Q t=- ? s-/*(* u. j: 7 DAYS r*5i& Analog Simulation of the Ground-Water System, Yuma, Arizona ?> GEOLOGICAL SURVEY PROFESSIONAL PAPER 4 8 6-1 [documents department MAR X 6 1977 LIBRARY ...... r v . . * t7.SU5.D- LB 1 fiRAnalog Simulation of the Ground-Water System, Yuma, Arizona By EUGENE P. PATTEN, JR. WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA GEOLOGICAL SURVEY PROFESSIONAL PAPER 48 6-1 UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1977UNITED STATES DEPARTMENT OF THE INTERIOR THOMAS S. KLEPPE, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress Cataloging in Publication Data Patten, Eugene P., Jr. Analog simulation of the ground-water system, Yuma, Arizona. (Water resources of Lower Colorado River, Salton Sea area) (Geological Survey professional paper ; 486-1) Bibliography: p. Supt. of Docs, no.: I 19.16:486-1 1. Water, Underground—Arizona—Yuma region. 2. Water, Underground—Electromechanical analogies. 3. Water, Underground—Data processing. I. Title. II. Series. III. Series: United States. Geological Survey. Pro- fessional paper ; 486-1. QE75.P9 no. 486-1 [TD224.A7] 557.3'08s [622'.18'7'0979171] 75-619430 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 Stock Number 024-001-02927-8CONTENTS Page Abstract____________________________________________________ II Introduction_________________________________________________ 1 The hydrologic model__________________________________________ 2 The electric analog model____________________________________ 3 Stress applied to the system_____________________________ 4 Verification of the analog model_________________________ 5 Page Results of model predictions___________________________ 15 Conclusions __________________________________________ 9 Summary ________________________________________________ 10 References _____________________________________________ 10 ILLUSTRATIONS Page Plate 1. Maps showing irrigated areas, well locations, and computed effects of irrigation and pumping, Yuma area, Arizona______________________________________________________________________________________________In pocket Figure 1. East-west cross section of Yuma area showing hydrologic model and analog representation------------------------- 12 2. Graphs showing computed change in ground-water flow across international boundaries, 1925-2000 ---------------- 6 3. Graph showing computed decrease in ground-water flow across international boundaries resulting from pumping in United States, 1965-2000 _____________________________________________________________________ 8 4. Profiles of change in water levels resulting from pumping, 1925-2000: cross section eastward from about Tecolote, Mexico_________________________________________________________________________________________ 9 TABLES Page Table 1. Well discharge and irrigation recharge programed on the Yuma analog model, in thousands of acre-feet per year________________________________________________________________________________________________________ ^ 2. Effects of Mexicali pumping on computed change in ground-water flow to Mexico across international boundaries, in acre-feet per year____________________________________________________________________________ 7 3. Effects of U.S. pumping on computed change in ground-water flow to Mexico across international boundaries, in acre-feet per year____________________________________________________________________________ 7 illWATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA ANALOG SIMULATION OF THE GROUND-WATER SYSTEM, YUMA, ARIZONA By Eugene P. Patten, Jr. ABSTRACT An electric analog model was used to simulate the ground-water system of the Yuma area, Arizona, and to predict the magnitude of southwesterly flow of ground water across the limitrophe section of the Colorado River. An evaluation of alternative ground-water recovery plans indicated that there would be little effect on the flow across the limitrophe section but a substantial decrease in flow across the Arizona-Sonora international boundary. INTRODUCTION This report summarizes the progress of the analog modeling of the ground-water system underlying parts of the United States and Mexico in the vicinity of Yuma, Ariz. The project was begun in April 1966 at the request of the U.S. Section of the International Boundary and Water Commission, and resulted in a cooperative scientific effort among personnel of the Boundary Commission, the Bureau of Reclamation, and the Geological Survey. As a result of that request and subsequent meetings among the U.S. agencies, it was agreed that an analog model would be constructed of the Yuma ground-water basin and of the contiguous areas in Sonora and Baja California, Mexico. The broad objectives of the model study were to be threefold: (1) to construct a three-dimensional electric analog model of the study area which would incorporate all known and inferred data pertaining to the geologic and hydrologic characteristics of the system; (2) to impose upon the model, as a criterion of validity, the time sequence of historical events that altered the equilibrium system of 1925 into the dynamic system of 1966; and (3) to utilize the model to describe more fully the regional effects of past hydrologic events, and to predict the future response of the system to proposed increases in ground-water pumping. The specific objectives under (3), above, included the prediction of the magnitude of the south- westerly flow of ground water across the limitrophe (international boundary) section of the Colorado River and an evaluation of the effects of alternative ground-water recovery plans on that southwesterly flow. The ground-water system underlying the Yuma area is a part of an extensive aquifer composed of permeable alluvial material deposited by the Colorado River, the Gila River, and the earlier drainage systems that created the delta of the Colorado River. The aquifer system of the delta area underlies parts of Arizona, California, and the Mexican States of Sonora and Baja California. The Yuma ground-water system, shown on plate 1A, is in the apex of the delta and includes the Yuma Mesa, an extensive desert area lying east and south of Yuma, Ariz., the Mexicali and Yuma Valleys to the west, and the South Gila Valley to the north. The entire delta area is in one of the driest regions of North America, with summers that are hot and winters that are mild, precipitation less than 5 inches annually, and agriculture possible only by irrigation. Historically, water diverted from the Colorado River has been the principal source of irrigation supply in both the United States and Mexico. Since before 1955 ground water has been pumped in Mexicali Valley to supplement the supply available from the Colorado River. In recent years the water pumped has supplied one-third of the irrigation demand. While the area irrigated by ground water in the Yuma Area of the United States is relatively small, it has increased since 1966. The application of Colorado River water to lands in the Yuma Mesa was started about 1924, but full-scale irrigation activity was not started until 1946. The ground-water recharge from irrigation on the permeable soils of the Yuma Mesa resulted in substantial rise in regional ground-water levels, which II12 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA eventually overwhelmed the capabilities of the existing drainage system in the adjacent valley areas. As a consequence, drainage wells were installed to control the ground-water levels. Prior to 1955 there were only privately owned wells operating in Mexicali Valley. In 1955 and 1957 the Mexican Government authorized drilling wells to supplement its canal-water supply and to control rising water levels. The influence that the water-level change in both countries has on water movement across the international boundary was part of the Geological Survey appraisal, which began in 1961, of the water resources of the lower Colorado River area. This report is one of a series that constitute an appraisal of the water resources of the Lower Colorado River-Salton Sea area. The analog model was first used to simulate the historical water-level changes that occurred in the Yuma Mesa to help define the hydraulic characteristics and water movement in the aquifer system. That aspect of the model study is described in Olmsted, Loeltz, and Irelan (1973). Later the model was used to assist in studies of the effects of pumping from the aquifer system under various assumed future conditions. This report summarizes the results of those studies. The present model is not the first electronic representation of the Yuma ground-water flow system; during the course of previous studies, Brown and Skibitzke (1956) used a steady-state cross-sectional model to demonstrate the effects of anisotropic permeability in the system, and Jacob (1960) used a differential analyzer to study the nature of the ground-water mound underlying Yuma Mesa. THE HYDROLOGIC MODEL Hydrologic data in the Yuma area have been collected by the Bureau of Reclamation since the first decade of the 20th century. Subsequently other agencies participated in the collection and interpretation of hydrologic data, principally the Yuma County Water Users’ Association and the Geological Survey. The Survey’s activity in the Yuma area culminated in 1969 with the publication of a comprehensive report by Olmsted, Loeltz, and Irelan (1973) that contained the hydrologic description upon which the analog-model analysis was based. It is beyond the scope of this report to recapitulate Olmsted’s findings except to note how his description of the hydro-logic system was simplified and translated into analogous electrical form. WEST EAST Analog Representation MEXICALI VALLEY YUMA VALLEY YUMA MESA 1-dimensional flow-resistors (Yuma Valley) 2-dimensional resistor-capacitor network 1-dimensional connection- resistors 2-dimensional resistor-capacitor network Figure 1.—Hydrologic model and analog representation.ANALOG SIMULATION OF THE GROUND-WATER SYSTEM, YUMA, ARIZONA 13 For the purposes of this analog study, the hydro-logic system is regarded as a three-dimensional flow field idealized into two two-dimensional transmissive layers and two zones of purely one-dimensional flow (fig. 1). The upper transmissive layer is composed chiefly of the “coarse gravel zone” which underlies most of the Yuma Mesa and river valleys, and in which most of the wells of the area have been completed. Overlying that zone are much finer sediments, which in the Yuma Valley have been modeled as a confining layer, allowing vertical flow between the gravel zone and land surface according to the direction of the hydraulic gradient. Elsewhere in the modeled area, the upper fine-grained material is lumped with the gravel zone. Underlying the gravel zone are alluvial sediments in a wedge-shaped body with a total thickness as much as 3,600 feet; that body of sediments has been modeled as a lower transmissive layer in hydraulic connection with the upper transmissive layer, and bounded by impermeable material or basement below. An effective parameter, representing the average vertical hydraulic conductivity and the average flow distances between the two layers, simulates the head loss resulting from vertical flow between the two aquifers. The analog model of the Yuma ground-water basin represents an area of about 1,600 square miles, and, where practical, the positions of natural hydrologic boundaries were used to terminate the model system. For instance, the poorly permeable Gila Mountains form the eastern boundary of the model, and the alinement of the northern boundary is represented by the decreasing permeability or decreasing saturated thickness of the sediments several miles north of the international boundary; the western boundary of the model is about 10 miles west of Tecolote, Baja California, roughly coincident with the increasing clay content of the Imperial Valley sediments; the southern boundary of the model, which is about 15 miles south of San Luis, is purely arbitrary and represents the ability of the sediments south of the modeled area to yield water in response to changes in water level. A constant-head surface represents the drains which maintain an effectively constant water table in the one-dimensional flow system that simulates the fine-grained material in the Yuma and South Gila Valleys. One of the important features of the hydrologic system for which there were no physical data was the fault zone extending southeast approximately through the center of the ground-water mound. The fault is a partial barrier throughout the “wedge” aquifer and along the southeast half of its trace in the upper transmissive layer; but on the basis of water levels, it appears to have little hydrologic significance in the upper transmissive layer northwest of the center of the mound. In general, the fault diverts water applied northeast of it to the east and southeast, but allows water applied southwest of it to flow to the south or southwest. The hydraulic significance of the fault zone is demonstrated in some places by wells on opposite sides of the fault that have a measured head differential of about 30 feet. In order to duplicate that differential on the model, an effective transmissivity of about 200 gpd/ft (gallons per day per foot) was required in a narrow strip of each aquifer along the fault trace. The effect of the fault on water levels is clearly demonstrated on plate 1B-N. Where the fault is shown as a solid line it is hydrologically significant in both aquifers, but where its trace is dotted it is significant only in the wedge-shaped lower transmissive layer. The values and areal distribution of transmissivity and storage coefficient, given by Olmsted, Loeltz, and Irelan (1973), were derived from their extensive field studies; owing to the difficulty in obtaining regionally significant data, however, the values of vertical permeability were inferred from the analog-model analysis. THE ELECTRIC ANALOG MODEL The electric analog model is basically a tool that the hydrologist uses to bring the hydrologic environment under study into the laboratory where it may be dissected and each of its individual hydrologic parameters evaluated. It should be recognized from the onset, however, that the model is not a literal replica of the real hydrologic system but is, rather, an approximation based on a considerably simplified set of idealizations that allows the highly complex hydrologic system to be modeled with an analog of manageable complexity. The power of the modeling procedure stems from the model’s ability to use all known geologic and hydrologic data applicable to the area, and to predict the results of hydrologic stress on the system. The construction of the analog model requires that each element of the hydrologic model be translated into an equivalent electrical parameter; thus transmissivity is represented in the electrical system by14 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA resistors, and the storage coefficient by capacitors. Other equivalents are given below. and 5,500 capacitors were used to construct the model. Hydraulic system Hydraulic head, feet Volume rate of flow, acre-feet per year Time, years Electrical model Voltage Current, amperes Time, seconds Each of these equivalents is established by a simple and essentially arbitrary constant of proportionality. Thus 40 feet of change in hydraulic head is represented by 1 volt on the model; 1 second of model time is the equivalent of 240,000 days of real time; and 1 ampere of electrical current equals a flow of 110,000,000 acre feet per year. A thorough treatment of the theory and technique of analog modeling is given by Skibitzke (1961), Wood and Gabrysch (1965), and Karplus (1958). The hydrologic system in the Yuma area is modeled by two resistor-capacitor networks that represent, respectively, the upper transmissive layer and the wedge-shaped lower transmissive layer. The two networks are connected at equivalent nodes by resistors that represent the average vertical hydraulic conductivity and distance along the flow path between the two aquifers. Resistors also represent the fine-grained sediment of Yuma Valley which overlies the upper transmissive layer and which provides a one-dimensional flow path to land surface. There are 10,500 nodes on the model, with a nodal spacing of i/2 inch = 1,500 feet on Yuma Mesa and 1 inch = 3,000 feet elsewhere. About 22,000 resistors STRESS APPLIED TO THE SYSTEM Although the major irrigation activity in the Yuma Valley started in the early 1900’s, the hydro-logic system probably had regained equilibrium by 1925 when irrigation started on the Yuma Mesa; that is, inflow equaled outflow and there was little or no change in storage with time. The initial condition of the analog model reflects that equilibrium, and the water levels and ground-water flows measured on the model are changes in water levels and changes in flow from those that existed in 1925. Effective or net recharge to the Yuma Mesa, which started in 1925, was computed on the basis of irrigation deliveries minus consumptive use. The net recharge was distributed areally according to the acreage irrigated in 1925, 1947, 1952, and 1957; and it was assumed that the acreage did not change appreciably after 1957. Table 1 shows the programed rates of recharge to Yuma Mesa for the seven time periods modeled. Note that it was assumed the 1965 recharge rate will continue into the future. Ground-water withdrawals from the system started in 1948 when the first of the “early” drainage wells were installed in Yuma Valley. Private pumping started on Yuma Mesa in 1965 and was followed in 1967 by pumping from the six “new” Yuma Valley wells. Pumping from the 12 Yuma Table 1.—Well discharge and irrigation recharge programed on the Yuma analog model, in thousands of acre-feet per year1 Recharge Pumpage Yuma Mesa 2 Early drainage wells New Yuma Valley wells Yuma Mesa wells Private wells Mexicali well field3 1925-47 3 4 1943-47 - 51 1948-52 .. 102 19 1953-57 157 36 1958-62 - 208 78 117 1963-64 .. 228 119 165 1965 188 126 4 212 1966 — (188) (126) 4 212 1967 (188) (126) 23 16 (212) 1968 (188) (126) 20 21 (212) 1969 . - (188) (126) 21 (21) (212) 1970 (188) (126) (21) (21) (212) 1971 (188) (126) (21) 12 (21) (212) 1972 — (188) (126) (21) (25) (21) (212) 1973 — (188) (126) (21) (37) (21) (212) 1974 - - (188) (126) (21) (50) (21) (212) 1975 _ - (188) (126) (21) (63) (21) (212) (188) (126) (21) (69) (21) (212) (188) (126) (21) (69) (21) (212) (188) (126) (21) (69) (21) (212) 2000 - (188) (126) (21) (69) (21) (212) 1 Figures in parentheses are projected. 2 Net quantity. 3 Auxiliary project.ANALOG SIMULATION OF THE GROUND-WATER SYSTEM, YUMA, ARIZONA 15 Mesa wells started in 1970. With the exception of the private wells, all data on pumping rates were provided by the Bureau of Reclamation; data on the private wells were provided by the Geological Survey, Yuma, Ariz. Pumping from the Mexicali Valley started prior to 1955, but few if any data were available to document the net draft on the ground-water system. Data were available, however, that showed the seasonal decline in water levels as the result of pumping. Lacking a better or more direct method of determining the net draft in the Mexicali Valley, the analog model was used to compute the net pumpage necessary to produce the average water-level decline observed from 1953 to 1965. The rate necessary to produce that drawdown was 212,000 acre-feet per year, and it was assumed that quantity would be representative of the net draft in the future. Because of the uncertainties in modeling the western and northern boundaries of the model, and because of the great water demand in Mexicali Valley, the derived pumping figure is probably conservative. VERIFICATION OF THE ANALOG MODEL The adequacy of the analog model of the hydro-logic system was tested according to the criterion of the 1925-66 water-level changes. The degree that the model could reproduce these changes according to the known recharge and pumping stresses would determine its usefulness in predicting the eifects of future stress that might be imposed on the system. The procedure and results of the model verification are described in detail by Olmsted, Loeltz, and Ire-lan (1973) and will not be given here. It is sufficient to report that the analog model duplicated the historic response of the system satisfactorily, and was deemed appropriate for use in predicting the future response of the system to new stresses. RESULTS OF MODEL PREDICTIONS The basic prediction obtained from the analog model is simply an extension to the year 2000 of the stress conditions that existed in 1965 and which are shown in table 1. Plate 15 and C, respectively, show the computed changes in water level in 1975 and 2000 resulting from recharge to the ground-water mound applied to the 1965 rate, and from pumping all wells that existed in 1965. As a result of those conditions, computed drawdown in the Mexicali well field will increase to a maximum of 30 feet by 1975 and to 35 feet by the year 2000; the ground-water mound underlying Yuma Mesa will attain its maxi- mum rise in water level of 55 feet by 1975. In the year 2000, the mound should still be rising in the area northeast of the fault, as is shown clearly by the position of the 20-foot change line on plate 15 and C; southeast of the fault, however, the mound will decrease slightly by the year 2000 as the result of diminished recharge to the mound after 1964, and because of the effects of Mexicali Valley pumping. Figure 2 shows that, as the result of those conditions, the change in ground-water flow to Mexico across the limitrophe section from 1925 to 2000 will be 72,000 acre-feet per year; during the same interval the change in flow to Mexico across the Arizona-Sonora boundary will be about 21,000 acre-feet per year. It should be noted here, and in the following discussion of results, that the predicted changes are changes from the 1925 base. Thus, the predicted rise in water levels under Yuma Mesa of 55 feet by 1975 is a rise of 55 feet during 1925-75. Plate ID and E show the effects of full development in the Yuma area as it is presently planned. The early drainage wells are pumping a total of 126,000 acre-feet per year, and the new Yuma Valley wells are pumping a total of about 21,000 acre-feet per year; the 12 proposed Yuma Mesa wells are pumping their proposed capacity of 69,000 acre-feet per year, and private wells account for the total pumping of 21,100 acre-feet per year. The location of these wells is shown on plate IF. Under those conditions, U.S. pumpage in 1975 will exceed recharge to the ground-water mound by about 50,000 acre-feet per year, and total ground-water withdrawals from the system, including Mexican pumpage, will exceed recharge by 260,000 acre-feet per year. As the result of that overdraft, the maximum height of the mound is'expected to be 40 feet by 1975, which is 15 feet less than the height to be expected if no new development occurred after 1965, as shown on plate 15. By the year 2000 the ground-water mound northeast of the fault will have declined substantially from its 1975 position, and almost all the area southwest of the fault will show water-level declines. Figure 2 shows that, as the result of pumping, by 1975 the change in flow to Mexico across the limitrophe section will have been reduced by 2,000 acre-feet per year to 66,000 acre-feet per year, and that by the year 2000 the total change in flow will be 69,000 acre-feet per year. The computed change in flow across the Arizona-Sonora boundary will be 5,000 acre-feet per year in 1975 and 3,500 acre-feet per year in the year 2000. Plate 1G and H show the eifects of development with Yuma Valley and Yuma Mesa wells added. By16 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA 1920 1940 1960 1980 2000 1920 1940 1960 1980 2000 EXPLANATION -------------- 1965 development extended to the year 2000 --------------With the addition of Yuma Mesa, Yuma Valley and private wells Figure 2.—Computed change in ground-water flow across international boundaries, 1925-2000. 1975 the maximum computed change of water level on the mound will be 50 feet (pi. 1G), or 10 feet higher than the equivalent situation when private development wells are included (pi. ID). Note from plate IF that eight of the private wells (as of 1968) are northeast of the fault, which probably accounts for the relatively large change in water level on the mound for only a rather small quantity of pumpage. By the year 2000 (pi. 1H), there will be only slight additional changes in water levels, principally in the Mexicali Valley and in the southern part of the Yuma Mesa where the long-term effects of the 1965 reduction of recharge and the effects of Mexicali pumping will alter the shape of the ground-water mound. The computed flow of ground water across the limitrophe section in the year 2000 is not affected by pumpage from the private wells, and therefore the change in flow will remain at 66,000 acre-feet per year in 1975 and 69,000 acre-feet per year in the year 2000. The flow across the Arizona-Sonora boundary, however, shows the effects of private development; the change in ground-water flow resulting from the water-level changes shown on plate 1G will be 8,500 acre-feet per year by 1975; by the year 2000 the change in ground-water flow will be increased to 9,500 acre-feet per year as the result of Mexicali pumping (pi. ID). Plate II and J show for 1975 and 2000, respectively, the computed changes in water levels for a situation in which it was assumed there was no Mexicali pumping and no private development; the changes in water levels will result only from the programed recharge to Yuma Mesa, and from Yuma Mesa and Yuma Valley pumping as shown in table 1. A comparison of plate 1/ with plate 11 shows that the ground-water mound on the northeast side of the fault will undergo little change from 1975 to 2000. The mound on the southwest side of the fault, however, will show a considerable change in areal extent. Table 1 shows that recharge to the ground-water system through infiltration of irrigation water will exceed U.S. pumping until 1973, but by 1975 pumping will exceed recharge to the mound by about 28,000 acre-feet per year. As a result of that continuing deficit, the ground-water mound southwest of the fault will decline, while the mound northeast of the fault will remain fairly stable. Under the foregoing conditions, the computed change in flow across the limitrophe section in 1975 is 2,000 acre-feet per year to the United States from Mexico. AtANALOG SIMULATION OF THE GROUND-WATER SYSTEM, YUMA, ARIZONA 17 Table 2.—Effects of Mexicali pumping on computed change in ground-water flow to Mexico across international boundaries, in acre-feet per year Change in flow of ground water to Mexico Across limitrophe section 1975 2000 Across Arizona-Sonora boundary 1975 2000 Total U.S. development1 with Mexacali Valley pumping 66,000 69,000 8,500 9,500 Total U.S. development1 with no Mexicali Valley pumping —2,000 —2,000 7,000 6,000 1 Excluding private development in United States. the same time, the computed change in flow to Mexico across the Sonoran boundary is 7,000 acre-feet per year. In the year 2000 the flow across the limitrophe section will be unchanged at 2,000 acre-feet per year, while the flow across the Sonoran boundary will have decreased to 6,000 acre-feet per year. Table 2 shows the effects of Mexicali pumping on the boundary flows. In order to assess more clearly the regional effects of present (1968) private pumping, and of the existing new Yuma Valley wells and proposed Yuma Mesa wells, a more detailed analysis was made. Plate 1K and L show the computed declines in water levels in 1975 and 2000, respectively, resulting from pumping the new Yuma Valley wells and the Yuma Mesa wells without any other stress applied to the system. Plate 1M and N show, respectively, the 1975 and 2000 declines resulting from pumping only private wells. This technique of showing the effects of only one of several stresses on the system is possible because the system is linear (in the mathematical sense) and the principal of superposition can be employed. That principal states that in a linear hydrologic system the total water-level change at a particular point and at a particular time is the (algebraic) sum of all the individual changes caused by separate stresses; for example, the water-level decline at a point between two wells is the sum of the drawdown caused by well “A” plus the drawdown caused by well “B.” In the present case, the technique was employed so that the rather small water-level changes caused by the private pumping and the new Yuma Valley and Yuma Mesa wells could be measured in greater detail without being masked by the much larger water-level changes caused by recharge to the Yuma Mesa, pumping from the early valley wells, or by pumping from the Table 3.—Effects of U.S. pumping starting in 1967 on computed change in ground-water flow to Mexico across international boundaries, in acre-feet per year [—indicates decreases in flow to Mexico] Change in flow of ground water to Mexico Across limitrophe section 1975 2000 Across Ariozna-Sonora boundary 1975 2000 Pumping from New Yuma Valley and Yuma Mesa wells- —1,400 —2,400 —8,500 —11,500 Pumping from private wells1 _ 0 0 —3,500 —6,000 1 At 1968 rates. Mexicali well field. The boundary flows associated with each well group are given in table 3, and are shown graphically in figure 3. The major significance of these data is the small change in flow across the limitrophe section resulting from that pumping in the United States. The reduction of flow of 2,400 acre-feet per year computed at the end of the year 2000 is small compared with either the net recharge to the Yuma Mesa (188,000 acre-feet per year) or to the net withdrawal from the early valley drainage well (126,000 acre-feet per year). The profiles of ground-water change shown in figure 4 suggest the reason for that small change; the dashed profile shows the effects of recharge to Yuma Mesa and of pumping from the early drainage wells, new Yuma Valley wells, and Yuma Mesa wells, excluding private pumping and pumping from the Mexicali well field. The solid curve includes the effects of pumping from private and Mexicali wells in addition to the above. The “X” curve includes pumping from the Mexicali Valley only, and excludes all pumping in the United States. Under full Mexican and U.S. development there will be a mound under the Yuma Mesa, a ground-water depression at the western edge of the Mesa resulting from new Yuma Valley and Yuma Mesa drainage wells, and a ground-water trough in the Mexicali Valley reflecting the effects of Mexican pumping. The other two curves show the effects, respectively, of no U.S. pumping and no Mexican pumping. Under each of those conditions there will be little, if any, water-level decline under the Yuma Valley, indicating that the Yuma Valley acts as a buffer or “hinge” that effectively separates the ground-water regimens of Yuma Mesa and Mexicali Valley. The greatest part of the water flowing westward across the limitrophe section to Mexico will be derived from salvaged water that would otherwise flow from the upper transmissive layer upward through the fine-grained sediments of Yuma18 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA EXPLANATION —X---------X— Limitrophe Section --------------- Arizona-Sonora Border Figure 3.—Computed decrease in ground-water flow across international boundaries resulting from pumping in United States, 1965—2000. Valley to be discharged either to the Yuma Valley drains or to the atmosphere as evapotranspiration. The hydraulic gradient that causes that salvage will be established principally by pumping in the Mexicali well field, although some salvage is effected by Yuma Valley and Yuma Mesa pumping. Under the pumping and recharge conditions shown in table 1, the computed rate of discharge salvaged from Yuma Valley by the year 2000 will exceed 100,000 acre-feet per year. Measurements were made on the analog model to predict the changes in flow that may occur across the international boundaries from 1925 to 2000. Those data are shown in figure 2. Measurements along the limitrophe section showed that little change in flow occurred before 1958, but that after that time there was a rapid increase until by 1966 the total increase in flow across the limitrophe to Mexico was about 58,000 acre-feet per year. The model shows that if the conditions of 1965 are extended to the year 2000 (no pumpage from the new Yuma Valley, Yuma Mesa, or private wells), the total change in flow across the limitrophe section will be 72,000 acre-feet per year increase. The graph also shows that when the additional wells are considered after 1965 (dotted curve), the change in flow in the year 2000 is decreased by about 3,000 acre-feet per year to 69,000 acre-feet per year, or only about 4 percent of the total change in flow. It is concluded from this illustration that the changes in flow across the limitrophe section are almost wholly influenced by pumping in the Mexicali Valley and that the effects of pumping in the United States are largely dissipated before they reach across Yuma Valley to the limitrophe section. The Arizona-Sonora boundary, however, showed changes in flow before 1958 when Mexicali pumping became significant. By 1958 the flow southwestward to Mexico had already increased by about 9,000 acre-feet per year in response to the rising ground-water mound on Yuma Mesa. By 1966 the ground-water flow from the United States to Mexico had increasedANALOG SIMULATION OF THE GROUND-WATER SYSTEM, YUMA, ARIZONA 19 Figure 4.—Profiles of change in water levels resulting from pumping, 1925-2000: cross section eastward from about Tecolote, Mexico. to 31,000 acre-feet per year, accelerated to some degree by water-level declines caused by pumping in the Mexicali Valley. The decrease in boundary flow to 17,000 acre-feet per year in 1975 will result primarily from the effects of pumping 111,000 acre-feet per year from the new Yuma Valley, Yuma Mesa, and private wells, and to a lesser degree from the reduction in recharge to the Yuma Mesa ground-water mound after 1964. The increase in flow to 21.000 acre-feet per year in the year 2000 includes the effect of the expanding cone of depression from the Mexicali Valley well field. Flow across the Arizona-Sonora boundary is also greatly affected by the Yuma Valley, Yuma Mesa, and private wells, as shown by the dotted curve in figure 2. By 1975 flow will have decreased by about 12.000 acre-feet per year as the result of pumping, and by the year 2000 the flow will have been reduced by about 18,000 acre-feet per year to 3,500 acre-feet per year. The effects of pumpage on the change in flow across the international boundary is summarized in figure 3. Note that private well development (as of 1968) is not sufficient to cause any measureable change in flow across the limitrophe section. CONCLUSIONS The results of the model analysis are shown most clearly in figures 2 and 3, and tables 2 and 3. The important conclusions that emerge from those data are as follows: 1. The major change in the flow of ground water to Mexico across the limitrophe section of the Colorado River started in 1958, coinc’dent with accelerated pumping in the Mexicali valley. Prior to that year, the increase in flow to Mexico across the limitrophe section was about 1,000 acre-feet per year, but by 1962 the flow had increased to more than 20,000 acre-feet per year; by the year 2000 the model study indicates the increase will be about 72,000 acre-feet per year. 2. The full development of existing and proposed wells in the United States by the year 2000 will diminish the increase in flow across the limitrophe section to Mexico by about 4 percent, from 72,000 to 69,000 acre-feet per year. 3. Flow across the Sonoran boundary to Mexico be- gan to increase in the 1940’s as the result of the growing ground-water mound under Yuma Mesa, and after 1958 was somewhat accelerated by water-level declines caused by the Mexicali Valley pumping. 4. Ground-water flow across the Sonoran boundary is sensitive to pumping in the United States, and under the full development shown in table 1, the model indicates it will diminish fromno WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA 31,000 acre-feet per year in 1966 to 3,500 acre-feet per year by the year 2000. That computed decrease includes the effects of pumping in the Mexicali Valley. 5. If Mexicali Valley pumpage were omitted, the computed changes in flow across the limitrophe section would be 2,000 acre-feet per year to the United States by the year 2000; thus the net effect of Mexicali pumping on the flow across the limitrophe would be an increase of about 71,000 acre-feet per year. 6. The largest part of the ground-water flow to Mexico across the limitrophe section is derived from water that would otherwise discharge to Yuma Valley; that is, if it were not for the gradients established by Mexicali Valley pumping, much more water would flow upward from the coarse gravel zone underlying Yuma Valley through the overlying finegrained sediments, and would discharge either to drains or to the atmosphere. 7. Taken as a whole, pumpage in the Yuma ground- water system now exceeds recharge to the ground-water mound underlying Yuma Mesa by about 65 percent, and by 1975 existing and proposed pumpage will be almost 2.5 times the annual recharge to the ground-water mound. 8. As a result of that imbalance, water levels will decline indefinitely and on a regional scale. The effects of the expanding cones of depression will be mitigated to some degree by ground water salvaged from areas that have been points of discharge. The model study indicates that by the year 2000 salvage in excess of 100,000 acre-feet per year will be recovered from the Yuma Valley. Owing to the present and proposed patterns of pumping, however, little water will be recovered from the South Gila Valley. SUMMARY The electric analog simulation of the ground-water system in the Yuma area has provided an abundance of detailed predictions on the response of the system to proposed hydrologic stress. It would be desirable here to give some quantitative measures of the accuracy of those predictions, measured against some set of independent standards. Unfortunately, the only standard is the prototype ground-water system itself, and that system was deliberately simplified so that a model of manageable complexity could be conceived and implemented; thus fundamental to the simulation procedure is the exchange of “accuracy” for insight. As an example, the model study predicts that under the proposed ground-water recovery plans almost 2 feet of water a year would be salvaged from the Yuma Valley by the year 2000; whether this is an “accurate” prediction is moot; it is accurate only to the extent that the hydrologic model is analogous to the prototype system, and that the analog representation is correct. In the Yuma analog model the upper fine-grained sediments of Yuma Valley are modeled as a vertical-flow system that allows upward ground-water flow to be discharged to the drains and by the evapotranspirative processes. Although that representation appears to be appropriate on the basis of regional analysis, it fails to distinguish locally, in the Yuma Valley, the components of that salvage; which portion is discharged to the drains, which to evapotranspiration, and which is possibly derived from the dewatering of the valley-fill sediments. Accordingly, while reasonably accurate on a regional scale, the model is inadequate in its representation of the Yuma Valley. If the model were modified to incorporate those variables, its adequacy for providing hydrologic predictions would be improved while its overall accuracy would be unchanged. An appraisal of the accuracy of the simulation study requires constant monitoring of the ground-water system and comparison of the analog-model predictions with the actual response of the system. REFERENCES Brown, R. H., and Skibitzke, H. E., 1956, Theoretical ground-water movement based on electrical analogs, in Analysis of basic data concerning ground water in the Yuma Area, Arizona, by R. H. Brown, J. W. Harshbarger, and H. E. Thomas: U.S. Geol. Survey open-file rept., p.32-44. Jacob, C. E., 1960, Ground water and drainage of Yuma Valley and contiguous areas: Consultants’ Report to the Yuma County Water Users Association by C. E. Jacob & Associates, Los Angeles, Calif., 50 p. Karplus, W. J., 1958, Analog simulation: New York, McGraw-Hill, 434 p. Olmsted, F. H., Loeltz, O. J., and Irelan, Burdge, 1973, Geohydrology of the Yuma Area, Arizona: U.S. Geol. Survey Prof. Paper 486-H, 227 p. Skibitzke, H. E., 1961, Electronic computers as an aid to the analysis of hydrologic problems: Internat. Assoc. Sci. Hydrology Pub. 52, p. 347-358. Wood, L. A., and Gabrysch, R. K., 1965, Analog model study of ground water in the Houston District, Texas, with a section on Design, construction and use of electric analog models by E. P. Patten, Jr.: Texas Water Comm. Bull. 6508, 103 p. UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY 115°00' 114°20' 45' 114*20' PROFESSIONAL PAPER 486-1 PLATE 1 A. MAP OF YUMA AREA. ARIZONA. SHOWING PRINCIPAL IRRIGATION AREAS. B. COMPUTED CHANGE IN WATER LEVELS. 1925-1975; 1965 PUMPING AND RECHARGE RATES EXTENDED TO 1975. C. COMPUTED CHANGE IN WATER LEVELS. 1925-2000: 1965 PUMPING AND RECHARGE RATES EXTENDED TO THE YEAR 2000. D. COMPUTED CHANGE IN WATER LEVELS, 1925-1975: YUMA VALLEY. YUMA MESA. AND PRIVATE WELLS INCLUDED: 1965 PUMPING AND RECHARGE EXTENDED. E. COMPUTED CHANGE IN WATER LEVELS. 1925-2000: YUMA VALLEY. YUMA MESA. AND PRIVATE WELLS INCLUDED: 1965 PUMPING AND RECHARGE EXTENDED. 115"05’ 45' 30' 114"20' SOUTH CALIFORNIA ..■ BAJA CALIFORNIA MEXICALI VALLEY r.A Somerton ^0 VALLEY Tecolote .Gadsden EXPLANATION Line of equal water level change. Interval 5 feet 32"20' 115-05' 32-50' 114-20' SOUTH _ CALIFORm|. BAJA CALIIwI VALLE YUMA MEXICALI VALLEY Somerton .V; VALLEY Tecolote Gadsden EXPLANATION --- Line of equal water level change. Interval 5 feet 32-20’ 115°05' 32°50' 115°00' F. LOCATION OF EARLY DRAINAGE. YUMA VALLEY. YUMA MESA. AND PRIVATE WELLS. G. COMPUTED CHANGE IN WATER LEVELS. 1925-1975; YUMA VALLEY AND YUMA MESA WELLS INCLUDED: 1965 PUMPING AND RECHARGE EXTENDED. H. COMPUTED CHANGE IN WATER LEVELS. 1925-2000; YUMA VALLEY AND YUMA MESA WELLS INCLUDED: 1965 PUMPING AND RECHARGE EXTENDED. I. COMPUTED CHANGE IN WATER LEVELS. 1925-1975; YUMA VALLEY AND YUMA MESA WELLS ONLY-ASSUMING NO PUMPING IN MEXICALI WELL FIELD: 1965 PUMPING AND RECHARGE EXTENDED. J. COMPUTED CHANGE IN WATER LEVELS. 1925-2000; YUMA VALLEY AND YUMA MESA WELLS ONLY-ASSUMING NO PUMPING IN MEXICALI WELL FIELD: 1965 PUMPING AND RECHARGE EXTENDED. 115-05' 115-00’ 45' 114-20' SOUTH CALIFORNIA -BAJA CALIFORNIA MEXICALI VALLEY VAUlEY Tecolote ladsden EXPLANATION --- Line of equal water level decline. Interval 5 feet with supplemental 1-foot line (dashed) 45’ 32-20’ K. COMPUTED DECLINE IN WATER LEVELS RESULTING FROM YUMA VALLEY AND YUMA MESA WELLS. 1967-1975. L. COMPUTED DECLINE IN WATER LEVELS RESULTING FROM YUMA VALLEY AND YUMA MESA WELLS. 1967-2000. 115-05' 115-00' 45' 30’ 114-20' M. COMPUTED DECLINE IN WATER LEVELS RESULTING FROM PRIVATE DEVELOPMENT. 1965-1975. N. COMPUTED DECLINE IN WATER LEVELS RESULTING FROM PRIVATE DEVELOPMENT. 1965-2000. Base map modified from U.S. Army Topographic Command NI 11-12 1:250 000 0 1 1 1 5 _l l 1 10 1 15 1 20 1 25 MILES 1 1 1 1 1 r 1 1 1 1 1 1 0 5 10 15 20 25 30 35 40 KILOMETRES IRRIGATED AREAS, WELL LOCATIONS, AND COMPUTED EFFECTS OF IRRIGATION AND PUMPING, YUMA AREA, ARIZONAGeohydrology of the Needles Area, Arizona, California, and Nevada GEOLOGICAL SURVEY PROFESSIONAL PAPER 486-J f) •Geohydrology of the Needles Area, Arizona, California, and Nevada By D. G. METZGER and O. J. LOELTZ WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA GEOLOGICAL SURVEY PROFESSIONAL PAPER 486-J UNITED STATES GOVERNMENT PRINTING OFFICE. WASHINGTON : 1973UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress catalog-card No. 72-600334 For sale by the Superintendent of Documents, TJ.S. Government Printing Office Washington, D.C. 20402 Stock Number 2401-02212CONTENTS Page Abstract________________________________________________ J1 Introduction_____________________________________________ 3 Purpose of investigation._____________________________ 3 Location of area______________________________________ 3 Methods of investigation______________________________ 3 Surface features____________________________________ 3 Climate_____________________________________________ 6 Acknowledgments_______________________________________ 7 Well-numbering systems________________________________ 7 Reporting of water-quality data_______________________ 8 Geologic units and events and the water-bearing characteristics of the rocks____________________________ 8 Perspective___________________________________________ 8 Bedrock_______________________________________________ 8 Unconformity at the base of the fanglomerate_____ 9 The fanglomerate______________________________________ 9 Unconformity between the fanglomerate and the Bouse Formation_____________________________________ 9 Bouse Formation______________________________________ 10 Lithology and thickness__________________________ 11 Basal limestone_____________________________ 11 Interbedded unit_____________________________ 11 Tufa________________________________________ 12 Paleontology and age_____________________________ 12 Water-bearing characteristics____________________ 12 Alluviums of the Colorado River and its tributaries. 13 Older alluviums__________________________________ 13 Unit B_______________________________________ 13 Piedmont gravels (unit C)____________________ 14 Unit D_______________________________________ 15 Unit E_______________________________________ 16 Younger alluvium_________________________________ 16 Age______________________________________________ 16 Water-bearing characteristics____________________ 16 Structure of sediments______________________________ 16 Page Ground-water resources of the Needles area_____________ J18 Occurrence_________________________________________ 18 Rocharge___________________________________________ 18 Dischargs__________________________________________ 19 Historicael ketch__________________________________ 19 Develepment of irrigation______________________ 20 River stages___________________________________ 21 Hydrologic characteristics of aquifers------------- 23 Definition of terms__________________________ 23 Soil-moisture studies__________________________ 25 Pumping tests__________________________________ 26 Ground water under natural conditions-------------- 28 Mohave Valley__________________________________ 28 Chemehuevi Valley______________________________ 29 Ground water in recent years_______________________ 29 Mohave Valley__________________________________ 29 Chemehuevi Valley______________________________ 31 Water-level fluctuations_________________________ 32 Mohave Valley ________________________________ 32 Chemehuevi Valley______________________________ 32 Depth to ground water______________________________ 33 Water budgets______________________________________ 33 Streamflow depletion___________________________ 33 Unmeasured runoff______________________________ 34 Ground-water inflow____________________________ 35 Ground-water outflow__________________________ 36 Consumptive use by natural vegetation---------- 36 Consumptive use by crops___________ — ----- 36 Changes in ground-water storage________________ 37 Evaporation from water surfaces._______________ 37 Colorado River valley between Davis Dam and Parker Dam___________________________________ 37 Future development of water resources______________ 40 Quality of water______________________________________ 41 Chemical character of Colorado River water_________ 41 Chemical character of ground water_________________ 42 Suitability of ground water________________________ 44 References______________________________________________ 45 Index___________________________________________________ 47 ILLUSTRATIONS Plate [Plates are in pocket] 1. Geologic map of the Needles area, Arizona, California, and Nevada. 2. Map showing generalized water-level contours during 1962-69 in Mohave Valley, Arizona, California, and Nevada. 3. Map and diagrams showing quality of ground water, Needles area, Arizona, California, and Nevada. inIV CONTENTS Page Figure 1. Index maps showing location of the Needles area______________________________________________________ J4 2. Surface features on the west side of Mohave Valley______________________________________________. .. 5 3. Graphs showing annual precipitation at five climatological stations in the lower Colorado River area, 1950- 65________________________________________________________________________________________________ 6 4. Sketches showing well-numbering systems...______________________________________________________________ 7 5-9. Photograph showing— 5. Fanglomerate overlain by the Bouse Formation________________________________________________ 10 6. Bouse Formation in Chemehuevi Valley________________________________________________________ 11 7. Interbedded unit of the Bouse Formation southeast of Needles, Calif_________________________ 11 8. Tufa of the Bouse Formation southeast of Davis Dam__________________________________________ 12 9. Red Spring------------------------------------------------------------------------------------ 13 10. Section showing the deposits of the Colorado River and its tributaries_________________________________ 13 11. Photograph showing Colorado River boulder gravel_______________________________________________________ 14 12. Diagrammatic section showing subunits of unit B of older alluviums_____________________________________ 14 13. Sketch map showing piedmont gravels near Black Mountains_______________________________________________ 15 14. Photograph showing depositional contact between unit D of the older alluviums and older units__________ 15 15. Lithologic sections from auger holes near Needles, Calif_______________________________________________ 17 16. Photograph showing deformed older alluviums of the Colorado River and its tributaries__________________ 17 17. Photograph showing east limb of syncline_______________________________________________________________ 18 18-21. Graph showing— 18. Yearly maximum and minimum daily discharge and stage of Colorado River at Topock and Needles river stage stations, 1933-67_______________________________________________________________ 22 19. Colorado River stages at selected sites in 1902-3 and 1962-63------------------------------- 23 20. Maximum and minimum discharges and stages of Colorado River at gaging station below Davis Dam, 1949-67________________________________________________________________________________ 23 21. Counts per minute at various depths below land surface obtained with neutron moisture probe at two sites in Needles area_________________________________________________________________ 25 22. Hydrographs of pumping-test data for selected wells---------------------------------------------------- 27 23. Graph showing depth to water in well (B-18-22)35aaa____________________________________________________ 32 24. Graphs showing annual depletion of Colorado River, average consumptive use, and net inflow------------- 39 25. Quality of water diagrams of Colorado River water------------------------------------------------------ 42 TABLES Page Table 1. Annual pumpage of ground water, in acre-feet, for irrigation, 1964-68______________________________________ J21 2. Results of pumping tests____________________________________________________________________________________ 27 3. Colorado River stages in 1902-3, estimated average stages of Havasu Lake, and increases in water-level stages at 5-mile intervals below stream-gaging station near Topock------------------------------------- 31 4. Annual streamflows, diversions to Metropolitan Water District, changes in contents of Havasu Lake, and streamflow depletions, 1950-66_____________________________________________________________________________ 34 5. Estimated average annual unmeasured runoff to the flood plain of the Colorado River------------------------- 35 6. Average annual ground-water recharge from precipitation------------------------------------------------- 36 7. Water budget for Colorado River valley between Davis Dam and gaging station near Topock-------------------- 37 8. Water budget for Colorado River valley between Topock and Parker Dam_____________________________________ 38 9. Chemical analyses of water from wells and from Red Spring--------------------------------------------------- 50 10. Records of test and selected wells___________________________________________________________________________ 52 11. Selected logs______________________________________________________________________________________________ 55WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA GEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA By D. G. Metzger and O. J. Loeltz ABSTRACT The Needles area, as defined in this report, includes Mohave and Chemehuevi Valleys, and extends from Davis Dam (57 miles south of Hoover Dam) southward to Parker Dam. It is in Mohave County, Ariz., San Bernardino County, Calif., and Clark County, Nev. The principal landforms are rugged mountains, piedmont slopes, and flood plain. Locally, a pediment is present on the bedrock of the mountains bordering the west side of Mohave Valley. The highest summit in the Black Mountains is 5,216 feet above sea level, and in the Chemehuevi Mountains in Arizona, 5,148 feet above sea level. The piedmont slopes have gradients that range from about 100 to 300 feet per mile. The Colorado River flood plain in Mohave Valley has a maximum width of 5 miles. The former flood plain in Chemehuevi Valley is covered by Havasu Lake. In 1968, the average altitude of the Colorado River at Bullhead City, Ariz., was about 500 feet above sea level; at Topock, Ariz., about 455 feet. The average altitude of Havasu Lake is about 448 feet above sea level. The consolidated rocks of the mountains, referred to collectively as bedrock, are relatively impermeable and form the boundaries of the ground-water reservoir. There is no evidence to indicate any sizable potential for development of ground water in the bedrock, although locally, small yields may be developed from fractures. The geologic units that are important in an evaluation of the water resources are the fanglomerate, the Bouse Formation, and the alluviums of the Colorado River and its tributaries. The fanglomerate of Miocene (?) age is made up chiefly of cemented gravel composed of angular to subrounded and poorly sorted pebbles and some fine-grained material that are thought to come from a nearby source. It varies widely in thickness because it was deposited on an irregular surface having considerable local relief. The fanglomerate probably is a potential aquifer on the basis of grain size and degree of cementation. However, only meager subsurface data are available for substantiating this supposition because most wells are drilled either into Colorado River deposits or the Bouse Formation. The Bouse Formation of Pliocene age is composed of a basal limestone overlain by interhedded clay, silt, and sand and by a tufa. The thickest known section is the 254 feet that was penetrated in well (B-16-20V2) llccd; a much thicker section probably is present beneath the central part of Mohave Valley. Only two wells produce water from the Bouse, and these have limited yields. Because of the clay beds in the Bouse, it can be anticipated that the Bouse lias a low permeability in the Needles area. The alluviums of the Colorado River and its tributaries are the result of several periods of extensive degradation and ag- gradation by the Colorado River. The alluviums are divided into older alluviums, which are the deposits of several degradations and aggradations by the Colorado River, and younger alluvium, which is the deposit of the youngest aggradation. The alluviums are heterogeneous mixtures of gravel, sand, silt, and clay. The alluviums are treated as a composite aquifer because of the obvious hydraulic continuity between the several alluviums and because of the difficulty of separating them on the basis of subsurface data. Most of the yield from wells that are perforated in these deposits comes from highly permeable beds of sand and gravel. Wells that tap a sufficient thickness of Colorado River gravels have specific capacities as high as 400 gallons per minute per foot of drawdown. Ground water in the Colorado River alluviums in the Needles area occurs under water-table conditions. Ground water may occur under artesian conditions in or below the Bouse Formation. Sources of recharge to the ground-water reservoir are the Colorado River, unused irrigation water, runoff from precipitation, and underflow from bordering areas. Of these, the Colorado River is by far the principal source. Recharge from unused irrigation water is, in a sense, a negative discharge inasmuch as practically all irrigation supplies are obtained from wells. Recharge by runoff from precipitation occurs in the sandy washes of the area. Recharge by underflow from bordering areas occurs where the major ephemeral streams such as the Sacramento, I’iute, and Chemehuevi Washes enter the Needles area. Ground water is discharged from the aquifers by wells and evapotranspiration. Discharge to the Colorado River, if it occurs at all. is negligible. Pumped ground water is used for municipal and domestic supplies and for irrigation. Ground water is discharged by evapotranspiration throughout the flood-plain area. Under natural conditions the Colorado River annually overflowed its banks and flooded large parts of the adjacent lowland. Natural vegetation, consisting mainly of arrowweed, mesquite, and willow, thrived in the flood plain. Attempts were made to divert water from the Colorado River as early as 1891, either by gravity or by pumping, but the early attempts were unsuccessful mainly because of the uncontrolled flows of the river. Early plans for irrigating flood-plain lands by pumping from wells also proved unsuccessful. As a result, irrigation agriculture was gradually abandoned to the point where, during the 1940’s, only a few hundred acres were being irrigated. However, irrigation agriculture was revived during the 1950's. During 1964-68, pumpage for irrigation ranged from about 12,000 to 21,000 acre-feet per year. However, diversion of river water for irrigation remained small, the acreage so irrigated being less than 2,000. J1J2 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA The closure of Hoover Dam, to the north of the area, in 1936, and of Parker Dam in 1938, caused major changes in the hydraulic regimen in the Needles area. The closure of Hoover Dam ended the annual spring floods and caused some scouring of the channel. The closure of Parker Dam and subsequent filling of Havasu Lake caused a rapid aggradation of the Colorado River channel in the immediate area of the lake. Within a few years the definable channel in the lower part of the flood plain east and southeast of Needles was obliterated. By 1944 the aggradation had caused river stages and consequently ground-water levels to rise sufficiently to threaten the town of Needles and the Atchison, Topeka, and Santa Fe Railway and to waterlog much land. To alleviate the situation, the U.S. Bureau of Reclamation initiated programs for dredging the river channel and for improving the channel geometry. Most of the dredging and channel improvement work in Mohave Valley was completed by July 1960. Work downstream from Topock was halted landing studies of the physical and ecological changes in the canyon downstream from Topock. The average river stage from the northern end of Mohave Valley to a point about 10 miles north of Needles is now about 4 feet higher than it was under natural conditions. The differences in stage increase southward, so that at Needles the stage is about 8 feet higher and at Topock about 27 feet higher than under natural conditions. These higher river stages, which have resulted in a higher water table and therefore in increased evapotranspiration, have caused additional depletion of the available water supply. The alluvial deposits commonly tapi>ed by irrigation wells east of the Colorado River are very permeable. Hydraulic conductivities of about 10,000 gpd (gallons per day) per square foot are indicated at several sites in Arizona. Hydraulic conductivities between 1.000 and 5,000 gpd per square foot are indicated by four pumping tests made in California. Transmissivities of several hundred thousand to about a million gallons per day per foot are common for the alluvial deposits underlying much of the flood plain and for Colorado River gravel where it occurs beneath the a 1 hi vial slopes adjacent to the flood plain. Limited soil-moisture studies suggest that in an area of rising water levels beneath the flood plain outside irrigated areas the capacity to store water is between 32 and 42 percent of the volume saturated by the rising water levels. Outside the flood plain, the capacity is less. Under natural conditions, ground-water discharge in Mohave Valley averaged about 170,000 acre-feet per year. Ground-water recharge was a similar amount. Owing to the much more limited area of flood plain and water-loving vegetation in Chemehuevi Valley, both ground-water recharge and discharge were much less in that valley than in Mohave Valley. Under present conditions in Mohave Valley about 150,000 acre-feet of water infiltrates directly from the river to the ground-water reservoir. Most of this infiltration occurs in a 37-mile reach of the river downstream from Bullhead City, Ariz. An infiltration rate of about 8,000 acre-feet per year per mile length of channel is indicated for a reach 2 miles upstream from Needles. This is twice the average rate of infiltration for the 37-mile reach. Most of the infiltration eventually supports the growth of phreatophytes which thrive on the flood plain. The impounding of Havasu Lake behind Parker Dam effected a new control for ground-water levels in the valley adjacent to and above the reservoir. The average altitude of Havasu Lake of 448 feet rather than the previous river level became the new control for ground-water levels. Currently, the average lake level ranges from 27 feet higher at the gaging station near Topock. to 76 feet higher near Parker Dam, than did the river levels prior to 1938. As a result of this increase in head, a substantial quantity of water from the lake has infiltrated to the ground-water reservoir in the process of establishing new equilibrium conditions between the surface water and ground water. In recent years a new equilibrium has been virtually attained. Consequently, the interchange between surface water and ground water in Chemehuevi Valley is small—only a fraction of the interchange that is occurring in Mohave Valley. Ground-water levels in the Needles area generally fluctuate within an annual range of 2 feet except near pumping wells, irrigated land, and the river. Water levels generally are between 9 and 12 feet below the land surface in the flood plain. On the alluvial slopes that border the flood plain, the depth to water is governed largely by the height of the land surface above the water level in the flood plain opposite a given site. In many areas the depth to water increases between 100 and 200 feet per mile with increasing distance from the flood plain. A water budget for the Colorado River valley between Davis Dam and the gaging station near Topock for the period 1950-66 shows an annual streamflow depletion of about 180,000 acre-feet, an average unmeasured inflow of 30,000 acre-feet, and a negligible unmeasured outflow. The total depletion or consumptive use within the area thus is about 210,000 acre-feet, based largely on differences in streamflow measurements at the upper and lower ends of the valley. On the other hand, the annual consumptive use, based on acreages and rates of use, is estimated to be 188,000 acre-feet by natural vegetation, 12,000 acre-feet by crops, and 41,000 acre-feet by evaporation from open water surfaces, a total of 241,000 acre-feet. Because of the quantitative uncertainty of many of the budget items, no attempt is made to adjust the budget to eliminate the imbalance of 30,000 acre-feet that exists between the two methods used for computing consumptive use. A similar budget for the Colorado River valley between Topock and Parker Dam shows an average annual streamflow depletion (after adjusting streamflow measurements for out-of-basin diversions and changes in content of Havasu Lake) of 151,000 acre-feet and an additional unmeasured annual net inflow of 24,000 acre-feet. The consumptive use in the area, based largely on differences between streamflow measurements, thus averages about 175,000 acre-feet per year. On the other hand, the annual consumptive use based on acreages and rates of use are estimated to average 4.000 acre-feet by natural vegetation and 140,000 acre-feet by evaporation. Consumptive use by irrigated crops is negligible. The difference of about 30.000 acre-feet between the total consumptive use computed by the two methods is equal to but opposite in sense to the difference that was indicated for the budget of the upstream river valley. The greatest potential for developing additional beneficial use of water is the substitution of crops for the natural vegetation that has a low economic value and a high water-consumption rate. A substitution of crops for mesquite would limit the additional depletion of the total water supply to about 6,500 acre-feet per year. Both the Fort Mohave and the Chemehuevi Indian Reservations have substantial, but as yet largely unexercised rights for diverting water from the Colorado River. Diversions of water by the Fort Mohave Indian Reservation will probably result in little additional depletion of the total supply because the average rate of use by crops is not likely to be greatly different from the rate of use by the natural vegetation they replace. Diversion of water for irrigation by the Chemehuevi IndianGEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J3 Reservation, however, will result in an additional depletion of the total supply because the diversion presumably will be to lands that are not now supporting the growth of water-loving natural vegetation. Additional water might be made available for beneficial use by affecting a reduction in the quantity of water consumed by natural vegetation. The U.S. Bureau of Reclamation (written commun., 1971) estimates that 45,000 acre-feet per year can be salvaged in the Mohave Valley by this method. Chemical analyses of water from wells in the Needles area indicate that ground water is of better quality than that in other parts of the lower Colorado River area. Of the 95 samples of ground water that were analyzed. 46 analyses had dissolved solids of less than 1,000 mg/1 (milligrams per liter) and six had less than 500; the smallest concentration found was 314 mg/1. On the other extreme, six analyses had dissolved-solids content of more than 2,000 mg/1; the largest concentration was 3,290 mg/1. The chemical composition of ground water indicates that irfuch of the water was derived from the Colorado River and that the ground water has been altered by three primary processes: concentration by evapotranspiration, precipitation of calcium and magnesium carbonates, and reduction of sulfate. Ground water that contains about the same concentration of dissolved solids as Colorado River water (between 600 and 800 mg/1 and less than 1.5 mg/1 fluorides) is acceptable to the residents for domestic use. Locally, where water of this quality is not available, water exceeding these concentrations is used. Concentration of dissolved solids in much of the ground water exceeds the usual standard for irrigation use. However, the fact that ground water is being used successfully indicates that other factors, such as salinity of soil, drainage, amounts of water applied, manner of application, and types of crops are also important. INTRODUCTION PURPOSE OF INVESTIGATION An investigation of the ground-water resources of the Needles area, Arizona, California, and Nevada, began in 1960 as a part of a Federal appraisal of the water resources of the, lower Colorado River area (fig. 1), which extended from Davis Dam south along the valleys of the Colorado River to the International Boundary, and to the Imperial Valley. The general objectives of the investigation in the Needles area were to determine the location, extent, and hydraulic characteristics of aquifers; the relation of the aquifers to the Colorado River and other conveyance channels; the amount of evapotranspiration; and the chemical character of the water. The investigation in the Needles area is less detailed than the investigations of the other areas of the lower Colorado River. Throughout this report, therefore, reference will be made to the more detailed investigation of the Parker-Blythe-Cibola area (Metzger and others, 1972), which is adjacent to the Needles area (fig. 1). Many of the interpretations for the downstream study may be transferred with reasonable confidence to the Needles area because the two areas are similar in many respects as regards geology, chemical character of the water, and surface- and ground-water hydrology. LOCATION OF AREA The Needles area is mostly in Mohave County, Ariz., and San Bernardino County, Calif. A small part is in Clark County, Nev. The term “Needles area” is here used to include all the Colorado River valley from Davis Dam to Parker Dam, and it includes Mohave and Chemehuevi Valleys. However, the base map (pi. 1) includes only that part of Chemehuevi Valley in which ground water has been developed. Needles, Calif., is near the center of the area. METHODS OF INVESTIGATION Forty-three holes, 4 inches in diameter, and ranging in depth from 12 to 167 feet, were augered with a powered rig. Although the material below the water table sloughed, sandpoints could be installed readily in the loosened material. These wells were used to collect water samples and for periodic measurements of the water level. In addition, three holes were drilled to depths ranging from 18 to 21 feet using a hand auger, and completed with 5-inch casing. These wells were equipped with graphic water-stage recorders. Two privately owned wells also were similarly equipped. Nine pumping tests were made to determine the waterbearing characteristics of the materials. Chemical analyses were made of 95 samples of ground water from sandpoint wells and other sources. Selected analyses of ground water are given in table 9. The ground-water samples were obtained from shallow test holes drilled by the Geological Survey, from privately owned wells drilled for domestic, municipal, irrigation, or industrial supply, and from wells drilled for other Federal agencies. All tabulated analyses represent samples collected directly by the Geological Survey and analyzed either in a field laboratory at Yuma, Ariz., using rapid analytical methods, or at the Survey's permanent water-quality laboratory at Albuquerque, N. Mex., using standard Survey procedures. The investigation was made under the general supervision of C. C. McDonald, project hydrologist. The ground-water section was prepared by the junior author ; the rest of the report by the senior author. SURFACE FEATURES The Needles area is in the Sonoran Desert section of the Basin and Range physiographic province (Fenne-man, 1931, p. 326-395). The section is characterized by roughly parallel mountains separated by alluvial basinsJ4 WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA 116° 115” 114” Figure 1.—Index maps showing location of the Needles area.GEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J5 and by an arid and hot climate. Generally, the basins lie between sea level and 1,000 feet. Although the Sonoran Desert section is, for the most part, one of ephemeral drainage, the Needles area is exceptional in that it contains a perennial stream with a wide flood plain. However, the ephemeral nature of the drainage applies to the tributaries of the Colorado River, the master stream in the area. The flood plain, as used in this report, is that part of the Colorado River valley (fig. 2) that has been covered by floods of the modern Colorado River p^ior to the construction of Hoover Dam. The flood plain is wider than the meandering course of the Colorado River, and it is bounded generally by a terrace. There are many indications of lateral shift of the channel R. 65 E. R. 66 E. Figure 2.—Surface features on the west side of Mohave Valley. of the Colorado River. This can be seen on aerial photographs which show many abandoned channels of the river. The maximum width of the flood plain in Mohave Valley is about 5 miles. From Davis Dam southward for about 10 miles, the Colorado River is confined to a narrow flood plain cut in alluvial deposits. Then the flood plain widens and reaches its maximum width near Needles. In Chemehuevi Valley the flood plain is now covered by the waters of Havasu Lake. In 1968 the average altitude of the Colorado River at Bullhead City, Ariz., was about 500 feet above sea level; at Topock, about 455 feet. The average altitude of Havasu Lake is about 448 feet, and it remains fairly constant because of the requirements of the pumps operated and maintained by the Metropolitan Water District. The mountains of the area are rugged and rise abruptly from the pediments, piedmont slopes, or the Colorado River in the bedrock narrows. The highest summits are in the Black Mountains (5,216 ft.) and in T. 14 N., R. 19 W. in the Chemehuevi Mountains (5,148 ft.). Many of the mountain crests are above 3,000 feet. Between the flood plain and the mountains are the dissected piedmont or alluvial slopes. Locally, a pediment has been cut on the bedrock of the mountains bordering the west side of Mohave Valley (fig. 2). The pediment is cut on granitic, metamorphic, and Tertiary sedimentary rocks. On the southeast part of the Newberry Mountains, the pediment is concave upward and has a slope that ranges from 400 feet per mile to 300 feet per mile near the river. On the Dead Mountains the pediment forms a narrow bench. South of Needles, the pediment has a slope of about 150 feet per mile and is very much eroded. The piedmont slopes have gradients that range from about 100 to 300 feet per mile. The steepest gradient occurs on the piedmont slope between the Newberry and Dead Mountains. It is 330 feet per mile, and the slope is concave upward. Near the flood plain the gradient is about 240 feet per mile. The piedmont slopes from the Black Mountains east of Needles have gradients that range from 100 to 150 feet per mile. East of Havsau Lake, the gradients range from about 150 feet per mile near the lake to about 260 feet per mile near the mountains. The washes generally have about the same gradient as the piedmont surfaces. In some localities, however, the washes have a gradient that is about 10 to 20 feet per mile more than that of the adjacent alluvial slopes. An example is the area west of Havasu Lake in T. 4 N. The washes near the edge of the map (pi. 1) are incised only about 20 feet below the adjacent alluvial slopes; 474-370 0-73-2J6 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA vet, near the lake, the washes are incised as much as 120 feet. CLIMATE The Needles area has a dry, warm climate, which is characterized by mild winters and hot summers, when temperatures above 100°F are common. The meager precipitation (fig. 3) is concentrated about equally in two periods, one in the summer and the other in the winter. The precipitation is the result of two different types of storm. In the summer, moist air from the Gulf of Mexico along with the high temperatures results in local thunderstorms. These can have high intensities, resulting in rapid, although local, runoff. The winter storms come from the Pacific Ocean and cause gentle rains with little or no runoff. The annual precipitation on the flood plain and piedmont slopes is about 5 to 6 inches and on the higher mountains about 10 inches (Ilely and Peck, 1964, pi. 3). Occasionally in August or September, moist air from tropical disturbances in the Pacific Ocean enters the desert and, coupled with the moist air from the Gulf of Mexico, causes heavy rains throughout the area. An example is the first of three storms in September 1939, which dropped 5.12 inches of rain on Needles, 2.70 c/i LlI X O z z o I- < D- o Ul OC CL Figure 3.—Annual precipitation at five climatological stations in the lower Colorado River area, 1950-65.GEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J7 inches of which fell between 4:30 a.m. and 10:30 a.m. on September 6. For the month of September 1939, 7.61 inches of rain was recorded, which is in sharp contrast to the average annual rainfall of less than 5 inches. ACKNOWLEDGMENTS The authors wish to thank the many citizens of the Needles area who furnished information on their wells. Organizations which willingly supplied information on their wells include the city of Needles, Lake Havasu Irrigation and Drainage District, Oasis Utility Co., and El Paso Natural Gas Co. WELL-NUMBERING SYSTEMS Three systems of well numbers are used in this report because the Needles area is in Arizona, California, and Nevada. These systems were developed by the Geological Survey for use in the three States and are based on the Bureau of Land Management system of land subdivision. In the Arizona system, wells are assigned numbers according to their locations in the land survey based on and Gila and Salt River base line and meridian which divides the State into four quadrants. For assignment of well numbers, these quadrants are designated counterclockwise by the capital letters A, B, C, and D, letter A being the northeast quadrant. Wells in the Needles area are in the B quadrant—that is, all are west of the meridian and north of the base line. For example, the first well inventoried in the NE14NEy4NE(4 sec. 35, T. 18 N., R. 22 W. is given the number (B-18-22) 35aaa. The capital letter indicates that the well is north and west of the intersection of the base line and meridian. The first set of numbers indicates the township (T. 18 N.); the second set of numbers indicates the range (R. 22 W.); and the third set, the section (sec. 35). Lowercase letters a, b, c, and d after the section number indicate the well location within the section (fig. 4). Figure 4.—Sketches showing well-numbering systems. The first letter denotes the 160-acre tract, the second the 40-acre tract, and the third the 10-acre tract. These tracts also are designated counterclockwise beginning in the northeast quarter. Where more than one well is within a particular tract, the wells are distinguished by adding consecutive numbers beginning with one after the lowercase letters. In the California system, wells are assigned numbers according to their locations in the land survey based on the San Bernardino base line and meridian. For example, the first well inventoried in the NE*4 NE14 sec. 30, T. 9 N., R. 23 E. is given the number 9N/ 23E-30A1. The part of the number preceding the slash (/) indicates the township (T. 9 N.), the number following the slash indicates the range (R. 23 E.), the number following the dash (-) indicates the section (sec. 30), and the letter following the section number indicates the 40-acre subdivision of the section (fig. 4). Within the 40-acre subdivision, the wells are numbered serially as indicated by the final digit. Thus, well 9N/ 23E-30A1 is the first well inventoried in the NE1/^ NE14 sec. 30, T. 9 N., R. 23 E. The letters N and E indicate that the entire area is north of the San Bernardino base line and east of the meridian. In the Nevada system, wells are assigned numbers according to their locations in the land survey based on the Mount Diablo base line and meridian. For example, the first well inventoried in the SW^SW^SW1/^ sec. 10. T. 33 S., R. 66 E. is given the number S33/66-lOccc. The number preceding the slash (/) is the number of the township (S33), the number following the slash is the range east of the meridian (66), and the number following the dash (-) is the section. The section is subdivided exactly as in the Arizona system described above. Thus, well S33/66-10ccc is the first well inventoried in the SW(4 S W (4 S W14 sec. 10, T. 33 S., R. 66 E. The capital S indicates that the area is south of the Mount Diablo base line. For numbers in all systems, if the location of a well is unverified, a “Z” is substituted for the letter following the section number. Where more than one well is reported for a section, the wells are numbered serially. Because the Colorado River at some locations has shifted its course since the land survey networks were established, some land that was surveyed using the California network is now in Arizona and vice versa. Because the number given a well is based on the land survey network at the well site, it sometimes happens that a well now in Arizona will have a number based on the California land survey network, and a well that is now in California may have a number based on the Arizona network. These instances are noted in the report. b j a b | a b b --a — c J d c 1 d c d b a b a c j d c d Arizona and Nevada systems D C B A E F G H M J L K J N P Q R California systemJ8 WATER RESOURCES OF LOWER COLORADO RIVER—SALTON SEA AREA REPORTING OF WATER-QUALITY DATA For water-quality data in this report, concentration of the various constituents is given in milligrams per liter, temperature is given in degrees Celsius (°C), and conductivity is given in micromhos at 25°C. The terms “parts per million” and “milligrams per liter” are practically synonymous for water containing as much as 5,000 to 10,000 mg/1 (milligrams per liter) of dissolved solids. Temperature data can be converted to degrees Fahrenheit (°F) by using the following: o F 0 c o F ° c O Y ° c O -p 0 c o y 0 c 32 0 51. _ _ 11 70.. 21 89... _ 32 108.. _ 42 33 i 52 __ _ 11 71.. .. 22 90. . 32 109.. . 43 34 i 53.. . 12 72.. 22 91... _ 33 110__ _ 43 35 2 54. _ . 12 73.. 23 92... . 33 111.. _ 44 36 2 55.. _ 13 74. _ .. 23 93. __ _ 34 112 . 44 37 3 56.. . 13 75. _ 24 94... . 34 113.. . 45 38 3 57.. _ 14 76.. _ 24 95.._ _ 35 114. . 46 39 4 58 __ _ 14 77.. _ 25 96. __ _ 36 115__ _ 46 40 4 59. _ _ 15 78. _ _ 26 97. _. _ 36 116.. _ 47 41 5 60. _ 16 79.. _ 26 98... _ 37 117 _ 47 42 6 61 . 16 80 _ 27 99.._ _ 37 118__ . 48 43 6 62. _ 17 81. _ _ 27 100__ . 38 119 . 48 44 7 63 _ 17 82. _ 28 101.. _ 38 120. _ _ 49 45 7 64 _ 18 83 . 28 102. _ _ 39 121. _ _ 49 46 8 65 _ 18 84. _ 29 103. _ _ 39 122.. _ 50 47 8 66... _ 19 85 _ 29 104.. . 40 48 9 67 . 19 86... _ 30 105. _ _ 41 49 9 68. _ 20 87... . 31 106.. _ 41 50 10 69... _ 21 88... . 31 107. _ _ 42 GEOLOGIC UNITS AND EVENTS AND THE WATER-BEARING CHARACTERISTICS OF THE ROCKS PERSPECTIVE The geologic units that are important in an evaluation of the water resources of the Needles area are the fanglomerate, the Bouse Formation, and the alluviums of the Colorado River and its tributaries. The consolidated rocks of the mountains, referred to collectively as bedrock, are relatively impermeable, and form the boundaries of the ground-water reservoir. There is no evidence to indicate any sizable potential for ground-water development in the bedrock. The absence of Paleozoic carbonate rocks precludes interbasin movement of substantial quantities of ground water through the mountains in a manner similar to that reported for the Paleozoic rocks of southern Nevada (Loeltz, 1960). Rather, the interbasin movement of water in the lower Colorado River area occurs, for the most part, in alluvium. However, some interbasin movement may occur through volcanic rocks, especially if the water levels in one basin are several hundred feet higher than those in an adjacent basin. Interbasin movement under these conditions is inferred to occur between Eldorado Valley, a basin of interior drainage west of the Colorado River below Hoover Dam, and the Colorado River valley. Rush and Huxel (1966, p. 18) conclude that the estimated average ground-water recharge of 1,100 acre-feet per year in Eldorado Valley must move eastward through volcanic rocks to the Colorado River valley because there is virtually no ground-water discharge in Eldorado Valley. (The water table beneath the playa in Eldorado Valley is at least 270 ft beknv land surface, and the water level there is about 800 ft higher than the Colorado River.) Likewise, ground water may also be moving from Sacramento Valley through the volcanics of the Black Mountains to the Needles area. Although this possibility exists, such movement does not detract from the statement that there is no sizable potential for developing ground water from bedrock. The quantity of such movement would be of academic interest only. It would be nearly impossible to develop even low-production wells because such movement would be only through fracture zones and possibly along bedding planes. Therefore, the bedrock was not investigated in detail, and the study of the geohydrology was oriented principally towards an understanding of the rock units that underlie the flood plain and piedmont slopes. BEDROCK Bedrock, as here used, includes all rocks older than the fanglomerate of Miocene (?) age, and is made up of igneous and metamorphic rocks of the basement complex, volcanic rocks of Mesozoic and Tertiary age, and sedimentary rocks of Tertiary age. Generally, the volcanic and sedimentary rocks are folded and dip steeply; this is in marked contrast to the overlying fanglomerate and alluvial deposits which dip gently. The only rocks that can be dated with assurance are some of the Tertiary sedimentary rocks. These occur in the Sacramento Mountains about 10 miles west of Needles in sec. 4, T. 8 N., R. 21 E. (not shown on pi. 1). There, a vertebrate-fossil locality contains a fairly primitive species of Merychippus, which is probably middle Miocene in age (J. F. Lance, written commun., 1960). Sedimentary rocks, which are similar in that both are unmetamorphosed and have steep dips, are exposed in the northwest quarter of T. 7 N., R. 23 E. The rocks at both locations may be of the same relative age, but no stratigraphic study was made during the present investigation to establish whether they were the same sequence or of the same age. All the rocks which are collectively referred to as bedrock are relatively impermeable. Thus, only small yields are likely to be developed and these principally from fractures. As an example, a bailer test made upon completion of well 7N/23E-10J1, which was drilled to aGEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J9 depth of 730 feet in the Tertiary sedimentary rocks and in which the depth to water was 90 feet, indicated that the maximum yield of the well was only iy2 gpm. UNCONFORMITY AT THE BASE OF THE FANGLOMERATE A major unconformity separates the bedrock and the fanglomerate, which is the basal deposit in the present valley. The rocks of the mountains had been severely deformed, and the outlines of the basin and ranges were probably formed prior to the deposition of the fanglomerate. The fanglomerate may have been deposited during the late phase of the structural deformation and the early phase of the present physiography. No attempt was made to define the structural history beyond the obvious differences in amount and direction of dip, intensity of faulting, and lithology, between the fanglomerate and older rocks. THE FANGLOMERATE The fanglomerate is composed chiefly of cemented sandy gravel that is probably from a nearby source. The fanglomerate of the Needles area has the same stratigraphic position and lithologic characteristic as the fanglomerate of the Parker-Blythe-Cibola area (Metzger, 1965); that is, the fanglomerate underlies the Bouse Formation and overlies tilted and faulted bedrock. Because the pre-Bouse fanglomerate can be differentiated from post-Bouse alluviums only where the Bouse Formation is present, the fanglomerate is differentiated only where it underlies the Bouse Formation. Elsewhere, it is arbitrarily assigned to the older alluviums. The fanglomerate is exposed about 8 miles southwest of Davis Dam, west of Topock, and in Chemehuevi Valley (pi. 1). The fanglomerate is also exposed locally beneath alluvium east of Havasu Lake in Chemehuevi Valley, although it is not shown as such on plate 1 because only one small outcrop of the Bouse Formation is present, and this is in the SE14 sec. 33, T. 14 N., R. 20 W. The gravel of the fanglomerate generally consists of angular to subrounded and poorly sorted cemented pebbles with a sandy matrix. The color of the fanglomerate depends on the predominant rock types represented by its constituent pebbles—gray where the material is derived from igneous and metamorphic rocks and brown or reddish brown where the material came from volcanic rocks or older consolidated sedimentary rocks of Tertiary age. Bedding surfaces of the fanglomerate generally dip from the mountains towards the basin. The fanglomerate, for the most part, has only gentle dips, ranging from 2° to 4°. It varies widely in thickness because it was deposited on an irregular surface. The fanglomerate represents composite alluvial fans built from the mountains towards the valley. The debris | of the fanglomerate probably represents a stage in the wearing down of the mountains following the severe structural activity that produced the basin-range topography in this area. The gentle and moderate tilting of the fanglomerate indicates that severe structural movements have not occurred since its disposition. No fossils have been found in the fanglomerate in the Needles area, and therefore, no age designation can be assigned on this basis. However, the fanglomerate was deposited after the last major mountain making activity in which the present basins and ranges were outlined, and it underlies the Bouse Formation. A maximum age for the fanglomerate can be inferred on the basis of the relation between the fanglomerate and rocks containing a vertebrate fauna west of Needles in the Sacramento Mountains, which is discussed under the section entitled “Bedrock.” The fauna, which occurs in steeply dipping sedimentary rocks, contains a fairly primitive species of Merychippus and is probably middle Miocene in age according to J. F. Lance (written commun., 1966). Similar sedimentary rocks are exposed south of Needles in the northwest quarter of T. 7 N., R. 23 E., and are overlain unconformably by the fanglomerate. Because of this weak stratigraphic relation, the fanglomerate is referred to the Miocene(?), although it may in part be Pliocene because the Bouse is not dated precisely within the Pliocene. Although the fanglomerate in the Needles area probably is an aquifer similar to that of the Parker-Blythe-Cibola area (Metzger, 1965), only meager data are available for substantiating this supposition because most wells are drilled either into the alluviums of the Colorado River and its tributaries or into the Bouse Formation. Only two wells are known to have pumped water from the fanglomerate. Well (B-16-201/^) 14bca in Mohave Valley about 4 miles east of Topock, Ariz., is perforated from 332 to 490 feet, and is reported to have yielded 56 gpm (gallons per minute) with a drawdown of 70 feet. Well (B-13-20) lcdd in Chemehuevi Valley was perforated from 625 to 950 feet and is reported to have been pumped at 500 gpm with a drawdown of 130 feet. The well was abandoned because of the high fluoride concentration of the water. UNCONFORMITY BETWEEN THE FANGLOMERATE AND THE BOUSE FORMATION The contact between the fanglomerate and the Bouse Formation is sharp (fig. 5) and represents a marked change in environment, from deposits laid down onJ10 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA Figure 5.—Fanglomerate (Tf) overlain by the Bouse Formation (Tb) in NWy4 sec. 12, T. 7 N., It. 23 E. The thin white layer is the basal limestone of the Bouse, and it thickens to 4 feet about half a mile to the east. land to those deposited in an extension of the Gulf of California. The fanglomerate represents alluvial fans that -were built from the mountains, and thus locally, it represents drainage from the mountains toward the basins. There is no evidence—rounding and rock type— of rocks from a distant area; the detritus is derived from the nearby mountains. Also, there is no evidence of a major through-flowing stream such as the ancestral Colorado River crossing the area during the deposition of the fanglomerate. The composition of the fanglomerate suggests interior drainage in a manner similar to the present-day closed desert basins of Nevada and part of California. Yet, no deposits that can be interpreted as having been deposited in a playa have been observed in outcrops. The subsurface data are too meager to warrant further speculations. Drainage during the time of deposition of the younger part of the fanglomerate may have been external prior to the invasion of the Gulf of California. This would afford a mechanism by which the gulf invaded the area, namely by proceeding up a river valley as the area sank. However, there is no evidence supporting this possibility because a substantial part of the fanglomerate was removed by erosion before the deposition of the Bouse Formation. If there was external drainage prior to the deposition of the Bouse Formation, the meager data from the Needles area do not indicate the direction of the drainage. However, regional studies indicate that highlands were northeast and east of the area (M. E. Cooley, written commun., 1968) and that, if through drainage occurred prior to the transgression of the Gulf of California, then the direction of drainage from the Needles area probably would have been southward or south westward. BOUSE FORMATION The Bouse Formation is a marine to brackish-water sequence that was deposited in an embavment of the Gulf of California. It is composed of three units, which are a basal limestone overlain by interbedded clay, silt, and sand; and a tufa (Metzger, 1968). Numerous outcrops are present in the Needles area (pi. 1); generally these have a thickness of only a few tens of feet. The thickest known section is 254 feet, which was penetrated in well (B-l 6-20(4) 1 Iced. However, the Bouse may be considerably thicker beneath the central part of Mohave Valley. The Bouse Formation rests unconformably on the fanglomerate. The Bouse Formation occurs as high as 1,800 feet above sea level on the flanks of the Black Mountains. The upper surface of the Bouse is ero-sional, each degradation of the Colorado River having removed some of the formation. In Mohave Valley the Bouse Formation occurs at several localities near the mountains along the west side of the valley and at a site about 3 miles west of Topock (pi. 1). Several outcrops also occur east of Topock along IT.S. Highway 66. Another outcrop is at an altitude of about 1,500 feet in T. 15 N., R. 20 W. The only outcrop found along the Black Mountains is in sec. 25, T. 20 N., R. 21 W. Six wells in Mohave Valley have been drilled into the Bouse, and of these, only two, in T. 16 N., R. 201^ W., have been drilled through the Bouse into the underlying fanglomerate. In well (B-16-20(4) 1 lccd the Bouse occurred from 189 to 443 feet below land surface. Three other wells that were drilled into the Bouse are in secs. 14. 26. and 36. T. 19 N., R. 22 (V. There, the Bouse is present at depths of 225, 211, and 240 feet or at altitudes of about 375, 390, and 370 feet above mean sea level, respectively. The Bouse also is present in well 7N/24E-6F1 from 44 feet to the total depth of the well at 190 feet. In Chemehuevi Valley, extensive areas of the Bouse Formation occur west of and bordering Havasu Lake. The only outcrop found east of the lake, and this covers only a few acres, is in sec. 33, T. 14 N., R. 20 W. No wells on the east side of Chemehuevi Valley are known to have been drilled into the Bouse. It appears that the wells pass from Colorado River or locally derived deposits into the pre-Bouse fanglomerate. Three wells on the west side of the valley in sec. 36, T. 5 N., R. 24 E. probably were drilled into the Bouse because of the close proximity of Bouse outcrops. No logs were available to indicate whether or not this assumption is true. The Bouse Formation also is exposed about 12 miles north of Davis Dam in Cottonwood Valley (fig. 1). In sec. 20. T. 23 N., R. 21 (V., where about 40 feet is exposed, both the basal limestone and the interbedded unit are present, The Bouse is underlain by locally derived fanglomerate and overlain by alluviums of the Colorado River and its tributaries.GEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA Jll LITHOLOGY AND THICKNESS The basal limestone of the Bouse Formation grades upward into the interbedded sequence of clay, silt, and sand. The tufa is distinct and was formed throughout the time of deposition of the basal limestone and inter-bedded sequence. There is always a sharp break between the tufa and either of the other two units, but it is not a | significant time break. BASAL LIMESTONE The basal limestone is a white marly limestone that ranges in thickness from less than 1 foot to as much as 26 feet. It is thin bedded for the most part, although in Chemehuevi Valley some beds are massive. Locally, thin crossbedded gravel underlies the limestone. About 9 miles southeast of Davis Dam, the basal limestone has a minimum thickness of 25 feet on the basis of an incomplete section. About 3 miles west of Topock, Ariz., the limestone ranges in thickness from less than 1 foot to as much as 4 feet. In Chemehuevi Valley in T. 4 N., R. 24 E., the limestone is at least 26 feet thick (fig. 6). In the latter two localities, the limestone is overlain by the interbedded unit. In the area west of Topock, the dip of the limestone is 5° to 6° northeast. West of Havasu Lake, the dip ranges from 1° to 5° ; the more gentle dips are near the lake. The basal limestone in the field may appear to be a tuff because it is white, fine grained, and contains many mica flakes. Noble (1931, p. 41H-2) interpreted it in the field as a very fine volcanic ash. Later, after a chemical analysis proved the deposit to be largely calcium carbonate, he called it a calcareous marl, or chalk. During the present investigation, several insoluble residue determinations were made on this limestone. The insol- Figure 6.—Bouse Formation in east-central part of T. 4 N., R. 24 E. (un-surveyed into sections) in Chemehuevi Valley. The basal limestone is 26 feet thick. Fanglomerate (T»), basal limestone (Tbl) and interbedded unit (Tbc) of Bouse Formation. uble residue was very fine grained and ranged from 10 to 30 percent; so it may well be, in part, volcanic ash. INTERBEDDED UNIT The interbedded unit is composed of clay, silt, and sand. The beds are generally thin, and only a few are thicker than 10 feet. In the locality about 3 miles west of Topock, Ariz., the beds appear “varvelike,” that is, they grade from fine sand upward to silt to clay. The represented cycles are seldom more than 10 feet thick, and probably do not represent varves but cycles of much longer periods. Most of the clay beds are pale olive to pale yellowish green. One characteristic of the clay is that it swells when moistened, which may indicate that some of the clay is montmoril Ionite. Because of this characteristic, much of the outcrops are mantled by an amorphous greenish mass. Other characteristics of the clay in Mohave Valley are the extreme fineness of the clay and the absence of sand grains. The silt and fine-sand beds are commonly grayish orange, or very light gray to very light pink. Most of the sand is only weakly compacted or cemented. The thickest exposed section of the Bouse Formation is about 50 feet in the SWi/4 sec. 1. T. 7 X., R. 23 E., west of Topock (fig. 7). The beds are fiat lying or have only a gentle dip. About half a mile to the south in sec. 12, the interbedded unit has a dip of 4° northeast. In this area, sand dikes occur in the Bouse Formation. Some of the dikes are vertical, only about 1 foot wide and fill a small fault or fracture zone. However, others are masses of sand that intrude beds composed mostly of clay. Seemingly, this sand flowed upward, probably during the time of deposition of the Bouse, but this cannot be verified. In other parts of the area, dips as high as 30° have been observed in the Bouse Formation. Although some of these dips may be the result of structural adjust- Figure 7.—Interbedded unit of the Bouse Formation in east-central part of sec. 1, T. 7 N.t R. 23 E. southeast of Needles, Calif. About 50 feet is exposed. The lighter beds are sand, and the darker beds are silt and clay.J12 WATER RESOURCES OF LOWER COLORADO RIVER-iSALTON SEA AREA ments, some of these must be the result of preconsolidation slumping during or soon after deposition of the Bouse. This can be demonstrated in T. 4 N., R. 24 E., in Chemehuevi Valley. One unit about 20 feet thick contains sand beds that dip as much as 15°. Because most of the unit is clay, which weathers into an amorphous slope, the exact nature of the disturbance cannot be determined. However, this unit rests on the basal limestone, which contains none of the abnormal features of the overlying unit. TUFA The tufa has been found at only three localities in the Needles area. One is in the SW1^ sec. 21, T. 9 N., R. 22 E., about 5 miles west of Needles where the tufa is on basement complex. Another is in the SW(4 sec. 25, T. 20 N., R. 21 W., about 9 miles southeast of Davis Dam where the tufa is on volcanic rocks (fig. 8). The third is in T. 4 N., R. 24 E. (unsurveyed), west of Havasu Lake, here, the tufa is on the two southernmost small outcrops of volcanic rocks. At the first two localities the tufa is light to very light gray and porous. Individual rocks weather to an uneven surface with very sharp ridges, which is typical of some limestones in a desert environment. In the third locality the tufa is a mottled olive-gray to dusky-yellow rock and has numerous holes. The odd coloring suggests this tufa probably contains more impurities than the other. The tufa weathers to dusky yellow with some dark streaks and also is not as rough as the other after weathering. The outcrops of the tufa that have been seen are very small, the total area being less than 1 acre. Yet, it is Figure 8.—Tufa of the Bouse Formation in the SW1^ sec. 25, T. 20 N., It. 21 W.t about 9 miles southeast of Davis Dam, Ariz. The tufa is light in color and rests on volcanic rocks. Pick in right center of picture (circle) gives scale. obvious that the original area covered by the tufa must have been considerable, so most of the tufa must have been subsequently eroded away. This inference is substantiated by the numerous boulders of the tufa that have been observed in Pleistocene local gravels. One such locality is west of Needles, where the local gravels are composed mostly of metamorphic rocks, yet a few boulders of unmetamorphosed limestone-—the tufa—are present. Another area is in sec. 13, T. 15 N., R. 20 W., where isolated boulders occur in local gravels overlying the basal limestone of the Bouse. The source of this gravel was the Mohave Mountains to the south; yet no outcrops of the tufa were found on those mountains. PALEONTOLOGY AND AGE Fossils are not common in the Bouse Formation of the Needles area. The most abundant of the meager fauna is ostracodes, which occur both in the basal limestone and in the interbedded unit. A few charophytes have been found in the basal limestone. Some casts of clams and snails occur in the basal limestone in Chemehuevi Valley, but these are poorly preserved. The age of the Bouse Formation is given as Pliocene (Metzger, 1968) with the understanding that some Colorado River deposits, which overlie the Bouse, are also Pliocene in age. Nothing was found in the Needles area to alter this interpretation. WATER-BEARING CHARACTERISTICS Only two wells in the Needles area probably produce water from the Bouse Formation. Well (B-16-20i/£) llccd, which is perforated from 189 to 420 feet below land surface, yielded 50 gpm with a drawdown of 74 feet. This yield indicates a specific capacity of about 0.7 gpm per foot of drawdown. The other well, 8N/23E-20J1, which is perforated from 478 to 480 and 517 to 520 feet below land surface probably taps the Bouse because of the proximity of outcrops of the Bouse, and the report from the owner on the amount of clay penetrated during drilling of the wrell also indicates this. One seep, Red Spring (fig. 9), issues from the Bouse in the NlVy4 sec. 30. T. 10 N., R. 22 E. Because the spring is at an altitude of about 840 feet and about half a mile from the bedrock of the Dead Mountains, it is inferred that the water issuing from the seep represents discharge from only a limited area. The amount of the water discharging from this seep is very small, and no well-defined outflow channel is present. In all probability, the few phreatopliytes at the spring use all the discharge in the summer. Because of the clay beds in the Bouse, it can be anticipated that the Bouse has a low permeability in theGEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J13 Figure 9.—Red Spring in NW% sec. 30 T. 10 N., R. 22 E. Spring in right center of picture is enclosed by wood fence and issues from Bouse Formation. Bouse Formation (Tb), alluviums of the Colorado River and its tributaries (QTa). Needles area. Other than this, little can be added about the water-bearing characteristics because the data are so meager. ALLUVIUMS OF THE COLORADO RIVER AND ITS TRIBUTARIES Alluviums of the Colorado River and its tributaries are the result of several broad periods of degradation and aggradation by the Colorado River. The alluviums are divided into older alluviums, which are the deposits of several degradations and aggradations by the Colorado River, and younger alluvium, which is the deposit of the youngest aggradation. The contact between the younger and older alluviums is the contact between the present flood plain of the Colorado River and the bordering terraces and alluvial slopes. Commonly, the contacts between the various units of the older alluviums can be differentiated only with great difficulty even in clear outcrops. The contacts are even more difficult to determine from subsurface data. Neither can the contact between the younger and older alluviums be separated readily as was done in the Parker-Blythe-Cibola area (Metzger and others, 1972). Only where the Rouse Formation underlies the younger alluvium, can the two be differentiated. The water-bearing characteristics of the four units of the older alluviums and the younger alluvium are not discussed separately because of the obvious hydraulic continuity between the various alluviums, and because of the difficulty of separating the various alluviums on the basis of subsurface data. OLDER ALLUVIUMS Cibola area (Metzer and others, 1972). Unit A is not recognized in the Needles area. Unit B includes all deposits of the Colorado River and its tributaries that are older than unit C and younger than the Bouse Formation. Units C (piedmont gravels), D, and E are the same for the two areas. UNIT B Unit B is a sequence of heterogenous fluvial deposits of the Colorado River and its tributaries that uncon-formably overlies the Bouse Formation, and is overlain in turn unconformably by younger deposits of the Colorado River and its tributaries. Because this unit includes all deposits older than unit C (piedmont gravels) but younger than the Bouse Formation, the unit is made up of a considerable variety of rocks, and contains several units separated by erosional unconformities. and at least in one locality, an angular unconformity. Although these relationships can be seen in favorable outcrops, it is virtually impossible to visualize them from the available subsurface data. Unit B is composed of silt, sand, gravel, and clay. A common lithology deposited by the Colorado River is a gray medium sand containing scattered well-rounded small pebbles. A unique lithology are the lenses of Colorado River pebble-cobble gravel, which are capable of yielding copious amounts of water to wells. The gravel consists of pebbles and cobbles that came from many miles upstream, and of others that came from the adjacent mountains. The pebbles and cobbles from upstream sources are rounded to well rounded and dense. Colorado River sand Local Colorado River gravel Erosional unconformity „ gravels Colorado- Local Erosional unconformity „ gravels Colorado River silt, sand, and clay Colorado River gravel Erosional unconformity 1 oca I vgravels Erosional unconformity > Local > gravels Colorado River sand with lenses of gravel £ Local gravels Angular unconformity Colorado River sand and gravel — Angular unconformity •Local \ Unit A gravel J >Younger alluvium Piedmont > gravels f Older alluviums (unit C) Unit B The older alluviums of the Needles area (fig. 10) are subdivided using the terminology of the Parker-Blythe- Figure 10.—Diagrammatic composite section showing the deposits of the Colorado River and its tributaries in the Parker-Blythe-Cibola area, Arizona and California. (From Metzger and others, 1972.) 474-370 0 - 73 -3J14 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA Some are recognized as coming from Cambrian quartzites (Tapeats and related sandstones), Mississippian crinoidal limestone, red cherts of the Pennsylvanian rocks, and drab cherts of the Permian limestones. Some black chert is also present, its source being the Shin-arump Member of the Chinle Formation of Late Triassic age (M. E. Cooley, written commun., 1968). Interfingering with the Colorado River deposits are local gravel derived from the adjacent bedrock. This gravel may be subangular. subrounded or rounded. Invariably. the largest pieces of gravel, more than 1 foot in diameter, are locally derived. A gravel deposit in the SE14 sec. 5, T. 7 N.. R. 24 E. deserves special mention because of the unusual size of the elastics (fig. 11). This is the coarsest gravel deposited by the Colorado River downstream from Grand Canyon. Some of the boulders are as much as 3 feet in diameter. Most of the boulders are subrounded to rounded and consist of highly-contorted gneiss and granitic and volcanic rocks, whose composition suggests local derivation. Several cobbles 8 to 10 inches in diameter are rounded to well-rounded quartzites which are rock types typical of those moved into the area by the Colorado River. The variety of deposits included in unit B is best shown by the outcrops along the north side of Sacramento Wash in the SW1/) sec. 26, T. 16 N., R. 21 W. Here are five subunits of unit B (fig. 12), which from oldest to youngest are (1) Silt and clay overlain by well-rounded Colorado River gravel, (2) interbedded silt, sand, and clay, (3) rounded boulder gravel (local debris) overlain by sand and rounded to well-rounded gravel (local debris), (4) thin-bedded silt and sand overlain by sand containing well-rounded Colorado River gravel, and this, in turn, overlain by more thin-bedded silt and sand, (5) thin-bedded silt and sand with a 5-foot sand bed at base. The geologic history of these subunits is as follows: (1) Deposition of subunit 1, (2) erosion of subunit 1. (3) deposition of subunits 2 and 3, the two apparently conformable, (4) erosion of subunit 3, (5) deposition of subunit 4, (6) structural adjustment, either as a result of a monocline, or a fault, (7) erosion of subunits 3 and 4. (8) deposition of subunit 5, and (9) erosion. How far these subunits persist is not known. Further, these subunits are not to be construed as the breakdown Figure 11.—Colorado River boulder gravel In the SEVi sec. 5, T. 7 N., R. 24 E. Most of the boulders (as much as 3 ft in diameter) are locally derived and subrounded to rounded. Several cobbles (8 to 10 in. in diameter) are rounded to well-rounded quartzites which are rock types typical of Colorado River gravel. Pick in right center (circle) gives scale. of unit B, but rather as being only a part of unit B and to show the complexity of the deposits referred to unit B. Time did not permit detailed mapping of the deposits. PIEDMONT GRAVELS (UNIT C) Piedmont gravels are made up of debris from the adjacent bedrock. The unit is composed mostly of gravel, but sand and silt are also present. The thickness of individual gravels is not great and ranges from 10 to about 50 feet. The gravels, although thin, have the greatest areal distribution of any of the units bordering the flood plain. This is the unit that effectively conceals much of the older alluviums, Bouse Formation, and fanglom-erate. The surfaces of some of the gravels have been exposed to weathering since before the deposition of unit I). Desert pavement has formed on the surfaces, and the gravel has a heavy coating of desert varnish. The gravels are cemented with calcium carbonate, and the oldest piedmont gravel bordering the Black Mountains contains much hard caliche. The term “piedmont,” as used herein, is the compound surface of the dissected, alluvial slopes between the mountains and the flood plain of the Colorado River. Figure 12.—Diagrammatic sketch along the north side of Sacramento Wash in SWJ/4 sec. 26, T. 16 N., R. 21 W., showing subunits of unit B of older alluviums. Dashed lines indicate trend of bedding.GEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J15 114*30' 114*20' EXPLANATION iiilQPiiii: Oldest piedmont gravel cr Consolidated rocks of Black Mountains Contact Figure 13.—Sketch map showing piedmont gravels near Black Mountains. The overall cutting of the piedmont is controlled by the Colorado River. The term “piedmont gravels” is given to certain gravels deposited on some of these surfaces. It is restricted to deposits laid down during the period of downcutting that followed the deposition of unit B and before the deposition of unit D. This, use of the term is not entirely satisfactory, but it seems to be the best term for these deposits which overlie erosional surfaces having local different levels. The problem conld be resolved, perhaps, by giving formal names or some numeral sequence to the surfaces. These gravels and some of the surfaces would be referred to by some geologists as “pediment gravels” and “pediments.” There is some merit to this because the gravels termed the “piedmont gravel” are thin and lie on the surfaces cut on older rock units, for the most part unit B. However, many 2__a_2__ Colluvium and alluvium Qp3 Youngest piedmont gravel Intermediate piedmont gravel people restrict the term “pediment” to an erosional surface developed on the bedrock of the mountains and not on the softer units upon which these gravels lie. The use of “pediment” for describing these surfaces is further complicated by the fact that these are compound or multiple surfaces and include capping gravel, each younger gravel having successive lower elevations. Three piedmont gravels near the Black Mountains (fig. 13) have a gradient towards the flood plain of 100 to 150 feet per mile. A projection of the surface on the highest gravel indicates that this gravel could have been graded to a point about 100 feet above the present flood plain. A projection of the surface on the lowest gravel intersects the present flood plain. UNIT D Unit D is made up of two facies: (1) interbedded sand, silt, and clay, and (2) local gravel. Although the basal gravel of unit I) was recognized in the Parker-Blythe-Cibola area (Metzger and others, 1972), it is not included in the definition of unit D in the Needles area because of the absence of adequate subsurface data to determine if the gravel is present. The first facies occurs near the edge of the flood plain and was deposited by the Colorado River. The second occurs at the margins of deposition by the Colorado River and is the contribution of tributary washes. Unit I) was deposited against and on the piedmont gravels and older units (fig. 14). Unit D occurs along both sides of the flood plain in Mohave and Chemehuevi Valleys and in the canyon between the two valleys. Near Davis Dam, it is 300 feet higher than the flood plain. The interbedded sand, silt, and clay is generally tan in color with a slight pinkish or reddish tint to the outcrops. Some of tlie clay beds are darker shades of brown. The gravel interfingers with the fine-grained unit, and is Figure 14.—Depositional contact between unit D of the older alluviums and older units in tlie NE1^ sec. 27, T. 17 N., It. 21 W. Unit D was deposited against erosional features cut on unit B and piedmont gravel. Unit B (QTa), piedmont gravel (Qp), unit D (Qc), unit E (Qs).J16 WATER RESOURCES OF LOWER COLORADO RIVER—iSALTON SEA AREA made up of subangular to subrounded pebbles and cobbles that were derived from the adjacent bedrock. UNIT E Unit E is made up of two facies: (1) Sand deposited by the Colorado River, and (2) gravel deposited by local tributaries. The sand has virtually the same areal distribution as the interbedded part of unit D. The sand was deposited on erosional surfaces cut into unit D and older units, and was laid down during oscillations of a major period of degradation by the Colorado River. Thus, sand capping the terrace bordering the flood plain is younger than sand of the same unit that occurs at a higher elevation. The sand is tan, unconsolidated, medium, and fairly well sorted and contains scattered rounded to well-rounded pebbles. Because of its unconsolidated nature, it is easily attacked and moved by the wind, and forms gentle dune-covered slopes. The gravel facies is composed of subangular to subrounded cobbles derived from the adjacent bedrock. The elevation and slope of the gravel surface reflects the local base level (the Colorado River) to which the gravel was graded. As the Colorado River degraded, local gravels occurred at successively lower elevations. YOUNGER ALLUVIUM The younger alluvium includes flood-plain deposits of the Colorado River, wash deposits, and colluvium. Only the flood-plain deposits are shown on plate 1. The younger alluvium (excluding the colluvium) represents the last aggradation of the Colorado River, which continued until the river was controlled by Hoover Dam. The part that was deposited by the Colorado River extends from terrace to terrace, although at some places it is only a few feet thick because the present river is actively cutting into the terraces. The wash deposits extend from the flood plain up the present washes. The younger alluvium was defined with confidence in the Parker-Blythe-Cibola area (Metzger and others, 1972). Rear Parker the younger alluvium was deposited in a trench cut into the Bouse Formation. However, near Blythe the younger alluvium was deposited in a trench cut into older Colorado River deposits, and it was difficult to define the contact between the younger and older alluviums because the basal gravel of the younger alluvium apparently was deposited on gravels of the older alluviums. From the meager data that are available, it seem9 that conditions in Mohave Valley are more similar to those near Blythe than near Parker. Five holes were drilled with a powered auger rig across the flood plain near Reedies in an attempt to define the contact between the younger and older alluviums. The holes (fig. 15) ranged in depth from 117 to 167 feet and were entirely in Colorado River materials. The depth to the first pebble to cobble gravel ranged from 37 to 87 feet. Most of the material above the gravel was sand to silty sand with scattered gravel. The results suggest that the deposits above the gravel are thinner than they are in the Parker-Blythe-Cibola area, and therefore, the thickness of the younger alluvium is probably less in the Reedies area than farther south. These auger logs and logs of other wells indicate that near Reedies the younger alluvium rests on older Colorado River deposits. AGE The oldest deposits of the lower Colorado River in the Parker-Blythe-Cibola area are at least late Pliocene in age and perhaps older (Metzger and others, 1972). The youngest is the modern flood-plain deposits of Holocene age. Ro basis for refining these age assignments was found during the study of the Reedies area. WATER-BEARING CHARACTERISTICS The alluviums of the Colorado River are a heterogeneous mixture of gravel, sand, silt, and clay. All but a few wells in the Reedies area yield water from sand and gravel of the alluviums. Many domestic wells are sandpoints installed only a few feet below the land surface. Large diameter wells are drilled generally only as deep as necessary into a pebble and cobble gravel. Therefore, very little is known about a composite thickness of the several Colorado River alluviums. The thickest known section is that in well (B-18-22)23bcc2, which was still in alluvial deposits at a depth of 310 feet. Most of the yield from wells that are perforated in the alluviums come from highly permeable beds of sand and gravel. The Colorado River gravel lias the highest permeability of any water-bearing rocks in the area. Wells that tap a sufficient thickness of these gravels have specific capacities over 100 gpm per foot of drawdown. The largest specific capacity determined during this investigation was that for well (B-19-22)36bab, which had a specific capacity of 400 gpm per foot of drawdown. STRUCTURE OF SEDIMENTS Ro attempt was made during this investigation to determine the structural history of the bedrock because the bedrock forms the boundary of the ground-water reservoir and is, for all practical purposes, a barrier to ground-water movement. Revertheless, it is obvious that the structural history of the bedrock is much more involved than that of the sediments of the valleys. The granitic and metamorphic rocks are much fractured. The sedimentary and volcanic rocks older than the fan-glomerate have been faulted and folded and commonlyGEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J17 VERTICAL SCALE GREATLY EXAGGERATED EXPLANATION Clay Sand and silt Sand and gravel Sand Gravel and sand Figure 15.—Lithologic sections from auger holes near Needles, Calif. have steep dips, which is in marked contrast to the gentle dips of most of the sedimentary rocks forming the ground-water reservoir. Although most of the outcrops of unit B have beds with gentle dips, some outcrops have beds that indicate structural adjustments during and following deposition of the unit. Because unit B was not studied in detail during the present investigation, its structural history is not fully known. The structural adjustments during the deposition of unit B at a selected site along the north side of Sacramento Wash was given under the section on unit B (p. J14). Figure 16 shows the deformed sediments. This locality was also visited by Lee (1908, fig. 10B). Also in this area, several normal faults of small throw are present. On the basis of only tho log of well (B-18-22)23bcc2, it may be tentatively concluded that unit B is dowmvarped beneath parts of the flood plain, in much the same manner as that noted near Blythe (Metzger and others, 1972). This is weakly substantiated by the presence of the Bouse at depths of 200 to 250 feet in T. 19 X., R. 22 W. In T. 4 X., It. 24 E. (unsurveyed into sections), in Chemehuevi Valley, unit B along with the underlying Bouse Formation has been deformed into a syncline (fig. 17). The syncline is exposed for about 1,000 feet along a wash and trends northwest. The piedmont gravels in T. 17 X., It. 20 W., are cut by a graben that has a displacement of about 10 feet. The graben is about a quarter of a mile wide and extends 2 miles northwest. It shows with particular clarity on aerial photographs because the gravels contain a heavy coating of desert varnish that make the linea-tions of the faults stand out. This is the only locality where displacement of the piedmont gravels was observed. Other lineations on the piedmont gravels have been noted, but in most places, these are scarps cut on the piedmont gravels that are now being exhumed. Figure 10.—Deformed older alluviums of the Colorado River and its tributaries along north side of Sacramento Wash in SE1^ sec. 26, T. 16 N., R. 21 W. 474-370 0 - 73 -4J18 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA RECHARGE Figure 17.—East limb of syncline in east center of T. 4 N., K. 24 E. (unsurveyed into sections). Bouse Formation (Tb) and locally derived alluvium (QTa). Nowhere in the area has unit I), unit E, or the younger alluvium been observed to have been displaced by structural adjustments. Units D and E are not continuous throughout the area, so minor displacements could be hidden. However, major displacements are not present, and from the time of deposition of unit I) to the present, major geologic controls have been stable. GROUND-WATER RESOURCES OF THE NEEDLES AREA OCCURRENCE All but a few of the wells in the Needles area are completed in the alluviums of the Colorado River, in which the ground water occurs under water-table conditions. Two wells that may contain water under artesian conditions are in T. 16 N., R. 20y2 W., about 3 miles east of Topock. These wells produce water from and below the Bouse Formation and fanglomerate, and similarly developed wells in the Parker-Blythe-Cibola area contain water under artesian conditions. However, there are no nearby wells in which to determine the depth to the water table. Some ground water also occurs under perched conditions. One small body of perched ground water occurs south of Chemehuevi Wash in T. 4 N., R. 24 E., as evidenced by the shallow depth to water of 5.7 feet in well 4N/24E-17Z1, which is an old dug well. Because of the nearby outcrops of the Bouse, it is assumed that this water is perched atop the Bouse. An interesting observation is that nearby Chemehuevi Wash is incised below the elevation of the water level in the well; yet, the wash contains only desert vegetation, which further suggests that the ground water tapped by the well is perched. Sources of recharge to the ground-water reservoir of the Needles area are the Colorado River, unused irrigation water, runoff from precipitation, and underflow from bordering areas. Of these, the Colorado River is by far the principal source. The role of the river as a source of recharge is given in more detail in the section in which ground water in recent years is discussed. Recharge of the ground-water reservoir from excess irrigation water is, in a sense, only a negative discharge, inasmuch as practically all irrigation supplies are ob-j tained from wells. The recharge from this source in recent years has been 5,000 to 10,000 acre-feet per year, if, as is likely, half the ground water that was pumped for irrigation was not used consumptively but returned to the ground-water reservoir. Additional details about pumpage for irrigation are given in the section in which the development of irrigation is discussed. Recharge by runoff from precipitation occurs in the sandy washes and along major ephemeral streams such as Sacramento and Piute Washes. Most storms probably cause little runoff, and even much of this runoff is lost by evaporation or transpiration in the streambed. Only runoff from rains of high intensity contribute to recharge. Heavy rains in the arid southwest may seem anomalous, but these occur as a result of moist air moving into the area from tropical disturbances off the coast of Baja California. During these rare storms, it is common for 2 or 3 inches of rain to fall in a few hours. Such an intensity results in rapid runoff. As an example, during a storm in September 1939, Piute Wash at a point 8.5 miles northwest of Needles is reported to have had a maximum discharge of 30,000 cfs (cubic feet per second) or 39.0 cfs per sq mi (cubic feet per second per square mile); and Sacramento Wash at its mouth near Topock is reported to have had a maximum discharge of 15,000 cfs or 10.5 cfs per sq mi (Smith and Heckler, 1955. p. 5). The sandy washes have well-developed channels from the bedrock areas to the flood plain, a feature that is in marked contrast to most ephemeral washes of the Mohave Desert. The major washes are incised and have well-defined banks and wide, flat bottoms that are mantled and underlain by sand and gravel. Thus, much of the runoff from the bedrock areas infiltrates into the sand and gravel and eventually part of the water recharges the ground-water reservoir. Another factor tending to accentuate the recharge possibilities in the washes is the cementation of the desert pavements of the piedmont gravels. Heavy rain on these gravels quickly becomes runoff that flows into the desert washes.GEOHYDROLOGY OF THE NEEDLES AREA. ARIZONA, CALIFORNIA, AND NEVADA J19 Recharge from areas bordering the Needles area occurs as underflow beneath Sacramento Wash, Piute Wash, and Chemehuevi Wash. The sources of this recharge are discussed in the section on “Water Budgets.” As stated in the discussion of the location of the area, the Needles area comprises the Mohave and Chemehuevi Valleys. These valleys are separated by the Chemehuevi Mountains except for a very narrow connecting section of the Colorado River valley. Although Chemehuevi Valley is recharged to the extent of the underflow through the alluvium of the river channel, this quantity is negligible and is also compensating when the entire Needles area is considered because it is outflow from Mohave Valley. This source of recharge and discharge, therefore, is not discussed further. DISCHARGE Ground water is discharged from the aquifers of the Needles area by wells and by evapotranspiration. Discharge to the Colorado River, if it occurs at all, is negligible. The ground water pumped from wells is used for municipal and domestic supplies and for irrigation of land. The two principal communities in the area— Needles and Lake Havasu City (which is being built on the east side of Havasu Lake)—both use wells for municipal water supply. The wells of both cities obtain water from the alluviums of the Colorado River. In addition to the cities, numerous blocks of land are being subdivided. In some of these, one or two wells supply water for all the lots, whereas in others, individual wells supply each lot. A common type of well construction, which is used on farms and homesites on the flood plain, is a sandpoint driven only a few feet below the water table. Another type is a cased hole drilled into the first “good” gravel, after which the casing is perforated in that gravel. Irrigation wells generally are between 12 and 20 inches in diameter, and all obtain water from the Colorado River deposits. Pumpage in 1968 was about 18,000 acre-feet (p. -T21). Ground water is discharged by evapotranspiration wherever the water table is near the land surface, which is throughout the flood plain area. This topic is discussed under the section, “Water Budgets.” The only area in Mohave Valley where discharge from the ground-water reservoir to the Colorado River might be occurring is along the east side of the river near Topock. Prior to the filling of Havasu Lake in Chemehuevi Valley, some ground water must have discharged into the nonbeclrock reaches of the river where the flood plain was narrow and did not contain water-loving vegeta- tion, or where there was practically no flood plain. However, the filling of the lake with an attendant reversal of ground-water gradients near the lake caused water to move away from the lake into the sediments. As far as can be detected from the limited data available, the water table is presently nearly flat; so evidence for ground-water discharge to the lake is inconclusive. Eventually, however, the recharge from the adjacent mountains, meager as it may be, will cause a reestablishment of a ground-water gradient and discharge to the lake. HISTORICAL SKETCH The first white man to enter the area, according to the records, was a Spanish priest, Padre Fray Francisco Garces, who in 1776 traveled northward from Yuma to visit the Mohave Indians. The next white man of whom records are available was Jedediah S. Smith, who visited the area 50 years later, in 1826. In 1858 a party under Lt. Joseph C. Ives (1861) explored the Colorado River from its mouth to the head of navigation at the lower end of Black Canyon, which is some 40 miles north of Davis Dam. The expedition was made by steamboat, a fact which proved the river to be navigable to that point. In 1861 a ferry was established across the Colorado River at Fort Mohave, Ariz. (about 15 miles north of Needles). In August 1883 the Southern Pacific Railroad was completed eastward to the Colorado River at Needles where it joined the Atlantic and Pacific Railroad and provided rail service between the west coast and the Mississippi River. Thus, the region became much more accessible to the early travelers, some of whom settled in the area. Needles, with a population of 2,807, was the only incorporated town in the entire Mohave Deseit region in 1920 (Thompson. 1929). The town was supported largely by railroad activities, being a division headquarters of the Atchison, Topeka, and Santa Fe Railway, which purchased the two railroads that originally joined at Needles. Needles was also a trade center for the mining camps in the area. In 1890 Fort Mohave was transferred to the Indian Service for use as a school. In 1922 the Fort Mohave Indian Reservation included several thousand acres near the school, as well as all the even-numbered sections on the lowlands in Arizona as far south as Topock. Thompson (1929) reported that at the time of his visit to the area in 1922 the water table was close to the land surface beneath the lowlands along the Colorado River and that water-loving vegetation was abundant. Cottonwood and willow thrived along the river and sloughs,J20 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA and large mesqnite trees, arrowweed, salt bush, and some salt grass occupied the rest of the lowland. Thompson also noted that although the river channel lay near the western margin of the flood plain in the reach between Fort Mohave and Topock, the many lakes and abandoned river channels were evidence that in the past the river had occupied all parts of the flood plain. He further stated that the river always carried a large amount of silt, sometimes as much as 3 percent by weight of the entire flow. The water was so muddy that it was not used for domestic purposes without first filtering it or allowing the silt to settle. The Indians were the only people using the river water in the early 1920’s. Before the coming of the white man, the Indians had farmed the flood plain by planting seeds after the annual floods subsided. During the dry season, they carried water from the river to irrigate their crops. Beginning in 1891, several attempts were made to divert water from the river, both by diversion canals and by pumping. None of the early attempts were successful because of the ever-changing channel and the annual floods. The settlers realized that levees were needed, both to protect the canals and to prevent flooding of the reclaimed land. As early as June 1915, the Cotton Land Co., which owned the odd-numbered sections on the Arizona side of the river, had spent $575,-000 for irrigation works and flood protection, but without success (U.S. Congress, 1922). Plans to use water from wells for irrigating flood-plain lands in the Indian Reservation also had been unsuccessful. A well drilled to a depth of 780 feet near the Indian School at Mohave City reportedly did not penetrate any extensive gravel beds and did not yield sufficient water for irrigation (Thompson, 1929). Prospects for irrigation by pumping from wells in the flood plain were believed to be poor principally because of the fine material likely to be found and the poor chemical quality of the ground water that had been obtained. Outside the flood plain, the prospects were also considered poor because of the greater depth to water, the inadequate yields, the dissected slopes, which would require extensive leveling, and the highly mineralized water that was obtained from a few existing wells. (Depths to water of more than 100 ft were considered impractical for irrigation.) Hydrologic conditions remained fairly stable from the 1920’s to the closure of two dams, Hoover Dam in 1936 and Parker Dam in 1938. The closure of Hoover Dam, 67 miles upstream from Davis Dam, ended the annual spring floods in the area and caused some channel scouring because relatively clear water was released from the dam. The closure of Parker Dam and the consequent filling of Havasu Lake caused a rapid aggrada- tion of the Colorado River upstream from the lake. As the aggradation continued and moved upstream, the definable channel in the lower part of the flood plain east and southeast of Needles was obliterated, and the river flowed through a series of swamps and sloughs. By 1944 the aggradation had caused river stages and consequently ground-water levels to rise enough to threaten the town of Needles and the main line of the Atchison, Topeka, and Santa Fe Railway. To alleviate this situation, the U.S. Bureau of Reclamation initiated a program of dredging operations and improvements on the river-channel geometry. Dredging operations and channel-alinement work from the Big Bend area below Davis Dam to Topock were completed in July 1960. Only a limited amount of dredging was done below Topock before operations were stopped pending studies of the physical and ecological changes in the canyon downstream from Topock. In addition to the aforementioned channel improvement, a levee system was also constructed so that flows of 50,000 cfs and more could be controlled. DEVELOPMENT OF IRRIGATION Following the unsuccessful early attempts to irrigate land, previously described, the development of land for irrigation agriculture was gradually abandoned. Irrigated acreage, principally by diversion of river water, dropped from about 2,400 acres in 1914 and 1915 to about 850 acres from 1916-23, to 730 acres in 1924, to 630 acres in 1925-27, and to about 200 acres from 1928^5 (U.S. Bureau of Reclamation, 1953). As interpreted from aerial photographs dated October 1947, only about 200 acres of the flood plain were being irrigated at that time. A similar acreage adjacent to the flood plain, principally in the Big Bend and Fort Mohave areas, also was being irrigated. During the 1950’s the development of land for irrigation agriculture again thrived. By 1962, 3,090 acres of the flood plain (U.S. Bureau of Reclamation, 1963) and 300 acres east of the flood plain were being irrigated. Of the flood-plain land, 1,960 acres was irrigated with Colorado River water. About 1,400 acres of the total acreage was irrigated by pumping ground water. Using an estimated withdrawal rate of 6 acre-feet per year per acre irrigated, the pumpage was 8,400 acre-feet. Total other pumpage by the city of Needles and other users of ground water probably resulted in a total withdrawal of somewhat less than 12,000 acre-feet in 1962. Beginning in 1964, the U.S. Geological Survey began an annual inventory of pumpage for irrigation from wells in the flood plain of the Colorado River and from wells adjacent to the flood plain as a part of its responsibility for measuring diversions, return flows, and consumptive use of Colorado River water in accordanceGEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J21 with Article V (B) of the decree of the Supremo Court of the United States in Arizona v. California dated March 9,1964. The results of the inventories as listed in annual administrative reports are summarized in the following table. The data in the table show that pumping of ground water for irrigation remained rather constant through 1966 at between 12,000 and 15,000 acre-feet per year but that beginning in 1967 pumpage increased 50 percent as a result of new wells drilled in 1966. The newly developed land is limited principally to the odd-numbered sections (non-Indian land) east and north of Needles. In addition to the above pumpage, the city of Needles pumps four wells for municipal use. Pumpage each year, 1964 through 1968, is listed as: 2,527; 2,113; 2,384; 3,230; and 2,946 acre-feet, respectively. Pumpage of ground water by other communities and the many resorts that line the river was an additional 1,000 acre-feet, and is continuing to increase as more resorts are built or existing ones are expanded. Thus, the total annual pumpage of ground water through 1966 was about 18,000 acre-feet or less; in 1967 about 25,000 acre-feet, and in 1968 about 22,000 acre-feet. Pumpage from the river for irrigation has also been small to date. As stated previously, 1,960 acres were so irrigated in 1962, but in later years the acreage has been less. Table 1.—Annual pumpage of ground water, in acre-feet, for irrigation, 1964-68 Year Arizona California Total in area Number of wells Number of acres Pumpage Number of wells Number of acres Pumpage Number of wells Number of acres Pumpage 1964 10 2, 250 13, 500 i 90 540 n 2, 340 14, 040 1965__ .. 8 1, 890 11, 520 2 140 840 10 2, 030 12, 360 1966 20 1, 885 11, 820 5 512 3, 132 25 2, 397 14, 952 1967 22 3, 107 18, 197 5 522 3, 132 27 3, 629 21, 329 1968 21 2, 336 15, 597 5 393 2, 358 26 2, 729 17, 955 RIVER STAGES Because the Colorado River is hydraulically connected to the ground-water system, river stages directly influence rates of recharge to and discharge from the ground-water system and also the quantity of ground water that is stored in the system. The interchange between surface water and ground water depends not only on the difference between the river stage and the head in the ground-water system, but also the period of time over which the difference exists. Although detailed analysis of the recharge to or discharge from the ground-water system caused by changes in river stage is beyond the scope of the present study, some generalizations can be made about the relative amounts of ground-water recharge or discharge that have occurred in past years on the basis of the influence of river stage alone. The earliest river stages that are considered to be representative of stages under natural conditions are those shown on a U.S. Geological Survey river profile and topographic map compiled in 1902-4)3. The river profile and stage are based on the altitude of the river at a discharge of 10,000 cfs. Changes in river stage from, stages under natural conditions, therefore, should be indicated by differences between the river stages in 1902-03 and those of later dates. The U.S. Geological Survey stream-gaging station near Topock has one of the longest records of stage and discharge on the lower Colorado River. Incomplete records dating back to February 1,1917, show that prior to the control of the Colorado River by Hoover Dam in 1935 maximum discharges varied from 51,000 cfs, June 6, 1925, to 175,000 cfs, June 22, 1921. Respective stages were about 438 feet and 451 feet above mean sea level. Minimum discharges generally ranged from 2.000 cfs to about 6,000 cfs, with minimum stages generally being between 427 and 429 feet above mean sea level. The river profile map of 1902-03 indicates a stage of about 427 feet for a discharge of 10,000 cfs, which suggests that the river may have aggraded a few feet between 1902-03 and 1917. Yearly maximum and minimum stages and discharges for the period 1933-67, which is principally a period of regulated flow, are shown in figure 18. It is seen that after 1935 the difference between maximum and minimum discharges averages only about 15,000 cfs. Differences between maximum and minimum stages likewise are small, ranging from only a foot or two in the middle 1940’s to 7 feet in the middle 1960’s. In contrast, earlier records show that prior to the regulation of flows by Hoover Dam in 1935, differences between yearly maximum and minimum discharges averaged about 100.000 cfs, and differences between maximum and minimum stages generally were about 15 feet, although in a few years differences were about 25 feet. Of greater significance as regards ground-water levels, however, are changes in average stage of the river. If it is assumed that a stage midway between the maximum and minimum stages shown is a satisfactory•J22 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA approximation of the yearly average stage, then the data show that from an average stage of 438 feet in 1938, when backwater from Havasu Lake reached the station, the stage rose to 450 feet by 1944. There it remained until 1950, after which it gradually rose to a peak of 455 feet in 1959 and I960. Between 1961 and 1967 the average stage gradually declined to 453 feet, which is about 15 feet above the stage in 1938, and about 25 feet above the stage for a comparable discharge in 1902-3. River-stage records have been published for a station at Needles since 1933. However, discharges are not measured at the Needles station; so the discharges near To-pock are used in this study to correlate stages and discharges. Average daily stages at Needles on dates of maximum and minimum discharge near Topock are plotted in figure 18 also. Again assuming that a stage midway between the average daily stages on dates of maximum and of minimum discharge in any one year is a satisfactory approximation of the average stage for that year, the following observations can be made: The changes in average stage of the river at Needles differ from those near Topcock. The average stage at Needles rose from an altitude of about 468 feet in the middle 1930’s to a maximum altitude of about 475 feet by 1945 and then gradually declined to 468 feet by 1952. This stage was maintained until 1960, after which it again gradually declined to about 465 feet in 1966 and 464 feet in 1967. It appears, therefore, that the 15-foot rise that occurred near Topock between 1938 and 1944 was accompanied by a rise of about 7 feet at Needles. Because the resultant rise of ground-water levels was causing some agricultural land to be waterlogged and causing damage to Needles and the railroad, the U.S. Bureau of Reclamation in 1947 began remedial measures for lowering water levels. Undoubtedly, the dredging and channel rectification work that followed were responsible for much of the 5-foot decline of average river stages that occurred between 1947 and 1952. Changes in river stage upstream from Needles between 1902-3 and 1962-63 can be inferred by comparing river stages for the earlier period with river stages for the latter period which are recorded at river-stage stations maintained by the U.S. Bureau of Reclamation. The data for this comparison (shown in fig. 19) indicate that for a discharge of 10,000 cfs, stages in 1962-63 were 2 to 4 feet higher than in 1902-3 in the reach between Davis Dam and a section about 10 miles north of Needles. Presumably a similar relationship existed for other rates of discharge, including the average yearly discharge. The foregoing comparisons show only the net change in stage between 1902-3 and 1962-63, not intermediate changes. More complete data at the U.S. GeologicalGEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J23 E CM T3 C 8 (/> a o CO 0> CD O TJ w oc 00 CO 0) ’> (C cr CD ffi (r Z Q co cc 01 5 D CD CD o CO CO D D m RIVER STAGE STATION Figure 19.—Colorado River stages at selected sites in 1902-3 and 1962-63. Discharge rate is 10,000 cfs. Survey gaging station below Davis Dam show that substantial intermediate changes may have occurred. The gaging station is half a mile downstream from the dam and 30y2 miles upstream from the river stage station at Xeedles. Discharge and stage records were begun in March 1949 at about the time Davis Dam was completed. The river profile map for 1902-3 indicates that the river surface was at an altitude of about 504 feet when the discharge was 10,000 cfs. In 1949 the altitude of the river surface was almost 511 feet for a like discharge. This suggests that the river channel probably had aggraded about 7 feet between 1902 and 1949. Discharge and stage data for the station below Davis Dam beginning in 1949 are shown in figure 20. Maximum discharges generally range between 25,000 and 30.000 cfs because of the regulation of releases from Hoover and Davis Dams. This rate of maximum discharge is only about one-fifth the maximum rates that were common under natural conditions. The decline of stage during years of rather constant yearly discharge indicates that the river channel continually degraded after 1950. On the basis of discharge-stage relationships, it is computed that in 1962 the river stage was about 502 feet above sea level when the discharge was 10,000 cfs, or about 2 feet lower than the stage for a comparable discharge under natural conditions. Thus, although the river channel near the gaging- station site below Davis Dam was not much different in the 19G0's from what it had been under natural conditions, in the interim the river channel evidently had aggraded at least 7 feet by 1949, and then had eroded back to near its natural altitude in a few years time following the l'elease of relatively clear water from Davis Dam. In summary, the average river stage from the northern end of Mohave Valley to a point about 10 miles north of Needles presently may be about 4 feet higher than under natural conditions. Southward from this point the differences in stage increase, so that at Needles the average river stage presently is about 8 feet higher than under natural conditions and at Topock, about 27 feet higher. These higher stages cause ground-water levels to rise a like amount near the river and a lesser although substantial amount at considerable distances from the river. Where the rise is sufficient to make ground water more readily available to water-loving vegetation or for evaporation, the rise results in additional depletion of the available water supply. Figure 20.—Yearly maximum and minimum discharges and stages of Colorado River at gaging station below Davis Dam, 1949-67. HYDROLOGIC CHARACTERISTICS OF AQUIFERS DEFINITION OF TERMS The term “aquifer” commonly is applied to a waterbearing formation or rock unit that is capable of yielding a satisfactory water supply. It may denote a single bed, or a sequence of beds whose individual permeable beds may be lenticular and vaguely bounded but which generally are not separated by extensive relatively impermeable beds. Because a satisfactory water supply depends in large part on the conditions that must be met, “aquifer” is aJ24 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA relative term for which good, fair, or poor are commonly used to denote the degree to which the supply is satisfactory. However, these general terms are inadequate for a quantitative appraisal of an aquifer or aquifer system, or for comparing one supply with another. For these purposes, more specific terms as explained in the following discussion are used. 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 coefficient.” The term “transmissivity,” which is equivalent to the term “coefficient of transmissibility” introduced by Theis (1935), has been used by an increasing number of hydrologists in recent years because it is a more exact word than transmissibility for the hydraulic characteristic that it describes. In units commonly used by the Geological Survey, transmissivity is 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 prevailing tem-perature of the water. In some applications it may be visualized more easily by expressing the width of aquifer cross section in miles and the hydraulic gradient in feet pei' mile. The water-transmitting characteristics of a rock may also be expressed on a unit-area basis. The term commonly used for this purpose is “hydraulic conductivity” (formerly coefficient of permeability), which is 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 reforred 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 material, it is necessary to differentiate between the horizontal and vertical hydraulic conductivity. The horizontal hydraulic conductivity of a particular bed ordinarily is substantially higher than the vertical hydraulic conductivity, owing to the size sorting and the alinement of tabular grains that occur during the deposition of alluvial materials. Values of horizontal hydraulic conductivity commonly range from a fraction of a gallon per day per square foot for clay and silt, to 10,000 gpd per sq ft (gallons per day per square foot) for well-sorted very coarse sand or less well sorted gravel. Transmissivity values generally are determined from pumping tests if it is practical to make the tests and if test conditions are favorable. They also can be computed on the basis of the theoretical relation between transmissivity and the specific capacity of wells (Theis and others, 1963). (Specific capacity is the yield of a well per unit of drawdown after a specified period of discharge. In this study it is expressed as gallons per minute per foot of drawdown at the end of 1 day.) Both the above methods for estimating transmissivity were used in the present study. The other 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, the storage coefficient (formerly coefficient of storage), which is the volume of water that is released from or taken into storage per unit surface area of an aquifer per unit change in the component 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 conditions, 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 compressibility of the aquifer materials and of the water in the saturated zone; so the volume of water resulting from compressibility can be ignored. The volume of water involved in gravity drainage divided by the volume of porous material through which the water table moves, has been defined as the specific yield. Under dewatering and unconfined conditions the storage coefficient therefore is, for all practical purposes, equal to the specific yield. When water is going into storage, that is, when the water table is rising, the storage coefficient may exceed the specific yield if the material in which the water is being stored contains less moisture than it can retain against gravity drainage. The upper limit of the storage coefficient in the latter example is the porosity of the material. Under water-table conditions, the storage coefficient for clay and silt commonly ranges fromGEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J25 almost zero to a few hundredths. For clean sand and gravel, it frequently ranges between 0.2 and 0.4. By definition, the storage coefficient is not a function 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 or months of drainage. Storage coefficients used in conjunction with transmissivities permit the determination of the relative amounts of ground water that will be involved in storage changes and of those that will be involved in movement of ground water toward or away from an area for a given change in the ground-water supply. Conversely, the change in position and shape of the water table or piezometric surface that results from a given change in the supply of ground water can be used to compute the two characteristics. Pumping tests are probably the most practical way for determining storage coefficients if artesian conditions exist, but they may be less practical than otlwr methods if water-table conditions prevail. The failure of pumping tests to provide valid data for computing storage coefficients is due in most instances to the slow rate at which many water-bearing materials drain. The mathematical formulas used for analyzing pumping tests assume an instantaneous change in storage with a change in head. Although this idealization may be closely approached under artesian conditions, it is rarely closely approached under water-table conditions. Therefore, storage coefficients computed from data obtained during pumping tests of unconfined aquifers are likely to be substantially less than the true storage coefficient unless the tests are made over a period of days and adjustments for protracted drainage are made. In some areas a more practical approach for determining storage coefficients under water-table conditions is 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 an indicator of the amount of water that will go into storage as the water table rises. This approach was used for estimating storage characteristics of material underlying the flood plain in the Parker-Blythe-Cibola area and the Yuma area and to a limited extent in the Needles area. The field investigation in the Needles area was limited because the results of studies made in the aforementioned downstream areas were considered to be applicable to similar deposits in the Needles area also The scientific principles which relate neutron-probe data to moisture content and the details of construction of access holes and of equipment used are explained in previous water-resources reports on the lower Colorado River area (Metzger and others, 1972 and Olmsted and others, 1972), and so will not bq repeated here. SOIL-MOISTURE STUDIES Figure 21 shows typical profiles obtained during the soil-moisture studies. At access hole (B-l7-22)llccc, the average counts at 1-foot depth intervals from land surface to a depth of 7 feet are related to the moisture content in the zone of aeration above the capillary fringe. The average counting rate of about 780 per minute represents an average moisture content of about ?> percent. The increase in counting rate in the depth interval from 7 to 10 feet is due to increasing moisture content below the top of the capillary fringe. The average counting rate of about 8,000 per minute below 10 feet is related to a moisture content of about 47 percent in the zone of saturation. As stated previously, the difference between the moisture content above the capillary fringe and the content in the zone of saturation, 44 percent, is the basis for estimating the ability of the deposits to store water as the water table rises. Although the above assumption may be considerably in error for any one profile, it is considered a valid assumption if applied to the mean values of a large number of profiles. The profile of access hole (B-18-22)35cad indicates that the water table and capillary fringe both were below a depth of 14 feet. It also shows that the moisture content in the zone of aeration is not uniform. The average counting rate of about 2,000 per minute between Figure 21.—Counts per minute at various depths below land surface obtained with neutron moisture probe at two sites in Needles area.J26 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA depths of 6 and 8 feet corresponds to a moisture content of about 10 percent, whereas the average counting rate of about 700 per minute from 10 to 12 feet corresponds to a moisture content of only 3 percent. If the moisture content in the zone of saturation is similar to that at site (B-l7-22)llccc, or 47 percent, the capacity to store water as the water table rises averages about 42 percent. The foregoing two profiles, in themselves, are not an adequate basis for estimating the storage capacity of deposits at shallow depths beneath the flood plain in the Needles area. The results of similar studies in the downstream areas therefore are summarized (Metzger and others. 1972 and Olmsted and others, 1972). At 11 sites in Parker Valley, the average moisture content in the zone of saturation was 45 percent, and in the zone of aeration above the capillary fringe, 6 percent. In Palo Verde Valley (also known as the Blythe area), average values at 16 sites for corresponding zones were 44 and 12 percent, indicating a storage capacity of 32 percent. Soil-moisture profiles of shallow flood-plain deposits in the South Gila Valley east of Yuma, Ariz., indicated a capacity for storage of about 37 percent and in the Yuma Valley, west and southwest of Yuma, about 42 percent. In contrast, the storage capacity at similar depths beneath Yuma Mesa was about 28 percent. In no place did the soil-moisture studies include any appreciable thickness of coarse gravel because it was impractical to drive access tubes into these deposits. However, on the basis of studies in other areas (Johnson, 1967, p. Dl), it is probable that the storage coefficient of gravel in the Needles area averages about 25 percent. The soil-moisture studies suggest that in an area of rising water levels beneath the flood plain outside of irrigated areas the storage capacity is likely to be between 32 and 42 percent. A similar amount of water can be expected to be released from storage as water levels decline if sufficient time elapses for practically all gravity drainage to be completed. The actual amount that can be expected during a seasonal or shorter period of decline of water levels may be considerably less than the above amounts because of the slow drainage of finegrained material. Storage coefficients beneath irrigated areas are likely to be less than beneath nonirrigated areas because the moisture content above the capillary fringe quite often exceeds the field capacity due to incomplete gravity drainage of excess irrigation water. No studies were made of the storage capacity of material outside the flood plain. However, it is probable that the storage capacity of the deposits beneath the piedmont slopes is less than that of the shallow flood-plain deposits. PUMPING TESTS The principal objective of the pumping tests was to determine within reasonable limits the transmissivity of the main water-bearing deposits. Accordingly, tests were made in existing wells of large yield. For most wells the test was limited to obtaining data on the rate of recovery of water level after the well had been pumped at a constant rate for a known period of time. A few wells also yielded data on drawdown versus pumping time. No wells other than the pumped well were available for satisfactorily observing the effects of pumping or shutting down the pumped well. Consequently, the pumping-test data were inadequate for computing storage coefficients. Where possible, the data were analyzed by use of the nonequilibrium formula of Theis (1935) or modifications thereof. However, because conditions at some of the sites were substantially different from those that were assumed in deriving the nonequilibrium formula, the plot of observed changes of water level with time sometimes deviated so far from the theoretical pattern that the Theis nonequilibrium formula obviously could not be used to compute even an approximate transmissivity value. Sometimes the plot, although conforming to the theoretical pattern, nevertheless indicated unreasonably high values of transmissivity on the basis of the theoretical relation between transmissivity and specific capacity. Under these conditions the transmissivity indicated by the recovery data was also evaluated against a probable value based on the estimated hydraulic conductivity and thickness of the water-bearing material tapped by the well. Recovery data for two wells are plotted in figure 22. The plot of recovery data versus time for well 11N/21E-36Q1 is typical of the pattern that was used for computing transmissivity by use of the Theis nonequilibrium formula. The transmissivity is inversely proportional to the slope of the plotted data during the early part of the recovery period at which time the slope is nearly constant. The plot of recovery data versus time for well (B-19-22)26ddd is typical of some of the plots that followed the theoretical pattern a minute or two after pumping stopped, yet which resulted in computed values of transmissivity that were considered unreasonably high when compared to values computed from drawdown data versus time or from specific capacity data. The results of the five pumping tests in Arizona and the four pumping tests in California that were made during the investigation are listed in table 2. Each of the transmissivity values computed by use of the TheisDEPTH TO WATER, IN FEET, BELOW LAND SURFACE GEO HYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J27 Figure 22.—Hyclrographs of pumping-test data for selected wells. nonequilibrium formula is classified as being a good, fair, or poor indicator of the transmissivity of the water-bearing deposits tapped by the well. A classification of good is assigned if the difference between computed transmissivity and the true transmissivity is thought to be less than 25 percent of the value listed; fair, if the difference is between 25 and 50 percent, and poor, if more than 50 percent. Consequently, none of the computed values is significant to more than two figures and most of them to one figure. The classification takes into account not only the degree to which the plotting of test data followed a theoretical pattern and the theoretical relation between transmissivity and specific capacity previously mentioned, but also the construction of the well, the possibility of leakage between strata tapped by the well, and any other known factors that might tend to invalidate the results. Also considered was whether the hydraulic conductivity, as computed by dividing the indicated transmissivity by the thickness of strata tapped by the well, greatly exceeds the probable maximum hydraulic conductivity. Studies in downstream areas (Olmsted and others, 1972 and Metzger and others, 1972) indicate that the average maximum hydraulic conductivity of alluvial deposits that are at least several tens of feet thick probably is not much larger than 10,000 gpd per sq ft. Table 2.—Results of pumping tests [Type of test: D, drawdown; R, recovery; S, specific capacity. All wells completed in alluviums of the Colorado River] Depth Indicated interval Conformance average Date Type tested Yield Draw- Specific Transmis- of test data Reliability field Well Owner or name of test of test (ft below (gpm) down capacity sivity T to theoretical of T hydraulic Remarks land-surface (ft) (gpm (gpd per ft) values conductivity datum) per ft) (gpd per s-. . I). Ilulet ..11- 1-62 R 60-05 1, 720 20.8 83 240,000 Fair ... Fair 6,900 S 240,000 6. 000 27bbc... . G. McKellip... .. 11- 1-62 D 80-126 3,420 21.5 160 600,000 Good ... Good 13,000 R s «K)0. 000 . ..do 20.000 240,000 5,200 2)26ddd_. . S. Joy, Sr .. 11- 2-62 R 117-100 1, 720 7.0 250 6,500^000 do.... ... Poor S 350.000 4, 700 36bab— dc .. 11- 1-62 R 147-250 1,870 4.6 410 6,000,000 Poor do S 650,000 6,300 36bac.-. do .11- 2-62 R 151-200 1,460 4.7 310 2,600.000 Fair do S 430.000 8,800 Only part of aquifer tested. California 9N/23E-29F1... .. City of Needles. 6-20-63 R S 7-65 650 3.0 220 600,000 300,000 Fair . Fair 10,300 5. 200 32K1-. do 6-20-63 R s 150-360 1,460 31.0 47 450,000 70.000 Excellent.. . Good 2,100 330 11N/21E-36G2... . Soto Bros Aj-18-63 R S 30-85 850 17.0 50 04, 000 75,000 do do 1.3(H) 1,400 Only part of aquifer tested. 36Q1... W. Riddle 6-19-63 1) R S 12-150 2,500 26. 0 06 160,000 170.000 140.000 Good Excellent... do do 1,200 1,200 1.000 Do.J28 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA Because there is no known reason why average maximum hydraulic conductivities should be substantially higher in the Needles area than in the downstream areas, the reliability of the computed transmissivity is given a lower classification if the implied hydraulic conductivity is substantially higher than 10,000 gpd per sq ft. The data show that the materials tapped by the wells in Arizona are very permeable, the hydraulic conductivity generally having a probable minimum value of 5,000 gpd per sq ft. The probable average hydraulic conductivity will be even higher to the extent that well losses are responsible for the observed drawdown. It is possible, therefore, that some of the actual hydraulic conductivities may be double the probable minimum values shown, in which case the deposits tapped by the wells are as permeable as any that are known to exist in the lower Colorado River area. The hydraulic conductivity values indicate that yields of several thousand gallons per minute with drawdowns of tens of feet can be expected from large diameter wells that tap at least several tens of feet of the alluviums of the Colorado River. The tests of wells in California suggest that similar yields and drawdowns can be obtained in the flood plain at Needles. Some 15 miles north of Needles, however, the yields for a given drawdown and depth of well are likely to be smaller because the hydraulic conductivity of the alluvium beneath the flood plain in this area apparently is more nearly 1,200 gpd per sq ft than the 5,000 gpd per sq ft which characterizes the water-bearing material tapped by the wells in Arizona that were tested. GROUND WATER UNDER NATURAL CONDITIONS MOHAVE VALLEY Under natural conditions, the Colorado River annually overflowed its banks during the early summer runoff and flooded large parts of the flood plain, some of which were remote from the river. The flood waters commonly spread across the flood plain via abandoned channels. Some of the water returned directly to the river, but much of it was trapped, thereby forming sloughs and oxbow lakes. Some of the water evaporated; some of it infiltrated into the ground and became soil moisture, only to be evaporated or transpired later; and some of it infiltrated to sufficient depths to recharge the ground-water reservoir. In addition to this recharge by floodwater, the ground-water reservoir was also recharged by the infiltration of water directly from the river. Over a period of years the recharge to the ground-water reservoir was equal to the discharge from it. The magnitude of the recharge therefore can be estimated by considering the quantity of ground water that was dis- charged. Ground water was discharged principally by the transpiration of water-loving vegetation and by evaporation from free water surfaces. The consumptive use by vegetation under natural conditions can be estimated on the basis of the consumptive use by natural vegetation during recent years, after making adjustments for the changes in that use that have occurred since natural condit ions prevailed. In the Mohave Valley, saltcedar was the dominant vegetation on about 25,000 acres in 1962, arrowweed on about 11,000 acres, mesquite on about 6,000 acres, and tules on about 4,800 acres (U.S. Bureau of Reclamation, 1968). Using data in the reference cited, it can be computed that the average rate of use in 1962 by saltcedar was 3.6 feet per year, arrowweed 3.5 feet per year, mesquite 2.5 feet per year, and tules 8.5 feet per year. To relate the above data to natural conditions, one must recognize that saltcedar was not present in the valley under natural conditions. The 25,000 acres of saltcedar noted in 1962 was established sometime after the early 1920’s. Because saltcedar is an aggressive plant, it is likely that it replaced other vegetation and also in some places became established on ground that up to that time had not supported the growth of water-loving vegetation. To the extent that saltcedar replaced arrowweed, it did not cause a significant change in the discharge of ground water because the average rates of use by the two species are about the same. However, where saltcedar replaced mesquite each acre of saltcedar resulted in an additional discharge of ground water of about 1 acre-foot per year on the average. Where the saltcedar became established on land that had not previously supported the growth of water-loving plants, each acre of saltcedar resulted in about 3.6 acre-feet per year additional discharge of ground water. The number of acres of saltcedar that were replacements for other types of vegetation and that were new acreages are not known. However, on the basis of the distribution of natural vegetation in 1962 it seems probable that about half the saltcedar was a replacement for mesquite and half for arrowweed. If this is true, then the discharge of ground water on land where saltcedar was the dominant vegetation in 1962 would have been 12,000 acre-feet less under natural conditions, or about 78,000 acre-feet per year. Other downward adjustments of consumptive use are needed because much of the acreage mapped as being dominantly tules in 1962 was probably mesquite or arrowweed under natural conditions. If it is assumed that equal acreages of these species were replaced by tules, the consumptive use of water under natural conditions on the 4,800 acres of land occupied by tules in 1962 would have been about 15,000 acre-feet per year. Likewise, evaporation fromGEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J29 free water surfaces was less under natural conditions than in 1962, principally because the open water that is now a part of the Havasu Lake National Wildlife Refuge did not exist until 1938. About 3,000 acres that was under water in 1962 probably supported vegetation under natural conditions. If an average rate of use of 3 feet per acre is assumed to have been used by the vegetation growing on this acreage, an annual consumptive use of 9,000 acre-feet is indicated. In addition, a like amount is assumed to have been consumptively used on the 3,000 acres of cropland that were irrigated in 1962, but which had supported the growth of natural vegetation before being cleared. The total discharge of ground water in the Mohave Valley under natural conditions, therefore, is the sum of the four estimates just made, 111,000 acre-feet, plus the consumptive use of natural vegetation on the other land in the area, 58,000 acre-feet (U.S. Bureau of Reclamation. 1963, table 4, p. D-10)-—a total of about 170,000 acre-feet per year. Because ground-water discharge and ground-water recharge were equal over a period of years, the foregoing figure is also an estimate of annual ground-water recharge under natural conditions. As was stated earlier, the Colorado River was the principal source of this recharge, either by infiltration of water from the river itself or by the infiltration of part of the flood water that annually covered large areas of the valley. If only half the ground-water recharge resulted from infiltration of water directly from the river, an average infiltration rate of 2,500 acre-feet per | year per mile of river length would suffice to supply the recharge in the 35-mile reach north of Topock where most of the consumptive use occurred. Thus, under natural conditions ground water moved from the river to areas of ground-water discharge much as it does today. However, because the river stages then were considerably lower relative to the adjacent ground-water levels than they presently are (1969), especially in the southern half of the valley, infiltration of river water directly to the ground-water reservoir was considerably less under natural conditions than it is today. The contour lines of a water-level map showing natu- | ral conditions would therefore extend away from the river at a considerably larger angle than those shown on plate 2. CHEMEHUEVI VALLEY Under natural conditions the ground-water regimen in Chemehuevi Valley was considerably different from that in Mohave Valley. Although both areas were subject to annual flooding by the Colorado River, the flooded area in Chemehuevi Valley was much smaller than in Mohave Valley. The only extensive area that was subject to flooding in Chemehuevi Valley was about 10 square miles upstream from Site Six. Elsewhere only relatively narrow strips of land along the river were subject to flooding. The depletion of the river as it passed through the valley was due principally to evaporation from the river itself and to the transpiration of water-loving vegetation whose source of supply was ground water that had infiltrated from the river or its flood waters. Depletion by evaporation is estimated to have averaged 32,000 acre-feet per year and by transpiration 20,000 acre-feet per year. The basis for the first estimate is an average width of the river of 0.15 of a mile for the 50-mile reach between the stream-gaging station near Topock and Parker Dam and a net annual evaporation rate of 6.75 feet (p. J37). The second estimate is based on an average rate of use of 3 feet per year by water-loving vegetation on 10 square miles of the flood plain upstream from Site Six. There was virtually no irrigation in the area; so the total consumptive use averaged only about 50,000 acre-feet per year. Any substantial infiltration of water from the river to the ground-water reservoir was limited to the area of water-loving vegetation above Site Six. For most of the valley, therefore, water levels in alluvial deposits bordering the river would have had the same altitude as the mean annual stage of the river, and would have had a comparable downstream slope. Stages of the Colorado River in 1902-3, adjusted for a discharge of 10,000 cfs, at intervals of 5 river miles below the stream-gaging station near Topock are listed in table 3. In general, water-level contours under natural conditions would have had similar values and would have been normal to the axis of the valley except in limited areas where substantial ground-water recharge from tributary areas or from precipitation in the bordering mountains was moving toward the river. In these areas the contours would trend slightly down valley from a line normal to the axis of the valley. GROUND WATER IN RECENT YEARS MOHAVE VALLEY The ground-water regimen in recent years differs considerably from what it was under natural conditions. One of the principal reasons for the difference was the control of the river by the building of dams. The completion of Hoover Dam in 1936 ended the annual flooding of much of the area and consequently eliminated or greatly reduced much of the recharge to ground water that formerly resulted therefrom. Another major change in the ground-water regimen occurred with the closure of Parker Dam in 1938. The aggradation of the river channel which resulted from the closing of the dam is discussed in more detail inJ30 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA the section “River Stages.” In addition to the aforementioned changes, changes in the ground-water regi-jnen also resulted from the building of levees and dredging operations to control the course of the river and to maintain river stages at acceptable levels. Although several thousand acres of land were cleared and irrigated by pumping ground water, this development did not greatly alter the ground-water regimen because the consumptive use by crops was not greatly different from the consumptive use by the natural vegetation which it replaced. Water-level contours for the Mohave Valley as of the 1960’s are shown on plate 2. The contours in the flood plain for the most part were drawn on the basis of water-level data obtained during 1961-62 from a network of shallow observation wells established for this purpose, and on the basis of continuous records of river stage at about 10-mile intervals during the same period of time. Contours outside the flood plain were drawn on the basis of water levels in wells at various times during the period 1962-69. Comparisons of water levels measured at different times during the above period indicated that water levels were quite stable in most parts of the area. Spirit levels were run to most of the wells in the flood plain and to about half the wells on the alluvial slopes on either side of the flood plain. The altitudes of other wells were determined by hand level from nearby bench marks or by interpolation between 10-foot contours shown on the topographic map compiled by the IT.S. Geological Survey from surveys made in 1902-3. The contour map indicates that the Colorado River is losing water to the ground-water reservoir throughout its course through Mohave Valley. The ground water moves from the river to other areas in the flood plain, where it is discharged either by transpiration or by evaporation. An estimate of the magnitude of the infiltration of river water can be obtained by making use of data contained in the 1963 U.S. Bureau of Reclamation study and of data contained in other parts of this report. The infiltration from the river in Mohave Valley is assumed to be equal to the consumptive use in the area that is not supplied directly either from surface water or from inflow other than the river. In the 1963 U.S. Bureau of Reclamation study, it is estimated that the annual consumptive use by saltcedar is 89,000 acre-feet, by arrowweed 40,000 acre-feet, by mesquite 16,000 acre-feet, and by other phreatophytes, excluding tules, 2,000 acre-feet. The 40,000 acre-feet consumed by tules, for the purposes of this analysis, is considered to be mostly river water that is diverted to the large body of open water in the Havasu Lake National Wildlife Refuge and therefore is excluded from the estimates of infiltration of river water. Infiltrated river water is also needed to re- place the net quantity of ground water pumped for irrigation, which is about 12,000 acre-feet. The total discharge of ground water is the sum of the preceding estimates, about 159,000 acre-feet per year. Unmeasured runoff and ground-water inflow from tributary areas is a minor additional source (probably not much more than 5,000 acre-feet per year) for the ground water that is discharged in the area. Therefore, the infiltration of water directly from the river to the ground-water reservoir is about 150,000 acre-feet per year. Most of the infiltration occurs in a 37-mile reach of the river downstream from Bullhead City, Ariz., which implies an average rate of about 4,000 acre-feet per year per mile length of river. However, the actual rate of infiltration at a particular section may be considerably different from the average rate. The actual rate of leakage will depend among other factors on the transmissivity of the deposits through which the ground water moves to points of discharge, the hydraulic connection between the river and the water-transmitting deposits, the distances to the areas of discharge, and the rate of the discharge. The resultant of these and other factors controlling the rate of infiltration are depicted in part by the location of the water-level contours on plate 2. A crude estimate of the transmissivity in certain areas can be obtained by computing the discharge that is occurring in a strip bounded by the river, two parallel or nearly parallel flow lines, and a section of no further significant movement of water away from the river. The following example illustrates the use of the method. Consider a 1-mile-wide strip of land extending northeast from the river at a reach about 2 miles upstream from Needles, Calif. The flow lines, at right angles to the contours, are nearly parallel and the section of no further movement of water from the river crosses near the northeast corner of sec. 1, T. 17 N., R. 22 W., or near the center of the closed 452-foot contour. The strip is about 4 miles long. The consumptive use by native vegetation, which is mostly saltcedar, and by crops within the strip is about 3.5 feet per year, or about 2,200 acre-feet per mile distance from the river, a total of 8,800 acre-feet per year. Presumably, this is the rate at which water infiltrates from the river in this particular 1-mile reach. The average river stage is 470 feet above sea level, and the average water level at the far end of the strip is 452 feet above sea level. Assuming that the consumptive use is at a uniform rate, at a point midway between the river and the section of no further movement of ground water from the river, the rate of movement is half the rate of infiltration, or 4,400 acre-feet per year. The hydraulic gradient causing this movement of water cannot be determined from the spacing of theGEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J31 water-level contours midway between the river and the section of no further movement of ground water from the river because the control for locating the contours is neither sufficiently detailed nor precise enough for this purpose. An indication of the probable gradient can be obtained, however, by using the average gradient of 4.5 feet per mile at the midway section. The transmissivity can be computed according to the following formula: T=893 where T is the transmissivity in gallons per day per foot, Q is the rate of movement of ground water through the midway section in acre-feet per year, I is the hydraulic gradient, in feet per mile, and L is the width, in miles, of the section through which the movement is occurring. For the values previously cited T=893 (4,400) 4.5 =870,000 gpd per ft Although the estimate is crude, it is consistent with the results of pumping tests that were made a few miles north of the above area. In other parts of the valley conditions are less favorable for computing transmissivity by the above method. The contours shown on plate 2 also indicate relative values of the transmissivities in some parts of the valley. The bunching of the contours east of the flood plain in the Fort Mohave area indicates either a zone of relatively low transmissivity or a hydraulic barrier somewhere between the 486- and the 474-foot contour. The 12-foot difference in gradient in 1 mile is about six times larger than the differences per mile upgradient and downgradient. No surface expression identifying the cause of this much steeper gradient was recognized. The gradients of about 2 feet per mile downgradient from the zone of relatively low transmissivity are compatible with the gradients that are common in areas of high transmissivity, such as are indicated by the pumping tests and specific capacities of the irrigation wells within the contours. Although there is no specific evidence to indicate the nature of the restriction to the movement of ground water east of the Fort Mohave area, it is possible that the northwestward projection of the alluvial slope in the Fort Mohave area is significant. Also, the fact that a well drilled to a depth of 780 feet in this area (p. J20) reportedly penetrated no appreciable thickness of gravel may be significant. For lack of adequate control, the westward and eastward extent of the movement of ground water out- side the flood plain could not be determined in most parts of the area. However, by recognizing that at least a small amount of ground water moves from the mountains towards the flood plain in all parts of the area, it follows that at some point between the river and the mountains there must exist a southward gradient and that between this point and the mountains the gradient must be toward the river rather than away from the river as it is in most areas where contours are shown on plate 2. The probable configuration of water-level contours showing this movement of water in opposite directions is indicated on the alluvial slope south of Needles, Calif., and also on the slope east of the flood plain northeast of Needles. CHEMEHUEVI VALLEY The completion of Hoover Dam in 1936 greatly improved control of the discharge of the Colorado River and eliminated the annual flooding of a limited part of Chemehuevi Valley. However, this did not greatly change the ground-water regimen in most parts of the valley. In contrast, the closure of Parker Dam in 1938 had a profound effect on the ground-water regimen because the surface elevation of Havasu Lake which resulted therefrom was 25 to 75 feet above the elevation of the ground water prior to the closure of Parker Dam. Changes in ground-water regimen that resulted from the impounding of water behind Parker Dam can be inferred from table 3. The increase in stage of surface-water levels is shown at intervals of 5 miles downstream from the stream-gaging station near Topock. The values of river stage were obtained from the plan and profile map of the Colorado River, adjusted for a discharge of 10,000 cfs, compiled by the U.S. Geological Survey from surveys made in 1902-3. These stages are considered to be representative of stages under natural conditions. Table 3.—Colorado River stages in 1902-3, estimated average stages of Havasu Lake, and increases in water-level stages at 5-mile intervals below stream-gaging station near Topock Feet above mean sea level Distance below stream-gaging station near Topock (river miles) Estimated average stages of Havasu Lake Colorado River stage in 1902-3 Increase of water-level stage (ft) 0 453 426 27 5 _ 451 420 31 10 449 414 35 15_ _ 448 410 38 20 1 448 405 43 25 448 398 50 30 448 389 59 35 _ 448 380 68 40 448 372 76 1 Site Six.J32 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA From table 3, it is seen that the water-level stage increased from 27 feet at the stream-gaging station near Topock to 76 feet 40 miles downstream, near Parker Dam. It follows that ground-water levels adjacent to the lake rose a like amount. At increasing distances from the lake, ground-water levels initially rose a lesser amount than near the lake; but with continuing infiltration from the lake they, too, eventually rose very nearly the same amount as did the lake. It is likely, therefore, that beneath the lower parts of the alluvial slopes, ground-water levels are very nearly the same altitude as the lake, about 448 feet above mean sea level. As the water from the lake recharged the ground-water reservoir, the recently infiltrated water displaced much of the prelake ground water and forced it away from the lake. The ground water that presently occupies the upper part of the saturated zone near the lake, therefore, is water that recharged the ground-water system after 1938. At a somewhat greater distance, the ground water is prelake water that has risen up through unsaturated deposits in response to increased heads resulting from the level of Havasu Lake being above prelake river levels. Only a limited amount of ground water has been developed in Chemehuevi Valley. The principal development is at Lake Havasu City, Ariz., where ground water is pumped for municipal and industrial use. Elsewhere, the pumpage is mostly for domestic and quasipublic supplies for trailer parks and resort areas. The total pumpage is estimated at 3,000 acre-feet per year. WATER-LEVEL FLUCTUATIONS MOHAVE VALLEY Ground-water levels in Mohave Valley generally fluctuate within an annual range of 2 feet. Exceptions are ground-water levels near pumped wells, irrigated land, and the river. Water levels near a well that is pumped will tend to fluctuate in response to the drawdowns and recoveries of water level resulting from the pumping. Water-level fluctuations in wells in or near land irrigated with surface-water supplies commonly show the effects of recharge from irrigation. They ordinarily reach peak stages shortly after the final irrigation and then recede to minimum stages just prior to the beginning of the next irrigation season. They also tend to rise from year to year until the increased gradient is sufficient to carry away the increase in ground-water recharge resulting from the irrigation. Ground-water levels also fluctuate in response to fluctuations of river stage. In the Mohave Valley the annual range of mean daily river stage is about 6 feet. Near maximum stages generally persist April through August ; near minimum stages, December through January. The daily range of stage at the gaging station below Davis Dam commonly is about 7 feet during the summer, owing largely to variations of releases through the turbines to meet the demands for electricity. The range in stage lessens downstream, although at Needles, Calif., daily ranges of 5 feet are common. The influence of river stage on water levels in the Parker Valley were studied (Metzger and others, 1972). It was found that the daily fluctuations of river stage of about 4 feet affected ground-water levels to a marked degree only a few hundred feet from the river and that there was little evidence of substantial seasonal changes in ground-water levels attributable to river stages at distances of more than half a mile from the river. On the basis of the foregoing study and on the water-level fluctuations observed in wells in Mohave Valley, it is inferred that a similar relation between river stages and ground-water levels exists in Mohave Valley. Fluctuations of water level in Mohave Valley result from the draft on ground-water supplies because of the transpiration of water-loving natural vegetation. A network of shallow wells having about a 1-mile spacing, east-west, and a 2-mile spacing, north-south, was constructed for the purpose of determining the pattern of these fluctuations. Observations were made monthly for more than a year in all the wells, and graphic water-stage recorders were maintained for almost 3 years on three wells. The general nature of the fluctuations that were observed are indicated by the hydrograph of water level in well (B-18-22) 35aaa, which is near the center of the area of transpiration by natural vegetation (figure 23). The hydrograph shows that the water level follows Figure 23.—Hydrograph showing depth to water, in well (B-18-22) 3oaaa, 1962-64. a pattern that is repeated on an annual basis and that is affected almost entirely by the seasonal transpiration of natural vegetation. At distances of a mile or more from the flood plain, water levels probably fluctuate very little except beneath limited areas subject to recharge from infrequent severe storms. CHEMEHUEVI VALLEY Ground-water levels in Chemehuevi Valley fluctuate in response to changes in stage of Havasu Lake. How-GEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J33 ever, the lake is usually maintained within 5 feet of the top of the regulating gates; so the fluctuations of groundwater levels due to changes in lake stage are limited to about 5 feet very near the lake and to smaller ranges at an increasing distance from the lake. At distances of a mile or more, water-level fluctuations due to changes in lake stage are likely to be only a small fraction of such changes. The fluctuations due to other causes, such as changes in rates of recharge or discharge, probably are very small also, except beneath limited areas that may receive a substantial amount of recharge from infrequent severe storms. DEPTH TO GROUND WATER Depth to ground water beneath most of the flood plain in Mohave Valley probably ranges between 9 and 12 feet. The depths to water in two-thirds of 25 shallow wells fairly well distributed over the flood plain were within this range. The minimum depth to water in the wells was 6 feet and the maximum, 20 feet. Depths to water beneath the alluvial slopes bordering the flood plain depend largely on the height of the site above ground-water levels in the adjacent flood plain. A close estimate of the depth to water can be made by noting the altitude of the ground-water level as indicated on plate 2, and subtracting this altitude from the altitude of the land surface at the site in question. In many areas, the alluvial slopes have gradients between 100 and 200 feet per mile toward the flood plain, so depths to water increase at similar rates with distance from the flood plain. Depth to water beneath most of the alluvial slopes of Chemehuevi Valley is governed largely by the height of a given site above the level of Havasu Lake. Exceptions, for which the depth may be much less are limited areas where the ground water is perched, or where the rate of recharge from a tributary area is sufficient to cause a steep hydraulic gradient between the well site and the lake. Depths to water in most existing wells in both valleys are shown in table 10. WATER BUDGETS A water budget is a convenient means of accounting for the water supply of a given area. It can be presented in many different formats as long as the principle that inflow minus outflow is equal to consumptive use plus any decrease of storage or minus any increase of storage is adhered to. In the present study, annual changes in storage are neglected for reasons given in the discussion of budget items in the section “Changes in Ground-Water Stor- age” (p. J’3T). The budget formula, therefore, reduces to the simpler form of inflow minus outflow equals consumptive use. Because of the nature of the data that are available for the budget items, it is further convenient to analyze the measured inflow and outflow items separately from the unmeasured inflow and outflow items. The difference between measured inflow and outflow is the measured streamflow depletion, to which need be added the difference between unmeasured inflow and outflow items to obtain total inflow minus total outflow. The difference between these totals is the consumptive use based on the inflow-outflow method. Following this analysis, consumptive use, based on areas and respective rates of use for these areas, is shown for the convenient categories of natural vegetation, crops, and evaporation from free water surfaces. The total should equal the difference between total inflow and total outflow as previously determined. Any inequality between the values is shown as an imbalance between the two methods for computing consumptive use. The various items of water budgets for the Needles area and the reliabilities of the items are discussed in the following sections, after which budgets are presented for Mohave Valley and Chemehuevi Valley. STREAMFLOW DEPLETION Streamflow depletion is the difference between stream-flow measurements made at the upper and lower ends of selected reaches. The U.S. Geological Survey maintains gaging stations below Davis Dam, near Topock, and below Parker Dam for measuring the discharge of the Colorado River and near Alamo, Ariz., about 32 miles eastward from Parker Dam, for measuring the discharge of the Bill Williams River. The Survey, by maintaining rigid standards for its equipment and stream-gaging procedures, attempts to keep measurement errors to a practical minimum, and is especially concerned about systematic errors which result in streamflow discharge figures being consistently too high or too low. Nevertheless, there exists a practical limit within which measurement errors can be kept. The significance of a given error depends on the use that is being made of the particular discharge measurement. For example, in the study area, an error of 1 percent in a stream-discharge measurement causes an error of about 20 percent in a computation of streamflow depletion. The percentage error is magnified to the above extent because the ratio of stream discharge to streamflow depletion is about 20 to 1. (See table 4.)J34 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA The one out-of-basin diversion is made from Havasu Lake by the Metropolitan Water District of Los Angeles. The computed Streamflow depletions are credited for this diversion and also for changes in storage content of Havasu Lake, where applicable, to obtain the values of streamflow depletion as used in the budgets and the discussion pertaining to the budgets. Table 4 shows yearly values of flow for the period 1950-66 passing the U.S. Geological Survey gaging stations, the change in contents of Havasu Lake, the diversions to the Colorado River aqueduct of the Metropolitan Water District of Los Angeles, and computed streamflow depletions, or the difference in yearly flow between the gaging stations after adjusting measured flows, where applicable, for the inflows, diversions, and storage Changes. The departure of annual depletions from mean values is seen to be as much as 165,000 acre-feet for the upper reach and about 225,000 acre-feet for the lower reach. Some of the yearly variations are due to errors of measurement, some are caused by differences in temperature and precipitation, and some by conservation measures such as dredging and improvement of channel geometry. The reliability of a single annual depletion or the average of even five annual depletions as a measure of the actual depletion is seen to be poor. Loeltz and McDonald (1969) determined to what extent streamflow measurements were a reliable indicator of long-term depletions barring consistent errors of measurement. They found that for any 17-year period of record, such as 1950-66, there was an even chance that the 17-year mean would not differ from a long-term mean, which is the true mean, by more than 14,000 acre-feet in the reach from Davis Dam to Topock, and by not more than 18,000 acre-feet in the reach from Topock to Parker Dam. Also, there was only one chance in 20 that differences would be more than 42,000 acre-feet for the upper reach and 55,000 acre-feet for the lower reach. These findings are used for evaluating the reliability of the streamflow depletion records when the budgets are analyzed in a later section of this report. UNMEASURED RUNOFF Unmeasured runoff consists of the runoff from hundreds of areas ranging in size from a fraction of a square mile to more than 1,500 square miles. It is impractical to measure the runoff from these small areas because of its small magnitude, infrequency of occurrence, and short duration. The runoff may range from practically nothing in an extremely dry year to many times the long-term average in a relatively wet year; this amounts to a range of several hundred thousand acre-feet in the study area. Consequently, unmeasured runoff can cause large differences in annual streamflow depletions. To date, data are inadequate for reliably computing runoff from desert areas. Estimates of runoff for ungaged areas are commonly based on precipitation data, rainfall-runoff relations, character of the terrain, and other parameters. Recently, Moore (1968) proposed a different method for estimating runoff using as a basis the channel geometry and precipitation-altitude rela- Tabli; 4.—Annual streamflows, diversions to Metropolitan Water District, changes in contents of Havasu Lake, and streamflow depletions, 1950-66 (Quantities in thousands of acre-feet] Calendar year Streamflow depletions Colorado River Colorado River Bill Williams Change in Diversion to Colorado River---------------------------------------------- below Davis near Topock, River near contents of Colorado below Parker Davis Dam Gaging Davis Dam Dam Ariz. Alamo, Ariz. Havasu Lake River Dam to gaging station near to Parker aqueduct station near Topock to Dam Topock Parker Dam 1950. 10, 830 10, 640 7 -53 179 10, 470 190 51 241 195U 9, 256 8, 973 96 + 21 231 8, 672 283 145 428 1952. 15, 760 15, 560 158 -54 175 15, 410 200 187 387 1953. 11, 160 10, 980 7 + 33 228 10, 650 180 76 256 1954. 10, 410 10, 139 8, 617 63 -3 341 9, 671 271 193 464 1955. 8, 836 35 -7 417 8, 141 219 101 320 1956. 7, 743 7, 519 7 -1 481 6, 869 224 177 401 1957. 9, 008 8, 882 16 -6 595 7, 997 126 312 438 1958. 11, 740 11, 630 61 + 8 540 10, 890 110 253 363 1959. 9, 196 9, 059 17 + 7 708 8, 186 137 175 312 1960. 8, 763 8, 683 23 -5 894 7, 794 80 23 103 1961. 8, 329 8, 035 6 -8 1, 103 6, 975 294 -29 265 1962. 8, 453 8, 288 19 -2 1, 073 7, 159 165 77 242 1963. 8, 533 8, 339 34 -5 1, 057 7, 251 194 70 264 1964. 8, 022 8, 006 32 + 4 1, 137 6, 652 16 245 261 1965. 7, 735 7, 652 274 + 17 1, 178 6, 356 83 375 458 1966. Average, 8, 169 7, 863 81 -18 1, 146 6, 684 306 132 438 1950-66 9, 526 9, 345 55 -4 675 8, 578 181 151 332GEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J35 tionships. Both methods are used herein for estimating unmeasured runoff'. Hely (in Hely and Peck, 1964) estimated runoff rates for the entire lower Colorado River -Salton Sea area. He used the first cited method of estimating runoff to prepare a map showing runoff rates from small tracts (10 to 20 square miles), making no allowance for infiltration of runoff. The rates shown by Hely therefore are larger than those that occur wherever infiltration of runoff is substantial. Runoff rates for several small drainage areas in Sacramento Valley (fig. 1) were determined by Moore using the second cited method (D. O. Moore, written com-mun., 1968). A comparison of local runoff rates as determined from the channel geometry method by Moore with rates computed by Hely shows large differences, even in the mountains where rates should be comparable. Because both methods are crude and because the results of one method are not known to be more nearly correct than those of the other, it is assumed that both methods have equal merit. On this basis it appears that reasonable rates of runoff from mountains can be obtained by multiplying the rates shown by Hely by a factor of 0.4. This same adjustment is considered applicable also to the Colorado River Valley for areas where the runoff from the mountains crosses only a few miles of alluvium before reaching the flood plain. Where the runoff crosses several tens of miles of alluvium as does the runoff from Sacramento and Piute Valleys and the subarea below the gaging station on the Bill Williams River near Alamo, obviously the runoff as computed from rates of local runoff must be reduced even more—perhaps to only 5 percent of the rates shown by Hely for the tributary valleys and to 10 percent for the Bill Williams River subarea. Estimates of average annual runoff to the flood plain of the Colorado River or to the river itself from the various subareas are listed in table 5. The above estimates are about half of the estimates made by Loeltz and McDonald (1969), principally because Loeltz and McDonald used 40 percent of the runoff rates shown by Hely for all areas rather than using substantially lower percentages of the runoff that originates in large narrow Table 5.—Estimated average annual unmeasured runoff to the flood plain of the Colorado River Runoff Subarea (acre-Jeet) Colorado River valley: Davis Dam to Topoek_______________________________12, 000 Topock to Parker Dam______________________________15, 000 Tributary areas: Piute Valley______________________________________ 1, 000 Sacramento Valley_________________________________ 2. 500 Bill Williams River subarea_______________________ 4. 000 Total unmeasured runoff___________________ 34, 500 tributary areas. Lower percentages for the tributary areas were not used in the earlier study because data for computing runoff on the basis of channel geometry were not available at the time the earlier study was made. Although the estimates of unmeasured runoff as computed for the earlier study are now thought to be too large, the principal conclusions of the earlier study remain unchanged because the unmeasured runoff is one of the smaller items of the budgets. GROUND-WATER INFLOW Ground-water inflow is not measurable directly. One method of computing it is to multiply the transmissivity of the section across which flow is occurring by the width of the section and by the hydraulic gradient normal to the section. A basis for estimating ground-water inflow that is especially applicable to inflow from tributary areas is the ground-water recharge resulting from precipitation in the tributary areas if ground-water recharge is due principally to precipitation and if the percentage of that recharge that eventually becomes inflow to the study area is known. Eakin and others (1951, p. 79-81) have proposed an empirical relation between precipitation and ground-water recharge for use in central Nevada which has proved satisfactory for reconnaissance ground-water studies in that State. The method assumes that ground-water recharge generally is related to average annual precipitation in the following manner: Average annual Percentage of precipitation precipitation that contributes to (inches) ground-water recharge More than 20__________________________________________________ 25 15 to 20_________________________________________________________ 15 12 to 15__________________________________________________________ 7 8 to 12________________________________________________________ 3 Less than 8____________________________________________________ 0 In the areas of Nevada for which the method was developed, three-fourths or more of the yearly precipitation occurs as snow which accumulates in the mountains during the winter. When the snow melts in the spring, it sustains the flow of streams for periods of weeks and months and thereby provides a very effective means of ground-water recharge. In the study area, however, and the lower Colorado River valley as a whole, only a very small percentage of the precipitation is snow. Almost all runoff, therefore, is in direct response to rain storms. As a consequence, most runoff persists only for a few hours, thereby limiting the depth of infiltration from a given storm. This fact, coupled with the infrequent occurrence of runoff, results in much of the infiltrated water being stored temporarily as soil moisture before being returned to the atmosphereJ36 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA rather than eventually recharging the main body of ground water. In recognition of the much poorer conditions for recharge of ground water from precipitation that exist in the study area as compared with central Nevada, half the percentages of precipitation shown in the preceding table are used in the present study for computing ground-water recharge from precipitation. Precipitation in the area is shown on maps prepared by Hely and Peck (1964, pi. 3). Using these maps and half the percentages shown in the preceding table, the recharge to ground water, and by inference also ground-water inflow for the various subareas, is estimated as listed in table 6. Table 6.—Average annual ground-water recharge from precipitation Subarea Recharge (acre-feet) Colorado River Valley: Davis Dam to Topoek_________________________Negligible Topock to Parker Dam______________________________ 880 Tributary areas: Piute Valley___________________________________ 2, 300 Sacramento Valley area_______________________ 12, 300 Chemehuevi Valley (that part west of the Colorado River valley)__________________________ 260 Bill Williams River subarea____________________ 4, 000 Total ground-water recharge (rounded)____ 20,000 The above figures are half those computed by Loeltz and McDonald (1969) because the earlier estimates did not incorporate the downward adjustment of the percentages of precipitation that are used in the present study. The fact that the adjustment was not made in the earlier study does not materially change any of the conclusions that were reached in that study because ground-water recharge is small relative to most other budget values. GROUND-WATER OUTFLOW Ground-water outflow from one area commonly is ground-water inflow to an adjacent area. Ground-water outflow therefore can be computed by the same methods that are used for computing ground-water inflow. Ground-water outflow from the area upstream from the Topock gaging station computed as the product of ground-water gradient, width of saturated section, and transmissivity of the water-bearing material, is at most, a few hundred acre-feet per year, and is therefore neglected. The underflow at Parker Dam likewise is estimated to be so small that it, too, need not be included in the budgets. CONSUMPTIVE USE BY NATURAL VEGETATION The consumptive use of water by natural vegetation is one of the larger budget items. Estimates of this use in the flood plain were made by the U.S. Bureau of Reclamation (1963). These estimates supplemented by estimates of use for areas that were not included in the Bureau of Reclamation study are used for the water-budget items. The estimates of the Bureau of Reclamation were based on a field vegetative survey to which was applied water-use rates developed for the area by Blaney and Harris (1952). Blaney and Harris (1952) utilized the Blaney -Criddle method (Blaney and Criddle, 1945), adjusting experimental data on water-use rates obtained in one area to make them applicable to another area having a different climate. The Blaney-Criddle method, expressed mathematically, is ZJ=KF, in which V is the seasonal consumptive use, K is an empirical coefficient for a specific plant, and F is the sum of the monthly consumptive use factors (sum of the products of mean monthly temperature and monthly percent of daytime hours of the year). In developing rates of use, Blaney and Harris (1952) utilized the results of studies of water use by natural vegetation made by the Geological Survey in Safford Valley, Ariz. (Gatewood and others, 1950). No K coefficients for saltbush were available, so coefficients that had been determined for comparable vegetation were used. To obtain additional data on water use by natural vegetation, in 1961 the Geological Survey, in cooperation with the Bureau of Reclamation, began a study near Yuma, Ariz., of the use of water by arrowweed, saltbush, bermuda grass, and tules. These species were grown in tanks in their natural environment. The results of these studies (Hughes and McDonald, 1966; McDonald and Hughes, 1968) indicate that the K coefficient for arrowweed may be about 50 percent higher than the coefficient that was used by the Bureau of Reclamation. Conversely, the K coefficient for saltbush, as indicated by the tank studies, may be only two-thirds of the coefficient that was used by the Bureau of Reclamation. If the differences are as large as these studies indicate, the estimate of consumptive use by arrowweed in the Mohave Valley would need to be increased about 20,000 acre-feet, whereas the estimate of consumptive use by saltbush would need to be lowered only 500 acre-feet. Because of the sparse acreage of vegetation in Chemehuevi Valley, no adjustments would be needed for that valley. CONSUMPTIVE USE BY CROPS The consumptive use of water by crops is a relatively minor part of the total budgets. In 1962, according to a survey made by the U.S. Bureau of Reclamation (1963), 3,050 acres in the flood plain north of Topock was beingGEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J37 irrigated. Aerial photographs indicate that upstream from Topock an additional 310 acres were being irrigated outside the flood plain, making the total irrigated acreage 3,360 acres upstream from Topock. Detailed information on the acreages of various crops is not available. In general, the crop mix is similar to that for the Parker and Palo Verde Valleys downstream from the study area. An average rate of use of 3.6 feet per year was used for computing consumptive use by crops in these valleys (Loeltz and McDonald. 1969). This rate of use is considered valid for computing consumptive use by crops in the present study also. CHANGES IN GROUND-WATER STORAGE Changes in ground-water storage are indicated by changes of water levels in wells. With an adequate network of observation wells and reasonable knowledge of the amount of water represented by an observed unit change of water level at each site, changes in the amount of ground water in storage can be computed. Significant changes in the trend of water levels over rather large areas for a period of a few years ordinarily result only from a major change or a combination of changes in: (1) the amount of land irrigated, (2) drainage systems, (3) the river channel alinement or profile, or (4) pumpage. The only major change that has occurred in the study area during the budget period is the improvement of channel alinement and geometry of the Colorado River in the reach between Big Bend and Topock which was begun in 1947 and completed in 1960. Although this improvement program lowered water levels over large parts of the flood plain, the average annual decrease in ground-water storage during the period 1950-60 is estimated to have averaged less than 1,000 acre-feet per year. Changes in ground-water storage in the study area, as stated earlier, therefore, are considered small enough to be omitted from the water budget. EVAPORATION FROM WATER SURFACES Evaporation, as a water-budget item in this report, is the net evaporation from a free water surface. It is based on the mean annual lake evaporation as shown by Ilely and Peck (1964, pi. 6), less the average annual precipitation. Hely and Peck found that the available data on evaporation did not warrant mapping evaporation rates at less than 4-inch intervals. Their map shows annual lake evaporation in the Colorado River valley to be about 86 inches. A precipitation map by Hely and Peck (1964. pi. 3) indicates a mean annual rate of about 5 inches in the flood-plain area. The evaporation item in the budgets therefore is computed on the basis of an average rate of 81 inches (6.75 ft) annually, the same rate used by Loeltz and McDonald (1969). The area of free water surface was computed from aerial photographs. COLORADO RIVER VALLEY BETWEEN DAVIS DAM AND PARKER DAM Water budgets for the Colorado River valley between Davis Dam and Topock, and between Topock and Parker Dam are presented in tables 7 and 8, which follow. The budget items are also shown in figure 24, which consists of graphs of the annual streamflow depletions (adjusted for out-of-basin diversions and changes in contents of Havasu Lake), the average of these depletions, the consumptive use estimates, and the unmeasured inflows to the several subareas. Figure 24 also shows the above information on a combined basis for the subarea, Davis Dam to Parker Dam. Values of average consumptive use by natural vegetation, irrigated crops, and evaporation are plotted at the left side of the figure. The net unmeasured inflow is added graphically to the average annual streamflow depletion to show the total estimated depletion based on inflow-outflow items. The difference between the total depletion and the sum of the estimated consumptive use values is the imbalance. Table 7.—Water budget for Colorado River valley between Davis Dam and gaging station near Topock, l!)o0-66 Budget item Quantity (acre-ft per yr) Inflow-outflow: Measured inflow minus measured outflow: Average annual streamflow depletion, 1950-1966 (table 4) _______________________________________ 181, 000 Unmeasured inflow minus unmeasured outflow: Unmeasured inflow (average) : Runoff1 ____________________________ 15, 500 Ground water from tributary areas2__ 14, 600 Total unmeasured inflow (rounded) 30,000 Minus unmeasured outflow (average)---Negligible Total unmeasured inflow minus unmeasured outflow________________ 30, 000 Total inflow minus total outflow_____________ 211, 000 Consumptive use: Natural vegetation (1962)_______________________ 188,000 Irrigated crops (1962)___________________________ 12,000 Evaporation (average)3___________________________ 41,000 Total consumptive use_____________________ 241, 000 Imbalance: Difference by which inflow minus outflow is less than consumptive use____________________ 30, 000 1 From table 5, slim of quantities for Colorado River valley from Davis Dam to Topock, Piute Valley, and Sacramento Valley. 2 From table 6, sum of quantities from Piute and Sacramento Valleys. 3 14,000 acre-feet from the Colorado River, and 27,000 acre-feet from other open water.J38 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA Table 8.—Water budget for Colorado River valley between Topock and Parker Dam, 1950-66 Budget item Quantity (acre-ft per yr) Inflow-outflow: Measured inflow minus measured outflow: Average annual streamflow depletion, 1950-1966 (table 4)__________________________________ 151,000 Unmeasured inflow minus unmeasured outflow: Unmeasured inflow (average) : Runoff1___________________________ 19,000 Ground watera_____________________ 5, 000 Total unmeasured inflow_________ 24, 000 Minus unmeasured outflow (average)___Negligible Total unmeasured inflow minus unmeasured outflow________________________ 24, 000 Total inflow minus total outflow_____________ 175, 000 Consumptive use: Natural vegetation (1962)________________________ 4,000 Irrigated crops (1962)_______________________Negligible Evaporation (average)__________________________ 140,000 Total consumptive use______________________ 144, 000 Imbalance : Difference by which inflow minus outflow is more than consumptive use____________________ 31, 000 1 From table 5, sum of quantities for Colorado River valley from lopock to Parker Dam and Bill Williams River subarea. 3 From table 6, sum of quantities (rounded) for Colorado River valley from Topock to Parker Dam, Chemehuevl Valley, and Bill Williams River subarea. The imbalance for the subarea, Davis Dam to Topock, is nearly equal to but opposite the imbalance for the subarea, Topock to Parker Dam. One might postulate, therefore, that the records of streamflow near Topock may be about 30,000 acre-feet per year too high, on the average. The implied error is less than one-half of 1 percent of the measured flows at the gaging station near Topock, which is within the limits of accuracy claimed by the U.S. Geological Survey for its measurements. Errors in streamflow measurement therefore could be responsible for much or all of the apparent imbalance. One might also postulate that much of the imbalance in the budgets is due to differences between the 17-year average depletion and the long-term or true depletion. As was stated in the discussion of streamflow depletion, there is an even chance that the 17-year mean depletion might vary as much as 14,000 acre-feet from the true mean. It follows therefore that there is one chance in four that the 17-year mean is too low by as much as 14,000 acre-feet. Finally, any one or a combination of errors in any of the larger budget items might be responsible for the imbalances. This fact becomes evident when budgets are computed for other periods and also when the budgets are analyzed relative to budgets for river valleys downstream from the study area. For example, a budget for the river valley between Parker Dam and Imperial Dam computed on the same basis as that used for the present study area shows the consumptive use estimates exceeding the inflow-minus outflow estimates by 150,000 acre-feet a year on the average. To obtain a balanced budget between Davis Dam and Imperial Dam for the period 1950-66, it is therefore necessary to adjust budget quantities 150,000 acre-feet. In making these adjustments, it is assumed that the same percentage adjustment applies to each of the budgets. If all the estimates of consumptive use by crops and by natural vegetation are assumed to be too large by 15 percent and all the estimates of evaporation too large by 10 percent, a virtual balance between inflow less outflow quantities and consumptive use is obtained. The following additional assumptions regarding published flow's at gaging stations are necessary to achieve balanced budgets for each of the three subareas: Average annual streamflow records: (1) Below Davis Dam are correct, (2) near Topock are too high by 4,000 acre-feet, (3) below Parker Dam are too low by 40,000 acre-feet, and (4) at Imperial Dam are correct. The foregoing approach for obtaining balanced budgets implies adjustments that differ considerably from those that appear warranted for obtaining balanced budgets only for the study area without regard to adjacent areas. The approach utilizing a uniform percentage adjustment for each of the subareas is considered a more logical approach than those which consider adjustments for each subarea without regard to adjacent subareas. In view of all the uncertainties regarding true values of all the budget items, no specific adjustments for achieving balanced budgets for the study area are suggested. The budgets, as shown, indicate within reasonable limits the relative quantities of water consumed by crops, natural vegetation, and evaporation. They show that the principal causes of stream depletion are evaporation and consumptive use by natural vegetation. Losses by evaporation can be lowered by suppressing the rate of evaporation and by reducing the area of open water. However, in the study area only a limited reduction of evaporation losses can be expected in the foreseeable future because large-scale evaporation suppression by chemical means on large bodies of open water that are subject to winds and currents is not presently practicable and because fish and wildlife interests oppose any large-scale draining of existing swamps and lakes. Depletion of streamflow due to consumption of water by natural vegetation is estimated at 192,000 acre-feet per year, most of which, 188,000 acre-feet, is in the flood plain upstream from Topock. A large percentage of this use by natural vegetation undoubtedly will beHUNDRED THOUSAND ACRE-FEET GEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J39 4 3 2 1 0 4 0 0.5 5 o a consumptive use, net inflow, and imbalance o rH C\J co ■'t in ID 00 cn o rH C\J co IT) in in in in in in in m in CD CD CD CD CD cn cn cn cn cn cn cn cn cn cn cn cn cn cn cn rH rH rH •—i 1“H «—• r—1 t-H rH rH rH rH rH rH in ID CTl Figure 24.—Graphs showing annual depletion of Colorado River, average consumptive use, and net inflow for selected segments of Colorado River valley between Davis and Parker Dams. 1966J40 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA used eventually for growing crops as additional land is converted to irrigation agriculture. FUTURE DEVELOPMENT OF WATER RESOURCES The greatest potential for developing additional beneficial use of water, as is pointed out in the section on water budgets, is the substitution of crops for natural vegetation having a low economic value and a high water-consumption rate. This kind of development is likely to occur in the flood plain north of Topock where arable land is available that presently supports the growth of native vegetation. In 1962 the vegetation in the flood plain upstream from Topock was predominantly mesquite on some 6,200 acres, mostly arrowweed on some 11,000 acres, and mostly saltcedar on some 24,000 acres. The average yearly rate of use of water was 2.54 feet by mesquite, 3.5 feet by arrowweed, and 3.6 feet by saltcedar (U.S. Bureau of Reclamation, 1963). If the consumptive use rate by crops is assumed to average 3.6 feet per year, the substitution of crops for natural vegetation will result in little, if any, additional depletion of the supply except where mesquite is the natural vegetation that is replaced. The latter substitution would cause an additional depletion of about 1 acre-foot per acre, thus limiting the total additional depletion to slightly more than 6,500 acre-feet per year. Eventually, Indians of the Fort Mohave and the Chemehuevi Indian Reservations probably will exercise their rights to divert water for irrigation. Under Supreme Court of the United States decree, article 8, Arizona v. California, et ah, dated March 9, 1964, subdivision (D), paragraph (1), the Fort Mohave Indian Reservation is entitled to divert main stream water in the lesser amount of 122.648 acre-feet annually or the quantity necessary to supply the, consumptive use for irrigation of 18,974 acres and for the satisfaction of related uses, with priority dates of September 18,1890, and February 2.1911, subject to certain provisions that lands conveyed to the State of California pursuant to the Swamp and Overflow Lands Act [9 Stat. 519 (1850)] as well as accretions thereto, and lands patented to the Southern Pacific Railroad pursuant to the Act of July 27,1866 (14 Stat. 292), shall not be included as irrigable acreage within the Reservation and that the above specified diversion requirement shall be reduced by 6.4 acre-feet per acre of such land that is irrigable. The quantities of the above provisions are subject to adjustment either by decree or agreement upon final determination of the reservation boundaries. Although the ultimate exercising of these rights will represent a sizable diversion from the river, the actual additional depletion of the river will be only a small fraction of the gross diversion because the diversions are likely to be to lands that already are using water at a rate comparable to that of the crops that are likely to be substituted for the natural vegetation. However, the legal depletion of the water supply may be substantial as it is based on measured diversions less measured return flows, a method that likely will give a computed depletion that is at least equal to the consumptive use by crops. Under the same decree, the Chemehuevi Indian Reservation is entitled to divert the lesser of 11,340 acre-feet of water from the main stem of the Colorado River or that quantity necessary to supply the consumptive use required for irrigation of 1,900 acres and for the satisfaction of related uses with a priority of February 2, 1907. Diversions to the Chemehuevi Indian Reservation, which is between Topock and Parker Dam, will result in additional depletion of the available supply both in fact and legally. The lands that are likely to be irrigated are far enough above the flood plain of the river so that the natural vegetation on them does not use appreciable amounts of ground water. Any consumptive use by crops or otherwise therefore will be an additional depletion of the water supply. The legal depletion probably will be the quantity diverted unless credit is received for return flows to the river, most of which probably will be subsurface returns. In contrast to the above developments, additional water might be made available for beneficial use by reducing the amount of water consumed by natural vegetation. A plan for effecting water salvage by eradicating natural vegetation and controlling its regrowth in selected areas where this procedure appears to be practicable has been developed by the Bureau of Reclamation. The U.S. Bureau of Reclamation (written commun., 1971) estimates that about 45.000 acre-feet per year in the Mohave Valley is salvable and thus is available for other needs either in that area or in downstream areas. Undoubtedly future development in Mohave Valley will also include substantial pumpage of ground water either for irrigation or other uses. Most of this development will be by private interests. The depletion of the overall water supply that will result from such development will depend on how much of the consumptive use, is an additional consumptive use rather than a substitute for an existing use. If the pumpage is for the irrigation of land presently supporting the growth of natural vegetation having a consumptive use reouire-ment equal to that of the crops which replace it, no additional depletion will result. However, if the pumpage is for the irrigation of land where the natural vegetation uses little or no ground water, such as much ofGEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J41 the land on the alluvial slopes bordering the flood plain, the consumptive use on such land will be entirely an additional depletion. QUALITY OF WATER Selected chemical analyses of water from wells and one spring in the Needles area are given in table 9. More than one analysis was available for many wells, so the analysis listed is either that of the first water sample obtained from a well or that considered to be the most representative. The chemical analyses indicate that ground water in the Needles area is much better than that in the Parker-Blythe-Cibola area to the south. This was unexpected because both areas have a shallow water table beneath the flood plain in which large-scale evapotranspiration occurs. Of the 95 analyses given in table 9, 46 had dissolved-solids contents of less than 1,000 mg/1 and six had less than 500 mg/1. The smallest dissolved-solids content was 314 mg/1 from well (B-16-20%) llccd. On the other extreme, only six analyses showed dissolved-solids contents of more than 2,000 mg/1. Of these, five were between 2,010 and 2,330 mg/1; the largest dissolved-solids content was 3,290 mg/1 from well (B-17-21)8cec2. Selected analyses are also shown graphically by diagrams based on a method devised by Stiff (1951, p. 15). In the preparation of a Stiff diagram, the chemical equivalent concentrations of the cations, calcium, magnesium, and sodium (plus potassium), are plotted as proportionate line segments on equally spaced parallel lines to the left of a central axis; the equivalent concentrations of the anions, bicarbonate (plus any carbonate), sulfate, and chloride (plus any nitrate), are plotted on the same lines extended to the right of the axis. The ends of the plotted line segments are then connected, thereby forming a geometric pattern characteristic of the mixture of minerals making up the dissolved-solids content of the water whose analysis is plotted. Because the area of a Stiff diagram is not strictly proportional to the dissolved-solids content of the water represented by the diagram and because of the differences in the equivalent weights of the cations and anions, the corresponding dissolved-solids concentration is indicated beneath the individual diagram. CHEMICAL CHARACTER OF COLORADO RIVER WATER Knowledge of the chemical character of Colorado River water is important for understanding the quality of the ground water because the Colorado River is the dominant source of recharge to the aquifers of the Needles area. Although ground-water recharge is chemically altered by several processes, the water generally retains some characteristics of the river water. The chemical character of the river was investigated by Ire-lan (Metzger and others, 1972) as a part of the investigation of the Parker-Blythe-Cibola area, and the discussion that follows is based on that study. The natural chemical regimen of the Colorado River was undoubtedly one of large seasonal variation in both composition and concentration because such variations have been documented by systematic sampling for chemical analysis. However, these sampling programs cannot be expected to duplicate the natural regimen because irrigation, which both reduced the natural river flows and added saline drainage water, was developed in the Upper Basin of the Colorado River before the sampling programs began. Records of a few years of sampling at Willow Beach (about 47 miles north of Davis Dam), Topock, and Yuma, prior to the construction of Hoover Dam, indicate that the usual salinity variations in the Lower Colorado River were very similar to those at the Grand Canyon gaging station (in Grand Canyon National Park). Therefore, the Grand Canyon record, with the qualification given above, probably is representative of the long-time dhemical variations in the Needles area. A relatively stable regimen of flow and salinity of the Colorado River at Grand Canyon existed from 1926, which was after most of the irrigation in the Upper Basin had been developed, until 1963, when Glen Canyon Dam (in Arizona but near Utah border) was closed. During spring floods in most years of this period, the Colorado River at Grand Canyon contained 200 to 300 mg/1 dissolved solids, mostly calcium and bicarbonate, and the sulfate content always exceeded the chloride content. During low-flow periods in fall and winter, the river often contained 1,500 mg/1 dissolved solids but rarely as much as 1,800 mg/1. The content was mostly calcium and sulfate, although considerable sodium and chloride were sometimes present. The variations in the composition and concentration of the Lower Colorado River began to decrease as a result of the closing of Hoover Dam in 1936. By 1941, when Lake Mead spilled, the downstream seasonal variations virtually ended. Since 1941 the annual weighted average dissolved solids (sum) at the sampling station below Hoover Dam has ranged between 606 and 813 mg/1; the sulfate has ranged between 261 and 355 mg/1 and the chloride between 62 and 108 mg/1. Day-to-day concentrations have been above or below’ the annual weighted average but in any one year they generally have departed less than 10 percent from the computed averages. The chemical quality of the Colorado River at specified times during the periods just cited is shown in figureJ42 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA 25. The diagrams indicate the maximum and minimum concentrations for the years of minimum, median, and maximum flow during the period 1926-62 at Grand Canyon and the annual weighted averages for 1950, 1956, and 1965 at Colorado River below Hoover Dam. The wide annual variability of the chemical quality prior to the filling of Lake Mead, and the relatively uniform quality of water released from Hoover Dam are readily apparent. 2 3 > 7> \ 0 ZE> DS 1890 DS 437 DS 1330 4 5 6 17 > I DS 258 DS 1520 DS 226 7 8 9 I Z 2Z DS 813 DS 606 DS 782 EXPLANATION Z f Calcium m Bicarbonate^ Z Sulfate > 2 Chloride J 5 <> O J Magnesium H j Sodium and ^ L potassium 777 w 20 10 10 20 MILLIEQUIVALENTS PER LITER DS 1520 Total dissolved solids, in milligrams per liter Figure 25.—Diagrams of selected chemical analyses of Colorado River water before and after the filling of Lake Mead. Colorado River at Grand Canyon, 1926-62 : 1. Minimum flow year, 1934, maximum concentra- tion, Sept. 21-30. 2. Minimum flow year, 1934, minimum concentra- tion, May 23-31. 3. Median flow year, 1936, minimum concentration, Jan. 1-10. 4. Median flow year, 1936, minimum concentration, May 21-31. 5. Maximum flow year, 1929, maximum concentra- tion, Oct. 11-28, 1928. 6. Maximum flow year, 1929, minimum concentra- tion, June 11-20. Colorado River below Hoover Dam, 1941-65 : 7. Maximum average dissolved-solids contents, weighted average, 1956. 8. Minimum average dissolved-solids contents, weighted average, 1950. 9. Weighted average, 1965. CHEMICAL CHARACTER OF GROUND WATER This section is principally a discussion of the chemical character of ground water obtained from the alluviums of the Colorado River because all but a few wells are perforated in these deposits. The discussion is divided arbitrarily into two parts on the basis of the depths of wells; one part pertains to shallow wells which are sandpoints driven only a few feet below the water table on the flood plain of Mohave Valley, and the other part pertains to all the other wells in both Mohave and Chemehuevi Valley. Irelan (Metzger and others, 1972) concluded from a study of chemical analyses of water from wells in the Parker-Blythe-Cibola area that most of the ground water came from the Colorado River and was altered mainly by three primary processes: concentration by evapotranspiration, precipitation of insoluble calcium and magnesium carbonates, and reduction of sulfate. Because the chemical character of water for the Needles area is similar in many respects to that of the Parker-Blythe-Cibola area to the south, the principal findings of the study of the latter area are considered to be applicable to the Needles area also and are therefore widely drawn upon in the discussion that follows. In making a hypothetical study of the processes by which the chemical composition of Colorado River water might be altered to the various concentrations of ground water in the area, Irelan assumed that the Colorado River initially contained 770 mg/1 total solids and had a chemical composition similar to that shown by diagrams 7-9 in figure 25. The study showed that the process of evaporation within certain limits could produce water similar to known ground water but that beyond these limits the bicarbonate concentrations exceeded those found in ground water. To rectify this, it was assumed that chemical precipitation of calcium and magnesium carbonates begins whenever bicarbonate concentrations reach some specific level, and that as the bicarbonate concentrations exceed this level, precipitation becomes more and more pronounced. This, however, results in sulfate concentrations greater than the chloride concentrations, a condition which is not found in the more highly concentrated waters of the area. One means of reducing the sulfate concentrations is by the precipitation of calcium sulfate; however, in order to do this, calcium concentrations must reach about 600 mg/1 and sulfate about 2,000 mg/1, concentrations which also are not found in real analyses. Another means by which the hypothetical concentrations of sulfate may be reduced is by changing the sulfate to colloidal elemental sulfur, to sulfide ion, or to gaseous hydrogen sulfide (gas having the familiar rotten-egg odor) as a result of bacterial activity, generally in an anaerobic environment, or as the result of an irreversible reaction between the sulfate ion and the wetted but not necessarily dissolved organic matter. During the drilling of the deep test wells of the Parker-Blythe-Cibola area, hydrogen sulfide odor was noticed on many occasions. This, along with organic debris inGEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J43 the deposits, strongly suggests that sulfate reduction has occurred in the ground water. These processes result in hypothetical analyses similar to many real chemical analyses of samples of water obtained in the Parker-Blythe-Cibola area, but there are analyses which are quite different. According to Ire-lan, some of the differences may be attributed to having assumed incorrect limits of concentrations at which various precipitates begin to form. Other differences, however, suggest that base exchange of calcium or magnesium for sodium, or of sodium for calcium or magnesium occurred during the transformation of some of the waters from river water to ground water at sites where the samples were obtained. On the basis of the hypothetical analyses, Stiff diagrams can be prepared, which by visual comparison with Stiff diagrams from real analyses, can be used to show the alteration of Colorado River water after it enters the ground-water reservoir. This procedure is especially applicable along the flood plain of the Colorado River where many wells have been sampled, and there is little doubt but that the ground water has as its source, the Colorado Kiver. The fact that diagrams of chemical analyses of water from two wells are similar and that the samples have nearly exact concentrations of chemical constituents does not of itself necessarily prove that the two samples were derived from the same source. Two examples will be cited to illustrate this point. One example is a com- i parison between water from well (B-17-22) 12ccc2 on the flood plain about 3 miles northeast of Needles (pi. 3) and water from well (B-22-18)12caa (not shown on pi. 3) in Sacramento Valley about 24 miles east of Davis Dam. Stiff diagrams prepared from the two analyses from these wells are very similar; in fact, the concentrations of individual constituents are also very similar. Yet, well (B-17-22) 12ccc2 produced water that had as its source Colorado Biver water, whereas well (B-22-18) 12caa produced water that had as its source local recharge from the mountains near King-man. Another example is a comparison between samples from well (B-20-22)29aec south of Bullhead City (pi. 3) and well 9N/21E-10B1 (not shown on pi. 3) about 9 miles west of Needles in Piute Valley. The Stiff diagram for water from these wells is an hourglass pattern. The water from well (B-20-22)29acc probably originated as Colorado Kiver water and was subject to a nearly complete sulfate reduction. The water from well 9N/21E-10K1 must have originated as local recharge within Piute Valley, a completely different source than that for the water from well (B-20-22)29acc. The chemical character of water from 21 shallow wells in Mohave Valley ranges from 630 to 2,100 mg/1 dissolved solids (sum). Stiff diagrams of analyses of water from these wells (pi. 3), in addition to the ground-water-contour map (pi. 2), which shows ground-water movement eastward from the river, suggest that the ground water was derived from the Colorado Kiver and has been altered principally by the combined processes of evaporation, precipitation of calcium and magnesium carbonates, and sulfate reduction. Diagrams for samples from wells near the river (wells 11N/ 22E-30N1, (B-18-22)22aaa; and (B-17-22)lOccc) are identical with that of the Colorado River since the filling of Lake Mead. Other diagrams (those for samples from wells (B-18-22)3ccc and (B-17-22)14ccc) are similar to that of the Colorado River but slightly more concentrated, which could have been caused by evaporation only. Sulfate reduction, along with the other processes, is apparent from the shape of some of the diagrams (those for samples from wells (B-18-22)2ccc and (B-17-21)6ccc). Diagrams of the more concentrated waters suggest that Colorado River water has been altered by all three processes. Of the 21 shallow wells, eight yielded water having less than 1,000 mg/1 dissolved solids. This concentration is lower than that found for most shallow water in comparable environment in downstream areas. As might be expected, Stiff diagrams prepared for the rest of the analyses from wells in the Needles area (pi. 3) show considerably more variety of chemical types than for the shallow wells. Again, diagrams for most of the wells indicate alteration of Colorado River water by the three primary processes. Diagrams of analyses of samples from wells near the river are a pennant pattern similar to those of Colorado River water (diagrams 7-9 in fig. 25). Some analyses are identical with that of water released from Hoover Dam after the filling of Lake Mead, and some show a slight increase in chemical constituents, which probably is caused by evaporation. Eastward from the river the concentrations of dissolved solids increase. If the water was derived from the Colorado River, the water has been altered primarily by evaporation, precipitation of carbonates, and sulfate reduction. For the area about 4 miles east of the river in Tps. 17 and 18 N., the ground wafer probably is altered Colorado River wafer because ground-water contours (pi. 2) indicate that ground-water movement is towards this area from the Colorado River and because evapotrans-piration occurs from the shallow water table beneath the flood plain. Thus, the ground water beneath this area probably is Colorado River water that had been concentrated by evaporation along with the other processes mentioned previously.J44 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA Although the explanation for the concentration is reasonable in the part of the flood plain just mentioned, some doubt about the validity of the explanation is cast when the analyses of samples from wells in T. 19 N., R. 22 W. (26aab, 26ddd, 36bab, and 36bac) are considered. These analyses show a range of dissolved solids from 1,120 to 1,620 mg/1 and Stiff diagrams similar to those discussed above. Water-level contours indicate that the movement of ground water is southward and that the Colorado River may be a possible source. However, if the river is the source, the chemical quality of the water would have had to have been altered by evaporation and perhaps by other processes because the concentrations of chloride of the samples from the wells are much higher than any known concentrations of chloride of Colorado River water during historic time. Sufficient concentration by evaporation seems unlikely, however, because the flood-plain area in which such evaporation could occur appears to be inadequate. Furthermore, evapotranspiration near the wells is impossible because the depth to water is 90 feet and more. It is possible that the water obtained from the wells represents a mixture of Colorado River water that has not been altered appreciably and of local recharge from ! precipitation on the mountains bordering the east side of the valley. However, the chemical quality of the local recharge probably is good because of the rock types composing the mountains. There are no wells east of the wells that were sampled for obtaining data regarding the chemical quality of the recharge from the mountains. Still another possibility is that the water in the wells is a mixture of Colorado River water and of water containing relatively high concentrations of sodium and chloride that might be leaking upward through the Bouse Formation. If any of the Stiff diagrams represent local recharge, the most probable is that of the sample from well (B-21-21 )21cbb (pi. 3). The water likely is recharge from the Black Mountains to the east, although definitive evidence is lacking. Stiff patterns similar to the above were constructed from the analysis of samples from two other wells, well 8N/23E-20J1 and a well (not shown on pi. 3) near Chemehuevi Wash west of the report area. The source of water for the first well could be either the Colorado River or local recharge. The source for the second well is local recharge because the well is about 20 miles west of Havasu Lake, and the water level in the well is more than 400 feet higher than the lake. Irelan (Metzger and others, 1972) suggests that Stiff diagrams of water in the Parker-Blythe-Ci’bola area that resemble an hourglass may be indicative of Colorado River water that has been altered by a nearly complete reduction of sulfate. Stiff diagrams of samples from several wells in the Needles area also can be explained on this basis. For example, wells (B-20-22) 29acc, (B-18-22)23bcc2, and (B-18-22)23ccc2 (pi. 3) all are near the Colorado River and are surrounded by wells containing altered Colorado River water. However, the same cannot be said about the hourglass diagrams of samples from the three wells that are near Topock and east of the Colorado River. Ground-water movement near the wells is westward to the Colorado River, the water from well (B-16-21)15add being'local recharge, whereas that from the two wells in T. 16 N., R. 2OV2 W., probably represents ground-water underflow from Sacramento Valley. Well (B-16-19)8dab, some 10 miles eastward and which probably also represents underflow from Sacramento Valley has an analysis that plots as a pennant pattern. However, this water eventually may be altered by sulfate reduction as it moves westward to the type of water found in the three wells nearer Topock. SUITABILITY OF GROUND WATER Along the Lower Colorado River, the suitability of water for domestic use is based on the concentration of ! dissolved solids as compared to that of Colorado River water. Any water containing about the same concentration as Colorado River water (between 600 and 800 mg/1 dissolved solids and less than 1.5 mg/1 fluorides) is acceptable to residents as water for domestic use. The more common constituents in drinking water are objectionable only when they are present in such concentrations as to be noticeable to the taste. Such concentrations are difficult to define because of differences between individuals. According to Hem (1959, p. 239-240): “A chloride concentration of 200 to 300 mg/1 in water containing an equivalent amount of sodium is enough to give a noticeable salty taste to most people. The presence of sulfate in similar concentrations will have a laxative effect on some of those who drink the water.” Many of the analyses given in table 9 contain or exceed the concentrations given by Hem. Nevertheless, where better water is not available, the water is used for domestic purposes. Most of the analyses in table 9 contain less than 1.5 mg/1 of fluoride, which is an upper limit on the amount of fluoride that may cause mottling of tooth enamel in children. Because the Needles area has an arid and hot Climate, more water than average is consumed per person, and consequently the upper limit for fluorides may be somewhat less. "Whether water is suitable for irrigation depends not only on the chemical character of the water being applied but also on other factors such as salinity of the soil, drainage, amounts of water applied, manner ofGEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J45 application, and types of crops to be grown. The most significant items relative to the chemical character of water are the dissolved-solids content, the amount of sodium relative to calcium and magnesium, and the concentration of substances, such as boron, that may be toxic to plants. The U.S. Salinity Laboratory (1954, p. 69-82) in its classification of irrigation waters lists the sodium hazard and the salinity hazard as two of the most significant factors to be considered. The sodium hazard is based on “the probable extent to which soil will adsorb sodium from the water and the rate at which adsorption will occur as the water is applied.” The salinity hazard is much simpler to define, and is based solely on the electrical conductivity of the irrigation water. The salinity hazard is defined as low if specific conductance values, in micromhos per centimeter, are between 0 and 250, as medium if between 250 and 750, as high if between 750 and 2,250, and as very high if more than 2,250. For the Needles area, none of the analyses would be classified as having a low salinity hazard and only four as having a medium salinity hazard. The balance of the analyses would be classified as having a high to very high salinity hazard. Some of the analyses showing specific conductances in the very high salinity hazard range are for samples from irrigation wells that are being used successfully to grow crops in the Needles area. This indicates that chemical character alone is not adequate criteria to determine if a water is suitable for irrigation and that other factors such as those given in the first sentence of this paragraph also must be considered. REFERENCES Blaney, H. F., and Criddle, W. D., 1945, A method of estimating water requirements in irrigated areas from climatological data: U.S. Dept. Agriculture, Soil Conservation Service, 59 p. Blaney, H. F., and Harris, Karl, 1972, Consumptive use of water rates in the lower Colorado River basin (provisional) in Report on water supply of the lower Colorado River basin, project planning report: U.S. Bur. Reclamation, Boulder City, Nev., 427 p. Eakin, T. E., and others, 1951, Contributions to the hydrology of eastern Nevada: Nevada Water Resources Bull. 12, 171 p. Fenneman, N. M., 1931, Physiography of Western United States: New York, McGraw-Hill, 534 p. Ferris, J. G., and others, 1962, Theory of aquifer tests: U.S. Geol. Survey Water-Supply Paper 1536-E, p. 69-174. Gatewood, J. S., and others, 1950, Use of water by bottom-land vegetation in lower Safford Valley, Ariz.: U.S. Geol. Survey Water-Supply Paper 1103, 210 p. Hely, A. G., and Peck, E. L., 1964, Precipitation, runoff and water loss in the lower Colorado River-Salton Sea area: U.S. Geol. Survey Prof. Paper 486-B, 16 p. Hem, J. D., 1959, Study and interpretation of the chemical characteristics of natural water: U.S. Geol. Survey Water-Supply Paper 1473, 269 p. Hughes, G. H., and McDonald, C. C., 1966, Determination of water use by phreatophytes and hydrophytes: Am. Soc. Civil Engineers, v. 92, no. HY2, Proc. Paper 4714, p. 63-81. Ives, J. C., 1861, Report upon the Colorado River of the West: U.S. 36th Cong., 1st sess., House Executive Doc. 90, 154 p. Johnson, A. I., 1967, Specific yield—Compilation of specific yield for various materials: U.S. Geol. Survey Water-Supply Paper 1662-D, p. D1-D74. Lee, W. T., 1908, Geologic reconnaissance of a part of western Arizona: U.S. Geol. Survey Bull. 352, 96 p., 11 pis., 16 figs. Loeltz, O. J., 1960, Source of water issuing from springs in Ash Meadow Valley, Nye County, Nevada [abs.] : Geol. Soc. America Bull., v. 71, no. 12, p. 1917-1918. 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, no. IR 1, Proc. Paper 6457, p. 65-78. McDonald, C. C., and Hughes, G. H., 1968, Consumptive use of water by phreatophytes and hydrophytes near Yuma, Ariz. : U.S. Geol. Survey Prof. Paper 486-F, 24 p. Metzger, D. G., 1965, A Miocene)?) aquifer in the Parker-Blythe-Cibola area, Arizona and California, in Geological Survey Research 1965: U.S. Geol. Survey Prof. Paper 525-C, p. C203-C205. ------1968, The Bouse Formation (Pliocene) of the Parker- Blythe-Cibola area, Arizona and California, in Geological Survey Research: U.S. Geol. Survey Prof. Paper 600-D, p. D126-D136. Metzger, D. G., Loeltz, O. J., and Irelan, Burdge, 1972, Geohydrology of the Parker-Blythe-Cibola area, Ariz. and Calif.: U.S. Geol. Survey Prof. Paper 486-G, (In press.) Moore, D. O., 1968, Estimating mean runoff in ungaged semi-arid areas: Internat. Assoc. Sci. Hydrology Bull., v. 13, p. 29-39. Noble, L. F., 1931, Nitrate deposits in southeastern California, with notes on deposits in southeastern Arizona and southwestern New Mexico: U.S. Geol. Survey Bull. 820, 108 p. Olmsted, F. H., Loeltz, O. J., and Irelan, Burdge, 1972, Geohydrology of the Yuma area, Arizona and California: U.S. Geol. Survey Prof. Paper 486-H, (In press.) Rush, F. E., and Huxel, C. J., Jr., 1966, Ground-water appraisal of the Eldorado-Piute Valley area, Nevada and California: Nevada Dept. Conserv. and Nat. Resources, Water Re-sources-Reconn. Ser. Rept. 36, 29 p. Smith, Winchell, and Heckler, W. L., 1955, Compilation of flood data in Arizona, 1862-1953: U.S. Geol. Survey open-file report, 113 p. Stiff, H. A., Jr., 1951, The interpretation of chemical analyses by means of patterns: Jour. Petroleum Technology, p. 15. Theis, C. V., 1935, Relation between the lowering of the piezometric surface and the rate and duration of discharge of a well using ground-water storage: Am. Geophys. Union Trans., pt. 2, p. 519-524. Theis, C. V., Brown, R. H., and Meyer, R. R., 1963, Estimating the transmissibility of aquifers from the specific capacity of wells in Methods of determining permeability, transmissibility and drawdown : U.S. Geol. Survey Water-Supply Paper 1536-1, p. 331-340.J46 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA Thompson, D. 6., 1929, The Mohave Desert region, Calif.: U.S. Geol. Survey Water-Supply Paper 578, 759 p. U.S. Bureau of Reclamation, 1953, Memorandum supplement to report on water supply of the lower Colorado River basin, project planning report, November 1952 : 48 p. ------1963, Lower Colorado River water salvage phreatophyte control, Arizona-California-Nevada, reconnaissance report: 57 p. U.S. Congress, House of Representatives, Committee on irrigation of arid lands, 1922, Hearings on H. R. 11449, A bill to provide for the protection and development of the lower Colorado River basin, Appendix A: U.S. 67th Cong., 2d sess., p. 138-148. U.S. Salinity Laboratory Staff, 1954, Diagnosis and improvement of saline and alkali soils: U.S. Dept. Agriculture Handb. no. 60,160 p.INDEX Page Age and paleontology of the Bouse Formation. J12 Age, Bouse Formation........................ 12 Colorado River aluviums................ 16 Alluvium, younger........................... 16 Alluviums, older............................ IS Alluviums of the Colorado River and its tributaries................... 8, IS Altitude of Havasu Lake...................... 5 Analyses, ground water....................... 3 samples from wells..................... 44 Aquifer, the term........................... 23 Aquifers, hydrologic characteristics........ 28 Arizona system of well numbering............. 7 Arrowweed, annual consumptive use of water. 28, 30, 40 Average daily stages at Needles............. 22 Basal limestone of Bouse Formation.......... 11 Bedrock...................................... 8 Black Mountains........................... 5,15 Bouse Formation...........................8,9,10 California system of well numbering.......... 7 Cambrian quartzites....................... 13 Changes in ground-water storage............. S7 Charophytes................................. 12 Chemehuevi Indian Reservation--------------- 40 Chemehuevi Mountains......................... 5 Chemehuevi Valley.....................5,9,29, Si ground-water levels.................... 32 Chemical analyses of water............41,42,51 Chemical character, Colorado River water_ 41 groundwater........................... 42 Chemical quality of the Colorado River.... 41 Clams....................................... 12 Climate...................................... 6 Coefficient of transmissibility, the term. 24 Colorado River alluviums, age............... 16 Colorado River Valley between Davis Dam and Parker Dam........................... S7 Colorado River water, chemical character-- 41 Concentration of water by evapotranspiration. 42 Consumptive use, crops...................... S6 natural vegetation...................28,86 Crops, consumptive use of water............. S6 Davis Dam.................................... 3 Dead Mounta ns............................... 5 Definition of terms............... ....... 28 Depletion of streamflow due to consumption of water................................. 38 Depth to ground water....................... 88 Discharge of ground water................... 19 Discharges and stages of river.............. 21 Diversion of water for irrigaton............ 40 Diversion of water from river............... 20 Driller’s logs of wells........... ....... 56 Drinking water constituents................. 44 Eldorado Valley.............................. 8 Evaporation from water surfaces............. 87 Evaporation losses.......................... 38 [Italic page numbers indicate major references] Page Fanglomerate............................... J8,9 Miocene age............................... 8 unconformity at base...................... 9 Fluctuations of water level in Mohave Valley. 32 Future development of water resources...... 40 « Geologic units and events...................... 8 Ground water, analyses......................... 3 chemical character....................... 42 depth.................................... 88 discharge in Mohave Valley............... 29 in recent years.......................... 29 inflow................................... 86 occurrence............................... 18 outflow.................................. 86 under natural conditions................. 28 regimen in Chemehuevi Valley............. 29 resources of the Needles area............ 18 storage changes.......................... 87 suitability............................. 44 Havasu Lake.................................... 5 Historical sketch............................. 19 Hoover Dam.................................. 5,29 Hydraulic conductivity, the term............. 24 Hydrologic characteristics oi aquifers........ 28 Imperial Valley........-...................- 3 Infiltration of water.......—.............. 30 Interbedded unit of Bouse Formation........... 11 Investigation methods.......................... 8 Irrigation of land.......................... 20 Irrigation water.............................. 44 Lake Havasu City.............................. 19 Lithology and thickness of Bouse Formation. 11 Location of area........................... 8 Losses of water by evaporation................ 38 Maximum discharges............................ 23 \lerychippu8............................... 8,9 Mesquite, annual consumptive use of water... 28, 30,40 Methods of investigation....................... 8 Mississippian crinoidal limestone............ 14 ground water in recent years............. 29 ground water under natural conditions -.. 28 water-level fluctuations............... 82 Mohave Valley.............................. 5,10 ground water discharge................... 29 Montmorillonite............................... 11 Needles, average daily stages..............19,22 Needles area, ground-water resources.......... 18 Neutron-probe data............................ 25 Nevada system of well numbering................ 7 Newberry Mountains............................. 5 Nonequilibrium formula of Theis............... 26 Occurrence of ground water.................... 18 Older alluviums............................... 18 Ostracodes.................................... 12 Page Paleontology and age of the Bouse Formation.. J12 Paleozoic carbonate rocks.................. 8 Parker Dam..................................... 3 Piedmont, the term......................... 14 Piedmont gravels, the term.................... 14 Piedmont gravels (unit C)..................... 14 Precipitation, area............................ 6 Nevada.................................... 35 Precipitation of insoluble calcium and magnesium carbonates............................. 42 Pumpage, total, in Chemehuevi Valley....... 32 Pumping of ground water for irrigation..... 21 Pumping tests..............................25,26 Quality of water.............................. 41 Rain in the arid southwest.................... 18 Recharge of ground water from precipitation. 36 Recharge of ground water reservoir............ 18 Recovery data versus time for well............ 26 Red Spring.................................... 12 Reduction of sulfate........................42,44 Regimen of flow and salinity of the Colorado River at Grand Canyon............. 41 River stage, changes.......................... 22 records................................... 22 River stages.................................. 21 Rocks, water-bearing characteristics........... 8 Runoff, unmeasured............................ 84 Runoff rates for Colorado River-Salton Sea area............................... 35 Salinity hazard of irrigation water........... 45 Saltcedar, annual consumptive use of water... 28, 30,40 Samples from wells, analyses.................. 44 Shinarump Member of the Chinle Formation. 14 Sodium hazard of irrigation water............. 45 Soil-moisture profiles........................ 26 Soil-moisture studies......................... 26 Sonoran Desert section of Basin and Range physiographic province.............. 3 Specific yield, the term...................... 24 Stages and discharges of river................ 21 Stiff diagrams..............................43,44 Storage coefficient, the term................. 24 Streamflow depletion.......................... 38 Structure of sediments........................ 16 Sulfate reduction............................. 43 Surface features of area....................... 8 Temperature of area........................... 6 Thickness and lithology of Bouse Formation.. 11 Transmissivity, the term...................... 24 Transmissivities, relative values............. 31 Tules......................................... 28 Unconformity at the base of the fanglomerate. 9 Unconformity between the fanglomerate and the Bouse Formation................ 9 Unit B of older alluviums..................... Is J47J48 INDEX Page Unit C (piedmont gravels)................ JIS U nit D of older alluviums............... 15 Unit E of older alluviums................ 15 Unmeasured runoff__________________________ H Use of river water.......................... 20 Vegetation, consumptive use of water......... 28,36 Volcanics of the Black Mountains........... 8 Page Water-bearing characteristics, Bouse Formation................L....................- Colorado River alluviums------------------ rocks..........—l...................... Water budgets......— L..................... Colorado River valley__________________ Water for domestic use_____________________ Water-level contours for the Mohave Valley.. J12 16 8 S3 37 4* 30 Page Water-level fluctuations in Mohave Valley__ J32 Water quality.............................. 41 Water-quality data........................... 8 Water resources, future development........... 40 Water surfaces, evaporation.................. 37 Well construction, common types.............. 19 Well-numbering systems______________________ 7 Younger alluvium----------------------------- 16TABLES 9-11J50 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA Table 9.—Chemical analyses of water from wells and from Red Spring, Needles area, Arizona-California-Nevada [Analyses in milligrams per liter, except as indicated. Analyses made in U.S.G.S. laboratory, Yuma, Ariz., Use of water: Irr, irrigation; PS, public supply; Dom, domestic; T, test hole; Un, unused; S, stock] Perfo- rated interval Silica Cal- Mag- So- Potas- Bicar- Sul- Chlo- Fluo- Dis- Hardness as CaC03 Calcium, Noncar- Specific conduct- ance Per- cent (SiOi) cium nesium dium sium bonate fate ride ride solved magne- bonate (micro- pH so- sampled land- surface datum) (Ca) (Mg) (Na) (K) (HCOj) (SO,) (Cl) (F) solids sium mhos at 25°C) dium Arizona (B-13-20) 4dbb 6-10-68 50-90 PS 24 127 52 212 172 450 268 1.1 1,220 530 389 1,970 7.4 46 6-10-68 117-165 PS 21 92 39 313 236 370 192 1.2 1,050 390 196 1,650 7.5 54 (B-14-20) 16ccd.._. 6- 6-68 180-280 S, PS 2 130 61 414 36 330 775 4.0 1,730 575 546 3,230 7.6 61 (B-16-19) 8 dab... 6- 5-68 . Dom 8 47 7.4 122 58 232 87 1.0 533 148 100 880 7.8 64 (B-16-20K)11 ccd. 3- 9-62 189-420 Dom 16 21 4.3 91 144 33 77 3.0 314 70 0 602 7.6 74 3- 9-62 332-490 16 36 8.5 158 120 73 201 3.2 558 125 26 1,060 7.7 73 (B-16-21) 15add . 9-11-62 PS 35 30 13 86 158 62 84 .9 390 129 0 664 7.1 59 (B-17-21)5bcd 4-23-68 PS 26 143 65 342 208 280 642 .7 1,600 625 454 2,930 7.5 54 5- 2-62 16-18 T 18 124 50 170 270 275 268 .. 1,040 515 294 1,910 7.7 42 7abd lrr 22 151 47 231 348 450 225 .9 1,300 570 284 2,100 7.7 47 7bbd 2-15-67 21 180 48 270 344 475 322 .6 1,490 645 361 2,390 7.9 48 7c bd lrr 19 204 72 237 392 500 338 .6 1,570 805 484 2,530 7.6 39 5- 1-62 15-17 T 27 182 79 429 452 800 362 .. 2,100 780 410 3,350 7.8 54 5-20-65 83-85 T 21 370 106 666 272 600 1,390 .. 3, 290 1,360 1,140 5,470 7.4 52 5- 1-62 13-15 T 17 138 76 178 360 525 145 .. 1,260 658 361 1,880 7.4 37 (B-17-22) lbaa 2-18-67 60-70 Dom 21 266 92 382 352 700 605 .8 2,240 1,040 752 3,580 7.7 44 lObbb.. 5- 1-62 10-12 T 21 221 76 135 410 550 178 .. 1,390 865 529 2,140 7.45 25 5-21-65 20-22 T 23 98 29 121 216 258 129 .9 765 364 187 1,250 7.7 42 lOddd 5-17-65 61-63 T 25 111 32 90 232 267 95 . 5 737 408 218 1,200 7.5 32 5- 1-62 16-18 T 18 94 61 144 248 412 118 .. 971 486 282 1,520 7.4 39 llbbb 5- 1-62 16-18 T 13 156 56 390 326 538 455 .. 1,770 620 352 2,770 7.4 58 4-14-67 Irr 23 146 50 229 352 450 220 .8 1,300 570 282 2,100 7.4 47 llcdd Irr 23 145 47 230 348 450 212 .8 1,280 555 270 2,030 7.5 47 5- 1-62 16-18 T 21 120 34 236 384 425 138 .. 1,170 438 123 1,850 7.35 54 5-18-65 70-72 T 24 153 48 124 420 317 123 .4 999 580 236 1,620 7.7 32 12ddd 5-19-65 72-74 T 21 122 35 314 436 462 208 .7 1,380 450 92 2, 220 7.7 60 5- 1-62 19-21 T 23 174 62 293 454 600 235 . 1,610 690 318 2, 470 7.5 48 Irr 24 238 82 301 480 675 345 .8 1,910 930 536 2,910 7.6 41 13bbb 22 158 43 230 356 450 218 .9 1,300 570 278 2,090 7.5 47 3- 2-67 64-143 Irr 25 150 45 313 380 538 260 1.2 1,520 560 248 2,420 7.6 55 13 15 T 13 143 42 179 306 450 141 .. 1,120 528 277 1,730 7.65 42 2-15-67 30-65 PS 23 121 32 157 264 362 128 .8 956 435 218 1,480 7.5 48 15ddc 3- 2-67 35-65 PS 20 102 31 125 200 317 111 .6 807 380 216 1,310 7.5 42 (B-18-22) 2ccc. 5- 2-62 16-18 T 16 89 23 99 220 167 126 . 630 316 136 1,080 7.3 40 16-18 T 16 126 43 143 226 433 117 . 991 490 304 1,390 7.6 39 Irr 17 80 25 177 228 192 212 .4 817 302 115 1,400 7.4 56 24-26 T 19 120 83 480 427 575 522 .. 2,010 640 290 3,420 7.85 62 60-95 Irr 20 105 30 120 256 733 136 .4 772 384 .. 1,290 7. 55 40 5- 2-62 21-23 T 19 102 28 108 236 242 111 .. 730 370 176 1,200 7.9 39 3- 1-67 65-95 Irr 19 71 17 94 204 no 119 .4 532 246 78 930 7.6 45 23bcc2 3- 1-67 60-304 PS 17 71 15 73 208 90 93 .4 461 238 68 829 7.6 40 20 78 22 102 2:6 145 113 .4 598 284 90 1,020 7.8 44 23cdh Un 19 180 48 218 288 470 278 .6 1,360 645 409 2,160 7.7 42 T 20 108 49 356 306 425 390 .. 1,500 470 219 2, 520 7.5 62 Irr 22 190 55 376 292 475 555 .6 1,870 700 460 2,990 7.7 54 25abb2 2-28-67 19 182 62 281 244 388 508 .6 1,560 710 510 2, 690 7.7 46 27bbc 11- 1-62 80-126 S, Irr 18 102 27 94 170 292 88 . 5 707 364 224 1,150 7.4 36 27dddl 5- 2-62 29-31 T 15 135 37 115 288 312 127 .. 885 490 254 1,500 7.5 34 27ddd2 PS 18 158 40 136 236 362 202 . 5 1,040 560 366 1,700 7.9 35 PS 18 102 28 108 216 258 111 .5 734 368 191 1,210 7.6 39 Irr 14 105 37 137 ‘254 325 117 .6 863 416 208 1,340 7.6 42 Irr 17 158 44 161 240 412 212 .6 1,120 575 378 1,800 7.2 38 5- 2-62 22-24 T 22 70 25 265 256 362 190 . 1,060 278 68 1,770 7.3 68 11hhd PS 24 105 34 159 224 238 148 1.2 921 400 216 1,530 7.6 46 Irr 19 82 31 348 220 375 365 1.1 1,330 332 152 2, 240 7.5 70 15 76 22 134 200 275 87 .4 709 282 118 1,120 7.2 51 18 79 24 121 182 283 82 .2 698 296 147 1,080 6.8 47 4-13-67 18 68 20 152 224 183 145 . 5 699 250 66 1,230 7.5 57 24 116 36 121 236 267 161 .4 843 437 244 1,350 7.1 38 4-11-67 150-220 Irr 21 87 27 279 228 250 342 1.1 1,120 326 139 2.050 7.7 65 Irr 22 150 53 293 182 400 468 .6 1,480 590 441 2,600 7.3 52 Irr 28 86 29 444 205 250 615 2.0 1,560 335 167 2,920 7.5 74 Irr 28 92 31 454 195 288 622 2.3 1,620 355 195 2,980 7.4 74 4 23-68 PS 18 174 56 200 272 540 222 .7 1,350 665 442 2,090 7.7 40 PS 24 180 50 145 154 400 302 .5 1,180 655 528 1,880 7.2 32 PS 28 92 29 142 180 267 163 .3 811 348 200 1,270 7.0 47 37 27 0.6 211 188 100 174 9.5 653 70 0 1,110 8.1 87 4-24-68 PS 38 73 3.4 212 152 120 282 4.0 808 196 72 1,430 7.4 70 4-24-68 PS 8 14 2.2 141 130 120 82 1.7 434 44 0 746 8.2 88 s 24 52 14 73 162 95 81 .4 420 188 55 724 7.2 46 44 65 10 805 128 140 1, 200 4.5 2,330 204 99 4,430 7.7 90 (B-21-21) 21 ebb.. 3- 7-62 . Dom 11 11 1.2 156 124 65 57 4.8 518 28 0 763 8.1 92 California 4N/24E-17Z1 5-13-68 Un 20 32 1.0 230 96 180 222 1.7 745 84 6 1,330 7.5 86 5N/24E I 6K1 3- 8-62 PS 16 112 25 241 250 462 158 1.1 1,140 384 179 1,810 7.6 60 36TC2 3- 8-62 PS 29 116 27 274 254 550 151 1.1 1,280 400 192 1,840 7.4 60 7N/24E-6F1... .. 3- 7-62 28-180 PS 26 104 34 378 124 288 675 1.2 1,470 398 296 2,520 7.6 67 8N/23E-15A1 . 2-16-67 30-85 Irr 20 118 35 140 340 267 132 .4 882 440 161 1,410 7.6 41 15G1 . . 2-16-67 39-51 10 108 29 114 192 300 118 .6 776 390 232 1,270 7.6 39 20J1 3- 7-62 478-520 PS 14 31 4.7 124 128 95 113 .8 446 97 0 785 7.7 74 9N/22E-1D1 6- 1-61 . 34 66 33 177 219 131 202 .4 711 300 120 1,220 7.5 49 1- 4-62 33 60 27 172 198 181 196 .9 772 260 98 1,280 7.5 59 9N/23E-28E1 5- 1-62 10-12 T 19 205 65 151 348 575 160 .. 1,350 780 494 2,050 7.65 30 29E1 .. 6-20-63 . PS 36 100 58 227 192 225 414 1.5 1,160 486 328 2,040 7.5 50GEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA J51 Table 9.—Chemical analyses of water from wells and from Red Spring, Needles area, Arizona-California-Nevada—Continued Well Date Perforated interval (feet below Silica Use (Si02) Cal- cium Mag- nesium So- dium Potas- Bicar-sium bonate Sul- fate Chlo- ride Fluo- ride Dis- solved Hardness as CaC03 Calcium, Noncar-magne- bonate Specific conduct- ance (micro- pH Per- cent so- sampled land- surface datum) (Ca) (Mg) (Na) (K) (HCOj) (SO() (Cl) (F) solids sium mhos at 25°C) dium California—Continued 9N/23E-29E2 .. 4- 5-61 . PS 28 94 26 114 208 277 86 .5 775 342 172 1,110 7.7 40 29E3 .. 4- 5-61 . PS 36 106 34 200 211 388 176 .9 1,050 404 231 1,600 7.7 50 29E4 .. 4- 5-61 40-76 PS 51 134 55 504 257 690 492 2.2 2, 060 560 350 3,140 7.9 64 29F1 .. 6-20-61 . PS 24 111 20 213 248 412 133 .8 1,040 358 154 1,490 7.3 56 30A1 .. 4-11-67 38-82 PS 16 102 31 101 192 288 105 .6 742 382 224 1,250 7.6 37 32K1 .. 6-20-61 150-60 PS 41 111 50 219 194 227 414 2.0 1,190 488 329 2,010 7.8 49 10N/22E-14C1... .. 5- 1-62 11-15 T 24 186 57 155 342 488 176 .. 1,260 700 420 1,990 7. 75 32 11N/21E-36K1 .. 6-18-63 30-85 Irr 19 116 29 117 220 283 134 .4 808 410 230 1,270 7. 45 38 36P1 .. 6-19-63 . Un 17 122 33 142 228 362 130 .5 921 440 •253 1,400 7. 45 41 11N/22E-30N1... .. 5- 1-62 14-16 T 17 111 32 110 190 333 104 .. 802 410 254 1,290 7.4 37 Nevada S33/66-10CCC....... 5- 2-62 21-23 T 17 130 42 124 214 400 124 ________ 944 498 322 1,500 7.4 35 Red Spring 10N/22E-30-C1___3-21-68 ..........S 52 36 5.4 166 344 60 77 8.0 576 112 0 910 7.9 76 Table 10.—Records of test and selected water wells, Needles area, Arizona-California-Nevada Well: Location cf well according to the Federal Land classification. See text for description of well-numbering systems. Other number: Number assigned to test wells of the Geological Survey; number assigned to wells of irrigation districts; informal number assigned to some privately-owned wells. Owner or user: Owner or user reported to the Geological Survey at the time the well was inventoried, not necessarily the original or present owner or user. L.H.I.D.D., Lake Havasu Irrigation and Drainage District. Year completed: Known or reported year of completion of well. Total depth: Greatest depth, in feet below land-surface datum, to which well was known or reported to have been drilled. Well may have been completed to a shallower depth, or filled in subsequently. Completed depth: Depth, in feet below land-surface datum, to which well was cased or subsequently plugged. Methods of construction: Letter symbols designate the following: D, drilled, method unknown; Dug, dug; C, drilled with cable-tool or percussion equipment; R, drilled with rotary-mud equipment; A, drilled with power or hand auger. Casing diameter: Nominal inside diameter, in inches, of casing or pipe used in well. Where more than one figure is given, figures refer to diameter of casing in each successive segment from land surface downward. Depth of perforated interval: Depth, in feet below land-surface datum, to top of highest perforations and base of lowest perforations. Water level: Date measured by the Geological Survey, or reported (R) by owner or other agency. Depth to water in feet below land-surface datum. Ordinarily, the measurement made at the time of the well inventory appears here. ' Type of pump: The following letters indicate the source of power: E, electric; G, gasoline; Ga, gas; D, diesel; W, wind; H, hand. The following letters indicate the type of pump: T, turbine; C, centrifugal; J, jet; S, submersible turbine; L, lift; P, pitcher. As an example, E, T refers to a turbine pump driven by an electric motor. For auger holes, G, J refers to gasoline operated compressor and airlift pump temporarily used to obtain water samples. Pumps are not maintained in auger holes. Use: The use of the water is indicated by the following symbols: Irr, irrigation; PS, public supply; Dom, domestic; Ind, industrial or mining; T, test hole or well; Un, unused; Des, destroyed or filled in above the water table; S, stock. Discharge: Measured or reported discharge of well, in gallons per minute. Drawdown: Measured or reported drawdown, in feet, accompanying discharge in previous column. Water quality: Date when water sample believed to be most representative of the present water at the depth of the perforated interval was obtained. Sum of determined dissolved constituents of water sample, in milligrams per liter by weight. Water temperature: Temperature, in degrees Celsius (°C), of most recent sample of water pumped or bailed from well believed to represent water from the depth of the perforated interval. Temperatures taken with a Fahrenheit thermometer. Other data available: Additional information about the well available in files of the Geological Survey. Some of this information is given in other tables of the present report. The type of information is indicated by the following letter symbols: L, driller’s log; PT, pumping tests. t 3 h © rs © x: a © c © © Water level Water quality © Well .O £ © ££ a £ o s: — © T3 •o © © © o 3 *3 is £ a *3 -3 © =11 Date of Depth £ 3 a o © 6 £ © Sum 2 a as o "3 6 c © — a 2” measure- to & j= * Date of © £ « * 5 © £ © s •ss cn &&.H ment water 8 Jo g solids 3 -2 2 aS o o Eh O s o Eh s o Arizona (B-13-20) lcdd... 4dbb_____ 9aab..... 13ccd____ 15bcc____ 15ddbl.. 15ddb2.. 20dab____ 21bba____ (B-14-19)28bcd___ (B-14-20) 7aaa___ 7ada----- Well 11.. Well 3... Well 8... Well 5... Well 2... Well 4... Well 6... Well 9... Well 1... Well 7... 16ccd.. (B-16-19)8dab... (B-16-20)13bcc_. (B-16-20^)llccd Well 1... 1 iKpo (B-16-21)15add...! Well 2. (B-17-21)5bcb. 6ccc L.H.I.D.D 1963 1,000 1,000 C 12,10 625-960 480 R L.II.I.D.D 1964 150 150 c 12 50-90 6-10-68 19.2 L.H.I.D.D 1967 155 155 c 12 20-110 17R L.H.I.D.D 1964 325 132 c 20-90 205 R L.H.I.D.D 1963 165 165 R 12,10 117-165 30 R L.H.I.D.D 1965 150 150 C 12 27-123 18R L.H.I.D.D 1965 153 153 C 12 28-150 14R L.H.I.D.D 1943 88 88 c 12 32-75 25 R L.H.I.D.D 1958 153 c 72-150 30R L.H.I.D.D 1963 740 c 8 325 R Pierce and Messer... 1964 158 158 I) 6 128-158 105 R 1963 150 150 I) 6 80 R Chemowth. Rolfs and Hetzel 1962 300 300 c 8 180-280 190 R 180 180 D 8 D 8 5-22-68 44.7 El Paso Natural 1950 880 880 D 8 189-420 214 R Gas Co. 1955 503 503 D 10 332-490 214R Golden Valley 1961 290 290 C 12 12-21-61 161.0 Land Co. Colorado River 100 100 D 6 2-27-67 14.1 Land Co. U.S. Geological 1962 18 18 A 1H 16-18 5- 2-62 9.0 Survey. Ga, T Ga, T Ga, T Ga, T D, T E, S E, S E, S E, S E, S E, S E, T E, S H, P Un PS PS Un PS PS,Irr Irr Un Irr Un PS Dom S, PS Dom Un Dom Dom PS PS T 500 130 6-10-68 1,220 6-10-68 1,050 .... 6- 6-68 6- 5-68 1,730 533 .... 50 56 74 70 3- 9-62 3- 9-62 9-11-62 4- 23-68 5- 2-62 314 558 390 1,600 1,040 33 21 L L L L L L L L L LJ52 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA Table 10.—Records of test and selected water wells, Needles area, Arizona-California-Nevada—Continued T3 © s: ft © Water level ft Water quality a 3 ft © a So B © ft 6 o si ft © T3 © © >— © s _CJ -3 T3 © Date of Depth © bo £ o Sum ta E a u. c © 'S ft c _S measure- to « S3 is Date of 5 o £ S s Kl ment water © CO to cS solids cS ® o O !» O S o Q 5 o is Arizona—Continued D D D U.S. Geological 1961 17 17 A Survey. 1965 122 85 A 1968 21 21 A 1961 15 15 A 1968 27 26 A 1962 18 18 A 1967 70 70 D lbbd Colorado River 1967 175 175 D Land Co. U.S. Geological 1961 12 12 A Survey. 1965 117 22 A 1965 132 63 A 1962 18 18 A 1962 18 18 A D D D U.S. Geological 1961 18 18 A Survey. do 1965 147 72 A 1965 167 74 A 1962 21 21 A 87 I) ]) D J. Vanderslice 1965 157 D R. Chesney 1965 154 154 R U.S. Geological 1961 15 15 A 15aba Survey. Bermuda Water Co. 1966 68 68 C do 1962 70 70 C D fB 18-21) 31bbb... U.S. Geological 1961 18 18 A Survey. 1968 22 21 A 1961 18 18 A do 1961 18 18 A 1957 63 D 90 D U.S. Geological 1961 26 26 A Survey. D. Hulet 1957 95 D U.S. Geological 1961 23 23 A Survey. 1945 85 85 C 1926 100 C 1966 100 D 23bccl G. McKelUp 1963 152 152 R 1963 310 304 D 250 250 R Transwestern 1965 287 287 D Pipeline. do .1960 79 79 D G. McKellip 1965 D U.S. Geological 1962 21 21 A 25abbl Survey. D D 27bbc G. McKellip 1957 126 126 D 27dddl.. U.S. Geological 1962 31 31 A 27ddd2 Survey. G. McKellip 1965 D 27ddd3._ Mohave Valley 1965 108 D 34bbb... School. U.S. Geological 1961 21 21 A Survey. 1961 21 21 A 35b bb. G. McKellip 1960 94 94 D 35bbc D 35bda 1963 150 150 R (B-19-22)3dbb U.S. Geological 1968 27 26 A Survey. 1968 21 21 A llbab 1962 24 24 A llbbd D 1965 230 230 D 130 130 D W. Highfill 120 120 D D 21bcb U.S. Geological Survey. 1968 32 32 A 1960 150 D 1964 228 228 D 26baa S. Joy, Jr D 20 2-15-67 12.2 E, T 4-14-67 1,260 22 E, T 2-15-67 l’ 430 22 20 E, T Irr 2-15-67 1,530 22 VA 15-17 8-10-61 9.9 H, P T 5- 1-62 2,100 22 1 83-85 G, J T, Des 5-20-65 3,290 23 VA 15-17 1-15-68 14.2 H, P T VA 13-15 8-10-61 9.2 h; p T 5- 1-62 1,260 20 24-26 1-15-68 23.4 T VA 16-18 5- 1-62 9.2 T 6 60-70 2-28-67 15.2 E, J 2-18-67 2,150 22 12 20 R E, S PS 1 A 10-12 8-10-61 6.8 H, P T 5- 1-62 1,390 20 VA 20-22 G, J T, Des 5-21-65 765 20 VA 61-63 g; j 5-17-65 737 20 Vi 16-18 5- 1-62 9.2 H' P T 5- 1-62 971 21 VA 16-18 5- 1-62 9.0 h; p T 5- 1-62 1,770 21 16 2-15-67 14.8 E, T Irr 4-14-67 1,260 22 16 2-15-67 35.1 E, T Irr 2-15-67 1,220 21 1-18-68 17.8 VA 16-18 8-10-61 9.4 H, P T 5- 1-62 1,170 21 IX 70-72 G, J T, 5-18-65 999 21 Des IX 72-74 G, J T, 5-19-65 1,380 22 Des l A 19-21 5- 1-62 10.4 II, P T 5- 1-62 1,610 21 16 17R E,' T Irr 2,500 33 3- 2-67 1,750 21 20 2-15-67 20.0 E, T Irr 4-14-67 1,250 21 16 2-15-67 15.4 Un 16 80-157 3- 2-67 14.3 D, T Irr 20,16 64-143 16R E, T Irr 3,000 65 3- 2-67 1,450 21 VA 13-15 8-10-61 7.2 II, P T 5- 1-62 1,120 22 16 30-65 E, T PS 2-15-67 888 22 16 35-65 E, T PS 3- 2-67 786 1A 1-15-68 13.1 5 1- 9-62 8.8 T VA 19-21 16.2 T l a 16-18 8-11-61 11.1 H, P T 5- 2-62 630 20 VA 16-18 8-11-61 13.5 H, P T 5- 2-62 991 19 20 3- 1-67 13.0 Un 20 6- 4-64 15.2 E, T 6- 3-64 817 23 IX 24-26 8-11-61 19.2 H, P T 5- 2-62 2,010 21 60-95 E, T Irr 1,720 21 11- 1-62 772 20 1 a 21-23 8-11-61 17.1 H, P T 5- 2-62 730 21 8 E, J 12 65-95 E, T Irr 1,350 3- 1-67 558 6 3- 1-67 17.1 E, S 12 112-152 20 60-304 3- 1-67 11.7 E, S PS 3- 1-67 497 6- 3-64 13.3 E, T Irr 8 E, T 6. E, S 3- 1-67 598 20 3- 1-67 13.0 Un 4-25-68 1,360 V/\ 19-21 5- 2-62 14.9 FT P T 5- 2-62 1,500 23 20 E, T Irr 2-28-67 1,790 23 20 2-28-67 22.2 E, S 2-28-67 1,610 23 20 80-126 20 R E, T 11- 1-62 707 19 VA 29-31 5- 2-62 18.9 H, P T 5- 2-62 885 21 8 16R E, S PS 2-28-67 1,020 8 17R e; s PS 2-28-67 726 5 T 5 1-10-62 13. 2 T 20 11-28-62 19. 8 E,T Irr 3- 6-62 863 21 PS 20 6- 3-64 18. 4 E,T Irr 6- 3-64 1,120 22 24-26 T V4 19-21 T VA 22-24 5- 2-62 17. 7 H, P T 5- 2-62 1,060 22 8 4-13-67 19.4 E, T PS 4-13-67 918 16 120 R E, T Irr 2,300 18 4-13-67 1,340 27 8 70 R E, T 6- 3-64 709 26 8 60 R E 9-18-62 698 8 4-13-67 97. 0 E, S 4-13-67 738 V/\ 30-32 6- 4-68 T 10 92 R E, S 9- 9-62 843 26 20 150-220 E, T Irr 4-11-67 1,230 28 14 6- 3-63 91.6 Un L L L L L L L L PT L L PT L L L availableGEOHYDROLOGY OF THE NEEDLES AREA. ARIZONA, CALIFORNIA, AND NEVADA Table 10.—Records of test and selected water wells, Needles area, Arizona-California-Nevada—Continued J53 T5 £3 D. © Water level Water quality © £2 | © © T3 _o 2 s s Well I® >-< d 6 a O o 3 a ©^ 3 Q, © 3 £ 2 05 ,© ©£> c e3 © •a © ® > Date of Depth O c Sum £ feS © a c measure- to S. J3 ■S Date of ss * s e © 8 a © — £3 ment water >> © OT Cj solids O O 1" O s O Q Eh s Q =s O Arizona—Conti nued (B-19-22)26ddd 1958 190 D 21 11- 2-62 117.4 Ga, T 1,720 7 11- 2-62 1,480 28 PT 113 D 8 4-11-67 68.4 W, L 36bab 1958 250 250 D 20 11- 1-62 147 Ga, T Irr 1,870 4. 6 11- 1-62 1,560 28 L, PT 130 D 6 5- 8-69 77. 5 E, S 36bac 1960 200 200 D 20 11- 2-62 150.7 Ga, T Irr 11- 2-62 1,620 28 PT (B-20-22)laca 120 120 D 12 27 R E, S PS 4- 3-68 1, 350 Court. 1962 249 249 D 12 153R E, S PS 6- 3-64 1,180 28 17bcd Well 3... 200. D 8 Un 17bdd Well 2... do 72 D 20 E, S PS 550 1960 150 150 D 16 E, J PS 9-18-62 811 D 18 6- 4-69 28.4 Un 23bcd Well 1... 1965 200 200 D 8 190-200 146 R E, S PS 135 4 L 25bab 1967 318 318 D 5 288 R e's 4-24-68 653 1968 165 D 6 5- 8-69 98.4 E, S PS 26cdb 1961 150 D 6 E, S PS 4-24-68 808 26dcd do 1968 220 220 D 6 E, S PS 4-24-68 434 80 D 20 s 4-18-62 420 1968 20 20 A IX 18-20 1-18-68 18.4 T Survey. 35bbb... 1960 104 D 8 94-104 48 R Un D 6 E, T 5- 7-68 2,330 J. Wilson 1968 168 D 6 5- 8-69 60.8 N L (B-21-21)21cbb O. Buck 1951 490 108 D 8 E, S 3- 7-62 518 California 4N/24E-17Z1 West well 8.4 8.4 36X42 5- 3-68 5.7 Un 5-13-68 745 5N/24E-36K1 1958 462 462 c 8 30 R E, S PS 150 3- 8-62 1,140 L 36K2 1958 428 428 c 8 80 R E, S PS 3- 8-62 i; 280 36L1 1958 520 520 c 8 130R Un 130 30 7N/23E-10J1 1957 730 C 16 4-24-63 89.7 Un 3 L Gas Co. 7N/24E-6F1 1961 190 190 c 10 28-180 3- 7-62 21.9 E, T PS 350 12.5 3- 7-62 1,470 L County. 8N/23E-16A1 1965 90 90 D 16 30-85 2-16-67 6.7 E, T Irr 1,800 42 2-16-67 846 19 L Wildlife Service. 15G1 1965 53 53 c 8 39-53 10R E, C 150 15 2-16-67 762 L 20J1 1950 521 521 D 6 478-520 250 R E, S PS 3- 7-62 446 34 20K1 1969 o94 D 6 280R E, S 20Q1 C. Tonjes 1957 396 396 c 12,10 373-385 295 R Un 15 55 34 9N/22E-1D1 Pacific Light and 1960 165 D 6 E, T 6- 1-61 ..711. Gas Co. 1E1 M. Johnson 120 112 D 8 1- 4-62 95. 7 E, J 1- 4-62 772 9N/23E-28E1 1961 12 12 A IX 10-12 8-10-61 6. 5 H, P T 5- 1-62 1,350 19 Survey. 29E1 Well 1... City of Needles D E, T PS # 6-20-63 1,160 23 29E2 Well 2... do D E, T PS * 750 4- 5-61 775 20 29E3 Well 3... do D E, T PS 1,000 4- 5-61 1,050 21 29 E4 Well 4... 1954 81 83 D 16 40-76 14R F. T PS \\ 500 ^28 4- 5-61 2,060 22 L 29F1 do 1961 65 D 16 6-20-61 10. 2 e| t PS 650 3 6-20-63 1,040 PT 29L1 Atchison, Topeka, 1929 200 C 16 1-26-61 12 Un and Santa Fe Railroad. 29Q1 do 92 I) 57-82 E, T Ind 1,200 L 29Q2 90 D E, T 30A1- 1967 98 98 c 20 38-82 4_10-fi7 8 F, T PS 2,800 26 4-11-67 750 17 L 30 A 2 1968 100 100 C 20 50-85 4-25-68 14.5 PS L 32K1 Well 5.. 1960 360 360 D 16 150-360 4- 6-61 50.1 E, T PS 2,250 18 6-20-63 1,190 30 L PT 10N/22E-10F1 U.S. Geological 1968 27 26 A l X 24-26 T Survey. 11B1 A IX 5- 7-69 13.0 T Reclamation. 13Q1. . 1968 22 21 A l 'A 19-21 6- 4-68 9. 2 T Survey. 14C1 1961 15 15 A 13-15 8- 7-61 11.1 T 5- 1-62 1,260 20 22D1 1968 57 57 A 1 55-57 6- 3-68 48.2 T 23C1 1961 A 1_10_68 9.1 T 23P1. 1961 23 23 A ik 21-23 8- 7-61 15 0 T 11N/21E-36G1 1950 50 50 D 16 30-50 4- 6-61 10 4 G, C Irr 36K1 1.950 85 D 16 30-85 12R G, T 6-18-63 808 21 PT 36P1 W. Riddle.. 1968 150 D 18 4- 6-61 10.6 Un 6-19-63 921 21 PT 11N/22E-30N1 1961 16 16 A IX 14-16 8- 7-61 11.3 T 5- 1-62 802 18 Survey. 31C1 W. Riddle 143 I) 18 4- 6-61 15.4 D, T Irr 31C2 D 18 4- 6-61 13.0 Un 31F1. 140 D 18 4- 6-61 13. 4 D, T Irr Nevada S33/66-10ccc. 17add. 20cdc. S34/66-5Z1.. 5Z2. _ U.S. Geological Survey. ____do_........ ___do......... ___do......... ___do......... 1962 1968 1968 1968 1968 23 48 27 30 27 23 A IX 21-23 5- 2-62 15.4 H, P T 48 A m 46-48 6- 4-68 29.6 T 26 A m 24-26 6- 4-68 15.3 T 30 A m 28-30 6- 4-68 18.5 T 27 A IX 25-27 6- 4-68 19.4 T 5- 2-62 944 21 availableJ54 GEOHYDROLOGY OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA Table 11.—Selected modified driller's logs of eight wells in the Needles area [Modified from original only by giving lithology first and by addition of geologic units by senior author] Thickness Depth (feet) (feet) Thickness Depth (feet) (feet) Well 8N/23E-20K1 [Location: NWKNWKSE]^ sec. 20, T. 8 N., R. 23 E.t San Bernardino base line and meridian] Well ( B-20-22)35dcc [Location: SW^SW^SE]^ sec. 35, T. 20 N., R. 22 W., Gila and Salt River base line and meridian] Alluviums of Colorado River and its tributaries: Composite 70 70 Sand and some gravel. 30 100 Bouse Formation: Bentonite and brown clay . 20 120 Shale, blue 170 390 Brown color, water . 4 394 Alluviums of Colorado River and its tributaries: Sand and boulders _ 75 75 Sand and gravel 65 140 Bouse Formation: Clay, blue 5 145 Clay, white 10 155 Fanglomerate: Sand and gravel 13 168 Well (B-13-20) 15bcc [Location: SWJiSWJiNWM sec. 15, T. 13 N., R. 20 W., Gila and Salt River base line and meridian] Alluviums of Colorado River and its tributaries : Surface_______________________________________ 46 46 Sand, fine, and gravel________________________ 24 70 Sand, fine____________________________________ 15 85 Sand, coarse, and gravel______________________ 65 150 Gravel, big__________________________________ 15 165 Well (B-16-20Vi)14bca [Location: NE'^SWKNWK sec. 14, T. 16 N„ R. 20K W., Gila and Salt River base line and meridian] Alluviums of Colorado River and its tributaries : Sand, surface__________________________ Sand, coarse, gravel___________________ Gravel, coarse, sand------------------- Clay, gray.................-........... Sand, medium___________________________ Gravel, medium_________________________ Bouse Formation: Clay, blue_____________________________ Fanglomerate: Sand and gravel________________________ Gravel_________________________________ Gravel, fine___________________________ Well (B-19-22)26aab [Location: NW^NEJiNEK sec. 26, T. 19 N., R. 22 W., Gila and Salt River base line and meridian] Alluviums of Colorado River and its tributaries: Sand, gravel, and boulders-------------- Sand and gravel_________________________ Sand____________________________________ Sand and gravel_________________________ Boulders________________________________ Bouse Formation: Clay and gravel_________________________ Clay, sandy_____________________________ Clay..._________________________________ 50 50 40 90 30 120 5 125 30 155 5 160 187 347 63 410 14 424 79 503 22 22 22 44 18 62 8 70 32 102 10 112 6 118 20 138 16 154 36 190 Well 7N/24E-6F1 [Location: SE^NWti sec. 6,T.7 N., R. 24 E., San Bernardino base line and meridian] Alluviums of Colorado River and its tributaries : Gravel, 3 in. to sand___________________ Gravel, 2 to 8-in. rock_________________ Bouse Formation: Clay.................................... Shale___________________________________ Clay, blue______________________________ Clay, gray, with rock___________________ Rock, gray solid________________________ Clay, gray with rock____________________ Clay, with softer rock------------------ Rock, with clay_________________________ Well 9N/23E-32K1 [Location: NWKSEJ4 sec. 32, T. 9 N., R. 23 E., San Bernardino base line and meridian] Alluviums of Colorado River and its tributaries: Boulders and sand_______________________ Clay........—........................... Boulders and sand_______________________ Clay------------------------------------ Sand, hard with 6 to 12 in. gravel lenses. Gravel, coarse__________________________ Bouse Formation: Bentonite_______________________________ Well ( B-20-22)23bcd [Location: SEMSWMNWK sec. 23, T. 20 N., R. 23 W., Gila and Salt River base line and meridian] 10 10 3 13 81 94 7 101 99 200 16 216 144 360 Alluviums of Colorado River and its tributaries: 130 130 Clay, gravel, and boulders... 45 45 35 165 Clay. 5 50 15 180 Clay, sandy . 10 60 20 200 Silt 10 70 11 211 Sand, coarse 10 80 Sand, fine 85 165 7 218 Gravel 5 170 7 225 Sand and gravel 13 183 3 228 Boulders, sand, and gravel 17 200 U. S. GOVERNMENT PRINTING OFFICE : 1973 O - 474-370 UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY PROFESSIONAL PAPER 486-J PLATE 1 21cbb lOcpc 17add 35cdd 3dbb (llbab llobd ,20cdc 9dca 21bcd 30N1 0.31C1 o—31C2 31F1 14C1 •lSaab 23abb 23bbd / 13cbc 25abbl,2 27 b be 27ddd 1,2,3, 34bbb, olDl 31bbb v31dcd 5bcd lObbb ,7bbd llcdd 1 Iced, lOddd, x •7 c bd 8cccl,2 lOccc 15aba 0 Ubbb^ 13 15ddc beb • »14ccc *2 31 bb n° o-_____28 \o E1 29Q1.2 \ 13aaa 13abb 17cdd 32K1 20K1 28bcd APPROXIMATE MEAN DECLINATION, 1972 4dbb 15bcc 21bba, 15ddbl,2 13ccd 20dab 17Z1 EXPLANATION Younger alluvium Sand, gravel, and silt. Gravel yields copious supplies and sand yields moderate supplies of water to wells Older alluviums Sand, gravel, silt, and clay. Unit B, piedmont gravels ( unit C), unit D, and unit E of the Colorado River and its tributaries. Gravel yields copious supplies and sand yields moderate supplies of water to wells > > * cr < < □ 1 -’1- ^ ui cr < |_ LlJ < P D O Bouse Formation SHt, sand, clay, limestone, and tufa. Yields small supplies of water to wells Tf Fanglomerate Cemented sand, gravel, and silt. Yields moderate to small supplies of water to wells Bedrock Sedimentary, igneous, and metamorphic rocks of the mountains. Mostly unimportant as source of water; locally may yield limited supplies of water to wells Approximate contact 36 PI Well in California A 36bab Well in Arizona or Nevada Number refers to section and location within section as described in text. Township and range must he determined from map in order to locate well in tables See figure 15 for section A-A' QTa laca • ladd QTa 17bdd 17bcd 23bcd 19ada* 19cda 25bab 26cdb ,26dcd 15abb 15acb • 14cab 15dad* *l4cbd 23ccc * • • \ 26aab 26baa 26ddd #36bab 36bac QTa 21abb 15A1 o 15G1 15add QTa 8dab 1 lccd 14bca 13bcc QTa #7aaa • 7ada 16ccd Q o QTa 36 K2 o o 36 LI 36K1 SCALE 1:125 000 2 4 6 10 MILES QTa 10 KILOMETERS CONTOUR INTERVAL200FEET DATUM IS MEAN SEA LEVEL GEOLOGIC MAP OF THE NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA Base from U.S. Geological Survey, 1:250,000 Kingman and Needles, 1963 Geology by D. G. Metzger 1967-68 474-370 0 - 73 (In pocket) No. 1UNITED STATES DEPARTMENT OF THE INTERIOR PROFESSIONAL PAPER 486-J MAP SHOWING GENERALIZED WATER-LEVEL CONTOURS DURING 1962-69 IN MOHAVE VALLEY, ARIZONA, CALIFORNIA, AND NEVADA 474-370 0 - 73 (In pocket) No. 2UNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY R. 65 E. R. 66 E. R. 21 W. 114°30' R. 20 W. R. 66 E. PROFESSIONAL PAPER 486-J PLATE 3 R. 21 W. 114°30' EXPLANATION Calcium laca a Magrnesium Sodium and V X Bicarbonate / Sulfate 1 potassium 1350 Chloride § 20 10 10 20 MILLIEQUIVALENTS PER LITER Well number (above diagram) refers to section and location within section as described in text. Number below is dissolved solids, in milligrams per liter DEEP WELLS 114° 15' R. 19 W. 4 MILES 2 I_________u 4 KILOMETERS R. 24 E. R. 25 E. 35°00' MAP AND DIAGRAMS SHOWING QUALITY OF GROUND WATER, NEEDLES AREA, ARIZONA, CALIFORNIA, AND NEVADA 474-370 0 - 73 (In pocket) No. 37 DAY 2^-7-sr t'UTrt tss? Geohydrologic Reconnaissance of the Imperial Valley, California GEOLOGICAL SURVEY PROFESSIONAL PAPER 486-K DOCUMENTS DEPARTMENT APf* l 5 1975 LIBRARY U»iV£P?>TV of CALIFORNIA i Geohydrologic Reconnaissance of the Imperial Valley, California By O. J. LOELTZ, BURDGE IRELAN, J. H. ROBISON, and F. H. OLMSTED WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA GEOLOGICAL SURVEY PROFESSIONAL PAPER 4 8 6 -K UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1975UNITED STATES DEPARTMENT OF THE INTERIOR ROGERS C. B. MORTON, Secretary GEOLOGICAL SURVEY V. E. McKelvey, Director Library of Congress catalog-card No. 75-600003 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, D.C. 20402 — Price $2.85 (paper cover) Stock Number 024-001-02609CONTENTS Page Abstract_______________________________________________________ K1 Introduction____________________________________________________ 2 Purpose of the investigation_______________________________ 3 Location and climate_______________________________________ 3 Previous investigations ___________________________________ 3 Methods of investigation___________________________________ 3 Acknowledgments ___________________________________________ 3 Well-numbering system______________________________________ 5 Geologic setting________________________________________________ 5 Landforms__________________________________________________ 5 Eastern Imperial Valley________________________________ 5 Central Imperial Valley________________________________ 6 Western Imperial Valley________________________________ 6 Structural features________________________________________ 7 Cenozoic stratigraphy______________________________________ 8 Lower to middle Tertiary sedimentary and volcanic rocks_________________________________________________ 8 Imperial Formation_____________________________________ 9 Upper Tertiary and Quaternary predominantly nonmarine deposits_______________________________________ 10 Paleohydrology of the Salton Trough____________________________ 12 Hydrology______________________________________________________ 13 The ground-water reservoir________________________________ 13 Water-bearing characteristics of the rock_____________ 14 Definition of terms_______________________________ 14 Pumping tests_____________________________________ 15 Soil-moisture studies ____________________________ 16 Page Hydrology — Continued Sources of ground-water recharge_______________________ K19 Colorado River______________________________________ 19 Imported water__________________________________ 19 Leakage from canals_____________________________ 19 Underflow from tributary areas _____________________ 20 Precipitation and runoff____________________________ 20 Movement of ground water________________________________ 23 Discharge of ground water_______________________________ 23 Springs_____________________________________________ 23 Wells_______________________________________________ 23 Drains, rivers, and upward leakage__________________ 24 Chemical quality of the ground water_________________________ 25 Eastern Imperial Valley ________________________________ 25 Chocolate Mountains piedmont slope__________________ 25 Pilot Knob Mesa-Sand Hills area_____________________ 25 East Mesa___________________________________________ 26 Central Imperial Valley_________________________________ 28 Western Imperial Valley_________________________________ 30 Lower Borrego Valley________________________________ 30 San Felipe Creek-Superstition Hills area____________ 30 Coyote Valley_______________________________________ 31 West Mesa and Yuha Desert___________________________ 31 References cited_____________________________________________ 32 Basic data___________________________________________________ 35 ILLUSTRATIONS Page Plate 1. Map showing water-level altitude in 1965, geology, and location of wells and springs_________________________________In pocket 2. Graphic logs of test wells and holes ____________________________________________________________________________In pocket Figure 1. Map showing area of report________________________________________________________________________________________________ K4 2. Photograph showing view across Pilot Knob Mesa____________________________________________________________________________ 6 3. Photograph of desert pavement_____________________________________________________________________________________________ 6 4. Photograph of fold in Brawley Formation of Dibblee (1954) ________________________________________________________________ 8 5. Composite column of Salton Trough, showing inferred time relations of stratigraphic units________________________________ 9 6. Photograph of upper shoreline____________________________________________________________________________________________ 12 7. Map showing location of pumping-test and soil-moisture-test sites________________________________________________________ 16 8. Graph showing relation between counts per minute obtained with the soil-moisture meter and moisture content of the soil 17 9. Graphs showing counts per minute obtained with the soil-moisture meter at different depths below the land surface at selected sites in Imperial Valley_____________________________________________________________________________ 18 10. Graphs showing water losses in selected reaches of the All-American and Coachella Canals_________________________________ 21 11. Map showing change in ground-water levels in East Mesa, 1939-60 _________________________________________________________ 22 12. Map showing location of flowing wells, 1960-64___________________________________________________________________________ 24 inIV CONTENTS TABLES Page Table 1. Results of pumping tests_____________________________________________________________________________________________________ K17 2. Moisture content and storage capacity of alluvium________________________________________________________________________ 17 3. Records of selected wells and springs____________________________________________________________________________________ 36 4. Drillers’ logs of selected wells_________________________________________________________________________________________ 39 5. Chemical analyses of water from selected wells___________________________________________________________________________ 49WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA GEOHYDROLOGIC RECONNAISSANCE OF THE IMPERIAL VALLEY, CALIFORNIA By O. J. LOELTZ, BURDGE IRELAN, J. H. ROBISON, and F. H. OLMSTED ABSTRACT The Imperial Valley occupies a broad lowland in the southern, wider part of the Salton Trough section of the Basin and Range physiographic province. The trough is a landward extension of the depression filled by the Gulf of California, from which it is separated by the broad, fan-shaped subaerial delta of the Colorado River. Much of the land surface is below sea level, and the valley drains northwestward to the Salton Sea, which was 232 feet below mean sea level in 1968. The Imperial Valley is bordered by the Chocolate Mountains on the northeast, the Peninsular Range of Baja California and southern California on the southwest, and the Salton Sea on the northwest; it is contiguous with the Mexicali Valley in Mexico on the southeast. The Salton Trough, which evolved during Cenozoic time, is a structural as well as a topographic depression in which the surface of the basement complex lies thousands to tens of thousands of feet below the basement-complex surface in the bordering mountains. The basement complex is composed of plutonic rocks of early and late Mesozoic age which intrude Mesozoic and older metamorphic rocks. The Salton Trough is traversed by the San Andreas fault system. Development of the trough involved both folding and warping as well as faulting; much of the folding is related to movement along the major faults. Structural relief caused by folding, faulting, and warping is inferred to exceed 14,000 feet. The pre-Tertiary basement complex of the trough is overlain by a thick sequence of predominantly nonmarine sedimentary rock that ranges in age from Eocene to Holocene. The Cenozoic rocks beneath the south-central part of the Imperial Valley probably are more than 20,000 feet thick. Rocks as old as Eocene crop out in the bordering mountains, but none of the fill in the central part of the trough appears to be older than about middle Miocene, and most of it is Pliocene and younger. The sedimentary and volcanic rocks of Eocene and Miocene age that are exposed in the mountains are moderately to strongly deformed and are semiconsolidated to consolidated. Consequently, these rocks constitute an insignificant part of the ground-water reservoir. A marine unit, the Imperial Formation of late Tertiary (Miocene or Pliocene) age, is extensively exposed in the western part of Imperial Valley, but apparently it was not penetrated in an oil test hole 13,443 feet deep in the central part of the valley. The Imperial Formation is overlain by a thick heterogeneous sequence of nonmarine deposits. Some of the deposits were derived locally, but most were brought in by the Colorado River. Generally, the river deposits consist of silt, sand, and clay, as contrasted with the locally derived deposits of coarse sand and gravel near the margins of the valley. The last major marine invasion of the Salton Trough is probably represented by the Imperial Formation. Subsequent incursions of the Gulf of California appear to have been minor and of short duration. The hydraulic phases of this study were concerned principally with water in the heterogeneous sequence of nonmarine deposits in the upper few thousand feet of the ground-water reservoir. At depths greater than a few thousand feet, the ground water commonly is too saline for irrigation and most other uses, and the hydraulic connection between the water in the deeper deposits and the water in the upper part of the ground-water reservoir is poor. Short-term pumping tests at several sites indicate that in both the eastern and the western parts of the Imperial Valley moderate to high yields can be obtained from wells that tap several hundred feet of the marginal alluvial deposits or deposits of the Colorado River. Transmissivities of several hundred thousand gallons per day per foot are characteristic of these deposits. Wells with specific capacities of 50 gallons per minute per foot of drawdown or more may be attainable in the more favorable areas. In contrast, the fine-grained deposits that are characteristic of the central part of the valley are likely to have transmissivities of only 1,000 to 10,000 gallons per day per foot to depths of 500 feet. At greater depths, transmissivities are likely to be even less for a similar thickness of deposits. The maximum transmissivity computed from pumping tests was 880,000 gallons per day per foot at well LCRP 6, near the head of the Coachella Canal on the East Mesa in the southeastern part of the valley. Other tests indicate that the transmissivity of the deposits decreases westward and northwestward from well LCRP 6. The extent of the high transmissivity eastward from LCRP 6 is not known but probably is several miles. Soil-moisture studies indicate that in an area of rising water levels in fine-grained alluvial deposits outside of irrigated areas, about 40 percent of the volume of the material in which the rise occurs acts as a storage reservoir. Beneath mesas and other areas where the deposits are not all fine grained, the storage capacity under similar conditions may be more nearly 30 percent. Smaller quantities of water per unit volume than those indicated by the foregoing percentages can be expected to be released from storage as water levels decline. Although the Colorado River was a major source of recharge under natural conditions, the areas where the recharge occurred varied widely depending on whether the river was flowing to the Gulf of California or to the Salton Trough. The last uncontrolled flooding of the Salton Trough by the Colorado River occured in 1905-7, when the present Salton Sea was formed. Importation of Colorado River water for irrigation beginning in 1901 caused the rate of recharge to the shallow part of the ground-water reservoir to increase over that prevailing under natural conditions. Much of the additional recharge in the irrigated area is due to leakage from the numerous conveyance channels and to the application of irrigation water in excess of crop requirements. Recharge to the ground-water system from excess irrigation water is estimated to be more than 400,000 acre-feet annually. However, this K1K2 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA added recharge is balanced largely by discharge from the system through an extensive drainage network, and therefore it does not appreciably affect the aquifers several hundred feet or more below the land surface. In 1942 the All-American Canal became the sole means for diverting Colorado River water to the Imperial Valley; in 1948 the Coachella Canal, which supplies water to the lower part of Coachella Valley, was completed. Leakage from these canals is a major source of recharge to the ground-water system. Leakage during 1950-67 totaled about 4.5 million acre-feet from the All-American Canal and 2.7 million acre-feet from the Coachella Canal. Along the All-American Canal the water-level rise generally was more than 40 feet between 1939 and 1960; along the Coachella Canal it was about 40 feet near the head of the canal and gradually increased northward to more than 70 feet. Recharge to the ground-water reservoir by underflow from tributary areas is small compared with recharge from the imported Colorado River water. Ground-water underflow from tributary areas in the San Felipe Creek drainage basin in western Imperial Valley is about 10,000 acre-feet per year. Total recharge to the ground-water system from precipitation within the valley is estimated to be somewhat less than 10,000 acre-feet per year. Ground water generally moves toward the axis of the valley and thence northwestward toward the Salton Sea. The principal area of discharge is the central, cultivated part of the valley. Ground water also is discharged to the lower reaches of the Alamo and New Rivers and through numerous small springs and seeps. Some of the springs probably are associated with discharge of ground water along the San Andreas fault system, and many are associated with leakage from the Coachella Canal. Wells discharge only a small part of the ground-water supply, because most of the hundreds of used wells furnish only small stock or domestic supplies. Many of the wells are in a 6- to 10-mile-wide flowing-well area between the Alamo River and the East Highline Canal that extends about 30 miles northward from near the international boundary. A few wells yield hot water used to heat homes, but most are utilized only for domestic and stock purposes. The average rate of discharge is about 10 gallons per minute, and the total average annual discharge is only a few thousand acre-feet. Most of the few wells that are used for irrigation are in the lower Borrego Valley, where alfalfa is the principal crop. A few hundred acre-feet of ground water is pumped for industrial, private, and public supplies in the western part of the valley near Ocotillo and Coyote Wells. The chemical quality of the ground water in the Imperial Valley differs greatly. Total dissolved solids range from a few hundred to more than 10,000 mg/1 (milligrams per liter). Generally, ground water that is derived locally from precipitation and that has not yet reached the more saline deposits of the central part of the valley contains only a few hundred milligrams per liter of dissolved solids. Highest concentrations of dissolved solids commonly occur in areas where ground water is discharged principally by evaporation. Water from 10 wells on the Chocolate Mountains piedmont slope in eastern Imperial Valley contained 360 to 4,930 mgA dissolved solids. Samples of water from wells in the Pilot Knob Mesa-Sand Hills area downslope from the piedmont area contained 370 to 2,080 mgA dissolved solids. Water from 51 wells on the East Mesa, southwest of the Pilot Knob Mesa-Sand Hills area, contained 498 to 7,280 mgA dissolved solids; more than three-fourths of the samples contained less than 2,000 mgA, which indicates that water of this quality or better can be obtained in much of the area. In areas of substantial recharge because of leakage from canals, the chemical quality of the water resembles that of Colorado River water, which is characterized by sulfate as the predominant ion. Where recent leakage has not been substantial, sodium or bicarbonnate is the principal ion. The extent to which ground water that is satisfactory for domestic or irrigation use occurs in the central part of Imperial Valley is not known, but on the basis of past attempts to develop usable water in this part of the valley, such occurrence is thought to be extremely limited. Concentrations of fluoride higher than the concentration recommended for drinking water are common, as are concentrations of boron higher than those recommended for certain agricultural crops. Test wells drilled to depths of 500 to 1,000 feet in the southern and western parts of the central Imperial Valley yielded water containing about 5,000 to 10,000 mgA dissolved solids. In the western part of Imperial Valley, water suitable for irrigation probably can be obtained in much of the lower Borrego Valley. Ground water beneath the developed area of Coyote Valley generally contains less than 400 mgA dissolved solids. The principal undesirable characteristic of the water is the high concentration of fluoride; half of the samples analyzed contained more than 2 mgA fluoride. Concentrations of dissolved solids apparently increase to the east. Test well LCRP 8, perforated from 135 to 560 feet, yielded water that contained about 2,000 mgA dissolved solids; two test wells a few miles farther east yielded water containing about 5,000 mgA dissolved solids. INTRODUCTION The Imperial Valley in southern California is the largest desert irrigation development in the United States. Half a million acres of otherwise parched desert lands have been transformed into one of the most productive agricultural areas in the Nation by the importation of Colorado River water. This importation is but one of many diversions of the river water that are being made by the Colorado River basin States. Recognizing that the ever increasing demands for Colorado River water might exceed the available supply, the U.S. Geological Survey in 1950 undertook a comprehensive study of the water resources of the upper Colorado River region, and in 1960, of the lower Colorado River region. This report on Imperial Valley is one of a series of reports resulting from the latter study. It presents the results of a reconnaissance of the geology, hydrology, and chemical quality of the ground water in the valley. The surface-water resources are described in other chapters (Hely and Peck, 1964; Hely and others, 1966; Hely, 1969; Irelan, 1971) of U.S. Geological Survey Professional Paper 486, the principal medium for publishing the results of the series of investigations. Original plans included a study of the water resources of the Coachella Valley, Calif., which is in the Salton Sea area northwest of the Imperial Valley. However, shortly after the investigation began in 1960, the California Department of Water Resources also began an investigation of the ground-water resources of the Coachella Valley. To avoid duplication of work, the Geological Survey and the California Department of Water Resources reached an informal agreement whereby investigations in the Coachella Valley by the staff of the Geological Survey were reduced in scope to assisting the California agency and to drilling two deep test holes. A report on the Coachella Valley was published in 1964 by the California Department of Water Resources. The investigation of Imperial Valley was made under the general supervision of C. C. McDonald, projectGEOHYDROLOGIC RECONNAISSANCE OF THE IMPERIAL VALLEY, CALIFORNIA K3 hydrologist for the Lower Colorado River Project from 1960 to 1968. J. H. Robison, geologist, was principal investigator from 1961 until 1966. F. H. Olmsted, geologist, assisted materially in completing the geologic section of the report. O. J. Loeltz, hydrologist, was responsible for the hydraulic phase of the investigation; Burdge Irelan, chemist, prepared the chemical-quality-of-water phase of the report. G. R. Vaughan and R. H. Westphal, of the Lower Colorado River Project staff, aided in the field investigations. PURPOSE OF THE INVESTIGATION The broad objectives of the investigation of Imperial Valley were (1) to describe the geology in relation to the occurrence of ground water, (2) to define the hydraulic characteristics (transmissivity and storage) of the aquifers, (3) to determine the sources of ground water, (4) to determine the direction of movement of ground water, (5) to determine the principal means by which ground water is discharged, (6) to determine the chemical quality of the ground water in various parts of the system, and (7) to relate differences in chemical composition of the water to differences in the sources of recharge and to man-caused and natural processes. LOCATION AND CLIMATE The Imperial Valley is a broad lowland in southeastern California just north of the boundary between the United States and Mexico (fig. 1). Most of the central part of the valley is below sea level and drains northwestward from the international boundary, which is near sea level, to the Salton Sea, a saline lake whose surface in 1968 was about 232 feet below mean sea level. The climate of Imperial Valley is characterized by extreme aridity and high summer temperatures. Average annual precipitation is less than 3 inches in a large part of the valley (Hely and Peck, 1964). Summer maximum temperatures commonly exceed 40°C (104°F), and winter minimums seldom are below 0°C (32°F). PREVIOUS INVESTIGATIONS The earliest geologic and hydrologic studies that included Imperial Valley were the regional reconnaissance studies by Mendenhall (1909a, b). Brown (1923) made a more detailed study, which included a general description of the geography, geology, and hydrology of the Salton Sea region. Other geologic studies include those by Woodring (1932), Tarbet and Holman (1944), and Dibblee (1954). In the 1960’s, during the present study, the results of many other geologic studies were published or made available to the writers. METHODS OF INVESTIGATION More than 300 wells were inventoried, and selected well data — such as depth of well, date drilled, depth to water, and discharge — are given in table 3. Drillers’ logs of wells are given in table 4. Both of these tables are in the “Basic Data” section of this report. Eight deep test wells in the Imperial Valley and two in the Coachella Valley were drilled for the U.S. Geological Survey by commercial well drillers. (All Geological Survey test wells are noted in this report by LCRP — Lower Colorado River Project.) The drilling of the two wells in the Coachella Valley was supervised by employees of the California Department of Water Resources; all other test drilling was supervised by employees of the Geological Survey. Electric logs were obtained for the test wells drilled with hydraulic-rotary equipment. Pumping tests were made on the Geological Survey test wells that were completed as permanent wells and on several privately owned wells. Lithologic, electric-resistivity, electric-potential, gamma-ray, and temperature logs of these test wells and information on well construction, static water level, and water movement under static conditions are shown on plate 2. Many small-diameter test wells, some of which are almost 200 feet deep, were bored by the Geological Survey using a power auger. Many of the holes were completed by casing with pipes fitted with sand points. Water levels were measured periodically in these and numerous other wells. Continuous graphic water-stage recorders were installed on most of the Geological Survey test wells, on several of the Imperial Irrigation District test wells, and on a few strategically located privately owned wells. Water samples were collected from the test wells, many of the augered wells, and many previously existing wells. Chemical analyses were made of these water samples, either in a field laboratory at Yuma, Ariz., or in the Geological Survey’s laboratories at Albuquerque, N. Mex., or Tucson, Ariz. Also, the results of hundreds of chemical analyses made prior to the present study were assembled and evaluated. Selected results of all chemical analyses are given in table 5, in the “Basic Data” section of this report. Large water samples from three test wells on the East Mesa, after being processed in Yuma according to standard procedures for concentrating their carbon content, were sent to Washington, D.C., for radiocarbon dating. Gravity and seismic-refraction surveys were made by the Geological Survey. A generalized geologic map for the area was compiled from reconnaissance geologic mapping and from published geologic maps. ACKNOWLEDGMENTS Many agencies, groups, and individuals provided valuable assistance to the U.S. Geological Survey. The U.S. Bureau of Reclamation, Yuma Projects office, furnished much information from its files regarding water levels and well logs on the East Mesa. The Imperial Irrigation District was most cooperative in making available theK4 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA 117° 116° 115° 114° 113° 112° 0 25 50 75 KILOMETERS Figure 1. — Area of report. large store of hydrologic data in its files. Several local water-well drilling companies — notably Coachella Valley Pump and Supply and the Desert Drilling Co., which are near Indio, Calif. — provided well logs and other pertinent information. Farmers and other land owners were most cooperative in permitting access to their lands and wells and in furnishing information about their wells.GEOHYDROLOGIC RECONNAISSANCE OF THE IMPERIAL VALLEY, CALIFORNIA K5 WELL-NUMBERING SYSTEM The well-numbering system used in this report is in accordance with the system employed in southern California by the California Department of Water Resources and the U.S. Geological Survey. The wells are assigned numbers according to their township, range, and section locations in the Federal land survey based on the San Bernardino base line and meridian. Each land section is subdivided into 40-acre tracts, which are lettered as shown in the well-location diagram: D C B A E F G H M L K J N P Q R WELL-LOCATION DIAGRAM. As an example, a well in the NEV4NEV4 sec. 32, T. 6 S., R. 9 E., has the number 6S/9E-32A. The part of the well number preceding the slash indicates the township (T. 6 S.); the part immediately after the slash indicates the range (R. 9 E.); the digits after the hyphen indicate the section (sec. 32); and the letter after the section number indicates the 40-acre tract within the section (NEV4NEV4). In a few instances, where more than one well was inventoried in a 40-acre tract or where the California Department of Water Resources had previously assigned the well number, a final digit indicates the order in which the well or wells were inventoried. For example, well 6S/8E-10A4 was the fourth well to be inventoried within the particular 40-acre tract. GEOLOGIC SETTING LANDFORMS The Imperial and Coachella Valleys of southeastern California are in a topographic and structural trough — the Salton Trough section of the Basin and Range phy- siographic province of Fenneman (1931, 1946; fig. 1). The trough, which is about 130 miles long and as much as 70 miles wide, is a landward extension of the depression filled by the Gulf of California, from which it is separated by the broad fan-shaped subaerial delta of the Colorado River. Much of the land surface is below sea level. The lowest part of the trough is occupied by the Salton Sea, whose surface in 1968 was about 232 feet below mean sea level. The Imperial Valley occupies the southern, wider part of the Salton Trough in the United States. On the northwest, the valley is bordered by the Salton Sea; and on the southeast, it is contiguous with the Mexicali Valley in Mexico — the part of the Colorado River delta that is above sea level. The Chocolate Mountains are on the northeast, and the Peninsular Range of Baja California and southern California is on the southwest. The land surface slopes northwestward from about sea level at the international boundary to the Salton Sea, 50 miles distant. Several shorelines of prehistoric Lake Cahuilla, at 42 to 50 feet above mean sea level, are well-preserved features in both the eastern and the western parts of the valley. EASTERN IMPERIAL VALLEY The northeast and east boundaries of eastern Imperial Valley are herein defined as being the northwesttrending Chocolate Mountains and a line extending southward from the Chocolate Mountains through the Cargo Muchacho Mountains and Pilot Knob near the international boundary (pi. 1). The Chocolate Mountains are a low rugged chain formed principally of pre-Tertiary plutonic and metamorphic rocks in the northwestern part and extensive Tertiary volcanic rocks in the southeastern part. The altitudes of the mountains generally are somewhat less than 2,500 feet; one especially low gap separating southwestward drainage in Imperial Valley from northeastward drainage to the Colorado River has an altitude of only about 1,100 feet. The smaller but equally rugged Cargo Muchacho Mountains and Pilot Knob are masses of pre-Tertiary rocks that reach altitudes of about 2,200 and 900 feet, respectively. The eastern Imperial Valley, lying between the mountains just cited and the eastern shoreline of prehistoric Lake Cahuilla, comprises four principal subareas: (1) Chocolate Mountains piedmont slope, (2) Pilot Knob Mesa, (3) Sand Hills, and (4) East Mesa. The Chocolate Mountains piedmont slope extends southwestward from the Chocolate Mountains to the northeast margin of the Sand Hills. The area is underlain by poorly sorted fluvial deposits of local ephemeral streams. The piedmont surface is extensively dissected by washes and is partly covered with desert pavement. Trees and large shrubs are sparse except along some of the larger washes, where small desert hardwood trees,K6 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA chiefly paloverde (Cercidium floridum) and desert ironwood (Olneya tesota), are abundant. Pilot Knob Mesa is a southerly extension of the Chocolate Mountains piedmont slope and is similar in most respects (fig. 2). The southeastern part of Pilot Knob Mesa is underlain by deposits of the Colorado River, as well as by local deposits. Desert pavement on the river deposits is characterized by lag gravel of well-rounded siliceous rocks of distant source, as contrasted with the more angular, generally less resistant pebbles of local derivation (fig. 3). FlC.URE 2. — View across Pilot Knob Mesa. Cargo Muchacho Mountains are in right background; Chocolate Mountains are in left background. Dark bands in fore and middle distances are areas of varnish-coated desert pavement. Ficurr 3. — Desert pavement consisting of rounded quartzitic gravels of the Colorado River. Near Cargo Muchacho Mountains. The Sand Hills, also referred to as the Algodones Dunes, occupy a belt that is more than 40 miles long and 5 to 6 miles wide. These dunes lie on a southwestward- to westward-sloping surface that is continuous with the Pilot Knob Mesa to the northeast and the East Mesa to the southwest. The southwestern part of the Sand Hills is marked by longitudinal southeast-trending ridges, but most of the belt consists of transverse ridges and smaller barchan or quasi-barchan dunes. Some of the ridges are as much as 300 feet above the mesa surface, which is exposed locally in blowouts in the southeastern part of the belt. The southwest margin of the dunes is adjacent to a lacustrine (or marine?) shoreline that probably furnished the sand for the dunes, as discussed in the section “Paleohydrology of the Salton Trough.” The East Mesa occupies a triangular area southwest of the Sand Hills, north of the international boundary, and east of the shoreline of prehistoric Lake Cahuilla. Phy-siographically, the East Mesa, which is an extension of the Pilot Knob Mesa to the northeast, is a sloping surface that merges gradually with central Imperial Valley. The East Mesa was formed mainly by fluvial processes but was locally modified by lacustrine (or marine?) processes. The broad, southern part of the East Mesa slopes west-south westward at about 6 feet per mile. The mesa surface is mantled extensively by irregular sheets of windblown sand that generally are less than 20 feet thick. The natural vegetation consists largely of scattered creosote bushes (Larrea divaricata). CENTRAL IMPERIAL VALLEY The large contiguous area of cultivated land constituting the central Imperial Valley is entirely within the shorelines of prehistoric Lake Cahuilla. The soils formed from the lakebed materials contain a large proportion of clay and silt, in contrast with the predominantly sandy soils of the adjacent East Mesa and West Mesa. Topographically, the central Imperial Valley is a broad flat trough whose axis slopes north-northwestward from about sea level at the international boundary to and beyond the shore of the Salton Sea, which had an altitude of 232 feet below sea level in 1968. The lowest point of the trough’s surface is beneath the southern part of Salton Sea and is about 275 feet below sea level (Littlefield, 1966). The average land-surface gradient from the international boundary to this point is 1.7 feet per mile. Most of central Imperial Valley is a monotonous plain dissected by two major drainages — the Alamo and New Rivers — which have cut trenches as much as 40 feet deep in the soft silty lacustrine deposits. Much of the cutting took place during 1905-7, when virtually the entire Colorado River flowed uncontrolled in these channels and established the present-day Salton Sea. Obsidian Butte and other nearby buttes, formed of rhyolite obsidian, and the mud volcanoes, built up by rising thermal water and mud highly charged with carbon dioxide, are small domical hills 20 to 100 feet above the valley near the southeast shore of the Salton Sea. Some of these hills became surrounded by water as the sea rose in recent years. WESTERN IMPERIAL VALLEY Western Imperial Valley is a topographically complex area between the central irrigated plain of ImperialGEOHYDROLOGIC RECONNAISSANCE OF THE IMPERIAL VALLEY, CALIFORNIA K7 Valley and the Peninsular Range to the west. The boundary between the western and central parts of the valley is less distinct than that between the eastern and central parts. The altitudes of the piedmont surfaces ranges from 100 feet or more below mean sea level near the Salton Sea in the northwestern part of the area to nearly 2,000 feet above mean sea level at the foot of the Peninsular Range in the southwestern part. Spurs and outliers of the main Peninsular Range, which are formed chiefly of pre-Tertiary basement complex, include the Fish Creek, Coyote, and Jacumba Mountains, and Superstition Mountain — the lowest and easternmost outlier, about 20 miles northwest of El Centro. In contrast to these rugged exposures of crystalline rocks are the low flanking hills and badlands underlain by deformed Cenozoic sedimentary and minor volcanic rocks. Western Imperial Valley is drained by San Felipe Creek, which has perennial reaches in the mountains but not in the valley, and by many ephemeral washes. The most prominent ephemeral streams are Fish Creek, Carrizo, Coyote, Yuha, and Pinto Washes. The most extensive alluvial slope in western Imperial Valley is the West Mesa, a broad flat plain straddling the Lake Cahuilla shorelines in the east-central part of the area. On the northwest, the West Mesa merges with lower Borrego Valley, and on the northeast, it merges with the dissected lacustrine deposits of Superstition Hills and with the downstream part of the flood plain of San Felipe Creek. To the southwest, along Palm Canyon Wash and Coyote Wash, is the informally designated Coyote Valley area, underlain by gravelly alluvium from the Peninsular Range. The Yuha Desert area extends south of West Mesa to the international boundary and includes the Yuha Buttes, which are colorful badland exposures of deformed Cenozoic sedimentary rocks. STRUCTURAL FEATURES The trough of the Gulf of California and its landward extension, the Salton Trough, are structural as well as topographic depressions in which the surface of the basement complex lies thousands to tens of thousands of feet below the basement-complex surface in the bordering mountains. The basement complex is composed of plu-tonic rocks of early and late Mesozoic age which intrude Mesozoic and older metamorphic rocks (Bushee and others, 1963). The Gulf of California and the Salton Trough evolved during late Cenozoic time. Hamilton (1961) attributed the formation of the Gulf of California to a combination of strike-slip displacement and cross-strike separation. According to Larson, Menard, and Smith (1968), the gulf resulted from ocean-floor spreading from the crest of the East Pacific Rise, which apparently extends landward (northward) near the present mouth of the gulf. These authors infer that the spreading has rafted the Baja California peninsula away from the mainland of Mexico, mostly within the last 4 million years (late Pliocene to Holocene), but that the northern part of the gulf formed earlier, probably at least by late Miocene time. The San Andreas fault system, the major strike-slip fault system that traverses the Salton Trough, probably was in existence in early Tertiary time. Although not conclusively demonstrated, possibly as much as 200 miles of aggregate strike-slip displacement has occurred in the region since the middle Eocene (Crowell and Susuki, 1959, p. 590). The various faults have been active at different times, however, so that the loci of major displacements have shifted substantially throughout the Cenozoic Era. The Elsinore fault is the southwesternmost fault of the San Andreas system in the United States part of the Salton Trough (Biehler and others, 1964, p. 139). The dip-slip component on the fault northwest of the Imperial Valley is as much as 3,000 feet (Jahns, 1954, p. 45). The strike-slip component is unknown, but conceivably it might be several times the dip slip. The Laguna Salada fault, which lies mostly in Baja California, Mexico, is an extension of the Elsinore fault; together, they coincide approximately with the southwestern boundary of the Imperial Valley. The San Jacinto fault of the San Andreas fault system begins in the San Gabriel Mountains, about 120 miles northwest of the Imperial Valley, extends southeastward, forming the northeast edge of Borrego Valley, and then splits into several subparallel faults before entering the Imperial Valley northwest of El Centro. The Imperial fault may be a part of this system (Biehler and others, 1964, p. 138). As much as 13 feet of right slip took place on the Imperial fault near the international boundary during an earthquake on May 18, 1940 (Dibblee, 1954, p. 26). The San Andreas fault and several parallel or en echelon faults lie along the northeast margin of Imperial Valley. Biehler (1964; oral commun., 1967) inferred the existence of the fault zone on the basis of an alinement of gravity lows that extend from the Salton Sea southeastward beneath the Sand Hills and the East Mesa to the Colorado River south of Pilot Knob. The gravity data are supported by seismic-refraction profiles that also indicate a fault beneath the northeast margin of the Sand Hills. The surface of the basement complex is down-thrown several thousand feet to the southwest along this fault (Kovach and others, 1962, p. 2867-2869). This fault (or possibly a parallel fault), named the “Algodones fault” by Olmsted, Loeltz, and Irelan (1973), extends southeastward across the Yuma area. The development of the Salton Trough in late Cenozoic time has involved folding and warping as well as faulting. Much of the folding is related to movementK8 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA along the major faults and indicates right-lateral drag. Some folding, generally not as tight as that near faults, apparently is unrelated or only indirectly related to faulting. Folding of Quaternary alluvial and lacustrine deposits and of Tertiary nonmarine and marine sedimentary rocks has been noted (fig. 4). This folding is in contrast to the relatively mild deformation—mainly warping—of upper Tertiary and Quaternary nonmarine deposits along the Colorado River to the east in the Yuma and Parker-Blythe-Cibola areas. (See Metzger and others, 1973, and Olmsted and others, 1973.) Figure 4. — Fold in Brawley Formation of Dibblee (1954) east of Niland. View is to the north. Lake Cahuilla shoreline is faintly visible in background. A measure of late Tertiary and Quaternary deformation in the Salton Trough is provided by the configuration of the base of the marine Imperial Formation (Miocene or Pliocene) and the possibly correlative Bouse Formation. Although the base of the Bouse Formation is exposed at an altitude of about 1,050 feet in a gap in the Chocolate Mountains about 15 miles northeast of Glamis, marine deposits similar to either the Bouse or the Imperial Formation apparently were not penetrated in a 13,443-foot-deep oil test well 7 miles northwest of Holtville, in the central part of the trough. In the Coyote Mountains along the west side of Imperial Valley, the base of the Imperial Formation is as high as 1,000 feet above sea level. Much of the inferred structural relief of more than 14,000 feet has resulted from large-scale downwarp of the Salton Trough and upwarp of the bordering mountains, as well as from folding and faulting. Warping continued at least through late Pleistocene time, as indicated by the tilting of lacustrine (or marine?) shorelines, which is discussed in the section “Upper Tertiary and Quaternary Predominantly Nonmarine Deposits.” Not all the warping was in the same direction; some shorelines on the west side of the trough appear to slope southeastward, whereas a prominent shoreline on the east side slopes northwestward. Explo- ration with geoelectrical methods has indicated a gentle southward dip of strata in the upper water-bearing deposits beneath central Imperial Valley (Meidav, 1969). CENOZOIC STRATIGRAPHY Overlying the pre-Tertiary basement complex in the Salton Trough and adjacent mountains is a thick sequence of dominantly nonmarine sedimentary rocks that ranges in age from Eocene to Holocene. The aggregate thickness of this sequence is many thousands of feet, both in exposures and beneath the Imperial Valley in the central part of the Salton Trough. Geophysical evidence indicates that the Cenozoic fill beneath south-central Imperial Valley probably is more than 20,000 feet thick (Kovach and others, 1962). Rocks as old as Eocene crop out in the bordering mountains, but the fill in the central part of the trough does not appear to be older than about middle Miocene, and most of the fill is Pliocene and younger (Durham, 1954, p. 27). The inferred stratigraphic relations of the generally recognized units and formations are shown in figure 5. For the purpose of the discussion below, the Cenozoic deposits are grouped in three broad categories: (1) a lower sequence comprising chiefly nonmarine sedimentary rocks of early to middle Tertiary age but including also volcanic rocks and minor marine sedimentary rocks; (2) a middle marine unit, the Imperial Formation, of late Tertiary (Miocene or Pliocene) age; and (3) an upper sequence composed of predominantly nonmarine deposits of late Tertiary (Pliocene) and Quaternary age. The upper sequence constitutes the main part of the ground-water reservoir beneath the Imperial Valley. LOWER TO MIDDLE TERTIARY SEDIMENTARY AND VOLCANIC ROCKS Sedimentary and volcanic rocks that range in age from Eocene to Miocene are exposed in the mountains on the margins of the Salton Trough but generally are believed to be thin or absent beneath the central part of the trough. These rocks are moderately to strongly deformed and are semiconsolidated to consolidated; they do not constitute a significant part of the ground-water reservoir and are described only briefly. Earlier geologists made several different interpretations of the stratigraphic relations of these rocks, but the differences are not pertinent to this report. The inferred stratigraphic relations of the lower to middle Tertiary sedimentary and volcanic rocks shown in figure 5 are based largely on the interpretations of Durham and Allison (1961) and Woodard (1961), adapted and modified by Robison. The Maniobra Formation (lower and middle Eocene) of Crowell and Susuki (1959) comprises the earliest known Cenozoic rocks of the Salton Trough region. TheGEOHYDROLOGIC RECONNAISSANCE OF THE IMPERIAL VALLEY, CALIFORNIA K9 Split Mountain Formation of Tarbet and Holman (1944),as redefined by Woodard (1961) Basaltic andesite or basalt of Chocolate Mountains Alverson Andesite Lava of Dibblee (1954) Older volcanic rocks of Chocolate Mountains "Unnamed Oligocene(?)" of Crowell and Susuki (1959) and Durham and Allison (1961) Maniobra Formation of Crowell and Susuki (1959) Basement complex: igneous and metamorphic rocks Prepared by J. H. Robison flows and sills of 01igocene(?) age (Crowell, 1962, p. 28). Similar, probably correlative rocks are exposed in the Chocolate Mountains northeast of Imperial Valley and in the Vallecito-Fish Creek Mountains and Jacumba-Coyote Mountains areas southwest of the valley (Durham and Allison, 1961). The volcanic rocks in the Chocolate Mountains are herein grouped in two units (pi. 1 and fig. 5): (1) older volcanic rocks, consisting of pyroclastic rocks and minor flows of andesitic to rhyolitic composition; and (2) basaltic andesite or basalt, a ridge-capping sequence of dark-gray to dark-brown flows and flow breccias. These volcanic rocks are associated with predominantly conglomeratic nonmarine sedimentary rocks. Volcanic rocks in the southeastern Chocolate Mountains and nearby Laguna Mountains east of the area shown on plate 1 have potassium-argon ages of 23 to 26 million years, indicating a middle Tertiary age for these rocks and associated nonmarine sedimentary rocks (Olmsted and others, 1973). In the Vallecito-Fish Creek Mountains and Carrizo Wash-Coyote Mountains areas on the southwest margin of the Imperial Valley, the sedimentary and volcanic rocks of middle Tertiary age include (1) the Split Mountain Formation of Tarbet and Holman (1944), (2) the Alverson Andesite Lava of Dibblee (1954), and (3) the Fish Creek Gypsum of Dibblee (1954). The Split Mountain Formation of Tarbet and Holman (1944) was redefined by Woodard (1961), who excluded the lower 1,800 feet of arkosic arenite (sandstone) and sedimentary breccia below an unconformity at the type section. Woodard (1961, p. 74) described this restricted Split Mountain Formation as consisting of two nonmarine members of very coarse grained sedimentary breccia separated by a middle member of marine arenite, which includes the Fish Creek Gypsum of Dibblee (1954) as an evaporite facies. The Alverson Andesite Lava of Dibblee (1954) underlies the Split Mountain Formation as redefined by Woodard (1961) and overlies the lower part of Tarbet and Holman’s (1944) Split Mountain Formation. Figure 5. — Composite column of Salton Trough, showing inferred time relations of stratigraphic units. Maniobra Formation is exposed in the Orocopia Mountains, about 5 to 10 miles beyond the northern limits of the geologic map (pi. 1). The formation consists of about 4,800 feet of fossiliferous marine clastic rocks of early to middle Eocene age, ranging from coarse conglomerate and breccia in the lower part to siltstone and sandstone in the upper part. In the Orocopia Mountains, the Maniobra Formation is overlain unconformably by about 5,000 feet of nonmarine sedimentary rocks and intercalated andesitic IMPERIAL FORMATION The Imperial Formation was redefined and renamed from the Carrizo Formation by Woodring (1932, p. 7). He defined the Imperial Formation as having a basal member of “conglomerate, sandstone, coralliferous limestone, and at places basalt flows and flow breccias” and a siltstone member of “buff siltstone with occasional hard beds of very fossiliferous limy sandstone.” Woodring (1932) described the Imperial Formation at the type locality to be “the entire series of marine deposits bordering Carrizo Mountain, and to exclude overlying nonmarine beds.”K10 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA Christensen (1957) described the Imperial Formation in its type area bordering the Coyote Mountains as follows (top to bottom):1 Unit Thickness Description Member_____ 600-900 Upper one-third: Reddish, tan, and yellow silty sandstone and tan, green, and gray claystone and siltstone. Grades upward and laterally into sand and clay of Palm Spring Formation. Some wood fragments and marine fossils. Lower two-thirds: Gray calcareous siltstone and light-tan and yellow fine-grained arko-sic sandstone. Flag and spheroidal weathering. Member — 900-1,500 Cream to buff arkosic sandstone and gray-green and light-gray calcareous siltstone. Sandstone contains Ostrea, Anomia, and Pecten. Locally recrystallized into coquina limestone that crops out as cuestas. Sandstone weathers dark brown; siltstone weathers yellow with green cast. Member_____ 20-250 Gray, light-tan, and olive-drab siltstone. Weathers yellow and greenish yellow. Thin lenses of fine-grained buff sandstone. (UndesignatedK10-150 Buff cobble conglomerate. Lithologically heterogeneous. Lenses of buff sandstone. Oysters, corals. (Undesignated)^!10-150 Red to brown massive cobble conglomerate and yellow to pink volcanic conglomerate. Although exposed extensively on the west side of Imperial Valley, the Imperial Formation has not been recognized in several oil test wells, one as deep as 13,443 feet, in the central part of the valley (see Muffler and Doe, 1968) and was not recognized in U.S. Geological Survey test well LCRP 6A (total depth 2,519 ft) on the East Mesa. In the Parker-Blythe-Cibola area along the Colorado River northeast of Imperial Valley, Metzger (1968) named and described the Bouse Formation, a Pliocene marine unit whose stratigraphic position and general lithology suggest possible correlation with the Imperial Formation, although the microfaunas of the two units generally are dissimilar (Smith, 1968). The Bouse Formation also has been recognized in the subsurface of the Yuma area, just southeast of the Imperial Valley (Olmsted and others, 1973). The apparent absence of the Imperial Formation in the intervening central Imperial Valley (although it may be present below the depths reached by oil test wells) is a problem of major paleo-geographic significance. The age of the Imperial Formation is uncertain; estimates range from early Miocene for the lower part (Woodring, 1932) to possible early Pleistocene for the upper part (Allison, 1964). Metzger (1968) presented evi- 'The members, as Christensen described them, were assigned names, but since these names have no official status dnd do not fully correspond with the units of Woodring (1932), they are not indicated here. dence that the possibly equivalent Bouse Formation is Pliocene. The present consensus is that at least part of the Imperial Formation is Pliocene. UPPER TERTIARY AND QUATERNARY PREDOMINANTLY NONMARINE DEPOSITS Overlying the marine Imperial Formation is a thick hetreogeneous sequence of predominantly nonmarine deposits. In some tributary valleys and marginal parts of the Imperial Valley these deposits are derived locally, but most of the deposits in the central part of the valley were brought in by the Colorado River. The deposits are many thousands of feet thick; Muffler and Doe (1968) reported that the Standard Oil Co. Wilson No. 1 oil test well near the center of Imperial Valley, between Braw-ley and Holtville was still in deposits of the Colorado River at its bottom depth of 13,443 feet. In general, the deposits of the Colorado River are finer grained than the locally derived deposits and consist predominantly of silt, sand, and clay, as contrasted with the locally derived coarse sand and gravel. Muffler and Doe (1968) stated that the deposits of the Colorado River are characterized by dominant quartz and calcite and subordinate dolomite, plagioclase, potassium feldspar, and the clay minerals montmorillonite, illite, and kaolinite; minor constituents are magnetite, zircon, leucoxene, cli-nozoisite, biotite, and chlorite. According to these authors (Muffler and Doe, 1968), the deposits derived from the margins of the basin are markedly different from the deposits of the Colorado River in that they contain much more feldspar, less clay, and very little or no calcite or dolomite. The deposits overlying the Imperial Formation have been subdivided by previous workers into several formations and informal units. In places the formations and units are separated by unconformities, but in general they are not well-defined time-stratigraphic units, and they appear to intergrade laterally (fig. 5). Each formation is therefore a crudely defined rock-stratigraphic unit and represents a particular facies. The various formations and informal units are described briefly in the following paragraphs. The Canebrake Conglomerate of Dibblee (1954) is a coarse pebble and cobble conglomerate composed of pre-Tertiary granitic and metamorphic detritus of local derivation. It occurs along the west margin of Imperial Valley, where it is generally several thousand feet thick; basinward it grades into the Imperial Formation and the overlying Palm Spring Formation. The Palm Spring Formation, named by Woodring (1932, p. 9-10) for exposures in lower Vallecito Creek, comprises many thousands of feet of fluvial and deltaic sand, silt, and clay deposited by the ancestral Colorado River. The Palm Spring Formation overlies the Imperial Formation gradationally, and its lower part containsGEOHYDROLOGIC RECONNAISSANCE OF THE IMPERIAL VALLEY, CALIFORNIA Kll probable brackish-water deposits. Both the Imperial and the Palm Spring Formations are weakly to moderately consolidated and are locally folded and tilted to a significant degree, especially near faults of the San Andreas system. The Palm Spring Formation grades toward the western mountains into the Canebrake Conglomerate of Dibblee (1954) and toward the center of the valley into the lacustrine silt and clay of the Borrego Formation of Tarbet and Holman (1944). The uppermost part of the Palm Spring Formation may include time equivalents of the Brawley Formation and Ocotillo Conglomerate, both of Dibblee (1954). The relatively coarse grained deposits mapped as older alluvium in the eastern Imperial Valley (pi. 1) and the older alluvium of the Parker-Blythe-Cibola area (Metzger and others, 1973) and the Yuma area (Olmsted and others, 1973) probably are in large part equivalent in age and source of sediment to the Palm Spring Formation. The Palm Spring Formation was regarded as middle or upper Miocene by Woodring (1932, p. 10), but because it overlies the Imperial Formation (which is probably younger than Woodring believed), it is unlikely to be older than Pliocene. Most workers who have studied the area more recently regard the Palm Spring Formation as Pliocene and Pleistocene. Downs and Woodard (1961, p. 21) found a middle Pleistocene vertebrate fauna in the upper 2,500 feet, and Merriam and Bandy (1965, p. 913) considered the Palm Spring Formation to be mostly Pleistocene. The Borrego Formation of Tarbet and Holman (1944) is a thick sequence of mostly fine-grained lacustrine deposits typically exposed northwest of Borrego Mountain. The Borrego Formation contains a microfauna similar to that occurring in deposits of prehistoric Lake Cahuilla and in the Salton Sea. Arnal (1961, p. 473) regarded the Borrego Formation as late Pliocene or early Pleistocene in age. In western and northwestern Imperial Valley the Borrego Formation of Tarbet and Holman (1944) is over-lain with local unconformity by the Ocotillo Conglomerate of Dibblee (1954), a coarse gray conglomerate composed chiefly of granitic detritus. The Ocotillo grades eastward into fine-grained lacustrine beds assigned by Dibblee (1954, p. 24) to his Brawley Formation. The Brawley Formation is similar to the underlying Borrego Formation of Tarbet and Holman, from which it is not readily differentiated where an angular unconformity does not exist between the two units. On the geologic map (pi. 1), the Brawley Formation of Dibblee (1954) is included in the unit designated as lake deposits. The unit shown as older alluvium on the geologic map (pi. 1) consists largely of coarse-grained alluvial-fan deposits and includes the Ocotillo Conglomerate of Dibblee (1954) in western Imperial Valley. Near the Chocolate Mountains, along the east edge of the valley, the older alluvium may constitute only a thin blanket overlying deformed sedimentary rocks of Tertiary age. Toward the center of the valley the older alluvium grades laterally into the lacustrine silt, sand, and clay of the Brawley Formation of Dibblee (1954). The older alluvium also may include deposits correlative with the upper part of the Palm Spring Formation. The unit designated on the geologic map (pi. 1) as terrace deposits is composed of thin blankets of gravel and sand overlying pediments cut on the Palm Spring and Imperial Formations in western Imperial Valley. In places the terrace deposits appear to thicken, and they may grade laterally into deposits classified as the older alluvium. The deposits of Lake Cahuilla are the uppermost lacustrine silt, sand, and clay in the central part of the valley within the shorelines of the lake. On the geologic map (pi. 1) the deposits are included in the unit designated as lake deposits, which also includes the somewhat older Brawley Formation of Dibblee (1954). In the subsurface, present data do not allow the deposits of Lake Cahuilla to be differentiated from those of the Brawley Formation. The unit designated as alluvium on the geologic map (pi. 1) consists of the youngest fluvial and deltaic deposits in the Imperial Valley. They lie along present ephemeral stream channels and also beneath broad gently sloping surfaces on both sides of the valley. In contrast to the soils formed on the older alluvium and the terrace deposits, the soils on the younger alluvium are immature and lack the profile development characteristic of the older soils. Well-sorted fine to medium sand of windblown origin is extensive on the sides of the valley, especially in the East Mesa and in the Sand Hills (Algodones Dunes). The Sand Hills are related to the water bodies that once occupied the Salton Trough. Brown (1923, p. 28-29) believed the dunes had been formed from sand blown eastward from Lake Cahuilla across the East Mesa. Norris and Norris (1961) also ascribed the source of the sand to Lake Cahuilla, but only from an area northwest of where the Lake Cahuilla shorelines adjoin the north end of the dunes. The present writers believe that an older, higher shoreline (discussed in the next section) was the local source of the sand in the Sand Hills. The Colorado River provided the sand by depositing a large volume in the East Mesa. When the water body associated with the high shoreline was present, wind and shoreline processes formed the dunes from this source, probably in a manner similar to that of dune formation along the present California and Oregon coasts. The position of the high shoreline and the dunes appears to have been determined by the Algodones fault and, possibly, by a parallel branch of the San Andreas fault (pi. 1).K12 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA Volcanic rocks crop out in a row of small domical buttes, one of which is called Obsidian Butte, along the southeast shore of the Salton Sea (pi. 1). Together with the nearby mud volcanoes — a series of fumaroles, which emit carbon dioxide and other gases — these knobs of obsidian, scoria, and pumice are evidence of geologically recent volcanic activity. A strong thermal anomaly characterized by abnormally high geothermal gradients is present in this area (Rex and Randall, 1969) and has been explored by several steam test wells. PALEOHYDROLOGY OF THE SALTON TROUGH Certain aspects of the geologic history of the Salton Trough are of particular interest here because they relate to the origin of the ground water in the Imperial Valley. If the trough was occupied (perhaps intermittently) by an arm of the Gulf of California until only a few thousand or tens of thousands of years ago, incompletely flushed marine water still may be present in the relatively young deposits, which are of primary interest in this study. On the other hand, if the trough has been isolated from the gulf during all or most of the period since the marine Imperial Formation was deposited, the ground water in the post-imperial deposits probably had a nonmarine source or sources. The first hypothesis was supported by Mendenhall (1909b, p. 16-18) and Brown (1923, p. 26), who concluded that the Salton Trough was part of the Gulf of California, having subsided prior to the seaward advance of the Colorado River delta, and that the trough was separated from the gulf only recently in geologic time, when the delta was built above sea level. The second hypothesis was proposed by Free (1914, p. 25-26) and expanded by Buwalda and Stanton (1930). According to this hypothesis, down warping of the central part of the Salton Trough below sea level was contemporaneous with the building of the Colorado River delta. The available data tend to support the second hypothesis rather than the first, although the possibility that the Gulf of California may have invaded the Salton Trough for short periods up to very late Pleistocene time cannot be ruled out. Some of the pertinent evidence is summarized in the following paragraphs. Stratigraphic evidence indicates that the major marine invasion of the Salton Trough is represented by the Imperial Formation, which is probably at least in part Pliocene. The late Cenozoic stratigraphic record is subject to some dispute, but most workers have agreed that nonmarine conditions predominated in post-imperial time. Downs and Woodard (1961) noted an “impoverished brackish-marine” fauna interbedded with Irvingtonian (early Pleistocene) vertebrates in the upper part of the Palm Spring Formation. However, the brackish or marine interbeds do not constitute a major part of the Palm Spring Formation. The Borrego Formation of Tarbet and Holman (1944), which is largely equivalent to the Palm Spring Formation, is chiefly lacustrine in origin, although, according to Arnal (1961, p. 471), it includes strata of shallow-marine origin. The deposits overlying the Borrego Formation of Tarbet and Holman (1944) and the Palm Spring Formation are mostly lacustrine in the central part of the trough and fluvial in the marginal parts. The lacustrine deposits are represented by the Brawley Formation of Dibblee (1954), which, according to Arnal (1961, p. 473), contains a freshwater fauna. The limits of the Brawley Formation are defined approximately by the highest extensive shoreline remnants in the Imperial Valley, and the Brawley Formation is inferred to be at least partly contemporaneous with these shorelines. One of the high shorelines has an altitude of 140 to 160 feet above mean sea level in western Imperial Valley near Plaster City. G. M. Stanley (oral commun., 1965) reported that this shoreline slopes southward in Baja California and crosses the younger, Lake Cahuilla shorelines at about 45 to 50 feet above mean sea level. In eastern Imperial Valley a high shoreline, possibly equivalent to that near Plaster City but sloping toward the northwest, extends northwestward along the southwest edge of the Sand Hills. This shoreline slopes from an altitude of about 160 feet near the south end of the Sand Hills to 120 feet at the northwest end; farther northwest, about 4 miles north of Niland, it is truncated by the younger shoreline of Lake Cahuilla (fig. 6). Several shoreline segments lie farther north, near the Riverside-Imperial County line, at altitudes of 160 feet or more. The segments probably were uplifted to these altitudes by a branch of the Banning-Mission Creek fault, which extends through a nearby hot mineral spa. Figure 6. — Upper shoreline, extending from left foreground to right background and cutting into the Brawley Formation of Dibblee (1954). Located north of Niland, near intersection of upper shoreline and Lake Cahuilla shoreline. Other, probably related shorelines are cut in bedrock on the northwest flank of Superstition Mountain, where they have been uplifted and tilted by movements along the San Jacinto fault. The oldest shoreline slopes aboutGEOHYDROLOGIC RECONNAISSANCE OF THE IMPERIAL VALLEY, CALIFORNIA K13 10° southwestward and has an altitude of nearly 500 feet at its northeast end. Remnants of a high shoreline farther north, on the west side of the Salton Trough, occur as far north as Travertine Point; but north of San Felipe Creek the shoreline is not apparent, probably because it is concealed by younger alluvial fans. The youngest and most prominent shorelines are those associated with Lake Cahuilla, a name given by Blake (1856) to the prehistoric lake that antedates the present, much smaller lake, the Salton Sea. The last main stages of Lake Cahuilla, which, prior to 1962, were the only ones with published reference, had altitudes of 42 to 45 and 47 to 50 feet above mean sea level (Stanley, 1962). Unlike the older, higher shorelines, the shorelines of Lake Cahuilla are virtually undeformed. Stanley (1962), Hubbs (in Hubbs and others, 1963), and Thomas (1963) all believed that the higher shorelines represent fresh-water lakes. The morphology, tufa coating, and molluscs associated with these shorelines all seem to indicate a fresh-water ecology. However, one of the present authors (Robison, 1965) noted several problems involved in this interpretation. One involves the containment of fresh water in the basin, or exclusion of sea water from the Gulf of California. The present divide between the drainage southward into the Gulf of California and northward into the Salton Sea has a minimum altitude of 47 feet (Arnal, 1961, p. 445) — about the right altitude to contain the latest stages of Lake Cahuilla, but far too low to account for fresh-water bodies at the higher levels of the older shorelines. Another problem involves the maintenance of sufficient inflow to keep the water in the lakes fresh. As Mendenhall (1909b, p. 18-19) pointed out, the average flow of the Colorado River (the predominant source of inflow at present and probably also during moister stages of the Pleistocene and Holocene Epochs) probably was insufficient to maintain a fresh Lake Cahuilla — the lake probably was somewhat brackish. The area within the older shorelines is greater than the 2,000-square-mile area covered by Lake Cahuilla; therefore, the older water bodies necessarily would have been more brackish than Lake Cahuilla if the Colorado River was the primary source of water. Another problem is the satisfactory explanation of events that are thought to have occurred within the time span indicated by dating of fossils and tufa deposits of the higher shorelines and early Lake Cahuilla. Fossils from one of the higher shorelines yielded a radiocarbon date of 37,100 ±2,000 years B.P. (before present) (Hubbs and others, 1963, p. 262) .The oldest tufa deposits from Travertine Point, 100 feet below the Lake Cahuilla shoreline, gave a date of 13,040 ± 200 years B.P. (Hubbs and others, 1963, p. 260). If these ages are valid, the maximum time interval between the high stage and an early stage of Lake Cahuilla was about 25,000 years. If the higher shorelines represent lakes and not an arm of the Gulf of California, then during the 25,000-year interval a topographic divide separating the Salton Trough from the Gulf of California was removed, and the higher shorelines were faulted and tilted. The problem of how the divide was removed does not, of course, exist if the higher shorelines are actually marine rather than lacustrine. The reconnaissance nature of the present study did not allow further study toward determining more definitely the nature and age of the higher shorelines and the hydrologic events that followed their formation. The dates of the last main stages of Lake Cahuilla have been well documented from radiocarbon evidence. A radiocarbon date of 1,510 ± 180 years B.P. was obtained from tufa associated with a beachline at an altitude of about 43 feet; other dates range from several hundred to about 1,900 years B.P. (Hubbs and others, 1963, p. 269-270). The Indians in Coachella Valley have legends about a large body of water (Lake Cahuilla) which disappeared slowly — probably by evaporation after the Colorado River ceased to flow into the Salton Trough and began to flow into the Gulf of California. When the first white men entered the region, the floor of the trough (Salton Sink) was a dry salt flat. The most recent major hydrologic event was a series of uncontrolled inflows of floodwater of the Colorado River into the Salton Trough during 1905-7, thereby forming the present Salton Sea. Diversion intakes on the Colorado River below Yuma, Ariz., which has been constructed in the late summer of 1904 to increase the amount of water available for irrigation in the Imperial Valley during that low-flow period, were breached by the spring flood of 1905. The diversion intakes were greatly enlarged by repeated floods, so at times virtually the entire flow of the river was westward and northwestward into the Salton Sea by way of the Alamo and New Rivers. In early 1907 the river was finally brought under control and diverted to its former course to the Gulf of California. At its maximum extent, the Salton Sea reached a stage of about 195 feet below mean sea level, covered an area of more than 500 square miles (less than one-fourth that of Lake Cahuilla), and had a depth of more than 80 feet (Hely and others, 1966). HYDROLOGY THE GROUND-WATER RESERVOIR The ground-water reservoir in Imperial Valley consists of Cenozoic valley-fill deposits; these deposits are underlain by rocks of pre-Tertiary age that are referred to as the basement complex. Although the valley fill probably is more than 20,000 feet thick, the hydraulic phases of this study are concerned principally with the heterogeneous sequence of nonmarine deposits in the upper few thousand feet of the ground-water reservoir. The studies were limited to depths of several thousand feetK14 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA because at greater depths the water is too saline for irrigation and most other uses and because the hydraulic connection between the water in the deeper deposits and the water in the upper part of the ground-water reservoir is poor. Near the margins of the valley, the deposits are derived locally and range from boulders to clay; coarse sand and gravel predominate. Colorado River deposits, which for the most part consist of sand, silt, and clay, underlie the central part of the valley and extend to the margins of the locally derived deposits. WATER-BEARING CHARACTERISTICS OF THE ROCK DEFINITION OF TERMS The term “aquifer” is applied to any water-bearing formation or rock unit that is capable of yielding an adequate water supply. The adjectives “excellent,” “good,” “fair,” or “poor” may be used to denote the degree to which the yield from an aquifer is adequate; but they are not specific enough for a quantitative appraisal of an aquifer or for comparing one aquifer with another. To be more specific, the water-bearing ability of an aquifer may be expressed in terms of the aquifer’s transmissivity. In this report, transmissivity is expressed as the rate of flow in gallons per day through a 1-foot-wide vertical strip of the entire saturated thickness of the aquifer under a unit hydraulic gradient at the prevailing temperature of the water. The water-bearing ability of an aquifer may also be expressed in terms of field hydraulic conductivity. As used in this report, the field hydraulic conductivity is the rate of flow in gallons per day that will occur through a 1-foot-square cross section of the aquifer under a unit hydraulic gradient. Generally, the horizontal hydraulic conductivity of an aquifer is greater than the vertical hydraulic conductivity. This is especially true for alluvial materials because of size sorting and the alinement of platy and ellipsoidal grains that occur during deposition of the material. The vertical hydraulic conductivity of some aquifers that consist of many different strata ranging from clay or silt to sand or gravel may be only hundredths or thousandths of the horizontal hydraulic conductivity. Horizontal hydraulic conductivities in Imperial Valley probably range from a fraction of a gallon per day per square foot for clay and silt to several thousand gallons per day per square foot for well-sorted sand and gravel. Transmissivities commonly are computed from the results of controlled pumping tests. They also can be computed on the basis of the width of a vertical section through which ground water is moving at a known rate under a known hydraulic gradient, or on the basis of the specific capacity, which is the rate of yield per unit drawdown, of a well (Theis and others, 1963, p. 331). In many areas the specific capacities of wells are the only data available for computing transmissivity. If only lithologic or good driller’s logs are available, transmissivity can be estimated if the relation between hydraulic conductivity and some physical parameter, such as median grain size, is known. Such a relation has been established for alluvial material in the Arkansas River valley, Arkansas (Bedinger and Emmett, 1963). To the extent that the relation is applicable to the materials of the area being investigated or that a new relation can be established, the transmissivity can be computed by summing the products of the different hydraulic conductivities and the thicknesses of the strata to which they apply. All the aforementioned methods were used in varying degrees during this study. In this report, most of the transmissivities computed from pumping-test data are for a section of the aquifer that is not much thicker than the strata tapped by the wells. The extent to which the computed transmissivities are representative of the entire saturated thickness must be judged on the basis of the thickness of the different kinds of material tapped by the wells and the thickness and kinds of material that comprise the entire reservoir. In many areas of the Imperial Valley the transmissivity of the entire thickness of saturated material is of little significance in the development of irrigation or municipal water supplies. As stated earlier, the hydraulic connection between the deposits at great depth and those in the upper part of the reservoir is so poor that the two parts are virtually completely isolated. However, the occurrence of highly transmissive material at depth may be greatly significant for other types of development, such as the generation of electrical power by utilizing the thermal energy of ground water, or the recovery of specific minerals from the deep water. The feasibility of developments of these types is beyond the scope of this study. Another important characteristic of a water-bearing rock is its capacity to store or to release water in response to changes in head. A measure of this characteristic is called the storage coefficient (formerly termed “coefficient of storage”) and is a dimensionless number that is defined as the volume of water that is released from or is taken into storage per unit surface area of an aquifer per unit change in the component of head normal to that surface (Ferris and others, 1962, p. 74). When water is confined — that is, when it occurs under artesian conditions — the changes in storage that result from changes in head are attributed entirely to compressibility of the water and of the aquifer materials. Storage coefficients under artesian conditions are small and generally range from about 0.00001 to 0.01. However, in Imperial Valley, the upper limit may be several times higher because of the unusually great thickness of the deposits.GEOHYDROLOGIC RECONNAISSANCE OF THE IMPERIAL VALLEY, CALIFORNIA K15 When water is unconfined — that is, when it occurs under water-table conditions — the changes in storage that result from changes in head are dependent mainly on the drainage characteristics of the aquifer material. In an unconfined aquifer the volume of water involved in gravity drainage ordinarily is many hundreds or even thousands of times greater than the volume attributable to compressibility of the aquifer materials and of the water in the saturated zone, so the volume of water involved in gravity drainage divided by the volume of the zone through which the water table moves is the specific yield. Under dewatering and unconfined conditions, the storage coefficient therefore is sensibly equal to the specific yield. However, when water is going into storage — that is, when the water table is rising—the storage coefficient may exceed the specific yield if the material in which the water is being stored contains less moisture than it can retain against gravity drainage. In this instance, the upper limit of the storage coefficient is the porosity of the material. Generally, however, storage coefficients under water-table conditions range from almost zero to a few hundredths for clay and silt, and from 0.2 to 0.4 for clean sand and gravel. Storage coefficients, especially those for artesian aquifers, are commonly computed from the results of controlled pumping tests. However, the computed coefficients have little significance if the field conditions differ markedly from the conditions that were assumed in deriving the mathematical formulas used for computing the coefficients. The pumping-test data obtained during this study either were not adequate or were otherwise considered unsatisfactory for computing meaningful storage coefficients. A neutron moisture probe, in conjunction with access tubes driven to depths of several feet below the water table, was used to determine storage characteristics of several types of material in Imperial Valley. Construction details and the scientific principles that relate neutron-probe data to moisture content at a particular depth are explained in previous water-resources reports on the lower Colorado River area (Metzger and others, 1973; Olmsted and others, 1973). The method is especially useful for determining the capacity of materials to store water when water levels are rising. Water levels have been rising for 20 or 30 years in the parts of Imperial Valley where the ground-water reservoir is recharged by leakage from the All-American and the Coachella Canals. The average difference between the moisture content of the material above the capillary zone and that of the material below the water table is an indicator of the quantity of water that will go into storage as the water table rises. The results of the neutron-probe moisture studies are given in a later section entitled “Soil-Moisture Studies.” PUMPING TESTS Short-term pumping tests were made at several widely scattered sites to obtain data for computing transmissivity. Although some of the short-term tests did not provide adequate data, most of the tests were satisfactory. The pumping-test sites are shown in figure 7, and pertinent data from the tests are listed in table 1. The test data were analyzed by the Theis (1935) nonequilibrium formula. The reliability of the computed transmissivity is classified arbitrarily as follows: Good, if the difference between computed transmissivity and true transmissivity is thought to be less than 25 percent of the values listed; fair, if the difference is between 25 and 50 percent; and poor, if it is more than 50 percent (table 1). None of the computed transmissivities are considered significant to more than two figures, and most, to only one figure. The classification takes into account not only the degree to which the test data conformed to theoretical values, but also other known factors that might influence the results, such as the theoretical relation between transmissivity and specific capacity previously mentioned and consistency of results obtained from drawdown data and from recovery data. The data indicate that in the eastern and western parts of Imperial Valley moderate to high yields can be obtained from wells that tap several hundred feet of the marginal alluvial deposits or deposits of the Colorado River. Transmissivities of several hundred thousand gallons per day per foot seem to be characteristic of these deposits, and wells with specific capacities of as much as 50 gallons per minute per foot of drawdown or more may be attainable in the more favorable areas. In the central part of Imperial Valley, the two pumping tests that were made by the Imperial Irrigation District prior to this study indicate that the transmissivity of the fine-grained deposits that are characteristic in this part of the valley is likely to be only 1,000 to 10,000 gallons per day per foot to depths of 500 feet. The geologic studies suggest that at greater depths the transmissivity may be even lower for a similar thickness of deposits. The exceptionally high transmissivity and hydraulic conductivity computed for deposits at well LCRP 6 (fig. 7; table 1) indicate that some of the Colorado River deposits at the site are very permeable. The values are similar to those obtained from pumping tests of large-yielding wells in the Mexicali and Yuma Valleys. The lower transmissivities and hydraulic conductivities at wells LCRP 11, 12, and 18 (fig. 7; table 1) indicate that the permeability of the deposits decreases westward and northwestward from well LCRP 6. The eastward extent from well LCRP 6 of the region of high transmissivity is not known, but consideration of possible past courses of the Colorado River suggests that it probably is several miles.K16 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA RIVERSIDE CO SOIL-MOISTURE STUDIES The moisture content of soil profiles was determined at 18 sites in Imperial Valley (fig. 7). A neutron probe was lowered inside access holes of 1.62-inch ID steel tubing, generally driven to depths of about 16 feet below the land surface, and a counting rate was determined at 1-foot intervals. From the counting rate the moisture content of the material at a particular depth was determined on the basis of the relation shown in figure 8. This relation was inferred from specific relations between laboratory determinations of moisture content or porosity of samples and the respective counting rate obtained with the soil-moisture meter for the samples in the field; it is valid only for the conditions under which the data were obtained. Experiments during this study showed that the relation changes if different methods are used for installing the tubing or if other kinds and diameters of tubing are used. Figure 9 shows graphs of the counts per minute that were obtained with the soil-moisture meter at different depths below the land surface at sev- eral sites in the valley. In the zone of saturation — that is, below the water table — the rate generally is 7,000 to 8,000 counts per minute, which corresponds to a moisture content of 41 to 48 percent by volume of the material. The high counting rate sometimes persists for several feet above the water table, which indicates that the lower part of the capillary fringe is saturated or nearly saturated. At three of the sites the counting rate was 1,000 or less per minute for a part of the depth tested. The low counting rate is related to the slight moisture content of the material above the capillary fringe; 1,000 counts per minute corresponds to a moisture content of somewhat less than 5 percent. The difference between the average moisture content of the saturated material and that of the material above the capillary fringe is an estimate of the quantity of water that will go into storage per unit volume of material as water levels rise in an area where the capillary fringe does not reach the land surface. Table 2 lists the moisture content below the water table and above the capillary fringe and the difference between these contents at each site whereK17 GEOHYDROLOGIC RECONNAISSANCE OF THE IMPERIAL VALLEY, CALIFORNIA T able 1. — Results of pumping tests [Type of test: D, drawdown; R, recovery. All wells completed in Quaternary alluvium. LCRP, Lower Colorado River Project of U.S. Geol. Survey] Date Type Interval Draw- Specific capacity Transmissivity Conformance Indicated average Well Owner or name of tested (ft Yield down in gpm computed from of test data Reliability field hydraulic (fig. 7) test test below land surface) (gpm) (ft) per foot of drawdown tests (gpd per ft) to theoretical values of computed transmissivity conductivity (gpd per sqft) Western Imperial Valley 12S/ 9E-22A2 _ _ T. M. Jacobs 7-29-63 R 285- 667 1,450 14 100 290,000 Excellent Good 760 12S/11E-18J1 LCRP 19 5-20-64 R 310- 650 150 4 38 100,000 Fair Fair 300 18J2 LCRP19A 5-20-64 R 35- 55 45 8.5 5 37,000 do Hn 1,800 14S/11E-32R LCRP 8 5-11-62 R 135- 165 218- 258 310- 354 390- 416 430- 560 250 13 19 130,000 Good Good 480 Central Imperial Valley 15S/14E-18C __ 17S/15E-10N . _ Imperial Irrigation District. do 5-9-58 5-16-58 R R 140- 440 110- 450 160 90 86 68 2 1.3 2,200 1,700 Good do Good do 7 5 Eastern Imperial Valley 12S/16E-9A . _ Southern Pacific 7-9-63 R 150-1,000 975 43 23 62,000 Excellent Good 73 Co. 7-9-63 D 150-1,000 675 27 25 47,000 Good Ho 55 15S/18E-15M _ _ . LCRP 11 5-10-63 R 309- 894 1,000 20 50 220,000 do Hn 380 5-10-63 D 309- 894 1,000 20 50 220,000 Excellent Hn 380 16S/18E-32R _ LCRP 18 6-29-64 R 140- 630 900 21 43 140,000 _ do _ do 240 16S/19E-11D . LCRP 12 5-14-63 R 300- 610 990 24 41 240,000 Good do 770 16S/20E-31K . LCRP6 5-2-62 R 340- 410 1,035 12 85 850,000 Excellent __ do 10,000 510- 520 5-2-62 D 340- 410 1,035 12 85 880,000 Good Ho 10,000 510- 520 16S/21E-16B _ _ R. G. Winder 12-4-62 R 598- 806 1,550 36 43 ■630,000 Poor Poor 3,000 12-4-62 D 598- 806 1,550 36 43 ■590,000 do do 2,800 'May be too high by a factor of 2. Figure 8. — Relation between counts per minute obtained with the soil-moisture meter and moisture content of the soil. The line is dashed where the relation was not determined for this study. T ABLE 2. — Moisture content and storage capacity of alluvium [All quantities in percent by volume] Average moisture content Field No. ------------------------------------ Storage (fig. 7) Location Below Above capacity water table capillary fringe 1 _______12S/14E-4K_______ 44 _____ ______________ 2 ______13S/13E-3E_______ 45 _____ ______________ 3 ______13S/16E-35M______ __________ 2 ____ 4 ______15S/15E-35A______ 41 _____ ______________ 5 ______15S/16E-27D______ 45 4 41 6 ______15S/16E-29D______ 44 _____ ______________ 7 ______15S/16E29Q_______ 44 _____ ______________ 8 ______16S/12E-1M_______ 44 _____ ______________ 9 ______16S/12E-11E______ 43 _____ ______________ 10 ______16S/13E-2H_______ 45 _____ ______________ 11 ______16S/14E-7K_______ 43 _____ ______________ 12 ______16S/14E-19D______ 46 _____ ______________ 13 ______16S/15E-35P______ 41 _____ ______________ 14 ______16S/16E-3D_______ 41 _____ ______________ 15 ______16S/16E-12P______ 44 _____ ______________ 16 _______16S/16E-12Q______ 43 3 40 17 _______17S/15E-5J_______ 43 8 35 18 ______17S/15E-10C______ 44 _____ ______________ Average_________ 43 4 39 such determinations were possible; the average for each of the determinations is also given. The average moisture contents for deposits in the Imperial Valley compare favorably with moisture contents for flood-plain deposits in the other valleys in the lower Colorado River area in which similar studies were made. For example, at 11 sites in Parker Valley, Ariz., the average moisture content was 45 percent in the zone of saturation and 6 percent in the zone above the capil-DEPTH BELOW LAND SURFACE, IN FEET K18 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA COUNTS PER MINUTE, IN THOUSANDS Figure 9. — Counts per minute obtained with the soil-moisture meter at different depths below the land surface at selected sites in Imperial Valley.GEOHYDROLOGIC RECONNAISSANCE OF THE IMPERIAL VALLEY, CALIFORNIA K19 lary fringe, which indicates a storage capacity of 39 percent. In Palo Verde Valley, Calif., average values for 16 sites for corresponding zones were 44 and 12 percent, indicating a storage capacity of 32 percent (Metzger and others, 1973). In the South Gila Valley east of Yuma, Ariz., the indicated storage capacity was 37 percent, and in Yuma Valley, it was about 42 percent. In contrast, the indicated storage capacity of shallow deposits beneath the Yuma Mesa was only about 28 percent (Olmsted and others, 1973). The lesser capacity of the mesa deposits for storing water probably is due to the smaller percentage of fine-grained material they contain. The capacity of the shallow deposits of the East Mesa of Imperial Valley for storing water likewise may be less than the average of 39 percent determined for the material in the valley. In summary, the soil-moisture studies indicate that in an area of rising water levels in fine-grained deposits outside of irrigated areas, the storage capacity is about 40 percent of the volume of the material in which the rise occurs. Beneath mesas and other areas where the deposits are not all fine-grained, the storage capacity may be more nearly 30 percent. Smaller quantities of water per unit volume than those indicated by the foregoing percentages can be expected to be released from storage as water levels decline, the quantities being dependent largely on the fineness of the material and the length of the drainage period. The storage capacities of materials beneath irrigated areas are likely to be less than beneath nonirrigated areas because of the incomplete gravity drainage of irrigation water in the profile above the capillary fringe. SOURCES OF GROUND-WATER RECHARGE The most important source of ground-water recharge in Imperial Valley is the Colorado River. Minor sources are underflow from tributary areas, precipitation, and local runoff. COLORADO RIVER The Colorado River has been recharging the ground-water reservoir of Imperial Valley since its delta was built sufficiently high to exclude the Gulf of California from the Salton Trough. However, the areas where the recharge has occurred have varied widely depending on whether the river was discharging to the Gulf of California or to the Salton Trough. When the river was flowing to the Gulf of California, recharge in Imperial Valley was principally underflow from Mexicali Valley and underflow through the alluvial section between the Cargo Muchacho Mountains and Pilot Knob. When the river was flowing to the Salton Trough, a substantial amount of recharge also resulted from the infiltration of river water in the eastern part of the Imperial Valley. IMPORTED WATER Recharge to the shallow part of the ground-water reservoir, as it occurred under natural conditions, was increased by the importation of Colorado River water to the Imperial Valley for irrigation beginning in 1901. Development of an agricultural economy based on irrigation was interrupted occasionally, notably by the uncontrolled flooding of the valley by the Colorado River in 1905-7, when the present Salton Sea was formed. However, irrigation agriculture continued to expand until, in the latter part of the 1960’s, more than 430,000 acres of cropland was being irrigated. Much of the additional recharge in the irrigated area is due to leakage from the numerous conveyance channels and to the application of irrigation water in excess of crop requirements, the latter practice being necessary to prevent an excessive accumulation of salts in the root zone. The quantity of recharge resulting from the application of excess water is difficult to determine. However, it may be estimated by multiplying (1) the rate of water delivery (in acre-feet per year per acre) by (2) the irrigated acreage (in acres), by (3) a rule-of-thumb figure of 25 percent as the minimum amount of water, in excess of crop requirements, needed to prevent an excessive accumulation of salts. Because 430,000 acres is irrigated and consumptive use is about 4 acre-feet per year per irrigated acre (Hely, 1969, p. 33), the recharge is estimated to be more than 400,000 acre-feet per year. However, this recharge to the ground-water system is balanced largely by discharge from the system through an extensive drainage network, and therefore it does not greatly influence recharge to aquifers several hundred or more feet below the land surface. LEAKAGE FROM CANALS The completion of the All-American Canal, which permitted the diversion of Colorado River water to Imperial Valley by an all-American route rather than through Mexicali Valley by the Alamo Canal, greatly increased the opportunity for recharge to the ground-water system. In February 1942 the All-American Canal became the sole means for diverting Colorado River water to the Imperial Valley. Six years later the Coachella Canal was completed and thereafter supplied water to the lower part of Coachella Valley. The canals are major sources of recharge because (1) they are unlined; (2) they are as much as 200 feet wide; (3) they flow across many miles of sandy terrain, especially in the eastern part of Imperial Valley; and (4) the water surface in the canals is much higher than the general ground-water levels along their alinement. In the Sand Hills area of the East Mesa the stage of the All-American Canal is about 80 feet above precanal ground-water levels; the difference between precanal levels andK20 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA canal stage is similar at the head of the Coachella Canal and northward. The rate of leakage of water from these canals cannot be determined precisely. However, the records of measured canal flows corrected for diversions and evaporation losses give a rough estimate of the rates of leakage. In 1948 the Imperial Irrigation District assumed responsibility for operation of the All-American Canal and the upper 50 miles of the Coachella Canal; since that time the canal flow, diversions, and evaporation losses have been recorded. Water losses in selected reaches of the All-American Canal and the upper end of the Coachella Canal, as compiled by the Imperial Irrigation District, are shown in figure 10. Errors in measurement probably account for a large part of the annual variations in the leakage rates as indicated on the graphs (fig. 10). The plotted values are residual differences in canal flow in the reaches and, therefore, include the net effect of any errors in measurement. The annual flows in the upper end of the All-American Canal generally are 3 to 4 million acre-feet, and at the head of the Coachella Canal, they are about 0.5 million acre-feet. A small percentage of error in flow measurement, therefore, can account for much of the year-to-year variations in computed rates of leakage. The total quantity of leakage from the All-American Canal between Pilot Knob and the East Highline Canal and from the Coachella Canal in the reach above the 6A check can be estimated as follows. The average annual rate of leakage from the All-American Canal from 1941, when the canal was first used for conveying large flows to Imperial Valley, to 1950 probably was about the same as the average annual rates for the first 3 years shown in figure 10. The rates were about, 90,000 acre-feet per year for the reach Pilot Knob to Drop 1 and about 130,000 acre-feet per year for the reach Drop 1 to East Highline Canal, or a total of about 220,000 acre-feet per year. From 1950 through 1967 (fig. 10), the leakage from the two reaches was about 140,000 acre-feet per year. Through 1967, therefore, the total leakage from the All-American Canal between Pilot Knob and East Highline Canal was nearly 4.5 million acre-feet. The leakage from the Coachella Canal in the reach above the 6A check averaged nearly 150,000 acre-feet per year; thus, from 1950, when the canal was first used to near capacity, through 1967, leakage amounted to about 2.7 million acre-feet. The ground-water recharge to the East Mesa as a result of leakage from these canals thus was about 7 million acre-feet through 1967. The leakage caused ground-water ridges to form beneath the canals almost immediately, and in time, the tops of the ridges intercepted the canals. The leakage also spread horizontally, thereby causing water levels over large areas to rise many tens of feet. Eventually much of the recharge due to the leakage, especially from the All-American Canal, caused additional discharge to drains and areas of natural discharge, rather than continuing to add to the quantity of ground water stored in the system. The rise in water levels that resulted from leakage from the canals between 1939, before the canals were completed, and 1960 is shown in figure 11. In 1960 the All-American Canal had been in operation for 18 years, and the Coachella Canal, for 12 years. Along the All-American Canal the water-level rise generally was more than 40 feet, and along the Coachella Canal it was about 40 feet near the head of the canal and gradually increased northward to more than 70 feet (fig. 11). Throughout most of the length of the East Highline Canal the change in water levels was small. UNDERFLOW FROM TRIBUTARY AREAS Recharge to the ground-water reservoir by underflow from tributary areas is small compared with recharge that results from the importation of Colorado River water. The tributary areas that provide the major part of the underflow are the Mexicali Valley and the areas drained by Pinto and Coyote Washes and Carrizo and San Felipe Creeks (pi. 1). Of these, the two that contribute most of the recharge are the Mexicali Valley and the area drained by San Felipe Creek. Upper limits for the probable magnitude of the inflow can be estimated on the basis of the transmissivity of the deposits through which most of the flow occurs, the hydraulic gradient, and the width of sections. Most of the ground-water inflow from Mexicali Valley occurs through a section that extends westward from Calexico, Calif., to the mountains, a distance of about 12 miles (pi. 1). The average hydraulic gradient is about 5 feet per mile, and the transmissivity of the deposits through which most of the water moves, as estimated from well logs and pumping-test results, is about 100,000 gallons per day per foot. Multiplying these parameters of width, hydraulic gradient, and transmissivity results in a computed average annual flow of ground water across the section of about 7,000 acre-feet. A similar computation indicates that the underflow beneath San Felipe Creek is about 10,000 acre-feet per year. Underflow from the area drained by Coyote Wash is considerably smaller, and the underflow from areas drained by Pinto Wash is estimated to be hundreds rather than thousands of acre-feet per year. PRECIPITATION AND RUNOFF Direct infiltration of precipitation to the ground-water reservoir is a minor source of recharge. Only on the higher alluvial slopes of the mountains bordering theANNUAL WATER LOSS, IN THOUSANDS OF ACRE-FEET GEOHYDROLOGIC RECONNAISSANCE OF THE IMPERIAL VALLEY, CALIFORNIA K21 1945 1950 1955 1960 1965 1970 Figure 10. — Water losses in selected reaches of the All-American and Coachella Canals.K22 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA Figure 11. — Change in ground-water levels in East Mesa, 1939-60.GEOHYDROLOGIC RECONNAISSANCE OF THE IMPERIAL VALLEY, CALIFORNIA K23 southwest side of Imperial Valley is the precipitation sufficient to provide recharge by direct infiltration. Recharge also results from infiltration of runoff, mainly in washes and drainageways that discharge to the central part of the valley or to the Salton Sea. This recharge is estimated to average somewhat less than that from the tributary area of San Felipe Creek. Thus, the average annual recharge due to precipitation within the study area probably is somewhat less than 10,000 acre-feet. MOVEMENT OF GROUND WATER The general direction of movement of ground water can be inferred from the water-level contour lines on plate 1. In general, the direction of ground-water movement is at right angles, or normal, to the contour lines and toward the next lower contour line. The contours were drawn on the basis of all known water-level altitudes that, in the authors’ judgment, provided useful information on the probable altitude of water levels in wells tapping the main water-bearing zones in 1965. Altitudes of water levels in wells that tap only water-bearing strata either above or below the main water-bearing zones, therefore, may differ from the altitudes indicated on plate 1. In some areas these differences may be as much as several tens of feet, but generally they are much smaller. The broad ground-water mound that extends westward from Pilot Knob (pi. 1) is the result of leakage from the All-American and Coachella Canals. Between the canals the direction of movement is principally westward, but south of the All-American Canal the movement is southward toward Mexico. The relatively wide spacing of the contours on the East Mesa is due to the high transmissivity in this region; immediately west of the East Mesa the transmissivity is much less. Ground water generally moves toward the axis of the valley and thence northwestward toward the Salton Sea. The principal area of discharge is the central, cultivated part of the valley. Substantial amounts of ground water move toward the Alamo River, as shown by the convexity of the contour lines in the upstream direction of the river, especially north of Holtville. Ground water also moves toward the New River, but the configuration of the lines suggests that considerably less water moves toward the New River than toward the Alamo River. The hydraulic gradients of 2 to 5 feet per mile that are common near the New River upstream from the -80-foot contour line contrast markedly with the gradients of 10 to 15 feet per mile that are common along the Alamo River at corresponding water-level altitudes. Although the wider spacing of contour lines in the western part of the valley floor, which includes the New River area, might be interpreted as an indicated that the transmissivity beneath this area is higher than that beneath the eastern part of the valley floor, the wider spacing more likely is an indication that the rate of movement of ground water, and consequently the annual discharge, is less in this part of the valley floor than in the eastern part. In addition to moving toward the Alamo and New Rivers, appreciable quantities of ground water move upward to the extensive system of drains in the irrigated area. Most of the movement in the irrigated area, however, is downward to the drains. The contours on plate 1 do not represent the altitude of the drain water. A wide range of hydraulic gradients is indicated on plate 1 for the ground water that moves from the adjacent mountains and tributary areas toward the valley floor or the Salton Sea. However, adequate control for drawing the contour lines for most of the marginal areas is lacking, so explanations for the wide range of gradients that are shown are somwhat speculative. Steep gradients — 20 feet and more per mile — in areas where the rate of ground-water movement is known to be small indicate that the deposits are poorly permeable. Some of the seemingly abrupt changes in gradient are caused by the barrier effects of faults. The very steep gradients west of the Coachella Canal near Niland and northwestward undoubtedly result from substantial leakage from the canal into poorly permeable deposits. DISCHARGE OF GROUND WATER SPRINGS Ground water is discharged by numerous small springs and seeps. On the northeast side of the Salton Sea they commonly are found in a zone that roughly parallels the San Andreas fault system, and many of them are down-gradient from the Coachella Canal. The fact that many of the springs and seeps postdate the completion of the canal in .1948 indicates that the source of many of them and the reason for increased flows from some of the historic springs are seepage from the canal. Springs and seeps southwest of the Salton Sea are less numerous and generally have smaller flows than those northeast of the sea. The total discharge of springs and seeps, excluding the discharge due to seepage from the Coachella Canal, is estimated to be only a few thousand acre-feet per year. WELLS Wells discharge only a small part of the ground water in Imperial Valley. Although there are hundreds of wells (table 3) in the area, most of them are small domestic or stock wells. Much of the ground water they tap is confined and therefore has some artesian head. In someK24 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA areas the head is sufficient to raise the water level above the land surface, and the wells flow. The principal area of flowing wells is in the eastern part of the valley, extending from about 2 miles north of the international boundary northward for about 30 miles in a 6- to 10-mile-wide belt between the Alamo River and the East Highline Canal (fig. 12). Most of the wells are 350 to 1,300 feet deep, casings are 2 to 3 inches in diameter, are either slot perforated or not perforated, and are open at the bottom in fine- to medium-grained sand (tables 3 and 4). Total dissolved-solids content of the water commonly ranges from 700 to 5,000 mg/1 (milligrams per liter), and the percent sodium is more than 90. Only the better quality water is used for domestic and stock purposes. A few wells that yield hot water have been used to heat homes. The discharge from each of the several hundred wells in this area averages about 10 gallons per minute, so the annual discharge is only a few thousand acre-feet. 116*00' Figure 12. — Location of flowing wells, 1960-64. Irrigation of crops by pumping from wells was attempted prior to 1915 (Hutchins, 1915); however, only a few wells were being used for this purpose in the 1960’s — mainly to irrigate alfalfa in the lower Borrego Valley. On the northeast side of Imperial Valley, the Southern Pacific Co. drilled well 12S/16E-9A (table 3) in 1963 to provide a water supply for irrigating saltcedar windbreaks along its track. Well 16S/12E-16B, in the Pilot Knob area, was used for a few years in an attempt to irrigate citrus, but it was no longer being used at the time this study was completed. A group of wells in the Ocotillo-Coyote Wells area in the southeastern part of T. 16 S., R. 9 E., has been developed for industrial supply at the gypsum-products plant at Plaster City; for local, private, and public supply; and for drinking water to be delivered to other communities in the area. Pumpage probably is only a few hundred acre-feet per year. The Imperial Irrigation District uses wells 17S/18E-4A and 17S/17E-3C (table 3) to supply cooling water for the electrical turbine generators at drops 3 and 4, respectively, on the All-American Canal. A few wells have been drilled near the Hot Mineral Spa in sec. 2, T. 9 S., R. 12 E., in an effort to tap the source of the ground water that was discharging as springs and seeps under natural conditions. Some of the wells flow; the discharge of well 9S/12E-2A1 (table 3) reportedly was 900 gpm in September 1948. In addition to the aforementioned wells, 15 deep wells have been drilled by private interests as part of the exploratory programs for assessing and developing the vast geothermal resources of the area. The drilling has been centered in the Buttes area southeast of the Salton Sea, although preliminary investigations indicate that the thermal area probably is much more widespread. The activities regarding development of this resource are beyond the scope of this study. Information on the geothermal resources of the area, their magnitude, and some of the problems that have arisen with their development are contained in California Department of Water Resources Bulletin 143-7 (1970), entitled “Geothermal Wastes and the Water Resources of the Salton Sea Area.” DRAINS, RIVERS, AND UPWARD LEAKAGE Most of the ground-water discharge in Imperial Valley is by an extensive network of drains that serve the irrigated land. The network discharges about 1 million acre-feet per year of ground water and surface waste water, most of which previously had been diverted to cropland for irrigation. Some of the discharge, however, is water that has moved upward to the drains from the deeper aquifers, principally near the east edge of the irrigated area. The water-level contours on plate 1 indicate upward leakage of water from the main ground-water body to the Alamo and New Rivers and in the vicinity of the Salton Sea. However, the amount of such leakage averages only a few tens of thousands of acre-feet per year.GEOHYDROLOGIC RECONNAISSANCE OF THE IMPERIAL VALLEY, CALIFORNIA K25 CHEMICAL QUALITY OF THE GROUND WATER The geographic and* geologic controls that govern the occurrence, movement, and chemical quality of the ground water of the Salton Trough vary widely. The variability of the chemical quality of the water contained in the rocks is due to differences in location with respect to the water table and opportunities for recharge, to compositional differences in sources of rechage, and to the high evaporation rate in the hot arid climate. Some of the deeper ground water may be moderately altered connate ocean water. At shallower depths, the water in the deltaic deposits probably consists of evaporation residuals of water from prehistoric Lake Cahuilla or earlier fresh-water lakes. Some of the residual water may be nearly fresh, and some, moderately saline. Locally, the ground water may have become somewhat saline because storm runoff has leached soluble evapo-rites from sedimentary rocks now above the water table. Some small lenses of fresh ground water may have resulted from impoundment of runoff from the ephemeral desert washes against sand dunes, as along the northeast margin of the Sand Hills. In the following discussion, interpretations of chemical relations are based mainly on chemical analyses of water samples collected from wells. However, interpretations about physical conditions near some rotary-drilled wells are based on electric logs. The chemical analyses specifically referred to are in table 5. The individual analyses are grouped according to specific geographic areas, and the order of analyses in the areas is by blocks according to township, range, and section. Each analysis is given an identifying number, and if it is one of two or more analyses for a particular well, it is also given an identifying letter. In the discussions, references to analyses are made by these identifying numbers and letters. EASTERN IMPERIAL VALLEY CHOCOLATE MOUNTAINS PIEDMONT SLOPE Chemical analyses of water samples from 10 wells and one mine shaft on the Chocolate Mountains piedmont slope (table 5, analyses 1-11) indicate considerable differences in the quality of the ground water. Although the number of sites sampled is small relative to the area (more than 500 sq mi), the analyses suggest some generalizations associated with well location and depth. Water at higher altitudes appears to be less mineralized than water at lower altitudes. Also, water from deep wells apparently is generally more mineralized than water from shallow wells. Most of the shallow wells are dug wells, and most of them yielded usable water. Calcium bicarbonate water containing less than 500 mg/1 dissolved solids was obtained from two rather deep dug wells (table 5, analyses 1 and 11) that probably penetrate pockets of alluvium in hollows of the crystalline rocks of the mountains. Three shallow dug wells yielded water containing a mixture of calcium and sodium sulfates, lesser quantities of bicarbonate and chloride salts, and 849 to 1,080 mg/1 dissolved solids (table 5, analyses 2-4). Water of this type commonly is produced from shaly sediments. Water from the drilled wells, all of which are much deeper than the dug wells, contained a little less to substantially more dissolved solids than the most mineralized water from the dug wells. One drilled well about halfway down the piedmont slope yielded a sodium mixed-anion water containing 1,350 mg/1 dissolved solids (table 5, analysis 6). Three other drilled wells farther down the slope yielded water containing 844 to 1,510 mg/1 dissolved solids, predominantly sodium chloride; the extreme concentrations were different samples from the same well (table 5, analyses 8a and 8b). Two samples (table 5, analyses 5 and 9) were too highly mineralized for continued use as drinking water. One was from a mine shaft and may not be representative of ground water beneath the piedmont slope; the other sample was obtained many years ago from a well, now destroyed, that was used to supply water for a mine and probably was not used for drinking water. PILOT KNOB MESA-SAND HILLS AREA Water from wells in the Pilot Knob Mesa-Sand Hills area (table 5, analyses 12-28) has less areal range in quality than that from the Chocolate Mountains piedmont slope. However, samples were available from only two wells in the northwest end of the area; hence, the quality of water there is not well defined. Samples from a deep well (table 5, analyses 12a and b) drilled to supply water for a windbreak along the Southern Pacific Co. railroad were the most mineralized of any in the entire Pilot Knob Mesa-Sand Hills area. Although the chemical composition of the water was still changing after sec-eral hours of pumping, the analyses indicate that the water contains more than 2,000 mg/1 dissolved solids and is a mixture of sodium chloride and bicarbonate and lesser quantities of other constituents. This type of water probably is suitable for growing salt-tolerant plants in permeable soils. A single water sample (table 5, analysis 13) obtained in 1917 during the drilling of a well for railroad use at Amos indicated that the water would have been satisfactory for domestic use. The well was not completed, however, because the yield was inadequate. Water from the part of the Pilot Knob Mesa-Sand Hills area that is south and southeast of Ogilby contains less than 1,000 mg/1 dissolved solids and is satisfactory for domestic use. Generally, bicarbonate or chloride is the principal anion, and sodium is the principal cation; however, water from several small-diameter wells augered by the U.S. Geological Survey near the All-K26 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA American Canal contained more sulfate than any other anion and resembled Colorado River water except for being somewhat softer. The quality presumably reflects leakage from the All-American Canal. Evidence of changes in chemical quality of ground water resulting from such leakage is the variation in the quality of water obtained from well 16S/20E-27D (table 5, analyses 17a-d). Analysis 17a shows that in 1941, before the utilization of the All-American Canal, the ground water was mixed-anion type; analysis 17b shows that by 1958 it resembled Colorado River water. The only deep well in the southeastern part of the Pilot Knob Mesa-Sand Hills area yielded water having sodium and chloride as the principal ionic constituents (table 5, analysis 22). The water was used to irrigate alfalfa and citrus for 2 or 3 years, but apparently the soil was so permeable that pumping costs were excessive and irrigation was discontinued. According to reports, the chemical quality of the water was not a consideration in the cessation of irrigation. Several of the wells that were sampled have served as rural domestic supplies for 10 or more years. EAST MESA Part of the East Mesa probably has a greater potential for new ground-water development than any other part of the study area, because of the substantial recharge due to leakage from the All-American and Coachella Canals and the proximity of the Colorado River. Therefore, a determination of the quantity and chemical quality of ground water that might be developed on the East Mesa was given high priority during this study. Four deep test wells were drilled on the mesa as an aid in making this determination. Chemical analyses of water from 51 wells on the East Mesa (table 5, analyses 29-79) show substantial differences in chemical characteristics. The dissolved-solids concentrations ranged from 498 to 7,280 mg/1. However, more than three-fourths of the samples contained less than 2,000 mgA dissolved solids, so water containing less than this concentration can probably be obtained in a large part of the mesa. During and after the construction of the All-American and Coachella Canals, the U.S. Bureau of Reclamation and the Imperial Irrigation District installed several hundred observation wells extending just below the original water table or to an average depth of about 50 feet to determine the effects of the canals on the water table beneath the mesa. The Geological Survey analyzed many water samples bailed from these wells during this study and also studied earlier analyses of water from some of the wells. Study of the analyses by plotting on maps and by comparing samples taken from the same well indicated that a large percentage of the analytical results were spurious. The spurious analyses may have resulted from insufficient pumping of the wells before sampling to remove water standing in and around the casings that possibly might have been differentially concentrated by evaporation, changed by microbial activity, or altered by reaction with the iron casings. Consequently, analyses of water from the shallow observation wells are not included in table 5, and the only generalization made about water in the top few feet of the aquifer is that it is variable in composition and may have chemical characteristics unlike the water a few tens of feet below the water table. Twenty-nine of the 51 wells for which water analyses are shown in table 5 were small-diameter holes augered by the Geological Survey during the project investigation. Most of these wells were sampled by pumping them immediately after well points had been installed, generally at depths somewhat less than the total depth drilled; the several wells not sampled upon completion were later sampled by bailing. The analyses of the water from the augered wells did not exhibit the peculiarities of those from the network of shallow observation wells previously described, and they were in general agreement with analyses of water from nearby test and production wells. We concluded, therefore, that these samples are valid representations of the chemical quality of the ground water near the well-point settings. However, the conclusions based on these analyses probably would not be valid for depths substantially below the well points. Water containing less than 1,000 mg/1 dissolved solids (table 5, analyses 59-61 and 68-79) has been produced from all wells near the All-American Canal and U.S. Highway 80, both before and after the canal was constructed. However, the analytical data indicate that the water quality may have changed gradually as a result of infiltration of Colorado River water from the canal. Of the six samples (table 5, analyses 60, 61, 69, 72, 73a, and 73b) obtained from wells near the present location of the canal prior to its construction, five contained more chloride than sulfate. All but two samples obtained from wells in the same area since the canal was constructed contained more sulfate than chloride. Because the Colorado River water in the canal contains substantially more sulfate than chloride, the change in the chemical quality of the ground water is assumed to have resulted from infiltration of water from the canal. Chemical analyses of water from the six test wells in the southeast quarter of the East Mesa indicate a rather large volume of ground water that is nearly as suitable for irrigation and other purposes as present Colorado River water, although ground water in at least part of the area has relatively more chloride and less sulfate than the river water. Some of the ground water may contain as much as two or three times the dissolved-solids content of the river water (800 mg/1).GEOHYDROLOGIC RECONNAISSANCE OF THE IMPERIAL VALLEY, CALIFORNIA K27 The easternmost of the test wells, LCRP 6, was drilled for the Geological Survey near the head of the Coachella Canal. It was completed to a depth of 1,000 feet by the cable-tool method in April 1962 and was deepened to 2,519 feet by the rotary method in March 1964. Analyses of water samples obtained at numerous times during the drilling of the cable-tool section of the well indicated no great changes in chemical quality with depth. Water entered the well, as originally completed, through perforations at a depth of 340 to 520 feet below the land surface. Three samples of water (table 5, analyses 71a-c) entering the well through these perforations during different extended test periods showed that the chemical quality of the pumped water was not greatly different from that of recent Colorado River water and that it more nearly approached the composition of river water as pumping continued. The electric log indicated fresh water to the total depth (2,519 ft) of the rotary section of the well. Information obtained from the Imperial Irrigation District’s test wells 3 and 3a, which were drilled for the district in 1958 at its experimental farm 2, about 5 miles west of LCRP 6, gave the first indication of a substantial body of fresh ground water at depth in the East Mesa. Although the records concerning formations penetrated in drilling were obtained for both wells, chemical analyses of water were available for only one well. The two wells were drilled to depths of 275 and 500 feet, respectively, and were perforated from 40 to 240 feet and 69 to 273 feet, respectively. Evidently, development of the deeper materials was not considered feasible. The water from test well 3 (table 5, analyses 68a and b) was similar to Colorado River water except that the first analysis, 68a, indicated a large amount of fluoride. No plausible reason can be given for the 5 mg/1 fluoride that was reported, as this was the only well water in the area having a large concentration of fluoride. The sample may have been contaminated, or the analysis may be in error. However, high fluoride concentrations also occur in ground water beneath the central Imperial Valley, so the reported concentration may represent some unusual local condition. The area known to be underlain by ground water of good quality was extended 5 miles farther west on the basis of information obtained from well LCRP 18, drilled in May 1964 near drop 3 of the All-American Canal. The well was drilled by the rotary method to a depth of 815 feet, and an electric log was made. The well was then cased, perforated from 140 to 630 feet below the land surface, and pumped to determine aquifer characteristics. A water sample (table 5, analysis 59) obtained during the aquifer test contained 874 mg/1 dissolved solids, 93 mgA hardness, and approximately equal concentrations of bicarbonate, sulfate, and chloride. Obviously the water had not been greatly affected by infiltration from the nearby All-American Canal. To determine whether fresh ground water, similar to that found in LCRP 6 in 1962, extends northwestward along the Coachella Canal, the Geological Survey in 1963 arranged for the drilling of two deep rotary test wells. The pilot hole for one well, LCRP 11, 13 miles northwest of LCRP 6, was drilled to a depth of 1,140 feet. Casing was installed to a depth of 900 feet, and selective perforations were made from 309 to 894 feet below the land surface. The electric log of the pilot hole indicated fresh water (specific conductance less than 3,000 micromhos) to a depth of 250 feet and brackish water throughout the rest of the saturated deposits penetrated. The chemical quality of the water produced from the well varied slightly after pumping began but became uniform at the end of three tests (table 5, analyses 45a-c). Water from this well contained considerably less bicarbonate and sulfate, more calcium and magnesium, and substantially more sodium and chloride than the water produced from LCRP 6 (table 5, analyses 71a-c). The data indicate that the pumped water contained no leakage from the Coachella Canal. The pilot hole for another test well, LCRP 12, 5Vi miles northwest of LCRP 6, was drilled to a depth of 1,000 feet. An electric log indicated fresh water throughout the depth drilled. The well was cased to 630 feet, gravel packed, and completed by perforating the casing from 300 to 610 feet. Water obtained from the well immediately upon completion of development (table 5, analysis 66a) contained slightly more dissolved solids, a little less sulfate, and about double the chloride that is characteristic of recent Colorado River water. A sample collected 8 months later (table 5, analysis 66b), however, contained water very similar to recent Colorado River water. The change in chemical composition indicates that leakage from the Coachella Canal had moved downward through the gravel pack surrounding the well and into the principal water-bearing zone. After the Geological Survey completed its test-well drilling on the East Mesa, the U.S. Bureau of Reclamation investigated the area to determine if ground water might be recovered to augment surface-water supplies in the Imperial and Coachella Valleys. Using its own rotary drilling equipment, the Bureau drilled a 500-foot test hole north of the junction of U.S. Highway 80 and State Highway 98 about halfway between the All-American and Coachella Canals. The well was completed by inserting small-diameter pipes to four different depths and then by hydraulically isolating each pipe from the others. Water samples for chemical analysis were obtained by pumping from each of the pipes separately. The samples (table 5, analyses 57a-d) showed a small range in dissolved-solids content (708-929 mgA) and small differences in anion ratios, possibly caused byK28 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA the manner in which the samples were collected. However, all four samples indicate that the chemical quality of the water is good. We concluded, therefore, that the area of good-quality water extends across the southeast corner of the East Mesa. Water samples from augered wells on both sides of the Coachella Canal but mainly west of the canal indicate that water of the same general composition as that from well LCRP 11 probably is present at depths of 50 to 150 feet or more in the area between the edge of the Sand Hills and a line within 2 or 3 miles of the main Lake Cahuilla shoreline that extends northward from the international boundary to a few miles north of the Brawley-Glamis highway. The dissolved-solids content of the water may increase westward and range from 1,000 to 3,000 mg/1. An artesian well was drilled in 1961 to supply water for a proposed citrus project east of Holtville. Water from the well was sufficiently low in dissolved solids — 787 mg/1 (table 5, analysis 41a) — to be satisfactory for the proposed use, but the percent sodium (96) was too high, and the project was abandoned. About 10 miles farther north an unused 2-inch artesian well has flowed uncontrolled for many years. Two analyses of water from this well (table 5, analyses 36a and b) indicate that the water may be somewhat different in origin from that yielded by the artesian well east of Holtville. The dissolved-solids content (1,190 mg/1) is higher and consists of relatively more sodium chloride and less sodium bicarbonate. About 6 miles farther northeast a cable-tool test well was drilled for the Imperial Irrigation District to a depth of 329 feet. The well flowed when completed in 1958 but was capped and not used. Water from the well (table 5, analysis 30) contained 1,660 mg/1 dissolved solids, mainly sodium chloride, and 2.3 mg/1 boron. On the basis of this analysis, the water was deemed unfit for irrigation. Water samples from the augered wells within a mile or two of the west edge of the East Mesa (table 5, analyses 31, 38-40, and 51) indicate that the chemical quality of the shallow water is not uniform and that the water is generally more mineralized and contains more sulfate than water from artesian wells. The difference in chemical quality suggests that water from the augered wells probably is separated from the artesian water by a confining bed or beds and that it is at least partly derived from seepage from the East Main Canal. The East Mesa narrows northwestward to the limiting boundary of the Sand Hills near Mammoth Wash, where it becomes difficult to define. However, for discussion, it is arbitrarily extended northwestward to include the areas where the land-surface altitudes are 30 to 160 feet above mean sea level. Two analyses of water samples (table 5, analyses 29a and b) from a private well in this northern extension of East Mesa indicate that the local ground water contains more dissolved solids (2,190 mgA) than most ground water in the southeastern part of the mesa. The well, drilled to a total depth of 550 feet, was perforated only from 25 to 150 feet below the land surface. The rather high ratio of sulfate to chloride suggests that the water, in part, may have been seepage from the nearby Coachella Canal. CENTRAL IMPERIAL VALLEY Deep exploration holes drilled to find oil or water have shown that most of the central Imperial Valley is underlain by great thicknesses of water-saturated lacustrine and playa deposits overlying older sediments. Studies elsewhere have shown that such deposits generally have low vertical permeability and that water from them may be moderately to highly mineralized in some zones and fresh in others. Thus, the shallow ground water (water immediately below the root zone of plants) may be saline, and the deeper water, which is separated from the shallow water by a layer of poorly permeable material, may be fresh. Many years ago widespread waterlogging developed as a result of repeated irrigation whose only drainage was slow seepage to the Alamo and New Rivers. Evaporation from the waterlogged areas increased the salinity of both the soil and the shallow ground water. Later, networks of ditch and tile drains extending throughout the cultivated area were constructed. Waterlogging is now virtually ended, and unconfined ground-water levels have been stabilized at depths between 5 and 20 feet below the land surface. However, white saline crusts still persist in uncultivated fields and along river, canal, and drain banks, indicating that the shallow ground water is still rather saline in most of the areas that formerly were waterlogged. Although the extent to which usable ground water occurs in the central Imperial Valley is unknown, the occurrence of such water certainly must be limited. Early attempts to construct wells to supply municipal water at Brawley and El Centro were failures. The only successful large-capacity wells drilled in the area are two drain wells adjacent to major canals. Many small artesian wells have supplied domestic water in an area east of the Alamo River extending from about 6 miles south of Holtville to several miles northeast of Calipatria. Old records indicate that wells west of the Alamo River are not likely to flow and that they have water of very poor chemical quality. Chemical analyses of water from 115 wells in the central Imperial Valley are shown in table 5. There are 86 privately owned artesian wells, 22 observation wells augered by the Geological Survey, 4 test and 2 drainage wells owned by the Imperial Irrigation District, and 1 test well drilled for the Geological Survey. Because allGEOHYDROLOGIC RECONNAISSANCE OF THE IMPERIAL VALLEY, CALIFORNIA K29 the artesian wells and several other wells are east of the Alamo River, the analytical data are greatly biased toward the eastern part of the area. Although the artesian water has a rather large range of dissolved-solids content, it includes only a small number of different compositional types. The dissolved-solids content of the artesian water ranged from 663 to 5,710 mg/1, but most of the concentrations ranged from 1,000 to 2,000 mg/1. Salts dissolved in the artesian water are mainly mixtures of sodium chloride and sodium bicarbonate, but the water from a few wells contains considerable sodium sulfate. Generally, the least concentrated artesian waters contain bicarbonate as the dominant anion or contain equal or nearly equal amounts of bicarbonate and chloride. As the dissolved-solids content increases, the bicarbonate content tends to become less than the chloride content until, in the most concentrated artesian water, the chloride content is several times larger than the bicarbonate content. The sulfate content of water samples from a large number of the artesian wells is less than 100 mg/1; one sample contained no sulfate. Sulfate contents greater than 100 mg/1 generally are associated with high chloride contents. However, the water that contained 5,710 mg/1 dissolved solids (table 5, analysis 110) contained 2,200 mg/1 sulfate and only 1,360 mg/1 chloride. Several characteristics make the artesian water rather undesirable for various uses. Most of the samples analyzed for fluoride content contained more than 0.8 mg/1 recommended as the upper limit for drinking water in hot climates, and many contained more than the 1.7 mgA recommended as the upper limit for cool climates (U.S. Public Health Service, 1962). All the samples contained more than 80 percent sodium, and most contained more than 90 percent. Because of these high percents sodium, the artesian water probably would be hazardous for continued irrigation. Boron concentrations were moderately high (0.67-2.50 mgA) for most of the samples analyzed for that constituent. However, in several analyses the boron content was greater than the upper limit (3.75 mgA) considered acceptable for any crop. Analyses of successive water samples from the same wells taken over a long period of time showed, for the most part, only small changes in the chemical quality of the water, such as might result from analytical errors or differences in analytical procedures. However, the analyses of samples from one well (table 5, analyses 134a-e) showed a considerable reduction in both chloride and dissolved solids that may indicate a real reduction in the mineral content of the water yielded by the well. Areal differences in the chemical quality of the artesian water were studied by plotting diagrams prepared from the chemical-analysis data at points on topogra- phic maps corresponding to well locations. The diagrams suggested some generalizations of chemical patterns, but the generalizations were far from conclusive. Apparently, the water from artesian wells near the East Highline Canal contains less dissolved solids and more bicarbonate than water from wells farther west. Also, the highest dissolved-solids contents were found mainly in water from wells within a few miles of the Alamo River. However, exceptions to both patterns indicate that there may be zones yielding fair to poor water between other zones yielding better water. With but two exceptions, both of which were flowing wells, the augered wells yielded water from below the root zone of plants and above the uppermost zone likely to yield artesian water. The chemical analyses of the water samples from the 20 nonflowing augered wells indicate that the prospects for obtaining water acceptable for domestic use at depths of less than 150 feet are poor. Only three water samples from nonflowing augered wells contained less than 2,000 mgA dissolved solids, whereas 11 samples contained more than 9,000 mgA dissolved solids. The chemical characteristics of the water from these wells were quite variable, but generally the bicarbonate content was less than the sulfate content, and the sulfate content was less than the chloride content. Although sodium was the principal cation in almost all the samples from these wells, the water contained enough calcium and magnesium to produce several hundred milligrams per liter noncarbonate hardness. Thus, the upper water can be differentiated from the deeper artesian water, because the latter generally contained much more bicarbonate than sulfate, rather low concentrations of calcium and magnesium, and moderately low to zero noncarbonate hardness. East of the Alamo River two augered wells penetrated artesian water under sufficient head to cause the wells to flow. A water sample from one well (table 5, analysis 83) had the highest specific conductance and the highest chloride content of any water sampled in the central Imperial Valley during this study. The water from the other well (table 5, analysis 122) was very similar to water from nearby privately owned flowing wells. Analyses of water from the five test wells in the central Imperial Valley support the generalizations based on the analyses of samples from the artesian and augered wells. A well drilled east of Calexico in 1958 for the Imperial Irrigation District was perforated between the depths of 110 and 450 feet and yielded water contained 5,610 mg/1 dissolved solids (table 5, analysis 192), most of which were a mixture of sodium chloride and sodium sulfate. A 1,000-foot well at the west edge of Calexico, drilled for the Geological Survey in 1962, yielded from strata below a packer set at 260 feet water containing 4,920 mgA dissolved solids (table 5, analysis 191), principally sodium salts, and the ratio of chloride to sulfate was higher thanK30 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA that for the water from the well east of Calexico. Farther north, at Imperial, a 500-foot test well that was drilled for the Imperial Irrigation District in 1958 yielded only a small quantity of water. The dissolved-solids content, most of which was sodium chloride, exceeded 10,000 mg/1 (table 5, analyses 149a and b). Two of the Imperial Irrigation District test wells drilled in 1958 penetrated artesian strata. One well, 603 feet deep, near the East Highline Canal southeast of Holtville, was perforated in three zones: 590 to 432 feet, 400 to 320 feet, and 234 to 46 feet below the land surface. Samples of water bailed from each of the two lower zones were of similar chemical composition (table 5, analyses 187a and b); each sample contained about 1,000 mg/1 dissolved solids of mixed sodium salts and was very much like water produced from several nearby privately owned artesian wells. Water bailed from the upper perforated zone (table 5, analyses 187c and d) was much more highly mineralized; the samples contained 5,750 and 6,890 mg/1 dissolved solids, respectively, consisting mainly of sodium sulfate and sodium chloride but also including considerable quantities of calcium and magnesium salts Water (table 5, analyses 171a-c) from the second artesian test well, about 3 miles northeast of Holtville, also was different in chemical composition, depending on the zone from which the water was obtained. Analyses (182 and 188, table 5) of water from two rather shallow drain wells on opposite sides of the central Imperial Valley suggest the possibility that careful exploration might disclose sites near major canals where ground water of good quality can be obtained from shallow permeable zones. Both wells were drilled in 1947 and were pumped for several years but were not in use when visited in 1962. The chemical quality of the water from the wells was very similar to that of Colorado River water. WESTERN IMPERIAL VALLEY Much of the area of the western Imperial Valley is referred to locally as the West Mesa. In this study, however, the term “West Mesa” is restricted to a smaller area, considered suitable for irrigation, that is immediately west of the Westside Main Canal. Major subdivisions of the western Imperial Valley are the lower Borrego Valley, the San Felipe Creek-Superstition Hills area, the Coyote Valley, and the West Mesa and Yuha Desert. LOWER BORREGO VALLEY The lower Borrego Valley, which has also been referred to as the Ocotillo Valley, extends north and northwest of the Fish Creek Mountains. The valley is mostly barren desert, but it contains scattered areas where ground water is pumped for irrigation; and old maps show numerous wells, many of which no longer exist. Most of the irrigation is in San Diego County. Water samples (table 5, analyses 195-198) were collected from four wells in San Diego County, although several times this number of wells may be in use. The chemical analyses indicate that the ground water is satisfactory for irrigating most crops grown in the Imperial Valley. One of the wells, used for domestic supply, yielded water of substantially better quality (table 5, analysis 196) than that obtained from the other three. Water from three irrigation wells (table 5, analyses 199-201) in the Imperial County part of the valley was more highly mineralized than the water from the irrigated area in San Diego County. Although chemical characteristics of water from the wells sampled in the lower Borrego Valley differed from well to well, without exception, sodium was the dominant cation, and bicarbonate was less abundant than sulfate or chloride. The analyses also indicate that the dissolved-solids content of the ground water increases eastward. SAN FELIPE CREEK-SUPERSTITION HILLS AREA The San Felipe Creek-Superstition Hills area, north of Superstition Mountain and between the central Imperial Valley and the lower Borrego Valley, is a somewhat dissected part of the western Imperial Valley surrounding the Superstition Hills. The surface drainage is mostly to San Felipe Creek and thence to the Salton Sea, but some washes flow directly into the sea. A part of the area is flat enough to be cultivated, and sufficient wells are indicated on old maps to suggest that attempts have been made to develop ground water. The lack of other evidence of development suggests that satisfactory ground-water supplies were not found. Three water samples (table 5, analyses 202a-c) collected from Harper’s Well in 1918, 1949, and 1962, respectively, were of a nearly uniform mixed sodium chloride sulfate type that could be used for drinking water but that probably contained too much sodium for irrigating clay soils. The water from nearby Harper’s Spring, sampled in 1949 (table 5, analysis 203), was somewhat more mineralized, but this may be partly the result of evapotranspiration of water seeping from Harper’s Well. Another old well yielded moderately saline water containing 3,920 and 4,520 mg/1 dissolved solids when sampled in 1949 and 1962, respectively (table 5, analyses 204a and b). Sodium chloride was the principal salt, and the sulfate ion concentration was low. Water from this well ordinarily would not be considered satisfactory for drinking by humans except in an emergency, although it probably could be drunk by animals. To determine whether substantial quantities of usable water could be obtained nearer the Salton Sea, the Geological Survey in 1964 contracted for the drilling of a deep rotary test well, LCRP 19, near the intersection ofGEOHYDROLOGIC RECONNAISSANCE OF THE IMPERIAL VALLEY, CALIFORNIA K31 California State Highway 78 and U.S. Highway 99, and a short distance from the channel of San Felipe Creek. The well was drilled to a depth of 958 feet; the casing was perforated from 310 to 650 feet below the land surface. When completed, the well flowed about 200 gpm. Water from the well (table 5, analyses 205a and b) contained slightly more than 1,400 mg/1 dissolved solids, mostly sodium salts; chloride was the principal anion, although considerable sulfate also was present. Boron content was 2.0 and 2.6 mg/1, respectively, in the two water samples. Water from this well, therefore, might be satisfactory for domestic use, whereas it might not be satisfactory for irrigation. A shallow test well was also drilled at the same site, and the casing was perforated from 35 to 55 feet below the land surface. The water (table 5, analysis 206) from the well contained 8,420 mg/1 dissolved solids consisting of a mixture of sodium chloride and sodium sulfate and slight amounts of other salts. At this locality the shallow water and the deep artesian water evidently are separated by very poorly permeable deposits. Springs formerly were used regularly as watering places in the Colorado Desert, but they have been used much less since the automobile replaced the horse as a means of travel. Thus, the apparent large increase in the dissolved-solids content of two water samples (table 5, analyses 207a and b) taken in 1917 and 1962, respectively, from Kane Spring may be more the result of differences in the way the area around the spring was maintained at the times of sampling than of real changes in water quality. If so, the much higher concentration (5,270 mgA) represents a change because of greater evap-otranspiration at the spring; cleaning the springs might result in a return to the 1917 quality. However, water of even this lower concentration (2,090 mg/1) would not be considered very satisfactory by most travelers today. COYOTE VALLEY Coyote Valley is the only area in the western Imperial Valley south of San Felipe Creek where development of ground water has been significant. The area extends from a boundary west of Ocotillo to a boundary east of the former railroad station at Coyote Wells. A few dozen wells scattered over several sections of land supply domestic and municipal water that is used both locally and at Plaster City, about 10 miles northeast. Water from wells near Ocotillo is hauled in tank trucks to Mexicali, where it is sold for drinking water. Most of the wells in Coyote Valley yield soft bicarbonate water containing less than 400 mg/1 dissolved solids (table 5, analyses 208-216 and 220b). Limited data indicate that most of the wells are screened or perforated between depths of 100 and 500 feet. Dissolved-solids content of the water is higher, and the depth of perforations in the casings of wells is shallower, toward the east end of the productive area. The principal undesirable characteristic of the water is the high concentration of fluoride. About half of the water samples whose fluoride concentrations were determined contained at least 2.0 mg/1 fluoride, and several samples contained more than 3.0 mg/1. WEST MESA AND YUHA DESERT The large, nearly barren area east of the Coyote Valley development and between the international boundary and Superstition Mountain is designated as the West Mesa for that part north of U.S. Highway 80 and as the Yuha Desert for that part south of the highway. Irrigation from wells was attempted on the West Mesa prior to 1915 (Hutchins, 1915), but apparently the undertaking was a failure. No information is now available as to the quantity or quality of the water that was developed. To obtain information concerning the availability and chemical quality of the ground water in the West Mesa, the Geological Survey contracted for a deep rotary test well, LCRP 8, at a site about 7 miles north of Plaster City. The well was drilled to a depth of 985 feet and was completed by perforating the casing from 135 to 560 feet. Two water samples (table 5, analyses 221a and b) obtained when the well was being tested differed slightly in mineral content. If the well had been fully developed as a production well, the water would have contained about 2,000 mg/1 dissolved solids, with sodium sulfate the dominant mineral salt. The water probably would be satisfactory for irrigating salt-tolerant crops. During its 1958 test-drilling program, the Imperial Irrigation District drilled one well about a mile north of Dixieland and about half a mile west of the district’s Westside Main Canal. A water sample from this well (table 5, analysis 224) contained 2,620 mg/1 dissolved solids, mainly sodium chloride and sodium sulfate salts. The water was not considered satisfactory for irrigation because of the availability of canal water of better quality. However, water having a chemical composition similar to that of the well water has been used for irrigation in other areas of the Colorado River basin. As a part of its exploratory program the Geological Survey drilled two wells with a power auger near the east edge of the West Mesa. The permeability of the materials penetrated appeared to be low, and the chemical quality of the water (table 5, analyses 222 and 223) was poor (5,210 and 4,680 mgA dissolved solids, respectively). The prospects for obtaining much usable water in this area also appear to be poor. Small quantities of good-quality ground water may be present in the west edge of the Yuna Desert, but information on chemical quality is sparse and undependable. A water sample (table 5, analysis 232) taken from an oil test hole about 5 miles southeast of Ocotillo contained 721 mgA dissolved solids, which consisted mainly of a mixture of sodium salts; chloride was the principalK32 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA anion. Water samples (table 5, analyses 228a and b) reported to have been obtained in 1952 and 1958 from an oil test hole that was finished as a water well contained 493 and 568 mg/1 dissolved solids, respectively. When the site was visited in 1962, the well was not found, but two water samples (table 5, analyses 229 and 230) taken from nearby shallow dug wells contained 13,000 and 2,630 mg/1 dissolved solids, respectively. The much higher concentrations in the water from the shallow dug wells suggest that better water might be obtained at greater depths. A water sample (table 5, analysis 233) from an auger hole drilled by the Geological Survey where Pinto Wash crosses State Highway 98 contained 2,770 mg/1 dissolved solids. REFERENCES CITED Allison, E. C., 1964, Geology of areas bordering Gulf of California, in van Andel, T. H., and Shor, G. G., Jr., eds., Marine geology of the Gulf of California (a symposium): Am. Assoc. Petroleum Geologists Mem. 3, p. 3-29. Arnal, R. E., 1961, Limnology, sedimentation, and microorganisms of the Salton Sea, California: Geol. Soc. America Bull., v. 72, p. 427-478. Bedinger, M. S., and Emmett, L. F., 1963, Mapping transmissibility of alluvium in the lower Arkansas River valley, Arkansas, in Geological Survey research 1963: U.S. Geol. Survey Prof. Paper 475-C, p. C188-C190. Biehler, Shawn, 1964, Geophysical study of the Salton Trough of southern California: California Inst. Technology unpub. Ph. D. thesis, 145 p. Biehler, Shaw, Kovash, R. L., and Allen, C. R., 1964, Geophysical framework of northern end of Gulf of California structural province, in van Andel, T. H., and Shor, G. G., Jr., eds., Marine geology of the Gulf of California (a symposium): Am. Assoc. Petroleum Geologists Mem. 3, p. 126-143. Blake, W. P., 1856, U.S. Pacific Railroad Exploration: U.S. 33d Cong., 2d sess., H. Ex. Doc. 91, v. 5, pt. 2, 50 p. Brown, J. S., 1923, The Salton Sea region, California: U.S. Geol. Survey Water-Supply Paper 497, 292 p. Bushee, Jonathan, Holden, John, Geyer, Barbara, and Gastil, Gordon, 1963, Lead-alpha dates for some basement rocks of southwestern California: Geol. Soc. America Bull., v. 74, p. 803-806. Buwalda, J. P., and Stanton, W. L., 1930, Geological events in the history of the Indio Hills and Salton Basin, southern California: Science, new ser., v. 71, p. 104-106. California Department of Water Resources, 1964, Coachella Valley investigation: California Dept. Water Resources Bull. 108, 145 p. ______1970, Geothermal wastes and the water resources of the Salton Sea area: California Dept. Water Resources Bull. 143-7, 123 p. Christensen, A. D., 1957, Part of the geology of the Coyote Mountain area, Imperial County, California: California Univ., Los Angeles, unpub. M.A. thesis, 188 p. Crowell, J. C., 1962, Displacement along the San Andreas fault, California: Geol. Soc. America Spec. Paper 71, 61 p. Crowell, J. C., and Susuki, Takeo, 1959, Eocene stratigraphy and paleontology, Orocopia Mountains, southeastern California: Geol. Soc. America Bull., v. 70, p. 581-592. Dibblee, T. W., Jr. 1954, Geology of the Imperial Valley region, in Jahns, R. H., ed., Geology of southern California: California Div. Mines Bull. 170, chap. 2, p. 21-28. Downs, Theodore, and Woodard, G. D., 1961, Middle Pleistocene extension of the Gulf of California into the Imperial Valley [abs.]: Geol. Soc. America Spec. Paper 68, p. 21. Durham, J. W., 1954, The marine Cenozoic of southern California, in Jahns, R. H., ed., Geology of southern California: California Div. Mines Bull. 170, chap. 3, p. 23-31. Durham, J. W., and Allison, E. C., 1961, Stratigraphic position of the Fish Creek Gypsum at Split Mountain Gorge, Imperial County, California [abs.]: Geol. Soc. America Spec. Paper 68, p. 22. Fenneman, N. M., 1931, Physiography of western United States: New York, McGraw-Hill Book Co., 534 p. _______1946, Physical divisions of the United States: U.S. Geol. Survey 1 : 7,000,000-scale map. Ferris, J. G., Knowles, D. B., Brown, R. H., and Stallman, R. W., 1962, Theory of aquifer tests: U.S. Geol. Survey Water-Supply Paper 1536-E, p. 69-174. Free, E. D., 1914, Sketch of the geology and soils of the Cahuilla Basin, in MacDougal, D. T., and others, The Salton Sea: Carnegie Inst. Washington Pub. 193, p. 21-33. Hamilton, Warren, 1961, Origin of the Gulf of California: Geol. Soc. America Bull., v. 72, no. 9, p. 1307-1318. Hely, A. G., 1969, Lower Colorado River water supply — its magnitude and distribution: U.S. Geol. Survey Prof. Paper 486-D, 54 p. Hely, A. G., Hughes, G. H., and Irelan, Burdge, 1966, Hydrologic regimen of Salton Sea, California: U.S. Geol. Survey Prof. Paper 486-C, 32 p. Hely, A. G., and Peck, E. L., 1964, Precipitation, runoff, and water loss in the lower Colorado River-Salton Sea area: U.S. Geol. Survey Prof. Paper 486-B, 16 p. Hubbs, C. L., Bien, G. S., and Suess, H. E., 1963, La Holla natural radiocarbon measurements III: Radiocarbon, v. 5, p. 254-272. Hutchins, W. A., 1915, Report on investigation of wells in Imperial Valley, 1914: California Dept. Engineering Bull. 1, p. 59-74. Irelan, Burdge, 1971, Salinity of surface water in the lower Colorado River-Salton Sea area: U.S. Geol. Survey Prof. Paper 486-E, 40 p. Jahns, R. H., 1954, Geology of the Peninsular Range province, southern California and Baja California, in Jahns, R. H., ed., Geology of southern California: California Div. Miles Bull. 170, chap. 2, p. 29-52. Kovach, R. L., Allen, C. R., and Press, Frank, 1962, Geophysical investigations in the Colorado delta region: Jour. Geophys. Res., v. 67, no. 7, p. 2845-2871. Larson, R. L., Menard, H. W., and Smith, S. M., 1968, Gulf of California — a result of ocean-floor spreading and transform faulting: Science, v. 161, p. 781-784. Littlefield, W. M., 1966, Hydrology and physiography of the Salton Sea, California: U.S. Geol. Survey Hydrol. Inv. Atlas HA-222. Meidav, Tsvi, 1969, Geoelectrical exploration of a geothermal area in southern California [abs]: Am. Geophys. Union Trans., v. 50, no. 4, p. 348. Mendenhall, W. C., 1909a, Some desert watering places in southeastern California and southwestern Nevada: U.S. Geol. Survey Water-Supply Paper 224, 98 p. _______1909b, Ground waters of the Indio region, California, with a sketch of the Colorado Desert: U.S. Geol. Survey Water-Supply Paper 225, 56 p. Merriam, Richard, and Bandy, O. L., 1965, Source of upper Cenozoic sediments in Colorado delta region: Jour. Sed. Petrology, v. 35, no. 4, p. 911-916. Metzger, D. G., 1968, The Bouse Formation (Pliocene) of the Parker-Blythe-Cibola area, Arizona and California, in Geological Survey research 1968: U.S. Geol. Survey Prof. Paper 600-D, p. D126-D136. Metzger, D. G., Loeltz, O. J., and Irelan, Burdge, 1974, Geohydrology of the Parker-Blythe-Cibola area, Arizona and California: U.S. Geol. Survey Prof. Paper 486-G, 130 p. Muffler, L. J. P., and Doe, B. R., 1968, Composition and mean age of detritus of the Colorado River delta in the Salton Trough, southeastern California: Jour. Sed. Petrology, v. 38, p. 384-399.GEOHYDROLOGIC RECONNAISSANCE OF THE IMPERIAL VALLEY, CALIFORNIA K33 Norris, R. M., and Norris, K. S., 1961, Algodones Dunes of southeastern California: Geol. Soc. America Bull,, v. 72, p. 605-620. Olmsted, F. H., Loeltz, O. J., and Irelan, Burdge, 1974, Geohydrology of the Yuma area, Arizona and California: U.S. Geol. Survey Prof. Paper 486-H, 227 p. Rex, R. W., and Randall, Walter, 1969, New thermal anomalies in the Imperial Valley of California [abs.]: Am. Geophys. Union Trans., v. 50, no. 4, p. 348. Robison, J. H., 1965, Environment of the Imperial trough, California, during the Quaternary — a paleogeographic problem [abs.]: Geol. Soc. America Ann. Mtg., Cordilleran Sec., Fresno, Calif., p. 47. Smith, P. B., 1968, Pliocene (?) Foraminifera of the lower Colorado River area, California and Arizona [abs.]: Geol. Soc. America Ann. Mtg., Cordilleran Sec., Tucson, Ariz., 1968, p. 111-112. Stanley, G. M., 1962, Prehistoric lakes in Salton Sea basin [abs.]: Geol. Soc. America Ann. Mtg., Houston, Tex., p. 149A-150A. Tarbet, L. A., and Holman, W. H., 1944, Stratigraphy and micropaleontology of the west side of Imperial Valley, California [abs.]: Am. Assoc. Petroleum Geologists Bull., v. 28, p. 1781-1782. Theis, C. V., 1935, The relation between the lowering of the piezomet- ric surface and the rate and duration of discharge of a well using ground-water storage: Am. Geophys. Union Trans., 16th Ann. Mtg., pt. 2, p. 519-524. Theis, C. V., Brown, R. H., and Meyer, R. R., 1963, Estimating the transmissibility of aquifers from the specific capacity of wells, in Bentall, Ray, compiler, Methods of determining permeability, transmissibility, and drawdown: U.S. Geol. Survey Water-Supply Paper 1536-1, p. 331-340. Thomas, R. G., 1963, The late Pleistocene 150-foot fresh water beach line of the Salton Sea area: Southern Calif. Acad. Sci.Bull., v.62, pt. l,p. 9-17. U.S. Public Health Service, 1962, Drinking water standards: U.S. Public Health Service Pub. 956, 61 p. Woodard, G. D., 1961, Stratigraphic succession of the west Colorado Desert, San Diego and Imperial Counties, southern California [abs.]: Geol. Soc. America Ann. Mtg., Cordilleran Sec., San Diego, Calif., 1961, p. 73-74. Woodring, W. P., 1932, Distribution and age of the marine Tertiary deposits of the Colorado Desert: Carnegie Inst. Washington Pub. 418, p. 1-25.BASIC DATAK36 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA Table 3. — Records of selected wells and springs Well location: See text section entitled “Well-Numbering System” for explanation. Owner or name: LCRP, Lower Colorado River Project (U.S. Geol. Survey). Altitude of land surface: Approximate altitude above ( + ) or below (-) mean sea level. Depth of well: Greatest depth to which well was drilled; well may have been completed or tested at a shallower depth. M, measured depth; all others reported. Type of well: D, dug; C, drilled by cable-tool method; R, drilled by rotary method; A, augered; G, gravel packed (if known or reported). Water level: F, flowing artesian, static level unknown; R, reported. Type of pump and power: T, turbine; S, submersible; J, jet; P, pitcher; N, none; E, electric; G gasoline. Use of well: Irr., irrigation; Ind., industrial or mining; PS, public supply; Dom., domestic; S stock; T, deep test hole; 0, shallow observation well; U, unused; Des., destroyed or filled in above the water table. Discharge: E, estimated; R, reported. Other data available: Data in files of U.S. Geol. Survey. D, driller’s log; E, electric log; G, gamma-ray log; T, temperature log; P, pumping-test data; W, hydrograph or periodic water-level measurements; C, chemical analysis of water.] Well location Owner or name Year completed Altitude of land surface Depth of well Type of Diameter (in.) Perforated interval Water level Feet above (+) Date or below (—) measured Pump and Use of Discharge Other data - ~Yb~ ~ 0.68~ 2,020 525 470 69 3,790 7.5 45c 1-14-64 23 158 43 504 59 200 1,000 1,960 570 522 66 3,790 7.3 19M1 155- 157 46 1-17-62 26 122 58 411 74 57 935 — — — 1,650 545 484 62 3,360 7.9 19M2 94- 96 47 3- 2-64 16 139 63 694 127 250 1,240 .8 2,470 606 502 71 4,541 7.9 26R 82- 84 48 5-16-63 32 87 32 204 200 317 211 .7 984 350 186 56 1,600 7.6 15S/19E28N 155- 157 49 2-19-64 39 143 5.6 885 94 225 1,410 1.9 2,760 380 303 84 5,060 7.8 33R 155- 157 50 3- 6-64 29 111 10 505 98 233 775 1.0 1,710 320 240 77 3,180 8.6 16S/16E-12Q 92- 94 51 1-22-62 13 101 55 750 265 600 900 — — 2,550 478 263 77 4,340 8.0 16S/17E-23R 155- 157 52 2-24-64 21 49 21 403 296 120 508 .9 1,270 210 0 81 2,340 8.0 16S/18E-2R 134- 136 53 2-16-65 30 127 49 860 123 412 1,320 2,860 520 419 78 4,900 7.7 6R 145- 147 54 2-16-65 28 94 30 574 120 275 865 1,930 356 258 78 3,480 7.9 13R 145- 147 55 4-22-64 22 47 16 287 104 225 345 __i!b~ 995 185 100 77 1,780 7.4 17R 155- 157 56 2-19-64 22 26 11 280 150 212 265 1.4 — — 892 112 0 84 1,530 8.0 23A 58- 60 57a 9-16-64 10 28 7.7 234 4.3 145 175 227 1.1 1.9 .41 761 102 0 82 1,300 8.1 148- 150 57b 9- 5-64 20 36 16 272 4.3 128 224 289 1.1 3.1 .46 929 156 52 78 1,570 8.2 298- 300 57c 9-16-64 21 23 7.7 216 5.4 134 171 192 1.3 3.7 0.36 708 89 0 83 1,200 8.1 498- 500 57d 9-15-64 26 24 7.8 213 13 122 156 211 1.0 3.7 .38 717 91 0 81 1,220 8.2 29J 155- 157 58a 1-22-64 30 16 7 282 186 180 242 — — — 850 68 0 90 1,450 8.2 58b 2-19-64 27 12 7.3 271 192 165 224 1.9 804 60 0 91 1,370 8.1 32R 140- 630 59 6-30-64 27 23 8.6 272 4.0 208 235 200 1.7 ""5" .64~ 874 93 0 86 1,460 8.0 35P1 60 12- 4-17 38 29 17 238 170 158 252 .34 818 142 3 78 35P2 61 2-14-41 12 16 257 96 279 215 1.0 828 96 18 85 ~M40 16S/19E-2N1 136^” 138 62 2- 3-62 _ 25 ~ 65 22 153 136 316 102 — — — 751 252 140 57 1,170 ~ 7.8 2N2 62- 65 63 2- 3-62 5 58 26 140 70 295 149 688 250 192 55 1,130 7.4 5J 82- 84 64 5-14-63 23 44 12 445 110 350 474 ~~iT 1,400 160 70 86 2,390 7.8 9E 134- 136 65 2-13-64 20 41 6.7 278 98 208 308 1.3 912 130 50 82 1,670 7.8 11D 300- 610 66a 5-14-63 26 52 7.4 253 131 285 216 .6 ~ rr ~ .24 905 160 52 77 1,490 7.7 66b 1-14-64 25 76 8.6 196 145 357 118 — 1.2 .14 854 232 113 64 1,300 7.3 15Q 72- 74 67 5-16-63 24 87 31 316 112 412 438 .6 1,420 344 252 70 2,390 7.5 32G1 40- 240 68a 5-29-58 19 54 29 202 6.1 163 343 150 5.0 ~~iY 891 255 120 63 7.8 68b 6-19-58 63 31 160 12 146 300 160 .8 800 287 166 54 8.0 36P1 69 1933 38 11 144 156 102 145 0 518 140 12 69 -_900 36P2 — 70a 3- 3-52 — 84 29 105 .4 176 265 103 .6 ~~2~b~ — 679 329 184 41 — ~~ 8.3 70b 5-13-58 104 38 140 178 380 140 900 416 270 44 1,400 7.9 70c 7-18-61 82 29 121 163 305 96 715 324 190 45 1,140 7.9 70d 9- 4-63 82 29 120 154 292 109 T 730 324 198 45 1,170 7.4 16S/20E-31K 340- 520 71a 5- 2-62 21 78 16 138 5.9 149 293 103 .1 .8 ” _.14~ 729 259 137 53 1,130 8.0 71b 6-26-63 21 81 18 142 152 300 104 .3 1.2 .14 743 276 152 53 1,140 7.4 71c 1-13-64 17 80 20 146 150 312 106 .3 756 280 157 53 1,150 7.4 32 72 12- 4-17 26 32 12 138 134 106 146 501 129 20 70 32R1 __ 73a 1933 44 12 138 149 102 155 ~ 0~~ 525 160 38 65 --900 73b 2-14-41 31 13 137 135 102 146 ” _.2(f 498 132 21 69 919 32R2 82- 84 74 7- 5-62 3 97 4.4 122 66 250 150 — — — 659 260 206 50 1,090 ~ 6.9 K50 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA17S/17E-3C1 75a 4- 4-50 65 30 126 171 75b 3-13-52 27 31 393 229 3C2 _ 76a 6-23-53 76 35 116 174 76b 9-27-61 — 76 32 149 162 17S/18E-4A 179- 195 77a 9-27-61 18 21 8.4 226 160 77b 6-15-64 26 23 8.1 213 162 4K 160- 175 78 11-24-47 37 17 159 165 17S/19E-4 25- 96 79 4- 2-52 7 ~ 102 19 15 195 280 91 678 286 146 49 1,080 116 525 1,210 196 8 81 298 96 708 335 192 42 "l"l50 342 110 — — — 803 320 187 50 1,210 7.8 215 158 726 87 0 85 1,190 8.0 208 143 ~'iT 704 91 0 84 1,170 7.8 115 179 0.2 589 162 27 68 1,100 277 160 820 332 172 1,380 ~ 5.5 CENTRAL IMPERIAL VALLEY 10S/14E-20N 80 4-28-61 210 6,050 2,440 2,270 19,200 8.0 11S/13E-22H 145- 147 81 5-10-62 3 134 49 384 100 275 710 1,600 535 453 61 3,120 7.4 12S/12E-25F1 __ 103- 105 82 2- 1-62 2 107 86 295 79 425 535 1,490 620 555 51 2,710 7.4 25F2 __ 14- 16 83 2- 1-62 1 944 242 4,570 20 1,200 8,530 15,700 3,350 3,330 75 24,700 6.9 12S/13E-15L 113- 115 84 7-10-62 2 476 202 1,300 40 700 2,900 — — 5,600 2,020 1,990 58 9,370 7.2 12S/14E-21J 145- 147 85 7-10-62 18 810 822 3,400 408 4,050 5,850 15,200 5,400 5,060 58 19,800 7.4 12S/15E-23M 285- 325 86a 2-26-58 28 31 25 628 5.1 334 457 568 " oir " 2.62" 1,910 178 0 88 3,120 8.1 86b 4-29-62 24 32 25 635 336 475 562 1.7 1,920 182 0 88 3,370 7.6 26J 304- 344 87 4-27-62 24 20 11 502 278 275 477 1.4 1,450 96 0 92 2,620 7.6 27R — 88a 3-10-36 — 23 12 539 273 301 579 1.4 ~ 3.1" ~ 2.20~ 1,530 107 0 92 2,680 7.9 88b 2-26-58 20 20 11 539 3.9 280 325 575 1.0 2.33 1,570 101 0 92 2,640 8.2 88c 5-18-62 20 20 12 525 268 275 520 1,570 101 0 92 2,690 7.8 12S/16E-31N 89 4-27-62 16 36 12 1,110 276 45 1,620 2,980 140 0 94 6,030 7.7 13S/13E-22G 145- 147 90 7-10-62 16 564 460 3,100 434 1,250 5,950 11,600 3,300 2,940 67 18,600 7.2 13S/14E-21K 145- 147 91 7-10-62 15 930 608 1,990 294 1,250 5,400 — — — 10,300 4,820 4,580 47 16,500 7.1 13S/15E-1B 92a 3-10-36 46 15 1,112 392 308 1,108 1.2 10.1 3,190 174 0 93 5,290 92b 4-16-48 20 35 1,132 407 605 1,195 .5 8.2 3,190 194 0 93 5,160 92c 8- 1-61 32 36 13 1,120 370 586 1,180 1.4 ~~2A~ 9.9 3,160 144 0 94 5,150 ~ 7.5 IQ ___ 93 4-27-62 19 16 6.8 460 252 110 528 1.4 1,270 68 0 94 2,530 7.6 2N — 94 2-21-62 12 12 4.1 491 352 155 428 1.6 — — 1,320 47 0 96 2,380 7.8 3N 95a 9-17-59 9.6 0.4 510 3 442 115 430 1.8 0 1,290 25 0 97 7.8 95b 3- 1-62 ” 34 ~ 9.3 4.1 486 2.9 441 112 445 2.1 .6 ~ 2.4 ~ 1,320 40 0 96 "2~2~70 7.7 3Q — 96 2-21-62 23 17 2.6 489 368 115 490 1.5 1,320 53 0 95 2,540 7.9 5D1 851- 886 97 3- 1-62 27 25 4.3 611 1,240 60 230 1.3 1,580 80 0 94 2,600 8.2 5D2 — 98 3- 1-62 29 40 2.9 613 1,170 55 302 1.2 — — 1,630 112 0 92 2,780 8.2 5D3 772- 812 99 11-13-63 23 4.8 10 546 1,150 0 208 1.5 1,470 54 0 96 2,310 8.0 12R 100 11-17-61 23 14 8.3 5$4 314 210 488 1,400 69 0 94 2,520 8.2 15G 101 2-16-62 16 13 1 488 508 140 378 ~~L8~ 1,290 38 0 96 2,230 8.2 21Q 102 11-15-61 29 8.0 2.7 452 656 92 269 1,180 31 0 97 2,040 8.2 22P — 103 11-15-61 32 6.2 3.5 504 672 130 312 — — — 1,320 30 0 97 2,270 8.3 23Q 104 2-21-62 18 31 8.6 952 424 525 915 2,660 113 0 95 4,660 8.1 24E 105 2-21-62 15 11 4.0 447 316 125 442 1,200 44 0 96 2,230 8.2 24N 106 2-21-62 23 10 3.6 481 482 89 422 1.6 1,270 40 0 96 2,380 8.3 28N 107 2-16-62 20 61 50 1,110 534 538 1,240 3,180 356 0 87 5,560 7.7 32D — 108 9-24-62 21 17 12 883 840 140 835 — — — 2,330 92 0 95 4,170 7.7 33A 1,269-1,389 109a 9-27-59 29 12 1,052 516 216 1,295 .7 3,090 123 0 94 7.7 109b 11-15-61 " 33 ” 27 15 1,090 530 240 1,290 2,960 128 0 95 ~5~360 7.9 33K 110 2-14-62 13 135 77 1,760 530 2,200 1,360 5,710 655 381 85 7,740 7.7 34J 111 2-21-62 27 11 4.0 555 748 145 342 "Ts" 1,460 44 0 97 2,420 8.2 34K — 112 2-14-62 29 13 2 562 816 121 328 1.7 — — 1,460 40 0 97 2,480 8.6 34M 936- 954 113 2-14-62 30 13 2 578 782 132 365 1.8 1,510 40 0 97 2,560 8.0 13S/16E-6A 114 4-27-62 14 14 9 448 268 160 467 1.5 1,250 72 0 93 2,340 7.8 6J 115 4-27-62 13 19 10 512 224 183 588 1.2 1,440 90 0 92 2,810 7.8 6N 116 11-17-61 3 19 9.8 572 210 205 672 1,610 88 0 93 2,950 8.1 6P — 117 3- 1-62 21 24 8.3 573 264 200 648 T — — 1,610 94 0 93 2,950 8.0 28R 118 8- 1-61 593 211 608 90 0 94 2,760 8.0 14S/13E-33K 124-" 126 119 1-23-62 ~~19~ 68~ 3{f 935 278 _ ~588~ 1,080 ~2~870 330 102 86 4,820 7.9 14S/14E-22G 82- 84 120 1-23-62 16 1,610 1,110 1,770 352 2,050 7,100 13,800 8,580 8,290 31 21,700 7.2 30N 124- 126 121 1-23-62 25 676 417 3,930 416 875 7,580 13,700 3,400 3,060 72 22,900 7.4 14S/15E-1B — 122 11- 6-61 22 23 13 436 314 105 485 ~Ye~ ~~5T " 1.4 ~ 1,250 112 0 89 2,180 8.0 6B 123 2-14-62 30 61 11 1,200 810 412 1,220 3,340 197 0 93 5,630 8.0 9D 124 2-14-62 21 60 53 1,050 510 575 1,160 3,170 366 0 86 5,250 7.6 9N 125 7-25-61 33 61 46 1,030 518 482 1,200 ~ rr "!u~ " 2.6 ~ 3,110 340 0 87 5,140 7.9 11D 126 7-25-61 529 760 79 344 41 0 97 2,380 8.2 12N 1,171-1,233 127 5-18-62 25 34~ 12 947 362 538 945 ~~1.3~ — — ~2~680 134 0 94 4,740 7.6 15B1 128a 3-10-36 15 6.0 628 762 87 510 1.3 4.3 4.13 1,630 61 0 96 2,840 8.1 128b 2-26-58 ~ 34 ~ 12 4.1 622 4 762 87 487 1.9 1.2 4.47 1,630 46 0 96 2,740 8.2 128c 9- 4-63 25 14 2.2 618 756 95 472 1.3 1,610 44 0 97 2,790 8.0 15B2 __ 129 9- 4-63 24 19 6.9 760 692 85 758 1.6 2,000 76 0 96 3,570 7.9 23M — 130 7-25-61 34 6.8 4.6 494 700 75 322 1.8 — — 1,290 36 0 97 2,250 8.0 27A 131a 3-10-36 27 27 756 847 194 651 2.6 6.8 2,090 182 0 90 3,430 131b 7-25-61 ~ 24 ” 26 17 530 616 292 342 1.7 6.8 1,530 136 0 89 2,450 "7.7 GEOHYDROLOGIC RECONNAISSANCE OF THE IMPERIAL VALLEY, CALIFORNIA K51Table 5. — Chemical analyses of water from selected wells — Continued K52 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA iisggi a§ « §■=] co 8 w £ c S Z a o a! i| ° a 2o is IIS S «o S go cq JjK 2 is 3d ■gs P B M §?.2S ■20 ts 6 Q 3 gz < — "C 5 — g-S-S-o 8 ttd) c ® -2 c eo£ 3 T3 V 3 #g ’■3 C o O >x H ►J < > i-) < s H a. § ►j < Pd w o 88888 188 !2 88288 OO-H-HftrH 00 N 05 1 CO t^-'J'OOC^OO COCO CO CO CO Ofl CO cm © © ooooo t'ffiinoo wtoqu-d; x-T xt* x-T ©' ©' II n n OOO I I OOOO I OMQOO CO © © I I x+ xi -CO t* r-T hn'mn 1 cm" cm" co co* co looo o iHCMH Tf 00 CS| I i-H i-T cm cm’ O Q CO CO't ©©Ml" I CO CMCOL- OOCOOW 00 05 00 CO CO 05 05 00 05 | 05 05 05 05 05 05 05 05 CO CO COC~ CM CO Q CM i-c i—c I 05 xH x-< CO i—c i-H i—I I CO CO CO CD I © © © © © © Int* I CO 05 05 05 05 05 05 I CO 05 05 CO CO CO CO | 05 05 05 05 I 05 05 05 05 05 05 | 05 05 | 05 OO OOOOO 00-3*00 ooooo ooooo (M 00 00 lO O CD O "t CM © © xt IMOtpOO CO CO Q O 05t't'in'f COlOlOIMN CO CO 05 CO CO — COHNNIM -HHU5 50000 OOOOO OOOOO 000500 ooooo ooooo ooooo o £ (M O 00 05 05 tO © CM CO to O © 00 00 00 CO CO IO to to Xj* 05 CO xH O I CM CM CM CM . (M CM (M Dt-coooo c- © © c 5 © cm © i © a . — . 00 Q © OO to -------j* xj* © co 051-* r- tr- •1 CM © © © (M CM CM CM CM CM © © © 00 X CM M © t- CJ © © © © CJ ©©©CM© © © © © CM rHrHCOCMrH H CO © © © © xj* xj< © © xf © © ©« CM 5 © © ©<>i © S © © S xj* xji © §5 5) ©© ©©!>©© © ©r-CCM L— N i- © © © CM © lO xt © © © © r-C © © x* lO © © o oi> ci to xt H CM CM © © © 05 CM L- 05 05 co_o 0*0 a> xt Xt xt Xt xt © © © © © © CM © xc CO © © © © © © © © HHHNIM © © © © © CM © © x-c —( © © © © © © CM CM CM © © © © © © © xH CO © H © © © © © © © © xH H © xt © © © CM © XH CM © © © © © © xH -3* © © H © CO © © © xC CO xH CM xH H © © © © © © Xt xH © © xHtxxtt~t~ CM CM CM c> © xL ci CM CM CM H © © © CM xH 1-H CM © Xj* Xt xH ci CM CM CM xC ©Ht-©H CM CM x-t CM CM ci CM ti xH ri x-t CM CM CM xH xt t1^- ci © CM CM xH 00 xt 05 x}< 00 H CM CM x-. ©05 at) CO CM CM ck CO xH C- ot fi- CM t> 05 M'C-NC- © CO ot) l> CM © © © © Nt'©(Mt' © © CM t~ tx CM 05 t^- CM CO t'ffirtNf' Xj* CO i- CM 00 00 -o o ajo u © © © © © © © © © © COX) COX) CO X) o CO X! O C— C"~ © © 05 © —i CM © xt xt xt © © © ©©©©© ©©©©© © © © © © CM © © xt CM CM © “or © xt ffi^ZCQCQ ©©©-lx- -HH-HCMIM QQWOW H CM xt CM CM CM © CM CM Z Jo © © —| C CM o X ZfcfflQt U.U. a © CM © © © © © xirtCMCMIM © © CM © © ©15P 170 7-27-61 21 7 3.3 426 552 155 237 3.2 1,130 31 0 97 1,920 8.0 18Q 171a 8-20-58 17 7.8 397 671 79 217 1.6 1.8 1,070 74 0 92 1,710 7.9 171b 8-20-58 41 31 706 360 220 880 1.9 1.6 2,040 230 0 87 3,360 7.8 171c 12-12-61 21 13 40 729 300 190 951 — — — 2,090 198 0 89 3,870 8.8 19E 172a 2-25-58 32 7.4 2.9 318 1.6 623 97 79 3.0 2.4 852 30 0 96 1,360 8.3 172b 7-27-61 327 622 110 82 28 0 96 1,390 8.1 22F 173 7-31-61 21 4.8 1.7 251 336 52 163 1.7 663 19 0 97 1,180 8.2 22L 174a 3-20-58 17 6 545 4 390 124 588 2.4 1,480 68 0 7.7 174b 7-31-61 29 17 5 571 404 135 588 1.7 — — 1,550 64 0 95 2,740 8.2 16E-23F 452- 542 175 2-14-62 11 9 1 385 548 185 151 3.5 1,020 26 0 97 1,600 8.3 27N _ 176 7-31-61 31 6 1 264 444 80 100 2.0 706 20 0 97 1,110 8.4 29Q1 537- 616 177 9-27-51 15 7.2 2.2 277 544 120 42 3.0 735 27 0 96 1,150 8.2 29Q2 __ 178 2-14-62 21 1.1 1 385 634 170 115 2.8 1,020 30 0 96 1,570 8.3 16S/12E-36E 103- 105 179 7- 9-62 11 72 23 461 145 80 762 — — — 1,480 275 156 78 2,820 7.8 16S/13E-13N 145- 147 180 7- 9-62 2 362 211 3,020 45 175 5,750 9,540 1,770 1,730 79 16,600 7.3 16S/15E-17L 145- 147 181 7- 9-62 14 376 214 2,920 267 400 5,350 9,410 1,820 1,600 78 16,100 7.4 16S/16E-1M 182 6- 1-50 81 35 153 189 310 142 811 346 191 49 1,320 3C 183a 7- 8-61 458 165 23 0 1,440 8.4 183b 9- 4-63 25 14 1 327 456 100 187 3.0 — — 885 38 0 95 1,530 8.2 14A 184 9-27-61 17 15 4.4 567 290 145 638 1,530 50 0 96 2,830 8.0 15B 864- 877 185a 2-24-58 24 11 3.9 425 2.0 445 112 345 2.3 1.6 2.2 1,120 43 0 95 1,960 8.3 185b 7-28-61 29 426 472 116 320 1.9 1.6 2.2 1,120 39 0 96 1,930 8.3 33D __ 186a 3-20-58 20 9 540 3 307 112 646 2.0 1,480 88 0 93 7.7 — 186b — 21 17 4.3 576 316 115 662 — — — 1,550 60 0 95 2,870 8.0 35F 432- 590 187a 8-18-58 21 5.4 349 214 192 320 1.2 9.3 1.1 1,000 72 0 91 1,620 7.8 320- 400 187b 8-19-58 20 4.6 367 228 179 352 1.3 6.8 1.2 1,040 69 0 92 1,680 7.7 46- 234 187c 8-20-58 196 117 1,670 274 1,970 1,650 2.4 11.2 2.9 5,750 970 745 79 8,260 7.6 46- 234 187d 8-21-58 235 144 1,980 299 2,490 1,880 2.9 12.6 3.2 6,890 1,180 934 79 8,930 7.6 16'«S/12E-2 — 188 7-31-50 — 97 34 122 198 312 114 — — — 791 382 219 41 1,190 — 17S/13E-20N 82- 84 189 1-31-62 29 160 70 766 394 1,000 725 2,960 720 396 70 4,540 8.2 17S/14E-14Q1 __ 71- 73 190 1-31-62 10 448 261 1,720 304 1,350 3,040 6,980 2,190 1,440 63 11,000 7.9 14Q3 191 3-62 5 175 122 1,480 199 800 2,240 4,920 940 777 77 8,350 7.7 17S/15E-10N 110- 450 192 4-21-58 18 253 143 1,541 19.4 299 1,450 2,040 .05 5,610 1,220 975 80 8,500 7.5 16K 150- 152 193 1-30-62 11 244 161 1,530 257 850 2,490 5,410 1,270 1,060 72 8,890 17S/16E-18B 150- 152 194 1-30-62 3 103 48 953 198 538 1,280 — — 3,020 455 292 82 4,800 7.5 WESTERN IMPERIAL VALLEY Lower Borrego Valley 12S/8E-15R 195 8- 1-63 24 81 10 482 116 650 365 2.5 1,670 244 149 81 2,640 7.6 22E 196a 1- 8-54 16 1.8 177 3.4 96 145 147 .3 538 48 0 88 936 7.7 196b 8- 2-63 " 20 ~ 18 .7 171 88 125 145 ” 4lf 529 48 0 88 911 7.5 22G 197 8- 2-63 24 76 7.4 309 88 325 335 3.8 1,120 220 148 75 1,870 7.6 23G — - 198 8- 1-63 20 82 15 420 96 575 350 4.0 — — 1,510 268 190 77 2,410 7.6 12S/9E-22A1 312- 412 199 7-29-63 19 450 184 1,360 96 1,850 2,000 1.3 5,910 1,880 1,880 61 8,630 7.2 22A2 __ 285- 667 200a 9-25-62 20 157 23 372 92 388 578 1,580 486 410 62 2,770 7.3 200b 7-29-63 19 130 29 383 100 400 550 .8 1,560 442 360 65 2,630 7.4 23D 250- 580 201a 9-25-62 19 162 31 381 84 388 628 1,650 530 461 61 2,920 7.3 2Qlb 7-29-63 20 163 31 409 84 425 645 ~"uf — 1,740 534 465 62 2,900 7.5 San Felipe Creek-Superstition Hills Area 12S/10E-26M 202a 1- 8-18 15 56 13 270 98 216 336 995 193 112 75 202b 1- 9-49 87 34 222 97 284 355 1,030 356 277 58 1,770 202c 9-25-62 15 61 14 292 96 233 370 0.8 1,030 210 132 75 1,920 7.2 26 203 1- 4-49 130 38 465 281 396 550 1,720 407 176 71 2,820 34G — 204a 1- 4-49 — 170 67 1,320 104 25 2,310 — — — 3,920 495 410 85 — — 204b 9-25-62 0 109 46 1,590 66 5 2,740 4,520 462 408 88 8,430 6.6 12S/11E-18J1 310- 650 205a 5-20-64 18 39 8.4 470 9.4 200 296 495 1.8 0.1 2.0 1,440 132 0 88 2,470 8.2 205b 7- 2-64 18 30 9.0 472 9.4 191 285 498 1.2 5.2 2.6 1,420 112 0 89 2,460 8.4 18J2 35- 55 206 5-20-64 19 348 197 2,380 248 2,400 2,950 8,420 1,680 1,480 76 12,600 7.2 21 207a 11-20-17 26 30 22 705 207 451 748 1.4 2,090 165 0 90 207b 9-25-62 — 28 32 1,930 567 800 2,200 — — — 5,270 202 0 95 9,180 7.8 Coyote Valley 16S/9E-25K 90- 247 208a 5-15-59 19 67 79 4.3 157 27 61 .6 3.2 279 75 0 68 8.3 208b 3- 6-62 15 20 3.2 73 152 25 49 1.0 262 63 0 509 7.3 25M 209 3- 6-62 17 23 4.5 82 152 32 67 1.1 303 76 0 70 532 7.3 26H 210 3- 5-62 29 18 3.9 93 160 30 68 1.1 3.9 326 61 0 77 540 7.8 35M 415- 495 211a 7- 2-62 — 1.4 .2 104 8.0 129 14 80 3.8 .1 — 330 4.5 0 94 — 9.3 211b 1- 9-63 48 1.5 .1 105 123 10 82 2.0 311 4 0 98 509 8.8 GEOHYDROLOGIC RECONNAISSANCE OF THE IMPERIAL VALLEY, CALIFORNIA K53☆ U.S. GOVERNMENT PRINTING OFFICE: 1975-677-309/34 Table 5. — Chemical analyses of water from selected wells — Continued Well location Interval sampled (ft below Analysis Date of Silica Calcium Magne- Sodium and potassium Potas- Bicar- Sul- Chlo- Fluoride Nitrate Boron Total dis- solved Hardness as CaC03 Non- Percent Specific conduct- ance (micro- land No. sample (SiOa) (Ca) sium Sodium sium bonate fate ride (F) (NO:,) (B) solids Calcium carbon- sodium mhos at surface) (Mg) (Na) (K) (HCO,) (SO,) (Cl) magnesium ate 25°C) pH WESTERN IMPERIAL VALLEY — Continued Coyote Valley — Continued 35 N 212 1- 9-63 35 6.1 2.2 114 162 14 84 2.0 338 24 0 91 577 7.8 36C1 _ 213a 10-27-52 22 20 6 76 143 24 69 .9 2.5 292 76 0 76 450 8.2 213b 2-19-58 14 5 102 9 149 30 78 3 315 56 0 77 582 8.1 213c 3- 5-62 10 14 3.2 106 130 33 94 2.2 0 — 326 48 0 83 583 8.0 36C2 _ 180- 300 214a 2- 8-61 16 4.9 93 43 156 27 69 1.6 4.8 299 60 0 76 8.3 214b 3- 5-62 14 19 2.6 101 168 28 75 1.5 325 58 0 79 584 7.3 36G1 199- 214 215a 5-27-57 25 5 4 124 178 39 71 .1 357 30 0 90 608 215b 2-19-58 5 1 128 6 177 35 78 .45 341 17 0 92 622 8.4 215c 3- 5-62 11~ 5.8 1.5 133 196 32 75 3.5 — — 356 20 0 94 628 7.7 36G2 __ 216 3- 5-62 9 5.8 1.6 141 188 39 87 4.0 381 21 0 94 679 7.7 36R 217a 9-17-48 24 7.2 7.8 141 224 69 72 433 50 0 86 7.8 217b 1953 12 3 144 207 63 84 410 42 0 88 217c 1958 — 10 3 160 10 207 85 85 — — — 456 38 0 87 764 8.6 16S/10E-20R 218 2-19-58 13 12 500 9 308 370 376 0 1,430 83 0 92 2,300 8.0 28D 219 12-16-48 3 14 3,140 1,620 ,520 2,510 8,000 0 0 99 30R 220a 6-27-59 40 32 12 129 5.3 166 95 128 2.5 527 130 0 67 910 7.8 220b 3- 5-62 20 25 7.4 108 156 43 109 1.0 — — 391 93 0 72 711 7.9 West Mesa 14S/11E-32R 135- 560 221a 4- 3-62 16 133 36 445 82 827 365 1.4 .2 1.6 1,870 480 413 67 2,800 7.5 221b 5-11-62 15 152 33 510 64 1,080 318 2,140 515 463 68 2,920 7.7 15S/11E-13K 93- 95 222 4-15-64 15 368 142 1,260 142 1,650 1,700 5,210 1,500 1,380 64 7,970 7.7 15S/11E-32R 138- 140 223 3-19-64 2 28 19 1,560 368 2,250 635 4,680 150 0 96 6,500 9.2 16S/12E-6P 262- 264 224 8-18-58 — 131 57 726 146 769 866 .6 4.3 0.74 2,620 564 444 74 4,030 8.2 Yuha Desert 16S/11E-23B 121- 123 225 3-19-64 3 148 96 4,150 184 3,330 4,380 12,200 765 614 92 17,800 8.2 16'/2S/10E-5D1 226 4-23-63 32 8.4 .7 260 272 160 141 2.2 742 24 0 96 1,220 8.2 5D2 227 7-17-62 31 8 2.9 155 220 58 86 2.8 454 33 0 91 750 8.1 6 228a 5- 8-52 7.0 1.6 183 270 55 95 12.0 4.3 .4 493 24 0 94 876 8.2 228b 3- 4-58 — 4 .5 215 6 265 100 110 — — .25 568 11 0 96 980 8.8 16'/2S/11E-6M1 229 8-23-62 0 2.4 5,010 5,940 2,700 2,280 13,000 10 0 100 17,600 9.4 6M2 230 8-23-62 11 2.6 1,010 1,500 400 420 2,630 38 0 98 4,150 8.5 17S/9E-1 l(i 231 7-17-62 34 1 .4 124 112 22 106 3.5 347 4 0 98 590 9.4 17S/10E-2E 232 4-22-64 11 23 3 238 137 158 219 .6 721 70 0 88 1,250 7.4 17S/12E-17A 233 3-19-64 15 188 73 690 236 825 865 — — 2,770 770 576 66 4,680 8.0 K54 WATER RESOURCES OF LOWER COLORADO RIVER-SALTON SEA AREA4IUNITED STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY '' Tv Side county :OUI\tJYr^ TORRES MARTINEZ INDIAN RESERVATION NAVAL RESERVATION Elevation 234 feet below sea lev li May 1959 Fault shown by infrared photographs' JriAl GUNNERY raj NTAliy SALTO N SEA TEST BA I Carbon dioxide r---------1 Mullet Island yvWvJijf SALTON SEA NATIONAL WILDLIFE REFUGE .MPEItlAI Ocotillo. Calipatria SALTON SEA NATIONAL , LDLIFE REFU' iMPERlAi lamer ’hi in i 'O'Connell NAVAL TARO AREA NO 'JSBkt i^PA(S^^Arfef)v OES^RT^SmTE PAR NEST MESA 525G1.2 °25R Om nt Lak i S NAVAL [ery ranq Naftl Air Technical ( GflTraining Unit! INTAIN Imperial Valley Juberculilsis Sanatorium rtoltville foxiliaryi 14mm- Xq15G Tq mwe\ station v* ‘■32VAAraz JUncfi Farm £)32G1,2 Geology compiled by J. H. Robison, 1961-66 Based partly on mapping by T. W. Dibblee, Jr. and California Division of Mines and Geology Hydrology by O. J. Loeltz Plat imperial Wistaria < 'anal\ SCALE 1:250 000 il’lL PROFESSIONAL PAPER 486-K PLATE 1 EXPLANATION r Qa Alluvium Alluvial and deltaic sand, gravel, and silt. Includes some dune sand (stipple pattern) where generally less than about 10 feet thick Q1 Lake deposits Lacustrine silt, sand, and clay. Include the Brawley Formation of Dibblee (1954), exposed along the perimeter of the trough, and the deposits of Lake Cahuilla, exposed in the middle of the trough Qs Windblown sand Well-sorted fine to medium sand, commonly in high dunes and ridges, where more than about 10 feet thick. In~ eludes Sand Hills (Algodones Dunes) Qt Terrace deposits Thin pediment gravel and sand, formed mostly on the Palm Spring Formation; may grade into fans of older alluvium Qb Niland Obsidian of Dibblee (1954) Obsidian, pumice, and scoria Qof Older alluvium Older alluvial and fan gravel and sand, distinguished in most areas by a surface of desert varnish; near the Chocolate Mountains may be only a veneer on older sedimentary rocks (Ts); in western Imperial Valley includes Ocotillo Conglomerate of Dibblee (1954) of Pliocene or Pleistocene age T3 C a c 3 2/ Cl QTb Borrego Formation of Tarbet and Holman (1944) Lacustrine and brackish-water deposits; light-gray silt, clay, and sandstone; grades laterally into Palm Spring Formation QTp Palm Spring Formation Unconsolidated to weakly consolidated terrestrial deposits;.light-brown sand, gravel, and silt; upper units may be equivalent in part to older alluvium Ti Imperial Formation Shallow marine deposits; basal conglomerate overlain by gray, tan, and yellow siltstone, sandstone, and claystone; fossil-iferous Ts Sedimentary rocks Mostly nonmarine coarse sedimentary rocks of several ages; include Split Mountain Formation (Miocene) of Tarbet and Holman (1944), and its proposed revisions by Woodard (1961) and Durham and Allison (1961); outcrops near the Chocolate Mountains are of Oligocenef?) age (prebasalt of Chocolate Mountains) be Igneous and metamorphic rocks Intrusive rocks of granitic to gabbroic composition, meta-sedimentary gneiss, schist, and marble, and metavolcanic rocks QTc Canebreak Conglomerate of Dibblee (1954) Coarse silty conglomerate and sandstone; grades laterally into Palm Spring Formation Volcanic rocks Tb, basalt, andesite, and scoria of Chocolate Mountains Tv, basalt, andesite, and rhyolite-, includes Alverson Andesite Lava of Dibblee (1954) and older volcanic rocks of Chocolate Mountains Contact Dashed where approximately located or gradational Shoreline of prehistoric Lake Cahuilla Former shoreline of Pleistocene to Holocene age; contact between units where shoreline is coincident Fault Dashed where approximately located; queried where inferred; dotted where concealed ------------100------------ -------------80------------ Water-level contour Dashed where approximately located. Shows altitude of water level in feet above (+) or below (-) mean sea level. Contour interval 20 and 100 feet j2f 23M Well or test hole, destroyed o24G Water well or test well Number and letter, 22G, is location of well within township. See text for explanation of well-numbering system -& Oil test Steam well or test hole Base from U.S. Geological Survey Santa Ana, 1944; Salton Sea, 1948; San Diego and El Centro, 1958 CONTOUR INTERVAL 100 FEET DATUM IS MEAN SEA LEVEL 1974 MAGNETIC DECLINATION VARIES FROM 14°00' TO 14°30' EAST MAP SHOWING WATER-LEVEL ALTITUDE IN 1965, GEOLOGY, AND LOCATION OF WELLS AND SPRINGS, IMPERIAL VALLEY, CALIFORNIA ☆ U.S. GOVERNMENT PRINTING OFFICE: 1975-677-309/34 PRE-TERTIARY TERTIARY QUATERNARYI united STATES DEPARTMENT OF THE INTERIOR GEOLOGICAL SURVEY COACHELLA VALLEY IMPERIAL VALLEY PROFESSIONAL PAPER 486-K PLATE 2 Self potential - 20 + LCRP 2 7S/8E-4A Altitude +155 feet (+47 meters) Resistivity point electrode ohm-meters LCRP 3 5S/6E-6R Altitude +225 feet (+69 meters) 20 I 40 I Self potential HmV + Resistivity point electrode ohm-meters 0 50 1 I 3 =4= 2 0-1 100 - 200- I- £ 300 400 - to DC UJ I— LU 500- 600 — 25 — 50 — 75 co cc UJ I— UJ — 100 —125 — 150 ■175 EXPLANATION LITHOLOGY Gravel WELL CONSTRUCTION Sand and gravel Sand Silty sand, very fine sand, or silty clay with sand Silty clay, clay silt, or silty clay with fine sand Clay Blank casing -Perforated casing LCRP 7 17S/14E-14Q (not completed as a well) Altitude -30 feet (-9 meters) Self potential -H20mv|«- + Resistivity 16 inches normal ohm-meters 0 10 I I Well Self potential LCRP 8 14S/11 E-32R1 Altitude +88 feet (+27 meters) Resistivity 16 inches normal ohm-meters 0-1 2° L . mv + 10 20 I 100- 200 — 300 — 400- £ 500- 600- 700- 800- 900 - 1000 -J 1—0 — 125 — 25 100 - — 50 200- — 75 300 — — 100 400 - CO •150 H t cnri uj uj 500 - — 175 600- — 200 700 — — 225 800 — -250 - 275 900 — *—300 1000 — 8-inch I D casing Static -water level Pilot hole 985 feet (300 meters) Temperature (completed well) 74° 86° F I I 23° 30° C Well Self potential --C°vP + LCRP 11 15S/18E-15M1 Altitude +120 feet (+38 meters) Resistivity 16 inches normal ohm-meters 20 I 0—1 100- 200 — 300 • 400 — 500 — 600 — 700 — 800 — 900- 1000 1100 - 1200—1 1—0 — 25 — 100 100- — 50 200- — 75 300- 400- 1—125 CP DC —150 £ UJ H UJ 500- -175 600- — 200 700 — ■225 800- - 250 — 275 900—1 F- 300 Well Self potential ' H mv P + Resistivity 16 inches normal ohm-meters 20 I 80° I 27° Gamma ray No scale LCRP 18 16S/18E-32R Altitude +118 feet (+36 meters) Temperature (pilot hole) 90 F I 32° C Temperature (completed well) Well 70° 90 F Self potential --*|1 OmvR - LCRP 12 16S/19E-11D1 Altitude +155 feet (+47 meters) Resistivity 16 inches normal ohm-meters Gamma ray No scale 20 I 0-i 100 - 200 - 300- 400- LU uj 500- LL CP CC 600 - 700 - 800 - 900 - 1000 -* Static water — level -J 10Vi-inch I D casing 8-inch I D casing Arrows indicate circulation under static conditions — A Pilot hole 1000 feet (305 meters) IMPERIAL VALLEY Percent of discharge vs. depth (Discharge, 605 gpm) 50 Well Self potential 100 r- 0 - 25 -50 — 75 — 100 — 125 100 — 200- 300- 400- CP CC -150 500- -175 600— — 200 700- — 225 800- — 250 *- 275 900- 1000—' Temperature (pilot hole) 60° 120° F I | 16° 49° C — 25 — 50 —75 —100 i 10 i --------Static ---------nmvr + (292 meters) —125 — 150 CP CC UJ F- LU -175 -200 — 225 -250 -275 >—300 LCRP 19 12S/11E-18J Altitude -175 feet (-53 meters) Resistivity 16 inches normal ohm-meters 10 i Gamma ray No scale Temperature (pilot hole) 20 I 80° l 27° 90° F I 32° C i—0 — 25 — 50 — 75 — 100 -125 cp DC -150 £ -175 — 200 — 225 -250 -275 F-300 100 — 200— 300— 400- 500 — 600 — 700 — 800— 900— 1000- 1100 — 1200- I- £ 1300- 1400 — 1500 — 1600— 1700 — 1800- 1900 — 2000 — ) 2100 — 2200 — 2300 — 2400 2500 — 2600 —1 LCRP 6 and 6A 16S/20E-31K Altitude +155 feet (+47 meters) LCRP 6 drilled by cable tool; LCRP 6A consisted of deepening by rotary method Well Static water — level 12-inches I D casing LCRP 6 LCRP 6A Gamma ray No scale Temperature LCRP 6 (completed well) 86° I 30° Temperature LCRP 6A (pilot hole) 95° A- 104°F 40° C — 25 — 50 — 75 — 100 -125 — 150 — 175 —200 — 225 — 275 — 300 — 325 —350 -250 — 375 — 400 -425 -450 —475 -500 — 550 — 575 — 600 —625 -525 -650 — 675 —700 — 725 — 750 L- 775 GRAPHIC LOGS OF TEST WELLS AND HOLES, IMPERIAL VALLEY, CALIFORNIA ■ftU.S. GOVERNMENT PRINTING OFFICE: 1975-677-309/34 METERS