7 DAY ‘Géohydrology of the Yuma Area, Arizona and California GEOLOGICAL SURVEY PROFESSIONAL PAPER‘486-H G€ohydrology of the Yuma Area, Arizona and California By F. H. OLMSTED, O. J. LOELTZ, and BURDGE IRELAN WATER RESOURCES OF LOWER COLORADO RIVER~SALTON SEA AREA GEOLOGICAL SURVEY PROFESSIONAL PAPER 486—H UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1973 UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress catalog-card No. 73-600011 For sale by the Superintendent of Documents, US. Government Printing Office Washington, D.C. 20402 — Price $11.60 Stock Number 2401—02391 CONTENTS Page Page Abstract ________________________________________ H1 Geology—Continued Introduction _____________________________________ 6 Stratigraphy—Continued Location of area _____________________________ 6 Volcanic rocks (Tertiary)—Continued History of water-resources development ________ 6 Basalt or basaltic andesite of unknown Yuma Valley ____________________________ 6 age _______________________________ H38 Yuma Mesa _____________________________ 9 Age of volcanic rocks ________________ 39 Other areas _____________________________ 9 Older marine sedimentary rocks (Tertiary)- 39 Mexicali Valley __________________________ 10 Bouse Formation (Pliocene) ______________ 40 Objectives of present investigation and scope of Transition zone (Pliocene) ________________ 45 report ____________________________________ 11 Conglomerate of Chocolate Mountains (Ter- Methods of investigation _____________________ 12 tiary and Quaternary) __________________ 45 Geologic mapping ________________________ 12 Older alluvium (Pliocene and Pleistocene) .. 45 Geophysical exploration __________________ 12 Distribution and thickness ____________ 46 Test drilling ____________________________ 12 Age and correlation __________________ 46 Studies of formation samples _____________ 13 Classification of deposits by source _____ 47 Wireline logging _________________________ 14 Deposits of local origin _______________ 47 Inventory of existing wells and well records- 14 Stream-terrace and piedmont deposits __ 47 Quantitative determinations of aquifer char- Deposits of mixed origin ______________ 48 acteristics _____________________________ 15 Deposits of the old Colorado and Gila Chemical analyses of ground—water samples _ 15 Rivers ____________________________ 48 Measurements of ground-water temperature- 15 Younger alluvium (Quaternary) ___________ 53 Analog-model studies ____________________ 15 Deposits of the Colorado and Gila Rivers 53 Earlier investigations ________________________ 16 Alluvial-fan deposits _________________ 56 Geologic studies _________________________ 16 Wash and sheet-wash deposits ________ 56 Hydrologic studies _______________________ 16 Windblown sand (Quaternary) ____________ 56 Acknowledgments ____________________________ 16 Structure ___________________________________ 57 Well-numbering systems _____________________ 17 Regional structural patterns ______________ 57 Geology _________________________________________ 18 Pre-Tertiary structural features __________ 57 Geomorphology ______________________________ 18 Basin and Range structural features (Ter- Regional setting _________________________ 18 tiary) ________________________________ 58 Classification of landforms ________________ 19 Late Tertiary and Quaternary structural Mountains and hills ______________________ 19 features _______________________________ 60 Dissected old river deposits _______________ 23 Algodones fault and related faults _________ 61 Dissected piedmont slopes ________________ 24 Ground-water hydrology __________________________ 63 Undissected piedmont slopes ______________ 24 The ground-water reservoir ___________________ 63 RiVer terraces and mesas _________________ 26 Major subdivisions of the reservoir ________ 63 Sand dunes _____________________________ 28 Definition of fresh water __________________ 63 River valleys ____________________________ 28 Poorly water-bearing rocks of Tertiary age _ 64 Stratigraphy ________________________________ 30 Nonmarine sedimentary rocks _________ 65 Classification of rocks ____________________ 30 Older marine sedimentary rocks _______ 65 Crystalline rocks (pre-Tertiary) __________ 30 Bouse Formation _____________________ 65 Nonmarine sedimentary rocks (Tertiary) _- 32 Transition zone ______________________ 66 Red beds ____________________________ 3 Water-bearing deposits of Pliocene to H010- Breccia and conglomerate ____________ 33 cene age __________________________ 66 Kinter Formation ____________________ 34 Wedge zone _________________________ 66 Other nonmarine sedimentary rocks ____ 37 Coarse-gravel zone ___________________ 67 Volcanic rocks (Tertiary) ________________ 37 Upper, fine—grained zone ______________ 68 Older andesite _______________________ 37 Older alluvium, undivided _____________ 69 Pyroclastic rocks of silicic to interme- Origin of ground water and sources of recharge _ 70 diate composition __________________ 37 Colorado River __________________________ 70 Basaltic andesite or basalt of Chocolate Gila River _______________________________ 71 Mountains _________________________ 38 Irrigation _______________________________ 71 Flows and vent tufl’ of Laguna Moun— Local precipitation _______________________ 72 tains _____________________________ 38 Local runoff _____________________________ 72 III {T327F‘5 IV Ground-water hydrology—Continued Hydrologic characteristics of aquifers _________ Definition of terms _______________________ Transmissivity ___________________________ Determinations by previous investiga- tors _______________________________ Determinations during present investi— gation ____________________________ Storage coefficient ________________________ Movement of ground water ___________________ Direction of movement under natural con- ditions __._ _____________________________ Rate of movement under natural conditions- Alluvial section between Pilot Knob and Cargo Muchacho Mountains _________ Limitrophe section of Colorado River __ Yuma Valley ________________________ Direction of movement in 1960 ____________ Rate of movement in 1960 ________________ Alluvial section between Pilot Knob and Cargo Muchacho Mountains _________ Limitroiphe section of Colorado River __ Yuma Valley ________________________ Movement after 1960 _____________________ Water budgets _______________________________ “Laguna Valley” subarea _________________ Reservation and Bard subarea _____________ The Island subarea ______________________ North Gila Valley subarea ________________ South Gila Valley subarea ________________ Yuma Mesa subarea ______________________ Yuma Valley subarea _____________________ Summary of subarea budgets _____________ Yuma area ______________________________ Ground-water discharge to the Colorado River between Imperial Dam and the northerly international boundary ________ Analog-model studies ________________________ Model characteristics _____________________ Transmissivity values _________; ______ Storage-coefficient values _____________ Stresses applied to the modeled system _____ Verification studies _______________________ Reliability of the analog model ____________ Temperature of ground water ________________ CONTENTS Page H72 72 75 75 75 78 82 84 87 87 87 87 88 91 91 91 93 95 95 98 99 100 100 100 101 102 103 103 105 107 107 108 109 109 113 113 113 Ground-water hydrology—Continued Temperature of ground water—Continued Variations in temperature with time _______ Vertical variations in temperature ________ Areal variations in temperature ___________ Chemical quality of ground water ______________ Chemical changes in ground water derived from the recent Colorado River ______ Concentration by evapotranspiration ___ Softening ___________________________ Carbonate precipitation _______________ Sulfate reduction _____________________ Hardening __________________________ Summary of hypothetical analyses _____ Subdivision of Yuma area for description of quality of water _____________________ Gila Valley subarea ______________________ Gila Siphon sector ___________________ East sector __________________________ East-central sector ___________________ West—central sector ___________________ West sector _________________________ Upper valley subarea _____________________ “Laguna Valley” sector _______________ North Gila sector ____________________ Bard sector _________________________ The Island sector _____________________ Winterhaven sector ___________________ Yuma Valley subarea _____________________ California sector ____________________ East sector __________________________ Central sector _______________________ Floodway sector ______________________ Yuma Mesa subarea ______________________ Fortuna sector ______________________ Arizona Western sector ______________ Citrus sector ________________________ City sector __________________________ South sector _________________________ References Appendix A. Records of wells _____________________ Appendix B. Selected logs of water wells __________ Appendix C. Chemical analyses of ground water ___ Appendix D. Selected pumping tests _______________ Appendix E. Moisture investigations _______________ Index ___________________________________________ ILLUSTRATIONS [Plates are in separate volume] PLATE 1. on ground-water levels, Yuma'area, Arizona and California. 91:593.“ Topographic map of the Yuma Mesa, Yuma area, Arizona and California. Geologic map of the Yuma area, Arizona and California. Geologic map of southeastern Laguna Mountains and north end of Gila Mountains, Yuma area, Arizona. Geologic sections A—A’, B—B’, C—C’, D—D’, and E—E’ across northern Yuma Valley and northwestern Yuma Mesa, Yuma area, Arizona and California. 6. Geologic sections F—F’ along limitrophe section of Colorado River and G—G’ along southerly international boundary, Yuma area, Arizona and California. 7. Map showing altitude of top of coarse-gravel zone, Yuma area, Arizona and California. Page H113 116 121 124 124 126 126 127 127 128 129 129 129 132 132 133 133 133 134 134 134 135 135 135 136 137 137 138 138 139 139 139 140 140 141 141 146 170 195 208 216 225 Topographic map of the “Upper Mesa” showing trace of the Algodones fault and the effect of the fault, PLATE FIGURE 10. 11. 12. 13—17. 5-“?pr 7—9. 10. 11. 12. 13. 14. 15. 16. 17—20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. CONTENTS V Geologic sections H—H’ across margins of Yuma Valley and Yuma Mesa southeast of Somerton and I—I' across eastern South Gila Valley and northeastern Yuma Mesa, Yuma area, Arizona and California. Map showing principal geologic structural features, Yuma area, Arizona and California. Block diagram of the Yuma area, Arizona and California. . . Map showing chemical character of water in the coarse-gravel zone, Yuma area, Arizona and California. Maps showing thickneSS of clay, silty clay, and clayey silt in the upper 100 feet of the alluvium in parts of the Yuma area, Arizona and California. Maps of the Yuma area, Arizona and California showing location of— 13. Water test wells and oil test wells. 14. U.S. Geological Survey auger test holes deep observation wells, and selected 15. Drainage and supply wells. 16. Irrigation wells. 17. Miscellaneous wells. and test wells, Yuma County Water Users’ Association U.S. Bureau of Reclamation observation wells. Page Map of the lower Colorado River region ShOWil’lg location of the Yuma area _____________________ H7 Map showing areas irrigated in 1966 _________________________________________________________ 8 Photograph showing the boring of a test well with a power auger 31/2 miles south of Somerton, Ariz- 13 Photograph showing the drilling of test well LCRP 26 11/2 miles west of Winterhaven, Calif ____ 14 Snetch showing subdivision of U.S. land-net sections for assignment of well numbers and locations of wells by grid coordinates _____________________________________________________________ 18 20 Geomorphic map of the Yuma area __________________________________________________________ Photographs of— 7. Westward view of a ridge in the southwestern Chocolate Mountains, Calif _______________ 21 8. Dissected piedmont surfaces of reentrant of “Picacho Mesa” in eastern Cargo Muchacho Mountains, Calif ________________________________________________________________ 25 9. Northern Gila Mountain from Fortuna Wash ________________________________________ 26 Photograph showing terraces in southern Laguna Mountains __________________________________ 27 Stratigraphic column _______________________________________________________________________ 31 Photograph showing granite breccia and conglomerate exposed in north bank of Colorado River at Yuma _________________________________________________________________________________ 34 Photograph showing exposure of Kinter Formation in railroad out along Kinter siding at north end of Gila Mountains ______________________________________________________________________ 36 Selected logs of test well LCRP 29 below a depth of 1,000 feet _______________________________ 41 Map showing inferred extent and configuration of the Bouse Formation ________________________ 43 Selected logs of test well LCRP 26 between depths of 1,000 and 1,450 feet ____________________ 44 Photographs showing— 17. Poorly sorted gravelly deposits of local origin exposed in west bank of Fortuna Wash near U.S. Interstate Highway 8 _______________________________________________ .- ______ 47 18. View of southeastern Chocolate Mountains, California, showing predominantly fine-grained older alluvium abutting basaltic andesite or basalt of Tertiary age __________________ 49 19. Crossbedded coarse sand and fine gravel in exposure of older alluvium 6 miles west of Yuma _________________________________________________________________________ 50 20. Well-rounded to subrounded Colorado River gravel in an exposure of older alluvium south- west of Pilot Knob ____________________________________________________________ 51 Map of the southwestern part of the Yuma area showing extent and altitude of top and bottom of clay A beneath Yuma Valley and northwest margin of Yuma Mesa ______________________ 54 Map of the central part of the Yuma area showing extent and altitude of top and bottom of clay B beneath Yuma Mesa __________________________________________________________________ 55 Map showing transmissivities computed from pumping tests made prior to the present investigation__ 76 Map showing wells for which pumping tests were made during present investigation __________ 77 Map of the Yuma area showing transmissiVity of alluvium __________________________________ 81 Hydrograph Showing mean annual stages of Colorado River at Y'uma _____' ____________________ 83 Map Of Yuma Valley showing average water-level contours in 1911 ____________________________ 85 Map Of the delta region showing aVerage water-level contours in 1939 _________________________ 86 Map showing average water-level contours in 1925 __________________________________________ 89 Map of the delta region showing average water-level contours in 1960 _________________________ 90 Map of Yuma Valley showing average water-level contours for upper part of coarse-gravel zone in 1960 ________________________________________________________________________________ 94 Map of the delta region showing average water-level contours in December 1965 _______________ 96 Sketch map showing water budgets for subareas, 1960—63, inclusive ___________________________ 97 Map of Yuma Valley showing average water-level contours for upper part of coarse—gravel zone in 1962 _________________________________________________________________________________ 104 VI FIGURE 35. 36. 37. 38443. 44. 45. 46. 47. 48. 49. 50—54. 55. 56758. TABLE 9" 12. 13. 5°!" PPWSP‘P‘?‘ CONTENTS Map of the delta region showing transmissivity of the upper transmissive layer simulated in the analog model ___________________________________________________________________________ Map of the delta region showing transmissivity of the lower transmissive layer simulated in the ana- log model _______________________________________________________________________________ Map showing storage coefficients of the upper transmissive layer simulated in the analog model __ Maps showing changes in— 38. Water level, 1925 to December 1957, as indicated by field measurements or as estimated __ 39. Head in the upper transmissive layer, 1925 to December 1957, as indicated by responses of the analog model ___________________________________________________________ 40. Water level, December 1957 to December 1962, as indicated by field measurements ______ 41. Head in the upper transmissive layer, December 1957 to December 1962, as indicated by responses of the analog model ________________________________________________ 42. Water level, December 1962 to December 1966, as indicated by field measurements ______ 43. Head in the upper transmissive layer, December 1962 to December 1966, as indicated by responses of the analog model _________________________________________________ Temperature profiles in well (C—9—24)11ccc for May and November 1967 and February 1968 _____ Graph showing change in temperature of water pumped by well (C—9—23)20bdc (USBR drainage well YV—13) from November 1966 to February 1968 ______________________________________ Temperature profile in well (C—8—23)33cdd (LCRP 13) for March 12, 1963 _____________________ Map showing temperature of ground water in coarse-gravel zone or at equivalent depth below the water table, 1965—68 _____________________________________________________________________ Diagrams representative of chemical character of water represented by selected chemical analyses in table 15 _______________________________________________________________________________ Map of the Yuma area showing subareas and sectors described in section on quality of water and listed in appendix C ____________________________________________________________________ Graphs in appendix D showing pumping-test data for wells-— 50. 168/23E—10Rcc (LCRP 23) _________________________________________________________ 51. 16S/22E~29Gca2 (LCRP 26) ________________________________________________________ 52. (C—9—22)28cbb (LCRP 25) __________________________________________________________ 53. (C—10—25)35bbd (LCRP 17) ________________________________________________________ 54. (C—11—24)23bcb (LCRP 10) ________________________________________________________ Graph showing relation between counts per minute and moisture content _____________________ Graphs showing counts per minute at various depths below land surface obtained by use of a neutron moisture probe at— 56. Ten sites in South Gila Valley ______________________________________________________ 57. Ten sites on Yuma Mesa ____________________________________________________________ 58. Six sites in Yuma Valley ____________________________________________________________ TABLES Irrigated acreage and water diverted to Yuma Mesa __________________________________________ Potassium-argon ages of volcanic rocks in the Yuma area _____________________________________ Summary of heavy-mineral analyses of alluvial sand (deposits of the Colorado River) of the Yuma area __________________________________________________________________________________ Selected data from analyses of gravel from wells in older and younger alluviums _______________ Depths of Tertiary and pre-Tertiary horizons in wells _______________________________________ Miscellaneous chemical analyses ______________________________________________________________ Results of pumping tests ____________________________________________________________________ Diversions, consumptive use, and ground-water recharge for Yuma Mesa _______________________ Summary of ground-water budgets of Yuma subareas, 1960—63 _______________________________ Ground-water discharge to the Colorado or Gila Rivers between Imperial Dam and northerly in- ternational boundary, 1960—63 ___________________________________________________________ Flow of the Colorado River at Imperial Dam and at Yuma, and differences between sum of all surface-water inflow items in the reach and flow of Colorado River at Yuma ______________ Flow of the Colorado River at Yuma and at northerly international boundary, and differences be- tween sum of all surface—water inflow items in the reach and flow of Colorado River at northerly international boundary __________________________________________________________________ Design stresses for analog model of Yuma area _______________________________________________ Page H110 111 112 114 115 116 117 118 119 120 121 122 123 130 131 209 211 213 214 216 218 221 222 224 Page H9 39 51 52 64 73 79 98 105 106 106 106 109 TABLE 14. 15. 16—20. 21. CONTENTS Effective year-end declines of water level, in feet, in Mexicali Valley at a site 12 miles west of the middle limitrophe section of the Colorado River __________________________________________ Hypothetical analyses of ground water resulting from specified chemical changes in Colorado River water _________________________________________________________________________________ In appendix A: 16. Water-test wells and oil-test wells ___________________________________________________ 17. U.S. Geological Survey auger test holes and test wells, Yuma County Water Users’ Associa- tion deep observation wells, and selected U.S. Bureau of Reclamation observation wells 18. Drainage and supply wells __________________________________________________________ 19. Irrigation wells ____________________________________________________________________ 20. Miscellaneous wells ________________________________________________________________ In appendix E: Moisture content and storage capacity of alluvium as indicated by neutron moisture probe study ____________________________________________________________________________ VII Page H109 125 147 150 158 160 164 219 WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA By F. H. OLMSTED, O. J. LOELTZ, and BURDGE IRELAN ABSTRACT The Yuma area includes the upstream part of the Colo- rado River delta within the United States, in one of the driest desert regions of North America. Except for very minor irrigation by the Indians and the Spanish before about 1850, irrigation with Colorado River water began in the late 19th century. By 1966, about 100,000 acres was being irrigated, chiefly in the river valleys (flood plains) and on Yuma Mesa (a river terrace). Ground water has been the' source of supply only in South Gila Valley east of Yuma and in small areas outside the established irrigation districts in the other river valleys and on Yuma Mesa. The valley lands were the first to be irrigated, and only a very small acreage was irrigated on Yuma Mesa before 1923. After the middle 1940’s the irrigated area on Yuma Mesa expanded rapidly so that by 1966 more than 20,000 acres was under irrigation. About two-thirds to three-fourths of‘the total of more than 5 million acre-feet of Colorado River water imported for irrigation on the mesa from 1922 through 1966 either went into ground-water storage to build a widespread ground-water mound or induced ground- water movement into the valleys west and north of the mesa. Drainage Wells were installed in the 1950’s and 1960’s in eastern Yuma Valley and in the 1960’s in South Gila Valley in order to alleviate drainage problems aggravated by the growth of the ground-water mound. - Irrigation with Colorado River water in Mexicali Valley, the northern part of the Colorado delta in Mexico, began shortly after the turn of the century. By 1955, more than 500,000 acres in the valley was irrigated. This area re- quired more water than the 1.5 million acre-feet of Colorado River water guaranteed annually to Mexico under a 1944 treaty plus the small supplementary supply pumped from private wells. Accordingly, the Mexican Government author- ized the drilling of several hundred wells to augment the total supply. P‘umpage of ground water increased during the next decade, so that by 1965 nearly 1 million acre-feet was pumped, of which about two-thirds came from Government wells. Ground-water pumpage is now carefully controlled by the Mexican Government, and the total area irrigated with ground water and surface water is restricted to about 415,000 acres—substantially less than the maximum area irrigated in the 1950’s. The Yuma area straddles the dividing line between the Sonoran Desert section and the Salton Trough section of the Basin and Range physiographic province and is char- acterized geomorphically by low north-northwest-trending mountains separated by much more extensive desert plains through which are cut the present valleys (flood plains) of the Colorado and Gila Rivers. The landforms include seven major types: (1) Mountains and hills, (2) dissected old river deposits, (3) dissected piedmont slopes, (4) undissected piedmont slopes, (5) river terraces and mesas, (6) sand dunes, and (7) river valleys. Mountains and hills composed of dense pre-Tertiary crystalline rocks and hard volcanic rocks of Tertiary age form the higher, more rugged exposures; less consplidated sedimentary and volcanic rocks of Tertiary age form the lower, more rounded hills. Some of the mountain blocks are buried or nearly buried by alluvium, particularly those in the southern and western parts of the area. Dissected old river deposits lie at some distance from the mountains; the chief example of this landform type is the “Upper Mesa,” a generally westward-sloping desert plain southeast of Yuma Mesa. Dissected piedmont slopes characterized by broad desert pavements cut by numerous washes lie along the margins of the hills and mountains. The undissected piedmont slopes, also near the hills and mountains, are distinguished from the older, dissected pied- mont slopes by the general absence of desert pavement and by the shallow depth of incision of the most recent washes. The river terraces and mesas are remnants of an exten- sive former valley and delta plain of the Colorado River and its major tributary, the Gila. The surfaces of the ter— races and mesas lie about 60—80 feet above the present river valleys except in the extreme western part of the area, where the terrace surfaces slope west or southwest toward the axis of the Salton Trough at gradients steeper than those of the river valleys. Yuma Mesa represents the principal river terrace in the area. Others are Imperial East Mesa, Wellton Mesa, and several distinct smaller terraces that extend upstream along both the Gila and the Colorado Rivers. Windblown sand is extensive in the Yuma area, although in only two sizable areas has the sand accumulated to form dunes more than 10 feet thick. The larger area, known as the Sand Hills or the “Algodones Dunes,” lies northwest of Yuma between the Imperial East Mesa and Pilot Knob Mesa; the smaller tract of dunes—the “Fortuna Dunes”—is in the southeastern part of the area, near the international boundary. The river valleys (Holocene flood plains of the Colorado and Gila Rivers) were flooded periodically before dams and reservoirs were constructed upstream on both the Colorado H1 H2 and the Gila Rivers. The principal valleys within the area of intensive investigation are Yuma Valley, “Bard Valley,” South Gila Valley, and North Gila Valley. The earth materials of the Yuma area range from dense crystalline rocks to unconsolidated alluvium and windblown sand. These materials are grouped in 10 generalized strati- graphy units: (1) Crystalline rocks (pre—Tertiary), (2) nonmarine sedimentary rocks (Tertiary) including a new formation, the Kinter, of Miocene age; (3) volcanic rocks (Tertiary) (4) older marine sedimentary rocks (Tertiary), (5) Bouse Formation (Pliocene), (6) transition zone (Plio- cene), (7) conglomerate of Chocolate Mountains (Tertiary and Quaternary), (8) older alluvium (Pliocene and Pleisto— cene), (9) younger alluvium (Quaternary), and (10) wind- blown sand (Quaternary). The crystalline rocks, which form a large part of the mountains and hills and unconformably underlie the Tertiary and Quaternary rocks, comprise a wide variety of meta- morphic, plutonic, and dike rocks, of which granite and quartz monzonite and various kinds of gneiss and schist are the most abundant. The ages of most of these rocks have not been established, although all of them appear to ante- date the Laramide orogeny (Late Cretaceous to early Tertiary). The nonmarine sedimentary rocks (Tertiary) consist of strongly to weakly indurated clastic rocks ranging from mudstone and shale, in part of lacustrine origin, to mega- breccia and boulder conglomerate. For the purpOse of this report all these rocks are grouped in one major unit, al- though detailed mapping in the Laguna Mountains and northernmost Gila Mountains resulted in the delineation of three mappable units: red beds, breccia and conglomerate, and the Kinter Formation (chiefly fanglomerate, with sub- ordinate breccia, arkosic sandstone and mudstone, and tufl‘aceous beds). Stratigraphic relations with radiometrically dated volcanic rocks indicate that the red beds and the breccia and conglomerate are pre-Miocene; the Kinter For- mation is designated Miocene on the basis of a potassium- argon date of 23 :2 million years for an interbedded ben- tonitic ash and of stratigraphic relations with overlying units. Associated with the nonmarine sedimentary rocks is a suite of volcanic rocks that includes an older andesitic se- quence (flows and tufl‘s), pyroclastic rocks of silicic to intermediate composition ranging from soft pumiceous ash- fall tufl’ to densely welded ash-flow tuf’f (ignimbrite) , basaltic andesite or basalt of the Chocolate Mountains (a sequence of dark-gray flows and flow breccias), flows and vent tufl‘ of the Laguna Mountains, and scattered masses of basalt or basaltic andesite of uncertain stratigraphic position and age. Potassium-argon dates for several of the volcanic rocks range from about 25 to 26 million years, indicating a prob- able middle Tertiary age for the unit. The older marine sedimentary rocks consist of more or less indurated fine sandstone and interbedded gray siltstone and claystone which occur entirely in the subsurface in the Yuma area. Fossils include foraminifers and mollusks indica- tive of a marine environment but not diagnostic as to age. The age of these beds and their correlation with units of other areas are uncertain, but their stratigraphic position suggests that they probably intertongue with the Kinter Formation in the upper part of the nonmarine sedimentary rocks. The Bouse Formation, a younger marine unit which prob- ably is unconformable on the older marine sedimentary rocks, WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA includes fossiliferous silt and clay, subordinate fine sand, hard calcareous claystone, and, locally in the basal part, calcareous sandstone or sandy limestone, tufl“, and possibly conglomerate of local derivation. The fine-grained clastic beds are predominantly greenish to bluish gray and contain small gastropods, pelecypods, and ostracodes, as well as several species of Foraminifera which indicate brackish to marine environments but are not diagnostic as to age. Other evidence, in part from the P‘arker-Blythe-Cibola area, indicates a Pliocene age, although a definite assignment within the Pliocene is not yet possible. Except for one small area of exposures 2—3 miles southeast of Imperial Dam, the Bouse Formation occurs entirely in the subsurface in the Yuma area. Throughout much of the Yuma area, the Bouse Formation is overlain by a transition zone in which marine strata like those of the Bouse alternate or intertongue with nonmarine strata like those in the overlying older alluvium. The tran- sition zone reflects the fact that marine or estuarine condi- tions did not cease abruptly but recurred at intervals for some time after the ancestral Colorado River entered the area. The conglomerate of the Chocolate Mountains occurs only in the northern part of the area, on the flanks of the Choco- late Mountains. This unit, which is composed predomi- nantly of volcanic detritus from nearby exposures of Ter- tiary volcanic rocks, includes strata probably equivalent in age to the upper part of the nonmarine sedimentary rocks (Kinter Formation) but also in part equivalent in age to the lower part of the older alluvium. The older alluvium is composed of basin-filling fluvial deposits of the Colorado and Gila Rivers and of local ephem- eral streams. The unit is actually a complex of alluvial fills separated by unconformities representing degradational cycles that resulted in extensive scouring. It is the most widely exposed unit in the Yuma area and reaches a maxi- mum thickness of more than 2,000 feet in the southwestern part of the area. Its age ranges from Pliocene to late Pleis- tocene. The older alluvium comprises a great variety of granular materials ranging from clay to cobble and boulder gravel; sand is predominant at most places. These materials are classified by primary source as deposits of local origin, deposits of the old Colorado and Gila Rivers, and deposits of mixed origin. In addition, relatively thin stream-terrace and piedmont deposits cap the older, thicker fills at many places. The deposits of local origin occupy the margins of the area and consist of poorly sorted, obscurely bedded gravel, sand, silt, and clay which were deposited probably as allu- vial fans. The stream—terrace and piedmont deposits are similar to the deposits of local origin, which they cap near the mountains, and are characterized by broad surfaces of so-called desert pavement. The deposits of mixed origin con- sist of intergradational or intertonguing deposits of local origin and old river deposits. The deposits of the old Colo- rado and Gila Rivers, which constitute the greatest bulk of the older alluvium, consist of relatively well sorted sand and subordinate silt and clay, at many places containing anasto- mosing tonguelike and ribbonlike bodies of gravel. The gravel includes abundant well-rounded pebbles and cobbles of siliceous rocks, chiefly quartzite and chert, which appear to have been derived from the Grand Canyon region and even farther upstream. The younger alluvium comprises all the alluvial deposits GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA of the most recent cycle of deposition. These deposits are classified in three categories according to the dominant agent of deposition: (1) Deposits of the Colorado and Gila Rivers, (2) alluvial-fan deposits, and (3) wash and sheet- wash deposits. The river deposits consist predominantly of sand and silt and underlie the present river flood plains; locally a basal gravel may be present at depths exceeding 100 feet. The alluvial-fan deposits, which consist of poorly sorted detritus derived from nearby exposures of granitic rocks, occur only near the southeastern and northwestern corners of the area. The wash deposits are thin, occur in channels cut into the older alluvium and prealluvial rocks, and consist of sand and gravel and thin lenses of silt. The sheet-wash deposits are similar to the wash deposits but occupy broader, less well defined areas. The windblown sand occurs as dunes, principally in the Sand Hills and in the “Fortune. Dunes,” and as relatively thin sheets on Yuma Mesa and “Upper Mesa.” Small dunes occur also in Yuma Valley and “Bard Valley.” The wind- blown deposits consist of well-sorted fine to medium sand which is probably derived from nearby sandy alluvium or, for the deposits of the Sand Hills, from old lacustrine or marine beaches. Structurally, the Yuma area is characterized by north- northwest-trending mountains separated by broader basins filled with Cenozoic deposits possibly as much as 16,000 feet thick in the “Fortuna basin” west of the southern Gila Mountains and Butler Mountains. Some of the mountain masses, especially in the western Sonoran Desert and east- ern Salton Trough, are buried or nearly buried by the Cenozoic deposits. Presumably the mountains and basins are separated by faults, but most of the present mountain fronts are fault-line scarps rather than fault scarps; the faults lie basinward and are concealed by alluvial fill. Early deformational episodes, which were Laramide and probably pre-Laramide (pre-Tertiary), resulted in faulting (including thrust faulting), folding, and metamorphism. In the Sonoran Desert—the eastern part of the Yuma area— structural activity continued into the Tertiary, and by middle Tertiary time the mountains and basins assumed approximately their present configuration. Subsequent def— ormation has involved only minor warping and normal faulting, probably associated with regional subsidence along the southwest margin, adjacent to the Salton Trough. In the Salton Trough in the southwestern part of the area, deformation has continued to the present, especially on and near the faults of the San Andreas system. Move- ment on these faults has involved large right-lateral com- ponents as well as apparently sizable vertical displacements. A major fault in this system, herein named the Algodones fault, has been delineated in the present study from topo- graphic, geophysical, and hydrologic evidence. In the south- eastern part of the area this fault forms a partial to nearly complete barrier to ground-water movement and is a feature to major hydrologic significance. Other faults, parallel or en echelon to the Algodones fault, have been identified from seismic and temperature data. The ground-water reservoir consists of two major sub- divisions: (l) poorly water—bearing rocks of Tertiary age, and (2) water-bearing deposits of Pliocene to Holocene age. The first subdivision constitutes the lower part of the reser- voir and includes (1) the nonmarine sedimentary rocks, (2) the volcanic rocks, (3) the older marine sedimentary rocks, (4) the Bouse Formation, (5) the transition zone, and (6) H3 the conglomerate of the Chocolate Mountains. These units contain some water, but much of it is highly mineralized, and the rocks are too poorly permeable or lie at too great a depth beneath most of the area to be significant sources of ground water. Local exceptions include fresh-water- bearing nonmarine sedimentary rocks, in the northern part of the area, and a conglomerate in the basal part of the Bouse Formation, also in the northern part of the area. (Fresh water is defined herein as water containing not more than 1,800 mg/l (milligrams per liter) of dissolved solids or having a specific conductance of not more than 3,000 micromhos.) The units of the second subdivision, which form the upper, principal part of the ground-water reservoir, include (1) the older alluvium, (2) the younger alluvium, and (3) the windblown sand. However, beneath the river valleys and Yuma Mesa, the upper part of the reservoir is most con- veniently subdivided into three zones, two of which cross stratigraphic boundaries. In ascending order, these zones are (1) the wedge zone (lower, major part of the older alluvium), (2) the coarse-gravel zone (uppermost gravel strata of the older alluvium and possibly a basal gravel of the younger alluvium), (3) the upper, fine-grained zone (uppermost strata of the older alluvium beneath Yuma Mesa, the upper, major part of the younger alluvium be- neath the river valleys, and small masses of windblown sand). Outside the river valleys and Yuma Mesa the alluvial deposits (almost entirely older alluvium below the water table) are not subdivided and are classified instead as older alluvium, undivided. The wedge zone, which extends to depths of about 2,500 feet in the south-central and southwestern parts of the area, constitutes the major part of the fre‘sh-water-bearing deposits of Pliocene to Holocene age beneath the river valleys and Yuha Mesa. The average grain size and prob- ably the average porosity and permeability of the wedge zone decrease with depth. The lower part of the zone con- tains more silt and clay than the upper part, but in gen- eral, the fine-grained strata are not sufficiently extensive or thick to cause significant hydraulic separation. The upper part of the zone locally contains coarse-gravel strata similar to those in the overlying coarse-gravel zone. Except in two small areas, one beneath the city of Yuma and the other west of the northern Gila Mountains, the water in the wedge zone contains less than 1,800 mg/l dis- solved solids. In both areas of more highly mineralized water, the overlying coarse-gravel zone is thin or absent and the wedge zone is thinner and probably less permeable than it is at most other places. In most of the northern part of the Yuma area, water in the wedge zone appears to be sub- stantially fresher than that in the overlying coarse-gravel zone. Beneath the southern part of the area the chemical quality of the water in the wedge zone is virtually indis- tinguishable from that of the water in the coarse—gravel zone. Relatively little is known about the chemical quality of the water in the older alluvium, undivided. Some of the water is undoubtedly similar to that in the adjacent wedge zone. Mineralized water in which the dissolved-solids con— tent exceeds 1,800 mg/l exists west of the northern Gila Mountains, beneath “Fortuna Plain” at the southerly inter- national boundary, and possibly between these two places. The coarse-gravel zone, which is the principal aquifer beneath the river valleys and Yuma Mesa, is a complex of H4 gravel bodies of different ages deposited by the Colorado and Gila Rivers. The zone ranges in thickness from 0 to possibly more than 150 feet; the top lies at an average depth of 100 feet beneath the valleys and 170—180 feet beneath Yuma Mesa in the central part of the area. Under natural conditions, the Colorado and Gila Rivers were the sources of almost all ground-water recharge in the Yuma area, but with the development of irrigation and the construction of upstream reservoirs on both rivers, irrigation water diverted from the Colorado River became the principal source. Local runoff and precipitation are very minor sources of ground-water recharge. The chemical regimen of the Colorado River has been ma- terially affected by man’s control of the river. Before the impounding of water in Lake Mead in 1935 the chemical composition of the water in the lower reaches of the river was highly variable, both seasonally and annually. Since 1935 the composition has varied much less; during the period 1941—65 the concentration of dissolved solids at Imperial Dam generally was between 700 and 800 mg/l. Sulfate was the major dissolved constituent, and calcium was the most abundant cation, although sodium was slightly more abundant than calcium when the dissolved-solids con- centration was highest. Precipitation and local runoff furnish ground-water re- charge of excellent chemical quality. In most places the overall effect of these sources on the quality of ground water is negligible; however, in several places, such as along Fortuna Wash near the northwest margin of the Gila Moun- tains, fresh ground water derived from storm runoff occurs as a thin lens or lenses not far below and above the water table. The connate water is likely to be rather highly mineral— ized; sodium and chloride are the chief ionic constituents. The coarse—gravel zone and the wedge zone are the prin- cipal aquifers in the Yuma area. Subordinate aquifers of only local significance include the nonmarine sedimentary rocks, the conglomerate in the basal part of the Bouse Formation, and a few relatively coarse grained beds in the upper, fine-grained zone. Outside the river valleys and Yuma Mesa, the older alluvium, undivided, is regarded as the principal single, heterogeneous aquifer. Transmissivity values for the principal aquifers were estimated on the basis of one or more of the following: (1) Step—drawdown tests, (2) short-term pumping tests, (3) specific-capacity data, (4) lithologic logs, (5) electric and sonic logs, and (6) seismic data. The studies of pre- vious investigators also were utilized. Critical evaluations of the reliability of computed values of transmissivity obtained from pumping tests made during the present investigation indicated that three of the values were within 10 percent of true values, 33 within 25 percent, 27 within 50 percent, and 10 more than 50 percent. Transmissivity values of the wedge zone generally increase in a southwestward direction from zero along the relatively thin east and north margins of the zone to values of more than 500,000 gpd (gallons per day) per foot beyond a north- westward-trending line about 4 miles southwest of the Algodones fault, where the wedge zone is more than 2,000 feet thick. Transmissivity values for the coarse-gravel zone range from zero to about 1,000,000 gpd per foot. Maximum values of transmissivity for the coarse-gravel zone occur in the South Gila Valley, south of the confluence of the Colorado WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA and Gila Rivers. Transmissivity values exceed 500,000 gpd per foot beneath The Island, north of the area just cited, and they also persist for about 6 miles southward beneath Yuma Mesa from the area of maximum transmissivity. Transmissivities of more than 500,000 gpd per foot occur also beneath the west edge of Yuma Valley and southwest- ward from a line 3—5 miles southwest of the Algodones fault, about along the boundary between southern Yuma Mesa and the “Upper Mesa.” Storage characteristics of the material saturated by the large ground-water mound built up beneath Yuma Mesa after 1947 were estimated on the basis of soil-moisture data obtained with a neutron moisture probe lowered into access tubes driven into the zone of saturation. The difference be- tween the moisture content above the capillary fringe and that below the water table was considered to be a valid estimate of the amount of water that would be stored as water levels rose. The storage coefficient at 10 sites in South Gila Valley averaged 38 percent; at six sites in Yuma Valley, 43 percent; and at 10 sites on Yuma Mesa, 28 percent. Stor— age coefiicients for the material penetrated by drainage Wells along the east edge of Yuma Valley as computed by earlier investigators ranged from 5.8X10“ to 3.6x10‘“ and averaged 1.2X10‘— values which indicate confined or artesian con- ditions for at least the periods of the tests. Data for com- puting storage coefficients under similar conditions were not obtained during the present investigation. Under natural conditions both the Colorado and the Gila Rivers were losing streams in the Yuma area. Infiltration from these streams was the principal source of ground- water recharge. Much of the infiltration replenished the draft on ground-water supplies caused by evapotranspiration, but some of the infiltration provided a source for the ground water moving out of the area. Movement of ground water through the alluvial section between Pilot Knob and the Cargo Muchacho Mountains under natural conditions was about 4,500 acre-feet per year. The movement of ground water westward from the limitrophe (International Bound- ary) section of the Colorado River is estimated to have been as much as 110,000 acre-feet per year. As much as 90,000 acre—feet of water that infiltrated from the Colorado River is estimated to have been discharged by evapotranspi- ration in Yuma Valley. The Colorado River continued to be a losing stream until the early 1940’s, at which time the channel near Yuma was deepened 5 feet or more by erosion, and ground-water levels rose as a result of irrigation and leakage from the All- American Canal. These conditions caused the Colorado above the limitrophe section to change from a losing to a gaining stream. For a distance of 25 miles west of Pilot Knob the ground-water ridge resulting from leakage of the All- American Canal was 30 feet or more high, with the result that the direction of ground-water movement south of the canal changed from westward to southward, and the gra- dient steepened from that existing under natural conditions. By 1960 many changes in rates of movement had occurred and the pattern of movement was more complex than it was under natural conditions. In the alluvial section between Pilot Knob and the Cargo Muchacho Mountains the west- ward flow is estimated to have been only three-eighths of the flow under natural conditions. The westward movement of ground water to Mexicali Valley adjacent to the limi- trophe section is estimated to have been 36,000 acre-feet in 1960. This estimate is corroborated by an estimate of GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA 20,000 acre-feet of outflow from Yuma Valley opposite the limitrophe section plus about 15,000 acre-feet for unac- counted depletion of the river in the limitrophe section during periods of low flow. In addition to the outflow from Yuma Valley to the limitrophe section, 7,250 acre-feet of ground water moved northward to the Colorado River and 5,000 acre-feet flowed across the southerly international boundary, making the total ground-water outflow from Yuma Valley about 33,000 acre—feet. After 1960 the principal changes in ground-water move- ment were a moderate increase in the size of the ground- water mound beneath Yuma Mesa and a lowering of water levels in Mexicali Valley. Water levels beneath Yuma Mesa continued to rise until 1962, but subsequent to that year, water levels northward and westward from the apex of the mound began a moderate decline, owing to increased pump- ing for drainage near the toe of the mesa in Yuma and South Gila Valleys. However, water levels continued to rise at greater distances eastward and southward from the apex of the mound. The generally lower water levels in Mexicali Valley resulted from the large-scale pumping for irrigation in that valley. Pumping by private interests for irrigation on Yuma Mesa, which began in 1962, caused only a moderate lowering of water levels through 1966. Average yearly water budgets for the period 1960—63, inclusive which were prepared for seven subareas designated for the Yuma area, had a net imbalance of 20,000 acre—feet out of a total inflow to the subareas of 1,192,000 acre-feet. The imbalance for individual subareas expressed as a per— cent of the inflow to the subarea ranged from zero for the Yuma Mesa subarea to about 7 percent for the Reservation and Bard subarea. Consumptive use in the subareas is 488,000 acre-feet, or about 40 percent of the total inflow. A water budget for the entire Yuma area for the 4-year period 1960—63 shows an imbalance of only 7,000 acre-feet— an imbalance that is well within the limits of accuracy for measuring inflow and outflow, each of which exceeds 6 million acre-feet per year. During the 1950-65 period the average yearly discharge of ground water to the Colorado River is estimated to have averaged about 21,000 acre-feet in the reach, Imperial Dam to Yuma, and 17,000 acre-feet in the reach, Yuma to north- erly international boundary. For the 4-year period 1960—63, comparable estimates are 45,000 and 27,000 acre-feet, re- spectively. Two electrical analog models of the hydrologic system of the delta region were constructed during the present inves— tigation for the purpose of verifying the estimates of hydrologic parameters that had been made as the result of geologic and hydrologic studies. The first model, built in 1964, simulated a single trans- missive layer connected to a constant-head surface through- out the flood—plain area in the United States by a vertical- hydraulic-conductivity parameter. It was abandoned because satisfactory correlation between model responses and his- torical changes was not achieved. However, the study did demonstrate that the model failed to simulate one or more significant hydrologic parameters beneath Yuma Mesa. Later, a more sophisticated model was constructed. The hydrologic system was simulated as a three-dimensional flow field idealized as tw0 two-dimensional transmissive layers and two layers of solely vertical flow, one of which served as the hydraulic connection between the two two-dimensional transmissive layers and the other as the hydraulic connec- H5 tion to constant-head boundaries. This second model incor- porated the newly discovered hydrologic-barrier effects of the Algodones fault and satisfactorily reproduced historical changes in water level. In the Yuma area, variations in ground-water tempera- ture are useful in corroborating vertical movement of water inferred from other evidence. Also, abnormally high tem- peratures at some places furnish supporting evidence for the presence of fault barriers or zones of low permeability. At many places, especially on Yuma Mesa, geothermal gra- dients have been modified greatly from natural conditions, owing to vertical movements of ground water induced by heavy applications of irrigation water or by large-scale pumping from wells. Faults, such as the Algodones fault and the inferred buried faults near the west margins of the Gila Mountains and the “Yuma Hills,” have produced warm anomalies which are caused by upward movement of deep water near the fault barriers. Upward movement of warm water along the east margin of Yuma Valley has been accelerated by pumping from drainage wells. The chemical quality of ground water in the Yuma area varies markedly, both areally and vertically. Differences in chemical characteristics of the recharge from several sources account for part of these variations, but the most important factors appear to be the chemical changes in the ground water that take place as a result of such processes as con- centration by evaporation or evapotranspiration, softening by ion exchange, precipitation of insoluble carbonates, sul- fate reduction, and hardening by ion exchange. Other processes probably include re-solution of precipitated salts, oxidation of dissolved organic substances, and mixing of waters of different chemical composition. It is possible to summarize the chemical characteristics of the ground water in the area by regarding it as chemi- cally altered recent Colorado River water, using a hypo- thetical-model approach in which the river water is assumed to have been evaporated and subjected to the chemical processes cited above. Most of the chemical characteristics of the ground water can be accounted for by these hypotheses, although not all the ground water is actually derived from recent Colorado River water. Among the various processes, concentration by evaporation or evapotranspiration and sul- fate reduction appear to be especially important at most places. The mineral content of the ground water in the coarse- gravel zone in the South Gila Valley and eastern North Gila Valley is greater, on the average, than it is in most other places, the sum of determined constituents generally exceed- ing 1,800 mg/l. However, information on the preirrigation chemical quality of the water is lacking, so that it is not possible to estimated how much of the present salinity has resulted from long-continued irrigation without drainage. Most of the water is of the sodium chloride type, and the proportions of sodium and chloride tend to increase with increasing dissolved-solids content. Two places, one near the east end of South Gila Valley, the other near the West end, have the most concentrated water, the dissolved-solids con- tent exceeding 3,600 mg/l. The water in the wedge Zone is much fresher than that in the coarse-gravel zone, as it generally contains substantially less than 1,800 mg/l dis- solved solids. In “Bard Valley,” “Laguna Valley,” and western North Gila Valley the water in the coarse-gravel zone appears to contain less than 1,800 mg/l dissolved solids at most places, H6 and the water in the wedge zone is even fresher. The upper, fine—grained zone in these valleys locally contains more highly mineralized water, especially where the water table is shallow. Water-quality variation is not well defined in most of Yuma Valley because of the sparsity of the data. Variations in the upper, fine—grained zone and the coarse-gravel zone appear to be erratic, although the freshest water—commonly containing less than 900 mg/l—occurs near the Colorado River. On Yuma Mesa the chemical quality of the ground water beneath the irrigated area has been affected by infiltrated Colorado River water, somewhat concentrated by evapo- transpiration. Sulfate is the major anion in most of this water. Outside the irrigated area the ratio of chloride to sulfate is higher, chloride generally exceeding sulfate in equivalent concentration. The dissolved-solids content of the water at most places is less than 1,800 mg/l, except in the area west of the northern Gila Mountains, and beneath the city of Yuma at the northwest corner of the mesa, where somewhat brackish water occurs. Pumping-test data for five Geological Survey test wells are presented in an appendix. Possible explanations are offered for some of the observed anomalies. The probable large differences that may exist between measured drawdown and drawdown in the aquifers are illustrated by the data collected using different pumping equipment. The movement of. water between strata is offered as an explanation for some of the anomalies. The reasons for some of the other anomalies are not known. The practical value of a deep- well current meter for determining the rates at which vari- ous strata yield water when a well is pumped is shown. Its value in connection with other geophysical logs for disclosing strata that are still sealed with drilling mud is also indi- cated. Soil-moisture data are presented in another appendix. The relation between counting rate and actual soil moisture of material in place for use with the neutron probe and access tubes is difficult to determine for material whose moisture content is half or more of the moisture content of the ma- terial when it is saturated. Because of the small variations in absolute specific gravity of the material for which mois- ture determinations were made, moisture content of satu- rated material in place was determined on the basis of the bulk density of the material and its absolute specific gravity. The absolute specific gravity of 25 samples of material as determined in the laboratory ranged from 2.66 for a sandy loam to 2.81 for a loamy clay. The absolute specific gravity for 14 samples of sand ranged from 2.66 to 2.70 and aver- aged 2.68; for five samples of silt, from 2.69 to 2.75 and average%2 2.72; for six samples classified as clay or clayey silt, from 2.72 to 2.81 and averaged 2.76. The relation be- tween counting rate and moisture content for moisture con- tents of more than 10 percent was interpolated between the relation determined for low moisture content and moisture content when saturated. The soil-moisture studies indicated the need for improved methods of constructing access holes, especially to depths greater than 20 feet. Minor differences in the relation between counting rate and soil moisture were found to be due to differences in the construction of the access holes and in the material used for casing the holes. INTRODUCTION LOCATION OF AREA The area investigated is near the downstream WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA end of the Colorado River basin, in one of the driest desert regions in North America. The south- western part of the Yuma area is within the Salton Trough, a lowland extension of the Gulf of Cali— fornia which includes the delta of the Colorado River; the northeastern part is in the Sonoran Desert, a region of barren, low, generally northwest- ward-trending ranges separated by extensive desert [basins (fig. 1). The city of Yuma, at the confluence of the Colorado and Gila Rivers, is 70 airline miles north of the mouth of the Colorado at the Gulf of California. HISTORY OF WATER-RESOURCES DEVELOPMENT The Yuma area is part of a very arid region where crops are entirely dependent on irrigation for their water supply. The dry climate, with its hot summers, mild winters, and practically year- long growing season, together with the availability of the Colorado River as a source of water supply, have encouraged the development of intensive irri- gated agriculture. Since irrigation began, before the turn of the century, the acreage under cultivation has increased so that, by 1966, about 100,000 acres was being irrigated (fig. 2). The first irrigation developments were in the river valleys (flood plains of the Colorado and Gila Rivers); the broad river terrace known as Yuma Mesa (fig. 6) was developed later—principally after the end of World War II—when citrus orchards were planted extensively on the favorable sandy soils. The Colorado River has been the source of supply except in the South Gila Valley (fig. 6) and in small areas in the other valleys and on Yuma Mesa, where ground water has been developed by means of wells of generally large capacity. YUMA VALLEY The first irrigation in Yuma Valley (fig. 6) began about 1897. By 1902, four privately owned canal systems were in operation. In 1904, Congress author- ized the Yuma Project, the first Federal irrigation project on the main stem of the Colorado River. At that time more than 10,000 acre-feet of water was being diverted annually from the Colorado River by pumps and gravity for irrigation. However, the supply was very undependable owing to the large fluctuations in stage of the river. Between 1904 and 1912 about 50,000 acre-feet per year was being pumped from the river to irrigate Valley Division (Yuma Valley) lands (fig. 2). In 1912 the Colorado River siphon was completed and thereafter until 1945 water was diverted at Laguna GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H7 117° 116° 115° 114° 113° 112° I \ l l | l o \\ Hoover Dam Lake V w _ 36 — \ ‘ Mead \\ O 4» 46W l @OVzo fig 1 Lake EXPLANA i'lON {Y \ Mohave _ _ _ _ __ _ \ \ Physiographic boundary \ \ Davis Dam \ \i o 25 50 MILES |__l__l__._|—l 35 ° — I “ i l N ’ d1 e€\esD ® \ Lake 81-0, / _ \ O ) Havasu ”moms \—\\ 4/0 lilarker Darn Bill W/fi \ DSanBernardino \—-——\\ I? $ h\\_// \\‘\ 34 ° — ,\ \ '7 x4 \ \ _ g \ \ \ 4/ ‘1' \ f \ \ \ < ., .— Q \ \\ \\ o: PHOENIX 0 Kg! \ O O ‘52: o i ) Q ‘70\ o 0 /® §<\\ L) 6 "I (< \ < a v a — \ ‘71, Imperial/D/aym‘ ) 6"le \ ‘7 ’ C ’ ' gfiSAN DIEGO ALL,AMERICANZ'- A// /4 A f. t' t‘ _ 7 ’ Y rea o inves 1ga ion \ _ __(:_A,I_41_F.91}%‘Ilé= 3r \ U MEXICALI y/ / um” BAJA C . / Sam I" / Luis, R. C. \ % A \ )‘ \ ‘ \RIZO \ \ 801%11’ 32° __ \\ ’90 \ RAT \\ — '6 (I \ \ \\U E k 06’ \\ {£12732 STA T a; ‘8 QQ \ XI% 435; Cg \ m \ v GULF OF \ ‘2. CALIFORNIA 1 l 1 I ‘ I FIGURE 1.—Map of the lower Colorado River region showing location of the Yuma area. Dam (pl. 3), and it flowed by gravity to the lands of the Valley Division of the Yuma Project. Continued irrigation resulted in a rise in ground- water levels and consequent drainage problems; construction of gravity drainage ditches began in 1916. The system generally was expanded to meet drainage problems as they arose. The Main Drain (pl. 3) extending southward down the middle of the valley carries the drainage to the southerly inter- national boundary where the boundary pumping plant (fig. 2) lifts the drainage water 12—15 feet and discharges it into Mexico. H8 WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA 114°45’ 30’ i . 114°15' Wvfl %"”/////"//////4¢//{//1 a 32°45’ — \ / 21113151529345 % mEXICO \\/ \—/ ). lu \I \I T > 3 q’ 0 8 Q >< ‘2' £14 3 n 1 Boundary pumping plant ‘41? so' — Y \ / (”J SONOI‘EA< ~ \\ \ K EXPLANATION \UiVITED ___,74_ ENATE'S A700“ :1 Alluvial escarpment \ \ ~22 Irrigated area 7i: ‘9» \\‘ 1. Reservation Division if" ‘2’ \\ 2' The [Slam Area of shallow bedrock 3‘ North Gm Valley Um't ’ \\\ 4. South Gm Valley Um't \ 5. Y 6. 7. uma Mesa Division Fault Yuma Au-I’ilim‘y PTOJ'ECt Dotted where concealed Valley Division 0 5 10 MILES | l | l l l J Mountains and hills 32°15’ FIGURE 2.—Areas irrigated in 1966. The yearly pumpage of drainage water at the age after 1945 is derived from drainage wells along boundary pumping plant at 5-year intervals is listed the east side of Yuma Valley. The pumpage dis- in the following table. Much of the increased p-ump- charges into the drainage system. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA Drainage water pumped at boundary pumping plant [Amounts rounded to nearest 5,000 acre-feet] Year Amount Year Amount 1920 _______________ 20,000 1945 _______________ 55,000 1925 _______________ 50,000 1950 _______________ 90,000 1930 _______________ 45,000 1955 _______________ 105,000 1935 _______________ 25,000 1960 _______________ 135,000 1940 _______________ 65,000 1965 ________________ 130,000 Between October 1940 and June 1945 diversion of water for the Valley Division lands was shifted from Laguna Dam to Imperial Dam (pl. 3) with its desilting works and thence into the newly completed All-American Canal (fig. 2) from which it was diverted into the Yuma Main Canal (pl. 3). This conveyance plan has remained in effect to the pres- ent time. YUMA MESA , Only a small acreage was irrigated on Yuma Mesa prior to 1923. Then about. 650 acres, an increase of more than 400 acres over that irrigated in 1922, was irrigated by lifting Colorado River water at the B-lift pumping plant (fig. 2) and distributing it to land east of the plant. This development, known as the Yuma Auxiliary Project (fig. 2) , was authorized by Congress in 1917. Records of the acreage irri- gated and the amount of water diverted under this ~ project are shown intable 1. The B-lift pumping TABLE 1.—-Irrigated acreage and water diverted to Yuma. Mesa1 [Diversions in thousands of acre-feet] Yuma Yuma Yuma Mesa Auxnliary Auxiliary division of Total PTOJect Project Gila Project Year Year Diver- Diver- Acres Diver- Acres Diver- Acres sions Acres sions sions sions 1922 ___ 220 1 1943 ___ 1,600 20 200 1 1,800 21 1923 ___ 660 7 1944 ___ 1,500 17 1,000 15 2,500 32 1924 ___ 640 5 1945 ___ 1,550 20 5,100 55 6,650 75 1925 ___ 540 5 1946 ___ 2,100 25 5,500 109 7,600 134 1926 ___ 720 3 1947 ___ 1,950 33 5,900 118 7,850 151 1927 ___ 880 4 1948 ___ 2,050 34 6,300 124 8,350 158 1928 ___ 1,040 6 1949 ___ 2,100 33 6,300 99 8,400 132 1929 ___ 1,160 7 1950 ___ 2,150 31 7,100 104 9,250 135 1930 ___ 1,190 9 1951 ___ 2,150 32 8,200 138 10,350 170 1931 ___ 1,240 8 1952 ___ 2,250 33 10,400 176 12,650 209 1932 ___ 1,260 8 1953 ___ 2,100 32 14,100 195 16,200 227 1933 ___ 1,240 9 1954 ___ 2,350 37 14,200 235 16,550 272 1934 ___ 1,210 10 1955 ___ 2,500 35 14,600 214 17,100 249 1935 ___ 1,220 10 1956 ___ 2,600 37 13,500 196 16,100 233 1936 ___ 1 210 11 1957 ___ 2,850 35 14,700 187 17,550 222 1937 ___ 1 240 12 1958 ___ 2,900 37 14,200 208 17,100 245 1938 ___ 1 260 13 1959 ___ 2,950 41 17,200 230 20,150 271 1939 ___ 1 270 13 1960 ___ 2,950 42 10,900 253 19,850 295 1940 ___. 1 250 14 1961 ___ 3,100 42 16,000 248 19,100 290 1941 ___ 1 250 14 1962 ___ 3,150 45 16,300 282 19,450 327 1942 ___ 1 400 15 1963 ___ 3,150 42 16,600 275 19,750 317 ______________ 1964 ___ 3,200 40 17,100 259 20,300 299 ______________ 1965 -.._ 3,200 36 17,000 229 20,200 265 ______________ 1966 ___ 3,300 39 16,800 236 20,100 275 1 Quantities (rounded) obtained from U.S. Bureau of Reclamation yearly project history reports. plant was abandoned in July 1953 when water be- came available to the project from an extension of the Yuma Mesa Division of the Gila Project. A substantial increase in irrigated acreage fol- lowed the initial development work done under the 507-243 0 - 74 - 2 H9 Yuma Mesa Division of the Gila Project. Under this project water diverted at Imperial Dam into the Gila Gravity Main Canal (pl. 3) is pumped to the mesa at a point about 9 miles east of Yuma. The irrigated acreage increased from about 1,000 acres in 1944 to about 17,000 acres by 1959, after which it stabilized (table 1). Because the project lands generally were about 90 feet above the water table when development began, drainage of these lands was not an immedi- ate problem. However, the drainage of these lands was of early concern to the ranchers and farmers of the Valley Division, who feared that their existing drainage facilities would be overtaxed by any sub- . stantial increase of inflow from the mesa. Conse- quently, they immediately began to improve and augment their drainage system. Additional drain- age wells were drilled near the foot of the mesa escarpment to control the rise of water levels in that area. As a result of this improvement program, very little, if any, land in the valley was lost to agriculture because of waterlogging. Several inves- tigations (p. H16) resulted from the development of the Yuma Mesa Division of the Gila Project (fig. 2). Most of the studies attempted to determine the extent of the adverse effect that the mesa develop— ment had on the valley lands adjacent to the mesa. Complete agreement as to the extent of the effects has not yet been reached. It is generally agreed that two-thirds to three- fourths of the total of more than 5 million acre-feet of water imported for irrigation of mesa land from 1922 through 1966 either went into ground-water storage to build a widespread ground-water mound or induced ground-water movement in the valley lands west and north of the mesa. The distribution of unused irrigation water among these three cate- gories is also controversial. OTHER AREAS The other principal areas where the hydrologic regimen has changed as a result of development are the lands of the Reservation Division, the North Gila Valley Unit of the Yuma Project, and the South Gila Valley Unit of the Gila Project (fig. 2). The Reservation Division of the Yuma Project generally is that part of the Colorado River flood plain lying north of Yuma and on the right side of the river or on the right side of an abandoned chan- nel of the river where the channel formed the west- ern boundary of The Island (fig. 2). Since the early 1900’s the irrigated acreage has ranged from about 5,000 to about 12,000 acres and has averaged about 9,000 acres. About 10,960 acres was irrigated in 1961. H10 A system of drains, begun in 1912, keeps water levels far enough below the land surface to prevent waterlogging. Leakage from the All-American Canal, beginning about 1939, made necessary the construction of additional drains whose principal function was to remove this leakage and discharge it into the river. The North Gila Valley Unit, now a part of the Yuma Mesa Division of the Gila Project, lies along the left side of the Colorado River north of its con— fluence with the Gila River (fig. 2). This unit, too, has had a long history of irrigation with Colorado River water. Since 1955, it has been served from a turnout on the Gila Gravity Main Canal; before that time water was diverted from Laguna Dam. About 6,080 acres was irrigated in 1961. Water levels rose because of irrigation, so new drains were constructed to keep the land from be- coming waterlogged. Leakage from the Gila Gravity Main Canal, which was completed in 1943, added to the drainage problems of the eastern part of the unit. South Gila Valley lies between Yuma and the narrows of the Gila River near Dome (fig. 2). It is bounded on the north by the Colorado and Gila Rivers and on the south by the Yuma Mesa escarp- ment. The South Gila Valley Unit is part of the Yuma Mesa Division of the Gila Project. Until 1965, irrigation was dependent largely upon pumping ground water. An exception was the authorization under the Warren Act of 1947 to divert surface water from the Gila Gravity Main Canal onto about 850 acres adjoining the canal. The first irrigation well in the valley was drilled in 1915. By 1925 about 1,000 acres was being irri— gated with ground water; by 1943 the acreage had increased to about 4,500, and by 1948, to almost 9,000 acres. The irrigated acreage increased at a slower rate through the fifties and the first half of the sixties, In 1955, 9,700 acres reportedly was irri- gated with pumped water. In 1965, surface water from the Colorado River became available to all the unit. Drainage wells were installed at the same time to keep water levels from rising to the point where the agricultural lands would become waterlogged. A substantial quantity of ground water continued to be pumped for irri- gation. In contrast to all the other areas, ground-water levels in the developed part of South Gila Valley declined from the levels of the early 1920’s, which probably represented natural levels, to the levels of 1946 and 1947, which were 10—15 feet lower. About 1947, levels began to rise, probably owing in part WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA to recharge of leakage from the newly completed Gila Gravity Main Canal and in part to lessened outflow to Yuma Mesa because of the growing ground-water mound beneath the mesa. As the ground-water mound continued to grow, the historic southward gradient in South Gila Valley was gradually decreased until in the 1950’s it was reversed and became northward. Waterlogging of lands near the mesa was widespread. In 1961 and 1962, nine large-capacity drainage wells were drilled near the foot of the mesa to reclaim the land that had become waterlogged and to prevent further waterlogging as the result of inflow from the mound beneath Yuma Mesa. The wells were drilled to the base of the coarse gravel zone, which is about 200 feet below land surface. The system was successful and was expanded in later years as the need for more drainage became apparent. Also three supply wells were drilled to depths of about 600 feet to obtain water of better quality which was used to augment the surface supply. MEXICALI VALLEY Irrigation with Colorado River water began in Mexicali Valley (fig. 2) about 1901. In 1915 about 40,000 acres was irrigated out of a total valley area of some 700,000 acres. By 1925 about 200,000 acres was irrigated, but in 1932 the total irrigated area was only 70,000 acres. From this low point the irri- gated area increased to more than 330,000 acres in 1949, and to about 540,000 acres in 1955. Realizing that this amount of land would require water in excess of the 1.5 million acre-feet of Colo- rado River water guaranteed to Mexico annually under the treaty of February 3, 1944, the Mexican Government in late 1955 authorized the drilling of 281 deep wells for augmenting the surface-water supply. In 1957 the Government authorized the drilling of an additional 100 irrigation wells. These wells were in addition to some 230 privately owned irrigation wells which had been drilled by that time. Since 1957, the total number of pumped wells has been limited to 495 upon recommendation of the Ministry of Hydraulic Resources. Notwithstanding the increased pumping for irrigation, the total acre— age irrigated was reduced in the early 1960’s from the 540,000 acres irrigated in 1955 to about 415,000 acres. The early history of pumping for irrigation is not well documented. Most of the wells were drilled by United States interests to furnish a supplemental supply to lands normally irrigated with Colorado River water. As early as 1934 a tract of 800 acres near Algodones (fig. 2), at the northeast corner of GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA Mexicali Valley, was receiving a supplemental sup- ply of ground water. The history of irrigation pumping can be inferred from records of well completions. Of more than 140 logs ‘of private wells drilled in Mexicali Valley by United States drilling firms (made available to the U.S. Geological Survey by Frank E. Leidendeker of Yuma), only the logs of three large-capacity irriga— tion wells showed drilling dates prior to 1950; all the other logs showed drilling dates from 1950 to 1957, inclusive, the latter being the year when the Well-limiting decree was enacted by the Mexican Government. Because these logs represent about half the privately owned irrigation wells in Mexicali Valley, the completion rate of these wells probably is indicative of the completion rate of all the pri- vately owned irrigation wells. If this is true, and if it is further assumed that pumpage was proportional to the number of wells drilled, then from 1930 (the first year of record of a large-capacity irrigation well, drilled by Mr. Lei- dendeker’s firm) until 1950 the annual pumpage for irrigation was small relative to the pumpage from private wells in 1957—‘probab1y ranging from a few thousand acre-feet in 1930 to a few tens of thousands of acre-feet a year by 1950. From 1950 to 1956 the pumpage probably increased at an annual rate of about 25,000 acre-feet to about 200,000 acre-feet annually by 1956. With the begin- ning of pumping from Government wells in 1956, the total pumpage increased to about 300,000 acre- feet annually by the end of 1956. With the installa- tion of additional Government wells, the pumpage more than doubled from 1956 to 1957 , and thereafter continued to increase, so that by 1965 the pumpage amounted to 940,000 acre-feet. (See table below.) [Pumpage (1,000 acre—feet) Calendar year Private Government All Wells wells wells 1956 __________ 200 100 300 1957 __________ 1 180 1 455 635 1958 __________ 1 250 1 310 560 1959 __________ 1 175 1 460 635 1960 __________ 1 230 1 470 700 1961 __________ 1 185 1 680 ,865 1962 __________ ____ ____ 845 1963 __________ ____ ____ 845 1964 _ _________ 225 710 935 1965 __________ 255 685 940 1Figure adjusted on basis of ratios of earlier figures of total pumpage furnished by Mexican Government in 1962 to figures for total pumpage furnished by Mexican Government in 1966. According to Paredes (1963) land irrigated prin- cipally with Colorado River water averaged about 256,000 acres during the period 1961 to 1963, in- clusive; much of the 1.5 million acre-feet per year of surface water guaranteed to Mexico under the 1944 treaty was applied to this acreage. This implies H11 an average annual diversion rate of 5.9 feet (5.9 acre-ft per acre) for surface water. Paredes (1963) further estimated that land designated as being irri- gated principally by water pumped from private wells averaged about 60,000 acres, and that land designated as being irrigated principally by water pumped from Government wells averaged about 100,000 acres. Based on the average total pumpage for each year of the period, the average rate at which pumped water was diverted was 5.3 feet. The average rate of diversion to all the irrigated land (415,000 acres) was 5.6 feet per year for the years 1961 to 1963, inclusive. In 1964, approximately 49,000 acres were irri- gated with water pumped from private wells, and 107,000 acres with water from Government wells; in 1965, figures for these same categories are 54,000 and 100,000 acres, respectively (Eduardo Arguelles and Eduardo Paredes, written commun., 1966). The figures for 1964 and 1965 indicate an average annual rate of pumpage of 4.7 feet from private wells and 6.7 feet from Government wells. A similar lesser rate of pumpage from private wells is‘indi- cated by figures furnished by Paredes (1963); his data suggest that pumpage from private wells in the 3-year period ending December 1963 averaged between 3 and 31/2 feet annually and that pumpage from Government wells averaged more than 61/2 feet annually. The reason for these apparent differences in with- drawal rates is not known. Part of the difference may be due to the fact that a larger percentage of the pumpage from private wells is basically a sup- plemental supply than is the pumpage from Govern- ment wells. Part of the difference also may be due to pumping some water from Government wells into canals and transferring it to other areas to supple- ment supplies on land that is designated as being irrigated principally with surface water. OBJECTIVES OF PRESENT INVESTIGATION AND SCOPE OF REPORT This report is one of a series of chapters of Geo- logical Survey Professional Paper 486, on the water resources of the lower Colorado River-Salton Sea area. The broad objectives of the study of the Yuma area were to (1) define the geology sufficiently to delineate the ground-water reservoir or aquifer sys- tem, ( 2) determine the sources of the ground water and the relations between ground water and surface water, (3) define the hydrologic characteristics (transmissivity and storage coefficient) of the aqui- fer system, (4) determine the movement of ground water in different parts of the area, (5) calculate H12 ground-water budgets for both past and present conditions, and (6) describe the chemical quality of the ground water and relate variations in chemi- cal quality to sources of recharge and to processes of chemical change. The report is divided into two principal sections: The first section describes the geology, with empha- sis on the younger, water-bearing rocks and de- posits; the second section describes the various aspects of the ground-water hydrology enumerated above. The geology is described in somewhat greater detail than usual for a report of this type, because relatively little previous detailed geologic investiga- tion had been done in the area. Basic data consisting of well records, well logs, and chemical analyses of ground water, and detailed descriptions of several pumping tests and of soil-moisture measurements, are given in five appendixes at the end of the report. The investigation, which was under the direction of C. C. McDonald, project hydrologist, was started in 1961 by G. E. Hendrickson and carried on from 1962 to 1968 by the present writers. Other members of the Geological Survey who assisted materially in the investigation were F. J. Frank, G. R. Vaughan, R. H. Westphal, and F. L. Doyle. Geophysical work was done by the Regional Geophysics Branch of the Survey, under the direction of D. R. Mabey. Assist- ance in well logging, sample analysis, and shallow test drilling was provided by the Hydrologic Labora- tory and the Ground-Water Equipment Pool of the Survey, both headquartered at Denver, Colo. METHODS OF INVESTIGATION The study of the geohydrology of the Yuma area included geologic mapping, extensive geophysical exploration and test drilling by the U.S. Geological Survey and the U.S. Bureau of Reclamation, inven- tory of existing wells and well records, quantitative determinations of aquifer characteristics, calcula— tions of ground-water budgets, and determinations of the chemical character and temperature of water in many wells. Major emphasis was placed on study of the Cenozoic deposits, which contain virtually all the ground water of usable quality, and on the delineation of geologic structures that affect the movement of ground water. Toward the end of the investigation, an electrical analog model was con— structed by the Geological Survey which incorpo- rated an idealized geohydrologic framework based on the results of the several types of studies. The various methods of investigation are summarized in the following paragraphs. GEOLOGIC MAPPING The geologic mapping, done chiefly in 1962-65, WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA included detailed coverage of the north-central part of the area: the Laguna Mountains, southeastern Chocolate Mountains, northern Gila Mountains, southeastern Cargo Mruchacho Mountains, and inter- vening piedmont, mesa, and valley areas. Some of this geology is shown on the geologic map of the Laguna Dam 71/2-minute quadrangle (Olmsted, 1972). The Cenozoic geology of the northwestern Gila Mountains and adjacent piedmont area was also studied in detail by F. L. Doyle in 1963. The remainder of the area was covered by a geo- logic reconnaissance, relying heavily on photogeo— logic techniques, with field checks along variously spaced traverses, mostly by vehicle. Reconnaissance of the southeastern part of the area was done chiefly 4ny F. J. Frank; that of the northern part, by F. H. Olmsted. GEOPHYSICAL EXPLORATION Geophysical surveys were made beginning in 1963 and continuing into 1967 to obtain subsurface in- formation in support of the geohydrologic investiga- tion. The work, which was done by the Regional Geophysics Branch of the U.S. Geological Survey under the direction of D. R. Mabey, included: (1) a gravity survey of about 900 square miles (most of the area shown on plates 3 and 9), (2) an aeromag- netic survey of an area of about 300 square miles in Yuma Valley and western Yuma Mesa, (3) nine seismic-refraction profiles in the northern part of the area, and (4) 14 resistivity profiles and lines of electrical soundings at several places throughout the area. In addition, four seismic-reflection profiles were made by a commercial firm under contract to the U.S. Bureau of Reclamation. The gravity and magnetic surveys furnished valu- able information about the gross distribution and thickness of the Cenozoic sediments forming the ground-water reservoir. The seismic and resistivity surveys yielded more detailed information on the thickness and structure of sediments along local profiles. Many of the interpretations of the geology in this report are based in part on the geophysical data. TEST DRILLING Test drilling by the U.S. Geological Survey and the U.S. Bureau of Reclamation provided the pri- mary basis for the interpretation of the subsurface geology and hydrology. For shallow-depth informa- tion, 134 test holes were bored with a truck- mounted power auger to depths ranging from 4 feet to more than 200 feet (fig. 3). Most of these test holes were completed as observation wells with 11/4- inch or 11/2-inch pipes fitted with well points. Simi- lar shallow wells were installed in the 1940’s and GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H13 FIGURE 3.—Boring a test well with a power auger, 31/2 miles south of Somerton, Ariz. later by the US. Bureau of Reclamation, particu- larly on Yuma Mesa, where few other well data were available. In addition, more than 100 wells were installed by the Yuma County Water Users’ Associa- tion in the 1950’s by jetting pipes into the upper part of the coarse-gravel zone in Yuma Valley. Deeper test drilling was done by private contrac- tors for the US. Geological Survey (fig. 4) and the US. Bureau of Reclamation and by Bureau equip- ment. Twelve US. Geological Survey test wells were drilled to depths ranging from 328 to 2,946 feet; one private well and one US. Bureau of Reclama- tion test well were deepened for additional informa- tion. The US. Bureau of Reclamation drilled or had drilled about 70 test wells from 1957 to 1967. Depths of these wells range from 64 to 1,427 feet. All these test wells were drilled by either the percussion (cable-tool) method or the mud-rotary method; drill cuttings and a few cores were collected for study; and most of the wells were logged by various Wire- line-logging methods. Ten of the US. Geological Survey test wells and several of the US. Bureau of Reclamation test wells were test pumped for infor- - mation about transmissivity of the materials and chemical quality and temperature of the water. STUDIES OF FORMATION SAMPLES In addition to megascopic identification of well cuttings made during drilling, several kinds of laboratory analyses of formation samples were made. Heavy-mineral analyses of alluvial sands and H14 WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA FIGURE 4.-——-Drilling of test well LCRP 26 with mud-rotary equipment 1% miles West of Winterhaven, Calif. X-ray diffraction analyses of clays were made by the Hydrologic Laboratory of the Geological Survey in Denver, Colo. Grain-size analyses were made of samples from several of its test wells by the Bureau of Reclamation. Pebble counts and studies of gen- eral lithology of alluvial sands and gravels and a few petrographic studies of older rocks were made by the Geological Survey in Yuma. Also, cuttings from several oil—test wells were examined at the Arizona Bureau of Mines office in Tucson, Ariz., by F. J. Frank and F. H. Olmsted. Paleontological studies of cuttings from marine deposits were made by Mrs. P. B. Smith, Branch of Paleontology and Stratigraphy of the US. Geological Survey, in Menlo Park, Calif. VVIRELINE LOGGING Wireline logs were used extensively to supplement and refine the information obtained from drillers’ logs, geologists’ logs, and sample studies. Logs were made of most of the test wells and also of as many private wells and drainage Wells as possible. The logs included the following types: Gamma-ray (natural gamma radiation), electric (resistivity and spontaneous potential), temperature, fluid- resistivity, caliper, contact-caliper (microresistivity— caliper), dip, and sonic (acoustic—velocity). Logging was done by three commercial logging companies and by the US. Geological Survey and the US. Bureau of Reclamation. INVENTORY OF EXISTING WELLS AND WELL RECORDS The bulk of the geologic and hydrologic informa- tion about the upper water-yielding zones was pro- vided by records of existing water wells, test wells, and observation wells. These data included descrip- tions of the wells and their locations, logs, produc- tion figures (pumping rates and drawdowns), chemical quality and temperature of the water, and water—level records. Many of these data were db- tained from files of the US. Bureau of Reclamation, irrigation districts, and other government agencies; other information was obtained from drillers and private individuals during a field canvass of the area. All wells except for a few that had been destroyed were inventoried in the field and their locations plotted on the latest Geological Survey GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA topographic maps. The information thus obtained is summarized in appendix A, tables 16—20; the locations of the wells are shown on plates 13—17. QUANTITATIVE DETERMINATIONS OF AQUIFER CHARACTERISTICS Transmissivity at specific sites was computed on the basis of results of short-term pumping tests of practically all the large-capacity wells in the area. The tests of private wells commonly were limited to observing rates of change of water level during and after pumping periods and to determining spe- cific capacity (yield per unit of waterlevel draw- down). Collection of data was limited to the pumped well because satisfactory observation wells were not available. Observation wells were utilized, however, for a few of the large drainage wells owned by the US. Bureau of Reclamation or the Yuma County Water Users’ Association. Step-drawdown and recovery tests were made for all the US Geological Survey test wells that were pumped, for several US Bureau of Reclamation drainage wells, and for a few newly drilled private irrigation wells. In addition to the tests made dur- ing the present investigation, previous pumping tests by others were utilized. Especially helpful were pumping tests made by the US. Bureau of Reclama— tion and by the Yuma County Water Users’ Associa- tion (Jacob, 1960). Where pumping-test data were lacking, transmissivity was computed on the basis of specific capacity or of lithologic logs. Storage coefl‘icients were determined on the basis of soil moisture as indicated by a neutron probe. Soil-moisture profiles which commonly included both the zone of aeration and the zone of saturation were obtained at some 30 sites. None of the pumping tests during the present investigation provided useful data for computing long-term storage coefiicients. As with transmissivity values, the work of earlier investigators was utilized in estimating storage co- efficients. Studies by Jacob (1960) were used as a basis for estimating storage coeflicients under arte- sian conditions; these studies were also the basis for estimating values for vertical hydraulic conductiv- ity and leakage (leakance as defined by Jacob). CHEMICAL ANALYSES OF GROUND-VVATER SAMPLES Variations in the chemical quality of the ground water were determined primarily by comparisons of analyses of samples obtained during the present in- vestigation; only a few earlier analyses assembled from other sources were used. Samples of water were collected from existing wells equipped with turbine pumps; from test wells by bailing, airlift H15 pumping, or pumping by turbine; and from unused wells and observation wells by airlift pumping, bail- ing, or sampling with a thief sampler. Many of the wells were sampled several times in order to deter- mine chemical changes occurring with the passage of time. Most of the chemical analyses listed in the present report (appendix C) made in a field laboratory at Yuma, using rapid analytical methods. A few analy- ses were made in the US Geological Survey’s per- manent water-quality laboratory at Albuquerque, N. Mex., using customary procedures. Most of the earlier analyses were obtained from the files or publications of the US. Geological Survey, the US. Bureau of Reclamation, other Federal or State agencies, or individuals. Some of these analyses were recomputed from originally reported values in order to agree with the format of the US. Geological Survey analyses. The analytical data were supplemented by field observations made with a conductivity meter and by electric logs of test holes. MEASUREMENTS OF GROUND-WATER TEMPERATURE Temperature of ground water was among the data collected in the routine inventory of well informa- tion. After the study was underway, it became ap- parent that water temperatures furnished useful evidence on the sources and movement of the ground water and the nature of the geologic framework through which it moves. Accordingly, a special study was made of vertical, and particularly areal, varia- tions in temperature, using thermistors as well as maximum thermometers and a standard mercury thermometer. ANALOG-MODEL STUDIES Two electrical analog models of the hydrologic system of the delta region (including both the Yuma area and the part of Mexicali Valley where much ground water is pumped for irrigation) were con- structed. The first model, begun in 1964, was a rela- tively simple simulation of the hydrologic system. In 1966 it was replaced by a more complex model which took into account the barrier effect of a fault (Algodones fault) that was not recognized as a barrier to ground-water movement when the first model was built. The second model not only repro- duces in generalized form the present and past hydrologic conditions but can be used to predict fu- ture changes in directions and rates of ground-water movement and changes in water level under various assumed schemes of ground-water development. H16 EARLIER INVESTIGATIONS GEOLOGIC STUDIES Previous geologic studies of the Yuma area con- sisted primarily of regional geologic reconnaissances by Wilson (1933; 1960) in Arizona and by Morton (1962) in California; more detailed studies of smaller areas such as the study of the Cargo Mu- chacho Mountains by Henshaw (1942) , or of special problems such as the origin of the “Algodones Dunes” by Norris and Norris (1961) and McCoy, Nokleberg, and Norris (1967) ; and geophysical studies such as those by Biehler, Kovach, and Allen (1964) in the Salton Trough, and of private oil companies (un‘pulb. data) in Yuma Valley and adja— cent parts of Yuma Mesa in connection with wildcat drilling in search for oil or gas. The earlier geologic study having the most direct application to ground- water geology, or geohydrology, is that by R. H. Brown and others (1956). In a sense, the present report updates and expands the work of Brown and others (1956) , although some of their geologic inter- pretations are modified substantially herein. In addition to the reports and data cited above, many papers have dealt with the general region that includes the Yuma area, or have discussed problems that relate to certain aspects of the local geology. Among these are papers describing the geology and geomorphic features of the Salton Trough by J. S. Brown (1920, 1923), Knifi'en (1932), MacDougal and others (1914) (a particularly exhaustive treat- ment), McKee (1939), and Sykes (1914, 1937). Reports describing the sediments of the Colorado River delta include those by Merriam (1965), Merriam and Bandy (1965) , and van Andel (1964). The geologic history of the lower Colorado River has long been a subject of much interest and specu- lation. A few of the papers discussing this problem are those by Longwell (1946, 1954), Lovejoy (1963b), Cooley and Davidson (1963), and McKee, Hamblin, and Damon (1968). Other papers describing previous work are cite-d in the section on geology and are listed in the bibli— ography. HYDROLOGIC STUDIES Most of the hydrologic studies have been made for or by agencies concerned with the management or use of water. The US. Bureau of Reclamation not only has collected a large amount of hydrologic data during the years but has made many hydrologic studies to appraise the results of its management practices and the probable results of proposed changes in these practices. The US. Bureau of Reclamation report by Sweet (1952), the report on on the water supply of the Lower Colorado River WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA basin (US. Bureau Reclamation, 1953), and the report on the Lower Colorado River water salvage and phreat‘ophyte control (US. Bureau Reclama- tion, 1963) were eSpecially helpful in the present study. In 1956, the US. Geological Survey, as a result of a recommendation from the Assistant Commis- sioner of Reclamation to the Secretary of the In- terior, reviewed the problem of high water levels in Yuma Valley and studied the need for additional information to define and control the problem. The results of that study were reported by R. H. Brown and others (1956). As a result of the preceding study, in September 1956 the Secretary of the Interior entered into a contract with the consulting firm of Tipton and Kalmbach, Inc., and C. E. Jacob, consultant, which called for an investigation of the ground-water and drainage conditions in the Yuma Valley and a study of the relation between these conditions and the irrigation on Yuma Mesa. The report of this inves- tigation (Tipton and Kalmbach, Inc., and Jacob, 1956) was the first attempt to estimate quantitar ively the underground flow of water from the Yuma Mesa to the adjacent flood plains. In 1960, C. E. Jacob, consultant, completed a study for the Yuma County Water Users’ Associa- tion (Jacob, 1960) for the purpose of obtaining a more accurate inventory of water use on Yuma Mesa and in Yuma Valley and to better evaluate aquifer characteristics. . In 1966, C. E. Jacob, at the request of the Com- missioner, United States Section, International Boundary and Water Commission, made additional studies of the ground-water regimen of the Yuma area, which included estimates of the flow of ground water across international boundaries (Jacob, 1966) . ACKNOWLEDGMENTS Many agencies, groups, and individuals provided substantial assistance to the US. Geological Survey in the present investigation. The US. Bureau of Reclamation, Yuma Projects Ofiice, furnished in— formation from its files, did exploratory drilling, contributed financial assistance toward the construc- tion of an electrical analog model, financed two reflection seismic surveys, and worked closely with the writers in all phases of the investigation. Both the United States Section and the Mexican Section of the International Boundary and Water Commis- sion gave freely of information from their files and of their general knowledge of the area. The United States Section also provided funds to assist in the construction of the analog model. The Yuma County Water Users’ Association furnished valuable infor- GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA mation from its files, such as well logs and water- level records, and the results of hydrologic studies. Several water-well drilling companies and drillers, notably Hamilton and Hood, Arizona Machine and Welding Works, Frank H. Leidendeker, and L. P. Cromer, provided well logs and other pertinent in- formation. Many farmers and other landowners gen- erously permitted access to their lands and wells, furnished various kinds of information, and cooper- ated in the scheduling of pumping tests. Information such as pumping-test data, well logs, chemical data, and geophysical data was made available from pri- vate consultants, including C. E. Jacob and Asso- ciates, General Atomic Division of General Dynamics Corp, S. F. Turner and Associates, and Water De- velopment Corp. Radiometric dating of several rock samples was done by the Geochemistry and Petrol- ogy Branch of the U.S. Geological Survey; Geochron Laboratories, Inc., of Cambridge, Mass; and the Geochronology Laboratories of the University of Arizona. WELL-NUMBERING SYSTEMS The well-numbering systems used in this report are based 0n the rectangular system of land sub- division used by the U.S. Bureau of Land Manage- ment. Two systems are used because part of the Yuma area is in California and part is in Arizona. In the Arizona system, the wells are assigned numbers according to their locations in the land survey based on the Gila and Salt River base line and meridian which divide the State into four quad- rants. For assignment of well numbers these quad- rants are designated counterclockwise by the capital letters A, B, C, and D; the letter A being the northeast quadrant. All wells in the Yuma area are in the southwest quadrant—the C quadrant. For example, the first well inventoried in the NEI/LNEMLSWML sec. 35, T. 8 S., R. 22 W., is given the number (0—8—22) 35caa1. The part of the well number in parentheses indicates the township and range in the southwest quadrant (T. 8 S., R. 22 W.) , the digits following the parentheses indicate the section (sec. 35), and the lowercase letters indicate the location within the section (fig. 5, graph A). The first letter (c) indicates the 160-acre tract (SW14 sec.), the second (a) the 40-acre tract (NElflLSWlAL sec.), and the third (a) the 10-acre tract (NE1/4NE14SW14 sec.). These tracts. are designated counterclockwise beginning in the north- east quarter (fig. 5, graph A). Where more than one well is inventoried within a 10-acre tract, the wells are distinguished by adding consecutive num- bers beginning with 1 after the lowercase letters. H17 In the California system, the wells are assigned numbers according to their locations in the land survey based on the San Bernardino base line and meridian. A modification of the system used by the California Department of Water Resources and by the California District of the Water Resources Divi- sion of the US. Geological Survey is employed in which the 40-acre tracts are further subdivided into 10-acre and 21/2-acre tracts. For example, the sec- ond well inventoried in the NE%SW%SW%,NE14 sec. 29, T. 16 S., R. 22 E., is given the number 16S/22E—29Gca2. The part of the well number pre- ceding the slash (168) indicates the township (T. 16 S.); the number following the slash indicates the range (R. 22 E.); the digits following the en dash indicate the section (sec. 29); the letter (G) following the section number indicates the 40-acre tract within the section (SW%NE%); and the lowercase letters (ca) indicate the 10-acre and 21/2- acre tracts (NE 1/4SW14) according to a subdivision similar to that used in the Arizona system (fig. 5, graph B). Within each 2%-acre tract, the wells are numbered consecutively starting with 1. A small area in Arizona west of Yuma and south of the Colorado River is subdivided according to the California system. Also, in The Island area north of Yuma, the California system is used in part of what is now Arizona, and the Arizona system is used in part of what is now California. In all these areas, State boundaries have been changed since they were originally established. In addition to the US. land-net well-location sys- tems just described, the location of each well is described according to a system of grid coordinates used by the US. Bureau of Reclamation. The Bureau of Reclamation coordinates are based on a zero point located at the Southern Pacific Co. railroad bridge across the Colorado River at Yuma. The grid utilizes section lines of the US. Bureau of Land Management net as mileage increments north or south and east or west of the zero point. For exam- ple, well (C—8—22)35caa1 has the coordinates 21/2S— 71/2E, which indicate that the well is half a mile south of the section line approximately 2 miles south of the zero point and half a mile east of the section line approximately 7 miles east of the zero point (fig. 5). Coordinates for each well are given to the nearest one-sixteenth of a mile, as measured on the 1:24,000-scale 71/2—minute series quadrangles of the US. Geological Survey published from 1955 to 1965. In some places these coordinates differ slightly from those assigned earlier by the US. Bureau of Reclamation using approximate locations shown on older maps. H18 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA Coordinates according 8E to U.S. Bureau of 7E 23 I I b I a b I sires Wag c I d c I bf a b + secui fig, c d c b a b O I I ACCIFA I +s ~—+—v—+~f—+&+—— +44 I I Am; I I + Q) Q. I 0) m?[ o. I D. 0' O U 0 0' I 0 —_+_+_+-}—+—+w+—— 25 Reclamation grid i a I b I a system r-+e+—— I d I c I d +—+—+—— IaIbIa ACAZJF:_dV—d_fi Well: (0—8—22) 35caa1 Coordinates: 21/28. -71/2E. I“I*i‘ “ i i I I’+ l I l b a b a b I a I b I a ——r— —Ie eIe ~+—— c I d c I d c l d I c i d 33 I L I | I 38 7E T. 8 8., R. 22 W., sec. 35 8E A. Arizona well-numbering system Coordinates according to U.S. Bureau of 4W 3W Reclamation grid IN I I I system | l I D I C I B I A I I I iiiii +,7_7+_7_i+_i,__s I I I I I I E I F I Well. I H I I I ‘ ##### —jLL!Yi—T#—il—T#—i—— 40-acretractG | l I M I L I K I J Well: 168/22E—29 I I ‘ Coordinates: O5/aN.-3%W. _____ T~#_i+mi_vet_ig_ie I | N I P I Q I R I I I O I l I 0 4w T. 16., R. 22 E., sec. 29 3W B. California well-numbering system FIGURE 6.—Subdivision of land-net sections for assignment of well numbers and locations of wells by grid coordinates. GEOLOGY GEOMORPHOLOGY REGIONAL SETTING The Yuma area includes the upstream part of the delta of the Colorado River, near the downstream end of the Colorado River basin, within the United States. The northeastern part of the area lies within the Sonoran Desert section, the southwestern part Within the Salton Trough section of the Basin and Range province, according to the widely adopted GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA physiographic (geomorphic) classification of Fen- neman (1931, 1946). (See fig. 1.) The Sonoran Desert east of Yuma is character- ized by generally elongate, low, rugged mountains separated by much more extensive desert plains. Many of the mountains trend about north-northwest (N. 20°—40° W.). The Colorado River flows across the region in an alternating series of narrow valleys or canyons through the mountains and much broader alluvial valleys through the desert plains. The Gila River, which is the principal southern tributary of the Colorado River, flows generally west-southwest across the mountains and desert plains of the Sonoran Desert to join the Colorado just east of Yuma. The southernmost valley in the Yuma area, Yuma Valley, merges with Mexicali Valley on the west and southwest, the latter broadens southwestward to form the present delta plain of the Colorado River. The delta plain, and some of the low—lying desert plains to the east, lie Within the Salton Trough, a northwestward lowland extension of the Gulf of California (fig. 1). The lowest part of the trough is occupied by Salton Sea, a large saline lake, the surface of which was about 232 feet below mean sea level in 1968. The northeast boundary of the Salton Trough section, where it'adjoins the Sonoran Desert section, is rather vague geomorphic- ally but may be considered structurally as being formed by the Algodones fault, the major fault of the San Andreas system in the Yuma area. The Salton Trough is bordered on the southwest by the Lower California (or Lower Californian) province (Fenneman, 1931, 1946). CLASSIFICATION OF LANDFORMS Apart from the regional geomorphic classification of Fenneman (1931) just described, the landforms 0f the Yuma area are divided in this report into seven major types: (1)mountains and hills, (2) dis- sected old river deposits, (3) dissected piedmont slopes, (4) undissected piedmont slopes, (5) river terraces and mesas, (6) sand dunes, and (7) river valleys. Each landform type occurs in several sub- areas shown on the geomorphic map (fig. 6) ; a few subareas include more than one type of landform. Several subareas have no formal geographic desig- nation and are given informal names from some geographic feature; these informal names are desig- nated by quotation marks. The term “mesa” has been given to some of the terraces, and to other surfaces—some terraced, some not—which stand a few feet to several tens of feet above adjacent valleys and plains. Other subareas have been called H19 “plains,” and still another, “desert.” This local usage is carried on in the assignment of informal names to some of the subareas; the terms have no geo- morphic significance. Several subareas beyond the limits of the principal geohydrologic study were not investigated in detail, and their landforms are described only briefly. MOUNTAINS AND HILLS The mountains and hills are composed of the older, more consolidated rocks of the region—rocks of Tertiary and pre-Tertiary age. The higher, more rugged parts of the ranges consist of dense pre- Tertiary crystalline rocks, or, in places, of hard volcanic rocks of Tertiary age. The lower, more rounded hills are exposures of less consolidated vol- canic and nonmarine sedimentary rocks of Tertiary age. Where the mountains are composed of hard crys- talline rocks, the topographic contrast between the mountains and the adjacent desert plains and river valleys generally is abrupt. Slopes of the hard-rock exposures are governed by joints and other physical characteristics of the rocks and are ordinarily much steeper than the slopes in the adjacent unconsoli- dated deposits of the plains and valleys. Slopes in exposures of metamorphic and plutonic rocks aver- age about 1,000 feet per mile (11°) and locally exceed 4,000 feet per mile (37°). Geophysical data indicate that many buried surfaces of the crystalline rocks are equally steep. Some exposures of hard volcanic rocks—lava flows and beds of welded tuff—are even more rugged than those of the crys- talline rocks; nearly vertical cliffs several hundred feet in height occur at several places in the volcanic rocks of. the Chocolate and Muggins Mountains. In contrast, the exposures of slightly to moder- ately consolidated nonmarine sedimentary rocks and volcanic rocks of Tertiary age are dissected or rounded hills of comparatively gentle slope. Instead of the sharp break in slope characteristic of the margins of the hard-volcanic-rock and crystalline- rock masses, a gradual transition from foothills to piedmont plains occurs Where semiconsolidated non- marine sedimentary rocks or soft volcanic rocks (tut-f and ash) border unconsolidated alluvial de- posits. Local relief in exposures of Tertiary sedi- mentary rocks or soft volcanic rocks rarely exceeds 400 feet, whereas that in exposures of crystalline rocks or hard volanic rocks commonly is 1,000 feet or more. The principal chain of mountains in the Yuma area comprises the Chocolate, Laguna, Gila, Butler, and Tinajas Altas Mountains (fig. 6). This chain WATER RESOURCES H20 115°OO’ 33°00' 45’ CALIFORN K \ ____—.. ,‘ BAJA CALIFORNlA . ' ......... Niel/SQ” 3.2. .:.: :.'YUM% 30' %. :31’:-:~:-:~. : 3:936:33; ~~\ ............... \\ «"5: >\~ . ~\- EXPLANATION Dissected piedmont slopes River valleys Sand dunes Dissected old river deposits River terraces and mesas Mountains and hills L...? OF LOWER COLORADO RIVER—SALTON SEA AREA ”14°OO’ Undissected piedmont slopes 32°15’ FIGURE 6.—Geomorphic map of the Yuma area. trends about N. 35° W.—roughly parallel with sev- eral other ranges in the Sonoran Desert farther east and forms the northeastern bedrock border of the area of the main geohydrologic investigation. The Chocolate Mountains, structurally and topo- graphically the most complex of the chain, are largely a series of southwestward-tilted fault blocks of exposed Tertiary volcanic rocks. The higher ridges, which reach altitudes of 1,500 feet in the southwest part, are capped by flows of basaltic ande- site or basalt (fig. 7) ; farther east, the lower ridges are of predominantly more silicic pyroclastic rocks. Exposures of pre-Tertiary crystalline rocks, not as extensive as in most of the other mountains of the Yuma area, are relatively low and are chiefly near the southeast end of the mountains, adjacent to Laguna and Imperial Dams. In some of the lower parts of the Chocolate Mountains, dissected hills composed of semiconsolidated sedimentary or vol- canic rocks of Tertiary age merge on one side with more rugged exposures of hard volcanic or crystal- line rocks, and on the other side, with more gently dissected exposures of late Tertiary and Quaternary alluvial deposits. The Laguna Mountains occupy a roughly equidi- mensional area about 6 miles across lying between the Colorado and Gila Rivers. The rugged northern and eastern parts of the mountains are underlain by pre-Tertiary crystalline rocks. The rest of the exposures are chiefly semiconsolidated, coarse— GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA / FIGURE 7.-—-Westward view of a ridge in the southeastern Chocolate Mountains, Calif. The ridge on the skyline is composed of pre-Tertiary cry- stalline rocks and Tertiary nonmarine conglomerate and breccia, capped by dark basaltic andesite or basalt. Surfaces in foreground and mid- dle distance are underlain by piedmont gravel deposits of local origin. grained nonmarine sedimentary rocks of Tertiary age. Sugarloaf, a volcanic knob near the west mar- gin of the mountains about 2 miles south of Laguna Dam, rises to an altitude of 668 feet; the highest point in the eastern exposures of crystalline rocks is the summit designated as Gila City, 1,080 feet above sea level. The drainage pattern of the Laguna Mountains is roughly radial. The northwestward-trending ridges characteristic of the Chocolate Mountains to the northwest are absent. Along the southwest mar- gin of the Laguna Mountains, the dissected hills underlain by Tertiary nonmarine sedimentary rocks are flanked by only slightly less dissected exposures of gravelly alluvium of local origin, which in turn are bordered by southwestward-sloping alluvial terraces. The Gila Mountains are fairly straight and elongate, trend north-northwest, and are about 27 miles long by 2—7 miles Wide. Toward the south, the mountains divide into two ridges about 5 miles apart; farther south, the eastern ridge becomes the Tinajas Altas Mountains, and the western ridge (Vapoki Ridge) becomes the Butler Mountains (fig. 6). The Gila Mountains contain some of the most rugged topography in the Yuma area. Only at the north end, and in a small area west of Telegraph H22 Pass, are there significant exposures of Tertiary nonmarine sedimentary rocks with their character- istic smoothly dissected hilly outcrOp forms; the bulk of the range consists of much steeper, more jagged exposures of pre-Tertiary crystalline rocks (gneiss, schist, and granitic rocks). Local relief is greater than 2,000 feet in the southeastern part of the mountains, which attain a maximum altitude of 3,150 feet above sea level. The central and north- western parts of the range are not as high; the highest summits are about 2,700 feet in the central part, south of Telegraph Pass, and 1,500—1,700 feet northwest of Telegraph Pass. The Butler Mountains consist of low ridges of pre-Tertiary crystalline rock (granite). The granite outcrops are crudely linear in plan, and oriented about N. 30°—-50° W. They are nearly buried by rock waste (local alluvium) that forms the pied- mont slope along the southwest flank of the Tinajas Altas Mountains to the east (Davis Plain). The ridges rise to a maximum of only 400 feet above the plain, but their slopes are as steep as most of the slopes in the higher mountains to the north and east. The Tinajas Altas Mountains are separated from the southeastern Gila Mountains by a low alluvium- filled gap known as Cipriano Pass. The highest peak has an altitude of 2,764 feet above sea level—about 1,700 feet above the adjacent desert plains. Except for Raven Butte, the mountains are composed en- tirely of buff-weathering, light-gray granite—the same as that in the Butler Mountains and the south- ern Gila Mountains. Raven Butte, near the north end of the mountains on their east flank, is a double- crested mass of nearly black basalt or basaltic ande- site, crudely pentagonal in plan, about 1 mile in diameter, and rising about 700 feet above the Lechuguilla Desert. The Tinajas Altas Mountains derive their name, Spanish for High Tanks, from the natural tanks near the east base of the mountains. The tanks, which are plunge pools beneath usually dry water- falls or cascades, have provided water to wildlife, and also to men traveling the historic Camino del Diablo (Devils Road) into Mexico. Southwest of the mountain chain just described is another, more crudely alined chain 0f mountains and hills comprising the Cargo Muchacho Moun- tains, Ogilby Hills, Pilot Knob, “Yuma Hills,” and “Boundary Hills.” The last two groups of hills are nearly buried by alluvium, and an intervening crys- talline-rock mass beneath Yuma Mesa is completely buried. The hills and mountains in this chain not only are less well alined than the mountains to the WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA northeast, they are also separated by substantial gaps in which the alluvial fill attains thicknesses ranging from 1,000 to more than 2,000 feet. Except for the Cargo Muchacho Mountains, they are gen- erally lower than the mountains to the northeast. The Cargo Muchacho Mountains are an irregular, deeply embayed mass about 10 miles long in a northwest direction by about 6 miles wide. Granitic rocks predominate, but there are sizable exposures of metamorphic rocks and associated dikes in the northern and western parts of the mountains. Sev- eral small hills, some of which are capped by basalt or basaltic andesite, lie as much as 2 miles beyond the margins of the main mass. The terrain in the main part of the mountains is rugged, like that in exposures of similar rocks elsewhere in the Yuma area. Highest altitudes are 2,100—2,200 feet—about 1,200 feet above the desert plains at the foot of the mountains. The northeastern part is generally much lower and less rugged than the rest of the moun- tains; the highest summits in that area are less than 1,200 feet above sea level and some of the intervening bedrock exposures are nearly reduced to pediments. Two small hill masses 1 to 2 miles south of the Cargo Muchacho Mountains are named the Ogilby Hills from the former settlement of that name on the Southern Pacific Railroad about 2 miles west of the hills. The hills are composed of pre-Tertiary crystalline rocks, capped by basalt or basaltic ande- site which forms extensive talus on the slopes. Pilot Knob, so named because of its use as a land- mark during early steamboat navigation on the lower Colorado River, is a low but rugged hill of pre-Tertiary crystalline rocks (chiefly gneiss) rising to an altitude of nearly 900 feet—600—750 feet above the adjacent valleys and desert plains. “Yuma Hills” is the informal designation applied to a chain of low hills or knobs of pre-Tertiary and Tertiary rocks in and adjacent to Yuma. The Colo- rado River flows between the northernmost two hills, which are exposures of granite fanglomerate and breccia. of Tertiary age (fig. 12). The remaining six outcrops to the south all are coarse-textured porphyritic granite or quartz monzonite similar to that occurring as detritus in the fanglomerate and breccia. The outcrops of granite are about a mile apart and are alined N. 20° W.—roughly parallel with the Gila Mountains to the east. The two hills of fanglomerate are slightly east of the axis of this trend. All the hills are the summits of a nearly buried ridge which is almost completely engulfed by the alluvium of the Colorado and Gila Rivers. The southernmost highest hill is about 320 feet above GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA sea level and 120 feet above Yuma Mesa; the north- ernmost granite outcrop, known as Sierra Prieta, rises to nearly 300 feet above sea level—160 feet above South Gila Valley to the east and 100 feet above Yuma Mesa to the west. The seemingly anomalous present position of the Colorado River between the northern two outcrops of Tertiary fanglomerate and breccia probably re- sults from superposition from a higher level, per- haps at a time when the flood plain was the present Yuma Mesa. At that time, the hills of Tertiary rock much have been buried or nearly so. The river pre- sumably exhumed these older rocks as it cut into this old flood plain, then backfilled to its present level. At other times as the river cut down, it flowed north of its present course; young river deposits extend from the northernmost hill of Tertiary rocks about 3% miles northward to the edge of the flood plain (“Bard Valley”). The “Boundary Hills” consist of a northwest- trending small chain of outcrops of pre-Tertiary crystalline rock (.porphyritic granite or quartz mon- zonite) near the southerly international boundary. Like the “Yuma Hills,” these low hills are the tops of a nearly buried ridge projecting only about 100 feet above the adjacent desert plains. The northern- most and largest of the hills attains an altitude of 529 feet above sea level just north of the interna- tional boundary; the other hills are in Mexico. East of the area of principal investigation are the Middle and Muggins Mountains and the Wellton Hills. The Middle Mountains are underlain chiefly by volcanic rocks and are low, rising to a maximum of about 500 feet above the adjacent desert plains. The Muggins Mountains, a notable exception to the nar- row, elongate, north-northwest-trending ranges in the southwest part of the Sonoran Desert (fig. 6), are underlain by pre-Tertiary crystalline rocks, hard volcanic rocks (Tertiary?), and nonmarine sedi- mentary rocks of Tertiary age. The Wellton Hills are a small group of northwestward-trending ridges of gneiss several miles east of the Gila Mountains, rising a maximum of 600 feet above the Lechu- guilla Desert. DISSECTED OLD RIVER DEPOSITS Somewhat dissected exposures of predominantly old river alluvium are represented by “Upper Mesa,” “Proving Ground Dome,” and the central part of “Laguna Mesa” (fig. 6). The old river de- posits are at many places blanketed with thin re- worked deposits left by local ephemeral streams. The informally named “Upper Mesa,” a generally westward-sloping area between Yuma Mesa and the H23 piedmont surfaces at the west base of the Gila Mountains, is the largest area of dissected old river deposits. The materials underlying “Upper Mesa” are composed of older alluvium of the Colorado and Gila Rivers and admixed alluvium of local origin. Near the land surface at many places are reworked materials deposited by local runoff after heavy storms and modified by wind erosion and deposition. A poorly formed desert pavement is preserved on remnants of some of the older river-formed surfaces but is lacking in most of the mesa. Parts of the mesa lie above intervening broad, shallow, stream- cut depressions, which are mantled with thin de- posits of Windblown sand and sheet-wash sand and gravel. The general westward slope of the land surface is interrupted by a northeast-facing escarpment 50—60 feet in height which traverses “Upper Mesa” from “Fortuna Dunes” on the southeast to the edge of Yuma Mesa on the northwest (pl. 1). Southwest of the escarpment the slope of the dissected surface is about 40 feet per mile toward the west-south— west— somewhat steeper than the average slope of the land surface northeast of the escarpment, which is about 30 feet per mile. The drainage from the east is diverted toward the northwest along the foot of the escarpment—an obviously anomalous direction for the mesa as a Whole. This unique feature is the trace of the Algodones fault, described in a later section (p. H61), an important member of the well— known San Andreas fault system. “Proving Ground Dome,” partly enclosed within the southern part of “Middle Mountains Plain” in the northeastern part of the Yuma area, is a low dome-shaped hill, roughly ellipsoidal in plan, about 41/2 miles long by 2 miles wide. The summit of the hill is 562 feet above sea level, about 100 feet above “Middle Mountains Plain.” “Proving Ground Dome” probably is primarily an erosional feature, a rem— nant of once more extensive Colorado River allu- vium which filled the area to a level somewhat higher than the present summit of the dome. (The altitude and form of the dome may result in part from warping, however.) The dome is similar in origin and form to classic desert domes (for example, see Sharp, 1957); but, unlike most desert domes, it is formed on unconsolidated sand, silt, and gravel, rather than on conSolidated rocks. Desert pavement, like that on adjacent “Middle Mountains Plain,” is absent; instead, a thin colluvium of pebbly sand and silt and eolian sand blankets most of the dome. “Laguna Mesa,” which is south of “Proving Ground Dome,” also includes dissected exposures of old river deposits. The mesa is a broad arch sloping H24 westward toward the Colorado River flood plain (“Laguna Valley”) and eastward toward Castle Dome Plain from a central area 320-340 feet above sea level. DISSECTED PIEDMONT SLOPES The third and fourth types of landforms in the Yuma area, which occur along the margins of the mountains and hills, are dissected and undissected piedmont slopes. In places, one type grades into the other, but in general, the dissected piedmont slopes represent areas where erosion is the dominant process today and probably has been dominant for at least the past several thousand years. In contrast, undissected piedmont slopes represent areas where either deposition is occurring or a rough balance exists between erosion and deposition. Many of the dissected piedmont slopes could be classified as dissected pediments under the broad meaning of the term “pediment.” However, unlike classic pediments in desert regions, the surfaces are cut chiefly on unconsolidated to semiconsolidated alluvium rather than on consolidated bedrock. The deposits, chiefly coarse grained older alluvium of local origin, are generally mantled with thin stream- terrace and piedmont deposits (gravel). The dissected piedmont slopes occur in “Picacho Mesa,” “Senator Mesa,” Middle Mountains Plain,” Castle Dome Plain, “Gila Mesa,” and “Ligurta Mesa” and in parts of Pilot Knob Mesa and “Laguna Mesa” (fig. 6). In all these subareas, desert pave- ment is generally conspicuous on the broad gravel surfaces and also conspicuous on the narrow terraces below the main piedmont levels. Several piedmont levels are present at most places. The most extensive of these appears to be graded to the level of Yuma Mesa. The narrow terraces are not paired, are gen- erally adjacent to present washes, and represent abandoned washes left behind as the ephemeral streams cut down to their present levels. “Picacho Mesa,” the broad piedmont between the Cargo Muchacho Mountains and the Chocolate Mountains, is drained by sub‘parallel southeast- to south-trending washes, of which Picacho Wash near the center of the area is the largest. The floors of the washes are incised as much as 80 feet below the adjacent piedmont surfaces near the Colorado River flood plain (“Bard Valle-y”), but the depths of in- cision become progressively less toward the north- west (fig. 8). The average slope of the piedmont surface is about 50 to 60 feet per mile. Near its north end, “Picacho Mesa” becomes more intricately dissected and merges gradually with low, hilly ex- posures of conglomerate of the Chocolate Mountains WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA and nonmarine sedimentary rocks along the south- west flank of the Chocolate Mountains. “Senator Mesa,” on the east side of the Choco- late Mountains, comprises several piedmont and terrace levels, all sloping about 70-120 feet per mile toward the east and southeast. The underlying ma- terials are alluvial gravel deposits of local deriva- tion which thin eastward and southeastward, where they overlie relatively fine grained older Colorado River alluvium. “Middle Mountains Plain” and the western mar- gin of “Laguna Mesa” are similar in most respects to “Senator Mesa,” except that the piedmont sur- faces and terraces slope westward rather than eastward or southeastward and generally are not quite as deeply incised as in “Senator Mesa.” Aver- age slopes of “Middle Mountains Plain” range from more than 100 feet per mile at the foot of Middle Mountains to about 60 feet per mile near the C010- rado River. » Castle Dome Plain, a gently sloping desert surface traversed by a network of shallow washes, slopes southwestward at gradients ranging from 100 feet per mile in the northeast to 45 feet per mile in the southwest. Dark-brown desert pavement is well de- veloped on the surfaces between the present washes, which are generally incised only a few inches to 4 feet below the pavement surfaces, except in the east- ern part of the plain, where depth of incision is locally as much as 40 feet. Much of Castle Dome plain is in some respects transitional between the relatively undissected and the dissected piedmont slopes. The chief difference between Castle Dome Plain and the Lechuguilla Desert farther south is the absence of dark desert pavement in the latter area. “Gila Mesa” and its homolog on the east side of the Gila Mountains, “Ligurta Mesa,” include some of the steepest and most deeply dissected piedmont slopes in the Yuma area. Slopes of desert pavement surfaces in the “Ligurta Mesa” area range from 160 feet per mile (1°45’) near the mountains to about 100 feet per mile (1°05’) at the lower ends. In “Gila Mesa,” slopes are somewhat flatter (55—- 120 feet per mile). Both areas contain deeply dis- sected older alluvial deposits of local origin on which desert pavement is generally lacking (fig. 9). Slopes of ridges in these exposures are as ’much as 300—350 feet per mile, and near the mountains some of the present washes are incised as much as 150 feet below the ridges. UNDISSECTED PIEDMONT SLOPES The undissected piedmont slopes are distinguished GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H25 FIGURE 8.—Dissected piedmont surfaces of reentrant of ”Picacho Mesa” in eastern Cargo Muchacho Mountains, Calif. Present wash crosses picture from right to left in foreground. Granitic detritus in this area forms poorly developed desert pavement. from the older, dissected piedmont slopes by the general absence of desert pavement and by the very shallow depths of incision of the most recent washes. Most of the deposits underlying the undissected piedmont slopes are classified as alluvial-fan de- posits (younger alluvium) (pl. 3); these deposits are being aggraded slowly in most places, and in some places, a rough balance appears to exist be- tween aggradation and degradation. The subareas representing undissected piedmont slopes are the Lechuguilla Desert, Davis Plain, “For- tuna Plain,” and part of Pilot Knob Mesa (fig. 6). The first three subareas are adjacent to the southern Gila Mountains and their southerly extensions, the Butler and Tinajas Altas Mountains. Light-colored fairly coarse grained granitic rock predominates in these mountains and furnishes the coarse granitic 507-243 0 - 74 — 3 sand and fine gravel that constitute the alluvial-fan deposits. As mentioned earlier, desert pavement is either poorly developed or absent; moreover, desert varnish has not formed to an appreciable extent on the larger fragments. In part, the absence of var- nish may reflect the fact that deposition is the dominant process. However, it probably is also a consequence of the tendency of varnish to form very slowly on the light-colored granitic rocks. Land-surface slopes in the Lechuguilla Desert, Davis Plain, and “Fortuna Plain” range from 70 to 100 feet per mile at the foot of the mountains to about 40 feet per mile at the lower edges of the piedmonts—substantially flatter than the slopes in the dissected piedmont areas (“Ligurta Mesa” and “Gila Mesa”) farther north. Present washes are poorly defined and entrenched only a few inches to H26 WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA FIGURE 9.—-—Northern Gila Mountains from Fortuna Wash. Beyond Fortuna Wash in the foreground are dark desert pavement surfaces; the light- colored exposures in the middle distance, and the somewhat darker smooth exposures near the center of the mountains beyond, are deeply dissected older alluvial deposits (chiefly coarse gravel of local origin). The high, rough exposures are of Dre-Tertiary crystalline rocks. a few feet below the general surface of the piedmont areas. In some areas, particularly in the southern part of the Lechuguilla Desert and in parts of Davis Plain, a distinctive rhomboidal pattern of shallow rills may indicate sheetflooding as the pri- mary geomorphic process. Except for its southeastern part, where it adjoins “Picacho Mesa,” Pilot Knob Mesa consists of a relatively undissected piedmont slope like the areas just described. Also, as in those areas, the detritus beneath Pilot Knob Mesa “is largely granitic, sheet- fiooding probably is common, and the present washes are poorly defined and very shallowly incised. The Southern Pacific Co. has had to protect its railroad tracks from washouts and inundation by a continu- ous line of revetments having a zigzag pattern, to concentrate the runoff through culverts. RIVER TERRACES AND MESAS The river terraces and mesas are the remnants of former valleys and the delta plain of the Colo- rado and Gila Rivers. Yuma Mesa, Wellton Mesa, and Imperial East Mesa are the subareas of this type (fig. 6). All these surfaces are nearly flat and lie above the present valleys (flood plains) of the rivers. The old valleys and delta plain were aban- doned when the rivers began to cut their present, narrower valleys. Wellton Mesa and northeastern Yuma Mesa lie respectively 60—70 and 70—80 feet above the adja- cent Wellton-Mohawk and South Gila Valleys. Ex- tensive river terraces at similar heights occur far— ther upstream on both the Colorado and the Gila Rivers. In places—for example at Laguna Dam, Imperial Dam, and the Gila River narrows between GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA the Gila and Laguna Mountains—the terraces are cut on pre-Tertiary crystalline rocks or on Tertiary sedimentary or volcanic rocks. Extensive piedmont surfaces formed by local runoff also are graded to this terrace level (fig. 10). The higher of the two prominent levels appears to be graded to the level of the Yuma Msa terrace 70 to 80 feet above the present flood plains. FIGURE 10,—Terraces in southern Laguna Mountains. The time when the streams were at the level 60— 80 feet above the present flood plains is not indi- cated by direct evidence. However, the terraces may have been formed at the time of the last major higher sea-level stand during the Sangamon Inter- glaciation. According to Broecker (1966) and Veeh (1966), the last sea-level stand significantly above the present level occurred about 120,000 years ago. Not all the Yuma Mesa represents the terrace just described. In the southwestern part of the mesa, one or two much-eroded terraces lie below the main surface of the mesa and 30-50 feet above adjacent Yuma Valley. These surfaces may be cor- relative with similar levels in the piedmont areas. The general slope of Yuma Mesa is much flatter than that of the “Upper Mesa” to the southeast and not greatly different from the slope of the present river valleys (flood plains). Northeastern Yuma Mesa has a southward gradient of about 2 feet per mile, but farther southwest the slope changes in direction to westward and steepens to about 6—8 feet per mile (pl. 2). The westward slope appears to be chiefly erosional in origin, although in part it results from downwarp along the east margin of the Salton Trough. Farther southwest, in Mexico, westward downwarp causes the mesa surface to intersect the surface of the present river flood plain at a point about 18 miles southwest of San Luis, Rio Colorado. H27 The Imperial East Mesa is similarly downwarped toward the axis of the Salton Trough, although the direction of tilt may be somewhat different from that of Yuma Mesa. The East Mesa surface has a west- ward slope of less than 2 feet per mile—substantially flatter than the slope of southwestern Yuma Mesa. The northeast margin of East Mesa is occupied by an old shoreline, either of an ancestral lake or of an arm of the Gulf of California. In the south- eastern part of the mesa the shoreline is about 160 feet above sea level, but 55 miles northwest of the international boundary it is only 70 feet above sea level .(Loeltz and others, 1972). This tilt probably results from the westward (or northwestward) downwarp described above. The west margin of the mesa is occupied by another shoreline—~that of ancient Lake Cahuilla at about 45 feet above sea level (Stanley, 1962). Unlike the higher, older shore- line, the Lake Cahuilla shoreline is Virtually unde- formed. The lacustrine origin of the 45-foot shoreline is unequivocal, but the origin of the higher shoreline is uncertain. Fresh-water shells dated at 37,100: 2,000 years before present have been described from this shoreline (Hu-bbs and others, 1963, p. 262), but evidence of the barrier across the delta required to contain the lake and exclude the Gulf of California is lacking (Robison, 1965). Unless sig- nificant warping has occurred in the Yuma area more recently than indicated by present evidence, remnants of this higher shoreline should be found elsewhere at altitudes similar to those along the southeastern Imperial East Mesa (140—160 feet above sea level). The widespread tufa “gravel” that occurs in the Yuma Mesa and even on parts of the “Upper Mesa” may be indicative of shorelines, but no other evidence has been found in those areas. Since the time the rivers began to cut their pres- ent narrower valleys, the older flood-plain surfaces represented by Wellton, Yuma, and Imperial East Mesas have been modified by erosion and deposition, chiefly by wind but also by water. The southeastern and eastern parts of Yuma Mesa, adjacent to the “Upper Mesa,” are occupied by thin blankets of windblown sand, and the areas farther west by broad, wind-scoured depressions. Undrained depres- sions as much as 10 feet in depth are common in the areas of wind scour and deposition. One par- ticularly large depression (whose origin may not be entirely wind scour), about 15 feet in depth and 2 miles in width, occurs in the northern part of the mesa, just west of the southernmost two outcrops of pre-Tertiary crystalline rocks of the “Yuma Hills”. (pl. 2) . On the Imperial East Mesa, low dunes H28 are extensive in places; in other places, sand accu- mulates around the bases of the larger shrubs, par- ticularly the creosote bush (Larrea tridentata.) . Notwithstanding the modification of the mesa surfaces by wind, traces of old river-formed features remain. On Yuma Mesa, the most noticeable of these features is a low ridge, perhaps a natural levee or channel ridge, which trends southwestward in the south-central part of the mesa (pl. 2). SAND DUNES Although windblown sand is extensive in the Yuma area, in only two sizable areas has the sand accumulated to form dunes more than 10 feet thick. One of these tracts—the Sand Hills, or, as they have been informally designated, the “Algodones Dunes” ——is on the northeast side of the Imperial East Mesa, chiefly in California. See also Norris and Norris (1961). The other tract informally called “Fortuna Dunes,” is in Arizona, near the southerly international boundary (fig. 6). The “Algodones Dunes” form an elongate north- west-trending belt about 45 miles long by 6 miles wide on the northeast side of the Imperial East Mesa. The surface on which the dunes rest is con- tinuous with the East Mesa and with the Pilot Knob Mesa to the northeast; this surface is exposed at several places in the southeastern part of the dunes. The southeastern part of the “Algodones Dunes” comprises three longitudinal belts: (1) A narrow southwestern belt generally less than a mile wide, (2) a main central belt averaging about 21/2 miles in width, and (3) a northeastern belt about 2—21/2 miles wide. Each belt is characterized by a distinc- tive type of dune topography. The southwestern belt is composed of narrow parallel longitudinal ridges. The higher ridges rise 60—100 feet above the East Mesa. Their remarkably straight southwestern edge has led some observers to believe that they are fault controlled, possibly by a branch or parallel branches of the San Andreas fault system. Loeltz, Robison, Irelan, and Olm- sted (1972) have shown that the southwest edge of the dunes is adjacent to an old shoreline, of either an ancestral lake created by the Colorado River or an arm of the Gulf of California (p. H27 ). The main central belt is composed of high trans- verse ridges and intervening depressions having a remarkably uniform spacing—the average distance between the ridge crests is about a mile. Smaller barchan crescent or quasi-barchan dunes are super- imposed on the general form of the transverse ridges, which rise 150—300 feet above the depres- sions. According to Norris and Norris (1961), the WATER RESOURCES 0F LOWER COLORADO RIVER—SALTON SEA AREA transverse ridges are related to an earlier wind regime, the barchan dunes to a later one. The south- east, leeward sides of the ridges are linear, steep slip slopes of about 32° inclination—the angle of repose for the dry fine to medium sand. The bar- chans are on the gentler, windward slopes of the ridges; these dunes are modified in shape during the summer when the prevailing winds are from the south-southeast rather than from the north and west, as they are during the rest of the year (US. Weather Bureau unpub. data for Yuma, Ariz.) . The depressions between the transverse ridges are gen- erally semicircular in plan, with the straight side on the northwest, and many are scoured free of sand. The northeastern belt consists of low, irregular dunes and small barchans. The dunes are much lower than the dunes in the other two belts; they range in height from about 5 to 15 feet. They ap- pear to shift and change form more than the other, higher dunes, although no measurements are avail- able to document this general observation. The informal name “Fortuna Dunes” is given to an area of windblown sand between “Upper Mesa” and “Fortuna Plain,” just north of the southerly international boundary. These dunes are merely the northwestern prong of a much more extensive dune area largely in Sonora, Mexico. The thicker sand deposits occur as closely spaced small transverse dunes as much as 30 feet high. The long axes of the dunes are all uniformly oriented N. 60° E., pre- sumably perpendicular to the strongest winds that formed them. It is not known whether the dunes are moving at present. RIVER VALLEYS The river valleys are the Holocene flood plains of the Colorado and Gila Rivers. Most of the flood plains are now farmed and are no longer subject to flooding since dams were constructed upstream and levees built along the Colorado River in the Yuma area. The flood plains are bordered by terraces and other higher desert surfaces into which the rivers cut down before starting the aggradational cycle that produced the present flood plains. “Laguna Valley” is the informal name given to the flood plain of the Colorado River between La- guna and Imperial Dams. It is the first broad flood plain along the river downstream from the Parker- Blythe-Cibola area. In its present form it is not a natural feature but is a surfaCe of aggradation caused by Laguna Dam, which was constructed in the early 1900’s. An estimated 14 feet of aggrada- tion has occurred behind Laguna Dam; the postdam GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA fill probably thins upstream toward Imperial Dam. Most of “Laguna Valley” is occupied by phreato- phytes and hydrophytes, and much is covered by shallow water. Mittry Lake (pl. 3) at the southeast edge of the valley is the largest water body. The flood plain of the Gila River between the town of Wellton (pl. 3) and the site of Mohawk 25 miles to the east is usually referred to as the Wellton-Mohawk Valley. The present channel of the Gila River follows a somewhat meandering course down the valley, which ranges in width from 2 to 4 miles within the area shown in figure 6. The flood plain is bounded by higher lands underlain by older, dissected alluvial deposits. Within the area shown in figure 6, the Wellton-Mohawk Valley slopes west- ward from an altitude of 255 feet above sea level to 205 feet above sea level in a distance of about 14 miles—an average gradient of about 31/2 feet per mile. Like most of the other valleys in the Yuma area, nearly all the area is presently irrigated. The flood plain of the Gila River between the North and South Gila Valleys and the Wellton- Mohawk Valley is referred to locally as Dome Valley. Dome Valley is somewhat narrower than Wellton- Mohawk Valley and ranges in width from 3 miles near its upper end to less than 1 mile at the lower end, where the Gila River flows between the Gila and Laguna Mountains. The average altitude of the flood plain decreases from 205 feet above sea level at the upper end to 150 feet above sea level at the lower end, in a distance of 15 miles. This gradient— 32/3 feet per mile—is slightly steeper than that of the lower end of Wellton-Mohawk Valley to the east. The part of the valley of the Colorado River in California downstream from Laguna Dam is in- formally designated “Bard Valley” from the com- munity of Bard in the upper part of the valley (pl. 3). “Bard Valley” is a broad, flat area, the southeastern part of which was traversed by a meander loop of the Colorado River within historic time. The abandoned meander is now occupied by two oxbow lakes: Haughtelin Lake (pl. 3) and Bard Lake about a mile to the east. Until August 1966, the meander channel formed the disputed boundary between California and Arizona. The area between the present channel of the Colorado River and the abandoned meander is known as The Island. The eastern part of The Island and the adjacent area to the east is covered by a thin sheet of windbvlowrn sand and a few low dunes (not shown in fig. 6 but shown on pl. 3). “Bard Valley” is an unusually flat segment of the Colorado River flood plain. It slopes southwestward from about 140 feet above sea level at Laguna Dam H29 to 125 feet above sea level along the Colorado River west of Yuma—an average gradient of about 11/2 feet per mile. The reason for the anomalously flat gradient is not fully understood; the presence of the nearly buried bedrock ridge (“Yuma Hills”) near the downstream end of the valley may be a contributing factor. The North Gila Valley is an L-shaped flood-plain area downstream from Laguna Dam, bounded on the east and north by the Laguna Mountains, on the west by the Colorado River, and on the south by the Gila River. The northern arm of the L is thus the eastern part of the Colorado River flood plain above the confluence of the Gila River; the eastern arm is the northern part of the lower Gila River flood plain. The northern arm is nearly flat, but the eastern arm slopes westward from 160 feet above sea level to 135 feet above sea level at the confluence of the Colorado and Gila Rivers—a gradient of 37/3 feet per mile. The South Gila Valley is south of the Gila River and of the Colorado River below the mouth of the Gila River. It extends westward from the Gila Mountains to the nearly buried “Yuma Hills.” The valley is about 12 miles long by 2 miles wide and slopes westward at an average gradient of about 3 feet per mile. The valley surface is not perfectly flat but consists of a series of low terraces decreas- ing in altitude northward toward the Gila River. (Similar terraces occur on the north side of the Gila River in North Gila Valley.) Old meander scars mark the edge of these terraces, the lowest of which is 10—15 feet below the southern margin of the flood plain. In places the form and outline of the terraces have been modified greatly by land leveling for farming and roadbuilding. The flood plain east of the Colorado River down- stream from Yuma is called the Yuma Valley. Yuma Valley is about 19 miles long by 2—9 miles wide. It slopes south-southwestward from 125 feet above sea level west of Yuma to 90- feet above sea level at the southerly international boundary—an average gra- dient of' 1.8 feet per mile. Small, sinuous sand dunes 5—20 feet high are scattered throughout the central and eastern parts of the valley; these dunes have formed on the lee- ward (southeast) side of abandoned meanders. Many of these old meander scars can be discerned from the air, even where the land has been farmed intensively for several decades. The soil is sandier and of a lighter color in the old channels than in the adjacent flood plain. The Yuma Main Drain, the principal surface drain in the valley, occupies an old river channel along most of its length. H30 The present channel of the Colorado River is 15—20 feet below the adjacent flood plain. Much of this cutting occurred since the construction of the upstream dams and the desilting works at Imperial Dam in the 1930’s and 1940’s, when the sediment load of the river decreased markedly. (See fig. 26.) The terraces along the Gila River in the South and North Gila Valleys may reflect the recent degrada- tion by the Colorado River below Yuma. The Mexican part of the flood plain of the Colo- rado River downstream from Pilot Knob is gen- erally called the Mexicali Valley. Mexicali Valley widens toward the south and west; together with Yuma Valley, it forms part of the delta of the Colo— rado River. The surface form of the delta is that of a large, flat fan having its apex near Pilot Knob and Yuma. The axis trends west-southwestward toward the Cucupas Mountains in Baja California; south of the axis, the surface slopes gradually toward the Gulf of California; to the north, toward the Salton Sea. The lowest point on the axis of the delta, near the Cucupas Mountains, is about 47 feet above sea level (Arnal, 1961). At times during the Holocene and latest Pleistocene, the Colorado River flowed westward rather than southward and main- tained large fresh-water lakes about 42—48 feet above sea level north of the delta axis. The average land-surface gradient along the east side of Mexicali Valley from Pilot Knob to the head of tidewater (Gulf of California) is about 2.2 feet per mile. The river has wandered back and forth across the valley frequently in historic time; be- cause of its meandering course, the gradient of the river itself has averaged only about 1 foot per mile in this reach. STRATIGRAPHY CLASSIFlCATION OF ROCKS The geologic materials of the Yuma area range from hard, dense crystalline rocks, such as gneiss, schist, and granite, to unconsolidated alluvium and windblown sand. For the purposes of this report these materials are grouped in 10 generalized strati- graphic units. The inferred stratigraphic relations of these units are shown in figure 11, the extent of their outcrops on plate 3, and their probable subsur- face extent and configuration on plate 10. The oldest unit—the crystalline rocks—is sepa- rated from the overlying units by a major uncon— formity (nonconformity) ; less significant uncon- formities are present throughout the Tertiary and Quaternary units. The amount of deformation of the various units decreases with decreasing age. Deposits younger than the nonmarine sedimentary WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA rocks and older marine sedimentary rocks of Ter- tiary age are only broadly warped and locally faulted. The only fossils diagnostic as to age found Within the area mapped in the present investigation were some bones of Equus sp. (a horse) and Odocoileus sp. (a deer) reported by Bryan (1923, p. 30—31) from a terrace near Ligurta (pl. 3). The bones indi- cate a Pleistocene age for the enclosing deposits of older alluvium. Lower Miocene vertebrate fossils have been reported from a locality about 10 miles east of the mapped area, in the eastern Muggins Mountains (Lance and Wood, 1958; Lance, 1960). In addition to the scanty fossil data, several radio- metric dates have been obtained for material col- lected in the Yuma area and, together with inferred correlations with units in adjacent regions, have been used to establish the general stratigraphic sequence. Most of the stratigraphic units (fig. 11 and pls. 3, 10) are useful subdivisions of the ground-water reservoir for describing the occurrence and move- ment of ground water. However, beneath the river valleys and Yuma Mesa, the alluvial and minor windblown deposits are subdivided into zones that differ in part from the stratigraphic units, as is explained in the section of the report on occurrence of ground water. The different geohydrologic clas- sification of these deposits is required because the boundaries of the water-bearing zones cross the stratigraphic boundaries. CRYSTALLINE ROCKS (PRE-TERTIARY) Crystalline rocks of pre-Tertiary age form a large part of the mountains and underlie the Ter- tiary and Quaternary rocks throughout the area. The crystalline rocks comprise a wide variety of metamorphic and plutonic rocks. For the purposes of this report all these rocks are grouped in one unit, as they are uniformly devoid of sizable sup- plies of ground water. The metamorphic rocks range from weakly meta- morphosed sedimentary and volcanic rocks to strongly metamorphosed gneiss and schist. In the Cargo Muchacho Mountains, Henshaw (1942) di- vided the metamorphic rocks into two formations: the Vitrefrax Formation, composed of quartzite, quartz-sericite schist, kyanite-quartz-sericite schist, sericite schist, biotite-hornblende schist, and a few other less extensive types; and the Tumco Forma- tion, composed largely of feldspar-quartz—biotite- hornblende rock, hornblende schist, and metamor- phosed arkose. Elsewhere in the Yuma area, the metamorphic GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA SUBSURFACE EXPOSURES g E YOUNGER Deggfgtzdog 2:: W'NDBLOWN smithvfgsdh Alluvial-fan YOUNGER :: o ALLUVIUM SAND ' - E Gila Rivers deposits deposrts ALLUVIUM < i E g Stream-terrace and E ' ' I D '3. 8 Deposits of the piedmont deposrts E S 2: 8 OLDER _, :3 O 3 ALLUVIUM old Colorado and Deposits of 0 j E Gila Rivers mixed origin < Deposits of local origin / “'5‘ Lu 2 TRANSITION ZONE '3: E m 8 __>_ m _, _z_ .2 g e : cT. BOUSE FORMATION 3 g z (.7 U 8 Z 2 Other nonmarine o g sedimentary rocks 0 Upper member Lu E OLDER MARINE + +++++++Tuff, ash E E v, SEDlMENTARY KlNTER FORMATION T ff h <2: Eé +++ + u ,as z _ ROCKS Lower member 0 o x 2 Lu V) B . . Basalt in US. Bureau of Reclamation asalzfolrjrb:::£:1caagnedeSIte test well CH—8RD 2 a.) U .2 E Flows and vent E tuff 0f Basaltic E Laguna Mts andesite or m if: basalt of 5 r— _ Chocolate 0 Pyroclastic rocks Mountains 0: and 2 minor flow rocks <2: of 3 silicic to 2 intermediate NONMARINE composition ? SEDIMENTARY ROCKS Older andesite: Flows and tuff d) C 8 g Breccia and >_ c1, conglomerate § 3:: a g 5 g ++ ++++Tuff,ash 353 Red beds 2 S (I) ++++++++Tuffl ash >- _'l . 0‘ < w E; CRYSJékélNE Metamorphic, plutonic, and dike rocks {>73 1% g E 5 tr FIGURE 11.—Stratigraphic column. H31 H32 rocks have not been named, although they have been described in a general way by Wilson (1933) in the Laguna, Gila, Butler, and Tinajas Altas Mountains, and they have been examined briefly in the Choco- late Mountains by F. H. Olmsted. The most exten- sive types in all these mountains are various kinds of biotite-bearing and hornblende-bearing gneiss, some of which is migmatitic and highly contorted. At the north end of the Gila Mountains, crystalline limestone, not known elsewhere in the Yuma area, is intercalated with schist. Gneiss of granitic to quartz monzonitic composition is abundant in the eastern Laguna MOuntains; some of this rock ap- pears to grade into porphyritic granite and quartz monzonite of probable plutonic origin. In the Chocolate Mountains, a suite of weakly metamorphosed rocks includes slate and phyllite o'f epiclastic and probable pyroclastic origin, sheared sandstone and arkose, metaconglomerate, sheared tuff breccia, and greenstone derived from mafic lava flows and shallow intrusive bodies. These rocks are similar to the McCoy Mountains Formation of Miller (1944) farther north, with which they may be at least in part correlative. Also present in the Choco- late Mountains are several types of schist similar to the Orocopia Schist of Miller (1944) in the Oro- copia Mountains to the northwest. The plutonic rocks include a wide variety of types, although quartz monzonite and granite are the most extensive. Other plutonic rocks include granodiorite, quartz diorite, diorite, and gabbro. Dikes of aplite, alaskite, pegmatite, and various fine-grained dark rocks, of which distinctive dark—green altered dia- base and basalt are most conspicuous, are abundant at many places. Most of the plutonic rocks clearly intrude meta- morphic rocks, but in places the relations of the two types are gradational. For example, in the Cargo Muchacho MOuntains, some of the granite appears to grade into meta-arkose, from which it may have been derived (Henshaw, 1942) ; the gradational relations of some of the gneiss and the porphyritic granite and quartz monzonite in the Laguna Moun- tains were cited above. The ages of most of the metamorphic and plutonic rocks in the Yuma area have not been established, although all these rocks appear to be no younger than the Laramide orogeny, which took place dur- ing the Late Cretaceous and the early Tertiary (Damon and Mauger, 1966). Some of the youngest plutonic and dike rocks might be of Tertiary age (Wilson, 1933, p. 185; 1960). For convenience, these rocks are grouped with the pre-Tertiary crys- talline rocks in this report. WATER RESOURCES 0F LOWER COLORADO RIVER—SALTON SEA AREA Ironically, the only two radiometric dates, which are for a coarse porphyritic quartz monzonite in Yuma, are widely disparate. Wasserburg and Lan- phere (1965) report a rubidium-strontium age of 73 million years for the biotite in a sample obtained in the Highway 95 cut just east of the railroad over- pass in Yuma. However, L. T. Silver (written commun., 1968) obtained a uranium-lead age of 1,440 million years for crystals of zircon in the same rock. The zircon age (Precambrian) presumably indicates the time of original crystallization; the biotite age (Late Cretaceous) may reflect a Lara- mide metamorphic event. The dated porphyritic quartz monzonite is wide— spread in the Yuma area and makes up almost all the detritus in some of the breccia and conglomerate of Tertiary age described in a later section (p. H33). The rock is generally coarse grained, contains ovoid to irregular phenocrysts (or porphyroblasts) of white to pale-pink microcline as much as 50 mm (millimeters) in diameter, and smaller grains of plagioclase, quartz, biotite, and minor accessory min- erals (chiefly magnetite and zircon). In places the rock is gneissose, and in ancient (pre-Laramide) fault and shear zones it is schistose and locally my— lonitic. It is cut by younger plutonic and dike rocks Whose ages are unknown. The porphyritic quartz monzonite grades into porphyritic granite and has been found in almost all wells that penetrate the pre-T‘ertiary crystalline rocks in the Yuma area. NONMARINE SEDIMENTARY ROCKS (TERTIARY) Unconformably overlying the crystalline rocks of pre-Tertiary age is a suite of sedimentary rocks and associated volcanic rocks of Tertiary age. This suite comprises several mappable units, all of which ap- pear to have been deposited before the Colorado River entered the Yuma area. For convenience, all the predominantly nonmarine sedimentary rocks, except conglomerate of volcanic composition in the Chocolate Mountains are included in one major unit, the volcanic rocks in another. Marine sedi- mentary rocks of Tertiary age comprise two addi- tional units; the younger marine unit is overlain by a transition zone of marine and nonmarine de- posits of late Tertiary age (fig. 11). All these other units are discussed in a later section. The nonmarine sedimentary rocks consist of strongly to weakly indurated clastic rocks ranging from mudstone and shale, in part of lacustrine ori- gin, to megabreccia and boulder conglomerate. Fanglomerate is most abundant, at least in the out- crop areas. Detailed mapping done during the pres- ent investigation resulted in the delineation of GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA several mappable units in the Laguna Mountains, southeastern Chocolate Mountains, and northern Gila Mountains. These units, one of which has been named the Kinter Formation, are described briefly in the following paragraphs. Exposures in a critical area in the southeastern Laguna Mountains and northernmost Gila Mountains are shown on plate 4. RED BEDS The basal part of the nonmarine sedimentary rocks exposed in the Laguna Mountains area is composed of arkose, conglomerate, mudstone, fine- grained tufi'aceous beds, and bentonitic ash, all re- ferred to herein as red beds from the predominant color in the exposures near McPhaul Bridge (pl. 4). The coarser beds are red, brownish red, brown, and yellow and contain subangular to rounded frag- ments of quartz and feldspar, hornlblende, biotite and other heavy minerals, and various kinds of plutonic and metamorphic rocks, including abund- ant- slightly metamorphosed volcanic rocks. These beds are of fluvial origin; the well-rounded char- acter of many of the pebbles indicates transport for a considerable distance, probably by a fairly well integrated drainage system. Tongues of coarse breccia and conglomerate in the upper part of the sequence suggest local high relief and rapid erosion toward the close of deposition of the red beds. The finer beds, generally more abundant in the lower part of the sequence, are mostly green, pale yellow, or gray and locally contain abundant thin seams of gypsum. These finer grained gypsiferous sediments probably are of lacustrine origin (no marine fossils have been observed) any may indi- cate the presence of local basins of interior drainage in the early stages of deposition of the red-bed se- quence. Intermittent volcanic activity is reflected by the presence of tuffaceous mudstone and a few thin beds of white bentonitic ash. In the Yuma area, the red beds are exposed only near McPhaul Bridge in the southeastern Laguna Mountains and at the north end of the Gila Moun- tains (pl. 4). The total exposed thickness in the Laguna Mountains is difficult to estimate because of faulting; probably it is on the order of 2,000—2,500 feet. The subsurface extent and thickness are largely unknown; varicolored sandstone, shale, and con- glomerate penetrated between depths of 4,937 and 6,007 feet in oil-test well Colorado Basin Associates Federal 1 may be at least in part correlative with the red beds exposed near McPhaul Bridge. Beds similar to those near McPhaul Bridge are exposed extensively in the Muggins Mountains 10—20 miles to the east, but fossil and radiometric evi- H33 dence indicates that the Muggins Mountains beds probably are younger, as discussed on, page H37. BRECCIA AND CONGLOMERATE The uppermost red beds in the southern Laguna Mountains intertongue with a thick sequence of generally coarse grained, poorly sorted breccia and conglomerate. These strata are made up of pre- dominantly angular and subangular fragments of all sizes up to boulders and blocks many feet across in a semiconsolidated matrix of clayey sand and silt. Thin interbeds of arkose, sandy siltstone, and felsic tuff occur locally. In the Laguna Mountains the lower part of this sequence consists of breccia and conglomerate com- posed entirely of the distinctive pre-Tertiary por- phyritic granite and quartz monzonite and associ- ated dike rocks found in nearby exposures. This monolithologic granite breccia and conglomerate sequence is obscurely bedded and very coarse—— blocks as much as 50 feet across have been observed. Some of this material appears to have formed as mudflows, talus, and colluvium, although most of it probably is fanglomerate. Obscure bedding and faults make estimates of thickness uncertain, but probably at least 4,000 feet is exposed in the south- ern Laguna Mountains. The granite breccia- conglomerate sequence is exposed also in Yuma, where the Colorado River has cut its present chan- nel through a low hill of this material (fig. 12). The upper part of the breccia-conglomerate se- quence is composed of more heterogeneous material but is otherwise similar to the underlying granite breccia and conglomerate. The two types intertongue in the southern Laguna Mountains (pl. 4) ; in the southeastern Chocolate Mountains, the heteroge- neous type predominates. Typically the heteroge- neous breccia and conglomerate has an earthy greenish-gray matrix in which are embedded frag- ments of all sizes as much as many feet across composed chiefly of fine-grained varicolored meta- sedimentary and metavolcanic rocks. The nearest exposures of similar low-grade metamorphic rocks in the pre-Tertiary crystalline-rock complex are in the Chocolate Mountains near the north edge of plate 3. Maximum exposed thickness of heteroge- neous breccia and conglomerate near the southeast end of the Chocolate Mountains is probably more than 5,000 feet, although poorly exposed faults of unknown displacement make this estimate somewhat uncertain. Both the red beds and the overlying breccia and conglomerate have been moderately deformed; bed- ding generally dips 30°—60°, most commonly in a H34 WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA FIGURE 12.—Granite breccia and conglomerate exposed in north bank of Colorado River at Yuma. westerly or southwesterly direction. Good exposures reveal high—angle reverse, or thrust, faults, as well as low to high-angle normal faults. In the southern Laguna Mountains, pre—Tertiary crystalline rocks in places are in contact with the red beds along high-angle reverse faults. KINTER FORMATION The name Kinter Formation is proposed in this report for a sequence of predominantly coarse grained nonmarine sedimentary rocks and minor intercalated beds of tufi' and ash exposed principally in the Laguna Mountains and at the north end of the Gila Mountains. The name is taken from a rail- road siding of the Southern Pacific Co. at the north end of the Gila Mountains, along which the forma- tion is typically exposed. The type section, desig- nated A—B—C on plate 4, is in secs. 3, 9, 10, and 11, T. 8 S., R. 21 W., Gila and Salt River base line and meridian, directly south of the Wellton-Mohawk Canal, 1.8 miles east to 0.8 of a mile south of McPhaul Bridge, and about 7 miles southeast of Laguna Dam. The Kinter Formation is divided into two unnamed members: the lower, composed of coarse unsorted breccia and tongues of brown and gray arkosic sandstone and gray to pink tuffaceous mudstone and the upper, composed of yellowish- gray conglomerate (fanglomerate) and some soft arkosic sandstone and mudstone. The type section is described below. Type section Thickness (feet) Top of section concealed by Quaternary alluvium. Upper member: Arkosic sandstone and pebbly sandstone, soft, yellowish-gray (5Y 7/2); interbedded pale— yellowish-brown (10YR 6/2) soft silty sand- stone ______________________________________ Mudstone, sandy, moderately hard, obscurely bedded, pale-brown (5YR 6/2); thin interbeds of pale-yellowship-brown (10YR 6/2) very fine to fine-grained sandstone. Mudstone has sub- conchoidal fractures; contains a few poorly pre- served small gastropods ____________________ 120 Arkosic, tufl’aceous sandstone, soft, yellowish—gray (5Y 7/2; 5Y 8/1) to pinkish-gray (5YR 8/1); lenses of pebbly sandstone containing granules and small pebbles of metamorphic and granitic rocks and pale-pink pumice; a few interbeds of pale-yellowish-brown (10YR 6/2) soft silty sandstone and sandy siltstone _______________ 280 700 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H35 Thickness (feet) Upper member—Continued Pumice tufl", soft, pale-pink (5RP 8/2) to pinkish- gray (5YR 8/1) ___________________________ 5 Arkosic sandstone, soft, yellowish-gray to pinkish- gray; thick, lenticular interbeds of yellowish- gray to gray conglomerate and pebbly sandstone Conglomerate, obscurely bedded to moderately well bedded, yellowish-gray to gray; composed chiefly of angular to subrounded clasts, as much as 3 ft across, of gneiss, schist, granite, and scattered pumice tufi'; thin, lenticular interbeds of yellow- ish-gray (5Y 7/2; 5Y 8/1) arkOSic sandstone. Lower part traversed by vertical fractures filled with grayish-brown sandy clay and silt ______ Tuffaceous sandstone or sandy tufl", soft, fine- to medium—grained, pinkish-gray (5YR 8/1); lens of conglomerate in upper part _______________ 120 950 01 Exposed thickness of upper member __________ 2,180 _— Lower member: Breccia, unsorted, obscurely bedded; contains an- gular to subangular fragments of metamorphic and granitic rocks as much as 5 ft in diameter in a light-brown (5YR 5/6) earthy matrix ____ Breccia, earthy, light-brown (5YR 5/6) to pale- olive (10Y 6/2); interbedded gray (N 7) to grayish-orange-pink (10R 8/2) sandy tufl" or tufi‘aceous sand _____________________________ 40 Breccia, coarse, earthy, greenish-gray (5GY 6/1) ; crude bedding indicated mainly by alinement of 250 larger slabs of gneiss and schist _____________ 150 Interval poorly exposed; probably similar to ma- terial above and below ______________________ 450 Breccia, fine to coarse, earthy, obscurely bedded and poorly sorted, light—brown (5YR 5/6), pale- olive (10Y 6/2), and yellowish-gray (5Y 7/2). Larger clasts include tufl“ as well as metamor- phic and granitic rocks _____________________ 510 Fault contact with upper member. Exposed thickness of lower member __________ l—Afill Total exposed thickness of Kinter Formation __ 3,580 The two members designated in the type section can be traced northward into the southern Laguna Mountains, but the coarse, unsorted breccia char- acteristic of the lower member has not been identi- fied in the central and northwestern parts of these mountains. In places in the northern Gila Mountains the lower member contains brown and gray arkosic sandstone and gray to pale-pink tufi'aceous mud- stone. The sandstone is generally more indurated than that in the upper member. The coarse, un- sorted, and virtually unbedded nature of the breccia that constitutes most of the lower member suggests a mudflow origin in a region of strong local relief. The upper member of the Kinter Formation is generally better sorted than the lower member. In exposures near Dome, east of the type section, con- glomerate makes up the entire exposed thickness of the upper member, and in most exposures in the Laguna Mountains, conglomerate seems to predomi- nate over finer grained deposits. The conglomerate (fanglomerate) was deposited on alluvial fans from local sources, as indicated by the angularity of most of the clasts and their similarity to pre-Tertiary rocks presently exposed in the area. The alluvial fans were bounded by flood plains on which were deposited the finer sands and muds. Both the upper and the lower members of the Kinter Formation contains beds of ash-fall tufi’, some of which have been reworked by streams. The most widespread of these beds is a biotite-bearing tuff and altered ash at or near the base of the upper member (fig. 13). This bed is only a few feet thick and is locally missing, probably because of subse- quent erosion. In addition to the extensive outcrops in the La- guna Mountains and northern Gila Mountains, the Kinter Formation is exposed in a narrow belt along the south flank of the hills southeast of Imperial Dam and also in the southwestern Chocolate Moun- tains just northeast of “Picacho Mesa.” Probable equivalents occur on the east side of the Chocolate Mountains as well, but these last exposures (mapped as conglomerate of Chocolate Mountains) consist chiefly of conglomerate composed of volcanic detri- tus rather than the predominantly metamorphic and granitic clasts typical of the Kinter. In the subsurface the Kinter Formation appears to have been penetrated in several test wells where it underlies fine-grained marine deposits of the Bouse Formation. The contact probably is an angu- lar unconformity, at least near the mountain blocks on the margins of the basins, as indicated by the discordance of several degrees observed in expo- sures southeast of Imperial Dam and by the rela- tively mild deformation of the Bouse Formation at most places in the subsurface (fig. 15). Metzger (1965) reports a similar angular discordance be- tween the Bouse Formation and an underlying Mio- cene(?) fanglomerate in the Parker-Blythe-Cibola area. The Miocene(?) fanglomerate appears to be at least in part equivalent to the Kinter Formation. In the Laguna Mountains the Kinter Formation locally overlies pyroclastic rocks (chiefly SlllClC ash- flow tufi's) mapped as volcanic rocks of Tertiary age (fig. 11 and pls. 3, 4). No angular discordance between these two units has been observed, al- though the abundance of clasts of silicic tuff in parts of the Kinter suggest at least local unconformity. On the southwest flank of the Chocolate Mountains, just northeast of “Picacho Mesa,” the Kinter over- lies basaltic andesite 0r basalt and contains abund- H36 WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA FIGURE 13.—Exposure of Kinter Formation in railroad out along Kinter siding at north end of Gila Mountains. Poorly consolidated fanglomerate overlies tbin bed of pale-purplish-gray tufl'aceous sand (Is) at base of upper member; unbedded mudflow breccia (br) below the tuflaceous sand at lower right corner of exposure is typical of much of the lower member of the formation. ant clasts of that rock in places. The basaltic ande- site or basalt also is part of the main sequence of Tertiary volcanic rocks (fig. 11). Both the Kinter Formation and the underlying volcanic rocks unconformably overlie the, red beds and the breccia-conglomerate sequence. The uncon- formity has several hundred feet of local relief. The angular discordance between the bedding of the Kinter Formation and that of the red beds is as much as 60° in a highly faulted area about 11/2 miles north of McPhaul Bridge (pl. 4). The vol- canic rocks and the Kinter Formation have generally been deformed by normal faulting and tilting or folding with bedding dips of less than 35°. This comparatively mild deformation contracts with the high-angle reverse faulting and moderate to steep tilting and folding characteristic of the red beds, breccia, and conglomerate of the older sedimentary sequence. However, in places in the central Laguna Mountains, the Kinter Formation appears to rest conformably on, or even intertongue with, hetero- geneous breccia and conglomerate presumed to be part of the older sequence. Evidently, deformation varied in time and intensity through the Laguna Mountains. The age of the Kinter Formation is well estab- lished as Miocene on the basis of radiometric dating and stratigraphic evidence. Biotite from a bed of bentonitic ash at locality VAW—60 : 29 near the base of the upper member in the southern Laguna Moun- GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA tains (pl. 4) has been dated by the potassium-argon method as 23:2 million years (US. Geological Sur- vey, written commun. 1963). (See table 2.) If the apparent age is correct, the ash and the enclosing fanglomerate can be assigned an early Miocene age according to the widely accepted time scales of Holmes (1960) and Kulp (1961). Beds similar to those in the lower member of the Kinter Formation and also resembling some of the underlying red beds occur in the Muggins Moun- tains 10—20 miles east of the Laguna and northern Gila Mountains. Lance and Wood (1958) assigned an early Miocene age to camel teeth from the Mug- gins Mountains beds; in a subsequent paper, Lance (1960, p. 156) stated that the fossils are “certainly no older than Upper Oligocene or younger than Middle Miocene.” P. E. Damon (written commun., 1968) reports a potassium-argon age of 21.9:09 m.y. (million years) for biotite in a tuff determined by F. H. Olmsted to be 350—400 feet stratigraphically below the fossiliferous bed; this corresponds to a late Arikaree age according to the Cenozoic mam- malian chronology of Evernden and James (1964), which supports the interpretations of Lance and Wood (1958) and Lance (1960). The Bouse Formation, which unconformably over- lies the Kinter Formation, is considered to be Plio- cene (p. H44). The volcanic rocks underlying the Kinter in the Chocolate and Laguna Mountains have yielded potassium-argon dates ranging from about 25 to 26 my (table 2). All the evidence cited above suggests a Miocene age for the Kinter Formation. The probable time equivalent of the Kinter in the western Salton Trough is the Split Mountain Formation of Tarbet and Holman (1944), a predominantly nonmarine fanglomerate and sandstone containing intercalated marine sandstone and shale. Marine beds have not been definitely identified in the Kinter Formation in the Yuma area, although in the subsurface the older marine sedimentary rocks underlying the Bouse Formation may be at least in part contempo— rary with the Kinter (fig. 11). OTHER NONMARINE SEDIMENTARY ROCKS In addition to the units described above, unnamed nonmarine sedimentary rocks of probable Tertiary age—chiefly coarse breccia and conglomerate— occur in the east-central Cargo Muchacho Moun- tains and at scattered localities in the Gila Moun- tains. The stratigraphic assignment of these de- posits is uncertain. In the Cargo Muchacho Moun- ains, coarse, loosely indurated conglomerate under- lies basalt or basaltic andesite of uncertain age and H37 alluvium of probable Quaternary age and uncon- formably overlies crystalline rocks of pre-Tertiary age. In the Gila Mountains, similar coarse deposits composed of detritus similar to nearby exposed crystalline rocks unconformably rest on the crys- talline rocks. and are overlain unconformably by coarse alluvial-fan deposits of probable Quaternary age. VOLCANIC ROCKS (TERTIARY) Volcanism took place intermittently throughout much of the time the nonmarine sediments of Ter- tiary age were accumulating. The volcanic activity was most extensive after the deposition of the red beds, breccia, and conglomerate and before that of the Kinter Formation and the unnamed conglomer- ate of the Chocolate Mountains. The thickest accu- mulation of these volcanic rocks within the area mapped (pl. 3) is in the Chocolate Mountains; far- ther southeast, in the Laguna Mountains, the vol- canic sequence is much thinner. Comparatively thick sections of volcanic rocks occur outside the mapped area, in the Muggins Mountains, Castle Dome Moun- tains, Middle Mountains, and several other ranges east and northeast of the Yuma area, but some of these rocks may be older than middle Tertiary. OLDER ANDESITE The oldest rocks in the main volcanic sequence are exposed chiefly in the easternmost part of the Chocolate Mountains near the Colorado River and in the adjacent area across the river in Arizona. These rocks consist of flows, pumiceous tuff, and some shallow intrusive bodies, agglomerate, and flow breccia, all apparently of andesitic composition. The flows are dull gray to dull red, are cut by closely spaced irregular fractures, and lack pronounced flow banding or other primary structures. Most of the flows are very fine grained and partly glassy; small phenocrysts of plagioclase, pyroxene, or horn- blende are present but not abundant. The tqu is light gray, soft, and pumiceous and contains scat- tered crystals of biotite, hornblende, pyroxene (mostly augite), and plagioclase, as well as scat- tered fragments of fine-grained andesite and abun- dant glass shards. The thickness of this sequence of andesitic flows and tufi‘s is diflicult to estimate but is probably less than 1,000 feet. PYROCLASTIC ROCKS OF SILICIC T0 INTERMEDIATE COMPOSITION Predominantly pyroclastic rocks overlie the older andesite in the eastern Chocolate Mountains, in places unconformably. These younger rocks range from light-colored soft, pumiceous ash—full tuf‘f to H38 red densely welded ash-flow tufi (ignimbrite). Sev- eral beds of water-laid tuff and tufi‘ breccia also are present. A few flows of light— to medium-gray ande- site or dacite occur in the upper part of the sequence near Picacho Peak. A hard pink trachyte is reported at Senator Wash about 2 miles northwest of Im- perial Dam (US. Bureau of Reclamation, written commun., 1963). Associated with these rocks are widely scattered dikes and, near Picacho Peak, a circular vent filled with a dull-grayraphanitic rock (probably welded tufi'). The softer beds of tuff form valleys, commonly mantled with thin gravel deposits of Quaternary age; the more resistant beds of welded tuff and the flows form ridges. The valleys and ridges are gen- erally oriented northwest, parallel with the strike of the beds. The tuffs, both welded and nonwelded, are com- posed chiefiy of glass Shards, with scattered crystals and small fragments of fine-grained to glassy vol- canic rocks. The low refractive indices of the glass and the abundance of biotite, sanidine, and quartz in some of the tuffs indicate probable rhyolitic or rhyodacitic (quartz-latitic) composition. Other tufi's contain more plagioclase, little or no sanidine and quartz, and augite or hornblende rather than biotite as the chief ferromagnesian constituent; these rocks probably are of andesitic or dacitic composition. The predominantly pyroclastic sequence appears to reach a maximum thickness of about 1,500 feet in the eastern Chocolate Mountains, although un- known displacements on poorly exposed faults make this estimate somewhat uncertain. A section about 1,100—1,200 feet thick was observed in upper Sena- tor Wash, but the base is not exposed at this locality. In the Laguna Mountains the older andesite is missing, and the younger pyroclastic rocks are much thinner than they are in the Chocolate Mountains. The pyroclastic rocks are chiefly welded to non- welded ash flows locally containing a small amount of black vitrophyre in the basal part. The sequence ranges in thickness from a few feet in the southern part of the mountains, northwest of McPhaul Bridge, to nearly 400 feet in the northern part, east of Laguna Dam. The pyroclastic rocks overlie coarse breccia and conglomerate with angular un- conformity and are overlain by the Kinter Forma- tion without significant angular discordance. BASALTIC ANDESITE OR BASALT OF CHOCOLATE MOUNTAINS The most prominent ridges in the southeastern Chocolate Mountains are formed of dark basaltic andesite or basalt (fig. 7). This rock comprises sev- eral distinct flows or flow units, some of which are WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA brecciated, probably from fiowage after the lava had begun to solidify. Most of the rock is medium gray to dark brownish gray, is more or less vesicu- lar, and on weathered surfaces is coated with dark- brown desert varnish. It breaks up into small- boulder-sized subangular fragments but on the whole is very resistant to erosion and forms long, promi- nent ridges. The rock typically has a groundmass composed of tiny laths of plagioclase and pyroxene (chiefly augite) and some brownish glass and opaque grains (probably magnetite), and it contains scattered phenocrysts of olivine (partly altered to iddingsite) , augite, and plagioclase (labradorite). The potassium content of 1.4 percent, determined in a potassium- argon analysis for dating (Geochron Laboratories, written commun., 1963), is considerably higher than that in most basalt (Nockolds and Allen, 1954) and suggests that the rock is more likely a basaltic ande- site or potassic basalt rather than a normal basalt. The flows of basaltic andesite or basalt overlie coarse breccia and conglomerate with angular dis- cordance and locally rest unconformably on the older andesitic sequence. At a few places the ba— saltic andesite or basalt is overlain by tufi' of silicic to intermediate composition, but most contacts of these two rocks are faults; their age relations are therefore uncertain. The maximum exposed thick- ness of the basaltic andesite or basalt in the south- eastern Chocolate Mountains is about 1,000 feet. FLOWS AND VENT TUFF OF LAGUNR MOUNTAINS Flows and vent tuff of uncertain stratigraphic position occur at a few scattered localities in the Laguna Mountains. A sizable exposure of very fine grained rocks of undertermined composition occurs near the west margin of the mountains, south of Laguna Dam. The concentric, steeply dipping struc- ture of the rocks in this exposure suggests an eroded volcanic neck or plug. The neck or plug appears to be capped by remnants of flows that issued from the central part. Other small remnants of flOWS or possibly shallow intrusive bodies occur at several scattered localities in the southern Laguna Mountains. The relations of these rocks to the other volcanic rocks in the area are not known. BASALT OR BASALTIC ANDESITE 0F UNKNOWN AGE Basalt or basaltic andesite of unknown age and stratigraphic position occurs at several localities scattered throughout the Yuma area. All the masses are small, and one was penetrated in US. Bureau of Reclamation test well CH—8 about 2 miles north of Yuma—the only known subsurface occurrence of GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA volcanic rock in the Yuma area. Four of the expo- sures are in the northwestern part of the area: two on the east flank of the Cargo Muchacho Mountains, one on the west flank of those mountains, and one in the Ogilby Hills. A fifth exposure occurs at Raven Butte on the east flank of the Tinajas Altas Moun- tains in the southeastern part of the area. The ex- posed bodies are either flat lying or gently tilted. The overlie crystalline rocks of pre-Tertiary age or, in places, conglomerate of uncertain age. The basalt penetrated in the well 2 miles north of Yuma is overlain by possibly a few feet of the Bouse Forma- tion and then by alluvium of the Colorado River. AGE OF VOLCANIC ROCKS The main masses of volcanic rocks in the Choco- late and Laguna Mountains have been dated with reasonable certainty by the potassium-argon method. The results of the determinations for five samples, and for a sixth sample from an ash bed in the over- lying Kinter Formation, are given in table 2. The samples are listed in approximate stratigraphic or- der, With the youngest at the top. The stragraphic position of the basaltic andesite or basalt is uncer- tain; it may be below rather than above most of the tuffs of silici-c to intermediate composition, but it definitely overlies the older andeside (represented by the lowermost two samples in table 2). TABLE 2,—Potassium-argon ages of volcanic rocks in the Yuma area Apparent age (million years ) Location, description, and stratigraphic position of sample H39 TABLE 2.——Potassium—argon ages of volcanic rocks in the Yuma area—Continued Apparent age (million Location, description, and stratigraphic position years) of sample Lat 32°56’56” N., long 114°33’12” W., Chocolate Mountains, Calif. Sample from a flow of horn- blende andesite that overlies dated pumiceous andesite tufl" (sample COL 2—7z38A). Sample COL 2—7:41A; Univ. Arizona lab. PED 1—67. K-Ar age of hornblende phenocrysts _________ Lat 32°56’37” N., long 114°32’52" W., Chocolate Mountains, Calif. Sample from a bed of pumi- ceous andesite(?) tuff that underlies dated horn- blende andesite flow (sample COL 2—7z41A). Both the flow and the tufi' appear to be strati- graphically below the dated felsic tufl’ and welded tuff and probably below the dated basal- tic andesite or basalt. Sample COL 2—7:38A; Geochron lab. BO 514. K-Ar age of biotite ____ 24.7:2.1 25.9:O.9 Lat 32°45'58” N., long 114°26'10” W., Laguna Mountains, Ariz. Sample from bed 2—4 ft thick composed of pink altered bentonitic ash in lower part of upper member of Kinter Formation. Lo- cally Kinter Formation overlies breccia and conglomerate of heterogeneous composition. Sample VAW—60229; USGS lab, 471—B. K-Ar age of biotite ______________________________ Lat 32°49'53" N., long 114°31’39” W., Chocolate Mountains, Calif. Sample from base of a se- quence of flows of basaltic andesite or basalt that unconformably overlies breccia and con- glomerate of heterogeneous composition. Sample HC2—15z35B; Univ. Arizona lab. (P. E. Damon, written commun., 1970). K-Ar whole-rock age __ Lat 32°48’13” N., long 114°28’50” W., Laguna Mountains, Ariz. Sample from top of a bed of pale-purple porous soft vitric crystal tufi' at top of section at least 200 ft thick composed of vitric tuff, welded tufi‘, vitrophyre, and pOSsible flow rock of felsic to intermediate composition. Vol- canic rocks unconformably overlie granite brec- cia and conglomerate and are overlain (uncon- formably?) by fanglomerate of the Kinter Formation. Sample 5—15z55A; Univ. Arizona lab. PED 4—65. K-Ar age of biotite ___________ Lat 32°55'15” N., long 114°31’12" W., Chocolate Mountains, Calif. Sample from a bed of hard grayish-purple slightly Welded felsic tuff within a sequence of tuff and welded tuff of felsic to intermediate composition. Sample COL 2—3521A; Geochron lab. F0 448. K-Ar age of sanidine __ 23:1.2 25.1:1.6 26.3:1.0 26.2:1.6 The apparent ages of the volcanic rocks have re- markably little spread and suggest that the entire sequence was erupted within a relatively short time. The precision of the age determinations is not sufficient to corroborate the inferred stratigraphic sequence. The potassium-argon dates all indicate a late Oligocene or early Miocene age for the volcanic rocks according to the widely used time scales of Holmes (1960) and Kulp (1961). However, until the problems of interpreting apparent radiometric ages and correlating them with standard Tertiary sedimentary sequences are worked out more thor- oughly than they are at present, it seems best to say only that the main volcanic sequence in the Yuma area is middle Tertiary. Volcanic rocks of similar age have been described from many other places in the Basin and Range province; Damon and Bikerman (1964, 1965) and Bikerman and Damon (1966) have described a middle Tertiary pulse of hypabyssal plutonism and volcanism which reached a peak between 25 and 30 million years ago in south- eastern Arizona and adjacent areas. The age and correlation of the flows and vent tuff of the Laguna Mountains, and of the scattered masses of basalt or basaltic andesite, are uncertain. Stratigraphic relations indicate that these rocks also are middle Tertiary. These scattered masses may be in part correlative with the basaltic andesite or basalt of the southeastern Chocolate Mountains, but some might be younger. OLDER MARINE SEDIMENTARY ROCKS (TERTIARY) Predominantly fine grained deposits that contain invertebrate faunas representing marine and possi- ble brackish-water environments have been pene- trated in several oil-test wells and water-test wells in the Yuma area. Data from US. Geological Survey test well LCRP 29 and two oil-test wells indicate that the marine sedimentary rocks in much of the H40 area are divisible into tw0 units: (1) An older, more indurated, and probably more deformed sequence, herein designated the older marine sedimentary rocks, and (2) a younger, generally finer grained sequence which is assigned to the Bouse Formation, a name given by Metzger (1968) to equivalent strata in the Parker-Blythe-Cibola area. A dip log of one of the oil-test wells—Colorado Basin Associates Federal 1 in the south-central part of the Yuma Mesa—indicates the presence of an angular unconformity between the two marine units and that the older sequence may be essentially con- formable on underlying nonmarine rocks. In con- trast to the Bouse Formation, which is mostly silt and clay with subordinate thin layers of sand, the older marine sedimentary rocks contain much more sand and are also more indurated. In test well LCRP 29 the greater degree of induration of the older sequence is shown by a caliper log made just after the pilot hole was completed (fig. 14). The log shows that the hole remained at or near the diameter of the drilling bit throughout the thickness of the older marine sedimentary rocks, even though the sequence is very sandy; whereas in the Bouse Formation, al- most all the thin strata of sand, and much of the clay and silt as well, washed out or sloughed, en- larging the hole. The older marine sedimentary rocks consist of more or less indurated light-gray fine—grained sand- stone and interbedded medium- to dark-gray silt- stone and claystone. The sandy strata make up about half the total thickness in all three test wells (LCRP 29, Colorado Basin Associates Federal 1, and Yuma Valley Oil and Gas Co. Musgrove 1). Beds of ash or tuff are reported in the tWO oil-test wells, and at least one bed of altered soft tuff or ash was penetrated in the lower part of the section in well LCRP 29 (fig. 14). Fossils in the older marine sedimentary rocks include foraminifers and mollusks indicative of a marine environment but not diagnostic as to age. In well LCRP 29, Smith (1968) reports the pres- ence of two foraminiferal faunas: the older (which occurs in what are herein designated the older marine sedimentary rocks) consists of abundant globigerinids, mainly Globigem'm'ta mmla with few to common Globquadem‘na hexagona and Sphaer- hoidinella dehiscens, plus a good shelf benthonic fauna including Planulina sp., Uvigem‘na sp., Han- zawayai sp., and Bolivim interjuncta. The younger fauna occurs in the overlying Bouse Formation and indicates much shallower, more restricted waters. The age of the older marine sedimentary rocks and their correlation with stratigraphic units of WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA other areas are not known with certainty. The strati— graphic position of these beds suggests that they probably intertongue with nonmarine beds of the Kinter Formation of Miocene age. Mrs. P. B. Smith (written commun., Oct. 12, 1969) reports that the planktonic foraminifer Sphaeroidinella dehiscens in the sample of older marine sedimentary rocks from well LCRP 29 is now regarded as post-Miocene and is, in fact, con- sidered to be a guide fossil to the Miocene-Pliocene boundary. The older marine sedimentary rocks therefore would be Pliocene, rather than Miocene. However, because of the apparent conflict with other lines of evidence, it seems best to defer assigning a definite age to the older marine sedimentary rocks until additional information becomes available. On the west side of Imperial Valley the Split Mountain Formation of Tarbet and Holman (1944) contains a poorly preserved, meager foraminiferal fauna of Miocene age in the middle part (Tarbet and Holman, 1944), or in the upper part (Durham and Allison, 1961). The Split Mountain is overlain unconformably by the marine Imperial Formation (Durham and Allison, 1961; Woodard, 1961). Be- cause of their similar structural and stratigraphic relations, the older marine sedimentary rocks and the Bouse Formation of the Yuma area may be cor- relative, respectively, with the marine part of the Split Mountain Formation of Tarbet and Holman (1944) and with the Imperial Formation. However, in both places the faunas are somewhat different in the presumably equivalent units, and it has not yet proved possible to trace the units from one area to the other beneath the intervening Imperial Valley. The maximum thickness of the older marine sedi- mentary rocks in the Yuma area may exceed 1,000 feet. A vertical interval of 1,135 feet was penetrated in Colorado Basin Associates Federal 1 oil test; however, if the average dip of 30° indicated by the dip log is correct, the stratigraphic thickness in this well is a little less than 1,000 feet. According to an interpretation of seismic-reflection data and the record of test well LCRP 29, the thickness may be somewhat greater near that well; it may be greater also near well LCRP 25, which, however, did not penetrate these rocks. BOUSE FORMATION (PLIOCENE) The Bouse Formation was named and described by Metzger (1968) in the Parker-Blythe-Cibola area along the Colorado River north of the Yuma area. The younger sequence of marine sedimentary rocks in the Yuma area is assigned to the Bouse on the basis of similar lithology and stratigraphic posi- GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H41 D th CALIPER LOG ELECTRIC AND LITHOLOGIC LOGS GAMMA LOG SD in Hole diameter, Spontaneous potential, Resistivity (18 in,), feet in inches in millivolts in ohms mZ/m Increasing gamma radiation 8 12 14 1 — 5 + 1000 6 10 6 —-| l-— o 30 ———> Transition zone 1045 ft '1100 Bit size 11in. 1200 3°“? Formation 1300 1320 ft 1400 1396 ft 1500 Bit size 1058 in. 1600 Older 1700 marine sedimentary rocks 1800 1900 T‘ D. 1997 ft 2000 6 8 10 12 14 16 Note: Lithologic explanation on plate6 FIGURE 14.—Selected logs of test well LCRP 29 below a. depth of 1,000 feet. 507-243 0 - 74 - 4 H42 tion and of an identical foraminiferal fauna (Smith, 1968). The Bouse Formation is widespread in the sub- surface, but the only known exposure in the Yuma area is 2 miles southeast of Imperial Dam, just east of the Colorado River flood plain (pl. 3). The Bouse appears to be more extensive than the older marine sedimentary rocks and is probably absent only in the mountains, in most of the foothills, and on the tops and upper flanks of buried ridges of pre— Tertiary and early to middle Tertiary rocks (fig. 15). Although it has been broadly warped and locally faulted (fig. 15), the Bouse Formation appears to be substantially less deformed than the nonmarine sedimentary rocks and the older marine sedimentary rocks, and it probably was deposited after the prin- cipal mountain masses in the Yuma area had as- sumed approximately their present configuration but not their present altitude. The thickness of the Bouse ranges from zero where it pinches out or is overlapped by alluvium to a maximum of about 950 feet in Yuma Valley Oil and Gas Co. Musgrove 1 test well near the southwest corner of the area. Except at some places in the northeastern part of the area where the con- tact with overlying older alluvium is sharp and may be an unconformity, the Bouse Formation is over- lain by a transition zone in which marine clay and silt are interbedded with nonmarine alluvial de— posits like those in the older alluvium. The Bouse Formation consists predominantly of silt and clay, with subordinate very fine to fine sand, hard calcareous claystone, and—locally in the basal part—calcareous sandstone or sandy limestone, tuff, and possibly conglomerate of local derivation. In the subsurface the clay and silt are pale-greenish gray to bluish gray (dark green to dark blue when wet) ; some strata are pink and brown. The very fine to fine sand is light gray and is well sorted. In the exposures southeast of Imperial Dam the predomi- nant color of the fine-grained beds is pale-greenish gray, but pale-yellowish-gray, light-brown, and pink beds are conspicuous in the upper part, which is transitional into grayish-brown and reddish-brown clay and silt characteristic of the overlying older alluvium. Organic remains, both plant and animal, are abundant in some zones. Small gastropods, pele- cypods, and ostracodes can be seen with the unaided eye. Plant remains consist of molds of twigs and roots, partly filled with brown ferric oxides or by- droxides. The microscope reveals also several spe- cies of Foraminifera, consisting of Ammonia bec- carii, Elphidium cf. E. gunteri, Epom‘della palmeme, WATER RESOURCES 0F LOWER COLORADO RIVER—SALTON SEA AREA and Rosalind columbz'ense. (P. B. Smith, written commun., 1969). The faunas are said to indicate brackish to marine environments but are not diag- nostic as to age (Metzger, 1968). The sandy limestone or calcareous sandstone locally present at the base ’of the Bouse Formation is very pale gray to grayish yellow and in places contains an abundant marine fauna, including corals as well as mollusks. This calcareous bed is equiva- lent to the basal limestone described by Metzger (1968) in the Parker-Blythe-Cibola area. In the Yuma area, this limestone was penetrated in test wells LCRP 26 and 23, in a private well (C—9— 21)14bdb, and probably in oil-test well Sinclair Oil Co. Kryger 1, but in other wells penetrating the base of the Bouse Formation it is either absent or unrecognized. In gamma-ray logs this basal lime- stone is a prominent zone of abnormally low natural gamma radiation. In test well LCRP 26 it uncon- formably overlies a nonmarine coarse fanglomerate, the top few feet of which appears to be weathered, probably representing a fossil soil zone. The weath— ered zone is characterized by high natural gamma radiation (probably owing to its clay content), which contrasts vividly with the very low gamma radiation of the overlying basal limestone (or cal- careous sandstone) of the Bouse Formation (fig. 16). In well LCRP 26 the basal limestone is 28 feet thick and is overlain by a bed about 9 feet thick that has abnormally high gamma radiation and is probably a tuff or altered tuff (fig. 16). Unfortu- nately, only a very few cuttings of this bed were recovered during drilling, so its exact nature is not known, and it could not be dated radiometrically. In test well LCRP 23 the clay, silt, and fine sand of the upper part of the Bouse Formation are under— lain by conglomerate and arkosic sandstone com- posed of granitic and metamorphic rocks containing a 3—foot bed of bluish-gray claystone similar to that higher in the section. These beds overlie a 6-foot stratum of sandy limestone, which in turn rests on conglomerate (fanglomerate?) much like that above. The stratigraphic position of the conglomerate, the interbed of claystone, and the sandy limestone are uncertain; no fossils were collected from these beds. Lithologically, the conglomerate resembles that in the Kinter Formation, which unconformably under- lies the Bouse Formation southeast of Imperial Dam and probably also at test well LCRP 14 at Laguna Dam. However, the presence of the bluish-gray clay- stone in the middle of the section and of the sandy limestone at the base suggests that the entire se- quence belongs to the Bouse Formation. The con- glomerate and sandstone beds may represent beach GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H43 114945, : ’ 114°15’ " Io. VII/fl WW/ I” I ,, ,, / //////. O / ///// 32°45, \ ——~— '0’ " ' I MEXIC -, Morelos Dam / Gk _ / ‘~ v \ ,_/ ‘-;7 v \/ \-/ % 2500139“? A .90 Q 30' o 5 MILES \~A£Izo l_l_.|___.l_l_l 80W A \ \\ \ i EXPLANATION \~K‘- _ \ \ Inferred subsurface margin .pTc ‘ ' \ 0f Bouse Formation Well penetrating pre-Bouse rocks '.'.'.:+z45 beneath alluvium Exposure of Bouse Formation pTc, pre- Tertiary ervstalline rocks,‘ Tn, *:‘\UNIT +245, altitude of top offormation, Tertiarunonmarine. sedimentary rocks; 71%) STAT infeet above mean sea level TV’ Tertiary volcanic rocks X% £6; _1350+ _ — ’500 Mountains and hills .° 2950 . Structure contour \‘ Well penetrating Bouse Formatlon Shows altitude of top of House Formation, —2950, altitude of top offormation, in feet Contour interval 500 feet. Datum is above mean sea level. Plus or minus mean sea level sign after number indicates an estimated 7 7 altitude,from geophysical data, for well . . ———_“— penetrating only the overlying transition Fault offsettlng Bouse Formatlon Alluvial escarpment zone Dashed and queried where uncertain 32° 15: | 1 FIGURE 15i—-Inferred extent and configuration of the Bouse Formation. gravels or offshore bars similar to those described The invertebrate fossils in the Bouse Formation by Metzger (1968) in the basal limestone of the are useful as indicators of a marine to brackish- Bouse Formation in the Parker-Blythe-Cibola area water environment, but none so far identified is to the north. diagnostic as to age except within broad limits. H44 WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA U Tl -VEL ITY LITHOLOGIC Depth A00 S LCOG OC LOG RESISTIVITY L0G GAMMA LOG in feet , Velocity, in feet per second R, in ohms mZ/m (18 in.) Increasing gamma radiation 4000 6000 8000 10,000 12,000 14,000 0 6 12 18 24 3O 36 ——> 1000 1 I r n 113 Older alluvium 2a 6 1033 ft T 1050 a 5 Transition zone 1b 1100 < 5 3 1115 ft 4~ 6 1150 5 6 .3; a E 1200 Bouse Formation 1250 E 5 é 21 1300 f 1343 ft E i 10 mm 1350 1352 ft 7 Basal 2 < limestone 138915 E 1380 ft 77 SK 1400 iNonmarine 1% 8 sedimentary rocks F (fanglomerate) 1450 l 1 1 15 1 I I 1 <2 —1 4000 6000 8000 10,00012,000 14,000 1 1 0 6 12 18 24 30 36 Note: Lithologic explanation on plate6 FIGURE 16,—Selected logs of test well LCRP 26 between depths of 1,000 and 1,450 feet. P. B. Smith (written commun., 1966) reports that 1 within the Pliocene, although a more definite age the foraminifers range from Miocene to Holocene, assignment is not yet possible. Metzger (1968) though none is living on the Pacific coast today. Metzger (1968) reviews other evidence for the the Bouse Formation between the Parker-Blythe- age of the Bouse and concludes that it belongs Cibola area and Imperial Valley which was dated describes a thin tuff within the basal limestone of GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA by the potassium—argon method as 8.1:44 m.y. (P. E. Damon, written commun., 1969). This tufl' may be correlative with that just above the basal limestone in test well LCRP 26 (fig. 16). Little additional evidence for the age of the Bouse Formation is available in the Yuma area. As men- tioned earlier, the Bouse overlies the Kinter Forma- (Miocene) with at least local angular discordance; a lower limit of Miocene (probably late Miocene) is therefore reasonably well established. As in the Parker—Blythe-Cibola area, none of the distinctive well—rounded siliceous gravel characteristic of Colo- rado River alluvium occurs within or below the Bouse Formation, so the Bouse antedates the estab- lishment of the Colorado River as a through-flowing stream within the present lower Colorado River region. In the Yuma area, the Bouse Formation is overlain gradationally by alluvium of the Colorado River; Metzger (1968) cites evidence that the earliest deposits of the lower Colorado River are no younger than late Pliocene. TRANSITION ZONE (PLIOCENE) Throughout most of the Yuma area, the Bouse Formation appears to be overlain conformably by alluvium deposited by the Colorado River and pos- sibly the Gila River. In much of the area, marine deposition did not cease abruptly, however, and the marine deposits are overlain by alternating or inter- tonguing marine and nonmarine (alluvial) strata. For convenience this interval, which is as much as several hundred feet thick in the southwestern part of the area, is designated the transition zone. The top of the transition zone is defined by the upper— most bed of fossiliferous gray clay or silt, the base by the lowermost bed of recognizable sand or grav- elly sand of fluvial origin just above the predomi- nantly fine grained marine beds of the Bouse Forma- tion. In a few wells, thin beds of bluish— or greenish- gray clay have been reported within the alluvium as much as 1,000 feet above the top of the deposits assigned to the transition zone. These beds, gen- erally less than 2 feet thick, may indicate later brief recurrences of marine conditions, but more likely they are not beds at all but are boulders of the marine clay reworked into the alluvium by the ancestral Colorado River. Such boulders have been observed in exposures of the older alluvium at many places. CONGLOMERATE OF CHOCOLATE MOUNTAINS (TERTIARY AND QUATERNARY) On the flanks of the southern Chocolate Moun- tains, the nonmarine sedimentary rocks and vol- canic rocks of Tertiary age are overlain by a slightly H45 to moderately indurated conglomerate composed chiefly of volcanic detritus derived from nearby ex- posures of the volcanic rocks. In places the contact of the conglomerate and the older rocks is an angu- lar unconformity with a discordance of as much as 15°, but in other places the discordance is slight or absent. Small angular unconformities have been observed within the conglomerate and probably record uplift of the Chocolate Mountains mass while deposition was going on. On the west flank of the mountains the conglomerate is overlain unconform- ably by older alluvium (old deposits of the Colorado River), but farther west the contact of these two units may be conformable or gradational. From the field relations it appears that the older parts of the conglomerate of the Chocolate Mountains may be equivalent in age to the upper part of the nonmarine sedimentary rocks (Kinter Formation of Miocene age), but that the younger parts are equivalent in age to the older alluvium (Pliocene and Pleistocene). (See fig. 11.) The conglomerate of the Chocolate Mountains is typically pale pink when viewed from a distance and is composed chiefly of pink and gray fragments of ash-flow tufl" and welded tuff. Most of the fragments, which range in size from granules to occasional slabs and blocks several feet across, are subangular or angular. Beds of pale-brown soft sandstone are locally conspicuous. The upper part of the unit contains abundant soft brown siltstone. The conglomerate generally is only mildly de- formed; the bedding dips less than 5° at most places but bedding as steep as 45° has been observed near normal faults. Small high-angle normal faults are abundant, especially in the more indurated parts of the unit and where the bedding dips more than about 4°. OLDER ALLUVIUM (PLIOCENE AND PLEISTOCENE) The older alluvium consists of basin-filling fluvial and deltaic sediments deposited by the Colorado and Gila Rivers and by local ephemeral streams. The unit does not represent a single cycle of aggrada- tion but rather is a complex of fills separated by degradational cycles during which extensive scour- ing occurred. The degradational and aggradational cycles probably were caused in part by fluctuations in sea level amounting to several hundred feet re- lated to glacial and interglacial stages and in part by both regional and local warping of the land sur- face. Erosion by the river probably occurred during times of lowered sea level or upwarping; deposition took place when sea level rose or downwarp oc- curred. The southwestern part of the Yuma area, H46 on the margin of the Salton Trough, subsided con- tinually under the load of the fluvial and deltaic deposits so that not all the deposits of the aggrada- tional episodes were removed during the ensuing degradational episodes. Farther northeast and adja- cent to the mountain blocks, however, many if not most of the earlier fills were removed and replaced by later fills. Although different alluvial fills separated by un- conformities have been identified in outcrop areas, subsurface delineation of all the fills has not been possible with present data. Accordingly, all the alluvial and deltaic deposits older than the most recent fill are grouped in one unit designated as older alluvium. The older alluvium occupies the stratigraphic interval between the transition zone (or the Bouse Formation where the transition zone is absent) and the younger alluvium (the most re- cent fill). DISTRIBUTION AND THICKNESS The older alluvium is the most widely exposed stratigraphic unit in the Yuma area. It is exposed in mesas, stream terraces, and piedmont areas and underlies the younger alluvium of the present flood plains of the Colorado and Gila Rivers and the young alluvial fans in the southeastern part of the area (pl. 3). At some places the older alluvium is concealed by a blanket of windblOWn sand. Expo- sures of older alluvium commonly are dissected, and many are characterized by desert pavement that formed on poorly sorted gravelly deposits (pl. 3). On the flanks of some of the mountains, coarse older alluvium of local origin forms low hills and dis- sected uplands similar to some of the exposures of coarse nonmarine sedimentary rocks of Tertiary age (fig. 9). The thickness of the older alluvium ranges from zero to as much as 2,500 feet in the southwestern part of the area, near San Luis, Ariz.; if the under- lying transition zone is included, the maximum thickness is about 3,400 feet (fig. 15 and pl. 10). This thickness is much greater than that attained by equivalent deposits north of the Yuma area; Metzger, Loeltz, and Irelan report that the maximum depth to the base of the older alluvium in the Parker-Blythe-Cibola area is about 600 feet. The great thickness in the Yuma area, and the much greater thickness of equivalent deposits of the C010- rado River in Imperial Valley, indicate subsidence during deposition. The oldest alluvial deposits (at the base of the transition zone), which are now more than 3,000 feet below sea level near San Luis (fig. 15), must have been deposited above or at least not far below sea level by the ancestral Colorado River. WATER RESOURCES 0F LOWER COLORADO RIVER—SALTON SEA AREA AGE AND CORRELATION The age of the older alluvium ranges from Plio- cene to late Pleistocene, according to several lines of evidence. The, underlying Bouse Formation is considered Pliocene (p. H44), and the overlying younger alluvium is Holocene and possibly latest Pleistocene. Recent studies of the erosional history of the Grand Canyon, summarized in McKee, Wilson, Breed, and Breed (1967), show that the canyon was cut to nearly its present depth by the middle Pleis- tocene. This seems to require an inauguration of the canyon cutting well before the beginning of the Pleistocene and would imply that the Colorado River had entered the downstream region including the Yuma area at least as early as some time in the Pliocene. The Gila River may not have entered the Yuma area until long after the advent of the Colo- rado River, but the scanty evidence is inconclusive as to the history of the ancestral Gila River down- stream from the Phoenix basin (M. E. Cooley, writ- ten commun., 1969). Three samples of carbonized wood from the upper part of the older alluvium in the Yuma area have been analyzed by the radiocarbon (0”) method. The results are listed below: Age in years before present (C—10—23)31bbb1. U.S. Geological Survey test well LCRP 1. Lignite from a depth of 472—474 ft. USGS lab. W—1428 _________________________ (C—10—24)12ccc2. U.S. Bureau of Reclamation drainage well YVI—28. Carbonized wood from a depth of 128—130 ft. Geochron lab. GXO—661--- 168/23E-10Rcc. U.S. Geological Survey test well LCRP 23. Carbonized wood from a depth of 224—234 ft. USGS lab. W—1538 ______________ >36,000 All three samples are older than the limits of the radiocarbon method of measurement, and the differ- ences in the minimum ages shown are not signifi- cant. The unconformably overlying younger allu- vium has yielded radiocarbon ages of less than 10,000 years in the Parker-Blythe-Cibola area (Metzger and others, 1972). Thus, the radiocarbon evidence indicates that the upper part of the older alluvium can be no younger late Pleistocene. The older alluvium of the Yuma area probably is correlative with the older alluvium of the Parker- Blythe—Cibola area (Metzger and others, 1973). Deposits near Gila Bend 120 miles east of Yuma, called older alluvial fill by Heindl and Armstrong (1963), probably are correlative with the older alluvium in the Yuma area. In the Imperial Valley region, units equivalent or partly equivalent to the older alluvium of the Yuma area include the Palm Spring Formation, the Canebrake Conglomerate of Di'bblee (1954), and the Borrego Formation of Tar— >42,000 >33,600 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA bet and Holman (1944); the Ocotillo Conglomer- ate and the Brawley Formation (both of Dibblee, 1954) may be equivalent to the uppermost part of the older alluvium. CLASSIFICATION OF DEPOSITS BY SOURCE The older alluvium comprises a great variety of granular materials ranging from clay to cobble and boulder gravel. On the geologic map (pl. 3) these materials are classified according to their primary source into deposits of local origin, deposits of the old Colorado and Gila Rivers, and deposits of mixed origin. In addition, many of the areas adjacent to the mountains are mantled with relatively thin sheets and ribbonlike bodies of gravelly deposits left behind as these areas were dissected. These deposits; referred to as stream-terrace and piedmont deposits, are included with the older deposits of local origin on the geologic map; their extent is indicated in a general way by the pattern representing desert pavement, which is characteristic of the exposures (pl. 3). DEPOSITS OF LOCAL ORIGIN The deposits of local origin occupy the margins of the area, adjacent to the mountains and expo- sures of older rocks, and were laid down by ephem eral streams and sheetfloods. Because most of the materials were deposited as flood-swollen, muddy masses of debris from nearby sources, they are obscurely bedded and poorly sorted. Typically they consist of angular to subangular gravel in a matrix FIGURE 17.—Poorly sorted gravelly deposits of local origin exposed in west bank of Fortuna \Vash 0.4 of a mile north of U.S_ Interstate Highway 8. H47 of silty or clayey sand (fig. 17). Scour and fill are common, and individual strata are poorly defined and lenticular. The composition of the gravel is closely related to the kinds of older rocks in the drainage area. Farther from the source, the deposits become finer grained and better sorted and the gravel more rounded. Most of the older alluvium of local origin probably was deposited as alluvial fans. The oldest exposed local deposits are comparatively thick masses of coarse ill-sorted gravel which characteristically form low hills and dissected uplands mantled with a blanket of coarse colluvium (fig. 9). STREAM-TERRACE AND PIEDMONT DEPOSITS Except for the scattered low hills and dissected uplands mentioned above, the older fills in the older alluvium are capped by relatively thin stream- terrace and piedmont deposits left behind as the older deposits were progressively dissected by local streams and sheetfloods. The stream-terrace and piedmont deposits consist largely of ill-sorted gravel associated with much sand, silt, and clay. At most places they overlie similar older fill from which they are often difficult to distinguish. According to F. L. Doyle (written commun., 1963), who inten- sively studied the piedmont area at the northwest corner of the Gila Mountains, the gravelly pied- mont deposits represent the bedloads of ephemeral streams that dissected the older rocks and alluvial fills. As their name implies, the stream-terrace and piedmont deposits occur in two principal environ- ments which, however, tend to intergrade. The stream-terrace deposits are found at different levels along the larger washes and also along abandoned washes, where they reach a maximum thickness of more than 50 feet. The terraces are not paired and are most extensive on the concave sides of large bends. The deposits undoubtedly are analogous to those now accumulating in the larger washes. The piedmont deposits underlie extensive piedmont sur- faces formed by a combination of sheetfloods and shifting ephemeral streams. These deposits are less than 10 feet thick at most places. Most exposures of stream-terrace and piedmont deposits are characterized by an armor of closely spaced pebbles or small cobbles which is called “desert pavement.” In many places these stones form a mosaic so that little sand or silt is visible. The stones are generally coated with a dark stain called “desert varnish,” which gives the pavement a dark aspect, like asphalt. Not all pavement is dark, however. Pebbles and cobbles of the lighter colored H48 granitic and quartzose rocks commonly lack a good coating of desert varnish (fig. 8). Most desert pavement contains a layer of silty sand and silt 2—4 inches thick just below the armor of pebbles and cobbles. The layer is impoverished in gravel and nearly everywhere contains some clay as a binder. It is underlain by a darker mixture of silty sand and gravel in a zone as much as 8 inches thick. The darker third layer contains seams of cal- cium carbonate (caliche) and may represent the B soil horizon. Owing to their clay and silt content, the second and third layers are not very permeable, and the dense mosaic of stones in the tOp layer does not allow water to penetrate rapidly from the sur- face. Infiltration rates from precipitation are low, and much of the water runs off pavement surfaces during storms. Infiltration rates are higher in the areas of light-colored granitic and quartzose pave- ment, which have thinner silty and clayey sub- strata. The desert varnish on desert pavement consists of oxides of manganese and iron brought to the sur- face by capillary action assisted by acid secretions of lichens (Laudermilk, 1931). Hunt (1954) cites archeological evidence that most coatings of desert varnish are at least 2,000 years old, although Engel and Sharp (1958) state that varnish is not neces- sarily an indicator of antiquity. If Hunt’s conclu- sions (1954) are correct, the widespread presence of varnish on even the lower stream terraces and on bedrock exposures attests to the general slowness of the processes of weathering and erosion in the region. DEPOSITS OF MIXED ORIGIN Where the deposits of local origin intertongue or grade laterally into old deposits of the Colorado and Gila Rivers, the materials are classified on the geo- logic map (pl. 3) as deposits of mixed origin. Much of this unit consists of river deposits that have been reworked by local ephemeral streams and sheetfloods and mixed with deposits of local origin. At many places, good exposures reveal a broad zone of dis- tinctive buff silt and fine sand which grades away from the mountains into well-sorted fine to medium river sand, and toward the mountains into ill-sorted gravelly deposits of local origin. From this relation- ship it is inferred that the old Colorado and Gila Rivers were bordered by broad flood plains into which discharged, during brief periods, local runoff carrying detritus from the adjacent hills and moun— tains. However, at some places the flood-plain silt and fine sand abut directly against older rocks and contain very little coarse detritus of strictly local derivation. This relationship has been observed on WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA the flanks of the Chocolate Mountains (fig. 18) and the almost—buried “Yuma Hills.” DEPOS/ITS OF THE OLD COLORADO AND GILA RIVERS The greatest bulk of the older alluvium in the Yuma area consists of deposits of the old Colorado and Gila Rivers. These deposits are noticeably dif- ferent from those of local origin. They are better sorted and stratified and less heterogeneous on a small scale than the local deposits; the river gravel is much more rounded than the local gravel and contains types of rocks derived from the middle and upper parts of the Colorado River drainage basin. In contrast with the local deposits, which are ex- tremely variable, both areally and vertically, the river deposits contain some beds or zones that can be traced for several miles. Sand is the most abundant material in the old river deposits. The river sand is much better sorted than the local sand and is more commonly cross- bedded (fig. 19). Also, the grains of river sand are generally more rounded than those of local sand. River sand is typically gray to pinkish gray, where- as local sand is yellowish to reddish brown. Crude analyses of several samples of fine to medium river sand from the older alluvium near Yuma indicate the following approximate composi- tion: Quartz, 65-75 percent; feldspar (not difier- entiated) , 10—20 percent; rock fragments, 5-15 per- cent; calcite and dolomite (in part as cement), 2—5 percent; and heavy minerals, 1—8 percent. The quartz is clear to translucent, mostly subrounded to subangular but occasionally rounded; feldspar is white, pink, or grayish-yellow and subangular to subrounded; rock fragments are chiefly small, angu- lar to subrounded, and composed of chert, quartzite, granitic, metamorphic, and volcanic rocks. Most of the river sand is feldspathic, according to the classi- fication of Krumbein and Sloss (1951). Results of heavy-mineral analyses of alluvial sand (chiefly older alluvium but including some younger alluvium) are summarized 'in table 3. Most of the samples represent river deposits; the two samples from well (C—8—23)33cdd (test well LCRP 13) rep- resent local sand and are quite different in composi- tion from the other samples. Amphiboles (chiefly green hornblende), pyroxenes (chiefly augite), and opaque minerals (magnetite, ilmenite, and pyrite) typically compose about three-fourths of the total; garnet and zircon are the other important heavy minerals. No significant variation in heavy-mineral composition with depth has been noted, with the possible exception that the orthorhombic pyroxenes (hypersthene and enstatite) are scarce or absent below depths of about 350 feet in the Yuma Mesa. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H49 FIGURE 18.—View in southeastern Chocolate Mountains, Other investigators in the region have reported similar conclusions. R. W. Thompson (written commun., 1963) states that amphiboles, pyr‘oxenes, and opaque minerals compose more than 80 percent of the heavy-mineral total in sand of the lower Colorado River delta and Gulf of California; epi- dote, titanite, garnet, and zircon also are present in significant amounts. Imbrie and van Andel (1964) describe the north end of the Gulf of California as an amphibole-augite-garnet heavy-mineral province in which the Colorado River is the probable source of the sediments. After sand, gravel probably is the most abundant material in the deposits of the old Colorado and Gila Rivers, especially in the upper several hundred feet of these deposits. Some of the gravel is coarse and contains many rounded cobbles and small boulders. Calif., showing predominantly fine-grained older alluvium abutting basaltic andesite or basalt of Tertiary age. River gravel is exposed at many places through- out the Yuma area. Along the southeast margin of “Picacho Mesa” a gravel tongue can be traced for a distance of about 10 miles. Similar tongues occur farther north as much as 560 feet above sea level and also in the “Upper Mesa” as much as 580 feet above sea level. The highest known occurrences of river gravel in the Yuma area are at 740 feet above sea level on the southwest flanks of the Chocolate Mountains. In the subsurface, river gravel occurs throughout the entire thickness of older alluvium and underly- ing transition zone to depths as great as 3,400 feet near the southwest corner of the area, although the coarse cobble—gravel strata probably extend no deeper than about 750 feet (pl. 6). The uppermost coarse-gravel strata beneath the river valleys and FIGURE 19.-~—Crossbedded coarse sand and fine gravel in exposure of older alluvium 6 miles west of Yuma. The more resistant sand laminae in these old deposits of the Colorado River have a slightly higher content of calcareous cementing material than the rest of the sand. Yuma Mesa constitute the principal aquifer in the Yuma area and are referred to collectively as the coarse-gravel zone (p. H67). Brown and others (1956), who named the coarse—gravel zone, described it as a widespread blanketlike deposit underlying at least part of their “upper terrace” (“Picacho Mesa” and “Upper Mesa”), as well as the interven— ing Yuma Mesa and river valleys. However, detailed studies by both the US. Bureau of Reclamation (J. W. Julian, written and oral commun, 1967) and the US. Geological Survey have shown that the coarse river gravel in the older alluvium occurs as a complex of several gravel bodies of different ages, although it has not yet proved possible to determine the boundaries of all these bodies. The top and bottom of the coarse-gravel zone are there- fore at different horizons and altitudes from place to place (pl. 7). Some of the irregularities in the zone are shown also in the geologic sections of the area (pls. 5, 6, 8). The coarse-gravel bodies, includ- ing those below the coarse-grave] zone, probably were deposited during the glacial stages of the Pleistocene, when the Colorado River was swollen by glacial melt water from the Rocky Mountains, and each gravel body fills a trench 0r valley scoured in older fills. The top of the coarse-gravel zone slopes generally southwestward from altitudes of about 90 feet above sea level at the east end of South Gila Valley and 40 feet above sea level at Laguna Dam to about WATER RESOURCES 0F LOWER COLORADO RIVER—SALTON SEA AREA 80 feet below sea level at the southwest corner of the area (pl. 7). Corresponding depths below valley surfaces are about 70 feet in eastern South Gila Valley, 100 feet at Laguna Dam, and 170 feet at the southwest corner of the area. The increasing depth toward the southwest results chiefly from southwestward gradation of the uppermost coarse- gravel strata into finer deposits, so that the top of the coarse-gravel zone is at a lower horizon in the southwest than in the northeast. Areas where the coarse-gravel zone does not ap- pear to be present include the southeast margin of northern Yuma Mesa, “Picacho Mesa” and adja- cent parts of “Bard Valley,” most of the “Upper Mesa,” and the northwest corner of Yuma Mesa and the adjacent northeast corner of Yuma Valley (pl. 7). The older alluvium of these areas is pre- dominantly sandy, with only minor, apparently dis— continuous streaks of fine gravel. The river gravel differs 'markedly in several re- spects from the local gravel of the older alluvium. Unlike local gravel, in which bedding is indistinct and crossbedding rare, river gravel commonly is crossbedded; foreset bedding dips about 20°—30° and is conspicuous in many exposures. Cementation, generally calcium carbonate, is a widespread char- acteristic of the river gravel, both in exposures and in the subsurface. Compared to the local gravel, the river gravel is better sorted, and the clasts are more rounded and include a large proportion of hard, siliceous rocks (fig. 20). Gray and tan quartzite are generally the most abundant types of siliceous rocks; other types include red and brown jasper, gray and black chert, and a distinctive crosslaminated tan and maroon quartzite very similar to some of the Tapeats Sandstone of Cambrian age in the Grand Canyon. Except for a few pebbles of brown jasper, these hard siliceous rocks are completely absent in the grave] of entirely local origin. In places the river gravel contains as much as 80 percent siliceous rocks, but the usual proportion is 30—60 percent (table 4). Other types of rocks include a variety of felsic plutonic (granitic) rocks; felsic to intermediate volcanic rocks (including abundant hard red welded tuff); various kinds of schist, gneiss, and fine-grained metamorphic rocks; vein quartz; pegmatite, aplite, and other dike rocks; and in places some limestone and dolomite. Worn, rounded fragments of silicified wood (probably desert iron-wood) also occur locally. Like the sili- ceous rocks, some of the plutonic, metamorphic, and volcanic rocks, especially the most resistant, well- rounded clasts, probably came from regions far upstream from Yuma, but others probably were con- GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H51 TABLE 3.—Summary of heavy-mineral analyses of alluvial sand (deposits of the Colorado River of the Yuma area) [Analyses by U.S. Geo]. Survey, Hydrologic Laboratory] Range in Percentage of total beavy minerals1 Well Number of depth of samples samples Amphlboles Pyroxenes Opaques Garnet Zircon . (feet) I (C—10—23) 31bbb1 __________________ 3 195-955 31 14 21 9 7 (C—10-23)15aab ___________________ 2 400—851 32 18 16 9% 12 (C—10—23) 5ddd ____________________ 14 0—500 44 34 11 5 1% (0—8—22) 35ccb - _ _ ______________ 10 85—600 40 34 16 4 2 168/22E—23Caa __ _ ________ 2 100—248 28 16 28 10 8 (C—11—24) 23bcb _________ __ 7 39—1,038 33 21 16 12 7 (C—8—23) 33cdd ’ ___________________ 2 705—1,080 12 2% 22 20 11 (C—7—22) 14bcd ____________________ 3 77—209 30 14 33 9 ‘yé 5 (0—10—25) 35bbd ___________________ 10 51—2,823 3O 18 23 9 5 Average for eight wells __________________________________ 34 21 20 8 ta 6 1Other heavy minerals present in significant amounts include epidote. biotite. tourmalne, apatite, and titanite. "Samples from (0—8—23)33cdd not included in averages; probably represent deposits of local origin. FIGURE 20.——Well-rounded to subrounded Colorado River gravel in an ex- posure of older alluvium southwest of Pilot Knob. Pebbles and cobbles are chiefly quartzite and chert in a matrix of lime-cemented coarse sand. Steel tape (extended to a little more than a foot) gives scale. tributed from local sources. Welded tuif derived from the local Tertiary volcanic sequence is locally abundant, and some of the granitic clasts, undoubt— edly had local s0urces. A few of the most significant characteristics of the gravel penetrated in test wells and deep private wells are summarized in table 4. Each sample con- sisted of 100 pebbles and small cobbles selected at random from the bulk sample obtained from the depth interval indicated. Clasts ranged in size from about 1/2 inch to 4 inches; most were in the range of 1—2 inches. Identifications were made by hand lens. Most of the samples appear to be river gravel, although in some of the samples the angularity of the clasts and the relatively low percentage of quartzite and chert suggest local origin. Possibly the most significant parameter in the gravel analyses is the percentage of black chert. Recent studies of the south-central Yuma area by the US Bureau of Reclamation (J. W. Julian and Earl Burnett, oral commun., 1966—67) have shown that the deeper, older gravel strata in the older alluvium have a noticeably higher concentration of black chert than the shallower, younger gravel strata. The figures in table 4 tend to substantiate that conclusion, although admittedly the data are too few to indicate more than a general trend. The source or sources of the black chert have not yet been identified with certainty; M. E. Cooley (oral commun., 1967) reports that similar black chert in the Grand-Glen Canyon region was probably de- rived originally from the Mescal Limestone (upper unit of the Precambrian Apache Group) of central Arizona, from which it was deposited in the Shina- rump Member and other conglomeratic sandstone units of the Chinle Formation (Upper Triassic), and whence reworked later by the Colorado River. M. E. Cooley (written commun., 1969) reports also that no black chert has been observed in the terrace gravel of the Gila River between Hyder and Phoe- nix, Ariz., although black chert is present in the Mescal Limestone in the canyon of the Salt River, a tributary of the Gila near Phoenix. The paleo- geographic significance of the relative abundance of black chert in the river grave] of different ages and different sources may be a fruitful subject for future investigation. Although generally less abundant in the older alluvium than sand and gravel, clay and silt strata are locally conspicuous, especially below depths of H52 TABLE 4,—Selected data from analyses of gravel from wells in older and younger allzwiums [Analyses by F. J. Frank. Average roundness (Wadell, 1932; Krumbein and $1055, 1951) derived by assigning the following roundness va ues to each of four categories described by visual inspection: Well rounded, 0.875; subrounded, 0.625; subangular, 0.375; angular, 0.125] Percentage Well Depth of Average sample roundness Quartzite Black (feet) and chert chert (C—7—22)14bcd ______ 111—125 070 52 (D 177—183 .60 36 (U (C—8—22)15bdd ______ 109—120 .54 45 6 135 .70 43 2 145—150 .53 41 10 260—280 .50 34 15 285—290 .43 47 21 415—420 .40 42 11 (C—8—22)19ccc ______ 225—235 .44 37 (U 355—375 .47 41 9 390—400 .58 36 16 440—465 .49 30 12 (C—8—22)330bb ______ 109—120 .58 35 5 (C—8—22)35caa1 _____ 89 .60 43 0 122 .59 22 2 548—556 .56 32 11 (C—8—22)35ccb ______ 150—185 .70 56 0 190—240 .68 50 0 240—245 .54 45 3 273—300 .42 54 20 415—425 .38 43 13 495—515 .36 55 20 560—570 .37 51 15 (C—lO—23)llccb _____ 131—163 .68 59 12 332—336 .66 56 11 (C—10-23)15aab ____ (?) 2.44 72 27 615—670 .61 72 22 730—754 .55 59 23 754—798 .48 62 19 848—856 .49 57 22 (C—10—23)31bbb1 ___ 137—150 .66 39 3 178—190 .60 41 7 395—407 .49 56 28 545—560 .49 62 26 (C—ll—24)23bcb _____ 186—196 .72 38 9 211—226 .62 46 10 370—379 .74 87 25 381—394 .77 79 26 398—410 .75 77 14 472—490 .74 80 30 523—540 .70 70 20 627—630 .74 76 27 682—685 .64 64 17 850—866 .69 65 24 987—990 .60 62 18 1&04—L006 .59 57 11 16S/23E—10Rcc _____ 110—155 .56 28 6 224—264 .58 43 13 334—364 .47 26 13 495—515 .45 51 8 1 Black chert not differentiated in count. d :IRoundness probably too low; many pebbles in sample were broken by r1 . LOGO—1,500 feet in the southern part of the area (pl. 6) and in the uppermost deposits, above the coarse-gravel zone (pls. 5 and 8). These fine-grained strata can be identified readily on electric logs by their low resistivity and on gamma logs by their relatively high natural gamma radiation. The high gamma intensity of most beds suggests a substantial clay content, although most samples from wells, together with evidence of at least moderate per- WATER RESOURCES OF' LOWER COLORADO RIVER—SALTON SEA AREA meability, indicate the presence of much sand and silt. Brown and others (1956, p. 20) report that particle-size analyses of samples from US. Bureau of Reclamation observation wells drilled on Yuma Mesa showed that pure clay is uncommon; particle- size analysis of a representative bed described by the driller as “silty clay with sand streaks” or “silty sand with clay streaks” might show about 55 per- cent clay, 30 percent silt, and 15 percent sand. The clay and silt strata of the older alluvium are typically brown to gray, in contrast with the greenish- to bluish-gray marine clay and silt of the underlying transition zone and Bouse Formation. A nonmarine origin for the fine-grained strata of the older alluvium is suggested by the abundance of fossil twigs, roots, and root fillings, the scarcity or absence of marine fossils, the close association with coarser strata of obviously fluvial origin, and the similarity to flood-plain clay and silt at the top of the younger alluvium. Slack-water deposition on broad flood plans is the most likely origin. Little work has been done on the determination of the mineral composition of the clay and silt in the Yuma area. Two samples of clay and silt from US. Geological Survey test well (C—10—23)31bbb1 (LCRP 1) were analyzed by X-ray diffraction in the Hydrologic Laboratory of the US. Geological Survey at Denver, 0010., with the following results: Approximate mineral content (percent) 115—120 ft 735—736 ft Clay minerals: Illite _______________________ 7.5 6.3 Kaolinite ____________________ 7.5 4.9 Montmorillonite _____________ 45.0 51.8 Mixed-layer _________________ 15.0 7.0 Quartz __________________________ 13 13 Calcite _________________________ 9 10 Dolomite ________________________ Trace 5 Potassium feldspar ______________ 2 __ Montmorillonite, the dominant clay mineral in both samples, is common in arid environments, especially where source rocks include volcanic ash or tuff. Montmorillonite has the property of expand- ing its crystal structure to accommodate variable amounts of water, and a body of it moistened with water tends to thus swell and become impermeable. Montmorillonite has a considerable capacity for base (cation) exchange. Seismic-reflection data indicate that some of the deeper beds of clay and silt extend several miles laterally. Extensiveness is suggested also by some- what uncertain correlation of several of the thicker fine-grained beds between wells (0—11—25) llab and (C—lO—25)35cab, which are about 2 miles apart (pl. 6). Some of the clay and silt strata in the uppermost GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA part of the older alluvium beneath Yuma Mesa can be traced several miles in wells and good exposures. One prominent bed 5—15 feet thick of fine sandy silt and clay is exposed in the escarpment along the northern and western edges of Yuma Mesa, Where it extends, with some interruptions, more than 15 miles. Two fine-grained beds in the t0p part of the older alluvium have been identified in wells beneath siz- able areas of eastern Yuma Valley and western Yuma Mesa. The lower bed, informally designated clay A (fig. 21 and pl. 5), is not far above the coarse-gravel zone beneath Yuma Valley and adja- cent parts of Yuma Mesa. This bed ranges in thick- ness from a few inches to about 35 feet. Parts of clay A appear to grade laterally into coarser ma- terials at different places, so it is difficult if not impossible to trace a single horizon far enough to determine the precise attitude of the bedding be- neath a large area. In general, however, the middle of the bed seems to have approximately the same slope toward the southwest as the present surface of Yuma Valley. Southeast of Somerton, where clay A is thickest and least sandy, its middle part lies about at sea level (pl. 5, geologic section E—E’ and fig. 21). In places along the margins of the bed the clay and silt grade laterally into pebbly clay and other ill- sorted gravelly deposits which, like the clay and silt, are characterized by high gamma radiation. Clay A underlies an area of at least 33 square miles. Clay B is the informal designation applied to another, higher fine-grained bed that occurs beneath western Yuma Mesa at an average altitude of . about 100 feet above sea level (fig. 22 and pl. 5). Clay B is even more extensive than clay A, under- lying an area of at least 42 square miles, and it probably extended farther west before it was re- moved by erosion when Yuma Valley was cut (fig. 22). Clay B is 10—15 feet thick at most places; more than half the thickness is clay and silty clay, the remainder is silt, fine sand, and scattered pebbles. Toward the northwest the bed is difficult to dis- tinguish from other strata of clay and silt above and below; possibly clay B underlies much of he city of Yuma. Like clay A, clay B grades laterally into pebbly clay and other heterogeneous gravelly deposits, particularly toward the southwest (fig. 22). Along its southeastern margin, clay B may abut older deposits that are exposed in the “Upper Mesa” farther southeast. YOUNGER ALLUVIUM (QUATERNARY) The younger alluvium comprises all the alluvial H53 deposits of the most recent major cycle of deposition. These deposits underlie the present river flood plains, the washes, and the alluvial fans. At these places, aggradation has been the dominant process during the last several thousand years, although locally. degradation seems to have occurred most recently. Soils on the younger alluvium are imma- ture and lack the profile development characteristic of the exposures of older alluvium. The younger alluvium has been classified in three categories according to the dominant agent of depo- sition: (1) Deposits of the Colorado and Gila Rivers, (2) alluvial-fan deposits, and (3) wash and sheet- wash deposits (fig. 11). Each of these three cate- gories or subunits is described briefly below. DEPOSITS OF THE COLORADO AND GILA RIVERS The deposits of the Colorado and Gila Rivers underlie the present river flood plains. Until Hoover Dam and other large dams were constructed on both the Colorado and the Gila Rivers, floods added increments of predominantly fine-grained deposits to the flood plains. The rivers continually shifted their courses across the flood plains in meandering channels. In Yuma Valley the sites of many of the old meanders are marked by long, narrow, arcuate or sinuous sand dunes which accumulated on the leeward sides of the channels. The river deposits consist predominantly of sand and Silt. Pebbly sand and silt are abundant in places, especially in the lower part, and beds of clay and silty clay, which are rarely more than a few feet thick, are locally extensive. One extensive bed of silt and clay lies immediately beneath the flood plains of the Colorado and Gila Rivers. It is not present everywhere, having been replaced by scour and fill of sand along channels occupied by the rivers dur- ing relatively recent times, probably within the last few hundred years. In northern and central Yuma Valley the silt and clay range in thickness from a few feet to as much as 30 feet (pl. 5). Deposition on the flood plain during times of overbank flow is the most likely origin. The river sand of the younger alluvium is gen- erally similar to that of the older alluvium, except that it is commonly looser. Van Andel (1964, p. 236) gives the following composition for a sand from the Colorado River near Yuma: Quartz, 73.3 percent; feldspar (chiefly potassium feldspar), 18.8 percent; and rock fragments, 7.9 percent. A gravel occurs at the base of the younger allu— vium of the Colorado River at depths of about 100—130 feet in the Parker-Blythe-Cibola area 30— 100 miles north of Yuma, where it has been dated H54 WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA 114°45' l 32°45’ UNITED STéTfis. _ _ _ ' mEXICO SMILES /quL_\ / EXPLANATION // _—_ '38 Subsurface margin of clay A l Dashed where doubtful or . . Well used for .contrOI I poorly controlled Solid Circle denotes well having gamma log; open /'\ / circle, well having only driller's log. Upper number / \V/ indicates altitude of top; lower number, altitude of ‘ \ bottom of clay A, in feet related to mean-sea-level. Letter symbols designate: S, sandy clay; VS, very \ \ 1V1 sandy clay; G, gravel and clay; M, clay missing or /\ \TE’D S m not identifiable; (?), clay not distinguishable from I MEXI\T{TES beds above and below 00 T .M .0) 32°30’ Area underlain by clay A Bedrock outcrop FIGURE 21.—Extent and altitude of top and bottom of clay A beneath Yuma Valley and northwest margin of Yuma Mesa. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H55 114°30' 32°45' EX P LA N ATI O N Subsurface margin of clay B Dashed where doubtful or poorly controlled Area underlain by clay B Bedrock outcrop 114 ' 98 Well used for control Solid circle denotes well having gamma log; open circle, well having only driller’s log. Upper number \ indicates altitude of top; lower number, altitude of 0M / bottom of‘clay B , in feet above mean -sea -level. 0386 ( Letter symbols designate: S, sandy clay; VS, very 32°15’ — \ sandy clay; G, gravel and clay; M, clay missing or _ .110 JVI l not identifiable; (?), clay not distinguishable from 83G ( beds above and below \ \ \\ o 5 MILES \ I I I l I I \ .9936 0'“ | FIGURE 22.—Extent and altitude of top and bottom of clay B beneath Yuma Mesa. H56 by the radiocarbon method as less than 10,000 years old (Metzger and others, 1973). This gravel prob- ably was the first material deposited during the most recent aggradation by the Colorado River as sea levels rose with the retreat of the last glaciers of the Wisconsin stage. Two samples of carbonized wood from overlying fine-grained younger alluvium in the same area gave radiocarbon ages of 5,380 and 6,250 years (Metzger and others, 1973). The basal gravel of the younger alluvium of the Colorado and Gila Rivers has not been dated or positively identified in the Yuma area; accordingly, the younger alluvium and older alluvium are not differentiated in the geologic sections (pls. 5, 6, 8). If present in Yuma Valley, this gravel must occur in the western part; no significant gravel strata overlie clay A of the older alluvium in eastern Yuma Valley, which is at a depth of 80—90 feet below the land surface (pls. 5 and 8). In SOuth Gila Valley, likewise, a basal gravel of the younger alluvium has not been definitely identified; if pres- ent, such a gravel must be nested in gravel of the older alluvium which extends southwest of the val- ley, beneath Yuma Mesa (coarse-gravel zone on pl. 8). ALLUVIAL‘FAN DEPOSITS Although surfaces somewhat similar to alluvial fans are common in the Yuma area, true young alluvial fans—that is, thick accumulations of young deposits having fan—shaped aggradational sur- faces—occur only in the southeastern part of the area, adjacent to the Tinajas Altas and Butler Mountains and at the northwest corner of the area, on the west flank of the Cargo Muchacho Mountains. In both these areas the deposits consist of poorly sorted granitic detritus derived from the exposures of granitic rocks in the mountains. US. Bureau of Reclamation test well CH—28YM on the southerly international boundary about 30 miles east of San Luis, Rio Colorado, Mexico, penetrated 310 feet of ill-sorted arkosic sand and silt with thin interbeds of calcareous clay, overlying older allu- vium consisting of interbedded river deposits and local deposits, probably also of alluvial-fan origin. (See log of well (C—13—20)2abd1 in appendix B.) The scattered shallow exposures in this area reveal granitic (arkosic) sand and fine gravel (chiefly angular clasts of granite, felsic dike rocks, quartz, and feldspar), and interbedded silt and clay. The fan surfaces are characterized by a network of broad, shallow channels having a dendritic pattern where degradation has been the dominant recent process, and a distinctive rhomboidal pattern where WATER RESOURCES 0F LOWER COLORADO RIVER—SALTON SEA AREA aggradation (perhaps by sheetfloods) has been dominant most recently. WASH AND SHEET-WASH DEPOSITS The wash deposits occur in washes and channels cut into the older alluvium and prealluvial rocks. The deposits are generally thin and consist of sand and gravel and thin, lenticular beds of silt. In many washes, degradation rather than aggradation is the dominant process at present, and even the most recent wash deposits have been subject to extensive scour during floods. The sheet-wash deposits are similar to the wash deposits but occupy broader, less well defined areas. They also resemble the alluvial-fan deposits. How- ever, instead of forming fairly thick wedges like the alluvial-fan deposits, the sheet-wash deposits are thin blankets on older rocks and deposits, and are probably formed by sheetfloods and thin mud- flows. Their most extensive development is in the “Laguna Mesa” north of the Laguna Mountains, where they consist of sand and silt reworked from the underlying older alluvium. WINDBLOWN SAND (QUATERNARY) The thickest and most extensive deposits of wind- blown sand are the Sand Hills (“Algodones Dunes”) on the East Mesa of Imperial Valley, northwest of the Yuma area, proper. The less extensive “For- tuna Dunes” occur on the “Upper Mesa” and “For- tuna Plain” in the southeastern part of the Yuma area (fig. 6). These. two dune areas are alined northwest and may once have been part of a con- tinuous belt before the Colorado River formed what is now the Yuma Mesa and, later, the Yuma and Mexicali Valleys. The belt appears to extend south- eastward into Mexico, where dunes are large and extensive. The “Algodones Dunes” and “Fortuna Dunes” are described earlier, in the section “Geo- morphology” (p. H28). Other, smaller dunes, as well as thin sheets of windblown sand, occur at many places throughout the area. One small area of low dunes and sand sheets is on the east side of The Island in Bard Valley, 3—4 miles northeast of Yuma. These deposits are adjacent to a meander channel of the Colorado River that was cut off within historic time. In Yuma Valley, long sinuous or arcuate dunes are wide- spread; they occur on the leeward sides of aban- doned meanders. Most of these dunes (or perhaps more properly, sand ridges) are less than 20 feet high and 500 feet wide. Some are long in proportion to their width; one ridge just east of Somerton is more than a mile long. On Yuma Mesa, the wind- blown sand occurs in somewhat discontinuous thin GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA sheets rather than in discrete dunes; most of this sand is on the inner margin of the Yuma Mesa, adj a- cent to the “Upper Mesa.” Other small masses of Windblown sand occur on the north flank of the Laguna Mountains and in scattered windrows on the “Upper Mesa.” The windblown deposits consist almost entirely of well-sorted fine to medium sand which is probably derived from nearby sandy alluvium or, with the “Algodones Dunes,” from old lacustrine or marine beaches. The sand grains are subrounded to rounded, include many frosted grains, and are com- posed chiefly of quartz, with subordinate feldspar, rock fragments, and heavy minerals. STRUCTURE REGIONAL STRUCTURAL PATTERNS The Yuma area lies at the southwest edge of the Sonoran Desert section and the northeast edge of the Salton Trough section of the Basin and Range province of Fenneman (1931, 1946). (See fig. 1.) The structural features of these two physiographic sections are somewhat different, both in pattern and in time of most actve development. The Sonoran Desert east of Yuma is characterized by subparallel, narrow, low but rugged mountain ranges trending generally north-northwest, sepa— rated by much more extensive desert plains under- lain by Cenozoic fill. The mountains probably owe their configuration at least in part to block fault- ing (Davis, 1903; Gilbert, 1928; Gilluly, 1946; Thornbury, 1965), although most of the marginal faults are concealed by the Cenozoic fill of the plains and must be inferred from geophysical and other indirect evidence (pl. 9). Some of the moun- tain masses, especially those adjacent to the Salton Trough, are buried or nearly buried by fill. The mountains and basins assumed approximately their present configuration by middle Tertiary time;'sub- sequent deformation has involved only broad-scale warping and minor normal faulting, probably asso- ciated with regional subsidence along the southwest margin of the Sonoran Desert. The Salton Trough, by contrast, has been tec- tonically active to the present time, especially west of the Yuma area, where movement on faults is still going on. The faults are part of the well-known San Andreas system. Along this major fault system, aggregate right slip (blocks southwest of the fault displaced northwestward relative to blocks northeast of the fault) in southern California has amounted to about 160 miles since earliest Miocene time, ac- cording to Crowell (1962). The faults of the San H57 what more northwesterly than the mountains of the Sonoran Desert and their inferred bounding faults, although the two trends appear to converge to the southeast, in Mexico. The Salton Trough has sunk rapidly during Ceno- zoic time and has accumulated as much as 20,000 feet of fill (Biehler and others, 1964). Much of this fill in the southern part of the trough consists of alluvial and deltaic deposits of the Colorado River. PRE-TERTIARY STRUCTURAL FEATURES The structural features of the Yuma area may be classified according to the time of their principal development. Some deformation has affected only the pre-Tertiary crystalline rocks; other features probably had their maximum development during Tertiary time; and still others such as the faults of the San Andreas system have been active through- out late Tertiary and Quaternary time, although most of these faults originally formed earlier. The structural features that affect only the crys- talline rocks of pre-Teriary age did not all originate at the same time, but no attempt was made in the present study to decipher the sequence of the older deformational episodes. The pre-Tertiary struc- tural features include old faults, metamorphic folia— tion and lineation, and joint systems. Most of the old faults are mineralized and filled with dikes and quartz veins. The last major deformation affecting only the crystalline rocks was the Laramide orogeny, which occurred at the end of the Cretaceous period and extended, in its waning phases, into the early Ter- tiary (Damon and Mauger, 1966). The Laramide orogeny resulted in extensive folding, reverse and normal faulting, igneous intrusion and extrusion, and recrystallization of many of the older rocks. The rubidium-strontium date of 73 million years reported by Wasserbur‘g and Lanphere (1965) for biotite in a porphyritic quartz monzonite at Yuma probably indicates a Laramide metamorphic event. Abundant evidence of Laramide plutonism and volcanism farther east in southern Arizona has been reported (Richard and Courtright, 1960; Creasey and Kistler, 1962; Lootens, 1966; Bikerman and Damon, 1966). Laramide and pre-Laramide structural features are expressed topographically where rocks of dif- ferent resistance to erosion are juxtaposed along faults, where faulting has formed easily eroded crushed or sheared rocks, and where extensive and conspicuous joint systems and metamorphic folia- tion have controlled patterns of erosion. The south- Andreas system in the Salton T‘rough trend some‘ i eastern Laguna Mountains afford good examples of 507-243 0 - 74 - 5 H58 the effects of probable Laramide faults on topog- raphy. Joint systems and foliation have profoundly affected the topography of the Gila, Butler, and Tinajas AItas Mountains. The present outlines of some of the ranges and basins in the Yuma area may be related to faulting and domal uplift that began during the Laramide orogeny and continued, at intervals, throughout much of the Tertiary, but present evidence on this question is inconclusive. Farther north, in the Great Basin section of the Basin and Range province, the block faulting that resulted in the present pattern of the basins and ranges is generally regarded as post-Laramide (Gilbert, 1928; Nolan, 1943; Mackin, 1960). However, some students of the basin-range problem have questioned this interpretation; Love- joy (1963a) has ascribed the product of so-called basin-range faulting of classical theory to normal erosional processes acting on Laramide structures. Later wbrkers have generally agreed with the inter- pretation of Gilluly (1946) that the faulting in southern Arizona (Ajo area) began earlier than it did farther north. In the Yuma area the outlines of the present basins and ranges resulted chiefly from Tertiary faulting, accompanied by domal uplift and basin subsidence, but some faults, particularly in the southeastern part of the area, date from the Laramide orogeny. Some of the Laramide faults thus became the loci of later activity. BASIN AND RANGE STRUCTURAL FEATURES (TERTIARY) The so-called Basin and Range structural fea- tures, as apart from Laramide and earlier structural features, are not well understood in the Yuma area. Except for parts of the Chocolate Mountains and possibly the southern part of the Tinajas Altas Mountains, the present form of the mountains and intervening basins seems to be only indirectly re- lated to faulting, uplift of the mountain blocks, and subsidence of the basins. The present mountain fronts are in most places erosional in origin. The faults that may determine the general pattern of the basins and ranges are mostly buried beneath alluvium and lie basinward from the mountain fronts, although a few faults within the G'ila Mountains have helped to determine the general outline of those mountains. The clearest evidence of Basin and Range block faulting in the Yuma area is found in the south- eastern Chocolate Mountains, where middle Tertiary volcanic rocks are offset by antithetical faults, with southwesterly to westerly tilting of the fault blocks and steep northeasterly dips of fault planes. The WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA sequence of volcanic rocks is probably repeated several times from northeast to southwest, although the actual throw on the faults and even some of their positions are uncertain. At some of the faults near Senator Wash Dam and Imperial Dam, nearly horizontal slickensides record strike-slip movement where the faults cut welded tuif or other hard vol- canic rocks. The fault pattern in part of the expo- sures of basaltic andesite or basalt farther west indicate left-lateral displacement on north-north- westward-trending faults; intervening tension faults and fractures trend west-northwestward. The pre- dominant trend of faults in the southeastern Choco- late Mountains is northwest, but another important set has a north-south trend. In the Cargo Muchacho Mountains to the west, the exposed faults strike northwest to west. Hen- shaw (1942) suggests that the range may be an elevated block between two now-buried strike-slip faults which are approximately parallel to the San Andreas fault system (northwest). In the north- central part of the mountains, Henshaw (1942) mapped a thrust fault on which the upper plate was thrust from the south. Most of the other faults within the range are normal faults, however. The quaquaversal attitude of several flows of basalt on the margins of the mountains suggests domal up- lift as well as faulting. In the Laguna Mountains, the straight northeast margin of the exposures of crystalline rocks, and seismic-refraction data as Well suggests a. high- angle fault trending about N. 60° W., downthrown to the northeast. South of this probable fault is a set of normal(?) faults trending about northward; the youngest rocks affected are middle Tertiary volcanic and sedimentary rocks. In the southeastern part of the Laguna Mountains is a set of concentric arcuate faults bending from an easterly strike on the west to northeasterly farther east. These faults are roughly parallel to the foliation and joints in the pre-Tertiary gneiss and probably developed before Tertiary time. At least one of the faults extends westward across exposures of early to middle Tertiary sedimentary rocks (pl. 4). Where the fault planes are clearly exposed they dip about 50°—80° north to northwest. Direction of net slip is generally unknown, but on two of the more southerly faults, pre-Tertiary gneiss is thrust over Tertiary nonmarine sedimentary rocks (red beds). Similar faults may extend be- neath the alluvium between the Laguna and the Gila Mountains. In the southeastern Laguna Moun- tains are several small northwestward-trending GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA normal faults. The throw on these faults is gen- erally no more than 100 feet. Bedding in the nonmarine sedimentary rocks in the Laguna Mountains dips generally west to south- west at angles ranging from a few degrees to more than 40°. The older part of the sequence, the red beds, dips west to north in an arcuate pattern; the attitudes of the bedding are generally similar to those of the foliation in the adjacent pre-Tertiary gneiss, but the dips are flatter. Evidently middle Tertiary deformation in this area had a pattern governed in large part by Laramide or older struc- tures and merely accentuated these structural fea- tures in the pre-Tertiary rocks. The Kinter Formation and the volcanic rocks in the southern part of the mountains overlie the older nonmarine sequence with marked angular discord- ance; dips of the Kinter are gentle toward the west and northwest where it fills an old valley trending west-northwest cut into the older rocks. In the northern part of the mountains the beds of the Kinter Formation have low, irregular dips and strikes indicating broad folding and warping. In the southwestern part of the Laguna Moun- tains, alluvium of local origin unconformably over- lying the Kinter Formation is very gently deformed. Bedding dips westward to southwestward at angles ranging from 1° or less to as much as 4°—not much more than the probable initial dips. The easterly to northeasterly trending fault pat- tern of the southeastern Laguna Mountains con- tinues southward into the northern Gila Moun- tains. A steep normal fault having a throw of more than 2,000 feet extends northeastward across the northern Gila Mountains, the Kinter Formation on the northwest being faulted against pre-Tertiary crystalline rocks on the southeast along the eastern part of its exposed length (pl. 4). Aeromagnetic data suggest that this fault continues southwest- ward beneath the alluvium of the South Gila Valley. The Kinter Formation is titled about 15°—30° toward the northwest along the northern margin of the Gila Mountains; foliation in the metamorphic rocks south of the fault dips southward to southeast- ward at about 40°—50°. In the central and southern parts of the Gila Mountains several large faults near the margins of the range trend northwest to west-northwest. Prob- ably other parallel faults exist farther out from the margins, where they are now buried by alluvium. The foliation and prominent joints in the crystal- line rocks in this area dip 30°—60° southeast to south-southeast; another joint set dips northwest. These trends are athwart the long axis of the range H59 and perpendicular to the margins. This pattern sug- gests that the margins of the mountains, which are fairly straight in most places, may be controlled at least indirectly by faults parallel or nearly parallel to the exposed faults. The western edge of the Tinajas Altas Mountains near the Mexican border is controlled in large part by such a fault (pl. 3). Farther northwest the parallel ridges of the Butler Mountains may result from en echelon faults trend— ing about N. 50°—60° W. (pl. 9). Between the Cargo Muchacho Mountains and the Chocolate Mountains, and farther south, between the “Yuma Hills” and the Laguna and Northern Gila Mountains, is a basin informally designated the “Picacho-Bard basin.” The depth to the pre- Tertiary crystalline rocks along the axis of the basin increases southward from about 1,500 feet to about 3,500 feet, according to an interpretation of gravity data. The presence of a few outliers of crystalline rocks near the margins of the basin and the complexity of the gravity and magnetic patterns suggest that the bedrock surface has considerable local relief. South of the Gila River the trough west of the Gila Mountains—essentially a continuation of the “Picacho-Bard basin” called the “Fortuna basin”— deepens rapidly and attains a depth estimated from gravity data to be about 16,000 feet. (See pl. 9.) As indicated by the log of well (C—9—22)28cbb (test well LCRP 25), only the upper one-eighth of the basin-filling deposits consists of alluvium of the Colorado and Gila Rivers; the lower seven-eighths probably is composed of marine and nonmarine de- posits older than the Colorado River (Bouse Forma- tion and older units). Farther south, the “Fortuna basin” does not ap- pear to be quite as deep. Estimates from gravity 'data and electrical soundings indicate that the base- ment (pre-Tertiary crystalline rocks) :surface is 10,000-13,000 feet below the land surface in the mid- dle of the basin just north of the southerly in- ternational boundary. Information from test well (C—13—20) 2 abdl (USBR CH—28YM) and from a profile of electrical soundings indicates that only the upper 1,200 or 1,300 feet of the overlying fill is alluvium; the bulk of the basin-filling deposits prob- ably are semiconsolidated marine and nonmarine sedimentary rocks of Tertiary age (pl. 10). On the west side of the trough formed by the “Picacho-Bard basin” and the “Fortuna basin”_ is an irregular chain of basement highs composed of, from north to south, the Cargo Muchacho Moun- tains (described earlier), the “Yuma Hills,” a buried ridge south of the “Yuma Hills” referred to H60 informally as the “Mesa basement high," and a southeast-trending basement high culminating in the row of low hills, known as the “Boundary Hills,” straddling the southerly international boundary (fig. 6). The north-northwesterly alinement of outcrops of the “Yuma Hills” and various kinds of geophysical data indicate that these hills are the summits of a nearly buried ridge approximately parallel to the Gila Mountains and other ranges of the Sonoran Desert farther east. The “Yuma Hills” basement ridge probably is bounded on both sides by faults whose precise location and attitude can be only a matter of speculation at present. The “Mesa basement high” is separated from the “Yuma Hills” to the north by a. saddle in which the basement surface is estimated on the basis of geo- physical data to be at a depth between 1,000 and 1,500 feet. Shallow test drilling by the US. Bureau of Reclamation and the US. Geological Survey, and geophysical exploration by the Geological Survey, have established that the highest part of the buried basement ridge, which is oriented northwest, is less than 100 feet below the surface of Yuma Mesa; well (0—9—23) 33cdd (USBR CH—ZOYM) penetrated porphyritic quartz monzonite at a depth of only 47 feet. The “Mesa basement high” is bounded on both northeast and southwest sides by faults (pls. 9, 10). The large fault on the southwest is the Algo- dones fault which is described on pages H61—H63; the other faults probably are parallel or en echelon to the Algodones fault. Geophysical data suggest that southeast of the “Mesa basement high” and on the southwest side of the Algodones fault, the surface of the crystalline rocks slopes steeply southward into a broad saddle and thence rises southeastward to the line of low outcrops straddling the southerly international boundary—the “Boundary Hills.” The “Boundary Hills” are composed of the same porphyritic quartz monzonite as that penetrated in test wells on the “Mesa basement high” and exposed in the “Yuma Hills” farther north. Between the “Yuma Hills” and Pilot Knob is a basement trough oriented north-northeast referred to informally as the “Yuma trough.” Geophysical data, supplemented by information from test wells 16S/22E—29Gca2 (USGS LCRP 26) and (C—8— 23)32caa1 (Sinclair Oil Co. Kryger 1) and from water well 168/21E—36Fca, show that the basement surface is deepest in the eastern part of the trough, where the sedimentary fill includes the Tertiary nonmarine sedimentary rocks below the less de- formed Bouse Formation, transition zone, and older WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA and younger alluviums. Farther west, within 2 or 3 miles of Pilot Knob, the crystalline basement is shallower and is overlain only by the older and younger alluviums or, in places, the transition zone and Bouse Formation. Gravity and magnetic data indicate a deep basin between the “Boundary Hills” and San Luis which is given the informal name “San Luis basin.” (See pl. 9.) The axis of the “San Luis basin” trends west- northwest along the southerly international bound- ary. Estimates indicate that the depth to basement in the middle of the basin is about 13,500 feet. Oil- test well (0—10-24)24cbb (Colorado Basin Associ- ates Federal 1) on the north side of the basin bottomed in Tertiary nonmarine sedimentary rocks at a depth of 6,007 feet (pl. 10). LATE TERTIARY AND QUATERNARY STRUCTURAL FEATURES The older and younger alluvium, the underlying transition zone, and the Bouse Formation, which range in age from late Tertiary (Pliocene) to Qua- ternary (Holocene), are substantially less deformed than the pre-Bouse rocks, from which they are separated by significant angular unconformities. Nevertheless, except for the younger alluvium and possibly the upper parts of the older alluvium, these late Tertiary and Quaternary units are affected by broad-scale warping and local faulting. Deformation of the older alluvium on the flanks of the mountains consists chiefly of slight tilting with dips as much as 6° away from the mountains, and, locally, of small-scale high-angle normal fault- ing. Uplift of the mountains in post-older alluvial time is indicated by the presence of Colorado River deposits as high as 740 feet above sea level on the flanks of the southeastern Chocolate Mountains and about 580 feet above sea level on the west flank of the northern Gila Mountains. Even greater uplift since the deposition of the Bouse Formation is indi- cated by the presence of basal limestone and tufl' of the Bouse at an altitude of about 1,000 feet above sea level in a gap in the Chocolate Mountains 10 miles beyond the north edge of plate 3 (Metzger, 1968). In the subsurface, a measure of the maximum deformation since the late Tertiary is provided by the configuration of the top of the Bouse Formation (fig. 15). The Bouse, being marine, presumably was nearly horizontal at the time of deposition; the basal beds of the overlying transition zone are the earliest deposits of the Colorado River, which must have been laid down not far above sea level. The maximum dip of the top of the Bouse Formation is about 9°—10°. These deposits have been downwarped GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA in the basins such as “Fortuna basin” and differ- entially upwarped along the margins of the moun- tain blocks (p1.'10). The top of the Bouse Forma- tion is more than 3,000 feet below sea level in the southwest corner of the Yuma area, near San Luis (fig. 15 and pl. 10). This probably reflects broad- scale downwarp or subsidence in the Colorado delta region as well as more local downwarp or down faulting in the basins. At least part of the down- warp results from differential compaction in the fine-grained deposits. Farther west, in the central part of the Salton Trough, probably nonmarine de- posits (possibly of the Colorado River?) have been penetrated in oil-test wells at depths exceeding 13,000 feet (Mufl‘ler and Doe, 1968), which indicates much greater downwarp or subsidence there. Structural activity has generally occurred more recently in the Salton Trough than it has farther northeast, in most of the Yuma area. The trough is crossed at acute angles by northwest-trending faults of the well-known San Andreas system. Many members of this system are well delineated by seismic and gravity data in the delta region (Biehler and others, 1964). One of these faults and several other probably related faults that cross the Yuma area are described in the following section. ALGODONES FAULT AND RELATED FAULTS The San Andreas fault system is a major crustal feature along the northeast margin of the Pacific Ocean. The Gulf of California—a southern exten- sion of the Salton Trough—was probably formed by oblique rifting across the system (Hamilton, 1961) and probably also by ocean-floor spreading (Larson and others, 1968). Displacements on the faults have been right lateral and, in southern Cali- fornia, may have amounted to as much as 160 miles since early Miocene time (Crowell, 1962). An earler date has been postulated for some of the faults by Hill (1965), who believes that possibly several hundred miles of right slip has occurred since the Cretaceous. One of the main branches of the San Andreas system extends along the northeast side of Coach- ella Valley southeastward to the northeast shore of Salton Sea. Allen (1957) calls this branch the Banning-Mission Creek fault; Dibblee (1954) con— siders it the San Andreas, itself. Southeast of Salton Sea the trace of the fault is concealed by unaffected alluvium and windblown sand, so its precise trend is not known. Biehler (unpub. Ph. D. thesis, 1964; oral commun., 1967) interprets a strong alinement of gravity lows as indicating the trace of the fault where it is concealed by the Sand Hills (“Algo- H61 , dones Dunes”). 0n the basis of this evdence and of further evidence from seismic data (Kovach and others, 1962), the fault appears to extend beneath the Sand Hills to a point on the Colorado River south of Pilot Knob; the exact location is uncertain. The fault just described (or possibly a parallel fault) appears to continue southeastward across the Yuma area from a point on the Colorado River about a mile south of Morelos Dam to the southerly inter- national boundary 26 miles east of the Colorado River at San Luis (pls. 3 and 9). It is herein named the Algodones fault from the village of Algodones just northeast of the trace of the fault in the north- eastern corner of Baja California, Mexico. The evi- dence for the Algodones fault is summarized: 1. Anomalous topography on the “Upper Mesa.”— The existence of the Algodones fault was first inferred from a topographic anomaly on the “Upper Mesa,” in the southeast part of the area of investigation. The anomaly con- sists of a northwestward trending drainage system approximately perpendicular to the normal, consequent streams draining south- westward from the Gila Mountains. The in- ferred fault trace is along this system, at the foot of an eroded northeast-facing alluvial escarpment. The mesa surface southwest of the fault is 30—60 feet higher than the surface to the northeast and slopes toward the west- southwest at about 30—40 feet per mile (pl. 1). Lineaments apparent on vertical aerial photographs suggest that the fault has a branching pattern in the central part of the “Upper Mesa.” 2. Offset of the water table and ground-water bar- rier effect—Test wells in the “Upper Mesa” indicate an abrupt offset in the water table along the inferred fault trace. Water levels northeast of the fault are more than 30 feet higher than those southwest of the fault near the northwest edge of the “Upper Mesa” and about 7 or 8 feet higher near the southerly international boundary (pl. 1). Measurements in private irrigation wells and government observation wells indicate that the water—table offset continues about 3 miles northwestward beneath Yuma Mesa, although this part of the fault trace is concealed. The water-table offset results from the func- tion of the fault as a barrier to ground-water movement. The barrier effects of faults in allu- vial materials are well known and are com- monly attributed to: (a) Pulverization of earth materials along the fault, (b) offset of bedding H62 so that impermeable beds are juxtaposed against permeable beds, (c) rotation of flat 0r elongate clasts parallel to the fault, thereby decreasing permeability normal to the fault plane, and (d) deposition of minerals along the fault surface (Davis and De Wiest, 1966, p. 396). The first and fourth factors listed above are probably most significant at the Algodones fault. Electrical-analog data, described on page H108, indicate that observed changes in water level on both sides of the fault are best mod- eled by assuming that the transmissivity of the fault barrier is less than one-thousandth of that of the alluvial deposits on either side. The configuration of the water table-water- level contours on both sides of the fault are nearly perpendicular to the fault trace—also supports the conclusion that very little ground water moves across the fault. 3. Magnetic gradients—A steep magnetic gradient along the southwest side of the buried “Mesa basement high” suggests a fault or series of step faults on which the basement is down- thrown to the southwest. The zone of steep gradient extends across Yuma Valley to the northwest and indicates that the inferred fault or fault zone crosses the Colorado River some- where between 11/2 and 4 miles south of Pilot Knob. 4. Gravity patterns.—Gravity data generally cor- roborate the magnetic data. Also, the gravity data indicate a very steep gradient on the northeast flank of the “Boundary Hills” base- ment high, which suggests downtlirow of the basement surface toward “Fortuna basin” along a fault about in the position of the fault inferred from topographic and hydrologic evi- dence. 5. Seismic-reflection data.—Seismic-reflection pro- files made by a commercial firm under contract to the US. Bureau of Reclamation revealed several faults including what is interpreted herein as the main Algodones fault. The faults oifset reflecting horizons such as the top and bottom of the Bouse Formation and the top of the transition zone, and locally are associated with steep dips of the reflecting horizons (Snodgrass, 1965, 1966). On a profile along the limitrophe section of the Colorado River, the top of the Bouse Formation was determined to be downthrown 500 feet to the south or southwest along a fault that is probably the main Algodones fault about 21/2 miles south of Pilot Knob (Snodgrass, 1966). (See p1. WATER RESOURCES 0F LOWER COLORADO RIVER-SALTON SEA AREA 10.) The faults inferred to be parallel to the Algodones fault near the “MeSa basement high” (pls. 9 and 10) all were determined from seismic-reflection data. 6. Seismic-refraction data.—A seismic-refraction profile extending southward from the crest of the “Mesa basement high” revealed that the basement surface is downthrown 350 feet toward the south or southwest along a steeply dipping fault in alinement with the projected extension of the ground-water barrier to the southeast. This fault is interpreted as being the main Algodones fault (pl. 10). 7. Ground-water-temperature anomalies.— Although the Algodones fault is concealed be- neath Yuma Mesa and Yuma Valley, its posi- tion throughout much of its extent across these features is revealed by an elongate body of anomalously warm ground water, mostly on the northeast side of the inferred fault trace (fig. 47). Similar temperature anoma- lies farther southwest probably reflect parallel or en echelon faults. The elevated temperatures of these anomalies are probably the result of upward movement of deep warm water in- duced by the barrier effects of the faults. However, the effect of the buried basement ridge at the “Mesa basement high” may in part account for the temperature anomaly along the Algodones fault. In addition to the methods of investigation de- scribed above, attempts were made to delineate the Algodones fault beneath Yuma Mesa by use of resistivity profiles and electrical soundings. Unfor- tunately, the resistivity surveys did not provide the expected information as to the location and nature of the fault or fault zone. Information on the atti- tude and width of the fault, and on whether the barrier eifect results primarily from pulverized material (gouge) or from cemented material, must await detailed exploration by test drilling or exca- vation. Likewise, unambiguous information on the direc- tion and amount of movement on the Algodones fault is not yet available. Analogy with other, bet- ter known faults in the San Andreas system sug- gests chiefly right-lateral movement; this inference is substantiated to some extent by gravity and mag— netic patterns. However, vertical components of movement also are indicated by some of the evi- dence summarized above. Northwestward from the vicinity of the “Mesa basement high” the southwest side is downthrown, but to the southeast, across the “Upper Mesa,” the throw is opposite. Such reversals GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA in throw along the strike are common along other faults in the San Andreas system which have had predominantly strike-slip movements. The last significant movement on the Algodones fault can be dated approximately by geology and topography. The fault is exposed on the “Upper Mesa” but is concealed beneath apparently unaf- ected alluvial deposits in both the Yuma Mesa and Yuma Valley. The uppermost coarse-gravel strata of the older alluvium (coarse-gravel zone) are not offset, at least vertically, beneath western Yuma Mesa and eastern Yuma Valley (pls. 5 and 8). The age of the Yuma Mesa surface is late Pleistocene— perhaps Sangamon (p. H27)—and the presumably unaffected gravel strata are somewhat older. The age of the “Upper Mesa” surface, which is offset, has not been established but almost certainly is older than latest Pleistocene. It is therefore inferred that significant movement on the Algodones fault ceased before the latest Pleistocene. Movement on the parallel or en echelon faults probably ceased even earlier; this is indicated by the lack of topo- graphic expression of these faults on the “Upper Mesa” and from the apparent absence of significant hydrologic effects (other than thermal effects) caused by these faults. By contrast, many faults of the San Andreas system crossing the Salton Trough farther west are still active, which indicates the more recent deformation of that region as compared to the Sonoran Desert. GROUND-WATER HYDROLOGY THE GROUND-WATER RESERVOIR The limits of the ground-water reservoir in the Yuma area are considered as being formed by the crystalline rocks of pre-Tertiary age. These rocks include many types, but all are dense and contain only small quantities of water in open fractures and weathered zones within a few tens of feet of the land surface and possibly to greater depths in faults and shear zones. In the arid environment of Yuma, most of the small quantity of water in the crystal- line rocks near the mountains and hills occurs far above the regional water table as small, discontinu- ous perched bodies. The ground-water reservoir is therefore composed of the Cenozoic basin-fill deposits overlying the pre- Tertiary crystalline rocks. The general configuration of the basins was discussed in the preceding section on structure. The thickness of fill in the deepest parts of some of the basins probably exceeds 16,000 but only the upper 2,000—2,500 feet at these places is composed of fresh-water-bearing alluvial deposits. For this reason, the ground-water reservoir is con- H63 sidered as being composed of two parts, which are discussed separately below. MAJOR SUBDIVISIONS OF THE RESERVOIR The ground-water reservoir consists of two major subdivisions: (1) Poorly water-bearing rocks of Tertiary age and (2) water-bearing deposits of Pliocene to Holocene age. The first subdivision con- stitutes the lower part of the reservoir and includes the following stratigraphic units: (1) The nonma— rine sedimentary rocks, (2) the volcanic rocks, (3) the older marine sedimentary rocks, (4) the Bouse Formation, (5) the transition zone, and (6) the conglomerate of the Chocolate Mountains. The vol- canic rocks and the conglomerate of the Chocolate Mountains appear to be of very minor subsurface extent within the area of principal hydrologic in- vestigation and are not considered further in this section of the report. The stratigraphic units of the second subdivision include: (1) The older alluvium, (2) the younger alluvium, and (3) the windblown sand. These units contain most of the fresh ground water. For convenience, the water-bearing deposits of the second subdivision are further subdivided into water-bearing zones that cross stratigraphic boundaries, as discussed on pages H66—H69. DEFINITION OF FRESH WATER In describing the fresh-water part of the ground- water reservoir, the term “fresh water” requires definition. Fresh water is an imprecise term prob- ably best defined as water that has a sufficiently low mineral content to be acceptable for ordinary uses. The Office of Saline Water defines fresh water as that containing not more than 3,000 mg/l of dis- solved solids. In many reports of the US. Geological Survey, fresh water is defined as that containing not more than 1,000 mg/l of dissolved solids—a use- ful limit in most parts of the United States where such water is widely available. However, in the Yuma area, as in many other desert areas, more highly mineralized water is used extensively; not many wells yield water containing less than 1,000 mg/l dissolved solids. On the other hand, water con- taining as much as 3,000 mg/l dissolved solids is injurious to some of the local salt-sensitive crops and is notconsidered acceptable for general domes- tic use. Accordingly, a limit of 1,800 mg/l probably is applicable to local conditions and is used in this report. This limit corresponds approximately to a specific conductance of 3,000 micromhos per centi~ meter (hereinafter abbreviated to micromhos), which is used as the upper limit for fresh water in the interpretation of electric logs of wells. H64 WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA POORLY WATER-BEARING ROCKS OF TERTIARY AGE Within the area of principal geohydrologic inves- tigation, the lower part of the ground-water reser- voir—the poorly water-bearing rocks of Tertiary age—includes, in ascending order: (1) The nonma- rine sedimentary rocks, (2) the older marine sedi- mentary rocks, (3) the Bouse Formation, and (4) the transition zone. Inferences as to the subsurface extent and configuration of these units (pl. 10) are based primarily on records of 31 test wells and water } wells (table 5) and on geophysical data. In parts of TABLE 5.—Depths of Tertiary and pro-Tertiary horizons in wells Depth, in feet, to top of—- Name of Altitude Well Well or of land Total Older Non Remarks owner surface depth Transition Bouse marine marine Crystalline (feet) (feet) zone Formation sedimentary sedimentary rocks rocks rocks (0—7—22) 14bcd --- USGS LCRP 14- 155.1 505 ---- 209 ---_ 471 ---- (0—8—21) 16bca --- Tanner Paving 195 396 _--- --_- -_-- 207(?) ___- Co. (0—8—22) 15bdd --- USBR CH—6 --- 140.5 501 ---_ 422 ___- 497 ___- 15dab ___ Gila Valley Oil 145 2,140 ---- 422 ---- 482 __-_ & Gas Co Kamrath 1. 35caa1 -- USBR CH—704 150.8 1,997 794(?) 1,045 1,396 ---- __-- Top of transition USGS LCRP zone may be at 29. 885 ft. (C—8—23) 21caa --- Yuma School 175 404 ---- ---- ---- 280(?) ___- District 1. 21cac --- Abe Marcus Pool- 175 478 ---- ---- ---- 300(?) 470 “Granite” at bottom. 320aa1 -- Sinclair Oil Co. 120 1,400 ---- 972(?) ---_ 1,243 1,398 Do. Kryger 1. 33cdd ___ Stardust Hotel 197 1,090 -_-- ---- ---- ---- 1,085 Porphyritic quartz USGS LCRP monzonite at 13. bottom. 35caa ___ S & W Ranches _ 141 191 ____ ---- ---- _--- 190 “Granite” at bottom. (0—9—21) 13ccb --_ B. Palon _______ 423 603 -_-- ---- ---_ ---- 563 14bac --- ---do __________ 395 1,085 _--- 700 ---- -__- 1,082 Do. (C—9—22) 28cbb --- USGS LCRP 25- 204.6 2,318 2,101 ---- ---- ---- ___- (C—9—23) 2cda --- Yuma County 212 306 --__ ---_ ___- -_-- 292 D0. Fairgrounds. 19bcd --- Colorado Basin 110 3,277 ---- _--- ---- ___- 1,431 Drilled 1,846 ft Associates into granitic Elliott 1. basement. 29aab ___ Old oil test _____ 118 730 ---- --__ ---- ---- 730 Reported in Ko- 32bad --_ USBR CH—21YM 188.0 285 ___- 33cbd ___ USGS AH _____ 195 90 ___- 33cdd --- USBR CH—20YM 196.0 64 ---- 33dab -_- USGS AH _____ 196 79 ---- (C—9—24) 8baa -_- USGS LCRP 28- 118.7 2,466 1,927 (0—10—23) 31aaa -__ M. P. Stewart 181 3,660 1,748 Co. Federal 1. (C-10—24) 24cbb ___ Colorado Basin 170 6,007 2,367 Assoc. Fed- eral 1. (0-10—25) 35bbd --- USGS LCRP 17- 94 2,946 2,514 (0—11—25) 11ab ---- Yuma Valley Oil 90 4,868 2,525 & Gas Co. Musgrove 1. (0—13—20) 2abd1 -- USBR CH—28YM 577.5 1,427 1,285 16S/21E 36Fca --- Arizona Public 117 978 (2’) Service Co. 168/22E 230aa --- USBR CH—SRD - 128.5 360 ___- 29Gca2 -- USGS LCRP 26- 125.4 1,777 1,033 35Hac _- San Carlos Hotel 145 173 ---- 16S/23E 10Rcc --- USGS LCRP 23- 143.8 715 -_-- vach, Press, and Allen (1962). ---- ---- ---- 267 Cored porphyritic quartz mon- zonite. ---- ---- ---_ 90 -_-_ ---- _--- 47 Do. ---- ---- ---- 79 (2) 2255(7) “Iii ____ ___- 3,112 3,802 4,937(?) ___- Top of nonma- rine sedimen- tary rocks may be at 4,302 ft. 31555 4,350 ___- -___ Bottom in allu- v1um or tran51- tion zone- 328(?) -_-- -__- ---- Baisalt 342—360 t. 1,115 -_-_ 1,380 ---- ---- ---- 173 ---- “Granite” boulder at bottom. 548 ---- 687 703(?) May be breccia at bottom. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA the area these wells are far apart (pl. 3), and by no means all the wells penetrate the units below the transition zone. Interpretations shown in figure 15' and plate 10 are therefore in part uncertain and generalized. The poorly water-bearing rocks are relatively unimportant in the hydrology of the area, and each of the units listed above is discussed only briefly. NONMARINE SEDIMENTARY ROCKS The nonmarine sedimentary rocks of Tertiary age occupy the basal part of the ground-water reservoir throughout much of the Yuma area. In the south- western part of the area, on the north flank of the “San Luis basin,” varicolored sandstone and con- glomerate of the nonmarine sedimentary rocks were penetrated in oil-test well (C—10—24)24cbb (Colo- rado Basin Associates Federal 1) from a depth of 4,937 feet to the bottom of the well at 6,007 feet; some nonmarine strata, possibly interbedded with marine strata (older marine sedimentary rocks) occur as high as 4,302 feet in this well (table 5). The electric log indicates very brackish—water— probably exceeding 15,000 micromhos specific con- ductance—throughout this interval. Farther north, in the “Yuma trough” and “Picacho-Bard basin,” several test wells penetrated coarse fanglomerate and breccia of the nonmarine sedimentary rocks. Electric logs and pumped water samples indicate much fresher water than that in well (C—10-24)24cbb—the specific conductance of most of this northern water is substantially less than 3,000 micromhos. However, at test well (C—7- 22) 14bcd (USGS LCRP 14) at Laguna Dam, analysis of a sample of water from fanglomerate (probably the Kinter Formation) indicated 3,420 mg/l dis- solved solids and 5,610 micromhos specific conduct- ance, which is too mineralized for most uses (appendix C, analysis 206b). The extent and thickness of the nonmarine sedi- mentary rocks beneath “Fortuna basin” in the southeastern part of the area are unknown (no wells in this basin are deep enough to penetrate these rocks) ; however, the nonmarine sedimentary rocks probably are present in at least part of the basin. On the southerly international boundary, deep electrical soundings and an electric log of test well (C—l3—20)2abd1 (USBR CH—28YM) indicated brackish to saline water in all the Tertiary deposits below the base of the older alluvium at depths of 1,200—1,300 feet. In summary, the nonmarine sedimentary rocks probably contain brackish water in the southern part of the Yuma area but contain fresh water in much H65 of the northern part of the area. These deposits are very coarse grained in places but are slightly to moderately indurated and therefore are generally less porous and permeable than the alluvial deposits in the upper part of the ground-water reservoir. Even the coarser phases, like the fanglomerate of the Kinter Formation, do not appear to be potentially very productive. In test wells (0—7—22) 14bcd (USGS LCRP 14) and 16S/22E—29Gca2 (USGS LCRP 26) in the northern part of the area, the productivity of the fanglomerate was much less than that of the alluvium. OLDER MARINE SEDIMENTARY ROCKS The older marine sedimentary rocks have been penetrated in three test wells (table 5), where bore- hole geophysical logs and drilling characteristics indicate that these rocks are moderately indurated and therefore probably less porous and permeable than the overlying Bouse Formation, transition zone, and water-bearing deposits of Pliocene to H010- cene age. Like the nonmarine sedimentary rocks, the extent of the older marine sedimentary rocks is not well known, but their absence below the Bouse For- mation in several test wells in the northern part of the area suggests that they are less extensive than the Bouse Formation. Although no samples of ground water from the older marine sedimentary rocks were obtained for chemical analysis, electric logs of the three wells penetrating the unit indicate brackish water (spe- cific conductance 3,000—15,000 micromhos) unfit for most uses. BOUSE FORMATION The Bouse Formation appears to be Widespread (fig. 15 and pl. 10), although it has not actually been penetrated by wells in the southern and south- eastern parts of the area, where its subsurface extent and configuration are inferred from geophysi- cal data. The unit consists chiefly of clay and silt having small hydraulic conductivity, but the inter- bedded very fine to fine sand probably would yield small amounts of somewhat mineralized water to wells. In places the basal part of the Bouse Forma- tion contains sandy limestone or limy sandstone, conglomerate, and tufl“; a conglomerate penetrated by test well 16S/23E-10Rcc (USGS LCRP 23) in the “Picacho-Bard basin” yielded large quantities of fresh water (1,180 mg/l dissolved solids) when that well was test pumped, but such coarse-grained productive strata have not been recorded elsewhere in the Yuma area. In the “Picacho-Bard basin” and the “Yuma trough” the predominantly clay and silt of the H66 Bouse Formation form an aquiclude between the underlying nonmarine sedimentary rocks (which contain fresh to somewhat brackish water) and the overlying water-bearing deposits of Pliocene to Holocene age, which constitute the upper, main part of the ground-water reservoir. Farther south, the Bouse is underlain by the older marine sedimentary rocks, and both units contain brackish water. TRANSITION ZONE The transition zone overlies the Bouse Formation throughout most of the Yuma area but is missing in the northeast and perhaps elsewhere along the margins of the Bouse embayment (fig. 15), where the Bouse Formation is overlain by the older allu- vium. The transition zone is as much as several hundred feet thick in the “San Luis basin” in the southwestern part of the area, where it is pene- trated by several test wells (table 5). Electric logs of wells (C—lO—Z4)24cbb and (0—11—25)11ab indi- cate that the specific conductance of the water in the zone increases from about 3,000 micromhos near the top to more than 8,000 micromhos near the base. Although the transition zone locally contains fresher water (less than 3,000 micromhos in some test wells) the unit is unimportant hydrologically be- cause of the generally small hydraulic conductivity inferred from the abundance of clay and silt and from the slight to moderate induration of the coarser strata. WATER-BEARING DEPOSITS OF PLIOCENE TO HOLOCENE AGE The upper, principal part of the ground-water reservoir—the water-bearing deposits of Pliocene to Holocene age—includes the following stratigraphic units: (1) The older alluvium, (2) the younger allu- vium, and (3) the windblown sand. However, be- neath the river valleys and Yuma Mesa—the areas of most intensive present and probable future water development—the upper part of the reservoir is more conviently subdivided into three zones, two of which cross stratigraphic boundaries, as shown below: Zones Stratigraphic units _ Upper, fine-grained zone ___Windb10wn sand (small dunes in valleys, sheets of sand on Yuma Mesa). Younger alluvium (upper, ma- jor part). Older alluvium (uppermost strata beneath Yuma Mesa). Coarse-gravel zone _________ Yotfiiger alluvium (basal grav- e . Older alluvium (uppermost) coarse-gravel strata). Wedge zone _______________ Older alluvium (lower, major part). These zones are not everywhere well defined; for example, the coarse-gravel zone is thin or absent WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA beneath the northwest corner of Yuma Mesa and the north-central part of “Bard Valley.” However, at most places beneath the river valleys and Yuma Mesa, the zones are useful subdivisions of the upper part of the ground-water reservoir. The wedge zone, the coarse-gravel zone, and the upper, fine-grained zone correspond respectively to the lower sandy allu- vium, the coarse-gravel zone, and the sandy and silty alluvium of Brown and others (1956, p. 15—22). Later writers have used classifications similar to that of Brown and others (1956), and it seems de— sirable to continue with this classification in the present report. . Outside the river valleys and Yuma Mesa, where the coarse-gravel zone is generally absent or un- recognized, the water-bearing deposits of Pliocene to Holocene age, which are almost entirely the older alluvium below the water table, are not subdivided and are classified instead as older alluvium, undi- vided. The older alluvium, undivided, is stratigraph- ically equivalent to the wedge zone and hydraulically continuous with it. WEDGE ZONE The wedge zone constitutes the major part of the water-bearing deposits of Pliocene to Holocene age beneath the river valleys and Yuma Mesa. Through- out most of its extent the wedge zone overlies the transition zone or the Bouse Formation and under- lies the coarse—gravel zone; laterally, beneath “Pi- cacho Mesa” and “Upper Mesa,” the wedge zone is adjacent to the older alluvium, undivided, to which it is largely equivalent. The zone extends to depths of about 2,500 feet in the “San Luis basin” and the northern “Fortuna basin” but wedges out beneath the coarse-gravel zone against the Laguna and Gila Mountains to the northeast and also against the buried and nearly buried “Mesa basement high” and “Yuma Hills” farther southwest, hence its name. The top of the wedge zone ranges from about sea level (depth 160 ft) near Laguna Dam and eastern South Gila Valley to nearly 200 feet below sea level (depth nearly 300 ft) in southern Yuma Valley. However, where strata of coarse gravel are abun- dant in the upper part of the wedge zone, as they are at many places, the boundary between the wedge zone and the overlying coarse-gravel zone is vague and arbitrary and is not shown at a definite horizon in the geologic sections of the area. (See pls. 5, 6, 8.) Scanty information indicates that the average grain size and probably the average porosity and hydraulic conductivity of the wedge zone decrease with depth. Clay and silt appear to be more abun- dant below depths of 1,000—1,500 feet than they are GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA at shallower depths, especially in the “San Luis basin.” However, except possibly for the lower 1,000 feet or so, fine—grained strata do not appear to be sufliciently extensive or thick to cause sig- nificant hydraulic separation. Thus, on a large scale, the wedge zone is considered to be a single hetero- geneous hydrologic unit. The chemical characteristics of the water in the wedge zone are not known in detail, owing to the small number and irregular spacing of wells from which samples have been collected (pl. 11). How- ever, electric logs of several test wells supplement the chemical data and help to provide reasonably reliable estimates of the extent and general char- acter of fresh water in the zone. Except for two small areas, the water in the wedge zone is fresh, as defined in this report. The two areas where the concentration of dissolved solids exceeds 1,800 mg/l (and the specific conduct- ance exceeds 3,000 micromhos) are roughly the city of Yuma at the northwest corner of Yuma Mesa and a strip along the west flank of the northern Gila Mountains (pl. 11). In these areas the overlying coarse-gravel zone is thin or absent and the deposits of the wedge zone are relatively thin and probably less permeable than they are at most other places. The body of somewhat brackish water along the west flank of the northern Gila Mountains, which is much more extensive farther south, in the older alluvium, undivided, may represent contamination from deeper water in the Bouse Formation and non- marine sedimentary rocks of Tertiary age which has risen along faults. Electric logs and a few chemical analyses indicate that in the northern part of the Yuma area the water in the wedge zone becomes fresher with depth. The wedge-zone water in this part of the area ap- pears to be substantially fresher than that in the overlying coarse-gravel zone, except for the two occurrences of brackish water described above. The decrease in dissolved-solids content with depth prob- ably indicates that some of the more concentrated water in the coarse-gravel zone has moved down- ward into the upper part of the wedge zone. Farther south, beneath central and southern Yuma Mesa and Yuma Valley, vertical variations in con- centration and chemical characteristics of water in most of the wedge zone appear to be relatively small. However, several electric logs in that part of the area indicate a gradual downward increase in spe- cific conductance of the water below depths of 1,500—2,000 feet, where clay and silt are more abun- dant in the zone. South of the irrigated area on Yuma Mesa, the water in the wedge zone not only H67 shows little vertical variation in concentration and chemical characteristics, but it is virtually indis- tinguishable from the water in the overlying coarse- gravel zone. (See pl. 11.) However, this condition may change when water from irrigation to the north moves farther southward, largely through the coarse-gravel zone. Scattered sample and electric—log data suggest that the freshest water in the wedge zone occurs beneath a strip along the Colorado River. This water is considerably fresher than the present Colorado River; four samples had dissolved solids concentra- tions ranging from 451 to 624 mg/l (pl. 11). Elsewhere, except in the two areas of brackish water described earlier, the concentration of dis- solved solids in wedge-zone water generally ranges from about 700 to 1,500 mg/l. At most places below a depth of 500 feet, the concentration generally is less than 1,200 mg/l. Expressed in chemical equivalents, wedge-zone water characteristically contains considerably less magnesium than calcium, and much of the water contains less sulfate than bicarbonate (pl. 11). Ex- cept for one sample (242a), for which the analysis represents a mixture of water from the coarse- gravel zone and the uppermost part of the wedge zone, the equivalent concentration of chloride ex- ceeds that of sulfate. The equivalent concentrations of sodium and chloride are generally about equal, although a few wells have yielded water in which calcium seems to have replaced sodium by base exchange, so that the chloride substantially exceeds the sodium. In general, the water in the wedge zone has a smaller range in concentration and chemical char- acteristics than that in the overlying coarse-gravel zone, and probably much less than that in the upper, fine-grained zone. C70 ARSE-GRAVEL ZONE The most permeable deposits in the Yuma area, and the ones that are tapped by nearly all the pro- ducing wells, are the coarse-gravel strata in the upper part of the older alluvium and locally, perhaps, at the base of the younger alluvium. These strata are herein referred to collectively as the coarse- gravel zone, which is the principal aquifer beneath the river valleys and Yuma Mesa. This zone, to which Wilcox and Scofield (1952) applied the term “deep aquifer,” has long been recognized as the primary source of ground water pumped in the Yuma area. Brown and others (1956) suggested that “deep aquifer” is not an appropriate designa- tion because of the presence of much deeper fresh- H68 water-bearing deposits; instead, they used both “coarse-gravel zone” and “coarse-gravel aquifer.” Usage of the term “coarse-gravel zone” is contin- ued in the present report. As described in the section, “Geology” (p. H50), the coarse—gravel zone consists of a complex of gravel bodies of different ages deposited by the Colo— rado and Gila Rivers; the top and bottom of the zone are at different altitudes and stratigraphic horizons from place to place (pl. 7): Delineation of the zone is necessarily arbitrary at many places; the upper part of the underlying wedge zone locally contains similar coarse gravel. The coarse-gravel zone generally ranges in thickness from 0 to more than 100 feet (or more than 150 ft, depending on which horizon is identified as the bottom). The zone generally dips southwestward at an angle somewhat steeper than the slopes of the valley surfaces and Yuma Mesa; in the central part of the area the depth to the top averages about 100 feet beneath the valleys and about 170—180 feet beneath Yuma Mesa. Somewhat saline water, in which the sum of de- termined constituents exceeds 1,800 mg/l, occurs in the coarse-gravel zone beneath most of South Gila Valley, eastern North Gila Valley, northwestern Yuma Mesa, a U-shaped area in northern Yuma Valley, and scattered other areas of small extent (pl. 11). At all these places except the northwest corner of Yuma Mesa (city of Yuma) and the east end of South Gila Valley, the water in the under- lying wedge zone is fresh. Elsewhere, the concentration of dissolved solids of the ground water in the coarse-gravel zone ranges from about 900 to 1,500 mg/l, although scattered wells of small capacity have yielded water contain- ing as little as 418 mg/l dissolved solids (pl. 11). As in the wedge zone, much of the fresher water in the coarse-gravel zone is near the Colorado River and presumably results from local recharge of river water. The scattered occurrences of fresher water at sites away from the river probably are due to local anomalous conditions such as excessive sulfate reduction. Beneath most of Yuma Mesa the water in the coarse-gravel zone has a smaller range in concen- tration of dissolved solids than it has beneath the valleys: most analyses from the mesa range in con- centration from 900 to 1,400 mg/l. As mentioned earlier, the water in the coarse-gravel zone in the southern part of the mesa is chemically about the same as that in the underlying wedge zone. The water in the coarse-gravel zone is more vari- able in chemical character as well as in concentra- WATER RESOURCES 0F LOWER COLORADO RIVER—SALTON SEA AREA tion of dissolved solids than that in the wedge zone. (See pl. 11.) In much of the coarse—gravel-zone water the concentration of sulfate (expressed in chemical equivalents) exceeds that of chloride, whereas in the wedge-zone water, chloride exceeds sulfate in equivalent concentration except for one analysis, and that analysis represents a strong admixture of coarse-gravel—zone water. The higher sulfate con- centrations probably indicate that river water (chiefly, but not entirely, the Colorado River) is a more recent source of the water in the coarse-gravel zone, and that sulfate reduction (explained in the section “Chemical Quality,” p. H127) has not gen- erally proceeded as far as it has in wedge-zone water. The water in the coarse-gravel zone is highly vari- able in proportions of the major dissolved constitu- ents, and the variations are not necessarily correla- tive with the variations in concentration of dissolved solids (pl. 11). Because the coarse-gravel zone is the overwhelmingly predominant source of ground water pumped in the Yuma area, a more detailed descrip— tion of the variations in the chemical characteristics of the water in the zone, and suggested explanations for the variations are given in the section, “Chemi— cal Quality.” UPPER, FINE-GRAINED ZONE The upper, fine-grained zone includes most of the younger alluvium, the uppermost deposits of the older alluvium, and the relatively minor deposits of windblown sand beneath the river valleys and Yuma Mesa. Although little water is pumped from these fine-grained deposits, the upper, fine-grained zone is significant hydrologically because most of the ground-water recharge and discharge Within the Yuma area take place through it and because the water table beneath the irrigated areas lies Within it. The upper, fine-grained zone generally ranges in thickness from about 70 to 240 feet and averages about 100 feet beneath the valleys and 170—180 feet beneath Yuma Mesa. Sand and silt are the most abundant materials in the zone, although beds of silty and sandy clay and sandy gravel are extensive in places. Because much ground water moves vertically through the upper, fine-grained zone, a special effort was made to determine the thickness and lateral extent of fine-grained beds that might impede or restrict vertical movement. Studies of geologic logs and gamma logs of numerous test wells and obser- vation wells in Yuma Valley and on Yuma Mesa were supplemented by careful examination of expo- sures along the escarpment along the northern and western edges of Yuma Mesa. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA Clay beds A and B of the older alluvium (p. H53) are two of the more extensive fine-grained beds mapped in the subsurface study, and other beds of clay and silt in both the older and younger alluviums in the upper, fine-grained zone may be extensive enough to be hydrologically significant. No attempt was made to trace these individual beds as was done with clays A and B. Instead, the aggregate thick- ness of clay, silty clay, and clayey silt in the upper 100 feet beneath three areas—Yuma Mesa, Yuma Valley, and South Gila Valley—was computed from well-log data (pl. 12). Because the thickness of the upper zone considered in each area is 100 feet, the aggregate thickness of the fine-grained materials is also equivalent to their percentage in this inter- val. The well-log data consist of drillers’ or geolo- gists’ logs of many wells, supplemented by gamma logs or other borehole geophysical logs. Using the gamma logs, the drillers’ or geologists’ logs were modified so that the thickness of the clay-bearing strata could be computed more precisely than would have been possible otherwise. The computations indicate that the average thick- ness of clay-bearing strata in the top 100 feet be- neath the river valleys and Yuma Mesa is only about 15 feet; however, the range is from 0 to more than 50 feet (pl. 12). The clayey deposits are thick- est in South Gila Valley (pl. 12). Somewhat lesser thicknesses occur beneath northern Yuma Mesa, west-central Yuma Mesa (in the vicinity of the apex of the large ground-water mound caused by irriga- tion), south-central Yuma Valley, and several other scattered localities. Beneath much of the Yuma area, the aggregate thickness of the fine-grained clayey deposits in the top 100 feet is less than 10 feet. Most of the clayey strata in the upper, fine-grained zone contain a considerable amount of silt and sand. Consequently, the permeability of these strata is not sufficiently low to cause extensive perching of ground water, even where these fine-grained strata, such as clays A and B described earlier, are thick and ex- tensive. However, although true perching is rare or absent, the fine-grained strata inhibit vertical move- ment of ground water, so that sizable differences in water levels exist at different depths where upward or downward movement occurs. One of the best ex- amples is in the west-central Yuma Mesa. In this area, which has been irrigated for about 50 years and which is the apex of the ground-water mound beneath Yuma Mesa, the water table locally is more than 35 feet higher than the piezometric level for the top of the coarse-gravel zone. Scattered chemical analyses suggest that the water in the upper, fine-grained zone is exceedingly H69 variable in chemical characteristics and concentra- tion of dissolved solids. The variations probably are related to several factors, among which are depth of the water table, proximity of canals, laterals, or surface drains, irrigation regimen, and upward or downward movement of water reflecting areal pat- terns of ground-water circulation. Not nearly enough wells tapping the upper zone are available to document adequately the pattern of chemical variation; wide differences exist between wells less than a mile apart. Where the water table is shallow, the dissolved solids are concentrated by evapotrans- piration, and brackish water, generally high in sodium chloride, is the result. At some other places, where infiltration of canal water occurs, the shal- low ground water is almost identical to the water in the canal (Colorado River water). OLDER ALLUVIUM, UNDIVIDED Outside the river valleys and Yuma Mesa, the coarse-gravel zone appears to be largely absent, and the older alluvium forms a single water-bearing unit which is stratigraphically equivalent to the adjacent wedge zone and hydraulically continuous with it. This unit, called older alluvium, undivided, consists chiefly of slightly to moderately indurated sand, silt, and a minor amount of gravel and clay of river origin, interbedded or mixed with deposits of local origin. Near the mountains, poorly sorted gravelly deposits of local origin predominate. As in the wedge zone, the permeability and porosity of the deposits probably decrease with depth, owing to compaction and cementation. However, because of the considerable thickness—as much as 2,000 feet beneath part of the “Upper Mesa”———the older allu- vium, undivided, stores and transmits substantial amounts of water. In “Fortuna Plain” and Davis Plain in the southeastern part of the Yuma area, the older alluvium is overlain by younger alluvial- fan deposits, but these fan deposits are largely if not entirely above the water table and are not con— sidered further here. Relatively little is known about the chemical quality of the water in the older alluvium, undi- vided. Beneath the “Upper Mesa,” three analyses indicate that the water is similar to that in the wedge zone beneath Yuma Mesa (pl. 11). Farther east, beneath “Gila Mesa,” the water is brackish and probably contaminated by deeper water rising along fault barriers. The southern limits of the brackish water are not known. The electric log of US. Bureau of Reclamation test well CH—28YM on “Fortuna Plain” at the southerly international boundary indicated water having a specific con— H70 ductance slightly exceeding 3,000 micromhos—the limit for fresh water in the Yuma area. However, there are no data to show Whether or not the brack- ish water at test well CH—28YM extends all the way north to the body of brackish water beneath “Gila Mesa.” ORIGIN OF GROUND WATER AND SOURCES OF RECHARGE Almost all the ground water in the upper part of the ground-water reservoir in the Yuma area is in- filtrated river water; precipitation and local runoff are very minor sources of ground-water recharge. The more highly mineralized water in the older rocks of the lower part of the reservoir may include some connate water which was not completely flushed out. Patterns of ground-water recharge have changed, both in geologic time and in historic time, so that the configuration of the water table and the chemical character of the ground water are in a state of flux. The relative importance and the chemical char- acteristics of each of the various sources of ground- water recharge are described in the following para- graphs. COLORADO RIVER Under natural conditions the Colorado River was the predominant source of ground-water recharge in the Yuma area, and it still is by way of diver- sions for irrigation. Water-level contours for 1925 (fig. 29) indicate that the Colorado River at that time was a source of ground-water recharge during low flows as well as high flows. The water table sloped away from the channel so that the river formed a ground-water ridge, and water moved away from the channel on both sides. Evapotrans- piration, in large part by the phreatophytes grow- ing on the flood plain, maintained the lower water levels away from the river. Considerable quantities of ground-water recharge occurred during floods, when most of the flood plain was covered with slow- moving sheets of water. Discharge of ground water by evapotranspiration WATER RESOURCES 0F LOWER COLORADO RIVER—SALTON SEA AREA in the flood plain probably resulted in increased salinity at shallow depth. The rest of the ground water moved slowly southward and southwestward into Mexico to areas of discharge in the Colorado delta around the head of the Gulf of California. The underground flow was a very small fraction of the flow in the river itself. After the construction of Hoover Dam, Imperial Dam, and other upstream dams, the Colorado River cut down, so that its channel now lies 10—20 feet below the adjacent flood plain from Laguna Dam to the southerly international boundary. The downcut- ting resulted from the clearer water in the river after its normal load of sediment was largely trapped by the dams. At the same time, irrigation has main- tained a high water table beneath the flood plain, hence the lowered river channel now acts primarily as a drain rather than as a source of ground-water recharge. However, some recharge from the river still occurs, during occasional high flows, and also at other times along reaches where significant quan- tities of ground water are pumped from adjacent wells, such as along the limitrophe section between Pilot Knob and the southerly international boundary. The chemical composition of ground-water re- charge from the Colorado River has been materially affected by control of the river by the upstream dams. Before the impounding of water in Lake Mead behind Hoover Dam, beginning in 1935, the chemical composition of the river water in the lower reaches was highly variable, both seasonally and annually. Concentrations of dissolved solids were relatively low during seasons and years of high flow and rela- tively high during periods of low flow. Because of their longer duration, periods of low flow and high concentration may have affected the chemical quality of ground-water recharge more than periods of high flow and low concentration. As shown by the summary below, the chemical characteristics of Colorado River water at Yuma were very similar to those at Grand Canyon during the two years of parallel sampling, 1927 and 1928. Constituent concentrations in Colorado River water prior to closure of Hoover Dam in 1.935 Grand Canyon Yuma Year Constituent Minimum Weighted average Maximum Minimum Weighted average Maximum 1927 Dissolved solids ______________ 238 569 1,450 287 612 1,300 1927 Bicarbonate _________________ 121 162 289 133 169 256 1927 Sulfate _____________________ 66 235 597 75 238 579 1927 Chloride ____________________ 18 53 248 25 73 278 1928 Dissolved solids ______________ 233 491 1,180 285 513 1,180 1928 Bicarbonate _________________ 126 162 240 132 163 234 1928 Sulfate _____________________ 66 187 525 79 195 557 1928 Chloride ____________________ 10 48 165 23 55 157 1934 Dissolved solids ______________ 437 960 1,890 ___ ___ ___ 1934 ' 145 206 280 ___. ___ ___ 1934 131 ' 392 827 ___ ___ -_- 1934 Chloride ____________________ 51 136 310 ___ ___ ___ GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA Concentrations were not determined at Yuma dur- ing 1934, the minimum annual flow year of record of the Colorado River prior to construction of Glen Canyon Dam, but were probably similar to those listed for Grand Canyon. Thus, the pre—Hoover Dam records indicate that the usual flow of the Colorado River water in the Yuma area contained less than 1,000 mg/l dissolved solids, with sulfate the major anion and with concentrations of bicarbonate exceed- ing chloride except during periods of low flow. Dur- ing flood flows, bicarbonate was the major anion. Sulfate always exceeded the chloride, regardless of flow. During the 25-year period 1941—65, the composi- tion of Colorado River water downstream from Lake Mead, although still somewhat variable on a year-t0- year basis, did not depart much from a character- istic concentration pattern. Thus, although the con- centration of dissolved solids at Imperial Dam fluc- tuated between 600 and 900 mg/l, it was generally between 700 and 800 mg/l. The chloride concentra- tion fluctuated between 70 and 140 mg/l. Sulfate, always the major dissolved constituent, usually ranged from 260 to 370 mg/l and amounted to about three-sevenths of the dissolved solids. The calcium con-centration, ranging from 80 to 115 mg/l, was generally about three times the magnesium concen- tration and was also usually a little greater than the sodium concentration when the dissolved solids concentration was lowest (about 700 mg/l), and somewhat less than the sodium concentration when the dissolved solids concentration was highest about 900 mg/l). No consistent relation existed be- tween the concentrations of any of the cations and anions, although the equivalent concentration of sodium was generally about twice the equivalent concentration of the chloride. GILA RIVER Under natural conditions the Gila River was peren- nial to its mouth near Yuma, except during pro- longed dry periods, when flow ceased during some months (Wells and others, 1954, p. 707—709). Regu- lation of the river began in 1911 with the' construc- tion of Roosevelt Dam on the Salt River, a major tributary near Phoenix. Thereafter, as irrigation increased east of the Yuma area, especially near Phoenix, the flow at the mouth generally decreased; after the late 1920’s, only occasional floods produced flow near Yuma. Water-level data for 1925 indicate the Gila River was a significant source of ground—water recharge to South Gila Valley at that time; by inference, the recharge under natural conditions was even greater. H71 Ground water beneath South Gila Valley moved southward beneath eastern Yuma Mesa, eastern “Upper Mesa,” and “Fortuna Plain”; therefore, under natural conditions, much of the ground water beneath the eastern part of the Yuma area was_de- rived from the Gila River. Unfortunately, no analytical records describe the natural variation of the chemical quality of the Gila River before the construction of upstream dams and the diversions for irrigation. Recent analytical rec- ords for the major tributaries above Phoenix indi- cate considerable differences in chemical character- istics among these tributaries, which are the former major sources of inflow to the lower Gila River. The natural chemical characteristics of water in the lower Gila River probably were quite variable, de— pending on the proportions of inflow from each of the major tributaries at any particular time. The Gila River flowed at the mouth during the winter of 1966 as the result of release of low-salinity water from the new Painted Rock Reservoir, about 100 miles east of Yuma. The water was stored as a result of flooding on the Salt and Verde Rivers (two of the major tributaries) when runoff in December 1965 filled the storage reservoirs. Analyses of sam- ples taken at various points from Painted Rock Dam downstream to Dome (12 miles upstream from the mouth) during release of the stored water showed that it flowed down the river without great change in composition. Similarity in chemical composition of this water to that produced from wells at many locations on Yuma Mesa supports the hypothesis that much of the original ground water beneath the mesa was derived from flood flows of the Gila River. IRRIGATION Irrigation with diverted Colorado River water is now the source of almost all ground-water recharge in the Yuma area. The principal exception until 1965 was the South Gila Valley which was irrigated with ground water and therefore received much recircu- lated ground water as well as some water from adja— cent areas irrigated with Colorado River water. Water applied in excess of crop requirements and the amount evaporated from the soil penetrates to the water table. In addition, leakage occurs from the canals and distribution system; a considerable proportion of this leakage also reaches the water table. Much of the ground water derived from irri— gation is discharged by surface drains or, in recent years, by drainage wells. Since the early 1920’s, but especially since the late 1940’s irrigation with Colo- rado River water on Yuma Mesa has resulted in the formation of a ground-water mound of considerable H72 size. Because of the sandy soils of low water-holding capacity and the need to reduce salt accumulation in the soil zone, the amount of irrigation water applied has been several times as much as the amount evaporated and transpired, so that ground- water recharge from this source has been sub- stantial. As discussed in the quality of water section of this report, there has been a significant change in the quality of water obtained from domestic wells in the part of the Yuma Mesa irrigated with Colo- rado River water. Older analytical data indicate that formerly the quality of the water obtained from wells in this area was of rather uniform character with sodium and chloride the principal ionic con- stituents and with much less sulfate than chloride being present. Domestic wells in the area now gen- erally yield water more like Colorado River water, with sulfate exceeding chloride, except that there apparently has been considerable softening as the water infiltrated from the land surface. Apparently surface application of large volumes of imported Colorado River water has resulted in a downward displacement of the original water accompanied by softening of the displacing water. LOCAL PRECIPITATION In the Yuma area, as in most desert regions, pre- cipitation is too scanty to allow deep penetration of moisture at most places. The mean annual precipita- tion in Yuma for the period 1931—60 was only 3 inches, and in the adjacent mountains, 4—6 inches (Hely and Peck, 1964, pl. 3). Even during relatively wet years and during periods of intensive rainfall, little or no water penetrates below the soil zone. Moisture measurements by the neutron-meter method made during the present study showed that the materials between the top few feet and the water table are nearly dry outside of the irrigated areas; moisture contents of less than 5 percent—far below field capacity—were recorded at most places. Deep penetration of precipitation, therefore, is a negligi- ble source of ground water recharge in the Yuma area, except possibly in irrigated areas where the soil is wet before rains occur. The addition from precipitation to the mineral content of ground water in the Yuma area is almost certainly negligible. Investigations by Feth ('1967) have shown that the dissolved mineral content of bulk precipitation (rainwater and incorporated dry fallout from the atmosphere) in the Mojave Desert region is generally very low; the specific conductance of most samples is less than 100 micromhos, al- though in a few samples of fallout it ranged from WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA 200 to 300 micromhos. Feth found that most of the samples having higher specific conductance came from locations where dry fallout might include dusts stirred up from the surface of desert playas. These more concentrated samples probably are not repre- sentative of bulk precipitation in the Yuma area because playas are absent. Otherwise, Feth’s results appear applicable. It appears reasonable to assume, therefore, that the average mineral content of rain- fall in the Yuma area has less than 100 micromhos specific conductance and contains 60 mg/l or less dissolved solids. Several of Feth’s analytical results representing samples collected near the Yuma area, are given in table 6. LOCAL RUNOFF Even the small amount of precipitation in the local mountains is enough to produce local runoff, especially during periods of intense storm rainfall. The mean annual runoff in the mountains near Yuma may exceed 1 inch (Hely and Peck, 1964, pl. 5). However, because of rapid infiltration in the sandy and gravelly washes, most of this locally generated runoff does not reach the Colorado and Gila Rivers. A major part of the infiltrated water is later evapo- rated and transpired, but a minor part eventually reaches the water table. Chemical-quality and water- level data from wells near Fortuna Wash show that local runofi“ has reached the water table and has also formed perched or semiperched bodies of ground water. Although no data have been gathered else- where, the large washes like Picacho Wash and Un- named Wash north of Yuma are likely sources of local ground-water recharge. However, the flat water-table gradients adjacent to the mountains indicate that the total quantity of recharge from local runoff is very small. Evidence that local runoff, particularly in the mountains, is low in mineral content is afforded by a number of analyses of samples collected from both natural and artificial tanks and one spring in moun- tainous areas near the Yuma area. An analysis of a sample from Little Picacho Wash, in California, and another from the Gila River near Texas Hill, Ariz., taken after a rain also show low mineral con- tents. (See table 6.) HYDROLOGIC CHARACTERISTICS OF AQUIFERS DEFINITION OF TERMS The term “aquifer” commonly is applied to a water-bearing formation or rock unit that is capa- ble of yielding appreciable quantities of water to wells. The term is flexible, in that it may denote a single bed, or it may refer to a relatively thick sequence of beds. The latter usage is especially GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H73 TABLE 6.—Miscellaneous chemical analyses [Values in milligrams per liter, except for specific conductance] Hardness as 05 .. E = E A § 3 ,2 Spe- N m 37, cific A A E A '5; v '2 A 0’3 '9; g u, gon- Sam le source Date " a d V "‘ A 6 *-’ uct- p g 8 g a E {3 8 8 5 E ”1 E g (ance 4. -- 1: V '13 .a micro- 5 33 E 5 .3 S :32) :2 8 E g 5 mhos _§ '5. E» :3 3 § £3 § E} E 2 E E at 25°C a: o .. ,_ -~ ... m 5 S :2 s. a: :3 5 rs. z r: :3 2 Bulk precipitation-s-Slasbes Ranch, Mar. 17, to 0.2 10.0 1.0 4.6 3_8 10 13 4.8 ____ 8.7 51 29 21 111 lat 33°17' N., long 114°43’ W. Apr. 18, In California.) (Data from Feth, 1965. 1967. table 1.) Bulk precipitation-a-Slashes Ranch Apr. 4 to ____ 18 1.7 120 11 94 16 16 ____ 2.5 124 50 0 259 Data from Feth. 1967, table 1.) 59%; 23. Bulk precipitation Singers, lat Mar. 17. 1965, 1.0 4.8 0.0 1.0 .8 8 4.0 .8 ____ 1.5 26 12 5 44 33°03’ N_. long 114°43' W. (In to Mar. 21. California.) (Data from Feth, 1966. 1967, tab e 1.) Bulk precipitation-Glamis, lat Mar. 17 to .6 __-—. ____ 5.0 2.0 29 18 4.1 ..___ 4.5 -___ ________ 99 33°00‘ N., long 115°04’ W. (In Apr. 4, California.) (Data from Feth, 1965. 1967 table 1.) Bulk precipitation-Glamis (In Cali- Apr. 4. 1965. .3 8.8 5 1.0 1.8 2 8.0 3.8 ____ 12 37 24 22 72 fornia.) (Data from Feth, 1967, to Jan. 20, ta. e l.) 1966. Owl Head Dam, Kofa Mountains, Aug. 11. 1965 11 45 4.7 ____ 8.7 152 6 14 ,3 0 166 132 8 295 Ariz. Budweiser Spring, Kofa Mountains, Jan. 14, 1965 25 25 5.7 ____ 14 102 17 9 5 .3 ____ 148 86 2.5 216 Ariz. High tank No. 7, Kofa Mountains, Jan. 14, 1965 12 38 3.6 __-_ 11 106 22 16 .3 --__ 156 110 23 253 Ariz. Charley Died tank, Kofa Mountains. Feb. 3, 1965 14 23 4.3 ____ 19 70 35 16 _2 ____ 146 75 18 219 Aria. Horse tank. Castle Dome Moun- Dec. 13, 1964 1 20 2.4 ____ 26 98 14 16 ____ ____ 128 60 0 232 ta' , Ar'z. l-Iorsliz‘stankl ___________________ Sept. 15. 1965 16 17 9 ___- 35 124 0 14 ____ ____ 145 46 0 238 Frenchman tank. Tank Mountains, Mar. 5, 1965 7 22 0 ___- 12 64 12 10 .2 1.3 97 55 2.5 143 Ariz. Black tank. Castle Dome Mountains, Jan. 12, 1965 5 30 4.6 ____ 15 120 7 14 .3 _-__ 136 94 0 236 riz. Arch tank. Castle Dome Mountains. Mar. 23, 1965 6 26 7 ____ 8.7 56 19 9 5 .2 8.8 107 68 22 166 riz. Bandy tank. Castle Dome Moun- Mar. 23, 1965 1 34 5.6 ____ 13 110 19 18 ,2 ____ 146 108 13 242 tains, Ariz. Saguaro tank, Castle Dome Moun- Feb. 17, 1965 7 38 1.9 ____ 14 80 27 16 .2 15 162 103 32 246 tains, Ariz. Ladder tank, Castle Dome Moun- Dec. 14, 1964 11 38 3.2 ____ 14 72 42 26 ____ -___ 170 108 49 297 tains. Ariz. Burnt Wagon tank, Castle Dome July 15, 1965 6 37' 2.8 -___ 6.9 116 9 10 .1 ____ 130 104 9 226 Mountains, Ariz, Salton tanks, Castle Dome Moun- Feb. 18, 1965 6 29 23 ____ 7.1 65 13 6.5 26 ____ 122 32 28 190 tains. Ariz. Carrizo tank, Chocolate Mountains. Feb. 5. 1962 11 32 1 ____ 5 66 30 7_0 ____ ____ 119 84 30 223 Calif. Little Pichacho Wash., near Burro Jan. 31. 1962 27 31 4 ____ 73 177 63 31 _____ ____ 317 96 0 513 Wash" in Calif. Gila River near Texas Hill. Ariz., Aug. 15, 1963 7 30 4.4 ____ 26 86 34 30 .3 __.._ 175 93 22 291 after rain, barely flowing. Gila River near Dome, Ariz. Flood Feb. 28, 1966 11 68 18 ____ 185 180 98 281 .3 ___._ 751 244 96 1,390 water being released from Painted Rock reservoir. Gila River near Dome, Ariz. Flood Mar. 18, 1966 10 70 16 _-_- 191 186 115 272 ____ ____ 767 240 88 1,360 water being released from Painted Rock reservoir. Well in nonmarine sedimentary Apr. 24, 1963 1 964 651 _-_._ 5,450 29 792 11,400 ____. ____ 19,300 5,080 5,060 31,300 rocks at North end of Gila Moun- ' tains. Ariz. Mine shaft near well at North end Apr. 24, I963 25 230 264 ____ 6,680 696 367 10,800 ____ ___.. 18,700 1,660 1,090 31,300 of Gila Mountains. Ariz. applicable to alluvial deposits in the Yuma area where individual permeable beds are lenticular or vaguely bounded and are not generally separated by extensive relatively impermeable beds. The principal aquifers in the Yuma area are the coarse-gravel zone and the wedge zone; subordinate aquifers of only local significance include the non- marine sedimentary rocks, conglomerate in the basal part of the Bouse Formation, and a few relatively coarse grained beds in the upper, fine-grained zone. Outside the river valleys and Yuma Mesa, the older 507-243 0 - 74 - 6 alluvium, undivided, is regarded as the principal single, heterogeneous aquifer. Further studies using more data than are presentlyavailable may indicate that the older alluvium, undivided, and the wedge zone actually comprise several distinct aquifers and interbedded relatively impermeable beds. Because what is considered to be an appreciable water supply varies widely from place to place, aqui- fer is a relative term which depends in large part on the conditions that must be met. The adjectives excellent, good, fair, or poor are commonly used to H74 denote the degree to which the supply is satisfac- tory. However, these general terms are inadequate for quantitative appraisal of an aquifer or aquifer system, or for comparing one supply with another. For these purposes, more specific terms are re- quired. The principal characteristics of an aquifer that permit a quantitative analysis of its response to changes in supply or withdrawal are designated by two terms: “transmissivity” and “storage coeffi- cient.” The term “transmissivity,” which is equivalent to the term “coefficient of transmissibility” intro- duced by Theis (1935), has been used by an increas- ing number of hydrologists in recent years because it is a more appropriate word than transmissibility for the property that is described. In units com- monly used by the US. Geological Survey, trans- missivity may be expressed as the rate of flow of water in gallons per day through a vertical strip 1 foot wide of the entire saturated thickness of the aquifer under a unit hydraulic gradient at the pre- vailing temperature of the water. In some applica- tions it may be visualized more easily by expressing the width of the aquifer cross section in miles and the hydraulic gradient in feet per mile. Hydraulic conductivity (formerly coefl‘icient of permeability) is the term that expresses the flow of water in gallons per day that will occur through a 1-square-foot cross section of the aquifer under a unit hydraulic gradient at a water temperature of 60°F (15.6°C). If the flow is that occurring at the prevailing temperature of the water, the term is referred to as the field hydraulic conductivity. Thus, the field hydraulic conductivity is related to the transmissivity by the formula Pm=T in which P is the field hydraulic conductivity, m is the saturated thickness of the aquifer in feet, and T is the transmissivity. Under certain conditions, especially in alluvial ma- terial, it is necessary to differentiate between the horizontal and vertical hydraulic conductivity. Gen- erally, the horizontal hydraulic conductivity of a particular bed is substantially greater than the ver- tical hydraulic conductivity because of the size sort- ing and the alinement of platy and ellipsoidal grains that occur during the deposition of alluvial mate- rials. The difference between average horizontal and average vertical hydraulic conductivity increases markedly with thickness if an aquifer is composed of a large number of thin beds whose conductivities cover a wide range, such as is common in the allu- vial deposits of the Yuma area. Thus, an alluvial WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA aquifer composed of many different strata ranging from clay or silt to sand or gravel may have a hori- zontal hydraulic conductivity that is hundreds or even thousands of times larger than the vertical conductivity. Values of horizontal hydraulic con- ductivity commonly range from a fraction of a gallon per day per square foot for clay and silt to 10,000 gallons per day per square foot for well- sorted gravel. Determinations of hydraulic conductivity are among the principal objectives of an appraisal of a ground-water system. Reasonably close estimates of hydraulic conductivity can be obtained by proper sampling and laboratory procedures. However, the results thus obtained apply only to the samples analyzed. It is seldom feasible to obtain a sufficient number of samples to adequately define hydraulic conductivity throughout a ground-water system. Rather, the average horizontal hydraulic conduc- tivity is computed on the basis of a known trans- missivity and a known thickness of saturated ma— terial. Vertical hydraulic conductivity can be computed from adequate pumping-test data for a leaky arte- sian system. It also can be computed for areas in which most of the flow is vertical, if data on vertical gradients, changes in water level with changes in rate of recharge or discharge, and storage coeffi- cients are known or can be estimated with reason- able accuracy. The costs of obtaining the data necessary to compute vertical hydraulic conduc- tivity often exceed the available funds, and thus in many investigations this parameter is not well de- fined. The inability to adequately define the vertical hydraulic. conductivity Will not of itself prevent a satisfactory appraisal of the total quantities of water involved in recharge, storage, and discharge. However, its absence will lessen the precision with which the response of the system to stresses placed on it by changes in rates of recharge or discharge can be predicted. In the Yuma area, values of vertical hydraulic conductivity had been computed for limited areas by Jacob (1960). Most of the values were for the alluvial material above the coarse-gravel zone be- neath the irrigated area of the Yuma Mesa and for the alluvial material both above and below the coarse-gravel zone for limited areas of the flood plain in Yuma Valley and the South Gila Valley that border the Yuma Mesa. These values were used as guidelines for determining values to be used in the electrical analog model of the Yuma area. Transmissivity generally is determined from pumping or aquifer tests for areas where adequate GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA data are available. However, the areas for which aquifer-test data are inadequate generally are much more widespread than the areas for which the data are adequate. For the areas where aquifer-test data are inadequate but the specific capacities of wells of known construction can be computed, the trans- missivity for the materials tapped by the wells can be estimated on the basis of the theoretical relation between specific capacity and transmissivity that exists under a given set of conditions (Theis and others, 1963). If data on specific capacity are lacking, transmis- sivity can be estimated for those areas Where litho- logic logs or good drillers’ logs are available if the relation between hydraulic conductivity and median grain size is known. Such a relation has been estab- lished for alluvial material in the Arkansas River Valley, Ark., (Bedinger and Emmett, 1963). To the extent that the relation found for the allu- vial materials of the Arkansas River Valley are applicable to the materials of the area being investi- gated or that a new relation can be established, possibly on the basis of pumping tests or laboratory analyses, the transmissivity can be computed by summing the products of the various hydraulic con- ductivities and the thicknesses of the strata to which they apply. Transmissivity can also be computed if the width of a vertical section through which ground water is moving at a known rate and the hydraulic gradi- ent normal to that section are known or can be esti- mated with reasonable accuracy. All the above methods were used in varying de- grees during the current investigation for estimat- ing transmissivity. TRANSMISSIVITY DETERMINATIONS BY PREVIOUS INVESTIGATORS Prior to the present investigation, Jacob (1966) analyzed the results of interference tests for 10 deep drainage wells along the eastern side of Yuma Valley. Transmissivities obtained as a result of these tests are shown in figure 23. He also analyzed the results of step-drawdown tests on six of these wells to determine the characteristics of the wells themselves. Step-drawdown tests also were made on 10 other wells, of which three were in the Yuma Valley, three in the South Gila Valley, and four on the Yuma Mesa. The location of these tests and the transmissivities, where considered reliable by Jacob, are also shown in figure 23. DETERMINATIONS DURING PRESENT INVESTIGATION In planning the phase of the investigation deal- H75 ing with regional transmissivity values it was de- cided that, for the time and funds available, more representative information could be obtained by making short-term pumping tests: of practically all the large capacity wells, even though some of the procedures might yield questionable data in some instances, than by making more detailed and much more expensive and time—consuming tests at only a limited number of sites. Consequently, advantage was taken of almost all opportunities to make pump- ing tests on existing large-capacity wells for which adequate tests had not been made. In most places, the procedure was limited to obtaining data on the rate of recovery of water level in the pumped well after it had been pumped at a constant rate for a known period of time. Although the reliability of this procedure was unpredictable it generally pro- vided useful information for computing transmis- sivity for the material tapped by the well. When it was possible to obtain rate-of-drawdown data also, the transmissivity computed from that data was compared with the value computed from the recov- ery data. A substantial difference between the two values was considered an indication that one or both was unreliable. Other measures of transmis- sivity, such as specific capacity, were considered in checking the reasonableness of the values computed from drawdown or recovery data. Step-drawdown tests were made for most of the test wells that were drilled and for a few other wells where it was practical to do so. Step-drawdown tests permit the separation of the observed drawdown into two components, one due to well losses and the other due to formation losses. A transmissivity com- puted on the basis of the specific capacity from which well losses have been excluded is likely to be closer to the true transmissivity than is a value that is based on the assumption that the well loss is average for the area. The Thiem method for computing the transmis- sivity was used for several of the large drainage wells for which observation wells were available for computing the hydraulic gradient toward the pumped well. All the pumping tests, except those which were analyzed by the Thiem method, in- volved the use of the nonequilibrium formula of Theis (1935) or modifications thereof. The nonequi- librium formula is based on the following assump- tions: (1) The aquifer is isotropic and homogenous, (2) the aquifer is of infinite areal extent, (3) the well taps the full thickness of the aquifer, (4) the well has an infinitesimal diameter, and (5) the re- lease of water from storage with decline of head is instantaneous. WATER RESOURCES 0F LOWER COLORADO RIVER—SALTON SEA AREA H76 . 114°45' 30' 114°15' "’/ / ‘- W "/ 9” ' J ' ’ / /// / A4,. a, , a ¢ ¢,///// ”I -/r'/(’;’/ I / // % %% /”” / 32°45' — "a. Pilotb a“ Kno / ,» UNIT§D_Sw§-—;‘T‘ - 1235101185 MEXICO (flu... Morelos Dam v9 lYUMAfi / .. VV 4603 v \\ / x: Q. ““720 A 5107\ 2:: 4/ Q) .30 \l A “20$ 130: if? V x, Y .619 190.) A? Q7 45‘ .“...310l 210 v \ 140 2r)! 4,9 V e 7- 440‘ ‘3.“— 0 .370 ~: )9- 0 K ' . to Q 340.} . é Vt: 430/.) 40¢? .' ~. % // [2“. ° ( /// N} __\ J ( o {J \ 30' — D .720 pg \ 7 ~J. l (P €202 801v$4x \\ \\ \ \ \ L EXPLANATION \ t; % .460 \ \ [TED P ' t 't — — — ‘ M\EX1£T\ TE “. ‘22 umplng: est 5‘ e Alluvial escarpment 00 fl Circle shows well—site location; numbershows ‘ ‘43 ‘_ transmissivity of materials tested, in thousands """ “RN \ 3‘ of gallons per day per foot D0 d 123-11113 l d We ‘\ tte \ w ere comeea e \ \ \ m \\ Mountains and hills N Area of shallow bedrock ('3 I 1 I 1 5" J“) was 32°15’ ' I FIGURE 23i—Transmissivities computed from pumping tests made prior to the present investigation. meaningful results can be obtained if the tests are It was realized that the actual conditions differed substantially from the ideal conditions that were assumed in deriving the nonequilibrium formula. Nevertheless, the results of previous pumping tests throughout the country have demonstrated that made and the results are analyzed in a way that minimizes the effects of any conditions that differ substantially from ideal conditions. Accordingly, pumping tests utilizing the nonequilibrium formula 32°45' — GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H77 114°45’ ‘ ’0; ' ”we /////,. 30' 114°15' \\ y / ome //// 6 1188.55: e ‘- \ /% 13bdd2 ‘ . J 21ddd 22caa . Q \ ’4///% 22cda| _, ' :4/ £53m 28a'aa 223933.; \ \ s é ’25:: b ' . \o 330ddd34aaa' agiacgfi (3%? l @cab 413%th \\ 2 27: 35°” 35ca\a1,2 A x \ 2?; /) lu ail/Q r17abc1 ‘1 '-.® ) / ‘1 Q7 lacdd a / 36838 30cbaZ—,~.—a‘ ZQadb 25dba2. 28cbb./ 35cbd / f: / A . lZabal 5/ 3 12mm; ( 3V 12bcc2° i [3" / 13bbdl_°/ e“ 153'ab \/ v fix i; Y‘ ‘. i I / 5“ / w” A0 A // .. Q _J 31bbb1 ( x j \ ’I R 24 W '2 bd R 23\W ’ F J ' "mg ’ \ ' q_ “34x ~\-\K i Q‘" “710 A1312 \ Q ‘4» SBA? 0N4 \ p) 0% ~~23bcb \ \N LANATION \ \ . EXP \\.§4bbc \ .28cbb \ . Well for which pumping test(s) were made \UNIT R. 22 w \B. 21 W. % and well number gbab‘sED ST ”1%)‘353 T. . 12 / \ . ”7% \~QN S. Mountains and hills ‘o. ‘ x" W 0 \ \ \ f if \‘ N Area of shallow bedrock \‘\ Alluvial escarpment ......... 0 5 10 MILES Fault l I l l | | Dotted where concealed I I 32°15’ FIGURE 24.—Wells for which pumping tests were made during present investigation. were made on practically all large-capacity wells on which pumping tests had not been made previous to the present investigation and for which satisfac- tory arrangements for a pumping test could be made, unless the geologic and hydrologic conditions obvi- ously precluded obtaining meaningful results (fig. 24). Because of this practice, some of the pumping tests yielded data that were not satisfactory for analyses by the nonequilibrium formula. Table 7 lists the results of the pumping tests that H78 were made during the present investigation. Each of the values of transmissivity is designated as being considered an excellent, good, fair, or poor indicator of the transmissivity of the material tapped by the well. The classification takes into account the construction of the well, the possibility of leakage between strata tapped by the well either within the well casing or the gravel envelope out- side the casing, the storage capacity of the well casing and the gravel envelope relative to the rate at which the well had been discharging, and other factors that might tend to invalidate the results. The degree to which changes in water level with time conformed with theory also was used to judge the reliability of the transmissivity. Another cri- terion was the ratio between the transmissivity and the specific capacity of the well, a method mentioned earlier in this report. For most of the wells that were tested, ratios of 2,000—3,000 were considered reasonable. Lower ratios were indicated when the drawdown used to compute specific capacity did not include well losses, when the specific capacity was considerably higher than it would be at the end of a 1-day pumping period, or when effective well diam- eters were considerably more than 24 inches. Another criterion for evaluating the reliability of the indicated values of transmissivity was whether the hydraulic conductivity as computed by dividing the indicated transmissivity by the thickness of strata tapped by the well greatly exceeded the probable maximum hydraulic conductivity of the material tapped by the well. In the Yuma area the average maximum hydraulic conductivity of allu- vial material several tens of feet thick probably is not more than 10,000 gallons per day per square foot. Thus, computed values of transmissivity that indicated hydraulic conductivities two or more times larger than the above figure were considered un- reliable. A classification of excellent for the reliability of the transmissivity was made where, taking into account all the aforementioned criteria, the com- puted transmissivity was thought to differ from the true value by less than 10 percent; good, if the difference was likely to be as much as 25 percent; fair, if as much as 50 percent; and poor, if more than 50 percent. Of the 73 evaluations of reliability of the computed values of transmissivity, three are classified as excellent; 33 as good; 28 as fair, and nine as poor. To adequately evaluate the transmissivity of the full thickness of saturated material at a particular well site, one must also have knowledge of the hy- draulic conductivity of all water-bearing strata not WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA tapped by the well, or at least a general knowledge as to what percentage of the transmissivity of the fully saturated section is represented by the com- puted value. A good understanding of the various kinds of water-bearing material and their positions in the geologic framework in which the ground water occurs is necessary for this evaluation and was at- tained during the present investigation. This knowl- edge together with pumping—test data and drillers’ logs of wells permitted the compilation of maps showing transmissivity (fig. 25 and others not shown), which were used as a basis for construct- ing the analog model of the Yuma area and for computing rates of ground-water movements. STORAGE COEFFICIENT An important characteristic of an aquifer is its ability to store or to release water in response to changes in head. This characteristic commonly is designated by a dimensionless number called the storage coefficient (formerly coefficient of storage), which has been defined as the volume of water that is released from or taken into storage per unit sur- face area of an aquifer per unit change in the com- ponent of head normal to that surface (Ferris and others, 1962, p. 74). The changes in storage that result from changes in head when water is confined, that is, when it occurs under artesian conditions, are due almost entirely to compressibility of the water and the aquifer. Storage coefficients under artesian condi- tions, therefore, are small, generally ranging from about 0.00001 to 0.01. The changes in storage that result from changes in head when water is unconfined, that is, when it occurs under water-table conditions, are dependent almost wholly on the drainage characteristics of the aquifer material. The volume of water involved in gravity drainage ordinarily is many hundreds or even thousands of times greater than the volume attributable to com- pressibility of the aquifer materials and of the water in the saturated zone; therefore, the volume of water resulting from compressibility can be ignored. The volume of water involved in gravity drainage divided by the volume through which the water table moves, has been defined as the specific yield. Under dewatering and unconfined conditions the storage coefficient therefore is sensibly equal to the specific yield. When water is going into storage, that is, when the water table is rising, the storage coefl‘i— cients may exceed the specific yield if the material in which the water is being stored contains less mois- ture than it can retain against gravity drainage. The upper limit of the storage coefficient in the latter con- GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA TABLE 7.—Results of pumping tests Type of test: D, drawdown; R, recovery; SD, step-drawdown. H79 Aquifers tested: B, Bouse Formation; C, coarse-grave] zone; N, nonmarine sedimentary rocksfii 0, older alluvium, undivided: W, wedge zone. ‘9 ~ 9 Depth EH '5’: Z c f interval Up on orm- tested, in Date of a a 'E 2““ E: ance of test Reliability Aquifers Well Owner or name feet below test ,0, M s? S 5; '5 5.", data .tO Of T teste Remarks land- H g B 9‘ E a theoretical surface 0 ""_ r8 3:) E 5-: values datum w w: B '5 e- = a a : r: a” a a a D (0.5 9.5 lGS/22E—29Gc32 -_.- USGS LCRP 26 _ 125—1,127 4713—65 R 1,390 9.6 140 570,000 See page 11le 1,368—1,769 for additional test data. l6S/23E78Ecc _____ USBR CH5 ___- 110—141 12716763 D 570 6 95 340,000 12718—63 R 570 6 95 750,000 22ch ___ H. Mitchell ___- (T) 10—29762 R 4,120 17 240 440,000 9Naa ___ M. E. Spencer __ 1247225 4720—63 R 3,900 19 200 >300,000 Only parts of aquifers tested. 10Rcc ___ USGS LCRP 23 _ 6347694 1-—21—63 D 1,230 22 56 260.000 Excellent __ Good _____ B See page H209 for additional data 1721—63 R 1,230 22 56 4,600,000 Fair ______ Poor ______ B 1207548 4— 6765 R 650 4 160 240,000 Excellent __ Good _____ C, W 31Dhc ___ Dover and Webb- 1007144 4730763 R 3,000 21 140 420,000 Fair ______ Fair ______ C (C— 7722) 14bcd ___ USGS LCRP 14 _ 4707490 4723—63 R 290 46 63 110,000 Good _____ ___do _____ N Only pfart of aqui er tested. {$13} 5—29—63 R 600 9 67 790,000 Poor ______ Poor _____ c (C7 8721) 19dad ___ F. J. Hartman _.. 1157165 9711—62 R 2,600 28 93 230,000 Good ______ Good _____ C 30cdc ___ ___do _________ 1207140 10— 9-62 R 2,050 11 190 1,800,000 Excellent __ Fair ______ C Gravel re- ported 807 150 feet. Only part of aquifer tested. (0— 8—22) 13bdd2 __ S. Sturges _____ 109—128 4— 9764 R 1,325 53 25 65,000 Good ______ Good _____ C In tight gravel. Only part of aquifer tested. 15¢de ___. Powers ________ 1107160 10716762 R 4,400 9 490 610,000 ___do _____ ___do _____ C 18ddd __- ___do _________ 1007155 10717762 R 4,600 24 190 800,000 Fair ______ air ______ C 3707390 Only parts of 19ccc ___ USBR CH702 -__ 3:5—435 } 11713763 R 1,060 35 30 68,000 Good _____ Good _____ W aquifer tested 4 5—463 21ddd ___ B Church _____ 1057150 10710762 R 2,820 16 180 390,000 ___do _____ ___do _____ C 22088. -..- 100—165 10—- 5762 R 3,200 15 210 430,000 Excellent __ _-_do _____ C 22cda1 __ (136 10— 4762 R 3,200 16 200 320,000 ___do _____ air ______ C T may below by about 25 percent be- cause Well 14 mile distant was shut off 10 minutes prior to re- covery test. Only part of aquifer tested. 220da2 __ ___do __________ 1007152 107 4762 R 2,600 10 260 380,000 Fair ______ C 25bad ___ F. J. Hartman _ 100—114 9720—62 R 2,600 14 190 400,000 ___ o _____ C Only part of aquifer tested. 26adb ___. S & W ________ ('3) 10— 8—62 R 2,400 20 120 290,000 Good _____ C 28aaa ___ B. Church ______ 1057150 10710762 R 2,600 18 140 350,000 C 30cab ___. O Lord _______ 115—170 107 4762 R 3,100 12 260 380,000 C 30ddd _ ___(lo _________ 130—160 107 9762 R 1,450 8 180 360,000 C Do. 34aaa W. R. Whitman _ 937177 10— 9762 R 2,560 26 98 960,000 Excellent __ C 34add USBR CH750 ___ 500—600 10— 7—64 R 2,700 60 45 150,000 Fair ______ W 35038.1 __ USBR CH704 ___ 435—445 480—490 )12—24—63 R 1,100 24 46 340,000 W Do. 507—570 997170 1— 7—64 R 1,620 8 200 1,100,000 C 35caa2 USBR CH751 ___ 4847585 10713764 R 2,750 65 42 190,000 W Do. 35cca ___ Aréfilna Western 1807248 9—30—62 R 690 30 23 230,000 C ege. 36cad ___ USBR CH752 ___ 5207621 10— 1764 R 2,600 82 32 200,000 W Do. (C7 8723) ldcc ___ K. Easterday ___ 1207145 11— 6762 R 2,900 22 130 600,000 C Ichb ___. ___ o __________ 1157171 117 8762 R 4,500 27 170 480,000 C 25acb ___. Gusnht'hlr and 115—175 10— 5762 R 2,230 20 110 260,000 C n- ey. 25dab ___ _-_do _________ 115—175 10— 5762 R 2,400 17 140 300,000 Excel‘ent -_ Excellent __ C 26bac ___ G. Ogram ...... 142—180 10—10—62 R 1,960 22 89 180,000 ___do _____ ___do _____ C Only Dart of aquifer tested. 27a“ "‘ USBR CH7“ --- 128§_lg§ )12— 3763 D 1,250 20 62 330,000 Fair ______ Fair ______ C 127 3763 R 1,300 19 68 230,000 Excellent __ Excellent __ C 27ddd1 __ Carter _________ 135—158 10— 8—62 R 1,725 35 49 120,000 air ______ air ______ C De. (C7 8724) 22CCd ___ McCLaren Produce 1177142 7715—30 D 2,850 39 58 300,000 Good ..... Good _____ C Do. 0. (C7 9—22) 28cbb ___ USGS LCRP 25 _ 862—2,002 1719765 D, R 600 11 54 200,000 Poor _____ W See page H213 for additional test data. Upper 500 feet of aquifer not included in test. (C7 9723) 1711ch ¥C¥UA 3 _____ 1307170 4729—63 D 4,700 42 110 230,000 Fair ______ ___do _____ C 20° d --— C UA 5 ----- $2.323} 14—25453 D 6,300 35 180 250,000 Good _____ ___do _____ C, w o'gétuggfieglxe zone included in test. H80 WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA TABLE 7.—Results of pumping tests—Continued \Vell Owner or name Depth interval tested, in Date of feet below test land- surface datum Transmissivity (T) , Specific capacity, in gpd per ft in gpm per ft Conform- ance of test data to theoretical values Aquifers Reliability of T tested Remarks (C— 9—23)‘25dba2 __ 293db ___ 30cba2 __ (0— 9—24) lscdd ___ (0— 9—25) 35cbd ___ 36aaa ___ (0-10723) 12aba1 __ 12bda _ _._ 15aab ___ 311)be (010—24) 12b002 __ 13bbd1 _, (C—10—25 lbba _____ cha 35bbd ___ 350ab 1-- (0—11—23) 34bbc -1- (Cell—24) 2abd ____ 2bbd ___ 23bcb ___ (C—11725) 3dac ___- (0-12—22) 9bab ___ USBR CH7B ___ Yuma Mesa Fruit Growers Unit B. YCWUA 6 _____ USBR CH3 ___- USGS LCRP 9 __ McDaniel & Sons, Inc. J. F. Nutt _____ _-_do _ _,_do _________ USGS LCRP 1 __ YCWUA 8 YCWUA 9 P. R. Sibley ___ F. Jeffries USGS LCRP 17 _ J. F. Barkley __ USGS LCRP 30 _ J. F. Nutt _____ USGS LCRP 10-- E. Hughes ______ USGS LCRP 24 _ 3718—64 12—23—55 U50 Type of test 160—250 1567207 140—160 170~203 139—170 )4725—63 12—31763 12—31763 436—1,108 1148—62 50:66 U 4367560 12411—62 1 2—1 1—6 2 130—180 11—19fl62 178*686 US$315 10431763 1 0—3 1—6 3 1 14 6—6 3 1 1~1 8-6 1 6*20e62 1507680 <890 2207280 E‘NW 150v178 1718—65 142~185 1v18765 160~285 11— 9762 158—295 10130432 520—1398 3—28764 NFU‘EUFU pg 1787293 160~600 11——21—62 8731765 130~300 1—14—65 1—14765 } 5* 3765 5— 3—65 51),}: 140—289 319—376 165—1,002 4—11~63 R 188—282 318—1346 10731—62 3‘16—65 R SD 3—16—65 5‘ Yield. in gpm O 0” Drawdown, in feet NH 3,700 40 22 22 71 4.000 520 520 100 92 79 92 79 3,620 44 4,150 28 4,150 3,700 1,940 1,320 84 4,940 33 2,060 120 5,200 22 3,820 25 388 5 39 11 4,000 1,340 11 11 1,660 1,620 3,700 3.700 19 2,500 18 29 4,560 600 66 66 Cl 00 3,000,000 180 600,000 200,000 300,000 300,000 300,000 1.2 18,000 1.2 82 220,000 160,000 150 210,000 150 140 100 16 260,000 500,000 270,000 280,000 150 260,000 170 540,000 443,000 460,000 160.000 150 78 100 120 600,000 1,300,000 150 150 190 190 1,100,000 1,100,000 1,600,000 9,000,000 140 740,000 160 9.1 730,000 200,000 9.1 3,500,000 Specific capacity is abnormally low because of high inter- nal well losses. 120 feet of screen in the 672- foot interval tested. Only part of aquifer tested. Only part of aquifer tested. Good ___do _____ ___do _____ Do. Only part of wedge zone tested. Do. Analyzed by us- ing leaky artesian formula and observation wells. Only part of aquifer tested. Only part of aquifer tested. Do. Fair See page H214 for additional data. Only part of aquifer tested. Fair ______ Excellent __ Only part of wedge zone tested, ___do _____ ___do _____ Good _ _ _ do _____ Do. T as indicated from recovery data. is 10 or more times larger than T based on formation specific ca- pacity. Only part of wedge zone tested. See page H216 for additional data. .231 feet of screen in the 837-foot interval tested. Only part of wedge zone tested. 18 feet of cas- ing perforated in the 28-foot interval tested. Only part of aquifer tested. 0 Above remarks apply to this test also. Poor ______ __ _do _____ GEOHYDROLOGY OF THE YUMA AREA, ARIZONA, AND CALIFORNIA H81 1 14°45’ 30' MM / / .d,<0 '. O ”.9 O > 0 . 32°45’ 30/ _ E X P LA N AT! 0 N —300— ' Line of equal transmissivity, in Alluv1al escarpment thousands of gallons per day per foot Fault Dotted where concealed Mountains and hills Area of shallow bedrock 32°15’ FIGURE 25.—Transmissivity of alluvium. dition is the porosity of the material. Under water the aquifer material increase and (or) sorting im- table conditions, the storage coefficient for clay and ‘ proves, the storage coefficient commonly increases. silt commonly ranges from almost zero to a few hun- For clean sand and gravel, it frequently ranges dredths. Generally, as grain size, and sphericity of ‘ between 0.2 and 0.4 H82 By definition, the storage coefficient is not a func- tion of time. It represents the ultimate change in storage, regardless of the time necessary to achieve the change. In practice, the ultimate change, is rarely, if ever, reached. Rather, it is approached within widely varying limits depending on the time since the change in head occurred and the physical properties of the water-bearing material. In a clean sand or gravel almost all the gravity drainage may be completed in a few hours or a few days, whereas in silt or clay, an appreciable part of the ultimate drainage may occur after weeks and months. Storage coefficients used in conjunction with transmissivities enable one to determine for a given change in the ground-water supply in a given area the relative amounts of ground water that will be involved in storage changes and those that will be innvolved in movement of ground water toward or away from the area. In other words, using these two characteristics one is able to determine the change in position and change in shape of the water or piezometric surface that results from a given change in the supply of ground water. Storage coefficients can be determined from pump- ing tests. Pumping tests are probably the most practical way for obtaining storage coefficients if artesian conditions exist, but many times they may be less practical than other methods where water- table conditions prevail. The failure of short-term pumping tests to provide valid data for computing a storage coefficient is due in most places to the slow rate at which many water-bearing materials drain. The mathematical formulas used in this analysis of pumping tests assume an instantaneous change in storage with a change in head. Although this idealization is approached under artesian conditions, it is not approached under water-table conditions. Most storage coefficients computed from data ob- tained during pumping tests of unconfined aquifers are likely to be substantially less than the true stor- age coefficient unless the test is extended for sev- eral days and adjustments for the protracted drain- 3 age are made. In most tests, therefore, it is impractical to meet all the conditions that are neces- sary to obtain valid data. A more practical approach for determining storage coefficients under water- table conditions in the Yuma area appears to be the use of a neutron moisture probe in conjunction with access tubes driven to depths of several feet below the water table. The average difference between the moisture content of material above the capillary zone and that of material below the water table is then considered a reliable indicator of the amount WATER RESOURCES 0F LOWER COLORADO RIVE‘R—SALTON SEA AREA of water that will go into storage as the water table rises. This approach was used for estimating storage characteristics of the material saturated by the large ground-water mound that built up beneath Yuma Mesa after 1947. The details of the investiga- tion of moisture content by means of the neutron probe are given in appendix E. Storage coefficients for artesian conditions were not computed from any of the pumping tests that were made during the present investigation because the conditions for the pumping tests were not ade- quate for obtaining valid results. Artesian storage coefficients for drainage wells along the eastern boundary of Yuma Valley, as computed by Jacob (1960, appendix E, table E—l) ranged from 5.8><10’* to 3.6><10“‘ and averaged 1.2X10‘3. In the Yuma area, the quantities of water that are involved in changes in storage under artesian conditions are very small relative to the quantities involved under water-table conditions. Thus, only a general knowledge of the storage coefficient under artesian conditions is needed to account for or pre- dict the principal changes in ground-water move- ment or storage resulting from stresses imposed on the system. MOVEMENT OF GROUND WATER As in surface flow, ground water moves in the direction of decreasing head, but its rate of move- ment through granular materials, such as those in the Yuma area, is only a small fraction of the rate of movement of surface water, and its path of move— ment is much more complex. During the present study, water-level maps were prepared to show the direction of movement of ground water under natural conditions and at se— lected times during the historical development of the water resources of the area. Because the Colo- rado River and the ground-water system are con- nected hydraulically, important controls for prepar- ing the water—level maps were the mean annual stages of the river (fig. 26). A river-profile map and a series of topographic maps of the Colorado River flood plain were pub- lished in 1927 by the US. Geological Survey from surveys made in 1902. These maps together with the early records of river stage at Yuma were used to estimate mean annual river stages under natural conditions and also during the period of water- resources development until the rapid degradation of the river channel in the early 1940’s. After 1940, considerable information regarding the river profile was inferred from river-channel-cross-section sur- STAGE, IN FEET ABOVE MEAN SEA LEVEL STAGE. 1N FEET ABOVE MEAN SEA LEVEL GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA 125 120 ~ 115 125 1905 1910 1915 1920 1925 1930 1935 120 115 1970 1970 110 ‘ 1940 1945 1950 1955 1960 1965 105 . I . 100 — Morelos Dam 95 l l I v 1 V, ,, 1940 1945 1950 1955 1960 1965 85 | | l I l I 80 — ‘ Southerly International Boundary 75 1965 1940 1945 1950 FIGURE 26.—Mean annual stages 1955 1960 of Colorado River at Yuma, Ariz. 1970 H83 H84 veys that were made periodically at selected sites by the US. Section of the International Boundary and Water Commission. Before 1942 the mean annual stage of the Colorado River at Yuma ranged from 120 to 125 feet above mean sea level; during the next few years the stage dropped about 5 feet, then continued to drop, but at a lesser rate, to a stage of about 113 feet in 1966 (fig. 26). Although the lowering of stage was due in part to decreased flow of the river, the principal cause of the rapid lowering in the 1940’s probably was the erosion of the channel by the clearer water that resulted from upriver storage. Stages were also dropping at the Morelos gaging station and at the southerly international boundary, undoubtedly for the same reasons as at Yuma (fig. 26). In the 1960’s a stage of about 74 feet indicated no measurable streamflow at the southerly interna- tional boundary. DIRECTION OF MOVEMENT UNDER NATURAL CONDITIONS Adequate water—level data are not available for determining directly the configuration of the ground- water surface beneath Yuma Valle-y or Mexicali Valley under natural conditions. The earliest year for which sufficient data are available for drawing a water-level map for Yuma Valley is 1911. Although the valley had been irrigated with Colorado River water for several decades priod to 1911, the effects of irrigation on the configuration of the ground- water surface probably was small, partly because under natural conditions Yuma Valley had been sub- ject to periodic flooding by the river and partly be- cause only one-eighth of the valley land was being irrigated. Therefore, ground-water levels in Yuma Valley in 1911 probably were similar to those under natural conditions. The inferred configuration of the water table in Yuma Valley in 1911 is based on widely scattered water-level data and estimated river stages (fig. 27). The water-level contours indicate that in 1911 and by inference, also under natural conditions, the Colorado River was a source of recharge to the ground—water body underlying Yuma Valley. The earliest year for which similar information is available for any part of Mexicali Valley is 1939. Water-level data for 1939 for that part of Mexicali Valley lying north of the Alamo Canal, together with water-level data for 1958 for that part of Mexicali Valley lying south of the Alamo Canal, were used as a basis for drawing a water-level map showing the probable configuration of ground-water levels in Mexicali Valley in 1939 (fig. 28). WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA The irrigation of land with surface water in Mexicali Valley, without provisions for drainage, caused water levels to rise above the levels that existed under natural conditions. By 1939, several places had been noted in which irrigated lands had become so waterlogged that farming was no longer feasible. Although the configuration of the water—level sur- face in Mexicali Valley in 1939 was similar to its configuration under natural conditions, its south- westward slope had decreased somewhat because its eastern boundary was hinged to the Colorado River and did not rise as did water levels beneath the irri- gated lands farther westward from the river. For these reasons a somewhat lesser rate of infil- tration of Colorado River water to the ground-water system, both beneath Yuma Valley and Mexicali Valley, is indicated by this map (fig. 28) than existed under natural conditions. The map shows that as late as 1939 the Colorado River was a source of recharge to the ground-water body, although ground-water levels had risen as much as 5 feet as a result of irrigation with surface water. Under natural conditions, then, the movement of ground water easterly from the river to the Yuma Valley and westerly to Mexicali Valley was substantially greater than that indicated by the 1939 data. In 1939 there was also a southward movement of water beneath Yuma Mesa and across the southerly international boundary (fig. 28). The available data for later years indicate that neither the direction nor the rate of movement across the southerly in- ternational boundary was greatly different from what it probably had been under natural conditions. Therefore, the movement of ground water across this boundary as shown by the 1939 water-level data is a good indication of the movement under natural conditions. The westward movement of ground water through the alluvium between Pilot Knob and the Cargo Mu- chacho Mountains as shown in 1939 probably also is a good indication of the direction and rate move- ment under natural conditions. However, after 1939, leakage from the All-American Canal greatly changed the ground-water gradients in this area. (Compare figs. 28 and 30.) In summary, the water-level data, for the delta area in 1939 also indicate the direction of ground- water movement under natural conditions. However, the rates of movement from the Colorado River to the ground-water system adjacent to the limitrophe section, as shown by gradients in figure 28, are less than under natural conditions. 32°45’ 32°30’ GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA 114°45’ H85 "‘ ' -mEXICO \ ALL-AME l 0 7 l RICAN CANAL \NfiTED ST ME \ATE XICO \ TS ’70 Shows altitude of water level. interval Sfeet; datum is mean sea level MESA EXPLANATION 9o Water-level contour Bedrock outcrop Alluvial escarpment Contour SMILES l FIGURE 27.—Average water-level contours in 1911 in Yuma Valley. WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA H86 .flommmmfifioc hon—:3 can hauvflsom _a=o$a:u3=H .fiomuowm 533st 05 >3 “53295 ho=a> :58on new Sun— ...833 afiwu we 5 223 E 253:8 ~w>w7uwua3 muauw>~\’\’ P“ 04 / v?‘ /// 6 32°45' — n‘df’ilot Knob Wg’ ES " - . UNITEILSFLT— — " modems MEXICO {/‘g‘ Morelos Dam ,-/j l' \\/f\\"/.\ 9% a . [a an /05 V A //\. V \I x. A? ‘5 ‘ \ V V 0 \ [0+ O é‘ Q ‘17 a: flf o 3 Q Q 30' — D f“ 7 i\ \ U \ {1751) EXPLANATION \ ST ME? ATES // -——95—'— :T: 100\ ‘ ~12 \/ Water-level contour :' i D? x J. Shows altitude of water level. Dashed where Area of shallow bedrock B \ \ approximately located. Contour interval 1, 2, \\ and 5feet; datum is mean sea level —'——— ‘\ Alluvial escarpment \\ \ . . Fault Mountalns and hllls Dotted where concealed o 5 10 MILES I L | l I J 32°15’ FIGURE 29.—Average water-level contours in 1925, changed considerably between 1939 and 1960 (and Yuma Mesa that had formed by 1960. The influ— also, by inference, between the time of natural con- ence of the mound extends in all directions: east- ditions and 1960; see figs. 28 and 30). A significant ward toward the Gila Mountains, southward toward change is the large ground-water mound beneath Mexico, northward into South Gila Valley, and west- 507-243 0 - 74 - 7 WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA H90 59335.58 flag was baud-50m Han—Omega; nun-300m 5—3wa 25 ha 335ch ham—db =5:wa you auda— dommwu 51% 05 5 an: 5 5:353 "2575.33 uuduw> _ K ~ 9 ha 11H _Om 2.3V .Ooam: haomfifi GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA ward into Yuma Valley. The very steep gradients westward toward Yuma Valley result in large part from the lowering of head by drainage wells in Yuma Valley albng the toe of the mesa. A more detailed discussion relative to the build up of the mound is given in the section on the analog model. (See p. H109.) Also significant is the change in the character of the Colorado River upstream from the limitrophe section. Under natural conditions and as late as the early 1940’s, the Colorado River was a losing stream. The mean annual stage of the river was higher than the mean annual water levels on either side of the river. However, during the early 1940’s the river chan- nel was eroded 5 feet or more in the Yuma area (fig. 26). This degradation of the river channel, plus rising ground-water levels as the result of irriga- tion and leakage from the All-American Canal, all tended to raise ground-water levels upstream from the limitrophe section above the mean stage of the Colorado River, thereby making the river a gaining stream in the reach above the limitrophe section. Marked changes also occurred in the limitrophe section area. Movement of ground water was still westward from the Colorado River into Mexico, but the direction of the movement in the northern part of the limitrophe section, principally as the result of leakage from the All-American Canal, had changed from westward to southward. A marked change in the direction of the contours in Yuma Valley near the Colorado River also oc- curred between 1939 and 1960. Under natural con- ditions, and as late as the early 1940’s, the mean stage of the river was above the adjacent ground- water levels in Yuma Valley. In 1960, however, and for some 10 years prior thereto, ground-water levels in western Yuma Valley were higher than the adjacent mean river stages. As a result, ground water moved from Yuma Valley toward the river. To what extent the ground water discharged into the river rather than moved west- ward beneath the river is not known, but consider- ing the westward gradient from the river to Mexi- cali Valley and the substantial thickness of pre- dominantly fine—grained materials beneath the chan- nel and above the coarse-gravel zone, which greatly inhibits interchange between the ground-water body and the river, it is doubtful that a large percentage of the outflow from Yuma Valley westward to Mexicali Valley was intercepted by the Colorado River. An estimate of the outflow from Yuma Valley is made in a later section of this report. (See p. H103.) H91 Leakage from the All-American Canal is the prin- cipal cause for the changes in the direction and rate of movement of ground water relative to the course of the Colorado River. Leakage from the All-Ameri- can Canal and the Coachella Canal branch of “the canal obviously had built a sizable mound beneath these canals by 1960. For a distance of 25 miles west of Pilot Knob, the height of the mound aver— aged 30 feet or more. The net result is that in a 30-mile reach the direction of ground-water move- ment south of the All—American Canal had been changed from westward, or practically parallel to the United States-Mexico boundary which existed under natural conditions and until some years fol- lowing the completion of the All-American Canal, to southward and at a gradient that was steeper than was the westward gradient before completion of the All-American Canal. RATE OF MOVEMENT IN 1960 Many of the same difficulties mentioned in the discussion of rates of movement under natural con- ditions also arise in making estimates of rates of ground-water movement after development of water resources by man. By 1960, many changes in rates of movement had occurred, and the pattern of move- ment was more complex than under natural condi- tions. Much of the complexity is due to the fact that many of the changes noted by 1960 were interim changes, which did not represent the ultimate re- sponse of the ground-water system to the develop- ment that had occurred. ALLUVIAL SECTION BETWEEN PILOT KNOB AND CARGO MUCHACHO IVIOUNTAINS The rate of movement westerly through the allu- vial section between Pilot Knob and Cargo Muchacho Mountains is difficult to estimate, principally because of lack of knowledge of the westward gradient. Only two control points are available for defining the gradient. One indicates that the altitude of the water level in well 16S/22E—2Hac which is less than half a mile west of the All-American Canal, was about 135 feet. The other indicates that the altitude of the water level in a well 8 miles west was 123 feet. Thus a westward gradient of 11/2 feet per mile is indicated. If this figure is accepted as a reasonable value of the gradient, then the westward flow through the section in 1960 probably was only three-eighths of the flow under natural conditions, or somewhat less than 2,000 acre-feet per year. LIMITROPHE SECTION OF COLORADO RIVER In 1960, the movement of ground water in the 2-mile reach downstream from the northerly inter- H92 national boundary was toward the Colorado River both from Mexicali Valley and Yuma Valley (fig. 30). The eastward movement of ground water to the river was due principally, if not entirely, to the discharge of part of the leakage from the All- American Canal. South of this reach, or beginning at a point about where the 100-foot water-level con- tour crosses the river, to a point about 5 miles down- stream, or where the 95-foot contour crosses the river, there was a westward gradient of about 3 feet per mile almost directly away from the river. Using an average transmissivity of 80,000 gpd per ft and the foregoing data, the westward flow is indicated to have been 12 mgd, or 13,500 acre-feet per year. Southward from this reach to the southerly inter- national boundary, the contours are so irregular that it is difficult to determine the many gradients that are implied. Undoubtedly, much of the irregularity is caused by pumping of ground water for irrigating land west of the Colorado River. However, in a gross sense, the contours in this reach leave the river at an angle of about 45°; the straight-line distance of the river reach is about 9 miles; and the contour difference is 20 feet. Using an average transmissivity of 1 mgd per ft and the foregoing data, the rate of movement of ground water southwestward into Mexicali Valley from the point where the 95-foot water—level contour crosses the river to the southerly international boundary is 20 mgd, or about 22,500 acre-feet per year. The total westward movement of ground water into Mexicali Valley adjacent to the limitrophe section, thus, was about 36,000 acre-feet in 1960. The data on which the foregoing estimate is based are very meager. The principal value of the estimate is that it shows the order of magnitude of the move- ment of ground water westward from the Colorado River to Mexicali Valley in 1960. Some support for the reasonableness of the foregoing estimate is obtained by examining its value relative to estimated outflow from Yuma Valley in the limitrophe section and estimates of streamflow depletion and other losses in the limitrophe section. The outflow from Yuma Valley in the limitrophe section is estimated to have been about 20,000 acre- feet in 1960 (p. H95). Estimates of streamflow de- pletion in the limitrophe section vary widely, de- pending on the magnitude of the flow and its relation to preceding flows and also the points between which the losses or gains are computed. Streamflow in the limitrophe section in 1960 was small relative to his- torical flows but somewhat larger than flows after 1960. WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA The streamflow depletion in 1960 and thereafter, therefore, probably is best estimated by noting the losses that occurred in years when the flows were near to and less than the 1960 flow. Estimates of loss between the northerly inter- national boundary and the southerly international boundary were computed by adding to the flow re- corded at the northerly international boundary the wasteway water from the Yuma project, then sub- tracting (1) the diversions to Mexico made at Morelos Dam, (2) the pumpage in the limitrophe section of the river, and (3) the flow at the south- erly international boundary. Years of relatively low flow of the Colorado River and rates of depletion in the limitrophe section of the river since 1950 are as follows: Flow at northerly international boundary ( a or e-feet) Loss between northerly and southerly international boundaries (acre-feet) 1,640,000 9,000 2,338,000 47,000 1,672,000 31,000 1,811,000 35,000 1,834,000 72,000 Average (rounded) _ 1,860,000 39,000 From the foregoing, it appears that for a flow of about 1.9 million acre-feet per year at the northerly international boundary, the computed loss in the limitrophe section averages about 39,000 acre-feet. This loss is only about 2 percent of some of the measured flows, which is within the probable limits of error of the data. Another evaluation can be made by computing the losses in the limitrophe section from Morelos gaging station to the southerly international boundary. Morelos gaging station is about 1.7 miles south of the northerly international boundary and about 0.5 mile south of Morelos Dam (fig. 30). The advantage of this evaluation is that the magnitude of the flows are much smaller than the flows at the northerly inter- national boundary and the diversions to Mexico from Morelos Dam which were used in the preced- ing analysis. According to water-level data for 1960 (fig. 30), the losses indicated for the reach between Morelos gaging station and the southerly international boundary should be a good indication of the net loss in the entire limitrophe section because northward from Morelos gaging station the Colorado River is a gaining stream. Estimates of loss were obtained by adding to the measured flow at Morelos gaging station the inflows from Eleven-Mile and Twenty-One—Mile wasteways, which are 31/4 and 171/2 miles respectively down- stream from Morelos Dam, and subtracting there- GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA from the pumpage from the limitrophe section and the flow at southerly international boundary. Years of relatively low flow and rates of unac- counted depletion since 1950 are as follows: Unaccounted depletion. Morelos gaging station to southerly interna- tional boundary Flow at Morales Year gaging station (acre-feet) (acre-feet) 1956 ____________________ 242,000 6,000 1960 ____________________ 540,000 18,000 1961 ____________________ 177,000 20,000 1962 ____________________ 313,000 23,000 1963 ____________________ 176,000 10,000 Average (rounded)- 290,000 15,000 The yearly inflows from the wasteways were about 25,000 acre—feet, and pumpage from the river generally was about 4,000 acre-feet. The average unaccounted depletion of the gross flow therefore is about 5 percent of the average maximum flow. Five percent is outside the probable limits of error of the data, and therefore the indicated unaccounted deple- tion by the latter method is considered the more reliable of the two estimates. Therefore, the loss of Colorado River water in the limitrophe section in 1960 and thereafter probably averages about 15,000 acre-feet yearly. The outflow of 20,000 acre-feet from Yuma Valley plus the unaccounted depletion of the riverflow of about 15,000 acre-feet suggests that in 1960 the out- flow westward to Mexico opposite the limitrophe sec- tion of the Colorado River was about 35,000 acre- feet minus evaporation losses from the free water surface of the river. The latter probably is less than 2,000 acre-feet at low stages of the river. This estimate of slightly less than 35,000 acre-feet per year, which is based largely on excess irrigation water and infiltration of river water, compares favorably with the estimate of 36,000 acre-feet per year, which was based Wholly on ground-water parameters in Mexicali Valley. YUMA VALLEY Ground-water outflow from Yuma Valley can be analyzed as the sum of the flows that cross its north- ern, western, and southern boundaries. An estimate of the ground-water outflow northward and west- ward from Yuma Valley is made on the basis that part of the outflow is ground-water recharge from irrigated land lying between the northern and west— ern boundaries of Yuma Valley and the ground- water divide southerly and easterly from these boundaries, less the use of ground water by phreato— phytes and the pumpage of ground water from be- neath these lands for irrigation, and that part is ground water moving westerly at depth. Detailed water-level contour maps compiled by the United States section of the International Boundary H93 and Water Commission (not shown) were used to determine the location of the divide for the ground- water recharge due to local irrigation. The contours were based on water-level altitudes in more than 200 shallow wells and on the altitude of the water sur— face in the drains. The ground-water divide that separates the area from which the outflow was prin- cipally northward coincided roughly with an easterly prolongation of the northerly international boundary. Most of the land north of the divide, about 2,500 acres, was irrigated. Based on reports of the Yuma County Water Users’ Association the diversion of water to land irrigated in Yuma Valley, including losses from laterals, averaged 6.5 feet for the years 1955 to 1960, inclusive. Estimates of consumptive use for crops was assumed to have been 3.6 feet, the same value as used throughout this study for crops grown in the flood plain. The recharge to ground water from irrigation thus averaged about 2.9 acre-feet per acre per year for lands that were irrigated. The out— flow from Yuma Valley northward of an imaginary extension of the northerly international boundary therefore was about 7,300 acre-feet. The area between the river, the ground-water di- vide, and the northerly and southerly international boundaries Which contributed to the outflow was 15,000 acres. Of this acreage, 3,100 acres supported the growth of phreatophytes, and 11,900 acres sup- ported irrigated crops. The recharge from irriga- tion, therefore, was 34,500 acre-feet per year, from which must be deducted the consumptive use by phreatophytes and pumpage for irrigation. The lat- ter two items are 8,200 and 13,000 acre-feet, respec- tively, based on data in the US. Bureau of Reclama- , tion (1963, p. 28 and 34) study. The net outflow from Yuma Valley to the limitrophe section as a result of local recharge from irrigation not diverted to drains, therefore, was about 13,000 acre-feet in 1960. Outflow also occurred in the deeper aquifers. Con- tours based on water levels in wells penetrating the top of the coarse-gravel zone are considered to be representative of the head in the coarse-gravel zone and the underlying wedge zone. Therefore, the con- tours are useful for estimating gradients and for selecting width of sections through which water is transmitted to or across the limitrophe section. Using the information shown in figure 31 and transmissivity values shown in figure 25 the flow to or across the limitrophe section through the coarse- gravel zone and the wedge zone is computed to have been about 6,400 acre-feet in 1960. The combined outflow of ground water from Yuma Valley to the H94 32°45’ 32°30’ WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA 114°45’ l ALL-AMERICAN CANAL ..____— _.—.—— _//—\ \\ U /\N’3EDS \ T M \AT l EXICO \ ills \ \ \\ we \ a \J/ ‘22; YUMA @- w E X P LA N AT] 0 N 90 Water-level contour Shows altitude of water level. Contour interval 5 feet; datum is mean sea level Bedrock outcrop Alluvial escarpment 0 5 MlLES FIGURE 31.—Average water-level contours for upper part of coarse-gravel zone in 1960 in the Yuma Valley. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA limitrophe section in 1960, therefore, is the above quantity plus the 13,000 acre-feet of local recharge from irrigation not diverted to drains, or about 20,000 acre-feet. The outflow across the southerly international boundary based on a transmissivity of 1 mgd per ft, a width of section of 1% miles, and a gradient of about 3 feet per mile is about 6,000 acre-feet per year. The total outflow from the valley in 1960 thus was the 20,000 acre-feet to the limitrophe section, plus the outflow northward of 7,300 acre-feet, plus the outflow across the southerly international boundary of 6,000 acre-feet, a total of about 33,000 acre-feet. MOVEMENT AFTER 1960 Both the direction and rate of movement of ground water continued to change after 1960. In general, the changes followed the pattern that was established prior to 1960. A comparison of water- level contours as of December 1965 (fig. 32), with the water-level contours as of December 1960 (fig. 30), illustrates the changes that occurred. The principal changes were: a moderate increase in the size of the ground-water mound beneath the Yuma Mesa and a lowering of water levels in Mexi- cali Valley. Water levels beneath Yuma Mesa con- tinued to rise until 1962. After 1962, owing to increased pumpage for drainage near the toe of the mesa in Yuma and South Gila Valleys, water levels northward and westward from the apex of the ground-water mound began a moderate decline. However, at greater distances eastward and south- ward from the apex, water levels continued to rise. More details on the areas and amounts of change of water level beneath Yuma Mesa are given in the section on the analog model (p. H107). The other principal change is the generally lower water levels in Mexicali Valley, which resulted from pumpage for irrigation. These lower water levels together with generally unchanged levels for most of Yuma Valley resulted in an increased westward component of the water-level contours crossing the limitrophe section of the Colorado River. The in- creased westward component plus an increased ground-water gradient away from the river imply an increased outflow of ground water from the United States. More details about the lowering of water levels in Mexicali Valley is given in the sec- tion on the analog model (p. H107). Movement of ground water in future years will depend on the changes in recharge to and discharge from the ground-water system. As long as ground— water levels in the United States remain relatively H95 stable or continue to rise and water levels in Mexi- cali Valley continue to decline, the outflow from the United States will increase. Water levels in the United States may be lowered by improving the irrigation efficiency to the point where only sufficient water is diverted for irriga- tion to satisfy evapotranspiration needs and to carry away the salts contained in the irrigation water. Water levels also may be lowered by pumping. The marked increased pumpage of ground water for drainage beginning in 1961 illustrates the effective- ness of this method for lowering water levels. Pump- ing of ground water by private interests for the irrigation of land on Yuma Mesa outside designated irrigation districts, which began in 1962, also has resulted in lower water levels. As of 1968 the pump- age and consequent lowering has been only moderate, but if the present rapid pace of developing new land for pumping irrigation is maintained for only a feW more years sufficient land will be developed in the southern part of Yuma Mesa to require the pump- ing of more ground water than presently is entering the area. Additional ground water will be diverted to the area because of the lowering of water levels, but if a ground-water sink is maintained, the chemi- cal quality of the pumped ground water eventually will deteriorate because of the continued reuse of much of the water. The extent to which the outflow of ground water from the United States eventually will be influenced by the control of water levels is likely to be governed not only by economic factors but also by interna— tional political considerations. WATER BUDGETS Water budgets provide an accounting for the water resources of an area during a specific period of time. The budget may be for either the surface— water system or the ground-water system or both, depending on the objective of the analysis. In the present study, the movement of ground water is of principal concern. Therefore, the budg- ets presented emphasize the disposition of the ground-water supply rather than the surface-water supply. The budget period was selected as the calen- dar years 1960—63, inclusive, because better-than— average data are available for most of the budget items during this period. The budget years also oc- curred near the end of a long period of continuous growth of the ground-water mound beneath Yuma Mesa. In order to obtain a better understanding of the complex movement of the ground water, the Yuma area is divided into subareas, mainly on the basis WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA H96 dommmmEEOO .533 was hang—5cm 3.853535“ 9: AA "$35.3 >2er “€8wa uom Sun 4330.. 33% $5 5 mg." uwnfiwown E mason—:8 $575095 owauojwslda NEE—h _ J m . _ mTNm A; 323363 msmfz NOSEQ 23$ \ _ _ _ _ _ _ _ _ V azwfiafiwoww FAN/31¢ mug: ma 9 m o g llllll O £09352 252,3? mo «MEAN 0 WW 7 \ 0 Ex: mid mfiwuzsog 9 § .V N33 33. :63: 3 4x383» .dmwkg 0 was: m ESSA: $8226 $8393 0 Eugesfigoxaas 232$ BEESQ €93 xwueg Kc 335.33 mgcqm .5038 E>3L3a>> I I new \VéV ZO_._. mmmocmm_ 18 @ #2118214 T % Subsurface-water inflow or outflow Mountains and hills XICBQ \ ‘0 ‘ -> 30 :2 v? \ \ Surface—water inflow or outflow ;; a \ \ g 25 Area of shallow bedrock V15\\ . — — —— \ \ \ Consumptlve use Alluvial escarpment \ +62 ------- Ground-water storage Fault gain (+) or depletion (_) Dotted where concealed 0 I l 7’ 1'0 MILES 1 | Numbers show quantities in 1,000 acre-feet 32°15' I | FIGURE 33.—Water budgets for subareas, 1960—63, inclusive. of the principal irrigation districts (fig. 33). These that valley and that the Yuma Mesa subarea in this subareas correspond to some of the subareas de- section of the report includes also the “Upper Mesa,” scribed in the section “Geomorphology” with the “Fortuna Plain,” and “Fortuna Dunes” subareas of exception that The Island area of “Bard Valley” is the geomorphic classification. herein made a subarea separate from the rest of Values for surface inflow and outflow items were H98 determined from records published either by the US. Geological Survey, or from operational records maintained by the US. Bureau of Reclamation or the irrigation districts. Unmeasured runoff, esti- mated to average less than 1,000 acre-feet per year, was not considered large enough to be distributed among the various subareas. Values for subsurface inflow and outflow items were computed on the basis of transmissivity, width of section, and hydraulic gradient, as indicated by the map of the Yuma area showing transmissivity (fig. 25) and maps compiled quarterly by the US Bureau of Reclamation show- ing water-level contours. The estimated average yearly recharge to ground water resulting from pre- cipitation was negligible and therefore was not in- cluded in any of the budgets. Estimates of leakage from the principal canals were in part based on unaccounted-for differences in flow between gaging stations and in part on trans- missivity, hydraulic gradients, and length of canal. Ground-water storage change was considered sig- nificant only for Yuma Mesa subarea. The change was computed on the basis of increase in volume of the ground-water mound multiplied by storage co- efficients of 31 per cent for the volume underlying Yuma Mesa and 18 percent for the volume underly- ing the “Upper Mesa” and “Fortuna Plain.” Volume changes were determined from water-level contour maps for year end 1959 and 1963. Values for consumptive use in the flood-plain areas, except where noted in a particular budget, were computed by multiplying the average net irri- gated acreage for the years 1960—63 as listed in US. Bureau of Reclamation records by 3.6 feet and by multiplying the remaining area by an average con— sumptive use rate of 2.5 feet. Consumptive use on Yuma Mesa was assumed to be the average of the annual consumptive use values for the years 1960—63 as shown in table 8. The con- sumptive use values were based on irrigated acreage of crop and noncrOpland and the following annual rates of use: (1) Alfalfa hay, 7 feet, (2) unhar- vested fields, 2.6 feet, (3) citrus and others, 3.9 feet, (4) urban and suburban, 2.5 feet, and (5) farm- steads and ditches, 2.5 feet. Budgets for the individual subareas are based on the principle that inflow less consumptive use equals change in storage plus outflow. Because of practical limitations on the accuracy of flow measurements and of limited knowledge about values to be used for computing indirect estimates and estimates of consumptive use an equality is rarely achieved. This fact, of itself, does not lessen the reliability of the WATER RESOURCES 0F LOWER COLORADO RIVER—SALTON SEA AREA TABLE 8.—Diversions, consumptive use, and ground-water recharge for Yuma Mesa [Quantities in 1,000 acre-feet] Calendar Consumptive Ground-water year Diversions 1 use recharge 1941 _______ 14 6 8 1942 _______ 15 7 8 1943 _______ 21 8 13 1944 _______ 32 14 18 1945 _______ 75 38 37 1946 _______ 134 50 84 1947 _______ 151 47 104 1948 _______ 158 50 108 1949 _______ 132 52 80 1950 _______ 135 56 79 1951 _______ 170 62 108 1952 _______ 209 72 137 1953 _______ 227 84 143 1954 _______ 272 95 177 1955 _______ 249 90 159 1956 _______ 233 77 156 1957 _______ 222 72 150 1958 _______ 245 74 171 1959 ....... 271 81 190 1960 _______ 295 78 217 1961 _______ 290 77 213 1962 _______ 327 79 248 1963 _______ 317 78 239 1964 _______ 299 82 217 1965 _______ 265 82 183 1966 _______ 275 82 193 1 Based on crop reports of the U.S. Bureau of Reclamation. estimates as long as the imbalances are less than the probable error and the imbalances do not tend to be in the same direction. None of the imbalances are thought to be unreasonable in View of the uncertain- ties of many of the items to which they pertain. Average annual budgets for the period 1960—63, inclusive, for the subareas of the Yuma area are given in the following sections. “LAGUNA VALLEY" SUBAREA The “Laguna Valley” subarea consists of the Colo- rado River flood plain between Laguna and Imperial Dams (fig. 33). Most of the subarea is covered by natural vegetation or shallow lakes and marshes (Mittry Lake is the principal water area) ; cropland is restricted to a small area immediately upstream from Laguna Dam. The water budget follows: (Acre-feet) Inflow, subsurface water: Leakage from All-American Canal1 ..__ Leakage from Gila Gravity Main Canal” Leakage beneath Imperial Dama ______ 10,000 Total Consumptive use: Crops, 80 acres ______________________ Natural vegetation Evaporation from free water surface other than river and canals5 ___ Total Inflow less consumptive use ______________________ vfliio Change in storage _____________________________ Negligible Outflow, subsurface water: To North Gila Valley subarea6 ________________ 700 To Colorado River 7 __________________________ 2,900 Change in storage plus outflow ___________________ 3,600 Imbalance ______________________________________ 13,000 33,000 O GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA 1Estimated on basis of 3-mile length of canal and average rate of leakage of 4,300 acre-feet per year per mile of canal, the average rate if leakage computed from U.S. Geological Survey measurements of canal ows. 2Estimated on basis of 5-mile length of canal and average rate of leakage of 2,000 acre-feet per year per mile of canal. 3Unaccounted-for pickup in flow of river between Imperial Dam and gaging station 0.6 of a mile below dam is about 11 cubic feet per second or about 8,000 acre-feet per year. This pickup probably is due to leak- age beneath the dam; an additional 1,000 to 2,000 acre-feet of leakage probably is still subsurface inflow 0.6 of a mile downstream from the dam, based on an estimated maximum coefficient of transmissivity of 500,000 gpd per ft, 11/2 mile width of section, and hydraulic gradient of 2 feet per mile. 4Estimated on basis of acreages of natural vegetation and rates of use by various species as computed from data in U.S. Bureau of Reclama- tion (1963) study. 5Areas of open water as determined from U.S. Geo‘ogical Survey topographic map Laguna Dam 75-minute series multipiled by a net annual rate of 6.2 feet. 6 Computed on basis of transmissivity of 0.3 mgd per ft, hydraulic gradient of 2 feet per mile, and 1 mile width of section. 7 Computed to balance budget. The network of observation wells does not extend into the “Laguna Valley” subarea nor are the inflow and outflow of the Colorado River known. The avail- able data therefore are insuflicient for obtaining a check as to whether or not estimates of inflow less consumptive use equal estimates of change in storage plus outflow. Rather, the budget was balanced by assuming that the amount needed to balance the budget was subsurface inflow to the Colorado River. The reasonableness of the various estimates there- fore depends to a large extent on the reasonableness of similar types of estimates in other subareas where data or estimates for all budget items were avail- able, because the basis for the estimates, other than the subsurface inflow to the Colorado River, is the same. RESERVATION AND BARD SUBAREA The Reservation and Bard subarea includes all “Bard Valley” except for The Island, which is as- signed to a separate subarea. More than half the subarea is in crOpland, irrigated with water diverted or pumped from the Colorado River (a small tract in the northeastern part of the subarea is irrigated with ground water). The water budget follows: Acre-feet Inflow: Surface water: Diversions to district lands _______ 95,100 Diversions to other lands 1 ________ 3,600 Total surface water _________________ 98,700 Subsurface water: Leakage from All-American Canal2 56,000 Leakage from Yuma Main Canal 3 _ 5,000 Total subsurface water _____________ 61,000 Total inflow ________________________ 159,700 Consumptive use: Irrigated cropland in district, 10,800 acres at 3.6 feet ___________________ 38,900 Other irrigated cropland, 630 acres at 3.6 feet ___________________________ 2,300 Other land in subarea, 8,190 acres at 2.5 feet _______________________ 20,500 Total __________________________________ 61,700 Inflow less consumptive use ______________________ 98,000 Change in storage _____________________________ Negligible H99 Outflow : Surface water: Araz Drain _____________________ 4,600 Reservation Central Main Drain __ 46,600 Total surface water _________________ 51,200 Subsurface water: To The Island subarea‘ __________ 14,000 To Colorado River5 ______________ 22,000 Total subsurface water ______________ 36,000 Change in storage plus outflow ___________________ 87,200 Imbalance: Inflow less consumptive use exceeds change in storage plus outflow _________________ 10,800 1Water pumped from river for irrigation at estimated rate of 6 feet on 600 acres. . 2"Based on average rate of leakage for the period 1958—64, inclusxve, of about 4,300 acre-feet per year per mile length of All-American Canal bordering the subarea as computed from U.S. Geological Survey meas- urements of canal flows, multiplied by the 13-mile length of canal border- ing the subarea. . “Based on rate of leakage of 2,000 acre-feet per year per mile length of canal. 4Computed on basis of transmissivity of 0.9 mgd per ft, hydraulic gradient of 4 feet per mile, and 3 mile length of section across northern part of The Island subarea boundary plus transmissivity of 0.7 mgd per ft, hydraulic gradient of 2 feet per mile, and 11/.» mile length of section at southwestern boundary. . 51n reach between Laguna Dam and The Island subarea, outflow is compupted as 6,000 acre-feet per year based on transmissivity at 0.6 mgd per ft, hydraulic gradient of 3 feet per mile, and length of reach of 3 miles; in reach between Yuma and All-American Canal, outflow is com- puted as 16,000 acre-feet per year based on transmissivity of 0.6 mgd per ft, hydraulic gradient of 6 feet per mile, and length of reach of 4 miles. Minor items of inflow and outflow that were not included in the budget are: (1) Ground-water re- charge from the tributary area west of the subarea, (2) unmeasured runoff to the subarea from the tributary area, and (3) subsurface outflow through the alluvial section between the Cargo Muchacho Mountains and Pilot Knob. The latter item is estimated to be about equal to the two minor inflow items, so the omission of these minor items has no appreciable effect on the budget. A substantial part of the imbalance of 10,800 acre- feet probably is due to an overestimate of the amount of water diverted for irrigation of district lands. Beginning in 1965, measurement procedures were improved, with the result that the average yearly diversion rate per acre irrigated apparently dropped 0.5 of a foot. An overestimate of 0.5 of a foot "would account for about half of the imbalance. The remaining imbalance is of the same magnitude but of opposite sense to the imbalance for The Island subarea. (See p. H100.) Part of the imbalance may be due to the use of the same rate of consumptive use for nonirrigated land (2.5 feet per year) for both subareas. The average depth to water in the Reser- vation and Bard subarea is several feet less than the average depth to water in the flood-plain subareas, whereas the depth to water in The Island subarea is several feet greater. Rates of consumptive use commonly decrease as the depth to water increases. Thus it is reasonable to infer that the consumptive use estimate for non- irrigated land is somewhat too low for the Reserva- H100 tion and Bard subarea and somewhat too high for The Island subarea. THE ISLAND SUBAREA The Island subarea is that part of “Bard Valley” south of an abandoned meander loop of the Colorado River (fig. 33). The subarea is outside the estab- lished irrigation district and the cropland (less than half of the total land area) is irrigated mainly with ground-water supplies. The water budget follows: Acre-feet Inflow: Surface water: Diversions from river for irrigation ______ 2,200 Subsurface water: Inflow from Reservation and Bard subarea 1 ______________________ 14,000 Inflow from North Gila subarea ___ 7,000 Total subsurface water _____________ 21,000 Total inflow _______________________ 23,200 Consumptive use: Irrigated cropland, 3,100 acres at 3.6 feet ______________________________ 11,200 Other land in subarea, 5,470 acres at 2.5 feet __________________________ 13,700 Total __________________________________ 24,900 Inflow less consumptive use ______________________ —1,700 Change in storage _____________________________ Negligible Outflow, subsurface water to Colorado River2 _____ 4,000 Change in storage plus outflow __________________ ‘4,000 Imbalance: Amount by which inflow less consumptive use is less than change in storage plus outflow -__ 5,700 1 See footnote 4 of budget for Reservation and Bard subarea. 3 Computed on basis of transmissivity of 0.7 mgd per ft, hydraulic gradient of 2 feet per mile, and 21/2,: mile length of reach east of Yuma. Much of the imbalance probably is due to an over- estimate of consumptive use on land that is not irri- gated (p. H99). NORTH GILA VALLEY SUBAREA The North Gila Valley subarea, an L-shaped area east of the Colorado River and north of the Gila River, is chiefly in cropland which is irrigated with Colorado River water except for the eastern arm of the subarea, which is now (1968) irrigated in large part with ground water. The water budget follows: Acre-feet Inflow: Surface water (Gila Gravity Main Canal) : Diversions at North Gila Main Canal turnout _________________ 88,400 Diversions at other points (Warren Act contracts) _________________ 11,600 Automatic canal spills ____________ 1,000 Total surface water _________________ 101,000 Subsurface water: From South Gila Valley subarea 1 __ 10,000 From “Laguna Valley” subarea and tributary areas eastward _______ 1,000 Leakage from Gila Gravity Main Canal 2 ____________________ 16,000 Total subsurface water _____________ 27,000 Total inflow ________________________ 128,000 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA Consumptive use: Irrigated cropland, 7,100 acres at 3.6 feet ______________________________ 25,600 Other land in subarea, 4,300 acres at 2.5 feet __________________________ 10,800 Total __________________________________ 36,400 Inflow less consumptive use ______________________ 91,600 Change in storage _____________________________ Negligible Outflow: Surface water: Laguna Canal Wasteway _________ 7,700 Levee Canal Wasteway ___________ 15,500 North Gila Main Canal Wasteway _ 8,300 Bruce Church Wasteway _________ 9,400 North Gila Drain No. 1 ___________ 7,300 North Gila Drain No. 3 ___________ 600 Bruce Church Drain _____________ 700 Total surface water _________________ 49,500 Subsurface water: To The Island subareaa __________ 7,000 To Colorado River‘ ______________ 23,000 To South Gila Valley subarea5 ___- 14,000 Total subsurface water _____________ 44,000 Change in storage plus outflow __________________ 93,500 Imbalance: Amount by which inflow less consumptive use is less than change in storage plus outflow ___ 1,900 1LInflow across southwest corner of subarea computed on basis of transmissivity of 1 mgd per ft, hydraulic gradient of 6 feet per mile, and length of section‘ of 11/2 miles. 2Computed as average of 16,000 acre-feet per year based on average rate of leakage of 2,000 acre-feet per year per mile length of canal as indicated by measurements of flows and diversions. 1‘ Computed on basis of transmissivity of 1.0 mgd ner ft, hydraulic gradient of 4 feet per mile, and length of section of 1%; miles. “Computed on basis of transmissivity of 0.6 mgd per ft, hydraulic gradient of 5 feet per mile. and 6-mile length of reach less 7,000 acre- feet to The Island subarea, plus outflow across southwest corner of subarea of 10,000 acre-feet. 5Computed on basis of transmissivity of 0.5 mgd per ft, hydraulic gradient of 8 feet per mile, and length of section of 3 miles. The imbalance of 1,900 acre-feet per year is con- sidered insignificant. SOUTH GILA VALLEY SUBAREA The South Gila Valley subarea, which lies south of the Gila and Colorado Rivers and north of Yuma Mesa, was until 1965 irrigated principally with ground water. A minor part was irrigated With surface water diverted from the Gila Gravity Main Canal under Warren Act contracts. About two- thirds of the total area of nearly 15,000 acres is in irrigated cropland. The water budget follows: Acre-feet Inflow: Surface water (Gila Gravity Main Canal): Diversions for irrigation, (Warren Act contracts) ________________ 5,100 Automatic canal spills ____________ 1,000 Total surface water _________________ Subsurface water: Leakage from Gila Gravity Main Canal 1 Leakage from Wellton-Mohawk Main Outlet Drain 2 ____________ Inflow from Dome Valley3 ________ Inflow from North Gila Valley sub- area ‘ _________________________ 14,000 Inflow from Yuma Mesa subarea5 _ 57,000 Total subsurface water ______________ Total inflow ________________________ 6,100 12,000 3,000 1,000 87,000 93,100 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA Consumptive use Irrigated cropland,“ 9,850 acres at 3.6 feet ______________________________ 35,500 Other land in subarea, 4,850 acres at 2.5 feet __________________________ 12,100 Total __________________________________ 47,600 Inflow less consumptive use ______________________ 45,500_ Change in storage7 _____________________________ —2,000 Outflow: Surface water: Deep Pump Outflow Canal No. 1 ___ 17,000 Deep Pump Outflow Canal No. 2 ___ 13,000 Total surface water ________________ 30,000 Subsurface water: To North Gila Valley5 ___________ 10,000 To Colorado River " ______________ 9,000 Total subsurface water ______________ 19,000 Change in storage plus outflow ____________________ 47,000 Imbalance: Amount by which inflow less consumptive use is less than change in storage plus outflow ___ 7 1,500 1 Based on 2,000 acre-feet per year per mile length of canal and 6-mile length of canal in subarea. 3 See discussion following budget. “ Computed on basis that transmissivity does not exceed 1 mgd per ft., hydraulic gradient of 2 feet per mile; and 1/2 mile-width of section. tComputed on basis of transmissivity of 0.5 mgd per ft., gradient of 8 feet per mile, and 3-mile length of section. 5 See discussion following budget for Yuma Mesa subarea. p. H101. " 9,420 acres in district plus 430 acres outside district. TComputed from water-level maps for December 1959 and December 1963, assuming a specific yield of 20 percent. aComputed on basis of transmissivity of 1 mgd per ft., hydraulic gradient of 6 feet per mile, and width of section of 11/; miles. 9Computed on basis of transmissivity of 0.7 mgd per ft, hydraulic gradient of 4 feet per mile, and width of section of 3 miles. The budget item “Leakage from Wellton-Mohawk Main Outlet Drain” requires some additional expla- nation. Flow in this drain, or conveyance channel, began in February 1961. Therefore, for practical purposes, the drain was in operation for 3 of the 4 years of the budget period, 1960—63. The flow in the drain is measured at a point 8 miles above its outlet to the Gila River. Except at the measure- ment sections, the drain is unlined. Leakage from the drain during the budget period could not be com- puted because measurements were first made near the drain outlet beginning in October 1965, at which time the Main Outlet Drain Extension to Morelos Dam was completed. A comparison of flows between the two stations shows that in each of the years 1966, 1967, and 1968 the flow near the outlet to the Gila River is about 9,500 acre-feet less than the corresponding flow at the station where the flow was measured during the budget period. Allowing that some of the indicated loss represents evapora- tion and that the loss may be somewhat more than during the budget period because of a slightly higher stage due to the Construction of the drain extension, a seepage loss of 8,000 acre-feet per year, or about 1,000 acre-feet per year per mile of chan- nel is indicated. To the extent that the leakage does not discharge to the Gila River, whose channel gen- erally is within half a mile of and north of the drain, the seepage is an inflow item to the South Gila subarea. The extent to which the above condi- hydraulic H101 tion exists is not known, but on the basis of obser- vations in the field and general ground-water condi- tions, at least half the leakage, or 4,000 acre-feet per year, is estimated to be inflow to the South Gila subarea. The rest of the inflow as measured at -the station 8 miles above the drain outlet is considered a through flow, or return flow to the Colorado River via the Gila River, and as such need not be consid- ered in the budget of the subarea. The imbalance of less than 1,500 acre-feet is con- sidered negligible in View of the uncertainty regard- ing true values for many of the budget items. YUMA MESA SUBAREA The Yuma Mesa subarea includes the “Upper Mesa” and “Fortuna Plain” as well as Yuma Mesa. This subarea is underlain by most of the ground- water mound which has developed from irrigation of citrus orchards on Yuma Mesa, mostly since the mid 1940’s. The water budget for the subarea follows: Acre-feet Inflow: Surface water: Diversions for irrigation _________ 307,000 City of Yuma (diversions in excess of sewage returns) ____________ 4,000 311,000 Consumptive use: Crops ‘ ______________________________ 78,000 Lawns ______________________________ 2,000 80,000 Inflow less consumptive use ______________________ 231,000 Change in storage2 _____________________________ 47,000 Outflow, subsurface: To South Gila Valley 3 ________________ 57,000 To Yuma Valleya ___________________ 97,000 Across international boundary east of San Luis ______________________ 30,000 Total __________________________________ 184,000 Change in storage plus outflow ___________________ 231,000 Imbalance ______________________________________ 0 1 Average of values shown in table 8. gComputed from map showing changes in water level, December 1959 to December 1963 and using coefiicient of storage of 0.18 for changes beneath “Upper Mesa," 0.31 for changes beneath nonirrigated land of Yuma. Mesa, and one-half of the foregoing coefficient for changes beneath irrigated land. 3 See discussion following budget. The outflow from the ground-water mound to the South Gila Valley subarea and to the Yuma Valley subarea was computed by determining the percent- age of the ground-water recharge that moves toward each of these subareas and to the area east and southeast of the mound. A contour map showing the head in the coarse-gravel zone beneath the irrigated area of the Yuma Mesa as of December 1962 was used for establishing the position of the ground- water divides of the mound. Although only a few data were available for con- trols as early as December 1962, by making use of all the data on water levels in both shallow and deep H102 wells over a period of years, and of more complete data in deeps wells in later years, it was possible to draw contours showing the head in the coarse- gravel zone and also the ground-water divides. Then by assuming that the yearly rate of ground—water recharge per acre irrigated was uniform for blocks of several thousand acres or more, the yearly re- charge that was diverted to the various subareas was computed by determining the percentages of the total irrigated areas that lay between specific divides. On the above basis it was found that about 25 percent of the irrigated acreage, and therefore of the recharge, or about 57,700 acre-feet, was within the divide diverting recharge to the South Gila Valley subarea. Of this amount, some 500 acre- feet went into storage beneath the mesa, leaving 57,000 (rounded) acre-feet as outflow to the South Gila Valley subarea. About 45 percent of the irri- gated acreage, and thus 45 percent of the recharge, or 104,000 acre—feet, was in the sector where re- charge was diverted westward toward the Yuma Valley subarea. Of this amount, about 7,000 acre— feet went into storage beneath the mesa leaving 97,000 acre-feet as outflow to the Yuma Valley subarea. About 30 percent of the irrigated land was in the sector in Which water moves eastward and south- ward from the mound. Of the 69,000 acre-feet of recharge to this sector, about 40,000 acre-feet went into storage beneath the mesa, and 29,000 acre-feet moved as outflow southward toward the interna- tional boundary. A small eastward or westward shift of the di- vides causes a pronounced change in the relative quantities of recharge that are diverted to the Yuma Valley subarea and to the subarea eastward and southward of the divide, but the shift causes only a relatively small change in the recharge that is diverted northward to the South Gila Valley sub- area. Although shifting the ground-water divides slightly westward would reduce the outflow to Yuma Valley and thus would reduce the rather large im- balance for that subarea, it would increase the recharge to the eastern and southern sector a simi- lar amount. A balance presently exists between the l recharge estimated on the basis of the ground-water divides and the recharge based on outflow and stor- age estimates in this sector, so any westward shift of the divides should be governed by the extent to which the outflow and storage estimates for the eastern sector might be too low. The storage coefficients used for the budget may be too low. The coefficients used for the budget are those that were simulated by the analog model dur- WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA ing the final stages of the vertification procedures. Although historical changes were verified to a bet- ter degree by using those coefficients than the larger coefficients of 0.25 for the material underlying the “Upper Mesa” and 0.35 for that underlying Yuma Mesa, the possibility that an excellent verification by using the larger coefficients and adjusting other parameters could be obtained was not fully explored because of a lack of both time and funds. The larger storage coefficients would increase the estimate of ground-water storage an additional 10,000 acre-feet per year. An increase of this magnitude would sig- nificantly reduce the imbalance of the Yuma Valley ' subarea, the algebraic sum of the imbalance of all the subareas (p. H105), and would change only the character of the imbalance for the whole Yuma area. The above observations suggest that the estimate of yearly increase of ground-water storage beneath the Yuma Mesa subarea as computed for the budget may be too low by 10,000 acre—feet. Further studies of the storage characteristics of the materials under- lying the Yuma Mesa subarea are needed in order to more reliably estimate the quantities of ground water represented by a given change in volume of saturated material. Outflow from the Yuma Mesa subarea also would be lessened if the average yearly recharge were not as large as is shown in the budget. Some justifica- tion for the possibility that the estimate of average yearly recharge is too high may be had from the fact that the estimated yearly recharge during the 4—year budget period was the highest of record, that it exceeded the average of the 4 preceding years by 62,000 acre-feet, and the average of the 3 following years by 31,000 acre-feet, whereas the average irri- gated acreages for these periods were only 1,800 l acres less and 7,000 acres more, respectively, than the average acreage for the budget period. Average rate of ground-water recharge during the budget period was 11.7 feet per year, whereas for the peri- ods preceding and following the budget period the ‘ rates were 9.4 and 9.8 feet per year, respectively. ‘ Part of the 2-foot lower rate of ground-water re- . charge following the budget period undoubtedly was due to a request by the US. Bureau of Reclamation ‘ to irrigation districts in the Yuma area to conserve i water by diverting less water for irrigation. \ The indicated 2.2 foot per year higher ground- water recharge rate during the budget period than the recharge rate preceding the budget period is not as easily explained. ’ YUMA VALLEY SUBAREA The Yuma Valley subarea includes about 62,000 ‘ acres, of which more than three-fourths is irrigated GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA cropland. Except for a narrow strip adjacent to the Colorado River, which is outside the irrigation dis- trict and is irrigated chiefly with ground-water supplies, the subarea is irrigated with Colorado River water by way of the Yuma Main Canal. The water budget for the subarea follows: Acre-feet Inflow: Surface water: Diversions for irrigation from Yuma Main Canal _____________ 341,000 Diversions for irrigation by pump- ing from river, 1390 acres at 6 feet __________________________ 8,000 Subsurface water: Inflow from Yuma Mesa __________ 97,000 Total inflow _______________________ 446,000 Consumptive use: Irrigated cropland, 45,270 acres of dis- trict land and 2,220 acres of nondis- trict land at 3.6 feet _______________ 171,000 Other land in subarea, 14,810 acres at 2.5 feet _______________________ 37,000 Total __________________________________ 208,000 Inflow less consumptive use ______________________ £8,000 Change in storage _____________________________ Negligible Outflow: Surface water: Cooper Canal Wasteway __________ 2,000 Eleven Mile Wasteway ___________ 16,000 Twenty-One Mile Wasteway ______ 8,000 East Main Canal Wasteway _______ 12,000 Main Drain _____________________ 135,000 Subsurface water 1 ___________________ 45,000 Change in storage plus outflow __________________ 218,000 Imbalance: Amount by which inflow less consumptive use is more than change in storage plus outflow __ 20,000 15,000 acre-feet across southerly international boundary (p. H103); 13,000 acre-feet to limitrophe section, resulting from net excess irriga- tion (1). H93): 20,000 acre-feet to limitrophe section in main aquifers (1). H103): 7,000 acre-feet to Colorado River between Yuma and northerly international boundary (p. H93). The estimates of subsurface outflow to the limi- trophe section and across the southerly international boundary were computed on the following basis. It was assumed that the head in the top of the coarse- gravel zone in the western half of Yuma Valley is the same as the head in the underlying wedge zone. This assumption is based on limited evidence of little or no measurable differences of head with depth that was obtained during the present study. The head near the top of the coarse-gravel zone was computed from water-level measurements in the network of observation wells constructed and mea- sured periodically by the Yuma County Water Users’ Association. Water levels as of December 1962 (fig. 34) are assumed to be good indicators of average heads for the period 1960—63, inclusive. The rate of ground-water movement toward the limitrophe section was computed as the product of the transmissivity, width of section, and hydraulic gradient. The transmissivity was that indicated in figure 25; the other parameters of width and hydrau- lic gradient were determined from the information H103 shown in figure 34. A flow net was used to facilitate computations of the amounts of flow toward various segments of the limitrophe section. The flow toward the limitrophe section as given for the budget contains some duplication to the extent that the flow in the coarse-gravel zone in- cludes some of the excess irrigation water that originated between the Colorado River and the shal- low ground-water divide east of the river. The amount of duplication is thought to be small, prob- ably less than 5,000 acre-feet. The subsurface flow across the southerly interna- tional boundary is the product of the transmissivity, width of Yuma Valley between the river and Yuma Mesa, and the hydraulic gradient as shown in or computed from figure 34. The budget imbalance of 20,000 acre-feet is quite large relative to the budget items, being almost 5 percent of the total inflow, about 10 percent of the estimated consumptive use, and about 10 percent of the estimated outflow. A significant part of the imbalance may be due to an overestimate of the subsurface inflow from Yuma Mesa as was explained in the discussion of the budget for the Yuma Mesa subarea. Other causes of the imbalance are possible overestimates of the surface-water inflow and under- estimates of the consumptive use, or the subsurface outflow. It seems quite unlikely, however, that the latter item is underestimated by much more than 5,000 acre-feet. Because of a lack of knowledge as to which estimates cause the imbalance, no adjust- ments of the estimates shown have been made to reduce the imbalance. SUMMARY OF SUBAREA BUDGETS The water budgets for all the subareas are sum- marized in table 9. The algebraic sum of the imbal- ances of 19,000 acre-feet apparently is due in large part to the imbalance for the Yuma Valley subarea, the probable causes of which are discussed in the section on the budget of the Yuma Mesa subarea (p. H102). The interrelations of the budgets for the various subareas and the principal items of these budgets are shown in figure 33. YUMA AREA A water budget for the entire Yuma area for the period 1960—63, inclusive, was also prepared. With the exception of consumptive use by evaporation from free water surfaces, the consumptive use values are the sum of the respective values given in the budgets of the subareas. Consumptive use by evaporation (total evaporation less precipitation) in- cludes evaporation from the Colorado River and the All-American Canal in addition to evaporation within H104 32°45’ 32°30’ WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA 114°45' I / Pilot Knob ,7 , 7/ z” \/ Q ’4 ? ALL-AMERICAN CANAL /W/4 //4 (\/ UNITEDSféfi-__—————————-—~-—:’/’_/ // @ MEXICO // Morelos \ / Darn / P \ 5 g, \ ,/ // \ /// f/ \\ // % \// — Q) A N Q Q Q ‘7 \\ Q 90 c ] MESA N7 /_/// Q / b // EXPLANATION 6’5 / 90 Water-level contour / Shows altitude of water level. Contour interval Sfé’é’f; datum is mean sea level // fifi \ Bedrock outcrop \ \ \ \ UN /\ {TED STA 0 45 M‘LES \ T K I MIME \ $19 / FIGURE 34.—Average water-level contours for upper part of coarse-gravel zone in 1962 in the Yuma Valley. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H105 TABLE 9.—Summary of ground-water budgets of Yuma subareas, 1960—63 [Quantities in acre-feet per year] Imbalance, Column 2 Change Column 5 column 4 Subarea Inflow Consumptive minus in Outflow plus minus use column 3 storage column 6 column 7 1 2 3 3 5 6 7 8 “Laguna Valley” __________________ 33,000 29,400 3,600 0 3,600 3,600 0 Reservation and Bard _____________ 159,700 61,700 98,000 0 87,200 87,200 10,800 The Island ________________________ 23,200 24,900 —1,700 0 4,000 4,000 —5,700 North Gila Valley _________________ 126,400 36,400 90,000 0 93,500 93,500 —3,500 South Gila Valley _________________ 93,100 47,600 45,500 _2,000 49,000 47,000 —1,500 Yuma Mesa ______________________ 311,000 80,000 231,000 47,000 184,000 231,000 0 Yuma Valley ______________________ 446,000 208,000 238,000 0 218,000 218,000 20,000 Total of subareas1 ___________ 1,192,000 488,000 704,000 45,000 639,000 684,000 20,000 1-Column totals are rounded to nearest 1,000 acre-feet per year. The rounded column totals therefore do not necessarily check by row. the subareas. Change in subsurface (ground water) storage is that indicated in the budgets of the sub areas. The other items of inflow and outflow are 'based on surface-water measurements or are esti- mated as explained in the footnotes pertaining to individual items. The boundaries of the budget area are quite evident except in the limitrophe section of the river where the boundary is the left or easterly edge of the river. Water budget for Yuma area, 1960—6‘3, inclusive [Mean annual quantities in 1,000 acre-feet] Inflow: Measured: Surface1 _________________ 6,719 Unmeasured: Surface 2 ________________________ 2 Subsurface 3 _____________________ 11 Total inflow ________________________ 6,732 Consumptive use: Irrigated cropland ___________________ 363 Natural vegetation and evaporation from other lands __________________ 118 Evaporation from free water surfaces _ 16 Total __________________________________ 497 Inflow less consumptive use ______________________ 6,235 Change in storage (subsurface) * _________________ 45 Outflow: Measured: Surface 5 __________________ 6,115 Unmeasured: Subsurface'3 ____________ 68 Total __________________________________ 6,183 Change in storage plus outflow ___________________ 6&8 Imbalance: Inflow less consumptive use exceeds change in storage plus outflow __________________ 7 1Sum of the average flows of the Colorado River at Imperial Dam, the Gila River near Dome, and the Wellton-Mohawk Main Outlet Drain ‘-' Estimate of average annual runoff from precipitation. sIncludes 10,000 acre-feet underflow below Imperial Dam; and 1,000 acre-feet underflow at the gap where the Gi‘a River enters the area. 4Increase in storage beneath Yuma Mesa subarea of 47,000 acre-feet less decrease in storage in South Gila Valley subarea of 2,000 acre—feet. 5Sum of: ,flows of All-American Canal above Pilot Knob Power Plant and Wasteway less flows through Pilot Knob Power Plant and Wasteway (3,634,000 acre-feet); diversion to Wellton-Mohawk Irrigation District f(399,000 acre-feet); and surface-water deliveries to Mexico (2,082,000 acre- eet). “ Sum of ground-water flow across southerly international boundary of 35,000 acre-feet, and ground-water flow across limitrophe section from Yuma Va‘ley of 33,000 acre-feet. The flows used to compute the average measured inflow are published flOWs except the flow of the Colorado River at Imperial Dam in 1960. The pub- lished flow for 1960 is adjusted downward 100,000 acre-feet to compensate for an overstatement of pub- lished flows at Imperial Dam prior to 1961 (Loeltz and McDonald, 1969, p. 67—69) . 5077243 0 - 74 - 8 The outflow item “surface-water deliveries to Mexico” under footnote 5 consists of the same flows as those used in the administration of the Mexican Water Treaty of 1944, namely “the sum of the C010- rado River at the northerly boundary, the drainage and waste waters which enter the limitrophe section and the southerly boundary from the United States, less the small (about 5,000 acre-feet annually) use within the United States in the limitrophe section.” The drainage and waste waters that are included in the computations are those measured at Cooper, Eleven-Mile, Twenty-One Mile, and East Main Canal Wasteways, and at the boundary pumping plant of the Yuma Main Drain. The small imbalance of 7,000 acre-feet has no sig- nificance because of the uncertainty of the true values of many of the budget items. The budget compares favorably with a longer term (1951—66), slightly different, and less detailed budget which was prepared for Hely (1969). GROUND-WATER DISCHARGE TO THE COLORADO RIVER BETWEEN IMPERIAL DAM AND THE NORTHERLY INTERNATIONAL BOUNDARY The water budgets for the various subareas of the Yuma area for the period 1960—63 indicate that ground water generally was being discharged to the Colorado River. The average yearly quantities of ground water discharged to the Colorado River or to the Gila River from each of the subareas between Imperial Dam and the northerly international boundary are listed in table 10. Of the 72,000 acre-feet of ground-water discharge to the river, about 45,000 acre-feet is indicated to enter the river upstream from Yuma and 27,000 acre-feet downstream. Surface-water records also indicate that ground water is being discharged to the river. However, be- cause of the large volume of surface water relative to the discharge of ground water to the river, which is computed as the difference between surface inflow H106 TABLE 10.—Ground—water discharge to the Colorado or Gila Rivers between Imperial Dam and northerly international boundary, 1960—6‘3 Average yearly quantity Subarea (acre-feet) Laguna Valley _______________________ 3,000 Reservation and Bard: Eastern boundary _________________ 6,000 Southern boundary ________________ 16,000 The Island ___________________________ 4,000 North Gila Valley _____________________ 23,000 South Gila Valley ____________________ 9,000 Yuma Valley: Northern boundary ________________ 7,000 68,000 Plus: Estimated leakage from All- American Canal to river between Res- ervation and Bard subarea boundary and northerly international boundary1 4,000 72,000 1Estimated on basis that only the leakage from about 1 mile of the 2-mile length of canal at rate of 4,300 acre-feet per year per mile reaches the river. and outflow, the errors inherent in surface-water measurements may be the principal influence on the yearly differences of ground-water inflow indicated by surface—water measurements. Sufficient surface- water data are published so that computations can be made as to the indicated discharge of ground water to the Colorado River for the reach Imperial Dam to Yuma for the period 1961—65, inclusive, and for the reach Yuma to northerly international boundary for the period 1950—66. The first computation involves the flow of the Colo- rado River, the Gila River, and 12 or more other inflows. The second involves the flow of the Colo- rado River and four other inflows. As many as four different agencies supply data for computing flows. The yearly difference for the period 1961—65, inclusive, by which the flow of the Colorado River at Yuma exceeded the sum of the flow of the Colorado River at Imperial Dam and all the known surface- water inflows to the river in the reach between Imperial Dam and Yuma, including the flow of the Gila River, are shOWn in table 11. TABLE 11,—F'low of the Colorado River at Imperial Dam and at Yuma and differences between sum of all surface- water inflow items in the reach and flow of Colorado River at Yuma [All quantities in 1,000 acre-feet] Surface-water Gaging station at— outflow exceeds Calendar surface~water year Imperial inflow 1 Dam Yuma 1961 _____________ 437 683 38 1962 _____________ 510 860 32 1963 _____________ 575 924 40 1964 _____________ 440 712 20 1965 _____________ 297 560 11 Average ___ 28 1After adjusting published return flows to Gila River from Wellton- Mohawk Outlet Drain downward 4,000 acre-feet per year to compensate for estimated seepage loss in 8-mi1e unlined channel between measuring point and river that does not reach Colorado River. WATER RESOURCES 0F LOWER COLORADO RIVER—SALTON SEA AREA For the period of record the yearly ground-water inflow less evaporation of river water (4,000 acre- feet) and water diverted for irrigation (6,000 acre- feet) ranges between 11,000 and 40,000 acre-.feet and averages 28,000 acre-feet. Adding 10,000 acre- feet because of annual evaporation of river water and diversions for irrigation indicates an average annual inflow or discharge of ground water to the river of 38,000 acre-feet. This discharge of ground water to the Colorado River in the reach between Imperial Dam and Yuma computed on the basis of surface-water inflows and outflows thus averages only about 7,000 acre-feet less than the discharge of 45,000 acre-feet indicated by the water budgets of the various subareas (p. H105). Because of the un- certainty of the true values of many of the items in all the budgets the difference of 7,000 acre-feet be- tween the two estimates is insignificant. The difference by which the flow at the northerly international boundary exceeds the sum of the flow at Yuma and the other return flows is a measure of the discharge of ground water to the river in the reach, if to the difference is added about 2,000 acre- feet for average annual evaporation from the river and about 2,000 acre-feet becauSe of pumpage from the river for irrigation. Table 12 shows a wide range in these annual differences—from an indi- cated loss of 85,000 acre-feet in 1952 to a gain of 74,000 acre-feet in 1954. It is quite apparent that the yearly differences are dominated to a large ex- TABLE 12.—Flow of the Colorado River at Yuma and at northerly international boundary, and difl'erenees between sum of all surface-water—inflow items in the reach and flow of Colorado River at northerly international boundary [All quantities in 1,000 acre-feet] Gaging station at— Surface- Surface- water water outflow outflow Calendar exceeds is less than year Yuma Northerly surface- surface- international water water boundary inflow inflow 1950 _________ 3,464 4,456 43 _______ 1951 _________ 2,764 3,639 _______ 48 1952 _________ 9,192 10,146 _______ 85 1953 _________ 4,095 5,224 44 _______ 1954 _________ 3,196 4,346 74 _______ 1955 _________ 2,118 3,058 17 _______ 1956 _________ 881 1,638 30 _______ 1957 _________ 1,167 2,853 _______ 2 1958 _________ 2,951 5,908 _______ 68 1959 _________ 933 3,051 25 _______ 1960 _________ 702 2,338 66 _______ 1961 _________ 683 1,672 25 _______ 1962 _________ 860 1,811 28 _______ 1963 _________ 924 1,834 42 _______ 1964 _________ 712 1,502 51 _______ 1965 _________ 560 1,524 31 _______ 1966 _________ 428 1,420 34 _______ Total ________________________ 510 203 NOTEr—Surt‘ace-water outflow exceeds surface-water inflow: For period of record ____ 307 Yearly average __________ 18 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA tent by errors of measurement. However, they also are influenced somewhat by the amount of flow in the preceding year. Generally, the ground-water discharge for a given year should be less than the ground-water discharge for the preceding year when the stream discharge for the given year is substan- tially larger than the stream discharge for the pre- ceding year. A large annual increase of stream dis- charge for a given year ordinarily implies an in- crease of river stage. An increase of river stage in an area of ground-water discharge to the river de- creases the gradient from the ground-water reser- voir to the river and consequently the ground-water discharge to the river. Similar reasoning shows that ground-water discharge to the river should increase in a year in which the stream discharge, and presum- ably the stream stage, is lower than in the preceding year. The average annual amount by which the discharge at the northerly international boundary exceeds the sum of the measured inflows for the years listed in table 12 is 18,000 acre-feet. The average annual discharge of ground water to the river is an additional 4,000 acre-feet because of evaporation and pumpage, or 22,000 acre-feet for the 17-year period 1950—66. For the period of the water budgets of the various subareas 1960—63 the discharge of ground water to the river is indicated to be about 44,000 acre-feet. The true value probably is somewhere between these two values unless consistent errors of measure- ment are involved. Even in years of relatively low flow, the flow at the northerly international bound- ary is between 1.5 million and 3 million acre-feet, so a consistent error of only 1 percent would cause the computed discharge of ground Water to the river to be in error 15,000—30,000 acre-feet. The indicated mean annual difference even for a 10-year or longer period therefore, may be reliable only to plus or minus 10,000—20,000 acre-feet. As a basis for comparison, the average annual dis- charge to the Colorado River in the reach Yuma to the northerly international boundary as indicated by the water budgets of the various subareas was about 27,000 acre-feet for the period 1960—63 (p. H105). This estimate is based on the ground-water parame- ters of transmissivity, hydraulic gradient, and width of section. It is 17,000 acre-feet less than the estimate for the same period computed from surface- water measurements and 5,000 acre-feet more than the estimate computed from surface-water measure- ments for the period 1950—66. In general, the estimates of ground-water dis- charge to the Colorado River computed on the basis of surface-water measurements and the estimates H107 computed on the basis of ground-water parameters agree as well as can be expected in View of the un- certainties of the values of the items used to obtain the estimates. ANALOG-MODEL STUDIES Because of the complex nature of the hydrologic system in the Yuma area and the continuing and varied development of the system, the use of mathe- matical formulas for directly computing the re- sponse of the system to this development becomes impractical. The electrical-analog method, however, is well adapted for solving the complex mathematics of the partial differential equations involved in de- scribing the hydrologic system. The construction of an electrical analog model of the Yuma area that would simulate responses of the actual system to stresses imposed on it therefore was one of the obj ectives of the present investigation. An initial attempt in 1964 to simulate observed changes of water level beneath Yuma Mesa by means of a one-layer model was not successful enough to warrant further work on the model. The model was useful, however, in demonstrating that some of the parameters of transmissivity, storage, and boundary effects in the southern and southeastern part of Yuma Mesa that were being simulated by the model were incorrect. In 1966, the barrier effect of the Algodones fault to the southward movement of ground water beneath Yuma Mesa was first recog- nized as the result of drilling exploratory wells on both sides of the fault. Discovery of this highly ef- fective barrier appeared to provide the boundary parameter that would permit reasonable agreement between observed changes in water level and those indicated by an electrical analog model using values similar to those assumed for the initial study. The United States Section of the International Boundary and Water Commission, and the US. Bu- reau of Reclamation were very much interested in obtaining a model that might be used in predicting the effect of future water development on the move— ment of ground water across international bounda- ries. ‘As a consequence, both agencies cooperated with the Geological Survey in building a more repre- sentative electrical analog model of the Yuma area and in providing additional hydrologic data, prin- cipally from exploratory drilling in the southeastern part of the “Upper Mesa” and “Fortuna Plain.” Also, these two agencies provided funds for addi- tional geophysical exploration. MODEL CHARACTERISTICS The analog model includes the Yuma area and con- tiguous parts of Sonora and Baja California, Mexi- H108 co; a total area of some 2,000 square miles. The actual hydrologic system is simulated as a three- dimensional flow field idealized as two two-dimen- sional transmissive layers and two layers of solely vertical flow. The upper transmissive layer generally corres- ponds to the coarse-gravel zone, but where that zone is missing, such as beneath the “Upper Mesa” and “Fortuna Plain,” it includes the upper part of the older alluvium, undivided. Beneath southwestern Yuma Mesa and southern Yuma Valley the upper transmissive layer includes all the alluvial deposits in which most wells have been completed or are likely to be completed. Thus, in those areas the upper transmissive layer includes the uppermost part of the wedge zone as well as the coarse-gravel zone. Overlying the materials modeled as the upper transmissive layer are much finer grained materials corresponding to the upper, fine-grained zone. In Yuma and South Gila Valleys these finer materials are modeled as a confining layer which allows ver- tical flow to or from the upper transmissive layer according to the hydraulic gradient between the con- stant-head surface assumed in these valleys and the head in the upper transmissive layer and the vertical hydraulic conductivity of the confining material. Elsewhere in the modeled area the upper confining layer is lumped with the upper transmissive layer. The lower transmissive layer is hydraulically con— nected to the upper transmissive layer and is mod- eled as a single transmissive layer. Beneath the river valleys and Yuma Mesa the lower transmissiVe layer includes most of the wedge zone, and beneath the “Upper Mesa” and “Fortuna Plain” it includes the lower, major, part of the older alluvium, undi- vided. The average head loss resulting from vertical flow between the upper and lower transmissive lay- ers at any site is simulated by a parameter repre- senting the average vertical hydraulic conductivity and average flow distances between the two layers. Wherever practicable, the model boundaries (part- ly shown in fig. 35) approximate natural hydrologic boundaries. The eastern boundary of the model coincides with the Gila Mountains and their south- ern continuation—the Butler Mountains; the north- ern boundary generally follows the Cargo Muchacho Mountains and a marked decrease in transmissivity in the alluvium about 9 miles north of the northerly international boundary; the western boundary is modeled as being about 30 miles west of Pilot Knob along a line that approximates the increasing clay content and consequent decreasing permeability of the deposits in Imperial and Mexicali Valleys; the WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA southern boundary is arbitrarily modeled as being about 15 miles south of San Luis, Mexico, and is a constant-head boundary so as to yield or receive water in response to changes in ground-water gradients. Also modelel as constant-head boundaries are the All-American Canal and the Colorado River. Their hydraulic connection with the upper trans- missive layer is a parameter representing the hydraulic radius, the permeability of the deposits underlying the river or canal, and the distance through which the water moves in the interchange process. Values for this parameter were selected by trial and error until reasonable agreement between interflow rates computed from model response and best estimates of historical rates were obtained. For computational purposes, both the All-American Canal and the river are divided into two segments, one end of each terminating near Pilot Knob. In the lower transmissive layer the Algodones fault is modeled as a partial barrier to the move- ment of water throughout its length, whereas in the upper transmissive layer, the fault’s barrier effect was modeled only southeast of the apex of the ground-water mound. This difference in the two layers was modeled because barrier effects of the fault were not recognizable during the present in- vestigation in wells bottoming in the coarse-gravel zone (principal part of upper transmissive layer) northwest of the apex of the ground-water mound. TRANSMISSIVITY VALUES Ranges in transmissivity for the upper and lower transmissive layers as finally modeled are shown in figures 35 and 36. The transmissivity values were adapted by the analog-model-unit laboratory from more detailed maps submitted to the laboratory from the project office, which showed respective trans— missivity values for the upper and the lower trans- missive layers. These estimates were based on the results of pumping tests, specific capacity of wells, drillers’ logs, lithologic logs, borehole geophysical logs, and probable thickness and permeability of sediments as interpreted from all the geologic, geo- physical, and hydrologic studies in the area. Verifica- tion studies of the model 'showed that increasing the original estimates 25 percent resulted in an im- proved correlation between model response and observed changes of water level. This increase, therefore, was incorporated into the model and is included in the values shown in figures 35 and 36, and in figure 25, which shows the sum of the trans- missivity values that were the basis for transmissivi- ty values simulated by the analog model. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA STORAGE-COEFFICIENT VALUES The storage coeffcients for the upper transmissive layer that were actually modeled are shown in figure 37. They were arrived at in the following manner. A first estimate of the storage coefficient for the nonirrigated areas of Yuma Mesa was 35 percent, based on soil-moisture studies with the neutron moisture probe (p. H219). Geologic studies indicated that the foregoing value was too large for the “Up- per Mesa” and “Fortuna Plain,” so a value of 25 percent was used for those areas. Subsequent verifi- cation studies, however, indicated that the smaller values shown in figure 37 resulted in model re- sponses that correlated with observed changes much better than did the original estimates. A storage coefficient of 20 percent was originally assumed for all the flood-plain land in Mexico and for land in the United States north and west of Pilot Knob. Verification studies indicated that a value of 18 percent as shown in figure 37 was as valid as the original 20 percent estimate. Construction of the model therefore was not modified to incorporate a simulation of the somewhat higher original value. The storage coefficient for the upper transmissive layer beneath Yuma Valley is 5X10“, an artesian coefficient. In this area, the changes in water level are assumed to be small because of the extensive network of drains in most of the area. The specific value to be assigned to the storage coefficient is not critical because storage in the upper transmissive layer beneath the flood plain in the United States has little effect on the response of the system. A storage coefficient of 0.31 was modeled for the flood-plain area north and northwest of Yuma Mesa. In addition, a constant head was modeled for North and South Gila Valley subareas. Modification of the model in the flood plain north of Yuma Mesa proba— bly would better simulate actual conditions. How- ever, the modifications were not essential to the prin- cipal objectives of the study and therefore they were not fully explored. One modification, which involved using a constant head and artesian storage coefficient for the entire flood plain north and northwest of Yuma Mesa, gave poorer correlations between model response and historical changes than did the present model with the supposedly less realistic values. A value of 5X 10‘4 was modeled for the storage co- efl‘icient throughout the lower transmissive layer. Hydrologic data were not available for making an estimate of this parameter, so a reasonable value that would result in the shortest travel time for pressure waves was selected. Under this design, the movement of ground water across international H109 boundaries as indicated by the model response is at a maximum rate. STRESSES APPLIED TO THE MODELED SYSTEM Recharge to the system was computed on the basis of imports to Yuma Mesa minus consumptive use, and was apportioned areally according to the acre- age irrigated during specific periods (table 13). Dis- TABLE 13.—Design stresses for analog model of Yuma area [Quantities in 1,000 acre-feet] Yearly Period rate Period Accumulated Recharge 1925—42 _______________ 95 95 1943—47 ________ 51 256 351 1948-52 ________ 102 512 863 1953~57 ________ 147 785 1,648 1958—62 ________ 208 1,039 2,687 1963—64 ________ 228 456 3,143 1965—66 ________ 188 376 3,519 Drainage-well pumpage 1948—52 ________ 19 95 95 1953—57 ________ 36 182 277 1958—62 ________ 80 400 677 1963-64 ________ 114 228 905 1965—66 ________ 126 251 1,156 charge of ground water by pumps in the United States from the coarse-gravel zone began in 1948 and was apportioned according to the location of the principal drainage wells along the western and northern margins of Yuma Mesa and the pumpage for specific periods (table 1). Pumpage in Mexicali Valley was determined on the basis of the stress that had to be imposed on the system to cause historical declines in head in the coarse-gravel zone underlying the Mexicali Valley well field. (See last column of table 14.) TABLE 14.—Eflective yearend declines of water level, in feet, in Mexicali Valley at a site 12 miles west of the middle of the limitrophe section of the Colorado River Average addi- Period Average decline tionaJ decline ending during irriga- due to draw- Decline since Effective year- December tion season down at wells December 1952 end decline 1952 ____ 0 0 0 0 1957 ___- 1 3 —2 2 1962 -___. 2 6 7 15 1964 -.__- 3 7 11 21 1966 ____ 3 7 15 25 The average decline of water levels since Decem- ber 1952 and the seasonal decline were based on water-level maps obtained by the United States Section of the International Boundary and Water Commission from the Mexican Section of the Com- mission. The average additional decline due to drawdown at wells was estimated to be about one- fourth of the average drawdown at the well sites. Points of stress were distributed uniformly through- out the Mexicali Valley well field. WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA H110 .5332 56c 05 E 335 M255 an» 5 E835? ~22: wimflfimnafi noun: 05 «o haymmmmflmnaufilém 552% _ _ m a E on A/ £33339 ”€336 ESQQQ / :sam \ _ _ O _ _ _ V uzwfiaawomo ~3>==< mug: E S m c K II‘IIII / I I v #02on 3312? we «95‘ / M II I I K I‘ll“ ..D j x “I . _ Eng q 0 £3: 9% 213552 . r 0 we . [lam _5.wn § O < i 7 med“ .m Q? I \ 0 3978A §€ swam 253:3 cmm mu“ 4 . / \ .3 SwimmwSm§at §§3 333% 3:3» v0. mom / I I v.% \ .eEV \c “ta “as .3936 “0383 Q. /$RVQ / V 33:5 \ngmmustmfisfi SSwfimE win ONNQV/ , .O .m Iswfifi \5 3333339 3.93 ufiwudxfii mom ... I [£54 =«m\l I\ 0 dock s»& 3% LmR wfigfiua fiSdeQS wow .2 /m~.l SS $39§3Em§§3 aw Lwe§§z _ mm (wk. .. 3% W /\ on: @3555 zfifimmmfinge I ‘om 0./ mom va \ S . My» \\ 04 x I E zo_F o 04 / «)4 Nmm l.... «BMW 7 o o \ l/|\ \ 3w «WW .. V4 )5 \ I\ /I \ b 9; \A/ i > / W mm mom m3 \mom 49 «V 7 Juv 14o \1 I/ W mom \ mo / .. 7V A Sm \ /.\ N \ mmm \/ I/ Nmm |\ ./ / k \ / \ \o v / \I 8”me .l .. . w l I \II I I I\../ 4/ L \ r\ . (I w 25% Ema . ‘II I I \l l ImflaZBm QHPHZD /.// 9 advection from various sources. Temperatures representative of the coarse-gravel zone or, where that zone is missing, of materials at equivalent depths below the water table (about 100—150 ft) were measured in nearly 500 wells (appendix A). In roughly one-third of these wells—— chiefly irrigation and drainage wells—the tempera- tures were measured at the discharge pipe with a mercury thermometer while the wells were pumping. In the rest of the wells the temperatures were mea- sured with a thermistor or a maximum thermometer inside the casings at depths corresponding to the middle of the coarse-gravel zone. In some places, particularly on the “Upper Mesa” and “Fortuna Plain,” temperatures at depths about 100—150 feet below the water table were estimated by extrapola- tion from water-table temperatures. Geothermal gradients observed in the nearest wells having such data were used. The configuration of the tempera- ture lines is uncertain beneath most of the “Upper Mesa” because of the paucity of reliable data (fig. 47). The coolest water in the coarse-gravel zone occurs beneath the river valleys. At most places in the valleys the temperature ranges from about 21°C to 23°C; a few areas underlain by somewhat warmer water are considered to be warm anomalies, as ex- plained farther on. The usual temperatures are slightly higher than the mean annual air tempera— H122 Water table 100 — 200 * Temperature measured with a WIDCO logger using a thermistor sensor 300 - 400 1 500 , DEPTH BELOW LAND SURFACE, IN FEET 600 — 700 1 800 I I I I I I 1 I I I I L 20 25 30 35 TEMPERATURE OF WATER, IN DEGREES CELSIUS FIGURE 46.—Temperature profile in well (C—8723)33cdd (LCRP 13) for March 12, 1963. ture at the Yuma Valley weather station in northern Yuma Valley, which was 20.7°C for period 1906—53 (Sellers, 1960). With certain exceptions, discussed later, the water in the coarse-gravel zone beneath Yuma Mesa is 2°-3°C warmer than that beneath the adjacent valleys. The higher temperatures beneath the mesa probably result from the greater average depth of the water table and the somewhat higher mean annual air temperature; the mean annual air tem- WATER RESOURCES OF'LOWER COLORADO RIVER—SALTON SEA AREA perature at Yuma (northwestern Yuma Mesa) for the period 1893—1957 was 224°C, as compared with 20.7°C for the Yuma Valley station for 1906—53 (Sellers, 1960). Beneath parts of Yuma Mesa, deep infiltration of irrigation water probably has cooled the water in the coarse-gravel zone to a temperature below what it was naturally. The close correspond- ence of the boundaries of the cooler water and the boundaries of the irrigated area at many places sup- ports this inference. (Compare figs. 2 and 47). In general, the warmest water in the Yuma area occurs beneath “Upper Mesa” and contiguous parts of “Fortuna Plain” and “Gila Mesa.” The coarseh gravel zone is absent in most of those areas, but at equivalent depths below the water table the tem- peratures (which are largely extrapolated from temperatures at the water table and therefore some- what uncertain) range from about 25°C along the northwest edge of “Upper Mesa” to more than 36°C at several places (fig. 47) . In large part, these higher temperatures are a consequence of the fact that the water table is deeper beneath “Upper Mesa,” “For- tuna Plain,” and “Gila Mesa” than it is elsewhere in the Yuma area. The geothermal gradient in un- saturated material is generally greater than that in saturated material, so that depth to water has a pronounced effect on temperatures below the water table; the average geothermal gradient for dry ma- terials beneath “Upper Mesa” is about 2.8°C per 100 feet. After taking into account the effects of the vari- able depths of the water table and of recharge from irrigation, as described above, a number of warm anomalies can be delineated throughout the area (fig. 47 ). Most of these anomalies appear to be re- lated to faults or fault zones such as the northwest- ward bulge of warm water beneath central Yuma Mesa and east-central Yuma Valley which is chiefly on the northeast side of the buried trace of the Algodones fault. Some anomalies may reflect hot zones in the pre—Tertiary crystalline rocks that are not related to faulting, but these possible sources of heat cannot be evaluated with the available data. Other anomalies related to faults or suspected faults are those west of the northern Gila Mountains, in north-central “Bard Valley,” along the west edge of Yuma Mesa in Yuma, on Yuma Mesa about a mile west of the west edge of the “Upper Mesa,” and on southern Yuma Mesa 1-3 miles north of the south- erly international boundary. The warm water in these areas probably has resulted from upward movement from the wedge zone into the coarse- gravel zone induced by the partial damming effect of the faults. Where the anomaly is related to the GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H123 114°45’ 30' Y‘ ‘1 114°15’ / 2/:/ qfl '26 Q:/ ’x//// d Q ///,,,, // 167 32°45' - Silo; v no I ES ' - . EEED—ST—g‘ " ’ Algodones Morelos‘Qa 30’ E X P LA N AT | O N _ _ 28— .— Line of equal temperature of water, in degrees Celsius Dashed where approximately located Fault Alluvial escarpment Dotted where concealed Warm anomaly % 20 25 30 35 °c ‘ I | | l llllllllll ll] l IJI III I]! III ll‘l I ll Illl | l l‘ Mountains and hills 7o 75 so 85 90 95 °F 7 A 7. o 5 10 MILES 7:24 I I | I l I I Area of shallow bedrock Coarse-gravel zone absent 32°15’ FIGURE 47.—Temperature of ground water in coarse-gravel zone or at equivalent depth below the water table. 1965—68. Algodones fault, the temperature data indicate that l of the buried bedrock ridge may also account for the barrier effect of the fault extends farther north- ' the northwestern part of the anomaly. west than can be demonstrated unequivocally from 5 Not all the warm anomalies are caused entirely or water-level and geologic data. However, the effect 1 even partly by faults acting as ground-water bar- H124 riers. Alluvium that is less transmissive than that in surrounding areas may account for the two anomalies in western “Upper Mesa,” for the broad anomaly at the northwest corner of Yuma Mesa in Yuma, and possibly for the southwest-trending band of slightly warmer water in south-central Yuma Valley (fig. 47). Another major anomaly is the elongate, some- what irregular band of warm water that extends along the west margin of northern Yuma Mesa and the east margin of the adjacent Yuma Valley. Two thermal maxima occur within the band: a northern one in the southwest part of Yuma, where the maxi- mum temperature exceeds 30°C and a southern one just south of the first major westward bend in the escarpment along the west edge of Yuma Mesa south of Yuma, where the maximum temperature is a little less than 29°C (fig. 47). The higher temperatures in this band result from the upward movement of ground water from the wedge zone through the coarse-gravel zone and into the upper, fine-grained zone, from which it is dis- charged by evapotranspiration or by surface drains. This movement has taken place since irrigation began on Yuma Mesa and the associated ground- water mound began to form. However, the northern thermal maximum, in Yuma, probably results also from natural upward movement caused by a con- cealed fault barrier, as mentioned earlier. Pumping of drainage wells along the east margin of Yuma Valley has accelerated the upward move- ment by providing additional discharge from the coarse-gravel zone with a consequent lowering of head in that zone, but the pumping has also induced downward leakage into the upper part of the coarse- gravel zone. The downward movement of relatively cool irrigation water from the upper, fine-grained zone has lowered the temperature in the coarse- gravel zone adjacent to the drainage wells, as illus- trated by the record for well (C—9—23)20bdc (fig. 45) and by less-abundant data for some of the other wells. CHEMICAL QUALITY OF GROUND WATER Chemical analyses of ground water in the Yuma area indicate marked differences from place to place in the percentage and concentration of the six ionic constituents that make up the bulk of the dissolved solids. (See appendix C; pl. 11). The chemical char- acter of the ground water depends on (1) the chemi- cal character of the source of recharge and (2) the chemical changes that have occurred since the water entered the ground. Separation of the effects of these two factors is ordinarily difficult. However, WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA the interpretation of the second factor—the chemi- call changes—is facilitated by the fact that the relatively shallow ground water beneath the irri- gated areas is derived mainly from recent recharge from the Colorado River by way of diversions for irrigation. The following discussion considers the processes of chemical change that produce the types of ground water observed beneath the irrigated areas, starting with the Colorado River as the recent source of ground-water recharge. CHEMICAL CHANGES IN GROUND WATER DERIVED FROM THE RECENT COLORADO RIVER An appraisal of ground water beneath the irri- gated areas as chemically altered recent Colorado River water requires consideration of the chemical processes capable of altering the river water to observed types of ground water, and also the estab- lishment of criteria for recognition of the altered river water. In the approach used, recent Colorado River water is assumed to have been evaporated and subjected to specified chemical changes while it evap- orated. Hypothetical chemical analyses computed from a 25-year weighted-average analysis of Colo- rado River water, and from two single-year weighted averages, then serve as examples that suggest how ground water represented by actual analyses might have been derived (table 15). The assumption that the recent Colorado River (indicated by the chemical-quality records at Im- perial Dam for 1941—65) is the source of ground- water recharge is most nearly valid for the rela- tively shallow ground water in the upper, fine- grained zone and the coarse-gravel zone beneath the irrigated areas of the valleys and Yuma Mesa. Deeper, older ground water beneath those areas and ground water outside the irrigated areas were de- rived from the Colorado River before regulation by upstream reservoirs and from the Gila River when it was still a live stream near Yuma. These sources of recharge may have differed substantially in chemical character from recent Colorado River water. The same chemical processes as those occur- ring in the younger ground water probably were operative in the older ground water, although the actual changes would have been different from those described below. The chemical-change processes probably operative in ground water in the Yuma area include: (1) Con- centration by evapotranspiration, (2) softening, (3) carbonate precipitation, (4) sulfate reduction, (5) hardening, (6) re-solution of precipitated salts, (7) oxidation of dissolved organic substances, and (8) mixing of waters of different chemical composition. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H125 TABLE 15.—Hypothetical analyses of ground water resulting fr om specified chemical changes in Colorado River water Relative Concen- Cal- Magne- Sodium Bicar- Sulfate Chloride Sum Hardness Specific volume tration cium sium plus bonate (804) (CI) ——-—-— con- No. Description factor (Ca) (Mg) potas- (H003) N on- ductance Percent sium Total carbon- (micro- sodium (Na+K) ate mhos at 25°C) Milligrams per liter Unchanged Colorado River water 1 ________________ J1941—65 1,000 1 94 28 110 165 309 93 730 350 214 1,120 40.6 2 1,000 1 84 27 90 163 265 77 625 320 187 985 38.0 3 1,000 1 106 34 142 173 375 128 872 404 262 1,340 43.4 Concentrated by evaporation, no other change 4 667 1.5 141 42 165 248 464 140 1,090 525 321 1,680 40.6 5 500 2.0 188 56 220 330 618 186 1,460 700 428 2,240 40.6 6 333 3.0 282 84 330 495 927 279 2,190 1,050 642 3,360 40.6 7 250 4.0 376 112 440 660 1,236 372 2,920 1,400 856 4,480 40.6 8 250 4.0 336 108 360 652 1,060 308 2,500 1,280 748 3,940 38.0 9 250 4.0 424 136 568 692 1,500 512 3,490 1,616 1,048 5.360 43.4 Concentration by evaporation with 50 percent softening 667 1.5 117 35 205 248 464 140 1,080 437 234 1,680 50.5 500 2.0 141 42 300 330 618 186 1,450 524 254 2,240 55.4 333 3.0 188 56 491 495 927 279 2,190 699 292 3,360 60.4 250 4.0 234 70 681 660 1.236 372 2,920 873 332 4,480 62.9 250 4.0 210 68 583 652 1,060 308 2,560 803 269 3,940 61.2 250 4.0 264 85 846 692 1,500 512 3,550 1,010 442 5,430 64.6 Concentration by evaporation, precipitation of insoluble carbonates at 380 mg/l HCOa 333 3 255 76 330 380 927 279 2,060 951 640 3,180 43.0 250 4 313 93 440 380 1,236 372 2,640 1,160 853 4,040 45.1 200 5 370 110 550 380 1,545 465 3,230 1,380 1,070 4,900 46.5 200 5 328 106 450 380 1,325 385 2,780 1,250 942 4,250 43.8 200 5 424 136 710 380 1,875 640 3,980 1,620 1,310 6,020 48_8 Concentration by evaporation, bicarbonate ceiling 380 mg/l, 25 percent sulfate reduction 667 1.5 141 42 165 339 393 140 1,050 525 248 1,680 40.6 500 2.0 155 46 220 380 464 186 1,260 576 266 2,010 45.3 333 3.0 160 48 330 380 585 279 1,590 596 284 2,500 54.7 250 4.0 162 48 440 380 696 372 1,910 603 292 2,970 61.3 200 5.0 161 48 550 380 795 465 2,210 598 286 3,420 66.7 125 8_0 142 42 880 380 1.040 744 3.040 528 216 4,650 78.4 100 10.0 126 37 1.100 380 1,190 930 3,570 468 157 5,450 83.6 100 10.0 134 43 900 380 1.030 770 3,070 510 199 4,700 79.3 100 10.0 135 43 1,420 380 1,430 1,280 4,500 515 204 6,860 85.7 As above but 33-1/3 percent sulfate reduction 667 1.5 141 42 165 371 367 140 1,040 524 220 1,680 40.6 500 2.0 141 42 220 380 412 186 1,190 524 212 1,910 47.7 333 3.0 133 40 330 380 489 279 1,460 496 184 2,310 59.2 250 4.0 121 36 440 380 548 372 1,710 449 138 2,680 68.1 200 5.0 106 32 550 380 600 465 1,940 395 84 3,030 75.2 125 8.0 57 1‘7 880 380 736 744 2,620 212 0 4,040 90.0 100 10.0 17 5 1,100 380 800 930 3,040 62 0 4,680 97.5 100 10.0 48 16 900 380 720 770 2,640 188 0 4,090 91.2 100 10.0 18 6 1,420 380 1,000 1,280 3,910 68 0 6,010 97.8 As above but 40 percent sulfate reduction --1941—65 667 1.5 137 41 165 380 346 140 1,020 510 198 1,660 41.3 -1941—65 500 2.0 129 39 220 380 371 186 1,140 482 170 1,830 498 __1941—65 333 3.0 113 34 330 380 416 279 1,360 420 108 2,170 63.1 __1941—65 250 4.0 92 27 440 380 445 372 1,570 342 30 2,470 73.9 __1941—65 200 5.0 70 21 550 380 470 465 1,770 270 0 2,770 82.1 __1941—65 125 8.0 0 0 880 380 533 744 2,350 5 0 3,650 100.0 -_1941—65 100 10.0 0 0 1,100 609 560 930 2,900 0 0 4,560 100.0 __1950 200 5.0 78 25 450 380 405 385 1,530 296 0 2,430 76.8 __1950 125 8.0 24 8 720 380 458 616 2,020 90 0 3,160 94.5 __1950 100 10.0 0 0 900 442 490 770 2,380 0 0 3,730 100.0 __1956 200 5.0 71 23 710 380 580 640 2,210 273 0 3,460 85.0 __1956 125 8.0 0 0 1,136 431 648 1,024 3,020 0 0 4.710 100.0 _________________ 1956 100 10.0 0 0 1,420 648 690 1,280 3,740 0 0 5,880 100.0 Concentration by evaporation, bicarbonate ceiling 380 lug/l, 40 percent sulfate reduction, hardening equivalent to sulfate equivalents increase resulting from evaporation 52 _________________ 1941—65 667 1.5 147 44 147 380 346 140 1.010 548 237 1,660 36.9 53 500 2.0 147 44 190 380 371 186 1,130 546 234 1,830 431 54 333 3.0 142 42 279 380 416 279 1,350 530 219 2,170 53.4 55 250 4.0 130 39 375 380 445 372 1,550 484 172 2,470 62.8 56 200 5.0 115 34 473 380 470 465 1,750 428 116 2,770 70.6 57 125 8.0 63 19 773 380 533 744 2,320 233 0 3,650 87.8 58 100 10_0 20 6 980 380 560 930 2,690 74 0 4,200 96.7 59 200 5.0 116 37 383 380 405 385 1,520 442 130 2,430 65.3 60 125 8.0 76 25 628 380 458 616 1,990 292 0 3,160 82.4 61 100 10.0 61 20 769 380 490 ‘770 2,300 234 0 3,630 87.7 62 200 5.0 127 41 612 380 580 640 2,190 486 174 3,460 73.3 63 125 8.0 63 20 1,006 380 648 1,024 2,950 242 0 4,630 90.0 64 100 10.0 19 6 1,270 380 690 1,280 3,460 73 0 5,400 97.4 H126 WATER RESOURCES 0F LOWER COLORADO RIVER—SALTON SEA AREA TABLE 15,—Hypothetical analyses of ground water resulting from specified chemical changes in Colorado River water—Continued Relative Concen- Cal- Magne- Sodium Bicar- Sulfate Chloride Sum Hardness Specific volume tration cium sium plus bonate (SOs) ( Cl) can- No. Dscription factor ( Ca) (Mg) potas- (11003) N on- ductance Percent slum Total carbon- (micro- sodium (NI-PK) ate mhos at 25°C) Milligrams per liter Concentration by vaponcion. bicarbonate ceiling 380 lug/l, 40 percent sulfate reduction, hardening until sodium equiv-lent concentration is reduced to chloride equivalent concentration 65 ___1941—65 667 1.5 180 54 91 380 346 140 1,000 672 860 1,660 22.8 500 2.0 187 56 121 380 371 186 1.110 698 386 1,830 27.3 333 3.0 200 60 181 380 416 279 1,330 744 432 2,170 34.6 250 4.0 208 62 241 380 445 372 1,520 7'74 463 2,470 40.4 200 5.0 215 64 302 380 470 465 1,710 800 489 2,770 45.0 125 8.0 233 70 483 380 533 744 2,250 869 558 3,650 54.8 100 10.0 240 72 603 380 560 930 2,600 894 582 4,200 59.5 200 5.0 192 62 250 380 405 385 1.480 723 421 2.430 42.6 125 8.0 206 66 400 380 458 616 1,940 788 476 3,160 52,4 100 10.0 215 69 499 380 490 770 2,230 821 510 3,630 56.9 200 5.0 239 77 415 380 580 640 2,140 914 603 3,460 49.7 125 8.0 258 83 664 380 648 1,024 2,870 986 674 4,630 59.4 100 10_0 269 87 830 380 690 1,280 3,350 1,030 718 5,400 63.9 1 Weighted average. The last three processes are not readily demon- strated from analytical evidence and are not readily demonstrated from analytical evidence and are not considered further here. Several combinations of the first five processes, carried out to varying degrees, are listed in table 15, beginning with the weighted-average chemical analysis of the Colorado River at Imperial Dam for the period 1941—65. In addition, the effects of mod- erate annual variations in the chemical character of the river water are shown by listing the calcu- lated analyses of substantially evaporated ground water derived from the weighted-average river water for 1950, when the concentration of dissolved solids was low, and the analyses for 1956, when the dissolved-solids concentration of the river was high. Several series of hypothetical chemical analyses are given as illustrations of specified chemical proc- esses, assuming that each process has operated ‘con- tinuously, and that the ground water it represents was sampled at specified evaporative volume reduc- tions. Generally each series is ended when the speci- fied chemical process results in hypothetical analyses with one or more ionic concentrations greater or less than those commonly observed in the many actual analyses of ground water from the irrigated areas. A few series are carried beyond these end points to illustrate particular hypothetical analyses. CONCENTRATION BY EVAPOTRANSPIRATION Evaporation is loss of water to the atmosphere across an air-water interface. Transpiration is loss of water from plants by permeation through a cell membrane. In both processes (commonly lumped to- gether as evapotranspiration) a more concentrated residual solution remains. Because of the prevailing high temperatures and low humidity and the pres- ence of phreatophytes in the river valleys of the Yuma area, probably very little water infiltrates from the Colorado River without considerable con- centration by evapotranspiration. Such concentra- tion is indicated wherever all constituents in a well water are nearly the same multiple of river-water concentrations. If concentration by evapotranspira— tion is the only chemical change occurring, dissolved ionic concentrations increase by the same multiple, but the percent sodium, which depends on the ratio of sodium concentration to total cation concentra- tion, both expressed in equivalents, does not increase. Thus, approximately equally increased ionic concen- trations in ground water compared to concentra— tions of Colorado River water, and unchanged or nearly unchanged sodium percentage, are indicative of evapotranspirative change. Bicarbonate concentrations greater than 500 mg/ 1 are extremely rare in Yuma area ground water and few analyses ShOW bicarbonate concentrations as great as 450 mg/l. These limits probably indicate the level at which calcium carbonate precipitation begins. Recent Colorado River water has contained from 150 to about 175 mg/l bicarbonate, which sug- gests that evapotranspiration by itself seldom ac- counts for more than a threefold increase in ground- water concentrations as compared to river-water concentrations. In order to allow for all possible strictly evapotranspirative effects and not go be- yond probable natural-process limits, the hypotheti- cal analyses were computed for as much as a four- fold concentration by evapotranspiration but no further. SOFTENING Softening, the replacement of the hardness-caus- ing constituents calcium and magnesium by a chem- ically equivalent amount of sodium, commonly oc- curs wherever hard water, such as Colorado River water, seeps through beds containing a large num- ber of clay-mineral particles. Softening is a particle-surface reaction between ions chemically attached to the clay-mineral particles and the ions GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA dissolved in the water. Although it can continue so long as dissolved calcium and magnesium ions in the water are available for replacement, softening rare- ly removes all these constituents from the water. In the calculated analyses, softening is assumed to have resulted in replacement of half the increases in cal- cium and magnesium resulting from a 50 percent evaporation. However, softening may occur where there is little or no evaporation. Softening and carbonate precipitation—the next change considered—both result in reduction in calci- um and magnesium concentrations in water, but they are almost mutually exclusive and probably can- not go on simultaneously. They can be distinguished by the fact that carbonate precipitation results in decreases in calcium, magnesium, and bicarbonate, whereas softening results in decreases in calcium and magnesium but not of bicarbonate. Softening is always accompanied by an increase in percent sodium. Because the equivalent weight of sodium is somewhat greater than that of calcium and substantially greater than that of magnesium, there is usually a somewhat greater increase in dissolved-solids concentration in water which is both concentrated by evaporation and softened than in water which is merely concentrated by evapora- tion. CARBONATE PRECIPITATION Water containing appreciable quantities of bi- carbonate and either of the alkaline earth ions cal- cium or magnesium precipitates the corresponding alkaline earth carbonate when sufficiently evapo- rated. Water containing both alkaline earths, such as Colorado River water, can precipitate mixed salts. The carbonate precipitation is indicated in pipes and boilers by the formation of scale. Carbonate precipi- tation is indicated wherever decreases in calcium and magnesium concentrations, in equivalents, are equalled by decreases in bicarbonates, in equivalents. However, because of temperature, pressure, and combination effects caused by other dissolved ions, the actual bicarbonate-concentration level at which insoluble carbonate precipitation begins is not readily predictable. Analyses from frequently sampled wells suggest that individual ceilings on bicarbonate concentration do exist, depending in some manner on well environ- ment, and that the concentration levels at which calcium and magnesism carbonate loss becomes an important control on dissolved-solids concentration may range from less than 200 mg/l to more than 450 mg/l. But after precipitation begins, the differ— ent bicarbonate-ceiling levels apparently have little effect on the general pattern of chemical change occurring with evaporation. Therefore, although H127 other ceilings were considered and carried through the evaporation sequence, model analyses are given in table 15 only for the arbitrarily selected bicar- bonate ceiling of 380 mg/l. Precipitation of insoluble carbonates with or with- out concentration by evaporation is best indicated by an increase in percent sodium because, as calcium and magnesium are lost by precipitation and sodium is not, the relative amount of sodium increases. For the same reason, the ratio of chloride to bicarbo- nate increases. Softening (described in the previous section) also results in an increase in percent sodium but not in an increase in the ratio of chloride to bicarbonate. Also, as the loss of dissolved solids caused by pre- cipitation of insoluble carbonates is often consid- erable, and as there is always a small increase in dissolved-solids content resulting from softening, the two processes can ordinarily be separated by inspection of the chemical analyses. SULFATE REDUCTION Most analyses of ground water from the irrigated areas indicated lower ratios of sulfate to chloride than those characteristic of recent Colorado River water. High-sulfate water is rare; even the analyses representing the greatest concentration by evapo- transpiration do not indicate sulfate concentrations nearly high enough for precipitation of calcium sul- fate to occur. Also, although hydrogen sulfide was not determined in the chemical analyses, hydrogen sulfide odor was reported when many wells were rumped. For these reasons, sulfate reduction is probably a major process occurring in Yuma area ground water. Sulfate reduction is an incompletely understood process, which probably occurs in several ways under diiferent conditions. Some may occur wherever or- ganic matter is in long-continued anaerobic contact with water containing sulfate. The process is more likely associated with the natural metabolic proc- esses of a widely distributed group of sulfate- reducing bacteria. These bacteria derive energy from oxidation of organic compounds and in the process obtain oxygen from the sulfate ions in water. Sul- fate reduction by the bacteria probably involves a series of steps in which polysaccharides and other complex organic compounds are depolymerized, hy- drolized, and oxidized simultaneously with the re- duction of sulfate ion to sulfide ion or hydrogen sulfide. Starting with cellulose, the organic substance (polysaccharide) making up most of the cell walls of plants, the complete process can be represented by the following steps: H128 1. Depolymerization of the cellulose to the monomer (sugar): (CeH1oO)x “é X'Csfliooa 2. Hydrolysis of the monomer to methane and carbon dioxide: CSH1005+H20 —> 30HH—3CO2 3. Reduction of sulfate ion to give bisulfide ion or hydrogen sulfide: (a) SCH—CH, -—> HS+HCOS+H20 (b) SO4+2CH4 -—> HZS+C03+H20 Other reactions have been written in which hy- drogen is an intermediate decomposition product which reduces the sulfate. An important point in considering sulfate reduc- tion is that for each chemical equivalent of sulfate ion reduced, one chemical equivalent of carbonate or bicarbonate is formed. These newly formed ions must be allowed for in constructing model analyses of reduced waters. Generally the bicarbonate con- centration is controlled as explained previously. Although sulfate reduction undoubtedly takes place, its extent is variable and uncertain. Hypo- thetical analyses resembling a considerable number of Yuma area ground-water analyses are produced by imposing sulfate reduction at three rates in which 25 percent, 331/3 percent, and 40 percent of the sul- fate disappear each time the river water is evapo- rated by one half, with the reduction process being continued until the original volume is reduced by nine-tenths. Some actual analyses indicate even greater sulfate reduction. Thus, some show chloride ; concentrations similar to those in recent river water analyses but show sulfate concentrations much less than those in the river water. Other analyses indi- cate chloride concentrations substantially greater than those in recent river water and sulfate con- ; centrations somewhat less than those of the river water. Although either of these water types might be explained by imposing large sulfate reduction rates on recently infiltrated river water, an environ- ment that could produce rapid reduction on the large amounts of water pumped by some wells does not seem very likely. Thus it appears that the low- . sulfate water may have been produced by slow sul- ‘ fate reduction acting over a long period and may not be related to recent river water. By comparing the sulfate and chloride concentra- trations in the Yuma area ground water with con- trations that would have occurred if the original water was average Colorado River water, the appar- ent sulfate reduction in the ground water can be described as follows: . Slight: Sulfate reduction somewhat less than that shown by the 25-percent model analysis series. WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA Moderate: Sulfate reduction nearly the same as that shown by the 25-percent model analysis series. Considerable: Sulfate reduction nearly the same as that shown by the 33-percent model-analysis series. Substantial: Sulfate reduction nearly the same as that shown by the 40-percent model-analysis series. High: Apparent sulfate reduction considerably more than 50 percent as indicated by sulfate concen- trations less than 300 mg/l but greater than 100 mg/l. Very high: Sulfate concentrations less than 100 mg/l with chloride concentrations equal to or greater than usual Colorado River concentrations. The rate of sulfate reduction apparently is not often much less than 25 percent, because reduction at lesser rates would result in the presence of more sulfate relative to chloride than is indicated by any of the analyses of more concentrated ground water. A 50-percent reduction rate would result in a sulfate level unchanged as chloride increases during evapo- ration. A reduction rate greater than 50 percent would result in decreased sulfate concentrations as chloride concentrations increase. In computing hypothetical analyses produced by sulfate reduction the calcium and magnesium con- centrations are also lowered as the sulfate is re- ‘ duced in amounts sufficient to maintain cation-anion balance, with the bicarbonate concentration main- tained at 380 mg/l. Comparison of hypothetical analyses so produced with actual Yuma area ground- water analyses indicates many close resemblances up to about a fivefold evaporative concentration. Beyond that concentration the quantities of dis- solved calcium and magnesium remaining in the water begin to be so lowered that the model analyses become softer than most Yuma area ground water. This difficulty disappears if. hardening, explained in the next section, is also assumed. HARDENING Hardening, the reverse of softening, is a base- exchange process in which sodium ions dissolved in I water are replaced by calcium and magnesium ions ! attached to clay-mineral particles present in water- ‘ bearing materials. Montmorillonite, which consti- tutes more than half the clay minerals in two sam- ples of older alluvium (p. H52), is noted for having the highest cation-exchange capacity of any of the common clay minerals (Robinson, 1962). Hardening, like softening, probably depends on clay-mineral E particle saturation. For this reason the hardening i reaction is likely to go to different completeness in ' different aquifer locations. Hardening is a hypothesis GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA helpful in accounting for the presence of moderately high concentrations of calcium and magnesium in ground water in which sulfate reduction appears to have been considerable. Hardening is strongly sug- gested by so-called calcium or magnesium chloride water. Two rates of hardening are considered in the series of hypothetical analyses (table 15). Sulfate reduction is assumed to be concurrent with evapo- ration, but the sulfate concentration increases if the reduction rate is less than 50 percent. In the first series of analyses computed so as to allow for hard- ening, the hardening is made chemically equivalent to the increase in sulfate concentration. The second series of analyses is calculated so that hardening occurs until sodium concentration is reduced to equivalence with chloride concentration. Both series of hypothetical analyses simulate some actual ground—water analyses, but the second series repro- duces more actual analyses than the first. SUMMARY OF HYPOTHETICAL ANALYSES To summarize, the table of hypothetical analyses represents the quality of the ground water that would be obtained from wells assuming that the water infiltrated from the recent Colorado River and was evaporated to the degree indicated and sub- j ected to the particular chemical processes described. Limits on concentration or process rates used in preparing the table were chosen for descriptive pur- poses and are not meant to imply that other limits or rates do not occur. Because of chemical consid- erations, some of the processes are terminated after less concentration by evaporation than others. Thus the evaporation process and the combination of evaporation and softening are terminated at the first step and produce bicarbonate concentrations above 500 mg/l, because that level represents about the maximum observed in Yuma area ground water. To facilitate visual comparison of the model analy- ses with analyses indicated in other figures in the report, selected chemical analyses from table 15 are shown diagrammatically in figure 48. The diagrams in figure 48 are arranged so that those in each row represent Colorado River water which has been subjected to uniform chemical proc- esses and those in each column have been evaporated to the same extent. Consequently, comparing the diagrams by rows or columns emphasizes different environmental effects. Generally speaking the dia- grams are not greatly different in shape up to a twofold concentration increase, regardless of the chemical processes assumed. Thereafter, the various combinations of chemical processes produce more H129 and more individualistic chemical patterns as con- centration increases. A general conclusion is that a dissolved solids value (or specific conductance) by itself is not a very good guide as to how much the original volume may have been reduced by evaporation. For example, dia- gram 17 represents a reduction to one-fourth the original volume with 2,640 mg/l dissolved solids. In contrast, diagram 59 represents a volume reduction to one—tenth the original volume and 2,600 mg/l dis- solved solids. SUBDIVISION OF YUMA AREA FOR DESCRIPTION OF QUALITY OF WATER Almost all information on chemical quality of ground water in the Yuma area is limited to the central part of the area, which includes the river valleys, Yuma Mesa, and the northern parts of “Upper Mesa” and “Gila Mesa.” In order to facili- tate detailed description of differences in water quality, this central part is divided into four sub- areas which are further subdivided into a total of 19 sectors (fig. 49). In the descriptions of the sec- tors, references are made to place names not shown in figure 49; these places are shown on the standard US. Geological Survey 71%z-minute series topo- graphic maps of the Yuma area. The four subareas correspond in a general way to some of the subareas described in the geomorphology section of the report (p. H18) and together constitute the part of the Yuma area investigated most intensively. A brief generalized description of the chemical characteris- tics of the ground water in each of the water-bearing units is given in the section on occurrence of ground water. The present discussion is more detailed and is concerned chiefly with water-quality differences in the coarse-gravel zone and, to a lesser degree, in the upper, fine-grained zone and wedge zone. Selected chemical analyses of ground-water sam— ples collected from wells in the Yuma area are given in appendix C, arranged according to the four sub- area-s and 19 sectors. In the discussion below, com- parisons are made between the ground water in the various sectors and present Colorado River water according to the hypothetical processes described earlier. GILA VALLEY SUBAREA The Gila Valley subarea consists of all South Gila Valley and the east leg of the L-shaped North Gila Valley (fig. 49). Because of the proximity of the relatively saline Gila River and Wellton-Mohawk conveyance channel, this subarea is the part of the Yuma area most likely to have the salinity of the WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA H130 .3 ~53 5 mama—«Ed 33530 Bunion .3 635.832 .5533 ac $3239 18...:qu we 3335833 misgualfiv umaEh comm on omoN x2 ooww xod ow om x9 2mm x2 .8: 3a mEEmzzE E 638 2:686 S Eam/ B «Owl MS: 5.38%; E 553.5850.\\‘L2V 0:: fl .3: in 3:23:35: _E E mzHG :E: 9:592 383 96% mm uEmm am 32 Q xm ONE Xm xe 32:6 E 388:. 3: 2 .33 9:592 33 :2,on mm mEmm ommw on: 0mg xm xm xq coco—52 323m “:8th ow .ufimtflowa fiBSoagm ommw 3: gm: M 3 m / mv m W N9 xw Xm xw :ozguE $8.5m EwEma m: mm .uSmtEoma fiBSoamE ONoN 0:3 32 xw Xm é concave 323m Egan mN .uBmtEoma .uBEonmE ovom S NN 22 82 xx Xm xv xm uBEEUEn ucm uEanmE ZO_P_m:< xv Xm ome omHN Q Q xe xm BE; 32: 2:228 owe omn mm? mmfi xma xH GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H131 114°45’ 30' 114°15’ //,./ % é WW/ % : % ~, é ;:\\ // o r ' I, ‘ B\D(‘)m \ 32 45 Pilot I // \I. e \ ...Knob/ // Q??? ATES_ _ a ”133%” ‘ .. = ' ' ////\\<\ J / 9° ° Io Q <“ s: ‘3: O : ,,,, O 30' — O f I .:.:. EXPLANATION \stI Q GILA VALLEY SUBAREA MA VALLEY SUBAREA #0 ST YU m EXTCBATES l. Gila Siphon sector 11, California sector \\ "x 2. East sector 12. East sector Mountains andvhills K \ ‘3‘ :. figt-cceelhtgglssegcbg‘r l: gigxalzezglm if We ~\\ 5. West sector 7 \ \ Area of shallow be rock \ ‘ UPPER VALLEV SUBAREA YUMA MESA SUBAREA _._.___d_ \\N 6, Laguna Valley sector [5. Fortum sector Alluvial escarpment 7. North Gila sector .6. Arizona Western sector 8. Bard sector 17. Citrus sector .3: aiésiizsefizzzzo. is: gamma. ‘1 - . . f go 32°15' ' ' FIGURE 49.—Subareas and sectors described in section on quality of water and listed in appendix C. ground water increased by induced infiltration. The 1965 most of the subarea was irrigated with ground natural drain of the subarea is the Gila River to its water pumped from wells perforated in the coarse- mouth and west of there the Colorado River. Until gravel zone. The pumping undoubtedly caused some H132 infiltration of Gila River water and, since comple- tion of the unlined part of the Wellton-Mohawk con— veyance channel across the eastern part of the sub- area, some infiltration from the conveyance channel. However, the hazard from induced infiltration was partly offset by the leakage from the unlined Gila gravity canal near the east end of the subarea, and by the fact that most of the South Gila Valley was converted in 1965 to irrigation with Colorado River water. Although recent analytical data indicate that the mineral content of the ground water in the coarse- gravel zone in the Gila Valley subarea is greater, on the average, than in any of the other subareas, in- formation On the preirrigation chemical quality of water is lacking so that it is not possible to estimate how much of the present salinity of the water has resulted from long-continued irrigation without drainage. Emplacement of irrigation canals has greatly changed the ground-water quality in some parts of the Gila Valley subarea and has produced only small effects elsewhere. Also, irrigation developments in the South Gila Valley and adjacent parts of the Yuma Mesa produced effects which have extended to only part of the subarea. Consequently, the subarea is divided for detailed discussions into five sectors, each of which differs in some respects from neigh- boring sectors. GILA SIPHON SECTOR The east leg of the North Gila Valley and a small area east of the south-flowing reach of the Gila River immediately downstream from the Gila Gravi- ty Main Canal Siphon are combined in the Gila Siphon sector of the Gila Valley subarea. The un— lined Gila Gravity Main Canal, which carries Colo- rado River water, is at the north boundary of the sector and turns southward across the sector near its eastern boundary. The Gila River, which gener- ally contains water three to four times as concen- trated as the canal water and with relatively more chloride, is the natural drain and flows southward across the sector from the Gila Siphon, then bends west at the south edge of the sector. The Wellton— Mohawk Conveyance Channel, which was placed in use in 1961 and which is unlined across the sector, flows south from the siphon and turns west south of the bend in the Gila River. The salinity of the water in the conveyance channel is controlled almost entire- ly by selective pumping of drainage wells in the Wellton-Mohawk area to the east but is generally greater than that in the Gila River although of somewhat similar composition. WATER RESOURCES 0F LOWER COLORADO RIVER—SALTON SEA AREA Formerly the North Gila Valley part of the sector was irrigated by diversion from the Gila Gravity Main Canal, but since 1965 it has mostly been irri- gated by pumping from recently drilled irrigation wells. The South Gila Valley part of the sector has also mostly been irrigated from wells, although there has been some diversion from the Gila Gravity Main Canal. Quality-of—water information for the sector is mostly limited to analyses of samples from the coarse-gravel zone. Chemical analyses of water samples obtained from a well at a gravel-washing plant at the east end of the sector, east of the Gila River, and from seven irrigation wells, of which two are east and five are west of the river, when ar- ranged from east to west, do not suggest any com- position pattern that can be related to well location alone. All the pumped water has been somewhat more mineralized than recommended for domestic use but has been less mineralized than water com- monly used in the main part of South Gila Valley for many years to irrigate salt-tolerant crops. Sev-. eral of the wells were sampled more than once, and it appears from successive analyses that there has been an erratic but generally upward change in con- centration of the pumped water, particularly in chloride concentration. However, none of the sam- pled water has reached concentration levels recently prevalent in the lower Gila River or the Wellton- Mohawk Conveyance Channel. In the future, water pumped from wells probably will contain increments derived from the Gila Gravi- ty Main Canal, Gila River, and Wellton-Mohawk Conveyance Channel, and from recirculation of ap- plied irrigation water. The proportions derived from these sources will vary with place and time, so that prediction of future water quality is not possible. However, the average concentration of dissolved solids and chloride probably will increase at sites near the Gila River. EAST SECTOR The east sector of the Gila Valley subarea lies east of County Avenue 10E and south of the Gila Siphon sector, in R. 21 W. of the Federal land net in Ari- zona. The sector is too far from the irrigated area on Yuma Mesa for the water quality to be affected by the water-table mound under the mesa. Water levels and water quality have been mainly affected . by the transition from limited development on the east side of the sector to complete irrigation on the west. The Gila Gravity Main Canal, which traverses the sector diagonally from northeast to southwest, is a possible source of infiltrating water. Before the GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA recent change to irrigation with surface supplies in the western part of the sector, pumpage of ground water was sufl‘icient to prevent a shallow water table, and the recent expansion of irrigation east of the canal may keep the water table far enough below the land surface to prevent salinization of soils and ground water. There are no drainage wells in the area, although one is just outside of it on the southwest. All chemical analyses from the sector represent water from the coarse-gravel zone. During the past few years the mineral content of the water has been higher than in most other parts of the Gila Valley subarea (pl. 11). In general, the water has been of the mixed chloride sulfate type in which the ratio of chloride to sulfate is greatest in the most concen- trated samples. EAST-CENTRAL SECTOR The part of the South Gila Valley bounded by County Avenues 7E and 10E, the Gila River, and the escarpment at the north edge of Yuma Mesa consti- tutes the east-central sector of the Gila Valley sub- area. Factors controlling quality of water in the sector are mostly like those in the east sector. How- ever, infiltration of canal water probably has con- siderably less influence on the quality of the ground water because the Gila Gravity Main Canal bounds the sector for only about 1 mile along its southeast corner. The intensely irrigated part of Yuma Mesa begins about 1 mile southwest of the west edge of the sector. However, this irrigated area is sufl‘lcient- ly far away so that the deep seepage from the irriga- tion probably has not affected the water quality of the east-central sector as much as it has affected the sector immediately west. The east-central sector, like most of the remainder of South Gila Valley, was irrigated for many years by pumping from wells perforated in the coarse- gravel zone but has been converted to primary de- pendence on Colorado River water. Therefore, re- cent ground-water-quality conditions are probably transient and may not closely resemble conditions which will exist after a few years. Many analyses of water pumped from both irriga- tion wells and new drainage wells in the sector indi- cate a general southward increase in the mineral content of the water in the coarse-gravel zone (pl. 11). Sodium and chloride are invariably the domi- nant constituents, but their relative amounts in- crease as total salinity increases. Water from some of the wells has had fluctuating concentrations ap- parently caused by different duration of pumping periods and by simultaneous pumping from other wells. H133 Information about the wedge zone is limited, but near-uniformity of water-quality characteristics in one sample from a test well in the northern part of the sector, and samples from three deep supply wells at the south edge of the sector suggest the presence of water of relatively, low salinity in the wedge zone under a considerable part, and perhaps all, of the sector. WEST-CENTRAL SECTOR The part of South Gila Valley bounded by County Avenues 4E and 7E, the Gila and Colorado Rivers, and the Yuma Mesa escarpment is called the west— central sector of the Gila Valley subarea. The sector is immediately north of the citrus sector of the Yuma Mesa subarea, and, as a result, both water levels and water quality have been considerably affected by irrigation on the mesa. All the original nine drainage wells drilled for the US. Bureau of Reclamation to control water levels in South Gila Valley are in the southern part of the sector. Periodic analyses of water samples collected from these wells have indicated a pattern of slowly declining salinity with long-continued pumping. Analyses of samples obtained from irrigation wells suggest that usual concentrations north of the drain- age wells may be less than those in the vicinity of the drainage wells. However, some of the irrigation wells appear to have produced water of slowly in- creasing salinity. Dissolved-solids concentrations throughout most of the sector have ranged from 1,800 to 3,600 mg/l, with fewer wells yielding con- centrations above 3,600 mg/l than in the east-central sector. Samples obtained from a domestic well, a public-supply well, and a test well (appendix C, analyses 56a, 66, 87a, b, c) indicate that the water in the wedge zone is less mineralized than the water in the coarse-gravel zone. WEST SECTOR The part of South Gila Valley between County Avenue 4E and the city of Yuma, in R. 23 W. of the Federal land net for Arizona constitutes the west sector of the Gila Valley subarea. Several factors that influence the patterns of ground-water move- ment probably affect the water quality in the sector. The sector is south of the COlorado River and west of the mouth of the Gila River, so the local infiltra- tion from the river channel probablv is less saline than in the sectors farther east. Pumping of ground water for irrigation in The Island across the C010- rado River to the north may reduce water movement south and southwest. The deposits flanking the buried slopes of “Yuma Hills” on the west side of the sector are less permeable than those to the north H134 and east (fig. 25). The east half of the sector is north of the citrus sector of Yuma Mesa, but the west half is north of the urban area of Yuma. Chemical analyses of water samples obtained from irrigation and drainage wells in the sector show the general southward increase in salinity that also oc- curs farther east (pl. 11). However, the analyses also indicate an increase in salinity toward the west and southwest, which suggests that recirculation of pumped water has been greater in the southwest corner of the sector than elsewhere in South Gila Valley. UPPER VALLEY SUBAREA The upper valley subarea is the part of the Yuma area where water quality in both the upper, fine- grained zone and the coarse-gravel zone is most nearly related to the average quality of the Colorado River. The subarea comprises “Laguna Valley,” “Bard Valley,” and the western part of North Gila Valley. The Colorado River flOWS through the east- ern part of the subarea and forms most of its south- ern boundary. The All-American and Gila Gravity Main Canals are emplaced mostly on cuts along the lower parts of the slopes at the sides of the valleys and are about 20—40 feet higher than the Colorado River. Consequently, ground-water movement is mainly away from the two canals toward the river. Most of the subarea is irrigated with Colorado River water except for The Island sector, where irri- gation is by pumping from wells screened in the coarse-gravel zone. Thus, most of the recharge in the subarea is Colorado River water infiltrating from the two principal canals or their diversions. In order to describe local conditions, the upper valley subarea is subdivided into five sectors. The “Laguna Valley” and the North Gila Valley are treated as individual sectors, whereas “Bard Valley” is subdivided into three sectors termed the Bard sec- tor, The Island sector, and the Winterhaven sector. “LAGUNA VALLEY” SECTOR The “Laguna Valley” sector, which is bisected by the Colorado River, includes the ovate part of the Colorado River flood plain between the All-American Canal and the Gila Gravity Main Canal above La- guna Dam and below Imperial Dam. Before the constructiOn of Hoover Dam most of the sector probably was flooded every year. Mittry Lake, a permanent water body between the river and the Gila Gravity Main Canal, is continually fed by ground-water seepage. Analyses of several samples of outflow from Mittry Lake indicate that evapo- transpiration has concentrated the lake water to two or three times as much as the river and that mod- erate sulfate reduction occurs in the lake. WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA Most of the remainder of “Laguna Valley” is low lying and swampy so that chemical processes just below the water table may be like those in Mittry Lake. Analyses of samples obtained from four hand- auger holes suggest that two patterns of chemical change occur in the shallow deposits on both sides of the Colorado River. Two of the analyses suggest concentration by evaporation, slight sulfate reduc— tion, and considerable softening. The other two indi- cated greater concentration by evaporation, moder- ate sulfate reduction, and hardening instead of softening. Nevertheless all samples contained less than 1,600 mg/l dissolved solids. A well at the Imperial Irrigation District’s Im- perial Camp, probably screened in the coarse—gravel zone, yields water very similar in composition and concentration to Colorado River water. Water ob- tained from the coarse-gravel zone at test well LCRP 14 just north of Laguna Dam is comparable to re- cent Colorado River water (appendix C, analysis 206a). Thus, water of the Colorado River type may be present in the coarse-gravel zone in much of the valley. Analyses of samples obtained from the mud scow during drilling of LCRP 14 did not show the pres- ence of water of better quality below the coarse- gravel zone like that found in “Bard Valley” to the southwest. Water pumped from the nonmarine sedi— mentary rocks perforated after the well was com- pleted at depths of 470—490 feet was the most saline of any water sampled in the entire upper valley area, with 3,420 mg/l dissolved solids, 1,450 mg/l chloride, and 660 mg/l sulfate (appendix C, analysis 206b). Water of this character could not have been formed from recent Colorado River water without being concentrated by evaporation ’about 10 or 12 times and being subjected to substantial sulfate reduction. It is difficult to explain the quality of the water at this site except by assuming that the water has been in the sediments for a long time. NORTH GILA SECTOR The North Gila sector, which is east of the C010- rado River across from the more comprehensively sampled Bard and The Island sectors and immedi- ately downstream from the “Laguna Valley” sector, includes the part of North Gila Valley irrigated with Colorado River water. The sector contains no irri- gation wells or other large-capacity wells in use. Consequently, appraisal of water-quality variation is based on analyses of samples of water obtained from small domestic and stock wells, auger-test wells, and a US. Bureau of Reclamation test well which may not have been pumped long enough for stabilization of water quality, and on the assumption GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA that test wells LCRP 14 and 23, which are in ad- jacent sectors, indicate conditions in this sector. The data indicate that ground water containing between 900 and 1,800 mg/l dissolved solids can'be obtained in most of the sector, although water con- taining as much as 2,500 mg/l dissolved solids and relatively high in chloride may be present locally in the upper, fine-grained zone. Water of better quality than that represented by the analyses may be gen- erally present in the wedge zone, and the best water is probably near the Colorado River. Most of the sampled water appears to be Colorado River water only moderately altered by concentration and softening. BARD SECTOR The Bard sector is the part of “Bard Valley” downstream from Laguna Dam, north of The Island, and east of the Yuma Main Canal. Chemical analy- ses of samples of water obtained from auger test wells drilled along washes outside the sector, a short distance north of the All-American Canal, are in- cluded in the tabulation (appendix C) because they indicate the presence of water similar to that ob- tained from auger test wells on the valley side of the canal. Most of the Bard sector is irrigated with Colorado River water, although strips of unculti- vated land overgrown with phreatophytes are scat- tered along the All-American Canal and laterals. Water quality along the east margin of the sector is probably similar to that indicated. by test wells LCRP 14 and 23 which are close by but in other sec- tors. Water samples obtained from scattered farm wells and auger test wells mostly tapping the top of the coarse-gravel zone indicate only moderate varia- bility of water-quality patterns. The composition ranges from water like Colorado River water to water from the river moderately evaporated and with somewhat reduced sulfate. Nine samples ob- tained from very shallow house wells used by Indi- ans at uncertainly designated sites in the western part of the sector indicate that the shallow water is generally more mineralized than Colorado River water; this is likely to be true for shallow water throughout most of the sector. A well drilled into the coarse-gravel zone a short distance east of the Yuma Main Canal near Indian Hill yielded water similar to recent Colorado River, which suggests that such water might be available in favorable areas close to many of the canals. US. Bureau of Reclamation test well CH—8, which pene- trated a buried volcanic hill (basalt or basaltic an- desite), yielded water containing 1,380 mg/l dis- solved solids from 355 feet which was softened and also appeared to have undergone considerable sul- H135 fate reduction (appendix C, analysis 231a). A well at the San Pasqual Valley School was perforated from 120 to 204 feet and yielded water closely re- sembling 1950 Colorado River water which had been concentrated about four times, had undergone mod- erate sulfate reduction, and had been considerably hardened (appendix C, analysis 241) . THE ISLAND SECTOR The Island sector includes the part of “Bard Val- ley” south and southeast of the Bard sector that is not supplied with Colorado River water by a canal system. The sector, somewhat larger than the aban- doned Colorado River meander cutoff known as The Island, contains a considerable acreage irrigated from wells and scattered acreages which are either covered with small sand dunes or overgrown with phreatophytes and which are not irrigated. Infor- mation about shallow water is not available for the sector, but such water is probably variable in com- position and more highly mineralized than the water in the coarse-gravel zone because of concentration by evapotranspiration and because there is no pro- vision for drainage in the sector. Chemical analyses of water samples obtained from 13 irrigation wells, probably all perforated entirely or mainly in the coarse-gravel zone, indicate that concentrations of dissolved solids in the pumped water ranges from about 900 to 1,900 mg/l. Some of the analyses indicate only moderately altered Colorado River water, slightly concentrated by evaporation, whereas others suggest more than 50 percent sulfate reduction and several times concentration. Test well LCRP 23 at the northeast corner of The Island sector probably indicates the general varia- tions in water quality with depth in parts of the Bard and North Gila sectors as well as in The Island sector. Water bailed from this well at 133 feet dur- ing drilling was somewhat like evaporated Colorado River water (appendix C, analysis 243a). Samples obtained when pumping from perforations extend- ing from a depth of 120 to 548 feet represent a mix- ture of water from the wedge zone and the coarse- gravel zone. This water contained less than 600 mg/l dissolved solids and was like highly reduced Colorado River water (appendix C, analysis 243C). Water from the interval 634 to 694 feet. which came from the Bouse Formation (marine), was higher in concentration than the river water and contained much more chloride and somewhat less sulfate than the river water (appendix C, analysis 243‘b). WINTERHAVEN SECTOR The Winterhaven sector, most of which is in the H136 Yuma Indian Reservation, includes the part of “Bard Valley” west of the Yuma Main Canal. Most of the sector is accessible to a network of irrigation canals but not all the valley land has been cultivated; a considerable acreage of scattered low-lying tracts overgrown with phreatophytes has accumulated sur- face salts as a result of evapotranspiration. Few wells have been drilled in the sector. Water- quality information is mainly limited to analyses of water samples obtained from auger test wells. Sam- ples from most of these small-diameter wells indi- cate the presence of water about like recent Colo- rado River water or like river water concentrated two or three times but with its sulfate slightly to moderately reduced. A water-quality problem exists at the village of Winterhaven, the only important trading point in the California part of the Yuma area. The chemical character of the water obtained from several wells drilled to supply the community is reported to have changed slowly from a water something like the recent river to water almost unacceptable for public supply. Hence, operators of the company supplying water have had to drill new wells and abandon old ones every few years. The latest well was drilled in September 1961 and by the spring of 1967 the water quality had deteriorated so that the well was con- sidered questionable as a continuing source for pub- lic supply. An auger test well southwest of Winterhaven be- tween the Colorado River and a flood-protection levee produced water containing 3,450 mg/l dis- solved solids With 1,160 mg/l chloride when sampled at 117 feet (appendix C, analysis 266). However, as very poor water originating upriver in the Wellton- Mohawk district constituted much of the river flow for many months prior to the time of sampling, the sample might represent local infiltration of miner- alized water from the river. A deep US. Geological Survey test well, LCRP 26, drilled by the mud-rotary method, cased, and gravel packed, yielded water containing only 712 mg/l dissolved solids (appendix C, analysis 26%). The well is perforated from 125 to 1,127 feet (throughout the coarse-gravel zone and the wedge zone) and also from 1,368 to 1,769 feet (in the non- marine sedimentary rocks), so that the water sam- ple represents a composite from three aquifers. Use of a flow meter in the well while making pumping tests indicated that relatively little water was yielded by the nonmarine sedimentary rocks, and electric and water-resistivity logs and thief samples showed that the water in these rocks was not quite as fresh as that in the wedge and coarse-gravel zones WATER RESOURCES 0F LOWER COLORADO RIVER-SALTON SEA/AREA of the alluvium. The logs also indicated fairly uni- form electrical conductivity for the water through- out the alluvium. Thus, it is inferred that the water yielded by the coarse-gravel and wedge zones alone would be slightly fresher than that actually pumped from the well and might contain less than 700 mg/l dissolved solids. A shallow well used to furnish water for drilling the test well yielded water con- taining 2,460 mg/l dissolved solids (appendix C, analysis 269a). This analysis indicates that the upper, fine-grained zone probably contains slightly to moderately saline water. The only irrigation well in the Winterhaven sec- tor, well 16S/22E—29Dba, less than a mile northwest of test well LCRP 26, obtains water of fair quality, though not as fresh as that in the test well (appendix C, analyses 267a, b). The irrigation well is per- forated from 118 to 143 feet, entirely in the coarse- gravel zone. YUMA VALLEY SUBAREA The Yuma Valley subarea, largest of the subareas, consists of all the Colorado River flood plain in Ari- zona south and west of the city of Yuma. The entire Yuma Valley except for a narrow strip adjacent to the river on the north and west is protected by a flood-control levee and is irrigated from the Yuma Main Canal system. The canal water enters the valley through an inverted siphOn beneath the Colo- rado River at Yuma but is originally diverted from the river at Imperial Dam and therefore has the chemical characteristics of the Colorado River water at the dam rather than the somewhat greater con- centrations that occur below the mouth of the Gila River. Irrigation in Yuma Valley began before 1900, and most of the valley has been irrigated with river water for at least 50 years. Consequently, rather complete leaching of soluble salts present in the up- per soil zones prior to initial irrigation probably has occurred. Nevertheless, some comparatively small areas are underlain by a high water table where white saline surface crusts appear from time to time as a result of evaporation from the capillary fringe. An extensive network of canals and laterals be- gins at Yuma and interfingers with an equally ex- tensive drain system which converges into a single main drain near the southerly international bound- ary. The drain water, although moderately variable in composition and concentration because it includes variable parts of irrigation wastes, is always con- siderably more mineralized than the applied Colo- rado River water. Nevertheless, it has been pumped across the southerly international boundary and used for irrigation in Mexico for many years. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA The Yuma Valley subarea is not as easily divisible into sectors on the basis of topography, geology, or’ analytical data as the other three subareas. Numer— ous chemical analyses are available which represent sampling from drainage wells near the Yuma Mesa escarpment on the east side of the valley and also from irrigation and other wells in the fioodway strip on the west side of the valley, but there are compara- tively few analyses that represent sampling from the far larger area between the drainage wells and the floodway strip. Consequently, the subarea is divided into three relatively narrow sectors along the north, east, and west margins, and a fourth sector that in- cludes the greatest part of the valley (fig. 49). CALIFORNIA SECTOR At the north end of Yuma Valley, west of Yuma, the Colorado River flows slightly north of west for about 5 miles, then turns abruptly toward the south- southwest. A small part of the valley near the river was once included in California and is still sub- divided according to the California system of the Federal land net. For convenience in identifying wells this small area is designated the California sector of the Yuma Valley subarea. Part of the sec- tor is not farmed, part is or has been irrigated by pumping directly from the Colorado River, and part has been irrigated by pumping from the Central Main and Cooper Canals of the Yuma Project. There is one irrigation well in the sector. Analyses of water samples obtained from several domestic wells in the sector indicate the presence of an unusual body of shallow ground water containing only a few hundred to about 1,000 mg/l dissolved solids. This water is moderately low in chloride and unusually low in sulfate. Although the water may be residual flood water, more likely it is Colorado River water that has undergone great sulfate reduc- tion. Water from two domestic wells and one obser- vation well was considerably higher in dissolved solids. This fact indicates that part of the local ground water represents considerably evaporated and moderately reduced Colorado River water. Two samples of water obtained 2 years apart from the irrigation well are so much like reCent Colorado River water that they suggest a considerable part of the water pumped from this well is recently infiltrated Colorado River water, even though the well is perforated in the coarse-gravel zone (ap- pendix C, analyses 308a, b). Two deep wells per- forated in the wedge zone which have supplied water for a steam-electric plant for about 10 years have yielded water containing much less dissolved solids than any other regularly pumped large-capacity 507-243 0 - ’74 - 10 H137 wells in the Yuma area (appendix C, analyses 303a, b, 304). EAST SECTOR Recent water quality in the coarse-gravel zone on the east side of Yuma Valley probably is rather well defined by chemical analyses of water samples col- lected from a line of drainage wells constructed near the eastern edge of the valley and west of the East Main Canal—the eastern distributary of Colorado River water in Yuma Valley. The drainage wells were constructed so that continuous pumping would relieve the high water table caused by the ground- water mound beneath Yuma Mesa to the east. The first drainage wells, placed in operation in 1947, did not extend into the coarse-gravel zone, so that most of the water pumped from them actually came from the upper, fine-grained zone, although undoubtedly replaced by upward movement from the coarse-gravel zone. The capacity of the shallow wells proved inadequate to control water levels and they were replaced, beginning in 1954, by large- capacity wells screened in the coarse-gravel zone. Although the shallow drainage wells obtained water from the upper, fine-grained zone, the old analyses of samples obtained from them probably do not repre- sent the quality of water in the upper zone near the well sites today. Consequently, the analyses of sam- ples from the old wells are not included in appen- dix C. Pumping from the high-capacity drainage wells screened in the coarse-gravel zone has generally been nearly continuous once a well has been placed in operation. Consequently, differences between chemi- cal analyses of water samples taken at intervals from these wells can be interpreted as showing actual changes in water quality in the coarse-gravel zone resulting from the continued pumping. Never- theless, some care must be taken in drawing con- clusions about salinity changes in the ground water as the chemical analyses came from several sources and are not always strictly comparable owing to differences in analytical methods used by individual laboratories and because some analyses suggest pos- sible chemical precipitation prior to analysis. None of the presently pumped wells yields water like the present Colorado River water. Yet each well tends to have a definite chemical pattern which is some- what different from that for adjacent wells, prob- ably because vertical and horizontal movement of water to the wells varies from well to well, and be- cause part of the water pumped from some of the wells may have come from considerable depths in the wedge zone. H138 The dissolved-solids content of water pumped from the drainage wells has ranged from about 1,100 to 2,300 mg/l and either has generally been rather constant for an individual well or has gradually de- creased after several years of pumping; however, water from the northernmost drainage well has trended upward in concentration rather than down- ward. The most northerly wells, whlch are west of the built-up part of the city of Yuma and farther from the irrigated area of the mesa than those farther south, yield water that is like moderately evaporated and greatly reduced Colorado River water. The drainage wells in the central part of the group and west of the heavily irrigated part of the mesa yield water that contains more sulfate and less chloride. Wells at the south end of the group yield water having the lowest dissolved-solids content and containing less chloride and much less sulfate than farther north. The different changes in composition of the water with time apparently result from dif- ferential movement to the wells of an increment of Colorado River water applied as irrigation water on Yuma Mesa. CENTRAL SECTOR Water-quality variation in the central part of Yuma Valley is not very well defined, because there are only a few wells for which depth information, logs, and sampling all are available. Wells used to supply Somerton are the only ones in central Yuma Valley that have pumped substantial amounts of water. Information is also available on a few wells of moderate capacity constructed to supply labor camps, cotton gins, and feed yards. Most of the analytical information is on samples collected from auger test wells and small-capacity domestic wells of which many of the latter are of unknown depth. The auger test wells were sampled through well points at their base. Some of the domestic wells also obtain water through well points or open bottoms. Thus the auger-well and domestic-well samples mostly represent point rather than zone sampling and water of different quality might be obtained at their loca- tions if wells of larger capacity perforated for lengthy intervals were constructed. Therefore, the central part of Yuma Valley must be appraised on a more tentative basis than the rest of the Yuma area, although the appraisal may not be far removed from describing average water-quality conditions. Chemical analyses of water samples collected from auger test wells and domestic wells, chiefly from the northern one-third of the valley, indicate consider- able erratic variation in the chemical quality of water in the upper and coarse-gravel zones. Appar- WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA ently many of the canal reaches serve as line sources of recharge so that the chemical character of the water obtained from shallow sources near them is very similar to that of recent Colorado River water. In contrast, wells of similar depths but closer to drains rather commonly yield water with chemical characteristics indicating moderate concentration by evaporation and some sulfate reduction. During 1962, the US. Bureau of Reclamation had two 500-foot test wells drilled in the valley. Analyses of water samples taken from the mud scow or with a thief sampler during drilling indicated irregular differences in water composition with depth. The wells were perforated in the coarse-gravel zone but not pumped and sampled until about 2 years later. The pumped samples agreed only in a general way with the samples obtained earlier. (See appendix C, analyses 360a—h, 376a—f) . In 1965 the city of Somerton had a deep test well drilled in order to prospect for water suitable for city use. Several samples (appendix C, analyses 37 5a—g) were obtained from the mud scow at depths ranging from 470 to 1,143 feet but they did not indi- cate the presence of the hoped-for good water, and the well was not completed at that time. It was completed later, however, and is now (1968) used for public supply. F LOODWAY SECTOR At the time the Yuma Project was developed by the US. Bureau of Reclamation a rather narrow strip along the Colorado River was separated from the rest of Yuma Valley by a flood-protection levee so that it did not receive canal water. Overgrown with bottom-land vegetation, the strip was mostly unused for many years. By 1940, however, some of it had been cleared and was irrigated by pumping directly from the river. Later the irrigated area was greatly expanded to cover most of the strip, and irrigation by pumping from wells replaced the pumping from the river. Several analyses of samples from two wells near the West Main Canal in the north-central part of the sector have shown that these wells have always yielded water containing 1,200,—1,400 mg/l dissolved solids which is Similar to evaporated Colorado River water that has undergone slight sulfate reduction (appendix C, analyses 344a—e, 395a, b). All the irri- gation wells farther south have yielded water that contains less dissolved solids, that appears to be less concentrated by evaporation, and to have undergone more sulfate reduction. Four analyses of samples taken from a cluster of auger test wells installed to determine differences in head (appendix C, analyses GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA 402—405) indicate that the water in the upper, fine- grained zone is most like evaporated Colorado River water near the water table and that its dissolved- solids content decreases with depth, mainly because of increased sulfate reduction. Several samples collected with packers from test well LCRP 9 (appendix C, analyses 399a—f) indicate that the quality of water obtained between depths of 310 and 1,108 feet (in the wedge zone) does not vary much with depth and that the wedge zone probably contains better water for an extended depth than that in the river. Samples obtained from test well LCRP 17, several miles farther south (appendix C, analyses 410a—h) consistently indicated a little more chloride and a little less sulfate than in well LCRP 9. All the analyses from irrigation wells represented by repeated samples showed small but definite in- creases in dissolved solids content after several years pumping, but the rate of increase was not sufficient to suggest that the water would become unsatisfac— tory for the general farming carried on in the area for many years. YUMA MESA SUBAREA The Yuma Mesa subarea includes small parts of “Upper Mesa” and “Gila Mesa” as well as the entire Yuma Mesa. All the subarea lies above the river valleys (flood plains) and consequently has not been subject to geologically recent (Holocene) flooding by the rivers. The subarea includes a large central acre- age irrigated by Colorado River water brought in by lined canal and scattered tracts where irrigation by pumping from wells has begun recently or is being planned. It also includes large sections where irriga- tion may be possible but where irrigation has not yet been planned. The alluvium beneath the Yuma Mesa subarea is hydraulically continuous with the alluvium under the adjacent river valleys so that a continuous water table extends from the South Gila Valley southward and southwestward under the Yuma Mesa subarea to the southerly international boundary and Yuma Valley. Early chemical records suggest that most of the subarea may have had ground water of uniform chemical quality before irrigation began in the South Gila Valley and on Yuma Mesa, and that some of the old water was replaced by water more like recent Colorado River water. Irrigation on the mesa un- doubtedly has altered the chemical quality of much of the ground water in the irrigated area so that the present patterns of ground-water-quality variation are best described by sectors. FORTUNA SECTOR The Fortuna sector, in the northeast corner of the H139 Yuma Mesa subarea, is named for Fortuna Wash, an ephemeral stream which originates in the Gila Mountains several miles south of Telegraph Pass and extends northwestward, but nearly parallel to the mountains, to South Gila Valley. Except for the city sector in and adjacent to Yuma, the Fortuna sector is the only extensive part of the Yuma Mesa su‘ - area where water of poor quality is widely present. The sector, a dissected upland 2—3 miles wide, lies chiefly within “Gila Mesa.” Crossed by US. High- way Interstate 8, the sector has particularly good access from Yuma so that it has been attractive to picnickers and has been the site of several proposed desert homesite subdivisions. Land developers and purchasers of individual homesites have drilled more than a dozen wells in the sector. Analyses of samples of water obtained from seven of the deeper wells during drilling and testing sug- gest the widespread presence of slightly to moder- ately saline sodium chloride type water which usual- ly would not be considered suitable for domestic use because of its mineral and fluoride content. Analyses of samples obtained from three wells in the sector but west of Fortuna Wash, which penetrated only short distances below the water table, indicated the presence of water containing less than 300 mg/l dis- solved solids with only a little fluoride. The fresh water near Fortuna Wash, derived from the occasional flood flows of the wash. occurs in a lens or thin lenses, in part perched, overlying the more saline water in the main water body. The known thickness of the fresh-water body does not exceed 40 feet; the extent is less well known but probably does not exceed a few thousand acres. Development of this water of superior quality would have to be limited to domestic wells of small capacity, carefully spaced and pumped so as not to draw in the more saline water from below. The origin of the somewhat saline water of the main water body is uncertain; possibly it represents contamination by upward leakage along faults of brackish water from marine and nonmarine sedimentary rocks of Ter- tiary age. The abnormally warm temperatures of the water support such an inference (fig. 47). ARIZONA WESTERN SECTOR Extending south from the escarpment along the south edge of South Gila Valley between the For- tuna sector and the citrus sector is a tract of mostly undeveloped land which is designated the Arizona Western sector of the Yuma Mesa subarea. Two wells at Arizona Western College (from which the sector derives its name) are the only heavily pumped wells in the sector. Other wells are commercial wells H140 of small capacity along US. Highway 80 (Interstate 8) and scattered exploratory wells drilled mainly to prove up land acquisition from the State of Arizona and generally not used after drilling. Water samples obtained from 11 wells in the sec- tor show similarly constituted sodium chloride water with dissolved solids ranging from 800 to 1,400 mg/l. The two wells at Arizona Western College are of different depth, and the water they produce is used for different purposes. The shallower well, per- forated in the coarse-gravel zone and used mainly for irrigation (appendix C, analyses 517a, b), has produced water of higher concentration than that of the deeper well. The deeper well, perforated in the wedge zone and used for public supply, produces water like that pumped from the US. Bureau of Reclamation wells now supplying part of the water in nearby South Gila Valley (appendix C, analyses 518a—c). Mud-rotary-drilled test well LCRP 25, about 5 miles southwest of Arizona Western College, is gravel packed and perforated from 862 to 2,002 feet (entirely in the wedge zone) and, when pumped during a test, yielded water similar to and only a little more concentrated than the water in the deeper college well (appendix C, analysis 521). Although the number of wells in the Arizona West- ern sector represented by water analyses is small, the near uniformity of water-quality patterns and the general similarity to the patterns of water quali- ty shown by the more numerous wells in the south sector of the Yuma Mesa subarea suggest that the general composition pattern of the deep supply well at Arizona Western College probably is representa— tive of water that might be produced from any new wells drilled in the sector. CITRUS SECTOR The principal irrigated part of Yuma Mesa is designated the Citrus sector because most of it has been planted to citrus orchards. Analytical evi- dence indicates that the chemical characteristics of the ground water in the Citrus sector have been or are in process of being altered, owing to the infiltra- tion of imported Colorado River water. Several older analyses, mostly from wells no longer in exist- ence, indicate that formerly most of the ground water in the sector had the same chemical pattern as that occurring today in the Arizona Western sector. Concentration of dissolved solids generally ranged from 800 to 1,000 mg/l, with sodium and chloride the principal constituents. Recent analyses of many samples collected from domestic wells scattered throughout the sector indi- WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA cate the general presence of water that can be char- acterized as Colorado River water moderately evapo- rated and partly softened. The modified Colorado River water has sulfate, rather than chloride, as the principal anion constituent. However, because most of the sampled domestic wells in the Citrus sector are no deeper than about 200 feet, some of the water below that depth (upper part of the coarse—gravel zone) may still be of the sodium chloride type. Analyses of samples obtained from a few wells in the northernmost part of the sector indicate water much like that produced from the coarse-gravel zone in South Gila Valley. The analytical evidence cor— roborates the water-level data which indicate that water moved southward from under South Gila Val- ley to under the mesa prior to the development of intensive irrigation on the mesa. After irrigation on the mesa, and particularly since drainage wells Were drilled in South Gila Valley, the direction of movement of water in the northern part of the Citrus sector has been reversed and some reduction of salinity may have occurred. CITY SECTOR Most of the city of Yuma is on or immediately south of a peninsulalike extension of Yuma Mesa at its northwest corner. Only a few wells now pump water in this sector. A municipal water department (formerly a private company) supplies Colorado River water to residents of the city and a consider - able quantity of this water is used to irrigate yards, trees, and shrubs, so that it must provide some local recharge. However, because of the rather high cost of the water, many of the larger grassy areas around some of the motels and public buildings and in parks and school yards are irrigated by pumping from wells. This pumped water, although considered sat- isfactory for irrigation of bermuda grass, has not been considered satisfactory for use on salt-sensitive trees and shrubs. The parts of Yuma Mesa south of Yuma, and Yuma Valley to the west, are irrigated with Colorado River water. The part of South Gila Valley east of the city was long irrigated with ground water and has only recently been converted to irrigation with Colorado River water. The “Yuma Hills” on the east side of Yuma form a partial barrier to ground- water movement from South Gila Valley. However, the chemical character of the water pumped from most of the wells in Yuma is more like that beneath the South Gila Valley than that beneath Yuma Val- ley or the adjacent part of Yuma Mesa to the south. Most of the wells in Yuma yield water containing between 1,800 and 3,600 mg/l dissolved solids which GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA is like Colorado River water that has been concen- trated several times by evaporation and has under- gone substantial sulfate reduction and hardening. Other wells near the west edge of the mesa yield water which appears to have a considerable incre- ment of infiltrated Colorado River water. In 1962 a well was drilled to a depth of 830 feet at the Stardust Hotel near the center of the sector in an effort to obtain water suitable for cultivation of flowers and shrubs and other uses at the hotel. Dur- ing the drilling, water-quality variation with depth was determined by frequent measurements of spe- cific conductance of the water brought up with well cuttings in the mud scow. Both the quality of the water and the quantity obtained were disappointing and the hotel left the well unused. In 1963 an agree- ment was made for the U.S. Geological Survey to have the well deepened to bedrock (as LCRP 13) in order to further test water-quality variation with depth. Water of better quality was not found and the well was not completed as a production well and has since been filled in. It was concluded from this test well that there is little variation in water quality with depth under this part of Yuma Mesa (appendix C, analyses 573a—d) . SOUTH SECTOR The largely undeveloped part of Yuma Mesa ex- tending south and southwest from the citrus sector constitutes the south sector of the Yuma Mesa sub- area. Most of the sector was once programed for irrigation with Colorado River water but was left out of the developed project because the Congress restricted the acreage that could be developed. How- ever, as the south sector includes considerable land with soil characteristics similar to those in the most favorable part of the citrus sector, there has resulted much interest in developing farms irrigated with ground water. The development of a ground-water mound under the citrus sector, resulting from inten- sive irrigation there, and the continuing spread of this mound outside that sector, indicated that the ground water in the south sector was being recharged from the citrus sector and that this re- charge would continue and replace water removed for irrigation. Consequently, well development and some irrigation farming in the south sector was begun by private developers about 1961 and has in- creased nearly every year since. The analyses of water samples obtained from wells in the south sector indicate that the quality of the native ground water was as good as the recent Colo- rado River water, although it had chloride rather than sulfate as the chief anion constituent. Wells in H141 the northern part of the south sector, adjacent to the citrus sector, have generally shown changing pat- terns of water quality with pumping. Commonly the first samples contain about 800 mg/l dissolved solids, mostly sodium and chloride; after pumping the rela- tive amount of sulfate tends to increase and the dis- solved solids also increase to 1,200—1,400 mg/l. This change is probably caused by admixture of water infiltrated from the citrus sector. Farther south all the wells show the predominance of chloride over sulfate in a pattern that is so char— acteristic as to be recognizable as the original “Yuma Mesa pattern.” The average mineral content ap- pears to decrease in the southern part of the sector. REFERENCES Allen, C. 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D., 1931, On the origin of desert varnish: Am. Jour. Sci., v. 21, 5th ser., p. 51—66. Loeltz, O. J., and McDonald, C. C., 1969, Water loss in the lower Colorado River Valley, Davis Dam to Imperial Dam: Am. Soc. Civil Engineers, v. 95, n0. IR 1, Proc. Paper 6457, p. 65—78. Longwell, C. R., 1946, How old is the Colorado River?: Am. Jour. Sci., v. 244, p. 817—835. 1954, History of the lower Colorado River and the Imperial depression, in Jahns, R. H., ed., Geology of southern California: California Div. Mines Bull. 170, chap. 5, p. 53—56. Lootens, D. J ., 1966, Geology and structural environment of the Sierrita Mountains, Pima County, Arizona: Arizona Geol. Soc. Digest, v. 8, p. 33—56. GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA Lovejoy, E. M. P., 1963a, Reevaluation of geomorphic cri— teria of “Classical basin range normal block faulting” [abs.]: Geol. Soc. America, Program 16th Ann. 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WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA Wells, J. V. B., and others, 1954, Compilation of records of surface waters of the United States through September 1950; pt. 9, Colorado River basin: U.S. Geol. Survey Water-Supply Paper 1313, 749 p. Wilcox, L. V., and Scofield, C. S., 1952, History of the ground-water conditions of the Valley Division of the Yuma (Arizona) Project prior to 1936: U.S. Salinity Lab., Riverside, Calif. Wilson, E. D., 1933, Geology and mineral deposits of south- ern Yuma County, Arizona: Arizona Bur. Mines Bull. 134, 236 p. 1960, Geologic map of Yuma County, Arizona: Ari- zona Bureau of Mines, Univ. Arizona, map, scale 1:375,000. Woodard, G. D., 1961, Stratigraphic succession of the west Colorado Desert, San Diego and Imperial Counties, southern California [abs]: Geol. Soc. America, Program 1961 Ann. Mtg., Cordilleran Section, p. 73—74. APPENDIXES A-E H146 WATER RESOURCES 0F LOWER COLORADO RIVER—SALTON SEA AREA APPENDIX A. RECORDS OF WELLS Appendix A represents records of 936 wells in the Yuma area inventoried by the US. Geological Survey during the period 1961—66. These wells provide much of the basis for the interpretation of the ground-water hydrology and the subsurface geology in the main part of this report. Logs of, and chemical analyses of water samples from, some of these wells are given in appendixes B and C, respectively. Appendix A comprises five tables (16 through 20), in which the wells are grouped according to type or major disc. Within each able, the wells are listed sequentially according to their location (well number) in the Federal land classifica- tion. A description of the well-numbering system is given in the introduction of the report (p. H17). Locations of the wells in tables 16—20 are shown on plates 13—17, respectively. _ Not all wells in the Yuma area were inventoried in the present investigation; domestic wells, shallow observation wells, and destroyed wells were generally omitted except where special information was available for a well. The well inventory was terminated in the spring of 1966, but some well data were obtained as late as 1968. 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E4234 .md B Tm 44 H ----- .3000 --------- -- ---- 04.40 00-4N-0 4\.4 < -- -- 0N: N004 -- ---- c4.--- 3 mum 44 --- 04.4.4440 -------- - -- - -- 00 40 N0-4Nl0 \44 < -- -- 0N: N004 -- ---- owl- 3 0-m 44 -..- 00.4440 04 --------- -- - - 04.40 N0-4N-0 44.4 4 004 NON 0.004 N004 -- ------- 00-} B 010 44 ----- 0.4.340 44 --------- -- -HHH 00.04. 40404-0 .444 < 00N NNN 004.4 N004 -- ------- 041! 3 0-m 44 ----- 2240 Q --------- -- - 40.00 N014N|0 4\44 < 004 N4N 0.N4.4 N004 -- ---H4- 041- 45 0-0 44 --- 00.540 . w>.444w 44 ------ -- -- ------- 00.40 N0|4N|0 40.4 < 004 NON 0.04.4 N004 -- 4840280 .m.D 3 01w 44 --- 0.2040 3 .0 .44 0.00 0.9N 00-3-0 4.0.04. 000N|0 N\.N 44 0N4 0N4 0N: 9404 -- ------- 041- B 0-m 44 --- 4.4.340 4.4034054:me .5 -------- - -- ------- 04.00 N0-4N-0 N 44 mNN 0NN :2 4004 -- 4.. 4:02:44 0.44 3 0-0 44 ----- 0.3.440 a --------- -- ------- 44.00 40040 44.4 4 $4 $4 0N: 4004 -- ---w- 00-} B 0-m 44 --- N250 . 94.44% --------- -- ---- 04.00 4044-4. 40.4 < 4.04 004 004 4004 -- 4840280 .044 B Nam 044 N4 --- 3200 45354044004 .94me .4335 B .9 .44 .4 .0 0.04N N.0N 00-0 44 04.40 00-3-0 4 4. 409NN «SNN 0.04.4 4004 N0 04550 «E45 3 m-m N4 ----- 05.004 .Eozflga—uwm 3 .0 .44 N0 SN 00|0N|0 N000 00-0NI0 «N 44 0N4 0N4 0.004 0404 -- 4° 4:84:44 .m.D B 0-0 N4 --- N83: 442044400034 .3me .4335 B .4 --------- -- ------ - {-J ------- 0.44 4. 4.400 4.400 0.044 504 00 .3550 5:84 .5 01m N4 --- 40804 40420444040044 3 .0 .04 0.00 N40 00-3-0 4.0.04. 000N140 «N 44 -- 404 0.004 4404 -- 40 sawwam .w.44 B Tm N4 ------ 4.4.4.94 . Siam - ----- -- -- ------- -- ------- 4\.4 4 4.0 -- 0.004 4004 -- 4340280 .md B N-w N4 ----- 00804 .0 |---- -- ---i -- .. ------ --.i 44 [-1- -- 0.004 -- -- ------- e -- B. Nlm N4 --- N08: .5 .44 0.00 0.0N 00-0N-0 0N.00 00-0NI0 «N 44 0N4 0N4 0.004 4.404 ---------- 041- 3 N-m N4 --- 482.4 3.0 .04 4.40 0.NN 21.410 4.4.4.0 00-070 «\40 44 404 404 N004 9404 -- - ----- 041- ? Num 44 ----- 2.4.44.4 n4 - -------- -- ------- -- ------- 4.44 44 00 00 N.N04 0004 -- ------- 041-- B N-m 44 --- 4444445 B .0 .44 0N0 NNN 90104-0 04.40 00-0NI0 0N 44 -- 004 0.004 4.404 -- ------- 00-} B Tm 44 - ----- 534.4 B .9 .0 .44 0.004 0.0N 001N4|N4 4.4.00 0000-0 «N 44 044 044 0.404 4404 -- ------- 041- 00 44 ----- a «$04 50520034 .memD .8035 WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA H156 . . u» H25". 3: I as“ m i: 3 :H .0 93 NNN $I2IH. 2 HH SINNIOH N\HH h. :2 SH H mm 32 NN éwgffummafi B N m 2 H N I00 3 .0 .0 .0 3w NsN NNINNIN 3.2. HxTNNIN N\HN NH NNH oNH .0.me IIII No sawwwmgw D B mIm NH .HSNN . . . I l u N . III 350 ow . . 3 “wIw mm llllll 0003 a d .0 2H H. NNV NNINHINH E E. 8 2 NH .5 < 222 \32 N EH :2 H.E..H§HEM$WD . . . . . I I . I I . . III o H32: . . .5 7m NH ....... 2.5 3 a 0 a N: H 0N 8 NN N mN we 3 NN N «\a m 2H oNH H0 H2 :2 “dossuwmmw: .mhwmp hwudB . . . I II . h :5 «3:5 I IIIIIII 9 o B ..H. :H .0 .0 EH w NN SINNéH NN I 20 NN 2 N\HH H. m2 3H 0 NN 22 N2 0 amiamw 3 N w H5: 2 a N . . . I I . II I EN 32 III Name 80 .m.D I H ....... 2.5 .H. 0 mam H. NN mm «H N E N H; aNéH \HH < .02 N2 Heosroowflw .5 N m m .mkwwp 032;? . . . . . I . l N H A mm»: 2: 3:00 05:? I H IIIIII .300 3 a. A 0 H SH m NN 5 NNA: I. a 8 NNIS \2 H. 03 on m m dosgwfluwm 3 NH; w w m . . . . . H N.» wwINHINH 8.2. meNNIN N\HN m oNH ONH wmmmH :2 NH moIIHHwIwmmm .m5 3 mtm 0H HHIIHI SumsNIHHIov 3 0 Ha. w .m “.me Nam $IN INH MESH SIEINH NE < 5: N2 o «NH 82 ac NH NIw HN ...... 2.; .H. .0 d 3.2 EN SIN. INH 2.3 SIEINH SH < «$2 5: N2 :2 III ...... oH.III 3 Him NIw HEN 2 ...... 353 ........ I IIII IIIIIII IIII IIIIIII 0.: < N? N2 2: :2 III III. 21: B in HIm 2; 2 :82 .%0>.~5m IIIIII . . .va N.H.N 5N INH :3: STEINH N2 < 2H N: 32 32 HH 5&280 .w.D NH me 2 IIIIII SEN 3 .W. .w .M 0 mm wSN wwlmNIa m.mw cwImNIa «\HN M ca ONH v 9.: ”.me IIIIIII ovIII 3 mlm M: 003: Ill .Somadfiddumm IIIIII N5 .6 .Q ww 0.0m wwlmNIm fiww amIaNIa «\HN M ONH ONH NUS: 5.3 III .«IOIIHHINWWNIHm .M.D 3 Him 3 IIIIII 000m: . . . . INHINH NH”: EIEINH N; < 02 HNH NEH $2 ow II 0 HIm NH IIIII 362 .H. 0 MHH mmmm IIIII WININI M0. IIIII IIII IIIIIII IMIIII < IIII HH. .2 32 III IIIIIII 211 m me NH "H.302 Sexism IIIIII rH. .0 . NINE EN SIN LNH $02 $I2INH «2 < 3: EH £me 32 Hm HINIuwmIeWwHU .m.b NH NIw NH IIIIIII H.H.H.NH B .0 .m N3 0.2 $INNIN 5.5 RTNNIN N\HN m ONH oNH H. 2H :2 .zosfiHmaHDWIII B HIm 2 .33 . u m IIIIII .5 .0 .Q Hg NsN wwINNIN 3.3 HEINNIN N\HN m ONH oNH ”H: 5.2 III we 53:5 .05 3 mIm 0H annENNIHHIDV .nomaflugmaw .2me .5035 IIII 3. . . .5: .mn Dolmmlon mafia wwINNIoH N\HH h. mm: mm: Rama. wmmfi am 3560 “Ed? chIm mH IIIIHI 030m .H. A m m IIIIIIII wIII IIIIIII $0.2 SISIN SH < NHH NHH :N :2 IIIIIIIIII ouIII 3 in oHIm mH\H «H IIIII 32mm 9 IIIIIIII I IIII IIIIIII No.3 SINHIN w: < mm mm mi 32 III IIIIIII ocIII B «\N oHIm 2\H NH IIIII 9133 Q IIIIIIIII IIII IIIIIII 2.: SINHIN SH < 8 H0 .35 :2 III IIIIIII owl- 3 Him oHIm 2\H H.H IIIII SEEN a IIIIIIIII IIII IIIIIII Nd: HwIONIN #H < NH. NH. mi. $2 III IIIIIHHI ouIII .5 «3 Elm NH\H NH 355 . 0?:Hm IIIIII a .n. d :2 3N SINNIOH «Ni $INNI2 SH < :2 N2 5. 32 III HISHNoHooo .w.D B cHIm N\H NH I IIIII SENN 3 ..H. :H .0 $2 RNN $INNIoH 2.2 $IHNI2 "E H. 2H 2H mg 32 on IIIIII ocIII B NIw HH SNNH domafloowmdw .mgme .5903 IIIIII B ..H. :H .0 H2: N.NN NNINNIoH 8.2 ETHNL: "x: 2. N2 N2 H.H2 32 Ho .0580 «ES» 3 oHIm HH IIIIII £62 a d IIIIIIIII IIII IIIIIII 8.2 SIZIN SH < 02 m2 :2 82 III IIIIIII 8.} B 22H cHIm mi N IIIIII SEN a d IIIIIIIII IIII IIIIIII NNNN HNIHNIN «N: < «N «N .32 $2 IIIIIIII . II oH.III .5 ¢H\HH cHIm S N IIIIII Neg—N a .Q IIIIIIIII I IIII IIIIIII NN.NN lewNIN «VHH < N0 N0 :2 82 III IIIIIHHI £11 3 0Q: oHIm 3H N NnNHHN . 0>k-m 0 d IIIIIIIII IIII IIIIIII 3.2 HwIwNIN SH 4 NN NN :2 :2 III $30280 .m.D B 22H oHIm mi N IIIII SENENISIO. .fiomufimoOmé .mxwwD .kuNB .5 ..H. :H as: «.mN $INHIHH SHHH $INNI2 «.2 2. 3H 3H «.5 $2 8 .3560 NEE» B wxm 7m 22 «H IIIIII ENNN n IIIIIIII I IIII I IIIIII IIII IIIIIII «\HH 4 N2 N2 «N 32 III IIIIIII oH.III 3 7m «H IIIIII NNNNN szsm .H. .0 .0 m2 NHN NEHIN £5 $INN$H £2 < N2 52 NN $2 III HSHMOH80 .w.D B N\H NIm NH HHIII 233 .5 .G .0. .0 d 3.: HEN NHTNHINH 2.2. wwINNIN «\HN m H02 H02 22 2.2 III IIIIIII oH.III B me E III SewN down—«53003 3 .0 d 5:. HEN SINNIN 212. $INNIN N\HN m IIII H02 52 2.2 III we $250 0.0 .5 Tm NH HHII .HaflN B .H. :H .0 3: EN SINNIoH :2. SINNéH N N 2; 2H 93 $2 2 IIIIIII ocIII .5 me NH I NENNN dofimmoommgw . . .mhme hwwwg .5 .q IIIIIIIII IIII IIIIIII oN.m SIN INH «2 N «2.2 «.32 93 32 N» .3550 «E; B mIm NH IIIII HannmNQNIcHIov “ m. m m m m m m m m w u m . pm a .m m. m. m m m n m m s u. u. m o .m. I n J n l. D. a D. D. 3 J u my D. 1. a a 0 u I. 1. o a d 0 m n a w: m a I. P 1 I. d w .63 033??» w W e m m D. u.. N. N W. .8 03050500 :03 3% .550 q m w u m u m. 1 .6550 w. 1 n m... m P P 0 m. u. m 003000953 0303 Hw>w~ 035$ umnfinqoolsNuS 0833333 :osafifiowfi .8 33935 $5 03033 30 :52: 203003039 @089 0833331 .335 5833 9:330 033..” $02: “we... 30 022* 3.3 $03.8 020.03% Naomqsgw .MSISH "35.8 H157 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA .mafiwfiwunmuvfi ousamuwafiwa omcomuwma £93,559 a .21: 02 H a .9 .9 $2 3N 212-2 2.“ 2-N -HH «2 4 NNH EH m2 H52 -- - ...... ocl- NH N2 72 N5 H IIIIIII £05 a d 92 SN ww-N -HH 2.2 5N -HH \HH < H5 H2 :2 $2 -- ---w- OHM- "H N5 72 m ...... £55 . >k= .e d :2 EN 5-2-HH 2H 5-H -: «2 < NNH 5H 52 H52 -- 333600 .m.D m H-z H ...... 8522\on B :H NHN :N 2-222 8.HN SEN-2 N\HH H. 52 N2 :2 22 52 ....... 81- 3 N5 o-c ...... .502 B .,H. :H .o :2 EN 5-2-2 2.: 2-2-2 N2 H. NHH NHH QHNH 2.2 5H ....... 8-} .3 w: H-o ..... BHHHN B _.H_ 4H 3: NAN 5-2-: 2.2 55-222 N2 H. NHH NHH :2 $2 52 ....... 81- B H-w 22 c ...... £55 .iOmadeOmm< .225 .533 B :H 5.me N.NN 5-2-2 22 5-wN-m “2 H. 2H OHH :2 22 52 3550 NE; 3 m-w 22 a ...... 83:». a .w d m.HNH-m.NNH NNN 5-2-5 -- ....... N2 4 2H2 N2 cNH $2 -- ---- 8-1 B N\H H-m H\H o - ..... 8m; a d 52-52 EN 5-5 -m -- ------- H2 < 52H 2H 2H 52 -- ------- 31- 3 H2 5-2 25 o ------ 852 a .H. d NdHH oNN 5-2-2 52 55-NNA2 H2 < NHH 5H 3.2 H52 -- --.- 21- B m\m “-2 55 c ----- 2302 0 .Q 87:: m.NN mw-m -m -- ------- H\HH < 8? SH ONH m2: -- ------- 2.1- B Him 72 H\H a ----- $25 a d 5NH-HNH 3N 55-2-5 -- ------- «H2 4 5NH 5H 2H H52 -- ------- 31- 3 72 H2 5 ----- «SEN o ”A .6 c.2H w.NN 5542-: Ha.” ww-m -HH H2 < 2H NNH WHNH H52 -- ------- 8-} B N\H o-z H ------ 3mg 0 .m ”.H. 3.: H.mN 5-2-2 2.: 5-HT: «2 4 2H N: 5.2 H52 -- ------- 8-: 5-2 N2 o -- N222 a ,H. a @mm-Ii mwN-N- mmme-MH-H NEH-H mmnw-MH- uH-Hm-I « Wo-H-H mmm- mum «WNW Hm ------- 3.--- B 2\ HH o-z N\ H H ------ HamNN . ------- o -- ------------------------ SomN .0 .Q NNH HEN 5-2-2 2;. 2-HT: H2 < 2H 5H 5.52 H52 -- ------- owl- B N}. H-z N\H H --- VouuNN a ..H. HH 0.52 w.NN 5-5 -H H55 5-5 -H «H: < NNH 5H 5.22 H52 -- ------- 21- B N-z N ----- HSQNN a .9 no :2 H.NN 5-2-HH 2.2 5-5 -H «H: < 2H 5H H.wNH H52 -- ------- ou-l 3 N12 H ----- EEHN a ..H. .n :2 H.NN 5-2-HH 2N 5-5 -H 2H 4 2H 5H 5.52 H52 --- ------- 31- 3 5-2 N\H H --- €ch 0 e a HNH EN 5-2-5 2.5 8-HT: «2 < mNH 5H 32 H52 -- ------- 8-} .3 N\H N-z N ----- 2&2 . .Q odm 9mm ww-N I: 5.5. ww-N I: H\HH < we I-- ad: $3 1- IIIIIII ov-II B \H mlz w\s N IIIII 33H: 0 ..H. .Q 32 HEN 5-2-2 5: 5-5-2 «2 < «$2 N2 :2 H52 -- ------- 31- ? NxH N-z m)“ N --- £52 0 H. m 9mm mfim bwlw Iv --I mw-bwlcfi NH“ <4 MWH M: a»: 1:: I-- ------- ow-I- B meH o-Z N\H m IIIII was: -------- - -- ---- -- ---- HH HH N2 H52 -- ---- o -- - --- a ..H. d 32 MEN 5-” -5 EH 5-5 -H SH < N2 32 :2 H52 -- ------- ow-i m H-zonHH M ----- "aw—mm” .Q IIIIIIII I IIII IIIIIII III| IIIIIIIIIIIII I 6- AHV bra HMH wwmm III IIIIIII owl-I B w\H H rz m .-|-I .. ofiflcn B .Q 95 HEN 55-N -: 2.2. 5N -HH «H: 4 .22 2H 32 N52 -- ------- 31- 322 5-2 22H H ------ 3 BEN a n 9N5 2N 2N -HH N85 55-N -HH «H: < ma EH N.N2 H52 -- ------- 31- 3 25 o-z H\N H --- Bwmm B w\H o-z N\H m NaumHH-MHNNEmH a .H. d N.N2 22 5-5 -NH :32 2-2-2 H2 4 N2 NON NNON $2 -- 1.55280 .m. --- . . . . . . D H H-m 2 N HN as B ,H- A o NNH N NN 5-2-2 Hm 2 55-NN-2 «2 H. N2 N2 92 22 o2 ------- 8}- 3 NS 2mm 2 ------- «amwANN-NH-o. WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA H158 ....... -- -- --- ---- ---- l- - - 3... -- ------ -l-- 8--- B S; Tm in m - 1.8.32. L0. O moa‘mmH .5355555fl ..H. .d d EH-mNH .EN RTE-N 0.... 3-”le -- -- 8 d ..H. EHImNH «H-VN 0mm EH SN 9me ENH 2750-0... 28:5 .m.D d {N Tm «\H N -- 2.3.. O .Q 2.73. EN 5-2-5 5.5.. $4..” In -- -- S d .5. EHémH «N 0 .2: EH N.ONH 5...... H ------ o..-- B N\H Him wH\HH N .- NoncNm .EOmufimUOmm< .thmp #853 ... .n ma QNN 5-.” I... -- ----------- -- ------------ -- Q - N\aNH N.ONH SNH m 5.me .3550 was... .5 N\H H-w 5H). N - . HoprN O ..H. d d NwHINNH E...N SIS-N N.HH EINN-v -- -- dd 9:12: «HIVN 0.... SH mNN NNH ENH mop-mo -------- 3.1- d N\H 0% «\H H -H nuaEN dad wNH-wNH 3N EIHNLN NE meNN-v --- -- ------ wNHIwNH «EN 55H EH NcN N.me ENH oHE-mo -------- 0..-} d «\m H-w «\N H - 5..ch ..H. dad «EH-«NH H.NN STEIN H... ENN-w -- -- 3 d ..H. EH-«NH vH-VN wmm EH EH ENH $3 mop-mo -------- o..-- d «\H Him N\H H -- 0.838le L... .9940... NN EN BEN-OH NEH EL. INH -- -- E d ..H. HNwéNm .H-ON 0m NNw 5... 5.3.. $2 $750 --------- 0.1- N. NE 515 5H\HH N -- .55....” .5... do... awn-«w. «.mN 5-HT... 5.: Elm. rNH -- -- E d ..H. £54.... .HIcN cm 23 H8 m5. 1.... HE-mo -------- o..-- d N\. Tm N\H N - N583 .EnH .A .9 85-25 A...NN HTS-N 5.8 31.. -NH -- -- E d ..H. 85-8... «HucN 3. 3.. 0H. 3.3 .me oE-mo -------- o..-- d Tm N}. N -- 2.3.5 o d .Q omH-oa N.NN wulcmlHH H.N Ho-EHIN .5... 83 a. d ..H. 2:12. 3-3 0.. 8H «oN N.N..H H5... m Snow -------- 8-: d m-m m -- 8on a d omHImHH 5.NN 51.. I5 N... SIS-m -- -- 8 d ..H. ONTEH 5-8 0m .5. EN 5...: SNH 5 250m -------- 21- d mlm N\H N -- .553 Q 37...: N.NN 2T... 4HH WHN 3-... -NH -- -- ------ 2.7.... 3-3 0.... .5 mm. 5...... E... 5. Snow“ ------- o..-- d N\. #5 N\H N - N583 a .5. d ------ N.NN H5$HIE 5 5-54 3.... com.” ------------ ZION om - SN New. HE: E 2505 ------- 0.1- d N\H mlw N\H N - Haaomm a ..H.nH ..H. .9 ETEH 5.NN STN INH SH NwlmHlm -- -- 8 d .,H. $7me 0N 0 EN HVN E2 NEH m 250m --------- 8-: d 05 N\H N -- .63» a d .n. ooNlo... YNN glow-S a... SIS-w mm... 8.3 2. d ..H. 8N0. 5-3 0... SN SN «.3. H2: .. 390m -------- 3.1- d N\H Tm N. -- EENN a d .9 «ON-«NH N.NN SIN IN -- ------- HN.¢H 03% co d ..H. ENINNH wH-oN om 3N wHN 2.3 H52 N 2505- ------- 31: d Tm m -- 8on a d .9 amH-vNH wNN SlaNéH hm. Hc-wN-m 3.2 +03..." 8 d ..H. NwH-vNH 518 .5 mm. EN 9:; HEH a Baum-MIN} o..-- d Tm N\H N -- 5.5% a d .Q EN-omH MEN SIS-N N...“ SIS-w $.NH NE... 8 d ..H. EN-cmH .H-oN 0.. EN wHN 3.... H2: N 35%.: ----- a..-- d N\. «15 N: N - H.555 a d ooN-cm. N...N 5-5 <5 .5 HmIHle ENN NE.» 3. d H... .313. 5-8 cm 8N mHN 5.me $2 . Baum-s- ---- 81- d «5 N\H N -- 85” a ..H. .q .n 5|on SN ENNIS E... mw-N INH -- -- 8””...8 1.7on 5-3 5.... EH .2 m..me Em. 5:150 ------- o..-- d N\H mlw 5H). H -.- 05......" a ..H. :H d SHIEH .25 3-3-3 3: «5-HT... -- -- 8 d .H. EwH-EHH «TON 0.... NS HEH 9m... 3:... 5750 ------ 21- d m-m N -- .oowN a ..H. .4 .Q EH-E N.NN 55-3-3 «.5 3-. 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N2: 1 :2; .m H N\H NHIm N\H m - H8»: a :2 NH” SINNIN $.va wwaNIN --------------- Eon ------ H. 0 Sn H5 NS. $2 - 32%»: m NH; «Tm 22H HI I- .unvNH .hD IEmhow c ------ II-I ------ I-I- -------------- Nd .H. :89 “com-3 w HH owN Hem mvm 2:: .H ..H. .3 m .33 NHIw S H. -II H23 . 55H. 0 ------ --I ------ -- -------------- .HH. :5: ------ N UHH mwN wwN 5m -- :H .o m NHIm N\H H. -- 8e: .333. ------ -- Ill :3 SIN IN II-I -- «\mfifi Eon -I--I m cm EN EN SN 25H .,H. .2 NH 33 aIm SSH m -I- News. ------ III- II---- 33 SIN IN -- -- ---- Eon III-I- N 0 SN oHN SN SS IESFMSHH NH 23 NIm H. -- HHoHaw .n 00 a ------ --I ------ I-II -------------- mi. :89 ------ N an RN 8N 3N --I .3 d H NIm SSH m I} 88 do a ..H. d 9me H23 SIHNIN @me SIHNIN --------------- Eon 27ch S 0 Hum Sm mg 32 553m 25 H m\ H mHIm «H N 1- HaunNHHNIa I9 .EHmh 39:05 .22me SSE-JV “Ho 0 d ------ -- ------ m.» HeIoNIH -------- N.H.H.H. ewes: NHHIHHH w o NNH NNH N: 32 $983.5 3 SE mIm H III SEN .§E:B a ------ -- ------ w NwIH Iw -------- N\H.NH .o :89 37% N .5 3 3. «NH IIII m .m .m B N\H N In Sb. H -- ESN . :55 Q IIIIII IIII IIIIIII H.» levmlv IIIIIIII N .mm .h Eon momlam wlcm 0 v: v: w: mama 5? .H 5? v)” nlw 3:: c III “ovum a ------ EN N: IN N N: IN -------- H .m .0 Son ------ m o N: EH wHH --------- 8-: 3 NH; mi H III HVENN 50 33.8% a .Bm .HH ------ -- ------ a.» SIHNIN -------- «\H .m .H. am .5 NHHINHH «N 0 EN «3 SH 82 :wHa-HOQHH B in mIm H -I- BONNGNIHH I0. .0 amok—Eco a .n ------ II-I ------ 92. SIN IN 9.3 mNN om .NH .8 E: ENImNH NH II NH.» New oHN NmmH Exam H.H v: NIm m -I- Haven 0 mulon vim «win In IIII IIIIIIIIIIIIII H .0 Son mmIom N\HH .HQ mm mm nNH ------ 8:5 .H B «\m Him m III 35% O mules Han main Iw IIII IIIIIIIIIIIIII m :89 mulcm «\HH .5 mm mm umH IIIIIIIII m McIII 3 m: HIw w: m III :on .hw MM 0 ------ HEN SIN In -I- -------------- H .m .0 Son ------ N II 5H SH SH I: ..H .H.H 3 NE Ta 3; N - Naaon 3:2: 0 mHIeH N.NN NHTH I3 3. NoIH IcH -------- m\H .NHH :59 NT“: «HH .5 NH NH SH 2:: m .HH .H. g NE HIm uH\H N -- NNSNN And: =w> a 97.2 N.NN NoIH I3 3. NHT IH. IIIIIIII ”\H fig. :59 £73 £3 .5 a. S. oNH 32 H W .0 3 NE HIw HE H N - HSENN do a E a EHIcNH H..HN NwINNIN n.NH NeIn IoH -------- Nd? HEH EHIcNH -- 0 SH SH uNH $2 ammbMom B «\H NIm SSH N 1- €ch . 2533 a .D INHHISH 3N 1TH. I... E HerHIv IIIIIIII ad ..H. HEH NHHIHSH w 0 ”NH eNH 3H 3.: Eco 55m 3 7m «\H H -- acuNN Q ----- --I ------ I-II --------------------- Eon NNHIEH m 0 3H 3H 3H NNNH - .655» .H. B a}. eIw N\.H H -- .ouwN .5552? n ------ I-I IIIIII NH HoIHEIH IIIIIIII N .H .9 am .88 IIIIII v 0 EN SN 9.: $2 .oomumB m waN elm NS H -I BEN Q IIIIII IIII IIIIII IIII IIIIIIIIIIIIII E .H .H. E: eNHImHH NH 0 N2 «mu mm: 33 amwgfiscm clm «\H c III 8:3 .hh—yHHHHaH a .n IIIIII I-I- IIIIII S ETNNIH. IIIIIIII Md HEH woNIoeH w o 8N EN 5: m2: 8 NHN puma SEEN 6.23 we 25 ad awn—@508 3w 3 «in Tm wS N. a 2‘5. HIM v\~ N. BmImw 3 v} eIm h. m a) NIw a m wk Tm m: w H w: Tm N} w H «\m NIw {H v H «\m wIw v} v a S} Tm 2: v a 23 on S) w. B S; oIm wk q B B N: oIm w B S; Tm 3 SE Tm B NIm Q B «Iw «E m 5? wH\_~. ofw m Mn w~\a elm v H NIw «\b m "A um\~. alww\m m "N V\H NIw SKHH m m S): Tm a} m m 32 me p m wH\r mIm 3}“ m Illl UUQN Ill NfifldN II Gwaiwula I3 I I I 9.33 III wucmn “33:" H moan” III 2.3» II £3; I I I unoaw I H awaaN ~ OUUWN III fig" III £53. III £34. 3.3% acum— oaawfi I m 93: III canon III :63 a Hogan IIII anav ovum «can IIII «can H can; . 2.58.1. In: agacm II. HaanNN III E62“ III 38: II H 35m.“ III :03." llll 669% WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA H168 .mEonzo a .M mmH-DHH «Q «mix-3‘}: ...... . IIIIIIII «.M.m mm .58 mmH-mHH H. 0 9: EH «2 82 co .m.D B «\H w-w in o - «253 . quanH M ...... -- ...... -- .............. M .m MMdnH 3-3 m 0 2: 2: ««H «2: Ewfiaow B «\H “Tm in o - HHBamm-M\H«m3 a llllll -- llll «.3 S HHI«H llllllll HM... Eon ...... H. M 3H SH EH $2 «$35 .9 M «H; mlz wH\HH m - 3M9.» Sofie: 455:5 a ...... -- llllll -- IIIIII -- -- H.M.H. son :25 w m 8H o2 «.2 $2 .5 .m .M M 3:. ”-2 «\m m -- uuMmm-Mmfimfi . Eflhw a ...... 9 3 «w-fi-H -- .............. H .M .H. Eon ...... m 0 8H 3H 8H HmmH :66 .md B SEH «J. «E S -- AH8«H .00 9335 a d IIIIII -- ...... SH. HATS-H 2 3H M.9 mm 8T9: m o «H« «S SH SH: ”:5 5m B a; «1m «3 S -- MHz—«H . 933m 0 .M 372: m«« «9-31 -- .............. $1M .H. ES 37me o b m2 «2 o2 H9: < «:35 B in «um «\m H: -- Sn«HS«-HH|3 a HH: -- ...... a «m-H. Ia uuuuuuuu «\H.M.H. Eon ...... « - SH SH mm MNm-H wise .m .< B «\H oH-m «\H «H -- EEK a - -- ...... H. «.1. $ ........ «\H .M .0 Son 111111 « SH SH «9 - mmfimfi .M B «\9 m-w «3 HH -- 5325-36. . M a ...... H. 3 $4«« H. -- .............. m.M .H. am .55 ...... w 0 9H« :« 2.. «Hz: .aH ..H B «\H w-m 3m MH -- £53 .HEH .oo 5:8 a d ...... -- llllll o9 3-H. 1m llllllll m M 9 Eco omH-«mH «H o «a. «NH. 2: $2 ExmwB B 23 m-w HH - «£an a IIIIII -- ...... -- .............. H M 0 am Eon ...... w -0 3H 3H 8H,}: - $.89 .M B S; m-m HH -- 2.2: a ..... -- ...... -- .............. H M .o Hm Eon ...... - -- 3H 8H -- $35.5 .M B m: M-m SE S -- was .33w 0 llllll In-I llllll III: llllllllllll «\H .m .0 Eon mwlmm « .HQ mm mm m3 -- 255:3 3 rlm m ..-- :9: .69; .90 £8.50 a d ...... -- ...... 9m «w-fi-m -- -- 91M .9 Eon $795 3 o «>me «$3 «2 «3H ESWB B 32 m-w «\m m -- 2:: .o H .muom Q . .0 ------ -- ------ -- -------------- 91M .0 H5 ------ a n -- SH 5: --- .383. .B B 1H Tm a -- nafiSN-eH-ov a o o ------ --- ------ Em s-«H-H. «H Sm M E: «mN-«HN «H 0 ms 5 2: H2: unfiwofimd B N-m S: «H - .523 a n ----- -- ------ -- -------------- $1M M. Eon 8«-§H E o m«« m«« 3: «NE M «:5 B «\H H-m oH -- 83 -- |-- ------ -- --------------------- Eon ------ c Q -- wwM wmu -- - a> am .3 3 oH\a le mi: a -- chon 9 .0 .M wwH «.5 MI. xHH «.8. 5T” -« --------------- Son .37an w 0 HH« HH« «.2: $2 353 .M .m B waH o-m «\H m -- H35 5030.. Jam-Hanna G IIIIII IIII IIIIII cdm wwlm lm III: : H .H .9. Eons :wMO w m c3 :2 m3 cog .< .m H wH\: 01¢ a IIII «5me a HmH-EH H.w« 8-HT» Hi. Hw-H.«-u -------- «E .M .9 son me-EH m o 2: 3: «3 $2 EmEMHa MW: M 23H o-m wH\ H a - «aaafifiéH-g . . VN . .0 2: 3a $IHH-H 32 wu-HH-H -------- w .w mnH ------ «H o «Hm. «Hm $3 mmmH Era-So .m. D M 23 w-m waH «H naa««A««-eH-ov a o M ------ -- ------ -- --------------------- mm ------ «H 0 3H H SH; «.2: 39H -- 21- B «\H m-m 33H m - 203m 0 ------ -- ------ -- --------------------- mm ------ S o -- -- «.SH -- ----- 8-: B «\H mum 33H m - «€31» .EOn—kwgow B .a .n ------ -- ------ H.«H Hw-«H-H -- 8o.« o«.M .0 mm ------ «H o mH« ms «.2: 82 MEWS B «\H m-m SEH m - H 393% .5an handoo c d H ----- -- ------ -- -------------- o« .M .9 mm an-EH «H o «3 «3 8H «3H 55.9 B «\H 7m «Em -- $3” a -- -- ------ --- --------------------- Eon ------ -- s- -- -- 8H -- - oo muooB B 7m «\H9 -- 033% do Eofion wozuohm a .n HHH- -- ------ -- -------------- «MM. Son :86 m o m«H mNH HHH 9:: {HES-92 BEE HT w w H} and? c - II ------ -- -------------- «\H .Md Eon -- m M SH SH SH -- :wwmmml B 3: Tm «\9 w - H363 a HHH -- ------ -- -------------- 91M .9 um .53 ------ m M 2: SH «HH -- 1.26 B «2 Tm 9 -- 25% a -- -- ------ -- -------------- {MM .H. can ES :25 « M «2 «2 5H HmmH Siam .M B 7m 3:. m - 2...: a ----- ---- ------ --- -------------- H .M .0 son ------ N S 1-- -I- 2: -1- 4.33:: M B 1H m-m 2... m --- 33H 0 -- III- ------ -- -------------- m .H .9. am .EoQ ------ w - 39 o«H a: --. ----- 21-1 B 33 Tm «\H m - «at: .00 2350 . ------ 53> -- a a ------ -- ------ 3H Hw-HH-H. -------- m. M ..9 $1.59 375 w o ”2 3H mHH 35H «5-;- B 1 H. m SE n -- £6: a ------ HH- ------ -- -------------- m M M. :89 ------ H. 0 3H 3H 2H -- ----- oH. - B {H mum ¢H\HH H. -- 33H G - ------ -- -------------- «\H M D :59 «19.9 « .5 H« H« wHH «m3 -- MED .w 3 «\H «I33 v E63 ------ do 235 - O --|- ------ -- -------------- m m 0 am ------ -- -- ow 3 M: -- mEMHaB 3 wlw H. - £33 mEEEB a ------ -- ------ -- -------------- «\H M 0 son 3-H: N -- 8 3 w: .1. .m .H. B S: m-m a: m 1- £33: A: II o u. l. “m a m m m m m :- 9. mm m. m m. m. w a PM a m m e a «a 9 mm m. m. m m u. m .r- q M w 9 a A u .w. o m - n n I. 1 o I o m... W0 D. a P w. m nu o u a ma 1. m o m m o m w I. m n n d B I. P 1. I. a 92:95: Sana-«>6 a a a w a m m P u. I N 55° nwaunmuuooo :03 33. 1 m... d n. m u a m M ES .53 .550 W 1 W m 1 m m. P .5 .3550 o P m n m M P W H m. a u m 333.5953 «335. E >2 M355 wwnzfisoolflfis mMSSEEQSEI. ow Mafia. H169 .509 .Ho .55? £58.52 335.3 E; cadadnomfiwu ”91:5 whammy; 05$ 05 35 39:59 N Had a m=o>P~ GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA 693.589: .63:un— .326m 0 d ooN-ONH H.HN lewHIm HHH SIS-H. -- 8N «Edd. mnH coN-oNH w 9 EN EN 2: $2 383m 5% H waH le an H - 2:22 85393. .uémhkon uuuuuu -- --- -- --- -- -- «\HfiHfi. :89 5.5 N - moH 3H NmH wmaH NH .3 NH ¢H\H HIZ «\H N - SHE: .95 cm a ...... -- IIIIII -- llllllllllllll «\H .mHH. Eon IIIIII N - -- mHH «NH 82 .m .HH mH NxH H-z v -- $3 50309 dot/om IIIIII -- --- -- --- -- -- «SEA. :89 550 N .5 8H 3H mm: 53 .m ..H H N\H m-Z SE H. -- 80v 111111 -- Ill ”5 Hw-HHINH -- -- Hdé Eon «NH-mm NH o HNH HNH mmH HmaH Jan—co .> .H. m SH 72 9H; H. -- 8m: .mfifihom a wHHImHH HEN SIHHINH -- llllllllllll «RAH;- .am.Eon wHH-mHH «\HN - mHH mHH 3H H2: 2H..mm..H. m 72 m -- asnm-fimNEwH .x . H. o d ...... -- llllll -- lllllllllllllllllllll Eon SHINNH H. 0 ”NH mmH «NH -- d M m 23 ale - 3mg .Eom a iiiiii -- ...... -- .............. Rind. 04 $12 NH 0 3H NS 3H 32 3.26 :«m B w\H HTm a; o - gamma :8: -£8mm< .2me Hen—35 3550 a IIIIII -- IIIIII -- llllllllllllll ma Eons; :T: w a g 2.. «NH -- £55 3 2b. cam 1H o - .3me ESSA a ...... -- llllll -- - lllllllllllll NamHH. .3 :25 m o ONH oNH ”NH 32 9:55 .3 .H. B 33 m-m N\H o -- uPHNm a .HH ...... -- llllll -- lllllllllllll ad. 5: Eon NNH-SH S O «NH EH mNH 35H lllll 2.1- 3 3H N-z 33 o - 25an a NHHIaoH H.HN EVAN-N -- lllllllllllllllllllll Eon NHH-SH n - NHH NHH wNH «me lllll 31- 3 m2 N12 SR o - NaammN a ..H. mmlmm N.HN EVAN-N -- uuuuuuuuuuuuuu mi Eon mum-mm «x: .5 mm mm wNH ...... 2:15 .HH 3 w\ H le 33 c - SSHNN a d uuuuuu -- llllll -- llllll - llllllllllllll Eon ...... a 0 EN NmN mNH N2: 45350 .2 B N\H le SE a - NuanHNN .«EHHV llllll -- --- -- --- -- -- ---- afiéon mHTOHH e o NHH mHH NH 3,: Ho 36 B «.12 NH O - BZNN Saxon a ------ -- ------ -- -------------- ad :8: :25 H o 2: 3H m: -- -2328 .2 3 NE N-z 23 c - 8an .35.? a ------ -- ------ -- -------------- ”\HfiH .0 am 589 mm-mm N\HH an mm mm A“NH N2: Ho 35 .5 oH\HH le 3H c - nompN a .n SHImMH EN HNH-NH;- SH 8-2;. -------- «Edd. mnH SH-mmH NH 0 SH SH 8H «m2 - 236m .vH 3 H12 N\H o - HaeEN n ------ -- ------ -- -------------- H A. Son ------ N - -- 3H NH $2 :862 .< .o B N\H H12 33 o - «SEN .wogaww . ------- . .anHH 0 .HH -- -- ----- 3 $1 IHH - - 3 ma. wnH SHISH 9H 0 2: «in: 3H 33 33am .w.D B 8:. clz NH; o -- 3ch a Q ”NH-HNH “AN mwllew 3H Hm-aNIoH -- -- Edd wnH ”NH-HNH NH 0 HHH HHH 8H 2:: - E958 .vH B 72 N\H o -- SEN 485m 9 ------ -- ------ 9m HwINHINH -------- oN.mH..H. mm ST: N o HNH HNH mNH ommH 5%.: .TZ N: o - SHEEN .8 2:35 .0 IIIIII HNH IIIIII HHH- III-II HNH. IIIIIIIIIII mm umHImmH w 0 5H 5H mvH mNaH Ewfisom 3 SD. HTZ w\m H I..- «ONT-"3&9; a n HEN a .8 EH AVE-HS 3 o :3 2:. SH SH: ----- awn-VI B in m-w m}. o - 32¢» 333m . ------ -- IIIIII . . 33an a a HH SIH 1e He 8.. m m .H. E: NHalem ON 0 «5 NS SH $2 2:52 3 wk m-m Sb. o -- 5&8 507-243 0 - '74 - 12 H170 WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA APPENDIX B. SELECTED LOGS OF WATER WELLS Appendix B presents logs of 61 water wells and water test wells in the Yuma area. These logs, which are selected from more than 700 logs in the files of the Geological Survey, are probably representative and give good areal coverage. Logs of most of the private wells are by the drillers; those of the test wells are by Geological Survey or Bureau of Reclama- tion geologists, based on sample studies and borehole geo- physical logs. The materials logged are assigned by F. H. Olmsted to the various water-bearing units described in the text. The well number given for each well is that given in Appendix A, tables 16—20. The name following the well num- bers is the Government agency that drilled the well or had it drilled, or the owner or user at the time the well canvass was made. The type or use of the well and its approximate location are also listed, as are the name of the driller and the type of drilling equipment used. The depths of perforated intervals are given where available; these are indicative of the productive horizons within the respective areas. Altitudes listed are of the land surface at the Well from which depths were logged (mean—sea—level datum). Altitudes given to the nearest foot are approximate and were estimated from topo- graphic maps; those given to decimal fractions of a foot were obtained by spirit leveling to a reference point at the well and are much more accurate. Other information about the wells is listed in Appendix A, tables 16—20. Selected logs of water wells Thick- ness (feet) Material Depth (feet) Well (C-7—22)14bcd [U_S. Geological Survey test well LCRP 14 at Laguna Dam. Drilled with cable-tool equipment by Hamilton and Hood. Log by F. H. Olmsted, F. L. Doyie, and F. J. Frank. Casing perforated from 118 to 128, 152— 162, and 4107490 ft. Altitude 155.1 ft] Upper, fine-grained zone: Sand and silt containing plant fragments; thin strata of clay and pebbly clay. Upper 14 ft represents fill accumulated since construction of Laguna Dam __________ 16 16 Sand, fine to medium ___________________ 4 20 Sand and silt containing plant fragments; some clay ____________________________ 8 28 Sand, scattered pebbles, and some clay and silt __________________________________ 9 37 Sand, medium, and subangular gravel ____ 3 40 Sand and silt containing plant fragments; some gravel and clay _________________ 13 53 Sand, fine to medium; interbedded pebbly silt and clay _________________________ 16 69 Sand, fine to medium, some gravel; thin beds of silt and clay _________________ 31 100 Sand and gravel, scattered cobbles. Gravel includes well-rounded siliceous rocks ___- 3 103 Sand, fine to medium, some gravel; thin beds of silt and clay __________________ 11 114 Coarse-gravel zone: Gravel, well-rounded to subrounded; con- tains cobbles as much as 5 in.; some coarse sand and cemented streaks ______ 14 128 Sand, medium to coarse; gravel contains rounded pebbles and cobbles as much as 3 in.; some silt ______________________ 7 135 Sand, fine to coarse; scattered pebbles ___- 4 139 Gravel, coarse, rounded _________________ 2 141 Sand, medium; scattered pebbles __________ 7 148 Selected logs of water wells—Continued Thick- ness (feet) Material Depth (feet) Well (C-7-22)l4bcd—Continued Coarse-gravel zone—Continued: Gravel, chiefly well rounded to subrounded; contains cobbles as much as 5 in. includ- ing abundant siliceous rocks; some coarse sand and cemented streaks _____________ 15 Wedge zone: Sand and gravel; thin streaks of conglom- erate. Gravel finer and contains more rocks of local derivation than that above- Sand, fine to medium, silty, brown; scat- tered granules and small pebbles includ- ing pebbles of clay and sandstone concre- tions ________________________________ 29 Bouse Formation: Clay, silty and sandy, tough, gray; contains concretions of clayey siltstone and sand- stone ________________________________ 5 Sand, silty, soft, micaceous; contains some carbonized wood Clay, silty and sandy, tough, gray; contains concretions of clayey siltstone and sand- stone ________________________________ 11 228 Clay, silty, gray; fossiliferous ____________ 15 243 Clay, silt, and fine sand; thin bedded greenish— to bluish-gray fossiliferous ___ 228 471 Nonmarine sedimentary rocks (Tertiary) : Conglomerate composed of angular to sub- rounded granules, pebbles, cobbles, and scattered boulders of plutonic, metamor- phic, and few silicic volcanic rocks in a sandy and silty matrix. Fairly hard drill- ing _________________________________ 34 Well (C—8—21)lbbc [U.S. Bureau of Reclamation test well 1 in Dome Valley. Drilled with cable-tool equipment by Hamilton and Hood. Log by Bureau of Re- ciamation. Altitude 171 ft] 163 17 180 209 214 217 505 Upper, fine-grained zone: No record _____________________________ 10 10 Sand (80 percent), fine to medium, slightly micaceous, light-grayish-tan; silt (20 percent), slightly clayey; with small clay balls ________________________________ 21 31 Sand (85 percent), fine to medium; silt (10 percent), light-grayish—tan; clay (5 per- cent), plastic, dark-brown _____________ 6 37 Clay (60 percent), dense, plastic, dark- brown; sand (30 percent), fine to me- dium, light-grayish-tan; gravel (10 per- cent), fine to coarse, angular to sub- angular; composed mostly of gneiss and granite ______________________________ 13 50 Sand (70 percent), slightly silty, fine to medium, light-grayish-tan; gravel (15 percent), fine to coarse (2 in.), rounded; with a few angular pieces (mostly quartz) ; clay (15 percent), dense, plastic, dark-brown __________________________ 18 68 Coarse-gravel zone: Sand (60 percent), fine to medium, slightly silty, light-gray; fine to coarse gravel (30 percent), with cobbles as much as 4 inches, smooth, rounded quartzite pre- dominant; dense dark-brown clay (5 per- cent); silt (5 percent) ________________ 11 79 Gravel (75 percent), fine to coarse, pre- dominantly rounded; a few cobbles as much as 3 in.; sand (25 percent), fine to coarse, clean, light-grayish-tan; some clay in upper part ________________________ 13 92 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA Selected logs of water wells—Continued H171 Selected logs of water wells—Continued Thick- Material ness Depth (feet) (feet) Well (C—S—2l)lbbc—Continued Coarse-gravel zone—Continued: Gravel 70—90 percent), fine to coarse, pre- dominantly smooth and rounded; sand (10—30 percent), clean, fine to coarse, light-grayish-tan _____________________ 48 140 Wedge zone: Gravel (85—90 percent), fine to coarse (2 in.); predominantly angular and sub- angular; composed of granite and gneiss; sand (10—15 percent), fine to coarse, light-grayish-tan _____________________ 20 160 Sand (60—75 percent), medium to coarse, angular to subangular, predominantly granitic and quartzitic; gravel (15—25 percent), subangular; composed predomi- nantly of gneiss and granite; some quartzite; clay (10 to 15 percent), fine, light-dun—colored _____________________ 9 169 Wedge zone(?) : Granite gneiss (large boulder; possibly bed— rock) _______________________________ 2 171 Well (C-8-21)l9dad [F. J. Hartman. Irrigation well in South Gila Valley. Drilled with cable- tool equipment by Frank H Leideneker (Arizona Machine & Welding Works). Casing perforated from 115 to 165 ft Altitude 158 ft] Upper, fine-grained zone: Silt ................................... 2 2 Sand __________________________________ 12 14 Silt and sand __________________________ 3 17 Sand, some pebbles _____________________ 1 18 Sand, silt, and clay strata _______________ 38 56 Clay with sand streaks __________________ 18 74 Clay, sand, and some pebbles ____________ 9 83 Coarse-gravel zone: Gravel with sand _______________________ 14 97 Gravel, large, with sand _________________ 11 108 Gravel, good ___________________________ 8 116 Gravel with sand _______________________ 6 122 Sand with some gravel streaks ___________ 3 125 Gravel with sand _______________________ 1 126 Gravel, good, with large rock ____________ 10 136 Sand __________________________________ 1 137 Gravel, good ___________________________ 19 156 Boulder, very large ____________________ 0 156 Wedge zone: Sand, packed; with clay layers __________ 35 191 Gravel with sand (increased salt in water) ___ 1 192 Well (C-8-22) 7ccd [Johnson and Drysdale. Irrigation we‘l in The Island area. Drilled by Henderson & Sons. Casing perforated from 110 to 160 ft; open bottom. Altitude 139 ft] Upper, fine-grained zone: Silt and sand, dry ______________________ 10 10 Clay, heavy ____________________________ 8 18 Water sand, water at 18 ft; rose to 15 ft _ 86 104 Sand, gravel ___________________________ 6 110 Coarse-gravel zone: Gravel, coarse; cobble stones and pea gravel _______________________________ 50 160 Wedge zone: Coarse water sand and small gravel ______ 84 244 Sand and gravel ________________________ 8 252 Well (C-8—22)l4cdd [S. Sturges. Irrigation Well in North Gila Valley. Drilled with cable- tool equipment by Hamilton and Hood. Casing perforated from 80 to 129 ft. Altitude 150 ft] Upper, fine-grained zone: Silty sand _____________________________ 75 75 Coarse-gravel zone: Gravel to 8 in. diameter _________________ 57 132 Gravel, cemented _______________________ 1 133 Thick- Material nesa Depth (feet) (feet) Well (C-8-22)15bdd [U.S. Bureau of Reclamation test well CH—6 in North Gila Valley. Drilled with cable-tool equipment by Hamilton and Hood. Log by E. L. Smith, Bureau of Reclamation: modified slightly by F. H. Olmsted. Casing perforated from 90 to 150 and 160 to 186 ft. Altitude 140.5 ft] Upper, fine-grained zone: Sand (about 75 percent), fine to medium, brown; subrounded grains of quartz; silt (about 25 percent) ; contains a few small clay balls ____________________________ 32 32 Sand (about 75 percent), fine to medium; subrounded grains of gray quartz; occa- sional fine gravel; silt (about 25 - cent); chocolate-brown plastic clay a ut 6 in. thick at 44 ft ____________________ 26 58 Sand (about 70 percent), fine; subrounded grains of gray quartz; occasional fine gravel; silt (about 30 ercent); contains thin layers of choco ate-brown plastic c ay _________________________________ Sand (about 65 percent), fine, gray; silt (about 20 percent); contains a little chocolate-brown plastic clay; gravel (about 10—15 percent), subrounded to well-rounded pebbles of quartzite ...... 9 85 Coarse-gravel zone: Gravel (about 85 percent), fine to coarse, well-rounded; predominantly quartzite with some volcanic rocks, a few clasts, cobbles as much as 4 in.; sand (about 10 percent), fine, gray; silt and clay (about 5 percent) Gravel (about 75 percent), fine to coarse; well-rounded, clasts predominantly quartzite; many cobbles as large as 6 in.; sand (about 25 percent), fine, gray; con- tains little silt and clay _______________ 36 130 Gravel (about 70 percent), predominantly fine and well-rounded; a few cobbles as much as 4 by 8 in.; sand (about 30 per- cent), fine to coarse, gray; contains little silt and clay _________________________ 5 135 Gravel (about 60 percent), poorly graded, well-rounded; some cobbles as much as 4 in.; sand (about 40 percent), fine to coarse, poorly graded; contains little silt and clay ____________________________ 15 150 Wedge zone: Sand (about 60 percent), granitic, coarse, gray; gravel (about 40 percent), fine, angular to subangular, granitic; contains a few pebbles of quartzite _____________ 8 158 Gravel (about 70 percent), predominantly fine, angular to rounded; composed of volcanic rocks; sand (about 30 percent), granitic, fine to coarse, angular to rounded,, gray _______________________ 11 169 Sand (about 70 percent), granitic, fine to coarse, gray; gravel (about 30 percent), granitic, fine, angular to subangular; a few well-rounded pebbles of quartzite __- 16 185 Sand (about 60 percent), fine to coarse, brown; gravel (about 30 percent), vol- canic, fine, subrounded to rounded; clay (about 10 percent), moderately plastic light-brownish-green _________________ 25 210 Sand, fine to coarse, brown and gray, angu- lar to rounded; scattered fine gravel; some yellowish-brown nonplastic clay from 233 to 244 ft ___________________ 60 270 Sand (about 60 percent), fine to coarse, subangular to subrounded, grayish- brown; gravel (about 40 percent), vol- canic, poorly graded, fine to coarse, sub- rounded to rounded ___________________ 10 280 18 76 H172 Selected logs of water wells—Continued WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA Selected logs of water wells—Continued Thick- ness (feet) Depth (feet) Material Well (C-8-22)15bdd——Continued Wedge zone——Continued: Sand, fine to medium, grayish-brown; scat- tered fine gravel ______________________ 45 Sand (60—70 percent), fine to coarse, sub- angular to rounded, gray; gravel (30—40 percent), volcanic, fine to 1-in. angular to subrounded ________________________ 14 Clay, silty, moderately plastic, light- grayish-brown ________________________ 2 Clay, gray, dense; plastic; a small amount of chocolate-brown clay; few lime concre- tions and gravel near 350 ft ___________ 34 Sand (about 80 percent), fine to medium, gray; gravel (about 10 percent), fine; composed of clasts of volcanic rocks and quartzite; silt (about 10 percent); a small amount of clay __________________ 18 Clay, dense, plastic, chocolate-brown; with a few green streaks __________________ 12 Clay, sandy, silty, limy, grayish-brown, moderately plastic ___________________ 7 Sand (about 75 percent), fine to coarse, gray; silt (about 15 percent), a small amount of clay; gravel (about 10 per- cent), fine; occasional cobbles as much as 4 in. Sand (about 65 percent), fine to coarse, gray; gravel (about 25 percent), vol— canic, fine to coarse; silt and clay (about 10 percent) __________________________ 4 Bouse Formation: Clay, silty, plastic, chocolate-brown and brown; gravelly and sandy moderately plastic clay; lime concretions from 439 to 441 ft. Fossiliferous __________________ 19 Clay. Thin interbeds of medium-brown plas- tic clay, dark-grayish-brown silty and sandy micaceous clay, and grayish-brown moderately plastic clay; all slightly ex- pansive on drying. Fossiliferous _______ 49 Sand (80—90 percent), fine to coarse, greenish-gray; gravel (10—20 percent), fine to 2-in., subangular; some pieces of limestone and sandstone Silt agd clay, greenish-gray; little very fine san Nonmarine sedimentary rocks (Tertiary) : Gravel, very coarse; consists of cobbles and possibly boulders; only broken pieces recovered ____________________________ 325 339 341 375 393 405 412 6 418 422 441 490 4 494 3 497 Well (C—8—22)l9ccc [U_S. Bureau of Reclamation test well CH—702 in South Gi‘a Valley. Drilled with cable-tool equipment by Hamilton and Hood. Log by E. L. Smith of Bureau of Reclamation: modified partly on basis of gamma log, by F. H. Olmsted. Casing perforated from 115 to 150, 370 to 390, 395 to 435, and 455 to 463 ft. Altitude 129.6 ft] Upper, fine-grained zone: Sand, uniform, fine, gray; brown above 10 ft ___________________________________ 25 25 Sand, gray; some gray clay and scattered fine angular volcanic gravel ____________ 18 43 Clay, sandy, grayish-brown to chocolate- brown; interbedded in thin layers with fine gray sand ________________________ 13 56 Sand, fine, gray (about 75 percent); silt, a small amount of clay, few pieces of sand- stone (about 25 percent) ______________ 14 70 Sand, uniform, fine, gray; little fine angu- lar volcanic gravel and rounded quartzite gravel _______________________________ 13 83 Sand and gravel _______________________ 5 88 Material Thick- ness (feet) Depth (feet) Well (C-8-22)19ccc—Cominued Coarse~gravel zone: Gravel, fine to coarse; consists of subangu- lar to rounded clasts of volcanic rocks and quartzite as much as 5 in.; some fine grayish-brown sand and a little gray clay at 93 ft _____________________________ Sand, fine to medium, gray ______________ Gravel, fine to coarse; predominantly well rounded clasts of quartzite (70 percent); sand, fine, gray (30 percent) __________ Sand, fine to medium, gray (90 percent) ; interbedded fine gravel (10 percent) ___ Gravel, fine to coarse, predominantly well rounded; some cobbles as much as 7 in.; _ interbedded sandy zones _______________ Wedge zone: Sand, fine to coarse, gray; consists chiefly of subangular to subrounded grains of quartz; scattered granules and pebbles of volcanic rocks and quartzite; some lime- stone fragments (concretions) _________ Gravel, volcanic, fine, subangular (about 80 percent); fine to coarse gray sand; some concretions and a little tan to grayish-green non-plastic clay (20 per- cent) Sand, fine to medium, gray; scattered fine gravel and a little grayish-green non- plastic clay __________________________ Limestone concretions Sand, fine, gray (75—90 percent); fine vol- canic gravel; with a few rounded clasts of quartzite __________________________ Sand, gravel, and tan to grayish-green sandy clay ___________________________ Sand, fine, gray; with a little brown sand and scattered fine gravel ______________ Gravel, predominantly volcanic, fine to coarse, subangular (25—50 percent); fine to coarse sand (50—75 percent); a little clay at about 390 ft ___________________ Sand, fiue to medium, gray; scattered fine gravel Sand, fine to coarse, gray (about 60 per- cent) ; fine volcanic and quartzitic gravel (40 percent); a few limestone concre- tions and some wood between 405 and 410 ft _______________________________ Sand, fine to coarse, gray (75 percent); gravel (25 percent) __________________ Sand (60 percent) ; fine to 1-in. subangular to rounded volcanic and quartzite gravel (40 percent) _________________________ Sand, predominantly coarse (80 percent); grayish-brown to grayish—green clay (10 percent); fine to 2 in. volcanic and quartzite gravel (10 percent) _________ Sand, fine to coarse, light-gray (95 per- cent); fine volcanic and quartzite gravel (5 percent) __________________________ Gravel, fine to 3 in., volcanic; quartzite (50 percent); fine to coarse gray (50 per- cent) sand Gravel, fine to 2 in., subangular, volcanic (80 percent); fine to coarse gray sand, and a few limestone concretions (20 per- cent) ________________________________ Sand, fine to coarse, gray (55 percent) ; fine to coarse volcanic and quartzite gravel (30 percent); lime-cemented conglom- erate (15 percent) ___________________ Clay, sandy, hard, nonplastic; light-gray lime inclusions (80 percent); coarse sand 27 134 11 13 20 15 20 12 102 106 122 126 153 287 292 337 339 350 357 370 390 395 410 430 435 447 453 455 460 463 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA Selected logs of water wells—Continued H173 Selected logs of water wells—Continued Thick- Thick- Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C-8-22)l9ccc—Continued Well (C-8—22)23dad—Continued Wedge zone—Continued: Wedge zone—Continued: . and fine gravel imbedded in the clay (20 Sand, fine to coarse; contains scattered peb- percent) _____________________________ 3 466 bles as much as 2 in.; thin bed of clay at Sand, fine to coarse, gray (80 percent) ; fine 250 ft _______________________________ 76 270 to 11/2 in. volcanic and quartzite gravel Gravel consisting mainly of pebbles as much (20 percent) _________________________ 3 469 as 2 in., partly cemented with CaCOs (50 Gravel, fine, volcanic, and quartzite (60 per- percent) ; well-graded sand (50 percent)- 5 275 cent) ; sand and a little green sandy (clay Sand, fine; and scattered pebbles _________ 10 285 (40 percent) _________________________ 5 474 Gravel _cons15t1ng mainly of pebbles as much Sand, fine to coarse, gray, and a few lime- as 2 m., partly cemented with CaCOa (50 stone concretions (90 percent); fine vol- percent); well-graded sand (50 percent)- 11 296 canic gravel (10 percent) _____________ 6 480 Sand (70 percent) and gravel (30 percent). Gravel, subangular to subrounded, volcanic Much of gravel subangular and cemented 14 310 (50 percent) ; fine to coarse gray sand (50 Sand, fine ______________________________ 12 322 percent) _____________________________ 4 484 Gravel, largely cemented (50 percent) ; and Sand, fine to medium; a few pieces of lime- sand _________________________________ 39 361 cemented sandstone ___________________ 6 490 Clay, red, soft __________________________ 2 363 Gravel, subangular to subrounded, volcanic Sand, fine; and scattered angular and sub- (50 percent) ; fine to coarse gray sand angular pebbles _______________________ 125 488 (50 percent) _________________________ 5 495 Gravel, sandy; cemented with C‘aCOs (con- Sand, fine to medium; a few pieces of lime- glomerate) ___________________________ 12 500 cemented sandstone ___________________ 5 500 Well (C—8—22)22cd52 [3. Church. Irrigation well in South Gila Valley. Drilled with cable-tool equipment by Frank H. Leidendeker. Casing perforated from 100 to 152 ft. Altitude 149 ft] Upper, fine-grained zone: Clay __________________________________ 15 15 Sand, silted ____________________________ 10 25 Sand, clay strata _______________________ 15 40 Clay, sticky ____________________________ 5 45 Sand __________________________________ 17 62 Clay, sandy ____________________________ 4 66 Clay, sticky ____________________________ 2 68 Sand, silted ____________________________ 7 75 Sand __________________________________ 16 91 Coarse-gravel zone: Gravel, water-bearing (good) ____________ 61 152 Wedge zone: Sand, some gravel ______________________ 5 157 Sand, packed ___________________________ 14 171 Well (C-8-22)23dad [U.S. Bureau of Reclamation test well CH~4 in South Gila Valley. Drilled with cable-tool equipment by San Diego We‘l Drillers. Log by Bureau of Reclamation; modified by F. H_ Olmsted, using gamma log. Casing perforated from 100 to 130 and 334 to 354 ft. Altitude 152.4 ft] Upper, fine-grained zone: Sand, fine; and alternate layers of brown and gray clayey silt and silty clay. Some sand contains mica and a considerable proportion of highly colored grains _____ 60 60 Sand, clayey, fine; and silt; contains thin layers of gray silty clay and brown clayey silt ____________________________ 20 80 Coarse-gravel zone: Gravel containing cobbles as much as 7 in. (65—70 percent); fine to coarse sand consisting of abundant colored grains (30—35 percent). ______________________ 30 110 Sand (60—70 percent) ; gravel contains cob— bles as much_as 8 in. (30—40 percent) ___ 10 120 Gravel containlng cobbles as much as 7 in. (65—70 percent) ; fine to coarse sand con- sisting of abundant colored grains (30- 35 percent) __________________________ 22 142 Sand, fine; and silt; contains 6-in. layers of light-green to gray clay _______________ 9 151 Gravel and sand ________________________ 6 157 Wedge zone: Sand, fine to coarse; and scattered pebbles - 35 192 Clay, hard, dry _________________________ 2 194 Well (C-8—22)32cdd [U.S. Bureau of Reclamation drainage well SGDW 4 in South Gila Val< ley. Drilled with mud-rotary equipment by Layne Texas Co. Cased and gravel packed to a depth of 200 ft; screened from 90 to 200 ft. Altitude 140.3 ft] Upper,_ fine-grained zone: S011 ___________________________________ 5 5 Clay ___________________________________ 21 26 Streaks of sand and clay ________________ 34 60 Clay and gravel ________________________ 10 70 Clay and sand __________________________ 15 85 Coarse-gravel zone: Gravel, coarse __________________________ 20 105 Gravel, fine ____________________________ 12 117 Gravel, coarse; and streaks of clay ________ 11 128 Gravel, fine; and streaks of sand _________ 17 145 Gravel, coarse; and streaks of clay _______ 22 167 Gravel and hard streaks _________________ 18 185 Gravel, coarse __________________________ 13 198 Wedge zone: Sand and gravel ________________________ 6 Clay, sandy ____________________________ 12 Well (C-8—22)35caal [U.S. Bureau of Reclamation test well CH7704; deepened by U.S. Geologi- cal Survey from 600 to 1,997 ft as test well LCRP 29; in South Gila Valley. Drilled to 600 ft with cable-tool equipment by Hamilton and Hood; deepened (pilot hole only) from 600 to 1,997 ft with mud-rotary equipment by Desert Water Drilling Co. Log to 600 ft by Bureau of Rec‘amation; modified by F. H. Olmsted using gamma log; from 600 to 1,997 ft, log by F. H. Olmsted Casing perforated from 99 to 170, 435 to 445, 480 to 490, 507 to 540, and 550 to 570 ft. Altitude 150.8 ft] 204 216 Upper, fine—grained zone: Sand, silty, light-brown; some clay and organic matter _______________________ 3 3 Clay, reddish-brown; sand and silt _______ 45 48 Sand, fine, light-brown (50 percent) ; brown plastic clay (50 percent) ; occasional sub- angular volcanic pebbles _______________ 41 89 Coarse-gravel zone: Gravel, fine to coarse; consists of rounded clasts of quartzite and, a few subangular clasts of volcanic rocks and scattered cobbles as much as 6 in. (65—80 percent); fine to coarse sand; a little clay (20—35 percent) _____________________________ 85 174 Wedge zone: Sand, fine to coarse, light-grayish-brown (80 percent) ; fine to coarse volcanic and quartzite gravel (15 percent); yellow moderately plastic clay (5 percent) _____ 13 187 Sand, fine to medium, light-brown; scat- tered fine pebble-s _____________________ 108 295 H174 WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA Selected logs of water wells—Continued Selected logs of water wells—Continued Thick- Thick- Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C—8—22)35caal—-Continued Well (C-8-22)35caa1—Continued Wed e zone—Continued: Bouse Formation—Continued; . Sand, fine to coarse, poorly graded, light- ClaY? bluish-gray and pinkish-brown, fos- brown (75 percent); predominantly fine _5111ferous ------- > -------------------- 17 1,110 volcanic and quartzite gravel ((25 per- Sllt and fine sand, well-sorted, gray ‘7'?" 8 1,118 cent) ________________________________ 10 305 Clay and s11tyc1ay, bluish-gray and pinkish- Sand, fine to medium, light-brown; and .brown, foss111ferous ------------------- 131 124,? occasional pebbles _____________________ 10 315 Sllt and Clay‘ey Sllt’ gray ---------- 7-1-" 1’25‘ Sand, fine to coarse, poorly graded, light- Clay and Sllty‘clay, bluish-gray and pmleh' brown (70—75 percent); predominantly _brown, fossiliferous ------- :r '''''''' 40 125” fine volcanic and quartzite gravel (20_25 Silt and clayey silt, gray, fossfliferous _.___ 33 1,330 percent) ; hard medium—brown clay balls Clay and silty.c.lay, bluish-gray and pmkISh' (0_10 percent) ______________________ 20 335 .brown, foss111ferous _______ _ ____________ 1 5 1,345 Sand fine‘ to medium light-brown' and Silt and clayey Silt, gray foss11ifer0us ___- 27 1,372 sca’ttered pebbles ___’_____________’ _____ 45 380 Clay and silty_c_lay, bluish-gray and pinkish- Gravel, predominantly fine, volcanic; and Old brown, fozsiliferous "-k". -------------- 24 1396 some quartzite (60 percent); fine sand er marine se imentary roc s. (40 percent) _________________________ 3 383 Sand, _fine, gray, somewhat indurated; some Sand fine to coarse light-brown' and scat— medium sand and Silt; foss1liferous _.____ 39 1,435 tered small pebbles _-_______: _________ 43 426 Clay, gray; and fine. gray sand, inter- Sand, fine to coarse; some gravel and green bfidtfied ; somewhat Indurated and fos- to brown plastic clay __________________ 4 430 S‘lSl 1 erous ''''''''' .— ----------------- 38 1,473 Sand, fine to coarse (70 percent); fine vol- itifgray, somewhat indurated and fos- canic and quartzite gravel (30 percent); 0151 1 erous. "a ‘‘‘‘‘‘ .“‘.“‘g""""": 1,506 chocolate-brown plastic clay at 445 ft ___ 15 445 ay, gray, an some pmleh'. rown clay, Sand, fine to medium, light-brown; and somewhat indurated and fossfliferous ___ 23 1,529 scattered pebbles and pieces of sandstone 18 463 Sand, fine, gray, somewhat indurated; some Sand, fine to coarse, light-brown (70_95 medium sand and 81113;. foss111ferous ___- 46 1,575 percent); fine to 1% in., volcanic and Clay, gray; and some pinkish-brown clay; quartzite gravel (5_30 percent) . a few somewhat indurated and fossdrferous ___ 16 1,5191 green bentonitic clay balls _____’ _______ 27 490 Sand, fine to medium, somewhat indurated; Sand and scattered fine pebbles __________ 17 507 interbedded gray clay and Sllt “"".'-" 24 1,615 Gravel (70 percent) and sand (30 percent- 8 515 Clayé (gray, fossfliferous, somewhat indu- Sand, fine to coarse, light-grayish-brown S ra efi ""'“‘7“""‘“"“1'"""—j 17 1,632 (60—70 percent); fine to 21/2 in. gravel; and, ne to medium, somewhat indurated, quartzite gravel (30—40 percent) _______ 25 540 Clinterbedded gdray clay _arliéi 511% ‘-------j 19 1,651 Sand and about 10—15 percent fine quartzite :3” gray, an some pm 15 '. Town Clay, and volcanic gravel ___________________ 5 545 osslhferous and samewhat indurated __ 17 1,668 Clay, slightly silty, medium-brown _______ 3 548 Sand, fine to medium, gray, somewhat indu- Gravel, chiefly subrounded volcanic and Clrated "1 """"""""""""""" 5"" 12 1,680 quartzite; contains a few cobbles as much ay, gray, indurated, somewhat foss111fer- as 4 in. (70—85 percent); fine to coarse S 013$ fi """"" T""""“"‘""""“'.""' 1,686 sand (15_30 percent) _______________-_- 22 570 an , ne t0 medlum, gray, somewhat indu- Sand, fine to coarse, light-grayish-bro-wn; lrated "". ------------------- . 'r--- 15 1,701 and occasional fine pebbles _____________ 11 581 C ay, gray, Indurated, somewhat fossilifer- Sand and about 30—35 percent fine volcanic S ous """"""" r"""""-"—"--7-"- 1,706 gravel _______________________________ 9 590 and, fine to medium, gray, somewhat indu- Sand, predominantly fine, grayish-brown; Clrated ”"1 """"""""""""""" .-.---- 16 1,722 and scattered fine pebbles _____________ 10 600 ay, gray, Indurated, somewhat fossihfer- Sand and gravel, interbedded ____________ 105 705 S ous "'“""“. ---------- .- ----------- 1,731 Clay, soft, brown _______________________ 9 714 and, fine to medium; some Silt; somewhat Gravel and sand ________________________ 14 728 Indurated . ————————————————————— .—:--- 26 1,757 Silt, clayey, brown ______________________ 3 731 Clay, gray, indurated, somewhat fOSSlllfer- Sand and gravel, interbedded _____________ 22 753 S.0usfi_________-_____1___ ---------------- 11 L768 Silt, clayey, brown ______________________ 6 759 llt, ne sand, and clay, interbedded, some- Sand some gravel ___ _ 35 794 what foss1hferous _____________________ 61 1,829 Transition 20,180). """"""""" Sandi, fine dto medium; some silt; somewhat , ' '~ _ . 1n urate ____________________________ 32 1,851 $33 S_°_ff::ef:y:i1:_‘:i‘:r::‘i‘??§€i¥f}fi: :2: sun fine sand, and clay, interbedded. some- Clay, soft, grayish-brown; some gray clay _ 15 831 Clwhat foss111fterous T‘. ---------------- . - 86 L937 Sand, some gravel ______________________ 54 885 ay, gray, entonitic (altered volcanic Transition zone: S aséi)fi "tn-_dr ------------ ll "1"" 1,942 Clay, brown and gray, fossiliferous; inter- an t, dne 0 me lum’ gray, somew at 1nd“' bedded sand _________________________ 59 944 Clra e "“"“‘. ------------ .- --------- 34 1,976 Gravel, somewhat cemented, and sand _____ 25 969 ay, sandy and Sllty’ pale-greenish-gray “ 21 L997 Sand and gravel; thin beds of fossiliferous Wcll (C-8—23)27ada gray silty clay _________________________ 76 1,045 [U.S. Bureau of Reclamation test well CH—701 in South Gila Valley. Bouse Formation: Dfrill'zed1witht‘cable-toglfieqiuigmelznt i313, léamiltoin and Hood. Log by Bureau . . . o ; . . . ‘ ' Cliliftls‘fih'gray and plum—brown, fos- 20 1 065 permeate; "mess r and ma restarts?MOW Silt and fine sand, well-sorted, gray _______ 6 1:071 Upper, fine-grained zone: Clay, bluish—gray and pinkish-brown, fos- Sand, predominantly fine, some medium and .Siliferous ____________________________ 17 1,088 coarse; small amount of silt and brown Silt and fine sand, well-sorted, gray _______ 5 1,093 clay balls ____________________________ 40 40 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA Selected logs of water wells—Continued H175 Selected logs of water wells—Continued Thick- Thick- Material ness De'pth Material ness Depth (feet) (feet) (feet) (feet) Well (0-8-23)27ada—Continued Well (C-8-23)33cdd—Continued Upper, fine-grained zone—Continued: Wedge zone—Continued: Clay, tough, brown, moderately plastic; Sand, very little gravel ................. 53 273 some interbedded sand ________________ 27 67 Clay, gray, hard ——————————————————————— 5 278 Sand, clean, quartz _____________________ 5 72 Sand, small gravel ————————————————————— 38 316 (Hay, tough, brown; some silt ____________ 10 82 Sand, 142 Inch gravel and “rock” ......... 14 330 Coarse-gravel zone(?): Sand, little gravel ————————————————————— 30 360 Gravel, predominantly to subangular to sub- Sand, Wlth Clay balls and streaks fI‘Om 372 rounded pebbles of volcanic rocks and '00 392 ft ———————————————————————————— 35 395 quartzite; about 20 percent fine to coarse Clay -—_ ———————————————————————————————— 15 410 sand ________________________________ 7 89 Sand, With clay streaks _________________ 15 425 Sand, silt, clay, and about 10 percent fine Clay —————————————————————————————————— 5 430 gravel _______________________________ 15 104 Sand —————————————————————————————————— 35 465 Sand, fine, brown, and silt; scattered small Clay —————————————————————————————————— 9 474 pebbles ______________________________ 18 122 Sand —————————————————————————————————— 26 500 Coarse-gravel zone: Clay and sand ————————————————————————— 15 515 Gravel, coarse; well-rounded pebbles and Sand —————————————————————————————————— 5 520 cobbles as much as 10 in.; 14—15 percent Clay —————————————————————————————————— 5 525 coarse gray sand _____________________ 38 160 Sand, packed __________________________ 42 567 Wedge zone: Clay, hard ____________________________ 8 575 Sand, gray; and scattered small pebbles __ 10 170 Sand __________________________________ 10 585 Clay, sandy, tough, grayish-green ________ 2 172 Sand and gravel ________________________ 15 600 Sand, fine, gray; and about 25 percent silt- 17 189 Sandstone _____________________________ 5 605 Clay, sandy and limy, grayish-green; con- Clay and gravel ________________________ 20 625 tains scattered small pebbles __________ 16 205 Sand __________________________________ 10 635 Clay balls as much as 5 in., with sand and Clay __________________________________ 58 693 fine gravel coating ___________________ 10 215 Sandstone ______________________________ 57 750 Sand, silt, and gravel; occasional cobbles Clay, hard _____________________________ 7 757 and a green clay ball at 220 ft ________ 12 227 Sand and sandstone _____________________ 11 768 Sand, fine, gray; and 40 percent silt, some Sand and gravel ________________________ 12 780 clay _________________________________ 21 248 Clay __________________________________ 45 825 Sand, fine; and loosely cemented fine sand- Casing reduced to 8 in. at 825 ft _________ stone, and 30 percent green sandy clay _ 2 250 Clay, gray sandy streaks of brown fine sand 30 855 Sand, fine on sandstone __________________ 2 857 Well (C-8-23)29daa Sand, gray and clay _____________________ 39 896 [0. C. Johnson School. Irrigation well on Yuma Mesa, in ”Yuma. Drilled Clay or shale ___________________________ 3 899 with cable-tool. equipment by Frank H. Leidendeker Casmg perforated Sand and S111; _ ___ 6 905 from 160 to 262, 265 to 270, 283 to 286, and 291 to 295 ft. Altitude """""""""""" 132 fi] Clay and streaks of sand ________________ 5 910 _ _ _ Sand, clay, and silt (thin layer), cemented Older alluv1um,.und1v1ded: sand and gravel at 917 ft _____________ 10 920 Sand and 51113 strata ———————————————————— 98 98 Sand, with cemented streaks, and streaks of Sand, some pebbles _____________________ 50 148 clay _________________________________ 30 950 Sand, packed_ ——————————————————————————— 7 155 Clay, brown ____________________________ 3 953 Clay, 50ft, sticky ——-_— ——————————————————— 7 162 Clay, gray, and sand ___________________ 12 965 Sand, packed; and th1n sandstone layers __ 32 194 Clay and sandstone ____________________ 5 970 Sandstone; some clay and sand layers ---_ 27 221 Sand, loose _____--___________________:_ 3 973 Quicksand _____________________________ 10 231 Clay and sandstone _____________________ 12 985 Sand With sandstone and clay layers ______ 9 240 Sandstone _____________________________ 3 988 Sand and gravel _______________________ 20 260 Clay, silt, sand, and sandstone ___________ 37 1,025 Sand __________________________________ 5 265 Sandy clay ____________________________ 43 1 068 Gravel and sandstone ___________________ 3 268 Sand, loose _____________________________ 3 1:071 Sand —————————————————————————————————— 14 282 Clay, sandy, and sandstone ______________ 14 1,085 Sandstone and clay ____________________ 3 285 Granite ______________________________ 5 1090 Sand, fine _____________________________ 5 290 " ’ Sandstone and sand _____________________ 6 296 [F d 1 C C I d Vt?“ (C's-23)3ficcd e era om 1‘ SS 0. 11 us 1‘] ' Sand, fine ---------------------- 7 303 Drilled withp ceable-tool equipnilen‘t’ellyml’rgdlzvae lg‘i'llalinkusgo‘faséagifngug: Well (C-8-23)33cdd [Stardust Hotel test well; deepened from 830 to 1,090 ft as U.S. Geologi- cal Survey test well LCRP 13. On Yuma Mesa, in Yuma. Drilled and deepened with cable-tool equipment by Hamilton and Hood. Log below 830 ft by G. R. Vaughan. Casing perforated from 182 to 200 ft. Altitude 197 ft] Upper, fine-grained zone: Sand __________________________________ Clay and sand _________________________ Clay ___________________________________ Coarse—gravel zone: Gravel and about 40—50 percent sand _____ Clay ___________________________________ Gravel _________________________________ Wedge zone: Clay __________________________________ 30 6 10 70 75 105 135 170 200 206 216 220 forated from 185 to 196 and 238 to 244 ft, open bottom. Altitude 216 ft] Upper, fine-grained zone: Sand __________________________________ Clay, sandy; water test _________________ Sand, loose ____________________________ Coarse-gravel zone: Gravel, coarse; little sand _______________ Sand Sand and gravel, mostly sand ____________ Gravel, coarse; looks like washed gravel __ Gravel and sand, loose (50—50) __________ 38 38 4 42 37 79 11 90 50 140 6 146 36 182 16 198 17 215 2 217 5 222 15 237 8 245 13 258 H176 WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA Selected logs of water wells—Continued Selected logs of water wells—Continued Th' k- Thick- Material “61:5 Depth Material ness Depth (feet) (feet) (feet) (feet) Well. (C-8-23)36ccd—Continued Well (C-9—22)l7dca Wedge zone. [P. flIairgrove. linubsed Arrigatiorn lv‘vell onDYfima Nllesa fDrilled with 3am;- ' . . to ' m . r. ' ’ 0 to 1 0 t Sandy Wlth some gravel, httle firmer ————— 37 295 mgdifiegimgy an. H.y Olmsted odcbglslis ofngfrrnfna 0lgog. x“gigging perforated Conglomerate __________________________ 3 298 from 165 to 190, 194 to 198, and 215 to 218 feet. Altitude 203.9 ft] Sand, loose, some gravel ________________ 4 302 Well (C-9-21)14bac [B. Palon, Unused irrigation well on “Fortuna Mesa” piedmont area west of northern Gila Mountains. Drilled with cable-tool equipment by Hamilton and Hood. Casing perforated from 914 0 1,040 ft. Altitude 395 ft] Older alluvium, undivided: Clay and rock __________________________ 22 22 Sandy clay and gravel __________________ 11 33 Sand __________________________________ 55 88 Red clay _______________________________ 2 90 Sand __________________________________ 131 221 Sand and gravel, 1%; in. maximum ________ 19 240 Sand __________________________________ 146 386 Sand and gravel ________________________ 4 390 Sandstone and gravel, 3 in. maximum ____ 8 398 Sand __________________________________ 16 414 Clay ___________________________________ 7 421 Sand __________________________________ 27 448 Clay ___________________________________ 2 450 Sand __________________________________ 1 451 Clay ___________________________________ 8 459 Sand and boulders, 41/2 in. maximum ______ 4 463 Granite gravel and boulders, 5 in. maximum 12 475 Clay __________________________________ 4 479 Sand and sandstone _____________________ 75 554 Clay __________________________________ 4 558 Sand and sandstone ____________________ 98 656 Granite gravel and boulders, 4 in. maximum 6 662 Sand and sandstone _____________________ 18 680 Sand and gravel, 11/2 in. maximum _______ 3 683 Sandstone _____________________________ 9 692 Decomposed granite and sandstone _______ 8 700 Bouse Formation: Clay __________________________________ 40 740 Sand and sandstone _____________________ 10 750 Clay __________________________________ 5 755 Sand and sandstone ____________________ 15 770 Clay and shale _________________________ 15 785 Sand __________________________________ 2 787 Clay and shale _________________________ 127 914 Sand __________________________________ 90 1,004 Sand and decomposed granite ____________ 65 1,069 Clay ___________________________________ 13 1,082 Crystalline rocks: Decomposed granite _____________________ 1 1,083 Granite ________________________________ 2 1,085 Well (C-9-22)9bba [Ketcherside Unused irrigation well on Yuma Mesa. Drilled with cable- tool equipment by F. E. Leidendeker. Driller’s log modified by F. H. Olmsted on basis of gamma log. Casing perferated from 150 to 182 and 230 to 250 ft. Altitude 208.0 ft] Upper, fine-grained zone: Sand __________________________________ 8 8 Sand and cemented gravel _______________ 8 16 Sand __________________________________ 19 35 Clay and sand _________________________ 9 44 Clay __________________________________ 26 70 Sand and gravel ________________________ 14 84 Clay and sand __________________________ 6 90 Sand __________________________________ 46 136 Clay and sand __________________________ 10 146 Sand __________________________________ 7 153 Coarse-gravel zone(?) : Sand and gravel ________________________ 11 164 Sand __________________________________ 6 170 Sand and gravel ________________________ 16 186 Coarse-gravel zone: Gravel, some interbedded sand ___________ 23 209 Sand __________________________________ 11 220 Gravel, sandy __________________________ 30 250 Upper, fine-grained zone: Silt, sandy _____________________________ 11 11 Sand __________________________________ 8 19 Silt and sand ___________________________ 16 35 Sand __________________________________ 13 48 Clay __________________________________ 10 58 Sand __________________________________ 20 78 Sand and gravel ________________________ 5 83 Sand __________________________________ 9 92 Clay, s1lt and fine sand __________________ 34 126 Sand __________________________________ 28 154 Sand and silt ___________________________ 12 166 Coarse-gravel zone: Sand and gravel ________________________ 7 173 Gravel _________________________________ 17 190 Sand __________________________________ 3 193 Clay ___________________________________ 1 194 Sand and gravel ________________________ 4 198 Sand ________________________________ 17 215 Gravel _________________________________ 3 218 Wedge zone(?) : Clay ___________________________________ 3 221 Sand __________________________________ 4 225 Clay, green ____________________________ 1 226 Sand, water ____________________________ 37 263 Well (C—9—22)28cbb [U.S. Geological Survey test well LCRP 25 on Yuma Mesa. Drilled with mud-rotary equipment by Evans Brothers. Log by F. H. Olmsted. Completed to 2,002 ft and gravel-packed; casing perforated from 862 to 2,002 ft. Altitude 204.6 ft] Upper, fine-grained zone: Sand, fine to medium, light-brown; some silt 25 25 Gravel and brown medium to coarse sand _ 20 45 Sand, medium to coarse, light-brown; gravel and some brown clay and silt __________ 24 69 Clay, silty, brown; gravel and some sand __ 13 82 Sand, silty, brown; some gravel and brown clay _________________________________ 27 109 Sand, brown; brown clay and some gravel and silt ______________________________ 33 142 Sand, fine to coarse, brown _______________ 18 160 Coarse-gravel zone: Gravel, cemented _______________________ 5 165 Clay, silty, brown _______________________ 10 175 Sand, fine to coarse; some silt in upper part 13 188 Gravel, cemented _______________________ 9 197 Sand, fine to coarse, brown; some gravel __ 10 207 Clay, silty, brown _______________________ 3 210 Sand, gravel, and some brown silty clay ___ 35 245 Coarse-gravel zone(?) Clay, silty, brownish-gray _______________ 4 249 Sand, coarse, gray ______________________ 5 254 Clay, silty, brownish-gray _______________ 7 261 Gravel and coarse sand, gray; much rounded quartzite and chert ___________ 43 304 Wedge zone: Sand, silt, and clay, gray to brownish-gray 13 317 Sand, fine to coarse; gravel and thin beds of brownish-gray silty clay and silt ____ 110 427 Silt, brownish-gray _____________________ 4 431 Sand, fine to coarse; gravel and thin beds of brownish-gray silty clay and silt ____ 95 526 Silt, brownish-gray _____________________ 4 530 Sand, fine to coarse; gravel and thin beds of brownish-gray silty clay and silt ____ 43 573 Silt, brownish-gray _____________________ 5 578 Sand, fine to coarse; some gravel and thin beds of brownish—gray silt and silty clay 83 661 Clay, silty, brownish-gray _______________ 4 665 Sand, fine to coarse; some gravel and thin GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA Selected logs of water wells—Continued Selected logs of water wells—Continued H177 Thick- Thick- Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C—9—22)28cbb—Continued Well (C-9-22)28cbb—Continued Wedge zone—Continued: Wedge zone—Continued: beds of brownish-gray silt and silty clay 68 733 Sand, fine to coarse; and gravel __________ 33 1,535 Silt, brownish-gray _____________________ 3 736 Clay, silty _____________________________ 4 1,539 Sand, fine to coarse; some gravel and thin Sand, fine to medium; some gravel _______ 37 1,576 beds of brownish-gray silt and silty clay 20 756 Clay, silty _____________________________ 4 1,580 Silt, brownish-gray _____________________ 4 760 Sand, fine to medium; a small amount of Sand, some gravel, and brownish-gray silt _ 11 771 gravel _______________________________ 10 1,590 Silt, brownish-gray _____________________ 3 774 Clay, soft, sticky, light-brownish-gray ____ 26 1,616 Sand, some gravel, and brownish-gray silt .. 8 782 Gravel (mostly plutonic, volcanic, and meta- Silt, brownish-gray _____________________ 3 785 morphic rock detritus, some chert and Sand and gravel; 'a small amount of quartzite) ; some sand _________________ 15 1,631 brownish-gray silt ____________________ 32 817 Sand; some gravel and grayish-brown silt _ 17 1,648 Silt. brownish-gray _____________________ 3 820 Silt, sandy, soft, grayish-brown __________ 3 1,651 Sand and fine gravel; some fine white sand- Sand, fine to medium; a small amount of stone ________________________________ 17 837 gravel _______________________________ 24 1,675 Clay, silty, brownish-gray ______________ 4 841 'Silt, sandy, soft, grayish-brown __________ 3 1,678 Sand, coarse; and gravel (chiefly metamor- Sand; beds of cemented sand and gravel __ 54 1,732 phic and volcanic); some fine to medium Clay, hard, light—grayish-brown __________ 9 1,741 sand and silt _________________________ 50 891 Sand, fine to medium ____________________ 13 1,754 Silt, brownish—gray _____________________ 3 894 Sand, somewhat cemented, and gravel ____ 13 1,767 Gravel and sand; some fine white sandstone 26 920 Clay, soft, light-brownish-gray __________ 5 1,772 Silt, sandy, brownish-gray _______________ 3 923 Sand, fine to coarse; a small amount of Sand, fine to coarse, gray ________________ 7 930 gravel _______________________________ 28 1,800 Sand, fine to coarse; and gravel (meta- Clay, silty and sandy, soft, pale-yellowish- morphic, volcanic, chert, quartzitic, and brown (10YR 6/2); much moderate- some granitic) _______________________ 11 941 brown (5YR 4/4) clay ________________ 23 1,823 Sand, fine to coarse, gray _______________ 3 944 Sand and gravel, somewhat indurated ____ 35 1,858 Sand and gravel _______________________ 11 955 Silt, sandy, grayish-brown _______________ 5 1,863 Sand, fine to coarse, gray ________________ 10 965 Sand, fine to coarse; some gravel _________ 70 1,933 Gravel and sand ________________________ 10 975 Clay, brown ____________________________ 10 1,943 Clay, silty, grayish-brown _______________ 3 978 Sand, fine to coarse; some gravel _________ 21 1,964 Gravel and sand ________________________ 8 986 Clay, brown ____________________________ 10 1,974 Sand, fine to coarse; and gravel _________ 34 1,020 Sand, fine to coarse; some gravel _________ 10 1,984 Silt, brownish-gray _____________________ 3 1,023 Clay, brown ____________________________ 13 1,997 Sand, fine to coarse; and gravel __________ 13 1,036 Sand, medium to coarse; some beds of Silt, brownish—gray _____________________ 4 1,040 gravel _______________________________ 104 2,101 Sand, fine to coarse; and gravel _________ 3 1,043 Transition zone: Sand, fine to medium, gray ______________ 11 1,054 Clay, hard; or pale-bluish-gray and pale Gravel and sand ________________________ 4 1,058 brown claystone; pelecypods ___________ 9 2,110 Sand, fine to medium, gray ______________ 8 1,066 Sand, fine to medium, gray _______________ 7 2,117 Clay, gray or brownish-gray _____________ 5 1,071 Clay, hard; or pale-bluish-gray and pale Sand, fine to medium; some gravel _______ 19 1,090 brown claystone; pelecypods ___________ 5 2,122 Gravel and sand ________________________ 37 1,127 Sand, fine to medium; and interbedded clay 9 2,131 Sand, fine to medium; some gravel ________ 32 1,159 Clay and clavstone, medium-bluish—gray and Silt, sandy _____________________________ 5 1,164 brown; pelecypods ____________________ 13 2,144 Sand, fine to medium; some gravel _______ 24 1,188 Sand and silt; some gravel ______________ 10 2,154 Clay, gray _____________________________ 4 1,192 Clay and claystone, medium bluish-gray Sand, fine to medium; some cemented sand and brown; pelecypods ________________ 31 2,185 and gravel ___________________________ 62 1,254 Sand, fine to coarse; somewhat indurated, Silt, gray ______________________________ 4 1,258 gray ________________________________ 31 2.216 Sand, fine to coarse; and gravel __________ 19 1,277 Clay __________________________________ 3 2,219 Silt, clayey ____________________________ 4 1,281 Sand, fine to coarse, somewhat indurated, Sand, fine to coarse; some gravel _________ 7 1,288 gray ________________________________ 34 2,253 Clay, hard, light-brownish-gray ————————— 11 1,299 Clay and claystone, bluish-gray, olive-gray, Sand, fine to coarse; some gravel ————————— 23 1,322 and brown; pelecypods; some interbedded Silt, sandy _____________________________ 3 1,325 sand and silt _________________________ 18 2,271 Sand, fine to coarse; some gravel _________ 25 1,350 Sand, fine to medium; some silt and clay in Gravel and sand ________________________ 7 1,357 thin beds ____________________________ 15 2,286 Sand, fine to medium; some cemented sand Clay and claystone, olive-gray, bluish-gray, and gravel ——————————————————————————— 21 1,378 and brown; pelecypods; some interbedded Clay, silty ————————————————————————————— 6 1,384 gray sand and silt ____________________ 8 2,294 Sand, fine to medium; a small amount Of Sand, fine to medium; some silt __________ 13 2,307 cemented sand and gravel ————————————— 36 1,420 Clay, hard; or tough sticky olive-gray clay- Silt, sandy ————————————————————————————— 4 1,424 stone; some pelecypods ________________ 11 2,318 Sand, fine to medium; a small amount of cemented sand and gravel _____________ 17 1,441 Well (C-9-23)7baa Silt, sandy ____________________________ E 3 1,444 [1%55” gureagl of fihecltamation . test twill SlgV175(P)f III; lYum: ValIIJey. Sand, fine to medium; a small amount 0 ‘f‘ ,e V“. P ,m“ 'm 3“" 9”“‘Pmen ." “fez“ 0 9“ am" 1"” 0g cemented sand and gravel ————————————— 10 1,454 }0Ve1la-pgi‘:11tnilivst:llgd E512; 321$"01‘01‘11331451Hf5321d’ttd5 litioi't‘imd' Clay. light-brownish-gray _______________ 7 1,461 . Sand, fine to medium, gray ______________ 6 1,467 Upper, fine-grained zone: Gravel and coarse sand __________________ 13 1,480 Silt, clayey, medium- to dark-brown ______ 4 4 Sand, fine to coarse; some gravel _________ 17 1,497 Sand, fine, light-brown, poorly graded ____ 2 6 Silt, sandy _____________________________ 5 1,502 Clay, fat, reddish-brown _________________ 2 8 H178 WATER RESOURCES 0F LOWER COLORADO RIVER—SALTON SEA AREA Selected logs of water wells—Continued Selected logs of water wells—Continued Thick- Thick- Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C—9—23)7baa—Continued Well (C—9-23)20bdc—Continued Upper, fine-grained zone—Continued: Upper, fine-grained zone—Continued: Sand, fine, poorly graded ________________ 10 18 Sand, poorly graded, light- to medium- Clay, silty, reddish-brown _______________ 6 24 brOwn; a few thin interbeds of fat clay Sand, fine to medium, gray _______________ 7 31 and weakly cemented sand; scattered Clay, silty ______________________________ 4 35 small pebbles ________________________ 38 45 Sand, fine to medium, gray; thin cemented Sand and clay, interbedde‘d. Fine gray sand layers _____________________________ 15 50 with scattered pebbles; silty light-brown Sand; thin beds of clay and silt ________ ’ -_ 12 62 clay _________________________________ 4 49 Sand, fine to medium, gray; thin cemented Clay, silty, light-brown _________________ 4 53 layers _______________________________ 10 72 Sand, predominantly fine, light-grayish- Clay, silty and sandy, bluish-gray ________ 3 75 brown _______________________________ 24 77 Sand, fine to coarse, poorly graded; a few Clay, silty, light-brown __________________ 1 78 small pebbles _________________________ 13 88 Sand, predominantly fine, light-grayish- Clay, fat, reddish-brown to brown; a few brown _______________________________ 27 105 silt layers ___________________________ 20 108 Clay, silty, grayish-brown _______________ 1 106 Sand __________________________________ 4 112 Sand, predominantly fine, a little medium Clay and sand, interbedded ______________ 14 126 and coarse; contains a few thin cemented Coarse-gravel zone: Gravel, poorly graded, containing abundant rounded pebbles of quartzite, chert, and volcanic rocks. Thin interbeds of fine sand 4 130 Gravel, well-graded, otherwise similar to that above. “Pea” gravel more abundant below 157 ft. Layer of fine sand from 160 to 161 ft _____________________________ 35 165 Wedge zone(?) : Sand, fine, poorly graded; occasional peb— bles or cobbles above 176 ft, thin layer of green clay at 176 ft ___________________ 37 202 Well (C-9-23)9bbb [Arizona Public Service Co. Industrial well on Yuma Mesa. Drilled with cable-tool equipment by A. G. Tschour. Casing perforated from 641 to 670 ft. Altitude 193 ft] Upper, fine-grained zone: Sand, mesa ____________________________ 14 14 Sand and clay streaks, some water at 74 ft 143 157 Clay, soft ______________________________ 29 186 Coarse-gravel zone: Gravel, good; water ____________________ 19 205 Wedge zone: Sand, quick; and fine broken sandstone strata _______________________________ 19 224 Sand, clay, sandstone streaks ____________ 16 240 Sand __________________________________ 76 316 Sandstone, gravel strata ________________ 8 324 Caliche ________________________________ 6 330 Sand, sandstone in layers; water bearing _ 55 385 Sand and some water ___________________ 41 426 Caliche and clay _______________________ 6 432 Sand __________________________________ 18 450 Clay ___________________________________ 3 453 Sand __________________________________ 79 532 Clay and sandstone _____________________ 3 535 Sand __________________________________ 19 554 Clay and sandstone _____________________ 18 572 Clay, tough ____________________________ 8 580 Clay, soft, sandy _______________________ 10 590 Sand and sandstone streaks _____________ 4 594 Sand __________________________________ 47 641 Sandstone, gravel, sand strata; water ____ 29 670 Sand __________________________________ 7 677 Clay, tough ____________________________ 5 682 Clay, sandy ____________________________ 68 750 Well (C—9—23) 120de [U.S. Bureau of Reclamation drainage well YV1713 in Yuma Valley. Drilled with reverse-circulation-rotary equipment by G. Maddox. Log by Bureau of Reclamation. Completed and gravel packed to 229 ft; screened from 95 to 167 ft. Altitude 112 ft] Upper, fine-grained zone: Clay, silty to highly plastic, light- to medium-brown ____-_____--____~_ _______ 7 7 layers _______________________________ 8 114 Coarse-gravel zone: Gravel, fine to 3 in., predominantly rounded (65 percent); sand, fine to coarse, gray (35 percent) _________________________ 7 121 Gravel, fine to 6 in., rounded (80 percent) ; coarse to fine sand (20 percent) _______ 30 151 Gravel, fine to 5 in. (65 percent); fine to coarse, gray sand (35 percent); thin layers of reddish- to grayish-brown clay between 170 and 172 ft ________________ 38 189 Coarse-gravel zone(?) : Sand, fine to medium, some coarse, gray; few thin interbeds of gravel (less than 10 percent) __________________________ 6 195 Gravel, predominantly subrounded, fine to 16 in.; about 20 percent fine to coarse sand _________________________________ 28 223 Gravel, subrounded to rounded, fine to 5 in.; about 30 percent fine to coarse sand; trace of greenish limy clay ____________ 6 229 Sand, gray, poorly graded; scattered peb- bles _________________________________ 8 237 Well (C-9—23 ) 2 5dba1 [U.S_ Bureau of Reclamation test well SH—7A on Yuma Mesa. Drilled with mud-rotary equipment by Bureau of Reclamation. Log by Bureau of Reclamation, modified by F. H. Olmsted on basis of electric log and gamma log. Altitude 204 ft] Upper, fine-grained zone: Sand, fine, light-grayish—tan _____________ 20 20 Sand, fine to coarse, grayish-tan _________ .65 85 Sand, fine to medium, grayish-tan; grains more rounded than in overlying sand ___- 35 120 Sand, fine to coarse, grayish-tan; scattered pebbles, chiefly silicic volcanic rocks ___- 20 140 Sand, medium to coarse, light-grayish-tan; a few lumps of dark-reddish-browu silty clay _________________________________ 25 165 Coarse-gravel zone: Sand, fine to coarse; and fine gravel com- posed mostly of quartz and silicic volcanic rocks ________________________________ 24 189 Sand and clay; scattered pebbles _________ 11 200 Gravel, fine. angular to subrounded; com- posed primarily of granitic rocks, silicic volcanic rocks, and some metamorphic rocks ________________________________ 17 217 Sand, grayish—brown; and some gravel ___ 13 230 Gravel, fine to coarse, angular to rounded; some quartzite, as well as other rock types ________________________________ 16 246 Wedge zone: Sand, fine to medium, some coarse; few streaks of brown sandy and silty clay, occasional greenish-black silt. Gamma GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H179 Selected logs of water wells—Continued Selected logs of water wells—Continued Thick- Thick- Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well— (C-9—23 ) 25dba1—Continued Well (C-9-23) 35cm: [U.S_ Bureau of Reclamation test well CH—13YM on Yuma Mesa. Drilled Wedge zone—Continued' laggttmgg$153311eggirfi'gcegtmgonmfiggifigg giggmamggfithmé 235:0 fé radiation significantly higher than from by F. H. plmsted on basis of gamma log. Well point installed at 248— sands above the coarlse-gravel fiene ____ 94 340 250 f“ A‘t‘t‘me 20“ “1 Sand, fine silty and c ayey, gra ing into _ - . fine gravel; high gamma radiation _____ 30 370 Uppgrén%n%§:a€§eggf;e'pebbly _______________ 20 20 Sagirdé 2:33;; dark-gray; scattered pebbles 40 410 Salnld, fine to medium, a few scattered peb- _____________________________________________________ 22 42 Sand, fine to coarse, dark-gray; about 25 es - percent bluish-gray sandy and silty clay- 40 450 3:23 22%;; radetigfiartmt; graarlel b—d—"f 6 48 Sand, compacted, fine to medium; about 5 bbl clae p es, a ew m e S o 9 57 nereent fine gravel and 5 percent gray to Salli clean y._::::::‘::::':::::“:::"': 3 60 Safgdlggébigwglealifi’n’Eafié‘égégge"aafig 120 570 Sand, scattered pebbles, a few thin beds of gray; about 50 percent gray to r’eddish- S cognpgct s11ty sand and pebbly clay """ 14 74 brown clay and 10 percent fine gravel __ 10 580 Gigvel ESn‘d-ahdurwilnl """"""""" i 3 Sand, compfacted, fine to Igledium, small Sand fine brown 8 c ay """"""" 6 86 2141;271:1111; a2] d cgagsgrcseahrtd ’g 331333315323; Clay, red, and thin beds of fine sand _____ 24 110 (pebbles?) ___________________________ 120 700 Sand, fine; brown ———7 —————————————————— 16 126 Sand, fine to medium; and gray clay and $1133 hgrfd’ £93, and Sllty sand """"" g 132 silt, thin-bedded ______________________ 10 710 a , e: 1" W’,‘ ---------------------- Clay, redd1sh-tan, some coarse sand ______ 2 137 we“ (C 9 23)32bad Sarid, fine, brown; some thin beds of red ‘ . ‘ ‘ c ay _________________________________ 11 148 I‘l-5;,1i:rzzutsfol‘eeasrafllzz‘ rill gal-3:234, :lumaleysagalal may, soft, reddish-tan —————————————————— 1 149 of Reclamation, Log by E. Burnett of Bureau of Reclamation. modified Sand and scattered pebbles ______________ 9 158 by F. H. Olmsted on basis of gamma log. Well point installed at 2671/2 Clay soft reddish-tan _________________ 1 159 to 2691/ ft. Altitude 188.0 ft] ’ ’ ' 2 C Sand and scattered pebbles ______________ 13 172 _ . _ oarse-gravel zone: UppfSrarfldnefiireaniifitihzclrilftle medium and coarse- Sanld and fine gravel; few thin beds 0f red 10 182 ’ ’ . . ’ c ay _________________________________ iiifiefigdié’ffi‘grEtfl‘ii’yf‘ivffilf‘.ff‘f‘f‘if’f 46 46 sand and scatter‘id Pebbles -------------- 6 188 Clay and silt, calcareous, medium-brown __ 4 50 Gravel,t fine t°d4 mi; well-rounded clasts Of Sand fine' few thin beds of medium-brown quar the an SP. rounded to subangular clay ’ 16 66 clasts of granitlic and volcanic rocks; 2 ‘-“."““‘—. """""""""""" some coarse san _____________________ 1 200 g;:% 3511‘; Sllt’ medium-brown """"""" g g? Eand inddscgttoelg‘ed pebble: ______________ 2 202 ’ "7 """" 7": """""""" -"‘_ ay, ar , ar -gray to rown; silt inter- 013% vgallcareous, med‘um br°wn t0 reddISh 8 79 beds below about 206 ft _______________ 16 218 Silt and dag, ““““““““““““““““ 3 82 Sand, fine, brown _______________________ 18 236 Sand fine """""""""""""" 6 88 Gravel, fine to 6 in., and coarse sand; small San d, an d Egan-‘61; """"""""""" 4 92 amount of dark-gray clay. Well-rounded Clay calcareous brovwn """"""""" 4 96 clasts of quartzite and subrounded to sub- Sand and layers’of brown—clay_:::::::: 10 106 angfizlar clasts Of granitic and volcanic 2 Sand, fine _____________________________ 8 114 W d m S, ------------------------------- 8 264 Sand, fine, and brown clay _______________ 6 120 e g‘e zone. - - Clay, medium-brown to reddish-brown _____ 5 125 gang, fi-Ifi3 to miedium, grayish-brogvn """" 32 296 Sand, fine and layers of brown clay ______ 8 133 an ’ 51 y,.an c ay m t in inter eds ““' 1 297 Sand fine' some weakly cemented sand Sand, grayish-brown, and scattered small scattered small pebbles ________________ 34 167 Clpebbées """"""""""""""""" 8 305 Clay, calcareous, brownish-gray to dark- :37in ark-gray, and abOUt 20 percent fine 3 308 Saifiayffnzome fine sand and gut """"" $53) :3: Sand, fine, grayish-brown _______________ 3 311 Coarse-gravel Z‘Jn'e’: """""""""""""" Clay, dark-gray, and about 20 percent fine Gravel, fine to 3 in., subrounded to rounded; S sand """" ,— """"""""" 7 """ 1 312 thin beds of sand. Pebbles and cobbles and, fine, grayish-brown; a few p1eces of include granitic and volcanic rocks, cemented sand and a few thin lenses of quartzite, and chert __________________ 17 222 Clg‘ray clay __lr_1‘_"_"_'_h """"""""" 17 329 Sand and scattered pebbles ______________ 3 225 S 338 sgn y, w lte to 11g t—g‘ray “““““ 2 331 Gravel, fine to 3 in., subrounded to rounded 18 243 Cim ’ n3 “Tl." """ 11-11}; """"""" 3 334 Sand, fine brownish-gray ________________ 11 254 s 33:; 5;“ Ye W “‘9 ‘30 1g gray --------- 1 335 Gravel, fine to 3 in., subrounded to rounded 5 259 Sal? ’ rée’ gray "‘b‘“1‘{ """"""""" 5 340 Sand, fine brownish-gray ________________ 5 264 S1 ,dsakn y, gray to lac """""""" 1 341 Gravel, fine to 3 in., subrounded to rounded- 3 267 San ’ ne, gray, scattered small pebbles “‘ 48 389 Crystalline rocks: . and, fine to coarse, and 20—30 percent fine Granite. Nx diamond core from 280 to 285 well—rounded quartmte to subangular ft contained friable to coherent grayish- S grgianflitlcland volcainlc gravel """"""" 6 395 white granite, coarse-grained, containing S212 ’ rile, scafizere smal pebbles ——————— 13 408 about 60 percent feldspar, 20 percent SI ’dsaf? y, 1g :gray """"" .— —————— 2 410 quartz, and 20 percent dark minerals an bblne, gray1sh-br0wn; occas1ona1 small (chiefly biotite). Dry-weight density 2.7 S pea 5315 “-"h' """"""""""""" 10 420 g per cm“ ____________________________ 17 285 an , 51 ty, 11g t3:951'5113’ ——————————————————— 2 422 Sand, fine, grayISh-brown _______________ 35 457 H180 Selected logs of water wells—Continued WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA Selected logs of water wells—Continued Thick- Thick. Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C—9-23)35ccc——Continued we" (C-9-24)8baa—Contlnued Wedge zone—Continued: . Wedge zone—Continued- Saéilg,S fine to coarse, s11ty, and small peb- 5 462 Sand, fine to medium; some silt __________ 20 810 Sand in; _______________________________ 5 467 gang, Ecattfige‘d eEfbbles ------------ 1 ------ i g 36g ’ ”“7“““""““_“‘. ““““ 7“ an , me In lum, gray; some Sit ___- 0 sand: dense, SlltYJ dark'gray) httle bluISh' Sand, medium to coarse, gray ____________ 10 918 s g3” Cla "Ft—21336 -------- 1- ----- :31- 4 471 Silt, light-brown ________________________ 5 923 afi‘ravsgme 1n er 9 e ne grave ’ grayis ' 33 504 Sand, fine to coarse, poorly sorted; granules """""""""""""""""" and small pebbles mostly of black chert Well (C—9—24)8baa _and 'silicic volcanic rocks ______________ 52 975 [U.S. Geological Survey test well LCRP 28 in Yuma Valley on east bank S1113, llght-brown _______________________ 4 979 are, ”#1:, mar-revserrate??? ““3 Sand! We gravel, fine t0 poorly J. H. lgkobison. Cgasell to'292' ft. SAltitu’de 11827 ft] ' ' ' a g an' an sorted; granules and small pebbles mostly of black chert and s111c1c volcanic rocks _ 21 1,000 Upper, fine—grained zone: Sand, fine to medium, and silt; a few thin Sand, fine, and silt; thin pebbly streaks __ 28 28 cemented streaks or flat sandstone con- Sand, fine to medium ___________________ 57 85 cretions ______________________________ 72 1,072 Clay, silty, brown ______________________ 8 93 Sand, fine to coarse, pebbly ______________ 6 1,078 Sand, fine to medium ___________________ 16 109 Sand and silt, fine to medium; a few thin Sand, some pebbles _____________________ 6 115 cemented streaks or flat sandstone con- Sand, fine to medium ___________________ 9 124 cretions ______________________________ 90 1,168 Coarse-gravel zone: Clay, brown to brownish-gray ____________ 7 1,175 Gravel, coarse, predominantly subrounded Sand and Silt, fine to medium; a few thin to rounded; some coarse sand __________ 62 186 cemented streaks or flat sandstone con- Wedge zone: CI‘BtIQnS ___—__7 _______________________ 202 1,377 Sand, silt, and clay; thin streaks of graveL 28 214 Clay, light-brownish gray _______________ 5 1,382 Sand, fine to coarse; thin beds of clay and Sand, fine to coarse, and fine gravel; scat- silt __________________________________ 76 290 .tered pebbles and small cobbles _________ 80 1,462 Sand, fine, and silt ______________________ 36 326 Sllt, light-brown, and light-brownish-gray Silt, pale-brown ________________________ 4 330 clay _________________________________ 9 1,471 Sand, fine to medium ___________________ 26 356 Sand and fine gravel ___________________ 9 1,480 Silt, light-brown ________________________ 6 362 Gravel, cemented _______________________ 5 1,485 Sand, fine to coarse, somewhat pebbly ____ 33 395 Sand, medium to coarse; scattered pebbles Silt, light-brown _______________________ 6 401 and thin beds of gravel _______________ 187 1,672 Sand, sparse small pebbles ______________ 7 408 Clay, gray and brown ________________ ‘_-_ 5 1,677 Silt, light—brown ________________________ 2 410 Sand, coarse, and gravel; thin cemented Sand, fine to coarse _____________________ 11 421 zones or flat concretions _______________ 22 1,699 Clay, silty, brown _______________________ 4 425 Silt and grayish—white clay; possibly a few Sand, fine to coarse _____________________ 23 448 pebbles ______________________________ 4 1,703 Silt, light-brown ________________________ 3 451 Sand, some gravel and clay balls _________ 37 1,740 Sand, fine to medium, some coarse and Sllt and clay, brown and gray ___________ 2 1,742 pebbly; a few thin streaks or pebbles of Sand, some gravel; thin cemented zones or gray and brown clay _________________ 79 530 concretions ____________________________ 14 1,756 Silt, light-brown ________________________ 4 534 Clay, silty, gray _______________________ 4 1,760 Sand, fine to medium, brownish-gray; a Sand, some gravel; thin cemented zones or little silt and scattered small pebbles ___ 15 549 concretions ___________________________ 34 1,794 Silt, light-brown _______________________ 3 552 Sand, coarse, and fine gravel, somewhat Sand, fine to medium; some coarse pebbly cemented ____________________________ 5 1,799 sand. Pebbles mostly plutonic, volcanic, Sand, some gravel; thin cemented zones or and metamorphic rocks; a few are well- concretions ___________________________ 16 1,815 rounded chert and quartzite. Many frag- Clay, grayiSh-brown _____________________ 5 1,820 ments of plants and carbonized wood u, 80 632 Sand, some gravel; thin cemented zones or Silt, light-brown ________________________ 5 637 concretions ___________________________ 40 1,860 Sand, some fine to medium gravel; some Sand, fine to coarse; trace of gravel, silt, coarse pebbly sand. Pebbles most plutonic, and clay ____________________________ 67 1,927 volcanic, and metamorphic rocks; a few Transition zone: are well-rounded chert and quartzite. Clay, gray, fossiliferous _________________ 11 1,938 Many fragments of plants and carbon- Sand and silt, gray _____________________ 17 1,955 ized wood ____________________________ 14 651 Clay, gray, fossiliferous _________________ 21 1,976 Silt, light-brown ________________________ 6 657 Sand, fine to coarse, gray; some fine gravel- 52 2,028 Sand, some fine to medium gravel; some Clay, gray, and fine sand, fossiliferous -__ 17 2,045 coarse pebbly sand. Pebbles mostly plu- Sand, fine to coarse, gray and subangular tonic, volcanic, and metamorphic rocks; a to rounded gravel composed of chert and few well-rounded chert and quartzite. quartzite in addition to plutonic, volcanic, Many fragments of plants and carbon- and metamorphic rocks _______________ 45 2,090 ized wood ____________________________ 23 680 Clay, gray, silt and fine sand, fossiliferous- 40 2,130 Sand; a few streaks or clasts of light-gray Sand, some fine gravel __________________ 13 2,143 clay; scattered pebbles ________________ 30 710 Clay, silty, gray, fossiliferous ___________ 13 2,156 Sand, fine to medium, some coarse, gray; Sand, fine to medium, gray ______________ 20 2,176 thin beds of fine gravel _______________ 40 750 Clay and silt, gray, fossiliferous __________ 4 2,180 Sand, medium to coarse; scattered sand- Sand and gravel, fine to coarse, gray, sub- stone concretions and pebbles of light- angular to rounded; composed of chert gray claystone; some carbonized wood. and quartzite in addition to plutonic, vol- Gravel rare __________________________ 40 790 canic, and metamorphic rocks _________ 38 2,218 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA Selected logs of water wells—Continued H181 Selected logs of water wells—Continued Thick- Thick- Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C—9—24)8baa—Coutinued Well (C-9—24)34dcb3 _ , _ [City of Somerton. Public-supply well in Yuma Valley. Drilled with TranSItlon zone—Continued: cable-tool equipment by Hamilton and Hood. Driller’s log modified by Clay, gray, fossiliferous _________________ 5 2,223 F. H. Olmsted on basis of gamma log. Altitude 106.2 It] Sand and gravel, fine to coarse, gray, sub- _ . , angular to rounded: composed of chert Uppgli'itfigfidglgéned zone. 14 14 and quartzite in addition to plutonic, vol- y """""""""""""" 42 56 canic, and metamorphic rocks __________ 69 2,292 2 58 Clay, gray, and fine sand, fossiliferous ___- 10 2,302 22 80 Sand and gravel, somewhat cemented -___ 48 2,350 5 85 glay, graly, and 1fine sand}; interbedded ___- :5 3,322 51 136 and an grave , somew at cemented ___- , Clay, gray; foss111ferous ________________ 20 2,466 CoarEZ-ngt'irsxgl 53:2?! """""""""""" 12 148 Well (C—9-24)13cdd Gravel _________________________________ 14 162 [U.S. Bureau of Reclamation test well CH—3 in Yuma Valley. Drilled with Sand ---------------------------------- 10 172 cable-tool equipment by San Diego Well Drillers. Log by Bureau.of Grave] ________________________________ 28 200 Reagamgtgmgrrfidgggdtbygb lg,- 941$??? 335133512,“ gamma 1°z- Cams Sand __________________________________ 12 212 per Ora e 0 0 . l e . Gravel _________________________________ 44 256 Upper, fine-grained zone: Wedge zone: Clay and fine sand and silt, brown, contain- Sand __________________________________ 304 560 ing much organic matter ______________ 12 12 Sand and clay __________________________ 44 604 Silt and fine sand, clayey, brown _________ 6 18 Sand, small amount of gravel ___________ 10 614 Sand, fine to medium; roots and bark at Sand __________________________________ 169 783 25 ft ________________________________ 18 36 Clay ___________________________________ 4 787 Clay, silt, and fine sand _________________ 6 42 Sand, some clay ________________________ 154 941 Sand, fine to medium ___________________ 12 54 Sand, clay, and gravel ___________________ 5 946 Clay, brown, plastic, and sand ___________ 2 56 Sand __________________________________ 19 965 Sand, fine to medium; scattered pebbles ___ 8 64 Clay ___________________________________ 4 969 Clay and sand _________________________ 5 69 Sand, some clay ________________________ 33 1,002 Sand, fine to medium; few thin layers of Sand __________________________________ 5 1,007 clay and silt __________________________ 57 126 Sand, clay, and gravel ___________________ 4 1,011 Coarse-gravel zone: Sand __________________________________ 67 1,078 Sand, fine to medium, and about 35 percent Sand, with small amount of gravel ________ 5 1,083 gravel _______________________________ 3 129 Clay, sandy ____________________________ 18 1,101 Sand, fine to medium, silty; a few pebbles _ 11 140 Sand __________________________________ 62 1,163 Gravel, fine to 8 in., much of it well-rounded (about 60—70 percent) ; sand, fine to W9“ (0-9-25>35¢bd coarse (30—40 percent) ________________ 26 166 [U'S't (geollgginalcfigi'vSY gist twellgrflllgRPfh igugestteam Yuan; Vatlleg’. $1 Sand, fine to medium (50—85 percent); ijasA “rs: Lo 3 °F ‘ff 'Om e w‘ 'r° ’3’ eq ‘ me“ y ' W d gravel, fine to 5 in. (15—50 percent) ___- 29 195 Screerfigd i: 5- agdblyo-fé intergalsstggorf '31J6 {oraleibsallg gitifidgal‘bihfil]. e ge zone: , Sand, fine to medium, containing some silt _ 25 220 Upper, fine-grained zone: . Sand, fine to medium ____________________ 20 240 Sand; some thln beds of 5111: and clay _____ 26 26 Sand, fine, containing some silt and clay __ 10 250 Sand; Silt; some W°°d ——————————————————— 11 37 Sand, fine; scattered angular to subang'ular Sand, fine gravel; some WOOd ------------- 10 47 pebbles ______________________________ 15 265 Sand; some Sllt and wood ________________ 44 91 Sand, fine, containing some silt and clay __ 15 280 Silt: clayey; some sand, gravel, and carbon- Sand, fine to coarse; scattered pebbles ___- 20 300 lzed W°°d ---------------------------- 10 101 Sand and gravel ________________________ 6 306 Coarse-gravel zone: . Sand, fine _______________________________ 18 324 Sand and gravel; thm clay at 103 ft _______ 17 118 Sand, silt, and some gravel ______________ 71 395 Gravel and sand ———————————————————————— 13 131 Sand and 20 percent gravel up to 2 in. ___- 10 405 Gravel, coarse —————————————————————————— 2 133 Sand, fine to medium, containing some silt Sand; some coarse gravel bEdS ———————— . ——— 19 152 and clay _____________________________ 35 440 Gravel and sand; some clay and carbonized Sand, fine, well-sorted; some coarse sand __ 35 475 W°°d --———-—-—, ——————————————————————— 6 158 Sand, fine to coarse; layers of well-cemented Gravel, coarse; thm beds 0f coarse sand -_— 21 179 sand _________________________________ 25 500 Coarse-gravel zone(?) : Sand; some gravel ______________________ 7 186 Well (C-9—24)19bad2 Sand; some silt _________________________ 14 200 [P. E. Sterling. Irrigation well in western Yuma Valley. Drilled with Gravel, boulders ________________________ 1 201 cable-tool eauipment _by San Diego Well Drillers. Casing perforated Gravel, fine; and sand ___________________ 4 205 from 145 to 180 ft‘ mm“ 107 f“ Sang; thdn bedslof clayeylsilt _____________ 17 222 . ‘ _ an an grave ; some sit _______________ 28 250 Upperrépfirgigramed zone. 5 5 Gravel, coarse; thin beds of sand _________ 29 279 Silt and decomposed wood ________________ 44 49 glay’ 511'“ and sand --------------------- 2 281 Sand and silt ___________________________ 4 53 and and fine gravel ____________________ 4 285 Sand and cla streaks 32 85 Gravel. boulders, and cobbles _____________ 17 302 y """""""""" Wedge zone: Brown clay ____________________________ 8 93 8'11: 'It 1 Coarse sand with small amount of gravel _ 23 116 S1 dor 3:! y c a}; --------------------- 4 306 Coarse sand with gravel _________________ 7 123 Sand an] grave """"""""""""""" 32 338 Coarse_gravel Zone, an , s1 ty or Sllt _______________________ 4 342 Gravel l/L—4 in ___________________ 57 180 Sand; Some b‘GdS 0f gravel _______________ 12 354 ’ .7 . ' """ Sand, s11ty _____________________________ 3 357 \Vedge zone( .). S d (1 fi 1 3 3 Coarse sand with gravel _________________ 15 195 Siltl an no grave ------------------- 2 3g; H182 Selected logs of water wells—Continued WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA Selected logs of water wells—Continued Thick- Thick- Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C—9-25) 35cbd—Continued Well ( 0-9—2 5) 3 5 ch d—C ontinu ed Wedge zone—Continued: ‘ Wedge zone—Continued: Sand; some beds of gravel _______________ 12 403 Sand; some gravel ______________________ 4 1,153 Sand, silty _____________________________ 4 407 Clay, white _____________________________ 5 1,158 Sand; some gravel _____________________ 13 430 Sand __________________________________ 2g 1,1;8 Silt, clayey _____________________________ 5 4 5 Sand, silty -_______-___, _________________ 1 1 and; --------------------------------- i ——1 ———————————————————————————————— 1:: as i t, c ayey ____________________________ and, si ty _____________________________ , Sand; some gravel .. _____________________ 16 448 Sand __________________________________ 2 1,201 Silt, sandy _____________________________ 3 451 Sand, gray, fine to coarse ________________ 23 474 Well (0—10-23)lldcd Silt” elayey’ gray """""""""""" 4 478 [F. Booth. Irrigation well on Yuma Mesa. Drilled with cable-tool equip- Sand, medium to coarse; some gravel ______ 11 489 ment by Hamilton and Hood. Casing perforated from 98 to 113, 192 to Sand __________________________________ 8 497 222, 260 to 280, 320 to 334, and 445 to 495 ft. Altitude 200 ft] Sand, silty _____________________________ 3 500 _ . _ Sand, marriage cfoarse .1 ................ $9 3110 Uppggngnggaggfighgone- 10 10 Sand; some s o grave _______________ 1 S nd """""""""""""" 19 29 sand’ Silty ----------------------------- 3 544 Giavef—3"ir_1“1na;(im11_rnnn-":“ZI-II: 2 31 gald “d """"""""""""""""" g 2%? Sand and gravel, 1 inch maximum ________ 32 63 sim’d san y """"""""""""""" 8 559 Sand and gravel, 5 in. maximum; with clay advert:::::::::::::::::::::::::::: 2 561 Sgglneses ------------------------------- 1 39 Sand __________________________________ 6 567 """"""""""""""""""" Gravelisome' sand —————————————————————— 5 572 Eiifleifi‘ii:iigariini‘:::::::::::::::::: 1% 3% Sand, Sllty """"""""""""""""""" 5 577 Sand and gravel _______________________ 18 113 Sand, some gravel ______________________ 1% 233 Sand 72 185 Silt _____________________________________________________________________ Coarse-gravel zone: Gravel and coarse sand __________________ 8 608 . . Sand; some gravel and silt ______________ 31 639 322% 22g ggaazill’ 5 1n. max1mum -------- 1% :32 Sand' coarse' some gravel _______________ 13 652 g ".""'". “““““““““ Silt ’ ’ 4 656 Sand and gravel, 4 1n. max1mum __________ 13,31 3%: """"""""""""""""""" Sand -_-__________________________-..___ Sand __________________________________ 8 664 . - - Gravel 3 1n max1mum __________________ 24 280 Silt ___________________________________ 6 670 ’ ' , Sand; some soft sandstone and fine gravel _ :8 ((3330 Coargg—rfgavel zone(?) ' 36 316 Silt ___________________________________ o ———————— a-—:—---——: --------------- Sand; some soft sandstone and very little 33 23 We diggirfél-d gravel, 3 1n. max1mum ''''''' 18 334 _fine gravel ___________________________ 7 Sand ' ________________ 6 340 Sllt’ sandy """""""""""""""" 10 733 Sand, cemented _________________________ 20 360 Sand, some gravel """"""""""" 52 $33 Shale blue 2 362 ilt’ sandy """""""""""""""" Sand,cementezlu-_::::::::::::::::: 3 365 333d and ”ft sandStone_:::::::"':- 1: 383 Sand: cemented lenses ___________________ 90 455 Sand; soft sandstone; some beds of gravel _ 59 868 Sand ------------------------------ 54 509 2323arsilf¥_::::::::::::::::::::::::::::: % 333 . We" (ti-wane». . , Sand __________________________________ 8 882 [U.S. Navy. Industrial wellholn Yuma Mesa. Drilled With cable-tool equip- ment by Weber Well Drilling Co. Log by G. E. Hendrickson. Casing gragel; 50ft sandstone —————————————————— Z 333 perforated from 212 to 232 ft. Altitude 189 ft] an __________________________________ _ Gravel; soft sandstone __________________ 3 892 Upper, fine-grained zone: Sand and silt ___________________________ 10 902 Sand, fine ______________________________ 5 5 an __________________________________ 6 908 Clay and caliche ________________________ 2 7 Sand, silty; brown clay __________________ 4 912 Sang, fine to coarse _____________________ 155» 3% Grave] and sand ________________________ 5 917 an __________________________________ Sand, fin to medium ____________________ 10 927 Sand, fine ______________________________ 3 30 Sand, silgy _____________________________ 4 931 Sang, coarse, with some gravel __________ :3 23 Sand __________________________________ 6 937 an , medium __________________________ Silt, sandy _____________________________ 4 941 D0 ____________________________________ 20 60 Sand; some beds of gravel _______________ 391 35832 gang, coairse ___________________________ 13 £8 Silt, sand _____________________________ * an , me lum ____ _______________________ Sand; sorge gravel ______________________ 8 992 31nd, mefiium, w1th sgnall pelables ________ ‘18 138 Silt ____________________________________ 5 997 'ay, wi some very ne san ___________ Sand; some gravel, silt, and fine white Sand, very fine _________________________ 10 110 sandstone ____________________________ 27 1,024 Sand, fine ______________________________ 10 120 Clay ___________________________________ 8 1,032 Sand, very fine _-________..____. __________ 10 130 Sand; some carbonized wood and gravel __- 32 ngg Sang, fiery fine, with tracgs of s11t or clay _ lg fig Silt, sandy _____________________________ 1, an , ne, some cemen _______________ Sand; some carbonized wood and fine white Sand, fine, trace of s11t or clay ___________ 5 150 sandstone ____________________________ 11 1,083 Sand, fine, Wlth about 10 percent gravel __ 2 152 Silt and white clay ______________________ 9 1,092 Coarse-gravel zone: Sand; some gravel ______________________ 22 1,114 Gravel 1%; (inland smaller, 5—15 percent fine 2 154 Sand, silt _____________________________ 7 1,121 sand an c ay ________________________ Sand; 50m); gravel and soft sandstone _____ 13 1,134 Gravel, with coarse sand ________________ 1 155 Sand, silty _____________________________ 3 1,137 Sand, fine to coarse, With about 25 percent Sand; some carbonized wood _____________ 12 1,149 gravel _______________________________ 5 160 GEOHYDROLOGY OF THE YUMA Selected logs of water wells—Continued AREA, ARIZONA AND CALIFORNIA Selected logs of water wells—Continued H183 Thick- Thick- Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (0-10—23)20bbb—Continued Well (C—10—23)31bbb1—Continued Coarse-gravel zone—Continued: Coarse-gravel zone—Continued: Gravel, small with coarse sand ___________ 10 170 and about 50 percent very fine to medium- Description missing _____________________ 5 175 grained grayish-brown sand ___________ 24 297 Sand, medium to very coarse, with clay Wedge zone: balls _________________________________ 7 182 Sand, very fine to medium-grained, grayish- Pebbles, sand, and clay __________________ 3 185 brown _______________________________ 28 325 Sand, fine to coarse, about 35—40 percent Sand, medium- to coarse-grained, brownish- gravel _______________________________ 5 190 gray; scattered pebbles and thin strata Sand, fine to medium; some silt or clay ___- 5 195 of blue clay __________________________ 70 395 Sand, very fine to fine; some silt or clay ___ 5 200 Gravel, 14—3 in., and a small amount of Sand, fine, with some silt and clay ________ 10 210 medium sand _________________________ 12 407 Sand, medium to coarse, with about 40 per- Clay, bluish-gray _______________________ 1 408 cent gravel ___________________________ 2 212 Sand, medium, brownish-gray ____________ 8 416 Gravel, with about 40 percent sand, medium Gravel, 14—3 in., and about 40—50 percent to coarse _____________________________ 8 220 medium gray sand; thin streaks of clay Gravel, with about 20 percent sand ....... 20 240 at 417 and 418 ft _____________________ 4 420 Wedge zone: Sand, fine to medium, brownish-gray, and Sand, fine to medium ____________________ 10 250 scattered small pebbles _______________ 13 433 Sand, fine to medium, with 5—10 percent Sand, brownish-gray, and about 30—50 per- pebbles ______________________________ 10 260 cent gravel; thin streaks of clay at 435 ft 7 440 Sand, fine to medium, with 0—10 percent Sand, brownish-gray, and a few small peb- pebbles ______________________________ 10 270 bles; streaks of clay at 457 and 459 ft -_ 32 472 Sand, fine to medium, with 5—10 percent Gravel, 14—94 in., and about 40 percent pebbles ______________________________ 10 280 sand; some wood embedded in bluish-gray Sand, fine to medium, with 15—20 percent clay from 472—475 ft _________________ 8 480 pebbles ______________________________ 10 290 Sand, coarse to very coarse, grayish-brown; Gravel, with some sand, had some water, no trace of silt and 1A-im gravel __________ 17 497 rise _________________________________ 4 294 Sand, coarse to very coarse, grayish-brown, Sand, medium ___________________ . _______ 21 315 and about 35 percent angular gravel; some cemented sand and gravel ________ 3 500 Well (C-10-23)28ccd Sand, medium to coarse, brownish-gray; [V. H. Ueckert: Unused irrigation well on Yuma _Mesa. Drilled with scatteI-ed graVel 14-3 in.; streaks of clay mud-rotary equxpment by Gregg. Gravel-packed. casing perforated from at 527 530 532 and 540 ft ____________ 42 542 230 to 293 ft. Altitude 185 ft] : _ , , _ Sand, medium to coarse, brownish-gray; Upper, fine-grained zone: and 10—40 percent gravel ______________ 13 555 Sand __________________________________ 45 45 Sand, medium to coarse, brownish—gray- Coarse-gravel zone: and less than 10 percent gravel, 14—3 in. 20 575 Gravel, cemented _______________________ 25 70 Sand, medium to coarse, pebbly, medium- Gravel _________________________________ 64 134 brown _______________________________ 15 590 Sand, fine ______________________________ 40 174 Sand, medium to coarse, grayish-brown; Gravel _________________________________ 6 180 some sandstone and gray clay balls _____ 14 604 Gravel, sandy __________________________ 45 225 Gravel, subangular to well-rounded, 14—2 Sandstone ______________________________ 25 250 in., and 30 percent medium to coarse Gravel, small __________________________ 20 270 grayish brown sand ___________________ 6 610 Gravel, sandy __________________________ 64 334 Sand, well-rounded, medium to coarse, medium-brown _______________________ 10 620 Well (C-10-23)31bbbl Sand, well-rounded, coarse, grayish-brown, U. . Geolo ica urve test wel LCRP on Yuma Mma. Drilled with [ wile-tool gequiprient 3by Arizonh Machinje and Welding Works. Log by 331%3s5’wfiaks 0f gray Shaly Clay from 630 21 641 F. J. Frank. Casing perforated from 220 to 280 ft. Altitude 172.8 ft] """"""""""""""" Sand, poorly sorted, fine to very coarse, Upper, fine-grained zone: and 15—20 percent gravel, 14—1 in. ______ 1 643 Sand, light-brown, and about 10 percent Sand, fine to coarse; scattered pebbles and gravel; thin strata of clay at 15, 25, 60, streaks of bluish-gray shaly clay and silt- 43 686 and 65 ft ____________________________ 82 82 Sand, medium to very coarse, and 15 per- Gravel, 14—2 in.; streak of clay and sand __ 2 84 cent well-rounded 174—34 in. gravel, Sand, light-brown, somewhat pebbly; streaks of greenish-blue clay ___________ 3 689 streaks of clay, cemented gravel, and Sand, poorly sorted, fine to very coarse, cemented sand from 115 to 123 ft _______ 53 137 gray ________________________________ 12 701 Coarse-gravel zone: Sand, medium to coarse, gray, and 20 per- Gravel, pebbles, and cobbles, and about 10 cent gravel, 14—174 in.; some clay at 708 percent sand; a few strata of weakly ft __________________ ' _________________ 9 710 cemented sand ________________________ 16 153 Sand, medium to very coarse, grayish- Gravel, pebbles, and cobbles, and more sand brown _______________________________ 25 735 than above; strata of conglomerate and Sand, medium, grayish-brown; and gray clay from 162 to 164 ft ________________ 17 170 platy clay ___________________________ 740 Sand, pebbly; streaks of reddish-brown clay 8 178 Sand, medium to coarse, grayish-brown; a Gravel, pebbles, and cobbles, and about 40 few pieces of broken lava rock _________ 5 745 percent sand; streaks of reddish-brown Sand, very fine to medium, poorly sorted, clay from 178 to 180 ft ________________ 12 190 grayish-brown ________________________ 35 780 Sand, pebbly, grayish-brown; pebbles 14—2 Sand, coarse to very coarse, grayish-brown; in. __________________________________ 6 196 some angular pieces of volcanic origin at Gravel, 14—4 in., and 10—30 percent sand; 780 and 787 ft ________________________ 15 795 some clay streaks and cemented zones ___ 77 263 Sand, medium to coarse, poorly sorted, Gravel, 14—1 in., scattered large cobbles, grayish-brown ________________________ 12 807 WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA Selected logs of water wells—Continued H184 Selected logs of water wells—Continued Thick- Material ness Depth (feet) (feet) Well (C—l 0-23) 31bbbl—Continued Wedge zone—Continued: Sand, medium, gray; 20—25 percent 14—1 in. gravel and a few gray clay balls _______ 2 809 Sand, medium to coarse, well-rounded, gray; silt and clay at 816 ft; and a few subangular volcanics at 820 ft _________ 9 818 Sand, very coarse, gray; 15 percent, 14—4 in., angular gravel ____________________ 2 820 Sand, very coarse, gray; some fine sand and gray silt _____________________________ 15 835 Sand, well-rounded, medium; some gray silt and a few gray clay balls at 805—850 ft _ 25 860 Sand, fine to medium, gray; contains more silt than preceding beds; poorly sorted, fairly well rounded ___________________ 20 880 Sand, medium to coarse, gray; silt and gray clay balls with a few large angular pieces of rock ______________________________ 2 882 Sand, medium to coarse, gray; more fine particles than in bed above; few gray clay balls from 885 to 890 ft ___________ 8 890 Sand, fine to medium, gray, subangular to fairly well rounded; very few coarse grains _______________________________ 25 Sand, fine, moderate-yellowish-brown, angu- lar to rounded; contains a few rounded pebbles 14—1 in. and some angular pebbles of volcanic rocks. Carbonized wood at 939 ft _______________________________ 25 940 Sand, fine to medium, dark-yellowish-brown, subangular to rounded; about 5 percent 915 granule gravel, rounded _______________ 5 945 Sand, fine to medium, moderate-yellowish- brown, and greenish-gray clay balls ____ 5 950 Sand, fine to medium, light-brown, subangu- lar, fairly well sorted ________________ 10 960 Sand, fine, fairly well sorted, subangular, pale-yellowish-brown; a few yellowish- brown clay balls ______________________ 5 965 Sand, fine, fairly well sorted, subangular, pale-yellowish-brown; a few yellowish- brown clay balls; contains a few rounded pebbles 1/2—1 in. ______________________ Sand, fine to medium, subangular, pale- yellowish-brown, fairly well sorted; some 03003 cementation and a few angular pebbles of volcanic rocks ______________ 10 895 Sand, fine to medium, subangular, pale-- yellowish-brown, fairly well sorted; about 20 percent light-gray platy clay ________ 5 990 Sand, fine to medium, subangular, pale- yellowish-brown, fairly well sorted; about 20 percent light-gray platy clay; a few 10 975 subangular pebbles of volcanic rocks ____ 10 1,000 Well (C—10-23)36ddd [U.S. Bureau of Reclamation test well CH722YM on “Upper Mesa." Drilled with mud—rotary equipment by Bureau of Reclamation. Log by E. Burnett of Bureau of Reclamation. We‘l point installed at end of 2—in. pipe at a depth of 2097211 ft. Altitude 285 ft] Older alluvium, undivided: Sand, fine, light-brown, poorly graded; scat- tered gravel _________________________ 7 7 Gravel, fine to coarse, well-graded, 1/2—11/2 in., a few 3 in. Well-rounded to sub- rounded clasts of volcanic rocks granite and quartzite (amber and purple) _____ 47 54 Gravel and sand, interbedded ____________ 3 57 Sand, fine, poorly graded; scattered gravel- 11 68 Sand, fine, and thin layers of fat light- grayish-brown calcareous clay _________ 6 74 Sand, fine, poorly graded ________________ 29 103 Sand, fine, poorly graded; a few thin layers of coarse sand and fine gravel. Well- rounded to subrounded clasts of volcanic rocks, granite, and quartzite ___________ 107 210 Thick- Material ness Depth (feet) (feet) Well (C—10—24)1bdd1 [US. Bureau of Reclamation test well CH—l on east edge of Yuma Val- ley, at foot of Yuma Mesa escarpment, Drilled with cable-tool equip- ment by San Diego Well Drillers. Log by Bureau of Reclamation, modified by F. H. Olmsted on basis of gamma log. Casing perforated from 144 to 170 ft. Altitude 110 ft] Upper, fine-grained zone: Sand, very fine to medium; a few thin streaks of silty clay __________________ 25 25 Sand and brown silty clay with black streaks ______________________________ 3 28 Sand, fine to medium ___________________ 6 34 Sand and brown silty clay _______________ 2 36 Sand, fine to medium; a few thin (14—2 in.) beds of silt, clay, and clayey sand ______ 51 87 Clay, sandy and silty ___________________ 2 89 Sand, fine to coarse; few thin beds of silty clay and about 2—3 percent pebbles _____ 23 112 Sand, clayey ___________________________ 4 116 Sand, fine to coarse, and about 10 percent gravel up to 3 in. _____________________ 25 141 Coarse-gravel zone: Gravel containing well-rounded cobbles up to 8 in.; about 25—30 percent sand ______ 40 181 Coarse-gravel zone(?) : Sand, fine to coarse; beds of gravel (25 per- cent) ________________________________ 24 205 Gravel containing 30—40 percent sand and a higher percentage of mafic rocks than gravel from 141 to 181 ft ______________ 5 210 Sand, fine to coarse, and gravel up to 2 in._ 17 227 Wedge zone: Sand, fine to coarse, and about 5 percent scattered granules up to 14 in. _________ 23 250 Sand, fine to coarse, containing pieces of silty clay ____________________________ 15 265 Sand, fine to coarse, containing angular granules and pebbles up to 2 in. composed of volcanic rocks _____________________ 15 280 Sand, very fine to medium, containing layers of cemented gravel 3-6 in. thick -- 20 300 Sand, fine to medium; some silt and clay, scattered granules and pebbles _________ 13 313 Sand, fine to medium ____________________ 19 332 Sand, fine to coarse; some silt and clay and 3—4 percent gravel ____________________ 43 375 Clay, very hard ________________________ 1 376 Sand, fine to coarse, containing layers of clay 3—4 in. thick and 2—3 percent gravel- 19 395 Sand, fine to coarse; some silt and 5-8 per- cent gravel __________________________ 10 405 Sand, fine to coarse; some silt, clay, and cemented sand ________________________ 10 415 Sand, fine to coarse; silt and clay; contains more clay than bed above ______________ 10 425 Sand, fine to coarse; 2—3 percent gravel; some cemented sand and a few pieces of light-gray sandy clay __________________ 25 450 Sand, fine to coarse; some silt and clay __-_ 35 485 Sand, fine to coarse; 2—3 percent gravel and some poorly cemented sand ____________ 15 500 Well (C-10—24)5ddd [U.S. Bureau of Reclamation test well CH72 in Yuma Valley. Drilled with cable-tool equipment by San Diego Well Drillers. Log by Bureau of Reclamation: modified by F. H. Olmsted on basis of gamma log. Casing perforated from 170 to 215 ft. Altitude 100 ft] Upper, fine-grained zone: Silt, sandy, and clay, brown ______________ 13 13 Sand, fine to medium; scattered pebbles in lower part _________________________ 73 86 Silt, brown, containing a few granules and small pebbles _________________________ 4 90 Clay, silty, brown; some gray clay _______ 6 96 Silt, brown ____________________________ 12 108 Sand, fine to coarse; a few thin layers of s11ty clay; scattered pebbles below 120 ft- 59 167 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H185 Selected logs of water wells—Continued Selected logs of water wells—Continued Thick- Thick- Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) We" (0-10-24l5ddd—C0Minfld Well (C-10—24)23ddd—Contlnued Coarse-gravel zone: U fi _ ' __ t' . Gravel: some fine to coarse sand --------- 13 180 ”gray?ifiiilfififisf°?§dd§§3‘bifi3ff'_ _________ 2 21 53113:): fine to medlum; pleces 0f W°°d at 18 198 Sand,dfine; scattered medium and coarse --—--------------------. -------- san _________________________________ 23 44 Gravel, rounded cobbles up to 6 in.; some Clay, calcareous, reddish-brown __________ 14 58 sand ,— -------------------------------- 22 320 Sand, fine to coarse _____________________ 4 62 Clay, Sllty -,--. ------------------ , -------- 1 21 Sand and fine gravel ____________________ 7 69 Gravel containing cobbles up to 8 in.; some Sand, fine to coarse _____________________ 4 73 sand 7 -------------------------------- 31 252 Sand and fine gravel ____________________ 4 77 Wedge zone. Sand, fine to coarse _____________________ 3 80 Sand, ‘fine to coarse; some pebbles up to Clay, calcareous, reddish-brown __________ 9 89 1 /2 1n. ------------------ .- ------------ 23 275 Sand, fine to medium; some silt, and scat- Sand, fine to coarse; few thin beds of ce- tered fine to 2-in. pebbles of volcanic merited gravel ________________________ 29 305 rocks ________________________________ 19 108 Sand, fine to coarse} and 10—15 percent ce' Sand and fine volcanic gravel ____________ 7 115 mented gravel w1th angular pebbles up Sand fine to coarse 7 122 to 2 in. —————————————————————————————— 13 318 Gravel _____________________ 1 123 Sand, fine to coarse; little gravel in thin Sand fig-6,1613%}; """"""""""" 5 128 cemented layers _____________________ 40 358 Gravel ____________::::: """"""""" 3 131 Sand,tfir§e. to coarse, and 20 percent gravel 5 363 Sand, fine, medium-brown; -sc-a:ttered_p_eb_- up 0 1n _____________________________ Sand, fine to coarse; some gravel in thin C-oarsel-Jgi‘ivel— "2&1;- """""""""""""" 35 166 cemented layers ------------------- 137 500 Gravel, subangular to well-rounded, up to Well (C-10-24)13bcc1 3 in., predominantly quartzite, quartz, [U.S. Bureau of- Reclamation test well YVI—27(P) in Yuma Valley. and granitic rocks, some volcanic rocks grilfid wit}; mug-gag e533??? 11333331”? figcgfgmafiog‘, nLogoigvt and sandstone ________________________ 17 183 lastalilimii :ndepth of 168—1700 a on end of 11/2 in. $1119. eAltiDtude Sand and gravel ------------------------ 5 183 101.0 ft] Upper, fine-grained zone: Clay ___________________________________ 15 15 Sandy clay, sand lenses __________________ 15 30 Clay ___________________________________ 4 34 Sand, with clay lenses ___________________ 36 70 Sand, pebbly, 1/3 in. maximum ____________ 27 97 Clay, with sand lenses 2 or 3 in. thick ____ 23 120 Sand, few gravel and clay lenses _________ 29 149 Gravel, sand lens 156 to 157 feet __________ 9 158 Gravel, cobbles, and sand ________________ 22 180 Sand, occasional gravel __________________ 23 203 Well (C—l 0-24 ) l 6b882 [Western Cotton Co. Industrial well in Yuma Valley. Drilled With cable- tool equipment by Arizona Machine and \Velding Works. Casing per- forated from 112 to 180 ft. Altitude 100 ft] Upper, fine-grained zone: Sand __________________________________ 46 46 Clay and wood, sandy ___________________ 12 58 Sand __________________________________ 17 75 Clay ___________________________________ 35 110 Sand __________________________________ 8 118 Clay ___________________________________ 20 138 Coarse—gravel zone: Rock and sand _________________________ 60 198 Clay ___________________________________ 8 206 Rock and sand __________________________ 19 225 Gravel and sand ________________________ 25 250 Wedge zone: Sand __________________________________ 25 275 Clay ___________________________________ 12 287 Sand __________________________________ 13 300 Rock and gravel ________________________ 5 305 Sand __________________________________ 118 423 Well (C-10-24)23ddd [U.S. Bureau of Reclamation test we‘] CHrl7 YM on Yuma Mesa. Drilled with mud-rotary equipment by Bureau of Reclamation. Log by E_ Burnett of Bureau of Reclamation; modified from a depth of 0 to 192 ft by F. H. Olmsted on basis of gamma log. Below 192 ft, interpretation of gamma log does not correspond to geologist’s log, as indicated be‘ow. Well point installed on end of ll/z-in. pipe at depth of 428 to 430 ft; later removed and reset at 198 to 200 ft. Altitude 166.9 ft] Upper, fine-grained zone: Sand, fine, light-brown; scattered pebbles of volcanic rocks and quartzite ___________ 19 19 507-243 0 - 74 -13 Gravel, subangular to well-rounded, up to in., predominantly quartzite, quartz, and granitic rocks, some volcanic rocks and sandstone ________________________ 4 192 (Gamma log indicates lower gamma in- tensity from 192 to 278 ft, then generally high intensity below 278 ft.) Gravel (geologist’s log) _________________ 51 243 Wedge zone: Sand and gravel, interbedded ____________ 8 251 Sand, fine, some medium and coarse; small amount of gravel, and traces of gray, limy clay and hard-brown clay _________ 95 347 Gravel, fine to 1 in.; thin layers of sand from 359 to 3612 ft ____________________ 18 365 Sand, fine, gray; traces of white limy ma- terial and gray clay. Scattered fine gravel from 412 to 419 ft ____________________ 54 419 Gravel. fine to 11/2 in.; pebbles predomi- nantly granitic rocks and quartz, with few volcanic rocks ___________________ 19 438 Sand, fine, poorly graded; thin beds of fine gravel at 441 and 450 ft _______________ 17 455 Sand and gravel, interbedded ____________ 7 462 Well (C-10—24)30baa [U.S. Geological Survey auger test well in southern Yuma Valley. Drilled with truck-mounted power auger by Geological Survey. Log by G. R. Vaughan; modified by F. H. Olmsted on basis of gamma log. Well point installed on end of 11/2-in. pipe at a depth of 183 to 185 ft. Altitude 93 ft] Upper, fine-grained zone: Clay and silt, brown _____________________ 10 10 Sand, fine, brownish-gray ________________ 38 48 Sand and silt, gray _____________________ 12 60 Sand, gray ............................. 5 65 Sand and silt, gray _____________________ 19 84 Sand, gray _____________________________ 16 100 Clay and sand __________________________ 6 106 Sand __________________________________ 14 120 Gravel ________________________________ 4 124 Sand, some pebbly zones _________________ 26 150 Sand and gravel ........................ 8 158 Coarse-gravel zone: Gravel, coarse _________________________ 20 178 Sand __________________________________ 5 183 Gravel, coarse __________________________ 4 187 H186 Selected logs of water wells—Continued Thick- ~Material ness Depth (feet) (feet) Well (C—10—25)lbba [P. R. Sibley. Irrigation well in Yuma Valley. Drilled with cable-tool equipment by Frank H. Leidendeker. Casing perforated from 160 to 180, 195 to 205, and 250 to 285 ft. Altitude 106 ft] Upper, fine-grained zone: S . 011 ___________________________________ 2 2 Clay ___________________________________ 2 4 Sand __________________________________ 3 7 Clay, soft, sticky _______________________ 10 17 Clay and sand strata ____________________ 22 39 Clay, tough, sticky ______________________ 24 63 Sand, clay, some sharp gravel ____________ 23 86 Quicksand _____________________________ 10 96 Quicksand and clay strata _______________ 9 105 Sand with approximately 10 percent gravel- 10 115 Clay, hard Clay, soft, sandy ________________________ 22 148 Coarse-gravel zone: Gravel in silted sand ____________________ 5 153 Gravel, sandy __________________________ 3 156 Gravel, good water ______________________ 19 175 Quicksand _____________________________ 12 187 Gravel and sand strata __________________ 18 205 Sand with scattered pebbles _____________ 8 213 Sand __________________________________ 4 217 Sand with pebbles ______________________ 17 234 Sand, packed, gravel, and clay ____________ 3 237 Sand and pebbles _______________________ 3 240 Gravel, sandy __________________________ 4 244 Gravel, good water ______________________ 35 279 Wedge zone: Sand, packed ___________________________ 16 295 Well (C—10-25) 23add [U..S Geological Survey auger test well in Yuma Valley. Drilled with truck-mounted power auger by Geologica‘ Survey. Log by G. R. Vaughan. Well point instelled on end of I‘d-in. pipe at a depth of 185. 7 to 187.7 ft. Altitude 97 ft] Upper, fine-grained zone: Clay and silt __________________________ 27 27 Sand and silt, clay streak at 81 ft _______ 99 126 Clay __________________________________ 3 129 Sand and silt ___________________________ 26 155 Gravel, small; with sand and silt _________ 9 164 Coarse-gravel zone: Gravel, heavy, with sand ________________ 28 192 Well (C—10-25)35bbd [U.S. Geological Survey test well LCRP 17 on east bank of Colorado River in southwestern Yuma Valey. Drilled with mud-rotary equip- ment by Roscoe Moss Co. Log by F. H. Olmsted, F. J. Frank, J. H. Robison, and G. R. Vaughan Gravel packed and cased to 1,988 ft: casing perforated from 520 to 1.998 ft, with a blank section from 1,398 to 1,438 ft. Altitude 94 ft] Upper, fine- grained zone: Sand and silt, some clay, gastropods, and carbonized wood _____________________ 71 71 Sand and gravel, some silt and clay _______ 103 174 Coarse-gravel zone: Gravel, coarse, probably somewhat ce- mented ______________________________ 32 206 Sand, some gravel ______________________ 25 231 Gravel, coarse, probably cemented, at least in part ______________________________ 45 276 Wedge zone: Sand and gravel ________________________ 30 306 Gravel, coarse, probably cemented in part _ 44 350 Sand, some coarse gravel beds ___________ 58 408 Gravel, coarse, probably cemented in part _ 64 472 Sand, some gravel ______________________ 122 594 Gravel, fine to medium, cemented in part __ 50 644 Sand, some gravel; a few thin beds of silt and cemented gravel __________________ 203 847 Silt, clayey, in two thin beds, with sand between them ________________________ 12 859 WATER RESOURCES 0F LOWER COLORADO RIVER-SALTON SEA AREA Selected logs of water wells—Continued Thick- Material ness Depth (feet) (feet) Well (C—lo—25)35bbd—Continued Wedge zone—Continued: Sand, some gravel; a few thin beds of silt and cemented gravel .................. 171 1,030 Silt ___________________________________ 8 1,038 Sand, some silt and fine gravel __________ 394 1,432 Clay __________________________________ 2 1,434 Sand, compact, silty and pebbly; thin clay beds at depths of 1,520, 1,688, 1,692, 1,750, 1,778, 1,920, and 1,934 ft _______________ 556 1,990 Clay ___________________________________ 10 2,000 Sand, compact; and cemented gravel ______ 30 2,030 Sand, silty; a few thin beds of cemented gravel _______________________________ 27 2,057 Clay, silty ______________________________ 3 2,060 Sand and thin beds of grayish-white com- pact silt _____________________________ 30 2,090 Sand, silty, and thin beds of cemented gravels ______________________________ 57 2,147 Silt, clayey _____________________________ 3 2,150 Sand, silt, and thin beds of clay and ce- mented gravel ________________________ 50 2,200 Sand, compact; and cemented gravel ______ 12 2,212 Clay ___________________________________ 8 2,220 Silt and sand __________________________ 13 2,233 Clay ___________________________________ 5 2,238 Sand, compact, silty; thin beds of clay ___ 62 2,300 Sand, silty _____________________________ 42 2,342 Clay, silty ______________________________ 6 2,348 Sand, compact; thin beds of cemented sand and gravel ___________________________ 67 2,415 Clay, silty _____________________________ 2 2,417 Sand, thin beds of silt and silty clay ______ 97 2,514 Transition zone(?) : Clay ___________________________________ 6 2,520 Sand, some cementation; some silt _______ 154 2,674 Clay ___________________________________ 2 2,676 Sand, silty; and thin cemented beds _______ 52 2,728 Cla ___________________________________ 2 2,730 Sand, silty; and thin cemented streaks ___- 74 2,804 Clay ___________________________________ 2 2,806 Sand, silty; and a few thin lenses of ce- mented gravel ________________________ 12 2,818 Clay __________________________________ 4 2,822 Sand, silt, and thin beds of clayey silt ____ 30 2,852 Sand and some silt and cementation ______ 40 2,892 Clay ___________________________________ 8 2,900 Sand, silt, and thin lenses of silty clay ___- 46 2,946 Well (C—ll—21)4ddc [U.S. Bureau of Reclamation test well CH—9 YM on (Yuma Desert). Drilled with mud-rotary equipment by Bureau of Reclamation. Log by J. Granchi of Bureau of Rec‘amation. Cased to 350 ft; perforated from 293.5 to 328.5 ft. Altitude 403.3 ft] “Fortune Plain” Older alluvium, undivided: Sand, fine, grayish-tan; lower 2 ft lime cemented Sand, fine to medium, silty and clayey, tan; scattered angular to rounded pebbles composed predominantly of volcanic and granitic rocks, a few metamorphic rocks- 7 10 Sand, medium to coarse, some fine, tan to grayish-brown. Thin beds of tan and reddish-brown clay ___________________ 27 37 Sand, cemented, fine to coarse, grayish-tan; of granitic and volcanic composition -__- 12 49 Clay, hard, chocolate-brown; a few angular to subrounded clasts of granitic and vol- canic rocks ___________________________ 5 54 Sand, cemented, fine to coarse, grayish- brown; fine gravel ____________________ 4 58 Gravel, fine to medium; abundant meta- morphic and basaltic rocks; some medium to coarse gray and brown sand _________ 11 69 Clay, reddish-brown _____________________ 4 73 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA Selected logs of water wells—Continued H187 Selected logs of water wells—Continued Thick- Thick- Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C-ll—21)4ddc—Continued Well (C—ll—22)24bab—-Continued Older alluvium, undivided—Continued: Older alluvium, undivided—Continued: Sand, fine to coarse, grayish-tan; a few ce- Clay, light-brown; small amount of fine mented layers. Scattered pebbles; a few gravel _______________________________ 1 99 thin layers of light-grayish—brown clay _ 27 100 Sand, fine, poorly graded; scattered pebbles Sand, fine to coarse, grayish-tan, loose ____ 10 110 and occasional trace of clay ____________ 8 107 Sand, predominantly fine to medium, gray- Gravel, predominantly fine; similar in com- ish-tan; scattered granules and pebbles position to gravels above; few thin layers of volcanic rocks; few thin beds of gray- of fine sand, some cemented ____________ 11 118 ish-brown limy clay __________________ 51 161 Clay, hard, reddish-brown _______________ 2 163 Sand, predominantly fine to medium, gray- ish-tan; scattered granules and pebbles of volcanic rocks; few thin beds of grayish- brown limy clay ______________________ 12 175 Gravel, cemented _______________________ 3 178 Sand, medium to coarse, grayish-tan to grayish-brown; occasional streaks of fine gravel _______________________________ 28 206 Sand, fine to medium, limy, and light- grayish-brown clay, possibly in thin layers or lenses _______________________ 30 236 Sand and fine gravel, cemented ___________ 2 238 Sand, fine to medium, limy, and light- grayish-brown clay, possibly in thin layers or lenses _____________________ 4 242 Clay, limy, light-grayish-brown and gray __ 14 256 Sand, medium to coarse, grayish—brown; scattered volcanic granules and pebbles _ ,20 262 Sand, lime-cemented ____________________ 2 264 Sand and scattered gravel, medium to coarse, grayish-brown; scattered volcanic granules and pebbles __________________ 21 285 Clay, sandy, limy, tuffaceous; a few sub- rounded to rounded granules and small pebbles ______________________________ 13 298 Sand, fine to medium, limy, grayish-brown to gray; scattered granules and pebbles, a few streaks of grayish- and reddish- browu clay ___________________________ 4 302 Sand, consolidated, limy and ashy ________ 4 306 Gravel, fine, and coarse cemented sand ____ 1 307 Sand, fine to medium, limy, grayish-brown to gray; scattered granules and pebbles, a few streaks of grayish- and reddish- brown clay ___________________________ 13 320 Sand, fine to medium, clayey, limy, tufi‘a— ceous, gray to light-grayish-tan; some coarse sand, and a few layers of light- grayish- and reddish-brown clay ________ 53 373 Well (C—11—22)24bab [U.S. Bureau of Reclamation test well CH~27 YM on “Upper Mesa.” Drilled with mud-rotary equipment by Bureau of Reclamation. Log by E. Burnett of Bureau of Reclamation. Well point installed on end of 2-in. pipe at a depth of 268—270 ft. Altitude 322.3 ft. Older alluvium, undivided: Sand, fine, light-brown, poorly graded; scattered pebbles _____________________ 6 6 Clay, calcareous, light-reddish-brown; inter- beds of coarse sand and fine gravel con- sisting of subrounded to well-rounded clasts of chert, quartzite, and granitic and volcanic rocks ____________________ 8 14 Sand, fine, well-graded; numerous thin lay- ers of fine to coarse sand and fine gravel- 36 5O Gravel, predominantly fine, some coarse; pebbles consist of subrounded to well- rounded amber and black chert, amber to white quartzite, granitic and volcanic rocks. Small amount of cemented sand __ 14 64 Sand, fine, poorly graded; scattered pebbles 30 94 Sand, fine; thin layers of light-brown clay; small amount of fine gravel and cemented sand _________________________________ 4 98 Sand, fine, poorly graded; scattered gran- ules and small pebbles; occasional trace of clay _______________________________ 14 132 Gravel, predominantly fine; thin layers of cemented sand (calcareous) ____________ 4 136 Sand, fine, poorly graded; thin cemented layers at intervals of about 10 feet; occasional silt ________________________ 134 270 Well (C-ll-23)34bbc [U.S. Geological Survey test well LCRP 30 on Yuma Mesa at southerly in- ternational boundary. Drilled with mud—rotary equipment by Desert Water Drilling Co. Log by J. H. Robison. Well cased and gravel packed to 600 ft; perforated from 160 to 600 ft. Altitude 163.0 ft] Upper, fine-grained zone: Sand, very fine to coarse, silty; some very fine angular gravel. Few pieces brown clay _________________________________ 53 53 Sand, very fine to coarse ________________ 19 72 Coarse-gravel zone: Gravel, very fine to coarse (pebbles and chips to 25 mm), with fine to very coarse sand. Gravel is subangular to subrounded, has relatively high percentage of tufi's and other light volcanic types. Partly cemented. (Coarse and very loose, 109— 115 ft; cemented, 119—124 ft) __________ 58 Gravel, very fine to coarse, and fine to very coarse sand. Somewhat finer and less ce- mented than previous interval __________ 12 142 Sand, fine to very coarse. Small amount of brown silt, silty clay, and very fine gravel 48 190 Gravel, very fine to medium, and fine to very coarse sand. Gravel is subangular to subrounded, to 15 mm or larger; includes chert, quartzite, tufi, andesite, and gran- ite __________________________________ 12 Sand, fine to very coarse. Small amount of very fine to fine gravel ________________ 7 Gravel, very fine to medium, and small amount of medium to coarse cemented sand. Gravel is subangular to rounded, pebbles and chips to 15 mm or larger. Includes granite, chert, quartzite, but less andesite than above, a very little tuif. Some of the quartzitic pebbles look typical of Colorado River deposits. ____________ 23 Sand, fine to very coarse, and very fine to medium gravel. Gravel similar to previous interval. Small amount of brown silt ____ 57 Gravel, very fine to medium, and small amount of medium to very coarse sand. May be partly cemented, but very per- meable ______________________________ 12 Gravel, very fine to medium, and fine to very coarse sand. Cemented ___________ 9 Wedge zone: Sand, fine to very coarse; some very fine to medium gravel. Few thin layers of brown silt __________________________________ 15 Gravel, very fine to medium, and sand, medium to very coarse. Cemented ______ 35 Sand, fine to very coarse; some very fine to medium gravel _______________________ 21 Gravel, very fine to medium (10 mm or larger) and medium to very coarse _____ 28 130 202 209 232 289 301 310 325 360 381 409 H188 Selected logs of water wells—Continued WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA Selected logs of water wells—Continued Thick- Thick- Materinl ness Depth Material nas Depth (feet) (feet) (feet) (feet) Well (C-ll-23)34bbc—Continued Well (C—ll—24)23hcb—Conti.nued Wedge zone—Contlnued: Upper, fine-grained zone—Continued: Sand, fine to_ very coarse and some very Sand, fine, and moderate-brown clay; scat- fine to medlum gravel. Small amount of tered pebbles _________________________ 12 161 brown s1lty clay. Fragments of carbon- Sand, coarse, pebbly, and streaks of ill- lzed w°°d below 442 ft ---------------- 57 466 sorted sandy silt; some flat sandstone Sand, fine to very coarse. Some very fine to concretions ___________________________ 9 170 medlum gravel ----------------------- 30 496 Sand, fine to medium, clean, well-sorted ___ 19 189 Sand, fine to very coarse. Small amount of Coarse-gravel zone: very fine to medlum gravel ------------ 48 544 Gravel, fine to coarse, subangular to Sand, fine to very coarse. Small amount of rounded; medium to coarse sand, some very fine to medlum gravel and some sandstone concretions _________________ 12 201 brown clayey silt. Loose, uncemented ___ 79 623 gand’lfinf? to coarse; some gé‘avel -___-__a_ 6 207 rave , ne to coarse, san y; some san - [Parker and others. Irrigmidln ((3117:; zo‘dllsitcthern Yuma Mesa Drilled Stone concretions """""""""""" 18 225 with cable-tool equipment by Hamilton and Hood. Casing perforated Sand and scattered'pebbles -—----.-.- ------ 10 235 from 148 to 160 and 187 to 212 ft. Altitude 166 ft] Gravel, sandy; 51m11ar ln compos1t10n and . size to gravels above __________________ 14 249 Upper, fine-gralned zone: Sand, fine to coarse; scattered pebbles and Sand __________________________________ 53 53 sandstone concretions _________________ 31 280 Clay‘and gravel as much as 3 in. ________ 8 61 Gravel, fine to coarse, subrounded to Sand __________________________________ 19 80 rounded; interbedded coarse gray sand -_ 51 331 Gravel as much as 3 in. _________________ 1 81 Wedge zone: Clay, tough ____________________________ 6 87 Sand, fine to medium, gray; some coarse Sand, cemented, and gravel ______________ 5 92 sand and thin beds of pebbly sand; Sand __________________________________ 9 101 chunks of brown to gray clay and white Clay, jointed, and gravel as much as 3 in. _ 3 104 sandstone concretions _________________ 38 369 Clay, tough ____________________________ 24 128 Gravel, coarse, and varying amounts of Silt and fine sand _______________________ 14 142 gray sand ____________________________ 16 385 Coarse-gravel zone: Sand and some gravel ___________________ 8 393 Sand, medium, and gravel as much as Gravel, coarse, and varying amounts of 2% in. _______________________________ 162 gray sand ___________________________ 16 409 Sand. medium __________________________ 18 180 Sand, scattered pebbles and granules _____ 8 417 Sand, medium, and gravel as much as Gravel, fine to medium; some coarse sand _ 10 427 41/2 in. _______________________________ 32 212 Sand, fine to medium, gray ______________ 4 431 Sand, cemented, and sandstone strata _____ 47 259 Sand and gravel ________________________ 6 437 Large rocks imbedded in sandstone _______ 7 266 Sand, medium to coarse, gray; thin beds of gravel, in part cemented _______________ 20 457 we" (01144)”be Sand, fine, silty ________________________ 9 466 [U.S. Geological Survey test well LCRP 10 on Yuma Mesa at southerly Sand fine to medium clean _____________ 5 471 international boundary. Drilled with cable-tool equipment by Roscoe Moss ’ ’ 9 Co. Log by F. H. Olmsted and F. J. Frank. Casing perforated atfol- Gravel and sand cemented( ) ----------- 5 476 13:)2vgiiégs degtgl 39%tengés1412;67:1720300908232’54213623710’632407324?6428807338055, Sand, medium to coarse, some- pebbly zones 11 487 V , 7 _ , _ ’ 7 , i ’ __ 1 m ' _. 705, 8557875, and 923571.002 ft. Altitude 1608 ft] Grri‘diidedi?eablt1?1dgiidpliblblegudfncfilratrarid) Upper, fine—grained zone; quartzite, as well as volcanic, plutonic, Sand, fine to medium, some coarse moderate— and metamorphlc I‘OCkS; some sand ————— 37 524 yellowish-brown; grains subrounded to Sand, fine to coarse, gray; sparse granules rounded, fairly well sorted _____________ 27 27 and pebbles —————. ————— _— ——————————————— 13 537 Sand, fine to coarse, moderate-yellowish- Gravel, fine 1'0 medlum; interbedded sand. brown; some fine gravel, and streaks or Gravel contains abundant subangular to pieces of silty clay ____________________ 26 53 subrounded pebbles of granitic and silicic Clay, silty and sandy, moderate-brown ___- 3 56 volcanlc I‘OCkS ———————————————————————— 43 580 Sand, ill-sorted, clayey and silty; streaks of Sand, fine, somewhat silty, grayish- o-range- gravel and coarse sand _______________ 6 62 Plnk ———————————————————————————————— 7 587 Sand, fine to medium; smaller amounts of Sand, coarse, and granule gravel ————————— 8 595 silt, clay, and gravel __________________ 17 79 Sand, fine to coarse, gray; thm beds of Sand, medium to coarse, some fine, grayish— fine to medium gravel 7 ________________ 30 625 orange _______________________________ 14 93 Gravel, fine to coarse; th1n beds of sand __ 30 655 Sand, fine to coarse, moderate-ye'llowish- Sand fine to medium, a small amount brown to grayish-Orange; about 15—20 coarse; sparse granules and pebbles ___- 29 684 percent granule and pebble gravel, scat- Sand and fine to coarse gravel, interbedded- 23 707 tered small cobbles ___________________ 7 100 Sand, fine to medium; scattered granules Sand, fine to medium ____________________ 5 105 and pebbles and thin lenses or chunks of Sand, medium to coarse, some fine, moder- clay ———-—7 ——————————————————————————— 12 719 ate--yellowish-brown; 10—30 percent fine Sand and film bEdS 0f gravel; a few clay to medium gravel, some of it well balls ________________________________ 10 729 rounded; a little yellowish-brown clay ___ 19 124 Sand and fine to medium gravel __________ 8 737 Sand, fine to medium ____________________ 7 131 Sand, fine to medium; a few clay balls and Sand, medium to coarse, moderate-yellow- sandstone concretions _________________ 9 746 ish-brown, pebbly _____________________ 7 138 Sand, fine, silty; some clay balls and sand- Sand, fine to medium ___________________ 4 142 stone concretions _____________________ 33 779 Sand, coarse, some fine to medium; about Sand, fine to medium, clean ______________ 10 789 30 percent subangular to rounded pebble Sand, Silt, and clay _____________________ 5 794 grave] _______________________________ 7 149 Sand, fine to medium, clean ______________ 9 803 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA Selected logs of water wells—Continued H189 Selected logs of water wells—eContinued Thick- Thick- Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C—11-24)23bcb—Continued Well (C-12—21)l7cbc—Continued Wedge zone—Continued: Older alluvium, undivided—Continued: Gravel, cemented (conglomerate) ________ 4 807 and small pebbles of well-rounded quartz- Sand and some fine to medium gravel _____ 13 820 ite and volcanic and granitic rocks _____ 4 4 Sand, fine to medium, gray, clean ________ 4 824 Gravel, similar in size and composition to Sand and gravel ________________________ 9 833 that above; thin layers or lenses of red- Sandy, silty, fine; a few clay balls in lower dish-brown clay ______________________ 7 11 part _________________________________ 22 855 Sand, fine to coarse, and rounded pebbles Gravel, coarse; interbedded medium to and granules of quartzite and volcanic coarse sand __________________________ 18 873 and granitic rocks ____________________ 10 21 Sand, silty, fine; scattered pebbles and Gravel, fine, rounded ____________________ 12 33 pieces of clayey sandstone _____________ 21 894 Sand, fine to coarse; layers or lenses of Sand, fine to medium, gray ______________ 9 903 gravel _______________________________ 11 44 Sand, clayey sandstone, and fine gravel; Sand, fine; layers or lenses of fine gravel small amount of wood _________________ 20 923 at intervals of 3—10 ft; traces of reddish- Sand, fine, silt, and sandy clay; scattered to grayish-brown clay _________________ 28 72 granules and pieces of carbonized wood _ 57 980 Sand, fine; scattered gravel _____________ 39 111 Sand, fine to coarse, and gravel, inter- Gravel, fine; similar in composition to that bedded. Some zones cemented __________ 26 1,006 above, with black chert pebbles also ____ 5 116 Sand, fine, and thin beds of brown and gray Sand, fine; scattered gravel ______________ 17 133 clay _________________________________ 7 1,013 Sand and fine gravel, interbedded ________ 25 158 Clay, brown, pebbly, and sand ___________ 14 1,027 Sand, fine; scattered gravel. More indurated Sand, some fine gravel, and thin streaks of or compacted below 235 ft _____________ 162 320 clay _________________________________ 11 1,038 Well (C—12—21)l4dnb [U.S. Bureau of Reclamation test well CH725YM near west edge of “Fortune. Plain," about 2 miles north of southerly international bound- ary. Drilled with mud-rotary enuipment by Bureau of Reclamation. Log by E. Burnett and E. Smith of Bureau of Reclamation. Well point installed at a depth of 367-369 ft. Altitude 422.2 ft] Younger alluvium (alluvial-fan deposits): Sand, fine, light-brown; intermixed white angular coarse granitic sand ___________ 6 6 Clay, sandy, calcareous, reddish-brown __.. 10 16 Sand, fine, lightrbrown; intermixed white angular, coarse granitic sand ___________ 2 18 Clay, sandy, calcareous, reddish-brown __-- 9 27 Sand, fine, light-brown; intermixed white angular coarse granitic sand ___________ 11 38 Clay, sandy, reddish-brown; streaks of coarse granitic sand __________________ 3 41 Sand, fine, light-brown; intermixed white angular coarse granitic sand; few thin seams of clay or silt __________________ 18 59 Clay, sandy, reddish-brown; streaks of coarse granitic sand ___________________ 3 62 Sand, fine, silty, medium-brown ___________ 10 72 Clay, silty, medium-brown; little fine sand- 4 76 Sand, fine, poorly graded _______________ 3 79 Clay, soft, calcareous, reddish-brown ______ 10 89 Sand, silty, fine; little medium to coarse sand ________________________________ 4 93 Older alluvium: Sand, fine; scattered granules of angular to well—rounded granite, chert, quartzite, and quartz; few thin layers or lenses of medium-brown to light-grayish-brown highly plastic fines ___________________ 8 101 Sand, fine, poorly graded ________________ 6 107 Sand, fine to coarse, and some fine gravel similar in composition to that from 93 to 101 ft _______________________________ 3 110 Gravel, fine to coarse, predominantly sub- rounded to well-rounded, similar in com— position to gravels above _______________ 11 121 Sand, fine, poorly graded; scattered gran- ules and pebbles ______________________ 248 369 Well (C—12—21)l7cbc [U.S. Bureau of Reclamation test well CH723YM on “Upper Mesa” at southerly international boundary. Drilled with mud-rotary equipment by Bureau of Reclamation. Log by E. Burnett of Bureau of Rec‘ama- tion. Well point installed at a depth of 318—320 ft. Altitude 356 ft] Older alluvium, undivided: Sand, fine, light-brown; scattered granules Well (C—l2—22)9bab [U.S. Geological Survey test well LCRP 24 on “Upper Mesa” at southerly international boundary. Drilled with cable-tool equipment by R. . Anderson. Log by F. J. Frank, Rex Anderson, and F. H. Olmsted. Casing perforated from 318 to 324, 330 to 336, and 340 to 346 ft. Altitude 233.5 ft] Older alluvium, undivided: Soil, brown, sandy; some pebbles _________ 2 2 Sand, pinkish-brown, tough, silty; gravelly lenses; white caliche throughout, gravels mostly rounded to subrounded and in- clude quartzite, chert, and granitic, meta- morphic, and volcanic rocks ____________ 20 22 Sand, light-brown, poorly sorted; with less than 5 percent well-rounded gravel ..... 4 26 Sand, light—brown, medium to coarse, poorly sorted _______________________________ 5 31 Sand, brown; with 40 percent rounded to subrounded gravel composed of mostly chert and quartzite ___________________ 4 35 Sand, brown, medium to coarse; poorly sorted with a few scattered quartzite and chert pebbles _________________________ 15 50 Sand, brown, medium to coarse, poorly sorted; some cementation and thin lenses of sandstone _________________________ 30 80 Sand, brown, medium to coarse ___________ 13 93 Sand, brown, medium to coarse; some small pebbles and granules __________________ 1 94 Gravel, with small amount of medium- brown sand; gravel mostly well-rounded quartzite and chert 14—94 in. ___________ 6 100 Gravel, with small amount of medium to coarse brown sand. Gravel includes well- rounded quartzite and chert as much as 3 in. with some subrounded gravel of local origin _______________________________ 25 Sand, brown, medium to coarse; with a few 14—1/2 in. subrounded, subangular graveL 46 171 Sand, brown, fine; silty with a few scattered subangular 1A-in. gravel; some cementa- tion _________________________________ 62 Clay, silty, reddish-brown to buif; coarse sand and a few subangular to angular metamorphic and volcanic pebbles ______ 2 Silt and fine buff sand; some clay; cemented in part ______________________________ 27 Sand, medium, brown; with cementation and thin sandstone lenses; some pinkish- brown clay balls _____________________ 13 _Sand, medium, brown; some cementation 125 233 235 262 275 H190 Selected logs of water wells—Continued WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA Selected logs of water wells—Continued Thick- Thick- Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well (C—12—22)9bah—Continued Well (C-l3—20)2abdl—Continued Older alluvium, undivided—Continued: Older and younger alluvium, undifierentiated—Continued: and thin lenses of sandstone; some clay Sand, fine; little silt and clay ____________ 175 635 balls and a few subangular pebbles of Clay, light-brown, silty __________________ 5 640 local origin ___________________________ 20 295 Sand, fine; little silt or clay ______________ 35 675 Sand, fine to medium, brown, somewhat ce- Clay, light-brown _______________________ 5 680 mented ______________________________ 7 302 Sand, fine ______________________________ 20 700 Sand, medium to coarse, brown; some sub- Clay ___________________________________ 5 705 rounded to subangular 14—37t-in. gravel; Sand, fine ______________________________ 10 715 some cementation _____________________ 8 312 Clay ___________________________________ 5 720 Gravel and sand. Gravel subrounded to sub- Sand, fine ______________________________ 5 725 angular, 1/1—3/3 in., mostly granite and Clay ___________________________________ 5 730 volcanic rocks with a few well-rounded Sand, fine; cemented layer at 755 ft ______ 30 650 pebbles of chert and quartzite; some ce- Sand, fine; clay layers, thin cemented zones, mentation and about 50 percent brown and scattered fine gravel ______________ 50 810 medium to coarse sand ________________ 12 324 Sand, fine; thin beds of clay; cemented Sand, medium to coarse, brown, somewhat layer at 810 ft _______________________ 60 870 cemented ____________________________ 6 330 Sand, fine; thin beds of cemented fine sand Sand and gravel; sand more than 50 per- from 870 to 880 ft, 890 to 895 ft, and at cent; medium to coarse subangular 14—1 940 ft; little silt or clay _______________ 100 970 in. gravel ____________________________ 6 336 Clay ___________________________________ 5 975 Sand, medium to coarse, brown ___________ 4 340 Sand, fine; thin cemented layers at 1,015, Sand and gravel; gravel mostly granitic 1,025, and 1,075 ft; little silt or clay ..-__ 110 1,085 and volcanic, subangular to subrounded _ 6 346 Claystone (probably calcareous) _________ 5 1,090 Sand, medium, brown, with a few angular Sand, fine; thin cemented layers at 1,145— - gravels _______________________________ 20 366 1,150 ft; little silt or clay _____________ 70 1,160 Clay and silt, buff _______________________ 4 370 Clay ___________________________________ 5 1,165 Sand, fine to medium, buff, somewhat ce- Sand, fine _' _____________________________ 5 1,170 mented ______________________________ 4 374 Clay ___________________________________ 5 1,175 Sand, very fine, silty, buff, somewhat ce- Sand, fine; little silt or clay ______________ 40 1,215 mented ______________________________ 18 392 Clay ___________________________________ 5 1,220 Sand, fine to medium; well cemented in part, Sand, fine; more indurated (higher acoustic thin gray clay and 5—10 percent subangu- velocity) than materials above _________ 55 1,275 lar to subrounded %—%g-in. gravel. Gravel Sand, coarse ___________________________ 10 1,285 mostly granitic and volcanic, with a few Transition zone: well-rounded pebbles of chert and quartz- Sand, fine, clayey, bluish to greenish-gray _ 20 1,305 ite __________________________________ 5 397 Clay, gray _____________________________ 5 1,310 Sand, fine to medium; a few thin lenses of Sand, fine, gray _________________________ 5 1,315 gray silty clay _______________________ 18 415 Clay, gray _________________h ___________ d 5 1,320 Sand, fine, clayey, gray; t in cemente .We“ (0"3'20’zab‘“ u , layers at 1,320 ft, 1,360—1,365 ft, and [U.S. Bureau of Reclamation test well CH728Y.M on Foxtuna Plan) at 1 370 ft 55 1 375 southerly international boundary. Drilled With mud-rotary equipment ’ ----------------------------- ’ :nEreaelrfpeexéaafizz- £4213 J? E)- i‘iu‘m i; Malawi??- S1”; ggay --1- ------------- , ism-mg; 10 L385 - S . . 4.‘ ‘ ' ’ an , ne, c ayey, gray; in cemen e 2 . 1 th 1' w 01 t installed in same hoe as well C—13v20 iéiiiiz if: aAdreopthe of dig—500nm Altitude 577.5 ft] 1 ( ) layers at 1385’ 1:405, and 1,410 ft ------ 42 1:427 Older and younger alluvium, undifferentiated: Sand, fine; few thin layers of clay from 0 to 21 ft; occasional thin layers or lenses of cemented sand below 62 ft __________ 95 95 Clay, calcareous, medium-brown _________ 5 100 Sand, fine; few thin layers of clay; occa- sional thin layers or lenses of cemented sand Clay, calcareous, medium-brown; inter- bedded medium to coarse granitic sand - 10 115 Sand, fine, predominantly quartz; abundant medium to coarse angular to subangular granitic sand; thin layers of cemented 105 sand _________________________________ 165 280 Clay, silty, medium-brown; interbeds of fine to coarse granitic sand ________________ 30 310 Gravel, fine; consists of angular to well- rounded clasts of chert, quartzite, quartz and granitic and volcanic rocks; fine to coarse sand __________________________ 15 325 Clay, brown, silty _______________________ 10 335 Sand, fine to coarse; considerable amount of fine gravel ________________________ 45 380 Clay, brown, silty _______________________ 5 385 Sand and gravel, fine to coarse ___________ 10 395 Sand, fine; thin beds of light-brown sandy to silty clay __________________________ 50 445 Clay, silty, light-brown __________________ 5 450 Sand, coarse ____________________________ 10 460 Well lGS/2lE—36Fca [Arizona Public Service 00., Industrial well in northwestern Yuma Val- ley. Drilled with cable-tool equipment by Roscoe Moss Co. Casing perforated from 518 to 560, 592 to 650, 706 to 740, 752 to 766, 864 to 880, and 904 to 912 ft. Altitude 117 ft] Upper, fine-grained zone: Topsoil ________________________________ 4 4 Clay, silty, water at 11 ft _______________ 7 11 Sand, fine, brown (quicksand action) ______ 28 39 Clay, bluish, silty ______________________ 1 40 Sand, bluish, fine, clay streaks, slow— draining _____________________________ 65 105 Silt, mixed, and clay with pebbles _________ 7 112 Coarse-gravel zone: Gravel, clean, possible clay layer 6 in. thick 8 120 Gravel, clean; fair gradation with rocks as much as 6 in. ________________________ 22 142 Gravel and coarse sand; rocks as much as 2 in ____________________________________ 10 152 Wedge zone: Sand, lightly cemented fine sand lumps, and some small gravel _____________________ 10 162 Clay ___________________________________ 5 167 Gravel, round and fractured, as much as 2 in.; brown dirty water _________________ 3 170 Gravel, small, round and fractured; lightly cemented sand laminae, 3 in. thick; piece hard to break _________________________ 14 184 Sand, mixed; gravel with clay an ash; GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H191 Selected logs of water wells—Continued Selected logs of water wells—Continued Thick- Thick- Material ness Depth Material ness Depth (feet) (feet) (feet) (feet) Well lfiS/ZlE—SGFca—Continued Well lGS/ZlE—36Fca—Continued Wedge zone—Continued: Wedge zone—Continued: soft, slimy, possibly colloidal clay _______ 16 200 Gravel, mixed, loose; angular as much as Sand and pea gravel; some lightly consoli- 3 in., with sand and silt filler __________ 14 766 dated sand streaks ____________________ 7 207 Clay, firm; grades to softer mixed clay; fine Sand and gravel as much as 1% in. ______ 8 215 silty sand ____________________________ 30 796 Sand, lightly cemented laminae, fine gravel, Sand and clay, mixed; very muddy _______ 16 812 few shale particles ____________________ 10 225 Sand, small gravel, and some clay ________ 8 820 Sand; gravel as much as 11/2 in.; brown silt 10 235 Clay with some sand and gravel __________ 8 828 gang, soft, some gliavel, bluiih “"13; _____ 15 250 Clay svdith fine sand, very little gravel, quite 2 an ; some grave as muc as 2 in.; mu y water _________________________ 1 840 lightly consolidated sand laminae _______ 16 266 Clay and sand; increased amount of sand Safnd; some gravel, few large rocks at 280 4 2 with small graVel, muddy water ________ 10 850 t ___________________________________ 1 80 Sand and small gravel ___________________ 4 854 Sand, fine; thin consolidated clay streaks at Sand and gravel as much as 2 in.; sand not S 280 fit _______________________________ g 235 S sharp and only moderately cllean _______ 16 870 and, ne ______________________________ 2 4 and with some fine grave , increased Firm clay strata with shale and gravel ___- 6 300 amount of sand _______________________ 14 884 Sand1 ; fslome lightly cemented laminae _____ a; 3&0 Eand, medium _1______-_h _________________ 16 900 San , ne ______________________________ O and and grave as muc as 2 in. ________ 12 912 Sand, mixed, and clay; some gravel _______ i 334 Sand with silt and clay __________________ 12 924 Sand, fine ______________________________ 38 Silt, tight; with mixed clay and sand _____ 12 936 Sanhd,1 lightly 1cemented laminae with few 2 Clay, silty red, hsome very firm ___________ 8 944 s a e partic es ________________________ 1 350 Clay, silty; wit granite pieces as much as Sand, megium; some clay balls at 335 ft __ 10 360 2 in. _________________________________ 4 948 and, me ium __________________________ 12 372 Granite detritus with clay and silt fill ___- 4 952 Sand, mediugn, and loose gravel. Apparently 0 382 Slay, firm, and brown silt ________________ 12 964 good aqui er _________________________ 1 ilt and sand with cemented layers _______ 8 972 Sand, medium, and gravel as much as 1% 6 388 Sand and gravel as much as 3 in.; granitic- 6 978 In. ___________________________________ Sand; gravel and Clay layer about 8 in‘ [U.S. Bureau of Reclamativg:ntels(:s€:lli:-él}ll)fi)4RD in western Bard Val- thlck at 390 ft ________________________ 4 392 ley. Drilled with mud-rotary equipment by Bureau of Reclamation. Log Sand, coarse, and fine gravel _____________ 6 398 by Granchi and Moffitt of Bureau .of Reclamation; modified by.F. H. Sagféveglrrgvii'éh 311111116 cliggigizrsand rounded 12 410 gégigifegofi" eii’ff‘irt’fiimimsifiiecirt‘c‘a “331)??? “iii” ifsgfiziveil. pi'fiitliié Sand medium; with very little 559611—018; - . ’ . . ’ Upper, fine-grained zone: safifif’irisvéli’ynfiiiag‘aa'y:zgagaegaga't‘aa 1" 42° gang, firgebtan ---1 ----------------------- 1g 2; ash layer 6 in. thick at 420 ft __________ 4 424 Sand 3; If“ C W -------------------- 14 3 Sand, gravelly; some clay balls and silt ___ 6 430 Cim ’ If? rgcvlmhh """"""""""" 6 Sand; some gravel pieces 0f lignite at 475 ft 44 474 S 213;}, SE ’ I; 15 ' 1103’“ k ------ to "6"": 3 39 Clay layer preceded and followed by dirty a; ' ne 1 coarse, dar égray) lrown, end wee cemented 5mm graind°qusizag31::t:°‘ u so Safi‘i‘iieafiéiafiihg'g'av'gi‘::::::::::::: i3 133 glayd, efgfte, brovge “ed““i ----- amen": 1 51 Sand, lightly cemented; some small gravel _ 8 506 arh"fl ne, Sf": .Er granu es an pee es, Sand, coarse; well-graded angular gravel as 5 Sacndle filr'lquoa cogrgej-fifié'éggé ----------- E E; much as 2 in. ________________________ 4 10 ’ ’ """""" Sand, coarse, and fine gravel _____________ 8 518 Coarae-gralvelfizoneéé . d f b Sand, coarse, and small gravel, some 2 in. _ 10 528 rave ’1 nte cgafis‘e’ corlnpose bbl) su d Sand and small gravel with clay streaks __ 10 538 231%}le 0% rgi‘lalniice giirlfafii pfiockess, :2 d Sand; some small gravel _________________ 22 560 ' . . ’ ’ Sand, medium; very little gravel; few thin quartmte, fine to coarse brown sand ___- 20 133 cemented sandy laminae _______________ 24 584 3223’ gggltfycoarse, brown """"""""" ; fig Sand, coarse; some small gravel __________ 16 600 ’ """""""""""""" Sand, small amount of gravel, some clay ___ 10 610 Sang, gne {’0 coarse, brownfi """""" 1 """" 1 4 156 Sandy gravel as 1much as 2 in., mixed round 2 SZEd, fig: t: $3§f§&s%r::wnne grave ----- i 12% and angular, C can ____________________ 12 6 2 ’ i ’ """""""" Gravel, sandy, clean; as much as 3 in.; few (Sland 3nd grivel """""""""""""" 19 184 cemented conglomerate zones ___________ 6 628 S a321, ersse, rorvn """"""""""""" 3 187 Sand, coarse, and small gravel; good grada- 4 We dgznzonzierlfig-rave """"""""""""" 5 192 tion _________________________________ 632 ‘ ' . Gravel, sandy, sharp and clean; as much as Eand,éine tobmedium, brown """"""" 31 223 2hin.; firmly cefmented sand layer 6 in. 8 83:53 Sfifiie’gfgxgh'gggva """""""""" 3 332 t ick near 638 t _____________________ 640 ’ ’ '. ' """""""" Gravel, sandy; as much as 2 in.; streaks of gfigd’dfinf’ grayish-brown """""""""" 12 249 hard clay and cemented sand laminae ___ 4 644 S1 ’d eince, gra-Y 11—1; """"""""""""""""" 2 251 Firm clay grading to sand and silt _______ 36 680 San ’ ne, grayls ‘ rown "“7 ----------- 19 270 S nd mixed and cla ___________________ 24 704 and, some gravel composed chiefly of gran- Sa (1’ d ’ 11 yl 4 708 1te and quartz1te 13 283 an an sma grave _______________________________________ Sand and small gravel as much as 2 in. ___ 32 740 (Shaiéelfi ----------------------------- 3 286 Sand, gravel, and clay and cemented vol- San ’ ne to coarse, gray "“"“"'. ““““ 8 294 canic ash ____________________________ 10 750 and and clay, interbedded; soft bluish to Granite pieces, larger fractured, as much as grayish-green clay -------------------- 16 310 6 in. with sand _______________________ 2 752 Sand, fine, brown ——————————————————————— 14 324 H192 Selected logs of water wells—Continued WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA Selected logs of water wells—Continued Thick- Material ness Depth (feet) (feet) Well lfiS/ZZE—ZlDbb—Continued Wedge zone ( ?)—Continued: Sand, fine to coarse, pebbly ______________ 28 352 Sand, fine, brown _______________________ 8 360 Sand, fine to coarse, pebbly ______________ 16 376 Sand, fine, brown _______________________ 12 388 Sand, fine to coarse, pebbly ______________ 8 396 Sand, fine, brown _______________________ 6 402 Sand, fine to coarse, pebbly; gravel more abundant below 415 feet _______________ 17 419 Sand, fine to medium, grayish-brown; scat- tered granules and pebbles _____________ 21 440 Clay, hard, and cobbles __________________ 4 444 Sand, fine to medium, some coarse, grayish— brown _______________________________ 15 459 Sand, medium to coarse, brown, and fine, well-rounded gravel ___________________ 14 473 Sand, fine to medium, brown _____________ 6 479 Gravel, fine, well—rounded, and fine to coarse brown sand __________________________ 5 484 Sand, silty, fine, and thin beds of bluish- gray clay ___________________________ 6 490 Sand, fine to coarse, brown, and fine gravel, interbedded __________________________ 17 507 Well 168/22E-23Cna [U.S, Bureau of Reclamation test well CH78 in Bard Valley. Drilled with cable-tool equipment by E. McBride. Log by E. L. Smith of Bureau of Reclamation; modified by F. H. Olmsted on basis of gamma log. Casing perforated from 96 to 104 ft. Altitude 128.5 ft] Upper, fine-grained zone: Sand, fine to coarse, light-brown (above 20 ft), and grayish—brown (below 20 ft); interbedded reddish-brown to dark-brown clay and silty sandy clay ______________ 38 38 Sand, fine to coarse; little reddish-brown clay; little gravel from 72 to 75 ft _____ 41 79 Sand, gray, and 10—40 percent gravel con- taining abundant concretions of limy sandstone ____________________________ 19 98 Coarse-gravel zone: Gravel, fine to 3 in., angular to well— rounded; about 35—40 percent coarse gray sand _________________________________ 6 104 Wedge zone: Sand, fine to coarse, gray; scattered pebbles, and some beds of yellowish—green and brown clay and silt ___________________ 57 161 Sand, gray, and gravel __________________ 26 187 Sand; little gravel ______________________ 7 194 Sand and gravel _______________________ 26 220 Sand; little gravel ______________________ 22 242 Gravel, fine to 2 in., and gray sand _______ 14 256 Sand, fine to coarse, gray; scattered gran- ules and pebbles ______________________ 12 268 Gravel and sand ________________________ 9 277 Sand, fine, and scattered “pea” gravel ____ 17 294 Gravel and sand; some cobbles and concre- tions of limy sandstone up to 8 in. ______ 26 320 Sand, fine to medium, and about 40 percent fine to l—in. subangular gravel _________ 8 328 Bouse Formation(?) : Clay, silty, dark-gray ___________________ 3 331 Sand, fine to medium, gray; moderately to firmly cemented _______________________ 1 332 Clay, silty, dark-gray, partly calcareous; thin layers of cemented sand ___________ 10 342 Volcanic rocks (Tertiary?): Basalt, fine-grained, dark-gray, slightly glassy; weathered and vesicular ________ 18 360 Thick- Material ness Depth (feet) (feet) Well 1 65/22E—29Gca2 [U.S. Geological Survey test well LCRP 26 in western Bard Valley. Drilled with mud-rotary equipment by Kalco Development Co. Log by F. H Olmsted, F. J. Frank, and A. G. Hely. Well cased and gravel packed to 1,769 ft; perforated from 125 to 1,127 and 1,368 to 1,769 ft. Altitude 125.4 ft] Upper, fine—grained zone: S11t, brown ____________________________ 7 7 Sand, fine to medium, brown _____________ 18 25 Clay, silty, medium-brown _______________ 10 35 Sand, fine to medium, and grayish-brown silt __________________________________ 11 46 Clay, silty ______________________________ 5 51 Sand, grayish-brown ____________________ 18 69 Silt, sand, and clay ______________________ 7 76 Sand, grayish-brown ____________________ 8 84 Silt, sand, and clay ______________________ 7 91 Sand, grayish-brown ____________________ 19 110 Sand; scattered granules and pebbles _____ 10 120 Coarse-gravel zone: Gravel, coarse, loose; contains abundant well-rounded pebbles and cobbles of sili- ceous rocks __________________________ 11 131 Gravel, coarse to fine, and sand ___________ 22 153 Coarse-gravel zone(?) : Sand, silty, brown, soft __________________ 3 156 Gravel and sand, loose; subangular to well— rounded pebbles, cobbles, and granules of a wide variety of rocks including abun- dant quartzite and chert ______________ 24 180 Wedge zone (gravel similar in composition to that above) : Sand and gravel ________________________ 30 210 Gravel and sand ________________________ 30 240 Sand and gravel ________________________ 52 292 Gravel and sand ________________________ 33 325 Sand and gravel ________________________ 10 335 Gravel and sand _______________________ 39 374 Clay, silty _____________________________ 2 376 Sand and gravel ________________________ 20 396 Gravel and sand ________________________ 14 410 Sand and gravel ________________________ 23 433 Sand, little gravel _______________________ 11 444 Gravel and sand ________________________ 8 452 Sand __________________________________ 8 460 Gravel and sand ________________________ 4 464 Sand __________________________________ 5 469 Sand and gravel ________________________ 19 488 Sand __________________________________ 11 499 Gravel and sand ________________________ 23 522 Conglomerate (cemented gravel and sand) _ 14 536 Sand __________________________________ 10 546 Sand and gravel ________________________ 18 564 Sand; scattered gravel __________________ 24 588 Gravel and sand ________________________ 11 599 Sand, some gravel ______________________ 12 611 Gravel and sand ________________________ 8 619 Sand, some gravel _______________________ 27 646 Gravel and sand ________________________ 25 671 Silt, sand, and clay _____________________ 6 677 Gravel and sand ________________________ 46 723 Sand and silt ___________________________ 20 743 Sand, some gravel and silt _______________ 40 783 Sand and silt ___________________________ 49 832 Sand, some gravel ______________________ 42 874 Sand and silt ___________________________ 56 930 Sand, some gravel; thin beds of clay ______ 16 946 Gravel and sand ________________________ 20 966 Sand, some gravel ______________________ 34 1,000 Gravel and sand ________________________ 17 1,017 Sand, some gravel ______________________ 16 1,033 Transition zone: Clay, silty, gray ________________________ 7 1,040 Clay and sand, interbedded ______________ 43 1,083 Gravel and sand; some chert and quartzite granules and pebbles __________________ 19 1,102 GEOHYDROLOGY OF THE YUMA Selected logs of water wells—Continued Thick- AREA, ARIZONA AND CALIFORNIA H193 Selected logs of water wells—Continued Thick- Material ness Depth Material ness Dept th (feet) (feet) (feet) (feet) Well 165/22E—296ca2—Continued Well 16S/23E-8Ecc—Continued Transition zone—Continued: Wedge zone—Continued: Sand, fine to medium, gray ______________ 13 1,115 Sand __________________________________ 5 184 Bouse Formation: Sand, locally cemented; streaks of gravel __ 18 202 Clay, silty, gray _______________________ 39 1,154 Gravel and sand ________________________ 7 209 Clay and fine to medium gray sand _______ 6 1,160 Sand; some gravel and silty clay _________ 4 213 Clay, silty, gray ________________________ 33 1,193 Sand, fine to coarse, and angular to sub- Sand, fine to medium, and gray clay -__,.__ 4 1,197 angular gravel up to 114 in. ____________ 19 232 Clay, silty, gray ________________________ 124 1,321 Gravel, granules and pebbles, up to 2 in. ; Sand, fine to medium, gray, and silty clay _ 7 1,328 sand _________________________________ 17 249 Clay, silty, gray ________________________ 15 1,343 Sand and scattered granules and pebbles __ 7 256 Tufi‘ or ash(?) _________________________ 9 1,352 Sand and gravel up to 2 in. ______________ 35 291 Limestone, sandy _______________________ 28 1,380 Sand, fine ______________________________ 9 300 Nonmarine sedimentary rocks: Gravel containing pebbles up to 3 in.; 40 Conglomerate composed of pebbles, cobbles, percent sand _________________________ 13 313 and boulders of gneiss, granite, pegma- Sand, fine; about 5 percent pebbles _______ 21 334 tite, vein quartz, and other crystalline Sand and angular granules and pebbles; rocks; some beds of coarse, gritty sand- about 10 percent cobbles; some zones con— stone ________________________________ 285 1,665 tain little gravel ______________________ 78 412 Boulder conglomerate or megabreccia: Gravel, up to 3 in., and sand _____________ 40 452 Blocks and boulders of crystalline rocks Sand, fine to coarse; 5—8 percent gravel __ 28 480 in an earthy sandstone matrix __________ 112 1,777 Sand, gravel, and carbonized wood ________ 10 490 w... S312;cff‘fi‘i:_C_°I‘ff‘_"3f_‘iffvif‘f‘i‘ilf‘fffl’: 10 500 [D. W. Haygood. Irrigation well in Bard Valley, near west bank of Colorado River. Drilled with cable-tool equipment by Frank H. Leidendeker. Casing perforated from 115 to 153 ft. Altitude 140 ft] Upper, fine-grained zone: Clay with wood roots ___________________ 8 8 Sand, silted ____________________________ 10 18 Clay, soft ______________________________ 2 20 Water sand and some sharp gravel _______ 25 45 Quicksand with some gravel and clay streaks ______________________________ 62 107 Coarse-gravel zone: Gravel, good ___________________________ 33 140 Gravel, small, coarse sand _______________ 13 153 Wedge zone: Gravel, very sandy ______________________ 6 159 Well lGS/23E—8Ecc [U.S. Bureau of Reclamation test well CH—5 in Bard Valley. Drilled with cable-tool equipment by San Diego Well Drilers. Log by Bureau of Reclamation; modified by F. H. Olmsted on basis of gamma log. Casing perforated from 110 to 141 ft. Altitude 130 ft] Upper, fine- grained zone: Sand, silt, and clay; l-ft layer of black organic silt and clay at 10 ft ___________ 11 11 Sand, fine, light—brown, grading downward into fine gray sand ____________________ 26 37 Clay, brown, silty, and fine sand __________ 3 40 Clay, pebbly ____________________________ 1 41 Clay, brown, silty, and fine sand; also layers of gray silty clay; scattered peb- bles in lower part ____________________ 19 60 Sand, fine, gray _________________________ 5 65 Clay, brown, silty, and fine sand; scattered pebbles ______________________________ 12 77 Sand, fine, varicolored; scattered pebbles and small cobbles up to 4 in., and a few lenses of clay _________________________ 32 109 Coarse-gravel zone: Gravel containing rounded pebbles and cob- bles up to 4 in.; 30—40 percent fine to coarse sand; more sand in lowest several feet _________________________________ 39 148 Wedge zone: Sand, fine to coarse; silt, clay, and scat- tered fine gravel ______________________ 18 166 Sand, fine to coarse, and fine gravel. Below 166 ft the materials are characterized by higher gamma radiation than those above; this is probably due to a high per- centage of both clay and gravel to coarse sand containing abundant silicic volcanic and granitic rocks _____________________ 13 179 Well IGS/Z3E—9Naa [M. E. Spencer. Irrigation well in Bard Valley. Drilled with cable-tool equipment by Frank H. Leidendeker. Casing perforated from 124 to 150, 154 to 164, 198 to 204, 205 to 217, and 218 to 225 ft. Altitude 137 ft] Upper, fine-grained zone: Soil ___________________________________ 4 4 Clay ___________________________________ 1 5 Sand, silt, and clay mixed _______________ 2 7 Sand, silted ____________________________ 30 37 Clay, sand with pebble strata ____________ 28 65 Sand and clay strata ____________________ 13 78 Quicksand ______________________________ 9 87 Clay and grave] in sand _________________ 10 97 Gravel, sandy __________________________ 6 103 Sand __________________________________ 11 114 Coarse—gravel zone: Gravel _________________________________ 36 150 Wedge zone: Sand __________________________________ 2 152 Sand, coarse, and fine pea size gravel _____ 12 164 Sand, some pebbles ______________________ 14 178 Gravel, sandy __________________________ 3 181 Clay ___________________________________ 1 182 Sand and some gravel ___________________ 6 188 Sand, coarse, and pea size gravel _________ 16 204 Sand, some pebbles _____________________ 6 210 Gravel, sandy __________________________ 8 218 Gravel, not too large ____________________ 7 225 Sand, some pebbles ______________________ 1 226 Sand __________________________________ 9 235 Well 16S/23E—10Rcc [U.S. Geological Survey test well LCRP 23 in eastern Bard Valley, on West bank of Colorado River. Drilled with cable-tool equipment by Hamilton and Hood. Log by F. H. Olmsted and G. R. Vaughan. Casing perforated from 120 to 548 and 634 to 694 ft. Altitude 143.8 ft] Upper, fine-grained zone: Sand, fine, silty, brown -1 ________________ 14 14 Sand, fine to medium, grayish-brown; scat- tered granules and pebbles _____________ 35 49 Clay, silty and sandy; some sand and scat- tered granules and pebbles _____________ 13 62 Sand, fine to medium, grayish-brown ______ 11 73 Sand, fine to coarse; some clay and silt, and about 10—15 percent gravel ____________ 28 101 Sand, fine to medium, grayish-brown ______ 11 112 Coarse-gravel zone: Gravel containing abundant well-rounded and subrounded pebbles and cobbles of quartzite, chert, silicic volcanic rocks and H194 Selected logs of water wells—Continued WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA Selected logs of water wells—Continued Thick- Material ness Depth (feet) (feet) Well 165/23E—10Rcc—Continued Thick- Material ness Depth (feet) (feet) Well l6S/23E—lORcc—Continued Coarse-gravel zone—Continued: various types of crystalline rocks; some medium to coarse sand, probably as lenses 43 155 Wedge zone: Sand, fine to coarse, and thin beds of ce- mented gravel ________________________ 11 166 Gravel, fine to coarse, subangular to well- rounded; chert and quartzite somewhat less abundant than in interval from 112 to 155 ft; medium to coarse sand, prob- ably as lenses _________________________ 49 215 Gravel containing abundant bluish-gray, pink, and green volcanic detritus; some vein quartz, quartzite, and chert and vari- able amounts of crystalline rocks (pre- Tertiary). Fine to coarse sand present in variable amounts throughout. Gamma ra- diation noticably higher than in overlying materials. Sample of charcoal from a depth of 224—234 ft gave an age of >36,000 years by the C“ method _______ 333 548 Bouse Formation: Clay, greenish-gray, and interbedded gray silt and fine sand; fossiliferous _________ 86 634 Conglomerate composed chiefly of angular to subrounded clasts of gneiss and gran- ite; some coarse sandstone _____________ 22 656 Clay or mudstone, bluish-gray ____________ 3 659 Conglomerate composed chiefly of angular to subrounded clasts of gneiss and gran- ite; some coarse sandstone _____________ 22 681 Limestone, pale-yellowish-gray ........... 6 687 Nonmarine sedimentary rocks: Fanglomerate composed chiefly of angular and subangular blocks and slabs of gran- ite, gneiss, schist, and various other crystalline rocks similar to those now ex- posed in Laguna and Chocolate Moun- tains ________________________________ 16 703 Quartz monzonite, porphyritic, coarse; either in large boulders and blocks or as bedrock (crystalline rocks of pre-Tertiary age) ................................. 12 715 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA APPENDIX C. CHEMICAL ANALYSES OF GROUND WATER Appendix C presents 776 chemical analyses of ground-water samples from 396 wells in the Yuma area. Most of the analyses were made in laboratories of the U.S. Geological Survey in Yuma, Ariz., or in Albuquerque, N. Mex., during the period 1961—67; a few earlier analyses were obtained from the files or publications of the Geological Survey, the Bureau of Reclamation, other Federal or State agen- cies, or from individuals. Some of these earlier analyses were recomputed from originally reported values in order to agree with the format of the Survey analyses. The 776 analyses were selected from a substantially larger number so as to pro- vide a representative sample of the various chemical types of ground water in the Yuma area. The analyses are grouped according to the four subareas and 19 sectors described in the chemical—quality section of the report (p. H129) and are listed se- quentially by well number (Federal land classification) within each sector. Most of the analyses are reported in terms of concentration, in milligrams per liter, of six principal ionic constituents (calcium, magnesium, sodium plus potassium, bicarbonate, sulfate, and chloride) and also silica, hardness as calcium carbonate (both calcium plus magnesium and noncarbonate), and sum of dissolved solids. Some analyses also include the concentrations of sodium and potassium separately, and of fluoride, nitrate, and boron. Additional information includes specific conductance, pH, and percent sodium. All the above characteristics adequately describe the chemical quality of the ground water as it relates to its suitability for common uses in the Yuma area. Almost all the analyses are identified according to depth (usually the depth of the perforated interval in a well) and the aquifer from which the sample was obtained. Most of the analyses represent water in the coarse-gravel zone—the zone of greatest hydrologic significance in the areas of present and probably future water development. Changes in water quality with time are documented by records of drainage wells for which analyses are listed for a period of years (commonly 1961~67). H195 WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA H196 IIII we MS OOO.m OO«.H own; O«O.« IIII IIII OOO.N Omm wwm ONH.H OOH OH« «N «OIONI« O OOHIOOH no“ III vuumN IIIII NON IIII OF ME OHb.m N«O OE. OOO.N IIII IIII NHw Ohm ODN «O« Ob me ON NOIO IOH O «:ch .3: III HXHUON IIIIII EN IIII OO m6 OOO..¢.. OH« wow OrmN IIII IIII OOH. OOm Ob« «mm Ob «OH wN NOIONIO U «HHIOOH E: III vwamN IIIIII ON IIII wv HS ON«.N mom ONO OO«.H IIII IIII mO« N«O ONO «ON NO O«H NN NOIvNI« U o«HIhO 5: III dou«N IIIIII ON IIII NO OS O«~..H OmH NO” ONO IIII IIII O«m OOH NON wNN ON mu m NOIONIN B OOOH E III $4“me IIIIII «N IIII hm OE OOM.N OOH OOH. 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OON.V ONN OOO.H ONv.N O. 1111 OON.H OOV ONN HOO HOH NON bN NO11ON1O D ONH1NOH 11111 JNO rV. OO V6 OOO.V ONN OOH.H ONN.N N.O 1111 OON.H OVV EN ONO OHH OON NO HO1ON1H O ONH1NOH .HhH 111 OOOON 11111 «NO 1111 VO OH. OOV.O OHO OE. OHO.H 1111 1111 OON OON OOO VHV ON. ONH NH NO1H 1O O NOH1NNH .EH 111 doHVNN 111111 HO 1111 OO N.b OOH.O OOO OOO OOO.H 1111 1111 NVb NON VVN HOV OO NNH ON OO1N 1O CLO NVNV a: 111 nHHENN 111111 OO 1111 NO 1111 OOb.V NHO NbN OON..N 1111 1111 OHN.H OOV N.HO HOO ON OON 1111 O bOHéHH 1111 N.oOO 1111 NO b5 ONO.V NNO OON OOON 1111 1111 OOH.H OOO ONN OOO VN NON ON 0 >OH1>HH . 11111 OOO 1111 OO OS OO0.0 VOO OON OOO.N 1111 1111 NHO NOV VON VOO NN VON HN O OOH :H hnH 111 oooNN 11111 «OO 1111 OO OH. OERN OHN ONO OVO.H 1111 O. OOO NON OOO OOO VO OVH VN O OOH OOH 11111 UNO 1111 VO OS ONO.N NOO OOO ObO.H 1111 1111 NNO ONN OOV OOO OO OOH VN O OOH OOH 11111 QNO 1111 OO OH OOO.N NOO OOO OOO; 1111 1111 OOO NON OOO OOO NO OOH ON 0 OOHOOH 9; 111 SEWNN 11111 5NO 1111 VO N6 OOO.N OON ONO ONV.H 1111 1111 NHV NOO VNO HHO OO OVH ON 0 OOH OOH 111111 fl:O 1111 NO ON OOV.N NON OOO OrV.H 1111 OH NNV ONO OOO OOO OO NOH ON 0 OOH...OOH .CH 111 OOOHN 11111 abO NN. OO OS ONN.N NNN NOV OOO.H N.H 1111 NOV NON ONO OON NV ONH ON 0 OOH1OOH P: 111 OeoOH 111111 rO OV. NO VS OVEN OOV OON OON.N b. 1111 OOO NHO NNV OOV HN OOH OH O OOH OHH 11111 AHOO ONO NV V.b ON0.0 OVO OVb ONO.H 0.0 V.O ONN. ONH VVN OHO OO NON VH OO1OH1HH 3 OOVIObO H. 111 QQUOHANNIQ In: 11111 NOO nceoom Hauuflauémua HN. HO N.» ODN.H VOH NNO OVO.H 1111 O. NVV ON ONN HON ON NO OH OO1ON1OH OP HNO ONO 1111 «OOO 1111 HO OH ONO.H OOH NvO OVO.H 1111 O. OVV ON NNN VON ON NO OH VO1H 1OH OP HNO ONO 11111 nHOO ON. OO NA. OOO.H NOH NOO OHO.H H. O. OOV ON ONN OVN vN rO OH VO1ON1O B HNO ONO NOH 111 vauOO 11111 MOO 1111 VO O6 OON.N ONN.H OOO.H OOO.V 1111 1111 OOH.N OON VNO ONN.H OOH VON HN OO1OH1O O OOH1OHH 11111 AHVO 1111 OO NE ONN.N NOV ONO OON.H 1111 1111 OON. NOH OVN DNO OO OOH VN NO1V 1OH O OOH .OHH A: 111 «NEON 11111 BVO 1111 ON. VS OOH.OH ONN.H OOO.H OHN.O 1111 1111 ONHN OOO.H OOO ONO.H OOH NrO ON OO1OH1O O OVHON 11111 nOOO 1111 NO V6 OON..O OOO OON. OON.N 1111 1111 NV> ONO NON OOO E. ONH NN NO1O 1OH O OVHION .ZH 111 AHUNOO 11111 NOO 1111 OO OS OOp.OH OVH.N OOV.N .ON0.0 1111 1111 OO0.0 ONO.H NOV ONV.H pON NOO ON OOIOH1O 0.9 OOH OOH F: 111 HHHHNOO 111111 NO 1111 OO OS OO0.0 OON ONO ONO.H 1111 1111 OON. OON NNN VOO hO NOH VN VO1ON1N. O ObHsOO 11111 nHO 1111 HO OS OOb.N OOO OOO ONV.H 1111 1111 NNO NOH OON VOO OO NHH HN OO1N 1O O OrHlOO hhH 111 HEHVOO 11111 .nHO 1111 NO VS OVO.H HO OON ONN 1111 O. NNO Ob NHN VNN NH NO bH OO1H 11H. O? ONO1VNV 11111 OOO 1111 NO ON OOO.H OO NON VON 1111 N. HOO Op VHN ONN OH OO ON VOJOH1OH B ONO1VNV 11111 AHOO 1111 bO NE OOO.H hm OON NHN 1111 OH OHO Ob HHN NHN pH VO NH VOIN. 1O B ONO1VNV .HnH 11 NwNUOO 11111 NOO 1111 OO V6 OON.O NNO OHN OOH.N 1111 1111 OOO ONN OON bOV NN NNH HN VOIP 1H O ObHOO 11111 A”HOV 1111 NO O.» OOO.H HO NNN NNN 1111 N. NNO ON. OHN ONN .OH OO ON OOINNNH >9 OrO1OOV .H. 11 Hnaomm 11111 uOV 1111 OO ON OHb.O OOO OVH.H OHN.O 1111 I111 ONO.H ONO. OON OOO NNH OON HN NOEN 1O O ONH1VN .HHH 11 HaanO 111111 NV 1111 OO O.» OOHN OOO.H OON.H OON.O 1111 1111 OOV.N OON. OOO OON.H OOH NHV NN OOIOH1O O rOHIOO 11111 aFV 1111 NO V.» OO0.0 OOO OON. OOO.H 1111 1111 NON ONO OON OHV ON EH VN NO1O 1OH O OOHIOO 5: 11 NdddOO 11111 NbV 1111 OO OS OH0.0 OOO ONN OOO.N 1111 1111 OOO bHN VVN VOV VN NNH bN NOION1O O VNHIOHH .5: 11 HuEHVO 1 11111 NV 1111 OO OS ONV.H OO NON VNO 1111 O.H NON NO OHN OON NH OO OH OO1NHIHH B OOO1OOO 11111 QOV 1111 NO N.H. OOV.H DV VNN ONN 1111 OH HNO NN. OHN NNN VH OO HN VO1> IOH B OOOIOOO .HQ 111 vcaVN 11111 NOV 1111 NO N.H. ON0.0 ONV OOO ONN.H 1111 1111 ONN ONN ONN NNV OO HOH ON OO1N 1O O bhH1OO 11111 uVV 1111 OO OS OHN.O ObV OOO OHb.H 1111 1111 NO... NON VVN Ohm OO OOH NN NO1O IOH O NBH1OO 11111 AHVV 1111 NO VS OOOF ONN.H OOV.H OOV.V 1111 1111 OVH.N OOO bON OOO.H OOH NOO OH OO1OO|O O va1OO .CH 111 “NHVO 11111 «VV 1111 VO 1111 ONN.V OOr OOO OOV.N 1111 1111 OOH.H OON OON NNO VO OON 1111 OOIN. lb 0 OOHIOO 1111 «OOV 1111 NO 1111 OO0.0 VVO NON OOH.N 1111 1111 O5 OON OON VOV HN NoN 1111 OOIO IV 0 OOHIOO 1111 «ONV I111 OO OS OOb.O VOO OHN OVN.N 1111 1111 OOO ONV NON OVO N.H. NOH HH VOIVHIO O OOHIOO hm— 111 OOHKN 11111 ”NV 1111 NO V.» ONN.N ONO OON ONO.N 1111 1111 OOO OON OON NOV ON VOH OH NOION1O O NHH1OOH .EH 111 HEEN 1 11111 NV 1111 NO 1111 OOV.O OHV OOO OOO.H 1111 1111 VON HON NON HOV OO OVH 1111 OO1N INH 0 OrHlOOH 1111 «eHV 1111 OO 1111 OO0.0 ONV NNO OrO.H 1111 1111 OON OON OON OOV VO OVH 1111 OOlb lb 0 OOHIOOH 1111 «HHHV 1111 NO ON OOO.V ONO OON OVV.N 1111 1111 OOH.H ONN OOO VOO OO OON ON VO1O IV 0 OrHIOOH an 111 coopN 11111 aHV 1111 bO OS ONN.V VVO OON OOO.N 1111 1111 ONO.H ObN OOO OOO DN VHN HN OOIVNIV O HVHIOO 11111 AHOV 1111 VO N.H. OHNaV ONO ONO OOO.N 1111 1111 OVO.H NNN NNN OOV OOH NOH ON NOIV IOH O HVH1OO .CH 111 vaubN 11111 NOV 1111 OO O H. OOH.V NNN. ONO OON.N 1111 1111 NNO OOO NVN NrV NO OHN ON NOIO IOH O HOH1ON F: 111 HVOAON 111111 ON 1111 NO VS OVN.N NNN NVV ONN.H 1111 N. ONV OVH NON NON OV OOH ON OOIOHIO CLO ANOHOHV ham 111 NOANN 1 11111 .1 NO 1111 NO 1111 OO0.0 .OOV ONN ONO.N 1111 1111 NVH. OHO OOV HHV NN OOH 1111 OOIH. lb 0 hVH1ON 1111 Norm 1111 NO ON ONO.V FOO OOO.H OOVN 1111 1111 NVO OOO NNO VOO VOH NVN ON OOINNIH O N.VHION 11111 AFN 1111 OO OE ONN.O OOO OOO OHN.N 1111 1111 OON NNO NNV NVV NO ONN ON VO1NHIV O N.VHION no” 111 nQObN 11111 «pm 1111 NO H. OO0.0 NOO OON ONO.N 1111 1111 O2. OON OOV ONV ON VON NN OOIVNIV U VOHINOH .EH 111 SEN 111111 ON 1111 HO 1111 OON“. OON.H OrO.H OOb.V 1111 1111 ONH.N OVN. VNO OOH.H OOH OOO I111 OOIN 1NH O OOHIOO 1111 «OON 1111 NO 1111 OOON Ohm; OOO.H OHb.V 1111 1111 ONH.N O: NO ONO.H ONH OOO 1111 OOIO 1V O OOHIOO 1111 «OOO 1111 NO ON OH0.0 NON ObH.H OVN.N 1111 N.H ONO.H NHO O5 O3. ONH NbN ON VOOOIO O OOH1OO kg 111 OOOON 11111 sum 1111 OO VS OrV.N NON OVO OOO-H 1111 N. NNO ONH NNN OON NV bOH HN OOIONIO B OOH1VNH Son 11 NNUHVON 1 11111 VO 1111 HO V8 OO0.0 VNV OOO OOO.H 1111 1111 NVN OON NNN VbV OO HOH ON NOIO 1OH O ONHIOO .5: 11 HdquON 1 11111 ON 1111 OO 1111 OO0.0 ONN. OOO OrV.N 1111 1111 OHH.H OOO HNN OOO 5O VNN 1111 OO1 1O U OOHIVO EH III HXHGON I1111 «NO 1111 NO 1111 ONH.N OOH OVV OON.H 1111 1111 HON OON VON NNN NV OHH 1111 OOIN. 1N. O VOHIVN 1111 «SO 1111 OO NS OVO.H OOH OOO OOH.H 1111 1111 NNO SON NNN rON pm NO ON OOION1V U VOHIVN 11111 nHHO Hm. NO VS OVN.N OHN OOV OOO.H H. O. NOV ONN NON VON NV VHH ON VOIVNIN O VNH1VN unH 111 AEOON 11111 «HO 1111 OO OS OVN.O OOO OOO ONH.N 1111 1111 OOO NON VNN ONV HO NNN HN NOIVNIV O OrHlOO .EH 111 HERON 111111 ON 1111 NO b4. oNH.N ONH ONV OOH.H 1111 1111 NNO NON NNN HEN NV NO ON OOINHIH U VNHV 11111 OON 1111 OO N6 OVN.N NNO OHO ONO.H 1111 1111 NOO NNN VVO OVN NO NVH NN NOIN IOH O VNHV 11111 A3N N0.0 rm O. OOO.N HON OVV OHN.H ON 1111 VHV SH NON NV NOH NO HOIONIH U VNHV 5H 111 nOaON 11111 «ON 1111 NO 1111 OONN OOO.H OON.H OOH.O 1111 1111 ONN.N OVO OOO ONH ONV 1111 OO1> Ir 0 OOH1OOH 1111 «ONN 507-243 0 - 74 -14 WATER RESOURCES 0F LOWER COLORADO RIVER—SALTON SEA AREA H198 -- 3. 9p 2% ms 83 $3 -- -- emu; m2 mmu E m: mpm mp ww-NN-H 0 87m: 5 -- 20mm --- «3 I: an p.p 83 26 Sm fig -- -- 3m «mm in 3; pm SN 3 Nm-w -: o C; ..... fix am. pm 3 8p.” «Np cum 92.x p. p. £3 «,3 SN oz. 5 amp 3 film-N o E --- 3w -- pv wp 3.3“ w; 2:; 83 -- -- 83 «mm 3N w: p: m3 mu Slap-H o :5 an - 38mm ----- 3w .-- mm wp 3.3 own 2w 3.3 -- -- can; amp :3. 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' § § =260,ooo god per ft _i 1.1.1 0 C > Z 5 5 34 Drawdown data ' 5 Jan.21, 1965 \ '2 3 35 I | | I | I I J l I l | I I | | | I | .— 10 100 TIME, IN MINUTES, AFTER PUMPING STARTED 14.6 14.8 15,0 15.8 H209 _ Prepumping IeLel/_—/7_/;\__\‘ I IIIIIIII I l I y, T: 264 (1230) 0.06 35 mgd per ft Recovery data Jan. 21, 1965 I IIIIIIII IIIIIIII 10 100 Perforated interval 120 to 548 _ feet below Iand surface T3264 (650) x 0.7 f a 240,000 gpd per ft / A / /l ‘ .- E Recovery data Apr. 6, 1965 _ IIIIIIII I IIIIIII 10 100 TIME, IN MINUTES, AFTER PUMPING STOPPED FIGURE 50.—Pumping-test data for well 165/23E—10Rcc (LCRP 23). Graphs A, B, C. and D, show data pertaining to the house Formation (con- glomerate) between depths of 634 and 694 feet, whereas graph E shows data pertaining only to the coarse-gravel and wedge zones between depths of 120 and 548 feet. eductor pipe was installed to a depth of 500 feet, and the well was pumped for 2 hours by the air-lift method. At the pumping rate of 650 gpm, the drawdown in the annular space between the eductor pipe and the casing was 4 feet, which indicates a specific capacity of about 160 gpm per foot of drawdown. The drawdown, as measured, is a mini- H210 mum value, and is less than the drawdown on any of the water-yielding strata except the uppermost. Granting that the specific capacity for computing transmissivity would be less than the above figure, the transmissivity computed from the recovery data appears reasonable. The drawdown data obtained during the test were not consistent enough for computing transmissivity. The oscillations of water-level that were measurable for at least 5 minutes after pumping stopped probably are due in large part to the imbalance between the head in the 500-foot long column of water inside the eductor pipe and the head in the hollow cylinder of water of comparable length between the eductor pipe and the casing that per- sisted after pumping stopped. WELL 16S/22E—29Gc32 LCRP 26 TEST Figure 51 shows selected pumping-test data for well 16S/22E—29Gca2, LCRP 26. The graphs are of the same general nature as those for well LCRP 23 which were ex- plained in the preceding section. Pertinent information regarding the well and the tests is as follows: Method of drilling -_-Mud rotary. Casing record ________ 12—inch diameter from land surface to depth of 121 feet; 12— to 8-inch reducer, 121 to 124 feet; 8-inch diameter, 124 to 1,765 feet. Horizontal-louver type perforations between depths of 124 and 1,105 feet; and between 1,345 and 1,765 feet. Gravel packed from land sur- face to depth of 1,105 feet. Aquifers tested _______ Coarse-gravel zone; wedge zone; non- marine sedimentary rocks. Test conditions: March 11, 1965: Recovery period followed 2 hours of continuous pumping at rate of 250 gpm at end of a 90-hour intermittent period of developing the well by the airlift-pressuring method. The 5-inch diameter eductor pipe was set 1,740 feet below land surface, and drawdown was measured in the annular space between the well casing and the eductor pipe. April 13, 1965: The well was pumped by means of a turbine pump and gasoline engine. An orifice was in- stalled on the end of the discharge pipe. A steady rate of discharge was maintained by manually con- trolling a valve in the discharge line to maintain a constant head on the orifice. Drawdown was meas- ured in the annular space between the pump column and the well casing. Step 1 consisted of pumping the well at a uniform rate of 380 gpm for 2 hours; step 2 of pumping at a uniform rate of 715 gpm for 2 hours, 30 minutes; step 3 of pumping at a uniform rate of 1,100 gpm for 1 hour, 30 minutes; and step 4 of pumping at a uniform rate of 1,365 gpm for 2 hours, 40 minutes. DISCUSSION OF TEST DATA The recovery data obtained on March 11, 1965 (graph C), shows surging, which also was noted in well LCRP 23. This phenomenon seems to be characteristic of recovery data following the airlift method of pumping when the recovery measurements show the changes in water level in one long column of water that is freely connected with another of comparable length. The drawdown of only 0.75 of a foot WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA while the well was being pumped at the rate of 250 gpm indicates a maximum value of 335 gpm per foot of draw- down as the specific capacity. Recognizing that this value is larger than the value that would be valid for computing transmissivity on the basis of specific capacity, it appears that the transmissivity of 400,000 gpd per foot computed on the basis of rate of recovery of water level shown in graph C is a reasonable value. The specific-capacity data in graph A imply specific capac- ities much less than the 330 gpm per foot that was com- puted for the airlift pumping test of March 11, 1965. Some- what lower specific capacities are to be expected as the discharge rates increase, because for any part of the system in which turbulent flow exists, (and this type of flow occurs in the vicinity of the perforations even at rather low rates of yield), the loss of head increases at a faster rate than the yield. This increase in rate of drawdown with yield is shown by the increasing slope of the line through steps 1, 2, and 3, as contrasted with the line of uniform slope which separates the drawdown into components of formation head loss and wellhead loss. However, at comparable yields one ordinarily expects comparable specific capacities. The reasons for the large differences in specific capacity at comparable rates of discharge between the two tests are not all known. A small part of the differences may be due to errors in measurements of yields or drawdown. Also, part of the differences are due to differences in the pumping equipment. The measurement of drawdown in the annular space between the eductor pipe and the casing as made for the airlift pumping test excludes all internal well losses, whereas the measurement of drawdown in the annular space between the pump column and the well casing as made for the test using a turbine pump includes all internal well losses. Furthermore, the distribution of drawdown along the perforated sections of casing is different for the two tests. When the well was pumped by the airlift method, the maximum drawdown oppOSite the perforated sections of the casing occurred near the bottom of the sections at a depth of 1,740 feet, whereas when the turbine pump was used, the maximum drawdown occurred near the top of the perforated section at a depth of 124 feet. It is also possible that the well sanded in below a depth of 1,100 feet between the times of the two tests. The transmissivity of 550,000 gpd per foot shown in graph B, which was computed on the basis of recovery data, appears somewhat high, although not unreasonably so, if a formation specific capacity of about 200 gpd per foot is accepted as a valid value. The transmissivity computed on the basis of recovery data, following the test in which the turbine pump was used, is only slightly higher than the transmissivity computed on the basis of recovery data fol- lowing the test for which the airlift method was used. Graph D shows that either the permeability of the strata below a depth of 730 feet is very low relative to the average permeability above that depth or these lower strata were not developed (cleared of drilling mud). The graph also shows that particular strata within the zone of average higher permeability differ greatly in permeability (or possi— bly in degree of development), some strata apparently being practically impermeable (or undeveloped) and others being very permeable (or well developed). The latter evidently occur at depths of about 390, 450, and 530 feet. A compari- son of the relative permeabilities as indicated by the current- meter survey shown in graph D with relative permeabilities GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H211 DISCHARGE (Q), IN GALLONS PER MINUTE 0 200 400 600 800 1000 1200 1400 0 I I I I I | 100 I r I I Top of perforated .. section of casing Lu “J . “' Step 1 Formation E 4 ” head loss — 200 « g 33 Step 2 g Well head Ioss 8 8 — — 300 - 3 Step 3 D 12 — Step 4 400 “ 0.014 — — g A E E 0012 _ SpeCIfIc capaCIty data , w 500 - r: 2 Apr. 13, 1965 m 5 E 3a. 0.010 ‘ Lu. c§ 2 E <1 3 0.008 — z 600 — \ _J 2 :5 < (I) <1 ‘5 a m 0.006 2 Lu 4 O. _I 0.004 ' 1 ' 1 1 1 g 700 - 0 400 800 ‘1200 1600 2000 2400 2800 3 Q,,,_,)+Q,,,IN GALLONS PER MINUTE ‘85 I I I I I | I I II I I I I | I | | I- E 800 - D .24 13.8 — T=264(1385) / _ LA. E g 0.67 / _,— 1” = 550,000 and per ft “. 900 — u; D .u' a E 14.2 — / ‘ -‘ _J .I'. D K g .o( . IE 3 .o 1000 mm data < 0' — Lu ' ’ 3 m 14 6 _ .fo . Recovery data Apr. 13, 1965 E / Apr. 13, 1965 LI. 1100 ‘ 150 I l | l I I | | | | | I | l l l I 1 10 100 TIME, IN MINUTES, AFTER PUMPING STOPPED 1200 ' 1 1 1 12.0 1 I I I I I I I r I I I I I I I I I I I I I 0 300 600 900 1200 1500 9’26“”0’ . / YIELD, IN GALLONS PER MINUTE 0.15 a / 5 12 2 _ a 400,000 gpd per ft _ L , z a: / _ Z / > to 5 5 12 4 — _ a: 2 1.1.1 I; g Recovery data 3% Mar. 11, 1965 I— 12.6 - — [LI LU u. 128 I I 1 I I I I I II I | l I 1 I I I I I I ' 0.1 1 10 40 TIME, IN MINUTES, AFTER PUMPING STOPPED FIGURE 51.—Pumping test data for well 16S/22E—29Gca2 (LCRP 26). suggested by the lithologic logs (appendix B) shows sub- stantial difi‘erences for some strata, although in general the relative permeabilities indicated by the two methods agree quite well. In the few places where the permeability indi- cated by the current-meter survey substantially exceeds that indicated by the lithologic log, the log probably is in error. WELL (C-9—22)28cbb1, LCRP 25 TEST Figure 52 shows selected test data for well (C—9-22) WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA H212 DISCHARGE (Q), IN GALLONS PER MINUTE 0 100 200 300 400 500 600 700 0 I I I I I I ._ U-l . E‘ FormatIon E 4 ; Step 1 head loss _ 4 V) \ E Step 2 Well head loss 0 8 h — D 3 < E . . . t 3 12 _ SpeleIC capaCIty data » S e” _ 5 ~ 0.03 — Jan. 19, 1965 — no on “u L“ E ’5 5 j E 0.02 // _ e< 2 , 31’: c: 0.01 — \ m 3 2:“- 0.00 I | l I I 0 200 400 600 800 1000 1200 1400 Q(n_1)+Qn’ IN GALLONS PER MINUTE ; 54 I I I I I O _l “J m I— <5 5 g 55 — _ “' < z o .__ u_ _I O “i n. 5 9 56 _ Recovery data ‘ 5 Jan. 18, 1965 ._ < 3 57 I I I I | I 0 4 8 12 16 20 24 28 TIME, IN MINUTES, AFTER PUMPING STOPPED 3 3 I I I I I I Lu m 54 — ’5 E E :2 z c :- “5 g n. 55 — Recovery data Lu —I 8 Jan. 19, 1965 Z HJ LT: 56 I I J I 3 0 4 8 12 16 20 24 28 TIME, IN MINUTES, AFTER PUMPING STOPPED 531 I|||II| I IIIIIIII I ||||||I ; - O . d -' _ m 54 — ._ E i E 2 U 5.1. 55 — — .4 0 W > 0. W O ; *- Recovery data : 56 - Jan. 19, 1965 — < 3 57 I IIIIIII I IIIIIIII I I IIIIII 1 10 100 TIME, IN MINUTES, AFTER PUMPING STOPPED DEPTH BELOW LAND SURFACE, IN FEET 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100 0 I | I Top of perforated section of casing E Yield data Jan. 19, 1965 Casing filled with sand below this depth Lower limit of perforated section I I I 100 200 300 400 500 YIELD, IN GALLONS PER MINUTE 600 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H213 52 . 1 1 l 1 l l N .5 a. Nonpumping level E 54 — _ a — E D. O G 56 — _ E Step-drawdown and recovery data 3; Jan. 19, 1965 s a _ 58 - — E 2 z 0 3 “a g m 60 _ Q=412 gpm _ u-I o —1 1- I! u: 1— < 3 62 — _ 64 — Q2595 gpm ‘ F 66 l 1 l I 1 I l 700 800 900 1000 1100 1200 1300 1400 1430 HOUR or DAV FIGURE 52.-—Pumping test data for well (C—9—22)28cbb1 (LCRP 25). 28 cbbl (LCRP 25). Pertinent information for the well and tests is as follows: Method of drilling ___Mud rotary. Casing record ________ 12-inch diameter blank casing from land surface to depth of 320 feet; 8-inch blank casing from 320 to 862 feet; 8-inch horizontal louver- type casing from 862 to 2,002 feet. Drilled hole, 16-inch diameter, gravel packed from 2,002 feet to land surface. Aquifer tested: Wedge zone. Test conditions: Pumped with turbine pump and gasoline engine; pump bowls 100 feet below land surface; orifice installed at end of discharge pipe; steady rate of discharge main- tained by manually controlling valve in discharge pipe to maintain constant head on orifice; deep-well current meter installed below pump. January 18, 1965: Further developed well with turbine pump after well had previously been developed by airlift method; developed for 2 hours and then made recovery measurements. January 19, 1965: Using same equipment as on preceding day made a step-drawdown and recovery test. Also made a rate of flow survey during the test. DISCUSSION OF TEST DATA Graph B shows recovery data following a 2-hour pump- ing period, the last hour of which the rate was kept fairly constant at about 700 gpm. The pattern of the recovery data is unusual in that after an initial recovery period of 3 minutes, recovery ceased for the next 6 minutes, but then resumed at a rate that appeared to be fairly normal and which resulted in a rise of 2 feet in 15 minutes. / 507-243 0 - 74 - 15 Graph C shows recovery data following the step-draw- down test shown‘in Graph F. The period of virtually no recovery is 2 minutes to 6 minutes after pumping stopped. The failure of the latter recovery data to follow the theoretical pattern, is shown by graph D. Theoretically, the recovery data should plot very nearly as a straight line sloping upward to the right. The reasons for the interruptions in recovery that were observed are not fully understood. A possible explanation is that there is considerable movement of water from deep strata to shallower strata when pumping is stopped. This is probable because when pumping is in progress, the draw- down in the deep strata is less than the drawdown in the shallower strata because of friction losses within the well. When pumping is stopped the friction losses within the well virtually cease and thus water from the strata that had the lesser drawdown will flow to strata where the drawdown was greater until the drawdown in both are equal, after which recovery in both will proceed at a uni- form rate. Evidence that this internal movement was occurring dur- ing the recovery period shown in graph B are the observa- tions of rate of flow through the deep-well current meter that was suspended in the well at a depth of 1,000 feet. This depth is near the bottom of the better-than-average water yielding zone near the upper part of the perforated section of casing (graph E). The current meter indicated an upward flow of at least 60 gpm during the early part of the period of non-rising water level. This rate gradually lessened to about 30 gpm 10 minutes after pumping stopped, and ultimately became less than that needed to actuate the meter. Graph F illustrates still another anomaly. The water level is lowest in the well immediately after an increase in the pumping rate and then recovers to a high stage for the pumping rate within a 10- to 20-minute period. H214 The reason for this phenomenon is not fully understood but it is probably due to a change in the distribution of drawdown with time along the 1,100-foot length of perforated casing following a sudden increase in pumping rate. Graph E shows the cumulative yield from strata below a given depth when the well was being pumped at the rate of 585 gpm. The rate of yield from strata between specific depths is easily computed by dividing the difference in yield between the given depths by the difference in the depths. It is seen that strata below 1,900 feet yield a relative small percentage of the total discharge; that between 1,900 and 1,300 feet the yield per unit thickness of strata gen- erally increases; that between 1,300 and 1,050 feet the yield is much less, with some strata apparently yielding no water; and that from 1,050 to about 920 feet, the yield per unit thickness is as high as, if not higher than anywhere in the entire section. A comparison of the yield data graph with the borehole gephysical logs shows that the correlation is good.‘ for rather WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA thick clay beds, but that it is only fair for beds logged as sand or gravel. This‘ lack of good correlation for sand and gravel strata may indicate either that the borehole geo- physical logs are not dependable guides as to the permeability of sand and gravel strata, or more likely, that some of the permeable sand and gravel strata were still sealed with drilling mud and therefore were not yielding water. Further development work confined to particular strata by the use of packers and use of chemicals to break down drilling mud would determine which of the above inferences is more nearly correct. Graph A indicates that when well losses are excluded, the specific capacity is about 100 gpd per foot. The specific capacity is considered to be the most useful value of all the pumping-test data for computing the transmissivity of the water-bearing material tapped by the well. WELL (0—10—25)35bbd LCRP 17 TEST Figure 53 shows selected test data for well (0—10—25) 35bbd (LCRP 17). l4.l 1 1 1 1 ! 1 500 [ 1 1 '1 , Top of perforat10n¢ 14.2 ~ — section of casing 600 - 1 g 1414 — ..W E M 2 - 700 — ~ (/7 .- 2 . < 1416 — 1 _l a _ - 8 A 800 Lu 1— m 148 7 Recovery data _ 3 1— ' 1.1. § , 2 Mar. 28, 1964 E g ' .5,— 900 ~ , -‘ E g 15.0 - — a: 11,4 3 5 g 1000 — ~ 2 .1 a 15.2 — ~ g 0 _. LLI m 1100 — A E 15.4 7 1 a C D Yield data 15.5 1 l | 1 | l l l l 1200 7 1 0 4 8 12 16 20 24 28 32 35 40 Apr. 21’ 1964 TIME, IN MINUTES, AFTER PUMPING STOPPED §142 1 1 1111111 1 1 1/1I111 1300—1 — LL 3 w T:264 (388) D z 1 0.64 ,_ 14.4 S 1400 a — 3 :160,000 gpd per ft 0 _J LLJ CD ’1; 14'6 _ T 1500 1 ‘ 1 ‘ :14 0 20 40 60 80 100 E Recovery data YIELD, 1N PERCENT E 14.8 1 Mar. 28, 1964 “J / g / g 15.0 I / l l | I II | 1 1 | 1 1 ll 1 10 100 TIME, IN MINUTES, AFTER PUMPING STOPPED FIGURE 53.—Pumping test data for well (0—10—25)35bbd (LCRP 17). v—"y—‘x— _ v ~vrv ——v— ertinent information regarding the well and tests is as follows: M thod of drilling ___Mud rotary. Casing record ________ 18-inch diameter blank casing from land surface to depth of 300 feet; 8-inch blank casing, from 270 to 520 feet; 8-inch horizontal—louver casing from 520 to 1,398 feet; 8-inch diameter blank casing 1,398 to 1,438 feet; 8-inch diameter screen from 1,438 to 2,000 feet. Drilled hole, 15-inch diameter, gravel packed from 300 to 2,000 feet. Test conditions: March 28, 1964: The well was pumped by the air-lift method. A 4-inch diameter eductor pipe extended to a depth of 1,420 feet below land surface. A packer to prevent upward movement of water from strata below a depth of 1,398 feet was set invthe sec- , tion of blank casing 10 feet below the eductor pipe. After an initial period of development of l the well, the well was pumped at the rate of ‘ 388 gpm for a 4-hour period. Pumping was then ‘ stopped and the recovery measurements shown ‘ on graphs A and B were made. , April 21, 1964. i A centrifugal pump was used to pump the well at ‘ the rate of about 165 gpm for a 2-hour period. ‘ During the pumping period a survey of the rate of upward movement of water within the well was made by means of a heat flow velocity meter furnished and operated by the Hydrologic Equip- ment Laboratory of the U.S. Geological Survey, Denver, Colo. DISCUSSION OF TEST DATA The oscillations of water level that are shown on graph A persisted longer than observed oscillations at any other site. Most of the same explanations that were postulated for oscillations noted at wells LCRP 23 and 26 are probably valid for well LCRP 17. However, the movement of water into and out of the formations tapped by the well may be more significant at this site than at the other test sites. Support for this probability is offered by the observations made on May 5, 1964. On that date the thermal velocity m ‘ter was lowered to a depth of 590 feet. An annular pl te had been attached to the meter so as to limit most of any movement of water within well casing to a path th ough the meter, thereby causing the meter to respond to very slow movements of water within the 8—inch casing. T e lowering of the meter to the depth of 590 feet was ac omplished over a period of more than an hour. The meter was being used in an attempt to determine if there was any movement of water in the well at the depth of 590 feet under non-pumping conditions. Movement of water in either direction through the meter was indicated on a chart by the trace of a pen, whose deflections increased from zero for no flow to a limit of 4 inches as the rate of flow through the meter increased. For a period of 53 minutes after observations began, the pen continued to move in an apparently erratic manner, throughout the 4-inch wide range. Much of the pattern, especially during the first 7 minutes suggested alternate times of zero and maximum flow through the meter; from 9 until 13 minutes, the deflec- GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H215 tions were less then 1 inch; after which they began to increase and reached the full-scale deflection 16 minutes after observations began. Other near-full-scale deflections were noted 21, 31, 33, 35, 36, 38, 41, 47, and 50 minutes after observations began. Less than one-half inch deflections generally were. observed between the above times. From about 37 to 53 minutes the deflections tended to stay in the neighborhood of 2 inches. Observations were discontinued after 53 minutes. The tendency of the deflections to center about a value of 2 inches suggests that after equilibrium was attained some vertical movement of water at a uniform rate probably occurred at the depth of 590 feet. The apparently erratic pattern of the deflections suggests that water was moving through the meter at varying rates which probably resulted from imparting an oscillatory movement to the 500-foot long column of water in the casing above the uppermost perforations and to a column of water of unknown length inside the casing below the upper- most perforations as the meter was lowered to the 590-foot depth. The rest of the oscillatory system presumably is water that was going into or coming from some of the strata that were tapped by the well. Water levels corresponding to the means of the oscilla- tions shown in graph A are plotted in graph B. Some of the higher than theoretical values of water levels that oc- curred during the first 6 minutes of the recovery period may have~been due to leakage of water from the pump suction hose to the well. The value of about 160,000 gpd per foot for the transmissivity appears to be reasonable, although not necessarily precise. The yield data in graph C shows that about 80 percent of the water was derived from strata between depths of 520 and 620 feet and that only 10 percent was yielded by strata below a depth of 900 feet. An average hydraulic conductivity of about 1,400 gpd per square foot is indi- cated for the strata between depths of 520 and 620 feet if the value of 160,000 gpd per foot is accepted as a reason- able indication of the transmissivity of all the strata tapped by the well. WELL (C—ll-Z4)23bcb LCRP 10 TEST Figure 54 shows selected data for well (C—11—24)23bcb (LCRP 10). Pertinent information regarding the well and the tests from which the data in figure 54 were obtained are as follows: Method of drilling _-_Scow and cable tool. Casing record ________ 16-inch diameter steel casing, land surface to depth of 240 feet; 12-inch diameter casing from 220 to 1,055 feet; horizontal-louver perforations made in place at following depth intervals in feet below land surface: 165-170; 190—202; 213—220; 240— 250; 280—305; 320—325; 375—395; 405—425; 475—500; 520—545; 630— 635; 643—648; 685-705; 855—875; 985—1,002. Test conditions: February 26, 1963, to March 1, 1963: Pneumatic packers were used to isolate the perfo- rated intervals shown in figure 54. The packers were placed in position by means of string of 4-inch pipe which also functioned as the eductor H216 WATER RESOURCES 0F LOWER COLORADO RIVER—SALTON SEA AREA 78-8 i iiiiiiii l lllllll i a 730,000 gpd per ft WATER LEVEL, IN FEET BELOW LAND SURFACE T: 264 (2500) :1 79.0 7 0.9 _ 200 Yield Drawdown Specific Permeability (gpm) (ft) capacity (gpdzper (gpm per ft ) ft) I i 1 ill 100 e 0 4 60 3600 ET 8 1. 1 1 Ii :1] 33 B90 105 3,2 2 —3 ‘ 300 j *— /B|ank casmg Lu /Perforated 7914 a . — 2 400 31— section of — /‘ 5; casing _‘ a ]} Interval / :1 tested 10 570 796 .~ 3 500 100 10.0 3 j . - —i ‘ ./ Recovery data ; :Jl— ./ Apr. 11,1963 3 ./ '35 79.8~ -/ a E 600 — / w ‘ /' E 31 / u // E ii 317 265 80.0 i i Iiilil 1 lllllill i llllll $700?}80.022.01 j _ 0.1 1 10 100 0 TIME, IN MINUTES, AFTER PUMPING STOPPED 800 M 4 6 332 }90 195 J J 900 ‘ 1000 Data obtained with packers Feb. 26-Mar. l, 1963 1100 FIGURE 54.—Pumping test data for well (0-11—24)28bcb (LCRP 10). pipe for the airlift method that was used for developing and pumping the well. Water levels were measured inside a string of 1/g-inch pipe whose lower end extended 21 feet below the 1%-inch pipe through which the air was intro- duced, both pipes being inside the 4-inch eductor pipe. April 10, 11, 1963: A turbine pump was used for this test. The well was pumped for 91/2 hours at varying rates to develop the well and then pumped steadily at 2,500 gpm for 8 hours prior to the recovery test shown in graph A. Discussion of test data: Graph A shows that during the first 2 minutes of the recovery period water levels were influenced considerably by the return flow of water from the pump column. After this initial period the recovery data followed the theoretical pat- tern quite well. The reliability of the transmissivity com- puted from the data is considered good. Graph B shows that the permeability of the deposits de- creases rapidly with depth. The deposits between depths of about 165 and 220 feet have a hydraulic conductivity of about 3,600 gpd per square foot, whereas, those that were tested between depths of 240 and 325 feet had an average hydraulic conductivity of almost 1,200 gpd per square foot. At greater depths the hydraulic conductivity is considerably less, ranging from 265 to 635 gpd per square foot. 0n the basis of specific capacity, it might be expected that strata above a depth of 325 feet (the coarse-gravel zone) will pro- vide about three—fourths of the total yield from all the strata that were tested. APPENDIX E. MOISTURE INVESTIGATIONS One of the major items of the water budget for the Yuma area appeared to be the water that went into storage beneath the Yuma Mesa and Yuma Desert (“Upper Mesa” and “For- tuna Plain”). It was desirable, therefore, to ascertain as closely as practical how much water was represented by a 14 v‘ 12 16 20 24 28 O GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA l l I (C-8-22)33daa Air drill Aluminum tubing Water level l H221 C (C-9—22)1Gaad Air drill Aluminum tubing 0 T I I l (C—8—22)31cbb _ 4 I Driven _ Steel tubing Water level _ 8 _ _ _ 12 _ _ _ 16 I I I I 0 2 4 6 8 10 ~ 0 I I I (C—8-23)250cc Driven 4 _ Steel tubing _ 10 8 — _ 12 — — Water level _ 16 l l l I 0 2 4 6 8 10 _ 0 I 163/22E-363 2 4 ” Driven ‘ Steel tubing Water level _ 8 — e _ 12 2 I _ 16 — e 20 | l l l 10 0 2 4 6 8 10 THOUSAND COUNTS PER MINUTE obtained by use of a neutron moisture probe at 10 sites in South Gila Valley. H222 WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA 0‘ I I r I I I I (C—9-23)27cbb (C—9-23)28aaa Driven Steel tubing 4 _ _ _ Water level Water level 8 .. _ .. 12 _ _ _ 16 | l l J l | 0 I I I ‘1 I I I (C-9-23)32caa V ‘ (C'—‘9—23)32ddd E LI. E 4 A _ — we 0 E D: D (I) D 8 _ _ _ :2: Water level below 9 feet _J 3 o _l Lu CD I 12 _ _ _ .— 0. Lu 0 16 l l | | | | l 0 4 6 8 10 0 I I I I (C-lO-23)2aaa 4 _ — 8 _ _ 12 — d 16 | l | | 0 2 4 6 8 10 THOUSAND COUNTS PER MINUTE FIGURE 57.——Counts per minute at various depths below ]and surface A ‘__’At_ _J_ I__H‘ ‘Ag -_._. " 4,‘ 4 GEOHYDROLOGY OF THE YUMA AREA, ARIZONA AND CALIFORNIA H223 0 l I I I I (C-9—23)28acd Water level Water level 12— l I | (C—9—23)28dcc l 16 | | 0 I I I I I (C—9-23)33bbb J} | | I 00 I | I Water level DEPTH BELOW LAND SURFACE, IN FEET 5 I l I I | (C-9-23)33bcd 16 I I I I I 0 I I I I (C—lO—Z3)8bbb 12- — 16 I I I I 0 2 4 6 8 10 THOUSAND COUNTS PER MINUTE obtained by use of a neutron moisture probe at 10 sites on Yuma Msa. 10 H224 WATER RESOURCES 0F LOWER COLORADO RIVER—SALTON SEA AREA 0 T I I 0 I I I I (C-9-24)18cdd (C-9—25)35dcd 4 _ _ 4 ,— fl 8 — — 8 — ~ 12 k _ 12 ‘ Water level # 16 16 I I 0 10 0 2 4 6 8 10 0 I I 0 I I I (C—9-25)36ddd (C—9-25)25bad '_ 4 7 — 4 , ‘ LLI LLI LI. E (Lg 8 ” " 8 e _ < LI. :3: 3 w 12 12 o _ e k A 2 Water level Water level < _l E _1 16 l I I 1 I I ‘55 2 4 6 10 6 O 2 4 6 8 10 :I: '— n. LIJ o I I I 0 I I i I (C-9-25)26ddd (C—lO-25)2dcd 0 - — 4 k _ 4 — - 8 e 7 Water level 8 - ~ 12 _ _ 12 I- e 16 f _ Water level 16 k _ 20 k a 20 I I I 24 I I I I 0 2 4 6 10 0 2 4 6 8 10 THOUSAND COUNTS PER MINUTE FIGURE 58.—Counts per minube at various depths below land surface obtained by use of a neutron moisture probe at six sites in Yuma Valley. \ Page A Age and correlation of older alluvium" H46 Age of volcanic rocks ________________ 39 Agriculture, use of irrigation ......... 6 Alamo Canal _________________________ 84 Alfalfa hay, use of water ___--__..____ 98 Algodones Dunes _______________ 16, 28, 56, 61 Algodones fault ....... 19, 23, 60, 61, 107, 123 All—American Canal ___ 9, 84, 91. 103, 108, 134 Alluvial-fan deposits _________________ 56 Alluvial section between Pilot Knob and Cargo Muchacho Mountains _______________ 87. 91 Alluvium, older - -_ 45, 66 Alluvium of Yuma area, younger _____ 53, 66 Ammonia beccarii ____________________ 42 Analog model, reliability _ _______ 118 verification studies ________________ 113 Analog-model studies ________________ 15, 107 Analyses, hypothetical ________________ 12.9 Andesite, older _______________________ 37 Apache Group ________________________ 51 Aquifer, the term _____________________ 72 Aquifer characteristics ___- 15 Aquifers, hydrologic characteristics ___- 72 Arizona system for numbering wells ___ 17 Arizona western sector of Yuma Mesa subarea __________________ 139 Arkose ___________________________ 32 Arrowweed in Yuma Valley _ 7 Artesian storage coefficients __________ 82 Average annual discharge of ground water ____________________ 107 B Banning-Mission Creek fault _________ 61 Bard Lake ___________________________ 29 Bard sector __________________________ 135 Bard subarea _________________________ 9.9 Bard Valley ........ 23, 29, 50, 56. 66. 97, 134 Basalt or basaltic andesite of unknown age ______________________ 38 Basaltic andesite or basalt of Cholocate Mountains ________________ 38 Basin and Range structural features (Tertiary) _______________ 58 Bicarbonate concentrations in ground water ____________________ 126 Block faulting in the Yuma area ______ 58 Bolivina. interjunctu __________________ 40 Borrego Formation ___________________ 46 Boundary Hills ___________________ 22. 60, 62 Bouse Formation (Pliocene) ___ 35, 37, 39, 1:0, 60, 6‘5 Brawley Formation ................... 47 Breccia and conglomerate _____________ 3.? Butler Mountains __________________ 19, 22. 56 C Cable-tool method of drilling _________ 13 California sector _____________________ 137 California system for numbering wells" 17 Camino del Diablo _____________________ 22 INDEX [Italic page numbers indicate major references] Page Canebrake Conglomerate -. ............ H46 Carbonate precipitation ............... 127 Cargo Muchacho Mountains ___ 12, 16. 30, 39, 66. 87 Castle Dome Mountains - ..... 37 Castle Dome Plain ___- _ 24 Cenozoic deposits _____________ _ 12 Central sector of Yuma Valley ....... 138 Chemical analyses of ground-Water samples _________ 15, 69, 124, 134 Chemical changes in ground water derived from recent Colorado River ___________ 124 Chemical quality of ground water .......... 15, 124, 136. 140 Yuma area ....................... 129 51. Chinle Formation _ -- 12. 33. 37, 45 Chocolate Mountains Cipriano Pass ________________________ 22 Citrus and other crops, use of water__-- 98 Citrus orchards ....................... 6 Citrus sector of Yuma Mesa _________ 150 City sector of Yuma Maa ___________ 140 Classification. deposits by source ______ $7 landforms ________________________ 19 rocks ............................ 80 Climate of area ..................... 6 Coachella Valley ...................... 61 Coarse-gravel zone, mineral content ._ 132 variations in temperature ......... 121 water-bearing deposits ____________ 67 Coefficient of storage __________________ 78 Coefficient of transmissibility ......... 74 Colorado Basin Associates Federal 1. 33.40.65 Colorado flood plain .................. 6 Colorado River, older alluvium deposits 48 source of ground water ___ - 70 younger alluvium deposits _________ 5.! Colorado River basin _________________ 6 Concentration by evapotranspiration __ 126 Conglomerate and breccia ____________ 83 Conglomerate of Chocolate Mountains" 45, 63 Consumptive use of water on Yuma Mesa ..................... 98 Corals ______________________________ 42 Correlation and age of the older alluvium .................. 46 Cottonwood in Yuma Valley 87 Creosote bush (Larrea tridentata) ___- 28 Crystalline rocks (Pre-Tertiary) ______ .90 Cucupas Mountains ___________________ 30 D Dacite __________________ 38 Davis Dam 88 Davis Plain _______________________ 22, 25. 69 Definition of fresh water _ 6.! Definition of terms __________________ 72 Deposits, Colorado and Gila Rivers --_ 5.? Deposits, old Colorado and Gila Rivers .68 Deposits, older alluvium classified by source .................... H47 Deposits, older alluvium of local origin .67 Deposits. older alluvium of mixed origin .58 Deposits. water bearing, Pliocene to Holocene age ............ 66 Desert pavement ...................... 47 Desert varnish ....................... 48 Distribution and thickness of older alluvium ................. 46 Dome Valley .............. 29 Dorelos gaging station ..... 92 Drilling of test wells ................. 18 E East-central sector of Gila Valley subarea 18.! East Mesa 27 East sector Gila valley subarea _____ 132.187 Electric logs of wells .............. 14.66.67 Elphidium gunteri .................... 42 Eponidella palmeme .................. 42 Emma sp __________________ 30 Evapotranspiration. concentration by -__ 1.96 Evapotranspiration on flood plain _____ 70 Exploration, geophysical ______________ 13 F Farmstead and ditches, use of water ...... 98 Faults, reverse and thrust ____________ 34,61 Flood plains of Colorado and Gila Rivers 6 Floodway sector of Yuma Valley ...... 1.18 Flows and vent tutf of Laguna Mountains ________________ J8 Foraminifers _________________________ 40. 44 Formation sample studies ____________ 18 Fortuna basin .................... 59, 61, 65 Fortuna Dunes ................ 23, 28, 66, 96 Fortuna Plain _____________ 25, 56, 69, 97. 109 Fortune. sector of Yuma Mesa ......... 139 Fossils of area ___________________ 30.40.43 Fresh water. definition ............... 6.! G Gamma-ray logs ..................... 14,42 Geologic mapping ____________________ 1: Geologic structures ___________________ 1'2 Geologic studies of Yuma area ......... 16 Geology of area ...................... 18 Geomorphology of area ............... 18 Geophysical exploration ............... 13 Gila City ............................. 21 Gila flood plain ...................... 6 Gila Gravity Main Canal ............. 9,132 Gila. Gravity Main Canal Siphon ....... 132 Gila Mesa __________________ 24. 122, 129. 139 Gila Mountains ___ - 12, 21. 33, 67 Gila River ............................ 71 older alluvium deposits ...... .---- is younger alluvium deposits ........ 5.! H225 H226 Page Gila Siphon sector ................ _ H182 Gila Valley subarea _ _ 129 Glen Canyon Dam ___ _______________ 71 Globigerim’ta uvula ___________________ 40 Globquaderina hexagona ______________ Gneiss ________________________________ Granite _______________________ Gravel deposits in Yuma area _ Great Basin section of Basin and Range province __________ 58 Greenstone ._.___--_.: ................ 32 Ground water, area] variations in temperature ____________ 121 rate of movement under natural conditions ________________ 87 sulfate reduction _________________ 127 Ground-water discharge for a given year _____________________ 107 Ground—water discharge to the Colorado River between Imperial Dam and the northerly inter- national boundary ________ 105 Ground-water hydrology ______________ 12, 69 Ground-water movement __ _ 82 after 1960 ________________ _ 95 toward limitrophe section ________ 103 Ground-water origin and source of recharge _________________ 70 Ground-water reservoir 61 major subdivisions 63 Ground-water samples _ 15 Ground-water temperatures __________ 15,119 Gulf of California ___________________ 6 H Hanzawayai sp _______________________ 40 Hardening of water __________________ 128 Haughtelin Lake ______________________ 29 Heavy-mineral analyses of alluvial sand 48 Hills and mountains of area _________ 19 History of water-resources development 6 Holocene flood plains _________________ 28 Hoover Dam _____________________ '70 Hydraulic conductivity, the term _____ '74 Hydrologic characteristics of aquifers__ 72 Hydrologic regimen ___________________ 9 Hydrologic studios ____________________ 16 Hydrology, ground-water _____________ 63 I Ignimbrite ___________________________ 38 Imperal Dam ______ __ 9, 42, 70, 98 Imperial East Mesa -- _______ 26 Imperial Formation -_ 40 Imperial Valley ______________________ 40 Indian Hill __________________________ 135 Inventory of existing wells and well records ___________________ 14 Investigation, objectives of present ___ 11 Investigation methods ________________ 12 Investigations of Yuma area, earlier - 16 Irrigation in Mexicali Valley _________ 10 Irrigation in Yuma Valley _____ 6, 10, 71, 136 Irrigation of area _________ 6 Irrigation well, first 10 K Kinter Formation ___________ 33, u, 39, 45, 59 L Laguna Dam ____________ 7, 12, 38, 50, '70, 98 Laguna Mesa _________________________ 23, 56 INDEX Page Laguna Mountains ........... H12, 33, 39, 59 Laguna Valley ...................... 28, 134 Laguna Valley sector -_ - 134 haguna Valley subarea _ _. 98 Lake Cahuilla __________ __ 27 Lake Mead _________________________ 70 Landform classification _______________ 19 Laramide faults ______________________ 58 Laramide orogeny ____________________ 32, 57 Lechuguilla Desert _. _ 22, 25 Ligurta Mesa ____________ _ 24 Limitrophe section of Colorado River" 87, 91 Location of area _____________________ 6 M McCoy Mountains Formation ......... 32 McPhaul Bridge _______________ - 33, 36 Main Drain _____________ 7 Marine sedimentary rocks (Tertiary) -- .99, 65 Measurements of ground-water temperature ______________ 15 Mesa basement high ..... - 60,62 Mescal Limestone ________ _- 51 Mesquite, use of water _ __ 88 Yuma Valley _____________________ 87 Metaconglomerate _____________________ 32 Metamorphic rocks ___________________ 30 Mexicali Valley _________ 10. 19, 30, 84, 92, 109 Middle Mountains Mineral composition of clay and silt in Yuma area .............. 52 Mittry Lake _____________________ 29, 98, 134 Model characteristics of analog model - 107 Modeled system, stresses applied __ _ 109 Mollusks _________________________ __ 40, 42 Montmorillonite _____________________ 52, 128 Morelos Dam _________________________ 61, 92 Morelos gaging station _______________ 84 Mountains and hills of area ___________ 19 Movement of ground water __ 82 after 1960 ________________________ 95 direction in 1960 _________________ 88 under natural conditions _________ 87 Mud-rotary method of drilling ________ 13 Muggins Mountains .................. 19, 30 N Nonmarine sedimentary rocks ........ 65 North Gila Sector 1.!“ North Gila Valley _______________ 29,68,132 North Gila Valley Unit of Yuma Project 9 North of Gila Valley subarea _________ 100 0 Objectives of present investigation____ 11 0cotillo Conglomerate 47 Odocm'leus sp _______________________ 30 Ogilby Hills __________________________ 22, 39 Older alluvium, undivided, water- bearing deposits ......... 69 Origin of ground water and source of recharge ................. 70 Orocopia Schist ...................... 32 P Palm Spring Formation ___ _- 46 Phyllite _________________ _- 32 Picacho-Bard basin ___________________ 59, 65 Picacho Mesa ..................... 24, 35, 49 Page Pioacho Peak ......................... H38 Picacho Wash _ 24 Piedmont and stream-terrace deposits__ 17 Piedmont slopes, dissected ____________ .84 undissected _______________________ 24 Pilot Knob -.-- 22, 30, 60, 61, 87, 91 Planulina. sp __________________________ 40 Pliocene and Pleistocene older alluvium 45 Pliocene transition zone ______________ 45 Plutonic rocks _______________________ 30 Potassium-argon age determinations- 37, 39, 45 Precipitation, local ___________________ 72 Precipitation of insoluble carbonates __ 127 Pre—Tertiary structural features ______ 57 Proving Ground Dome ________________ 23 Pumping tests in area ............... 82 Pumping wells for irrigation ________ 10 Pyroclastic rocks of silicic to inter- mediate composition ______ 97 Q Quality of water, subdivision of Yuma area ______________ 129 Quantitative determinations of aquifer characteristics ____________ 15 Quartz monzonite ____________ - 32 Quaternary alluvium, younger __ - 58 Quaternary windblown sand _________ 66 R Radiocarbon dating method ........... 46,56 Rate of movement of ground water under natural conditions __ 87 Raven Butte _________________________ 22, 89 Recharge diverted to Yuma Valley subarea __________________ 102 Recovery tests for wells ______________ 15 Red beds _____________________________ 8.! Reservation Division of Yuma Project" Reservation subarea __________________ 99 River deposits, old dissected - 23 River terraces and mesas __.___.____Q 26 River valleys _________________________ 28 Rocks of Yuma area, classification ___- :0 Rosalina, columbiense _________________ 42 Rubidium-strontium age determination" 32, 57 Runoff, local ............... . .......... 75 S Salton Sea ___________________________ 19, 61 Salton Trough ___________ .-_ 6. 16, 18, 37. 57 San Andreas fault system - ______ 28, 57, 61 San Luis basin ______________________ 60,65 Sand, windblown ..................... 56 Sand deposits in Yuma area ......... 48 Sand dunes ___________________________ 28 Sand Hills -_ _ 28, 56, 61 Sandstone _______________ ___ 32 Sangamon Interglaciation .- 27 Schist ................................ 30 Scope of report _____________________ 11 Sedimentary rocks, nonmarine ........ 92,65 older marine ___________ :9, 65 other nonmarine _ -_ .97 Senator Mesa ........................ 24 Senator Wash ........................ 48 Senator Wash Dam .................. 58 Sheet-Wash and wash deposits ______ 56 Shinarump Member .................. 51 Sinclair Oil Co. Kryger 1 test well --- 42 Slate _________________________________ 32 Softening of water __________________ 126 Soil-moisture studies ................. 109 M 7“ Page Sonoran Desert _______________ H6, 18, 57, 60 Source of recharge of ground water __ 70 South Gila Valley _______ 6, 50, 59, 68, 88, 139 South Gila Valley subarea ____________ 100 South Gila Valley Unit of the Gila Project ________ 9 South sector of Yuma Mesa 141 Specific capacity of the well 78 Specific conductance _______ 129 Sphaerhoidinella dehiscens _ 40 Split Mountain Formation _ 40 Spontaneous potential logs ____________ 14 Step-drawdown tests _________________ 15,75 Storage coefficient, the term __________ 74,78 Storage coefficient determinations ___ 15,102 Storage-coeflicient values _____________ 109 Stratigraphy of area _________________ 3‘0 Stream-terrace and piedmont deposits _ 47 Stresses applied to the modeled system 109 Structural features, late Tertiary and Quaternary _______________ 60 pre-Tertiary _____________________ 5 7 Structural patterns, regional “"7“" 57 Structure of area ______________ __ 57 Subdivision of Yuma area for description of quality of water ______ 12.9 Subsurface outflow to limitrophe section 103 Sugar-loaf volcanic knob _______________ 21 Sulfate reduction _____________________ 127 Surface water deliveries to Mexico ___ 105 ’1‘ Tapeats Sandstone ____________________ 50 Telegraph Pass ___________ 22, 139 Temperature of ground water ______ 15,113 variations with time _____________ 113 vertical variations ................ 116 Tertiary and Quaternary conglomerate 45 Tertiary and Quaternary structural features __________________ 6’0 Tertiary marine sedimentary rocks ___ 39 Tertiary sedimentary rocks ___________ .92 Tertiary volcanic rocks _______________ 37 INDEX Page Test drilling .......................... H12 The Island _-_ _______ 9, 17, 56. 99, 134 The Island sector ___________________ 135 The Island subarea ___________________ 100 Thickness and distribution of older alluvium _________________ 46 Thiem method for computing transmissivity ____________ 75 Tinajas Altas Mountains _______ 19, 22, 39, 56 Trachyte _____________________________ 38 Transition zone (Pliocene) _____ 45, 60,63, 66 Transmissivity ___________________ 75, 88, 108 the term _________________________ 74 Transmissivity at specific sites _ _ 15 Transmissivity values __________ - 108 Tufi‘, ash-flow ___________ _ 38 water-laid ___________ _ 38 Tuff breccia ___- 32, 38 Tumco Formation ................ -_ 30 U Unharvosted fields, use of water ______ 98 Upper, fine-grained zone, water-bearing deposits ____________ 6'8, 124, 139 Upper Mesa ___- 23, 27, 49, 56. 61, 97, 108, 139 Upper Valley subarea ________________ 1.9.6 Uranium-lead age determination ______ 32 Urban and suburban use of water ..... 98 Uvigerina sp ......................... 40 V Valley Division (Yuma Valley) ...... 6 Variations of temperature with time-_ 11.9 Verification studies of analog model ___ 113 Vertebrate fossil from Miocene ________ 30 Vertical hydraulic conductivity ________ 74 Vertical variations in temperature ___- 116‘ Vitrefrax Formation _________________ 30 Volcanic rocks, age _____ 3.9 Volcanic rocks (Tertiary) ____________ 37,45 W Wash and sheet-wash deposits ________ 56 Water, fresh. definition _____________ 63 H227 Page Water-bearing deposits of Pliocene to Holocene age ___________ H66 Water-bearing rocks ..... 12 Tertiary age _____________________ 66 Water budget for Yuma area ......... 105 Water budgets _______________________ 95 Water hardening 128 Waterlogging of lands near Yuma mesa 10 Water movement direction in 1960 _____ 88 Water quality in Bard Sector ________ 136 Water-resources development, history -- 6 Water samples from Arizona western sector ____________________ 140 Water softening _____________________ 126 Wedge zone of water-bearing deposits_- 66 Well-numbering systems ______________ 17 Well records, inventory ______________ 14 Wellton Hills 23 Wellton Mesa 26 Wellton-Mohawk Conveyance Channel-- 132 West-central sector of Gila Valley subarea __________________ 1.” West sector of Gila Valley subarea 188 Wildcat drilling for oil ......... _ 16 Willow in Yuma Valley ______ _ 87 Windblown sand (Quaternary) ______ 56, 66 Winterhaven sector __________________ 135 Wireline logging of wells ............. 11 Y Yuma area ........................... 103 Yuma Auxiliary Project -_ ______ 9 Yuma Hills ____________ 22, 29, 48, 59 Yuma Main Canal . _- 9, 185 Yuma Main Drain ____________________ 29 Yuma Mesa __ _--_ 6, 9, 16, 26, 50, 53, 67, 97 Yuma Mesa Divxsion of the Gila Project 10 Yuma Mesa subarea ________________ 101,139 Yuma Project ________________________ 6 Yuma trough ________________________ 60,65 Yuma Valley ____________ 6, 19, 29, 50, 87. .93 Yuma Valley Oil and Gas Co. Musgrove 1 test well _______________ 40, 42 Yuma Valley subarea ______________ 102, 136 U. S. GOVERNMENT PRINTING OFFICE: 1974 O - 507-243 UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 486—H GEOLOGICAL SURVEY PLATE 1 EXPLANATION O107.6 Well Number is altitude of water level, in feet above mean sea level 85 Water-level contour, fall 1966 Shows altitude of water level. Contour interval, 5 feet. Datum is mean sea level Trace of Algodones fault Short dashed wheue concealed Base from US Geological Survey \ Vopok: Ridge and South of Yuma I:62,500, \\ 1964—65; Fortuna SW and Yuma SE 124,000, 1965 32°25’ 114°3o\~ K, . L 27, 1‘ SCALE 1,62 500 \‘ngzow j 1 3 MILES 07‘ ‘ A I, l l ‘VOI§\~L\ I, 1 2 3 KILOMETERS \2124‘ l I I ~o / ‘ CONTOUR INTERVAL 20 FEET Geology by F. H. Olmsted; DATUM IS MEAN SEA LEVEL hydrology by F. H. Olmsted and O. J‘ Loeltz TOPOGRAPHIC MAP OF THE “UPPER MESA” SHOWING TRACE OF THE ALGODONES FAULT AND THE EFFECT OF THE FAULT ON GROUND-WATER LEVELS, YUMA AREA, ARIZONA AND CALIFORNIA 507-243 0 - '74 (In pocket) No. l 32°45’ PROFESSIONAL PAPER 486—H UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY PLATE 2 114°45' 3730" 114°3o' 32045, I T I EXPLANATION W Bedrock outcrop SOUTH GILA VALLEY Base from US. GeologicaI Survey \ \ \ Yuma West, Yuma East, Fortuna, Gadsden,\ Somerton, and Yuma SE 1:24.000, 1965; T I a a South of Yuma 1:62,500, 1964 ‘ ~ 0 O O —I 3730" 32°30’ SCALE 1:62 500 I 112 o I I 3 MILES I I I ‘5 (I) I1 2 3 KILOMETERS | CONTOUR INTERVAL 10 FEET DATUM IS MEAN SEA LEVEL \ Geology by F. H. Olmsted; ‘ \ hydrology by F. H. Olmsted ‘ ‘ | [130” and O. J. LoeItz |\‘~‘ 37 114°30’ TOPOGRAPHIC MAP OF THE YUMA MESA, YUMA AREA, ARIZONA AND CALIFORNIA 507-243 0 — 74 (In pocket) No. 2 UNITED STATES DEPARTMENT OF THE INTERIOR : PROFESSIONAL PAPER 486—I—I VGEOLOGICAL SURVEY ‘ PLATE 3 l IIT‘)I:“I/fll l3 l‘fi'l' If, “:9 , . , \mpvtlrlmez / ~34? .\ ”'3 R I I T «1 . e. We 3) L W £1 8“”) I ( ft.» , a . «323%; e es: PEAKQL_/:c (é. O'.OU 1” .k\‘ 5/ 0&0 . 3W . t D .. ~ I” ' sherslcandlnngWMW 0 ll : ; x _ §\250 . . . 1 ‘7 < I: \‘\:‘:\:\\\ ' ‘ l: “‘55? I” :olllfioeio e lo “es I« I ' e? t 4/ / ’ gel/51 rep/l I) a fi ) _> w, ”M . Wle/ / 1/ l 1/ P1, // ,/ f"‘l""' t’ f/M' yTSS l l “"“ l x \ hone TEsn fr 1 , , I: _ 440- Alf" '/ / f Kama (ye/fl ”7/3 gel ,, u y/ 32°45’ 5 I I , Il'elll‘l «[ :‘ ‘“ - * c’ ‘ / T. s s _ ’ :’ l n l \ 23 7 i,“ a _ _lw AL ‘ka'd. I30 I I” I; : 0 L. A 4 k 00—6: I“ \ V "J ' . K» (/5 0g g :3, “’Qsd l- ing Gila Valley 1;“ .‘ [/1 m: L.“ , I I MW Base from US. Geological Survey lgb d l T 7* I ‘ Q» , f2 ma l 33 , B6ccc 316, C: GabbJ ' . ‘\ d 5 3 ~ ‘e..\% 3 b‘gzabbw J 6bbb 3 : 32Ecc’ Q ‘ 3e Yu inerale’ J0‘s its? ' EXPLANATION ’3. g.“ l ID Qsd :- :5 ‘ V 3 le \ 8b '* Q l a ‘ _\-§ M /(1_“‘. l N: Q3” [>12 M L ' . “' 5bbb ’4‘” 14b {it 7ccc I e - . -‘ .- ‘3 16b ' ‘ U s” ~ E Younger alluv1um Wmdblown sand 4: " if‘ A Max 102dd “900 ,_ 2: 8ccc Sdcc E Alla vial sand, gravel, silt, and clay Well—sorted fine to medium sand E f' / x) Q fill: A ‘5 of most recent cycle of deposition Qs, sheets and small dunes less than , 3 £0“ 5 MMI’” e' l ‘l‘e ‘9 z . . , _ LIJ “J. t ,‘ _‘ lo I] . l I n 3 er, deposits oj the Colorado and ltlfeet thick I— 19 1. r \ /LUI“‘ .3 \J “r . '5 Gila Rivers Qsd, dunes generally more than I!) <3: stiff! It; / \/ ]B&C-\‘ mm ‘X‘ T q S ‘2 le, wash, sheet—Mash, and allitt‘ial- feet [hie/I- ,"L 3 A L, l I . . . I.Mmm;:‘”‘“w“ - \ h ’ A V g fan, deposits oflocal origin 0 Q I 9CC , 30333 20ddd 2 j / [LUSI [)lldln MK 95 20 WW \i \W ,\ the ~ . 2” 1 l l E / ""27'a5‘ar'r' “ .. , View .- j” m A: , g COCO; R (F’ b 26 aaa g-‘IBCCC s‘.29b‘b 31L ’ 4.? 15016613 FLIIZA'S .\ - mmllNDlAlx f“ - '* cl \ l h .4. , IS .e- , £63} twee: ~\ 3 ill 3. , ,/ / Qsd ,: t,“ ‘r‘ 0 § Older alluvium _ “i f f ll 3 ( ( m ‘ ' ;N *3: Allullial sand, gravel, silt, and clay I 3‘5wa J‘ l 32ddb0/ 34dd1'3d -.: ‘ a 00 ' Q t S of several aggradational and de- l D \\ ' , , 1 \ id beb -' g. \\ P '14 gradation cycles preceding the l 23an E elc o‘fiifl‘je {—2 : ‘. Clo] E most recent cycle of deposition. / fl 5 V ' {I o 6 Includes strea m—terrace and l ’02 ': \ 2ad Q\ l°C~ :1 pied mont deposits (chiefly in I l -" . 1 O O :; areas of desert pa U6 ment) I / “v 18323 e 'I “LOO 5 QToI. deposits of local origin . 'J :5 3‘ i (3“ V3\‘ ‘14 QTom, deposits of mixed origin, l N: 6b 1 (\ @lm \ (both local and river) 1 NM 83 2 \ . J 3 Q QTor. deposits of the old Colorado “355 16!; U 14bbblsldcaca§ '. ' <2 and Gila Rivers , , I .. § 13bcc 1' 2 \p . Ni . ( 8i} Conglomerate of Chocolate 3‘ “T 14 \\ o O . .. N. L O Mountains s r (VH2glonierdfe and gravel composed E Qsd@; . T , IO 5 ‘ chiefly of volcanic detritus. Prob— ‘ . , E Bouse Formation ably includes deposits eqniralent -~ {Q Q ‘5 Y , ,. "ine sedimentar rocks in age to both the nonmarine sed— i I‘ N C onnge) .mm .’ .' y .‘ imentary rocks and the older :. ){7 RI consisting offossil’tferons clay, Silt, alluln'n m ., . @ and fine sand. Exposed only at a ' locality J to :3 miles southeast of a ,, ‘ In'lperial Dam E < r I: [I Lu 3 l— ,_ / . . r , ‘ E ‘ ' V 1 ' .k .52“ 50 M e Nonmarlne sedimentary rocks . 0 came 1‘00 S . _: _~ 39°30. g (‘lastic sedimentary rocks ranging Pyroclastic and flow TOM‘S "Witt/Wt! 113, . l 3 from megabreccia and fanglom— 77’ COMPOSTtWflfWH/t l‘lllfldlle (0 G\ :. s erate to mudstone and shale, in basaltic a’ndesite 0"” basalt I?“ ‘ _ , _ , . q " . - 93> part oflacustrine origin. AI'nclade clade basalt or basaltic andesite \ 3 ‘ . fl . -. I ‘ _‘ Q, I, Lr 3 L e A V A > ’ , " . : . _ _ _ _ ' _ :3." . ' _ \ H ‘ .' ', '. S red beds, breccia and conglomerate, of 1’08“be Quaternary “ye “’1 ‘ - ‘ - : ‘V'II, - ' "eI LE1, ' L qr L" l w , ' . ~.‘ ‘. .. . ~ \ and Kinter Formation (shown on {tanks oj;(1a)rgo MighgtCho M5717," \ m , ~ I ‘M ' 7 "i V" i ' " " g . \ \\ l K - . . 111.4): Locally interbedded with “W‘s, 0‘ . “”9” ”4 . e, an m , ~ . . 3 .’ 1‘ L I-IIlmniI- rocks Ogilby Hills. Locallymterbedded 114°45\ ~. [Vt/ ' \ \ .u ‘ I . ' ‘ - :_ “3,: I L ‘9’“) :1 L , j ‘ r 1:3,} v I " "l ‘ . ‘ . * / —- . ' ':,".. ‘ I. . I ‘ ‘ . ,‘ .o . . ' \ ' ‘, with nonmarine sedimentary rocks \ w i y‘ ‘ ‘e 7 ,' 5 , 9‘: , -. - ' ' M,”- , fl :_ , - ‘ -" / I \ ‘ \W I , 3 . R’ZAW' " ’ -, T” 7;; r ‘ i I” l’f’w'fl‘ " i : 'K ' J” 1' ‘ I z '- / . // / / \. '\ ,' - “ ” - - _ ‘ ,e, t ‘ ;: - . . - ' . / ‘ ’ ’ . \ ' MAJOR U/‘VCONFOR’MITY . 4’ / .. . ,‘ - ‘ ' ./ .. \ ' 'k . . - ’ / / \ Crystalline rocks Chiefly granitic rocks, gneiss and schist. Also include weakly metamorphosed sedimentary and volcanic rocks, crystalline limestone (at R23 w.~~ PRE-TERTIARY Upper Cretaceous and older north end of Gila Mountains), and a wide Contact ”my,” 0f dike ”MAS Dashed where gradational or uncertain U _______7 ______ D Fault """ Dashed where uncertain, dotted Desert pavement where concealed, queried where 1 ”030, Gently sloping, somewhat dissected surfaces location so niezchat doubtful. U, characterized by closely packed gravel apthrown side: D, downthrown underlain by compact silt. Commonly side. Arrows indicate inferred formed on stream-terrace and piedrnont displacement in horizontal plane deposits which form thin caps on older rocks or deposits. Dense-dot pattern tndi— _L6 cates well-developed pavement in which . . . pebbles are coated with desert varnish. Strlke and dip 0f beddlng Open-dot pattern indicates light-colored A Baaa A, granitic or quartzose pavement having a less well developed silty substratum and generally lacking desert varnish Well used in geologic section Geologic section .5 an SCALE 1:125 000 3 2 O 2 4 6 8 10 MILES g f l l : l : +———-——-————-—l l—-———l 2 O 2 4 6 8 10 KlLOMETERS APPROXlMATE MEAN l—l l-——l l——-—l T:—l l——-——l DECLINATlON, 1973 CONTOUR INTERVAL 200 FEET DATUM IS MEAN SEA LEVEL 4?: e 32°15 INTERIORfiGEOLOGICAL SURVEY. WASHNGTON. D.C.~l973 *W7lO34 GEOLOGIC MAP OF THE YUMA AREA, ARIZONA AND CALIFORNIA GeologereomsIQd,Fleancstm’ F. L Dole, 1962—68 UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY Base from US. GeoIogIcaI Survey Laguna Dam and Dome. 1955; ‘Fortuna and LIgmta, 1965 ‘—I _4 Ifl I—I I—a I PROFESSIONAL PAPER 486—I—I PLATE 4 °47A r5 32°45’ MWLJ ‘ ;, MILES ‘ i I O INDEX MAP Contact Dashed where approximate or gradational U D Fault Dashed where approximatedotted where concealed. U, upthrown side," D, doumthrown side 33 7* -«I~ EB Inclined Vertical Horizontal Attitude of beds 58 W Li, 74— Inclined Vertical Attitude of foliation [I 19 (7 I , a 7 i I , v , ...,i . I Location of type section of Kinter Formation Pliocenel?) and Pleistocene Miocene Pleistocene Alluvium Unconsolidated sand, gravel, silt, and clay in flood plain of Gila River and tributary washes. Younger alluvium Qt Terrace deposits Poorly sorted gravel underlying stream ter- races at several levels above present flood I plain of Gila River and tributary washes. I\ Part of older alluvium QTog Old gravel Slightly tilted, somewhat consolidated coarse gravel of local origin. Part of older alluvium Kinter Formation Tku, upper member, gray fanglomerate,‘ some soft arkosic sandstone and mudstone TkI, lower member, coarse unsorted breccia,’ tongues of brown and gray arkosic sandstone and gray to pink tufi’aceous mudstone / W TERTIARY AND I J I QUATERNARY TERTIARY QUATERNARY Miocene and older EXPLANATION Tuff Ash-flow and ash-fall tuff of silicic to inter— mediate composition; some beds of reworked tuff. Occurs both below and within the Kinter Formation Breccia and conglomerate Tbh, coarse, unsorted breccia and conglomer- ate of heterogeneous composition Tbg, very coarse granite breccia and conglom- erate," lower part intertongues with the red beds Red beds Varicolored arkose, conglomerate, mudstone, and bentonitie ash Crystalline rocks Gneiss, schist, granite, and various kinds of light and dark dikes Geology by F. H. Olmsted, 1962—64 TERTIARY PRE—TERTIARY GEOLOGIC MAP OF SOUTHEASTERN LAGUNA IILE" " INTERIORiGEOLOGICAL SURVEY WASHINGTON D( \N I073 W7I034 MOUNTAINS AND NORTH END OF GILA MOUNTAINS, YUMA AREA, ARIZONA PROFESSIONAL PAPER 486—H PLATE 5 UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY >WLW.WL< __ L _ Buoflmwimiov 3 6 3 6 3 ABmEonEqm c0589 625.52: Lo: ,LLm; 85:39 Sommmeimdv 3 4 MEL/Dig 0ELO< It“ 4 5 Yuma 53 pTC Ta .1. Sommflmmedv _ l .\ MDZN>< Qmmfimmimdv ___L LL LL j 235 qqzqo ZLQE KwmL 0ELO< \ 3 3,564 P323 33 3 MESA AIRSTRIP aggmimmimlov IILILlLiLITLiL, A M U V. mzooow 83280. _ _ __ __ SEA LEVEL 50’ — 50’ ~ 100' — 150’ 200’ 250’ QTa : _. «SmAmNioiov 3 .5. 3 5:3“ 3 53% q m32m>mm&i8 LL mmnvifimimlov 13 gravel zone Coarse— fine—grained Upper, VALLEY 80. .QmimiQL .i 2.. ...;N 2.. :Ew 3 UUooivmimlov YUMA 205m Zfimlmlov E SQ $.32 zone gravel Coarse— Bgoxemimiov _ F: __ 4 343434 343435 3 UUEQNASV qfiZfio 231% ROME l mm>oL\ 07:0 in. Zwfiiebom QQxQR CQVQQQQD/ QTa pTc B 250’ — 200’ — 150’ — 100’ — 50' 4 50’ — 100’ — SEA LEVEL 150’ — 200’ — 250’ / C —250’ O U 0 5 2 1 _ L L SEA LEVEL 50' — 50' 100' 150' — 200' 250' Mm MDmeLv/ gnomwflmmimiov E. mtoou Staci Summflmmimiov 4 2 3 2 3 e m w 0 08833-9 LLlLlLJI: e .m S a, E m M U B y a o Neowmamale flLLlLLLLiTTILL zone QTa grained QmmwmAMNIOIQV L YUMA 1 NDZM>< Clay 8(7) mammmNAmNASV/ _ $150 2:3. emgmL/ Hmnmmmawimiov mmnmmmflmmlmiov DammmAmwimlov 4 343453, 3 zone Uboomflmwimig 3 anmmnmmlmiov L Wedge Li- ’23 zone zone grained gravel Boozmmimiov _ LL 23 fine! Coarse— Upper, mmmwmfldmimlov Al 1- 3 53 3535353 2 mammmgwimlov VALLEY 4wL kmeQ CQTQCQCL/ lILLLLlILLiLEL 3 55343632 3331345333 3 II Wedge zone C _ NV 5 2 200’ “ 150’ — 100' — 50' — 50' — 100’ — 150’ — 200’ — 250’ SEA LEVEL / D —— 250’ — 200’ 150' — 100’ SEA LEVEL — 50' — 50' 100' ~ 150' — 200i 250’ Mm m32m> q oooomAmmimlov ooummflmmimiov L L_L I L QTa QLVZLYU .\ 5 3 2 4 3 5 4534 Clay B L L MESA ZbOM. UBUwELnL movammlOHloL memo Bagel cuommLmNioiov ELEM. chL>L m/ # Mo00mmAMNl®lOL L _ LL L zone Wedge g zone gravel pTc Coarse— . NooummflmmlmlUv 3 6 364L56 fine— YUMA Clay B mUSNmLmNAroV 5: 53 zone NSQNQRAQ 3 _5_3_ 5 35 4 Luggmflmmimiov L L L L UUQHMAmmlmiov L 38.8679 L .... .... Clay B 43/30 ZEE Emir”; QmpiqmloTQL 53 53535 Clay A zone mmmNQNéTB t Toz 93m QQQNQNATB lLlllII :2on ZOme§ow\.fi 4 1 gravel Clay A Coarse— mLOmo 388$ mauvfimfivmlmiov 6 Somerton ztooa BEBE zone zone SSQNISQ 2a 5 EQ L... SQ». W VALLEY i:\Z.\O qfikkzmo fl Wedge grained z o n e pcvmmgmimiov L YUMA ztooR 8820i _ 2b fine— g r a v e Upper, C o a r s e BSQNSTB 5 . JWZWO Z:.\.\< kwmgl ULMQOVQ ZQMIPDOW 893N678 LL QTa moi: LiliL unommflmmimlov zone Wedge 23 23 WIFQQ CQ TQCQCL / .4- D 200’ «l 250’ — 150' - 100’ — 150’ —— '- 200’ — 2:5 250’ SEA LEVEL / — 250' 200' 150’ 507~243 O - 74 (In pocket) Nol 5 SEA LEVEL 100' 50' — 50' 100’ 150' 200’ 250' E Mm, NDZMC. .\ $323679 L la Bu.:mmioL-ov LL L LL finiflmwiofov lI+TLTIlTI QTa $3236.18 43mm ,3 EL 32 3 922.8678 + $818678 lLLiLlLLlLlLlLIL MESA fine— QWZVD .V ELEM. m mmmmimmioTov YUMA NggnmzmmioTov NUUUSQNIOLIQL 4330 23:. ewqm/ QQQMHQNIOHIQV ESQ <23er NUUQNZLVNiOTQV NUSNLQNSTB 382330.05 finisumiedv gnomgmlofiiov VALLEY SEQ 3:3 ESSQNSTB NGESQNSTB mmmtAewioTov YUMA 253N679 mllTlLLliL+lL|L 2.. SAQ 3.30,: .2 :Qm mammimmloTov CUE .AmmioTov L :2 <0 Z. <2 kmmi. wm>mL 23 Clay B wedge zones (limits uncertain) a Coarse—gravel and 2 zone grained 3 232454 63 3 /C|ay A 10 000 FEET 8000 1500 METERS 6000 1000 4000 500 VERTlCAL EXAGGERAIlON <20 B—B’, C—C’, D—D’, AND E—E’ ACROSS NORTHERN YUMA VALLEY AND NORTHWESTERN YUMA MESA, YUMA AREA, ARIZONA AND CALIFORNIA zone Note: Trace of sections shown on plate 1 zone 2000 500 gravel 7 Coarse— I grained Clay A 5-- Wedge zone 1b GEOLOGIC SECTIONS A—A Upper, 5—— Clay A zone gravel Coarse— QTa 2a 1] E WQ>QQ QQWQQQQD/ 250’ 200’ -— 150’ '— 1oo' — 50' — 50' — 100’ — 150’ — 200’ — 250' SEA LEVEL UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 486—I-I GEOLOGICAL SURVEY PLATE 6 I I— Q: F A 5’1 F 3 A E E N M .Q (\J m u Q U o m t; D <6 (D m m m g 8 g; 8 E n 8 to g e g g 3 g g t: g 03 Q .Q o LO KO <1, 0 a.) Lg ‘0 .0 U Q Q (VJ Z (Y) 00 k9 (\I FEET : 53 5; m 91 H (,1 g m a S I\ 02 90; Ln 0 m m ”3 3 UL FEET A A A A Lo A LO A A A A A _ ~ a __ — 4 __ 4:: __ . 3 . . . . __ 3 . 3 . 2 __ 5—— 4 —— 3 —— —— < __ 4 6_: 21*. 4 Upper, flne— __ gralned 4 zone : ej== 3 4:: 2* 3 3— Upper. 5_ fIne- 3—— gramed 4 zone 32:; Alluv1um and mlnor w1ndblown dep0s1ts A E: 5a== 53:: —: 6:: 4 _ 5;— 64== 6:_ 3 3" 93:: 4 4 __ 23__ Include both older and younger (LIILLI'IIHILS, (“Id locally. (\- Z SEA LEVEL ,.__ 6 2__ §_ _ a__ 23__ 2“ lie“; 233:: 13:: if: 5 2a -— ' 1:: _‘ SEA LEVEL thin deposits of IIIIIIdbloII‘II sand Af mos-f [dares >>‘_ 0: 4 4 45:: 2 4 —' 6 1_ 1b _ 1_= T" 1:: 3:: 1__ 1_ 1 C 0 a I’ 5 e ' g T a V e I Z O n 9—12,: _——- beneath the flier Irrtlleys (LIId Yuma Mesa include Hie (I I-IJ 4 2 Coarse 41— gravel zone 1 I 1 — _E r“ 4 .. , . ,_ 58:: 3:: 5a== 4 1-— 1—— __ 4155 1 2:: fl_ 2 3E2: 2 jollouIIItg hydrogeologIc u'IIII‘s: Wedge zone; course- :5 < 23 1b_: — gl;;—1 ,__ llgzz 1h 2E; 22:: 1_r 5241:: 2A: 4—— 6 58 I: __ glare] zone; and upper, fine-grained zone E 3 la 1 1 a :: '— 1 :: 6~ = __ ‘— 1b 2a- Coarse 2b— ~— 2," 31 Coarse—gravel 3__ 4__ 2__ 4g 2-- -- ’UJO la_— g r a V e I 25 l —— Z O n e 3 21:: 2—— 3 23 2 Tt \ *— —_ Z 0 n e 7 1 an 155E 7 2l__ 2:“ I 1:: lb—_ Transition zone , — 1 : - — —= . . . . 200’ _ 2-_ 3:: 2a__ —— 1—— — _ _1 6:: __ __ J_ 7 2 : — 200’ Interbedded or IIIIerfoIIgIIIrIg (LIIMZ'IZHH and marine la la 6== 1b sedimentary roe/cs __ __ 3 5a:: 23 1b:: 2.- 28 2a 2 1b—— Tb > __ __ | 23—4— 32:... . 0: 22-13;: 5__ 2 QTa 3 :: Bouse Formation <( la la 23 ‘_ I _ 2:: Marine sedimentary rocks > ; __ _ __ __ 5—= 3 , 25: _ T__ D: 400’ _ —— -— — 2a L: I 2 13;; — 400' Tu L: 23 2a 3__ 35:: _ T" Wedge zone 2%— Undivided marine and nonmarine 7 / ______ —————- " lb “ 23 I 28 2E; sedimentary rocks ~- — —— ————— f f ’— _————— 5:: —— 2a:— 18 13 _———— 7 fl- ! 2 2 5:: l 1b 1b“: Tn “ -— _ _ __ #— ————- {I ' 85-: __ _= . . —— 2a _ * 5_{__ 5‘ Nonmarlne sedimentary rocks 600’ 2a 2a 4—”— 3 l 42— 1!: j E — 2 " :- — 600’ :___ 2 52¢ 4—— pTc L11 it __ -— -_ _ 2 . Ia__ 1a—I: 2a 3 1L: a___ Crystalllne rocks g E 5:: 4__ 5"— 4 LL, 23 36== —_ 24:: __ 7 I— 2a 55“ 23 Contact 8—— 5:: W. 2 —-— Dashed where approximItfelj/ located; 4 — 4 queried .H'here don/)UIII 800’ — 23 QTa 3:” — 800’ , 5:: 4__ 23:: _,_» 3 2a 53:: 1‘3-— ‘ 3 23:: 45a;:‘ 2a Fault _ a __ 2 4 — 22—- Dashed where apmm‘lmaz‘ely located. I— 2; __ 4 6‘: Arrows indicate diI’ecI‘Ion of relay— 5:_ TI 5 tire IIIoI'eIIIeIII‘ 3 2——_- _ . 5 32:: I I 15: A— I _ :: ’__ _ I ’1000 4__ 23 4 6 1000 LITHOLOGIC SYMBOLS __ 3 5:: 3 6:: b_: 6__ 1 5 = 3 Tb 4-— -.. Gravel, coarse ravel, clean ravel b _ 3 g g 36;; 5.1L Wedge zone 3 __ 6 b___ 3 1a 5: 4 Conglomerate, cemented gravel 1200' - 3 LI: g2: — 1200’ g=E 10:1: 10 6:: e 7 _ Gravel and sand, fine gravel, 3 _F \ sandy gravel, pea gravel 5d: 2 22 6 2a_: _ 2 5—— 2168;; Sand and gravel, gravely sand 1400' ~ 3 — 1400’ 23 6—: 8 Sand and scattered gravel 3 5F? 23 e:—- 3 Tt 2b 32— 54: ' Sandstone, cemented sand EE— 3 e-- e: 35=I= 27—: 3 I 3 ‘ 5=I= e _ 1600 — ,__ 2a pTC —1600I Sand 6__ 3 2a 6 L 2 e 3 "’ 2a _ 4 —— 5:- 28,6 Sand and silt, silty sand, sand 5 6 . __ and little clay 3 3 2a 6:: 5“ Tn 5 <__ a - . V V 1800’ __ 2a 3__ __ 1800’ Silt, sand and clay, sandy clay, 5 g clayey sand 6:: _— 6 23 3__ 2a 5a 5:: 6—— _ Clay and gravel; clay, sand, 3 Za 5 — and gravel 2 6:: 6:: __ T I 3 4TI’ 5 b e 2000 T 2n__ 23 23:- _ 2000 Clay, silty clay, clayey silt §_— :I 6*: 5:— b _ 8:: 7 2 2 . . :__ a__ 6:: leestone, IImy sandstone __ 5:: 3‘__ 6:: 2 8 36‘“ Tt g, :: 4 5:: Coarse fanglomerate 2200' ~ 4 4— la — 2200' 10 3 __ ,__ 6:: 5 Tuff or ash 5 —I— __ 2a 2 I a__ 6:; a_I_ TU 4 B—I— g: 4 y 2400' ‘_ 6_ 2400' _ SCALE 1:48 000 5000 0 5000 10,000 15.000 20,000 25,000 FE ET I I I I I I I I I I J 1000 0 1000 2000 3000 4000 5000 METERS ' G ’ I I I I I I I I I I I VERTICAL EXAGGERATIONX2O ,_I — 800’ U D (U E CA J 8 :I U «'3 G E ‘3 “ I l K J i i K L” J ’ Q YUMA YUMA MESA UPPER MESA I FORTUNA g PLAIN v/I/Lm VALLEY g :3 E 8 H I X o U —I J V __ N I <1 5__ (\I .0 m “T 400’ — 8 8 — 400' o A 3 A .D Q N E a n N 1 E61+53+21°ii% 3323‘) 60 942 +7243 0+ster i 0 8 . \\ \ . P4443 m \ +12OO+13 ~ 347C3L430+46 O+52 +50 +73 0+69 +63 Ar \ \ ' —22 4.2? O ' \ /——~\ +41 +18 +21 +35 +47 + 55 /9‘ \.+62 /,._3 \ +5 0 o_1\5 M} 3 323 OJ: \ c o o +30co /O/~O\ / +77\ o+68 / \ +1 +2 C+)124+13 .+6 +16 +7 -1 —5 ‘Ql-s /) 24 ‘T‘\ +21+55 644/ 0+78 +8241) \qu4 l _5 +12 +9 1380V278 ll Ohfi/ U+20 U+33 +40? $333457 .+53 +70 8+67 +68 910 . +I14 \/ +265 +32 d+35 +25 01630 / +2 —10 +9 O 9/ 7 +19 0 00 . 0—1 c o o oo 3 0 0+8 6 +54 .+55 +56 I 53 75 0 +22/ +46 . / Q3 .—2 ’13 (2919+1 o+8 I Q) +10 +3 +20 -9 +19V5+1ss +22 —3 ‘59.“ / / A o o o o / c o \ / (W / _ o 0+1o / (y/ 2 ) I /'\ / —8 +43 +20 +285 / +21 +8 / I +40 0 +43 0 o / 0 +15 0000 «+7 I 0 +35 0+48 / o+130/ / 1 +2374 / / / // .—15 00 K I / // _‘19 _ +41 0—26 0—22 0—23 (‘16 _loo 2&3 24/ 0 V‘ /9{120 4‘ _24O—19 14 / % o+37 % \/ 0—27 ‘34—18.—170/.—18 64/ Q/ +.39 ‘45/// \‘8/ —28 / o#o/-6 9 L O / V. .—38 ‘30 #20 .318 8 15 69 // V“ / / q. A ’+17 +9 / I Q, / ? ° / / Q J / .+36 q./ // 0Q o~42 ‘03 / U .+3o / z c —32 646 '26 —26 / .+19 / / 0*36 0 _31 I / / —38—‘33 .0 _32 +23 / 0—25 . i140 +31 II .4213 .+33 +90 / / +38_ ,/ +54 ‘320 o :2 \331' ”38 -/ ’ +688+93 +524\ \ /" o+65$ O / EXPLANATION .+45 7 37 144—34339; 4° / V‘ / / ®+17o +45 / / .+ 27 ‘4503‘ .+l33./ é / +167 0+168 0 /’ W11 t t‘ t f 1 ._47 / 3:317 .+31 0 +185 e pene ra mg op 0 coarse-grave zone .— 38 / / 0/ /+31 _\ / \ Solid circle denotes well having gamma log; open /0/ .+11/ ~ +21 d+32 +37 / +91 +162 +124 +153 +202 \ circle, well having only driller’s log. Number / / . 0 64-40 0 O O . /Q 0 \ indicates altitude of top of coarse-gravel zone, 0 +198 . / +16 / / +142 0+ 174 / \ infeet above (+) or below (—) mean sea-level. f age / O+67 / Letter symbols designate: s, sandy gravel; vs, / 1 +59 .5 very sandy gravel; M, gravel missing / we w I0 / I / fl _ 3 — — —— — —— / (\I_ / / Major discontinuity in top of coarse-gravel zone / +36 +190./V Stratigraphic position of top of zone changes I ( markedly, and altitudes differ by several tens 1 offeet across discontinuity. Only major dis- tinuities shown \ 6071 +29 I ~ , .3- +66”, 0+ 39 {I n... “3 41 Nu 1;;43, an 4 u . 4,“ 32°30, _ T 115 +32 ///\ +£9/ \ \ 7 .‘84I I I ( O\\ l I \{750—14 I l \0+ 24 { R,25W- + ‘L —056I +86\ _012 3 +24 \ I \QNITE I l —28\ O \ / ‘ \0 87 I I \ \ \ /\,// MExfaATEwl / \ \ \\ / O T ‘\ / \\ \ \\ _______ T 11 s < R 24 W ¢34Q-32 \ c\_ \\ Alluvial escarpment f IE S I WES \324 \ \ ~ 1 + \ \AfiIZ \ 2 1 o 2 4 KILOMETERS 6‘0]inij \ l 1:2, l l l | I [34 ‘ + \ +91 \ ‘1 R 23 W73 \\ I \‘ \ l \\ . 114345, R.22W1 114030! R.21W1 R.ZO W. 1140151 Base from US. Geological Survey MAP SHOWING ALTITUDE OF TOP OF COARSE—GRAVEL ZONE, YUMA AREA, ARIZONA AND CALIFORNIA Geology by F. H, Olmsted, 1968 507~243 O - 74 (In pocket) No. '7 PROFESSIONAL PAPER 486—H PLATE 8 UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY m / U D g YU MA MESA 3; YUMA VALLEY H EXPLANATION m , N 1 200' —? 200 —I 3 __ 4 > C g g Clay and gravel; clay, sand, and gravel 2a lb 5 lay A 5 , :— 7 _ , b —— ' 3-: 1b -" :2." —‘_fi— ‘5- E: S‘- 3 SEA LEVEL SEA LEVEL 1b__ 5 S Clav siltv elav Clavev silt Gravel 1:1; 5 5 5 /_§ ClayA HS: 24 J . . , I . __ __ 1b .7“ 3 C14 >33,600yrs B.P. '— 2 2a _ ? 3 4 3 3 4 26 . __ 2__ __ .1- w M , 1 1— Lithology uncertain below 3 3 2 , 1b: _S-yl‘ 2 Z 113 -_ . _— _l TE _l. 1 thIs depthzgammalog e :2“ 3+ gJ— ‘3 ’ 50, _ does not corroborate 2 1 " 1_L 3 — 50' geologIst's log 3“ __ 1 COarse— 1 gravel zone 1:: 1b 3__ __ 24‘ __ 23 4 23 TL L 213:1 — 100’ 100' — —— -- 150’ 150’ — 200’ 200’ SCALE 1:12 000 1000 0 1000 2000 3000 4000 0000 FEET | I l 1 l l l l I l l 200 O 200 400 600 800 METERS l I I I l l l l l E) VERTICAL EXAGGERATIOIX2O \l 4": 9 <2: a r.._ .mn saswww 7- .6.” .. ‘ I, Q Q _o L) 300- a YUMA «I 23 g MESA. 5,3 2 SOUTH GILA VALLEY 300 U D Of Q (VS m \ D a it w 1 i A E A ‘ a: Z I (\I (\J g (\I (\J a (\I <( E N N ' >‘ .—I U '0 D | I oo Lu H (g 13 n “C .Q I | O O on m I m N ‘O (a _o m ‘0 m OR o" to <0 C) L.) Q :l 8 “3 8 S 8 8 ’\ '8 0 O pr—l‘v V V V L” rug L“ N m H 1 H V V > m A N A A A '4 2 53 _ A (\I A (\l H ‘—' N / 200’ 4 la ': A" 3 3 <( RI 3V S (T ‘T' N. ob CIV 200 3 — 2 : _“ K :1 (XS 00 05 00 00 0‘0 I 010 4 21):: __S 0 I I I I I o O — #——————— } e o I o o g v V 3i ___—_— ?—> 5 S:— 5 Clay and SIIt 5 \N\8 V 9 V v | 6 5 __ , K 4 _ 4 \IL/ 5f 3 K ? 3 II: 4; 5_ 5 . z; 3 _ 6 42: :E 4 2 “ 2 4 1 6 __ 4 j j —- j: . . 5 4 3—— 5 6 Upper, fIne—graIned zone 3 3 __ 6 5 :: . , 2 4 5 2a _ -- Upper, 6 == fIne—gralned zone _ 6a 10 ,_ 5 elb=— l 6 —100’ O 3 1b: 4 4 5 3 3 “ 5 3 __ 5a —— “)4 == 7 __ 2a 5a :: 5 5a “ \ L5 __ 4 3__ 1b __ = 63"— ) I 3 3* —— 2b: / .1- <——= —— 1b 1 __ /——— 2 “‘ 6 “ 1 1 I 1 1 4 1 T_ 5a __ 3 :_ _I_ 11) __ 2__ _ _— __ 1 2 1 Coarse—gravel zone 2 ? Coarse 5 gravel 1 zone 2a Th 1 5 :_ 24$ 7 1b 5a _ __ 1 3 -- 1 —-————-‘— SEA LEVEL 6 3—1 g 3 1 1 _ 04— SEA LEVEL _ __ f 5 _ 4 4 1 1 __ __. -‘— 1433: 7—5—— J -— 7 2-- E. 2 _ 3 / _ . 3 .. 2 —— 3 100’ — — 100’ 23 Wedge zone I Wedge zone — ..... _ 2-_ .z. , , y 3 __ 26 200, _ 2:“ 3 — 200' 2:: 3 1b: ~2 2a 1b: 2” 3—~ 6:: 300' — 2-- — 300' 3 3 2a: 2“ 3 __ _— ---b- 2 1b-- 31 2 6:1: 400' — 1b — 400' 2a 2 500’ 500' SCALE 1:24 000 2000 O 2000 4000 5000 8000 10 000 FEET l I I I l l l I l l 4000 O 4000 8000 12 000 16 000 METERS l I I I l l l l l VERTICAL EXAGGERATIONX20 GEOLOGIC SECTIONS H'—H’ ACROSS MARGINS OF YUMA VALLEY AND YUMA MESA SOUTHEAST OF SOMERTON AND I—I’ ACROSS EASTERN SOUTH GILA VALLEY AND NORTHEASTERN YUMA MESA, YUMA AREA, ARIZONA AND CALIFORNIA 507-243 0 ~ '74 (In parka!) No, I“: UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY 115°OO' _—.—- I‘— 115°OO’ Base from US. Geological Survey MAP SHOWING PRINCIPAL g9 [ll/1; 0 'II 4 // //0 "9% I’ 4.9, X” // ' , / ., I//%////% @/ I, "é,"4/’I{,;3 3. <9 . ' Q— . In '. <50 ’95 v-Sinclair on; 63:23; ‘9 “‘4; Kryger 1.5 I“ o 0’) a 23. (~- a: &W A, 3.. “39¢ -o ‘68 up) .. , .0) ~57 3.9 Q7 .3, 6‘ o LCRP 25 . .97 PROFESSIONAL PAPER 486—I-I PLATE 9 EXPLANATION I 3')“ II I //7//¢ Outcrop of fl‘ertiary and ’ pre-Tertlary rocks 30' 15, / I ~.’ I , / /’ ‘ I I4. /%WY / ‘ I; $532 ’ I ’01,; a.“ I ¢//I/% 2:0/ / lo, /// we}, <’ “I WI” / ’ I 0 ’0 ‘ ' «s ”eh W < WI ........ x // eel/I //I,I. //// .7 e // 9/1/33 3/ ///, /% 1g —ange ault (33’ l/fl 49/ ‘~{// @@ Dashed where uncertain; dotted where 0 g 9”" eojrjceailed; queried where doubtful or \G : A 7/” are .7 .~. Q0 ’p \ I "~. 2. o P" III/z" I, 4., /' I~. Thrust fault \~\ v : y’fl/WI‘I/ 5 M 5-. C P‘ g 5 ////§¢// ? a! Sawteeth on upper plate 3‘ ‘ 1% .: / / // a... VV\ 65 5 I/r M,” .CH—28 YM ER \0 29 / / /{/{///IIII,,I5/%’ P Test well referred to in text . A M ._ q, // WM ‘ ’3‘“ ““1 ~' /4,’v l”, Way: - ' 0 " f} / Colo Basin Assoc Federal 1 10 MILES l J' 5 1o KILOMETERS | l 30’ GEOLOGIC STRUCTURAL FEATURES ,YUMA AREA, ARIZONA AND CALIFORNIA Geology by F. H. Olmsted, 1968 UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PLAT GEOLOGICAL SURVEY EXPLANATION O I Z l l < l ‘ ‘ >- Alluvial and minor windblown deposits E Alla vial sand, gravel, silt, and clay deposited by the E ('olorado and Gila Rivers, and by local ephemeral K streams. Include both older and younger alluviums, Lu and, locally, thin deposits of windblou'n sand I— Transition zone J Interbedded or intertonguing allai’ium and ma rine sedimentary rocks Bouse Formation Fossiliferous clay, silt, andfine sand, and, locally, a basal limestone or sandy limestone Older marine sedimentary rocks >_ Fossiliferousfine sandstone, siltstone, and clayswne; [I ma induratezl, generally coa rser. a ml probably more <( deformed than House Formation F. [I L|J l- Nonmarine and older marine sedimentary rocks, undivided Volcanic rocks ‘ Altered basalt pcnelratecl at test well I USER CHAS RD Well N01 Name USGS LCRP 14 [7868 IICRP 23 I'SBR Cllrré RI) ISSGS IK'RI’ Z USGS LCRP 28 @ (C77~22)14bcd @ 16S/23Eelllkcc @ 168/22E723(7aa 16S/22i172mnaz (C79724)8baa (C~11725)11ab (C78722)35caa1 (C79722)28cbb (C79723)33cdd (€710,24)24cbb (C713720)2abd (C712721)253dd (C712A21)17chc (€712,22)9bab ((1711723)34bbc (C—11724)23bcb USGS LCRP 25 USBR CH720 YM USBR CH728 YM USBR CH724 YM USBR CH423 YM USGS LCRP 24 USGS LCRP 30 USGS LCRP 10 6®6®®©6®©®©®® 114°45’ 32°45’ i OUATERNARY Yuma Valley 0i] and Gas Musgrm‘e 1 USBR CH7704; USGS LCRP 29 Colorado Basin Associates Federal 1 5 41/155 A AQUA/,4 DAM Nonmarine sedimentary rocks Clastic sedimentary rocks ranging from claystone to boulder conglomerate and megabrect-ia Horizontal scale variable m other durec; lions. Vertical exaggeration 5:1 along northrsouth and eastrwest lines , pTc 5 AIMEE Crystalline rocks Fhiefly granitic rocks, gneiss, and schist 100 O PRE- TERTIARY TERTIARY 200 0 __ __ fl .. - -— —"' ‘n 44035405 Contact Dashed where poorly controlled or uncertain. Surface ofrrystalline rocks is shown diagrammatically as an erosional surface oflow to moderate local relief 3000 4000 5000 Surface trace of Algodones fault Dotted where concealed. Arrows indicate inferred displacement in horizontal plane EA LEVEL 6000 FEET R We 4— Vertical trace of fault Dashed where uncertain, Arrows indicate displace- ment in vertical plane 8 Alluvial escarpment Sea level IS shown by a light lll’le near the top of each section, bottom of each SeCllOn lS 6,000 feet below sea level Total depth (feet) 505 715 360 1,777 2,466 4,868 1,997 2,318 64 6,007 1,427 410 320 7105 VALLEY 114°15' l \ / —\ _ River 32°30’ \ R. 22 w. x. 0 5 10 MILES \Q‘ T'12 S ‘ l l “ R. 21 w. ‘~\ \~© I R. 20 w N INDEX MAP INTERIOR—GEOLOGICAL SURVEY, WASHINGTON. D C 77719737W71034 ‘ a. PAPER 486—H E 10 . SEA LEVEL Geology by F. H. Olmsted, 1967 -BLOCK DIAGRAM OF THE YUMA AREA, ARIZONA AND CALIFORNIA T9539 is \NN“ UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY 114°45’ / 77 ”’,/7‘:Z7/'/ ’ ., //7 .. 71° 6’0 I " ,7" %v7/ Q R 21 E E“ 7% 1% l 635 \51, W ARNNN 2400 351 356 A 1030 \ $ 4c 372 706 240 § \\\\\j§\\\\\\‘> \NNN‘ \"Z Ii/iy” \ Z // /Z////// I “BARD VALLEY” \ GIL 248 1290‘ 9 smm 218 . .‘ , ,‘ 7‘, , I! I H 1’02le / (7,7371! / // 7/7 7 ////7 QZ'Z I‘Z/Ilé / 7 / K / 5 \\ A. \\\\\\\j\\\\\\\ 4 NM 6 \\ AMWMM 1 2020 SOUTH G I LA VALLEY NMNR 28b 1.1»sz \\\\\\\\\\\\\\\\\\\\\\\\\\ 7“, WWW M m cl \\\\§N\\ M R. 21 W. ,,, , 7 // Z ’ I 7’ Zn, /4 '7 7 1777;13777‘Z/r' m I / Q] 7 77, '77/ /7 @9 4 \ sw 2830 . 2070 2550 5160a / ” 3f \ \ PROFESSIONAL PAPER 486—11 PLATE 11 R.21w. R.ZO w. 114°15’ 12.20 W. 114°15' 114°45' {Z @ ‘Zzz 7 /w77 7 ear/77’ // 97/7 ' ' 7% ./ a V 4 , , /° 02 Q 0 6 ° 0 Ogilby Hills 6° // 2439 I I AM&\\\\\ 380C 90b \\\\ Ca\ 575 Mg \\\\\\\\\ \\ 4 \Ns\\\ 3060 Stiff diagram Shows concentration of major constituents, in millequiv- alents per liter according to scale below. Black circle shows location of well sampled; 575, number of sam- ple in appendix C; 3060, sum of determined constit- uents in milligrams per liter 0 50 MILLIEQUIVALENTS PER LITER 50 I_I_I__|__.L_I_;I_I_L_J Boundary of consolidated rocks \\} //%//////%/ 7 T165 “BARD VALLEY” 581 VALLEY I: WW7,’M \. \ ‘ /////77/////7/l . ‘K \\ % a? 77// R 211: \\ 7 2171; 7\‘// \\__7 1c .2 x ‘ (/%% K \ 1 {% \, \\ Wg/Zjé/%I4Z v/ 1080 % ~'\» \\ / . \1 07/777,? :: \} Gila River /i\ \. T.8S , \ sis-157* NW 017,, Z '\. I 1 ’7 , / \\\ '~.\. / T 85 LA VALLEY 923 " %/ \\\\"\. [I ,/ / \\<§.\.\‘_‘,,. \I‘ ~\\ //_\//93 1360 55c//d{A ,, \<:.\i‘\""/T\~, %fi//// T19 s. W Z ///// 7 @///j T, 9 5. Z //’7 / ' l7 //’//’7 7 / ,7 , , , , , . / 7 - 7 1R 7/// <7 Zf/ ( 7 (@j/ 777/ 5‘? 77/ ' / ZZZ % , .1 587 592 \\ 522 EXPLANATION @7; /////777 ° ’ / 77 ’ ’ “Pi/j 8“?de ////Z7Z/ / ,, Z9 ,a , ‘ l mfmmmfmm 23:7: 7 _ Z/,% 0 3230 {l 3&7 7 47% 32 3o } // \\ 1,800 milligrams per mire Z, % \\\\ W T ” S / \ Boundary 0f consolidated rocks T H S /Z777/ ‘\~ \\ ’ A \ \ R 2§w\e\ \ 015, 1141451 \\\ \ R22 w. 114130: i R‘izl‘wf' R.20 w. “4°15 0 'Ogilby Hills Z° R122 W- 114930' R: 21’W.’ CHEMICAL CHARACTER IN COARSE GRAVEL ZONE Geology by F. H. Olmsted, 1968 CHEMICAL CHARACTER lN WEDGE ZONE 114°15’ / 4 ' 7 a y {a M’" ‘ J: W» a a 4 \ "‘ «7,7727% 7 “BARD VALLEY” 95,260 .233 .252 .949b 6 7200011.; 253c1230234- 77 / 7777 7% / 7 7 1210 1870 . .5311; .51: 3333333 1320 1160 1090 1020 1130 1730 382b V‘ O 1320€3837 ~385b 0 614 833 Sum of de EXPLANATION O 1420 Well from which sample was obtained 549, number of sample in appendix C; 1420, sum of determined constituents, grams per liter Sum of determined constituents less than Sum of determined constituents 1,8 constituents exceeds 3,600 mg/l Boundary of consolidated rocks in milli- r/ 7 / \\ \\\\\\\ §\\\\‘ Z7 1 ZZZ/7777 \a %/7 1777/7777 I I ’ 7. WEDGE ZONES, YUMA AREA, ARIZONA AND CALIFORNIA 77//// , 7 / / MAPS SHOWING QUALITY OF WATER IN THE COARSE-GRAVEL AND /,°0 /7 //’/’4 3230 TIIS / \ \ \ I Base from U.S. Geological Survey .388 1240 r ‘“ / 5 l 9490b // \J// 1150 / 7, r . l l \QNIT A E'D S A MEXicb TES \ ~ @OSa R.271vv. ‘EIL \ l 114°45' R,22w. 114030 RJ21w, SUM OF DETERMINED CONSTITUENTS IN COARSE-GRAVEL ZONE UNITED STATES DEPARTMENT OF THE INTERIOR 32°45’ GEOLOGICAL SURVEY PROFESSIONAL PAPER 486—H 3230' j} 32°30’ 32°45’ Base from US. Geologlcal Survey | PLATE I2 32°45, 114°45’ ' / / o , 32° 45, _ / — 32 45 / $.- '-:'V:'l’:‘ L: v ”/ .::: ///'4/’\ Uzi-'57 fl%/% .:-1. ALL 'AMERICAN CANAL — _ 4 V u,S_.§.______.—————"“’T_— //”‘/ — — MEXICO / Morelos Dam .' ///fi\\ ......... O Q ‘5‘ 5., DC: Q IQ Q Q) 32°30 _ 32°30' " ‘ ~ L2; 3» 71%%4- l I XICB\ L / 114°30’ 114°45 YUMA MESA YUMA VALLEY EX P LA N ATI O N Aggregate thickness of clay, silty clay, and clayey silt, in feet, in upper 100 feet of alluvium <10 30—40 40—50 >50 0 Well having driller’s log 0 Well having gamma-ray log Bedrock outcrop AmanSC—aLITp—UTEM l l 1 14° 30’ GILA AND BARD VALLEYS 0 2 4 6 8 MILES I I l 4| 4 6 8 KILOMETERS l MAPS SHOWING THICKNESS OF CLAY, SILTY CLAY, AND CLAYEY SILT IN THE UPPER 100 FEET OF THE YUMA AREA, ARIZONA AND CALIFORNIA OF THE ALLUVIUM IN PARTS 5077243 0 - '74 (In pocket) No. 12 UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 486—I-I GEOLOGICAL SURVEY PLATE 15 $565000 30' R.22wi R,Zl w. RIZO w. 114°15' T58 4%eu‘ %%%7”%7 wm / [‘11, 1/ ///// ,/ '/ ' / ;/ , / VII/l A 4, // //////// . I 1". / W / // m7 Wine/g? / ‘ . :.. / ' ’ r ”I; 4 / /: /, ' V / , / ,/;/// , 0/ / //; g // l / / x . 1/ / /,'/: / / / / // / 7 / / ”/ / :/ /./.Y/' 9 4 n / // / 7 / : , / ’ / fa . a M” m / ’4’, i ,/ 7Wym / W V// t weeez / / g/ / 2 6/ ,/ ,. ///\I’ . , V34? r // ~ , 4 //j ”7/, Vex/fl I // ,/ /e4' 9" I : W// flag} ., I, /‘/27//’?/7 2 / z // / ’ , "he... /I 00% a ' 4/ @ ’W 4 4 / / I a 0/ V/ V I; ///// I//Z///Z/l % Q g - ’/ ‘ / 7% ’1 , %¢’/4{:?’, // I I '/¢e,' / [I ”I. /// ‘Zféey / " :7; it: i/ / 4 ‘ fl 0 '1’, ”‘ / / " I Q; 4‘ 7 e /. / "~.., 2, ”g / ‘e / /% £9 %/ " 31 1/ * 4% 'e/ e / ///;/ W / ///f//// %f% / /I ,I "n / Q” % 1' “7’?“ "’4- 1/1 9 {fin/I; % I 'I / fl ’0 ' , '6’ Z // / '. M 3/; \ \ W SS Ogilby Hills 1 @° .' // { / /' / / // / 75/ / // /! //://l// ,/ ,’ / :’ / // ,“ y, ’6? /f 7/ l / ,/ /, , /' / , // ,r// m / / ' a // 1/ / / / [,1/ X , / ,'/ ,/ ,; .v ,/ , / ,/ ,, / / e g/Mj/f/ ,/ ’, ////:/ ,: @ Win, «:4 77:: ' Q” " ”fly/:fi/ /;//////1/ 41/ :7 ’ o / y z /' / o , l / W a ’ / /1 fig 43% 6 0 D 09 a \§§\\\\\\\\\ _. \“\ ///////( [’7 W ,W‘" MW'Z // N , . I , <37 flgfi’gWC/T% ’/‘;}%E% 14‘ ) ' % : e I // VALLEY o~ , x e/ @ {6/5 ‘9 59/ 76, ,, , l A kge/Inaeg/ . // % b g / \ , ‘J. ‘ 0. ' “\g/ \\ _’ ."‘.’¢"173 7 l7bbal 17bab \ ' dab a 15ddd Gilli River ¢ GlLA VAL_EY LCRP29 Ar /“\ /’_ \.350aa1 ,l/‘Tf \ \ /‘\/ \c‘ / @‘Q/ \ \ / / // M7/////¢%V/// l i a / / / / ’ 4 / rein”, ‘ / / I // I 7/ , ’ 1/ T._9 s. / ,1 ’ / 0 I : 25dba1,2O Listzcsby/ «’9? ? rv/fi/ / // / v“ m , /» :. g I Q/Q‘ / e . / / Q r ’ “/1; / 0Q // // , / C‘ o I , I 9/ I // / "W // l W / . /_/ /// \\ % I; ’/ A \ T 10 syog/ / \ ’/// / / / , J / / / / 0 ’ / %/ 36dd " ’ 4ddc o 13ac o I II S LCRP3 l '3 \ 1V \ ' EXPLANATION \[Z‘ED ST \ / , $3,311 ME%04TES LCRP30 \ 0 US. Geological Survey water test Well ~ . we \ OZabd1,2 R,Z3 W. ‘\\ \ US. Bureau of Reclamation water test well \ \ \ 4} 15dab \ ‘\\ % Oil test well \ \ \ LCRP24 % The number preceding the letters is the section \ \ftlab number; the. number, or numbers separated \ b ,ll ' thltt ' d't'— ‘~ giiii’ffiaiufibé’mid $23215? thaififie R» 22 W- \ t \ well is within the 10-acre tract designated \ ~ by the letters ‘ T 12 S' E SCALE 1:125 000 2 1 o 2 4 6 8 MILES l | l I l l I 2 1 0 2 4 6 8 KILOM ETERS L l I I | I I \ \ \ e \ \ R. 20 we \\ (013-20) ‘\Q 3 d 2 \ \ \ J 3215’ I l , 115°oo' ' 45' 30' 32°15 Base from US. Geological Survey 114°15’ Geology by F. H. Olmsted, 1968 MAP SHOWING LOCATION OF WATER TEST WELLS AND OIL TEST WELLS, YUlVIA AREA, ARIZONA AND CALIFORNIA UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 486—I—I PLATE 14 w. GEOLOGICAL SURVEY é? 0000 ’ /%/ MM/‘flfl ’7 , % / ‘ ~ " I %% ” /’Z%//%{/ / 00 % %%/ ”/{;%ég/'&? vr//// ~ of??? I , //////%~Wz /,§,//47 //////////////§/ ,/ / % %/////////%W/// //6/ /////// / // ,W/////% w//// %///Z%/% fi/i % 4, ‘II/l/ / % / Q2) 2'? a %’ '/ T65 %% 4%%/ D \\ Z5?” %, 1 /, /"’ Qéijaawg/ I I 0 a 11111 // // I / // %’ 7 7/77! / ’/ /,, / ¢ ///¢ / \ /%%// I '1; fl ¢ 7/’ My“ // ’ z ////////}///,/ \\ ///// // 1 M Kh/v/ /, I ‘_/ \_,/ @” \\ ”HTAX XS: ,1 ,/ ‘////% , \Ilb‘xgu/‘x o aaaaa 012137 aaaaaaa 0833a %“;@/%///////// / \ x aaaaa CCCCCC / v // // ,% / / EXPLANATION ‘ ‘\‘§ 28'dcc1,2 Auger test hole or well 888888 EEEEEEEEEEE MAP SHOWING U.S. GEOLOGICAL SURVEY AUGER TEST HOLES AND TEST WELLS, YUMA COUNTY WATER USERS ASSOCIATION DEEP OBSERVATION WELLS, AND SELECTED U.S. BUREAU OF RECLAMATION OBSERVATION WELLS, YUMA AREA, ARIZONA AND CALIFORNIA UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 486—I-I GEOLOGICAL SURVEY PLATE 15 e/ ’ ’ ’ ' M4 %f% / 115°OO’ 33°OO’ [ T58 3 44// e///// , *1/44 7 /%//%%/V / // a / e4%? / \ o . /// /;;// , , . / ”4/47“ ’ ‘ H l t .- 4 / / " M / 0’ ', 4. 0% . r . #0,, a ¢ 1 0 ‘ ’ ‘ I, I 4 e /. I / I ”I 'oo "4” w r 6/0 4 7/ %W"/”’4 J.// /‘ 6% I w 4 . ”U ///// I "x’/ 1’ v, I , % . ‘/ . // , , gm ’ M. y// ac ///IT4'/ .,’..<,,”", ' , A/jw e4 /// g 9' C22) ' , “3197/, / /, A "I y / e ., V / // WV/fl/ / , ,4 g ,, m J / / I I '4 / I a '/// 4 K ,, / 2/, ,/r/’,,/ “ / // // 4/,” '-..4,,,’} 4 , // 4 I e "M «V/ _if/,:4,;,,,;/4, , 4/4 47/ ’ 7/0’ /4 // ‘ 4, .. / // ~/ , '4 Wm , '9, / / a / ES /// a / e”! 11’, / / 77/ / 1, // . / , 4 a 0 . -' 4 14 ,/ ’ a a) / / / 44"" ’I I 7 ' a 'Il/I / //// / ’ ¢ 3” ’4 r ' ‘ “W //,///, / /, $ ‘& //////// 7/, ///A / / / y , [IV/{:4 . ///’l / / 44/44 / / /'// o a / / / / / //// / ////; $ R22E //// ,’7/ 'I / /”/,’/h“ 0e 3., / / 0 ’/// o9 ‘ / / ‘ 4 7p / ,~ 1:" / /// .0; I / I; //A/////////%, m /.‘ ‘Z ‘ ? / // I], 17:“; '0 V / ”’I/ 133‘. "1 z A if. "I I‘ '//// ' l’}! 77/ / 4 6’” V a / / // i I ‘4 Q / //C7// / I; J! v‘ / / U ’4 W ‘9’ , , m a I’ / __.’——-—' ”BARD VALLEY" C 14cdd 13dad O 30adc 29ddb\ o <6cda\o\0250a a 30cab 30dddA o a d33aaa 302;;ng [03:53?!) 2 3 a I. 34bac / b 32daalo /03;db?/26dca1 \ / Base from U.S. Geological Survey 1199mm 819bda1,2 \/ Y. A O5dbb Y. a“ x) .L Ol5cb f 1 I / / / /7 \ / / / O32a \/ {/ O32ddb ) J / \L 9ddd IOcdd nodduddd O O EXICB\E§ o\\ / / O23cbb 24abd lldca 11CCb1o *0 12dbc O KIBab 14aa 20abd. 22m, 2 O labb 2 ad 23abb OO 22lobcQ 28 @223“ / \ 20863 20add 21d/ag 22acc 22ad 02”“ 922cm: O 28cad / R24 w. \\O\\ EXPLANATION 035aaa1,2 Irrigation well The number preceding the letters is the sectian number; the number, or numbers separated by commas, following the letters is a distin- guishing number used when more than one well is within the 10—acre tract designated by the letters Alluvial escarpment 45’ 8 KILOMETERS Geology by F. H. Olmsted, 1968 MAP SHOWING IRRIGATION WELLS, YUMA AREA, ARIZONA AND CALIFORNIA UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 486—I-I GEOLOGICAL SURVEY PLATE 17 ' R21 E. // / ’ Mr 22 W' / ”W/ , «¢(¢.I %% ' ,’ Maw/I 4 / ’9 Z / , "/// K /‘ W/ bbbbb / / / 6 . I; > , ,, m%é Zgfl/ZW/ 27f,” A% é . \\\\l \ \ “ \ ’4 x/ -\ 4 ,,/ a M \ ' “"”""” I ” , 4386 O4aad /. A I Adi :1” VALLEYI‘ IQ: /////%% 01 1bbc lé/ @ 5dd g Q ’ l? 7 VC\ . , L, Ollb ' ”Z I” / ’4 r' ,o/ // 4g, “ ’I’. o 4%!» tb ’. 1 4/ Q, ‘ \ O / \\\\\\\ \‘I . \.‘.‘ ../// W / %/ ///1/ I/ (4,) 4% 30' // MAP SHOWING MISCELLANEOUS WELLS, YUMA AREA, ARIZONA AND CALIFORNIA