£15425, eace%_ Alluvial Fans in the Death Valley Region California and Nevada J&.-S GEOLOGICAL SURVEz/LROFESSIONAL PAP ER 466 Alluvial Fans in the Death Valley Region California and Nevada By CHARLES S. DENNY G EOLOGICAL SURVEY PROLESSIONAL PAP E R 466 A survey and interpretation of some aspects of desert geomorphology UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1965 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director The U.S. Geological Survey Library has cataloged this publications as follows: Denny, Charles Storrow, 1911- Alluvial fans in the Death Valley region, California and Nevada. Washington, U.S. Govt. Print. Off., 1964. iv, 61 p. illus., maps (5 fold. col. in pocket) diagrs., profiles, tables. 30 cm. (U.S. Geological Survey. Professional Paper 466) Bibliography : p. 59. 1. Physical geography-California-Death Valley region. 2. Physi- cal geography-Nevada-Death Valley region. 3. Sedimentation and deposition. 4. Alluvium. I. Title II. Title: Death Valley region. (Series) EARTH sciences LIBRARY For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C., 20402 '"Canyon sen 411,045 ~.$Sz, ee, a '<» cany" lNIWVNVd ( ~Yo, 2. --* $ 36°00'- 30° 116°15¢ I FicUrE 1.-Map of the Death Valley region, California and Nevada, showing the location of more detailed maps included in this paper. A1, plate 1; A2, plate 1 insert ; B, plate 2; C, figure 13; D, plate 3; E, plate 4 ; F, plate 5. tape was laid across the wash or pavement; whatever material lay beneath each 4-foot mark (4, 8, 12, 16, etc.) was picked up, and the length of the intermediate axis of the particle was tallied within a size class. A sample of 25 particles was obtained in this manner. The Wentworth size classes denoted by the phi nota- tion are used. Experience has shown that the sizes of the particles on a streambed or fan surface form a pop- ulation that has approximately a log normal distribu- tion. In order to apply statistical methods to the figures obtained, therefore, the sizes must be expressed in units on a logarithmic scale. This conversion is most conveniently done by using the phi units of Krumbein based on logarithms to the base 2 (g=-logn, where n= grain size, in millimeters). The size classes increase in a geometric progression as follows: Phi unit size (mm) -1 2 -2 4 -B 8 -4 16 -B 82 The actual particles picked up were tallied in size classes by means of a scale graduated as follows: Size class (¢) Size range (mm) ize class (¢) 0. 2 ~I) rad. Cons LaLa bak mM 2.83-5.T mT! ash _ 90.5-181.0 ToD 5.T-11.3 mab 181.0-361.8 i auc ank s cress 11.3-22.6 tU in 361.8-728.8 f aos Bo oe paar 22.6-45.2 4 ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA The number of particles in each size class was plot- ted as a cumulative curve (fig. 2), and an estimated mean size, in phi units, was determined by inspection as follows: Estimated mean size =fii2gi where Q;, is the first quartile, or the 25 percentile, and Qs is the third quartile, or the 75 percentile (both in phi units). The estimated mean size was then con- verted into millimeters. The values of mean size obtained by this method refer only to the surface of the material sampled. They are not directly comparable to the sieve analysis of a bulk sample. - Such a grid method is usable provided that the material on the surface does not include too many par- ticles in phi size class -1 (less than about 3 mm). Not all the individual measurements may be repre- sentative of the surface material, but the values for the entire length of a wash-from mountain crest to toe of fan-when plotted on a graph group about a trend line that seems to be representative of the surface of the wash and can be compared with similar curves for the washes on 'other fans. These estimates suggest the size of the material of which a fan may be built and indi- cate how the size of the material on one fan may differ from that on a neighboring fan. The accuracy of the grid sampling method can be determined on the basis of well-known statistical princi- ples. If the individual particle measured are as- sumed to be selected randomly, then the error in any estimate of the mean size of all the particles within the sampled area or transect depends, first, on the actual variation in size of all the particles within the area and, second, on the number of particles actually measured. Thus if the deposit on the surface is poorly sorted and contains a wide range of sizes, the estimate of the mean size obtained by the grid sampling method is apt to be much further from the true mean than it would be if the deposit at the surface were well sorted. The error involved may be reduced by measuring a larger number of pebbles. Experience as well as statistical theory shows, however, that with increasing number of meas- urements accuracy increases at a gradually decreasing rate. The improvement in accuracy from a count of 2 particles to one of 25 particles, for example, is much greater than that from 25 to 100. The probability that a certain accuracy has been attained can be estimated by simple statistical methods and is expressed as the confidence limit. An estimate of the confidence limit can be obtained as follows : Estimated confidence limit, in g units =5-u=%’ where z=estimated means, «=true means, s=estimated standard deviation (all in phi units) ;. » is the number of individuals in the sample, and ? is a statistic (Dixon and Massey, 1951, app., table 5, p. 307). The estimated standard deviation, which is a measure of the sorting or range in size of the sample, can be obtained from the cumulative curve of size classes (fig. 2) as follows: Psa Pis Ty where P;, is the 84 percentile and P,, is the 16 percentile (both in phi units). The Trask sorting coefficient, another measure of sorting, can be obtained from the cumulative curve of range in size (fig. 2) as follows : Estimated standard deviation = i 25 where P;; is the 75 percentile and P;; is the 25 percentile (both in millimeters). To illustrate the use and accuracy of the method, counts at three localities in subgroups are shown on figure 2 and table 1. As shown in the table, sample AM 38 has a standard deviation of 2.18 phi. The esti- mated confidence limit or maximum difference that can be expected between the mean of the sample and the mean of the deposit as a whole (9 times out of 10) is 0.6 phi. For sample AM 35, which has a lower standard deviation and a larger number in the count, the con- fidence limit is 0.2 phi. For a pavement (sample AM 39) where the sorting is very good (estimated standard deviation 1.6 phi), the confidence limit is low compared with that of other samples having a similar number of individuals. In practice it was deemed advisable to sample the fans at many places using a count of 25 individuals at each place rather than to measure many particles at a small number of places. On the average the mean values obtained at most sample sites can be expected to be within 0.5 phi unit of the true values. The values of estimated mean size used in this report are true geometric means because the original measure- ments and the calculations were in phi units. These values are comparable with those measured by Hack in streams in the Appalachian region (Hack, 1957). Since the size distribution of such alluvial deposits is approximately log normal, Hack's median grain sizes are estimated geometeric means and thus are compa- rable with those from the Death Valley region. Measurements of size bed material in streams in the southern Rocky Mountains made by Miller (1958) yielded values that also appear to be comparable. The estimates from all three regions are based on a grid method of sampling of the surface of the deposits. For each locality sampled in the field, one or more of the following measurements were made from topo- Trask sorting coefficient= graphic maps in the laboratory: (1) altitude, (2) dis- tance to divide, (3) fall or difference in altitude be- tween drainage divide and sample locality, (4) slope, and (5) drainage area above the sample locality. Most sample sites were selected along a main fan-building PERCENT Ficurs 2.-Cumulative curves of samples from surface of washes floored with unweathered desert pavement, Ash Meadows quadrangle, Nevada-California. INTRODUCTION 100 109 Ps Fs 90 |- -I 90 |- A B 80 |- - 80 20 - 70 |- 60 |- = 60 |- & 50 |- e St sol- & Total sample i 40 |- - 40 |- Subsample 35A |- -R- mol t Total sample 34 Subsample 35B m tly _- 2 +---O=-- Subsample 38A 20[< Subsample 35C a 20 |- ssg nos 7 Subsample 38B 10 Subsample 35D =I 10|- 3 - g Ge: 1s At fe te 3 C pists: sl 0 1 2 3 5 6 7 8 9 0 1 2 4 5 6 7 8 9 $ CLASS $ CLASS 100 T | I } @ 90 |-- - C 80 |- - - 60 |- = 50 |- - sample AM 39. 185-932 0O-64--2 PERCENT ---B#-- 40 ~ Total sample —x— 30 Subsample 39A I Ciera... 20 Subsample 39B =I enna} eames 10 Subsample 39C sd 0 | | | | 0 1 2 3 4 5 6 7 $ CLASS gravel and from weathered gravel of A, wash, sample AM 35; B, wash, sample AM 38; C, pavement, 5 wash, and the distance to divide was measured along the wash. For sample sites on areas of desert pavement and on fans or parts of fans where no single, well- defined wash occurs, distance to divide was measured along a radius from the apex. In this paper all slope 6 ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA TABLE 1.-Size analyses of samples of unweathered gravel on the surface of washes and of the weathered gravel of desert pavement, Ash Meadows quadrangle, Nevada-California Difference between Estimated mean of whole sample | Estimated | Standard | confidence Mean size and means of sub- standard | deviation | limit (90 Number of samples deviation percent of Sample Subsample individuals the time) in sample ¢ Milli- ¢ Error 6 6 6 meters (percent) AM3S . ts 50 -38. 8 14.0 |_ mes [Dane. 2. 5 2. 18 0. 60 25 -8. T 13. 0 0.1 2 2. 6 2. 44 . 80 25 -4. 2 18. 5 . 4 10 2. 2 1. 95 . 70 XMS5 (Wash): .: ens an e- os an » 350 -2. 7 esas 2. 3 1. 98 . 20 100 -3. 0 8. 0 3 11 2. 4 2. 06 . 85 100 -2. 9 7. 4 2 T 2. 2 1. 95 . 85 100 -2. 5 5. 6 2 7. 2. 9 ..- sl. 50 -2, 1 4, 2 6 22 2. 0 1. 84 . 40 KM3Q - LiL 100 -8. 7 130 {.vce cell 1. 6 1. 57 . 30 25 -38. 6 12. 0 Me p4 1:8 1. 59 . 60 25 -8. 9 15.0 vB 5 1. 7 2.09 . 60 50 -3. T 13. 0 . 0 0 2, 1 1. 65 . 50 data are taken from a topographic map, unless other- wise stated, because experience shows that measure- ments of slopes over a long distance from a topographic map give more consistent results than do measure- ments over a short distance in the field. All the field and laboratory measurements used in this report are presented in table T (p. 43). DEFINITIONS AND SYMBOLS The following definitions and symbols are used in the text unless otherwise specified : The area of fan or fan segment (Af) is measured by planimeter on a map, in square miles. The drainage or source area (Am) is the area of the basin above sample locality measured by planimeter on a map, in square miles. Width (W) is the width of a wash at a sample locality, in feet. GEOGRAPHY The fans discussed in detail are in the Amargosa Valley east of the Greenwater Range and east of the southeast end of the Funeral Mountains (fig. 1). This segment of the valley is a broad area of sloping alluvial plains bordered by low moutains that rise about 3,000 feet above the river and are bordered by piedmonts 1 to about 6 miles long, measured at right angles to the mountain front. The foot slopes are largely alluvial fans, and the total area of pediment is small. The Shadow Mountain fan, east of Death Valley Junction, is part of the alluvial apron at the northwest end of the Resting Spring Range. The Bat Mountain fan, north- west of Death Valley Junction, is close to the southeast end of the Funeral Moutains. These two fans, and the others briefly described, are listed in table 2, and their approximate location is shown on figure 1. Two of the other fans are in Greenwater Valley, which lies between the Amargosa River and Death Valley. One, perhaps in part a pediment, is north of Funeral Peak ; the second, a small one, is on the east side of the valley southwest of Deadman Pass. Five fans in Death Valley are dis- cussed briefly : three are on the west side of the valley east of the Panamint Range, at the mouths of Trail, Hanaupah, and Johnson Canyons; and two, Copper Canyon fan and Willow Creek fan, are at the foot of the Black Mountains east of the valley floor. The climate of the region is warm and dry. Trees are absent except in the higher parts of the Panamint Range. Climatological data are given in the following table: Summary of climatological data [U.S. Weather Bur., 1932, 1935; Troxell and Hofmann, 1954; C. B. Hunt, written commun., 1960 Average annual Temperature (°F) Area precinitation (inches) Summer Winter Floor of 3-4; snow Average Minimum for Amargosa rare. maximum for Decem- Valley. for July, ber and >100. January, <32. Mountains Slightly= 3" [2 : Lt cringe oli o- exienge adjacent to more than Amargosa f Valley. occasional snow. Floor of Death Average for | Minimum Valley. July, rarely below >100. freezing. Higher parts of 1218 ua Wr H eir acc ale crs see ane Panamint (es- Range. timated) ; snow common. SHADOW MOUNTAIN FAN TaBus 2.-Fans and washes described in this report Source area Piedmont Areas in square miles (values in parenthesis are in percent.) Alti- | Relief Ap- Regional subdivision Name and location (fig. 1) tude of! apex | age | proxi- | Relief Area Bedrock sum- | to di- | area | mate | toe to Area Area |of var- mit | vide (sq |length] apex ofdes-| Area | of un- nished (feet) | (feet) | mi) |(miles)] (feet) | Total] ert |ofvar-|weath-| and area | pave- [nished] ered un- ment | gravel | gravel | weath- ered gravel Shadow Mountain fan, east of | Quartzite and subordinate | 5,071 | 1,591 | 2.73 6.0 | 1,450 [18.95 | 3.26 | 3.65 | 1.71 5.36 Death Valley Junction, Ash shale, limestone, and dolo- (100) | (36.4) | (40.8) |(19.1) | (59.9) East side of Amargosa Valley, Meadows quadrangle mite west of Shadow Mountain - - - Fan east of Alkalai Flat, south- | Quartzite and subordinate | 5,071 | 1,721 | 1.10 4.0 | 1,350 | 3.68 :18 2. 95 east of Death Valley Junction, shale (100) | (19.6) (80. 2) Ash Meadows quadrangle West side of Amargosa Bat Mountain fan, northwest of | Limestone, dolomite, fan- | 4,963 | 2,123 1.14 4.5 750 | 3.93 | 0.78 | 22.30 | 0.76 3.15 Valley, east of Funeral Death Valley Junction, Ash glomerate, and subordi- (100) | (19.8) | (60.8) |(19.4) | (80.2) Mountains Meadows quadrangle nate sandstone, and shale Wash northwest of Lila C mine, | Volcanic and sedimentary | 4,006 786 .23 8.5 | 1,000 | Individual fans merge on lower half Funeral Peak quadrangle rocks, chiefly basalt, rthyo- of piedmont. lite, vitrophyre, tuff, sand- Wash southeast of Lila C mine, stone, and conglomerate 4,276 | 1,476 | 2.80 6.0 800 Funeral Peak and Eagle Moun- tain quadrangles West side of Amargosa Valley, east of Greenwater | Wash west of Eagle Mountain, 4,982 | 1,742 | 4.11 7.0 | 1, 240 Range Funeral Peak and Eagle Moun- tain quadrangles Segment of piedmont between 4,982 | about | 16.31 | 4.7- | 1,250 | 19.96 | 8.85 |.______]_____._. 11.11 Lila C mine and Deadman 2, 000 7.0 | (max) | (100) |(44.3) (55.7) Pass, Funeral Peak, Ash Meadows and Eagle Moun- tain quadrangles Wash southwest of Deadman 4, 056 696 14 2.0 530 | Fan merges with adjacent ones on Passi Eagle Mountain quad- | Monzonite lower half of piedmont. rangle Greenwater Valley Wash north of Funeral Peak, 6, 287 | 1, 087 . 50 3.0 | 1,240 | Fan merges with adjacent ones. Funeral Peak quadrangle Mayt be thin mantle over pedi- ment. Willow Creek fan, Funeral Peak | Metadiorite, monzonite, | 6,317 | 6,417 | 22.35 .6 150 | 0.41 | 0.03 | 0.00 | 0.38 0. 38 quadrangle and volcanic rocks (100) (7) (0) (93) (93) East side of Death Valley, west of Black Mountains Copper Canyon fan, Funeral | Sandstone, siltstone, fan- | 6,160 | 5,980 | 22.26 1.5 440 | 2.28 . 20 .72 | 1.36 2. 08 Peak and Bennetts Well quad- glomerate, and metadio- (100) (0) (32) (59) (91) rangles rite Trail Canyon fan, Emigrant | Quartzite, argillite, and | 9,064 | 7,504 | 23.76 5.0 | 1,810 | 11.47 | 3.14 | 4.68 | 3.65 8. 33 Canyon and Furnace Creek dolomite (100) (27) (41) (32) (73) quadrangles West side of Death Valley, | Hanaupah Canyon fan, Tele- | Quartzite, argillite, and [11,049 | 9,009 | 25.68 5.5 | 2,200 | 13.12 | 6.47 | 3.18 | 3.47 6. 65 east of Panamint Range scope Peak and Bennetts Well granitic rocks (100) (49) (24) (27) (51) quadrangles Johnson Canyon fan, Telescope | Quartzite and argillite 9,636 | 7,336 | 17.88 6.5 | 2,550 | 14.53 | 8.76 | 2.67 | 3.10 5.77 gfak Hand Bennetts Well quad- (100) (60) (18) (21) (40) angles ' Includes 0.32 sq mi (3.7 percent) underlain by fine-grained beds of Quaternary age. The maximum air temperature recorded in Death Valley at Furnace Creek Ranch is 134°F (U.S. Weather Bur., 1935). In the Amargosa Valley the highest recorded temperature, at Clay Camp in the Ash Meadows quadrangle, is 118° F in July; the lowest is 3°F in December. On the floor of Death Valley, ground temperatures as high as 190°F have been re- ported (C. B. Hunt, written commun., 1960). During the summer of 1957, a reading of 162°F was recorded on a desert pavement in Amargosa Valley. * Includes areas where individual patches of pavement, varnished gravel, or un- weathered gravel are too small to be mapped separately. SHADOW MOUNTAIN FAN Shadow Mountain, rising about 3,000 feet above the Amargosa River, is bordered by a sloping piedmont 3-6 miles wide underlain by Quaternary alluvial deposits. In the area mapped (pl. 1), this piedmont is a complex alluvial fan bordered by small areas of older rocks that have been beveled by erosion and form pediments. Near the mountain front where the fan has a maximum slope of 700 feet per mile (fig. 3), the fan is a complex of narrow ridges and washes as much as 50 feet in ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA FEET 12,000 Fans in Death Valley s 11,000 10,000 9000 8000 7000 6000 5000 4000 3000 2000 1000 0 FEET ___ Fans in Greenwater a Valley Fans in Amargosa Valley 3000 # 2000 1000 1% 0. 2% =3 |_ 4 MILES } (___ FisurE 3.-Longitudinal profiles of fan-building washes in the Death Valley region. Profiles extend along the main wash from the drainage divide in the mountains to the toe of the fan. Position of the apex of a fan is shown by tick mark. The vertical exaggeration is about X 10. SHADOW MOUNTAIN FAN depth. Broad washes separated by extensive areas of desert pavement appear a short distance down the fan, but the pavements narrow and come to an end before reaching a point half way between the apex and the toe. An expanse of braided channels and gravel bars dotted by small areas of pavement, especially near the toe, extends westward to the flood plain of Carson Slough. The geoloy of the fan was mapped on a scale of about 4 inches per mile (pl. 1), and the size of material at the surface was measured at sample sites along a traverse from the toe of the fan to the summit of Shadow Mountain and at other localities The sample sites are shown by number on plate 1, and the data from the measurements are recorded in table 7. In some places the boundary between wash and pave- ment is arbitrary. The determination of the boundary is especially difficult on the western part of the fan, where both the local relief between pavement and wash and the size of the individual areas decrease toward the toe. GEOLOGY Shadow Mountain is underlain by east-dipping beds of probable Cambrian age, which are composed of gray and brownish quartzite and subordinate micaceous shale and quartzite-pebble conglomerate. Along the west base of the mountain is a narrow band of limestone and dolomite, probably also of Cambrian age, that is faulted against the quartzite. Low hills north of Shadow Mountain consist largely of fanglomerates of late Cenozoic age that rest unconformably on the Paleozoic rocks and are themselves somewhat tilted and faulted. The Quaternary deposits that form most of the pied- mont west of Shadow Mountain are a little-deformed accumulation of arid-basin sediments that rest uncon- formably on the older rocks. The fragments are com- posed largely of quartzite and, near the mountain front, range in size from silt to boulders. Away from the mountain the proportions of the larger sizes decrease, and silt, sand, and clay are dominant near the toe. Most of the deposits are cemented by caliche. At the north and south edges of the fan (pl. 1) are small out- crops of eastward-dipping beds of sandstone and clay, veneered with gravel, and low hills of fanglomerate. | The flood plain of Carson Slough and Alkali Flat, west of the fan, are floored with unconsolidated silt, sand, and clay. GEOMORPHOLOGY The surface of the Shadow Mountain piedmont can be divided into four geomorphic units (pl. 1)-modern washes, abandoned washes, desert pavement, and pedi- ment (fig. 4)-which differ in topographic form and in the nature of the material at the surface. The mod- ern washes are those segments of the piedmont that appear to be areas of active erosion or deposition at the present time. Desert shrubs are absent. The material that floors these washes is unweathered and lacks the coating of desert varnish characteristic of much of the surface of the fans in this région. The modern washes constitute only a small portion of the surface of any fan, a fact suggesting that most of them have a complex history. The abandoned washes support a growth of desert shrubs and are floored with stones that have a coating of desert varnish. They are stream channels in which shrubs have grown and whose floor has acquired a coating of varnish since the last time they were flooded. Unforunately, it is not known how long ago such a flood took place. Nevertheless, the greater extent of the abandoned washes as compared with that of the modern ones suggest that the regimen of the modern streams may differ from that represented by the aban- doned washes. The size of the bed material in these two types of wash also differs. Desert pavements are armors of rock fragments that rest on and protect a layer of silty material apparently weathered from the gravel below. - The fragments have a coating of desert varnish and are tightly packed to- gether. A pavement is dark colored, gently sloping, and smooth surfaced and lacks the channels and bars of a wash. The areas of pavement on the Shadow Mountain fan show as a dark stippled pattern on an aerial photograph (fig. 4). A pavement is a segment of a fan on which no new sediment has been deposited for a long time. The range in size of the constituents of the pavements depends not only on the size of the gravel from which the pavement is derived but also on the weathering, mass movements, and erosion that have combined to transform the channeled surface of a wash into a smooth pavement. The pediments on the piedmont northwest of Shadow Mountain occupy small areas marginal to the fan, where deformed rocks largely of Tertiary age have been beveled and mantled by gravel and are now dis- sected to expose the buried pediment. 10 ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA 'I ut umoys 324} St gary 'us; urejunop; mopeqy oy} ;o ydeaSojogd SHADOW MOUNTAIN FAN MODERN WASHES Braided channels and gravel bars with a microrelief ranging from 1 to 3 feet constitute the modern washes. Those mapped range in width from 50 to several hun- dred feet. The channels and bars, generally lacking vegetation, are underlain by bouldery to pebbly gravel and sand ; the coarse fragments are angular to subangu- lar blocks and slabs that are almost unweathered, and the exposed fragments are not coated with desert varnish. The modern washes are not uniformly distributed over the fan but are most extensive near the mountain front, in midfan downstream from the mouths of washes heading in pavements, and near the toe. On the lower part of the fan, on plate 1 in the vicinity of the 2,200-foot contour, a broad indefinite zone occurs where the modern washes divide into many channels that nar- row westward. Some of the channels finger out and end in a broad area of abandoned washes, whereas others continue westward as narrow channels too small to map at the scale of plate 1. Where small pavements and fine-grained arid-basin sediments occur near the toe, modern washes are also present, but near the south- ern part of the toe of the fan, the fine-grained beds are absent and the surface is a mosaic of abandoned washes. The mean size of the gravel that floors the modern washes-that is, the surface layer-ranges from about 20 mm near the mountain front to less than 5 mm near the toe (fig. 5). The microrelief of the surface also decreases downfan. These values of mean size are smaller than those of the gravel on the surface of the abandoned washes or the pavements, although the rate 11 of decrease in size downfan is about the same as that for the gravel in the abandoned washes. A very rough estimate of the effects produced by present-day runoff in the modern washes is afforded by measurements of erosion of the Old Traction Road. Built about 1905 but not maintained, the road is a con- tinuous 15-foot-wide embankment whose top is about at the level of the highest part of the adjacent wash. Part of this embankment has been washed out, and the amount of material removed is a measure of the total erosion on the Shadow Mountain fan during the last 50 years. Near the Old Traction Road, about a third of the area mapped as modern or abandoned washes has been subject to overflow during this time, and of the third, about half shows evidence of erosion. The evi- dence comprises 24 cuts through the roadway ; the cuts range in depth from 6 inches to about 3 feet and in width from 4 feet to as much as 180 feet. The direction of flow of the stream in a modern wash on the northeast edge of the Shadow Mountain fan has recently changed. Such diversion or piracy is an im- portant element in the history of this fan and doubtless of many others (Rich, 1935; Hunt and others, 1953). The modern wash running westward just south of the State line (pl. 1) narrows abruptly and then passes as a single channel through as mall area of fanglomerate (near loc. 74) into an extensive pavement. The floor of the modern wash is only 5-10 feet below the smooth surface of the fanglomerate and only a foot or two below the surface of the large area of abandoned washes just north of locality 74 that extends northwestward beyond the mapped area. Clearly, the stream in the I * T I I ! EXPLANATION 100.0 & ® Unweathered gravel on Varnished gravel on floor _ 7 d floor of modern wash of abandoned wash ias o o & x A ha 3 0 e o Gravel of desert Unweathered gravel on floor _| a § & 0 pavement of meandering wash head- S ing in a pavement ig # C Xa A © e o] a bas O a; o 0 y * x us 10.9 A A X FS 6 X x o x = N -I o ""g" #: - ~ o o 91 .S z % o o - a A x - 3 ® -] Divide at head of meandering ® _ wash heading in pavement 1.0 I1 I | 1 I | {> 0 1 2 S 4 6 6 DISTANCE FROM DIVIDE, IN MILES FrGurE 5.-Semilogarithmic scatter diagram showing the relation between the mean size of material at sample sites on the surface of the Shadow Mountain fan and the distance of these sites from the divide (pl. 1). forming the desert pavement and of the gravels that floor both modern and abandoned washes. gravel on the floor of a meandering wash heading in a pavement. The diagram includes size measurements of fragments Data are also shown for unweathered 12 ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA modern wash once flowed northwestward. The present course of the wash through the fanglomerate probably resulted from overflow or from lateral cutting by the stream, which thus spilled into the head of a west- flowing gully whose floor was at a lower level than that of the wash. This diversion could have taken place during the last few hundred years, and a cloudburst might even now send water and debris down channels in both directions. ABANDONED WASHES Abandoned washes, the most extensive geomorphic unit on the fan, are the somewhat subdued remnants of braided stream channels in which water has not flowed for a long time. The channels contain faint broad ridges and swales having a relief of several feet and spaced 5-20 feet apart. The ridges and swales are covered by gravel and boulders; commonly, the ridges are more bouldery than the swales. Desert shrubs a few feet to as much as 15 feet apart are scattered over the surface. Abandoned washes are floored with gravel whose exposed stones are varnished but otherwise not greatly weathered. The intensity of the varnish varies: in some places the pebbles have only a faint coating, and in other places the floor of the wash appears dark colored because the exposed fragments are thickly coated. The estimated mean size of the gravel on the surface of abandoned washes from near the apex to the toe of the fan (pl. 1; table 7, varnished gravel in abandoned washes) generally ranges from 7 to 25 mm (fig. 5). These means are slightly larger than those for the un- weathered gravel of the modern washes at the same distance down the fan. Presumably, when the aban- doned washes carried water, the flood discharges were greater than they are today. The fragments are slightly rounded, and in general are distinct from the angular fragments of a pavement. The surface of an abandoned wash has a slightly greater relief than does a modern one. An abandoned wash may lie as much as 2 feet above the level of an adjacent modern one, or their positions may be reversed, the modern wash being either built out over the adjacent abandoned wash or separated from it by a higher-standing area of desert pavement. The character of the abandoned washes changes to some extent from the apex to the toe of the fan. Al- though the spacing between the individual ridges and swales is constant, the relief between them decreases from as much as 5 feet near the apex to a maximum of about 2 feet on the lower half of the fan. The local relief near the toe is seldom more than a few inches. The color of the varnish that coats the fragments at the surface changes from place to place, being slightly lighter colored near the apex and the toe than elsewhere on the fan. The varnish that coats quartzite fragments flooring the abandoned washes is evidence that these washes have not carried water for many years. If the time when the stones were coated could be determined, a minimum age for these abandoned water courses could be estimated. Engle and Sharp (1958) described a locality where desert varnish has formed on fragments of rhyolite in 25 years, and C. B. Hunt (1954) and A. P. Hunt (1960) cited abundant archaeological evidence that most varnish coatings are at least 2,000 years old. During the building of the Old Traction Road about 1905, pavements were disturbed and the varnished stones removed from areas adjacent to the road (a situation not unlike that described by Engel and Sharp (1958) at the South Stoddard locality near Barstow). The road was never maintained, and the areas of moved stones and of bare ground adjacent to it probably have not been disturbed for more than 50 years. These quartzite fragments, moved or disturbed during road construction, have not acquired a visible coating of var- nish in about 50 years. Thus the time since the last water flowed down these abandoned channels is in ex- cess of 50 years and doubtless is much more, perhaps more than 2,000 years. Other considerations, however, suggest that an esti- mate of thousands of years is too large. On the lower part of the fan, the floor of a modern wash is in many places less than a foot below the surface of the adjacent abandoned one. Therefore, water deeper than 1 foot has not flowed down a modern wash on the lower part of the fan. The magnitude of the occasional floods that have occurred in the Death Valley region during the last century make it seem likely that during the last 2,000 years many floods reached the toe of the Shadow Mountain fan with depths of more than a foot. Thus, I believe that the last flows down the abandoned washes are more likely to have occurred within the last few hundred years than prior to the beginning of the Christian era. ORIGIN OF WASHES The modern and abandoned washes are those parts of the fan where erosion and sedimentation have taken places during the last few hundred to few thousand years. The distribution of the modern washes suggests that at present these processes are vigorous on only a small part of the fan-namely, at the moutain front, downfan from areas of pavement, and near the toe. These areas are the areas of more rapid runoff-the bedrock slope of the mountain and the smooth surface of a pavement-compared with the broad areas of aban- SHADOW MOUNTAIN FAN 13 doned washes, where little erosion or deposition have occurred for a long time. The abandoned washes, on the other hand, record a time when flooding of the fan was more extensive than at present, and presumably a time of more active erosion and deposition. This condition is suggested both by the coarse debris on the floors of the abandoned washes (fig. 5) and by the much greater areal extent of the washes as compared with the modern ones. Although a gradual lateral shift of the modern washes would cover some of the areas of abandoned wash, large areas of abandoned wash on the lower part of the fan are not traversed by mappable areas of modern wash. When the abandoned washes were active areas of erosion and deposition, floods must have spread downfan much further than they do at the present time. When these large areas of abandoned washes were flooded, the total discharge presumably was greater, because of either greater yearly or summer rainfall, less evaporation, or a combination of both. Such flood- ing may have occurred at various times, from only a few hundred years ago to as far back as the beginning of the Christian era, when Death Valley contained a shallow lake (C. B. Hunt, written commun. 1960). Both erosion and deposition take place along a wash, and it is difficult to be certain whether during some time interval the net result has been to build up or to lower the surface of the wash. The surfaces of some areas of wash, however, have the form of the segment of a very low cone, suggesting that these washes are areas where deposition has been dominant. A good example is the circular area of abandoned washes near the apex of the Shadow Mountain fan, between localities 430 and 426 (pl. 1). On a map, the contours crossing this area are convex downfan. This depositional segment, shown on figure 64 as area 2d, was built up by debris carried to it from a small area on the northwest slope of Shadow Mountain (area 2s, fig. 64) and can be described in- formally as a "fan on a fan." Just north of locality T8, varnished gravel of an abandoned wash laps over the edge of the adjacent pavement. Some water was lost by percolation and evaporation in this depositional segment ; the remainder flowed westward between pave- ments in channels where erosion and transportation were the dominant processes. Three additional areas of washes whose surfaces are cone shaped are present on the Shadow Mountain fan, and their locations are shown on figure 64 as deposi- tional areas 1d, 3d, and 4d. These three depositional segments and their source areas are briefly described in the following paragraphs. Their conical surface form is too subdued to be shown by the 200-foot con- tours on plate 1, but the reader will find that the conical 735-932 0O-64--3 form is suggested by the 40-foot contours on the topo- graphic map of the Ash Meadows quadrangle, Nevada- California, published by the U.S. Geological Survey. The first area is west of the segment of the Old Trac- tion Road that lies between sample localities 73 and 69 and south of the extensive pavement along the north edge of the fan (pl. 1)). This is a large area of aban- doned washes with a faintly cone shaped surface (area 1d, fig. 64) whose western limit is about midway be- tween altitudes of 2,200 and 2,400-feet. This deposi- tional segment received sediment from much of the east- ern half of the pavement along the north edge of the fan (area 1s). The depositional segment previously mentioned near the apex of the fan (area 2d) is also a part of the area that drained to the larger segment 1d. The smaller segment, however, is not considered a source of sediment for the larger one because it was itself an area of deposition. The source area of depositional segment 1d is drawn on figure 64 to exclude a large area, near the State line, that now drains to it (roughly the same as area 5s, fig. 6B). We can assume that the source area of deposi- tional segment 1d did not include area 5s because, as mentioned on page 11, the diversion of drainage that caused area 5s to drain into area 1s took place only a short time ago, probably after much of the gravel in area 1d had acquired its coating of desert varnish. When the gravel of area 1d was being deposited, area 5s was supplying sediment to areas of wash north of the fan. \ Two other areas of wash with slightly cone-shaped surfaces are shown on figure 6. Area 3d is a small diamond-shaped segment of abandoned washes south of area 1d, between it and the Old Traction Road, that was fed by drainage from source area 3s, the long nar- row pavement just to the east (pl. 1, locs. 69-78). Area 4d includes two areas of deposition : one just north of the area of pediment near the southern edge of the map and the other farther north separated from the first area by a large diamond-shaped pavement. Area 4d re- ceived sediment from the west slope Shadow Mountain and adjacent areas of pavement (source area 4s). In order to show the significance of these three areas as well as other depositional segments in the formation of the Shadow Mountain fan, one of the conclusions of this paper (p. 38) must 'be mentioned in advance of the presentation of all of the facts on which it is based. Plate 1 shows that the Shadow Mountain fan consists of segments of modern and abandoned washes and of areas of desert pavement. The analysis of the data of several fans in the Death Valley region demonstrates that the areal extent of the segments of a fan is related to that of their source areas in the mountains. The size of the depositional segments of which the fans are com- 14 ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA EXPLANATION Desert pavement Pediment Hills and mountains Outline of drainage area in mountains 2d Area of deposition or of pavement 2s Source area or possible source area of the gravel beneath pavement N Shadow XX Mountain C 1 0 1 2 MILES rom CE ca a E 1 ] FIGURE 6.-Areas of deposition on the Shadow Mountain fan and their possible source regions. A, Areas of deposition in washes-areas with faintly cone-shaped surface-and their possible source areas that supplied water and sediment; B, three pavements and the possible source areas of the gravel that underlies them; C, one pavement and possible source area of the gravel that underlies it. Related source and depositional areas shown by same number. Maps generalized from plate 1. SHADOW MOUNTAIN FAN posed is roughly equal to one-third to one-half the size of their source areas. On the Shadow Mountain fan, the four areas of depo- sition having slightly cone-shaped surfaces range in areal extent from 0.08 square mile to 0.46 square mile whereas their source regions range from 0.27 square mile to 1.26 square miles, as given in the following table : 15 Depositional _ Source area Segment (fig. 6) segment (sq mi) (sq mi) Pr rew 2 Puan cane ap rane o nas rain ale sa g 0. 46 1. 26 arenes sinhankars ad ol A0 . 43 n pI IPT c ae a naaa on ak o ain ale . 08 . 27 Tel nee abe ed akane s n=n nent ars ans o . 23 . 95 A logarithmic plot of these values (fig. 7) shows that they fall about a line, drawn by inspection, that in- I I cSt Ft 1] | t EE AE TTI I sxy T TTP] 100.0|- EXPLANATION - ~CE HILLS NORTH OF rs Z DEVILS HOLE WEST OF SHADOW MOUNTAIN CJ H s 5% Fa Small fans west Fan east of Alkali Flat __ Shadow Mountain Fan [C % of hills Quartzite and quartzite - Quartzite and quartzite tx: r— > Limestone and conglomerate conglomerate - J dolomite § C $ f A 2 E EAST OF GREENWATER RANGE EAST OF FUNERAL MOUNTAINS 5 < & . + IE; [- Depositional segments Depositional segments TI < on piedmont on piedmont (D) Volcanic rocks, conglomerate, Dolomite, limestone, quartzite, A A ® and sandstone fanglomerate, and sandstone A < 10.0 |- ~ ir ha.) EAST OF BLACK MOUNTAINS A = 5 -S > A - E __§ % Depositional segments 4% 5 | $> on piedmont & > z (3 Monzonite a. - 5 e o EAST OF PANAMINT RANGE WEST OF BLACK MOUNTAINS eg [ £3 © @ s a * gé Depositional segments Fans on east sie of Death Valley A ,/ 3 | o> on piedmont Mixed lithology #G C- <4 Mixed lithology I, € a >- DEATH VALLEY REGION + // fast A A Af=0.5 Am98 # o|- + e - 3 1.0|- Entire piedmont or + »". ~ i - entire fan x Pid © - f- Fan east of Alkali Flat, Bat Fa 2] a! -- Mountain fan, Shadow x I, ~A g L_ Mountain fan, segment of 1 F4 - had predmont between Lila C X Q 4 F 5 T mine and Deadman Pass, @8 # g @ =I 0 Trail Canyon fan, / 6 ©D '\ fi [- Hanaupah Canyon fan, 8D} Q A I, Af=0.1 Am*© s 2 Johnson Canyon fan / D4 C© ©/, 0 ~ / I6) neu Z 7 re # lk % 591, ® orl 4 A ? (g < E Af=0.33 Am} -] u [- 3 ad &C < k- a & _ -I C I LAA LMA 111 1 Lf THI I $5014 LT TTA | Loc t}] 0.01 int + ares 0. 0.1 1.0 10.0 100.0 Am, SOURCE AREA (DRAINAGE AREA ABOVE APEX), IN SQUARE MILES FIGURE 7.-Logarithmic graph showing the relation between the area of a fan or depositional segment on a fan and its source area in adjacent mountains. on figure 6. mapped by C. S. Denny and Harald Drewes (unpub. data). Points for about 60 fans are shown and are grouped with the highland from which they are derived. Data used in construction of the graph are given in tables 2 and 7. Letters for fans west of the Black Mountains are shown on plate 4. Numbers for areas on the Shadow Mountain fan are shown Fans west of the hills near Devils Hole were 16 ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA dicates that these four depositional segments are roughly equal to one third of the area that drains to them (4f=0.334m). Their size and also apparently their location appear to be independent of the position of the toe of the fan. - This plot shows four other points representing areas on the Shadow Mountain fan. These are segments of desert pavement and are dis- cussed on page 22. The graph on figure 7 confirms the view that the piracy believed to have taken place near the north edge of the Shadow Mountain fan is a recent event. If in the graph on figure 7 the source area of desposi- tional segment 1d is assumed to include the area near the State line that now drains to it-that is, to include area 1s plus most of area 5s (fig. 6), or about 3.18 square miles-then the point on the graph representing de- positional segment 1d would fall to the right of the three other points for the Shadow Mountain fan and would also fall outside of the cluster of points for most of the other fans described in this paper. Thus the graph on figure 7 supports the assumption that the di- version of most of the drainage from area 5s into deposi- tional area 1d took place so recently that it has not yet caused an enlargement of depositional area 1d. DESERT PAVEMENT Desert pavements, common to most fans in the Death Valley region, are smooth, gently sloping surfaces com- posed of closely packed rock fragments ranging in diameter from a fraction of an inch to several feet. The fragments of a desert pavement constitute an armor that promotes rapid runoff and protects the underlying silty material from removal by water or wind. Desert pavements occur on all parts of the Shadow Mountain fan but are most extensive near the border- ing highlands. The largest single area of pavement, along the northern edge of the map (pl. 1; fig. 4), is about 1,000-3,000 feet wide and more than 4 miles long. The east end of this pavement, forming the embayment in the northwest face of Shadow Mountain, is broken into narrow ridges separated by gullies as much as 50 feet deep. Only the tops of the narrow ridges are typical pavement; most of the land is steeply sloping. The western part of the pavement, however, consists of extensive fan-shaped surfaces trenched by narrow gul- lies; probably 90 percent of the area is pavement, and only 10 percent is gully. In the eastern half of the map area, most pavements stand a few feet to several tens of feet above adjacent washes. West of the Old Trac- tion Road, pavements are close to or even slightly below the level of the adjacent washes; the streams in the washes may have either scoured the pavement or depos- ited material on top of it. Near the toe of the fan are many small pavements and narrow outcrops of fine- grained arid-basin sediments. Both the pavements and the fine sediments are absent near the southern edge of the mapped area. The fragments forming pavements are largely var- nished pieces of quartzite and quartzite conglomerate and range in size from pebbles to boulders a foot or more in diameter. Near the west base of the moun- tain, etched fragments of limestone and dolomite are abundant. The fragments rest on several inches of silty material, which is transitional downward into weathered gravel cemented by caliche. Presumably at greater depth the gravel is little weathered. The armor and underlying silty material probably constitute a weathered mantle developed in the coarse detritus of the arid-basin sediments. The stones forming the pavements are the weathered relies of the coarse gravelly part on the arid-basin sedi- ments. Many stones are angular fragments, and in some places, adjacent pieces can be fitted together to form the parent cobble or boulder. Most fragments of quartzite and of quartzite conglomerate have weather- ing rinds a quarter to half an inch thick. The tops of the stones have a dark coating of desert varnish, but the undersides are brown or reddish brown. Some stones have little varnish except for a dark-brown band close to ground level, and still others appear as if they had lost most of an older film of varnish or had recently been overturned or otherwise dislodged from the pave- ment. Adjacent fragments whose shape and position suggest that they were once part of a single boulder are commonly varnished on all exposed surfaces. The limestone and dolomite fragments of a pavement gen- erally have flat, rough and pitted upper surfaces and rounded undersides coated with caliche. They are un- varnished, except for chert nodules in them. Clearly the limestone fragments have acquired their form by solution while part of a pavement. Estimates of the mean size of fragments on pave- ments were made at several localities along a traverse down the fan from the apex (loc. 424-447, pl. 1). The results are given in table 7 and are shown graphically on figure 5. These means generally range from 10 to 20 mm, except near the toe (loc. 447), where the mean is about 4 mm. - Size does not markedly decrease down- fan, as is true for the gravel in adjacent washes, where the estimated mean sizes are smaller than those of the pavement. The difference is expectable because the fragments on the pavement are part of a weathering profile, whereas those of the washes reflect their mode of transport. SHADOW MOUNTAIN FAN 17 oC Sw FEET 40 - Abandoned wash floored Pavement with varnished gravel 30 / - A - Modern wgsh floored with 20 Miniature terrace Meandering gully 10 unweathered gravel $ rts -t- pay, ~> 0 40 80 120 160 200 FEET FicurE 8.-Profile across a pavement and a wash on the Bat Mountain fan, Ash Meadows quadrangle in California. Profile trends roughly northeastward at right angles to the regional slope. At the southwest end, the profile crosses a meander- ing wash that heads in pavement; the northeast segment of the profile intersects abandoned and modern washes. For location see plate 2. profile is drawn to scale ; the datum is assumed. In surface form, the Shadow Mountain pavements resemble those found throughout the Death Valley region. The typical pavement is virtually a plain sur- face that slopes downfan, whereas in a transverse pro- file, a pavement is commonly slightly convex upward with steeper slopes along its lateral margins (fig. 8). Pavements are relatively smooth near the lower end of the fan; farther upfan, the pavement surface becomes more irregular, apparently as the number and size of the large fragments increase. Most of the pavements in the Death Valley region are traversed by meandering washes that head on the pavement. From a shallow swale in a pavement, marked by a line of shrubs, a gully descends abruptly to a level that is commonly slightly below that of an adjacent wash (fig. 8) and follows a meandering course downfan to the lower end of the pavement, where it joins a modern wash. Commonly, the gradient of the FIGURE 9.-Desert pavement composed of angular fragments of var- nished quartzite. A few unvarnished pieces are visible in upper left hand corner of photograph. Stones touch or overlap and generally range from 1 to 12 inches in diameter. The larger stones in the middle distance form a curving line, concave to the camera, that extends from the pick handle to the slate. 'The smaller stones in the background are piled up against the larger ones and form the tread of a miniature terrace. The locality is on Shadow Moun- tain fan, Ash Meadows quadrangle, California and Nevada. The meandering gully is less steep and the grain size of the material on its bed (fig. 5) is smaller than in neighboring washes. In the embayment at the head of the Shadow Mountan fan are several such steep-walled gullies-for example, the one that begins near locality 465. Few pavements are completely smooth ; rather, when examined in detail, miniature steps or terraces less than an inch high can be seen (fig. 9). These miniature breaks are generally only a few feet long and range from 1 to several feet in width (fig 10). Near the edge of a meandering gully or of an adjacent wash, a terrace riser may run parallel to the regional slope of the fan (fig. 8), and near the center of an area of pavement, the miniature terraces commonly trend across the fan at right angles to the regional slope. Details of several such miniature terraces are shown in plan and profile view on figure 10. Although these examples are on the Bat Mountain fan, similar features are found on the Shadow Mountain fan. The plan view shown on this figure is diagrammatic, but the larger fragments and bands of unusually small fragments are shown in their true positions on the pavement. Actually, the fragments which are generally 1 or 2 inches in diameter touch each other or overlap (fig. 9). The overall slope of the profile is about 4° (375 feet per mile). Only the terraces of small fragments are easily seen; the others are indistinguishable in sur- face material and are conspicuous only when they cast a shadow. In some places the terrace scarp is a single large fragment of rock, and rarely a continuous band of large fragments marks the riser. Elsewhere, the risers can be traced for 10 feet or more as faint topo- graphic breaks in material of similar size. Most of the stones are uniformly varnished and no variation in extent or appearance of varnished fragments is ap- parent in either terraced or unterraced pavements. Desert shrubs grow generally 20-30 feet apart on pavements ; but in some places shrub-free areas measure 18 ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA 10 d 10 1 Azimuth N. 85° W. 210 3|0 INCHES FIGURE 10.-Diagrammatic plan and profile of small area of pavement showing miniature terraces, Bat Mountain fan, Ash Meadows quadrangle in California (loc. 255, pl. 2). hundreds of feet in diameter, and in other places these plants are spaced every few feet. The ground around a shrub is commonly bare of stones and, in some places, forms a pedestal an inch or so in height on which the plant grows. Small areas of pavement near the toe of the Shadow Mountain fan adjacent to fine-grained Quaternary de- posits (pl. 1) are the top of a thin bed of gravel, a few inches thick, that overlies unconsolidated silt, sand, and clay. The mean size of the fragments is small, and many of them lack desert varnish; the quartzitic frag- ments have rough exteriors, and the few pieces of car- bonate rock are well-formed rillensteine. Between pavements the surface of the Quaternary deposits has abundant surface efflorescences of salt. The ground beneath these pavements is soft, even in dry weather. The rain that falls on a pavement runs off much more rapidly than that falling elsewhere on a fan (C. B. Hunt, written communication, 1960). Runoff moves not only small particles across a pavement but larger fragments as well. For example, the desert shrubs common to most pavements are surrounded by animal burrows, and the surface is strewn with small white pieces of the caliche that cements the underlying gravel. In some places the pavement downslope from a bush is strewn for distances as great as 8 feet with these frag- ments carried across the pavement by surface wash. The extensive pavement along the north edge of the Shadow Mountain fan was studied in a small area just east of the Old Traction Road (loc. 435, pl. 1). Obser- vations were made following a heavy rain, and a trench was dug across the pavement to expose the material be- low the armor of stones. The material exposed in the trench is shown diagrammatically on figure 11 and is described in table 3. The cross section on figure 11 shows that the pave- ment cut by the trench slopes to the southwest. The surface is not smooth but is interrupted by miniature steps a few inches wide whose risers are formed by boulders. All but the largest stones under the pave- ment rest on a thin layer of loose silt (unit 2), which in turn lies on a porous friable silt (unit 3) that is tran- sitional downward (unit 4) into weathered gravel (unit 5). Many of the openings in the porous silt are lined with secondary material, a fact suggesting repeating solution during rains and redeposition when drying. This condition is perhaps caused by the capillary rise of vadose water. The silty material exposed in the trench between the layer of stones under the pavement and the weathered gravel resembles that found through- out this part of the Amargosa Valley, except that the silt generally has a vesicular structure throughout, the fragments beneath the pavement resting directly on firm porous silt (unit 3) and not on loose silt (unit 2), as in SHADOW MOUNTAIN FAN 19 NE INCHES SW 10 0 EAE OTO 20 30 INCHES 1 5 FIGURE 11.-Section of material exposed in trench dug beneath pavement on Shadow Mountain fan, Ash Meadows quadrangle, California and Nevada. the trench. Scattered observations suggest that the silt beneath the stone armor tends to be thicker where the underlying gravel is finer grained and to be thinner where the gravel is more bouldery. On fans where the gravel contains many fragments of limestone and dolo- mite, such as the Bat Mountain fan (p. 25), the silt appears to be thicker than on the Shadow Mountain fan, at least in those places where the grain sizes in the underlying gravel are comparable. Observations made on the pavement at the site of the trench following a heavy rain suggest that some of the silt beneath the armor of stones became saturated with water and tended to flow downslope, carrying the smaller stones with it. Meanwhile the larger stones, imbedded in firm dry silt, did not move; they impeded the lateral flow of the silt and caused the stone-covered surface of the silt to remain slightly higher on the up- slope side of the boulder than just downslope from it. When the pavement at the site of the trench was first reached on the afternoon of April 7, 1958, following about 24 hours of intermittent rain, a faint tinkling sound was heard which continued for about 20 minutes. The pavement was not firm; the jeep tires had made shallow ruts. When one of the smaller fragments of the pavement, such as fragment A shown on figure 11, was pushed horizontally, all the stones within a radius of 3-4 inches jiggled. The material beneath the pave- ment had the consistency of jelly, and when a stone was removed from the pavement, the surrounding silt tended to flow into the depression left by the stone. If, however, a large fragment set deeper in the under- lying silt, such as fragment B shown on figure 11, was pushed horizontally, it did not move. The silt beneath the pavement was saturated with water to depths rang- ing from 1 to 2 inches; below, the ground was dry. The Units are described in table 3 (loc. 435, pl. 1). Fragments A and B are referred to in text. fact that the large stable fragments form the risers of miniature steps indicates that such steps probably form when the water-saturated surface layer moves in small increments downslope, carrying along the small frag- ments of the pavement. Such movement is checked where it meets a boulder firmly embedded in the under- lying dry silt. ORIGIN OF PAVEMENT The pavements on the Shadow Mountain fan are the floors of very old abandoned washes where no deposition has taken place for a long time. The fragments on the surface of these washes have been broken into smaller pieces by mechanical processes such as expansion and contraction due to temperature changes or to freezing of water and by chemical decay. The fine material has been removed from the surface by running water and by wind, and a concentrate of closely packed fragments the pavement-has been left. Such a mechanism, how- ever, does not seem adequate to transform a rough sur- face of channels and gravel bars into a smooth pave- ment. For this transformation some kind of lateral redistribution of material seems required. A lateral movement of the fragments of a pavement is indicated by the miniature terraces, and this move- ment appears to be caused by the flowage of the silt on which the fragments rest. When saturated with water, the silt becomes plastic and tends to flow down- slope, either toward an adjacent wash or downfan. Expansion of the silt due to wetting also has a small horizontal component that increases with increase in slope and may result, after many cycles of wetting and drying, in a slight net movement of the silt downslope. When the paement and underlying silt creep down the steep banks of a wash, the downslope support of the 20 ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA gently inclined surface layer of saturated silt is re- moved farther up the pavement. The saturated silt tends to flow, and tension cracks tend to form in the wet silt, displacing the pavement. The risers of the miniature terraces are the surface expression of these 3.-Material exposed in trench dug beneath pavement on Shadow Mountain fan, Ash Meadows quadrangle, Nevada- California [Units shown in section of figure 11. Trench dug on May 1, 1958. Material dry to depth of about 5 in. Locality 435, pl. 1] Range in Average thickness depth (inches) (inches) Unit 1. Pavement. Pebbles and angu- lar fragments of quartzite; 1 in. or less is a common size but includes a few larger fragments; form a single layer of fragments resting directly on or in the under- lying silt. 2. Silt or clayey silt, light gray (10¥R 7/2), loose; basal con- tact sharp, wavy ; microrelief about 0.5 inch..--_--.-____-s- 1 .0-1.75 3. Silt or clayey silt; contains a few sand grains; light gray (10¥R 7/2); very firm in place; very friable, porous, has vesicular structure; open- ings commonly 0.05 in. in diameter, a few are 0.1 in. in diameter ; locally openings are larger near - base. Some openings contain skins of silt or clay that under the hand lens resemble tallow that has run down the side of a can- dle and hardened. Lower contact gradational________- 1 .0-2.0 4. Silt or clayey silt; contains a few small pebbles; light yellowish-brown (10¥R 6/4) to very pale brown (10VR 7/4); firm in place, very friable, porous; has vesicular structure and silt or clay skins similar to those of unit 3. Some openings are lined with brown crystalline material (caliche?). Distri- bution of openings gives this unit a faint thin wavy hori- zontal banding. Lower con- tact gradational____________ 0. T5-2. 0 5. Gravel, silty, yellowish-brown (10¥VR 5/4), loose to slightly firm, very friable; contains angular fragments of rock as much as 4 in. in diameter. Caliche on underside of many fragments is in the form of small lath-shaped crystals as much as 0.1 in. long. At depth of 10 in. below the pavement, the silt is brown (T.5YR 5/4) and contains thin flakes of caliche. Below depths of 15-20 in. the mate- rial is loose and faintly stratified and contains angu- lar and very slightly rounded pebbles as much as 7 in. in diameter; 0.25-2 in. is a com- mon size. Base not exposed. 0 .0-1 .5 1 .5-3 .0 3. 0-4. 5 15+ 4.5-20+ tension cracks. This mechanism seems adequate to form long and evenly spaced terraces. In other places, where a pavement includes boulders that are anchored in firm dry ground, the saturated material creeps down- slope and either piles up behind the boulders or flows by them. In either occurrence, the segment of pave- ment behind a boulder stands slightly above the surface in front of it. The presence of the silt beneath the pavement requires further explanation. The pavement acts as an armor that protects the underlying fine material from removal by water and wind. This armor is the top of a weather- ing profile; the material beneath it has been formed by the weathering of the gravel of which the fan is made. Perhaps the silt is formed largely by mechanical weath- ering, because the fragments scattered through it are not greatly weathered. The mechanism might involve the loosening and breaking up of the parent gravel by wetting and drying, and the resulting expansion and contraction of a surface layer causes the larger frag- ments to be raised to the surface in the same way that stones are raised by repeated freeze and thaw. As ex- plained by this theory, the silt beneath the pavement is the matrix of the parent gravel and, as a corollary, gravel having abundant matrix should form a thicker layer of silt than one having little interstitial material. Gravels derived from the volcanic rocks of this region contain much fine material, and the pavements on such fans do in fact rest on thick silt layers. On the other hand, the silt is thicker where the underlying gravel is composed of fragments of easily weathered carbo- nate rocks than where resistant quartzite is its principal constituent; this fact suggests that chemical weather- ing is also a factor. The origin of the vesicular structure of the silt be- neath a pavement is not entirely clear. Thorough wetting apparently destroys the structure; therefore, its occurrence not only under all pavements but throughout the surface layer=of most silty deposits in this region suggests that it forms rapidly after wetting. The openings may contain air or carbon dioxide trapped in the saturated silt by some sort of crust. Perhaps some of the irregular openings resulted from solution and redeposition rather than the entrapment of gas. Nikiforoff (oral commun., 1961) suggested, on the basis of personal observation, that during rains a curtain of moisture descends through the dry silt, trapping air in pockets. On drying, the air is warmed, expands, and rises toward the surface where it is held in by a crust composed of a very thin layer of micaceous mineral flakes. Although on the Shadow Mountain fan are found many typical pavements and abandoned washes, many SHADOW MOUNTAIN FAN 21 areas also occur where the surface of this fan has charateristics both of pavements and of washes. These areas, intermediate between the two types, can be grouped to represent a continuous series of steps in the process of transforming a wash into a pavement. Dissection of a pavement by washes heading on it has apparently gone on hand in hand with its formation. No large "undissected" pavements occur on this fan or elsewhere in the region. Thus the tendency for the surface of an abandoned segment of the fan to be trans- formed into a pavement is opposed by the local runoff, which carves gullies in the surface. In many places the two forces-smoothing and dissection-appear to be in balance. The amount of pavement and underlying silt that creeps down into the wash is balanced against the ability of ephemeral streams to transport this ma- terial down the fan. A pavement, once formed, may persist for a long time. All well-formed pavements, under conditions of this theory, need not have been in existence for the same period of time, nor are the many small pavements on one part of a fan necessarily part of a single once more extensive pavement. For example, the many small pavements on the central part of the Shadow Mountain fan, near locality 453, could have come into existence long after the large pavement on the north edge of the fan. The area of narrow flat-topped ridges separated by ~ deep washes that forms the eastern end of the Shadow Mountain fan is perhaps its oldest segment (p. 22). The gravel beneath this segment, whose western limit is approximately at an altitude of 2,800 feet, is probably slightly older than that beneath the rest of the pave- ment to the west. Dissection of the surrounding parts of the fan has permitted the surface runoff on this seg- ment to carve. deep gullies, thereby greatly decreasing the area of pavement. PEDIMENT Along the northern and southern sides of the fan are small areas of pediment (fig. 6) underlain by Tertiary sandstone and clay and a younger fanglomerate (pl. 1). These weakly cemented but deformed rocks are exposed in shallow gullies and are overlain unconformably by a few feet of gravel, which is not shown on plate 1. The unconformity at the base of the gravel is an erosion surface that bevels the deformed rocks-in other words, a pediment that has been mantled by a younger gravel and has subsequently been dissected. Other areas of pediment not shown on figure 6 are the small outcrops of Tertiary fanglomerate and of Cambrian (?) Quartzite that are situated along the northeast edge of the fan east of locality 4 (pl. 1). 735-932 O-64--4 The two areas of pediment north and south of the fan (fig. 6B) are places where erosion has dominated over deposition to the extent that rocks of early Pleisto- cene(?) and older age are exposed beneath only a few feet of gravel. While on the fan itself extensive bodies of detritus have been deposited, weathered, and eroded, slightly consolidated and tilted beds have been beveled by weathering and erosion in these small areas to either side. These two small segments of the piedmont re- ceive water and sediment from only small drainage areas in the adjacent highland. Even this small amount of runoff has removed all the local detritus and has eroded these weak rocks to the level of the adjacent fan. ORIGIN OF THE SHADOW MOUNTAIN FAN Although detritus from the mountain is transported down the fan and ultimately reaches the toe, the history of any given particle of quartzite from its bedrock source to the toe is clearly not one of continuous move- ment. - Sediment is not now being deposited uniformly over the entire surface, nor can deposition be assumed to have ever been uniform over the entire fan. Instead, the surface of the fan has probably always been a mosaic of pavements and washes. The following discussion attempts to decipher the history of the fan from its present configuration. The relative ages of some parts of the surface of the fan are obvious. The modern washes are the youngest unit; in times of flood they carry water that erodes, transports, and deposits the material on their beds. The abandoned washes are older; they have not been flooded, nor has their bed material been moved for a long time. Many of the pavements are on deposits that are older than the gravel that floors the abandoned washes. Inspection of plate 1 and figure 62 will show three areas of pavement that have the relations common to most pavements; the areas are (1) the large pavement (No. 5d) that extends about 4 miles along the north edge of the fan, (2) the two-pronged pavement near the center of the fan (No. 6d) that extends eastward from the Old Traction Road for about a mile and in- cludes localities 69 and 78, and (3) the oval-shaped pavement (No. 7d) just west of the belt of limestone and dolomite at the foot of Shadow Mountain. The gravels beneath these three pavements were deposited prior to those in the adjacent washes, although the pave- ments themselves may be younger. The gravels of the washes lie in channels cut generally below the pave- ments; in a few places however, as north of locality 78, gravel in a wash laps over the edge of the adjacent pavement. 4 ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA The large pavement along the north edge of the fan appears to be developed on parts of two adjacent fan segments. One segment (No. 8d, fig. 6C) had its apex near that of the modern fan, near locality 424 (pl. 1), and sloped rather steeply northward and westward for a distance of almost a mile to the place where the slope of the existing pavement decreases a little and changes in direction from northwest to slightly south of west. This change in amount and direction of slope is only suggested by the 200:foot contour lines on plate 1; it coincides roughly with the are of a circle passing through locality 440 whose center is at locality 424. When segment 8d was receiving sediment from Shadow Mountain, of course, no gully occurred east of it, as is there today. The second segment of the large pave- ment (No. 5d) had its apex about a mile north of and about 500 feet lower than the first one-that is, at a point about half a mile east of locality 74. This seg- ment sloped westward. The first segment (No. 8d) has its source on a part of the northwest slope of Shadow Mountain (segment 8s), perhaps in a somewhat larger area than now drains to the apex (to loc. 298). The second segment (No. 5d) received its detritus from the hills of quartzite and fanglomerate shown in the north- east corner of the map (segment 5s). The reconstructions (figs. 6B, C) of segments 5d and 8d show an overlap of their source areas, which indi- cates that deposition of segment 8d preceded that of 5d. An age difference between these two segments is reasonable also because the surface of segment 8d now stands much higher above the surrounding washes than does segment 5d and because segment 5d is much more extensive. - Because the area of deposition on a fan is proportional to the source area (fig. 7), the large size of segment 5d suggests that its source area was much larger than that of segment 8d. Within the framework of the existing highlands such a difference can be under- stood only by assuming a diversion of drainage, such as described on page 11. The two-pronged pavement near the center of the fan (No. 6d, fig. 6B) extends eastward from the Old Traction Road nearly to the mountain front. The gravel beneath this pavement was probably derived in part from the northwest face of Shadow Mountain and partly from the gravel of area 8d (fig. 6C). The sedi- ment on which the oval-shaped pavement (No. 7d) formed west of the gap in the belt of carbonate rock probably came from a small area (No. is) on the west slope of Shadow Mountain. $ The four areas of pavement just defined were loci of deposition at some time in the past. Because the extent of deposition in the washes bears a fairly con- stant relation to the size of their source areas, perhaps the size of the four pavements is similarly related to the size of the areas that may have supplied the sediment that underlies them. The size of each of these four segments of pavement and of the possible source areas of the gravel beneath them are given in the following table: Area of pavement segment Source area Pavement segment (fig. 6) (sq mi) (sq mi) 1, 04 1. 92 . 80 1. 22 . 18 . 85 . 28 . 72 A logarithmic plot of these values (fig. 7) shows that they fall near the points for the areas of deposition in the washes (Nos. 1, 2, 3, and 4), suggesting that these pavements were, in fact, once areas of deposition. A part of the history of the Shadow Mountain fan may be reconstructed by an analysis of these four pave- ments; the history started with the deposition of the gravel beneath segment 8d (fig. 6C). This gravel was deposited by a stream heading on the northwest slope of Shadow Mountain. Assume that the stream flowed northward on the east edge of segment 8d in a channel that was below the top of the gravel near the south edge of the segment. A west-flowing stream in a small wash heading in the southern part of the segment eroded its bed to a level below that of the fan-building wash to the east (the small wash is analogous to those that head in pavements). Ultimately the divide of gravel between these two washes was breached, probably by a lateral swing of the larger northward-flowing stream, which was thus diverted westward and cut down; fan segment 8 was thereby abandoned. The west-flowing stream from the mountain cut a gorge through segment 8d (fig. 6C) and began to deposit its load farther downfan in the area of pavement 6d (fig. 6B). At the same time, the gravel beneath pave- ment 5d was laid down by a stream heading in area 5s. Another stream, flowing down the east edge of the abandoned segment 8d carved a valley in the under- lying bedrock, diverting some of the drainage off the quartzite from segment 6d to 5d. Most of the remain- der of segment 8d also drained to segment 5d. Mean- while, the gravel beneath the oval-shaped pavement (No. 7d, fig. 6B) was laid down by a stream that drained a part of the west slope of Shadow Mountain and flowed northwestward through the belt of limestone and dolo- mite. While the alluvian beneath pavements 5d, 6d, and 7d was being laid down, streams in washes heading in re- entrants on the fan between these segments deepened their beds and set the stage for additional diversions of drainage. In time the stream that carried sediment SHADOW MOUNTAIN FAN 23 to 5d was diverted northward into a wash that flowed to the northwest through the hills of fanglomerate that are traversed by the Old Traction Road. In like manner the fan-building washes on segments 6d and d were diverted to the north or to the south. These diversions brought to an end the deposition of gravel in segments 5d, 6d, and d. Weathering and erosion then became the dominant processes on these segments of the fan and transformed an irregular surface of channels and gravel bars into the smooth pavements of the present day. With the close of deposition in segments 5d, 6d, and Td, the modern and abandoned washes became the prin- cipal places of transportation and deposition on the fan. Deposition, however, has not been equal in amount over all the washes but has been concentrated either in areas near the mountain front, such as depositional area 2d (fig. 6A), or downstream from pavements, such as areas 1d, 3d, and 4d. Sedimentation continues at the present time although the amount deposited during perhaps the last few thousand years is small in comparison with the total volume of material now exposed on the fan. Only a short time ago the northwest-trending wash that car- ried the drainage from the hills along the State line was diverted southwestward. Water from these hills now flows in a narrow wash through the eastern part of pavement 5d (fig. 623) to depositional area 1d west of the Old Traction Road. The small areas of exposed pediment on the north and south sides of the Shadow Mountain fan (fig. 6) are now areas where erosion is dominant over deposition. These gravel-capped ridges are probably younger than the gravel beneath the adjacent pavements; at least the uncovering of these buried erosion surfaces was coinci- dent with formation of the adjacent abandoned washes. These pediments may in time be buried again. The pediment along the southern edge of the fan, for ex- ample, is traversed by a very small wash heading in a small area on the bedrock slope to the east. The floor of this small wash is more than 40 feet below the adjacent broad wash to the north and is separated from it by a low ridge of gravel on which is a pavement. At some time in the not too distant future, the stream in the large wash may cut through the gravel ridge, spill over into the small wash, and bury it with many feet of gravel to form a new fan segment. , This partial history of the Shadow Mountain fan does not deal with areas near its toe, because the events just described are conditioned by changes that have taken place on the upper part of the fan or on the adja- cent highlands. The position of the toe is controlled primarily by the level of the alluvium along Carson Slough and is largely unaffected by changes that may have taken place near the apex. The overall size and shape of the Shadow Mountain fan and perhaps, in part, its downfan gradient are dependent primarily on the kind of rock that forms the highlands and the structural history of this part of the Amargosa Valley. Although the highlands clearly owe their elevation primarily to faulting, no convincing evidence exists that faulting has disrupted the fan's surface since deposition of the oldest gravel now exposed on it (beneath pavement 8d, fig. 6C). A gradual rise of as much as 200 feet in the level of Carson Slough would have little effect on the formation of the upper part of the fan because such a change would not. affect either the discharge of the streams in the fan-building washes or the size of their load. However a rise of several hundred feet would obviously cause radical changes on the Shadow Mountain pied- mont. Gradual lowering of the broad flood plain of Carson Slough might lead to deposition of detritus from the mountains along the east side of the plain, thereby moving the position of the toe westward. Carson Slough could lower its bed several tens of feet without noticeable changes taking place on most of Shadow Mountain fan. As a further illustration of the way in which the Shadow Mountain fan has been formed-a sequence of events that is doubtless common to many fans in this region-consider the history of a particle of detritus, from its source in the bedrock of Shadow Mountain to its lodgement at the toe. The particle in question is a boulder of quartzite in the gravel be- neath pavement number 8d at the head of the fan. The boulder was once part of the bedrock on the northwest slope of the mountain. It was produced by weathering on the bedrock slope; it moved down to the wash and ultimately was carried to its present position in seg- ment 8d. Erosion, lowering the surface of the deposit, will in time bring the boulder into the weathered zone where it may break into angular fragments of pebble size that in time may reach the surface as part of the pavement. Creep and wash will move these pebbles to the adjacent narrow gully where flood waters will carry them down a gentle gradient to the end of the pavement near the Old Traction Road and deposit them in area 1d (fig. 64). Here the pebbles may in time weather to still smaller fragments, perhaps once again becoming part of a pavement armor. Ultimately, these small particles may be carried to the toe. The movement of detritus downfan thus takes place during short periods separated by long intervals during which the material is comminuted by weathering. Boulders near the apex are reduced to pebbles and sand before they reach the toe. This change in size from place to place, rather than along a single wash from '.\‘\‘ 24 ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA apex to toe, produces the marked concavity in the longitudinal profile of the fan. Such a concavity is a common feature where boulders are abundant near the apex of a fan but are not carried by floods to the toe. The processes of erosion, transportation, deposition, and weathering are operating on the Shadow Mountain fan, but their intensity varies from place to place. Erosion and sedimentation are dominant in the washes, while weathering is more important in areas of pave- ments. - During the life of the fan, these processes have been in operation at more or less constant rates. The mode of fan formation presented here does not require that these processes were much more active during the last glacial age than they have been since that time. Rather, the location of the places where one or another of these processes are dominant shifts from time to time (Eckis, 1934, p. 101-104). That is not to say that changes in the activity of these processes may not have taken place. Perhaps weathering and erosion were more active during the last glacial age than they have been since that time. Such increased activity may have permitted the transformation of an abandoned wash into a pavement in a shorter period of time than it does at present. But once formed, the pavement will persist for a long time because of the tendency for the processes that produce it to balance the erosive activity of the local runoff that is tending to destroy it. The existence of narrow pavements and washes near part of the toe of the Shadow Mountain fan indicates that the net result of the processes active near that part of the toe has been erosion, not deposition. Such ero- sion is easily explained by assuming a slight lowering of the level of Carson Slough. However, the presence of narrow washes and pavements where the underlying arid-basin sediments are fine-grained and the absence near the southern part of the toe of the fan (pl. 1), where the surface material is entirely gravel, suggests a causal relationship. - Perhaps channels and ridges are the result where streams in the washes are eroding sand and silt, whereas a broad plain is produced where the streams are flowing on gravel (Thomas Maddock, Jr., oral commun., 1960). Where the bank of a wash is composed of gravel, the impinging of the current against the bank may undermine it and cause the peb- bles to fall to the floor of the wash but not move down the fan any great distance. The stream is more effec- tive in eroding the bank of the wash than in moving I I I (7 EXPLANATION # O yx Unweathered gravel on Gravel of desert pavement 100.0 |- floor of modern wash - E Unweathered gravel on floor of meandering l [= wash heading in a pavement = & > levi a E Sample localities 254-260 = E 0 - I Sample localities 263-267 3 - 73 x < x Sample localities 241-248 u J 0 $ ia" ®: xo T. ~ 100|- P 8 < 2 3] 2. 19.0 o :x e a*. ¢ * *o x~ o > g i> o 8 o} w o_ 9g ? 0 s 2 3 un A B 3 a as A0 l O xe! SS] < 0 > i N \I% ~ N \\?féwq s. ‘\\ '% 36°20} EXPLANATION CZ Depositional segment Areas dominantly either pavement or wash, < commonly with slightly cone shaped surface Source area Drainage basin tributary to fan segment, largely hills and mountains Bedrock Tertiary or older, largely hills and mountains -- —<-\_.‘/\,' ) osy Limit of Bat y Swe ~ Death Valley Juncti : $ MILES figure 7. FiGurE 13.-Distribution and source areas of fans near the eastern end of the Funeral Mountains, California. Size measurements of the numbered geomorphic units are listed in the table showing size of depositional segments and of their source areas (p. 26) and are plotted on 27 bo CoO MEAN SIZE, IN MILLIMETERS MEAN SIZE, IN MILLIMETERS ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA 100 T T T T T T = T T T T C ®® ® m 10 |X] Fan north of Funeral Peak = - X § - Fan east of Alkali Flat 4 4 [® K Kq TI LJ a 5 |- Fan southwest of A 8 C .D 3 Deadman Pass < e a 3 Shadow Mountain fan z < { j : { - 21 t t t t Au ~. e .e e 3 H 10|- "s "* ** a o = > & - o o 00 =e 03 o T a .[. Bat Mountain fan ® o ® - 1 | | | | I [ g L P a 0 1 2 3 4 5 6 7 f- a al DISTANCE FROM DIVIDE, IN MILES p: l 1 | 1 | R 0 1 l S 4 5 DISTANCE FROM DIVIDE, IN MILES T T I I I I I I I T I | I 10 © ® Fan southeast of Lila C mine _] E \ in _ M -if... = E: mm a e 3 - 3 C C ® 3 Fan west of Eagle Mountain - & t sal ® [~ hs p 3 t 4 e s tx T + + 0 * Fan northwest of Lila C mine 1 | | | | | | | | 100 [- IL_A__<=_____I_ | J T I T T F / Z a Fan building stream in Virngi-a --------- =- i ~* [ 2 # X x g [O] ® A - © = @ y " X % @ @ x A | * _s "e se t A ~If m ® s 4, Fans on east side of Panamint Range / i y 10 - - - ® A js | | | I | I 1 | | | | | | 1 | | I | | I 0 1 2 3 4 5 6 , 8 9 10 11 12 13 14 DISTANCE FROM DIVIDE, IN MILES FiGURE 14.-Semilogarithmic scatter diagrams showing the relation between the mean size of material on floor of wash and the distance from the divide, at sample sites along fan-building washes in the Death Valley region. For comparison, the median size of bed material at sample sites along East Dry Branch of Middle River, Va., a fan-building stream on the west side of Shenandoah Valley (Hack, 1957) is shown by a dashed line. 735-932 O - 64 - 5 Death Valley Greenwater Valley f Amargosa Valley BAT MOUNTAIN FAN EXPLANATION 29 Sample locality and principal lithologic types comprising the bed material on the surface of the main fan-building washes EAST OF PANAMINT RANGE A % Hanaupah Canyon fan Quartzite, argillite, and granitic rocks Trail Canyon fan Quartzite, argillite, and dolomite WEST OF BLACK MOUNTAINS © A Willow Creek fan Copper Ca Metadiorite, monzonite, and volcanic rocks EAST OF BLACK MOUNTAINS © Johnson Canyon fan Quartzite and argillite nyon fan Sandstone, siltstone, fanglomerate, and metadrorite bed ® Fan north of Funeral Peak Fan southwest of Deadman Pass Monzonite Monzonite EAST OF GREENWATER RANGE + 0 Fan southeast of Lila C mine Volcanic rocks, conglomerate, and sandstone Fan northwest of Lila C mine Volcanic rocks, conglomerate, and sandstone Fan west of Eagle Mountain Volcanic rocks, conglomerate, and sandstone WEST OF SHADOW MOUNTAIN S o Shadow Mountain fan Quartzite and quartzite conglomerate Fan east of Alkali Flat Quartzite and quartzite conglomerate EAST OF FUNERAL MOUNTAINS Bat Mountain fan Dolomite, limestone, quartzite, fanglomerate, and sandstone 30 erosion or pavement formation depend on the spatial relations of mountain and basin-that is, on the struc- tural history-and thus may differ from range to range. FANS EAST OF GREENWATER RANGE ~The volcanic rocks of the Greenwater Range yield a relatively fine grained detritus, which has been depos- ited by east-flowing streams, in the form of a broad piedmont 4-8 miles wide that slopes gently toward the Amargosa River (fig. 1). In comparison with the Bat Mountain and Shadow Mountain fans, previously de- scribed, those fans east of the Greenwater Range are longer from apex to toe and have a finer grained bed material. On no other of the fans studied in the Death Valley region are the pavements more extensive (pl. 3). The fine size of the bed material and the gentle slope may be a function of the bedrock, but the structural history of mountain and basin probably determines the length of the fans and the extent of the areas of pavement. The Greenwater Range from Greenwater Canyon southward to Deadman Pass is made up dominantly of late Tertiary and early Pleistocene volcanic rocks and associated sediments; andesite and basalt, rhyolite and rhyodacite, vitrophyre, tuff, sandstone, and conglomer- ate are the principal lithologic types (Drewes, 1963). The piedmont east of the range is underlain almost exclusively by an unkown thickness of Quaternary deposits-largely bouldery to pebbly gravel, sand, and silt. - The several small outcrops of Tertiary rock in the ~embayment west of the Lila C mine suggest that the embayment may be in part a pediment thinly veneered with gravel. The piedmont has a gentle slope, from about 250 feet per mile near the mountain front to less than 100 feet per mile near the Amargosa River. Estimates of mean size and of slope were made at sample localities (pl. 3) along three washes from the crest of the Greenwater Range to the Amargosa River (table 7). Both within the range and on the piedmont; the slope of these washes is virtually constant for long distances (fig. 3), and the mean size of the material on the surface is small and decreases downwash at a low rate (fig. 14). The ex- tensive areas of desert pavement show that on much of the surface of the piedmont, weathering and erosion are the dominant processes. The pavements resemble those on the Shadow Mountain fan, except that the coating of varnish on the stones is darker and the silty layer be- neath the pavement is thicker-about 10 inches in some places. Boulders resting on an otherwise smooth sur- face are characteristic of the pavements east of the Greenwater Range (fig. 15). « ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA Ficurs 15.-Desert pavement on gravel derived from volcanic rocks of the Greenwater Range. The desert shrubs beyond the man are along a wash. The view is northward toward the east end of the Funeral Mountains from a point about 2 miles north of Lila C mine (loc. 133, pl. 3). The slope is eastward at about 140 feet per mile. The esti- mated mean size of the stones forming the pavement is about 10 mm. Only three segments of wash on the piedmont have slightly cone-shaped surfaces, a fact suggesting that they are areas of deposition. However, the several large areas of pavement are also slightly cone shaped surfaces, a fact suggesting that they too were once areas of deposition. The extent of these pavements and seg- ments of wash and the location of the source areas that may have supplied the gravel of which they are com- posed are shown on figure 16, and their extent is given in the following table (these measurements are dis- cussed on page 38) : Size of depositional segments and of their source areas on the east side of the Greenwater Range Depositional segment Source area Segment (fig. 16) (sq mi) (sq mi) [SSSR aes aet ad enane. ae 0. 90 3. 88 B «rosen ble tke seo cen babi nere ale 1. 41 4. 04 O rcs! - susan s tak sinh ae ae dens 3. 34 9. 46 IJ. panes Peed a uk akan aan oar on 3. 70 6. 50 ArE .oo. be ue aces ae cain 2. 43 6. 14 6s r ra ce nna ok ani ooe an an aeebak 1. 27 1. 00 a rac ak due c akin ae sae an en ne abl 1. 08 1. 05 $A cone ean ou Loc eeu cid 2. 20 6. 99 Although the overall configuration of the piedmont is related to the structural history, the location of pave- ment and wash near the mountain front is the result of diversions of drainage similar to those that have taken place on the Shadow Mountain fan. On figure 16, for example, fan segment 3 appears to have been deposited by the stream that had previously built fan segment 8, and fan segment 4, where material is now being de- posited, came into being when drainage was diverted northward from segment 3. - Near.the Amargosa River, on the other hand, the extensive pavements doubtless owe their formation to downcutting by the river. FANS EAST OF GREENWATER RANGE The fans west of the river are about 2 miles longer and slope more gently than the Shadow Mountain fan to the east (fig. 3) ; perhaps these differences are entirely due to an eastward tilting of the valley, which is clearly the explanation for a similar contrast between the east and west sides of Death Valley. On the other hand, the differences in lithology and in size of fragments be- tween the Amargosa Valley fans may account for the 116°30' 31 asymmetry of the valley-a short fan having markedly concave-upward profile on the east side of the valley and a long slightly concave profile on the west. The Shad- ow Mountain fan east of the Amargosa River is built of bouldery material, and its profiles is markedly con- cave. This concavity, as mentioned on page 23, may be due to the bouldery detritus from the quartzite moun- tain ; the detritus is deposited high up on the piedmont 116°25" RYAN QUADRANGLE ASH MEADOWS QUADRANGLE y159 \ 36°15" ci, <{ALKALI FLAT \y 9 a? a ‘_/ ,,{1é‘fl'\g S xe - 9 §: l, J/f sa oe. . 1 2 ~A J I Pa /> & f -2 / \ N" f", / ’}‘ - } A rat 54: "uy oy 13 . /A’2322 / / b > > % 36°10' ¢ - : P FUNERAL PEAK QUADRANGLE EAGLE MOUNTAIN QUADRANGLE 3 EXPLANATION & cz» Depositional segment Area dominantly either pavement or wash; commonly with slightly fan-shaped surface --"*~~ ye a } s Sut "s / Drainage basin tributary to deposi- tional segments; largely hills and mountains Numbers refer to related fan segment x15 Sample locality 2 MILES ] |- i- FIGURE 16.-Map of the piedmont east of the Greenwater Range showing depositional segments and related drainage basins in adjacent mountains. Related segments and basins as shown by the same number. 32 ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA and does not move farther downfan until it is com- minuted by weathering. The contrasted fans adjacent to the Greenwater Range west of the river are composed of pebbly material including cobbles of vesicular vol- canic rocks; the low density of the rocks doubtless per- mits their transport a longer distance downfan than that of the quartzite cobbles on the opposite side of the river. FANS IN GREENWATER VALLEY Two fan-shaped segments of piedmont mantled by detritus from hills composed of granitic rocks were investigated in Greenwater Valley (fig. 1). These round-topped hills, in common with many other areas of granitic rocks in the Southwestern United States, have a high drainage density-many closely spaced washes-and are partly mantled by gruss (Sharp, 1954, p. 7). The longitudinal profile of one of the segments is nearly straight, whereas that of the other is marked concave upward. Both are floored with fine-grained debris (table 7). The floor of Greenwater Valley ranges between 3,500 and 4,000 feet in altitude and has a luxuriant growth of desert shrubs. The valley is asymmetric; the axial wash runs close to the base of Greenwater Range (pl. 4) and, to the west, a piedmont mantled by Quaternary gravel and sand extends 2-3 miles into an embayed mountain front. The Black Mountains tower more than 6,000 feet above the floor of Death Valley (fig. 1), whereas Greenwater Valley, east of the mountains, lies only about 2,000 feet below their summit. One of the two washes studied has a steep slope and a long narrow drainage basin in an area of monzonite north of Funeral Peak (fig. 3; locs. 41-36, pl. 4). The wash can be traced for about half a mile east of the mountain front (to loc. 35), where it is lost on a slightly cone shaped segment of the piedmont (segment M, pl. 4) that is grooved by many small and discontinuous washes only a few feet in depth and width. The size of material in the wash changes little, except near the toe (fig. 14). The second wash, southwest of Deadman Pass (pl. 3), rises in low hills composed of monzonite surrounded on three sides by a sloping piedmont under- lain by Quaternary gravel and sand. The longitudinal profile of the fan shows a pronounced concavity, and the material underlying it decreases in size toward the toe. Near the apex, the wash is incised and slopes more steeply (between locs. 9 and 8) than farther south, where no individual channel is continuous. The wash north of Funeral Peak owes its steepness perhaps to an eastward tilting of the Black Mountains that may be still in progress (Drewes, 1963). In plate 4, depositional segment M and a part of the larger area of pavement just to the south, labeled segment N, have cone-shaped surfaces, a fact suggesting that the gravels beneath them are segments of fans that had their sources in the granitic and volcanic rocks north of the peak. The size of these two segments and of their source areas are given in the following table: Size of depositional segments and of their source areas on east side of Black Mountains Depositional segment Source area Segment (pl. 4) (sq mi) (sq mi) r pel ieee ane o 2. 38 1. 49 Neues aap ee ee bie on e aan an ae 1.16 . 94 Both segments are slightly larger than most other fans or fan segments having a comparable source area (fig. 7). Perhaps the deposits on the surface of these segments are veneers over broad pediments. (See p. 38.) Several small bedrock hills rising above the piedmont northeast of Funeral Peak also suggest that the alluvial cover is thin. The decrease in grain size and the pronounced up- ward concavity in longitudinal profile of the fan south- west of Deadman Pass are related to the spatial rela- tions of this fan. The fan is compound. Near the apex it receives sediment from only a small area in the ad- jacent hills, but the lower part of the fan, which has no continuous channel, is part of a broad piedmont whose source includes a much larger segment of the Greenwater Range. This difference in size of source area between those of sample localities 8 and 7 results in a marked decrease in slope and in size of material. DEATH VALLEY FANS The Death Valley fans clearly show how continuing structural deformation influences the size of the indi- vidual fan or of an entire piedmont. Death Valley is bounded by high mountains (fig. 1) and, in the area near Badwater, is asymmetric. The precipitous west front of the Black Mountains is fringed by small semicircular fans, which contrast with the broad apron of coalescing fans that spreads eastward from the base of the Pana- mint Range. The Black Mountains (pl. 4) are built of sedimentary, igneous, and metamorphic rocks, and their dominant structural feature is a fault zone at the west front of the range. The mountains have been elevated several thousand feet relative to the valley floor; per- haps more than 100 feet of the displacement has taken place during the last few thousand years. The surface of the fans west of the mountains consists of modern or abandoned washes and of a few small ribbon-shaped areas of desert pavement. The size of 12 fans between Badwater and Mormon Point and the extent of their source areas are presented in table 5. Copper Canyon has a straight and steep gradient from divide to mountain front (fig. 3), where the DEATH VALLEY FANS 33 TaBLs 5.-Size of fans or depositional segments in Death Valley and of their source areas in the Black Mountains and the Pana- mint Range Fan or fan Fan or fan segment (Letters refer to pls. 4 and 5) segment Source area washes only (sq mi) Eastside: (sq mi) uaa Cents sean ne win 0. 26 2. 28 Belle ilia snene . 88 2.28 Orie a ee er ala ec ; 23 1. 50 D rl NNUAL I rs 198 2, 87 Bice dee c aan ea £ & 42 1.13 Coffin Canyon (F)____.. R . 41 1.47 Copper Canyon (G).-__.. hex 2. 08 22. 26 Sheep Canyon (H).-.----.. £ . 82 10. 60 Willow Creek (J)..<-.......sg1.° . 38 22. 35 Keel Neder agent tea areas ss A2 1. 65 Dred nece deen na bie uis ae as 18 2. 13 West side: Trail Canyon (0).-...._._-....... 8. 33 23. 76 Death Valley Canyon (P)-_____---. 3. 92 11. 76 3 ______________________________ 2. 12 5. 94 anaupah Canyon (R)-_____----.- 6. 65 25. 68 erie ees Np aaa cleanse nee 5. 04 8. 37 Starvation Canyon (T).___.____... 4. 99 19. 48 Johnson Canyon (U)...___.._._... 8.17 17. 88 Six Spring Canyon (V)___.___----.- 4, 24 19. 03 ephermeral stream has built a symmetrical fan with a radius of a little more than a mile (table 2). The local relief on the fan is only a few feet except near the apex, where a small terrace underlain by weathered gravel rises 10 feet above the canyon floor. The upper half of Willow Creek flows down a gentle slope within capacious Gold Valley, which is carved in granitic rocks. To the west beyond Willow Spring, the creek enters a deep canyon and descends over several dry falls to emerge on a small fan (table 2).. The Willow Creek fan (Segment J, pl. 4) is cut by low fault scarps that displace both unweathered gravel and desert pave- ment. - Measurements of the size of bed material were made along Copper Canyon, Willow Creek, and on their fans. The lofty Panamint Range, whose crest lies between altitudes of 9,000 and 11,000 feet, is composed of sedi- mentary and metasedimentary rocks of late Precam- brian and early Paleozoic ages and, near Telescope Peak, of granitic rocks. Alluvial fans 3-6 miles long (pl. 5 and table 2) form the piedmont east of the range from Trail Canyon southward to Six Spring Canyon. In the mountains the floors of the main washes are sev- eral hundred feet wide along their lower courses and, at their mouths, are as much as 200 feet below the surface of the fan. These high banks commonly persist down- fan and gradually decrease in height over a distance equal to one-half or two-thirds of the fan's radius. The piedmont east of the Panamint Range is under- lain by alluvial deposits of Pleistocene age that are divided into three geomorphic units on plate 5: un- weathered gravel in the modern washes, varnished gravel in the abandoned washes, and weathered gravel generally forming a desert pavement. Pavements cover from one-quarter to two-thirds of the piedmont (table 2) and, near the mountain front, cap mesas that rise as much as 200 feet above the modern washes. Both the modern and abandoned washes are cut in the older gravel and are floored with similar material. Gravel is now deposited on only small parts of the fans (table 2), chiefly near their toes, and is finer grained than the varnished gravel in the abandoned washes. Historical and archaeological evidence gathered by A. P. Hunt (1960) and' by C. B. Hunt (written commun., 1960) indicate that only a small amount of material has been moved down the Death Valley fans during the Recent epoch. These workers believed that the varnished gravel dates from a pluvial period that immediately preceded the Christian era or from a still earlier period. Trail Canyon fan, the smallest of the Panamint Range fans studied in the field, has about three-quarters of its surface covered by either modern or abandoned washes (table 2), and the flat-bottomed canyon at its head is more than 500 feet wide throughout its lower 31/, miles. The chief lithologic types either in the fan gravel or exposed in the source area are quartzite, argil- lite, and dolomite, but, in addition, granitic rocks are present near the headwaters. The surface of the Hanaupah Canyon fan is about equally divided between wash and pavement (table 2). The canyon heads on the east slope of Telescope Peak, the highest point on the Panamint Range, and the fan is built chiefly of fragments of quartzite and argillite and a subordinate amount of granitic material. The main wash leaves the mountains as a channel nearly 1,000 feet wide whose banks decrease in height from almost 200 feet near the apex to only a few feet in the middle of the fan (pl. 5; fig. 17). Elongate areas of desert pavement extend from near the apex of the fan to a point about four-fifths of the distance to the toe; areas north of the main wash end in an east-facing fault scarp about 50 feet high. Desert pavement mantles three-fifths of the surface of the fan at the mouth of Johnson Canyon; the rest, chiefly in the northern part and near the toe, is about equally divided between modern and abandoned washes. The fan gravels are composed largely of fragments of quartzite, argillite, and dolomite. The broad gravel-floored washes that head in the Panamint Range have smooth longitudinal profiles that are slightly concave upward (fig. 3). No change in gradient occurs at the mountain front or at the head of the fan-shaped areas of modern or abandoned washes (pl. 5). Although the washes are hundreds of feet wide in their lower courses, they are not wider in pro- portion to the size of their catchment areas than are 34 - : ALLUVIAL FANS IN THE FiGURE 17.-Aerial photograph of the Hanaupah Canyon fan on the west side of Death Valley. For location, see outline on plate 5. of desert pavement. other washes in this region (fig. 18). The material on their beds is coarse grained (fig. 14) and is comparable in size only with that near the apex of the fans west of Shadow Mountain (fig. 19). The rate of decrease in size downfan is small; this low rate of decrease is equaled only by that in the washes east of Greenwater Range and in the wash north of Funeral Peak. The large areas of pavement on the Panamint Range: piedmont are cone-shaped surfaces that were probably inherited from the original depositional form of the gravels that underlie them. - Some time ago the streams in the fan-building washes were diverted from these areas into new channels The streams in the new washes cut down, abandoning the old depositional seg- ments, which have since been transformed into pave- ments. Changes of this sort have occurred on many parts of the piedmont. The pavements on the Ha- naupah Canyon fan are described in the following para- graphs to illustrate these changes. Note the meandering washes heading in areas Inspection of plate 5 shows that about halfway down the Hanaupah Canyon fan, near locality 6, is the apex of a fan-shaped area of washes that extends to the edge of the saltpan and, in the following discussion, is called the "modern fan." The modern fan has a slightly cone-shaped surface and is the place where deposition has gone on during the last few thousand years. The reader will find that the form of the modern fan is well shown by the topographic map of the Bennetts Well quadrangle, California, published by the U.S. Geologi- cal Survey. North of the main wash, a segment of pave- ment, labeled Z (pl. 5), has its apex near locality 8, and another such segment of pavement south of the main wash, shown as Y, has an apex near locality 51. The arithmetic plot on figure 20 shows that the eastward slope of segment Z is slightly less than that of segment Y and that both are a little steeper than the modern fan. DEATH VALLEY FANS 35 CEL ETI I fe f TFT TAI I I I f TAT I od EXPLANATION Sample locality and principal lithologic types comprising the bed material on the surface of the main fan-building washes EAST OF PANAMINT RANGE A X © s. Trail Canyon fan _ Hanaupah Canyon fan Johnson Canyon fan Al Quartzite, argillite, Quartzite, argillite, and Quartzite and argillite $ and dolomite granitic rocks £ 1 WEST OF BLACK MOUNTAINS & C Willow Creek wash in Gold Valley Metadiorite, monzonite, and volcanic rocks EAST OF BLACK MOUNTAINS f E1!" $ fe. K & 10,000 |- g 'l Wash north of Funeral Peak - E- O L Monzonite ran EZ if [EAST OF GREENWATER RANGE WEST OF SHADOW MOUNTAIN g S C < ‘>u ® o ¥ X -| -- A e gofi Fan west of Eagle Mountain Fan east of Alkali Flat \- © Volcanic rocks, conglomerate, Quartzite and quartzite img E C and sandstone conglomerate §x [m & i : A j © X W- 1000|- Floodplain of Little River, = [- Va., in mountains x t f- X & 3 X Z F E T fa) -- c Fal - C w Ma te 3 Pa [e] 7 - 100|- 2 - z (+ 3 o - M - C O 10 T -l (dal 0.01 0.1 1.0 DRAINAGE AREA, IN SQUARE MILES FIGURE 18.-Logarithmic scatter diagram showing the relation between width of wash and drainage area at sample sites along seven washes in the Death Valley region. Lines representing generalizations from similar data for channels in N. Mex. Miller, 1958) and in the Appalachian region (Hack, 1957 ; Hack and Goodlett, 1960) are shown for comparison. (Leopold and Miller, 1956 ; 36 MEAN SIZE, IN MILLIMETERS ALLUVIAL FANS IN THE DEATH VALLEY REGION , CALIFORNIA AND NEVADA 100 T T T T T 3 A99 I I & x . [> #3 € 0] Hanaupah Canyon C2 - i A® % |- ® Johnson Canyon _ __| [ s North of Funeral Peak 33 A Trail Canyon = 10 - A ~ K 4 [c) Copper Canyon - - A Fik I [- 'A AR [- o xs l [~ (G A ag t 4 r— Southwest of - Willow Creek 3 Deadman Pass - ~I1- td ~ f C _1 3 1 1 | | | | | 3 | | 100|- t { I T | 73 2100 I $ S k- - up T - - i - -- C |- -| a -|- - - ~I Z I" = i East of Alkali Flat ~ S £ g 3 Lo r f- 3 M ® » Bat Mountain 10 |-- *~ 10k. - - 3 - @ _o re fia— w West of Eagle Mountain im [~ = \- 22 s? ~~ P i an - Shadow Mountain a~~-. 4 |- Ma l --I 0 1 2 3 4 5 0 1 2 S DISTANCE FROM APEX, IN MILES DISTANCE FROM APEX, IN MILES EXPLANATION Sample locality and principal lithologic types comprising the bed material on the surface of the main fan-building washes ( EAST OF PANAMINT RANGE ( EAST OF GREENWATER RANGE A x ® Trail Canyon fan Hanaupah Canyon fan Johnson Canyon fan Fan west of Eagle Mountain Quartzite, argillite, Quartzite, argillite, and Quartzite and argillite Volcanic rocks, conglomerate, E and dolomite grantic rocks and sandstone 6 # al g WEST OF BLACK MOUNTAINS % WEST OF SHADOW MOUNTAIN ® > & @ A g C o 0 Willow Creek fan Copper Canyon fan & Shadow Mountain fan Fan east of Alkali Flat Metadiorite, monzonite, and Sandstone, siltstone, fanglomerate, g Quartzite and quartzite Quartzite and quartzite C volcanic rocks and metadiorite . conglomerate conglomerate 93 ( EAST OF BLACK MOUNTAINS EAST OF FUNERAL MOUNTAINS $5 § E I ® % & Wash north of Funeral Peak Fan southwest of Deadman Pass Bat Mountain fan Monzonite Monzonite Dolomite, limestone, quartzite, C fanglomerate, and sandstone FicUrE 19.-Semilogarithmic scatter diagram showing the relation between the mean size of material on the surface of the wash and the distance from the apex at sample sites on 11 fans. The apexes of the fans are at the mountain front. Lines, drawn by inspection, show depositional areas where a wash has the form of the segment of a very low cone-commonly the areas where wash is wide. Sm ennis ws 2" 20 DEATH VALLEY FANS 3° These two pavement segments on the Hanaupah Can- yon fan are old; when they were the loci of deposition, the modern fan was not in existence. Pavement Y has a steeeper slope and is more deeply dissected than pavement Z a fact suggesting that the gravel beneath Y is perhaps older than that below Z, The two gravels, however, could be parts of the same fan, be- cause the area of the modern fan is about equal to that of pavement segment Y plus segment Z. The gravels 600 | | | EXPLANATION Pavement segment Z © fo Pavement segment Y € © Modern fan Fan-shaped area of washes with apex at locality 6 500 |- ea O O] X X O] [0] X bre © e © < X 3 o X X X a i- & ] 6 le % X < bad ul a. 0 +d in € 300 r—— Teal © | | | 200 1 5 § A DISTANCE FROM UPFAN END OF PAVEMENT SEGMENTS OR OF MODERN FAN, IN MILES FicurE 20.-Slope of pavement segments and of a part of the main wash on the Hanaupah Canyon fan. Locality 6 is at the apex of a fan-shaped area of washes-the modern fan-that extends to the edge of the saltpan. Pavement segments Y and Z are shown on plate 5. Arithmetic scatter diagram showing the relation between slope and distance from upfan end of pavement segments or of the modern fan. under the pavements pass downfan beneath the gravels of the adjacent washes. Presumably the toe of the old gravel fan is now buried at an altitude lower than the surface of the saltpan, but whether it is east or west of the toe of the modern fan is unknown. Pavement segments Y and Z perhaps include most of the area of an earlier fan whose toe was about half a mile west of the toe of the modern one. At the toe of Starvation Canyon fan, however, weathered boulder gravel of Quaternary age exposed in a small fault block (C. B. Hunt, written commun., 1960) is part of an ancient fan that must have extended further eastward than the edge of the saltpan. The contrast between the east and west sides of Death Valley reflects, in large part, its structural his- tory and is influenced to only a small extent by the difference in altitude between the two opposing high- lands. The Black Mountain fans are small in com- parison with those west of Death Valley and even with all the other fans studied (fig. 7). Copper Canyon fan, for example, with an area of about 2 square miles, would have to be about three times its present size to bring it in accord with other fans in this region. On figure 7, the average trend line of the graph lies above the point that represents the Copper Canyon fan. Dur- ing the Quaternary period, the floor of Death Valley was depressed relative to the west front of the Black Mountains and tilted eastward (C. B. Hunt, written commun., 1960). This deformation lowered the Black Mountain fans and caused most of the sedimentation on the saltpan to be localized along its eastern edge at the foot of the mountains. The surface of the saltpan has risen faster than the surface of the Black Mountain fans. Deformation and eastward tilting of the Black Mountains themselves are suggested by the steep east- erly slope of their piedmont in Greenwater Valley (p. 30). The mouths of the canyons in the Panamint Range have been the sites alternately of erosion and of deposition. After the mouths of the canyons were eroded at least to their present depth, they were filled with gravel to a height 200 feet above their present floors. It is reasonable to suppose that the greater rainfall intercepted by the lofty Panamint Range results in more frequent flooding and more rapid erosion or deposition on its fans. From this supposition we might infer that the fans east of the range should be exceptionally large ones. However, the areal extent of the washes on the piedmont east of the range compared with that of their source areas (fig. 7) follows the general relation for all fans in the region. The areas of these washes is 38 ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA proportional to the size of their source areas. The entire piedmont east of the range has probably never been at one time an area of wash but has always in- cluded large areas of pavement. This probability is supported by data shown on figure 7. When the total areas-pavement plus wash (table 2)-of the Trail Canyon, Hanaupah Canyon, and Johnson Canyon fans are plotted on the graph, these points fall well above the general line, and slightly above the field:-of scatter of all other points. CHARACTERISTICS OF FANS SIZE AND RELATION TO PEDIMENTS The size of an alluvial fan is related to the size of the source area. The description of the several fans presented in the first part of this paper has shown that if values for the area of a fan or of the area of deposi- tion on a fan is plotted on a logarithmic graph against the size of the drainage area above the apex, the field of scatter of many of the points (fig. 7) is restricted ; a line can be drawn through the points by inspection and may be expressed by the relation Af=0.5 Am**, which states that the size of a fan or fan segment is equal to half of the eight tenths power of the size of its source area. This graph includes values for fans of varying size and material-from the small fans ringing the isolated hills near Devils Hole to the Trail Canyon fan having an area of 8 square miles-and clearly rep- resents a valid relation. Nevertheless the data are not precise, and it is perhaps more meaningful to say that in the Death Valley region the area of deposition on a fan is roughly one-third to one-half that of its source area in the desert mountain. This relation, however, does not hold if the entire fan or entire piedmont is considered and either one in- cludes extensive areas of desert pavement. Values for several entire piedmonts are also plotted on figure 7, and the points lie well above the trend line. The ex- planation for this divergence appears to lie partly in the structural history of mountain and basin and partly in drainage changes. On the large piedmont east of the Panamint Range, for example, the local runoff carves lowlands in part of a fan while deposition takes place on a higher segment near by. Drainage diversions cause the stream in the fan-building wash to leave the higher segment and flow down into the lowland incising a channel across the breached divide and depositing sedi- ment in the lowland. Thus the loci of deposition shift whereas, on the contrary, the size of the area of deposi- tion remains the same. The fans west of the Black Mountains, on the other hand, are notably small in relation to the size of their source regions (fig. 7). These fans do not follow the equilibrium relation of size to source area that is gen- eral for fans in the Death Valley region. Clearly this lack of adjustment is related to the recent eastward tilt- ing of the floor of Death Valley and the resultant over- lap of the playa beds onto the fans (C. B. Hunt, written communication, 1960). This evidence does not neces- sarily imply, however, that the volume of fan debris at the base of the Black Mountains is of a smaller order of magnitude than the debris which underlies the fans on the west side of the valley. A large volume of fan debris from the Black Mountains may lie beneath the valley floor. The arrangement on the graph of sizes of the fans west of the Black Mountains from Badwater south to Copper Canyon (fans A to G in fig. 7 and pl. 4) is not haphazard but is orderly, a fact suggesting that these fans follow a different equilibrium relation of size to source area than is represented by the other fans stud- ied. Inspection of figure 7 shows that these seven fans are roughly equal to one-tenth the size of their source areas in the Black Mountains (4f=0.1 Am**). These fan-building washes, therefore, are maintained in some sort of equilibrium with their surroundings in spite of continuing deformation. A third example is the entire Shadow Mountain fan, which is about three times larger in proportion to its source area than called for by the general relation. Only the valves for the many depositional segments of which the fan is composed plot close to the trend line shown on figure 7. On many piedmonts distinguishing alluvial fans from pediments either by field observation or from map study is difficult at best. -It would be of considerable practical value if one could distinguish a fan underlain by many hundreds of feet of alluvium from a pediment thinly veneered with gravel. Conical segments of the allu- vial fans that have been studied show a consistent rela- tion between size of depositional segment and extent of source area. This relation implies that all conical segments are in fact depositional and, therefore, that a piedmont made up largely of conical segments is a con- structional landform. - Such a generalization should be used with caution, but in its support, note that the Panamint Range piedmont, clearly built up of thick CHARACTERISTICS OF FANS 39 alluvial deposits, consists of cone-shaped segments of pavement and of wash. Only parts of the Shadow Mountain fan, on the other hand, are cone shaped, and a considerable part of its surface (pl. 1) is either a more or less sloping plain or actually scoop shaped. The same is true also of the fans that slope southwestward from the Funeral Moun- tains (fig. 1) near Chloride Cliff to the north end of the saltpan (C. B. Hunt, written commun., 1960). Whether or not these scoop-shaped areas are pediments cannot be answered with certainty. On the Shadow Mountain fan, however, the pavements near the toe and the small segments of pediment along its north and south borders are areas where erosion has dominated over deposition in the recent past. It is not unreason- able, therefore, to suppose that the gravels that now crop out on the western half of the fan are not more than a few tens of feet thick, whereas to the east the thickness may reach several hundred feet. The total area of the Bat Mountain fan (fig. 13) and of the fan-shaped segment of the piedmont traversed by the wash north of Funeral Peak (segment M, pl. 4) is several times larger than that indicated by the gen- eral relation of fan area to source area (fig. 7). Per- haps parts of these two fans are actually veneers on a pediment, for small bedrock hills rise within them and suggest that the alluvium is thin. In regions where the mountains are small relative to their piedmonts, as in southeastern Arizona, the areas demonstrable as pediment are much larger in propor- tion to the areas that drain to them than are the Death Valley fans (Tuan, 1959, fig. 47). At best, once a con- siderable number of observations on the relation of area of fan to source area are available for a given re- gion, a plot of size of fan against size of drainage area, such as figure 7, may aid in guessing which segments of a piedmont are fan and which are buried pediment. FAN-BUILDING WASHES The desert washes, both modern and abandoned, are broad, flat-floored troughs with or without distinct banks and consist of channels and gravel bars. They are generally steeper and wider than stream channels in humid regions; these differences are related perhaps to the regimen of the ephemeral streams and the absence of a protective blanket of vegetation. The material on the floor of the desert washes is finer grained than that on the beds of perennial-streams, but the actual sizes pres- ent depend primarily on the local geology. The slopes of the larger washes in desert mountains- those having drainage areas greater than about 1 square mile-are generally steeper than stream chan- nels in humid regions, although both commonly have concave-upward longitudinal profiles and, along both, the slope decreases with increasing drainage area, as is illustrated by the diagram on figure 21. If drainage area is a factor directly affecting discharge, then this diagram shows that at the same discharge, the slope of a desert wash in the mountains is steeper than that of stream channels in more humid regions, perhaps because water is lost by evaporation and by flow into the gravel beneath the bed of the desert wash. Although most desert washes are wider than are stream channels in humid regions, both increase in width in a downstream direction at roughly the same rate as drainage area increases (fig. 18). Many of the desert washes vary widely in width with little or no corresponding change in slope (fig. 22), but where a stream channel has the same width as a desert wash, the gradient of the perennial stream is much lower. This apparent greater width of the desert washes may be related to the nature of their banks. The stabilizing effect of vegetation is absent and perhaps in a desert wash, as mentioned on page 24, gravel banks are more easily eroded than are those built of finer materials. The difference in width between channels in humid and those in arid regions, however, may be more appar- ent than real because most washes whose widths are represented in these diagrams actually consist of several braided channels separated by gravel bars. Because we do not know which part of the floor of a wash was covered with water at any one time, the width of a wash is possibly more comparable to flood-plain width in a humid region than to channel width. For exam- ple, the flood plain of the Little River in the mountains west of the Shenandoah Valley, Va. (Hack and Good- lett, 1960) has widths and slopes that are comparable to those of washes in the California desert (figs. 18 and 22). This segment of the Little River flood plain in- cludes both bare channels and forested areas and forms the entire floor of a narrow valley in the mountains. The material on the surface of the fan-building washes ranges in size from boulders to clay, but the amount of silt or finer sediment is small. The range in esti- mated mean size for 115 samples of material at sites on the surface of washes from headwaters to toe of fan, is shown as a cumulative curve on figure 23. The mean value for all samples is 8.5 mm (table 6). No estimates ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA I CSF I TT TEETH I FET FFH I Fs T AH EXPLANATION Sample locality and principal lithologic types comprising the bed material on the surface of the main fan-building washes EAST OF PANAMINT RANGE A X © Trail Canyon fan - Hanaupah Canyon fan Johnson Canyon fan _q>_>' Quartzite, argillite, Quartzite, argillite, and Quartzite and argillite E and dolomite granitic rocks £ © & WEST OF BLACK MOUNTAINS ~ ~a A Willow Creek fan Copper Canyon fan Metadiorite, monzonite, and _ Sandstone, siltstone, fanglomerate, volcanic rocks and metadiorite EAST OF BLACK MOUNTAINS H Wash north of Funeral Peak Monzonite Greenwater Valley EAST OF GREENWATER RANGE ® & Fan southeast of Lila C mine _ Fan west of Eagle Mountain eal ® 10,000 |- 3 Volcanic rocks, conglomerate, Volcanic rocks, conglomerate, - [c > and sandstone and sandstone s |- g wel 58 C WEST OF SHADOW MOUNTAIN ~I - § k O hk 5 R i ba < Shadow Mountain fan Fan east of Alkali Flat C Quartzite and quartzite Quartzite and quartzite -- conglomerate conglomerate T [m] m OQ [m I 1000 FFEL! I elev SLOPE, IN FEET PER MILE 100 1 1 | | 0 10.0 100.0 10 £_s J: Cu -t T 1 1-1 £51 T C1 "J 1 14 | 0.01 0.1 1: DRAINAGE AREA, IN SQUARE MILES FIGURE 21.-Logarithmic scatter diagram showing the relation between slope and drainage area at sample sites along 10 washes in the mountains of the Death Valley region. For comparison, lines on the diagram show the generalized slope-drainage area relation for stream channels in other regions. Those in Maryland and Virginia are from Hack (1957, fig. 16) ; those in the Sangre de Cristo Range, N. Mex., are based on data collected by Miller (1958, fig. 20), and those for ephemeral streams in the Rio Grande Valley are from Leopold and Miller (1956, fig. 24). CHARACTERISTICS OF FANS 41 de Cristo Range, N. Mex. 1000 Willow Creek in f _ Gold Valley Ephemeral streams in Rio Grande Valley, N. Mex. SLOPE OF WASH OR CHANNEL, IN FEET PER MILE I L =t 44 I T F SHEET I mann tar I I EXPLANATION Sample locality and principal lithologic types comprising the bed material on the surface of the main fan-building washes EAST OF PANAMINT RANGE A X © m Trail Canyon fan _ Hanaupah Canyon fan _ Johnson Canyon fan = Quartzite, argillite, Quarry/e», argillite, and Quartzite and argillite > and dolomite granitic rocks é WEST OF BLACK MOUNTAINS 3 g] a Willow Creek wash in Gold Valley Metadiorite, monzonite, and volcanic rocks 5 EAST OF BLACK MOUNTAINS 6 » $s a $S Wash north of Funeral Peak East of Alkali Flat & Monzonite , - g EAST OF GREENWATER RANGE WEST OF SHADOW MOUNTAIN 7 $2 o fe. fol Fan west of Eagle Mountain Fan east of Alkali Flat 2 Perennial streams in Sangre o g > Volcanic rocks, conglomerate, Quartzite and quartzite and sandstone conglomerate A X & aA ye Trail Canyon O] C Hanaupah Canyon HC C E] Johnson Canyon H Wash north of Funeral Peak Floodplain of Little River, 100 |- Va., in mountains 3 [> Gillis Falls, Md. x L Calfpasture River, Va. H 10 1 I1 124 [4 1 | I E ofc L -L LLL l L504 CJCL 1.0 100 1000 10,000 WIDTH OF WASH OR CHANNEL, IN FEET FIGURE 22.-Logarithmic scatter diagram showing the relation between slope and width at sample sites along seven washes in the Death Valley region. Lines representing generalizations from similar data for channels in N. Mex. (Leopold and Miller, 1956; Miller, 1958) and in the Appalachian region (Hack, 1957 ; Hack and Goodlett, 1960) are shown for comparison. TaBus 6.-Particle size and sorting coefficients for bed material from various regions [All samples were selected by use of a grid. Values for the Appalachian region are from Hack (1957, table 8); values for the Southern Rocky Mountain region are from Miller (1958, tables 15-18)] Mean diameter Trask sorting coefficient (millimeters) Region Mean | Mini- | Maxi- | Mean | Mini- | Maxi- ofall | mum | mum | ofall | mum | mum samples| value | value |samples| value | value Death Valley.. 8.5 2.4 74.0 1.9 1.25 4.00 Appalachian... 147.0 5.0 | 630.0 1.95 1.1 21.0 Southern Rocky 105.0 48.0 | 312.0 1.6 1.20 2.05 1 Median diameter. were made of maximum size, but the 90 percentile size of the material at the sample localities is given in table 7. These values generally are 3-5 times larger than the mean diameters. Of 115 analyses from the Death Valley region, about.two-thirds are unimodal, the most abundant modal class being 4 phi units. The remainder are bimidal; 6 phi units is the most cemmon primary mode, and 1 phi unit is a secondary mode. Washes draining areas of granitic rock are floored with uni- modal gravel; on the other hand the high Panamint Range, which has a diverse lithology, furnishes a detri- tus that is bimodal at two-thirds of the sample localities. Ha bo ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA ",~ Sts w [=] I BOM 70 |- Washes in Death Valley 60 |- region (mean diameter) Streams in Appalachian 50 /- 20 CUMULATIVE PERCENT OF NUMBERS OF SAMPLES 10 . ' h t t | | | I region (median diameter) I | I od I Streams in Southern Rocky Mountains (mean diameter) | | | | I | | | 1 | | 20.30 . 40 -. 50-60. : 70+ - 90 :100 110 120 130 140 150 160 170 180 190 200 210 220 MEAN OR MEDIAN DIAMETER, IN MILLIMETERS FisurB 23.-Cumulative curves showing the range in mean or median diameter of material on the floors of washes in the Death Valley region and in streams in the Appalachian region (Hack, 1957, table 8), and the southern Rocky Mountains (Miller, 1958, tables 15-18). Numerical values are given in table 6. The samples from the floors of the desert washes are not well sorted. The standard deviation ranges from 0.45 to 2.85 phi units and is slightly higher for samples from fans compared with those from washes in the ad- jacent mountains. Sorting is nearly independent of mean size of material. The range of standard devia- tion varies slightly from fan to fan. The change in size of bed material downwash does not seem to follow any general law but varies from fan to fan (fig. 14). On the east side of the Panamint Range, for example, the changes in size of bed material from one sample site to the next are considerably greater than any overall decrease in size from headwaters to toe of fan. No clear explanation can be given for this lack of order. In part, the debris supplied to the Panamint Range washes may vary in size from place to place be- cause of bedrock differences. The explanation may lie in the regimen of the washes. The high altitude of the range induce occasional great floods that move coarse debris nearly to the saltpan, but floods of lesser magni- tude or covering only a part of the source area merely cause deposition along washes in the mountains. Thus the material on the floor of the washes results from varying combinations of formative processes. The quartzite debris of the washes west of Shadow Moun- tain, decreases markedly in size downfan because the floods from this low mountain carry coarse debris only a short distance down the fan, where it remains until comminuted by weathering. No overall change in the slope of a wash occurs with change in the size of bed material, as indicated on figure 24; however, the plot of values suggests that at less than a slope of about 500 feet per mile and where size is not more than about 15 millimeters, there is a slight tendency for slope to increase with increasing size of bed ma- terial. [Data used in constructing graphs presented in this paper are included in this table. was measured on a topographic map between sample localities; slope, measured, was determined in the field by use of an Abney level. downslope) ] CHARACTERISTICS OF FANS Tapu 7.-Principal measurements at sample localities 43 The location of each sample locality is shown on the plate indicated. Slope, calculated, c Distance to apex, at head of cone- shaped area of wash is to the head of the area where the wash has a cone-shaped surface (on a topographic map the area where the contours crossing the wash are convex y Distance to apex (miles) 90 percentile size Dist t Quadrangle and locality No. Altitude 3131115: is Drainage area | Slope (feet | Mean grain| Width (feet) (miles) | (square miles) | per mile) | size (mm) (feet) At moun- | At head of tain front |cone-shaped 6 Millimeters area of wash EAST OF PANAMINT RANGE Trail Canyon fan (pl. 5) Emigrant Canyon Calculated eC eae ner cnd be mae aad ae an anes 4, 640 2. 22 3. 61 800 21. 0 150 1.c.s -t. use. 5. 9 60. 0 14 AIAN E Ha o a min aia a mamas a 3, 840 8.37 5. 00 696 TAO: 7T 105. 0 1 s ALi l. a bee an 3, 240 4. 40 13. 45 583 17. 0 200 1. uc cr 6. 3 79. 0 TBL ls Ace aoa Pa nace as a alel 2, 680 5. 52 18. 38 500 37. 0 600 |-: : s 6. 9 120. 0 TN EEI eda a 2, 240 6. 44 19. 72 478 20. 0 700; {_c 0 cue ie | ar aoe ous 6. 1 69. 0 Furnace Creek SH sic n aa ii nt ous Clan's aie 1, 840 7. 39 20. 89 421 13. 0 {O0 {ers eee abuses 5. 9 60. 0 102: rec: le cd Auli 1, 440 8. 35 23. 81 417 26. 0 2, 000 0:25. | 30... 6. 2 74. 0 Bee il eis e eee Poss : canker san 5. 8 56. 0 LH 4a s aan n a ae g ae male 2, 420 7. 63 9. 77 505 37. 0 700 1-2-2: l na ue 6. 7 105. 0 D EA IAE H aln an i eine io Coe i ge tae 2, 040 8. 44 25. 68 469 34. 5 600 0:00 |-; vere 105. 0 Bers iol en da al k on nona aes 1, 680 9. 17 27. 54 493 26. 0 1, 100 Te 12 222. 6. 8 112. 0 HD-. unl oats aela'n ae o o ol aln 1, 220 | £10. 16 27.79 465 45. 0 700 172 6. 8 112. 0 Meare reer ao ae ne e menis 840 | 11. 07 27. 96 418 18. 5 900 208 7.2 150. 0 Abre re n lds, T uo a u ain ale mine 560 | 11. 86 28. 05 354 24. 0 2, 500 3. 42 0. 50 .A 140. 0 Tree aa rebar aun oa n'a ei mie aas 280 | 12. 53 28. 11 418 11. 2 5, 000 4. 09 107 5. 2 37. 0 a n aaa an hae diia n' s nals ula l 100 | 13. 05 29. 27 346 22. 0 D 4. 61 1. 89 722 150. 0 Ieee ae a u Aa a a aa nena and a -220 | 14. 08 30. 38 311 19,0] 5. 64 2. 92 5. 9 60. 0 44 ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA TABLE 7.-Principal measurements at sample localities-Continued Distance to apex (miles) | 90 percentile size Distance to| Drainage area | Slope (feet | Mean grain] Width Quadrangle and locality No. Altitude divide | (square miles)| per mile) | size (mm) (feet) At moun- | At head of (feet) (miles) tain front |cone-shaped 6 Millimeters area of wash Johnson Canyon fan (pl. 5) Unweathered gravel on floor of modern wash Telescope Peak Calculated e Bec eed nen cale a onan anns aaa 4, 880 2. 80 3. 40 762 18. 5 15. 7. b 185. 0 reel kel coon cas- walks 4, 640 3. 09 4. 21 828 8. 5 60 wee 6. 2 74. 0 eerie cuca rk cans rank = none asss a 4, 130 3. 95 6. 92 593 13. 0 50 eel ail o 5. 8 56. 0 Dee eer eee ee neo ewan an 3, 670 4. 81 8. 23 535 24. 0 200 I: sete clr 6. 6 98. 0 Bennetts Well 10 s y l nla en no n nce rasan 3, 360 5. 46 13. 78 477 34. 5 550 1. 6.5 91. 0 f ens s 2, 990 6. 21 14. 41 493 30. 0 400 {: leat 6. 8 112. 0 Tae ena een ll ev dien, 2, 660 6. 91 16. 59 471 21. 0 200 a 5. 9 60. 0 Te bes ae ud o o m G2 af bine bile i ain ain a n ie a 2, 300 7. 67 17. 88 474 26. 0 400 6. 8 112. 0 ik canne wanes ass a 1, 980 8. 41 18. 68 4832 26. 0 400 A Ml 6. 9 120. 0 Ure s er creed iene ssn as 1, 600 9. 27 18. 88 442 21. 0 300 1127-1... 6. 4 85: 0 Meer rea e bana eke nin siena 1, 340 9. 94 18. 99 388 32. 0 800 1.914 6. 9 120. 0 Mace e err en cee nine ne e aa s 860 | 11.11 19. 25 410 20. 0 400 3. 11 0. 50 5. 9 60. 0 DU renee rie eae =e= sas 540 | 11. 93 19. 52 390 17. 0 400 3. 93 1. 32 6. 7 105. 0 er ei navi 4 been. 180 | 12. 90 19. 95 464 16. 0 1, 200 4. 90 2. 29 6. 4 85. 0 TOs ile L yes -180 | 14. 02 22. 01 321 15. 0 4, 000 6. 02 3. 41 6. 2 74. 0 Wash heading on the fan (pl. 5) Bennetts Well Calculated fors 2 nso inc id cnc 2, 000 0. 21 0. O1 571 49. 0 HHA inin h nes eleeties ale ine. ayy Nera LL cea an eee 1, 920 . 84 . 02 615 18. 5 S |E. tole vics eros. cs Reede i ne ieee nacre cane ls 1, 680 . 83 . 06 490 37. 0 29, sa rea- Le ru on onle - |e e aer oe ats ee neenee n dee n ada ales aeg 1, 200 1. 87 "AB 462 28. 0 I0 nine ira | Rance ct aces gear acne n dle anns ane sats 700 3. 15 . 98 391 10. 5 100 -c cnt conn cleus Teese aeon eca s.. 120 4. 90 1. 83 331 14. 0 400 1. acne ele av ie c WEST OF BLACK MOUNTAINS Willow Creek fan (pl. 4) Funeral Peak Calculated Ts Heel batik eben ans oor s a asl 4, 435 0. 05 0. O1 300 5. 2 I tt 3. 9 15. 0 e ree ite each -b ees 4, 370 .19 . 04 464 8. 0 Bene ed WW 4. 7 26. 0 wy le 1 a one a ai penn o enna nre ual o 4, 340 . 29 . 09 300 4. 9 20 | nse es aa 3. 6 12. 0 Eee r nen rece sansa s 4, 210 + 97 . 85 464 4. 9 55 3. 6 12. 0 ora eel ia aer an ana ans we asan s 3, 910 1. 34 91 390 6. 5 100] ce 3. 9 15. 0 f es en aan an ne nan e peso o el 3, 520 2. 50 3. 55 336 7. 0 135 >_ e: la 220 3. 8 14. 0 Te re een bee aan a an nn anl ae 3, 300 3. 28 9. 07 282 9. 8 200 1 » ese cll coa ue 5. 3 39. 0 etree eres r b seen t aio o nere sls aie a 2, 960 4. 36 16. 87 315 12. 0 150 4 5. 6 49. 0 es re en boe e awan ao bd aa ae onn a a 2, 660 5.15 18. 70 380 9. 2 80 |_ seas dla. n te 4. 9 30. 0 oil nas ails Jak 2, 480 5. 57 19. 47 429 9. 8 80: logs 4. 9 30. 0 ee n na iii n dl den ee ono 2, 400 5. 74 19. 65 470 9. 8 508. cour eel oer tke 5. 9 60. 0 I Tees av iY nan e sae we * «390 7. 88 21. 32 T78 9. 8 ed (s tien alin sees 6. 2 74. 0 TSHR mPanel 200 8. 41 21. 78 358 11.2 200 s es e ee iad 5. 6 49. 0 Tose rales eol ents sew tna. -100 9. 26 22. 86 353 9. 8 100 0:00 {-. 8:7 52. 0 Tees e ean noen riles fend gs -130 9. 39 22. 36 231 6. 0 500 AAB Nits ts 5. 8 56. 0 Ee rae e rea r nL de nene oe Be a c al- -230 9. 70 22. 38 326 3. 4 2, 000 744 Is 6. 3 79. 0 CHARACTERISTICS OF FANS TABLE 7.-Principal measurements at sample localities-Continued 45 Distance to apex (miles) | 90 percentile size Distance to| Drainage area | Slope (feet | Mean grain} Width Quadrangle and locality No. Altitude divide (square miles) | per mile) | size (mm) (feet) At moun- | At head of (feet) (miles) tain front |cone-shaped p Millimeters area of wash Copper Canyon fan (pl. 4) Funeral Peak Calculated TY es ELH c toad 2, 160 5. 21 7.76 600 18.0" | Ie ENCs cae na Eales 5. 5 45. 0 (I LL. ie as cie nanos 1, 870 5. 74 9. 45 547 TONS Escient esi caa. 4. 9 30. 0 1299 e erea s cn cane ense nau 1, 180 6. 88 13. 76 605 10:5 | sn e eee 2 al a ae nal alace a aio a 5. 9 60. 0 Tore eet sin acers oen 990 7. 45 21. 48 333 B0 .l ce ele nere aan ine 4. 8 28. 0 MM ACT uce e alana nn aan ane eee 460 8. 51 22. 04 321 13:0 |- Ln sil Arlie cues 5. 8 39. 0 1D reena dean cen ce anna ae s £6 280 8. 85 22. 21 529 SAD {2 4. 6 24. 0 Bennetts Well Der naal cee ank i- a ne c anes wo 180 9. 06 22. 26 476 I A | 0,00 |...... 4. 7 26. 0 STi GTA Ideen nen la cn e 60 9. 34 22. 29 429 b ALL .3i:2. aS Is 3. 9 15.0 gsar c: l tric aol. I 9 72. |- 229. 33 421 gis | " "66 [=> 3s" %. 6. 1 69. 0 sar ile r afe =240 | 10. 21 22. 36 286 80 | 118] 3°. 4. 5 29.6 EAST OF BLACK MOUNTAINS Wash north of Funeral Peak (pl. 4) Funeral Peak Measured irs ma Ga a a aG eca egen 6, 240 0. 04 0. O1 5 12. 0°} L 6. 3 79. 0 Mer eep VY La wae aise ~s ase 6, 200 . 09 . O1 1, 000 8. 0 AEA. anneals s 5.2 37. 0 AEE nner ier reh a cet ts aa c 6, 120 .16 . 02 554 4. 0 12 [_c s 3. 8 14. 0 Calculated Ure ltd el LE LT. a ty aan 6, 000 . 84 . 08 828 4. 5 80 clin 3. 4 10. 5 Gee ae 5, 840 . 63 . 16 552 6. 0 80 | __.. 3. 9 15. 0 cn tel ee lns ns en t 5, 580 1.06 . 85 590 4.9 80 {_ :c. ein: 3. T. 13. 0 Trakr eee reuses non beet see 5, 320 1. 53 . 48 550 8. 0 SD 1... res 4. 2 18. 5 GUR He aar rao ge wale mele b aan ene 5, 040 2. 03 . 53 560 8.0 45 0. 25 4. 7 26. 0 Dee rele t's reina uae s oie bale ao oal 4, 710 2. 63 . 58 550 $0 . 85 0. 00 4. 1 17.0 Sig- roa -a eeu aeons 4, 440 3. 26 . 62 429 8.0 {-. 1. 48 . 63 4. 1 17.0 oer ALIN LCD - e 9a a a ound 4, 170 3. 94 . 67 397 T AY.-ce.l.i. 2. 16 1. 31 3. 8 14. 0 aru n. nee cale a ed e a t nee 3, 980 4. 68 . 78 257 £0 1:...32.. 2. 90 2. 05 3. 9 15. 0 Wash southwest of Deadman Pass (pl. 3) Eagle Mountain Calculated 11s eee dag neo e raga s aa aaa 8,120 0. 25 0. 03 1, 320 15.0 |.. L ni n 6. 8 112. 0 10. el e e nea be a aia blo ah 3, 580 . Al . 05 875 13. 0 |_2l __.. APE deren 5. 6 49. 0 Q rin n sw es on 3, 360 . 76 14 629 14/0'1..:...... 0.001 6. 2 74. 0 Perel c . ce- ads - a nts hie 3, 120 1. 19 . 18 558 B O0: ce claw UB 4. 5 22-0 eri «uca re- an 2, 980 1. 69 . 89 280 6-0 |- 03.1 5. 2 37. 0 eee ece ce cana r nan ae nh i wid aie 2, 890 2. 19 . 63 180 £2 12 Uie.ed 1748 3. 8 14. 0 eal s apna ae a a aint a n a oad 2, 830 2. 68 . 70 122 3.4 .s 1:02 3. 9 15. 0 46 ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA TABLE 7.-Principal measurements at sample localities-Continued Distance to apex (miles) | 90 percentile size A Distance to| Drainage area | Slope (feet | Mean grain] Width Quadrangle and locality No. Altitude divide (square miles) | per mile) | size (mm) (feet) At moun- | At head of (feet) (miles) tain front |cone-shaped 6 Millimeter area of wash EAST OF GREENWATER RANGE Fan west of Eagle Mountain (pl. 3) Funeral Peak Calculated e pe h ania a sl b 2a an 4, 065 0. 55 0. 29 188 7. 0 100 }. 3.9 15. 0 B eo ee en dice oak aln os aa Bw a aoe 3, 870 1852 1.72 204 8. 0 200. |. 4.9 30. 0 g e a an satan vida eis 3, 680 2.11 2. 88 267 12. 0 4001. esc eld. 5:2 37. 0 Eagle Mountain (2s r de l IP weer ee o n el ale mo 3, 450 2. 95 4. 00 274 11. 2 600 1. .22 -c 4. 1 17. 0 Ne USTC Uva acd a a wil e us an ild anld 3, 240 3. 74 4. 11 266 6. 0 600 0:00 4. 2 18. 5 (14 :e a r e L ann o a aaa alle a 2, 990 4. 70 4. 28 260 6. 5 450 06 .-. 4. 2 18. 5 The res a ua d d an a 2, 700 5. 93 4. 68 236 8. 0 5, 200 2. 19 0. 90 4. 8 28. 0 10. sr rd Al uke o . in Lk an a alg 2, 420 7.39 4. 77 192 $A 3. 65 2. 36 4. 5 22. 5 ( re Ue «Us o cin a ule a ea aan e 2, 200 8. 86 4. 85 150 40 [...... 5. 12 3. 83 4. 9 30. 0 TSN pC Ll L a ead ware io wile 2, 020 | 10. 43 4. 93 117 3.4 |...... 6. 69 5. 40 3. 5 11. 2 Wash northwest of Lila C mine (pl. 3) Funeral Peak Calculated Perse a in an a biet a bial nln al wie ale a wn 3, 580 0. 29 0. 04 1, 44 Bed |L A eel lace n ee lee ewan la aes a sles a aed f e ea o ee a e o Us Ce an < an a's 6 o 3, 220 . 87 . 23 620 pA - Nxt rent. clgess Easel. edu e lsu deen ue TLP a uC iela a ine foe s awd ak 3, 020 1. 35 . 41 417 PMe lve es dle ce eae als boa ien ene e aaa an 1 2 a al a darn a al a a ob nl 2, 710 2. 38 . 49 300 n A ITE «eae ane ae ane na af ant an s (an an eae Ash Meadows Mere ec ee gin ce ce ana a alena e 2, 490 5 00 (Are cere- cats .s Bed EE ACAI er release ae loo een ae Trees e le ENVY cca nge a+ 2, 420 tA2 IL Lats uo I2: ieee aloes an clean ls aol 120. e: AC ce bd. tenes ien 2, 300 SHD fs ets oll t ant Ad (REAE LEE OIA ares anne eset eee il LOTE a ea aa a 2, 240 (o. c ercesa eli ace. rO | aa es ela ands lee rece le enas le aar aes 155. on r L oi 2 ea il anl ae male's a 2, 110 6:05 {oce cece ILI: IL ELE a 4 |e ca beck ales =n s olen d 188 MeL Ld e aca so 2, 035 $."95 sol. 2B (El fle tere lea nline cnn aa ts Wash southeast of Lila C mine (pl. 3) Funeral Peak Calculated eee eee be tin a ae ore a- ane aan abe ale 3, 380 1.17 0. 63 479 6:0: {22 el- ova e slc anl teas - lek oke Meo T Be Sa n e LL a w earn wis ae a te a 3, 070 2. 34 1. 79 265 BABE. SNL acer eal ease { ane aad Eagle Mountain (fee oa ee c aE HZ wie se an a ale 2, 830 3. 29 2.71 253 LAM A LCC. I. Airy ile e ase A ka e ana ee ak a ue aig b 2, 660 4. 08 3. 24 215 $.0 :.. .se cl. rveenclctes ta usle =s alkalies Wee sie ee a aE a s red H a Ma o Hin ul nthe arly o wie 2, 420 5. 07 3. 65 242 T0 |- ar l ale soren eas aa nae d A ea ano ei ara n eee sice 2 rian alek 2, 320 5. 56 3. 68 204 AME: cL. ol ns sen eles cece sala sles an sss i e d oun a dele rele an a ee E bao aa 2, 200 6. 59 577 117 SAO {2 2 ee en le sore eel bean a na ll ia are | ayn a ole' s ag Ash Meadows 19g e e ag oor a n nes a le ae 2, 030 8. 90 3. 96 74 Pre (resec- e de eli iv ae Pauls beat a anis k aie CHARACTERISTICS OF FANS TaBtr 7.-Principal measurements at sample localities-Continued 47 Distance to apex (miles) 90 percentile size Distance to| Drainage area | Slope (feet | Mean grain] Width Quadrangle and locality No. Altitude divide (square miles) | per mile) | size (mm) (feet) At moun- | At head of (feet) (miles) tain front |cone-shaped [J Millimeters area of wash WEST OF SHADOW MOUNTAIN Fan east of Alkali Flat (pl. 1) Ash Meadows Calculated ASBL ILL dane cem s 4, 640 0. 18 0. 02 2, 394 34. 5 15 {. cecal ele ctf isn. ana :c cll dab ss onn 4, 860 . 84 . 05 1, 750 21. 0 S5 |_. (ae MBTA eer ede faci 4, 160 . 50 A41 1, 250 52. 0 G0 1. sari TSA 214. 0 ABE EC LU aaa ca n <= Haen n 3, 920 . 78 . 28 857 13. 0 50 {2-2 6. 2 74. 0 ABYX eR LZ e S s aa en a aao a= camas 3, 640 1. 16 214 737 13. 0 100 |2 .- s. 5. 4 42. 0 Eagle Mountain AL en EEV a als ne al nee 3, 500 1. 49 91 424 34. 5 130 1s cle RASA 7.2 150. 0 109=. sell ee ne 3, 310 1. 86 1. 09 514 11.2 85. | eer 5. 2 37. 0 Ec il sien - news ias 3, 220 2. 07 1. 16 429 21:0 110 0.14 |:. 6. 5 91. 0 1102.4 Le a s ask eine 3, 030 2. 47 1. 19 475 30. 0 700 . 54 0. 44 7.1 140. 0 M2; ANE: cense eso ae 2, 740 3. 07 1, 23 483 21. 0 1, 600 1. 14 1. 04 5. 8 56. 0 Ash Meadows THB}: rre NFI. -e 2, 380 3. 92 1. 28 423 10. 1. 99 1. 89 5. 7 52. 0 SOH iL Iv aki aL =s 2, 110 4. 983 1. 35 267 9. 2 3. 00 2. 90 5. 3 39. 0 Tiss elev cel cease 18 eus 2, 040 5. 44 1. 39 137 8.0] 3. 51 3. 41 4. 6 24. 0 Da LLEN C- o a a ea pic a aa mee 2, 000 5. 92 1. 43 83 2. A {t _ {el -L ras 3. 5 11. 2 Shadow Mountain Fan Unweathered gravel on floor of modern wash (pl. 1, Qg) Ash Meadows Calculated OE rend Ale ere d eni ea aa ean as 5, 040 0:00 - {2 2 rea a ae =a e S90 |_ 6. 7 105. 0 eerst eK Lee can - 5, 040 106 HLL RET LILY AL Je a el 60.0 12. : 2. ile n |» s aas tl. 0.8 112. 0 lern sC a Lola's uh 4, 340 : 96 0. 04 2, 470 08.0 1. 2 Colen ened e a uue ees 127 214. 0 C00 rs dl ~~~ seuss 3, 980 . ler 1, 567 42. 0 100 /L. cises T4 140. 0 RYU: ege el- - whun -- ss aan 3, 680 . 85 . 24 1, 111 32. 0 30. | XSi 7. 5 185. 0 BSc cest 2 cE TVL . be amai 3, 480 1. 10 . 40 800 320 0.00 | >. sss. 6. 9 120. 0 2 ea LL Hea! ank ans a 3, 380 1.850 . 42 500 17. 0 80 vB0 1.ict is- 6. 6 98. 0 Aae Hg ire cna nenas 3, 120 1. 70 . 45 650 13. 0 30 00:1 /-. 6. 2 74. 0 df. Z IAC uas s ananas a nob a bie 2, 665 2. 47 £58 592 14. 0 8 1:87 5. 8 56. 0 AOT eleven tie? -our ews alw =o 2, 545 2. 96 1.11 245: 6. 0 100 1, 56 4. 9 30. 0 LOT} 2 ! remus ney cale - a ald anh am 2, 475 3. 25 1. 15 218 8. 5 10 2. 48 5. 5 45. 0 MOP: e eti o:. ecb a ane ano aa an 2, 480 8. 25 3. 29 224 6. 0 80 AT 5. 4 42. 0 A55. cl :e tet nose cl tet cee p 2, 370 3. 88 3. 29 183 8. 5 50 o. O7: [« 5. 8 39. 0 ID eed e IN t a a ua tl a a amin an 2, 280 4. 25 3. 29 248 8.2.2 25.2.0 4. 9 30. 0 109.. 2: elie ct aude nants anos nul 2, 200 4. 74 3. 29 163 5. 6 16 5.03 |-.2.%*.-. 5. 2 37. 0 MDa roe Eel eile uh a a ak mlnte a anes 2, 130 5. 22 3. 29 146 4.012. 4 41 5. 8 56. 0 bol: cer sale {cg aln tha seas 2, 066 5. 80 3. 29 111 3. 2 10 4,009 |....-.i-- 4. 2 18. 5 HR f e p dea ae e a aaa ann a ae a 2, 035 | 6. 24 3. 30 70 2. 3 20 0.49 la..... 2.7 6. 5 Varnished gravel in abandoned wash (pl. 1, Qgy) Ash Meadows Calculated (20: eir acelin ans ann 3, 120 1. 70 0:45 26: 0 |....cc cul. .l we M25: r eet -a coa an c cosas 2, 940 2. 00 . 47 600 B8. 0 |. cull ccc. cla s O0 EU Peer cn e ece ca nae en's 2, 670 2. 45 . 53 600 2A. O .c. l ele cs ce alt coas oal (Da kere Laren nab as 2, 610 2. 69 . 66 250 22, 5.1. ...l l . eect oal - same eos (op- Per acer tir. ale. 2, 550 2. 94 . 67 240 15. 0 EL... ~~. dpa ny lactic. coriolis 2, 475 | 8. 30 1.15 208 :|: 18x00] {col ...li- sole .do ace e ooo ss Ien ic angles 2, 370 3. 88 3. 29 181 12. 0 ID naan 2, 280 4. 25 3. 29 243 16, 0 | ._ ul Cree ec c cn a 2, 199 4. 74 3. 29 165 T. MEZ ELLIE AG Ata eens ail a anu a -' | ale me o e ae M51 rre r Unie cual === aaa 2,150 5. 22 3. 29 144 0, 8 |.. ufc. oon anl o ann ul [t aim 'win m he era ae t a barri stin lens ". 2, 066 | 5. 80 3. 29 110 6. 5. | oe |e iaa ariel bau fade tne dag t c le Lil :no fut. 2, 035 | 6. 24 3. 30 70 7D este tall { f e eal andes 1 Small unmapped area of varnished gravel. 48 ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA TABLE 7.-Principal measurements at sample localities-Continued Distance to apex (miles) | 90 percentile size Distance to| Drainage area | Slope (feet | Mean grain] Width Quadrangle and locality No. Altitude divide (square miles) | per mile) | size (mm) (feet) At moun- | At head of (feet) (miles) tain front |cone-shaped 6 Millimeters area of wash Desert pavement (pl. 1, Qgp) Ash Meadows Calculated dr ne ered en 3, 380 s 18:5 |- < es Mr er rn ne are eae aol a niece tain 3, 100 h T2 J sulci. ored ar Mil erect dels le- ae {ea ne an a al aio min ae lack a ale anl a rre e ns pea e nae a ae win's aad 2, 720 P A6 l aes e M 1.2 ore balon iew ns (a anna n anl esas awa aie aioe Nad et eN IAIN Ln net inane ak 2, 650 2 OY Here UB Ne ere neon eae nal ean slain =s ln wi away a To Piscina es dc lee eo- ap ab es 2, 520 B. - rat. 190 14.k penal. ssn whent 60 na un da a iia whe aan 2, 460 POE 2 |. 1230 1-. 4s ccie alata lms s ae tm a far a oes cue o a nates ig 2, 360 400 10.5 |« 2 eee ei lenee an in as c+ aan h ank s O0 e ries isin oul eon ue nee 2, 350 G: B1. |- 1620 122 sc E n ee eun ele ren as c ASU eee L Uri. aaa k eas 2, 280 T 2D ile cece 19 0 «<== aiken TDI renee eke aren acne nu ee ee ae 2, 180 LBJ. Me eel e naik s 9. 2 |.. e endl on ene eine eels ee Pue | aca ek s a Es care- s saul oen s 2, 185 enne [eee ana fe 12:0 (.ll ciel. Greet ie ue nn anen nre ass s 2, 066 570 ils cn cella K gS |e nl in le leven eal ere eon ile ae be cles ols - a MATER ENEECE anh wick ancer s aie ae a> 2, 035 6.29 |-. ID Ile el sel dea clon nae oue Wash heading on the fan (pl. 1) Ash Meadows Measured AOE eA r cele ced oo s a's 3, 240 0. 000 00000 |__:..... 17.0. 12 z. LLA fe none sa lean ine + (LOE Lad ae e niin nee wakes a ae = 3, 190 . 085 . 0024 660 16. 0 E won pluie ees .r RDC a ne c nene an -on a 3, 110 . 180 . 0072 582 30. 0 10 acnes ok ang ADTs ened e nari ee nel anis 3, 040 . 8303 . 0167 740 14. 0 19 {sc elan a alan t oon a TODs ree ee e Pree e enn nen anes. 2, 980 . 4837 . 0262 365 21. 0 T4 .r earn sls oes Sind naal c ale ane ole a OBL e ert nei neer aan none enne n 2, 910 . 682 . 0428 343 9. 8 ID ese THe e eee eee ieee ieee ae ae bo 2, 840 . 833 . 0618 290 9. 8 SD [LLE clo ire. a aale ale a MoU e n te cena anais aas 2, 760 1. 174 . 1428 238 7. 0 RS (ELLEN cleat a al = a a aaa Oben caer aba nes ts 2, 690 1. 477 . 2832 211 6. 5 50 |. en dec nei niels Ie aTe N Percoll aon a aoe anna 2, 640 1. 780 . 3592 185 4. 0 BD (ee EY rae las. iew e eed e eee lawl eb n> k sa 2, 560 2. 102 . 83782 158 7. 4 00 \c 1 aas EAST OF FUNERAL MOUNTAINS Bat Mountain fan Unweathered gravel (pl. 2, Qg) Ash Meadows Calculated Te edie i wel. lea bas san wal 2, 940 1. 35 0:03° {{ oA {are ale ares o sp 1: 6 185. 0 OIE ILC c ne newb aln wee 2, 840 1. 64 1. 14 345 12.0 1-4 cl... -... 4. 9 30. 0 M ea a an hen an nee m banned au moe mara ao 2, 780 1. 79 1. 14 400 98 .cc. £19 5. 2 37. 0 Tepe EL nll dc 2, 700 2. 02 1. 15 348 8:0 !: OB Icl... -s 4. 9 30. 0 I deere oen ns aan a 2, 640 2. 17 1. 15 400 14:0 N M Lf 5. 7 52. 0 OIE PERU on cana ao ain bane a'nls aa ale 2, 560 2. 07 400 $. 0 MO 12 ieee cs 4. 4 21. 0 s re ee AZ nen eran d ane a als 2,510 | 2. 53 1.17 313 14 0:1: .2..... o A vea k 4. 9 30. 0 UAE es o ae ein y cer e lc nc 2, 440 2. T2 1. 18 368 nly |p eta ancl 1:08 4. 6 24. 0 OPL oe Aanes cole eee eac naa a+ Sb 2, 380 2. 91 J. 21 316 eA desycsell. 1. 27 0. 19 4. 2 18. 5 TBA nae tense nn co's 2, 290 3. 29 1.283 237 1. 65 . 57 4.9 30. 0 TOE ian v aed o oe aioe wow ae clan 2, 2350 8. 54 1. 42 240 y A reacik' 1. 90 . 82 3. 9 15. 0 Mie ed nol a ae e ann - nee as 2, 170 | 3. 89 1. 43 171 cX 2. 25 1.17 | 8. 4 10. 5 Nees ei oo eL cu oak. 2,130 | . 4. 12 1. 43 174 2. 2. 48 1. 40 |: 2.9 7. 4 Parra ae e eae eee e o heat aas. 2ATe0 'l 2.00 ono.. netkas. 11.0 (-ac ec i san 5. 6 49. 0 dp tone nen UL eee wen as 2000 (42. 45 - Sc MLC -r esi 8:0. n:: s cil 5. 1 34. 5 Ls: a lll leila ade bor nl 2,455 |i 2 4 ! _--: 200 OB Uke ceil sno 4. 8 28. 0 Oa aa ore nnn ene nene ase re 2,870 |. 8.16 r pl misc tote Hat . 5. 9 60. 0 f ideas iin ca eda bag.. 2,860] 0. 1 c_ ane 90 esis iii ne 4. 5 22. 5 oE rerio ceca na p 2851. 3: Ba ln g 0 aii r A i 5.9 60. 0 Mere sr nee er roan eevee 2,250. 18/8, 74 {.s :c -t g-... r Ones er cece sli 4.9 30. 0 TOP e eee ee ea nee eae ren cece 2,220 B BL. c C60 {. Ell NE ele [lara 5. 1 34. 5 IO selene iin l neer ick en.. 2,140] 402 |L _} BTH ere |-. wee 5. 4 42. 0 fai Pe LP INI IIs. n 2,660 .( 2 18 20 LM c ecs 11.9. ]. C 0:49 !. e ie meen nr Onan e sock -s 2y885 |- 2. 08 to: 1.29 -£: css Nese Urei a neg cea az .less 2040] S. 14° (": a tgt 7.4 1. 50 . |2.o:e aet doe oa en ion onn oo.. 21076 |. A TL cl: ...t... 26. e 07 sole _o ll cases s" CHARACTERISTICS OF FANS 49 TABLE 7.-Principal measurements at sample localities-Continued Distance to apex (miles) | 90 percentile size Distance to| Drainage area | Slope (feet | Mean grain] Width Altitude divide (square miles) | per mile) | size (mm) (feet) Quadrangle and locality No. (feet) (miles) At head of % At moun- {cone-shaped 6 Millimeters tain front |area of wash Desert pavement (pl. 2, Qgp) Ash Meadows Calculated M1 Pe n e eddie nan snes sb 2,040 | 2.07: 14. 0: Lo EL er lenee sole eel Caen cee s $55. ien iv n eous uae a aa a aaa im 2, 545 2: 4D 11.0 | ce ALL eca cle aim:: a frc AEI 3,480 ( 2. 094 | cel c.}. g: 0 | LO LPO Dt o rec footies A49... ie e aa iela nes - a ane 2, 380 3 A4, |-. .c Aes slags. 032 |- el-» sie aan e- [eon becn 3. ar ini 2, 330 3. 95 - s 9.2 {eon neer | Enes ona alan s ae a's a le an ain a ea aie nle 2 as on 2, 700 1.93 | .s dral ee ae aan 0.2 | L eL e ene e ne » elena revela ea nn Lr HEL! suck co am on 2, 600 2 AS. . _ num «-l ae ne 16. 0 I_. e non tue [aie tale a | o leona i ag TEDL in bed onan ae ous a a oe mea aan am 2, 470 2.02 eel ee Pir lea an a ark 0. 2 s lane seuss .. lca a #5 2, 400 ABE ale lle can o celens sloan. 14, 0:12:22 asa th -l slags une asd ic . __.: sofia c 9: 390: s 12 >| closer... 13. 0 | OIL A en ml rent |e ien. ane Tct e ino ae s b tol a 2, 665 2.0 eze 12.0 nl bae es edi. c n N "pin. P aso t, (10: :c _c rl akc" 11.0} lolol gleet 20 od de n aa o o o o ule a alel o oo tile o a ion teral ae mee 2, 075 A Tl Meas. te cc ue une LCIE siad = a =| 2+ anl ~a ae a aloles Washes heading on the fan (pl. 2) Ash Meadows Measured MML IN «anale calne s s nk 2, 529 0. 189 0. 007 290 11. 0 § |. icts aan bolan nnle tel m 290. ee oleic s dar o a all ul a alin me he an 2, 501 . 813 . 020 343 6. 5 16 | 4 isa -~ TDE cn vies ben ans ues a= tun alnlan aa ae s 2, 476 . 445 . 029 238 4. 6 Z| xine eae ee bes ms ale s a aln a | i tale ie le toad IBL IAL LIN. oo ce relce s an be a me m an 2, 451 . 568 . 039 211 7. 4 26 |L inl el erie an ela u eee | ao aaa tials) OYE 24 oh ole a Hin an a aa ming aa male 2, 413 . 720 . 056 211 6. 5 34 es sl s ail cr eee nn anc ab nm ai bles 2, 385 . 871 . 062 290 $.0 |e n e PEI H EY eu a a aa | ale a n m a | a a alee mae tit QI. ll cn an ans s 2, 461 . 189 . 006 317 9. 2 J |- coun la aos a | am seee OFE EPE uaa al ne aa a an mie wn mc m 2, 430 . 294 . 011 343 13. 0 8 |L nsec [Lr .as ak MOBLEY U 0 3 | EAST OF BLACK MOUNTAINS 3 K ® 2 Wash north of Funeral Peak Fan southwest of Deadman Pass g Monzonite Monzonite O ( EAST OF GREENWATER RANGE s h ® Fan northwest of Lila C mine Fan southeast of Lila C mine Fan west of Eagle Mountain Volcanic rocks, conglomerate, Volcanic rocks, conglomerate, Volcanic rocks, conglomerate, and sandstone and sandstone and sandstone > WEST OF SHADOW MOUNTAIN T % g l 6 Shadow Mountain fan Fan east of Alkali Flat g, Quartzite and quartzite Quartzite and quartzite E conglomerate conglomerate < 51 52 ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA A relation between size of load, slope of wash, and drainage area, such as Hack (1957, fig. 19) demonstra- ted for streams in the Appalachian region, does not ap- pear to hold true in the desert. For his sample sites Hack plotted channel slope against the ratio of the size of bed material to drainage area and found that the points of the resulting scatter diagram cluster about a line that may be expressed by the relation M 0.6 8 ——IST; where S8 is channel slope, JZ is median particle size of bed material, and 4 is drainage area. A similar dia- gram for sample sites along the desert washes, not in- cluded in this paper, shows a large field of scatter and indicates that for a wide range of values of slope remains nearly constant. Geological differences appear to have more effect on the form of the individual desert 'wash than any equilibrium relation between size, slope, and drainage area. Perhaps the streams in Shenandoah Valley, for example, constitute a single system in equi- librium, whereas in the desert, each wash represents a different system. The material that floors the desert washes is appar- ently finer grained than the bedload of some streams in more humid regions (table 6). Fan-building streams on the west side of the Shenandoah Valley have a bed- load that is slightly coarser than the bed material in the fan-building washes from the Panamint Range (fig. 14). The Appalachian streams, in turn, have a finer grained bedload than do the streams in the southern Rocky Mountains described by Miller (1958). It is not clear why these differences in size of bed material occur. Perhaps a sample selected by means of a grid on the bed of a perennial stream is not closely com- parable to one selected in the same way from the dry bed of a desert wash. Fine material remains on the bed of a dry wash, whereas it is removed from the bed of a perennial stream by the low flow. The size differences shown by the samples may be related to differences in channel characteristics, in vegetation and in weathering on adjacent slopes, or in the amount and frequency of precipitation. WASHES HEADING ON A FAN Areas of desert pavement in the Death Valley region are traversed by meandering washes that are both nar- row and steep-sided (fig. 17). Near the upper end of an area of pavement, a shallow channel marked by a line of shrubs descends steeply and becomes a few to several tens of feet deep. Thence to the downfan end of the pavement the channel has a meandering course and a downvalley gradient less than that of the adjacent pavement or of a neighboring wash heading in the mountains. As mentioned on page 21, the erosion in these meandering washes appears to work in opposi- tion to the processes forming pavements. Indeed, the two processes may be part of an open system that at times approaches a steady state of balance. The meandering washes that head in pavements dif- fer in some respects from fan-building washes that head in the mountains. The meandering washes have drainage basins that are long and narrow compared with those of the fan-building washes. At a point about 1 mile from the headwaters of a meandering wash, the area draining to that point is about 0.1 square mile, but 1 mile from the headwaters of a fan-building wash, the drainage area is about 0.5 square mile. The width of a meandering wash increases with an increase in drainage area (fig. 25) at the same rate as does the width of a main wash (fig. 18). On the Bat and Shadow Mountain fans, meander lengths range from about 150 to 450 feet, and radius of curvature ranges from about 50 to 250 feet. These size parameters con- form to the empirical relations of meander length to channel width or to radius of curvature determined by Leopold and Wolman (1960). At its headwaters a meandering wash has coarse bed material and a steep slope. Both size of bed material and slope decrease downwash and become a little smaller than those of the adjacent wash or pavement (figs. 26 and 27). Perhaps a meandering wash has a gentle slope because its bed material is fine grained ; the fine material comes to it from the weathered gravel beneath the ad- jacent pavement or underlying silt. A meandering wash on the Johnson Canyon fan has coarser bed mate- rial (fig. 28) and a steeper gradient than do those on the other two fans, probably because the surface of the Pan- amint Range fan is covered by much coarser material than are either the Bat or the Shadow Mountain fans. On the Johnson Canyon fan, however, the rate of de- crease in size of bed material downwash is for some reason much less rapid than is that in meandering washes on the other fans. The slope of a meandering wash is comparable with that of ephemeral-stream channels in the Tertiary rocks of the Rio Grande Valley, near Santa Fe, N. Mex. (Leopold and Miller, 1950, fig. 24). CHARACTERISTICS OF FANS wW=122 A °5 100.0 TTV WIDTH OF WASH, IN FEET I 10.0 EXPLANATION TT 111 m Shadow Mountain fan © Johnson Canyon fan I iG Bat Mountain fan X Sample locality numbers 254-260 ® - ® Sample locality numbers 264-267 H Sample locality numbers 241-248 1.0 ests Ett eld fase t $0 I 12) Jl 4 F3 | -V "4 TS HIs I Fl I T ts T EJ 1d e LI {£13 } I | 0.001 0.01 0.1 1.0 DRAINAGE AREA, IN SQUARE MILES 10.0 FIGURE 25.-Logarithmic scatter diagram showing the relation between the drainage area and the width at sample sites along five meandering washes that head in pavements on fans in the Death Valley region. | ty te es. -T 14s I Ts Ash AET I at I EXPLANATION L. Shadow Mountain fan © Johnson Canyon fan Bat Mountain fan X Sample locality numbers 254-260 - J 1000.0 Sample locality numbers 264-267 C> Sample locality numbers 241-248 > # |___ Bat Mountain fan _ Johnson Canyon fan Shadow Mountain fan SLOPE, IN FEET PER MILE | {-f 13 | L 100.0 1 te" C T Ll | I poo ac T TEL 11 I I L AL L114 I I 1: 0.001 0.01 0.1 DRAINAGE AREA, IN SQUARE MILES 5.0 FIGURE 26.-Logarithmic scatter diagram showing the relation between the drainage area and the slope at sample sites along five meandering washes that head in pavements on fans in the Death Valley region. 54 ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA SLOPE, IN FEET PER MILE 800 700 600 500 400 300 200 100 / ] | | # EXPLANATION © [i> Shadow Mountain fan Johnson Canyon fan __| Bat Mountain fan X Kh Sample locality numbers 254-260 ® (-- f Sample locality numbers 264-267 =- H l Sample locality numbers 241-248 © l © - © te O] A 4 © X @ x n_ ® © 8 C x " um x # ® * = ® H ® HG SB | | | | 10 20 30 40 50 MEAN SIZE, IN MILLIMETERS FIGURE 27.-Arithmetic scatter diagram showing the relation between the size of bed material and the slope at sample sites along five meandering washes that head in pavements on fans in the Death Valley region. CONCLUSIONS 55 100.0 - | - | | | pet EXPLANATION C3 0 as lu jen |-@ Shadow Mountain fan -I - * © 2 Johnson Canyon fan "4 w Ex © o X £ |-- s- Bat Mountain fan a- € © 3 # Q x. © = X e 10.0 |- C_ < xx 3 ® ss K E= xX m T N - med a E *SC % y " r : z L- al § x** 3 m 4 tA | | | | 1.0 0 1 2 3 4 5 DISTANCE FROM DIVIDE, IN MILES FIGURE 28.-Semilogarithmic scatter diagram showing the relation between the mean size of material on floor of washes and the dis- tance from the divide at sample sites along meandering washes that head in pavements on fans in the Death Valley region. CONCLUSIONS Alluvial fans are accumulations of detritus at the point where a debris-carrying stream from a highland leaves a confined channel and enters a place where it is free to migrate from side to side. In the Death Valley region the highland may be 10 feet or 10,000 feet high. The fan-building wash has a smooth profile and passes without a break in slope from the highland out onto the fan. Compared with stream channels in more hu- mid regions, the desert washes are generally steeper and their bed materials appear to be finer grained; per- haps they are also wider, but the data on comparative widths are inconclusive. The gradient and cross sec- tion of a desert wash are probably adjusted to the avail- able discharge and load. The wash is more or less in equilibrium-in quasi-equilibrium, to use the less con- troversial term of Leopold and Maddock (1953)-al- though hydrologic data and measurements of bedload are not numerous enough to demonstrate that this is so. The stream in a fan-building wash forms and main- tains its gradient by erosion and deposition. In order for the wash to acquire a smooth profile from the head- waters to the toe of the fan, deposition may take place both in the confined channel and where the stream is than the gradient upstream. El‘he fan-building wash _ channel is unconfined if the gradient at that place is has; free to migratfl Eeposition will take place where the] Lfik (m "Uh C f Stream is Tree to miqrake. Pepesit l? (6&1 kuLfl/UL Uxfi Chet/mul \$ “A um imine d ‘ auxilQ-‘J‘ eX "thak §JW~UL (s" Mess. 3 HAW} ‘t’ NL 6&th QM)” st - The hew (JNMXKKIMS f 3p: M ( {Cal/A cf/‘th/l" Crew) A m9 inet _c han ML} oud «hou tha é {on wi \\ 4“ka [f the. acquires a profile whose form can best be discribed as Tgraded, much as a highway is graded. The point of termination of the confined channel varies from fan to fan and, doubtless, from time to time. On some fans it is at the mountain front ; on others, it is more than half way down to the toe. The location of the point of ter- mination is related to the structural history of the area and to drainage diversions that have taken place on the fan. The slope of a fan or fan segment depends in some degree on the size of the debris of which it is built, although a comparison of the measurements of size and slope recorded on figure 29 lends only moderate support to this view. Nevertheless, a relation of size to slope appears to be part of the explanation of why some fans are markedly concave upward in longitudinal profile. Although all fans have concave profiles, on many the concavity is slight, and these fans have nearly uniform slopes for long distances. Fans having only slight con- cavity include those that are largely without areas of desert pavement. Such fans are small. Some large fans with extensive areas of pavement, such as those in longitudinal profile, whereas others, such as those east of the Panamint Range, are only slightly concave west of Shadow Mountain, are markedly so. The tion of the size of the material deposited on different explanation for these differences may lie in a considera- Sc,wUUf\’L ‘cm'b Mh’fl “H aSiVe {mac‘s 6 quum¢4fl Stath an Vii/(AU)? #06 [la khé, (“fulfil 4+ “(A/”2?!" otk c,“ gfi‘mxH cpncaud i N Apr f’rthAf’ka I t+ ) j F f | | L [_\’\r\/,\_'>'VS win oo wéat 06 Shokan #4 h» gic s»eaked kg $s . & whmnea 56 ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA parts of a fan. If steeply sloping pavements on coarse detritus high on a fan are the source of fine debris deposited on a gently sloping segment lower down, as on the Shadow Mountain piedmont, the fan is markedly concave upward in longitudinal profile. In contrast, if the fan is built of coarse debris and pavements con- tribute fine sediment only to points near the toe, as on the piedmont east of the Panamint Range, the longi- tudinal profile of the fan is only slightly concave. The piedmonts adjacent to the Panamint Range and Shadow Mountain are approximately the same size. Both have lengths, measured at right angles to the mountain front, of 5-6 miles (table 2). The two pied- monts have contrasting source areas and differ also in the size of their fan-shaped segments of wash-that is, in the size of their areas of deposition. The areas of deposition on the Panamint Range fans are larger per- haps in part because washes from the range drain an area of high rainfall but principally for the reason that the source areas are many times greater than those on Shadow Mountain. The surface features of a piedmont are to a large extent independent of the position of the toes of the fans. On the piedmont east of the Panamint Range, for example, the fan-shaped segments where deposition has taken place during the last few thousand years are large enough to extend from the mouth of the main fan-building wash to the edge of the saltpan, whereas on the Shadow Mountain piedmont, the depositional segments are not large enough to extend from the mouth of the main fan-building wash to the edge of Alkali Flat. Coarse detritus from the mountain is deposited on the upper part of the Shadow Mountain fan. Far- ther from the mountain front, the finer gravel on the surface comes from the erosion of areas of pavement upfan. If Eagle Mountain should be elevated, dam- ming the Amargosa River and causing the level of Alkali Flat to rise so that the lower half of the Shadow Mountain fan were buried, the exposed upper part would still have a relatively straight slope. The longi- tudinal profile of the fan would resemble those of fans east of the Panamint Range and would probably main- tain such a slope because a rise of the surface of Alkali Flat, unaccompanied by any change on Shadow Moun- tain, would not alter the load or flood regimen of the fan-building wash. It is a commonplace that the size of a fan is related to the size of the source region. Measurements of the size of many fans, or of some segments of their washes or pavements, compared with the size of their source areas, indicate that the size of a fan is roughly equal to one-third to one-half of the size of the source area. The data presented on figure 7 can be expressed by the relation Af=0.5 Am**, which states that the area of a fan or fan segment is equal to half the eight-tenths power of its source area (all measurements are in square miles). This relation is only a first approximation, for the delineation of the individual segment is not always easy, the number measured is not large, and the field of scatter is con- siderable. The relation, also, seems to vary slightly from range to range. If it is restricted to include only the data from the Shadow Mountain piedmont, the size of these fans or fan segments more closely approxi- mates the 1 : 3 relation than if all the measurements are included. Because the relation holds good for fans that are composed of various rock types and have di- verse geologic histories, the probability is high that a general relation exists. It follows that the confluration of a fan depends upon some functional relation be- tween the bedrock and the processes acting upon it and not upon a fan's stage of development in an evolution- ary sequence. The height of the source area above a fan may be as important as its extent in determining the size of a fan. The piedmont east of the Greenwater Range, for ex- ample, is slightly larger in relation to its source area in the neighboring hills than are the fans east of the lofty Panamint Range. The size measurements suggest that the Panamint Range supplies much coarser grained bed material than is found on the floor of the washes west of the Amargosa River. The bedrock of the Pana- mint Range is not more massive than that elsewhere, for it includes extensive areas underlain by argillite, thin- bedded quartzite, and granitic rocks. The coarseness of the material is probably explained by the effects of the height of the Panamints, which reach up into a zone of relatively great precipitation and of deep canyons hav- ing precipitous walls where runoff is rapid. The coarse debris on the floor of the Panamint Range washes seems to be clearly related to the adjacent steep slopes and to the large discharge as compared with those in the washes of the Amargosa Valley. The type of rock that makes up the highland source plays a part in alluvial-fan formation. - Shale hills may be bordered by very small fans-commonly the adjacent piedmont is largely pediment-whereas hills of massive bedrock may have extensive aprons composed of coarse detritus (Hunt and others 1953, p. 189-204). - The long gently sloping fans west of the Amargosa Valley con- trast with the shorter, steeper fans east of the river; the fans differ perhaps because of bedrock differences in their source areas. The mountains on either side of the valley are more or less the same height, although CONCLUSIONS 57 the source areas on Shadow Mountain are a little smaller than those in the Greenwater Range. 'The grain-size measurements suggest that the volcanic rocks of the Greenwater Range supply a finer-grained bed material to the washes that traverse them than does the quartzite of Shadow Mountain. If one assumes that the occa- sional discharges in the washes on both sides of the valley are of the same order of magnitude, the difference in length of these fans possibly reflects the size of the debris supplied by the highlands. Fine debris from the western highlands may be carried a longer distance and down a gentler gradient than is the coarse debris from the mountains to the east. The asymmetry of the Amargosa Valley, as explained by this theory, reflects the mechanism of fan formation. Casual inspection of many piedmonts in 'this region suggests that many of the longer ones, as measured at right angles to the moun- tain front, adjoin highlands composed of volcanic rock. The structural history determines the capacity of the depositional basin relative to the amount of debris sup- plied, and thereby, in large measure, fixes the outline of the piedmont-the extent of fan and of pediment. The continual deformation of many of the highlands and basins of the Death Valley region promotes the maintenance of large alluvial fans and retards the ero- sion of broad pediments. On the Shadow Mountain fan, for example, the areas of demonstrable pediment are small and are restricted to small segments between the large fan-building washes. These small segments are traversed by washes that drain correspondingly small areas on the mountain front. Within certain limits, the form of a large complex fan depends upon the size, elevation, and lithology of its source and not upon the position of its toe or the floor of the adjacent basin. I believe that the complex of wash, pavement, and pediment that constitutes many piedmonts is not a cy- clic phenomena related to an evolutionary sequence but is the result of present-day processes. Hack (1960, p. 81) stated that a piedmont "and the processes molding it are considered a part of an open system in a steady state of balance in which every slope and every form [every area of pavement, wash, or pediment] is ad- justed to every other." The form of the piedmont is explainable in terms of the bedrock and the processes acting on it, and the differences between one piedmont and another are accounted for by differences in the spa- tial relations of mountain and basin. As long as Shad- ow Mountain and the adjacent segment of the Amar- gosa Valley had or continues to have about the same spatial relations, one to another, the general configu- ration of the piedmont has been and will continue to be much as it is today. The location of pavement, wash, or pediment on the piedmont will change from time to tims, but the proportion of pavement, wash, and pediment will remain roughly constant. A change in the proportion of pavement, wash, and pediment on a piedmont will take place when the ero- - sional or depositional processes or the spatial relations of mountain and basin change. The great extent of varnished bouldery gravel on many fans as compared to the area of unweathered more pebbly gravel in the active washes indicates greater flooding of the fans in the past, perhaps more than 2,000 years ago. Such a change in process-an increase in flood discharge- doubtless also took place during the pluvial periods of the Pleistocene. The small size of the fans at the west base of the Black Mountains and the irregular longi- tudinal profiles of their fan-building washes show that along this mountain front erosion and deposition have 'not been able to keep pace with changes in the relative position of highland and basin floor. Eastward tilting of the floor of Death Valley during the Recent Epoch has resulted in the burial of an unknown volume of fan debris beneath the saltpan. If no further deformation takes place, however, the Black Mountain-fans will probably grow in surface area until they are two or three times their present size. The ubiquitous desert pavement dissected by mean- dering washes is a part of the system of alluvial-fan formation. - The processes of weathering and of erosion that flatten an area of braided channels and gravel bars into a smooth desert pavement are opposed by surface runoff, which collects in channels and is continually dissecting the pavement. The processes of pavement formation and destruction tend to balance each other. A pavement once formed may persist for some time and adjacent pavements are, for this reason, not necessarily of equal age. A general lowering of the piedmont by erosion because of structural changes or because of gen- eral mountain degradation ultimately causes pavement dissection to proceed more rapidly than pavement for- mation, and the pavement is consumed. Meanwhile new areas of pavement are developed elsewhere on the fan. Thus the maximum life expectancy of one pave- ment is probably much less than that of the mosaic of pavements and washes on the entire piedmont. Pediments are segments of a piedmont where erosion dominates over deposition. The areas of pediment in this region are very small; most of them are bed rock surfaces veneered with gravel and are exposed only where gullies dissect the gravel veneer. Pediments are, of course, limited because the mountains are high and extensive relative to the valleys; deformation is prob- ably a continuing process in much of the region. - Pedi- ments occur between fans either where the adjacent 58 ALLUVIAL FANS IN THE DEATH VALLEY REGION, CALIFORNIA AND NEVADA highland is low or where the streams traversing the pediment have small source areas. The pediments north and south of the Shadow Moun- tain fan, for example, are small areas of desert pave- ment traversed by small meandering washes that have dissected a gravel veneer 5-10 feet thick and exposed deformed Tertiary rocks. The pediment is the planed top of these weakly cemented sands and clays. The small wash has a lower gradient than adjacent fan- building washes and is floored with fine debris (Hunt and others, 1953, fig. 106). The pediment was cut by a wash similar to that which now exposes it and ends downfan, where it descends beneath the floor of the wash. -The planed surface now visible is the floor of such a wash; the pediment was perhaps "born dis- sected" (Gilluly, 1946, p. 65) and was never a smooth plain but was always ridged as at present. Clearly, the activity of the stream in the small wash that exposes the pediment is a part of the equilibrium of the entire piedmont, for the floor of the small wash cannot be eroded below the level at which it meets the adjacent fan. The bed of the small wash up stream from its mouth may lie 10-20 feet below the bed of the adjacent fan-building wash and may be separated from it by a low gravel ridge. In time, the stream in the larger wash may breach the ridge and empty into the small one, filling the wash with gravel and burying the pedi- ment beneath a new fan segment. In the meantime, erosion elsewhere on the piedmont may expose or erode another segment of pediment. As long as Shadow Mountain and the Amargosa Valley maintain about their present size and shape, no extensive pediments will form on the piedmont. But if, in time, mountain degradation exceeds uplift of the range, then the amount of debris deposited on the pied- mont will decrease with respect to the amount removed by erosion. The general level of the piedmont will be gradually lowered, and the areas of pediment will in- crease. Parenthetically, a pediment may be difficult to recognize where carved in undeformed alluvial-fan deposits. The mountain that was once surrounded in large part by sloping alluvial fans is in time reduced to hills bordered by a wide pediment that at some dis- tance from the hills passes beneath an alluvial cover. Many such pediments are areas where shallow gullies expose bedrock veneered with gravel. This study offers no new criteria for the identifica- tion of alluvial-fan deposits-fanglomerate-in the geo- logic column. It merely emphasizes how many different combinations of geomorphic factors could be postulated on the basis of what can be seen in outcrop or inferred from geologic relations. Size estimates based on point counts on the surface of a wash are not closely com- parable to similar counts on the surface of an outcrop, although further study might make such a comparison possible. The trace of a desert pavement might per- haps be preserved in a cross section through a fanglom- erate. In one exposure near Devils Hole (fig. 1), a band of solution-faceted pebbles of carbonate rock that suggests a buried pavement was observed in a cut through a small alluvial cone. However, pavements are easily disturbed by running water and are probably destroyed in the process of burial. The weathered zone beneath a pavement stands a much better chance of _ being partly preserved (Eckis, 1934). The presence of a thick sequence of fanglomerate in the geologic column indicates that deformation and sedimentation were con- current processes. - If deformation slows down, the area of pediment increases, and the alluvial deposits are removed. This theory of alluvial-fan formation postulates that when a steady state of balance is reached, such a state will be maintained as long as the spatial relations of mountain and basin are maintained. Let us assume that material is supplied by a recently elevated high- land at a constant rate. A fan at the base of the high- land will grow in surface area year by year. In time drainage diversions will take place, however, and the area of deposition may be displaced downfan. Aban- doned segments of the fan near the apex are continually being eroded while they are transformed into pave- ments. - Pediments may be eroded in areas between fans. The area of the piedmont being eroded-that is, the amount of material being removed-will increase, until it equals the amount supplied. The system will there- after be in a steady state of balance and will remain so as long as the topographic position of mountain and basin and the geologic processes remain the same (Niki- foroff, 1942). - The total volume of detrital material on the piedmont will not change; the volume of fine mate- rial reaching the adjacent playa or floodplain is bal- anced by the amount of coarse detritus supplied by the highlands. The hills and mountains in much of arid southern California and adjacent States are surrounded by broad, sloping, gravel-covered piedmonts. Where the moun- tains are recently elevated, as in much of the Death Valley region, the piedmonts consist largely of fans. Where the mountains are small compared with the adjacent basin, as in parts of the Mojave Desert, the piedmonts include extensive areas of exposed pediment, especially near the highlands. These mountains in the Mojave may always have stood above their sloping piedmonts, much as they do today rather than having been once surrounded by broad alluvial plains. The debris on the piedmonts is carried to them by mountain REFERENCES CITED floods and dropped where the banks of the washes termi- nate. Once deposited the debris is not easily moved by local runoff on the piedmont until it has weathered to smaller-sized particles. A sloping apron of waste will gradually encroach more and more onto the mountain block until equilibrium is reached and the transport of debris out onto the fan equals the rate at which the material on the fan is weathered into a size trans- portable further downfan. The mountain will appear as if it was resting on top of a very broad and very low pyramid. However, as the mountain is reduced in size, it will supply less and less debris to the washes. Erosion will become the dominant process on a large segment of the piedmont and will cause the area of pediment to increase. Near the mountain front, more and more bedrock will be exposed, whereas further away from the highlands the fan deposits will be eroded. Tuan (1959, p. 120) suggested that the pediments in southeastern Arizona are exhumed erosion surfaces that were once buried under a vast sheet of waste whose gradual removal is now exposing an extensive bedrock surface, the pediment. However, some of his maps (Tuan, 1959, fig. 8) appear to show a contrast in gra- dient and position between washes having large drain- age basins in the mountains and those having small catchment basins, and several localities occur where drainage diversions similar to those described in the Death Valley region can be reasonably inferred to have taken place. I believe that the pediments in Arizona have probably formed in the manner just outlined for the California region and to postulate their burial beneath a thick alluvial cover is unnecessary. REFERENCES CITED Blissenbach, Erich, 1954, Geology of alluvial fans in semiarid regions: Geol. Soc. America Bull., v. 65, no. 2, p. 175-190. Bryan, Kirk, 1922, Erosion and sedimentation in the Papago Country, Arizona : U.S. Geol. Survey Bull. 730, p. 19-90. Denny, C. S., 1961, Landslides east of Funeral Mountains, near Death Valley Junction, California, in U.S. Geological Sur- vey, Short papers in the Geologic and Hydrologic Sciences, Art. 293-435: U.S. Geol. Survey Prof. Paper 424-D, p. D85- D89. Dixon, W. J., and Massey, F. J., Jr., 1951, Introduction to sta- tistical analysis: New York, McGraw-Hill, 370 p. Drewes, Harald, 1963, Geology of the Funeral Peak quadrangle, California: U.S. Geol. Survey Prof. Paper 413, 78 p. Eckis, Rollin, 1928, Alluvial fans of the Cucamonga district, 59 southern California: Jour. Geology, v. 36, no. 8, p. 225-247. 1934, South coastal-basin investigation; Geology and ground-water storage capacity of valley fill: California Water Res. Div. Bull. 45, 279 p. Emery, K. O., 1955, Grain size of marine beach gravels: Jour. Geology, v. 63, no. 1, p. 39-49. Engel, C. G., and Sharp, R. P., 1958, Chemical data on desert varnish : Geol. Soc. America Bull., v. 69, no. 5, p. 487-518. Gilluly, James, 1946, The Ajo mining district, Arizona: U.S. Geol. Survey Prof. Paper 209, 112 p. Hack, J. T., 1957, Studies of longitudinal stream profiles in Vir- ginia and Maryland: U.S. Geol. Survey Prof. Paper 204-B, p. 45-97. 1960, Interpretation of erosional topography in humid temperate regions: Am. Jour. Sci., Bradley Volume, v. 258-A, p. 80-97. Hack, J. T., and Goodlett, J. C., 1960, Geomorphology and forest ecology of a mountain region in the central Appalachians: U.S. Geol. Survey Prof. Paper 347, 66 p. Hunt, A. P., 1960, Archeology of the Death Valley salt pan, California: Utah Univ. Anthropol. Papers, no. 47, 313 p. XHunt, C. B., 1954, Desert varnish: Science, v. 120, p. 183-184. Hunt, C. B., Averitt, Paul, and Miller, R. L., 1953, Geology and geography of the Henry Mountains region, Utah: U.S. Geol. Survey Prof. Paper 228, 234 p. Leopold, L. B., and Maddock, Thomas, Jr., 1953, The hydraulic geometry of stream channels and some physiographic impli- cations: U.S. Geol. Survey Prof. Paper 252, 57 p. Leopold, L. B., and Miller, J. P., 1956, Ephemeral streams- Hydraulic factors and their relation to the drainage net: U.S. Geol. Survey Prof. Paper 282-A, p. 1-37. Leopold, L. B., and Wolman, M. G., 1960, River meanders : Geol. Soc. America Bull., v. 71, p. 769-794. Miller, J. P., 1958, High mountain streams : effects of geology on channel characteristics and bed material: New Mexico Bur. Mines and Mineral Resources, Mem. 4, 53 p. Nikiforoff, C. C., 1942, Fundamental formula of soil formation : Am. Jour. Sci., v. 240, p. 847-866. Rich, J. L., 1985, Origin and evolution of rock fans and pedi- ments: Geol. Soc. America Bull., v. 46, no. 6, p. 999-1024. Sharp, R. P., 1954, Some physiographic aspects of southern Cali- fornia, pt. 1 of chapter 5 of Jahns, R. H. ed., Geology of southern California: California, Div. Mines Bull. 170, p. 5-10. Troxell, H. C., and Hofmann, Walter, 1954, Hydrology of the Mojave Desert, pt. 2 of chapter 6 of Jahns, R. H., ed., Geol- ogy of southern California: California, Div. Mines Bull. 170, p. 13-17. Tuan, Yi-Fu. 1959, Pediments in southeastern Arizona: Cali- fornia Univ. Pub. Geography, v. 13, 163 p. U.S. Weather Bureau, 1932, Nevada see. 19 of Climatic summary of the United States, climatic data to 1930 inclusive: 34 p. 1935, Southern California and Owens Valley, sec. 18 of Climatic summary of the United States, climatic data to 1930 inclusive : 38 p. 5 Wolman, M. G., 1954, A method of sampling coarse river-bed material: Am. Geophys. Union Trans., v. 35, p. 951-956. Page Abandoned washes, Bat Mountain fan...... 25 Death Valley fans................~ $ 33 defined: - 9 desert pavements formed on...........__. 19 estimated mean size of gravel on...... 12 prigin 12 Shadow Mountain fan. 12 Alkali 56 TSH 2... ran 25 Alluvial fan, area of, defined...............--- 6 2, 55 Alluvial fans, characteristics of._..........--- 38 formation egy o 58 See also particular fan. Amargosa 6 Animal burrows.... 18 Appalachian 4 Arizona, pediments in...__._..________.____._. 59 :. IOL -.. oc cic scan 32, 38 Bat Mountain fan, abandoned washes 25 desert pavements On..._......._____.____. 25 drainage diversion......_.....__.._...__.. 26 general discussion....-..:..___........... 25 20-0200 loll conect es 6 MglOty 22-2. none nese ener es 26 miniature terraces on..........._..__..... 17 modern waghe8...._c_.._____._.._._l..cl.. 25 size related to source area. 30 washes, meander lengths......__....._..- 52 Bed material, Death Valley washes..._....... 42 Panamint Range washes........_._......- 43 Shadow Mountain washes...............~ 49 BiblMography............... Black Mountain fans.. Black Mountains...... Bonanza King Formation..._.....__....__... 25 Carson 9, 23, 24 Chloride Cliff. 30 .C o out cn rine os 6 Climatological data for region, summary.... 6 CORCIHSIONL 2.222 712.20 sys- coos rome cal alos 55 Copper Canyon... 32, 33, 38 Copper Canyon fan. 87 @CORTADHY .: IIID COA ues 6 Deadman Pasgi__....-....-2cscclll.lccocl. 6, 30, 32 Death Valley, contrast between east and west ee nn conk 37 Death Valley fans, general discussion...... 82 size related to source area...... & 39 24 Depositional segments, Black Mountains s 32 Greenwater Range fans...._._._..___..... 80 Shadow Mountain fan............._...... 18 Desert pavement, Bat Mountain fan.. 4 25 Death Valley fans........ & 83 defingd-.......__../...... . 9,16 Greenwater Range fans......_._....__.... 80 Hanaupah Canyon fan..................- 84 lateral movement of fragments............ 19 INDEX [Italic page numbers indicate major references] Desert pavement-Continued meandering gullies in....._..____.__.____.. miniature terraces __. on Panamint Range piedmont............ ONI@IA OL. 2... .L oolecoulvec cit. ? relation to areas of deposition......_.. relation to source area........._...... go Shadow Mountain fan... gilt beneath. ..-. Desert shrubs. See Shrubs, desert. Desert varnish.. Devils Hole... fans near.... fans surrounding hills near....._._......_.~ Diversion of streams. - See Stream piracy and Drainage diversion. Drainage area, defined............__......_.... See also Source area. Drainage diversion, Bat Mountain fan...... Shadow Mountain fan....._......__...... Eagle 000. EIOBION: 2. (Leos cones ere sno doe s nek bue a Fan-building wash, profile of............~ va Fan-building washes, change in size of material cc. cone. general Fanglomerate.......... FiCIOWOTKLLL . . . . «noose nle el ee Pet ls Funeral Mountains... Funeral Far CEOETADHY . 10-1 cron oce cue Corrie ove cher Gold Grain size, estimation of mean..............~- TOCS. . ... .- o ece cee cece ados aah Greenwater Canyon.... Greenwater Range... T9HS Of. .L. .- . ue dee dene cer an on piedmont east of..._..____..._.__... Greenwater Valley......._________.... fong In..... c.... Grid sampling method, accuracy of.........~- general CTUSEL LL A2. ICARE aa venn ane seas Hack, 3. 'P., AuObOUL L200. 200 cer ce Hanaupan Hanaupah Canyon fan............ Highlands, significance of type of rock...... History, Bat Mountain fan..................~ Shadow Mountain fan, reconstructed from analysis of four pavements. ..... .. structural, significance of......._._._...-. Investigation, method of study............... Johnson olen Johnson Canyon 88, -A, Page 26 17,19 34 19 EH 22 16, 21 19 12,16 6 26 22 56 24 55 43 39 25, 89 2 6 38, 52 Page LandgHdes /+ . (L1. L.- 25 Little River, Va..: 3.0... 20.0. dou. .sp 30 Meandering gullies in pavements............. 26 Meandering washes..........-- ure 62 Modern washes, Bat Mountain fan. s+ 25 Death Valley fans. ...... .. 88 ...... .N. ooo tel 9 a 12 Shadow Mountain fan.. &e 11 Mojave Desert......_.... a 58 Mormon Point? -. . . ..- cus a swe uve 32 Movement of detritus, downfan.............. 23 Old: Traction 11,12 Panamint R&nge. -. .L... 2121 [220 lie 6, 32, 33, 38 Panamint Range fan........--. 52 Pavement. See Desert Pavement. Podiment, defined.... cr ener 2, 57 Shadow Mountain fan...... 21 ...... 9 formation Of.... ._.. ues 68 north and south of Shadow Mountain.... 58 size and relation to fans...............---- 88 Piedmont, defined... -... ._. ._... 2 Greenwater Range fans..________.....---- 80 Greenwater Valley......__...____._.__ _... 82 Shadow Mountain........._............. 56 surface features deus 56 Ploy BK.. A ANI ice- 38, 58 Quaternary alluvial deposits...._.._.......... 7 Resting Spring 6 Rillensteine........ 18 Rio Grande Valley, N. Mex___.._.__........- 52 Rocky L... ec eus 4, 52 Salt efflorescence$. ..... Shadow Mountain... Shadow Mountain fan...._............_.._._. _ 56 abandoned washes.............._........- 12 depositional segments on.... 13 desert pavement............... 16 general description...........- 7. lout 6 §OOIOEY L...... «.ll. con 9 * 9 3 EH 3 11 prIgih Of SL.... L L1 .oo 000000 esp rea ate 21 pedithent Of-. -- Ite andes. 21, 28 pediments near............ 9 size related to source area............_.-.- 38 washes, meander lengths_._._...........- 52 Shenandoah Valley, Va................._..... 390, 52 Shrubs, desert, on fans in Greenwater Valley... 32 desert, on pavements.....____..__..._....- 17 in abandoned washes...._._.............. 12 61 62 Page Silt, beneath pavement....._...._____________ 10 flow 20 formation of.. 20 origin of vesicular structure of......_..... 20 fix Spring Canyon.. _. 33 Slope. of fan......" Z ALLA AAC iet 55 Source area, alluvial-fan size related to...... 38, 56 defined.... es saa chs 6 See also Drainage area. Starvation Canyon 87 Stream piracy, on Shadow Mountain fan.... 11,22 Structural history, significance of.........._.. 67 System of alluvial-fan formation......._...__. 67 INDEX Page Telescope FRealc..2.... licen cr el NZ s 33 .... (2 .a ccs LAT 7 Terraces, miniature, on pavements..__..___. 17 Trail -. 6,33 Trail Canyon fan.......__._... - $8788 Transportation, process of...... h 24 Trask sorting coefficient...._________________ 4 Vesicular structure of silt, origin of......__... 20 Volcanic Fooks sue. _ 20s .ll soles e 30 Wash channel width, compared with that in humid 39 Washes, Panamint Range S- :o 1003000002, See also Fan-building washes. See also Meandering washes. See Modern washes and Abandoned washes. Weathering 2.21. 20. 0.1 cous o ooo over Wentworth size classes. ._..__________________ WAlow ©Cregik -- . 220000000900 oot L Apacs Willow Creek fgh. 222. .s 21 . 22 ca eus en geography;... 2220.00.20. 00. Its AF Witiow Spring... 3s. seqdlooll lineage eon t Page 39 33 24 33 33 33 U.S. GOVERNMENT PRINTING OFFICE : 1964 0O-735-932 GEOLOGICAL SURVEY 116" 22:30" UNITED STATES DEPARTMENT OF THE INTERIOR 1730" PROFESSIONAL PAPER 466 PLATE 1 116°15" 5°17'830" B6°I6'15" <_ F\\\\“ X ""Tea s to trg oar r «8.9. < vo bru, e 9 c - 36° 17:30" d\\\§\§\\ 36°16 15" INSERT MAP SHOWS FAN EAST OF ALKALI 3 MILES soOUTHWEST OF SHADOW MOUNTAII\|I 116"°15 FLAT AND f Mountain 5071 V302 TRUE NORTH APPROXIMATE MEAN DECLINATION, 1964 116° Base map from Topographic Division U.S. Geological Survey multiplex compilation sheet. Outlines of channels, pavements, and washes drawn with Kelsh plotter from aerial photo- graphs Recent Pleistocene and Recent MAP OF SHADOW MOUNTAIN FAN, ASH MEADOWS QUADRANGLE, CALIFORNIA AND NEVADA 17:30" 1000 0 5000 10,000 FEET S-- r= === msm a rm 1000 0 1000 2000 METERS c E. X PL A N A T. | ~O N Unweathered gravel Boulder to pebbly gravel and sand. Fragments both slab-shaped and bilocky with angular to slightly rounded edges Surface form of deposit Braided channels and ridges-the modern washes-with a microrelief ranging from Alluvium along Carson Slough and on Alkali Flat Sand, silt, and clay 1 to 3 feet Arid-basin sediments Qs, silt, sand, clay, and subordinate gravel Qgv and Qgp, bouldery to pebbly gravel, breccia, sand, and silt; fragments dominatly quartzite, commonly cemented by caliche Surface form of deposit Qs, plain commonly with salt crust, and shallow washes. Includes small areas of abandoned wash Qgv, abandoned washes floored with layer of varnished rock fragments. Surface consists of broad ridges and swales with a micro- relief commonly of about 1 foot, but not more than 2 feet, that are the somewhat subdued remmants of braided channels. Includes many narrow modern washes floored with unweathered gravel (Qg), especially on lower part of fan Qgp, desert pavement. - Armor of varnished fragments forming a nearly plain surface. Fragments range from pebbles to boulders and touch each other. Fragments are commonly angular and appear considerably weathered QUATERNARY Middle or Upper Pliocene or Pleistocene Pliocene and older Cambrian Lower Cambrian Fanglomerate Conglomerate, breccia, sandstone, and sub- ordinate tuff. - Underlies low hills north of fan and small areas of pediment along its southern margin Tso Sandstone and clay Chiefly brown, yellow, or gray sandstone and clay, with subordinate siltstone, shale, tuff, limestone, and conglomerate. - Underlies a pediment Fanglomérate Reddish-brown conglomerate and breccia. Forms hills Unidentified limestone and dolomite Stirling(?) Quartzite Light-gray, reddish-brown, and greenish-gray quartzite with subordinate micaceous shale and quartzite pebble conglomerate; a little of the underlying Johnnie(?)Formation may be included 116°15' Geology mapped by C. S. Denny, assisted by H. F. Barnett, J. P. D'Agostino, and Jack Rachlin, 1956-58 INTERIOR-GEOLOGICAL SURVEY, WASHINGTON, D. c.-1964-Gé3289 C~ Z iy Contact I4 Contacts between units of Pleistocene and of Ji. Recent ages are generalized or diagrammatic [ral id LU 3% C 958 Arbitrary north and south i- boundary of Shadow Mountain fan Outline of drainage area &e < --- § Contour Pf” Interval 200 feet i— 63 x Sample locality Z - T Segment of fan east of Alkali Flat C Area of wash with slightly g cone-shaped surface (0.55 sq mi) < U ee homed hack hans Arbitrary north and south boundary of fan east of Alkali Flat UNITED: STATES DEPARIMENT OF THE INTERIOR GEOLOGICAL SURVEY 116"°30' PROFESSIONAL PAPER 466 PLATE 2 EXPLANATION Unweathered gravel Bouldery to pebbly gravel and sand. Frag- ments both slab-shaped and blocky with angular to slightly rounded edges Surface form of deposit Braided channels and ridges -the modern washes- with a microrelief ranging from 1 to 3 feet Bouldery to pebbly gravel and sand Fragments dominantly limestone, dolomite, sandstone, and quartzite; commonly cemented by caliche Gravel and sand, undifferentiated Surface of deposit is a mosaic of modern and abandoned washes and desert pavement. Microrelief not more than 2 feet. Individual ; tches to U t Surface form of deposit C4 See aks Qgv, abandoned washes floored with layer of varnished fragments. Surface consists of broad ridges and swales, with a micro- relief of about 1 foot, that are the somewhat subdued remmants of braided channels and of bars QUATERNARY Qgp, desert pavement. - Armor of fragments forming a nearly plain surface. Frag- ments range from pebbles to boulders and touch each other; commonly angular and considerably weathered. Quartz-rich rocks varnished; carbonate rocks faceted or pitted; many are thin slabs Pleistocene and Recent Landslide Tabular bodies of limestone and fanglomerate, highly brecciated. In large part mantled by rubble , 36°20" 36°20 Gravel beneath landslide Pebble, gravel, and sand MAJOR UNCONFORMITY e 9 9 569 I* se 8 Fanglomerate Reddish-brown cobble fanglomerate; includes some pebble conglomerate and sandstone Limestone Yellowish-gray thick-bedded limestone and reddish shale; subordinate sandstone and tuff Miocene and older(?) TERTIARY Conglomerate Red pebble conglomerate, subordinate sandstone and siltstone SS Cherty limestone, limestone, and dolomite Subordinate samcstone, siltstone, and quertzite ~~Toe of fan TRUE NORTH APPROXIMATE MEAN DECLINATION, 1964 DEVONIAN AND MISSISSIPPIAN Contact Generalized or approximate; Radio telephone station includes fault contacts RYAN QUADRANGLE ASH MEADOWS QUADRANGLE Outline of drainage area Shown only in mountains STATE ROUTE 1 90 3200 Generalized contours 100-foot interval on fan; 200-foot interval in mountains (above 2800 feet) 116° 30 INTERIOR-GEOLOGICAL SURVEY, WASHINGTON, D. C-1964-G63289 Base map from Topographic Division U.S. Geological Survey multiplex compilation sheet. Outlines of channels, pavements, and washes drawn with Kelsh plotter from aerial photo- graphs MAP OF BAT MOUNTAIN FAN, ASH MEADOWS QUADRANGLE IN CALIFORNIA Quaternary geology mapped by C. S. Denny, assisted by H.F. Barnett and J. P. D'Agostino, 1956-58; pre- Quaternary rocks mapped by x24? Drewes and Denny, 1958 f Sample locality 10,000 FEET 1000 0 5000 I r --- 2000 METERS UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY 6°35 30 RYAN QUADRANGLE ASH MEADOWS QUADRANGLE 25" 15: ,1A,\ V £: >V>’g < "0 4 > < ~s "CR A 71LA—<'m’\,’)L /7/_A\21\/ru £: 354 8k ew 3 y (Bag ©: $ t .% gv 3 A >\"g\7V1 € Fum ig s iC\/‘J/\< > mg . Gree Pleistocene and Recent 25" TRUE NORTH Deadman Pass APPROXIMATE MEAN DECLINATION, 1964 r FUNERAL PEAK QUADRANGLE 6°35' 30' Base from U.S. Geological Survey isei-essces 15-minute quadrangles, Ryan, Ash Meadows, Funeral Peak, and Eagle Mountain. EAGLE MOUNTAIN QUADRANGLE 2004 Arid-basin sediments Pebbly to bouldery gravel, sand, and silt. Frag ments dominantly: of volcanic rock; commonly cemented by caliche. Include un- consolidated gravel in washes Surface form of deposit Qg, modern and abandoned washes consisting of braided channels and gravel bars. Fragments on surface of abandoned washes are varnish coated; those on surface of modern washes are essentially unweathered Qgp, desert pavement. fragments forming a nearly plain surface. Fragments are largely of volcanic rock and range in size from pebbles to boulders Outline of drain x11 25" INTERIOR-GEOLOGICAL SURVEY, WASHINGTON, D. C MAP OF PIEDMONT EAST OF GREENWATER RANGE, CALIFORNIA 1 Ya 0 1 2 3 4 5 MILES a % _——Em—~—ifi 1 8 20 1 2 3 4 5 KILOMETERS PLATE 3 116 °20' S] QUATERNARY Armor of varnished Volcanic rocks and associated sediments Basalt, andesite, rhyolite, rhyodacite, vitro- phyre, tuff, sandstone, and conglomerate. Include small masses of pre- Tertiary rocks. Form hills and mountains TERTIARY Granitic rocks Chiefly mongzonite; form hills Contact Generalized or approximate nra Northern and southern boundary of segment of piedmont between Lila C Mine and age area Sample locality 16°20" Geology generalized from Drewes (1963), and Jennings (1958) PROFESSIONAL PAPER 466 715’ 08" 36°00 36°20° PROFESSIONAL PAPER 466 + UNITED STATES DEPARTMENT OF THE INTERIOR # GEOLOGICAL SURVEY PLATE 4 116°50' 4 40" 116° 35" < aes £ 56°15" pmo ms wass EXPLANATION Rant i+ ;//:\/>_/\\ xI’/\\/7\\/Z\;/ 4 DEATH VALLEY GREENWATER VALLEY 'p€r % 1/3/63‘: A345 ( 3 £ ish wla yo o 4 te J by Z 4 dass Beas s. - ose: ® + Silt and evaporites _ Unweathered gravel in modern washes Gravel, sand, and silt t Saltpan on floor of Loose pebble and cobble gravel Form irregular beds, commonly cemented by Death Valley caliche. Include unconsolidated gravel in washes & 0 Surface form of deposit 70 S ( Qg, modern and abandoned washes consisting $ of braided channels and gravel bars. Frag- i * Y“ fq ; , ments on surface of abandoned washes are < m no Varnished gravel in abandoned washes varnished; those on surface of modern wash | z * § Pebble to boulder gravel; fragments at are essentially unweathered ?Df z gfi surface strongly varnished but firm Qgp, desert pavement. Armor of varnished [ll * $ fragments forming a nearly plain surface; E é 8 frag ments range in size from pebbles to 3 7 é boulders 0 & A Q4 « m Weathered gravel Pebble to boulder gravel and sand, commonly & w 24 cemented by caliche. Locally faulted and 3 3865 as probably tilted. Surface of deposit is 10 commonly a desert pavement, an armor of 10° 3 angular fragments from less than 1 inch to r f : : XE A ¢ Wf ist / several feet in diameter. Varnish on sur- § : % It' Ap Cal #5 "*y ALC hya" = . Dl/J/ €] « face of deposit less distinct than on gravel F # (3 ~ : in washes. Fragments in weathered zone g R U _ commonly much disintegrated J J { C & f TVV [s 7 ~ * > m T4 . >- L A \ or y Fav f \ g/ cf acy a l:- * g mp Sedimentary rocks predominate Volcanic rocks predominate Granitic rocks i } t O Includes some beds of early Includes small areas of Chiefly monzonite Lu * i \ Pleistocene age Paleozoic sedimentary rocks +- ¥ . E \ //\>/\|>/\|; C. Ar pCr/ \\//\ mM ) : 33. /\//l\' < * / C vze> < / Metamorphic rocks U ¥ 3917 Metadiorite, schist, gneiss, marble L : © P © m # tov. 4 "y fis i L. C Q ; Funeral, Peak + " - "« ) S 41L74'L1v>bLcL me- mates, be I ( (4 y as [A_ Wes Contact j 7 y A 9. y. t 3 7|> § f s / ; 4 ely t "gf ? Generalized or approximate; / i*:"'." ~" va includes faults "G i ; 2 474 yk 3 N. K J | p+ejz ant mod 3597 s j Y.» UB « !" + f d At aes 05 's C.. [I €, ® <2, € o \ j \ Ae . 1A *n ys, B \ Fault scarp on fan B w \ ss vos 54 2 Many small scarps omitted 'we 4 > v # \ i \ r”(7(V:VL\_A<" a* == k» ; 3 jA [r : ays fs Outline of drainage area * \ y & 3 L) f v.> j * mag 5 Shown only in mountains f » 7 7° 3 3 % \ L." Fa < A51 #: eas a Mormon‘ééht‘. N 3 ' ¢ * \\ &\ J (L.74>4FtL¢\>L-r £ e : K : y ome ..- 2 121 2200... . 320 2040, 0 onle o see a ol Feats To. Cee sa e sol ch a aet a i. | Ce n Wl he Tacs. Oot t fe on algae tan ooc iar menues ass hin; on raat coset mas % f € yore 2 >i e: <7?» at. 2% se- Outline of fan or c* \\\ Z \ Willow Sprifg 4 ves t as t fan segment x3 o xmas a Pees tag iin sir. oa yrs: Alps. \ ay ya als , I A vil ws 2 $ j I/l(\j§\‘/\V//\ 2s rat) V>VJALL7 s | j (/\/i\\/:Vl> \ >/\7\J/\Z\7\/: r- i \ v <7 27 5 £. V y 3... / i IC re \/, % * se Vrv>firh> a]" Pas ac f > A bl“ AN O4 34 y 8 F f t APPROXIMATE MEAN 2 r) pf a R an OI: an spgmen DECLINATION, 1964 € 4 / mentioned in text r 5 * 45g? 4 yl < { g w f . f * g% \’4 36°00" BENNETTS WELL QUADRANGLE FUNERAL PEAK QUADRANGI 3 ’ c x4 3 y § sway 116° f 45" 40" intERrion-eroLocicAt WasHINGToN. 5. C iig*35' %f 36°00 Base from U.S. Geological Survey 15-minute Geology generalized from Drewes(1963) and C. B. Hunt (unpublished data) quadrangles, Bennetts Well, and Funeral Peak f MAP OF BLACK MOUNTAINS, CALIFORNIA, SHOWING ALLUVIAL FANS j 1 ~6 i 2 3 4 5 MILES E--__E-- --- a m 0 1 2 3 4 5 KILOMETERS . I 36°20 19't 10 36°05" UNITED STATES DEPARTMENT OF THE INTERIOR y GEOLOGICAL SURVEY 117"°05" 117° 55 & Telescope Peak ~~ yp 74 2 < Wildrose 116°50' Rogers Peak Bennett Peak a A renga st Eps . g [s 5s. .0Dv°°°°-°0 gas oquw s 0 80% 0% TRUE NORTH APPROXIMATE MEAN DECLINATION, 1964 ‘Pbrier Peak Base from U.S. Geological Survey 15- mlnute quadrang|es Emigrant Canyon Furnace Creek, Telescope Peak, and Bennetts Well 117°55' 30550 s 4° af o s AACS o . 8 .. [+ no ge 8+ bs g ® n 9o'rs ® Pate . tus 81 + 898 t+ e 8+ te O80 94. Put, a a 0 a 8 (+0900 59, 5s B £85 Q0‘Bno°0> + 10' .v“ouufl0‘§°a°0'g‘ *%" £ MAP OF PARTS oF THE PIEDMONT EAST Or: THE PANAMINT RANGE, CALIFORNIA HANAUPAH AND JOHNSON CANYON F ANS MAPPED IN DETAIL 5 MILES ] 1 Ya 0 1 p v3 ras foo fee- 1 5 'O 1 2 % 3 4 5 KILOMETERS CE-H E= f--- ] INTERIOR-GEOLOGICAL SURVEY, WASHINGTON, D. C 1964- G 63289 w 116°50' Geology generalized from C. B. Hunt (unpublished data) 36°20 Upper Precambrian Pleistocene and Recent and Lower Paleozoic Saltpan.on floor of Death Valley EXPLANATION FANS AT MOUTH OF TRAIL, HANAUPAH, AND JOHNSON CANYONS Ose. | Silt and evaporites Varnished gravel in abandoned washes Pebble to boulder gravel; fragments at surface strongly varnished but firm Weathered gravel Pebble to boulder gravel and sand, commonly cemented by caliche. Locally faulted and probably tilted. Surface of deposit is commonly a desert pavement, an armor of angular fragments from less than 1 inch to several feet in diameter. Varnish on sur- face of deposit less distinct than on gravel Unweathered gravel in modern washes Loose pebble and cobble gravel in washes. Fragments in weathered zone commonly much disintegrated MOUNTAINS Sedimentary and metasedimentary rocks Include small areas of granitic rocks and volcanic rocks of Tertiary age PROFESSIONAL PAPER 466 PLATE 5 OTHER FANS ,n_.,_,‘goé€1ffu‘3;}1 Gravel Both unweathered and varnished. Includes both modern and abandoned washes y. . < 4 t LU 1—— < km 0 = ® Q 5 Fa ¢|~ " / INDEX MAP SHOWING AREA OF THIS REPORT - ammmons e Tz 3 |CLarkDALE _ COCONINO COUNTY _ _| 3 Q {MU/l YAVAPAI COUNTY°¢(‘ ts 2204 a //,/// (Sn 4> "Ty ® . g" \'A 1, 7, § (00 / 70\ ”Mu/lunowl/L' 5 & 4}; «Perkinsvill ¢." > cals & } z metes ser ig = 3" N x 47 [ Anal \ & 38 ®, £1~ * Ig Ly orp Qx-Ql'fp/(oSimmons E E % + g f pA a 8 ws ec C !$ E 7 Valley l o irRon,sprines % PRESCOTT MINGUS MTN ugk, / > Cottonwood s s ¥3 ( d ", s 0 | 'm of 2 | $ § \ - o 4 ¢ & (< ai £ 9/6 / o % /4.@e ia E; / rescott /(J Dewey \ » Copper a & g 30 Basin ; ' o e KIRKLAND MT UNION T pl as J ag p , ce # / 4 £ & B efor T Fas ? .o Walker e J) y vG" o & Aj I (0) #" f > &/ % h $ z ol & 0 $] ly $ :$ H / 72. \ g 15 & x.: Ag 34°15" [ ¢ To Wickenburg {To Phoenix 112°45" and Phoenix 5 0 5 10 15 20 MILES Caco | 1 | | FicUrE 1.-The study area. Inset shows location of the two quadrangles in relation to Yavapai County and the State and the approximate position of the three topographic regions. 6 GEOLOGY OF THE PRESCOTT AND lying but is related to the plateau by its flat-lying Paleo- zoic rocks. The southwest-facing escarpment of Black Mesa, largely northwest of the area, is part of, but not continuous with, the plateau margin to the east. Gran- ite Creek has been deeply incised into the resistant Mazatzal Quartzite (pl. 2), and gorges have been cut in Paleozoic rocks and overlying basalt flows by the Verde River (fig. 2) and its tributaries. An isolated block of granite northeast of Prescott has been eroded into rec- tangular and picturesque forms owing to strong joint control (fig. 14). Other forms include volcanic cones, andesitic plugs (fig. 19), buttes and mesas, which are remnants of once more extensive basalt flows of Paleo- zoic rocks, and a few narrow hogback ridges formed by erosion of monoclinally folded sedimentary rocks. Fisurs 2.-The view is to the east-northeast along the Verde River, Paulden quadrangle, from near 1,410,500 N., 384,300 E. The follow- ing units are exposed : Precambrian quartz diorite (ad), Tapeats Sand- stone (€+], Martin Limestone (Dm, units A-D), and Redwall Limestone (Mr). Note figure (arrow) for scale. Altitudes range from 6,968 feet near the south margin of the area (pl. 1) to about 3,875 feet along the Verde River in the northeastern part (pl. 2). Much of the area is between 4,500 and 5,500 feet in altitude. High- est altitudes in surrounding areas are between 7,500 and 8,000 feet. PAULDEN QUADRANGLES, ARIZONA Drainage.-The Verde River and parts of two of its tributaries are the only perennial streams. The prin- cipal tributaries of the river (fig. 30) are Granite Creek, which flows northward across the area, and the washes in Hell Canyon and Big Chino and Williamson Valleys. The southeastern part is drained by the Agua Fria River and its major tributary, Lynx Creek. Dams im- pound water to form Sullivan Lake-the headwaters of the Verde River (pl. 2)-and Watson Lake and Wil- low Creek Reservoir in the Granite Dells north of Pres- cott (pl. 1). COlimate.-Arizona has a wide range in climatic con- ditions owing to a wide range in surface altitudes. The Prescott-Paulden area lies between the extremes of both altitude and climate. Only rarely does the tem- perature reach 100°F in Prescott, where below-zero tem- peratures are not common. Incomplete weather reports are available for Prescott since 1872 and for the Pres- cott Municipal Airport, 8 miles north of Prescott, since 1942. These data are summarized in table 2. Summer and winter are the periods of greatest precipitation. TaBus 2.-Temperature, humidity, and precipitation in the Prescott area [Unless otherwise noted, length of record is as follows: For temperature and humidity Prescott, 40 years; Prescott Municipal Airport, 10 years. For precipitation: Prescott, 28 years; airport, 10 years) Prescott Airport Temperature, in degrees Fahrenheit: January average.....k_..l_ll. ._" 35 35.6 July 72.5 75 Annual 1 54 57 1 105 102 Minimum... 1 -21 -5 Summer T0 rs Winter average......cl..-........ 80% 8 Humidity, in percent: Annual Average.... l cled PELLE U 47 December 66 JUNC AVETARCOL LEE rela rre! aan 26 Average precipitation, in inches: se cunel cole 1. 80 1.19 __. 2. 20 . 69 so 1.56 . 88 rentes seaon 1. 20 rd May...... lle loo nomen . 44 49 TUHC. ..:: cro oes 34 A11 July... _: N MMO.... 2. 62 2. 69 2:1 !. CE E: 3.39 2. 81 1.98 1. 20 October-... . 99 . 64 November. -one 1. 08 . 60 2. 38 1. 31 AnfRUAL L LOE tee -eq 19. 98 13. 02 pnowfall.-. c 20 ! Length of record: 80 years. July and August are generally the wettest months of the year, most of the precipitation falling during local thunderstorms. Snowfall is common above an altitude of 5,000 feet but rarely accumulates at this altitude. The average winter snowfall at the air- port is 20 inches. Compared with lower altitudes, higher altitudes have cooler summer and colder winter temperatures and greater accumulations of snow and GENERAL GEOLOGY I. somewhat greater rainfall. Recorded precipitation at the airport is lower than at Prescott because of the air- port's lower altitude and greater distance from the mountains and also because the airport records were taken during a period of drought. Vegetation.-Pine forests, pinyon-juniper woodland, grassland, and chaparral constitute the four types of vegetation in the area. Pine forests are limited to the southern part of the area, mostly above an alitude of 5,500 feet. Sparse pinyon-juniper woodland (fig. 2) covers a large part of the northern half and a little of the southern half. The chaparral areas (southwestern brush- or shrub-type vegetation) occur principally in the southern part along the margin of Chino-Lonesome Valley. Most of Chino-Lonesome Valley (figs. 19, 28) and the area east and south of Drake is in grassland. For a more detailed account of the vegetation of adja- cent areas, see Anderson and Creasey (1958, p. 5-6) and Lehner (1958, p. 518-519). GENERAL GEOLOGY Rock formation in the Prescott and Paulden quad- rangles belong to the Precambrian, Paleozoic, and Ceno- zoic Eras. The distribution and structure of these for- mations are shown on plates 1 and 2. The formations are shown diagrammatically in figure 3. The older Precambrian formations consist of volcanic, sedimen- tary, and intrusive rocks. Volcanic rocks belong to the Alder Group of the Yavapai Series; the sedimentary rocks belong to the Mazatzal Quartzite. The Mazatzal Quartzite is in fault contact with the Alder Group. Precambrian igneous rocks intrude the Alder Group but not the Mazatzal Quartzite. The intrusive rocks consist of gabbro, granodiorite, granite, and alaskite of Precambrian age and are probably closely related in time. Paleozoic rocks of Cambrian and Devonian through Permian ages presumably overlay the Precambrian rocks throughout the area but have been stripped from the southern half. Mesozoic rocks, with the possible exception of the Moenkopi Formation of Triassic age, were not deposited here. The Cenozoic rocks consist of andesite dikes of Tertiary(?) age, volcanic and sedi- mentary rocks of late Tertiary (?) age, and Quaternary gravel and alluvium. The sedimentary rocks of late Tertiary (?) age consist of gravel, sand, silt, clay, and thin beds of rhyolite tuff and freshwater limestone of fluviatile and lacustrine origin. The interbedded vol- canic rocks are basaltic flows, tuffs, and cinder cones and andesitic plugs, domes, flows, breccias, mud flows, tuffs, and gravels. The sedimentary and volcanic rocks filled Chino-Lonesome Basin and covered much of the area northeast of the basin. These rocks are westward extensions of Pliocene(?)-Pleistocene( ?) rocks, which are separated to the east into the older Hickey and younger Perkinsville Formations on the basis of rela- tion to structure (Anderson and Creasey, 1958; Lehner, 1958). Locally in the Prescott-Paulden area andesite separates older from younger gravel and basalt, but elsewhere no clear-cut division of an older and a younger formation could be made. < Rocks of the Alder Group have been intensely de- formed ; in most places bedding and foliation are about parallel, and the formations dip steeply. Many of the Precambrian intrusive rocks have also been intensely deformed. Distributive shear characterizes much of the older Precambrian deformation. The Mazatzal quart- zite, however, although folded, has not been intensely deformed in this area. Paleozoic and late Cenozoic rocks, most of which are nearly horizontal, have locally been displaced by high-angle faults, and the Paleozoic rocks have been folded into sharp monoclines. OLDER PRECAMBRIAN ROCKS The Precambrian rocks of Arizona have been divided into older and younger Precambrian (Butler and Wil- son, 1988, p. 11) on the basis of a major unconformity. The older Precambrian rocks include the Pinal Schist . in southeastern Arizona, the Yavapai Schist and the Mazatzal Quartzite and associated formations in cen- tral Arizona, the Vishnu Schist in the Grand Canyon region, and the granitic rocks that intrude the schist and quartzite. Wilson (1939, p. 1153) correlated the quartzite in the Paulden area with the Mazatzal and recognized only one period of deformation and intru- sion, which occurred after the deposition of the Mazat- zal. - In the Paulden quadrangle, evidence suggests that the quartzite is younger than deformation of both schist and granitic rocks; the quartzite was not intruded by granitic rocks or deformed to the extent that the schist and granite were. - Younger Precambrian rocks- the Grand Canyon Series to the north and the Apache Group to the southeast-are not present in the Prescott- Paulden area. The regional correlation of the Pre- cambrian rocks was discussed by Anderson and Creasey (1958, p. 44-45). YAVAPAI SERIES-ALDER GROUP In the Jerome area Anderson and Creasey (1958, p. 9) recognized two groups (Alder and Ash Creek) in rocks previously called the Yavapai Schist. They therefore redefined the Yavapai as a series. Only the Alder Group is represented in the Prescott-Paulden area. Rocks of the Alder Group were described by Ander- son and Creasey (1958, p. 20-32), who redefined strata previously called the Alder Sreies (Wilson, 1989, 8 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA SYSTEM SERIES FORMATION AND MEMBERS THgggngss a 1 & © ® E (3 "C € ® Pediment and terrace 0-50 + * C £ gravels and alluvium, Qg of each type S 8 of deposit 3 § TRE arms: @ MZ "am & UNCONFORMITY 7 & & = Sedimentary rocks, Ts e g Volcanic rocks: < ,< Andesite, Ta 0-1700 + ie 5 Basalt, Th , F # Basaltic cinder cone, Tc => UNCONFORMITY 3 Coconino Sandstone, Pc 400 + 4 ® 4 E Upper member, Psu 700+ < £ Supai & 5 Formation a. z 0 C 5 Middle member, Psm 250+ 6 ? -+ -2--- Lower member, PIP sI 600+ 3 | 22 6 | $5 = 5 | ¥ € t | £ * Mr g > ags rana n anata UNCONFORMITY 7 m | 2 5.2 .o < | gk) $378 Redwall Limestone, Mr 219+ o = 9 -% 7 t o ~~~ UNCONFORMITY ~~~~ : 4 C & < l P3 & % i o $o Martin limestone, Dm ~>50-439 Ls <5 € o = a # 5 *% UNCONFORMITY ~ g & € Tapeats Sandstone, €t 0-154 9 ANGULAR UNCONFORMITY 10 g Mazatzal Quartzite has??? LOgCKgsg s Mazatzal o & nlin mp. Quartzite u) a mq, ma}, Map Alder Group of ~ AFK Wok a E me, , mc, Yavapai Series . 4000+ \Wgb)dg) yr al /+ \- 0 o av, gv, cv, ik, sv, iu, tu Alder Group ; Kw} «olor 1 be Fault contact, Mazatzal may be unconformable 30,000+ t a Te ge fa g fck we above Alder Group and intrusive rocks Ficur® 3.-GENERALIZED STRATIGRAPHIC SECTION, OLDER PRECAMBRIAN ROCKS GENERAL DESCRIPTION AND REMARKS Gravel veneer on pediment surfaces; gravel, sand, and silt on terraces; alluvial and colluvial material on slopes and valley bottoms; sand and coarse gravel in stream channels. Unconsolidated except where locally ce- mented by caliche Sedimentary rocks: fanglomerate, coarse to fine gravel, sand, silt, clay of fluviatile and lacustrine origin, thin beds of fresh-water limestone, and minor amounts of interbedded rhyolitic tuff, Ts; volcanic rocks: andesite flow, plug, breccia, mud flow, tuff, and gravel composed largely of andesite fragments, Ta; basalt flow, Th; basaltic cinder cone, Tc. In places andesite separates older from younger sedimentary and basaltic rocks Massive pale-orange to grayish-orange sandstone characterized by crossbedding on a large scale. In most places forms a sheer cliff Chiefly strongly crossbedded reddish-orange sandstone separated by horizontally bedded and thinly laminated fine-grained pale-reddish-brown sandstone and siltstone; forms cliffs, buttresses, and pinnacles Chiefly pale-red to grayish-red somewhat calcareous siltstone interbedded with conglomerate and cross- laminated sandstone; very irregularly and thinly bedded; forms a subdued topography Thin-bedded reddish-orange shale, siltstone, sandstone, and some gray limestone; chert and limestone breccia at base; thicker bedded and contains less shale upward; pink crossbedded sandstone at top; forms steplike slope Comprises four units: unit 1 consists of 0 - 35 feet of thin-bedded reworked Devonian material and 23 feet of bluish-gray oolitic limestone; unit 2 consists of 80 feet of fine-grained cherty limestone; unit 3 consists of 81 feet of coarsely crystalline limestone; and unit 4 consists of 35 feet of bluish-gray micro-oolitic to pellety limestone, locally underlain by crystalline and cherty limestone and by a solution breccia. Formation forms a cliff in most places Comprises four units: unit A is 0 - 21 feet of cliff-forming crossbedded impure clastic dark-gray dolomitic limestone; unit B is 0 - 97 feet of slope-forming light-gray thin-bedded lithographic limestone with shale partings; unit C is 0 - 75 feet of thicker bedded mottled cliff-forming dark-gray dolomitic limestone; unit D is less than 50 to 255 feet of alternate thin beds similar to units A, B, and C, with some siltstone, shale, and sandstone; forms a steep, steplike slope Comprises two units: a lower unit of cliff-forming dark-reddish-brown and buff crossbedded sandstone 0 - 142 feet thick that averages at least two-thirds of the total thickness, and an upper unit of slope-forming reddish- to yellowish-gray mudstone, siltstone, and shale, and locally conglomerate, 0 - 22 feet thick 10 Intrusive rocks: (from oldest to youngest) gabbro, gb; Government Canyon Granodiorite, gg; Prescott Grano- diorite, pg; alaskite, al; and Dells Granite, dg; (not shown are coarse-grained granite, fine - grained granite, and younger diabase and fine-grained gabbro-diorite). Mazatzal Quartzite: includes lavender, reddish, and grayish massive to crossbedded fine- to coarse-grained quartzite and minor granule conglomerate, mq; interbedded lower and upper red argillite, ma , and may,; and lower and upper conglomerate containing quartz and jasper pebbles, cobbles, and small boulders, in- terbedded with quartzite, me, and me, Alder Group rocks: unnamed basaltic flows and tuffaceous rocks of the Alder(?) Group, av; Green Gulch Volcanics, basaltic flows, breccias and tuffs, and rhyolitic and basaltic tuffs and flows, gv; Chaparral Volcanics, andes- itic and rhyolitic tuffs, cv; Iron King Volcanics (not exposed), andesitic tuffs and andesitic or basaltic flows, ik; Spud Mountain Volcanics, andesitic breccia and andesitic tuffs, sv; Indian Hills Volcanics, rhyolitic and an- desitic or basaltic flows, a few tuffaceous rocks, iu; Texas Gulch Formation, largely rhyolitic tuffaceous sedimentary rocks, some rhyolite flows or massive tuffs, andesitic flows and tuffs, and minor amounts of conglomerate and jasper-magnetite beds, tu PRESCOTT-PAULDEN AREA, ARIZONA. 10 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA p. 1121, 1159). In general the group consists of basaltic, andesitic, and rhyolitic flows and tuffaceous sedimen- tary rocks. Of the six formations described by Ander- son and Creasey, five were recognized in the Prescott- Paulden area; these are the Texas Gulch Formation and the Indian Hills, Spud Mountain, Chaparral, and Green Gulch Volcanics. The sixth formation, the Iron King Volcanics, is beneath Cenozoic deposits in the ex- treme southeast corner of the area (pl. 1, see. E-E'). In addition, isolated masses of basaltic flows and tuffa- ceous rocks probably belong to the Alder Group but are not given formation names or assigned to one of the previously named formations. f The Alder Group has been regionally metamor- phosed, and many of the textures, structural features, and mineral assemblages are typical of rocks of the green schist facies; some are the result of higher grade metamorphism. The principal metamorphic minerals are chlorite, actinolitic hornblende, epidote, clinozoisite (zoisite), albite, sericite, and quartz. Microcline is a common stable relict mineral in the rhyolitic rocks. Biotite, muscovite, hornblende, oligoclase-andesine, garnet, and staurolite(?) indicate local higher grade metamorphism. Although the Alder Group has been metamorphosed, unravelling its stratigraphy and structure was of great- er importance in the search for clues to ore deposits in the Precambrian rocks than was the study of meta- morphic features. A careful search was therefore made for relict textures and structural features. If relict amygdules or pillow structures can be recog- nized in chlorite or hornblende schist, the rocks are classed as andesite or basalt. Rocks of the same gen- eral composition that show relict bedding are called andesitic or basaltic tuffs or tuffaceous sedimentary rocks; those containing abundant phenocrysts or crys- tal fragments of plagioclase are called andesite. Seri- citic schists or fine-grained rocks composed of quartz and alkalic feldspar and containing flow structures and phenocrysts of quartz and feldspar are classed as rhy- olite; similar rocks having relict bedded structures are classed as rhyolitic tuff or tuffaceous sedimentary rocks. Siliceous-looking flows containing a greater amount of mafic minerals and calcic plagioclase than normal rhy- olites are called dacites. Some fine-grained rocks orig- inally lacked features indicating that they were a vol- canic flow, massive tuff, or a fine-grained intrusive rock. The original textures and structures in other rocks have been obliterated by intense deformation, higher * Although muscovite and sericite are the same mineral, in this re- port the term "sericite" is used for fine-grained metamorphic or see- ondary muscovite ; the term "muscovite" is used for the primary igneous mineral and also for the larger (generally more than 2 mm) crystals formed by higher grade metamorphism. grade metamorphism, or later retrograde metamorph- ism. Fortunately, many of the rocks in which original diagnostic features were lacking or were later destroyed can be traced along the strike into rocks in which relict textures and structural features indicate the original character of the rock. Because of the almost complete absence of sedimen- tary rocks such as limestone, sandstone, and shale and because of the abundance of volcanic material in the Precambrian rocks in this area, much of the bedded ma- terial has been interpreted as of tuffaceous, rather than terrigenous, origin. Bedded tuffs and a few pil- low lavas indicate deposition in water, probably in a marine environment. Attempts to work out the stratigraphy and structure of the Alder Group in the area met with little success. The rocks have been isoclinally folded and foliated. They are separated into isolated masses by faults and intrusive igneous rocks or are exposed only in windows in Paleozoic and Cenozoic rocks. Some masses may lack internal continuity; a displacement may not have been recognized because it paralleled lithologic trends and brought similar rocks of different formations into apparent continuity, or because it had been injected by igneous rocks. Little evidence was found to indicate the direction in which tops of beds face. In many places where the orientation of a bed could be determined, only the local rather than the regional structure was indicated be- cause of known or inferred isoclinal folding. Rocks of the Alder Group were injected by and caught up in intrusive igneous rocks. Where mixing of volcanic and intrusive rocks is difficult to show on the map (pls. 1, 2), a stippled pattern has been placed over the pattern used for the principal rock type in the area. Data on these complex areas are given in sections on the principal rock type involved. The formations of the Alder Group dip so steeply that outcrop widths would approximate stratigraphic thickness except for several complications: (1) Isoclinal folds and small unmapped masses of igneous rocks cause outcrop widths to be greater than stratigraphic thickness, and (2) flowage, shearing out of beds, and unmeasured amounts of rocks of the Alder Group in adjacent intrusive rocks cause outcrop widths to be less than stratigraphic thickness. Because of these complications and because neither the top nor the bottom of the Alder Group is exposed, the thickness of the group is not known ; however, it is probably at least 20,000 feet. In the Jerome area An- derson and Creasey (1958, p. 20) estimated the Alder Group to be 20,000-30,000 feet thick. Their figures in- clude thicknesses of the Spud Mountain, Chaparral, OLDER PRECAMBRIAN ROCKS 11 and most of the Green Gulch Volcanics in the southeast- ern part of the Prescott quadrangle but not thick- nesses of the unnamed volcanic rocks that are probably in the Alder Group and thicknesses of additional units in the Texas Gulch Formation and Green Gulch and Indian Hills Volcanics. TEXAS GULCH FORMATION DISTRIBUTION The Texas Gulch Formation was named and described by Anderson and Creasey (1958, p. 28-30) for exposures in Texas Gulch in the southwestern part of the Jerome area. The principal exposure of the Texas Gulch For- mation in the Prescott-Paulden area is in the south- central part (pl. 1). Three small exposures are in the northern part along Granite Creek about 1 mile south of its junction with the Verde River (pl. 2; fig. 5). Lithologic units have not been mapped, except for four units in the largest exposure (pl. 1). They are units containing respectively, jasper-magnetite beds, andesite flows and tuffs, rhyolite crystal tuffs, and rhyolitic flow or massive tuff. The andesitic rocks have been mapped in three places; the other units, in only one area each. THICKNESS, STRATIGRAPHIC RELATIONS, AND CORRELATION The thickness and stratigraphic relations of the Texas Gulch Formation are not known. Structural and stra- tigraphic features suggest that the main mass occupies a south-plunging syncline within which are small folds, the top and the bottom are both absent, the oldest beds are on the east and west sides, and the youngest part is the rhyolitic flow or massive tuff unit near the center of the outcrop. This interpretation is based on jasper- magnetite float and beds of rhyolite tuff, slate, and con- glomerate in the western part of the mass that may be correlative with similar beds on the east; on generally west-facing beds in the eastern part; and on south- plunging lineation, interpreted as the 6 axis of the struc- tural coordinate system. The greater outcrop width of the formation (about 12,000 ft) along the southern border of the quadrangle, in contrast with a narrower width (less than 5,000 ft) about 2 miles to the north, is probably due to duplication of beds by folding and to the southward plunge of the syncline. The formation must be 3,000-4,000 feet thick in this area. © No normal stratigraphic contacts of the Texas Gulch Formation with other Precambrian formations are ex- posed. Its western contact with unnamed basaltic flows of the Alder(?) Group appears to be a fault or shear zone (pl. 1). To the north and east the Texas Gulch Formation is intruded by igneous rocks. The eastern contact is sharp, but the granite adjacent to it contains abundant inclusions of volcanic rocks, which probably 758-447 O-65--2 are part of the formation. One small outcrop is in fault contact with the Mazatzal Quartzite (pl. 2). Anderson and Creasey's interpretation (1958, p. 28) of the regional structure of the Alder Group in the Jerome area is that the Texas Gulch Formation is the oldest formation in the group. Whether it directly un- derlies the Indian Hills volcanics or is separated from it by other formations is not known, as the two are not in contact. In the Jerome area Anderson and Creasey (1958, p. 28) applied the name Texas Gulch Formation to rocks formerly referred to as quartz-sericite schist, conglom- erate, and slate by Lausen (1930) and as arkosic sand- stone, squeezed conglomerate, and slate by Wilson (1939, p. 1155-1158). Wilson correlated these rocks with his Alder Series in the Mazatzal Mountains. In the south- ern part of the Prescott-Paulden area, many of the rocks mapped as Texas Gulch Formation are lithologically similar to those in the type locality. Similarities in- clude the abundance of fine- to coarse-grained rhyolite tuff that locally grades into lithic tuff, the considerable amounts of slate, and a distinctive conglomerate. Not all the lithologic types are found in both areas. Thin beds or layers of marble occur in the Jerome area ; none occur in the Prescott area. Thin beds of jasper-mag- netite and scattered jasper-magnetite pebbles in con- glomerate occur in the Prescott area but not in the Jerome area. In the Prescott area the slate is gray; in the Jerome area it is chiefly purple or maroon and only locally gray or green. Another difference is the presence of dacite(?) and andesite in the Prescott area but not in the Jerome area. If rocks in the Prescott and Jerome areas are correctly correlated, these differ- ences may be because neither area contains a complete section. Near Granite Creek (pl. 2) the abundance of quartz-sericite schist that may represent metamorphosed slate and rhyolitic tuff suggests a correlation with the Texas Gulch Formation to the south. Also, Wilson (1939, p. 1153) termed these rocks "phyllite and argil- laceous sandstone of Alder type." Inclusion of rocks here called Texas Gulch Formation in the Alder Group and their correlation with the Texas Gulch Formation in the Jerome area are both tentative but the best that can be done on the basis of present knowledge. LITHOLOGY AND INTERNAL STRUCTURE The Texas Gulch Formation is composed largely of rhyolitic tuff but it includes rhyolite flows( ?), andesite tuffs and flows, slate, conglomerate, dacite( ?) flows and tuffs, and jasper-magnetite beds. Much of the descrip- tive material in the section on undifferentiated rocks applies to rocks in differentiated units; some rocks are described only under an individual unit. 12 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA The rocks are variably foliated ; the finer grained ones have a smoother, more regular foliation than the coarser grained ones; conglomerates have a hackly foliation. Lineation, which is widespread, results from elongation of sericite or chlorite flakes, elongation of pebbles, and intersection of cleavage and bedding. Except for min- eral streaking, which is parallel to the a axis, most linea- tion is parallel to the plunge of minor drag folds and to the b axis of the structural coordinate system. Thickening on crests and thinning on limbs of small drag folds is characteristic of the jasper-magnetite beds. Some pebbles in conglomerates are attenuated to lengths as much as 10 times widths. The rhyolite tuffs are various shades of gray. Many of them are very fine grained and finely laminated, especially in the area extending 1,500 feet west of the unit containing jasper-magnetite beds. Relict bedding is preserved in places. Some tuffs are coarse grained or contain sparse to abundant crystal or lithic fragments. Lithic fragments range from about 1 mm to 15 ecm in length. In some beds, crystal or lithic fragments are massed almost without matrix. The tuffs grade into slate and into sandstone and conglomerate of question- able tuffaceous origin. The matrix of the tuff consists of quartz, sericite, alkali¢ feldspar, and lesser amounts of biotite, chlorite, muscovite, epidote, and sparse ac- tinolite. Magnetite is a fairly abundant accessory mineral in some tuff. Most fragments in the lithic tuffs have the same composition as the matrix-mainly thy- olite-but some are composed of quartz, chalcedony, or andesite. Except for a distinctive conglomerate, discussed in the next paragraph, the lithic tuffs are most abundant west of the rhyolite flow or massive tuff unit. A distinctive conglomerate lies east and west of the unit containing jasper-magnetite beds (fig. 4). Similar conglomerate is exposed near the western edge of the largest exposure (1,285,400 N., 352,600 E.). West of the unit containing jasper-magnetite beds, the conglo- merate is a maximum of 50 feet thick; east of this unit the conglomerate is mostly less than 10 feet thick. The conglomerate is similar to rhyolitic lithic tuffs except for the presence of pebbles and cobbles of red chalcedony and jasper-magnetite ; the conglomerate also contains a few fragments of andesite and of graphic intergrowths of quartz and alkalic feldspar. Gray slate, which may be a normal terrigenous sedi ment," is associated with the jasper-magnetite beds and with conglomerate and tuffaceous rocks for about 1,500 3 Anderson and Creasey (1958, p. 29-30) considered purple slate in the Jerome area to be terrigenous on the basis of a higher alumina content and a higher ratio of potash to soda as compared with rhyolite tuffs of the area. feet west of the jasper-magnetite beds. Quartz-sericite schist, associated with lithic tuffs (pl. 1; near 353,500 E., north of 1,281,500 N.) and with micaceous quartzite in the two western outcrops near Granite Creek (pl. 2), may be metamorphosed gray slate. Some of these schists are spotted. In the southern exposures the spots, as much as 2 cm by 0.6 cm, are pseudomorphs after staurolite( ?) and now consist of sericite, magnetite, and chlorite in a matrix of quartz, sericite, chlorite, magne- tite, and some alkalic feldspar. In the northern ex- posures the spots are biotite metacrysts as much as 3 mm in diameter that poikilitically enclose quartz grains. Dacite( ?) rocks, probably flows and tuffs, occur west of the rhyolite flow or massive tuff unit (south of 1,281,000 N.). They interfinger with rhyolitic lithic tuff and with rocks of uncertain origin. The dacite(?) is medium dark gray and well foliated. Some contain large amygdularlike areas of granular quartz; others contain fragments of a slightly different composition; some are bedded. The very fine grained matrix or groundmass consists of sericite, quartz, alkalic feldspar, chlorite, minerals of the epidote group, and abundant magnetite. Altered plagioclase grains are mostly less than 2 mm long; many are less than 0.5 mm long. Rocks of uncertain origin are characterized by sparse to abundant flattened white fragments of feldspar(?) or rhyolite. The fragments are angular and are ran- domly oriented in the plane of foliation, but they are somewhat augenshaped at right angles to foliation. Many of them are as large as 1.5 cm by 0.4 cm; some are much larger. They consist of a mixture of zoisite, epidote, sericite, alkalic feldspar, quartz, and a little chlorite. The matrix is composed of alkalic feldspar, quartz, chlorite, epidote-zoisite, and magnetite. Unit containing jasper-magnetite beds.-The unit that contains thin beds of jasper-magnetite consists of tuffaceous sedimentary rocks composed of rhyolite, some andesite, and a little gray slate; jasper-magnetite beds form a very minor part of the unit. Thin inter- beds of jasper-magnetite are concentrated in layers 25- 50 feet thick, which are separated by at least 100 feet of tuffaceous rocks free of jasper-magnetite. Individual jasper-magnetite beds range from paper thin to about an inch in thickness. They are dark gray to blackish red-except for iron-poor, silica-rich interbeds, which are a lighter gray. A few beds have been traced along the strike for as much as 1,000 feet. The jasper- magnetite beds are composed of very fine grained mag- netite-locally of hematite or the specular variety of hematite-in a matrix of microcrystalline quartz and variable amounts of quartz, sericite, albite, chlorite, and minerals of the epidote group. These beds resemble the Precambrian iron formation of the Lake Superior region OLDER PRECAMBRIAN (Leith and others, 1985, p. 21) and probably had a similar origin. James (1954) concluded that the high iron content of the iron formation is the product of iron-rich sedimentation in marine waters. Andesite flows and tuffs.-The eastern mass of an- desite is largely tuff ; the middle one is largely flow, and the western one is largely a porphyritic rock of uncer- ROCKS 13 tain origin. Much of the andesite, in both differenti- ated and undifferentiated areas, is very fine grained and well bedded; some is medium grained and massive. The andesite is medium dark to medium greenish gray. Some is porphyritic or contains clusters of large flat- tened plates of saussuritized plagioclase. A few of the coarser grained rocks are vesicular or contain quartz EXPLANATION Younger rocks As pastas Texas Gulch Formation tu, undifferentiated Texas Gulch Formation ti, unit containing jasper-magnetite beds tc, conglomerate beds in undifferentiated Texas Gulch Formation and unit containing jasper-magnetite beds Dashed where approximately located,; dotted where concealed Fault Strike and dip of beds 1,280,000N 34°30" Direction in which top of bed faces, based on graded bedding, channelling, bedding- foliation relations, or pattern of drag folds TRUE NORTH APPROXIMATE MEAN DECLINATION, 1965 Ya 1 MILE ] FiGURB 4.-Distribution of conglomerate in the Texas Gulch Formation, Prescott quadrangle. 14 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA or calcite amygdules. Small crystal fragments or phenocrysts of saussuritized plagioclase are erratically distributed through some of the rock. The andesite consists of chlorite, albite, and variable amounts of sericite, epidote, actinolite, calcite, quartz, magnetite, and ilmenite. Chlorite and sericite (from rhyolitic detritus) are abundant in the finer grained fissile rocks; actinolite, in the coarser grained ones. Hornblende (actinolitic) forms some metacrysts. The porphyritic rock contains plagioclase, actinolitic hornblende, epi- dote, magnetite, and sphene. Rhyolite crystal tuff. -Rhyolite crystal tuff is fine to coarse grained. Quartz and feldspar crystal frag- ments, as much as 2 mm in diameter, are sparse to abundant; either mineral may predominate; locally they are absent. Lithic fragments are composed of rhyolite and chalcedony. The matrix consists of quartz, sericite, alkalic feldspar, and a little chlorite and epidote. Rhyolite flow or massive tuff. -The rhyolite flow or massive tuff is dark to medium gray or pale red to pinkish gray ; it weathers pinkish gray to light brown- ish gray. The dark-gray rocks are very fine grained and dense, almost flinty in appearance. Massive rhy- olite grades into and interfingers with foliated rhyolite, but the micaceous minerals have a preferred orienta- tion, even in massive-appearing rhyolite. Most of the rock lacks features that might indicate whether it is a flow or massive tuff ; its length does not support a flow origin. The tiny phenocrysts or fragments of quartz and albite and a few of orthoclase are not conspicuous or abundant; they are mostly less than 1 mm in diam- eter. The matrix consists of quartz, alkalic feldspar, and sericite. Green biotite, magnetite, pyrite, epidote, or irregular aggregates of biotite, calcite, and magnetite were observed in some of the rhyolite. Muscovite forms metacrysts in some of the coarser textured rock. INDIAN HILLS VOLCANICS DISTRIBUTION The Indian Hills Volcanics, named by Anderson and Creasey (1958, p. 20) for exposures in the Indian Hills in the western part of the Jerome area, extend into the east-central part of the Prescott-Paulden area, where they crop out north of Route 89¢ (pl. 1) and in four places south of 1,381,000 N. and east of 395,000 E. (pl. 2). The formation consists of interbedded andesitic and rhyolitic flows. The two units are differentiated on plate 1 but not on plate 2. Tuffaceous material, in areas mapped as contaminated Indian Hills Volcanics and in adjacent contaminated intrusive rocks, is in- cluded in the formation ; tuffaceous rocks are not part of the formation in the type section. THICKNESS AND STRATIGRAPHIC RELATIONS The maximum outcrop width of the Indian Hills Volcanics within the area is about 4,000 feet. The thickness is probably less than outcrop width because the formation is probably folded and because the out- crop includes a considerable amount of granodiorite and gabbro too small or too poorly exposed to map. In places sheets and pods of gabbro compose as much as one-third of an area mapped as rhyolite. Gabbro may be as abundant as andesite in some areas mapped only as andesite, but it is not as apparent as in the rhy- olite. In areas mapped as contaminated Indian Hills Volcanics, the volcanic rocks appear to make up about half of the outcrops. Granodiorite and some alaskite and gabbro, however, may be more abundant but are not apparent because the volcanic rocks crop out better. The volcanic rocks occur as angular to lenticular xeno- liths in the intrusive rocks and as large masses into which the intrusive rocks were intimately injected. In the Prescott-Paulden area the Indian Hills Vol- canics are not in contact with other formations of the Alder Group. In the- Jerome area (Anderson and Creasey, 1958, p. 21) the Indian Hills and Spud Moun- tain Volcanics appear conformable, but the direction in which tops of beds face was not determined. Because the Iron King Volcanics probably overlie the Spud Mountain Volcanics, the Indian Hills Volcanics were interpreted as underlying the Spud Mountain Volcan- ics. Although the base of the Indian Hills Volcanics is not exposed, Anderson and Creasey interpreted the volcanic rocks as presumably overlying the Texas Gulch Formation. LITHOLOGY AND INTERNAL STRUCTURE, Interbedded andesitic and rhyolitic flows and some tuffaceous sedimentary rocks make up the Indian Hills Volcanics. The main exposures of the flows are in the Jerome area; they are described in detail by Anderson and Creasey (1958, p. 21). The rocks are foliated but less so than other forma- tions of the Alder Group. Foliation is absent in some outcrops in the Jerome area; it is more pronounced to the west, especially in the areas of fine-grained bedded tuffs. Some contacts between rhyolite and andesite flows are shear zones. Rhyolitie flows.-The rhyolitic flows are grayish orange pink to light gray or greenish gray, except for dense siliceous, almost flinty rhyolite, which is medium gray to medium dark gray. Textures and structural features typical of rhyolite flows-such as flow banding, flow breccia, amygdules, and vesicles-occur locally but are generally inconspicuous. Phenocrysts consist of quartz, albite, and a little potassium feldspar; few of OLDER PRECAMBRIAN ROCKS 15 them are conspicuous. Most phenocrysts are less than 1.0 mm long; where abundant, they may be more than 2 mm long. The groundmass is composed of micro- crystalline aggregates of alkalic feldspar, quartz, and a little sericite; accessory minerals are chlorite, min- erals of the epidote group, and magnetite. Sericite is abundant in the more sheared rocks. In some northern outcrops (pl. 2), biotite is concentrated in widely scat- tered thin layers and lenses, and quartz phenocrysts are recrystallized. Andesitic and basaltic flows.-The andesitic and basaltic flows are greenish black. The flows are blocky, except where they are somewhat fissile owing to folia- tion or shearing. - Amygdules, composed of minerals of the epidote group, and vesicles are widely distributed. Phenocrysts of altered plagioclase and less commonly of hornblende are widespread and are as much as 2 cm long. The holocrystalline commonly fine-grained groundmass consists of granular albite and minerals of the epidote group, small flakes of chlorite, and some biotite, magnetite, and calcite. Most chlorite has a slight preferred orientation; some is well oriented. Tuff aceous sedimentary rocks.-Most of the andesitic and rhyolitic tuffaceous sedimentary rocks are fine- grained fissile foliates of light to dark color. Graded bedding and drag folds were observed in a few places. Mafic minerals are more abundant in some siliceous tuffs than in the rhyolite flows. Quartz, alkalic feld- par, and variable amounts of sericite make up the rhyo- litic tuffs. Albite, minerals of the epidote group, chlorite, and some actinolitic hornblende compose the andesitic tuffs. Epidote is conspicuous in many of the rocks, even those composed largely of rhyolitic detritus. SPUD MOUNTAIN VOLCANICS DISTRIBUTION The Spud Mountain Volcanics (Anderson and Creasey, 1958, p. 21-26) were named for excellent ex- posures on Spud Mountain, in the extreme southeast corner of the area (pl. 1), where they crop out as one large and several smaller masses. An outcrop of brec- cia, mapped with the Indian Hills Volcanics but prob- ably part of the Spud Mountain Volcanics is in the east- central part of the area (pl. 2, 1,367,500 N., 398,100 E.). The breccia is faulted against Indian Hills Volcanics and Martin Limestone. In the type locality the forma- tion consists of two units: (1) andesitic tuff lying east of (2) andesitic breccia. - Elsewhere in the Jerome area, some rhyolitic tuff and andesite flows are intercalated in the andesitic tuff and breccia units. THICKNESS AND STRATIGRAPHIC RELATIONS The thickness and stratigraphic relations of the Spud Mountain Volcanics are uncertain because the forma- tion is cut off on the west by the Spud fault and buried to the north and east by Cenozoic rocks. It has an outcrop width within the area of about 5,500 feet, of which about 4,000 feet is the breccia unit and 1,500 feet, the tuff unit. - The tuff unit may be approximately 1,500 feet thick in this area ; the breccia unit may not be more than 2,000 feet thick, as the structure of the unit may be anticlineal (pl. 1, see. E-E'), as interpreted by Ander- son and Creasey (1958, p. 72). To the southeast the volcanics appear to be conform- ably and gradationally overlain by the Iron King Vol- canies (pl. 1, see. E-E') (Anderson and Creasey, 1958, p. 23). The andesitic breccia is interpreted as occupy- ing the lower part and the andesite tuff, the upper part of the formation. LITHOLOGY AND INTERNAL STRUCTURE The Spud Mountain Volcanics are various shades of grayish green to greenish gray; actinolitic hornblende produces the darker shades. Lighter shades are due to sericite from admixed rhyolitic detritus. The rocks weather brown or reddish brown to yellowish gray. Most of the breccia within the map area is foliated, but it does not readily break parallel to this foliation be- cause of abundant fibrous actinolitic hornblende. Fine- grained tuffs in any one locality are more intensely foliated than coarser grained crystal tuffs or breccia beds. Some fragments in the breccia facies show little or no evidence of stretching; others, even in adjacent beds, have been attenuated to lengths as much as 12 times the widths. Relict bedding is preserved in some tuffaceous beds. Graded bedding, brought out by the distribution and size of plagioclase grains, can be recognized in places. The principal constituents of both breccia and tuff are chlorite, albite and albite-oligoclase, minerals of the epi- dote group, some carbonate, and accessory magnetite, sphene or leucoxene, and apatite. Clinozoisite (or zoisite) is more abundant than epidote; actinolitic horn- blende is found only in the andesitic breccias. The dis- tribution of quartz is very erratic. Except in saus- suritized plagioclase, sericite is largely confined to finer grained tuffs and was derived probably from admixed rhyolitic detritus. Andesitic breccia.-Included within the breccia facies of the Spud Mountain Volcanics are beds of breccia, granular crystal tuff, and fine-grained tuffaceous sedi- mentary rocks. The unit is predominantly andesitic in composition. Breccia beds, which range from less than 1 foot to possibly 500 feet in thickness, are more abun- dant than the tuffs in the breccia facies. The fragments, from less than 1 inch to 18 inches long, are sparsely to abundantly distributed through- out the breccia beds. Within individual beds most of 16 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA them are rather uniform in size. Their shape, which is generally subrounded, is due, in some places, to the original form or, in other places, to later deformation. Fragments in the breccia are composed largely of porphyritic andesite. A few andesite fragments are amygdaloidal or vesicular. Other fragments consist of rhyolite, fine-grained dark rocks of undetermined ori- gin, and mixtures of quartz and epidote of probable metamorphic origin. Rhyolitic fragments are locally abundant on the west side of Spud Mountain. Pheno- crysts in the andesite fragments occur as individual crystals and clusters of crystals.. They consist principal- ly of equant saussuritized plagioclase and have a maxi- mum size of 1 em. The character, size, and distribution of the phenocrysts are identical in many places with those of the crystal fragments in andesitic crystal tuff, which forms the matrix of some of the breccia. Else- where the matrix is fine-grained andesitic tuff. Fine- grained tuff and crystal tuff similar to the matrix occur as interbeds in the breccia and are identical with andesitic tuff described in the following paragraphs. Andesitic tuff. -The contact between the tuff and breccia is gradational and is arbitrarily located. Away from the contact, breccia or conglomerate and coarse crystal tuff beds are thin and less abundant, the frag- ments are smaller, and finer grained tuff beds are more prevalent. Conglomerate beds as much as 10 feet thick are common in the part of the tuff within the Prescott quadrangle; however, to the east and presumably higher in the section, coarse-grained crystal tuff beds and as- sociated conglomerates are much less abundant, and more of the unit is fine grained (Anderson and Creasey, 1958, p. 24-25). The andesitic tuff is a sedimentary rock composed largely of andesitic volcanic detritus. Most individual beds are not more than a few inches thick; grain size varies from bed to bed. The particles range from clay to cobbles, but most of them are between silt and coarse sand in size. Some variation in grain size is due to dif- ferential shearing, but most of it is probably a primary sedimentary feature. Visible minerals in the tuff are chlorite, saussuritized plagioclase, and variable amounts of quartz and seri- cite; saussuritized plagioclase is the most conspicuous mineral. The plagioclase grains give the rock a per- phyritic appearance or bring out its bedding depending on their distribution. The finer grained facies are phyllites or slates. Chlo- rite and some sericite produce a sheen on cleavage sur- face that is characteristic of these rocks. Small grains of quartz or saussuritized plagioclase can be seen with a hand lens in some of these beds. Fissility is more pro- nounced and regular than in the coarser grained tuffs. CHAPARRAL VOLCANICS DISTRIBUTION The Chaparral Volcanics (Anderson and Creasey, 1958, p. 30-31), named for exposures in Chaparral Gulch (1,277,000 N., 392,000 E.), trend northeastward for about 3 miles across the southeast corner of the area (pl. 1). The volcanics consist of two lithologic units : rhyolitic tuff and andesitic tuff. Most of the andesitic tuff lies east of the rhyolitic tuff. A narrow layer of rhyolitic tuff occurs in andesitic tuff (pl. 1), and a narrow layer of andesitic tuff that tapers to a point from a width of about 50 feet occurs in rhyolitic tuff (shown only on pl. 1 of the Jerome report, Anderson and Creasey, 1958). At the north, the outcrop of the rhyolitic tuff is split into three parts by the south-tapering masses of Pres- cot Granodiorite and alaskite. South of the tongues of intrusive rocks, the separate belts of rhyolite join to form a single belt. At the many places where quartz- sericite schist was formed at the contact between rhyo- litic tuff and intrusive granitic rocks, the location of the contact is indefinite because the schist that was pro- duced by intense distributive shear could have origi- nated from either the tuff or the granitic rocks. THICKNESS AND STRATIGRAPHIC RELATIONS No estimate of the thickness of the Chaparral Vol- canics can be made, and its stratigraphic relations to other formations are unknown. The formation is sepa- rated from adjacent formations by major faults that are occupied by intrusive igneous rocks (pl. 1). The Chaparral fault separates it from the Green Gulch Volcanics on the northwest, and the Spud fault sepa- rates it from the Spud Mountain Volcanics on the southeast. Structural complications-isoclinal folding, strong phyllonitization (Knopf and Ingerson, 1938, p. 190), and shearing out of beds-make an attempt to estimate original thickness hopeless. The formation has an outcrop width of 1,500-2,600 feet. At the north end the distance between the two bounding faults is about 3,800 feet, but approximately 1,500 feet of this distance is occupied by intrusive rocks. The outcrop width of the rhyolitic tuff is much greater than that of the andesitic tuff at the north but less than that of the andesitic tuff to the south. The stratigraphic relation of andesitic tuff to rhyolitic tuff is not known, as the direction in which tops of beds face was not determined. ‘ Although lithologically some of the Chaparral Vol- canics resemble parts of other formations of the Alder Group, evidence currently available is insufficient to justify any correlation. The faults and shears in the area suggest that the Chaparral Volcanics may have OLDER PRECAMBRIAN ROCKS 17 been moved for a long distance and may not even be part of the Alder Group. LITHOLOGY AND INTERNAL STRUCTURE Rhyolitic tuff. -The rhyolitic tuff is a fine-grained predominantly sedimentary rock that ranges from fis- sile, finely laminated foliates to more massive rocks. - The rocks included in the rhyolitic tuff grade from com- partively pure rhyolite to those containing added an- desitic material. On a broad scale the rhyolite tuff con- sists of three types; each variety predominates in a separate area, but some interbedding of and gradation between the types occur. The eastern belt consists mostly of white fissile quartz-sericite schist ; the western 'belt, of massive pink rhyolite; and the middle belt, of finely laminated greenish-gray tuff having contorted bedding. A single belt composed largely of white tuff occurs south of the tongues of intrusive rocks. Rhyolitic tuff of the eastern belt is very light gray to yellowish gray, very fine grained, and finely lami- nated. Scattered tiny grains of quartz and a few of feldspar are the only visible minerals, although the sheen of the rock attests to the presence of sericite and a green tinge indicates admixed chlorite. Most of the feldspar grains are albite; a few are orthoclase. The matrix is composed of quartz, sericite, and variable amounts of alkalic feldspar. Much of the rhyolitic tuff in the middle belt is a finely laminated greenish-gray to dark greenish-gray rock. Fissility is less well formed than in the rocks of the eastern belt. Contorted beds and small drag folds are common. The rock contains some epidote, actinolite, and biotite or chlorite; sericite is less abundant than in rocks of the eastern belt. Rhyolitic tuff of the western belt is largely a mas- sive pale-red rock; some is yellowish gray. Some grains of quartz and feldspar are a little larger and more abundant than those in the tuffs of the east. The matrix is mainly quartz and feldspar; a little epidote occurs locally. In much of this belt, no textures or structural features resembling primary flow or bedded features were found. The massive rhyolite is interpreted as a massive tuff on the basis of its extremely long strike length in contrast to its width ; most rhyolitic flows are lenticular. Andesitic tuff. -The andesitic tuff is fine grained, well foliated, and fissile, except for interbeds of more mas- sive, coarser grained tuff. The finer grained tuff is commonly greenish gray to olive green ; some is blotched and streaked with variegations of light yellowish green. Much of the lighter color is due to admixed rhyolitic material; where crosscutting, it is due to alteration. The matrix is composed of chlorite, sericite, albite, epi- dote, and quartz. The coarser tuff, in beds 1-50 feet thick, is more plentiful in the eastern than in the west- ern part of this unit. It is grayish green and less well and more irregularly foliated than the finer grained tuff. Its principal constituents are chlorite, albite, and epidote. Feldspar grains are saussuritized. GREEN GULCH VOLCANICS DISTRIBUTION The Green Gulch Volcanics (Anderson and Creasey, 1958, p. 31-32) were named for excellent but incomplete exposures along Green Gulch (between 1,282,000 N., 393,500 E. and 1,281,900 N., $86,500 E.). The forma- tion crops out in the southeast part of the area (pl. 1) west of the Chaparral fault. Scattered outcrops pro- trude above the Cenozoic cover north of the main ex- posures. The formation is cut out near the south border of the area by the fault and by gabbro. It is not ex- posed elsewhere in the Prescott-Paulden area or the Jerome area. The formation has been divided into a basaltic flow unit and a tuffaceous unit ; the basaltic flow unit lies east of the tuffaceous unit, which is split into two parts by intrusive rocks. THICKNESS AND STRATIGRAPHIC RELATIONS If outcrop widths approximate thickness, the forma- tion must be more than 5,000 feet thick; the outcrop width of the basaltic flow unit is 7,000 feet, and that of the tuffaceous unit is 4,500 feet. The stratigraphic relations could not be determined as the Green Gulch is not in normal contact with other formations of the Alder Group. Except locally, the lithology of the Green Gulch Volcanics is not sufficiently like that of any other formation in the group to permit a correlation. Although beds face east and west in the basaltic flow unit, west-facing beds are more prevalent than east- facing ones. For this reason, the tuffaceous unit is be- lieved to overlie the basaltic flow unit. LITHOLOGY AND INTERNAL STRUCTURE Basaltic flow unit.-The basaltic flow unit consists of flow, breccia, tuff, and conglomeratic tuff. Most of these rocks are medium to dark gray and have a green cast. Rocks rich in metamorphic hornblende are dark bluish gray ; those rich in chlorite are grayish green. Relict pillow and breccia structures, amygdules, vesi- cles, and bedding are preserved here and there and are well exposed in the water-polished exposures in the larger gulches. Pillows were recognized only in Green Gulch and the next gulch to the south (indicated by symbol on pl. 1). Many of the pillows are attenuated to as much as 15-20 times the width. Amygdules, com- posed of quartz and quartz-epidote, and vesicles are more widespread than the pillows. Relict bedding and drag folds are preserved in tuffaceous interbeds separat- 18 GEOLOGY OF THE PRESCOTT AND ing flows and breccias. Bedding symobls in the basaltic flow unit on plate 1 indicate the location of some of these interbeds. Fragments in the breccia and conglomeratic tuff are composed of rhyolite and more abundant ande- site or basalt and of crystal fragments from these rocks. The fragments range from less than 1 mm to about 15 cm. Some are attenuated; lengths in places exceed widths by as much as 10 times. Some fragments are angular to subangular. Small saussuritized plagioclase phenocrysts and porphyroblasts or aggregates of hornblende are the most abundant megascopic minerals. Some phenocrysts (or fragments in the tuffs) are clustered. Chlorite is visible locally. Relict felty texture was recognized in one place, but metamorphism has obliterated many original textures. The principal constituents are actinolitic hornblende, albite, and epidote ; chlorite and carbonate are abundant where the rocks were highly sheared. Higher grade metamorphism in the northeasternmost exposures pro- duced hornblende, oligoclase, and some brown biotite, sphene, and apatite. Here narrow veinlets that resem- ble ptygmatic folds consists of minerals of the epidote group and some quartz, chlorite, plagioclase, sphene, and muscovite, all of which were probably formed by metamorphic diffusion. The predominance of mafic constituents and the lack of abundant plagioclase phenocrysts suggest that this unit is basaltic rather than andesitic. The presence of pillows likewise suggests a basaltic composition; Sat- terly (1941) pointed out that most of the analyzed pil- low lavas of Canada are basalts, and an analysis of the Iron King Volcanics (Anderson and Creasey, 1958, p. 27), which contains pillow lavas, indicates a basaltic composition. Tuff aceous unit.-The tuffaceous unit consists of tuffs and breccias and very minor rhyolitic flows. The clas- tic rocks are principally rhyolitic and admixed rhyolitic and andesitic in composition, but a few are mafic. The mafic tuffs and breccias are identical to the tuff and breccia in the basaltic unit and predominate for about 1,000 feet west of the arbitrarily located contact between the two units. Most of the rhyolitic rocks are dark gray ; some have a green, olive, or pink cast; they weather olive gray or pinkish gray. A few are light-gray porcelaneous slates. In the eastern exposures those that weather olive gray have a characteristic sheen due to abundant sericite and a little chlorite. Here the rhyolitic tuffs are fine grained and range from finely laminated fissile foliates to more massive locally coarser grained rocks. Relict bedding and drag folds are apparent in water-worn out- crops along Green Gulch. An additional indication of PAULDEN QUADRANGLES, ARIZONA the sedimentary origin of at least the eastern part of the unit is the abrupt variation in composition and texture across the trend of the unit. No relict bedding was observed in the western outcrops; flow banding was ob- served in one place (1,280,800 N., 382,200 E.). Phenocrysts and crystal fragments are visible in many places, but few of them are more than 1 mm long. They consist mostly of clear albite-oligoclase, quartz, and magnetite. Some plagioclase has saussuritized centers; larger ones are completely saussuritized. The ground- mass or matrix is composed of quartz, orthoclase, albite, sericite, minerals of the epidote group, magnetite, sphene, and sporadic chlorite and actinolite or actino- litie hornblende. Saussuritized plagioclase, epidote- group minerals, and magnetite are locally abundant. The plagioclase and epidote minerals together with chlorite and actinolite probably represent admixed an- desitic or basaltic detritus. The rhyolitic tuffs in the eastern outcrops are composed largely of quartz and sericite. In the western outcrops quartz and alkalic feldspar are the principal constituents. The unit contains a few rhyolitic breccias. Frag- ments are composed of rhyolite and andesite or basalt; some are angular, others are rounded. They range from a fraction of an inch to 10 inches in length. UNNAMED VOLCANIC ROCKS OF THE ALDER(!) GROUP DISTRIBUTION Volcanic rocks that may belong to the Alder Group, but which could not be correlated with known forma- tions in the group, are mapped as two lithologic units; basaltic flows and tuffaceous rocks. These rocks crop out in four places along the southern border of the area (pl. 1) and in two places in the northern part (pl. 2). They are referred to as (1) the southwestern basaltic flows and tuffaceous rocks, (2) the south- central basaltic flows, (3) the south-central tuffaceous rocks, (4) the southeastern basaltic flows and tuffaceous rocks, (5) the northern tuffaceous rocks, which extend south-southeastward from upper King Canyon (1,392,- 500 N., 381,000 E.), and (6) the northern basaltic flows, which form six small outcrops (fig. 5) east and south- east of the Pinnacle (1,400,000 N., 353,000 E.). Small unmapped amounts of these lithologic units occur in adjacent intrusive rocks. THICKNESS AND STRATIGRAPHIC RELATIONS On the basis of outcrop widths, individual masses of these unnamed volcanic rocks are estimated to be 1,000- 3,000 feet thick, but the relations are unknown. No correlation of individual masses with one another has been made. Lithologically some or all of the masses of tuffaceous rocks could be stratigraphic equivalents, as could some of the basaltic flows. OLDER PRECAMBRIAN ROCKS 19 Where mapped, the individual masses are surrounded by younger rocks. Many of them occur only as roof pendants or lenses in intrusive rocks (pl. 1, sec. B-B' and E-E'). Only the south-central basaltic flows are adjacent to another formation of the Alder Group, but a fault or shear zone separates the two. - The southwest- ern basaltic flows and tuffaceous rocks interfinger or are repeated by folds along the contacts between the two units. The relations of the southeastern basaltic flows and tuffaceous rocks is not known; on the east, along, and west of Charcoal Gulch, a fault or shear zone prob- ably separates the two units. LITHOLOGY AND INTERNAL STRUCTURE Basaltic flows.-Rocks mapped as unnamed basaltic flows comprise basaltic flow, breccia, tuff, and some interbedded rhyolitic tuff. The basaltic rocks are medium to dark gray with a slightly green or blue cast. Foliation except in some sedimentary breccia and tuff, is variable but generally less well defined than in most of the formations of the Alder Group. Intense shear has produced zones of retrograde metamorphism and abundant chlorite. The northern basaltic flows and some of the southeastern and southwestern ones are poorly foliated to nonfoliated. Amygdules, vesicles, agglomeratic structures, and pil- lows(?) indicate a flow origin for some rocks. Bedding, a fragmental character, and abrupt changes in lithology indicate or suggest a sedimentary origin for others. Amygdules are composed of quartz, epidote, or calcite. Pillows (?) were noted in the southwestern basaltic flows (especially near 1,276,100 N., $37,900 E.). The closely packed rounded, ellipsoidal, or irregularly shaped pil- low (?), mostly less than 1 foot long, have thin fine- grained dark selvages, which are probably chilled bor- ders. The irregular shape and small size are sugges- tive of bombs, lapilli, and other agglomeratic fragments, but triangular chalcedonic fillings are reminiscent of the chalcedonic fillings between most pillows in the area. The enclosing matrix is rich in zoisite (or clinozoisite). The northern basaltic flows consist largely of closely packed fragments having the same composition as the enclosing matrix. Some of these fragments resemble the small lapilli and bombs of an agglutinate (Tyrrell, 1931, p. 66). Sedimentary breccias are largely confined to the south-central basaltic flow. Fragments in the breccias are 1 mm to 15 ecm long and consist of saussuritized plagioclase, basalt, and a little rhyolite. The frag- ments are angular, rounded, or attenuated. Recogniz- able tuff interbeds are confined to the south-central and to the western parts of both the southeastern and south- western basaltic flows. Much of the rock is massive, fine grained, and non- descript ; it has no features that indicate a flow, tuff, or intrusive origin. Scattered saussuritized plagioclase phenocrysts, crystals fragments, or clusters of them, are generally visible and may be abundant. Many of them are about 1 mm in size; some are as much as 7 mm. Most of them are equant to lath-shaped. In distribution and abundance the phenocrysts in fragments are sim- ilar to, or contrast with, those in the matrix. Saussuritized plagioclase and magnetite are generally the only relict primary minerals, but a little relict py- roxene was observed in the northern and southeastern basaltic flows. Some unaltered zoned plagioclase laths occur as phenocrysts and in the groundmass in the northern and south-central basaltic flows. The felty to diabasic texture and subparallel orientation of plagio- clase laths are interpreted as primary. Most minerals and textures are metamorphic. The rock is composed of a granular assemblage of albite or oligoclase, actinolite or actinolitic hornblende, minerals of the epidote group, and some quartz, chlorite, calcite, sericite, and accessory magnetite, sphene, and apatite. Hornblende or actinolitic hornblende forms sparse to abundant large porphyroblasts, poikiloblasts, or aggre- gates. Hornblende, brown biotite, and muscovite are common in areas of higher grade metamorphism. A subparallel dimensional orientation of actinolitic horn- blende and variations in the relative proportions of hornblende and plagioclase in thin layers are probably metamorphic features. Tuff aceous rocks.-The unnamed tuffaceous rocks are principally a sedimentary series composed of volcanic detritus of basaltic (or andesitic) and rhyolitic composi- tion; some may be terrigenous siliceous sediments. A few small unmapped basaltic flows and questionable flows are included with the tuffs. The tuffs are mostly fine grained, finely laminated, and well foliated ; where micaceous minerals are abundant, the tuffs cleave read- ily. Mineral streaking, plunge of drag folds, and inter- section of cleavage and bedding give some of the rock a pronounced lineation. Some pebble- to cobble-sized fragments have the same composition as the enclosing matrix; the composition of other fragments contrasts with the matrix. The basaltic or andesitic tuffs are medium dark to dark gray and have a green or blue cast ; some layers are light yellowish or greenish gray. Some tuffs contain visible crystal fragments of saussuritized plagioclase; others contain poikiloblastic or porphyroblastie actino- 20 litic hornblende as much as 1 ecm long. The matrix is composed of metamorphic albite or oligoclase-andesine, actinolitic hornblende, and minerals of the epidote group. Accessory minerals are magnetite, apatite, sphene, and pyrite. Quartz, potassium feldspar, bio- tite, chlorite, muscovite, or sericite sporadically occur. Zoisite or clinozoisite is more abundant than epidote. Much of the quartz and feldspar represent admixed rhyolitic detritus, but some may have been derived from granitic veinlets that cut the tuff. Except for sericite formed from alteration of plagioclase, micaceous min- erals are generally absent unless the rocks contain rhyo- litic detritus or have been sheared. The typical finely laminated rocks are composed of layers of different combinations and proportions of the principal min- erals; hornblende is especially abundant in the dark layers; and zoisite, or clinozoisite, in the light-colored layers. Some light-colored layers contain abundant tremolite-actinolite. Many rhyolitic tuffs are medium-dark to light shades of bluish, greenish, or yellowish gray ; some are nearly white; others are pale or grayish red to grayish orange pink. They are composed of quartz, variable amounts of alkalic feldspar, muscovite, sericite, biotite, chlorite, minerals of the epidote group, and accessory magne- tite, pyrite, and sphene. The tiny angular to sub- rounded erystal fragments, some visible in hand speci- men, are composed of quartz, potassium feldspar, and albite; a few are composed of saussuritized plagioclase. Many of the rocks are quartz-sericite schists, but higher grade metamorphism of the southwestern tuffaceous rocks has formed some quartz-biotite and quartz-musco- vite schists. In the southeastern exposures some tuf- faceous rocks are composed of quartz and alkalic feld- spar but contain little or no sericite. In one place along Bannon Creek (near 1,274,200 N., 336,200 E.), pseudo- morphs after poikilitic tremolite(?) are now composed of biotite, chlorite, epidote, sphene, and a little relict amphibole. They are as much as 1 ecm long and en- close many quartz and feldspar grains. Tremolite(?) metacrysts are unusual in a rock composed largely of quartz and calcitic albite. Some schists contain mag- netite metacrysts as much as 4 mm in diameter; others (near 1,290,500 N., 375,800 E.) contain tiny red garnets. Garnet-epidote-quartz alteration zones and quartz- magnetite veins or alteration zones are common in the southwestern and south-central areas of tuffaceous rocks; some occur in the southeastern areas. - The quartz-magnetite veins are discussed under veins and silicified and alteration zones in the section on older Precambrian intrusive rocks (p. 48). GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA The garnet-epidote-quartz alteration formed largely in the mafic tuffs as concordant and crosscutting thin layers and lenses and locally, as knots and ptygmatic- like veinlets. The minerals formed during the altera- tion are epidote, grayish-red garnet, and quartz in vary- ing proportions. Sparse to abundant zoisite, tremolite, sericite, sodic plagioclase, magnetite, and sphene occur in various combinations in the alteration zones. MAZATZAL QUARTZITE DISTRIBUTION The Mazatzal Quartzite, named by Wilson (1922, p. 299 ; 1939, p. 1124) for exposures in the Mazatzal Moun- tains (southeast of Pine, inset, fig. 1), crops out south of the Verde River in the central part of the Paulden quadrangle (pl. 2), where it is referred to as the Del Rio area. Within an area of about 23 square miles, the quartzite forms 1 large and 21 small outcrops (fig. 5), which total about 3 square miles in area. THICKNESS AND STRATIGRAPHIC RELATIONS About 4,000 feet of Mazatzal Quartzite was measured in the Del Rio area, but the total thickness is not known, as neither the top nor the bottom of the formation is exposed. Wilson (1939, p. 1155) measured only 1,780 feet, but he believed the formation to be cut by a thrust fault. The stratigraphic position of the Mazatzal is not known. The quartzite is in fault contact (fig. 5) with the Texas Gulch Formation (1,402,500 N., 347,000 E.) and with basaltic flows of the Alder(?) Group (near 1,393,500 N., 353,300 E.). Quartzite apparently sur- rounds the basaltic flows to the north, but contacts are covered. The probable stratigraphic position of some of the small outcrops of the formation is shown in figure 5. The Mazatzal Quartzite is unconformably overlain by the Tapeats Sandstone, or Martin Limestone, of Paleozoic age or by Cenozoic rocks. LITHOLOGY AND INTERNAL STRUCTURES The Mazatzal Quartzite comprises a series of fine- to coarse-grained quartzite, granule to boulder conglom- erate, and a little argillite. In ascending order the formation consists of quartzite, 260 feet (0-1) ; lower conglomerate, 440 feet (2-5); lower argillite, 50 feet (6) ; quartzite and minor conglomerate, 940-1,100 feet (T-11); upper argillite, 60 feet (12); quartzite and minor conglomerate, 835 feet (13-17) ; upper conglom- erate, 1,150 feet (18-26) ; and quartzite, 325 feet (27- 28). (Figures in parentheses refer to units described in the measured section.) The formation is described OLDER PRECAMBRIAN ROCKS 1,410,000 RDE r 1,405,000 <"' LII? mq and me tu s + { FIND s: W t e £9 1,400,000 & ind 4 Pinnacle a\, p 1,395,000 1,390,000 1,385,000 1 L i 1,380,000 N I inx r! 340,000 E 345,000 350,000 355,000 360,000 ‘fiéfifi 365,000 370,000 "a 75 EXPLANATION wad P Anticline Texas Gulch Formation Showing plunge; dashed where f eet approximately located Contact =e Dashed where approximately located; Minor fold dotted where concealed Nearly horizontal, or plunge unknown samt 51 94% so Mazatzal Quartzite Fault , me,, upper conglomerate Dashed where approximately located; Strike and dip of beds ma,, upper argillite dotted where concealed 22 ma ;, lower argillite ag me ;, lower conglomerate f Strike of vertical beds Stratigraphic position of me (conglomerate) Thrust fault and ma (argillite) unknown Saw teeth on upper plate msr Area of jointed rock Unnamed basaltic flows of the Alder(?) Group ? FIGURE 5.-Outcrops of the Mazatzal Quartzite and of Precambrian rocks adjacent to the Mazatzal in the Paulden quadrangle. 'The structure and probable correlation of isolated outcrops to the main mass of the Mazatzal are shown. 22 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA in detail in the following sections (note that two differ- ent figures, sections 1 and 1a, were obtained for units T-11) : Mazatzal Quartzite, Del Rio area, Arizona [Color terms and numerical designations are those used in the "Rock Color Chart," National Research Council, 1948] Section 3 [Top located at 1,395,600 N., 347,600 E.] Top eroded and covered by Cenozoic deposits. Quartzite (27-28) : 28. Quartzite and a little granule conglomerate, pale red-purple (5RP 6/2), medium- grained, thin bedded (beds are about 6 in. thick), cross-laminated, well-indurated (quartz cement) ; conglomerate contains subrounded to subangular granules of quartz and a few of red chalcedony_____ 27. Quartzite and a little granule to small- pebble conglomerate, grayish-red (5R 4.5/ 2), rarely pale-red (TR 5/2) ; weathers dusky red to very dark red (5R 3/4- 2/6) ; medium-grained, thin-bedded (6 in. to 1 ft), cross-laminated, well-indurated (quartz cement) ; contains a few very thin partings of red argillite and mica- ceous sandstone, granules and small peb- bles of quartz, a little red chalcedony, and, locally, red argillite 1% in. across__ Thickness (Jeet) 50 275 Total thickness of exposed quartzite (27- 2B) ss o a t 1 he nee arie to on oe in hale mace m he nid hele to an wile Hice to m ae Upper conglomerate (18-26) : 26. Conglomerate and medium- to coarse- grained quartzite, grayish red-purple to grayish-red (5RP 4/2-5R 5/2); unit weathers very dusky red (10R 2/2) ; very thin to thin bedded, well-indurated ; subrounded granules and pebbles (as large as 3% by 2 in.) of quartz, red and dark-gray chalcedony, grayish and red- dish quartzite, and quartz porphyry; some angular red chalcedony pebbles; conglomerate beds 6 in. to 2 ft thick; pebbles at least as abundant as matrix in one 25. Quartzite, medium- to coarse-grained, less abundant granule to pebble conglom- erate; light brownish-gray, very pale brown to brownish-gray (5YR 6/1-6/2- 4/1), mostly thin-bedded (1 ft to rarely 7 ft), cross-laminae accentuated by black hematite; quartzite contains scattered pebbles (%-%4 in. in size) of quartz and a few of red chalcedony ; most pebbles in conglomerate are of quartz and less than 1 in. in diameter ; a few cobbles (as much as 1 ft in diameter) occur near base in a very coarse grained matrix____________ 325 30 280 Section 3-Continued Upper conglomerate (18-26)-Continued 24. Sandstone, sandy and micaceous, and shale, grayish-red (10RP 5/8-5R 4.5/3), fine-grained to silty, weakly cemented, locally ripple-marked, slope-forming; estimated thickness, less than-_________ The same conglomerate bed (23) that forms the top of section 2 forms the bottom of section 3. [Bottom of section located at 1,395,000 N., 348,100 E.] Section 2 [Top located at 1,391,500 N., 347,200 E.] 23. Conglomerate and a few reddish-brown quartzite interbeds as much as 1 ft thick, light brownish-gray (5¥YR 6/1)-locally light olive-gray (5Y¥ 6/1) and pale red (TR 5/2) -grayish red-purple (5RP 4/2) near base; weathers blackish red to dusky-red (5R 2/2-3/2) ; some black he- matite grains concentrated in laminae; medium to very coarse grained, thin (6 in.) to thick-bedded; pebbles of sub- rounded to subangular quartz, and a few of quartzite, quartz porphyry, and angu- lar red chalcedony; red and dark-gray chalcedony more abundant toward base ; pebbles, generally as abundant as ma- trix, mostly less than 1 in. in size near top, mostly about 2 in. near base ; largest pebbles (3-4 in. in size) in middle ; a few triangular fragments of blackish-red (5R 2/2) chalcedony and grayish quart- zite are 6 by 4 in. in gize_______________ 22. Quartzite, medium-grained, and granule to small-pebble conglomerate; - weathers dark, like base of unit 23; thin layers (as much as 1 ft thick) of coarser con- glomerate like lower part of unit 23____ 21. Pebble conglomerate and a little quartzite ; weathers very dusky red to grayish brown (10R 2/2-5YR 3/2) ; pebbles of red chalcedony and quartz about equally abundant; a few of quartzite, quartz porphyry, and gray chalcedony and some angular fragments of grayish-red (5R 4/2) argillite (as much as 1 ft in size) __ 20. Conglomerate, chiefly quartz pebbles and small cobbles generally 2 in. in size; a few as much as 8 in. across____________ 19. Conglomerate and some quartzite; weath- ers light brownish gray to light olive gray (5¥YR 6/1-5Y 6/1) near base; some finer grained beds weather dusky red (5R 3/4-3.5/5) ; pebbles composed of quartz, red chalcedony, or a little quartzite and quartz porphyry ; pebbles are mostly less than 2 in. in diameter but range from granules to cobbles, smaller ones near base; some finer grained beds are cross 1a In ALGA... =--. L - Coe onne ren Mazatzal Quartzite, Del Rio area, Arizona-Continued Thickness (feet) 140 50 25 448 OLDER PRECAMBRIAN ROCKS Mazatzal Quartzite, Del Rio area, Arizona-Continued Section 2-Continued 18. Quartzite, granule conglomerate, and some thin beds of small-pebble conglomer- ate; unit weathers dusky red; some beds in the middle of the unit weather to a lighter Total thickness of the upper conglomerate (BRD ) L 2 nne ee e ee a tae he ha me me ne mee cane i ba oe mee e A saddle near the middle of the ridge separates the predominantly conglomerate beds (above) on the west from the predominantly quartzite beds (below) on the east. Quartzite (13-17) : 17. Quartzite and granule conglomerate, largely grayish-red (5R 4/2-5/2) to slightly red-purple; finer and more even grained beds are dark reddish-brown (5R 38/5); cross-laminated; quartz grains in a reddish matrix___________-- 16. Quartzite and granule conglomerate, very pale red-purple (5RP 7/2), grayish orange-pink (5¥YR 7/2), and pale-red (10R 6/2), cross-laminated____________ 15. Conglomerate; pebbles (as much as 2 in. in size) of quartz and some red chalced- ony ; a few other rock fragments________ 14. Quartzite, pale-red (10R 6/2), fine to very coarse grained, a few some- what friable medium-grained beds ; some interbeds as much as 5 ft thick contain quartz pebbles (less than 1 in. in diam- CLET ) 23 22 L eae d oa a eee tep Fera ae e me on aan ance e matase 13. Quartzite and sandstone, pale reddish- brown (10R 5/4), moderate-red (5R 5/4- 4/6), grayish-orange-pink (10R 7/3- 5YR 7/2), thin-bedded (less than 6 in.), cross-laminated, medium- to coarse- grained; basal beds contain angular pieces of red argillite. Approximate thickness. :c o_. oce oll uue coc curiae Total thickness of quartzite (13-17) -_____- Upper argillite (12) : 12. Argillite (very fine grained mudstone), some micaceous shale and sandstone; various shades of red (mostly 6R 4/6-7R 4/6; some 5R 4.5/5-8.5/3-4.5/3) ; weath- ers lighter shades, numerous light spots due to leaching of iron oxide; massive to very thinly laminated. Estimated thickness of argillite (12) -_____- Thickness (feet) 220 1, 158 85 95 25 602 T5 25-60 Nots.-Bottom of section located at 1,391,800 N., 349,600 E. 28 Mazatzal Quartzite, Del Rio area, Arizona-Continued Section la [Top located at 1,386,500 N., 349,700 E.] Top overlain by upper argillite (unit 12). Quartzite (7-11) : 11. Quartzite (the typical lavender quartzite of the Mazatzal) and well-indurated sandstone, pale-red (5R 6/2-5.5/3-5/2), very pale red-purple (5RP 7/2), to light brownish-gray (5¥YR 6/1); weathers light brownish gray, light olive gray, yel- lowish gray, to very pale yellowish brown (GYR 6/1-5¥ 6/1-5Y¥ 7/2-10¥VR 7/2); medium- to fine- and even-grained, locally cross-laminated; composed almost en- tirely of quartz; redder quartzite is fine to medium grained and well sorted ; lay- ender quartzite is slightly coarser and less well sorted. Thickness approxi- mate, it grades down into unit 10_______ 10. Quartzite and a few beds (as much as 1 ft thick) of granule and pebble (as much as half an inch in size) conglomer- ate, light brownish-gray (5YR 6/1-7/1) ; weathers pale yellowish brown with a rough surface, locally, pale red (10R 6/2- 7/1); medium to very coarse grained, cross-laminated; grades upward into medium- to fine-grained lavender quartz- ite (pale-red, 5R 7/2, to very pale red- purple, DRP 1/2)... ___ CZs 9. Conglomerate, light olive-gray (5Y¥ 6/1) to light brownish-gray (5YR 6/1) ; rounded to subangular pebbles as much as half an inch in diameter____________ 8. Sandstone, well-cemented ; some quartzite and a few thin beds of granule and small-pebble (as much as 1 in. in size) conglomerate; pale-red (5R 6/2) to light brownish-gray (5¥YR 6/1); weathers pale red (10R 6/2); cross-laminated (less so than is unit 7C); dark-gray hematite grains in some cross laminae. 7C. Quartzite; weathers medium gray to brownish gray (5N-5YR 4/1-3/1), lo- cally grayish red (TR 5/4) ; medium- to coarse-grained; scattered (locally abun- dant) granules and small pebbles (as much as 1 in. in size) of quartz and a few of red chalcedony; prominently cross-laminated ; cross laminae accentu- ated by abundant grains of dark-gray HEMALIEE :.. . - con Leanne cera aan in 7B. Conglomerate and some quartzite lenses as much as 6 in. in thickness; pebbles and cobbles (as much as 3% in. in size) of subrounded quartz, subrounded to subanguler red and dark-gray chalced- ony, and, a few of quartzite and quartz pOTDHYIY ... .. ...... cll. Ln cua naan alel dele mn teem Thickness (feet) 408 330 67 27 24 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA Mazatzal Quartzite, Del Rio area, Arizona-Continued Section 1a-Continued Quartzite (7-11)-Continued TA. Quartzite, light brownish-gray to pale grayish-red (5¥YR 6/1-5/1-5R 6/1); weathers pale brown (5YR 5/2) with a rough surface; weathers darker brown- ish-gray near top; coarse to very coarse grained; scattered granules and very small pebbles; cross-laminated__.._ Total thickness of quartzite (7-11), as meas- tired in 'section 18.-..__-_-_.__________ __ Thickness (Jeet) 265 1, 105 [Bottom of section is located at 1,384,700 N., 350,800 E. and is underlain by lower argillite (6)] Section 1 [Top located at 1,383,900 N., 356,200 E.] Top overlain by upper argillite (unit 12). Quartzite (7-11) : 11. Quartzite (same as unit 11, section 1a), lavender, becoming reddish at top; crossbedded, even-grained_____________ 10. Quartzite and some granule to small-peb- ble conglomerate; weathers light brown- ish gray (BYR 06/1) uel eel anal 9. Conglomerate, same as unit 9 of section la. 8. Quartzite and some small-pebble (as much as a quarter of an inch in size) con- glomerate, pale-red (5R - 6/2-5/8), coarse-grained, cross-laminated; some laminae accentuated by hematite grains. 7. Quartzite, poorly exposed; some is like unit TC of section Total thickness of quartzite (7-11), as meas- ured in section Lower argillite (6) : 6. Sandstone, micaceous, sandy micaceous shale, and a little argillite; grayish-red (5R 4/2-5/2) to pale reddish-brown (8R 5/4), white or light-colored spots due to leaching of iron oxide, medium- to fine-grained; angular to subrounded closely packed grains of quartz and some muscovite in a reddish matrix. Thickness of lower argillite, estimated_____ Lower conglomerate (2-5) : 5. Conglomerate and quartzite; weathers brownish gray (5YR 4/1) at top; peb- bles are smaller, and beds of quartzite are thicker and more abundant than in unit: 4.0.00-0000002 0000000000801 -_ 4. Conglomerate; lighter colored than unit 3; contains abundant cobbles and small boulders (as much as 12 in. in size) of quartz and a few of red chalcedony____ 480 230 40 188 942 25-50 305 15 purple; much of it has a lavender tint. Mazatzal Quartzite, Del Rio area, Arizona-Continued Section 1-Continued Thickness (feet) Lower conglomerate (2-5)-Continued 3. Conglomerate; red and gray chalcedony fragments are more abundant than in unit 2; weathers dusky red (5R 3/4) ___ 100 2. Conglomerate and a little quartzite, pale- red (5R 6/2) to grayish orange-pink (5YR 7/2) ; rounded to angular quartz and some angular red chalcedony, rang- ing in size from granules to cobbles 6 INA L.. n ece ln eanaans 20 Total thickness of lower conglomerate (2-5) 2 + a ae c eee oo oe ne n n he ae ue a he h he Se ie a Be alan haren an od Bn 440 Quartzite (0-1) : 1. Quartzite, grayish orange-pink (5YR 7/2) to very pale red (5R 7/2) ; weathers yel- lowish gray, light brownish gray, light olive gray, to pale yellowish brown (5¥YR 8/1-5YR 6/1-5Y¥ 6/1-10VR 6/2): medium- to coarse-grained and very coarse grained, mostly well-indurated ; massive, bedding is indistinet__________ 208 0. Quartzite, weathers dark reddish brown at base; unit was not measured, but is exposed below unit 1 ; approximate thick- ial =n wens sun 50 Total exposed thickness of quartzite (0-1), .. . « <- Eder aa one- 258 Base concealed by Cenozoic deposits. [Bottom of section located at 1,382,700 N., 354,900 E.] Total thickness exposed, approximate______ 4, 000-4, 200 Section 1a was measured as a check on the correlation of the western and eastern outcrops of upper argillite and on the stratigraphy of the rocks between the upper and lower argillite in the two areas. The difference in measured thickness (about 160 ft out of a total of about 1,000 ft) could be due to several factors: (1) errors in measuring caused in part by the gentler dip of the rocks in section 1a ; (2) original differences in thick- ness; and (3) the fact that upper and lower contacts of the two argillites in section la were covered and may actually have been farther west and therefore higher up in the section than estimated. QUARTZITE AND CONGLOMERATE Most of the quartzite and conglomerate are hard vitreous rocks that form cliffs and rugged topography, but some beds are less resistant. The fresh rock is vari- ous shades of red, grayish pink, and brown to pale red The rock weathers dark to light shades of gray, red, and brown. From a distance the outcrops are dark colored. OLDER PRECAMBRIAN ROCKS 25 Bedding ranges from thin to thick or massive and from indistinct to conspicuous. Crossbedding is com- mon in much of the finer grained rocks and is sporadic in conglomerate. Most lamination planes are 1 foot or less in length; some are as much as 3 feet long. In places grains of dark-gray hematite accentuate cross laminae and some bedding planes. Some laminae, com- posed principally of hematite, are more than 5 mm thick. The hematite grains, which are subrounded and mostly less than 0.5 mm in diameter, represent original concen- trations, not later replacement. Textures range from fine grains to boulders 12 inches in diameter (fig. 6). Most of the lavender quartzite below the upper argillite (unit 11, measured sections) is even grained, but elsewhere much of the material is poorly sorted. Pebbles are very sparsely distributed to closely packed. Many of them are subrounded, but some large pieces of argillite and red chalcedony are subangular to angular. The pebbles are milky quartz, variable amounts of red, reddish-black, and dark- and light-gray chalcedony, a little grayish and reddish quartz porphyry and quartzite, schistose and more mas- sive dark volcanic rocks, and argillite. Argillite frag- ments are common immediately above the upper argil- lite. No granitic pebbles were seen. The quartzite and matrix of the conglomerate are composed of quartz and a little chalcedony, black hematite, argillite, and muscovite. - Grains of magnetite and ilmenite, observed in most thin sections, are rounded to angular; smaller grains are more angular. FigURrE 6.-Lower conglomerate in the Mazatzal Quartzite, Granite Creek (near 1,388,200 N., 353,600 E.) ARGILLITE Argillite forms thin partings in the Mazatzal Quartz- ite and two thicker beds-lower (unit 6) and upper (unit 12) argillite. The lower argillite, consisting of micaceous sandstone, sandy micaceous shale, and a little argillite, forms two narrow bands in the central part of the main mass of the formation. The upper argillite, consisting of argillite, micaceous sandstone, and sandy micaceous shale, forms three bands in the main mass- a western, a central, and an eastern one. The argillites crop out poorly and form grassy slopes and flats over which small chips of the material are scattered. The upper argillite was first noted and mapped because of small pits dug on it by Indians, who used the material for pendants. Most of the pits are on the two eastern outcrops; only one was noted on the western outcrop. The argillite is similar to the pipe- stone or catlinite used by Minnesota Indians for pipes of peace and other artifacts. The argillite is shades of grayish red, reddish brown, and red purple. It weathers moderate orange pink; much of it contains numerous spheroidal-, ellipsoidal-, and disk-shaped spots that are the same color as the weathered surface or very light gray. The spots range from less than 1 to 10 mm in diameter; they are formed by leaching of iron oxide from the matrix. Scattered small white grains are also visible. The argillite ranges from a very fine grained, dense rock to one composed of rounded and ellipsoidal grains as much as 1.5 mm in diameter. Much of the argillite is massive, but some is thinly laminated; the slightly darker laminae are about 1 mm thick, and the lighter colored ones are 3-10 mm thick. The laminated rock tends to break parallel to the bedding, but it does not split readily. The massive rock has a very irregular fracture, except where cut by numerous closely spaced joints. Slickensides have formed where the rock has been shattered, but the argillite shows no internal evi- dence of having been deformed. Micaceous sandstone and sandy micaceous shale grade into argillite and into quartzite. These rocks are me- dium to fine grained, thinly bedded (2-3 em), and in places ripple marked. The color is similar to that of the argillite. The rock is composed of grains consisting of quartz, residual muscovite, aggregates of fine sericite, and minor amounts of chalcedony, tourmaline, mag- netite, and ilmenite in a fine-grained reddish matrix that is composed principally of sericite and iron oxide. Many quartz grains are angular, and most of them are less than 0.2 mm long; a few are as much as 1 mm long. + According to Laudermilk (1944), the source of all red pipestone was believed to be in Minnesota until the Del Rio locality was discovered. 26 Although quantitatively unimportant, the argillite is discussed in some detail because of its interesting min- eralogical composition and the light its composition may throw on its probable origin and on the age of the Mazatzal Quartzite. The mineralogy of five specimens of argillite was determined by use of X-rays (table 3). Specimens from the central outcrop (Nos. 1, 4, and 5, table 3) are composed of quartz, pyrophyllite, and minor amounts or traces of mica, chlorite, and hematite. One speci- men (No. 3, table 3) from the western outcrop con- sists of kaolinite and minor pyrophyllite and hematite; the other (No. 2, table 3) consists of quartz, mixed lay- ered mica-montmorillonite, and traces of hematite. The fine-grained finely laminated argillite (No. 4, table 3) from the central outcrop contains angular to rounded colorless grains and aggregates of a mineral having a moderately high birefringence. The grains, as much as 0.1 mm in diameter, are enclosed in a fine- grained ferruginous matrix that, where iron oxide has been leached, has birefringence similar to that of the larger grains; both probably are pyrophyllite. The elongated grains in the argillite from the western out- crop (No. 3, table 3) are composed of ecryptocrystalline material of very low birefringence, presumably kaolin- ite. No quartz was recognized in thin sections of either specimen. TABLE 3.-Mineralogy of argillite from the Mazatzal Quartzite, Paulden quadrangle [Analyses based on X-ralg studies. Analysts: J. C. Hathaway, H. C. Starkey, and lackmon, U.S. Geol. Survey Tr., trace] Specimen............. 1 2 3 4 5 Fraction after grind- l Clay | Silt | Clay | Silt | Clay | Silt | Clay | Silt | Clay | Silt Percent of sample.....| 24 76 20 80 21 79 28 72 21 78 Estimated amount of minerals present, in parts in ten: € leslie 6 5 6 6 5 2 2 5 2 4 ........... 1] Tt. 1. Tr: a t Tr. [Tr Ts. | Pr. | Tr.] Tr. Mixed layered mica-montmor- iMoRife3. 2.2.1. 220120 20 8 Breese eee els «Souk Kaolinite. ...... P fera 8 BME LCL cels ece ss ORIOMIEE 2 22. Ine snel s raed ele ee Aue deer le cca s Th. Tr. |.ciee 1 About 20 percent montmorillonite layers. 1. Mgrssiggfignf-gralned argillite, central outcrops (1,381,000 N., 359, 400 E.). Lab. 2. Mfissgve “$30?“ purplish argillite, western outcrops (1,388,200 N., 350,000 E.). a 3. Mfisslvwzanular argillite, western outcrops (1,388,200 N., 350,000 E.). Lab. 0. 4. Finely laminated fine-grained argillite, central outcrops (1,381,000 N., 359,400 E.). Lab. No. 266394. 5. Massive fine-grained argillite, central outcrops (1,381,000 N., 359, 400 E.). Lab. No. 266398. The chemical composition of one specimen (No. 1, table 3) is given in table 4 and compared with the chemical composition of other argillaceous rocks; the minor elements in specimen 1 are given in table 5. GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA TABLE 4.-COhemical analysis of argillite from Mazatzal Quartz- ite, Paulden quadrangle, compared with analysis of other argillaceous rocks S@MDpIG: -. .s 0.1.10 1 2 3 4 5 62.2 60. 96 60. 15 61. 54 19. 4 16.15 16. 45 16. 95 .75 . 86 .76 .82 7.5 5.16 4. 04 2. 56 . 30 2. 54 2. 90 3. 90 .02 . 07 'Trace |..«--... ~. 1.6 3. 06 2. 82 2. 52 . 08 31 1.41 1.76 .8 1.5 1. 01 1.84 .6 5. 01 3. 60 3. 45 a £0 3 AB 99 100. 25 100. 23 1. Rapid analysis of argillite from Mazatzal Quartzite, Paulden quadrangle (1,381,000 N., 359,400 E.). Analysts: P. L. D. Elmore, S. D. Botts, K. E. White, U.S. Geol. Survey. Lab. No. 148371. * 2. Rapid analysis of purple slate, south of Shylock mine (1,312,900 N., 418,500 E.), Mingus Mountain quadrangle. Analysts: S. M. Berthold and E. A. Nygaard From Anderson and Creaseg‘r0958, table 10). 3. Purple slate, Castleton, Vt. om Clarke (1924, p. 554). 4. Composite analysis of 51 Paleozoic shales by H. N. Stokes. From Clarke (1924, p. 552). 5. Average composition of pelitic rocks. From Shaw (1956, table 10). * TaABu® 5.-Semiquantitative analysis for minor elements in argillite from Mazatzal Quartzite, Paulden quadrangle [Analyst, H. J. Rose, Jr., U.S. Geol. Survey. Lab. No. 148371] Element Percent Element Percent CUs 0. O01 La... 0. 003 PD.: . O01 1 . O1 . 01 eled s . O01 0 if Ne ¥ 303 Be elsa lie . 0003 see nl 3 ofl ai . oon, NES >-- o vii r: sooty CA- -< if . o par . 10. 0 d da aia . 008 Oa . 008 - d . 001 ee, 4 asan . 003 . 0083 Looked for but not found: Ag, Au, Hg, Ru, Rh, Pd, Os, Ir, Pt, Mo, W, Re, Ge, Sn, As, Sb, Bi, Zn, Cd, Tl, In, Ce, Nd, Hf, Th, Ta, U, P. The silica content is higher (about 17 percent) in the argillite than in other argillaceous rocks. This higher content makes the other components of the argillite seem lower, but they generally retain the same relative proportions as the other argillaceous rocks. The alkali ratios of the five specimens are given in table 6. All have a high ratio of potassium oxide to sodium oxide. - The amount of sodium oxide varies only slightly (0.04-0.18 percent) and is lowest in the kaolinite-rich sample (No. 3, table 6). The amount of potassium oxide is more variable; it ranges from 0.96 to 1.6 percent in the specimens composed of quartz and pyrophyllite (Nos. 1, 4, and 5, table 6) ; it is lowest (0.11 percent) in the kaolinite-rich sample (No. 3, table 6) and highest OLDER PRECAMBRIAN ROCKS 27 (2.9 percent) in the specimen containing the mixed- layered (mica-montmorillonite) clay mineral com- ponent (No. 2, table 6), where it is contained mostly in the mica mineral structure. TaBu® 6.-Alkali ratio in five specimens of argillite from Mazatzal Quartzite, Paulden quadrangle [Specimens 2-5.-Rapid analyses for Na;O and K;O only. Analyst, I. H. Barlow, U.S. Geol. Survey] Na:0 K0 Specimen (percent) (percent) TPE: :o eela s oa den aa male a 4 on Sd am 0. 13 1.8 . 14 2. 9 . 04 A4 . 18 1. 6 £16 . 96 . Massive fine-grained argillite, central outcrops (1,381,000 N., 359,400 E.). From chemical analysis 1, table 4. . Mgssivg3 gne grained, argillite, western outcrops (1,388,200 N., 350,000 E.). Lab. 0. 1 350,000 E.). Lab. No. 1 2 3. Massgége granular argillite, western outcrops (1,388,200 N., 4. Flfiglby. 113113mat§d fine-grained argillite, central outcrops (1,381,000 N., 359,400 E.). 5. Massive fine-grained argillite, central outcrops (1,381,000 N., 359,400 E.). Lab. No. 15334. Kaolinite, montmorillonite, and pyrophyllite are un- expected constituents in older Precambrian rocks. Grim (1953, p. 356), pointed out that montmorillonite is generally absent in sedimentary rocks older than the Mesozoic, whereas it is abundant in many Mesozoic and Cenozoic rocks, in Recent marine sediments, and in present-day weathering products; kaolinite is less abundant in rocks older than the Devonian than in younger ones. Montmorillonite and kaolinite are gen- erally not formed under the same conditions (Grim, 1953, p. 355-356). All three minerals are common prod- ucts of mild hydrothermal alteration in nature. Pyro- phyllite forms at higher temperatures (above 350° C) than does kaolinite, according to laboratory experiments by Hemley (1959) ; at a low pH it forms at a lower temperature than does mica. The significance of these minerals is not understood. There is no evidence that they formed under hydrothermal conditions, though possibly the higher temperature represented by pyro- phyllite may be related to late Tertiary(?) andesite plugs; kaolinite and montmorillonite may represent products of weathering. The relation of temperature of formation or degreee of metamorphism indicated by pyrophyllite to that of the formation of the green schist facies common in rocks of the Alder Group is not known. The high K,0 to Na,0 ratio of the argillite may indi- cate derivation from normal terrigenous clay, as this ratio is typical of normal clays (table 4, Nos. 2-5) ; Pre- cambrian rhyolite tuffs of the area have a high Na,0 to K,0 ratio. On the other hand, montmorillonite is com- mon in bentonitic clays derived from volcanic ash. Ex- tensive leaching of the argillite is indicated by the high silica content, but it must have occurred under different weathering conditions than exist today. 758-447 O-65--3 Laudermilk (1944) stated that specimens of argillite from the Del Rio locality had the same general chemical composition as the pipestone from Minnesota: S10;, A1;0;, Fe;0;,:FeQ, and minor amounts of CaO, MgO, Na,0, K0, and rare elements. However, he stated that a different alkali ratio (high K0 to Na,0 in the Minne- sota material; a reverse ratio in the Del Rio material) and different amounts of certain other elements (copper, silver, calcium, strontium, and barium) distinguish the material from which Minnesota and Arizona artifacts were made. Laudermilk's conclusions were based on spectrographic and petrographic studies by Howell (1940, p. 51), who stated : "Potassium, a constant con- stituent of the northern material, is either extremely minute or entirely missing in the southern samples ex- amined. Sodium and lithium show a similar decrease between specimens from these two sources." Howell stated further (p. 55) that the Minnesota material is "composed predominantly of pyrophyllite, hematite, and a sericite-like mineral as against a predominance of kaolinite for the Arizona shales." The present X-ray and chemical studies of Del Rio material (tables 3-6) do not agree with Howell's results. His material may have come from the eastern outcrop, which was not ex- amined chemically or by X-ray during the present study, or from variations that may occur across or along the strike of an outcrop band. AGE AND CORRELATIONS The Mazatzal Quartzite in the Del Rio area is older than the Tapeats Sandstone. It may be younger than the metamorphism of the Alder Group and than the granitic intrusions that cut the Alder Group. The composition of the argillite, the absence of foli- ation, and the unstrained character of quartz grains in folded quartzite indicate that the Mazatzal in this area was at most only slightly metamorphosed. In contrast, rocks of the Alder Group have been foliated and meta- morphosed to green schist and higher grade facies. A granitic terrane older than the Mazatzal is indicated by the abundance of pebbles, cobbles, and small boulders of vein quartz in the conglomerate and by the absence of quartz veins or granitic rocks intruding the Mazat- zal; quartz veins and granitic rocks are abundant in the Alder Group. Although lack of granitic pebbles and feldspar grains in the quartzite might indicate deposition prior to the granitic intrusions, their absence may be attributed to vigorous and long-continued ero- sion that removed particles of earlier granite or reduced them to clay-sized particles, now represented by thin argillaceous partings in the quartzite. Southeast of Pine (fig. 1, inset) the Mazatzal Quartz- ite is assigned to the older Precambrian because it was folded, intruded by granite, and eroded prior to depo- 28 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA sition of the younger Precambrian Apache Group. This deformation and granitic intrusion mark the Mazatzal Revolution (Wilson, 1939, p. 1134), which separates older from younger (Apache Group and Grand Canyon Series) Precambrian rocks (Butler and Wilson, 1988, p. 11). Wilson (1922, p. 299) first correlated the quartzite in the Del Rio area with the Mazatzal Quartzite in the Mazatzal Mountains and adjacent areas. Although a correlation from Pine Creek to the Del Rio area, a dis- tance of more than 60 miles, may be open to question, the lithology of the thick quartzites and conglomerates in the areas mapped as Mazatzal is similar, and the correlation does have merit. According to E. D. McKee (oral commun., 1957), the quartzite in the Del Rio area resembles the Shinumo Quartzite of the Unkar Group, which is the older of the two groups that make up the younger Precambrian Grand Canyon Series in the Grand Canyon, more than 90 miles north of the Del Rio area. The fact that younger Precambrian rocks overlie the Mazatzal to the southeast does not preclude the possibility that the Mazatzal is equivalent to the Shinumo Quartzite, as the relative ages of the younger Precambrian rocks north and southeast of the Del Rio area are unknown. Because of the possibility that the Mazatzal Quartz- ite in the Del Rio area has been moved along faults from an area of very low grade metamorphism that was not intruded by granitic rocks, the formation has been left in the older Precambrian. The quartz cob- bles and pebbles in the Del Rio area may have been de- rived from a terrane older than the Alder Group, such as is now known to have existed (see footnote T, p. 49), and the granitic intrusions that cut the Mazatzal to the southeast may be younger than the granitic intrusions in the Prescott-Paulden area. Age determinations made by analysis of enclosed zircon grains in granitic rocks, in quartzite in the Grand Canyon, Del Rio, and Mazatzal Mountain areas, and in rhyolitic tuff in the Alder Group may eventually help to solve this problem of age relations. INTRUSIVE ROCKS Jaggar and Palache (1905) proposed the name Brad- shaw Granite for most of the quartzose intrusive rocks south of the Prescott-Jerome area, and Lindgren (1926, p. 16, pl. 2) extended the term Bradshaw Granite to rocks in the Prescott-Jerome area. Lindgren con- sidered the "diorite" and some quartz diorite or grano- diorite to be younger than the Bradshaw Granite and believed that younger quartz-bearing intrusive rocks were possibly Laramide in age. Studies in the Jerome and Prescott-Paulden areas show that (1) the so-called Bradshaw Granite consists of several different intru- sives ranging from granodiorite, which is the most abundant, to granite and alaskite, (2) much of the "diorite," now called gabbro, is older than the Brad- shaw Granite, and (3) one of the "younger quartz di- orite or granodiorite stocks" is Precambrian in age and older than at least some of the Bradshaw Granite. In this report the name Bradshaw Granite is aban- doned and new names are assigned to some of the in- trusive rocks that formerly were part of the "Bradshaw Granite." The major intrusives in the Prescott-Paul- den area, and their probable age relations from oldest to youngest, based largely on field evidence, are: (1) gab- bro and quartz diorite, (2) Government Canyon Grano- diorite, (3) Prescott Granodiorite, (4) quartz monzo- nite and alaskite, (5) coarse-grained granite, (6) Dells Granite, and (7) fine-grained granite. The relationships of the various intrusive masses are obscure for the following reasons : 1. The gabbro includes diabase and fine-grained gab- broic to dioritic rocks, some of which are younger than quartzose intrusive rocks but cannot be dis- tinguished from the older gabbroic rocks petro- graphically or in the field in most places. 2. Mafic volcanic rocks of the Alder(?) Group may have been misidentified as fine-grained gabbro older than the quartzose intrusive rocks. 3. Dikes of granodiorite, granite, alaskite, and aplite cut the intrusive rocks, but correlation of these dikes with a given intrusive mass is doubtful or impossible in some places; in addition, the aplites are of more than one age. 4. Compositional and textural features of the quartz- ose intrusive rocks differ from place to place, some of the differences being due to contamina- tion of the magma by the intruded rocks; there- fore, a mass may be erroneously assigned to a different intrusion. 5. Intense shearing masked and destroyed primary fea- tures of some rocks and resulted in mechanical rather than normal intrusive contacts; most of the north-trending contacts are zones of shear, and many contacts were located arbitrarily because of mechanical mixing of adjacent rocks. 6. The various masses mapped as the Prescott Granodi- orite are not contiguous, and their relationships to one another could not be determined exactly in the field; they are considered consanguineous be- cause of similarities in modal, chemical, and nor- mative compositions. 7. Some of the quartzose intrusive rocks may possibly be pre-Alder Group in age (see footnote 7 on p. 49). OLDER PRECAMBRIAN ROCKS The available modal, chemical, and normative data on the intrusive rocks are given in tables 7-10. Varia- tion diagrams show the modal and normative quartz- orthoclase-plagioclase composition of the different groups of intrusive rocks. Figure 9 represents the Gov- ernment Canyon Granodiorite; figure 11, the various masses of Prescott Granodiorite; and figure 13, the gra- nitic rocks. Modes, norms, and average mode are plotted. Figure 7 shows (4) the quartz-orthoclase- plagioclase norm and average mode of all the rocks, (B) modal and normative quartz-feldspar-mafic and accessory minerals, (C) plots of oxides on Si0.-K,0: Na,0-FeOQ-Fe,0, : MgO :-CaO diagrams, and (D?) ox- ides plotted against SiO,. The distribution of the vari- ous masses is shown in figures 8, 10, and 12. Included in these tables and figures are data on gabbro from the Mingus Mountain quadrangle and north-central part of the Mayer quadrangle, on granodiorite of the Walker area (Lindgren, 1926, p. 21) in the north-central part of the Mount Union quadrangle, and on the quartz diorite of the Jerome area (Anderson and Creasey, 1958, p. 40, table 13). The quartz diorite is considered part of the Prescott Granodiorite and is referred to as the Yarber Wash, Big Bug Creek, and Chaparral masses (fig. 10). The Big Bug Creek mass (McCabe area of Lindgren, 1926, p. 21, pl. 2) and the granodiorite of the Walker area are among the "younger granodiorites" of Lindgren. Modes and norms agree fairly well. Most average modes, however, are lower in orthoclase than are the norms, because in the norm all potash has 29 been assigned to orthoclase whereas in the mode some potash is tied up in the micas. GABBRO AND RELATED ROCKS DISTRIBUTION Gabbro and related rocks are widely distributed throughout the Precambrian rock outcrops of the Prescott-Paulden area. They form two large and sev- eral smaller bodies. Innumerable lenticular to dike- like masses, many of them too small to show on the geo- logic maps, intrude the Alder Group and quartzose intrusive rocks. The largest mass extends from the southern border of the area (pl. 1, west of 370,000 E.) northward for nearly 5 miles. The second largest mass forms the high ridge east of Prescott and extends from the south- ern border of the area (pl. 1, near 344,000 E.) north- ward for 3%4 miles. Scattered gabbro masses, the largest occupying not more than 1 square mile, are in the southeastern (pl. 1) and east-central (pls. 1, 2) parts of the area. Dikelike masses occur in the Chaparral and Spud faults (pl. 1). A small mass of quartz diorite, probably a facies of gabbro, crops out along the Verde River (pl. 2, between 375,500 E. and 390,000 E.) and is the northernmost exposure of Precambrian rocks in the area. Diabase dikes cut the Alder Group and some of the intrusive rocks but have not been mapped. They are abundant in the alaskite porphyry near Charcoal Gulch (pl. 1, between 377,000 E. and 378,000 E.) and in the Tamur 7.-Modal composition of quartzose intrusive rocks in the Prescott-Paulden-Jerome area [See figs. 8, 10, and 12 for locations; figs. 9, 11, and 13 for plots of norms and modes on Qu-Or-PI diagrams; fig. 7 for other triangular and variation diagrams; table 8 for chemical and table 10 for normative composition] 1 2 3A 3B 3C 4 5 6 7 8 9 10 11 12 Map ad ee - |pgy-1 pgy-2 | pgy-3 pgs pge pel PEP pgm qm al cg dg 17 16 27 26 27 | 32. 0 | 29. 0 28 | 28. 0 22 23 | 35. 0 | 33. 0 36 Orthoclase............._.. 5 14 9 4 7 5. 0 8. 0 10 | 10. 0 9 28 | 26. 0 | 19. 0 28 Plagioclase...:...:..:..... 54 52 56 61 58 | 52. 0 | 56. 0 52 | 54. 0 56 | * 837 | 38.0 | 39. 0 25 .... 16 8 2 4 B (e leew alle = ss aa l= ale ns seee lge =a Mica ®. 5 T 5 4 4 | 10.0 | 4.0 7 6. 0 T 7. 1.0 | ; 9.0 9 Epidote 2 2 1. 0 3. 0 2 2. 0 2 I ( ear ee ions a ale ut aan Accessory minerals_____.___. 1 1 1 1 1 | <. 5 | <. 56 1 | <.5 i 1T | <.5 2 Total...."......... 100 100 100 100 100 |100. 0 |100. 0 100 (100. 0 100 100 |100. 0 |100. 0 100 Percent of feldspar that is ; 8 21 14 6 10 9 12 16 16 14 48 40 33 58 1 Approximate composition based on X-ray diffraction, Anis«s. ? Largely white mica; includes primary and metamorphic biotite, chlorite, and muscovite-sericite. % Mostly secondary epidote derived from mafic minerals; includes some derived from plagioclase. a . Quartz diorite, Verde River, Paulden quadrangle, average of two thin sections (not shown in figs. 8, 10, or 12). 2. Government Canyon Granodiorite, average of 14 thin sections. 3. Yarber Wash mass, Prescott Granodiorite: 3A, western facies, average of four thin sections; 3B, eastern facies, average of five thin sections; 3C, average of western and eastern facies (Anderson and Creasey, 1958, table 13). . Salida Gulch mass, Prescott Granodiorite, average of 11 thin sections. . Chaparral mass, Prescott Granodiorite, average of six thin sections. ou 6. Lynx Creek mass, Prescott Granodiorite, average of eight thin sections. 7. Prescott mass, Prescott Granodiorite, average of seven thin sections. 8. Mineral Point mass, Prescott Granodiorite, average of four thin sections. 9. Quartz monzonite, average of two thin sections. . Alaskite, average of four thin sections. . Coarse-grained granite, average of seven thin sections. . Dells Granite, average of four thin sections. 30 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA TaBu® 8.-Chemical analyses of quartzose intrusive rocks and gabbro of the Prescott-Jerome area [See figs. 8, 10, and 12 for location, figs. 9, 11, and 13 for plots of norms and modes on Qu-Or-PI diagrams, fig. 7 for other triangular and variation diagrams, table 7 for modal; and table '10 for normative composmon Analyst: W. W. Brannock and others, U.S. Geol. Survey, rapid rock analyses, except for granodiorite of Walker area (from Lind gren, 1926, p. 21, No. 3) and gabbro (from Anderson and Creasey, 1958, p. 38, table 12, No. 8)] M Bol lb 2 3 4 5 6| 7. 8 9| 10 11 12 ap sym W G m f hate.. s 1&8ee |...... s tér | hee | | fier | ihe | | | wiege | ©10;........... 48. 57 61. 4 65.74 65.6 69. 5 70.1 67.7 64. 5 T1i9 76.8 76. 2 78. 2 _c 20. 32 16. 7 16. 76 16. 2 16. 0 16. 6 15.8 17.4 13. 2 18. 4 13.7 13. 0 2. 6 3. 99 2. 5 1.3 1.2 2. 0 1.6 O1 . 8 . 69 . 6 FeQ.:..:..... 8. 87 PT leds 2. 8 1.5 . 81 1.6 2.2 . 06 . 48 A7. . 35 4. 87 2.8 1.70 1.7 1.1 72 1.5 2. 1 . 05 . 26 . 10 . 10 9.15 4.7 3. 78 4. 6 3.2 2.9 3.3 4. 5 . 22 . 49 . 50 .74 2. 66 4. 2 3. 37 3. 6 4.3 4.7 4. 0 4. 4 4. 1 3. 9 4. 2 4. 4 (Q- ce canna 34 3. 4 3. 55 2:1 2.1 2.0 2. 6 1.9 4. 5 3. 7 4.5 1.9 . 64 OD . 38 . 23 . 20 . Al . 36 AAT . 10 . 04 . 06 B0 . 14 . 09 . 05 . 13 . 15 . 00 . 02 . 00 . 00 MnrnQ......".. 12 08: c. . 08 . 04 . 05 06 . 06 . 00 . O1 . 03 . O1 H;O..._..5:0... 4. 02 . 62 . 99 . 84 T0 . 07 . 64 1.0 . 80 . 50 . 56 . 39 CO;... 00 {ew . 07 . 84 . 24 . 28 . 16 . 08 "-fs 18 . 36 Total Sulfur As §.-.ec .e? sy.:01, |-. -.-.... <, 01 <. O1 . Of . 04 <. O1 <. 01 <. O1 <. 01 . 02 Total._..| 99.56 | 100 99.88 | 100 100 100 100 100 101 100 101 100 1. Gabbro, composite of five specimens from loc. 49 and one from loc. 50 (fig. 10). 7. Prescott mass, Prescott Granodiorite (loc. 7, fig. 10). 2. Government Canyon Granodiorite (loc. 5, fig. 8). 8. Mineral Point" mass, Prescott Granodiorite (loc 36, fig. 10). 3. Granodiorite of Walker area (loc. 48, fig. 10) 9. Alaskite (loc. 16, fig. 12). 4. Yarber Wash mass (western facies), Prescott Granodlorite (loc. 47, fig. 10). 10. Coarse-grained granite (loc. 13, fig. 12). 5. Salida Gulch mass, Prescott Granodiorite (loc. 23, fig. 10). 11. Dells Granite (loc. 1, fig. 12). 6. Lynx Creek mass, Prescott Granodiorite (loc. 12, fig 10). 12. Fine-grained granite (loc 6, fig. 12). TABLE 9.-Semiquantitative analyses for minor elements in quartzose intrusive rocks of the Prescott-Jerome area [See table 8 for explanation of map symbols. Analyst: H. J. Rose, Jr., U.S. Geol. Survey] Prescott Granodiorite Government Coarse- Dells Fine- Canyon Alaskite grained Granite grained Grano- Yarber Salida Lynx Prescott Mineral granite granite diorite Wash Gulch Creek mass Point mass mass mass mass Map | c La bp Ny _______________________ 15566 lgsggfil 1253562 15541233 123,64 1452215 142369 148568 14125570 118567 . _ 0. 003 0. 003 0. 001 0. 00083 0. 003 0. O01 0 0. 001 0. 0001 0. O01 . O01 . O01 . O01 . O01 . 003 . O01 . O01 . O01 . 003 . O01 MnNcc.s. cles ec eeeve . 03 . 03 . 08 . 03 . 03 . 03 . O1 01 . 03 . O1 (COPE ek Lue. cae bens . O01 . O01 . 0008 . 0003 . O01 . O01 0 0 0 0 . 003 . O01 . O01 . O01 . O01 . 003 0 0 0 0 3 3 3 3 3 3 . 8 . 8 +8 e CF crc ere aia ans . O01 . O01 . 00083 . 0008 . O01 . O01 0 . O01 0 . 00083 Yean nae eel e o . O1 O1 . 003 . 003 . 003 . 003 . O01 . O01 . 003 . O01 ML.. cie aoe santana 10 10 10 10 10 10 10 10 10 10 Ga...: n 9." /a . 003 . O01 . O01 . O01 . 003 . 003 . 003 . 003 . 003 . O01 . O01 . O01 . 0008 . 0008 . O01 . O01 0 . O01 0 . 00083 sine acane . 003 . O01 . O01 . O01 . 008 . O01 . 003 . 008 . O1 . O01 p Mommas to ate fos... . 003 . O01 . 003 . O01 . 003 . O01 . O01 . 003 . O01 . 003 Tilgin se cil seat cene e 8 8 74 9 I he | . 03 . 03 . O1 . 03 Tee ene ae ial rhe s . O1 . 003 . O01 . O01 . 003 . O01 . OO1 . 003 . 003 01 ND nee an ee a 0 0 0 0 0 0 0 0 . O1 0 . 00083 . 0001 . 0001 . 0001 . 0001 . 0001 . 0008 . 0003 . 00083 . 0001 tk .t" t 3 1 1 1 1 1 . 03 [A4 & . "I Cal. lue eee aat t 3 3 1 1 1 3 <% . 8 - 8 #0 ToL. sie ia 4 . 03 . 03 . 03 <3 ¥1 . O01 y 01 . O01 O1 rer . 083 . 03 . 03 . 08 . 03 . 03 . 003 . 03 . 003 . 03 NA... 3 3 3 3 3 3 3 3 3 3 D 0 0 0 0 0 0 0 0 . 003 . O01 Looked for but not found: Ag, Au, Hg, Ru, Rh, Pd, Os, Ir, Pt, Mo, W, Re, Ge, Sn, As, Sb, Bi, Zn, Cd, Tl, In, Ce, Nd, Hf, Th, Ta, U, P. OLDER PRECAMBRIAN ROCKS 3l TaBu® 10.-Normative composition of quartzose intrusive rocks and gabbro of the Prescott-J erome area [See figs. 8, 10, and 12 for locations; figs. 9, 11, and 13 for plots of norms and modes on Qu-Or-PI diagrams; fig. 7 for other triangular and variation diagrams; table 7 for modal composition and table 8 for chemical composition 1 2 3 4 5 6 7 8 9 10 11 12 Mapsymbol.........-l.:.c._.c...c. gb ge we pgey pgs pg! PEP pgm al eg dg tg Quarts 5. 64 | 10. 68 | 21.96 | 24. 00 | 27.90 | 28. 14 | 24.96 | 18. 36 36. 30 | 38. 10 | 33. 24 43. 74 Orthoclase..............._.. 1.07 | 20.02 | 21.18 | 12. 25. | 12.28 | 11.08 | 15. 57 | 11. 12 26. 69 | 21. 68 | 26. 69 11. 12 cn 22. 58 | 55. 68 | 28.30 | 30. 30 | 36. 15 | 39. 82 | 34. 06 | 37.20 34. 58 | 33. O1 | 35. 63 37. 20 Amnorthite:.....__....c...0.. 42. 58 | 16.68 | 18. 90 | 21.96 | 15.01 | 13. 62 | 15.57 | 21.41 1.11 2. 50 2. 50 3. 61 Hypersthene_......._.__.__ 11. 50 7. 05 | } 4. 20 5. 88 4. 25 1. 93 4. 36 7. 44 1.10 Nye 1.20 1 , 20 Miopside......__...._.... 2. 38 BT e: nl i | eager anl e haled ana i ala aula a a le a nia nee aler ae te a gll a me aind i a al aie a aln ie Magnetite_._._.........._. 8. 12 or Ta aU 8. 71 1. 86 1. 86 3. 02 2.02 1. 16 . 46 . 98 1. 22 1.8 . 76 . 46 . 46 . 76 1G 718 >. Ab .l. cree lease awes 2d . 84 . 34 . 84 . 84 (ere sans le anale nin mbH |. 1. 22 1.18 01 . 81 1. 12 2. 04 . 92 2. 35 cece. 4-00 |:. :.. cease inn abla are #82 Total......-...-.... 95. 59 | 99.58 | 99. 00 | 99.27 | 99.42 | 99. 58 | 99. 25 | 99.26 | 100. 69 | 99.37 | 99. 96 99. 30 Percent of feldspar that is orthociase.............. 2. 5 28 31 19 19 21 24 16 43 38 41 21 Plagioclase composition.... 2 Ang | $Ang | *tAns | *Ang | | Ang | %Angx | *Ang | | 5 An; | 5 Any; 5 An p 1 Tron free (enstatite). 2 Labradorite-bytownite. 3 Oligoclase-andesine. 4 Andesine. 5 Albite. 1. Gabbro, composite of 5 specimens from United Verde mine at Jerome and 1 from 6. Lynx Creek mass, Prescott Granodiorite. Yarber Wash (locs. 49 and 50, fig. 10). In the chemical analysis, iron is reported 7. Prescott mass, Prescott Granodiorite. as FeO; in calculating norm ratio of FerOs, FeO is arbitrarily taken as 5:3. 8. Mineral Point mass, Prescott Granodiorite. . Government Canyon Granodiorite. 9. Alaskite. . Granodiorite of Walker area. 10. Coarse-grained granite. . Yarber Wash mass (western facies), Prescott Granodiorite. . Salida Gulch mass, Prescott Granodiorite. @r im 00 ho Prescott Granodiorite west of the largest mass of gab- bro, but they are sparse in the Government Canyon Granodiorite and in the mass of Prescott Granodiorite that is north of the largest mass of gabbro (one was noted near 1,279,800 N., 333,700 E., and another near 1,300,000 N., 268,000 E.). Diabase dikes are probably abundant in gabbro but are not as obvious as in the granitic rocks, where they contrast in color. Larger masses of diabasic rock are included with gabbro because of the difficulty in distinguishing diabase from gabbro and because of the uncertainty as to age relationships between the rock types. GENERAL CHARACTER Gabbro.-The gabbro is a variable generally dark- colored granular rock. Where fresh, much of it is medium dark to medium gray, but the color ranges from nearly black to light gray, greenish gray, and grayish green. Much altered gabbro is green tinted. Weathered outcrops are various shades of brown. Grain size ranges from coarse to fine. Most of the gabbro is medium grained, the crystals ranging from 2 to 5 mm. Crystals in coarse-grained rocks are 5-10 mm long; some euhedral pyroxene crystals are several inches across. Rocks that may have been coarse grained are now finer grained because of cataclastic deformation. Some are now coarse grained because . Dells Granite. . Fine-grained granite. of the development of more or less equant porphyro- blastic or poikiloblastic hornblende several inches across. Textures include the ophitic (or poikilophitic), hy- pidiomorphic-granular, diabasic, and porphyritic tex- tures of intrusive rocks and the foliated, cataclastic, granularly recrystallized, or porphyroblastic to poikilo- blastic textures of metamoprhic rocks. Most of the younger diabase has well-defined diabasic texture and chilled margins. Some is porphyritic or contains large saussuritized plagioclase xenocrysts. The gabbro in some parts of the two largest masses is layered. Many of the pyroxene-rich, plagioclase-rich, and locally olivine-rich and magnetite-rich layers range from 14, inch to 3 inches in thickness. Some lay- ers probably resulted from crystal settling. Where alternating layers are now composed of metamorphic minerals-dark-colored hornblende and light-colored zoisite (or clinozoisite) and tremolite (or anthophyl- lite) -the origin of the layering is in doubt. Original minerals in the gabbro were plagioclase and monoclinic pyroxene (augite?); accessory magnetite, ilmenite, apatite, and zircon; and some pyrite and al- lanite. Olivine and quartz are erratically distributed. Metamorphism has saussuritized the plagioclase, re- placed pyroxene by amphibole, and serpentinized the olivine. 32 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA. Mafic and accessory minerals A, Plots of norms (a) and average modes («) on quartz-orthoclase- plagioclase diagram B, Plots of norms (a) and average modes («) on quartz- feldspar- mafic and accessory mineral diagram (included with the mafic minerals in the mode are white mica and epidote) Alaskite C a. va PI 10 33% 66% Or Feldspar Quartz Si , : Q" 22 C, Plots of oxides on Si0»-Na20, o K,0-FeO, Fez03, MgO, x' 20 |- : CaO diagram § 11 . | & o 18 |- * .} 1 2 w 10°F - a 7 0 - - 8 pu} 7 o o 4 = 5 8, | 3 412} 7 8 :E .;! ] fer “5, 10 |- _ a. Ci,“ L 4 < 8] 7 & [ -I 5 °f 8 L § 4} ~ o. - 4 9 |- 4 50 55 m 65 70 75 PERCENT SILICA aq D, Plots of oxides against silica FeO, Fe,0; K20 MgO, CaO Na,0 gb - Gabbro pg! - Lynx Creek mass, Prescott Granodiorite qm - Quartz monzonite qd _ Quartz diorite (not located in fig. 10) pgs - Salida Gulch mass, Prescott Granodiorite al Alaskite gg - Government Canyon Granodiorite pge Chaparral mass, Prescott Granodiorite cg - Coarse-grained granite wg - Granodiorite of Walker area pgm Mineral Point mass, Prescott Granodiorite dg - Dells Granite pgp Prescott mass, Prescott Granodiorite pgy - Yarber Wash mass, Prescott Granodiorite tg Fine-grained granite FrGURE 7.-Variation diagrams of quartz-bearing intrusive rocks and gabbro in the Prescott-Paulden-Jerome area. See figures 8, 10, and 12 for location of masses; figures 9, 11, and 13 for quartz-orthoclase-plagioclase plots of individual thin sections; and tables 7, 8, and 10 for modal, chemical, and normative analyses. Plagioclase in parts of the two largest masses forms Pyroxene is preserved in diabase dikes and in a few euhedral to anhedral clear unaltered crystals that range - places in the two largest masses of gabbro. Most of it in composition from andesine to labradorite or more is partly to completely replaced by amphibole. The calcic plagioclase. Some of it is packed with minute amphibole ranges from actinolite to hornblende; most unidentified inclusions (probably magnetite, spinel, of it is actinolitic hornblende. Actinolite forms fibrous and others). In fresh diabase the plagioclase is zoned. masses and needles; hornblende forms fine to coarse Much of the plagioclase has been partially to completely _ equant crystals or grains. altered to a granular aggregate of clinozoisite and Olivine, much of it altered to serpentine, occurs in zoisite associated with albitic plagioclase and sericite; the northern part of the second largest mass (mostly some has recrystallized to clear granular oligoclase- north of 1,285,000 N.) and in small amounts elsewhere. andesine. Some rocks that may have had the composition of OLDER PRECAMBRIAN ROCKS 33 periodotite are now composed largely of either anti- gorite and narrow chrysotile veinlets or of tale, serpen- tine, and a few unaltered olivine remnants. Interstitial quartz and potassium feldspar occur as original, minor constituents, but some quartz and micro- cline were derived probably from granitic emanations that locally permeated the gabbro. Quartz appears to be much less common as an original constituent in the largest masses than in some of the smaller ones, but its source in the more sheared rocks is problematic. A little primary (?) biotite was noted in some of the least altered gabbro ; much of the biotite is metamorphic and intergrown with magnetite. Chlorite replaces pyroxene, amphibole, or biotite, commonly forming rims around these minerals or forming aggregates with epi- dote, quartz, and other minerals. It is most abundant along shear zones. Locally, more or less feathery masses of tremolite, anthophyllite, and zoisite, or clinozoisite) have partly to almost completely replaced plagioclase and pyroxene in the two largest masses of gabbro. The thermal meta- morphism that formed these minerals was caused by adjacent quartzose intrusive rocks. Some gabbro has been extensively epidotized, and some of it in the southwestern part of the second largest mass contains piedmontite as veinlets and dissemina- tions (see p. 105). Iron-rich gabbro occurs in parts of the two largest masses and in small masses (near 1,288,700 N., 374,000 E., especially the one near 1,290,500 N., 374,500 E.). Locally, layers are composed almost entirely of mag- netite and ilmenite. Plagioclase is the principal sili- cate mineral, almost to the exclusion of pyroxene or hornblende in some of these rocks. Apatite is generally abundant. Although euhedral magnetite crystals are common in the gabbro, in the iron-rich rock most mag- netite and ilmenite occupy interstitial positions between and are molded on plagioclase and pyroxene. The granular intergrowths of magnetite and ilmenite are of secondary or late-stage origin and replace pyroxene and hornblende. Magnetite appears to be later than ilmen- ite in iron-rich rocks but earlier than ilmenite in the more normal gabbro.> Chemical analyses of gabbroic rocks from the area have not been made. The average silica content (Anderson and Creasey, 1958, table 12, No. 8, p. 38) of 5 The magnetic susceptibility of several specimens of gabbro from the Prescott quadrangle was tested in the Physical Properties Laboratory of Newmont Exploration, Ltd. The susceptibility of most of the speci- mens ranges from 4,200 X 10-%®s to 7,100 X 10%®s (1,680-2,840 gammas). The susceptibility of some specimens of light-colored al- tered gabbro and of serpentine ranges from 19 X 10-* to 200 X (7.6-80 gammas). A specimen rich in magnetite and ilmenite gave a reading of 13,000 X 10-*s (5,200 gammas). The susceptibility of the gabbro is sufficiently high to give rise to magnetic anomalies (U.S. Geol. Survey, 1950) over gabbro areas. five specimens from the United Verde mine at Jerome and one from southeast of the Prescott quadrangle (see fig. 10, table 8, and also fig. 7 and table 10) is 48.57 percent compared with a silica content of 48.24 percent for average gabbro and 56.77 percent for average dio- rite (Daly, 1933, p. 16-17). Much of the least meta- morphosed parts of the two largest masses appears to be a saturated gabbro in which the plagioclase is at least as calcic as labradorite; it is likely that most of the smaller more metamorphosed masses had a similar com- position. The presence of olivine in some and quartz in others indicates a range from undersaturated to over- saturated rocks. Quartz gabbroic to quartz dioritic facies occur, but only the quartz diorite along the Verde River is large enough to map and describe separately. Quartz diorite.-Quartz diorite along the Verde River is a medium- to coarse-grained rock composed prin- cipally of light pinkish-gray feldspar and greenish- black to dark olive-gray hornblende and some biotite. Grain size of much of the rock is 4-5 mm, but some horn- blende crystals are as large as 5 by 10 mm. The rock varies slightly in relative proportions of dark and light minerals and in the amount of quartz and potassium feldspar (largely microcline). The plagioclase is seri- citized or saussuritized. Chlorite replaces hornblende and biotite. The rock contains some coarse epidote and accessory magmetite, apatite, zircon, sphene, and allan- ite. Because the quartz content is greater than 10 per- cent (table 7; fig. TA), the rock is classed as quartz diorite. The higher content of hornblende, biotite, and epidote suggests correlation with gabbro rather than with one of the granodiorites. RELATIONS TO OTHER ROCKS Gabbroic rocks are younger than the Alder Group, as they clearly intrude the volcanic rocks and contain xenoliths of them. The large-scale intrusive relations are illustrated on the geologic map (see pl. 1, near 1,283,000 N., 350,000 E.). Most of the gabbroic rocks are older than the quartzose intrusive rock, but some are younger. Gabbro is cut out by Prescott Granodiorite (for example, at the northern end of the largest mass of gabbro). It is brecciated, and fractures are filled with granitic to aplitic material, especially along the sides of some of the masses and in some areas of contami- nated gabbro and Prescott Granodiorite. In the east- central part (northeast part, pl. 1) intrusive breccia, formed by the invading Prescott Granodiorite and aplite, are common. The east side of the largest mass and the southwest part of the second largest mass of gabbro have been contact metamorphosed, and zoisite (or clinozoisite) and tremolite (or anthophyllite) ex- tensively replace primary plagioclase and pyroxene. 34 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA Mainly because of spatial relations, the intrusive rocks that probably produced both the alteration and the veinlets are thought to be alaskite, quartz monzonite, and Government Canyon Granodiorite. Some gabbroic rocks, mostly diabase, have intruded gabbro, alaskite porphyry, and some masses of Prescott Granodiorite. The dikes in gabbro fill clean fractures and have chilled borders. Larger masses of fine-grained mafic rocks, especially in areas mapped as contaminated gabbro and Prescott Granodiorite in the south-central part of the area, contain xenoliths or xenocrysts of granodiorite. These xenoliths, however, could have come from a pre-Alder Group intrusive rock (see foot- note 7, p. 49). Much of what is shown as contam- inated gabbro in the westernmost lenses in this area may be volcanic in origin. GOVERNMENT CANYON GRANODIORITE DISTRIBUTION The Government Canyon Granodiorite, herein named for good exposures along Government Canyon (1,280,- 000 N., 341,000 E.), forms two masses in the south west- ern part of the area (pl. 1; fig. 8). The western mass, which is separated into two parts by Cenozoic rocks, must end somewhere between its northernmost expo- sures and the Dells Granite, less than 2 miles to the north. Minor amounts of granodiorite, too small to show on the geologic map, occur in the southern part of the adjacent unnamed volcanic rocks of the Alder( ?) Group. GENERAL CHARACTER The Government Canyon Granodiorite forms topo- graphic lows, many of which are covered with pine forest. The rock weathers light yellowish brown to light brown. It disintegrates to a sandy soil, through which protrude scattered more or less spheroidal boul- ders of relatively fresh rock. The fresh rock is medium to medium light gray and has a salt and pepper ap- pearance. The granodiorite ranges from a massive rock to one having a fairly pronounced planar and linear structure. Primary planar and linear flow structures are brought out by alinement of xenoliths, of plagioclase, horn- blende, and biotite crystals, and in places of porphy- ritic and nonporphyritic layers. A secondary foliation locally cuts the western mass. Xenoliths of various sizes are abundant in the western mass. In the eastern mass xenoliths, mostly less than 6 inches long, are rather sparsely but uniformly distrib- uted, except near the contacts with the volcanic rocks, _ where they are abundant and of many sizes. The xeno- liths are composed largely of mafic volcanic rocks and of fine-grained gabbro( ?). RESCOTT QUADRANGLE Hd 1,300,000 eg 09 f lle 12] 8g \ « \ «< / A X | MT UNION QUADRANGLE 330,000 E 0 1 2 3 MILES (LU rd c n 200 " 1,260,000 N gg Government Canyon Granodiorite Contacts dashed where overlain by younger rocks FicUurE 8.-Distribution of the Government Canyon Granodiorite in the Prescott and Mount Union quad- rangles, showing location of specimens used for modal, chemical, and normative analyses. No. 13 is from a small mass in schist. Typical granodiorite is a medium-grained rock hav- ing a seriate texture. Some of it is porphyritic. The maximum length of plagioclase, hornblende, and bio- tite crystals is about 1.5 cm. In addition to these min- erals the rock contains orthoclase, quartz, epidote, and accessory minerals (see tables 7, 8, 9, and 10, and figs. and 9 for modal, chemical, and normative composition). Plagioclase is somewhat zoned and has an average composition of sodic andesine;, normative plagioclase is An. The plagioclase forms euhedral to anhedral grains. The centers of most crystals are slightly seri- citized or saussuritized; a few are highly altered. Microcline and perthite fill interstices and locally form poikilitic grains 3 mm in diameter. Quartz is intersti- tial to plagioclase and mafic minerals. Most of it shows wavy extinction, but little of it is granulated. Green hornblende and greenish-brown biotite are in euhedral crystals and in very ragged grains and aggregates. OLDER EXPLANATION U Mode of individual thin section Qu U Average mode of mass A Norm PI Or 33% 66% FiGur® 9.-Government Canyon Granodiorite. Plots of modes and norms on quartz-orthoclase-plagioclase diagram. Numbers refer to individual thin sections or to chemically analyzed specimens; loca- tion of numbers is shown in figure 8. See also figure 7 and tables 7, 8, and 10. Some are intergrown with other mafic and accessory minerals or altered to chlorite. Some hornblende is poikilitic. Sphene is commonly conspicuous as well- formed crystals as much as 1.7 mm long and as ragged and poilkilitic grains. Apatite and magnetite form euhedral crystals less than 0.4 mm in size. Biotite con- tains tiny zircons. A few euhedral epidote crystals were observed; much of the epidote is secondary and forms intergrowths with mafic and accessory minerals. Veins and disseminations of piedmontite occur locally (see p. 105). RELATIONS TO OTHER ROCKS The Government Canyon Granodiorite is younger than unnamed volcanic rocks of the Alder(?) Group; the intrusive relations are manifested by the very ir- regular contact between the two rocks (south of 1,284,000 N.), by widespread intrusive breccias, and by grano- diorite injected along bedding, fracture, and foliation planes in the volcanic rocks. Erratically and conform- ably oriented volcanic xenoliths from a few feet to 3,500 feet long are abundant in the southern part of the west- ern body of granodiorite. The granodiorite is probably younger than gabbro (see the discussion in the pre- ceding section). The western mass of Government Canyon Grano- diorite is cut by many dikes of Prescott Granodiorite and occurs as xenoliths in the Prescott Granodiorite; however, no dikes of Prescott Granodiorite were noted in the eastern mass of Government Canyon Grano- PRECAMBRIAN ROCKS 35 diorite. The possibility that the eastern and western masses are not part of the same intrusion or that the western mass contains two granodiorites has been con- sidered, but no supporting field evidence was observed. The eastern mass is the northern part of what Lindgren (1926, p. 21-22 and pl. 2) called the Groom Creek area of granodiorite, which he considered probably Late Cre- taceous to early Tertiary in age. The lead/alpha age of zircon in the granodiorite, however, is Precambrian (see p. 50). PRESCOTT GRANODIORITE DISTRIBUTION The Prescott Granodiorite, herein named for ex- tensive exposures in the western part of the city of Prescott, forms isolated masses in the southern and east- central parts of the Prescott-Paulden area. For ease in discussion, the various masses are given locality names: the Prescott, Salida Gulch, Lynx Creek, Chapar- ral, and Mineral Point masses (fig. 10). Small out- crops, dikes, and lenses and much granodiorite in areas of contaminated rocks are part of the Prescott Grano- diorite. The quartz diorite of the Jerome area (Ander- son and Creasey, 1958, p. 38-41) is considered to be part of the Prescott Granodiorite and is referred to as the Yarber Wash and Big Bug Creek masses. The Chap- arral mass was also called quartz diorite by Anderson and Creasey. In the present report, a rock is consid- ered to be a granodiorite if more than 10 percent of the feldspar is orthoclase. On this basis, only the eastern facies of the Yarber Wash mass is a quartz diorite; the Salida Gulch mass is on the dividing line between quartz diorite and granodiorite (fig. 7, 11). As the Prescott mass, which gives its name to these rocks, is a granodiorite and as the norms of all the rocks fall within the granodiorite field, the term granodiorite is used. The Prescott mass forms a triangular-shaped outcrop in the southwest corner of the area. The Salida Gulch mass is a long, narrow north-trending body in the south- central part. The Lynx Creek mass lies at the north end of the largest body of gabbro. All of these masses are buried to the north or northeast by Cenozoic de- posits, and their extent beneath these deposits is un- known, except that the Prescott mass cannot extend for more than 2 miles to the northeast before it is cut out by or faulted against the Dells Granite (pl. 1, sees. C-C" and Two narrow north-northeast-trending bodies of granodiorite in the Chaparral zone form the Chaparral mass. The larger one, whose extent to the northeast is unknown, is in the Chaparral Volcanics; the smaller one occurs along the Spud fault. The Min- eral Point mass is in the east-central part of the area 36 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA 1,390,000 «pei fol pgi © WI a \ <1 {pgm |/\/\ PAULDEN QUADRANGLE "4G M CLARKDALE QUADRANGLE PRESCOTT QUADRANGLE CV MINGUS MOUNTAIN # 6 ig] QUADRANGLE Qéofiss 923 Logi 36 A);\ gm P7 y‘l No 06] bfi L/ s + It J+. . +1... s+ 1+ 'P /+ + !4 +-P\ p + Y f + \ eous 19 k - f ) 4. 4. 4 4 4 A |. \ $8 + |+. + ;' 4 -+ 4 AZ (g y I 33 + '+ + JJ’) Fa .- {ie 14) 3C a "s) 1:11/7 2.11 [ % # £ ni- + . 1 |\_’\,34 ken Lg; ++ ++++-+ ".' a] a) $8 2 + pey |+ ~ s414 vae " + ALP 915 I '+Bg4] + [+ +434] . +: +/] aba" 3.14 a_ rea a f Of % C. +~ =. p | £ +!* s i ++ Joan—bx | f+++4 +40+ 4 +t+ #44 4 |1 +‘\ - J.) a WW 28, ¢ > ar +/ Has+ ++++) f a 4 V ef 12/4 4 42503031 d s} mst T> 3 32.33 5B 4/8 . 4/ MT UNION QUADRANGLE - ¥ b MAYER QUADRANGLE § 50 1,260,000 N f r jag (2&3 o .s) s o/s miles os $2 | B esen EXPLANATION 470,000 S14 JJ w 7 5 h; 7 -PEP s Nogm/ 4_-_ -A f” Prescott mass Numbers 1-8; number 8 from a dike F- +pgy+ + _+ 4 Yarber Wash mass Western facies, numbers 38-41, 47; eastern facies, numbers 42-46 Lynx Creek mass Numbers 9-16 =+ to." n~pgb~ a= 4 Big Bug Creek mass No data available Salida Gulch mass Numbers 17-27 pgi Miscellaneous outcrops, lenses, and dikes Probably related to Prescott Granodiorite Contact Dashed where overlain by younger rocks Chaparral mass Numbers 28-38 Granodiorite of Walker area Location of specimen Number 48 Mineral Point mass Numbers 34-87 Gabbro Composite of five specimens from number 49 and one from number 50 FicurE 10.-Distribution of masses of the Prescott Granodiorite, showing location of specimens used for modal, chemical, and normative analyses ; locations of granodiorite of the Walker area and of gabbro samples are also shown. OLDER PRECAMBRIAN ROCKS 37 (pls. 1, 2) and is exposed intermittently for about 10 miles. Its extent to the south and southwest beneath Cenozic deposits is unknown. GENERAL CHARACTER The various masses of Prescott Granodiorite have been correlated on the basis of similarity in modal, chemical, and normative composition (figs. 7, 11; tables T, 8, 9, 10). The Prescott mass is the least altered and deformed and is described in detail; brief mention of differences in the other masses are also given. Weathering of the Prescott mass characteristically re- sults in large erosional mounds of relatively fresh rock surrounded by sand flats formed by accumulation of angular fragments, some of crystal-grain size. Dis- integration along joints results in piles of rounded boulders, some balanced, whose form depends largely on the spacing and attitude of joints. The Prescott mass is a fine- to medium-grained mas- sive slightly altered rock, having a poikilitic, hypidio- morphic-granular texture. Fresh granodiorite is medium gray, light gray, or greenish gray. Slightly darker or lighter shades are principally a function of grain size, but lighter shades in places are due to less abundant biotite or to the opaque character of the more altered plagioclase. The weathered surface is grayish orange pink to grayish orange; some is reddish brown owing to baking by basalt or is light brown owing to weathering of introduced pyrite. The granodiorite contains plagioclase, quartz, potas- sium feldspar, biotite, epidote, and accessory minerals. Most plagioclase is translucent to greasy ; some is glassy, and some is chalky or greenish. Individual grains are hard to distinguish in hand specimen. The plagioclase forms zoned subhedral laths and anhedral grains, mostly less than 1 mm long. A few euhedral laths are 2 mm long; sparse phenocrysts are larger. Some plagioclase encloses other mineral grains; the margins of some are intergrown with quartz and microcline. Cloudy sodic plagioclase surrounds microcline in places. The centers of the plagoiclase, which is about andesine in composi- tion, are cloudy because of slight argillization, sericiti- zation, or saussuritization. The margins are clear albite (Ans-,). Normative plagioclase in this mass is An; ; it ranges from Ans; to An»; in the other masses. Quartz occurs as glassy colorless to light-gray slightly strained anhedral grains, mostly less than 1 mm in diameter. Some of it forms myrmekitic or graphic intergrowths with plagioclase. Where microcline is not abundant, quartz is interstitial to plagioclase. Most of the potassium feldspar is microcline, but some occurs as orthoclase and as perthitic or microperthitic intergrowths. Microcline forms clear, colorless square to rectangular, poikilitic crystals having irregular margins. The crystals average about a quarter of an inch long; some are as much as 11/4 inches across. The poikilitic microline is scattered sparsely to abundantly throughout the rock and encloses the other minerals. Commonly, the inclusions are distributed rather evenly through the microcline; some are so abundant that the enclosing microcline is easily overlooked. Locally the inclusions are concentrated around the margins of the microcline. Biotite forms greenish-black flakes, books, and gran- ular aggregates, which average about 0.5 mm in diameter; a few are as much as 1-2 mm. Pleochroic halos around zircon are common. Some biotite is re- placed by magnetite (or ilmenite), epidote, or chlorite. Epidote is widely distributed, from minor quantities to amounts nearly as abundant as biotite. Some grains are euhedral, but epidote is probably metamorphic; it also occurs in veinlets. Veinlets and disseminated grains of piedmontite (see p. 105) are abundant in the granodiorite northwest and west of Prescott. Accessory minerals are sphene, magnetite, ilmen- ite(?), apatite, and zircon. Sphene forms euhedral crystals as much as 0.6 mm long and granular rims around magnetite. Leucoxene has formed from sphene and from ilmenite or titaniferous magnetite. Although most of the Prescott mass is uniform, some of it is spotted, layered, or altered. Contamination from mafic rocks produced sparse to abundant rounded, irregular, or angular spots (especially near 1,295,500 N., 340,500 E.; and 1,294,000 N., 336,000 E.). Most of the spots are about a quarter of an inch in diameter. They are composed of green biotite and minor amounts of epidote, sphene, magnetite, apatite, and leucoxene. Parallel dikes of aplite and pegmatite produced lay- ered rocks in a few places (1,296,400 N., 334,500 E.; 1,295,500 N., 340,800 E.; and 1,308,000 N., 327,300 E.). The layers strike north-northeast and dip about verti- cally. Individual layers average 1-3 feet wide, but range from 1 inch to more than 10 feet. Some can be traced along the strike for several hundred feet. Some layers consists of compound dikes, the centers being aplitic and the margins pegmatitic, or vice versa ; others are made up of irregular aplitic and pegmatitic zones. The layers are cut by younger pegmatite and aplite dikes. Most of the Prescott mass has been altered by mild regional metamorphism. - For about 3 miles north of the southern border of the area, a more intense alteration is probably the result of hydrothermal solutions asso- ciated with quartz, quartz-tourmaline, and tourmaline veins. It formed a mafic-poor aplitic-looking rock containing dark specks composed of granular mixtures 38 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA V V. V. V % Or V PI Or PI 33% 66 YARBER WASH MASS (pgy) 10 33% 66% MINERAL POINT MASS (pgm) Qu 10 EXPLANATION Mode of individual thin section Average mode of mass (Yarber Wash mass: y-1, average of western facies; y-2, average of eastern facies; y-3, average of mass) a Norm (no norm of pgc) Or COMPOSITE Ficure 11.1-PRESCOTT GRANODIORITE. PLOTS OF MODES AND NORMS ARE ON QUARTZ-ORTHOCLASE-PLAGIOCLASE OF NUMBERS AND EXPLANATION OF LETTER SYMBOLS ARE OLDER PRECAMBRIAN ROCKS a t Or 33% 66% 33% 66% PRESCOTT MASS (pgp) LYNX CREEK MASS (pg!) Qu Qu Or <:: PI Or 10 33% 66% CHAPARRAL MASS (pgc) 33% 66% SALIDA GULCH MASS (pgs) DIAGRAMS. NUMBERS REFER TO INDIVIDUAL THIN SECTIONS OR TO CHEMICALLY ANALYZED SPECIMENS: LOCATION SHOWN IN FIGURE 10. See also figure 7 and tables 7, 8, and 10. 39 40 of magnetite, specular hematite, and leucoxene that are pseudomorphic after magnetite, pyrite, or original mafic minerals. The saussuritized centers of plagio- clase have been replaced by coarse sericite. Microcline is somewhat mottled owing to intergrowth or replace- ment by sodic plagioclase or myrmekitic quartz. Specu- lar hematite occurs as veinlets, and coarse sericite coats fractures in places. Except for small parts of the Lynx Creek and Min- eral Point masses, the other masses do not resemble the Prescott mass. They are more deformed and altered, lack poikilitic microcline, and are generally coarser grained. The northern part of the Salida Gulch mass is intensely foliated quartz-feldspar-biotite schist and augen gneiss. Much of the Chaparral mass is a cata- clastically deformed mafic-poor rock. Grain size in undeformed parts of these masses ranges from 1 to 5 mm, but the size of some of the feldspar augen suggests an original coarse-grained or porphyritic rock contain- ing feldspar crystals more than 8 mm long. The calcic cores of plagioclase are highly saussuritized. Quartz occurs as granular aggregates or is drawn out into long thin plates. Potassium feldspar forms fine inter- growths or granular mixtures with quartz and albite. Hornblende was observed only in the Mineral Point mass; allanite, in the Salida Gulch, Chaparral, and Mineral Point masses. No primary mafic minerals are preserved in the Salida Gulch and Chaparral masses, with the possible exception of a few large biotite flakes. Most boitite and chlorite occur as granular aggregates associated with epidote and accessory minerals. In the intensely foliated rock in the northern part of the Salida Gulch mass, metamorphic brown or greenish-brown biotite is concentrated in plates or thin lenses. In the less foliated rock to the south, the biotite is green or brownish green. This part of the Salida Gulch mass contains more chlorite than the more schistose rock to the north. In the Chaparral mass mafic minerals have been largely sheared out and completely altered to chlorite, epidote, calcite, and leucoxene. RELATIONS TO OTHER ROCKS The conclusion that the rocks mapped as the Prescott Granodiorite are part of the same intrusion is based primarily on similarities in modal, chemical, and nor- mative composition, but this correlation is open to question. Refinements in age determinations may prove or disprove this conclusion. On the basis of the amount of deformation the rocks have undergone, the Prescott, Yarber Wash, Big Bug Creek, Mineral Point, and Lynx Creek masses could be interpreted as younger than the Salida Gulch and Chaparral masses. GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA Field relations prove that most of the masses of Pres- cott Granodiorite intrude the Alder Group or contain xenoliths of the Alder Group, but because of intense deformation and mechanical mixing, relations are ob- secure in- some places. The Lynx Creek mass clearly intrudes tuffaceous rocks of the Alder(?) Group and gabbro. The Mineral Point and Yarber Wash masses also intrude gabbro; most of the other masses contain xenoliths of gabbroic(?) rocks. The Prescott mass intrudes the western mass of Government Canyon Granodiorite. Pink aplite dikes, some spatially related to alaskite, cut all the masses; coarse-grained alaskite cuts the Mineral Point mass. The Salida Gulch mass is cut by coarse-grained granite, fine-grained granite, and fine-grained gabbroic to diabasic rocks. A few diabase dikes also cut the Lynx Creek mass, but none cut the other masses. The Dells Granite and Prescott Granodiorite are not in contact, but the Prescott mass is cut by dikes of aplite and pegamatite and veins of quartz, quartz-tourmaline, and tourmaline that are probably related to the granite; the granite contains xenoliths that resemble the granodiorite. The fine-grained granite rather thoroughly perme- ated some of the Salida Gulch mass. This mass con- tains numerous dikelike bodies, too small to map, and larger irregularly shaped bodies of mafic rocks that are mapped as gabbro. Some of the bodies may be older volcanic or gabbroic rocks; others have a diabasic tex- ture, cut the granodiorite, contain xenoliths of grano- diorite, or have chilled margins against the grano- diorite. The granodiorite bodies in the Chaparral-Spud fault zone parallel the regional foliation within the zone. The bodies were intruded prior to final deformation within the zone or, more probably, were dragged into it. Postintrusive deformation produced augen gneiss and mylonite in the granodiorite and obscured the original relations of granodiorite to Chaparral Volcanics and to gabbro. The contacts are gradational, and the grano- diorite may nowhere be in contact with rocks that it originally intruded. ALASKITE AND RELATED ROCKS DISTRIBUTION , Alaskite and related rocks crop out in the southeast- ern and east-central parts of the Prescott-Paulden area (pls. 1, 2; fig. 12). These rocks are mapped as quartz monzonite, alaskite, and alaskite porphyry ; the alaskite porphyry includes aplitic alaskite and aplite. Quartz monzonite lies west of the eastern mass of the Green Gulch tuffaceous unit. It is separated into two parts and buried to the north by Cenozoic deposits. OLDER PRECAMBRIAN ROCKS 41 PRESCOTT QUADRANGLE, SOUTHERN PART 1,320,000 /+ 1,280,000 N Hm ¥ ~ qmz 6 330,000£ tne sou > ng+ lit. -+ . Dells Granite Numbers 1-5; number 5 from boulder in gravel an I 5 Coarse-grained granite Numbers 7-18 390,000 Fine-grained granite Number 6 f \\/\/, Pal d LL\ mi Alaskite and related rocks al, alaskite; numbers 14-18 ap, alaskite porphyry and aplite am, quartz monzomite; numbers 19-20 Contact Dashed where overlain by younger rocks FiGURE 12.-Distribution of granitic rocks, showing location of specimens used for modal, chemical, and normative analyses. Alaskite forms two large and several small discrete bodies in the southeastern part of the area, all of them east of the largest mass of gabbro. Five small lenses and pods, one of them occurring largely south of the map area, are in the southwestern part of the tuffaceous rocks of the Green Gulch Volcanics ; a long, narrow body of alaskite is in the Chaparral Volcanics. Eight small bodies of alaskite extend south-southeast from Upper King Canyon (pl. 2, 1,396,500 N., 379,100 E.). Un- mapped sheets, pods, and irregular dikes of alaskite are found in the Prescott Granodiorite and gabbro south of these exposures. Alaskite porphyry forms one large mass in the south- eastern part of the area. Two narrow masses of aplitic alaskite occur in the northern part of the Green Gulch tuffaceous unit, and an elongated lens lies immediately east of Chaparral fault. Unmapped aplite dikes, probably related to alaskitic rocks, are common in the 42 Mineral Point and Lynx Creek masses of the Prescott Granodiorite (fig. 10) and cut other intrusive rocks. GENERAL CHARACTER Alaskite and alaskite porphyry are resistant rocks. In the southern part of the area the largest masses form high ridges having local steep to precipitous slopes. The crests of the ridges that extend northward from the wider parts of the larger alaskite masses are occupied by narrow dikelike masses of alaskite augen gneiss. A sub- dued topography, formed on alaskite in the east-central part of the area and on the quartz monzonite, is the result of proximity to old erosion surfaces-pre-late Tertiary on the quartz monzonite and pre-Paleozoic on the alaskite. Quartz monzonite-Quartz monzonite is medium grained, locally coarse grained or porphyritic, and has a massive to foliated structure. The rock is mottled olive gray and light brownish gray and is composed of micro- cline, plagioclase, quartz, and mafic and accessory min- erals. The modal composition is given in table 7. The Plagioclase is a somewhat zoned oligoclase (Ani;.; as determined by X-ray diffraction). The cores are par- tially sericitized and saussuritized. Chlorite, less abun- dant biotite, epidote, and muscovite, and a few relics of hornblende form irregularly shaped aggregates. Ac- cessory minerals are magnetite, apatite, zircon, and al- lanite. Alaskite and alaskite porphyry.-The alaskitic rocks are similar in color and composition. They differ in degree of deformation and amount of contamination but principally in texture. Textural gradations between alaskite and alaskite porphyry occur in a few places. Most alaskitic rocks are pale red to grayish orange pink, some are moderate red, and some are nearly white because of alteration. The rocks weather light shades of brown ; exceptions are the northern part of alaskite in the Chaparral Volcanics and some of the aplitic alaskite east of Chaparral fault, which weather dark to moderate reddish brown. Alaskite ranges from a massive rock through augen gneiss to mylonite. Augen gneiss is characteristic of many of the narrow dikelike masses, some unmapped, in gabbro and volcanic rocks; it forms only narrow zones in the large masses. Alaskite in the Chaparral Volcanics is mostly equigranular at its northern end and augen gneiss in the middle; its southernmost 1,000 feet is a tail of mylonite less than 50 feet wide. Much of the granitic-textured alaskite is medium grained. In augen gneiss, however, the size of some feldspar augen suggests that some of the original rock was coarse grained or porphyritic. Most alaskite porphyry is massive and fine grained. Its sparse to abundant phenocrysts, 2-6 mm in diameter, GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA consist of feldspar and quartz. Aplite and aplitic alaskite are fine grained and have a sugary texture. Slight recrystallization of mylonite may also have formed a sugary texture. Some aplitic alaskite, espe- cially on the eastern edge of the large mass of alaskite porphyry, contains phenocrysts of quartz and feldspar, generally less than 1 mm and rarely as much as 2 mm in diameter. Modal, chemical, and normative compositions of medium-grained equigranular alaskite are given in tables 7, 8, 9, and 10, and figures 7 and 13. The rock consists of potassium feldspar, albite, quartz, a little mica, and accessory minerals. The feldspar is albite, microcline, orthoclase, and perthite. Some potassium feldspar has been partly replaced by late albite. Most of the augen are potas- sium feldspar. Albite, in many places, is slightly sericitized; most potassium feldspar is fresh. Norma- tive albite is An,. Quartz is strained, crushed, or granulated in most alaskite but is only slightly strained in the finer grained rocks. In augen gneiss it forms lenticular or plate-like aggregates or granular mixtures with feldspar. In unsheared and uncontaminated alaskitic rocks poor in mafic minerals, primary biotite, muscovite, magnetite (or ilmenite), zircon, and sphene are sparse. In some of the sheared rocks, aggregates of fine flakes of biotite, chlorite, or sericite are concentrated in thin plates or lenses. In some intensely deformed alaskite in the Chaparral zone, mafic minerals have been com- pletely sheared out. Contaminated alaskitic rocks contain sparse to abundant biotite, chlorite, amphibole, and epidote, which were derived from mafic volcanic rocks and gabbro that have been sheared into the alaskite or were picked up by it from the intruded rocks. The aggregates of chlorite, sericite, epidote, leucoxene, and some calcite were derived from original or xenolithic biotite or other mafic minerals. Biotite has altered to chlorite. Tiny pyrite cubes are abundant in some alaskitic rocks and appear to be related to mild sericitization. RELATIONS TO OTHER ROCKS Alaskite, alaskite porphyry, and quartz monzonite are probably consanguineous; the alaskite porphyry is slightly younger, and the quartz monzonite is slightly older than the alaskite. If consanguineous, then alas- kite and related rocks are all younger than the gabbro and the granodiorites but older than some diabase. Quartz monzonite.-Quartz monzonite probably in- trudes gabbro. Many pink aplite dikes in quartz monzo- nite suggests that is a slightly older facies of the alaskite and alaskite porphyry. OLDER PRECAMBRIAN ROCKS x Or yH. viv 10 33 % 66% 33% DELLS GRANITE (dg) ALASKITE (al) Qu Qu PI o & or PJ 10 33% 66% 10 33% 66% COARSE-GRAINED GRANITE (cg), QUARTZ MONZONITE (qm) COMPOSITE EXPLANATION Mode of individual thin section Average mode of mass (no mode of fg) a Norm (no norm of gm) 43 FIGURE 13.-Granitic rocks, Plots of modes and norms are on quartz-orthoclase-plagioclase diagrams. Numbers refer to individual thin sections or to chemically analyzed specimens; location of numbers and explanation of letter symbols are shown in figure 12. figure 7 and tables 7, 8, and 10. 758-447 O-65--4 See also 44 GEOLOGY OF THE PRESCOTT AND Alaskite.-The larger masses of alaskite intrude the unnamed volcanic rocks of the Alder(?) Group. Al- though the actual contacts are poorly exposed, the out- crop pattern of the basaltic flows that separate the two largest bodies of alaskite indicates intrusion by alaskite, an indication strongly supported by the many aplite dikes in the basaltic flows. Part of the outcrop pattern of the tuffaceous rocks northeast of these alaskite masses is due to intrusion of the alaskite. In upper King Canyon (pl. 2) alaskite is clearly intrusive into the tuffaceous rocks. Unmapped masses of alaskite in gabbro north of the largest masses of alaskite and alaskite porphyry have dikelike form. They are 1-50 feet wide and as much as half a mile long. The margins are zones of shear, and the alaskite is an augen gneiss, but much of the adjacent gabbro is relatively massive. Presumably shearing was taken up in alaskite rather than in gabbro. Alaskite porphyry.-Alaskite porphyry and aplite clearly intrude unnamed basaltic flows of the Alder ( ?) Group and form distinctive intrusive breccias, especially along Green Gulch (near 1,284,500 N., 378,300 E.; and 1,284,400 N., 381,100 E.) and along Charcoal Gulch (near 1,283,200 N., 377,700 E.; and 1,277,800 N., 377,400 E.). The elongated subrounded to angular xenoliths are alined roughly parallel to the regional trend of the foliation and range from individual biotite or horn- blende crystals or aggregates a fraction of an inch long to masses measured in tens of feet. Some xenoliths are dikelike in form. Xenoliths make up about 40 percent of some outcrops, and in these places many of them are about 3 feet long. Narrow diabase dikes in alaskite porphyry along Charcoal Gulch are also parallel to the regional north-trending foliation. Narrow dikes of aplite intrude gabbro and the Lynx Creek and Mineral Point masses of Prescott Grano- diorite in the southeastern and east-central parts of the area. Although most of the alaskite and alaskite porphyry masses parallel the regional formation, some aplite dikes are crosscutting. COARSE-GRAINED GRANITE DISTRIBUTION Coarse-grained granite forms a long narrow north- trending mass in the south-central part of the area (pl. 1,284,500 N., 359,500 E., and fig. 12). Adjacent areas mapped as contaminated Prescott Granodiorite and contaminated fine-grained granite contain some coarse- grained granite. GENERAL CHARACTER Coarse-grained granite is a medium-light-gray to light-gray rock. Where intensely foliated it has a silvery sheen due to abundant sericite. The rock is PAULDEN QUADRANGLES, ARIZONA medium to coarse grained and locally porphyritic, con- taining phenocrysts as much as 1 cm long. Most of the massive rock has an equigranular granitic texture. Some of the foliated rock is augen gneiss. The granite is composed of plagioclase, quartz, microcline, biotite, sericite, chlorite, and accessory minerals (see tables 7, 8, 9, and 10, and figs. 7 and 13 for chemical, modal, and normative compositions). Quartz is strained, granulated, or drawn out into thin, platelike, fine granular masses. Microcline and mircrocline-perthite are subordinate to albite, which shows slight replacement by or alteration to coarse- grained sericite. Normative plagioclase is An,. Some of the rock contains a few large altered plagioclase (oligoclase-andesine) crystals. Epidote is generally lacking. Metamorphic biotite occurs as aggregates of small flakes or is concentrated in lenticular areas or as thin plates. In most places it is not abundant and is generally subordinate to the white mica, most of which is also of secondary origin. Accessory minerals are zircon, magnetite, apatite, and sphene( ?), which is now largely altered to leucoxene. RELATIONS TO OTHER ROCKS In a few places coarse-grained granite clearly in- trudes the Salida Gulch mass of Prescott Granodiorite and is intruded by fine-grained granite. Most contact between coarse-grained granite and granodiorite, how- ever, are gradational and arbitrary. Because biotite, epidote, and saussuritized plagioclase gradually increase in abundance toward the granodiorite contact, it was difficult in the field to distinguish the granite from the granodiorite. Prescott granodiorite may occupy more of the area mapped as coarse-grained granite, or coarse- grained granite may occupy more of the areas mapped as contaminated granodiorite. Modal, chemical, and normative analyses of the granite resemble those of both alaskite and the Dell Granite, but the coarse-grained granite has been mapped separately because it does not resemble either rock megascopically and because the analyses do not clearly indicate that it belongs to either the alaskite or the Dells Granite. © DELLS GRANITE DISTRIBUTION The Dells Granite, herein named for the Granite Dells, lies about 5 miles northeast of Prescott (pl. 1; fig. 12). It forms a somewhat triangular-shaped mass about 5 square miles in area. Its extent beneath the surround- ing Cenozoic cover is probably limited by faults on the southeast and southwest to a mile or less (pl. 1, sees. B-B', 0-C"', D-D', and F-F"' ) ; its extent to other direc- tions is unknown. OLDER PRECAMBRIAN ROCKS 45 FIGURE 14.——Aétial photograph (Cou-8-73) of Granite Dells and Glassford Hill, showing joint pattern in the Dells Granite (dg) and the overlying rocks of late Tertiary (?) age: basalt flows (Tbl, lower; Tom, middle; Tou, upper); sedimentary and tuffaceous rocks (Ts) ; cinder come (Tc); branching dike (Td); and andesite flow (Ta). GENERAL CHARACTER The form of the bold outcrops of the Dells Granite is controlled by joints and shows up well in aerial photo- graphs (fig. 14) and on the topographic map, where con- tour lines make right-angle bends. In two places, northeast of Storm Ranch (1,308,800 N., 354,300 E.) and between Entro (1,312,000 N., 353,500 E.) and Route 89, N. 15°-40° W. joints have exerted more control on the topography than the principal set, which is N. 25° E. and N. 70° W. (fig. 26). Where the rocks are more disintegrated, especially northwest of Storm Ranch, Light areas east and north of Glassford Hill are caliche. bold hills and pronounced valleys are absent, and the area is more extensively covered by trees and brush. Weathering along joints has formed large and small rounded boulders, some balanced boulders, and other unusual forms. It has also produced a checkerboard appearance (fig. 15) where iron oxide has migrated in- ward from horizontal, vertical, and sloping joint sur- faces. Successive migrations of iron oxide resulted in concentric envelopes that become more spherical inward. The weathered surface is rough owing to rounded knobs or pits. - The knobs consist of masses or individual large 46 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA FIGURE 15.-Checkerboard appearance formed in the Dells Granite due to weathering along joint planes; southwest of Willow Creek Reser- voir (1,310,000 N., 343,900 E.). crystals of pegmatitic minerals or of xenoliths of schist or gneiss. The pits, 3-6 inches deep and 1-2 feet in diameter, noted northwest of Watson Lake, are formed by weathering along joints or by removal of pegmatitic minerals or of xenoliths. Much of the granite is crum- bly because its present surface is near an old erosion surface. A green claylike material coats joints and is disseminated through the rock near the surface in some places. The Dells Granite is a fairly uniform massive medium- to coarse-grained rock having a granitic (seriate), locally porphyritic, texture. The principal minerals generally range from 2 to 5 mm in diameter. Phenocrysts of feldspar are erratically distributed and are almost completely absent in some areas. The pheno- erysts have a maximum size of about 2 inches and average from 14 to 1 inch in length. Most of them, and the larger ones, are microcline; some are albite. Fresh surfaces of the granite are very light gray to almost white, and weathered surfaces are vari- ous shades of orange pink and light brown. The granite is composed of white feldspar, light smoky-gray quartz, and variable amounts of biotite. Black tourma- line, purple fluorite, magnetite, specular hematite, and a little apatite occur either as accessory minerals or as introduced hydrothermal minerals. The modal, chemi- cal, and normative compositions are given in tables 7, 8, 9, and 10, and in figures 7 and 13. Quartz occurs as rounded, anhedral, slightly strained grains, many containing inclusions of other minerals. Microcline is the principal potassium feldspar. It forms interstitial anhedral grains; some of it poikilit- ically encloses albite, quartz, and biotite; some pheno- erysts have poikilitic margins. Perthite forms irregu- lar areas in the microcline. Albite occurs as subhedral crystals, perthitic intergrowths, and a few phenocrysts. Some of it encloses other minerals, especially around the margins. It ranges from about An:s to Ani; normative plagioclase is An,. A few phenocrysts show slight zoning. Much of the albite is slightly cloudy because of minor sericitic or argillic alteration. Locally in the northeastern part of the mass, dark- green biotite forms books ranging from 1 to 4 mm in size, but in much of the rock, biotite is bleached and forms smaller flakes that have a ragged outline and a pale-olive color. Under the microscope this mica is nearly colorless and nonpleochroic or slightly pleo- chroic. Darker pleochroic halos occur around some of the tiny zircons. The index of refraction on cleavage flakes is slightly less than 1.61,° in contrast to the index of the fresh mica, which is nearly 1.64. The 2V of this colorless mica is too small for muscovite. Alternate platelike areas of iron oxides (magnetite, specular hem- atite, ilmenite, and leucoxene) occur in some of the bleached biotite. The bleaching appears to be associ- ated with the introduction of deuteric or hydrothermal fluorite. Most of the specimens used for modal analy- ses contain bleached biotite; the chemically analyzed specimen contained fresh biotite. Alteration of the rock might account for the poor agreement between the norm and average mode of the granite (figs. 7, 13). Accessory minerals are magnetite, specular hematite, and some leucoxene. Veinlets and granular masses of individual crystals generally less than 1 mm in diameter of purple to colorless fluorite can be seen in most thin sections and in many hand specimens. Crystals of black tourmaline range from less than 0.1 mm to more than 5 em in length ; some are concentrated in irregular areas as graphic intergrowths with quartz and feldspar. Tiny red garnets are present in some places but are more abundant in some aplites that cut the granite. A few diamond-shaped reddish areas, now largely altered to hematite(?) and leucoxene(?), probably represent original sphene. LATE-STAGE PRODUCTS OF CRYSTALLIZATION Deuteric and hydrothermal alteration slightly sericitized albite, bleached biotite, and introduced peg- matitic and aplitic minerals and quartz, quartz-tourma- line, and tourmaline veins. The abundance of these minerals, together with fluorite, suggests that the ® The index checks reasonably well with partly altered biotite from Santa Rita (Kerr and others, 1950, p. 321). OLDER PRECAMBRIAN ROCKS 47 granite was rich in water and mineralizers. These min- erals are erratically distributed and do not appear to be as abundant in the northeastern part and along the northwestern border as elsewhere. Pegmatitic material permeated the granite and formed dikes, irregular veins, pods, and individual crystals. Many of the dikes are only a few feet wide; individual microcline crystals are as long as 12 inches; pods of quartz and tourmaline and individual tourma- line crystals are several inches long. The dikes are composed of coarse quartz and microcline, some finer grained graphic or platelike intergrowths of quartz and albite (about An,), dark-green biotite, muscovite, and tourmaline. Some dikes contain alternating layers of pegmatite and aplite; the aplite is fine grained, sugary, and white to grayish orange pink. RELATIONS TO OTHER ROCKS The Dells Granite is surrounded and unconformably overlain by Cenozoic rocks (fig. 14). The concealed contact between the granite and the Precambrian vol- canic and intrusive rocks southeast of the Granite Dells is thought to be a fault trending north-northeast that passes beneath GHlassford Hill (pl. 1, sees. B-2', D-D' ). The concealed contact between the granite and the Gov- ernment Canyon and Prescott Granodiorites southwest of the Granite Dells may be a fault trending west-north- west close to the southwestern outcrops of the granite- that is, between the granite outcrops and a 1,000-foot well in late Tertiary(%) deposits (pl. 1, sees. C-C", D-D', F-F'). The granite is probably younger than the Prescott Granodiorite, as discussed on page 40. FINE-GRAINED GRANITE DISTRIBUTION Two areas of fine-grained granite are found in the south-central part of the area (pl. 1, fig. 12). One is east of the Texas Gulch Formation and extends north from the southern border of the area for about 4 miles. The other is north of the Texas Gulch Formation and west of the unit containing jasper-magnetite beds. It is ' separated into two parts by a surficial cover of Cenozoic rocks. GENERAL CHARACTER Fine-grained granite is greatly contaminated with older rocks. The granite is massive, light, slightly pinkish, yellowish, or greenish gray. - Individual grains are mostly less than 1 mm long. The granite is com- posed of plagioclase, orthoclase, quartz, and traces of mafic and accessory minerals. Chemical and normative compositions of what appeared to be a relatively uncon- taminated sample from the eastern area are given in tables 8, 9, and 10, and in figures 7 and 13. The compo- sition falls in the granodiorite field (fig. 7), but the plagioclase is albite; therefore the rock is a granite. The following petrographic data were obtained from study of thin sections of specimens from the eastern mass. - Much of the quartz occurs as graphic or myrme- kitic intergrowths, in places having a radial arrange- ment; some quartz encloses plagioclase. The irregular margins of the plagioclase are sodic albite, but the more or less euhedral centers of some are more calcic and slightly sericitized. Normative plagioclase is An,. Large quartz grains as much as 5 mm in diameter, large saussuritized and sericitized plagioclase, and erratically distributed lenticular aggregates of mafic and accessory minerals probably were picked up from intruded quartz porphyry, the Prescott Granodiorite, gabbro, and the Alder Group. The mafic and accessory minerals are biotite, chlorite, epidote (zoisite), magnetite, apatite, sphene, leucoxene, actinolitic hornblende, zircon, calcite, and pyrite. Same granite in the western area resembles the aplitie alaskite or aplite in texture and in the almost complete absence of mafic and accessory minerals. RELATIONS TO OTHER ROCKS Fine-grained granite intrudes the Texas Gulch For- mation, quartz porphyry, gabbro, the Salida Gulch mass of the Prescott Granodiorite, and coarse-grained gran- ite. In places it thoroughly permeates older rocks. The aplitic material in the western outcrops may not be related to the fine-grained granite of the eastern area ; it may be older, as indicated by local foliation. The east- ern mass may not be consanguineous with the other quartzose intrusive rocks; its chemical and normative composition (tables 8, 10; figs. 7, 13) differs from that of the other rocks. OTHER INTRUSIVE ROCKS Quartz porphyry and rhyolite dikes, too small to show on the geologic map, occur in the south-central part of the Prescott-Paulden area, mostly in areas mapped as contaminated Prescott Granodiorite and contaminated fine-grained granite. QUARTZ PORPHYRY Quartz porphyry intrudes the Alder Group and is intruded by the Prescott Granodiorite, coarse-grained granite, and fine-grained granite. It is a light gray porphyritic rock; some of it has a primary flow struc- ture and embayed pheonocrysts, but much of it has been intensely foliated. It is composed of quartz and albite phenocrysts as much as 10 mm long in a ground- mass composed of quartz, alkalic feldspar, variable amounts of sericite, a little biotite or chlorite, a little epidote or zoisite, and accessory magnetite and apatite. 48 Some intensely foliated quartz porphyry consists of al- ternating layers of sericite and quartz-sericite; but some of the augen of quartz in the layers show little strain or granulation. RHYOLITE DIKES Rhyolite dikes are confined largely to the southern part of the area of fine-grained granite east of the Texas Gulch Formation. The dikes intrude the Alder Group and fine-grained granite. The rhyolite is fine grained, massive and light to medium light bluish to greenish gray; it weathers white. Quartz and albite phenocrysts are as much as 3 mm in size. Quartz is euhedral or resorbed. Some albite crystals are clus- tered. Large areas of epidote are scattered erratically through the rock. The groundmass is quartz, alkalic feldspar, and very minor amounts of epidote, sericite, and chlorite. VEINS, SILICIFIED ZONES, AND ALTERATION ZONES Veins, silicified zones, and alteration zones include quartz, quartz-tourmaline, and tourmaline veins (iden- tified on pl. 1 by the letter q), quartz-magnetite veins or replacements (identified on pl. 1 by the symbol m), and to avoid the use of a separate symbol, silicified and alteration zones (identified on pl. 1 by the symbol si). The silicified and alteration zones include silicified breccia zones and economically important mineralized and alteration zones; many quartz veins have been min- eralized. Mineralized veins and zones are discussed in the section on "Economic geology," page 104. Quartz veins are widely distributed in the Precam- brian rocks, except in the Mazatzal Quartzite. They are especially abundant in the east-central and southeastern parts of the area. Quartz-tourmaline and tourmaline veins cut principally the Dells Granite, Government Canyon Granodiorite, Prescott and Lynx Creek masses of Prescott Granodiorite, and the aplite and pegmatite dikes in these rocks. The veins fill shear zones and a few joints. Some are parallel to and others are at an angle to the foliation _ in the host rock. The veins, pods, and lenses of quartz range in width from a few inches to, rarely, 50 feet. They are generally discontinuous within a shear zone. The longest quartz vein, about 1,000 feet, is in quartz diorite north of the Verde River (pl. 2, 1,413,500 N., 382,300 E.) ; other large veins and pods are found in the extreme southwest corner of the area and in alaskite in the Chaparral zone (pl. 1, 1,284,000 N., 398,000 E.). The largest tourmaline vein seen is 5 feet by about 100 feet. Some tourmaline veins form thin coatings on joints. GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA The quartz veins consist principally of milky or white quartz. Some contain appreciable amounts of tourma- line and grade into veins composed principally of tour- maline. Others contain minor amounts of gold, and many of them contain sufficient pyrite, chalcopyrite, or other metallic minerals to have induced prospectors to dig many shallow pits and adits. Few of the quartz- tourmaline and tourmaline veins contain enough me- tallic minerals to encourage exploration. The tourma- line ranges from hairlike needles to thicker crystals 2 mm long. The crystals form a network or mesh con- taining minor amounts of quartz. Quartz-magnetite veins, pods, and lenses are most abundant in the southwesternmost and south-central masses of unnamed tuffaceous rocks of the Alder Group (?), but they occur also in the Spud Mountain Volcanics and the basaltic flow unit of the Green Gulch Volcanics. Those in intrusive rocks are probably part of a xenolith of volcanic rocks. The veins are parallel to foliation or bedding in the host rock and do not appear to have any stratigraphic significance. Some are en echelon, an eastern one lying to the north of an adjacent western one. They range from a few inches to 20 feet in width,; a few fill all but a minor part of a 50-foot zone. Some have been traced as much as 1,500 feet. The quartz-magnetite is medium gray to medium dark gray and has a purple or blue cast. - Most of it is finely laminated ; some is massive. Laminae range from paper thin to several feet in width and are formed by variations in amount and grain size of quartz and mag- netite. Minute magnetite grains, 0.01-04 mm in diameter, are scattered or occur in ramifying streaks and bands, some of them more than 1 mm long. Most quartz grains are elongate and range from 0.01-0.8 mm in length, except in magnetite-free layers, where the individual grains are as much as 4 mm long. Small to large variations in the proportions of quartz and mag- netite are common ; the layers range from pure quartz to almost pure magnetite. Some veins enclose minerals characteristic of the host rock. The quartz-magnetite zones may represent recrystallized sedimentary jasper- magnetite beds or, more probably, a replacement of the tuff by hydrothermal quartz and magnetite. In the Prescott quadrangle portion of the Jerome area, these veins are referred to as jasper veins by Anderson and Creasey (1958, p. 43), but the veins here are more crystalline than the jasper veins farther east. Silicified breccia zones occur in the Dells Granite west and northwest of Storm Ranch and in the Prescott and Lynx Creek masses of Prescott Granodiorite (pl. 1). Most zones are narrow, ranging from less than an inch to a few inches or feet wide. A number of narrow zones may be concentrated to form a wider zone, such as the OLDER PRECAMBRIAN ROCKS 49 one in the Prescott mass (1,301,000 N., 329,000 E., to 1,305,300 N., 327,800 E.). The widest breccia zone has a maximum width of 50 feet and was traced intermit- tently for about half a mile (from 1,295,800 N., 370,700 E., to 1,297,700 N., 369,000 E.). This zone contains fragments of Precambrian volcanic and intrusive rocks, some of which are more than a foot long, and smaller ones of quartz, feldspar, tourmaline, and other minerals. The fragments are cemented by chert and other forms of silica. - Limonitic areas suggest alteration of introduced pyrite or other iron oxide or sulfide-bearing minerals. CONCLUSIONS AGE The Precambrian quartzose intrusive rocks in Arizona have generally been thought to belong to one period of orogeny that octurred before the deposition of the Ma- zatzal Quartzite, although Hinds (1986, p. 100) sug- gested two periods, one prior to and one after deposition of the Mazatzal. Until the recent discovery of a grano- diorite older than the Texas Gulch Formation," all the intrusive rocks of the Prescott-Paulden area were con- sidered younger than the Alder Group. As relations are obscure in many places, the possibility exists that locally pre-Alder Group rocks may have been included in the Government Canyon or Prescott Granodiorites. No evidence, however, of intrusion of any granitic rocks into the Mazatzal Quartzite was found in the area. Gabbro and the Yarber Wash mass of Prescott Granodiorite in the Jerome area, quartz diorite in the northern -part (pl. 2), and alaskite and the Mineral Point mass of the Prescott Granodiorite in the east- central part (pls. 1, 2) of the Prescott-Paulden area are unconformably overlain by lower Paleozoic rocks. Elsewhere Paleozoic rocks are absent, and the Precam- brian age of the intrusives is less certain. The lead/ alpha age of zircon in the Government Canyon Grano- diorite (see p. 50), however, is Precambrian. The intense deformation of some intrusive rocks in the southern part of the area-especially alaskite, coarse- grained granite, and the Chaparral and Salida Gulch masses of the Prescott Granodiorite-likewise indicates a Precambrian age for these rocks. If the correlation of the Yarber Wash and Mineral Point masses with the Prescott mass is correct, then the Prescott mass also is Precambrian, even though it has undergone only mild regional metamorphism. Also the Prescott mass "Mapping in the Mount Union quadrangle about 10 miles south- southwest of the southeast corner of the Prescott quadrangle by P. M. Blacet of the U.S. Geological Survey in the summer of 1961 has shown that the Texas Gulch Formation rests unconformably on an older granodiorite (quartz diorite) (C. A. Anderson, oral commun., 1962). This is the first known occurrence of granitic rocks older than the Alder Group. resembles granodiorite that is overlain by Tapeats Sandstone in the southeastern part of the Simons quadrangle (fig. 1). The age of the massive Dells granite is less certain, but it is considered Precambrian because it is cut by quartz and tourmaline veins, which have not been found cutting Paleozoic rocks to the north, and because it resembles granite that is overlain by Cambrian rocks in the Camp Wood quadrangle (see fig. 16) about 25 miles to the northwest. Fine-grained granite is considered Precambrian only because it is cut by diabase dikes, which have not been observed cutting Paleozoic rocks; its massive unaltered character sug- gests that it may be younger. The massive rhyolite dikes were intruded after regional deformation ; they may be related to upper Tertiary rhyolite tuff, but be; cause they are more altered than the rhyolite lapilli in the tuff, they are included in the Precambrian instrusive rocks. Quartz, tourmaline, and quartz-magnetite veins are presumably Precambrian; none were observed cutting Paleozoic rocks. They were formed probably after the major Precambrian deformation, as they are fractured but otherwise undeformed. The fragmental character of the breccia zones implies that brecciation occurred close to the surface in very late Precambrian or, possibly, in post-Precambrian times. RELATIONS The various masses of the Prescott Granodiorite are correlated on the basis of modal, chemical, and norma- tive compositions (tables 7-10, figs. 7, 9, 11, 13, 15). The similarity in hand specimen between some of the masses is less striking. The Prescott mass is finer grained than all the other masses except parts of the Lynx Creek mass; it is characterized by large poikilitic microcline; the others are not. The Lynx Creek mass consists of finer and coarser grained rocks that are con- sidered to be facies but conceivably represent different intrusions. The Yarber Wash and Mineral Point masses both have hornblende; no hornblende was ob- served in the Prescott and Lynx Creek masses, and if originally present in the Salida Gulch and Chaparral masses, it was destroyed during shearing. The composition of most of the Prescott Granodiorite is sufficiently different from that of the Government Canyon Granodiorite-lower in modal and normative quartz and in total silica, higher in modal and norma- tive mafic and accessory minerals (fig. 7)-to conclude that the two granodiorites are not part of the same in- trusion. The presence of hornblende in the Yarber Wash and Mineral Point masses suggests a possible correlation with the Government Canyon Granodiorite, as does the somewhat lower quartz content of the Min- eral Point mass compared with that of the other masses 50 ' GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA of Prescott Granodiorite. The amount of contamina- tion of the Mineral Point mass, however, makes inad- visable any firm conclusion that it is consanguineous with either the Prescott or the Government Canyon Granodiorite or that more than one granodiorite is present. The lead /alpha age of zircon in the Government Can- yon Granodiorite is 930 million years and that of the Yarber Wash mass is 1,045 million years. These ages were determined by H. W. Jaffe of the U.S. Geological Survey in 1954. The age of the Government Canyon Granodiorite was reported as 910 and that of the Yarber Wash mass as 1,050 million years by Anderson and Creasey (1958, p. 39). The change in age is due to slight revision in the constants used in the calculations (Jaffe, written commun., 1957). The results indicate only that these rocks are Precambrian ; they should not be considered as indicative of the relative ages. If the Yarber Wash mass is a facies of the Prescott Granodio- rite and if both areas mapped as Government Canyon Granodiorite are the same age, then the Government Canyon Granodiorite is older than the Yarber Wash mass. Because alaskite and some masses of Prescott Granodiorite were intensely deformed, they appear to be older than Government Canyon Granodiorite and the Prescott mass of Prescott Granodiorite. Alaskite, coarse-grained granite, and the Dells Granite are similar in modal, chemical, and normative composition, but megascopically alaskite is too different from the two granites to be considered correlative; the amount of deformation and metamorphism of coarse- grained granite compared with that of the Dells Gran- ite appears to preclude a correlation of the two granites. All or most of the intrusive rocks of the area may have been derived from the same parent magma. The gradual shift of points from the plagioclase corner of the field towards the center of the field in figure 7A conforms to experimental data on silicate melts. The curves of oxides plotted against silica in figure 7D are relatively smooth and likewise conform to curves that would be expected from differentiation of a magma. Both are in general agreement with relations established in the field. As the point representing the potassium oxide content of fine-grained granite does not fall on the curve, this granite may have had a different source. New and additional age determinations using the potassium,/argon and strontium/rubidium methods to be made on Government Canyon Granodiorite, the Yarber Wash and Prescott masses of Prescott Grano- diorite, and the Dells Granite may resolve some of the uncertainties. UNCONFORMITY AT THE BASE OF THE PALEOZOIC ROCKS The older Precambrian rocks of north-central Ari- zona are separated from Paleozoic formations by a major angular unconformity. Paleozoic rocks were laid down on the eroded edges of the older Precambrian volcanic, sedimentary, and intrusive rocks. Where local hills or monadnocks stood above this surface, the basal Paleozoic formations were deposited around them. In most places these hills rise to heights of little more than 50 feet above the general level, but part of the area underlain by the Mazatzal Quartzite (southwest-central part, pl. 2) was so high that about 500 feet of lower Paleozoic beds (Cambrian and most of the Devonian) are absent (fig. 17). PALEOZOIC SEDIMENTARY ROCKS GENERAL FEATURES Paleozoic rocks are largely limited to the area north- east of Chino-Lonesome Valley, where they are widely exposed but are concealed in many places by Cenozoic rocks. Their presence beneath these deposits in Chino- Lonesome Valley is uncertain. The southernmost exposures of the Paleozoic rocks (northeast corner, pl. 1) consist of the Tapeats Sand- stone of Cambrian age and the basal beds of the Martin Limestone of Devonian age. Successively younger formations appear to the north. They are the upper beds of the Martin Limestone, the Redwall Limestone of Mississippian age, the Supai Formation of Pennsyl- vanian and Permian age, and the Coconino Sandstone of Permian age. The youngest Permian formations, the Toroweap Formation and the Kaibab Limestone, crop out northeast of the area. The present distribution of Paleozoic rocks is due to uplift of the area to the southwest, which resulted in gentle titling of the rocks to the northeast, in local modifications of the northeast structure by faults and sharp warps, in burial by upper Tertiary (?) rocks; and in erosion prior to and after accumulation of the upper Tertiary (?) rocks. Northeast of the basin this distri- bution is illustrated in part by the maps showing the structure contours of the base of the Redwall Limestone (pl. 5) and the map showing the present thickness of Paleozoic and Cenozoic rocks (fig. 31). The Tapeats Sandstone can be divided into two units; and the Martin and Redwall Limestones, into four units each. These units have not been mapped, but their recognition is helpful in working out offsets along mono- clinal structures and faults of small displacement. The three members of the Supai Formation, a red-bed de- posit, have been mapped (pl. 2). The Paleozoic rocks are probably about 2,800 feet thick in the northeast PALEOZOIC SEDIMENTARY ROCKS corner of the area. The thicknesses of the formations and their units in north-central Arizona are shown in table 11. TAPEATS SANDSTONE DISTRIBUTION Outerops of the Tapeats Sandstone are limited to the extreme northeast corner of the Prescott quadrangle and to the southern part of the Paulden quadrangle (fig. 16). Northeast of the outcrops, the formation probably lies beneath younger Paleozoic rocks; it was not deposited in much of the area that is underlain by the Mazatzal Quartzite (fig. 17). The southernmost exposures of the Tapeats Sandstone are on the hill near 1,364,000 N., 392,500 E. (pl. 1), and near the eastern margin of the quadrangle between 1,357,900 N. and 1,361,100 E. An outcrop, too small to show on the geologic map, occurs beneath basalt near 1,358,000 N., 398,500 E. | 51 The most continuous exposures of the Tapeats (see pl. 2) are along the Verde River east-southeastward from Hubbel Ranch (1,417,500 N., 374,500 E.), in the headwaters of King Canyon (1,390,000 N., $83,000 E.), and north and northwest of St. Mathews Mountain (1,870,000 N., 399,000 E.). The sandstone forms iso- lated exposures along the Verde River west of Hubbel Ranch, near the mouth of Granite Creek (1,403,000 N., 346,000 E.), in upper and lower Bull Basin Canyon (south of Hubbel Ranch), in the headwaters of Gold Basin Canyon (1,398,000 N., 382,000 E.), and 3-314 miles south-southwest of Paulden (near 1,398,000 N., 330,000 E.). The last occurrence is the only outcrop within the area that is not northeast of Chino-Lonesome Valley. About 100 feet of mudstone, siltstone, and sandstone of the Tapeats was penetrated about 1,150 below the surface in a wildcat oil well (No. 1, sec. 20, T. 18 N., R. 2 W.; pl. 1, sees. B-B', C-C") about 314 miles northwest of Paulden. TaBu® 11.- Thickness, in feet, of Paleozoic formations in north-central Arizona [Inc., incomplete: Abs., absent because of nondeposition or erosion; U, undifferentiated or unrecognizable. Figures given in parentheses are approximate range of thickness in the quadrangles involved; they are listed because the thickness of the formation or unit at the indicated section is not given. See figs. 16 and 17 for approximate locations. The sections in Paulden quadrangle were measured by Krieger] AE. L cr 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Coconino Sandstone. . . . . . -... .. ..- |.. 2; 020- [ neben bul h he [ex ee cle as (es nie o on |euibaner ece eron abends €500-080) | : (500-650) |. ... 2: 21 220 eous elena de efe a cele 1, 000 Supai Formation: ssl clive l EEA IONA |- duck 2s 17005 iL ec L cor |L ede 2650—750) 1, 140 250-300) 390 (580-625) 2670 Total Supai Formation.......|.___..__|..______ L s. sxe ivi n LOl we deus Inc | 1, 550 2, 200 Redgailtgimestone: 3 (a ¥ nit 4. 51 5 r 1a]. fin -|} 151 (me.) 80 )| _ (56-80) * 74 28 (25-55) (25-55) 30 Total Redwall Limestone....| - Inc. Inc. 275 Inc. Inc. Inc. Inc. 219 252 241 256 (Inc.) 286 30 Marttsjmiggnestone: U U U U 0 218 | (260-270)| (260-270) 255 260 250 Af D-. none 3 ® I > e o > @T9NYVHGYNO | HTONYHIYNO m LLOOSTHd NOHI I A 6. ;; > [Ara ille Z 100 aToNvuavnd «TvaxuyT D)) NadTavd w padi by"" i aT9Nvuavnd SNONWIS 'oSuripenb 04} JO JoUuI0d ow1jxo ay} UI jdoo%o aul st) JO YJnos 10 Suore no doo syoo1 OU St 'pojoouuoo aq j0uUutd> TJ put g 'umoys st [¥z]ezEpt oy} 4q powno; ySty orydeasodoj oy} : stout quoot{pé pus ajSuripenb uop[nEB4 94} UI SUOTJEWLIOJ J10209[BA J9MO[ PUB UBLIQWEIIJ-'LT ues puse a - "s p3uy 143ug > -eqqg- z Wk W I auojsowt?t Aenp vum auogspuns asamof _ y + sas pou aqniow01Bu09 z fi asinoa 10f qdaoza abyss Robin; 'run aeddn ' {9 47 pur y 'ewug auopspueg syeadey, pun g 'quug fra rum 9 'oug : o pun g 'pug H 0 WA ewa > qwa r A wq aug pug @TDNVIGVNO COOM dWYO »S€ iSTeEIL @TONVHCVAO OE ETT % NOANYD AZXHUAL WTONVHCYNO ZLLNY OHOVOId Ste ETL 56 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA Evidence of a break in deposition between the Ta- peats(?) Sandstone and the Martin Limestone can be seen near the mouth of Granite Creek. The contact be- tween the conglomeratic facies of the shale unit and the overlying A unit of the Martin is sharp and indicates an abrupt change in conditions of deposition. The sur- face on which the A unit-that is, the discontinuous bed of reworked ( ?) sandstone-was deposited locally bevels slightly the underlying conglomerate. The surface is relatively smooth and even, but small irregularities pro- trude a few inches to a foot above it (fig. 18). The overlying limestone abuts against and dips away from these protruding masses; the dips are probably due to a combination of compaction and initial dip. pied 1 AT FIGURE 18.-Conglomerate at the top of the Tapeats Sandstone (€), and the overlying Martin Limestone (Dm) (1,403,500 N., 345,000 E.). Note the abrupt change from conglomerate to limestone, the relatively flat surface cut on the conglomerate, the local irregularities where cobbles in the conglomerate protrude into the overlying limestone, and the compaction and initial dip of the limestone around the irregulari- ties. See hammer for scale (arrow). About four-tenths of a mile (near 1,402,800 N., 347,- 000 E.) east-southeast of the exposures of conglomerate shown in figure 18, the Tapeats(?) Sandstone rests on the Texas Gulch Formation of the Alder Group. The basal 20 feet of dusky-red sandstone grades upward into buff sandstone about 127 feet thick. Except in color and the presence of some calcareous cement, the buff sandstone differs little from the underlying sand- stone. Pebbles of limestone and sandstone, in addition to the pebbles normally found in the sandstone, occur near the base of the buff sandstone; however, no pebbles derived from the Mazatzal were observed in the sec- tion, although a topographic high of Mazatzal cuts out the sandstone less than 500 feet to the east. The upper 4 feet of sandstone at the Simmons section immediately below the reworked sandstone contains similar limestone and sandstone pebbles, as does the upper 50 feet of sandstone in the Black Mesa section. The origin of these pebbles is an enigma. If the pebbles were derived from Cambrian formations (Ta- peats and Muay to the northwest), then the sandstone that contains them must be Devonian, and probably all the sandstone in the area is also Devonian. However, a Devonian age is not necessary and is not considered likely, because the limestone pebbles do not resemble the Muay and because a thickness of sandstone, such as occurs at Black Mesa (279 ft) has not been reported elsewhere in the Devonian in northern Arizona. The limestone pebbles do not resemble thin beds of marble in the Texas Gulch Formation of the Jerome area-the only other known pre-Devonian carbonate rock nearby. The limestone and sandstone pebbles may have been derived from the younger Precambrian Grand Canyon Series or Apache Group. Limestone and sandstone form part of these younger Precambrian rocks, and, according to E. D. McKee (oral commun., 1957), a thick sequence of limestone has been reported in a drill hole underlying the Tapeats in the Grand Canyon. Be- cause the area from the Grand Canyon to Paulden is covered by younger deposits, the southwestward extent of the Grand Canyon Series is unknown. Likewise, be- cause of deep erosion of the Precambrian rocks in pre- and post-Paleozoic times south of here, the former ex- tent of the younger Precambrian rocks is unknown. Immediately east of the thick section of sandstone just described, the Texas Gulch Formation is in fault contact with the Mazatzal Quartzite, and the Mazatzal and adjacent schist form a topographic high. The sandstone is absent east of the fault, and the conglom- erate that overlies 140 feet of sandstone west of the fault rests directly on the Mazatzal Quartzite east of the fault. The area near the fault is largely talus covered, so the relation of the Tapeats( ?) to the Mazatzal is not obvious, but one small exposure proved that the sand- stone is in depositional contact with a small sliver of the quartzite that lies just west of the main fault be- tween the two Precambrian formations. The sand- stone, therefore, is not older than the fault, as might be assumed from its absence east of the fault and from the absence of Mazatzal pebbles in the sandstone immedi- ately west of the fault. According to E. D. McKee (oral commun., 1957) this deposition of Tapeats Sand- PALEOZOIC SEDIMENTARY ROCKS 57 stone against a quartzite high is typical of the situation in the Grand Canyon, where the Shinumo Quartzite of the Grand Canyon Series forms sharp peaks surrounded and buried by Tapeats Sandstone; the sandstone may contain a few angular fragments of quartzite close to the contact but contains none within a short distance of it. The outcrops of Mazatzal that supplied the rounded pebbles and cobbles in the overlying conglom- erate may not have been exposed at the time the sand- stone was deposited. The amount of rounding of the resistant pebbles and cobbles of quartzite and conglom- erate from the Mazatzal indicates that this material was derived from some distance away and not from the nearby outcrop of the Mazatzal. The similarity be- tween the relation of the Tapeats(?) Sandstone to the Mazatzal and of Tapeats to the Shinumo Quartzite in the Grand Canyon area contrasts with the relation of known Devonian sandstone to the Mazatzal Quartzite in the Paulden quadrangle; this contrast also suggests that the questionable sandstone in the Paulden-Jerome area is Cambrian. In view of the foregoing evidence, the Cambrian age of the basal Paleozoic sandstone in the Paulden-Jerome area is no longer questioned. MARTIN LIMESTONE DISTRIBUTION Outerops of the Martin Limestone are found mostly northeast of the Tapeats Sandstone and are more ex- tensive than those of the Tapeats. Northeast of Chino- Lonesome Valley, the formation is widely distributed across the northern part of the area (pl. 2) along a northwest-trending strip that has a maximum width of about 9 miles. The formation is exposed almost contin- uously (1) along the Verde River from Stewart Ranch Headquarters (1,406,000 N., 341,500 E.) nearly to the mouth of Hell Canyon, (2) from the southeast corner to the Verde River, principally east of King Canyon (1,- 397,000 N., 378,000 E.), and (3) along the southwest side of Black Mesa for 5 miles from the northwest corner of the study area. The Martin is buried by younger rocks northeast of a line running parallel to but at least a mile southwest of Hell Canyon. It is not exposed in or west of Chino Valley, except for two small outcrops south-southwest of Paulden (near 1,397,000 N., 330,000 E.). A wildcat oil well (No. 1, see. 20, T. 18 N., R. 2 W.) northwest of Paulden cuts more than 400 feet of the Martin beneath about 700 feet of Cenozoic de- posits. The southernmost exposures of the formation are in the same area as those of the Tapeats; a small outcrop, too small to show on plate 1, occurs near 1,359,000 N., 397,200 E. THICKNESS AND STRATIGRAPHIC RELATIONS The Martin Limestone thins to less than 50 feet over the topographic high of the Mazatzal Quartzite (fig. 17). Elsewhere in the Paulden-Jerome area the forma- tion has a relatively uniform thickness of 390-479 feet, as it does for many miles to the northwest and southeast (table 11). Four units, from botton to top the A, B, C, and D units,° are recognizable in the southeast of the Paulden-Jerome area; they are less distinct northwest of the area. The units thin and are successively cut out around the topographic high of Mazatzal Quartzite. Away from the topographic high, the A unit is 15-21 feet thick, and the B unit is 55-97 feet thick. The C and D units are 65-75 feet and 218-255 feet thick, respec- tively, in the eastern part of the area, but to the west the position of the contact between the two units is uncertain. Except where topographic highs on the Precambrian surface cut out the Tapeats, the Martin Limestone rests on the Tapeats, as described on page 52. The aMrtin is overlain disconformably by the Redwall Limestone of Mississippian age; the maximum relief on the Martin surface is about 35 feet and averages 10-15 feet. LITHOLOGY The Martin Limestone comprises dolomite, dolomitic limestone, limestone, disseminated argillaceous and arenaceous material, and minor amounts of limy silt- stone and sandstone. The dark color, thinly and evenly bedded character, and steplike slopes to which the for- mation weathers serve to distinguish it from the over- lying Redwall Limestone. Some beds in the C and D units are fossiliferous, and fish plates have been reported from sandstone beds near the top of the B unit near Jerome.. The fauna of the Martin at Jerome was described by Stoyanow (1936, p. 495-500). A UNIT The A unit is largely dolomitic limestone, but near Granite Creek (1,402,800 N., 347,000 E.), it contains interbedded sandy and conglomeratic layers and is underlain by a 2-foot bed of reworked (?) sandstone. Lehner (1958, p. 525) reported a similar, nonpersistent basal sandstone in the Clarkdale quadrangle. The well sorted medium to coarse grained sandstone is composed principally of well-rounded frosted grains of quartz. It is light gray or light olive gray to nearly white and has local limonitic spots. *The units were so designated by Lehner (1958, p. 525) but were called lower, lithographic, middle, and upper units by Anderson and Creasey (1958, p. 50). 58 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA The A unit is a very impure quite uniform clastic cliff-forming dolomite and dolomitic limestone that emits a strong fetid (petroliferouslike) odor when freshly broken. According to Curt Teichert (written commun., 1956), the rock contains no hydrocarbons, and the odor may be due to ammoniacal salts. The rock is light brownish gray to light olive gray and weathers to slightly darker shades. Coarser beds are, in general, darker than the finer grained beds. Impuritie- largely clay and silt-impart a pink or yellow cast. Most beds are medium to coarse grained, but some are fine grained. Dolomite forms larger grains than does calcite. The weathered surface is pitted because of the weathering out of scattered coarse calcite grains, as much as 1 cm in diameter, whose origin is uncertain. The beds range from 1% inch to 4 feet in thickness. The clastic character of the unit can be observed where etching has revealed crossbedding, channels, or frag- ments. - Massive beds are coarse grained, possibly owing to recrystallization. The upper part of the A unit near Granite Creek (especially near 1,403,000 N., 347,000 E.) is coarser grained and lighter colored. In places it is a breccia abundantly and irregularly replaced by dark- brown chert-the chert may be related to late Terti- ary (?) basalt flows. At this place the basal 4 feet of the unit is the typical dark dolomitic limestone, but it contains many sand grains and small pebbles derived from the Mazatzal Quartzite. East of the fault that separates the Texas Gulch Formation from the Mazat- zal, the coarse-grained light-colored limestone rests di- rectly on the conglomerate bed at the top of the Tapeats. B UNIT The B unit (fig. 2) contrasts sharply with the olive- gray A and C units. It is an aphanitic evenly and thinly bedded light-colored slope-forming dolomitic limestone containing shale partings. The limestone beds are pinkish gray, locally darker gray or lavender, and weather light gray to white. Beds range from 3 inches to 3 feet and average about 8 inches in thickness. Few of them show internal stratifi- cation. The beds are separated by shaly partings- from thin films to 3 inches thick-which are exposed only in road cuts and cliffs. The shale is dark gray to grayish yellow green and pale yellowish green. The unit, which is more calcite than dolomitic, is very fine grained ; it is virtually a lithographic limestone. The weathered surface is smooth, except where disseminated grains of sand project above the surface and where it has a wrinkled appearance because of solution along joints. Light-yellow and dark-gray chert, as nodules, lenses, and thin layers parallel to the bedding, is fairly abundant in some of the beds. A persistent sandstone, locally called the red marker bed, lies within a few feet of the top of the unit. Even though in places it is represented by only thin sandy lenses in the limestone, this horizon marker was recog- nized wherever the upper part of the unit is exposed in the Paulden-Jerome area. It ranges from a few inches to about 61% feet in thickness. Locally it consists of several beds of sandstone, of scattered sand grains, or of lenses of sandstone interbedded in aphanitic lime- stone through an interval of more than 10 feet. In places the rock is more nearly an orthoquartzite. Rip- ple marks and crossbedding are locally conspicuous. The sandstone is generally various shades of light red- dish brown to pale red ; some is buff to light gray. At one place in the southeastern part of the Paulden quad- rangle the sandstone contains fragments of aphanitic limestone as much as 8 inches in maximum size. Near the mouth of Granite Creek and in an exposure as far east as Bull Basin Canyon (1,401,500 N., 373,700 E.), small pebbles as much as 214 inches in diameter of Ma- zatzal Quartzite occur in the sandstone or in limestone immediately below the sandstone. Much of the upper part of the B unit beneath the red marker bed in the Granite Creek area is a yellowish- brown chert that weathers very light gray to white. The origin of this chert is in doubt, but in the south- eastern part of the quadrangle, the local association of similar chert beds in the unit which late Tertiary (?) basalt flows suggests that the chert is a replacement as- sociated with volcanism. West of Hubbel Ranch (1,417,700 N., 374,500 E.) the upper part of the B unit, below the red marker bed, contains beds of a very light gray massive friable medium-grained sugary limestone or dolomite that weathers light yellowish or reddish. Some beds are as much as 8 feet thick and lack internal stratification, except for a few greenish sandy, shaly partings. C UNIT The C unit (fig. 2) is darker colored, coarser grained, and thicker bedded than the B unit; it forms weak cliffs. The typical rock of the unit is light to moderate olive-gray dolomitic limestone mottled by fine-grained light-pinkish-gray areas. The mottled areas, which are due to recrystallization, are irregular in size and shape but, in general, are several inches long. Beds range from less than 1 inch to 4 feet in thickness; few of them show internal stratification. Beds that resemble those of the A unit and have the same fetid odor occur in the C unit, especially near the base. A bed of light-weath- ering aphanitic limestone, similar to beds in the B unit, commonly lies 7-12 feet above the base of the C unit. In the southeastern part of the Paulden quadrangle, the contact between the C and D units is placed below the first bed of aphanitic white-weathering dolomitic lime- PALEOZOIC SEDIMENTARY ROCKS 59 stone (B-unit type) at the top of the typical beds of the C unit. West of Hubbel Ranch the contact between the C and D units occurs either about 35 or 65 feet above the base of the C unit-about 30 feet of mottled lime- stone (C-unit type) overlie one or more beds of aphanitic light-weathering limestone (B-unit type), which are about 35 feet above the base of the C unit. D UNIT The D unit is characterized by diverse lithology. It comprises alternating beds typical of the three lower units and some interbedded calcareous shaly siltstone, mudstone, and sandstone. Much of the lower part of the D unit consists of inter- bedded rocks of A, B, and C lithologies. The bottom 50 feet or so of the unit in upper King Canyon contains beds, as much as 5 feet thick, of A and C lithologies and a few beds of B lithology. Above this part of the D unit, the beds are thinner (ranging from a few inches to 2 ft.) and contain more abundant aphanitic beds that weather light gray, bluish gray, lavender, and purple. The upper part of the unit contains some shaly mud- stone, platy siltstone, and a few thin beds of sandstone. Some beds contain chert. In places, the top of the unit is a grayish-orange-pink medium-grained dolomitic limestone. Where the uppermost beds of the unit overlap the Mazatzal Quartzite (near 1,382,500 N., 358,000 E.), nu- merous beds of sandstone and conglomerate derived from the Mazatzal interfinger with beds typical of the D unit. The beds dip gently to steeply away from the Mazatzal because of initial dip or compaction. In places only the sandstone and conglomerate are ex- posed-as on the east side of the largest mass of Mazat- zal Quartzite and the two small outcrops near the south side of this mass (northeast of 1,380,000 N., 362,500 E. and at 1,382,300 N., 357,200 E. and 1,384,000 N., 353,700 E.)-but these beds can be distinguished from the Tapeats(?) by their thin-bedded, flaggy character and darker, but not red, color. Several distinctive beds can be used as key or marker horizons, at least for short distances. One is a massive bed, generally about 2 feet thick, which is olive gray mottled with conspicuous yellow to orange colorations on weathered surfaces. AGE AND CORRELATION The Devonian limestone at Jerome was originally named the Jerome Formation by Stoyanow (1930) and later described bx him in detail (1936, p. 495-500). Stoyanow (1936, p. 503) considered the Temple Butte Limestone (named by Walcott, 1890, p. 50) of the Grand Canyon as correlative with his Jerome Formation. In the southeastern part of the state, the Devonian lime- T58-447 O-65--5 stone was named the Martin Limestone by Ransome (1904, p. 33). According to Stoyanow the Devonian rocks thin towards and are largely absent from the area between Pine (fig. 1, inset) and Theodore Roosevelt Lake (60 miles southeast of Pine). Because of certain differences in lithology and in sequence, Stoyanow (1936, p. 495) postulated a land mass-Mazatzal Land- to separate the Devonian seas northwest of Mazatzal Land from those southeast of it. He considered the upper part of his Jerome Formation to be equivalent in age to the Martin Limestone. Huddle and Dobrovolny (1945) found that in spite of local thinning the Martin Limestone could be traced from Globe into the Pine area, even though it is locally only 30 feet thick in the areas Stoyanow called Maza- tzal Land. They pointed out that the lithologic sim- ilarities and the indication of original continuity of the Devonian rocks are sufficient to justify the extension of the name Martin Limestone into the Pine area. They believed that the Martin can be traced into the Temple Butte Limestone of the Grand Canyon region. Because the Martin Limestone in the Pine area, as described by Huddle and Dobrovolny, is without doubt the same as the Devonian rocks in the Jerome area, Anderson and Creasey (1958, p. 51) applied the name Martin to these rocks at Jerome. McNair (1951, p. 516) correlated the Devonian rocks of Jerome with those at Hurricane Cliffs in the western part of the Grand Canyon and called them all Martin Limestone. Huddle and Dobrovolny (1945; 1952, p. 73) subdivided the Martin Limestone in the Pine area into three members. Their lower member apparently includes the A and B units and a basal sandstone. Their upper members differ from the C and D units in con- taining greater amounts of sandstone and shale. Where I have observed the formation in the Pine area, the four units can be recognized in sections where the for- mation is not adjacent to or partly cut out by topogra- phic highs of the Mazatzal Quartzite. According to Curt Teichert (oral commun., 1956), the four units can be recognized as far as Theodore Roosevelt Lake, al- though they become less distinct southeast of Pine. Northwest of the Paulden quadrangle, the A unit was recognized (furing reconnaissance, but the other units were not recognized much beyond the western boundary of the quadrangle. At Fort Rock and farther north- west, the formation consists entirely of cyclothems, each of which comprises one or more of six broadly defined lithologic types and phases, according to W. H. Wood." Huddle and Dobrovolny (1952, p. 67 and 86) placed the Martin Limestone of central Arizona in the Upper Devonian, except for the lower part, which may be ® Wood, W. H., 1956, The Cambrian and Devonian carbonate rocks at Yampai Cliffs, Mohave County, Arizona : Arizona Univ. Ph. D. thesis. 60 equivalent to the lower part of the Devils Gate Lime- stone (Middle and Upper Devonian) of Merriam (1940, p. 16-17) in central Nevada. The Martin in the Pres- cott and Paulden area, therefore, is assigned a Mid- dle(?) and Late Devonian age. REDWALL LIMESTONE DISTRIBUTION The distribution of the Redwall Limestone is about the same as that of the Martin Limestone, except that its outcrops extend farther to the northeast. Its most extensive exposures in the Paulden quadrangle are in the northwestern part, the east-central part, and along the Verde River in the central part. Its most north- easterly exposures are along Hell Canyon and along the Verde River east of its junction with Hell Canyon. THICKNESS AND STRATIGRAPHIC RELATIONS The Redwall Limestone is about 220 feet thick where measured in the Paulden quadrangle and somewhat thicker in the Clarkdale and Mingus Mountain quad- rangles (table 11). To the northwest towards the Grand Canyon, it thickens to 500 feet (McNair, 1951, p. 515, 519). To the southeast it thins locally to about 30 feet in the Pine area (Huddle and Dobrovolny, 1945). The Redwall Limestone lies unconformably between the Martin Limestone of Devonian age and the Supai Formation of Pennsylvanian and Permian age. The relief on the Martin surface is low and gently undula- tory; the Martin and Redwall therefore appear con- formable. Depressions on the Martin surface are filled with material derived from the Martin and not readily separable from the Martin. For mapping purposes, the base of a massive light bluish-gray oolitic limestone that overlies the Martin or the reworked Martin was used as the contact between the Martin and Redwall. In many places the relief on the Redwall surface is more than 50 feet in a horizontal distance of little more than 100 feet. LITHOLOGY The Redwall Limestone is a cliff-forming massive, thick- to thin-bedded, white to light-gray coarsely crystalline to aphanitic limestone. Solution channels and caverns, in places collapsed or filled, are common. The filling consists of fragments of limestone or chert, or both, cemented with a bright red claylike sediment or with silica. In several places large blocks of the Supai Formation rest on the lower part of the Redwall or even on the upper part of the Martin. Some of these blocks may have been let down along faults, but some probably were let down as a result of solution and collapse within the Redwall. Much of the limestone is fossiliferous, but local zones are barren. 7 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA In the Jerome area Wooddell (Stoyanow, 19836, p. 512- 513) divided the Redwall Limestone into six members. Gutschick (1943; see also Easton and Gutschick, 1953), who studied the Redwall from the Pine area northwest- ward to beyond Seligman (fig. 1, inset), subdivided it into four members designated, from oldest to youngest, members I, II, III, and IV. His members II and III are about the same as Wooddell's members 3 and 4. Gutschick's four members have been recognized in the Paulden and Clarkdale (Lehner, 1958, p. 530-531) quad- rangles and are called units 1, 2, 3, and 4. In the Jerome area Anderson and Creasey (1958, p. 52) did not distin- guish between units 3 and 4. UNIT 1 Unit 1 consists of two parts: reworked Martin Lime- stone and oolitic limestone. The lower part, 0-40 feet thick according to Gutschick (1943), consists of thin- bedded clastic dolomitic limestone, arenaceous limestone, and calcareous sandstone that resembles the Martin. The beds are finely crystalline and light to very light brownish gray and olive gray, locally tinged with pink or lavender because of impurities. Much of the upper part of the unit is a conspicuous, massive aphanitic very light bluish-gray oolitic lime- stone. In most places in the Paulden quadrangle it forms a slope or bench between the weak cliff-forming lower part of unit 1 (or the upper part of the Martin Limestone) and the cliff-forming unit 2; it is 23 feet thick where measured. - Locally the bed grades laterally into crystalline limestone. A bed of finely crystalline darker limestone or dolomitic limestone that resembles the Martin lies 2-5 feet above the base of the oolitic limestone in many places. The top of the unit is a coarsely crystalline fossiliferous limestone, generally only a few feet thick. Fossils include cup corals, brachiopods, and gastropods. UNIT 2 Unit 2 is 80 feet thick where measured and is a fine- to medium-grained porous limestone containing abundant chert nodules, lenses, and layers. The lime- stone ranges from nearly white or very light gray to yellowish gray. The chert is white, grayish yellow, and locally dark gray; it weathers reddish brown. Beds are 2-5 feet thick. Fossils are scarce and consist of corals, crinoids, and brachiopods. Solution and col- lapse have produced widespread breccias, especially in the southeastern part of the area. The breccia consists of fragments of chert and a few of limestone that are cemented by silica or by a red claylike sediment. Some of these breccias resemble fault breccias, except in their blanketlike distribution. PALEOZOIC SEDIMENTARY ROCKS 61 UNIT 3 Unit 3 is 81 feet thick where measured and is a thick- bedded coarsely crystalline massive fossiliferous pure limestone of uniform character. It is yellowish gray to very light gray and weathers yellowish gray; the weathered surface is rough owing to the unit's coarse grain size and to the abundance of crinoid discs. Corals are relatively abundant; other fossils include bryozoa, blastoids, gastropods, trilobites, and fish (Gutschick, 1943). UNIT 4 A solution breccia and overlying light-gray limestone compose unit 4, which forms weak cliffs. 'The solution breccia consists of irregular cobble- to boulder-sized limestone fragments surrounded by red silty material. Most of the limestone resembles that of the upper part of unit 1, except that much. of it is micro-oolitic to pellety. In the northwestern part of the area, the limestone is partly crystalline in the lower part and partly cherty in the middle part. Local fossil zones contain corals, gastropods, cephalopods, pelecypods, fish teeth, formanifera, and ostracodes (Gutschick, 1943, written commun. to Lehner, 1955; Easton and Gutschick, 1953). Gutschick interpreted the solution breccia to be a residual deposit representing an un- conformity. I am not sure of its significance. Lehner did not observe the breccia or the crystalline and cherty beds and placed the contact between units 3 and 4 at the base of the oolitic limestone. The oolitic limestone is better exposed in the Paulden quadrangle than are the underlying beds of the unit. Where measured, the breccia is 15 feet thick, and the oolitic limestone is 20 feet thick. AGE AND CORRELATION Mississipian rocks in the Jerome area were called Redwall by Ransome (1916, p. 162), Lindgren (1926, p. 9), Stoyanow (1936, p. 512-514), and Gutschick (1943). The name Redwall was first applied to Mis- sissipian limestone in northern Arizona by Gilbert (1875, p. 162, 177-186), who included rocks older and younger than Mississippian. Later, Noble (1922, p. 54) restricted the name Redwall to rocks of Missis- sippian age. In southeastern Arizona, limestone of Mississippian age was called Escabrosa Limestone by Ransome (1904, p. 42), and this term has been widely used in that part of the state. According to Stoyanow (1936, p. 505), the Escabrosa and Redwall "are not exactly taxonomic equivalents * * * but, rather, over- lap each other." He stated that the deposition of the Redwall began somewhat later than that of the Esca- brosa. In central Arizona, Huddle and Dobrovolny (1952, p. 86) found that the two formations are prob- ably a continuous, mappable unit, which they called the Redwall Limestone. Fossils collected by Ransome (1916, p. 162) indicate an early Burlington age (lower Osage series) , and those collected by Wooddell (Stoyanow, 1936, p. 514) indicate a late Kinderhook to Keokuk age (largely late Kinder- hook and Burlington). Gutshick (written commun. to Lehner, 1955) placed unit 1 in the Kinderhook and the other members in the Osage. He correlated unit 2 with the top of the Alamogordo and base of the Nunn Members of the Lake Valley Formation of Laudon and Bowsher (1941, 1949) of New Mexico. He correlated unit 3 with the Burlington Limestone of the Mississippi Valley. He tentatively placed unit 4 in the uppermost Osage (Keokuk affinity) but stated that it may be Meramec, especially if the "conspicuous solution bouldery zone" between units 3 and 4 does represent a break in the sedimentary sequence. The Redwall Lime- stone in this area is considered to be Early Mississipian in age. SUPAL FORMATION DISTRIBUTION The Supai Formation, principally a red-bed deposit, is confined to the northeastern half of the Paulden quadrangle. The southeasternmost exposure lies about 4.3 miles north of the southeast corner of the quadrangle. The most extensive exposures are in the northeastern part, north of Limestone Canyon in the northwestern part, and north and south of the Verde River in the central part. The formation comprises three members (pl. 2); the middle and upper members have been eroded from all but the northeastern corner of the area. THICKNESS AND STRATIGRAPHIC RELATIONS The thickness of the Supai Formation is not known, as faults cut out some of the upper member and a con- tinuous section of the middle member is not exposed, although most of this member is problably exposed in Red Butte. In the northeast part, the formation is pre- sumably about as thick as in the east part of the Clark- dale quadrangle, where it is 1,550-1,665 feet thick (Lehner, 1958, p. 533; E. D. McKee, oral commun, 1953). It probably thins to the northwest, as Hughes (1949, p. 33; 1952, p. 643) measured about 1,100 feet in Black Mesa about 20 miles northwest of the Paulden quadrangle. The formation thickens to the southeast (table 11). The three members into which the Supai Formation can be subdivided have been recognized to the east and southeast. In the Clarkdale quadrangle (Lehner, 1958, p. 535-537), the lower member is 580-625 feet thick; the middle member, 250-300 feet; and the upper mem- ber, 650-750 feet. In Black Mesa, Hughes (1949, p. 62 33; 1952, p. 643) recognized only two members; the lower is about 150 feet thick, and the upper, about 1,000 feet. In the northwestern part of the Paulden quadrangle, the exposures include the lower part of his upper mem- ber and probably his lower member. The Supai Formation unconformably overlies the Redwall Limestone, as described on page 60. The con- tact is generally marked by a basal limestone or a chert breccia or conglomerate in a red-purple to grayish-red mudstone and silty shale. In the northwestern part of the area, however, the contact between the Redwall and Supai, because of poor exposures, was arbitrarily considered to be at the base of a light-gray to lavender limestone that has been partly to completely replaced by chert. At least 25 feet of the formation probably underlies the cherty limestone. Along Limestone Can- yon about 3 miles northwest of the quadrangle bound- ary (Ashfork quadrangle, NW14 see. 17, T. 19 N., R. 2 W.), the sequence between the top of the Redwall and the cherty limestone is (1) chert breccia, (2) olive-gray fetid limestone, (3) light-bluish-gray to lavender non- cherty limestone, and (4) a thin zone of red beds. The cherty limestone and underlying beds probably cor- respond to the lower unit of Hughes (1952, p. 643), which comprises interbedded limestone, red siltstone, and basal conglomerate. f The contact of the Supai Formation with the overly- ing Permian Coconino Sandstone is gradational and intertonguing. In the upper part of the Supai, tor- rential-type and some eolian-type cross-laminae occur in thick sandstone beds. These cross-laminae are bev- eled and covered by thinly laminated horizontally bedded siltstone and fine-grained sandstone. The Co- conino Sandstone has large-scale eolian-type cross- bedding and lacks the horizontal silty layers. Because where examined at close range the crossbedding in the sandstone of the upper member of the Supai resembles that in the Coconino, it may be impossible to determine to which formation isolated outcrops belong. The con- tact can locally be determined by color, as most of the Coconino is buff and the Supai is reddish. Some Co- conino, however, has the same color as the Supai, and vice versa. Hughes (1952, p. 642), like Huddle and Dobrovolny (1945), considered the contact to be "* * * at the base of the lowest massive sandstone with well- developed Coconino-type crossbedding." McKee (oral commun., 1953), on the other hand, arbitrarily placed the upper limits of the Supai at the top of the upper- most flat-bedded siltstone or sandstone. McKee's cri- terion was used to map the contact in the Paulden and Clarkdale quadrangles. In the Grand Canyon area the Hermit Shale separates the Coconino Sandstone from the Supai; there the contact between the Hermit GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA Shale and the Supai Formation is an erosional uncon- formity (Noble, 1922, p. 63-64). LITHOLOGY The Supai Formation, largely a red-bed deposit, con- sists of sandstone, siltstone, shaly mudstone, and minor amounts of limestone and chert near the base. The limestones are marine in origin, as northwest of the area they contain a brachiopod-pelecypod fauna (Hughes, 1952, p. 639, 652-656). The detrital mate- rial is deltaic or flood-plain in origin, according to Mc- Kee (1940, p. 822). McNair (1951, p. 532) suggested a marine mud-flat environment. LOWER MEMBER The lower member comprises sandstone, siltstone, minor amounts of shaly mudstone, some limestone beds-especially in the lower part-and basal chert breccia or limestone conglomerate. It forms a steplike topography, except for a cliff of sandstone at the top. The basal chert breccia is almost universally present. It consists of angular to subangular fragments of chert and some of limestone as much as several inches across. The chert is gray, black, and red ; it occurs in a very dusky purple, dusky-red, or black shaly, silty, or sandy matrix, some of which is hematitic. Limestone con- glomerate occurs locally at the base and is also inter- bedded with red beds higher in the section. It contains chert, limestone, and siltstone pebbles as much as 4 inches in diameter in a light-gray to brownish-gray limestone that weathers pale reddish brown. Chert in siltstone and sandstone occurs as nodules and more or less spherical concretionary masses. These masses reach dimensions of 314 by 2 feet and are composed of alter- nating concentric bands of white chert and red silt. The limestone, which occurs in beds 1-6 feet thick, is mostly fine grained to aphanitic and olive gray, light gray, or light bluish, yellowish, or brownish gray. In the northwestern part of the area, especially south and east of Rock Butte (1,453,000 N., 342,500 E.) and about 41, miles east-northeast of Paulden (near 1,424,000 N., 356,500 E.), some light-gray and lavender limestone has been partially to completely replaced by chert. Some of the chert is banded white, lavender, purple, and red. The chert forms thin layers and irreg- ular stringers parallel to the bedding. Veinlets of red and white chert cut the bedded chert. Most of the member in the eastern part of the area and the beds that overlie the cherty limestone in the north- western part consists of alternating siltstone, very fine grained sandstone, some mudstone, and some silty and cherty limestone. Sandstone is more abundant in the upper part. These rocks are pale to dark reddish brown and have a somewhat orange cast. PALEOZOIC SEDIMENTARY ROCKS 63 MIDDLE MEMBER The middle member remains only in the northeastern part of the area (north of 1,435,000 N., and east of 392,- 000 E.). This member contrasts with the underlying and overlying members, especially in topography and color. It forms slopes having a few subdued rounded ledges and some rounded hills-such as Red Butte (1,436,500 N., 394,500 E.). The color is generally gray- ish red to reddish brown; the weathered surface has a purple cast that contrasts with the more orange red color of the other members. The principal constituent is siltstone; minor con- stituents are conglomerate, sandstone, and a very little limestone. Beds range from less than 1 inch to about 3 feet in thickness. Some siltstone is calcareous or con- tains calcareous nodules and grades laterally into lime- stone. Conglomerates are composed of a pale-red to reddish-brown siltstone and pebbles as much as 5 inches long composed of pale-brown to pale-red siltstone and some light brownish-gray to medium-gray limestone. The beds are typical "intraformational conglomerates." The few sandstone beds are 5-10 feet thick, light brown to pale reddish brown, and fine grained. They form rounded ledges. Some are calcareous and prominently cross-laminated. The limestones are very light brown- ish gray, cross-laminated to structureless, aphanitic, and sandy or silty. UPPER MEMBER The upper member of the Supai Formation crops out in the extreme northeast corner of the area. It contrasts sharply with the middle member in topography, li- thology, and color and consists of sandstone and a little siltstone that form cliffs, buttresses, and pinnacles. The sandstone is medium to coarse grained; some is finer grained. Current cross-lamination is conspicuous in the sandstone beds; the cross-laminae are generally larger than those in the middle member. Near the top some of the cross-laminae are eolian. A reddish-orange color characterizes this member, but some of it is light brown or moderate reddish brown. It weathers to slabs and plates or to a sandy soil. Some sandstone is cal- careous. Bedding is massive; some sets of beds, accord- ing to Lehner (1958, p. 538), are 150 or more feet thick. Siltstone beds are a few feet to 30 feet thick but aver- age 6-8 feet. The siltstone is pale reddish brown and has irregular wavy laminae. Some is cross-laminated on a small scale. It weathers to smoothly rounded ledges that, together with its horizontal beds, contrast markedly with the large-scale crossbedding of the sandstone. AGE AND CORRELATION The name Supai Formation was applied by Darton (1910, p. 25-27) to red sandstone and shale occurring between the Redwall Limestone and overlying Coconino Sandstone in the Grand Canyon area. Noble (1922, p. 59) redefined the Supai by removing from the top about 300 feet of red shale and sandstone of Permian age, which he called the Hermit Shale, and by adding about 250 feet of red shale, purple and gray limestone, and calcareous sandstone to the bottom. These lower beds are Pennsylvanian in age and had previously been in- cluded in the Redwall Limestone. Noble (1922, p. 62) regarded the Supai as probably Pennsylvanian in age. Darton (1925, p. 72, 89) believed that most if not all of the red beds are Permian in age, except for the lower beds that Noble had included in the formation. Much of the Supai Formation outside the Grand Canyon area includes beds of known or inferred Penn- sylvanian age as well as those of Permian age. Wher- ever possible in recent years, these Pennsylvanian beds have been separated from the Supai or have had their probable Pennsylvanian age pointed out. In the Paul- den-Jerome area, lack of fossils and of a distinctive lithology makes this separation impossible, although it is probable that the lowest beds are Pennsylvanian. In northwestern Arizona the Supai Formation is underlain by and interfingers with the Callville Lime- stone, named by Longwell (1921, p. 46-47) for lime- stone lying between Mississippian rocks and Permian red beds in the Muddy Mountains of Nevada. Longwell placed the Callville in the Pennsylvanian but later stated (1949, p. 930) that the Callville contains some Permian strata. McNair (1951, p. 520) restricted the name Callville in northwestern Arizona to Pennsylva- nian limestones and removed from the Callville the over- lying dolomitic limestones of Permian age. The basal member of the Supai in Black Mesa northwest of the Paulden quadrangle (Hughes, 1952, p. 654-656) contains brachiopods, pelecypods, and trilobites; these fossils in- dicate marine conditions this far to the southeast. The fossils are not diagnostic as to age, but the beds contain- ing them may be equivalent to the upper part of the Call- ville (Upper Pennsylvanian) or to lower part (Lower Pennsylvanian), depending on whether the seas were transgressive (McNair, 1951, p. 520), or regressive (Hughes, 1952, p. 656, fig. 10). In southeastern Arizona the name Naco Limestone was applied by Ransome (1904, p. 44) to Pennsylvanian rocks. In central Cochise County the Naco has been assigned to a group and subdivided into several forma- tions of Pennsylvanian and Permian age (Gilluly, Cooper, and Williams, 1954, p. 15-42). Beds of Naco Limestone interfinger with Supai red beds to the north 64 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA and northwest of the type locality. Huddle and Dobrovolny (1945) extended the name Naco to beds at Fossil Creek and at Fort Apache (40 and 140 miles, respectively, southeast of Jerome). In these two areas, R. L. Jackson "* (1951) and Winters (1951) likewise applied the name Naco to beds of Pennsylvanian age that had been included in the Supai. E. D. McKee (oral commun., 1953) correlated the bottom 332 feet of the lower member of the Supai in Sycamore Canyon (Clarkdale quadrangle) with the Naco and placed the boundary between it and the overlying Supai Forma- tion along an arbitrary plane. Huddle and Dobrovolny (1945) stated that the Supai transgresses time lines and probably varies in age from Des Moines (Middle Pennsylvanian) through Leonard (Early Permian) and that the lower member in south- eastern Arizona differs in age from place to place and probably ranges from Des Moines through Wolfcamp (Early Permian). Huddle and Dobrovolny assigned the middle member to the Wolfcamp(?) and Leonard and correlated it with the Abo Formation of New Mex- ico. It may represent the main part of the Supai For- mation and the Hermit Shale of the Grand Canyon. They stated that the upper member is Leonard in age and is about equivalent in age to the Yeso Formation in New Mexico. The Supai Formation of the Paulden quadrangle is assigned a Pennsylvanian and Early Permian age to conform to usage immediately to the east and northwest, although the basal part contains no diagnostic fossils and cannot be definitely correlated with either the Call- ville or the Naco Formations. COCONINO SANDSTONE DISTRIBUTION The Coconino Sandstone is found only in the extreme northeastern corner of the Paulden quadrangle. These exposures are its southwesternmost limit in this area; the formation underlies much of the Colorado Plateau in northern Arizona. In the Paulden quadrangle about half the area underlain by the sandstone is covered by basalt of late Tertiary (?) age. THICKNESS AND STRATIGRAPHIC RELATIONS Less than 400 feet of Coconino Sandstone is exposed because of faulting and because of removal of the upper part of the formation prior to its burial by late Ter- tiary(?) basalt. In the Clarkdale quadrangle the formation is 500-650 feet thick (Lehner, 1958, p. 541). It thickens to the southeast (table 11) and thins and 1 Also see Jackson, R. L., 1951, The Stratigraphy of the Supai for- mation along the Mogollon Rim, Central Arizona: Arizona Univ. M.S. thesis. pinches out to the north and northwest (McNair, 1951, p. 532-534; Noble, 1922, p. 67). The Coconino Sandstone conformably overlies the Supai Formation and intertongues with it as described on page 62. Northeast of the quadrangle the sandstone is beveled by the Toroweap Formation along a sharp, remarkably smooth contact. McKee (1938, p. 15) con- cluded: "Extensive truncation of sloping Coconino laminae to a perfectly flat surface can be accounted for only by beveling of the sediments while still uncon- solidated." LITHOLOGY The Coconino Sandstone is a homogeneous massive fine-grained sandstone having conspicuous large-scale crossbedding. Most of it is very pale orange to grayish orange or grayish orange pink. Quartz is the major constituent; clay and iron oxides and traces of feldspar and heavy minerals are very minor constituents. The quartz grains are rounded to subangular. Many of them are frosted and pitted ; some are stained with iron oxide; a few are clear. Silica forms the cement. Some beds are nearly as resistant as quartzite; some are friable, but many of them are moderately firm. The crossbedding is eolian and individual laminae are as much as 50 feet long. The sandstone weathers to slabs and blocks; it splits readily along bedding planes. Ripple marks and tracks are common. AGE AND CORRELATION The Coconino Sandstone was named by Darton (1910, p. 21 and 27) for exposures in the Grand Canyon, where it is underlain by the Hermit Shale of late Early Permian age (White, 1929). To the southeast the Coconino is underlain by the upper member of the Supai Formation which is Leonard in age. As the Kaibab Limestone (as redefined by McKee, 1938, p. 12) is likewise Leonard in age, the underlying Toroweap and Coconino Formations are also considered to be Leonard (Early Permian) in age. UNCONFORMITY AT THE BASE OF THE CENOZOIC ROCKS A major unconformity and long period of erosion separate the Paleozoic rocks from the Cenozoic rocks in north-central Arizona. Although the thickness (about 300 feet) of the Triassic Moenkopi Formation in Sycamore Canyon (Price, 1949), about 17 miles east-northeast of the Paulden quadrangle, indicates that the formation extended farther south and west, no other formations are known to have been deposited in this part of Arizona until late Tertiary; the oldest known " See also Price, W. E., Jr., 1948, Rim rocks of Sycamore Canyon, Arizona : Arizona Univ. M.S. thesis, 92 p. CENOZOIC ROCKS Cenozoic rocks reported from this area are early Plio- cene (20 miles south of Prescott, J. F. Lance, oral com- mun., 1950). During this period more than 3,000 feet of Paleozoic rocks and an unknown amount of Precam- brian rocks were eroded from the southern part of the Prescott-Paulden area, and lesser amounts were eroded from the northern part. Recurrent uplift and erosion probably occurred in Late Triassic, Late Cretaceous to early Tertiary, and possibly other times. McKee (1937) cited the Shina- rump Conglomerate of Late Triassic age and the gravel deposits of Pliocene(?) age beneath the basalt flows on the Colorado Plateau as evidence of extensive uplift in central Arizona prior to these times. Both contain pebbles and cobbles ranging from Precambrian to Per- mian in age that could only have come from the south- west. The uplift tilted the Paleozoic rocks northward a few degrees and erosion beveled them ; so, successively older Paleozoic rocks and finally Precambrian rocks are found beneath basalt of late Tertiary(?) age as one goes southward across the Prescott-Paulden area. CENOZOIC ROCKS Cenozoic rocks in the Prescott-Paulden area consist of andesite dikes of Tertiary (?) age, sedimentary and volcanic rocks of late Tertiary (?) age, and gravel and alluvium of Quaternary age. ANDESITE DIKES DISTRIBUTION Andesite dikes cut the Precambrian rocks in the south- ern part of the area (pl. 1). They range from a few inches to more than 50 feet in width; some were traced for more than 2 miles. The dikes trend mostly north- ward or east-northeastward. The longest ones trend (1) northward in the Texas Gulch Formation, (2) east- northeastward across the largest mass of gabbro, alas- kite, and alaskite porphyry, and (3) northward in the eastern mass of unnamed tuffaceous rocks of the Alder (?) Group. LITHOLOGY The dike rocks are distinctive in appearance. They are light gray to medium light gray or, rarely, very light or medium dark gray. Fairly fresh outcrops are char- acteristically light brownish gray; brown, yellow, or red shades are typical of weathered surfaces. Mafic minerals may weather out leaving well-defined molds or may alter to limonite. Plagioclase is chalky on weathered surface. Phenocrysts are conspicuous and range from about 1 to 10 mm in length, averaging a little less than 5 mm. plagioclase phenocrysts are generally more abundant 65 and larger than mafic phenocrysts. Most plagioclase is zoned ; some has been resorbed. It ranges from about An,, to Ang,. Locally phenocrysts of hornblende and biotite are more abundant than those of plagioclase; some dikes contain only hornblende phenocrysts. Tiny magnetite and apatite crystals are generally present. The groundmass is aphanitic and consists of plagio- clase microlites and tiny laths in a cryptocrystalline base. The texture is felty. Flow structure, where pres- ent, is brought out by the arrangement of microlites. Some dikes have been slightly altered-the groundmass to calcite, the plagioclase to sericite, and the mafic min- erals to chlorite, calcite, and magnetite or to limonite. Part of the north-trending dike in the eastern mass of the unnamed tuffaceous rocks of the Alder (?) Group is a pebble dike locally packed with fragments of Pre- cambrian rocks ranging from less than 1 to more than 60 mm in length. AGE The andesite dikes are younger than the Precambrian and older than the upper Tertiary (?) rocks. They have been intruded along faults, shear zones, and joints in Precambrian rocks, but none were observed cutting the upper Tertiary (?) rocks. Other evidence in support of a pre-late Tertiary (?) age are (1) the pebbles of dike material in fanglomerate beneath basalt south of Glass- ford Hill (near 1,294,400 N., 358,200 E.) and south of Willow Creek (near 1,304,250 N., 335,400 N.), (2) the apparent cutting off of a dike by the andesite plug south of Glassford Hill, (3) the lithologic dissimilarity be- tween dikes and andesite plugs and flows-most of the dikes contain large plagioclase and hornblende or bio- tite phenocrysts, whereas the plugs and flows lack plagioclase phenocrysts and have generally small mafic phenocrysts-and (4) the slight propylitic alteration of some dikes in contrast to the general lack of altera- tion of the flows and plugs. The andesite dikes intrude faults which may have im- mediately preceded the accumulation of the upper Ter- tiary (?) rocks. On the other hand, uplift and faulting probably occurred intermittently between Late Triassic and late Tertiary ( ?) times, and the dikes may have been intruded at one of these times. A late Precambrian age is unlikely because of the relatively fresh, unrecrys- tallized character of the groundmass. On the other hand, they have not been reported cutting Paleozoic rocks to the north and east. The andesitic dikes are tentatively assigned a Tertiary ( ?) age. UPPER TERTIARY(?) ROCKS The rocks of late Tertiary (%) age in the Prescott- Paulden area are westward extensions of rocks mapped as the Hickey Formation in the Jerome area (Anderson 66 and Creasey, 1958, p. 56-61, (9-83) and the Hickey and Perkinsville Formations in the Clarkdale quadrangle (Lehner, 1958, p. 549-557, 563-566, 551-579) . The terms Hickey and Perkinsville, however, are not used in this report because of uncertainties as to correlation. East of the Prescott-Paulden area the Hickey and Perkins- ville Formations were distinguished largely by struc- tural and physiographic evidence, the Hickey Forma- tion being older and the Perkinsville Formation young- er than the last major post-Paleozoic deformation. No such distinction was possible in the Prescott-Paulden area, where all the rocks appear to be younger than the major post-Paleozoic deformation. The upper Tertiary (?) rocks filled Chino-Lonesome basin and covered most if not all of the area northeast of the basin. They consist of (1) fanglomerate and channel gravel, (2) sand, silt, and clay of fluviatile and lacustrine origin, (3) basaltic flows, dikes, and cinder cones, (4) andesitic flows, plugs, breccias, tuffs, and gravels, and (5) some rhyolitic tuff. Andesite locally separates older gravel and basalt from younger gravel and basalt. Elsewhere, relations of the various litho- logic types, as well as the significance of the andesite and its relation to the Hickey and Perkinsville Forma- tions, are uncertain. Plates 1 and 2 show only the lithol- ogy of the upper Tertiary(?) rocks. Some strati- graphic relations and possible correlations with rocks to the east are shown on plate 4. DISTRIBUTION Upper Tertiary (?) rocks at one time covered most of the Prescott-Paulden area and now occupy about three- fourths of it, although they are largely concealed throughout much of Chino-Lonesome Valley by thin Quaternary deposits. BASALT The most extensive exposures of basalt flows are in the northeastern part of the area, in the north-central part from Paulden southeastward to St. Mathews GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA Mountain, and in the southwestern part. One cinder cone is in the northern part west of the Pinnacle (1,401,000 N., 351,000 E.) ; two cones are in the southern part-the cone that makes up the central part of Glass- ford Hill (fig. 14) and an older cone to the south-south- west. One basalt dike has been mapped in the north- central part (near the center of pl. 2) ; and four in the southwestern part (two a short distance southwest of Granite Dells and one cutting each of the cinder cones, pl 1). ANDESITE n Andesite is widely distributed in the northern part of the Prescott-Paulden area, especially in a belt that ex- tends northwestward from St. Mathews Mountain, a volcanic cone, in the southeast corner (pl. 2). The iso- lated peaks (fig. 19) east of Granite Creek on the north- east side of Chino Valley are plugs or plug domes. Thick accumulations of andesitic gravels, tuffs, mud flows, breccias, massive flows, and plugs or domes ex- tend northwest then west from these peaks. Small plugs and remnants of flows, mud flows, tuffs, and ande- sitic gravels are found north and south of the main ex- posures. - The northernmost outcrops are on and east of Red Butte (1,436,500 N., 394,500 E.). Five isolated masses of andesite are in the Prescott quadrangle-three in the southern part and two in the northern part. A small plug is found south of Glass- ford Hill, and a flow remnant (fig. 14) is found on the northeast side of the Granite Dells; the form of the other masses is unknown. The various forms of andesite are not differentiated on the geologic maps, although the location of some mud flows and gravels are shown (pl. 2). The best ex- posures of the fragmental rocks are west (fig. 21), east, and south of the Pinnacle (1,400,000 N., 353,000 E.). SEDIMENTARY ROCKS The sedimentary rocks that filled Chino-Lonesome basin (pls. 1, 2) are best exposed in the southern part. FiGurE 19.-Andesite plug or dome remnants, north side of Chino Valley. The view is to the north-northeast from east of Granite Creek (near 1,368,500 N., 370,000 E.). extreme right are Precambrian and Paleozoic formations. The dark rocks at the left are the southernmost exposures of Mazatzal Quartzite. Photograph by Museum of Northern Arizona. The rocks at the CENOZOIC ROCKS 67 Northeast of the basin they are well exposed from near Puro (1,391,000 N., 342,500 E.) northeastward to Hell Canyon but are generally less well exposed elsewhere. They are more abundant than the volcanic rocks at the surface, except locally in the southwestern part, in the northeastern corner, and in a northwest-trending belt immediately northeast of the basin. Available data from deep wells (table 12) indicate that sedimentary material is also more abundant than volcanic material, except in the Chino artesian area near the village of Chino Valley. - Unmapped remnants of thin but widespread rhyolitic tuffs occur mainly in the southwestern part of the basin. These tuffs are more widespread than would appear from outcrops, as they are easily masked by pediment gravel and alluvium. They are best exposed in small gullies, prospect pits, and roadcuts-notably the cut at the top of the hill on the new alinement of State Route 69 (pl. 1, 1,292,100 N., 352,100 E.). Thin unmapped beds of fresh-water limestone are rather widely distributed in gravels northeast of the basin, especially (1) south and locally north of the Verde River eastward from its junction with Hell Canyon, (2) along Hell Canyon for about 4 miles south- east of Drake, where the limestone forms a very thin bed above gravel and below basalt, and (3) south of Granite Creek (1,386,200 N., 353,600 E.) and about 1.2 miles to the northeast (1,390,500 N., 358,000 E.). In the southwestern part of the basin a little fresh-water limestone is below the uppermost basalt flow on the ridge south of Willow Creek (near 1,305,500 N., $39,700 E.) and beneath basalt on the south side of Glassford Hill (near 1,300,800 N., 360,500 E.). LITHOLOGY BASALT Flows and dikes.-Basalt flows in and northeast of the basin are similar; those in the southwestern part were studied and are described in more detail than the flows elsewhere. The basalt spread out as sheets, 10-20 feet but locally 50 feet or more thick. Most flows are nearly horizontal and maintain a fairly uniform thick- ness for considerable distances. Many individual flows stand out clearly, but in some places no evidence of in- dividual flows or their attitude can be observed. Rem- nants of a thick sequence of many thin flows can be seen on Glassford Hill (pl. 1; fig. 14), on the north side of St. Mathews Mountain (southeast corner of pl. 2), and elsewhere; but in many places only a few thin flows accumulated between sedimentary rocks, or the overly- ing sequence of flows has been eroded. Few source areas were observed ; most of the basalt probably came from dikes. Much of the basalt in the northern part flowed from the Colorado Plateau rim north of the area along drainage lines into the Hell Canyon-Verde River low- land. Some flowed into this lowland from Black Mesa, northwest of the area. - Some of it may have flowed northward towards the Verde River. The basalt is typical of plateau basalts. Most of it is medium dark to dark gray; some is lighter or darker gray or shades of red. The weathered surface is dark gray or brownish black to very light gray, brown, or olive. Most of the flows have massive interiors and blocky, brecciated tops and bottoms that may be vesicular to scoriaceous or agglomeratic. Thicker, more massive flows generally form steep-walled cliffs along canyons. A few inches of basaltic tuff underlie many flows. Vesicles range from microscopic openings to almond- shaped ones more than 3 inches long; they are rounded, elongated, flattened, and irregular. Many vesicles are filled with calcite; others, with quartz, opal, chalcedony, cristobalite, zeolites, and (or) epidote. Cristobalite spherules are generally about 0.2 mm in diameter ; a few are 1 mm. Flow structure is brought out in places by alinement of vesicles and by alternating layers of vesicu- lar and nonvesicular basalt; it indicates only local flow direction but not the direction from which a flow came. Splatter cone type of accumulations are associated with some flows. On the east end of the ridge south of Willow Creek (pl. 1, 1,306,500 N., 341,000 E.), vesicu- lar basalt grades upward into brecciated and ropy lava that contains abundant lava fragments and bombs. The largest bomb seen was 3 feet long. The bombs may have been carried for some distance on the surface of a flow, possibly from the Glassford cinder cone, as there is no evidence of explosive activity at this place sufficient to eject bombs of this size. Columnar, platy, and spheroidal joints occur in many places in the basalt. Prominent columnar joints are in basalt on the north side of the tilted flow remnant or plug(?) south of Prescott (pl. 1, 1,281,000 N., 338,700 E.), along Hell Canyon, and along the Verde River west of Stewart Ranch (pl. 2) ; crude columnar joints are widespread. Platy and spherical joints are espe- cially abundant in the thicker finely vesicular or non- vesicular portions. Gently dipping platy joints in the basal part of some flows are replaced upward by columnar joints. Linear striations on some platy joints, especially along the gulch east of the east-trending ridge south of Willow Creek, resemble grooves on slick- ensides. Spheroids in this gulch are as much as 6 feet long. The basalt contains phenocrysts of olivine, magnetite, augite, and plagioclase (listed in general order of de- creasing abundance). Phenocrysts make up 5 to rarely 68 GEOLOGY OF THE PRESCOTT AND 25 percent of the rock. Except for those of magnetite, which are generally smaller, the phenocrysts average 'about 1 mm in size, but some are as long as 7 mm. Along Hell Canyon, especially near King Spring (near Gila and Salt River Meridian), large augite and olivine phenocrysts and clusters of phenocrysts measure as much as 4 em across. The large augites are black and have a vitreous luster. In thin section they are light brownish gray, whereas the augite of most of the basalt is colorless to light greenish gray. Some basalt north- east of the basin contains elongated black pyroxene phenocrysts that in hand specimen resemble hornblende. In other places, especially west of the Pinnacle and be- neath the andesite 2,000 and 3,000 feet northeast of St. Mathews Mountain, the basalt contains phenocrysts of light-green pyroxene. These elongated and green pyroxene phenocrysts and a few phenocrysts of biotite make distinguishing basalt from basaltic andesite diffi- cult in places. Much of the olivine is fresh, yellowish or greenish, transparent to irridescent; some is partly altered to iddingsite or less commonly to serpentine and magnetite. Much of it is euhedral, some is resorbed or skeletal, and some is zoned. Plagioclase phenocrysts are zoned; the centers are calcic labradorite, and the margins are sodic labradorite. The groundmass, which is fine grained or micro- crystalline, is felty ; some is intergranular or trachytic. It is composed of plagioclase needles in a base of mafic material, which, where it can be resolved, consists of augite, olivine, magnetite, and a little apatite. The volcanic rock penetrated in water wells is re- ported as basalt or "malapais" ("malpais"), a term used for mafic volcanic rocks. It may be basalt, or some or all of it may be andesite. Most of this volcanic rock is described as red or black and as "coarse" or "porous"- water in the Chino artesian basin comes from "porous malapais." The volcanic material is interbedded with clastic material, some of which is undoubtedly pyro- clastic in origin; some pyroclastic material probably was reported as sand and gravel, and some as "mala- pais." The well-log data suggest that the upper surface of the basalt ( ?) is fairly even and slopes gently upward from the northeast side of the basin to southwest of the village of Chino Valley (fig. 20). This surface should merge near where basalt masses protrude above the Quaternary cover. The buried volcanic rocks, however, may not be part of the outcropping basalt, and the upper surface of the buried volcanic rocks may not have been formed completely by related rocks. Basaltic dikes are lithologically similar to the flows. Platy joints and flattened vesicles occur parallel to their chilled margins. The interior of the branching dike or neck that cuts the Glassford cinder cone is coarser PAULDEN QUADRANGLES, ARIZONA grained than most flows and dikes and has a diabastic texture. Cinder cones and tuffs.-The cinder cone west of the Pinnacle (1,401,000 N., 351,000 E.) is well exposed in the west-flowing gulch that partially dissects the cone. Beds dip 15°%-55° away from its probable center. The rock is moderate brown, moderately dark reddish brown, or very dusky red. It is composed principally of frag- ments of porphyritic, vesicular to scoriaceous basalt. The phenocrysts of greenish pyroxene and brownish al- tered olivine, as much as 2 mm in diameter, are enclosed in a finely vesicular, frothy dark-colored unresolved groundmass. The cinder cone which forms the center of Glassford Hill (1,307,000 N., 362,000 E.) is exposed only around the craterlike depression at the top of the hill and along the northeast-trending gulch that has cut through the overlying basalt and partially dissected the cone (pl. 1, see. D-D' ; fig. 14). Beds dip away on all sides from the dike or neck that is exposed in the depression. No interbedded flows or sills of basalt were observed. This cone was probably built up to a height of about 700 feet and then completely buried by basalt flows, some of which issued from the T-shaped dike or neck near the top. The basalt is conformable to the underlying cinder cone where exposed. Elsewhere around the hill the eroded edges of flows are exposed, and where their attitude could be determined, they are nearly horizon- tal. On the south side (near 1,301,400 N., 359,500 E.) the flows dip gently northward. The thick sequence of nearly horizontal to gently northward-dipping flows on the south side of the hill were at one time continuous with the thick sequence on the ridge to the south. The northward dip of the flows and the surface on which they are deposited (fig. 24 A and B) appears to be a nor- mal feature related to basin filling. This surface sloped gently away from the southern margin of the basin. If the cinder cone was nearly buried by basalt from the south, as appears likely, then the present shape of Glassford Hill is due largely to erosion. The material that makes up the cinder cone is pale to dark reddish brown, grayish red, or pale red. It is well indurated, generally well bedded, and composed of crystal, lithic, and vitric fragments derived from basalt. The basaltic particles are fine ash (shards and pumice), lapilli, bombs, and blocks ; large blocks and bombs are common. A tilted and eroded cinder cone (1,300,000 N., 357,000 E.) southwest of Glassford Hill is largely concealed by float from overlying basalt, but it is well exposed through a vertical distance of about 150 feet in a few gullies. Beds in the lower part dip steeply northward or are nearly vertical; beds in the upper part dip 25° 40°-about normal for cinder cones. The cinder cone CENOZOIC ROCKS R. 2 W. 3986 ® 3925 4070, 3906. , 3888 Iw w ~ "4049 4240 .4245\\ U U 4240. 4246» a 4230 +4255 + 4202~ ©4225 41207, 34 °45)|__ PAULDEN 4440 , \\ , 4480 ms. 4458, s w 4506 "~.. 4349 "4408 4500 *- _ 4459 4537+ -.. . 4442 , 4450 \\o 4366 ~ \\ - » 4450 ~- , 4361 x 23954 Cp PRESCOTT +4563 4568 ~ x ©4650 4590 . 4663 a4spe .* 4449 U , 4530 Is \\ 4618 *~ 4548 x 4560 \\ w x 112°30' i ¥» 0 kes 1 1 3 MILES I 69 EXPLANATION 4900 Outcrop of basalt Outcrop of Mazatzal Quartzite y 4750 Altitude of outcrop , 4054 Well Number indicates reported alti- tude of top of basalt. Some wells also reported basalt at higher or lower altitudes, separated by sedimentary deposits. Wells which were not deep enough to reach basalt or for which no log is available have been omitted --- 4200 --- _--««s. Structure contour on top of buried basalt Dotted where projected from southernmost wells to basalt outcrops FicurE 20.-Structure-contour map of the top of buried basalt in Chino artesian basin. 70 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA material ranges from well to poorly sorted and from friable to fairly well indurated. The lower part is soft, probably because of thermal alteration. In contrast to the Glassford cone, the material that makes up this cone ranges from yellowish gray through yellowish brown to pale or light brown and has a somewhat mottled appear- ance. It consists of well-bedded basaltic ash, lapilli, blocks, and small bombs. The fragments range from less than 1 to more than 60 mm long and are of two types: (1) yellowish or brownish lapilli and shards of basaltic pumice and (2) medium-gray to medium-dark- gray lapilli of scoriaceous, vesicular, and some non- vesicular basalt. Some beds are cemented by calcite; others contain tiny cristobalite spherules. The cinder cone is older than the surrounding basalt and gravel, a fact proved by its more altered character and by its steep dip in contrast to the nearly horizontal attitude of the basalt and gravel that bury it. 'The cone is not part of the Glassford cone, as it dips steeply north. Its rela- tion to the nearby andesite plug is unknown. Some basaltic tuffs are similar to the material that composes the cinder cones, but they are generally finer grained. These tuffs are gray, brown, reddish brown, or red, depending on the color of basaltic lapilli, scoria, and pumice or on the abundance of calcite cement. ANDESITE The topographic expression of the andesitic rocks varies from a subdued rubble-covered surface to sharp peaks, such as the Pinnacle and the peaks east of Granite Creek (fig. 19). The rubble-covered surface formed from fragmental andesite-gravel, mud flow, breccia, and agglomerate-and may make recognition of the form of an andesite mass difficult or impossible. The sharp peaks are composed of massive to flow-banded or platy-jointed andesite or of consolidated flow breccia or agglomerate. Some weathered surfaces are lumpy due to abundant inclusions or to autobrecciation. Prominent columnar joints were observed only in the flow remnant northeast of the Granite Dells-one of the few recognizable flows in the area. Flow bands and platy joints, mostly steeply dipping and parallel, but in places fan shaped, are common in much of the non- fragmental andesite; flow bands are visible in some blocks in fragmental rock. Phenoccrysts, plagioclase microlites, and some basic inclusions are parallel to the flow or platy structure but may have random orienta- tion within the plane of flow. Fragments in mud flows are angular to rounded; most of those in breccia and agglomerate are subangular. They range from little larger than groundmass par- ticles to several feet or even tens of feet in size; many rounded ones in mud flows are about 2 feet in diameter. Angular to subrounded basic inclusions are abundant in and near source or probable source areas. They are as much as 5 inches long and consist of (1) granular aggregates of light-green pyroxene (diopside?) con- taining or lacking reddish garnet, (2) aggregates of - biotite containing minor plagioclase, (3) large crystals of dark-colored pyroxene, mostly altered to aggregates of coarse hornblende, (4) greenish-brown hornblende, (5) basaltic(?) hornblende containing or lacking mag- netite, and (6) various mixtures of the foregoing min- erals. The andesite consists of hornblende andesite, biotite andesite, and basaltic andesite. Gradations are com- mon between biotite and basaltic andesite; most con- tacts between basaltic and hornblende andesite are abrupt. Lithologic types have not been separated on the maps. Biotite andesite is most abundant, especially on St. Mathews Mountain and on some of the peaks east of Granite Creek. The most extensive biotite-ande- site mud flow is east of the Pinnacle and underlies hornblende andesite mud flow near the base of the sec- tion. Hornblende andesite is confined principally to the area south of the Verde River for about 5 miles east of Route 89 (pl. 2) and to the andesite (pl. 1) northeast of the Granite Dells and west of Granite Creek (near 1,359,000 N.). As many as three horn- blende andesite mud flows interfinger with andesitic gravel and tuffaceous deposits beneath andesite breccia and massive andesite in the southwest-trending gulch south of the Pinnacle. The principal areas of basaltic andesite are west of the headquarters of King Canyon and about 114 miles east-southeast of the Pinnacle (pl. 2, near 1,384,000 N., 380,000 E., and 1,397,900 N., $60,- 300 E.), each area occupying about half a square mile. - The scarcity of mafic minerals (low color index) sug- gests that the hornblende andesite may be a dacite rather than an andesite. The index of refraction of obsidian and of some white pumice tuff associated with andesitic gravel is about 1.50; it indicates andesite or dacite (George, 1924, p. 368). Hornblende andesite.-The hornblende andesite is a medium light gray to medium dark gray dense siliceous- looking rock containing phenocrysts of hornblende. Some glassy rocks are nearly black and have tiny horn- blende needles; others have light grayish-brown zones, probably caused by slight devitrification, that gives a brecciated appearance. Vesicles are generally lacking. The flow on the north- east side of the Granite Dells (pl. 1), however, contains miarolitic cavities with small transparent light olive- gray hornblende prisms about 1 mm long associated with orthoclase and spherules of cristobalite. Hornblende is the only megascopic mineral, except CENOZOIC ROCKS TI for minerals in basic inclusions and for scattered light- green pyroxene crystals. The hornblende crystals are 0.1-5 mm and rarely 1 cm long. Some crystals are clustered. Most hornblende is fresh, but some is partly to completely altered to aggregates of granular mag- netite. Some is resorbed or skeletal. Most of it is pleo- chroic in shades of green to brown, but some is reddish brown to yellow. Microscopic phenocrysts are of unzoned plagioclase 0.1 to 0.3 mm long and minor amounts of magnetite or ilmenite, apatite, sphene, pyroxene, and, in a few places, quartz, possibly as xenocrysts. Pyroxene is colorless or slightly green in plain polarized light. The ground- mass is cryptocrystalline to glassy and contains micro- lites and small laths of plagioclase, mostly less than 0.01 mm long. Biotite andesite.-Included in the discussion of bio- tite andesite-more properly biotite-pyroxene ande- site-is much andesite that contains little or no biotite but that otherwise resembles biotite andesite. Biotite andesite is various shades of gray to nearly black. Much of it has a brownish or olive cast; some is reddish. Some biotite andesite mud flow is light brown to yellow- ish orange. A mottled appearance is due to alteration or devitrification of glassy groundmass or to differences in abundance of small vesicles. Vesicles are flattened and alined parallel to flow banding or to platy joints. Calcite, chalcedony, cristobalite, opal, quartz, tridymite, or zeolites (or combinations of these minerals) line or fill the cavities. Phenocrysts are of pyroxene, which is generally the most abundant, biotite, magmetite, apatite, and, very rarely, plagioclase. Pyroxene phenocrysts are 0.1-1 mm or, rarely, 1 cm in maximum dimension. Larger crys- tals and glomeroporphyritic aggregates are probably inclusions or basic segregations, not phenocrysts. Most pyroxene is light green, glassy, and granular. Few biotite crystals are larger than 1 mm in diameter by 0.1 mm thick, but some are twice that size. Most biotite is pleochroic, ranging from greenish brown to light yellow; some is reddish brown. Biotite is fresh, altered around the margins, or completely altered to aggregates of granular magnetite. Tiny needles and plates composed of granular magnetite are common in some andesite that contains no unaltered biotite. Some of these aggregates have the shape of hornblende. Mag- netite phenocrysts are rarely as much as 0.5 mm in diameter. The groundmass is aphanitic to glassy and composed of glass, devitrified glass, or an unresolved crypto- crystalline base containing plagioclase microlites or laths. The laths are mostly less than 0.1 by 0.11 mm in size; many are less than 0.02 mm long.. Pyroxene and magnetite can be recognized in the groundmass in a few thin sections. The texture is hyalophitic or felty and locally trachytic. Some groundmass has been par- tially replaced by calcite. Basalitic andesite.-The mineralogy of the basaltic andesite is for the most part similar to that of the biotite andesite, but both light-green pyroxene and bio- tite may be absent from some of the rock. The basaltic andesite is darker than much of the biotite andesite. Olivine phenocrysts are common in rock that may or may not contain needlelike or platelike aggregates of granular magnetite, light-green pyroxene, or basic in- clusions. Some olivine is partly to completely altered to iddingsite or to iddingsite having centers of antig- orite(?). Some is unaltered or only slightly altered, even in rocks that contain the aggregates of granular magnetite. Altered olivine, biotite, hornblende( ?), and, rarely, pyroxene are reddish or orange in these rocks. Some basaltic andesite has a speckled appearance caused by abundant phenocrysts as much as 1 ecm across composed of light-green pyroxene and other mafic min- erals. Origin of the andesite-The andesite was probably extruded and spread out from volcanic domes-endog- enous and exogenous domes and plug domes (Wil- liams, 1932). Evidence for this conclusion includes the steep to vertical flow planes and platy joints-some fan-shaped-the abundance of basic inclusions in ande- site close to source and probable-source areas, and the abundance of fragmental material that in many places grades upward through andesitic gravel, tuff, and brec- cia to massive andesite (fig. 21). Basic inclusions prob- ably represent early segregations from the magma and not xenoliths, as they are similar over widely scattered areas. Forceful intrusion of andesite is suggested in several places; an example is the plug east of the Pin- nacle that is partly surrounded by steeply dipping Pale- ozoic rocks (pl. 2, see. The attitude of a steeply dipping zone of tuff and glassy welded or fused tuff that is conformable to the north side of a hill of Paleo- zoic rocks (near 1,378,800 N., 377,800 E.) is probably due to flow of a mass of the nuée-ardente type against the limestone hill. Fragments of limestone in the tuff are bleached and altered owing to the high temperature of the tuff. SEDIMENTARY ROCKS The exposed sedimentary rocks in the southern part of Chino-Lonesome basin consist of fanglomerate, mud flows, and some interbedded rhyolitic and basaltic tuf- faceous material around the margins; in the interior of the basin these sedimentary rocks include channel gravel, sand, silt, clay, and marl and some rhyolite tuff. From the exposed Precambrian rocks to the south, the fanglomerate grades outward and upward into finer 72 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA FIGURE 21.-Volcanic and sedimentary rocks of late Tertiary(?) age near Granite Creek (1,401,500 N., 348,300 E.). Tob, massive andesite breccia ; Tas, lighter colored bedded tuff, breccia, and andesitic gravel ; Th, basalt flow ; and Tg, gravel. particles; some interfingering of coarse and fine mate- rial occurs. Most of the material that is 1-2 miles away from the Precambrian rocks is fine sand, silt, clay, and marl. The coarse and fine materials are not shown separately on the geologic map (pl. 1), but their ap- proximate distribution is indicated on plate 4. Logs of wells in Chino Valley show a large amount of fine material, either "clay" or "volcanic ash." In the north- western part of the area (pl. 2), the sedimentary mate- rial is so poorly exposed that little about its character is known with certainty. Both coarse and fine material is exposed locally. Northeast of the basin most of the sedimentary material is coarse grained and accumulated in channels; some (southwest of Drake) resembles the finer grained beds in the interior of the basin. The sedimentary rocks have a wide range of color. Many gravels are various shades of greenish or yellow- ish gray, but in the northeastern part of the area, many of them are shades of red owing to abundant material derived from the Supai Formation; others are gray owing to abundant basalt fragments. Mud flows are generally pale red to yellowish brown (buff); the rhyolitic tuffs are white, buff, pale red, or shades of orange pink, reddish orange, and reddish brown. The clay, silt, and fine sand of the interior of the basin are pale orange to moderate or grayish orange pink; the interbedded marly layers are very pale orange to nearly white. Gravels in the southern part of the area are composed of Precambrian fragments, generally a heterogeneous mixture, except close to a source area, where the frag- ments may be largely of one kind. Where granitic rocks were deeply weathered, the overlying gravel con- tains little granite. Northeast of the basin many gravels, especially south of the Verde River, are com- posed of about equal amounts of fragments of Precam- brian and Paleozoic rocks, but locally, rocks of one era may predominate almost to the exclusion of rocks of the other era. The Precambrian fragments in this area are largely from the Alder Group but include intrusive rocks and Mazatzal Quartzite; the Paleozoic rock frag- ments are largely from the Martin and Redwall. In the northeastern part of the area the Paleozoic fragments are largely from the Supai and Coconino Formations. Scattered basalt fragments, composing generally less than 1 percent of the gravels at any one locality, are widely distributed in the coarser sedimentary rocks, especially in the southern part of the basin. Basalt fragments, however, may be very abundant in some gravels that are interbedded with or overlie basalt flows, and some of these were derived from penecontempora- neous flows. In the northeastern part of the area, much of the gravel is composed largely of basalt. Basaltic gravels have been reported in deep wells. The fragments are angular to subrounded ; many are subangular, but channel gravels are generally more CENOZOIC ROCKS 73 rounded. Those composed of schistose Precambrian rocks are platy ; many of those from the Coconino Sand- stone are slabby. The degree of sorting varies from bed to bed and from one locality to another. Some beds or lenses, especially along Hell Canyon, consist of closely packed pebbles or cobbles and a minimum amount of fine-grained material; others consist largely of sand or silt and only a few scattered pebbles, cobbles, or bou!l- ders. Some of the material, especially in the south west- ern part, accumulated as mud flow on alluvial fans. Some mud flows are composed largely of tuffaceous ma- terial. Accumulation as mud flows is suggested by the local chaotic jumbling of cobbles and by scattered boul- ders, some more than 6 feet long, in nonbedded and non- sorted fine sand, silt, or clay. A good example of fine- grained mud flow is exposed in the gulch east of the road to Williamson Valley and Simmons (pl. 1; 1,313,500 N., 326,000 E.). Away from the margins of the basin the nearly hori- zontal well-bedded fine-grained character of much of the sedimentary material (fig. 25), the intercalated cross- bedded sands, and the sand- and pebble-filled channels indicate a lacustrine origin, possibly in playa lakes. This material is well exposed along lower Lynx Creek and the Agua Fria River and in roadcuts along the new alinement of State Route 69 near Fain Ranch (pl. 1; 1,298,000 N., 397,000 E.). The sedimentary rocks are variably cemented, some sufficiently enough to form cliffs ; others are almost com- pletely unconsolidated. Consolidated and unconsoli- dated material is interbedded in places. Along Hell Canyon the gravel is virtually a conglomerate and is so firmly cemented that it breaks across pebbles. Chalce- dony, opal, or zeolites, probably formed by hot springs associated with volcanism, cement some gravels and tuffs. Much of the cement in gravels is calcium car- bonate, but little or no calcium carbonate, silica, or zeo- lites cements the clay, silt, and many of the rhyolitic tuffs. Some rhyolitic tuffs, however, have a calcareous cement, and calcite crystals that poikilitically enclose grains of tuff are as much as 1 cm in diameter. Spheri- cal concretions in sandy tuff a short distance south of the Granite Dells (1,306,400 N., 347,300 E.) are 8-10 cm in diameter and consist of an exterior shell of sandy tuff in which the calcite cement has a radial arrange- ment. The centers (about 4 cm in diameter) of the con- cretions consist solely of coarsely crystalline calcite. Tuff aceous rocks-Relatively pure tuffs that are rhyo- litic in composition and mixed tuffaceous sedimentary rocks form part of the sedimentary sequence; most of them are associated with the basin deposits. The pure tuffs are much less abundant than the mixed tuffaceous rocks, which may contain basaltic material. Some silt and clay in the southeastern part of the area and prob- ably some so-called clay and volcanic ash reported from deep wells in the Chino Valley area is rhyolitic tuff. The tuffs and tuffaceous rocks are variable in texture, composition, color, degree of sorting, bedding, consoli- dation, and type of cement. Interbedding with and gradations into nontuffaceous rocks are common. The tuffaceous rocks range from clay to gravel and locally contain scattered cobbles and boulders. Most tuffaceous - deposits observed are 1-2 feet thick; some are as much as 25 feet thick. Most pure rhyolitic tuffs are white, except where they are shades of red owing to baking by overlying basalt; some are buff. They are massive to thinly bedded, local- ly crossbedded, well to poorly sorted, and fine to coarse grained; they contain lapilli as much as 5 em long. Most particles are angular, but some quartz grains (original phenocrysts?) are rounded. The tuffs are composed of vitric, crystal, and lithic fragments. The vitric fragments are shards, grains, and pumice lapilli ; the lithic fragments are gray rhyolite lapilli ; the crystal fragments are quartz, orthoclase, plagioclase, and a little biotite and magnetite. These same minerals occur as phenocrysts in pumice and rhyolite lapilli. The plagio- clase is about An,, ; some is zoned. The groundmass of the rhyolite is eryptocrystalline to glassy ; some has been devitrified. The index of refraction of the shards is about 1.485 and suggests a rhyolite (George, 1924, p. 368). A prominent 10-foot thick bed of gray tuff, used for building stone, is well bedded, locally crossbedded, or massive. The medium-grained, coarse- to fine-sand particles consist of round gray vitric grains (index of refraction of 1.495) and sparse to abundant shards, dust, and tiny pumice lapilli. Some thin layers resemble sandstone and are composed of well-sorted pumice and rounded vitric grains; the vitric grains appear to be molded on each other and on scattered crystal grains. The best exposures of this rock are near 1,305,000 N., 331,800 E. (pl. 1). f An orange-colored tuffaceous sedimentary rock from a few inches to about 10 feet thick generally underlies the "middle" basalt flows north and northeast of Pres- cott (fig. 24A). It grades downward into pure white rhyolite tuff or into fanglomerate and upward into ba- saltic tuff. The "orange tuff" contains fragments com- mon to these rocks. Its color is due in part to altered mafic, lithic, and crystal fragments, to basaltic scoria, pumice, lapilli, and shard, and, in part, to limonitic and hematitic staining of the matrix caused by baking. Fresh-water limestone.-The fresh-water limestone, . which ranges in thickness from a few inches to about 10 feet, is thinnest along Hell Canyon and near Granite Creek and thickest along the Verde River, where more than one bed occurs in gravel. Some of the limestone 74 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA is more resistant to erosion than is the gravel ; it forms weak cliffs and breaks into very angular chunks. Clastic grains and pebbles of quartz and other mineral and rock fragments are common and abundant where the lime- stone grades into grayel. The rock weathers rough, owing to exposed pebbles and grains or to holes left by their removal. The dense limestone has a very low siliceous content and contains microfossils, gastropods, and stem molds(?). Much of the limestone is massive, but some is finely laminated. It ranges from white to shades of gray and very pale yellowish brown ; some is mottled. The dark-gray color, characteristic of some limestone along Hell Canyon, is due to amorphous or- ganic material. The fossils indicate deposition in shal- low temperate to cold fresh to brackish or saline water (see p. 80). THICKNESS The thickness of the upper Tertiary(?) rocks in Chino-Lonesome basin was probably at least 2,000 feet in the deepest portion before the top was removed by erosion. Gravel-strewn pediment remnants and the superposition of Granite Creek across the Dells Granite and Mazatzal Quartzite (pls. 1, 2; figs. 29, 30) prove that the upper surface of the upper Tertiary (?) rocks is one of erosion ; the creek was let down from the over- lying upper Tertiary(?) rocks or from pediment gravels cut on them. That some of the local thick ac- cumulations of basalt originally were more extensive is indicated by the eroded edges of thin nearly horizontal flows. The greatest known thickness of sedimentary material is about 1,000 feet, and the thickest uninter- rupted basalts are about 500 feet. Much of the infor- mation on the thickness of the basin fill has been obtained from logs of wells. Deep wells near the center of the basin have not penetrated bedrock; the basin apparently becomes deeper towards the northwest at least as far as the headwaters of the Verde River. The distribution of the wells is shown on plate 3; the prob- able configuration of the basin, in figure 22; and the present minimum thickness of deposits, in figure 23. The well-log data are summarized in table 12. About half a mile southwest of the Granite Dells, well 1 in see. 14, T. 14 N., R. 2 W. (1,306,200 N., $45,000 E.), penetrated 1,013 feet of sedimentary material but did not reach bedrock. Above the collar of the well, about 325 feet of interbedded basalt flows and sedi- mentary rocks are exposed to the top of the east-trending ridge (1,305,500 N., 336,500 E.). Thus a total of at least 1,338 feet is indicated in this area. The uppermost flow on this ridge was at one time continuous with the uppermost flow (1,301,500 N., 350,000 E.) east of Gran- ite Creek (pl. 1, sec. B-2'). More than 300 feet of basalt may have overlain this uppermost flow if the Iq +8 A o « A Ist //// X y * A f \( A A\ y L TZ¥ - # %\ ax PAULDE:\ \\ C \ %: \ QUADRANGLE eB \ \ PRESCOTT ‘\ fa é UADRANGLE | F 34°45" § / 34°30 EXPLANATION Contact between Precambrian and Paleozoic basement rocks (lined pattern) and upper Tertiary(?) volcanic and sedimentary rocks -- -4500 --- Contour showing probable configuration of Chino-Lonesome basin as extrapolated from outcrops and well data FisURrE 22.-Probable configuration of Chino-Lonesome basin in which volcanic and sedimentary rocks were deposited. nearly horizontal basalt flows that form the ridge south- southwest of Gassford Hill extended westward. In the southeastern part of the area, about 800 feet of nearly horizontal sedimentary material is exposed in- termittently from near the point where Clipper Wash leaves the quadrangle (1,291,300 N.) to the base of the basalt flow on the south side of Glassford Hill. East of the southern part of the map area, a well (No. 1, sec. 11, T. 13 N., R. 11 E.; 1,282,300 N., 405,500 E.) entered Precambrian bedrock about 740 feet below the lowest exposures on Clipper Wash; the total amount of sedi- mentary material, therefore, may be 1,600 feet. Near the village of Chino Valley, many wells that tap the Chino artesian area bottom in upper Tertiary (?) rocks as much as 768 feet below the surface; some of CENOZOIC ROCKS 75 PAULDEN Q PRESCOTT QUADR - ¥ } 1 I 1 2. MILES Lemna e PLO 12°15" EXPLANATION smu Contact between Precambrian and Paleozoic basement rocks (lined pattern) and upper Tertiary(?) volcanic and sedimentary rocks 2 0-500 500-1000 More-athan 1000 Present minimum thickness, in feet, based on well data Ficurm 23.-Approximate present minimum thickness of volcanic and sedimentary rocks of late Tertiary(?) age in and adjacent to Chino- Lonesome basin. them cut as much as 500 feet of "malpais." One well (No. 1, see. 17, T. 16 N., R. 1 W.) is reported to have bottomed in basalt 1,085 feet below the surface. A wildeat oil well (No. 1, sec. 32, T. 18 N., R. 2 W.) re- 758-447 O-65--6 portedly entered bedrock about 1,000 feet below the surface. Another wildeat oil well (No. 1, see. 20, T. 18 N., R. 2 W.) closer to the margin of the basin entered bedrock 600 feet below the surface. An additional 200 feet or more of sedimentary material remains above the collars of some of these wells and below the pediment gravels that cap nearby hills. Erosion has been greater in this area, which is the headwaters of the Verde River, and at the southeast end of the basin than elsewhere. Northwest of the Prescott-Paulden area, the deepest well for which I have a record is 700 feet. Northeast of the basin, the upper Tertiary (?) rocks are thinner, except for thick accumulations of volcanic rocks, probably around vents. Basalt ranges from 10 to more than 500 feet in thickness (at the north side of St. Mathews Mountain) ; accumulations of 200-300 feet are on the mesa about 3 miles northwest of St. Mathews Mountain, near the headwaters of Muldoon Canyon (1,395,000 N., 366,500 E.), and south of Stewart Ranch (1,407,800 N., 354,500 E.). The maximum known thick- ness of andesite is 850-1,000 feet on the Pinnacle, St. Mathews Mountain, and the two peaks between them; some thick accumulations may represent plug or domal material intrusive into earlier andesite. About 300 feet of massive andesite breccia underlain by breccia, tuff, and andesitic gravel is exposed (fig. 21) along Granite Creek south of the Verde River. Gravel in the central part of the area northeast of the basin filled shallow de- pressions and local channels and is mostly less than 200 feet thick. It is thickest near the lowland along the Verde River, where it may have been downwarped when the structural low was formed rather than have accu- mulated in the lowland. The top of the gravel, which is a relatively level surface beneath basalt or andesite, may be erosional. Northeast of Hell Canyon the max- imum thickness of combined basalt and gravel is about 300 feet, but in many places, especially along Hell Canyon, it is less than 150 feet thick. Basalt generally makes up most of the known thickness. The gravel portion is very thin; some gravel along Hell Canyon forms a sheetlike deposit less than 50 feet thick. Thicker sections of gravel are in the general area where the gravel is most extensively exposed-in the neighbor- hood of Bar Heart Ranch and Schwanbeck Tank. AGE During Cenozoic times volcanic and sedimentary rocks accumulated throughout Arizona. Volcanic ac- tivity was dominant at various times and places, depo- sition of clastic material was dominant at others, and at still other times volcanic and sedimentary material were deposited in nearly equal amounts. Discovery of diagnostic fossils or physiographic and structural re- lations locally indicate that many of these rocks are 76 TABLE 12.-Summary of well-log data in Chino-Lonesome Valley, Arizona GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA [Compiled from data supplied by H. C. Schwallen, State Land Office, University of Arizona, Tucson, Ariz., and by drillers and ranch owners and from data on file with the U.S. Geological Survey. Not all data are reliable, and the table reflects the author's interpretation of the available data. Some well altitudes are approximate. Basalt refers to volcanic rocks reported in logs as "malapais (malpais)," "lava," and "basalt'"-some may be andesite; where more than one figure is given for altitudes of the top and bottom of basalt, the lavas are separated by clastic deposits; figures for some thin beds of clastic deposits have been omitted from the calculations. Where the figure for the bottom altitude of a well is underlined and followed by the symbol "br," the well entered bedrock at the given altitude] Well Basalt Thickness, in feet, of overlying (a), intervening, and Section and well Altitude (feet above sea level) Altitude (feet above sea level) underlying (b), Depth (feet) ‘Thickness (feet) sedimentary | deposits Top Bottom Top Bottom T. 18 N., R. 3 W. ‘ Seo. o, well 1.......:......... 4, 450 3, 750 700 'Me 700 22 wel 1:.._.....;.:0.... 4, 417 3, 917 500 Mer esen i| n a rena ren as 500 T. 18 N., R. 2 W. See. 20, well' 4, 500 2, 440 2,000: |. c ile narnia t 600 |=. ns l _E calan ank s= sr S2, well 4, 385 3, 385br 1,000 |. cle rei ren are aas (?) T. 17 N., R. 2 W. See. 26, well- 4, 446 4, 171 275 4, 441 4, 429 12 ba 4, 416 4, 408 8 13 4, 396 4, 388 8 12 217b 4, 489 3, 986 503 4, 486 4, 469 17 3a 4; 4, 457 4, 447 10 12 4, 427 4, 417 10 20 229 or 431b 84, well 4, 500 3, 925 575 4, 325 4, 314 11 175a 3, 986 3, 925 61 328 sensilla cosas 4, 500 4,115 SBB Ee err ien ir nece os $- 4, 500 3, 913 587 4, 290 (?) STT! { 4, 070? (?): c |e via ewa slack r as 4, 514 3, 792 722 4, 291 4, 229 62 228a 3, 906 3, 792 114 323 4, 515 3, 795 720 3, 9257 3, 9047? 217 588g]? 1 95, well 1........-..e.-.= 4, 508 3, T78 730 4, 446 4, 108 338 62a 3, 888 3, 808 80 220 3, 801 3, 778? 11? 7 12?b P te- scams 4, 525 3, 808 717 4, 090 4, 075 157 435a 4, 0607 3, 8157 2457 15? 7?b sans. 4, 510 4, 190 $20 |. is.... egen icc es.. 320 T. 16 N., R. 2 W. See. I, well 1_:.._i...z.le.... 4, 591 3, 891 700 3, 954 3, 891 63 637a 2, well 4, 550 3, 988 562 4, 054 4, 048 6 428?) Re Ao 4, 550 3, 830 720 (?) (?) (?) ( 55m o, well cL. .s cule 4, 532 4, 016 516 4, 049 4, 016 88 483a 4, 574 4, 045 520 |_ :. Lole eel e tesa iL a er ~- 4, 575 4, 075 500 4, 202 4, 185 17 373a 4, 099 4, 075 24 86 4, 575 4, 075 500 4, 225 4, 075? 150? 350a $:. cc ci cde. 4, 582 4, 050 532 4, 262? 4, 2597 3? 3207a 4, 0957 4, 059? 367 163;b luces 4, 584 3, 918 666 4, 0497 3, 918 131? 535a Ts 4, 592 4, 010 582 4, 142 4, 0107 132? 450a S NE. 4, 575 4, 034 541 4, 132 4, 034 98 443a . irilecaes 4, 597 4, 010 587 4, 162 4, 010 152 435a 4, 602 4, 013 589 4, 1207 4, 013? 107? 482?a CENOZOIC ROCKS TABLE 12.-Summary of well-log data in Chino-Lonesome Valley, Arizona-Continued T7 Well Basalt Section and well Altitude (feet above sea level) Altitude (feet above sea level) Thickness, in feet, of overlying (a), intervening, and underlying (b), Depth (feet) Thickness (feet) sedimentary deposits Top Bottom Top Bottom iT. 16 N., R. 2 W.-Continued Seer 4, well 1.........._..... 4, 568 3, 948 620 4, 068 4, 038 30 500a 3, 9937 3, 948 457 45? des 4, 600 4, 100 500 4, 110? 4, 100 10 4907a elec i anns 4, 600 4, 115 485 4, 240 4, 210 30 360a 4, 150 4, 115 35 60 Ar ai 4, 600 3, 900 700 4, 436 4, 420 16 164a 4, 246 3, 900 346 174 el.. 4, 600 4, 040 560 4, 230 4, 200 30 370a 4, 140 4, 115 25 60 T5b Uncen. ue 4, 600 3, 988 M12: IAL 2s aon ane o t ans sm ss ao 4, 600 4, 020 580 4, 240 4, 210 30 368$b 19 ne .. 4, 600 4, 080 520 4, 240 4, 220 20 360a 4, 150 4, 080 70 70 Yee 4, 650 3, 882 768 4, 340 4, 320 20 310a 4, 255 4, 140 115 65 3, 985 3, 915 70 155 33b 5, well 4, 567 3, 870 697? 1222, snes snes -s 6977 o well 1l.-.:...........C. 4, 650 3, 885 7657 4, 278 3, 885 393 372a TO, well 4, 650 4, 050 600 4, 3527 4, 064 288? 2???) ee s= nsa 4, 600 3, 919 681 4, 000 3, 919 81 6007a erea 4, 654 3, 954 700 4, 304 4, 204 100? 350a 2507b ________________ 4, 633 4, 037 596 4, 309 4, 037 272 324a lif well 4, 621 3, 921 700 4, 231 3, 9217 3107 390a ce: 4, 560 4, 000 560° |. 22 sl re reale noe c 560 G s es 4, 611 4, 111 500 4, 261 4, 111 150? 3507a cs 4, 600 3, 956 644 4, 050? 3, 986 64 5383?) 4, 628 3, 989 630. (|. RALI Ee lene taa co aps 4, 600 4, 065 535 4, 210 4, 138 72 390a 4, 135 4, 065 70 3 A 4, 600 3, 980 620 4, 185 3, 980 205 415a sus 4, 582 4, 042 540 4, 382 4, 042 3407 200a Uterine dle nan 4, 600 4, 020 580 4, 185 4, 020 165 415a 4, 600 3, 900 700 4, 000? 3, 900 100? 600a 12, well 4, 600 3, 956 644 4, 150 3, 970 180 $32?) este 4, 600 3, 856 744 4, 285 3, 8567 429 315a Seuss ne eact 4, 700 3, 7407 9607 4, 530 3, 7407 7907 170a 14, well 4, 600 4, 100 500: |i c_s.2n Leili. (un unases cass Melle eac eties. 4, 602 4, 052 550 4, 102 4, 052 50 5007a evere neenee 4, 650 4, 063 587 4, 250 4, 063 187? 4007a As ec 4, 650 3, 953 697 4, 330 3, 953 377 320a sab 4, 656 4, 016 640 4, 351 4, 029 322 305a 4, 018 4, 016 2 11 to well 4, 700 4, 134 566 4, 405 4, 155 250 2331) A tees 4, 664 4, 059 605 4, 274 4, 059 215 390a 4, 700 4, 200 500 4, 366 4, 200 166 334a eee ncr senna 4, 689 4, 169 520 4, 349 4, 169 180 340a aa mesys 4, 699 4, 389 510. {cece :a see onan 310 4, 700 4, 109 591 4, 440 4, 109 331 260a Si, well 4, 750 4, 347 403 4, 480 4, 347 133 270a ( 4, 750 4, 337 413 4, 476 4, 337 139 274a ..a 4, 700 4, 300 400 4, 440 4, 300 140 260a 4, 775 4, 348 427 4, 568 4, 348 220 207a el 4, T75 4, 368 407 4, 563 4, 385 178 2g?) Messi lae aka ces 4, 750 4, 350 400 4, 500 4, 350 150 250a va, well 1.............-.- 4, 735 4, 134 601 4, 4597 (?) (?) (gash y Fle ro ne angie a 4, 737 4, 136 601 4, 537 4, 242 295 200a 4, 232 4, 136 96 10 78 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA 12.-Summary of well-log data in Chino-Lonesome Valley, Arizona-Continued Well Basalt Thickness, in feet, of overlying (a) intervening, an Section and well Altitude (feet above sea level) Altitude (feet above sea level) underlying (b), Depth (feet) Thickness (feet) sedimentary deposits Top Bottom Top Bottom 'T. 16 N., R. 2 W.-Continued Seo. 22, well 8:.::.:........2. 4, 725 4, 125 600 4, 458 4, 230 228 267a 4, 210 4, 125 85 20 TR Ige c ae aab 4, 700 4, 270 430 4, 5007? 4, 270 2307 2007a Dere o- sant 4, 750 4, 550 200 IIR rine camas nae lass h ald a a nee 200 Cie: 4, 725 4, 025 700 4, 450 4, 102 348 23? b ________________ 4, 725 4, 177 548 4, 442 4, 177 265 283a 25, well 1:."_;:_..;.0_ 033 4, 703 4, 403 800 (BE: iN: NAI av ee ases eee 300 saul ea 4, 650 4, 132 518 4, 361 4, 132 2297 289a \ fern oli reala t' 4, 650 4, 315 335 4, 450 4, 3157 135? 2007a 26, well 1 4, 750 4, 300 450 4, 560 4, 3007 2607 1907a 27, well 000 4, 763 4, 345 418 4, 449 4, 3457 104? 314a 4, 764 4, 311 453 4, 528 4, 404 124 236a 4, 368 4, 345 23. 36 34b BVH... cua 4, 725 4, 525 200 4,580f: 12. .. 57 195?a PLLA I3 4, 800 4, 610 190 4, 618 4, 610 8 182a 4, 820 4, 153 667 4, 663 4, 346 329 145a 4; 161br? |- .. coe ie re rr -le s rea sake sea Inas anew cack 1857b s, well 1 -... _ 4, 850 4, 600 2507 4, 650 4, 600 50 200a ________________ 4, 820 4, 420 400 4, 640 4, 420 220 180a So, well 4, 850 4, 530 320 4, 590 4, 530 60 260a 34, well 1-.._......._._.L 4, 799 4, 529 270 4, 729 4, 529 200 7Oa a ee as neues 4, 829 4, 590 200 |: cries on eens 35, well1 _.. 4, T78 4, 543 235 4, 548 4, 548 5 2307a Pee det ~* < auks ae 4, 800 4, 258 542 4, 650 4, 2587 392? 150a T. 15 N., R. 2 W. gee 17, ._ 5, 057 4, 627 4850" |...... NLL I els ele lr 19, well lc. 5, 150 4, T72 378 5, 070? 4, 900? 1707 138?) Si, 5, 069 4, 709 100} |L cee e an sss anes 28, well _s 5, 076 4, 498 DTB il a e lass =s etka awe 5787 95, well 1-..l._...._.._.ZL_C.. 5, 010 4, 171 839 4, 360 4, 213 147 650a 4, {L .e ce ele cn an en er ne - l- c noe eae a 42b or br? Pede aaa -a ale alas 5, 014 4, 202 812 4, 364 4, 222 142 628?) 26; well 5, 025 4, 663 Bb2 (ees al: oen irae sa ans 362 50, well 1: 5, 185 5, 035 150, AIE ase 150 PSLE a creas 5, 199 5, 019 180 5, 049? 5, 019 30? 1507a Sewell 5, 300 5, 168 192 .L. Loca ane we na an [e's eau anes a - 30, well 5, 050 4, 680 SM 2C Le salen 370 T. 14 N., R. 2 W. Rec. 1, well 1_:.....l..:.:.l.__. 5, 025 4, 854 171 12: 8: so Ens aL Ar s: sash 171 10, well 5, 220 4, 326 894 4, 6207 4, 580 407 222338 14, well 5, 196 4, 973 225. |k c n 223 ene 5, 200 4, 920 280 seen sms 280 ________________ 5, 200 4, 187 1, 013 5, 200 5, 190 10 1, 003b 21, well 5, 350 5, 060 290 . |:: 120 D 200BL : |. c aes s bl m 5, 565 5, 261 304 5, 4657 5, 4137 527 £311) Susie. e us staal 5, 525 5, 250 210 ESET ELL IEEE. reac nen sla ane ad ans - o 2307 § 1. }. L 2G ~a ane dinaln a abs a Kale a ain [ale £s nae ae bn s a Nal... lsc Is 5, 550 5, 230 +320 5, 380 5, 360 20 ggfi Te, well 1... 5, 340 4, 764 576 5, 340 5, 290 507 257 5, 265 5, 140 125? 3767b ________________ 5, 453 4, 603 850 |. EL Leva ask ae ss lacs in annals a 850 vo well 5, 197 4, 718 479 |L UL aa enue a nen 479 CENOZOIC ROCKS TABLE 12.-Summary of well-log data in Chino-Lonesome Valley, Arizona-Continued 79 Well Basalt Thickness, in feet, of overlying (a), intervening, and Section and well Altitude (feet above sea level) Altitude (feet above sea level) underlying (b), Depth (feet) Thickness (feet) sedimentary deposits Top Bottom Top Bottom 'T. 14 N., R. 2 W.-Continued well 5, 200 4, 690 MO.. 12. s.. cnl ene ceo on aos Paran [ale aln bra in ala in in 510 ________________ 5, 214 5, 065 149 : (Een nel een ea + aie a aa a an mle a in ie B e e a a on ie 147 5,007br "|; L aus =- sos s 27, Well 5, 273 4, 860 M19 | {LE :E Us- a ece nals | alee an o a a 243 5, -- 1. co ee saa dn aln |e = a an a o oa he ele he |a on e oe m n n cule a oe | on in e at ac n e n or he e as [haren ine A aa n im e a S, well 5, 377 5,125 202) he- enses ae[ak sk nants sro 252 S3; 5, 350 5, 137 213 5, 300 5, 288 12 1???) Bie 1 athe aat i- 5, 350 4, 980br? 370 5, 340 5, 330 10 10a 350b Jackie a. 5, 400 5, 282br 118 {l ca eL PLI a aia eames 118 B4 well 1: 5, 350 4, 878 |. NAV IR IC:. (@?) ? ele en nne 5, 350 5, 085 265 |e lenee nua aa - clr aan agin ien 265 ell s ti bances 5, 425 5, 169 250 :|}... ...en cll ue e nan a's aus |a nie a a amen a aln tebe a an io hao hve as lke 5, 400 5, 040 360 5, 400 5, 040 300 T. 13 N., R. 2 W. See. A, well 5, 350 5, 050 B00 :|. nce ee n a nee t tut a n (ane an oe cam inn 300 T. 16 N., R. 1 W. Sec. 6, well 1.........-.-«.... 4, 717 4, 567 150 4, 5777 4, 567 107 140?a T well 4, 750 3, 665 17085? cl ()e: Ien aas S/ well 4, 725 4, 415 310 4, 429 4, 415 14 206a 14, well 1........s..c_... 4, 830 4, 560 270 12.00 lns oe alie ale + alg and aie alel | a a a e tia hr ane is is ie 2707 I7, well 4, T7O 4, 258 $12 |_ (27) 5127 18, well 4, 764 4, 459 805 : "|: cc ti gl dell n be ecs ae ales s 305 20; Wel 4, 775 4, 865 M10; |- |= [-- nsane sms 410 er welll .._." 4, 804 4, 444 B00. |... le... clare nn ale ner 29, 4, 840 4, 447 399) |. ___.. nese MCL VIA lee nea nea o 393 G4) well 1..........._...-- 4, 810 4, 508 $02) {c nen ue. an s En ale cls (2) 3027 T. 15 N., R. 1 W. Set. 5, well 1._...__...____:. 4, 820 4, 520 800-1 >>. ...-- «anal- !> Be anla us =n sun nt 300 G well 1... _:0.l}.0... 4, 820 4, 555 205 (| cur lil l e eu [ae men' ans a a 265 gar wel 4, 914 4, 596 B18) | Epee leone eee neo rana al ane aman SI, well 1....._:......... 5, 000 4, 585 MLD | {L EET E a bie m (tn bs a ale aa ana Mk hall cous te a hs me see h e n e 415 eben IEIC ILL 4, 783 4, 283 500 :: |: 2 n LLE n oe nee n eu |e aidan pae a amd fa ae an ii a a ml in T. 14 N., R. 1 W. Sec. 2, wellil....:............ 4, 950 4, 600 5950 (.%... balan - anns 350 6 well 1.........l...... 5, 045 4, 702 49 |: .o .l as sanns ans s 340 4, TObbr?! {*e IL. cl. _ LCL set lll sous sess s snow T. 15 N., R. 1 E. Sec. 20, well 1..:.......}..... 5, 825 5, 175 150, {. 2s. nected elan ene ns iin aol amie a an ain s a's s 150 28, well 5, 060 4, 660 400 :|: T noen nt ie sa 2 noe = on an i 400 1 Basalt penetrated at top of well. 2 Basalt penetrated at bottom of well. 80 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA Taste 12.-Summary of well-log data in Chino-Lonesome Valley, Arizona-Continued Well Basalt Thickness, in feet, of overlying (a), intervening, and Section and well Altitude (feet above sea level) Altitude (feet above sea level) underlying (b), Depth (feet) Thickness (feet) sedimentary deposits Top Bottom Top Bottom T. 14 N., R. 1 E, Seci11, well 4, 875 4, 525 850 . ie c clic lla rio, 350 16, well 1....;...s...l... 4, 817 4, 217 600: 22 ree o ar er oa s oona r o | nan enn, 600 SS, 4,675 3, 845 850 : | - aw ane ens aes 830 ss can ere 4, 725 4, 325 100 |S ine e eee ede e erea nn eee ue arenes 400 T. 13 N., R. 1 E. peer 2, well 1....:l.._>:.5%}. 4, 550 3, 911 639 3, 964 3, 934 30 532g 11, 4, 540 3, 690 $50 : cnn emale eee be anl nan ea eee es 745 s; TOBDT ila -case irie aas a nam ale bn ain eae a eae laa nana alee e en e probably Pliocene or Pleistocene, but in many places such evidence is lacking or inconclusive. In 1946 K. K. Kendall of the Water Resources Di- vision of the U.S. Geological Survey found fragmen- tary antelope and llamalike camel bones in the basin de- posits north of Prescott. C. L. Gazin of the National Museum stated : "The lama-like camel * * * may rep- resent a small species of Pliauchemia, * * *" possibly of Pliocene age (written commun. to C. A. Anderson, 194%). These bones were found along the William- son Valley road (near 1,313,500 N., 326,000 E.), in a roadcut on the west side of Route 89 (near 1,301,200 N., 344,200 E.), about a mile south of Willow Creek (near 1,302,900 N., 340,500 E.), and in the NW 1 see. 23, T. 14 N., R. 2 W., probably due east of the preceding loca- tion. During the present investigation, an unidentifi- able bone fragment was found south-southwest of Glassford Hill (near 1,297,500 N., $55,000 E.). All these bones came from about the same stratigraphic hor- izon-below the middle basalt flows (fig. 244) in orange-colored tuff or in the immediately underlying gravel. The Williamson Valley road area is the most promis- ing locality for fossils and contains fairly abundant bone fragments. J. F. Lance (oral commun., 1956) found an antelope leg bone that he thought is not younger than middle Pliocene and may well be the same age as a vertebrate fauna 20 miles south of Prescott. These fossils (Reed, 1950; Bryant, 1951) were discov- ered along Milk Creek (fig. 1) in the Mount Union quadrangle; they are early Pliocene in age according to Lance. The bones occur in sedimentary rocks that resemble the rocks north of Prescott except for having been tilted slightly. The similarity is increased by iden- tical white rhyolite tuff beds in both. Specimens of fossiliferous fresh-water limestone northeast of the basin were studied by E. B. Leopold (1955 and 1957), by D. W. Taylor, R. W. Brown, and R. Rezak (1955), and by K. E. Lohman (1957) of the U.S. Geological Survey. The limestone is reported to be moderately organic-the organic material is in an amorphous or macerated condition. Fossils include a medium-sized gastropod-probably a Lymnaea-frag- ments of dicot wood, rootlets, corroded conifer grains- probably Juniperus-fungal hyphae, filamentous green algae, spores, an undetermined Silicoflagellate-like or Heliodiscoaster-like form, diatoms, corroded sponge spicules, concretionary laminated algal deposits around pebbles-similar to water biscuits of modern fresh- water lakes-and crisscrossing tubes of undetermined origin, possibly stem molds or worm burrows. None of the material is diagnostic as to age, but it does indi- cate a subaqueous shallow dominantly fresh-water environment. According to Lohman, the diatoms consist of fresh- water and brackish- or saline-water forms (table 13). The largest number of species are fresh-water forms, whereas the largest number of individuals are brack- ish- or saline-water forms. The identification of Hyalodiscus radiatus and its variety artious, the most abundant diatom, is uncertain. The badly leached or corroded condition of all specimens of both, in contrast to good preservation of delicate structures of most other diatoms, suggests reworking of an older deposit or transportation from a different habitat. Eyalodiscus of. H. radiatus var. artice was originally described from Franz-Josef Land associated with marine and some brackish- and fresh-water species; this association sug- gests a tidal estuary. The diatoms have known geologic ranges of Miocene or Pliocene to Recent, except for CENOZOIC ROCKS 81 Navicula bituminosa, which has been found previously only in late Tertiary (Miocene or Pliocene) beds in Hungary. Two forms, Gomphonema bohemicum and Hyalodiscus cf. H. radiatus var. artica, live today only in cold water. The others, except the extinet Navicule bituminosa, are temperate-water species. Because of the foregoing associations, Lohman suggested that the limestone was deposited in a shallow somewhat saline lake fed by streams of temperate water and by streams originating in higher, colder country (such as the Colo- rado Plateau and its volcanic peaks). TABLE 13.-Diatoms from fossiliferous limestone of late Ter- tiary(?) age. Limestone underlines basalt and overlies andesitic gravel, 5 miles northeast of the village of Chino Valley (1,386,200 N., $53,600 E.) [Report by Kenneth E. Lohman, August 30, 1957. Occurrence: A, abundant; C, common; F, fairly common; and R, rare.] Cymbella ehrenbergii Kiitzing (F) parva (Wm. Smith) Cleve (F) Fragilaria cf. F. pinnata Ehrenberg (R) Gomphonema angustatum (Kiitzing) Rabenhorst (F) bohemicum Reichelt and Fricke (F) intricatum Kiitzing (F) lanceolatum Ehrenberg (R) Hyalodiscus cf. H. radiatus (O'Meara) Grunow (C) cf. H. radiatus var. arctica Grunow (A) sp. (F) Navicula bituminosa Pantocsek (F) lucidula Grunow (R) Nitzschia commutata Grunow (A) cf. N. commutata Grunow (F) palea (Kiitzing) Wm. Smith (R) Pinnularia gibba var. parva (Ehrenberg) Grunow (F) interrupta Wm. Smith (R) microstauron var. biundulata Muller (F) microstauron var. brebissonii (Kiitzing) Hustedt (R) Some of the white rhyolite tuff above the vertebrate fossil locality east of Williamson Valley road contains abundant pollen ; pollen studies of this material are now being made at the Geochronology Laboratories of the University of Arizona (Jane Gray, written commun. 1959). The Colorado Plateau northeast of the Prescott- Paulden area is covered by volcanic rocks that, accord- ing to Robinson (1913, p. 38), were erupted in three stages: (1) widespread eruption of basalt from small cones, (2) eruption of lava of andesitic to rhyolitic composition from isolated large cones and a large num- ber of small ones, and (3) eruption of basalt from many small cones. The last period of eruption con- tinued until Recent times; it was widespread, but not as widespread as the basalt eruptions of the first stage. Although not based on stratigraphic and fossil evidence, Robinson's assumption (1913, p. 91-92) that the first stage of eruption occurred in the late Pliocene has been widely quoted. Gravels beneath the plateau basalts were deposited as a result of uplift to the south that probably occurred in late Miocene or early Pliocene, according to Longwell (1946, p. 832). Although fossils are lacking, the Hickey Formation of the Jerome area and Clarkdale quadrangle is con- sidered to be Pliocene ( ?), and the younger formations, Pliocene(?) to Pleistocene(?) (Anderson and Creasey, 1958, p. 58, 61; Lehner, 1958, p. 554, 561-562, 565-566). STRATIGRAPHIC RELATIONS AND CORRELATIONS The upper Tertiary (?) rocks rest on Precambrian rocks in the southern half of the area (pl. 1) and on successively younger rocks to the northeast across the northern half of the area (pl. 2, see. L-Z'). This is illustrated in part by the map showing the approxi- mate present thickness of Paleozoic and Cenozoic rocks (fig. 31), as northeast of Chino-Lonesome basin the thickness is due largely to Paleozoic rocks. The sur- face on which the upper Tertiary(?) rocks were de- posited had considerable relief, The rocks are over- lain by Quaternary pediment gravel and Recent gravel and alluvium. Attempts to correlate the upper Tertiary (?) rocks in the Prescott-Paulden area with the Hickey and Perk- insville Formations to the east have so far proved fu- tile. The volcanic and sedimentary rocks in the Prescott- Paulden area are obviously westward continuations of rocks mapped as Hickey and Perkinsville to the east, but the criteria used to distinguish the two formations do not apply in the Prescott-Paulden area. The distribution and possible relations of the upper Tertiary(?) formations in the Prescott-Paulden-Je- rome-Clarkdale area are shown on plate 4. As shown on this plate, the Hickey Formation consists of upper Tertiary (?) basalt and sedimentary rocks in the south- western part of the Jerome area and of older (pre- andesite) basalt and gravel, andesite, and younger (post- andesite) basalt in the southwestern part of the Clark- dale quadrangle. (See Anderson and Creasey, 1958, p. 56-59, pl. 1, also p. 78-83, figs. 5, 6; Lehner, 1958, p. 549-556, pl. 45, also p. 568-576, for descriptions of the Hickey Formation and its distribution, as mapped by them, in these areas; the volcanic rocks of the Hickey Formation according to them consist largely of basalt.) On plate 4 the name Perkinsville Formation (Lehner, 1958, p. 563-566, pl. 45, also p. 556-563) has been ap- plied to the upper Tertiary (?) rocks in the northeast corner of the Paulden quadrangle. In the Jerome-Clarkdale area the Hickey Formation was distinguished from the younger formations on the basis of relation to deformation and erosion. The Verde Formation is east of the Black Hills and east of the Verde fault; the older Quaternary gravels-called older Quaternary gravels in the text but braced as Pliocene (?) to Pleistocene on the map explanation and correlated with the Verde Formation by Anderson and 82 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA Creasey (1958, p. 61, pl. 1)-are west of the Black Hills and west of Coyote fault; the Perkinsville Formation is north of the Black Hills The Hickey Formation forms a thick sequence of basalt flows on top of the Black Hills, downfaulted flows east and west of the two bounding faults, and downwarped flows north and south of the Black Hills The flows are underlain locally by gravel that is limited to northward-draining channels, except in the southern part of the Jerome area where sedimentary material is more abundant and gen- erally predominates over basalt. East of the Verde fault the Verde Formation unconformably overlies the Hickey Formation. Except where downfaulted or downwarped, the Hickey Formation is confined to topographic highs, where it occurs as erosion remnants.: Erosion, initiated by post-Hickey deformation, resulted in about 1,300 feet of relief and in the present south- ward drainage, according to Lehner (1958, p. 555). The younger formations are more closely related to pres- ent topography. They accumulated mainly in topo- graphic lows. The stratigraphic relations within the upper Ter- tiary (?) rocks in the Prescott-Paulden area are not clearly understood. The sequence, as worked out in the central part of the Paulden quadrangle, consists of gravel and a little basalt-referred to here as older gravel and older basalt-overlain by andesite that in turn is overlain by basalt and gravel. During recon- naissance in much of Yavapai County, andesite (or dacite) was observed in many places above gravel and below basalt. To conclude that all the andesite (or dacite) is contemporaneous and is important as a strati- graphic marker is tempting, but such conclusions have not been proved. The andesite may be older than, an early facies of, or younger than basalt of the Hickey Formation, or it may be of several ages. The presence of basaltic-looking rocks related to andesite and of ande- sitic-looking rocks related to basalt have complicated the picture. The upper Tertiary (?) rocks all appear to have been deposited after the last major deformation in the area. The older basalt, which is quantitatively unimportant and may possibly be an early basaltic facies of andesite, occurs in four areas: (1) west of the Pinnacle (1,400,000 N., 353,000 E.), (2) on the eastern edge of the area, 2,000 and 3,000 feet northeast of St. Mathews Mountain, (3) 1,000 and 2,000 feet southeast of Stewart Ranch (1,407,- 500 N., 354,500 E.), and (4) in the headwaters of Bull Basin Canyon (1,396,000 N., 372,500 E.). It consists of flows, except at the first locality, where it includes a cinder cone (pl. 2). | The older gravel extends from northeast of Chino- Lonesome basin nearly to Hell Canyon. Included with the older gravel are the gravels along the western mar- gin of the area, which are probably older than andesite and which extend for about 4 miles north of the latitude of the village of Chino Valley ; a small patch of gravels in the northeast corner of the area (1,453,000 N., 397,000 E.) is also included. The gravel beneath basalt along Hell Canyon, some of which is too thin to show on plate 4, and that beneath basalt north and south of the Verde River near the eastern edge of the area may also be part of the older gravel. Fragments of Precambrian vol- canic and intrusive rocks are characteristic of the older gravels. These Precambrian fragments must have been derived from rocks south or southwest of Chino-Lone- some basin, probably prior to the formation of the basin. The small patch of gravel in the northeast corner is prob- ably older gravel because it contains Mazatzal Quartzite pebbles that must have come from rocks south of the Verde River lowland. : The pebbles of Mazatzal Quart- zite and some of the Precambrian fragments along Hell Canyon and the Verde River may have been derived from older gravels. . The older gravel is intruded by andesite plugs and overlain by andesite flows, breccias, mud flows, and gravels composed largely of andesite fragments. The contact between older gravel and overlying andesitic gravel, tuff, and mud flow is well exposed on the sides of the gulches west (fig. 21), east, and south of the Pin- nacle (1,400,000 N., 353,000 E.) and appears to be con- formable and gradational. At only one place was a pos- sible discon formity observed. Most of the basalt northeast of the basin rests on ande- site or on older gravel that generally contains andesite fragments at the top. In places these andesitic gravels are only a few inches thick. Most, if not all, of the thin andesitic gravels are related to the andesitic period of volcanism and not to a period of erosion following erup- tion of andesite; they are lateral extensions of andesitic gravel and mud flows that underlie andesite breccia and massive andesite (fig. 21). Erosion prior to eruption of the basalt, however, may have removed overlying andesite breccia, massive andesite, and much of the andesitic gravel. The Hickey Formation (as mapped by Lehner) in the southwest corner of the Clarkdale quadrangle consists of the same sequence: older gravel and a little basalt, andesite, and post-andesite basalt (pl. 4). Lehner (1958, p. 553) recognized andesite in the area but in- cluded it with and considered it a facies of the basalt of the Hickey formation. Basalt and overlying gravel in the northeast corner of the Paulden quadrangle are part of the Perkinsville Formation. The basalt flowed from the Colorado Plateau rim southward into the Verde River lowland. CENOZOIC ROCKS Basalt of the Perkinsville Formation has been arbi- trarily distinguished (pl. 4) from the basalt south of Hell Canyon and the Verde River. As the base of some of this basalt slopes northward toward the Verde River lowland, the basalt may have been erupted after forma- tion of the lowland and at nearly the same time as the Perkinsville basalt. On the other hand, the base of some of this basalt and of some of what is shown as Perkinsville basalt along Hell Canyon upstream from King Spring (west of 376,500 E.) has the same attitude as the underlying Paleozoic rocks (pl. 4, see. A-4') ; it may have been downwarped into the lowland. Nearly all the basalt in the Paulden quadrangle, including Per- kinsville basalt just north of the area (near 384,000 E.), overlies andesite; andesite, therefore, cannot be used as evidence for distinguishing basalts of different ages, ex- cept for the small amounts of basalt beneath andesite. Gravel and interbedded fresh-water limestone beneath the lowest basalt (Perkinsville) in the northwest corner of the Clarkdale quadrangle is continuous with the gravel and limestone beneath basalt immediately to the west. Lehner mapped them as Perkinsville; I found it impossible to distinguish the gravel from the older gravel to the southwest. It is lithologically similar and contains Paleozoic and a few Precambrian fragments, whereas gravel of the Perkinsville in most places, ac- cording to Lehner (1958, p. 563-564), is composed largely of basalt derived from older basalts. The lime- stone along Hell Canyon southeast of Drake is between underlying gravel and overlying basalt. Limestone south of Granite Creek (1,386,200 N., 353,600 E.) un- derlies basalt and overlies older gravel, which contains andesite fragments at the top. The limestone north of Granite Creek (1,390,500 N., 358,000 E.) probably oc- cupies the same position, but it may underlie the andesite. The sequence as far as known in the southern part of the basin consists of sedimentary material and a few interbedded basalt flows. North and northeast of Pres- cott, the sedimentary material is overlain by three basalt flows or flow series that are separated by as much as 100 feet of gravel and rhyolitic tuffaceous rocks. Figure 14 (southwest corner) shows lower, middle, and upper basalt flows and the gravel and tuff beneath these flows. The middle and upper flows rest on relatively gently northward-dipping surfaces (fig. 24). The middle ba- salt flows rest on Precambrian rocks in places and on increasingly thicker basin deposits to the north. In the exposed part of the basin, fanglomerate and coarse fluviatile deposits grade into and interfinger with the finer grained lacustrine deposits of the interior of the basin. Rhyolite tuff deposits east and west of Glassford Hill suggest correlation of the underlying 83 deposits. The tuff on the west side is above gravel and below the middle basalt flows. The tuff east of Glass- ford (near 1,299,500 N., 384,700 E.) is above gravel that to the west underlies the upper basalt flows. Where exposed in the central part of the basin, the fine-grained lacustrine deposits are similar to those ex- posed to the southeast. East of Granite Creek (pl. 1, 1,345,000 N., 360,000 E.) these deposits are overlain by basalt that is probably about contemporaneous with the basalt north of Prescott and with basalt to the east (pl. 1, northeast corner). The eroded edges of thin nearly horizontal flows in the northeast corner suggest that these flows spread out westward on a relatively level surface (pl. 1, see. 4-4") after the basin was largely filled. At one place (1,354,600 N., 394,000 E.) a tuff bed beneath basalt contains large white rhyolite pumice lapilli ; the tuff is identical lithologically with tuff that underlies the upper basalt flows on the south side of Glassford Hill. The contemporaneity of the rhyolite tuffs, however, has not been proved. Basalt at the headwaters of the Verde River (Sulli- van Lake, pl. 2) also appears to rest on basin deposits. The continuity of the basin and its deposits northwest and southeast of Sullivan Lake, however, cannot be proved because of absence of subsurface data. Certainly the basin is much narrower south of Sullivan Lake than elsewhere, if the small exposures of Paleozoic rocks east and west of Del Rio Ranch represent the margins of the basin ; the Paleozoic rocks could be xenoliths in andesite. Basalt near Sullivan Lake is part of the basalt north- east of the basin, which to the east is underlain by older gravel that contains andesite fragments at the top. The relationships of the upper Tertiary (?) rocks of the basin to older gravel and to andesite are uncertain. The andesite plug south of Glassford Hill and the flow on the northeast side of the Dells Granite, however, are considered contemporaneous and are interpreted as probably older than the upper basalt flows of Glassford Hill. The deposits in Chino-Lonesome basin appear to be the result of continuous and contemporaneous deposi- tion in a single basin, but this cannot be proved or dis- proved because of the extensive cover of Quaternary pediment gravel and alluvium. This cover masks pos- sible structural discordances or erosional unconformi- ties within various parts of the basin. The sedimentary rocks mapped as part of the Hickey Formation in the southwestern part of the Jerome area are unquestionably the same as the sedimentary rocks in the southeastern part of the Prescott quadrangle and probably the same as those in the basin as a whole. The sedimentary record for the most part indicates drainage into the basin-the coarser material is near the 84 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA EXPLANATION Twr -~ --- Base of the middle basalt flows (shaded); solid line where underlain by orange tuff inmed sag L\x/ (lined pattern) (outcrop width greatly 3 M/ > exaggerated) # # Try U \\\L $5 5 aol _ 1,310,000 "ng Fault 6650 Dashed where approximately located; queried where doubtful; U, upthrown side; D, downthrown side Structure contour Drawn on base of the middle - Structure contour Drawn on base of the upper basalt flows Outline of base of basalt of Glassford Hill & 5850 Altitude of basalt-granite contact ©5500 Altitude of basalt-alluvium contact, base concealed ©5500 Altitude of contact of basalt with under- lying cinder cone x P x $5 basalt flows \_ ~ psc 3s. , 5300 5850 °o\ G # Altitude of base of the middle(?) basalt flows in down-faulted block 1,300,000N w p- - s 8 E sy B § C 3 3 lud c ® id E E E E S : y 3) -s ® 3 © ap alias (= m ~ m Fiagk . d/ n 1,310,000 \(5500 \ 1,310,000 A \ 5750 55007 tes 8600 \ 5250 - s [5750 wz ~a, ~2 ( ~ % \ ~- < \ EXPLANATION S. s250 / Yth Fw Base of the upper basalt flows (shaded); g "ast" underlain by tuff and gravel TS o ron n 1,300,000 FiGURE 24.-Structure contour of the base of basalt flows of late Tertiary(?) age north of Prescott. 0 1 MILE Upper map: base of the middle basalt flows, showing outcrops of underlying orange tuff ; lower map : base of the upper basalt flows. CENOZOIC ROCKS 85 margins-but other drainage directions east of the Prescott area may mean that the sediments do not all belong to the same period. In Tex Canyon (pl. 4, 1,304,000 N., 435,000 E.) the gravel is composed chiefly of Paleozoic rocks, which must have come from the north, possibly when drainage was southwestward into Chino-Lonesome basin. On the other hand, along the eastern margin of Lonesome Valley (roughly between 1,295,000 N. and 1,300,000 N. and between 410,000 E. and 420,000 E.) and farther east, the gravel contains frag- ments of alaskite that must have come from the south- west, possibly after the basin had been filled sufficiently for them to be carried across. A northward drainage, possibly before formation of the basin, is indicated by gravel beneath basalt on Kendall Peak (pl. 4, 1,330,000 N., 480,000 E.) ; this gravel is composed solely of Pre- cambrian fragments, although Paleozoic rocks lie a short distance to the north. In the Jerome-Clarkdale area north of Kendall Peak, gravel beneath basalt of the Hickey Formation filled northward-draining chan- nels (Anderson and Creasey, 1958, p. 57, 58). Lehner (1958, p. 554) considered it to be possibly correlative with scattered remnants of once extensive gravel de- posits beneath basalt on the Colorado Plateau (Koons, 1948; Price, 1950) ; if so, this gravel may be consider- ably older than the gravel in the southern part of Chino-Lonesome Valley. It is tempting to correlate the thick sequence of volcanic rocks in the Chino artesian basin (pl. 1, sees. A-A', F-F"' ; pl. 2, sees. H-H', J-J' ; table 12) with the thick sequence of basalt of the Hickey Formation on top of the Black Hills. If it is downfaulted Hickey, then the overlying basin deposits may have accumulated after post-Hickey faulting. The basalt mapped as Hickey west of Coyote fault apparently is the same as the basalt in the east-central part of the area (pl. 4, sec. B-2'), which is tentatively correlated with the basalt that over- lies sedimentary rocks of the basin to the west and south- west (pl. 1, see. A-A'). If basalts of two ages are pres- ent, they have not been distinguished. The many similarities between Chino-Lonesome basin and Verde basin and their deposits suggest a correla- tion. Arching of the Black Hills and major movement on the two bounding faults undoubtedly occurred at the same time and may have resulted in simultaneous forma- tion of the two basins. Both basins were filled with fanglomerate and finer fluviatile and lacustrine deposits interbedded with basalt flows. The basin deposits have since been cut by pediments, and the pediments them- selves have been dissected during a more recent cycle of erosion. The Verde Formation contains Silicoflagellate- or Heliodiscoster-like forms (E. B. Leopold, written commun., 1958) similar to those in fresh-water lime- stone in the Paulden quadrangle (see p. 80, this report), but it contains an abundance of limestone and a paucity of rhyolite tuff compared with the deposits in Chino- Lonesome basin. Paleozoic limestones surround much of the Verde basin but are absent around much of Chino- Lonesome basin; this difference may account for the difference in carbonate content in the two basins. Although rhyolite tuff had not been previously reported from the Verde Formation, some was recovered from three drill holes (A. R. Still, oral commun., 1956). The occurence of rhyolite tuff in the Hickey Forma- tion (Lehner, 1958, p. 553-554; Anderson and Creasey, 1958, p. 56) also suggests a correlation of the Hickey with the deposits in Chino-Lonesome basin. On the one hand, contemporaneity of rhyolite tuffs has not been proved, and on the other hand, the rhyolite tuff in the Hickey is located in places where its inclusion in the Hickey might be questioned (pl. 4, 1,376,000 N., 407,500 E. and 1,305,000 N., 436,800 E.). No definite conclusions as to stratigraphic relations and correlations of the upper Tertiary (?) rocks have been made as a result of the present study. The fore- going discussion is an attempt to point out some of the difficulties in correlating these rocks with formations to the east. Some of the problems will undoubtedly be solved by more fossil finds, by determinations of the potassium-argon age of biotite in volcanic rocks, and by other methods of study now being developed. The situa- tion may be more complex than is suggested by the two formations now recognized to the east. QUATERNARY DEPOSITS The Quaternary deposits include Pleistocene pedi- ment and younger terrace gravels and Recent gravel and alluvium. In Chino Valley, both east and west of Gran- ite Creek, and in many other places, pediment and terrace gravels and the Recent material grade imper- ceptibly into one another. The Recent material has been mapped separately only along larger gulches and washes. PLEISTOCENE GRAVELS DISTRIBUTION Pediment gravels at one time covered much of the Prescott-Paulden area. The largest remnant (figs. 28, 29) lies east of Glassford Hill; smaller patches remain, mainly around the margins of the basin. Gravels cap flat-topped hills-remnants of the main pediment-that form a row on each side of Granite Creek from the Granite Dells northward to the north side of Chino Valley. In the relatively flat country southwest and east of Drake (northern part of pl. 2), pediment or terrace gravels are difficult to differentiate from gravels of late Tertiary (?) age. Younger terrace gravels are 86 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA widely distributed along most of the gulches that cross the upper Tertiary (?) sedimentary rocks, especially along Lynx Creek and the Agua Fria River valleys (pl. 1). THICKNESS AND STRATIGRAPHIC RELATIONS The Pleistocene gravels are veneers on pediment and terrace surfaces. They are generally 0-25 feet thick but locally are as much as 50 feet thick. The pediment gravels are about conformable to the nearly horizontal upper Tertiary (?) rocks but in a few places overlie them with an angular unconformity of 2°-3°. The pediment gravels overlap the upper Terti- ary (?) rocks onto the Precambrian and Paleozoic rocks in a few places on the north and northeast sides of the basin and, locally, in the southern part-for example, north of Green Gulch and west of Lynx Creek (pl. 1, between 1,285,000 N. and 1,291,000 N.; near 380,500- 381,000 E.; and near 1,292,000 N., 361,000 E.). They are overlain by Recent gravel and alluvium only near hills, such as Glassford Hill. The younger terrace gravels overlie the upper Terti- ary (?) deposits but at altitudes lower than the pediment gravels in any one area. They are locally overlain by Recent gravel and alluvial and colluvial material. LITHOLOGY j The Pleistocene gravels are a heterogeneous mixture of boulders, cobbles, pebbles, and finer grained material derived from Precambrian, Paleozoic, and upper Ter- tiary (?) rocks. Cobbles and boulders of alaskite and gabbro as much as 8 feet long are not uncommon in the southern part of the area, where other Precambrian rock fragments are pebble to cobble sized. Away from the southern margin of the area, few fragments are larg- er than cobbles, and on the terraces few are larger than pebbles and small cobbles. Sorting is characteristical- ly poor, but some material is sorted. The color ranges from dusky red and grayish brown through lighter shades of brown and gray. Most pediment gravels are dark red or brown, but some pediment gravels and many terrace gravels are lighter colored. On aerial photographs the pediment gravels on the hills that par- allel Granite Creek and on the large pediment remnant east of Glassford Hill resemble, in their dark color, basalt-capped hills. The dark color is due to iron oxide coating on quartz and other grains of the matrix. These dark pediment gravels contrast markedly with the un- derlying light-colored silt, clay, and marl of the upper Tertiary (?) deposits. Other dark-colored gravels are aprons of basalt or andesite around many volcanic hills-for example the apron on the northeast side of Glassford Hill (fig. 14). Some of these aprons are pedi- ment gravels, but many are more recent deposits. In the southern part of the area most of the gravels are composed of Precambrian rocks that were derived from the south or west or from reworking of the upper Tertiary (?) rocks. Along the eastern margin (pl. 1) the gravels contain Precambrian and Paleozoic rocks that were derived from the east. In the northern part of the area (pl. 2) the gravels are composed of Paleozoic and less abundant Precambrian rocks or of upper Ter- tiary (?) volcanic rocks. Near basalt or andesite masses, volcanic fragments are very abundant but generally be- come scarce away from the volcanic rock outcrops. The gravels contain fragments of Mazatzal Quartzite near outcrops of this formation and for some distance to the northeast of these outcrops, where they have in part been derived from upper Tertiary (?) gravels that con- tained fragments of the quartzite. In the southern part the terrace gravels are sub- angular to subrounded. Lack of rounding is due in part to the strongly foliated or jointed character of the Pre- cambrian rocks. Angular cobbles and boulders in grav- els near the southern margin of the basin probably rep- resent upper Teritary(?) material that accumulated on steep alluvial fans and that was let down during erosion of the fanglomerate without being moved far. The large boulders of alaskite and gabbro on flat pedi- ment surfaces several miles from higher Precambrian hills probably attained their present positions in this way, although they could have been carried there dur- _ ing flash floods. RECENT ALLUVIUM DISTRIBUTION The distribution of the larger areas of Recent al- luvium is shown on plates 1 and 2. In addition narrow ribbons occur along most of the smaller gulches and washes, especially where they cross the upper Ter- tiary (?) or some areas mapped as Pleistocene gravels. Finer grained alluvium covers the flats bordering drain- age lines; coarser material is in the stream beds, and both coarse and fine colluvial material covers slopes be- tween pediment or terrace surfaces and the valley bot- tom. Andesitic and basaltic alluvium surrounds hills of upper Tertiary (?) volcanic rocks, effectively con- ceals underlying rocks, and merges with pediment and younger gravels. THICKNESS AND STRATIGRAPHIC RELATIONS The thickness of the alluvium varies, and its maxi- mum thickness is unknown. Presumably the deposits are thin, as most streams are degrading, but where there is an abrupt decrease in gradient, small alluvial fans are being built up. This is especially true east of Glassford Hill, where small gullies descend abruptly from the - STRUCTURE 87 pediment surface to the alluvial flat along the Agua Fria River and its tributaries. Where gullies dissect the al- luvial flats, 5 to 10 or, locally, 20 feet of fine-grained al- luvium is exposed. The alluvium is separated from the underlying upper Tertiary (?) lacustrine deposits by a few inches to a few feet of reddish-brown gravel. Along Coyote Wash (pl. 1, 1,317,000 N., 391,500 E.) a gully 25 feet deep in the lacustrine deposits has exposed an older gravel-lined channel that is filled with fine-grained alluvium (fig. 25). - River gravels where placered along Lynx Creek, are as much as 25 feet thick. FIGURE 25.-Recent alluvium in channel cut in fine-grained sedimentary rocks of late Tertiary(?) age and exposed in a recent gully along Coyote Wash (pl. 1, 1,317,000 N., 391,500 E.). To the left, the channel extends nearly to the bottom of the gully. Rounded cobbles line the bottom of the channel, but much of the overlying material is fine-grained alluvium-largely clay. Note the light-colored well- bedded character of the older deposits, which consist of sand, silt, clay, and marl; some marly layers are nearly white. LITHOLOGY The fine-grained alluvium is gray or yellowish brown to brownish black. The darker color is characteristic of alluvium derived from upper Tertiary (?) basalt or from some of the mafic Precambrian rocks. Light yellowish- brown colors are common along the Agua Fria River and its tributaries, where the alluvium has been derived from fine-grained sedimentary rocks of late Tertiary ( ?) age. Much of the alluvium is composed of clay, silt, and fine sand, and locally it contains abundant plant mate- rial. Coarser material forms thin layers or fills channels. The coarser material, which is concentrated along drainage channels, is composed of sand, pebbles, cob- bles, some silt and clay, and scattered boulders several feet in diameter. Many fragments are subrounded. Sorting and stratification are generally absent. Coarse colluvial gravels cover some slopes below pediments and may largely conceal underlying fine-grained sedimen- tary rocks of late Tertiary (?) age (fig. 28). AGE The pediment gravels were laid down after the upper Tertiary (?) rocks were deposited and the upper part removed by erosion. They were probably deposited after the last faults that cut the younger of the upper Tertiary (?) rocks, although a fault scarp probably of Recent age can be traced on aerial photographs along the north side of Big Chino Wash for more than 20 miles from the northwestern part of the area (pl. 2, 1,437,200 N., 330,000 E.). On the basis of the amount of dissection that the pediments have undergone, of the amount of downcutting through Precambrian rocks be- low the pediment surface, and of the presence of mam- moth teeth in younger terrace deposits, the pediment gravels are considered Pleistocene in age. The terrace gravels are younger than the pediment gravels, and some of the lowest ones may be of very recent age. A mammoth tooth, found by G. H. Hazen, Water Resources Division, U.S. Geological Survey, in terrace gravels 50-100 feet above Granite Creek (pl. 1, near 1,301,200 N., 344,200 E.) was identified by C. L. Gazin of the National Museum as MammutAhus sp.; it indicates a Pleistocene or possibly a late Pleistocene age. A mammoth tooth (?) was found in clay in the southeastern part of the area (pl. 1, 1,309,400 N., 399,300 E.) during the present investigation. A Pleistocene horse (genus Z'guus) was reported by Hay (1927, p. 55) from Lynx Creek (location not given) probably from alluvium deposited during erosion of the upper Ter- tiary (?) rocks. Some alluvium is Recent in age. Small nonpetrified mammal bones, associated with the remains of bugs, twigs, droppings, and carbonized wood fragments, occur in silt and clay in the bottom of valleys tributary to the west side of the Agua Fria River (southeast part of pl. 1) and in coarser gravel underlying the alluvium 5-10 feet below the top of the gullies. STRUCTURE The major structural features in the Prescott-Paulden area are tight folds, shear zones, and strike faults pro- duced by major deformation in Precambrian time; normal faults, sharp monoclines, and gentle folds were produced by less severe disturbances during the period since the close of the Paleozoic Era. STRUCTURE OF OLDER PRECAMBRIAN ROCKS Precambrian deformation in the Prescott-Paulden area may have been the result of one period of orogeny 88 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA which included intrusion of igneous rocks, preceded and followed by deformation. It produced isoclinal folds, foliation parallel to bedding, and strike faults in many of the Alder Group rocks and foliation and shear planes in intrusive rocks (S-tectonites). In the Mazatzal Quartzite, deformation produced open folds (B-tecto- nites) and no foliation. The structure of the Precambrian rocks of Arizona has been summarized by Anderson (1951) and by An- derson and Creasey (1958, p. 45 and 62). They stated that the degree and type of metamorphism of the older Precambrian rocks varies from place to place and ranges from thermal metamorphism related to granitic intru- sions to mild or intense dynamic metamorphism but that the structures are similar in a broad way. The folds trend north, northwest, and northeast and indicate an east-west compression that may have occurred during a single period of orogeny. Until the recent proof of a pre-Alder granitic intru- sion (see footnote 7, p. 49), only one major orogeny in Arizona during the Precambrian had been proved; it separated older Precambrian rocks from younger Precambrian rocks in northwestern and southeastern Arizona. In central Arizona, where younger Precam- brian rocks are absent, it separated older Precambrian rocks from Paleozoic rocks. Wilson (1989) called it the Mazatzal revolution, because it involved the Mazatzal Quartzite. He stated that no pre-Mazatzal deforma- tion or granite has been recognized, although a minor unconformity separated the quartzite from older rocks. Hinds (1986, p. 100), on the other hand, suggested two periods of orogeny and accompanying granitic intru- sion : one prior to and the other after the accumulation of the Mazatzal Quartzite. It is unlikely that only one period of major orogeny occurred in the tremendous length of time represented by the Precambrian, but little evidence for more than one has been found. In the Paulden quadrangle the abundance and size of the quartz pebbles in the con- glomeratic facies of the Mazatzal Quartzite, the very low grade of metamorphism of the quartzite, and the absence of granitic rocks or quartz veins intruding the quartzite suggest that the Mazatzal was deposited after the major deformation and granitic intrusions in this area. Because the quartzite is in fault contact with the Alder Group, the difference in degree and type of deformation and metamorphism does not prove a pre- Mazatzal orogeny. STRUCTURE OF THE ALDER GROUP Alder Group rocks occur in small windows in younger rocks or are so isolated by intrusive rocks or separated by faults or zones of intense shear that stratigraphic re- lations are uncertain. Consequently, the broad struc- tural pattern has not been unraveled, although struc- tural continuity apparently exists within individual "blocks." Northeast-trending structures occur in the discordant Chaparral fault zone, a zone characterized by distribu- tive shear and bounded by Spud and Chaparral faults (pl. 1, southeast corner). Elsewhere, Precambrian de- formation produced generally north-trending steeply dipping structures: (1) isoclinal folds, strike faults, and foliation parallel to bedding in the Alder Group and (2) foliation and shear planes in intrusive rocks. Most postintrusion structures are about parallel to pre- intrusion ones. The probable large displacement on the Chaparral fault zone makes any correlation of the stratigraphic units and of the structure on the two sides of the zone highly questionable. For this reason, the structures within and west of the shear zone are dis- cussed separately. Deformation, which may have been part of a single orogeny, probably preceded and followed intrusion of igneous rocks. Kenoliths of foliated volcanic rocks in unfoliated Government Canyon Granodiorite prove that some structures are preintrusive. The preintru- sion structures in the Alder Group are isoclinal folds and foliation that, except in the noses of folds, are about parallel to bedding. Postintrusion structures are folia- tion, distributive shear, and strike faults. The north- trending structures may have been produced during suc- cessive surges, and the northeast-trending structures in the Chaparral zone may have formed slightly later. West of the Chaparral zone postintrusion structures in intrusive rocks are parallel to structures in the volcanic rocks that are presumed to antedate the intrusive rocks. Northeast-trending foliation and shear planes in vol- canic and intrusive rocks in the Chaparral zone are dis- cordant to the north-trending structures both east and west of the shear zone. A few minor zones of north- east-trending shear cut north-trending structures in volcanic rocks east and west of this zone; none were ob- served cutting north-trending structures in intrusive rocks outside the zone. The relation of north- to north- east-trending postintrusion structures, therefore, is un- certain. STRUCTURE EAST OF THE CHAPARRAL ZONE The Alder Group east of the Chaparral zone includes the Spud Mountain Volcanics in the southeastern corner (pl. 1), the Indian Hills Volcanics in the east-central part (pls. 1, 2), and probably the unnamed tuffaceous rocks of the Alder(?) Group farther north (pl. 2). The Spud Mountain and Indian Hills Volcanics are part of a large structural block in the western part of STRUCTURE 89 the Jerome area (Anderson and Creasey, 1958, p. T1- 44). The unnamed tuffaceous rocks of the Alder(?) Group are separated from these volcanics by intrusive rocks. Spud Mountain Voleaniecs.-Thé Spud Mountain Volcanics were isoclinally folded prior to the formation of the northeast-trending Chaparral zone. Near Spud Mountain the strike of bedding and early foliation ranges from N. 20° E. to N. 45° W., but the general strike is about north. On Spud Mountain the strike swings from north to N. 45° W., and close to the Spud fault it swings back to the northeast. As bedding and foliation both make the swing, they were probably folded by drag on the major fault zone. Narrow zones of foliation, zones of breccia, or single planes of shear that strike N. 45° E. to N. 65° E. near Spud Mountain are clearly at an angle to early foliation. The struc- ture near Spud Mountain is probably an anticline; a syncline may lie to the east (pl. 1, see. Z-") ; both probably plunge gently southward. No evidence of the direction that tops of beds face was found near Spud Mountain, but Anderson and Creasey (1958, p. 72) found sufficient evidence nearby to propose this inter- pretation of the structure. Indian Hills V oleanies and unnamed tuff aceous rocks of the Alder(?). Group.-In the east-central part of the Prescott-Paulden area, lithologic units trend north and northwest, as do sparse bedding in the volcanics and foliation in volcanic and intrusive rocks. Dips are vertical to steeply east or west. Small drag folds in the tuff unit of the Indian Hills Volcanics plunge north 25°-35°, but drag folds in the unnamed tuffaceous rocks plunge south 45°%-60°. Although foliation and drag folds in the volcanics are for the most part parallel to foliation and mineral streaking in the adjacent intru- sive rocks, the drag folds and some foliation are con- sidered preintrusion because foliation and drag folds in the unnamed tuffaceous rocks in upper King Canyon (1,389,500 N., 382,400 E.) are cut at a slight angle by an alaskite dike. STRUCTURE WEST OF THE CHAPARRAL ZONE Green Gulch V oleaniecs.-Liithologic units and struc- tures in the Green Gulch Volcanics trend northward ex- cept next to the Chaparral fault. Here gabbro (mostly south of the map area) and the volcanics have been dragged into the fault, and northeast foliation cuts the earlier structures in the volcanics. West of the fault, bedding and foliation are steep and, with few exceptions, dip west. Scattered determinations of the directions in which tops of beds face suggest that, except for minor reversals, the beds face west. Sparse 6 lineation, formed by intersection of foliation and bedding, plunges north 10°-25°, parallel to the plunge of minor drag folds. The a lineation was observed in a few places. Steeply north- plunging crenulations in foliation and bedding are prob- ably related to later cross fractures. Based on the few determinations, the formation (at least east of 386,000 E.) is interpreted as the east limb of a north-plunging tightly folded syncline. Lineation in the western out- crops of the formation (near and east of 380,000 E.) plunges south or southwest 40°-75°. Some of it is streaking on a plane of shear that is postintrusion in age; it is parallel to sparse lineation in associated in- trusive rocks. Lenticular and dikelike masses of alas- kite, aplite, and gabbro, many too small to show on the geologic map, trend northward, parallel to the struc- tural and lithologic trends in the tuffaceous rocks. Some of these intrusive rocks have a north-trending foliation. Texas Gulch Formation.-The largest structural unit within the Prescott-Paulden area is the Texas Gulch Formation in the south-central part. The formation is bounded on the east by intrusive rocks and apparently separated on the west by a sheer zone from the un- named basaltic flows of the Alder(?) Group. Data suggest a south-plunging syncline, within which are numerous smaller isoclinal or near isoclinal folds. Reasons for assuming a major syncline are as follows: (1) Lineation, believed to be the b direction of the structural coordinate system and related to deformation that produced the folds, plunges southward; (2) the outcrop of the formation progressively widens to the south; (3) tops of beds on the east generally face west (fig. 4) ; and (4) unmapped beds of gray staurolite( ?) schist and conglomerate and float of jasper-magnetite are present on the west (near 1,285,400 N., 353,000 FE.). Jasper-magnetite and some of the conglomerate are identical to the eastern beds of jasper-magnetite and conglomerate ; the schist may represent metamorphosed gray slate such as is associated with the eastern beds of conglomerate. Lineation consists of plunge of minor drag folds, intersection of cleavage and bedding, and elongation of pebbles. The pattern of drag folds, graded bedding, channeling, and cleavage bedding relations give con- sistent information on the direction in which tops of beds face, especially in the southern part of and im- mediately west of the unit containing jasper-magnetite beds. North of 1,285,000 N. the pattern of drag folds indicates numerous reversals of dip. Identical beds of conglomerate on both sides of the unit containing jasper- magnetite beds complicate the picture of a south-plung- ing syncline. The conglomerate bed west of this unit has been repeated by folding. Along the southern bor- der of the area (near 1,274,000 N., 358,000 E.), rhyolite crystal tuff caps small hills, and its contact with the underlying andesitic rocks plunges south as do minor 90 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA folds in the tuff. Foliation, lineation, and boudinage structure in a few lenticular and dikelike masses of in- trusive rocks, too small to map, indicate postintrusion deformation. Because outcrops of the Texas Gulch Formation along Granite Creek south of the Verde River (pl. 2) are too small, its structure or relations to the formation in the southern part of the area cannot be determined. Beds in the western outcrops strike east and dip south, whereas foliation trends north. In the eastern outcrops, drag folds plunge 50°%-70° S. Intense north-northeast foliation parallels the fault that brought the formation in contact with the Mazatzal Quartzite, but the Mazat- zal is not foliated. Unnamed volcanic rocks of the Alder(?) Group.- The unnamed basaltic flows near 350,000 E. in the south- ern part of the area (pl. 1) are separated from the Texas Gulch Formation by a shear zone. All the other masses of unnamed volcanic rocks in the southern part of the area are separated from one another by intrustive rocks. Foliation and zones of distributive shear in igneous rocks that intrude the volcanic rocks are about parallel to foliation in the volcanics. Between the largest mass of gabbro on the west and alaskite porphyry on the east, deformation of volcanic and intrusive rocks was erratic. The unnamed basaltic flows and much of the alaskite are nonfoliated, except along the east and west margins and along narrow zones within them. Distributive shear was more intensive in and adjacent to the unnamed tuffaceous rocks, especially in the northwestern part, where deformation resulted in mechanical mixing of the rocks and in. the formation of narrow dikelike masses of alaskite augen gneiss and, locally, of mylonite. Except in one area near 1,291,000 N., 376,000 E., where trends are north-northwest, bed- ding, lithologic units, and foliation in volcanic and in- trusive rocks trend northward and are vertical or dip 65° or more west. A few small north-plunging drag folds in tuff may be related to earlier deformation. Most lineation is postintrusion, it plunges south 35°%-60° and consists of mineral streaking and intersection of two cleavages or of bedding and foliation. In the unnamed tuffaceous rocks along 364,000 E., bedding and foliation strike northward and dip steep- ly west or are vertical. The pattern of a few north- plunging drag folds indicate east-facing beds. North of 1,292,000 N., steeply south-plunging lineation of post- intrusion origin parallels lineation in the Prescott Granodiorite to the west. East and west contacts with intrusive rocks are largely narrow zones of shear. Bedding, flow-banding, and foliation in the unnamed basaltic flows near 350,000 E. trend northward and are vertical or dip more than 80° west. The direction that tops of beds face was determined in only one place where graded bedding in a tuffaceous bed indicated that the bed faces east. Breccia fragments have been stretched in some beds, but considerable areas of the rock are massive. ' Deformation may have been prein- trusion, as most of the gabbro is massive. The northern part of the westernmost mass of un- named volcanic rocks trends northward, except at its northern end, where its trend is northeast at an angle to foliation in the volcanics. The northeast trend is probably due to a fault or shear zone. A pronounced lineation plunges gently south in places; and elsewhere a faint lineation plunges steeply north or south; the structural significance of the lineation is unknown. In the southern part of the volcanic rocks, foliation and bedding trend northeast ; the trend becomes more east- erly to the south. Less intense postintrusion deforma- tion in the area may account for the more easterly strikes. Lit-par-lit injection of granodiorite along straight and contorted beds and inclusions of schistose and folded volcanics in the granodiorite prove deforma- tion occurred prior to intrusion of the granodiorite. The unnamed basaltic flows north of the large out- crop of Mazatzal Quartzite (pl. 2) are mostly massive but are locally cut by a very faint foliation. The vol- canics are probably separated from the quartzite by a fault. STRUCTURE IN THE CHAPARRAL ZONE-THE CHAPARRAL YVOLCANICS AND CHAPARRAL AND SPUD FAULTS Rocks of the Chaparral Volcanics are separated from other formations by faults, and their stratigraphic po- sition in the Alder Group is not known. The volcan- ics and associated intrusive rocks probably occupy a wide fault zone that is characterized by distributive shear. The bounding faults, foliation, and lithologic units trend northeast at an angle to the earlier north- ward trends in adjacent rocks. Deformation within the zone was so intense that some alaskite was reduced to augen gneiss or to a dense mylonite. Most contacts are mechanical, and volcanic and intrusive rocks grade into one another owing to mechanical mixing. The volcanic rocks were probably folded during an earlier period of deformation that produced north- trending structures in adjacent rocks. This early period is suggested by a faint north-trending foliation in the northwest part of the volcanics, and by contorted bed- ding and bedding at an angle to the northeast foliation locally found in tuff that lies between alaskite and the Prescott Granodiorite. Northeast-trending foliation is the dominant struc- tural feature within the zone. It dips 65° W. to 80° E., the dips to the west predominating. Lineation in STRUCTURE ' 91 both volcanic and intrusive rocks is related to the de- formation that produced the northeast structure. It plunges southward 10°-35° and consists largely of min- eral streaking, but some of it consists of the plunge of minor drag folds. A few north-plunging axes of folds in crenulated foliation are due to later cleavage. In the eastern andesitic tuff, a gentle north-plunging pen- cil structure was formed by the intersection of north- east foliation and later cleavage. The Chaparral and Spud faults (pl. 1, sees. B-2', E-E") bound the Chaparral zone. This zone strikes about N. 30° E. within the map area, but to the south- west the trend is about N. 50° E. In detail within the map area, the Chaparral fault trends about N. 25° E. and the Spud fault trends about N. 35° E. The faults may dip steeply west if their dips are parallel to the dip of foliation in volcanic and intrusive rocks within the zone. The northwest side of the zone moved north- eastward relative to the southeast side, and in detail similar drag is found along all the narrow zones of late foliation within and adjacent to the Chaparral zone. Displacement may be as much as several miles. To the northeast the fault zone is buried and does not reappear near Indian Hills (Mingus Mountain quadrangle, 1,324,000 N., 410,000 E.) along its strike extension. A fault zone of this magnitude would be unlikely to die out in this short distance; unless offset by a fault, its strike must continue to change to a more northerly and then a northwesterly direction - These changes would bring the fault zone west of the low hills in the east-central part of the area, where the structures trending north-northwest in the volcanic and intrusive rocks may be related to the zone. STRUCTURE OF THE MAZATZAL QUARTZITE Precambian deformation of the Mazatzal Quartzite (pl. 2) produced open folds and local zones of small tight folds and small-scale thrusts but no foliation. As the formation is separated from Alder Group rocks by faults (1,402,300 N., $46,700 E.; and 1,393,300 N., 353,500 E.), its stratigraphic position and the relation of its structure to that of the Alder Group are unknown. The major structures in the Mazatzal Quartzite (fig. 5; pl. 2, see. G-G') are two northeast-trending anticlines that plunge gently southward. The anticlines are sep- arated by a fault. The fault is not exposed, but its trend and approximate location are determined by structural discontinuity of the rocks on the two sides of the fault and by the close proximity of discordant outcrops of the upper argillite. The fault presumably continues northwest and separates the Mazatzal from the unnamed basaltic flows of the Alder(?) Group (1,393,300 N., 353,500 E.). A conspicuous feature of the western anticline is that 758-447 O-65--7 it plunges to the north on the south end of the exposure and that its eastern limb in this area swings abruptly to the southeast and has nearly vertical dips. Similarly, the western limb swings away from the axis toward the southwest. These features suggest that the original structure, formed by northwest-southeast compression, was later deformed by forces acting at right angles to the earlier forces. Wilson (1939, p. 1156) explained the steeply upturned structure as caused presumably by a northwest-trending fault to the south whose trace is concealed by alluvium. The eastern limb of both anticlines is somewhat steeper than the western limb. Dips of the western limbs average about 20° in the eastern anticline and 30° in the western anticline, except in the northwestern exposures, where dips average about 55°. East of the crest of the western anticline, a small thrust fault (Wilson, 19839, pl. 3, fig. 1, p. 1156) cuts the quartzite along Granite Creek (1,386,600 N., 355,- 000 E.; indicated by symbol, fig. 5). Slickensides and some breccia formed, and small drag folds lie above the plane of the thrust to the east (1,386,000 N., 355,- 300 E.) and beneath the plane of the thrust to the west (1,386,700 N., 354,700 E.); displacement is probably minor. Along the north-trending part of Granite Creek (1,389,600 N., 351,300 E. to 1,391,200 N., 351,000 E.) and for several hundred feet to the east, the rocks are shattered (the area is indicated by joint symbol on fig. 5). Slickensides formed on small thrust faults that parallel, or nearly parallel, bedding planes ; breccia occurs along steeply dipping joints Except in one place the beds dip consistently about 30° W. and can be traced across brecciated joints. This shattered area may be the place where Wilson (1939, p. 1155) believed that his measured section was ended by a fault. It is doubtful, however, that major displacement occurred; the upper argillite a short distance to the west has not been displaced, and the beds exposed to the south in the west-flowing part of Granite Creek are not affected. The shattering is too irregular in pattern to have been caused by a fault; it may be due to intrusion of an un- derlying andesite plug of late Tertiary (?) age or to collapse following withdrawal of andesitic magma. Steep reversals of dip occur at several places-in the extreme southeastern part, in the southwestern part (near 1,387,000 N., 348,000 E.), and on the east side of Granite Creek at the north end of the shattered zone. Some of these may be due to intrusion of andesite. The one east of Granite Creek is a tight east-trending fold about 200 feet wide. Along the south edge of the fold, beds are vertical and are marked by slickensides, by breccia, and by gouge containing ellipsoidal "pebbles" 92 ' GEOLOGY OF THE PRESCOTT AND of quartzite. The east-trending fold does not continue to the west side of the creek. The Mazatzal Quartzite formed topographic highs during several periods since the Precambrian; during Cambrian and Devonian times, when both the Tapeats Sandstone and Martin Limestone cut out against it, and during Late Tertiary (?) times, as proved by the pres- ence of pebbles of the quartzite in gravels near Hell Canyon and beneath basalt in the extreme northeast corner of the quadrangle. Much of the quartzite today stands above the surrounding younger formations. Whether it has remained as a monadnock, been ex- humed at various times, or been successively uplifted is not known. In places it now stands at least 150 feet above outcrops of the Redwall Limestone. As pebbles of the Mazatzal have not been observed in adjacent Red- wall Limestone and as the Redwall does not obviously cut out against the Mazatzal, it seems likely that the area underlain by the quartzite was relatively uplifted in post-Paleozoic times. This conclusion is supported by the steep dips of the upper Martin where it abuts against the Mazatzal south of Granite Creek ; these dips may be due partly to compaction and initial dip. STRUCTURE IN THE INTRUSIVE ROCKS Most of the structures in the intrusive rocks in the area have been mentioned in the discussion of the struc- ture of the Alder Group. Brief summaries and addi- tional data are given here. Many of the intrusive rocks have been foliated, in places intensely so; lithologic trends and structures are about concordant to north-trending structures in the volcanic rocks, to northeast-trending structures in the southwestern part, or to the discordant northeast-trend- ing structures in the Chaparral zone. Many intrusive masses form narrow lenticular sill-like or tonguelike masses within the volcanic rocks. Small lenses or tongues of gabbro are about as abundant as basaltic flows for about 1,000 feet west of the tongue of gabbro that partially splits the volcanic rocks near 350,000 E. in the southern part of the area. Discordant-appearing contacts-for example, north and south of the gabbro near 1,289,000 N., 374,000 E.-may be more apparent than real, as narrow prongs of volcanic rocks extend into the gabbro and vice versa owing to injection or to later distributive shear. Where the intrusive rocks are relatively undeformed, intrusive breccias are widely preserved and indicate magmatic stoping. Good examples can be seen in alas- kite porphyry along Charcoal Gulch and along Green Gulch near its junction with Charcoal Gulch in the southeastern part, in the Government Canyon Granodi- orite in the southwestern part, and in the Prescott Gran- odiorite in the east-central part (pl. 1). PAULDEN QUADRANGLES, ARIZONA Aerial photographs reveal a north-trending lineation in the largest mass of alaskite porphyry and, to a lesser extent, in the largest body of alaskite. This lineation is not particularly evident on the ground; it is probably caused by a greater density of vegetation along faults, joints, or shears because of more abundant soil and water where the rocks are broken. A few north-trend- ing zones of sheared or foliated alaskite separating mas- sive alaskite support this conclusion. Most gabbro bodies, particularly along their east and west margins, are foliated, and the foliation parallels their northward trends. The two largest masses, how- ever, also have a northeast- to east-trending planar structure, which may be partly caused by crystal set- tling. Faint foliation, joints, shear zones, and quartz veins parallel to the layering suggest that some of the layering is due to postintrusion deformation and meta- morphism. Some postinstrusion structures may be ten- sion and thrust fractures related to deformation that produced the north-trending distributive shear. Gabbro, Prescott Granodiorite, and alaskite masses within the Chaparral zone were probably dragged into the shear zone and rotated to their present position, al- though preexisting northeast-trending structures could have guided the intrusions. Post-Precambrian faults cut the older Precambrian rocks, but where Paleozoic or younger rocks are absent, they are difficult to recognize. Gouge along fault or shear zones is interpreted as indicative of post-Precam- brian movement, as gouge apparently was not produced during or before the deformation that formed the Chap- arral zone. Gouge, breccia, and shears, some along line- aments that shows up on aerial photographs, were ob- served between the Government Canyon Granodiorite and the second largest mass of gabbro (north end), in the Prescott Granodiorite in Miller Valley (near 1,292,- 600 N., 333,000 E.) and about half a mile north (near 1,303,000 N., 324,500 E.) and half a mile west (west of quadrangle) of Forbing Park, and in the Dells Granite near the junction of Routes 89 and 89A. These zones cut some quartz and tourmaline veins; they also parallel north-northeast joints in the Prescott Granodiorite and Dells Granite (fig. 14). The joints may have formed at the same time as the gouge-filled shears, or recurrent movement may have occurred along them. Parallelism of the north-northeast and west-northwest joints in Paleozoic rocks to the north to the major joints in the Dells Granite suggest a common age, but the parallelism may be fortuitous; the joints may be related to cooling and crystallization of the granite. The steeply dipping major system of joints-those trending north-northeast and west-northwest-in the Dells Granite is illustrated on figure 26, which also shows a N. 25° W. nearly ver- C200 he Cece %g sd ' 33 z _ g ' %(({W STRUCTURE EXPLANATION 983 mes: s 5x RX * 8 So \\"\0k XS Cya. 1.0‘0 XX C GP O-1 percent 6-8 percent 1-2 percent 2-3 percent 8-10 percent 10-12 percent 3-4 percent 4-6 percent 12-14 percent FiGUrE 26.-Contour diagram of 274 joints in the Dells Granite; the poles are plotted on the lower hemisphere. 04 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA tical set and a few gently dipping (0°%-50°) joints that strike about parallel to the major system. The gently dipping joints may be more abundant than appears, be- cause little attention was paid to them in the field. STRUCTURE OF PALEOZOIC AND CENOZOIC ROCKS Major post-Paleozoic structural features are shown on the structure contour map of the Paulden, Clarkdale, and Mingus Mountain quadrangles (pl. 5). Structures in the Prescott quadrangle are not shown, because Pale- ozoic rocks have been eroded from all but the extreme northeast corner. Structures in the Clarkdale and Mingus Mountain quadrangles are included to illustrate the regional setting. The contour of the base of the Redwall Limestone eliminates the effect of the topo- graphic high of Mazatzal Quartzite (pl. 2) that re- sulted in nondeposition of the Tapeats Sandstone and most of the Martin Limestone. Within the area under- lain by the Mazatzal, some irregularities may be due to forcible intrusion of andesite (notably near 1,400, 000 N., 356,500 E.) or to subsidence due to withdrawal of andesitic magma. Although the Paulden quadrangle lies largely south of the Mogollon Rim, the present boundary of the Colo- rado Plateau, and most of the younger Paleozoic rocks have been stripped from it, structurally this area be- longs to the Plateau province; the rocks are generally flat lying, having a gentle north to northeast dip " in- terrupted by shallow folds, sharp monoclines, and faults. The general north to northeast regional dip of the Paleozoic rocks of north-central Arizona is interrupted in the Paulden quadrangle (pl. 5). Interruption of the regional dip by west-facing Bull Basin monocline re- sulted in a northwest-plunging anticline that meets southwest-plunging Black Mesa anticline near the cen- ter of the quadrangle. Black Mesa anticline is bounded on the northeast by Limestone Canyon monocline and on the southwest by Big Chino fault or monocline. From Black Mesa anticline the rocks dip gently east- ward across the northern part of the quadrangle. The rocks are also deformed along other monoclines and disrupted by faults. Structural relief along the eastern margin is about 3,250 feet; along the northern edge, 2,750 feet; along the southeastern anticline, 1,500 feet; and along Black Mesa anticline, 1,000 feet. Structural relief along the southwest side of this anticline is at least 1,400 feet; and south of here along the western margin of the quadrangle, 1,500 feet. For purposes of description the headings "Older structure" and "Younger structure" are used. Only !" The absence of dip and strike symbols on the map (pl. 2) generally indicates that dips are less than 10°. those structures that clearly deform the rocks of late Tertiary (?) age are called younger structures. OLDER STRUCTURE MONOCLINES Although smaller in size, monoclines in the Paulden quadrangle exhibit many of the features characteristic of the monoclines of the Colorado Plateau. Many of the terms used by Kelly (1955) in his discussion of monoclines are used in this report ; some types of mono- clines are illustrated in figure 27. _- bend /Synclinal bend Simple monoclines Broad anticlinal bend 2. Mlinm bend With regional dip Opposed to regional dip With normal faults Broad (Kaibab) type sus \f\ I %. ay A_. Horst type After Kelley, (1955, figure 2) 27.-Variations of monoclines in cross sections. Monoclines are characterized by great ratio of length to width; the length may be measured in miles, the width in a few hundred feet. Most of the monoclines in the area are exposed for less than 2 miles. The longest one is more than 6 miles long; one has been traced for more than 17 miles, largely northwest of the quadrangle. Most of the monoclines are tight and where poorly exposed may be confused with drag along a fault. Sharpness of flexure, especially of synclinal bend, is characteristic; a bed may change from nearly STRUCTURE horizontal to vertical within a few inches. Anticlinal bends are generally broader. The monoclines are straight, curved, or branching and include double mono- clines-broad (Kaibab) or horst types (fig. 27). Most of them trend northwest or north; a few small ones trend northeast to east; they face northeast, southwest, or south. Many are associated with faults. They can- not be traced across Precambrian rocks, and small ones are difficult to trace in massive rocks such as the Red- wall Limestone. The Verde monocline is a horst type of structure; Black Mesa anticline might be described as a broad (Kaibab) type of structure. Limestone Canyon monocline-Limestone Canyon monocline (pl. 2, sees. B-2', 0O-C", H-H"' ; pl. 5) lies on what appears to be the northeast side of Black Mesa within the Paulden quadrangle, although to the north- west it actually runs approximately through the middle of the mesa. The monocline faces northeast and has been traced from about half a mile southeast of Lower Limestone Tank (1,452,700 N., 337,300 E.) for more than 17 miles to the northwest. At its northwest end (north of the center of Piccacho Butte quadrangle, fig. 1), it is buried by basalt of late Tertiary (?) age. At its southeast end it is buried by gravel and appar- ently dies out. Throughout its exposed length the zone of deformation is less than 1,000 feet wide. Martin, Redwall, and Supai beds are exposed along the struc- ture. Dips range from about 30° to vertical; the strata northeast of the monocline are about horizontal or dip gently eastward ; those southwest of it are nearly hori- zontal except south of the southeast end of the mono- cline, where dips are gently southeast. Structural relief across the monocline is between 300 and 500 feet near and northwest of the quadrangle boundary and de- creases to the southeast. The exact amount of structural relief was not estimated, as a known stratigraphic hori- zon is not exposed in the synclinal bend. Big Ohino monocline or fault.-A major structure, Big Chino monocline or fault, forms the boundary be- tween Black Mesa and the northwestern part of Chino- Lonesome basin ; it extends from north of Paulden for- at least 26 miles to the northwest. For more than 4 miles northwest of Route 89, the Martin and Redwall strata dip southwest 10°-40°. Many small northwest- trending faults (pl. 2, see. C-C"), most having the northeast side downdropped, however, displace the beds. Northwest of the quadrangle the exposed Paleo- zoic beds are about horizontal; southwest of here they are buried by upper Tertiary(?) rocks. Conclusive proof of major displacement was obtained from a wild- cat oil well (No. 1, see. 20, T. 18 N., R. 2 E.; 1,430,800 N., 326,200 E.) that penetrated the Tapeats-Martin contact about 1,400 feet below the estimated altitude of 95 this contact about 2 miles northeast of the well. Whether this structural relief is due largely to faulting or to warping is unknown. Verde monocline.-The Verde monocline (pl. 2, sees. J-J' and JI-M' to T-T") is a complex branching horst- type (fig. 27) structure that extends from the east edge of the Paulden quadrangle (near 1,403,000 N.) for about 4 miles to the west-northwest. It becomes a fault in the Clarkdale quadrangle, where it is exposed for about 1 mile. The monocline forming the south side of the horst- type structure faces south and is opposed to the regional dip; that on the north side faces north in the direction of the regional dip. Structural relief is at least 300 feet on the south-facing monocline and is probably less on the north-facing one. Southeast of the Verde River, the south-facing monocline forms a narrow hogback in which the average dip of the beds is 30°-50°. The anti- clinal bend involving Precambrian quartz diorite, Tap- eats Sandstone, and basal Martin Limestone is well ex- posed half a mile southeast of the Verde River; the quartz diorite-Tapeats contact in places is almost ver- tical. The synclinal bend, involving Redwall and Supai beds, is well exposed about 114 miles southeast of the Verde River. Near the Verde River (1,410,500 N., 388,000 E.) the monocline splits into two branches, one trending slightly south of west, the other continuing northwest for about 2,000 feet, then swinging more nearly due west. Here the contact between quartz dio- rite and Tapeats is vertical or slightly overturned. Paleozoic rocks on the anticlinal bend have been re- moved by erosion. The synclinal bend, involving beds in the B unit of the Martin, is well exposed on the north side of the Verde River (1,411,500 N., 386,500 E.), where the beds make an abrupt turn from nearly hori- zontal to vertical. The north-facing monocline on the north side of the horst-type structure lies only 200-300 feet northeast of the south-facing monocline near the east edge of the quadrangle; but some 3,000 feet from the quadrangle boundary, it swings northwest until it is about 2,000 feet from the south-facing monocline, where it resumes its west-northwest trend for about 1 mile. Here it is offset to the north a few hundred feet by a north-trend- ing fault. West of here displacement is largely along a fault, which dies out abruptly. A north-facing monocline branches off the south-fac- ing monocline a short distance northwest of the Verde River (1,412,000 N., 386,000 E.) and extends northwest for about 3,000 feet, where it horsetails out into at least five north-trending faults or faulted monoclines. Cumu- lative vertical separation on the branches is close to 500 feet. 96 Bull Basin monocline-The west-facing Bull Basin monocline (pl. 2 sees. A-A', J-J', K-K' ; pl. 5) on the west side of the southeastern anticline lies near and largely west of Bull Basin Canyon and trends north-northwest and then north from 1,390,000 N., 379,000 E. for about 4 miles. Faults mark its trend over some of this distance. South of about 1,400,000 N. the monocline appears to branch, the west branch trending nearly south. Total structural relief is 600- 700 feet. The monoclines and faults may continue to the southeast for at least another 4 miles (pl. 5) ; the southernmost outcrop of the contact between the Martin and Redwall Limestones (1,372,600 N., 378,000 E.) is about 800 feet below the contact's altitude about 2 miles to the east, and only one fault, which has a stratigraphic throw of about 250 feet, was found (1,372,000 N., 387,500 E.). South of the Verde River, the monocline is buried by gravel, beneath which it is offset about half a mile to the southeast by a northwest-trending fault ; it reappears near Hubbel Ranch (1,418,000 N., 373,700 E.), where it has been mapped as a fault; poorly ex- posed, steeply dipping beds, however, suggest a mono- cline (pl. 2, see. Structural relief here is about 700 feet. Other monoclinal - structures.-Other monoclinal structures occur in the area : 1. A south-facing arcuate monocline is north of St. Mathews Mountain. A younger fault has down- dropped the Tapeats on the north giving the effect of anomalous (reverse) drag (pl. 2, sec. L-'). 2. A south-facing monocline (pl. 2, see. A-4') trends east-northeast from 1,377,000 N., 387,000 E., and is exposed for a little more than 1 mile. Struc- tural relief appears to be about 500 feet and to decrease to the east, where the monocline may pass into a fault. 3. A northwest-facing monocline trends northeast from 1,414,500 N., 365,700 E., for about 4,000 feet and dies out abruptly to the southwest; structural relief at the northeast end is about 300 feet and appears to be due entirely to a fault. 4. A southeast-facing monocline trends northeast from 1,400,000 N., 344,800 E., for about 4,000 feet. East-dipping beds exposed to the south-south- west suggest that it has a length of at least 1% miles. At the southwest end of the main exposures, the structure is narrow ; at the north- east, it becomes broader. FAULTS Vertical to high-angle faults trend northwest to north and northeast to east. Most of them are shown as GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA vertical in structure sections, as the amount and direc- tion of dip on fault planes was determined only locally. Few are exposed for more than 2 miles. Some die out; others pass into monoclines. Stratigraphic throw ranges from less than 100 feet to at least 750 feet; some of the larger displacements represent vertical separation across several faults or across faults and monoclines. The amount of displacement on minor faults in the Paleozoic rocks can be determined only where the con- tact between formations or a thin unit within a forma- tion is cut. In the massive Redwall Limestone, faults are difficult to trace. One low-angle thrust was ob- served; it displaced unit 1 of the Redwall Limestone and had an apparent dip slip of about 8 feet, as ex- posed in a cut near 1,425,600 N., 344,000 E. Faults with vertical displacements of 250-700 feet are exposed for short distances in the northeast corner of the area (pl. 2). Most trend eastward, although a few trend northward. The north side of most east- trending faults is downthrown ; the accumulated vertical separation (pl. 2, see. L-L') is about 1,200 feet. An eastward-trending fault (pl. 5), probably part of this group, is exposed for a short distance in Bear Canyon about a mile east of the Paulden quadrangle (Lehner, 1958, p. 570; pl. 45) ; it has a stratigraphic throw of about 600 feet, the north side being downthrown. The major north-trending fault in the northeast cor- ner of the area (near 1,450,000 N., 398,200 E.) has a vertical separation of at least 700 feet, the east side being downthrown (pl. 2b, see. L-L'). Farther west a buried fault trending north-northeast is indicated on plates 2 and 5. Its trace is suggested by topographic expression and by slight displacement of basalt and gravel in Hell Canyon. Just north of the quadrangle boundary (near 385,000 E.), the fault brought the Supai Formation on the west up into contact with the Coconino Sandstone on the east. Four miles farther north the vertical separation of the contact between the Coconino Sandstone and Kaibab Limestone is an estimated 400- 500 feet, and this movement was largely pre-Perkins- ville in age. Several faults in the southeastern part of the Paul- den quadrangle are westward extensions of faults in the Clarkdale quadrangle (Lehner, 1958, pl. 45). The southernmost one trends northeast from 1,380,000 N., 395,000 E. The north side is downthrown, and the ver- tical separation is about 300 feet (pl. 2, sec. L-'). East of the quadrangle boundary the fault curves north then north-northwest and re-enters the quadrangle near 1,393,500 N., where the west side is downthrown. A fault trending east-northeast having the south side downthrown about 300 feet extends for about 114 miles from 1,386,500 N., 392,500 E. (pl. 2, see. L-') and STRUCTURE continues for 1%4 miles into the Clarkdale quadrangle, where it is buried by gravel. It offsets slightly the fault just described, whereas most of the east-trending faults in the Paulden area are offset by north-trending faults. Near the northeast side of Chino Valley, east of Gran- ite Creek, northwest-trending displacements have re- sulted in a total vertical separation estimated at about 800 feet (pl. 2, see. G@-G'). A fault, in which the west side is downthrown about 250 feet, is indicated by a small outcrop of Tapeats Sandstone (near 1,372,000 N., 387,500 E.) and by a sliver of probable Tapeats a mile to the northwest. Another fault or monocline about 2 miles to the west is indicated by the altitude of the contact bet ween the Martin and Redwall Limestones, as mentioned in the discussion of Bull Basin mono- cline (p. 96). A fault near the headwaters of King Canyon (1,8387,- 900 N., 385,000 E.) trends eastward. The north side is upthrown; the stratigraphic separation is about 150 feet near where the fault swings to the northeast and decreases west and northeast of here. The Tapeats Sandstone on the south side is steeply upturned. The northwest-trending fault that probably offsets Bull Basin monocline south of the Verde River is ex- posed for about half a mile. Near the Verde River (1,416,000 N., 368,000 E.) the stratigraphic throw is about 400 feet, the east side being downthrown. The fault is buried by gravel and basalt (near 1,415,000 N., 370,000 E.). About 1,300 feet northwest of the Verde River, the fault meets a northeast-trending fault or monocline; the fault was not recognized to the north- west. West of Bull Basin monocline the top of the Redwall Limestone is about 150 feet lower than the base of this same limestone 1,500 feet to the southwest (near 1,- 395,000 N., 370,000 E.) ; the structural relief, therefore, is about 400 feet (pl. 2, sees. J-7' and K-K'). Al- though buried, this structure probably trends northwest (from near 1,391,500 N., 374,000 E.), but whether the displacement is due to a fault or a monocline is un- known. The 20° NE. dip of the Redwall south of the structure suggests a flexure. The structure marks the probable northeast side of the topographic high of Mazatzal Quartzite. The irregular southwestern margin of Chino-Lone- some basin suggests an erosional valley, but the rather straight trends of parts of the eastern and northeastern boundary suggest structural displacement, as does the depth of wells in basin fill close to Precambrian or Paleozoic bedrock outcrops (figs. 20, 22, 23). Except for Coyote fault in the western part of the Mingus Mountain quadrangle and the structure on the south- 97 west side of Black Mesa (see "Monoclines") structures that may have partly outlined the basin have been com- pletely obscured by basin fill, by subsequent pedimen- tation, and by wearing back of fault scarps by erosion during and after deposition of the upper Tertiary (?) rocks. Faults may in part outline the Dells Granite (pl. 1). The fault on the southwest side is suggested by the known minimum depth of the basin a short distance southwest of granite outcrops (pl. 1, see. The one on the southeast side is suggested by the change, be- neath basalt, from intensely foliated north-trending rocks to massive granite on what may be an extension of the fault that separates gabbro from Government Can- yon Granodiorite to the southwest; it may have local- ized the Glassford cinder cone. In the southern part of the area, a few high-angle north- and northeast-trending faults offset lithologic units of Precambrian rocks and have horizontal dis- placements of 100-1,000 feet. The faults are intruded by Tertiary (%) andesite dikes. JOINTS In many places the Paleozoic rocks are well jointed, especially in the Martin Limestone and to a lesser ex- tent the Tapeats Sandstone. In general these joints strike N. 30° E. and N. 60° W. Their origin is un- known, but the two directions are about the same as those of the major joints in the Dells Granite and as those of some faults. In the northeastern part of the Clarkdale quadrangle, Lehner (1958, p. 542, 571) re- ported well-defined joints especially in the Coconino Sandstone, that trend N. 50° W. and N. 45° E. and are about parallel to nearby high-angle faults. YOUNGER STRUCTURE STRUCTURE FORMED BY INTRUSION OF ANDESITE PLUGS Some steep dips in Paleozoic rocks are interpreted as due to forceful intrusion of andesite plugs, but the pos- sibility of deformation associated with a fault or a monocline at an earlier time cannot be eliminated. The best example of structure probably formed by intrusion of andesite is found about three-fourth mile east of the Pinnacle (pl. 2, near 1,400,400 N., 356,500 E.). The Paleozoic rocks east of the plug dip steeply (65°) east; those southwest of the plug dip steeply southwest (pl. 2, see. F-F"'). A short distance west of the plug the unnamed basaltic flows of the Alder(?) Group are about 100 feet above the Redwall Limestone on the southwest side of the plug, an occurrence suggesting that the basaltic rocks were uplifted by an underlying plug. Small outcrops of Tapeats Sandstone and Martin 98 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA Limestone at the north end of the large area of andesite west of Route 89 (pl. 2) may have been dragged up by the andesite. If not, and if the Paleozoic-Precambrian basement is close to the surface here, then Chino-Lone- some basin is relatively narrow at this place (figs. 22, 23) or is separated into two parts. FAULTS Faults having displacements as much as 2,800 feet cut Hickey basalt in the Jerome area (pl. 5), but no faults of this magnitude were observed cutting the upper Tertiary (?) rocks in the Prescott-Paulden area. Four faults cut these rocks in the area between Prescott and the Granite Dells and Glassford Hill (pl. 1). Or- ange tuff underlies the basalt on both sides of the north- east-trending fault southwest of the Granite Dells (fig. 24A) and the basalt south of fault near Prescott. If the orange tuff in each place represents the bed beneath the middle basalt flows, then vertical displacement may have been about 200 feet in the first locality and 300-400 feet in the second. In the southern part of the Paulden quadrangle, a few faults cut basalt and have displacements of not more than 100 feet. Actual displacement is hard to prove because of the difficulty in tracing faults through basalt. In a few places where apparently faulted, the basalt flowed against fault scarps, or slight movement along an older fault disrupted the basalt. Faults trending north-northeast cut basalt and older rocks about 1,500 feet above the junction of Rattlesnake Wash with Hell Canyon and in two places along Hell Canyon-one just east and one about half a mile west of King Spring. Vertical displacement of the base of the basalt is 50-100 feet. Post-basalt movement on the westernmost structure probably was largely in the form of a flexure; fine sand beneath basalt on the south side of the canyon dips steeply (35°) east and the basalt is downwarped. One basalt flow overlies a thin bed of fresh-water limestone above sand and gravel west of the flexure; four flows overlie the limestone east of it. Three flows lie west of the fault east of King Spring, and at least four flows are east of it. A low fault scarp cuts upper Tertiary(?) gravel along the northeast side of Big Chino Wash (southwest side of Black Mesa), largely northwest of the Paulden quadrangle. It shows up well on aerial photographs for a distance of about 26 miles. Its course is somewhat sinuous, and it locally branches; in places a grabenlike depression was probably carved out by a stream that temporarily followed the fault. The scarp probably formed during renewed movement along an older struc- ture-Big Chino monocline or fault. AGE OF THE STRUCTURES Structural disturbances are known to have occurred intermittently since the close of the Paleozoic Era, but the sedimentary record in this area yields little infor- mation as to when they occurred. Price (1949) re- ported a conspicuous disconformity between the Kaibab (Permian) and the Moenkopi (Early Triassic). Mc- Kee (1951, p. 494) stated that the first major uplift in central Arizona after the Precambrian probably oc- curred in the Late Triassic. Monoclines on the Colo- rado Plateau are Late Cretaceous to early Tertiary in age (Babenroth and Strahler, 1945, p. 148-149; Kelley, 1955, p. 797). Remnants of once extensive gravel de- posits beneath basalts on the Plateau and in north- and northeast-trending channels beneath basalt south of the Plateau margin indicate uplift to the south probably in the late Miocene or early Pliocene (McKee, 1951, p. 498). East of the Prescott-Paulden area, Anderson and Creasey (1958, p. 78-83) and Lehner (1958, p. 568-579) recognized two major periods of deformation. One af- fected only Paleozoic and older rocks; the other, the stronger, followed accumulation of the Hickey forma- tion but continued in milder form during and after accumulation of the Verde and Perkinsville Formations. It is characterized chiefly by normal faults trending north and north-northwest. None of the major structures in the Paulden quad- rangle are clearly younger than the upper Tertiary (?) rocks, and because of uncertainties as to the relations of the basalt to Hickey and Perkinsville basalts, the rela- tions of these structures to post-Hickey deformation are uncertain. The terms "older and younger structures" do not imply deformation in pre- or post-Hickey times. MONOCLINES The possibility of a Late Cretaceous-early Eocene age for monoclines in the Paulden quadrangle is appealing because of the similarity of the monoclines to those on the Colorado Plateau that are of this age. However, a monocline in the southeastern part of the Clarkdale quadrangle has tilted Pliocene(?) basalt of the Hickey Formation (Lehner, 1958, p. 579) ; the Verde fault of post-Hickey age passes northward abruptly into a mono- cline (Anderson and Creasey, 1958, p. 80). The young- est beds involved in monoclines in the Paulden quad- rangle are those of the Supai Formation, but younger Permian beds, since removed by erosion, undoubtedly also were folded. The monoclines were probably formed after the Paleozoic rocks were regionally tilted to the northeast (pl. 5), and they are older than at least some of the north- and northwest-trending faults. No in- volvement of any upper Tertiary (?) rocks in the mono- clinal structures was observed; some monoclines are buried by upper Tertiary (?) rocks. PHYSIOGRAPHY 99 Bull Basin monocline is older than the gravel east of it. This gravel was probably deposited in a valley carved into the uplifted side of the block. Limestone Canyon monocline is older than the gravel northeast of the monocline, as is indicated by the presence in the gravel of pebbles of Martin Limestone derived from the uplifted block to the southwest. Limestone Canyon monocline northwest of the quadrangle and the fault extension of the Verde monocline east of the quadrangle are buried by basalt, but these basalts may both be Perkinsville in age. The monocline north of St. Mathews Mountain is older than basalt that buries it at the east edge of the quadrangle. To the east this basalt is called Hickey by Lehner (1958). Bull Basin and Verde monoclines are older than the Verde River; the intervening uplifted area (pl. 2, see. D-D' ; pl. 5) was worn down before the river took its present course. FAULTS Lehner (1958, pl. 45) mapped many faults in the Clarkdale quadrangle that cut basalt of the Hickey Formation (pl. 4). Most of the faults are east of Coyote fault. Of those that extend into the Paulden quadrangle, none clearly displaces the upper Ter- tiary (?) basalt more than a minor amount, although displacement of Paleozoic rocks may be 300 feet or more. The fault that curves northward east of the area and reenters it near 1,393,500 N. does not obviously disturb the older gravel. The northwest-trending fault that offsets Bull Basin monocline south of the Verde River does not disturb the older gravel or the overlying (post-andesite) basalt that conceals the probable trend of the fault. The faults that cut Precambrian rocks in the southern part of the area (pl. 1) are probably younger than the Precambrian, but older than the upper Tertiary (?) rocks; the faults are intruded by andesite dikes that also probably have the same age limits. The principal move- ment on the faults, however, may have taken place at a much earlier period than the intrusion of the dikes. Quartz veins and zones of mild silification, presumably of Precambrian age, occupy or parallel some of the faults; the first movement, therefore, may have been in the Precambrian. In the southwestern part of the area, movement on some faults occurring after basalt deposition may have been as much as 400 feet, if the orange tuff bed on which the displacement was measured is everywhere correla- tive. Only small faults cut the basalt (Perkinsville?) in the northeast part of the area. Recurrent movement probably occurred along the structure on the southwest side of Black Mesa (largely northwest of the area ) ; the most recent movement form- ing the low fault scarp in upper Tertiary (?) gravel. CONCLUSIONS The structural low in which the Verde River flows eastward from Chino-Lonesome basin may have formed at the same time that deformation arched the Black Hills, faulted and downwarped basalt of the Hickey Formation north of the Black Hills, and produced the major movement on Coyote and Verde faults. How- ever, the underlying structure does not appear to have controlled the course of the Verde River to any extent (pl. 5), except where the Verde leaves the basin and for a short distance south of its junction with Hell Can- yon. The structure was probably buried by upper Ter- tiary (?) rocks when the river's course was determined. The covering rocks would be considered Perkinsville were it not for the fact that they include older gravel that probably antedates the formation of Chino-Lone- some basin. Until the relation of the upper Tertiary (?) rocks to the Hickey and Perkinsville Formations in the type areas is known, the age of the major deformation cannot be determined. If basalt in the southeastern part of the Paulden quadrangle is Hickey, then most of the structure there is pre-Hickey in age; if these rocks or some of them, however, are Perkinsville in age, then some of the structure may also be post-Hickey in age. Similarly, some or all of the rocks mapped as Hickey west of Coyote fault in the Jerome-Clarkdale area may be Perkinsville in age and may have accumulated after Chino-Lonesome basin was formed. PHYSIOGRAPHY GENERAL FEATURES The major physiographic feature of the Prescott- Paulden area is the broad Chino-Lonesome Valley, which extends from a short distance southeast of the area for 60 miles to the northwest (figs. 1, 30). The southwestern boundary of the valley is quite irregular and consists of a series of mountain ranges, of which only the northern part of the Bradshaw Mountains ex- tends into the area. The southeastern part of the valley is bounded on the east by the uplifted Black Hills block (Mingus Mountain quadrangle) ; the northwestern part is bounded by the uplifted Black Mesa block (mostly northwest of the area). Between these two blocks is a low relatively flat but locally dissected area that ex- tends northeastward to the southwestern boundary of the Colorado Plateau (the Mogollon Rim). Chino-Lonesome Valley is an erosional and struc- tural basin filled with upper Tertiary (?) rocks. Ex- terior drainage commenced when the basin was filled sufficiently for water to spill over a low point into the Verde River drainage. This point is located near the 100 center of the northeastern boundary (near 1,406,000 N., 337,000 E.), not at one end, as in normal valleys. The existence of temporary base levels allowed forma- tion of gravel-strewn pediments and terraces. Drainage in the southern half of the valley was northward until the Lonesome Valley portion was captured by head ward erosion of the Agua Fria River. Rapid dissection of the pediment followed the stream capture. The Verde River (fig. 2) and its tributaries northeast of the basin have cut steep-walled canyons in the generally horizon- tal Paleozoic and Cenozoic rocks. The surface forms are largely erosional, except for some formed by alluviation along valley bottoms. MOUNTAINS The mountains and hills are of several types, each type depending primarily on the rocks and structure involved but locally on the erosional history of the area. In the southern part, erosion of schistose rocks having nearly vertical structures produced long sharp ridges separated by north-trending gulches. Higher ridges and peaks reflect a greater resistance to erosion. In the southwestern part of the area, some subdued, rounded hills, generally composed of massive granite, represent a weathered erosion surface that was buried during late Tertiary (?) time and later exhumed. The topographic form of the isolated Dells Granite is controlled by nearly vertical joints (fig. 14). Square to rectangular hills, locally having precipitous sides, rise 50-200 feet above the valleys. The major valleys in the granite trend approximately N. 25° E. and N. 70° W., parallel to the major joints. The valleys are 200- 1,000 feet apart and as much as half a mile long. In the southwestern part of the area (pl. 1), flat- topped mesas and buttes are part of a maturely dissected GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA lava plateau or plain. Flat-topped hills in Chino-Lone- some Valley are remnants of once extensive pediments (figs. 28, 29). Northeast of the basin, flat-topped hills are capped by nearly horizontal Paleozoic rocks or basalt flows of late Tertiary (?) age. Hogbacks were formed by erosion of steep monoclines. Flatiron-shaped slopes (dissected dip slopes) are fairly common in folded Mazatzal Quartzite. Glassford Hill (fig. 14) in the southwestern part of the area is a cinder cone; the cone was partly buried by nearly horizontal basalt flows that were eroded to form a roughly circular hill. St. Mathews Mountain in the east-central part (pl. 2) is a dissected cone of ande- sitic flow, breccia, and intrusive-plug material and was also partly buried by basalt. Dissected andesitic plugs or domes form isolated hills (fig. 19) on the north side of the Chino-Lonesome Valley east of Granite Creek. Erosion of andesite that is cut by steeply dipping joints and flow planes produced sharp peaks such as the Pin- nacle (pl. 2, 1,400,000 N., 353,000 E.). Erosion of ande- sitic gravel and breccia produced rounded hills covered with andesitic rubble. PEDIMENTS A broad pediment, strewn with sand and gravel, cov- ered much of Chino-Lonesome Valley. The pediment sloped from the margins toward the center and then along the axis of the valley to the Verde River. It prob- ably formed at the time that a temporary base level occurred along the river; much of it was subsequently destroyed by erosion. Lower pediments or terraces formed during shorter periods when temporary base lev- els had occurred along Granite Creek and the Verde and Agua Fria Rivers. FicurE 28.-Pediment east of Glassford Hill. The eroded edge of the pediment is across the Yaeger-Agua Fria alluvial flat. Glassford Hill is on the extreme right. It conceals fine-grained sedimentary rocks of late Tertiary (?) age such as are shown in figure 25. The view is to the southwest from the east edge of the area (pl. 1, 1,310,000 N., 398,000 E.). The Bradshaw Mountains are in the background, and Coarse gravel in foreground is largely colluvial material from pediment gravel to the east. 34°55" 34°45" © 34°35" PHYSIOGRAPHY 112'15' 101 I EXPLANATION Younger alluvial surfaces Pediment surfaces 7 Volcanic and sedimentary rocks of late Tertiary(?) age Precambrian and Paleozoic rocks 3 4 MILES FIGURE 29.-Distribution of pediment remnants in Chino-Lonesome Valley, Ariz. 102 The pediment is cut largely on basin fill, but in a few places it can be traced onto Precambrian and Paleo- zoic rocks around the margin. It is easy to recognize where its gravels are underlain by fine-grained lacus- trine deposits, but it is difficult to recognize where cut on fanglomerate or on basalt if the pediment gravels are composed largely of basalt fragments. The major pediment remnant is east of Glassford Hill (figs. 28, 29). Smaller remnants occur on both sides of Granite Creek and around the margins of the basin. The east side of the pediment remnant east of Granite Creek slopes imperceptibly into lower terraces and into allu- vium of the valley floor. In other places, where erosion has been rapid, the pediment remnants end abruptly. GEOLOGY OF THE PRESCOTT AND DRAINAGE CHINO-LONESOME VALLEY One of the interesting physiographic features of the area is the drainage pattern in Chino-Lonesome Valley ; the pattern records the history of drainage changes (fig. 30). Unlike a normal valley, which has an outlet at one end, the major outlet, the Verde River, of the 60-mile long valley is near the center of the northeast side. Northwest and west of the headwaters (Sullivan Lake), of the Verde River, drainage is southeastward (Big Chino Wash) and eastward (Williamson Valley Wash). South of Sullivan Lake drainage was entirely to the north and northwest until its southern part was cap- tured by headward erosion of the south-flowing Agua Fria River because of its steeper gradient. Route 89A follows the inconspicuous present divide between north- and south-flowing drainage for most of its distance across the valley. Water falling north of the highway (pl. 1, near the Gila and Salt River meridian; fig. 1) travels, via Granite Creek and the Verde and Salt Rivers, almost twice as far to the Gila River near Phoenix, as does water falling south of the highway, which reaches the same point in the Gila River via the Agua Fria River. The capture resulted in deep dissection of the pedi- ment. The existence of temporary base levels along the Agua Fria and its tributaries, especially along Lynx Creek, resulted in the formation of lower pediments or terraces and may account for some of the slight allu- viation that occurred along the river and its tributaries. Recent rapid erosion due to lowering of base level or to climatic changes has cut gullies 5-25 feet deep into alluvium and basin deposits (fig. 25). The northward drainage of the valley consists of three parts. About 40 percent of the area is drained by Granite Creek and its tributaries. The remainder is almost equally divided between the washes east and west of Granite Creek, which were formerly the prin- PAULDEN QUADRANGLES, ARIZONA cipal northward drainage lines. After capture of its headwaters by the Agua Fria River, the wash east of the creek could no longer remain a major drainage line; some stagnation and alluviation has occurred along it. The wash west of Granite Creek at one time drained all the area west of Granite Creek (west of the dotted line that extends northward from the Granite Dells, fig. 30) and possibly the area southwest of the Granite Dells. This drainage was captured by headward erosion of tributaries on the west side of Granite Creek, two north of and one south of the airport. © Granite Creek is a superimposed stream. It was let down onto resistant Dells Granite and Mazatzal Quartz- ite from overlying upper Tertiary (?) rocks or from a pediment cut on the upper Tertiary (?) or Precam- brian rocks. Had its course been a short distance to the west, the creek would now be on softer basin deposits. At the time the course was determined, however, the softer rocks may have been concealed by resistant vol- canic rocks. From the Dells Granite to the Mazatzal Quartzite, a distance of about 12 miles, the Granite Creek drainage was confined to a strip 1-214 miles wide (fig. 30, east of the dotted line) that is bounded by flat-topped hills, which are pediment remnants. The creek bottom within this strip is a quarter to more than half a mile wide. The wide valley flat probably formed because the creek had a very low gradient caused by the temporary base level formed by the resistant Precambrian rocks. The creek could widen its valley upstream from the resistant rocks but could do little downcutting. The reason why the creek was originally confined to this narrow strip is obscure. Granite Creek now drains a large mountainous area that received more rainfall than do the areas drained by the washes to the east and west since their headwaters were captured. Granite Creek enters the Verde River about 100 feet lower than does the wash to the west. This lower base level may explain why the creek captured the head- waters of the drainage system to the west. This wash may now be cutting back more rapidly because it is on softer material and also because of permanent stream flow below Del Rio Springs, which taps the Chino-Ar- tesian basin. NORTHEAST OF CHINO-LONESOME VALLEY The area northeast of Chino-Lonesome Valley as far as the Verde River is quite deeply dissected, but north of the river it is largely a flat land. The low relief appears to be due mainly to smoothing out of irregu- larities by basalt that flowed south from the Colorado Plateau. It could, however, be an extension of the pediment in Chino Valley. The lowland extends north- ward from the north-central part of the area and forms a break in the escarpment of the plateau (fig. 1). The PHYSIOGRAPHY 1083. 112°45" 112°30' Base and drainage compiled from U.S. Geological Survey 15-minute topographic quadrangles, Paulden and Prescott; U.S. Army Map Service 2° maps, Williams and Prescott; and Soil Conser- vation Service aerial photographs 112185" 35°00" e RANGLE ~- APRANGLE ~ 34°45" EXPLANATION Cenozoic rocks Precambrian and Paleozoic basement rocks Contact west of long 112°80' and north of lat 35°00' taken from reconnaissance mapping 1955-56 Drainage divide ||| Upper Granite Creek drainage basin 34°30' aw Agua Fria drainage basin 1 0. 1% , 3 4 Milcs FicuRE 30.-Drainage pattern in Lonesome, Chino, and Williamson Valleys, Prescott-Paulden area, Arizona. 104 southwest-facing Black Mesa escarpment, mostly west of the area, appears to be an offset part of the Mogollon Rim. The Verde River and its tributaries have cut steep-walled gorges as much as 300 feet deep into the relatively flat basalt and gravel plane and into the un- derlying Paleozoic and Precambrian rocks. Structure in the Paleozoic rocks apparently had little control on the course of these streams, except that the Verde River leaves Chino-Lonesome Valley near a structural low. The faults and monoclines were probably buried by upper Tertiary (?) rocks or by pediment gravels at the time that the stream courses were determined. ECONOMIC GEOLOGY ORE DEPOSITS HISTORY Mining in the Jerome-Prescott area prior to the ex- ploration of Arizona and New Mexico by the Spaniards was carried on by Indians. The presence of hammers and other stone implements in ancient workings at the site of the Silver Belt mine, a short distance southwest of the Iron King mine, indicates mining in the Prescott area during prehistoric time (Galbraith, 1947, p. 42). The first recorded discovery of an economic deposit was made in 1863, when Joe Walker and a party of pros- pectors found gold in Hassayampa River and Lynx Creek in the Prescott region (Hamilton, 1883, p. 47). The Lynx Creek placers have contributed a considerable part of the placer gold of the state and county. A little placer mining has been done on other creeks in the area. Lode mining during historic time close to the Prescott area commenced with the rediscovery of the ore deposits at the site of the Silver Belt mine in 1870 (Lindgren, 1926, p. 128). Rich silver ore was mined at this mine until 1880. The Iron King lead-zinc mine (southeast corner of pl. 1) is the only important lode deposit discovered within the Prescott-Paulden area. It has been the lead- ing mine in the Prescott-Jerome area since the closing of the United Verde mine at Jerome in 1953. Mining was begun at the site of the present Iron King mine probably about 1880. Production was sporadic and minor until 1937, when the present operation was started. Except for the Mazatzal Quartzite, the Precambrian rocks in the Prescott and Paulden quadrangles are rid- dled with prospect pits, tunnels, and shallow shafts, largely dug on quartz veins. A small amount of ore, mostly gold, has been produced from some of them. Many of these veins were prospected during the early days of mining, but prospecting and small-scale devel- opment work have continued intermittently since then. GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA MINERALOGY Brief descriptions of the minerals directly related to the ore deposits are given in this section. The list in- cludes hypogene ore and gangue minerals-formed by ascending ore-forming solutions-and supergene ore minerals-formed by descending waters-but not the common rock-forming minerals. Some hypogene and supergene ore minerals are of no economic importance. The data on mineralogy have been obtained from brief examination of material on dumps of small prospects and from the following sources: Anderson and Creasey (1958, p. 91-95), Galbraith (1947), Wilson and others (1934), and Lindgren (1926, p. 24-31). HYPOGENE MINERALS ORE MINERALS Arsenopyrite (FeAsS).-Small crystals of arsenopy- rite are scattered throughout the massive sulfide ore body at the Iron King mine. It was also noted in specimens on some of the dumps of small prospects (near 1,274,600 N., 390,500 E. and 1,282,700 N., 393,800 E.). Chaleopyrite (CuFeS,).-Small quantities of chalco- pyrite occur in many of the fissure vein deposits and in the copper vein a short distance west of the Iron King mine. Galena (PbS). as scattered medium to large crystals, is common in many of the fissure veins in the area. In the Iron King massive sulfide ore it is an important constituent, where it occurs as very fine to microscopic grains. It is present in the Gold Coin group (1,293,600 N., 368,300 E.) and was noted in small prospects in the following areas: 1,287,200 N., 371,500 E.; 1,274,600 N., 390,500 E.; 1,282,700 N., $93,800 E.; and along 393,300 E., between 1,282,100 N. and 1,283,400 N. Near the east edge of the Paulden quadrangle south of the Verde River (1,422,400 N., 396,000 E.), cubes of galena, more than 1 inch square, occur in calcite veins in the Mississippian Redwall Limestone. Galena was also reported by Lindgren (1926, p. 102) in a quartz vein (the "Peters silver mine") in the southeastern part of the Paulden quadrangle, probably in see. 7, T. 16 N., R. 1 E. Gold (Au). -Gold is economically important in the Iron King mine, in many of the small quartz veins in the area, and in the placer deposits along Lynx Creek. The gold at the Iron King mine is free-milling and oc- curs in galena, sphalerite, and pyrite, as indicated by metallurgical tests and assays. Chiefly because it is most abundant, pyrite carries most of the gold. Visible gold has been reported from some of the quartz veins, nota- bly the Gold Coin group (1,293,600 N., 368,300 E.), the White Horse prospect (1,285,500 N., 370,500 E.), a prospect near 1,274,000 N., 369,200 E., and in Precam- ECONOMIC brian rocks north and south of the boundary between the Prescott and Paulden quadrangles. Placer gravels glong Lynx Creek near Walker (about 3 miles south of the Prescott quadrangle) have yielded nuggets of about 5 ounces, whereas the gold from lower Lynx Creek ranges from finely divided material to nuggets of about three-tenths of an ounce (Wilson, 1952, p. 48). Hematite (Fe,0,) -Specular hematite is widespread as veinlets in Precambrian rocks. Hematite is an abun- dant constituent in some of the beds of jasper-magnetite in the Texas Gulch Formation. It is concentrated along cross laminae and bedding planes in some of the Mazat- zal Quartzite. Magnetite (Fe,O.,) -Although of no economic im- portance at present, magnetite is a major constituent in the narrow beds of jasper-magnetite in the Texas Gulch Formation and in some of the quartz-magnetite veins in Alder Group rocks, especially in the unnamed tuffa- ceous rocks. Magnetite-rich zones occur in gabbro, es- pecially in and east of the largest mass (near 1,289,000 N., 371,600 E.; 1,288,700 N., 374,000 E.; and 1,290,500 N., 374,500 E.) and in some of the western part of the westernmost mass. Magnetite in the gabbro is associ- ated with ilmenite. Magnetite is also present in black sands in an area locally called the Nugget Patch (1,290,000 N., 370,000 E.) and in gulches that drain areas of gabbro and late Tertiary.(?) basalt. Molybdenite (MoS). -Scattered flakes of molybde- nite were observed in large quartz veins in the extreme southwestern corner of the Prescott quadrangle. Mo- lybdenite also occurs in Copper Basin (Kirkland-Iron Springs quadrangles) about 7 miles west-southwest of the city of Prescott. Platinum (Pt). -Platinum has been reported from the black sands near Prescott (Galbraith, 1947, p. 10). Pyrite (FeS,) . -Pyrite is the principal ore mineral in most of the fissure veins in the area and is a major con- stituent in the massive sulfide deposit at the Iron King mine. Scattered pyrite crystals are widespread wher- ever there has been even minor hydrothermal alteration. It is sparsely disseminated as tiny cubes in some areas of alaskite, Prescott Granodiorite, and Alder Group rocks. Pyrite is recovered in the concentrator at the Iron King mine largely for its gold content but partly because of the demand for its use as a smelter flux. Scheelite (CaWO,).-Scheelite occurs in quartz veins in the Gold Coin group (1,293,600 N., 368,300 E.) and has been reported from quartz veins in the Prescott Granodiorite south of Prescott. Serpentine minerals (antigorite and chrysotile, H, -Serpentine minerals, of no economic im- portance, occur in some gabbro, especially in the north- ern part of the western mass. 105 Aphalerite (ZnS).-Sphalerite, as minute grains forming streaks and aggregates in the pyritic massive sulfide and as grains interstitial to the pyrite, is the most abundant ore mineral in the Iron King mine. Many of the fissure veins in the area contain scattered crystals of sphalerite. It was noted at the New Strike prospect (1,276,200 N., 357,200 E.) and at a small pros- pect at the southern edge of the Prescott quadrangle (near 384,700 E.); it was also reported by Lindgren (1926, p. 102) in a quartz vein (the "Peters silver mine") in the southeastern part of the Paulden quad- rangle. Stibnite (Sb,8,). -Stibnite has been reported from the Malley Hill mine (Galbraith, 1947, p. 22) on Lynx Creek (the exact location is unknown ; it may be south of the map area). Tennantite [ (Cu, Fe) ,, As,8:;].-Silver-bearing ten- nantite in the Iron King mine adds to the silver content of the ore. GEOLOGY GANGUE MINERALS Barite (BaSO,) -Barite is reported (Lindgren, 1926, p. 25) in the Silver Belt vein, southwest of the Iron King mine. Carbonate minerals.-Several varieties of carbonate minerals occur in the ore deposits Ankerite [CaCO,: (Mg, Fe, Mn) CO;] is the principal carbonate mineral at the Iron King mine. Calcite (CaCO;) is found in many of the fissure veins in the area, as are ankerite and dolomite [(Ca, Mg) CO;]. Brown car- bonate, possibly siderite (FeCO,;), was noted in a few of the fissure veins. Chlorite (complex silicate of Fe, Mg, A1,0,). -Alter- ation zones associated with some of the fissure vein deposits contain chlorite. Piedmontite - (mangamese-bearing - epidote). -Al- though of no economic importance and probably not related to any ore-bearing solutions, piedmontite is de- scribed here because it is a relatively rare mineral and is widely distributed in the southwestern part of the Prescott quadrangle. It forms small veinlets and dis- seminated grains in the southwestern part of the west- ernmost mass of gabbro, in the Government Canyon Granodiorite, and in Prescott Granodiorite north- northwest of Prescott. It is pink, but as seen under the microscope, the color is not evenly distributed; it grades on the edges into a yellow mineral having yellow absorption but the same indices of refraction. The indices of refraction of the piedmontite are: a, 1.738; B, 1.758; y, 1.773 and X, yellow; Y, purple; and Z, purple (as determined by Marie L. Lindburg of the U.S. Geological Survey in 1949). Quarts (S10). -Quartz is the principal gangue min- eral in most of the ore deposits of the Prescott quad- 106 rangle and is the most abundant one in the fissure veins of both quadrangles. At the Iron King mine it occurs as rather pure masses associated with the massive sul- fide or is interstitial to the sulfide grains. It is the main constituent in the quartz-magnetite veins in some Pre- cambrian volcanic rocks. Quartz has been mined for flux from a quartz vein (1,284,000 N., 398,000 E.) about 2 miles north of the Iron King mine. Considerable amounts are in the large quartz veins on the hill in the extreme southwestern corner of the Prescott quadrangle and in a large quartz vein in quartz diorite along the Verde River (1,413,500 N., 382,300 E.). Sericite [ HK Al; (810.);].-Sericite is a fine-grained variety of muscovite that is widespread in the alteration zone associated with the Iron King massive sulfide ore bodies and occurs in many of the narrow alteration zones associated with the fissure veins. Tourmaline (complex silicate of B, Al, Fe, Mg).- Black tourmaline occurs in some of the fissure veins. Tourmaline-quartz and tourmaline veins are abundant in the Dells Granite and the westernmost mass of Pres- cott Granodiorite, where much of the tourmaline occurs as fine hair-like needles. Some of it forms dikelike or podlike masses as much as 5 feet wide. Tourmaline veins may be younger than some of the quartz veins. SUPERGENE ORE MINERALS Anglesite (PbSO,) and cerussite (PbCO,).-Angel- site and cerussite occur in the oxidized parts of the Iron King mine and may be present at the surface of some of the fissure veins that carry galena. Cerargyrite (AgCl).-Cerargyrite has been reported from the Silver Belt mine, southwest of the Iron King mine, where it was found associated with cerussite in ancient workings (Galbraith, 1947, p. 42). Chateocite (Cu,8).-Small quantities of chalcocite are found in many of the fissure veins that contain pri- mary chalcopyrite. It was noted specifically in a pros- pect near 1,274,000 N., 369,200 E. Chrysocolle (CuSi0, ' 2H,0).-Films of chrysocolla are common at the surface of the fissure veins that carry chalcopyrite and at the United States mine (1,423,900 N., 399,300 E.). Limonite (hydrated iron oxide). -Limonite gossan developed at the surface over the Iron King massive sulfide deposit and in minor amounts over most of the fissure deposits. Some limonite (gossan) was mined at the Iron King mine for its precious metal content in the early days of mining. MU a lac hite [CuCo,:Cu(OH),] and azurite [2CuCO,;-Cu(OH),].-The green and blue copper car- bonates malachite and azurite occur as scattered films at the surface of many of the fissure veins, in Tapeats Sandstone, and in calcite veins and disseminations in GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA the Supai Formation at and south of the United States mine. Manganese oxides.-Minor amounts of manganese ox- ides are associated with many of the fissure veins. V anadinite [PbCI-Pb,(VO.);].-Vanadinite occurs as yellow to yellowish-green and light-brown needles and crusts in galena-bearing calcite veins in Redwall Limestone south of the United States mine (1,422,400 N., 396,000 E.). Wuifenite (PbMoO,.)-Wulfenite occurs with vana- dinite as thin orange wedges south of the United States mine. GENERAL CHARACTERISTICS The ores deposits of the Prescott-Paulden area consist of Precambrian massive sulfide deposits, Precambrian and possibly younger fissure veins, a few noneconomic post-Paleozoic fissure veins and disseminated deposits, and Quaternary gold placer deposits. Practically all the base metal production and much of the precious metal production has come from the Iron King lead-zinc mine in the southeastern corner, the only known massive sulfide deposit within the area. Fissure veins have been mined largely for their precious metal content, prin- cipally gold ; production from them has been small, but the amount is unknown. Placer deposits have probably supplied less than one-sixth of the gold produced in the area. . As most ore deposits in north-central Arizona are Precambrian in age, a knowledge of the thickness of the overlying Paleozoic and Cenozoic rocks is important in exploring for ore deposits in Precambrian rocks. For this reason a map (fig. 31) showing the approximate thickness of Paleozoic and Cenozoic rocks in the Paul- den quadrangle has been compiled. The approximate minimum thickness of Cenozoic rocks in Chino-Lone- some basin is shown on figure 23. The configuration of the Precambrian surface is illus- trated in the structure contour map of the Paulden, Clarkdale, and Mingus Mountain quadrangles (pl. 5). As the contours are drawn on the base of the Redwall Limestone, the Precambrian surface is about 500 feet below the altitudes shown on plate 5, except in an area of about 23 square miles that is probably underlain by the Mazatzal Quartzite. Within this area the Pre- cambrian surface may be as little as 10 feet below the base of the Redwall. The area that is underlain by the Mazatzal is economically unimportant, as no ore de- posits occur in exposed portions of the Mazatzal and the quartzite has not been intruded by granitic rocks or by quartz veins. __ MASSIVE SULFIDE DEPOSITS Deposits composed of granular aggregates of sulfide minerals and little or no gangue minerals are referred to ECONOMIC as massive sulfide deposits. The Iron King mine at Humboldt, the only massive sulfide deposit in the Pres- cott-Paulden area, and the United Verde and United Verde Extension mines at Jerome are examples of this type of deposit. Pyrite is the dominant mineral, but variable amounts of other sulfides, especially chalcopy- rite, sphalerite, and galena are present. Where appreci- able amounts of these minerals (other than pyrite) oc- cur, the ore is generally banded. Most massive sulfide deposits exhibit sharp contacts with host rock, but local- ly they grade into disseminated deposits. Silification and sericitization of the host rocks are common. Minable ore shoots are formed where the pyrite-rich facies was fractured and base or precious metals were added. This type of deposit was formed probably by hydrothermal mineralizing solutions that replaced schistose rocks. FISSURE-VEIN DEPOSITS The fissure veins were formed principally by fissure filling, but replacement of the wall rock occurred along some of them. They occupy shear zones, some of which are parallel to the foliation in the enclosing rocks. Lindgren (1926, p. 37-48) described two types of fissure-vein deposits in the Jerome and Bradshaw Moun- tains quadrangles : gold-quartz veins of undoubted Pre- cambrian age and gold and silver veins that he con- sidered younger than the gold-quartz veins and possibly late Mesozoic or early Tertiary in age. The gold- quartz veins are widely distributed throughout the Pre- cambrian rocks of these two quadrangles; the younger veins are confined apparently to the southern part and south of the Prescott quadrangle. The gold-quartz veins are massive or have a crude banding. The quartz, which is glassy to milky, occurs as pods or lenses in shear zones, which strike parallel or at an angle to the foliation in the country rock. Few of the veins can be traced for as much as 1,000 feet. Calcite, ankerite, or siderite may be present. Tourma- line occurs in many of them. The sulfides, which are not abundant, consist of pyrite, chalcopyrite, sphalerite, and galena. Gold, some of it in visible particles, is pres- ent in many of the veins. Scheelite has been noted in some of them. In the eastern part of the Prescott and Paulden quadrangles, north and south of the boundary between them, unmineralized Paleozoic rocks overlie Precambrian rocks that contain quartz veins, an occur- rence suggesting that the mineralization is Precambrian in age. Locally, as in the headwaters of King Canyon (1,885,400 N., 385,100 E.), copper carbonate occurs in the Tapeats Sandstone. The copper was probably dis- solved out of quartz veins in adjacent alaskite and re- deposited in the sandstone by ground water. Quartz, 758-447 0O-65--s 107 GEOLOGY quartz-tourmaline, and tourmaline veins are abundant in the Dells Granite and in the southwestern mass of Prescott Granodiorite, but gold and sulfide minerals are generally absent from or very sparsely distributed in these veins; few of these veins have been prospected. Most younger fissure veins are straight and narrow and have well-defined walls The quartz gangue is milky and has a drusy structure. Carbonate accompa- nies quartz in many of the veins, which also have minor and variable amounts of arsenopyrite, sphalerite, chal- copyrite, galena, and some tetrahedrite and tennantite. Gold and some native silver occur in the oxidized zone; gold is not visible in the primary ore. According to Lindgren (1926, p. 42) many of the veins are associated with rhyolite porphyry dikes, which are younger than the regional metamorphism and deformation that in- volved the Precambrian rocks. Other veins, according to Lindgren, are apparently related to stocks of quartz diorite or granodiorite that he considered possibly post- Precambrian in age. One of these stocks has been proved to be Precambrian in age (see p. 96, 35, 50). POST-PALEOZOIC MINERALIZATION Most of the ore deposits in Yavapai County are Pre- cambrian in age or are probably Precambrian, as are the quartz-bearing intrusive rocks from which mineral- izing solutions were probably derived. A few are con- sidered Late Cretaceous to early Tertiary in age, partly because of similarities to the porphyry copper deposits of this age. In the Copper Basin copper-molybdenum deposits (W. P. Johnston '*; Johnston and Lowell, 1961) about 7 miles west-southwest of Prescott (Iron Springs and Kirkland quadrangles, fig. 1), pyrite, chal- copyrite, bornite, and molybdenum occur in breccia pipes in the Copper Basin stock (predominantly quartz monzonitic). Surrounding the central copper-molyb- denum zone are zinc-lead-silver deposits in which galena occurs as cubes as much as 2 inches on a side. The Bagdad porphyry copper deposit (about 40 miles west of Prescott) is likewise considered to be Late Cretaceous or early Tertiary in age (Anderson, Scholz, and Stro- bell, 1955, p. (9-80). Lack of overlying Paleozoic rocks in these areas makes a positive age assignment impossible. In the eastern part of the Paulden quadrangle, the Supai Formation of Pennsylvanian and Permian age has been mineralized, a fact thus proving the existence of mineralizing solutions of post-Paleozoic age. Near the Verde River from a short distance east to about eight-tenths of a mile west of the quadrangle boundary, much of the fine-grained red Supai sandstone has been " Johnston, W. P., 1955, Geology and ore deposits of the Copper Basin mining district, Yavapai County, Arizona: Utah Univ. Ph. D. thesis, p. 96-98. 108 GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA 390,000 1,450,000 1,370,000 2 3 4 MILES I EXPLANATION THICKNESS OF PALEOZOIC AND CENOZOIC ROCKS, IN FEET Area of outcrop of Precambrian rocks r 0-250 1500-1750 Isopach [2] sso-500 1750-2000 Solid isopachs are drawn on exposed tacts: 0-foot isopach is the tact bet Precambrian and Paleozoic or Cenozoic rocks; 500-foot isopach is the contact El J E 3 between the Martin and Redwall Limestones, except in the area of the Mazatzal 500-750 2000-2250 Quartzite; and 750-foot isopach is the contact between the Redwall and Supai Formations. Dashed isopachs are approximately located; queried isopachs are E 750-1000 10 2250-2500 doubtful [_s ] 1000-1250 2500-3200 5 Fa_ult or monocline f 6 | 1250-1500 Shown only where different unit thicknesses are brought into contact or where thickness lines are offset FIGURE 31.-Thickness of Paleozoic and Cenozoic rocks, Paulden quadrangle, Arizona. ECONOMIC GEOLOGY bleached white, the silty layers remaining red. At the prospect called the United States mine north of the river (1,423,900 N., 399,300 E.) and in some of the Supai beds south of the river, hydrous copper carbonate and silicate minerals are disseminated in bleached sandstone or are associated with coarse calcite veinlets in sand- stone. Material on dumps from small prospect pits in the Redwall Limestone south of the river (1,422,400 N., 396,000 E.) consists of coarse calcite, cubes of galena more than an inch on a side, and a little wulfenite and vanadinite. The area has been explored by shallow pits in the Redwall and by several shafts of unknown depth in the Supai (United States mine), but the de- posits are probably too small and low grade to be of value. The date of the workings is unknown ; it may be later than 1922, as the area is not mentioned by Lindgren (1926). PLACER GOLD DEPOSITS Placer gold deposits occur in Quaternary gravels along the present streams and locally as a mantle on pediment surfaces. These gravels rest on Precambrian bedrock or on the upper Tertiary(?) deposits. The placer gravel is well rounded except near the headwaters: of the streams. Small nuggets have been recovered from the upper reaches, but most of the gold down- stream from the Precambrian bedrock is finer grained. The gold has been derived from gold-quartz veins. DESCRIPTIONS OF INDIVIDUAL DEPOSITS IRON KING MINE The Iron King ore deposit was studied by Creasey; for a detailed account of the deposit, the reader is re- ferred to the report on the Jerome area (Anderson and Creasey, 1958, p. 155-169) , from which the present brief summary has been taken. (See also Creasey, 1950, 1952; Mills, 1941, 1947.) The Iron King lead-zinc mine is in the southeastern corner of the Prescott quadrangle and in the northern part of the Big Bug mining district. It is the leading mine in the district and the only mine in operation since 1953. The mineralized outcrop extends for only about 300 feet into the quadrangle, although the de- posit is being mined for some distance to the north beneath the Cenozoic cover. Since 1986 production from this mine has come largely from north of the quadrangle boundary, although earlier production was largely from south of the boundary. Production from the Iron King mine from 1906 to January 1, 1952, included about 21,486 ounces of gold, 6,624,101 ounces of silver, 72,573,620 pounds of lead, 209,199,140 pounds of zinc, and 6,345,740 pounds of copper from approximately 1,640,060 tons of ore (An- 109 derson and Creasey, 1958, p. 155). Production from 1952 through 1956 included about 97,397 ounces of gold, 3,280,850 ounces of silver, 46,790,978 pounds of lead, 117,014,330 pounds of zinc, and 2,206,888 pounds of copper from approximately 1,043,152 tons of ore (U.S. Bureau of Mines, 1953-58). The mine has been devel- oped by seven shafts; only two of these are used and both are north of the mineralized outcrop. Some of the older shafts are caved. Levels are at 100-foot inter- vals, except below the 1,200-foot level, where intervals are greater ; the 2,100-foot level was under development in 1958. Drifts are driven along the veins, and raises extend above them. The deposit was localized in a sheared and deformed zone in the andesitic tuff unit of the Spud Mountain Volcanics and is about parallel to the regional foliation. Intense cataclastic deformation occurred along this zone. The rocks were then hydrothermally altered, and early vein minerals were introduced. These vein minerals were granulated, and a still later period of deformation produced a fracture cleavage on the earlier deformation. During the early period of mineralization or hydro- thermal alteration following the early period of defor- mation, quartz, pyrite, and ankerite were concentrated in well-defined veins in en echelon shears along the east or footwall side of the sheared zone. Disseminations and narrow veinlets of these minerals and of sericite were deposited west of the veins. The veins and the sporadically mineralized zones to the west were then intensely sheared, especially the northern parts, and in these new openings sphalerite, arsenopyrite, galena, tennantite, sparse chalcopyrite, sericite, and probably pyrite, ankerite, and quartz were deposited. Except where it occurs in veinlets, the quartz of the early phase of mineralization or hydrothermal alteration cannot be distinguished from the quartz originally pres- ent in the metamorphic rocks. Pyrite and ankerite form veinlets and disseminated crystals and grains. Pyrite is associated with other alteration minerals. Ankerite is associated with pyrite and quartz; it also veins the late-stage sulfide minerals. The twelve sulfide veins that lie along the footwall (east) side of the alteration zone are well defined, and most of the production of the mine has come from them. They crop out in an area that is about 2,500 feet long by 100 feet wide. The other sulfide veins in the alter- ation zone west of the footwall crop out erratically and are mostly nonproductive. Fracturing and shearing controlled the size and shape of the alteration zone and the widths, lengths, and spe- cial relations of the veins. The veins appear to be slightly discordant to the structure of the alteration zone. 110 Each of the twelve en echelon veins extends in a hori- zontal plane farther north than the adjacent vein to the east. In a vertical plane, each vein extends to a higher altitude than its eastern neighbor. The veins strike about N. 22° E., dip 71° W., and plunge northward between 55° and 60°. They range in width from 1 to 14 feet and are hundreds of feet long. The contact between massive sulfide and wallrock is abrupt. Fine-grained massive sulfides and massive quartz. make up the vein material. The color of the massive sulfides ranges from pale yellow to nearly black, depend- ing on the ratio of pyrite to sphalerite and carbonate. Quartz is gray, white, and greenish gray. Differences in the relative amounts of pyrite, sphalerite, or gangue pro- duce a fine banding in most of the ore; banding is in- distinct or absent in nonproductive parts of the veins. Pyrite, arsenopyrite, sphalerite, chalcopyrite, galena, and tennantite comprise the sulfide minerals, of which pyrite is dominant. Ankerite, quartz, sericite, and a little residual chlorite constitute the nonsulfide min- erals; of these minerals quartz and ankerite are domi- nant; either one may be more abundant except in the northern ends of the veins, where quartz is almost the only nonsulfide mineral. Deposition of ore-forming minerals (chiefly sphaler- ite) in fractures or microscopic shear planes in early vein filling and variation in relative rates of deposition of the vein minerals probably caused the banding in this deposit. Mineral zoning is characteristic of the deposit and is generally similar in each vein. The northern end of each vein consists mostly of massive quartz, south of which the vein is massive sulfide- largely sphalerite and galena-the content increasing to a maximum and then decreasing gradually to the south as the pyrite content increases. Postmineralization structures include faults, joints, and probably fracture cleavage. Larger faults that off- set veins are reverse strike faults and are nearly parallel to the veins. GEOLOGY OF THE PRESCOTT AND FISSURE VEINS IN THE SOUTHERN PART OF THE PRESCOTT QUADRANGLE Although mineralized fissure vein deposits are wide- spread in the Precambrian rocks along the southern part of the Prescott quadrangle, none appears to be of any economic importance, and production from them has been very small. They have been prospected inter- mittently since the early days of mining, and shafts 100 or more feet deep have been sunk along some of them. The veins are in the northern margins of the Big Bug, Walker, and Groom Greek districts and in the Prescott and Lynx Creek districts. Because of the similarity of the deposits and the indefinite boundaries of the districts, they are not discussed by district. PAULDEN QUADRANGLES, ARIZONA The Silver Belt-McCabe vein is about 1,500 feet north- west of the Iron King deposit. It was traced by Creasey (Anderson and Creasey, 1958, p. 169) for about 14,000 feet; only about 1,200 feet of the vein is within the Prescott quadrangle. The Kit Carson vein lies about 1,300 feet northwest of the Silver Belt-McCabe vein and was traced by Creasey (Anderson and Creasey, 1958, p. 174) for about 4,000 feet, only about 500 feet being exposed within the map area. Both veins are buried to the north beneath the upper Tertiary (?) gravels. The strike of the northern sectors of these veins is about N. 30° E., about parallel to the Iron King zone. The Silver Belt-McCabe vein dips 70° 80° NW., but the Kit Carson vein dips steeply south- east. - The veins may intersect at depth. Several pros- pect pits and shallow shafts were dug in the part of the veins within the map area. Gold and silver ore was produced from three mines on the Silver Belt- McCabe vein, south of the Prescott quadrangle, in the early days of mining in the district. The shear zones containing the veins consist of fissile rock containing abundant chlorite. The wall rock, Spud Mountain breccia, is foliated but not fissile, because ac- tinolitic hornblende rather than a micaceous mineral is present. Fissile somewhat bleached areas, generally only a few feet wide, make up the veins, but some bleached zones on the Silver Belt-McCable vein south of the map area are 15 feet wide. The ore shoots are lenses or pods, most of which are narrower than the part of the vein in which they occur. The drusy character of these veins, in contrast to the massive character of the Iron King deposits, and some of the quartz veins in the area suggest that these de- posits formed at moderate depths and after the major Precambrian deformation. The shear zones in which the vein material occurs, on the other hand, are mica- ceous; they parallel the structure produced by Precam- brian deformation in the area, so that a Precambrian age for their formation is probable. On the west side of the Spud Mountain about 3,000 feet northwest of the Kit Carson vein, shear zones oc- cur in breccia of the Spud Mountain Volcanics adjacent to the Spud fault and in gabbro and granodiorite within the fault. They strike N. 20°-45° E. and dip steeply east or west. Several veins have been prospected. Quartz, carbonate (at least some of which is probably ankerite), pyrite, arsenopyrite, galena, and chalcopyrite were noted on some of the dumps along these shear zones. Many of the quartz pods and lenses in por- tions of the shear zones contain minor amounts of pyrite and copper carbonates. East-trending steeply northward-dipping shear zones and quartz veins in granodiorite and gabbro north and ECONOMIC GEOLOGY south of the old State Route 69 (near 1,295,500 N., 370,000 E.) have been prospected, some of them by shafts 100 or more feet deep. The highly sheared zones are generally 1-4 feet wide, but locally pods of quartz are as much as 10 feet wide. Chlorite or sericite has been formed along some of the shear zones. Large areas of the granodiorite to the northeast show minor silicifica- tion, sericitization, and some chloritization. Minute pyrite crystals are rather widely disseminated, and quartz, quartz-tourmaline, and tourmaline veins are abundant. Both massive and drusy quartz veins occur in the area. Pyrite and chalcopyrite were noted in specimens from the drusy quartz. Carbonate, fine tour- maline needles as individual crystals and as masses, pyrite, and locally chalcopyrite and malachite occur in the massive quartz veins. During development work on the Gold Coin group (1,293,600 N., 368,300 E.) in 1950, scheelite was found together with chalcopyrite and minor amounts of galena ; gold in pockets was reported. Two tons of gold ore were shipped in 1950 ; 110 tons, in 1946; 1 carload, in 1939; and 2 carloads, in 1935 (U.S. Bureau of Mines, 1935-58). The New Strike prospect (1,276,200 N., 357,200 E.) is located on a strong shear zone that strikes about N. 12° W. and dips about 80° W. about parallel to the foliation in the rhyolitic tuff host rock, Texas Gulch Formation. The prospect has been explored by an adit and several shallow shafts and pits for a distance of about 1,500 feet. According to the U.S. Bureau of Mines (1935- 58), 1,171 tons of zinc-lead ore was shipped in 1942, 1943, 1946, and 1949. The prospect was reopened briefly in the fall of 1952. The rocks in the shear zone have been silicified and sericitized and contain quartz, sericite, carbonate, chlorite, and epidote. Pyrite and sphalerite were noted on the dump. The Bull prospect (1,291,000 N., 352,000 E.) in what has been called the Prescott district occurs in unnamed basaltic flows of the Alder(?) Group that have been intruded by gabbro. According to Blake (1898, as quoted in Wilson and others, 1934, p. 28), the mine "sometimes called the Bowlder claim * * * is notable for bearing coarse gold of high grade in a small quartz vein. The vein varies in thickness from a few inches to a foot * * *. There is apparently one ore 'shoot' or chimney pitching northward. The claim has been worked to a depth of 132 feet by a shaft, and most of the pay ore [has been] extracted (1886) to that depth." The shaft was caved at the time of Lindgren's visit (1926, p. 108). Additional prospecting has been done since then, as several shafts in the vicinity were observed that are not mentioned in either of the reports. According to Lindgren the "vein of massive quartz is 111 several feet wide and trends N. 18° E., probably with the schist * * *. The massive milky-white quartz con- tains a little pyrite in crystals and stringers." Calcite is associated with quartz in some of the specimens on the dump, and a little malachite coats fractures. About seven-tenths of a mile east-northeast of the Bullwhacker prospect, several shallow shafts and pits have been dug in a quartz vein that trends about N. 25° W. and dips about 80° E. In places the quartz vein is as much as 5 feet wide. Copper stains are abundant on the quartz specimens on the dumps. The Whitehorse prospect (near 1,285,500 N., 370,500 E.) is dug in quartz veins in gabbro that is cut by many pegmatite, aplite, and granodiorite dikes. The exact vein from which some of the high-grade gold ore was produced about 1900 (Mr. G. S. Fitzmaurice of Pres- cott, oral commun., 1955), is not known as several adits and pits have been dug in quartz veins in the area. The gold is reported to have been in visible flakes. Speci- mens on some of the dumps contain pyrite and a little chalcopyrite. The quartz is vuggy and the vugs contain quartz crystals, a botryoidal manganese mineral, and fibrous malachite. About 2,000 feet northeast of the Whitehorse pros- pect, an east-trending shear zone, which dips about 65° N., contains a milky vuggy quartz vein. Limonitic stains after sulfide are abundant. Galena and pyrite are in fractures, and crystals of pyrite, one-eighth inch in size, are imbedded in the quartz. Near the quartz vein, epidote veins are abundant in the gabbro. Their relation to the quartz veins and to mineralizing solu- tions is not known, but epidote is not abundant in the adjacent areas. FISSURE VEINS IN MINERAL POINT DISTRICT AND ADJACENT AREAS Some prospecting has been done on quartz veins in Precambrian rocks in the Mineral Point district (east- central part of the Prescott-Paulden area) and along the Verde River in the eastern part of the Paulden quadrangle. Lindgren (1926, p. 102) mentioned Ford's copper prospect and "Peter's silver mine" in the Mineral Point district (probably near see. 7, T. 16 N., R. 1 E.). He stated that shafts were sunk in copper-stained schist at Ford's prospect and that at Peter's mine a 2-foot vein of quartz in sheared red granite (alaskite) contained a little pyrite, galena, sphalerite, and 'black streaks of felty tourmaline. The Old Hopkins mine (pl. 1, 1,345,700 N., $94,500 E.) produced some gold, according to G. S. Fitzmaurice (oral commun., 1953) of Prescott. Production of gold, silver, and copper from the Min- eral Point district from 1932-57 is given in table 14. 112 TABLE 14.-Value of gold, silver, and copper recovered from the Mineral Point district, 1982-57 [Minerals Yearbooks, U.S. Bur. Mines, 1932-57] 0: ~AMO-~Luil $7, 844 1995... . ZLL. '$9,.288 1041._._._____L_LL__-- TO 1980- 9,462 1042-45____._______._ 0 ene 0 . 1946 35 5.217 1947-07..........-.- 0 19992. uo 2, T53 Potal=......_. 28, 619 * According to Minerals Yearbook, the 1935 production from the dis- trict was entirely from lode mines, but according to Wilson (1952, p. 57), $3,194 of placer gold was produced in 1935. Most quartz veins in the Mineral Point district are 6 inches to 4 feet wide and occur in shear zones. They strike from north-northwest to northeast, except for a few that strike eastward. The dips are steep. The quartz is massive and glassy or milky. Pyrite occurs in small cubes, and minor amounts of copper staining (malachite, azurite, and chrysocolla) indicate the pres- ence of primary copper minerals, probably chalcopyrite. LYNX CREEK PLACER DISTRICT Gold placer deposits occur over a distance of more than 16 miles along Lynx Creek and some of its tribu- tary gulches from near Walker (fig. 1), about 3 miles south of the Prescott quadrangle, to its junction with the Agua Fria River, just east of the map area. HISTORY OF OPERATIONS AND PRODUCTION Operation of the Lynx Creek placers can be briefly summarized as follows: (1) early (prior to 1885) small- scale operations, and (2) later large-scale operations, mostly unsuccessful, and intermittent small-scale oper- ations, especially during economic depressions. The placers were discovered in 1863 by a party of California miners headed by Captain Joe Walker, and more than 200 men were soon working them, according to State Historian Hall (Wilson, 1952, p. 39). Active work with hand rockers, pans, and small sluices contin- ued for several years before the richest gravels were exhausted. Of the 100 men reported to be working these placers prior to 1885, some recovered about $20.00 a day, according to Gilmore (Wilson, 1952, p. 39), and one man is reported to have recovered $3,600 in 11 days from the lower reaches of the creek, according to Shananfelt (Wilson, 1952, p. 39-41). Much money has been spent in efforts to work the placers on a large scale; these operations have been con- fined to the area near the highway bridge over Lynx Creek (1,292,500 N., 362,700 E.) and near the Fitz- maurice property along the east-trending portion of the creek (sec. 22, T. 14 N., R. 1 W., through see. 19, T. 14 N., R. 1 E.; 366,700 E., to 387,700 E.). These opera- GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA tions are summarized below, mostly from data given by Wilson (1952, p. 41-42). In the late 1880's, an Englishman, B. T. Barlow-Mas- sick, built a small dam above the highway bridge across the creek and installed a 30-inch pipe from the dam for about 2 miles down the creek for use in hydraulic min- ing of the gravels. The dam was soon destroyed by a flood. From 1892 to 1895 a steam shovel was in operation on a gravel flat about half a mile below the bridge. About 1900, the Speck Co. tried out an old dredge a short distance below the bridge, but the roughness of the bedrock prevented success. Later, Mr. F. G. Fitz- maurice of Prescott, who owned placer claims on lower Lynx Creek for many years, operated the Speck Co. dredge for a short time, but after recovering about $800 worth of gold, the dredge fell apart. A large expensive patented gold-saving machine was tried out nearby at about this time but, also, without success. In 1927, the Lynx Creek Mining Co. attempted large- scale operations with a movable plant consisting of an excavator, a stacker, sereens, and sluices. A large yard- ago of material was treated. In 1932, a California-type dredge was installed on the Fitzmaurice property below the lower dam (see. 22). The dredge was operated from March to July 1933 by the Calari Dredging Co. In one 60-day period, 60,000 cubic yards of gravel, yield- ing approximately 32 cents per cubic yard, was treated. The operation is described in some detail by Wilson (1952, p. 41-42). Upper Lynx Creek from the area called Bigelow Flat (1,279,000 N., $59,700 E.) to half a mile below the high- way bridge was leased by a Mr. Barnes, according to F. G. Fitzmaurice (oral commun., 1953) and operated by doodle bug during 1940-41. Doodle bug is a term used in placer operations for unconventional methods of getting the gravel to a conventional gold-saving ma- chine. It is used where lack of water or other factors make conventional dredging operations impractical. It may consist of dragline, power shovel, or other impro- vised equipment. Other dredging operations are summarized by Wilson (1952, p. 42) as follows: Arizona Dredging and Power Co.: Latter part of 1933. Lynx Creek Placer Mine Co., 1934-40: Treated 556,115 cubic yards of gravel in 1938 and 542,815 cubic yards in 1939 with large floating washing plant and two draglines; was largest producer of placer gold in Arizona (mostly on Fitzmaurice property). Phoenix Lynx Creek Placers Co. : 1934. j Rock Castle Placer Mines Co.: Last quarter of 1939; handled about 12,000 cubic yards of bench gravel (above the Lynx Creek Placer mine dredge) by ECONOMIC means of a dry-land dredge equipped with four bowl-amalgamators. Placer King Mines, Inc.: In September 1940 took over property and equipment of Lynx Creek Placer Mine Co. Big Bug Dredging Co. : 1941. Minona Mining Co. : 1948-49, on Fitzmaurice property. Other dredges at several properties : 1940-42. Parker and Raymond : 1952-53, dragline dredge. Intermittent small-scale placer operations have been carried on for many years. According to A. S. Konsel- man (Wilson, 1952, p. 42), the average earnings dur- ing the spring and summer of 1983 amounted to 50 cents per day per man; at this time approximately 30 men were recovering gold by rocking and sluicing largely in dry side gulches on upper Lynx Creek. According to F. G. Fitzmaurice (oral commun., 1953) as many as 500-600 men worked the placers during 1933-34. One 160-acre plot is reported to have had 100 men working on it. Total production from Lynx Creek was probably about $2 million. Records of early-day yield are not available, and much of the recovery by individuals has not been recorded or the records were not accurately kept. The principal producing periods were prior to 1885 and 1933-42. It is not possible to make sense out of the various estimates and records of production from the district, nor to be certain how much of the produc- tion has come from the portion of the district that lies within the Prescott quadrangle. Most of the produc- tion, however, probably came from within the Prescott quadrangle, as all the large-scale operations have been from this part of the district. Production from 1914 to 1957 is given in table 15. The district has accounted for about 20 percent of the placer gold produced in the State and about 34 percent of that produced in Yavapai County. GEOLOGY AND OCCURRENCE OF THE GOLD The geology along Lynx Creek is shown on plate 1. A stock of granodiorite considered by Lindgren (1926, p. 21-22) as possibly post-Precambrian but by Wilson (1937, fig. 5, p. 34) as Precambrian in age is south of the map area near Walker. Wilson's map also shows schist and undifferentiated diorite and granite in this area. Within the Prescott quadrangle, the north- trending part of Lynx Creek is cut on Prescott Grano- diorite, gabbro, unnamed tuffaceous rocks of the Alder(?) Group, fine-grained granite, coarse-grained granite, and rocks of the Texas Gulch Formation. The east-trending part of the creek east of coordinate line 370,000 E. is cut on upper Tertiary (?) rocks that con- sist of well-cemented coarse gravel close to Precambrian bedrock but grade eastward into fine-sand, silt, clay, GEoLoGgyY 113 TABLE 15.-Value of gold and silver production of the Lyna Creek placers, 1914-57. [Mineral Resources of the United States, U.S. Geol. Survey, 1914-23, and U.S. Bur. Mines, 1924-31; and Minerals Yearbooks, U.S. Bur. Mines, 1932-57. Data for the years 1914-31 taken from Wilson, 1937 facing p. 16.] $8,100 1980......_____._. $144,828 1915._..-.._..____ 4,587 - 1987-38_.________ 73,981 1916.:.......-..s 1872 92,824 1917....-.__._____ 2424 ~ 1040..........___ 71,257 1,047: AQ41..._.____.__ _. 153,650 10919.:_.......... 1,225 .. I1942......_._.._. 3,055 1920.-............ 0 :: 1945....__._.__... 280 1921......_..____ 1,104. 41044......._..___ 0 1225 J045.._._i._.__.. 0 2856. Aon _s=__}.... 1,859 765 0 814 1,969 1920... 445 : 1040......_.____L 12,822 1027. -one TO 1025.......2.__.t 01951... 105 - #764 foss: :.... 0 2886 ' :10568.-____LC____-- 1,896 1.084 '1084.....L.._._._ 0 4.508 1955.............. 35 1999 26672 1956........_.___.._ 0 1084. _> . 1937....-.....__-.: 0 100,905 m Total----_. * 848,825 1 Total may include values of some placer gold from the part of the district that lies south of the Prescott quadrangle. and limy beds. The Precambrian formations and foli- ation within them trend northward; dips are steep to vertical. Gold is found in gravels along the entire length of Lynx Creek. It was probably derived from gold-quartz veins in the Walker district. Where the creek bed is cut on Precambrian rocks, a distance of about 8 miles, placers occur as thin benches or bars a few yards in width. Where the creek bed is cut on upper Tertiary(?) deposits, placer gravels attain a maximum width of about 1,000 feet and a thickness, according to Wilson (1937, p. 35), of 8-24 feet. Wilson stated that some gold was said to be present through- out this thickness, but the richest material is at the bot- tom of the gravels and in a 4-foot streak about 2 feet higher. Gold occurs along some small dry side gulches tributary to upper Lynx Creek. Lindgren (1926, p. 109) stated that the average value of the placers was reported at 18 cents per cubic yard. He reported: "At Walker the placers yielded nuggets worth as much as $80, about $16 an ounce. Lower Lynx Creek produced a finer grained gold of higher value, worth about $18 an ounce. Such an enrichment in the value of the gold is common and indicates a solu- tion of the silver by the waters." According to Wilson (1952, p. 43), the "gold of lower Lynx Creek ranges from finely divided material up to $6 to $8 nuggets, and 114 is associated with considerable hematitic and magnetitic black sand." During the operations of the Calari Dredging Co. in 1933, 85-90 percent of the gold in the gravels was extracted. "It ranged in size from flour up to fragments 0.1 inches in diameter * * *" (Wil- son, 1952, p. 42). OTHER PLACER DEPOSITS Placer gold occurs along the upper branches and main course of Granite Creek, mostly south of the Prescott quadrangle, although gold has been recovered nearly as far north as the Granite Dells. Some gold has been reported in washes and in pediment and terrace gravels along Granite Creek north of the Granite Dells and near Del Rio, about 20 miles north of Prescott (Lind- gren, 1926, p. 54). The Granite Creek placers were discovered in the 1860's and worked to a considerable extent during the 1880's. The New England Gulch, a tributary, was reported to have been very rich ; one old- time placer miner recovered about $20,000 worth of gold prior to 1922 (Wilson and Tenney, 1932, p. 37). Some small nuggets were found when excavating for build- ings in Prescott, according to Mr. H. R. Wood (Wilson, 1952, p. 56). Granite Creek placer production from 1931 to 1957 is given in table 16. TaBue 16.-Recorded production of placer gold from Granite Creek, 1981-57 [Mineral Resources of the United States and Minerals Yearbooks, U.S. Bur. Mines, 1931-57] 1991: -- -s OOL $590 1041...__._L_________ $245 1002... 6285 _L 0 #14 TO 1994: 144 I19M5-40...__.________ 0 SE) eas 35 70 - 0 1997-88. 0 1989 IX 385 * 8, 020 IMO 560 * Wilson (1952, p. 57) listed Granite Creek placer production 1931-49 as $1,983. An area locally called The Nugget Patch (1,290,000 N., 370,000), between the headwaters of Clipper Wash and a wash that enters Lynx Creek below the Lower Dam, is reported to contain gold in black sands, prob- ably derived from the underlying quartz veins in gabbro. A little development work was done in 1948 by Mr. D. P. Lawson, but the operations were hampered by lack of water. NONMETALLIC DEPOSITS BUILDING STONE Precambrian, Paleozoic, and upper Tertiary (?) rocks are used as building stone and in road construction. The Prescott Granodiorite near Prescott is the most GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA widely used of the Precambrian rocks, principally for foundations and trim in homes and larger buildings- for example, the trim on Yavapai County Court House (1916) in downtown Prescott. The granodiorite is fine to medium grained and takes a good polish; the large poikilitic microcline crystals, as much as an inch across, give a pleasing effect when the light is reflected from their cleavage planes. Mazatzal Quartzite and some interbedded conglomerate are used in and near the vil- lage of Chino Valley for foundations and home construction. Upper Tertiary (?) rocks used in home construction include some of the tuffaceous sedimentary rocks, espe- cially the orange-colored tuff used for trim and other construction when sufficiently indurated. A gray rhyo- lite tuff bed north of Prescott was used in constructing the Armory in Prescott and a few fireplaces. The tuff (described on p. 73) crops out beneath basalt near the tops of two hills south of Willow Creek: (1) On the east side of the hill near 1,306,700 N., 332,200 E., and (2) on the north end of the hill near 1,305,000 N., 331,800 E., where it has been quarried. Attempts have been made to quarry the Glassford cinder cone for cinder blocks, but apparently the large bombs and blocks of basalt make the material undesirable. Sandstone is quarried in the extreme northeastern corner of the Paulden quardangle (sees. 26, 27, 34, and 35, T. 19 N., R. 1 E.). Many more quarries are north and east of the quadrangle. The Coconino Sandstone and some of the sandstone beds near the top of the Supai Formation are strongly crossbedded on a large scale, and much of the rock splits readily along cross- beds into thin slabs and sheets. Sandstone that splits into pieces not more than 2 inches thick and as much as 4-6 feet square (minimum of 18 inches on a side) is sold as flagstone for exterior use, chiefly in steps, side- walks, and patios. Sandstone that is more than 2 inches thick is cut into strips 2-4 inches thick and about 3% inches wide for use as exterior decoration or veneers on buildings. Very large pieces are cut into building blocks. A more detailed account of this resource is given by Lehner (1958, p. 587-588). LIMESTONE Limestone is widespread in the Paulden quadrangle, but only parts of units 1, 2, and 4 of the Redwall are pure enough to be suitable for use as raw material for cement and lime. Limestone was being quarried in 1928 (Tenney, 1928, p. 109) at Cedar Glade (Drake) in the north-central part of the quadrangle. The broken limestone was trammed to the kiln, where it was burned and shipped as lime. The Drake operation was one of ECONOMIC GEOLOGY the three principal producers in Yavapai County for a long period prior to 1928 (Wilson and Roseveare, 1949, p. 25). Open pits and remnants of kilns are (1) along Limestone Canyon see. 34, T. 19 N., R. 2 W.), (2) about three-fourths mile southwest of Drake, and (3) about 1%, miles north-northeast of Paulden. In 1956, the limestone near Drake was drilled, but the project was dropped, in part because of lack of sufficient water and good clay in the area. WATER RESOURCES OF THE PRESCOTT AREA A study of the water resources of the Prescott area was made in 1945 and 1946 by personnel of the Ground Water Branch of the U.S. Geological Survey. The study was made under a cooperative agreement at the request of the Honorable James Whetstine, at that time Mayor of Prescott, and an informal report on the pre- liminary results of the study was submitted to the city in September 1945. Geologic and hydrologic fieldwork was carried on by K. K. Kendall and H. M. Babcock of the Ground Water Branch with assistance and cooperation by Mayor Whetstine and by Mr. Charles Shaw, at that time Water Superintendent for Prescott. sented in this section is condensed from the preliminary results of K. K. Kendall and H. M. Babcock. Record of wells and springs in the Prescott area, collected dur- ing the investigation, is shown in table 17. The loca- tion of these wells and of other wells in Chino-Lonesome Valley is shown on plate 3. HISTORY OF USE OF GROUND AND SURFACE WATER Prescott was founded in 1864, and since then the prob- lem of an adequate water supply has been an ever-pres- ent concern. Until 1884 the inhabitants of the city depended entirely on shallow wells for their water sup- ply. At that time a dam was constructed on Miller Creek to impound the surface flow, and water was pumped from the storage reservoir to a tank above the city. As this supply was inadequate and the water of poor quality, a large portion of the water supply con- tinued to be obtained from wells. In 1891, an infiltra- tion gallery, a permeable structure equivalent to a hori- zontal well, was constructed in the channel of Granite Creek. As the city continued to grow, the supply from this gallery became inadequate, and in 1899 another gal- lery was constructed nearby. The demand for water soon outgrew the supplies available from the infiltra- tion galleries, and in 1901 a pipeline was constructed to Del Rio Springs (near Puro, 1,391,000 N., 342,200 E., pl. 2), about 19 miles north of Prescott. An adequate supply was available from this source, but the cost of The information pre-. 115 pumping a distance of 19 miles and lifting the water about 1,000 feet was considered excessive. In an attempt to obtain a cheaper water supply, a dam (Goldwater Lake) was built in 1923 on Bannon Creek about 3 miles south of Prescott (1,253,500 N., 337,300 E.). Later, another dam was built a short dis- tance upstream, and several small dams were constructed on nearby streams. Water was piped from these smaller dams to the reservoirs on Bannon Creek. Upon completion of these storage reservoirs, the pipeline to Del Rio was abandoned and later removed. In 1945 Prescott was dependent primarily on this system of surface storage reservoirs for its water sup- ply. Some additional water was obtained from the infiltration galleries on Granite Creek and from a pri- vately owned well about 4 miles north of the city-No. 1, see. 14, T. 14 N., R. 2 W. These sources were inade- quate, and a period of severe drought complicated the situation. As the investigation by the U.S. Geological Survey in 1945 and 1946 did not indicate an adequate water sup- ply close to Prescott, in 1947 the city drilled two wells (Nos. 6 and 7, see. 22, T. 16 N., R. 2 W.) that tapped the Chino artesian basin. The wells were located ap- proximately 5 miles south of Del Rio Springs, thereby reducing the piping costs by an estimated $140,000. The first well was completed in October 1947 and yielded more than 1,000 gpm (gallons per minute) during a pumping test of several hours. The second well, a quar- ter of a mile to the north, was completed in December of the same year. The yield here was about 1,850 gpm, which equaled the capacity of the testing equipment. Water from these wells was piped to Prescott in May 1948, and the wells are now the principal source of supply. Surface water from Goldwater Lake is still used, and much of the water that supplies Miller Valley comes from wells tapping a small artesian basin in the area. Water for domestic use outside the city of Prescott is obtained principally from wells. Water for irriga- tion near the village of Chino Valley is obtained from deep wells that tap the Chino artesian basin and is sup- plemented by water brought along an irrigation ditch to Chino Valley from artificial Watson Lake in the Granite Dells Water from springs along Del Rio Creek, at and south of Puro (1,391,000 N., 342,200 E.) and from nearby wells, for many years supplied water to Grand Canyon Village and still supplies Ashfork and Seligman on the Santa Fe Railroad. Water for stock on the range is obtained from "tanks"-basins formed mostly by earthen dams across gullies where runoff is impounded. This supply is supplemented by water pumped from shallow or deep wells. 116 TaBum 17.-Record of wells and springs in the Prescott area GEOLOGY OF THE PRESCOTT AND PAULDEN QUADRANGLES, ARIZONA [All wells are drilled unless otherwise noted in the remarks column. 'Well and sgring records were collected by H. M. Babcock and K. K. Kendall of the U.S. Geol. Survey and by John Gibbs (1945-46). Pump and power: Cf, centrifugal; J, jet; N, none. Use of water: D, domestic; S, stock; I, irrigation; P, public supply; and N, none. pipe clamp, or top of well curb) , cylinder; T, turbine; B, bucket; G, gasoline; E, electric; H, hand; W, windmill; and Measuring point was generally top of casing, top of pump base, top of water- Well Water level ; (depth | Date of Pump Temper- Section and well Owner Driller Altitude below | measure- and Use of ature Remarks (feet Depth | Diam- | meas- ment power water (°F) above (feet) eter uring sea (inches)] point level) in feet) T. 13 N. R., 2 W. Sec. 2, well 1..... J: ine eects renee ce Leslee sane o 30 60 | 22.3 6/ 5/46 | Cf, G D 56 l Dus well; reported 3, well 1...._ F. H. Smith..._;....\ Aol ccr 107 I, E P 2.0000] (Boyd: Tehny. 2.2. Aus Pile s cleans bales 25 C, W L 4, well 2..... OB. Jones .-.. cer AEL EVO Hova ne iaa ne eeu cleve ca s 16 C, E D, 5, well 1... H. -Cory.........:.lll Boh 360 8 (1100.0 T, E D 2:2. M. B.Claw...;....... 20 60 8.6 6/17/46 | J, E I 9, well 1..... A. F. Bumpas........ 130 6 eee eevee. 1 E D 12, well l..... H. B. Warbass....._.. 22 60 B, H D T. 14 N., R. 2 W. Bec. 10, well 1..... San White & Kuhne.._... 5,219.9 894. 0 6 | 84.7 7/ 1/46 | N N 14, well1..:..| E. Weston....:....... E. Weston....._..___. 5,196. 2 223.0 10 | 1 48.0 9/ A6 | T, E D, 8, P. 1 1 Bere (0.--ser.clesice .do. -| 5,200. 0 | 1, 013.0 141 N N 16, well 1..... Johnson...... -| 5,206. 8 120.0 6 | 28.2 8/10/46 | Cf, E D ..... do.... -..| 5,209. 1 130. 0 6 | 17.3 7/ 1/46 | C, W S Ralph Murphy. 5,227. 5 30.0 80 1 22.4 [..._do...! C, W D, I W AH. ARandonelk: 203281222 000000000 LIS LANT ATLL cns BO {cero rar cabe C, W D, S Roy Haines... 30.0 60 | 10.5 6/13/46 | C, H D 10.0. . 22 | Her?. ALRI ne rE e cnn | 's sale co biens aler sen oo sabe e be D, 8 D. W. Fuller. diese 60. 0 6 | 11.9 6/13/46 | Cf, G D B. A. Logan. ORC: 100. 0 [FH A [oes § g 19, well 1..... L. C. Holmes......... Fred 97.0 Oe eens sau J, E 2. P. A: LOGAH : s Leeds Lede lec e cense eer den ars (us oe nanos 100.0 6 | C, E fa (pl (C2, 7 it at A c 48. 0 60 {eines elec estoy s C, E 20, well Roy C. Baling. 022.020] EIA ALOO AET erin na hct cage 12.0 60 6. 4 6/13/46 | Cf, E 21, well 1..... Dan Sidel. Bob Kubne........._. 5,350.0 | 290.0 leeve lee ece C, w J. C. Brown Fred Green......._... 5, 565. 0 304.0 6 | 170.0 7/18/46 | J, G 48 | 49.2 7/ 5) N N 4 | 212.0 8/12/46 | N N 36 13.5 7/ 5/46 | N N 6 | 1 55.0 1946 | N N 60 1.45 | 12/1/46 | N N 3 61.0 60 | 26.8 7/ 9/46 | C, H D 24, well 1.. 91. 0 48 | 83.2 8/ 8/46 | C, W I 26, well 2._... City of Prescott...___. I Pulleum>.......... 5, 214. 0 149. 0 8 5.8 11/ 7/45 | N rn £ about 3 gpm, with 14-it drawdown, July 1946. Test well 2. Originally Pumped at 40 gpm; | ater, it produced less than 3 gpm. $.... U.S. Veterans 5, 215. 8 25.0 72 1 11/ 9/45 | N N* Big Bug Creek mass, Prescott Granodiorite. Big Bug mining district. _._.......__..._._._. Big Chino monocline or fault........_.._...... iBig Chino Wash.,... {Biotite andesife. sco l Black Mesa Page 4 3 50 50 102 41 41 7 110. 70, 82 71 71, 97 65 65 15 13 70 17 16 106 104 107 105 INDEX [Italic page numbers indicate major references] Page Blackmon, P. D., analyst. ...... 26 Botts, S. D., analyst.... 26 Brannock, W. W., anglyst.............__..._. 30 Bright Angel 53 Building stone......... 114 Bull Basin monocline... 94, 96 Bullwacker progpect..............._..__.._._.. 111 C 105 Catlinite. See Argillite. (CERORGIC TOCKE. . -. - 200 on ule nn ou 65 L . . ool Deven Erron sia ese ous 106 OOFHSEIEDL. . .. . . coon ee ec oan coba n 106 Chalcocite........... 106 ChalcopyTIfe.. . . . » orer e eee n neenee 104 CHADATALIAUIE :L C crece e 16, 89, 91 Chaparral mass, Prescott Granodiorite....... 35 Chaparral Volcanics, andesitic tuff ...._...... 17 «-. AG internal structure. ......_.._.._.......... 17 IItHOIOGY . .... .! ae means 17 EAL on 17 stratigraphic relations. 16 . . .. y-. TL r remus 90 ce cC cl. 89, 90, 91 "Chemical character of water.._.______________ 120 Chino artesian basin.... 115, 122 Chlorite......... yu 106 Chrysocolla . . ... -.. "300 Cinder Cones - . 1 u. ..o, epee shes 67, 68 Olitmafe. -.. ._ c cones 6 Coconino Sandstone, age. ..._.......__....... 64 correlation.......... 64 distribution . .. 64 lithology ........-- 64 stratigraphic relations.._......_....._..... 64 thickness............~ 64 use as building stone.. 14 Contliifiong. . 2. . 0. ee recess cena 122 Conclusions, relations of structures to upper Tertiary?) 99 Copper Basin deposits. . .... 107 C., olfed reroll ccs 109 D Dacite (?), Texas Gulch Formation........... 12 Dells Granite, distribution........_..__.....- 44 general O2 45 late-stage products of crystallization. ..... 46 relations to other rocks.. ...... s 47 Del Rio 2s M5 Description of individual ore deposits........~ 109 Dinbase dikes . -- es 20 ool core udon £ 70 - 6, 102 Drainage, Chino-Lonesome Valley -... -u northeast of Chino-Lonesome Valley.. . _. 102 Drainage direction in late Tertiary(?) time... 83, 85 Drainage pattern in Lonesome, Chino, and Williamson Valleys...........-..- 103 E Economic £oolO#y . 12... . 104 Eimore, P. L. D.. anSlyst..-....__.....:....s 26 F ans Fanglomerate, ground water in.............. -L ceo - Faulis, f§e....-.._....s.« 2 Fissure-vein deposits. Fissure veins, Big Bug district.............-. Groom Creek district.._...__.....__..__.. Mineral Point district and adjacent area.. PreSOOLE cus southern part of Prescott quadrangle.... Walker «- cn cree enous is. west side of Spud Mountain.............. Fresh-water G ose Gabbro, relation to other rocks.......~ Gabbro and related rocks, general character. . fron-rich gabbro. LCL Galena... Garnet-epidote-quartz alteration zone......... Gazin, C. L., Glassford Hill area, cinder cones.. Cold .. .. (Gold CON @FOUD. ... .._. cloe Gold deposite, Goldwater Lake on Bannon Creek... Government Canyon Granodiorite, age...... distribution. 0d. L general character. .c.._.._.._cucl.1clll.. relation to other rocks........._...~...---- Granite, coarse-grained, distribution. coarse-grained, general character. relations to other rocks.. fine-grained, distribution................~ general relations to other rocks. Granite Creek, drainage history. infiltration galleries....~.~.. Granitic rocks, ground water in. ...........~~ . .... .. cou crs » ot rae tab be ao Gravel, older...-- younger......~- Green Gulch Volcanics, basaltic flow unit.... brecels ...s distribution. . . .. .. LC. internal structure HEROIGEY - +. 2. .. LEL. pHIOWEL . .. (1 . cope Zeus stratigraphic relations. ..........-.---.-.-.-- SHTUCHUNG .. L.-. o.oo onle d thickness.... - tuffaceous unit...... Ground water, chemical quality........-....- fanglomerate...........- granitic rocks.... movement.. OCOUTTONOB-L... .- volcanic rocks.... Ground-water resources . . Gutschick, R. C., H Hathaway, J. C., analyst......_....._...._.... HeMaAtite.. .-... ew 125 Page 71 121 96, 98 99 106 110 110 67 29 33 31 26 105 126 Page Hickey Formation, Jerome and Clarkdale LL IER deus we 81 History of use of ground and surface waters... 115 Hornblende andesite.........l.__:....1L.l... 70 Howell; DH., ACC 27 Hubbel Ranch..........__._...... 59 Huddle, J. W., and Dobrovolny, E., cited.... 59, 64 Huighes, P. W.; Humidity, average, in Prescott area.. . _...... 6 Hypogene minerals, gangue minerals......... 105 Ore mingrals. c.... LINC 104 I Igneous intrusions, in Alder Group........... 10 Indian Hills Volcanics, andesitic flows 15 basaltic flows................ 15 distribDUMOn..............c_- 14 infernal SHUCBUTG-: .c. 1.1... 14 Cleese ceri eran oh ceasar ro an 14 rhyolite flows.. 14 stratigraphic relations... ..... 14 alvin ea 89 thickness... 14 tuffaceous sedimentary rocks............. 15 Indian FUNS 4 Infiltration galleries, Granite Creek. 115 TRAHUSIVE 28 Intrusive B06. :.:. s 49 conclusions as to age............._....___. 49 conclusions as to relations... 1 ~ 49 older than Alder Group....--. ines abe bae cen 47 Iron Formation. See Texas Gulch Formation jasper-magnetite beds. Tron KI@ Oc- 109 J Jaffe, H. W., age determination by........... 50 Jasper-magnetite beds, Texas Gulch Forma- SL uc: an 12 Jerome Formation. See Martin Limestone. Joints, Dells 97 K Kaolinite, in argillite................ 27 Kit Carson cc 110 L Lacustrine deposits, fine-grained 72, 78 Lake cus si MB Late-stage products of erystallization......... 46 Loudermilk, Jerry, cited.......___..___.._._._. 25 Lehner, R. E., cited... 60, 64, 81, 96 ols Cen cale anne 114 Limestone, fresh-water. 73 Limestone Canyon monocline................ 94 Limonite... 106 Lindburg, M. L., analyst.... 105 Lindgren, Waldemar, cited...____._.... 107, 111, 113 1LOCAHOR Of ATCR- r- cock 4 Longwell, C. R., cited..........._... 63 Lynx Creek mass, Prescott Granodiorite... .. 35 Lynx Creek placer district..._....__...___._.. 112 M McKee; E. D., 52, 65, 98 MeNair, A. H., cited .-.... 53, 59, 63 Magnetite... 105 Malachite. ... 106 Malapais (malpais), defined ....... 68 Manganese oxide.........._.__....:__________. 106 INDEX Page Martin Limestone, age.........__._._____.___ 59 Correlation:: o. 0020-0 cect recs 59 distribution... 57 lithology, A unit 57 B unit.... 58 O UNIEL... .us neve ba Pce cus 58 D UhIE. . , - 59 stratigraphic relations. 57 thickness............ 57 Massive sulfide deposits. 106 Mauy LimestOns..10. AICI. 53 Mazatzal Quartzsite, age....._..._..._...____. 27 alkali ratio . ..... 27 n .... 12.000 00s eL ILL 91 ~. ~.. cool cl oone ooo # 25 chomical analyseg......_..._..__..l...._... 26 .. . . eno 27 . C. l le eos 20, 21 infernal L...! C.-L.. 0. 20 1ithol08y .. .>: LIA. ode 20 measured section, Del Rio area........... 22 . 26 quartzite and conglomerate. 24 stratigraphic relations.................... 20 SUHCVIFO. 20. -.- INEC -e cements 91 IOU CLL race a 20 use as a building stone......._..._.____._._. 114 Mazateal Revolution......._......._..___.___ 88 Measured section, Mazatzal Quartzite, Del RIO ATCA... 22 Mineralization, ABG. 1 - 000.0000. 0000. 106 Mineral Point mass, Prescott Granodiorite... 35 Moenkopi Formation...._...___..._____._._._.. 64 Molybdenite. .... . 105 Monoclinal structures, other.................. 96 Monociings, 4@6. ..... 98 Montmorillonite, in argillite.................. 27 ... s.. -.. shoul iol NSHE 100 Mud flows sL. TL slo 70, 72 N New Strike Prospect. ....c.cl...l_l.l.l._cuscl. 111 Nonmetallic deposits.. cen Nygaard, K. A., 26 0 (Ore ). 2-11 .l bere cl 104 P Paleozoic and Cenozoic rocks, structures.... 98 Paleozoic rocks, general features........._.... 50 thickness in north-central Arizona.. a 51 Paleozoic sedimentary rocks............ P 50 Paleozoic sedimentary rocks, measured se MOUS. 1 . ;- - sole io; DL Pediment gravels. - See Pleistocene gravels. Pediments... 22221 12.20 THT G eca e e.. 100 Perkinsville Formation, Clarkdale area. het 81 Phyrophyllite, in argillite . ....___....._ os 27 Physical features :... . ...o clues ecu IF 4 ThySIOETADhY. . ... . ...n rac len us 99 Piedmontite....... skip 105 PHOW 19996. . .. .oo recs. nua rales - 17,19 Pipestone. See Argillite. Placer deposits, Oher... 114 PIAVINUMELLL L . 02. oo noo 00000000 oe ee d uu 105 Pleistocene gravels... .. 85 Population and industry.. 4 Post-Paleozoic mineralization.........__.._._. 107 Post-Precambrian structures.... 92 Precambrian orogeny... 87 Precambrian rocks, older. 7 IL. oo cence URINE ee 7 Precambrian structures.........__...._._ Precipitation, average, in Prescott area. ._.___ Prescott Granodiorite, distribution.... .._... general character...._...._... relations to other rocks... ... use as building stone.......__.. Prescott mass, Prescott Granodiorite. .______. Previous work.... Price, W. E., Jr., cited. oon Leet Q QUBTIEL L soon eer auew an an bbl oul Quartz diorite, Jerome area. See Yarber Wash mass, Prescott Granodiorite. Quartz diorite, relations to other rocks.._.___. Quartz diorite. See Gabbro. Quartz-magnetite veing...._._._______________ Quartz monzonite. See Alaskite. Quarts porphyry.....___...___... QUATHL NOMB. 112: r een eg Quartzose intrusive rocks, chemical analyses... gabbro, chemical analyses......_____.___. normative composition. variation diagrams.........._.. modal analyses normative composition.........._____._.. variation diagrams. Quaternary deposits.... Quaternary deposits, age........___.._.______ ground water Quaternary gravels, Jerome area.. ._....___.. Recent alluvium... Recent alluvium, age. LTL Rent ehe nanan acess ground water Record of wells and springs, Prescott area.. .. Redwall Limestone, age.........__.....__.._.. correlation.......... distribution.. s -u 2.2L EOC lithology, Unit uhit2..-.-..-.. MINS: 3. iTune Beas deur NAIP A2 clover cen cies ee bere mineralization in. ...... stratigraphic relations. . oti 24. Relations of buried volcanic rocks in Chino artesian basin to Hickey Forma- HOH. 1% bee be rea Rhyolite crystal tuff, Texas Gulch Formation. Rhyolite dikes.... /! SEER ORAC Rhyolite flow or massive tuff, Texas Gulch A0 ce. Rhyolitic flows, Indian Hills Volcanics Rbyolitictuff........._:_.._. Rhyolitic tuff, Chaparral Volcanics... Rose, H. J., It., SLL 0.2.00 S Salida Gulch mass, Prescott Granodiorite. ... -s 1 eRe rob Chad Sedimentary rocks. Serpentine Silicified breccia zones........_...___....___.. Sflicified 20008. LEL cee a a+ Silver Belt-McCabe vein......_._...___...__. Similarities of deposits in Chino-Lonesome basin to Verde Formation........ 105 33 119 35 105 106 105 48 110 85 Page Spud Mountain Volcanics, andesitic breccia... . 15 andesgitic tuff.............._.._......_..... 16 15 internal 15 HEROIOGY. ... 15 stratigraphic relations......-.-~.--------- 15 structure............ 89 a 15 Starkey, H. C., analyst. x 26 105 Stoyanow, A. A., cited.... 59 Stratigraphy, Alder Group... 3+ 10 Stream capture, Agua Fria River. 102 Structure, Alder Group.....- 87 east of the Chaparral zone. 88 in the chaparral zone.... 90 older Precambrian rocks se clot west of Chaparral zone.. 89 Structures, age...------ 98 .. JSS. cece ce -- 96, 98 formed by intrusion of upper Tertiary(?) andesite plugs..._._._..._._;.._.. 71, 97 in intrusive rocks....- 92 in Paleozoic and Cenozoic rocks. 94 monoclines..................~ 94, 98 94 97 Sullivan Lake, headwaters of Verde River 102 Supai Formation, age...... 63 correlation........~. 63 distribution....-..--.-.-..- 61 lithology, lower member.... 62 middle member....---- 63 upper member............ 63 mineralisation... 107 relations to Callville and Naco limestones. _ 63 stratigraphic relations. 61 NHICKNGSS. Lil nt 61 Supergene ore minerals............_.....----- 106 Superposition, Granite Creek..............~.~ 102 Surface water, chemical quality ..... 120 T Tapeats Sandstone, 53 conglomerate in upper part........~.-- 52, 53, 56 53 disconformity below the Martin Lime- ILEC. cn eens 56 ede roar 51 INDEX Tapeats Sandstone, age-Continued distribution of central Arizona............ limestone and sandstone pebbles lithology, lower unit...... upper unit...... stratigraphic relations. thickness.............-..- thickness in central Arizona.... Temperature, average, in Prescott area.. .cc scone Tertiary andesite... ...- Tertiary(?) andesite dikes. Pertlary bogalt Hows. Texas Gulch Formation, andesite flows and tuffs.... conglomerate. correlation........ dscite(?).........~ distribution.... internal structure......- jasper-magnetite beds... rocks of undetermined origin.. . rhyolite crystal tuff..........~ rhyolite flow or massive tuff. rhyolitic . 1.10000 es stratigraphic relations. . . ... -. De neces .-... one seule. 29.00. The Pinnacle, cinder cones west of........~... Topographic highs formed by Mazatzal Quartz- ite since the Precambrian......... 'PoUraling. . . . /-- onne s Tourmaline Tuffaceous rocks, rhyolitic......._............ unnamed Volcanics, Alder(?) Group....-- tise as building stong.....L...._......._.... Tuffaceous unit, Green Gulch Volcanics...~.~ (Puffs. --:... nous cus U Unconformity, at base of Cenozoic rocks.... .. at base of Paleozoic rocks.........__...... Unnamed volcanic rocks of the Alder(?) group, basaltic flows.............. distribution......:-...2-..... garnet-epidote-quartz alteration... ....... infernal -.... s Page 54 56 52 62 52 52 54 6 105 92 106 48 73 19 114 18 70 127 Page Unnamed volcanic rocks of the Alder(?) group, basaltic flows-Con. PHIOWE : $. urne asa cen oes bee cels 19 stratigraphic relations. 18 structure......... 89, 90 thickness.... 18 tuffaceous rocks.... 19 Upper Tertiary(?) rocks, age.. 75 correlations........... 81 distribution. 66 fossils.... 80 ground water. 118 HEHOIOGY : .. .co.cc ec 67 relations to Hickey and Perkinsville For- . o. ey lsu at nea 82 sequence, central Paulden quardangle.... 82 southern part of basin..........._._.._.__. 83 stratigraphic relations. . .................. 81 . 12-0 leeds sa bh aes 74 v Valley fill, water-bearing properties........... 120 Vanndnife: sur./.00 .s haren at 106 L... ._. .oo cove one cuses 7 -ur -e rere cont ues cen oo 48 oce en's 81 Verde Formation, Jerome and Clarkdaleareas. _ 81 95 Verde Cece ene eate nac 102 Verde River, relation to monoclines........~- 99 Volcanic rocks, ground water........___..._.. 121 W Water, for domestic use and irrigation.... 115 Water-bearing properties of valley fill......... 120 Water resources, Prescott area._............-- 115 White, K. F., analyst...-...._-...._._ 26 Whitehorse prospect...............~.. 111 Williamson Valley Wash............. -- : 108 Wilson, E. D., cited.....__........ 28, 88, 91, 112, 114 Wilson, E. D., and others, cited............-- 111 ... nece 106 ¥ Yarber Wash mass, Prescott Granodiorite... 35 Yavapai Schist. . See Yavapai Series. Yavapai Series. . _ eer 9 U.S. GOVERNMENT PRINTING OFFICE: 1965 - O-758-447 e & . PROFESSIONAL PAPER 467 PLATE 1 Government Canyon Granodiorite Stippled where contaminanted with volcamic rocks, gabbro, and Prescott Granodiorite Gabbro Includes diorite, diorite porphyry, and diabase of more than one age. Stippled where contaminated with volcanic rocks, Prescott Granodiorite, and other intrusive rocks VOLCANIC AND SEDIMENTARY ROCKS Unnamed volcanic rocks of the Alder(?) Group ab, basaltic flows, including breccias and minor tuffs at, tuffaceous rocks of basaltic and rhyolitic composition, with some basalt flows Stippled where contaminated with Government Canyon Granodiorite or gabbro SEPARATED BY INTRUSIVE ROCKS Green Gulch Voleanies ggb, basaltic flow unit, includes flow, breccia, tuff, and conglomeratic tuff get, tuffaceous unit, includes tuffs and breccias of rhyolitic and admized rhyolitic and andesitic composition, and minor rhyolitic flows and mafic tuffs and breccias. Stippled where contaminated with Prescott Granodiorite, gabbro, and alaskite FAULT CONTACT Chaparral Volcanics cr, rhyolitic tuff. ca, andesitic tuff FAULT CONTACT Iron King Volcanics Shown only in section E- E" Spud Mountain Volcanics sb, andesitic breccia, with interbedded andesitic tuff st, andesitic tuff sr, interbedded rhyolite tuff. Shown only in section E-E' ir, rhyolitic flows. ia, andesitic and basaltic flows it, tuffaceous sedimentary rocks of basaltic and rhyolitic composition, and minor flows. Stippled where contaminated with Prescott Granodiorite, gabbro, and alaskite FAULT CONTACT (? P i‘t‘a * Texas Gulch Formation tu, undifferentiated Texas Gulch Formation, includes rhyolitic tuffaceous sedimentary rocks and crystal tuff, slate, spotted schist, conglomerate, andesitic tuffaceous sedi- mentary rocks and flows (?), and dacitic (?) rocks tr, rhyolite flow or massive tuff tt, rhyolite crystal tuff ta, andesite flows and tuffs ti, unit containing jasper-magnetite beds in tuffaceous sedimentary rocks V &" f & O41? UNITED STATES DEPARTMENT OF THE INTERIOR 03 L/ C fice GEOLOGICAL SURVEY tarde 34°45 Ameen 'a °A5' . A 34°45 EXPLANATION *, 9, [21 22- ; to Qal & $ . > T. 16 N. T.16 N § Gravel and alluvium t Includes placer dumps along Lynx Creek. Omitted from sections except where they fis conceal large areas of older rocks 5 L o m 1,360,00 g < § | i 3 Bs 0 é Pediment and terrace gravel E Includes some unmapped sedimentary rocks of late Tertiary (?) age and Recent gravel and alluvium. Largely conceals the upper Tertiary (?) rocks UNCONFORMITY ts | & Volcanic and sedimentary rocks ' ‘ g Th, basaltic flows 8 To, basaltic cinder cone ‘ .$ Td, basaltic dike & ~w Ta, andesite flow or plug ; a Ts, fanglomerate, gravel, and fine-grained fluviatile and lacustrine deposits; some t g interbedded tuffaceous rocks, largely of rhyolitic composition. - In one locality < a contains Pliocene fossils rel é 1,350,000 Some of upper flows and sedimentary rocks may be Pleistocene in age 14 B L g ] E # UNCONFORMITY? Q 2 A "& Tad o E 80 Andesite dike I B u UNCONFORMITY § 3 § Z, § § m a $ 1 A & f o & M £ ______ g £ Martin Limestone Lu & o a tD UNCONFORMITY 1,340,000 cA S .$ 2. ® $ | & C. w 5 & m 's G 3 a Tapeats Sandstone < § -£ 0 s | 4 R4 T.45 N T.i5 N. UNCONFORMITY INTRUSIVE ROCKS 40" 40 g o Fine-grained granite "(g Contaminated with volcanic rocks, gabbro, aplite, Prescott Granodiorite, and sd coarse-grained granite E 8 dg 2 1,330,000 45 Dells Granite ra tn x € C A m 3 = 9 s 3 < A Coarse-grained granite U Stippled where contaminated with Prescott Granodiorite and fine-grained granite [Si-I Q. [1d Lu o Alaskite and related rocks 6' al, coarse-grained alaskite ap, alaskite porphyry, aplitic alaskite, and aplite, stippled where contaminated with Green Gulch Volcamics, gabbro, and Prescott Granodiorite am, quartz monzonite probably related to alaskite PB _.. 1,320,000 in X4. I x a z Prescott Granodiorite y g E Stippled where contaminated with gabbro, fine-grained granite, coarse-grained E granite, and volcamic rocks l C (O o 2 O] 2 < e S a. s Contact Dashed where approximately located; dotted where concealed meee moe #1771 cap. ° _ Fault V Dashed where approximately located; queried where probable or \\\\ 514. doubtful; dotted where concealed. U, upthrown side; D, down- thrown side illow ghjeek Reservoir Mir Ref . Shear zone, showing dip 1,310,000 Dashed where approximately located; queried where doubtful 8 75 Approximate strike and dip of pillow structure Showing direction in which top of pillow faces 50 55 TAD tr _ "y] fy1 45 60 Pattern of drag folds and plunge of axes T, indicates direction in which top of bed faces, where known T. 14 N. $ T. 14 N. 2 39% % dee afe, p U 35 Inclined Vertical Overturned 1,300,000 Base map by Topograp! ivision Strike and dip of beds 85 Strike and dip of foliation 25 65 Strike and dip of joints 80 Inclined Vertical dip where known q, quartz vein m, quartz-magnetite vein si, silicified zone +p Well on section to section UNION) R1 W 340,000. " h vet 25 350,000 360 wo j % INTERIOR-GEOLOGICAL SURVEY, WASHINGTON, D.C.-1965-G6é3295 .S. Geological Surve * SCALE 1:48 000 Geology by M. H. Krieger, 1947-52; W. E. Bergquist, g s ¥ 1 Ya o 1 2 3 MILES s 1947-49; and R. L. Kupfer, 1950 s m Emmer e - ft Ft - I st s f f z lu 1 15 0 1 2 3 KILOMETERS & a H H F-------- pm enn - CONTOUR INTERVAL 50 FEET DATUM IS MEAN SEA LEVEL APPROXIMATE MEAN DECLINATION, 1965 wie Inclined Vertical --i <--» Inclined Horizontal Direction and plunge of lineation May be combined with bedding or foliation symbol seg- Inclined Vertical Veins and silicified (or alteration) zones, showing Showing total depth; dashed where projected more than 0.3 mile Location of wells shown on sections is given on map of Chino-Lonesome Valley and surrounding areas PS & $ xa Z| © A z ~s 8 < we a $ H ae C cla SJ $ § 26 A' C S $5 g10 o 2 - I 8 WW | uy r # 4 = F ml 3 t © r § f 6g up} g 8 & M | p 6000 6000 Tb Prescott é big Miller Valley b| g F eco s 1 : 9 5 5000' 5000' [ : es “Eu“ 5000' 4000" 4000" |- 4000" f . 3000 3000' | M Connects with section B-B' on map of the 3000' Prescott-Paulden-Jerome-Clarkdale area f a3 a 2 $ $. 2 8 ¢ al. & 8 § c w* § 2/8 oi; x & clo $ > g s, 9 : s 910 $id $5 g" & . $ & ses $ g ] § if | j : § ' "j f y z 6000' 7 § C8 8 Tb $ € ©8900. § £ j N to | Sg .; les § z s x i . 5 g T {ngb Toss 0 5000' pE PE \gb. 4000' 3000" 3000' £ ¢ 2 o 3 2 0 8 * G @ > - (6) @ < I Fa pa ne ps 2] p- 6% § a H $ $ 91, @ ©© 4 0 215 5 & (€] £ [k. £ © - 0 n whi .$ O I a & ) & e a Olu c a f 4 P $ s § $ ay g 3 % 4 & § Prescott | 3 F4 w gg a D ® CG Is.! 0.1% n 5 ® 6000" U & 5000 < 4000' : PE ooo 3000' 2 C - $ S G £ & R C 2 T Cl 9 < § > 2 - 3 3 n > F4 0 os § o G (0 3 | & £ G .P $ $ Os l lu % & : hd 0 o & Fo 2l& 2 A l > 5 i- c Rd G .. 3 aj R A Cas) U] I a = $ 0 c - & E 7000' § a 0 £ / 3 0 to G 2 m 2 A 3.3 5s W | £ SaY £ C . m < 0 0 l [G) r g § g ml 6 Ea g g g o Lc. & g a 2 7000 6000' $& § i a 0 S me 2 ~ 5s 88 o &. "t"" g T m & ~ ] 9 3 U l 0 > | é? 0 g a. FA s z 6000 5000" if 85 - % s 3.2.8 0 pg i TS 5000' 4000" 4000" 3000 cree 2 | 2] E o 70o0' 6000" | é w é T Bs o v i g Prescott > 2 2] 0 0| J § 3 T & 6 § fo 6 & Municipal s C m/ tl I a a J a 6000" Is I < f z T - © T Qg | Airport < | C 3 hs 8 a.. sms Qa Qal Qg __ Qal | Tb T 8 Qg 8 Chino Valley 8 5000' ## o 4000" I | g 4000' 3000 | hess GEOLOGIC MAP AND SECTIONS OF THE PRESCOTT QUADRANGLE, ARIZONA OLDER PRECAMBRIAN D- (0 4 ~ ~ he FQ ft. \ / | / \ & f \ [ \ Bt \ My a MW \\ \ --- SCC -S zZ ~ Feist / / [ op: | a a o @ / / M | | || ¢» . ) \\ \ "o 3 | | 7 i N $ m \ \ o m d A | ip S \\\M/ r/l/l/l/ 4 if W. iL. / / | 7 e 76 ///L7/////1 i O $ $ [ \ 7 & " F "-l ee ® 3 Ae 0 be Tse d > al ? | -> f [e- + © & C | pg a { d p 53 s €3 \\\\\\\\\\\\\\\\\\\\\\\\\\\\\ $ Lud = 3 am ea x do am F4 - | p o | 7, | pign | as al | d p D pood found > E ew 7. & g Wu $ % # \ o L MG G be 7, W s i I 4." a <- ) 7. C N 3 m 4 M (2 | il | _C °I I m al [/f al" l f " pound 5 ““““““““““““““““““““““““““““““““ WW D 3; 7, n ca ea | da CC Bs as L--. Ad wwwwwwwwwwwwwwwwwww Ett u [l le we ais d p] C we 7, ‘‘‘‘‘‘‘‘‘‘‘‘ fix | -A ly- § E x < j=] 5 > b A 3 st 471 ® E t M 3 onHzofzcwsz A O HINON 3ni1 WW E mm» y AEs: 3 £ 92" &/ pud tz 3 4&1 _s z M I # ._ f 7 & ? & 5 i- JUJ nAfl N I 3 Fad .. ; g s 7 m p S fi i. 5 a 3 a 5 Ad Fm ”MM We /‘m.~/.w/w M t m r | < I3 a. [ 40° & < 2 aa 5.5 f a s $ 3 7 3 | 9 8 3 , < £5 f C D § 5 3a 1 9 4 it igs a ast pf | at 13 ] . : & 2 2 S$ -f f |a 13 // € is «L t 8 naif a i |b 1st s $ < f o 5 .~ 48 g .j 8 "R$ Nz Ne B « 's 5, 8 $a : § | $: $. C: NZ jz 3 a 5 E mg m" vo bs s - f a 5 f § a "~A § f £ 2 - 9 BC & 3 : oo N 8 < w m w / /,N%/// i-: *. 19 Be () m/ mm % N S 1 E z e am PROFESSIONAL PAPER 467 UNITED STATES DEPARTMENT OF THE INTERIOR PLATE 4 GEOLOGICAL SURVEY AH¥VN¥Y3LYNO y srs (i) AYHVNHI3LY¥NO QNYV AHVILHM3L AdVILH3L-38d Fret ~ hs & s 3 3 2 & %" ~ 5: & =s. § ma &: P aC 5 $4 ; & A to u S < 2 s & Fe & = § 's C s~ § a -S % Gva > < C3 § 85 » QTv QTvg, QTw ion salt 00' o 00 35 45" 34°30' lle Format QTpv. volcanic rocks, largely ba 112° QTps, sedimentary rocks InSsv1 Perki ion A 7 JEROME AREA CLARKDALE QUADRANGLE Lehner (1958 p1.45) 10n 15" 112°00' Anderson and Creasey (1958 pl.1) UNCONFORMITY UNCoONFORMITY Contact Dashed where approximately located Fault Dotted where concealed. U, upthrown Monocline Showing direction of downwarp UNCoNFOoRMITY Well on sect Line of section Location of sections also shown on map of Hickey Format volcanic rocks, largely basalt EXPLANATION Gravel and alluvium gravel side; D, downthrown side Dotted where concealed U D Lonesome Valley and surrounding » » Thy Ths Basement rocks A Chino- areas PAULDEN QUADRANGLE This report PRESCOTT QUADRANGLE Older gravel This report 30° 112°30 5! 35° 00° 4 Some of the upper flows and sedimentary ions are rocks may be Pleistocene in age and older gravel The Hickey lle Format ite, insvi arbitrarily separated from the pl. 45) are shown here as sedimentary rocks Th, basalt Ts, gravel Tsf, fine-grained lake beds Ta, andesitic rocks Tho, older basalt Tgo, older gravel Rocks mapped as the Hickey Formation by Anderson and Upper Tertiary(?) volcanic and rocks in the southwestern part and basalt in the southwestern part of the Clarkdale quadrangle and as basalt and sedimentary Note Creasey (1958, pl. 1) and Lehner (1958, basalt, andes of the Jerome area. and Perk upper Tertiary (?) rocks. fl Pe- W- 1\¢ $ < fimfi r G GRESC g j XAP & CnC _ p . C M A8 A > «f fimwuwfianfi . eee: Zee «W. & SAS fAAXX® 1,450,000 1,440,000 1,430,000 45" 1,410,000 1,400,000 1,390,000 4 1,380,000 1,360,000 4 1 1,370,000 1,350,000 +30 1128 34 INDEX MAP OF AREA SHOWING SOURCE OF DATA 1965 » HINON 3NHL APPROXIMATE MEAN DECLINATION Sisd 34 112°00' Geologic map modified from sources indicated on index map 9 Reservoir Granit y: SY PRESCOE/ (“f X 30' 0 000 470, ces295 ,000 460 GEOLOGICAL SURVEY, WASHINGTON, D. C.-1965- 450,000 INTERIOR- 430,000 440,000 420,000 T 370,000 300,000 7 1,320,000 1,310,000 1,290,000 1 4, SCALE 1:96 000 5 MILES L 5 KILOMETERS INTERVAL 200 FEET IS MEAN SEA LEVEL CONTOUR DATUM Al mak- Paleozoi NoOILOSS rocks 3000' Ni ON38 Ni an3a © 4 cks "-- Paleozoic ro: ME I NOILO3S Precambrian rocks NI QN NOILDSS 38 at Paleozoic rocks Ni aN3 a o P3 © a £ 0 a 's a o F J, E e £ T «B a o I3 9 Al o 0 o V -C w 3s --' E ££ o a o Z o o 0 o o o o o o o O o i P w < ® 4oury mug onby: o i- of TI yoing usais oar mu] onby w x o nollos3s £ NI aN38 © G & a E G o 0 + a. worry muy onby o o © o o o o o o o O o © i st m e o 3 el 6 O ~ 1 St Ths Paleozoic rocks A- Precambrian | rocks P AND SE ‘iiTIONS SHOWING DISTRIBUTION AND RELATIONS OF UPP ARIZONA 9 CLARKDALE AREA JEROME - ER TERTIARY AND LOWER QUATERNARY(?) VOLCANIC AND SEDIMENTARY ROCKS IN THE PRESCOTT-PAULDEN UNITED STAT ES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY PROFESSIONAL PAPER 467 PLATE 5 47Q,OOO 112°00' 3500" STRUCTURE TRUE NORTH APPROXIMATE MEAN DECLINATION, 1965 35oéég°30' 330,000 t S & 5500/ I I + a w. 3500 % ed - 1,450,000 1,450,000 N 3500 - YC Ms O \ ; C < f ~ & - 4 & | ¢ x | % | 0 I & O 6 I bul / a el $ & 0 yf & Q. O $ A0 # | o $93) $ / 8 : 3 K Ub fol X / 3280-7 5: d ; / ad lie is to b th 63 o $ s] 6 Sullivan Lake L 3 "NQ s 3 € i- $a c coca § 7 a E >, Df <. 4 : [4 Px & z A m $*%a 4 yy 3 | HIChmo Valley % 112°30' 330,000 E (200 yip sistas ~~. 34°45" ¥ x Ok ; I+ polu £ at o ie - - m y" or / x " \6000 and o U /,\/ 0 ; 6 & m . & EXPLANATION XA $ 6000 - -- (. ig 0“? Structure contour Drawn on base of Redwall Limestone. Dashed where approximately located; queried where (950); projected from outside of area or where sufficient control is not available. - Contour + interval is 250 feet; datum is mean sea level. Thicknesses assumed below and above base \ of Redwall are: base of Tapeats Sandstone, 500 ft; base of Supat Formation, 250 ft; base of middle member of the Supai, 850 ft; base of upper member of the Supai, 1075 ft; base of Coconino Sandstone, 1750 ft. In the area of the Mazatzal Quartzite, the base of the a Paleozoic rocks in places is less than 50 ft below the base of the Redwall; in areas where [- * e there is no control on the thickness of the Martin and Tapeats Formations, hills of Pre- \ cambrian rocks may protrude into the Paleozoic rocks & U monn ~210 D ~950) Fault & Dashed where approximately located; dotted where concealed. U, upthrown side; D, down- x thrown side. Number indicates estimated throw of base of Redwall Limestone. Number s ) in parenthesis indicates structural relief measured on displacement of basalt across the [:s (1200)\ Cal Coyote fault and the Verde fault and associated fault zones (from Anderson and Creasey, D\U 1958, fig. 6) | Se ot o BL ..a. Monocline Dashed where approximately located; dotted where concealed. Arrow shows direction of downwarp * ¥) sary 112°00' 112°30 112°15 CLARKDALE Modified from unpublished PAULDEN m a p b y This report Fle'h-n'e r. Compiled on base of Ta- peats Sand- § stone 34°45! O T MINGUS MTN A pg e Compiled from W 6000 Anderson (o] Aart and Creasey //, (1958, pl 1) - z, fi | 6 f 34°30" I INDEX MAP OF AREA, SHOWING ‘ sOURCE OF DATA (100k) D/u / [| I, h ree a > S2 | I - 1,280,000 1,280,000 I 4 4 | | | { ; Taa | 34°30" " ® 470,000 - 112°00' 2 3 MILES ere -o Ya 0 1 3 KILOMETERS CONTOUR MAP ON BASE OF THE REDWALL LIMESTONE, PAULDEN, CLARKDALE, AND MINGUS MOUNTAIN QUADRANGLES, ARIZONA 158-447 O - 65 (In pocket) Crystal Chemistry of Beryllium By MALCOLM ROSS G E 0 LO GI C A L SURVEY PROF ESS IO NAL PAPER 468 A detailed discussion of the crystal chemistry of all the known beryllium minerals UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1964 UNITED STATES DEPARTMENT OF.THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director The U.S. Geological Survey Library has cataloged this publication as follows : Ross, Malcolm, 1929- Crystal chemistry of beryllium. Washington, U.S. Govt. Print. Off., 1964. iv, 30 p. illus., diagrs., tables. 29 cm. (U.S. Geological Survey. Professional paper 468) Bibliography : p. 28-30. 1. Beryllium. 2. Crystallization. I. Title: (Series) For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS Page -:: eile arie e. ante ~s K1 The beryllium minerals-Continued Introduction. cl 5. lo dilo 1 Gugiaite____. 'The beryllinm mincrals.. :: 1 leuc'ophawte _______________________________ co. ce ltt. q § 11.1e11phan1te ________________________________ i ls. $1100. 0. ONE ia cs. ... ir nals sens no ene recant cL 2 M erice a oro ape e.. Oraesite c.... on oo 8 clei ca ita ted .a. an 3 Phenakite con... _c eee ELIE asa a' Kin bek 5 ." '. le le. Battle. :a avremcernntinerc¥e tnd s amens 6 Js. cc Le... _ -new. aul s 6 Spherobertrandite._.._.._.._..____..____.___.____li.. aso r- 7. Fi Taafleiye _______________________________________ . 8 Te.nger¥te ______________________________________ Promellitel =--... se- trou- se ss 8 $lt1mentettje___-____-_-_____..___________:::::::: lobe - e n ence idee ace aas Mee Prine ol: o en pecan d.. eco- 2 The beryllium aco cue coo c 9 10 can Pec we asma css Faheyite ...= lo cel. ell ie swe Bas o 10 L_... 10 BeCGeO4.: :# cage sll. rtl. 10 Bes Sac.... lL. ral tie ec vane aie =a nr Marstigite .. .- 2202s bens sol c A ageal .. 11 PELL . cein e ice inne eens ads nine a ab ean bas se il. ust ll car.. ull 11 ss des 2,2 200 LACE cs «iirc e cal scales nne ae 11 BESINQ ________________________________________ ------- BeéQls. : Clt oon cane - Centhelyite _ cy. L_ t _ rat _L 11 e.. o or Lil... HMerderife:E ic. 2.0000 000 MGL iol oo.. 13 Basic beryllium acetate, Be,O(CH,COO)s--.-------.- Gadolinibtel .. loll tole nn... 18 Beryllium phthalocyanine, Hslanghualite... . till. 0 14 'The beryllium 2. :: 2 o cous 2 enn nan l rene seee. ak. 14 | Conciusions ... .L lL IM. sw .s arpinskyIb6_. .- s 10 | Referenced cr «sins uamies's s ILLUSTRATIONS . 1. The crystal structure of . llc etn. el c AT ll ino 2.> The crystal structure of bertrandite (after Ito and. West). _ 3. The crystal structure of bertrandite (after Solovieva and 4. The crystal structure of beryl. = /. dere. le cet eannch ean tanker $00 ame 5. The structure of the SisO;s ring in P8 ooc, . Ged cll gout ow a de one cel n o meals pice cole 6. The orystal structure of berylIOhite 2 2... neice ener nae -an 7. The arrangement of tetrahedra and octahedra in layers I and II of chrysoberyl.____________________-------- $. The crystal structure of hambergite. .. = 1 252. nl celle nle .n rence ei- eins - anand 9. 'The crystal structure of cdg _ cL: lL _ i MILL ates 10. The arrangement of the calcium polyhedra in -s 11. The arrangement of the yttrium and iron polyhedra in 12. The ory stal structure of c_ cld LLE LL LL.. 13, The crystal structure of A0 J.D.. 14. Phe arrangement of the calcium polyhedra in melilite. ecs 15. The crystal structure of milarite projected on (1010). e IH IV CONTENTS Freun® 16. The crystal structure of milarite projected on l ls 18 17. :A comparison of the beryl and milarite Lets 19 18. The érystal structure of swedenborgite - .c... . neon ren onl leon non UC eu GCU e ana ae egen aan bae cn enss . eae 21 19. A comparison of the vayrynenite -and cuclase structures. 80 LLQ 23 20. Tic beryllium plithalocyanine molecule- . _ _ : ce. L nnn sone cea bls cee leve nels » Bed anes s 25 TABLES Page TaApt's: 1. The beryllium minerals c 28 LL.B _ cE c- on.. 2 2 Chemical composition of ...s: leo. n .c ch cue adns ances ass bene cent emel o 3 3. Charge distribution on the oxygen atoms in hurlbutite and 15 4. Bond lengths in the hurlbutite structure. .._. ___ .__cakent otto nuo _ oben i e nee agl cs. 15 5. Crystallography of gugiaite, leucophanite, meliphanite, and the related minerals melilite and hardystonite . _ ___ 16 6. Chemical composition of gugiaite, leucophanite, and meliphanitel L 17 7 Bondlengths in milarite. .._. c - .o peces oul cl en bolo o Anode o uue eit econ tool iia ni ay monet 19 $.: The beryllium cComMpOUNUS.>. - -_. .- as ..o odo 23 9. The beryllium fluoride compounds and their structural 26 10. The beryllium-anion bond length$#. \ _>. see de s Bake 27 CRYSTAL CHEMISTRY OF BERYLLIUM By Marcoum Ross ABSTRACT The present study is a compilation of the X-ray crystallogra- phy, chemistry, and crystal chemistry of all the known minerals containing essential amounts of beryllium. These minerals are: aminoffite, barylite, bavenite, bazzite, bearsite, bertrandite, beryl, beryllite, beryllonite, beryllosodalite, bityite, bromellite, chkalovite, chrysoberyl, danalite, epididymite, euclase, eudidy- mite, faheyite, gadolinite, gelbertrandite, genthelvite, gugiaite, hambergite, harstigite, helvite, herderite, hsianghualite, hurl- butite, karpinskyite, leucophanite, meliphanite, milarite, morae- site, phenakite, rhodizite, roschérite, spherobertrandite, sweden- borgite, taaffeite, tengerite, trimerite, and viyrynenite. The X- ray crystallography and crystal structure of the following in- organic and organic beryllium compounds are also given: B-Be(OH):;, BeSO,, BeGeQ,, BeS, BeSe, BeTe, BeSiN:, BeCl;, Be(CH:):», Be0 (CHCO0)«, BeC»HNs, and the beryllium fluorides. In all but one compound (beryllium phthalocyanine) beryllium is reported to be tetrahedrally co- ordinated. In beryllium phthalocyanine Be. is in planar coor- dination. A summary of the bond distances between beryllium and the coordinating anions is presented. The average berylli- um-oxygen bond distance in those structures believed to be accu- rately determined is 1.636 A ; the average Be-OH bond distance is 1.650 A. INTRODUCTION Beryllium is one of the less abundant elements; recent estimates (Fleischer and Cameron, 1955; Warner and others, 1959) give 0.0005 to 0.0006 percent for the con- tent of the earth's crust. This element occurs primarily in the igneous rocks where it is one of the last compo- nents to crystallize. In the early stages of magmatic crystallization the concentration of beryllium is low and it is thus not incorporated in any appreciable quantities in the structures of ferromagnesian silicates and felds- pars. It tends to be concentrated in the late magmatic and early hydrothermal stages and crystallizes as an - essential constituent in such minerals as beryl and chrysoberyl. Sandell (1952) found the average Be content of seven granitic composites to be 3 ppm where the SiO; content varied between 68 and 78 percent. He found 4 ppm Be in An;sAb;», 1 ppm in microcline, and 4 ppm in biotite. Sandell suggests the mechanism Be+ Ca for Na+ Al to account for the presence of Be in the feld: spars. The beryllium ion (Be*) has a radius of 0.33 A (Green, 1959) and appears to be of a size that will per- mit it to readily substitute for tetrahedral Si*, Al*, P" and 8%. If such a substitution occurs, the deficiency of positive charge must be adjusted for by replacement of other cations with ones of higher charge. For ex- ample, Rankama and Sahama (1950, p. 126) postulate that the small content of lanthanum sometimes present in potassium feldspar is a result of the substitution of La® for K+ simultaneously with Be* for Si*. As will be discussed later, such substitution mechanisms, if they do occur, occur only to a very limited extent. This is probably because of the rather unsatisfactory distribu- tion of charges on to the anions such that Pauling's rules are not very well obeyed. The first part of this report is a compilation of the X-ray crystallography, chemistry, and crystal chemis- try of all the known minerals containing essential amounts of beryllium. The second part is a presenta- tion of the crystallography and crystal chemistry of a number of inorganic and organic beryllium compounds. I would like to thank several of my colleagues for their help: C. L. Christ suggested this study of the crystal chemistry of beryllium, and he and Michael Fleischer made numerous suggestions for improving the manuscript ; Douglas C. Alverson translated a num- ber of Russian publications into English for me. I am also particularly indebted to Michael Fleischer for bringing to my attention much of the current Russian literature on the beryllium minerals. THE BERYLLIUM MINERALS Apparently, 43 minerals have been described that contain an essential amount of beryllium. These are listed in table 1. Some of these minerals are of doubtful validity and several have questionable chemical formu- las. The various minerals are discussed individually. If known, the unit-cell dimensions, space group, densi- 1 For the purposes of this report an "essential amount of beryllium'"' is defined as the amount of beryllium needed to fill at least 50 percent of the equipoints of one set of equivalent positions in the crystal structure. 1 2 CRYSTAL CHEMISTRY OF BERYLLIUM ties, and number of formulas per unit cell are given." Chemical analyses or references to lists of chemical analyses are given for most of the minerals. For a few minerals, where there appears to be no question of the validity of the chemical formula, the chemical compo- sition is not discussed. The crystal structures of more than half of the beryllium minerals are known or partly known and these are discussed in detail. The present study will not touch on the mineralogy or petrology of these minerals. These subjects are con- sidered in great detail in the recent book, "The Geo- chemistry of Beryllium and Genetic Types of Beryl- lium Deposits," by the Russian mineralogist, A. A. Beus (1960). The mineral kolbeckite, once believed to be a phos- phate or silicophosphate of beryllium, has been shown TABLE 1.-The beryllium minerals Name Formula Aminoffite. __.... Ca,(Be, Al) Si;O0,(OH)» ..... ... BaBe;S8i;0; Bavenite.. ___ ___. Ca4(Be,A1)4(Sl, Al) 9026(OH)2? Bazzite_...__..._. R+(Sc, Al, Fe, Mg)BesSisO;s? Bearsite......... Be,(As0,) (OH).4H;0? Bertrandite._ ___.. Be,Si;0;(OH); Beryl ____________ AlzBeasieols Beryllite_-____-_ Ph B85Si207(0H)4.2H20? Beryllonite.__.... NaBePO, Beryllosodalite. . . Na, BeAISi,0Cl Bityite_ (0216 Igla, K) (Al, Li, Mg) :-;(Si, Al, Be)1010 )2 Bromellite. __ ___. BeO ___. Na,(BeSiz04) Chrysoberyl____ __ Al;BeQO. Danalite_________ Fe,BesS8iz0;».8 Epididymite. _ ___ NaBeSi;0;(OH) AlBeSiO,(OH) Eudidymite. _ _.___ NaBeSi;0;(OH) Faheyite.__..__... (Mn, Mg, Na) Be:Fe;#+(PO,)1.6H;0 Gadolinite. ._.... FegiYBe 10.4.0 Gelbertrandite._ ___ Be,8i;0;(OH);.3H;0?- Genthelvite ______ anBeasi30|z.S Guginite._._...._. Ca;BeSi;O; Hambergite. ___. Be;(BO;) (OH) Harstigite________ (Ca, Mn, Mg);Be,Sis(O, OH, F)»3-»4? Helvite __________ MmBea isolz. Herderite._______ CaBePO,(F, OH) Hsianghualite. _ __ LijCa;Be;(Si04) ;F; Hurlibutite.:.:.... CaBe;(PO4): Karpinskyite. _ ___ Na;(Be, Zn, Mg) Al;SisO16(OH);? Leucophanite.____ (Ca, Na);Be(Si, Al);(O, F, OH); Meliphanite__ ___ (Ca, Na);Be(Si, A);(O, F, OH); Milarite. .._. -_. KCa,(BesA)) (Si120»).4H20 ___. Be;(PO,) (OH).4H;0 Phenakite_____ ___ e;8i0, Rhodizite ________ NaKLigAlgBeaBmO'n? Roschérite_______ (Ca, Mn, Fe);Be;(PO,);(OH);.2H;0 Spherobertrandite Be; (Siz0;) (OH)? Swedenborgite___ _ aBe,SbO; ... (Be, Mg) (Al, Fe):04 Tengerite..__._____ (¥, Trimerite._______ Ca (Mn, Fe, Mg)(BeSiO,); Viyrynenite______ (Mn, Fe) BePO,(OH) * The following abbreviations will be used in this work: a, b, c; a, B, y-unit-cell edges; unit-cell angles ¥=volume of unit cell D. =measured density D.=calculated density Z=number of formula units per unit cell A=angstrom unit (10-tem) kX=0.997984 times A. Unit-cell edges are assumed to be in angstrom units for substances described after 1948 and in kX units for substances de- scribed prior to 1949. Unless otherwise noted, the numerical values of the unit-cell edges are those originally presented in the references. by Mary E. Mrose, U.S. Geological Survey (oral com- munication, 1962), to be a scandium phosphate with the formula Sc(PO,).2H,0. AMINOFFITE CM(Be,ADSizoa(0H)2 CRYSTALLOGRAPHY (Hurlbut, 1937] Tetragonal: , @:.L... 13.8 kX Du-? so 2.94 g/cm 9.8 kX avg Hees cake 12 1866 kX D; i= aac. 3.03 g/cm} Space group: 14/mmm CHEMICAL COMPOSITION [Hurlbut , 1937, p. 202. Numbers of ions on the basis of Si=2.00] Weight W eight percent Ratios percent Ratios S10;-.e«cc.. 42.49 2.00 | CaO_______._ 40. 27 2. 03 Al;Os...c... 4. 41 AS ' 6. 45 - 1. 01 BeQ...... s: 6. 20 . 70 . B1 . O1 100. 32 MnQO........ .19 . O1 Caz.03(Be, Al, Fe) .ss3iz.:0006.15 (OH); .02 CRYSTAL STRUCTURE This mineral may be related structurally to the min- erals of the melilite group. BARYLITE BaBe:Siz0; CRYSTALLOGRAPHY [Smith, 1956; Abrashev and Belov, 1962] *+ Orthorhombic: a rate' - 9.80 +0.01 A Da se; -At: 4.03 g/em 11.65+0.03 A C i <+ 4 *s cukses ise 4.71+0.02 A 4.08 VeR elke ece 526 A* Space group: Pn2Zia, piezoelectric -ray powder data (Smith, 1956) CHEMICAL COMPOSITION [Numbers of ions on the basis of Si=2.00] Palache and _Aminoff (1923) Bauer (1930) __ Weight Weight |__ __ percent _ Ratios percent Ratios -+ 35. 51 2.00 36.42 2.00 16.01 2.17" 15. T7 <2.08 88.8 ________________________ 47. is 1.05 46.49 _ 1100 IUS - 2 s t's wel nie ain all ol a uble ot + nu Feld is - Usa n - nate MgO.. .t l 21." $_ ad PDO: .... co- .e i Faes Al.: "saree FeO... 2 o cee ia so aas o » ae oke Cae aie "19. gir cll. ._ mo " $7... ::" aao. :s 100. 24 99. 67 CRYSTAL STRUCTURE [Abrashev and Belov, 1962] The barylite structure is found to be composed of linked BeQO, and SiO, tetrahedra. Each of two corners THE BERYLLIUM MINERALS of the BeO, tetrahedra are shared with another BeQO. group and one SiO, group. Each of the other two corners are shared with an SiO, group. The SiO. groups link together in pairs to form Si@O,; double tetra- hedra. One corner of each SiO, tetrahedron is shared with a like group, one corner with two BeQ, groups, and two corners with a single BeQO, tetrahedron. The BeO. tetrahedra link to form pyroxenelike chains oriented parallel to the c-axis. The repeat distance along the chains is 4.71 A (the c-dimension), and is the length measured parallel to c of two linked BeQ, tetra- hedra. The Si,O; groups are oriented with the Si-Si axes parallel to b and link the (BeO,;),*"*~ chains to- gether to form the three-dimensional structure shown in figure 1. Large cavities appear in the framework and are composed of four SiO; groups and four BeQO, tetrahedra, two each from two different (BeOQ;),*"*~ chains. Into these large cavities fit the barium ions. These ions are in approximately twelvefold coordi- nation. The bond lengths were found to have the following range in angstroms : Angstroms (8) Ni-O:__._._.._. 1. 63-1. 70 (8) Be-O._____. 1. 64-1. 70 (12) Ba-O.___.__. 2. 82-3. 34. BAVENITE Ca, (Be, Al), (Si, CRYSTALLOGRAPHY [Claringbull, 1940. For chemical composition of bavenite see table 2] Orthorhombic: a z.. 19.34 kX Daz lees. 2.74 g/em} b.... -C 23.06 kX a ica tin. e 4 4.95 kX 2.80 g/cm} ¥. 2208 kX X-ray powder data (Fleischer and Switzer, 1953) BERTRANDITE 136451307 (OH); CRYSTALLOGRAPHY [Solovieva and Belov, 1961; Ito and West, 1932] Orthorhombic: 8.73 A 612 A 15.31 A @- 4 C 4.58 A 2.58 g/em> Space group: C'mec2,, pyroelectric CHEMICAL COMPOSITION [Dana, 1892, p. 546. Numbers of ions on the basis of Si=2.00] Weight percent Ratios ( (2) (8) (1) (2) (3) 49. 60 49.26 51.8 2.00 2.00 2.00 _. 42. 62 42.00 39.6 4.13 4.10 3.67 CaO: _ S22. oes) d! 11:0 .....: we. . 04 Fe203 ________ Tr. 1.40 u- 02 c..... 12 TFs. 2 ces e eG e a s aie a «=+ ok s nm H;O0.....:.l... 7. 94 6. 90 8.4 ° 1.07 - .95 108 100. 16 .-99. 56 100.8: - -... CRYSTAL STRUCTURE [Ito and West, 1932; Solovieva and Belov, 1961] The bertrandite structure, as Ito and West postulate it, is built up of linked SiO,, BeQO,, and BeO,(OH):; tetrahedra. The structure is based on an arrangement of close-packed oxygen atoms with beryllium and silicon occupying tetrahedral holes. This model is depicted in figure 2 which shows the bertrandite structure pro- jected on (001). One half of the silicon tetrahedra form infinite SiO; chains parallel to c which alternate with two infinite BeQO; chains to form strips of the composition Be;Si0,. The BeO. and SiO, tetrahedra within this strip are po- sitioned with their bases parallel to (001). Successive tetrahedra in this strip are joined up in such a way that TaBu® 2.-Chemical composition of bavenite [Samples 1-5, Fleischer and Switzer, 1953; 6, Beus, 1960, p. 45-49; 7, Switzer and Reichen, 1960. Numbers of ions on the basis of 26.00 oxygens and 2.00 OH] 1 2 3 4 5 6 7 Weight | Ratios | Weight | Ratios | Weight | Ratios | Weight | Ratios | Weight | Ratios | Weight | Ratios percent percent percent percent percent percent 5g. gs 8. 91 5g 92 9.13. 59.13 9. 22 5g. 64 9.11 55. g 8. 82 53 g; 9.05 . . 88 7.00 ¢ . 46 . 60 8. I . .10 } 91 . O7 } EAX er ee eet cus arene eevee efeceececens Lis |f _ >85 . 60 } 94 6. 33 2. 38 7.72 2. 88 7.14 2. 67 7. 66 2. 91 7.00 2. 69 5. 52 2.10 24. 35 4.06 28. 26 3. 86 23. 90 3. 98 28. 96 4.06 24.15 4.13 28. 44 3. 99 .................... M | POT {-o en ch el er coon abe d|tk ubs ece [ut we ana wel a bs sheen se [1 sed an {an en nle as on .................... 13 .03 . 05 AOL ovu teri | e ede] -c reuse es» (B2 JA .................... 44 . 07 . 10 108 [oo cease esau te chen ab ereens cans (ee vede be Soane un abe a[ asan an 1.90 . 99 , 2.41 1. 25 2. 46 1.28 3. 56 1.88 4.00 2.13 2.86 1. 51 .................... £00 OB es ABB [z. e] oul cut -as |= = paws ae ae S16 |-- sess SBL M0 16 ccie eal enn reac [# Exc cers MTE |e acl | eben cls an nh wares 100-19 |--<->..... 90.04 ]..c.... .. 100.01] :-... .>... 99.00 100.58 99. 44 )......... Cai .os(Be, Al)1.15(Si, Al)s.00(OH)2 Cai os(Be, Al)1.1 (Si, Al)o.00n(OH)2 . (Ca, Mg, Na)i.s(Be, AD1.uSio.1s302(OH)2 (Ca, Mg, Na)1.0s(Be, A1)3.s58i9.3s02(O H)2 5. Cairss(Be, 6. Cais(Be, Al)«.1 (Si, ADs.c002(OH)2 7. Cas.00(Be, ADs.ss8i0.0s02(OH)2 a goro r 4 CRYSTAL CHEMISTRY OF BERYLLIUM FrauRE 1.-The crystal structure of barylite, BaBerSi20 7. Reprinted from A brashev and Belov, 1962. 'The stippled tetrahedra are the BeO4 groups; the lined tetra- hedra are the SiO, groups. The large circles represent barium atoms. The (BeO;) , !*~- chains run parallel to the c-axis. the apex of one becomes a corner of the base of the next. The two types of chains link into the Be;Si0, strips by sharing two corners of each base. All oxygen atoms in the BeQ, tetrahedra coordinate two beryllium atoms and one silicon atom. The basal oxygens in the SiO. tetrahedra coordinate two Be atoms and one silicon atom. The apical oxygens of each SiO, tetrahedra coordinate two silicon atoms only. The BeSi0O, strips alternate with strips of the com- position Be;O;(OH),. These latter strips consist of infinite BeO.(OH) chains lying parallel to c. The BeO;(OH) tetrahedra that form these chains link in the same manner as the BeQ, and SiO, tetrahedra but are oriented so that the apices point in the opposite direction. The BeQ;(OH) chains are linked into the strips by sharing one corner of each base. The two types of strips link into a three-dimensional network as shown in figure 2. Additional SiO, tetra- hedra are situated between the strips. Each oxygen atom of these tetrahedra coordinates one silicon atom and two beryllium atoms. The two oxygen atoms of Y Y 6s BeQ4 S104 B602(OH)2 Figurz 2.-The bertrandite, BesSizO:(OH)2, structure as postulated by Ito and West (1932). THE BERYLLIUM MINERALS 5 k _ //,; } > FIGURE 3.-Bertrandite, Reprinted from Solovieva and Belov, 1961. tetrahedra, unshaded; tetrahedra shaded. the BeQO.(OH): tetrahedra also coordinate one Si and two Be atoms. The two (OH) groups coordinate two beryllium atoms only. Ito and West's structure is a model only and prob- ably, in view of the work of Solovieva and Belov (1961), is not correct. Solovieva and Belov (1961) recently determined the crystal structure of bertrandite from analysis of AkO and 0kZ intensity data. Their structure is different from that given by Ito and West as can be seen in figure 3 which shows a projection of the structure on (001). Each BeO;(OH) tetrahedron shares the (OH) corner with another (OH) tetrahedron, and each of the oxygen corners with one SiO, tetrahedron and one Be03(OH)‘ tetrahedron. The SiO, tetrahedra share one corner with another SiO, tetrahedron and each of the other three corners with two BeO; (OH) groups. In this way a three-dimensional framework structure is formed. The structure may be also viewed as being formed of linked double SiO); and Be,0,(OH) tetra- hedra. BERYL AlzBeasisOm CRYSTALLOGRAPHY [Bragg and West, 1926] Hexagonal: @...... B21 kX reali. ee, 2 9.17 kX Dy. aco ios 2.63 g/cm V. 673.6 kX Space group: P6/mee CHEMICAL COMPOSITION Beus (1960, p. 66-90) gives a very complete descrip- tion of the chemistry of beryl including 38 chemical analyses. Schaller, Stevens, and Jahns (1962) have 695-379 O-64--2 proposed two main solid-solution series for the beryls. They are given as follows: 1. Ri(Al,-.Li,) (Bes--Al,)SisOi1snH;0 (where z=0 to 0.5) and 2. RF(Al;-.Mg,) BesSiiOisnH;0 (where z=0 to 0.55). If z»=0 we have the ideal end-member Al;Be;8ie$O1s which is never found in nature. R* may be Cs, Rb, Na, or K. Fe* may replace Al in the octahedral sites, and Mn* and Fe* may replace Mg in the octahedral sites. Only small smounts (0 to 2.5 percent) of HO appear in the beryl analyses. CRYSTAL STRUCTURE [Bragg and West, 1926; Belov and Matveeva, 1951; Schaller, Stevens, and Jahns, 1962 The beryl structure contains rings of the composition and are composed of six SiO, tetrahedra sharing corners. Figure 4 shows these rings projected on (0001). Figure 17 shows a projection of the beryl structure perpendicular to c. The Si;O;; rings are linked together into a three-dimensional structure by Al octahedra and BeQO, tetrahedra as shown in figures 4 and 17. In the solid solution series described above Al, Li, Mg, Mn*, Fe, and Fe® can appear in the octahedral sites. In the tetrahedral sites outside the SizO0;s rings, Be and Al can appear. There appears to be no substitution of other cations for silicon. The cesium, rubidium, sodium, and potassium ions and also the water molecules are probably situated within the tunnels running through the center of the rings. The openings in the rings are shown in figures 4 and 5. In figure 5 the possible location of a cesium ion is shown. The role of Nat, K*, Rb, and Cs 6 CRYSTAL CHEMISTRY OF BERYLLIUM F1GuRE 4.-The beryl, AlsBesSisOis, structure projected on (0001). represent Be# ions, and the open circles ions. in the beryl structure is much disputed and we must wait for an accurate structure determination of a beryl containing a large amount of these alkalies before we can be sure of their true position in the lattice. It is interesting to note that the presence of appreciable amounts of the alkali metals, particularly the large cesium ions, causes an increase in the c dimension. The a-dimension is apparently not affected by the alkali content. Belov and Matveeva (1951) found the following bond lengths in beryl: Angstroms 1.64 Si-O -::....~: 1.00 Al-O. ¢.«=..~. 1.95 BAZZITE R*(Sc, Al, Fe, Mg)9Be38ioOm? CRYSTALLOGRAPHY [Peyronel, 1956] Hexagonal: iet Lines sam oul 9.51 A c Haras aan s un asain a a ana awa 9.11 Vass ti onl ro eee l pre LLC- 718.5 A ill. s 1n unul ee ins waren 2.819 g/cm cna cise 2 sacs ayes 2.809-2.825 g/cm} Space group: P6/mec CHEMICAL COMPOSITION Bazzite is a rare mineral and has only been analyzed Each ring of shaded tetrahedra represents an SisO3~ group. The solid black circles Reprinted from Schaller, Stevens, and Jahns, 1962. spectrographically. The major constituents appear to be Be, Si, Al, Mg, and Sc. Lesser amounts of Fe, Na, and Ba are present. Minor amounts of Cu, Ga, V, Sn, Y, Yb, and Ag have been found (Huttenlocher, Hugi, and Nowacki, 1954). CRYSTAL STRUCTURE [Peyronel, 1956] Peyronel (1956) worked out the crystal structure of a bazzite containing Sc, Fe, Na, Y, Yb, Al and Si. He found the mineral to be isostructural with beryl. Scan- dium appears to occupy the octahedral sites. BERYLLITE Bessi207 (OH) 421120? CRYSTALLOGRAPHY [Kuz'menko, 1954] Da=2.196 g/cm} X-ray powder data given CHEMICAL COMPOSITION [Beus, 1960, p. 103. Numbers of ions on the basis of 7.00 oxygens and 4.00 OH] Weight Weight percent _ Ratios percent Ratios 34 10 . 1.83 | CaQ....._.. ~00 =.... AlsOs---.--.. 1. 63 } 05 NaiQ._..... 2-42 ...... Fe:sQs....... 12 f 18. 95 } 3. 98 10-.....s. 3. 25 F MaQ::.....- Tt» BeQ-...:... 40. 00 _ 5. 17 100: 97 ...... B65 7 (Si, Al, Fe) 1 ,9301(0H)4(H20) 1.08 THE BERYLLIUM MINERALS. T Si4+ ion Cst ion FiGurE 5.-The structure of the SisO}$~ ring in beryl projected on (0001). The opening in the center of the ring is apparently sufficiently large to accommodate a Cs+ ion, one of which is shown in the center of the diagram. Reprinted from Schaller, Stevens, and Jahns, 1962. BER YLLONITE CRYSTALLOGRAPHY (Wehrenberg, 1954] Monoclinic: a...... 8.10% V__. < 8905 A 7.79 A D.... 2.81 g/cm cil 14.08 A al. 42 P... 90% g... - 2.831 g/oms Space group: P2 /n X-ray powder data (Mrose, 1952, p. 938) CHEMICAL COMPOSITION [Beus, 1960, p. 111] CRYSTAL STRUCTURE [Golovastikov, 1961] Golovastikov, 1961, using the unit-cell data of Wehrenberg, 1954, solved the crystal structure of beryl- lonite by three-dimensional Patterson techniques. Each BeQO, tetrahedron shares corners with four PO, tetra- hedra and likewise each PO, tetrahedron shares corners with four BeQO, tetrahedra. The BeQO, and PO. tetra- hedra link-up to form pseudohexagonal rings as shown in figure 6. The rings are joined to similar rings above and below through the sharing of six apical oxygens, three of which point up and three of which point down. Within the rings are found channels running parallel to the 6 axis. The rings link together as shown in figure 6 to form a continuous three-dimensional network. The sodium atoms lie within the channels. Na, is found to be in ninefold coordination; Na, and Na; in octa- hedral coordination. The range of values for the various bond lengths were found to be as follows: Angstroms PNL auks .., 1. 48-1. 56 BesO as _o. 1. 58-1. 66 e. 22. eal esa rse eon 2. 51-2. 82 Nas; cgl -an imu=sl.s 2. 22-2. 68 BERYLLOSODALITE Na4BeAISi4OnCl CRYSTALLOGRAPHY [Semenov and Bykova, 1960] Pseudocubic: a...%... ms8.7 A 2.28 g/em' Desi.... 2.36 g/cm‘ (for Z=2 and V=658.5 A}) Anisotropic X-ray powder data given CHEMICAL COMPOSITION [Semenov and Bykova, 1960] Weight percent Theoretical OF:... +e weet c lnm < non colbie c wine cic 50. 45 51. 33 AO;... . =e be - Lpc annal is 12. 56 10. 92 0:13.20; ______________________________ O0 cible «anh aun =s ains arai ss 5. 30 5. 85 Cad ann ans ane a OU.: - s . « as. ius ion cual o 23. 26 26. 52 n se lau lane nae aunt b A0 ler cud. 1: 50 :. 20_ _______________________________ 1 51 x CL . .z. Len sew ara - abl sie 6. 04 7. 59 101. 56 101. 71 tes mr _> 1. 40 1:71 100. 16 100. 00 CRYSTAL STRUCTURE This mineral is probably isostructural with sodalite, Na, Al;81,041,C1, with (BeSi) replacing (2A1). In the well-known sodalite structure (Pauling, 1930), each oxygen atom is coordinated by one silicon, one alumi- num, and one sodium atom. Each sodium atom is co- ordinated by three oxygens and one chlorine atom. The chlorine atoms are coordinated by four sodium atoms. The aluminum and silicon atoms are coordinated tetra- hedrally by four oxygens. The aluminum and silicon atoms are ordered. Semenov and Bykova state that the X-ray powder pattern cannot be indexed with a cubic unit cell. The deviation of beryllosodialite from cubic symmetry is perhaps due to the ordering of Be, Al, and Si, which requires lower symmetry than that of sodalite (P487). 8 CRYSTAL CHEMISTRY OF BERYLLIUM C FiGURE 6.-The crystal structure of beryllonite, NaBeP O4, showing the arrangement of the BeOs« (stippled) and PO; (lined) tetrahedra. 'The sodium atoms are shown as circles. Reprinted from Golovastikov, 1961. If in this mineral we retain the P43n symmetry with one Be, Si, and Al atom statistically distributed in the six-fold aluminum position (64), the bond strengths about each oxygen atom will vary between 1% and 244. This leads, probably, to an unstable structure. BITYITE (Ca, Na, K) (Al, Li, Mg) -s (Si, A1, Be)4010(OH); CRYSTALLOGRAPHY [Strunz, 1956] Monoclinic: @-. csi 4.98 A Vl. terete. 809.1 As 8.67 A 3.07 g/cm C. <.-k% 18.74 A 4 m90° 3.14 g/cm} Probable space group: C2/c X-ray powder data given CHEMICAL COMPOSITION [Strunz, 1956. Numbers of ions on the basis of 10.00 oxygens and 2.00 OH] V eight percent Patios \ (1) (2) (1) 2 31.95 33.37 2. 14 (2). 17 BeO.z:z:..: fei inde ce 2. 27 7. 30 . 36 1. 14 cr 41. 75 36. 24 1. 64 1. 39 con eck *a ase sa . O1 0 718 . 04 1130: .% lcs e cece .c... 2. 73 2. 39 37 31 . 40 . 29 02 02 ; (olo _ Maa era one. . 16 . 04 01. : .a.. A0. lee eels eer cn aeon 14. 30 - 14. 42 1. 02 1. 01 HyO: :.. 2 sa sel cs seas 6. 50 b: 72 1. 45 1. 24 (1) - (Ca, Na, K)1.0s(Al, Li, Mg)2.s3(8i, Al, Be)40;10(OH); (2) (Ca,Na)1.05(Al, Li, Fe):.72(Si, A1, Be)1010(OH)2 In calculating the formulas from these analyses I assume that (1) the tetrahedral positions are completely filled (4 atoms per formula unit) ; (2) all Si and Be atoms go into the tetrahedral positions; (3) the remain- ing vacancies in the tetrahedral positions are filled by aluminum; (4) the excess aluminum plus all lithium, iron, and magnesium go into the octahedral positions; (5) calcium, sodium, and potassium go into the inter- layer sites; and (6) no water in the form of oxonium ions replaces the interlayer cations. CRYSTAL STRUCTURE Bityite is a beryllium margarite. The beryllium re- places some of the aluminum and silicon in the tetra- hedral sites. To balance the charges lithium goes into some of the vacant octahedral sites. f BROMELLITE BeO CRYSTALLOGRAPHY [Aminoff, 1925] Hexagonal: 2.68 kX str 3.02 g/cm Cig. .ss 4.36 kX uu 27.12 kX* D;. siege.. 3.04 g/cm Space group: P6;me THE BERYLLIUM MINERALS 0 CHEMICAL COMPOSITION [A minoff, 1925] Weight percent $D;0¢. .s . 29 MsOg. cise . 14 . 85 100. 95 CRYSTAL STRUCTURE Bromellite has the wurtzite structure. Pure synthet- ic bromellite gives Be-O bond lengths of 1.655 and 1.647 A, and O-Be-O bond angles of 109.0° and 110.0° (Jef- frey, Parry, and Mozzi, 1956). The unit-cell size of pure BeO is Angstroms a = 2.698 c = 4.379 CHKALOVITE Na,(BeSizO4) CRYSTALLOGRAPHY [Pyatenko, Bokil, and Belov, 1956] Orthorhombic: @... 3% 21.1 A 21.1 A C.. ITL 6.87 A Space group: Fddd V RME 3059 A Mt aat... 24 2.66 g/cm CHEMICAL COMPOSITION [Beus, 1960, p. 38. - Numbers of ions on the basis of 6.00 oxygens] Weight Weight percent Ratios percent Ratios $10;........ 56. 81 1.98 | 0.13 ..: ..s eil. --.... !l -an Fe103 _______ 30: 20— ______ A29 - FeQ...:...... , A2. Biz.. TP E Les.. sharen beo..:..... 12.67: 1:06 | 8O.;_....._.... 22 Cad........ + Onis les's N#0-...... 28. 93 - 0. 98 900.758" Na1.95Be1-0s8i1.9080s CRYSTAL STRUCTURE [Pyatenko, Bokil, and Belov, 1956] Chkalovite has the high cristobalite structure with beryllium substituting for one out of three silicon atoms in the SiO, framework. The sodium atoms occupy two-thirds of the large voids in the structure. A struc- ture similar to this was predicted by Buerger (1954) for the compound Na,BeSiO, which represents the fully "stuffed" Na-Be derivative of cristobalite. The for- mulas of chkalovite and Na,BeSiO, expressed as diox- ides are Na»,;(Beis8iz3)0O and Na(Bey»Si1,2)O0;, respectively. In chkalovite sodium possesses a some- what irregular coordination, one sodium being in ten- fold coordination, the other in elevenfold coordination. Ideally the sodium atom in an undistorted high cristo- balite structure would have twelvefold coordination. The unit cell of chkalovite (chk) is related to that of high cristobalite (crist) by : Gonk= bonk Z23Gor ist Conk CHRYSOBERYL A12B804 CRYSTALLOGRAPHY [Bragg and Brown, 1926] Orthorhombic: @- .. 5.47 kX V 227.0 kX bX -is 9.39 kX eee -C 4 6.2.... 4.42 kX Dea 3.69 g/cm Space group: Pbnm CRYSTAL STRUCTURE [Bragg and Brown, 1926] The oxygen atoms in this structure are approximate- ly in positions of hexagonal close packing, with the two layers perpendicular to (001) repeating every 4.42 ZX. The beryllium and aluminum atoms fill, respectively, certain tetrahedral and octahedral holes. Figure 7 shows the linked polyhedra of the two layers of the hexagonal close-packed repeat unit. The structure may be visualized by superimposing figure 7A on figure 72. Chrysoberyl is isostructural with olivine and also with the compounds AlGaBeQ,, AlFeBeQ,, and AICrBeQO, (Gjessing, Larsson, and Major, 1942). EPIDIDYMITE NaBeSi,0, (OH) CRYSTALLOGRAPHY [Ito, 1934; see also Pobedimskaya and Belov, 1960] Orthorhombic: as. 2. s 12.63 kX 1255 kX 7.32 kX a na ce 8 6.2.2. : 13.58 kX F) ) ¢. agen ay sia 2.58 g/cm} Space group: Pram CHEMICAL COMPOSITION Beus (1960, p. 37) gives seven chemical analyses of epididymite and its polymorph eudidymite. The com- position of these minerals is close to the theoretical composition NaBeSi,O0;,(OH). Minor amounts of aluminum and ferric iron appear to substitute for Be or Si. Also, minor amounts of Ca and Mg probably substitute for Na. Epididymite loses water at 700° to 800° C indicating that hydroxyl groups are present in the structure. CRYSTAL STRUCTURE [Ito, 1934; Pobedimskaya and Belov, 1960] The structure proposed by Ito (1934) has been con- tradicted by Pobedimskaya and Belovy (1960). The 10 FiGurE 7.-The arrangement of tetrahedra and octahedra in (A) layer I of chryso- beryl, and (B) layer II of chrysoberyl. atomic parameters proposed by Ito give unusually poor Be-O and Si-O bond lengths which led the Russian workers to reexamine the structure. The atomic pa- rameters proposed by these workers give plausible bond lengths. Their structure cannot, however, be accepted at this time. The epididymite unit cell contains 56 oxygen atoms and 8 (OH) groups. Pobedimskaya and Belov list coordinates for 60 oxygen atoms and 8 (OH) groups. EUDIDYMITE NaBeSi;0;(OH) CRYSTAL CHEMISTRY OF BERYLLIUM CRYSTALLOGRAPHY [Ito, 1947; see also Pobedimskaya and Belov, 1961] Monoclinic: 12.62 kX V 1264 kX sct 7.37 kX Dnuk=-<=-.2. 2.553 g/cm} it. 13.99 kX p pV axe So. 8 Mlle 103°43" DJ. 2.561 g/ems Space group: C2/c CHEMICAL COMPOSITION [See the discussion of the chemistry of epididymite] CRYSTAL STRUCTURE [Ito, 1947; Pobedimskaya and Belov, 1961] Ito (1947) has proposed a structure for this mineral. The bond distances are, however, so grossly in error that the structure cannot be considered correct. Pobedim- skaya and Belov (1961), as they did with epididymite, proposed a structure with 60 oxygen atoms and 8 (OH) groups in the unit cell. FAHEYITE (Mn, Mg, Na) Be;Fe;#+ (PO,)1.6H0 CRYSTALLOGRAPHY [Lindberg and Murata, 1953] Hexagonal? : Mee l- teres 9.48 A 2.000 g/om' 16.00 A se alec aas 3 V2. enas 1232 As 2.670 g/cm} X-ray powder data given CHEMICAL COMPOSITION [Lindberg and Murata, 1953. Numbers of ions on the basis of 16.00 oxygens) Weight Weight percent Ratios percent Ratios P;0,.......4 38. 11 1. 99 ,0.... 30:_ Ir." sz sus Fe;O;...=... 21. 42 . 99 Tre * A1;Os-... .% . 10 . O1 H;0.. ...... 14. 90 6. 11 beo:-.__-.. 1.20 2.15 Insol: ...... 9.44 - __ Mno.....-. 5. 99 . 62 MaeQ-:.:.._. 1. 14 . 21 99.20 (...... Na20 _______ . 84 . 10 (Mn, Mg, Na) 1.03Be2.1s(Fe**, Al)2.00P3.esO16(H20)s .11 GELBERTRANDITE BhSizOflOH) 3.31170? CRYSTALLOGRAPHY [Semenov, 1957] D,,-=2.176 g/cm} X-ray powder data given CHEMICAL COMPOSITION [Semenov, 1957. Numbers of ions on the basis of 7.00 oxygens and- 2.00 OH] Weight Weight percent Ratios percent Ratios £103. .-. »« 38.70... 1:02 |. Hi0O+.::... 15. 62 } 3. 93 Als03...,. .-.. 1. 20 . 04 | 8. 17 ' 34. 16 4. 06 Ces 1:09 ...:... 100. 11 (Na,K);0 . .. S9 e-- Beas (Si, Al) 2.0007(OH) 2 (H20) 2 .9s This mineral may be a poorly crystallized bertrandite (Fleischer, 1958). THE BERYLLIUM MINERALS 11 HAMBERGITE Be,(BO;) (OH) CRYSTALLOGRAPHY [Zachariasen, 1931b; Zachariasen and Plettinger, 1958] Orthorhombic: resort aon 9.755 +0.002A tige 12.201 +0.002A Cinc! .» ake 4,426 +0.001A V.le venn ALCLLL.. La 526.79 A F...... 8 c 2.34 g/cm? Space group: Pbca CRYSTAL STRUCTURE [Zachariasen and Plettinger, 1958] The beryllium atoms are coordinated tetrahedrally by three oxygen atoms and one (OH) group. Each oxygen atom of the BeQO,;(OH) tetrahedra is shared with another BeO,(OH) group and a BO; triangle. The (OH) group is shared between two BeO,(OH) tetrahedra. The boron atoms are in triangular coordi- nation by three oxygens at distances of 1.33+0.02 A. Each of these oxygens is also shared with two BeO;,(OH) tetrahedra. The triangles lie in a plane parallel to the c-axis. Figure 8 shows a portion of the hambergite structure projected on (001). The BeOQ; (OH) groups are shown as shaded polyhedra in this figure. As can be seen the structure is a three-dimen- sional one formed by the linking of tetrahedra in in- finite spirals parallel to c. There appears to be a hy- drogen bond of 2.89 A between the (OH) groups (shown as dashed lines in fig. 8). Zachariasen found Be-O bond lengths of 1.655, 1.639, 1.657, 1.636, 1.663, and 1.667 A. Be-(OH) lengths of 1.637 and 1.645 A were observed. The average Be-O (OH) lengths is 1.650 A. HARSTIGITE (Ca, Mn, 23- »? CRYSTALLOGRAPHY [Flink, 1917] Orthorhombic CHEMICAL COMPOSITION [Flink, 1917. Numbers of ions on the basis of Si=6.00] (1) (2) W eight Weight percent - Ratios percent Ratios 39.92 6.00 40.70 6.00 11.57 4.18 11. 40 4. 10 Tr. Trk "eck. 7.07 ~.90 7. 03 . 89 ,. 94 -.. 21 . 93 . 21 37.78 6.08 37.86 6.08 2 48 A8 ©_.. 000 clic. ______ anes 15 . 07 99.76 ~.... O7.4t ._... Less ass. O0 agen ites "07.08 i.... (1) (Ca, Mn,Mg);-10Be1.1sSie.00(O,O0H,F) 23.50 (2) (Ca, Mn, Mg);-1sBei-108is.00(0,0H,F) 23.35 HELVITE MmBeashOwS‘ DANALITE Fe4BeaSi30n-S GENTHELVITE Zn4Beasi30 12° S CRYSTALLOGRAPHY [Glass, Jahns, and Stevens, 1944; Pauling, 1930] Extrapolated X-ray data for the Mn, Fe, and Zn end members are given as follows : Ko "us; z:qim - "Cids" Helfite....-_~..... 8.27 565.6 2 3.20 P43n Danalite.......... 8.18 547.3 2 3.35 Pz3n (probable) Genthelvite.. ___. 8.10 531.4 2 3.70 P43n (probable) CHEMICAL COMPOSITION [Glass and others 1944; Beus, 1960] Helvite, danalite, and genthelvite are names designat- ing the manganese, iron, and zinc end members, respec- tively. There is apparently a complete solid solution formed between these end members. Inspection of the chemical analyses given by Beus (1960, p. 43) indicates that some aluminum substitutes for beryllium with a concomitant substitution of Na for Mn, Fe, or Zn. A limited solid solution towards the (R,**Na) (Be:Al) 81,0; 8 end. member may thus exist. CRYSTAL STRUCTURE [Pauling, 1930] Helvite has the sodalite structure with Mn replacing sodium, Be replacing Al, and S re- placing Cl. Helvite, by analogy to sodalite, possesses a framework structure with each SiO, tetrahedron shar- ing corners with four BeQO, tetrahedra and with each BeQO, tetrahedron similarly sharing all corners with SiO, tetrahedra. The two types of tetrahedra link into a three-dimensional network in which there appear large cages. In these cages, composed of 24 tetrahedra, lie the sulfur atoms. In helvite the Mn atoms lie within six-sided orifices and according to Pauling are coordi- nated by one sulfur and three oxygen atoms in a tetra- hedral arrangement. The electrostatic valence rule is satisfied. The bond strength from Si, Be, and Mn is 1, 14, and 14, respectively. Each oxygen atom is in contact with one Si, one Be, and one Mn atom to give a charge balance of two. Each sulfur atom is in contact with four Mn atoms to give a charge balance of two. Danalite and genthelvite are isostructural with hel- vite. 12 CRYSTAL CHEMISTRY OF BERYLLIUM (C) BO; Triangle & FrGure 8.-The crystal structure of hambergite, Bes(BOs)(OH). The BeO;(OH) tetrahedra link to form spirals parallel to the c=axis. THE BERYLLIUM MINERALS 13 HERDERITE CaBePO,(F,0H) CRYSTALLOGRAPHY [Pavlov and Belov, 1960] Monoclinic: @. Sas 9.80 A Y...: saan uh 361.3 A bess 7.68 A 3.00 g/cm} Agr ini s.: 4.80 A a aree ald alie 4 oue 90°6' D.:: - 2.98 g/cm} §g>ace group: P2;/a -ray powder data (Mrose, 1952, p. 938) CHEMICAL COMPOSITION There is apparently a complete solid solution be- tween herderite, CaBePO,F, and hydroxyl-herderite, CaBePO. (OH). CRYSTAL STRUCTURE [Pavlov and Belov, 1960] The herderite structure consists of infinite sheets of linked Po, and BeO;F tetrahedra. Each BeO;F tetra- hedron shares three oxygens with three adjacent PO tetrahedra. The PO. tetrahedra share three corners with three adjacent BeO;F tetrahedra. Between the (BePO.F),""~ sheets lie the calcium atoms. These atoms are coordinated by six oxygen atoms and two fluorine atoms; F, O,, O;, and O; of one sheet and by F, O,, O;, and O, of the second sheet. The structure of the sheets is shown in figure 9. The arrangement of the calcium polyhedra is shown in figure 10. FiGurE 9.-Herderite, CaBePO,;(F,OH), showing the structure of the infinite (BePO«F),#*~ sheets. Dashed lines denote the calcium-oxygen (fluorine) bonds. The PO tetrahedra have their 4 axes approximately perpendicular to the a-b plane; the BeOsF tetrahedra have their threefold axes approximately perpendicular to the a-b plane. 695-379 O-64--3 FrGurz 10.-Herderite, CaBePO,(F, OH), showing the arrangement of the calcium polyhedra. Reprinted from Pavlov and Belov, 1960. The bond lengths are given as follows : Angstroms Angstroms 1. 51 Be-F:_...:.._z..2 1. 67 Pop ::.: _s": 1. 52 ...:::} 2. 40, 2. 40 P—Oa _____________ 1. B7 Ca—Oz ____________ 2. 44 1. 51 CS 0, -;. 2. 61, 2. 70 Be—Oz ____________ 1. 64 Ca—O4 ____________ 2. 44 :-... 1. 55 ._. ::.. __. 2.71, 2. 58 BesOilis. ...... 1. 67 Herderite is isostructural with datolite, CaBSiO,(OH) (Ito and Mori, 1953). In datolite Be"*P5* is replaced by B*%S8i*. Herderite is also struc- turally related to gadolinite, FeMYBeSiO,.0, which will be described next. GADOLINITE FeW Y BeSi0,.0 CRYSTALLOGRAPHY [Ito and Mori, 1953; Pavlov and Belov, 1960] Monoclinic: a____ 9.89 +0.01 A 90°33" b____ 7.52 A 350.3 A c____ 4.71+0.01 A ra eas a 4 Space group: P2;/a CHEMICAL COMPOSITION Gadolinite is a complex rare earth silicate ; it is often in the metamict state owing to the presence of radio- active thorium and uranium in the structure. Fe, Be, 14 CRYSTAL CHEMISTRY OF BERYLLIUM and Si are apparently essential constituents although small amounts of Fe*, Al, and Mn* may substitute for these ions. Yttrium and the yttrium earths are usually present to the extent of 22 to 46 percent by weight (Dana, 1892, p. 511). Other elements including the cerium earths, thorium, uranium, calcium, magnesium, sodium, and potassium may substitute for yttrium and the yttrium earths. Nakai (1938) reports a calcium- lanthanum gadolinite containing 11.93 percent Ca (see also Beus, 1960, p. 59). CRYSTAL STRUCTURE [Ito and Mori, 1953; Pavlov and Belov, 1960] The formula of gadolinite is derived from that of herderite, CaBePO.,F, by replacing Ca with Y*, PO. with SiO, and F with O* to give the radical (¥BeSiO,.0)-. Fe* is placed in the special positions 2a (000,440) of space group P2,/a which are unoccupied in the herderite structure. The other atoms are in the general positions (4e) so that we have one Fe atom for every two Y, Be, and Si atoms. The formula can thus be written Fel Y¥BeSiO,.0. The iron atoms occupy a position within the rings of six YO; polyhedra as shown in figure 11. HSIANGUALITE Lizca3B63 (Si04) aFy CRYSTALLOGRAPHY [Huang, Tu, Wang, Chao, and Yu, 1958; Fleischer, 1959; Beus, 1960, p. 60-61] Cubic: (hss . «Abe SSH gie ae a an abe tho 12.879 +0.004 A ane 2136 A bas san 2.97-3.00 g/cm T BE .l. neta ns » der aes aem ll an 8 D... AEO ln Pade __ 2.95 g/cm Space group: 14,32 CHEMICAL COMPOSITION [Huang and others, 1958; Beus, 1960, p. 60-61. Numbers of ions on the basis of 12.00 oxygens and 2.00 F] (1) (2) Weight Weight percent Ratios _ percent Ratios BIO jie. eden n beeen an will 35.66 2.93 36.64 2. 95 CaO. .: 34.60 3.05 35.18 3.04 BeO:.l.l.- cer aus 15. 78 "8.12 46. 30 - 3. 16 i h:B5b -©97 5. 60 . 90 250 ie 2-2? ' aao ca 700: 2° Aes ABB 22 lr ss.. Cs 49 09. K;0....'... 00; . e. 1:09) \- -s __________________________ 7.81. 2 03 T. B7 »A, 85 LOSE! L xl names oue band g ol 1a2B. ee t dt oll 102.07" 101.28. _._. Less O= .t.. S20 -__- $500:=:- .._ .s. amu. 98:78... -=. 98,22 ° ___: FiGuRE 11.-Gadolinite, Fel/gYBeSiO4.0, showing the arrangement of the YO; and FeQs polyhedra. Reprinted from Pavlov and Belov, 1960. HURLBUTITE CaBez (P04) Pi CRYSTALLOGRAPHY [Bakakin and Belov, 1960] Monoclinic: | dx>.3. 8.29 A Me:... 569.8 A* 8.80 A i-... 4 C- 7.81 A D..... 2.89 g/em} $m... ~%90° Space group: P2,/a X-ray powder data (Mrose, 1952, p. 937-938) CRYSTAL STRUCTURE Hurlbutite is isostructural with danburite, CaB, (SiO,), (Dunbar and Machatschki, 1931 ; Bakakin, Krauchenko, and Belov, 1959; Bakakin and Belov, 1960). The hurlbutite structure is also related to that of the feldspars. Compare the hurlbutite structure (fig. 12) with that of sanidine (Eitel, 1958, fig. 56, p. 85). For convenience of presentation a sheet of the com- position (BePO,;) *" is isolated from the three-dimen- sional structure and is shown in figure 12. This sheet is connected above and below through sharing of apical oxygens to two nearly identical (BePO;),*"~ sheets. Each BeQO, tetrahedron is linked by sharing corners to four PO. tetrahedra. Likewise, each PO. tetrahedron is linked to four BeQO, tetrahedra. The phosphorus and beryllium atoms in adjacent sheets are interchanged so THE BERYLLIUM MINERALS 15 O ca 0 Be O :P FIGURE 12.-The hurlbutite; CaBe:s(PO;);, structure showing the arrangement of the infinite (BePO;)»!*~ sheets. that only beryllium atoms are adjacent to phosphorus atoms. The calcium atoms lie between the (BePO;) ,**~ sheets and are in sevenfold coordination. The Ca-O bonds are shown as dashed lines in figure 12. In danburite, the SiO, and BO, tetrahedra link up in much the same manner as in hurlbutite. In danburite, however, each SiO, tetrahedron is linked to three BO« tetrahedra and one SiO, tetrahedron. Each BO, tetra- hedron is linked to three SiO, tetrahedra and one BO, tetrahedron. The two different distributions of tetra- hedrally coordinated cations in hurlbutite and dan- burite are necessary in order to balance charges on the oxygen atoms. The charge distribution on the oxygen atoms is given in table 3. Although danburite is orthor- hombic, it has a unit cell similar in size and shape to that of hurlbutite (@=8.01A, b=8.75A, and e=7.71¢A). The calcium atom in danburite is also in sevenfold coordi- nation. TABLE 3.-Charge distribution on the ozygen atoms in hurlbutite and danburite HURLB UTITE DANB URITE (4) 0, -..: 2036 |. (8) O:... 2. 036 (1 o;: ° 2 036 | (s) 0.°. ~.. 2. 036 (4):07....>.2 2. 036 | ts) O;... 2. 036 (4 2 036 {=(4) 0. °. 2. 000 (4y 2. 036) t4) 0;- >.>"! 1. 784 ":: 2. 036 (40,1... .-: 1. 750 E:": 2. 036 TaBu® 4.-Bond lengths in the hurlbutite structure I Angstroms Angstroms Pr—Ol ________ 1. 60 Bea—02 _______ 1. 60 P1—03 ________ 1. 58 Beg—04 _______ 1. 58 P1—05 ________ 1. 56 B62—Og _______ 1. 59 Pl—‘Og ________ 1. 59 B82”Os _______ 1. 61 PjO:...-."¢.- 1.:55 | 2. 52 1.87 | Ca-O;..:..... 2. 49 1.56. | 2. 46 y-O;: 801... 1.858 | 2. 42 Be,—O, _______ 1. 57 08—05 _______ 2. 48 Bei-Os3.-----.-- 1. 59 | Ca-O,4.....-.. 2 46 Bei-O0;.....-..- 1. 59 | Ca-O;-._..... 2. 47 16 Table 4 gives the bond lengths found in hurlbutite by (Bakakin and Belov, 1960). The average phosphorus- phosphate oxygen distance is 1.57A. The average beryl- lium-beryllium oxygen distance is 1.59A. It appears that this structure needs further refinement for we should expect the average P-O and Be-O bond dis- tances to be 1.52 and 1.64A respectively. KARPINSKYITE Nag (B'e, Zn, Mg) AlgSloO 16 (OH) 2? CRYSTALLOGRAPHY [Shilin, 1956] Trigonal: 2.545 g/cm} G.2.2% 14.24 A BAE: .c. 6 4.83 A v.:: 848.2 a: Diffraction symbol: P... X-ray powder data given CHEMICAL COMPOSITION [Shilin, 1956. Numbers of ions on the basis of 16.00 oxygens and 2.00 OH] CRYSTAL CHEMISTRY OF BERYLLIUM Weight Weight F percent Ratios percent Ratios 56. 68 5.94. Nam,OQ......: ; 1. 04 16. 40} 1. 02 1. 55 § F9203 _______ . 06 y H30+ ______ 5. 00 1. 75 BeO..:..#..: 2. 58 ; 0b. 2. 50 . 87 3. 26 25 MgO -c... ~ 19 97: 99» --e-, Figure 13.-Melilite (CaeMgSiz)»). The MeO, tetrahedra are located at 0,0 and, § t . ra a (Na, K): 0s (Be, Zn, Mg) 1 .02(Al, Fe) 2 .048is.040 16(OH) : guigiizgsgtzrogrfsfmTge(?eiifi3u'rgzz)it%§$lss are digicteg bygcir‘clgs. tte: ./ n, GUGIAITE CagBeSi207 LEUCOPHANITE (Ca, Na) Be (Si, Al) ;(0,0H, F); MELIPHANITE (Ca, Na) ;Be(Si, Al) ;(0,0H, F); Table 5.-Crystallography of gugiaite, leucophanite, meliphanite, and the related minerals melilite and hardystonite (2) (1) (3) (4) (5) Gugiaite, tetragonal Leucophanite, Meliphanite, tetragonal ! Melilite, tetragonal Hardystonite, tetragonal ! orthorhombic ! 7. 484-0. 02 7. 4040.02 10. 6240.02 7. 78940. 005 7.87 ............................ T- A002 .|. 210-00... . ... L ooh een couch | a alee bre nak s bel aoe = n ae Blas sau seu 44 a o's oh 2200 ane mean 5.04440. 008 10. 0+0. 02 9. 924-0. 02 5.01840. 005 5.01 282. 2 548 11 304. 4 31(2) 4 Space group.-....-........... PTO |. sree. Adee e tle ese icle ive .. clve . on en on P342im P42m Pseudocell: Gelee ee een Cub Arico cde bles soe pae dione cines 7.39 |. neal oe e dh nils bones s suenan on aab an 4a bo » anale ah Ul e= * i- Colson ee aa bien ao g 5.0 £. 901: s 0-1 ch ace na a ade be |e eek ban t a+ b+ aa e baa nas pade aie Reference.. Peng and others, 1962 Zachariasen, 1930, 1931a Zachariasen, 1930, 1931a Smith, 1953, 1954 Warren and Trautz, 1930 Chemical composition ?...... See analysis (8) See analysis (4) See analysis (5) From Smith, 1953 From Palache, 1935, p. 94 ' Unit cell edges have been converted from kX units to angstrom units. 2 For analyses see table 6. CRYSTAL STRUCTURE Zachariasen (1930, 1931a) has shown that there is a close structural relationship between leucophanite, meliphanite, and the melilites. Peng and others (1962) demonstrated that gugiaite is a beryllium melilite. Before discussing the structure of leucophanite, meliph- anite, and gugiaite it will be useful to first consider the structure of the melilites. Warren (1930) found the structure of a melilite, of the composition (Ca,Na) (Mg, A1) (Si, A1) :0;, to consist of sheets composed of groups linked to MgO, tetrahedra through the sharing of the oxygen atoms. Figure 13 shows a sheet of this type projected on (001). These sheets, of the ideal composition (MgSi:O;)1*"~, are held together by calcium and sodium atoms. The calcium (and sodium) polyhedra are in the form of square Archimedean antiprisms and are shown in figure 14. * THE BERYLLIUM MINERALS Smith (1953) has accurately determined the structure of a melilite of the composition C&1. es NQ. 20K. oo Mg. 1s Al, ssFe®**. 4207. He finds that sodium and potassium may substitute for calcium; Mn*, Fe*, Fe*, and Al for Mg; and Al and Fe* for Si. A review of the papers discussing the melilite min- eral group, for example, Berman (1929), Goldsmith (1948), Andrews (1948), Smith (1953), and Neuvonen (1955), gives a fairly good picture of the cationic sub- stitution found in these minerals We may give the following general formula for the melilites: Caz—zNazMg 1-z- ”Al”. ”Sig-”Aly07 where small amounts of K may substitute for Na, small amounts of MnO and FeO for MgO, and moderate amounts of Fe;,0;, for Al;,0O0;3. From the analyses given by Berman (1929) we find that as much as 0.52 atom of Na may substitute for Ca, up to 1.00 atom of Al may substitute for Mg, and as much as 0.78 atom of Al may substitute for Si. The theoretical end members in this mineral group are gehlenite, Ca;Al.SiO;, and aker- manite, Ca,MgSi.0,;. Hardystonité, is the rare zinc-containing end member (Palache, 1935, p. 94). We have already compared the unit cell dimensions of melilite and hardystonite to those of leucophanite, meliphanite, and gugiaite. We see that the minerals of the leucophanite group have unit cells or pseudo-unit cells similar in size to those of the melilites. Leucophanite, meliphanite, and gugiaite may be con- 17 Og 41 FrGurE 14.-The arrangement of the CaOs polyhedra in melilite, CarMgSi:0; Some aluminium replaces silicon and some fluorine and (or) chlorine replaces oxygen in the structure. The H0 reported in the analyses probably occurs as (OH) groups substituting for oxygen. If we examine figure 13 we see that four of the 14 oxygen atoms within the sidered to be calcimum-sodium beryllium melilites. | unit cell are not shared between two tetrahedra. It is 6.-Chemical composition of gugiaite, leucophanite, and meliphanite (Samples 1-6, Dana, 1892, p. 418; 7, Semenov, 1957; 8, Peng and others, 1962. Numbers of ions on the basis of 0O+F-+OH=7.00] 1 2 3 4 5 6 7 8 Weight Weight Weight Weight Weight Weight Weight Weight & percent] Ratios | percent] Ratios | percent| Ratios | percent] Ratios | percent| Ratios | percent| Ratios | percent] Ratios | percent| Ratios 45. 98 1. 85 . 90 1. 91 . 22 06 PH 2.82 G 2.17 . 05 1.11 . 97 NOlaHIe§21.10000.: 0222201000000. . Less FORMULAS OF SAMPLES 1. .so 2. A1)2.000s.14F.ss 3. (Ca,Na,K)1.4B€1.178i1.0808.13F .at 4. (Ca,Na)1.0s(Be, Mg) se(Si, A1)2.000s.04(F, OH) 1.0 5. (Ca,Na)1.00(Be, Mg)1.00(8i, Al)2.0006.2sF .12 6. (Ca,Na,K)1.0(Be,Mg)1.20(8i, Al)1.90s.16(F, OH) .s 7. (Ca,Na,K)1.ss(Be,Mg)i 1s(8i, Al, Fe)1.070s.00(F , 0H)1 11 8. (Ca,Na,K)1.0(Be, Mg) .s9(8i, Al)2.00s.10(F, C1, OH) .so 18 these oxygen atoms that are probably replaced by F, Cl, and (OH). Examination of the chemical compositions of various minerals belonging to the leucophanite group given previously suggests the following general chemical formula : Car-Na,B6éSiz-yAlyOr-z-3(F,CL, OH) 4+, where O= (e+y)=<2. Small amounts of K substitute for Na, and Mg and Mn for Be. The substitution of (OH) groups for oxygen atoms in the melilites has been postulated by Goldsmith (1948). Smith (1953, 1954) also discussed this but did not consider the mechanism important. The names leucophanite, meliphanite, and gugiaite are synonymous. The mineral aminoffite is probably a member of the leucophanite group, perhaps having a formula similar to that of gugiaite. A synthetic beryllium melilite (Ca,BeSi@O;) close to gugiaite in composition, has been reported by Goria (1953-54). The compound is tetragonal with a=7.501 A and c=4.931 A (Z=2). The probable space group is P42,im. The synthetic compound Na,LiBe;F;, re- ported by O'Daniel and Tscheischwili (1948) is tetrag- onal with a=7.5 A and c=5.03 A4 (Z=2). From a comparison of X-ray powder patterns Na.LiBe.F; was found to be isostructural with the melilites. Here Na plays the role of calcium, Li that of Mg, Be that of Si, and F that of oxygen. MILARITE KCEABGQAD (Silgom) $4 Hzo CRYSTALLOGRAPHY [Belov and Tarkhova (1951)] Hexagonal: Dines... 2s sate 2.57 g/cm} eo ._ ic. 2 Dr. .-- 2.52 g/ecm* 18.85 A A... 1304 A} Space group: P6/mec 10.43 A l [Ito, Morimoto, and Sadanaga (1952)] Hexagonal: sade. 10.54 A 2.55 g/cm} t r:... 13.96 A 2 | r 1343 A Dec .at 2.45 g/cm} Space group: P6/mee CHEMICAL COMPOSITION [Palache, 1931. Numbers of ions on the basis of 30.00 oxygens] Weight Weight percent Ratios percent Ratios §10;........ 71.66 11.93 | Na,0....__. 0. 46 _ 0. 07 .... 4. 68 . 46 | H,0O+1..... 1. 02 . 57 5.24 2.10 | H;O-._.._._. +00: Cad:l...l... 11.70 2.09 1530..-...,..- 4. 91 . 52 99. 72 ..... CRYSTAL CHEMISTRY OF BERYLLIUM CRYSTAL STRUCTURE [Beloy and Tarkhova, 1951; Ito, Morimoto, and Sadanaga, 1952] The milarite structure is composed of double hexag- onal rings of the composition (Si:z0;,). These rings are shown in figure 15 and 16. The rings are joined to- e-- =10,48 A _____sf . I 13,85 C FiGurE 15.-The crystal structure of milarite, pro- jected on (1010). The double SizO»!~ rings are shown linked together by BeO4 and A1O; tetrahedra and by CaO; octahedra. Solid circles represent the calcium atoms. Reprinted fron Belov and Tarkhova, 1951. Figur 16.-The crystal structure of milarite, KCa;(BerA!)(SinO»).14H20 pro- jected on (0001). _The SizOs!?- groups are shown linked together by (Be, Al) O4 tetrahedra and CaOQs octahedra. The circles represent potassium atoms lying between the SizO»!- groups. Reprinted from Belov and Tarkhova, 1951. THE BERYLLIUM MINERALS 19 A > (() l\ bee | 1.8<2.0 g/cm 12 2.20 g/cm} (unit-cell constants deter- mined from X-ray powder data) X-ray powder data given 20 CRYSTAL CHEMISTRY OF BERYLLIUM CHEMICAL COMPOSITION [Kopchenova and Sidorenko, 1962] Theoretical Theoretical Weight composition Weight composition percent _ bearsite percent _ bearsite 16. 75. -: 20.35 1:04 :- Al;Os. Ls 2-..s 6.00 As;Os... @... y25b. 5 46. 72 Fe;O;...:--... 1:08 .s... >20. 0 32. 93 Cad... ...see 1:40 .@... i GH 100. 00 The close similarity of the X-ray powder pat- terns led Kopchenova and Sidorenko to propose that bearsite is the arsenate analogue of moraesite, Be, (PO.) (OH) 4H.0. Further work is needed to verify the unit cell and chemical composition of bearsite. PHENAKITE Bezsi04 CRYSTALLOGRAPHY [Bragg and Zachariasen, 1929] Rhombohedral: 7.68 kX NNEC 6 108°01' Déz: 2.99 g/cm} 367.5 kX Space group: RS CHEMICAL COMPOSITION [Dana, 1892, p. 463] Unessential amounts of Al;0;, Fe:0Os, Na:0, CaO, and MgO are present in the chemical analyses of phenakite. CRYSTAL STRUCTURE [Bragg and Zachariasen, 1929] The beryllium and silicon atoms are in tetrahedral coordination. The SiO, tetrahedra share each of all four corners with two BeQO, tetrahedra. The BeQO, tetrahedra share each corner with one SiO, tetrahedron and one BeQO. tetrahedron. The two types of tetrahedra link to form a complex three-dimensional network. The B&a-O distance in phenakite is 1.65 A ; the Si-O distance is 1.62 A. RHODIZITE NaKLi4A14Be3Bsz-l? CRYSTALLOGRAPHY [Strunz, 1943] Cubic: a-. 7.303 kX A4 x's ¥.> 390 kX: D1. 3.25 g/cn+ Space group: P43m CHEMICAL COMPOSITION [Palache, Berman and Frondel, 1951, p. 330] (1) (2) (3) Wciaht‘ Weiazi 11,2035 percent perce 1140... Pe- e ne cana s 7. 81 7. 30 0. 68 NA-... 22 cca 4. 05 3. 30 1. 78 -:. r- '= cons 4% k 1. 41 RD3O- Leve. rent es- 6. 16 5. 90 2. 29 CSzO _____________________________________ 3. 47 c =s ik aime 26. 65 - 30. 50 27. 40 COLLE RAIL -ac. sakes - ao 9. 81 10. 10 14. 93 ob sal aie 45. 52 40. 60 [43. 33] Rem...... 1. 81 1.41 100. 00 _ 99. 51 [100. 00] Dn-zcc«s nn s aoe oie g/cm". ': _I. 3. 305 3. 344 1. 2. Antandrokomby, Madagascar. 3. Sahatany Valley, Madagascar. CRYSTAL STRUCTURE [Strunz, 1943] Strunz gives a partial description of the structure. The structure cannot be considered solved on the basis of this work alone. ROSCHERITE (Ca, Mn, Fe) ;Be;(PO,);(OH) ;.2H.0 CRYSTALLOGRAPHY . [Lindberg, 1958] (1) (2) (3) R 15. 884-0. 04 15. 89040. 04 11. 9540.04 _ 11.904-0.03 11. 9040.03 6. 624-0. 04 6. 664-0. 03 6. 594-0. 03 94°30'+15' - 94°30'+15' 94°50" (assumed) 1257 1254 1242 2. 9834 2. 916 2. 936 4 4 4 2. 98 2, 90 2. 04 Calc Cale Cale CHEMICAL COMPOSITION [Lindberg, 1958. - Numbers of ions on the basis of 12.00 oxygens and 3.00 OH] Weight-percent Ratios (1) (2) (3) (1) (2) (3) 7. 60 11. 48 10.11 - 0.75 - 1.13 1.00 10. 04 14. 47 8. 66 38 (118 . 68 6.26 10.13 16. 49 . 48 75 1.27 19.96 <. ...... .90 (AD .03 12. 58 13. 74 13.01 2.78 3.04 2. 89 37. 60 38. 01 38.74 - 1.46 - 1.48 1. 51 11.56 12.17 12.00 - 3.55 3.74 3.72 280 S1 e 99.80 100.00 _ 100.00 (1) (Ca,Mn Fe, Sapucaia pegmatite mine, Minas Germs Brazil. (2) (Ca, Mn,Fe*);. mBes.uP2.1012(OH)s(H20):.», Greifenstein, Saxony. (3) (Cf/fig? , Fe#, FeS)3.01 Bez.soP3.02012(0 H) s(H20) 2.22, Nevel - Quarry, - Newry SPHEROBERTRANDITE Be;(8i;0;) (OH)? CRYSTALLOGRAPHY [Semenov, 1957] X-ray powder data given THE BERYLLIUM MINERALS 21 CHEMICAL COMPOSITION [Semenov, 1957] [Numbers of ions on the basis of Si+Al4-Fe=2.00] Weight Weight percent _ Ratios percent Ratios 41.03 1.90 | H,0+-.---. 11.70 : 1.81 AbQO;- ... s.~ 1. 40 . 04 | NQ F8303 _______ . 07 . O1 :.:... 45. 20 - 5.02 99. #0 %..:.. Be; .02(Si,A-1,Fe)2 0007 16(OH) s s2 The X-ray powder data of this mineral indicates that it is closely related to bertrandite (Fleischer, 1958). SWEDENBORGITE NaBe4Sb07 CRYSTALLOGRAPHY [Pauling, Klug, and Winchell, 1935] Hexagonal: 2 " mano 5. 47 kX -... 4.18 g/cm? 'ole ia. 8.92 kX V _._. 1281. 1IKX8 Space group: POsme CHEMICAL COMPOSITION [Palache, Berman, and Frondel, 1951, p. 1028] CRYSTAL STRUCTURE [Pauling, Klug, and Winchell, 1935] In this structure each beryllium atom is coordinated tetrahedrally by four oxygen atoms at approximately 1.63 A. Each antimony atom is coordinated octahe- drally by six oxygen atoms at approximately 1.93 A. The swedenborgite structure is based on a four-layer closest packing of the form . . . ABAC . . . such as is found in the mineral topaz. This is referred to by Paul- ing as double-hexagonal closest packing. Of the 16 close-packed oxygen positions in the unit cell, only 14 are occupied by oxygens; the other two positions are occupied by sodium atoms. The sodium atoms are thus coordinated by 12 oxygen atoms. The antimony atoms occupy 1, of the octahedral holes of alternate double layers. The beryllium atoms occupy 14 of the tetra- hedral holes within the double layer holding the anti- mony atoms. Within the double layers not occupied by antimony the beryllium atoms occupy % of the tetra- hedral holes. Each O; atom is shared with four BeQO. tetrahedra. The unusual sharing of four tetrahedra with a common oxygen atom is also found in the basic beryllium acetate, Be,0 (CH,CO00),, structure. Each O. and O; oxygen atom of swedenborgite is coordinated by one antimony atom, two beryllium atoms, and two sodium atoms. The arrangement of the various poly- hedra of the swedenborgite structure is shown in fig- ure 18. FiGURE 18.-The crystal structure of swedenborgite, NaBe,SbO;, showing the SbOs octahedra, the groups of four BeQ; tetrahedra, and the sodium ions (spheres). 'The oxygen and sodium ions together form a double hexagonal close-packed ag- gregate. Reprinted from Pauling, Klug, and Winchell, 1935. TAAFFEITE (Be, Mg) (Al, Fe):04 CRYSTALLOGRAPHY [Anderson, Payne, and Claringbull, 1951] Hexagonal: Dm. 3. 613 g/cm 5.172 A s ~ ar 8 18. 38 A v_... 520.8 A Space group: P6;22 X-ray powder data given CHEMICAL COMPOSITION [Anderson and others, 1951]. [Numbers of ions on the basis of 32.00 oxygens] Weight Weight percent Ratios percent Ratios A103... .=. 70.0 - 7.47 1 BeQ...... . 11.0 " 4. 79 Fe;0Q;:-.::.:- b. 9 - 0.359 --- :.. 13. 4 3. 64 100.8 .s .z... (Bei .sMgs.4)s.1(Fe.sAlin 9) 15.1108 CRYSTAL STRUCTURE [Anderson and others, 1951] The structure of taaffeite appears to be based on a close-packed oxygen framework with eight close-packed oxygen sheets in hexagonal stacking. The distance be- tween adjacent sheets (18.38/8=2.30 A) agrees closely with the corresponding dimensions for spinel, MgAl,0,, where the sheets are 2.32 A apart. In spinel, however, 20 CRYSTAL CHEMISTRY OF BERYLLIUM the oxygen atoms are in a cubic close-packed arrange- ment. The oxygen atoms within the sheets of taaffeite are 2.86 A apart ; in spinel they are 2.85 A apart. The data given by Anderson, Payne, and Claring- bull indicate that one of the following structures is the correct one for the oxygen framework of taaffeite. The oxygen atoms appear to form a subcell with a=2.86 A and c=18.38/n A, where n»=1, 2, or 4 (eight, four, or two oxygens per subcell). There are six possible hexagonal eight-layer stacking sequences for a subcell with c=18.38 A but only two are compatible with space group P6,22. These two sequences are . .. 4242ACAC . and . .. 4BCABACB ... The only possible hex- agonal four and two layer stacklng sequences for sub- cells with e=9.2 A and 4.6 A are . .. AB{€ . and . . AB ..., respectively. These structures require the oxygen atoms to lie on or near the 6 and 6, axes of the subcell in a close-packed array. The cations must lie in the tetrahedral and octahedral voids of the oxygen framework. TENGERITE (¥,Ce)BeCO,(OH);? CHEMICAL COMPOSITION | [Hidden, 1905. Numbers of ions on the basis of Y+Ce+Fe=1.00] Weight Weight percent _ Ratios percent _ Ratios 20 r= a 42 40. 8 4. 1 1. 82 1965283 __________ Z 0 }0. 500 1134200~i _________ (de " ©1053. 2.1... . 0 OSS -L LLL. B i atras Beo..'..'_:_ ~ 5 7 a 200). .s (s Sai CO...... ...th 19. 6 1. 04 100.0 : _._&. SlOz ____________ Sec og Tengerite is also reported as having approx1mately the composmon CaY,(CO;),(OH);.3H.0 and appar- ently is not the same as Hidden's matejlal which contains beryllium (Iimori, 1938). | TRIMERITE Ca (Mn,Fe, Mg) .(BeSiO,): CRYSTALLOGRAPHY [Strunz, 1949, p. 223] Monoclinic: (.in. see, 16. 11 3411 As $.5= >_. 7 Pii... 3. 47 g/em Cec: ices. 27. B0 A | Zu. 16 90°09" :s. 3. 53 g/cm" (for Ca Mn;Be;38i;O0;;) Space group: P2;/c (pseudobexagonal by twinning) CHEMICAL COMPOSITION [Dana, 1892, p. 460. Numbers of ions on the basis of 12.00 oxygens] Weight Weight percent Ratios percent Ratios g10;-;...2..:..9390. 77. 2. 97-1 Cs0..2...2:;___ 12. 44 - 1. 00 17.08 3. 06 MnO._._._.__. 26. 86 100-063}. FreQ...:.4 .... 3. 87 | 2. 01 MgO-_..;}_. x. . 61 CRYSTAL STRUCTURE Trimerite may be structurally related to beryllonite, NaBePO.. VEYRYNENITE (Mn,Fe) (OH) CRYSTALLOGRAPHY [Mrose and Appleman, 1962] Monoclinic: Ci 5. 411+ 0.005 A | V_________ 361. 7 A* b..--..:s 14.40 (£0.02. A | Da.:::.:.51 3. 215 g/cm 6-:..4s., 4. 780+ 0.005 A { Z_::....}_. 4 p.ciycus 102°45" +05" Dg: sy itl 3. 23 g/em' Space group: P2;/a CHEMICAL COMPOSITION [Mrose and von Knorring, 1959] The two analyses of viyrynenite indicate that the ratio of Mn+* to Fe*+ is about 85 to 15. A small amount of aluminum is present and probably substitutes for Be. Small amounts of Ca, K, and Na are also present and probably substitute for Mn#+* and Fe#*. CRYSTAL STRUCTURE [Mrose and Appleman, 1962] The viyrynenite structure consists of zigzag chains of the composition [Be,(OH):(PO.):].**~ (fig. 194). The chains are linked together by the Mn atoms and also by hydrogen bonds. 'The manganese atoms are co- ordinated by two oxygen atoms and one hydroxyl group (O;, O;, OH) of one chain and by one oxygen atom (0',, O',, O,) from each of three adjacent chains. Within the chain each beryllium atom is coordinated tetrahedrally by two oxygens (O;, O';) and by two (OH) groups (OH, OH'). Each phosphorus atom is coordinated tetrahedrally by four oxygen atoms (Ola 02a O3, O4) f The BeO;,(OH); tetrahedra share the two hydroxyl. corners with like tetrahedra and the two oxygen corners with PO, tetrahedra. The PO, tetrahedra share two corners (O;, O;) with two adjacent BeO,(OH); tetra- hedra. The remaining two oxygen atoms (O;, O.) of the PO, groups coordinate the manganese atoms. A hydrogen bond exists between the (OH) group of one chain and the oxygen atom O; of an adjacent chain. The bond lengths found in this structure are as follows : Angstroms 1.63, 1.65 Be-OH G Pol :s. ak..". 1.53, 1.53, 1.55, 1.51 2.08, 2.24, 2.14, 2.18, 2.23 Mn-OH.........o....... 2.97 Viyrynenite bears an interesting relation to euclase which will be described next. THE BERYLLIUM COMPOUNDS 23 FIGURE 19.-A comparison of the [Ber(OH)2(PO;):)a@*~ chain of viyrynenite (4) with the chain of euclase (B3): large single circles, oxygen; large double circles, hydroxyl groups; small open circles, beryllium; and small solid circles, silicon or phosphorus. Reprinted from Mrose and Appleman (1962). EUCLASE AlBeSi0,(OH) - CRYSTALLOGRAPHY [Mrose and Appleman, 1962] Monoclinic: a.-. 4.763+0.005 A V... 309.3 A* b___- 14.29 A D.... 3.095 g/cm} c---- 4.618 A i Paar. B._._- 100°15 +05" D,... 3.115 g/cm} Space group: P2,/a CRYSTAL STRUCTURE [Mrose and Appleman, 1962] The structure of euclase consists of zigzag chains of the composition [Be,(OH);(Si0.):].""* (fig. 192) cross-linked by aluminum atoms. These chains are oriented within the unit cell in the same manner as the chains in v@yrynenite. The aluminum atoms are co- ordinated octahedrally by O, and O;, of one chain, by O, and (OH) of a second chain, and by O; and O, of two additional chains. The SiO, tetrahedra share one corner (O;) with an adjacent BeO;(OH); tetrahedra and another corner (O;) with two additional BeO,(OH) tetrahedra. The two remaining corners are free to coordinate the aluminum atoms. The BeO;(OH); tetrahedra share one corner (O;) with an S10, tetrahedra and each of two more corners (O;, O';) with an SiO, group and a BeQO,(OH);, group. The fourth corner (OH) coordinates aluminum. There ap- pears to be no hydrogen bond in this structure. The bond lengths are as follows : Angstroms Bed:... s nll. 1.60, 1.63, 1.64 Be.~ 1. 655, 1. 639, 1. 657, 1. 636, 1. 663, 1. 667 1. 64, 1. 55, 1. 67 fuributite...........~-.- 1. 60, 1. 58, 1. 59, 1. 61, 1. 57, 1. 59, 1. 59, 1. 59 1. 65 swedenborgite.___.._..... 1. 63 1. 63, 1. 65 *cuciase..........*..eske. 1. 60, 1. 63, 1. 64 «c=. 1. 655, 1. 64 BeSO; __________________ 1. 56 *Be,0(CH;CO00);.---.----- 1. 666, 1. 624 Be-(OH) *hambergite..-.._........ 1. 637, 1. 645 *vAyrynenite............. 1. 69, 1. 63 FEUCIASC- 2 1. 68 1. 57, 1. 68, 1. 61. 1. 69 Be-H;0 Be(H;0)§0,.. _. ..-... 1. 62 Be-F herderite............__.. 1. 67 Be-S 2. 10 Be-Se ..._.._..ic:llil. 2. 18 Be-Te BeTox.:s. _i 2. 48 Be-Cl 2. 04 Be-C Be(CH3)z ________________ 1. 93 1 After this report went to press, two important papers describing refinements of the hamburgite and chrysoberyl structures came to my attention-Zachariasen, W. H. Plettinger, H. A., and Marezio, M., 1963. The structure and birefringence of hamburgite, Be,B0,.0H: Acta cryst., v. 16, p. 1144-1146; Farrell, E. F., Fang, J. H., and Newnham, R. E., 1963. Refinement of the chrysoberyl structure : Am. Mineralogist, v. 48, p. 804-810. Be-O bond lengths of 1.629, 1.621, 1.678, 1.644, 1.612, and 1.638 A, and Be-OH bond lengths of 1.619 and 1.629 A were found in hamburgite. Be-O bond lengths of 1.579, 1.687, and 1.631 A were found in chrysoberyl. If these values are included with others listed for the accurately determined structures in table 10, the average Be-O and Be-OH bond lengths would be 1.636 A and 1.650 A, respectively. consists of two Be(OH) (H0): tetrahedra sharing the (OH) corner. The complex (H0); is prob- ably also a tetrahedron. The Be; (OH); (H0) ,** complex is the most stable of the three. Kakihana and Sillén find the most likely structure to be a six-membered ring, three tetrahedra being linked by sharing (OH) corners: 28 CRYSTAL CHEMISTRY OF BERYLLIUM (H, 0), (OH) 7 Be (H2 O)2 -—Be/ \ \ (OH) (OH)—Be/ y (H2O0)2 The compounds Be(OH) (H0) :HgC1;, Be(OH) (H,0).HgBr; and Be;(OH); (H:0),Hg:; have been prepared and it appears that the ring-shaped complex described above may be found in them. It may be asked in what other minerals beryllium may crystallize in moderate to trace amounts if avail- able in the rock-forming magna or solution. The close similarity of beryllium and silicon in their crystal chem- istry suggests that many of the silicates may crystallize with a certain amount of beryllium within the struc- ture. Certain silicate minerals, owing to their struc- tural resemblance to the beryllium minerals described above, appear to be possible sources of beryllium. These are olivine, the humites (closely related to oli- vine), the micas, sodalite, the melilites, cristobalite, tri- dymite, danburite, willemite, and datolite. The micas and the humites appear to be the only minerals among those reported by Fleischer and Cameron (1955) to contain abnormally large amounts of beryllium. Re- ports of high beryllium content in a number of min- erals such as thorite, uraninite, and fergusonite, which appear to possess structures into which beryllium can- not readily substitute, suggest that the beryllium con- tent may here be due to small amounts of an admixed beryllium mineral and not to solid-solution phenome- non. It is suggested by the present study that a greater effort should be made to analyze for beryllium the minerals that bear a close structural resemblance to the beryllium minerals and compounds described above. REFERENCES Abrashev, K. K., and Belov, N. V., 1962, Crystal structure of barylite, BaBe:Si.0;: Akad. Nauk SSSR Doklady, v. 142, p. 636-638. ' [In Russian.] Aminoff, G., 1923, Om en association med barylit och hedyfan vid LAngban: Geol. foren. Stockholm forh., v. 45, p. 124. 1925, Uber Berylliumoxyd als Mineral und dessen Kristallstruktur : Zeitschr. Kristallographie, v. 62, p. 113- 122. ' Anderson, B. W., Payne, C. J., and Claringbull, G. F., 1951, Taaffeite, a new beryllium mineral, found as a cut gem- stone: Mineralog. Mag., v. 29, p. 765-772. Andrews, K. W., 1948, The lattice parameters and interplanar spacings of some artificially prepared melilites : Mineralog. Mag., v. 28, p. 374-379. Bakakin, V. V., and Belov, N. V., 1960, Crystal structure of hurlbutite: Akad. Nauk SSSR Doklady, v. 135, p. 587T- 590. [In Russian.] Bakakin, V. V., Krauchenko, V. B., and Belov, N. V., 1959, Crystal structure of danburite, CaB:Si:Os, and hurlbutite, CaBeP:0,: Akad. Nauk SSSR Doklady, v. 129, p. 420-423. [In Russian.] Beevers, C. 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Oosthoek's TUitgevers Mij. 1959, Structure Reports, v. 16, 1952, International Union of Crystallography, Utrecht, N.V.A. Oosthoek's Uitgevers Mij. 1961, Structure Reports, v. 18, 1954, International Union of Crystallography, Utrecht, N.V.A. Oosthoek's Uitgevers Mij. Zachariasen, W. H., 1926a, The crystal structure of beryllium oxide and beryllium sulfide: Zeitschr. physik. Chemie, v. 119, p. 201-218. 1926b, The crystal structure of the selenides of beryllium, zinc, cadmium, and mercury: Zeitschr. physik. Chemie, v. 124, p. 436-448. -- - 1926¢, The crystal structure of the tellurides of beryllium, zinc, cadmium, and mercury: Zeitschr. physik. Chemie, v. 124, p. 277-284. 1930, On meliphanite and leucophanite: Zeitschr. Kristallographie, v. 74, p. 226-229. 1931a, Meliphanite, leucophanite and their relation to melilite: Norsk geol. Tidsskr. v. 12, p. 577-581. --- 1981b, The crystalline structure of hambergite : Zeitschr. Kristallographie, v. 76, p. 289-302. Zachariasen, W. H., and Plettinger, H. A., 1958, A re-examination of the crystal structure of hambergite: American Crys- tallographic Association Program and Abstracts, p. 23. p £75 y ~We tafe Cambrian Rocks of the Pioche Mining District Nevada GEOLOGICAL SURVEY PROFESSIONAL PAP ER 469 gh ao, Pp 2a Q\ nov 9 1964 " & g $ h Co science $ Cambrian Rocks of the Pioche Mining District Nevada By CHARLES W. MERRIAM With a section on PIOCHE SHALE FAUNULES By A. R. PALMER GEOLOGICAL SURVEY PROFESSIONAL PAPER 469 Stratzgrapfiy of a western zinc-lead district with emphasis on lz't/zo/og y and correlation qf ore-bearing strata UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1964 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director The U.S. Geological Survey Library has cataloged this publication as follows : Merriam, Charles Warren, 1905- Cambrian rocks of the Pioche mining district, Nevada. With a section on Pioche shale faunules, by A. R. Palmer. Washington, U.S. Govt. Print. Off., 1964. iv, 58 p. illus., maps (1 col.) diagrs., tables. 28 ecm. (U.S. Geo- logical Survey. Professional paper 469) Part of illustrative matter fold. in pocket. Bibliography : p. 54-55. 1. Geology, Stratigraphic-Cambrian. 2. Geology-Nevada-Ely Range. I. Title II. Palmer, Allison Ralph, 1927- Pioche shale faunules. (Series) For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 CONTENTS Abstract.... ~ enn ool lein eed nos Introduction.." ._. ___ c_ l clan c cri ask Purposes and Stratigraphy and ore deposits..____________________ History of stratigraphic Aeknowledgments: .-. _-_ 21.000 Lesso oon dy Geologic structure of the Ely Range___________________ Normal faults. n. Thrust faults. . . 8.4... 001.00 ode oan n edd Stratigraphic column of Cambrian rocks._.__._________. Prospect Mountain ___ Basal Cambrian of the eastern Great Basin.... Relation to theoretical base of the Cambrian... Pioche Shale. cov. Lc d OL Previous Pioche Shale reference section-______________. Stratigraphic division D-shale member. l=} Combined Metals Member._.___________. Combined Metals Member as ore host. C-shale member. my te Susan Duster Limestone Member.... d F] ES ® © 00 ~I ~I Or Ot A wa bo ho - Stratigraphic column of Cambrian rocks-Continued Lyndon cll telos Chisholm Shale" C21 [_L LCS 2 Chisholm Shale as ore host.___________-_-__---- Highland Peak Lower part of the Highland Peak Formation.. Peasley _L Burrows Burnt Canyon Member_________________. Step Ridge Condor Meadow Valley Member-_______________- Upper part of the Highland Peak Formation.. UnIb TYZZL ~ UniIh olen n o LLC LOL ean k sal Unit :s. %.. .cc glade Unit /i ren rout lae Unit 12.20.2000 ce- irene nae an Unit 13... u oe o hen and Upper Cambrian and Lower Ordovician rocks..___.._._. B-shale 22 Mendha _ mem ice. 'A-gshale 0, 28 Mendha outlier at Step Pages Pioche Shale faunules by A. R. Palmer.-._-_-.. 25 | Locality rate ais Lek Early Cambrian faunules-_--__________ _. 26 | References i_. oo L Lett rsd Middle Cambrian faunules.-_________.__-.- 27 { x. : Mal. uae aan a ga ILLUSTRATIONS [Plates are in pocket] PratE 1. Detailed geologic map of a part of the productive area, Pioche mining district, Lincoln County, Nev. o gig s ro Fraur® w so ~I & prgm oo bo - kot pest gt ht o N i- O . Generalized geologic map of the Pioche area, Lincoln County, Nev. . Index map of the northwestern part of the Ely Range, Pioche mining district, Lincoln County, Nev. Comparison of columnar sections of the Pioche Shale in the Ely and Highland Ranges. Correlation diagram showing possible relation of Cambrian rocks at Pioche, Nevada, to those of other Great Basin sections. Measured section (M-M') of Highland Peak Formation at Warm Spring, northeast of Panaca, Nev. . Index map showing location of the Pioche mining district, Lincoln County, . Geologic structure section (B-B') extending northeast across Churndrill Valley-_L______________L____LL_____ -. View from. Churndrill Valley northeastward to Tank Ridge.. seus. - Nov,, view northward from Treasure Hill.. l View northwestward from Treasure Hill, Pioche mining district, i View northwestward at: Ploche Divide.. -.. . _.... . . } coun oan ea paso nea gear nona b wae aa ~ View northeastward through Pioche _L. .L L000 o c_ 0 00 uus 0 aco is i oue h o a pot ton a 2. _ View eastward across Valley to Tank Ridge. al . Columnar section (K) of the Lyndon Limestone and Chisholm Shale at the Shodde ._. . Measured section (D-D') of Highland Peak Formation south of Gray . Limestone facies of the Burrows Member of the Highland Peak Formation; smoothed . View northward across Prince mine road toward crest of Step . Typical mottled oolitic tiger stripe limestone facies in unit b of the Step Ridge Member of the Highland Peak Formation; weathered surface >.... nec check can ai ank abn errs ae HI Page 3 6 7T IV Freur® TABLE 1. 2. 8. 4. 5. Stratigraphic names for lower part of the Highland Peak Formation, compared with equivalent terms proposed by CONTENTS 14. Smoothed surface of typical limestone in the Meadow Valley Member of the Highland Peak Formation-.-.----. 15. Flat-pebble mud-breccia pocket in unit 9 of the Highland Peak TABLES Paleozole column; Pioche mining district, _.... Pioche Shale, composite Ann dl lini Lec oben un- annees Stratigraphic subdivisions of the Combined Metals Member of the Pioche Shale at Pioche Divide, showing equiv- alent terms used by mining companies... 0s Stratigraphic occurrence of Pioche Shale faunules based on paleontologic studies by A. R. Palmer______---_------ Wheeler and Lemmon (1939) and those used by mining . Stratigraphic units of the upper part of the Highland Peak Formation, Warm Spring, Nev-___-__________-------- Page 47 49 Page 9 17 19 25 34 48 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA By Cnarurs W. Marrtan ABSTRACT The Pioche mining district in the Ely Range, southeastern Nevada, is one of several districts in the Great Basin where Cambrian rocks are hosts of important ore deposits. Cambrian strata underlying the Ely Range are intruded by porphyritic granite and other dikes. Tertiary volcanic rocks and Pliocene fresh-water clastic deposits of the Panaca Formation occupy adjacent valleys and extend over the Cambrian strata on the south and east. The Pioche mining district reached a production peak in 1872, followed by a long interval of decline. In 1924, success- ful application of the flotation process to previously valueless sulfide ores of zinc, lead, and silver brought about revival of the mining industry, which has continued to recent times. Mining at Pioche during the initial production period was along fissures in the Lower Cambrian Prospect Mountain Quartz- ite. Much of the later mining was in the overlying intensely faulted Pioche Shale. Fissures which transect these shales brought about replacement of limestone layers by sulfide ores in such manner as to preserve initial bedding features. To these deposits, the term "bedded ore" has appropriately been applied. In this district a detailed understanding of stratig- raphy is essential to mining and ore search, as the richest sulfide ores are in large part confined to specific limestone members. Cambrian strata of the Pioche area are dissected into mul- titudes of blocks by high-angle normal faults. Evidence of earlier thrust faulting is adduced from low-angle faults and one outlier of Upper Cambrian on Middle Cambrian strata; but in general late normal faulting obscures the results of thrust movement. In the Pioche region the Cambrian section, about 10,000 feet thick, includes rocks of Early, Middle, and Late Cambrian age. In the Ely Range the Upper Cambrian was recognized only in a possible thrust outlier, but these strata are well represented, together with Lower Ordovician beds, at nearby Arizona Peak. Siliceous clastic rocks of the Prospect Mountain Quartzite and Pioche Shale are of Early and early Middle Cambrian age; these rocks which compose the lower 3,200 feet of the column, are overlain by 7,000 feet of mainly carbonate sedimentary rocks that are Middle and Late Cambrian. The Middle Cambrian rocks are about 5,500 feet thick and in- clude the upper part of the Pioche Shale, Lyndon Limestone, Chisholm Shale and Highland Peak Formation, in ascending order. Except for some of the upper part of the Pioche and the Chisholm Shale, the Middle Cambrian is represented mainly by carbonate rocks. Of these the Highland Peak Formation, 4,500 feet thick, is the greater part. The lowest fossils that have age significance are Early Cam- brian olenellid trilobites in the lower part of the Pioche Shale; this fossil-bearing shale grades downward into the barren Prospect Mountain Quartzite. The Pioche Shale, about 800 feet thick, straddles the Lower Cambrian-Middle Cambrian boundary and embraces the largest number of clearly definable lithologic-paleontologic zones of any single Cambrian formation in the region. Certain of these zones are loci of bedded ore deposits. Though referred to as shale the Pioche is actually diverse, comprising micaceous and nonmicaceous shale, siltstone, sand- stone, and fossiliferous limestone. The limestone members are in part bioclastic, including beds composed largely of trilobite shell material. Disseminated carbonaceous matter is abundant in some of these limestones. Although susceptible to sulfide re- placement, almost none of the limestone in the Pioche Shale is dolomitized. Dolomitization seems to have preferred the thick, fairly pure, and fine-textured nonbioclastic carbonate rocks of the higher Middle Cambrian such as the Highland Peak Formation. Study of the varied Pioche Shale depositional record reveals a fluctuating, more or less cyclic repetition of lithologic units. Features of special interest are alternating micaceous and non- micaceous shales, and a repeated pairing of a basal quartz sand- stone with an overlying limestone. The last is well illustrated by the Combined Metals Member, most important ore unit of the district. The Combined Metals Member, whose average thickness is about 50 feet, has great lateral continuity and extends at least 12 miles westward through the Highland Range, where it con- tains replacement sulfide ore. The member lends itself to rather detailed yet fairly consistent lithologic division. Knowledge of its lesser stratigraphic subunits is of practical value to the mining geologist and engineer. The Combined Metals Member gives unparalleled opportunity to study detailed structure of some of the earliest trilobites. Through much of its extent, the fossil shells are silicified and may be removed in large quantities by acid solution. Es- pecially numerous in the residues are minute larval stages of olenellids. The Highland Peak Formation comprises 13 principal litholo- gic units. The lower six of these have been mapped in the Pioche mining district, where they are designated as members. The seven units representing the upper part of the Highland Peak Formation are absent in the productive part of the dis- trict; these are assigned reference numbers ranging from 7 through 13. j The designated units of the Highland Peak Formation, al- though mappable, must be used with caution, for they are largely barren of fossils and nearly identical carbonate facies are re- peated vertically. These units are identifiable with assurance only where a fairly large part of the stratigraphic column is exposed. Stratigraphic study of the thick Highland Peak Formation entails complex facies problems, especially as related to dia- genetic dolomitization. The fine-grained unfossiliferous car- 1 2 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA bonate rocks that make up much of the formation are believed to be in large part of chemical rather than organic origin. The lower six carbonate units lend themselves to possible alteration studies in connection with ore search, because they overlie potential ore-bearing ground. INTRODUCTION The Pioche mining district is in the Ely Range of southeastern Nevada, 20 miles from the Utah State line (fig. 1). As used in this report, the name "Pioche min- ing district" is restricted to the Ely Range or "Pioche Hills" vicinity, a natural geographic and geologic unit and a convenient one for use in connection with the min- ing industry. Pioche district in a broad sense has pre- viously been employed (Westgate and Knopf, 1932) for a much larger area, including several mining districts (pl. 2). The Ely Range (pl. 2) is a minor geomorphically discordant mountain uplift about 14 miles long. It strikes northwest toward a near-junction with the elongate Highland-Bristol chain, which has the north- erly orographic trend more characteristic of the Great Basin.* Meadow Valley and Lake Valley flank the range on the south and north. These are exceptions to the Great Basin interior drainage, for they empty south into the Colorado River. The Cambrian rocks which underlie most of the Ely Range are intruded by diabasic and porphyritic granite dikes. Upper Tertiary volcanic rocks and fresh-water clastic beds of the Panaca Formation occupy adjacent valleys and cover the Cambrian rocks on the south and southeast. Silvor, gold, and base-metal mining reached a peak at Pioche in 1872. There followed a lengthy period of decline and virtual abandonment, lasting until about 1905. A revival in metal production began here in 1924, when the flotation process was introduced to beneficiate zinc-lead sulfide ores previously of no value (Westgate and Knopf, 1932, p. 54). In the early period of large production, the mines at Pioche were opened on outcropping fissure veins in Prospect Mountain Quartzite, oldest exposed rock of the region. After 1924 during the later period of major production, the principal ores were limestone- replacement sulfide deposits in Cambrian strata (Young, 1948) which overlie the quartzites. These de- posits are bedded or blanket ore bodies confined to a few stratigraphic zones. In most places no outcrop- ping indicated their presence, but the existence of feeder veins or fissures was either demonstrated or sus- pected. Stratigraphic control of ore, coupled with per- vasive and exceedingly complex faulting, encouraged Early reports (Howell, 1875, p. 243; Hague, 1883, p. 256) errone- ously interpret the Ely Range as a spur of the Highland Range. the use of geologic techniques in connection with ore search by drilling, and in exploitation of known ore bodies. PURPOSES AND METHODS Detailed geologic mapping of the structurally com- plex Pioche mining district is dependent upon corre- spondingly detailed subdivision of the stratigraphic column. In this area, pervasive faulting coupled with rapid lateral facies change of some units, and vertical repetition of nearly identical, commonly nonfossilifer- ous carbonate rocks greatly increase possibilities of mis- identifying strata. The principal aims of this study are description and age classification of rock units for map representa- tion, establishment of superposition, elucidation of facies changes, and, finally, geologic correlation by pale- ontologic and other means with strata of nearby moun- tain ranges and with more distant areas of the Cordil- leran belt. At the outset of this investigation preliminary recon- naissance in search for the least faulted sections was unrewarding, the best sections for stratigraphic meas- urement being disclosed only after geologic mapping and structural interpretation were well advanced. Sections as far removed as the Highland Range, although less disturbed, were in general not wholly satis- factory for reference because of lateral changes in the rocks. The great number of fault blocks into which the Ely Range is dissected (pl. 1) prevents observation of con- tinuous lithologic change. Accordingly the fieldwork resolved itself into many individual structural-strati- graphic problems. Sequences studied and measured in one block were compared and matched with those in adjacent or more distant blocks for purposes of strati- graphic integration. - Some reference sections are there- fore composite. Most reference sections were measured by tape and Brunton compass. Many of the stratigraphic con- clusions, however, are based on planetable geologic mapping at field scales ranging from 1 inch equals 100 feet to 500 feet, rather than upon simple one-plane measurement. Paleontology rendered trustworthy, but relatively minor service; most of the Middle Cambrian carbonate units yielded no significant fossils. Lithologic criteria were relied upon for identification, checked wherever possible by rigid tests of mappability. The rocks are described mainly in terms of gross hand specimen petrology applicable in the field. Briefly touched upon are thin-section petrology and problems of sedimentation as related to the stratigraphy. INTRODUCTION 43°|2I° nge o 12° lize l16° l15° 4° 113 41° | innemucea -- 1 -~ n I ~! Elko Saz) - BM 1/ Mountain \\ e Gold Hill 40° 1 | \ | ( l vu to - & H ) 1 lRe‘n "7 | . eFallon ha » Austin! Eureka | 8, «Nd 1 _ MWirginia, Z { o g £ Chy >.. € j ) »Ely I E 6°“ 3a Aterson city, __ __ ___ (LL._.-.-: reik, | - & | " *Yerington 's I% a < 1 I \\ L 4 3, B _4| \i / \\ .Manhufl0n fiF-fio-ve—Vulley *s "Hawthorne > i 1 7 \\ | \ I // & ‘ \ B | #. woh / ll allele. = S }|6CHE MINING a R/ [ Pioche DISTRICT \ \. __ Goldfield,) | | (age : Caliente < \ \\ i | ® Delamar I \o ~ | ! 4 Groom H3 K | = § x | 6 1 3 \ »Beatty 1 <2 \\ r,_ _____ germ Gordo \\ 1 €" | °;4\ I ty 3x | Las yv &, | Las Vegas, RF v _I . A § % 3 .Tecopu\ N % 100 MILES FIGURE 1.-Index map showing location of the Pioche mining district, Lincoln County, Nev. 4 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA The Pioche mining district is one of several mining districts in the Great Basin wherein Cambrian rocks are either ore hosts or closely associated with ore bodies. Among these are Delamar (Callaghan, 1937), Groom (Humphrey, 1945), Bristol (Westgate and Knopf, 1932), Comet (Westgate and Knopf, 1932), and Eureka in Nevada (Nolan, Merriam, and Williams, 1956) ; and Gold Hill (Nolan, 1935), Ophir (Gilluly, 1932), and Tintic (Lindgren and Loughlin, 1919) in Utah. Stratigraphic and paleontologic comparisons are made with several of these, and with the important House Range section of western Utah (pl. 5). Comparisons will be made eventually with the nearby Snake Range, where detailed mapping is now in progress. STRATIGRAPHY AND ORE DEPOSITS Though economically inspired, the present undertak- ing might otherwise be viewed as yielding purely scien- tific values in terms of Cambrian history. Occurrence of bedded replacement ores of zinc, lead, and other base metals in discrete stratigraphic units, however, gives practical value to stratigraphy in this district. This applies specifically to such ore-bearing units as the Combined Metals and Susan Duster Limestone Members of the Pioche Shale, the Lyndon Limestone, and the Chisholm Shale. But for exploration purposes all stratigraphic details in overlying rocks have value. Much of the exploratory drilling was done from the surface by churn drill and diamond drill, for which predictions of stratigraphic thickness and depth to po- tential ore-bearing beds are needed. In a theoretical sense, knowledge of the stratigraphy as well as the geo- logic structure is of value in conjunction with investi- gation of the little understood petrologic, geochemical, and geophysical factors that affect selective replace- ment of limestone beds by sulfide ores, as typified by the Pioche occurrences. HISTORY OF STRATIGRAPHIC INVESTIGATION Study of the Ely Range Cambrian rocks began in 1871 when G. K. Gilbert of the Wheeler Survey ex- amined the active mines at Pioche and recorded ob- servations on geologic structure. The following year E. E. Howell (1875, p. 259) continued work of the Wheeler party; his published map and cross sections are the first to illustrate stratigraphic and structural relations in the district. Fossils collected by Howell from the lower part of the Pioche Shale fixed the Cambrian age of these beds. Shortly thereafter, the common Lower Cambrian trilobite at Pioche was de- seribed as Olemnellus gilberti by F. B. Meek (in Gilbert, 1875; see also White, 1877). Discovery of abundant Cambrian fossils at Pioche en- couraged C. D. Walcott to visit the area in 1885, shortly after his pioneering study of Cambrian and later Pale- ozoic rocks at Eureka, Nev. (Walcott, 1884). He col- lected also from Cambrian sections in the House Range, Utah, at about this time. Thenceforth these three areas together with the Grand Canyon, the Silver Peak area, Nevada, and the Inyo Mountains, California, figured importantly in discussions of western Cambrian history. Walcott's 1885 fieldwork in the Pioche region included measurement of a section on the west side of the High- land Range (Walcott, 1886, p. 33-35), where the Cam- brian rocks are less deformed than at Pioche. Fossil collections that served to correlate the Pioche Cambrian section with that of the Highland Range and more dis- tant parts of the Cordilleran and Appalachian belts were described in part by Walcott (1886). The de- scribed fossils came mainly from shale units now recognized as Pioche Shale and Chisholm Shale. From 1886 to 1916, Walcott's comprehensive paleon- tologic and stratigraphic studies of the North American Cambrian touched frequently on problems involving Pioche and the Highland Range (Walcott, 1888, p. 162; 1891, p. 317; 1908a; 1908b; 1912, p. 189-192; 19162; 1916b). His stratigraphic and paleontologic revisions led to the naming of the Pioche Shale (Walcott, 19082) and the Chisholm Shale (Walcott, 1916b). A geologic study of the Pioche area by Pack (1906a, 1906b) aug- mented data on the stratigraphic order of lithologic units and faunas. Burling (1914, p. 4-6) reinterpreted observations of both Walcott and Pack in proposing a solution of the Lower Cambrian-Middle Cambrian boundary problem. In 1922 the U.S. Geological Survey initiated a com- prehensive study of the Pioche region. Geologic map- ping of the Ely Range and the Highland-Bristol chain continued through four seasons to 1926 (Westgate and Knopf, 1927, 1932). This work resulted in an excellent geologic map delineating the more distinctive stratal and igneous subdivisions. Stratigraphic units adopted for the Cambrian were fully adequate for purposes of a moderately detailed map compiled on a scale of 1 inch equals 1 mile. Renewed interest in Great Basin Cambrian paleon- tology and stratigraphy about 1936 drew attention to the geomorphically spectacular Highland Range, which awaited more detailed stratigraphic investigation. At this time Mason (in Grabau, 1936, p. 274-276) studied the Pioche Shale and its trilobite faunules in that area and proposed changes in nomenclature. Also forth- coming were revised correlations of Cambrian faunal zones in the Highland Range and the Ely Range with those of other North American successions (Howell and Mason, 1938; Mason, 1938). Deiss and Mason (Deiss, 1938) measured and zoned GEOLOGIC STRUCTURE paleontologically the lower part of the Highland Range Cambrian. As a result of these field studies Deiss re- defined the Pioche Shale and proposed transfer of type sections from the Pioche area in the Ely Range to the Highland Range. Work by. Wheeler and Lemmon (1939, p. 33-57) re- lated mainly to the previously undifferentiated High- land Peak Limestone of Westgate and Knopf. Detailed measurement and range-to-range comparison demon- strated that many of the unfossiliferous units in this 4,500-foot carbonate section had lateral continuity and could be used effectively in mapping ; similar conclusions were being made concurrently by mining company geologists. The lithologic units proposed by Wheeler and Lemmon were assigned informal letter symbols. Wheeler (1940) later proposed restriction of Highland Peak Limestone and applied the new formation names Peasley Limestone and Burrows Dolomite to the bottom part of the interval, as delimited initially by Westgate and Knopf. By 1941 the Pioche mining district and the Comet dis- trict in the Highland Range had come to be regarded as harboring large unproved reserves of zinc, lead, and other base metals (Young, 1948). Moreover, mining company experience had fully demonstrated the tech- nological value of stratigraphy as an ore search tool in this region. Under stimulus of the war-time strategic minerals program the U. S. Geological Survey in 1943 began de- tailed structural-stratigraphic studies at Pioche. Areas considered promising for drill exploration in the Ely, Highland, and Bristol ranges (pl. 2) were mapped geologically by planetable. Among areas so covered are the northwest tip of the Ely Range between Mount Ely and The Point (pl. 3), a 3¥4-mile strip east of the Comet and Pan American mines, Highland Range, and smaller areas near the Bristol mine. This initial map- ping was done by C. D. Campbell and J. A. Reinemund, assisted by the late Irvin Gladstone. Planetable geo- logic mapping was undertaken concurrently in the Mount Ely vicinity by American Metal Co., Ltd., re- sults of which were made available to the U.S. Geological Survey. From January 1944 through August 1945, geologic mapping of the Ely Range was continued by means of planetable and aerial photographs, the work being carried out by a U.S. Geological Survey party consist- ing of C. 8. Bacon, L. C. Craig, R. L. Griggs, C. W. Merriam, and P. D. Proctor. Surface work was sup- plemented by mine mapping. In addition small areas at the Shodde mine and the Forlorn Hope mine (pl. 2) in the Highland Range were mapped and studied in detail. 727-989 0O-64--2 OF THE ELY RANGE 5 During the winter of 1945-46, Merriam began com- pilation and integration of the large volume of map, drill log, and stratigraphic information assembled dur- ing the war years by the U.S. Geological Survey and various mining companies. - It was planned at that time to complete detailed geologic mapping of the Ely Range when scheduled topographic base maps became avail- able. During the summer of 1949, members of the U.S. Geological Survey resumed geologic mapping by plane- table and completed a preliminary geologic and topographic map of the Ely Range in 1952. During this period the party consisted of C. F. Park, Jr., and C. M. Tschanz, assisted by J. E. Frost and P. D. Proctor. The mapping was carried out in cooperation with Paul Gemmill, of the Combined Metals Reduction Co. Merriam continued stratigraphic studies in the Ely and Highland Ranges at intervals through 1954. In 1952, A. R. Palmer assumed responsibility for the paleontology of the Cambrian strata and thereafter assembled and studied all Cambrian fossil collections made by the U.S. Geological Survey parties in this region. A reconnaissance of Cambrian and Ordovician rocks at Arizona Peak was made by Palmer in 1954. Upper Cambrian and Ordovician strata of that area had not been differentiated previously. ACKNOWLEDGMENTS Mining company officials have been helpful during the course of the Pioche studies in supplying subsurface data, especially drill logs and maps of inaccessible mine workings. Among these are E. H. Snyder, S. S. Arentz, E. B. Young, and Paul Gemmill of Combined Metals Reduction Co., and John Janney of the Ely Valley mine. Valuable geologic maps and drill logs have also been made available by P. A. Lewis, of Ameri- can Metal Co., Ltd., George Bowen, of Bamberger Brothers, Salt Lake City, and the late W. H. Pitts, of Amalgamated Pioche Mines and Smelters Corp. Fossil collections from the Ely Range and the results of surface geologic mapping by C. F. Park, Jr., and C. M. Tschanz of the U.S. Geological Survey in col- laboration with Paul Gemmill of the Combined Metals Reduction Co. were transmitted for use in connection with the present stratigraphic study. All determinations of Cambrian fossils were made by A. R. Palmer, and of Ordovician fossils by R. J. Ross, Jr., of the U.S. Geological Survey. GEOLOGIC STRUCTURE OF THE ELY RANGE Detailed geologic mapping of the fault-bounded Ely Range has revealed a complex closely spaced network CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA [sal (dg) suzuend urejunopy joodsoig Shows intricate normal (od3) 1aqwap seja pue (sdg) 12qwap auops -owr1 1alsng uesng yiim (dg) ajeyg ayoolq Step Ridge C C © € . C 6 5 a E © 3 © OD hel [est a. F4 4 puejyB jo 1aqwaiy uofuey juing W/ QMAL v (qyg) uonewoy 429q puejySi4 jo Jaquwaiy ’ (dyg) uonewno4 4294 puejyBip jo aqua Aaseaq € € ie up c Nonna wl 8, (13) _ / 6 S Z & 4 x B s (qy3) uonewio4 y2aq 1 > i- _ puejySip jo jeqwap smoung Cy pe w 0 AHbL | 2g O/ le! & § $ FAM AA A UU o pak: (dyg) 4294 Wa HW €., § puejySsip jo aqua [ | ll" sf a; \ ater (] 3 aa" pri || 1 $ (93) [I [ [/ e sy 2 Sos cea § 2% (ogy3) uoneuno4 yead I” y77 7 # 8 q puejySip jo 1aqwaiy uofueo uing / / * m bs F 3 £ #E $- > A S (qy3) uonewnoy yeaq 3 $ = puejySiH jo Jaqwap; smouung 3 G © E, E { $f 6 3 ¢ (wuyg) uonewno4 4224 lal a 6 puejySip jo 1eqwapy AajjeA ‘ 3 3 [ 4 ] o- a ‘,.’.’.’lll":’; 10 $8 grr, | is (oy3) uonewno4 429g I," ll l, [] sd" ~3 8 puejySsip jo aqua jopuo9 V’llllllll I lll/ $- s B 8 3 (sqpreugesum .I.l!'".l_.' | ”Ill. g 3 a (oy3) uoneuno4 yeaq I?” puejysip jo 1aqwapy 1opuo) _ / f I, h 1,3 wr te oe o o hen Coun TAM AMN % I m a 0 S & 0 i > 9 - § i E: 0 38 1 a & a [5] g Fa GEOLOGIC STRUCTURE of high-angle normal faults (pl. 1). Although the principal structure of the range was once (Walcott, 1886, p. 33-35) believed to be anticlinal, no incontro- vertible evidence of major folding in the ordinary sense was recognized. Something of the net effect of broad warping is brought about by distributive throw on great numbers of high-angle faults (fig. 2). Bedding dips are moderate to low, except where drag has occurred in the immediate vicinity of faults. Magnitude and direction of bedding dip vary from fault block to fault block; but commonly within con- tiguous blocks of a fault set, the direction of dip is fairly uniform. NORMAL FAULTS Normal faults-both frontal and internal-have exerted the principal geomorphic control in the Ely Range. Whereas the neighboring Highland-Bristol chain (pl. 2) extends more nearly northward, the Ely Range trends northwestward in the direction of its predominating normal faults. These northwest lon- gitudinal breaks are more continuous than the northeast transverse faults which intersect or cross them locally. North-south normal faults, less numerous than the others, are present on the south and southeast flanks of the range. Many faults of the Ely Range occur in distributive sets with downthrown hanging-wall blocks (fig. 2). Sets of this kind are commonly opposed by others of roughly parallel strike, but opposite dip, such that Ficure 3.-View from Churndrill Valley northeastward to Tank Ridge. (€hsa) of the Step Ridge Member of the Highland Peak Formation in small fault blocks; top of ridge mainly Burnt Canyon Member (€hbe) overlying Burrows Member (€hb) of the Highland Peak Formation The intensely block-faulted terrane overlies important stopes of the Pioche No. 1 mine in Pioche Shale. Tank Ridge OF THE ELY RANGE 7 total block displacement is like that of a graben or horst. Some individual blocks in this fault patchwork (fig. 3 and pl. 1) seem to have moved independently almost as monoliths, one bounding fault apparently terminat- ing against another without cutting or displacing it. Carbonate rocks of this intensely block faulted area reveal closely spaced, concordant, knife-sharp shear surfaces which parallel normal faults through widths of many feet. Sympathetic shears of this kind are commonly mineralized. THRUST FAULTS Thrust faults were recognized by Westgate and Knopf (1932, p. 42-43) on the west side of the High- land-Bristol chain. In the Ely Range, structural fea- tures of compressional origin are masked and obscured by pervasive late normal faults superposed upon them. Presumptive evidence of thrusting includes low-angle faults and bedding-plane slippage in the Chisholm and in other incompetent shale units. An outlier of Upper Cambrian rocks on Middle Cambrian at Step Ridge (pl. 1) is explainable by thrust displacement. This significant occurrence is discussed below. Mine workings along the northeast margin of the Ely Range show low-angle faults of possible thrust origin. For example, in the Alps mine (pl. 3) a flat fault dipping 28° E. separates Prospect Mountain Quartzite from Pioche Shale, which is the next over- lying formation in depositional sequence. Flat faults were recognized also in the Raymond Ely Extension White cliffy outcrops are unit & 8 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA mine east of Lime Hill (Young, E. B., written com- munication, 1946). The Wheeler Monument fault at the west base of Lime Hill (fig. 4) is a thrust. This low-dipping fault brings Middle Cambrian limestone of the Highland Peak Formation into contact with Lower Cambrian Prospect Mountain Quartzite, with nearly 2,000 feet of intervening strata cut out. According to Paul Gemmill, of Combined Metals Reduction Co. (written communication, 1960), drill holes through valley alluvium west of the Ely Range showed limestone and dolomite of the Highland Peak Formation in flat fault contact upon Tertiary volcanic rocks. This anomalous relation may be interpreted as the result of either late thrusting or major landslides. On the west side of Step Ridge (loc. 17), a small discordant exposure of coarse limestone breccia (pl. 1) includes large jumbled limestone blocks bearing Upper Cambrian fossils of the Mendha Formation. The brec- cia is surrounded by and is presumably underlain by nearly flat-lying Middle Cambrian strata assigned to the Step Ridge Member of the Highland Peak Forma- tion. A Late Cambrian Aphelaspis faunule in this outlier would normally be expected 3,000 feet strati- graphically above contiguous beds of the Step Ridge. No adequate explanation of this phenomenon is pro- vided by the mapping of normal faults in the vicinity ; emplacement by thrusting, therefore, seems reasonable. Other, but seemingly more speculative, explanations are surficial transport by mud slides, or downward migration of large blocks of the Mendha in a breccia pipe. Submarine filling of caves or fissures in Middle Cambrian limestone of the Step Ridge by Mendha sedi- ments is improbable, in view of the brecciated and jum- bled nature of the erratic materials. STRATIGRAPHIC COLUMN OF CAMBRIAN ROCKS No Paleozoic rocks younger than Cambrian were rec- ognized in the Ely Range. Lower Ordovician strata are present at nearby Arizona Peak in the eastern Highland Range (pl. 2). To the west and northwest are rocks of Ordovician, Silurian, and Devonian ages, as in the Ely Springs, Bristol, and West ranges. Cambrian strata of the Ely Range are divided into 17 map or potential map units (table 1). Of these, 10 are named units; 7 are not employed as map units in connection with this study and therefore are designated by number only. The 10 named units represent the lower part of the stratigraphic column and comprise the country rock in the northwest Ely Range, that is, in the vicinity of the productive mines. These rocks are of Early and Middle Cambrian age. Except for the Mendha outlier at Step Ridge, elsewhere discussed, no Upper Cambrian beds were recognized. There is thus near Pioche a major gap in the Cambrian record, a FIGURE 4.-Pioche, Nev., view northward from Treasure Hill. ings (sh) on the Meadow Valley fissure (MF) in Prospect Mountain Quartzite (€pm). of center shows limestone of the Highland Peak Formation (€h) in thrust contact overriding Prospect Mountain Quartzite along the Wheeler Monument fault. In foreground are dumps of old shaft work- Lime Hill right STRATIGRAPHIC COLUMN OF CAMBRIAN ROCKS t hiatus partly filled by more complete sections in the southeastern Ely Range (Panaca Hills) near Warm Spring (pl. 2). TaBur 1.-Paleogoic column, Pioche mining district, Nevada Thick System Formation ness (feet) Lower 3233]; Ordovi- clan Mendha Formation (Upper Cambrian and Lower | 2,000 U Ordovician at Arizona Peak) Cain. brian g Unit 13 125 #5. | Uniti2 170 Unit 11 245 552 aA ct Unit 10 240 5C a £55 | Unito 840 € Highland pg Unit 8 500 ea Cam- Forma- Unit 7 310 brian | Middle tion (10,000 Cam- | (4,500 ft) Pm Meadow Valley Member 430 ft) brian E o 4 ial 333 Condor Member 110 SAZ 45:53 Step Ridge Member 740 ag Egg Burnt Canyon Member 190 ® 'o a Ea 8 Burrows Member 300-500 o F Peasley Member 160 Chisholm Shale 100 Lyndon Limestone 380 Lower Pioche Shale 800 l(fa'm- Prospect Mountain Quartzite 2, 400 rian PROSPECT MOUNTAIN QUARTZITE NAME AND OCCURRENCE Reddish brown Prospect Mountain Quartzite is the oldest rock exposed in the Ely Range, where it occupies the largest area of any single formation. Present-day exploitation of sulfide ores in stratigraphically higher Cambrian limestone gives this quartzite a less signifi- cant economic status than it formerly had; yet as host rock of rich fissure ores worked exclusively in the early days, it deserves more than passing consideration (figs. 4, 5). The Prospect Mountain Quartzite was named by Hague (1883, p. 253 ; 1892, p. 34) for exposures on Pros- pect Peak in the Eureka mining district, Nevada, 140 miles northwest of Pioche (Nolan, Merriam, and Wil- liams, 1956, p. 6). In early all respects the quartzite at Pioche resembles closely that of the type area, and in both districts these strata conformably underlie Lower Cambrian strata containing QZemelZus. There is little doubt that the name is appropriately applied at Pioche. Siliceous clastic rocks of Cambrian age that have the appearance of Prospect Mountain Quartzite are widely distributed in the Great Basin, and extend from south- eastern California to north-central Nevada and east- ward into Utah. Many of the outcrops are small, highly disturbed, and lack an exposed stratigraphic base. Although the Prospect Mountain Quartzite at Eureka, Pioche, and elsewhere is predominantly quart- zite, it includes through its vertical extent an appreci- able amount of interbedded micaceous shale, silty shale, and siltstone. Pebbly conglomerate and coarser con- glomerate are present locally. In the Ruby Mountains (Sharp, 1942, p. 652) intercalated shale is altered to micaceous schistose deposits. THICKNESS Absence of an exposed stratigraphic base in the Ely Range eliminates determination of true thickness. A partial measurement of about 2,400 feet was obtained northwest of Red Hill, along a line extending south- westward from the Alps mine (pl. 3). In that section the outcrop is more than a mile wide and seemingly unbroken by large faults. Exposed Prospect Mountain strata are generally low dipping, and single fault blocks show only a few hundred feet of continuous section. At Eureka, Nev., where again no precise measurement is possible, the Prospect Mountain can be no less than 1,400 feet thick. In the Ruby Mountains, Sharp (1942, p. 652) measured 1,400 feet of this formation. At the Groom mine, 85 miles southwest of Pioche, a T,855-foot section of Prospect Mountain Quartzite is reported by Humphrey (1945, p. 15). As noted by Humphrey, further investigation of geologic structure and stratigraphy is needed to confirm this great thickness. AREAL DISTRIBUTION Prospect Mountain Quartzite occupies an area of 314 square miles in the Ely Range, where its surface extent greatly exceeds that in the type area at Eureka, Nev. Outerops of the Prospect Mountain Quartzite extend for 4 miles southeast of Pioche through Treasure Hill and Red Hill, forming the greater part of the Ely Range within this belt. The quartzite is well exposed in the northeast foothills between Pioche and the Ely Valley mine. In these foothills it forms several flat- topped spurs and hillocks. Float material probably derived from the Prospect Mountain Quartzite occurs near The Point and was traced to a fault breccia. West of Pioche (pl. 2) where the surface rocks are younger, mine openings have penetrated the topmost Prospect Mountain at depths greater than 1,400 feet. Fissure veins, similar to those that have been followed downward from the surface at the town of Pioche, cut through these deeply buried quartzites to enter overly- ing Cambrian shale and limestone, thus to feed the blanket ore bodies for which the district is noted. 10 - CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA Tank Ridge Niece (Ph. tn Shqft FicurE 5.-View northwestward from Treasure Hill, Pioche mining district, Nevada, through saddle in which lies a fault contact of Pioche Shale (€p) and Prospect Mountain Quartzite (€pm). shows Burrows and Burnt Canyon Members of the Highland Peak Formation (€h). Tank Ridge on left Pioche No. 1 mine in Pioche Shale left middleground ; Greenwood shaft (Gs) center middleground. LITHOLOGY AND BEDDING FEATURES The Prospect Mountain Quartzite is typically a rose- colored to reddish-brown dense vitreous orthoquartzite showing moderately good sorting and a wide variation in grain size. Color of fresh surfaces ranges from white and light gray to pale red, grayish red, reddish brown, and limonitic brown. Grayish-red shades are especially characteristic. Shale interbeds vary from grayish red to drab, yellowish tan, and green. The darker reddish brown of weathered quartzite surfaces is generally confined to an outer skin a half-inch thick; internally these rocks are commonly white or light gray. Solutions responsible for iron staining of otherwise light phases commonly followed a plexus of fractures from which they diffused outward. Diffusion-ring pat- terns of reddish or brown coloration are characteristic. The quartzite consists mainly of clear quartz grains with rare feldspar. Well-sorted varieties are common ; these contain about 30 percent of well-rounded grains, the remainder being subrounded to angular. Grain size of coarse-textured varieties ranges from about 0.5 to 1.5 mm. Finer varieties, with average grain size less than 0.5 mm, have a greater proportion of angular grains. Finely divided angular detrital quartz occurs as interstitial matter in a quartzose cement that con- tains widely varying amounts of ferruginous pigment. The quartz grains are distinctly sutured in a mosaic texture where recrystallization has taken place. Arkosic facies of the Prospect Mountain Quartzite occur at Cave Valley, 55 miles north of Pioche. These have a laminated appearance and contain about 10 percent of feldspar grains, many of which are plagi- - oclase and microcline. Layers of coarser material contain occasional rounded quartz fragments as much as 1 cm in diameter. Al- though such pebbles are uncommon in this formation at Pioche, they are abundant elsewhere in the Prospect Mountain and in more or less equivalent Lower Cam- brian clastic rocks of the Cordilleran belt. Pebble conglomerates and conglomerates with abundant larger rounded quartz fragments make up a considerable part of the comparable Stirling Quartzite in the Spring Mountains of southwestern Nevada. Many of the fragments in the Stirling exceed 1 inch in diameter. The intercalated shales are commonly reddish or streaked with red, and in general strongly micaceous. Bedding surfaces are usually very uneven or lumpy, and the shiny interfaces reveal coarse sericitic-appear- ing micaceous flakes. These shales are in places bleached white or light gray, as for example, the punky- appearing beds near the mouth of Slaughterhouse Gulch. The shale beds locally contain a large amount of silty and fine sandy debris. Micaceous shales similar to those of the Prospect Mountain also occur in the overlying Pioche Shale. Reddish color, though uncommon in the Pioche, occurs sporadically in its upper members. Reddish-brown, near-vitreous quartzite like that of the Prospect Moun- tain is also present in the "sandstone marker" at the base of the A-shale member of the Pioche. Because it is brittle, the Prospect Mountain Quartzite has become much jointed, fractured, and brecceiated in PROSPECT MOUNTAIN QUARTZITE 11 response to stresses. Talus and surface mantle derived from it are composed of irregular blocks and rubble; breakage to flat slabs or flagstones is uncommon. Silica-cemented quartzite breccia of the Prospect Mountain forms prominent outcrops near the north- eastern margin of the Ely Range. The breccia is well exposed adjacent to frontal faults north of Slaughter- house Gulch (pl. 3), where northwest-southeast frac- ture cleavage is developed in massive quartzite. Frac- tures and gashes are commonly filled with white quartz. Certain of the larger quartz veins are continuous and attain widths as great as 40 feet. Erosion has sculptured the resistant Prospect Moun- tain Quartzite into prominent features such as Treas- ure Hill and Lookout Hill (fig. 5) ; the more massive beds produce low cliffy rises, or form the caprock of hills and flat-topped spurs. Where the quartzite is intensely shattered, response to erosion differs, and more subdued or even rounded surfaces are developed. In the Ely Range, as is common in the Great Basin, quartzite is less prone to form commanding heights than carbonate rocks. The bedding of the Prospect Mountain is nonuni- form, ranging from thinly laminated shales to massive quartzite layers more than 4 feet thick. The quartzite beds which predominate, normally range from 2 inches to 1/4, feet in thickness. Vitreous quartzite layers are characteristically bounded by thin, sometimes paper- thin, bumpy micaceous shale partings. Color banding and rather coarse color lamination occur within otherwise fairly homogenous quartzite beds. Some color-laminated layers exhibit an almost rhythmic alternation of laminae high in iron with laminae of low iron content, a change possibly related to fluctuating sedimentary conditions. The thicker quartzite beds commonly exhibit well-defined cross lamination. - Shale layers show occasional ripple marks and, more rarely, mudcracks; these features indicate a range from shallow water to subaerial conditions. Mud castings, burrows, pits, tracks, and irregular vermiform lumps of undoubted organic origin are com- mon bedding features. Shiny micaceous shale inter- faces and shale-quartzite interfaces show them particu- larly well. Burrows and castings are of two types: (1) those which are essentially parallel to bedding and produce an interlaced, anastomosing fabric; and (2) those which are normal to bedding. The first occur in shales or at shale-quartzite interfaces. The vertical type, cor- responding to the well-known form genus SeolitAus, was observed only in reddish vitreous quartzite. The burrows and castings lack annulations. Flat-lying castings are usually thick and heavy, attaining a maxi- mum cross-section diameter in excess of half an inch. STRATIGRAPHIC RELATIONS Only the upper limit of the Prospect Mountain Quartzite is definable at Pioche, and this boundary is arbitrary, for the quartzite grades upward into the overlying Pioche Shale. In mapping, the contact was drawn above a vitreous quartzite layer that marks the top of an interval the rocks of which are grayish red. Below this topmost vitreous layer, and classified with the Prospect Mountain, is a transitional zone roughly 50 feet thick, in which vitreous quartzite occurs as 2- to 6-inch beds intercalated within crinkly, lumpy, and only partly red-stained micaceous shales in beds 2 or more feet thick. Passing downward through the transition zone, the amount of vitreous quartzite in- creases relative to that of shale until it predominates in the lower part. Exposures of the transition are well shown in flat- topped spurs southeast of the Ely Valley mine. Here the lowest OQlenellus-bearing strata of the Pioche Shale lie 40 feet stratigraphically above the top of the Pros- pect Mountain as defined above. Between mines known as the Garrison and the Gold Eagle, 3,000 to 4,000 feet southeast of the Ely Valley mine (pl. 3), a transitional zone 35 to 50 feet thick bridges the gap from massive vitreous Prospect Mountain Quartzite to typical D-shale. Churn-drill holes on the west side of the Ely Range reveal alternating shale and quartzite in a transition zone as much as 75 feet thick. On the east side of the range at Slaughterhouse Gulch, churn-drill logs indicate a comparable transition zone that is at least 40 feet thick. No key beds or horizon markers useful in the strati- graphic division of the Prospect Mountain were recog- nized. Ncolithus beds have possible stratigraphic value; at Treasure Hill, Lookout Hill, and Red Hill the Scolithus beds seem to be in the upper part of the formation. In general, the thicker sections of this formation exhibit a monotonous repetition of similar lithologic types. Combinations or groupings of beds are de- finable locally as members, but as these were not traced from one fault block to another, they serve no useful purpose in mapping. - These possible unit combinations of beds are as follows: 1. Massive thick-bedded cross-laminated quartzite al- most lacking in shaly partings; 2. Thick-bedded cross-laminated quartzite with thin micaceous shaly partings and interbeds as much as 6 inches thick; shale partings pitted and lumpy, of reddish and greenish color; shale less than 2 per- cent of the rock; 12 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA 3. Thin-bedded flaggy to platy quartzite in beds 1 to 6 inches thick; shale nearly equal to quartzite in amount; shale, reddish and greenish, rarely bleached light gray and punky. ORIGIN Quartzose clastic material forming the bulk of this unit was derived mainly from decomposing crystalline rocks. Coarse, pebbly quartz sands and local con- glomerates give evidence of fairly high standing, if not mountainous, crystalline sources situated at no great distance from the depositional sites. The gross lithologic character of the formation is much the same at exposures hundreds of miles apart; this characteristic suggests that accumulation in very extensive basins near sea level is more likely than deposition in great numbers of small intermontane basins. Tectonic and climatic conditions responsible for this siliceous clastic cycle of deposition affected vast regions, possibly of continental extent. Students of Cambrian history (Walcott, 1915, p. 183) earlier speculated in terms of continental as op- posed to marine origin of the Prospect Mountain Quartzite. - In support of this reasoning are ubiquitous presence of cross-laminated red sands, and muderacks in reddish shale. At present this formation is believed by the writer to be of nearshore, partly subaerial, partly shallow water origin under fluctuating conditions of rise and fall of the strand. The basins were prob- ably joined from time to time with the open sea. The Prospect Mountain interval foreshadowed one in which advanced shell-bearing marine fossils abruptly became abundant; hence, the little-understood physical and biotic environments under which these sediments accumulated are of special interest to paleontologists. The Prospect Mountain sedimentary record seems to be one of inhospitable biotic environments, ill suited for fossil preservation. Absence of fossil shells and seem- ing lack of organic matter have been attributed to the grinding action of continually shifting silica sands under aeolian, fluviatile, and deltaic conditions. In spite of the seeming biologic inhospitability of the normal Prospect Mountain Quartzite, local reddish- brown shale facies with abundant organic castings and burrows remind us that the mud bottoms of this interval were not everywhere inimical to life. Organic material as a food supply must have been abundant initially to sustain this biota. Unfortunately the producing orga- nisms left no trace of taxonomic identity ; their burrows and castings give no clue as to whether the mud bottoms underlay fresh, brackish, or marine waters. Similar organically produced mud structures are found in Cam- brian rocks above the Prospect Mountain ; these higher rocks are known by their trilobites and other fossils to be marine. By analogy the Prospect Mountain shales that contain castings are likewise believed to be marine rather than continental. The analogy may be extended also to organically stirred mud facies in the upper part of the Lower Cambrian Johnnie Formation east of Death Valley. These Johnnie strata, which are con- sidered to be older than the upper part of the Prospect Mountain Quartzite, include shell-bearing fossil beds of undoubted marine origin. AGE AND CORRELATION The Prospect Mountain Quartzite has yielded no fossils of definitive age significance. Its provisional classification as Early Cambrian is predicated upon up- ward depositional intergradation with the OQlemellus- bearing Pioche Shale. Such OQ/Zenellus-bearing shales, which rest upon the quartzite at Eureka, Nev., were originally included by Hague (1883, p. 254) in the Prospect Mountain, but in later years these have been assigned to the Pioche Shale (Nolan, Merriam, and Williams, 1956, p. 7). The Prospect Mountain Quartzite at Pioche, in the Highland-Bristol chain, and at Eureka probably cor- relates westward toward Death Valley with the Stirling Quartzite and overlying strata that are stratigraphi- cally beneath beds containing QlemelZus. Correlative quartzites occur also in the House Range of western Utah (pl. 5). BASAL CAMBRIAN OF THE EASTERN GREAT BASIN Barren reddish brown quartzites are commonly the lowest Cambrian rocks exposed in the Great Basin. Gradationally overlying shales in the central and west- ern parts of this physiographic section commonly con- tain Early Cambrian olenellids. Toward the eastern Great Basin and toward the Colorado Plateaus Pro- vince, overlying shales appear to become progressively younger, or to rise eastward in the stratigraphic column. Such problems call for the detailed study and compari- son of the lowest Cambrian fossils of the eastern part with those of the central and western parts, as at Pioche and Eureka, Nevada, and the Death Valley region. In the Tintic and Ophir (pl. 5) districts of Utah, where Ophir Shale overlies Tintic Quartzite, contained fossils suggest that the topmost Tintic may be younger than the topmost Prospect Mountain Qaurtzite at Pioche. According to A. R. Palmer, reports of olenellids in the Ophir Shale of both Utah districts have not been confirmed by recent collecting. On the con- trary, the Ophir contains faunules linking it, not with the Pioche Shale, but with the Chisholm Shale of Mid- dle Cambrian age at Pioche, and with the lower part of the Bright Angel Shale of the Grand Canyon. If, as suggested, the entire Ophir is Middle Cambrian, the PIOCHE SHALE 13 uppermost part of the Tintic Quartzite may likewise be of this age. McKee's (1945, p. 11-36) findings and the studies of Wheeler (1947; 1948) bear out similar relations in the Grand Canyon region. For the eastern Grand Canyon, McKee showed that olenellids are seemingly absent in the lower part of the Bright Angel Shale, the lowest fossils discovered above the Tapeats Sandstone being Middle Cambrian trilobites of the genera @lossopleura and Alokistocare ; these link the lower part of the Bright Angel of the eastern Grand Canyon with the Chisholm Shale of Middle Cambrian age at Pioche, rather than with the Pioche Shale of Lower to Middle Cambrian age. According to McKee, as the Bright Angel Shale is followed west from the eastern to the western Grand Canyon, the shale-quartzite boundary appears to de- scend in the column, figuratively transecting imaginary time lines, until in the western Grand Canyon, olenellid trilobites of Early Cambrian age are above the quartzite. These data suggest progressive landward overlap of basal Cambrian clastic rocks from west to east, accom- panied by eastward rise (in time) of the intergrada- tional shale-quartzite boundary and by eastward thinning of the great sandstone wedge. RELATION TO THEORETICAL BASE OF THE CAMBRIAN The Cambrian System in a world sense has no objec- tively definable base. Ideally its oldest beds constitute the OZenellus zone, a rock-time-fossil range concept, in accordance with which the first appearance of Olenellus or olenellid trilobites (Wheeler, 1947, p. 157 ; Longwell, 1952) would seemingly provide a theoretical criterion. In the practical sense the base of the system might arbitrarily be indicated immediately below the lowest horizon in any particular section where olenellids hap- pen to have been discovered. First appearance of olenellids in the rocks un- questionably varies greatly in time from section to section and from region to region, depending upon dis- tributional, environmental, and preservational factors. Absence of these life forms in lower strata of a par- ticular section may involve lag in geographical spread, local facies conditions inimical to bottom life, or con- ditions of burial unfavorable to shell preservation. In considering this question, factors of chance or proba- bility as related to fossil entombment and fossil dis- covery should be added to the vagaries of depositional and life environment. The fact is inescapable that olenellids are an ad- vanced form of invertebrate life and had certainly been in existence long before deposition of the lowest dis- covered trilobite bed of the Pioche Shale. A theory that these forms possessed no preservable shells until 727-989 0O-64--3 a late evolutionary stage, when protective investment was abruptly acquired, has little appeal. In theory the olenellids could well have flourished in favored spots as shell-bearing arthropods during the entire Prospect Mountain depositional interval without leav- ing an objective record in rocks of the familiar Prospect Mountain facies. Current studies east of Death Valley may be expected to elucidate the question of where the theo- retical base of the Cambrian might reasonably be drawn in the Great Basin. The Stirling Quartzite (Nolan, 1929) of the Spring Mountains, Nevada, resembles and is believed correlative with part of the Prospect Moun- tain. Stratigraphically under the Stirling is a thick quartzite-shale-dolomite sequence which comprises the Noonday Dolomite below and the Johnnie Formation above. The Pahrump Series (Hewett, 1956, p. 25), un- equivocally assigned to the Precambrian, underlies the Noonday. At Bare Mountain, Nevada, (Cornwall and Klein- hampl, 1960) rocks provisionally assigned to the upper part of the Johnnie include a significant fossil bed con- taining spines and possible head-shield fragments of trilobite origin. These fragmentary remains add sup- port to the theory that the Stirling and correlative parts of the Prospect Mountain are younger than the base of the Cambrian System. How much of the sequence between the Pahrump and the Stirling should even- tually be retained in the Early Cambrian remains to be determined. PIOCHE SHALE The ore-bearing Pioche Shale (fig. 6), economically the most important rock unit in the district, is actually diverse lithologically, comprising micaceous and non- micaceous shale, siltstone, sandstone, and limestone. The limestones are varied, being in part dense and bar- ren of fossils, and in part bioclastic, including some beds composed largely of trilobite shell material. Some of the limestones contain an abundance of very finely divided carbonaceous matter. In general, the lime- stone beds of the Pioche Shale are very impure and almost none are dolomitized. This is true even where these limestones are cut by fissures and fractures which appear to have been responsible for local hydrothermal dolomitization of carbonate strata higher in the strati- graphic column. Dolomitization seemingly preferred the thick, fairly pure, and fine-textured nonbioclastic carbonate rocks like those of the Highland Peak Forma- tion of Middle Cambrian age. The Pioche Shale depositional record reveals a fluc- tuating, more or less cyclic repetition of lithologic units. Features of special interest are alternations of mica- 14 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA ceous with nonmicaceous shales, and a repeated pairing of a basal quartz sand with an overlying limestone. The last is well illustrated by the Combined Metals Member, most important ore unit of the district. This formation, which contains the oldest known carbonate rocks and the oldest significant fossils of the region, was investigated paleontologically and named as a formation by Walcott (19082) before realization of the large replacement ore bodies within it. The Pioche Shale separates two nearly unfossiliferous for- mations, the Prospect Mountain Quartzite below and the Lyndon Limestone above. Strata of similar lith- ology and more or less equivalent Cambrian age are known at many localities in the central and southern Great Basin, at least as far east as the House Range, Utah. PREVIOUS INVESTIGATION Observations on the Pioche Shale were recorded at Pioche by G. K. Gilbert (1875, p. 257-261) and by E. E. Howell (1875, p. 259), during field work in 1871 and 1872. Discovery of well preserved Cambrian fossils by these pioneers led to more extensive work by Walcott (1886, p. 35) 13 years later. Fossil col- lections were made by Walcott in the Pioche vicinity, but his detailed Cambrian section was measured in the Highland Range 8 miles west of Pioche. This meas- ured Highland section shows 23 stratigraphic units, of which 20 pertain to the Pioche Shale of present usage. In subsequent contributions Walcott (1888, p. 162; 1891, p. 317; 1908a, p. 11; 1912, p. 189-192) again referred to the measured Highland Range section, giv- ing revised fossil lists. Pack (1906a, p. 285-312), in discussing stratigraphic and structural relations near Pioche, did not formally name or describe the shales in question, although he estimated their thickness conservatively to be about 400 feet. The structure of the Ely Range was erroneously viewed as anticlinal at the time of Walcott's early Pioche work. Some of his fossil collections from that area are accordingly referred to localities on "* * * the east side of the anticlinal arch at Pioche 20 miles east of the Highland Section, the strata resting on quartzite * * *". Study of these collections in the light of present understanding indicate that they were made in two or more rather widely separated zones, but the exact localities from which they came remain in doubt. Areal distribution and broader structural relations of the Pioche Shale were outlined by the U.S. Geologi- cal Survey in mapping the Pioche region (Westgate and Knopf, 1927, 1932). Again, the representative Pioche Shale section was measured at Lyndon Gulch, in the Highland Range, rather than at Pioche. Although the potential value of individual limestone members for correlation and structural interpretation was recognized, no attempt was made to divide the for- mation for mapping purposes. In dealing with prob- lems of mining geology, enlightening details of stratig- raphy relative to the economically important Com- bined Metals Member and other ore-bearing stratal units in the Pioche Shale are given (Westgate and Knopf, 1932, p. 54-55). During the 1930's, academic students of Cambrian history were attracted by the spectacular Highland Range Cambrian rocks, while at Pioche a more prac- tical interest continued to grow as stratigraphy was successfully applied to search for bedded ore. Mason in 1936 (in Grabau, 1936, p. 275) restudied the Highland Range succession and proposed Forlorn Hope shale and Comet shale for Lower and Middle Cambrian parts of the Pioche Shale, respectively. Deiss (1938, p. 1152-1156), following joint field studies by Deiss and Mason, likewise proposed adoption of two units in the Highland Range. To these were given the names Pioche shale : restricted for Lower Cambrian and Comet shale for the Middle Cambrian part. Wheeler and Lemmon (1939, p. 34-35), briefly sum- marized Pioche Shale stratigraphy, rejected the Deiss separation into Comet shale and Pioche shale: re- stricted in the Highland Range, and concluded that the entire sequence is lithologically best treated as a single formation. AREAL DISTRIBUTION In keeping with its lack of resistance to erosion, the Pioche Shale underlies depressions and foothills. Three main areas of outcrop may be defined in the Ely Range as follows (pl. 3) : (1) The northeast area ex- tending from Slaughterhouse Gulch along the northeast side of the range almost to The Point, (2) the central area extending from Lookout Hill past the Pioche No. 1 mine and southward over Pioche Divide west of Treasure Hill, (3) the southeast area, a narrow de pressed belt extending from the Alps mine 114 miles southeast of Pioche, past Gray Cone, thence southward across the eastern Ely Range. Small fault-block ex- posures are found in greatly disturbed terrane along the west base of the Ely Range, beginning 3,000 feet south of The Point, and continuing thence as small more or less isolated segments to the mouth of Buehler Gulch north of Caselton. An isolated, much faulted low-lying exposure is found northeast of the Prince mine. Much of what is known about the Pioche Shale is subsurface information gained through churn-drill exploration and geologic mapping of mines. PIOCHE The most continuous Pioche Shale exposures of the region lie in the western foothills of the Highland Range (pl. 2), where they may be followed due south without break from a point near Stampede Gap to the union of Black Canyon Range and Highland Range, a distance of 10 miles. Elsewhere in the Great Basin, strata identified as Pioche Shale extend from Eureka, Nev., on the north- west, southward 200 miles to Frenchman Flat, and east- ward at least to the House Range, which lies 140 miles east of Eureka, Nev. THICKNESS No unbroken exposures of the entire Pioche Shale were found during mapping of the Ely Range. At Pioche Divide (pls. 1, 4) the Pioche Shale is about 620 feet thick; this is the most nearly complete section recognized. About 130 feet of shale at the top and roughly 75 feet of shale at the bottom are cut out by faulting. Average thickness of composite Pioche Shale sections in the Ely Range is, thus, of the order of 820 feet. The measured Pioche Shale section at Lyndon Gulch, Highland Range, is 975 feet thick; 2% miles north of Lyndon Gulch the formation thins to 780 feet at the Forlorn Hope mine (pl. 2). Unrecognized strike faults conceivably account for this discrepancy of nearly 200 feet. PIOCHE SHALE REFERENCE SECTION The Pioche Shale section at Pioche Divide (pls. 1, 3, 4 and figs. 6, 7) is proposed as the standard or reference SHALE 15 section for this formation. In the past there has been no established Pioche Shale yardstick in the Ely Range. Walcott's only measurement of these strata in the High- land Range rather than at Pioche doubtless explains the tendency among stratigraphers to regard the Highland occurrence as typical. Walcott (1908a, p. 11) designated no type section when he formally described and named the Pioche Shale in 1908. It is nonetheless fairly clear in context that he intended the Pioche vicinity as the type area, reference being made to exposures "southeast of the town of Pioche, Nev., on the road to Panaca, Utah." Hence, by priority, acceptance of a general type area embracing the shale belt "southeast" of town would seemingly be called for. That the Pioche Shale belt "southeast" of Pioche is by itself illsuited for purposes of stratigraphic investi- gation is demonstrated by recent detailed mapping of the U.S. Geological Survey. In fact, the nearest Pioche Shale outcrops of consequence in this direction lie 1% miles from town along the old Pioche-Panaca foothill road; moreover, all shale exposures in the southeast foothill belt were found to be so badly deformed as to lend themselves poorly to definitive stratigraphy. Less disturbed shales of this formation occur half a mile "southwest" of town at Pioche Divide (pl. 3) through which another and more devious Pioche, Panaca road passed in Walcott's day." Furthermore * Inadvertent directional confusion is possible in connection with Wal- cott's reference to Pioche Shale "southeast" rather than "southwest" of town. FicurE 6.-View northwest at Pioche Divide. road is Pioche Shale (€¢p) ; cliffy slopes in middle distance are Lyndon Limestone. Susan Duster mine (SD) right foreground. Foreground on The dark gray unit is member A (€LA) and the overlying white unit is Member B (CLB). 16 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA Ficur® 7.-View northeast through Pioche Divide. (€pm). ioche Divide Treasure nih * Cpa Neots, Pera "1 /a f- a % y ~~ baited : *. * Cul& *% Lis: # for" 4" > Treasure Hill on right is Prospect Mountain Quartzite Tank Ridge on left shows member A (€/A) and member B (€]B) of the Lyndon Limestone. Fore- ground and middleground are Pioche Shale (€p) of the reference section. Walcott (1908 b, p. 184) actually refers in another pub- lication to Pioche Shale fossils collected "southwest of Pioche, Nevada on the Panaca road," probably in the Pioche Divide vicinity. In any event, that Walcott studied and collected in these better exposures of Pioche Shale is a reasonable assumption. Westgate and Knopf (1932, p. 8) concluded that Walcott's original Pioche Shale exposures were "doubtless the shales which are well shown at the west of the pass south of Pioche along the old road (not the present road) to Panaca." The pass alluded to is Pioche Divide. The Pioche Divide reference section was selected after mapping and stratigraphic appraisal of all exposures of Pioche Shale in the Ely Range. This easily accessible section embraces in continuous and seemingly little broken or duplicated condition about two-thirds of the composite Pioche Shale column (pl. 4). However, the top and bottom relations are better shown in the north- west part of the Ely Range, because the uppermost and lowermost parts of the formation are faulted out in the reference section. Zoned fossil collections made at Pioche Divide include five of the six important Pioche Shale faunules. Future studies may be expected to prove the less dis- turbed sections of Pioche Shale in the Highland Range to be better suited on the whole for stratigraphic pale- ontology than those of the intensely faulted Ely Range. However, no valid necessity would seem to exist for abandoning a type area and appropriate reference see- tions near the geographic location after which the formation is named.} __ STRATIGRAPHIC DIVISION Since the early 1920's, exploration for and develop- ment of bedded limestone replacement ores in the Pioche Shale have called for more refined stratigraphic pro- cedures as the economic bearing of stratigraphic ore controls became increasingly more evident. Detailed geologic mapping and exploratory drilling by the min- ing companies demonstrated that this formation was not, as earlier believed, a monotonous repetition of similar beds. The mining companies divide the Pioche Shale into six principal lithologic units, each traceable throughout the Ely Range. Of these, the lower four are clearly differentiated to the west, in the Highland Range. Minor subunits have a local utility in parts of the Ely Range, and at least one of these is recognizable also in the western part of the Highland Range. Pioche Shale divisions here adopted (table 2) are virtually those successfully used by the Combined Metals Reduction Co. The stratigraphic nomenclature which came into be- ing as the ore bodies in the Pioche Shale were exploited is expressive of exploration from the surface downward (table 2). Four of the units are assigned letter symbols MS, p. 1159) seems to have interpreted Westgate and Knopf (1932) as implying transfer of the Pioche Shale type section to Lyndon Gulch, Highland Range. Actually reference is made (Westgate and Knopf, 1932, p. 9-10) to a type locality at Pioche. PIOCHE A through D in descending order, the uppermost unit being A-shale and the lowermost D-shale. As these letter symbols are firmly established among geologists and engineers in the district, we are hesitant to modify or to reverse them for sake of convention. Table 2 presents the Pioche Shale column here adopted. TABLE 2.-Pioche Shale, composite column System _| Formation Member Thickness (feet) g A-shale member 310 é g 3 B-shale member 170 E8 i Susan Duster Limestone Member 5-20 alm g C-shale member 80 5 £59 Pa Combined Metals Member 40-70 55 E D-shale member 200 The terms "Forlorn Hope shale" and "Comet shale" proposed by Mason (1936), as well as "Comet shale" and "Pioche shale: restricted" of Deiss (1938) are not adopted herein. Fossil ranges rather than lithology are seemingly the criteria upon which these proposed units depend, and the unrealistic boundaries which separate them in the Highland Range were not recog- nized in the Pioche mining district. In addition to the lithologic criteria upon which di- vision of the Pioche Shale is based, paleontology serves effectively in zoning the formation. All members ex- cept B-shale and C-shale contain distinctive trilobite faunules. - B-shale has yielded no fossils, but C-shale is sparingly fossiliferous; the few trilobites thus far col- lected from C are not stratigraphically distinctive. The occurrence and distribution of the Pioche Shale fossils are treated below under "Age and Correlation." D-SHALE MEMBER OCCURRENCE Vertically continuous exposures of the entire D-shale member were not found in the Ely Range. Composite columns were therefore compiled from overlapping par- tial sections measured on the surface, in the mines, and logged in churn-drill holes. Incomplete sections may be studied south and southeast of the Ely Valley mine and in the Pioche Divide area south of Pioche. The D-shale sections three-fourths of a mile southeast of the Ely Valley mine (pl. 3) though attenuated by faulting, show the normal gradational relation with underlying Prospect Mountain Quartzite. The lower part of the member is cut out by faults in the Pioche Divide section. In the southeast belt of Pioche Shale, the relations of D-Shale to the overlying Combined Metals Member may be observed along the main highway southwest of Gray Cone. All deep mines of the district have SHALE £7 penetrated D-shale to get below the productive Com- bined Metals Member for stoping and exploration purposes. On the west side of the Highland Range, the D-shale is on the whole poorly exposed, lying in an alluviated foothill belt between upstanding Prospect Mountain Quartzite and, to the east, steeper slopes formed by higher Pioche Shale and the overlying limestones. LITHOLOGY AND STRATIGRAPHIC RELATIONS On fresh surfaces the typical D-shale is light olive gray to dusky yellow and has partings of much darker, slightly greenish olive gray. Weathered surfaces are in many places khaki colored or moderate yellowish brown and marked by streaks of limonite brown. Interfaces have a distinct sheen, for D-shale is char- acteristically micaceous, having in fact been mistaken for mica schist (Pack, 1906a, p. 294). The flakes range from finely divided sericitic material to coarser green chlorite plates more than half a millimeter in diameter. Chlorite flakes are more concentrated in the greener partings and laminae, which are commonly the layers in which trilobites occur. Green layers with coarse chlorite flakes alternate with finer grained layers hav- ing fewer flakes visible to the unaided eye. Bedding tends to be uneven, crinkly, and bumpy. A multiplicity of intersecting minor joint surfaces causes the rock to weather into rather small hackly pieces. Similar lumpy micaceous shales are found also in A- shale and B-shale members, although the percentage of coarse green chlorite in D-shale is somewhat greater. Innumerable large olenellid carapaces occur in some of the D-shale layers. The trilobites are preserved as smooth limonitic, sometimes reddish-brown coated im- pressions showing relief. No filmy carbonaceous shell material or silicification of shells like that in the over- lying Combined Metal Member was noted in D-shale. In addition to trilobite impressions, the bedding sur- faces show various types of tracks and other markings of organic origin. However, the thick, lumpy, inter- laced castings so common in the underlying transition zone of the Prospect Mountain Quartzite were not recognized in the D-shale. The stratigraphic relation of D-shale member of the Pioche to the underlying Prospect Mountain Quartzite was investigated by underground studies, by examina- tion of churn-drill cuttings, and by surface mapping in the area southeast of the Ely Valley mine. All the evidence points to gradual passage from quartzite into D-shale, seemingly without break in sedimentation. The transition zone, varying in thickness from 35 to 75 feet (see p. 11), is arbitrarily included with the Prospect Mountain. 18 Red iron staining so characteristic of the Prospect Mountain disappears in the lower beds of D-shale and the amount of coarser arenaceous debris decreases up- ward. Sandy beds in D-shale are of finer grain, lack- ing the dense vitreous appearance of the quartzites in the Prospect Mountain. Southeast of the Ely Valley mine abundant olenellid trilobites appear about 40 feet stratigraphically above the uppermost reddish brown vitreous quartzite bed which defines the top of the transition zone. In the Pioche Divide reference sec- tion similar olenellid trilobites cccur in a somewhat higher position, 70 feet stratigraphically below the base of the Combined Metals Member. Within the upper 25 feet of D-shale there is at some places a thin calcareous fossil bed ranging from less than 1 inch to about 6 inches in thickness. Called the 20-foot marker in the Prince and Caselton mines, this fossil bed is locally mineralized and has served as a use- ful underground datum. A similar bed is found in the Pioche Divide section, but was not recognized in the Ely Valley mine. In the Prince mine, it is roughly 24 feet below the so-called lower bed (table 3) of the Combined Metals Member; on the 1,400-foot level of the Caselton mine, it was identified about 20 feet below the lower bed. The contact separating D-shale from the quartz sands, which characterize subunit 1 of the Combined Metals Member, is abrupt but conformable. THICKNESS The average thickness of D-shale member is about 175 feet in the Ely Range. Faulted sections southeast of the Ely Valley mine show about 80 feet of the lower part of the D-shale only. Underground in the Ely Valley mine, the member ranges in thickness from 114 to 158 feet; churn-drill logs at Slaughterhouse Gulch give thicknesses ranging from 120 to 175 feet. In the standard Pioche Divide section, only 130 feet of this unit is exposed, but total thickness in that vicinity may exceed 200 feet. Underground in the nearby Pioche No. 1 mine, D-shale is estimated to be between 225 and 250 feet thick (Westgate and Knopf, 1932, p. 54). Churn-drill records on the west side of the Ely Range give D-shale thicknesses from 170 to 230 feet. Near the Pan American mine (pl. 2) on the west side of the Highland Range, this unit is estimated to be 260 feet in thickness; this increase suggests overall westward thickening. COMBINED METALS MEMBER NAME AND OCCURRENCE Bedded zinc and lead ores have been mined exten- sively from this predominantly limestone unit by the Combined Metals Reduction Co., and the name "Com- CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA bined Metals bed" (here changed to Combined Metals Member) is now firmly established among mine operators and geologists. There are few good exposures of the Combined Metals Member in the Ely Range. Scarcity of surface outcrop is offset, however, by underground access. On the sur- face the member may be studied to advantage near the Gold Eagle, West End, and Gelder mines, 3,500 to 5,000 feet southeast of the Ely Valley mine (pl. 3). Small exposures occur southeast of the Pioche No. 1 shaft. In the Pioche Divide reference section (pl. 3) the Com- bined Metals Member shows a nearly continuous outcrop length of 1,000 feet, this being the best surface outcrop recognized in the district. Three miles south- east of Pioche, the member crosses the main highway near Gray Cone; it can be observed at several points between the highway and low limestone ridges south of Gray Cone. On the lower west slope of the Highland Range are many good exposures of the Combined Metals Member; these may be followed from the Pan American mine north to the Forlorn Hope mine (pl. 2), a distance of 3/, miles. The Pan American inclined shaft is collared in low-dipping beds of the Combined Metals Member. THICKNESS The Combined Metals Member ranges in thickness from less than 40 feet to about 70 feet in the Ely Range, the average being about 50 feet. Measurements were obtained from surface exposures, mine openings, and drill holes. Whereas some lateral variation in thickness _ is due to factors of original deposition, it is the perva- sive faulting that accounts for many of the recorded differences in thickness. Some exploratory drill holes were located on faults where the potential ore beds have been partly cut out or apparently thickened. Exag- gerated figures of thickness were obtained where the drill followed steeply dipping dragged beds. Thickness measurements reported by mine operators vary to some extent because the basal sandstone beds were in some places logged with the upper part of the D- shale member rather than with the Combined Metals Member. On the west side of the Highland Range, sur- face thickness measurements range from 25 feet near the Pan American mine to about 60 feet west of the Forlorn Hope mine.* LITHOLOGY AND STRATIGRAPHIC RELATIONS The Combined Metals Member may be divided at Pioche into an upper well-bedded argillaceous limestone + Results of drilling by the U.S. Bureau of Mines (Trengove, 1949, p. 3) in Lyndon Gulch give thickness ranging from 80 to 100 feet, which appears excessive, for the Combined Metals Member. PIOCHE 35 to more than 50 feet thick, and a lower heavier bedded part about 17 feet thick, comprising fine calcareous sandstone and arenaceous limestone. In this lower part, calcareous sandstone predominates and shows a varied concentration of micaceous debris from bed to bed. These two units are referred to informally as upper and lower parts of the Combined Metals Member, and are mappable separately throughout the district. Both parts lend themselves to further subdivision into sub- units having more than local stratigraphic value (table 3). Adopted terminology is based on study of the Pioche Divide reference section (pl. 1). The lower arenaceous part of the Combined Metals Member is partitioned into 3 subunits, called subunit 1, subunit 2, and subunit 3 in ascending order. Two lithologic subunits are rec- ognizable in the upper limestone part; these are a lower, thicker bedded part (subunit 4) and an upper thinner bedded part (subunit 5). TABLE 3.-Stratigraphic subdivisions of the Combined Metals Member of the Pioche Shale at Pioche Divide, showing equivalent terms used by mining companies Pioche Divide section, C. W. Merriam, this report Mining company terms Subdivisions Lithology Thin-bedded nodular lime- stone of fine grain, with | Upper part of Subunit 5 shale partings; dark gray upper bed (40 ft). to black; shale partings (U.P.U.B.). g locally pale to purplish 8 Upper lime- red. & stone £ (53 ft). o io 9 i eavier bedded, medium- wer part of i Sltgflrélgg grained limestone of medi- | - upper bed = * um to dark gray. (L.P.U.B.). 5 g Very fine grained gritty cal- 5 Subunit 3 careous sandstone with | Micaceous shale = (24 ft). abundant micaceous rib. a flakes. fel ® | Lower cal- A careous Subunit 2 | Fine-grained calcareous 3 sandstone (4 ft.) sandstone and sandy lime- | Lower bed. E and limestone. 3 sandy g limestone 8 (17 ft.) Siliceous shale rib. Subunit 1 | Fine- to medium-grained (8-10 ft). calcareous sandstone. Footwall bed, overlying sili- ceous footwall shale. Subunit 1, which is 8 to 10 feet thick, is a fine- to medium-grained slightly calcareous sandstone of yel- lowish olive brown to light brownish olive; it weathers tan or limonitic brown. The sandstone is well sorted, containing about 90 percent of subrounded to angular grains of clear quartz, 2 to 6 percent of micaceous min- erals resembling chlorite and sericite, and about 1 per- cent of dark ferruginous matter. Calcite fills inter- stices. Because of its abundant angular quartz grains and mosaic texture the term fine grit is not inappropri- ate. Normally this sandstone is speckled with micace- 19 SHALE ous flakes and has on the whole a rather dull nonvitreous appearance. Locally it becomes denser and subvitreous, containing little or no micaceous matter visible to the unaided eye. Subunit 2, about 4 feet thick, is a fine-grained fairly well sorted highly calcareous gritty quartz sandstone changing here and there to sandy limestone. It is me- dium gray to light brownish and pinkish gray. Fine to medium clear quartz grains make up 40 to 80 percent; the remainder is turbid calcite. These quartz grains are subrounded to angular, the latter in places pre- dominant. Subrounded detrital grains of reworked turbid calcite enclose quartz grains. Fragments of trilobite and brachiopod shells are common. Subunit 2 is an important ore zone, being quite susceptible to sul- fide replacement. Subunit 3, about 2% feet thick, is a very fine grained well-sorted gritty calcareous sandstone containing abun- dant flakes of micaceous minerals. This bed is a useful marker and is termed "micaceous shale rib" by the min- ing companies. A distinct sparkle imparted by the finely divided micaceous mineral is clearly evident to the unaided eye. The rock is light gray to grayish tan and is composed of subrounded to angular quartz grains (80 percent), chlorite or sericite (8 percent), and calcite as cement (5 to 15 percent). Some calcite is present in the form of turbid detrital grains. Fine-grained argillaceous and silty carbonaceous limestones about 53 feet thick make up the upper part of the Combined Metals Member in the Pioche Divide section. Two lithologic subunits are recognizable in this interval, subunit 4 below being heavier bedded and subunit 5 above prevailingly thinner bedded. The impure limestones of these two upper subunits prove to be the principal hosts of Pioche zinc-lead ores. Subunit 4 is a limestone 8 to 12 feet thick, of medium to dark gray color, and speckled with limonite brown. It is of medium grain, showing scattered rather coarse calcite cleavage faces. In thin section this limestone reveals a considerable admixture of very fine sand and silt grains, composed mostly of quartz. These grains are in the main less than 0.1 mm in diameter, are sub- angular to angular in shape, and make up 10 to 25 per- cent of the rock. The main body is granular turbid calcite. Locally this rock is essentially bioclastic, or- ganic debris being abundant as spines, needles, and frag- ments of brachiopod and trilobite shells. Subunit 5, about 40 feet thick in the Pioche Divide section, consists of dark-gray very fine grained thin- bedded carbonaceous limestone intercalated with argillaceous shale. These strata exhibit a characteristic pinch-and-swell bedding, individual beds ranging in thickness from less than 1 inch to 3 inches. Uneven 20 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA nodular limestone beds are separated by thin, uneven crinkly shale layers. On the weathered surface, shale partings and intercalations are locally pale red, purplish, or tan. A decrease in quartz grain content was noted near the top of subunit 4, where the limestone layers become pro- gressively thinner and more argillaceous upward. Ac- companying this change, the limestone, as seen in thin section, takes on a detrital texture, exhibiting abundant round to subangular calcite granules that range in di- ameter from less than 1 to 3 mm. Scattered throughout are larger ovoid limestone bodies that resemble Girvanelle and are as much as 1 ecm in diameter. Al- though of possible algal origin, none showed concentric lamination. Fossil shell material forms less of the rock in subunit 5 than in the somewhat coarser textured beds of subunit 4. Local beds of subunit 5, however, contain vast numbers of silicified trilobites, including larval growth stages (Palmer, 1957, 1958). These silicified shells weather out on limestone-shale interfaces. The quantity of finely divided sooty carbonaceous or graphitic matter associated with the upper limestones of the Combined Metals Member in the vicinity of ore bodies is surprising. When freshly exposed, some of the low-grade bedded ores with a good deal of black unre- placed limestone remind one of a low-grade coal seam. Knopf's (1932, p. 55) description is particularly ap- propriate; he stated that these beds ". . . are com- monly so nodular as to suggest that they are made up of layers of more or less flattened potatoes. These nodules are coated with a thin black carbonaceous (?) skin." Not infrequently when the limestone layers in these pinch-and-swell bedded ores are almost completely re- placed by sulfides, the more inert clayey interbeds re- main essentially unreplaced. The upper limestone and lower sandy parts of the Combined Metals Member are distinguishable through- out the Pioche district, but the three numbered subunits of the lower sandy part are not everywhere recogniz- able. Such is the case in the Ely Valley mine. Surface exposures near the Gelder and West End mines (pl. 3) show the well-developed lower sandy part of the member, but details of thickness and lithology in this lower part are slightly at variance with the Pioche Di- vide reference section. On the other hand, lithologic details of the thick upper limestone division at the Ely Valley mine and neighboring prospects are about the same as in the Pioche Divide standard column. Where the Pioche Shale is badly faulted and poorly exposed, it is possible to confuse the thicker limestones of A-shale member with those of the Combined Metals Member. The distinction as a rule can be made by detailed lithologic examination. Paleontology is of spe- cific aid in this connection, for Lower Cambrian faun- ules of the Combined Metals Member are wholly dif- ferent from Middle Cambrian faunules in the A-shale limestones. Depositional changes noted in the Combined Metals Member reveal a transition from basal quartz sands up- ward into impure limestones, concomitant with a more or less progressive decrease in grain size of the admixed siliceous debris and a corresponding increase in the pro- portions of clayey and carbonaceous matter. The his- torical meaning of this succession is not understood, but a similar cycle is repeated in the limestone units of A-shale member, some of which have a basal quartz sand. COMBINED METALS MEMBER AS ORE HOST The Combined Metals Member is host for the largest manto-type zinc and lead ore bodies of the district. As evidenced by the great number of prospect holes and dumps, this fairly uniform and laterally persistent unit has been extensively prospected through the Ely and Highland Ranges. Surface studies of the Combined Metals Member were supplemented by underground mapping, and by meas- urement and sampling of ore-bearing beds in the Casel- ton, Prince, and Ely Valley mines (pl. 3). Caving and waste-filling of large flat-back stopes in most places prevented satisfactory stratigraphic observations where the member had been most completely mineralized. Details of differential sulfide replacement, however, are well shown in exploratory headings penetrating un- mined low-grade ore, where only partial sulfide replace- ment has taken place. In addition to structural relations of the bedded ores, attention was given to such factors as bed-by-bed change in ore mineralization through the member and to stratigraphically controlled ore boundaries. The initial depositional differences which make possible subdivision of the member are clearly reflected by change of ore grade and metallurgical character across the section. These vertical differences seem to manifest stratigraphic selectivity on the part of fissure-intro- duced mineralizing solutions. Hydrothermal alteration commonly obscures bound- aries of subunits in the vicinity of ore bodies, especially the contacts separating the three lower siliceous sandy subunits. But even where the member is in consider- able part replaced by sulfides, some gross bedding features, and, to a more limited extent, traces of original sedimentary texture, may survive. Inert shale or clay interlayers are generally unreplaced. Recognition underground of stratigraphic position within the Combined Metals Member has practical min- PIOCHE ing significance. -Not only is this true with reference to stratigraphic change in ore, but in the engineering sense because of the varied physical strength of beds. Dur- ing selective mining, certain beds or zones are found to be better adapted than others to support load, and to stand without timbering after the removal of material beneath. In view of these factors, it is not surprising that the exigencies of ore search and mine development have encouraged at Pioche a high consciousness of the significance of stratigraphic details. Much speculation has been indulged in relative to geochemical, geophysical, and stratigraphic factors that make the Combined Metals Member so favorable a locus for replacement ores in the presence of feeding fissures. Among the more obvious of these is the rather impure carbonaceous nature of the limestone beds, some of which are bioclastic and all of which are seemingly not subject to dolomitization. The limestones are evi- dently prone to fracturing under stress, and the member is confined above and below by relatively im- permeable shale units not at all susceptible to sulfide replacement away from the immediate influence of strong feeding fissures. Where transecting fissures carry sulfides, the lowest significant carbonate beds of a stratigraphic section are expected loci of abundant replacement ore (Prescott, 1926, p. 247). By virtue of its low position, the Com- bined Metals Member appears to satisfy these con- ditions ideally. No stratigraphically or structurally lower carbonate beds of consequence are known in the Pioche region; however, older and deeper carbonate rocks may be inferred in depth even below the Prospect Mountain Quartzite, as is true for the Death Valley region. Discovery of large, bedded ore deposits at Pioche and presence of ore in the Combined Metals Member as far away as the western Highland Range have encouraged prospecting for zinc and lead in similar beds of more distant areas. Limestones resembling those of the ore- bearing Combined Metals Member in mountain ranges of the central and southern Great Basin have long at- tracted the attention of prospectors. Such limestones also occur as members in Middle to Lower Cambrian shales; however, they have not been correlated specifi- cally by fossils with the Combined Metals Member or with other potential ore units of the true Pioche Shale. Search in these more distant beds for replacement zinc and lead deposits has not in recent years been rewarded by significant discoveries. Negative results of this kind support the elementary deduction that massive zinc- lead replacement ore bodies of the Pioche type are not T27-989 0O-64--4 SHALE 21 reasonably to be expected in supposedly favorable beds unless strongly mineralized fissures are also present. C-SHALE MEMBER OCCURRENCE This lithologically distinctive and relatively uniform shale is recognizable in most Pioche Shale exposures of the Ely Range and is present likewise along the west slopes of the Highland Range. The C-shale member may be studied to advantage in the Pioche Divide sec- tion on the Prince mine road, in the vicinity of Gray Cone near the main highway, and on the slopes of Mount Ely about 2,000 feet northeast of the summit. The C- shale member is separated from the Combined Metals Member below and from the Susan Duster Limestone Member above by sharp conformable contacts. LITHOLOGY The C-shale member is more uniform in color and texture than are other members of the Pioche Shale. Its color is normally fairly light, slightly brownish olive gray, ranging to darker shades of grayish olive. Weathered surfaces are tan or light brown. The mem- ber is easily recognized by its smooth, even bedding and commonly very fine grain. A high proportion of inter- faces or parting surfaces do not show micaceous flakes readily visible to the unaided eye; however, fine mica- ceous beds with a distinct sparkle do occur rarely in this member. - Unlike other members of the Pioche, the C- shale member normally includes no sands or silty inter- beds, nor have limestone beds been recognized within it. Crinkly and lumpy interfaces are conspicuously absent. As occasional interbeds, smooth C-type shale is re- peated in the upper part of A-shale member. Because it is fine grained and relatively nonmicaceous, the C- shale member may be confused with the Chisholm Shale. The latter may be distinguished by its reddish color and color banding; it is almost everywhere highly fossiliferous, whereas fossils are exceedingly rare in the C-shale member. Limestone interbeds, absent in the C- shale member, are numerous in the Chisholm. Although the C-shale member is normally devoid of organic traces, a few poorly preserved trilobite impres- sions were found in this member at Pioche Divide and near the Pan American mine in the Highland Range. THICKNESS The C-shale member is 80 feet in the Pioche Divide section. Its average thickness in the Ely Range is about 100 feet, and its maximum is 120 feet in churn-drill holes. Near the Forlorn Hope mine, Highland Range, 110 feet was measured. 22 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA SUSAN DUSTER LIMESTONE MEMBER OCCURRENCE This important marker, lying 80 to 100 feet above the Combined Metals Member and separated from it by the C-shale member, is named for the Susan Duster mine near Pioche Divide on the Prince mine road (pl. 4). Contacts with the C-shale member and with the overly- ing B-shale member are characteristically sharp and conformable. The Susan Duster Member has been recognized throughout the Pioche mining district and is found likewise in the Highland Range. It is replaced heavily by sulfides in the Ely Valley mine, being one of the im- portant ore zones. The member is well exposed 1,500 to 2,000 feet northeast of the summit of Mount Ely (pl. 3) in the vicinity of the West End mine and along the Prince mine road in the Pioche Divide section. LITHOLOGY The Susan Duster Limestone Member is a well-bedded medium- to medium-light-gray limestone, which has a few argillaceous partings. The partings are olive colored and weather tan. Bedding tends to be uneven or crinkly, especially as seen at limestone-shale inter- faces. Megascopically the Susan Duster Limestone Member may appear medium grained, but in thin section it is usually observed to be very fine grained. Frag- mentary trilobite and brachiopod shells are embedded in a matrix of turbid aphanitic limestone with thin seams and spots of clearer crystalline calcite. Locally these beds are bioclastic ; shell fragments are so numer- ous as to constitute a coquina. This light-colored and very distinctive organic lime- stone is relatively pure, lacking the admixture of sand grains, clay, and carbonaceous matter that character- izes the dark-gray limestones of the Combined Metals Member. The Susan Duster Limestone Member shows little variation in lithology as far away as the west side of the Highland Range. This unit contains an abundance of well-preserved fossils, considered below under the heading of age and correlation of the Pioche Shale. THICKNESS The Susan Duster Member ranges in thickness from 5 to 20 feet in the Ely Range, averaging about 15 feet. Near the Susan Duster mine (fig. 6) it ranges from 8 to 10 feet; in churn-drill holes at Slaughterhouse Gulch its thickness is 13 feet, and in the Ely Valley mine 14 feet. Average thickness reported in churn-drill holes on the west side of the Ely Range is 20 feet. West of the Forlorn Hope mine, Highland Range (pl. 2), the thickness of the Susan Duster ranges from 7 to 13 feet. B-SHALE MEMBER OCCURRENCE The B-shale member lies between the Susan Duster Limestone Member and the sandstone marker bed gen- erally recognizable at the base of the A-shale member in the Ely Range. The B-shale member is especially well exposed in the Pioche Divide section and near the West End mine (pl. 3) northeast of Mount Ely. Where the sandstone marker bed (pl. 4) is not identifiable with assurance, as in parts of the Highland Range, it is doubtful that B-shale and A-shale members can be differentiated. LITHOLOGY AND STRATIGRAPHIC RELATIONS The B-shale member comprises grayish olive brown, crinkly, unevenly bedded, strongly micaceous shales, silty shales, and fine sandstones. Interfaces are lumpy and pitted, some showing organic castings and tracks. Smoother, finer-grained and less micaceous intercalated shales occur near the bottom of the unit. Red-stained patches, the first such recognized above the Prospect Mountain Quartzite, are present in the B-shale member, recurring also in the A-shale member. On the whole the B-shale member is more micaceous, more crinkly and pitted than the D-shale member, and differs also in lacking the numerous green chlorite-rich laminae, especially as noted in the OQZenelZus beds of the D-shale member. No limestone layers were found in the B- shale member, which lacks fossils except for the organic traces mentioned. The B-shale member is conformable upon the Susan Duster Limestone Member and passes without break into the sandstone marker bed at the base of the A- shale member. In some sections of the B-shale member, sandy and silty intercalations become progressively more numerous from the middle toward the top of the member. THICKNESS The B-shale member is 170 feet thick at Pioche Divide but thins to about 135 feet on the west side of the Ely Range as shown by drill cores. This thinning, however, is accompanied by the corresponding increase in thickness of the overlying sandstone marker bed to about 30 feet. Although the sandstone marker is for convenience classified with the A-shale member, its thickening may actually take place at the expense of the upper part of the B-shale member. Existence of precisely the same basal sandstone marker bed of the A-shale member in the Highland Range is doubtful. A measured section west of the Forlorn Hope mine includes a dense fine-grained sand- stone overlain by gray crystalline limestone 95 feet PIOCHE stratigraphically above the Susan Duster Limestone Member. Should this sand actually represent the sand- stone marker in question, it must follow that the B- shale member thins westward from 170 feet in the Pioche Divide section to less than 100 feet on the west side of the Highland Range. A-SHALE MEMBER OCCURRENCE The A-shale member, thickest member of the Pioche, is also the most widely exposed in the Ely Range. This heterogeneous member includes sandstone and thick- bedded limestone as well as shale and is more resistant than the other members to erosion, in part owing to protection by the Lyndon Limestone. The A-shale member is commonly the only part of the formation well exposed; as for example, on the east side of the Ely Range near The Point, where a large outcrop was mapped from a position 1,000 feet southeast of The Point nearly to the Alliance mine (pl. 3), 2 miles dis- tant. QOutcrops of badly faulted A-shale are present northwest of the Pioche No. 1 shaft, whence they extend south into the Pioche Divide section (pl. 1). The member is fairly well shown in the depressed, much faulted southeastern Pioche Shale belt from Gray Cone southward. The normal stratigraphic relation of the A-shale member to the underlying B-shale member appears to be gradational through the basal sandstone unit of the A-shale member. Because of faulting, good exposures of the contact of the A-shale with the Lyndon Lime- stone are uncommon. Near the Forlorn Hope mine, Highland Range (pl. 2), this upper boundary is sharp and suggests disconformity. THICKNESS Northwest of the Alliance mine, the A-shale member is 310 feet thick and seemingly unbroken. Because of faulting, only 150 feet of this member is exposed in the Pioche Divide section. At Lyndon Gulch, in the High- land Range, the A-shale member has a possible thick- ness of 450 feet, but, followed north to the Forlorn Hope Mine, it seemingly thins to 175 feet (pl. 4). However, the accuracy of this deduction rests on correct identifi- cation of the "basal sandstone marker." A variation in thickness of the A-shale member as a result of a dis- conformity between it and the Lyndon Limestone is also possible. LITHOLOGY AND STRATIGRAPHIC RELATIONS Lithologic heterogeneity distinguishes the A-shale member from other members of the Pioche Shale. The A-shale member comprises strongly micaceous, as well as nonmicaceous, shales, siltstones, sandstones, and 283 several distinctive varieties of limestone. Micaceous shales, which predominate, resemble those of the B- shale member; they are relatively coarse grained or silty, unevenly bedded, crinkly, lumpy, and pitted and contain organic castings. A noteworthy textural var- iant of the upper part of the A-shale member is a smooth nonmicaceous phase like that which character- izes the C-shale member. The normal color of the A-shale member is the gray- ish olive brown widely noted throughout the formation ; it weathers to shades of tan and limonite brown. Patches of red are fairly common, especially in the up- per part of the unit, as noted above the Susan Duster shaft and at the Forlorn Hope mine in the Highland Range. Nonmicaceous AZbertella-bearing A-shale in the northwestern part of the Ely Range lacks the olive shade, being dark gray and streaked with grayish red and limonite brown. Brown-weathering, commonly fine grained, locally calcareous quartz sandstones are associated with the micaceous shales and limestones. The widespread sandstone marker (pl. 4), lowest bed of A-shale mem- ber, is typical of these. Limestone makes up roughly 23 percent of the A- shale member in the northern Ely Range, occurring mainly in the upper half. The limestone subunits, which range in thickness from 1 inch to 40 feet, may be seen to advantage northwest of the Alliance mine and above the Susan Duster shaft at Pioche Divide. The limestones range in texture and composition from fairly pure dense fine-grained detrital types to oolitic lime- stones and impure argillaceous and silty limestones. The dense purer limestones usually lack identifiable fossils, whereas the impure and oolitic limestones con- tain abundant trilobites, brachiopods, and nodules of presumed algal origin (@irvanella). No dolomite was recognized. Mapping of the A-shale member was facilitated by distinctive and laterally persistent subunits within it. Among these, in ascending stratigraphic order, are (pl. 4) (1) basal sandstone marker, (2) blue limestone marker, (3) oolitic zone, and (4) upper fossil zone. Basal sandstone marker.-This bed is the lowest sub- unit of the A-shale member and ranges in thickness from 4 feet at Pioche Divide to 35 feet in churn-drill holes on the west side of Ely Range. Though unrec- ognized in Slaughterhouse Gulch churn-drill holes, it reappears near Alliance mine (pl. 3) at Mount Ely, where it is 16 feet thick. - The basal sandstone marker is commonly reddish and is usually paired with an over- lying, richly fossiliferous limestone bed into which it grades, as at Pioche Divide. Blue limestone marker.-This subunit is well shown SHALE 24 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA in the northeastern foothills between Slaughterhouse Gulch and The Point, where it lies near the middle of the member. It ranges in thickness from 40 to 15 feet, thinning as it is traced from Alliance mine toward The Point. As shown by Slaughterhouse Gulch churn drill- ing, its top is 130 feet below the Lyndon Limestone, whereas near the Alliance mine it is 160 feet below the Lyndon and its base about 100 feet above the sandstone marker. Limestone interbeds are few in the A-shale member below the blue limestone datum, but relatively common above it. The blue limestone marker is the thickest and most distinctive of 'the limestone in the A-shale member. It is dense, of medium to fine grain, thick bedded, and dark bluish gray mottled lighter and darker, and in some places shows buff or limonite-brown spots. Oolitic texture was noted near the base. Thin sections disclose a fine detrital structure with rounded and subrounded calcite granules as much as 0.5 mm in diameter. Calcite of the granules is turbid gray and of exceedingly fine grain. - Also present are calcareous plates, curved tubu- lar pieces, shreds, and needles as much as 2 mm long. These fragments are assumed to be organic. The lime- stones of this subunit are fairly pure and relatively uni- form, in these respects differing from the Combined Metals Member with which the blue limestone marker has been confused. That the blue limestone marker of the eastern Ely Range is correlative with the so-called 20-foot lime of the Prince mine is somewhat doubtful. At that mine the limestone is reported to lie 30 to 55 feet beneath the Lyndon and therefore closer to the top of the A-shale member. Conceivably, however, the A-shale member may be thinned here at the top, either by faulting or discon formity. Limestone beds are common above the blue limestone marker (pl. 4). In general these differ in that they are impure argillaceous or sandy and have coarser texture. Unlike the marker, they may contain identifiable fossils. Some are thin limestone layers that alternate with cal- careous shales; others occur in flaggy to fairly thick bedded limestone sequences several feet thick, separated by shales. On fresh surfaces these impure limestones range from medium to light gray or, more rarely, darker bluish gray. They are usually streaked or mottled with limonite brown, buff, or pink and tend to weather to various shades of tan, buff, and brown. The granular texture is medium to rather coarsely crystalline. Most of the individual limestone beds are lenticular and not traceable more than a few hundred feet. Thin sections show some of these limestones to be oolitic, others are oolitic-detrital pellet combinations. Trilobite, brachio- pod, and algal remains are abundant in certain layers. Oolitic zone.-The oolitic zone occupies an interval from 40 to 100 feet above the blue limestone marker and is characterized by an abundance of oolitic limestone interbeds in shale. It has been mapped from Slaughter- house Gulch toward The Point. Upper fossil zone.-The upper fossil zone occupies the upper 50 to 75 feet of the A-shale member above the oolitic zone. Thinly layered medium to coarsely granu- lar limonite-stained limestone beds are here associated with calcareous shale. This zone is generally the most fossiliferous part of the A-shale member. Nonmicaceous smooth C-type shales are present in the oolitic zone and upper fossil zone. The smooth in- tercalated shales contrast sharply in texture with the crinkly micaceous shales and silty sandstones in these subunits. Smooth C-type intercalated shales appear about 55 feet above the blue limestone marker and the highest observed were about 25 feet below the top of the A-shale member. Attention is elsewhere directed to characteristic pair- ing of a basal quartz sand with overlying limestone, as illustrated by the Combined Metals Member. Such pairing is again noted in the A-shale Member, as ob- served at Pioche Divide near the Susan Duster mine, and in the Highland Range at Lyndon Gulch and the Forlorn Hope mine. A repeated depositional cycle is suggested by this phenomenon. Westgate and Knopf (1932, p. 64) call attention to similar features in the upper part of the Pioche Shale at the Prince mine. The A-shale interval in the Highland Range contains limestone and sandstone subunits similar to those noted in the Ely Range (pl. 4). Obvious changes in lithologic facies and thickness have, however, taken place within the 8 miles separating the two exposures. In Lyndon Gulch, strata having the character of the A-shale mem- ber are 440 feet thick, which is about 140 feet greater than the typical A-shale member of the Ely Range. The base of the A-shale member, however, cannot be established precisely in that area, where the basal sand- stone marker is unrecognized. It is possible that the lower part of the 440-foot upper interval in question may embrace a time-stratigraphic equivalent of the Ely Range B-shale member, which is usually devoid of lime- stone beds. At Lyndon Gulch (Deiss, 1938, p. 1152- 1153) a 25-foot limestone unit 178 feet below the Lyndon Limestone probably represents the blue limestone marker. An oolitic zone is present 90 feet above the supposed blue limestone marker. Ore in limestones of the A-shale member.-Where mineralizing fissures are present, the A-shale limestones have yielded replacement ore. In the Prince mine, ore was extracted from the so-called 20-foot lime and other limestone beds of the A-shale member. On the north- PIOCHE east side of the Ely Range, the A-shale member lime- stones have been prospected extensively and the blue limestone marker occasionally mistaken for the produc- tive Combined Metals Member. Unlike the Combined Metals Member, the blue limestone marker does not possess a basal sandy zone. AGE AND CORRELATION Four of the six members contain diagnostic trilobite assemblages. In ascending order, these are: D-shale, Combined Metals, Susan Duster, and A-shale. C-shale member is sparingly fossiliferous; B-shale member seemingly contains no fossils. Especially well preserved material was collected during this study from limestones of the Combined Metals Member, Susan Duster Member and A-shale member. Upper beds of the Combined Metals Member yielded abundant silicified material amenable to acid preparation. Most of the fossils first collected by Walcott and others came from shale layers; all fossils obtained from D-shale member were in shale, as this basal unit includes very little limestone. The Pioche Shale faunules range in age from the Early Cambrian OQZenellus zone to the Middle Cambrian Albertella zone. Upward disappearance of olenellid trilobites is the criterion employed for the separation of Early from Middle Cambrian. This trilobite group was not recognized above the Combined Metals Mem- ber in the Ely Range. Accordingly D-shale and Com- bined Metals members are classified as Early Cambrian ; the Susan Duster Limestone Member and all younger beds of the formation are Middle Cambrian. Burling (1914) noted the presence of Middle Cam- brian trilobites in the higher part of the Pioche Shale at Pioche; in spite of this announcement there has until recently existed a tendency to place the entire forma- tion in the Early Cambrian. In other districts as at Eureka, Nev. (Nolan, Merriam, and Williams, 1956, p. 8-9), only Early Cambrian fossils have thus far been found in the Pioche Shale. In the Highland Range, Deiss (19838, p. 1158) drew the Lower Cambrian-Middle Cambrian boundary pale- ontologically at a horizon where the trilobite Kochaspis liliana is reported about 365 feet below the Lyndon Limestone. Walcott's type of K. liliana came from the Pioche area, but the type locality and stratigraphic oc- currence of this species are unknown. In the Ely Range, the genus Kochaspis ranges from the Susan Duster Limestone Member upward to limestone beds in the A-shale member. The contact separating C-shale member from the underlying Combined Metals Member seems to be the physical boundary most nearly approxi- mating that between Lower and Middle Cambrian. Poorly preserved ptychoparioid trilobites from the C- shale member do not controvert this interpretation. 25 Of six Pioche Shale trilobite faunules identified by A. R. Palmer in the Ely Range (table 4), all but the highest or Albertella faunule, are present in the stand- ard reference section at Pioche Divide. SHALE TABLE 4.-Atratigraphic occurrence of Pioche Shale faunules based on paleontologic studies by A. R. Palmer Sys- Formation Fossils tem Lyndon Limestone No fossils § 6. Albertella faunule 'Is A-shale member Plagiura f g 5. Kochaspis and Policlla? l O 2 B-shale member No fossils 3 | 3 A & | Susan Duster Limestone 4. Poliella faunule ‘g Member 3. Strotocephalus-Mezicella faunule A 9 f: C-shale member Ptychoparioids, fossils rare Combined Metals Member | 2. Olenellus gilberti-Paedeumias clarki E faunule N 2 use D-shale member 1. Fremontia fremonti-Bristolia bristo- al lensis faunule § ¥ Prospect Mountain Quartzite >5'¢.'olithu1.]ss and castings only, no fossil she) Large collections of fossils from the Pioche Shale have been studied by A. R. Palmer, whose findings in terms of biologic affinity, age, and geologic correlation are set forth below. PIOCHE SHALE FAUNULES By A. R. PALMER EARLY CAMBRIAN FAUNULES Fremontia fremonti-Bristolia bristolensis faunule.- Two species of olenellids characterize this faunule, which occupies the lower part of D-shale member. Both are short-eyed forms, as distinguished from Qlen- ellus gilberti, a long-eyed trilobite generally found in younger Early Cambrian beds. The ¥. fremonti-B. bristolensis faunule is also the lowest assemblage of Early Cambrian trilobites in the Pioche Shale at Eu- reka, Nev. (Nolan, Merriam, and Williams, 1956, p. 8), and in the Cadiz Formation of the Marble Mountains, southeastern California (Riccio, 195%, p. 27). Distinc- tive but less common associates are Bristolia imsolens, another short-eyed form, and Paedeumias nevadensis, a long-eyed olenellid with long frontal area. Collections representing the F. fremonti-B. bristo- lensis faunule were made at several localities in the D- shale member. The best of these localities are in the Pioche Divide reference section and on the north slope of Mount Ely (USGS loc. 1398-CO) near the Gold 26 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA Eagle mine (pl. 3). The following assemblage was ob- tained at the last-named locality : Bristolia bristolensis (Resser) Bristolia insolens (Resser) Fremontia fremonti (Walcott) Paedeumias nevadensis (Walcott) Olenellus gilberti-Paedeumias clarki faunule-This faunule was found in the Combined Metals Member only. Characteristic elements were obtained through- out the unit, but the greatest numbers of individuals came from the upper few feet. In addition to the ole- nellids, Crassiftmbra waleotti is common ; less abundant is Zacanthopsis levis. Present also are phosphatic brachiopods referable to Dictyonina, Acrothele, and "Acrotreta." Association of the non-olenellid trilo- bites Crassifimbra walcotti and Zacanthopsis levis with olenellid forms is considered indicative of late Early Cambrian. Early Cambrian assemblages containing olenellid and non-olenellid trilobites are believed ap- proximately contemporaneous, though the species may differ from one region to another. Approximately cor- relative assemblages of this nature are recorded from Pioche Shale in the Eureka district, Nevada (Nolan, Merriam, and Williams, 1956, p. 8), the Buelna Lime- stone of northwestern Mexico (Cooper and others, 1952, p. 71), and the Peyto Limestone member of the St. Piran Sandstone in British Columbia (Rasetti, 1951, p. 82). Fossils were collected from 2 horizons in the Pioche Divide section of the Combined Metals Member: Subunit 2, about 10 feet above base of the member (USGS loc. 1391-CO) Antagmus? sp. Crassifimbra sp. Olenellus gilberti Meek Zacanthopsis sp. Subunit 5, about 3 feet below the top of the member (USGS loc. 1892-CO) Acrothele sp. "Acrotreta'" sp. Antagmus sp. Crassifimbra sp. Dictyonina sp. Kutorgina? sp. Olenellus gilberti Meek Paedeumias clarki Resser Zacanthopsis levis (Walcott) Collections were made also near the West End mine (USGS loc. 1399-CO) on the lower north slope of Mount Ely 5,000 feet southeast of the Ely Valley mine. These are from upper subunit 5 near the top of the Combined Metals Member. Trilobites from this ho- rizon are silicified, with larval stages especially abun- dant (Palmer, 1957; 1958). The faunule includes the following forms: "Acrotreta" sp. Crassifimbra walcotti (Resser) Dictyonina sp. Olenellus gilberti Meek Paedeumias clarki Resser Whether or not the five subunits of the Combined Metals Member can always be distinguished faunually as well as lithologically has not been determined with assurance. It is reasonable to suspect that the sandy beds of subunits 1, 2, and 3 might carry faunas differing in facies from those in limestones of subunits 4 and 5. MIDDLE CAMBRIAN FAUNULES Ptychoparioids in C-shale member.-The few poorly preserved trilobites obtained from the C-shale member are questionably Middle Cambrian. These are gener- alized and flattened ptychoparioids, which at present have by themselves no specific age significance. On the other hand, the apparent absence of olenellids in asso- ciation points up a post-olenellid, and by definition, post-Early Cambrian age. Strotocephalus-Mexicella fawnule.-Elements of this faunule were collected from the lower part of the Susan Duster Limestone Member only. Strotocephalus cf. 8. arrojoensis and Mexicella sp. are abundant, while cal- careous brachiopods referable to Diraphore are com- mon. The phosphatic brachiopod genera listed below occur also in the Combined Metals Member. A species of Mexicella, one of the two abundant trilo- bites, occurs also in the A-shale member, where it is associated with Albertella. The lower Susan Duster faunule lacks AZbertella, and combined with the faunule from the upper horizon of the Susan Duster, charac- terizes a pre-A4ibertella early Middle Cambrian faunule with elements of the Wenkchemmia-Stephenaspis and Plagiura-Kochaspis faunules (both pre-Albertella) described by Rasetti (1951, p. 87-92) from the Mount Whyte Formation in British Columbia. AtrotocepA- alus arrojoensis is known from the earliest Middle Cam- brian Arrojos Formation of northwestern Mexico (Lochman, in Cooper and others, 1952, p. 157). A collection from the lower 3 feet of the Susan Duster Limestone Member in the Pioche Divide section (USGS loc. 1393-CO) includes the following: "Acrotreta" sp. Acrothele sp. Dictyonina sp. Diraphora sp. Kochaspis? sp. Mexicella sp. Onchocephalus cf. 0. maior Rasetti Strotocephalus cf. 8. arrojoensis Lochman Poliella faunule.-Elements of this faunule were ob- tained from the upper few feet of the Susan Duster LYNDON LIMESTONE 227. Limestone Member. Its affinities are the same as those of the previously discussed faunule. A. collection from the basal limestone bed of the Tatow Limestone of Deiss (1938, p. 1143) in the House Range, Utah, has two genera in common with this as- semblage. Collections from the upper part of the Tatow have affinities with those from the upper part of the Pioche Shale, suggesting correlation of A-shale, B- shale, and Susan Duster Members with this House Range unit ( pl. 5). In the Pioche Divide section (USGS loc. 1394-CO) the following fossils were collected near the top of the Susan Duster Limestone Member : "Acrotreta" sp. Acrothele sp. Fieldaspis sp. Kochaspis sp. Onchocephalus cf. O. depressus Rasetti Poliella cf. P. denticulata Rasetti Schistometopus sp. Unassigned faunules.-T wo collections from the A- shale member of the Pioche Divide section correlate either with the Plagiura-Kochaspis faunule from the Mount Whyte Formation in British Columbia or with the Albertelle fauna widespread in the Cordilleran re- gion. Neither collection contains sufficient well-pre- served material to establish its faunal affinities. Basal limestone of A-shale member, Pioche Divide section (USGS loc. 1895-CO) Helcionella sp. Kochaspis sp. Poliella? sp. About 40 to 50 feet below top of exposed part of A-shale member, Pioche Divide section (USGS loc. 1396-CO) Plagiura sp. Albertella faunule.-Elements of this faunule char- acterize the upper part of A-shale member in the Ely Range and the Highland Range. Albertella and other indicators of this zone have been recognized throughout the Cordilleran region and are best known in the Cathe- dral Formation of British Columbia (Rasetti, 1951), and the Arrojos Formation of northwestern Mexico (Lochman, in Cooper and others, 1952). Closest af- finities of the trilobites in this faunule at Pioche are with the Albertella faunule of the Arrojos Formation. The Albertelle faunule was collected from dark-gray shales of A-shale member on the top of the Ely Range northwest of the Tulloch mine (USGS loc. 1405-CO) Albertella cf. A. proveedora Lochman Mexicella sp. LYNDON LIMESTONE Massive, cliff-making light- and dark-gray limestones (figs. 6, 7, 8) between Pioche Shale and Chisholm Shale were named Lyndon Limestone by Westgate and Knopf (1932, p. 10). The type section of this forma- tion is in Lyndon Gulch (pl. 2) on the west side of the Highland Range near the Shodde mine. This limestone unit, with an average thickness of about 375 feet in the Ely Range, assumes economic im- portance as host rock for replacement ores in the Ely Valley and Prince mines. In fact, the name "Prince lime" has long been used for this unit in the Pioche min- ing district. The disturbed and altered condition of these rocks at the Prince mine, however, make them a poor stratigraphic standard. Throughout the Ely Range all exposures of Lyndon Limestone are consider- ably deformed, and the less faulted, more continuous sections of this formation in the Highland Range prove more satisfactory for stratigraphic study. AREAL DISTRIBUTION The largest Lyndon Limestone exposures in the Ely Range occur to the northwest between the Half Moon mine and The Point. Small discontinuous outcrops occur on the north slopes of Mount Ely, near the Pioche No. 1 mine and at the Prince mine (pl. 3). From Gray Cone southward, a narrow faulted outcrop crosses the range. In the Highland Range the Lyndon may be traced northward along the west flank from the junction with the Black Canyon Range, through the type area of the formation to Stampede Gap. For 9 miles, limestones of this unit produce a nearly continuous bold cliffy outcrop along the lower front. Less precipitous slopes are formed below and above by the Pioche and Chisholm Shales. LITHOLOGY AND STRATIGRAPHIC RELATIONS The Lyndon Limestone is characteristically dense, fine-grained, or porcellaneous limestone ranging in color from white to dark gray or nearly black. The rock com- monly has the texture and general appearance of a litho- graphic limestone, normally containing only a small percentage of such impurities as iron and silica. It varies from platy to heavy bedded and massive, the latter being predominant. The limestones of this formation fall into two color groups: the purer light-gray or white limestones and the less pure carbonaceous medium-gray to almost black limestones. Most of the thinly bedded limestones are dark gray, whereas the light-colored phases tend to be massive. In thin section the purer light-gray and white varie- ties are observed to be partly detrital and rather uni- formly composed of round white turbid calcium carbon- ate granules set in a somewhat clearer calcite matrix. 28 Tank Ridge CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA FicurB 8.-View eastward across Churndrill Valley to Tank Ridge. White colored member B (€[B) overlying member A (€[A) of the Lyndon Limestone in fault contact with Peasley Member of Highland Peak For- mation (€hp) on left. Burrows Member of Highland Peak Formation (€hb) on extreme left. Step Ridge Member of Highland Peak Formation (€hsb) is in fault contact with Lyndon Limestone (€/A) and Pioche Shale (€p) west of California Pioche shaft ((). Treasure Hill. The round granules are mostly less than 0.3 mm in size and appear to have been mechanically rounded. In general these granules do not exhibit a concentric structure. The darker-gray carbonaceous limestones are detrital and range from oolitic to nonoolitic; all intermediate gradations are found between them. Nonoolitic car- bonaceous types range from medium gray to dark gray, some having a slightly bluish shade. In thin section the dark nonoolitic limestones are observed to be made up of rounded, grayish turbid granules most of which are less than 0.3 mm in diameter, a few exceeding 1 milli- meter. - All grains, including even the smaller ones, are rounded. Calcite cement, though turbid, is somewhat clearer than the granules, which contain finely divided carbonaceous pigment. Narrow calcite veinlets are nu- merous, some being less than 1 millimeter in width. A faint pinkish secondary iron staining is common along fractures. The medium-and dark-gray oolitic limestones com- monly have a speckled salt-and-pepper appearance. The oolites show well-defined concentric layering, aver- age about 1 mm in diameter, and are set in a matrix of turbid calcite. Individual oolites have an outer pellicle containing dusty carbon pigmentation. The nucleus is sometimes more coarsely crystalline carbonate than the surrounding matter. Crossbedding, common in other oolitic limestones of this area, was rarely noted in the Lyndon. Prospect Mountain Quartzite (€pm) underlies A variety of oolitic limestone in the Lyndon shows layers with numerous round or ovoidal dark-gray bodies averaging 5 mm in diameter. These bodies do not, like calcareous algae or the associated oolites, show concen- tric layering. Some have the appearance of cemented clumps of detrital limestone granules. Dense, aphanitic fairly pure limestones megascopi- cally like those which characterize the Lyndon are com- mon in the Middle Cambrian of the Great Basin. As noted by Westgate and Knopf (1932, p. 10), the High- land Peak Formation includes lithologic types so similar to parts of the Lyndon as to render distinction difficult or almost impossible in situations where faults obscure the stratigraphy. Most likely to be confused are clean light-gray or white, massive, more or less porcellaneous lithographic limestones, which occur in the Lyndon, in undolomitized portions of the Burrows Member of the Highland Peak Formation, and as a local facies in the Step Ridge Member of the Highland Peak Formation. In thin section white lithographic limestones of the Step Ridge Member show a fairly uniform finely erys- talline to aphanitic texture. Surficially similar Lyndon limestones reveal in thin section a less crystalline detri- tal granular fabric which preserves more of the original depositional features. Dolomitization in the Lyndon Limestone is uncom- mon, being confined mainly to the immediate vicinity of faults and fractures. Incipient dolomitic mottling like that characteristic of the Meadow Valley Member of the Highland Peak Formation is noted locally. LYNDON LIMESTONE 29 The absence of laterally extensive and uniform dolo- mite in the Lyndon is not easily explained. Higher in the stratigraphic section the Burrows Member of the Highland Peak Formation is extensively dolomitized, but resembles the Lyndon closely where undolomitized. If we assume the Burrows to have been dolomitized by the action of magnesian solutions which ascended along fissures, the hydrothermal activity might reasonably be expected to bring about similar changes where the same fissures transect the stratigraphically lower Lyndon Limestone. Such does not appear to be so, nor are lime- stones in the Pioche Shale dolomitized to any extent. Marine-connected diagenetic processes, effective during the Burrows depositional interval, and nonoperative in Lyndon time seem to offer a more logical explanation of the differences noted. The possibility of disconformity between the Pioche Shale and the Lyndon Limestone is suggested by good exposures of the contact near the Forlorn Hope mine, Highland Range (pl. 2). The boundary is a sharply incised, slightly undulant surface, but no angular dis- cordance was noted. The basal Lyndon at this locality is thick-bedded dark-gray oolitic limestone with limo- nite brown streaks and parting lines, whereas the top- most Pioche is a bed of brown-mottled argillaceous limestone 114 feet thick grading downward into limy micaceous shale. The Lyndon-Chisholm contact is rarely well exposed. The basal Chisholm as observed at the Shodde mine in Lyndon Gulch is a limestone bed 114 feet thick, of much lighter gray than the topmost Lyndon. Although the change is abrupt, no evidence of disconformity was noted. Three members are recognized in the Lyndon Lime- stone (fig. 9) ; these are designated in ascending order as members A, B, and C. Member B in the middle is distinguished by the light-gray and white limestones within it, whereas the other two members are prevail- ingly dark gray. The three members are best shown in stratigraphic continuity in the Highland Range type area but are recognizable also in the Ely Range. Member A of the Lyndon is well exposed in the lime- stone hill just west of Pioche Divide (fig. 7) and again half a mile northwest of the summit of Mount Ely. It may be observed also at Gray Cone (pl. 3). In the Lyndon type section near the Shodde mine (pl. 2) member A is about 185 feet thick and exhibits a massive ledge-forming dark-gray basal zone 15 to 25 feet thick. The same ledge former is present at the Forlorn Hope mine and is recognizable west of Pioche Divide. It is usually mottled light and dark gray and, though mas- sive weathering, shows faint undulant parting lines %; to 3 inches apart; these partings are sometimes stained pink or limonite brown. The limestone is markedly oolitic and contains larger ovoidal bodies having the outline of G@irvanella but revealing none of the internal structure of such calcareous algae. The remainder of member A is prevailingly heavy bedded, medium to dark gray, and, sometimes mottled and forms rough-weathering massive cliffy exposures. Lo- cal intercalated argillaceous limestone shows thinner bedding and platy weathering. A persistent thin-bedded and laminated dark-gray limestone 12 to 35 feet thick occurs at the top of member A. It superficially resembles platy beds in the Condor Member of the Highland Peak Formation, but is not dolomitic like the Condor. This topmost subunit of member A of the Lyndon was recognized also in the Ely Range near Pioche Divide and at Gray Cone. Dark-gray heavy-bedded limestones of member A of the Lyndon closely resemble the Peasley Member of the Highland Peak Formation, both being partly ocolitic and both containing rounded bodies of larger-than- oolite size. However, some of the Peasley inclusions are more specifically algal, having concentric structure, and are on the average larger, attaining a diameter of about an inch. The Peasley nodules, unlike those of the Lyndon, often enclose a fragment of fossil shell. Small patches of striped and mottled oolite of member A resemble the tiger stripe oolitic phase of the Step Ridge Member of the Highland Peak, but crossbedding, so common in the oolite of the Step Ridge, is rare in the Lyndon. Member B of the Lyndon is generally massive and cliff forming. It varies in color from medium and light gray to white; the conspicuous lighter phases usually show darker patches, mottlings, and bedding streaks. Dense and largely of lithographic texture, this lime- stone weathers more smoothly than that of member A, and forms rounded outcrop surfaces. The bedding, not everywhere apparent, is normally heavy, thin in very few places, and on the whole not as well defined as that in member A. Member B also differs from A by being more uniform and purer with less of the argillaceous and limonitic mottling and streaking. Pale-pinkish staining of outcrop surfaces is fairly common. Near its base, member B shows a coarse lamination or band- ing and may intergrade with the underlying thinly bedded zone at the top of member A. Being dense, brittle, and massive, the limestones of member B are cut by many joints and commonly ex- hibit cleavage. Recrystallized white calcite as fracture and pocket filling is characteristic. In the field the cliff- forming light-gray or white lithographic limestones of member B are easily confused with those of the Step 30 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA FEET 500 - Peasley Member of Highland Peak Formation Chisholm Shale 135 ft 400 - 300 - 200 - Lyndon Limestone 345 ft 100 - 50 4 Pioche Shale Alternate shale and limestone; fossils abundant Member C (20 ft) The "upper dark Lyndon''. Dark gray medium- to thick-bedded rough-weathering lime- stone; patches of tan argillaceous matter and nodules of possible algal origin Member B (140 ft) The "white Lyndon". _ White and light- to medium-gray massive, thick-bedded dense cliff-forming limestone in part of litho- graphic texture Thin-bedded zone (12-35 ft) _ Member A (185 ft) The "lower dark Lyndon". Medium- to dark- gray largely thick-bedded limestone of fine grain, with oolitic facies and nodules of possible algal origin. Topmost subunit thin-bedded; basal beds ledge-forming Basal ledge-forming zone (15-25 ft) Thick-bedded dark-gray oolitic limestone POSSIBLE DISCONFORMITY Brown-mottled argillaceous limestone A-shale member of Pioche shale FicsurE 9.-Columnar section (K) of the Lyndon Limestone and Chisholm Shale at the Shodde mine, Lyndon Gulch, Highland Range. See plate 2 for location of section. CHISHOLM Ridge Member of the Highland Peak Formation, and with undolomitized phases of the Burrows Member. Member C of the Lyndon, the topmost division, is especially well exposed at the Shodde mine in Lyndon Gulch (pl. 2). It may also be studied at Gray Cone in the Ely Range. Topmost Lyndon at the Prince mine, possibly representing this member, is mineralized and has there been called the big bed (Knopf, in Westgate and Knopf, 1932, p. 63). Member C forms a ledge below the less resistant Chisholm shale in the Highland Range. Limestones of member C resemble those of member A, being dark gray, medium to heavy bedded and rough weathering. Some are mottled, showing patches of limonitic and buff to pinkish-colored argillaceous mat- ter. No oolitic beds were recognized, but the member contains @irvamello-like bodies which lack internal structure. THICKNESS The Lyndon Limestone as measured near the Shodde mine in Lyndon Gulch (fig. 9) is 345 feet thick, which agrees with the measurement by Deiss (1938, p. 1151) on the south side of Lyndon Gulch. On the north side of the gulch, the formation is thinned somewhat by faulting. In the Shodde mine section, member A is 185 feet thick, member B 140 feet thick and member C at the top of the formation 20 feet thick. Westgate and Knopf; (1932, p. 10) measured 400 feet of Lyndon 1% miles north of Lyndon Gulch on the ridge south of Peaslee Canyon. In the Ely Range 380 feet of Lyndon was measured half a mile northwest of the summit of Mount Ely. At Gray Cone, 300 feet of the formation is exposed, of which 160 feet is member A, 115 feet light-gray member B, and 25 feet member C. In the conspicuous white- topped limestone hill west of Pioche Divide (fig. 7) , 150 feet of member A is overlain by 80 feet of member B, which is incomplete because of faulting and erosion. No unfaulted sections of Lyndon Limestone were recognized in the Ely Range. AGE AND CORRELATION The Lyndon Limestone, like most of the Highland Peak Formation, is singularly barren of fossils. Its early Middle Cambrian age is, however, well established by intermediate position between the fossiliferous A- shale member of the Pioche and the richly fossiliferous Chisholm Shale. 5 Mr. Paul Gemmill of the Combined Metals Reduction Co. (oral communication, 1954) reports a small fossil collection from Lyndon Limestone near the Bristol mine, 20 miles north of Pioche. The fossils were referred to Dr. Christina Lochman Balk, who identified Nisusie and Hyolithes, together with indeterminate trilobite frag- ments. A Middle Cambrian age was indicated. SHALE 31 The Lyndon may correlate with part of the Eldorado Dolomite at Eureka, Nev., which is also barren of fossils. The Eldorado differs from the Lyndon by being extensively dolomitized, ranging from nearly pure lime- stone to nearly pure dolomite (Nolan, Merriam, and Williams, 1956, p. 9-1 In the House Range, Utah (fig. 1), the Lyndon is probably represented in lime- stone strata overlying the "Pioche shale" and below a fossil-bearing dark-gray argillaceous limestone which is correlated with Chisholm Shale (pl. 5). The House Range beds in question have been called Howell Lime- stone (Deiss, 1938, p. 1141) and include strata assigned to "Millard limestone" and "Burrows limestone" by Wheeler (1948, fig. 5). Lithologically, they resemble member A and member B of the Lyndon, in addition to occupying about the same stratigraphic interval. CHISHOLM SHALE NAME AND OCCURRENCE The name Chisholm Shale was given by Walcott (1916b, p. 409) to strata between the Lyndon Limestone and the Peasley Member of the Highland Peak Forma- tion of present usage. The type area of the formation is the Chisholm mine vicinity (pl. 3), 1,000 feet west of the summit of Mount Ely. This lithologically distinc- tive and highly fossiliferous unit provides a valuable Middle Cambrian datum. Despite thinness and struc- tural incompetency, the Chisholm is one of the discrete and readily mappable units of the region. The total Chisholm outcrop is relatively small, for as a thin and structurally weak unit it became a locus of movement and was more or less completely faulted out locally. Not uncommonly its former presence is indi- cated only by pinkish tan or gray clay gouge. The largest exposures of Chisholm Shale in the Ely Range lie on the flanks of Mount Ely, especially the west side in the vicinity of the Chisholm, Whale, Blue Eagle, and Half Moon mines. These mines were partly developed in the Chisholm Shale, and their dumps have long been a fruitful ground for fossil collecting. On the north side of Mount Ely, the Alliance and Lost Treasure mines are likewise in Chisholm. Smaller ex- posures are found near the Prince mine, on Tank Ridge above the Pioche No. 1 mine, and in the west foothills about the Whiskey Barrel and Demijohn mines. Chis- holm Shale is well exposed at Gray Cone and occupies a narrow discontinuous belt stretching south from Gray Cone and thence across the Ely Range. The most continuous Chisholm exposures and those best suited for stratigraphic study are on the west side of the Highland Range. A nearly unbroken belt of these strata may be followed from the junction of the Black Canyon Range and the Highland Range north- 32 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA ward to Stampede Gap (pl. 2). No Chisholm outcrops are known north of this gap. THICKNESS An undisturbed section of Chisholm Shale in the Highland Range at the Shodde mine, Lyndon Gulch, is 135 feet thick (fig. 9). In the Ely Range the thickness ranges from 55 feet north of Mount Ely to about 100 feet at Gray Cone. Thickness measurements of Chis- holm in the Ely Range are generally unreliable because of faulting. LITHOLOGY AND STRATIGRAPHIC RELATIONS The Chisholm Shale consists of very fine textured, smooth noncalceareous clay shales, calcareous shales, and limestones. Clay shale predominates, but locally as in Lyndon Gulch, 30 percent of the formation consists of limestone (fig. 9). In color the shales are characteris- tically a pale, slightly pinkish brown, ranging to shades of grayish red, moderate brown, tan, buff, and in very few places pale grayish green. When weathered and bleached the beds become very light tan, cream colored, or even white. Concentric color diffusion rings of gray- ish red, tan, and light greenish gray are common fea- tures. The surface mantle over Chisholm Shale is usu- ally pink or reddish in color. Joints, fractures, and weathered surfaces are sometimes coated with dark- brown or reddish limonitic matter. Fossils stand out sharply in the light-colored shales by reason of their contrasting dark limonitic brown color. Fresh exposures of Chisholm Shale commonly appear massive and homogeneous, with only an occasional color band to reveal bedding. Weathering develops the shaly layering, though evidence of very thin lamination is seen in very few places. The shale breaks down on weathering to form thin irregular plates as much as 10 inches long, shapes of which are determined in part by intersecting joint surfaces. Chisholm Shale commonly forms topographic saddles. To the unaided eye Chisholm Shale does not as a rule appear micaceous, differing in this respect from nearly all Pioche Shale except the C-shale member. The C- shale member of the Pioche may be distinguished by the lack of the pinkish Chisholm color ; the C-shale member tends to be greenish and shows a small amount of mica- ceous material. Lumpy or bumpy interfaces are un- common in the Chisholm. In thin section Chisholm Shale reveals a large amount of reddish brown and orange ferruginous pigment in the form of irregular granules scattered through an exceedingly fine grained nearly colorless matrix. The Chisholm includes many limestone interbeds ranging in thickness from a few inches to about 8 feet (fig. 9). Where thick, the limestone beds have argilla- ceous partings. At the Shodde mine about 30 percent of the formation is limestone; it includes 12 limestone units within a total formation thickness of 135 feet. The limestone beds are fine grained and range from light olive gray to medium gray, usually mottled or stained pink and limonite brown. Fossils are abundant in limestone interbeds as well as in the shales. In ad- dition to shell material, these limestones contain ovoidal bodies which suggest G@irvamella. The Chisholm is conformable with the Lyndon Lime- stone below and the Peasley Member of the Highland Peak Formation above; lithologic change at both con- tacts is abrupt and seemingly without intergradation. Because of the structural weakness and intermediate position of the Chisholm Shale between two rigid lime- stone units, both top and bottom contacts may show evidence of slippage parallel to bedding. CHISHOLM SHALE AS ORE HOST Limestone interbeds of the Chisholm Shale were evi- dently very susceptible to replacement by sulfide, as were those of the Pioche Shale. Around Mount Ely are several small mines where these limestones contain gossany iron matter and sporadic pockets of rich silver- bearing sulfides. The Chisholm has been much pros- pected throughout the district, its narrow outcrop being studded by pits, adits, and pinkish-tan-colored dumps. Presence of Chisholm ore has encouraged deeper ex- ploration in the Pioche Shale, on the theory that the same feeding fissures might be reasonably expected to have mineralized limestone beds of the Pioche Shale at depth. AGE AND CORRELATION Fossils are nearly every where abundant and well pre- served in the Chisholm Shale of the Pioche vicinity. In spite of extensive collecting by amateur and professional collectors, the weathered Chisholm continues to yield fossils. Most of the material, however, has come from shales, whereas the limestone members have been ne- glected. The Chisholm fauna remains an excellent sub- ject for monographic study. Studies of Chisholm faunas were initiated by Walcott (1886), who established their position in the early Mid- dle Cambrian. Subsequently, Pack (1906b), Walcott (1916b), Resser (1935, 1937, 1942), and Palmer (1954) described and illustrated some of the Chisholm species. To date, most of these studies were based on float mate- rial from shales, and zoned collections have not been made. Most abundant Chisholm fossils are Zacanthoides typicalis (Walcott), Alokistocare piochensis (Walcott) and Alokistocare packi Resser. Presence of G@lossopleu- ra packi Resser places the formation in the @lossopleura zone. HICHLAND PEAK FORMATION 33 Beds probably equivalent to the Chisholm in age are known in the Abercrombie Formation at Gold Hill, Utah, in the Ophir Formation of the Tintic and Ophir districts, Utah, and in the Langston Limestone of the Wasatch Range. The Chisholm is correlated also with beds of the Cadiz Formation of southeastern California and part of the Bright Angel Shale at Grand Canyon. In the House Range, Utah, argillaceous limestone beds just below the Dome Limestone contain a @lossopleure fauna and are probably correlative with the Chisholm.® Shales which might be confused lithologically with the Chisholm in complex structural situations occur spar- ingly in the Burnt Canyon Member and in the lower part of the Mendha Formation at Arizona Peak near the Highland Queen mine (pl. 2). Lists of common Chisholm Shale fossils identified by A. R. Palmer are given below. USGS colln. 1403-CO ; 8 feet above base of Chisholm Shale on south side of Burrows Canyon, Highland Range: Alokistocare cf. A. subcoronatum (Hall and Whitfield) Athabaskia howelli (Walcott) Diraphora sp. USGS colln. 1406-CO; from dump of Abe Lincoln mine, west side of the Ely Range : Alokistocare packi Resser Alokistocare piochense (Walcott) Eocrinus longidactylus (Walcott) Glossopleura packi (Resser) Glyphaspis kempi (Pack) Zacanthoides typicalis (Walcott) USGS colln. 1410-CO ; on east side of Lime Hill on dump of prospect pit: Alokistocare piochensis (Walcott) Athabaskia howelli (Walcott) Glyphaspis kempi (Pack) Zacanthoides typicalis (Walcott) USGS colln. 1414-CO; canyon south of Ely Valley mine, dump high on slope: Alokistocare packi Resser Zacanthoides typicalis (Walcott) USGS colln. 1415-CO ; dump at Half Moon mine. Alokistocare packi Resser Alokistocare piochense (Walcott) Athabaskia howelli (Walcott) Glossopleura packi Resser Zacanthoides grabaui Pack Zacanthoides typicalis (Walcott) HIGHLAND PEAK FORMATION Carbonate rocks 4,500 feet thick lie between the Chis- holm Shale and the Mendha Formation and form the highest peak of the Highland Range (pl. 2). To these geomorphically prominent rocks, Westgate and Knopf (1932, p. 11) gave the appropriate name Highland Peak ® Wheeler (1948, p. 38) assigned these House Range beds to the "Burnt Canyon limestone" of the Pioche column. The true Burnt Can- yon Member of the Highland Peak Formation is herein correlated with the lower part of the Swasey Formation of the House Range. Limestone, here changed to Highland Peak Formation. To the uninitiated observer this thick and largely mas- sive formation gives a first impression of stratigraphic monotony ; closer examination, however, shows it to be a diverse limestone-dolomite sequence having for the most part highly variable facies composition. An added deterrent to stratigraphic division is the absence of fossils in most Highland Peak beds. As mineral exploration continued near Pioche, it was found that Highland Peak strata occupied much of the surface where blanket deposits of zinc and lead were known or expected in depth. More detailed investi- gation of these strata demonstrated that the original Highland Peak Limestone can be divided into 13 litho- logic units. Six of these have been mapped throughout the Ely Range, and most can with fair assurance be traced or correlated throughout the region of the High- land and Bristol Ranges. It is nonetheless recognized that the almost wholly lithologic criteria as applied here have definite limitations where correlation is con- cerned, and must be used with caution in a facies-vari- able carbonate sequence of this type. Only where see- tions are sufficiently continuous to reveal established vertical groupings, distinctive sets of beds, or sedimen- tary cycles, are these criteria dependable. Where the Highland Peak sections are short, as in isolated fault blocks, known repetition of similar carbonate facies through the column entails the obvious risks attending strictly lithologic identification and correlation. A sixfold subdivision of the lower part of the High- land Peak has been used successfully by the mining pro- fession in the Pioche and Bristol districts since the 1930's. The classification here adopted is virtually in agreement with that of the mining companies, except for the objectionable geologic names. Geologic names used by the mining companies are as follows in strati- graphic order: 6. Bristol lime . Platy dolomite . Newport lime . Black Davidson lime . Gray Davidson dolomite . Blue Davidson lime Np go wa Ot pa Davidson, Newport, and Bristol have previously been used as formation names in other areas; "platy dolo- mite," being a lithologic term, is inappropriate. An informal division of the Highland Peak was pro- posed by Wheeler and Lemmon (1939). In this scheme, 17 lithologic units were described, and each was given a letter designation, A to Q inclusive. With refer- ence to the lower part of the formation, table 5 shows equivalence of the present scheme to those of Wheeler and Lemmon and of the mining companies: 34 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA TaBt® 5.-Atratigraphic names for the lower part of the High- land Peak Formation, compared with equivalent terms pro- pogre'd by Wheeler and Lemmon (1939) and those used by mining companies Formation C. W. Merriam, Wheeler and Mining company this report Lemmon, 1939 terms Meadow Valley Highland Peak G | Bristol lime Member Condor Member Highland Peak F | Platy dolomite Lower part of | Step Ridge Member Highland Peak E | Newport lime Highlimi Highland Peak D ca Formation Blémt Canyon Mem- | Highland Peak C | Black Davidson lime er Burrows Member Highland Peak B | Gray Davidson dolo- mite Peasley Member Highland Peak A | Blue Davidson lime Wheeler (1940, 1948) in subsequent contributions named the Peasley Limestone, Burrows Dolomite, and Burnt Canyon Limestone with designated type sections on the west side of the Highland Range. Except for Highland Peak units A, B, and Q, all originally lettered divisions of Wheeler and Lemmon are typified by ex- posures in the Warm Spring section northeast of Panaca. These divisions include the Condor or "High- land Peak F." The name Condor was initially applied (Wheeler, 1948, p. 39) to "Condor member" of the "Swasey limestone," a House Range, Utah, formation. However, the type section of the Condor proposed by Wheeler is near Pioche, Nevada, in the Warm Spring vicinity. This unit is here designated as a member of the Highland Peak Formation. Type sections of the new Step Ridge Member and the Meadow Valley Mem- ber are proposed in the Ely Range, where each is well exposed and readily accessible. For this study the Highland Peak is preserved with original content as a geologic formation, and its prin- cipal units are classified as members. Such a course seems preferable at present to removal of six or more formational units from the lower part of the original formation, thereafter retaining the term Highland Peak solely for the upper residuum. The named mem- bers occur in the productive part of the Pioche mining district where detailed mapping has been done. Group rather than formation status would be appropriate when all members are named and their type sections des- ignated, at which time elevation of member to forma- tion may be in order. The fairly continuous Highland Peak section at Warm Spring provides a valuable yardstick (pl. 6), especially for those units above the Burnt Canyon Mem- ber. However, this section, like all others in the dis- trict, is considerably faulted and thickness measure- ments of some divisions are unreliable. In the course of this investigation, the six named members that make up the lower part of the Highland Peak Formation were studied intensively with respect to stratigraphy, gross petrology, and geologic structure. In the northwestern Ely Range, these units occupy a large part of the surface above potentially ore-bearing ground (pls. 1,2). Because of faulting and erosion, the seven upper divisions of the Highland Peak are seem- ingly absent from this area. In connection with drill exploration from the surface, correct identification of the thick Highland Peak units is especially important in estimating the position of deeply buried potential ore beds. Rocks of the Highland Peak Formation extend through the Ely, Highland, and Bristol ranges and continue northward into the southern Shell Creek Range, north of the area shown in pl. 2. Certain of its members such as Peasley and Burrows Members are re- ported (Humphrey, 1945, p. 22-23) in the Groom dis- trict 75 miles southwest of Pioche. Middle Cambrian carbonate rocks having the general character of this formation are present over a much larger territory in the central and eastern Great Basin, where they attain a thickness of several thousand feet, and generally form prominent geomorphic features. In most places these strata are sparsely fossiliferous and in general are too poorly known at present for meaningful detailed com- parison with the Pioche section. During the course of these studies, field comparisons were made with similar rocks of the House Range, Utah, and the Eureka dis- trict, Nevada (pl. 5). Preliminary comparisons have been made by others (Drewes and Palmer, 1957) with the Snake Range. The results seem to indicate that members of the Highland Peak Formation are not traceable with assurance into these outlying districts, although sporadic and nearly identical carbonate facies characteristic of the Highland Peak are recognized throughout. As the formation is traced into outlying districts, individual members tend to lose lithologic in- dividuality or discreteness, with shift of depositional facies. Lithologic units wedge out and local units of limited extent are introduced as the overall content of the formation changes appreciably. How far the name Highland Peak Formation should be carried laterally from the Highland Range belt remains to be determined by areal mapping and facies analysis. Paleontologic correlation of some Highland Peak units at Pioche with House Range units (pl. 5) indi- cate that nearly matching carbonate facies and even comparable stratigraphic sequences can be misleading in point of time equivalence. Peculiar carbonate facies which characterize the lower part of the Highland Peak near Pioche are recognizable also in the House Range Middle Cambrian, but in differing vertical order. Paleontologic control, while still inadequate, serves in LOWER PART OF THE HIGHLAND PEAK FORMATION 35 this case to emphasize the risks of wholly lithologic cor- relation with distant sections in these facies-variable carbonate rocks. LOWER PART OF THE HIGHLAND PEAK FORMATION PEASLEY MEMBER NAME AND OCCURRENCE The Peasley Member takes its name from "Peaslee Canyon" " on the west side of the Highland Range (pl. 2), where it rests upon Chisholm Shale and is overlain by Burrows Member. As indicated by Wheeler (1940, p. 17), the type section is on the spur of Comet Peak south of "Peaslee Canyon". Westgate and Knopf (1932, p. 12), in the original description of the High- land Peak Formation, distinguished this unit as "dark- blue limestone" 90 feet thick above the Chisholm Shale south of "Peaslee Canyon". As here delimited, Peas- ley Member is essentially "Highland Peak A" of Wheeler and Lemmon (1939, p. 47), originally de- seribed at Comet Peak as "dark-gray, medium grained, thickly bedded massive limestone with numerous cal- cite stringers." In the Pioche mining district these beds have been known as "blue Davidson lime." The outcrop area of this relatively thin unit is small in the Ely Range, the narrow band forming a somewhat cliffy slope above the subdued and even narrower Chis- holm Shale. The Peasley Member is exposed in small fault blocks near The Point and has been mapped dis- continuously along both sides of the Ely Range to Gray Cone, thence southward across the hills toward Panaca. Fault contacts with the incompetent Chisholm Shale, coupled with uncertainty as to the exact position of the upper depositional boundary with the Burrows, make most sections of the Peasley unsatisfactory for strati- graphic study. Good exposures are found on the north, west, and south sides of Mount Ely and at Gray Cone (pl. 3). Less continuous faulted sections lie north and northeast of the Prince mine and south of the Pioche No. 1 mine (fig. 8). The Peasley is poorly exposed in the Warm Spring section. By far the most continuous outcrops of this unit follow the Chisholm along the west side of the Highland Range. THICKNESS The type section of the Peasley Member is 150 feet thick. In the Ely Range the member is 152 feet thick at Gray Cone, 160 feet north of Mount Ely, and 98 feet at Warm Spring, where it is faulted at the valley edge. Faulting along the Chisholm-Peasley boundary com- monly reduces the measureable thickness of both units. 7" On the Highland quadrangle (1916) and Highland Peak quadrangle (1953), this canyon is shown as "Peaslee Canyon." The spelling Peas- ley is probably correct. The Peasley seems to thicken and thin appreciably along the strike because the Peasley-Burrows contact undulates. To some extent the waviness of the contact may reflect the mapper's uncertainty as to where from point to point the actual boundary should be drawn. LITHOLOGY The Peasley Member is medium-dark- to medium gray limestone that is slightly bluish gray, detrital, less commonly oolitic, and medium to fine grained. It tends to be heavy bedded, massive, rough weathering, and more or less cliffy, with local intervals of thin bedding or color banding that range from half an inch to more than an inch in thickness. Light- and dark-gray mot- tling and streaking is characteristic, and in places, an alternation of light and dark color bands. In the lower 10 feet, a maroon or limonitic brown mottling is noted in some places. Three principal types of limestone in- tergrade and show various intermediate phases; these are detrital limestone, oolitic limestone, and algal limestone. The detrital limestone is composed largely of well- rounded granules of very fine textured calcium carbon- ate, ranging from silt size to about 2 mm in diameter; scattered oolites and a few algal bodies are present. The oolites in thin section average less than a milli- meter in diameter. Only rarely do they show good con- centric structure. Associated with the oolites are larger and smaller, much more irregularly rounded detrital granules of non-oolitic calcareous matter. The matrix is whitish, somewhat turbid calcite. The principal im- purity is finely divided carbonaceous material, present in both oolites and detrital granules, but not in the calcite matrix. Oolitic Peasley resembles oolitic phases of the Step Ridge Member and the lower part of the Lyndon Lime- stone. It exhibits the peculiar "tiger stripe" color dif- ferentiation like that of the Step Ridge. Only locally, however, is crossbedding, so characteristic of the oolitic limestones of the Step Ridge, noted in the Peasley. The algal limestone is composed in large part of ovoidal bodies averaging about 10 mm in greatest diam- eter, a few exceeding 25 mm. In the interstices are scattered oolites and numerous rounded calcium car- bonate granules ranging from less than 0.1 mm to about 1 mm. The cement is whitish turbid calcite. Although the texture of the cement, carbonate granules, and algal bodies is in general extremely fine, spots of medium to rather coarsely crystalline granularity are found in the calcite cement. The algal bodies do not as a rule show well-defined concentric structure. Many have formed around a piece of brachiopod or other shell which served 36 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA as a nucleus. Fragmentary shell remains, some possibly Hyolithes, are likewise scattered through the matrix. Fairly large algal nodules containing a shell fragment as the nucleus appear to be a distinctive feature of the Peasley. Some of these nodules exceed one inch in di- ameter. Algal nodules in the Lyndon do not, so far as known, attain such size, and all the many nodules ex- amined from the Lyndon were devoid of the shelly material. The coloration of the Peasley is very similar to that in parts of the Step Ridge and to the darker-gray phases of the Lyndon Limestone The Peasley exhibits throughout, however, a slightly more bluish shade than the Lyndon and is rarely as dark as the darker-gray Lyndon. None of the Peasley as here defined is light gray or white like the light-colored phase of the Lyndon Limestone. STRATIGRAPHIC RELATIONS Good exposures of the normal Chisholm-Peasley con- tact are uncommon in the Ely Range because faults are localized in the incompetent shale of the Chisholm. On the west side of the Highland Range an abrupt but con- formable contact may be seen near the Shodde mine in Lyndon Gulch (pl. 2). The lower few feet of Peasley at this locality has a pinkish mottling and contains edge- wise limestone breccia. At Peaslee Canyon the type Peasley is conformably overlain by dolomite of the Bur- rows Member. Limestones interpreted by Wheeler (1940, p. 17, 19) as lowermost Burrows in this section and at Warm Spring near Panaca are regarded by the author on lithologic grounds as uppermost Peasley rather than lowermost Burrows. Slight local angular discordance within these upper limestones of the Peasley (emended) is probably the result of subaqueous scour and fill ® rather than an unconformity of regional importance. The Peasley-Burrows boundary is difficult to recog- nize where the upper part of the Peasley is dolomitized, or where the lower part of the Burrows is limestone rather than doiomite. In some places where both Peasley and Burrows are limestone, the boundary is seemingly gradational. At many points the contact is undulant, or markedly uneven, suggesting discon- formity. The upper part of the Peasley is more or less dolo- mitic northwest of the Pioche No. 1 shaft (loc. 26), in upper Buehler Gulch (loc. 27), and on the east side of Slaughterhouse Gulch at Tank Ridge (loc. 28). At the first-mentioned locality (26) dolomite interbeds occur ® In a later contribution, Wheeler (1948, p. 33, 36) deemphasized the stratigraphic importance of these minor discordances, considering them "diastems." in the bluish-gray upper part of the Peasley and are overlain with seeming gradation by mottled saccha- roidal dolomite of the Burrows containing algal nodule ghosts. The Peasley-Burrows contact relations are fur- ther discussed under the Burrows Member. AGE AND CORRELATION The lower age limit of the Peasley is fixed as early Middle Cambrian by the abundantly fossiliferous Chis- holm Shale, which conformably underlies it. Frag- mentary fossil material in the Peasley itself provides nothing of age significance. Peasley and Burrows to- gether may well be roughly correlative with the Dome Limestone of the House Range, Utah (pl. 5). The similarity of the Peasley to the House Range Millard Limestone of Wheeler (1948, p. 35) is probably deceiv- ing, for paleontologic evidence in higher strata (see "Lyndon Limestone") suggests that the Millard Lime- stone and superjacent light-gray carbonate rocks are best alined with the Lyndon Limestone of the Pioche district, with which they agree in stratigraphic position. BURROWS MEMBER NAME AND OCCURRENCE The name Burrows Member applies to dolomite and limestone between the Peasley and Burnt Canyon Mem- bers. Type sections of both Burrows and Peasley (Wheeler, 1940, p. 27) were designated in the same sequence on the northwest spur of Comet Peak south of "Peaslee Canyon." The exposures are continuous south- ward from the type section to Burrows Canyon, from which the name is taken. Dolomite of the Burrows changes laterally to limestone at many exposures; hence, the term "member" is more appropriate than a lithologic modifier. The Burrows Member is virtually Highland Peak B of Wheeler and Lemmon (1939, p. 47). As presently interpreted the Burrows is, however, slightly less in- clusive than the original definition, for 30 feet of lime- stone regarded by Wheeler (1940, p. 27) as lowermost Burrows is herein viewed as part of the underlying Peasley. Thus restricted, the Burrows type section is almost exclusively dolomite. Although Westgate and Knopf do not specifically differentiate and name this unit, it is probably the "gray limestone" 560 feet thick measured by them south of "Peaslee Canyon." In the Ely Range, strata of the Burrows interval are known to the mining companies as "Gray Davidson dolomite." Discontinuous fault-block exposures of the Burrows occur along the west flank of the Ely Range from a posi- tion 1,500 feet south of The Point to the vicinity of Caselton, thence southward to the hills northeast of the Prince mine (pl. 3). The intermediate slopes of Mount LOWER PART OF THE HIGHLAND PEAK FORMATION 37 Ely are underlain by interfingering limestone and dolo- mite of the Burrows. In this belt of lateral facies change, the stratigraphy is complex and confusing. Dolomite of the Burrows forms large blocky outcrops on Tank Ridge west and south of the Pioche No. 1 mine, and the formation is exposed on the east slope of Lime Hill and in the southeast foothills near the Alps mine. Burrows outcrops may be followed southward from Gray Cone across the Ely Range in several fault blocks, the most southerly being that at Warm Spring (pl. 2). Continuous exposures of dolomite of the Burrows are found in the Highland Range, being especially well shown from Burnt Canyon southward to the slopes east of the Pan American mine. Factors of thickness and resistance to erosion make the Burrows, like the Step Ridge Member, a geomorphi- cally prominent and areally extensive unit. THICKNESS The type Burrows (Wheeler, 1940, p. 28-29) as rede- fined is about 370 feet thick. Elsewhere in the High- land Range greater thicknesses were measured, for ex- ample, both north of Lyndon Gulch and along the first spur north of Burrows Canyon where it is about 520 feet thick.: The section north of Burrows Canyon however, is thickened somewhat by faulting. In the Highland Range, Westgate and Knopf (1932, p. 12) measured 560 feet of the "gray limestone" which seem- ingly corresponds to the Burrows Member. Faulting makes most measurements of the Burrows in the Ely Range untrustworthy, but in general the thickness is extremely variable from one locality to another. For example intertonguing dolomite and limestone of the Burrows at Mount Ely is only about 300 feet thick, but the seemingly unbroken section south of Gray Cone measures about 490 feet (fig. 10). Be- cause of faulting, only about 90 feet of Burrows was measurable at Warm Spring. In view of the faulting it can not be concluded that the variations in thickness are related to conditions of deposition. LITHOLOGY Dolomite predominates in the Burrows Member but here and there changes to fairly pure, generally very fine grained limestone. Locally in the Highland Range, the section of this member is almost entirely dolomite, but in the Ely Range, it is commonly limestone over a considerable extent. In few places is the Burrows see- tion wholly limestone. Typical dolomite of the Burrows is light to medium gray and medium dark gray. Bedding is usually thick, * Measurements scaled from mapping by C. D. Campbell and J. A. Reinemund, U.S. Geological Survey, in 1943. and the outcrops massive and blocky with a ragged cliffy expression at many points. Like most rigid dolo- mites subjected to deformation, the Burrows is gen- erally much jointed and fractured. Texture is sac- charoidal, ranging from medium to coarse crystalline. Some weathered surfaces show a faint limonitic brown- ish stain, but in general the iron content is low. Silica in the form of chert or jasperoid is seemingly negligible. At Gray Cone and the first hill to the south (fig. 11), the Burrows is represented in considerable part by fine- textured or lithographic limestone, which is light gray or almost white to medium and medium dark gray in color. Streaks and patches of dark gray occur in the light phases, while in the darker areas the opposite is true. The limestone facies of the Gray Cone area is in general thick bedded, massive, and not uncommonly shows a banded color differentiation parallel to bedding. The bands range in thickness from less than 1 inch to several inches. Such massive limestones develop smooth knobby exposures which contrast with the ragged, blocky surfaces formed on normal dolomite of the Burrows. Common features of the Burrows limestone facies are irregular white calcitic inclusions for which the term "bluebird structure" is adopted. The name is derived from the Bluebird Dolomite of Middle Cambrian age at Tintic, Utah, wherein these peculiar structures were first described (Lindgren and Loughlin, 1919, p. 28). As observed in limestone facies of the Burrows at Gray Cone the bluebird structure (fig. 11) exhibits a great variety of shapes, sizes, and patterns, ranging from highly irregular branching and vermiform bodies to those which were originally globular or tubular before collapse. The diameter of tubular forms ranges from 2 mm to about 5 mm. Locally the collapsed tubes ex- hibit a median partition in longitudinal section. On both sides of the partition, calcite crystals form thick walls with long crystal axes oriented perpendicular to the outer surface of the tube. Certain of the ramifying calcite networks associated with bluebird structure suggest "Stromatactis-like frame builders" described by Lowenstam (1950, p. 440-441) in Niagaran reef bodies. Bluebird structure is especially characteristic of dark- gray limestone patches in the Burrows limestone facies, where the white calcitic material of the structure stands out in sharp contrast. In thin section the dark-gray limestone matrix shows traces of rounded granules and is presumably detrital. It is possible that localization of abundant bluebird structure in the more highly car- bonaceous dark facies indicates a locus of more vigorous organic growth than in surrounding areas of light-gray limestone. That bluebird structure is itself a product of organic activity has not, however, been demonstrated. CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA 38 10069 10009 10019 10029 (wy3) 1aqwapy Kafe mopeap A Jo co; g pus zg sored sog 'ouo; {tip Jo yjnos uopBulog X894 PUBIYSIH JO (,@G-G) UO1j998 poin§tap(-'0T HHODLT . T 1334 O0¢ O0€ O 1011 (043) 10puo39 T T T T OOT 0 OOT auopsowr] uopu/7 oz NNN Sst Fi csm t Spoor trot ean auopsawut) Ajeys Sywojog "'/”/"""""’ """'”/I’/V’oz (paziusooaiun ut sjisso4 /””0/”””’”"”""' "'/'”'”VV' AI 10009 aeqwap aSpiy dors jo. a mun) e seroe; ayiuojog /,%””””””””§WWV" & \ “Wu m § Rss" . £15 ons q up ,, eamon.}s paigen|q ,, 159m07 Aquseddy _ s 3 2 W 0029 1022 (0443) 12qwapy 106+ (443) seroey MN C 0 S98 (sy3) oSpiy dag jung quopsou1| Ajurew 'Uaquwap smoung CA s (ied 19moj) , uopewno4 4eaq LOWER PART OF THE HIGHLAND PEAK FORMATION FIGURE 11.-Limestone facies of the Burrows Member of the Highland Peak Formation. Smoothed surface of specimen from the measured section south of Gray Cone shows mottled and fine texture. White patches are bluebird structure. Natural size. Bluebird structure occurs also in dark limestones of the Step Ridge Member. It is present in the Lynch Dolomite of the Ophir area, Utah (Gilluly, 1932, p. 16), in the Young Peak Dolomite at Gold Hill, Utah (Nolan, 1935, p. 11), and in the Eldorado Dolomite at Eureka, Nev. (Nolan, Merriam, and Williams, 1956, p. 10). Although most occurrences of this structure in the Pioche area are in limestone, the commonest en- vironment elsewhere would seem to be dolomite. At Gold Hill, Utah (Nolan, 1935, p. 11), bluebird struc- ture is reported in both limestone and dolomite. Thin sections of the light-gray or white lithographic limestone facies reveal indications of detrital origin, although no oolites or fragments of organic origin were recognized. Present are numerous minute seams and irregular inclusions of clear calcite that resulted from partial recrystallization. Many small fault block exposures of lithographic and oolitic carbonate rocks were recognized during the course of detailed mapping; these commonly occur in structural situations that leave their correct strati- graphic identity uncertain. Confusing situations of this kind were found in upper Slaughterhouse Gulch (pl. 3) and near the head of Churndrill Valley, especi- ally where the Step Ridge Member and lithologically similar undolomitized Burrows Member are in fault contact. Much confusion stems from the fact that the Burrows lithographic limestone facies are megascopi- 39 cally indistinguishable from those of the upper part of the Lyndon and the Step Ridge. Moreover, bluebird structure occurs in dark-gray carbonaceous limestone patches of both the Step Ridge Member and the un- dolomitized Burrows. Factors to be considered in dis- tinguishing these carbonates are the scarcity of oolites in the undoubted Burrows, and the general absence of dolomitization in the unquestioned Step Ridge. Neither Lyndon nor Step Ridge seem greatly suscep- tible to dolomitization in the Pioche area, whereas the Burrows is more often dolomite than not. Fault blocks of crossbedded oolitic dolomite texturally reminiscent of the Step Ridge Member are therefore perplexing. BTRATIGRAPHIC RELATIONS Stratigraphic problems which arose during mapping of the Burrows relate especially to the position and char- acter of its boundaries, to much variation in thickness, and to complex facies change from dolomite to lime- stone within the member. To these must be added the possibility of confusion with other carbonate units of the Pioche area, facies of which resemble those of the Burrows. Lack of marker beds eliminates division of the mem- ber or determination of stratigraphic position within it by lithology alone. The lower part of the Burrows, however, may sometimes be distinguished from higher beds by abundant ghosts of ovoidal algal nodules and by its light- and dark-gray mottled pattern. Three sets of local conditions were recognized as the Peasley-Burrows contact was mapped through the Ely Range: (1) normal limestone of the Peasley overlain by normal dolomite of the Burrows, (2) limestone of the Peasley overlain by Burrows limestone facies, (3) both the upper part of the Peasley and the lower part of the Burrows dolomitized. Where dolomite is in contact with dolomite or limestone with limestone, de- lineating the precise boundary between the two members becomes difficult or impossible. Limestone of the Peasley is overlain by dolomite of the Burrows at Gray Cone. In its lower part this dolo- mite includes tongues and patches of limestone, the amount of limestone increasing upward. Only 1,000 feet away in the hill south of Gray Cone, the Peasley Member is directly overlain by the Burrows limestone facies (fig. 10). For mapping purposes the Peasley- Burrows boundary here was arbitrarily placed at the base of the lowest light-gray lithographic limestone body ; the boundary relation appears to be transitional. Limestone persists upward to make about 85 percent of the member. In this section, which is 490 feet thick, the lower 300 feet exhibits an irregular patchy distri- bution of massive light-gray, medium-gray, and me- 40 dium-dark-gray lithographic and fine-grained lime- stones with color bands that follow bedding. Bluebird structure appears 290 feet above the base. In this pre- dominantly limestone column, irregular pods of sac- charoidal dolomite occur 320 feet above the base, and the upper 15 feet of the member is mainly dolomitic. Possible existence of unconformities between the Bur- rows and members above and below is suggested by variations in thickness from point to point, and locally by contact features." At the mouth of Buehler Gulch (pl. 3) 1,600 feet north of Caselton (locs. 29, 30), the limestone of the Peasley is overlain by dolomite of the Burrows with so undulating a contact as to invite sus- picion of disconformity. At one exposure (loc. 30) a pinkish stain on the contact surface might be inter- preted as evidence of emergence and weathering. A similar highly uneven Peasley-Burrows contact was recognized on the east side of Lime Hill (loc. 31). In Churndrill Valley (loc. 32) the same contact shows no appreciable relief. Close study of these uneven con- tacts actually reveals no unequivocal evidence of ero- sion, but on the contrary suggests rapid gradational passage from limestone below to dolomite above. Although an unconformity between the Burrows and the overlying Burnt Canyon Member has previously been postulated (Wheeler, 1940, p. 28), the mapping of this contact gave no compelling evidence of a break. Normally this boundary is characterized by a change upward from thick-bedded saccharoidal dolomite, or less commonly massive fine-textured limestone, to thin- bedded rather fine grained dark-gray locally fossilifer- ous limestone. Not uncommonly, however, dolomitiza- tion did not cease abruptly with the topmost Burrows, but also affected the lowermost Burnt Canyon, which is a zone of alternating and interfingering dark-gray limestone and dolomite. Northwest of the Pioche No. 1 shaft (loc. 33) and near the head of Buehler Gulch (loc. 34), this partly dolomitic basal Burnt Canyon zone is about 25 feet thick. It is well exposed on Tank Ridge (loc. 35), comprising interbedded limestones and magnesian limestones, which change abruptly upward to well-bedded dark-gray limestones. At other points in this vicinity (loc. 36), the lower part of the Burnt Canyon shows only patches of dolomite in the limestone. On the whole, detailed study of the bound- ary of this member gives the impression of transition or intergradation rather than formity. DOLOMITIZATION Stratigraphic study of the Burrows Member unavoid- ably leads into familiar but as yet unresolved structural, " Evidences of Peasley-Burrows unconformity cited by Wheeler (1940, p. 27-28) are not relevant here ; they occur locally within what is pres- ently regarded as the upper part of the Peasley Member and are seem- ingly manifestations of subaqueous scour. CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA geochemical, and oceanographic problems of dolomite origin. Capricious lateral intertonguing of limestone and dolomite is present in all parts of the member. Where the rock is prevailingly dolomite, one finds sporadic islands or tongues of lithographic limestone 30 feet or more across. Conversely, in predominantly lithographic limestones, there are bodies of saccharoidal dolomite. Limestone-dolomite relations were mapped and studied in some detail at Mount Ely, at Gray Cone, and at the north end of Tank Ridge. The contacts behave fantastically, following a bedding plane for perhaps several feet, then swinging diagonally through a bed to a higher bedding plane. Where the Burrows Member is limestone rather than dolomite, the limestone is generally dense, fine-textured or lithographic. From this it is reasoned that the pri- mary carbonate which altered to dolomite was also of the same general lithographic character; however, it is possible to reason that the initial pre-dolomite carbonate facies differed texturally and chemically from the litho- graphic phase and because of these differences was the part which became dolomite. By the same token, the finer and denser limestone survived as such because it was less susceptible to the change. Behavior of the Burrows dolomite-limestone boundaries in the Ely Range brings to mind similar phenomena noted by Gilluly (1932, p. 16) in the Lynch Dolomite of the Ophir district and by Nolan (1985, p. 10) in the Young Peak Dolomite at Gold Hill, Utah. In all three there is abrupt change from limestone to dolomite within a single bed. According to Gilluly the changes at Ophir are apparently unrelated to fissures, a conclusion which seems inescapable for many of the abrupt changes in the Burrows at Pioche. Among geologic factors considered in connection with the present stratigraphic study were the presence or the absence of fracturing or brecciation of the dolomitized rock, the presence or the absence in the dolomite of fer- ruginous matter and silica (jasperoid), the sharpness of the limestone-dolomite contact, and structural or bedding control. At many observed exposures the lateral boundaries of unfractured massive limestone with dolomite are knife-edge sharp, jagged and have zigzag configuration. These reaction contacts seem to represent the advancing front of a magnesium-rich zone. Many Burrows exposures reveal that fracturing has a definite bearing upon the dolomitization problem, whether the dolomite be clearly hydrothermal and re- lated to fissuring or whether it be of supposedly pri- mary or diagenetic origin. For example, relatively iron-free and silica-free, homogeneous, and presumably diagenetic dolomite was followed at one outcrop to a LOWER PART OF THE HIGHLAND PEAK FORMATION 41 point where it terminated against a sharp fracture on which no evident displacement was noted. At other points, fractures seem to have played a role in facilitat- ing secondary or late movement of magnesum-bearing solutions. Supposedly primary dolomite masses which adjoin limestone have locally been subjected to leaching, and the derived magnesian solutions have migrated along fratures into contiguous limestone. In this man- ner secondary and nonhomogeneous dolomitic alteration took place in rocks which escaped the initial additive diagenetic reaction. Near the mouth of Buehler Gulch (pl. 3) the uneven Peasley-Burrows contact previously mentioned (loc. 29) gives evidence of dolomite control by minor fractures. At this contact numerous steeply dipping fractures, which show no clear evidence of displacement, cross from the dolomite above into limestone of the Peasley below. Magnesium derived by leaching from the Bur- rows apparently moved downward along these fractures to various depths within the limestone of the Peasley, bringing about secondary dolomitization therein. As a result, the uneveness and irregularity of the Peasley- Burrows contact is accentuated. Most of the dolomite of the Burrows is evidently a product of additive alteration which affected a wide area of buried sea bottom during one rather specific in- terval of geologic time. The extent or the intensity of the dolomitization process varied greatly with geo- graphic position and was influenced by the character and initial structure of the original carbonate sediment and by local differences in chemical, physical, and biologic factors of marine environment. At the one ex- treme, dolomitization of the member approaches com- pleteness in the Highland Range. To the east in the Ely Range, the sections at Mount Ely and Gray Cone illustrate the opposite extreme, in which sporadic dolo- mite, makes up only about 15 percent of the rock, with various intermediate stages. In theory the additive diagenetic changes came about shortly after accumulation of the carbonate mud, but quite probably after initial consolidation. Sea water is assumed to have been the source of magnesian solutions responsible for the reaction. These solutions may, to be sure, have circulated at considerable depths in the solidifying sediment, well below the interface between sea and mud. Given proper conditions of porosity and permeability, trapped or connate waters high in mag- nesium might continue to bring about dolomitization long after lithification. The predominance of diagenetic or primary dolo- mitization in the Burrows does not rule out the possi- bility that local dolomite bodies in this unit may be the result of fissure activity. Late hydrothermal dolomiti- zation was recognized in the overlying limestone of the Burnt Canyon ; locally in the Burrows such dolomitiza- tion may well be superimposed upon earlier formed diagenetic dolomite. AGE AND CORRELATION Undiagnostic algal nodules (@@irvanella) and blue- bird structure provide no evidence of age. However, the Burrows is conclusively Middle Cambrian, being bracketed by overlying fossiliferous Burnt Canyon and by the richly fossiliferous Chisholm Shale below, from which it is separated by the Peasley Member. The Burrows probably correlates with the Dome Limestone in the House Range, Utah (pl. 5), as sug- gested by faunal ties between the Burnt Canyon Mem- ber at Pioche and the lower part of the Swasey Forma- tion in the House Range." Lithologic similarities invite comparison of the Burrows with the Lynch Dolo- mite at Ophir, Utah, the Young Peak Dolomite at Gold Hill, Utah, the Bluebird Dolomite at Tintic, and por- tions of the Eldorado Dolomite at Eureka, Nev. Ab- sence of fossils, however, obviates direct correlation. BURNT CANYON MEMBER NAME AND OCCURRENCE The name Burnt Canyon Member is adopted for dark- gray well-bedded fossiliferous limestones that lie be- tween the Burrows Member and the Step Ridge Mem- ber. Described by Wheeler and Lemmon (1939, p. 47) as "Highland Peak C," these rocks were later designated as "Burnt Canyon limestone" by Wheeler (1948, p. 36) with the type section on the west side of the Highland Range between "Peaslee Canyon" and Burnt Canyon. In the Ely Range this unit has long been known as "Black Davidson limestone," so named for its occurrence together with underlying "Gray Davidson dolomite" and "Blue Davidson limestone" at the Davidson shaft. The Burnt Canyon Member with its well-preserved fos- sils and distinctive lithology proves to be a reliable stratigraphic datum and a valuable unit for correlation with distant Cambrian sections. Large exposures of the Burnt Canyon Member occur at Mount Ely a short distance below the summit and at the head of the north fork of Slaughterhouse Gulch. Faulted and incomplete sections are found on Tank Ridge, west and south of Pioche No. 1 mine, and along the east side of Churndrill Valley near its head. Dis- continuous badly faulted exposures on the west side of the Ely Range extend from the area east of Caselton southward to hills east of the Golden Eagle mine (pl. 3). Isolated Burnt Canyon exposures have been " This interpretation is somewhat at variance with that of Wheeler (1948, p. 36, fig. 5), who regards the Burrows as correlative with lime- stones herein alined with the light-gray Lyndon Limestone. 42 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA mapped north of Pioche at Williams Hill and southeast of town in conspicuous Lime Hill. The member crops out in the southeastern part of the Ely Range northwest and south of Gray Cone. For purposes of stratigraphic study, the sections at Mount Ely, the hill south of Gray Cone (fig. 10), and Warm Spring north of Panaca (pl. 6) are most satisfactory. In the Highland Range, the Burnt Canyon is much less faulted than it is near Pioche, and the sections are more continuous laterally. THICKNESS Burnt Canyon Member of the type area (Wheeler, 1948, p. 47) is about 300 feet thick. Measured sections in the Ely Range give the following thicknesses : Mount Ely, 200 feet; Gray Cone, 220 feet; Warm Spring, 162 feet. Average thickness of 190 feet in the Pioche area thus implies thickening westward toward the Highland Range type area. LITHOLOGY AND STRATIGRAPHIC RELATIONS The Burnt Canyon Member is predominantly thin- bedded medium-dark-gray to dark-gray commonly very fine grained limestone similar to that of the upper part of the Combined Metals Member of the Pioche Shale. Individual beds commonly range in thickness from %% inch to more than 1 inch, averaging about half an inch. Locally, thin beds show laminations no more than a millimeter thick; at the other extreme a few beds attain a thickness of 114 feet. Bedding ranges from fairly even to undulating and nodular, with marked pinch and swell features. On the weathered surface, some of the highly carbonaceous beds are medium light gray. Characteristic features are grayish-red to moder- ate-red splotches and partings of argillaceous matter. Fossils are abundant locally in thin reddish clayey in- tercalations, which at some points thicken to several inches of shale. In such argillaceous zones the limestone beds weather in platy fashion, showing extremely bumpy interfaces with highly irregular, sometimes vermiform depressions filled by the reddish clay material. Oolitic limestone beds and lenses contain ovoidal nodules of probable algal origin (Girvanella). The algal bodies average about 3 mm in diameter and are larger than oolites but smaller than the comparable algal bodies in the Lyndon and other Cambrian units of the region. By reason of its thin-bedded and locally shaly charac- ter the Burnt Canyon weathers in somewhat subdued fashion as compared with the massive limestones above and below. Such is particularly true of the lower half, which not uncommonly forms depressions and saddles, whereas the upper part may show greater relief, to- gether with the overlying Step Ridge. As elsewhere noted, the Burnt Canyon lies conforma- bly upon the Burrows Member, being gradational with it at some places. A precise contact is not everywhere de- finable by reason of the alternating dark-gray limestone and dolomite beds which locally occupy this boundary zone. Nowhere in the Ely Range was clear evidence of disconformity recognized (Wheeler, 1940, p. 28; 1948, p. 87). Burnt Canyon Member is conformably overlain by unit a of the Step Ridge Member. Although the change to light-gray lithographic limestone of unit a is abrupt, close examination of the actual boundary gives the impression of gradation in some places. At least three lithologic zones are recognizable within the Burnt Canyon Member. A lower zone about 25 feet thick is characterized by interbedded dark-gray lime- stone and light-gray dolomite. The overlying zone some 75 feet thick shows reddish mottling and argilla- ceous partings or interbeds with fossils. Edgewise limestone conglomerate occurs in this zone (locs. 37, 38). An upper zone about 90 feet thick is somewhat thicker bedded and in part is medium to light gray. The Burnt Canyon tends to be oolitic and crossbedded especially in the upper 25 feet and resembles the tiger stripe facies of Step Ridge unit 6. Good exposures of the reddish tan fossil-bearing shales of the Burnt Canyon Member are found near the head of Churndrill Valley on the east side (loc. 18), on the east side of Lime Hill (loc. 22), and south of Gray Cone. At locality 18 the reddish tan clayey material occurs as thin interbeds in dark-gray fossiliferous lime- stone. At the Lime Hill locality a 10-foot bed of fossil- iferous shale suggests Chisholm Shale lithology. The excellent shaly fossil bed south of Gray Cone lies 80 feet stratigraphically above the base of the member. The precise horizon of the other fossil occurrences is unknown; presumably they fall near the middle of the Burnt Canyon Member. The limestone of the Burnt Canyon Member was sus- ceptible to dolomitization throughout its entire thick- ness. In this respect it resembles the underlying Burrows, but differs from the overlying Step Ridge. Laterally continuous primary or diagenetic dolomite appears to be more or less restricted, however, to the lower 25 feet of the member. In the higher part, dis- continuous, patchy, and irregular dolomitization was noted at many points. In several places these patches are clearly related to feeding faults or fissures, from which magnesian solutions passed outward along favor- able beds. Shattering of the dolomite is characteristic of these occurrences, and magnesian solutions usually failed to penetrate far along bedding from the highly disturbed rock. Local fissure-fed dolomites of this sort include jasperoid and ferruginous matter. Limestone LOWER PART OF THE HIGHLAND PEAK FORMATION 43 of the Burnt Canyon has been brecciated and dolo- mitized along a fault on the east side of Churndrill Valley just north of the Prince mine road. AGE AND CORRELATION According to A. R. Palmer, fossil assemblages col- lected from the Burnt Canyon Member in Churndrill Valley (loc. 18), at Lime Hill (loc. 22), and in the vicinity of Gray Cone (loc. 25) contain undescribed species of Kootemia and ptychoparioid trilobites. This distinctive assemblage is known only from Burnt Canyon Member of the Ely Range. The unit identified as "Burnt Canyon" in the House Range by Wheeler (1948, fig. 5) contains species of Glossopleura and is here considered correlative with Chisholm Shale (Palmer, 1956, p. 672). The Ely Range true Burnt Canyon Member seemingly correlates with the shaly lower part of the Swasey Formation in the House Range (pl. 5), to which Wheeler erroneously applied the name "Condor Formation." STEP RIDGE MEMBER NAME AND OCCURRENCE Here named for Step Ridge (pl. 1), this limestone member (fig. 12) occupies the stratigraphic interval between the Burnt Canyon Member and the Condor Member. In the type area along Step Ridge, and on the east side of Churndrill Valley, the unit is widely ex- posed but discontinuous, being broken by many high- angle faults. The Step Ridge is fully exposed in the southern part of the Ely Range near Warm Spring, where it embraces the combined "Highland Peak D" and "Highland Peak E" of Wheeler and Lemmon (1939, p. 47). The preoccupied name "Newport lime" has been used for this unit by mining companies. The Step Ridge Member occupies large areas in the northern Ely Range, where it makes prominent geo- morphic features. The unit has been mapped from Mounty Ely southeastward through upper Slaughter- house Gulch (pl. 3), thence along both sides of Churn- drill Valley. In the east foothills north of Pioche, it crops out at Williams Hill and southeast of the town in conspicuous Lime Hill (fig. 4) where the summit and west slope are made by resistant, cliffy portions of the member. Good outcrops are found in the foot- hills northwest and south of Gray Cone and again farther south in the Condor Canyon-Warm Spring vicinity. THICKNESS In the mapped area at Step Ridge (pl. 1), this mem- ber is about 740 feet thick; at Warm Spring it is 775 feet thick (pl. 6). Initial variation in thickness of some magnitude is suggested by the fact that a measured section (fig. 10) in the hill south of Gray Cone reveals only 365 feet of Step Ridge Member. This part of the section does not seem badly faulted. At most exposures where faulting is not an important factor, the thickness probably exceeds 600 feet. Unit a of the Step Ridge ranges in thickness from 35 feet in Churndrill Valley to about 70 feet south of Gray Cone and at Warm Spring. Unit c ranges from less than 30 feet to 50 feet as it is followed along the crest of Step Ridge. LITHOLOGY AND STRATIGRAPHIC RELATIONS The Step Ridge exhibits a wide range of lithologic types, from white and dark-gray dense lithographic limestones to mottled oolitic limestones. Most preva- lent and distinctive is a striped oolitic variety to which the name "tiger-stripe limestone" is given (fig. 13). Commonly a dull medium bluish gray, these oolitic limestones are generally crossbedded, showing long sweeping foreset beds. To a lesser extent, nearly identical limestones occur in the Peasley and the Lyn- don. Mottling is common in all phases of the Step Ridge; where the rock is very light gray, patches are darker gray, or the converse is true. Bedding on the whole is obscure or thick and the outcrops are generally massive and cliffy. Dense resistant beds of the Step Ridge are the cap rock of prominent geomorphic fea- tures such as Mount Ely. Bluebird structure is char- acteristic of the Step Ridge Member as well as of the Burrows Member. In the vicinity of Churndrill Valley (pl. 1), it was feasible to divide the Step Ridge into three map units, which from bottom to top are called unit a, unit 6, and unit c. Units a and ¢, the thinner subunits, consist mainly of light-gray and white, massive lithographic limestones very similar to the white limestone member B of the Lyndon Limestone, and white undolomitized lithographic lime of the Burrows Member. Both units a and c are dense and resistant to weathering and form bold cliffy exposures." Unit a is well exposed at the summit of Mount Ely and on the east side of Churn- drill Valley near its head. Unit c occurs in a series of discontinuous light-gray cliff exposures along Step Ridge (fig. 12) from Mount Ely southward. At the top of this unit just beneath the contact with the over- lying Condor Member is a massive 3- to 5-foot dark- gray limestone containing an abundance of bluebird structure. Scattered darker-gray phases occur in the light-gray limestone of unit c. Unit c of the Step " The mining companies refer to unit c of the Step Ridge Member as "false Prince A" and unit a of the Step Ridge Member as "false Prince B". The dense lithographic limestones in each are quite similar to the "white Prince lime" of the mining companies which is member B of the Lyndon Limestone of present usage. 44 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA FicurE 12.-View northward across Prince mine road toward the crest of Step Ridge. Light gray cliffy unit c (€hsc) of the Step Ridge Member of the Highland Peak Formation stepped down by northeast faults. Condor Member of Highland Peak Formation (€hc) at ridge crest on left. (€hsb) of the Step Ridge Member. Fisurs 13.-Typical mottled oolitic tiger stripe limestone facies in unit b of the Step Ridge Member of the Highland Peak Formation. Weathered surface. Natural size. Ridge was not recognized in the more southerly out- crops of this member at Gray Cone and Warm Spring. The greater part of the Step Ridge Member falls in unit 5, which is characterized by large lenticular bodies of crossbedded tiger-stripe oolitic limestone. Unlike Lyndon oolitic limestone, these bodies seldom include algal nodules. Also present in unit b are massive light- and dark-gray-mottled fine-grained limestones having the appearance of magnesian limestone of the Meadow Valley Member. Bold lenticular masses of light-gray Foreground is unit b lithographic limestone like those of units a and c are uncommon in unit 5; however, on Step Ridge west of upper Churndrill Valley small lithographic bodies as much as 20 feet thick are present in the upper 80 feet of this middle unit. Unit a of the Step Ridge is "Highland Peak D" of Wheeler and Lemmon (1939, p. 47). "Highland Peak E" is approximately equivalent to combined units 5 and c of the Step Ridge Member. Very little dolomite was found in the Step Ridge. Near Warm Spring a weak incipient dolomitization was noted locally in the lower part. Scarcity of dolo- mite in the Step Ridge is rather surprising, for light- gray lithographic limestones of the Burrows were quite susceptible to magnesian replacement. Exposures of «dolomitized oolitic tiger-stripe limestone at the head of Slaughterhouse Gulch have the appearance of the Step Ridge oolites. In this intensely faulted area, identity remains uncertain and the dolomitic rocks in question may be part of either Peasley, Burrows, or Step Ridge. Whereas the Step Ridge Member is readily distin- guishable when top and bottom contacts or a consider- able part of the member are exposed, identity may re- main in question when only small segments of the member are in view. Incomplete fault block exposures (fig. 3) may easily be confused with Lyndon, uppermost Burnt Canyon, Peasley, Burrows, or Meadow Valley, all of which include facies indistinguishable from parts of the Step Ridge. The Step Ridge is conformable upon the Burnt Can- yon Member and is overlain by the Condor Member LOWER PART OF THE HIGHLAND PEAK FORMATION with apparent conformity. Uppermost beds of the Burnt Canyon in places closely resemble the mottled middle Step Ridge facies. AGE AND CORRELATION The Step Ridge Member has yielded no fossils, but its lower age limit is firmly established by the fossiliferous limestone of the Burnt Canyon Member which lies con- formably beneath. Paleontologic correlation of the Burnt Canyon Mem- ber at Pioche with the lower shaly part of the Swasey Formation in the House Range, Utah, suggests that Step Ridge and the upper part of the Swasey are also correlative (pl. 5). Moreover the upper limestone of the Swasey shares lithologic features of the Step Ridge, such as the oolitic tiger-stripe facies and the cliff-form- ing tendency. But lithologically the Step Ridge even more closely resembles the House Range Dome Lime- stone, which is quite probably older. Both are unfossil- iferous massive cliff-forming limestone comprising dark mottled facies with lighter gray lithographic phases. Both are characterized by oolitic tiger-stripe cross- bedded limestone and bluebird structure. CONDOR MEMBER NAME AND OCCURRENCE The Condor Member is named for Condor Canyon (pl. 2), 244 miles north of Panaca (Wheeler, 1948, p. 39). This is the most distinctive map unit of the High- land Peak Formation. Mining-company geologists re- fer to it as the platy dolomite because of the dolomitic nature and platy weathering of some beds. Actually the Condor is diverse lithologically, containing cal- careous sandstone and limestone as well as impure sili- ceous dolomite. Westgate and Knopf (1982, p. 12) recognized the potential value of this member in inter- pretating the complexly faulted structure. Although unnamed by them, its occurrence north of the Prince mine was correlated with that near Gray Cone and with a 98-foot unit east of Panaca. This member was first designated as "Highland Peak F" by Wheeler and Lemmon (1939, p. 47), it was later assigned the name "Condor member" by Wheeler (1948, p. 39) and considered by him a member of the "Swasey limestone," a House Range, Utah, formation. But in naming the Condor, Wheeler stated that the type sec- tion "* * * is in the Panaca Hills, Pioche district, Nevada * * *." However, the unit "* * * takes its name from Condor Canyon about two miles north of the type section where it is exposed on the north wall near the canyon mouth." In accord with this definition the Condor Member as here interpreted is typically exposed in the Warm Spring reference section measured by 45 Wheeler and Lemmon and remeasured in connection with this study. The Condor Member is represented in the central part of the Pioche district, where it serves well as a key unit in mapping the stepped-down fault blocks along Step Ridge (pl. 1). At several points in this vicinity, it is either the youngest bedrock exposed or is overlain by only a capping of Meadow Valley Member. Small Condor outcrops occur northeast of the Golden Eagle mine (pl. 3) and at lower elevation in minor fault blocks near the mouth of Churndrill Valley. South of Gray Cone the Condor reappears at the surface, whence it may be followed discontinuously southward toward Warm Spring and Panaca. THICKNESS The Condor Member varies little in thickness throughout the district. Three measured sections give the following: Warm Spring, 105 feet; Gray Cone, 110 feet ; Step Ridge, 120 feet. LITHOLOGY AND STRATIGRAPHIC RELATIONS The Condor Member is nonuniform, showing a con- siderable range of lithologic types. Among these are impure silty dolomites and dolomitic limestones, cal- careous silty sandstones, and fine-grained limestones. Fairly pure, clean uniform saccharoidal dolomites so characteristic of the Burrows and other carbonate units of the district are uncommon. Dark-gray and black chert nodules are present, though not in abundance. The fine silty dolomite is light or medium light gray on weathered surfaces. Limestone interbeds usually weather darker gray, although the calcareous siltstones and sandstones weather tan or light limonitic brown. On fresh fracture the silty dolomites are medium to dark gray, the limestone interbeds usually medium-dark gray, and siltstones and sandstones range from pale pink or reddish brown to very light tan gray. Thin bedding and fine lamination are characteristic of the member; as a consequence weathered surfaces tend to be platy or flaggy. Although the light-gray- weathering platy beds predominate, these layers are separated here and there by darker limestone and sand- stone beds ranging from less than 1 inch to more than a foot thick. A few fairly uniform, almost unlaminated dolomite beds as much as 2 feet thick were noted. Weathering of the laminated rocks imparts a rilled or grooved pattern like weatherbeaten wood where resist- ant laminae stand sharply in relief. The black chert does not occur in continuous layers, but as scattered nodules and lenses as much as 2 feet long and 8 inches thick. 46 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA Of interest with respect to conditions of accumulation are the fine bedding laminae, ripple marks, pits, and castings. Many of the laminae are less than 1 mm thick, and some exhibit the alternation of dolomite with fine limestone layers. These alternations appear to be pri- mary or diagenetic, rather than results of selectivity during late magnesian additive hydrothermal action. Highly undulating and broken laminae are common, giving evidence of flowage and slumping prior to lithifi- cation. At one exposure the laminae were observed to be molded concentrically around a chert nodule. Ripple marking noted in brown-weathering silty beds is of the oscillation variety having nearly symmetrical ridges, wave length of about 30 mm and amplitude of 24, mm. A ripple index of 12 suggests that these fea- tures formed by wave action in a partly inclosed body of shallow water, little affected by currents or tides (Pettijohn, 1949, p. 131). Interfaces show pits and mud castings that suggest organic activity. Supposed worm castings are abun- dant just beneath the 4-foot tan sandstone which caps the member near Warm Spring. No other fossils were found in the Condor. Thin sections of average dolomite of the Condor Member reveal a finely crystalline texture generally lacking traces of rounded carbonate granules, oolites, pellets, or organic structures of any kind. Laminated varieties range in character from dolomite or dolomitic limestone, of which 65 percent is carbonate and 35 per- cent quartz grains, to what is virtually fine quartz sand- stone, of which about 80 percent is quartz. The quartz grains are angular or subangular, almost never rounded, are concentrated in the coarser quartz-rich laminae, and are for the most part larger than average grain size. Intervening carbonate laminae are finer grained and contain only an occasional angular quartz granule. Flakes of a micaceous mineral are present. The fine- grained more or less magnesian limestones show coarser dolomite rhombs in a finely granular calcite matrix. Also present are a few angular quartz grains. In these limestone layers are abundant traces of rounded and subrounded carbonate granules, but no organic shapes were recognized. The Condor Member rests conformably upon the Step Ridge Member and is overlain concordantly by Meadow Valley Member."* Massive dark-gray lime- stone with abundant bluebird structure at the top of the Step Ridge gives way abruptly to laminated dolomite of the Condor. The top of the Condor is marked by a conspicuous bed of light-brown-weathering fine dolo- ® A minor unconformity between the Condor and Step Ridge is re- ported at a locality about 2,000 feet west-northwest of the Pioche No. 1 shaft (Park, C. F., Jr., Gemmill, Paul, and C. M. Tschanz, written communication, 1955). mitic sandstone, which was traced south from the Pioche area to the vicinity of Warm Spring. Across the Condor section, the lithologic sequence shows a more or less rhythmic repetition of similar layers. The dark-gray chert nodules are limited mainly to the upper half; platy character and tan color- ation on weathering are better defined in the lower half. The Condor is one of three units of the Highland Peak Formation in which chert is characteristic. The others are unit 7 and unit 9 in the upper part of the Highland Peak Formation. The Condor Member is the lowest unit of the Cam- brian section in this area that is typified by the rather uncommon finely laminated dolomites. Similar rocks are repeated in units 7, 9, and 13 in the upper part of the Highland Peak Formation. Platy laminated beds at the top of member A of the Lyndon Limestone re- semble the Condor, but are not dolomitic. Elsewhere in the Great Basin, laminated Middle Cambrian car- bonate rocks, recalling those of the Condor, occur at Gold Hill and in the Ophir district, Utah. Condor lithology also resembles that of the fine-textured Lower Devonian dolomites of the Sevy Dolomite, which occur widely in the Great Basin. AGE AND CORRELATION Identifiable fossils have not been found in the Condor Member. The lower part of the Swasey Formation of the House Range, Utah, with which the Condor has been correlated (Wheeler, 1948, p. 39) does not possess the lithologic peculiarities of the Condor. Fossils in the lower part of the Swasey, moreover, suggest a correlation of that unit with the Burnt Canyon Member of the Pioche district (Palmer, 1956). At present it would be hazardous to suggest that the Condor of the Pioche area is correlative with any of the Middle Cam- brian units elsewhere in the Great Basin which include similar fine-grained laminated dolomitic strata. MEADOW VALLEY MEMBER NAME AND OCCURRENCE The Meadow Valley Member is here named for beds that are conformably underlain by the Condor Mem- ber and conformably overlain by unit 7 of the Highland Peak Formation. In the past this unit has been called "Bristol lime" by the mining companies, in reference to its occurrence at the Bristol Silver mine. The type section of the Meadow Valley Member lies in the measured Warm Spring section northeast of Panaca (pl. 6) on the edge of Meadow Valley. The Meadow Valley Member is virtually equivalent to "Highland Peak G" of Wheeler and Lemmon (1939, p. 47). The Meadow Valley Member is the youngest Cam- brian unit of areal importance, known to be exposed in LOWER PART OF THE HIGHLAND PEAK FORMATION 47 the northern Ely Range near In this vicinity the member is represented by several fault-bounded erosion remnants on the crest of Step Ridge from the head of Slaughterhouse Gulch southeastward for about one mile. A large exposure is found on west-facing slopes 2,400 feet northeast of the Caselton shaft; a rem- nant caps a knoll 2,600 feet northeast of the Golden Eagle mine (pl. 3). Meadow Valley Member is exposed over a larger area in the southeastern Ely Range where it reappears 3 miles southeast of Pioche in the hill south of Gray Cone; from this locality it has been followed discon- tinuously southward toward the type section at Warm Spring. THICKNESS No complete section of Meadow Valley suitable for . measurement was found in the northern part of the Ely Range where the greatest thicknesses remaining after erosion are of the order of 200 feet. The type section east of Warm Spring is 430 feet thick, which agrees with the measurement by Wheeler and Lemmon (19839, p. 47) for "Highland Peak G." ** LITHOLOGY AND STRATIGRAPHIC RELATIONS The Meadow Valley Member comprises medium-gray to dark-gray medium-grained to exceedingly fine grained mottled limestones, which are in the main thick bedded and massive. In several zones, however, bed- ding becomes thin, yielding platy debris on weathering. The limestone has a characteristic and peculiar mottling (fig. 14). Weathered surfaces reveal a decided textural difference between irregular or vermiform splotches of medium grain and the intervening aphanitic limestone matrix. The medium-grained splotches, being less sol- uble, weather in sharp relief, producing a rough, pitted, and pointed surface recalling that of a bath sponge. Granular texture of the coarser material is that of saccharoidal dolomite, and is evidently due to patchy incipient dolomitic recrystallization. On freshly broken surfaces the coarser spotches commonly are lighter gray than the enclosing aphanitic limestone. On weathered faces the reverse may be true, for the dark fine-grained material bleaches to a rather light gray, as is common with weathered sedimentary rocks rich in carbonaceous matter. Medium-grained mottlings occasionally show a limonitic or pinkish coloration. Where the Meadow Valley becomes more argillaceous and platy, it tends to exhibit pinkish mottling and buff or pink argillaceous "* Jumbled blocks at locality 17 contain Upper Cambrian fossils but have only small areal extent. In the southeastern Ely Range an average thickness of 340 feet was measured by Park, Gemmill, and Tschanz (written communication, 1955), which suggests a possible thinning of the Meadow Valley north of the type area. FIGURE 14.-Smoothed surface of typical limestone in the Meadow Val- ley Member of the Highland Peak Formation showing mottled char- Lighter areas are limestone; darker, coarser grained areas are Specimen from measured section south of Gray Cone. Nat- acter. dolomite. ural size. partings. Edgewise limestone conglomerate was noted where the Meadow Valley is well bedded. In thin section the irregular dolomitic parts are rela- tively coarse internally; the size of rhombs decreases outward toward the boundaries with very fine textured calcite matrix. The calcitic matter contains clearly de- fined invertebrate shell fragments, which are absent in the completely recrystallized dolomitic patches. At Warm Spring the type section of the Meadow Valley is divided into two parts by a 30-foot zone of thinly bedded, somewhat pinkish more or less platy ar- gillaceous limestone, the base of which lies 178 feet above the bottom of the member. Above the argilla- ceous zone, through a thickness of about 140 feet, the higher part of the Meadow Valley shows better defined bedding than the lower part of the member, as in places it is rather thinly bedded. The Meadow Valley Member rests conformably upon the brownish silty sand bed which caps the Condor member. At Warm Spring the unit is terminated sharply above by the basal 22-foot light-gray laminated dolomite of Highland Peak unit 7. AGE AND CORRELATION Two small collections made by A. R. Palmer in 1952 and 1953 from the Meadow Valley Member in the Panaca Hills are not sufficiently distinctive for assign- ment to a named faunule. According to Palmer (writ- ten communication, 1955), these collections contain ptychoparioid trilobites and @Zyphaspis. No fossils 48 have been found in the Meadow Valley strata of the northwestern Ely Range. Wheeler's (1948, p. 39-40) correlation of "Highland Peak G" or Meadow Valley Member with the upper part of the Swasey Formation of the House Range, Utah (Deiss, 1938, p. 1133), is con- tingent upon his correlation of the lower part of the Swasey with the Condor, which is improbable. It seems more likely, on paleontologic evidence, that the lower part of the Swasey is of Burnt Canyon age and the upper part of the Swasey roughly equivalent to the Step Ridge Member, rather than the Meadow Valley (pl. 5). UPPER PART OF THE HIGHLAND PEAK FORMATION Of 13 major stratigraphic units representing the Highland Peak Formation in the Ely Range, 6 have been given member names. These comprise the lower part of the formation, crop out over a large area in the productive part of the Pioche mining district, and have withstood the practical test of mappability. The re- maining seven units, which constitute the upper part of the Highland Peak Formation, are well exposed at Warm Spring near Panaca (pls. 2, 6) and in the High- land-Bristol chain but were not recognized in the north- ern part of the Ely Range. These upper divisions have received only cursory stratigraphic study in the Highland Range itself. Because of interpretive differences, the contacts sep- arating the three upper units of the Highland Peak in the Warm Spring measured section of this report do not agree with comparable unit boundaries in the Wheeler and Lemmon (1989) section. To avoid con- fusion it therefore seems appropriate to designate units by number. Table 6 gives the provisional scheme here adopted, in comparison with the Wheeler and Lemmon informal letter designations. Units 10 through 13 agree with divisions M through P of Wheeler and Lemmon. The interval of units 7 through 9 inclusive corresponds to the stratigraphic range of Wheeler and Lemmon divisions H through L, but constituent unit boundaries differ somewhat. The seven units comprising the upper part of the Highland Peak Formation have not all been used as map units; whether they are mappable and worthy of eventual member or formation status remains to be determined. UNIT 7 This unit, which is 310 feet thick (pl. 6) near Warm Spring, includes division H of Wheeler and Lemmon plus the lower part of division I. It is characterized by fine-grained, medium- to dark-gray mottled lime- stone beds, which alternate with dolomite and dolomitic limestone. The dolomite and dolomitic limestone is CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA TaBL® 6.-Stratigraphic units of the upper part of the Highland Peak Formation, Warm Spring, Nev. C. W. Merriam, this report Wheeler and Lemmon Formation (1939) Unit Thickness (feet) 4 Unit 13 125 Highland Peak P © o Unit 12 170 Highland Peak 0 E Unit 11 245 - | Highland Peak N 2 £8 Unit 10 240 Highland Peak M & 32% Highland Peak L 28 hes S 8 Unit 9 840 Highland Peak K E75 Highland Peak J e {is Unit 8 500 Highland Peak I s Unit 7 310 Highland Peak H in part finely laminated, very fine grained, and weath- ers light gray to almost chalky white. On fresh frac- ture the distinctive laminated beds are commonly medium gray tinted slightly pinkish. The laminae are closely spaced, varying from one per millimeter to about 3 per millimeter. The laminated lower 22 feet of the unit is composed mainly of dolomite con- taining small amounts of quartz and calcite." Some dolomite laminae are speckled with finely divided cal- cite." These fine-grained dolomites differ in texture from the coarser saccharoidal types so characteristic of the lower Paleozoic column in this region. The laminated dolomite of unit 7 is similar to that found in the Condor Member, and in units 9 and 13 of the Highland Peak Formation. Similar strata are reported in the Trippe Limestone of Middle Cambrian age at Gold Hill, Utah (Nolan, 1935, p. 12, pl. 5, B.) and in the Lynch Dolomite of Middle(?) and Upper Cambrian age in the Stockton and Fairfield quad- rangles, Utah (Gilluly, 1932, p. 16, pl. 6, C.). Unit 7 of the Highland Peak is conformable with the Meadow Valley Member below and unit 8 above; the relation at both contacts is gradational. Wheeler and Lemmon (1939, fig. 11) have identified rocks of this interval in the Bristol Range. The presence of black chert in the lower part (see below), and the large amount of light-gray laminated dolomite are factors which should facilitate local correlation on a lithologic¢ basis. Absence of fossils obviates correlation with strata in more distant areas. Following is a detailed section of unit 7 of the High- land Peak Formation as measured near Warm Spring: !) Determined by X-ray powder analysis. '" Shown by staining with copper nitrate solution, following the tech- nique devised by Rodgers (1940). UPPER PART OF THE HIGHLAND PEAK Measured section, unit 7 of the Highland Peak Formation near Warm Spring, Nev. Thickness Subunit (feet) Ti. Limestone, dark-gray, mottled ; thinly laminated inter- beds; some laminae and bands are light gray_____- 34 h. Limestone, dark-gray mottled, thin-bedded________-- 38 g. Limestone, dark-gray, well-bedded; alternating with light-gray laminated dolomite____________________ 60 f. Dolomite, light-gray, laminated ; similar to subunit Ta. 39 e. Limestone, dark-gray, mottled, like subunit Te______-- 40 d. Dolomite, light-gray-weathering laminated, similar TOSUDUNIE TA >_ LL soon n cans en 28 c. Limestone, dark-gray mottled, fine-grained ________-_ 3T b. Limestone, medium- to dark-gray, mottled, fine- grained; intercalated light-gray dolomite; black chert. nOdWIOS... ... £.. _> 2. o eee nes iets. 12 a. Dolomite, light-gray-weathering, laminated, of fine grain; color medium gray and pinkish on broken surface az etn L 22 810 UNIT 8 This unit, having a thickness of 500 feet (pl. 6), consists largely of dark-gray, mottled rather thick bed- ded limestone and a few intervals of thinner bedded limestone. Its relation to unit 7 below and unit 9 above is gradational. Unit 8 embraces most of division I and the lower part of division J of Wheeler and Lemmon, both of which were recognized also in the Bristol Range. UNIT 9 This well-bedded unit is 840 feet thick (pl. 6) and comprises dark-gray, mottled, thick-bedded limestones and intercalated thin-bedded laminated dolomite and dolomitic limestone ; the dolomitic strata tend to weather very light gray, providing a strong color contrast. Chert or jaspery silica occurs in at least three zones within the lower 350 feet as follows: (1) A 2-foot bed of light-brownish-gray laminated jaspery matter 50 feet above the base, (2) large concentrically laminated spheroids of dark-gray and black chert weathering brown in a light-gray bed 162 feet above the base, (3) scattered chert nodules about 350 feet above the base. Except for the upper 70 feet of this unit, the dark- gray, mottled limestone predominates greatly over light-gray laminated dolomite or dolomitic limestone, intercalations of which range in thickness from a few inches to about 7 feet. Near the top of the unit, light- colored laminated beds (fig. 15) become so numerous that in the upper 70 feet they constitute about one-third of the rock; nine such beds range from less than 2 feet to 5 feet in thickness. Unit 9 includes most of division J and divisions K and L of Wheeler and Lemmon. Relations to units 8 and 10 of the Highland Peak Formation are grada- tional. Rocks of unit 9 have been recognized in the Bristol Range by Wheeler and Lemmon. 49 FORMATION FIGURE 15.-Flat-pebble mud-breccia pocket in laminated calcitic dolo- mite 95 feet below top of unit 9 of the Highland Peak Formation. Some of the coarser patches and laminae are partly calcitic. Warm Spring measured section northeast of Panaca, Nev. Natural size. Fossils identified by A. R. Palmer from the middle part of unit 9 (basal part of division K of Wheeler and Lemmon ; U.S.G.S. colln. 1808-CO, Warm Spring area) include the distinctive upper Middle Cambrian trilobite Eldoradia. This genus is known from many localities in the Great Basin. Among these localities is the Eureka mining district, Nevada (pl. 5), where it is found in the upper part of the Secret Canyon Shale (Nolan, Merriam, and Williams and others, 1956, p. 16). In the Gold Hill area, Utah, Zidoradia occurs in the upper part of the Trippe Limestone; in the Tintic dis- trict, Utah, it is present in the upper part of the Cole Canyon Dolomite. According to Palmer (in Gilluly, 1956, p. 22, 23) Eidoradia has also been recognized in the lower part of the Abrigo Limestone of southeastern Arizona and in the House Range, Utah, where its hori- zon has not been determined. Presence of in unit 9 indicates that up to the horizon of its occur- rence, the Highland Peak Formation is Middle Cam- brian. Whether some of the overlying beds in this formation are Upper Cambrian has not been ascer- tained. - Palmer concludes that the lowest fossils from the Mendha Formation are well up in the Crepicephalus zone of early Late Cambrian age, and are thus not the oldest fossils of the Late Cambrian to be expected. UNIT 10 This unit, with a thickness of 240 feet (pl. 6), consists of medium- to fine-grained dark-gray, mottled, thick- 50 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA bedded limestone, which lacks the light-gray laminated interbeds. It is gradational with unit 9 below and with unit 11 above, and corresponds to division M of Wheeler and Lemmon. UNIT 11 This unit is almost entirely dolomite (pl. 6), differ- ing in this respect from all others in the upper part of the Highland Peak Formation. One measured section 245 feet thick consists of a lower dark-gray mottled, mostly saccharoidal, thick-bedded dolomite 198 feet thick and an upper light-gray saccharoidal dolomite 47 feet thick. Another section of unit 11 measured only 110 feet. The difference may be due to unrecognized faults or to dolomitization having affected only the lower part of the unit. Theoretically, undolomitized carbonate rock of unit 11, like undolomitized Burrows Member, could well be a fine lithographic limestone in- distinguishable from the lithographic limestone of over- lying unit 12. Division N of Wheeler and Lemmon corresponds to this unit. UNIT 12 Unit 12 is about 170 feet thick in the measured Warm Spring section (pl. 6) and consists of fine-grained, por- cellaneous or lithographic limestone ranging from white and light gray to dark gray. Locally it exhibits a faint pinkish staining. The beds are rather thick. The limestone of this division resembles white limestone of the Lyndon and is similar to the undolomitized litho- graphic facies of the Burrows Member. Unit 12 is con- formable with underlying and overlying units. Unit 12 corresponds to division O of Wheeler and Lemmon, and has been recognized also in the Bristol Range. UNIT 13 Unit 13 comprises dark-gray, mottled saccharoidal dolomite, fine-grained medium- to dark-gray limestone, and light-gray laminated fine-grained dolomite like that in units T and 9. No true thickness can be given as this division is faulted in the measured section (pl. 6) ; it is believed to be at least 125 feet thick. Follow- ing is the order of beds in the measured section, partly repeated in a fault block to the east at the top of the column : Thickness Top. (Jeet) Dolomite, dark-gray, mottled, sugary, blocky-weather- AME A La LC s te il bek ar c os ae anenil sede 60 Limestone, medium- and light-gray thick-bedded, fine- grained; interbeds of light-gray, laminated dolomitic limestone 1. 2. c. secs SO cube 37 Limestone, fine-grained, medium- to dark-gray, with inter- beds of fine white-weathering dolomitic limestone hav- ing pinkish Linge 00 LU 28 125 Unit 13 corresponds to division P of Wheeler and Lemmon, recognized also by them in the Bristol Range. UPPER CAMBRIAN AND LOWER ORDOVICIAN ROCKS Strata of Late Cambrian age are represented in the Ely Range by a small outlier at Step Ridge (pl. 1). This occurrence has been discussed above under Geo- logic Structure. - Rocks of the same interval are present to the west in Arizona Peak (pl. 2), where they were described by Westgate and Knopf (1932, p. 13) as Mendha limestone, named for the Mendha mine. As now understood the Mendha type area includes beds of both Early Ordovician and Late Cambrian age. Until the structurally complex Arizona Peak area is mapped in detail geologically, a satisfactory differentiation of these rocks is not possible. Eventually it may be ex- pedient to establish new formations and treat the Mendha as a group. In this report the strata in ques- tion are referred to as the Mendha Formation of Late Cambrian and Early Ordovician age. It is probable that the Mendha Formation extends eastward beneath valley alluvium and volcanic rocks between the east spur of Arizona Peak and the Ely Range. Limestone pieces in fault breccia near The Point (pl. 3) suggest a facies of the Mendha lithologi- cally, but unlike the occurrence at Step Ridge, have yielded no fossils. Geologic mapping by Merriam and Proctor at the Highland Queen mine in 1945 pointed up the structural and stratigraphic complexity of the Arizona Peak vicinity, and fossils collected in that area by A. R. Palmer show that Ordovician as well as Late Cambrian strata are represented. MENDHA FORMATION The original definition of the Mendha given by West- gate and Knopf (1932, p. 13) is as follows: The Mendha limestone, named from the Mendha mine, on the west side of Arizona Peak, which is entirely composed of these rocks, includes nearly 2,000 feet of limestones and dolomites which lie with apparent conformity above the Highland Peak limestone. The formation is not seen in normal position under the Ordovician, as the contact with the Ordovician is every- where a fault contact. If, in keeping with the original definition, Arizona Peak is the type area, the Mendha Formation may now be interpreted as comprising not only a lithologically diverse and rather complex sequence of Upper Cam- brian rocks, but strata of Early Ordovician age as well. LITHOLOGY AND STRATIGRAPHIC RELATIONS The contact between the Mendha and the Highland Peak Formation is not exposed at Arizona Peak. UPPER CAMBRIAN AND LOWER ORDOVICIAN ROCKS 51 Farther south along the east slope of the Highland Range the two are reported to be conformable (West- gate and Knopf, 1932, p. 13). The lower beds of the Mendha are described as follows by Westgate and Knopf: The basal beds of the Mendha formation are thin-bedded gray limestones, in places stained yellow or rusty-red on weathering, which in the hand specimen are rather coarsely crystalline, locally oolitic and rusty-specked. They contain abundant fossil debris, almost wholly fragments of trilobites, most of which are specifically unidentifiable. By reason of their contrast with the underlying Highland Peak limestone these beds mark an easily recognizable horizon, which has helped greatly in working out the structure of the main Bristol-Highland Range. South of Dead Deer Canyon, Westgate and Knopf measured a section across the lower part of the Mendha, as quoted below : Feet White massive dolomite in beds as much as 8 feet thick. The beds show close-spaced parting planes but break info large DIOGkS .. - 1 -L __ uso ll nnn oin eee ee Ue eles. 85 Gray limestone, thinly parted, making the lower part of the cliff at the top of the hill. Layers throughout more or less oolitic and mottled. White chert in sheetlike lenses is found from the base Up-___________________- Thin sandstones and layers of alternating sandstone and limestone, weathering to flat rusty debris____________. 10 285 Gray thick-bedded erystalline limestone______________-_ 230 Gray limestone, some beds 5 feet thick, most of it crystal- tine, oolitic and mottled 220 Gray, rather thick-bedded limestone, 60 feet thick, passing up into well-bedded limestone in beds 1 or 2 feet thick. Layers commonly oolitic, rarely conglomeratic and yellow streaked. - Breaks down easily into slaty debris. _ 165 945 As at present understood the Mendha embraces at least seven principal lithologic divisions; three of these are limestones and four are dolomites. The lowest unit is a limestone of Late Cambrian age above which ap- parently follows the sequence of four dolomite units. A second Upper Cambrian limestone overlies the dolomite sequence. Stratigraphic relations of the Lower Ordo- vician limestones are unknown, for they occupy an inlying belt of fault-bounded rocks. Limestones of the lower part of the Mendha Forma- tion are exposed about 1 mile southeast of the Mendha mine. They crop out on a northwest-trending spur half a mile northeast of the mine and at various points northwest of Arizona Peak. At the Highland Queen mine in Sheridan Canyon, the lower part of the Mendha includes brownish-weathering medium- to fine-grained medium- to light-gray limestone resembling the white limestone of the Lyndon. This rock, which is similar to the Lyndon Limestone, is mottled with limonitic spots or patches, exhibits a pinkish staining and con- tains a small amount of chert. Argillaceous shale inter- beds of light tan to greenish color in this predominantly limestone unit resemble Chisholm Shale, with which they have been confused. Near the Highland Queen, these older Upper Cambrian limestones appear to be overlain normally by medium- and light-gray, mottled dolomites. A drill hole (Stone, J. B., in Wheeler and Lemmon, 1939, p. 43-44) in this area disclosed several hundred feet of limestone with oolitic facies and red- dish-brown shale partings. The unexposed beds may represent lower, partly oolitic Mendha, like that near Dead Deer Canyon described by Westgate and Knopf. Dolomites are present at the Mendha mine on the west side of a north-south fault. - The higher part of Arizona Peak is also dolomite, which is estimated to be more than 600 feet thick. On the south side of hill 7771 (in the Highland Peak quadrangle) three-quarters of a mile south of the Arizona Peak summit, the dolomite sequence comprises four lithologic divisions in the following stratigraphic order : 4. Light-gray dolomite (capping hill 7771) 3. Dark-gray cherty dolomite 2. Mottled light- and medium-gray thick-bedded dolomite 1. Dark-gray dolomite The lower dark-gray dolomite contains concentrically laminated stromatolites or algal bodies, some of which have diameters of several inches. Brachiopod frag- ments and EZyolithes occur in mottled beds of unit 2. In unit 3, chert lenses and nodules are more abundant than in any of the cherty units of the Highland Peak Formation with which it might be confused. The youngest fossil-dated Cambrian limestones rec- ognized crop out on the west slope of Arizona Peak south of the Highland Mary mine and cap hill 7569 a mile southwest of the summit of Arizona Peak. Whereas these beds resemble limestones beneath the dolomite sequence, of hill 7771, latest Cambrian trilo- bites identified by A. R. Palmer as Zurekic and Dikelo- cephalus suggest that they are younger. Moreover, on hill 7569 these younger limestones conformably overlie dolomites probably equivalent to those of hill T771. Strata of Early Ordovician age occur east of the Mendha mine and extend southeast to the Highland Mary mine. Consisting of well-bedded fossiliferous fine-grained bluish gray cherty limestones, these iso- lated Ordovician strata are separated by north-south faults from dolomites at the Mendha mine and from the main Arizona Peak dolomite body to the east. Their stratigraphic relations to the latest Cambrian limestones are obscured by a disturbed zone paralleling the road to the Highland Mary mine. MENDHA OUTLIER AT STEP RIDGE Jumbled limestone blocks occur with red gougy matter in a breccia on the west side of Step Ridge (pl. 52 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA 1, loc. 17) ; the larger blocks are several feet long. Sur- rounding and presumably underlying the breccia is unit b of the Middle Cambrian Step Ridge Member of the Highland Peak Formation. According to A. R. Palmer, fossils in the breccia blocks are of Late Cam- brian (Dresbach) age and strongly suggest derivation from the Mendha. Stratigraphic separation between the horizon of the Dresbach faunule and unit 5 of the Step Ridge would normally be of the order of 3,000 feet. As discussed under geologic structure these out- lying blocks are believed to represent a possible upper plate thrust remnant. Fossiliferous limestones of the breccia blocks are medium dark gray, very fine textured, and contain argillaceous inclusions and reddish-brown to tan mot- tlings. Some limestone blocks have a dull, chalky red- dish-tan laminar incrustation of caliche where exposed to weathering. Oolites are present but uncommon in these breccia limestone blocks. AGE AND CORRELATION Fossils indicate that the rocks described as Mendha Formation range in age from early Late Cambrian to Early Ordovician. A. R. Palmer reported early Late Cambrian trilobites of the Crepicephalus zone in limestones near the High- land Mary mine, and at a locality about 1 mile south- southwest of the summit of Arizona Peak. Between this summit and hill 7203, half a mile northeast, Elvinia occurs in shale layers in limestone. These Elvinia-bearing strata are probably correlative with Dunderberg Shale of Eureka, Nev. (Nolan, Merriam, and Williams, 1956, p. 19), which is of early to middle Late Cambrian age. Limestones with Zurekia occur in the upper part of the Mendha on the west slope of Arizona Peak. The Eurekiq-bearing strata are uppermost Cambrian, cor- relative with Windfall Formation, which overlies the Dunderberg at Eureka, Nev. Fossils from the Mendha outlier on Step Ridge (pl. 1, loc. 17) are of early Late Cambrian (Dresbach) age and include the trilobites Aphelaspis sp., Glaphyraspis sp., and Coosina sp. A. R. Palmer (written communi- cation, 1955) referred to collections from this locality as follows: All except one piece of rock contain abundant specimens of Aphelaspis sp., and G@laphyraspis sp., both widespread guides to the latest Dresbach. The presence of Glaphyraspis further in- dicates the very basal part of the Aphelaspis zone. This agrees well with a single piece of slightly oolitic limestone with a cranidium of Coosin@ sp., the characteristic guide to the beds immediately preceding Aphelaspis. These collections should have come from the interval above the sublithographic oolitic limestones of the lower part of the Mendha and below or as- sociated with the thin interval of succeeding sandy beds. Lower Ordovician fossils of the Mendha at Arizona Peak were submitted to R. J. Ross, Jr., of the Geological Survey, who provided the following report : All these are of early Early Ordovician age. I am unable to give ages of the collections relative to one another, which would be desirable in a structurally complex area. All four are cor- relative with the interval zones A-D [Ross, R. J., Jr., 1951] of the Garden City Formation. The presence of Kainella suggests zone D, but in Nevada this genus may range lower than else- where. Locality 39 (APN-1-54), southwest slope of Arizona Peak near Highland Mary mine, altitude about 7,400 feet. Symphysurina sp. (rounded genal angle) Syntrophid brachiopod Locality 40 (APN-2-54), near top of southwest spur of Ari- zona Peak northwest of Highland Mary mine, in noncherty limestone. Apheoorthis? sp. Nanorthis? sp. sp. Kainella sp. Hystricurus sp. Locality 41 (APN-4-54), west end of southwest-trending spur one-quarter of a mile west-southwest of Highland Mary mine. Same fauna and lithology as Locality 40. Locality 42, west side of Arizona Peak, 200 yards west of Highland Mary mine. Leiostegium? sp. Symphysurina sp. Nanorthis sp. Lower Ordovician cherty limestones provisionally included with the Mendha are correlative with the Goodwin Limestone of the Eureka, Nev., region. The Goodwin (Nolan, Merriam, and Williams, 1956, p. 25- 27) is the lowest formation of the Pogonip Group. Like the Ordovician part of the Mendha, it contains abundant chert, which tends to be light gray or white. However, cherts of the Lower Ordovician beds at Arizona Peak differ in being dark gray or black. In the section given by Westgate and Knopf south of Dead Deer Canyon the higher cherty limestone includes lenses of white chert reminiscent of the Goodwin. LOCALITY REGISTER Important localities in the Ely Range and Arizonia Peak to which reference is made. (See pls. 1, 2 and 3) Locality No. 12____ Pioche Shale, A-shale member, Albertelle collections. One mile southeast of The Point on crest of ridge near trail and near Evans mine. Altitude 6,359 ft. 13-___ Pioche Shale, D-shale member, Olenellus collections. Half a mile southeast of Ely Valley mine, near Gar- rison mine. Alt 6,480 ft. 14____ Pioche Shale, D-shale member, Olenellus collections. Three-fourths mile southeast of Ely Valley mine, near Gold Eagle mine. Alt 6,450 ft. 15.___ Pioche Shale, D-shale member, Olenellus collections. One mile southeast of Ely Valley mine, 600 ft north of West End mine. Alt 6,850 ft. 11.2" 18... 19... 20-:.>._ PL.... a 23.... 24-.. 23°... 20°... 2742.3 28... $12... 33-___ S415. 80... S1--: 38... _L LOCALITY REGISTER Chisholm Shale fossil collections in saddle. On Tank Ridge 400 ft southwest of Pioche No. 1 shaft. Upper Cambrian fossil locality, outlier of Mendha For- mation. West side Step Ridge three-fourths of a mile west of Pioche No. 1 shaft. Jumbled blocks of fos- siliferous limestone may represent remnant of thrust sheet. Burnt Canyon Member of Highland Peak Formation, fossil-bearing shaly bed. West side Tank Ridge near head of Churndrill Valley. Pioche Shale, Combined Metals Member with fossils. Pioche Divide section. Pioche Shale, D-shale member with Olenellus. Pioche Divide section. Pioche Shale, Susan Duster Limestone Member with fossils. Near edge of road in Pioche Divide section. Burnt Canyon Member of Highland Peak Formation, fossil-bearing shale bed. Northeast side Lime Hill near tramline. Prospect Mountain Quartzite, Scolithus bed. Southeast side Lookout Hill. Alt 6,340 ft. Prospect Mountain Quartzite, Scolithus bed. West side Treasure Hill, 1,300 ft southeast of Pioche Divide. Alt 6,620 ft. Burnt Canyon Member of Highland Peak Formation, fossil-bearing shaly beds. Near road 1,350 ft south- east of top of Gray Cone. Alt 5,925 ft near measured section D-D'. Upper part of Peasley Member of Highland Peak Forma- tion; 1,200 ft northwest of Pioche No. 1 shaft. Alt 6,500 ft. Upper part of Peasley Member of Highland Peak Forma- tion. Buehler Gulch, half a mile north of Caselton. Alt 6,520 ft. Upper part of Peasley Member of Highland Peak Forma- tion. East side Slaughterhouse Gulch, 3,000 ft north- west of Pioche No. 1 shaft. Alt 6,480 ft. Undulating Peasley-Burrows contact. Mouth of Buehler Gulch. Undulating Peasley-Burrows contact. Mouth of Buehler Gulch. Undulating Peasley-Burrows contact. Lime Hill. Peasley-Burrows contact. East side Churndrill Valley 1,300 ft southwest of Pioche No. 1 shaft. Alt 6,370 ft. Lower part of Burnt Canyon Member of Highland Peak Formation ; 2,000 ft northwest of Pioche No. 1 shaft. Alt 6,780 ft. Lower part of Burnt Canyon, Member of Highland Peak Formation. Near head of Buehler Gulch 1,400 ft east of Abe Lincoln mine. Alt 6,960 ft. Lower part of Burnt Canyon Member of Highland Peak Formation. On Tank Ridge 1,250 ft west of Pioche No. 1 shaft. Lower part of Burnt Canyon Member of Highland Peak Formation. West side Tank Ridge near head Churn- drill Valley on east side. Alt 6,760 ft. Burnt Canyon Member of Highland Peak Formation with edgewise limestone conglomerate. On Tank Ridge 1,400 ft west of Pioche No. 1 shaft. Burnt Canyon Member of Highland Peak Formation with edgewise limestone conglomerate. Near head Churndrill Valley. West of Southeast side 53 39____ Lower Ordovician beds. Peak near Highland Mary mine. (APN-1-54). Symphysurina. 40____ Lower Ordovician beds. Near top of southwest spur of Arizona Peak northwest of Highland Mary mine, Southwest slope of Arizona Alt about 7,400 ft in noncherty limestone (APN-2-54). Kainella, Symphysurina. 41____ Lower Ordovician beds. At west end of southwest- trending spur a quarter of a mile west-southwest of Highland Mary mine, Arizona Peak (APN-4-54). Same lithology and fauna as loc. 40. 42____ Lower Ordovician beds. On west side of Arizona Peak, 600 ft west of Highland Mary mine. Symphysurina. 48____ Churndrill hole No. 2, Combined Metals Reduction Co.; 1,400 ft northeast of Prince shaft. U.S. Geological Survey fossil localities, Ely Range and High- land Range, Nevada USGS 1213-CO, Ely Range, Warm Spring measured section near Panaca. Meadow Valley Member of Highland Peak Formation, probably above middle. Ely Range, Warm Spring measured section. Meadow Valley Member of Highland Peak Formation, near top. Pioche Divide section, Combined Metals Mem- ber of Pioche Shale, subunit 2, about 10 ft above base of member. Lower Cambrian faunule with Olenellus gilberti. Pioche Divide section, Combined Metals Mem- ber of Pioche Shale, subunit 5, about 3 ft below top of member. Lower Cambrian faunule with Olenellus gilberti and Paede- umias clarki. Pioche Divide section, lower 3 ft of Susan Duster Limestone Member of Pioche Shale. Middle Cambrian Atrotocephalus-Mezxicella faunule. Pioche Divide section, near top Susan Duster Limestone Member of Pioche Shale. Middle Cambrian Poliella faunule. Pioche Divide section, basal limestone of A- shale member of Pioche Shale. Middle Cam- brian faunule with Kochaspis and Poliella. Pioche Divide section, 40 to 50 ft below top of exposed part of A-shale member of Pioche Shale. Middle Cambrian with Plagiura. lower north slope of Mount Ely near Gold Eagle mine, about 4,000 ft southeast of the Ely Valley mine. Lower Cambrian Olenellus fremonti-O. bristolensis faunule. lower north slope of Mount Ely about 5,000 ft southeast of the Ely Valley mine, near West End mine. In upper part of subunit 5 of Combined Metals Member of Pioche Shale. Lower Cambrian faunule with Olenellus gilberti and Paedeumias clarki. Silicified larval trilobites. Highland Range, south side of Burrows Can- yon. Chisholm Shale 8 ft above base. Pioche Shale, A-shale member with Albertella. Same as loc. 12. 1214-CO, 1391-CO, 1392-CO, 1393-CO, 1394-CO, 1395-CO, 1396-CO, 1398-CO, 1399-CO, 1403-CO, 1405-CO, 54 CAMBRIAN ROCKS OF THE PIOCHE MINING DISTRICT, NEVADA 1406-CO, west side Ely Range on dump of Abe Lincoln mine. Chisholm Shale. 1407-CO, west side Ely Range on dump of Half Moon mine. Chisholm Shale. 1408-CO, Ely Range, east side of Lime Hill. Shale. 1410-CO, Ely Range, east side of Lime Hill on dump of prospect pit. 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Peking Press, 680 p. Hague, Arnold, 1883, Geology of the Eureka district, Nevada: U.S. Geol. Survey Ann. Rept. 3, p. 237-290. 1892, Geology of the Eureka district, Nevada : U.S. Geol. 'Survey Mon. 20, 419 p. Hewett, D. F., 1956, Geology and mineral resources of the Ivan- pah quadrangle: U.S. Geol. Survey Prof. Paper 275, 172 p. Howell, B. F., and Mason, J. F., 1938, Correlation of Middle Cambrian faunas of North America: Jour. Paleontology, v. 12, p. 295-297. Howell, E. E., 1875, Report on the geology of portions of Utah, Nevada, Arizona, and New Mexico : U.S. Geog. Geol. Survey, W. 100th Meridian (Wheeler), v. 3, p. 227-301. Humphrey, F. L., 1945, Geology of the Groom district, Lincoln County, Nevada : Univ. Nevada Bull., v. 39, no. 5 (Geol. and Mining Ser. no. 42), 53 p. Knopf, Adolph, 1932, Part 2. Economic geology, in Westgate, L. G., and Knopf, Adolph, Geology and ore deposits of the Pioche district : U.S. Geol. Survey Prof. Paper 171, p. 45-75. Lindgren, Waldemar, and Loughlin, G. F., 1919, Geology and ore deposits of the Tintic mining district, Utah: U.S. Geol. Survey Prof. Paper 107, 282 p. Longwell, C. R., 1952, Lower limit of the Cambrian in the Cordilleran region: Washington Acad. Sci. Jour., v. 42, no. 7, p. 200-212. Lowenstam, H. A., 1950, Niagaran reefs of the Great Lakes area : Jour. Geology, v. 58, no. 4, p. 430-487. Mason, J. F., 1936, Communication quoted in Grabau, A. W., Paleozoic formations in the light of pulsation theory, v. 1, Lower and Middle Cambrian pulsations : 2d ed., Natl. Univ. Peking Press, p. 274-276. 1938, Cambrian faunal succession in Nevada and Cali- fornia : Jour. Paleontology, v. 12, p. 287-294. McKee, E. D., 1945, Cambrian history of the Grand Canyon region : Carnegie Inst. Washington Pub. 563, 168 p. Nolan, T. B., 1929, Notes on the stratigraphy and structure of the northwest portion of Spring Mountain, Nevada: Am. Jour. Sci., 5th ser., v. 17, p. 461-472. 1935, The Gold Hill mining district, Utah: U.S. Geol. Survey Prof. Paper 177, 172 .p. Nolan, T. B., Merriam, C. W., and Williams, J. S., 1956, The stratigraphic section in the vicinity of Eureka, Nevada: U.S. Geol. Survey Prof. Paper 276, 77 p. Pack, F. J., 1906a, Geology of Pioche, Nevada and vicinity : Columbia Univ., School of Mines Quart., v. 27, p. 285-312, 365-386. 1906b, Cambrian fossils from the Pioche Mountains, Nevada : Jour. Geology, v. 14, p. 290-302. Palmer, A. R., 1954, An appraisal of the Great Basin Middle Cambrian trilobites described before 1900 : U.S. Geol. Survey Prof. Paper 264-D, p. 55-86. 1956, The Cambrian system of the Great Basin in western United States, in Rodgers, John, ed., El Sistema Cambrico, su paleogeografia y el problema de su base-symposium, Pt. 2: Internat. Geol. Cong., 20th, Mexico, D.F., 1956, p. 663-681. 1957, Ontogenetic development of two olenellid trilobites : Jour. Paleontology, v. 31, no. 1, p. 105-128. 1958, Morphology and ontogeny of a Lower Cambrian ptychoparioid trilobite from Nevada : Jour. Paleontology, v. 32, no. 1, p. 154-170. Park, C. lF., Jr., Gemmill, Paul, and Tschanz, C. M., 1958, Geologic map and sections of the Pioche Hills, Lincoln County, Ne- vada: U.S. Geol. Survey Mineral Inv. Field Studies Map MF 136. Pettijohn, F. J., 1949, Sedimentary rocks: New York, Harper and Brothers, 526 p. Prescott, Basil, 1926, The underlying principles of the limestone replacement deposits of the Mexican province: Eng. Mining Jour., v. 122, no. 7, p. 246-253; no. 8, p. 289-296. Rasetti, Franco, 1951, Middle Cambrian stratigraphy and faunas of the Canadian Rocky Mountains: Smithsonian Misc. Colln., v. 116, no. 5, 277 p. Resser, C. E., 1935, Nomenclature of some Cambrian trilobites : Smithsonian Misc. Colln., v. 93, no. 5, p. 1-46. 1937, Third contribution to nomenclature of Cambrian trilobites: Smithsonian Misc. Colln., v. 95, no. 22, p. 1-29. REFERENCES CITED 55 Resser, C. E., 1942, Fifth contribution to nomenclature of Cam- brian fossils: Smithsonian Misc. Colln., v. 101, no. 15, 58 p. Riccio, J. F., 1952, The Lower Cambrian Olenellidae of the southern Marble Mountains, California: Southern Cali- fornia Acad. Sci. Bull., v. 51, pt. 2, p. 25-49. Rodgers, John, 1940, Distinction between calcite and dolomite on polished surfaces: Am. Jour. Sci., v. 238, no. 11, p. 788- 798. ' + Ross, R. J., Jr., 1951, Stratigraphy of the Garden City formation in northeastern Utah, and its trilobite faunas; Peabody Mus. Nat. History, Yale Univ. Bull. 6, 161 p. Sharp, R. P., 1942, Stratigraphy and structure of the southern Ruby Mountains, Nevada : Geol. Soc. America Bull., v. 53, p. 647-690. Trengove, R. R., 1949, Investigation of Comet Coalition lead- zine deposits, Lincoln County, Nevada: U.S. Bur. Mines, Rept. Inv. 4541, 6 p., 8 figs. Walcott, C. D., 1884, Paleontology of the Eureka district, Nevada : U.S. Geol. Survey Mon. 8, 298 p. 1886, Second contribution to the studies on the Cambrian faunas of North America : U.S. Geol. Survey Bull. 30, 369 p. 1888, Cambrian fossils from Mt. Stephens: Am. Jour. Sci., 3d ser., v. 3, p. 161-166. 1891, Correlation papers; Cambrian: U.S. Geol. Survey Bull. 81, p. 317. 1908a, Cambrian geology and paleontology ; no. 1, Nom- enclature of some Cambrian Cordilleran formations: Smithsonian Misc. Colln., v. 53, p. 1-12. 1908b, Cambrian geology and paleontology; no. 5, Cam- brian sections of the Cordilleran area: Smithsonian Misc. Colln., v. 53, p. 167-230. Walleott, C. D., 1912, Cambrian Brachiopoda : U.S. Geol. Survey Mon. 51, Part I, 872 p. 1915, The Cambrian and its problems in the Cordilleran region, in Problems of American geology : Yale Univ. Press, New Haven, p. 162-233. 1916a, Evidences of primitive life: Ann. Rept. 1915, p. 235-255. 1916b, Cambrian Trilobites: v. 64, no. 5, p. 409-410. Westgate, L. G., and Knopf, Adolph, 1927, Geology of Pioche, Nevada and vicinity: Am. Inst. Mining and Metall. En- gineers Trans., v. 75, p. 816-836. 1932, Geology and ore deposits of the Pioche district, Nevada: U.S. Geol. Survey Prof. Paper 171., TO p. Wheeler, H. E., 1940, Revisions in the Cambrian stratigraphy of the Pioche district, Nevada: Univ. Nevada Bull., v. 34, no. 8 (Geology and Mining ser. no. 34), 42 p. 1947, Base of the Cambrian system: Jour. Geology, v. 55, no. 3, pt. 1, p. 153-159. 1948, Late pre-Cambrian - Cambrian stratigraphic cross section through southern Nevada: Univ. Nevada Bull., v. 42, no. 3 (Geol. and Mining ser. no. 47), 61 p. Wheeler, H. E., and Lemmon, D. M., 1939, Cambrian formations of the Eureka and Pioche districts, Nevada : Univ. Nevada Bull., v. 33, no. 3 (Geol. and Mining ser. no. 31), 60 p. White, C. A., 1877, Report upon geographical and geological ex- plorations and surveys west of the one-hundredth meridian : v. 4, pt. 1, paleontology, 219 p. Young, E. B., 1948, The Pioche district [Nevada], in Dunham, K. C., ed., Symposium on the geology, paragenesis and re- serves of the ores of lead and zinc: Internat. Geol. Cong., 18th, London, p. 98-106. Smithsonian Inst. Smithsonian Misc. Colln., A Page A-shale member, Pioche Shale.... .. ® 23 lithology and stratigraphic relations.. ._.. 23 23 oolitic zone.... 24 ore in limestones. 24 thickNess..-....-....._.__.~ 23 upper fossil zone............ 24 Abercrombie Formation. 33 Abrigo 49 Acknowledgments..._._.._.____.___._________.. 5 Acrothele sp...... - 26, 27 ccc ell one sooo. 26, 27 22s. c xas .o cuss o cre oh amnackics 26, 27 faunule.. 27 .~. JL .%. 200 dc oen enc cal an 27 e: acer ae oben ca nich an one nik ae 25 Alliance mine.. 23 A- coc cecal cuck m 13 DOOR EYEE -e - clench iss aoc news 32, 33 piochense. R 33 222... 0-000 cone eins ona on ias 32, 33 -. cuses 33 Alteration, hydrothermal 20 MDS MiRG:2 122... cre Seve es 7,9, 14 oo coon one See ced ces 26 Apheoorthis sp. 52 Aphelaspis sp R 52 Arizona Peak.... 50, 51, 52 important localities 3 52 Arrojos Formation. & 27 Afhabaskin Rowellt 33 B Bare Mountain, Nev.. 13 Blige Eagle 31 B-shale member, Pioche Shale................ 22 lithology and stratigraphic relations.. ._.. 22 c. lloc oe. 22 020. coon e nannies 22 Basal sandstone marker. . & 23 Base-metal mining. . z 2 Bibliography........ & 64 Black Davidson lime y 33 Blue Davidson lime... oice c Blue limestone marker. yar 23 Bluebird structure................ 37, 39, 40, 41, 43, 46 Bright Angel Shale of Grand Canyon.. -+- 12,88 a 33 Bristolin bristolensis.. ...... .. 26 PROCNE, 1-208 r 2222002 10. 2T OS i ode 26 Bristol Silver 46 Burnt Canyon Member, Highland Peak For- mabton.....-.....2..._..s00 34, 36, 40, 41 age and correlation.... 43 lithology and stratigraphic relations.. ._.. 42 name and occurrence. ........_______.___.. 41 22-2 00000002. 0,000 0.0 Cian eau l+ 42 Burrows 5 INDEX [Italic page numbers indicate major descriptions] Page Burrows Member, Highland Peak Formation. - 29, 34, 36, 50 age and correlation......._.._____._____.. 41 dolomitization......._..... 40 name and OCCUFFeNC@.._..__.____......... 36 SithOI08Y 2. [uc tc coon ce Eul oer eous 37 stratigraphic relations. 39 L CEIC O onl eevee neer hane 37 C C-shale member, Pioche Shale.............~.. 21 lithology. -: :.... cs ss 21 occurrence. R 21 thickness.... s 21 Cadiz Formation_........_........ 2ut98 Cambrian and Ordovician rocks._............ 50 Cambrian founuiles.. 25, 26 Cambrian rocks, eastern Great Basin......... 12 stratigraphic column .........__.....___.. 8 Cambrian System, relation to theoretical base. 18 Caselion 18, 20, 41, 47 Cathedral 27 Cave Valley, Prospect Mountain Quartzite . . 10 'Ohigholmm 31 Chisholm 4,12, 81 age and correlation. ..... ax 32 AS AN OTe -L concen cornea cocks 32 lithology and stratigraphic relations.. .... 32 name and occurrence.........._....._---- 31 Shick 1088, :>. 22. LUXE Lect ema arene 32 Ohurndrill Valley :-. 40, 42, 43, 45 Cole Canyon Dolomite..............._.......- 49 Combined Metals Member, Pioche Shale.... 4, 14, 17, 18, 21, 26 lithology and stratigraphic relations. ..... 18 name and OCCUrreNcée.....___...__..._---- 18 Of - e. Acier ea rel bau bes 20, 21 thickness.... a 18 Oaselton sic" 20 Combined Metals Reduction Co - 8, 16, 18 Comet 3 5 Comet mine..... f 5 Comet :- 2 ee g. Peanut. 14, 17 Condor Member, Highland Peak Formation. _ 34, 44, 45, 46, 48 age and correlation............ Coe . CHOE .L: Ee DEET cheat 46 lithology and stratigraphic relations....... 45 name And OCCUrrence....... . ..____.__.__. 45 ripple marking.. 10, I0 46 Sickness ©... 12.1 CL. 91 Lec 45 WOrBLCASMNES-L n .e. ccc 46 (COOSIRA SD: . . .n EEA ec ce nene naa eres 52 Conglomerate, edgewise limestone............ 47 Crasstfimbra wileoi. :: 0. 22 21. 26 re eee eed doe e ioo o oue ee epe 26 Crepicephalus tohne......_c......l.ll.ccl.icclls 49, 52 D Page D-shale member, Pioche Shale................ 17 lithology and stratigraphic relations. . .... 17 OCCUFTONOS..... 17 $hickHes§: .. «.-- ells core conc renee 18 Detljohn 31 Dictyontnia gp... ...l cu. icin coves ows 26 'Dikelocephaltts .> .--. oe cue ee ou 51 Dikes, #4 2 porphyritic granite. . F 2 "Diraphord. \ v0.22. [ac eous .l eevee do 26 §D. /.. l e- icu Tee boner sean 26, 33 Dolomite, laminated 46, 47, 48, 49, 50 Dolomitization : 2.21. coll. cence eedee 40 HAECNCNIC- ~.. : oc neo- nu 40, 41 fissure-fed..._....- sA. 42 hydrothermal: .~. ......... .._ ST 13, 40 Dolomitization of the Burrows Member...... 40 Dolomitization of the Burnt Canyon Member. 42 Drilling, 0220. 4,5 Dunderberg Shale.... 52 E :s. 20.0. . +0020. uus ue uae oe aes a 49 Eldorado Dolomite... - 31,39 BIMIMIL . ous 1.2 coon 2020008 Pue uk bee uis ie aie we wet 52 Ely Range.....--- --- 2, 4,5, 8, 14, 28 fossil ..... 53 geologic structure.. 6 important localities... 52 Meadow Valley strata....... 48 Prospect Mountain Quartzite...._....... 9,11 Ely Valley mine..._...........- 9, 11, 17, 18, 20, 22, 27 Eocrinus longidactylus....._...____.._____.____. 33 Eureka district, Nevada...___.._.__.____....-- 34, 49 2. couche oo ne nece una pene 51 F Faults, normal. ..... use 7 $HMISE. . .. 2. 2. 2120. 400 cous rls haunt ne 7 Pielduspls sp...... ...... 02000330 27 Fissure veils. .-..... . 2 Flotation process. 00.0. IEE 2 Forlorn Hope ming................ 5, 15, 18, 21, 22, 290 Forlorn Hope shale.. c.... c. 14,17 Fossils, A-shale member, Pioche Shale........ 23, 27 Bright Angel 13 C-shale member, Pioche Shale.... ..... 21, 25, 26 Combined Metals Member, Pioche Shale. _ 20, 25, 26 D-shale member, Pioche Shale. 22,25 Highland Peak Formation................ 49 Johnnie Formation.................._.... 13 Lower Cambrian strata . 9, 12, 13, 14, 25 Meadow Valley Member................. 47 Mendhba Formation... .. 8, 51, 52 Ophir Shale: , .. 12 Ploche shale 4, 11, 13, 16, 17, 25 Prospect Mountain Quartzite_.._....... 11 Susan Duster Limestone Member........ 22, 25 57 58 Page Fr tio fr ti 26 Fremontia fremonti-Bristolia bristolensisfaunule. . 25 a (GATHISON MING. . 23 se uals re eee eed eles 11 Gelder mine...... wass 18 Geologic map units...............~ 8 Geologic structure of the Ely Range.. 5 GirBARENE -}-» um 20, 28, 32, 41, 42 Glaphyraapza SDE scant neues 52 a ___ 13, 43 DOMAIN a onne nne 32, 33 CIJDROSDIEE. I< ECL IL- ec cess ades sul 47 been cines St eek 33 Golden Eagle mine... ... 41,47 Gold Eagle niing............_...__Q___..._ 11,18, 26 GOC HUNINE. L.-. coleen 2 Goodwin Limestone. 52 Gray Davidson lime...................._.._... 33 9 H Half Moon 31 8D. - ol ele ne dele sien 27 Highland-Bristol chain.................... 2, 4, T, 48 Prospect Mountain Quartzite . _._.___.... 12 Highland Mary mine............_.__._____... 51, 52 Highland Peak Formation........... 8 13, 28, 83, 49 IOWOF PATEL 85 UDDOF DATE LAL ALTAR eee bea cence 48 (AMIE versus ae as bene 48 MIE EAE EU- n ucc 49 NDI Y- EL 49 NIE IO SL c Lune ee ius cba ns bal 49 cre cca cause 50 NDI IR peel coco eee rec l- ece end 50 AY]: e ene een Adee ec noun buena ne d+ 50 Highland Peak Limestone. Highland Queen mine...._..............__... 50 Highland Range...............~~ 4, 5, 14, 17, 24, 37, 51 : 21.220 ents 53 House Range, Utah... 4, 12, 14, 33, 34, 36, 43, 46, 48, 49 canis 36, 51 BD. L.. IIL 52 I Igneous rocks, diabasic and porphyritic granite :- -u clei sends 2 Tertiary volcanic rocks.. 2 ..- 2 J Johnnie Formation:.......................... 12, 13 K ROME.. - cane 52 Sp... 52 ROChOSDHAHIOHE..22 . .. 2122 Loans ea sas 25 cache e 26, 27 Kooteni 43 TE LEL - s race es hack 26 L canbe 2 Leiostegi §p..:..s tees 52 Limestone-replacement sulfide deposits....... 2 Lithographic limestone............ 37, 39, 43, 44, 45, 50 Locality register._........ sess ) 68 Lookout Hill, Pioche Shale.... 14 INDEX Page Lost Treasure ming........_....._......_...._ 31 Lynch - 22... 2 .. 39, 40, 41, 48 Lyndon Limestone................ 4, 14, 28, 25, 27, 51 age and correlation.. 31 areal distribution........................0 27 lithology and stratigraphic relations.. .... 27 MEMDOT A. .2. ..o 20 MOMbOr Bell. 2.0000. 00 cus h 20 RETAbCT C... cloe c TEES » 31 eus 31 U M Meadow. Valley, .... 000 2 Meadow Valley Member, Highland Peak .\ 34, 44, 46 age and correlation....._........ 47 lithology and stratigraphic relations. 47 name and occurrence..........._..__..._. 46 thickness 47 Mendha Formation... 8, 50 age and correlation. 52 lithology and stratigraphic relations. 50 Mendha mine......... as 50, 51 Mendha outlier at Step Ridge. 61 Methods of investigation.......... 2 .. --..... - 26, 27 Millard Limestone.. 36 Mining, selective. .-... 21 Mount Whyte Formation.................... 27 N NOROMMS BD .se 4: s 9s whe ce sel 52 Newport lime.... 33 Noonday Dolomite...................... 13 0 Olenellus. 9, 12, 13, 22 X ILC. 4, 26 zOng..... 13, 25 Olenellus gijberti-Paedeumias Llafki faunule.... _ 26 Onchocephalus depressus....._.......... 27 TL once one bene cee 26 OOIIHC ZONE. 1 , 26 conc 24 Ophir - 12, 33 Ordovician and Cambrian rocks.............. 50 Ore bodies, bedded or blanket............... 2, 9, 21 9 L.: 20 manto-type zinc and lead.......... 20 repl nt. MUS 14 sulfide 9 Ore -.. 0. Lc einen 4 Ore in limestones of the A-shale member...... 24 P Paed ias clarki. 26 HEUAIERSISL 2.0 26 Pahrump Serigs. . .. 0.0 e rece 13 Falcontology . ... .cc ollie era ale 2, 4, 5, 17, 20 Pan-American ming........................ 5, 18, 21 Panaca Formation.... 2 Peéasley Limestone........__......_...___._._._ 5 Peasley Member, Highland Peak Formation. 32, 34, $5, 36, 39 age and correlation......_......__._._._.... 36 2 12 ERE VTLE. 35 name and occurrence. 35 stratigraphic relations 36 .L v. r Livery lise arse ang 35 Page: PBHTOIORY : . ue 22 AET Hh CUs ee iea de al 2 Pioche Divide, A-shale member 23 B-shale member........... 22 Ploche Shale. 7. (S LCIE ACIS: 15, 18 Pioche Divide reference section, adopted terminology 19 A-shale member. 23 Oshale menber. s. 220. 2s cl. il, 21 Pioche No. 1 mine.. Pioche Shale.... Arshale 28 age and correlation.. 25 areal 14 B-shale LL. 22 blue limestone marker, A-shale. -. 23, 24 C-shale member...__......... 21 columnar section........... 16 Combined Metals Member. Lac. 14, I8 D-shale 17 faunules 25 previous investigation......._..._._.____.. 14 reference section.. 15 sandstone marker, A-shale silicified trilobites... . . .2.2000 20 stratigraphic division.............._.____. 16 thicknoss........._._. 15 Plagiura-Kochaspis faunule...._._.___._______ 26, 27 Plagtura 8D - unde pve er s odc es 27 Platy dolomite... -- 33, 45 Policlla denticulata...... 27 faunule..... } 26 8p: rid... 27 Pogonip ._ 52 Pritice mine..... \ _} - 14, 18, 20, 24, 27, 31, 35 Prospect Mountain Quartzite.. ___. 2, T, 8, 9, 14, 17, 22 age and correlation....._.......____._._._._. 12 areal distribution. 9 arkosic facies. ..... ... ease benet send 10 @FORIOHLL L221... ILL .l bee s oven 11 fossils.. 3. A evince enn -. 11,12 lithology and bedding features............ 10 mud castings and burrows...._........ 11,12, 17 name and occurrence. .. as 9 -C. 1 oon eel aoi ed ec ben Eel dea 12 stratigraphic relations.. .........._....... 11 101 in 0000, rupee 9 Prospect Peak, Prospect Mountain Quartzite. 9 Prospecting for zinc and lead.._....____._.... 21 Ptychoparioid trilobites. ... -. 26, 43 Purposes of investigation . : 2 R Raymond Ely Extension mine............... 8 8 Schistometopus gp. .:.. 2: .... 22. t 27 - 2~ .~ ecm tes 11 Secret Canyon Shale. 49 Shodde ning.. . °... . ... .2 00920 22 5, 27, 29, 32 Silver Mining.... .. .. LIL. 1. 2 Slaughterhouse Gulch............ 10, 11, 14, 18, 22, 39 Stop Ridge. ..... 8, 50 Step Ridge Member, Highland Peak Forma- tlon. ..... gs 8, 34, 39, 42, 48, 46, 52 age and correlation.. tes. 45 bluebird structure..........._._.._._____.. 39 lithology and stratigraphic relations. ..... 43 name and occurrence. 43 co .c. 21 codell ene eee oen 43 Page Sfifiing Quartzite......................._. 10, 12, 13 Strategic minerals program.._......_..______. 5 Stratigraphic column of Cambrianrocks.... .. 8 Stratigraphic investigation, history_.-.....--. 4 SHrAHIEFADRY -. 2-2 2.00. sO 00.02 4, 16 Strotocephalus arrojoensis......__._..____.__.._. 2% Strotocephalus-Mezicella faunule.............. 26 .s. s see oo bec ne 9 Susan Duster 26 Susan Duster Limestone Member,Pioche Shale: 4, 21, 22, 26 .- ecu e Lol dee ec nde eo 22 2 +2002. IIL Save unls whee 22 Phicknoss . ..>. II np wus 22 Susan Duster . 22, 24 Swasey Formation.........._....._.... 43, 45, 46, 48 INDEX Page: 8D :1 IOI CIL es. 52 T Tapoats Sandstone... ..-... 13 Tatow Limestone.. e 27 'The Points 1. .us sin AEs cie 30s 9, 14, 23, 36 Tiger-stripe limestone..........__...._..... 43, 44, 45 QUBMETIGG LA EECCA RTO Ock. 12 Treasure Hill, Prospect Mountain Quartzite. _ 11 Trippe AIL 48, 49 Tulloch ming... :.2.2. ._. .C 27 U Upper fossil zone.: O cc. 24 v Volcanic rocks, Tertlary._......._.__.._.____. 2,8 & 59 w Page Wenkchemnia-Stephenaspis faunule........... 26 West End 18, 22, 26 Whale mine._......._. F 31 Wheeler Monument fault...... 8 Whiskey Barrel mine...... C 31 Windfall Formation.. 52 Y ¥oung Peak Dolomite................_...; 39, 40, 41 Z Zacanthoides grabaui._.......__________.___._.. 33 fy plealis: saci c 2202000000 0 aCe Sai 32, 33 Zaecanthopsls levis_2 0.12000, 000.0000. 0C. 26 BD- iri ferent cae ecn o nor e 26 PROFESSIONAL PAPER 469 UNITED STATES DEPARTMENT OF THE INTERIOR PATE , GEOLOGICAL SURVEY EXPLANATION 1 & >. Qal‘ E ft 5 <4 é Alluvium 8 § $; z & ~U Z x € 8 O€m , a) 2 4 €.. & 48 ~ no R 533 68 a £ oz $ f f BZ a A28 Mendha Formation 5 < 8 & Si Breccia with fossiliferous limestone a: I S $ blocks; possible thrust fault outlier J 0 nl MVN a & AMA * Z f o: [jz/M/ %// Meadow Valley Member & Che 2d © Condor Member (+ 8 Chsb & é LZ )) 2 ~ Step Ridge Member 8 2 ; E & Chsc, unit c ‘ Ag O €hsb, unit b 2* $ & €hsa, unit a A. i % 8 "e / §S :- , k | Cs €hbc I (t x; Burnt Canyon Member £ \ $ t y- § / g 7 1 & Burrows Member <2): 13 a (+ m > t . \ J p -_ 4 (. Nenst Che S JP L - \ a A 7 | j I 11;- Che [67 Chsaf/(yxf/W Peasley Member ¥ \| s T al. \ L / r p f Snbe ) €hsc \ X GZ c/ r f / XT /* *+ _ y Chisholm Shale _ AX "a * ; J_ [£3553 J/y __ HP L, wae, RKTT /M ss\,"\//, \( LZ \ AC X) ¥ Lyndon Limestone * f TERT . 4 + z Pioche Shale €ps, Susan Duster Limestone Member €pc, Combined Metals Member Lower Cambrian pt 0% P /4/ “f/WZ P, G7 NWA /// Prospect Mountain Quartzite 16%, T ________ es Contact showing dip 51 /g Dashed where approximately 2) located S APPROXIMATE MEAN DECLINATION, 1964 ___1'._..__.—.7 66 Fault showing dip Dashed where approximately located, queried where probable Concealed fault 12 ak Strike and dip of beds A A427 30" INTERIOR-GEOLOGICAL SURVEY, WASHINGTON. D. C Base from U.S. Geological Survey topographic quadrangle: Pioche 1953 1964-G s3300 al Geology mapped by plane table methods Shaft at surface by C. W. Merriam, assisted by L. C. Craig and R. L. Griggs in 1944-1945; o20 7 revised and replotted in 1957 by C. W. Merriam on U.S.G.S. topography, Fossil localities and other J 7 Pioche, Nevada quadrangle (1953) localities referred to in text. See locality register DETAILED GEOLOGIC MAP OF A PART OF THE PRODUCTIVE AREA, PIOCHE MINING DISTRICT, LINCOLN COUNTY, NEVADA 500 1000 1500 FEET ' m= 1 500 0 500 METERS 1 CONTOUR INTERVAL 40 FEET DATUM IS MEAN SEA LEVEL PROFESSIONAL PAPER 469 UNITED STATES DEPARTMENT OF THE INTERIOR PLATE 2 GEOLOGICAL SURVEY 114°40" 5 - y tal | (~ Pass EXP L A N A T 1 O N Dr r, Lucky Star Mine Ciao! Me!! Igneous Rocks Sedimentary Rocks O€m \Jackrabbit Mine a a Lava and tuffs Alluvium 11°20" NARY di Dr AN Diabase dikes Rocks undifferentiated TERTIARY(?) qm Sr Quartz monzonite Rocks undifferentiated and associated intrusives Or Rocks undifferentiated IL Measured stratigraphic section O€m M i-----AM' Structure section CL end ORDOVICIAN SILURIAN DEVONI- QUATER- AN Mendha Formation €h Highland Peak Formation De/mues Wel! €lc Lyndon Limestone and g 6 k> Chisholm Shale un- 3 e differentiated The Point CAMBRIAN €pp Prospect Mountain Quartz- ite and Pioche Shale _ | PIOCHE Ely Valley Mine v $ C Lu M OCm' Or D (re MmeAArizgna Peak | £pD < 48 Highland Queen €le Mt,Ely & t Highland If Mine AL C. cp Tank Hill ary MinezTVv £! = { Ag fl Er ciogi B Vn €pp-67 €h x2 Pioche ! y/ Alps Mine Caselton'? Pg Mine (2 Ch Mine 67610 oy Cone hx ao d.. ~. [p E2 £, A Peak ' epp €h % Biz.... «1 ) on can? ao¢ con > €hZ-? Warm Sprin gM 5 MILES i U.S. Geological Survey Professional Paper 171, Plate 1, 1932 S O & Geology based on Westgate and Knopf, Q7- é 37°45" GENERALIZED GEOLOGIC MAP OF THE PIOCHE AREA, LINCOLN COUNTY, NEVADA, SHOWING MAJOR MINES, LOCATION OF CHIEF STRATIGRAPHIC SECTIONS, AND AREA OF THE DETAILED GEOLOGIC MAP 727-989 O - 64 (In pocket) 37°55 UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY 114°27:30" PROFESSIONAL PAPER 469 PLATE 3 Pacific U A _4f| The Poin1\\\ ase ia Pioche Metals ~, MineI > F Marion Mine 4*~~& / re ~ 5.3 $97 Tulloch purges 0 PWS: _/ 6400 Garrison Mine mine o 14 o'él/l Ming "West End Mine B -A ~~ U Gold Etlglf’é> 1 Whale Mine ll Blue Eagle “PM @" I (0 / EXPLANA ¢. 5600 y TION IV Paved highways and surfaced roads Unimproved roads and vehicular trails / l, // \ Dr V Geologic structure section In Measured stratigraphic section 25 ol Locality referred to in text; see locality register Outlined area is that of detailed geologic map 8 L ime Raymond Ely Hillfi 3bL\Extension Mine & Wneelter A Treasure o Hill 24 \ \ Lflé Y \ I Wide Awake «" Mine / Meadow [Valley U 1 I 1 To Panacea i and Caliente w 74 L Base from U.S. Geological Survey topographic quadrangle: Pioche 1953 INDEX MAP OF THE NORTHWESTERN PART OF THE ELY RANGE, PIOCHE MINING DISTRICT, LINCOLN COUNTY, NEVADA SHOWING POSITION OF MINES, STRATIGRAPHIC SECTIONS, AND OTHER LOCALITIES REFERRED TO IN TEXT 0 5 2 MILES aed 2 KILOMETERS Ex- --- -- CONTOUR INTERVAL 200 FEET = - ket) DATUM IS MEAN SEA LEVEL 727-989 O - 64 (In pocke UNITED STATES DEPARTMENT OF THE INTERIOR FEET 10,000 - 9000 - 8000 - 7000 - 6000 - 5000 - 4000 - 3000 - 2000 - 1000 - PROFESSIONAL PAPER 469 GEOLOGICAL SURVEY PLATE 5 1 2 3 4 5 PIOCHE, EUREKA, HOUSE RANGE, GOLD HILL, OPHIR, NEV NEV UTAH UTAH UTAH ' IDAHO 3 .% [e da l remit aarad te craw a as mal. 3 1 < Great Salt €] l Lake , = a Sone anl . shoes y Wells S 4 & pact. Fax- (e] f - Battle % 7/ Notch Pefrsgylmestonev \ f Mountain l 5; = 4 o i- |_ NEVADA oral 9 / Chokecherry Dolomite I, //\ tel mo hoe minke y r * mme il 0-1000 | 2( & g \ / / Eureka L g Mendha Formation 2000' / $ Coa mel gkn C cok Ph #8 C L vier 6 (includes Lower Ordovician) / Ort Formation 1825) Hicks Formation ire J/ y ?- 590-1200" h oo \ l ze §__ Lu g % / s 3" N S \ / we". e eas o wees phd ued & hi wero ad # ae psy cX f I—Cedar City ," o 7 unnamed ~ Windfall Formation 650' Lamb Dolomite 1080' (-- Calientes - [- *c, "pol -- £ ithologic f ha % c units 2530’ \\ mere ande iy | I St George j ° & o \\ Dunderberg Shale 265" _, Weeks Limestone ser oun -< 1 M I vn 7 1940' ; f in: * 5 E 3 I» ck Pee -* Trippe Limestone:750 INDEX MAP SHOWING LOCATION 32:9 acy Hamburg Dolomite 1000' e> 4 OF STRATIGRAPHIC SECTIONS 33“ A $". / \'§‘ 0 50 100 MILES 4 DI '* Young Peak D 5 T-' - x aar t -> ce / Dolomite 600' \o g \\ Secret Canyon Shale 650° s 7; < Meadow Valley Member 430' . \<% O| o f ; can' Marjum Limestone / a Condor Member 110" = Geddes Limestone 330\ 1530" \'7 El 83 g \\ / - 3 Step Ridge Member 740' ~<> 74 rag e: sto. on ee i i ? 255“? Burnt Canyon Member 190' g Wheeler Formatiorfiig’ Abercromztygoformatlon & Lynch Dolomite 1000'+ pPER CAMBRIAN ;._ o .= mund sam .._. w 2222200 ios memes $4 Burrows Member 300-500' . Swasey Formation 395! MIDDLE CAMBRIAN easley Member 160' Eldoradzrgo?)?lomnte Ss 4 f Bowman Limestone 280' Chisholm Shale 100' Dome Limestone 310 F U Seel Lyndon Limestone 380 Hartmann Limestone 650' Howell Formation 835" Busby Quartzite Pioche Shale 800' 450° 24 Ophir Shale 320' : f Tatow Limestone of Cabin Shale Tintic Quartzite Ree kl _ ges Pioche Shale 100-500 Deiss (1938) 165" 500 4 309 p Z Pioche Shale 265" E Prospect Mountain “53 Prospect Mountain Quartzite 1000'+ S Prospect Mountain Quartzite 1500'+ oc Quartzite 2400° + Prospect Mountain L : r B haaa Quartzite 4750 > okt CORRELATION DIAGRAM SHOWING POSSIBLE RELATION OF CAMBRIAN ROCKS AT PIOCHE, NEVADA TO THOSE OF OTHER GREAT BASIN SECTIONS 727-989 O - 64 (In pocket) GEOLOGICAL SURVEY UNITED STATES DEPARTMENT OF THE INTERIOR E-L Y. R A N G E H 1 G H L A N D PROFESSIONAL PAPER 469 PLATE 4 R A N G E I A. 1 2 3 A 1' pl Lyndon Gulch (Section K) Mount Ely (Section C) Forlorn Hope Mine (Section Z) Slaughterhouse Gulch (Section /7) Northeast of Prince Mine (loc 43) Pioche Divide (Section A) 1% miles 1% miles 1% miles 8 miles 2% miles Lyndon Limestone 38Q' + Fossils abundant in limestone interbeds Oolitic limestone beds oa Fault contact Fossils abundant in limestone interbeds ye" A-shale member 225: +# 250' +- Blue limestone marker MIDDLE CAMBRIAN ossiliferous limestone Sandstone marker B-shale member Susan Duster Limestone Member Pioche Shale C-shale member Combined Metals Unexposed Member ? £ ? D-shale member LOWER - CAMBRIAN NP.» 13 hy tew T+ * Quartzite 2400' + \ eer" Prospect Mountain "A. COMPARISON OF COLUMNAR SECTIONS OF THE PIOCHE SHALE IN THE ELY AND HIGHLAND RANGES, NEVADA, TO SHOW CONTINUITY AND LATERAL VARIATION OF MEMBERS 727-989 O - 64 (In pocket) UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY Lower part of Highland Peak Formation" __ * Step Ridge Member 775" % Burnt Canyon Memb'er 162" 5: % + & o Is ® i; 5 § a & £ 0 0 P = Fd Fs B $- | f $ 3 a. co *Thickness unreliable because of faulting & a Condor Member 105'. ppt Meadow Valley Member 430' Argillaceous limestone 290 I 0 1 Upper part of Highland Peak Formation 200 pds 4(|)O 690 8?0 FEET Unit 12 PROFESSIONAL PAPER 469 PLATE 6 Upper part of Highland Peak Formation Unit 9* Unit 10* |Unit 11" Unit 12* Unit 13* 200' 4+. [110'+ 170° 120' + 727-989 O - 64 (In pocket)