iii? 7 3" .4595» 4?” Landslides Along the Columbia River Valley Northeastern Washington GEOLOGICAL SURVEY PROFESSIONAL PAPER 367 («j/‘74. flaéefl’fl/m, @575 flé . v, 7’53 EARTH SCIENCE LIBRARY ’/7 T: m 131962. 6;, . * ; g r ' f '1' NEG—$3 ' Landslides Along the Columbia River Valley Northeastern Washington By FRED O. JONES, DANIEL R. EMBODY, and WARREN L. PETERSON Witn a section on Seismic Surveys By ROBERT M. HAZLEWOOD GEOLOGICAL SURVEY PROFESSIONAL PAPER 367 Descriptions of landslides anaI statistical analyses 0f data on some 200 landslides in Pleistocene sediments UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1961 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director The US. Geological Survey Library has cataloged this publication as follows: Jones, Fred Oscar, 1912- Landslides along the Columbia River valley, northeastern Washington, by Fred 0. Jones, Daniel R. Embody, and Warren L. Peterson. With a. section on Seismic surveys, by Robert M. Hazlewood. \Vashington, US. Govt. Print. Ofl'., 1961. v, 98 p. illus., maps (part col.) diagrs., tables. 30 cm. (US. Geological Survey. Professional paper 367) Part of illustrative matter in pocket. Bibliography: p. 94—95. 1. Landslides—Washington (State)—Columbia River valley. 2. Seismology—Washington (State) I. Embody, Daniel R., joint author. 11. Peterson, Warren Lee, 1925— ,joint author. III. Hazle- wood, Robert Merton, 1920—IV. Title. (Series) For sale by the Superintendent of Documents, US. Government Printing Oflice Washington 25, D.C. CONTENTS Abstract ___________________________________________ Introduction, by Fred 0. Jones _______________________ Regional physiographic and geologic setting ________ Cultural developments __________________________ Acknowledgments _______________________________ Landslides, by Fred 0. Jones and Warren L. Peterson--- Topography on the surficial deposits _______________ Types of landslides ______________________________ Slump-earthflow landslides ___________________ Multiple-alcove landSIides ____________________ Slip—off slope landslides ______________________ Mudflows __________________________________ Landslides along Franklin D. Roosevelt Lake ______ Areas of extensive landsliding ____________________ Reed terrace area __________________________ Culture ________________________________ Geology _______________________________ Geologic history ..... , ___________________ Surface-water and ground-water conditions- Landslides____-__------_---__--- _______ Lake fill in the Reed terrace area _________ Cedonia area _______________________________ Ninemile area ______________________________ Geology _______________________________ Landslides _____________________________ Seatons Grove—Koontzville area ______________ Seatons landslide (No. 7) ________________ Seatons mudflow (No. 320) ______________ Koontzville landslide (No. 5) _____________ Nespelem River area ________ ’ ________________ Geology _______________________________ Glacial history _________________________ Landslides _____________________________ Landslides in the Columbia River basalt ___________ Summary of possible causes of landslides ___________ Economics _____________________________________ Landslides at Grand Coulee Dam _____________ Costs of landslides __________________________ Statistical studies __________________________________ Field observations and methods, by Fred 0. Jones- Landslide type groups _______________________ Classification units and measurements of the geologic environment ______________________ Material-classification categories __________ Ground water __________________________ Terrace height _________________________ Drainage of terrace surface _______________ Original slope of terrace scarp ____________ Submergence ___________________________ Culture ________________________________ Material removal _______________________ } Time ________________________________ ,. - _ , Landslide measurements H C: VC ratio- _--_ _ _ _ - Page NNQGGWWU$WHH .34 7-3 48 'FARTH SCIENCES LIBRARY Statistical studies—Continued Statistical analyses, by Daniel R. Embody and Fred 0. Jones ------------------------------------ Analysis and interpretation of landslide data_ __ Recent slump-earthflow landslides -------- Qualitative variables ---------------- Quantitative variables --------------- Tests of significance for materials and ground water --------------------- Equation for the prediction of H C 2 VC ratios of landslides ___________________ Ancient slump-earthflow landslides ________ Slip-off slope landslides ------------------ Multiple-alcove landslides ________________ Landslides ofl" bedrock ------------------- Uniformity experiment ---------------------- Summary of analysis of H C : VC ratio of landslides ---------------------------- Summary of analysis of original slope- - _ __ Summary of analysis of submergence percentage --------------------------- Summary of ground-water analysis ________ Summary of material analysis ____________ Summary and interpretation of uniformity experiment results ------------------- Slope-stability investigation __________________ Summary of analysis for the discriminant function Summary of analysis of variance for the discriminant function ------------------ Use of the discriminant function ---------- Results of experiment ___________________ Application of landslide and slope stability data, by Fred 0. Jones and Daniel R. Embody ___________ Recognition of potential landslide areas ________ Estimation of landslide extent in this and similar geologic settings -------------------------- General application of methods ______________ Illustrations of application of landslide and slope stability data ____________________________ Ninemile area (Franklin D. Roosevelt Lake) - Geology and landslide classification of the Alameda Flat area (Lake Rufus Woods)- Statistical techniques, by Daniel R. Embody __________ Assumptions made in the analysis of variance ------ Reconciliation of properties of field data and theo- retical requirements for validity ---------------- Experimental logic, tests of significance and precision- Specific methods and sources _____________________ Summary of reconnaissance seismic surveys, by Robert M. Hazlewood _____________________________________ Field measurements _____________________________ Results ________________________________________ Reed terrace area _______________________________ m 194 Page 46 46 46 47 48 49 54 55 55 55 56 57 57 58 IV CONTENTS Summary of reconnaissance seismic surveys—Con. Page Page Ninemile area __________________________________ 74 Tables of landslide data _____________________________ 74 Nespelem River area ____________________________ 74 Selected references __________________________________ 94 Conclusions ____________________________________ 74 Index _____________________________________________ 97 ILLUSTRATIONS [Plates are in pocket] Geologic map of the Reed terrace area. Hydrography and landslide fill in Franklin D. Roosevelt Lake. Geologic map and landslide classification of Ninemile area. Sections of Seatons and Koontzville landslides. Geologic map of the Nespelem River area. Geologic map and landslide classification of the Alameda Flat area. Page General index map of the Columbia River valley of northeastern Washington____ _ _ _ _ _ _ - _ _ _ _ _ _ _ _ _ - _ _ _ _ I. - - _ _ 2 Nomenclature of the parts of a landslide ______________________________________________________________ 6 An ancient slump-earthflow landslide exposed by recent sliding __________________________________________ 7 Aerial view of a recent multiple-alcove landslide _______________________________________________________ 8 Multiple-alcove landslide and cr0ss section ____________________________________________________________ 8 Photograph of a typical slip-off landslide ______________________________________________________________ 9 Slip-off slope landslide and cross section _______________________________________________________________ 9 Slip-off slope landslide, Kettle Falls area ______________________________________________________________ 10 Mudfiow in Hopkins Canyon ________________________________________________________________________ 11 Index map of the Columbia River valley of northeastern Washington _____________________________________ 12 Aerial oblique photograph of the Reed terrace taken May 15, 1951 _______________________________________ 16 Aerial oblique photograph of the Reed terrace taken on August 1, 1952 ___________________________________ 17 Slump-earthflow landslide, Reed terrace area __________________________________________________________ 19 Terrace of sand with some interbedded silt and clay ____________________________________________________ 20 Aerial photograph of Seatons landslide ________________________________________________________________ 22 Diagram of Seatons landslide ________________________________________________________________________ 23 Slickensides showing the upward and riverward movement of the Seatons landslide _________________________ 24 Mudflow at Seatons Grove __________________________________________________________________________ 25 Photograph showing the Koontzville landslide _________________________________________________________ 26 Diagram of the Koontzville landslide _________________________________________________________________ 27 Aerial photograph showing landslide in Bailey Basin ____________________________________________________ 30 Ancient slump-earthflow landslide and cross section ____________________________________________________ 30 Histogram showing estimated frequency of all‘ landslides along Franklin D. Roosevelt Lake, 1941 to 1954 _____ 31 Slump-earthflow landslide in lacustrine silt and clay ____________________________________________________ 32 Great Northern Railway landslide near Marcus, Wash __________________________________________________ 34 Deadman Creek landslide ___________________________________________________________________________ 35 Landslide data card (front) ____________________________________________________________________________ 36 Landslide data card (back) __________________________________________________________________________ 37 Slump-earthflow landslide limited by bedrock __________________________________________________________ 38 Failure of an artificial slope _________________________________________________________________________ 39 Dry earthflow ________________________________________________________________ . _____________________ 40 Sediments included in material category 1, Reed terrace area ___________________________________________ 41 Sediments included in material category 1, Hunters-Nez Perce Creek area _____________ L ____________________ 41 Sediments included in material category 2, Ninemile area _______________________________________________ 42 Sediments included in material category 2, Wilmont-Jerome area _________________________________________ 43 Sediments included in material category 3, Hawk Creek area ____________________________________________ 43 Sediments included in material category 4, Cedonia area ________________________________________________ 44 Sediments included in material category 5, Cedonia area ________________________________________________ 45 Cross section of a landslide showing H C and V0 measurements __________________________________________ 46 A slope on sand judged to be very stable ______________________________________________________________ 59 A slope on interbedded silt, clay, and sand judged to be nearly stable _____________________________________ 59 A slope on silt and clay judged likely to be affected by landslides ________________________________________ 60 Sample time-distance curves and bedrock profiles for Reed terrace area ___________________________________ 72 CONTENTS v TABLES Page TABLE 1, One hundred sixty recent slump-earthflow landslides used in statistical analysis ______________________________ 75 2. Forty-two slip-off slope landslides used in statistical analysis ______________________________________________ 79 3. Thirty-seven ancient slump-earthflow landslides used in statistical analysis __________________________________ 80 4. Classification and landslide data _______________________________________________________________________ 82 5, Landslide-classification data, Alameda Flat area. _________________________________________________________ 84 6. Miscellaneous landslides—data recorded for special studies, including landslides not sufficiently complete for type-group analyses or summaries ___________________________________________________________________ 85 7. Uniformity experiment—recent slump-earthflow landslides ________________________________________________ 87 8. Slope-stability investigation, Franklin D. Roosevelt Lake _________________________________________________ 89 9. Landslide date and time data _________________________________________________________________________ 92 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON By FRED O. JONEs, DANIEL R. EMBODY, and WARREN L. PETERSON ABSTRACT Landslides occur so frequently in the surficial depOsits along the upper valley of the Columbia River that they affect greatly engineering developments and land use. Most of the recent landslides took place in the Pleistocene deposits bordering Franklin D. Roosevelt Lake, the Grand Coulee Dam reservoir, which was slowly and intermittently filled during the construction of Grand Coulee Dam (1933 to 1942). Many landslides occurred while the lake was filling; many have occurred since. Down- stream from Grand Coulee Dam landsliding has occurred in several places since the beginning of construction. Geologic investigations were made intermittently from 1942 to 1948 and continuously from 1948 to 1955 in an effort to establish criteria for predicting the probable amount of land that will be affected by sliding. The area of study extends along the upper 200 miles of the Columbia River valley in Washington, reaching upstream from Grand Coulee Dam along Frankliri D. Roosevelt Lake to Canada and downstream from Grand Coulee Dam along the Columbia River nearly to Chief Joseph Dam. Many fresh land- slides in a nearly uniform physical setting presented an unusual opportunity for a study of geologic processes and for a statisti- cal analysis of landslide data. More than 300 landslides in the Pleistocene terrace deposits were examined. Slides were classified into type groups, so that each type might be analyzed and compared with the others. The geologic environment was subdivided into the classification factors—material, ground-water conditions, terrace height, drain— age, original slope, submergence, culture, and material removal. These factors were again subdivided into quantitative or qual- itative categories that could be determined by field examinations. The key measurement of a landslide was taken to be the ratio HC: VC, where HC and V0 are, respectively, the horizontal and vertical distances from the foot to the crown of the landslide taken at midsection normal to the slope. The HC:VC ratio was correlated with the classification units of the geologic en- vironment. The most extensive statistical analysis was done on data from slump-earthflow landslides. Of the eight classifi- cation factors analyzed, only material, ground water, original slope, and submergence proved to be significantly related to the HC:VC ratio. A formula was developed for predicting the H C : VC ratio of slump-earthflow landslides. The stability of natural slopes was investigated by comparing data from slopes on which slides have not occurred with data from slopes on which slides have occurred. The analysis in- cluded a consideration of material, ground water, terrace height, original slope, and submergence. A formula was developed for predicting the stability of natural slopes. The glacial geology of selected areas was mapped. The land- slides in these areas are described. To illustrate the practical application of the slope stability and landslide data, detailed landslide-classification studies were made of the lakeshore land in the Ninemile area along Franklin D. Roosevelt Lake and in the Alameda Flat area along Lake Rufus Woods (the Chief Joseph Dam reservoir). The techniques of geologic classification and statistical analysis described in this report will assist geologists and engineers in judging the stability of natural slopes and in estimating the extent of impending landslide action. INTRODUCTION By FRED O. JONES Landslides occur so frequently in the surficial deposits along the upper valley of the Columbia River that they become an important factor in engineering develop— ments and land use. Geologic investigations of the landslides were made intermittently from 1942 to 1948 and continuously from 1948 to 1955. This report sum- marizes the results of these investigations. The area included in these studies extends along the upper 200 miles of the Columbia River valley in Washington, reaching upstream from Grand Coulee Dam along Franklin D. Roosevelt Lake to the international bound- ary, and downstream from Grand Coulee Dam along the Columbia River nearly to Chief Joseph Dam (fig. 1). Such a large number of fresh landslides in a nearly uniform geologic setting presented an ideal opportunity for study of landslide processes and for a statistical an- alysis of landslide data. The application of statistical methods is a new approach to the analysis of landslides and the stability of natural slopes. Most of the recent landslides have been related to the construction of Grand Coulee Dam, especially tothe consequent filling of Franklin D. Roosevelt Lake (the Grand Coulee Dam reservoir). Construction of the dam was begun in 1933. The level of the backwater was slowly and intermittently raised as construction proceeded, until the dam was completed and full reser- voir level was first attained in 1942 thus creating a lake 144 miles long and raising the water level 350 feet at the dam. Landslides occurred with unusually great and unex- pected frequency in the bordering Pleistocene deposits as Franklin D. Roosevelt Lake filled. Because of the damage to property adjacent to the reservoir and the 1 2 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON 49a駰°°°' 119'00’ CANADA "1520: __ YK__3o_' __ . DU) 6 l {- (oMetaline d]. Northport /A (02' «6" 5 Falls 3 0 < 0 +— @ 2 K D lane 1‘ O z a arena 9 Republic > Kn”: FALLS ‘Kettle Falls % 8’ ‘ BRIDGE" g 30' >\. In N. W 69 Z lu < .1 , m I~ I~ ‘3 Twin ‘3? 2 Lu Lakes} h - - 65‘ 3 x " "0 e‘l‘lm ‘ Ifford \ n / I r)- gNespelemz 3‘. PLATEAU g; r1 g [a Mom Brewster '< #29 M Hunters $31.4 e . b» 9V v1 [U I 48'00' fa 7 Bridgeport amuse-FM Gfirildeéogleme couu: DAM ”O; m 0g \ 3 a: Fort E Q Q Spokane 11‘ oln Mansfield C . O L m \ \\ U "as M \Ceek 60 Davenport x073. P Spokane 30' L I 20 O 20 I_ 1 I l l I 4‘0 MILES FIGURE 1.—General index map of the Columbia River valley of northeastern Washington. threat to.human lives, a study of the landslides was begun by the senior author in 1942 for the Bureau of Reclamation. The geologic conditions and topographic relations were examined, and the 600 .to 700 miles of lakeshore lands were classified generally into five groups: landslides likely, landslides unlikely, slide areas, bed- rock, and indeterminate. The indeterminate classifica- tion was necessary as data were often insufficient to make a valid determination of the landslide potential. Particular attention was directed to areas where land- slides might destroy private property or endanger lives. Where privately owned land was found to be potentially dangerous, the US. Government ofl’ered to purchase the property. In 1948 the Geological Survey began research studies on Franklin D. Roosevelt Lake in technical cooperation with the Bureau of Reclamation and the National Park Service, the two Federal agencies most concerned with administrative problems of property adjacent to the lake. In 1950, in cooperation with the Corps of Engineers, investigations were extended to include a section of the Columbia River valley between Grand Coulee and Chief Joseph Dams. A geologic setting similar to that of Franklin D. Roosevelt Lake exists in the upstream part of the Chief Joseph reservoir (Lake Rufus Woods). Landslides had been frequent along the river in this stretch, and because it was possible to study the valley before flooding by Lake Rufus Woods, investigations were extended to include that part of the reservoir which had similar geologic conditions. The investiga— tions were discontinued in 1955. The practical purpose of these investigations was to establish criteria for predicting the probable amount of INTRODUCTION 3 land which will be affected by landslides so that maxi- mum use may be made of lands along the lake. More than 300 landslides have been studied in relation to their geologic environment. Classifications were de- vised to subdivide the environmental factors so that their separate and combined effects on groups of similar landslides could be analyzed and evaluated. Statistical methods employed consisted of the analysis of variance and covariance, chi-square tests, multiple regression, and discriminant-function analysis. Each important analysis is presented in brief summary and computational detail is omitted. The section headed “Statistical techniques,” page 69 discusses methods used and the purposes which they were intended to accomplish. The only topographic maps available for studies made along Franklin D. Roosevelt Lake in the years 1942 to 1946 were the river survey sheets, “Plan of Columbia River, International Boundary to Rock Is- land Rapids (below Wenatchee) Washington, Depart— ment of the Interior, US. Geological Survey,” which were surveyed in 1930. These maps were used though they were limited in extent and accuracy and were inade- quate for the work. To provide a basis for detailed geo- logic and engineering studies, as well as for other uses, the Geological Survey began the topographic mapping of all the 15-minute quadrangles along the Columbia River valley from the Omak Lake valley to latitude 48°30' N. These new topographic maps became available during the last few years of investigation. The Coast and Geodetic Survey made a hydrographic survey of Franklin D. Roosevelt Lake in 1947 and 1948. This hydrography and the new topography of most of the project area, along with repeated aerial photography, have provided an invaluable basis for the geologic and engineering studies of the landslide features. REGIONAL PHYSIOGRAPHIC AND GEOLOGIC SETTING Northeastern Washington is comprised of two strik- ingly different physiographic subdivisionsflethe moun- tainous highlands to the north and the nearly flat Columbia Plateau to the south. The boundary be- tween these subdivisions, with minor exceptions which are outlined later, follows the general east—west trend of the Spokane and Columbia Rivers (fig. 1). The plateau on the south is a part of the vast lava plains which spread over a large part of the Pacific Northwest. The highlands, which lie north of the boundary, are made up of north-south trending valleys between low subparallel mountain ranges. The principal north— south valley is occupied by the Columbia and Kettle Rivers and is a southern extension of the Selkirk Trench. Of the several minor extensions of the plateau lavas north of the Spokane-Columbia River valley, only two are particularly significant. One of these is the tri- angular-shaped Okanogan Plateau bounded on the south by the Columbia River, on the northeast by the Omak Lake valley and on the northwest by the Oka- nogan River valley. Omak Lake valley is an informal name used here for the large valley that contains Omak Lake and extends from the Okanogan River valley to the Columbia River valley. The second significant minor extension is the Spokane Plateau, an irregular group of tongues of the Columbia Plateau which extend north of the Spokane River (Weaver, 1920). The Columbia River enters the United States at about longitude 117°38’ (fig, 1). It flows southwest- ward for 40 miles in a moderately broad valley which is between the Rossland Mountains on the northwest and the Chewelah Mountains on the southeast. At the southern tip of the Rossland Mountains the Columbia River is joined by the Kettle River from the north and the Colville River from the southeast. Downstream from these junctures, the Columbia flows southward for 60 miles in a broad valley which lies between .the Kettle River Mountains on the west and the Huckle- berry Mountains on the east. The rocks exposed in the valley walls along this upper 100 miles are princi- pally limestone, marble, quartzite, schist, gneiss, and granite of Paleozoic and Mesozoic ages (Pardee, 1918; Weaver, 1920). A few miles below its confluence with the Spokane River, the Columbia turns sharply to the westward and follows a sinuous north-northwest course along the edge of the Columbia Plateau. The sharp change in the course of the river resulted from the creation of the lava plateau in Miocene time. From the mouth of the Spokane River to the Omak Lake valley, bedrock for- mations on the left bank1 of the valley are principally lava flows of the plateau and bedrock formations on the right bank are granitic rocks of the Colville batholith. During the Pleistocene epoch the Cordilleran con— tinental glacier formed one or more times in the inter- montane plateau region of British Columbia (Dawson, 1891; Johnston, 1926). The number of ice invasions into the United States area is not known but during the 'Wisconsin stage ice lobes pushed down southward- trending valleys into eastern. Washington, Idaho, and western Montana. Three of these ice lobes entered the area considered here: the Okanogan lobe which occupied the Okanogan River valley, the Sanpoil lobe which occupied the Sanpoil River valley and the Columbia lobe which occupied the part of the Columbia River valley north of the Columbia Plateau. The 1 Left and right bank refer to the left and right as one is facingdownstream. 4 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON maximum extent of these lobes has been mapped by Bretz (1923) and Flint (1937). During the times of ice invasion and recession glaciofluvial and glaciolacustrine sediments were depos— ited in the Columbia River valley. Deposits in the Columbia River valley upstream from the Nespelem River were first described and named the N espelem silt by Pardee (1918). These deposits are preserved in terrace remnants the highest of which occur on both sides of the valley at altitudes ranging from 1,720 to 1,900 feet (the Nespelem silt terrace of Flint, 1935). This terrace is found in the Columbia River valley upstream from Omak Lake valley. Pardee concluded that the Nespelem silt was aglaciolacustrine fill depos- ited in a lake ponded in the Columbia River valley. The first extensive work on the glacial deposits and erosional features of the Grand Coulee area was done by Bretz (1923, 1932), who concluded that the Nespelem silt was deposited in a lake that was ponded in the Columbia River valley by the Okanogan glacier lobe. The lake drained through the Grand Coulee which had been cut during one or more earlier glaciations. Subsequent work by Flint (1935), and Flint and Irwin (1939), on the Pleistocene sediments of the Columbia River valley upstream from the mouth of Okanogan River confirmed Bretz’s conclusions. Flint and Irwin concluded that all or most of the Pleistocene sediments of the Columbia River valley near Grand Coulee Dam were apparently deposited during a single major ad- vance and recession of the Okanogan glacier lobe, which occurred subsequent to the advance or advances associated with the cutting of the Grand Coulee. Pardee’s definition of the Nespelem silt is based on the interpretation that only one lake stage is involved in the deposition of the Pleistocene sediments. Evi- dence found this during investigation, shows that more than one lake' stage occurred. The name “Nespelem silt” now means little other than Pleistocene lake and stream deposits of the upper Columbia River valley and tributary valleys. The word “silt” in the term “Nespelem silt” is misleading, because, as pointed out by Flint (1936), much of the fill is not composed of silt- sized particles. Probably from 25 to 50 percent of the fill in the Columbia River valley between the Omak Lake valley and Kettle Falls is sand and gravel. The name “Nespelem silt” is not used subsequently in this report. CULTURAL DEVELOPMENTS David Thompson, surveyor, geographer, and fur trader, who explored the Columbia River valley of British Columbia beginning in 1800, was the first white man known to record his presence in the upper Colum- bia River valley of Washington (Elliot, 1918, p. 14). His journal records that on June 19, 1811, he reached the Kettle Falls of the Columbia River. Thompson and his men constructed a canoe at the site of the falls and journeyed downstream to the river’s mouth (Fuller, 1931, p. 81). Many legendary figures of the exploration and fur- trading era followed. The most noteworthy events of the exploration period were the arrival of Lewis and Clark in the Northwest in 1805 (Fuller, 1931, p. 63), and the Canadian Boundary expeditions of 1812 (Ful— ler, 1931, p. 101). The fur-trading enterprise was punctuated by the rivalry and feuds of the American and Canadian fur companies. Two of the earliest industries were lumbering and gold mining. Small individual sawmills were operating in the area by 1870 (Durham, 1912, p. 184), and gold placering of gravel deposits began after the gold dis- coveries of 1852 (Fuller, 1931, p. 304). The U. S. Army established military Fort Colville in 1859 on the banks of the Columbia River near Kettle Falls. Fort Spokans was established in 1880 on a ter- race overlooking the confluence of the Spokane River with the Columbia, and in 1882 Fort Colville was abandoned (Western Hist. Pub. Co., 1904, p. 73—74). Many settlers soon followed. They cultivated bench- lands near the river and grazed stock on the uplands along the valley sides. The lower part of the valley had been extensively developed by 1933 When the con— struction of Grand Coulee Dam was begun. Many of the lower terraces along the Columbia had been irri- gated and orchards had been planted on them; 4 saw- mills were in operation in the valley between Lincoln, Wash., and the international boundary; and the valley was served by many miles of roads, 2 spur lines of the Great Northern Railway, a bridge at Kettle Falls, and 6 ferries. With the completion of Grand Coulee Dam in 1942 a reservoir was created which averages about 4,650 feet in width and contains about 9,600,000 acre-feet of water (Hall, 1952). Approximately 70,500 acres of land was flooded, and a lakeshore of more than 600 miles was created. Within the reservoir area were 3,000 people, 2 railroads, 3 primary state highways, about 150 miles of country roads, 14 bridges for rail and vehicular traffic, 11 townsites, 4 sawmills, 4 telegraph and tele- phone systems, and many powerlines and cemeteries. Major developments were either purchased or relo- cated by the US. Bureau of Reclamation. The relo- cated Nelson Branch of the Great Northern Railway (15.3 miles) now follows the left shore of the reservoir from Kettle Falls northward to a point 4 miles south- west of N orthport. The relocated Republic Branch (13.1 miles) runs north along the right bank of the reservoir to the Kettle River confluence and then skirts LANDSLIDES 5 the left bank of the Kettle River to Boyds (fig. 1). Relocated State Highway 22 now follows the left bank of the reservoir from Fort Spokane to Northport, and US. Highway 395 follows the right bank of the river from the Kettle Falls bridge to Boyds. A relocated highway follows the right lakeshore generally from Kettle Falls to the mouth of the Spokane River (fig. 1). Franklin D. Roosevelt Lake, the reservoir created by Grand Coulee Dam, first reached its maximum level in June 1942. There was little human activity along the lakeshore for several years because of the dislocation of roads and industries required by the submergence. However, after a few years, private development and land use increased noticeably near the newly created lakeshore. As many terraces were within easy reach of the reservoir, pumps were installed at many locations to supply sprinkler irrigation systems. Logging operations were accelerated by formation of the lake, and lumber mills were reestablished. The Great Northern Railway constructed a loading dock at Kettle Falls to serve the lumber industry. This loading dock connected 'lake transportation to the railroad systems. The use of the lake for recreational and industrial developments had hardly begun by 1955. Chief Joseph Dam at Bridgeport, Wash., was under construction in 1955. Its backwater, Lake Rufus Woods, will extend throughout the area below Grand Coulee Dam included in these investigations. Chief Joseph Dam is a relatively low dam, and the resulting cultural changes should be less pronounced than those caused by the construction of Grand Coulee Dam. On a smaller scale, there will be a movement away from the river and then a movement toward it, as lands adjacent to the reservoir shore are used for agricultural and engineering purposes. ACKNOWLEDGMENTS The authors express their sincere appreciation for the wholehearted interest and support they received from so many individuals and organizations. The following government agencies cooperated by furnish— ing data, suggestions, and field facilities: Bureau of Reclamation and National Park Service, Department of the Interior; Corps of Engineers, US. Army; Coast and Geodetic Survey, Department of Commerce. Other organizations that aided in the work are: the Statistical Engineering Laboratory of the National Bureau of Standards; officials of Ferry County, Wash. ; Lincoln Lumber Co.; Marchant Transportation Co.; Lafferty Transportation Co.; and the Great Northern Railway Co. Among those who generously assisted in this program are the following: W. H. Irwin, A. S. Cary, C. E. Erdmann, Karl Terzaghi, Arthur Casagrande, D. J. Varnes, W. C. Krumbein, F. A. Banks, P. R. Nalder, A. F. Darland, T. Torkelson, Thomas Mutch, L. C. Russel, Wm. Cowals, W. R. Power, Jr., C. F. Erskine, W. E. Davis, W. G. Schlecht, R. E. Wallace, Keith Essex, H. H. Waldron, C. E. Greider, Hugh Peyton, Robert Coombs, A. F. Bateman, Jr., A. E. Weissenborn, W. J. Youden, Churchill Eisenhart, William Clat- worthy, Neil Maxfield, Ralph Main, Hal Marchant, Gale Beals, Cecil Houtz, W. L. Parrott, Arlene Penitte, W. F. Ford, Frank Moore, Alice Hendrickson, and Eula Thune. LANDSLIDES By FRED O. JONES and WARREN L. PETERSON Landslides have been an important factor in the removal of the Pleistocene deposits by the Columbia River during the formation of its present terraced valley. Many terrace slopes are scarred with the veg- etation-covered forms of old landslides and some ter— races are underlain by landslide debris. Landsliding of surficial deposits apparently began with the first inci- sion by the Columbia River and has continued to the present. The frequency of landslides was increased by the construction of Grand Coulee Dam, which ponded the Columbia River in a 144-mile stretch of the upper Columbia River valley and raised the water level at the dam 350 feet. Many terrace slopes became unsta- ble under saturation by the reservoir waters. Down- stream from the dam, fluctuation in river level imposed by the variable demands for power and housing devel- opment in old landslide areas have apparently contrib- uted to the reactivation of old landslide areas. Most of the landslides described in this report have occurred in the Pleistocene and Recent surficial de- posits of the upper Columbia River valley. These surficial deposits veneer the bedrock valley and have a terraced surface. They consist of glaciolacustrine sand, silt, and clay, glaciofluvial deposits, fluvial sand and gravel, alluvial-fan deposits, and windblown sand. TOPOGRAPHY ON THE SURFICIAL DEPOSITS About 90 percent- of the shoreline of Franklin D. Roosevelt Lake is bordered by Pleistocene sediments. On these deposits, there is a topography of terrace remnants separated by stream-cut scarps. The flatness of the terrace surfaces has been modified by deposition of extensive alluvial fans from higher slopes so that a terrace commonly rises gently away from the center of the valley. The terraces and stream-cut scarps have been extensively modified by gullying, landslid— ing, and creep. Some important factors that determine the morpho- logy of the interterrace scarps and the gully slopes are: (a) presence or absence of fluvial gravel on the terrace; 6 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON (b) type of sediment composing the terrace; (0) degree of saturation of sediment by ground water; ((1) age; and (e) erosive processes. Terraces underlain by dry silt and clay tend to have steep scarps. Silt and clay when dry are strong, and resist gravity movements such as creep and landsliding. These scarps are modi- fied primarily by gullying that, in places, has produced spectacular badland topography. Wet silt and clay are weaker, and subject to movement by creep and landsliding. Creep makes a slope more gentle. Land- sliding tends to make the lower part of a slope near the foot of a landslide more gentle but the upper part near the crown steeper. Commonly, however, slopes on wet silt and clay are gentle. Dry sand lacks cohesive strength and runs easily downslope, so that stream-cut scarps underlain by sand become more gentle until the angle of repose of the sand is attained. Sand, being permeable, is commonly dry and is not influenced by mass movements induced by excessive ground water. However, where silt and clay are interbedded with sand to form hydraulic barriers, excessive ground water may accumulate in the sediment and landsliding and related processes may modify the terrace scarp. Dry silt and clay tend to stand with the steepest slopes and wet silt and clay with the gentlest slopes. Slopes on sand are intermediate. At the time of initial filling, shorelines along Franklin D. Roosevelt Lake ranged from unembayed along scarps with minor gullies to deeply embayed along severely gullied terraces. Generally, the most intri- cately embayed shorelines occurred where dry silt and clay had been severely eroded. T YPES OF LANDSLIDES Landslides that occurred in the entire area of investi— gation before and during this investigation were principally of four types: slump—earthflow, slip-off slope, multiple-alcove and mudflow. These types are distin— guished by the form of the scars and by the kinds of movement in the sliding. The nomenclature of the parts of a landslide used here is shown on figure 2. In the data collected for the statistical analyses under the heading “Landslide—type groups” (p. 35), the land- slides have been divided into 10 type groups. However, for the purposes of the discussion presented here the fourfold subdivision will suffice. SLIIMP-EARTI-IFLOW LANDSLIDES Slump—earthflow landslides combine the processes of sliding and flow. The upper part slides downward in one or more blocks that commonly rotate slightly about axes that are horizontal and parallel to the slope in which the landslide forms; the lower part flows as a FIGURE 2.—Nomenclature of the parts of a landslide (adapted from Varnes, 1958). viscous liquid. The movement of the upper part is similar to slump, as described by Sharpe (1938, p. 65). The movement of the lower part corresponds to earth- flow or lateral-spreading described by Terzaghi (1950) and Varnes (1958). Slides of this type are illustrated on figures 11, 13, and 14. The surface of rupture is commonly concave toward the slip block in horizontal cross section. The shape in vertical cross section varies with the character of the materials. In fine grained, almost horizontally bedded materials, the surface of rupture cuts steeply from the surface to a bedding plane and then follows the bedding plane—similar to the com- posite surface of sliding described by Terzaghi and Peck (1948, p. 191). In vertical cross section the steep upper part of the surface of rupture in some slides shows curva— ture; in others it is straight. Figure 3 shows the composite surface of rupture of an ancient slide exhumed by a more recent one. The surface of rupture in coarse— grained, disturbed, and heterogeneous material in verti- cal cross section commonly takes the form of of a circle, an arc of an ellipse, or a logarithmic spiral. Slump-earthflow landslides have been more frequent and have affected more land in the area of investigation than any other type of landslide. These slump earthflows are similar to the deep de- formational slides described by MacDonald (1947) which plagued the construction of the Panama Canal. MULTIPLE-ALCOVE LANDSLIDES Multiple-alcove slides form large, basinlike features by the repeated processes of sliding, flow, and fall. This repeated action commonly results in an inter- locking group of landslide alcoves. The movement processes are chiefy those of slump-earthflow slides, but they also include mudflows and headward caving of the main scarp. When the vegetation-covered scars of ancient multiple-alcove slides were first examined, it was believed that their development took place over a period of many years. However, in the spring of 1952, LANDSLIDES 7 FIGURE 3.~An ancient slump—earthflow landslide exposed by recent sliding. Note that lower part of the surface of rupture follows a bedding plane. Fort Spokane area, lake mile 42.3 left bank. the only known recent multiple-alcove slide developed in a few days (figs. 4, 5, Reed terrace landslide 261). The large alcove continued to enlarge slowly for more than a year. In general multiple-alcove slides form in fine—grained materials Where deep channels in the bedrock are filled with deposits of surficial materials. They are similar to the Riviere Blanche slide in Quebec described by Dawson (1899), the Falles on the coast of Zeeland described by Miiller (1898), and the landslides in south- eastern Norway described by Holmsen (1929). SLIP-OFF SLOPE LAN DSLIDES Slip-off slope landslides combine in varying propor- tions the processes of sliding, fall, and flow. They are landslides in which the mass of material shows little backward rotation but slides or rolls forward. Land- slides of this type do not cut deeply into terraces. They occur most frequently in materials of medium- and coarse—grain size on slopes that lose support at the toe due to undermining by stream erosion, wave action, saturation, excavation, or similar causes. Unlike most of the slump earthflows, these landslides seldom reach their maximum development in one failure but continue to enlarge by ravelling and caving for a long period. Illustrations of this type are shown on figures 6, 7, 8. They are similar to the slope readjustments and undermined strata defined by Ladd (1935), debris slides and falls defined by Sharpe (1938), and include the sand runs defined by Varnes (1958). Because slip—off slopes have been numerous along Franklin D. Roosevelt Lake in recent times, they form the next to the largest group studied. Although damage and destruction from indi- vidual slides are less than from individual slump earth- flows, the slip-ofl' slope landslides are an important fac— tor in determining land use. M UDFLOWS Mudflows are rapid failures in which the mass of material moves like a thick fluid. Small slumps and 8 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON FIGURE 4,—Aerlal view of a recent multiple-alcove landslide. See cross section In figure 5. 1600' Varved silt and clay inter- bedded with thin beds and lenses of fine sand. Fine sand becomes thicker at depth Landslide surface Maximum lake altitude 1290 ft Underwater profile of slide from hydro- graphic surveys September 1952 _________g<1_'W_SL5flfa_°L// \‘___<:__ Old river channel ’_ ______._.._” 600 O 6OOFEET | l l I | l l | FIGURE 5.—Multiple-alcove landslide and cross section. Another View and details are given In figure 12. Rot-d terrace area, lake mile 98.65 right bank. Roosevelt Lake in left foreground. Franklin I). LANbSLIDEs 9 FIGURE 6.—Photogtaph of a typical slip-off slope landslide. See cross section in figure 7 1700‘? —1700’ 1600'— —1600’ \( Profile of original ground surface 1500'— . . —1500' Profile of landslide 1400'—- ——1400' Spokane River Bay 1300’— Maximum lake-surface altitude 1290 ft 1300' \\,/ 1200' 1200' 500 0 500 FEET l l l I l l J FIGURE 7.—S1ip—ofl slope landslide and cross section. Wave erosion or saturation of sediment by lake water caused a thin skin of material to lose support and ravel off the terrace scarp. Cross section is exaggerated vertically 3 X. Slide 105, Spokane River arm, mile 22.1 right bank. 10 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON FIGURE 8.—Slip-ofl slope landslide in sand. Slide blocks show little or no backward rotation. Surface of rupture is at shallow depth beneath surface of the slide debris. Slide 268, Kettle Falls area. falls are common along the sides and upper part of the surface of rupture. Only two mudflows have been recorded in the area in recent years (figs. 9 and 18). LANDSLIDES ALONG FRANKLIN D. ROOSEVELT LAKE Many landslides occurred along Franklin D. Roose- velt Lake in terrace scarps that became unstable when the reservoir was filled. Slides occurred in all sediment types. One cause of landslide occurrence has been the fluctuation of the surface of Franklin D. Roosevelt Lake, necessitated by power demands at Grand Coulee Dam. Consequently, the surface of the lake has been lowered different amounts during the winter and spring of each year, the maximum being 85 feet in 1955. The lowering of the reservoir surface left saturated silt and clay above the lake surface without the additional sta- bilizing effect of the weight of water against the slope. Ground water moved toward the scarp and seepage pressures developed that made the scarps less stable. The most important type of landslide on Franklin D. Roosevelt Lake has been the slump-earthflow, which has developed in all sediment types. The feet of these slides almost invariably occur well below the surface of the lake, and the crown commonly cuts into the terrace above the lake. A slide that develops in sand com- monly consists of one failure that apparently stabilizes the terrace scarp so that repeated sliding does not oc- cur. In contrast, repeated sliding occurs in silt and clay. Slides commonly have cut farther into silt and clay terraces than into sand terraces. Slip-off slope landslides have developed along much of the shoreline of Franklin D. Roosevelt Lake. This type of landslide has occurred most frequently along sand terraces. During the initial filling of the lake, LANDSLIDES 11 saturation of terrace materials weakened the sediments and caused failure. Subsequently, undermining by wave erosion has been the principal cause. Along most of the shoreline of the lake, low wave-cut clifl's had formed by 1955, except where shorelines were bor- dered by bedrock, were composed of Pleistocene sed— iments with very gentle surface slope, were in protected embayments, or had been recently modified by slump- earthflow land slides. One multiple-alcove landslide (fig. 4), at the Reed terrace, has formed since the filling of the lake. Landslides commonly aflect only the lowest terrace at a given place on Franklin D. Roosevelt Lake. Most slides occurred in terraces at altitudes of 1,450 feet and below, but a few occcurred in the 1,600—f00t terrace. The deep lake standing against the scarps in which the landslides originate provides an avenue of escape for the slide debris from the site of a slide. Upon descend- ing the slope, the debris enters the water and, mixing with the water, moves as an underwater mudflow or a turbidity current into deeper parts of the lake. This action occurs in all sediment types. Sand, lacking cohesion, forms a mixture of sand grains and water which flows away across the underwater surfaces. Two kinds of mudflow action probably occur with silt and clay debris. Where silt and clay are dry, the chunks of debris probably remain largely intact but are lubri- cated by water and by some mud, which enables the mass to descend the underwater slopes. Where the silt and clay are saturated, the disturbance causes this sediment to lose its form-retaining strength and in part become a Viscous mud. Water is added to the FIGURE 9.—Mudflow in Hopkins Canyon occurred on February 2, 1953, at about midnight; it lasted an estimated 7 minutes and destroyed a small house. flow originated in the alcove in the background which before the mudflow was an area of seeps. right of the alcove. so mobile that a mudflow resulted. 581004 0—61 2 This feature is analogous to the slump-earthilow landslide with slumpblock above and earthflow at the toe. Slide 295, N espelem River-Omak Lake valley area. The mud- A slump block which settled during or after the mudflow lies to the In this instance, the earthflow was 12 mass as it enters the lake and the debris moves down- slope as an underwater mudflow. The slide alcoves are completely empty of slide debris along most of the shore of Franklin D. Roosevelt Lake (figs. 12 and 14). Notable exceptions occur in the Sanpoil valley where large masses of slide debris remain in some slide alcoves. AREAS OF EXTENSIVE LANDSLIDING Five areas in the Columbia River valley were 'selec- ted for detailed study and description because they each contain many slides of considerable interest. These are the Reed terrace, Cedonia, and Ninemile areas along Franklin D. Roosevelt Lake, and the LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON Seatons Grove-Koontzville and Nespelem River areas downstream from Grand Coulee Dam (fig. 10). RED TERRACE AREA The Reed terrace area is on the right bank of Franklin D. Roosevelt Lake about 3.5 miles south of Kettle Falls bridge (figs. 1 and 10; pl. 1). This area has been one of the most active landslide areas along the upper Columbia River valley in recent years and geologic mapping suggests that landslides also occurred here in the distant past. The area includes the Main terrace at an altitude of about 1,480 feet and '3 smaller terraces. Of these, the Sherman Creek terrace is the highest, 119°30’ 119°00’ 118°30' 118°00' - _ _ __ _ _ _ _ _‘ _ _ _ _ __ _ _ _ _ 1440/ / Northport—lnte EXPLANATION // Bos ‘ Area in which landslides were Investigated Kettle River arm e; *Marcus—Ev ans ,_ _ _ _ _‘ 0.0 / : ; 104,0 : : //‘,l‘ r33 “ / | 4, Ancnent landslide mategal ///// KTTVAX¥$YT Seep area ‘ ”Tins Mm .m- 4 //// \:\ W/ t: / (’47—wa DAM / p f l\ ///// . ////, // 414’“, $W‘T‘rT—rj. 7‘7: TT xSp'rim Granite . //// \}§\:~ (fTTTT-r Line of section ”I: FT // ‘ ‘ ‘ x (pl.4) 7 // i FTTTTTTTTTT Tr» //' /- DDH ll *s~ \' STATE VOA / DDH yo ////’////’- ///////////§/7/Z7 9/ we I I ’V Granite 777% 7/”th "I” , lllilllllll' II” ‘ {/I‘lff'il l / Il”limi- l« l“ ,W/l / //// //// ////. .l Granite "I! ” «11mm % Ill/v ///// l //n / ///// , /////%¢, , Granite 2' 9/0 /' 57, /’///; ,/ , ’///. Ancient landslide material Seep area —/ EXPLANATION DDH 12 Diamond-drill hole TTTTT Ancient slide scarp ‘l—‘l—‘l—‘l—fi— Recent slide scarp T‘PT‘V‘T Ancient and recent slide scarp in surficial materials “WV—.— Ancient and recent slide scarp along bedrock FIGURE 16.—Seatons landslide. An area of ancient landslides that was reactivated in 1948 and moved intermittently through. 1953. The diagram shows the major slide scarps as of April 12, 1949, and the position of the cross section plate 4. Grand Coulee Dam-Belvedere area, river mile 5.1 right bank. Many factors influenced the renewed landslide action in this area, of which the following seem the most important: 1. The unusually heavy rainfall during the spring and summer of 1948. 2. The high water in the Columbia River during the flood of May and June, 1948, undoubtedly resulted in a higher water table throughout the entire slide area. 3. The flood eroded and unloaded the toe of the slide, which is on the outside of a bend in the river where erosion would be greatest. 4. Melt water from the heavy snowfall in the winter of 1948 and 1949 kept the slide lubricated and moving after sliding began. 5. Very deep freezing in the winter of 1948 and 1949 may have had some effect in extending old slide cracks and in damming ground water. 6. Seatons Lake was created in a key position at the head of the ancient slide so that it kept much of the lower part of the ground saturated. Springs on the lower slopes of the hill produced more water when the level of Seatons Lake was higher, and 7. the lake surface was raised purposely at times to make the springs at lower altitudes flow at a greater rate for irrigation. The material at the toe of the slide consisted of silt and clay thinly mantled with sand, gravel, and boulders (fig. 17). Silt and clay could be observed pushing through the gravels at several places along the toe of the slide. Since the construction of Grand Coulee Darn, a replacement supply of sand and gravel to cover and protect the silt and clay from erosion had been largely cut ofl’. The extensive use of this area for homes, gardens, irrigated tracts, and roads had undoubtedly been a factor in encouraging the renewed activity of the slide. Renewed activity might have been postponed if the natural cover of grass and sagebrush had not been removed and if the streams had been kept in their natural channels. The principal spring (fig. 16), which flowed a full stream through a 2}é—inch pipe, supplied the entire area with domestic water. The other two springs in the drainage above were about the same size. The small stream, which was seasonally diverted into Seatons Lake, flowed between 0.5 and 0.6 cfs, even in dry years. The stream probably flowed about 1 cfs in the early spring and during unusually wet seasons 24 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON The supply of water to the main spring was cut ofl’ during the slide of November 1948, but the flow of water was restored to about normal by driving a pipe into a small seep which broke out near the spring. The spring water was milky for several days before it cleared. In 1953, the Corps of Engineers drilled three test holes in the slide to obtain undisturbed samples of the underlying materials and to install gages to record the pore—water pressures in the soils throughout the year. The material penetrated in the test holes and the ground-water data are shown on plate 4. The main scarp of much of this slide exposes granite, and the upper part of the surface of rupture follows the contact between surficial deposits and this bedrock. In the initial movement on November 29, 1948, the FIGURE 17.—Slickensides showing the upward and riverward (right) movement of the downstream side of the Seatons landslide. Striations are on the moved block which is composed of lacustrine silt and clay overlain by liver gravel (rock at top of the photograph is a large boulder). Undisturbed material in the foreground. Photo- graph by H. W. Fuller for U.S. Bureau of Reclamation. LANDSLIDES 25 slide sank 12 inches at the scarp. During the winter SEATONS MUDnowmo'm) and spring of 1950—51 the slide sank 9 inches; during On March 17, 1949, a mudflow occurred on the edge the same season in 1951—52, 7 inches; and during 1952— of the Seatons landslide (fig. 18). The materials of 53, 3 inches. No movement was observed or recorded this mudflow were predominantly silt and clay that during 1953—54. filled a steep-sided valley in granite. The mudflow was FIGURE 18,—Mudflow at Seatons Grove, in the foreground, occurred March 17, 1949, at 6:30 p.m. Severalobservers were almost trapped by the advancing mud. Stria- tions at extreme left were formed as the mudflow crossed undisturbed material. Slide 320, Coulee Dam-Belvedere area, river mile 5.1 right bank. 26 caused by the lowering of the main unit of the Seatons landslide, which removed support, and by the high ground-water already described. People had been watching the bank for several hours, having been at- tracted by the noises and small bursts of mud and water. Suddenly, at 6:30 p.m., the whole mass burst and flowed as soft mud over the area. A large quan- tity of water was released from the materials as they ruptured; simultaneously, a new spring broke out near the top of the main scarp. Several observers were almost trapped by the advancing mud and water. The left foreground of figure 18 shows a mud—slickensided surface over which a part of the mudflow flowed. KOONTZVILLE LANDSLIDE (N0. 5) The Koontzville landslide involved the entire village of about 35 houses, one store, and a section of State Highway 10A. The village was built in 1934 and 1935. LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASIIINGTON The general setting is shown on figures 19 and 20. Old landslide materials extend from river level almost to the top of the terrace, or to an altitude of about 1,600 feet. Little or no landslide activity was noticed before the 1948 flood. There may have been some slight highway settlements or minor movements owing to irrigation and river-bank erosion below the highway, but no prop- erty damage from landslides was reported. In the fall of 1948 (about the time of the Seatons landslide movement) one resident of the area had trouble with water pipes parting and resorted to flexible hose con- nections to keep his water system operating. So far as is known, this marked the beginning of reactivation of the ancient slide. The slide has moved many times since. Movements are recorded on the following dates: December 23, 1951; November 10 or 11, 1952; Novem- ber 27, 1952; and January 10, 1953. FIGURE 19.—Photograph showing the Koontzville landslide and its relationship to the Seatons landslide (see diagram, fig. 20). LAN DSLIDES 27 Ancient landslide material (”f-(111’ k K k ,\ 3‘ X x ‘A f i J i ,3 i X 1 1%”:— ii 1 Spring/(3; yyy \ DDH 9 1 y)’ a} ;y* Line of section X i}. r} (0L4) * kg / 7 )1) F‘s 7’ ntzville/ llandslideyi / / 1 Spring area y” »\ .9" ./ \/):'yy >’ / . )a’»} y }yy y)’ ’Aa 4—”) ,v/ y” EXPLANATION )’ )/ y) X 2’ J.)— DDH 9 X A..Lm14¢4— *“*’ Diamond-drill hole TTTTT Ancient slide scarp T‘T-TTf Recent slide scarp \ '\ 3 TT‘l—TT 1 Ancient and recent slide scarp A . t ' a n d 5 | i d e m a in surflcial materials n c l e n ”(TTTT‘W‘FFF Seatons landslide ,z‘bi / 1‘ r// r I " \ IV/ 2/ Z/ 55x riite Zl/ " 7 Ancient «, Ali} " 7/ landslide ill ' material [27/ T'V_I_"‘_'— Ancient and recent slide scarp along bedrock FIGURE 20.—The Koontzville landslide showed signs of reactivation in 1948 and movements occurred in 1951, 1952 and 1953 which damaged many houses and State High- way 10A. Diagram shows the location of cross section plate 4. Coulee Dam-Belvedere area, river mile 4.6 right bank. In contrast to the diminishing rate of movement observed in the Seaton slide since 1948, the Koontz- ville slide seemed to move more and at more frequent intervals in successive years to and including the spring of 1953. Local residents have noticed that their houses cracked and moved each weekend during low stages of the Columbia River, which corresponded to drops in river level due to power operations at Grand Coulee Dam. Many houses and the store have been severely damaged, the springs have changed their courses, large fisSures have crossed the village area, and each year the slide has worked farther back into the hillside. In 1952, a fissure connected the Koontzville slide with the Seaton slide along the silt-granite contact (fig. 20). The displacement in 1955 extended all along the bed- rock outcrops between Seatons Grove and Koontzville. Vertical movement along this bedrock scarp ranges from a few inches to 5 feet. Before the 1948 movement 581004 o—eL—a there was a light-colored zone on the granite immedi- ately above the contact with the surficial deposits which ranged in width from 0 to 15 feet. Above this zone, all the granite wall is much darker due to weathering and organic growths. This light—colored zone may rep— resent the amount these slides moved down following an earlier Columbia River flood such as the one in 1896. Geologically, Koontzville is in a setting Where the sequence of Pleistocene deposits is the most favorable for landsliding. A preglacial channel of Peter Dan Creek underlies Koontzville and because of this geo- logic setting ground-water conditions are very high. Conditions similar to this have been described in the Reed terrace area, and they can be anticipated, almost without exception, where deposits of silt and clay now occupy the area of confluence of preglacial valleys with the main valley. 1 28 The causes of the initial reactivation of this ancient landslide seem to parallel those outlined for the Seatons landslide. The causes of the periodic movements, how- ever, are not well understood. In 1953, the Corps of Engineers drilled three test holes in the slide to obtain undisturbed samples of the soil and to install gages to record pore-water pressures throughout the year. The materials found in the test holes and the ground—water data are shown on plate 4. NESPELEM RIVER AREA The N espelem River area (pl. 5; fig. 10) contains large masses of landslide debris and the scarps of many ancient landslides. The area lies about 10 miles down- stream from Grand Coulee Dam and is within the area of the Chief Joseph reservoir. GEOLOGY Bedrock of the Nespelem River area is mostly the granite of the Colville batholith, although in the south- western part of the area the Columbia River basalt crops out. A granitic gravel which crops out in the lower part of the valley is probably the oldest unconsolidated deposit in the area (pl. 5). This gravel extended from below present river level to an altitude of at least 1,200 feet. It was largely removed by erosion before the deposition of the overlying sediments. Remnants are composed of stratified angular to rounded fine gravel and angular coarse sand consisting almost entirely of granite and minerals derived therefrom. The next younger sediment is a lower lacustrine sequence of which 20 feet of fine sand overlain by at least 100 feet of varved silt and clay is exposed in Kaiser Canyon. The top of this exposure is at an altitude of 1,400 feet. About 0.5 mile north of Kaiser Canyon, in the SE1/4SW1/4 sec. 14, T. 30 N., R. 30 E., fine to very fine sand with minor thin beds of silt and clay is exposed between altitudes of 1,400 and 1,520 feet. Still higher beds in the sequence crop out in gullies in the SEl/4 sec. 11, T. 30 N., R. 30 E. Here the following section is exposed. (digiti- mate) Sand, fine-to coarse, with lenses of fine gravel (exposed up to altitude of 1,700 ft) ____________________________ 20 Covered interval, probably sand ______________________ 80 Sand, fine to coarse, contains lenses of fine gravel 2 to 6 in. thick with cut and fill bedding; beds are deformed- _ _ _ 10 Very fine to medium sand with minor silt and clay, con- tains lenses of fine gravel 12 in. thick at an altitude of 1,550 ft __________________________________________ 70 Very fine to fine sand containing some silt and clay in beds 1/16 to 1/5 in. thick; base of exposure at an altitude of 1,500 ft _________________________________________ 20 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON Immediately overlying the lower lacustrine sequence is a basalt gravel a few feet to 50 feet thick that is over- lain by 3 to 8 feet of silty gray compact till that contains basalt stones. After deposition of the basalt gravel and till, melt water flowing southward along the wasting glacier formed ice-marginal terraces and channels along the east side of the Columbia River valley between altitudes of 1,760 and 2,400 feet. These terraces are underlain by sand and gravel of undetermined thickness. Stream erosion occurred after the deposition of the ice- marginal gravels and before the deposition of the next younger deposit, an upper lacustrine sequence. The upper lacustrine sequence consists of faintly graded silt and clay varves 5 to 15 inches thick with a distinctive yellowish-gray color. Scattered ice—rafted pebbles and calcareous concretions occur in the se- quence. Just south of the Nespelem River map area the original thickness of the upper lacustrine sequence must have been between 500 and 700 feet; in the map area, however, the thickness probably does not exceed 50 feet. Gravel in terraces at and below 1,400 feet in the Columbia River valley was deposited by the river during postglacial dissection of the upper lacustrine sequence. This gravel ranges in thickness from a few feet to at least 7 0 feet and consists mostly of subrounded pebble gravel. Overlying the fluvial gravel are alluvial fans of sand and silt as much as 50 feet thick which have been built on top of the terraces at the mouths of tributary valleys. (menu. HISTORY The first glacial event recorded in the Nespelem River area is the deposition of the granitic gravel, which is inferred to be of glaciofluvial origin. A subsequent ad- vance of the Okanogan glacier lobe blocked the Colum- bia River valley downstream from the Nespelem River area and formed a lake in which the lower lacustrine se- quence was deposited. Further advance of the glacier lobe into the area caused overriding of the sequence and deposition of basalt gravel and till. After the lobe re— treated, the Columbia River cut down to the profile of the modern flood plain. Later, the Okanogan lobe again blocked the Columbia River valley and formed the lake in which the upper lacustrine sequence was deposited. LANDSLIDES An elongated area of ancient landslide topography lies on the east side of the Columbia River valley from the N espelem River southward to Kaiser Canyon (pl. 5). The southern part of this area is bounded on the west by the Columbia River and the northern part is separated from the Columbia by a terrace at an alti- tude of about 1,160 feet. The slide topography in the LANDSLIDES 29 northern part of section 10 consists of narrow north- ward-trending ridges, suggesting that a series of slices broke away from the scarp of the 1,400-foot terrace and descended westward. Aerial photographs show that the west edge of this higher terrace forms a scarp slightly concave westward. Strongly disturbed lacus- trine beds are exposed where the north ends of the ridges are exposed in the N espelem River valley. These slides in the northern part north of section 10 occurred during the cutting of the 1,160-foot terrace. This inference is based on the interpretation that the west edge of the slide topography is a stream-cut scarp. Apparently the slide material became stable enough to maintain a low scarp while the river still ran at its toe. South of the center of sec. 10, T. 30 N., R. 30 E., the boundaries of the area of slide topography diverge to the east and west. Exposures in the small south- westward-trending stream valley in the NW% sec. 14, show that the beds underlying the north-south trend- ing ridges dip steeply eastward. Initial sliding here was probably contemporaneous with the sliding to the north, though the sliding cannot be dated any closer than being younger than the cutting of the 1,400-foot terrace. There has been movement since the cutting of the 1,160-foot terrace. The slides south of the middle of sec. 10, T. 30 N., R. 30 E., may have been caused largely by the abun- dant ground water in the sediments that fill the buried bedrock valley of the Nespelem River. Underground water passing southward through the sediments in the N espelem River valley reaches the surface in springs that issue into gullies in the SE% sec. 11, and the N EM sec. 14, T. 30 N., R. 30 E., at altitudes of 1,400 to 1,550 feet. This altitude range generally coincides with the transition zone from silt and clay to sand in the lower lacustrine sequence. The high concentration of ground water combined with river erosion at the toes of slopes on silt and clay has provided an ideal setting for land- slides. Erosion of the gullies in the SEM sec. 11, and the NE% sec. 14, T. 30 N., R. 30 E., has been accom- plished largely by spring water since the development of the slide topography north of Bailey Basin. Bailey Basin, landslide 13 (figs. 21 and 22), in the southern part of the map area is a huge ancient slump- earthflow landslide, the finest example of its type in the entire area studied. It is in the right bank of the Columbia River, 11.86 river miles downstream from Grand Coulee Dam in the Chief Joseph Dam reservoir area (pl. 5). The altitude difference from the crown of the slide to the estimated position of its foot is 700 feet, and the horizontal distance between these points is 3,600 feet. The width along the terrace scarp is 3,000 feet. ' The Columbia River in this area begins a long sweep- ing left turn. Bedrock outcrops in the left bank de- flects the erosive power of the river into the bank of surficial deposits at the toe of the slide. It seems likely that this erosion, along with very high ground-water conditions, set the stage for failure. Seismic studies of the configuration of the bedrock surface beneath the slide indicated that bedrock in the half of the basin nearest the river is at about the same altitude as the riverbed, 940 feet, and that near the bottom of the main scarp it has an altitude of 880 feet (fig. 21). Bedrock was indicated at an altitude of 1,315 feet in the terrace just behind the crown, and on the terrace east of the crown at altitudes between 1,100 and 1,516 feet. From these data it may be interpreted that the upper part of the surface of rupture has been controlled by a steep slope on the underlying bedrock and that the lower part of the surface of rupture generally fol- lows the contact between bedrock and the overlying silt. As can be seen from plate 5 and figures 21 and 22, the river channel is now narrowed by landslide debris. As the river erodes the toe, small new landslides devel- op in the ancient slide material. The channel and shoreline are dotted with large basalt erratics which were carried down by the slide. LANDSLIDES IN THE COLUMBIA RIVER BASALT Scars from landslides that occurred during and after Pleistocene time are numerous in the cliffs of the C0- lumbia River basalt which forms the upper part of the Columbia River valley downstream from the conflu- ence of the Spokane River. Examples of landslides that have occurred since the last invasion of glacial ice are to be found at the following localities: (a) east end of the town of Grand Coulee; (b) west side of the Grand Coulee near its intake; (0) sees. 15, 22 and 23, T. 30 N., R. 28 E.; and (d) on the west side of the Omak Lake valley near its junction with the Columbia River in sec. 6, T. 30 N., R. 28 E., sec. 31, T. 31 N., R. 28 E., and sec. 36, T. 31 N., R. 27 E. These landslides defi- nitely postdate the last glaciation, because the debris retains its characteristic form and is not covered with glacial deposits. Examples of landslide scars older than the last glaciation occur at the following localities: in sees. 20, 21, and 22, T. 28 N., R. 31 E.; and in the left Columbia River bluff between 3% and 6% miles downstream from the junction of the Omak Lake val- ley with the Columbia River valley. The basalt flows lie on a fairly even surface with altitudes ranging from 2,000 to 2,200 feet, in the area from Grand Coulee Dam to the Omak Lake valley. Between and beneath the basalt flows are lacustrine 3O LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON FIGURE 21 .—-Aerial photograph showing landslide in Bailey Basin. Columbia River in foreground. Note recent landslides at the river's edge. Landslide 13, Nespelem River area, river mile 11.86 right bank. Cross section shown in figure 22. 1700’ [— _ J Lacustrine silt and fine sand é“‘Crossbedded basalt gravel 1500' — 1300' 1100’ '? Landslideedehr-is Sf s'a'nd,‘.5_,‘. ,- ‘ - gravel, silt, and Clay 3 . ' . ’ ' .a__.a‘ Columbia Bed rock/ 900' — 1200 0 1200 FEET L | 700’ FIGURE 22.—— Ancient slump-earthflow landslide and cross section. This well-preserved ancient landslide is designated Bailey Basin on the Nespelem River geologic map (pl. 5). Distance from side to side of the landslide scarp is about 3,000 feet. Several intermittent springs rise in the slide debris. Abundant ground water coupled with river erosion set the stage for sliding. LANDSLIDES \ 31 and fluvial sediments of silt, sand, and fine gravel. These sediments are well exposed in the Grand Coulee and in the Omak Lake valley and probably occur throughout most of the area. They are more than 100 feet thick in the Omak Lake valley in sec. 25, T. 31 N., R. 28 E. The landslides that form huge alcoves in the basalt have apparently failed on these sediments. A notable feature of the Columbia River valley between the mouth of the Spokane River and Bridge- port is a steplike effect produced by the-recession of the basalt clifl’s acoss the granite base away from the part of the Columbia River valley incised in the granite. Several explanations are possible but landslide scars and masses of disturbed material suggest that much of the retreat of the basalt cliffs was due to landsliding. The sporadic nature of the widening indicates that some localities were more susceptible to landsliding than others. SUMMARY OF POSSIBLE CAUSES OF LANDSLIDES The principal cause of the landslides in the area was the weakening of sediments by ground water. The sediments generally have a lower shear strength when saturated or partly saturated than when dry. During the filling of Franklin D. Roosevelt Lake the sediments bordering the lake became saturated and many land— slides occurred. Apparently, buildup of ground water in certain areas downstream from Grand Coulee Dam has been the principal cause of landsliding there. In an attempt to determine if other factors could have triggered the landslides, the dates of occurrence of 50 landslides that were accurately known were plotted on correlation charts against several possible influenc- ing factors. These landslides occurred between 1941 and 1953. The factors considered were: (a) fluctua— tions of the level of Franklin D. Roosevelt Lake, (b) riverflow, for slides in the part of the area down- stream from Grand Coulee Dam, (c) barometric pres- sure, (d) maximum and minimum temperatures, (e) precipitation, (f) earth tides and (g) earthquakes. Most of these factors showed no obvious correlation with the times of landsliding. Some relations, however were brought out. Landslides along Franklin D. Roosevelt Lake were most frequent during the filling stage of the reservoir (fig. 23). Since the filling of the reservoir, landslides have been most frequent during periods of drawdowns and during or shortly after periods when the temperature was below freezing. Landslides, along the Columbia River downstream from Grand Coulee Dam were most frequent following and apparently related to a sharp reduction in riverflow and following a 9-month period when precipitation was above the 13-year average. Reservoir filling _ , (_A_‘3O~ft reservonr 65-ft reservmr drawdown drawdowns r—Kfi 1 , . . 60 Minor reservow fluctuatlons r— _._—4__ ._ . _ 150 100 50 ESTIMATED NUMBER OF SLIDES 1515 15 15. 1953 FIGURE 23.— Histogram showing esimated frequency of all landslides along Franklin D. Roosevelt Lake, 1941 to 1954. Number of landslides during this period estimated to be about 500. ECONOMICS Landslides cost at least $20 million in the upper Columbia River valley from 1934 to 1955. Most of this cost has been paid by the taxpayers through federal, State, and county agencies engaged in the con- struction of engineering works. Some of the cost of landslide damage has been borne by private companies and individual property owners. The most skillful geologic and engineering analyses and construction practices could not have saved all of this money, but a large part of it could have been saved had presently known geologic facts been available and had engineers applied them in designing and construction work. This section briefly summarizes the landslides at the site of Grand Coulee Dam and summarizes the cost of remedial measures to correct landslide action for a few locations. LANDSLIDES AT GRAND COULEE DAM2 The construction of Grand Coulee Dam was hindered by a succession of major and minor landslides along both banks of the river (fig. 24). More than 100 sep- arate slide movements were recorded between January 1934 and January 1952, many of which caused damage to structures or other features of the work. In the re- cent geologic past, erosion and landsliding had reduced 3 Summarized from memorandum to Chief Engineer, Bureau of Reclamation, Denver, Colo., from B. A. Hall, acting supervising engineer, Grand Coulee Dam, Wash., Historical record of riverbank slides at Grand Coulee Dam, Columbia Basin Project, Wash., 1952: published by permission of Bureau of Reclamation. 32 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON FIGURE 24.—Slump~earthflow landslide in lacustrine silt and clay. One of the many landslides that hindered the construction of Grand Coulee Dam. Located in what is now the pumping plant area at the left abutment of the dam. the surficial deposits at the damsite to slopes which were relatively stable to the normal flow and fluctua— tions of the river. This temporary stability was dis- turbed by excavation of material at the toe of the slopes, mechanical overloading of existing banks, shift— ing of the river course, and controlled fluctuations of the river level. Landslides during the early years of construction (1934—37) were caused primarily by excavation along the toe of riverbank slopes. Many of the later slides may have been due in part to earlier excavation or overloading near spoil banks. To facilitate construc- tion work, the river was often shunted from one side of the channel to the other. Such diversions were (Photograph by F. B. Pomeroy, Bureau of Reclamation.) accomplished by the use of temporary closure gates which, when lowered into position, sometimes caused rapid drops in the water level below the dam and con- Sequent landsliding. There were very few landslides after the dam had been nearly completed and before the time when the operation of the powerplants re— quired sharp fluctuations of discharge to meet varying powerload demands. There were no slides during 1944 and 1945. As the installed capacity of the power- plants increased, greater regulation of turbine discharge was necessary to meet varying power demands. Dur— ing this time landslides in the tailrace area of the dam, as well as those in the areas immediately downstream, were closely related to the sharp fluctuations in the STATISTICAL STUDIES river level during periods of low discharge. Excessive river scour due to the 1948 flood was probably also a major cause of increased slide movements in 1948—52. Frequency of recorded landslides at Grand Coulee Dam and in the area just downstream Year Number Remarks of slides 1934 _____ 11 Excavation and construction; many di- 1935 _____ 16 versions of river from one side of the 1936 _____ 9 channel to the other and accompanying 1937 _____ 21 fluctuations. 1333 """ 1? Construction, fewer river, changes and fluc- 1940 """ 6 tuations than in 1934—37. 1941 _____ 1 1942 _____ 4 1943 _____ 2 Minor sharp river level fluctuations. 1944 _____ 0 1945 _____ 0 1946 _____ 2 l 947 _____ 1 1948 _____ 3 Period of increasing river fluctuations due to 1949 _____ 1 greater installed capacity of Grand Coulee 1950 _____ 7 powerplant. Columbia River flood of 1951 _____ 3 1948. 1952 _____ 5 1953 _____ 1 COSTS OF LANDSLIDES Information on costs of remedial measures to correct landslide activity is available for a few locations. Left tailrace landslide area, Grand Coulee Dam?— Landsliding of the Pleistocene deposits in the bluff near the left tailrace of Grand Coulee Dam began on March 27, 1934, when as a result of excavation the hillside dropped vertically about 100 feet. The cost of stabi- lizing this landslide area was more than $6 million. The initial failure required an estimated 1% million yards of additional excavation. Movements and en- largements of the slide continued to 1950, and although renewed activity is not impossible, engineers of the Bureau of Reclamation consider the area to be stabi- lized. The stabilization was accomplished by extensive excavation to unload the slope; by installation of a system of underground drainage shafts, drifts, and radiating weep holes; by the construction of a rock-fill plug at the toe of the slope Where the slide mass was confined in a narrow bedrock gorge; and by loading and protecting the toe of the slope with a heavy blanket of riprap. Great Northern Railway slide 4, No. 272.——The Great Northern Railway landslide near Marcus, Wash., cost $239,000 for railroad relocation and the excavation of slide material from the highway (fig. 25). This slide of ' Published by permission of U.S. Bureau of Reclamation. 4 Published ’by permission of Great Northern Railway. 33 Tabulation of costs of landslides at Grand Coulee Dam [Less engineering supervision and costs] 1934—35 Excavation _________________________ $1, 500, 000 1936-40 Drainage shafts and tunnels ___________ 259, 000 1936 Rock dam at toe of part of slide _______ 215, 000 1936 Gravel blanket above rock dam at toe of part of slide ___________________ 84, 000 1940—41 Unloading and resloping ______________ 668, 000 1948 Riprap and riverbank protection _______ 363, 000 1949—51 _____ do ____________________________ l, 390, 000 1951~53 _____ do ____________________________ 1, 580, 000 $6. 059. 000 February 23, 1951, destroyed several hundred feet of track of the Nelson branch of the Great Northern Rail- way, blocked State Highway 22 with slide debris, and narrowly missed a school bus full of children. It was necessary to excavate a bench in bedrock to restore rail- road operations—the cost of which was $230,374. Clearing the highway cost $8,719. Deadman Greek slide 5 No. 271.——Relocation of Wash- ington State Highway 3 around the Deadman Creek landslide cost $112,000 (fig. 26). This slide is located in the Kettle River valley 5.5 miles north of the Kettle Falls bridge. Sanpoil valley landslidesfi—Many landslides damaged or destroyed parts of relocated Washington State High- way 4 along the west side of the Sanpoil River bay of Franklin D. Roosevelt Lake. The Washington State Highway Commission estimates that landslides along these 9 miles have cost $327,000, and that it will cost an additional $500,000 to provide a permanent roadbed in this section. STATISTICAL STUDIES During this investigation data were collected on more than 300 landslides. Enough data were collected only on recent slump-earthflow landslides to justify detailed statistical treatment. Two formulas that apply to a geologic environment similar to Franklin D. Roosevelt Lake resulted from the statistical analysis: (a) a formula predicting where slump-earthflow landslides will or will not occur, and (b) a formula predicting how far into a terrace a slump-earthflow landslide will cut. FIELD OBSERVATIONS AND METHODS BY FRED O. JONES Studies were made on more than 300 landslides in the Pleistocene deposits along the upper Columbia River valley. Early examinations along Franklin D. Roose- velt Lake revealed a wide range in the size and shape of landslides. These differences seemed to be related to the particular geologic settings of the slides. However, 5 Published by permission of Washington State Highway Commission. 0 Published by permission of Washington State Highway Commission. 34 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY NORTHEASTERN WASHINGTON FIGURE 25.—Great Northern Railway slide near Marcus, Wash. This landslide occured from 7 to 9 a.m.. on February 23, 1951. way track (roadbed shown at the crown of the slide). up to 1949, studies were inconclusive as to why slides oc- curred in one place and not in another, and as to why slides out deeply into one terrace and shallowly into another. A comprehensive study begun in 1950, attempted to relate the occurrence, magnitude, and location of the slides to the geologic environment. The first field problem was to differentiate between the various types of landslides. The second field prob- lem was to establish a satisfactory breakdown of the geologic controls. A data card was devised on which all obtainable information was catalogued. Figures 27 and 28 show both sides of one of these data cards for a typical land— slide case. This illustration shows the original classi- fication categories and their subdivisions. As the work of classifying and measuring progressed, it became ap- It destroyed several hundred feet of rail- Repair of the roadbed cost $230,374. Cost of removing slide debris from a highway shown at left side of the photograph was $8,719. Photograph by courtesy of the Great Northern Railway Co. parent that some classification subdivisions were unreal- istic and some unnecessary. Early statistical analyses indicated that others should be combined or expressed in different forms; for example ground water was orig- inally expressed in four classification categories. Pre- liminary statistical tests indicated that 3 of these were almost identical for all practical purposes, so the factor, ground water, was divided into only 2 categories. The factors—terrace height, original slope, and submer- gence——were originally classified into arbitrary cate- gories, but statistical studies indicated that a more precise appraisal of these factors could be made by using the true numerical value. This scheme was adopted. The definitions of classification categories given in the following sections were revised many times during STATISTICAL STUDIES Slump-earthflow landslide that destroyed several hundred feet of Washington State Highway 3 in the Kettle River valley. Cost of relocation of the highway was $112.000. FIGURE 26.—Deadman Creek landslide. the investigations. All landslide data referred to or used in any part of this report are tabulated on tables 1—9 under the heading “Tables of landslide data,” p. 74. Each landslide was located by geographic subdivi- ision, lake, or river mile distance from Grand Coulee Dam and its position on the right or left bank of the river or lake. Figure 10 shows the location and extent of the geographic subdivisions. Theoretical lake mile stationing was established along the center of Franklin D. Roosevelt Lake beginning with zero at the spillway of Grand Coulee Dam. The same system of river mile stationing was adopted downstream from Grand Coulee Dam, again with the spillway as river mile zero. Land- slides in bays of the lake were located by distances from the mouths .of the bays and whether on the right or left bank. Almost all these bays are at the mouths of trib- utary streams. Owing to the large number of landslides, numbers have been assigned to all landslides mentioned in any part of the report. The numbers are not necessarily related to the order of occurrence of the landslides or to the order in Which they were studied. LANDSLIDE TYPE GROUPS The landslides were classified into 10 type groups, which is an expanded classification of the 4 general types of landslides previously discussed. They conform only in part with the general landslide classifications estab- lished by Baltzer (1875), Terzaghi (1925), Ladd (1935), Sharpe (1938), Varnes (1958), and other investigators. The factors which were considered in establishing the type groups were: age, relation to bedrock, and proc- esses of movement (mainly sliding, flow and fall). The 35 term “recent” in type-group classifications and else- where in the report refers to landslides whose times of occurrence are recorded or can be recalled by local in- habitants. The term “ancient” in type-group classi- fication refers to landslides Whose times of occurrence are not recorded or cannot be recalled by local inhabi- tants and therefore presumably occurred long ago. All slide scars classified as ancient are now covered with vegetation indicating a great lapse of time since the ‘slide occurred. Almost all of the recent slides since 1940 have been due, either directly or indirectly, to the effects of major engineering projects. The nomenclature of the parts of the landslide used here is shown on figure 2. The 10 landslide type groups included in the study; with the number of each are as follows: Number 0 land— : idea in study 1. Recent slump earthflows ________________________ 184 2. Recent slump earthflows limited by bedrock _______ 4 3. Ancient slump earthflowe ________________________ 41 4. Slip-off slopes __________________________________ 51 5. Multiple alcoves _______________________________ 9 6. Landslides ofi bedrock ___________________________ 10 7. Talus slumps __________________________________ 3 8. Landslides in artificial slopes, including some natural materials ___________________________________ 7 9. Mudflows _____________________________________ 2 10. Dry earthflows _________________________________ 3 Unclassified ___________________________________ 7 Total in study ________________________________ 321 Recent slump-earthflow landslides.—Slump-earthflow landslides have been described in a foregoing section of the text under the heading “Types of landslides” p. 6. ‘This type group includes slope failures in which the surface of rupture intersects the slope at or above its toe, and base failures in which the surface of rupture lies at some depth below the toe of the slope. It has been impossible to determine this difference from field examinations for most of the landslides in this study; consequently, it was necessary to group them together. Landslides of this type have been found in about equal number in all material categories. Recent slump-earthflow landslides limited by bed- rock—Many slump-earthflow landslides are limited in their extent by bedrock (fig. 29). This group is similar in every respect to the recent slump-earthflow group except that the uppermost part of the surface of rup- ture follows the contact between surficial deposits and bedrock. Ancient slump-earthflow landslides—The terraces of the upper Columbia River valley show the scars of innumerable ancient landslides, most of which appar- ently date back to a time when river and lake levels 36 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASIEHNGTON I | I I | I I | | l I | I I | I I E 3 4 6 7 2| 22 23 2‘ 3| 32 33 ll 42 41 5| 5! 53 94 VERY WET DRY VERY 0'. I00: DVE’.‘ GOOD EMU POOR OVEN III ZII 3H ‘J ”NDEK MATERIAL WET DIV I00 20° 200 III ZII SCI 41' 5] 5CI GROUND WATER TERRACE HEIGHT DRAINAGE ORIGINAL SLOPE 0F CONDITIONS OR ELEVATION TERRACE SCARP DIFFERENCE See/)5 6f sand 350' 2'5 ‘ / members NAME QEED TEPPACE AIDE/I LOCATION A M 98.4. Q6 TYPE —-.A _D _C —° Shape SLIDE NUMBER 258 SURFACE WATER RELATIONSHIPS H above lake 2/0 H below lake /4O °/o submerqence 4O % s4 —- 37% w/ren as — j/I'r/e occurred CULTURE NONE 1| — IIMUI 7i — MAM 1! ’- MATERIAL REMOVAL A L on II - '4 SY mrzn— u -— MEDIATE VEIV I! — LITTLE TIME Ancient 9| - Pre-Reservoir 92 — Recenf FbsI-Reservoir s: - Dene-how u — IS known Apri/ /6’. /944- 6 JJOAM NOTES PHOTOGRAPH NO. 233 S/x'de w/I‘nessed by ME. H. E. Qeea’. [2‘ occurred in fwo (1/7/75 as f/nz s/rape of #72 prof/72 surges/5. 777:2 fai/are of f/ze f/‘raf 00/7" was insfan— faneous and #12 second fol/owed in ,/2/5f a maflar of acconds. vc 350’ HC /520’ 7 30' I00’ mo w' :00 I000' I I I I II' I | I |lI|||I | I‘IIIIIIIIIIIII II IIIIIIIII FIGURE 27.—Landsllde data card (front). I2aaxssgsc DEPARTMENT OF THE INTERIOR STATISTICAL STUDIES 37 UNITED STATES GEOLOGICAL SURVEY ENGINEERING GEOLOGY BRANCH COLUMBIA RIVER LANDSLIDE PROJECT —WASHINGTON Nof'e .' 7?“ was observud by HE Qe ed /0 be ap; roxi/pafe/y sfa/ion IZ fa /6 immed/a/e/g afhr slit/e , and o’er/I79 fol/on ivy week //7e free moved 5/ow/y across reservoir . fo Dosifion 5/20 vn‘ EXP/5 aha/7 /6 00 - d d / lVafeI Wave 0/7 appos/Ye sic/e of reservoir was - San Ian yralva 02/11/22” 25'any 30‘l7/gh. [El ’ S/Um/D mafW/a/ 7772 reservoir 1': approx/Ina a/y 5000’ E - Van/ad 5/7/ and day wide 51‘ fh/j p0 'nf. - Sand l500 Org/rial 5 ”face? / /F/'r5f pha / of o/ide 1m 1 I I IrIOA/IIIuI/I l-OK‘L LVVIL / __LLW_/¢£- if/flefl'ié’L/éé‘fi’ _ _/_ __ _ __ __ ’____/ Surface 07 s/fa’a debrs / A; xf / I_/ \ M —— ——\ __ A / “xkffiimafed posif/on of \ / /_ _- — " f . \ “h __ ~ _____ __,_,.—- 30" ace of square/mp //00 /000 VO/de of /a/705/Ue was esflmafza’la be b¢fwzzn 4 4 S‘m/Hior/ cul fc yards C / 0 2 0 3 Ufeef FIGURE 28,—Landsllde data card (back). 070 826300050“ 38 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON FIGURE 29.—Slump-earthflow landslide limited by bedrock. Basalt crops out at the crown of the slide. The distance into the slope that this slide out was apparently limited by the bedrock surface. The slide is in lacustrine silt and clay with some interbedded sand. Initial movement was in August 1941, and minor movements occurred each year through 1953. Slide 63, Hawk Creek area, lake mile 37.2 left bank (Hawk Creek Bay 1,600 feet right bank). STATISTICAL STUDIES were much different from those of today. Many of the slides are well preserved and can be studied from their topographic form in almost as much detail as some of the recent landslides. The processes involved seem to have been the same as in recent slump-earthflows. The best preserved slides of this type are in the finer sized material categories. Figures 21 and 22 illustrate the ancient slump—earthfiow group. Slip-of slope landslides and multiple—alcove land- slides.—Slip-off slope and multiple-alcove landslides have been described in a foregoing section of the text, pages 6—7. Landslides 01f bedrock.—In landslides off bedrock, the surface of rupture follows generally the contact be- tween surfical deposits and bedrock. The processes and characteristics of the surficial materials include those described for both the recent slump—earthfiow and slip-off slope type groups. Talus slumps—Talus slumps sometimes appear to be similar to the slump—earthflow landslides and, at other times, to be similar to the slip-off slope landslides. Talus accumulations in the investigation area are commonly underlain by clay, silt, and sand, which are veneered against steep bedrock cliffs in many places. Landslides in artificial slopes, including some natural materials.—Artificial-slope landslides consist of failures in cut slopes or in fills where some of the underlying formation also is included in the slide. They are spec- ial cases of slump-earthflows because the same move- ment processes are involved. An illustration is shown on figure 30. Mudflows.—Mudflows have been described in a fore- section of the text, pages 7—8. Dry earthfiows.—Dry earthflows are a combination of fall and flow Where there are steep cliffs of silt and clay materials. During prolonged dry seasons, large chunks apparently break off the cliffs and fall. Upon striking, the chunks burst apart and flow like water The flow material is principally a light fluffy powder that contains small fragments of silt and clay. Figure 31 shows a dry earthflow. CLASSIFICATION UNITS AND MEASUREMENTS OF THE GEOLOGIC ENVIRONMENT The scheme of classification and analysis used in this landslide study was conceived on the theory that by subdividing the geologic environment into broad units and categories, geologic factors related to groups of landslides could be analyzed by field exmainations and measurements. The classification units and cat- egories are arbitrary. Probably no two investigators would establish identical classifications, even for the same locality. ~17. ~. »-.-. . ..., Landslide induced by a roadcut in lacus- Toe of landslide FIGURE 30.—Failure of an artificial slope. trine silt and clay (one-fourth mile southwest of Cedonia, Wash.). was probably removed at intervals as it encroached on the road. MATERIAL-CLASSIFICATION CATEGORIES The surficial deposits were classified into six cate- gories which are based primarily on the percentage of lacustrine silt and clay as opposed to the percentage of lacustrine and fluvial sand and gravel in the given sediment and on whether or not the bedding is deformed. Material category 1.—The materials in category 1 consist predominantly of silts and clays which are in almost their original position of deposition. Terrace deposits of these materials may or may not have a cap of sand or gravel. The silt and clay may be inter- bedded with lenses or beds of sand, gravel, or till. In general the sand does not exceed 30 percent of the materials lying below the terrace cap. Gravel and till seldom constitute more than 10 percent of the ma- terial in this category. They are characteristically poor-draining deposits. Figures 32 and 33 illustrate the materials of this category. Material category 2,—The materials of category 2 are similar to those in category 1 except that they are in a disturbed or distorted position owing to previous land- slide action, slumping, ice shove, or other glacial pro- cesses. Figures 34 and 35 illustrate the materials of this category. Material category 3,—The materials in category 3 consist of alternating beds of silt, clay, and sand in nearly their original position of deposition. Terrace deposits may or may not have a cap of sand and gravel. The silt, clay, and sand may be interbedded with lenses of gravel or till. Gravel does not exceed about 30 percent of the materials lying below the 40 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON It is believed that one or more blocks of dry lacustrlne silt and clay fell at the same time from a high bluff in the background and disinte- grated upon striking the base of the blufi, forming a solid-in-air density current which flowed downslope. Common alluvial cones at left of dry earthflow. Nespelem River area, river mile 9.7 right bank. FIGURE 31.—Dry earthflow. STATISTICAL terrace cap. Till members seldom constitute more than 10 percent of the materials. In general, materials of this category may consist of as much as 60 percent silt and clay or 60 percent sand and gravel. They are partly free-draining and partly poor draining (fig. 36). Material category 4.——The materials of category 4 are similar to those in category 3 except that they are in a disturbed or distorted position owing to previous land- slide action, slumping, and ice shove or other glacial processes (fig. 37). Material category 5.——The materials in category 5 consist predominantly of sand and gravel. The depos- its may be in their original position of deposition, disturbed, or reworked. They may contain cemented zones or sparse layers of silt and clay, but they are free draining. Figure 38 illustrates the materials of this category. Material category 6.——These materials consist of talus accumulations which may be made up in part of silt, sand, gravel, and boulders. Talus deposits overlie stratified silt, clay, and sand in many places in the area. Material in category 6 is used only in the FIGURE Ell—Sediments included in material category 1 (silt and clay in, or nearly in, their original position of deposition). This photograph shows varved silt and clay in the Reed terrace area. Ligrit-colored bands are silty, dark-colored bands are clayey. Smooth surfaces of the exposure are vertical joints. STUDIES 41 This photograph shows These varves are minutely sublaminated as are all varves in the area investigated. Hunters—Nez Perce Creek area. FIGURE 33.——Sediments included in material category 1. thick varves of silt and clay with contortions in the clay zone. materials classification of talus slumps—landslide types which are special cases. The material classification for each landslide case was determined from an examination of the exposures opened by the slide and from detailed study of the adjacent area. Individual classifications recorded in the tables of landslide data do not always correspond to the map units on plates 1, 3, 5, and 6 because of local variations in the lithology which are too limited in extent to be depicted on these maps. GROUND WATER Ground-water conditions were classified into two categories, high or low, based on observable field criteria. The criteria consisted of the presence or absence of springs, seeps, water-loving vegetation, and high level sources of surface or ground water. The nature and movement of ground water in surficial deposits of the types involved in this study have been adequately described by Terzaghi (1949), Baver (1949), Meinzer (1949), and Meinzer and Wenzel (1949). Ground-water conditions vary from season to season 4:2 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON FIGURE 34.—Sediments included in material category 2 (disturbed or distorted silt and clay beds). This photograph shows varved silt and clay deformed by the thrust of glacial ice. Ninemile area. STATISTICAL STUDIES 43 FIGURE 35.——Sediments included in material category 2. This photograph shows lacustrine silt and clay deformed by overriding glacial ice. Wilmont-Jerome area. and from year to year, but the two classification cate- gories are so distinct that a locality would be classified the same regardless of the season of the year it was examined. Ground water category 21 (high).~—Springs, seeps, and abundant water-loving vegetation above the midpoint of the exposed terrace slope; lakes or springs on the terrace surface or situated at higher altitudes in a posi- tion to feed ground water into the terrace deposits. Ground water category 22 (low) .—Springs, seeps, and abundant water-loving vegetation absent or limited to zones below the midpoint of the exposed terrace slope; terrace may have a faint line of water-loving vegetation along the base of sand or gravel cap; no springs or lakes on the terrace surface or at higher altitudes to feed ground water into the terrace deposits. TERRACE HEIGHT Terrace height is the general altitude diiference between the top and bottom of the slope in which the landslide occurred. Commonly it is the altitude dif- ference between two adjacent terraces. Terrace height was originally divided into three categories, and data for many of the slides are tabulated in that form. 581004 O——61)——4 Category Terrace height (feet) 31 __________________________________________ 0—100 32 __________________________________________ 100——200 33 __________________________________________ 200 or more These categories were abandoned as a result of pre- liminary statistical study and the numerical value of the terrace height was used instead. DRAINAGE 0F TERRACE SURFACE Drainage category 41.#Drainage lines on the terrace are sufficiently well developed to channel rain and snowmelt rapidly off the area. Drainage category 42.—-Lines of drainage are less well developed and have no significant closed depres- sions on the terrace surface. Drainage category 43.~Closed depressions are on the terrace surface; drainage channels are so poorly devel- oped that most of the rain and snowmelt infiltrates the terrace deposits. FiGURE 36.—Sediments included in material category 3 (alternating beds of silt, clay, sand and gravel in nearly their original position of deposition). In the central part of the photograph there are megavarves, composed of sand grading upward into silt, which are overlain by many thin silt and clay varves. Hawk Creek area, lake mile 38.0 left bank. FIGURE 37.—Sediments included in material category 4 (disturbed or distorted alter- nating beds of silt, clay, sand and gravel). In the photograph, the beds of gravel, sand and silt are tilted, faulted and fractured. Deformation was probably caused by slump over melting glacial ice. Cedonia area. ORIGINAL SLOPE 0F TERRACE SCARP Six categories were initially defined to study the effect of the original slope on the landslides. Category Slopes 51 ____________________________________ Steeper than 1:] 52 ____________________________________ 1:1-2:1_ 53 ____________________________________ 2:1—3:1 54 ____________________________________ 3:1—4zl 55 ____________________________________ 4:1—5:1 56 ____________________________________ Flatter than 5:1 These categories were useful in preliminary statisti- cal studies, but it was possible to make a more detailed analysis of this element by using the numerical values expressed as the cotangent of the original slope angle. The measurements were determined for each landslide either from topographic maps made before the slide occurred or by field measurements in the vicinity of the slide. SUBMERGENCE Submergence is a measure of the percentage of the mass of the terrace deposit that is submerged and, LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON therefore, subject to the hydrostatic conditions imposed by the lake or river. Six categories of this classifica- tion were initially defined. Height Category (percent) 60 No relation between lake (or river) level and the ter- race or slope in which the slide occurred. 61 River running at the toe of the slope in which the landslide occurred. 62 Slope submerged by lake at high-water level _______ 0—25 63 _____ do _______________________________________ 25—50 64 _____ do _______________________________________ 50-75 65 _____ do _______________________________________ more than 75 Preliminary statistical studies demonstrated no measurable differences between catergories 60 and 61 and the lake submergence percentages established in categories 62, 63, 64, and 65 as they are related to the landslide elements being considered. Consequently, a more accurate evaluation of the submergence factor was made possible by considering river and lake submer- gence alike and by regarding category 60 as zero per- cent submergence. The submergence value for each case is the percentage of the terrace height of the slope that is below river or lake surface at high-water level. CULTURE This factor was studied to determine the effect of man’s cultural and engineering developments on certain landslide elements. The following three categories were established: Category 71 ______________ None. 72 .............. Minor, on or near slide, such as farm build- ings, plowed fields, farm access roads, or logging trails. 73 ______________ Major, on or near slide, such as deep high- way or railroad cuts and fills, irrriga- tion systems, towns, or storage reservoirs. Developments MATERIAL REMOVAL The landslides exhibit Wide differences in the amount of movement of the mass of landslide material. In some, particularly those along the lakeshore, practi- cally all of the material slides out, leaving an empty alcove resembling a glacial cirque. In others, the material moves slightly, outlining the shape of the slide. All degrees of movement of the slide material are in between these two extremes. Where several landslides occur side by side and the material is nearly all cleaned out of the scarp, the resulting terrace slope may be steeper than before the landslides. This situation may induce another series of slides cutting farther back into the terrace. STATISTICAL STUDIES 45 FIGURE 38.—Sedlments included in material category 5 (sand and gravel). The slides were classified into one of the following three categories: Category Removal 81 ______________ All or most of the mass of landslide material removed from the scarp. 82 ______________ Intermediate. 83 ______________ Very little movement of mass of landslide material. For illustrations of landslides in these categories see figure 12, category 81, and figure 26, category 83. TIME To help determine the activating causes of landslides, all data obtainable which related to the age of land- slides have been recorded. The following gen eral cate- gories were established, but where exact data were available they also were recorded: Cedonia area. Category Time 91 ______________ Ancient. 92 ______________ Recent, before filling of reservoir. 93 ______________ Recent, after filling of reservoir. 94 ______________ Date of initial - sliding or re—movement known. LANI)SLIDE MEASUREMENTS HC: VC RATIO The measurements made of each landslide were designated: horizontal component (H0), vertical com- ponent (V0), and length component (LO). H0 The horizontal component is the horizontal dis- tance from the foot of the landslide to the crown, taken at midsection of the landslide normal to the slope (figs. 2, and 39). V0 The vertical component is the difference in alti- tude between the foot and the crown, taken at midsection of the landslide normal to the slope (figs. 2 and 39). 46 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON FIGURE 39.—Cross section of a landslide showing H C’ and V0 measurements, which are respectively the horizontal and vertical distances from foot to crown. L0 The length component is the maximum horizontal distance from side to side of the slide measured parallel to the slope it descends. The H0 and V0 for each landslide were determined either from topographic maps and field measurements or by field measurements alone. Frequently the foot of the landslide was obscured by slide material or by lake water. Its position was arbitrarily placed at the topographic breakpoint (fig. 39) where examinations produced no other criteria for placing it. The LC was determined either by map measurements, field measure- ments, or by estimation. H02VC is the ratio of the horizontal component to the vertical component of a landslide or the cotangent of the angle of slope of a line between the foot and the crown. Environmental factors have been analyzed with relation to this ratio. For almost every landslide HO 1V0 ratio has been determined independently from the original slope value. In the tables of landslide data (p. 74—93) very shallow slides may have a H0zVC ratio less than the original slope owing to local slope changes and inaccuracies of measurements. STATISTICAL ANALYSES By DANIEL R. EMBODY and FRED O. JONEs ANALYSIS AND INTERPRETATION OF LANDSLIDE DATA Of the 10 landslide type groups, only 5 were repre- sented by sufficient data to warrant statistical study and interpretation. These five type groups were: Group Type 1 ________ Recent slump-earthflow landslides. Type 3 ________ Ancient slump-earthflow landslides. Type 4 ________ Slip-off slope landslides. Type 5 ________ Multiple-alcove landslides. Type 6 ________ Landslides off bedrock. For only 3 of the 5 groups were enough data collected to warrant consideration of a statistical analysis. These three type groups were: Group Type 1 ________ Recent slump—earthflow landslides, 160 cases. Type _3 ________ Ancient slump-earthflow landslides, 37 cases. Type 4 ________ Slip-off slope landslides, 42 cases. Statistical methods consisted of the analysis of vari- ance and covariance and multiple regression. Each important analysis is presented in a brief summary with computational detail omitted. For the methods used and the purposes which they were intended to accomplish, the reader is referred to the section headed “Statistical techniques” (p. 69) where an explanation and references to the literature are given. The analysis of variance method was used to test the significance of the various geologic classifications and to determine whether they could be used as a basis for prediction. Some of the field classifications were found to be significant, others were not; the classifica— tions that were not significant were omitted in arriving at the final analyses and interpretations. Of the many classifications and measurements made on landslides, the H OzVO ratio was the only one which described the landslide itself in numerical terms. Consequently, this ratio was defined as the dependent variable. The other factors, both qualitative and quantitative, were defined as independent variables. The problems considered were: 1. Determining which factors were related to the H0 1V0 ratio to a significant degree. 2. The derivation of formulas by which the H0:VC ratio of an impending landslide could be predicted. The first analyses were made to determine if any real differences existed in the three larger landslide groups—recent slump earthflow, ancient slump earth- flow, or slip—off slope landslides. Preliminary studies revealed that there were large interactions between classifications of geologic materials and the three land— slide groups, and between ground—water classifications and the three landslide groups. The interactions in- dicated that the effects of materials and ground water on the HCzVC' ratio of the landslides were not con- sistent in the three groups. It was judged, therefore, that each group would have to be analyzed separately. Only the recent slump-earthflow group of 160 land- slides contained enough data to justify a detailed statistical treatment. Classifications and measure- ments of these landslides are tabulated in table 1. RECENT SLUMP-EARTHFLOW LANDSLIDES Classifications and measurements were made on eight factors that were initially considered to be of importance in controlling the H0:V0 ratio of land- slides. These were as follows: STATISTICAL STUDIES Qualitative factors Quantitative factors 1. Materials 6. Terrace height 2. Ground water 7. Submergence 3. Culture 8. Original slope 4. Drainage 5. Material removal Ideally, the statistical analysis would include simul- taneous tests of main effects and interactions of all eight variables. The absence of observations in some of the combinations of factors indicated that such an all-inclusive analysis was not practical since dispropor- tionate subclass methods would be involved. Preliminary analyses indicated that materials, ground water, and original slope were correlated with the H0:VO ratio of the landslides. The influence of the above three factors had to be considered in testing the significance of the remaining factors. Each of the re- maining factors; namely, culture, drainage, material . removal, submergence, and terrace height, were tested individually in a series of analyses that included mate- rials, ground water, and original slope. Had more than one of the remaining factors shown significance in these analyses, it would have been necessary to perform a further analysis to insure that both factors have effects which are independent of each other. The further analysis, however, was not necessary. Q UALITATIVE VARIABLES The first analysis was made to determine whether culture was associated with the H02V0 ratio of land- slides. Observations of the 160 recent slump-earth- flow landslides were arranged in a table which was clas- sified according to material, ground water, and culture. The original slopes and the H 0 :VC ratios of the land- slides were the independent and dependent variables. Statistical operations were made with logarithms. Ref- erences to the method of analysis of covariance for three classifications with disproportionate items in the subclasses is given under the heading “Statistical techniques” (p. 69). Summary of the analysis . Degrees Sums of Mean Source of variance of squares squares Ratio Significance freedom Pooled interactions + 151 1. 49058251 0. 00987141 residual. Interactions ........... 13 .16814048 .01293388 1.35 Not significant. Residual ______________ 138 1. 32244203 . 00958291 ...... Culture + interac- 153 1.49695583 __________________ tions + residual. Culture _______________ 2 .00637332 .00318667 .32 Do. The pooled interactions of materials X ground water, materials >< culture, ground water >< culture, and materials >< ground water X culture were not 47 significant. The main effect for culture was also not significant. These results were interpreted to mean that within the situation represented by these data, no relation between culture and H01VO’ ratio of the landslides was detected. Cultural developments may be related to ground water or activating causes of landslides, but they could not be judged to relate directly to the HOzVC ratio of the landslides from these data. The absence of significant interactions supports the con- clusion. This may be interpreted to indicate that within each culture classification the effects of materials and ground water on the HC:VO’ ratio of landslides may be accounted for by chance variation. The second analysis was made by the same method to determine whether drainage was associated with the HOtVC ratio of the landslides. The following table shows a summary of the statistical analysis: Degrees Sums of Mean Source of variance of squares squares Ratio Significance freedom Pooled interactions 151 1. 44284331 0. 00955525 ...... + residual. Pooled interactions. 12 .10416158 .00868013 0.90 Not significant. Residual .............. 139 1. 33868173 . 00963080 ______ Drainage + inter- 153 1. 49695564 __________________ actions + residual. Drainage ______________ 2 .05411233 .02705616 2.83 Do. Neither the pooled interactions nor the main effect for drainage was significant. It was judged, there- fore, that the factor, drainage, was not associated with the HOzVO ratio of the landslides, even though it might be highly correlated with ground water. The third analysis was made to determine whether the factor material removal was associated with the HOIVO ratio of the landslides. Data were classified according to material removal, material, and ground water. The original slope was the independent vari- able. The HOZVC' ratio of the landslide was the dependent variable. Summary of the analysis Degrees Sums of Mean Source of variance of squares squares Ratio Significance freedom Pooled interactions 147 1. 43322298 0. 00979816 ______ + residual. Pooled interactions. 10 .08315798 .00831580 0.84 N 0t significant. Residual ______________ 137 1. 35006500 . 00985449 ______ Material removal + 149 1. 46175654 .01051623 ______ interactions + residual. Material removal. 2 .02853356 .01426678 1. 46 Do Neither the pooled interactions nor the main effect for material removal was significant. It was judged, therefore, that material removal was not associated with the H C’ : VC' ratio of the landslides. The material- 48 removal factor was not expected to be related to the HCzVC ratio of the landslides. This factor was studied to determine in which geologic setting a series of landslides would tend to load the toe area and con- tribute to slope stabilization, and in which geologic setting landslides would develop steep scarps and create conditions conducive to additional landslide action. The 160 observations of material removal which were made on recent slump-earthflow landslides indi- cated that it was correlated with submergence. Where submergence was high the slide alcove was generally emptied of material which spread over a large area on the bottom of the lake. In places where slides occurred side by side along a terrace,‘as they have in the Cedonia and Reed terrace areas, this emptying of the slide al- coves resulted in conditions which seemed conducive to a second series of slides cutting deeper into the terrace. This second series has started in the Reed terrace area. The landslide material had a tendency to load the toe area where submergence was lower. Lake and river fluctuations may have caused many re-movements of the material, but new landslides which cut deeper into the terrace have seldom occurred where much of material remains in the slide alcove. The above analyses completed the simultaneous tests of variables that can be expressed in qualitative terms. Culture, drainage, and material removal were not sig- nificant and were consequently judged to be of little importance as they related directly to the H 0 :V0 ratio of recent slump-earthflow landslides. QUANTITATIVE VARIABLES The three quantitative variables, terrace height, sub- mergence percentage, and original slope 7 were next considered. The analysis of covariance method was used and the significance of the quantitative variables was judged from the partial regression coefficients and their standard errors. References to the technique of analysis of covariance and the methods of computation are given under the heading “Statistical Technique” (p. 69.) The regression equation used Was Y = aii‘l’ bm + bzx2+ b33133 where Y=log HCzVC’, a.-,- (i=1, 2; j=1,2,3,4,5) =constants which represent the 10 sets of material (j) and ground water (1) conditions. b,, b2, b3,=regression coefficients for the three independent variables x1=log terrace height z2=submergence percentage expressed as equivalent angle $3=log of original slope " Original slopes and HC:VC ratios of landslides are identical geometric measure- ments, to avoid confusion the term "HC:VC ratio" has been eliminated in describ- ing original slope. LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON The value for submergence is a true percentage in that its value cannot be less than 0 percent nor more than 100 percent. The transformation from percent- ages to equivalent angles is often useful for variables with this characteristic. References describing the equivalent angle transformation and sources of pub- lished tables are given under the heading “Statistical Techniques” (p. 69). In the correlation analysis to be described, the orig- inal data were transformed as follows: Variable Transformation Terrace height ________________________ Logarithm Submergence percentage _______________ Equivalent angle Original slope ________________________ Logarithm H C : VC ratio slide ____________________ Logarithm Following standard procedures, regression coefficients for the three independent variables were as follows: Partial Standard Variable regression error t Significance coefficient Terrace height ............. 0.051028 0.036416 1.40 Not significant. Submergence percentage... .302550 .059582 5.08 Highly significant. Original slope .............. . . 407675 .049948 8. 16 Do. Coeflicient of determination R2=0.389. The t-test of significance indicated that the partial regression coefficient for terrace height was not signifi- cant, while coefficients for submergence percentage and original slope were highly significant. It was judged, therefore, that in this situation submergence percent- age and original slope were important controlling fac- tors with respect to the H0:VC’ of slides and that terrace height was not an important factor. Another important consideration was the consistence of the regression equation under the various combi- nations of materials and ground water. The covari- ance method requires that the true relation among the variables be parallel for each set of conditions and that any deviations from parallelism in the data be no greater than might be expected from chance causes. The test for parallelism among regression coefficients is made by fitting separate regression equations to the data of each of the 10 combinations of materials and ground water. If the total sums of squares accounted for by the individual regression are greater than the total sums of squares accounted for by the combined regression equation to a degree that is significant, then the regressions are judged to be not parallel. Of the 10 sets of data representing the 10 possible combinations of material and ground water, 1 set con— tained no slides; 2 other sets contained 1 slide each; and a 4th set contained only 5 slides. The remaining 6 sets contained 17 or more slides. The test for depar- tures from parallelism was made with the latter 6 classes, since including the 4 others would add very STATISTICAL STUDIES 49 little new information and would greatly compllcate . Partialre_ Standard the calculations. Variable grassion €o~ error t Significance e cien Test of significance gubnlierlgelnce percentage... 0. 2373211 _0. 0:13:31 4. 34 Highly significant. L a f M -t s" m rig. a sope .............. - . . 5 4. 72 Do. Source 0‘ variance gfgggigr Egiiifirgs ”:2; f est 1gn canoe Original slope (quadratic).- 8. 067515 1.336 6.04 Do. Pooled regressions _____ 2 0.677822 _ Coefficient of determination R3=0. 503. Individual regressions- 12 . 033487 Depatiimmm 10 255665 Highlty 5mm. Submer ence ercenta and both li d d aralie ism. can. 6 near 8.11 11 - iiesidual ______________ 135 980200 g p g ‘1 a A reference to the details for the test for parallelism is given in the section on “Statistical Techniques,” (p. 69). The test for significance showed that the regression equation derived from the combined data of the six classes did not adequately represent the data in the individual classes. It was necessary, therefore, to reex- amine the interrelations among the two independent variables (submergence and original slope) and the dependent variable (H0:VO ratio of slide). Use of a linear function to represent this relation implied that for a given change in the logarithm of the original slope a proportional change would be expected in the log- arithm of the H 0 : VC ratio of the slide without regard to the level of original slope. It can be easily under- stood that such a relation is not realistic. To develop a regression equation which properly represented the data, a quadratic term for logarithm of the original slope was added to the equation. The new regression equation then became Y: a’ ii+ 51,371+ 172,132 + 173'13 where Y: log H CzVC, al’, bl’, bz’, b;’=intercept and regression coefficients, x1=submergence percentage (equivalent angles), zz=log original slope, I 23=a+go original slope (quadratic). A new test of parallelism was then made using the new function as follows: Source of variance Degrees of Sums of Mean f-test Significance freedom squares square Combined regressions. 0.915676 .................. Individual regressions. 18 1. 062212 .................. Departures from 15 . 146536 0. 00976907 1. 3 Not significant. parallelism. Residual .............. 129 . 851475 00600581 ...... Using the equation with the quadratic component for original slope, departures from parallelism were not significant. We can assume that the regressions are parallel in the six classes and that a single regression relation is operating with respect to the landslides. A new covariance analysis was made employing all of the 160 observations of landslides. Estimates of the partial regression coefficients are as follows: ratic terms of original slope were highly significant. Some idea of the overall gain in precision due to adding the quadratic term is seen from the coefficient of deter- mination (square of multiple correlation coefficient), in the previous analysis R2=0.389, while in the last analysis R2=0.503, or an increase of 0.11. The coefii— cient of determination measured the proportion of total sums of squares accounted for by the independent variables. Adding the quadratic term brought about a sizable increase in precision. TESTS OF SIGNIFICANCE FOR. MATERIALS AND GROUND WATER The final analysis of H0zV0 ratios devolved about tests of significance for the two qualitative factors, materials and ground water. These tests were made from an extension of the above-described covariance analysis. A summary of the test of significance for the interaction between materials and ground water is as follows: Degrees Sums of Mean Source of variance of squares square f-test Significance freedom Pooled interactions re- 151 1.015135 ................ sidual. Residual ................ 148 1. 000239 0. 006758 ...... Pooled interactions ______ 3 .014896 .004965 0.73 Not significant. The f-test showed that the interaction was not sig- nificant. The absence of a significant interaction may be interpreted to mean that the effect of ground water on the H0zVC ratio of the slide is additive over the entire range of material categories or that within each materials classification the H0: V0 ratio of landslides increases uniformly with increases in ground water. The summary of tests of significance for main effects is as follows: Degrees Sums of Mean Source of variance of squares square f—test Significance freedom Materials pooled inter- 155 1.101047 ________________ actions. Pooled interactions re- 151 1.015135 0.006723 ...... siduals. > Materials ............... 4 .085912 .021478 3.19 Significant. Ground water pooled in- 152 1. 150310 ................ teractions residual. Pooled interactions re- 151 1.015135 006723 ______ sidual. Ground water __________ 1 . 135175 .135175 20.11 Highlysignifi- cant. 50 The test of significance showed materials to be sig- nificant and ground water to be highly significant. It was judged that both of these factors are very impor- tant in controlling the H 0 : V0 ratio of the landslides. In the statistical analyses summarized above, 10 inde- pendent variables were tested for possible correlation with the HCIVC ratio. Four factors were highly significant, and one factor was significant. They are as follows: f-test i-test Significance Ground water _________ 20. 11 _ A _ _ Highly significant Original slope (linear) r 1 ______ 4. 72 Do. Original slope ______ 6. 04 Do. (quadratic) Percentage submergence ______ 4. 34 Do. Materials _____________ 3. 19 - _ _ _ Significant. All five significant factors exercised important control- ling effects on the H O : V0 ratio. Perhaps other factors were related to the H C’ : V0 ratio, but if relations existed they were too small to be detected and therefore, were not important. EQUATION FOR THE PREDICTION OF HCZVC RATIOS OF LANDSLIDES In the foregoing statistical analyses, the importance of different factors affecting the landslides has been studied. Five factors in particular were important in controlling the H02VC ratio. The two qualitative factors ground water and materials showed no inter— action. The two quantitative factors original slope and submergence showed no departures from parallelism within the 160 slides studied. It has been established with this information that the H 0 : V0 ratio is a predic- table phenomenon that may be expressed in a single unified equation. If the predication equation is derived from the ana— lysis of covariance used in making the tests of signifi- cance, 10 independent variables are involved and the algebra becomes somewhat unwieldy for field use. Ground water, which contained only 2 levels, was simple to quantify by merely assigning the value of 0.1 to the high level and 0 to the low level. By this device the regression analysis gives an answer identical to that of the analysis of variance. It would be possible to quantify the five material classifications using the method of least squares as described by Fisher (1946, p. 299—306). The authors were not in a position to conduct such an exhaustive analysis as Fisher’s method would require. As an alternative action, numerical values were arbitrarily chosen as follows: Material designation Assignment numerical level +0. 1 MHBWNJH HOOD LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON Using the quantitative values for ground water and materials combined with submergence, and original slope, linear and quadratic, analysis folloeing the mul- tiple regression pattern was made. The computational pattern described by Fisher (1946) was followed. The method of multiple regression is also described by Davies (1954), Youden (1953), Goulden (1952), Mather (1943), Snedecor (1946), and Kempthorne (1953). Using the redefined variables in a new regression analysis, the reduced prediction equation was developed: Y: 0.6328+ 0.2460X1—1.4121X2+ 7.5583X3+1.0338X4 +0.4015X5 where Y: Logarithm of predicted H 0’: V0 ratio of slide X1=Submergence percentage (equivalent angle) X 2: Original slope (logarithm) X 3: Original slope (quadratic) X4: Ground water (low takes value 0. High takes value 0.1) X5=Materials (1 takes value +0.1; 2, 3, and 4 take value 0; 5 takes value —0.1) An estimate of the loss in precision which occurred by quantifying the two qualitative variables can be obtained from the analysis of covariance as follows: Source of variance Degrees of Sums of Mean freedom squares square Total._ : ______________________________________ 159 2. 919848 ............ Reduction due to fitting constants ____________ 8 1. 904713 0.238089 Resrdual ..................................... 151 1. 015135 . 006723 From the reduced regression analysis Total ......................................... 159 2. 919848 Reduction due to constants .................. 5 1. 893696 0.378739 Resrdual _____________________________________ 154 1. 026152 . 00666332 Source of variance Degreesoi Sums of Mean Ratio Significance freedom squares square Residual from 154 1. 026152 __________________ regression. Residual from 151 1. 015135 006723 ...... covariance. Loss of precision ______ 3 .011017 003672 0 546 Not significant. The analysis showed that the loss of precision brought about in the simplification of the prediction equation was not significant. For prediction purposes, therefore, the reduced equation can be used in place of the com— plete equation. Tests of significance were made for the individual re- gression coefficients as follows: Partial Standard Variable regression error t-test Significance coefficient Y intercept _______ —0. 6328 0. 1209 5. 23 Highly significant. Submergence ........ . 2460 2 0538 4. 58 Do. Original slope (linear) _ —1. 4121 .3036 4. 65 Do. Original slope (quadratic)_. 7. 5583 1. 248 6. 05 Do. Ground water ______________ 1. 0338 .2261 4. 57 Do. Materials __________________ . 4015 . 1198 3. 35 Do. STATISTICAL STUDIES 51 The final consideration concerned the precision with which predictions can be made of H 0: VC' using the re- duced equation. The 95-percent confidence limits for the prediction was considered a satisfactory level of precision. Such confidence limits for a six-variable equation, however, require a somewhat involved cal- culation and would be entirely impractical for field use (see section headed “Statistical techniques”, for amplifi- cation of this concept). A somewhat less exact meas- ure of precision can be derived from the standard error of estimate of the reduced prediction equation (8“,). The standard error of estimate in the logarithm scale s.,=0.08163 This statistic describes the distribution of observed values of HOzVC’ ratio in logarithms about their respective predicted values. If the data are normally distributed (in this situation it is judged that the data are normally distributed) approximately 95 percent of the observed points will fall within the range described by i (tsa). The 95-percent confidence limits describe a range which brackets the true value with a 95-percent prob— ability. The standard error of estimate describes the variation of the data about an estimated mean. The two kinds of limits will be almost identical within the normal range of the landslide data. The standard error of estimate remains constant over the range of the data, while the 95—percent confidence intervals increase as predictions are made with data which depart from their means. As an example of the use of the reduced prediction equation and the calculation of limits of variability, consider slide 65. Values of the independent variables for this slide have been estimated as follows: Variable Numerical Transformed Transformation value value Xi Submergence percentage-, 31 0.338 Equivalent angle. X: Original slope (linear) _____ 1.27 .230 Iioglarithm. X 3 Original slope (quadratic). 91—30% . 151 (_}-Oo_g) X4 Ground water ____________ Low (0) 0 None. X5 Materials _________________ 1 .1 None. The above values were substituted into the reduced prediction equation as follows: Regression Transformed Variable coefiiciem value Product Submergence ______________ 0. 2460 0. 338 0. 0831 Original slope (linear) ______ —1. 4121 . 230 —. 3248 Original slope (quadratic)-__ 7. 5583 . 151 1. 1413 Ground water _____________ 1. 0338 0 0 Materials ____________ / _____ . 4015 . l . 0402 Intercept (constant term in equations) ______________________________ —. 6328 0. 3070 Estimated value of Y Antilog (0.3070)=2.03 As indicated above, the standard error of estimate was s,,,=0.08163 as estimated with 154 degrees of freedom. The value of (t) for 154 degrees of freedom representing a 95-per- cent probability in one direction was t=1..65 and ts,¢=0.1347 In using the equation to predict the H02V0 ratio, interest was centered only on the upper limit, because it was important to know the most probable value of the H 0 : V0 ratio and an upper limit representing the great- est extent to which the slide would cut. Original values Logs (anliloga) Predicted log H 0: VC' ratio ________ 0. 3070 2. 03 (1. 65) 8x, _______________________ . 1347 Upper H 0: VC’ ratio limit . 4417 2. 76 For slide 65 the predicted H0tVC' ratio was 2.03 and the approximate upper 95—percent variability limit was 2.76. The measured HOzVO ratio of the slide was 2.5 and it cut back 1,150 feet into the terrace. The predicted H0: V0 ratio of 2.03 estimated that the slide would cut into the terrace only 920 feet. With the confidence interval added, the approximate variability limit for the slide was 2.76. Using this estimated ratio, the slide would have cut into the terrace 1,260 feet, or 110 feet farther than it did. ANCIENT SLUMP-EARTHFLOW LANDSLIDES Ancient landslides were studied to determine whether the H0zVC’ ratio for these slides followed the same general pattern in relation to the classification units as the recent slump-earthflow landslides and to try to evaluate how much HC:V0 might increase for the recent landslides during a long period of weathering and erosion. The classification data of the 37 slides of this type group are tabulated in table 3, page 80. An example of the group is shown in figures 21 and 22. Classifica- tion problems were immediately apparent in studying these ancient features. Ground-water conditions at the time of the slides were difficult to appraise. Only two classifications were established, high and low, and these were determined by the general physiographic form of the area behind the landslide. If the shape and trend of the bedrock valleys behind the landslide seemed conducive to channeling an abundant supply of ground water to the landslide area, the ground water 52 was classified as high and, if not, it was classified as low. Only 9 of the ancient landslides were in the low category, and they have a mean H02VC ratio of 3.1, as compared to a mean HCiVO ratio of 3.7 for the 28 classified as having high ground water. Surface-water relations or the submergence factor of this group were also unknown. The factor, original slope, which was determined to be important in the recent slump—earthflow group, could not be determined for the ancient landslides. Preliminary statistical tests indicated that the ancient slump-earthflow landslides could not be included with the recent slump-earthflow landslides in a statisti- cal analysis, because this group did not provide ade- quate data for a detailed statistical analysis. A test was made, however, of the material classifications as they related to the H01VU ratio, and the f—test was significant, indicating that in the different material classifications represented the mean H 0 : VC ratios were significantly different. The minimum, maximum, and mean HCIVO ratios of ancient landslides for the material and ground-water groups represented in the data are as follows: HC': V 0 ratios Ground Number Material water in group Mini- Maxi- Mean mum mum 19 2. 4 5. 1 3. 8 5 2. l 5. 9 3. 2 4 3. 6 6. 1 4. 8 0 ______________________________ 5 1. 7 3. 2 2. 6 4 2. 6 3. 4 3. 0 The following is a comparison of the mean H01V0 ratios of recent and ancient slump-earthflow landslides for all classes of materials and ground water contained in the ancient type group: Recent slump- Ancient land Material Ground earthflow slides slides (arithmetic water (estimated mean mean) of HC:VC' ratio 3. 27 3. 8 2. 43 3. 2 2. 92 4. 8 2. 16 __________________ 2. 87 2. 6 2. 13 3.0 In material category 1 and ground-water categories high and low the general pattern of relation between H C 2 V0 ratios was similar to that in the recent slump— earthflow landslides. In the other groups, no similar relation was found, but they were represented by such a small number of landslides that conclusions were probably unwarranted. Only the slide group having material category 1 and high ground water contained enough landslides (19) to give any validity to a com- parison of the mean value with that of the recent slump- LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON earthflow slides. The mean value of the ancient slides was 3.8 and of recent slides 3.27. This larger mean HO: V0 ratio could be indicative of an increase in time by weathering and erosion, but it could also indicate that only the larger ancient landslides have been pre- served in sufficient detail to be recognized in the field and included in the study. SLIP-OFF SLOPE LANDSLIDES This group was the second largest included in the study. The classification data of 42 landslides of this group are tabulated in table 2. Figures 6 and 8 illustrate this group. The classifications and measure- ments made of these landslides were the same as those made for the recent slump-earthflow group. Preliminary statistical tests indicate that the slip-off slope landslides could not be included with the recent slump-earthflow landslides but would have to be studied independently. The group did not contain data on a sufficient number of landslides to justify detailed statistical treatment. However, a test of significance was made of the material and ground—water classifica— tion categories as they related to H0: V0 ratios. Neither ground water, material classifications, nor their interactions were significantly related to the HCzVC ratio of the slip-ofl' slope landslides. The HCzVO ratios for this group ranged from a minimum of 1.0 to a maximum of 2.6 and the mean ratio of the 42 land- slides was 1.78. The data showed a high degree of correlation between original slope and the H C : V0 ratio which, as explained in the description of type groups, was an independent determination. The mean value of the original slope was found to be 1.62, or just 0.16 less than the mean HOzVC ratio. This type of landslide rarely cuts deeply into a terrace. The causes of these slides can generally be attributed to undermining processes by lake, stream, or excavation. This type of failure occurs more frequently in coarser grained and dry materials. Of the 42 slides classified, only 4 were in silt and clay, or material category 1, and the remaining 38 were in silt, sand, and gravel cate— gories. Of these remaining 38 slides, 26 were in sand and gravel. All 42 landslides were in the low ground- water classification categories (22, 23, and 24). Landslides of this type tend to stabilize at the angle of repose of the material involved where a protective wave bench has been built at the toe of the slope and undermining processes are not operating. None of these landslides in the area of investigation could be considered stabilized because of the lack of a protective wave bench in the Franklin D. Roosevelt Lake areas and unusual river fluctuations in the areas below Grand Coulee Dam. STATISTICAL STUDIES 53 MULTIPLE-ALCOVE LANDSLIDES Although small in number, this group of nine land- slides warrants special attention. The particular geologic setting in which slides of this type are found is described in a foregoing section of the report (p. 7). Perhaps all of these complex slides should be studied individually. More detailed knowledge of them might indicate that they should not be studied together; but because of similarities in the geologic environment they have been grouped in this study. Only one slide of this kind occurred during the investigations (figs. 4, 5, and 12). A detailed description of this slide is given on pages 16—18. The other eight are ancient landslides which have generally a similar physio- graphic form. Landslides of the multiple-alcove type are indi- vidually the most destructive of the 10 types of slides because of the tremendous area and volume of material involved. The HCIVC ratio in slide 276 reaches a maximum value of 9.7; however, this measurement may represent much postslide erosion which should not be attributed to the sliding. The mean value of the H02VC ratios for these 9 slides is 5.9, and the HO: V0 ratio of the new multiple-alcove slide (No. 261) which occurred in the Reed terrace in 1952 is 6.2. The locations of multiple-alcove slides are limited sharply to deep terrace deposits overlying channels in. the bedrock. They are also probably limited to fine—grained materials supersaturated by ground water. Summary of multiple-alcove slide data Slide N0. Material Ground H 0 VC H 0: V0 L 0 water 3 22 1 900 400 4. 8 3, 000 3 21 1 600 400 4. 0 1, 500 1 21 4, 700 510 9. 2 5, 500 1 22 4, 200 850 4. 9 5, 000 1 21 2, 600 600 4. 3 2, 000 1 21 1, 650 270 6. 1 l, 300 l 21 l, 650 400 4. l 3, 400 1 21 2, 100 340 6. 2 1, 400 1 21 3, 200 330 9. 7 4, 200 LANDSLIDES OFF BEDROCK Landslides in which the surface of rupture generally follows bedrock are common in the area. Summarized below are six of the landslides studied: Slide Material Ground Original H 0 VC H C: VC LC No. water slope 59 ________ 5 24 1. 4:1 210 160 1 3 90 84 ________ 2 22 5. 7:1 230 42 5. 5 160 86 ________ 1 24 2. 1:1 95 45 2. 1 140 110 _______ 2 21 3. 5:1 570 163 3. 5 250 171 ....... 1 24 2. 1 :1 33 16 2. 1 43 240 _______ 1 24 1. 7:1 120 70 1. 7 100 H 0' : V0 ratio of these slides is nearly the same as the original slope. The most important fact revealed by this group is that the flattest slopes fail in a setting where superficial deposits are shallowly underlain by bedrock. The flattest slope to slide in all the investi- gations was in slide 84, where the original slope was 5.7:1. It is interesting to note that ground—water conditions here were dry. The mass of landslide material in landslide 110 flowed around projecting bedrock points which seemingly should have given enough support to resist sliding. The mean H0zV0 ratio of this group was 2.7, but it has little significance in studying the possible occurrence or extent of a landslide of this type at other locations. UNIFORMITY EXPERIMENT All the basic data used in the statistical analysis of landslides were collected by Mr. Jones. The ques- tion arises, therefore, as to whether these data are conditioned in some manner by his long period of ob- servations and by personal methods of making the meas- urements. If this is so, other workers might find it difficult or impossible to get similar results. To gain some insight into this problem, a uniformity experi— ment was conducted to determine whether field obser- vations of independent workers, using the same concept of HCzVC ratio and the same classification categories of ground water, original slope, material, and percent submergence, would reproduce the results of Mr. Jones’ field observations. The uniformity experiment was planned so that two geologists who were not familiar with the Pleistocene deposits or the landslides in the area were assigned to make a series of measurements. The men were briefed for 2 days before going into the field on the methods used to secure the original data, definitions of the class- ification categories, and the organization and purpose of the test. Detailed explanations and answers to their questions were given as they requested. All data and results of the author’s measurements were withheld until the fieldwork was completed. The first half day in the field was devoted to practice measurements of landslides not included in the experiment and to obser- vations of a few exposures. After this the two geolo- gists, Christopher Erskine and Warren Peterson, used their notes and the definitions which had been estab- lished by the author, but no further explanations or guidance were given. The experiment was conducted on recent slump- earthflow landslides, 160 cases of which were analyzed in the preceding section. Available resources limited the investigation to a sample of 42 slides. The ideal sample would have been 42 slides picked and measured 54 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON completely at random from the 160 slides available. Under such conditions each of the 160 slides would have had an equal and independent chance of getting into the sample and, as such, it would have been represent- ative of the area as a whole. However, it was imprac- tical to measure 42 of the slides in a random order since some of them were nearly 100 miles apart. Irre- spective of the order of measurement, 7 areas were arbitrarily choosen Where 6 or more landslides could be measured in 1 day. A random sample of six slides was chosen from each area for inclusion in the test, and the order in Which the slides were chosen was the order in which they were measured. The randomization was performed with published tables of random permuta- tions. Landslides Were selected for experimental ob- servations for 7 days in the above manner. GeologistsPeterson and Erskine made observations on the 42 slides from April 13 to 23, 1953. Measure- ments and classifications recorded for each slide were the H0:V0 ratio or dependent variable and the four independent variables determined to be important controlling factors from the analysis of the recent slump-earthflow landslides—ground water, original slope, submergence, and material. Table 7 summar- izes the data obtained from this test together with du- plicate measurements taken from table 1 by the senior author. SUMMARY 0!" ANALYSIS 0]? H0: VC RATIO OF LANDSLIDES The problem was to determine whether the means of the H0:V0 ratio in the test differed significantly from the originals. The results showed that the mean values of the H0: V0 ratios did not differ materially; consequently, they were found to be reproducible by other geologists. Because H0: V0 ratios were contin- uous variables, the statistical analysis followed the standard pattern for the analysis of variance. The computations and tests of significance were made with the logarithmic form of the data. Sample computa- tions, together with references, are given under head- ing “Statistical Techniques” (p. 69). Degrees Sum: of Mean Source of variance of freedom squares squares f-test Significance Total ___________________ 83 1. 9038 Landslides .............. 41 1.3954 0.0340 2. 86 Highly significant. ---. l .0207 .0207 1.74 Not significant. Rheaesidualn .-___._.._'»_1. 41 .4877 .0119 In original numbers Mean H 0: VC' ratios In logarithms (antilogs) Test ___________________________________________________ 0.2670 1. 850 Original measurements ................................ .2986 1.989 Difierence ............................................. . 0316 . 139 The tests of significance show that the difference between slides is highly significant, while the difference between men is not significant. It is judged, there— fore, that the H0: V0 ratio is a sensitive measurement of a landslide, and the ratio could be reproduced in this situation by at least two other workers. The sen- sitivity of the H0: V0 measurement is presumably due to significant variations in the four classification fac— tors—material, ground water, original slope, and sub— mergence percentage, which are defined and analyzed in preceding sections. Measurements and classifications were made by Mr. Jones a few years before this test; thus the lack of a significant difference between men leads to the judgment that H02V0 values are stable over a short span of time. SUMMARY OF ANALYSIS OF ORIGINAL SLOPE The problem for original slope was the same as for the H0 : V0 ratio—to determine whether the means of original slopes measured in the experiment differed to a significant degree from the originals. It was found that they did not and that this factor was reproducible by the men in the experiment. Original slope, like the H0: V0 ratio, was a continuous variable, so the analy— sis and computation followed the same pattern. Degrees Sum! of Mean of Source of variance of freedom squares squares f-lest Significance Total ___________________ 83 1. 6618 Landslides. - 41 1.3140 0.0321 4.05 Highly significant. ____________________ 1 .0229 .0229 2. 89 Not significant. Residual ________________ 41 . 3248 . 00792 In original numbers Mean original-slope ratio: In logarithms (antilogs) Test ................................................... 0. 3476 2. 227 Original measurements ________________________________ .3806 2. 402 Difference ............................................. . 0330 . 175 The difference between landslide means is highly significant, whereas the difference between men is not significant. It is judged, therefore, that original slope is a controlling factor in the environment of a land- slide and its measurement can be reproduced by other geologists. SUMMARY 0!" ANALYSIS OF SUBMERGENGE PERCENTAGE Since submergence was also a continuous variable, the problem and its solution were the same as in the two previous analyses, except that the percentages were transformed to equivalent angles instead of logarithms. Degrees Sum: of Mean of Source of variance of freedom squares squares f—teat Significance Toat1._._._._.._______ 83 1.1263 Landslides. _ 41 1. 0274 0. 0251 14.2 Highly significant. Men ____________________ 1 .0264 . 0264 14. 9 Do. Residual ________________ 41 0725 . 00177 In original numbers Mean submergence values In angles (antilogs) Test ___________________________________________________ 0. 4224 45. 2 Original measurements ________________________________ . 4579 51. 4 Difference _____________________________________________ . 0355 6. 2 Both landslides and men were highly significant. It is judged, therefore, that submergence percentage is also a controlling factor in the geologic setting of a landslide. Statistically, the mean difference of 6.2 in STATISTICAL STUDIES submergence percentage indicates: (a) that submer- gences were measured differently at the time of the ex- periment than when they were measured originally, or“ (b) that the measurement for submergence is not re»- producible among geologists. From a practical stand- point this mean difference of 6.2 percent is probably not large enough to be important. SUMMARY OF GROUND-WATER ANALYSIS The qualitative variable ground water, with two categories, was reproducible by geologists Erskine and Peterson. Of the 42 landslides classified, only 1 dif- fered from the original. Had the‘ men in the experiment been unable to duplicate the ground-water categories at all, their results would have reflected chance vari- ation. With 2 classifications where chance alone dic- tated the choice, each classification would have a prob- ability of 1 :2 of being correct or erroneous (assuming the original classification to be correct), or it would have been expected that on the average, of the 42 slides, 21 would be classified right and 21 wrong. The results deviated from what would have been expected by chance alone; therefore, it is judged that the men were able to classify ground water in the same way as the author. Actual and expected results are: Ezpected (by chance alone) Actual Classifications right _______________ 21 41 Classifications wrong ______________ 21 1 x2: 38. 1 Degree of freedom= 1 Probability = 0.01 The chi-square of 38.1 is greater than would occur on a chance basis once in 100 times. Chance alone cannot explain these data. Consequently, it is judged that ground—water classifications are reproducible. SUMMARY OF MATERIAL ANALYSIS The qualitative variable material, with five catego- ries was not reproducible by the men in the experiment. The method of analyzing the material classifications was the same as for ground water except that material was divided into five categories. Here, if chance alone operates in the classification, the probability of its being correct is one—fifth and of its being incorrect four-fifths. Actual and expected results are: Expected (by chance alone) Actual Classifications right _______________ 8. 4 10 Classifications wrong ______________ 33. 6 32 x2 = 0.396 Degrees of freedom = 1 Probability = 0.30 The value of chi—square of 0.396 indicates that the test results are about what would be expected by chance alone; consequently, it must be judged that the men in the experiment were not to classify materials into the five categories. This is not surprising because of the com- plex nature of Pleistocene deposits in the area and the 55 brief incomplete field review of the deposits given the men in the test before their first attempt at this kind of classification. Classification is one of the most dif- ficult tasks for research workers in any scientific investi- gation. Geologists Erskine and Peterson could prob- ably have more nearly duplicated the original measure- ments if the illustrations showing the different types of material (figs. 32-38) had been available to them, and if they hadbeen provided with a working knowledge of all the pertinent material exposures in the investi- gational area. SUMMARY AND INTERPRETATION OF UNIFORMITY EXPERIMENT RESULTS 1.. The H02VC ratio was a precise measurement of a landslide. It was also a measurement reproduc— ible by other geologists unfamiliar with the details of the landslide or the particular geologic setting. 2. The original slope of the terrace scarp was one of the controlling factors in the environment of a land- slide. It was also a reproducible measurement. 3. Submergence percentage was also determined to be a controlling factor in the geologic setting of a landslide but was not reproducible by the geolo- gists in the test. 4. Ground-water classifications were reproducible, qual- itative measurements. . Material classifications were not reproducible in the experiment. The geologists could probably have more nearly duplicated the original classifications if they had been provided with clear-cut defini- tions, illustrative material, and a working knowl- edge of the stratigraphy of the Pleistocene deposits. While the uniformity experiment indicated that ma- terial classifications may not be reproduced, the analysis of recent slump-earthflow landslides showed that mate- rial classifications were correlated with the HO: V0 ratio of the landslides. Since both of these variables had demonstrated their usefulness in predicting the slide ratio, they were not rejected. Because of the results of the test, definitions of the material-classifica— tion categories were painstakingly revised to include many details which were not incorporated at the time of the experiment. 01 SIDPE-STABILITY INVESTIGATION In an effort to determine which sections of the banks along Franklin D. Roosevelt Lake were safe from land- slides and which were unsafe, a slope-stability investi— gation was undertaken. The study was designed to combine the data of the 160 recent slump-earthflow landslides with data for 160 representative locations in which there were no landslides. The analysis used the discriminant-function method, in which quantitative and qualitative factors influencing slid- 56 ing were combined into an equation that provided maximum discrimination between slopes that are likely to fail by landsliding and those that are not. The 320 values of the discriminant function ranged from —0.0019 to +0.0404. The lower values were generally associated with stable slopes, and the higher values with landslides. A value of 0.0106 was found to be the theoretical lower 95 percent confidence limit for slides, and although much overlapping of discriminant values was found between slides and stable slopes, there are clear-cut conditions where nearly all slopes have slides and other conditions where nearly all slopes are free of slides. For the purpose of this study, a stable slope was defined as a slope on which there was no recent slide. The investigation of stable slopes was made by classi- fications and measurements in the same manner as the investigation of landslides. Locations were chosen so that the group of 160 stable slopes represented as nearly as possible a random sample of all slopes along Franklin D. Roosevelt Lake which have not been affected by sliding in its first 14—year history. Measurements were made of the slope of the terrace scarp, submergence percentage, and terrace height. Classifications were made of the qualitative variables, ground water and material, following the same definitions and classifi- cation categories used for the landslides. The locations of the slopes studied and the classification data are summarized in table 8 (see section headed “Tables of landslide data”, p. 74). SUMMARY 0!" ANALYSIS FOR THE DISCRIMINANT FUNCTION The discriminant function employed in this experi- ment is an equation designed to differentiate slopes that are potential slide areas from slopes that are not po- tential slide areas. The form is y = bixi-l' bfl2+ bsxa‘l' bm+ bfls'l‘ boxa‘l’ 171137 + biz/178+ 179109 Where y=the dependent variable or discriminant function b1, b2 . . . b9=coefiicients derived from the analysis of factors influencing sliding in 160 landslides and 1.60 stable slopes x1, x2 . . . x9=independent variables determined to be sig- nificant factors influencing sliding: original slope. submergence percentage, terrace height, ground water, and materials The independent variables, original slope, submer- gence percentage, and terrace height, are quantitative and can be used in their numerical form. To use multiple regression methods, the qualitative variables ground water and materials must be quantified. Ground water is a qualitative variable, and since it has only two levels it presents no problem in quantifi- cation. The number 0.1 was arbitrarily assigned to LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON high ground water and the number 0 to low ground water. Materials were represented by five independent var- iables, with the following assigned values. 25:0.1 for material 1 and 0 for other materials 10:0-1 for material 2 and 0 for other materials x7=0.1 for material 3 and 0 for other materials $g=0.1 for material 4 and O for other materials x.=0.1 for material 5 and 0 for other materials Data for orignial-slope and terrace-height variables were transformed to logarithms. Data for submer- gence percentage were transformed to equivalent angles. For the 160 landslides, the discriminant values are listed in table 1; those for the 160 stable slopes in the experiment are listed in table 8. Regression coefficients and tests of significance for the discriminant function are as follows: Standard t—test Symbol Variable Cbefficient error 1 Significance b1 Original slope ........... -0. 0213 0.0016 13. 33 Highly significant. 1), Submergenoe... .0028 .0019 1. 44 Not signiflean cant b; Terrace height._ .0102 .0013 7. 85 Highly significant ()4 Ground water. . .0616 . 0104 5.89 Do. in Material 1.... ..... -. 0082 (I) b. Material 2. .0106 .0066 1.60 Not significant. b7 Material 3. .0037 .0070 . 53 Do. bs Material 4. .. . 0186 .0076 2. 44 Significant. be Materials ________________ -. 0247 .0071 3.46 Highly significant. 1 Not estimated. The variables, original slope, terrace height, ground water, and material 5, showed high significance. Mater- ial 4 showed significance at the lower level. Submer- gence percentage was not significant. The standard error for the coefficient of material 1 could not be readily estimated from the analysis, but since the standard errors for the other materials were approximately equal it was assumed that material 1 was not significant. The analysis of variance for testing the significance of the discriminant function was as follows: Source of Degrees of Sum: of Mean variance freedom squares square f—leat Significance Total _______________ 319 Between groups..._ 9 0. 000710936 0. 00639842 24. 6 Highly significant. Within groups ...... 310 . 00894317 .0000288488 The high degree of significance between groups may be interpreted to mean that the variables included are related in some manner to the stability of slopes in this area. Nonsignificance of material classifications in categories 1, 2, and 3 is not surprising because these categories contain principally fine grained sediments which when dry stand in clifflike slopes and when wet rest on gentle slopes. When taken together as material groups, both situations are combined. Some different method of quantification based on grain size, amount of compaction, cohesion, or shear strength might provide a way of incorporating them into the slope-stability formula, but this was not within the scope of the inves- tigation. Because of the lack of significance of three of STATISTICAL STUDIES the material categories, it was decided to derive a re— duced equation excluding all of the material categories. The variables, original slope, terrace height, and submergence percentage were all transformed to loga- rithms. In the case of submergence percentage, preliminary studies indicated that the logarithm trans- formation would be more highly correlated than the equivalent angle transformation used before. Ground water was defined as 0.1 for high ground water and 0 for low ground water. The reduced discriminant function and the summary of the analysis of variance is given as follows: (y=0.0216247 log x1+0.00334811 log z;+0.00944030 log Z3 +0.00673l26 x4) where y=Discriminant function z1=0riginal slope 2:2: Submergence percentage x3=Terrace height 2:4 = Ground water (high = 0.1) (low = 0) SUMMARY OF ANALYSIS OF VARIANCE FOR THE DISCRIMINANT FUNCTION Analysis of variance Degrees of Sums of Mean Source of variation freedom squares square f-test Significance Total ______________ 319 0. 001519 . Between groups... 4 0.006076 .0000277 54.90 Highly significant. Within groups. _ - - 315 . 008715 ________ Coeflicients of the discriminant function and their standard errors Variable Coefficient Standard t-test Significance error Original slope ................ —0. 021625 0 001531 14.12 Highly significant. Submergence. . . .. . 003348 000791 4. 23 Do. Terrace height. - .009440 001234 7. 65 Do. Ground water... .006731 00988 6. 82 Do. Nora—Degrees of freedom=315 t=2.6 for P=0.01 The high degree of significance between groups may be interpreted to mean that the variables taken to- gether are related in some manner to slope stability. The fact that the ratios of the coefficients divided by their standard errors exceed the value of (t) for a 1 percent probability warrants the judgment that each of the 4 variables is related to slope stability in such a way that prediction of potential landslide conditions is possible. use or THE DISCRIMINANT FUNCTION The discriminant function may be used to differen- tiate stable from potentially unstable slopes where any combination of values of the four variables exists. Cal- culations of the discriminant functions for the 320 57 landslides and stable slopes gave values ranging from —0.0019 to +0.0404. In general, the lower values of the discriminant func— tion represented stable slopes, and the higher values represented landslides. Less than one percent of the landslides had a discriminant value below a theoretical value of 0.0106; consequently, it will be safe to judge that a slope will not be affected by sliding if its discrim- inant value is below this level. Less than 5 percent of the landslides had a discriminant value below 0.0142; consequently, it will be relatively safe to judge that a slope will not be affected by landslides if its discrim— inant value is below 0.0142. The mean value of the discriminant functions for the two categories was i Landslides _______________________________________ 0. 02282 Stable slopes _____________________________________ . 01411 Midpoint value ___________________________________ 0. 01846 In theory, when the discriminant function is less than the midpoint 0.01846, the slope will be classified as stable, and when the discriminant function is greater than 0.01846, the slope will be classified as unstable. The difference between either mean and the midpoint is 0.00435. From the analysis of variance the standard deviation is 0.00526. The ratio of the difference to the standard deviation gives a value of _ .00435 t— .00526 =0.827 for 315 degrees of freedom From standard tables of Student’s t a value of 0.827 is exceeded about 21 percent of the time. Approxi- mately 21 percent of slides will have discriminant values below the midpoint 0.01846. Table of actual frequences of landslides and stable slopes for various levels of the discriminant function: Frequency Frequency of stable Class limits for discriminant function 0] slides slopes —0.0051—0.0000 ____________________________________________ 5 00001—00050. . ._ ______________ 00051—00100. . 00101—00150. . 00151—00200. _ 0.0%1—00250. . 00251—00300. _ 00301-00350. . 00351—00400. _ 00401—00450 .................................. Total _____________________________________ 160 160 320 Total Although there is much overlapping of discriminant values for slides and stable slopes, there are clear-cut levels where nearly all values represent landslides and 'other levels where nearly all values represent stable slopes. 58 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON The use of the midpoint value of the discriminant function 0.01846 as a theoretical dividing line between landslides and stable slopes results in the following misclassification: ' Landslides classified as stable slopes ___________________ 15 Stable slopes classified as landslides ___________________ 41 Total misclassifications ________________________ 56 Theoretically the misclassification in either direction should be equal. A chi-square test of significance gives a value of X2: 15.9 degrees of freedom=1 According to tables of X2 (see references under heading “Statistical techniques,” p. 69) a value of 15.9 will occur by chance less than 1 percent of the time. It is judged, therefore, that the discriminant function misclassifies stable slopes as slides more frequently than it mis- classifies slides as stable slopes. Since an important use of the function is to identify stable slopes, the dis- criminant function may err somewhat on the conserva- . tive side. The value of t for 315 degrees of freedom and a prob- ability of P=0.01 in one direction is t=2.326 Multiplying by the standard deviation st: (0.00526) (2.326) =0.0122 The mean value of the discriminant function for slides is 5:00228 and 5—st=0.0106 lower limit of the discriminant function for slides RESULTS OF EXPERIMENT Of the 160 slopes selected for stability studies, anal- ysis by the discriminant function method indicated that: 39 were very stable, having discriminant function values of 0.0106 or less; 36 were relatively stable, having discriminant function values between 0.0106 and 0.0142; 85 were likely to be affected by landslides, having dis- criminant-function values above 0.0142. Of the 39 locations judged to be very stable because of the low value of the discriminant function, the 5 listed below have the steepest slopes. The data for the locations indicate that low values of submergence percentage, terrace height, and ground water counter- balance the steepness of the slope to such a degree that the slope is stable. The photograph, figure 40, shows a slope judged to be very stable, and the photograph, figure 41, shows a slope judged to be relatively stable. Five stable slopes with steepest measured slope [LM, lake mile; RB, right bank; LB, left bank] Discrim- Submer- Terrace Slope Original inant gence height Ground No. Location and area slope value (percent) (feet) water 9 LM 8.2 RB Swawiila Basin.._- 2.8 0.0105 8 65 Low 122 LM 64.7 LB Hunters-Nez Perce .............. 2.8 .0097 10 50 Do. 43 LM 27.5 RB Helgate- Whitestone ........ 3.1 .0106 5 100 Do. 69 LM 43.7 LB Fort Spokane ______ 3.3 .0056 0 60 Do. 38 LM 23.9 RB Hellgate- Whitestone ........ 4.3 .0104 50 90 Do. Of the 85 locations judged to be susceptible to land- sliding due to the high value of the discriminant func- tion, the 5 listed below have the highest values. The photograph, figure 42, shows a slope judged to be susceptible to sliding. Five stable slopes most likely to be afiected by sliding [LM, lake mile; RB, right bank; LB, left bank] Discrim- Submer- Terrace Slope Original inant gence height Ground No. Location and area slope value (percent) (feet) water 99 LM 51.5 RB Ninemile .......... 2. 5 0. 0286 58 400 High. 24 LM 19.0 RB Keller Ferry _______ 1. 8 .0278 50 220 Low 17 LM 14. 7 LB Swawiila Basin.... 1. 5 .0254 30 370 Do. 64 LM 41.5 RB Fort Spokane ______ 2. 9 .0246 30 270 High. 50 LM 34.6 LB Hawk Creek _______ 1. 4 .0245 24 275 Low APPLICATION OF LANDSLIDE AND SLOPE STABILITY DATA By FRED O. JONES and DANIEL R. EMBODY Application of the methods and techniques developed in this research may contribute to the practical useful- ness of geologic studies of land stability. The relatively uniform physical setting along the upper Columbia valley not only provided an opportunity to develop new geostatistical techniques for such studies but also presented an ideal opportunity to apply and test the results. This section illustrates the way these data may be used to identify potential landslide areas and estimate the extent of impending landslide action. The most immediate application of this study should be in land utilization along Franklin D. Roosevelt Lake and Lake Rufus Woods. In future land acquisition programs along these lakes, both the Bureau of Recla- mation and the Corps of Engineers may be better able to determine just how much land needs to be withdrawn from public use and just how much is safe for public use. In managing federally owned lands along Franklin D. Roosevelt Lake, the National Park Service may use these methods in its administrative decisions. When STATISTICAL STUDIES 59 FIGURE 40.—A slope on sand judged to be very stable because of a discriminant function value of 0.0106. The lake is drawn down from its maximum level. Slope no. 43; lake mile 27.5 right bank; Hellgate-Whitestone area. See table 8 for classification data. FIGURE 41 .—A slope on interbedded silt. clay and sand judged to be relatively stable because of a discriminant function value of 0.0138. The lake is drawn down from ’ its maximum level. Slope no. 131; lake mile 71.5 left bank; Cedonia area. See table 8 for classification data. 581004 0—61—5 60 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON FIGURE 42,—A slope on silt and clay judged likely to be affected by landslides because of a discriminant function value of 0.0242. Slope 160; lake mile 107.0 right bank; Marcus-Evans area. future landslides sever highways and railroads in the area as they have in the past, these data may be helpful in selecting relocations. Owing to the fact that geologic conditions are so similar the data may be espe- cially useful in the land acquisition and relocation work on the Rocky Reach and Wells projects in Washington and on the Libby project in Montana. Pleistocene surficial deposits of the types studied are not limited to the area of the present investigations. Similar deposits are found along approximately a thou- sand miles of river valleys in northern Washington, Idaho, and Montana. They are also found along many thousands of miles of valleys of British Columbia in both the Columbia and Frazier River systems. The Columbia River system alone has a potential hydro- electric generating capacity of about 30 million kilo- watts of electricity, of which only 10 million have been developed. The dams, reservoirs, and other engi- neering works related to this development will encounter deposits similar ,to those in this investigational area in countless places. See table 8 for classification data. RECOGNITION OF POTENTIAL LANDSLIDE AREAS The recognition of natural slopes in which land- slides may occur is of primary importance in land use. By using measurable data and their own experiences and observations, many geologists and engineers have developed criteria for estimating stability. These sta- bility analyses of natural slopes, for the most part, result from personal judgment of a group of factors; such as, steepness of slope, topography, ground water, spring areas, material, and nearness to recent slides. The discriminant—function method described in this report uses the well-recognized criteria but goes a step further. It provides a numerical value to aid in judging whether or not a slope may slide by classifying the significant factors, transforming them into quantified units, and combining them into a formula. The resulting numerical value cannot be any better than the geologic classification from which it is derived. The discriminant-function method of identifying poten- tial slide areas and stable areas is not intended to replace personal judgment but is offered as a tool to assist the geologist and engineer whose responsibility it is to appraise the stability of natural slopes. STATISTICAL STUDIES 61 ESTIMATION OF LANDSLIDE EXTENT IN THIS AND SIMILAR GEOLOGIC SETTINGS An understanding of gelolgic and physiographic rela— tions is fundamental to the estimation of landslide extent and to a practical application of the landslide data assembled in this report. The first step in apply- ing the landslide data should be to determine the dif- ferent types of landslides which could occur in a par- ticular geologic setting, as in most places more than one type may occur. Examination of the mean and maxi- mum HC:VO ratios for these groups will provide a basis for judging the average and maximum depths to which a slide of any of the different types will cut. If the slump-earthflow slide is the type having the greatest possible H0zVC ratio, the formula in the preceding section may be used to estimate how far a landslide might cut back from the toe of the slope. The formula cannot replace competent, experienced judgment, but it should aid in arriving at appraisals which have more basis in fact than a guess. GENERAL APPLICATION OF METHODS The system of collecting and assembling field data employed here may be useful in landslide investigations in other geologic settings. The statistical techniques of testing geologic classifications and of combining quantitative and qualitative variables in the develop- ment of numerical formulas may prove effective in other landslide areas. Statistical methods similar to those developed in this landslide study should produce worthwhile results in other fields of geologic engineering research. ILLUSTRATIONS OF APPLICATION OF LANDSLIDE AND SLOPE STABILITY DATA To illustrate the practical application of the slope stability and landslide data, detailed landslide classi- fication studies were made of lakeshore land in the N inemile area along Franklm D. Roosevelt Lake and in the Alameda Flat area along the reservoir behind Chief Joseph Dam. The classification of the Ninemile area (pl. 3) is presented according to sections of the lake- shore which have a constant geologic setting. Some of the analyses are based upon only a specifically selected profile location, Whereas others are based upon com- posite data where several hundred feet of the lake banks have similar conditions. The classification data for the Alameda Flat area (pl. 6) is presented in tabular form (table 5). Research investigations did not provide data to predict when any Specific potential slide area will slide, and it seems doubtful they ever could. The following classifications were made on the premise that in land—use problems we are concerned only with areas which may fail in the foreseeable future—which future might be defined as the next 50 to 100 years. From a theoretical standpoint, landsliding may continue until all of the surficial deposits are removed from the rock valley of the Columbia, but consideration of time meas- ured on the geologic scale was not thought to be a practical premise for the landslide classification. Where landslides are likely to affect the lakeshore land under prevailing conditions, the estimated maxi- mum extent of landslide action is shown on the maps by a line designated A. This is an estimate based on the best available data and applies to conditions of maximum submergence by the reservoirs involved. In certain areas the lakeshore land is suitable for develop- ments such as irrigated farming, which could change ground-water conditions from low to high. A study has been made in these areas of the probable extent of landslide action under these postulated changes. This estimate of maximum landslide action is shown by the line designated B. Two mimeographed computation sheets were used in the fieldwork—one for the prediction of slope stability by the discriminant-function method, and one for the prediction of HOzVO ratio of slump-earthflow land— slides where it was applicable. Samples of both sheets are shOWn below. All computations were made with a slide rule in the field at the time of examination and are considered sufficiently accurate for the use to Which they were put. NINEMILE AREA (FRANKLIN D. ROOSEVELT LAKE) The following is a detailed description of a landslide classification on the shoreland along Franklin D. Roosevelt Lake in the Ninemile area using the data and guiding formulas developed in the landslide and Slope stability research. To aid in following the de- scription, the reader is referred to plate 3. The classi- fication begins at lake mile 49.7 on the left bank and extends uplake along the left bank to lake mile 55.25. It then begins at lake mile 49.7 on the right bank and extends to lake mile 55.25. Lake mile 49.7 to 50.8 left bank—The lakeshore land in this section consists of a broad terrace which has a surface altitude of 1,900 feet. The scarp of the ter- race has been cut into a series of alternating ridges and alcoves by ancient landslides and subsequent erosion. Materials of the lower part of the terrace are predomi— nantly silt and clay of material category 1; materials of the upper 200 to 400 feet of the terrace are princi- pally sand and gravel. Exposures of bedrock in the area suggest that ancient sliding may have been limited or controlled to some extent by bedrock. The ancient sliding was of the slump—earthflow type, and several small recent slump-earthflow slides have cut into the LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON Example of slope stability field sheet Sheet No. 5 Date 8/18/54 COLUMBIA RIVER LANDSLIDE PROJECT, WASHINGTON Computation sheet for predicting slope stability (by the discriminant-function method) Location. Ninemile area, lake mile 53.5 right bank Formula. Y= —0.021625 log X1+0.003348 log Xz+ 0.00944 log X3+0.006731 X4 where Y=the discriminant function X1=original slope X 2 = submergence percentage X3=terrace height X4=ground water: high=0.1 low=0 Tramforma- Transformed Variable Numerical value hon value . Regression coefficient Product X1 Original slope 2.0 : 1 Log 0.301 —0.021625 —0.0065 X 2 Submergence percent- age 85 Log 1.930 .003348 .0065 X3 Terrace height 270 Log 2.430 .009440 .0229 X 4 Ground water low = 0 None 0 .00673 1 0 .0229 Should ground water be changed from low to high the discriminant-function value would be 0.0296 Slopes having discriminant-function values of 0.0106 or less are very stable. Slopes having discriminant-function values of 0.0106 to 0.0142 are relatively stable. Slopes having discriminant-function values of above 0.0142 are likely to be affected by land- slides. Types of landslides which could develop in this geologic setting slump-earthflow Remarks: Terrace surface is smooth and favorable for development. Example of HC:VC field sheet Sheet No. 5 Date 8/ 1 8/54 COLUMBIA RIVER LANDSLIDE PROJECT, WASHINGTON Computation sheet for predicting HC:VC ratio of landslides (slump-earthflow type) Location. Ninemile area, lake mile 58.5 right bank Formula. Y=—0.6328+0.2460 X1—1.4121 Xz+7.5583 X3+ 1.0338 Xvi—0.4015 X5 Where Y=log HC: VC ratio of slide X .=submergence percentage (equivalent angle) X 2=log of original slope X3: (X2+1)2/10 X4=ground water (takes value of 0.0 for low and 0.1 for high) X 5=materia1s. Takes numerical values as follows: 1 = + 0.1 2, 3, & 4=0 5 = — 0. 1 Tramforma- Transformed Regression Variable Numerical value lion value coefiicient Product X 1 Submergence 85 Equivalent 0.672 0.2460 0.165 percentage angle X2 Original slope 2.0 Logarithm .301 — 1.4121 ——.423 (linear) X3 Original slope (1 +0.301)2 (1+log)2 .170 7.5583 1.285 (quadratic) 10 10 X4 Ground water Low=0 None 0 1.0338 0 X 5 Materials #2 = 0 None 0 .40 1 5 0 Intercept — .6328 .394 Y: Predicted HC:VC 0.894 2.5 95% confidence limit constant .134 Upper limit of HC:VC ratio .528 3.4 ihguld ground water be changed from low to high, upper limit of HC:VC ratio would be Remarks: Under present ground water conditions it is estimated that slides could cut back 400 feet from lake shore. If ground water conditions were changed to high due to irrigation or other causes, slides may cut back 760 feet from lakeshore. STATISTICAL STUDIES 63 banks. Slope—stability studies of the lakeshore land from an altitude of 1,300 to 1,400 feet gave discrimi— nant-function values ranging from 0.0166 to 0.0269, which indicate that all of the lakeshore land is likely to be affected by sliding. A composite study of slope stability considering the lakeshore land from the lake to the top of the high terrace gave a discriminant-function value of 0.0194. Basic data were: slope, 3.9:1; submergence, 25 percent; terrace height 810 feet; ground water, low. Of the 160 slump—earthflow landslides studied in the statis— tical work only 2 had original slopes as gentle as 3.9: 1, and these were located where water conditions are nat— urally high. These data and the suggestion that the ancient sliding may have been limited by bedrock lead to the conclusion that future sliding in the area should be considered only insofar as it affects the land at lower altitudes. The broad high-level terrace is favorable for developing irrigation farming. Should ground- water conditions be changed to high because of this or other developments, sliding may extend to about the present front edge of the terrace. Sliding has devel- oped at other places similar to this where terraces have been irrigated, but‘in no place has it been observed to cut far back into the terrace surface. The B—line on the map delineates the possible extent of sliding under such postulated changed conditions. At lower altitudes on the irregular terrace scarp, the type of landslide expected in this setting is the slump earthflow. A slope-stability study of the area at lake mile 49.7 left bank gave a discriminant-function value of 0.0225, and the H0zVC’ prediction formula indicated that slides in this area may cut back as far as 750 feet from the present lakeshore. Basic data were: slope, 2.13:1; submergence, 65 percent; terrace height, 310 feet; ground water, low; material category, 1. A slope—stability study in the small bay at lake mile 49.8, which has a spring area just above it, gave a discriminant-function value of 0.0269. Basic data were: slope, 2.85:1; submergence, 75 percent; terrace height, 350 feet; ground water, high. A similar study of the area between lake mile 49.85 and 50.0, left bank, resulted in a discriminant—function value of 0.0204, and the H01VU prediction formula indicated that slides may cut back as far as 975 feet from the lakeshore. Basic data were: slope, 2.56:1; submergence, 64 percent; terrace height, 310 feet; ground water, low; material category, 1. A composite slope-stability study of the area at lake mile 50.15 left bank gave a discriminant-function value of 0.0166, and the prediction formula indicates that slides may cut back as far as 650 feet from the present lakeshore. Basic data were: slope, 2.2 :1 ; submergence, 5 percent; terrace height, 200 feet; ground water, low; material category, 1. From these data the A—line was drawn on the map to outline what is the maximum extent to which land- slides are likely to cut into this area under present conditions. Lake mile 50.3 to 52.5 left bank—Along this section of lakeshore, slopes are gentle both above and below full lake level. The materials are silt, clay, sand, and gravel disturbed by ancient landslides or glacial processes. Slope-stability studies indicate that landslides are not likely in this section under present conditions. Should ground water be increased from low to high by irriga- tion of the lakeshore land or other developments, the slopes will probably remain stable. Summary of four slope-stability studies Location (lake mile, Submer- Terrace Ground Discrim- left bank) Slope gence height water inant (percent) (feet) function 50. 4 ___________________ 5. 7 42 120 Low ...... 0. 0087 51.2.... _._ 7.7 23 130 -._do _______ .0121 51.7.... ... 3.7 75 _..do _______ .0082 52.3 ................... 4.6 53 150 ...do ....... 0120 Wave banks are not present between lake mile 50.3 and 51.3, but they range in height from 2 to 10 feet between lake mile 51.3 and 52.5. Lake mile 52.5 to 53.55 left bank.— The lakeshore land along this section has a rolling surface which ranges from 20 to 90 feet above lake level. The topography probably reflects ancient landsliding or glacial proc- esses. Exposures along the entire section show dis- torted and disturbed silt and clay mixed with varying amounts of sand and gravel. For convenience the area will be described in two parts—— the lakeshore land paralleling the lake, and that part along the bay at lake mile 53.55. Nearly all the lakeshore land paralleling the lake has been cut by landslides. Six of the slump-earthflow landslides included in the research study are in this stretch. The following table gives a summary of the slope stability and H0: V0 data of those six slides: Summary of the slope stabilily and HC:VC ratio Sub- Dis- Pre- Mate- Ground Ter- mer— crim- Actual dicted Landslides rial water race gence Slope inant HC’:VC maxi- height (per- func- mum cent) tion HC:VC 2 Low__ 100 10 l 8 0.0167 2.4 2.4 2 _._Do__ 140 64 2.1 0193 2.3 3.2 2 .__Do._ 150 80 1.8 .0214 2.3 3.0 2 -._Do._ 110 82 1.7 .0207 3.3 3.0 2 ..-Do.- 80 62 1 8 .0185 2.0 2.8 2 ___Do._ 120 76 2 7 .0166 3.0 3.9 The discriminant-function value of each landslide indi- cated that the lakeshore land would be affected by sliding. Only one landslide, at lake mile 53.2, has cut 64 back farther than the H0: V0 prediction formula indi- cated it would. These slides all occurred soon after the lake was filled. Beach erosion and caving are tending to waste the points of land between them, and the banks are steeper than they were originally. The landslide material tends to flatten out on the bottom of the lake and has little effect of loading the toe area or of creating a more gentle slope. For these reasons it is believed that as the shoreline be- comes straightened by erosion and sloughing, conditions conducive for another series of landslides will form. Consequently, the A-line on the classification map has been drawn, using the H0: V0 prediction formula and then doubling the computed distance slides may cut into the bank. The tabulation below gives the esti- mated distances landshdes may cut in the foreseeable future. An estimate has also been made of the distance back slides might out if ground-water conditions were increased from low to high. Distance from shore Distance from present landslides may culif ahoreline landslides ground water is in- Location may extend creased to high (lake mile, left bank) (A-line) (B—line) 52.6 ____________________ 300 375 52 .7 ____________________ 330 41 5 53 .1 ____________________ 31 0 3 80 53.2 ____________________ 100 1 40 53 .4 ____________________ 320 400 53.5 ____________________ 280 380 Small landslides have cut the banks of the bay at lake mile 53.55 from its mouth to points‘on both banks about 540 feet from the opposite end. Near this end slopes become more gentle and submergence becomes less, so a study was made to determine whether the banks in this area are likely to fail. A composite slope-stability study was made on the right bank 250 feet from the end and on the left bank 300 feet from the end. The discriminant—function value was 0.0107, which indicates that under present conditions the banks are very stable. Should the ground~water conditions be changed to high, the discriminant-function value would be 0.0174, which indicates the likelihood of slides. Basic data: slope, 2.35:1; submergence, 33 percent; terrace height, 30 feet; present ground-water condition, low; material category, 2. Slope—stability and H0zVO studies were made on both sides of the bay to determine the probable extent LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON of landslide action in the outer part of the bay. The classification data and results are: Sub— ’I‘er- mer- race Ground Matc— Discrim— HC’:VC Location Slope genes height water rial inant H 0: VC (high (per- (feet) function ground cent) Water) 440 it from end of bay on right bank... 1.8 60 50 Low... 2 0.0164 2.8 3.5 700 ft from end of hay on left bank _________ 1 65 44 57 ..-do_.__ 2 .0174 2.4 3.1 At the location 440 feet from the end of the bay on the right bank, slides under present conditions may af- fect the land 90 feet back from shore. If ground-- water conditions were changed to high, they could affect the land 125 feet back from shore. At the location 700 feet from the end of the bay on the left bank, slides could cut back 85 feet under present conditions and 125 feet under high ground-water conditions. Lake mile 53.55 to 54.42 left bank—Slopes both above and below water along this section are very gen- tle and studies indicate that they will not be affected by landslides. A measurement at lake mile 53.6 gave a slope value of about 10:1, and no landslides have oc- curred in the surficial deposits in the area on so gentle a slope. A slope—stability study by the discriminant- function method at lake mile 54.0 gave a value of 0.0127, which indicates a nearly stable condition. Basic data: slope, 2.8:1; submergence, 29 percent; ter- race height, 70 feet; ground water, low. A study at lake mile 54.35 gave a discrimimant—function value of 0.0126 with basic data as follows: slope, 3.9:1; sub- mergence, 42 percent; terrace height, 120 feet; ground water, low. Lake mile 54.42 to 55.25 left bank.—The lakeshore land in this section consists of broad ridges and steep- sided valleys alined normal to the lakeshore. Slope— stability studies indicate that this area is likely to be afl’ected by landslides, and a few minor ones have al- ready occurred. The type of slides most likely to cut these banks is the slump earthflow. At the upstream end of the section they may be limited by bedrock or slides off bedrock may occur. The following is a summary of three slope-stability studies which have been used as guides in drawing the Summary of three slope-stability studies H C : VC under pres- H 0: VC under wet ent ground-water ground-water con- Location Slope Submergence Terrace height Ground water Material Discriminant conditions and dis- ditions and distance (Wrcent) (feet) function value tance back from back slides might shore slides might cut (feet) out (feet) Lake mile 54.45—54.55 ________ 2. 2 30 100 Low _____ 4 0. 0164 2. 9—180 3. 6—250 5 . _______________ 3. 3 25 200 ___do _____ 4 . 0149 3. 9—600 5. 0—900 55.05—55.27 ________ 3. 0 28 320 ___do _____ 4 . 0181 3. 6—1, 050 4. 6-1, 400 STATISTICAL STUDIES line on the classification map which delineates the area of potential landslide danger under present conditions and under high ground-water conditions should they be changed by developments in the area. Lake mile 49.7 to 50.33 right bank—The bank in this section is a steeply dipping bedrock surface which is covered thinly in places with talus and slope wash. Bedrock gullies contain minor accumulations of sand and gravel mixed with bouldery slope wash. There have been minor talus slides and one small rock slide along this section. Additional slides of this type will occur but they are insignificant in relation to land use. Lake mile 5033 to 50.70 right bank—In this section the lakeshore land with which we are concerned consists of two small areas of surficial deposits resting against steeply dipping bedrock. A slope-stability study of the larger area (lake mile 50.33 to 50.55) gave a discrimi- nant-function value of 0.0200. Basic data: material, category 2; disturbed silt and clay; original slope, 2.85:1; submergence, 61 percent; terrace height, 330 feet; ground water, low. These data indicate that the point is likely to be affected by slides. Three types of slides may develop in this setting—slump earthflow, slump earthflow limited by bedrock, or slides off bed- rock. Using the prediction formula for slump-earth- flow slides, it was determined that the H0: V0 may be as great as 3.9 : 1, which would cut back into the terrace 700 feet from shoreline. This is about 100 feet from the bedrock line when measured at the broadest part of the terrace point. It seems more likely that if failures occur, a part of the surface of rupture will follow bedrock; consequently, the entire area of sur- ficial deposits is likely to be affected by slides. A slope-stability study of the smaller terrace point between lake mile 50.55 and 50.70 gave a discriminant- function value of 0.0171, which indicated that it also may be affected by slides. Slides off bedrock seem most likely here, as they did in the larger terrace point. Thus the entire section is likely to slide into the lake. Lake mile 50.7 to 51.1 right bank—The lake bank along this section is steeply dipping bedrock covered thinly in places with talus accumulations. Minor talus- slump landslides may occur, but they would not affect use of the lakeshore land. Bay at lake mile 51.05 right bank (lake mile 51.1 to 51.25), including Ninemile Bay.—Lake banks along this area are alternating sections of steeply dipping bedrock and thin patches of surficial deposits of silt, clay, and sand resting on bedrock. Landslides have cut the highway in two places. Future landslide action will be of the following types: slides off bedrock, slip-off slopes, and slump earthflows limited by bedrock. All the surficial deposits in this section are expected to be affected by slides from lake level to the A—line on the 65 map. Bedrock areas Will be free of slides generally, but small areas of silty and clayey slope wash mixed with talus and rubble will fail. Lake mile 51.25 (silt-bedrock contact on left bank of Ninemile Bay) to 51.8 right bank—The lakeshore topog- raphy in this section contains the finest example of an ancient multiple-alcove slide found in the entire invest- igation. The slide overlies the deep preglacial channel of N inemile Creek. Materials are principally silt and clay of material category 1. Ground-water conditions are high. Sections of the surface of rupture of the ancient slide can be observed in new wave banks and minor recent slides along the shore. The high-level position of this part of the surface of rupture suggests that the slide occurred before the Columbia River had cut down to its present level. The probable base of this old slide is at an altitude of 1,360 feet, or 70 feet above maximum lake level. The river channel, which averages 220 feet below maximum lake level, follows close to this bank. Some new sliding of the slump- earthflow and slip-off slope types has already taken place. Slope-stability studies indicated that the entire area is likely to be affected by future sliding. A study of a part of the material within the slide scarp at lake mile 51.5 gave a discriminant-function value of 0.0286. Basic data: material category, 1; ground water, high; slope, 2.511; terrace height, 400 feet; submergence, 58 percent. A slope-stability study of the entire terrace taken through the center of the ancient slide resulted in a discriminant-function value of 0.0217. Basic data: material category, 1; original slope (generalized), 6.221; submergence, 29 percent; terrace height, 820 feet; ground water, high. There may be either slump-earthflow or new multiple- alcove landslides in this setting. On the average, multiple-alcove slides have a much larger H0 : V0 ratio than the slump earthflow and, consequently, the pre- diction formula cannot be used to estimate the extent of landslide action. The average H0 : V0 ratio of the 9 multiple-alcove slides measured was 59:1 The ancient multiple-alcove slide (133) in the Ninemile terrace has a measured H0 : V0 ratio in excess of 9.2 : 1. (See table 4.) Neither of these ratios seems realistic in estimating how far new slides could cut. It seems likely, however, that new major sliding in which the foot of the slide is lower than the ancient one might tend to rupture along the same general scarp at higher altitudes. Following this reasoning, the A—line delineating potential- landslide action was drawn on the map. Lake mile 51.8 to 52.75 right bank—An area of ancient landslides which extends to an altitude of 1,925 feet makes.up the shoreland topography along this section. The area is thought to be underlain by channels in the 66 bedrock which extend beneath the broad fill in the Ninemile Creek valley. Ancient sliding seems to have been of the slump-earthflow and multiple-alcove types. There is one recent slump earthflow at lake mile 51.8 to 52.0. Surface materials are disturbed silt and clay of material category 2, but at depth and a short distance back in the terrace at an altitude of 1925 feet, materials are regarded to be in about their original position of deposition, or in category 1. Slopes which have been studied between lake mile 51.8 and 52.1 range from 0.7:] to 4.3:1. The under— water slope is extremely steep down to the old riverbed, a depth of 220 feet. The slopes are somewhat more gentle between lake mile 52.1 and 52.75, and the water depth is about 110 feet down to a submerged terrace. A slope—stability study at lake mile 51.95 gave a discriminant-function value of 0.0401. Basic data: material category, 2; ground water, high; original slope, 0.7:1; submergence, 63 percent; terrace height, 350 feet. The predicted value of H02V0 ratio of a slump— earthflow landslide at this point would be 3.10:1. Thus a slide would extend 800 feet behind the present shoreline. A slope—stability study in the small bay at lake mile 52.2 showed the discriminant-function value to be 0.0149. The H 0 :VO prediction formula here indicated that a slide could cut back on a slope of 4.621, or 100 feet from the back of the bay. Basic data: original slope, 2.5:1; submergence, 72 percent; terrace height, 70 feet; ground water, low; material category, 2. A composite slope—stability study was made of the section between lake mile 52.3 to 52.65. The discrim- inant-function value was 0.0154. The predicted H 0 :VO’ ratio was 4.75:1, which indicates that landslides could cut back 420 feet from the shore. Basic data: material category 2; ground water, low; submergence, 71 percent; original slope, 3.4:1; terrace height, 155 feet. A study was also made of H0zVO' ratio should ground water be changed from low to high, and it was 5.9 :1. In plotting these data to determine the distance back from shore the slide could cut, it was found that this slope did not intersect the upper surface of the lower terrace made up of landslide debris, but passed into the upper terrace at an altitude of 1,925 feet before intersecting the surface. At this point a study was made of the stability of the high terrace, using a gener— alized slope, from altitude 1,925 to the toe of the scarp at the bottom of the lake. Using an original slope of 4.3 :1, submergence, 15 percent, terrace height, 740 feet, and low ground water, the discriminant-function value was 0.0162, or 0.0020 above the mathematical dividing line between relatively stable slopes and slopes which are likely to be afiected by slides. Should ground- LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON water conditions be changed to high, the discriminant- function value would be 0.0229. Slides will not affect the upper terrace under present ground-water conditions; consequently, the A—line delineating the anticipated extent of landslides in this area was drawn from the three studies of land at lower altitudes. It seems entirely possible, however, that development of the broad Ninemile terrace behind this potential—slide area could change ground-water condi- tions to high and induce sliding which would extend from the lake to the terrace surface. A study of the probable H0zVU ratio of slump- earthflow slides showed that they might extend back from the present lakeshore as much as 4,500 feet, or on a ratio of 6.6:1. This is an even larger ratio than the average for multiple-alcove slides of 5.9. Both types have occurred here, and it seems likely that under high ground—water conditions and new submer- gence conditions they could recur. The B—line delin- eating the possible-extent of slides under these condi- tions was drawn from these data and reasoning. Lake mile 52.75 to 53.6 right bank.—Lakeshore land here consists of a gentle sloping terrace just above maximum lake level. Its surface ranges from an alti- tude of 1,290 feet at shoreline to 1,400 feet at a distance of 1,000 to 1,500 feet back from the shore. The shore- line is indented by several small bays which extend back from the main shoreline 200 to 350 feet. Mate— rials comprising the terrace are principally silt and clay which are distorted and disturbed due to ancient land- slide action or glacial processes or both (category 2). Slopes of the terrace scarp which are mostly submerged range generally from 2.021 to 3.521. Between lake mile 53.25 and 53.60 the terrace scarp slopes generally to the old river channel or to a depth of 200 feet. Between lake mile 52.75 and 53.25 the terrace scarp slopes evenly to a depth of 140 feet, the depth of an underwater terrace. A composite slope—stability study of the section between lake mile 52.7 and 52.85 showed original slope, 2.32:1; submergence, 81 percent; terrace height, 155 feet; ground Water, low. The discriminant—function value was 0.0191, which indicates that the terrace may be affected by landslides. The type of slide in this setting which would have the maximum HO: V0 ratio is a slump earthflow. The prediction formula indi- cates that the HC:VC ratio here would likely not exceed 3.56 :1 or cut back more than 290 feet from shore. A study at lake mile 53.1 resulted in a discriminant- function value of 0.0167. Predicted H C : VC ratio of a possible slide was 4.75:1. Thus a slide would cut back 350 feet from shore. Basic data: material category, 2; ground water, low; submergence, 97 percent; original STATISTICAL STUDIES slope, 3.1:1; terrace height, 155 feet. A study at lake mile 53.5 resulted in a discriminant—function value of 0.0229 and a predicted HC’IVO ratio of 3.4:1, which indicates that slides could cut back as far as 400 feet from shore. The A—line delineating the probable extent of slide action was plotted on the map from these three studies. This terrace has a desirable lakeshore location. Its smooth surface and nearness to a supply of water make it seem favorable for an irrigated farm development; consequently, the slide potential was studied, assuming that such a development was made and that ground- water conditions were to be changed from low to high. The discriminant-function value at lake mile 52.75 to 52.85 would rise from 0.0191 to 0.0258; at 53.1 it would rise from 0.0167 to 0.0234; at 53.5 it would rise from 0.0229 to 0.0296, which suggest a much greater likeli— hood of landslide action with high ground water. The HOW/O ratios and the distance slides would likely cut back from the lakeshore are: Distance slides Predicted could cat back HC: V0 from shore (feet) Lake mile 52.7—52.85 _____________ 4. 51 480 53 __________________ 6. 0 750 53.5 __________________ 4. 3 760 Using these data, the B—line was drawn on the map to indicate the probable limit of potential slides if for any reason ground-water conditions Were changed from low to high. Lake mile 53.6 to 53.85 right bank—In this section a narrow strip of surficial material rests on a steeply dip- ping bedrock surface. Minor sliding of the slump- earthflow and slip—off slope type has already taken place. Its extent has been limited in places by bed- rock. The principal materials are disturbed and distonted silt and clay, although above high-water sand, gravel, and slope wash predominate. For slope— stability studies materials were classified as category 2. A composite slope-stability study was made of the bank between lake mile 53.6 and 53.7. The original slope was 2.40:1; submergence, 83 percent; terrace height, 205 feet; ground water, low. The discriminant- function value was 0.0191. A second composite study was made from lake mile 53.7 to 53.85, with the fol- lowing basic data: original slope, 2.06:1; submergence, 87 percent; terrace height, 240 feet; ground water, low. The value of the discriminant function was 0.0289. Both parts of the section are likely to be affected by future landsliding. The types of slides most likely in this setting are slides off bedrock or slump earthflows limited by bedrock. It was judged from these data that the line delineating the extent of probable land-- slide sction should follow the contact between surficial deposits and bedrock. 67 Lake mile 53.6 (altitude 1,600 feet) to lake mile 54.9 right bank—Landslides have already cut into about two-thirds of the shoreland between lake miles 53.6 and 55.0 and will likely affect the remainder. Slide types in this section are multiple-alcove, slump-earth- flow, slump-earthflow limited by bedrock, slides off bedrock, and slip-off slopes. These slides out into a ter- race which averages 1,900 feet in altitude. Only the multiple-alcove slide at lake mile 53.6 to 54.0 cuts into terrace surface. This slide (145) enlarged in 1906 following the San Francisco earthquake, and slide material partly dammed the flow of the river for about 45 minutes. This multiple-alcove feature is shown on the geologic map (pl. 3) and on the Wilmont Creek quadrangle map as “The Slide.” Surficial materials of the high terrace are silt and clay interbedded with sand and gravel (material category 1). Openwork gravel just above an altitude of 1,290 feet shows crack- ing and crushing Which suggest that a part of the terrace has been overridden by ice. The terrace scarp betWeen lake mile 54.5 and 54.9 becomes less steep and joins a lower terrace which has an altitude of 1,300 to 1,400 feet. The materials in this transition zone and in the lOWeI‘ terrace are predominantly disturbed silt and clay of material category 2. Bedrock projects through the surficial deposits at several places but neither in suffi- cient amount nor in a position to limit future land- sliding. The slope of the terrace scarp ranges from 1.3:1 to 2.921. The old channel of the Columbia River followed the toe of the terrace scarp at an alti- tude of 1,900 feet between lake mile 53.6 and 54.6 where the water is about 225 feet deep. Water depths along the terrace scarp lessen to 80 feet between lake mile 54.6 and 54.9. Ground water is high in the multiple-alcove slide area where there are many springs and seeps. There are seeps and wet areas as high as 30 feet above maximum lake altitude between the upstream edge of the multiple-alcove slide between lake mile 54.0 and 54.4. Above this, on the terrace scarp, are patches of water-loving vegetation. Slope-stability studies indicated that all of this sec- tion may be afiected by future sliding. A slope- stability computation at lake mile 54.3, where original slope is 1.5:1, submergence, 30 percent, terrace height, 755 feet, and ground water is high, gave a discriminant- function value of 0.0350. A computation at lake mile 54.84, Where the slope is 2.9 :1, submergence, 61 percent, terrace height, 130 feet, and ground water is low, gave a discriminant-function value of 0.0159. This entire section of surficial deposits overlies an area of preglacial channels in the bedrock. One of these channels leads directly to the multiple-alcove slide at lake mile 53.6 to 54.0. The remaining part of the section is probably underlain by the preglacial chan— 68 nel of Wilmont Creek. In this geologic setting, any of the following types of slides may occur in the future, and some form of all of them is presently recognizable— multiple alcove, slump earthflow, slump earthflow limited by bedrock, slides off bedrock, or slip-off slopes. The type of slide which has the maximum H0:VC’ ratio that may cut into this lakeshore land is the multiple alcove, so for this type the formula for pre- dicting the H01VC ratio of slump-earthflow landslides is of no assistance in judging how far back future slides will cut. Examination of table 8 showed that the average HO: V0 ratio for multiple-alcove slides was 5.9 :1 and that the only recent slide of this type had a ratio of 6.2 :1. Using this as a guide, it was judged that slides in this area may cut back as far as 6.0 :1 from the toe of the terrace scarp. At lake mile 53.8 the distance is 3,200 feet from the shoreline; at lake mile 54.2 it is 3,000 feet; at lake mile 54.3 it is 3,300 feet. The line delineating the area of potential landslides in this section was drawn on the map from the above data. Lake mile 54.9 to 55 .25 right bank—Slopes along this section are generally similar both above and below lake level. One small bay indents the shoreline. The terrace, which averages about 70 feet in height, is sub— merged 86 percent at full lake level. The terrace scarp has an average slope of 5.7 :1 except in the small bay at lake mile 55.0 where slopes are more gentle. Present ground-water conditions are low. Materials in this section are not exposed at full lake level, but exposures examined during stages of lake drawdown revealed that they are principally disturbed silt and clay of category 2. A composite slope-stability study resulted in a discrimi- nant-function value of 0.0071 which indicates that the terrace is very stable. This section of lakeshore terrace is favorable for developing irrigation farming. A study was made to determine whether this section would remain stable if ground-water conditions were changed from low to high. This composite slope- stability study resulted in a discriminant function value of 0.0138, which indicates that the terrace would be relatively stable. Wave-cut banks along the lake front range from 3 to 8 feet in height. Wave-cut banks in the small bay are minor. GEOLOGY AND LANDSLIDE CLASSIFICATION OF THE ALAMEDA FLAT AREA (LAKE RUFUS WOODS) The Alameda Flat area of Lake Rufus Woods was also selected to illustrate the practical usefulness of the landslide and slope—stability research. The land— slide-classification data are summarized on table 5. The results of the classification studies are shown on plate 6 and the geology of the area is discussed below. LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON Bedrock of the Alameda Flat area is chiefly the granite of the Colville batholith. Interbedded till and angular basalt gravel are exposed in secs. 7, 17, and 18, T. 30 N., R. 29 E. The till has a matrix of sandy silt and is dark gray; stones in it are predominantly basalt. Relations between the deposit and the other map units are not known but it is probably older, at least in part, than the fluvial sand and gravel unit discussed below. A fluvial sand and gravel is exposed in the bluffs above the Columbia River between altitudes of 910 and 970 feet at the west end of the Alameda Flat area. The gravel is composed of rounded pebbles and cobbles in beds 2 to 4 feet thick that are foreset down- stream. The stones are predominantly granite; although a small percentage of basalt is present. They are conspicuously fractured and crushed though gener— ally unweathered. Coarse-grained to very coarse- grained sand is interbedded in layers 6 inches to 10 feet thick; it is composed of unweathered fragments of granite minerals. A few feet of undifferentiated lacustrine silt overlies the fluvial deposit and immedi- ately underlies the gravel surface on the 1,000-foot terrace on the north bank at Mah—kin Rapids (pl. 6). Lacustrine silt and clay is exposed in the bluffs above the Columbia River and in the numerous trib— utary gullies from river level to an altitude of 1,200 feet throughout most of the Alameda Flat area. Its lower contact was not observed. The unit is com- posed primarily of silt and clay in finely laminated beds }6 to 2 inches thick. Varve structure generally is not well developed though some grading is faintly discernible. BetWeen altitudes of 1,000 and 1,200 feet, fine and very fine sand is interbedded with the silt and clay. The sand almost invariably occurs in graded beds; those measured range in thickness from 3 to 27 inches. In bulk, these graded sand beds prob- ably make up less than 20 percent of the deposit. Ice-rafted pebbles are scattered throughout the unit. In parts of the lacustrine deposit the bedding is greatly contorted. The contortion is commonly con- fined to layers several feet thick that are overlain and underlain with sharp contact by undisturbed beds. This deformation was probably caused by slump or flowage on a lake bottom when the distorted material formed the lake bottom. A lacustrine sand that occurs between altitudes of 1,200 and 1,300 feet overlies the lacustrine silt and clay unit with abrupt contact. The sand is composed almost entirely of fine- and medium-grained sand in beds 1 to 4 inches thick although thin beds and lenses of coarse-grained sand are present in the deposit between altitudes 1,280 and 1,300 feet in the extreme STATISTICAL TECHNIQUES northwest corner of sec. 4, T. 30 N., R. 29 E. In con- trast to the underlying sequence, the beds are undis- turbed. The lacustrine sand is overlain, with erosional contact, by the gravel of the 1,320- to 1,360-foot terrace deposit. The upper surface of the sand deposit proba- bly was never much higher than at present; only minor erosion occurred during the deposition of the overlying gravel. Other surficial deposits in the Alameda Flat area include channel gravel, alluvial-fan deposits, and wind- blown sand. These deposits are included in one map unit because contacts between them are not well ex- posed. Channel gravel forms terraces at and below 1,400 feet and was deposited by the Columbia River during postglacial dissection of the valley-fill deposits. The gravel is a few feet to at least 70 feet thick and is mostly of pebble size. Large areas of the terraces are overlain by alluvial fans of sand and silt as much as 50 feet thick. Windb10wn sand that forms small dunes and thin sheets also veneers the terrace deposits. Some time after the cutting of the 1,120-foot terrace in secs. 3 and 4, T. 30'N., R. 29 E. landslides occurred along the scarp at the back of the terrace; the debris of these slides forms long narrow ridges on the surface of the 1,120-foot terrace. STATISTICAL TECHNIQUES By DANIEL R. EMBODY In this investigation a particular group of landslides was selected for study. Modern statistical methods were used to solve the problems of indentification and prediction. As far as the writers are aware, this in- vestigation is one of the first attempts to study land- slides by statistical methods. Very little recorded experience has been available for guidance. During this work many intuitive judgments were made to obtain some of the answers. Only as later investigators test these judgments in other situations will their overall usefulness be appraised. This section of the report discusses the overall experimental logic, the statistical concepts employed, the assumptions implied, and the interpretations drawn. Statistical work was not begun until all the measure- ments of the slides had been made and recorded. The first attempts to analyze the data consisted of averaging the H C : V0 ratios for the various classifications. From preliminary analysis it appeared that a number of the factors under study might affect the slides, and a series of more comprehensive analyses were made. Grad- ually the data were examined in greater detail until the final analyses presented in the report were made. The analysis of slides and stable slopes indicated that both the occurrence of slides and their resultant H 0: V0 ratio could be predicted. In drawing conclusions from 69 the data an important factor is the reproducibility of the field measurements. The uniformity experiment was planned and executed to evaluate this reproduci- bility. ASSUMPTIONS MADE IN THE ANALYSIS OF VARIANCE The assumptions, logic, and numerical details of the commonly used statistical methods are described by Davies (1954), Fisher (1946), Fisher (1947), Goulden (1952), Kempthorne (1953), Mather (1943), Snedecor (1946), Youden (1953). No attempt will be made in this section to give numerical details. Generally the statistical methods used in the land- slide inquiry were specific applications of the general technique of analysis of variance originated by R. A. Fisher in the late 1920’s. Briefly, this technique pro- vides a uniform pattern for designing experiments, analyzing data, and making statements of probability regarding certain hypotheses. Scientists in nearly all fields have accepted the analysis of variance as a proper basis for constructing the various judgments which are the products of their inquiry. For data to be analyzed properly by the analysis of variance, a number of requirements must be fulfilled. Complete statements of these requirements and the consequences to be expected if they are violated are given by Cochran (1938), Cochran (1947), and Eisenhart (1947). In the landslide investigations careful attention was given to the data so that the requirements for analysis could be met. In this section a brief summary of requirements will be given so that the landslide data and the validity of the analyses made may be discussed. The three major requirements for experimental ob- servations are as follows: 1. Experimental errors must be distributed normally. 2. Experimental errors must be uncorrelated. 3. Experimental errors must form a homogeneous dis- tribution with a single variance. For detailed definitions of the ' term “experimental errors,” see Cochran (1938), Cochran (1947), and Eisenhart (1947). A fourth requirement is generally mentioned at this point; namely, that the effects of the classifications ground water and materials must be additive over the range of the data. This factor is extremely impor- tant and was the subject of a detailed test with each of the landslide analyses. As will be noted, with each of the analyses for the H0: V0 ratio, a test for interaction was made which indicated whether the treatments and conditions were additive. It is generally argeed that the requirement for nor- mality of the experimental errors is the least important 70 of the three. Except Where departure from normality is very large, the consequences can be ignored. Correlation among experimental errors is a more serious requirement. It can be seen that if the errors for a particular treatment tend to be in one direction (postively correlated) then part of the error will become entangled with the treatment effect. As such, the estimate of the treatment effect may be biased on the high side, whereas estimate of experimental error may be biased on the low side. The exact opposite would be true if errors were negatively correlated; that is, if one error in a series is associated with an error in the opposite direction. The requirement that the errors must form a single homogeneous distribution with a single variance is also a critical requirement. For the tests of significance to be valid, this requirement must be fulfilled. RECONCILIATION OF PROPERTIES OF FIELD DATA AND THEORETICAL REQUIREMENTS FOR VALIDITY Of the 12 combinations of ground water and material, 6 contained observations on 17 or more slides. The table below shows the number of slides, the mean HCzVC ratio, the standard deviation, and the low- high extreme values. Mean Lower Upper Number E C : VC Standard eItreme extreme of slides ratio deviation observation observation 17 _____________ 3. 35 0. 869 2. 0 5. 3 22 _____________ 2. 55 . 764 1. 5 3. 8 21 _____________ 2. 22 . 753 1. 1 4. 3 39 _____________ 2. 22 . 592 1. 5 3. 8 33 _____________ 2. 05 . 470 1. 2 3. 3 21 _____________ 1. 84 . 344 1. 3 2. 5 The method by which the means and standard devi- ations were calculated is described by Snedecor (1946, p. 17—20). Means are slightly but consistently nearer the lower extreme in each of the six groups, indicating that the data are not normally distributed. Standard devi-' ations are obviously correlated with means so that the larger means have the larger standard deviations. Thus, these rather primitive tests indicate that experi- mental errors violate 2 of the 4 requirements listed and statistical analyses made would not necessarily yield valid results. The question as to Whether errors are correlated cannot be examined simply. Correlation among errors might arise from two causes: first, the observations may not have been obtained in a random order and slow changes in measurement techniques may have brought about similar errors in adjacent slides; second, several slides with almost identical measurements may fre- quently occur side by side. Such slides may not be independent, and the experimental errors may tend to be correlated. LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON No formal randomizing was performed (except in the uniformity experiment) in measuring the slides. How- ever, some slides were measured and remeasured many times. It is believed that by these repetitions in many different orders, the methods of measurement were applied vm'thout significant trends. The question of the independence of adjacent slides must be left for later investigations. It was judged, however, that the effect was not serious. The problem of heterogeneous errors was solved by transforming the H0: VC observations to base-10 log— arithms. The logarithm transformation and the kinds of situations where it is useful are thoroughly described by Bartlett (1947) and Cochran (1938). Data for the 6 groups with 17 or more slides are converted to log— arithms as follows: Mean log Standard Standard error Number of slides HC:VO ratio deviation of estimate 17 _________________ 0. 512 0. 113 0. 1040 22 _________________ . 388 . 132 . 0844 21 _________________ . 323 . 146 . 0956 39 _________________ . 333 . 111 . 0662 33 _________________ . 300 . 099 . 0884 21 _________________ . 258 . 081 . 0534 The method by Which the standard errors of estimates were calculated is described by Snedecor (1946, p. 274—285). The observations in logarithms showed no apparent correlations between means and standard deviations. To further examine the situation, the independent effects of original slope, both linear and quadratic, and submergence percentage were removed by regression methods to give standard errors of estimate for each of the six groups. No correlation between means and standard deviations was apparent. It was judged that the variances of the transformed data were substan- tially equal. Deviations from the upper and lower extremes of the data converted to logarithms are shown for the six groups: Mean log EC:VC ratio Deviation to upper Deviation to lower eztreme extreme 0.211 __________________ 0.512 0.212 0. 212 __________________ . 388 . 192 0. 287 __________________ . 323 . 306 0. 144 __________________ . 258 . 140 0. 221 __________________ . 300 . 162 0. 157 __________________ . 300 . 247 The means appear to be approximately at the centers of the ranges. Of the 6 groups, 3 show larger deviations on the high side and 3 show larger deviations on the low side. The distributions of errors are substantially symmetrical. Since no previous experience with landslide data was available upon which to draw, it was arbitrarily judged that the experimental errors of the landslide data when converted to logarithms were approximately normally STATISTICAL TECHNIQUES 71 distributed with equal variances. It was further judged that the data transformed to logarithms could be prop— erly analyzed and interpreted by the method of analysis of variance. In forecasting the HCzVO ratio the regression equa— tion gives the logarithm of the H 0 :VC ratio. The antilogarithm gives the geometric mean of the estimate rather than the arithmetic mean. The writers made no effort to convert to arithmetic means but recognize that such a step might be desirable. Finney (1941) discus- ses this problem for those who wish to study it in further detail. EXPERIMENTAL LOGIC, TESTS OF SIGNIFICANCE AND PRECISION Attention will now be directed toward the logical patterns which were followed. In general, the experi- mental logic as set forth by R. A. Fisher (1947) was followed. In each analysis the problem at issue was developed in specific terms to fit the pattern for the analysis of variance. The null hypothesis became the possible solution and the f-test provided the test of significance. For a discussion of the concept of the null hypothesis, the test of significance, and the basic principles of inquiry, reference is made to the paper of C. M. Mottley and Daniel R. Embody (1942). The test of significance evaluates the probability that our result (correlation, differences among means, and other factors) could occur because of chance causes alone. As a result of experiences by many scientists in many fields it is customary to attach the term “signifi— cant” to a result if it could occur by chance with a probability of 1 to 20 or less. The term “highly signif- icant” is attached to results where the explanation in terms of chance causes is 1 to 100 or less. It is recog- nized that these specifications are arbitrary conventions. The test of significance is the evidence upon which the scientific judgment is constructed. If the f-test shows high significance, it becomes apparent that chance can— not reasonably explain the results. If all other consid- erations appear to be in proper form, then the scientist makes the judgment that a real effect has in fact been demonstrated. The judgment is based upon the test of significance, but the scientist in charge must make the judgment. When significance but not high significance occurs in the test then the judgment can be made, but the data do not give as strong support. If no significance is indi- cated, chance may then provide a satisfactory explana- tion. The efl’ect may be real, but the experimental observations do not have the capacity to demonstrate its existence. Further study can be made in these tests to determine the power of the test of significance; that is, possible to estimate the smallest difference that could be detected with a specified probability. If this smallest difference appears to be of no economic consequence, inquiry may be terminated. If economic importance could be attached to the smallest difference, then further inquiry may be indicated. A detailed discussion of the subject of the power of tests with tables and references is given by Kempthorne (1953). The desirable precision of H C :VO ratio predictions is a 95—percent confidence limit. In designed experi- ments where the correlations among independent vari— ables are zero, the 95-percent confidence limits are relatively simple to calculate. In the landslide investi- gation, however, the independent variables were all highly correlated and the calculation of 95-percent confidence limits for a predicted value would be tedious. For a complete discussion of the subject see Schultz (1930.) In the landslide study the standard error of estimate was used to describe the precision of predictions. This measure, although crude, would have immediate prac- tical use in the field. A discussion of the standard error of estimate is given in Snedecor (1946). It should be strongly emphasized that the results of the research in this investigation have not proved that landslides are predictable by statistics. The statistical analyses merely were used as tools to obtain probability statements. The conclusions and judgments made in the statistical parts of this report were made by the writers and responsibility must rest on them. These judgments can be considered as true and proper only if the community of scientists tests and accepts them. Other workers who plan to use the results of the in- quiries must test and retest the various concepts presented. SPECIFIC METHODS AND SOURCES The various statistical methods employed in the landslide investigation are listed as follows: 1. Simple analysis of variance. The uniformity experiment was patterned after simple analysis of variance. Davies (1954), Fisher (1946), (1947), Goulden (1952), Snedecor (1946), and Youden (1953) describe this method. 2. Analysis of covariance with disproportionate num- bers in the subclasses. This technique was used in the analyses with the H0:VO ratio. Patterns were obtained from Kempthorne (1953), Snedecor and Cox (1935), Tsao (1945)1, (1942), (1946), and Yates (1933). 1 Tsao, Fei, 1945, General solution of the analysis of variance and covariance in the case of unequal or disproportionate numbers of observations in the subclasses: Unpub. thesis, Univ. Minnesota, 115 p. 72 3. Multiple regression analysis. Final prediction equations were developed by this method. Techniques were obtained from Fisher (1946), Kempthorne (1953), and Snedecor (1946). 4. Discriminant functions. References for this method are Durand (1941), Fisher (1936; 1946), Goulden (1952), Mather (1943), Park and Day (1942). 5. Transformations. References, Bartlett (1947), Cochran (1938; 1947), Snedecor (1946). 6. Tests for parallelism. Reference Snedecor (1946). SUMMARY OF RECONNAISSANCE SEISMIC SURVEYS By ROBERT M. HAZLEWOOD Refraction seismic surveys of four small areas in the upper Columbia River valley were made to determine the position of the bedrock surface underlying the Pleistocene terrace deposits because landsliding in the terrace deposits may be influenced by the position and the configuration of that surface. The terrace deposits are composed of clay, silt, sand, and gravel which range in thickness from a few feet to 700 feet or more. Paleozoic and Mesozoic metamorphic and igneous rocks form the bedrock. They consist principally of quartzite, schist, gneiss, and granite. The seismic-refraction method was applicable here because of the contrast in velocities between the meta- TRAVERSE 13 0.400 0.320 0.240 0.160 TIME, IN SECONDS 0.080 O. 000 l I I I I I l l I I | I I I I | l I l I L Shell 200 400 600 800 1000 1200 1400 1600 1800 2000 Shot‘ pom pm 26 DISTANCE, IN FEET 27 d GROUND SURFACE : i 1400— 3; 1300- g1200- SURFICIAL DEPOSITS g 1100- ‘ 1000/ E u 900 u. z 800- :5 700.. BEDROCK 8 600~ +— : 500 _J < LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON morphic and igneous rocks and the surficial deposits composed of clay, silt, sand, and gravel deposits. Reconnaissance seismic measurements were made along the shores of the northern part of Franklin D. Roosevelt Lake in the Reed terrace and Ninemile areas and also along the Columbia River in the Nespelem River area, which is 12 miles downstream from Grand Coulee Dam (figs. 1, 10). Fieldwork was done from July 15 to August 28, 1952, and additional work in the Reed terrace area was done from June 8 to 26, 1953. Fred 0. Jones, who was in charge of the geologic stud- ies, selected the areas for investigation and furnished the necessary maps and geologic information. FIELD MEASUREMENTS The survey was made with a portable 12-trace refraction seismograph unit, and the reversed profile method of shooting was used for bedrock depth deter- minations. In this method the geophones are arranged in a straight line and dynamite is detonated alternately in shotholes at the ends of the line. Because the depth to bedrock ranged from less than 50 to more than 750 feet, profiles were 500 to 2,400 feet in length to obtain the necessary depth of penetration. Geophones were spaced at 100-foot intervals along the 1,200-foot profiles and at 200 feet along the 2,400—foot profiles. The geophones were placed in shallow holes 4 to 6 inches in depth to reduce background noise caused by wind. Because the material lying near the surface of the ground was extremely dry, large charges of ex- TRAVERSE 8 0.400 0.320 0.240 0160 TIME. IN SECONDS 0.080 000 I | I l I Shot 200 400 point 15 I I I l l I | I I l | I l l l | 600 800 1000 1200 14001600 1800 2000 Shot DISTANCE, IN FEET “I"? GROUND SURFACE 1400 *— 1300 — 1200 — 1100 1000 900 800 700 600 500 SURFICIAL DEPOSITS BEDROCK ALTITUDE. IN FEET ABOVE SEA LEVEL FIGURE 43.-—Sample time-distance curves and bedrock profiles for Reed terrace area, Franklin D. Roosevelt Lake, Wash. SUMIMARY 0F RECONNAISSANCE SEISMIC SURVEYS plosives were needed to send seismic impulses to distant geophones. From 10 to 50 pounds of 60 percent dyna- mite was used per shothole. Electric seismic blasting caps were used to detonate the explosive. A power auger mounted on a jeep was used where possible to drill shotholes to depths from 10 to 25 feet. Where it was not possible to use the power auger, shotholes 4 to 6 feet deep were dug by hand. A total of 50 profiles were shot: 37 in the Reed terrace ' area, 9 in the Ninemile area, and 4 in the Nespelem River area. Depths were computed by a critical-distance formula, assuming a single dipping layer, and were checked by means of the time-intercept method. The measure- ments were made over even ground and few altitude corrections were necessary. A sample of travel-time curves for Reed terrace area is shown on figure 43. RESULTS The terrace deposits varied greatly in their moisture content. Where the deposits were dry or nearly so, the velocity ranged from 1,500 to 3,500 feet per second. Where the terrace materials were water soaked, the velocity was uniformly 5,000 feet per second. The velocities in the individual beds Within the terraces were so similar that lithologic changes were not evi- dent. The velocity in the bedrock ranged from 15,000 to 19,000 feet per second. A bedrock contour map was prepared for the Reed terrace area. In the Ninemile and Nespelem River areas suflicient data were not available to prepare contour maps, and only the location of the shotpoints and the depths to bedrock are given. REED TERRACE AREA The Reed terrace area includes one large terrace and several smaller terraces at higher and lower levels. The surficial deposits are composed of clay, silt, sand, and gravel (pl. 1). The bedrock is quartzite, gneiss, and schist. Depths to bedrock are shown in the table below. Shotpoints and bedrock contours are shown on plate 1. Measurements in the uppermost terrace in the north- western part of the Reed terrace area (the Sherman Creek terrace) show an old valley in the bedrock surface draining southeast into the sediments underlying the largest terrace (Main terrace). The velocity in the material underlying the Sherman Creek terrace is is 1,500 to 3,000 feet per second. This velocity is lower than that in water-soaked material, and it suggests that there is little or no movement of water in the channel from the upper terrace to the lower main terrace. The possibility of seasonal movement of water is not excluded. In the other parts of the Seismic results Reed terrace area 73 Depth to Shotpoint Shotpoint Bedrock bedrock altitude altitude 1 __________________ 90 1,490 1,400 2 __________________ 150 1,490 1,340 3 __________________ 422 1,490 1,068 4 __________________ 410 1,490 1,080 5 __________________ 597 1,470 873 6 __________________ 47 1,493 1,446 7 __________________ 53 1,496 1,444 8 __________________ 328 1, 496 1, 168 9 __________________ 439 1,491 1,052 10 _________________ 441 1, 482 1, 041 11 _________________ 2'15 1, 585 1, 370 12 _________________ 204 1,535 1,331 13 _________________ 220 1,601 1,381 14 _________________ 220 1,584 1, 364 15 _________________ 333 1,490 1,157 16 _________________ 765 1,450 685 17 _________________ 560 1,310 750 18 _________________ 144 1,310 1,166 19 _________________ 240 1,450 1,210 20 _________________ 237 1,450 1,213 21 _________________ 459 1,479 1,020 22 _________________ 553 1,470 917 23 _________________ 541 1,458 917 24 _________________ 520 1,470 950 25 _________________ 385 1,490 1,105 26 _________________ 576 1,478 902 27 _________________ 455 1,490 1,035 28 _________________ 175 1,515 1,340 29 _________________ 401 1,491 1,090 30 _________________ 170 1,455 1,285 31 _________________ 225 1,455 1,230 32 _________________ 245 1,795 1,550 33 _________________ 230 1,805 1,575 34 _________________ 66 1,780 1,714 35 _________________ 126 1, 790 1, 664 36 _________________ 155 1,700 1,545 37 _________________ 91 1,660 1,569 38 _________________ 91 1,650 1,559 39 _________________ 45 1,590 1,545 40 _________________ 525 1,340 815 41 _________________ 102 1, 325 1, 223 42 _________________ 226 1, 438 1, 212 43 _________________ 252 1,490 1,238 44 _________________ 37 1, 622 l, 585 45 _________________ 115 1,515 1,400 46 _________________ 220 1,470 1,250 47 _________________ 190 1,510 1,320 48 _________________ 185 1,475 1,290 49 _________________ 265 1, 475 1, 210 50 _________________ 632 1, 299 667 51 _________________ 305 1,290 985 52 _________________ 110 1,800 1,690 53 _________________ 221 1,790 1,569 54 _________________ 148 1,785 1,637 55 _________________ 218 1,802 1,584 56 _________________ 535 l, 450 915 57 _________________ 241 1,500 1,259 58 _________________ 390 1, 490 1, 100 59 _________________ 469 1, 485 1, 016 60 _________________ 425 1,485 1,060 61 _________________ 550 1, 479 929 385 1,490 1,105 504 1,470 966 64 _________________ 170 1,500 1,330 65 _________________ 320 1, 490 1, 170 66 _________________ 90 1, 490 1, 400 67 _________________ 221 1,455 1,234 68 _________________ 256 1,500 1,244 69 _________________ 539 1,470 931 70 _________________ 118 1,775 1,657 71 _________________ 255 1, 798 1, 543 72 _________________ 120 1, 800 1, 680 73 _________________ 88 1, 841 1, 753 74 _________________ 220 1, 800 1, 580 75 _________________ 220 1, 790 1, 570 74: LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON Reed terrace area, a uniform velocity of about 5,000 feet per second was observed in the surficial deposits, indicating water-soaked material; and, in fact, the silt and sand were saturated with water where holes were drilled through the overlying dry surface. The average velocity in bedrock throughout the area. was 17,000 feet per second. NIN EMILE AREA The seismic investigations were done on Ninemile Flat (pl. 3) and in the ancient multiple-alcove land— slide to the south. Pleistocene deposits, chiefly silt and clay with some sand and gravel, overlie Paleozoic and Mesozoic metamorphic rocks in this area. Depths to bedrock are shown in the table below; the locations of the shotpoints are shown on plate 3. The depths to bedrock indicate that there is an old valley in the bedrock beneath N inemile Flat. The line shot west to east (shotpoints 3, 5, 6 and 7) shows the bedrock surface to be dipping to the west into the valley. The velocity of 3,500 to 4,000 feet per second in the over- burden along this line indicates that these materials were not water soaked. The velocity of 5,000 feet per second in the overburden in the buried valley, however, indicates water—soaked conditions and suggests that the subsurface drainage probably follows the old valley. Seismic results, Ninemr'le area Shotpolnt Depth to Shotpolnt Bedrock bedrock altitude altitude 599 l, 885 1, 286 630 l, 860 1, 230 477 1, 890 1, 413 475 1, 900 1, 425 275 1, 900 1, 625 278 1, 920 1, 642 265 1, 940 1, 675 361 1, 860 1, 499 315 1, 460 1, 145 406 1, 440 1, 034 385+ l, 390 l, 005— 1 Incomplete, at least 385+. NESPELEM RIVER AREA In the Nespelem River area, seismic profiles were run across Bailey Basin (pl. 5). The overburden is com- posed of clay, silt, sand and gravel. The bedrock is granite. The east end of Bailey Basin is formed by a landslide scarp; the floor is landslide debris. The sur- face material was exceedingly dry sand with a large amount of very coarse gravel, making it almost impossi- ble to dig shotholes. Depths to bedrock are shown in the table below; the locations of the shotpoints are shown on plate 5. On the floor of Bailey Basin velocities of 5,000 feet per second indicated that the overburden was water soaked. On the terrace above and to the east of the landslide scarp, velocities of 2,700 to 4,000 feet per second indi- cated that the overburden was dry. Seismic results, N espelem River area Shotpoint Depth to Shotpoint Bedrock bedrock altitude altitude l __________________ 140 1, 040 900 2 __________________ 210 1, 120 910 3 __________________ 74 1, 244 1, 170 4 __________________ 285 1, 600 1, 315 5 __________________ 164 1, 680 1, 516 6 __________________ 300 1, 560 1, 260 7 __________________ 440 l, 540 1, 100 CONCLUSIONS The results of this investigation indicate that the seismic-refraction method can, be used successfully over terrace deposits to determine depths to bedrock. This method was ideally suited to the area because of the large contrast between the velocity of the overly— ing material and the velocity of the bedrock. From the observed velocities it was possible to determine whether the terrace materials were dry, relatively dry, or water soaked. The velocities in the individual beds of the terrace were so similar that lithologic changes were not evident. TABLES OF LANDSLIDE DATA All landslide and slope-stability data used or referred to in any part of the study are tabulated in the following tables (tables 1—9, inclusive). More complete defi— nitions of classification categories are given in the section on statistical studies under heading “Field observation and methods” on page 33. 75 TABLES 0F LANDSLIDE DATA .0145“ HO Uflmv a.“ mwuofiaocw mum AAAA. A .A AAA AAA AAA ........................ AA AA AA AA AA .A AA AAA A A .AA AA AAAA . A .A AA AAA AA ........................ AA AA AA AA AA .A AA AA A A .A 85 AA AAAA. A .A AAA AAA AAA --.EAAAEEA 8:: AAAA AA AA AA AA AA A AA AAA A A .A RAE AA AAA. AA AAA AAA AAA ..... AAAA 2:: Annmwm AA AA AA AA AA .A AA AAA A A .A AA .56 AAAA ABBA. AAAA. A .A AAA AAA AAA AAAAEEAE 8328A AA AA AA AA AA .A AA AAA A A .A AA AAAA . A .A AAA AAA AA AA AA AA A ”A .A AA AAA A A .A AA AAA. A .A AAA AAA AA AA AA AA AA .A AA AAA A A. 25 -383 AAZAA ASAAAA AA AAA . AA A AA AA AA AA AA AA A uA A AA AAA A A .AA AAA-AA .......... 838m AAA-A AA . mm . . ....... . AA AAAA AB A85 AAAA. A .A AAA AAA A AAA A - - - AAAA AA ABA AA AA AA AA AA .A AA AAA A A .AA ABAAAA A380 MEAAA AA . mm A AAAA AS A85 AAAA. A .A AAA AAA AAA ........... AAAA .AA AA; AA AA AA AA AA .A AA AAA A A .AA 36 ABAAAA A85 AAAAAA AA AAA. A .A AAA AAA AAA ....................... AA AA AA AA AA .A AA AAA A A .AA AA AAAA. A A AAA AAA AAA ........................ AA AA AA AA AA A AA AAA A A .AA ........... A380 ABAAA AA 38. A .A AA AAA AAA ........................ AA AA AA AA AA .A AA AAA A A .AA 85 AA AAAA . AA .A AAA AAA AAA A ................. AA ..... AA AA AA AA AA .A AA AAA A A .AA AA AAAA. A .A AAA AAA AAA A ..... AAAA 2:; 8 AAFA AA AA AA AA AA A AA AAA A A .AA AA AAAA. A .A AAA AAA AAA ........................ AA AA AA AA AA .A AA AAA A A .AA AA 88. A .A AAA AAA AAA ........................ AA AA AA AA A ”A .A AA AA A AA .AA AA AAA. A .A AAA AAA AAA ........................ AA AA AA AA A“ A .A AA AA A A .AA 55 BE 33 --8AA=AAA.AAAAAAAEB AA AAAA. A .A AA AAA AA ........................ AA AA AA AA AA .A AA AAA A A .A AA AAAA. A .A AAA AAA AAA ........................ AA AA AA AA AA .A AA AAA A A .A AA AAAA. A .A AA AAA AAA ........................ AA AA AA AA AA .A AA AA A A .A 85 AA AAA. A .A AA AAA AAA ..................... AA AA AA AA A uA .A AA AAA A A .A AA AAAA. A .A AAA AAA A AAA A ........... AAAA .A .52 AA AA AA AA A "A .A AA AAA A AA .A AAAAA AA AAA. A .A AAA AAA ......................... AA ..... AA AA AA AA A “A .A AA AA A A .A AAAAAA AA AAAA. A .A AAA AAA ........ .155858 AAAA AAAA AA AA AA AA AA .A AA AA A A .A 3.: ..... AAA BEA Edam AA 63m 25sz Ava AAAA . A .A AA AAA ........................ AA AA AA AA A "A .A AA AA A A .A A5 A3 53m 225% AA AAA-AA AAAEAAA $.58 AAAA. AA AA AAA ..... AA AA AA AA A .A AA AA A AA 85 AS 53m macaw AA AAAA. A .A AAA AAA ....... mAAA Aw--- AA AA AA AA A .A AA AA A A .A AA .2 And AAAAEAMAAA :AATAHBOmVBQHV 0M3 AAAA. AA AAA AAA ........ AAAA AAAAEASE 5A2 AA AA AA AA .A AA AAA ..... AA:- A AA 85 AA AAAA. A .A AAA AAA .A AAA :EsAABAAA AAAAAAAAAAMAA AA AA AA AA .A AA AAA ..... AA-.- A A .A AA .AA .54 AAAAAAAAMAAA AAAA. A .A AAA AAA AAA .A .5 AAA AAA—A. 8 EPA AA AA AA AA .A AA AAA ..... AA--- A A .A 85 AA AAAA. A .A AAA AAA AAA ..... AAAA 2:: 3 EPA AA AA AA AA .A AA AAA ..... AA--- A A .A AA AAAA. A.A AAA AAA AAA ----------------- AAA ..... AA AA AA AA .A AA AAA ..... AA-.- A A .A AA .AAA .AA AAA: AAA. AA AAA AAA AAA AA; AA 25A. EASE-AAA AA AA AA AA .A AA AAA ----- AA-.- A AA .A AA AAAA. A .A AAA 8A AAA ----------------- AA ----- AA AA AA AA .A AA AAA ..... AA--- A A .A AA AAA. A .A AA AAA AAA ----------------- AA ----- AA AA AA AA .A AA AAA ----- AA--- A A .A AA AAAA. A .A AAA AAA AAA ----- AAAA 2:: 8 SE AA AA AA AA .A AA AAA ----- AA-.- A AA AA AAAA. A .A AAA AAA AAA ------------------------ AA AA AA AA .A AA AAA ----- AA-.- A A. AA AAAA. A .A AA AAA AAA ------------------------ AA AA AA AA .A AA AAA ..... AA--- A A. AA AAAA. A .A AAA AAA AAA ------------------------ AA AA AA AA .A AA AAA ----- AA..-- A A. 55 AA 88 .A A .A AAA AAA AAA ----- AAAA AAA—A. 8 EPA AA AA AA AA .A AA AAA - - -33 A A .A $5 25 ----- AAA 53m AAAAAAam AA 2.1 :23 .AA 53:95 AAAA. A .A AAA AAA AAA A ----- ,---AAAA 8 Sim AA AA AA AA AA .A AA AAA ----- AA-.. A A .AA - AA AAAA. A .A AAA AAA +AAAA EAAAA AAAA AAABAWMAom AA AA AA AA AA .A AA AAA ----- AA-.. A A .AA ------ 33m 82%sz AA . A . 258258 wok-«EPA A: coma .AAALN AAA—ma AAAA. A .A AAA AAA AAA .AAAA HAS-ASE AAEAA AA AA AA A 1AA AA AAA ---AAAAAA A A .AA .55 SEA SAAAAAAZ AA AAAA. AA AAA AAA AAA ------------------------ AA AA AA A AA .A AA AAA 5.33 A AAA AA AAAA. A .A AAA AAA AAA ------------------------ AA AA AA A AA .A AA AAA ----- AA:- A A AA AA AAA .A A .A AA AAA AAA ...AAAA AAAA AAAABAAAAA AA AA AA AA AA .A AA AAA --._AAAAA A A .AA 85 2E 53m ------- 32m 82832 AA Ea...— oo—ficU via-AU Eek-A 5555—39... ~0me HES—00 AA AAAAAAE 3:8 A 98A A Eon nose-AAA“ = own A. EASE A AAA: .58 33.5» A 0mm 33: A ASA-5 .33 ASE :0: 5m = P» 2 0AA .. DA 2% AA 2&9 9E -8 a: -30 A 88» AA AAAAA ESQ A332 2520 AA: AAA .AAEAAAAQ .AAAM -SASA .AAEAAAm AAAAAMAAO AAA-AAA? -354 A A5583 A A AAA-AAA 35‘“ .AE 35A AAAAAAAEA AS. SAAAEAAAAO AAAAAAAAAAA. AAAEAAAEA AAA AAA: AAAAAAAAAAAS Se§.H.a.moH-. 8 HHH HH HN HHH.H HH 8N HHH 35 $me Hozégnam NHH So; #980 mHSHHHHm «0 Has a .m on SN .8o 95% H8: HNHH SS4 ........ 8 «H 8 NH 2: H .NH 6.5 8H .Mooho Has. e .N 8H SH SH -. . 8 mm HH Hm. HH 8m H .NH 85 85m SZHHSHHHHHH HHH HwNo. N.” HNN 8H 83 :........:$2 on HHH; 3 Ha HH HHH «H SN 9% 3H HcHo. N .N SN c8 83 ..H3H an 2:: S SE 8 Hm HH H» 3. SN H .3 HHH nHNc. H .N 8N HHNH Sn ........................ 8 Ha HH HHH NH %N n .3 H5: ...... oEcHeoHHsHEHE 8H . mg C an; ham eHHHoHoUV 28. m .N 8H 8» oNH ........................ 8 HH HH HHH H H H .N HH SN a .HH NaaHeoécHSHHB EH . m3 t 8m ham oEonOv SN? 2 oHH HHH eNH ........................ 3 HH HH NH HHN.H HH oHN ..... 8... u w .H» eEoHao.HHHoHBHHH> HHH . HHH a :8 mam 082mg 88. c .N HHH S» can ..... HHS 8H: 8 HcHHnH 2 Hm NH HHH H5 .N HH SH ..... 8.-. H w .Hn Ed eEoHao.HHHHoEHHHHB 3H . mm 8H.» 53 238:? HHNo. c .N cHH SN :8 ........................ 8 N» HH HN Hum .H HH eHN ..... 8... H n .8 oaoHoc.HHHHoaHH3 N2 . mm HH 8H.N mam HSEHHBV 88. H .H 8H EN. 8» ................. 8 ..... 8 NH HH an H5 .H HH oHN ..... cu... H n .8 wEoHaoHHHsEHHHW HHH . mm SH; Ham HHSEHHE «4.8. o .N SN 8H SN ...§8H§HH. 8:: NEH .3 Hm HH HHH Ha .H HH 8N H n .3 NEEHOHMSNHHHHB SH . G— no 55 HHSHHHHHBV 88. N .N HHH an S» Hm HH 8 H n H .N HH HHH N a .8 sEoHoo.HHHcEHHH> NHH 82. o .N 8H 8» SH mm HH mm HHH .H HH 3H N a .8 85 HHH $8. a .n 2: 8» SH Hm HH HHH HHH .N HHH oNH N m .3 «HH 38. c .N 9: SN 2:. Hm HH NH HHN .H «H 8 N H an NHH 88. m .m 8 8m 8H Hm HH Nu H ”H .H HHH H: N N .2 HHH HHNo. m .N 8 SN 2: Hm HH on HUN .H mH 8H N H .8 8H 38. m .N 9: RN ONH Hm HH 3 H" H .N HHH 3H N H .NH HHH HHS. H .N NH 8» 8 NN HH 2 Hum .H pH 2: N H. .NH 85 SH as. N .H 9: 8m 8w ..... HHH: 2:: 3 BE HNNN Nw HH 8 HHH. «H S» N 8 .HH HHH 38. m .N oNH 8N 8N ............ NHNH .m Him 3 NH MH 2 Hum .H HH 8n H H .3 85 HHH 58. N .H “H 9H 8H ........................ 3 3 NH 8 H H H .N HH SH H N .NH NNH NHNo. N .H oHN 8a SN ...Esou§HHH SE N2: 8 Hm NH «H H5 .H NH oHN H o .NH NH 38. H .N HHH 8H 8N ........................ 2 8 HH 8 HHH .N «H 8N H N .HH .............. 2H8 2:2 ONH .QBOUBWHU 3:: N2: mar—HHH. .CNEHHIHHonHHaO 88. n .N HHH 8H 8m Haaaapoa 332$ 8 NH HH 8 HHH .N HH HHH ..... 8.-- H 3H 3.5 23on tom HHH . AH3HHo|HBMHHaO HHS. c .m SH 8» 8H ...E>oHENHHH BE NmNH 2 N» HH a He .m HH OHH -533 H N HHH no.5 $325 HHPH HHH .AHeHHEIgoO 8a: HHNo. o.N 8 8H 8H ........................ 8 3 NH NH H6 .H HHH 8 ..... 8--- H n .nH .295 83on HHPH HHH .AHSHHoIoEHO Ea: 8N? H .N 9: 8m 8N 8 NH 8 H5 .H a. oNH Edam H a .HH .EHHS 332; tom HHH NHNo. H. .H HHH SH 8H. NH HH nH HHH .H NH 3H m m .NH 2:: 0H3 .......... 353% gm HHH NnNo. H .H 8H :8 8H Hm «H H H5 .H «H 8n n 3 .NN 9: $2. H .H 8H 8N 8H Hm ”H H Hum .H «H 8n n a .NN 8H Has. a .H nNH 8N 8H Hm «H H HHH. .H «H Sn n m .wN H2 88. H .H %H SN 8” Na HH NH Hum .H NH SH H H .2 SH .gofigde 3H2 N8H MESH. $8“ a .H 8H BN 8» Ewaesa 3398: 8 Nm HH ”N HHH .H NH 8» ..... 8... H e .NH 9: 38. e .N 8 SN HNH 8 Hm HH 8 HHH .N HH 3 ..... 8... H H .NH 8 HHS. n .H 8N HHH» 8H 8 HQ HH NH H": NH 8» 3-33 n H.HH .3 NHNH. a .H 2: En 8H NN Hm HH m H5 .H HHH 8H -3:me a m HHH 85 Ha .HHBcUBHHHu 33 NHNH “5:6 3%. H .H SN 8m 8m H5833. Hakeem ma 8 HH 8 H5 .H NH 8N ..... .6-.. m m .NH . Ho 38 .c m N 8 saw 9: . ........................ ma mm HH Hm H5 .m «H on” 1133 n c .NH Ammv 0:2 {:33 55m 3395 8 EvflflmafiaoLu—J u—D>OO°OM— .9 Ema—Esau HH 32: Gave H 938 H PS» 550an H. can 2 ESE H 85 .58 @353 H emu 38: H H895 .Swo H5: HSHHGE H. 0.; 20m = on 253.. SHE. 3: -2 EH .30 H 85» S $on .595 .323 3:85 3.: .oz Havana Nam -33: .5895 3535 03:3. -SHHS N .3383 H H no: mflmfl 3.3V 03363— 65 nomaaogmma—O fiodnmpnoolfiafiege 39:33? 5 wow: @Efiwgg SQHEHENAHSEH 382 $8.3 $3355 HHHDIA H1548 77 0F LANDSLIDE DATA TABLES ~ ~ ~N~H~AAAdddNAAAfiNNHNN m H flaw mammmnm~« MHNNHHNHNH H dHNNHH HNNHHNH (“@l-IF‘W‘DOwON Q MNI‘OI‘B coaehtoooo CD 00 wnawmamamevmmchmmwnww no V‘ GM": NOSQDV‘IDIOHQDM In .4 $2 @858 ”5:6 332$ .33. £58.: e35 8 3:338 $2 .8 E: g .54 ..... $3 van—H 3 32m ............ wag aflon< £2 .E .80 Ea 2 .Eom $2 .fi .32 ............ 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A .A emu 8A. can Aw AA. on A x... A «A. cum n a .amA .ansefilfiasfioz ham wmmo. m A 3A 8: So .A Am Ah am An» .A a. 8A A. a AAA «mm won. A .m 8A 0mm EA Am Ah «A A "w A MA. SA A. o .nAA Ammv .............. mm: nag .o m A EA 8» 8: .A ..... $2 28;. 3 SE 8 Am an AA. A5 A MA. EA m A. AAA 35 ”Eammom «ma ‘0==m¢=°O|Qu—fl a—Obfimccm .AH Emu—Elk:— s was?» 3:8 5 88m » Eon 8288a : own 2338 . 8:..— .anV 888 a sum 3qu . .533 .33 88 20> "Um = Ox» 2 Di 2 0% 2:2 3 08E. g: .2 E: -80 a 85» Ho 82m -895 A Ems: 8595 A2.— 67A .8835 83A -SaE .5825 383.5 88.8,: .832 . :oSaooA « . no: “Wm” 38. 3:38: :5 89588820 woanmunoo‘flmflagu 30:33:» 5 wow: megvfigs Sofifisgéfifim 288.. 38.2. “8:253: “EQIIA 884,: TABLES OF LANDSLIDE DATA 79 TABLE 2.—Forty—two slip-of slope landslides used in statistical analysis Classification and landslide data Land- . slide Area I 1 Location I Mate- Original Sub- No. rial Ground Terrace Drain- slope of mer- Cul- Mate- Time cate- water 4 height 5 age 0 terrace gence 9 ture 9 rial re- 0 LC” H013 VC 1‘ H0: V0 15 gory 5 (feet) scarp 7 (per- moval 1" slide 11 cent) Columbia River downstream from Grand Coulee Dam 12 N espelem River ........... River mile (RB) 11.77 2 Low- _ 135 43 1. 2:1 5 71 81 92 200 70 60 1. 2 22 (LB) 15. 3 1 -__do_ _ 335 43 1. 6:1 3 71 81 92 200 400 300 1.3 Franklin D. Roosevelt Lake 23 Keller Ferry .............. Lake mile (RB) 16. 2 5 Low- - 500 41 1. 5:1 28 71 81 93 400 360 250 1. 4 52 Hellgate-Whltestone ...... (LB) 23. 4 5 .-.do_ _ 420 43 1. 5:1 72 72 81 93 1, 200 450 210 2. 1 53 24. 1 5 -..do- _ 420 43 1. 4:1 73 72 81 93 2, 000 740 360 2.1 54 (RB) 25. 3 5 ...do- . 785 43 1. 5:1 35 71 81 93 500 1,000 560 1. 8 67 Hawk Creek .............. (LB) 37. 5 3 ... 0. _ 440 42 1. 1:1 20 71 82 93 250 70 47 1. 5 68 37. 55 3 -..do- _ 510 42 1. 8:1 31 71 81 93 300 130 80 1. 6 69 37. 9 3 _.-do_ _ 480 43 1.7:1 52 71 81 93 200 200 110 1.8 70 38. 1 3 .-.d0_ _ 170 43 2. 1:1 53 71 81 93 200 100 40 2. 5 72 Spokane River arm ....... Mlle (BB) .2 5 ___do. - 115 43 2. 8:1 48 71 81 93 250 90 35 2. 6 73 (LB) . 5 5 ___do_ _ 480 42 1. 2:1 46 71 81 93 200 70 55 1. 3 75 . 8 5 --_do_ _ 400 42 1. 8:1 52 71 82 93 150 90 60 1. 5 76 .9 5 .-.d0. _ 230 42 1. 7:1 35 71 81 93 200 100 70 1. 4 85 10.8 5 190 42 1. 7:1 63 71 81 93 350 290 165 1. 8 89 (RB) 12. 5 3 300 42 l. 2: 1 17 71 81 93 300 130 105 1.2 92 (LB) 13. 2 5 210 43 1. 4:1 55 72 81 93 800 120 80 l. 5 105 (BB) 22.1 3 380 43 1. 5:1 12 71 81 93 1, 500 630 380 1. 7 106 28. 2 5 140 43 1. 3:1 14 71 81 93 150 200 120 1.7 138 N inemile .................. Lake mile (LB) 52. 9 2 180 43 1. 5:1 67 71 81 93 140 400 170 2. 4 139 53.0 2 170 43 1. 5:1 71 71 81 93 200 450 170 2. 6 169 Hunters-Nez Perce Creek. (RB) 64. 45 1 360 41 1. 0:1 53 71 81 93 900 350 350 N 1.0 174 65. 1 1 290 41 2. 0: 1 62 71 81 93 1, 650 740 290 2.6 189 Cedonla ................... (LB) 68. 2 5 290 43 1. 6:1 62 71 81 93 200 600 280 2. l 192 Cedonla (Bay 840 ft RB _ 68. 2 5 130 41 1. 7:1 38 71 82 93 220 260 130 2.0 203 Cedonia ................... 69. 1 5 340 43 .9:1 56 71 81 93 150 400 275 1.5 204 Cedonla (Bay 100 ft LB)_. 69. 2 5 190 42 1. 7:1 45 71 81 93 150 250 170 1.5 206 Cedonla (Bay 200 ft LB)._ 69. 2 5 180 42 1. 7: 1 39 71 81 92 75 260 170 1. 5 207 Cedonla (Bay 300 ft LB)-. 69. 2 5 180 42 1. 7: 1 39 71 81 93 180 290 165 1. 8 208 Cedonia (Bay 400 ft RB)_. 69. 2 5 170 42 1. 7:1 12 71 82 93 110 160 75 2. 1 209 Ceconia (Bay 500 ft LB) .. 69. 2 5 180 42 1. 7:1 33 71 81 93 150 255 135 1. 9 210 Cec 0111a (Bay 600 ft RB).. 69. 2 5 125 42 1.711 8 71 82 93 300 165 85 1. 9 218 Cec 0111a (Bay 400 ft LB)._ 70.0 2 155 43 1. 5: l 17 71 82 93 75 70 68 1.0 234 Cec. l 70. 9 5 300 43 1. 5:1 60 71 81 93 7 550 270 2.0 239 G111 (RB) 84. 8 l 110 43 2. 6: 1 55 71 81 93 1, 000 110 50 2. 2 245 Rice-Chalk grade ......... (LB) 88. 6 5 280 43 1. 8:1 68 71 81 93 700 220 105 2. l 247 (RB) 90. 3 5 210 43 1. 6:1 52 73 81 93 100 150 85 l. 8 254 Roper Creek .............. 96. 9 5 160 43 1. 7:1 28 71 81 93 700 210 124 l. 7 268 Kettle Falls (200 ft east of (LB) 103. 7 5 300 43 1. 6:1 13 71 82 93 100 270 160 l. 7 Coast and Geo~ detic Survey control station “EAT” in Mar- cus Bay). 270 Kettle Falls (1,200 ft west 103. 7 3 -.-do_ - 170 42 1. 5:1 35 71 81 93 300 150 100 1. 5 g “EAT" in Marcus BY). 290 Ngthpgn-lntematlonal 124. 8 3 _-.d0- - 160 43 1. 5: 1 43 73 81 93 80 160 85 1.9 on ary. 291 125.6 5 .-.d0. . 165 43 1. 4:1 55 73 81 93 300 170 90 1.9 lSee figure 10. 2 River mile, miles along centerline of Columbia River downstream from Grand Coulee Dam; Lake mile, miles along the centerline of Franklin D. Roosevelt Lake upstream from Grand Coulee Dam; Mile, miles from the mouth of a bay on Franklin D. Roosevelt Lake (bays commonly occur at the mouths of tributary streams); RB, right bank as one is facing dowstream; LB, left bank as one is facing downstream; a description such as “ (Bay 600 ft RB) Lake mile (LB) 69.2” means that 69.2 miles upstream from Grand Coulee Dam, there is a bay on the left bank of Franklin D. Roosevelt Lake and the site of the landslide is on the right bank of the bay 600 ft from the mouth. 8 (1), Predominantly lacustrine silt and clay in its original position of deposition; (2), predominantly iacustrine silt and clay with bedding disturbed by landsliding, glacial processes; (3), alternating beds of clay, silt and sand in nearly their original position of deposition; (5), predominantly sand and gravel. 4 High—springs, seeps and abundant water-loving vegetation above the midpoint of the exposed terrace slope; lakes or springs on the terrace surface or situated at higher altitudes in a position to feed water into the terrace deposits. Low—springs, seeps and abundant water-loving vegetation absent or limited to zones below the midpoint of the exposed terrace slope; no springs or lakes on the terrace surface or at higher altitudes to feed water into the terrace deposits. 5 The altitude difference in feet from the top to the bottom of the slope in which the landslide occurred, commonly the vertical distance between two terraces. ‘5 (41), Drainage lines on the terrace sufficiently well developed to channel rain and snowmelt rapidly 011 the area; (42), lines of drainage less well developed with no significant closed depressions on the terraced surface; (43), closed depressions on terrace surface; drainage channels so poorly developed that most of the rain and snowmelt infiltrates the terrace deposits. 7 The ratio of the horizontal distance from the top to the bottom of the slope to the vertical distance from the top to the bottom. . 8 Percentage of the distance from the bottom to the top of a slope that 15 under water. 0 (71), No cultural or engineering developments on or near slide; (72), minor devel- opments on or near slide such as farm buildings, plowed flelds, farm access roads. or logging trails; (73), major developments on or near slide, such as deep highway or railroad cuts or fills, irrigation systems, towns or storage reservoirs. 1° (81), All or most of the landslide material removed from the scarp; (82), part of the landslide material removed from the scarp. H (92), Recent prereservoir landslides; (93), recent postreservoir landslides. _ 12 The length component (LC’) is the maximum horizontal distance from Slde to side of the slide measured parallel to the slope it descends. 13 The horizontal component (H0) is the horizontal distance from the foot of the landslide to the crown. '4 The vertical component (V0) is the difference in altitude between the foot and the crown of a landslide. lb The ratio of the horizontal component to the vertical component. 10 Major enlargement May 11, 1953, on slide 169. 80 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON TABLE 3.—Thirty-seven anoient slump-earthflow landslides used in statistical analysis Classification and landslide data Land- slide Area 1 3 Location 3 Mate— Terrace Present Mate- Remarks and re—movement data No. rial Ground heightD drain- rial re- LCs HC'n V010 HC’:VC'11 cate- water 4 (feet) age 6 moval1 gorya Columbia River downstream from Grand Coulee Dam 1 Grand Coulee Dam-Bel- River mile (RB) 4.2 1 High__ 790 43 82 3, 500 3,350 790 4.2 Some renewed activity of material vedere. near river level since 1948 flood. 3 Grand Coulee Dam-Bel- 4.3 1 _-.do_._ 400 43 82 1,800 1,220 400 3.0 vedere (Peter Dan Creek 5,000 ft RE). 4 Grand Coulee Dam-Bel- 4.3 1 _-.do__. 260 43 82 400 560 230 2.4 Landslide 5, minor movements vedere (Peter Dan . Dec. 23, 1951; Nov. 10 or 11, 1952; Greek, 5,000 ft LB). ‘ Nov. 27, 1952; and weekend of Jan. 10, 1953. 5 Grand Coulee Dam-Bel- 4.6 2 ._.do._. 250 43 82 2,700 1,400 230 6.1 Renewed activity following com- vedere. munity development, irrigation, and 1948 flood. Major enlarge- ment Nov. 23, 1948. 6 4.4 1 _-.do... 820 43 82 2,100 3,900 790 4.9 Landslide 51s situated in landslide material of the toe of this slide. 7 5.1 2 .-.do... 380 43 82 2,000 1,800 380 4.7 Renewed activity following com- munity develo ment, irrigation, and 1948 flood; ec. 23, 1951; Nov. 10 or 11, 1952; Nov. 27, 1952; and weekend of Jan. 10, 1953. Major flogement on slide 7, Nov. 23, 94 . 8 Nespelem River __________ 11.2 2 ...do..- 550 43 83 500 1,270 260 4.9 9 11.4 1 ._-do... 550 43 82 3,000 2,570 530 4.8 13 11.86 1 ._‘do_.. 735 43 82 3,000 3,600 700 5.1 15 12.1 2 _..do__. 150 43 82 900 430 120 3.6 18 Nespelem River (Nes— 14.2 1 ...do..- 230 43 82 900 600 230 2.6 pelem Creek, 7,900 ft LB). 19 Nespelem River .......... 13.2 1 _..do.-_ 210 43 82 600 680 200 3 4 Franklin D. Roosevelt Lake 47 Sanpoil River bay ________ Mile (RB) 8.15 1 High._ 125 43 82 500 450 125 3.6 Renewed activity following lake filling and highway construction. 66 Hawk Creek (Hawk Lakemile (LB) 37.2 1 Low__ 470 43 81 850 1,270 380 3.3 Creek bay, 6,300 ft RB). 81 Spokane River arm ...... Mile 7.1 3 _._do,__ 280 43 82 1,200 920 270 3.4 96 17.15 3 H1gh-- 360 43 81 200 570 330 1.7 97 17.2 3 .-. o... 360 43 81 300 600 340 1.8 99 18.4 3 .-. o... 380 43 82 1,200 1,200 370 3.2 102 19.3 3 LOW__ 470 43 82 1,000 960 370 2.6 112 Fort Spokane ............ Lake mile 42.6 1 High-_ 670 42 81 1,400 1,940 670 2.9 123 Ninemile _________________ 48.3 1 ,--do.__ 670 43 82 1,300 2,600 670 3.9 124 48.8 1 ..-do... 800 43 81 700 2,450 580 4.2 126 49.2 1 -.-do._. 800 43 82 1,500 2,250 540 4.2 127 49.6 1 ..- o... 800 43 82 1,200 1,650 540 3.1 128 49.8 1 -.-do... 800 43 81 700 2,500 670 3.7 ' . _ 162 Hunters-NezPeroeCreek. 62.5 1 --.do.__ 410 43 81 850 1,270 410 3.1 Renewed activity followmg irriga- tion of terrace in 1920’s; addi- tional re—movement when lake was filled, and in years through 1953. 163 Hunters-Nez Perce Creek 64.8 1 --_do_.. 280 43 81 780 900 210 4.3 Renewed activity following irriga- (Hunters bay, 1,000 tion of terrace in 1920’s. It LB . 164 Hunters-Nez Perce Creek 64 8 1 .._do_-_ 270 43 81 720 850 180 4.7 Do. (Hunters bay, 1,600 ft LB). 185 Cedonia .................. (RB) 67 9 3 Low” 400 42 81 500 960 320 3.0 194 68 3 3 _._do_.. 400 42 81 300 820 280 2.9 196 68 4 3 High- 500 42 81 500 1,200 370 3.2 197 685 3 .._do... 540 42 81 500 1,180 410 2.9 See footnotes at end of table. TABLES 0F LANDSLIDE DATA 81 TABLE 3.— Thirty-seven ancient slump-earthflow landslides used in statistical analysis—Continued Classification and landslide data Land- slide Area 1 1 Location 9 Mate— Terrace Present Mate- Remarks and re-movernent data No. rial Ground height"j drain- rial re- LCB HOD V010 HO:VCH cate- Water 4 (feet) age 6 mova17 gory ' Franklin D. Roosevelt Lake—Continued 237 Gifiord-Inchefium (Hall Lake mile (RB) 79. 4 1 Low. _ 300 43 81 700 620 300 2.1 Renewed activity following irriga- Creek bay, 1,000 RB). tion of terrace before Franklin D. Roosevelt Lake and minor activity from the lake. 253 Roper Creek (Roper 95.2 1 ...do..- 150 43 82 700 890 150 5.9 Renewed activity of slide material Creek bay,1.800ft LB). * following partial inundation by Franan D. Roosevelt Lake. 275 Marcus-Evans ........... 106.0 1 ...do..- 140 43 82 200 360 140 2. 6 Do. 278 106. 8 1 High._ 320 43 82 1,670 1,130 320 3. 5 D0. 294 Hawk Creek (Hawk (LB) 37.2 1 Low-. 470 4.3 81 1.100 840 380 2. 2 Greek bay, 4,500 ft RB). I See figure 10. the exposed terrace slope; no springs or lakes on the terrace surface or at higher alti 2 River mile miles along centerline of Columbia River downstream from Grand Coulee Dam; Lake mile, miles along the centerline of Franklin D. Roosevelt Lake upstream from Grand Coulee Dam; Mile, miles from the mouth of a bay on Franklin D. Roosevelt Lake (bays commonly occur at the mouths of tributary streams); RB, right bank as one is facing downstream; LB, left bank as one is facing down- stream; a description such as “ (Bay 600 ft RB) Lake mile (LB) 69.2” means that 69.2 miles upstream from Grand Coulee Dam, there is a bay on the left bank of Franklin D. Roosevelt Lake and the site of the landslide is on the right bank of the bay 600 ft from the mouth. 3 (l), Predominantly lacustrine silt and clay in its original position of deposition; (2), predominantly lacustrine silt and clay with bedding disturbed by landsliding, glacial processes; (3), alternating beds of clay, silt and sand in nearly their original position of deposition. 4 High—springs, seeps and abundant water-loving vegetation above the midpoint of the exposed terrace slope; lakes or springs on the terrace surface or situated at higher altitudes in a position to feed water into the terrace deposits. Low—springs, seeps and abundant water-loving vegetation absent or limited to zones below the midpoint of tudes to feed water into the terrace deposits. 5 The altitude difference" in feet from the top to the bottom of the slope in which the landslide occurred, commonly the vertical distance between two terraces. 6 (42), Lines of drainage less well developed with no significant closed depressions on the terrace surface; (43), closed depressions on terrace surface; drainage channel so poorly developed that most of the rain and snowmelt infiltrates the terrace deposits. 7 (81), All or most of the landslide material removed from the scarp; (82), part of the landslide material removed from the scarp; (83), very little movement of the land- slide material. 5 The length component (L C') is the maximum horsizonta] distance from side to side of the slide measured parallel to the slope it desce n 9 The horizontal component (H0) is the horizontal distance from the foot of the landslide to the crown. I0 The vertical component (V0) is the difference in altitude between the foot and the crown of a landslide. H The ratio of the horizontal component to the vertical component. LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON 82 .223 «o ES 3 $352.“ 3w n.H 2 8H 8H Hm H» um HKH av cHH 1-3-.. H cg 1:850 xinwmwmfl 3a 2 8o.H .25 M85 63:8 8.5m soZv “H85 3: 932° aomflnaokon Suwmsannm Hd 2 mm «a. Hm E 3 H”; Hv ......... -353 H xiv 82$ $2.235m :H .358 #08 manumoE H.585 332w H32 Sank-Ami BBB mwwwmwag n .m 8H En can an H» aw Hun.» «w mam -1:me u Haw as can mic-H ......... 2.53am ”to-H oHH ”on 3sz «o E $3523 Snomuofinsm H .N 5. 3 3H mm Hp mm HNH .N HH~ ......... - 22....- H a .HH ...... .. ..... cw--. aw ad NH. Sm 9: mm HH. mm Hg .n HH. ......... .18--- m «.3 £5 32 ...82 Six 2:38am E m .H R: 2a 8 Ha HH. 3 H; .H HH. So .. .33 m an .3 as 0:8 SEA .......... 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Location 1 by— ratio category 3 water‘ of tertafe (percent) scarp Sanpoil River bay area Group 1 31 _______________ Mile (LB) 2. 05 P&E 3. 4 3 Low _____ 3. 6 68 J 2. 4 3 _ _ _do _____ 2. 2 66 30 _______________ l. 8 P&E 2. 7 3 _-_do _____ 2. 1 66 J 2. 5 3 ___do _____ 2. 4 74 35 _______________ (RB) 3. 1 P&E 2. 5 1 _-_do _____ 3. 0 65 J 3. 5 1 _ _ _do _____ 2. 6 61 27 _______________ (LB) . 8 P&E 2. 8 5 -_-do _____ 2. 4 74 J 2. 0 5 _-_do _____ 2. 6 69 33 _______________ 2. 4 P&E 1. 6 1 _-_do _____ 1. 3 40 J 3. 2 3 ___do _____ 3. 0 68 29 _______________ 1. 6 P&E 1. 6 1 _-_do _____ 1. 3 40 J 2. 1 3 ___do _____ 2. 1 68 Group 2 42 _______________ 6. O5 P&E 4. 2 1 _--do _____ 2. 6 21 J 5.3 1 High _____ 3. o 45 36 _______________ 3. 2 P&E 3. 2 3 Low ..... 3. 0 65 J 3. 8 1 _ _ _do _____ 3. 7 71 40 _______________ 3. 8 P&E 2. 7 1 __ -do _____ 2. 2 54 J 3. 4 1 ___do _____ 2. 8 62 . 43 _______________ 6. 7 P&E 2. 8 2 __-do _____ 3. l 17 J 3. 6 1 _ _ _do _____ 2. 9 33 41 _______________ (RB) 4. 3 P&E 2. 9 3 ___do _____ 2. 5 76 J 3. 2 1 _ _ _do _____ 2. 3 82 44 _______________ 6. 8 P&E 3. 7 1 High _____ 3. 7 13 J 4. 0 2 _ - _do _____ 3. 9 22 Ninemile are: Group 3. 143 ______________ Lake mile (LB) 53. 5 P&E 2. 4 5 Low _____ 1. 7 71 J 3. 0 2 _ - _do _____ 2. 7 76 125 ______________ 49. 0 P&E 1. 9 3 -__do _____ 1. 7 73 J 1. 9 4 _ _ _do _____ 1. 6 73 131 ______________ (RB) 51. 4 P&E 2. 2 5 ___do _____ 1. 6 15 J 2. 3 1 _ _ -do _____ 1. 8 16 150 ______________ Wilmont Bay (RB) 1, 750 ft P&E 2. 5 3 ___do _____ 1. 7 45 J 2. 0 1 _ _ _do _____ 1. 8 43 152 ______________ 3, 700 P&E 2. 0 3 ___do _____ 1. 2 24 J 2. 0 1 _ _ _do _____ 1. 8 25 141 .............. Lake mile (LB) 53. 2 P&E 2. 7 5 ___do _____ 1. 4 64 J 1. 7 2 _ _ -do _____ 3. 3 82 Cedonia area Group 4 193 ______________ Lake mile (LB) 68. 2 P&E 1. 4 3 Low _____ 1. 6 42 (Bay 360 ft LB) J 1. 9 2 ___d0 _____ 1. 5 53 195 ______________ (LB) 68. 3 P&E 2. 0 5 ___do _____ 2. 0 71 J 3. 3 4 _ _ -do _____ 2. 7 73 183 ______________ 67. 75 P&E 1. 7 5 ___do _____ 1. 7 35 J 1. 8 3 _ _ _do _____ 1. 8 30 187 ______________ 68. 0 P&E 1. 6 5 ___do _____ l. 6 33 J 1. 8 4 _ _ -do ..... 1. 4 33 190 —————————————— 68. 2 P&E l. 6 5 _-_do _____ l. 5 33 (Bay 800 ft RB) J 1. 2 2 _--d0 _____ 1. 8 27 186 .............. Lake> mile (LB) 67. 9 P&E 1. 9 5 __-do _____ 1. 6 19 J 2. 0 4 --_do _____ l. 3 33 See footnotes at end of table. 88 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON TABLE 7.——Uniformity experiment—recent slump-earthflow landslides—Continued [Landslides classified by Peterson and Erskine (P&E) and Jones (1)] Landslide gro§p and landslide . Classified H0: V0 1 Material Ground Original slope Submergence ' 0. Location 1 by— ratio category 3 water 4 of terrace (percent) scarp 6 Cedonia area—Continued Group 5 217 ______________ Lake mile (LB) 69. 9 P&E 1. 7 5 Low _____ 1. 3 53 J 2. 0 4 - _ -do _____ 1. 6 43 212 ______________ 69. 3 P&E 1. 5 5 _-_do _____ 1. 5 50 J 1. 6 4 - _ -do _____ 0. 7 55 202 ______________ 69. 0 P&E 1. 7 5 _--do _____ 1. 9 56 J l. 7 5 -_-do _____ 1. 7 54 213 ______________ 69.4 P&E 1. 5 5 ___do _____ l. 5 50 J 2. 9 4 _ _ -do _____ 1. 3 59 215 ______________ 69. 6 P&E 1. 7 4 ___do _____ l. 4 53 J 1. 7 4 _ _ -do _____ 1. 3 59 222 ______________ 70. 1 P&E 3. 0 4 ___do _____ 1. 6 67 l. 4 2 __-do _____ 1. 4 60 Group 6 22 ______________ 70. 45 P&E 2. 2 5 __ -do _____ 1. 4 50 J l. 9 4 - - _do _____ 1. 5 47 231 ______________ 70. 6 P&E 1. 9 5 __-do _____ l. 6 52 J 2. 6 4 ___do _____ 1. 3 66 232 ______________ 70. 65 P&E 2. 0 5 ___do _____ 1. 6 52 2. 4 4 _ _ _do _____ 1. 3 63 229 ______________ 70. 5 P&E 1. 6 5 ___do _____ 1. 5 56 J 1. 9 4 ___do _____ 1. 8 56 230 ______________ 70. 55 P&E 1. 8 5 ___do _____ 1. 5 57 J 2. 3 4 _ - -do _____ 1. 3 66 225 ______________ 70. 25 P&E 2. 0 5 ___do _____ 1. 4 49 J 1. 8 4 - _ _do _____ 1. 3 49 Roper Creek—Reed Terrace are. Group 7: 252 ______________ Lake mile (RB) 95. 2 P&E 1. 8 4 Low _____ 1. 7 27 (Bay 1300 ft RB) 1. 4 2 __-do _____ 1. 7 25 250 ______________ Lake mile (RB) 95. 2 P&E 2. 6 4 ___do _____ 1. 9 10 (Bay 800 ft RB) J 2. 4 2 ___do _____ 2. 2 37 251 ______________ Lake mile (RB) 95. 2 P&E 3. 5 4 High _____ 3. 5 22 (Bay 900 ft LB) J 3. 8 2 -__do _____ 3. 7 28 259 ______________ Lake mile (RB) 98. 5 P&E 3. 1 1 _-_do _____ 3. 0 41 2. 9 1 _ _ _do _____ 2. 3 38 271 ______________ Mile (RB) 2. 0 P&E 2. 3 4 Low _____ 1. 2 11 J 4. 3 2 - _ -do _____ 3. 5 18 257 ______________ Lake mile (RB) 98. 37 P&E 3. 8 1 High _____ 2. 3 45 J 4. 5 1 _ _ _do _____ 2. 5 50 1 Lake mile, miles along the centerline of Franklin D. Roosevelt Lake upstream from Grand Coulee Dam. Mile, miles from the mouth of a bay on Franklin D. Roose- velt Lake (bays commonly occur at the mouths of tributary streams); RB, right bank as one is facing downstream; LBY left bank as one is facing downstream; a description such as“(Bay 600 ft RB) Lake mile (LB) 69.2" means that 69.2 miles upstream from Grand Coulee Dam there is a bay on the left bank of Franklin D. Roosevelt Lake and the site of the landslide is on the right bank of the bay 600 ft from the mouth. 2 The horizontal component H C, is the horizontal distance from the foot of the land- slide to the crown; the vertical component V0, is the difference in altitude between the foot and the crown of a landslide; HC:VC’, the ratio of the horizontal component to the vertical component. ' (1), Predominantly lacustrine silt and clay in its original position of deposition; (2), predominantly lacustrine silt and clay with bedding disturbed by landsliding, glacial processes; (3), alternating beds of clay, silt and sand in nearly their original position of deposition; (4), alternating beds of clay, silt and sand disturbed by land- sliding and glacial processes; (5), predominantly sand and gravel. 4 High—springs, seeps and abundant water-loving vegetation above the midpoint of the exposed terrace slope; lakes or springs on the terrace surface or situated at higher altitudes in a position to feed water into the terrace deposits. Low—springs, seeps and abundant water-loving vegetation absent or limited to zones below the midpoint of the exposed terrace slope; no springs or lakes on the terrace surface or at higher alti- tudes to feed water into the terrace deposits. 5 The ratio of the horizontal distance from the top to the bottom of the slope to the vertical distance from the top to the bottom. 0 Percentage of the distance from the bottom to the top of a slope that is under water. TABLES 0F LANDSLIDE DATA TABLE 8.—Slope-stab2'lity investigation, Franklin D. Roosevelt Lake 89 Slope N 0. Location I Classification and measurement data Discriminant function values 7 Material Ground water 3 Terrace height 4 Original slope of Submergenoe ‘5 category 9 (feet) terrace scarp ‘5 (percent) Gland Coulee Dam 1 Lake mile (RB) 0. 5 5 Low _________ 130 8. 8: 1 85 0. 0060 2 (LB) 2. 5 2 _____ do _______ 120 11. 6:1 50 . 0023 Swawilla Basin 3 Lake mile (LB) 4. 5 1 Low _________ 155 3. 4:1 6 0. 0118 4 5. 5 1 _____ do _______ 150 2. 3: 1 7 . 0155 5 6. 3 2 _____ do _______ 110 15. 3: 1 73 —-. 0001 6' 7. 5 2 _____ do _______ 110 2. 6: 1 55 . 0161 7 (RE) 7. 5 1 _____ do _______ 330 4. 7:1 3 . 0108 8 8. 0 1 _____ do _______ 80 1. 8:1 0 .0125 9 8. 2 1 _____ do _______ 65 2. 8: 1 8 . 0105 10 8. 6 1 _____ do _______ 85 6. 0:1 13 . 0051 11 (LB) 9. 6 1 _____ do _______ 290 5. 2:1 66 . 0139 12 ’RB) 10. 1 1 _____ do _______ 155 5. 7:1 73 . 0106 13 (LB) 11. 3 2 _____ do _______ 45 12. 4: 1 67 —. 0019 14 (RB) 11. 9 5 _____ do _______ 285 2. 7:1 70 . 0200 15 12.8 1 _____ do ______ 235 2. 8: 1 83 .0191 16 14. 1 5 _____ do _______ 30 5. 1:1 50 . 0043 17 (LB) 14. 7 5 _____ do ________ 370 1. 5: 1 30 . 0254 18 15. 0 3 _____ do _______ 200 1. 8: 1 75 . 0225 19 15. 8 1 _____ do _______ 25 5. 7:1 20 . 0012 Keller Ferry 20 Lake mile (LB) 16. 8 2 Low _________ 25 6. 8:1 52 0. 0010 21 17. 5 2 _____ do _______ 40 3. 5:1 20 . 0077 22 17. 8 2 _____ do ______ 230 3. 4:1 83 . 0172 23 (RB) 18. 3 5 _____ do _______ 350 2. 6:1 14 . 0189 24 19. 0 3 _____ do _______ 220 1. 8:1 50 . 0278 25 20.0 3 _____ do _______ 130 2. 5:1 31 . 0163 26 20. 3 3 _____ do _______ 270 3. 5:1 67 . 0173 27 (LB) 20. 8 4 High _________ 150 8. 3: 1 43 . 0129 Sanpoil River boy 28 Mile (RB) 0. 9 3 Low _________ 80 2. 0: 1 0 0. 0163 29 1. 0 3 _____ do _______ 92 2. 0:1 13 . 0206 30 1. 1 3 _____ do _______ 130 1. 5:1 31 . 0211 31 4. 5 l _____ do _______ 170 2. 7: 1 82 . 0181 32 (LB) 5. 2 2 _____ do _______ 240 5. 0:1 50 . 0130 33 (RB) 7. 5 1 _____ do _______ 40 4. 5:1 20 . 0054 Hellsate— Whilestone 34 Lake mile (LB) 21. 0 4 High _________ 300 9. 3:1 57 0. 0151 35 21. 3 4 Low _________ 260 2. 4: 1 13 . 0183 36 21. 6 4 _____ do _______ 320 2. 7:1 16 . 0184 37 22. 3 5 _____ do _______ 190 3. 0:1 95 . 0178 38 (RB) 23. 9 5 _____ do _______ 90 4. 3:1 50 . 0104 39 24. 3 5 _____ do _______ 100 2. 1:1 10 . 0153 40 24. 4 5 _____ do _______ 100 1. 4:1 10 . 0191 41 (LB) 24. 8 5 _____ do _______ 300 3. 4:1 77 . 0182 42 25. 1 5 _____ do _______ 340 6. 5: 1 65 . 0124 43 (RB) 27. 5 5 _____ do _______ 100 3. 1:1 5 . 0106 44 28. 0 5 _____ do _______ 90 2. 6: 1 11 . 0130 45 28. 7 5 _____ do _______ 125 3. 2:1 28 . 0137 46 29. 0 5 _____ do _______ 90 3. 3: 1 22 . 0117 47 31. 7 5 _____ do _______ 220 3. 8: 1 27 . 0144 48 32. 7 5 _____ do _______ 110 6. 1:1 9 . 0055 See footnotes at end of table. 90 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON TABLE 8.——Slope-stability investigation, Franklin D. Roosevelt Lake—Continued Classification and measurement data ‘ 1 f Diiicrlminimt 7 Slope No. Location Material Ground water 3 Terrace height 4 Original slope of Submergenoe 0 uric on Va ues category 2 (feet) terrace scarp 5 (percent) Hawk Creek 49 Lake mile (LB) 34. 0 5 Low _________ 270 1. 4:1 41 0. 0252 50 34. 6 5 _____ do _______ 275 1. 4:1 24 . 0245 51 35. 1 5 _____ do _______ 260 2. 5:1 35 . 0194 52 35. 4 5 ..... do _______ 280 1. 8: 1 40 . 0230 53 35. 5 5 _____ do ....... 280 2. 5: 1 65 . 0206 54 (RB) 37. 0 3 _____ do _______ 190 1. 7:1 21 . 0210 55 38. 0 5 _____ do _______ 230 5. 5:1 26 . 0110 56 (LB) 38. 8 3 _____ do _______ 280 2. 8: 1 75 . 0197 57 38. 9 3 _____ do _______ 200 2. 4:1 60 . 0195 58 (RB) 38. 9 3 _____ do _______ 210 3. 8: 1 5 . 0117 Fort Spokane 59 Lake mile (RB) 39. 6 3 Low _________ 60 2. 8: 1 17 0. 0112 60 40. 5 3 High _________ 40 12. 0:1 25 . 0032 61 (LB) 40. 8 3 Low _________ 170 2. 2: 1 53 . 0194 62 (RB) 41. 1 1 High _________ 170 2. 5:1 0 .0192 63 (LB) 41. 3 3 Low _________ 170 2. 1:1 53 . 0199 64 (RB) 41. 5 1 High _________ 270 2. 9: 1 30 .0246 65 (LB) 42. 3 1 Low _________ 220 2. 3:1 68 . 0204 66 (RB) 42. 9 5 _____ do _______ 100 5. 7:1 80 . 0089 67 43. 2 5 _____ do _______ 210 8. 2:1 91 . 0087 68 (LB) 43. 4 1 _____ do _______ 270 3. 6:1 78 . 0173 69 43. 7 1 _____ do _______ 60 3. 3:1 0 . 0056 70 (RB) 43. 8 5 _____ do _______ 250 2. 0:1 68 . 0223 71 (LB) 44. 0 1 _____ do _______ 70 1. 8: 1 l4 . 0157 72 44. 5 1 _____ do _______ 210 3. 5:1 5 .0125 73 44. 8 2 High _________ 120 10. 7:1 50 . 0098 74 (RB) 44. 8 2 Low _________ 250 4. 6: 1 60 . 0143 75 45. 3 2 _____ do _______ 160 3. 7:1 82 . 0146 76 45. 9 2 _____ do _______ 50 2. 9:1 30 . 0110 77 46. 9 2 _____ do _______ 120 6. 7: 1 92 . 0083 Spokane River arm 78 Mile (RB) 0. 5 1 Low _________ 105 2. 7: 1 38 0. 0151 79 (LB) 1. 1 3 _____ do _______ 240 2. 9: 1 42 . 0179 80 (RB) 5. 8 5 _____ do _______ 80 4. 3: 1. 25 . 0089 81 6. 7 5 High _________ 40 6. 4: 1 0 . 0044 82 (LB) 7. 1 4 Low _________ 220 3. 1:1 23 . 0161 83 (RB) 7. 6 5 _____ do _______ 365 1. 7:1 4 . 0212 84 (LB) 7. 7 4 _____ do _______ 210 2. 7:1 5 .0149 85 (RB) 7. 8 4 High _________ 70 5. 4:1 29 . 0132 86 (LB) 9. 7 3 Low _________ 160 1. 8: 1 43. . 0208 87 (RB) 10. 2 3 _____ do _______ 460 3. 4:1 30 . 0186 38 (LB) 10. 9 5 _____ do _______ 80 2. 6:1 75 . 0153 89 11.8 1 _____ do _______ 160 3.8:] 75 .0145 90 (RB) 11.9 1 _____ do _______ 140 2. 3:1 14 .0163 91 (LB) 12.8 5 _____ do _______ 105 2. 4:1 28 .0157 92 (RB) 13. 5 5 _____ do _______ 130 2. 1:1 85 . 0195 93 (LB) 13. 9 5 _____ do _______ 210 1. 8:1 62 . 0224 94 16. 7 3 ______ do _______ 320 1. 8:1 12 .0217 95 (RB) 17. 8 5 _____ do _______ 170 10. 5:1 41 . 0044 See footnotes at end of table. TABLES 0F LANDSLIDE DATA 91 TABLE 8.—Slope—stability investigation, Franklin D. Roosevelt Lake—Continued l Classification and measurement data 1 f Distal-11111218111; 7 slope No. Location ‘ Material Ground water 8 Terrace height 4 Original slope of Submergenoe 6 one on v ues category 3 (feet) terrace scarp 5 (percent) Ninemileueu 96 Lake mile (LB) 48 0 2 165 4. 4:1 64 0. 0131 97 (RB 48. 4 2 150 5. 7: 1 87 . 0174 98 (LB) 51.2 2 130 7. 7: 1 23 .0121 99 (RB) 51. 5 1 400 2. 5:1 58 . 0286 100 (LB) 51.6 2 75 1. 7:1 7 .0156 101 (RB) 51. 7 2 125 3. 0:1 44 . 0217 102 (LB) 52. 3 2 150 4. 6: 1 53 . 0120 103 (RB) 52. 6 2 450 5. 1 :1 49 . 0154 104 53. 1 2 155 3. 1:1 97 . 0167 105 53. 5 2 270 2. 0:1 85 . 0229 106 (LB) 54. 0 2 70 2. 8:1 29 . 0127 107 54. 45 2 130 2. 2:1 54 . 0184 108 (RB) 54. 84 2 130 2. 9:1 61 .0159 Wilmont-Gerome 109 Lake mile (RB) 55. 5 2 Low _________ 100 4. 4: 1 60 0. 0109 110 56. 0 2 _____ do _______ 90 4. 2:1 56 . 0108 111 56. 4 2 _____ do _______ 95 3. 4:1 95 .0138 112 56. 5 2 _____ do _______ 140 6. 0: 1 _ 86 . 0099 113 57.0 2 _____ do _______ 130 3. 8:1 46 . 0130 114 (LB) 57.5 4 _____ do _______ 90 1. 6: 1 33 . 0191 115 57. 9 4 _____ do _______ 210 3. 0:1 95 . 0182 116 58. 3 4 _____ do _______ 140 3. 5:1 21 .0129 Hunters-Nez Perce 117 Lake mile (LB) 59. 0 4 Low _________ 470 3. 0:1 38 0. 0202 118 (RB) 59. 9 5 _____ do _______ 60 10. 7: 1 33 . 0004 119 62.8 2 _____ do _______ 80 3. 6:1 62 .0119 120 63. 6 1 _____ do _______ 230 2. 9:1 52 . 0181 121 (LB) 64. 1 1 _____ do _______ 190 2. 4:1 79 . 0197 122 64. 7 1 _____ do _______ 50 2. 8:1 10 . 0097 123 (RB) 64. 9 1 _____ do _______ 155 3. 2:1 29 .0147 Cedonia 124 ' Lake mile (RB) 66. 2 3 Low _________ 80 3. 6:1 50 O. 0116 125 (LB) 66. 9 1 ______ do _______ 500 2. 5:1 40 . 0222 126 (RB) 67. 0 3 _____ do _______ 100 2. 1:1 50 . 0176 127 67. 8 1 _____ do _______ 130 4. 0:1 77 .0133 128 68 3 ' 1 _____ do _______ 170 6. 0:1 35 . 0094 129 68. 45 1 _____ do _______ 120 2. 7: 1 50 . 0160 130 68. 6 1 _____ do _______ 120 4. 7:1 66 .0112 131 (LB) 71. 5 4 _____ do _______ 110 2.8:] 18 .0138 132 (RB) 72. 4 2 _____ do _______ 250 8. 5:1 24 . 0072 133 (LB) 72. 5 4 _____ do _______ 95 9. 5: 1 84 . 0040 134 (RB) 72. 6 2 _____ do _______ 135 8. 4:1 41 . 0055 135 (LB) 72. 7 4 ..... do _______ 75 10. 4:1 80 . 0021 See footnotes at end of table. 681004 0—61 ——7 92 LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON TABLE 8.——Slope-stability investigation, Franklin D. Roosevelt Lake—Continued Classification and measurement data Discriminant Slope No. Location 1 function values 7 Material Ground water I Terrace height ‘ Original slope of Submergence 0 category a (feet) terrace scarp 5 (percent) Gill'ord—Inchelium 136 Lake mile (RB) 73. 0 * 2 Low _________ 170 6. 7:1 41 0. 0086 137 73. 3 2 _____ do _______ 190 7. 8:1 53 . 0080 138 73. 6 2 _____ do _______ 200 4. 5: 1 35 . 0128 139 73. 8 2 _____ do _______ 90 5. 1:1 55 . 0090 140 74. 2 2 _____ do _______ 370 3. 4:1 62 . 0187 141 74. 4 2 _____ do _______ 150 2. 3:1 13 . 0164 142 75. 7 2 _____ do _______ 90 3. 0:1 78 . 0145 143 76. 4 2 _____ do _______ 200 2. 8:1 95 . 0187 144 (LB) 76. 8 2 _____ do _______ 110 14. 5:1 54 —. 0003 145 (RB) 77. 0 2 _____ do _______ 60 12. 0:1 67 —. 0004 146 77. 5 2 _____ do _______ 50 4. 6:1 60 . 0077 147 (LB) 77. 5 2 _____ do _______ 210 11. 6:1 43 . 0044 148 77. 9 2 _____ do _______ 85 6. 0:1 35 . 0066 149 (RB) 78. 3 2 _____ do _______ 210 3. 3:1 0 . 0107 150 78. 8 1 _____ do _______ 270 1. 9: 1 19 . 0212 151 79. 2 1 _____ do _______ 85 4. 2:1 ’ 59 .0107 152 81. 2 1 _____ do _______ 95 2. 1:1 95 . 0183 153 81. 4 1 _____ do _______ 95 3. 2:1 95 . 0144 154 82. 3 1 _____ do _______ 100 3. 2:1 60 . 0139 155 82. 7 1 _____ do _______ 120 1. 9: 1 92 . 0202 Rice—Chalk Grade 156 Lake mile (RB) 86. 0 1 Low _________ 100 1. 7:1 50 0. 0196 157 (LB) 89. 6 5 _____ do _______ 185 2. 5: 1 19 . 0171 158 (RB) 94. 6 2 _____ do _______ 70 1. 9: 1 86 . 0179 Reed terrace 159 Lake mile (RB) 99. 4 1 Low _________ 70 2. 8:1 86 0. 0142 Marcus—Evans 160 Lake mile (RB) 107. 0 1 High _________ 130 2. 3:1 , 38 0. 0242 1 River mile, miles along centerline of Columbia River downstream from Grand Coulee Dam; Lake mile, miles along the centerline of Franklin D. Roosevelt Lake up- stream from Grand Coulee Dam; Mile, miles from the mouth of a bay on Franklin D. Roosevelt Lake (bays commonly occur at the mouths of tributary streams); RB, right bank as one is facing downstream; LB, left bank as one is facing downstream; a description such as “(Bay 600 ft RB) Lake mile (LB) 69.2" means that 69.2 miles upstream from Grand Coulee Dam, there is a bay on the left bank of Franklin D. gloosiaveltii1 Lake and the site of the landslide is on the right bank of the bay 600 ft from c mou . 7 (l), Predominantly lacustrine silt and clay in its original position of deposition; (2), predominantly lacustrine silt and clay with bedding disturbed by landsliding, glacial processes; (3), alternating beds of clay, silt and sand in nearly their original position of deposition; (4), alternating beds of clay, silt and sand disturbed by land- slitding, glacial processes, etc.; (5), predominantly sand and gravel; (6), talus accumu- ia ons. 3 High—springs, seeps and abundant water-loving vegetation above the midpoint of the exposed terrace slope; lakes or springs on the terrace surface or situated at higher altitudes ina position to feed water into the terrace deposits.» Low—springs, seeps and abundant water-loving vegetation absent or limited to zones below the midpoint of the exposed terrace slope; no springs or lakes on the terrace surface or at higher altitudes to feed water into the terrace deposits. 4 The altitude difference in feet‘ from the top to the bottom of the slope in which the landslide occurred, commonly the vertical distance between two terraces. 5 The ratio of the horizontal distance from the top to the bottom of the slope to the vertical distance from the top to the bottom. 0 Percentage of the distance from the bottom to the top of a slope that is under water. 7 Value of the discriminant function for the terrace scarp. TABLE 9.—Landslide date and time data Land- slide No. Area Location or name 1 Date and hour | Time of slides and remarks Major landslides 2 { Minor landslides and re-movements 3 Columbia River downstream from Grand Coulee Dam 5 Grand Coulee Dam-Belve- dere. 7 Seatons slide“- _________ Hopkins Canyon mudflow- __ _ 295 Nespelem River—Omak Lake valley. See footnotes at end of table. Koontzville slide ________ Dec. 23, 1951 (initial). Nov. 10 or 11(?), 1952. Nov. 27, 1952. Weekend, Jan. 10, 1953. Nov. 23, 1948 _____________ Feb. 2, 1953, 12 p.m___--__ TABLES OF LANDSLIDE DATA TABLE 9.—Landslide date and time data—Continued 93 Date and hour Time of slides and remarks Land- Area Location or name 1 Slide N ' Major landslides a Minor landslides and re-movements ’ Columbia River downstream from Grand Coulee Dam—Continued 297 Grand Coulee Dam-Belve- Tail Tower slide _____________ Sept. 6, 1949 ______________ dere. 298 East tailrace slide ____________ ' ......................... Aug. 25, 1943. _____ do_______---_--__-_-___ ____-___-___--_____-_____- Aug. 31, 1943. 1, _____ do _______________________________________________ Sept. 8, 1950. 299 Elmer City slide ______________________________________ Do. ; _____ do _______________________________________________ Sept. 26, 1950. § _____ do _______________________________________________ Aug. 11, 1952 (midnight to daylight). _____ do_______-_--_-_-______ __-__-__-----___-____-__-_ Sept. 1, 1952. 300 Washington Flats slide _______ Sept. 8, 1950 ______________ 301 Main west slide _______________________________________ Oct. 16, 1941. _____ do_________--___--____- __________-------____-____ Oct. 8, 1942. _____ do--______--____--____- __--_------_-_-______---_- Sept. 8, 1950. 302 Lone Pine slide ______________ Nov. 20, 1946 (initial) ______ _____ do____-__-_-____-______ ___---___--___---_________ Oct. 7, 1950, 3, 6 a.m. _____ do_-___________________ __-_______________-_______ Nov.10,1952. 303 Downstream launching ramp__ Feb. 5, 1951 ______________ _____ do_-__-____-___-_______ -_____-_____---_-_________ Dec. 17, 1951. 307 Drydock ____________________________________________ Mar. 10, 1942 (re-move- ment) . _____ do___-__________-__-___ ______________-___-_______ Nov. 24, 1947 (re-move- ment). 308 CBI machine shop _____________________________________ Apr. 27, 1942 (re-move- ment) . 320 Seatons mudflow ____________ Mar. 17, 1949, 6:30 p.m__ - _ Franklin D. Roosevelt Lake 34 Sanpoil River bay __________ Sorimpt slide _______________ Apr. 13, 1953 (major en— largement). 36 Mile (LB) 3.2 _________________________________________ Apr. 13, 1953 (re-move- ment) . 37 3.7 _________________________________________ Do. 42 Hughes slide ________________ Nov. 8, 1942, 5, 7 am _____ 64 Hawk Creek ______________ Lake mile (LB) 37.2 _________ July 26, 1949, 5 :30 p.m- _ _ _ Hag}; Creek bay 4,200 ft 65 4 Lake mile (LB) 37.2 _________ July 27, 1949, 10:00 a.m---- ‘ (HavBVI; Creek ba-y 5,000 ft R . 131 Ninemile __________________ Lake mile (RB) 51.4 _________ July 3, 1949, 2, 4 p.m ______ 169 Hunters-Nez Perce Creek- _ _ 64.45 __________________________________ May 11, 1953 (enlargement). 257 Reed terrace ______________ 98.37 ________ Mar. 12, 1952, 1 1:30 a.m- - 98.37 ________ Sept. 12, 1952, 2:00 p.m__- . 98.37 __________________________________ Oct. 13, 1952, 5, 6 a.m. 258 i 98.4 _________ Apr. 8, 1944 ______________ 259 98.5 _________ Apr. 1, 1944 ______________ 261 Multiple-alcove slide _________ Apr. 10, 1952, 3:00 a.m. » (particularly active first . 4 days). 272 Marcus-Evans _____________ Great Northern Railway Feb. 23, 1951, 7, 9 a.m-- _ _ - slide. 296 Coulee Dam _______________ Lake mile (LB) 2.05 _________ June 3, 1952, 9 :30, . 10:00 a.m. 304 Reed terrace ______________ Main terrace____ _ ___________ Feb. 14, 1953, 8:15 p.m- _ _ _ 305 i _____ do _____________________ Feb. 16, 1953, 3:43 a.m- _ - _ 306 Spokane River arm ________ Mile (RB) 9.1 _______________ Mar. 30, 1953 _____________ 312 Hunters-Nez Perce Creek- _ _ Lake mile (RB) 64.3 ___________________________________ May 1)3, 1953 (re-move- , ment . 321 Reed terrace ______________ Center of Farm terrace____ _ _ _ __________________________ Aug. 19, 1953, 11:00 a.m. 1 Lake mile, miles along the centerline of Franklin D. Roosevelt Lake upstream from Grand Coulee Dam; Mile, miles from the mouth of a bay on Franklin D. Roose- velt Lake (bays commonly occur at the mouths of tributary streams); RB, right bank_ as one is facing downstream; LB, left bank as one is facing downstream; a description such as “ (Bay 600 ft RB) Lake mile (LB) 69.2” means that 69.2 miles up- stream from Grand Coulee Dam, there is a bay on the left bank of Franan D. Roose- velt Lake and the site of the landslide is on the right bank of the bay 600 it from the mouth. 2 New landslides in areas which have been stable in the known past or major en- largements of recent landslides; in general, both of above involve more than 5,000 on yds of material. 5 Slight movements and displacements of a few feet in large masses of material: or small enlargements involving less than 5,000 cu yds of material. 94 SELECTED REFERENCES Baltzer, A., 1875, Ueber einen neuerlichen Felssturz am Rossberg, nebst einigen allgemein n Bemerkungen iiber derartige Er- scheinungen in den Alpen: Neues Jahrb. Mineral. p. 15—26. Bartleet, M. S., 1947, The use of transformations: Biometrics, v. 3, no. 1, p. 39—52. Baver, L. D., 1949, Retention and movement of soil moisture, in Meinzer, O. E., Hydrology (Physics of the earth IX), New York, Dover Pubs. p. 364—384. Bretz, J H., 1923, Glacial drainage on the Columbia Plateau: Geol. Soc. America Bull., v. 34, no. 3, p. 573—608. 1932, The Grand Coulee: Am. Geog. Soc. Spec. Pub. 15, Chap. 4, 89 p. Cochran, W. G., 1938, Some difficulties in the statistical analysis of replicated experiments: Empire Jour. Expt. Agri., v. 6, no. 22, p. 157—175. 1947, Some consequences when the assumptions for the analysis of variance are not satisfied: Biometrics, v. 3, no. 1, p. 22—38. Culver, H. E., 1936, The geology of Washington, pt. 1, General features of Washington geology: Washington Dept. Conserv. and Devel., Div. Geol. Bull. 32, 70 p. Daly, R, A., 1906, The nomenclature of the North America Cordillera between the 47th and 53d parallels of latitude: Geog. Jour., v. 27, p. 586-606. 1912, Geology of the North American Cordillera at the 49th parallel: Canada Geol. Survey, Mem. 38, pt. 2, p. 577-— 598. Davies, 0. L., and others, 1954, The design and analysis of indus- trial experiments: London, Oliver & Boyd. Dawson, G. M., 1891, On the later physiographic geology of the Rocky Mountain region in Canada, with special reference to changes in elevation and to the history of the glacial period: Royal Soc. Canada Proc. Trans., v. 8, sec. 4, p. 3—73. 1899, Remarkable landslip in Portneuf County, Quebec: Geol. Soc. America Bull., v. 10, p. 484—490. Durand, David, 1941, Risk elements in consumer installment financing: Nat. Bur. Econ. Research, Studies in consumer installment financing, no. 8, 163 p. Durham, N. W., 1912, Spokane and the Inland Empire: Spokane, Wash., S. J. Clarke. Ehrenhard, P. E., 1945, Foundation investigations for the North Coulee Dam: U.S. Bur. Reclamation, Coulee Darn, Wash. Eisenhart, Churchill, 1947, The assumptions underlying the an- alysis of variance: Biometrics, v. 3, no. 1, p. 1—21. Elliot, T. C., 1918, David Thompsons journeys in the Spokane country: Washington Hist. Quart., v. 9, no. 1, p. 14. Fenneman, N. M., 1931, Physiography of western United States: New York, McGraw-Hill Book Co., 534 p. Finney, D. J ., 1941, On the distribution of a variate whose log- arithm is normally distributed: Supp. Jour. Royal Statis- tistical Soc., v. 3, no. 2, p. 155-161. Fisher, R. A., 1936, The use of multiple measurements in taxo- nomic problems: Annals Eugenics, no. 7, pt. 2, p. 179—188. 1946, Statistical methods for research workers: 10th ed., London, Oliver & Boyd. 1947, The design of experiments: 4th ed., London, Oliver & Boyd. Flint, R. F., 1935, Glacial features of the southern Okanogan region: Geol. Soc. America Bull., v. 46, no. 2, p. 169—194. LANDSLIDES ALONG THE COLUMBIA RIVER VALLEY, NORTHEASTERN WASHINGTON 1936, Stratified drift and deglaciation of eastern Wash- ington: Geol. Soc. America Bull., v. 47, no. 12, p. 1849-1884. 1937, Pleistocene drift border in eastern Washington: Geol. Soc. America Bull., v. 48, no. 2, p. 203—232. Flint, R. F., and Irwin, W. H., 1939, Glacial geology of Grand Coulee Darn, Washington: Geol. Soc. America Bull., v. 50, no. 5, p. 661-680. Fuller, G. W., 193], A history of the Pacific Northwest: New York, Alfred A. Knopf. Goulden, C. H., 1952, Methods of statistical analysis: 2d ed., New York, John Wiley & Sons. Hall, B. A., 1952, Final construction report on Lake Roosevelt reservoir: U.S. Bur. Reclamation, Coulee Dam, Washington. Holmsen, Gunnar, 1929, Lerfaldene ved Kokstad, Gretnes 0g Braa [English summary—Landslides of Kokstad, Gretnes, and Braa]: Norges geol. unders¢ke1se, no. 132, p. 41—45. Johnston, W. A., 1926, The Pleistocene of Cariboo and Cassiar districts, B. 0., Canada: Royal Soc. Canada, Proc. Trans., 3d ser., v. 20, pt. 2, sec. 4, p. 137—147. Karpofl, K. P., 1952, Stabilization of the slide area at the right switch-yard of Grand Coulee Dam: U.S. Bur. Reclamation Rept. SP—32, Denver, Colo. Kempthorne, 0., 1953, Design and analysis of experiments: New York, John Wiley & Sons. Ladd, G. E., 1935, Landslides, subsidences, and rock-falls. Am. Railway Eng. Assoc. Bull., v. 37, no. 337. Landes, Henry, 1902, An outline, of geology of Washington. Washington Geol. Survey, v. 1, p. 11—35. MacDonald, D. F., 1947, Panama Canal slides, the Panama Canal, Third locks project: Dept. Operation & Maint. [re- printed August 1947], p. 27. Mather, K., 1943, Statistical analysis in biology. New York, Interscience Pubs. Meinzer, O. E., 1949, Occurrence, origin, and discharge of ground water in Meinzer, 0. E., Hydrology (Physics of the earth IX); New York, Dover Pubs, p. 385-443. Meinzer, O. E., and Wenzel, L. K., 1949, Movement of ground water and its relation to head, permeability and storage in Meinzer, O. E., Hydrology (Physics of the earth IX), New York, Dover Pubs, p. 444—477. Mottley, C. M., and Embody, D. R., 1942, The effect of the full moon on trout fishing. Am. Statistical Assoc. Jour., v. 37, p. 41-47. Muller, Friedrich, 1898, Das Wasserwesen der Niederlandischen Province Zeeland: Berlin, W. Ernst. Pardee, J. T., 1918, Geology and mineral deposits of the Colville Indian Reservation, Washington: U.S. Geol. Survey Bull. 677. Park, B. C., and Day B. 8., 1942, A simplified method for deter- mining the condition of whitetail deer herds: US. Dept. Agr. Tech. Bull. 840, 60 p. Schultz, Henry, 1930, The standard error of a forecast from a curve: Am. Statistical Assoc. Jour., v. 25, p. 139—185. Sharpe, C. F. S., 1938, Landslides and related phenomena: New York, Columbia Univ. Press. 136 p. Snedecor, G. W., 1946, Statistical methods, 4th ed.: Ames, Iowa Iowa State Coll. Press. Snedecor, G. W., and Cox, G. M., 1935, Disproportionate sub- class numbers in tables of multiple classification: Iowa State Coll. Research Bull. 180, p. 234—272. SELECTED REFERENCES 95 Terzaghi, Karl, 1925, Erdbaumechanik, Leipzig and Vienna, Franz Deuticke, 391 p. 1949, Soil moisture and capillary phenomena. in soils. in Meinzer, O. E., Hydrology (Physics of the earth IX), New York, Dover Pubs, p. 331L363. 1950, Mechanics of landslides, in Application of geology to engineering practice, (Berkey volume): Geol. Soc. Amer- ica, p. 83—123. Terzaghi, Karl, and Peck, R. B., 1948, Soils mechanics in engi- neering practice, art. 31, New York, John Wiley & Sons. Tsao, Fei, 1942, Tests of statistical hypotheses in the case of unequal or disproportionate numbers of observations in the subclasses: Psychometrica‘, v. 7, no. 3, p. 195—212. 1946, General solution of the analysis of variance and covariance in the case of unequal or disporportionate num- bers of observations in the subclasses: Psychometrica, v. 11, no. 2, p. 107—128. Walker, F. C., and Irwin, W. H., 1954, Engineering problems in Columbia Basin: Am. Soc. Civil Eng. Proc., v. 80, Sep- arate no. 515. Weaver, C. E., 1918, Geological history of Washington: North- west Mines Handb., v.1, p. 143-145. 1920, The mineral resources of Stevens County: Wash- ington Geol. Survey Bull. 20. Western Historical Pub. Co., 1904, History of the Big Bend Country, p. 73—74. ' Varnes, D. J ., 1958, Landslide types and process, in Landslides 7 and Engineering Practice: Washington, D.C., Highway Re- search Board, Spec, pub. 29, chap. 3, p. 20—47. Yates, 15"., 1933, The principles of orthogonality and confounding in replicated experiments: Jour. Agr. Sci., v. 23, no. 1, p. 108—145. Youden, W. J., 1953, Statistical methods for chemists: New York, John Wiley & Sons. INDEX Page Acknowledgments ____________ . . . . . . 5 Age of landslides. - . . . . 45 rock units ........ 3 Alameda Flat area. .............. 68 geology ................... 68-69 landslide classification- __-. 84; pl. 6 slope-stability data. ._ ....... . 61, 68-69 Altitude at which landslides occur.. _.__ 11 Analysis, discriminant function 56 variance . 56, 69-70 original slope ____________________________________________________________ 54 reduced regression..- .-. _. 50 submergence percentage __________________________________________________ 54 material.. _.._ ...... --_ 55 Ancient landslides . .. . 29, 30, 35, 51, 61, 65 Artificial-slope landslides ..................................................... 39 Bailey Basin, landslide in .................................................... 29, 30 seismic survey.. Bedrock profiles. . -. Cedonia area, landslides. Chief Joseph Dam .......... .._- 5, 29 Chronologic order of landslides. .- 14—19 Classification categories_._. .................. 34, 39—41, 74 environmental factors in._ . . .. ............. 3 material. -_. .. ..- 39—41 landslides. . ..__-. . 2, 3 landslide type groups--. -_. 35 Columbia glacier lobe. . .. 3, 14 Columbia River basalt. . . ......... 29 landslides in._ 29-31 Colville batholith. . .._. _- 3, 28, 68 Conclusions. . .. 74 Cost of landslides ........... .. 31,33 Covariance analysis. . 49 Culture ..... ---. 4—5, 13, 44 Data card___.-._ 34,36,37 Deadman Creek slide 33, 35 Discriminant function, analysis for ........................................... 3, 56 use... 57 Drainage categories _____ _- 43 terrace surface... 43—44 Dry earthflows. . .. ..... 39, 40 Equation, prediction of H 0: VC .............................................. 50 Farm terrace, altitude ............. 13, 14 ground-water condition: 13,14 landslides. . . . ..... 14—19 lithologic description. . . _..- 14 Field observations._ ._ _ .. .. 33 Field sheet, slope stability... ______ 62 Franklin D. Roosevelt Lake, landslides along ............. . ..._ 10 Frequency of landslides ................................................... 1, 5, 31, 33 Geologic setting .......................................................... 3—4, 33, 61 Glacial geology. . _______ 3, 4, 14, 28 Grand Coulee Dam, landslides at ........................................... 5, 31—33 left tailrace landslide area... 33 Great Northern Railway slide ................................................ 33, 34 Ground-water categories ................................................ 34, 41, 43, 52 conditions .......... 14 test of significance of ...................................................... 49 H C : V0 ratio _______________________________________________________ 46, 47, 48, 49, 50 Hopkins Canyon, mudflow in ________________________________________________ 11 Page Ice lobes 3 Industries. . 4, 5 Kettle Falls area, landslide in 10 Koontzville landslide 26—28 Lake Rufus Wood. See Alameda Flat area. Landslides, chronologic order. 14—19 data card 34, 36, 37 frequency of occurrence 1, 5, 31,33 interpretation of data 46 lithologic description. . . p 5 numerical designation. . . 35 011 bedrock. .. 39, 53 relation of geologic conditions to. 2 relation of topographic conditions to ...................................... 2 types 5—10 type groups 35, 46 Location of landslides 14—19 Main terrace, altitude. 12, 14 ground-water conditions 13, 14 irrigation 13 land lidn 14—19 lithologic description. . . .. 14 Material categories. . 39—41, 56 removal. . 44-45, 47 Measurements, geologic envirnnment 39 landslides... 45—46 Methods, of analysis . _. -- - 71 investigation ........ - . 33, 34, 46, 61 seismic-refraction ..... . . . 74 Methods, statistical. - - . 71 Morphology of scarps 5, 6 Movement of slide material.... 44, 45 Mudflows. 6, 7—8, 10, 11, 39 Multiple-alcove landslides .................................. 6, 7, 8, ll, 21, 39, 51, 53, 65 Nespelem River area. . . 28, 29 geology .- 28 glacial history of .......................................................... 28 landslides in 28—29, 30 seismic surveys 72, 73,74 topography... . 28, 29 Ninemile area. . . -. 21 extensive landsliding in _.._ 20 geology of 20—21, 28 landslides in._ 21, 65 seismic surveys 72, 73, 74 slope-stability data in 62—62 Nomenclature of parts of landslide 6, 35 Okanogan glacier lobe. . . .-- .-_ 3, 4, 14, 28 Orchard terrace, altitude ..... 13,14 irrigation on .............................................................. l3 ground-water conditions in. . . 14 Original slope 44, 48, 54, 56 Physiography. . . ...... 3—4 Potential landslide areas ._ 60—61 Prediction equation ..... 50, 51 Qualitative variables. _. _____ 47, 56 Quantitative variables ........................................................ 48, 56 Recent slump-earthflow landslides 35, 40 limited by bedrock..- 35,38 Reduced regression analysis __________________________________________________ 50 97 98 INDEX Pale Bred Terrace area 12 culture. . 13 1 extensive landsliding in-.. 12 ‘ geologic history 13-14 geology of ..... 13-14 ground-water mndiflnns 14, 27 , initial movement of a landslide ___________________________________________ 15,16 ‘ lake fillin..._ 19 landslides 14—19 lnoaflnn __ 12 multiple-alcove landslide in.. 8,11 number of landslides in 14 seismic surveys- 72, 73 surface-water conditions _______ '14 Regression equation. . 48 Sanpoil ice lobe. . 3 Sanpoil Valley landslide 33 Seatons Grove area, ancient landslide in ______________________________________ 21 Seatons landslide, description of ..... 21-26 ‘ mudflow -... 25—26 Sediment, types of.... .-- 5 Seismic surveys ..... 72—74 Selkirk Trench. . 3 Sherman Creek terrace, altitude.. 12, 13 ground—water onndifinne 14 Page Slip-oi! slope landslides 6, 7, 9, 10, 39. 52 Slope ‘ ‘lt-‘s 44 Slope stability, application of data 61 field sheet- . 62 results of experiment 58 studies. . . 55, 61—64, 74 Slump-earthflow landslides ............................... 6, 10, 19, 21, 29, 30, 32, 33, 51 Sources of analyses. . . . 71, 72 Statistical analyses. 33, 46, 47 methods 3 Stratigraphic “Mn“ 28 Submergence 44, 48, 56 Surface-water. conditions... 14 Surficial deposits, classification N" ies , 39—41 topography of. . . 5 Talus 5111mm 39, 41 Ten-ace height 43, 48, 56 Tests of preann 71 significance. 71 for ground water.... 49 for materials 49 The Slide 21; pl. 3 Time not in 45 Types of landslides 6, 35, 46 Uniformity experiment 53—54, 55, 69 :U. 5. GOVERNMENT PRINTING OFFICE: 1961 O - 581004 U_ONOmm:>_ AKOV >K\ ‘ . . ~..-_--3--*- ~—~--- —— Details of geology and landslides in Reed prelandsllde proflle‘ \x.‘ terrace area shown on plate 1 ' an... , 1100’ 4......“ ‘ ...~.~........... _ 1100’ a a 5 C $ w 0' 1300'— Maximum lake-surface altitude 1290 ft r1300, Profile of landslide fill 1200’- 1200' _ _ _ JETS ‘°_V°'__. _____ 1 100' HYDROGRAPHY AND LANDSLIDE FILL IN FRANKLIN D. ROOSEVELT LAKE, REED TERRACE AREA, SEPTEMBER 1952 581004 0 -61 (In pocket) 1 000 O L l l | l l UNDERWATER CONTOUR DATUM IS MEAN SEA LEVEL lNTERVAL 10 FEET 3000 FEET l PROFESSIONAL PAPER 367 PLATE 5 R. 35 E. 118°20’ R. 36 E. UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY 118° 25’ ..... Pleistocene and Recent A Pleistocene A b“ . II >: ° > I" g'xab' M i: "f" 'o ' @fW/gf—f ; 7 \GT\ ' . I a i .i L/v )> ”3 \‘z x -- - ,rféi-a:;I\:‘fi1s//K’/LL3I=I: 98 /‘ A 7m WILL-WI 118°-00’ fl ' '-. - “ ‘ ‘ ' ‘ 4““ A 48°OO’ 118°25’ R. 35 E. 118° 20’ R. 36 E. Base from. U. 8, Geological Survey Wilmont Creek Geology by W: L. PQIEISOI‘: 1954- Bedrock-surficial topographic quadrangle. Underwater contours contact on right bank by W. R. Power, Jr, 1951. interpreted from hydrographic survey by the Landslide classification by F. 0. Jones, 1954 U- S coaSt and GeOdEtiC sun/9y INTERIOR-~GEOLOGICAL SURVEY. WASHINGTON. D, 0710206 GEOLOGIC MAP AND LANDSLIDE CLASSIFICATION OF THE NINEMILE AREA, FRANKLIN D. ROOSEVELT LAKE, WASHINGTON SCALE 131680 1 O 1MlLE | CONTOUR INTERVAL 40 FEET UNDERWATER CONTOUR INTERVAL 40 FEET DATUM IS MEAN SEA LEVEL EXPLANATION SURFICIAL DEPOSITS AVQDA <7 4 646‘ A V AA Channel gravel and Landslide debris alluvial-fan debris -Qi. Glaciolacustrine deposits Bedded silt, carved silt and clay, lesser amounts of fine lacnstrine sand. Dashed pattern where inferred to be present beneath slope wash Undifferentiated Outwash sand and gravel terrace deposits Undifferentiated drift Commonly thinly mantling bedrock ,I BEDROCK \ L \:\:I7 \/\/I/ , .. Contact Dashed where approximately located Lake mile upstream from Grand Coulee Dam O 2 Seismic shot point _———. A———_ __.__ B ...____ Landslide classification A, estimated extent of landslide action under present conditions. B, estimated extent of landslide action should ground-water con- ditions in the area be changed from low to high TRUE NORTH APPROXIMATE MEAN DECLINATION,196O QUATERNARY PALEOZOIC AND (OR) MESOZOIC UNITED STATES DEPARTENT OF THE INTERIOR PROFESSIONAL PAPER 367 GEOLOGICAL SURVEY PLATE 4 —-—1 100’ EXPLANATION Granite DDH' diamond—drill hole Ground-surface alt 1058.9 ft . . DDH 12. Top-of-casing alt 1060.92 ft Water table denotes apprOXimate water table in pervious overburden at time of drilling _ _ Seatons Lake alt 1071-0 ft Sept. 16- 1953 Irrigated field (é P, denotes zone of material from which pore pressures . . F ' are obtained by piezometers Irrigated field 1060 Gravelly sand Slide scarp Ditch 3 ft wide 1 ft deep Silty sand with basalt cobbles Ground-surface alt 1004.9 ft _ DDH 11. Top—of—casing alt 1006.83 ft way-tame 3” 1030 ft \ Gravelly sand — 1020' Ground-surface alt 1003.6 ft DDH 10. ‘ Top-of—casing alt 10051Wx.1 fi , — Sand _ Gravelly sand with boulders _ _ Piezo metric —Sandy gravel, with cobbles and boulders _;— Gravelly, Silty sand surface alt —— Silty gravel, sandy, QER— Piezometric-surface alt 977 ft Water-surface open-hole alt 9735 ft W;::;:T:;;SQ72 ft ’ " / Water—table alt 976 ft Sandy, lean clay, With basalt boulders _ 980’ 4 ~—————————— — Coarse, sandy gravel — Very fine silt, sandy. " ‘ Water—surface alt 939-0 ft - , with boulders —— Coarse, sandy gravel, With cobbles Sept. 15, 1953 ., '— . — Sandy gravel i— 940' F»— Fine sand p{ :— Clayey gravel __ Fine, silty sand " —— Silty, sandy gravel . , ' s — Slit [— Silt I —P ;-— Lean clay . _ . 4 .7' _ ‘ \ Fat clay 900’ ' . . c. , , - . l 900, H - 50 0 100 150 200 FEET- }, l l l l J ! See figure 16 for location 1100,? . fwd,“ , ' » ‘ Ground-surface alt 10772 ft _1100r Piezometric-surface alt 1091.7 ft DDH 9‘ Top-of—calsmg alt 1079'31 ft —— Sandy silty gravel 1060’ ! j Piezometric-surface alt 1072 ft F _ :17 , _ . —1060' ‘ . '» DDH (group: 2:223: 12531-326; 78 ft Slide scarp 1.5 ft Water—table _ Coarse gravel, sandy, ~. ' p g ' alt 1057 ft with boulders Slough—surface water 7 Slide scarp 1 ft 1020'- 'A Ground-surface alt 980 1 ft - I d '| — Sandy Silt With —1020’ ' - *—-— t ravel DDH 7. Top-of-casing alt 982.08 ft Sliced scarp 4 ft l /San y SI y g // boulders down I Water-tab e alt 1007 ft — / to 50 ft +Coarse sandy gravel / ' ,, " L ‘—— ‘ d 'It Water-surface alt 939.9%ft STATE IOA *- Very fine san y 5' Sept, 16, 1953 _ ‘ —— Silty gravel, sandy, with boulders 980"" Waterltab‘le alt 966 ft —- Finej‘é‘iltysand Clean fine sand — 980’ > , » _ =/ Jointed lean clay Piezometric—Surfacealt gaffl —— Clean véw'mse sand _ . Jointed silt ~> Clean fine sand , 7 . . ,2 ‘1 : ———Fine sandy Silt l , . . _ _, Varved clay :— Crumbled-Jean clay _ xe’y :ine sang 'It Silt —:> Clean fine sand _\ . g» ‘3 :/ ery ine san y si — girliemstflgglsilt _r— Crumbled gray sandy silt _ Eat clafy d 940, _ _ . . 1 . -— ean ine san _/ Very fine silty sand Silty sand With gravel as much as 1/2 in. P{-i— Fat clay ,_ 940' _—/ Medium-fine sand :_ Silty sand 2* Silt - - _ ~\ Crumpled lean clay Very fine sandy 5'” Fat clay P \ Medium-fine silty sand — Lean clay _'— Varved lean clay _/ Very fine silty sand :_ Silt _— Very fine Sllty sand 3— Very fine sandy silt __ Fat clay P{j— Sand 900’ 900’ Based on investigation by Seattle District, Corps of Engineers, U. 8. Army, 1953 581004 0 -61 (In pocket) 50 O 200 FEET 100 150 l l l See figure 20 for location SECTIONS OF SEATONS AND KOONTZVILLE LANDSLIDES, WASHINGTON UNITED STATES DEPARTMENT OF THE INTERIOR . PROFESSIONAL PAPER 567 GEOLOGICAL SURVEY PLATE 5 S 00°: :éogo avogoé) ‘ E E) 000° °g0°aou 8 8 00m °'°¢o°'3 N fag: ‘31 Channel gravel and S . a g alluv1al- fan debris “ Upper lacustrine sequence , " 3- Glaciolacustrt'ne varved silt “(Ki/Q and clay '1 ' M‘ ‘\ . . ’ . lflg‘ . ‘ ~ ‘ ‘ . - . le ki ‘ i. . o ' - .-‘ .> _ _ ' 3 ‘3 Ice marginal sand 3 and gravel Q) s .E Till and basalt gravel N E Lower lacustrine sequence Glaciolacustrz’ne clay, silt, and sand ‘ Qgs w ' , Jilly-l Granitic gravel "Ill Glacioflum‘al sand and "' gravel composed offrag- ments of granite and ‘ g granite minerals .‘ ’7 filfii b, A . 4 1- flier . / o : ‘/V/ f?‘ 6 b /" r 4 . \ veer/444 -- .‘a ‘i\?’Ji/Z£€-.‘ ro «$4,432, ‘ é“ ,. ’y’ , t W ’444. s E 48°05’ 119°OO’ Base from U. 8. Geological Survey Alameda Flat , Geology by W. L. Peterson, 1954—55. Bedrock- ur .u find Nespelem topographic quadrangles 7;: as» ewe“ ' surficial contact by W, R. Power, Jr., with -...,..,. ,. slight modification by W. L, Peterson A/ 1800’ 271359 1300' T VERTICAL EXAGGERATION x 4 I 3 1 g e0 GEOLOGIC MAP OF THE NESPELEM RIV ER AREA 3 3 5 LAKE RUFUS WOODS, WASHINGTON Wmfm DFCLINATIDN,1960 SCALE 1:31680 1 O IMILE LI I I I | l I l I l CONTOUR INTERVAL 40 FEET DATUM IS MEAN SEA LEVEL EXPLANATION SURFICIAL DEPOSITS Landslide debris Basalt talus ,Qlu Undifferentiated lacus— trine deposits Includes upper and lower lacustrine sequences and perhaps other unrecog- .. ‘ .. . s u n- 23:02:55.,:3;":;;?acio_ Undifferentiated drift lacustrlne clay, silt, and sand V QUATERNARY Ground moraine B E D R O C K >_ [I S l.— (I Columbia River basalt E 2 O N . O Crystalline rocks 5' < E]. Contact Dashed where approximately located e River mile downstream from Grand Coulee Dam 04 Seismic shot point AND (OR) MESOZOIC ES DEPARTMENT OF THE INTERIOR UNITED STAT ' ‘ ' GEOLOGICAL SURVEY PROFESSIONAL PAPER 567 PLATE 6 Base from U. 8. Geological Survey Alameda Flat 29 E. 119010, Geology by W. L, Peterson, 1954. Landslide topographic quadrangle Classification by F. 0. Jones, 1954 [NTERIORiGEOLOGICAL SURVEY. WASHINGTON, D. C.~ 10206 GEOLOGIC MAP AND LANDSLIDE CLASSIFICATION OF THE ALAMEDA FLAT AREA, LAKE RUFUS WOODS, WASHINGTON SCALE 1:31680 o lMILE | l | l CONTOUR INTERVAL 40 FEET DATUM IS MEAN SEA LEVEL Pleistocene and Recent Pleistocene A EXPLANATION SURFICIAL DEPOSITS r V- q V V v A q ,Ql8 Va v .7 v D 7 Channel gravel, alluvial- Landslide debris fan deposits, and wind- blown sand K r- N Glaciolacustrine sand Dashed pattern where inferred to be present beneath slope wash QISC; Glaciolacustrine silt and clay f Undifferentiated drift Fluvial sand and gravel L J BEDROCK Contact Dashed where approximately located @ River mile downstream from Grand Coulee Dam ._.—___ A -_.____ _._.__ B __...._ Landslide classification A, estimated extent of landslide action under present conditions. B, estimated extent of landslide action should ground-water con- ditions in the area be changed from low to high TRUE NORTH APPROXIMATE MEAN DECLINATION, 1960 Ffi' PALEOZOIC QUATERNARY AND (OR) MESOZOIC 7:75“ ’ % Hall and MacKevett—GEOLOGY AND.0RE DEPOSITS OF THE DARWIN QUADRANGLE, INYO COUNTY, GAME—Geological Survey Professional Paper 368 a? .\ (so 7%”: Geology and Ore Deposits of the Darwin Quadrangle Inyo County, California GEOLOGICAL SURVEY PROFESSIONAL PAPER 368 Preparea’ in cooperation wz'tfl t/ze State of Ca/zform'a, Department of Natural Resources, Dz'w'rz'orz of Mine: «" Geology and Ore Deposits of the Darwin Quadrangle Inyo County, California By WAYNE E. HALL and E. M. MACKEVETT, JR. l GEOLOGICAL SURVEY PROFESSIONAL PAPER ‘368 PrepareaI in cooperation wit/E tne ‘State of Calzfornz'a, Department of Natara/ Reroarces, Dz'w'yz'on of Miner UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1962 UNITED STATES DEPARTMENT OF THE INTERIOR STEWART L. UDALL, Secretary GEOLOGICAL SURVEY Thomas B. Nolan, Director For sale by the Superintendent of Documents, U.S. Government Printing Office Washington 25, D.C. CONTENTS Abstract ___________________________________________ Introduction _______________________________________ Location ______ : ________________________________ Purpose and scope _______________________________ Climate and vegetation __________________________ Topography ____________________________________ Water supply ___________________________________ Previous work and acknowledgments _______________ Fieldwork ______________________________________ Paleozoic rocks _____________________________________ General features ________________________________ Ordoviciansystem ______________________________ Pogonip group ______________________________ Eureka quartzite ____________________________ Ely Springs dolomite ________________________ Silurian and Devonian systems ____________________ Hidden Valley dolomite ______________________ Devonian system _______________________________ Lost Burro formation ________________________ Mississippian system ____________________________ Tin Mountain limestone _____________________ Perdido formation ___________________________ Mississippian and Pennsylvanian(?) systems ________ Lee Flat limestone __________________________ Pennsylvanian(?) system _________________________ Rest Spring shale ___________________________ Pennsylvanian and Permian systems ______________ Keeler Canyon formation ____________________ Lower unit _____________________________ Upper unit _____________________________ Owens Valley formation _____________________ Lower unit _____________________________ Middle unit ____________________________ Upper unit _____________________________ Undifferentiated Paleozoic silicated limestone _______ Gneiss _________________________________________ Mesozoic rocks _____________________________________ Intrusive rocks _________________________________ Biotite—hornblende-quartz monzonite __________ Leucocratic quartz monzonite ________________ Aplite and leucogranite ______________________ Dikes __________________________________________ Altered andesite porphyry dikes ______________ Diorite _____________________________________ Cenozoic rocks ______________________________________ Pliocene (?) ____________________________________ Pyroclastic rocks ____________________________ Lower pyroclastic unit ___________________ Upper pyroclastic unit ___________________ Andesite ___________________________________ Old fanglomerate from the Inyo Mountains- _ __ Coso formation _____________________________ "d p In a: wmczmo‘musthuaoowmmw Cenozoic rocks—Continued Pleistocene _____________________________________ Olivine basalt _____________________________ Old fanglomerate marginal to Darwin Wash- __ _ Lakebeds __________________________________ Recent ____________________________________ _ _ _ _ Unconsolidated gravels and alluvium ______ _ _ _ _ Structure _____ 1 ________________________________ _ _ _ _ Structure of the pre-Tertiary rocks ____________ _ - - - Unconformities _________________________ _ _ _ _ Folds __________________________________ _ _ - _ Darwin Wash syncline _______________ _ _ _ _ Darwin Hills overturned syncline _____ _ _ _ _ Talc City Hills syncline _____________ - _ _ _ Santa Rosa Hills warp _______________ _ _ - _ Faults _________________________________ _ _ _ _ Thrust faults _______________________ _ _ _ _ Talc City thrust ________________ _ _ _ _ Davis thrust ___________________ _ _ _ _ Strike-slip faults ____________________ _ _ _ _ Mineralized steep strike faults ________ _ _ _ _ Foliation ______________________________ _ _ _ _ Summary ______________________________ _ _ _ _ Cenozoic structures _________________________ _ _ _ _ Metamorphism_____________-__; ________________ ____ Igneous metamorphism ______________________ _ _ _ _ Metamorphism within the igneous rocks- - _ _ _ _ - Metamorphism of limestone __________________ Recrystallization to marble ______________ Dolomitization _____________________ ‘_ _ _ _ Alteration to calc-hornfels, calc-siliicate rock, and tactite __________________ 1- _ _ _ Alteration to feldspathic rock ________ _ _ _ _ Alteration to amphibolite ____________ _ _ _ _ Geologic history ________________________________ _ - _ _ Ore deposits ____________________________________ _ _ _ _ History and production ______________________ _ _ _ _ Lead-silver-zinc deposits _____________________ _ _ _ _ Distribution ___________________________ _ _ _ _ Character of ore ________________________ _ _ _ _ Forms of ore bodies _____________________ _ _ _ _ Bedded deposits ____________________ _ _ _ _ Irregular replacement ore bodies ______ _ _ _ _ Vein deposits _______________________ _ _ - _ Ore bodies in flat-lying fractures ______ _ _ _ _ Ore controls ____________________________ - _ _ _ Nearness to intrusive contacts ________ - _ _ _ Relationship of ore deposits to stratigra} hy- Relationship of ore to folds __________ _ _ _ _ Relationship of ore to faults __________ _ _ _ _ III Page IV CONTENTS Page Page Ore deposits—Continued Ore deposits—Continued Lead-silver-zinc deposits—Continued Tungsten deposits ______________________________ 76 Mingalogy ..... ""i —————————————————————— 58 Distribution ________________________________ 76 y pg:n:n‘31:$g:é;lifiéglé ““““““““ :3 Previous work and acknowledgments __________ 76 Gangue minerals___-___::::::::::::: 62 Deposits in the Darwin district ............... 76 Supergene minerals _____________________ 63 Geology. """"""""""""""""" 76 Sulfide zone ________________________ 63 Ore bodles """""""""""""""" 77 Oxide zone _________________________ 63 Grade- ' ' ' ' ' ' -’ """"""""""""" 77 Paragenesis ____________________________ 64 01:6 contrds """"""""""""""" 77 Primary zoning _____________________________ 66 Mineralogy """"""""""""""""" 77 Oxidation and enrichment ___________________ 66 D 813081175 111 the 0030 Range ------------------ 79 Classification and origin _____________________ 68 Other deposits ---------------------------------- 79 Darwin lead-silver-zinc district _______________ 69 Nonmetallic commodities ____________________________ 79 Geochemical prosiiecting _________________ 71 Steatite-grade talc ______________________________ 80 Future of the district ____________________ 72 Geolo 80 Zinc Hill district ............................ 73 gy‘ """""""""""""""""" . . Talc ore bodies _____________________________ 80 Lee district ________________________________ 74 Origin 81 Deposits in the Inyo Mountains and Talc City . ___.' """""""""""""""""""""""" Hills ____________________________________ 75 Chlorlte depos1ts ________________________________ 81 Santa Rosa mine _______________________ 75 Literature cited _____________________________________ 81 Deposits in the Talc City Hills ___________ 76 Index _____________________________________________ 85 FIGURE 1. ,«rcscn encore ozooo 11. 12. 13. 14. 15. 16. 17. ILLUSTRATIONS [Plates are in pocket] . Geologic map and sections of the Darwin quadrangle Inyo County, Calif. . Geologic map of the Talc City Hills. . Geologic map and sections of the Darwin mine area. . Map of part of 400 level and section of the 430-stope ore body of the Defiance workings. . Maps of the No. 6 and No. 10 levels of the Christmas Gift mine, showing localization of ore. . Map showing distribution of total copper-lead-zinc from soil samples over the Defiance and Bernon workings of the Darwin mine. . Map showing distribution of antimony, bismuth, and silver in residual soil over the Defiance—Bernon workings of the Darwin mine . Maps and section of upper workings of the Zinc Hill mine. . Geologic map and sections of the Main stope of the Silver Reid mine. . Geologic map of the Durham, Fernando, and St. Charles mines, Darwin district, Calif. Page Index map showing location of the Darwin quadrangle __________________________________________________ 2 , Index map showing the locationof Inyo County lead-silver-zinc deposits __________________________________ 3 . Simplified geologic map of the Darwin quadrangle showing the geologic setting of the ore deposits ____________ 7 . Photograph of the Tale City Hills near the Viking mine showing the overturned Paleozoic section of the Pogonip group, Eureka quartzite, Ely Springs dolomite, and Hidden Valley dolomite _____________________________ 9 . Lee Flat limestone viewed south from the Lee mine _____________________________________________________ 18 , Correlation of Carboniferous formations of the Quartz Spring area and Darwin quadrangle ___________________ 20 . Photograph showing the folded, incompetent nature of the Pennsylvanian and Permian strata in contrast to the throughgoing nature of the adjacent Lost Burro formation of Devonian age ______________________________ 21 . Owens Valley formation at Conglomerate Mesa in the northwest part of the quadrangle _____________________ 25 . Triangular diagram showing percentages of essential minerals in the biotite-hornblende-quartz monzonite ______ 30 . Partial sections of Pliocene(?) pyroclastic basaltic rocks in the Inyo Mountains 1% miles southwest of the Santa Rosa mine _______________________________________________________________________________________ 34 Lower well-bedded unit of Pliocene(?) pyroclastic rocks in the southern Inyo Mountains ____________________ 34 Agglomerate in the poorly bedded upper unit of Pliocene(?) pyroclastic rocks in the southern Inyo Mountains- __ 34 Photograph of a sawed volcanic bomb of olivine basalt showing its internal structure __________________________ 35 Local angular unconformity in the lower unit of the Owens Valley formation in Darwin Canyon _________________ 39 View looking south 1,800 feet southeast of the Christmas Gift mine showing the tight folds of the calc-hornfels of the lower unit of the Owens Valley formation on the east side of the Darwin stock ___________________________ 41 Photograph of an overturned isoclinal syncline in the Lucky Jim mine area____ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ __________ 41 Talc City thrust at the Alliance talc mine _______________________________________________________________ 42 CONTENTS FIGURE 18. View of the west flank of the Argus Range from Darwin Wash showing a step-faulted basalt flow ___________ 19. Photomicrograph of medium-grained light-gray calc-silicate rock from the inner zone of contact-metamorp osed limestone from the Defiance area ___________________________________________________________________ 20. Photomicrograph of light-green tactite composed predominantly of garnet __________________________________ 21. White fine-grained calc-hornfels _______________________________________________________________________ 22. Photomicrograph of light-greenish—gray tactite composed of coarse-grained wollastonite that is partly relilaced by andradite garnet ______________________________________________________________________________ 23. Photomicrograph of specimen of low=grade ore showing replacement of garnet and idocrase tactite by sulfide minerals _________________________________________________________________________________________ 24. Photomicrograph of partly feldspathized calc-hornfels ____________________________________________________ 25. Photomicrograph of kalisyenite dike from the Defiance workings of the Darwin mine __________________________ 26. Photomicrograph of andorite that contains inclusions of bismuth __________________________________________ 27. Photomicrograph of sphalerite from the Thompson workings of the Darwin mine ____________________________ 28. Exsolution pattern of chalcopyrite in sphalerite from the Darwin mine _____________________________________ 29. Galena and its alteration product cerussite with elongate inclusions of matildite _____________________________ 30. Photomicrograph of ore from the Darwin mine. Pyrite occurs as corroded relicts in pyrrhotite and galena- _ _ _ _ 31. Photomicrograph of zinc-rich ore from the Darwin mine showing replacement of garnet by sulfide ore ___________ 32. Photomicrograph of ore from the Darwin mine. The paragenesis is pyrite, chalcopyrite, and galena ____________ 33. Photograph of partly oxidized ore from the Lee mine- _____________________________________________________ 34. Maps of underground workings and vertical projection of the Durham mine _________________________________ TABLES TABLE 1. Sequence of rocks exposed in the Darwin quadrangle ____________________________________________________ 2. Correlation of late Cenozoic volcanic and sedimentary rocks _____________________________________________ 3. Analyses of limestone and calc-hornfels from the Darwin Hills ____________________________________________ 4. Gold, silver, copper, lead, and zinc produced from the Darwin quadrangle _________________________________ 5. Talc produced from the Talc City mine _______________________________________________________________ 6. Analyses of bismuth, selenium, and silver in galena from the Darwin mine _________________________________ 7. Paragenesis of principal primary ore and gangue minerals _______________________________________________ 8. ZnS-FeS content of sphalerites from the Darwin quadrangle ________________________________________ j _____ 9. Geologic column of the Zinc Hill district _______________________________________________________________ 10. Assay data of ore shipped from the Lee mine, 1951 to 1955 ______________________________________________ 33 50 54 55 61 64 69 75 GEOLOGY AND ORE DEPOSITS OF THE DARWIN OUADRANGLE, INYO COUNTY, CALIFORNIA By WAYNE E. HALL and E. M. MACKEVETT, JR. ‘ AB STRACT The Darwin quadrangle encompasses 240 square miles in the west—central part of Inyo County between long 117°30’ W. and 117°45’ W. and between lat 36°15’ N. and 36°30’ N. It includes parts of the Inyo Mountains, Coso and Argus Ranges, and Darwin Hills. Paleozoic rocks range in age from Ordovician to Permian in a conformable sequence more than 13,000 feet thick. They are predominantly carbonate rocks that in large part correlate with widespread formations in the eastern part of the Great Basin. Pre-Devonian rocks are predominantly dolomite and quartzite; Devonian rocks are limestone, dolomite, quartzite, and shale; and Mississippian and younger Paleozoic rocks are chiefly limestone. Silurian and Ordovician rocks are restricted to the Talc City Hills. Ordovician strata are about 3,000 feet thick and include the Pogonip group, Eureka quartzite, and Ely Springs dolomite. The Ely Springs is overlain by about 1,000 feet of massive light-gray Hidden Valley dolomite of Silurian and Devonian age. Devonian and Mississippian strata are best exposed in the Santa Rosa Hills and include 1,700 feet of Lost Burro for— mation of Devonian age, 435 feet of Tin Mountain limestone and 330 feet of Perdido formation of Mississippian age, and more than 960 feet of Lee Flat limestone of Mississippian and Pennsylvanian(?) age. Part of the Lee Flat limestone is a time—stratigraphic equivalent of the Rest Spring shale, which occurs only within or adjacent to major fault zones in the northwestern part of the quadrangle. Pennsylvanian and Per- mian strata are more than 6,000 feet thick and are the most widespread Paleozoic rocks. They are divided into the Keeler Canyon formation of Pennsylvania and Permian age and the Owens Valley formation of Permian age; both consist pre- dominantly of thinly bedded calcilutite and calcarenite. The Paleozoic rocks are intruded by several plutons of quartz mon- zonite of Mesozoic age. Limestones are commonly altered to calc-hornfels, calc-silicate rock, and tactite near intrusive contacts. Cenozoic rocks include sedimentary and volcanic rocks of Pliocene(?) and younger age. The sedimentary rocks are divided into the Coso formation, fanglomerate from the Inyo Mountains, fanglomerate marginal to Darwin Wash, lake beds in Darwin Wash, and Recent alluvium. Volcanic rocks in- clude a basaltic pyroclastic section as much as 920 feet thick that locally contains andesite interbedded near the top of the unit and younger olivine basalt flows that cover most of the northern half of the quadrangle. As the different lithologic units occur in separate areas with little interfingering or inter- layering between the units, their relative ages are nft definitely known. . The Paleozoic rocks are deformed into broad open folds except near plutonic bodies where the structure ‘is complex owing to forcible intrusion. The Paleozoic strata about the northeast margin of the biotite—hornblende-quartz onzonite in the Coso Range are tightly folded and are disrupt, d by many faults. Left-lateral strike~slip faults and thrust faults are both structurally important. The extensive volcanic c ver in the northern part of the quadrangle prevents a study of the defor- mation around the quartz monzonite in the north ‘astern part of the quadrangle. Formation of the basin-range topography began, before late 'Pliocene as shown by the fanglomerates of that age marginal to the Inyo Mountains and Coso Range. The Inyo Mountains, the Argus Range, and possible the Coso Range ar east-tilted fault blocks. Extensive basalt covers on the e t flanks of both the Inyo Mountains and Argus Range dip 5° to 15" E. Step faults are conspicuous features on the west ank of both ranges. The quadrangle contains important deposits of lead-silver; zinc and steatite-grade talc, and some tungsten, copper, gold, and antimony. The total value of the mineral production up to 1952 was $371/2 million. The Darwin lead-silverizinc district produced $29 million and the talc deposits about $5 million. Tungsten mines and small lead-silver-zinc mines produced $31k million. Nearly all of the lead-silver-zinc deposits occur in limestone or altered limestone. The most productive deposits surround quartz monzonite in the Darwin Hills in thinly bedded Penn- sylvanian and Permian strata that are largely alt red to calc- hornfels and tactite. Individual ore bodies occur as bedded replacements, vein deposits, and as steep pipe-shaped ore bodies in or near feeder fissures that strike N. 50° to 70° E. The hypogene ore consists of galena, sphalerite, pyrit , pyrrhotite, chalcopyrite, tetrahedrite, scheelite, andorite, m tildite, and clausthalite. Near the surface the ore is in large part oxidized to a crumbly mass of limonite, jarosite, cerussite, and hemi- morphite. The talc deposits occur as elongate pods or lenses in massive dolomite and to a lesser extent in quartzite peripheral to leuco- cratic quartz monzonite in the Tale City Hills. Shear zones in dolomite or contacts between quartzite and olomite may localize talc. Tungsten ore has been mined in the eastern parl of the Dar- win Hills and from the Thompson workings of the Darwin mine. The deposits are in calc-hornfels, tactite, and mainle of Penn- , 1 2 sylvanian and Permian age close to the contact of the biotite- hornblende-quartz monzonite in the Darwin Hills. Scheelite replaces pure limestone or tactite close to intersections with mineralized faults that strike N. 70° E. Most of the ore is within three limestone beds locally known as the Durham, Frisco, and Alameda beds. The ore bodies are mostly small. INTRODUCTION LOCATION The Darwin quadrangle is in eastern California in the central part of Inyo County. The area is between long 117°30’ and 117°45’ W. and lat 36°15’ and 36°30’ N. (fig. 1). Darwin, a small mining town in the south- ern part of the quadrangle, has a population of several hundred. A large modern mining camp is maintained GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. by The Anaconda Co. at the Darwin mine 1 mile north of Darwin, and residences are maintained at some of the smaller mines and at the principal water supplies in Darwin Wash and at China. Garden Spring. Lone Pine, 27 miles northwest of the quadrangle, is the principal marketing center for the area. It is on a branch line of the Southern Pacific railroad from Mo- jave to Owenyo. Paved State Highway 190, extending from Lone Pine to Death Valley, passes through the center of [the quadrangle. A paved road extends from State Highway 190 to Darwin and to the Darwin min— ing camp. An improved dirt road leads from State Highway 190 through the northern part of the quad— rangle to Saline Valley. Many secondary roads lead to mines and prospects from these main roads. / NEw YORK BUTTE \\ UBEHEBE PEAK N QUADRANGLE \\ QUADRANGLE o l’ / //l ”7 I5‘ 0 \\ “\\ \ 0 \\ \\ ’1’ //\\ \\ N/ \\ // \\ sg //‘7 \\ \\ \ // / \ \\ // }} \\\ —/’/ 7’ “Sss \\ (—EERRO \S‘ [I \§\\ §=jll A GORDO Conglomerate\\ /¢¢ fi’ 1 36530' 44 [Mesa \\ ___/¢/ I KEELER / 2/5? W PANAMINT BUTTE Keelei' OUADRANGLE §§\SANTA\\\ // DARW'N QUADRANGLE o \\\ ROSA \\// OUADRANGLE A \\ \‘1 4 \\\H|LLS \\ Lee Flat \\ /» \‘Fe ’1’ “ \v ll /¢fi’ \"‘\ql‘?e’/"'é’~ 7 =\ / " a" \\ ll/x II Darwin a SANTA \\,/ ll Pl 1: ROSA V \\ a eau ll \\ 5 . / // ll \\ “"?-”>o // // 1 //// Talc City//// /// Hills // Panamint A //// // i, Springs 4’ SIERRA Darwin China // //// // TALC Hills Garden . TO DEATH VALLEY» // // Ophir Spring .- I8 ZINC HILL 4 // // ~ \ //// / Mountain 1 J} '7 I/ O 6/ A Darwin {xv 1) 7 Olancha .— l/ O a DAR W’ N 5 O 6‘ SD . c r o §§s====§ /¢ " 36.15. 55/ AV )4? m r HAIWEE RESERVOIR coso PEAK \lF “ ,. OUADRANGLE ’9 QUADRANGLE\\§§\JJ x m ‘\\\K ‘7 \\ DD ”’ \l\ 3, 4 Upper Haiwee 0 \\ Z Reservoir ll Cactus « \\ O u Flat \ m 118°00’ 117°45' 117°30' 5 o 5 10 15 MILES g. 4. . . I 1 I J FIGURE 1.—Index map showing location of the Darwin quadrangle. INTRODUCTION PURPOSE AND SCOPE The investigation of the Darwin quadrangle is part of a long-range program by the US. Geological Survey in cooperation with the California Division of Mines to study the Inyo County lead-silver-zinc deposits that occur between the Cerro Gordo district in the Inyo Mountains on the northwest and the Resting Springs district on the southeast (fig. 2). As part of this pro- gram the Ubehebe Peak quadrangle was mapped by McAllister (1952, 1955), the New York Butte quad- rangle is being mapped by C. W. Merriam and W. C. Smith, and the Darwin quadrangle has been mapped by the writers (fig. 1). The Darwin investigation is published in two reports. Detailed descriptions of the mineral deposits and large- scale maps of most of the principal mines were pub- lished in an earlier report (Hall and MacKevett, 1958). In the present report, emphasis is given to a descrip- tion of the general geology of the Darwin quadrangle and to scientific aspects of the mineral deposits. 118° 1 3 CLIMATE AND VEGETATION ‘ The climate in the Darwin quadrangle is typically desert, and is characterized by scant rainfall, frequent strong Winds, and/a wide range in tempera ure. The climate of the closest weather station, at an ltitude of 3,830 feet at Haiwee Reservoir 14 miles southwest of the Darwin quadrangle, is probably representative of most of the quadrangle except for the lower altitudes in P'anamint Valley where the temperature‘is uncom- fortably hot in the summer. The US. Weather Bu- reau’s publication “Climatological Data” (A‘ on,, 1948, p. 350-362) lists the following data for t e Haiwee Reservoir station: ‘ Annual rainfall ______________________________ inches" 6. 06 Average January temperature__(degrees Fahrenhbit)“ 40.4 Average July temperature ______________________ do---- 81.7 Maximum recorded temperature in 1948 __________ 30-“- 102.0 Minimum recorded temperature in 1948 ---------- --__ 14. 0 Vegetation is mostly sparse. Sagebrush, Mormon tea (Ephedm), creosote brush (Larrea) , J oshra (Yucca 117° ‘ 116. «‘49 \ .rge NEW YORK BUTTE 1 QUADRANGLE; r“ ,0, Ubehebe district 4 UBEHEBE PEAK ” OUADRANGLE x X K R A n \I\?OSA\/,D’ Ltee‘ IS I'IC X j X X Darwin 0' t . IS ricé¢ Quartz Spring area i311" (-1 flinc Hill District a $0 6‘ 36° 1 \ EXPLANATION Stovepipe Wells Panamint \ \s X i Mine Distri KERN COUNTY I X X _INYO C_OUNTY _ Shosh ne ; Resting Spfing District SAN BERNARDINO COUNTY ‘ 10 O 10 20 MILES ‘ I FIGURE 2.—Index map showing the location of Inyo County lead-silver-zinc deposits. ‘ 4 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. brevifolz'a) , and cacti cover all except the northwestern part of the quadrangle near Conglomerate Mesa and the higher altitudes in the Coso Range, where pifion pines and junipers are prevalent. Joshua trees grow abundantly on Lee Flat. TOPOGRAPHY The Darwin quadrangle is in the western part of the Basin and Range physiographic province. Altitudes range from a maximum of 7,731 feet in the Inyo Moun- tains to a minimum of 1,960 feet in the canyon 2 miles north of Rainbow Canyon, which drains into Panamint Valley (fig. 1). The south end of the Inyo Mountains occupies most of the northwestern quarter of the quad— rangle. The north end of the Coso Range extends into the southwestern part and the northwest end of the Argus Range extends into the southeastern part of the quadrangle. The rest of the area is mainly an alluvial and lava-capped plateau with altitudes of 4,500 to 5,500 feet. The most rugged topography is in the eastern part of the quadrangle where narrow, deeply incised canyons draining into Panamint Valley are cut into the lava—capped Darwin Plateau. Rainbow Canyon has steep walls that are in places more than 1,000 feet high. The principal drainage is into Panamint Valley. Darwin Canyon drains the southeastern part of the quadrangle, including the Argus Range, the Darwin Hills, and the alluviated area west of Darwin. The east. slope of the Inyo Mountains and the west slope of the Santa Rosa Hills are drained by Rainbow Canyon, and Lee Flat and the east slope of the Santa Rosa Hills are drained by Lee Wash. Drainage of the southwest- ern part of the quadrangle is to the west into Owens Valley. WATER SUPPLY Darwin Canyon provides the principal water sup- ply. Small quantities of water have also been obtained from Black Spring in the Coso Range and from Mill Canyon in the northeastern part of the quadrangle. Shallow wells or springs in Darwin Canyon provide the water supply for the Darwin mine, a small tungsten mill in Darwin Canyon, a small mill and residence at China Garden Spring, and the motel at Panamint Springs. The Darwin mill and mining camp are supplied by 3 wells less than 60 feet deep in Darwin Canyon from which about 180 gpm (gallons per minute) of water are pumped, with a lift of about 1,840 feet. The water is supplied from a drainage basin of 165 square miles on the west flank of the Argus Range and the northeast flank of the Coso Range, and is funneled into the nar- row mouth of Darwin Canyon. Water for the town of Darwin is piped 8 miles from springs in the Coso Range and must be trucked from Lone Pine, Keeler, or Darwin to the Santa Rosa mine, the Talc City district, and the Lee district. PREVIOUS WORK AND ACKNOWLEDGMENTS The earliest discussions of the geology of the Darwin area are in reports of the California State Mineralogist (Crawford, 1894 and 1896; De Groot, 1890, p. 209— 218; and Goodyear, 1888, p. 224—309) and by Burchard (1884) and Raymond (1877, p. 25—30). These reports deal primarily with discussions of mining activity, but they also have notes on the geology of local mine areas. Knopf (1914) visited the Darwin area in May 1913 dur— ing his reconnaissance study of the Inyo Mountains, and in a separate report he discusses the geology and ore deposits of the Darwin Hills. The first comprehensive study of the Darwin district was made by Kelley (1937; 1938) during the summers of 1935—36. He made a geologic map of the Darwin Hills on a scale of 1,000 feet to the inch and mapped a few of the mines on a larger scale. In 1937 Schultz described some late Pliocene or early Pleistocene vertebrate fauna from the Coso Range, but most of his work was west of the quadrangle. Hop- per (1947) mapped about 90 square miles across the southern part of the quadrangle in his study of a strip 6 miles wide from the Sierra Nevada to Death Valley. The US. Geological Survey had geologists working in the Darwin quadrangle during World War II in its commodity-study program. C. W. Merriam and L. C. Craig studied the lead-zinc deposits; D. M. Lemmon and others studied the tungsten deposits of the Darwin Hills; and B. M. Page (1951) and L. A. Wright studied the tale deposits of the Talc City Hills. T. E. Gay, Jr. and L. A. Wright (1954) mapped the Talc City dis- trict. Several mine geologists have published reports on the Darwin district. L. K. Wilson, (1943), former resident geologist for the Pacific Tungsten Co., dis— cussed the geology and tungsten deposits on the east side of the Darwin Hills. D. L. Davis (Davis and Peterson, 1948), former resident geologist of the Anaconda 00., described the geology and ore deposits of the Darwin mine. Work in the field was greatly benefited by dis- cussions with J. F. McAllister and C. W. Merriam of the US. Geological Survey, M. P. Billings of Harvard Uni- versity, and C. E. Stearns of Tufts College. The writers especially wish to express their thanks for the wholehearted cooperation of the mining people in the area. Dudley L. Davis and Malcolm B. Kildale of the Anaconda Co. particularly facilitated the work in the Darwin district, and the writers greatly benefited from many discussions of the geology with them. Spe- cial thanks are also due to John Eastlick, Reginald Skiles, Joel Teel, and Fred Tong of the Anaconda Co.; PALEOZOIC ROCKS E. H. Snyder of Combined Metals Reduction C0,; A1- fred Glenn, lessee of the Lee mine; and Mrs. Agnes Reid of Panamint Springs. FIELDWORK The fieldwork began in April 1951 when E. M. Mac- Kevett, J r., and L. A. Brubaker mapped the Santa Rosa. mine and several smaller mines in the quadrangle and wrote preliminary reports on their work (MacKevett, 1953). W. E. Hall and E. M. MacKevett, J r., mapped the quadrangle on a topographic base at a scale of 1: 40,000 from January to October 1952 and from May to October 1953 and the mines between May and Sep- tember 1954 and in March 1955. The writers were ably assisted for short periods by Santi das Gupta, José Hernandez, Victor Mejia, E. H. Pampeyan, Dallas Peck, H. G. Stephens, and D. H. Thamer. PALEOZOIC ROCKS GENERAL FEATURES The Paleozoic motion in the Darwin quadrangle con— sists predominantly of carbonate rocks similar to forma- tions in the eastern part of the Great Basin. Pre- Devonian rocks are mainly dolomite and quartzite, De- vonian rocks are dolomite, limestone, quartzite, and shale, and Mississippian and younger Paleozoic rocks are mainly limestone (pl. 1). No volcanic or phos- phatic material, and only minor carbonaceous material was recognized in the Paleozoic rocks. Most formations are well exposed and some units form bold, clifl’like out- crops. The Paleozoic rocks have an aggregate thickness greater than 13,000 feet. Poor exposures in parts of the section preclude a more accurate appraisal of the total thickness. The Paleozoic rocks are similar to those described by McAllister (1952, 1955) from the ad- jacent Ubehebe Peak quadrangle and Quartz Spring area, and Merriam (1954), Bateman and Merriam (1954, map 11), and Merriam and Hall (1957) from the southern Inyo Mountains. , Outcrops of Paleozoic rocks are confined largely to five areas within the quadrangle. These areas, which are separated by alluviated or volcanic terrane, are: the Conglomerate Mesa area, the Santa Rosa Hills, the Tale City Hills, the Darwin Hills, and the Argus Range—Zinc Hill area (fig. 1). Pre-Devonian rocks are confined to the Tale City Hills. Devonian and Mis- sissippian rocks crop out in the Santa Rosa Hills, the Talc City Hills, and locally in the northwestern part of the Darwin Hills. Pennsylvanian and Permian rocks, which constitute the thickest and most wide- spread sequence, occur in each of the five areas. 5 Formation names used by McAllister ( 952, 1955) for the Ubehebe Peak quadrangle and Qu rtz Spring area are generally applicable and have b en utilized (table 1). Thick continuous stratigraphic Tections are lacking because of volcanic or alluvial cove structure. probably represent short-time intervals. r or complex Unconformities are apparently limited to Pennsylvanian and Permian parts of the Tection and Lee Flat TABLE 1.—Sequence of rocks exposed in the Darwin quadrangle Age Name Character Thick- uess (feet) Recent Alluvium Unconsolidated alluvium, playa deposits, fanglomerate, landslide debris. Pleistocene —7—?—?— Pliocene Lakebeds White to light-gray fine- grained pumiceous ash silt, clay, and diatoma..eous earth. 58+ Fanglomerate marginal to Darwin Wash Gravels composed mainly of subrounded fragments of Pennsylvanian and Permian limestone, quartz monzon- ite, and basalt in a sandy matrix. ‘ 25+ Olivine basalt Mainly flows 10—100 it t ick. Aiewundifferentiated ows in Darwin Oanyon‘ are younger than fanglomerate marginal to Darwin Wash. 0—600 Fanglomerate from Inyo Mountains and . Coso formation Gravel. Angular to sub- rounded fragments of rdo- vician and Silurian rocks up to 18 in. in diameter in a clay and silt m trix. Probably is contempoiane- ous with the 0050 form ‘ tion. Arkose and clay, poorly bed- ded, white to buff, fine- to medium-grained. 30+ 30+ Andesite and Pyroclastic rocks Forms broad dome in upper pyroclastic unit; conains phenocrysts and clusters of plagioclase and hornblende in an aphanitic groundIEass. Upper unit: poorly bed ed, mainly tufi-breccia an ag- glomerate and cinders. Lower unit: well-bedded lap- illi-tufl, scoriaceous b salt, and tufi-breccia. 1 0—1, 230 0-910+ Cretaceous ('I) Cretaceous Hypabyssal rocks Andesite porphyry, diorite, alaskite porphyry, anc al- tered quartz 1atite(?) dil es. Aplite and leucogranite Includes aplite, and leucogranite. pegmatite, Amphibolite Includes amphibolite, epidote amphibolite, hornblende gabbro, and diorite. Biotite -horn b1 ende- quartz monzonite and leucocratic quartz monzonite. Mainly quartz monzonite With other granitic rock types. Permian Owens Valley forma- tion Upper unit: limestone hon- glomerate 60 it thick over- lain by siltstone, calcarenite, and orthoquartzite ‘ 180+ Middle unit: brick-red Land yellowish-brown shale, ub- ordinate siltstone and lime- stone. 200 Lower unit: mainly ne- grained calcarenite in eds l to 2 ft thick; some t ick limestone lenses, shale and siltstone. ‘ 2, 800 6 GEOLOGY AND ORE DEPOSITS, DARWIN TABLE 1.——Sequence of rocks exposed in the Darwin quadrangle—Continued Thick- ness (feet) Age Name Character Upper unit: calcilutlte and fine-grained calcarenite with lesser pink fissile shale and limestone pebble conglom- erate. l, 700 Permian and Keeler Canyon forma- Pennsylvanlan tion Lower unit: thin-bedded lime- stone with intercalated lime- 2, 300 stone pebble conglomerate. Thin-bedded dark-medium- gray limestone that is equiv- alent to Rest Spring shale and upper part of the Perdido. Rest Spring Lee Flat shale lime~ 0—50+ stone Pennsylva- nian (‘1) 960+ Mississippian Perdido formation Limestone and bedded chert 330 Fossiliferous thin- to thick- bedded limestone with chert 435 lenses and nodules. Tin Mountain limestone Coarse-grained white and light-gray marble; dolomite Devonian Lost Burro formation and limestone in lower part of formation; minor quart- 1, 770+ zite. Brown fissile shale locally in upper part. Devonian and Hidden Valley Light-gray massive dolomite- _ 1,0005: Silurian dolomite Upper Ely Springs dolomite Dark-gray dolomite with chert Ordovician beds and lenses; lesser light- 920:}: gray dolomite Middle Eureka quartzite Light-gray to white vitreous 440 Ordovician orthoquartzite Lower Pogonip group Light- and medium-gray Middle(?) and thick-bedded dolomite; 1. 570+ Lower lesser thin—bedded dolomite Ordovician and limestone. Unknown Gneiss limestone, a time-stratigraphic equivalent of part of McAllister’s (1952, 1955) Perdido formation and his Rest Spring shale, was described as a new formation by Hall and MacKevett (1958). Part of the Lee Flat limestone correlates with the Chainman shale in the southern Inyo Mountains (Merriam and Hall, 1957, p. 4). Nomenclature used by Merriam and Hall (1957, p. 4) has been adopted for the Pennsylvanian and Permian formations. Most of the formations are fossiliferous, but large barren stratigraphic thicknesses occur between many collections in pre-Carboniferous rocks. The paleon- tologic record is best documented by an abundant Penn- sylvanian and Permian fusulinid fauna and by corals and brachiopods in the Tin Mountain limestone of Mis- sissippian age. ' Three sedimentary rock names used in this report follow the usage of Pettijohn (1949). These are: Orthoquartzite (Pettijohn, 1949, p. 237)—a sedi- mentary quartzite. Calcarenite (Pettijohn, 1949, p. 300)—“* * * de- trital carbonate rocks of sand-grain size (1/16 to 2 mm in diameter) that are with or without calcite cement and are composed mainly (more than 50 percent) of carbonate detritus.” QUADRANGLE, INYO COUNTY, CALIF. Calcilutite (Pettijohn, 1949, p. 307 )—detrital car- bonate rock of grain size less than sand-grain size. ORDOVICIAN SYSTEM POGONIP GROUP NAME AND DISTRIBUTION The name Pogonip limestone was originally applied by King (1878, p. 187—195) to all beds on Pogonip Ridge at White Pine (Hamilton), Nev., between Prospect Mountain quartzite (Lower Cambrian) and Eureka quartzite (Middle Ordovician). The name was sub- sequently revised and restricted by Hague (1883, p. 253~263) to include beds between the Dunderberg shale (Upper Cambrian) and the Eureka quartzite, but some' Upper Cambrian beds were still included in the Pogo- nip. Walcott (1923, p. 466) proposed restricting the formation further, but his proposal was not generally accepted and the US. Geological Survey continued to use the name as defined by Hague (Wilmarth, 1938, p. 1689). Merriam and Anderson (1942, p. 1683) pro- posed that the Pogonip be elevated to a group status, with inclusion of both the Upper Cambrian and the Ordovician. Hintze (1951, p. 11) proposed that the Pogonip be elevated to a group status to include only Ordovician rocks. Nolan and others (1956, p. 24) in their Eureka section accepted this and subdivided the Pogonip group into three formations—the Goodwin limestone, the Ninemile formation, and the Antelope Valley limestone listed from oldest to youngest. The Pogonip group is undifferentiated in our mapping and follows the usage of McAllister (1952, p. 11) for the rocks above the Nopah formation (Upper Cambrian) and below the Eureka quartzite (Middle Ordovician). The Pogonip has been described by McAllister (1952, p. 10—12) from the Quartz Spring area, and from the Ubehebe Peak quadrangle (McAllister, 1955, p. 10) and equivalent rocks were described in the Inyo Moun- tains by Kirk (in Knopf, 1918, p. 34),,Phleger (1933, p. 1—21), Merriam (1954, p. 10) and Langenheim and others (1956). Pogonip group in the Darwin quad- rangle occurs only in the Talc City Hills (pls. 1, 2). Most outcrops of the Pogonip are faulted and folded; the thickest and most continuous exposures are about a mile northeast of the Alliance talc mine (fig. 3). The thick-bedded strata are erosion resistant and form bold outcrops. The thin-bedded strata form smooth, rounded slopes and in places slight topographic depressions. THICKNESS AND STRATIGRAPHIO RELATIONS An almost complete section of Pogonip is probably present in the Darwin quadrangle, although the base PALEOZOIC ROCKS EXPLANATION Cenozoic terres r deposits Inc/miss allay/um, like blds, m1 fang/omen): Cenozoic volcanic rocks Inc/odes base/I, ewes/re, and pyroc/asfl'c rocks \ Mesozoic plutonic rocks Mat/14y quartz Moran/lite Mississippian and younger Paleozoic sedimentary rocks Devonian and aloe! Paleozoic sedimentary rocks Contaci Mines and prospects o I 0 Lead-zinc-silver Talc Tungsten A I y Gold Copper Antimony ‘ lceiand spar ' Cactus . I' V ovwenfl' F.4I E. 4 MILES Geology by W. E. Hall and E. M. 1952—54 FIGURE 3.—Simplifled geologic map of the Darwin quadrangle showing the geologic setting of the ore deposits. 8 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. of the formation is not exposed. The measured over- turned section northeast of the Alliance talc mine is about 1,560 feet thick, but parts of this section lack good exposures and the base is faulted. McAllister (1952, p. 11) reports a thickness of 1,440 feet for a composite section of Pagonip in the Quartz Spring area. The Pogonip group is conformably overlain by Eureka quartzite. LITHOLOGY The Pogonip group in the Darwin quadrangle is characterized by a prevalence of light- and medium- gray thick-bedded dolomite and lesser amounts of thin- bedded dolomite and limestone. Crossbedded sandy dolomite is common at the top. The upper part of the Pogonip contains several conspicuous brown siliceous zones 8 to 178 feet thick that contain thinly interbedded sandy dolomite, limestone, and iron—stained chert re- ferred to as having crepe structure by McAllister ( 1952, p. 10) because of their wavy nature. At some places in the measured section the crepe beds are folded and have a pronounced slip cleavage that produces marked crenu- lations. A zone of large gastropods is present 100 to 250 feet below the base of the Eureka quartzite nearly everywhere in the Pogonip. The crepe beds, the zone of large gastropods, and the conspicuous overlying Eureka quartzite distinguish the Pogonip from similar appear- ing younger dolomite in the section. Section 5,000 feet N. 40° E. of the Alliance talc mime Eureka quartzite. Conformable contact. Pogonip group : Feet (1 Dolomite, light— and medium-gray; and sandy dolomite, both thick bedded. Minor light-gray limestone. Contains two brown-weathering siliceous beds 10 and 25 ft thick. Crossbed- ding common near the top. Palliseria. robusta Wilson is present 150 ft below top _____________ c Dolomite, brown-weathering silty and sandy, and limestone with abundant thin limonitic- stained chert interbeds. Crenulations abundant. Referred to as crepe beds _____________________ 178 b Dolomite, light- to dark-medium-gray, sandy in upper part. Locally contains lens-shaped brown- weathering chert nodules. Contains 4 beds 8 to 45 ft thick of gray thinly bedded limestone and dolomite with abundant thin siliceous, limo- 540 nitic interbeds _______________________________ 393 a Dolomite, medium-gray and light-gray, thick-bed- ded to massive. Contains minor sandy medium- gray dolomite _______________________________ 448 Total _________________________________ 1, 559 Base unexposed. Unit a, the lowermost 448 feet exposed, consists pre- dominantly of thick—bedded light-medium-gray and medium-gray dolomite interbedded with some thick- bedded sandy medium-gray and light-gray dolomite. Reuben J. Ross, J r., suggests that this unit may belong to the Upper Cambrian Nopah formation (written communication, 1962), but fauna] evidence is lacking. Unit b is 393 feet thick and consists mainly of light- medium-gray to dark-medium-gray dolomite. Sandy dolomite is abundant in the upper part. Lens-shaped medium-gray brown-weathering chert nodules as much as 6 inches long are abundant in some of the thick- bedded dolomite. Unit b contains four zones of crepe beds; the maximum thickness is 45 feet. This unit cor- relates roughly with units 4 and 5 of McAllister (1952, p. 11). Unit 0 is a conspicuous crepe bed 178 feet thick. It consists of brown-weathering silty and sandy dolomite and thinly bedded highly iron stained irregular chert beds. Locally slip cleavage is well defined and produces conspicuous crenulations. Unit (1, the upper 540 feet of the Pogonip, consists of light- and medium-gray thick-bedded dolomite and a few beds of light-gray limestone 1 to 2 feet thick. Sandy dolomite that is locally crossbedded is increas- ingly abundant high in the section. Brown-weather- ing erosion-resistant zones of crepe beds are present; the highest of these forms conspicuous outcrops about 100 feet below the top of the Pogonip. Chert nodules are numerous locally, and remnants of large gastropods are abundant in a zone 150 to 260 feet below the contact of the Eureka quartzite. The genus Giwanella is common at the Viking mine (fig. 3). This unit includes Mc- Allister’s units 7 and 8 (1952, p. 11). Abundant sandy crossbedded dolomite in the upper part of the formation marks a transition between Pogonip group and Eureka quartzite. AGE The Pogonip group is Early and possibly very early Middle Ordovician in age. The only fossils found in the Darwin quadrangle in the Pogonip group are in unit (1 from a zone above the highest crepe beds of unit c, and stratigraphically 150 to 260 feet below the top of the formation; they are late Early or early Middle Ordo- vician age. Fossils were observed nearly everywhere this zone is exposed. Collections were made at the Viking talc mine and at the same stratigraphic zone 5,000 feet N. 40° E. of the Alliance talc mine. They were studied by Reuben J. Ross, J r., of the US. Geolog- ical Survey, who reported as follows (written communi- cation, 1954) :“Pogonip limestone—high Lower or very low Middle Ordovician Pallisem'a robusta (Wilson). Unidentified cystoid plates belonging to Paleocystites, “Receptawlites”? sp.” Nolan and others (1956, p. 25) consider the fossils from the upper Pogonip group a Chazy fauna and Mid- PALEOZOIC ROCKS i 9 die Ordovician in age. Helen Duncan (1956, p. 215), however, stated that G. A. Cooper and Edwin Kirk considered the fauna in the upper part of the Pogonip to be pre-Chazy and of Early Ordovician age. McAl- lister (1952, p. 11) reported fossils from his shaly unit 5, below the Pallisem zone, were identified by Josiah Bridge, in consultation with G. A. Cooper, who wrote: “This fauna * * * is definitely of Lower Ordovician (Canadian) age.” R. J. Ross, Jr. (in McAllister, 1956) studied a collection of McAllister’s from another local- ity in the same shaly unit and reported the collection of fossils to be equivalent to the fauna of his J zone of the Garden City formation in northeastern Utah, and that the age is probably very late Early Ordovician. EUREKA QUARTZITE NAME AND DISTRIBUTION Hague (1883, p. 253, 262) named the Eureka quartz— ite from exposures near Eureka, Nev. ,Lone Mountain was designated the type locality by Kirk (1933, p. 34), because the section is easily accessible and is the nearest satisfactory section to the town of Eureka. The forma- tion crops out in the Tale City Hills mainly in faulted areas and as blocks and slivers in fault zones (pls. 1, 2). The most extensive exposures are at the north end of the Talc City Hills where the Eureka is exposed in a discontinuous band 31/2 miles long along the flanks of a southward-plunging syncline. The most accessible complete section is north of the White Swan mine. The Eureka quartzite is widely distributed through— out southeastern California and Nevada. It was de- scribed by McAllister (1952, p. 12, 13; 1955, p. 11; 1956) from the Quartz Spring area and the Ubehebe Peak quadrangle, by Merriam (1954, p. 10) from the Inyo- Death Valley region, and by Langenheim and others (1956, p. 2092) from the Inyo Mountains. Hopper (1947, p. 407) described the Eureka quartZite on the west side of Death Valley and Hazzard (1937, p. 324) described it at the north end of the Nopah Range. The formation is erosion resistant and commonly makes sharp and precipitous outcrops; where strongly jointed it weathers to large angular blocks. THICKNESS AND STRATIGRAPI-IIG RELATIONS A thickness of 440 feet of Eureka quartzite was measured in a northeastward-trending section from a point 1,200 feet N. 40° E. of the White Swan mine (pl. 2). This thickness is slightly greater than the 400 feet measured by McAllister (1952, p. 12—13) in the Ubehebe Peak quadrangle and Quartz Spring area and the 250 feet measured by Hopper (1947, p. 407) on the west side of Death Valley. Both upper and lower con- tacts of the Eureka quartzite are apparentlyi conform- able depositional contacts. The lower contact is marked by a change from light-gray sandy dolomite and lime- stone to very light gray vitreous orthoquaftzite that weathers brown. Although the contact is well defined, the increase in arenaceous detritus near the op of the carbonate rocks of the Pogonip group indicat a transi- tion prophetic of Eureka deposition. The pper con- tact is denoted by a sharp lithologic change f om light- brown weathering vitreous orthoquartzite to dark-gray cherty Ely Springs dolomite. ‘ LITEOLOGY The Eureka quartzite, which is the best marker zone in the Paleozoic section, is a distinctive orthoquartzite characteristically light-gray to white and with a glis- tening vitreous luster. The orthoquartzite is well in- durated and cemented 'by secondary silica.‘ Despite thorough cementing and local minor metambrphic ef- fects, individual quartz grains are megascopically dis- cernible in some specimens. The distinctive (lithology, luster, and light color, especially when contrasted with the overlying dark-gray Ely Springs dolomite, make it a reliable mappable unit (fig. 4). i FIGURE 4,—Photograph of the Tale City Hills near the Viking mine showing the overturned Paleozoic of the Pogonip group (Op). Eureka quartzite (0e). Ely Springs dolomite (Gas), and Hidden JValley dolo- mite (Dsh). The Eureka quartzite and the overlying d rk-gray Ely Springs dolomite are the most conspicuous Paleozoic stratigraphic horizon markers. View looking northwest. The lowermost 120 feet of the formation ciinsists of yellowish-brown to dark-brown-weatheri g iron- stained orthoquartzite in beds 1 to 6 feet t ick that range from white to light gray on fresh surfaCes. Less abundant bluish-black stains are probably nianganese oxide. Very thin crossbedding is conspicuo s in this unit. Joints, spaced at about 5-foot intervjls, inter- 10 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. sect stratification at high angles locally in the basal unit. The uppermost 30 feet of the unit is marked by a zone of irregularly streaked and blotched bluish-gray, white, and brown orthoquartzite. The streaks, which are commonly less than an inch thick, are probably sec- ondary features. Thick-bedded white vitreous orthoquartzite and mi- nor light-gray orthoquartzite in beds 1 to 2 feet thick constitute the middle 250 feet of the Eureka. This or- thoquartzite weathers white and buff and to a lesser extent light brown and bluish gray. The uppermost 70 feet is locally thin—bedded light-gray vitreous orthov quartzite that weathers to sandy surfaces of variegated brown. Section 1,200 feet N. 41° E. of the White Swan mine Ely Springs dolomite. conformable contact. Eureka quartzite : Feet (1 Orthoquartzite, light-gray, vitreous, thin-bedded. Brown with sandy appearance on weathered surface. The contact with the Ely Springs is sharp_-__ ___- _ 70 c Orthoquartzite, white and light-gray, vitreous, thick-bedded. Weathers white, light brown, or bluish gray ___- 250 b Orthoquartzite, irregularly streaked white, bluish- gray, and brown _____________________________ 30 a Orthoquartzite, white to light-gray; weathers yel- lowish brown to dark brown. Beds 1 to 6 ft thick. Crossbedding is common _______________ 90 Total ___ __ Conformable contact. Pogonip group. 440 Thin—section study shows that the Eureka quartzite consists of well-rounded and sorted quartz grains that are tightly packed and cemented with silica. Individ— ual quartz grains are fine- to medium-sand size and range mostly from 0.2 to 0.4 mm in diameter. Second- ary overgrowths are indicated by thin peripheral rims of clear quartz grains in optical continuity with the original quartz grains. The quartz grains have strain shadows and are dotted with submicroscopic specks. Minor amounts of zircon and of late calcite and limo- nite are in most sections. AGE No fossils were found in the Eureka quartzite, but its age is fairly well substantiated by stratigraphic position. The upper part of the underlying Pogonip group is late Early or early Middle Ordovician in age; the overlying Ely Springs dolomite contains Richmond (Late Ordovician) fossils. It is reasonable to conclude that the Eureka quartzite is mainly if not entirely Middle Ordovician. The basal Eureka quartzite in the southern Inyo Mountains locally contains fossils of Black River or Trenton age (Merriam, 1954, p. 10). Langenheim and others (1956, p. 2092) correlate the Barrel Spring formation of Phleger (1933) in Maz- ourka Canyon in the Inyo Mountains with the lower part of the Eureka quartzite and consider it to be Mo- hawkian in age. ELY SJPRINGS DOLOMITE NAME AND DISTRIBUTION Ely Springs dolomite was named by Westgate and Knopf (1932, p. 15) from exposures in the Ely Springs Range about 12 miles west of Pioche, Nev. In the Darwin quadrangle the formation is mainly in the northwestern part of the Tale City Hills where it is one of the most widespread formations (pls. 1, 2). It crops out at the northernmost workings of the White Swan mine, and occurs in a continuous band 2 miles long on the flanks of the overturned syncline west of the Hard Scramble talc prospect (fig. 3). Most exposures of the Ely Springs are bounded by one or more faults, and the west flank of the Talc City Hills north of the White Swan mine is the only place where a complete section is present. Ely Springs dolomite has been described in the Quartz Spring area and the Ubehebe Peak quadrangle (McAllister, 1952, p. 15), in the Inyo-Death Valley area by Merriam (1954, p. 10), and in Mazourka Can- yon in the Inyo Mountains by Langenheim and others (1956, p. 2095). Hazzard (1937, p. 325) and Hopper (1947, p. 407) provisionally correlated dolomite over- lying Eureka quartzite in the Nopah Range and on the west side of Death Valley with the Ely Springs (fig. 2). Like most dolomitic rocks of the area, the Ely Springs dolomite forms bold, rough outcrops. The dark-gray color of the cherty dolomite overlying white vitreous quartzite renders the lower part of the Ely Springs readily recognizable. THICKNESS AND STRATIGRAPHIO RELATIONS A measured section of Ely Springs dolomite 2,200 feet northeast of the White Swan mine is approximately 920 feet thick (pl. 2). The accuracy of this section is somewhat impaired by a minor fault and a small basalt plug. McAllister’s (1952, p. 13) measured sections of Ely Springs dolomite in the Quartz Spring area are 940 and 740 feet thick. The contact between Ely Springs dolomite and Eureka quartzite is conformable and is marked by a sharp change in lithology and color. The upper con- PALEOZOIC ROCKS tact is conformable but transitional with the Hidden Valley dolomite. The Ely Springs—Hidden Valley con- tact is placed at the top of a dark-medium-gray dolo- mite band about 40 feet thick that overlies light-gray Ely Springs dolomite and is overlain by massive light- gray Hidden Valley dolomite. LITHOLOGY Ely Springs dolomite is largely dolomite and a les— ser amount of chert. The lower unit of the Ely Springs, 320 feet thick in the measured section, consists mainly of dark-gray thick—bedded dolomite but includes abundant black chert. The chert in this distinctive unit occurs as conspicuous beds 1/2- to 2-inches thick separated by 1/2- to 2—foot thicknesses of dolomite and as thin lenses and irregularly shaped nodules. Brown- weathering sandy dolomite about 15 feet thick is in the lower part of this unit. Light-gray dolomite and minor amounts of medium- gray dolomite constitute most of the massive-appearing upper unit, which is about 600 feet thick. A dark— medium-gray dolomite band about 40 feet thick is at the top of t e formation. Chert is rare in the upper unit, but a few chert nodules are in the basal part. Locally the olomite is mottled by different shades of gray, but ost of the unit is uniformly light gray. Outcrops of he light-gray massive-appearing dolomite that lack st atigraphic continuity are difficult to dis- tinguish fro similar dolomite in the Pogonip group and Hidden alley dolomite. AGE The lower unit of the Ely Springs is Late Ordovician in age; palebntologic evidence is lacking in the upper unit. The best preserved and most diversified fossil assemblage donsists of silicified specimens in the dark- gray dolomite that forms the prominent hill half a mile N. 30° E. of the Viking talc mine. C. W. Merriam (oral communication) collected and provisionally identified the following fauna from this site. Brachiopods: H eterorthis sp. Glyp torthis cf. imculpta Thwerodonta sp. Lepidocyclus n. sp. (probably at least two species, one large) Platystrophiw sp. me’ella cf. quadrata Wang Zygospim 11. ID. Strophomem n. sp. POpikma n. sp. Plaesiomys sp. Corals: H alysites, large form Columnam'a cf. wlveolata (Goldfuss) Several solitary streptelasmid types both large and small 620626 0—62—2 l 11 Another collection of brachiopods mad in cherty dark-gray dolomite about 15 feet strati aphically above the base of the Ely Springs on 3. sm ll exposure 6,300 feet N. 18° W. of the White Swa mine was studied by Reuben J. Ross, Jr. (written communica- tion, 1954) of the U.S. Geological Survey wlio reported: f130:D142 Resserella aft. R. corpulemta ‘ This is the only species present but it is dbundant and nicely silicified. The specimens at hand are not strictly R. corpulenta and bear some resemblance‘to R. multi- secta. The former is a Maquoketa and tihe latter an Eden form. It therefore is clear that the collection comes from Upper Ordovician rocks but these may not be upper- most Ordovician. i Ross also studied a collection from the upper unit 3,000 feet N. 15° E. of the Viking mine. his collec- tion was in light—gray massive dolomite of the upper unit of the Ely Springs. Ross reported (w‘ritten com- munication, 1954) : ‘ f132=D143 ‘ Thaeromlonta cf. T. digmztw Wang ‘ Daniella cf. 0. quad/rate Wang Silica cast of a shell, possibly referable to Parastropht— nella. Small silicified shell similar in shape to Zygoepim but not referable to that genus. The same or a very nearly identical species is known but is as ye undescribed from the uppermost Bighorn formation niear Buffalo, Wyoming. Numerous tetracorals. There is a strong suggestion that this colleciiion is essen- tially correlative with the Late Ordovician Maquoketa beds of Iowa, with the Stony Mountain formation of Manitoba, and with the uppermost Bighorn beds on the east flank of the Bighorn Mountains. SILURIAN AND DEVONIAN SYSTEiMS‘ HIDDEN VALLEY DOLOMITE , NAME AND DISTRIBUTION ‘ Hidden Valley dolomite was named by McAllister (1952, p. 15) for exposures on the east side (of Hidden Valley in the Quartz Spring area. Outcrops of folded and faulted Hidden Valley dolomite are in the Tale City Hills, and the largest and most westerly exposures are the core of a syncline that forms the ridge south- west of the Hard Scramble mine (pl. 2). The forma- tion is also exposed at the Victory prospect, and near the Alliance, Talc City, and Trinity talc mines (fig. 3). Regionally the formation is exposed in e Quartz Spring area (McAllister, 1952, p. 15), the Ubehebe Peak quadrangle (McAllister, 1955, p. 11), (and in the Inyo Mountains (Merriam, 1954, p. 11). THICKNESS AND STRATIGRAPHIO RELATIjNS Probably most of the Hidden Valley olomite is represented within the quadrangle, but continuous out- 12 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. crops are lacking because of faulting. Lack of distinc— tive lithologic units and the massive character of the rocks preclude an accurate measurement of the thick- ness. The formation is 1,365 feet thick at its type local- ity in the Ubehebe Peak quadrangle (McAllister, 1952, p. 16). No satisfactory section of the Hidden Valley was found for measurement, but it has a probable thick- ness of about 1,000 feet on the hill half a mile north of the Viking talc mine where the top of the formation is eroded. Hidden Valley dolomite conformably overlies the dark-gray dolomite at the top of the Ely Springs. The only exposures of the upper contact are at the Talc City mine, where the contact is placed at the base of a bed of interbedded orthoquartzite and sandy limestone 65 feet thick. The contact also marks a change from light- gray massive Hidden Valley to the prevalent mottled, dolomite and limestone characteristic of the lower part of the Lost Burro formation. LITHOLOGY Within the Darwin quadrangle the Hidden Valley is uniformly light-gray massive to very thick bedded dolo- mite with little diversification in lithology or color. Two sandy quartzite beds 5 and 20 feet thick are inter— bedded in the massive dolomite on the ridge west of the Hard Scramble mine. A few calcite aggregates 2 to 3 inches in diameter are widely scattered in parts of the formation. A representative thin section of Hidden Valley dolomite is made up of a granoblastic mosaic of dolomite crystals that average about 0.3 mm in diame- ,ter. Quartz occurs in small quantities as rounded sand grains and along grain boundaries of dolomite. AGE The only Hidden Valley fossils found are in massive light-gray dolomite a few hundred feet northwest of the Alliance talc mine. The fossils are poor in quan- tity and state of preservation, and consist of an orna- mented solitary coral and a colonial coral, probably a favositid. McAllister (1952, p. 16) reported the lower fossiliferous part of the Hidden Valley dolomite in the Quartz Spring area is Silurian, probably equivalent in age to the top of the Clinton group in the Niagaran series. McAllister (1952, p. 17) also reported that fos- sils from the upper part of the Hidden Valley from a zone 50 feet thick lying 15 to 65 feet below the top of the formation in the Andy Hills were identified by G. Arthur Cooper and determined as Lower Devonian in age. The zone was correlated with the Oriskany part of the restricted Nevada limestone (Merriam, 1940, pp. 52—53). DEVONIAN SYSTEM LOST BURRO FORMATION NAME AND DISTRIBUTION The name Lost Burro formation was applied by McAllister (1952, p. 18) to exposures at Lost Burro Gap in the northeastern part of the Ubehebe Peak quadrangle. In the Darwin quadrangle the Lost Burro is present at the southeast end of the Santa Rosa Hills, at the Talc City mine in the Tale City Hills, and locally on the west side of the Darwin Hills (pl. 1). A belt of Lost Burro crops out as a discontinuous band of white marble on the east side of the Santa Rosa Hills for 21/2 miles near the Lee mine. The Lost Burro for- mation forms a northwestward-trending band 1,000 feet wide and 2 miles long at the Talc City mine, and a small outcrop of marble of the Lost Burro is on the west side of the Darwin Hills 2.2 miles N. 24° W. of Darwin. Two small enclaves of marble about 3.7 miles S. 27° W. of the northeast corner of the quadrangle lithologically resemble the Lost Burro, and are assigned to it. Outside of the Darwin quadrangle the formation is well exposed near the Cerro Gordo mine in the New York Butte quadrangle according to Merriam (oral communication, 1954) ; it is abundant in the Ubehebe Peak quadrangle and Quartz Spring area (McAllister, 1952, p. 18; 1955, p. 11) and Hall and Stephens (1962) have mapped the formation on the south side of Towne Pass in the Panamint Range and at the Modoc mine in the Argus Range. The Lost Burro formation generally is erosion resistant, and is well exposed. THICKNESS AND STRATIGRAPHIC RELATIONS A stratigraphic thickness of 1,773 feet was measured for an incomplete Lost Burro section that trends north- eastward from a point 2,000 feet S. 14° W. of hill 5525 near the southeast end of the Santa Rosa Hills begin- ning at a conformable contact with the overlying Tin Mountain limestone. The lower part of the formation is not exposed. The accuracy of the measured thickness is impaired by apparently minor faults in the middle part of the section. The only exposure of the base of the formation in the quadrangle is in the Tale City Hills on the east side of the Talc City mine where the formation contact is placed at the base of a 65-foot- thick band of interbedded orthoquartzite and sandy limestone that conformably overlies massive light-gray Hidden Valley dolomite. The folded and faulted ex- posures in the Talc City Hills are not amenable to stratigraphic measurement. McAllister’s (1952, p. 18) section of Lost Burro at the type locality in the Ubehebe Peak quadrangle is PALEOZOIC ROCKS 13 1,525 feet thick, but he also reported a section from the Quartz Spring area that is questionably 2,245 feet thick (McAllister, 1952, p. 19). LITHOLOGY The Lost Burro formation consists of white and light- gray medium- to coarse-grained marble, light- and dark-gray dolomite, shale, orthoquartzite, and silty limestone. The lower part of the formation is mainly dolomitic, and the upper part is mainly limestone. Almost all the formation is exposed in the Talc City Hills, although the upper contact is eroded. The basal part of the Lost Burro formation is exposed only on the east side of the Tale City mine where it conformably overlies light-gray massive dolomite in an overturned section. The lowermost 65 feet of the formation con- sists of thinly bedded silty gray limestone and light- gray Vitreous orthoquartzite, both of which weather light brown. The lower 40 feet of this unit consists of quartzite beds 1 to 4 inches thick interbedded with gray sandy limestone that weathers brown. The upper 25 feet is vitreous light-gray quartzite that resembles the Eureka quartzite, and it is apparently repeated by faulting. This unit is correlated with the Lippincott member in the Ubehebe Peak quadrangle (McAllister, 1955, p. 12). The Lippincott member is overlain by about 300 feet of light—gray massive— to thick-bedded dolomite and has a faint mottled appearance due to irregular relicts of dark-gray dolomite. Several discontinuous beds of dark-gray fine—grained limestone about 40 to 50 feet thick are interbedded in the dolomite. The beds are discontinuous because of local dolomitization, partic- ularly at the crests of folds. The dark-gray fine- grained relicts of dolomite in the light-gray medium- grained dolomite are probably relicts of the original dolomite that was recrystallized during intrusion of leucocratic quartz monzonite. The mottled effect of the dolomite distinguishes it from the Hidden Valley dolo- mite. The mottled dolomite unit is overlain by light-gray fine- to medium-grained limestone that has a strong, steep lineation. Locally the limestone has abundant fragmentary masses of stromatoporoids and cladopo- roid corals. The limestone is estimated to be 450 to 500 feet thick. A brown-weathering fissile shale about 150 feet thick overlying the limestone is the uppermost unit exposed in the Talc City Hills. The middle and upper parts of the Lost Burro forma— tion are exposed in the Santa Rosa Hills near the Lee Mine in a section more than 1,700 feet thick; the base of the formation is not exposed. Dolomite is absent in the Lost Burro formation here in contradistinction to the predominantly dolomitic section at the type locality (McAllister, 1952, p. 18—19). The lower 300 feet of the exposed section in the Santa Rosa Hills consists predominantly of interbedded white marble and medium-gray limestone in beds about 1 foot thick that locally/contain stromatoporoids and cladoporoid corals. The upper part of the Lost Burro consists almost en- tirely of white and light-gray banded and streaked marble, but contains a few thin quartzite beds. The top of the formation is a 2-foot—thick light-gray sandy quartzite bed that conformably underlies dark-gray Tin Mountain limestone. The limestone and marble beds of the formation are generally free of sand, silt, and clay. Partial section of the Lost Burro formation measured north- eastward from a point 1,280 feet N. 65" W. of the main shaft of the Lee mine Tin Mountain limestone. Conformable contact. Lost Burro formation : Feet Marble, white, streaked and locally banded, bedding generally poor _____ 760 Marble, massive, mottled light- and medium-gray--- 140 Limestone, medium-gray, fine-grained. Streaked with thin calcite veinlets and tremolite rosettes ________ 53 Marble, coarsegrained, white, in beds about 3 ft. thick; locally handed and streaked by gray marble- 190 Limestone, medium-gray, fine-grained ______________ 12 Marble, white, coarse-grained; locally streaked with light-gray hands 48 Marble, mottled white and light-gray; calcite vein- lets 72 Marble, white, coarse-grained, thick—bedded ________ 89 Limestone, medium-gray ___________________________ 5 Marble, white, banded, coarse-grained ______________ 6 Limestone, medium-gray, fine-grained ______________ 2 Marble, white, coarse-grained _____________________ 8 Limestone, medium-gray, fine-grained, a few chert nodules 2 Marble, white, coarse-grained, locally banded, beds 1 to 4 ft thick ___ 69 Limestone, light-gray, poorly preserved corals and bryozoa--- 6 Orthoquartzite, light-gray, light-brown-weathering, subvitreous 1 Marble, banded white and medium—gray; cladoporoid- bearing beds 1 to 3 ft thick; a few stromatoporoids- 69 Limestone biostrome, mottled medium- and light— gray; consists mainly of stromatoporoids and cladoporoid corals ______________________________ 12 Marble, White and medium-gray, interbedded coarse grained- 49 Limestone, medium-gray ; contains calcareous nodules 6 Limestone, medium—gray, fine-grained; in beds about 1 ft thick. Poorly preserved gastropods(?) in lowermost exposure _____________________________ 174 Total ________________________________________ 1, 773 Base unexposed. 14 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. The shale unit is exposed near the top of the Lost Burro formation in a tight syncline in the Talc City ' Hills northwest of the Tale City mine. The ‘unit is about 200 feet thick and consists of green and brown thinly bedded shale and small amounts of siltstone. Examination of thin sections of the white marble shows that the rock consists almost entirely of an inter- locking mosaic of calcite that ranges from 0.5 to 3.0 mm in maximum dimension. Subordinate constitu- ents that generally constitute less than 1 percent of the sections are an opaque mineral, probably graphite, and in one section highly calcic scapolite (meionite), and wollastonite. AGE Stromatoporoid and cladoporoid corals, the most abundant Lost Burro fauna in the Darwin quadrangle, help to establish the Devonian age of the formation, but are inadequate for precise dating within the system. Most specimens of these genera, particularly those from the Tale City and Darwin Hills, are stretched and poorly preserved. McAllister (1952, p. 19) believes that the Lost Burro formation in the Quartz Spring area and Ubehebe Peak quadrangle is Upper Devonian and in part questionable Middle Devonian. Stroma- toporoids and cladoporoid corals are associated with Stringocephalus in the lower part of the Lost Burro formation in the New York Butte quadrangle according to C. W. Merriam (oral communication, 1954) and are upper Middle Devonian. It is likely that the Lost Burro formation is, by lithologic correlation with dated units in adjacent areas, both Middle and Late Devonian in age. MISSISSIPPIAN SYSTEM TIN MOUNTAIN LIMESTONE NAME AND DISTRIBUTION Tin Mountain limestone was named by McAllister (1952, p. 20) from exposures at the northernmost peak in the Panalmint Range, but as this site is somewhat inaccessible, he designated the type locality on the southern slope of the hills about 21/2 miles southeast of Quartz Spring. The formation crops out in the Darwin quadrangle in two bands along the crest and east flank of the Santa Rosa Hills, near the Lee mine, and locally in the north- western part of the Darwin Hills (pl. 1). It is also part of a thrust plate in the eastern Talc City Hills about three-quarters of a mile north of the Silver Dollar mine (pl. 2). Tin Mountain limestone was described by McAllister (1952, p. 20—22; 1955, p. 12) from the Quartz Spring area and the Ubehebe Peak quadrangle and by Merriam (1954, p. 11) in the Inyo Mountains. It has been mapped by Hall and Stephens (in press) in the Argus Range at the Surprise mine (fig. 2). The cliff—forming propensity of the lower part of the forma- tion is well displayed on the eastern face of the Santa Rosa Hills. Except for a few beds, the remainder of the formation is moderately erosion resistant and is well exposed. THICKNESS AND STRATIGRAPHIC RELATIONS A stratigraphic thickness of 435 feet of Tin Mountain limestone was measured in the southern part of the Santa Rosa Hills from a section trending S. 16° W. from a point 1.5 miles N. 51° W. of the main shaft at the Lee mine. The abnormal apparent thickness of more than 500 feet at the Lee mine is due to repetition of part of the section by faulting. The Tin Mountain limestone is 475 feet thick at its type locality in the Quartz Spring area and 425 feet thick where measured in the Ubehebe Peak quadrangle (McAllister, 1952, p. 21). Contacts with the underlying Lost Burro formation and overlying Perdido formation are conformable. The Lost Burro-Tin Mountain contact is distinct and marked by lithologic and color changes, whereas the Tin Mountain-Perdido contact is gradational and rep- resented by the inception of bedded chert in the lower- most part of the Perdido formation in contrast to lenticular and nodular chert in the Tin Mountain limestone. eronoer Tin Mountain limestone consists predominantly of pure fine-grained, medium- to dark-gray limestone. Most of it is calcarenite and calcilutite. Some limestone beds consist almost entirely of crinoid fragments—en- crinite of Pettijohn (1949, p. 301) ; they are abundant in the upper part of the formation. Chert lenses and nodules are common throughout most of the Tin Moun- tain limestone, but bedded chert is absent; these features distinguish the Tin Mountain from the overlying Per- dido formation. Veinlets of white calcite are locally abundant. Tremolite and actinolite as individual crys- tals and aggregates are commonly formed in the lime- stone as a result of low-grade metamorphism. Near fault zones the limestone is commonly bleached and recrystallized and resembles the Lost Burro formation, but it generally lacks the banding characteristic of the Lost Burro. The formation is divisible into two major units. The lower unit, 130 feet thick, is mainly dark—medium-gray limestone in beds 6 inches to 2 feet thick intercalated with iron-stained shaly partings 1%“; to 1 inch thick. A few scattered chert nodules are in this unit. The upper unit is 305 feet thick and consists mainly of light- to dark—medium-gray limestone in beds rang- ing from 6 inches to 12 feet in thickness. Chert lenses as much as 4 feet long and 6 inches thick are present, and crinoid-rich beds are abundant. PALEOZOIC ROCKS 15 The band of dark-gray fine-grained limestone at the Lee mine and on the east flank of the Santa Rosa Hills 6,500 feet N. 54° W. of the Lee mine can definitely be assigned to the Tin Mountain limestone on the basis of lithology and stratigraphic succession. The limestone 1 mile S. 80° W. of the Lee mine and in the band at the north end of the Santa Rosa Hills 3.2 miles N. 45° W. of the Lee mine is less certainly assigned to the Tin Mountain. Lithologically the limestone is similar to Tin Mountain. It is mainly a fine- to medium-grained medium-gray limestone that locally contains chert lenses and nodules. Individual beds are a few inches to sev- eral feet thick. Crinoid stems, solitary corals, and syringoporoid corals are abundant in the limestone. However, the‘beds are isoclinally folded and are cut by many faults so that no continuous stratigraphic succes- sion is present and the correlations are mainly lithologic. The fauna] evidence is inconclusive. Section trending S. 16° W. from a point 1.5 miles N. 51° W. of the main shaft of the Lee mine Perdido formation. Conformable contact. Tin Mountain limestone: Feet Limestone, light—gray crinoid-rich, with thin iron- stained partings; chert in lenses attaining .a maxi- mum length of 4 ft and thickness’of 4 in increas- ingly abundant near top of section _______________ 19 Limestone, medium-gray, in beds about 6 in thick; some iron-stained partings and chert lenses _____ 20 Limestone, light-gray, crinoid-rich, in beds 1% to 2 ft thick; small amounts of chert in lenses as much as 4 ft long and 6 in thick ______________________ 31 Limestone, dark-medium-gray; in beds about 1 ft thick; abundant medium-gray, dark-brown weath- ering chert lenses as much as 4 ft long and 4 in thick 41 Limestone, light-gray; a few interspersed crinoidal remnants___ 12 Limestone, medium-gray; abundant chert lenses 3 to 4 ft long and 2 to 4 in thick; moderately abundant crinoids, solitary corals, and brachiopods _________ 14 Limestone, light-gray, crinoidal; moderately abun- dant brown-weathering chert lenses ______________ 43 Marble, white, medium—grained; chert lenses altered White 63 Limestone, light-medium-gray, crinoid-rich; contains dark—gray, dark-brown weathering chert lenses and nodules; maximum dimensions of lenses 18 in long and 2 in thick 62 Limestone, dark-medium-gray; in beds 176 to 2 ft thick; iron-stained reddish-brown shaly partings 1,4 to 1 in thick; widely scattered chert nodules; some syringoporoid corals, solitary corals, and brachiopods 130 Total 435 Conformable contact. Lost Burro formation. Microscopic examination of thin sections shows that the rock is partly recrystallized fine-grained calcarenite. Calcite, which constitutes between 95 and 99 percent of the rock, occurs as subrounded grains of fine-sand size, as subangular recrystallized crystals as large as 0.5 mm in maximum dimension, and as cementing material. Some opaque minerals are generally present. Quartz occurs in very small amounts as cementing material. Randomly oriented tremolite laths that attain maximum dimensions of 5.0 mm in length and 0.2 mm in width are abundant in the bleached white limestone. AGE AND CORRELATION Tin Mountain limestone is Mississippian and prob- ably at least in part equivalent to the Madison group. Numerous corals and brachiopods are in the formation, but the internal structures of most specimens have been obliterated by silicification and recrystallization. Mc- Allister (1952, p. 21), on the basis of paleontologic evidence cited in his Quartz Spring area report, pro- poses that the Tin Mountain limestone is equivalent to the lower part of the Madison group. Several collections of Tin Mountain fossils from the Santa Rosa Hills were examined by Helen Duncan and Mackenzie Gordon, J r., and their findings substantiate an Early Mississippian age for the formation. Col- lections USGS 17 564 and 17567 are from the limestone, band about 3,000 feet S. 25° E. of the Lee mine that can definitely be correlated with the upper unit of the Tin Mountain on the basis of stratigraphic succession. A report by Mackenzie Gordon, Jr. (written communica- tion, May 26, 1953) on brachiopods in collection USGS 17564 is given below: Two of the brachiopod species are represented by at least one well preserved specimen each. These may represent un- described species or variants of known species and appear to have affinities with late Kinderhook or early Osage forms. No definite age determination can be made on these few brachio- pods, but it can be said that they appear to be of Early Mississippian age. The containing rocks are probably referrable to the Tin Mountain limestone of the Quartz Spring area. USGS 17564, Santa Hills, 3,100 feet S. 27° E. of the main shaft of the Lee mine at an altitude of 5,130 feet. Rhipidomella aff. R. dalyaha (Miller) Schizophoriasp. Oleiothyridimt cf. 0. hirsute aff. 0'. mouti (Swallow) The following are excerpts of a report by Helen Dun- can (written communication, June 12, 1953) : The corals in USGS 17564 and USGS 17567 are comparable to genera and species that occur in the Tin Mountain lime- stone. ‘ ‘ ‘ The specimens in USGS 17564 are crudely silicified. The small horn coral cannot be identified because internal structures 16 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. are destroyed. The corallites of the Syrmgopara have about the same size and spacing as those of S. sweater-ta Girty, a species that is widespread in Lower Mississippian rocks of the West. USGS 17567. Santa Rosa Hills, 2,300 feet S. 25° E. of the Lee mine along the saddle in the ridge. Syringopom cf. S. aculeata Girty cf. S. surcularta Girty Yavorslcta? sp. indet. Vemlophyllum sp. indet. * * * The Syringoporas are types common in the Lower Mississippian of the West. Vesiculophyllum seems to be diag- nostic of the Lower Mississippian in the Great Basin and the Southwest. This coral assemblage is appropriate for the Tin Mountain. Several collections of corals and brachiopods were made from the limestone beds about 1 mile S. 80° W. and 3.2 miles N. 45° W. of the Lee mine, which are as- signed to the Tin Mountain on the basis of lithology. Several collections from the limestone in the area 1 mile S. 80° W. of the Lee mine were reported on by Macken— zie Gordon, Jr. (written communication, Feb. 25, 1953) : This report is based on 20 partly silicified and fragmentary fossil brachiopods from limestones collected at three localities in the southern part of the Santa Rosa Hills * * ". The corals and bryozoans were examined by Duncan. Taken as a whole, the fossils indicate an Early Mississippian age for the contain— ing rocks. USGS 144418. South end of Santa Rosa Hills 1 mile S. 80° W of the Lee mine. Horn corals, indet. Brachiopod Spirife'r sp. A USGS 14419. Santa Rosa Hills 6,100 feet S. 85" W. of the main shaft of the Lee mine. Horn corals, indet. Bryozoan Ertdopom? sp. indet. Brachiopods Rhipidomella? sp. indet. Camamtoeeht'a? sp. Oyrtma n. sp. Composite? sp. indet. USGS 14421. Santa Rosa Hills, 1 mile S. 80" W. of the main shaft of the Lee mine at an altitude of 5,380 feet. Horn corals Brachiopods Leptaena analoga (Phillips) Productid, genus and species indet. Rhiptdomella cf. R. owem? (Hall) Schizophom‘a sp. indet. Tetracamem? sp. Sptm'fer sp. A. The three collections appear to represent approximately the same faunal assemblage. The small narrow Spirifer sp. A, with rather long dental plates and about 5 ribs on each side of a narrow sinus in the pedicle valve, occurs both in USGS 14418 and USGS 14421 along with poorly preserved horn corals that have a general Early Mississippian aspect, according to Miss Duncan. Oyrtma and Leptaena are genera that range through Silurian and Devonian rocks and into the Lower Mississippian. In the western United States Leptaena analoga, (Phillips) is typical of the rocks of Madison age but at one locality is known to range slightly higher. In the mid-continent this species and several Cyrtmas are known in rocks of Kinderhook and Osage age and are not known to range as high as uppermost Osage. Rhtptdomella oweni (Hall) with which several partly crushed silicified specimens are here compared is a widespread lower Osage form. The presence of the large productid, though too poorly preserved to identify even as to genus, precludes a De vonian age for the assemblage. The rest of the specimens are not well preserved or entire enough to add any evidence to that discussed above. In summary, the fossils can be said to represent an Early Mississippian (Madison) fauna. In terms of mid-continent stratigraphy they are believed to be not younger than Osage in age and may be Kinderhook in age. Regarding the corals in USGS 14421, Helen Duncan (written communication, Feb. 25, 1953) reported: This collection contains several specimens and fragments of horn corals. The smaller forms appear to be zaphrentoids. The two larger corals show indications of dissepiments and are probably either caninoids or clisiophyllids. Corals of this general type occur in the Tin Mountain limestone of the Pana- mint Range. Three collections of corals were reported on from the band 3.2 miles N. 45° W. of the Lee mine. Fossils collected by J. F. McAllister from this band were ex- amined by James Steele Williams and Helen Duncan. Williams (written communication, Jan. 18, 1949) reported: USGS 17663. Four miles N. 39° W. of the Lee mine on the south side of the first gully south of the basalt capping. Zaphrentoid horn corals, small, indet. Lithostrotion sp. indet. (phaceloid type) Crinoid columnals Composite? sp. indet. Of the corals, Miss Duncan says: “The small horn corals are fragmentary and silicifled and indeterminate but they seem to be the zaphrentoid types that are common in Early Mississip- pian faunas. The'presence of Lithostrotion in this collection is a strong support for a Mississippian age assignment. Al- though the specimen is recrystallized and not specifically iden- tifiable, there can be little doubt that it is a simple lithostro- tionoid type with a styliform columbella. Such corals first ap- pear in the Lower Carboniferous. Phaceloid lithostrotionoids ‘seem to have developed somewhat later than the massive forms, which occur sporadically in assemblages of late Kinderhook age.” Two other collections from the same band but prob- ably higher in the formation were examined by Miss Duncan (written communication, June 12, 1953). USGS 17566. 3.45 miles N. 46° W. of the main shaft 01' the Lee mine at an altitude of 6, 080 feet. ’ ~ This collection consists of several pieces of lithostrotionoid corals and a single fragment of a zaphrentoid. The material is so thoroughly recrystallized that sections are useless. The weathered surfaces indicate that one of the species is a phace- PALEOZOIC ROCKS 17 loid Lithostrotion. The other colonial coral is a massive form that belongs to either Lithostrotion or Lithostrotionella. The presence of lithostrotionoid corals suggests that the rocks are probably Mississippian * * * USGS 17565. 3.7 miles N. 44° W. of the main shaft of the Lee mine at an altitude of 6,080 feet. This collection consists of a number of silicified and frag- mentary corals and bryozoan. Silicification is so crude that structures needed to identify the corals are obliterated. In addition to the bryozoan Custodietya sp. indet, this lot contains a small piece of a lithostrotionoid coral that is probably either Eithostrotionella or Thysanophyllam and at least three types of zaphrentoid corals. USGS 17565 and 17566 appear to have come from beds of approximately the same age. The corals, however. are difier- ent from any that I have previously studied from this region. The fauna is apparently of Mississippian age, and might even be from the Tin Mountain, though it could be later. Although this limestone at the north end of the Santa Rosa Hills lithologically resembles Tin Mountain lime- stone most closely, it can not be ruled out that it is not part of the Perdido formation or Lee Flat limestone. It does not resemble beds as young as the basal Keeler Canyon formation (Atoka). PERDIDO FORMATION NAME AND DISTRIBUTION The Perdido formation was named by McAllister (1952, p. 22) from exposures in the Quartz Spring area. Rocks of the formation are best exposed in the Darwin quadrangle on the two prominent hills less than a mile south of the Lee mine. They are also in the northern part of the Santa Rosa Hills and in a narrow belt ex— tending southeastward from the southern part of the Talc City Hills to the northwestern part of the Darwin Hills (fig. 2). McAllister (1952, p. 23—24; 1955, p. 12) described Perdido rocks from the Quartz Spring area and Ubehebe Peak quadrangle, and Merriam (1954, p. 11) described them in the Inyo Mountains. The Perdido formation crops out at the north end of the Argus Range in the Modoc district and on the west flank of the Panamint Range in the Panamint Butte quadrangle (Hall and Stephens, in press). THICKNESS AND STRATIGRAPHIG RELATIONS The Perdido formation ranges in thickness from 177 to more than 334 feet in the Darwin quadrangle. Most contacts of the Perdido are faulted, but the maxi- mum thickness seems to be about 334 feet. A thickness of 610: feet was measured for the Perdido formation at its type locality in the Quartz Spring area by Mc- Allister (1952, p. 24), Who stated that the formation varies greatly in thickness. The Perdido formation conformably overlies Tin Mountain limestone, and in the Darwin quadrangle is conformably overlain by Lee Flat limestone. The con- tact With the underlying Tin Mountain limestone is gradational and is placed at the first bedded chert in the section. The contact with the overlying Lee Flat limestone is sharp. The Rest Spring shale, which over- lies the Perdido formation in the adjacent Ubehebe Peak quadrangle and Quartz Spring area (McAllister, 1952, p. 25; 1955, p. 13) is present only in fault zones in the Darwin quadrangle. LITEOLOGY The Perdido formation consists predominantly of gray medium-bedded limestone and interbedded chert. The lower part of the Perdido is predominantly lime- stone and thin beds of chert, whereas chert is prevalent at many places in the upper part. The limestone is mostly fine grained, although coarse elastic beds com- posed mainly of crinoid columnals are common. The color ranges from bluish-gray to dark-gray, and near intrusive rocks the limestone is bleached White. The lower part of the Perdido resembles the upper part of the Tin Mountain limestone. However, the Tin Moun- tain contains lenses and nodules of chert, and the Per- dido contains thin chert beds. The chert is gray on fresh surfaces and weathers dark brown. Chert is in beds generally less than 4 inches thick interbedded with limestone in the lower part of the Perdido. In the Santa Rosa Hills near the Lee mine, A partial section of the Perdido 331, feet thick measured from a southward-treading traverse from a point 0.90 mile S. 39“ E. of the main shaft at the Lee mine Lee Flat limestone : Conformable contact. Perdido formation: Feet Metamorphosed zone consisting of marble and white calcsilicate rock, some interbedded chert in beds 1 to 4 in thick, and 1-ft-thick beds of unsilicated medium-gray silty limestone _____________________ 62 Siltstone, medium-brown, dark-brown weathering; in beds 1 to 2 in thick ______________________________ 9 Limestone, medium gray, in beds 1 to 4 in thick, and interbedded chert in beds that average about 1 ft in thickness; a few limestone lenses within the chert ___________________ 21 Chert, white, in beds 1 to 2 ft thick ________________ 61 Limestone, medium-gray, in beds commonly 2 to 8 in thick with interbedded dark-gray, dark brown weathering chert 1 in to 1 ft thick; limestone in upper part of unit locally silty ___________________ 117 Limestone, medium- and light-gray, bleached; in beds 2 to 4 in thick and containing interbedded chert 2-in-thick, chert is pinkish white and limestone partly silicated _____ 64 Total ____________________________________ Fault contact with Tin Mountain limestone. 334 18 GEOLOGY AND ORE DEPOSITS, DARWIN chert beds as much as 61 feet thick and some siltstone are more abundant than limestone in the upper part. However, most stratigraphic sections of Perdido lack thick beds of chert in the upper part, and the forma- tion mostly has a uniform appearance of limestone and thin beds of chert. The Perdido band that trends southeastward from the southern part of the Talc City Hills into the Darwin Hills consists of thinly bedded chert and limestone (pl. 1) . The limestone and chert, which weather brown, are thinly bedded. No thick beds of chert are present. The upper clastic siltstone, sandstone, shale, and lime- stone unit of the Perdido at the type locality (McAl— lister, 1952, p. 22) is not present in the Darwin quad- rangle except for one fossiliferous locality in the eastern part of the Tale City Hills. The Darwin Perdido sec- tion correlates well lithologically and in thickness with the lower limy part of McAllister’s type Perdido section. Thin sections of limestone from the Perdido forma- tion consist largely of irregular and rounded calcite crystals 0.02 to 0.03 mm in diameter that are in part recrystallized to coarser calcite rhombohedrons. Chert partly replaces calcite in all sections. Iron oxides, pyrite, and late calcite veinlets occur in small quanti- ties. Tremolite in crystals as much as 3.0 mm long and 0.3 mm wide is interspersed throughout most sections. AGE The only Perdido fossils found in the Darwin quad- rangle besides ubiquitous fragmentary crinoid colum- nals are in the eastern Talc City Hills in an area com- plicated by thrust faulting. The fossils are in a 2-foot- thick limestone bed within a predominantly siltstone unit, which includes large solitary corals, crinoid columnals, and brachiopod fragments. The fauna is too poorly preserved to provide diagnostic age infor— mation. McAllister (1952, p. 24, 25) presents evidence that the formation is Mississippian and includes rocks ranging in age possibly from Osage or late Kinderhook into Chester. MISSISSIPPIAN AND PENNSYLVANIAN(P) SYSTEM LEE FLAT LIMESTONE NAME AND DISTRIBUTION The Lee Flat limestone was named for exposures on the southwest side of Lee Flat (Hall and MacKevett, 1958, p. 8). The type locality Of the formation trends southward from an altitude of 5,280 feet near the top of the prominent hill 0.9 miles S. 36° E. of the main shaft of the Lee mine to the contact with alluvium at the foot of the hill at an altitude of 5,000 feet. The most accessible good exposure of the formation is on the hill 3,000 feet south of the Lee mine where a section QUADRANGLE, INYO COUNTY, CALIF. FIGURE 5.—Lee Flat limestone (PMI) viewed south from the Lee mine. The Lee Flat limestone conformably overlies the Perdido formation (Mp). This is the most accessible section of Lee Flat limestone, but was not designated as the type locality because of the interruption of the section by steep faults (f). which, in turn overlies the Tin Mountain limestone (th). from the Lost Burro formation to Lee Flat limestone is exposed. This exposure was not designated as the type locality as the section is faulted (fig. 5). The Lee Flat is also exposed in a strip 4% miles long along the north- east slope of the Santa Rosa Hills, and in a band that extends from the northwestern part of the Darwin Hills into the southern part of the Talc City Hills, generally in fault-bounded outcrops (pl. 1) . The formation is in a horst at the Zinc Hill and Empress mines in the Argus Range. Calc-hornfels exposed in Rainbow Can- yon and adjacent canyons in the eastern part of the quadrangle is probably mainly metamorphosed Lee Flat limestone. The formation commonly weathers to smooth surfaces that retain the dark-medium-gray of the unaltered rock. Locally, parts of the formation form craggy outcrops and minor cliffs. THICKNESS AND STRATIGRAPHIG RELATIONS Lee Flat limestone conformably overlies the Perdido formation, but its upper contact is not exposed in the Darwin quadrangle. The contact between the Lee Flat limestone and Perdido formation is marked by a change from interbedded limestone and chert near the top of the Perdido formation to thin-bedded Lee Flat lime- stone. The formation is at least 520 feet thick at its type locality—this thickness represents an incomplete section that was measured southwestward from the apparently conformable contact with the Perdido for- mation to a point where alluvium conceals the bedrock. The formation has an estimated maximum exposed thickness of 960 feet in the Santa Rosa Hills 4,7 00 feet N. 67° W. of the main shaft of the Lee mine, and the PALEOZOIC ROCKS 19 thickness is at least as great 3,000 feet south of the Lee mine on hill 5594. Owing to complex folding and faulting in both places, however, the section was not designated as a type locality. LITEOLOGY Lee Flat limestone consists mainly of thin-bedded fine-grained dark-medium-gray limestone admixed with small amounts of silt and clay. The formation is gen- erally uniform in appearance and consists largely of calcilutite. Locally the limestone contains iron-stained partings or small lenses or thin beds of chert. The formation is divisible into two units at the type locality. The lower unit, 136 feet thick, is predomi- nantly thin—bedded, dark-medium-gray limestone but includes a few dark—gray, brown-weathering chert lenses and nodules and locally crinoid—rich beds. Iron— stained partings are moderately abundant near the top. The upper unit, which is at least 384 feet thick, differs from the lower unit by its absence of chert and the moderate abundance of 11/2- to 3-inch.thick iron-stained partings in parts of the section. The prevailing dark— medium-gray thin-bedded limestone of this unit is 10- cally cut by narrow veinlets of white calcite. Thin section study of the Lee Flat limestone shows that the rock is calcilutite and consists chiefly of small subrounded calcite grains that are less than 0.05 mm in average maximum diameter but that attain maximum diameters of 0.10 mm. Quartz, opaque minerals, and limonite make up about 1 to 2 percent of most sec- tions. Elongate tremoli-te crystals as much as 4.0 mm long are abundant. AGE, CORRELATION, AND ORIGIN Crinoid fragments are the only fossils found in the Lee Flat limestone. The formation is probably a time- stratigraphic equivalent of the upper elastic part of the Perdido formation and the Rest Spring shale of the Ubehebe Peak quardrangle (McAllister, 1956) and is Mississippian and Pennsylvanian(?) in age (fig. 6). Time equivalence is indicated by Rest Spring shale con— formably overlying the Perdido formation in the Quartz Spring and Ubehebe Peak areas (McAllister, 1952, p. 23; 1955, p. 13) and the Lee Flat limestone conform— ably overlying limestone and bedded chert that corre- lates with the lower unit of the Perdido formation at the type locality (McAllister 1952, p. 23). The Rest Spring shale in the Ubehebe Peak quadrangle is con- formably overlain by thinly bedded limestone of Atoka or early Des Moines age (McAllister, 1956). The upper contact of the Lee Flat is not exposed in the Darwin quadrangle, but in the adjacent Panamint Butte quad- rangle the writers have mapped'Lee Flat limestone that is conformably overlain by thinly bedded limestone of Atoka or early Des Moines age. The lower rocks of the Perdido are Mississippian and probably are Osage or late Kinderhook (McAllister, 1952, p. 24). The Lee Flat limestone therefore is younger than late Kinder— hook or Osage (early Mississippian) and older than Des Moines (Middle Pennsylvanian). In a reconnaissance of parts of the Argus Range south and east of the Darwin quadrangle in the Modoc district the writers observed marble of the Lee Flat limestone. The marble underlies the Keeler Canyon formation and overlies limestone and bedded chert of the Perdido formation. No shale is present between the Perdido formation and the Fusulinella zone at the base of the Keeler Canyon formation. The lithology of the Lee Flat limestone is transitional between the elastic Upper Mississippian and Pennsylvanian( ’4’) section in the Ubehebe Peak area and the massive, cliff-forming upper Monte Cristo limestone of the Nopah-Resting Springs area (Hazzard, 1954, p. 880). The cliff-forming Lee Flat limestone observed by the writers in‘ the Argus Range lithologica'lly resembles the Bullion limestone member of the Monte Cristo limestone described by Hazzard (1954, p. 881). PENNSYLVANIAN ( P) SYSFI‘EM REST SPRING SHALE Rest Spring shale was named by McAllister (1952, p. 25) in the Quartz Spring area. Shale in the Darwin quadrangle that is mapped as Rest Spring on the basis of lithologic similarity is found only in several small outcrops in fault zones at the north end of the Santa Rosa Hills, at four places in the thrust fault in the Talc City Hills, and in a fault in the hills south of State Highway 190 about 2 miles N. 57° E. of the Silver Dol- lar mine (pl. 1). In the Tale City Hills 0.7 miles south of the Talc City mine both Rest Spring shale and Lee Flat limestone are present, but the exposures are poor; so the nature of the contacts is not known. It is likely that the association of Rest Spring shale with Lee Flat limestone indicates interfingering of the two formations. The Rest Spring shale in the Darwin quadrangle is at least in part equivalent to the Chainman shale north- west of the Darwin quadrangle in the Inyo Mountains (Merriam and Hall, 1957, p. 4). The Chainman in the Inyo Mountains is the same unit as the black shale referred to the upper part of the White Pine shale of the Inyo Mountain (Kirk, in Knopf, 1918, p. 38; Merriam, 1954, p. 11). In the Darwin quadrangle the Rest Spring shale consists predominantly of dark-brown fissile argillace- ous shale and minor siltstone. Discoidal siliceous con- cretions that have a maximum dimension of about 6 inches are in the shale in the thrust fault at the Silver Dollar mine and at the northwest end of the Tale City 20 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. QUARTZ SPRING AREA CALIFORNIA McAIlister (1952) PENNSYLVANIANl?) PENNSYLVANIAN MISSISSIPPIAN DEVONlAN Lower (?) Mississippian Tihvipah limestone Fossils of late Atoka or early Des Moines age Rest Spring Upper unit Perdido f/ormation / / / r: c 3 L a: 3 o _l Tin Mountain limestone Lost Burro formation @ Limestone, thick bedded Bedded chert % Limestone. thin bedded Slltstone DARWIN QUADRANGLE CALIFORNIA This report Keeler Canyon formation Fossils of Atoka or }' Lee Flat limestone Perdido formation Tin Mountain limestone Lost Burro formation EXPLANATION Sandy limestone Shaly limestone Limestone containing chert nodules Kv 9‘0, “ - E 3“.) Shale and sulty shale Marble Dolomite qunm 6.—Correlatton of Carboniferous formations of the Quartz Spring area and Darwin quadrangle. PENNSYLVANIAN MISSISSIPPIAN AND PENNSYLVANIANC’) MISSISSIPPIAN DEVONlAN 200 400 FEET PALEOZOIC ROCKS 21 Hills 1.3 miles north of the northernmost workings of the White Swan mine (pl. 2). The Rest Spring shale may be allochthonous in the Darwin quadrangle. Wherever Mississippian and Pennsylvanian rocks are exposed in normal strati- graphic sequence in the quadrangle, the Lee Flat lime- stone is below the Fusulinella. zone of the Keeler Canyon and shale is absent. Several major faults trend N. 20° W. in the Santa Rosa Hills; they are probably left- lateral strike-slip faults. Except for a small outcrop at the north end of the Talc City Hills the Lee Flat limestone is either east of the westernmost strike-slip fault (the Santa Rosa Flat fault) in the Santa Rosa Hills or south of the Darwin tear fault, and the faulted exposures of Rest Spring shale are all west of the Santa Rosa Flat fault. Although the Rest. Spring shale is found only in fault zones, so many faulted slivers of it are exposed in the Tale City Hills that it probably oc- curs in the northwestern part of the quadrangle under a deep cover of younger rocks. The shale and limestone facies may be contiguous in the Santa Rosa Hills be- cause of left-lateral strike—slip faulting on the Santa Rosa Flat fault (pl. 1). AGE AND CORRELATION The Rest Spring shale is the time equivalent of part of the Lee Flat limestone of the Darwin quadrangle (fig. 6). The upper black shale of the Chainman in the Inyo Mountains is also correlative with the Rest Spring shale (McAllister, 1952, p. 26). The age of the Rest Spring is equivocal. No fossils were found in it in the Darwin quadrangle. Kirk (in Knopf, 1918, p. 38), Merriam (1954, p. 11), and Mer- riam and Hall (1957, p. 5) considered the dark shale beds of the Chainman in the Inyo Mountains to be Late Mississippian. McAllister (1952, p. 26) considered the Rest Spring shale to be Pennsylvanian( ?). In this report the Rest Spring in the Darwin quadrangle is considered Pennsylvanian ( ?) . PENNSYLVANIAN AND PEBMLAN SYSTEMS Pennsylvanian and Permian rocks predominate in the northwestern and southeastern parts of the quad- rangle and constitute the most widespread and thickest Paleozoic sedimentary rocks; they have an aggregate thickness greater than 5,900 feet. These rocks are mainly silty limestone but include pure limestone, shale, siltstone, arenaceous limestone, and conglomerate. Well—defined lithologic changes that could be used as formational boundary markers are lacking. Pennsyl- vanian and Permian rocks are similar to those described by Merriam and Hall (1957) from the southern Inyo Mountains, and their names—Keeler Canyon and Owens Valley formations—are used in this report. Because of the gradational nature of the rock types, some contacts may not be precisely at the same strati- graphic position as at the type locality. Lateral varia- tions in lithology in parts of the Pennsylvanian and Permian section are also a deterrent to precise strati- graphic correlation. McAllister (1955, p. 13) provi- sionally used the name Bird Spring( ‘9) formation for similar Pennsylvanian and Permian rocks in the Ubehebe Peak quadrangle. The Keeler Canyon and Owens Valley formations consist largely of clastic and limy deposits whose con- stituent particles range in size from silt to boulders. Characteristics indicative of shallow-water, nearshore deposition, such as crossbedded calCarenites and coarse conglomerate with subangular limestone fragments, are common. Disconformities in the Keeler Canyon and Owens Valley section are indicated by recurrence of fossiliferous pebble conglomerates that contain limestone pebbles of the Keeler Canyon in the lower part of the section and coarse conglomerate at Con- glomerate Mesa. Local angualr unconformities are present but are not common. Broad undulatory folds and moderate relief char- acterize most exposures of the Keeler Canyon and Owens Valley formations. Where the rocks are sili- cated, the relief is more rugged. The formations can commonly be recognized from a distance by the folded nature of the incompetent rocks in contrast to the throughgoing nature of the older strata (fig. 7). FIGURE 7.—Photograph showing the folded, Incompetent nature of the Pennsylvania and Permian strata (PP K) in contrast to the through- going nature of the adjacent Lost Burro formation (le) of Devonian age. The contact is a fault. View looking west at the east side of the Talc City Hills near the Silver Dollar mine. 22 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. HELER CANYON FORMATION NAME AND DISTRIBUTION The name Keeler Canyon formation was proposed by Merriam and Hall (1957, p. 4) for the thick sequence of rocks east of the Estelle tunnel portal at the head of Keeler Canyon in the New York Butte quadrangle 2 miles southwest of CerroiGordo Peak. Exposures of the formation in the Darwin quadrangle are on the west flank of the‘northern part of the Santa Rosa Hills, in the adjacent low hills to the northwest, and in the Talc City Hills and Darwin Hills (pl. 1). Conspicuously folded Keeler Canyon strata crop out in the eastern Talc City Hills and northwestern Darwin Hills and can be readily seen from State Highway 190. Generally the formation weathers to smooth slopes, but locally re- sistant beds form riblike outcrops and shaly parts form subdued topography. THICKNESS AND STRATIGRAPEIC RELATIONS There is no complete Keeler Canyon formation sec- tion suitable for stratigraphic measurement in the quad- rangle. Partial sections were measured east of the Conglomerate Mesa road in the northwestern part of the quadrangle, in the Darwin Hills northeast and southwest of the Darwin Antimony mine, and on the west flank of the Santa Rosa Hills west of hill 6170 (pl. 1). These sections indicate a minimum thickness of 4,000 feet for the formation. The contacts with the underlying Lee Flat limestone or with the Rest Spring shale are faults. The conformable upper contact is gradational and difficult to define accurately. It is placed at the top of a predominantly pinkish shale unit stratigraphically below the inception of a chiefly silty and shaly limestone containing lenses of pure limestone or limestone conglomerate. LITI-IOLOGY The Keeler Canyon formation is divided into two units, a lower unit at least 2,300 feet thick consisting mainly of bluish—gray limestone and limestone pebble conglomerate, and a 1,770-foot-thick upper unit com- posed largely of pinkish shales and shaly limestone. Limestone pebble conglomerate, although not confined to Keeler Canyon rocks, is sufficiently abundant to be a characteristic of the formation. LOWER UNIT The 500 feet of the lower unit is best exposed in the northern part of the Santa Rosa Hills. Thinly bedded dark-gray limestone and intercalated 1- to 4-foot—thick gray limestone pebble conglomerate beds containing small fusulinids about 2 mm long and minor chert ’ nodules constitute the lowermost 100 feet of the mem- ber. Spheroidal, black chert nodules about 1/2 to 2 inches in maximum diameter are conspicuous in the thicker limestone beds near the base. This zone is a reliable stratigraphic marker and is referred to as the “golfball” horizon. The superjacent 400 feet of sec- tion consists mainly of medium-gray shaly limestone intercalated with medium-gray limestone pebble con- glomerate in beds 1 to 4 feet thick that contain fusuli- nids 3 to 5 mm long. Some of the pebbles are com- posed of subrounded chert. Minor iron-stained part- ings and scattered crinoid debris are in parts of the thinly bedded limestone. West of the Darwin Antimony mine and southwest of the Darwin tear fault, strata of the lower member appear to be at least 2,300 feet thick, but the section is folded and faulted. It consists mainly of thin-bedded medium- and light-medium-gray limestone but includes local chert nodules, iron-stained partings, and crinoidal beds. Light-gray, brown-weathering silty limestone and calc-hornfels are abundant in the upper part of the member. The contact between the lower and upper units is gradational and is marked mainly by prevalent interbedded limestone and pink shale in the overlying unit. Pink shale is present but is not abundant in the lower unit. Metamorphosed rocks in the central part of the Dar- win Hills at the Darwin mine are correlated with the lower part of the Keeler Canyon formation ontpale- ontologic and lithologic evidence. Thinly bedded bluish-gray limestone and calc-hornfels containing spheroidal chert nodules '15 to 1 inch in diameter are interbedded with calc-hornfels in the inverted syncline on the south slope of Ophir Mountain (pl. 3). Locally poorly preserved tiny fusulinids were observed in the limestone. This limestone and calc-hornfels zone, which is in fault contact with limestone lithologically identical to the Lee Flat limestone, is undoubtedly the golfball horizon at the base of the Keeler Canyon formation. UPPER UNIT The upper unit of the Keeler Canyon formation crops out in the Darwin Hills on hill 5979 east of the Darwin Antimony mine, in the low hills for 3 miles northwest of hill 5979, and in the northwestern part of the quad- rangle 3 miles east of Conglomerate Mesa (pl. 1). It consists of thinly bedded bluish-gray calcilutite, fine- grained calcarenite, and pink shale and forms pinkish- gray slopes where unmetamorphosed in contrast to the grayish hue of slopes underlain by the lower member. This is particularly apparent in the low hills north of the Darwin Antimony mine. In the eastern part of the PALEOZOIC ROCKS , 23 rphosed to calc— orown on weath- {Xg aces. The dark- e‘o‘cia" ‘1”, in sharp contrast €96 ‘0?)9 “s 09 pholsed lower unit. . \ea. $9 a 4it a on a traverse ‘2") $296 €$e90140 feetg east of the X9 9 . . .564 \‘b‘b' 009 gQ .¢;§\Viony mine are sum- 9 ’6’» a?» 0 \x . .9049 60‘ a)?” $9 (35:36 1s overturned; the e ' - ' Q; 0‘19 «‘9‘ KO sage west, but their tops ‘0‘ ‘92) \0‘59 ‘Q 0" ”€90 5% :15; X)‘ e9 gs, the south ahwft at Darwin ’8‘ sp. a“ $9 eV'w ’39 .39 ‘0 \3 . e,3 n 90 {b \E ‘0 35’ V Feet e 0V 6-" :mation: ‘5 (filly and silty limestone; fa $°°:stone and pebble con- 39/ ‘ istitute about 60 percent '32-. 0». _______________________ 410 2% C; . .h-gray, 2 to 10 ft thick 6 ‘9‘ nkish-gray, locally brown- ‘j‘ 50 ft thick. Crossbedding one ______________________ 175 «my __________________________ 100 ., pinkish-gray, containing a 10-ft .ale; section cut by minor faults ______ 135 light-pinkish-gray, massive; locally cut .icite veinlets 200 .estone light- and medium-gray, sandy and silty; in beds 1 to 2 ft thick; minor shaly partings ______ 190 Limestone and fusulinid—bearing limestone pebble conglomerate containing a 15-ft thick pink limy shale 190 Limy shale, largely pink, and shaly limestone; brown and grayish-brown-weathering silty limestone and locally crossbedded fusulinid-bearing limestone pebble conglomerate are interbedded with pink shale in lower part of the section _________________ 300 Total ___ 1, 700 Gradational contact. Lower unit of the Keeler Canyon formation : The upper part consists mainly of light-mediums gray limestone with iron-stained partings and medium-gray fusulinid—bearing limestone pebble conglomerate in beds 1 to 2 ft thick. Shaly lime- stone is progressively more abundant near the upper contact. The higher parts of the upper unit are well exposed 3 miles east of Conglomerate Mesa where pink shale and subordinate brownish-gray-weathering silty lime— stone of the upper unit of the Keeler Canyon forma- tion grade into a conformable sequence of predom- inantly brown-weathering platy and silty limestone and subordinate shale of the lower part of the Owens Valley formation. Pink shale makes up about two- thirds of the upper 800 feet of the Keeler Canyon formation; the remainder is brown-weathering shale and silty limestone in beds 6 inches to 2 feet thick, and minor fusulinid-bearing limestone pebble conglomer- ates. The pink shale is underlain by 150—foot-thick light-gray to buff, tan-weathering siltstone. Below the siltstone the Keeler Canyon formation consists mainly of medium-gray and pinkish-gray, light-brown weath- ering thin-bedded silty limestone interbedded with lesser amounts of pink shale for an exposed thickness of 450 feet. AGE AND connnurrox The Keeler Canyon formation ranges in age from probable Atoka or Des Moines (Middle Pennsylvanian) to Wolfcamp (early Permian). Fusulinids are the most abundant fossils, but in many places their struc- tures are obscured by silicification and deformation. The lower unit of the Keeler Canyon formation con— tains fossils that range in age from probable late Atoka or early Des Moines to Wolfcamp. The lowermost ap- proximate 200 feet of the formation is in part equiv- alent to McAllister’s (1952, p. 26—27) Tihvipah lime- stone and paleontologically is characterized by small fusulinids of probable Atoka age. The following is a summary of a report by Lloyd G. Henbest (written communication, 1953) on a col- lection made near the base of the Keeler Canyon for- mation in the Santa Rosa Hills. £9591. Pennsylvanian, Atoka or Des Moines age. Locality 1.65 miles S. 79° W. of the Lee mine at an altitude of 5,270 feet. Calcareous algae Olimacammim sp. Endothym sp. Millerella? sp. Fusulinella or Wedelamdellma sp. Fueulmella or possibly an early form of Fusulma sp. The specimens are poorly preserved. The fusulinids are identified generically with only fair assurance and indicate Atoka or possibly very early Des Moines age. The other foraminifers listed give support but of very limited value to this age determination. The species of calcareous algae that seems to be represented here is a fossil of common occurrence in rocks of Atoka and Des Moines age. Though all of the species listed agree in indicating Atoka or possibly early Des Moines age, it is not certain that they are not of early Permian age. A collection made about 400 feet stratigraphically above the base of the formation in the Santa Rosa Hills is considered to be probable late Wolfcamp in age by R. C. Douglass (written communication, 1953) in a summarized report as follows: £9647. Permian. Locality in Santa Rosa Hills 3.60 miles N. 50° W. of the Lee mine at an altitude of 5,650 feet. Olimacammmw sp. Schubertella? Stafellahp. Triticites? Schwagefim spp. at least two forms The material in this collection is poorly preserved. mian, probably late Wolfcamp, in age. It is Per- 24 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, 1. The occurrence of Wolfcamp and probable Middle Pennsylvanian fossils within a stratigraphic interval of a few—hundred feet in the northwestern part of the quadrangle compared with a much thicker Pennsyl- vanian section elsewhere in the southern Inyo Moun- tains (Merriam and Hall, 1957, table 2) and Darwin quadrangle suggests a hiatus within the lower unit of the Keeler Canyon. The possibility of an un— conformity cannot be ruled out, but the only physical evidence for it is the limestone pebble conglomerate beds that are concordant in the stratigraphic sequence and show no effects of erosion. TWO collections from near the upper contact of the Keeler Canyon formation were examined by R. C. Doug- lass (written communication, 1954). These collections, which are from the rolling hills northwest of the Santa Rosa Hills, contain Ulimaoammz'm sp., Schwagem'na‘, probably two or three fairly advanced species, and Pseudoschwageri’na. sp. Douglass believes this fauna is probably late Wolfcamp. Douglass (written communi- cation, 1954) studied a collection from the northern Dar— win Hills from the upper unit and provided the follow- ing faunal list and comment: f9746. Locality in Darwin Hills 1.70 miles N. 48“ W. of the Darwin Antimony mine at an altitude of 5,200 feet. Small indeterminate forams. Climacamxmi/rw sp. Tetratamfis sp. Schubertella! Sehwagem‘na spp. at least three species This collection contains a fauna characteristic of the upper- most part of the type Wolfcamp, but it may be as young as early Leonard. Two collections from the transitional zone between the Keeler Canyon and the lower part of the Owens Valley formation in the northern Darwin Hills were examined by Douglass (written communication, 1954) : F9748. Locality 0.93 miles N. 15° W. of the Darwin Antimony mine at an altitude of 5,290 ft and 1.20 miles N. 33° W. of VABM 5979. Oltmacammina sp. Tetratawis? Endothyra? Schwagerina spp. One aff. S. compacta (White) Douglass believes this fauna probably represents Wolfcamp, possibly middle to late Wolfcamp. F9749. Locality at north end of Darwin Hills at an altitude of 5,400 ft. Located 660 feet north of VABM 5979. Calcitornellids Climacammma sp. Tritim’tes sp. Schwagerma spp. (possibly 3 species) One aff. S. diverstformis Dunbar and Skinner Another aff. S. linearis Dunbar and Skinner Pseudoschwagerma sp. Parafusu'lma ? Douglass states :OOQV ?7 This assemblage cox. 1 most part of the Wolft formations. -It can proba. with fair certainty. The Keeler Canyon fo<‘oQ Q correlates reasonably well '01. 012 t in the Inyo Mountains (Men or o [be However, because of lateral véoo be 0.01, 0’ o 91-. the contact between the Keeler . <99, 09,0, ley formations cannot be place 800.9 graphic horizon on the basis of 11%.] Canyon is partly equivalent to the 16‘ of the Quartz Spring area (McAll. and to part of the Bird Spring( ?) _ Ubehebe Peak quadrangle (McAlliste Pennsylvanian rocks that correlate with t yon formation were recognized in the Ar Hopper (1947, p. 411). 0 4 £11,: OWENS VALLEY FORMATION NAME AND DISTRIBUTION The Owens Valley formation was named by Me and Hall (1957, p. 7) for strata of Permian age that exposed in the foothills of the Inyo Mountains abou miles north of Owenyo (fig. 2). The Owens Valle formation near the type locality includes two forma- tions previously described by Kirk (in Knopf, 1918, p. 42—43)——the Owenyo limestone and Reward con- glomerate, now considered local members of the Owens Valley. The formation is well exposed in the northwestern part of the Darwin quadrangle east and southeast of Conglomerate Mesa, in the southeastern part of the quadrangle in the Argus Range, and at the north end of Darwin Wash between the Argus Range and Darwin Hills (pl. 1). The formation is subdivided informally into three units. The lowest unit is the thickest and is the most widely distributed. It is the only formation in the southeastern part of the quadrangle, and it underlies most of the low rolling hills east of Conglomerate Mesa. The middle unit occurs as a narrow band surrounding Conglomerate Mesa, while the upper unit forms the resistant capping and cliff exposures Of Conglomerate Mesa (fig. 8). LOWER UNIT THICKNESS AND STRATIGRAPHIO RELATIONS Where best exposed east of Conglomerate Mesa, the lower unit is about 2,800 feet thick. This thickness was computed from a measured stratigraphic section east of Conglomerate Mesa, but many minor folds and faults PALEOZOIC ROCKS . 23 Darwin Hills,'the member is metamorphosed to calc- hornfels and hornfels that are dark-brown on weath- ered surfaces and gray on fresh surfaces. The dark- brown metamorphosed upper unit is in sharp contrast to the white and light—gray metamorphosed lower unit. Lithologic details of the upper unit along a traverse that trends N. 70° E. from a point 140 feet east of the south shaft at the Darwin Antimony mine are sum- marized below. The section here is overturned; the beds strike north and dip steeply west, but their tops are to the east. Section of upper unit 140 feet east of the south shaft at Darwin Antimony mine Lower part of Owens Valley formation. Conformable contact. Feet Upper unit of the Keeler Canyon formation: Limy shale, pink and gray; shaly and silty limestone; and fusulinid-bearing limestone and pebble con- glomerate. Shaly rocks constitute about 60 percent of section Silty limestone, light-pinkish—gray, 2 to 10 ft thick inter-bedded with light-pinkish-gray, locally brown- weathering shale 10 to 20 ft thick. Crossbedding present locally in limestOne ______________________ Limy shale, pinkish-gray __________________________ Limestone, massive, pinkish-gray, containing a 10-ft thick pink shale; section cut by minor faults ______ Limestone, light-pinkish-gray, massive; locally cut by calcite veinlefs Limestone light- and medium-gray, sandy and silty; in beds 1 to 2 ft thick; minor shaly partings ______ Limestone and fusulinid—bearing limestone pebble conglomerate containing a 15-ft thick pink limy shale Limy shale, largely pink, and shaly limestone; brown and grayish-brown-weathering silty limestone and locally crossbedded fusulinid—bearing limestone pebble conglomerate are interbedded with pink shale in lower part of the section _________________ 410 175 100 135 190 190 300 1, 700 Total Gradational contact. Lower unit of the Keeler Canyon formation : The upper part consists mainly of light-mediumu gray limestone with iron-stained partings and medium-gray fusulinid-bearing limestone pebble conglomerate in beds 1 to 2 ft thick. Shaly lime- stone is progressivgly more abundant near the upper contact. The higher parts of the upper unit are well exposed 3 miles east of Conglomerate Mesa where pink shale and subordinate brownish-gray-weathering silty lime- stone of the upper unit of the Keeler Canyon forma- tion grade into a. conformable sequence of predom- inantly brown-weathering platy and silty limestone and subordinate shale of the lower part of the Owens Valley formation. Pink shale makes up about two- thirds of the upper 800 feet of the Keeler Canyon formation; the remainder is brown-Weathering shale and silty limestone in beds 6 inches to 2 feet thick, and minor fusulinid-bearing limestone pebble conglomer- ates. The pink shale is underlain by 150-foot-thick light-gray to bufl', tan-weathering siltstone. Below the siltstone the Keeler Canyon formation consists mainly of medium-gray and pinkish—gray, light-brown weath- ering thin-bedded silty limestone interbedded with lesser amounts of pink shale for an exposed thickness of 450 feet. AGE AND comnurzox The Keeler Canyon formation ranges in age from probable Atoka or Des Moines (Middle Pennsylvanian) to Wolfcamp (early Permian). Fusulinids are the most abundant fossils, but in many places their struc- tures are obscured by silicification and deformation. The lower unit of the Keeler Canyon formation con- tains fossils that range in age from probable late Atoka or early Des Moines to Wolfcamp. The lowermost ap- proximate 200 feet of the formation is in part equiv- alent to McAllister’s (1952, p. 26—27) Tihvipah lime— stone and paleontologically is characterized by small fusulinids of probable Atoka age. The following is a summary‘of a report by Lloyd G. Henbest (written communication, 1953) on a col- lection made near the base of the Keeler Canyon for- mation in the Santa Rosa Hills. f9591. Pennsylvanian, Atoka or Des Moines age. Locality 1.65 miles S. 79° W. of the Lee mine at an altitude of 5,270 feet. Calcareous algae Oltmacam/mxmasp. Endothyra sp. Mtllerella? sp. Fusultnella or Wedelaindelltna sp. Fusulinella or possibly an early form of Fusultna sp. The specimens are poorly preserved. The fusulinids are identified generically with only fair assurance and indicate Atoka or possibly very early Des Moines age. The other foraminifers listed give support but of very limited value to this age determination. The species of calcareous algae that seems to be represented here is a fossil of common occurrence in rocks of Atoka and Des Moines age. Though all of the species listed agree in indicating Atoka or possibly early Des Moines age, it is not certain that they are not of early Permian age. A collection made about 400 feet stratigraphically above the base of the formation in the Santa. Rosa Hills is considered to be probable late Wolfcamp in age by R. C. Douglass (written communication, 1953) in a summarized report as follows: f9647. Permian. Locality in Santa Rosa Hills 3.60 miles N. 50° W. of the Lee mine at an altitude of 5,650 feet. Oltmacammtna sp. Schubertella? Stafietlakp. Trtttcttes? Schwager'i/na spp. at least two forms The material in this collection is poorly preserved. It is Per- mian, probably late Wolfcamp, in age. 24 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. The occurrence of Wolfcamp and probable Middle Pennsylvanian fossils within a stratigraphic interval of a few hundred feet in the northwestern part of the quadrangle compared with a much thicker Pennsyl- vanian section elsewhere in the southern Inyo Moun- tains (Merriam and Hall, 1957 , table 2) and Darwin quadrangle suggests a hiatus within the lower unit of the Keeler Canyon. The possibility of an un- conformity cannot be ruled out, but the only physical evidence for it is the limestone pebble conglomerate beds that are concordant in the stratigraphic sequence and show no effects of erosion. Two collections from near the upper contact of the Keeler Canyon formation were examined by R. C. Doug- lass (written communication, 1954) . These collections, which are from the rolling hills northwest of the Santa Rosa Hills, contain Olimaoammz'na sp., Schwagerina, probably two or three fairly advanced species, and Psewfloschwagem'na sp. Douglass believes this fauna is probably late Wolfcamp. Douglass (written communi— cation, 1954) studied a collection from the northern Dar— win Hills from the upper unit and provided the follow- ing faunal list and comment: £9746. Locality in Darwin Hills 1.70 miles N. 48° W. of the Darwin Antimony mine at an altitude of 5,200 feet. Small indeterminate forams. Olimacamrmma sp. Tetratamfis sp. Schubertella! Schwagem’na spp. at least three species This collection contains a fauna characteristic of the upper- most part of the type Wolfcamp, but it may be as young as early Leonard. Two collections from the transitional zone between the Keeler Canyon and the lower part of the Owens Valley formation in the northern Darwin Hills were examined by Douglass (written communication, 1954) : F9748. Locality 0.93 miles N. 15° W. of the Darwin Antimony mine at an altitude of 5,290 ft and 1.20 miles N. 33° W. of VABM 5979. Olimacammma sp. Tetratams? Endothyra? Schwagem’na spp. One afi. S. compacta (White) Douglass believes this fauna probably represents Wolfcamp, possibly middle to late Wolfcamp. F9749. Locality at north end of Darwin Hills at an altitude of 5,400 ft. Located 660 feet north of VABM 5979. Calcitornellids Olimacammina sp. Triticites sp. Schwagerina spp. (possibly 3 species) One aft. S. diversiformis Dunbar and Skinner Another afi. S. linearis Dunbar and Skinner Pseudoschwagem’na sp. Parafusu'lina ? Douglass states : This assemblage contains elements common to the upper- most part of the Wolfcamp and lower part of the Leonard formations. It can probably be correlated with boundary zone with fair certainty. The Keeler Canyon formation in the Darwin Hills correlates reasonably well With that at the type section in the Inyo Mountains (Merriam and Hall, 1957, p. 4). However, because of lateral variations in the formation, the contact between the Keeler Canyon and Owens Val- ley formations cannot be placed at a precise strati- graphic horizon on the basis of lithology. The Keeler Canyon is partly equivalent to the Tihvipah limestone of the Quartz Spring area (McAllister, 1952, p. 26) and to part of the Bird Spring( ‘9) formation in the Ubehebe Peak quadrangle (McAllister, 1955, p. 13). Pennsylvanian rocks that correlate with the Keeler Can- yon formation were recognized in the Argus Range by Hopper (1947, p. 411). OWENS VALLEY FORMATION NAME AND DISTRIBUTION The Owens Valley formation was named by Merriam and Hall (1957 , p. 7 ) for strata of Permian age that are exposed in the foothills of the Inyo Mountains about 3 miles north of Owenyo (fig. 2). The Owens Valley formation near the type locality includes two forma- tions previously described by Kirk (in Knopf, 1918, p. 42—43)——the Owenyo limestone and Reward con- glomerate, now considered local members of the Owens Valley. The formation is well exposed in the northwestern part of the Darwin quadrangle east and southeast of Conglomerate Mesa, in the southeastern part of the quadrangle in the Argus Range, and at the north end of Darwin Wash between the Argus Range and Darwin Hills (pl. 1). The formation is subdivided informally into three units. The lowest unit is the thickest and is the most widely distributed. It is the only formation in the southeastern part of the quadrangle, and it underlies most of the low rolling hills east of Conglomerate Mesa. The middle unit occurs as a narrow band surrounding Conglomerate Mesa, while the upper unit forms the resistant capping and clifl' exposures of Conglomerate Mesa (fig. 8). LOWER UNIT THICKNESS AND STRATIGRAPHIC RELATIONS Where best exposed east of Conglomerate Mesa, the lower unit is about 2,800 feet thick. This thickness was computed from a measured stratigraphic section east of Conglomerate Mesa, but many minor folds and faults 25 PALEOZOIC . ROCKS 638:8 933 h¢=d> 3530 23 no mnmmouauofi 05 £033 Scum ad“ 3:32 wniawnflmma mm 03 as 53:2: «momma—0.3 0:8 6:59.533 05 E hnmdnmonou M55...— 05 was“ :35 in: .533 2—H. Asian: #5— 0833 5.23 unwuwafioofl one age Mafia—do 339395 a mun—.8“ «a5 wuduofiofinoo anon—moi: E323.— .ofinaucdnv c5 no «.23 53335.8: 25 5 dmcfi ouauefioumnoo ad :oflafihcu 3:5? meBOld “553% a E 2505 2:: him: 25 A5398 0.: “83958 05 no BE: 8.5» 2:. 26 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. in the section make this figure only an approximation. Lower strata of the Owens Valley in the southeastern part of the quadrangle are deformed into broad un- dulatory folds and are not amenable to stratigraphic measurements. The upper and lower contacts of the lower unit are gradational. The contact with the Keeler Canyon formation is generally marked by the lithologic change from predominantly pink shale in the upper part of the Keeler Canyon to predominantly silty and sandy lime- stone with lenses of pure limestone and limestone brec- cia in the lower unit of the Owens Valley formation. In the Darwin Hills the contact of the base of the Owens Valley formation was placed at the base of a 450-foot- thick, brown-weathering siltstone 2,500 feet east of the Darwin Antimony mine. The contact of the lower and middle units of the Owens Valley formation is at the base of predominant fissile shale. LITHOLOGY The lower unit of the Owens Valley formation con- sists mainly of fine-grained calcarenite commonly in beds 1 to 2 feet thick. Shaly limestone, lenses of pure limestone and limestone breccia, shale, and siltstone are common. Lenses of massive bluish-gray limestone and limestone breccia as much as 40 feet thick are character- istic of the unit; these lenses are probably bioherms and are commonly highly fossiliferous. Limestone peb- ble conglomerates are not as abundant as in the Keeler Canyon formation. A poorly sorted limestone breccia along the Darwin Wash road 114 miles S. 33° E. of China Garden Spring is interpreted as formed by sub- marine slump. The limestone breccia contains rounded and subrounded fragments of dark-gray limestone in a light—brown sandy and silty limestone matrix. Frag- ments are mostly 1 to 3 inches in diameter, but some reach a maximum length of 2 feet. Fragments consti- tute about 20 percent of the rock. The fine- grained calcarenite is commonly crossbedded. It is generally light or medium gray on fresh surfaces and weathers light brown. Associated thick, massive lens-shaped limestones are bluish gray on both fresh and weathered surfaces. Shale beds in the formation are variegated in pinks, grays, greens, and browns. The buff and brown siltstone weathers medium brown. Algal nodules 2 to 3 inches long are present in calcare- nite in Darwin Canyon near Millers Spring, and meta- morphosed ellipsoidal forms in calc—hornfels east of the Christmas Gift mine probably are metamorphosed algal nodules. The nodules contain abundant sponge spic- ules( ?) and fusulinids, although the enclosing calcare— nite is nearly devoid of fossils. Summary of an eastward-trending stratigraphic section of the lower unit measured from the base of the middle unit of the Owens Valley formation east of Conglomerate M esa about half a mile south of the quadrangle boundary Owens Valley formation: Middle unit. Conformable contact. Lower unit: Thickness 1 (feet) Limestone and siltstone, largely yellowish gray, silty and sandy; massive bluish-gray limestone lenses in lower part Of section as much as 40 ft thick ; most thick limestone lenses are fusulinid bearing; some contain brachiopods, gastropods, and crinoidal debris; thin beds of greenish— brown shale and limestone pebble conglomerate high in section Limestone, interbedded thin-bedded, gray, sandy and silty; and gray and yellowish-brown shale; minor pure gray limestone in beds 2 to 4 ft think 822 Limestone, mainly brown-weathering, silty and platy; moderately abundant fusulinid-bearing medium-gray limestone beds and lenses 2 to 30 ft thick; some contain limestone fragments; minor amounts of pink and brown silty fissile shales with cleavage transecting bedding _____ Limestone, brown-weathering, platy and silty; and minor amounts of interbedded brown- weathering shale and fusulinid-bearing lime- stone pebble conglomerate ___________________ 1,440 265 300 Total Conformable contact. Keeler Canyon formation. 1 Approximate. _ 2, 827 In the Darwin Hills a 450-foot-thick brown-weather— ing siltstone bed is at the base of the formation. This siltstone and its metamorphosed equivalent crop out abundantly on the eastern slopes of the Darwin Hills. Shaly and silty limestone containing lenses of massive bluish-gray limestone and limestone breccia overlies the siltstone. AGE AND CORRELATION Paleontologic evidence indicates that the lower unit ranges in age from late Wolfcamp into Leonard. The faunal assemblage consists largely of fusulinids, but includes large brachiopods, corals, ammonites, and gastropods. Most specimens are poorly preserved. Five collections of fusulinids from the lower unit of the Owens Valley in the area east of Conglomerate Mesa were studied by R. C. Douglass. He reported a range in age from late Wolfcamp into Leonard. A collection from near the base of the Owens Valley was identified by Douglass (written communication, 1954) as follows: PALEOZOIC ROCKS 27 f9645 Permian. California, Inyo County, Darwin quadrangle. Locality 2.85 miles S. 86° E. of the NW. corner of the quadrangle. Schubertella sp. Tritim‘tes ? sp. Schwagermc spp. Pseudoschwagerim? sp. The material in this collection is fractured and silicified. It is of Permian age, probably late Wolfcamp. Concerning a collection at the top of the lower unit of the Owens Valley, Douglass reports: f9650 Permian. California, Inyo County, Darwin quadrangle. Locality 1.20 miles S. 70° E. of the northwest corner of the quadrangle. There are many small forms in this collection, most of which seem to be immature individuals of the following genera, but some of which may be Endothym and Schubertella. Schwagem‘m spp. advanced forms related to S. guembeli iDunbar and Skinner Parafusulma sp. This sample is the youngest of the lot studied for this report. It is Permian in age and is probably equivalent to the Leonard. The lower unit of the Owens Valley does not corre- late precisely with the lower fauna] zone of the Owens Valley given by Merriam and Hall (1957, p. 11). The lower unit in this report includes the thick sequence of silty limestone, sandy limestone, shale, and siltstone that underlies the predominantly shaly varicolored unit at the base of Conglomerate Mesa. Parafusulz'm sp., which is placed in the middle faunal zone of the Owens Valley formation, is in the upper part of the lower unit of the Owens Valley as mapped by the writers. James Steele Williams summarized results of paleon- tologic studies of a megafossil assemblage collected about 200 feet stratigraphically below the top of the lower unit near Conglomerate Mesa. This collection was made from a thick, lenticular, craggy bioherm. Williams’ summarjy follows: USGS 17569 Darwin quadrangle, 1.32 miles S. 58° E. of the NW. corner of the quadrangle. Byrozoa (identified by Helen Duncan) Stenodiscus? sp. indet. {no close age significance) Brachiopoda M eekella sp. indet. large to rm Dictyoclostus sp. indet., re lated to D. West basst’ McKee Dictyoclostus? sp. indet., possibly related to D. ivesi (Newberry) Enteletes? sp. indet. Gastropods Three specimens of gastro pods were reported on sepa- rately by Ellis Yochelso: 1. Two are indeterminate and one represents an undeter- mined species of the gems Peruvispim which was de- scribed from beds said to be Lower Permian age in Peru but has been found in beds that range from Wolfcamp to Word in age. The large Dictyoclostus in the above list is crushed and in- complete but as nearly as one can tell it is probably a D. West 620626 0—62——3 variety bassi McKee. The smaller one is related to D. West (Newberry) as restricted by McKee but it appears to have coarser costate and a deeper sulcus than are typical of that species. The Meekella in mature individuals is larger than most Pennsylvanian species. On these rather slender grounds I believe that the collection is probably of Leonard or younger Permian age. It is not the typical Owenyo fauna but appears to me to be older than that fauna. I do not believe it is as old as typical McCloud. It may however be an unusual facies of one of these faunas ‘ * *. Poorly preserved solitary corals, crinoid columnals, and fragments of brachipods are in several thicker lime- stone lenses near Conglomerate Mesa. One lithostro- tionoid coral was collected near the top of the lower unit. Twelve collections of fusulinids from the lower unit in the southeastern part of the quadrangle were ex- amined by Douglass. Pseudoschwagerina, Schwage- rim, or both, are present in all the collections. Olim- camnm'm is in eight. Other less widespread genera rep— resented in the collections are Schubertella, Pam- schwagem'na, Parafusuli’na?, and P8eud0fusulina?. Tm'ticites sp. is present in only one collection from near the base of the formation. Douglass believes that these collections indicate late Wolfcamp or early Leonard age. Pseudoschwagerim is the prevailing fusulinid in collections from the lower unit from the Talc City Hills and the extreme southern part of the Inyo Mountains. Additional megafossils were found in the Owens Valley formation, but they were either badly preserved or were not diagnostic for age determination. Ammo- nites, which are too poorly preserved for generic deter- mination, occur in sandstone on the east slope of the Darwin Hills. Bernard Kummell (written communi- cation, 1954) reported they might be either Permian or Triassic. Solitary corals and crinoid colunmals are abundant in fusulinid—bearing limestone in the Argus Range. Owing to the poor state of preservation, the corals were not studied. MIDDLE UNIT THICKNESS AND STRATIGRAPHIC RELATIONS The middle unit is exposed only around the base of Conglomerate Mesa in the northwestern part of the quadrangle. Because of tight folds and poor outcrops resulting from the incompetence of this unit, a good section could not be measured. The mapped outcrop pattern indicates that the thickness is about 200 feet. The contact with the silty and sandy limestone of the lower member is gradational and conformable. LIT HOLOGY The middle unit consists predominantly of shale but contains subordinate siltstone and limestone. Most of 28 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. the shale is brick red or yellowish brown on fresh and weathered surfaces. Other shale beds are dark gray to nearly black, greenish gray, and light gray; these beds commonly weather to several shades of green and brown. The minor intercalated siltstone is yellowish gray on fresh surfaces and weathers yellowish brown. It is generally thinly bedded and contains abundant siliceous silt. Interbedded limestone layers are medium gray and weather brownish gray. They range from 1 to 4 feet in thickness and commonly contain abundant siliceous silt and sand. The cleavage’of the fissile shales dips steeply westward across bedding. Quartz veins, which are less than 100 feet long, fill tension fractures in the shale. UPPER UNIT THICKNESS AND STRATIGRAPHIC RELATIONS A minimum thickness of 180 feet of limestone con- glomerate of the upper unit of the Owens Valley for— mation crops out at Conglomerate Mesa. The unit is restricted to this area in the Darwin quadrangle. Its present distribution is probably close to its original extent. The lower contact with the shale of the middle unit is sharp and disconformable. Local angular dis— cordance along this contact mainly reflects minor slip- page between the competent limestone conglomerate and incompetent shale, but at the south end of the mesa. the discordance may be a local angular unconformity. LITH OLOGY The lower part of the upper unit consists of a 60-foot- thick limestone conglomerate that is overlain by a 30- foot—thick light-gray fine-grained orthoquartzite. The upper 90 feet of the unit is made up mainly of light- yellow and yellowish-brown-weathering siltstone and light—gray calcarenite with minor yellowish-weathering pebble conglomerate. Clastic fragments greater than sand size generally constitute 40 to 60 percent of the yellowish-brown— and brown-weathering conglomerate—a unique rock in the Darwin quadrangle ‘Paleozoic section. Coarse frag- ments that range in size from 1 to 4 inches in maximum diameter are most abundant but a few larger fragments are present. Gray silty limestone and, to a lesser extent, pink and light-gray chert form most of the rudaceous material. The limestone fragments commonly are sul} rounded to rounded and the chert fragments are sub- angular. The sand-size matrix constituents are mainly siliceous. In places the conglomerate has been largely replaced by chert. Several small isolated outcrops of coarse-grained sandstone south of Conglomerate Mesa near the western boundary of the quadrangle are stratigraphic equiva- lents of the limestone conglomerate. The light-gray locally crossbedded sandstones are composed largely of subangular and subrounded siliceous and limy grains. AGE AND CORRELATION No fossils were found in the upper unit within the Darwin quadrangle. The upper unit of the Owens Val- ley at Conglomerate Mesa is correlated with the upper part of the Owens Valley at the type locality in the Inyo Range (Merriam and Hall, 1957, p. 11), where it contains Neospz'm'fe'r- psewiocamemtus and Puncto- spirifer pulcher and is probably Word (middle Per— mian) 0r Guadalupe (late Permian) in age. UNDIFFERENTIATED PALEOZOIC SILICATED LIMESTONE Calc-hornfels that cannot be correlated definitely in the stratigraphic column occurs near the eastern border of the quadrangle in Rainbow and nearby canyons and as inliers surrounded by basalt (pl. 1). The calc horn— fels is mainly a white to light-gray, dense diopside-rich rock, but locally some relict bluish-gray limestone with tremolite needles remains. It occurs between a small inlier of probably the Lost Burro formation to the north in an unnamed canyon 3.70 miles S. 63° W. of the northeast corner of the quadrangle and the lower unit of the Owens Valley formation to the south in the Argus Range (pl. 1). The calc-hornfels is probably both Carboniferous and Permian in age. GNEISS Gneiss crops out only in the southwestern part of the quadrangle as several small r’oof pendants or screens marginal to biotite-hornblende-quartz monzonite (pl. 1). The rock is a fine- to medium-grained gneiss con- sisting mainly of biotite, quartz, and feldspar. Folia- tion strikes north to northwest and dips steeply. The gneiss is cut by some sills of biotite-hornblende-quartz monzonite. Its age is not known. MESOZOIC ROCKS INTRUSIVE ROCKS Plutonic rocks are exposed in about 10 percent of the quadrangle, and possibly an additional 10 percent of plutonic rocks underlie a cover of basalt or alluvium. The plutonic rocks are divided into two lithologic types—biotite-hornblende-quartz monzonite and leuco— cratic quartz monzonite. Minor leucogranite, aplite, and pegmatite are common in small bodies at the border of bodies of quartz monzonite and as thin dikes intrud- ing it. Quartz monzonite as used in this report is a granitoid rock that contains essential quartz, potas- MESOZOIC ROCKS 29 sium-feldspar, and plagioclase; the ratio of potassium- feldspar to plagioclase is between 1 to 2 and 2 to 1. Otherwise names of plutonic rocks in this report follow the definitions of Johannsen (1939, p. 141—161). BIOTITE—HORNBLENDE-QUARTZ MONZONITE Biotite—hornblende-quartz monzonite is the predom- inant plutonic rock type in the northeastern part of the quadrangle, in the Coso Range and in the central Dar- win Hills. Unaltered biotite-hornblende-quartz mon- zonite crops out in the northeastern part of the quadrangle in steep, eastward-trending canyons where the rock has been exposed by faulting or by erosion of the overlying basalt. The quartz monzonite extends northward into the Ubehebe Peak quadrangle where itis called the Hunter Mountain quartz monzonite by McAllister (1956). The name Hunter Mountain quartz monZonite may be extended to the biotite-horn- blende—quartz monzonite in the northeast quarter of the quadrangle. The name has not been applied to the other bodies of biotite-hornblende-quartz monzonite because of the uncertainty of correlating widely sepa- rated intrusive bodies whose age cannot be closely dated, and because the intrusive bodies have a heterogeneous appearance owing to the assimilation of a large amount of silty limestone. Biotite-hornblende-quartz monzonite is the most easily weathered rock in the Darwin Hills and Coso Range, where it forms gentle grus—covered slopes. slopes are marked by outcrops of resistant leucogranite or aplite that does not reflect the composition of the grus-covered areas. Therefore few fresh quartz mon- zonite specimens were found for petrographic study. PETROGRAPHY The biotite-hornblende-quartz monzonite is a light- gray rock that has a specked appearance produced by scattered mafic minerals. The texture ranges from equigranular, with an average grain size of 2 to 3 mm, to porphyritic, Where 10 to 20 percent phenocrysts of pink potassium feldspar as much as 1% cm long occur in a finer grained light-gray equigranular ground- mass. The uncontaminated rock is predominantly quartz monzonite, but it ranges in composition from granodiorite to quartz monzonite. Essential minerals are quartz, potassium feldspar, plagioclase, and more than 5 percent hornblende and biotite (fig. 9). F eldspar makes up 62 to 76 percent of the rock with nearly equal amounts of plagioclase and potassium feldspar. Plagioclase ranges from calcic oligoclase (Ann) to andesine (Ana) ; it connnonly shows normal zoning. The potassium feldspar is microperthitic, and some of it has microcline twinning, particularly the phenocrysts. The quartz content ranges from 5 to The ' 30 percent. It is more abundant in the quartz monzo- nite from the Coso Range than that in the northeastern part of the quadrangle. The mafic minerals include biotite, hornblende, and, in the northeastern part of the quadrangle, augite; they range from 8 to 30 percent by volume. Hornblende is predominant in the biotite- hornblende—quartz monzonite from the Coso Range and the northeastern part of the quadrangle, and biotite is predominant in the quartz monzonite underlying the low hills west of Darwin. Minor accessory minerals are sphene, apatite, magnetite, and tourmaline. Tour- maline is particularly abundant in the quartz monzon- ite at the south end of the Santa Rosa Hills. The stock in the Darwin Hills is a heterogeneous intrusive mass compOsed predominantly of biotite- hornblende-quartz monzonite and granodiorite, but the rocks are deeply weathered and few unaltered speci- mens were found for study. Near the Definance and Thompson workings of the Darwin mine the intrusive mass is hybrid and consists largely of granodiorite, quartz diorite, and diorite. Megascopically the biotite-hornblende—quartz mon- zonite from the northeastern part of the quadrangle, Coso Range, and the least contaminated parts of the stock in the Darwin Hills are similar in color and tex— ture. However there are some overall differences be- tween quartz monzonite from the various bodies. The quartz monzonite in the Coso Range contains more quartz and less mafic minerals than the quartz monzon- ite from the northeastern part of the quadrangle. Aug- ite is common in the quartz monzonite in the northeast— ern part of the quadrangle but was not observed in the quartz monzonite in the Coso Range. Hunter Moun- tain quartz monzonite in the Ubehebe Peak quadrangle (McAllister, 1956) is also low in quartz, and it is prob- able that the exposures of the ‘batholith are closer to the former roof than the exposures of biotite-hornblende- quartz monzonite in the Coso Range. The border facies of the Hunter Mountain quartz monzonite are quartz- poor rocks that include monzonite, syenodiorite, and gabbro. Generally the border facies rocks are slightly coarser grained and are darker than the typical biotite- hornblende-quartz monzonite, but in some exposures the two are indistinguishable. The border facies rocks are not distinguished on our map (pl. 1). These quartz- poor rocks probably formed by assimilation of the silty limestone and dolomite country rock by the biotite- hornblende-quartz monzonite. Except for the low quartz content, monzonite is similar to quartz monzonite in mineralogy and texture. Syenodiorite megascopically also is similar, except for containing more plagioclase than the monzonite. Lo- cally syenodiorite also contains small amounts of tour- 30 EXPLANATION 0 Normal granitoid rock X Border facies rock 80 Length of line indicates percent of mafic and accessory minerals; top of line is percent of total feldspar and bottom of line is percent of quartz, For example sample No. 1 con- GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. tains 59 percent feldspar, 30 percent quartz, and 11 percent mafic and accessory minerals 60 \s 90 Potassium feldspar ‘55 70 ”5 ‘90 "a Plagioclase FIGURE 9.—Triangular diagram showing percentages of essential minerals in the blotlte-hornblende-quartz monzonite (after Johannsen, 1939, v. 1, p. 152.) maline and scapolite, variety dipyre, in veinlets tran- secting and replacing plagioclase. AGE The granitoid rocks in the Darwin quadrangle in- trude Permian strata and are overlain by late Cenozoic rocks. In the Inyo Mountains they intrude shale and volcanic rocks of Late Triassic age (Knoff, 1918, p. 60). Two intrusions of biotite-hornblende-quartz monzonite in the Argus Range several miles east of the Darwin quadrangle were dated by the lead-alpha and potas- sium—argon methods as 180 million years (T. W. Stern and H. H. Thomas, written communication, 1961). Thus they are very Early Jurassic (Kulp, 1961). These dated intrusions are correlated by the writers with the biotite-hornblende—quartz monzonite in the Darwin quadrangle. They are considerably older than the Sierra Nevada batholith with which they were previously provisionally correlated by Hall and Mac- Kevett (1958). The geologic quadrangle map was com- piled before these age determinations were made, and the biotite-hornblende-quartz monzonite is shown as Cretaceous( ?) on the maps for this report. The two dated samples of biotite-hornblende-quartz monzonite were collected from the east side of the Argus Range a few miles east of the Darwin quadrangle. Sample DW—l was collected in Darwin Canyon 1 mile west of Panamint Springs at an altitude of 2,120 feet. MESOZOIC ROCKS 31 The locality is at the north end of the Argus Range in the Panamint Butte quadrangle. Sample TC—l is from Thompson Canyon 1.4 miles S. 85° W. of the Modoc mine at an altitude of 3,910 feet on the east side of the Argus Range in the Maturango Peak quadrangle. It is from the north end of the large mass of quartz mon- zonite that underlies Maturango Peak. Herman H. Thomas (written communication, 1961) dated sample DW—l as 182 million years and sample TC—l as 178 million years by potassium—argon. Data for the calculations are given below: Radiogenic argon Age (million Sample No. Arm (ppm) K“J (ppm) Arm/K40 (percent) years) DW—l __________ 0.0915 8.07 0.0113 94 182 TC—l __________ . 0671 6. 07 . 0110 93 178 Potassium analysis is by C. O. Ingamells, Pennsylvania State University. Constants used : xp=4.76 >< 10-‘°/year ke=0.589>< 10'1°/year K“°/ K =0.000120qg./ g. Possible error about 5 percent of determined value. T. W. Stern (written communication, 1961) dated the zircon of the same samples by the lead-alpha method. Sample TC—l was determined as 1801-20 million years and sample DW—l as 210:25 million years. Data for the samples are given below : Sazcnple Pb Calculated age 2 o. a/mg per hr (ppm)1 (million years) DW—l ___________________ 134 11.1 210 i 25 TC—l ____________________ 188 13.7 180 i 20 1 Analysts: Charles Annell and Harold Westley. aThe lead-alpha ages were calculated by T. W. Stern from the follow- ing equation: T=0 Pb/a where T is the calculated age in millions of years, 0 is a constant based upon the U/Th ratio, Pb is the lead content in parts per million, and a is the alpha counts per milligram per hour. The following constants were used : Assumed U/Th ratio 0 1 2485 Age is rounded off to nearest 10 my. The error quoted is that due only to uncertainties in analytical tech- niques. LEUCOCRATIC QUARTZ MONZONI’I‘E DISTRIBUTION Leucocratic quartz monzonite crops out in stocks in the Talc City Hills and at Zinc Hill in the Argus Range. Most slopes underlain by leucocratic quartz monzonite in the Tale City Hills are grus covered, and only a few shallow gullies expose relatively unweath- ered rock. Leucocratic quartz monzonite at Zinc Hill is in an area of rugged relief, and is well exposed. PETROGRAPHY Leucocratic quartz monzonite is a medium- to coarse- grained light-grayish-pink rock that generally contains less than 5 percent mafic minerals. The texture ranges from equigranular to porphyritic; locally the rock con- tains pink feldspar crystals as much as 11/2 cm long in a medium-grained equigranular groundmass. Dark fine— grained inclusions less than 11/2 inches long are dis- seminated sparsely through the quartz monzonite. The leucocratic quartz monzonite is lighter colored and coarser grained than the more widespread biotite-horn- blende-quartz monzonite. Essential minerals in the rock are quartz, sodic oli- goclase, and orthoclase. F eldspars constitute 70 to 75 percent of the rock and occur in about equal quantities. Orthoclase is microperthitic and commonly forms phenocrysts that poikilitically enclose all other min- erals. Biotite, the predominant mafic mineral, gen- erally constitutes less than 5 percent of the rock, although as much as 7 percent has been observed; it is in part altered to chlorite. Hornblende may be present in small quantities. Minor accessory minerals are allanite, apatite, magnetite, pyrite, sphene, and tour- maline. AGE The relative age of the biotite-hornblende-quartz monzonite and the leucocratic quartz monzonite is un- certain, but the leucocratic quartz monzonite probably is the younger rock. They are in contact only in the low grus-covered hills west of Darwin where the rocks are poorly exposed. The shape of the southeast end of the stock in the Talc City Hills suggests a tongue of a younger leucocratic quartz monzonite intruding the biotite-hornblende—quartz monzonite. The more sodic composition of the plagioclase and the smaller mafic mineral content of the leucocratic quartz monzonite sug- gests from the Bowen reaction series that it is a later differentiate and hence the younger rock. Lithologically the leucocratic quartz monzonite most closely resembles in texture and mineralogy the ortho- clase-albite granite at Rawson Creek in the Sierra Nevada (Knopf, 1918, p. 68). According to P. C. Bate— - man (oral communication, 1957) this is a widespread rock type along the eastern front of the Sierra Nevada. APLITE AND LEUCOGRANITE The youngest ‘batholithic rocks are leucogranite, aplite, and minor pegmatite. They are concentrated in small bodies near the borders of quartz monzonite in- trusions and in thin dikes cutting quartz monzonite (pl. 1). Leucogranite is most common in the north- eastern part of the quadrangle where the largest body is 4,200 feet long and 900 feet wide. Aplite and peg- 32 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. matite are in dikes mostly less than 100 feet long and 1 inch to 3 feet wide. Aplite and leucogranite are com- mon in dikes and small irregular bodies in the Coso Range and Talc City Hills, and a body of leucogranite is 2,500 feet northeast of Darwin on the west side of the stock of biotite-hornblende-quartz monzonite in the Darwin Hills. The leucogranite is a pinkish—white fine-grained rock that consists predominantly of feldspar and quartz. Minor accessory minerals are apatite, biotite, horn- blende, magnetite, and sphene. Tourmaline is locally abundant in the bodies in the northeastern part of the quadrangle. The rock contains 50 to 58 percent orthoclase, 30 to 33 percent quartz, 9 to 15 percent plagioclase of composition An8 to An“, 1 to 2 percent biotite, and less than 1 percent each of the other acces— sory minerals. Biotite is in large part altered to chlorite. Orthoclase is microperthitic; some is re- placed ‘by albite. The leucogranite and aplite in the Darwin Hills contain more plagioclase than most of the other bodies. Plagioclase and orthoclase are present in about equal quantities and make up about 70 percent of the rock. Plagioclase is albite (Ang) ; orthoclase is microperthitic. ' Hematite coats the feldspar and produces a light-pink or purplish color. The feldspar is in large part hydro- thermally altered to sericite, and pyrite is sparsely dis- seminated through the rock. Within the weathered zone pyrite is altered to limonite. BIKES ALTERED ANDESITE PORPE‘YRY BIKES Highly altered fine-grained, porphyritic greenish- gray dikes of andesitic composition crop out in the San- ta Rosa mine area, the eastern part of the quadrangle south of Rainbow Canyon, and near Conglomerate Mesa (pl. 1). Similar dikes have been described from the U‘behebeyPeak quadrangle as altered porphyritic dikes by McAllister (1956). The dikes are part of an extensive swarm that extends at least from the north end of the Argus Range in the Panamint Butte quad— rangle northwestward across the Darwin Plateau and Inyo Mountains to the Sierra Nevada—a distance of more than 50 miles (fig. 1). This dike swarm was described recently by Moore and Hopson (1961). The andesite porphyry dikes range from 2 to 6 feet in thickness. They strike predominantly between N. 70° W. and west, and dip about vertically. They are greenish gray on freshly broken surfaces and weather to several shades of brown. The dikes exposed at low altitudes develop dark-brown desert-varnished surfaces similar to that on basalt. The andesite porphyry dikes consist mainly of saus- suritized plagioclase phenocrysts in a fine-grained pilo- taxitic groundmass composed largely of elongate saus- suritized plagioclase. The plagioclase phenocrysts average about 1 by 2 mm, and the groundmass plagio- clase is about 0.2 mm long and 0.03 mm wide. The rock is altered mainly to albite, epidote, calcite, and chlorite. Quartz, limonite, sericite, clay minerals, and stilbite are less common secondary minerals. The meager assemblage of primary minerals includes a few skeletal remnants of augite phenocrysts, and very Small amounts of apatite, sphene, magnetite, and pyrite. The dikes cut granitic rocks in the northeastern part of the quadrangle. Elsewhere they cut Paleozoic rocks. The dikes were emplaced after consolidation of the batholithic rocks and before late Tertiary volcanic activity, and they probably are Cretaceous or early Tertiary in age. DIORITE Dikes of several compositions crop out in the south- ern part of the quadrangle. These are mainly diorite but include altered quartz latite, syenite, and one alas— kite porphyry. They are grouped with diorite dikes on the map. The most abundant are altered dark greenish-gray diorite dikes that cut biotite-hornblende- quartz monzonite in the low hills west of Darwin and Paloezoic rocks near Darwin Falls. The dikes are re— stricted to the margins of plutonic bodies or to contact metamorphosed zones about plutons. A porphyritic texture is common. The least altered are fine-grained, porphyritic dikes that consist mainly of hornblende, oligoclase, epidote, and magnetite. Most are com- pletely altered to chlorite, albite, calcite, clinozoisite, and magnetite. Felsic dikes are present both in the Darwin Hills and in the Talc City Hills. Dikes in the Darwin Hills in- clude both alaskite porphyry and syenite. An alaskite porphyry dike 3 feet thick, which crops out half a mile east of Ophir Mountain, contains phenocrysts of quartz and albite about 2 mm long in a, light—gray aphanitic groundmass composed mainly of albite and quartz and minor accessory magnetite, apatite, and sphene. Syen- ite is common in the Darwin mine area, and it is probab- ly formed by feldspathization (pl. 3). It is described under rock alteration. Felsic dikes are exposed in the pit at the Frisco talc mine and at the surface at the Tale City mine in the Talc City Hills. They are light-gray fine-grained dikes that are partly to wholly replaced by chlorite and minor tale. The dikes probably were quartz latite. They have a pilotaxitic texture and consist of quartz, ortho- clase, and oligoclase. No primary mafic minerals re- CENOZOIC ROCKS 33 main. The feldspar is partly to completely replaced by chlorite. The alteration of these dikes is closely re— lated to talc ore bodies. CENOZOIC ROCKS Late Cenozoic deposits include both sedimentary and volcanic rocks. Sedimentary deposits are mainly fan- glomerates, but also include lacustrine deposits in Darwin Wash and on Darwin Plateau. Volcanic rocks include andesite, minor pumice, basaltic pyroclastic rocks, and basalt flows and dikes. The probable cor- relation of the late Cenozoic rocks is given in table 2. TABLE 2,—Correlation of late Cenozoic volcanic and sedimentary rocks Age Volcanic rocks Sedimentary deposits Alluvium including fanglomerate, playa deposits, landslide deposits, and slope wash. Recent Olivine basalt: Lake deposits Old fanglomerate marginal to Darwin Wash. Olivine basaltic flows some tufi and small basalt intrusive rocks. Pleistocene Old tanglomerate from the Inyo Mountains. 0050 formation Upper pyroclastic unit and andesite: Basaltic agglomerate and tuft-breccia; minorpumice. Ande- site is interbedded in this unit. Pliocene(?) Lower pyroclastic unit: Well-bedded basaltic tuft, lapilli tail, and tufl-breccia, mainly yellow and yellowish- brown. Unconformity PLIOCENE ( P ) PYROCLASTIC ROCKS Pyroclastic rocks are distributed extensively throughout the northern half of the quadrangle. Par- ticularly good sections of pyroclastic rocks are exposed in the Inyo Mountains west and north of the Santa Rosa mine and in the large canyon 11/2 miles southwest of the Santa Rosa mine. They are exposed in many places on Lee Flat and in most of the deep canyons that drain eastward into Panamint Valley in the northeastern part of the quadrangle. ' The pyroclastic rocks are readily eroded except lo- cally near cinder cones, where they are very permeable and are resistant to erosion as they have little or no sur- face runofi'. In places spires 3 to 4 feet high are formed that commonly are capped by bombs or fragments of basalt. Cavernous erosional features are locally formed in the agglomerate and tuif—breccia. THICKNESS AND RELATION TO OTHER ROCKS The thickness of the pyroclastic section ranges from 0 to more than 910 feet and is greatest at local vents; it thins quaquaversally from them. The maximum thickness of 910 feet was measured on the north side of the canyon 11/2 miles southwest of the Santa Rosa mine. A partial section 730 feet thick was measured on the south side of the canyon. The bottom of the pyroclastic section is not exposed at either place. The pyroclastic rocks rest nonconformably on sili- cated limestone of Paleozoic age and on granitic rocks in Rainbow Canyon in the eastern part of the quad- rangle. The andesite south and southeast of the Santa Rosa mine is interbedded near the top of the pyroclastic section. The base of the andesite is conformable upon bedded pyroclastic rocks 2,200 feet S. 30° E. of the Santa Rosa mine and small concordant bodies of ande- site are interbedded with pyroclastic rocks near the main body of andesite south of the Santa Rosa mine and on the east slope of hill 557 2 in the central part of the quadrangle. The pyroclastic rocks are overlain unconformably by olivine basalt and a few intercalated thin lapilli-tufi' beds. Most of the rocks dip less than 25°, probably rep- senting initial dips away from volcanic centers. How- ever, in the basin 11/2 miles southwest of the Santa Rosa mine dips up to 41° were measured in pyroclastic rocks underlying nearly horizontal basalt; these dips indicate a period of tilting between the deposition of the pyro- clastic rocks and the extrusion of the basalt. LITHOLOGY The pyroclastic rocks include agglomerate, tuft— breccia, lapilli-tufl', scoria, and volcanic Cinders—all of basaltic composition—and some intercalated olivine basalt flows, andesite, and pumice. The pyroclastic section is divided into two units. The lower unit is well-bedded tuff, lapilli-tuff, and tuff—breccia; the upper unit is poorly bedded basaltic agglomerate, Cinders, and lapilli-tufl' and varies greatly in thickness, ranging from 0 to more than 500 feet. It is localized near the volcanic vents, Whereas the lower unit is more wide- spread. Two partial sections of pyroclastic rocks in a canyon 11/2 miles southwest of the Santa Rosa mine are shown in figure 10; these sections are 7 20 and 910 feet thick. The base of the pyroclastic rocks is not exposed in either section. LOWER PYROCLASTIC UNIT Light-brown and yellowish-brown well-bedded tufl', lapilli-tuff, and tufl-breccia in beds mostly 2 to 5 feet thick make up most of the lower pyroclastic section (fig. 11). The tufi' and lapilli-tufl" are yellowish brown, 34 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, ALTITUDE North side South side (FEET) of basin of basin >7000 + + + Ollvme basalt 9: Loose cinders and Iapilli-tulf g . _. . . _. Dark red. Poorly bedded .. <3 '3 DO ‘ a, 9005 Agglomerate. Dark red to redr & A dish-purple. Bombs up to 3 > 3 feet in diameter \ \ 6600 t + \ + Olivine basalt Red lapilIi-tull and unconsolidated cinders. Poorly bedded x Lower unlt A .A. / / / Upper uml Yellowish-brown Iapillitufl Dark- red tuN-breccia / ’41 . 6200 ish-brown Iapilh-tuff. well bedded Light-brown, well bedded tuff and tulf»breccia - 5800 FIGURE 10.——Partial sections of Pliocene”) pyroclastic basaltic rocks in the Inyo Mountains 1% miles southwest of the Santa Rosa mine. light brown, or grayish brown. The most abundant tufl‘aceous rock is lapilli-tufi' with rounded fragments of scoria, red basalt, and cinders from ‘1/8 to 1 inch in diameter that is somewhat indurated though may be crumbled easily in the hand. Lapilli-tuff is inter- bedded with tuff-breccia that contains irregular to rounded fragments and bombs of olivine basalt and scoria in a tuff or lapilli-tufl' matrix. The fine—grained interbedded tuifs are composed mainly of fragments of basalt and cinders, but also contain some fragments of quartz, augite and olivine crystals, and volcanic glass. FIGURE 11.-—Lower well-bedded unit of Pliocene(?) pyroclastic rocks in the southern Inyo Mountains. The pyroclastic rocks consist of tuif-breccia and lapilli-tutf of basaltic composition. View looking south from the basin 11/2 miles southwest of the Santa Rosa mine. INYO COUNTY, CALIF. FIGURE 12.—Agglomerate in the poorly bedded upper unit of Pliocene( ?) pyroclastic rocks in the southern Inyo Mountains. The agglomerate contains bombs and ropy and irregular fragments of basalt as much as 3 feet long in a lapilli-tuff matrix. View looking north in the basin 1% miles S. 70" W. of the Santa Rosa mine. They are more indurated than lapilli-tufl', and are cemented with calcite and chalcedony. UPPER PYROCLASTIC UNIT The upper proclastic unit is composed of agglomer- ate, cinders, volcanic breccia, tuff-breccia, and red scoriaceous basalt; the color is red, reddish brown, or a deep reddish purple. Bedding in this unit is mostly indistinct. The agglomerate consists of volcanic bombs, loglike masses of ropy lava, and irregular fragments of basalt and scoria in a lapilli—tufl matrix (fig. 12). The ag- glomerate is poorly indurated and has poor to indistinct bedding; it occurs only near vents. Volcanic breccia and tufl-breccia are interbedded with the agglomerate. The tuff—breccia consists of 10 to 20 percent bombs and fragments of basalt in a lapilli—tuff matrix. It is gen- erally moderately indurated and well bedded. Figure 13 is a photograph of a sawed volcanic bomb, which shows its internal structures. The bulk specific gravity of the bombvis 2.33 compared to 2.76 for the dense part of an olivine basalt flow in the same area. Very little of the bomb is scoriaceous. The center of the bomb is dense, and, in general, it becomes more vesicular out- ward. Nearly all the vesicles are less than 0.5 mm in diameter. The vesicular parts form discontinuous con- centric bands. Volcanic breccia contains fragments of scoria and basalt mostly ranging from 1 to 6 inches in diameter with little or no matrix material. The frag- ments are mainly subrounded. Small cinder cones are present locally on top of the pyroclastic section. The cinders are mostly bright red, but some are gray to red- dish gray. They are uncemented and show no bedding. CENOZOIC ROCKS 35 FIGURE 13.——Photograph of a sawed volcanic bomb of olivine basalt The center of the bomb is dense and The vesicles are mostly less than 0.5 Specific showing its internal structure. the border is more vesicular. mm in diameter and form discontinuous concentric bands. gravity of the bomb is 2.33. A few thin lenticular pumice beds are near the top of the pyroclastic section. They range from 3 to 8 feet in thickness and can be traced only a few hundred feet. The pumice is impure and contains as much as 20 percent rounded grains of quartz and fragments of basalt. ANDESITE Andesite is exposed south and southeast of the Santa Rosa mine over an area of 3.square miles; several smaller bodies are in the central part of the quadrangle on hill 5572. Andesite is resistant to weathering and com- monly forms bold reddish-colored cliffs. Joints are sharply defined, and in areas of moderate relief bouldery outcrops are formed. Cavernous weathering occurs in places on north slopes. Andesite south of the Santa Rosa mine forms a broad dome interbedded in the upper pyroclastic unit. The base of the dome is exposed resting concordantly on tuff— breccia 2,200 feet S. 65° E. of the Santa Rosa mine. Elsewhere the base of the dome is not exposed as the flanks are covered by basalt or alluvium or, in places, the contacts are faults. Flow structures are well de- fined in places and suggest the presence of a dome- shaped mass. The maximum exposed thickness of andesite is 1,230 feet on hill 6950, 11/2 miles southeast of the Santa Rosa mine, but the base is not exposed there. The andesite is a porphyritic rock that contains phenocrysts and clusters as much as 10 mm long of plagioclase laths and euhedral phenocrysts of horn- blende up to 4 mm long in an aphanitic groundmass. There are two color varieties of the rock. One is light gray on fresh surfaces and weathers dark gray; the other is reddish to reddish gray on fresh surfaces and weathers reddish brown. The two color varieties occur throughout the dome and have no recognized strati- graphic significance within the dome. PETROGRAPHY The gray porphyritic andesite contains phenocrysts of plagioclase, hornblende, and minor biotite, augite, and quartz in a fine—grained and in part glassy ground- mass. Plagioclase constitutes 60 to 65 percent of the rock as subhedral phenocrysts of andesine that are normally zoned from A1146 to A113. and as microlites of composition A1135 to Ame. Carlsbad twinning is pre- dominant, although some phenocrysts have broad albite twinning. Hornblende, the main mafic mineral, forms as much as 30 percent of the rock and occurs as euhedral lath-shaped phenocrysts that are strongly pleochroic With X=yellowish green, Y =brownish green, and Z=dark olive green. Biotite phenocrysts up [to 1 mm long constitute as much as 7 percent of the rock; they are extremely pleochroic from light brown or greenish brown to very dark brown. Augite, quartz, and ortho- clase may be present in small quantities as phenocrysts. The groundmass consists predominantly of plagioclase, hornblende, and volcanic glass and contains minor quartz, orthoclase, biotite, augite, apatite, and zircon. The groundmass has a trachytic texture. The andesite has a few small vesicles that are in part filled with calcite and chabazite. Texturally and mineralogically the reddish andesite resembles the gray andesite except that'oxyhornblende and hematite occur in the reddish andesite instead of common green hornblende. The oxyhornblende occurs as euhedral lath-shaped phenocrysts similar in size and shape to the hornblende in the gray andesite. The oxyhornblende is extremely pleochroic from light brown to very dark reddish brown and has thin opaque borders of hematite. Hematite occurs as euhedral thin plates and as tiny disseminated specks through the groundmass, giving the rock its reddish color. AGE The andesite is probably late Pliocene in age. It is interbedded in the upper unit of pyroclastic rocks, is overlain by flows of olivine basalt, and is cut by basin- range faults in the Darwin quadrangle. In the Haiwee Reservoir quadrangle, southwest of the Darwin quad- rangle, the andesite appears to be identical with the porphyritic andesite in the Darwin quadrangle. Hop- per (1947, p. 414) states that the andesite in the Haiwee Reservoir quadrangle unconformably underlies the tufl’s and lakebeds of the C050 formation of late Plio- cene or early Pleistocene age, and he suggests that the andesite may correlate with the andesite of late Mio- cene age described by Hulin (1934, p. 420) in the 36 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. Searles Basin quadrangle. The writers made a recon- naissance traverse over the andesite in the Coso Range between Cactus Flat and Haiwee Reservoir (fig. 1), and they believe that the andesite is interbedded in the Coso formation. The Coso formation west of the andesite body contains andesite fragments, but at Cac- tus Flat beds identical with and contiguous with beds known to be part of the Coso underlie the andesite. Therefore the andesite at Cactus Flat is contempora- neous with beds low in the Coso formation and is prob- ably of late Pliocene age. OLD FANGLOMERATE FROM THE INYO MOUNTAINS Erosional remnants of fans marginal to the Inyo Mountains occur southwest of the Talc City Hills near State Highway 190 (pl. 1). They form small hills that rise 15 to 30 feet above the surrounding Recent alluvium. The fans are composed of angular to sub- rounded fragments as much as 18 inches in diameter of sedimentary rocks of Silurian and Ordovician age in a clay and silt matrix. The fragments are limestone, bufl' to dark—gray dolomite, and quartzite from the Pogonip group and the Eureka, Ely Springs, and Hidden Valley formations. A quarry at the Frisco talc mine in the Talc City Hills exposes similar older fan material containing an indurated lens of well- bedded elastic limy shale and siltstone faulted against Hidden Valley dolomite. The limy shale probably formed in a small pond on the alluvial plain. South of State Highway 190 the fanglomerate is overlain by 5 to 20 feet of basaltic tuff, minor pumice, and olivine basalt flows. The source of the fanglomerate must have been the Inyo Mountains and Talc City Hills to the north and northwest. No other remnants of fanglomerate remain in that direction, but this is the only direction for a local source of Silurian and Ordovician rocks. In addi- tion south of State Highway 190 fragments in the fanglomerate are smaller and more rounded than those in remnants north of the road, closer to the Tale City Hills. The fanglomerate underlies olivine basalt of Quater- nary age and is probably the same age as the nearby Coso formation. COSO FORMATION The Coso formation so designated by Shultz (1937) is exposed locally in the west-central and southwestern parts of the quadrangle northeast and east of the Coso Range, where it is part of extensive fans west of the quadrangle marginal to the Coso Range. Early writers described these deposits as lake-beds (Fair- banks, 1896, p. 69; Campbell, 1902, p. 20; Trowbridge, 1911, p. 726), but later writers demonstrated that the beds are in large part alluvial fans, the lower reaches of which interfinger with or are overlain by lacustrine deposits (Schultz, 1937, p. 78; Hopper, 1947, p. 415). In the mapped area the Coso formation forms low, w‘hite hills that rise 5 to 30 feet above the Recent allu- vium. The beds are predominantly white to buff fine- to medium-grained arkosic sand and clay in indistinct beds 1 to 2 inches thick. These materials were de- rived nearly entirely from disintegration of granitic rocks of the Coso Range. At the north end of the Coso Range in the Darwin quadrangle the Coso forma- tion is overlain by a 5- to 15-foot-thick bed of fine- grained light—brown basaltic tufl', which, in turn, is overlain by olivine basalt. Elsewhere in the quadrangle the formation is dissected and in part covered by Recent alluvium. The Coso formation dips 1° to 8° NE. away from the Coso Range. No volcanic material was seen in the arkosic beds within the mapped area, but fragments of agglomerate are present in the Coso formation on the west side of the Coso Range between Cactus Flat and Haiwee Reservoir. Therefore the Coso formation is younger than at least some of the pyroclastic rocks, but is older than the Quaternary olivine basalt and asso- ciated thin tufl' beds; Schultz (1937, p. 98) found vertebrate fossils in coarse-grained arkosic beds in the Coso formation west of the Darwin quadrangle that are late Pliocene or early Pleistocene in age. PLEISTOCENE OLIVINE BASALT Basalt covers a large part of the surface of the north- ern two-thirds of the quadrangle as thin flows on a mature erosion surface and as dikes that cut all the older rocks; it occurs in several isolated patches in the southern third of the quadrangle. Thin dikes, which are in part feeders for the basalt flows and are in part contemporaneous with the underlying pyroclastic rocks, out all the older rocks but are especially abundant around vents. Basalt probably at one time covered all the northern part of the quadrangle, but in the south- ern part it is localized around vents and probably orig- inally did not cover a much larger area than at present. The flows range from 10 to about 100 feet in thick- ness, and the aggregate of flows totals a maximum thickness of about 600 feet in the east-central part of the quadrangle. Some lapilli-tufl' beds 5 to 10 feet thick are interbedded with the basalt. Basalt flows unconformably overlie a thick sequence of pyroclastic rocks, or where the pyroclastic rocks are missing, basalt nonconformably overlies granitic rocks or Paleozoic sedimentary rocks. Individual basalt flows commonly CENOZOIC ROCKS 37 have a systematic internal structure. A rubble zone at the base is 6 inches to 2 feet thick. Above the basal rubble zone the basalt flows have a platy structure over a thickness of 2 to 4 feet, and this grades upward into massive basalt that contains a few stretched vesicles. The massive basalt ranges from a few feet to 50 feet in thickness; locally it has columnar jointing. Mas- sive basalt grades upward into scoriaceous basalt and scoria at the top of a flow. Overlying flows repeat the sequence. PETRO GRAPHY The basalt is a finely porphyritic rock containing phenocrysts of olivine, plagioclase and augite in an aphanitic groundmass. It is dark gray on fresh sur— faces and weathers to dark yellowish brown; in many places it is blackened by desert varnish. Vesicles are common near the top and bottom of flows; those near the" bottom are elongated parallel to the direction of flow. Thin sections show that the phenocrysts are predomi— nantly olivine, but include small amounts of plagioclase and augite in a groundmass of plagioclase, olivine, augite, biotite, and glass. The olivine phenocrysts are euhedral to subhedral crystals 1 to 2 mm in diameter and are partly altered to iddingsite, antigorite, or goethite. Near the Santa Rosa mine the basalt contains fragments of quartz surrounded by thin reaction rims of sphene. The quartz fragments are probably xeno— crysts. The groundmass mainly has a trachytic texture, but, where much glass is present, it has an intersertal tex- ture. Plagioclase constitutes at least 60 percent of the groundmass. It is in elongate laths 0.1 to 0.3 mm long of labradorite of composition An57 to Aneo. Tiny sub— hedral olivine grains and glass each constitute about 20 percent of the gréundmass and are interstitial to plagio- clase. Augite is the predominant pyroxene mineral, although pigeonite was observed in some thin sections. AGE The extensive cap of olivine basalt flows is early Pleistocene or younger in age. The basalt sheets may be of several ages. Olivine basalt overlies the Coso formation of late Pliocene or early Pleistocene in the Coso Range. Kelley (1938, p. 513) and Hopper (1947, p. 417) consider that the olivine basalt is older than the lakebeds of middle or late Pleistocene age in Darwin Wash. The writers agree although the evidence is not conclusive. The contact between basalt and lakebeds is masked by talus, and lakebeds east of the road in Darwin Wash contain no basalt fragments although they are only 200 feet from basalt and lie 60 feet lower in elevation. Some olivine basalt definitely is older than the lake- beds because older fanglomerate marginal to Darwin Wash contains fragments of olivine basalt. The fan- glomerate is the same age or slightly older than the lakebeds. In Darwin Canyon a flow of olivine basalt also overlies older fanglomerate and is probably younger than the lakebeds. OLD FANGLOMERATE MARGINAL TO DARWIN WASH Remnants of large fans are widespread marginal to Darwin Wash. The fans have been broken into isolated patches by uplift along basin-range faults and erosion from the rejuvenated streams. Gullies cut the fan east of Darwin Wash on the west flank of the Argus Range and expose as much as 25 feet of fanglomerate, but the base is not exposed. The fanglomerate is overlain by a few feet of lakebeds in secs. 16 and 21, T. 19 S., R. 41 E. F anglomerate may in part interfinger with the lakebeds but the gullies are not deep enough to show whether it does. The fanglomerate is composed mainly of subrounded fragments of limestone of Pennsylvanian and Permian age, quartz monzonite, red basaltic agglomerate, and a little olivine basalt in a pebbly sand matrix. The frag- ments are mostly 1 to 4 inches in diameter, although a few fragments reach a maximum length of 2 feet. The fanglomerate marginal to Darwin Wash is probably middle Pleistocene in age. Locally it is tilted eastward by basin-range faults. It is older or possibly in part contemporaneous with the lakebeds of middle to late Pleistocene age, but is younger than the basaltic pyroclastic rocks of probable late Pliocene age and younger than at least some of the flows of olivine basalt. LAKEBEDS Conspicuous White medium-bedded lakebeds crop out in Darwin Wash 11/2 miles east and southeast of Lane mill. A thickness of 58 feet of nearly horizontal lake- beds is exposed in gullies, but the base is not exposed. In Darwin Wash the lakebeds interfinger to the south with older fanglomerate, and to the west they mainly underlie but also interfinger near the top with older fanglomerate. On the east 25 feet of lakebeds are ex- posed overlying the fanglomerate on the west flank of the Argus Range, but gullies do not cut sufficiently deep into the fanglomerate to determine if the lakebeds also interfinger in part with the fanglomerate. Recent fans from the Darwin Hills cover the lakebeds on the west side of Darwin Wash, and on the east side of the Wash the lakebeds have been uplifted and tilted by basin-range faults and are at present being eroded. The lakebeds consist of a mixture of White to light- gray fine-grained pumiceous ash, silt, clay, and diato- maceous earth in beds 6 inches to 4 feet thick. The 38 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. grains range from 0.05 to 0.1 mm in diameter. One bed 18 inches thick and 5 feet below the top of the exposure of lakebeds in the SE14 sec. 20, T. 19 S., R. 41 E. on the east side of the main gully in Darwin Wash re— sembles tufa but is a bentonitic clay that shrank and cracked in drying. At the surface the bed has a porous, cellular texture, but on freshly broken surfaces the cells are seen to be filled with clay balls. The cells are 1 mm to 11/2 cm in diameter. Cross sections of the cells are mostly rectangular with rounded corners, but some are irregular. The cell partitions are fine-grained calcium carbonate. The clay balls are friable and easily eroded away, leaving a cellular texture at the surface. Kenneth E. Lohman of the US. Geological Survey made 11 collections of diatoms from the lakebeds in Darwin Wash and concluded that the beds were middle to late Pleistocene in age. His report of June 15, 1954, is given below : Diatoms from lakebeds 1'11 Darwin Wash [Relative abundance .is indicated by A, abundant; 0, common; F, frequent; and R, rare. Asterisk (*) indicates Darwin species that also occur in the Utah formations] Uses diatom locality 4225 4224 4226 4227 4228 4229 4233 Stratigraphic interval in feet below Ice. 4225 0 7 9 14 19 25 58 Amphora ovalis Kiitzing* ____________________________________________________________________________________ C Anomoeoneis polygramma (Ehrenberg) Pfitzer* _________________________________________________________________ A sculpta Ehrenberg _______________________________________________________________________________________ C sphaeropom (Ehrenberg) Pfitzer __________________________________________________________________________ F sp ____________________________________________________________________________ R ____________ R Caloneis bacillum (Grunow) .Mereschkowsky* _________________________________________________ F R ______ schumam'ana (Grunow) Cleve* _______________________________________________________________ R ...... s1'l1'cula var. truncatula Grunow ___________________________________________________________________________ F Campylod1'squs clypeus Ehrenberg-___________________________‘ _________________________________________________ F cf. 0. clypeus Ehrenberg _________________________________________________________________________________ F Cocconeis placentula Ehrenberg* __________________________________________________________________ R ______ Cymatopleura solea (Brebisson) Wm. Smith* ___________________________________________________________________ F Cymbella mexicana (Ehrenberg) Schmidt* ______________________________________________________________________ R parva (Wm. Smith) Cleve* _______________________________________________________________________________ F n. sp. A* ______________________________________________________________________________________________ F turgida Gregory* _______________________________________________________________________________________ F sp __________________________________________________________________________________ R ____________ F Dent1cula cf. D. tenm’s var. mesolepta Grunow ______________________________ F ______________________________ thermal’is Kiitzing ___________________________________________________ A F C F A F C Diploneis ovalis (Hilse) Cleve* ____________________________________________ R R ______ R ____________ Epithemia argus (Ehrenberg) Kiitzing* ____________________________________ C F F F F ______ F zebra var. saxom'ca Kiitzing* _________________________________________ R ______ R R F ______ Fragilaria brevistriata Grunow* _________________________________________________ ' R R __________________ R Gomphonema angustatum (Kiitzing) Rabenhorst _____________________________ R __________________ R ______ bohemicum Reichelt and Fricke _______________________________________ R ______________________________ lanceolatum Ehrenberg* ________________________________________________________________ R F ______ lanceolatum var. insignis (Grunow) ____________________________________________________________ R ______ Huntzschia amphioxys Grunow* __________________________________________ F ____________ F F R F Mastogloia elIl‘1rpt1'ca (Agardh) Cleve* ______________________________________ F ______________________________ N av1cula cf amphibola Cleve __________________________________________________________________ R ______ car1' Ehrenberg _____________________________________________________ R ______________________________ cf. N. eusp1data var.amb1'g11a (Ehrenberg) Cleve ____________________________________________________________ R guatamalensis Cleve and Grunow _________________________________________________________ . ________________ C oblonga Kiitzing* _______________________________________________________________________________________ A peregrina (Ehrenberg) Kiitzing ___________________________________________________________________________ R cf. N . radiosa Kiitzing* __________________________________________________________________________________ F cf. N.s1'mple:1 Krasske _______________________________________________ R ______________________________ Sp _______________________________________________________________ R ____________ R R ______ F N e1d1um 1'r1'd1's (Ehrenberg) Cleve _____________________________________________________________________________ R N 1tzsch1a amphibia Grunow ______________________________________________ R ______________________________ angustata (Wm. Smith) Grunow __________________________________________________________________________ R tryblionella Hamtzsch* ___________________________________________________________________________________ R Pinnularia microstauron (Ehrenberg) Cleve* _______________________________ R ______ F ______ F ______ R microstauron var. brebissonii (Kiitzing) Hustedt _________________________ R __________________ F ______ F viridis (Nitzsch) Ehrenberg* _________________________________________ R ____________ R F ______ C Rhopalodia gibba (Ehrenberg) Muller* _______________________________________________________ R F ______ C gibberula (Ehrenberg) Muller* ________________________________________ F F F ______ C R gibberula var. succincta (Brebisson) Fricke _____________________________ F ______________________________ gibberula var. margaritifera Rabenhorst ________________________________ R ______________________________ Scol1'opleura pe1'son1's Grunow* ______________________________________________________________ R ____________ C Stauroneis cf. S. phoenicenteron Ehrenberg ___________________________________________________ R ____________ Stephanodiscus astraea (Ehrenberg) Grunow ___________________________________________________________________ F astraea var. intermedia Fricke ____________________________________________________________________________ R carconensis var. pusilla Grunow ___________________________________________________________________________ R Surirella spp _______________________________________________________________________________________________ C STRUCTURE 39 Lohman reported, This assemblage of nonmarine diatoms is indicative of a lake basin in which the earliest beds (loc. 4233) were deposited in water having a fairly high salinity, possibly as high as 1,000— 2.000 parts per million of NaCl, culminating in much fresher water at the top of the section, representing the last recorded level of the lake at this locality. The relatively high frequen- cy of several species characteristic of hot springs, such as Denticula thermalis, throughout the section strongly suggests that hot springs were active in the vicinity during the time represented by the 58 feet of sediment studied. It is entirely possible that the hot-spring activity was localized near the site of the collections, but as all the collections came from an area not exceeding a few acres, nothing regarding the areal ex- tent of such activity is indicated. The lake as a whole was certainly not a hot-spring basin, as many diatoms not character- istic of hot springs are also present. The hot-spring assemblage was merely contributed to a normal lake of moderate tempera- ture and may have come from hot springs feeding a small stream which emptied into the lake basin not too far from the site of the collections. A considerable quantity of calcium carbonate (another common byproduct of some hot springs) is present in all the collections (they all effervesced with hydrochloric acid) and this also may have been contributed by hot springs, but, of course, not necessarily so. The best age assignment that can be made for this assemblage is middle to late Pleistocene, based in part upon the high per- centage of species still represented in living assemblages and in part upon a comparison with very similar assemblages from the Provo and Bonneville formations in Utah. The Darwin species that also occur in the Utah formations are indicated in the list of species by an asterisk (*). Cymbella n. sp. A. has been described from the Provo formation in a manuscript I now have in preparation. The Provo and Bonneville formations are considered to be late Pleistocene in age by Charles Hunt and others who have worked in that area. It should be mentioned that one diatom hitherto known only from late Pliocene rocks, Stephanodiscus carcanensis var. pusilla, was found in the low- est diatomaceous bed in the Darwin Wash section, but only one individual was found. and its battered condition suggests that it was reworked from older beds. A small area of dissected lakebeds is exposed on the Darwin Plateau in secs. 1 and 12 (projected), T. 18 S., R. 40 E. The beds are composed of fine—grained light- gray silt and clay and have a minimum thickness of 15 feet. The beds grade westward into fanglomerate to- ward a group of low hills of quartz monzonite. The sediments were deposited in a basin behind a flow of olivine basalt. RECENT UNCONSOLIDATED GRAVELS AND ALLUVIUM Recent deposits consist mostly of alluvial fan mate- rial, but include slope wash and stream gravels. The largest areas of alluvium are Lower Centennial Flat, Santa Rosa Flat, Lee Flat, and Darwin Wash (pl. 1). Recent alluvium includes some older alluvial fan mate— rial on Lee Flat that has been uplifted and is currently being dissected. STRUCTURE Structurally the Darwin quadrangle consists of folded Paleozoic rocks that are intruded by several plutons and interrupted by many faults (pl. 1). Bed- ding strikes north t0.N. 30° W. except in the central part of the quadrangle from the Talc City Hills east- ward to Panamint Valley where bedding trends N. 60° to 85° W. and has been tightly folded. Faults have broken the Paleozoic rocks into several structural units. Thrust faults and steep faults, some with pos- sible large strike-slip movement, were formed during the late Mesozoic orogeny. Normal faults of late Cenozoic age were important in tilting the beds and forming the present basin and range topography. STRUCTURE OF THE FEE-TERTIARY ROCKS UNCONFORMITIES No major unconformities were recognized within the Paleozoic section, although owing to the discontinuous outcrop pattern due to faulting and erosion the nature of some of the contracts was diflicult to evaluate. Bed- ding was conformable wherever unfaulted contacts were observed. The only recognized major uncon- formity in the area truncates Paleozoic rocks and in- trusive rocks of late Mesozoic age. Local unconformities and disconformities occur within the Pennsylvanian and Permian strata (fig. 14). A local unconformity in crossbedded calcarenite in the lower unit of the Owens Valley formation can be seen from the road 3,000 feet north of Millers Spring. This unconformity can be traced only several hundred feet FIGURE 14,—Local angular unconformity in the lower unit of the Owens Valley formation in Darwin Canyon. View looking north from the road 3,000 feet north of Millers Spring. The unconformity is within a block between two branches of the Darwin tear fault. 40 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. as it is within a block between two strands of the Dar- win tear fault (pl. 1). The contact between the middle and upper units of the Owens Valley formation is disconformable. The limestone conglomerate of the upper unit at Conglom- erate Mesa contains limestone pebbles and boulders as much as 8 inches in diameter that have been eroded from the underlying Permian rocks. Locally at the south end of Conglomerate Mesa near the western bor— der of the quadrangle the contact is probably an angular unconformity although the contact is poorly exposed. Minor hiatuses may be represented by pronounced changes in lithology, particularly in the change from massive dolomite and limestone to pure quartzite, as between the Pogonip group and the overlying Eureka quartzite. The stratigraphic sequence from Lower Or- dovician to Permian is virtually complete, however, judging from the incomplete fossil record, but a hiatus may exist between the Pennsylvanian and Permian. The faunal zones in the Pennsylvanian strata have a wide range in thickness. This may be due both to cut- ting out of part of the section by faults and to original variations in thickness. For example, the Tm'm'cites zone (Upper Pennsylvanian) in the Keeler Canyon formation at the type locality in the New York Butte quadrangle is about 2,000 feet thick (Merriam and Hall, 1957, p. 6—7), but on the west flank of the Santa Rosa Hills in the Darwin quadrangle the Twlticites zone is only several hundred feet,,thick. The Tm’ticites zone in the Darwin Hill is possibly as much as 4,000 feet thick, but this figure is uncertain as the fossils are not abun- dant, and the structure is complex. The writers believe that this variation in thickness of Upper Pennsylvanian strata is due to local nondeposition in a nearshore en- vironment as no evidence of erosion at the top of the Triticites zone was found in the Darwin quadrangle. FOLDS Paleozoic strata were deformed into a series of broad open folds with axes trending north to N. 20° W. during the early stages of the late Mesozoic orogeny. This folding is reflected in the Paleozoic rocks east of Con- glomerate Mesa in the northwestern part of the quad- rangle, in the Santa Rosa Hills, and in the southeastern part of the quadrangle in Darwin Wash and the Argus Range (pl. 1). The Pennsylvanian and Permian rocks are thinly bedded incompetent strata that formed many small drag folds superposed on the limbs of the major folds (fig. 7), but the drag folds are not reflected in the underlying strata. The axial planes of the drag folds in general parallel those of the major folds. DARWIN WASH SYNCLINE The major fold in the southeastern part of the quad- rangle is a broad open syncline with an axis trending northward in Darwin Wash (pl. 1, section 0—0’) . The east limb of the syncline is approximately a dipslope on the west slope of the Argus Range except for several minor folds. The west limb is largely covered by alluvium in Darwin Wash, but it is exposed in the low hills at the north end of Darwin Wash. The west limb is tightly crumpled adjacent to the biotite-hornblende- quartz monzonite in the Darwin Hills, and most of the beds are overturned. The axis of the syncline is hori- zontal south of the Darwin tear fault, and north of the fault to Darwin Falls the syncline plunges northward (pl. 1). North of Darwin Falls the syncline loses its identity, and the rocks probably become progressively older northward, although silication of the limestone makes correlation uncertain (pl. 1) . DARWIN HILLS OVERTURNED SYNGLINE The major structural feature in the Darwin Hills is an overturned syncline that was intruded near its axis by a stock and is cut by many faults (pl. 1, section C—Cl). This fold is a complex crumple on the west limb of the Darwin Wash syncline, and is caused by forceful intrusion of the batholith of the Coso Range. West of the stock the dips are generally homoclinal to the west, but the beds are overturned. North of the Darwin tear fault on the north side of hill VABM 5979 abundant crossbedding in thin—bedded limestone in the upper part of the lower unit and the upper unit of the Keeler Canyon formation show that the westward- dipping beds are overturned. South of the tear fault the Keeler Canyon formation is mostly altered to calc-hornfels, and all internal struc- tures have been destroyed. However, the strata can be shown to be progressively younger toward the east (pl. 1). “(hite marble on the hill 4,000 feet N. 45° W. of Ophir Mountain is identical with marble of the Lost Burro formation and contains fragmentary remains that. resemble cladoporoid corals. The gray medium to thickly bedded limestone band adjacent on the east is lithologically similar to the Lower Mississippian Tin Mountain limestone. It contains poorly preserved syringoporoid and solitary corals, which are compatible with correlation to the Tin Mountain. The next lime— stone band to the east on bill 5654 is a medium—gray limestone that includes abundant bedded chert and is mapped as the Perdido formation. This is followed to the east in strata on ()phir Mountain by limestone similar to the Lee Flat limestone and then by the golf- ball horizon that contains sparse tiny fusulinids at the STRUCTURE FIGURE 15.-—View looking south 1,800 feet southeast of the Christmas Gift mine showing the tight folds in the calc-hornfels of the lower unit of the Owens Valley formation on the east side of the Darwin stock. length of the Darwin Hills. base of the Keeler Canyon formation. Strata on the east side of the Darwin Hills at the Lane mine are calc- hornfels of the lower unit of the Owens Valley forma- tion. F usulinid collections from near the Lane mine and south of the Keystone mine are considered by R. C. FIGURE 16.—Photograph of an overturned isoclinal syncline in the Lucky Jim mine area. Strata in the lower left (a) are right-slde-up; bedding is nearly horizontal at (b); strata overturn at (c); and are overturned in the upper right (d). View looking south in Lucky Jim Canyon 550 feet N. 57° E. of the Lucky Jim main shaft A belt about 800 feet wide of tight folds can be traced the The belt is transitional between gently folded strata to the east and overturned. strata to the west. Douglass (written communication, 1954) to be char acteristic of the latest Wolfcamp (Permian). The axis of the overturned syncline in the Darwin Hills is in a belt of tight folds on the east side of the Darwin stock (pl. 1, section C—C’; fig. 15). At some places the most westerly fold in the belt is readily recog- nizable as an overturned syncline, but in other places the folds are not well exposed, and it is difficult to demonstrate convincingly that the strata on the west limb are overturned. The folds are difficult to photo- graph, and figure 16 is given mainly to show a locality Where overturning can be demonstrated. It shows an overturned syncline in the Lucky Jim mine area involv- ing partly silicated thinly bedded limestone of the Keeler Canyon formation. Fracture cleavage that dips steeper than bedding is sharply defined where the. beds are right side up and is an aid in determining the struc- ture. Where bedding is overturned the cleavage is much more poorly defined and tends to parallel bedding. A similar overturned syncline is well exposed in the Fernando mine area 250 feet southeast of the eastern- most workings (fig. 3). This is the westernmost fold recognized in the belt of isoclinal folds, and all the strata west of this fold are considered overturned. Several small open folds are superposed on the over- turned limb of the syncline, for example, the open an- ticlinal folds in the Defiance mine area and on the 42 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. southwest flank of Ophir Mountain (pl. 3). Both folds have younger beds in the center and older beds on the flanks and are actually inverted synclines on the basis of relative ages of the rocks as described, for example, by White and J ahns (1950, p. 196). TALC CITY HILLS SYNCLINE Ordovician and Silurian rocks at the north end of the Talc City Hills form an overturned syncline plunging southeastward that is broken by many faults (pl. 2). Hidden Valley dolomite is in the core of the syncline and Ely Springs dolomite, Eureka quartzite, and Pogo- nip group are in successive bands on the flanks. The syncline loses its identity in many fault blocks and tight folds at the southeast end of the Talc City Hills between the Homestake mine and the Alliance talc mine (fig. 3; pl. 2). The axis of a second faulted syncline 1,800 feet south of the Alliance talc mine passes through the Talc City mine. Devonian limestone and shale are in the core of the syncline, and Ordovician quartzite and dolo- mite and Silurian dolomite are on the flanks. South of the Silver Dollar mine the overturned syncline bends toward the south and is warped into several steeply plunging folds. The folds are shown on plate 2 by the trace of the contact of limestone and dolomite in the Lost Burro formation. As the main syncline is over- turned, folds superposed on the overturned limb have overturned bedding. Thus anticlinal folds superposed on the overturned limb of the syncline have younger beds in the core and are inverted synclines. smminosn mus wear The Paleozoic rocks in the Santa Rosa Hills and in the low rolling hills east of Conglomerate Mesa dip mainly west or southwest except for small open folds in the area east of Conglomerate Mesa (figs. 2, 16A). Devonian and Mississippian rocks in the Santa Rosa Hills strike about N. 30° W. and dip to the southwest. Southeast of the Lee mine the strike changes from N. 30° W. counterclockwise to about N. 80° W., and the strata dip southerly. Marble of the Lost Burro forma- tion crops out in a canyon 3.7 miles S. 27° W. of the northeast corner of the quadrangle under a basalt cover. This marble, which probably is a continuation under the volcanic cover of the band of Lost Burro marble in the Santa Rosa Hills, shows a swing or warp in the pre- volcanic structure. This swing in structure is inter- preted as warping of beds concordantly around the south end of the pluton of Hunter Mountain quartz monzonite by forcible intrusion. FAULTS Faults are largely responsible for breaking up of the Paleozoic strata into many isolated blocks that are sepa- rated by alluvium or volcanic cover. The faults can be divided into four groups as follows: thrust, strike-slip, mineralized strike, and basin-range faults. The last group is late Cenozoic in age while the others are of late Mesozoic age. rnnus'r mums Thrust faults are localized along the margin of the biotite-hornblende-quarte monzonite in the Coso Range. Two thrust faults have been mapped—the Talc City thrust in the Talc City Hills (pl. 2) and the Davis thrust in the Darwin Hills (pl. 3). The thrusting along both faults was toward the east or northeast away from the intrusive mass. TALO CITY THRUST‘ In the Talc City Hills rocks of Mississippian to Ordovician age have been thrust principally over folded Pennsylvanian and Permian strata. The thrust sheet originally was at least 5 miles long in a northwesterly direction and 2 miles wide, but it subsequently was broken by many steep faults trending N. 70° to 80° W., and it has been in part removed by erosion (fig. 4). The thrust is exposed at only a few localities. The most accessible exposures are at the Alliance talc mine and at the Silver Dollar mine (pl. 2). At the Alliance talc mine Eureka quartzite and Ely Springs dolomite are thrust over folded thinly bedded limestone of the Keeler Canyon formation (fig. 17). Two klippen of Eureka quartzite and Ely Springs dolomite thrust over Penn— sylvanian limestone of the Keeler Canyon formation are exposed a few hundred feet south of the Alliance talc mine. The thrust is also exposed at the Irish lease FIGURE 17,—Talc City thrust at the Alliance talc mine. Two klippen of Ely Springs dolomite (Oes) and Eureka quartzite (09) over Penn- sylvanian and Permian Keeler Canyon formation (PPk) are exposed near the center of the picture several hundred feet south of the AllianCe talc mine. At the Irish lease the thrust fault is displaced locally by a steep fault; so the contact in the workings is steep, but it continues as a flat-lying thrust contact east of the workings as shown by its sinuous trace. View looking north at the Alliance talc mine. STRUCTURE 43 in the southeast part of the Alliance mine where shale lithologically similar to Rest Spring shale is present in the fault zone. A steep fault has displaced the thrust ' fault in the workings of the Irish lease but the trace of the fault is flat-lying to the east of the mine. At the Silver Dollar mine, massive bufl' dolomite of the Devonian Lost Burro formation is thrust over the Keeler Canyon formation. The thrust is exposed 300 feet north of the main pit of the lead-silver workings. Rest Spring shale is also present here in the fault zone. About 3,000 feet north of the Silver Dollar mine an imbricate structure is exposed. Medium-bedded gray Tin Mountain limestone is thrust over the Perdido formation, which, in turn, is thrust over Rest Spring shale and the Keeler Canyon formation. At the north end of the Talc City Hills 1.3 miles north of the north- ernmost workings of the White Swan mine the Pogonip group and Eureka quartzite are thrust over Rest Spring shale, Lee F lat( ?) limestone, and the lower unit of the Owens Valley formation of Permian age. The thrust sheet moved toward the northeast, but as the area southwest of the Talc City Hills is covered by alluvium, the net slip cannot be measured. The stratigraphic throw of the fault is locally as much as 5,900 feet where the Pogonip is thrust over the Keeler Canyon formation. The net slip is probably about 3 miles, but this is not much more than a guess based on projecting the geology from the southern Inyo Moun- tains (Bateman and Merriam, 1954, map 11). DAVIS THRUST A thrust fault that strikes northerly and dips 23° to 60° W. crops out in the Darwin mine area (pl. 3). Where exposed it involves only strata of the lower part of the Keeler Canyon formation. The fault is exposed at the surface at the Essex and Independence workings of the Darwin mine, 500 feet west of the portal of the Thompson adit, and 600 feet west of the portal of the Defiance adit (pl. 3). Many drag folds are localized in thinly bedded limestone in the hanging wall of the thrust. The largest and more conspicuous is the open anticlinal shaped fold in the southwest side of Ophir Mountain (pl. 3). The drag folds have a dextral pattern and most plunge gently to the north. They indicate a thrust movement toward the north- east, but the net slip is not known. All the contacts between formations on the west side of the Darwin Hills are faults that are parallel to but above the Davis thrust (pl. 1). The limestone and marble within a few feet of the faults are intensely drag folded, but the drag folds have a sinistral pattern in- stead of a dextral pattern like those near the Davis thrust. Most of the drag folds plunge gently to the 820628 0—62——-—4 north. A strong lineation that plunges steeply down dip in the a direction is developed in some of the drag folds (pl. 3). The lineation is shown by stretching of rounded chert nodules in the golfball horizon and by the disruption of sandy limonitic beds 14 to 1/2 inch thick into pencillike units 6 to 8 inches long. Drag folds bordering the faults overlying the Davis thrust indicate that they are normal faults. The Davis thrust was caused by forceful intrusion of the batholith of the Coso Range, which overturned the Keeler Canyon and thrust it up and toward the northeast. The overlying normal faults probably indicate minor readjustments upon relaxation of the push from the intrusion, but they could be formed if each footwall block was thrust up farther than the corresponding hanging—wall block. STRIKE-SLIP FAULTS Strike-slip faults are present both in the Santa Rosa Hills and in the Darwin Hills. The faults characteris- tically have a left-lateral displacement. Those in the Santa Rosa Hills trend about N. 30° W. parallel to the strike of bedding and dip 55° to 60° SW., whereas those in the Darwin Hills are steeply dipping trans- verse faults (pl. 1). The two major faults in the Santa Rosa Hills are the Lee and the Santa Rosa Flat faults (pl. 1). Both trend about N. 30° W. parallel to the strike of bedding and dip about 60° SW. Small calcite-filled gash frac- tures that strike about N. 80° W. and dip steeply north are localized near the faults. The block of Mississip- pian Tin Mountain limestone between the two faults is tightly folded and has axial planes that dip steeply westward. The folds are poorly exposed except in a few gullies as the limestone in the crests of the folds is shattered. The plunge of the folds could not be de- termined. The amount and direction of displacement on the Santa Rosa Flat and Lee faults are not known, but a left-lateral strike-slip displacement with the east block moving N. 30° W. is postulated. The faults must have a reverse component also as older beds are brought up to the west. The strike-slip movement is postulated on the basis of near juxtaposition of the Lee Flat lime- stone and Rest Spring shale on opposite sides of the faults. Part of the Lee Flat limestone in the Darwin quadrangle is a time-stratigraphic equivalent of the Rest Spring shale. It occurs only on the east side of the Lee fault in the Santa Rosa Hills, Whereas Rest Spring shale occurs locally in the Santa Rosa Flat fault zone and to the southwest in fault zones in the Talc City Hills. Reconnaissance work has shown that Lee Flat limestone is present and shale is absent in the Argus Range to the southeast. The facies change from Rest Spring shale to Lee Flat limestone on opposite 44 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. sides of the faults in the Santa Rosa Hills is abrupt, and the Lee Flat limestone probably was faulted from the southeast to near juxtaposition with the Rest Spring shale. The gash veins along the Santa Rosa Flat and Lee faults also indicate a left-lateral displacement for these faults. The Tin Mountain limestone between the two faults was tightly drag folded. The limestone, which probably was under shallow cover at the time of faulting, shattered like a brittle rock at the crest of folds instead of flowing plastically. Two systems of transverse strike-slip faults occur in the Darwin Hills. The major set strikes N. 60° to 80° W.; the minor set strikes N. 60° to 80° E. Faults of both systems have left-lateral displacement. The major fault is the Darwin tear fault, which was de- scribed previously by Kelley (1938, p. 518) and Hopper (1947, p. 420). It trends N. 70° to 80° W. from the Argus Range at the south end of the stock of leucocratic quartz monzonite at Zinc Hill to the Talc City Hills, where it merges with the local N. 60° to 80° W. struc- tural trend in the tale district (pl. 1). The displace- ment of the Darwin tear fault is 2,200 feet, with the north block moving westward relative to the south block. The direction of movement is shown by drag, nearly horizontal slickensides, and mullion structures. The displacement is shown by the following displaced units: the contact between the Keeler Canyon and Owens Valley formations, the axis of the syncline in Darwin Wash, and a conspicuous limestone bed 10 feet thick that contains abundant solitary corals and cri- noidal debris that crops out 2,200 feet N. 28° W. of Millers Spring. The vertical displacement is negligi— ble as both steeply dipping and horizontal beds in flat topography have the same offset. Another left-lateral transverse strike-slip fault—the Standard fault—is between the Darwin tear fault and the Independence workings of the Darwin mines (pl. 1). The Standard fault is a mineralized fault zone as much as 50 feet thick that cuts biotite-hornblende-quartz monzonite in the Darwin Hills; the fault passes through the Stand— ard group of claims in sec. 18, T. 19 S., R. 41 E. The long adit on the Standard claim is along this fault (fig. 3). The displacement on the fault apparently is several hundred feet, north side west. The second set strikes N. 60° to 80° E. These faults are abundant at all the principal lead-silver-zinc and tungsten mines in the Darwin Hills south of the Dar- win tear fault. They are mineralized faults that cut biotite—hornblende-quartz monzonite, and they are one of the important ore controls for both tungsten and lead—silver-zinc ore bodies. Displacement is small on these left-lateral faults. The north block has moved west less than 200 feet relative to the south block on all of them. Faults in this set include the Copper, Water tank, Lane, Bernon, 434, and Defiance faults (pl. 3) and northeastward-striking faults near the Fernando and St. Charles mines (fig. 3). The direction of move— ment is shown by offset of biotite—hornblende-quartz monzonite and by abundant nearly horizontal slicken- sides. Most of the faults that strike N. 60° to 80° E. are cut off by the Davis thrust, but some faults displace the thrust (pl. 3). The Copper fault displaces the Davis thrust 90 feet, north side west. The two sets of transverse strike-slip faults cannot be complementary shears as both are left-lateral faults; one set would have right-lateral displacement if they were complementary. Nor does it appear likely that the faults that strike N. 60° to 80° E. are tension frac- tures, as the displacement is mainly strike-slip and the fault zones are too sheared to be formed under tension. McKinstry (1953, p. 404) in his report on shears of the second order used the Darwin faults as one of his ex- amples, and he called the faults that strike N. 60° to 80° E. shears of the second order. He defined a shear of the second order as one caused by change in orientation of the planes of maximum shearing stress due to fric- tion during movement along a shear plane. The maxi- mum shearing stress changes from 45° before move- ment to an approximate angle given by the formula (we where ¢ is the angle of kinetic friction. A shear of the second order seems a reasonable explanation for these faults. mnmmznn sun? STRIKE mum's Steep mineralized strike faults are in both the Darwin Hills and the Talc City Hills. In the Darwin mine, ore is localized in steep north-striking faults. The faults are concentrated near the faults that strike N. 60° to 80° E. and die out away from these transverse faults. Displacement on the northward—striking faults is negligible. They are probably tension fractures formed at about the same time as the transverse N. 60° to 80° E. faults. In the Tale City Hills the overthrust sheet is dis— placed by several N. 60° to 80° W. faults that are parallel to‘the strike of the beds in the thrust sheet. These faults are mineralized and commonly localize talc ore bodies. The Talc City thrust is displaced vertically by the faults, but the north side may have been either raised or lowered (pl. 1, section B—B’). The vertical displacement of the thrust could be caused by strike- slip movement, vertical movement, or by a combination of both. STRUCTURE 45 FOLIATION Foliation is poorly defined in the Paleozoic rocks in the Darwin quadrangle. Locally the Keeler Canyon and Owens Valley formations have a fracture cleavage. It is well-defined in the middle unit of fissile shale in the Owens Valley formation on the east side of Con- glomerate Mesa (pl. 1). The fracture cleavage is as much as 90° to bedding, and the shale must be examined closely for bedding. Fracture cleavage is also locally developed in the belt of tightly folded rocks on the east side of the Darwin stock. At the Lucky Jim mine the fracture cleavage is an aid in working out the structure. SUMMARY The probable sequence of events during the late Meso- zoic orogeny is summarized below. The Paleozoic strata were first deformed into a series of broad open folds that formed the Darwin Wash syncline and tilted the Paleozoic rocks in the Santa Rosa Hills homoclin— ally westward. These folds have flat-lying axes that trend northward. The gently folded Paleozoic strata were then forcefully intruded by biotite-hornblende- quartz monzonite in the Coso Range and in the north- eastern part of the quadrangle during the Jurassic period. In the Darwin Hills older strata brought up by the intrusion in the Coso Range were overturned, tightly folded, and faulted. With release of pressure by cooling and crystallization of the batholith, minor adjustments took place onthe west limb of the Darwin syncline and formed normal bedding plane faults (pl. 1, section C—Cl). The Paleozoic rocks were folded and faulted before silication of the limestone around the in- trusive body. The tight folds spatially are directly re— lated to the periphery of the batholith, but the folding cannot be due to a buttressing effect of a large intru- sive body during late compression. The tightly folded structures in calc-hornfels reflect plastic deformation of incompetent beds and indicate that the folding pre- ceded silication of the limestone. The Paleozoic strata in the Tale City Hills and south— ern Santa Rosa Hills were squeezed between the two major intrusive masses (pl. 1). The beds were rotated from a northerly to a N. 60° to 80° W. strike. Defor- mation caused rupture along the Darwin tear fault and Standard fault. The Darwin tear fault must have moved both before and after silication. It controlled in part the silication of the limestone in the Darwin Hills, but the silicated limestone has also been sheared. After rotation of the beds, older Paleozoic rocks were thrust northeast over Carboniferous and Permian beds in the Talc City Hills, and the thrust sheet was broken by steep strike faults. CENOZOIC STRUCTURES The Darwin quadrangle is on the east flank of a broad regional warp of probably late Pliocene age that had an axis along the east side of Owens Valley. All the mountain ranges and basins in both the Darwin quad— rangle and adjacent Panamint Butte quadrangle on the east are east-tilted fault blocks. This includes the southern Inyo Mountains, Coso Range, Darwin Hills, Argus Range, and Panamint Range. The Sierra Ne- vada is the west side of the warp. Although the broad warp is the principal Cenozoic structural feature, it is only evident where late Cenozoic basaltic flows form extensive dipslopes. Examples of basaltic dipslopes are in the southern Inyo Mountains northwest of the talc mines and on Darwin Plateau, which slopes toward Panamint Valley. The warp has been broken by north—trending faults into a series of east-tilted blocks that form basins and ranges. The faults may have either normal or reverse movement, although in the area as a whole normal faults are more abundant. The observed displacement on most faults is only a few tens of feet, although a few have displacements of hundreds of feet. Northward-striking late Cenozoic faults form con- spicuous topographic features in the eastern part of the quadrangle. A swarm of steep faults, most of which are downthrown on the east, displace the extensive ba- saltic capping in the northeastern part of the quad- rangle and in part caused the depression of Panamint Valley. The displacement of basalt on most of the faults is less than 50 feet, but the basin-range fault that passes through Darwin Falls is downthrown more than 400 feet on the east. Another swarm of steep faults south of these faults is on the west flank of the Argus Range, but this swarm has the opposite displacement with the east side up. Blocks between these faults, though, are tilted toward the east. The faults in the Argus Range cannot be traced north of the lower reaches of Darwin Wash, and they probably are not continuations of the faults in the northeastern part of the quadrangle. The Argus Range is an east-tilted fault block. Oli- vine basalt on the west flank of the Argus Range has been displaced about 1,600 feet in a series of step faults (fig. 18). The basalt on the east flank dips mostly 10° to 15° E. and basin-range faults are much less common. Most of the faults on the tilted east side are normal faults that are downthrown on the mountain side. The south end of the Inyo Mountains is also an east- tilted fault block. Knopf (1918, p. 88) described the step faults on the west flank of the range. The total displacement of the step faults on the west flank of the 46 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. «29%. FIGURE 18.—View of the west flank of the Argus Range from Darwin Wash showing a step-faulted basaltic flow. The range is an east- tilted fault block. Inyo Mountains in the Keeler quadrangle is about 2,000 feet. Basalt flows on the east flank of the southern Inyo Mountains are tilted to an average dip of about 10° E. and are broken by a few basin-range faults (pl. 1). The most conspicuous fault on the east flank, the Santa Rosa fault, drops the east side about 400 feet. Other faults on the east flank show only small displace— ment of the basaltic flows, but most of them are down- thrown on the mountain side. North of the Keeler and Darwin quadrangles, late Tertiary and Quaternary up- lift of the Inyo Mountains on both the east and the west sides must be much greater, but basalt is absent, so no readily recognizable displaced marker bed is present. Some of the strike faults in the Santa Rosa Hills have had renewed movement of late Tertiary or Quaternary age. The fault zones are jumbled masses of breccia. and gouge in contrast to the healed fault zones of the older faults, and they have excellent topographic expression. Remnants of basalt flows in the Santa Rosa Hills have been uplifted about 500 feet relative to the flows on Lee Flat by late Cenozoic movement. The Coso Range extends only slightly into the Dar- win quadrangle, and owing to the lack of an extensive basalt cover the structure is not definitely known. The most conspicuous fault is a fault downthrown on the west along the northeast front of the range. Such faults are common at the foot of east-tilted fault blocks. METAMORPHISM Most of the Paleozoic sedimentary rocks and a few of the Mesozoic intrusive rocks are somewhat altered. The alteration has been caused mainly by igneous meta- morphism and to a lesser extent by regional metamor- phism. The recrystallization of the Hidden Valley dolomite and the limestone of the Lost Burro formation may have been done by regional metamorphism, but both formations in the quadrangle are located near borders Of areas affected by igneous metamorphism. Only igneous metamorphism is described. IGNEOUS METAMORPHISM Igneous metamorphism includes all' the physical, mineralogical, and chemical changes induced in a rock by intrusion of a plutonic body. The changes are either endomorphic, induced within the intrusion, or exomorphic, induced within the invaded rock. Alter- ation of the igneous rocks has been on a small scale, but changes in limestone near intrusive bodies are wide- spread. The most important exomorphic change is the contact metamorphism and contact metasomatism of limestone—the formation of calc-hornfels and tactite. METAMORPHISM WITHIN THE IGNEOUS ROCKS The major intrusive bodies in the Darwin quadrangle are not altered. The northern part of the biotite-horn- blende-quartz monzonite in the Darwin Hills, however, probably was intensely altered at or slightly after the time of emplacement. Quartz monzonite at the surface near the Thompson workings of the Darwin mine is a highly iron-stained, deeply weathered rock, whereas at the south end of the stock the quartz monzonite is unal— tered (pl. 3). Because of the deep weathering, it was impossible to find fresh specimens to study. It is prob- able that the weathering was'due to previous argillic alteration of the quartz monzonite. METAM ORPHI‘SM 0F LIMESTONE The various limestones of post-Silurian age have re- acted difl'erently to metamorphism. The Lost Burro formation of Devonian age was bleached and nearly completely recrystallized to marble, but the Tin Moun- tain limestone and the Perdido formation were only slightly affected by metamorphism. The Lee Flat lime- stone, Keeler Canyon formation, and the Owens Valley formation were extensively altered to calc-hornfels and tactite near intrusive bodies. The original composition of the limestone is chiefly responsible for the type of alteration. Limestone in the Lost Burro formation is clean and recrystallized to marble, whereas the lime- stone beds Of the Lee Flat, Keeler Canyon, and Owens Valley formations are mostly silty, sandy, or argil- laceous and formed silicated limestones. RECRYSTALLIZATI ON TO MARBLE The Lost Burro formation of Devonian age was the most susceptible limestone for recrystallization to marble. The upper 1,100 feet of the Lost Burro forma- METAMORPHISM 47 tion in the Darwin quadrangle is entirely recrystallized to white or light-gray marble. About half of the lower 650 feet of the exposed section of the Lost Burro forma- tion northeast of the Lee mine is bleached and recrystal— lized. The Tin Mountain limestone is bleached and recrystallized to marble in a band about 1,000 feet wide on the west side of the Lee Flat fault 5,000 feet S. 70° W. of the Lee mine. The Lee Flat limestone is also bleached and recrystallized to marble in a band 500 to 600 feet wide north of the Darwin mining camp along the west side of the Darwin Hills. In the Argus Range the Lee Flat limestone north and south of the stock of leucocratic quartz monzonite at Zinc Hill is bleached and recrystallized to white marble for 500 to 900 feet. Locally, pure limestone lenses in the Owens Valley for- mation are recrystallized to marble. On the whole re- crystallization to marble in the Mis'sissippian and younger limestones is on a small scale and is limited to strong fault zones and close to contacts with igneous bodies. DOLOMITIZATION Dolomitization is not widespread in Paleozoic rocks in the Darwin quadrangle. Most of the dolomite in the quadrangle is in Devonian, Silurian, and Ordovician strata in the Tale City Hills. Regional mapping by the US. Geological Survey in adjacent areas (McAllister, 1952, 1955; Merriam, 1954) has shown that these strata are sedimentary dolomite. However, the dolomite over much of the Talc City Hills is recrystallized and does not resemble its counterpart in less altered areas. The Silurian and Devonian dolomite is massive and buff colored in the Tale City Hills but is more commonly medium-bedded, light- to medium-gray dolomite where unaltered. At some places in the Talc City mine area relicts of light- to medium-gray dolomite remain in the massive buff dolomite, and several beds of limestone can be traced discontinuously in the dolomite. The original Lower Devonian and Silurian strata were light-gray medium—bedded dolomite but included thin beds of medium-gray limestone in the Devonian. The dolomite was recrystallized near the stock of leucocratic quartz monzonite to bufi' massive dolomite, and the thin lime- stone beds were in part dolomitized, particularly at the crests of folds. In the Darwin mine area and at the Zinc Hill mine, limestone locally has been dolomitized along faults. At the Darwin mine 2,500 feet south of Ophir Mountain, the Lee Flat limestone is altered to massive buff dolo- mite along a bedding plane fault for about 150 feet (pl. 3). At the Zinc Hill mine Mississippian limestone is also altered to dolomite along or near faults. All the dolomite in the Talc City Hills was consid- ered by Page (1951, p. 8) to have formed by hydro- thermal alteration of limestone. Quadrangle mapping by McAllister (1955), C. W. Merriam and W. C. Smith (Bateman and Merriam, 1954, map 11) in the New York Butte quadrangle, and by the writers, however, has shown that most of the dolomite in the Ordovician, Silurian, and lower part of the Devonian has a regional distribution. Peripheral to the stock of leucocratic quartz monzonite in the Talc City Hills much of the stratified dolomite is recrystallized to a massive, buff dolomite that does not resemble dolomite in equivalent stratigraphic positions in unaltered sections. Relicts of the unaltered dolomite in the massive buff-colored dolomite commonly give it a mottled appearance. The limestone-dolomite contact in the Lost Burro formation is well exposed 2,500 feet east of the Talc City mine; it is virtually conformable but is locally irregular owing to the dolomitization at the crests of folds (pl. 2). Several limestone beds less than 50 feet thick that are interbedded with the dolomite are in part dolomitized and have a discontinuous outcrop pattern. ALTERATION T0 CALG-HORNFELS, CALC-SILICATE ROCK, TACTITE AND Alteration of limestone and impure limestone to calc- hornfels, calc-silicate rock, and tactite has been wide- spread about the major intrusive bodies. The altera- tion is shown by an overlay pattern on the regional map (pl. 1). C‘alc-hornfels is a dense aphanitic light- colored rock generally considered to form by the vir- tually isochemical recrystallization of impure limestone. The mineralogy of calc-hornfels varies, but it contains some or all of the following minerals: diopside, wol— lastonite, idocrase, garnet, relict calcite, plagioclase, orthoclase, quartz, tremolite, and epidote. Tactite (Hess, 1918, p. 378) is a rock formed by contact meta- morphism of limestone or dolomite into which foreign matter has been introduced by hot solutions or gases from the intruding magma. In the Darwin Hills light- colored tactite, composed predominantly of wollaston- ite, idocrase, and garnet, and calc—hornfels have grada- tional contacts, and they are not everywhere distin- guished on the mine maps. Light-colored tactite is shown as medium-grained calc-silicate rock on the Dar- win mine map (pl. 3) ; however, a dark-colored tactite composed of epidote, idocrase, or andradite that is local- ized at intrusive contacts or along faults, especially at intersections with pure limestone beds within several hundred feet of an intrusive contact, may readily be distinguished (pl. 3). The Lee Flat limestone and Keeler Canyon and Owens Valley formations were particularly susceptible 48 to alteration to calc-hornfels and tactite minerals. The largest area of calc-hornfels is in the Darwin Hills as a contact metamorphic alteration around biotite—horn- blende-quartz monzonite. Impure limestone beds of Pennsylvanian and Permian age are altered to calc- hornfels and locally to tactite in an area 41/; miles long and 1 mile wide (pl. 1) . The Darwin tear fault is the approximate northern limit of the alteration. Parts of a. large area of calc—hornfels are exposed under basalt in the eastern part of the quadrangle near Darwin Falls and in all the canyons draining into Panamint Valley from Darwin Canyon to the canyon 2 miles north of Rainbow Canyon. Calc-hornfels must underlie much of the extensive basalt cover in this area. Calc-hornfels also crops out around the intrusive body at the south end of the Santa Rosa Hills and in the southern Inyo Mountains at the Santa Rosa mine (pl. 1) . In the Darwin Hills the altered rock ranges in gen- eral from medium-grained light-colored calc-silicate rock and minor dark tactite close to the contact of biotite-hornblende-quartz monzonite through dense white, light—gray, brown or greenish-gray calc-hornfels to partly silicated limestone at the outer margins of the altered zone (pl. 3) . Although the alteration generally is more intense and the altered rock is coarser grained near the intrusive body, many exceptions occur because of differences in composition of the original beds and because of more intense alteration close to ore bodies and faults. For example, at the Defiance workings of the Darwin mine (pl. 3) dense white calc-hornfels is in a band 50 to 100 feet wide adjacent to the biotite— hornblende-quartz monzonite, and medium-grained calc-silicate rock occurs westward for the next 500 feet to the Davis thrust. West of the Davis thrust the calc- hornfels is dense and grades into partly silicated lime- stone interbedded with unaltered limestone. Samples of silicated limestone were taken at 25-foot intervals away from the Defiance ore body on the 570, 700, and 800 levels and at irregular intervals over the surface for a study of the alteration (pl. 3). At the outer margin of the altered zone silication is selective; impure limestone beds are partly or completely altered to calc-hornfels but purer limestone beds are unchanged. Differences in color, grain size, and mineralogy occur between adjacent thin calc-hornfels beds. The silty limestone beds are readily converted to calc-hornfels. The grain size is commonly 0.02 to 0.05 mm. Tremolite, orthoclase, scapolite, clinozoisite, and sphene may be present. In the Defiance area east of the Davis thrust, the alteration is more intense (pl. 3). The calc-hornfels and calc-silicate rock here typically is a white to light greenish gray rock that consists predominantly of wol- GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. FIGURE 1,9.—.Photomicrograph of medium-grained light-gray calc-silicate rock from the inner zone of contact-metamorphosed limestone from the Defiance area. The rock consists almost entirely of wollastonite (we) and diopside (dl). A veinlet of calcite (ct) cuts the rock. The initial stage of replacement of diopside and wollastonite by garnet (gn) is shown. Plane polarized light, 40 X. lastonite and diopside (fig. 19). Garnet idocrase, orthoclase, clinozoisite, oligoclase, forsterite, tremolite, sillimanite, sphene, and apatite may be present. Grain size is mostly 0.5 to 2 mm, but locally it is coarser. Gar- net and idocrase replace diopside and wollastonite (fig. 20) as the grade of metamorphism increases. The dense White calc-hornfels in the inner zone of contact meta- morphosed limestone at the Defiance workings (pl. 3) is composed nearly entirely of wollastonite (fig. 21). It forms felted masses of laths less than 0.1 mm long with diopside in dense calc-hornfels. Near intrusions wollastonite forms megacrystalline radial masses and a few large crystals as much as 6 inches long that are replaced by garnet and idocrase (fig. 22). As the amount of garnet and idocrase increase, the rock be- comes greenish gray to light green. Garnet and ido- crase, the principal late minerals formed during the period of silication, are common gangue minerals in the replacement ore bodies (fig. 23). The garnet is light-green andradite. It is slightly birefringent and very commonly it is zoned. The specific gravity ranges from 3.627 to 3.872, and the index of refraction is 1.826 to 1.885. Garnet is Widespread through the calc-silicate rock and tactite, but it increases in grain size and abun- dance near ore bodies and intrusive contacts. Locally tactite composed entirely of garnet is found along in- trusive contacts or in faults near them. Idocrase is generally‘associated with garnet but is much less abun- dant. It occurs as euhedral to subhedral prisms in the medium-grained calc-silicate rock (pl. 3). METAMORPHISM 49 FIGURE 20,—Photomicrograph of light-green tactite composed predomi- nantly of garnet (gn). Corroded relictl of diopside (di), wollastonite (wo) and calcite (ct) are in the garnet. Specimen from the 800 level of the Defiance workings. Crossed nicols, 44 X. v v .112», i ’é‘.. 3 ‘53:) . ’4" ‘ ‘ . FIGURE 21,—White fine-grained calc—hornfels. The rock is composed of tabular and radial crystals of wollastonite (wo) with interstitial calcite (dark). Only one diopside (di) crystal is present in the photomicrograph, but the mineral is disseminated in small amounts throughout the rock. Plane polarized light, 22 X. Some material was added to the medium-grained Gale-silicate rock that is so widespread in the Darwin mine area. Two analyses of unaltered limestone from the Fairbanks mine and from an area near the Lead Hope mine (fig. 3) were compared with one analysis of oak—silicate rock from the surface between the Ber- non and Defiance workings of the Darwin mine (pl. 3). These samples were taken from strata believed to be the approximate unaltered equivalent of the medium- grained Gale-silicate rock in the Defiance area of the Darwin mine. The calc—silicate rock consists predomi— FIGURE 22.———Photomicrograph of light-greenish-gray tactite composed of coarse-grained wollastonite (wo) that is partly replaced by andra- dite garnet (dark mineral). Specimen from the inner zone of meta- morphosed limestone in the Defiance workings of the Darwin mine. Crossed nicols, 22 X. FIGURE 23.—Photomicrograph of specimen of low-grade are showing replacement of garnet (ga) and idocrase (id) tactite by sulfide min« erals (dark). Some relict calcite (ct) is present in the garnet. Specimen from the 800 level of the Defiance workings. Plane polarized light, 30 X. nantly of wollastonite but contains some garnet, ido- erase, and diopside. The results of the analyses are given in table 3. The most pronounced chemical changes during silication are an increase in silica and 50 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. decrease in carbon dioxide. It is probable also that some alumina was added. Iron, magnesia, lime, and alkalies remained Virtually unchanged. TABLE 3.—Analyses of limestone and calc-hornfels from the Darwin H ills [Rapid analyses by P. L. D. Elmore, K. E. White, and P, W. Scott, U.S. Geologi- cal Survey 1954-55] :2. US 0 A1203 ..... Total Fe as MgO _____ N“ 2".” fiwpafi p—I (glob-‘QQD-IWH “cmgmm .5 .10 .10 34.8 .40 S??fi... Total _________________________________________ 99 100 A. Limestone of the Keeler Canyon formation from the Lead Hope mine. B. Limestone of the Keeler Canyon formation from the Fairbanks mine. 0. Medium-grained calc-silicate rock from the surface between the Bernon and Defiance workings of the Darwin mine. Dark-green tactite locally replaces calc—hornfels and medium—grained calc-silicate rock along faults near intrusive contacts. Garnet generally is the predominant mineral and may be the only mineral present, forming the rock garnetite. Tremolite, garnet, epidote, zoisite, and coarse-grained calcite are commonly present. The dark tactite forms mainly as a replacement of pure limestone and marble. It is in small bodies a few inches to several feet wide and generally less than 50 feet long. ALTERATION TO FELDSPATEIC ROCK Locally calc—hornfels is altered to a feldspathic rock at the margins of the stock of biotitehornblende-quartz monzonite in the Darwin Hills and around some of the small satellitic bodies. The most conspicuous felds- pathic rock is in the Defiance workings of the Darwin mine and along the crest of the ridge 600 feet southwest of the Defiance inclined shaft (pl. 3). It is exposed on the 800 level of the Defiance workings 185 feet N. 15° E. of the main shaft in a dike. It probably formed by replacement and contains perthitic orthoclase, pyrite, fluorite, and sphalerite. The feldspathic rock ranges from a porphyroblastic rock that contains euhedral porphyroblasts of perthitic orthoclase as much as half an inch square in a ground- mass of orthoclase 11/2 to 1 mm in diameter, to calc- hornfels containing diopside, garnet, and calcite or wollastonite, diopside, and calcite that is partly replaced by feldspar (fig. 24). Where the replacement is com- plete, orthoclase makes up nearly 100 percent of the rock, and the rock is a kalisyenite. Kalisyenite occurs as thin dikes of probable replacement origin that cut calc-hornfels and as irregular zones within masses of partly feldspathized calc—hornfels. Sulfide minerals FIGURE 24.—Photomicrograph of partly feldespathized calc-hornfels. 0n the left side of the photomicrograph is a fine-grained mixture of wollastonite (we) and calcite (ct). Perthitic orthoclase (for) cor- rodes and replaces the fine-grained calcite and wollastonite and coarsely crystalline calcite. A veinlet of sphalerite (s1) (dark min- eral on the lower right) cuts the rock and is the youngest mineral. Crossed nicols, 30 X. and fluorite are abundant (fig. 25). Pyrite and sphal- erite are the most abundant sulfide minerals and com- monly constitute more than 10 percent of the rock. Galena may be present. Fluorite is a deep purple variety and may constitute several percent of the rock. ALTERATION T0 AMPHIBOLITE Amphibolite crops out for 2 miles in Darwin Canyon near Darwin Falls, for 0.2 miles in the canyon three- FIGURE 25,—Photomicrograph of kalisyenlte dike from the Defiance working of the Darwin mine. The dike consists of coarse-grained orthoclase (or) that is partly replaced by purple fluorite (f), pyrite (py), and sphalerite (sl). Minor calcite (ct) is a relict mineral between grains of orthoclase. Crossed nicols, 30 X. GEOLOGIC HISTORY 51 fourths of a mile north of Darwin Canyon, and for 1 mile in the canyon 1% miles north of Darwin Falls (pl. 1). It nonconformably underlies olivine basalt in the canyons, and it probably underlies basalt in most of the area between the canyons. A few small areas of amphibolite are present around the Christmas Gift and Darwin mines. Amphibolite is characterized by its nonhomogeneity. 'Most of it is a fine-grained greenish-gray rock that is cut by stringers and lenses of epidote. It grades locally into a porphyritic rock but includes porphyroblasts of hornblende in a fine-grained groundmass. The weathered surface is dark green to dark brown. Small pegmatitic lenses of hornblende and plagioclase are irregularly distributed through the diorite; the con- tacts of the pegmatite lenses are gradational. Bedding, which is readily recognized in the adjacent calc-horn- fels, locally can be recognized in the amphibolite. Amphibolite grades outward in a transition zone ‘10 to 20 feet wide into calc-hornfels in Darwin Canyon below Darwin Falls. Near the contact of amphibolite the calc-hornfels contains small irregular masses of epidote and thin veinlets of amphibolite that are mostly parallel to bedding. Abundant dikes and small plugs of amphibolite cut calc-hornfels and limestone close to the main body of amphibolite at Darwin Falls. The amphibolite map unit is composed principally of amphibolite, epidote amphibolite, hornblende diorite, and hornblende gabbro. They are fine-grained rocks composed of hornblende, plagioclase, and clinozoisite and small amounts of quartz, calcite, scapolite, apatite, and magnetite. The amount of plagioclase ranges from zero in some of the amphibolites to a maxi- mum of about 50 percent in diorite and gabbro, and it ranges in composition from albite to labradorite. The calcic plagioclase fOrms euhedral crystals with promi- nent albite twinning; the sodic plagioclase is anhedral and lacks twinning. Hornblende forms porphyro— blasts commonly 6 to 8 mm long that poikilitically en- close all other minerals. Clinozoisite is finely dissemi- nated through the groundmass and also forms large porphyroblasts. Hornblende is the predominant mafic mineral in the rocks with calcic plagioclase; clino- zoisite is more abundant where the plagioclase is albite. Highly calcic scapolite is common in epidote amphibo- lite but is much less abundant in the diorite and gabbro. Epidote amphibolite contains hornblende, clinozoisite, zoisite, and scapolite, and it differs from the diorite mainly in the lack of plagioclase. Some relict textures and structures of the silty lime— stones are recognizable. Locally relict bedding struc- tures can be recognized in the amphibolite near the contact with calc-hornfels. Corroded calcite grains dis- seminated through the groundmass of the epidote am— phibolite and some of the diorite are interpreted as relicts. The paragenosis is interpreted as follows: 1. Intrusion of quartz monzonite into silty limestone. 2. The impure limestone is altered to epidote amphi- bolite with clinozoisite, albite, scapolite, and minor hornblende and chlorite. Some relict calcite is present. 3. Epidote amphibolite is further altered to amphi- bolite and diorite. Clinozoisite is converted to horn- blende; plagioclase becomes more calcic. The grain size is increased and locally becomes pegmatitic. Epidote amphibolite is believed to be the first step in the alteration of calc—hornfels to amphibolite. The epidote amphibolite is finer grained and more hetero- geneous than amphibolite and diorite. It contains abundant corroded relicts of calcite disseminated through the groundmass. Clinozoisite locally has a network of amphibole through it, which is interpreted as replacement of clinozoisite by amphibole. The groundmass of the epidote- and clinozoisite—bearing rocks is much finer grained than the diorite. If the epidote andclinozoisite were formed by saussuritic al- teration of a diorite, the granularity of the original rock should have been somewhat preserved. GEOLOGIC HISTORY The Paleozoic era was marked by nearly continuous deposition of marine sediments from the Early Ordovic- ian to well within the Permian; no major unconformi— ties or hiatuses were recognized. Lithology and fossils of the Lower Ordovician Pogonip group, the oldest rocks in the quadrangle, indicate that the predominantly carbonate rocks were formed in a deepwater marine environment. Local admixing of sand grains and cross- bedding near the top of the formation manifest a transi- tion from deepwater deposition for the older dolomites and limestones to shallow-water conditions during the Middle Ordovician. Littoral subzone or beach condi- tions probably prevailed during Middle Ordovician time and resulted in the deposition of well-sorted quartz sand of the Eureka quartzite, probably a second cycle orthoquartzite. Ely Springs dolomiteand Hidden Vale ley dolomite were formed in seas that covered the area during Late Ordovician time and during the Silurian and Devonian. Marine deposition continued through the Devonian, mainly forming limestone in contrast to the preponderance of dolomite in pre-Devonian seas. Marine sedimentation continued throughout the Mississippian. The limestone units of the Tin Moun- tain limestone and Perdido formation were largely formed in placid seas devoid of foreign detritus. Cal- cilutite of the Lee Flat limestone records marine deposi- tion that was likely derived from a low-relief landmass. 52 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. Continued marine deposition in a nearshore environ— ment formed the calcarenite and calcilutite character- istic of the Pennsylvanian and Permian. Recurrent emergences are indicated by intercalated limestone con- glomerate and minor unconformities, and widespread crossbedding indicates a nearshore environment. Most of the emergences probably were short lived and of limited extent, but locally folding was concomitant with uplift. The coarse limestone conglomerate of the upper part of the Owens Valley formation probably accumulated in a local basin as a result of rapid local differential uplift. . Orogeny was the dominant feature of the Mesozoic era, although the exact age of the diastrophism is not well documented. The Paleozoic rocks were uplifted and folded before the advent of the Mesozoic intrusions. The Paleozoic rocks were then regionally warped in response to the forceful intrusion of the Hunter Moun- tain batholith and the Coso batholith. Faulting and fracturing, some subsequent to the partial solidification of the granitic rocks, preceded the deposition of ore and gangue minerals during the late stages of orogeny. Subareal erosion probably was active throughout most of the era. There is a gap in the geologic record between the Mesozoic intrusions and ore deposits and the advent of volcanism during the late Pliocene. This gap prob- ably represents a period mainly of erosion. By late Pliocene time the land surface had been eroded to a ma- ture surface of low relief. This surface has been corre- lated by Hopper (1947, p. 400) with the late Pliocene Ricardo erosion surface of Baker (1912, p. 138; Mer- riam, 1919, p. 529) out across tilted lower Pliocene beds in the El Paso Range about 75 miles to the south. The Darwin senesland of Maxson (1950, p. 101) between the Argus Range and the Inyo Mountains contains part of this mature surface. The present basins and ranges had their inception at least as far back as late Pliocene time when uplift of the Coso Range and Inyo Mountains caused the forma- tion of extensive piedmont fans that interfinger with lacustrine deposits in Owens Valley. Volcanic activity was common during the iPliocene, and it continued intermittently into the Quaternary. Pyroclastic rocks of basaltic composition are abundant in the lowermost beds of the late Pliocene or early Pleistocene Coso formation at Cactus Flat on the west flank of the Coso Range in the Haiwee Reservoir quadrangle. Andesite, which locally is interbedded in the Coso formation at Cactus Flat and is interbedded in basaltic pyroclastic rocks in the Inyo Mountains near the Santa Rosa mine, was extruded as domes during the late Pliocene or early Pleistocene. The pyroclastic rocks were tilted locally before the outflow of the extensive olivine basalt flows that cap most of the northern part of the Darwin quadrangle. Uplift of the Argus and Coso Ranges, and the Inyo Mountains continued through the Pleistocene and 8 Recent. The olivine basalt flows of Pleistocene age have been tilted and step faulted. A lake was formed in Darwin Wash during middle or late Pleistocene. Headward erosion of Darwin Canyon subsequently captured the drainage of Darwin Wash and in this way lowered the base level of erosion to Panamint Valley and caused dissection of the lakebeds. Erosion and intermittent uplift have continued in the Recent. ‘ORE DEPOSITS The Darwin quadrangle contains commercially im- portant deposits of lead-silver—zinc and steatite—grade talc, and some tungsten, copper, gold, and antimony (fig. 3). Large deposits of limestone, dolomite, and quartzite are known, but they have not been exploited owing to remoteness from market and railroad trans- portation. The total value of mineral production to 1952 is about $371/2 million. The Darwin lead-silver- zinc district has accounted for $29 million and the talc deposits for about $5 million. The remainder of the production has come from other lead-silver-zinc de- posits scattered throughout the quadrangle and from the tungsten deposits in the Darwin Hills. The major lead-silver—zinc deposits are in the Darwin Hills, but smaller deposits have been developed at Zinc Hill in the Argus Range, the Lee district in the northeastern part of the quadrangle, and the Santa Rosa mine in the Inyo Mountains. Steatite—grade talc has been mined continuously since 1917 from the Talc City Hills, prin- cipally from the Talc City mine. Scheelite was first mined in 1940 from deposits about 1 mile east of Dar- win, and production has been intermittent since then. Small amounts of copper, gold, and antimony have been recovered from deposits in the Darwin Hills. HISTORY AND PRODUCTION The following history of mining before 1945 was compiled entirely from the literature. The following references supplied most of the information: Burchard (1884), Chalfant (1933), Kelley (1938), Norman and Stewart (1951), and Robinson (1877). Statements of history'prior to 1945 not otherwise credited originally came from one of these articles. Mining in the Darwin quadrangle dates back to November 1874 when rich silver ore was discovered in the Darwin Hills by a Mex— ican reportedly searching for a lost pack mule (Chal- fant, 1933, p. 274). During the ensuing decade the ORE DEPOSITS 53 rich silver ores were extensively exploited, and by 1883 more than $2 million in bullion had been recovered. During this time Darwin is reported to have had a pop- ulation of 5,000. The Christmas Gift, Lucky Jim, Defiance, and Independence mines produced most of the ore the first few years. The New Coso Mining Co. obtained the Lucky Jim and Christmas Gift mines in May 187 5, and they developed both properties rapidly during the following few years. A report to the stock- holders, dated April 1, 1877, gives the production from the two properties as 226,672 ounces of silver and 1,920,- 261 pounds of lead worth $410,350. The Defiance and Independence mines were in production by 187 5 as re- ported in the Coso Mining News of December 24, 1875, and by 1883 they produced $1,280,000 of bullion (Bur- chard, 1884, p. 164). The ores in the district were treated at Darwin in three smelters—the capacity of the Cuervo was 20 tons per day, the Defiance 60 tons, and the New Coso 100 tons (Goodyear, 1888, p. 226). Bullion was hauled by teams of horses to Los Angeles. At the time of Goodyear’s visit in 1888, the district was nearly dormant, and the smelters were permanently closed owing to exhaustion of the easily mined, high- grade near-surface ores (Goodyear, 1888, p. 226). From 1888 until World War I the Darwin mines were operated intermittently on a small scale by the New Coso Mining Co., Inyo County Mining and De— velopment Co., Independence Mining Co., and- others. From 1915 until 1928, when the price of lead and zinc was too low to be mined profitably, the district was fairly active. In 1915 the Darwin Development Co., later called the Darwin Lead and Silver Mining and Development Co., and finally the Darwin Silver Co., consolidated the Lucky Jim, Promontory, Lane, and Columbia mines and about 1918 obtained control of the Defiance and Independence mines. In 1925, C. H. Lord leased the properties and operated them from 1925 to 1927 as the American Metals, Inc. In 1928 the Lucky Jim mine was gutted by a fire and rendered in- accessible. The district was idle from 1928 until 1936. From 1937 until August 1, 1945, the properties were controlled by the Darwin Lead Co., the Imperial Smelt- ing and Refining Co., Imperial Metals, Inc., and Dar- win Mines. On August 1, 1945, The Anaconda Co. purchased the Bernon, Defiance, Driver, Essex, Independence, Lane, Lucky Jim, Promontory, Rip Van Winkle, and Thomp— son mines, and other small properties in the Darwin quadrangle and the Columbia mine at the south end of the Darwin Hills in the Coso Peak quadrangle, and they have operated some of them continuously since 1945 except for brief shutdowns in 1948 and from March 1954 to January 1955. The Defiance, Essex, In- dependence, and Thompson mines produced most of the ore. The Lucky Jim mine was rehabilitated in 1948 but did not produce any ore. Talc was probably first mined in the Talc City Hills in 1915. Waring and Huguenin (1919, p. 126) de— scribed operations at the Talc City mine under the name Simonds talc mine in their biennial report for 1915—16. In 1918 the Simonds talc mine was purchased by the Inyo Talc Co., which later was renamed the Sierra Talc and Clay Co. They have operated the Talc City mine and several smaller deposits continu— ously since then. Scheelite was first described in the Darwin Hills by Hess and Larsen (1922, p. 268) ; Kelley (1938, p. 543) mentioned scheelite at the Bruce mine in the Darwin Hills, but the tungsten deposits remained undeveloped until 1940 when Frank Watkins, C. W. Fletcher, and others organized the Darwin Consolidated Tungsten Co. to develop them. The Pacific Tungsten C0. leased the claims in 1941, and the following year they pro- duced 30,940 tons of ore that averaged about 1 percent W03 (Wilson, 1943, p. 544). The ore was treated at a mill near Keeler owned by the West Coast Tungsten Corp. Howard Miller and Louis Warnken operated the Durham-Fernando, Hayward, and St. Charles mines from 1951 to 1953 and the Hayward and St. Charles mines during 1954—55. Location of mines are shown in figure 3. The ore was treated in a mill in Darwin Wash. The Ajax Tungsten Corp. obtained a lease on the Durham-Fernando property in 1954, and they shipped their ore to Bishop for treatment. The lead—silver ore at the Thompson mine of the Darwin group contains some scheelite. At present it is not re— covered, except for local high-grade concentrations that are stockpiled. The total metal production from the Darwin quad- rangle through 1951 was approximately 6,300 ounces of gold, 8 million ounces of silver, 1,000 tons of copper, 65,000 tons of lead, 23,000 tons of zinc, and 35,000 short ton units of W03. Norman and Stewart (1951, p. 29) gave the production of antimony from the Darwin Antimony mine as “50 to 100 tons of ore assaying more than 30 percent antimony.” The annual production from 1875 to 1951 excluding tungsten and antimony is given in table 4. Talc is the only nonmetallic commodity produced in the area. No record was found of the total production from the Tale City Hills. The production from the Talc City mine, which has produced most of the talc in the district, is given in table 5. The total produc- tion of the Talc City mine from 1915 through 1947 is 218,485 tons. 54 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. TABLE 4.—G’old, silver, copper, lead, and zinc produced from the Darwin quadrangle 1 See footnote at end of table. Year Gold (ounces) Silver (ounces) Copper (pounds) Lead (pounds) Zinc (pounds) Operators 1875-83 ________________ 1, 571, 000 ________________________________________ Defiance, Independence, New Coso Mining ‘ (estimated) Co. 1888—92 ______ 23. 51 ____________________________________________________ Phoenix. 1893 _________ 7. 26 26, 759 ________________________________________ Custer mine, J. A. McKenzie, H. Mettler, Phoenix. 1894 ___________________ 70, 095 ________________________________________ Christmas Gift mine, Henry Mettler. 1895 ___________________ 19, 362 ________________________________________ Custer mine, J. . McKenzie, Henry Mettler. 1897 ___________________ 5, 517 ________________________________________ J. A. McKenzie and W. W. Boswell. 1898 _________ 64 54, 800 ________________________________________ R. C. Troeger. 1899 ___________________ 37, 349 ________________________________________ Custer, Last Chance Mining Co., J. A. McKenzie, Phoenix. 1900 _________ 741 13, 178 ________________________________________ W. W. Boswell, J. A. McKenzie, Phoenix 1901 _________ 591 14, 333 ________________________________________ Do. 1902 ___________________ 4, 360 _________________________________________ J. A. McKenzie, Phoenix mine. 1903---- _-__ _ 39 14, 814 ______________ 11, 905 ______________ J. A. McKenzie. 1904 --------- 25 12, 276 ______________ , 20 ______________ Inyo County Mining & Development Co., J. A. McKenzie. . 1905 _________ 24. 19 5, 036 2, 600 2, 042 ______________ Christmas Gift mine, Inyo County Mining & Development Co. 1906 ___________________ 3,970 ______________ 36,842 ______________ C. R. Bradford, Inyo County Mining & Development Co., New Coso Mining Co. 1907 ___________________ 12, 600 ______________ 100, 000 ______________ New goso Mining Co. 1908 _________ 4 17, 785 ______________ 182, 405 ______________ 1909 _________ 23. 87 3,271 462 75, 235 ______________ ChrisDtmas Gift mine, New Coso Mining Co., S. H. Reynolds. 1910 _________ 75 16,718 904 277, 609 ______________ New Coso Mining Co , S. H. Reynolds, Silver Dollar mine. 1911 _________ * 9. 80 24,494 4,760 427,467 ______________ C. A Bradford, Custer mine, New Coso Minin Co., S. H. Reynolds, Santa Rosa mine, ilver Dollar mine. 1912 _________ 38. 32 11, 210 13, 210 215, 710 ______________ Christmas Gift mine, Independence Min- ing Co., New Coso Mining Co. 1913 _________ 64. 44 29, 291 6,097 475, 998 ______________ Christmas Gift mine, Custer mine, New Coso Mining Co., J. C. Roeper, M. J. Summers. 1914 _________ 6. 02 13,043 1,256 195, 667 ______________ Christmas Gift mine, New Coso Mining 0. 1915 _________ 3 10, 998 543 122, 713 ______________ Christmas Gift mine, Darwin Develop- ment Corp. ., Theo Peterson. 1916 _________ 38 132, 836 38, 658 2, 046, 618 ______________ Christmas Gift mine, Darwin Mines Corp. ., Santa Rosa mine. 1917 _________ 339 221, 634 374, 222 4, 063, 758 78, 586 Christmas Gift mine, Custer mine, Darwin Mines Corp., Theo Peterson, Santa Rosa mine, M. J. Summers, Zinc Hill m1ne. 1918 _________ 202. 61 145, 381 76, 741 3, 614, 161 1,040,000 A. A. Belin, Custer mine, Darwin Silver Co., Rooney and Bradford, Santa Rosa mine, Zinc Hill mine. 1919 _________ 40. 97 46,082 39,926 980, 945 291,540 Custer mine, Darwin Silver Co. ., Theo Peterson, Santa Rosa mine, J. Summers, Zinc Hill mine. 1920 _________ 19. 66 31, 773 23, 313 683, 436 669, 140 Buckhorn, Custer mine, Darwin Silver Co., Jackass, Lee, Theo Peterson, Santa Rosa mine, M. J. Summers, Zinc Hill . m1ne. 1921 _________ 2. 15 3, 886 2, 791 109, 613 ______________ Darwin Silver Co., A. G. Kirby, Santa Rosa mine. 1922 _________ 61. 6 89, 736 8, 097 957, 815 83,540 A. G. Kirby, Santa Rosa mine, Zinc Hill m1ne. 1923 _________ 154. 8 127, 716 19, 088 2, 087, 763 ______________ Christmas Gift mine, A. G. Kirby, Santa Rosa mine. 1924 _________ 69. 68 49,102 17,617 1,048,588 76, 947 A G. Kirby, Santa Rosa mine 1925 _________ 3 23, 723 18, 218 573, 648 150, 430 A. A. Belin, L. D. Foreman & Co., Santa Rosa mine, Zinc Hill mine. 1926 _________ 44. 25 39, 745, 10, 803 1, 202, 855 86, 060 American Metals, Inc. ., Christmas Gift mine, Santa Rosa mine, Zinc Hill mine. 1927 _________ 53. 44 41, 004 10, 156 1, 301, 323 ______________ American Metals, Inc. ., Christmas Gift mine, L. D. Foreman & Co., Santa Rosa mine. 1928 _________ 13. 11 7, 209 13,050 202, 459 ______________ American Metals, Inc. 1929 _________ 4. 01 3, 568 4, 509 117, 228 ______________ Santa Rosa mine. 1930 --------- 7. 65 904 .1, 631 25, 285 -------------- D0. 1931 _________ 0. 45 1, 349 270 31, 650 ______________ Do. 1932 _________ 9. 35 22, 515 6, 835 572, 164 ______________ Do. ORE DEPOSITS 55 TABLE 4.—G’old, silver, copper, lead, and zinc produced from the Darwin quadrangle 1——Continued Year Gold (ounces) Silver (ounces) Copper (pounds) Lead (pounds) Zinc (pounds) Operators 1933 _________ 4. 20 2, 609 1, 325 104, 112 ______________ Do. 1934 _________ 6. 39 7, 777 8, 364 242, 415 ______________ Do. 1935 _________ 95. 14 5, 575 10, 290 155, 457 ______________ Custer mine, Santa Rosa mine. 1936 _________ 14. 25 9, 755 16, 563 .269, 850 ______________ Santa Rosa mine. 1937 _________ 174 70, 526 14, 417 1, 240, 741 ______________ Custer mine, Darwin Keystone Ltd., Darwin Lead Co., L. D. Foreman & Co., Santa Rosa mine, Louis Warnken, Jr. 1938 _________ 26 7, 860 2, 846 143, 756 ______________ Darwin Keystone Ltd., Darwin Lead Co., Santa Rosa mine, Louis Warnken, Jr. 1939 _________ 5 146 ________________________________________ J. B. Anthony. 1940 _________ 7 748 170 32 712 ______________ Custer mine, Keystone mine, Theo Peter- son. 1941---" _ ___' 81 32, 915 16, 501 1, 434, 884 383, 720 Imperial Metals, Inc., Keystone mine, Zinc Hill mine. 1942 _________ 185 54,935 4,422 1,543, 824 650, 400 Im erial Metals, Inc., L. D. Foreman & 0., Zinc Hill mine. 1943 _________ 0. 31 138, 880 ______________ 4, 901, 412 38, 760 Darwin Mines, Zinc Hill mine. 1944__-_ ______ 4. 00 252, 900 10, 327 5, 218, 000 1, 110, 000 Darwin Mines, L. D. Foreman & Co., Wonder mine. 1945 _________ 377 575, 069 130, 931 10, 428, 000 1, 992, 000 The Anaconda Co., L. D. Foreman & Co. 1946 _________ 443 871, 621 200, 340 15, 450, 891 1, 720, 539 The Anaconda Co., Empress mine, L. D. . Foreman & Co. ' 1947 _________ 557 1, 126, 906 148, 949 14, 055, 988 1, 231, 641 The Anaconda Co., Custer mine, Empress mine, L. D. Foreman & Co., Santa Rosa mine, Wonder mine, Zinc Hill mine. 1948 _________ 495 418, 263 165, 708 12, 773, 984 9, 016, 300 The Anaconda Co., Custer mine, Empress mine, L. D. Foreman & Co., Santa Rosa mine, St. Charles mine. 1949 _________ 232 354, 861 131, 583 9, 994, 337 8, 148, 444 The Anaconda Co., Custer mine, Em- press mine, Santa Rosa mine, Zinc Hill mine. 1950 _________ 365 602, 263 208, 118 16, 991, 027 10, 474, 000 The Anaconda Co., Santa Rosa mine. 1951 _________ 422 ' 574, 765 223, 091 14, 395, 209 9, 441, 670 The Anaconda Co., Empress mine, Lee mine. 6, 296. 43 8, 089, 256 1, 989, 702 131, 122, 098 46, 683, 717 994. 9 65, 561 23, 341. 9 (tons) 1 Compiled from records of the US. Bureau of Mines and from Minerals Yearbook. The data for the Darwin district from 1888 to 1942 was compiled by Charles W. Merrill of the U.S. Bureau of Mines (from Hall and MacKevett. 1958). TABLE 5.—Talc produced from the Talc Olly mine ‘ Year Tons Year Tons 300 1 4, 398 428 3, 402 620 3, 640 2, 000 3, 766 3, 398 6, 667 7, 087 9, 829 4, 300 8, 800 5, 325 7, 640 5, 685 9, 691 5, 202 5, 890 4, 517 12, 600 5, 462 15, 526 5, 273 13, 325 6, 195 14, 908 6, 370 11, 113 5, 561 15, 169 4, 398 218, 485 1 Published with the permission of the Sierra Talc and Clay Co. Compiled by 1195?. VV'711i)ght of the California State Division of Mines (from Hall and MacKevett, p. . 2 Estimate. LEAD-snyEazmc DEPOSITS DISTRIBUTION The lead-silver-zinc deposits are concentrated in Paleozoic limestone close to intrusive contacts. The largest deposits are adjacent to the stock in the Darwin Hills in the southern part of the quadrangle. The prin— cipal mines are the Darwin, Lucky Jim, Christmas Gift, Lane, Custer, and Promontory. Other ore deposits are near the stock at Zinc Hill at the north end of the Argus Range, the Santa Rosa mine in the Inyo Mountains, the Lee mine on the east side of the Santa Rosa Hills, and a few small deposits in the Talc City Hills (fig. 3) . The name “Darwin mine” is used in this report to include all the properties through Which the Radiore tunnel passes (pl. 3). This includes the former Bernon, Defiance, Essex, Independence, Rip Van Winkle, and Thompson mines, and each of these properties will be referred to as workings of the Darwin mine. CHARACTER 0F ORE Both primary and secondary lead-silver—zinc ore is mined in the Darwin quadrangle. Prior to 1945 mainly oxidized lead-silver ore was mined, but since then more primary than oxide ore has been produced. ‘ In the Dar- win district sulfide minerals generally constitute more than 75 percent of the primary ore. The ore consists 56 . GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. principally of galena and sphalerite and lesser amounts of pyrite, chalcopyrite, and pyrrhotite. The average grade of ore is about 6 percent lead, 6 percent zinc, 6 ounces of silver per ton, and a small amount of copper. Gangue minerals are calcite, fluorite, jasper, and the relict host-rock minerals garnet, idocrase, diopside, wollastonite, quartz, and feldspar. Jasper and calcite are the abundant gangue minerals in most of the fissure deposits and relict host-rock minerals in the replace- ment ore bodies. The texture of the primary ore ranges from very fine grained steel galena to coarsely crystalline ore contain- ing galena and sphalerite crystals 1/2 to 1 inch in diam- eter. Steel galena is particularly abundant in the Essex vein. Banded ore, although not characteristic of the Darwin district, occurs in some of the mines where pyrrhotite is abundant. The oxidized lead-silver ore in the Darwin district, except where jasper is the principal gangue mineral, is a soft friable mass consisting principally of cerussite and limonite, and most of it can be disintegrated easily by hand. Silver ore containing a little galena occurs near the margins of some of the lead-silver-zinc ore bodies in the Darwin mine. The silver ore contains andorite, clausthalite, galena, matildite, and pyrite in a gangue of calcite and relict host rock. Matildite and claustha- lite are in exsolved laths in galena. Whereas sulfide minerals are predominant in the lead-silver-zinc ore, the silver ore commonly contains only several percent of metallic minerals. The ore in the Zinc Hill district contains more zinc than that at Darwin. Primary ore from the Zinc Hill mine averages 22 percent zinc and 1.3 percent lead. The ore consists of medium- to coarse-grained sphal- erite, galena, and minor pyrite in a calcite gangue. Most of the ore mined from the Santa Rosa and Lee mines was oxidized. Oxidized ore at the Lee mine is much harder than that from Darwin and consists of a hard light— to dark-gray porous mass composed mainly of hemimorphite, and includes thin coatings and crystals of cerargyrite. Some relict primary ore is present that consists of coarse galena and small amounts of sphalerite in a gangue of calcite and barite. FORMS OF ORE BODIES The ore bodies occur as bedded deposits, irregular re- placement bodies close to major faults, fissure or vein deposits, and small ore bodies in flat—lying fractures. BEDDED DEPOSITS Bedded deposits economically are the most important. They are common in the Darwin and Zinc Hill districts. Notable examples in the Darwin district are the bedded ore bodies in the Independence workings (pl. 3) ; the 430 stope ore body; the Blue and Red veins in the De- fiance workings; and the ore bodies at the Custer, Jackass, and Promontory mines. Small bedded ore bodies are also at the Empress and Zinc Hill mines in the Zinc Hill district. The ore bodies contain from a few tens to more than half a million tons of ore. The contacts between the bedded deposits and barren or slightly pyritized wallrock are sharp. However the grade within the ore body is not uniform along strike, and some lower grade parts have been left behind as pillars. 13.3mm.“ REPLACEMENT on: 30mm The only important irregular replacement ore body is in the Defiance workings of the Darwin mine (pl. 3). It is a vertical pipe-shaped zone about 250 by 350 feet V in horizontal section and contains many isolated ore bodies. It has been mined vertically for about 550 feet. The downward extent has not been determined. Ore bodies within the zone have gradational contacts with barren or pyritized calc-silicate rock. VEIN DEPOSITS Fissure or vein deposits are present in the Darwin dis- trict, at the Santa Rosa mine in the Inyo Mountains, and at a few small deposits in the Talc City Hills. In the Darwin district the veins are as much as 460 feet long; they average 2 to 8 feet in thickness and are as much as 35 feet thick. The Essex vein has been mined for 800 feet downdip (pl. 3) ; the Lucky Jim vein for 920 feet. All the other veins apparently have a lesser length downdip. Contacts of the veins with barren country rock are sharp. Minable high-grade ore is commonly localized in ore shoots within the veins. At the Christ- mas Gift and Lucky Jim mines, the ore is localized in the parts of the veins that have approximately a north- east strike, and the parts that have a more easterly strike are nearly barren. These ore shoots plunge to- ward the west. ORE BODIES IN FLAT-LYING FRACTURES Small silver-rich ore bodies are localized is flat-lying fractures in the Lee district at the Lee mine and Silver Reid prospect (pl. 9). The flat-lying fractures are in part parallel to bedding and in part transect bedding; they are localized between steep faults. The largest. known ore body was about 40 feet long, 35 feet Wide, and averaged about 6 feet in thickness. Most of the ore bodies mined in the past 20 years were smaller and yielded 50 to 100 tons of ore each. ORE DEPOSITS . 57 ORE CONTROLS Most of the lead-silver-zinc ore bodies in the Darwin quadrangle are in calc-hornfels close to intrusive con— tacts with quartz monzonite. A few smaller deposits are in limestone or marble. Anticlinal structures are important in localizing some ore bodies in the Darwin mine. A fault control is evident for nearly all the de- posits. Thrust faults, steep strike-slip faults, and high— angle normal faults have each played a part in localiz- ing certain ore bodies. NEARNESS T0 INTRUSIVE CONTACTS Deposits in the Darwin and Zinc Hill districts are generally within a few hundred feet of an intrusive con- tact. In the Defiance and Independence workings of the Darwin mine, much of the ore is adjacent to the stock of biotite-hornblende-quartz monzonite, and all the ore is close to quartz monzonite as the workings cut many small satellitic offshoots of the stock. The mines on the east side of the stock, in general, are farther from the intrusive mass than those on the west side. The Lane mine is 2,500 feet from the stock, the Keystone 1,000 feet, the Wonder 600 feet (fig. 3). Two excep— tions, the Custer and Fernando mines, are within 100 feet of quartz monzonite offshoots of the stock (fig. 3). The deposits in the Zinc Hill district are clustered about the stock of leuoocratic quartz monzonite at Zinc Hill (fig. 3). The Empress mine is on the contact of the stock, and the Zinc Hill mine is 2,300 north of it. At the Santa Rosa mine, quartz monzonite does not crop out, but a plutonic mass probably lies a short dis- tance below the surface. The original limestone is metamorphosed to calc-hornfels, and an inclusion of quartz monzonite is in an andesite porphyry dike; both the calc-hornfels and the inclusion indicate proximity to a plutonic mass. The deposits in the Lee district are the farthest from a known intrusion. The Lee mine is in unaltered limestone 6,500 feet northeast of the closest exposure of quartz monzonite, and the Silver Reid prospect is 7,600 feet distant. RELATIONSHIP OF ORE DEPOSITS 1'0 STRATIGRAPHY No one formation in the Darwin quadrangle seems to be especially favorable for lead-silver-zinc deposits. In general, limestone is favorable and dolomite, quartzite, and shale are unfavorable. No lead- silver-zinc deposits in the quadrangle are in beds older than Devonian (pl. 1; 3). The Silver Reid prospect in the Lee district and the Cactus Owen and Homestake prospects in the Talc City Hills are in the Lost Burro formation of Devonian age, as is the Cerro Gordo mine in the New York Butte quadrangle 31/2 miles northwest of the Darwin quadrangle. In the Talc City Hills small lead—silver-zinc deposits are in limy parts of the Lost Burro formation; the more extensive dolomite contains only talc deposits. The Lee, Zinc Hill, and Empress mines are in Mississippian limestone. The Silver Dollar mine in the Talc City Hills is in the Keeler Canyon formation of Pennsylvanian and Permian age. The deposits in the Darwin district are in calc-hornfels of the lower unit of the Keeler Canyon formation. The Santa Rosa mine is in calc-hornfels of the lower unit of the Owens Valley formation of Permian age. Dolomite seems to be unfavorable for lead-silver-zinc deposits in the Darwin quadrangle, but it is the host rock for at least two lead-silver—zinc deposits 9 and 17 miles north of the Darwin quadrangle in the Ubehebe district (McAllister, 1955, p. 23, 32). Ore at the Ubehebe mine is in Ely Springs dolomite and that at the Lippincott mine is in dolomite of the Lost Burro formation. Although lead-silver—zinc deposits occur in all forma- tions from Devonian to Permian in age and no one formation is particularly favorable, within mineralized areas certain beds are favorable. Generally one or more other favorable ore controls are instrumental in localiz— ing ore within a favorable bed. At the Zinc Hill mine all the known ore is in a favorable marble bed 200 feet thick and the overlying and underlying limestone is only slightly mineralized. The favorable marble bed is replaced by ore close to steep faults, and these faults are only slightly mineralized where they cut the over- lying and underlying limestone beds. At the Darwin mine the ore deposits are restricted to a favorable stratigraphic zone between the Davis thrust and the stock of biotite-hornblende—quartz monzonite (pl. 3). The ore is in a medium-grained, light—colored idocrase- garnet-wollastonite rock formed by contact metamor- phism of a fairly pure limestone bed, whereas the dense gray and white calc-hornfels west of the Davis thrust is unfavorable for ore. Folds and faults play an important role in localizing ore within this favor- able zone. RELATIONSHIP OF ORE T0 FOLDS In the Darwin district, anticlinal—shaped folds (in- verted synclines in part) are important in localizing some bedded ore bodies. An inverted synclinal axis that plunges gently northwestward extends from the main opencut near the Defiance shaft N. 30° W. to the Bernon mine (pl. 3). The Blue and Red veins are along the crest and west flank of the fold, An inverted syncline localizes the large bedded ore body in the Inde- pendence mine between the 200 and 3A levels (pl. 3). Steep north-striking faults localize ore along the crest 58 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. of the fold. Anticlinal structures are evident at the Custer mine and the Wonder mine on the east side of the stock of biotite—hornblende-quartz monzonite in the Darwin Hills (fig. 3). annnnonsmr or on: T0 mums A fault control is evident for all the ore bodies in the Darwin quadrangle. In the Darwin district four groups of faults have been instrumental in localizing ore. They are: (a) steep N. 70° E. faults; (b) steep N. 70° W. faults; (c) the Davis thrust, which strikes north and dips west; and (d) steep north-striking faults that have little displacement. Steep N. 70° E. faults apparently served as feeder channels for the ore solu- tions, and all ore bodies in the Darwin district. are localized along them or close to them by other favorable controls. Ore at the Lucky Jim and Christmas Gift mines and in the Darwin mine in the Bernon, 434, and Water tank faults (pl. 3) is localized in these faults. The bedded ore bodies and the irregular replacement ' ore body in the Defiance workings are localized close to the N. 70° E. Defiance fault (pl. 3). The Essex is the only ore body localized in a N. 70° W. fault (pl. 3). The other two major N. 70° W. faults—— the Darwin tear fault and the Standard fault—are mineralized but contain very little ore. The Davis thrust fault is a premineralization fault that apparently confined the ore solutions between it and biotite-hornblende-quartz monzonite. All the known ore bodies in the district lie below the thrust, and premineralization faults above the thrust are only slightly mineralized. Steep north-striking faults are an important ore con- trol in the Thompson and Independence workings in the Darwin mine. The northward-striking faults are most intensely mineralized close to a major N. 70° E. fault. Commonly the ore replaced a favorable bed that is transected by a steep north-striking fault, as in the Independence ore body (pl. 3). At the Zinc Hill mine ore replaces a favorable bed near a series of steep north- to northeastward-striking premineralization faults that probably were instru- mental in localizing ore (pl. 8). Flat-lying fractures localize ore between major steep faults in the Lee district. The flat-lying fractures are tension fractures that have had little or no displace- ment and were probably formed by differential dis- placement on the major steep faults. At the Santa Rosa mine in the Inyo Mountains ore is in northward-striking faults that dip mostly 30° to 65° W., although a few dip to the east. Pinching and swelling of the faults localizes some of the ore shoots. MINERALOGY A list of the minerals identified or reported in the lead—silver-zinc deposits of the Darwin quadrangle is given below. The list is divided into two major groups—hypogene minerals and supergene minerals. The hypogene minerals are subdivided into (a) Ore and sulfide minerals and (b) Gangue minerals. The supergene minerals are subdivided into minerals in the sulfide zone and those in the oxide zone. The minerals are listed alphabetically under each heading. The identification of the more uncommon minerals was verified by an X-ray diffraction pattern .if the mineral was sufficiently abundant and could be sepa— rated. The X-ray spectrograph was utilized to deter- mine qualitative compositions of some minerals and of minute inclusions that are common in the steel galena and in some of the sulfosalts. Minerals identified by previous workers but not verified by the writers are listed and credit or reference for the identification is given under description of the mineral. Hypoame minerals Ore and sulfide minerals: Andorite _________________ PbAngsso Arsenopyrite _____________ FeAsS Bismuth (?) ______________ Bi Bismuthinite _____________ BiaS3 Bornite __________________ CusFeS4 Chalcopyrite _____________ CuFeSa Clausthalite ______________ PbSe Enargite (?) ______________ CU3A584 Galena __________________ PbS Guanajuatite (?) __________ BiaSe3 Matildite ________________ AgBiSz Pyrite ___________________ Fesg Pyrrhotite _______________ Felfls Scheelite _________________ CaWO. Sphalerite ________________ ZnS Stannite _________________ CuzFeSn84 Tetrahedrite—Tennanite- __ _ (Cu,Fe) ”Sb4sla-(Cu, Fe) ”A1548”; Gangue minerals: Barite ___________________ BaSO; Calcite __________________ CaCOa Chalcedony-----_____l_-_ SiO; Deweylite ________________ Mg4Si3010. 6H 20 Diopside- _ _ _‘ _____________ CaMgSizos Fluorite _ _' _______________ Can Garnet sp (andradite) _____ Ca3(Al, Fe) ZSi3012 Idocrase _________________ Cam (Mg, Fe) 2(OH) 2Al4SioO 34 (OH) 2 Jasper ___________________ SiOz Montmorillonite __________ (A1, Mg)3(Si40m) 3- (OH) 10- 12H 20 Orthoclase _______________ KAlSi303 Quartz __________________ Si02 Sericite __________________ (H , K) AlSiO4 Wollastonite _____________ CaSiOa ORE DEPOSITS 59 Superaene Minerals Sulfide zone : Argentite ________________ Agzs Chalcocite _______________ Cuzs Covellite _________________ CuS Oxide zone Anglesite ________________ PbSO; Antlerite _________________ Cu; (OH)4SO4 Aurichalcite ______________ (Zn, Cu) 5(OH)3(003) z Autunite _________________ C3(U02)2(P04)2-10-12H 20 Azurite __________________ Cua (OH) 2 (003) z Bindheimite ______________ Pngb;Oo(0,0H) Bismutite ________________ (BiO) a( 003) Bro chantite ______________ Cu; (804) (OH) 0 Cale donite _______________ Cusza ($04) 3 (00;) (OH) 0 Cerargyrite ______________ Ag Cl Cerussite ________________ Pb CO; Chalcanthite _____________ CuSO4- 5H 20 Chrysocolla ______________ CuSiOg-2H20 Creedite _________________ Ca3A12F4(OH,F)a(SO..) -2H 20 Crocoite _________________ Pb Cr04 Cuprite __________________ 01120 Goslarite ________________ ZnSOy7H 20 Gypsum _________________ CaSOyZHzo Hematite ________________ Fe203 Hemimorphite ____________ HaZn,Si05 Hydrozincite _____________ ZD5(OH)3(003) 2 Jarosite __________________ KF63(SO4) 2(0H)o Leadhillite _______________ Pb4(804) (003) (OH) 2 Limonite _________________ Hydrous iron oxide Linarite _________________ Pb Cu (80;) (OH) 2 Malachite ________________ CU2(OH) 2(003) Melanterite ______________ FeSO4- 7H 20 Mimetite ________________ (Pb Cl) Pb, (AsO;) 3 Plumboj arosite ___________ PbFea ($04) 4 (OH) , 2 Pseudomalachite __________ Cu,o(P04)4(OH)s-2H20 Pyrolusite _______________ MnOz Pyromorphite ____________ Pbs (P04, As04) 301 Silver (native) ____________ Ag Smithsonite ______________ ZnCOa Stolzite __________________ PbWOa Sulfur ___________________ S Tenorite _________________ CuO Vanadinite-- _ _ -; _________ Pb5(VO4)3Cl Vi vianite ________________ F63P203'8H 20 Wulfenite ________________ Pb MO, HYPOGENE MINERALS ORE AND SULFIDE MINERALS Andom'te (PbAnggse) .—Andorite was identified by Charles Milton (written communication, 1954) of the US. Geological Survey from specimens from the A437 stope above the 400 level of the Thompson workings of the Darwin mine (X-ray film 6794). It forms a silver- rich ore‘with pyrite and minor Chalcopyrite and sphal- erite at the margin of a galena-rich ore body. The andorite occurs in thin tabular crystals generally less than 2 mm long that are conspicuously striated. In polished section the colorof the andorite is galena white, and it is moderately anisotropic in shades of gray. The andorite is in a gangue of coarsely crystalline calcite 620626 0—62—5 and less abundant garnet and idocrase. Minute irregu- lar, white strongly anisotropic inclusions of native bis- muth( ’9) are disseminated through the andorite (fig. 26). Andorite( ’9) has been provisionally identified by Milton (written communication, 1954) from the Round Valley mine in the Bishop district, Inyo County. Arsenopym'te (FeAsS).—Small amounts of arseno- pyrite occur in the ore at the Darwin and Santa Rosa mines. It is associated with pyrite and pyrrhotite and was one of the first sulfide minerals deposited. It is in diamond—shaped grains that are less than 0.5 mm long. BismutM .9) (Bi) .—Assays and spectrographic anal- ysis show bismuth minerals to be present in the Darwin ores, but the mineralogy is not well known. Steel ga- lena from the Essex workings gives distinct bismuth peaks on the X-ray spectrometer. Minute white, strongly anisotropic inclusions in the galena and in andorite may be native bismuth. Bismuthz'nite (Bizsa) .—Bismuthinite associated with scheelite was identified at the north end of the Durham ore body near the Fernando fault (fig. 2, 2A). The mineral is mostly altered to bismutite. The bismuthi- nite is in bladed masses as much as 1 inch long that are coated with powdery green bismutite. Bomite (Cu5FeS4).——Small amounts of bornite are in the Darwin and Santa Rosa mines. At the Darwin mine bornite occurs as a rim about some pyrrhotite inclusions in sphalerite and as inclusions in galena (fig. 27). Chalcopyrite (CuFesz) .—Most lead-silver—zinc de- posits contain small amounts of Chalcopyrite; it is the principal mineral in copper prospects on the east side of the Darwin Hills. Chalcopyrite occurs as minute blebs in sphalerite that undoubtedly formed by exsolu- tion, and commonly occurs with pyrite and pyrrhotite in the Darwin mine (fig. 28). Clausthalite (PbSe) .—Clausthalite was identified by X-ray diffraction pattern in a “galena” from the Darwin mine that contained 7.8 percent selenium, 6.13 percent silver, 20.67 percent bismuth, and 2.4 percent tellurium. Clausthalite and matildite had exsolved from the “galena”, but a homogeneous galena solid solution was formed by heating at 500°C for 5 hours. Enargite(?).——(Cu3AsS4)—Enargite( ?) was identi- fied by Charles Milton (written communication, 1954) from specimens of silver-rich ore from the 534 stope of the Thompson workings of the Darwin mine. Galena (PbS).—Galena is the predominant sulfide mineral in the Darwin district and at the Santa Rosa mine. It ranges in texture from steel galena to coarsely crystalline masses that average as much as half an inch in diameter. Some coarse-grained galena in the De- fiance workings of the Darwin mine has warped cleav- 60 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. FIGURE 246.—\Phobomicro‘graph of andnrite that contains inclusions of bismuthfl). Specimen from the 437 stope of the Thompson workings, of the Darwin mine, Plane polarized Fight, 60 X. B. Some of the pyrrhotlte inclusions have rims of bornite (bo). Plane polarized light, 250 X . A. (the sphalerite contains corroded relicts of pyrite (py), and is in turn, veined by gale‘na' (gn). Pyrrhotite (po) inclusions form a triangular pattern in the sphalerite. This is interpreted as an exsolu- tion pattern. Plane polarized light, 40 x. FIGURE 27.—PHor0MICROGRAPHs or SPHALERITE (SL) FROM THE THOMPSON WORKINGS OF THE DARWIN MIN E- A. ORE DEPOSITS 61 FIGURE. 28.—Exsolution pattern of chalcopyrite (light) in sphalerite (medium gray). from the Darwin mine. Chalcopyrite occurs as ori- ented segregation veinlets and blebs in the sphalerite. Plane polar ized light, 40 X. age faces. ' The warping is apparently due to transla- tion gliding. The (II-values and relative intensity of the lines in the X-ray diffraction pattern of the warped crystal agree precisely with those given in the “ASTM Diffraction Data Cards” for galena. The galena is all argentiferous, and chemical analyses _ show that some of it contains appreciable amounts of bismuth, selenium, and tellurium (Hall, 1959, p. 940). Analyses of 12 galena samples from the Darwin mine are given in table 6. In general, selenium, silver, and bismuth are most abundant in galena from ore bodies in the northern part of the Darwin mine area in the Essex and Thompson TABLE 6.—-Analyses of bismuth, selenium, and silver in galena from the Darwin, mine 1 ‘ Location Unit cell Name of workings o Selenium Silver Bismuth (pure sample (percent) (percent) (percent) galena= (level) 5.936A) 1200 0.018 0. 14 0.48 5. 9313i. 001 570 .025 . 12 .080 5. 9307 400 . 030 . 12 . 06 5. 9298 700 . 0088 . 26 <. 004 5. 9387 700 .39 .76 .26 ______________ 700 1.16 .018 .018 5. 9452 500 011 . .035 5. 9422 500 74 .058 <. 004 5. 9440 3A 39 . ll . 16 5. 9350 200 1 24 2.47 4.65 5.9146 200 2 11 3.79 7.86 5.923 400 1 7 8 6.13 20. 67 5. 88 1 Analyst S. M. Berthold Joseph Budinsky, Esma Campbell, M. K. Can-on, and Janet D. Fletch her. 1 In addition there IS 2.4 percent tellurium in this galena. workings (pl. 3). Minute inclusions of matildite (AgBiSz) were identified by X-ray diffraction pattern in the last three galena samples listed in table 6. A min- eral count was made of matildite in the galena contain- ing 2.11 percent selenium, 3.79 percent silver, and 7.86 percent bismuth. This galena contains 1.8 percent microscopic inclusions of matildite, which account only for about 20 percent of the silver and bismuth. The rest of the silver and bismuth is either in solid solution in the galena or is in inclusions too small to be seen under the microscope. The “galena” containing 7.8 percent selenium, 6.13 percent silver, 20.67 percent bismuth, and 2. 4 percent tellurium is a mixture of 3 phases—galena, clausthalite (PbSe) , and matildite. The identification is based on X-ray- -defraction pattern, polished- -seCtion study, and on chemical analysis. Megascopically this “galena” looks like a sulfosalt and is the mineral listed by Hall and MacKevett (1958, p. 16) as an unknown lead-bismuth-selenium sulfosalt. It forms thin tabular crystals as much as 1 centimeter long that are commonly warped and are conspicuously striated parallel to its - long dimension. By heating the “galena” with 3 phases for 5 hours at 500°C and quenching in water, a homo- geneous galena was obtained. It is evident that the three phases—galena, matildite, and clausthalite in what megascopically looks like one mineral—originally crystallized at a high temperature as a homogeneous galena but included abundant bismuth, selenium, tellu- rium, and silver in solid solution and exsolved into three phases on cooling. Guanajuatite( ?) (BiZSea) .-——Spectrographic and chemical analyses show that both bismuth and selenium are present in andorite and in some of the galena from the Thompson and Essex workings of the Darwin mine. Both minerals contain minute blebs that are white in polished section and have strong anisotropism and may be guanajuatite. Matildite (AgBiSZ) .——Tiny oriented lamellar in- clusions of matildite are intergrown with galena in ore from the Essex vein of the Darwin mine. The lamellae ‘ are gelena white in polished section and are moderately anisotropic. They are not visible in plane polarized light, but are readily seen under cressed nicols or When the section is etched with nitric acid (fig. 29). The identification is based on similarity to matildite de- scribed by Palache, Berman, Frondel (1944, p. 429) and by Edwards (1954, p. 111), on X-ray-defraction pattern, and on chemical analyses of galena showing the presence of silver and bismuth. The lamellae probably formed by exsolution from a bismuthian and 'argentian galena stable at high temperature, as the matildite readily goes into solid solution in the galena when heated at 500°C. 62 FIGURE 29.—Galena (gn) and its alteration product cerussite (ce‘) with elongate inclusions of matildite (AgBiSa) (ma). The polished section is etched with nitric acid to show the matildite, as the inclusions are not visible in plane polarized light in unetched specimens. Specimen from the Essex workings of the Darwin mine. Crossed nicols, 50 X. Pyrite (FeSz).—Pyrite is abundant in all the lead- zinc deposits in the Darwin district and at the Santa Rosa mine, but it is a minor constituent of the ores at the Lee and Zinc Hill mines. Pyrite is also widely dis- seminated in the biotite-hornblende-quartz monzonite and in the calc-hornfels near the Darwin mine. , It oc- curs both as cubes and pyritohedrons as much as 1 inch in diameter, and is the earliest sulfide mineral deposited. Some pyrite has an exploded bomb texture, and the fractures are filled with later sulfide minerals. wa'hotz'te (Fe1_xS).—Pyrrhotite is common in the primary ore in the Darwin mine; it commonly forms a banded ore. It replaces pyrite but is replaced by sphalerite, galena, and chalcopyrite. It also forms irregular blebs oriented along cleavage in sphalerite and probably formed by exsolution (fig. 27). Scheelz'te (CaWOg) .—Scheelite is common in the lead—silver-zinc ore bodies in the Darwin district and as discrete tungsten ore bodies that contain little or no sulfide minerals. It is associated with galena in the Thompson workings of the Darwin mine and at the Jackass mine. In the Thompson workings subhedral to euhedral scheelite crystals commonly 3/8 to 1/2 inch in diameter are embedded in fine-grained galena. In the oxided zone the scheelite is loosely embedded in a crumbly mass of cerussite, limonite, and jarosite. Sphalem'te (ZnS).—Sphalerite is present in about equal quantities as galena in most of the primary ore in the deeper ore bodies being mined at the Darwin mine in 1956, and it is the predominant mineral in the primary ore at the Zinc Hill mine. The sphalerite is generally coarser grained than galena and is commonly GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. in crystals as much as 11/2 inches in diameter. The color of the sphalerite in calc-hornfels and tactite is dark grayish brown at the Santa Rosa mine and in the Darwin district. At the Zinc Hill mine, where the ore is in marble, the sphalerite is a much lighter color—~ being pale brown. It is lightest in color at the Lee mine—a light grayish yellow—where it is in unaltered limestone. The color of sphalerite darkens as the FeS content increases. The dark iron-rich sphalerites formed at a higher temperature than the light-colored sphalerite. Iron analyses of 20 sphalerites and their significance are given on page 69. Stannite (CuzFeSnS4).—Stannite was identified by Charles Milton (written communication, 1954) from silver-rich ore containing matildite and galena from the Thompson workings of the Darwin mine. Tetrahcdwlte- temantite (Cu,Fe) 12‘Sb4Sm— ( Cu,Fe) 12 AsiSlg.—Small amounts of tetrahedrite or tennantite are in galena in the Darwin mine. The mineral is most commonly near the border of galena in grains too small to determine whether arsenic or antimony is predominant (fig. 31). Kelley (1938, p. 544) reports tennantite in the ore, and Carlisle and others (1954, p. 46) report tetrahedrite. GANGUE MINERALS Barite (BaSO4) .—-Barite is one of the predominant gangue minerals at the Lee mine and the Silver Reid prospect. It was not identified in ore from the Darwin or Zinc Hill districts. Calcite (CaCOS) .—Calcite is one of the predominant gangue minerals in most of the lead-silver-zinc deposits in the Darwin district. It is abundant at the Custer mine, the Defiance workings of the Darwin mine, and at the Darwin Iceland Spar prospect. It ranges in color from milky white to brownish gray, and rhombo- hedrons as much as 18 inches on a side are common. Calcite also occurs as an interstitial mineral in the calc- hornfels and as late veinlets that cut the ore. Chalcedony (SiOz).—Chalcedony is a common gangue mineral at the Santa Rosa mine. It forms light- tan to light-gray cryptocrystalline masses in the veins associated with ore minerals. Deweylite (Mg4Si3010-6H20).—Deweylite was iden- tified from the 570 level of the Defiance workings. The identification was based on an X-ray study by Fred A. Hildebrand (written communication, 1953). It forms pale greenish-yellow amorphous masses that are inter- grown With montmorillonite. Pyrite in the form of pyritohedrons as much as 11/2 inches long that have thin black coatings of chalcocite is disseminated through the deweylite. ORE DEPOSITS - 63 Diepside (CaMg‘Sizos).—Diopside is a common gangue mineral in the replacement lead-silver-zinc ore bodies in the Darwin mine and it is a major constituent of the Gale-silicate country rock. Fluorite (Can) .-——Fluorite is associated with galena in many deposits in the Darwin district. It is in anhe- dral to subhedral grains mostly a few millimeters in diameter that range in color from white to shades of blue, green, and rose. The mineral is most abundant in ore bodies close to igneous contacts. Garnet sp. ardradite (Ca3(Al,Fe)2Si3012).—Garnet is a characteristic gangue mineral in the lead—silver deposits in the Darwin Hills. It is a pale-green variety that occurs in dodecahedrons a few millimeters in diam- eter. The garnet is slightly birefrigent, and it has an index of refraction of 1.848 to 1.850. The specific grav- ity averages about 3.75, and ranges from 3.583 to 3.885 as determined on a Berman balance. The garnet is near the andradite end of the grossularite-andradite series. ' I docrase (Ca.10 (Mg,Fe)2 (OH) 2Al4Si9034 (OH)2) .— Fine- to medium-grained idocrase is common in the lead—silver-zinc deposits in the Darwin district, and it is abundant in calc—silicate rock. It occurs in subhedral to euhedral prismatic grains mostly 2 to 4 mm long that are light olive in color. The idocrase is coarser grained and more abundant near intrusive contacts. Jasper (SiOz) .—Jasper is a common gangue mineral in the veins at the Santa Rosa mine and in the veins that trend N. 70° E. in the Darwin district. Montmorillonit e (A1,Mg)8(Si4Om)3- (OH)10 -12H20) .—Montmorillonite, intergrown with dewey— lite in a fault zone in the irregular replacement ore body in the Defiance workings of the Darwin mine, was identified by Fred A. Hildebrand (written communica— tion, 1953). It forms amorphous pale greenish—yellow masses. Orthoclase (KAlSigos) .—Orthoclase is abundant locally in the replacement ore in the Darwin mine, and it is present in coarse-grained masses near intrusive con- tacts southwest of the Defiance workings. Quartz (SiOz).—Q,uartz is not abundant in most of the lead—silver-zinc deposits, but some is present with calcite and garnet in the ore at Darwin. Seriez'te ((H,K)AlSiO4) .—~Sericite is a common alteration product along fault zones in the Darwin mine. Plumbojarosite is commonly associated with it. Wollastomlte (CaSiOa).—Wollastonite is one of the most abundant minerals in the calc-silicate rock close to intrusive contacts, and locally coarsely crystalline aggregates consist of prismatic crystals as much as 6 inches long. The grain size decreases rapidly away from intrusive contacts. SUPERGENE MINERALS Most of the near-surface, high-grade supergene ore was mined out in the 1870’s so little of this ore was seen in place. The minerals were identified in specimens kindly given to the writers by The Anaconda Co. or in specimens collected from dumps. Specimens of low— grade oxidized ore were collected in the Darwin and Santa Rosa mines. The occurrences of the supergene minerals are not well known and, therefore, the writers have not described each mineral separately as they have with the primary minerals. SULFIDE ZONE Very little supergene enriched ore remains in the ore deposits in the Darwin quadrangle, but small amounts of chalcocite, covellite, and sooty argentite are present locally. Chalcocite and covellite form black coatings on pyrite, and thin veinlets of the minerals replace the primary ore minerals. Some of the high-grade oxidized silver ore contains sooty argentite. It undoubtedly was abundant in the rich oxidized ore mined in the 1870’s. OXIDE ZONE The zone of oxidation is deep at most places in the Darwin quadrangle, and the ore is largely oxidized to a crumbly mass composed mainly of cerussite, limonite, and hemimorphite except where protected by an im- permeable zone or in the deep levels of a few mines. At the Lucky Jim mine, the ore is oxidized and only a few relicts of galena remain in the deepest working on the 920 level. At the Darwin mine the ore is largely oxidized to the 400 level, and both primary and sec- ondary minerals are present to the deepest level (in 1955)—the 1100 level of the Defiance workings. Cerussite, the principal secondary lead mineral, forms radial aggregates of euhedral crystals as much as 1- inch long that rest upon porous finer grained masses of limonite, cerussite and other oxidized lead minerals. The larger crystals are White and have a vitreous lus- ter; the smaller crystals are yellowish or brownish owing to surface coatings of iron oxides. Anglosite, crocoite, mimetite, plumbojarosite, pyromorphite, vanadinite, and wulfenite are less abundant secondary lead min- erals in the Darwin mine. Anglesite commonly forms a thin dense zone between relict galena and cerussite. Clusters of stolzite in oxidized lead ore at the Thompson mine are reported by Tucker and Sampson (1941, p. 567) and by Dudley L. Davis (oral communication, 1955). The occurrence was not verified by the writers. Leadhillite was questionably identified from the Santa Rosa mine, but was not observed in the Darwin district. Secondary copper minerals are common in the oxi- dized lead-silver ore at the Darwin mines, and Santa 64 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. Rosa, and formerly both linarite and caledonite were common ore minerals from Darwin. Antlerite, aurich- alcite, azurite, brochantite, chalcanthite, chrysocolla, cuprite, malachite, and tenorite were also identified. Pseudomalachite has been reported by Woodhouse (in Murdoch and Webb, 1956, p. 260). Oxidized near-surface ore mined during the early history of the Darwin district is reported to have con- tained as much as 950 ounces per ton in silver (Ray- mond, 1877, p. 30). Native silver, cerargryite, and sooty argentite are reported in the oxidized ore at Dar- win (Kelley, 1938, p. 546; Davis and Peterson, 1948, p. 2; Carlisle and others, 1954, p. 46). Gypsum, hematite, jarosite, and limonite are common gangue minerals in the oxidized lead-silver ore, and bismutite, creedite, goslarite, melanterite, pyrolusite, and sulfur are less abundant minerals. Vitreous white prismatic crystals of creedite line cavities in partly oxi- dized lead ore containing galena and fluorite. Vivian- ite crystals on quartz have been reported by Woodhouse (6m. Murdoch and Webb, 1956, p. 343). Goslarite and melanteriteare in some of the workings in the Darwin mine. Bismutite was observed in the Fernando mine as coatings on bismuthinite crystals, but it may have been in the oxidized ore from the Essex vein of the Darwin mine as this vein contained a large amount of bismuth. Hemimorphite is the predominant secondary mineral in the oxidized zinc ore at the Zinc Hill and Lee mines. It has a mammillary habit, and the color ranges from colorless to white, pink, green, gray, or brown. The local pink color at the Zinc Hill mine is due to a thin coating of hematite. Hydrozincite and smithsonite are near the borders of the secondary zinc ore bodies and in fractures below them. Cerargyrite and bindheimite are associated with hemimorphite at the Lee mine. Euhe- dral crystals of cerargyrite 1 to 2 mm in diameter in the form of cubes commonly modified by octahedral faces locally are abundant in cavities in the hemimorphite. Autunite occurs in small pockets in oxidized ore in the Zinc Hill district, but none was found in the Darwin district. PARAGENEsm The paragenesis of the principal ore and gangue minerals is shown diagramatically in table 7. The mineralization is divided into an early stage of silication of limestone and a later stage of sulfide mineralization. A period of fracturing separates the two stages. Limestone was first altered to dense, aphanitic calc- hornfels. The composition of the calc-hornfels de- TABLE 7.—Pamgenesis of principal primary ore and gangue minerals Early Stage of silication Plagioclase Orthoclase __ _ _ Diopside Wollastonite Idocrase Garnet Epidote Scheelite Fluorite Pyrite Arsenopyrite Pyrrhotite Bornite Sphalerite Chalcopyrite Galena Matildite and clausthalite Tetrahedrite-tennantite Andorite Late Stage of sulfide mineralization ORE DEPOSITS 65 pended upon the purity of the original limestone. Im- pure limestones recrystallized to a very fine grained rock containing orthoclase, oligoclase, diopside, and quartz. Purer limestones were altered to fine-grained wollastonite-diopside calc—hornfels (fig. 19). Silica was added and carbon dioxide lost by this alteration. As the intensity of alteration increased, wollastonite in- creased in grain size and was replaced by andradite gar- net and by idocrase, forming a coarse—grained idocrase— garnet—wollastonite calc-silicate rock (fig. 22). Locally orthoclase replaces calc-silicate rock (figs. 24, 25). Scheelite, the earliest ore mineral, is in part later than the period of silication as shown by its common occur- rence along fractures, but at the Jackass mine scheelite, disseminated in calc-silicate rock, formed during the last stage of silication. Pyrite is the earliest sulfide mineral. is later than scheelite as shown by its veining of filling between euhedral scheelite crystalsin scheelite ore from the Thompson workings. Pyrite occurs as corroded relicts or is veined by all the other sulfide minerals. It is corroded by pyrrhotite (fig. 30) but apparently is contemporaneous with rare arsenopyrite. Sphalerite, chalcopyrite, and galena contain corroded relicts of pyrite (fig. 31). Pyrrhotite contains corroded relicts of pyrite (fig. 30), and occurs as oriented blebs in sphalerite (fig. 27A). Bornite forms thin borders on some pyrrhotite blebs (fig. 273). Chalcopyrite occurs mainly as oriented inclusions in sphalerite. Sphalerite and chalcopyrite are replaced by galena (figs. 31, 32), but galena and tetrahedrite-tennantite show mutual boundaries and are contemporaneous. Matildite occurs only as oriented laths within galena, possibly exsolved FIGURE 30.—Photomicrograph of ore from the Darwin mine. (py) occurs as corroded relicts in pyrrhotite (po) and galena (gn). Pyrite Pyrrhotite is corroded by andoccurs as relicts in galena. polarized light, 44 x. Plane It replaces garnet and idocrase (fig. 23) and . FIGURE 31.—-Photomicrograph of zinc-rich ore from the Darwin mine ' showing replacement of garnet (ga) by sulfide ore. Partly corroded garnet occurs as relicts in a groundmass of galena (gn), sphalerite (sl) pyrite (py ), and minor tetrahedrite (tet). Pyrite is the earliest sulfide mineral as it is in corroded relicts in sphalerite and galena. Sphalerite is veined and corroded by galena. Galena and tetra- hedrite have a mutual pattern and are contemporaneous. Plane polarized light, 40 X. from it (fig. 29). Clausthalitevalso exsolved from galena. The relative ages of andorite and galena are not known definitely but andorite is probably younger. Small galena ore bodies show a primary zoning with galena and sphalerite in the center and andorite and galena with abundant bismuth, selenium, and silver on The para- Pyrite is corroded by and occurs as relicts in chalcopyrite and galena and the FIGURE 32.—Photomicrograph of ore from the Darwin mine. genesis is pyrite (jpy'), chalcopyrite (up), and galena (gn). chalcopyrite in turn occurs as irregular relicts in galena. Plane polarized light, 40 x. 66 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, IN'YO COUNTY, CALIF. the borders. On the nebulous basis of this zoning andorite is considered the younger. PRIMARY ZONING The hypogene mineralization within the Darwin area shows a general zonal distribution, which probably can be correlated with an overall temperature gradient at the time of ore deposition. In general the near- surface ore contains more lead and silver, but with depth, the zinc-to-lead content increases and the silver content decreases. The Defiance workings of the Dar- win mine will be used as an example (pl. 3). The near- surface primary ore in the bedded deposits consisted mainly of galena with an above-average content of silver. The gangue minerals are largely calcite, fluo- rite, and jasper. The upper part of the steep pipelike Defiance ore body in the vicinity of the 400 level con- sisted predominantly of galena that contained less silver than the bedded deposits. Some sphalerite is present in this ore. With increasing depth in the pipelike ore body the ratio of zinc to lead increases and the silver content decreases slightly. Pyrite markedly increases in the deeper levels of the mine, and chalcopyrite locally is abundant. The gangue minerals are predominantly garnet, wollastonite, and calcite. It must be empha- sized, however, that many local variations occur within this general zonal distribution. The relative position of the lead-silver and tungsten ore bodies on the east side of the Darwin'stock also suggests zoning. The lead-silver ’ore bodies are farther out along the same faults that control tungsten ore bodies. Scheelite with little or no associated galena is found along the Fernando fault in calc-silicate rock and calc- hornfels in the Fernando adit as far as 660 feet from the contact of the stock of biotite-hornblende-quartz mon- zonite (pl. 1; fig. 3). Lead—silver ore is found along the same fault 450 feet farther from the stock than scheelite, although it is close to a small satellitic in- trusion. Similarly the scheelite ore at the St. Charles No. 3 workings is close to the biotite-hornblende-quartz monzonite and the lead-silver ore on one of the same fractures at the Custer mine is farther from the in- trusive contact. In Lane Canyon, scheelite in calc- silicate rock along the crest of an anticline is 450 feet from the intrusive contact but silver-lead ore at the Lane and Santa Ana mines to the east is even farther from the intrusion. The Jackass mine, where both scheelite and lead- silver ore are found Within a few feet of each other, is an exception to the spatial zoning on the east side of the stock. Scheelite is disseminated in calc-silicate rock, whereas the lead-silver ore with no scheelite is in a bedding plane fault at the footwall contact of the tactite with calc-hornfels and is undoubtedly later. OXIDATION AND ENRICHMENT Prior to 1942 mainly oxidized lead-silver ore had been produced from the mines in the Darwin quad- rangle. At most places the zone of oxidation is deep except where local conditions restrict the circulation of groundwater, and oxidized ore is known to a depth of more than 1,000 feet. All northeast—striking faults have permitted deep circulation of groundwater, and the ore in or near them is mostly oxidized. In the Darwin district some oxidized ore is present on the deepest levels of all the mines. At the Lucky J im_mine nearly all the ore is oxidized to the deepest level on the 920 level. In the Darwin mine most ore below the 570 level in the irregular replacement ore body in the Defiance workings is hypogene, but along or near the Defiance fault the ore is partly oxidized to the bottom workings (the 1,100 level in 1955). On the other hand, sills have restricted the circulation of groundwater in the Darwin mine, and the ore under them is mainly primary. Most of the ore at both the Santa Rosa and Lee mines in the northern part of the quadrangle is oxidized. At the Santa Rosa mine the ore is oxidized at the bottom of the Hesson workings 350 feet below the surface. Oxidation is shallow in the Zinc Hill district. The upper ore body at the Zinc Hill mine was oxidized for 20 to 40 feet below the surface, and at the Empress mine primary ore extends to the surface. TWO factors are responsible for the shallow depth of oxidation in the Zinc Hill district. First, the topography is rugged and rapid erosion prevents deep weathering. Second, strong basin—range fault zones uphill from both the Empress ore body and the upper ore body at the Zinc Hill mine drain of]? a large part of the descending sur- face and groundwater before it reaches the ore zone and thereby inhibits oxidation of the ore. Residual enrichment by leaching of calcium, iron, sulfur, zinc, and probably silica has been important in the Darwin district and at the Santa Rosa mine. The oxidized ore consistent-1y averages less zinc and more lead and silver than the primary ore. At the Darwin mine the primary ore during 1950 to 1954: averaged about 6 ounces of silver per ton, 6 to 6% percent lead, and 61/2 to 7 percent zinc. The oxidized ore mined from the same general area during the same period averaged about 7 ounces of silver per ton, 71/2 percent lead, and 41/2 to 5 percent zinc. Old records and the early literature both indicate that the near-surface oxide ore was much richer in lead and silver. Complete smelter returns of the New Coso Mining Co. from 1875 to 1877 ORE DEPOSITS 67 show that they recovered 20.5 percent lead and 47 ounces of silver per ton of ore from the Christmas Gift and Lucky Jim mines (Robinson, 1877, p. 38). Burchard (1884, p. 164) states that the Defiance and Independence ore averaged 30 percent lead and$40 (31 ounces) of silver per ton. The zinc content of this high-grade oxide ore was low. Small pods of high—grade ore ob- served in the Darwin mine by the writers consist pre- dominantly of cerussite, relict galena, and small amounts of gangue. The grade is erratic, but typically the ore assays 12 to 25 ounces of silver per ton, 20 to 25 percent lead, and 3 to 4 percent zinc. The mineralogy of the oxide ore depends upon the nature of the primary ore. The lead-silver—zinc depos- its with abundant pyrite, which liberates sulfuric acid when oxidized, are enriched in lead and silver and lose zinc in weathering. Examples are the deposits in the Darwin district and the Santa Rosa mine. There is little transportation of lead, and the oxide ore, com- monly with relict galena through it, has the same struc- tural control as the primary ore. Galena altered first to anglesite and then to cerussite, Which is insoluble and formed virtually in place. Sphalerite was attacked by the ground water, and much of the zinc was removed in solution, although some was precipitated as hemi- morphite and hydrozincite. The oxidation of the ore at the Zinc Hill and Lee mines, where the ore is in limestone and contains little pyrite, apparently was done by ground water that con- tained no free acid, and the stability relationships of the supergene minerals are different from those prevailing at Darwin where oxidation was done by acid ground water. The stable zinc mineral, hemimorphite, forms high-grade zinc—rich ore bodies virtually in place. The silver mineral is cerargyrite. Very little lead—mostly as relict galena—is present in the ore. This is in marked contrast to Darwin where zinc is leached, and the oxidized ore is rich in lead and silver and is low in mm. The oxidized ore at the Lee mine consists mainly of hemimorphite, chalcedony, bindheimite, cerargyrite, and relict galena. Cerussite and anglesite are in thin bands surrounding relict galena, and very little is pres- ent in the cellular oxide ore admixed with hemimorphite (fig. 33). Evidence indicates that under the environ- ment prevailing at the Lee mine that hemimorphite and cerargyrite are stable minerals and formed virtually in place. Very little sphalerite is found in the ore as it is unstable and readily alters to hemimorphite whereas galena is less readily altered and remains as corroded relicts. Similarly at the Zinc Hill mine the supergene ore consists predominantly of hemimorphite. The Zinc FIGURE 33.—Photograph of partly oxidized ore from the Lee mine. Galena (gn) and calcite (ct) occur as reiicts in a cellular mass of hemimorphite (hm), chalcedony (cl), bindheimite (bn) [Pngszn 0,0H)], and cerargyrite listed in order of decreasing abundance. Cerargyrite is present locally in vugs in hemimorphite but cannot be distinguished in the photograph. Cerussite (ce) and anglesite are limited to a thin rim about galena. Hill ore difl’ers from that at the Lee mine; it has a low content of silver. The primary ore from the upper ore body at Zinc Hill averaged 22.28 percent zinc, 1.33 percent lead, and 1.43 ounces of silver per ton (Hall and MacKevett, 1958). Oxide ore from the same ore body averaged 36.9 percent zinc, but the lead and silver con- tent of the ore is not known. Oxide ore that was mined from 1917 to 1920 averaged approximately 45 percent zinc, 1 percent lead, 3 ounces of silver per ton, and 11/2 percent iron, but this ore came from different ore bodies and no primary ore remains. Hemimorphite is the principal supergene mineral in all the oxidized ore bodies. It formed virtually in place as the oxide ore has the same structural control as the primary ore and relict galena remains in most places. Hydrozincite and smithsonite are also present. Hydrozincite is mainly concentrated near the borders and the bottom of the flat-lying ore bodies. Smithsonite is rare, but is found in thin veinlets beneath the ore bodies and was transported farther than the other supergene zinc min- erals. Cerussite and anglesite occur only in small quantities. 68 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. CLASSIFICATION AND ORIGIN The ore deposits in the Darwin district occur in light- colored calc-silicate rock and calc-hornfels as irregular replacement ore bodies, bedded replacement ore bodies, and as fissure fillings. Other lead-silver-zinc deposits in the quadrangle are in veins or bedded deposits in calc-hornfels, marble, and limestone. The Darwin dis- trict lead-silver—zinc deposits were considered by Knopf (1914, p. 7) to range from contact metamorphic de- posits to fissure fillings of hydrothermal origin at mod- erate temperature, and by Kelley (1937, p. 1007; 1938, p. 550) to be mesothermal deposits. The distribution of deposits shows a close spatial control between ore deposits and intrusive bodies. However, the ore deposits are younger than both the intrusive rock and the surrounding contact metamor- phic aureole, as shown in the Darwin district where ore is localized in fractures that cut both the Darwin stock and calc-hornfels. Because the sulfide minerali— zation is younger than the silication in the contact aureole and because some of the deposits are fissure fillings that have a regularity in strike and dip, Kelley (1937, p. 1007) considered all the deposits to be meso thermal and to be genetically identical. The writers, however, agree with Knopf that the deposits were deposited throughout a range in tempera- ture. In places a mineral zoning can be demonstrated, as on the east side of the Darwin stock where chalcopy- rite and scheelite bodies are nearly adjacent to the stock and lead—silver ore bodies are more distant. Ore in the Defiance workings shows a vertical zoning. The near— surface ore is in bedded deposits that contain coarsely crystalline calcite, jasper, and fluorite as common gangue minerals. On the deeper levels the ore is in an irregular replacement ore body that has andradite, wol— lastonite, idocrase, orthoclase, and calcite as common gangue minerals. In the replacement ore body the ratio of zinc to lead, the chalcopyrite content, and the pyrite content increase with depth. The writers believe the irregular replacement ore body in the Defiance workings should be classified as a pyrometasomatic deposit on the basis of mineral association. Andradite and idocrase are the princi- pal gangue minerals. Pyrite is widely disseminated through the calc-silicate rock, but the other Sulfide minerals are late in the sequence and are controlled by brecciated zones in the silicated limestone. There appears to have been a nearly continuous sequence of mineralization. The limestone was first altered to calc- hornfels and light-colored calc-silicate rock, and this resulted mainly in an increase in silica and decrease in carbon dioxide. Scheelite was deposited during the last phase of the silication. A period of fracturing separated the silication of the limestone from the intro- duction of sulfide minerals. The early formed lead- zinc ore bodies are replacement ore bodies that have mainly a silicate gangue, as the pipelike vertical re- placement ore body in the Defiance workings (pl. 3). With falling temperature the hydrothermal solutions apparently became less reactive, and the resultant meso- thermal deposits filled fissures. Calcite and jasper are the main gangue minerals in these mesothermal deposits. Examples are the Blue and Red veins exposed at the surface of the Defiance workings, the Essex vein, and ore at the Lucky Jim, Christmas Gift, and Santa Rosa mines (pl. 3; fig. 3). Ore at the Zinc Hill and Lee mines was deposited under even less intense pressure-temperature condi- tions, and they might be considered leptothermal de- posits. Ore at the Lee mine is in faults in unaltered limestone. Calcite and barite are the main gangue minerals. Galena, light—colored sphalerite, and a lit- tle tetrahedrite are the principal ore minerals. Pyrite is rare. Possibly the antimony deposit in unaltered limestone at the north end of the Darwin Hills is a still weaker phase of the sequence of late Mesozoic miner- alization. However, this is an isolated deposit, and it is not known whether or not it belongs in the miner- alization sequence related to the Darwin stock. In order to get further data on the temperature of deposition of the lead—silver—zinc ores, 20 samples of sphalerite were analyzed for the iron sulfide content, which might be used as a temperature indicator as shown by Kullerud (1953) and as applied by Fryklund and Fletcher (1956) to sphalerite from the Star mine in the Coeur d’Alene district. Kullerud (1953) has shown that under equilibrium conditions with pyr- rhotite the amount of iron sulfide in sphalerite is a function of temperature, and can be used as a geologic thermometer. Sphalerite deposited in equilibrium only with pyrite is not a useful geologic thermometer as shown by Barton and Kullerud (1958, p. 228), because sphalerite with a definite percentage of iron sulfide formed in equilibrium with pyrite can be deposited under a large range in temperature. Much of the sphalerite in the Darwin quadrangle is deposited in equilibrium only with pyrite. Sphalerite deposited in equilibrium with pyrite in the Darwin quadrangle has an iron sulfide content of 0.24 to 6.98 molecular percent (table 8). This sphal- erite may be deposited from less than 200°C to about 600°C (Barton and Kullerud, 1958, p. 228). The lowest iron sulfide content of sphalerite is 0.24 molecular per- cent from colorless sphalerite from the Lee Mine. The lead-silver—zinc ore is in unaltered fine-grained lime- ORE DEPOSITS 69 stone, and the temperature of deposition was probably less than 125°C. TABLE 8.—ZnS-FeS content of sphalerites from the Darwin quadrangle Mole Indicated Sample No. Mine Level percent Mineral association tempera- 1 FeS ture of deposition Dsl—l ........ Lee _____________________ 0.24 Calcite, barite, ga— Not deter- lena. minate. Dsl-2 ........ Zinc Hill ________________ . 74 Calcite ______________ Do. Dsl—3 ........ Santa Rosa _____________ 6. 46 Pyrite, galena, jas- Do. per. 2 _________ Defiance work- 1,100 3 6. 4 Pyrite, galena, diop- Do. ings, Darwin side. mine. 4 .............. do ........... 1 100 6. 98 Pyrite, garnet, di- Do. opside. 5 _________ Defiance work- 1,000 3 3. 4 Pyrite, galena, cal- Do. ings. cite. 6 .............. do .......... 1,000 3 92 Pyrite, diopside, Do. garnet. 7 ______________ do ........... 1,000 4 83 Pyrite, galena _______ Do. 10 ______________ do ___________ 00 6 25 Pyrite, diopside, Do. garnet. 14 .............. do“ 800 5. 09 _____ do _______________ Do. 15 .............. do.. 700 3 4. 6 Pyrite, galena ....... Do. 23 ______________ do ___________ 250 5 44 Pyrite, diopside, Do. garnet. 3479 _________ Thompson 200 7. 88 Pyrrhotite, pyrite, 285°C. workings, galena. Darwin mine. 3481 ______________ do ___________ 100 3. 90 Pyrite, calcite, Not deter- diopside. minate. 3482 ______________ do ___________ 3A 8 8. 7 Pyrrhotite, galena... 320°C. 3483 ______________ do ___________ 3A 2.45 Pyrite, calcite, di— Not deter- opside. minate. 3489 .............. do ........... 700 2320 Magnetite, pyrrho- 560°C. tite, galena, pyrite. 3491 .............. do ........... 600 1 14. 2 Pyrrhotite, pyrite, 480°C. galena. 3505 .............. do ........... 700 “19.6 Pyrrhotite, pyrite, 560°C. galena, magnetite. 3508 .............. do ........... 600 3 17. 5 Pyrrhotite, magne- 520°C. tite, pyrite, ga- lena, garnet, tetra- hedrite. 1 Analyst: L. E. Reichen. 1 Contains exsolution blebs of pyrrhotite. ‘ Analyzed by H. G. Stephens and W. E. Hall by fluorescent X—ray spectrographic analysis. Six samples of sphalerite from the Defiance workings of the Darwin mine contained 3.92 to 6.98 molecular percent iron sulfide. The sphalerite in the Defiance replacement ore body was deposited in equilibrium with pyrite, and no pyrrhotite is present. This sphalerite could be deposited at a temperature between approxi- mately 500° and 650°C (Barton and Kullerud, 1958, p. 228). Much of the sphalerite in the Thompson and Essex workings of the Darwin mine was deposited in equilib- rium with pyrrhotite and can be used as a geologic thermometer. Some of the sphalerite has oriented pyrrhotite blebs as shown in figure 27, and this is inter- preted as an exsolution texture. Two samples of sphal- erite from the 700 level of the Essex and Thompson workings contained 19.6 and 20 molecular percent iron sulfide. Two samples 100 feet higher on the 600 level contained 14.2 and 17.5 molecular percent iron sulfide. A sample 447 feet higher in the Thompson workings contained 7.88 molecular percent iron sulfide. The range in temperature indicated by the range from 7 .88 to 20 molecular percent iron sulfide is about 300°C in the upper part of the Thompson mine to 550°C on the 700 level. The iron sulfide content of the sphalerite in the Thompson and Essex workings indicates that the ore in the Darwin mine was deposited under a consider- able range in temperature. However most of the sphalerite in the mine is deposited in equilibrium with pyrite, and not enough is deposited in equilibrium with pyrrhotite to get a good idea of the range in temperature for the whole mine. The temperatures indicated by the sphalerite confirm Knoff’s (1914) early statements that the Darwin ores were deposited under a consider- able range in temperature, and the deposits Should be classified as contact metasomatic ranging to meso- thermal. Description of pyrometasomatic lead-silver—zinc de- posits are not abundant in the literature. Knopf (1933, p. 552) lists only the Darwin district as an example of a lead-silver-zinc pyrometasOmatic‘ deposit. Lindgren (1933, p. 724—725) includes the Magdalena mine in New Mexico, zinc deposits at. Hanover, N. Mex., the Sirena mine near Zimapan, Mexico, and the Darwin district. More recently Simons and Mapes (1956) have described the deposits of the Zimapan district which, like the Dar- win deposits, grade from pyrometasomatic replacement deposits in a silicate gangue to mesothermal deposits in a carbonate gangue. Jasper is not as common as it is in the mesothermal deposits at Darwin. In addition to a change of gangue minerals, the mesothermal deposits at Zimapan contain less arsenopyrite, chalcopyrite, and pyrrhotite and the sulfide minerals are coarser grained than the pyrometasomatic deposits. The lower tem- perature deposits in the Darwin quadrangle, like those at Zimapan, are coarser grained and show an approxi- mate similar zonation of ore and sulfide minerals. DARWIN LEAD-SILVER-ZINC DISTRICT The Darwin lead-silver—zinc district comprises the area of the Darwin Hills in the south-central part of the Darwin quadrangle. It lies within the organized New Coso mining district. The district has produced an estimated $29 million in lead, silver, zinc, and minor copper. Most of the ore came from the Darwin mine, which consists of consolidation of the former Bernon, Defiance, Essex, Independence, Intermediate, Rip Van Winkle, and Thompson mines. GEOLOGY The Darwin Hills are underlain by a thick sequence of limestone, silty and sandy limestone, shale, and siltstone that ranges in age from Devonian on the west side of the Darwin Hills to Permian on the east (pls. 1, 3). The formations represented are Lost Burro forma— tion, Tin Mountain limestone, Perdido formation, Lee 70 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. Flat limestone, Keeler Canyon formation, and Owens Valley formation. The Paleozoic rocks are intruded by a stock of biotite-hornblende-quartz monzonite in the central part of the district and in the Coso Range. The Paleozoic rocks dip predominantly to the west except for local folds. Within 4,000 feet of the stock of the Darwin Hills the sedimentary rocks are mostly meta- morphosed to calc-hornfels. A description of the unaltered rocks is given under “Paleozoic rocks,” and the alteration is described under “Metamorphism.” STRUCTURE Structurally the Darwin Hills are an overturned syncline with an axial plane that dips about 50°‘ W. A stock of biotite-hornblende-quartz monzonite in- truded Paleozoic rocks near the axis of the syncline. The Paleozoic rocks west of the stock strike northward and dip mainly 30° to 70° W. in an overturned section on the west limb of the major syncline. Small open folds are superposed on the overturned limb of the syncline, and these folds localize some of the principal ore bodies in the Darwin mine. The folds are all inverted structures. One is on the west flank of Ophir Mountain and can readily be seen from the Darwin mining camp. Similar inverted folds are be- tween the Defiance and Bernon workings, in the In- dependence workings, and on the west side of the Darwin Hills adjacent to the Darwin mining camp. The Paleozoic rocks in the Darwin district are broken by four sets of faults. The strongest set is left-lateral strike-slip faults that strike N. 70° W. and dip steeply (pls. 1, 3). Examples are the Darwin tear fault and the Standard fault. Another set of left-lateral strike- slip faults strikes N. 70° E. and dips steeply. These faults are the feeder fissures for the lead-silver-zinc and for the tungsten deposits of the Darwin district. The horizontal displacement is shown by offset of beds, axial planes of folds, and by abundant nearly hori- zontal slickensides and mullion structures. The other two sets of faults strike north. One set dips steeply and the other dips 30° to 55° W. The steep faults have little displacement but are important in localizing ore in some of the mines. The west-dip- ping faults include both thrust faults and normal faults. The most important is the Davis thrust, which is ex- posed along the side of the hill above the Independence, Essex, and Bernon workings and at the water tanks near the Water tank fault (pl. 3). The net slip is not known. The Ophir fault is parallel to, but west of, the Davis thrust. It is a bedding-plane fault that probably has little displacement. ORE DEPOSITS Three of the four structural types of lead-silver-zinc ore bodies in the Darwin quadrangle are in the Darwin district. They are bedded deposits, irregular replace- ment ore bodies, and vein deposits in fissures. Bedded deposits are the most common. Notable examples are the bedded ore bodies in the Independence workings, the 430 stope ore body and Blue and Red veins in the Defiance workings, and the ore bodies at the Custer, Jackass, and Promontory mines. The largest bedded ore body is in the Independence workings between the 200 and 400 levels along the crest of an anticlinal-shaped fold between two quartz monzonite sills, and directly below the Davis thrust (pl. 3). This ore zone is 400 feet along strike, a maxi- mum of 160 feet thick, and 700 feet across the crest and down the west limb of the fold. It must be emphasized that this zone is not all ore. Individual stopes within the zone have maximum dimensions of about 140 feet in length, 60 feet in width, and 40 feet in height. The contacts of individual ore bodies in this ore zone are mostly sharp, and only barren calc-hornfels or highly pyritized calc-hornfels lies between individual ore bodies. Two readily accessible bedded ore bodies—the Blue and Red veins—are well exposed at the surface of the Defiance workings of the Darwin mine. The shapes of the ore bodies may be inferred from the surface stopes, which have remained open since the ore was mined in the 1870’s (pl. 3). The bedded veins are along the crest and west limb of an anticlinal-shaped (inverted syncline) fold between two sills of quartz diorite (pl. 3). On the Defiance tunnel level the Blue vein is about 300 feet long, 2 to '8 feet thick, and has been mined discontinuously for 400 feet downdip. The Red vein is exposed intermittently by stopes for a strike length of 400 feet. It is 2 to 6 feet thick and has been mined 500 feet downdip. The contacts of the veins and pyritized calc-hornfels country rock are sharp. The grade of ore within the veins, however, is erratic. The ore body mined from the 430 and 520—12 stopes is another important. bedded deposit in the Defiance mine (pl. 4). The ore body was about 150 feet long, 40 feet thick, and extended about 360 feet downdip. The shape, nature of the ore, and method of minlng of this ore body is described in detail by Davis and Peter- son (1948, p. 3—6). It extended from the 110 to the 520 level. Below the 520 level the ore occurs as a steep irregular replacement of calc—silicate rock. The only important irregular replacement ore zone in the Darwin district is in the Defiance workings .ad— jacent to the Defiance fault (pl. 3). It is a vertical mineralized zone that has been developed from the bot- ORE DEPOSITS 71 tom of the bedded ore bodies at the 520 level to the 1000 level. The average cross sectional area of the mineralized zone is about 350 feet long and 200 feet wide. On the 700 level 12 percent of an area 400 feet long and 130 feet wide is ore, and on the 800 level 15 percent of an area about 320 feet long and 220 feet wide is ore. Contacts of individual ore pods within this zone are gradational. The premineralized Defiance fault, which strikes northeast and dips steeply to the northwest, cuts diagonally through the mineralized area, and many small faults are localized close to this fault and formed a strongly brecciated zone that served to localize later ore solutions. Vein deposits are in persistent faults in many mines in the district. Three sets of faults have localized ore— they are steep N. 70° E. faults, steep N. 70° W. faults, and steep north-striking faults. The most notable N. 70° E. veins are at the Christmas Gift, Darwin, Lane, and Lucky Jim mines. At the Christmas Gift mine an ore shoot has been mined from the Christmas Gift vein between the surface and the No. 6 level, a vertical dis- tance of 146 feet (pl. 5). The ore shoot has a strike length of 160 feet and an average thickness of 3 feet; it plunges steeply southwestward. The ore shoot at the Lucky Jim mine has a maximum strike length of 460 feet on the 200 level, and it plunges steeply to the southwest. The ore shoots at both mines are localized in parts of the faults that strike nearly northeast, and the parts of the faults with more easterly strike are mostly barren (pl. 5). Other smaller northeastward- striking veins are the 229 and 235 ore bodies in the Thompson workings, ore bodies along the Mickey Sum- mers and Water tank faults (pl. 3) and the Lane vein in the Lane mine (fig. 3). The only economically important steep northwest- striking vein is the Essex vein in the Darwin mine (pl. 3). This high-grade vein has a maximum length of about 500 feet, an average thickness of 8 feet, and has been mined 650 feet vertically. The other two major northwestward-striking faults—the Darwin tear fault and the Standard fault—contain very little ore. Steep north—striking faults have had some effect in localizing ore. The bedded ore bodies commonly make out along bedding from an intersection of a steep fault. GEOCHEMICAL PROSPECTING The distribution in residual soil over calc-hornfels of lead, zinc, copper, silver, antimony, and bismuth in re- lation to lead-silver-zinc ore bOdies in the Defiance-Ber- non area of the Darwin mine was investigated in August 1954. About 400 residual soil samples were collected 011 a grid at 50-foot intervals by James Prentice, of the US. Geological Survey, in the Bernon and Defiance area, and about 100 chip samples were collected on the Defiance tunnel level and the 570, 700, and 800 levels of the Defiance workings by the authors. Each sample was analyzed for lead, zinc, and copper and about a third were analyzed for antimony, bismuth, and silver; these trace analyses were made by H. E. Crowe of the US. Geological Survey. The area around two veins that crop out in the open- cuts in the Defiance workings along the crest of an open inverted syncline near the Defiance fault was sampled as a known control area (pl. 6). The fold is continuous between the Defiance and Bernon workings, but little ore is known in this geologically favorable area, and it was sampled as an area favorable for undiscovered hidden ore. It is cut by two N. 70° E. faults—the 434 and Bernon. Some ore was mined from the Bernon workings, but it does not crop out at the surface. Very little ore is known along the 434 fault. Soil samples were taken on a 50-foot grid system over the Bernon and Defiance area. The samples were taken at a depth of about 4 inches. Each sample was screened through an 80-mesh screen and the coarse ma— terial was rejected. Each sample weighed about 2 pounds. Chip samples were taken at 25-foot intervals in the underground workings of the Defiance ore body. Small chips were collected from the back if possible or from the wall over a radius of 3 feet. About 15 grams was collected for each rock sample. Distribution of Zead—zz'nc-copper.—The distribution of total lead-zinc—copper in residual soil is shown in plate 6. The distribution of the plutonic rocks and the location of the principal faults are also given. The strongest anomaly of total lead-zinc-copper, expressed in parts per million (ppm), is over the Defiance work- ings. This anomaly is probably much greater than 7,000 ppm, but the maximum quantities determined in the laboratory at the time of the exploration was 4,000 ppm for lead and 3,000 ppm for zinc and all the samples within the 7,000 contour were more than the maximum. The copper assays were mostly less than 200 ppm. Near the Defiance workings the 7,000 ppm contour outlines the area over the known ore bodies, and the anomaly is elongated along the Defiance fault, which probably is the feeder channel. The anomaly decreases in about 300 feet to a background in the mine area of 1,000 to 2,000 ppm. The background of soil over un- altered limestone several miles from the mine area is only 120 ppm of total heavy metals. Most of the area near the 434 fault is low in total lead-zinc-copper. A small high anomaly is near the west end of the fault near the intersection with the Davis thrust, but no ore is known in this area. As a 72 GEOLOGY AND ORE 'DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. whole the 434 fault has much less lead-zinc-copper than the other N. 70° E. faults that were sampled. The hidden Bernon ore body 70 feet below the collar of the Bernon shaft is reflected by a geochemical high, which extends farther south than known ore. Two geo- chemical anomalies between the Bernon and Copper faults have not been explored. ' One anomaly is 300 feet N. 5° W. of the Bernon shaft in an area that has a large quantity of disseminated limonite at the surface. The other anomaly is at the contact of biotite-hornblende- quartz monzonite midway between the Bernon and Cop- per faults. The whole Copper fault is another geo- chemical high, similar to the Defiance fault, but only a small amount of exploration work has been done along it. Antimony, bismuth, and silver were determined on about a third of the samples (pl. 7). The bismuth con- tent of the residual soil ranges from less than 10 to 250 ppm. The bismuth anomalies agree in general with the anomalies shown by total lead—copper-zinc. Adjacent to the Defiance ore bodies, bismuth ranges from 100 to 250 ppm, and it drops off to 10 to 15 ppm beyond 80 feet from ore. Another bismuth high, 260 feet S. 80° W. of the Defiance shaft, is about 300 feet above the 430 and 520—12 stope ore body in the Defiance workings and may be an anomaly reflecting it. Most of the area between the Defiance and Bernon workings contains less than 10 ppm of bismuth. The bismuth increases to 70 to 90 ppm over the Bernon ore body. Several analyses of samples from the north- eastern part of the area tested suggest that the bismuth is greater than above background, but the data are sparse. The total lead—zinc-cop-per anomaly is high in this area also, but no ore is known. Antimony and silver seem to be unsatisfactory in reflecting ore. The content of antimony and silver in the ore is high, but the content of each in residual soil falls off to background values generally within a few feet of ore. The antimony content of the Defiance ore is 45 to 100 ppm. Twenty feet from ore in residual soil the antimony content falls off to less than 15 ppm. Most of the soil between the Bernon and Defiance work- ings contains less than 4 ppm of antimony. Over the Bernon embody the antimony content increases to 15 to 40 ppm. The ore in the Defiance pit assayed from 4 to 9 ounces of silver (140 to 315 ppm), but the silver content dropped to less than 3 ppm in soil a few feet from ore. No anomaly in silver was apparent over the Bernon ore body. Throughout most of the tested area the silver content was less than 2 ppm. In conclusion, geochemical prospecting of soil could be a useful tool 1n the Darwin district. Heavy metals (total lead- -zinc-copper) and bismuth tests both gave promising results in the Defiance-Bernon area. The two known ore bodies in the tested area were reflected ' by pronounced anomalies. Two anomalies were also found in unexplored areas. Antimony seems less prom- ising than bismuth in reflecting ore. The antimony content decreased rapidly away from the Defiance ore body, so it provided very little larger target‘ than that of the ore body itself. The antimony was more satis- factory 1n reflecting the Bernon ore body. Silver gave unfavorable results. Nearly all the residual soil has less than 2 ppm of silver, and only the ore itself has a high silver content. . Rock chip samples were not as satisfactory in re- fleeting ore as the soil samples. Some rock chip sam- ples taken as a comparison with residual soil samples in general contained less total heavy metals and gave more erratic results. The underground rock chip sam- ples, in general, increased in total heavy metal content toward ore bodies, but the analyses were erratic and many samples gave anomalous results. i FUTURE OF THE DISTRICT New ore in the Darwin district has been found in the past mainly by following downward ore bodies exposed at the surface or in the upper workings of the mine. This procedure has proved highly successful, but dur- ing the past few years most of the major ore bodies have bottomed. The future of the district lies in finding new major ore bodies rather than extensions of old ones." The possibilities for finding new ore bodies have not been exhausted. A mastery of the stratigraphy, struc- ture, and rock alteration and their relationship to ore is essential for a successful program. Many areas re- main to be explored from the present workings of the Darwin mine, but enough drilling has been done to make chances of discovery of another large ore body like the Defiance seem dim. Ore in the Darwin mine is in a medium-grained idocrase-garnet-wollast0ni’oe rock; dense dark calc-hornfels like that west of the Davis thrust and unaltered limestone are unfavorable. Nearness to an intrusive body is important, and the largest ore bodies are within a few hundred feet of granitic rock. Faults play a part in localizing all the known ore—even the bedded deposits are localized close to N. 70° E. faults, whichappear to be feeder faults. Anticlinal structures are particularly favorable, al- though Ore is not restricted to them. Recognition and intelligent use of these ore controls will undoubtedly result in the discovery of new, probably small, ore bodies near the present workings in the Darwin mine. In the, Thompson-Essex-Independence workings the Davis thrust is an important ore control, and little or no ore has been found on the west or hanging-wall side ORE DEPOSITS of it. The ore above the thrust shown on plate 3 is projected and actually is on the footwall of the thrust. To the south in the Defiance workings the contact of the Darwin stock and the Davis thrust diverge, and the fault seems to be less important in localizing ore except near the satellitic body of quartz monzonite southwest of the,Defiance_ workings. At present the shape of the Darwin stock is'not known, and the writers only use the term “stock” because it has been used extensively. However, the west side of the intrusive body ends in a series of sills that bottom in the Defiance workings (pl. 3r),'and a diamond-drill hole extending 700 feet east from the 800 level" did not cut granitic rock. The writers feel that the intrusive mass may have a floor and be a laccolith. If so, a large area under the out- crop of the intrusive mass may contain undiscovered ore bodies. Little exploration has been done southeast of the Defiance mine along the Water tank and Mickey Sum— mers faults near the intrusive mass (pl. 3) where the alteration is similar to that in the Defiance area, and much of the outcrop is iron stained. A few prospect ' pits have been dug, but no exploration has been done at depth. Another area of extensive garnet-idocrase-wollasto- nite rock that may be favorable for ore is north of the Standard fault on the footwall side of the westward- dipping fault that passes through the Belle Union mine and the west side of the Lucky Jim mine (pl. 1; fig. 3). This fault is similar to the Davis thrust in that it local. ized intense silication of limestone below it. A geo— chemical prospecting program similar to the one de— scribed in this report for the Defiance area might help pinpoint areas favorable for further prospecting! ZINC HILL DISTRICT ‘ The Zinc Hill district is 31/; miles N. 65° E. of Dar- win on the west slope of the Argus Range. Relief in the area is rugged, and access to some places is difficult. The average slope in the district is about 30°. Indi- vidual properties are described in a previous report by the writers (Hall and MacKevett, 1958), and only a generalized description of, the district is given here. The Zinc Hill and Empress mines are the only prop- erties with a recorded production up to 1952. The Dar- Win Zinc mine has several hundred feet of workings, but no record of production was found for it. The re— corded production for the district from 1917 to 1951 is about 3,560,000 pounds of zinc, 285,000 pounds of lead, 8,500 ounces of silver, and 14,000 pounds of copper? 1Compiled from Hall and MacKevett (1958, p. 41—45). GEOLOGY 73» The Zinc Hill district is underlain by limestone and marble of Mississippian and Permian age that is in- truded by leucocratic quartz monzonite and by dikes and small irregular plugs of diorite (pl. 1). The stra- TABLE 9.—Geologz‘c column of the Zinc Hill district . Age Name Lithology , Thickness (feet) Cretaceous(?) Diorite dikes and . plugs. Leucocratic quartz monzonite. Permian Pennsylvanian(?) and Mississippian Owens Valley formation Limestone, thinly bedded, silty. ~Fau1t contact Lee Flat limestone Marble white Limestone, bluish-gray, thinly bedded. Con- tains interbedded chert. Marble (ore zone at Zinc Hill mine). 130+ 130 180 Mississippian Perdido formation Marble with 2- to 4-inch chert beds. ' 20 Limestone, bluish-gray, 100 containing bedded chert. Limestone, bluish-gray 20+ Tin Mountain(?) and mar 1e. limestone . tigraphy of the area is given in table 9. Both the Empress and the Zinc Hill mines are underlain by mar- ble and limestone of Mississippian age in a northward- trendinghorst about 1,000 feet wide that can be traced from the Darwin tear fault north for 2 miles (pl. 1). A minimum thickness of 580 feet of unfoss-iliferous marble and limestone crops out in the horst. The sec- tion is correlated with the Mississippian on the basis of lithologic similarity to Mississippian formations found elsewherein the quadrangle. The upper part of the Tin Mountain limestone, the Perdido formation, and the Lee Flat limestone are probably represented within the horst, but it is all mapped as Lee Flat as most of the marble within the horst resembles it. I The Owens Valley formation of Permian age crops out on the east and west sides of the horst. It con— sists of thinly bedded silty bluish-gray limestone and shale. .- The Zinc Hill stock, a small intrusive mass 5,000 feet long and 2,000 feet wide, crops out between theEm- press mine and the Darwin tear fault (pl. 1). It is medium-grained leucocratic quartz monzonite. Locally close to the stock the Mississippian limestone is altered to calc-hornfels and dark-brown tactite. Dikes and irregular plugs of fine-grained greenish—gray diorite and quartz diorite intrude the Mississippian marble and limestone in many places between the Empress and Zinc Hill mines, but most of these intrusive masses are too small to show on the quadrangle map (131- 1)- 74 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. STRUCTURE The horst containing the productive mines is bounded by steep north-trending faults. Bedding within the horst strikes predominantly northwest to west and dips 10° to 40°N., and that in the Permian limestone on either side strikes mainly N. 45'0 to 75° E. and dips 17° to 63° NW. The Zinc Hill fault, which bounds the horst on the west, and the major fault that bounds the horst on the east each have a stratigraphic displacement of more than 2,700 feet. Within the horst the lime- stone and marble are cut by many steep faults that trend N. to N. 45° E. and N. 45° to 70° W. These faults have had several periods of movement and many of them are mineralized or dolomitized. The latest movement on the northwestward-trending faults is very young. These faults displace the Zinc Hill fault (Hall and MacKevett, 1958) which has late Tertiary or Qua- ternary displacement. The leucocratic quartz monzonite is within the horst and is cut off on the West by the Zinc Hill fault. The Empress mine is in a roof pendant of Mississippian limestone. ORE DEPOSITS Ore occurs as small replacement bodies parallel to bedding and to a lesser extent along faults where they cut a favorable limestone or marble bed. Both primary and oxidized zinc ore is present. The primary ore from the Zinc Hill mine is predominantly sphalerite but in- cludes small amounts of galena, pyrite, and chalcopy— rite in a predominantly calcite gangue containing some quartz, jasper, and gypsum. The oxidized ore con- sists mainly of hemimorphite, but hydrozincite is abundant locally near the margins of some ore bodies, and smithsonite is rare in veinlets below a few. Ore at the Empress mine consists mainly of galena, but con- tains lesser amounts of sphalerite, chalcopyrite, and pyrite in a quartz-rich gangue. Secondary ore min- erals are anglesite, azurite, cerussite, chrysocolla, mala- chite, and wulfenite. At the Zinc Hill mine a favorable marble bed 180 feet thick crops out for 1,500 feet in a northwesterly direction. It is cut ofl" on the east and west by the faults bounding the horst. Minable ore bodies are in four localized areas within the favorable bed. Inter- sections of north to N. 45° E. faults with the favorable bed are apparent ore controls. The largest ore body is shown in plate 8. It is a bedded replacement of the favorable marble bed, called the Colorado bed by the owners. The lower stope in the upper workings is about 80 feet long, 60 feet wide, and 10 to 16 feet high. The outline of the stope reflects approximately the shape of the flat-lying, disk-shaped ore body. Approximately 9. third of the ore removed from this stope was primary and the rest was oxidized zinc ore. Primary ore extends to within 40 feet of the surface. Several smaller bedded deposits were mined from the lower, westernmost workings on the property. Small oxidized zinc ore bodies in the lower workings of the Zinc Hill mine are localized along northwest- ward-trending faults (Hall and MacKevett, 1958, p. 49) . The most strongly mineralized fault, which strikes N. 60° W. and dips 30° to 50° NE., is stoped discontinuously for 200 feet along strike and 50 feet downdip for a thickness of 3 to 12 feet. The lead—zinc ore body at the Empress mine is a bedded replacement of limestone near the contact with leucocratic quartz monzonite, and the deposit extends into the intrusive mass as a quartz vein. Ore can be traced on the surface about 400 feet, where it ranges in thickness from a few inches to 6 feet. The north end of the ore body within the quartz monzonite is thicker and higher grade than the more discontinuous south end, which is in limestone. Locally the ore in the Empress and Zinc Hill mines is slightly radioactive. At the Empress mine local radio— activity ranged from 0.04 to 0.15 mr per hr compared to a background of 0.02 mr per hr. At the Zinc Hill mine ore containing hydrozincite in the lower workings had a local radioactivity of 4 to 10 times background. The source of the radioactivity was not definitely deter- mined, although one specimen contained a small amount of a micaceous orange mineral, probably autunite. LEE DISTRIGI‘ The part of the Lee district in the Darwin quadrangle comprises a small area in the southern part of the Santa Rosa Hills (fig. 2). The Lee-mine (formerly known as the Emigrant mine) and the Silver Reid prospect are the only properties that have been developed. Produc- tion, which is recorded only from the Lee mine, was mainly during the 1870’s and early 1880’s. De Groot (1890, p. 213) mentioned that activity in the district was waning by 1888. Since then the Lee mine has been operated only intermittently on a small scale by lessees. The total ”“production of the district is not known. Tucker and Sampson (1938, p. 443) reported that 250 tons of ore shipped during 1927 averaged $49 (64 ounces) per ton in silver. L. D. Warnken shipped 226 tons of dump material in 1938 that contained 750 ounces of silver.2 The production since 1951 was furnished by the mine owners and is given in table 10. 2Published with permission of the mine owners. ORE TABLE 10.—-Assay data of are shipped from the Lee mine, 1951 to 1955 1 Copper Lead Zinc Silver Gold Year Tons (percent) (percent) (percent) (ounces (ounces per ton) per ton) 41 0.45 2. 4 16. 3 61. 3 0.025 35 . 1. 5 l7. 6 48. 0 .025 44 45 l. 5 22. 75 89. 76 .035 35 425 9.85 21. 05 93. 95 . 037 42 24 7. 9 17. 75 59. 6 .025 49 2 4.5 24.0 53.9 .......... 1 Published with permission of the mine owners. GEOLOGY The south end of the Santa Rosa Hills in the Lee dis- trict is underlain by a conformable sequence of lime— stone and marble of Devonian and Mississippian age. The Silver Reid prospect is in the Lost Burro formation, which crops out in a narrow band along the east flank of the Santa Rosa Hills. The formation consists of 1,770 feet of white and light-gray medium— to coarse- grained marble. The Lost Burro is conformably over- lain by the Tin Mountain limestone, which underlies most of the Lee mine area. The formation is about 400 feet thick and consists of medium-gray cherty limestone in beds 1/2 to 2 feet thick. STRUCTURE The Paleozoic rocks strike N. 45° W. to west and dip mainly southwest in a concordant sequence. They are cut by two sets of faults. One set strikes N. 70° W. ap- proximately parallel to the strike of bedding and dips steeply. The other set strikes N. 20° to 70° W. and dips , gently southwest. The low-angle faults have no ap- preciable displacement and occur between the major steep faults. In the Lee mine the beds dip gently and the flat—lying faults are approximately parallel to bed— ding. At the Silver Reid prospect they transect the steeply dipping bedding. ORE DEPOSITS Small discontinuous ore bodies are localized along the flat-lying faults that are in part cOntrolled by bedding. Most of the steep faults are only slightly mineralized except at the intersection with the mineralized flat-lying faults. Locally the ore bodies steepen adjacent to the major steep faults. At the Lee mine the largest ore body was about 40 feet long, 35 feet wide, and averaged 6 feet in thickness. Most of the ore bodies mined during the past few years are much smaller and have produced less than 100 tons of ore. , At the Silver Reid prospect the largest known ore body in 40 feet long, and 20 feet wide, and averages 2 feet in thickness (pl. 9). The ore body is localized in a nearly horizontal fault between two steep N. 70° W. 620626 0—62——6 DEPOSITS 75 faults that are 22 feet apart. At least five other flat veins are exposed on the property, but they are not extensively developed. The workings at both the Lee mine and the Silver Reid prospect are shallow; most of the ore is oxidized, and only relicts of the primary minerals remain. The ore at the Lee mine consists mainly of hemimorphite and cerargyrite. Angelsite, aurichalcite, azurite, bind- heimite, native copper, cerussite, and chrysocolla have also been identified. Gangue minerals are principally barite, calcite, chalcedony, and quartz. Cerargyrite occurs as euhedral cubes less than 1 mm on a side modi- fied by octahedral faces. Galena is the most abundant remaining primary mineral. It occurs as coarsely crys- talline relicts in masses of hemimorphite. Cerussite and anglesite occur mainly as thin rims a few milli- meters thick between the galena and cellular oxide ore. Small amounts of sphalerite, pyrite, and tetrahedrite remain. Sphalerite probably was originally an abun- dant ore mineral, but it is more readily attacked by ground water than galena, and little of it remains. DEPOSITS IN THE INYO MOUNTAINS AND TALC CITY HILLS The only lead—silver-zinc deposits in the Inyo Moun- tains and Talc City Hills are the Santa Rosa mine and several small deposits in the Tale City Hills, including the Cactus Owen, Homestake, and Silver Dollar mines (fig. 3). The Santa Rosa mine was described by Mac— Kevett (1953, 9 p.) , and the other deposits are de- scribed by Hall and MacKevett (1958). The Santa Rosa mine is an isolated lead-zinc deposit in the Inyo Mountains (fig. 3). It is in an inlier of calc-hornfels of Permian age in an area almost com- pletely covered by andesite and basaltic flows and pyro- clastic rocks of Cenozoic age. The mine was discovered in 1910, and was operated continuously until 1938, ex- cept during 1912—15. It has been operated only inter— mittently since 1938. Total production is 36,854 tons of ore from which 11,990,792 pounds of lead, 487,347 pounds of copper, 4,105 pounds of zinc, 426,543 ounces of silver, and 479 ounces of gold were recovered (Mac- Kevett, 1953, p. 4). The Silver Dollar mine is the only lead—silver-zinc deposit in the Tale City Hills that has a recorded production. It produced 469,782 pounds of lead and 19,694 ounces of silver during 1910—15 (Hall and MacKevett, 1958, p. 57). SANTA ROSA MINE The Santa Rosa mine is a vein deposit in an inlier of the lower unit of the Owens Valley formation that is metamorphosed to calc-hornfels. The inlier is about 2,000 feet long and 600 feet wide and is encompassed by Cenozoic volcanic rocks of andesitic and basaltic 76 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. composition. The calc-hornfels is intruded by steep andesitic porphyry dikes that are 2 to 6 feet thick and strike about N. 70° W. The calc—hornfels and the sur- rounding pyroclastic rocks are cut by basalt dikes. Structurally the Santa Rosa mine is in a horst that is bounded by steep north-trending faults. The calc- hornfels within the horst strikes northward and dips 30° to 70° E. It is cut by three sets of mineralized faults (MacKevett, 1953, p. 1), two of which strike north. Most of these dip 30° to 60° W., but a few dip 55° to 80° east. The third set strikes east and dips about vertically. Ore occurs in veins in the three sets of faults within the horst. The veins are 100 to 700 feet long and aver- age 3 to 4 feet thick. Those that dip west are the most important economically. The ore is mostly oxidized and consists mainly of cerussite and hemimorphite in a gangue of limonite, jasper, and calcite. Some pri— mary ore is in the lower crosscut, and locally relict primary minerals are in oxide ore. The primary ore contains galena, sphalerite,’ pyrite, chalcopyrite, and ar- senopyrite listed in order of decreasing abundance. DEPOSITS IN THE TALC CITY HILLS The lead-silver-zinc deposits in the Talc City Hills are small (fig. 3). They are all in limestone, and dolo- mite and quartzite are unfavorable host rock. The de- posits are in steeply dipping faults that strike N. 40° to 75° W. At the Silver Dollar mine, the only mine with a recorded production, the Lost Burro formation of Devonian age is thrust over the Keeler Canyon for- mation of Pennsylvanian and Permian age (Hall and MacKevett, 1958 p12). The thrust fault is exposed 300 feet north of the main pit where a sliver of Rest Spring shale has been dragged along the fault. The ore is in the Keeler Canyon formation in a shear zone that strikes N. 50° W. and dips steeply northeast. The size of the ore body, estimated from the size of the main pit, was about 35 feet long, 30 feet thick, and was mined 90 feet down dip. The nature of the ore is not known as little remains in the workings. The Cactus Owen and Homestake prospects are in thin-bedded bluish-gray limestone of the Lost Burro formation that is in part bleached and recrystallized to marble. Steep strike faults are abundant in the lime- stone. The faults are iron stained and locally contain pockets of cerussite, hemimorphite, and oxidized copper minerals in a gangue of quartz and calcite. TUNGSTEN DEPOSITS DISTRIBUTION Tungsten has been recovered from the Darwin quad- rangle principally from [mines in the eastern part of the Darwin Hills 1 to 11/2 miles east and northeast of Darwin (fig. 3). The deposits are all contact metamor- phic. Scheelite is the principal tungsten mineral. It has also been recovered from the Darwin mine from small high-grade concentrations in lead-silver-zinc de- posits, and stolzite has been reported in the oxidized ore by Tucker and Sampson (1941, p. 567) and by Dudley L. Davis (oral communication, 1955). A small amount of scheelite has also been mined from small deposits on the northeast slope of the Coso Range about 8 miles west and southwest of Darwin, mainly just south of the Dar- win quadrangle. One deposit—the Lone Pinyon—lies ' within the quadrangle in sec. 26, T. 19 S., R. 39 E. PREVIOUS WORK AND ACKNOWLCEDGMENTS Hess and Larsen (1922, p. 268) first mentioned the occurrence of scheelite in the Darwin district. The tungsten deposits were mapped by a US. Geological Survey party under D. M. Lemmon from November 3, 1941, to March 4, 1942. Their maps are published in the report on the ore deposits of the Darwin quadrangle by Hall and MacKevett (1958, see section on tungsten deposits by Hall, MacKevett, and Lemmon). L. K. Wilson (1943, p. 543—560), geologist for the Pacific Tungsten Co., described the tungsten deposits and the operations of the Pacific Tungsten Co. from 1941 to 1943. The US. Bureau of Mines trenched and sampled nine properties in the Darwin district from November 1941 to January 1942 and published assay maps of their results (Butner, 1949). Bateman and Irwin (1954, p. 34) briefly described the deposits. DEPOSITS IN THE DARWIN DISTRICT GEOLOGY Contact metamorphic tungsten deposits in the Darwin district are peripheral to the Darwin stock of biotite- hornblende—quartz monzonite. Most of the deposits are in the eastern part of the Darwin Hills in the lower unit of the Keeler Canyon formation of Pennsylvanian and Permian age. The tungsten deposits are localized mainly in the pure limestone beds interbedded with silty and sandy limestone that is metamorphosed to calc- hornfels. The relatively pure limestone beds are in part unmeta- morphosed and in part recrystallized to marble. Lo- cally the marble and limestone are altered to tactite within a few hundred feet of the intrusion. The tactite consists mainly of garnet (grossularite—andradite) and idocrase, but some contains epidote, orthoclase, diopside, wollastonite, and calcite. The Paleozoic rocks are tilted into an overturned sec- tion that strikes north and dips 30° to 78° W. The Paleozoic and plutonic rocks are broken by several pres ORE DEPOSITS 77 mineralization left-lateral strike-slip faults that strike N. 70° E. can BODIES Scheelite locally replaces pure limestone and tactite beds close to and within faults that strike N. 7 0° E. (pl. 10). Most of the ore is found within three limestone beds known as the Durham, Frisco, and Alameda beds. Only the Durham ore body extends more than 60 feet vertically (fig. 34). The Durham and Alameda ore bodies replace pure limestone and tactite near the Fernando shear zone. The Durham ore body is a re- placement of the Durham limestone bed near the contact with the underlying calc-hornfels. The ore body is 350 feet long at the surface and has been mined to a depth of 350 feet where the ore body is only 30 feet long (pl. 10). Its thickness ranges from 21/2 to 35’ feet. Three replacement ore bodies have been mined from the Alameda beds near N. 70° E. faults (pl. 10). Two are at the intersection of the Alameda beds with the Fernando shear zone; the third is 1,000 feet northwest of the Fernando shear at the Alameda shaft ('pl. 10). The largest of these ore bodies is at the intersection of the Alameda beds with the Fernando shear 950 feet S. 80° W. of the Fernando adit. It has been developed by an opencut 50 feet long parallel to the strike of the enclosing limestone, 60 feet wide, and about 20 feet deep. A drift was being driven in 1955 under the pit to develop ore that remained at the bottom. The)ore in the St. Charles-Hayward area is in N. 70° E. faults that dip steeply to the northwest (pl. 10). The largest ore body is developed by the St. Charles No. 1 workings. The ore shoot was 140 feet long, 2 to 10 feet thick, and was mined from the surface to an average depth of about 45 feet. Most of the scheelite exposed in the Sthharles No. 2 and No. 3 workings is in thin veins or streaks along N. 7 0° E. faults, and no scheelite is disseminated in the wallrock between faults. The streaks range from a fraction of an inch to 6 inches in thickness and can be mined only by highly selective methods or where fractures are sufficiently close that several can be mined together. Some streaks contain 10 to 30 percent W03, but the grade of ore over a mining width would probably average only about 0.2 to 0.3 percent W03. GRADE The grade of ore mined from the district has av- eraged about 0.75 percent “703. Wilson (1943, p. 558) reports that from 1941 to 1942 about 32,000 tons of ore averaging more than 1 percent WO3 was mined from the Darwin Hills. The ore at the Durham mine av- eraged 1 percent W03 for an average width of 15 feet on the 200 and 300 levels (Wilson, 1943, p. 558). The grade of ore at the St. Charles No. 1 mine was high and ranged from 2 to 10 percent W03. Ore in the district mined from 1951 to 1955 averaged about 0.5 percent WOS. Submarginal ore is present at the Fernando mine and to a lesser extent at the St. Charles N0. 3 mine. The submarginal ore at the Fernando mine is exposed in the main Fernando adit along the Fernando fault (pl. 10). Scheelite is localized along fractures for a length of 610 feet and a width up to 50 feet; some parts of this area are estimated to contain 0.2 to 0.5 percent W03. ORE commons The ore controls for scheelite are both stratigraphic and structural. Pure limestone, and tactite formed as an alteration of it, are more favorable for ore than dense calc-hornfels. However, the dense c-alc-hornfels cannot be eliminated as a possible host rock as some ore has been mined from it. The bedded replacement body at the Durham mine selectively replaced tactite and pure limestone. Most other occurrences of scheelite in the district are along faults that strike N. 7 0° E.‘; scheelite may be present whether the wallrock is tactite, lime- stone, or calc-hornfels. Commonly the scheelite zone is widest where a fault cuts tactite and thins to a narrow stringer where the fault cuts calc-hornfels. In the St. Charles No. 1 workings and in the Hayward mine, ore has been mined from veins in calc-hornfels. At the Hayward mine the ore is widest in tactite, and the vein thins to a stringer to the east where the wallrock is calc-hornfels. The ore body rakes to the west parallel with bedding. Granitic rocks must be nearby to form either tactite or scheelite. The most favorable places for ore are where small satellitic intrusive bodies crosscut structure. The tactite and scheelite do not necessarily form on the intrusive contact, but are within a few hundred feet of intrusive rocks. The deposits are commonly localized by faults. MINERALOGY The primary tungsten ore contains scheelite in a gangue of marble or calc-silicate rock containing gros- sularite-andradite, calcite, fluorite, idocrase, wollaston- ite, diopside and pyrite. Bismuthinite is present at the Fernando mine. At the Thompson workings of the Darwin mine, scheelite is associated with galena, spha- lerite, pyrite, chalcopyrite, fluorite, and calcite in light- colored calc-silicate rock composed of idocrase, garnet, wollastonite, diopside, and epidote. 78 DURHAM INCLINED SHAFT 0 LEVEL _ — 100 LEVEL I Altitude 4523 ft 200 LEVEL Akitude 4423 ft FERNANDO SHAI-‘l' 200 LEVEL \\\\\\ \\ \\\\¥\~\ \\\\\\\ \ \ DURHAM INCLINED SHAFT 300 LEVEL Altitude 4323 ft Vertical projection looking east Mapped by D. M Lemmon and M R. Klepper, 1942 40 4o 0 80 FEET DATUM IS MEAN SEA LEVEL FIGURE 34.—Map of underground workings and vertical projection of the Durham mine. GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. EXPLANATION Canyon formation Limestone and marble Keeler Tungsten ore, 0.5—1.5 percentWO3 /—"“\ l \ t y‘ Tactile with minor tungsten :2! Collar of shaft m Shaft going above and below level W Foot of shaft Projection of slope FENNSYLVANlAN AND PERMIAN NONMETALLIC COMMODITIES 79 The scheelite is commonly in euhedral crystals as much as 2 inches in diameter. At the Darwin mine euhedral to subhedral crystals of scheelite predomi- nately 1% to 34 inch in diameter are surrounded and in places veined and slightly corroded by sulfide minerals. Davis and Peterson (1948, p. 2) described euhedral scheelite crystals in a powdery matrix of limonite, j aro- site, and clay minerals from the oxidized ore in the Thompson mine. At the Durham, Fernando, and St. Charles mines tungsten ore bodies contain only small amounts of galena and sphalerite, but they occur else- where along the same ore controlling structures farther from the Darwin stock. The Durham ore body contains bismuthinite and py- rite near the intersection of the Durham bed with the Fernando fault (pl. 10). The bismuthinite is in tabular crystals as much as 2 inches long in calcite veinlets that cut the tactite. It is mostly pseudomorphously replaced by light-green powdery bismutite. The tungsten ore mined from the Durham ore body had an average bis- muth metal content of approximately 0.05.percent, but none was recovered. Most of the ore is oxidized and consists of euhedral to subhedral crystals and grains of scheelite in a crum- bly matrix of limonite, calcite, and partly decomposed calc-silicate minerals. Chrysocolla, azurite, malachite, and gypsum coat some of the fractures. The scheelite in- the upper stopes of the Thompson workings of the Darwin mine is embedded in a crumbly matrix of limo- nite, j arosite, cerussite, and clay minerals. The scheelite remained virtually unaltered, but all the other minerals were oxidized or partly leached; thus, the ore has un- dergone residual enrichment of tungsten. DEPOSITS IN THE 0080 RANGE A few small tungsten deposits are on the northeast slope of the Coso Range 8 to 10 miles southwest of Darwin, but only the Lone Pinyon prospect near Black Springs lies Within the quadrangle (fig. 3). The de- posits are within roof pendants or screens of metasedi— mentary rocks in quartz monzonite of the Coso batho- lith. None are extensive. OTHER DEPOSITS A small amount of antimony and copper have been mined from the Darwin district. The only antimony produced is from the Darwin Antimony mine, which is about 31/2 miles north of Darwin (fig. 3). The produc- tion from the mine is reported by Norman and Stewart (1951, p. 29) as “50 to 100 tons of ore assaying more than 30 percent antimony.” Ore is localized along a bedding-plane fault in thinly bedded limestone of the Keeler Canyon formation of Pennsylvanian and Permian age. Stibnite is exposed intermittently at the surface and in the underground workings over a strike length of 120 feet. Ore consists of stibnite containing minor secondary antimony minerals in sheared lime- stone and ranges from a few inches to 3 feet in thick- ness. Calcite and limonitenare the main gangue min- erals. All the ore was mined from a small stope in the footwall between the 100 and 150 levels about 40 feet south of the main shaft. Small discontinuous seams and pods of stibnite less than 1 inch thick are exposed on the 100 and 150 levels north of the main shaft. Copper minerals are associated with nearly all the lead—silver-zinc deposits and some of the tungsten de— posits. In a few deposits in limestone, copper minerals are the principal ore minerals. The copper prospects are in the vicinity of the Giroux mine about half a mile east of Darwin. Mining activity was mostly during the late 1890’s and the first few years of this century. A blast furnace was built at the Lane mine in 1898, and a small amount of copper matte was recovered (War- ing and Huguenin, 1919, p. 99). Chalcopyrite is the primary ore mineral, but it is mostly oxidized to azu- rite, chrysocolla, and malachite. All the prospects are small and have not been worked for many years. NONMETALLIC COMMODITIES Nonmetallic commodities in the Darwin quadrangle include steatite-grade talc, massive chlorite (which locally is called pyrophyllite), limestone, dolomite, and quartzite. Only steatite-talc and chlorite are important commercially at present. The term “steatite” is used herein in the restricted sense of Engel (1949, p. 1018) for virtually pure, massive, compact talc containing less than 1.5 percent CaO, 1.5 percent combined FeO and F8203, and 4 percent A1203 and that is suitable for the manufacture of certain ceramics. Massive chlorite, associated with some of the talc deposits, is used in cor- dierite ceramics and in insecticides. The deposits of limestone, dolomite, and quartzite have not been exploited, owing to remoteness to rail transportation and market and because similar ma- terials are more readily available on the east side of Owens Valley adjacent to a branch line of the Southern Pacific railroad. The upper part of the Eureka quartz- ite is very pure and could be used for super refractory silica brick. Limestone is prevalent in the Santa Rosa and Darwin Hills. The Lee Flat limestone and lime- stone of the Keeler Canyon and Owens Valley forma- tions are predominantly silty. Two analyses of lime— stone in the Darwin Hills are given in table 3. The Tin Mountain limestone and upper part of the Lost 'Burro formation are purer limestones, but no analyses are 80 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. available. Massive dolomite in the Devonian and older formations is abundant in the Talc City Hills, but no analyses of it are available. STEATITFrGRADE TALC Steatite-talc deposits are restricted to an area of about 6 square miles in the Talc City Hills about 6 miles northwest of Darwin (pl. 2). One of the deposits, the Talc City mine, has been one of the principal domestic sources of steatite-talc since 1915. From 1915 to 1948 the Tale City mine produced 218,485 tons of ore (table 5). The production of the other deposits is not known, but is much smaller than that of the Talc City mine. The tale deposits were studied by B. M. Page and L. A. Wright for the US. Geological Survey in 1942, and Page (1951) subsequently published a comprehen- sive report describing steatite-talc deposits in Inyo County. T. E. Gay, J r., and L. A. Wright (1954, map sheet 12) mapped the geology of the Talc City Hills, and briefly described the stratigraphy and structure. GEOLOGY The Tale City Hills are underlain by sedimentary rocks of Early Ordovician to Permian age that are in- truded by leucocratic quartz monzonite of Creta- ceous( ?) age and by felsic dikes. Silurian and Ordo- vician rocks are mainly dolomite and quartzite; Mississippian and younger Paleozoic rocks are predom- inantly limestone. The lower part of the Devonian rocks consists of dolomite, limestone, and quartzite; the upper part is limestone and shale. The Devonian and older rocks are thrust over younger Paleozoic rocks. The most important deposit—the Talc City—is in the Lost Burro formation of Devonian age. It is in the basal siliceous and limy Lippincott member, which is described from the type locality in the Ubehebe Peak quadrangle by McAllister (1955, p. 12). At the Talc City mine the Lippincott member is highly faulted so the thickness is not known, but it seems to be about 75 feet thick and is repeated by faulting. This member is shown as stratified dolomite and limestone and as silica rock on the large-scale surface map of Page (1951, pl. 1). The talc is localized in the massive dolomite close to quartzite of the Lippincott member. The Lippincott member is overlain by about 300 feet of light-gray to buff massive dolomite. A few beds of limestone are within the dolomite, and these beds are in part dolo- mitized, particularly at the crests of tight folds. The dolomite is overlain by light gray fine- to medium— grained limestone, which is exposed at the north and east sides of the hill containing the Tale City mine. The Paleozoic rocks are intruded by a stock of leuco- cratic quartz monzonite at the south end of the Talc City Hills. At the Frisco mine thin highly altered light-colored dikes are exposed in the main chlorite pit. The dikes are completely altered to clay minerals, chloi- rite, and sericite; they originally probably were quartz latite. Fine-grained highly altered dark-green dikes 2 to 6 inches thick also intrude Devonian rocks at the Talc City mine. TALC ORE BODIES The talc deposits are only briefly described here, as excellent descriptions and maps of individual proper- ties are given by Page (1951) from whom much of the following description is taken. The writers mapped the surface geology of the Talc City Hills on a scale of 1: 40,000, but did not map the tale deposits. The talc deposits are localized mainly in shear zones in massive buff dolomite and to a lesser extent in quartz- ite and along contacts between dolomite andcquartzite or dolomite and dolomitic limestone near leucocratic quartz monzonite. Dolomite of the Lost Burro forma— tion is the principal host rock, although some deposits are in dolomite of the Pogonip group, the Ely Springs, and the Hidden Valley. Both the Eureka quartzite and the quartzite in the Lost Burro are replaced by talc at some places. The steatite-talc bodies are irregular elongate lenses and pods that dip steeply. The largest ore bodies are at the Tale City mine where two are exposed for a length of about 500 feet and have a maximum width of 50 feet. One extends about 400 feet below the surface and the other about 100 feet. The other talc deposits are much smaller, and most of them have yielded only a few thousand tons each. In general, the size of the ore bodies diminishes with increasing distance from the stock of leucocratic quartz monzonite. Tale in the Alliance mine (pl. 2) is in a sheared zone about 200 feet long and a maximum of 30 feet thick; at the Trinity mine the glory hole, which probably represents the ap— proximate size of the ore body, is about 150 feet long, 50 feet wide, and 50 feet deep. The walls of most of the ore bodies are irregular, and horses of unreplaced country rock are common in some of the tale bodies. Page (1951, p. 13, 16) reported that gradational con- tacts and false walls are common and that large olf- shoots containing hundreds of tons of ore extend from the main talc masses following joints and shears. The steatite-talc is grayish green, pale green, gray, or dull white. Some is massive, but much of it is highly sheared. Fractures commonly are lightly limonite- stained or contain small dendrites of manganese oxides. The run—of—mine ore is exceptionally pure. The follow- ing analyses are from Klinefelter, Speil, and Gottlieb (in Page, 1951, p. 12). LITERATURE CITED Sample Theoretical Ignition loss ______________________ Total ______________________ 1A. Probably from Talc City mine. 1B. From Talc City mine. 1E. From Talc City mine. ORIGIN The talc deposits replace dolomite and quartzite and were formed by thermal waters traveling along shears and, contacts. Spatially the deposits are peripheral to the stock of leucocratic quartz monzonite, and the size of the deposits is approximately proportional to near- ness to the intrusive contact. Both suggest that the thermal waters were given off by the intrusive body dur- ing a late stage of crystallization and explain the dis- tribution of deposits around the stock and the diminish- ing size of deposits with increasing distance from the pluton. It is also possible, however, that the intrusive mass was the source of heat and the alteration was caused by recirculation of heated ground water. It is not necessary to postulate a large-scale introduction of magnesia or silica. Most of the deposits and, without exception, all the large talc bodies, have both dolomite and quartzite in close proximity, so that a local source of magnesia and silica is at hand. No talc alteration was observed in limestone or shale, and only small pods of talc were found in massive dolomite that has no local source of silica. On the negative side, the quartzite does not show evidence of large-scale corrosion or replacement. At most places the quartzite is massive and only slightly replaced, and talc is restricted to places where it is fractured. CHLORITE DEPOSITS A large part of the production of the Frisco mine is massive green chlorite that locally is called pyrophyllite. The chlorite occurs in shear zones 2 to 15 feet thick in dolomite and in felsic dikes that are altered to chlorite, sericite, and clay minerals. Chemical analysis of the chlorite [Analyzed by P. L. D. Elmore and K. E. White of the U.S. Geological Survey] Percent Percent Si02 ___________________ 29.0 K20 ___________________ .02 A1203 __________________ 25. 0 TiO: __________________ . 40 F6203 __________________ . 7 P 205 __________________ - 22 FeO ___________________ . 82 MnO __________________ .01 MgO __________________ 30 6 H20 ___________________ 12. 6 CaO ___________________ .36 002 ___________________ <. 05 N320 __________________ 0.04 81 The chemical analysis suggests that the chloritic rock is a mixture of approximately 87 percent amesite and 13 percent talc. Optical, X-ray, and differential thermal analysis data show that the chlorite is amesite with a chlorite structure. The chlorite has the following optical prop- erties: optic Sign +, 2V small, m: 1573:0003; m3 = 1.574 i 0.003; nu: 1.583 i 0.003. This closely fits the optical properties of amesite given by Winchell (1936, p. 643). X -ray diffraction pattern dA I ntensity dA Intensity 1. 397 __________________ 10 2. 44 __________________ 16 1. 537 __________________ 12 2. 54-; _________________ 20 1. 57 ___________________ 10 2. 85 __________________ 20 1. 82 ___________________ 5 3. 56 ___________________ 83 1. 88 ___________________ 8 4. 745 __________________ 83 2. 00 ___________________ 16 7. 14 ___________________ 100 2. 26 ___________________ 8 14. 255 __________________ 45 2. 38 ___________________ 8 The X—ray data confirm that the mineral has a chlorite- type structure. It has a strong 14A series of basal re- flections and is not similar to amesite from the type locality, which has a kaolin—type structure (Gruner, 1944, p. 422). Nelson and Roy (1953, p. 1458) have shown the existence of both types of amesite—the 7A kaolin type and the 14A chlorite type. The differential thermal analysis curve also fits a 14A chlorite. LITERATURE CITED Baker, C. L., 1912, Physiography and structure of the western El Paso Range and the southern Sierra Nevada: California Univ. Dept. Geol. Bull. 7, p. 117—142. Bateman, P. C., and Irwin, W. P., 1954, Tungsten in southeast- ern California, in Jahns, R. H., ed., Geology of southern California: California Div. Mines Bull. 170, chap. 8, p. 31—40. Bateman, P. 0., and Merriam, C. W., 1954, Geologic map of the Owens Valley region, California, in Jahns, R. H., ed. Geology of southern California: California Div. Mines Bull. 170, map sheet no. 11. Barton, P. B., Jr., and Kullerud, G., 1958, The Fe-Zn-S system: Carnegie Inst. Washington Yearbook 57, p. 227—229. Burchard, H. C., 1884, Report of the U.S. Director of the Mint upon the statistics of the production of precious metals in the United States for the calendar year 1883. Butner, D. W., 1949, Investigation of tungsten occurrences in Darwin district, Inyo County, California: U.S. Bur. Mines Rept. Inv. 4475, 6 p. Campbell, M. R., 1902, Reconnaissance of the borax deposits of Death Valley and Mohave Desert: U.S. Geol. Survey Bull. 200. Carlisle, Donald, and others, 1954, Base metal and iron deposits of southern California, in Jahns, R. H., ed., Geology of southern California: California Div. Mines Bull. 170, chap. 8, p. 41—49. 82 GEOLOGY AND ORE DEPOSITS, DARWIN QUADRANGLE, INYO COUNTY, CALIF. Chalfant, W. A., 1933, The Story of Inyo: Revised ed., Los Angeles, Calif., Citizens Print Shop. Crawford, J. J., 1894, Argentiferous galena, Inyo County, in Twelfth Report of the State Mineralogist: California Min— ing Bur. Rept. 12 (2d biennial), p. 23—25. 1896, Argentiferous galena, Inyo County, in Thirteenth Report of the State Mineralogist: California Mining Bur. Rept. 13 (3d biennial), p. 32—34. Davis, D. L., and Peterson, E. C., 1948, Anaconda’s operation at Darwin mines, Inyo County, California: Am. Inst. Min- ing Metall. Eng. Tech. Pub. 2407, 11 1). De Groot, Henry, 1890, Inyo County, in Tenth Annual Report of the State Mineralogist: California Mining Bur. Rept. 10, p. 209—218. Duncan, Helen, 1956, Ordovician and Silurian coral faunas of western United States, US. Geol. Survey Bull. 1021—F, p. 210—236. Edwards, A. B., 1954, Textures of the ore minerals and their significance: Melbourne, Australasian Inst. Mining and Metallurgy. Engel, A. E. J ., 1949, Talc and ground soapstone, in Industrial Minerals and Rocks: Am. Inst. Mining Metall. Eng, p. 1018—1041. Fairbanks, H. W., 1896, Notes on the geology of eastern Cali- fornia : Am. Geologist, v. 17, p. 63—74. Faul, Henry, 1954, Nuclear geology: New York, John Wiley & Sons, 414 p. Fryklund, V. C., J r., and Fletcher, J. D., 1956, Geochemistry of sphalerite from the Star mine, Coeur d’Alene district, Idaho: Econ. Geology, v. 51, p. 223—247. Gay, T. E., Jr., and Wright, L. A., 1954, Geology of the Talc City area, Inyo County, in Jahns, R. H., ed., Geology of southern California: California Div. Mines Bull. 170, map sheet no. 12. Goodyear, W. A., 1888, Inyo County, in Eighth Annual Report of the State Mineralogist: California Mining Bur. Rept. 8, p. 224—309. Gruner, J. W., 1944, The kaolinite structure of amesite, (OH)5 (Mg,Fe)4 A12(SizA12)Oio, and additional data on chlorites: Am. Mineralogist, v. 29, p. 422—430. Hague, Arnold, 1883, Abstract of the report on the geology of the Eureka district, Nevada: US. Geol. Survey 3d Ann. Rept., p. 237—272. Hall, W. E., 1959, Geochemical study of Pb-Ag-Zn ore from the Darwin Mine, Inyo County, California: Mining Eng, p. 940. ‘Hall, W. E., and MacKevett, E. M., Jr., 1958, Economic geology of the Darwin quadrangle, Inyo County, California: Cali- fornia Div. Mines Spec. Rept. 51. Hall, W. E., and Stephens, H. G., 1962, Economic geology of the Panamint Butte quadrangle and Modoc district, Inyo County: California Div. Mines Spec. Rept. (In press.) Harcourt, G. A., 1942, Tables for identification of ore minerals by X-ray powder pattern: Am. Mineralogist, v. 27, p. 63— 113. Hazzard, J. 0,1937, Paleozoic section in the Nopah and Resting Springs Mountains, Inyo County, California: California J our. Mines and Geology, v. 33, p. 273—339. 1954, Revision of Devonian and Carboniferous sections, Nopah Range, Inyo County, California: Am. Assoc. Petro- leum Geologists Bull., v. 38, p. 878—885. Hess, F. L., 1918, Tactite, the product of contact metamorphism : Am. J our. Sci., 4th ser., v. 48, p. 337—378. Hess, F. L., and Larsen, E. S., Jr., 1922, Contact-metamorphic tungsten deposits of the United States: U.S. Geol. Survey Bull. 725—D, p. 245—309. Hinitze, L. F., 1951, Lower Ordovician detailed stratigraphic sections for western Utah: Utah Geol. and Mineralog. Sur- vey Bull. 39. Hopper, R. H., 1947, Geologic section from the Sierra Nevada to Death Valley, California: Geol. Soc. America Bull., v. 58, p. 393—432. Hulin, C. D., 1934, Geologic features of the dry placers of the northern Mojave Desert, in Thirtieth Report of the State Mineralogist: California Jour. Mines and Geology, v. 30, p. 417—426. J ohannsen, Albert, 1939, A descriptive petrography of the igneous rocks, v. 1, Introduction, textures, classifications, and glossary: Chicago, 111., Chicago Univ. Press, 318 p. Kelley, V. C., 1937, Origin of the Darwin silver—lead deposits: Econ. Geology, v. 32, p. 987—1008. 1938, Geology and ore deposits of the Darwin silver-lead mining district, Inyo County, California: California Jour. Mines and Geology, v. 34, p. 503—562. King, Clarence, 1878, Systematic geology: U.S. Geol. Expl. 40th Par. Rept., v. 1. Kirk, Edwin, 1933, The Eureka quartzite of the Great Basin region: Am. Jour. Sci., 5th ser., v. 26, p. 27-44. Knopf, Adolph, 1914, The Darwin silver-lead mining district, California: US. Geol. Survey Bull. 580—A, p. 1—18. 1918, A geological reconnaissance of the Inyo Range and the eastern slepe of the southern Sierra Nevada, California, with a section on the stratigraphy of the Inyo Range by Edwin Kirk: U.S. Geol. Survey Prof. Paper 110, 130 p. 1933, Pyrometasomaltic deposits, in Ore deposits of the western states (Lindgren volume): New York, Am. Inst. Mining and Metall. Eng. Kullerud, Gunnar, 1953, The FeS-ZnS system——a geologic thermometer: Norsk geol. tidsskr, v. 32, p. 61—147. Kulp, J. Lawrence, 1961, Geologic time scale: Science, v. 133, p. 1105—1114. Langenheim, R. L., J r., and others, 1956, Middle and Upper( ‘2) Ordovician rocks of Independence quadrangle, California: Am. Assoc. Petroleum Geologists Bull., v. 40, p. 2081—2097. Lindgren, Waldemar, 1933, Mineral Deposits: New York and London, McGraw-Hill Book Co., 930 p. MacKevett, E. M., Jr., 1953, Geology of the Santa Rosa lead mine, Inyo County, California: California Div. Mines Spec. Rept. 34, 9 p. Maxson, J. H., 1950, Physiographic features of the Panamint Range, California: Geol. Soc. America Bull., v. 61, p. 99—114. McAllister, J. F., 1952, Rocks and structure of the Quartz Spring area, northern Panamint Range, California : California Div. Mines Spec. Rept. 25, 38 p. ' McAllister, J. F., 1955, Geology of mineral deposits in the Ubehebe Peak quadrangle, Inyo County, California: Cali- fornia Div. Mines Spec. Rept. 42, 63 p. 1956, Geology of the Ubehebe Peak quadrangle, Cali- fornia: U.S. Geol. Survey Geol. Quadrangle Map GQ—95. McKinstry, H. E., 1953, Shears of the second order: Am. Jour. Sci., v. 251, p. 401—414. Merriam, C. W., 1940, Devonian stratigraphy and paleontology of the Roberts Mountains region, Nevada: Geol. Soc. Amer- ica Spec. Paper 25, 114 p. 1954, Rocks of Paleozoic age in southern California, m Jahns, R. H. ed., Geology of southern California: Califor- nia Div. Mines Bull. 170, chap. 3, contr. 2, p. 9-14. LITERATURE CITED 83 Merriam, C. W., and Anderson, C. A., 1942, Reconnaissance sur- vey of the Roberts Mountains, Nevada: Geol. Soc. Amer- ica Bu11., v. 53, p. 1675—1727. Merriam, C. W., and Hall, W. E., 1957, Late Paleozoic stratig— raphy of the southern Inyo Mountains: U.S. Geol. Survey Bull. 1061—A, 15 p. Merriam, J. C., 1919, Tertiary mammalian faunas of the Mohave desert: California Univ., Dept. Geol. Bull., v. 11, p. 438- 585. Moore, J. G., and Hopson, C. A., 1961, The Independence dike swarm in Eastern California: Am. J our. Sci., v. 259, p. 241— 259. Murdoch, Joseph, and Webb, R. W., 1956, Minerals of Califor- nia : California Div. Mines Bull. 173. Nelson, B. W., and Roy, Rostum, 1953, Structural-chemical classification of the chlorites-the magnesian chlorites (abs.) : Geol. Soc. America Bu11., v. 64, p. 1458. Nolan, T. B., and others, 1956, The stratigraphic section in the vicinity of Eureka, Nevada: US. Geol. Survey Prof. Paper 276. Norman, L. A., J r., and Stewart, R. M., 1951, Mines and mineral resources of Inyo County: Calif. J our. Mines and Geology, v.47, p. 17—223. Page, B. M., 1951, Talc deposits of steatite grade, Inyo County, California: California Div. Mines Spec. Rept. 8, 35 p. Palache, Charles, Berman, Harry, and Frondel, Clifford, 1944, The system of mineralogy of James Dwight Dana and Ed- ward Salisbury Dana, v. 1, Elements, sulfides, sulfosalts, and oxides: 7th ed., New York, John Wiley & Sons. Pettijohn, F. J., 1949, Sedimentary rocks: New York, Harper &Bros. Phleger, F. B., Jr., 1933, Notes on certain Ordovician faunas of the Inyo Mountains, California: Southern California Acad. Sci. Bu11., v. 32, p. 1—21. Raymond, R. W., 1877, Statistics of mines and mining in the States and Territories west of the Rocky Mountains: US. Dept. Treasury, 8th Ann. Rept., Washington, U.S. Govern- ment Printing Office, p. 25—30. Robinson, L. L., 1877, Annual report to the stockholders of the New Coso Mining Co.: San Francisco, 39 p. Schultz, J. R., 1937, A late Cenozoic vertebrate fauna from the Coso Mountains, Inyo County, California: Carnegie Inst. Washington Pub. 487, p. 75—109. Simons, F. S., and Mapes, Eduardo, 1956, Geology and ore de- posits of the Zimapan mining district, State of Hidalgo, Mexico: U.S. Geol. Survey Prof. Paper 284. Spencer, A. C., 1917, The geology and ore deposits of Ely, Nevada: U.S. Geol. Survey Prof. Paper 96, 189 p. Trowbridge, 'A. C., 1911, The terrestrial deposits of Owens Valley, California: Jour. Geology, v. 19, p. 706—747. Tucker, W..B., and Sampson, R. J ., 1938, Mineral resources of Inyo County, in Thirty-fourth Report of the State Min- eralogist: California Jour. Mines and Geology, v. 34, p. 368—500. 1941, Recent developments in the tungsten resources of California, in Thirty-seventh Report of the State Miner- alogist: California Jour. Mines and Geology, v. 37, p. 565— 588. Walcott, C. D., 1923, Nomenclature of some post—Cambrian and Cambrian Cordilleran formations: Smithsonian Misc. 0011., v. 67, p. 457—476. Waring, C. A., and Huguenin, Emile, 1919, Inyo County, in Fifteenth Report of the State Mineralogist: California Min. Bur. Rept. 15, p. 29—134. Westgate, L. G., and Knopf, Adolph, 1932, Geology and ore de- posits of the Pioche district, Nevada: US Geol. Survey Prof. Paper 171. White, W. S., and Jahns, R. H., 1950, Structure of central and east-central Vermont: J our. Geology, v. 58, p. 179—220. Wilmarth, M. G., 1938, Lexicon of geologic names of the United States (including Alaska): US. Geol. Survey Bull. 896, pt. 2. Wilson, L. K., 1943, Tungsten deposits of the Darwin Hills, Inyo County, California: Econ. Geology, v. 38, p. 543—560. Winchell, A. N., 1936, A third study of chlorite: Am. Miner- alogist, v. 21, p. 643—651. Anonymous, 1948, Climatological data for the United States by’ sections '(California section): US Dept. Commerce, Weather Bur., v. 33, p. 350—362. A Acknowledgments ................ Actinolite ........ Agglomerate ........................ .. 33,34 Ajax Tungsten Corp ................ 53 Alameda beds.... Alliance talc mine .................... 8, 11, 42, 43, 80 Alluvium ................................... 5, 36, 39 Alteration. Se'c Metamorphism. Altitude of area ............................... 4 American Metals, Inc ........................ 53, 54 Ameslte ............ 81 Ammonites ................................... 26, 27 Amphibolite .................................. 50, 51 2, 53, 55 Andeslne ..................................... 29,35 Andesite, age ................................ 37 petrography.. 37 Arsenopyrite ................................. 59,76 Antler-its ..................................... 64 Argus Range .......................... 4, 5, 17, 18,24, 28, 30, 31, 32, 37, 40, 44,45, 52, 55, 73 _- 29, 32, 34, 35, 37 Azurite ................................. 64, 74, 75, 79 B Butte ..................................... 62, 68, 75 Basalt. 5,33, 34, 36, 37,45, 46, 52, 75, 76 Belle Union mine.. .._ 53, 55, 58, 69, 70, 72 _____________ 64, 75 29, 30, 31, 32, 35 . _____________ 21 ...... 59,60, 61, 65, 72 Blsmuthlnite ................ 59, 77, 79 Blsmutlte ................... 59, 64, 79 _________ 56, 57, 68, 70 Bornite ...................................... 59, 65 Brachiopods ................... 11, 15, 16, 18, 26, 27, 28 Breccia .................................... 26, 33, 34 Brochantite ....................... 64 53 Bryoman .................................. 16, 17, 27 Buckhorn mine ............................... 54 C Cactus Owen mine ........................... 75,76 Calcarenite .............................. 6, 22, 26, 52 Calcite .............................. 56, 62, 68, 76, 77 Calcilutite .................. 6, 22, 52, figs. 21 and 24 Calc-hornfels ................................. 28, 46, 47, 48, 50, 57, 64, 65, 68, 73, 75, 76, 77 Cale-silicate rock ................. 47, 48, 50, 65, 68, 70 Caledonite ................................... 64 Carboniferous formations ............... 18, 19, 20, 21 INDEX Page Cenozoic rocks. . ............ 33, 35, 36, 37, 38, 39 andesite ...... ... 5, 35, 36, 75 Coso formation. ...... 5, 36 lakebeds ............... .. 5,37, 38, 39 old fanglomerate from the Inyo Moun- tains ............................. 5, 36 old fanglomerate marginal to Darwin Wash ............................. 5, 37 olivine basalt... 5, 36, 37, 75, 76 pyroclastic rocks .................. 5, 33, 34, 35, 75, 76, figs. 11, 12 and 13 structural features of ___________________ 45, 46, 74 unconsolidated gravels and alluvium. . .. 5, 39 Cerargyrite ............................ Cerro Gordo mine. Cemssite ...... Chabazite . _ . Chainman shale. Chaleanthite. ._- Chalcocite. . _ Chalcedony ................. -- 35 Chalcopyrite.._..--....- Chert ............. China Garden spring .......... Chlorite ....................... deposits _______ Christmas Gift mine ....... 26, 41, 54, 55, 58, 67, 68, 71 Chrysocolla.........._..-..-. .......... 64, 74, 75, 79 Cinders ........................ 33, 34 Classification of ore deposits .................. 68 Clausthalite ............................ 56, 59, 61, 65 Climate ....... 3, 4 Clinozoisite ............................. . 32,48, 51 Columbia mine _______________________________ 53 Combined Metals Reduction 00 ............. 5 Concretions ................................. 19 Conglomerate ....................... 21, 22, 23, 24, 25 Copper ................... 52, 53, 54, 55, 71, 72, 75, 79 Copper fault ................................ . 44, 72 Corals ...................... 11, 12, 13, 14, 15, 16, 17, 18 Coso formation ............................. 5, 35, 36 Coso Range ................................ 4, 29, 36 tungsten deposits ......................... 79 Covellite ..................................... 63 Creedite ...................................... 59,64 Crinoids ............................... 14,15,16,18 Crocoite... . 63 Cuprite . . . ............................. 64 Custer mine ___________________ 54, 55, 56, 57, 62, 66,70 Cystoids ..................................... 8 D Darwin ............................... 2, 4, 31, 32, 52 Darwin Antimony mine ............. 22,23, 26, 53, 79 Darwin Canyon .......... 4, 26, 30, 32, 39, 48, 50, 51, 52 Darwin Consolidated Tungsten Co.. 53 Darwin Development Co ............. 53 Darwin district .................. 56,57, 64,66, 68,79 tungsten deposits in .................... 76, 77 Darwin Falls .......... Darwin Hills .............. 5,,,,,,,,,:1,2l42224262932374142 43,44,,,,,,,.48505253697079 Darwin Hills syncline ........................ 40 55 55 Page Darwin Lead 3: Silver Mining and Develop- ment Co ___________________________________ 53 Darwin lead-silver-zinc district 52, 69, 70 future of mining in ....................... 72 ore deposits ........ . ..................... 70 structure" 70 Darwin mine ................................. 2, 43,44,4849,,,,,,,,,5051535556575860 61, 62,,63,64 65, 66,69, 71, 72, 73, 77. Darwin Plateau ............................ 4,33, 39 Darwin Silver Co ____________________________ 54 Darwin stock ............................. 20,68, 73 Darwin tear fault ............. 21, 22, 40, 44, 45, 48, 73 Darwin Wash.. _ ___________ 24, 33, 37, 38, 39, 40, 44, 52 Darwin Wash syncline ....................... 40 Darwin zinc mine ............................ 73 Davis thrust _______________ 42, 43, 48, 57, 58, 70,71, 72 Defiance fault ................................ 71, 72 Defiance mine.... 48, 49, 50, 53, 54, 55, 56, 57, 58, 62, 66, as, 69, 70, 71, 72 Devonian rocks, distribution ............... 5,11, 12 lithology ............................ 5, 13,51, 80 stratigraphic relations ................. 11, 12, 13 thickness ____________________________ 5, 11, 12, 13 Deweylite ........ 62 Diatoms ..................................... 38, 39 Dikes, basalt ____________ andesite porphyry. diorite ........... felsic _ _ . . Diopside . . . . Dolomite. . . . Dolomitization ________ Douglass, R. 0., quoted. Driver mine ............. Duncan, Helen, quoted- Durham mine .......................... 53,77, 78, 79 E Ely Springs dolomite, age .................... 11 lithology ........................ stratigraphic relations ........... thickness ............ Empress mine .................... 55,56, 57, 66, 73,74 Encrinite .............................. _ 14 Enargite.. 59 Epidote ................................... 24, 47, 51 Erosion ....................................... 52 Essex mine .......... 53,55, 58, 61, 64, 68, 70, 72 Eureka quartzite, age ......................... 10 distribution ............................... 9 lithology ......... 9,10,80 stratigraphic relations .................... thickness ................................. 9 F Fairbanks mine .............................. 49, 50 Fanglomerate ..... . 5,36, 37 Faults- 39, 42, 43, 44, 45, 46, 52, 58, 71, 72, 73, 74, 75, 77, 79 Fernando fault. .-- ........... 66,77 Fernando mine_- 53, 57,64, 77, 79 Fieldwork .................................... 5 Flow structures .............................. 35 Fluorite ............... 56, 63, 64, 68 Folds ................. 21, 39, 40, 41, 42, 43, 45, 52, 57, 58 Foliation ..................................... 45 85 86 , Page Foreman, L. D., And Co ...................... 54, 55 Forms~of ore bodies... Forsterite .......... Fossils ....................... 8, 9, 11, 12, 13, 14,15, 16, 17, 18, 19, 21, 23, 24, 25, 26, 27, 28, 38, 39, 41 Frisco talc mine ..................... 32, 80, 81 Fusulinids ........................ 19, 23, 24, 26, 27, 41 G Gabbro ....................................... 51 Galena ............ 56, 59, 60, 61, 62, 65, 66, 67, 74, 75, 76 Gangue minerals. ............ 52, 56, 74, 75 Garnet ........................ 47, 48, 49, 50, 63, 65, 68 Gastropods ............................... 8, 9, 26, 27 Geochemical prospecting. - . - 71, 72 Geologic history .............................. 51, 52 Giroux mine .................................. 79 Glass. volcanic. . Golfball horizon .............................. 22,43 Gordon, Mackenzie, Jr., quoted .............. 15, 16 Goslarite ...................... - 59,64 Granodiorite ................................. 29 Graphite. ..J ................................. 14 Gravels 1: 5, 39 Guanajuatite ................................. 61 Gypsum .............. ' .................... 5 9, 64, 74 H Hayward mine ............................... 77 Hematite ________ Hemimorphite ................ 59, 63, 64,67, 74, 75, 76 Henbest, L. 0., quoted ............ 23 Hidden Valley dolomite, age 12 distribution .............................. 9, 11 lithology ................................. 6, 12 stratigraphic relations. . ll. 12 thickness _______________________________ 6, 11, 12 History of mining ............................ 52, 53 Homestake prospect- 57, 75, 76 Homblende ............................... 29, 35, 51 Horsts ..................................... 73, 74, 76 Hunter Mountain quartz monzonite. 29 Hydrozincite ___________________________ 59, 64, 67, 74 Hypogene minerals ________________________ 58, 59, 66 I Iddingsite .................................... 37 Idocrase ___________ . 47, 48, 63,65 Imperial Metals Inc ______________________ 53, 55 Imperial Smelting and Refining Co ___________ 53 Independence mine _______________ 53, 55, 58,69, 70, 72 Intermediate mine ............................ 69 Intrusive rocks ___________________ 28, 29, 30, 31, 32, 36 Inyo County Mining and Development Co._- 53,54 Inyo Mountains ............. 4, 10, 19, 21, 24, 45, 46, 52 ore deposits in ............................ 75, 76 J Jackass mine ______________________________ 56, 66, 70 J arosite.. . . Jasper-.. Joints ...................................... 9, 35, 37 K Kalisyenite ................................... 50 Keeler Canyon formation, age ............. 23, 57, 70 correlation ................................ 23 distribution ........................ 22, 70, 76, 79 lithology ........................... 22, 46, 47, 79 lower unit ............................. 22 stratigraphic relations ......... 17, 21,22, 70, 75 structure ........................... 41, 42, 43, 76 thickness INDEX L Page Labradorite .................................. 37 Mad deposits, distribution. . 3, 52, 55, 57, 66, 71, 75, 76 production and grade ..................... 52, 53, 54, 55, 66,67, 69, 70, 75, 76 Leadhillite ................................... 59, 63 Lead Hope mine ....................... 49 Ice district, geologic setting ...... - 56, 74, 75 structure ........................... 58, 75 are deposits in ................ 75 Lee Flat ____________________ -.- - 4, 18,39 Lee Flat limestone ............. 6, 18, 20, 51, 69, 70, 73 age ....................................... 19, 73 correlatiom-.. 19 distribution .............................. 18 lithology ................................. 19, 79 stratigraphic relations-.. -- 17, 18, 19, 69, 70, 73 thickness ............................... 6, 18, 19 Lee mine ............. 15, 16, 55, 56, 62, 64, 66, 67, 68, 75 Lee Wash ...................... -.-_ 4 Leuoocratic quartz monzonite ---------------- 28, 31 Leucogranite ............................... 5, 31, 32 Limestone ________ 5, 6, s, 13, 14, 15, 17, 18, 19, 21,22, 2‘], 26, 27, 43, 46, 47, 48, 49, 50, 51, 64, 65, 73, 76 Limonite-._ .-.- 32, 43,59, 64, 76, 79 Linarite.- .......... 59, 64 Lineation ..................................... 43 Lin- ‘ “ mine _ 57 Literature cited ------------------------------ 81—83 Location of area .............................. 2 Lohman, K. E., quoted ---------------------- 38,39 Lippincott member_ . . lithology .......... --- 6,13,14, 28, 75, 79. 80 ore in ------------------- 57,69 stratigraphic relations-- _---- ...... 12, 13, 69 thickness.--...-. ............. -.-- 6,12,13,69 Lower Centennial Flat ______ 39 Lucky Jim mine ...... 41, 45, 53, 55, 56, 58, 62, 67, 68, 71 M Madison group ------------------------------- 15 Magnetite--. - 32,51 Malachite - _ . Marble...- Matildite.. Melanterite. Mesothermal deposits- Mesozoic rocks ------ aplite ..... biotite—hornblende quartz monzonite dikes .............................. gabbro _ - leucocratic quartz monzonite leucogranite ................. monzonite"- - 59, 64 , 13, 15, 42, 46 syenodionte- Mesozoic orogeny ............................. 45 Metamorphic rocks -------------------- 22, 28, 46—51 Metamorphism .............................. 46—51 dolomitization ............................ 47 46 recrystallization to marble ................ 46, 47 to amphibolite ---------------------------- 50, 51 to ealc-hornfels, calc—silicate rock, and tactite ............................. 47, 48, 49 to feldspathic rock ........................ 50 within igneous rocks ...................... 46 Mickey Summers fault ....................... 71, 73 Page Mill Canyon ................................. 4 Millers Spring ................................ 26, 39 Munptm 59 Mineralogy ....................... 56, 58-67, 74, 75, 77 Mines and prospects--._ 53—58, 66-71, 73, 75—77, 79, 80 Mining history .................... 52, 53, 75 Missisflppian rocks.-. .. 5,6, 14-19, 57,73 Montmorlllonite ........ New Coso Mining Co ...... New York Butte quadrangle ...... 3, 12, 14, 22, 40,47 N N onmetallic commodities ..................... 79-81 0 Oligoclase ................................. 29, 31, 32 Olivine 37 Olivine basalt ........................ 5, 33, 34, 36, 37 Ophir Mountain ....................... 22,40, 42, 47 Ordovician rocks ....... . 6,18, 9, 10, 11, 51 distribution ............................. 6, 9, 10 lithology ........................... 6, 8, 9, 10, 11 stratigraphic relations. --- 6, 7, 9,10 thickness ------------------------------ 6, 7, 9, 10 Ore controls, lead-zinc-silver deposits ........ 57, 58 nearness to intrusive contacts". 57 relationship of ore to faults --------------- 5s relationship of ore to folds ................ 57 relationship of ore to stratigraphy- 57 Ore deposits, antimony ....................... 79 copper .................................... 79 lead-zinc-silver - -- 3. 52 bedded deposits.... 56 character- . . . ....... . 55 classification 68 controls ...................... 57, 58 distribution ---------------- 55 forms of ore bodies 56 gangue minerals ...... ._ 62,63 geochemical prospecting .. 71,72 geothermometry ...... ...- 68, 69 grade --------- 53 67, 74, 75 history ......... ---- 52, 53 hypogene minerals .............. 59, 60, 61, 62 in Darwin lead-silver-zinc district ..... 69, 70, 71, 72 in the Inyo Mountains and Talc City Hills ............................ 75,76 in the Lee district- -. 74, 75 in Zinc Hill district ........ -- 73,74 irregular replacement bodies 56 mineralogy ------------------ 58, 59, 60, 61, 62 ore bodies of flat-lying fracture.. origin ........................ oxidation and enrichment- paragenesis .............. primary zoning.- production ................. supergene minerals, oxide none ._ 63, 64 sulfide zone ------------------ 63 veins- . 56 talc ---------- 79,80 geology oi _ - - 80 are bodies. - . 80 origin of ------- 81 steatite-grade talc__ .- 80 tungsten ................. . 76 77, 78,79 controls_ - - ------- 77 d1stribution ------------------ 76 form of _______________________________ 77 grade ------------------------------ - _ . 77 in the Coso Range -------------------- 79 in the Darwin district ................ 76, 78 mineralogy --------------------------- 77 Orthoclase ........................ 31, 32, 35, 48, 63, 76 Orthoquartzite.-....----_.- -------------- 6, 9, 10,13 Page Owens Valley formation .............. 5, 24—28, 43,73 26, 27, 28, 43,73 correlation. ........................ 26, 27, 28 distribution. . _________________________ 24, 25 lithology _______________ 21, 26,27, 28, 46, 47, 73, 79 lower unit ................... _ . 24 middle unit ................. .__. 27,28 stratigraphic relations ______________ 24, 26, 27, 28 structural features ..................... 39, 40, 44 thickness ______________ 24, 26, 27, 28 upper unit. ...... _._ 28 Oxide zone . . . ...... 59, 63, 64, 66-69 Oxidized ore _______________________________ 66, 67, 79 Oxyhornblende _______________________________ 35 P Pacific Tungsten Co. ________________________ 53 Paleozoic rocks ............................... 5—28, 39, 40, 42, 43, 45, 46, 47, 48, 51, 52, 55, 70, 73, 75, 80. Panamint Butte quadrangle ............ 17, 19, 31, 45 Panamint Range .......................... 12, 17,45 Panamint Springs. ........... 4 Panamint Valley. ...... 3,4,33,39,48 Paragenesis- . .-- ...... _.._ 64 of amphibolite ............................ 51 of ore and gangue minerals ............... 64 Pegmatite ......................... __ 28, 31, 51 Pennsylvanian rocks. .. 5, 6, 18, 19, 20, 22, 23, 24, 73 distribution . . . .......... 5, 18, 19, 21, 22, 24 lithology ........................... 19, 21, 22,23 structural features ........................ 21 thickness ...... 5, 18, 19, 21, 22, 24 Perdido formation. ........ ..- 17, 18,69, 73 age ................ _. 18 distribution .............................. 17 lithology .............................. 17, 18, 73 stratigraphic relations ....... 14, 15, 17,69, 73 thickness ................................. 17 Permian rocks ...................... 5, 6, 21, 24—28, 73 distribution .............................. 5, 21 lithology ..................... 21, 22, 23, 26, 27, 28 structural features. 21 thickness ............................ 5, 21, 22, 24 Petrography .................... 29, 31, 32, 34, 35, 36 mstocene rocks ........................ 5, 36-39, 52 Pliocene rocks ............................. 33—36, 52 Plumbojarosite Pogonip group. age ......... distribution .............................. 6 lithology ................................. 8 stratigraphic relations ..... .. 6, 7, 8 thickness ...................... ._ 6, 7, 8 Potassium-argon age determinations. __ 30, 31 Previous work .............................. 4, 5, 76 Production ....................... 53, 54, 55, 73, 75, 77 antimony ................... 53 copper . . ....... 53, 54, 55, 73, 75 gold.. ...... _-._ 53, 54, 55 lead ................... . ......... 53, 54, 55, 73, 75 silver ............................ 53, 54, 55, 74, 75 talc-.-- _.._ 53,55 tungsten. ........................... 53, 77 zinc ....................... 53, 54, 55, 73, 75 Promontory ............................ 53,55, 56, 70 Prospecting, geochemical ..................... 71, 72 Prospects. See Mines and Prospects. Pseudomalachite . . Purpose of report ............................. 3 Pyroclastic rocks ........................ 5, 33, 34, 52 33 lithology ............................... 5,33, 34 l Page Pyroclastic rocks—Continued ‘ lower unit.........__-___._1 ............... 33,34 relation to other rocks .................... 33 thickness ................................. 33, 35 upper unit.. ._ 34, 35 Pyrite ....... 31,32, 50, 56, 62, 65, 66, 67, 68, 69, 74,75, 77 Pyrometasomatic deposits.- .. 68,69 Pyrolousite ................................... 59, 64 Pyromorphite ................................ 59 Pyrrhotite ........................... 56, 50, 62, 65, 69 Q Quartz ............. 9, 10, l2, 15, 19, 28, 29, 31, 32, 34, 35, 37, 47, 51, 56, 58, 63, 64, 74, 75 Quartz diorite ................................ 29 Quartzite .......... ' ........... 6, 12, 13, 76, 79—81 Quartz latite ................................. 32 Quartz monzonite ___________ 5, 28—31, 46, 57, 73, 79, 80 Quartz Spring area ......... , ....... 6, 8—12, 14, 17, 19 R Radioactive minerals ......................... 64, 74 Radiore tunnel ............................... 55 Rainbow Canyon. 4, 28, 48 Recent rocks ................................. 33, 39 Red vein ............................... 56, 57, 68, 70 Rest Spring shale. ...... 6, 17, 19, 20, 21, 43, 76 ...... .. 21 ...... 19, 20, 21 lithology ______ stratigraphic relations .................... 19 Rip Van Winkle mine ............ 53, 55,69 Ross, R. J. Jr., quoted ........................ 8,11 S St. Charles mine .......................... 44, 77, 79 Sandstone ............... ... 18,28 Santa Ana mine. ........ . 66 Santa Rosa fault ........ _ 46 Santa Rosa flat ............................... 39 Santa Rosa Hills- . . 4, 12, 14, 17, 18, 22, 23, 46, 48, 75, 79 Santa Rosa Hills warp ........................ 42 Santa Rosa mine ...... 35, 48, 52, 54—58, 62, 63, 66, 67, 68, 75, 76 Scapolite .................................. 30, 48, 51 Scheelite ................... 52, 53, 62,65,436, 76, 77, 79 Selenium.. ..- 61,65 Sericite-.-- ..... 32, 63 Shale .......... 5, 6, 13, 14, 18, 19,21, 22, 23, 26,27, 28, 36 Silicated limestone .................. 28, 45,49, 50, 68 Sillimanite ................................... 48 Sills ....... 66 Siltstone. .. 5,17,18,19,21,26,27,28,36 Silurian rocks. .................... 11, 12 Silver ...................... 52, 55, 59, 66,68, 70, 71, 72 distribution ..... _.._ 52, 55, 57,68, 71, 72, 75,76 native ....... 64 production ...................... 52-55, 69, 73-76 Silver Dollar mine ....... 14, 19,21, 42, 43, 54, 57, 75,76 Silver Reid prospect .................... 56, 57, 74, 75 Smithsonite .................................. 67 Sphalerite. _. 56, 62, 65, 66, 67, 68, 69, 74, 75, 76, 77 Sphene ................................. 29, 31, 32, 48 Standard fault ....................... 44, 58, 70, 71, 73 Stannite ................. 62 Steatite talc... ....... 52, 79, 8D deposits ............... 80 production ............................... 55, 80 Stibnite ...................................... 79 Stilbite ........ _.._ 32 Stolzite ................ .. 76 Strike-slip faults..- . 4.2 43,44 Stratigraphic sections ......................... 5, 6,8,,,101113,15,1617,2326,73 Structure ............. .. 39—46 Zinc Hill district. . . 74 87 Page Sulfide minerals._ ..... 54-62, 68, 69 Sulfur ....................... 59, 64 Supergene minerals ........................ 59,63, 67 Syenite ....................................... 32 '1‘ Tactite ......... 46, 47, 48, 49, 50, 73, 77 Talc City Hills ..................... 5, 6, 9—14, 17—19, 21, 22, 36, 39, 42—45. 47,53, 55, 56, 75, 76,80 Talc City Hills district, ore deposits .......... 75,76 Talc City Hills syncline ...................... 42 Talc City mine. ........ 11-14, 32, 47, 52, 53,55, 80, 81 Talc City thrust. ................... 42,44 Talc deposits ........................... 52, 79,80, 81 origin ..................................... 81 production ..... . 52,55 structural features ..... 80 Tenorite ...................................... 59, 64 Tertiary rocks ........................ 32, 33, 52 Tetrahedrite-tennantite ................... 62, 65, 75 Thompson mine ......... 53,55, 58, 60—62, 69, 72,77, 79 Tin mountain limestone.. .. 13—17, 40, 43, 47, 69, 73, 75 age ....................................... 15—17 distribution 14 lithology ........................ 14, 15,47, 73, 79 stratigraphic relations. . . . _ 14, 69 thickness ................................. l4 Thrust faults ................................. 42,43 Topography_. 4 Tourmaline. _ ............ 29, 31, 32 Tremolite. . . _ 14, 18, 19,28, 47, 48,50 Trinity mine ................................. 11 Tuff ....................................... 33,34, 36 Tufl-breccia ...... _ 33,34 Tungsten deposits, 0030 Range._ .. 76, 79 Darwin district .......... -. 52,53, 66, 76,78 distribution .............................. 76 grade ..................................... 77 mineralogy- - 77, 79 production. . . 52 U Ubehebe mine ................................ 57 Ubehebe Peak quadrangle ............. _.._ 3, 5,,,,,69101112,14,17,,,,19212932 Unconformities ............. 21, 24, 28, 33, 39 40, 51, 52 V Vanadim’te ................................... 59, 63 Vegetation ....... __ 3, 4 Vein deposits, lead-zinc-silver .............. 56, 75, 76 Victory prospect.... 11 Viking mine.......- 9 Vivianite ...................................... 59, 64 Volcanic bombs 33, 34, 35 Volcanic rocks ............................. 33—37, 52 W Water supply of area ......................... 4 Water tank fault ....................... 44, 58, 70, 71 West Coast Tungsten Corp __________ 53 White Swan mine ....................... 9, 10, 11, 21 Williams, James Steele, quoted _______________ 16 Wollastonite ............................... 47—50, 63 Wonder mine ................................. 55,57 Wulfenite .................................... 59 Z Zinc deposits ........................ 52, 55,56, 66—72 distribution .............................. 55 production ...................... 54, 55, 69, 75, 76 Zinc Hill district. ......... 52,57, 73,74 geologic setting ........................... 57,73 ore deposits ............................ 57,73, 74 structural features ................. 74 Zinc Hill fault ................................ 74 Zinc Hill mine.. 54—58, 62, 64, 66, 67, 68, 73, 74 Zircon ..................................... 10, 31, 35 SEA LEVEL _ UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY 117°45’ 36°30’ - 25 7 20' N 30’ (UBEHEBE PEAK) 420 000 (PINAMINT BUTTE) 36°30’ AIIuvium Fan deposits, stream gravels, wash deposits, and slope wash Recent Ql FEET Lake deposits Mainly white, medium-bedded pumi— ceous ash that interfingers with older gravel in the Argus Range; diatoms of middle to late Pleisto- cene age locally present Pleistocene Qb Olivine basalt flows Thin tuff beds are shown by dots. A few undifferentiated flows in Darwin Canyon are younger than Qof Coso formation Arkosic sand, silt and clay Tpu Tpl ”Sm Pyroclastic rocks Tpu, uppw unit, agglomerate, lapilli tuff, and tuff breccia of basaltic composition; includes some basalt flows, intrusive basalt, and minor pumicc Tpl, lower unit, bedded lapilli tuff; includes olivine basalt flow, Tb. Pliocene(?) /. Andesite porphyry dikes EXPLANATION le Landslide deposits Qof Old fanglomerate marginal to Darwin Wash F anglomerate in Darwin Wash and Argus Range, overlain and under- lain by olivine basalt flows We Intrusive basalt Dikes, sills, and irregular plugs localized near Or in vents Old fanglomerate from the Inyo Mountains Contains fragments of Paleozoic rocks in a clay and silt matrix Tan Andesite Interbedded near top of pyroclastic rocks MAJOR UNCONFORM/TY Diorite dikes Includes aplite, pegmatite, and leucogranite Jimphibolite Includes amphibolite, epidote, amphibolite horn- bleMe gabbro, and diorite qul qu2 TABS. 2 370 000 FEET A Conglomerate Mesa 6000' Mp 2000' _ 2000' ‘ h . 39 E. 117045, Base from U. 8. Geological Survey map of Darwin quadrangle, California, 1950 Qal QTI Qal qu2 sandstone. Rest Spring shale Dark—brown and dark greenish-gray fissile shale and minor siltstone. Occurs only in fault zones Perdido formation Interbedded thin- to medium-bedded gray limestone and brown—weath- ering chert. Some limestone beds consists predominantly of crinoid columnals. Correlates with lower part of type Perdido formation (Mo Allister, 1952) except in east- ern part of Talc City Hills, where equivalents of upper part of type Perdi' i0 are present. Silicated zones shown by overlining Quartz monzonite qu., biotite—hornblende-quartz monzonite. Border facies are medium-grained quartz-poor rocks that include monzonite, syenite, syenodiorite, and gabbro,’ not differentiated on map. Includes Hunter Mountain quartz monzonite in northeast corner of quadrangle. Kq m2, light—colored quartz monzonite MAJOR UNCONFORMITY Paleozoic Silicated rocks, undifferentiated Owens Valley formation Pou, upper unit, limestone conglomerate, siltstone, and Po, middle and lower units, undifferentiated, Middle unit, brick—red and yellowish-brown shale, siltstone and blue-gray limestone. Exposed only around base of Conglomerate Mesa. Lower unit, mainly thin to medium bedded bluish—gray calcarenite. Contains lenses of pure limestone and limestone breccia that are abundantly fossiliferous, and lesser siltstons and shale. Silicated zones shown by overlining Keeler Canyon formation Pku, upper unit, interbedded gray, thin- to medium- bedded calcarenite, calcilutite, pink fissle shale, silt- stone, and limestone pebble conglomerate. PlPkl, lower unit, thin- to medium-bedded calcarenite, containing some limestone pebble conglomerate beds with abundant fusulinids; in basal part of unit, spheroidal chert nodules 1/.) to 11/2 inches in diameter and sparse Fusulinella of Middle Pennsylvanian age. Silicated zones shown by overlining Lee Flat limestone Thinly bedded, dark-gray limestone with thin sandy iron-stained part— ings. Locally contains chert lenses and thin beds. Lee Flat is a time- stratigraphic equivalent of the Rest Spring shale and the upper part of the Perdido formation in the Ubehebe Peak quadrangle (Mc- Allister, 1956). At Zinc Hill, includes Tin Mountain limestone and Perdido formation. Silicated zones shown by overlining A‘ Upper Ordovician h QUATERNARY Middle Ordovician Lower and M iddle( ?) Ordovician TERTIARW?) CRETACEOUS l?) CRETACEOUS(?) PERMIAN V PENNSYLVANIAN AND PERMIAN PENNSYL- VANIAN(?) MISSISSIPPIAN , 36°19 ooso PEAK) Geology by W. E. Hall and EM. MaCKevett, Jr., 1952—54 117°30’ A! w 6000’ 4000' 2000' SEA LEVEL 0‘0 Talc City Hills BEND IN d Dll D's Oe Darwin Hills 4\ PM! PlPkl 0T Tin Mountain limestone Predominantly dark-gray fine—grained limestone in beds 1% to 12 feet thick; chert nodules and crinoid columnals common throughout the formation. Lime- stone is bleached white at south end of the Santa Rosa Hills. Siliciated zones shown by overlining I ,aDls " p'Du Did ‘u qu Lost Burro formation DIS, shale unit, brownfissile shale restricted to upper part of Lost Burro formation in the Talc City Hills. DH, limestone and marble unit, thinly bedded white and light-gray limestone and marble, characteristically banded by streaks and thin beds of gray marble. Dark-gray limestone beds near base of unit contain cladoporoid corals and stromatoporoids Dld, dolomite unit, light-gray, massive to thickly bedded dolomite with a mottled appearance and minor quartz- ite. Contains several dark-gray limestone beds 40 to 50 feet thick that are partly dolomitized. qu, white, vitreous quartzite at the base of the formation. Correlates in part with the Lippincott member described by McAllister (1955) g.— \F DEVONIAN PROFESSIONAL PAPER 568 PLATE I \ a (Z: 2 08h S . Z z S 0 Hidden Valley dolomite g: Light—gray massive dolomite -J D U) Ely Sprlngs dolomite Thickly bedded'dolomite, dark-gray in lower part and lighter gray in upper part. Black chert nodules and thin beds are in the lower part Z . 5 Eureka quartzite 9 White to light-gray vitreous quartzite; lower part is 5 stained dark brown Q 0: O Pogonip group Mainly light to medium gray, thickly bedded dolomite and minor limestone. Upper part contains several dark-brown siliceous units 8 to 178feet thick that contain interbedded iron-stained chert, sandy lime- stone, and dolomite. Dolomite in upper part contains abundant large gastropods (Palliseria robusta Wilson) Z w E 0 z 4 x Gneiss Z 3 Contact Dashed where approximately located; Indefinite contact Includes gradational contacts and indefinite boudaries of surficial deposits 4— U _’ D I 60 Fault, showing dip Dashed where approximately located. U, upthrown side; D, downthrown side. Arrows show relative movement 90 Vertical fault Concealed fault Thrust fault Saw teeth on side of upper plate Anticline Overturned anticline Synbline Showing direction of plunge of axis Overturned syncline 25 _1._ Strike and dip of beds 41. 7O Strike and dip of overturned beds 90 —l—— Strike of vertical beds 63 Horizontal beds __fi 70 Strike and dip of fracture cleavage at Strike of vertical fracture cleavage T 50 Strike and dip of joints + Strike of vertical joints _V_ 5 Strike and dip of flow banding Horizontal flow banding TRUE NORTH APPROXIMATE MEAN DECLINATION,196] 4000' 2000’ SEA LEVEL 2000’ MAP OF THE DARWIN QIADRANGLE AND SECTIONS, INYO GEOLOGIC 1 l—-ll--ll—-ll—-—l CONTOUR INTERVAL 40 FEET DATUM IS MEAN SEA LEVEL 3M|LES [NTERIORgGEOLOGICAL SURVEY. WASHINGTON. D, c 110212 COUNTY, CALIFORNIA UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 368 GEOLOGICAL SURVEY PLATE 2 g , , ,.. a , , EXPLANATION g Qal Oes Q: Alluvium Ely Springs dolomite z E s < § Qb //b 2 0e ‘3) 8 . . 33 8 1,3, 011v1ne basalt 2 Eureka quartzite a: ‘3 Flows, Qb; dikes, b. Tu)?“ bed shown by dots 8 O N l m I ‘ 1131'. ' p Op I QTf - I E | . . [ Pogonip group ' Fanglomerate | 5 __ «S. E Contact § Tp S Dashed where approximately located m +— 8 . Ir __________ .s m . . E P y roclastlc rocks I— Indeflmte contact Includes tufl~breccia, agglomerate, and basalt cinders A 75 2 an % Overturned contact, showing dip _ 3 £50 . . O — Ande31te porphyry dlke 8 Fault, showing dip < Dashed where approximately located qu2 E 90 r ‘ , 1 l , 5 U _I—_ ; > -, l. ‘ > y . ,‘i m x ‘ .. I“ . . , \,\ Quartz monzonite Vertical fault , , _ 7, , 4 . , 022 ES I32 ' " . 2 Thrust fault, showing dip Owens Valley formatlon j Z Saw teeth on side of upper plate >- Z < m ”- , Inverted anticllne 3 Showing direction and dip of plunge > 2 U) 2; «Ja— ‘ ‘ u 5 <>t Inverted syncline Rest Spring IPMI EL Showing direction and dip of plunge W 1Lee Flat 2 Syniline 1mestone 3 Showing trace of axial plane Perdido formation 3‘ Silicated zones shown g — by overlmmg a Overturned syncline APPROXIMATE MEAN @345th 9 Showing trace of axial plane and direction ofdip of DECLINATION, 1960 Qbimk’ DH 2 limbs. Dashed where approximately located \ 'h' \ / . rDld - . . J i2 Qb 4.1 . Tm Mountam llmestone N Strike and dip of beds ./ 1 w W} x / I I /V T h d'f' ' l G | b W E E M K t J 1953 ‘DIS 7%" opogrfag y mo iéed trorti'] U. Sa Geol'ogulcgsiurvey e0 ogy y . . Hall and .M, ac evet, r., DH 2 Strike and dip of overturned beds map 0 arwm’ -mlnu equa rang 6" INTERIOR-rGEOLOGICAL SURVEY. WASHINGTON,D. c.7710212 <_( Dld z 90 , o . ‘l— . GEOLOGIC MAP OF THE TALC CITY HILLS, IN YO COUNTY, CALIFORNIA mq r5 Strike of vemcal beds ' D is SCALE 132400 Lost Burro formation Mine 1 O :i MILE Shale, Dls; limestone, DII; dolomite, Dld; l—_—l l"——l l ' quartzite, qu J X CONTOUR INTERVAL 100 FEET z 2 Prospect DATUM IS MEAN SEA LEVEL 4: E .'.'.'.'. DSh E E Z Talc T 3