PRELIMINARY APPRAISAL OF 

GROUND WATER IN STORAGE 

WITH REFERENCE TO 

GEOTHERMAL RESOURCES IN THE 

lrfftPERIAL VALLEY AREA, 

RNIA 

Preliminary Appraisal of 

Ground Water in Storage 

With Reference to 

Geothermal Resources in the 

Imperial Valley Area, 

California 

By L.C.Dutcher,W.F.Hardt,and W.R.Moyle,Jr. 

GEOLOGICAL SURVEY CIRCULAR 649 

Prepared in cooperation with . 

the U.S.Bureau of Reclamation 

Washington 1972 
United States Department of the Interior 

ROGERS C. B. MORTON, Secretary 

Geological Survey 

V. E. McKelvey, Director 

Free on application to the U.S. Geological Survey, Washington, D.C. 20242 
CONTENTS 

Page 

Abstract -------------------------------------- 1 

Introduction ----------------------------------- 2 

General geologic and hydrologic setting _____ 2 

Previous work and reports _________________ 6 

Purpose and scope of this report ____________ 7 

Acknowledgments __________________________ 7 

Sources and adequacy of data ______________ 8 

Well- and spring-numbering system _________ 8 

Geology --------------------------------------- 9 

Setting ----------------------------------- 9 

Structure --------------------------------- 13 

Stratigraphy ------------------------------ 13 

Hydrologic characteristics of aquifers _______ 15 

A conceptual model of the system _______________ 16 

Basic concepts ----------------------------- 16 

Sources of heat and high-temperature anomalies ------------------------------------ 17 

Metamorphism and changes in porosity and 

permeability ____________________________ 19 

Age or duration of the steady-state flow sys- tenl ____________________________________ 22 

Geothermal gradients ______________________ 24 

Heat flow by conduction _______________ 25 

Heat flow in water convection cells _____ 27 

The dynamic system _______________________ 28 

Mechanism of recharge and discharge __ 30 

Quality and quantity of water and concentration of salts __________________ 30 

Page 

A conceptual model of the system-Con. 

The dynamic system-Con. 

Relation of salinity of recharge and deep 

brine ------------------------------- 32 

Estimated porosity and specific yield of the rocks 

and deposits -------------------------------- 32 

Available data ____________________________ ,_ 32 

Methods of computation --------------------- 33 

Usable and recoverable water ___________________ 33 

Criteria for defining terms ----------------- 33 

Method of estimating usable and recoverable 

water ----------------------------------- 38 

Thickness of water-bearing rocks and deposits_ 3S 

Areal and vertical extent of storage units ___ 38 

Thickness, areal extent, and specific yield or 

porosity of vertical zones 1-4 ____________ 41 

Water at temperatures more than 150" C ____ 46 

Summary of usable and recoverable water ___ 46 

Reliability of the estimates --------------------- 47 

Significance of production methods __________ 47 

Possible changes in the flow regime _________ 50 

Possible environmental hazards _________________ 50 

Land subsidence --------------------------- 51 

Seismic activity --------------------------- 52 

Air, water, and noise pollution ______________ 52 

Additional data needs -------------------------- 53 

Selected references ---------------------------- 54 

ILLUSTRATIONS 

COVER. Photograph courtesy of the Imperial Irrigation District. 

Page 

FIGURE 1. Index map ------------------------------------------------------------------------------- 3 

2. Map showing location of wells, springs, and hydrologic sections in Imperial and Mexicali Valleys _ 4 

3. Geologic map of Imperial and Mexicali Valleys'---------------------------------------------- 10 

4. Map showing depth to basement complex ----------------------------------------------------12 

5. Composite stratigraphic section ------------------------------------------------------------ 14 

6. Model for Salton Sea geothermal system, involving a vapor phase _____________________________ 18 

7. Map showing inferred direction of ground-water movement in deep aquifer system to generalized 

areas of known geothermal anomalies in Imperial and Mexicali Valleys ---------------------20 

III 
Page 

FIGURE 8. Modified model for Salton Sea geothermal system, showing source of recharge and water-quality 

changes ------------------------------------------------------------------------------23 

9-11. Hydrologic section9. A-A' ----------------------------------------------------------------------------26 

10. B-B' ----------------------------------------------------------------------------27 

11. C-C' ----------------------------------------------------------------------------28 

12. Schema for a pipe model for water and dissolved solids input-output of the Salton Trough hydrothermal system -----------------------------------------------------------------------31 

13. Map showing ground-water-level contours of shallow aquifer system, 1962 and 1964, in Imperial 

and Mexicali Valleys ------------------------------------------------------------------ 34 

14. Graph of estimates of formation porosity from wells 82 and 92 ------------------------------- 36 

15. Map showing thickness of deposits with total usable water ----------------------------------- 39 

16-20. Map showing thickness of deposits with usable water16. In zone 1 ------------------------------------------------------------------------40 

17. In zone 4 ------------------------------------------------------------------------42 

18. In zone 3 ------------------------------------------------------------------------44 

19. In zone 2 ------------------------------------------------------------------------45 

20. Of more than 150°C --------------------------------------------------------------48 

TABLES 

TABLE 1. Analyses of water from geothermal wells at Niland, Cerro Prieto, and Arizona ----------------- 29 

Usable and recoverable water at temperature of 150°C or more ------------------------------- 46 

Summary of usable and recoverable water in\the Imperial Valley area, California, contaJning less 

2. 

3. 

4. 

IV 

than 35,000 mg/1 dissolved solids ------------------------------------------------------- 46 

Summary of usable and recoverable water in storage derived from the Colorado River and local 

sources -------------------------------------------------------------------------------47 
Preliminary Appraisal of Ground Water 1n Storage 

With Reference to Geothermal Resources 1n the 

Imperial Valley Area. California 

By L. C. Dutcher, W. F. Hardt. and W. R. Moyle. Jr. 

ABSTRACT 

Imperial Valley occupies part of a deep sedimentfilled structural basin that extends south from the 

Coachella Valley in California to the Gulf of California. The Gulf of California coincides with the intersection of the East Pacific rise and the North American 

Continent, and heat flow through the thick (as much 

as 20,000 ft) young water-saturated sediments deposited in the delta of the Colorado River is greater than 

the world-wide average. Superimposed on the broad 

heat-flow anomaly are several small areas that have 

heat flow 4-10 times average. Electric power will soon 

be generated using geothermal energy at Cerro Prieto, 

Mexico. Deep wells at the Salton Sea geothermal field 

near Niland, Calif., have been tested for electric power 

production, but because the very hot water contains 

about 260,000 mg/1 (milligrams per liter) dissolved solids, commercial production of electricity is not yet economically feasible. 

Because of the extremely high temperatures at depth 

throughout the basin and at relatively shallow depth 

in areas of anomalously high heat flow, the deposits 

are undergoing metamorphism. The active metamorphism has caused changes in the original porosity and 

permeability of the rocks and deposits. 

Temperature gradients range from about 1 o to 3°C 

per 10 feet through most of the sediments where heat 

flow is dominantly by conduction, but in some exceptional areas the gradients range from 7o to 10oC or 

more per 100 feet. Where heat flow is dominated by 

water convection in deep cells, the geothermal gradients are only slightly below the pressure reference 

boiling-point curve for the brine solution. The temperature is probably slightly below the boiling curve because of partial pressures of gasses in the system. 

Our conceptual model of the hydrothermal system 

mechanisms includes recharge to the deep convection 

cells for about 50,000 years at a rate of about 30 liters 

per second. The discharge is mainly flow in the vapor 

phase through fractures into overlying shallow aquifers or to the surface. According to our conceptual 

model, the dissolved minerals in the recharge water 

are accumulated in the brine of the deep convection 

cells. Thus, the salinity of the deep water is dependent 

1 

on the recharge-discharge rate, the duration of flow, 

and the salinity of the inflowing water. On the basis 

of preliminary data and the conceptual model, wherever the salinity of the recharge \Vater from the base 

of overlying shallov;er aquifers exceeds about 

4,000-5,000 mg/1, the salinity of deep brines in convection cells may exceed 35,000 mg/1. 

Estimated porosity and specific yield of the deposits 

were used to estimate recoverable \Yater. The percentage of recoverable water in storage ranges from an 

average of about 5 percent of the volume for deposits 

at depths greater than 8,000 feet to about 20 percent 

of the volume for shallow deposits in the ground-water 

recharge area. 

The total usable and recoverable water in the Imperial Valley is estimated to he 1.1 billion acre-feet 1 of 

which about 200 million acre-feet is at a temperature 

of 150oC or greater. This estimate includes water 

probably containing less than 35,000 mg/1 dissolved solids regardless of temperature. About 62 percent of the 

total usable and recoverable water was derived from 

the Colorado River and about 38 percent from local 

sources. 

The combination of low well yields, energy costs in 

excess of $100 per acre-foot for lifts greater than 

5,000 feet, and very high capital costs of wells will 

probably prevent pumping most of the estimated usable and recoverable water. If as much as 1,000 feet of 

pumping lift would be economically justified, about 100 

million acre-feet of water might be recoverable from 

the shallow aquifers. 

Thus, economic studies are needed to determine the 

feasibility of recovering the estimated 1.1 billion acrefeet of water. Such studies may indicate that usable 

and recoverable \\·ater is only about 100 million acrefeet at a temperature less than 100°C, and less than 

200 million acre-feet at higher temperatures. 

The probable percentage error for the estimates of 

water in storage cannot be determined because data 

are not available. Therefore, the logic on which great 

extrapolations of meager data could be based had to be 

developed by formulating a conceptual model of the 

sedimentary basin and by considering the elements and 
mechanisms of the hydrothermal system. Thus, the accuracy of the estimates of usable and recoverable 

water in the system is directly related to how adequately the conceptual model of the system represents 

the prototype. Only further drilling, testing, experiments, and studies can provide a firmer basis for determining what amount of water can be recovered economically. 

As in other heavily pumped basins of the arid West, 

extractions in Imperial Valley that cause water levels 

to decline to new low levels each year will cause continuing surficial subsidence. In parts of the valley 

long-term subsidence might be of little consequence; in 

other areas damages would probably be prohibitive. 

Large-scale water production or injection, particularly 

involving the deep high-temperature rocks, may constitute a seismic hazard; this problem will require extensive research. 

Questions of poise generation, air pollution, and 

water pollution also will require answers prior to 

large-scale development of the potential resource. 

INTRODUCTION 

GENERAL GEOLOGIC AND HYDROLOGIC SETTING I 

Imperial, Mexicali, and ~oachella Valleys occupy the sediment-filled nprthern extension of 

the deep structural basin occupied on the south 

by the· Gulf of California. Imperial Valley is 

the name given to the large part of the basin 

south of the Salton Sea in the United States. 

The southern part of the basin in Mexico is 

called Mexicali Valley (fig.1). North of the 

Salton Sea the basin is called Coachella Valley. 

The entire depression is commonly called the 

Salton Trough and is filled primarily with clay, 

silt, and find-grained sand deposited 'by the 

Colorado River as part of its delta (Muffler 

and Doe, 1968). 

Under natural conditions ground-water recharge to the basin, both in the United States 

and in Mexico, was largely from fresh-water 

runoff in the Colorado River. But some recharge was derived from precipitation on the 

bordering uplands along the east and west 

1 basin margins. All ground-water discharge was 

by evapotranspiration from the shallow water 

table beneath the basin floor or, at times when 

large or sn1all lakes existed in the basin, by inflow to shallow lakes. Since 1900 large-scale irrigation using wate1· imported from the Colorado River has caused changes in the 

ground-water recharge and discharge relations. 

The Gulf of California coincides with the intersection of the East Pacific rise and the 

North American Continent. The general positive heat-flow anomaly of the East Pacific rise 

extends north at least the full length of the 

Salton Trough. The few available measurements of heat flow in the central and southern 

parts of the Gulf of California average about 

3.3 microcal/cm:.!/sec (mierocalories per square 

centimeter per second) (Von Herzen, 1963), 

more than doubled the oceanic average of about 

1.5 microcal/cm~;sec. However, a reasonable 

average background conductive heat flow in the 

continental part of the Salton Trough may be 

about 1.7 microcal/cm:!/sec (A. H. Lachenbruch 

·written commun., 1971). Superimposed on the 

broad heat-flow anomaly are several small 

areas that have heat flow 4-10 times average 

(Rex, 1966). The high heat flow has created 

greater than average geothermal gradients. 

There are two known areas of Quaternary volcanism and several local areas of hot-spring 

activity. The high geothermal gradients in the 

thick young water-saturated detrital sediments 

have created a potential geothermal energy resource that might be extensively exploitable. 

The Mexican Government has explored one 

area at Cerro Prieto, Baja California, Mexico, 

about 25 miles southeast of Mexicali (fig. 2) 

for geothermal energy (Alonso Espinosa and 

Mooser, 1964; Anda and Paredes, 1964). Development of a major steam field is underway for 

electric power production. The capacity of existing wells is reported by Rex ( 1970, p. 5) to 

be great enough to supply steam for 100-megawatts of power; a plant is now under construction to produce about 75 megawatts. 

2 

A second area of anomalous heat flow is in 

the United States at the Salton Sea geothermal 

field, sometimes called the Obsidian Buttes field 

or the Niland field. Exploration has consisted 

of deep drilling and pilot production of water 

and steam from several wells (Helgeson, 1968; 

Muffler and White, 1969). Because the water 

at the Salton Sea field is highly saline-as 

much as 260,000 mg/1 (milligrams per liter) 

dissolved solids-technical problems, mainly 

due to its highly corrosive nature, have deterred commercial production of electricity and 

recovery of minerals from the brine. 
124" 123 

40 N 

1 118 0 50 MILES 38 ~·--~~--~~--~· 

0 50 KILOMETERS 

0 

33° --+-------+-~-=-~-=A+-1-tk?"'m~~ 

120c 

FIGURE 1.-lndex map. 

Nevertheless, the large deep structural basin 

filled with low to moderately permeable rocks 

having substantial porosity and therefore containing a substantial quantity of water in an 

area of higher than average heat flow has created widespread interest in the Salton Trough 

3 

geothermal basin. Research and exploration of 

the gothermal, water, and chemical resources 

of the basin are being continued by public and 

private agencies. The goal is to determine the 

extent and value of the resources and the technical means of their economic use. 
Base from U.S. Geological Survey State of 

California (south half) 1!500.000, 1970. and 

U.S. Department of the Interior Reconnaissance 

Map of the Salton Sink, California 1:500,000. 1908 

FIGURE 2.-Location of wells, springs, and hydrologic sections in Imperial and Mexicali Valleys. 

4 
Geoth~rmal wells in Mexico from California 

Department of Water Resources (1970) 

FIGURE 2.-Continued. 

5 

EXPLANATION 

046 

Location of well or spring data 

used in report 

OMI 

Geothermal well in Mexico 

---1-··· 

Fau It 

Dashed where approximately located; 

dot ted where concealed; queried 

where doubtful 

A A' 

Line of hydrologic section 

APPROXIMATE MEAN 

DECLINATION 1971 

10 15 

CONTOUR INTERVAL 50 AND 50(1 FEET 

DATUM IS MEAN SEA LEVEL 

20 Ml LES 

Elevations and topography in Mexico are approximate 
PREVIOUS WORK AND REPORTS 

The earliest geohydrologic studies of the Imperial Valley were in the early 1900's and consisted of soil surveys (Holmes and party, 

1930; Strahorn and others, 1922; and Kocher 

and others, 1923) of the Imperial Valley, El 

Centro, and Bra\vley areas, respectively. Early 

water studies consisted mainly of locating and 

describing springs and wells (Mendenhall, 

1909, and Brown, 1920). The first reconnaissance report of the geohydrology of the Salton 

Sea region was by Brown ( 1923) . 

From these early reconnaissance studies, the 

geohydrology of Imperial and Coachella Valleys 

-the Salton Trough section of the Basin and 

Range physiographic province of Fenneman 

( 1931) -has been studied in increasing detail. 

Significant geologic studies of the Salton 

Trough were made by Tarbet and Homan 

(1944), Tarbet (1951), Dibblee (1954), Woodard (1961), Durham and Allison (1961), 

Downs and Woodard (1961), Merriam and 

Bandy ( 1965) , and Morton ( 1972) . 

West of the Salton Trough, the Peninsular 

Range province has been studied by Larsen 

(1948), Beal (1948), Jahns (1954), and Merriam ( 1958) . The geology of the mountains on 

the north and east were described by Bailey 

and Jahns (1954), Rogers (1961), Crowell 

( 1962), and Olmsted, Loeltz, and Ireland 

(1972). 

Several water-resources studies of the Salton 

Sea area have been of particular value: Bradshaw and Donnan (1952), California Department of Public W~rks (1954), Rely and Peck 

( 1964) Rely, Hughes, and Irelan ( 1966), Rex 

(1968): California Department of Water Resources (1970), and 0. J. Loeltz (written commun., 1971). Water-level measurements and 

chem1cal analyses are tabulated in California 

Department of Water Resources Bulletins 39 

and 1 since 1956, 130 series. 

The discovery of the geothern1al resources at 

Cerro Prieto, Mexico, and the high temperature hypersaline brine at the Salton Sea geothermal field stimulated a great increase in 

scientific study of the area and in research related to the e~tent and mode of occurrence of 

the geothern1al and mineral resources. Numerous papers have been published in recent 

years on a broad scope of subjects. 

6 

The published geologic studies have been related prinicipally to the geology of the Colorado River delta deposits (Muffler and Doe, 

1968; Merriam and Bandy, 1965; and Sykes, 

1937a b) and active metamorphism of the sediment~ (Muffler and White, 1969; White and 

Muffler, 1965). Biehler, Kovach, and Allen 

(1964), Kovach, Allen, and Press (1962), Biehler (1964), Rex (1970), and Griscom and Muffler (1971) studied the geophysical framework; 

Helgeson (1968) studied the geologic and thermodynamic characteristics; Allison ( 1964) 

studied the geology of the bordering areas; 

Arnal ( 1961) studied the sedimentation and 

fossils; Dibblee (1954) mapped the valley sediments; Kelley and Soske (1936) discussed the 

volcanic domes near the Salton Sea;. and Robinson and Elders (1970) discussed xenolit~s in 

the volcanic rocks. 

The mineralogical studies have included the 

hydrothermal minerals (Keith and others, 

1968) sulfide minerals (Skinner and others, 

1967): base-metal ore deposits (Whit~, 1968), 

and silicate metamorphism and genesis of ore 

solutions (Helgeson, 1967a). 

Aspects of the water quality and chemistry 

of the geothermal brines are included in several papers published since 1940. Included in 

these are descriptions of solution chemistry 

(Helgeson, 1967b) ; possible sources of lead and 

strontium in geothermal basins (Doe, Hedge, 

and White, 1966); origin of carbon dioxide and 

description of carbon dioxide wells in the system (Muffler and White, 1968; Rook an~ Williams, 1942; and Lang, 1959); general character of the Salton Sea geothermal brines 

(White, Anderson, and Grubbs, 196~; White, 

1968); sources of the water (~ra1g, 1966, 

1969; Berry, 1966, 1967; and Crmg and Gordon, 1965); and oxygen isotopes of rocks and 

water (Clayton and others, 19G8; \Vhite, 19G8). 

Aspects of temperature and heat flow in the 

region have been described by White, Muffler, 

and Truesdell (1971); Rex (1966); Helgeson 

(1968); Koenig (1967, 1969, and 1970); Menard (1960); Von Herzen (1963) ; lVIcNitt 

(1963, 1965); and Alonso Espinosa and Mooser 

(1964). 

Several studies have recently been completed 

that deal mainly with prospects for developing 

the water, mineral, and geothermal resources 
of that part of the Salton Trough within the 

United States. In two of these papers (White, 

1968; Berry, 1966) the authors developed conceptual models of part of the geothern1al system. Koenig ( 1967) described the resources in 

general terms. The potential geothermal resource of the Salton Trough was analyzed by 

Rex (1970). In that paper the author stated 

that it is feasible to develop 10-15 million 

acre-feet of geothermal brine annually, yielding 5-7 million or more acre-feet of distilled 

water and 20,000-30,000 megawatts of electric 

power. He also estimated that the volume of 

water in storage within the United States but 

south of Westmoreland, Calif., and excluding 

the hypersaline brine, is 1.6-4.8 billion acrefeet (Rex, 1970, p. 14). 

Finally, the U.S. Bureau of Reclamation 

(1971) summarized the work of Koenig (1967) 

and Rex (1970) and outlined a proposed program of additional studies and pilot projects. 

PURPOSE AND SCOPE OF THIS REPORT 

The primary purpose of this study, ·within 

the time and funds available, was to estimate 

the total recoverable water in storage in the 

sedimentary basin having dissolved-solids concentration equal to or less than that of sea 

\Vater (approximately 35,000 mg/1). Because 

the term "recoverable water" could mean 

very different things in different engineering 

and economic contexts, it was decided that the 

estimate should include all water in storage 

which could probably be withdl~awn from 

wells, considering present water-use pattei·ns 

and practices, without regard to water temperature or content of specific ions. The estimate 

of recoverable \Vater in storage was made 

without regard to costs or to the number and 

spacing of :required production or injection 

wells; thus, it does not consider important economic and engineering factors. The time and 

funds available for the work did not permit a 

thorough evaluation of the environmental or 

hydrologic consequences of removing all or part 

of the water from storage in the basin. A brief 

discussion of such consequences is included, 

however. 

Three secondary purposes of this study were 

to estimate the following: ( 1) The percentage 

7 

of the total recoverable water in storage that 

underlies Federal Lands in Imperial Valley 

,,;hich have been withdrawn from the public 

domain for reclamation purposes-the 'Imperial Valley is being considered as a potential 

source of water to augment the Colorado River 

supply, (2) the total water in storage having a 

temperature greater than approximately 

150°C, and (3) the total recoverable water in 

storage derived from both the Colorado River 

and local sources in California. 

The scope of the work included: 

1. Collecting for analysis and study pertinent 

available geologic, geophysical, and hydrologic data for the area, including logs 

of wells. 

2. Analyzing available data and formulating a 

conceptual geologic and hydrologic model 

of the sedimentary basin. 

3. Compiling an estimate of the basin's total 

recoverable water containing 35,000 mg/1, 

or less, dissolved solids. 

4. Describing the possible hazards that might 

accompany water production, including 

lmtd subsidence, possible seismic activity, 

and changes in the water inflow-outflow 

relations of the basin. 

5. Appraising the accuracy of the estimates of 

recoverable water and describing the additional data needed to refine the estimates. 

6. Preparing a report summarizing the results 

of the study. 

All the foregoing work was accomplished between May 20 and July 10, 1971; thus, the 

results presented herein are preliminary and 

should be regarded as subject to revision. 

This report was prepared by the U.S. Geological Survey in cooperation with the U.S. Bureau of Reclan1ation as part of an investigation of the water resources of the Imperial 

y alley area. The work was done during 1971 

under the general direction of R. Stanley Lord, 

district chief in charge of water-resources investigations in California. 

ACKNOWLEDGMENTS 

We are greatly indebted for discussions and 

consultation with many individuals and colleagues during this study. We have had imInense benefit from such discussions with our 
colleagues D. E. White, L. J. P. Muffler, Ivan 

Barnes, Alfred Clebsch, Jr., J. H. Feth, and P. 

H. Jones of the U.S. Geological Survey. 

We are greatful for the help of Mr. Bill 

Creel, Schlumberger Well Services, Inc.; Mr. 

Kent Crowder, Standard Oil Co. of Calif.; and 

many representatives of commercial oil companies who also supplied data for wells; and for 

the assistance given by J. B. Combs and Walter Randall, staff scientists at the University 

of California, Riverside, and R. T. Littleton of 

the Bureau of Reclamation. 

We are especially greatful for the assistance 

of 0. J. Loeltz, U.S. Geological Survey, Yun1a, 

Ariz., who supplied n1uch data, helped with 

analysis and interpretation of data, and assisted with the computations, as did W. R. 

Powers III of the Garden Grove office. 

Special thanks and recognition is due Ben E. 

Lofgren, U.S. Geological Survey, Sacramento, 

Calif., who wrote the section "Land Subsidence" in the report. 

Without the enormous help, assistance, and 

data supplied by these individuals the report 

could not have been completed. These acknowledgements of course do not commit any of the 

above individuals to views and interpretations 

expressed herein. 

SOURCES AND ADEQUACY OF DATA 

Time was not available for new fieldwork 

during this study. A detailed study \Vas made 

of previous publications (see section "Previous 

Work and Reports"), and discussions were 

held with personnel of the U.S. Bureau of Reclamation, Boulder City, Nev.; Institute of 

Geophysics and Planetary Physics, University 

of California at Riverside; Schlumberger Well 

Services, Inc.; selected oil companies; and personnel of the U.S. Geological Survey. 

The sources of data included a primary network of about 50 deep oil exploration and 

geothermal wells, supplemented with about 75 

shallow water wells and springs. Figure 2 

shows locations of wells and springs and hydrologic sections. 

Electric logs were available for many of the 

deep wells, but other geophysical logs, such as 

neutron porosity, neutron, sonic, gammagamma, and temperature logs were available 

8 

for only a few wells. Only a few chemical analyses of water from the deeper zones of the 

basin sediments were available. Temperature 

logs were helpful but not always indicative of 

the true forn1ation temperature. Data from the 

water wells consisted of drillers' logs, waterlevel measurements, and chemical analyses. 

Without the data from many shallow wells, 

analysis of the deeper geothermal zones would 

have been more difficult. 

The previously mapped surface geology (fig. 

3) was used in this study. Of prime importance was the delineation of the boundary between the water-bearing materials of the 

ground-water basin and the areas of non-water-bearing igneous and metamorphic rocks of 

the mountains. The map of thickness and configuration of the basin sediments as determined by Rex (1970) was used for this study 

(fig. 4), and his map was utilized in virtually 

unchanged form. 

In appraising the adequacy of data for subsurface analysis, it became apparent that although numerous reports have been prepared 

they are based on a paucity of basic data. 

Many of the reports were keyed to a few selected data, and the authors reached various 

conclusions. lViuch of the inadequacy of the 

data is largely the result of extremely high 

formation temperatures encountered during 

drilling. 

WELL- AND SPRING-NUMBERING SYSTEM 

vVells and springs (fig. 2) are numbered according to their location in the rectangular 

system for the subdivision of public land. For 

example, in the number 11S/13E-27M1, the 

part of the number preceding the slash indicates the township (T. 11 S.), the part between the slash and the hyphen indicates the 

range (R. 13 E.), the number between the hyphen and the letter indicates the section (sec. 

27), and the letter indicates the 40-acre subdivision of the section. Within the 40-acre tract 

wells are numbered serially, as indicated by 

the final digit. Thus, well 11S/13E-27M1 is the 

first well to be listed in the NW1,4SW1,4 sec. 

27, T. 11 S., R. 13 E., San Bernardino base line 

and n1eridian as shown in the following diagram. 
SAN BERNARDINO BASE LINE _ 

iffiffiT.lS. 

o T.2S. z: 

8 

~ T.lOS. 

i m 

R.lE. R.2E. w~,~-------- R.12E.\R.13E . ......_ ---- ' ....... -- \ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

' 

\ 

\ 

6 .5 4 

7 8 9 

18 17 16 

19 20 21 

30 29 28 

31 32 33 

Geothermal wells in Mexico are preceded by 

the letter M and numbered serially. These 

numbers were retained from previous reports. 

Springs are numbered similarly to wells except that an S is placed between the 40-acre 

subdivision letter and the final digit as shown 

by the following spring number: 11S/13E24ES1. 

GEOLOGY 

SETTING 

The southern part of the Salton Trough in 

the United States is called Imperial Valley. 

The Salton Sea (fig. 1) is about 30 miles long 

and 10 miles wide and occupies the lowest part 

of the trough ( 232 ft below mean sea level in 

- 3 2 1 

10 11 12 

15 14 13 

22 23 24 

........ - 27 ........ --- - r---~ 25 ....... -- -- [\\4 

........ , 

35 36 

-- ........ , -- ~----~----~----~~----, 

I 

9 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

D C I 8 A 

I I 

---- ---+--- ----

E F H 

I 

~--- +---27- --..... ---- 0 ll s I 1 3 E - 27M I . I 

M I L 

I 

K 

~---

\ I 

---+ ---

\ N I p Q 

J 

R 

\\ I L_ ____ lL---~----~----~ 

1968) . The crest of the Colorado River delta in 

Mexicali Valley protects the Salton basin from 

inundation by water from the Gulf of California. The land surface slopes northwest from 

about sea level at the international boundary 

to the Salton Sea. The shoreline of prehistoric 

Lake Cahuilla is well preserved along the east 

and west sides of the valley at 42-50 feet 

above mean sea level. 

Imperial Valley is bordered on the west by 

the Peninsular Ranges, which are mostly granitic rocks (figs. 1, 3) of probable Cretaceous age (Dibblee, 1954, p. 21). On the east 

are the Chocolate Mountains, which in the 

northern part are principally plutonic and metamorphic rocks, of pre-Tertiary age, and to 

the south are extensive volcanic rocks of Ter-
Base from U.S. Geological Survey State of 

California (south half) 1:500,000, 1970, and 

U.S. Department of the Interior Reconnaissance 

Map of the Salton Sink, California 1:500,000, 1908 

FIGURE 3.-Geologic map of Imperial and Mexicali Valleys. 

10 
Qo 

's l7rt / 

A I I u vi urn 

Gravel. sand, silt. 

and clay. Includes 

waterborne and 

windborne uncons o I i d a t e d d ep o s i t s 

of Quaternary age 

Geology complied by W R Mayle J r , after mapping 

by Cal1forn:a DIVIsion of M1nes and Geology, 

San Diego-EI Centro (1962), Santa Ana (1965). and 

Salton Sea (1967) Geologic Map Sheets and by 

Eduardo Paredes (1964) 

EXPLANATION 

[i] 

Lakebeds Yo I can i c rocks 

Si It, clay, and 

some evaporites 

of Quaternary 

age 

Rhyolite of Holocene 

age 

Sedimentary rocks 

Marine and nonmarine 

rocks o f T e r t i a r y 

age 

Basement complex 

Igneous and metamorphic rocks of 

Precambrian to Tertiary age 

Geologic contact 

Dashed where approximately I ocated 

~-?-··· Fau It 

Dashed where approximately located; 

dotted where concealed; queried 

where doubtful 

4~; 

~ i 0 

z 

~ ~-~ 

APPRO X I MATE MEAN 

DECLINATION 1971 

I 0 

CONTOUR INTERVAL 50 AND 501) FEET 

DATUM IS MEAN SEA LEVEL 

20 MILES 

Elevations and topography in Mexico are approximate 

FIGURE 3.-Continued. 

11 
1--' 

tv 

C' It 11s03o' 115°oo' 

~-~-~-r-:.)fo -7----..---+f-- --~~ .... 1tr',T~ K '""- . '""'Of < ·· , g . · I '\ l ; ( 

. 1' • -.. ,, ""l'/J~ ~ I -- -_ f ·--1~-~ 4 ;_, ~:: _ ____ 1 __ Q,:~ .... "'~ -.• 1 \f£.1 h 1 I"' xI ~1 ~-""" T ~~f;J~,·t ~. "c, 'f• tj 

_;-/1- cl0 · I '1 

' t f:l /'' ~ \ I"'~~ ~-,\ I' I 1\. I j·.., I - \.' \~. ~ ,..._~ '--'\:: ~ ..... 

116°oo' 

EXPLANATION 

--5000--

Line of equal depth to basement 

complex. Interval 5,000 feet. 

Datum is land surface 

---?-··· Fau I I 

Dashed where approximately located; 

dotted where concealed; queried 

where doubtful 

33000

'ifot-H~~(.; .... J._- '~, f(=S~~ Jl~w'lr\\1!-l\'\ \l-\ \~,·~ .... ~.jj L jj ~-- <p~- \<':" ·;~·r_- 2 't\ 133000 ' 

Base from U.S. Geo log1 cal Survey State of 

California (south half) 1:500,000.1970 

FIGURE 4.-Depth to basement complex. 

114°30' 

lap rrom R.I. Rex (1970) 

u -.. 

APPROXIMATE MEAN 

DECLINATION 1971 

0 5 10 15 20 Ml LES 

CONTOUR INTERVAL 500 FEET 

OATUM IS MEAN SEA LEVEL 
tiary age. The valley between 4 ~ mountains is 

identified from east to west by .ocal residents 

as the Sand Hills, East Mesa, main valley, and 

West Mesa areas (see fig. 16). 

The Sand Hills (Norris and Norris, 1961) 

along the east valley margin are more than 40 

miles long and as much as 6 miles wide. These 

hills lie on the surface sloping southwest to 

west. In the southwest part of the area there 

are longitudinal southeast-trending sand ridges 

as much as 300 feet above the adjacent mesa 

surface. 

The East Mesa area is a triangular area between the Coaehella and East Highline canals. 

The area was formed by fluvial processes, locally modified by lacustrine or marine processes, and merges gradually with the main valley. 

The main valley area consists primarily of 

cultivated agricultrual land and is entirely 

within the shorelines of prehistoric Lake Cahuilla. The soils from the lakebed materials 

contain a large proportion of clay and silt of 

low permeability, in contrast to the sandy soils 

of the adjacent East and West Mesas. 

The Alamo and New Rivers are the two 

main drainages to the Salton Sea and have cut 

trenches as much as 40 feet deep, mostly during 1905-07 when the Colorado River flowed 

uncontrolled aeross the valley floor to the lake 

then formed. Obsidian Butte, Red Island, Rock 

Hill, and Mullet Island are small domical hills 

20-100 feet above the general surface along 

the southeast Bhore of the Salton Sea. 

West Mesa is a broad plain between the main 

valley and the~ Peninsular Ranges to the west. 

Many ephemeral streams drain this area. The 

soil is sandy and has less clay than in the central part of thE! valley. 

STRUCTURE 

Three major right-lateral fault zones strike 

into Imperial Valley (fig. 3). The San Andreas 

fault zone (also called the Mission Creek-Banning fault zone) strikes along the east side of 

the valley, and the Elsinore and San Jacinto 

faults have been mapped along the west margin. 

The position of the San Andreas fault zone 

has been inferred on the basis of an alinement 

of anomalously low gravity measurements that 

extend from the Salton Sea southeastward to 

the Colorado River. The gravity data are supported by seismic-refraction profiles (Kovach~ 

and others, 1962) and aeromagnetic profiles 

(Griscom and Muffler, 1971). That fault, or 

possibly a parallel fault, has been traced into 

Arizona, south of Yuma, by Olmsted, Loeltz, 

and Irelan (1972), where it is named the Algodones fault. 

The Elsinore fault is the southwesternmost 

right-lateral fault related to the San Andreas 

system in the United States (Biehler and others, 1964, p. 139). The vertical component of 

movement on the fault is as much as 3,000 feet 

northwest of Imperial Valley {Jahns, 1954, p. 

45). This fault extends into Baja California 

and is locally called the Laguna Salada fault. 

The San Jacinto fault, which is related to 

the San Andreas fault system, splits into several subparallel faults west of Imperial Valley. 

The Superstition Hill and Superstition Mountain 

faults are probably part of this system. Imperial fault may be a part of this system (Biehler and others, 1964, p. 138). As much as 13 

feet of right-lateral movement occurred on the 

Imperial fault east of Calexico during the 

earthquake of May 18, 1940 (Dibblee, 1954, p. 

26). 

The Calipatria and Brawley faults in the 

central valley were shown on maps by Rex 

(1970). The mapping was based on unpublished work by E. A. Babcock (written commun., 1969). Gravity surveys across the basin 

(Kovach and others, 1962, p. 2:869-2870) were 

not particularly successful in demonstrating 

the continuity of major fault zones within the 

trough, although these data confirm the presence of large vertical displaeements beneath 

the valley alluvium. For this study, the Calipatria and Brawley faults are shown where postulated by previous workers, although further 

work is needed to substantiate their existence 

and effect on the basin-filling rocks and deposits, and especially to determinE~ their effects on 

ground-water circulation. 

STRATIGRAPHY 

13 

The clastic sediments filling Imperial Valley 

represent almost continuous deposition since 

Miocene time (fig. 5). The sediments were derived mainly from the Colorado River drainage 
1---l 

~ 

Geologic 

Age 

Stratigraphic 

column 

-

Stratigraphic unit 

and symhol Stratigraphic nom~clatur~ 0 Maximum 

thickn~ss 

(f~t) 

DESCRIPTION 

~ Volcanic Rocks (V) 

. . . I 

. .II ) O.po•ih 1 . ahuila (Cahur a 

.,- • _ 

_ 

··-

. Ql _ 

• 

_ -:_ ~ Lake D ep 

Deposits(Qt) oslls (QI) I Quat~mary Lok• Co N~mori•• T••~• O.po•H• l --.- ·-· . - •_.<•/ 54 - 0 4 •• Terrace UNCO NFORMITY 

~· 

Dun~ Sand (Q•) R~c~nt Dun~ Sand 

Alluvial D~posits (Qol) R~c~t Alluvium 

R~c~nt Volcanic Rocks 

> 

IX 

< 

z 

IX 

t.J 

I-

< 

::::> 

0' 

f 

~ 

Wind~lown sand, local dun~s Locally distributed around Salton Sea 

Grav~l. sand, silt, and clay Occurs along river chann~ls and at footh1lls abov~ th~ anc1ent shoreline of Lake 

Coahuila 

Obsidian, rhyolite,and pumic~ compos1ng volcaniC domes on the southeast shor~ of Salton Sea. Locally lnterbedd~d obs1d1an flows and lake deposi Is. 

Cl:b:.v~il~~:i:~• s~~~~ing;a;ttak:d c::rus~e ~n~Ji~~ll~f ~~dJf:::.rti:~~~::r:v::~~~:~~i~usdes old~r lake beds 

Ext~nsively dissKted and locally folded str~am temice d~posits of fanglom~rate, grav~l, and sand,1n Borrego 

Vall~ 

> 

IX 

< 

1= 

IX 

t.J 

INonmarine Sediments (Qc) 

·ac _ -- . Volcanic Rocks (V) 

·--~ ;:_ . -. ~·I Phoc~e formations (P) : •A • 6 A~ • 

/ 

- p 

/ / 

.. 

/ 

... 

• : 0 

. . . - . .... .•• .# I I 

.. ~ ' " ~ ~ .. --: / ~ ::/v·. ...... . ___.;/~o v"v 

• v • v\1 v 

• :' 

0

:,3--/v v 

Mioc~ne-Eoc~e 

formahons (M) 

Volcan1c Rocks (V) 

B111wley formation 

Ocotillo Conglomerate 

Pl~istocene Volcanic Rocks 

Unnamed Pliocene-Pleistocene Nonmarine Sedimentary Deposits 

Canebrake Conglomerate 

Palm Spring formation 

Borrego formation 

Mecca formation 

lmpenal formahon 

Spht Mountain formation 

Unnamed Oligoc~ne Nonmarine Sedimentary Rocks 

Maniobra formalton 

• ?--~ Undiffer~t1ated Tert1ary Volcamc and 

M I Intrusive Rocks 

A--------uNCONFORMITY 

Und1ffer~t1ated Mesozoic Gran11tc 

2,000 

2,500 

9,000 

Red-gr~ clayston~, siltslont'1 sandston~, and p~bbly grav~l deposits 

Gr:!~:::;(i~Y i~fo~~~~;~er!=~'l!~rg cf~~~w:rate, grading basin ward into pink sandstone and clayston~ Distribut~d 

Quaternary thyolite plugs along Salton Cr~ek. 

110::t~':.~Y~Ye:r,':.:~:fi~~T:';:'~~~~~n\~~ ~o~~fyma~~~~~~~Yc~~rc"~~i~s"r'sconsrsttng of unsort~d, poorly consolidat~d, 

Gr2'~t'i~!~~~I"~~::i~nd fanglomerate of granitic and m~tamorphic d~bris Unsorted and poorly consolidated 

7 000 I I L1pt-cray arl<osic sandston~ and r~ddish clayston~, cradin11. into Can~brak~ conglomera!~ Cont1n~ntal or111n 

Contains Pltocene andjorPie1stoce1e vertebrate fosstls west of Salton Sea 

0 

6,000 g I Lichl-lf,r~v clayston~ and n.inor amounts of buff sandstone of lacuslrlne ori~"' <"Oilt«lns " 1." u~1 nnl' I dun.~ ot 

~ m1nute mollusks, ostracods and rare foram1ntfew; grades laterally tnlo Palm Spnn~ form«llon. 

1,000 

4.000 

2,700 

Gr~ish-r~d to yellowish-brown basal conr,lomerate, overlatn boJ a'icose and arkos1c conglom~rate of granitic and metamorphic d~bns. Continental oncin. 

Light-grey claystone and lt>ssor interbedd~d arl<osic sandstone with calcerous oyster-sh~ll "reds " Shallow- water, manne in origin . 

R~d or gr~y c~m~nted basal cong)om~rat~ or fanglomerat~ and sandstone of granitic and m~tamorphic d~bris 

~ft'~a::~':;:;~tfe ':.fi~!~~ !:!:;'~!~:!:~.=!:rinC:ii:~rCf~f:k Gypsum member). Th~ upp~r m-ber 1s marin~, 

Conclomerat~, sandstone, breccia, mudstone, and ~vaporit~ rocks (Orocopia Mountains). 

Marin~ Eoc~e, siltstont'1 sandstone1 conclom~rat~, and br~ccia with som~ sandy Jim~ston~ (Orocopia Mountains). 

Local lava flows and tuffs. Flows are andesitic, myolitic,or basaltic rocks of variou,. aces. Also includes intrusive acidic rocks and r~lated diabasic dik~s. Alverson andesite dated as Miocene 

Gr..,itic rocks. 

"' • Gran11tc and Metamorphic Rocks • • Orocop1a Sch1st Pr~-Cretac~s schist. 

~ 

' < ~ i= 0. :: 

I-

~ .. + .... 

.. + .. .. 

~ + + 

Rocks (m) Other Pre-C~ozo1c Gran11tc and Metamorphic Rocks 

• After Cahfornia Division of Mines and Geology Salton Sea ( 1967) and 

Santa Ana ( l'loo) Geologic Map Sheets. Does not conform to U.S. 

Geological Survey stratigraphic nomenclature 

Gn~iss, lim~ston~, schist, and cranitic rocks, ranpnc in ag~ from M~sozoic to PrKambrian. 

From California Department of Water Resources ( 1970) 

FIGURE 5.-Composite stratigraphic section. 
area and partly from the adjacent mountain 

areas. The sediments attain a maximum exposed thickn,ess of 16,500 feet in the southwestern part of Imperial Valley and 18,700 

feet in the northwestern part (Dibblee, 1954, 

p. 21-22). Geophysical evidence (fig. 4) indicates that the fill is probably more than 20,000 

feet thick in the center of the basin (Kovach 

and others, H)62, p. 2864). 

In general, earlier studies, as shown by 

figure 5 (California Dept. Water Resources, 

1970), have grouped the basin rocks into three 

broad categories: (1) A lower sequence of 

chiefly nonmarine sedimentary rocks of early 

to middle Tertiary age, but including some volcanic rocks and minor marine sedimentary 

rocks; (2) a middle marine unit, the Imperial 

Formation, of late Tertiary (Pliocene?) age; 

and (3) an upper sequence of mainly nonmarine deposits of late Tertiary and Quaternary 

age derived primarily from the Colorado 

River. 

The late Tertiary and Quaternary deformation in the Salton Trough is indicated by the 

configuration of the base of the marine Imperial Formation. In the Chocolate Mountains 

about 15 miles northeast of Glamis, deposits 

similar or correlative to the Imperial Formation are exposed at an altitude of about 1,050 

feet. However, 22 miles southwest of Glamis in 

the center of the trough these deposits were 

not penetrated in an oil test well 13,443 feet 

deep. Along the west side of the Imperial Valley, the base of the Imperial Formation is exposed at altitudes as great as 1,000 feet above 

sea level. 

The geologic units of the Imperial Valley as 

shown in thE! geologic map (fig. 3) have been 

grouped into four main units. The four units 

include: (1) The igneous and metamorphic 

rocks of the surrounding mountains; (2) sedimentary rocks of marine and nonmarine origin 

of Tertiary age; ( 3) lake beds consisting of silt, 

clay, and sorne evaporites of Quaternary age; 

and ( 4) alluvium consisting of gravel, sand, 

silt, and clay of Quaternary age. 

The Niland Obsidian (Dibblee, 1954) crops 

out in a row of small domical buttes along the 

southeastern shore of the Salton Sea. These 

young knobs of obsidian, scoria, and pumice, 

with the nearby hot springs, are evidence of 

15 

geologically recent volcanic activity (Muffler 

and White, 1969, p. 162). 

HYDROLOGIC CHARACTERISTICS OF AQUIFERS 

The hydrologic characteristics of the sediments to a depth of about 1,000 feet are known 

generally from pumping tests of numerous 

shallow water wells. Water yield and formation permeability of the deeper rocks and deposits are difficult to estirnate because few 

quantitative data were available for examination. 

A large area in the central part of the valley 

contains flowing domestic wells; these extend 

from 6 miles south of Holtviile to several miles 

north of Calipatria. The Alamo River flows 

along the western limit of the area of 

flowing wells. Shallow wells drilled by the Geological Survey show that the area of artesian 

pressure extends farther west, but west of the 

Alamo River the pressure is insufficient to 

cause wells to flow. 

An inventory of more than 100 flowing 

wells, ranging in depth from 350 to 1,300 feet, 

shows that the discharge ranges from 10 to 

100 gallons per minute. Data indicate unfavorable conditions for development of large quantities of usable ground water within the area 

of flowing wells, and almost the entire central 

part of Imperial Valley. Aquifer tests at wells 

about 500 feet deep at Imperial and east of 

Calexico showed low transmissivity, about 

2,000 gpd per ft (gallons per day per foot). 

Thus, specific capacity of wells may be about 1 

gallon per minute per foot of drawndown. (The 

specific capacity of a well is the yield, in gallons per minute, divided by the drawdown, in 

feet, from the nonpumping water level in the 

well.) Ordinarily, wells having specific capacities less than about 10 are considered of marginal value for irrigation use .. 

A test well drilled to a depth of 560 feet by 

the Geological Survey on the West Mesa (fig. 

16) , 8 miles north of Plaster City, was tested. 

The transmissivity of the aquifer may be about 

150,000 gpd per ft. 

In the East Mesa area, about 8 miles southeast of Holtville, the Bureau of Reclamation 

drilled a well (well 92, U.S. Bur. Reclamation 

127) to a depth of 1,406 feet on a high heatflow anomaly. Determination of permeability 
in millidarcies from a sidewall neutron log 

and a formation density compensated log, in 

the depth interval 204-1,400 feet, indicated 

the following: 

Depth interval 

~ ·(feet) I 

Average permeability 

Millidarcies Gpcl per 

sq ft 

204- 300 ----------------------------------- 7 43 14 300- 400 ----------------------------------- 1,276 23 

400- 500 ----------------------------------- 376 7 500- 600 ----------------------------------- 628 11 600- 700 ----------------------------------- 787 14 

700- 800 ----------------------------------- 966 18 

800- 900 ----------------------------------- 147 3 900-1,000 ----------------------------------- 610 11 

1,000-1,100 ----------------------------------- 937 17 1,100-1,200 ----------------------------------- 654 12 1,200-1,300 ----------------------------------- 537 10 1,300-1,400 ----------------------------------- 651 12 

Average -------------------------------- 700 13 

Multiplying the average permeability value by 

the well depth gives an aquifer transmissivity 

of about 18,000 gpd per ft. By comparison, a 

well drilled 1,000 feet deep at the junction of 

the All American and Coachella Canals had an 

aquifer transmissivity about 10 times greater. 

A CONCEPTUAL MODEL OF THE SYSTEM 

If needed measurements of geologic, hydrologic, and physical parameters were available in 

great detail and quantity throughout the Salton Trough geothermal basin, it would be a 

straightforward process to assemble and analyze the data and make the necessary calculations required to estimate usuble and recoverable water in storage. However, this would 

require knowledge of parameters and boundary 

conditions and locations and rates of planned 

production of water. Parameters required 

would include three-dimensional distributions 

of temperature, water quality, rock conductivity, permeability, and porosity. Knowing the 

natural flux of water and heat through the system would also be required, as well as changes 

in the natural inflow and outflow of water and 

heat caused by production, if detailed estimates were required. 

Making the many necessary measurements 

of parameters would be extremely costly and 

very difficult, if not impossible at present. 

Many parameters would have to be computed, 

based on indirect measurements of physical, 

geologic, or hydrologic variables. 

Even if the best techniques were used to collect and interpret such a large volume of detailed data, inaccuracies might still reside in 

the computations of usable and recoverable 

water in the system. The scarcity and inaccuracy of the existing information plus the fact 

that most of it is from wells that are not particularly strategically placed for the purpose of 

making such estimates make the task extremely difficult. 

The only recourse is to formulate a conceptual model of the hydrodynamics of the 

sedimentary basin, considering also the quality 

and temperature of the contained water. In the 

remainder of this section of the report the 

basic concepts and assumptions used in formulating a conceptual model of the Salton Trough 

hydrothermal system are outlined. On the basis 

of these assumptions and the model, the few 

available data for the basin were extrapolated 

throughout the system as lines of equal temperature, porosity, specific yield, and water 

quality. Ultimately these lines formed the basis 

for the estimates of usable and recoverable 

water derived herein. Thus, assumptions about 

the basin geometry, its water and heat inflow 

and outflow, duration of the quasi-steady-state 

flow system, and many aspects of the water 

chemistry, all based on very limited data, have 

critical bearing on the estimates derived. 

Undoubtedly the estimates are inaccurate; 

unfortunately the magnitude of the error cannot be estimated until many additional data 

are collected. 

BASIC CONCEPTS 

16 

A hydrothermal system is considered as a 

heat-transfer mechanism relying for its operation on the transport of water, but not necessarily on a discharge of water at the surface. 

The system, however, includes at or below the 

surface a volume of rock and water in which 

heat flow is greater than in the surrounding 

area and is probably greater than average. 

Most of the system, then, consists of a water 

reservoir in hot rock. Under natural conditions 

little fluctuation of water level occurs but 

water is discharged; thus, recharge to the 

system must also occur. 

The basic elements of a hydrothermal system are: (1) A heat source, (2) a recharge 

mechanism, (3) a circulation (or recirculation) mechanism, and ( 4) a discharge mechanism. 
Prior to this study three presently actively 

supported conceptual models of the Salton 

Trough hydrothermal system had been proposed. All three models were formulated in an 

effort to explain data obtained from wells 

drilled at the Salton Sea geothermal field. All 

three models (Berry, 1966; Helgeson, 1968; 

and White, 1968) were in agreement that the 

origin of the water in the system was at least 

substantially if not entirely meteori~. All were 

in agreement that the source of the heat was 

almost surely a local magmatic body at relatively shallovv depth, but probably at least 

7,000 feet below the surface (Griscon1 and 

Muffler, 1971). 

There were fundamental differences proposed for the water recharge-discharge mechanisms, for the age of the system, and, most importantly, for the source or mode of occurrence 

of the hypersaline brines produced. There was 

also disagreement concerning whether or not 

the source of the meteoric water was the Colorado River or the bordering uplands ( Chocolate Mountains). Thus, basic assumptions concerning water source, age of the system, and 

source of salts led to fundamental differences 

in the models proposed. Because the conceptual 

model of the system and its mechanisms have 

such critical bearing on the interpretations of 

the limited data available, the choice of the 

model must strongly influence any estimates of 

usable and recoverable water in the system. A 

brief summary of the mechanisms proposed by 

the three actively supported models may be 

helpful here. 

Berry (1966) depended entirely upon semipermeable membrane filtration of capping 

shales to increase the total salinity of the 

water in the reservoir rocks to 155,000 mg/l 

chloride from an unspecified concentration in 

the ground water derived from the Colorado 

River. 

Helgeson's model (1968) assumed that thermal evaporative concentration of water derived 

from the Colorado River occurred during a 

stage prior to the deposition of the upper 

2,500-3,000 feet of predominantly fine-grained 

sediments of low permeability. 

White (1968) actually proposed two slightly 

different versions of his model; they differed 

mainly in vapor content of the fluid, mode of 

17 

discharge, and thermal gradient. We accept 

White's model as substantially correct and are 

proposing only a few modifications. One of 

White's models (1968, fig. 3) is reproduced in 

figure 6. A slight difference exists between our 

model (this paper) and that of White, however. \Vhite relies on evaporites in the system 

to supply the salts of the hypersaline brine at 

the Salton Sea field, whereas ours does not. 

Craig (1969) emphasized the significance of 

the isotope data and convincingly pointed out 

weaknesses in Helgeson's model. White (1968, 

p. 312-318) also presented an excellent analysis of available chemical and isotope data that 

forms a sound basis for modifying the previous models of Berry (1966) and Helgeson 

(1968). 

SOURCES OF HEAT AND HIGH-TEMPERATURE 

ANOMALIES 

On the basis of seismic refraction and gravity studies by Biehler, Kovach, and Allen 

(1964), Koenig (1967) estimated that the total 

crust is only 12-15 miles thick beneath the 

Salton Sea and is much thinner to the southeast beneath the Gulf of California. The crustal thickness even in the north part of the Salton Trough is considerably thinner than in the 

bordering mountain areas of the Peninsular 

and Transverse Ranges (Biehler, 1964). 

Heat-flow measurements reported by Rex 

(1966) are abnormally high in the Salton Sea 

(Niland) and Cerro Prieto areas but are not 

unexpectedly high in most of the area. There 

is, however, considerable variation in the 

heat-flow pattern within the trough. A pattern 

of randomly located hotter spots has been observed (Rex, 1970, U.S. Bur. Reclamation, 

1971). The known hotter spots are represented 

as circles in figure 7; the diameters shown are 

intended to represent only very approximately 

the size of the anomaly. 

Assuming that the heat source lies within 

uppermost mantle, the 4 miles of water-saturated sediments above the granitic basement 

provides a near-perfect environment for development of hot-water convection cells. These 

cells speed the transfer of heat from the granitic-metamorphic basement toward the surface. 

Where relatively impermeable clay, shale, or 

other rocks occur, the upward movement of 
...... 

00 

1..&... 

~ 

~ 

::r: 

1-

::; 

Cl 

oc 

0~~----~~u~u~-=----~~~vv~-------,--r------

Temperature qradient to 3,000 feet dominantly 

conductive; some heating by 

upward flow, cooling by near- surface dilution 

Temperaturesin up-flowing 

fluids are below reference curve because of partial 

pressures of gases 

no 

<;urface 

Channel oreatly 

exaggerated 

0------------------------~~-----------------------------

1,000- ...., 

~ c:: 

·e 

.g 

(I) 

"' 2,000- i5i 

3,000-

4,000-

5,000-

6,000-

(I) 

c: 

0"0 

....,(I) 

v>S-

-o::;, 

c:...., 

n:su 

"'"' S- •'1-

S-

.... "0 

oc: 

>n:s 

S- Q.>...., 

CllC: 

Q.ln:l 

S-c: QJ.E 

c::o 

.... "0 

Sec 

+-- +-- +-- +-- +-- +--

Gas bubbles Near-surface 

meteoric dilution 

+---+--<t--+--+---+--4------+-- 4------ +-- +--- r 

A little brine escapes 

upward; ratios of metals to S, C02, dnd H20 

decrease in shale, 

metal sulfides 

Vaoor escapes upward; most 0 and H2S condenses 

C02 is enriched by 

release in carbonatesilicate reactions 

I 

I 

j 

1 

precipitated @ "' s...J (I) ~ 

,.__.. ~ ~ ~ ----. "- ' /" -------~ t(--+--.. '\ ~ : 

i! j.t \~ ~J~ l ~ i t Vapor (H20. C02 • H2S) ~ l ~ J ~ ~ l ""'t brine t .1 i l ! J : 

l rema1ns i . . l j ;:, 1 . 0 

Con~ect~ n(l ~rl ne 1 (#, .8 .. 1n j 1sh1gh1n -t ,; tt> 

l I reservoir t ~eta~s, low 1 I 1ij 15 -t t 1n d1ssolved -t -t t& t sulfide; DS / 1 tf·· t 260~~~tmg/l i i / 

\.. "'---.-+ __... / 0 '"" .__ ....-- +- / j // -..... ---+ ---+ ~ "'-..:: +- +- +-- ......... ..--- ..-

) ) ) ; t 

M a g m a 

) ) 

t 

i c 

l >·Jt) ) ) 

/ 

Model modified after White (1968, fig. 3) 

FIGURE 6.-Model for Salton Sea geothermal system, involving a vapor phase. 
these heated fluids is impeded. Such confined 

heat fields may have little or no expression at 

the surface. However, where major faults cut 

through the permeable and impermeable layers, heat seeps and other evidences of the 

convection cell system may show clearly at the 

surface. 

The presence of Quaternary volcanic rocks 

at Niland and at Cerro Prieto has suggested 

the possibility of the existence of a magma 

chamber at a depth greater than 7,000 feet 

(Elders and Robinson, 1970). The local gravity 

high at Salton Sea and metamorphism of sediments at Salton Sea and Cerro Prieto are cited 

as supporting evidence. However, ·metamorphism was encountered in a deep well (No. 71, 

13,443 ft) about 8 miles northwest of Holtville 

without Quaternary volcanic rocks being present at the surface. 

A magnetic anomaly has been mapped in the 

Salton Sea area (Griscom and Muffler, 1971; 

Kelley and Soske, 1936) . This anomaly corresponds closely to the outcrops of Quaternary 

volcanic rocks and to the positive gravity 

anomaly at Salton Sea. This association is considered by some (Griscom and Muffler, 1971; 

Biehler, 1964; and McNitt, 1963) as evidence 

of a buried, cooling, magmatic mass that is 

the source of heat for the geothermal field at 

Salton Sea. 

METAMORPHISM AND CHANGES IN POROSITY 

AND PERMEABILITY 

In places the intense heat is sufficient' to 

cause metamorphism of sediments. White, Anderson, and Grubbs ( 1963) and Muffler and 

White (1969) discussed metamorphism of 

upper Tertiary and Quaternary sediments 

found in geothermal wells in the Salton Sea 

area. Evidences of metamorphism of young 

sediments also are found in wells at Cerro 

Prieto according to Bernardo Dominguez (Koenig, 1967). The laboratory determinations 

were made by L. J. P. Muffler, using samples 

from wells M-3 through M-6 provided by the 

Commission Federal de Electricidad. Evidences 

of low-grade metamorphism were found in a 

deep well (No. 71) near Holtville in the Imperial Valley (Rex, 1966). On the basis of examination of electric logs from other wells, metamorphism is probably common at depth 

19 

throughout the entire length and breadth of the 

Salton Trough. 

Several workers have suggested that the 

thick, relatively impermeable shale or clay and 

volcanic units near the surface of the trough 

serve as an insulator and thermostat preventing the dissipation of the major part of the 

geothermal fluid-and therefore the heat-to 

the surface. At Salton Sea, the shales of the 

Borrego Formation as used by Koenig (1967), 

form the impermeable cap. The Borrego Formation becomes increasingly sandy at depth 

and gradually interfingers with and merges 

into the Palm Springs Formation (Koenig, 

1967). This largely sandstone sequence is the 

reservoir rock at Salton Sea. Simil&rly, a metamorphosed argillite cap overlies sandy bedsthe reservoir-at Cerro Prieto (Paredes, 1964). 

Metamorphism may reduce permeability of the 

shaly cap rock still further. 

Estimated average horizontal permeability 

of the· fine-grained deposits dominant in the 

upper 2,500-3,000 feet at the Salton Sea 

geothermal field is only 1 gpd per sq ft (gallon 

per day per square foot) ; the vertical permeability is probably very much less. Thus the 

transmissivity may be about 2,500-3,000 gpd 

per ft. 

At the time of deposition, all the sediments 

consisted of sand, silt, and clay of uniform 

original mineralogic composition, but under 

the elevated temperatures and pressures of the 

geothermal system they are being transformed 

to low-grade metamorphic rocks of the 

greenschist facies. Muffler and White (1969) 

studied these transformations by X-ray, petrographic, and chemical analyses of cuttings and 

cores from deep wells that penetrate the sedimentary section. They reported, simply stated, 

that the reactions are: 

montmorillonite -+ illite 

T <100°C 

illite-montmorillonite -+ K-mica 

T <210°C 

dolomite+ ankerite+ kaolinite 

+ Fe+!! -+ chlorite+ calcite+ CO!! 

T=125°C to <180°C 

calcite+ silicates -+ epidote+ co!! 

T >290°C 
Base from U.S. Geological Survey State of 

California (south half) 1:500,000, 1970, and 

U.S. Department of the Interior Reconnaissance 

Map of the Salton Sink, California 1:500,000, 1908 

FIGURE 7.-lnfPrred direction of ground-water movement in deep aquifer system to generalized areas of known 

geothermal anomalies in Imperial and Mexicali Valleys. 

20 
--r:rr--, Plllo Vero.f I /.=,...__; 'II~ 

I 

I ' ~\ 

Geothermal anomalies in Mexico from California 

Department of Water Resources (1970) 

FIGURE 7.-Continued. 

21 

EXPLANATION 

Known geothermal anomalies 

Oi rection of ground-water movement in 

deep aquifer system 

Line dividing source of water derived 

from local mountains and water 

derived from Colorado River area 

APPROXIMATE MEAN 

DECLINATION 1971 

10 1.5 20 MILES 
The compositions of the sediments presently 

undergoing metamorphism in the Salton Sea 

area show a marked decrease in carbon dioxide 

with depth. 

On the basis of these findings and examination of drillers' logs, electric logs, gamma-ray 

logs, and neutron logs of wells, where temperatures exceed about 250°C most of the original 

interstitial sediment permeability has probably been greatly reduced or entirely eliminated. 

Fractures have formed extensively and may 

now account for virtually all available permeability. Even at shallower depth and where temperatures are lower than 250°C but greater 

than 100°C, significant changes in permeability presumably ;Llave accompanied metamorphism. 

On the basis of available data, estimates of. 

average permeability cannot be derived for the 

deposits deeper than about 3,000 feet. Deep 

wells at Salton Sea and Cerro Prieto, however, 

individually yield up to 200 or more tons per 

hour of steam and water-a quantity great 

enough to make production of water· and steam 

economically feasible if technical problems can 

be overcome. · 

High temperatures and pressures that 

caused metamorphism and resulted in reduced 

natural permeability of the rocks have also 

contributed to reduced porosity. Presumably, 

porosity has been reduced mainly through compaction of the sediments due to continuous 

deposition from the Colorado River. Porosity 

may also be substantially reduced locally near 

the margins of deep convection cells by cemen~ 

tation of the rocks and deposits with calcium 

carbonate, calcium sulfate, and perhaps silica 

carried toward the cells by recharge water. 

For estimates on the assumed average porosity 

of the deposits see the section "Estimated Porosity and Specific Yield of the Rocks and Deposits." 

AGE OR DURATION OF THE STEADY-STATE 

FLOW SYSTEM 

Near the Salton Sea geothermal field five 

domes of pumiceous rhyolite of late Quaternary age are exposed. The surface volcanic 

rocks have a probable age of 16,000 years as 

determined by potassium-argon dating (Muffler and White, 1969, p. 162), but that age may 

be in error by as much as 40,000 years. This 

certainly does not provide a precise age for the 

steady-state flow system, but it does suggest 

that the intense heat anomaly at the Salton 

Sea hydrothermal field is probably related to 

volcanism not older than about 55,000 years. 

The deuterium content of the brine (White, 

1968, table 1) is nearly identical with that of 

the overlying saline springs in the area and 

spring water from the Chocolate Mountains. 

The deuterium content is unlike that of ocean 

water, marine connate water, and water from 

the present Colorado River or the Salton Sea. 

Thus, only water from the bordering Chocolate 

Mountains can be the sburce of water in the 

deep brine reservoir. 

Helgeson (1968) considered that 12 sq mi 

(square miles) (30 km2 (square kilometers) ) 

have been proved by drilling to contain hypersaline high-temperature brine at the Salton 

Sea field. However, White (1968) considered 

this estimate conservative and that the brine 

probably underlies about 20 sq · mi (50 km2 ). 

Additional data are not available and White's 

estimate is still considered the best available of 

the size of the area underlain by the hypersaline brine reservoir. 

Available data indicate a probable average 

effective porosity of about 10 percent in the 

rocks of the brine reservoir. If the rocks containing the high-temperature brine in the convecting system (fig. 8) are assumed to be 

about 50. km:! in area, 1 km thick, and the po-

. rosity is 10 percent, the 50 km3 (cubic kilometers) of rock then contains 5 km3 of brine. 

White (1968) computed that 50 km3 of meteroric water containing 8018 ;:::: - 11 per mil 

(similar to that from the nearby Chocolate 

Mountains) would be the total flow necessary 

through the rock to convert the 50 km3 of delta 

sediments originally COI;ltaining oO 18 ;:::: + 18 

per mil to the present observed 0 18 values of 

the reservoir rocks, or 8018 ;:::: + 8 per mil. 

White (1968) also estimated the rate of discharge and recharge to the brine reservoir at 

about 500 gpm (gallons per minute) or 30 Ips 

(liters per second). This was based on 50 km3 

of meteoric water flowing through the brine 

reservoir during a total assumed time of 

50,000 years .. 

22 
~ 

~ 

Surface 

/ 

/ 

........... 

Channel areatly 

exaggerated 

-- - -- ____ ........,____ ___ _ Near surface ....._ -- - --- ~- - ------

meteoric dilution ............._ "-. __ ------- -- - --

/ 

~----- / / i ---............._/ ~ /'--... 

-------~--""' --- -Inflowin'"! ------ wat2r lo-. ,_.- in ~0 18 relative to 

Vapor escapP.s u ;ward·. most -- y ,;r;l 6 , low in cfl·. QJ 

"' ..c:; 

H20 and H2S condenses ¥ "'- moderately hiah ;.. 

A little brine escaoesl1 C02 is enriched by / CaSI"J.,, dissol·i<>d Vl 

/ \ / 

uoward; ratios of metals release in carbonate- ""- solids ab_out to S, C02 , and H

2

o · silicate rP.actions I " __.15,800 mn/1- ---

-----" decrease in shale, "- __.., 

metal sulfides · X 

precipitated <lJ / / • 

I\ \ ~;~=== ;:;,t ~;=:=:=:=:~\ ~~~ / 

" / ll f Vapor (H 20, C02, ~) l -:;1 I ~ I \ ", ll. r 1 l l cc<l;7 , 0 

J ~ / \ "\ 11 Cir:ula~ina 1-1ater l , l CC~n~ect~na ~rine l 1

1

/ '1>'/ s.. "":..: \ll h1g!1 1n aols 0 1s h1qh 1n l -c:-/ 

·c;-g /""' '\. relative to oOl6 l j metals, low 1 /

0 

1:"' "- l and enriched in in dissolved 4 '<- c, e 

~~ 1 """ '\.. 1 lao by evaporation l l sulfide; DS l 1 ~Y s.. c::: '\.... "'\.. ' 1 l i about l I '<' ~·g I """ '\.... l " 260,000 rnq/1 I l eY 

·s: " "-.__ "' l t i ' ~ co I "--- "-.__ ~ \ ' . \\ - J J / / -- ........._'-...,...... ___ -/ \~---.,/L/ / 

I ---- ---- "-...----Y" ~ 

I ------

( ( ( ( ( ( 

Reservoir rocks high in aQlB 

relative to 0016 

and low in 60 

( 1 ( ( H e ~ t ~j f 1? o w ( ( ( ( ( ( ( 

"' \. ----- ----- ~~Zone of !><>at flow / · bv CCI:ld•Jction and 

/ i'1Cl011inc; 1·1ater, 

/ \ temnrat~:r<: increases 

/ toward c•Jnvection c=ll 

\ 

\ 

Zone nf CaC0 3 a"d :::~s·;., 

precipitatior., c;u<:in:; 

reduced ::erme'1bi l i tv 

\ 

\ 

z..,ne of Si02 sol•.1':i"n 

causinn ·ir.cr:!aser! 

oermeabi 1 i t·t 

( ( ( 

FIGURE B.-Modified model for Salton Sea geothermal system, showing source of recharge and water-quality changes. 
Thus, one possible estimate of age or duration of the steady-state flow system is 50,000 

years. Because of the great possibility of errors in estimating reservior depth and area, 

rock porosity, and chemistry of water recharging the brine reservoir, the duration of the 

flow through the system can be varied. For example, if the reservoir area is larger, if it is 

deeper, or if the rock is more porous, either 

the rate of recharge would be greater or the 

duration of flow longer. Although buried volcanic rock presun1ably could be older than 

50,000 years, it seems unlikely that the estimate of reservoir size is too conservative. We 

arrive at this conclusion because the recharge 

rate ( 500 gpm) seen1s to us to be about the 

right n1agnitude for the region. On the other 

hand, that rate of recharge is about the maximun1 that could reasonably be expected from 

the Chocolate Mountains during the 50,000-

year period. During late Pleistocene time the 

average rainfall and runoff presumably were 

greater than those under present conditions, 

and the greater recharge presumably was sufficient to supply an average of about 500 gpm 

for the entire period, even though the area 

now has a very low average rainfall and runoff, and presumably supplies less than 500 gpm 

recharge. 

If the area of the reservoir is smaller or it is 

shallower, or if the rock is less porous, the rate 

of recharge would be smaller or the duration 

of flow shorter. Data are not available to provide a basis for selection among possible alternatives. On the basis of all the evidence now at 

hand we favor the possibility of a somewhat 

smaller brine reservoir, a somewhat shorter 

duration of flow in the system, and a somewhat smaller rate of recharge. 

GEOTHERMAL GRADIENTS 

A large number of measurements of fluid 

and rock temperatures have been made in 'veils 

in the Imperial Valley area. Even so, many reported measurements are probably grossly in 

error. Because of the paucity of data from 

deep wells, ten1erature data from shallow wells 

were extrapolated downward. This was necessary to estimate the three-dimensional distribution of temperature throughout the system; 

temperature was the only widely available information that could be used as an index of the 

degree of metamorphism of the rocks. Because 

the degree of metamorphism strongly influences the rock porosity and permeability, temprature 'vas also used as an index of the probable total porosity and the percentage of the 

contained water that might be produciblethat is, recoverable by wells. We assumed that 

if sufficient change in hydraulic pressure (or 

head) is imposed during production, water 

yielded from the rocks and deposits will exceed 

the specific yield and approach the porosity 

where temperature is greater than 100°C. 

Many temperature data are recorded on electric logs of wells. Many of these data, however, 

do not represent formation rock temperature. 

In some cases, reliance was placed in the recorded bottom-hole temperatures, if other more 

accurate measurements were unavailable. Errors in the data also result from flow of drilling fluid in test holes, water flow in the rocks 

or wells, salinity of the fluids, and, of course, 

instrument malfunctions caused by the high 

pressure and temperature commonly encountered. The overall problem of obtaining representative and reliable depth-temperature 

curves for wells in the Salton Trough area has 

been illustrated by many authors (Clayton and 

others, 1968, p. 973; McNitt, 1963, fig. 15). 

Data from a typical well at Cerro Prieto, Mexico, are used by the U.S. Bureau of Reclamation (1971, fig. 2) to illustrate the problem of 

obtaining meaningful temperature data from 

test wells. 

24 

Bullard (1947) and Jaeger (1956) found 

that once a test hole is drilled it takes 

about 20 times the time taken to drill the test 

hole for thermal equilibrium to be reestablished. However, spot temperatures can be used 

before they return to equilibrium if temperatures at several depths are measured at intervals after drilling is stopped. The drilling 

period is very short, of course, if temperatures 

are measured near the bottom after drilling 

stops. According to Lachenbruch and Brewer 

(1959) the equilibrium temperature T ( oo) can 

then be determined for any given depth z from 

the equation 

T(t)-T(oo)=C ln(1+tt/t2 ), 

where T(t) is the temperature observed at the 

time t 2 after drilling stopped, 
t1 is the time between when the drill reached 

depth z and the time drilling stopped, 

and C is a constant which depends on the diameter of the hole, the temperature, the depth, 

and the temperatures and thermal properties 

of the fluid and surrounding rock. 

Errors in the extrapolations can also result 

from unknown variations: ( 1) In the thermal 

conductivity of the rocks (McBirney, 1963); 

(2) from uncorrected effects due to water movement (Jaeger and Sass, 1963); (3) unknown 

intrusions of volcanic rocks or other sources of 

high-heat flow (Griscom and Muffler, 1971); 

( 4) the effects of changing surface conditions 

in one area or time as compared to another 

(Lachenbruch, 1957); and (5) the effects of 

nearby topography and rock types (Jaeger and 

Sass, 1963; Jeffrys, 1940; and Bullard, 1940). 

Needless to say, available temperature data 

for the Salton Sea hydrothermal system were 

not corrected for the above-listed effects. 

Available time, accuracy of the basic data, and 

desired accuracy of the estimates of recoverable water did not warrant that such corrections even be attempted. 

Despite all the questions about reliability of 

the temperature measurements and the many 

possible sources of errors that can be introduced when extrapolating shallow temperatures downward to great depth, such extrapolations had to be made in order to estimate 

recoverable and usable water in storage in the 

basin. The geothermal gradient, oT /oz, is the 

rate of increase of temperature with depth. In 

the Imperial Valley area the heat flux toward 

the surface ( q = K (aT /az) ) is areally variable, 

and the largest sources of errors in the temperature-depth extrapolations probably have 

occurred because data are lacking to determine 

one or another of the three following variables: 

1. The thermal conductivity of the rocks and 

water throughout the system. 

2. The mechanism of the heat flux: Whether 

the heat flows through the rock and 

water mainly by conduction or mainly by 

convection of water. 

3. The rate of heat flux toward the surface: 

In some areas high heat flux may remain undetected and the geothermal gra25 

clients may be considerably different than 

those extrapolated (figs. 9, 10, and 11). 

Item 1, above, causes the geothermal gradient to vary vertically in zones where heat 

flows dominantly by conduction. Item 2, above, 

can also cause the geothermal gradient to vary 

vertically in the rocks. The depth-temperature 

variations were heat flux is dominantly by 

convection and where it is dominantly by conduction are discussed in the following sections 

of this report. 

The criteria for distinguishing conductive 

and convective regimes from the temperature 

data were as follows: 

1. Conductive: Uniform gradient (allowing 

for conductivity increases with depth) 

that extrapolates to a (meterologically) 

reasonable mean surface temperature. 

2. Convective: High temperatures with small 

gradients that extrapolate to high surface temperatures. 

On the basis of these criteria and available 

temperature data we assumed that heat flow in 

the entire Salton Trough is mainly conductive 

except at the two hydrothermal fields (where it 

was observed to be otherwise). 

Our preliminary interpretation of the temperature-depth relations along sections A-A', 

B-B'. and C-C' (fig. 2) is shown in figures 

9, 10, and 11. Areas where Rex (1970) computed variations in the geothermal gradients in 

Imperial Valley are shown in map 1215-300-3 

(U.S. Bur Reclamation, 1971). In some areas 

the temperature-depth relations shown in figures 9, 10, and 11 are somewhat different from 

geothermal gradients obtained by Rex (1970) 

by measuring temperatures in very shallow 

wells. The differences arise mainly from assumptions about the physical properties of the 

rocks, water chemistry, and heat flux used to 

extrapolate the temperature data to much 

greater depth. 

HEAT FLOW BY CO:\'DUCTIO~ 

In the entire Salton Trough hydrothermal 

system, except in the hot spots of high-temperature anomalies and in the Salton Sea and 

Cerro Prieto hydrothermal fields, heat flux to 

the surface is probably mainly by conduction 

from about 3,000 and 2,400 feet, respectively. 
A 

:::1 

~~ 

~~ 2000' ~~~ ~ 

IQ 2000' 

I~ 

·- SO. LEVEl 

'00 

000 

8000' 

EXPLANITION 

---- Fault 

l T04729 

OS2fi0.000 

Selected well for sectton 

TO. total well depth '" leet. OS, diSsolved sol1ds 

10 water. 1nmtlltgrams 

per ltter 

--50°--

L1neot equal temperature 

1 n t e rv a I 50° ~~ e I s 1 us 

Ltne sholtngtuseofusaolewater 

tless thanJ5000mllllglamspel 

ltler dtssolved scltdst 

YERTICIL DEPTH-ZONES 

Numoers are spect ftc yt el d 

o I deposils. to percent 

0 16 

m [] Zone I lone J 

13 5 

m 

lone 2 • Zone4 

D later wt th more than 35 000 mtlltipams 

per ltter dtssol¥ed soltds 

Basement 

~"'\~ campi ei 

Quelled ohe~edouottul 

Ytrlltllllllltrlt!On2DIJJ:I See ''rure2 tor local10n 22.000'L,____:_:___:_:_:........:..:.. _ _;__ ___________________ _;____:.:__~-----'l2.00G' 

FIGURE 9.-Hydrologic section A-A'. 

At the Salton Sea hydrothermal field, the 

geothermal gradient in zone 1 (in the deposits 

extending to a depth of about 3,000 ft below 

the surface) averages nearly 10°C per 100 feet 

(fig. 6). In that entire zone heat flux is probably dominated by conduction. At depths 

greater than 3,000 feet heat flux is probably 

dominated by convection. At Cerro Prieto the 

geothermal gradient in zone 1 (the deposits 

extending to about 2,400 ft below the surface) 

also averages about 10°C per 100 feet and heat 

flow is also probably dominated by conduction 

in those deposits; at depths greater than 2,400 

feet heat flow Is probably dominated by 

convection. 

26 

At well 85 (U.S. Bur. Reclamation well 116) 

southeast of Holtville the average geothermal 

gradient in zone 1 (only 1,400 ft tested) averages about 7°C per 100 feet, in a zone where 

conduction presumably dominates. 

In the areas outside the known hot spots, in 

most of the system, all available data indicate 

that in zones having heat flux probably dominated by conduction, geothermal gradients 

range from less than 1 oc per 100 feet across 

some thick zones to as much as 2° or 3 oc per 
B 

2000' 

4000' 

6000' 

EXPLANITIOM 

--?--

Fault 

Ouerledwheredouottul 

T04729 

OS260,000 

Selected wt:ll lor sect1on 

TO. total well depth.'" 

teet OS, d1ss.otved s.oltds 

1n water. JnmJIIJgrams 

per l1tet 

l1neol equal temperatu1e 

QuerJed•hereunknown 

Interval 50° Cels1us 

ltne shoa1ngoaseof usable water 

(less than 35000mrllrgransper 

liter diSSOlved soltdSJ 

VERTICAL OEPTH-ZOMES 

lfumne rs are spec1 11 c y1 eld 

of depOSits. 1npercent 

D IS 20 

ro ooo' I:::::::J;x;"'j::: J 

1],000' 

14,000' 

16,000' 

18.000' 

Zone t 

13 

Zone 

~ 2 

[] 

Zone3 

5 

D water ., th more than 35.000 mr t 11 grams 

per ltter dissolved sol1ds 

Basement complex 

Setfllillrel for locetton 'Verl1tal uauerellon20833:1 

10.ooo'L------- -----=----------' 10.ooo' 

FIGURE 10.-Hydrologic section B-B'. 

100 feet across other thick parts of the total 

sedimentary section (figs. 9, 10, and 11). 

HEAT FLOW IN WATER CONVECTION CELLS 

Within the deeper parts of the Salton Sea 

and Cerro Prieto hydrothermal systems, heat 

flux is probably dominantly by convection. In a 

circulation system where downfiowing water 

recharging a deep convection cell is dilute and 

relatively low in temperature, and upfiowing 

water is a hot, 25 percent sodium chloride solution, the temperature of the brine must be 

about 200°C higher than the dilute water for 

convective circulation to occur, according to 

data determined by L. J. P. Muffler and re27 

ported by White ( 1968, table 2). For this reason we believe it is impossible to predict on the 

basis of available temperature and chemical 

data whether or not deep convective cells remain undiscovered in the Salton Trough area 

outside the known hydrothermal fields at Salton Sea, Calif., and Cerro Prieto, Mexico. Near 

deep well 71, however, northwest of Holtville, 

there are a few temperature measurements 

available for examination; these and waterquality data indicate that the temperature and 

water quality from near the bottom of the well 

exhibit a sufficiently great contrast when compared with data from only slightly shallower 

depth, that a deep convection cell may exist at 
C' 

D 

EXPLlUTION 

--!-- Faull 

Ouelledllleredouotlul 

1 

Toe OS 13000 

Selected well for sectron 

TO. total well depth. rn 

feel. OS. dr ssol ved sotrds 

1n water. 1n m1 llt&JIIIIS 

per ltlet 

--50°--

Lrneoloqual t•p01ature 

Interval 50°Colsrus 

Lrno sho~rn&baseal usablouter 

tl oss than 35.000 mrllrarams per 

lrterdrssolved solrdsl 

iERTIClLDEPTH-ZONES 

NutODersarespecrlrcyreld 

of deposrl s. rn percent 

IS 2D 16 

~::::::lX.;l : : : :I §ill Zone I ZoneJ 

~ s 

Zone 1 • Zone4 

D Water ., th more than 35 DOD mrllr a rams 

per l1ter diSSOl-ved SOlidS 

~~ Basement co"'lex 

Outrledwheredounlful 

FIGURE 11.-Hydrologic section C-C'. 

a depth only slightly greater than that reached 

by the drill. 

At well 61, southeast of Holtville, a deep 

convection cell probably exists at a depth several thousand feet deeper than that reached by 

the drill. 

Within the convection cells at the Salton Sea 

and Cerro Prieto fields, the temperature gradients are much lower than where the heat 

flux is dominantly by conduction (fig. 6). Presumably the temperatures of the upftowing 

fluids throughout the cell are only slightly 

below the reference boiling-point curve for the 

brine solution analyzed. The ten1perature is 

slightly below the reference curve probably be28 

cause of partial pressures of gasses in the systenl (fig. 6). 

THE DYNAMIC SYSTEM 

Most basic elements and mechanisms of the 

In1perial Valley area hydrothermal system cannot yet be measured directly. A satisfactory 

conceptual model of the system must represent 

the mechanisms and elements of the prototype, 

insofar as the available data permit the system 

to be understood. The mechanisms proposed 

for the system must be compatible not only 

with available data but also with principles of 

chemistry and physics. 
The model proposed must provide for operation of a system in which the following elements are known or assumed: 

1. The recharge and discharge mechanism. 

2. The source of the recharge water. 

3. The average rate of long-term recharge. 

4. The manner, rate, and location of discharge. 

5. The chemical quality of recharge and 

discharge. 

6. The spatial variation in water chemistry 

throughout the system. 

7. The size of the reservoir. 

8. Changes caused in the system by the flux 

of heat, water, gas and vapor, and 

chemicals. 

9. The distribution of water, gas, and vapor, 

and rock temperature, porosity, an 

permeability. 

10. The age of the system or the duration of 

the quasi-steady state of flow. 

Thus rates of water flow in the system are 

very important. Because rates of recharge and 

discharge have not been measured, and these 

still cannot be measured directly, they must be 

computed indirectly for purposes of formulating the model. The only practical means of 

computing recharge and discharge is by estimating the size of the reservoir, the chemistry 

of the inflowing water, the assumed and observed induced changes in water chemistry in 

the reservoir, the chemistry of the discharge 

water, and the length of time the system has 

operated. 

Explaining the observed data by using a 

simple model applicable to the entire Salton 

Trough hydrothermal system is desirable. On 

the basis of the data available, it seems that 

this is possible. For example, Koenig (1967) 

showed that although the concentration of 

salts is much greater at Salton Sea than at 

Cerro· Prieto (table 1) there is remarkable 

agreement in the ratios of ionic concentration 

at both sites. 

Therefore, it is important to formulate one 

model for the whole hydrothermal system and 

TABLE !.-Analysis of water from geothermal wells at Niland, Cerro Prieto, and Arizona, 

in milligrams per liter 

Well 39 Element (White, 

1968, 

table 1, 

analysis 2) 

Sodium -------- 50,400 

Potassium ------ 17,500 

Calcium -------- 28,000 Lithium ________ 215 

Magnesium ----- 54 

Strontium ------ 400 

Barium -------- 235 

Rubidium ------ 135 

Cesium _________ 14 

Iron ----------- 2,290 

Manganese ----- 1,400 

Lead ----------- 102 

Zinc ----------- 540 

Silver ---------- (2) 

Copper --------- 8 

Silica ---------- 400 Chloride ________ 155,000 

Boron ---------- 390 

Fluoride ------- 15 

Sum of sulfur ________ (2) 

Dissolved 

solids -------- 258,973 

1 Includes potassium. 2 Not reported. 

Niland 

Well 36 (Helgeson, 

1 967b) 

53,000 

16,500 

27,800 

210 

10 

440 

250 

70 

20 

2,000 

1,370 

80 

500 

( 2) 

(2) 

400 

155,000 

390 

(2) 

30 

259,000 

Cerro Prieto 

Well 57 (California M-3 Dept. Water (Alonso Espinosa Resources, 

1970) and Mooser, 1964) 

10,600 5,610 

1,250 1,040 

1,130 320 

40 14 

74 (2) 

85 27 

3 57 

(2) 

(2) 

.7 (2) 

6.4 (2) 

(2) 

(2) 

.05 

.09 

120 (2) 

19,700 9,694 

100 312 

1 .88 

~10 

34,800 ~17,000 

3 Recalculated from H3BQ3. 

29 

Arizona 

Musgrove 1 (Olmsted and others, 

1972) 

1 141 

148 

43 

18 

188 

1,000 
important to determine the duration of time 

during which the system has operated at an assumed steady state. 

MECHA:\'"ISM OF RECHARGE A:\TD DISCHARGE 

The model first proposed by White (1968) 

and reproduced herein (fig. 6) has been modified somewhat in figure 8 to show our concept 

of the Salton Sea (or Cerro Prieto) hydrothermal field as an evaporative convective system. 

In this model some precipitation falling on the 

local mountains east of the basin (Chocolate 

Mountains) becomes ground-water recharge 

near the basin margin. All the ground water 

flows toward the Salton Sea but some descends 

to a depth greater than 6,000 feet beneath the 

surface in the Niland area. As the water flows 

west and descends to depth, the content of dissolved solids increases, presumably through redissolution of salts contained in the finegrained deposits accumulated in this area of 

long-continuing evaporation near the lowest 

part of the valley. No evaporites (as distinct 

beds) have been found in any drill holes, but 

there is appreciable anhydrite (probably initially gypsum) in drill cores (Muffler and 

White, 1969). At the surface there were extensive evaporites prior to 1906. Furthermore, the 

geologic history of the northern part of the 

Colorado River delta throughout the late Tertiary and Quaternary was probably alternating 

flooding and evaporation (Muffler and Doe, 

1968; Sykes, 1937a, b). Evaporites are difficult 

to recover in drill cuttings. Even though their 

detection is difficult, evaporites probably exist 

at depth, particularly in the upper 3,000 feet 

of the sediments. Water near the base of the 

shale-dominant zone near the Salton Sea field 

probably contains 25,000-35,000 mg/1 dissolved 

solids (see well 57, table 1). 

Some of the water moves down in response 

to the greater hydrostatic pressure outside 

than inside the convection cell, to eventually 

recha1·ge the deep system. 

The descending water is relatively low in 

8018 and oD, and moderately high in calcium 

sulfate. Because the Colorado River delta deposits were originally high in o01 R, a disequilibrium exists, hence the 0 18 shift observed by 

Craig (1966) and Clayton, Muffler, and White 

30 

( 1968). The deuterium content of the brine 

proves its Chocolate Mountains source. Presumably some precipitation of calcium sulfate 

and calcium carbonate takes place because of 

heating of the descending water as it intercepts heat flowing toward the surface by conduction. The abundance of carbon dioxide, a 

product of the metamorphism taking place at 

depth, may affect the calcium carbonate solubility to an even greater extent than the increased temperature. 

Upon entering the convecting system the 

water rises; some is eventually evaporated, and 

vapor and gas escape upward. Carbon dioxide, 

ammonia, boron, and hydrogen sulfide are enriched as explained by White ( 1968) and 

Barnes (1970). The salts remain in the reservoir and are progressively concentrated. As explained previously, this mechanism presumably 

persisted during a period calculated to be not 

longer than 50,000 years, but probably more 

than 25,000 years. 

QUALITY A:\'D QU.\~TITY OF WATER 

A~D CO:\'CE:\'TR.\TIO~ OF SALTS 

Assuming that the brine reservoir at the 

Salton Sea field is in a maximum rock volume 

of about 50 km\ that this has an average 10 

percent porosity, and that the recharge has 

been 50 km~ during 50,000 years, the average 

recharge rate is about 500 gpm ( 30 Ips) or 

about 800 acre-feet per year. This is somewhat 

larger than would be expected using historic 

rainfall-runoff relations from the Chocolate 

Mountains, but very probably was considerably 

less than the available recharge during the late 

Pleistocene and Holocene fluvial periods which 

contributed water to large perennial lakes in 

the basin (Hubbs and others, 1963). Runoff in 

the Colorado River, of course, was the principal source of the lake water. 

Our concept of the water recharge-discharge 

relations for the shallow anct cteep aquifer 

systems and the water-quality changes within 

the system are schematically shown in figure 

12. This pipe model for the Salton Trough 

fresh-water and hydrothermal system indi<:ates 

our concept that both the Salton Sea and Cerro 

Prieto deep convection systems have a con1n1on 

mechanism and mode of origin. The only substantial difference in the two systems is the 
ILJ..J 

LJ..J 

1.1-

1.1-

0 

t/) 

Cl 

z: 

c:l: 

t/) 

:::> 

0 

CJ.!) :c 

......... Iz: 

........ 

:c 

I0.. 

LJ..J 

Cl 

0-

1-

2-

1,000-2,000 acre-ft per year 

j 3~0 acre-ft per year 

Discharge 

15,000-16,000 acre-ft per year 

t United States : Mexico ~ 

+J 

c 

tO 

c .E 

0 

"'0 

Q) 

rIO 

..s:: 

t/) 

I I 

I I 

Surface 

• + 

Recharge from 

local sources 

I 

I 

I 

I 

I 

Recharge from 

Colorado River 

OS about 

20,000 mg/1 9 OS 2,000-5,000 mg/1 

17,000 acre-ft per year Recharge 

OS 500-1,000 mg/1 1 1 unknown I I 1 I 

D. h I I Discharae lSC arae 1 1 

"800 acre-ft OS about 400-500 acre-ft per year : 

1/ 11er year 25,000-35,000 mg/1 OS 1, 500-2,000 mg/1 1 

3

-§ if·~ -~~1 1~ ~~~ '~ rr----~ ~(~--~~. ~ 1; ~ +J 1 I • 

1 • I >., i •.0... 1. T l\ • ~ 

4 - ~ +-' t t . I ~ OS about i • / ~ I 1 • o !. OS about I /{ 

\f)~ tR~c1rcula-\ \260,000 mg/\ t /+J t '

1 

Recircula-\ \20,000 mg/1~ • ~'rt: ;:.;:~ , t1on much • • ! /~ ~ ttion much ~ o • ~ I 1 ' 

E I I greater ' I I I Q) i. t I . t J s....q_, 

\f) 0 t • Vapor *. • / s.- grea er i. Vaoor v 5- ~-o • than t • . 1 u 1 than • ·. 10 ttr 

d. h I I I ' tO . I • s:::> B • 1. s c a rg e 1 

1 . ~ • J t : d i s charge j• . c:::s u • h j 0 • • ,co 

6 -~ ~~-=:~ l:-~.~~~ .)~ l~-=:~3 ( :=_:-:--~ /~~ Recharge abo~ Rec~rge 

((((((((((( (II iiilil ililll 1)) H e a t f 1 o w 

FIGURE 12.-Schema for a pipe model for water and dissolved solids input-output of the Salton Trough hydrothermal system. 
quality of the recharge water, which is much 

less saline at Cerro Prieto. 

The total ground-water recharge to the Imperial Valley area from the Colorado River 

under natural conditions was probably about 

17,000 acre-feet annually (0. J. Loeltz, U.S. 

Geol. Survey, written commun., 1971). This 

17,000 acre-feet does not include the unestimated recharge presently occurring as a result 

of losses from irrigation canals and from irrigated land. The recharge estimate is based on 

data from the water-level contour map (fig. 

13) showing the hydraulic gradient and width 

of the aquifer in the area of ground-water recharge in the southeast part of the valley and 

an estimated aquifer transmissivity of about 

500,000 gpd per ft in the recharge area. 

Only a small part of the recharge reaches 

the Salton Sea as continuous flow in the aquifers. We estimate this flow to be 300 acre-feet 

per year, on the basis of the water-level contour map (fig. 13) and an estimated transmissivity of 3,000 gpd per ft for the deposits containing water probably derived from the 

Colorado River in the area of inflow to the sea. 

The remainder of the recharge, 16,700 acrefeet per year by subtraction, discharges directly or indirectly by upward flow to either 

the land surface, the river channels, or the 

drainage-tile network widespread in the irrigated area. Part of this discharge may follow a 

very indirect route. A small part may descend 

to great depth to recharge deep undiscovered 

convection cells in the hydrothermal system to 

rise again, leaving most of its dissolved salts 

behind, to eventually rejoin water in the upper 

zones and ultimately reach the surface to evaporate, be transpired by plants, or to enter some 

part of the surface-drainage system. 

Under very long term average conditions, 

recharge to ground water in the Imperial Valley area from local sources may have averaged 

about 3,000-4,000 acre-feet annually. Under 

present conditions of rainfall and runoff, the 

average annual recharge from local sources is 

probably considerably less; it may even be less 

than half the very long term average, or about 

1,500 acre-feet per year. Discharge occurs as 

direct inflow to the Salton Sea, by evapotranspiration where the water table is shallow and 

presumably in small part to local drains' and 

the river channels in the area of irrigated 

land. 

32 

Recharge to the deep aquifers is by groundwater inflow from the shallow aquifers, presumably mainly near the basin margins, but 

probably also by descending flow near the 

deep, hot convecting cells. The recharge and 

discharge to the deep convecting cells, both at 

Salton Sea and Cerro Prieto, are estimated to 

average 500 gpm (30 Ips). 

RELATIO~ OF SALI:\'ITY OF RECHARGE 

AND DEEP BRI~E 

During the 25,000-50,000 years that the 

mechanisms of the hydrothermal system are 

presumed to have operated, about 50 km3 of recharge water originating in the overlying zone 

from 1,500 to 3,000 feet and presumably containing about 25,000-35,000 mg/1 dissolved solids (see well 57, table 1) probably has flowed 

into the deep convection cell at Salton Sea. The 

discharge has been virtually salt-free flow in 

the vapor phase. Thus, during that time the 

salinity of the deep brine has increased to 

about 260,000 mg/l. 

At Cerro Prieto, using the same age, volume 

of rock and porosity, and recharge and discharge, the deep brine salinity has increased to 

only about 15,000-20,000 mg/1, because the dis~ 

solved-solids content of the recharge water 

originating in the overlying 2,400-foot zone 

presumably has averaged only about 1,500-

2,000 mg/l. In this area evaporites, as distinct 

beds or nodules in the sediments, could not 

be expected because the area south of the delta 

axis has not been within a closed basin. 

On the basis of the model proposed and an 

assumed uniform duration of high heat flow in 

all the hot anomalies, we postulate that the dissolved-solids content of water in all deep 

convection systems yet to be discovered may 

exceed 35,000 mg/1 wherever the concentration 

of dissolved solids in the recharge water from 

the overlying deposits is greater than 

4,000-5,000 mg/l. 

ESTIMATED POROSITY AND SPECIFIC 

YIELD OF THE ROCKS AND DEPOSITS 

AVAILABLE DATA 

Factual data for determining porosity and 

specific yield of the rocks and deposits derived 
from geophysical logs are lacking in most of 

Imperial Valley. The most common geophysical 

logs available are electric logs from several 

oil-test and geothermal wells. These logs are 

not suited to the needs in calculating formation 

porosity unless supporting information is 

available. More useful logs for this purpose 

include sonic, formation density, neutron porosity, and the gamma ray-neutron. Inspection 

of the available log data revealed five logs 

from four wells that were particularly useful 

for porosity evaluation. T~?-ese wells are shown 

below. 

Well 

Location No. Name Type of log depth Log interval Date (feet) (feet) logged 

39 ____ Geothermal Gamma ray- 6,141 64-1,700 1962 Inc.-liD 1 neutron 7L ___ Standard Oil- Sonic 13,443 99-9,484 1963 Wilson 1 82 ____ American Sonic 10,624 1,530-7,988 1966 Petro fin a 92 ____ Bureau of Formation 1,406 204-1,400 1971 Reclamation density and 127 neutron 

porosity 

In the deep wells, drilled years ago, the 

logged interval does not reach the bottom of 

the wells. The formation temperatures encountered during the deeper drilling were higher 

than the maximum allowable limits of the logging equipment. 

Geological Survey hydrologic studies on 

water wells generally less than 1,000 feet deep 

in the valley indicate average specific-yield values of about 10, 15, and 20 percent for the 

shallow deposits. (The specific yield of a rock 

or soil is the ratio of ( 1) the volume of water 

which, after being saturated, it will yield by 

gravity to (2) its own volume. The definition 

implies that gravity drainage is completed.) 

On the basis of geologic data, we assume these 

values can be extrapolated to a depth of 3,000 

feet. Studies in other desert basins of California and Arizona indicate similar values. For 

basin depths more than 3,000 feet, specificyield values are not readily determinable. However, based on evaluation of different types of 

geohydrologic data, the specific yield and the 

quantitiy of recoverable water from the deeper 

aquifers (see section "Thickness, Areal Extent 

and Specific Yield or Porosity of Vertical 

Zones 1-4") probably is about 5 percent for 

deposits greater than 8,000 feet deep, about 16 

percent for deposits shallower than 8,000 feet 

but with water temperatures exceeding 100°C, 

and about 13 percent for deposits greater than 

3,000 feet deep but with water temperatures 

less than 100°C. 

METHODS OF COMPUTATION 

The most reliable estimates of porosity were 

determined with a computer program utilizing 

data from a formation-density log and neutron-porosity log of well 92 (Bur. Reclamation well 127). The porosity was computed at 

1-foot intervals and averaged about 25 percent 

for the logged interval of 204-1,400 feet below 

land surface (fig. 14). Unfortunately, the well 

is only 1,406 feet deep. However, only 5 miles 

northeast of this well, a sonic log was run in 

an oil test well (No. 82) to a depth of 7,988 

feet below land surface. Porosity values from 

this sonic log were corrected for hole diameter 

and compaction of the formation with depth. 

The sonic porosity curve was then adjusted by 

shifting to provide a better correlation with 

the data from the shallow well. Computations 

of porosity from sonic logs are commonly too 

high in these types of sediments. Porosity values 

estimated by J. B. Combs (written commun., 

1971) prior to this report by using data from 

a sonic log of well 82 are plotted for comparison (fig. 14). 

Elsewhere in the valley, 6 miles southwest of 

Niland, the porosity computed from a gamma 

ray-neutron log of well 39 (liD 1) for the interval 64-1,700 feet below land surface was 

about 35 percent. Seven miles southeast of 

Brawley, the porosity from a compaction compensated sonic log of well 71 (Wilson 1) 

ranged from 18 to 28 percent below 4,000 feet. 

Both of the above values may be too large; the 

methods of computation are unreliable. 

33 

Utilizing the three logs from wells 82 and 

92, a porosity-depth relation was determined 

(fig. 14). Usin_g these values as a guideline, average , porosity i and specific yield were assigned for the rocks and deposits from the 

land surface to a depth of about 15,000 feet 

(figs. 9, 10, and 11). 

USABLE AND RECOVERABLE WATER 

CRITERIA FOR DEFINING TERMS 

The water-quality criterion for usability of 

the water in storage is that the water shall 
Base from U.S. Geological Survey State of 

California (south half) 1:500,000, 1970, and 

U.S. Department of the Interior Reconnaissance 

Map of the Salton Sink, California 1:500,000, 1908 

FIGURE 13.-Ground-water-level contours of shallow aquifer system, 1962 and 1964, in Imperial and Mexicali 

Valleys. 

34 
I 

r---

! 

EXPLANATION 

Ground-water basin boundary 

-----?-··· 

Fault 

Dashed where approximately located; 

dotted where concealed; queried 

wh e r e do u b t f u I 

--+lo--?--

water-level contours 

Shows a I t i tude o f wa t e r I eve I i n 

shallow aquifer system for 1962 

and 1964. Dashed where approximately 

located, queried where doubtful. 

Contour interval, in feet, is 

variable. Datum is mean sea level· 

line dividing source of water derived 

from local mountains and water 

deri.ved from Colorado River area, 

prior to importation of water 

APPROXIMATE MEAN 

DECLINATION 1971 

10 15 

CONTOUR INTERVAL 50 AND 500 FEET 

DATUM IS MEAN SEA LEVEL 

20 MILES I 

I 

/ / 

\'\,~ Elevations and topography in Mexico are approximate 

Water level data in Arizona and Mex1co from 

Olmsted and others, (1972) 

FIGURE 13.-Continued. 

35 

\ 

\ 
1 0 20 

POROSITY. IN PERCENT 

30 40 50 60 

EXPLANATION 

t:::::s:) 

Dots indicate range of porosity values 

from lowest to highest, taken from 

computerized gamma-gamma and neutron 

porosity log for well 92 (map number). 

Dark line indicates average porosity 

fo1 204-1.400-foot depth interval 

Dots indicate porosity determination 

for well 82 prior to this report. 

(Source of data unknown.) Dashed 

line indicates poros1ty determination 

from a son1c log adjusted for 

compaction. Solid line indicates the 

adjusted porosity from sonic log. 

C 1 r c I e on so I i d I 1 n e i n d i cat e s 

porosity determination at 9. 730 feet 

from induction electrical log 

Velocity, fluid=5.300 teet per second 

Veloc1 ty. sandstone= 18.000 feet 

per second 

Data from Schlumoerger (1969. p. 16) 

FIGURE 14.-Estimates of formation porosity from wells 82 and 92. 

36 
contain fewer than about 35,000 mg/1 dissolved 

solids, regardless of the concentration of any 

specific ions. This decision by the Bureau of 

Reclamation was reportedly based on the following considerations: 

1. It is unlikely that in Imperial Valley, wells 

can be drilled that will produce dry 

steam only, or even essentially only 

steam. 

2. If wells produce both water and steam, the 

dissolved-solids content of the production 

water will sensitively control the economics of the operations. After separating 

the high-temperature steam, it would be 

possible to desalt a large percentage of 

the coproduced water, thus leaving as a 

hypersaline brine only a small percentage 

of the total, if the original water were of 

good quality. This brine could then be 

disposed of presumably either by reinj ection into the aquifer system, by evaporation, or by some other means. To accomplish steam production and to provide 

water for desalting, it was decided that 

the water be classified as usable only if 

its initial dissolved-solids content is no 

greater than about 35,000 mg/l. 

3. If wells produce only water at temperatures below the boiling point, intended 

for desalting (using supplemental energy), the same economic considerations 

outlined above apply to a large degree. 

4. If wells produce water intended for blending directly with a source of desalted 

water, the lower the dissolved-solids content of the pumped water the greater the 

volume of the final blend; thus, an economic benefit results from starting with 

water containing fewer than 35,000 mg/1 

dissolved solids. 

Determining whether or not water in storage is economically recoverable must ultimately be based on detailed knowledge of the 

aquifer system, the physical state of the fluid, 

and the type, kind, and location of wells, 

pumps, and production facilities designed for 

recovering the water. The operating procedures and practices also must be known in detail. Obviously such operating criteria cannot 

be developed for the Imperial Valley area at 

this stage of exploration and testing. Therefore, estimates of recoverable water, as the 

term is used in this report, are based on three 

assumptions: 

1. Engineering plans can be made and sound 

operating procedures could be devised for 

withdrawing the water from wells over a 

very long period, if economical to do so. 

Limits would be imposed by economic 

considerations and the characteristics of 

the aquifers penetrated. Because economics are not considered, many usually limiting considerations, such as well spacings, pumping rates, and drawdowns, 

were ignored when classifying the water 

as being recoverable. 

37 

2. The physical characteristics of the aquifer 

system and the physical state of the fluid 

were the principal factors considered 

when deciding whether or not the water 

in storage is recoverable. Thus, the aquifer gross transmissivity and the permeability of the deposits, the porosity and 

lithology of the deposits, the thickness of 

the saturated deposits, and the temperature of the water were taken into account. In some parts of the basin-filling 

deposits the recoverable water was estimated to be virtually equal to the total 

porosity; in other parts, the recoverable 

water will be only as great as the estimated specific yield of the deposits. This 

distinction was made because we assumed that under some production procedures the water yielded will exceed the 

specific yield of the rocks where temperature is greater than 100°C. 

3. The present pattern of water use in the 

central part of the valley and the irrigation practices there cause an aquifer 

boundary condition that would virtually 

preclude any dewatering of the shallow 

aquifers by pumping from wells. Annually more than a million acre-feet of 

water are applied to the land in excess of 

the consumptive use of crops to control 

soil salinity. Any reasonable attempt to 

mine water from the underlying shallow 

aquifers of very low transmissivity 

would meet with limited success because 

water available for diversion from the 

overlying network of shallow drains and 
irrigation canals would ultimately prevent further d-rawdown. For this reason 

dewatering the upper water-bearing zone 

beneath the irrigated area seems infeasible. The recoverable water in that area, 

therefore, is considered nearly zero, and 

water storage in that area is not included 

in the estimates. 

METHOD OF ESTIMATING USABLE 

AND RECOVERABLE WATER 

To estimate usable and recoverable water in 

storage in the Imperial Valley area the following steps had to be completed: 

1. Map the thickness of water-bearing deposits containing fewer than 35,000 mg/1 dissolved solids. 

2. Divide the water-bearing rocks and 

deposits into several convenient units or 

depth zones on the basis of approximately uniform permeability, porosity, 

specific yield, and temperature. 

3. Determine the average porosity, permeability, and, in some cases, the specific yield 

of the water-bearing rocks and deposits 

of each unit or depth zone selected. 

4. Map the thickness of water-bearing deposits in each selected unit or depth zone. 

5. Measure the areal extent of the water-bearing deposits mapped in each selected unit 

or depth zone. 

6. Compute the usable recoverable water in 

storage using the following equation: 

Su.,.=AmSy or Sur=Am,Pt, 

in which Sur is the approximate usable recoverable water in storage, 

A is the area of the storage unit, 

m is the thickness of saturated deposits, 

and Sv, and Pt are the specific yield or approximate total porosity of the water-bearing deposits, whichever is applicable. 

THICKNESS OF WATER-BEARING ROCKS 

AND DEPOSITS 

To estimate usable and recoverable water in 

storage in the Imperial Valley area, the first 

step necessary was to estimate the maximum 

thickness of water-filled rocks and deposits. 

Fortunately, the maximum thickness of waterbearing rocks was previously estimated by Rex 

(1970). His map was based mainly on gravity 

studies by Biehler (1964), supplemented by 

some seismic data. During this study, available 

logs of wells drilled near the basin margins 

were examined. In general, these data confirm 

the interpretations of the bedrock structure 

shown by Rex, and his map is reproduced in 

essentially unmodified form in figure 4. That 

map was also used in preparing the hydrologic sections (figs. 9, 10, and 11). Our criterion for usability (35,000 mg/1) and our conceptual model of the system exclude the deeper 

parts of the basin, however. 

All available water-quality data, including 

both chemical analyses of water and electrical 

logs of test wells, were examined. These data 

were considered in terms of the elements and 

mechanisms proposed for the conceptual model 

of the system and were then interpolated 

throughout the basin between points of control 

to estimate the total thickness of water-bearing rocks and deposits containing fewer than 

about 35,000 mg/1 dissolved solids in the contained water. Our concept of the thickness of 

the rocks and deposits containing usable water, 

therefore, is shown in the sections (figs. 9, 10, 

and 11) and in figure 15. 

38 

On the basis of this interpretation of available data, the deposits of interest are a maximum of about 15,000 feet thick a few miles 

south of Holtville and about 13,000 feet thick 

north of Brawley. They thin to zero locally 

along the basin margins on the east and west, 

but elsewhere, particularly along the north 

margin of Imperial Valley and along the international border, they extend beyond the area 

where usable and recoverable water in storage 

was estimated. 

AREAL AND VERTICAL EXTENT 

OF STORAGE UNITS 

For purposes of estimating usable and recoverable water in storage, four areal units 

(fig. 16) and four vertical water-bearing zones 

were established (fig. 9). The average porosity 

or specific yield of the deposits, whichever is 

applicable, was · estimated for each vertical 

zone. The four areal storage units are called 

Sand Hills, East Mesa, main valley, and West 

Mesa (fig. 16). The four vertical zones are 

numbered 1-4 (fig. 9). 
C/!) 

~ 

115°00 1 

--t·?~ .. ~c .. ~l:~V••"( ... T:.(:J' - "-~-~' e/ 

,s, 1~~ ~ ,, 

EXPLANATION 

Ground-water basin boundary 

----?-··· Fault 

Oashed where app rox ima te I y I oca ted; 

dot ted where concea I ed; queried 

where douot fu I 

--6--

L1 ne of equal thickness of deposits 

con ta 1 n 1 ng usab I e water in the 

basin, in thousands of feet. 

Interval, 1, 000 feel 

Usable water, I ess than 

JJ•oo'r· ~-~~~~~~~ ~1{§> 1~,·~~ 't?t:=tl~3 'oo' 35.000milligramspellltel "'!:"~t.o_ ~ _, ~ • 1:\;, h ·· ra~leff«-. , ',,\ ,\' ~ • . · · · il..~ dissolved sol1ds 

116°oo' 

Base from U.S. Geological Survey State of 

California (south half) 1;500,000· 1970 

114°30' 

FIGURE 15.-Thickness of deposits with total usable water. 

•J..',. 

~ j ~ !: i ~ 

APPROXIMATE MEAN 

DECLINATION 1971 

0 S 10 lJ 20 Ml LES 

CONTOUR INTERVAL 500 FEET DATUM IS MEAN SEA LEVEL 
~ 

0 

--i;;.~~.T-:.:7 

~~ t i '("' 

~~Mlf&1f\l\%t-lli~ -~l.····_t··~=lt~t ·~~··f-· P 

ZONE 1: Usable water, less than 35,000 mi II igrams 

per liter dissolved solids 

Temperature, less than 100°C 

Depth, 0-3,000 feet 

Formation porosity, 25 and 30 percent 

Recoverable water, 0, 15, and 20 percent 

EXPLANATION 

Ground-water oasin boundary 

0 15 20 

f::::::t?Q<t:/ nl A 1 ea of ground-wale r storage unr t s. 

Numbers are spec if 1 c yield of 

deposr ts, in percent 

330001 

r~~?f~~~~~~~,~~$.48ij~~~~~~~t4~j:~~~~~~~~~~~~~m~3§g~:~~=--~t~-l ____ , ___ _ 33000 ' Lrne of equal thickness of deposits 

con tarn i ng usao\ e water in zone 1. 

116°00' 

Base from U.S. Geolog1 cal Survey State of 

California (south hall) 1:500.000.1910 

114°301 

FIGURE 16.-Thickness of deposits with usable water in zone 1. 

1 n thousands of feet. Interval, 

I. 000 feet 

V

·r ., 

~ 

~ 

~ APPRO X I MATE MEAN 

OECLINAT ION 1911 

0 5 10 15 20 Ml LES 

CONTOUR INTERVAL 500 FEET DATUM IS MEAN SEA LEVEL 
As a second objective, usable and recoverable water probably having a temperature 

greater than about 150°C was also estimated. 

This estimate was made because a temperature 

of at least 150°C is considered marginal to 

produce commercial steam for power generation; under present technology a temperature 

of 180°C may be required. Finally, the quantity of water in storage that was probably derived from local sources and from the Colorado 

River was estimated. This was accomplished in 

zone 1 by using the ground-water flow lines 

shown in figure 13 to subdivide the storage 

units into areas where water is derived from 

local sources and the Colorado River. The estimates were accomplished for zones 2, 3, and 4 

by using the ground-water divide shown in 

figure 7 to subdivide the storage units into 

areas where water is derived from the Colorado River and local sources. 

Ground-water flow in the aquifers deeper 

than about 3,000 feet is probably downward 

from the shallower aquifers and radially toward each area of anomalously high heat flow 

where water-convection cells exist (Salton Sea 

and Cerro Prieto geothermal fields) or are postulated at great depths. Inferred ground-water 

flow lines are represented by arrows in figure 

7. The position of the ground-water divide, as 

shown in figure 7, is inferred on the basis of 

the assumed flow lines. 

The separation of water in zone 1 derived 

from local sources and the Colorado River was 

made on the basis of our concept of the flow 

system under natural conditions before a large 

part of the area, called the main valley area 

herein, was placed under irrigation. Therefore, 

some water derived from the Colorado River 

and used for irrigation may now be in storage 

in the area shown as containing locally derived 

water in figure 13. This storage, however, is 

probably minor in amount and is probably restricted to the upper part of the deposits in 

zone 1. 

THICKNESS, AREAL EXTENT, AND SPECIFIC YIELD 

OR POROSITY OF VERTICAL ZONES 1-4 

Four vertical zones were established on the 

basis of having approximately similar rock 

properties. The generally similar conditions 

and rocks made it possible to assume and then 

compute an average porosity or specific yield 

for the entire volume of rock within the depth 

intervals considered. Because the thickness of 

each depth zone varies areally, maps of each 

zone were prepared showing lines of equal 

thickness (figs. 16, 17, 18, and 19). The thickness of each zone is also shown in the three hydrologic sections (figs. 9, 10, and 11). 

Zone 4 (fig. 17) is the deepest of the four 

vertical subdivisions of the water-bearing 

rocks and deposits. As established for purposes 

of this report, it contains all the reservoir 

rocks that contain usable and recoverable 

water in storage at a depth greater than 8,000 

feet. Thus, vertical depth-zones 3 and 4 are 

separated by a somewhat aribitrary line about 

8,000 feet below the surface. The basis for this 

separation was the estimated downward decrease in porosity, the lithologic changes 

caused by increased metamorphism with increasing temperature at depth, and the indicated very low permeability of the rocks penetrated by wells below a depth of about 8,000 

feet, as determined by interpretation of electric logs. Conditions of temperature and pressure in the deep wells make interpretations 

based on existing electric logs uncertain. 

Convection, or caking of drilling mud, or 

unexplained phenomena, make it impossible to 

interpret the formation-water quality for 

many wells or even to detect the presence of 

relatively permeable or impermeable beds. 

Nevertheless, on the basis of available data, in 

general the rocks below 8,000 feet probably 

have very low permeability, are fractured, and 

have an average porosity of about 5 percent. 

41 

Because most of the contained water is at a 

high temperature, above 150°C, most of the 

water could probably be recovered from wells. 

The entire volume of water, estimated at 5 

percent of the total volume of the rock, could 

be recovered, however, only if pressures are 

eventually reduced sufficiently to allow flow in 

the vapor phase. 

The maximum thickness of zone 4 is about 

7,000 feet in an area south of Holtville (fig. 

17) . The line of zero thickness encloses an area 

of about 1,000 sq mi in the southcentral part 

of the storage units beneath the valley floor. 

The estimated total volume of the rocks is 
M::-. 

f.\:) 

116°00' 115°oo' 

--t· ~< -J;;..-(:1.(~;.::;7 ' 

_ '-. ~-~ I ~~-+---+---- ~~~<> ~~' • '~ ~~-,r.L ... I --+ -,_, ',_~ •. ~."' .. _,.- ·''-- j ," 9 

1( 

' ~ 

<,.,., 

-... 

ZONE 4: Usable water, less than 35,000 milligrams 

per liter dissolved solids 

Temperature, more than 100°C 

Depth, more than 8,000 feet 

Formation porosity, 5 percent 

Recoverable water, 5 percent 

EXPLANATION 

Ground-water basin boundary 

---?-··· Fault 

l"oo'r-~tt.?_\2~~-J'"' ~~ ~·> ~~~ ~ -I"~J\\•~ -~I] L.ll ~,,. r ~- 33'oo' 1 ; :_ ~wJe:{t~j ~ \ \ ~ =:',' 1 (6~ ) 

Oashed where approximate I y located; 

dotted where concealed; quer1 ed 

where doubtful 

---4--

Base from U.S. Geologtcal Survey State of 

Calo for no a (south hal f) 1:500,000, 1970 

FIGURE 17.-Thickness of deposits with usable water in zone 4. 

114°30 1 

Li ne of equal th1 ckness of depos1 t s 

containing usable wate 1 in zone 4, 

in thousands of feet. Interval, 

I, 000 feet 

U ;.ff 

z: ~ 

~: 

:; APPROXIMATE MEAN 

DECLINATION 1971 

0 5 10 15 20 Ml LES 

CONTOUR INTERVAL 500 FEET 

DATUM IS MEAN Sf A LEVEL 
about 1.9 billion acre-feet; about 100 million 

acre-feet of recoverable water is in storage in 

zone 4 (see table 3) . 

Zone 3 (fig. 18) overlies zone 4; it is much 

larger in areal extent than zone 4, not as thick, 

on the average, but contains much more water 

in storage. The porosity is estimated to average 20 percent, and the temperature of all the 

contained water is 100°C or greater (figs. 9, 

10, and 11). The low permeability of some of 

the rocks, the small thickness in some localities, and the lack of very high water temperatures in most of the depth zone, however, probably will make it impossible to rocover water 

from some of the rock pores. We believe that 

the low permeability will necessitate using 

closely spaced wells. It will probably not be 

economically feasible to drill wells at such 

close spacing as would be required to recover 

all the water; therefore, we believe that a significant percentage of the water will probably 

be retained in pores of the rocks, regardless of 

production methods used. The recoverable 

water will probably average more than the 

specific yield but less than the total porosity; 

the recoverable water may average about 16 

percent of the total volume of saturated reservior rock. 

The maximum thickness of zone 3 is about 

7,000 feet in a small area about 20 miles east 

of Holtville (fig. 18) . The line of zero thickness 

encloses an area of about 1,700 sq mi. The estimated total volume of the rocks is also about 

1.9 billion acre-feet; and about 300 million 

acre-feet of recoverable water is in storage in 

zone 3 (see table 3). 

As defined earlier, zone 2 extends from 

about 3,000 feet downward to the top of zone 3 

at the 100°C isothermal surface; thus, zone 2 

contains water at a temperature less than 

100°C (figs. 9, 10, and 11). 

The average porosity of the materials of 

zone 2 (fig. 19) probably is about 20 percent. 

However, because of the low temperature of 

the water, the total porosity is not a good 

index of the recoverable water in storage. 

Rather, the specific yield of the rocks and deposits must be used, assuming full drainage by 

gravity, to estimate the amount of recoverable 

water. An acceptable estimate of specific yield 

can be derived by multiplying estimated porosity by two-thirds, if sufficient data from well 

logs are unavailable on which to base direct estimates of specific yield. Thus, the specific yield 

of the deposits in zone 2 is estimated to average 13 percent. 

The maximum thickness of zone 2 is about 

4,000 feet in three areas of anomalously high 

temperature (fig. 19). In two areas of anomalously high heat flow in the southeast part of 

Imperial Valley, zone 2 is presumably absent 

because of the high water temperatures at 

shallow depth (figs. 11, 19). The lines of zero 

thickness enclose an area of about 1,650 sq mi. 

The total estimated volume of the reservoir of 

zone 2 is about 2.8 billion acre-feet; about 360 

million acre-feet of recoverable water is in 

storage in zone 2 (see table 3) . 

Zone 1 (fig. 16) extends downward from the 

water table near the surface to a maximum 

depth of 3,000 feet, or to the bedrock surface 

or the 100°C surface, whichever was less. Only 

in this zone was it possible on the basis of 

available data to portray the areal as well as 

the vertical variation in specific yields of the 

deposits. The Bureau of Reclamation requested 

that water in storage beneath each of the subunits be estimated separately because much of 

the land is Federally owned and has been withdrawn from the public domain for reclamation 

purposes. Thus, zone 1 was subdivided into 

four storage subunits (fig. 16). From east to 

west these are called the Sand Hills, East 

Mesa, main valley, and West Mesa storage 

units. 

43 

The average specific yield of the deposits of 

zone 1 beneath the Sand Hills subunit is estimated to be 20 percent. Beneath the East and 

West Mesa subunits, the specific yield of the 

deposits of zone 1 is estimated to be 15 percent, except in a small part of the southeast 

corner of East Mesa where it is estimated to 

be 20 percent. Beneath the main valley area, 

however, the irrigated area constitutes a recharge-boundary condition for the aquifers underlying the irrigated land, and dewatering the 

deposits is probably not feasible. Therefore, 

draining water from zone 1, main valley subunit, is probably not feasible, and the specific 

yield is considered to be virtually zero (see 

table 2). If water is pumped from this main 

valley area, it will almost certainly be derived 
~ 

~ 

rrs 0oo' 115°oo• 

--r ~--r~~ .. ~rv-:.7 

I 0 ~ I\ \ \~<> .. j ' I .,.,. f!;r 

"'"' I I s., 1 ~ $.1 ( .>'r;> j y 

( 

ZONE 3: Usable water, I ess than 35,000 mi IIi grams 

per liter dissolved solids 

Temperature, more than 10ooc 

Depth, less than 8,000 feet 

Formation porosity, 20 percent 

Recoverable water, 16 percent 

EXPLANATION 

Ground-water nas1n boundary 

---?-··· Fault 

Dashed where approximately located; 

dot ted where concealed; queried 

where doun t fu I 

33000·r ·~~~'\ '%'?7 ~~fuiM~i ')\41" t r fl~·~ij~ L.±L 'f ~"' . [ .· '\' 330000 

~- - ·· . '--~ \. ,. l~ ra~lev I . . \ \ , , . . ( jl,;_ I ---3-?-

116°00' 

Base from U.S. Geological Survey State of 

California (south half) 1:500,000,1970 

114°30' 

FIGURE 18.-Thickness of deposits with usable water in zone 3. 

/ 

Line of equal thickness of deposits 

containing usable water in zone 3, 

1n thousands of feet. Queried 

where doubtful. Interval 1,000 feet 

l4·~ 

... "' 

: ... 

APPROXIMATE MEAN 

DECLINATION 1971 

10 15 

CONTOUR INTERVAL 500 FEET 

DATUM IS MEAN SEA LEVEL 

20 MILES 
~ 

01 

115°oo• 

--~ _ -.-~--rs-,--:J~ ~loY•rOII!i: ! ,..._-

• ' i '(~ "'<,, I • • ~ .. 

\. ~~~., .... { .. - --~ ,." ~~ ? 

( 

ZONE 2: Usable water, less than 35,000 mi II igrams per 

liter dissolved solids 

Temperature, less than 100° C 

Depth, more than 3,000 feet, tess than 8.000 feet 

Formation porosity, 20 percent 

Recoverable water. 13 percent 

EXPLANATION 

Ground-water oasin ooundary 

---?-··· Fault 

Dashed where approximately located, 

dotted where concealed; quer1 ed 

where douotlul 

JJ"uo'j ~~~ ~~~~ ~ ~r, ~ ~ ~~~~i L-jl '~ ~·00 ~ 1 'i ~ JJ"oo· 

.~~~'"_:~:-~:s:;;ts; ~- \\~; ~\~-_( ~:~~ I --4--- line of equal !hi ckness of deposits 

containing usaole water in zone 2, k 

116°oo' 

Base from U.S. Geological Survey State of 

Cali fo roo a (south half) 1:500.000, 1970 

114°3o' 

FIGURE 19.-Thickness of deposits with usable water in zone 2. 

in thousands of feet. Interval, 

1, 000 I eel 

·'i~ 

~ 

.. 

: APPROXIMATE MEAN 

DECLINATION 1971 

10 15 

CONTOUR INTERVAL 500 FEET 

OATUI IS lEAN SEA LEVEL 

20 MILES 
TABLE 2.-Usable and recoverable water at temperature of 150°C or more 

[Estimates in millions of acre-feet] 

Storage in areal subunits 

Source Sand East Main West Rounded Percentage 

Hills Mesa valley Mesa total of total 

Colorado River ---------------- 10 48 69 0 127 64 

Local ------------------------- .91 2.9 60 5.6 70 36 -------------------------------------------------------- Rounded total ____________ 11 51 

directly from the canals that drain the irrigated land. 

The area of the Sand Hills subunit is about 

450 sq mi, that of the East Mesa subunit about 

350 sq mi, and that of the West Mesa subunit 

about 465 sq mi. About 350 million acre-feet of 

usable and recoverable water is contained in 

zone 1 (see table 3). 

WATER AT TEMPERATURES MORE THAN 150°C 

The areal extent of usable water at a temperature more than about 150°C is shown in 

figure 20. Such water is widespread; we believe 

it underlies almost all of the Imperial Valley 

area and is absent only along the marginal 

parts of the valley beneath strips of land a few 

to 10 or more miles wide. The thickness of 

rocks containing usable water at 150°C or 

more ranges from 0 to more than 8,000 feet. 

The estimated average porosity of the reservoir rock is about 10 percent. 

Figure 20 shows the thickness of four 

known areas with deposits containing usable 

hot water at more than 150°C. Southeast of 

Holtville the deposits are more than 8,000 feet 

thick, near Heber about 5,000 feet thick, and 

near both Ogilby and Westmoreland about 

6,000 feet thick. In much of the area, however, 

129 5.6 197 

the thickness of deposits with usable water at 

a temperature of 150°C or greater is only 

1,000-2,000 feet. 

The total estimated usable water in storage 

having a temperature of 150°C or more (table 

2) is rounded to about 200 million acre-feet. 

On the basis of the data available regarding 

the probable source of the water, about 64 percent or about 127 million acre-feet is derived 

from the Colorado River, and 36 percent or 

about 70 million acre-feet is from local sources. 

SUMMARY OF USABLE AND RECOVERABLE WATER 

Preliminary estimates of total usable and recoverable water in storage are summarized in 

table 3. Total usable and recoverable water in 

storage is estimated to be 1.1 billion acre-feet. 

This compares to a quantity in storage of 

1.6-4.8 billion acre-feet previously estimated 

by Rex (1970, p. 14). Of that amount, about 

190 million acre-feet is contained in the four 

vertical depth zones beneath the Sand Hills 

storage unit (fig. 16), about 280 million acrefeet underlies the East Mesa area, about 430 

million acre-feet is beneath the main valley irrigated area, and about 215 million acre-feet is 

beneath the West Mesa area. 

TABLE 3.-Summa?·y of usable and 'recoveTable water in the Imperial Valley aTea, 

California, containing less than 35,000 mg/l dissolved solids 

Vertical 

depth 

zone Sand Hills 

1 ---------------- 126 

2 ---------------- 28 

3 ---------------- 38 

4 ---------------- .1 

Rounded 

[Estimates in millions of acre-feet] 

Storage in areal subunits 

East Mesa Main valley West Mesa 

103 0 120 

89 181 63 

67 170 29 

19 77 2.4 

280 

Percentage in each Total depth zone 

349 31 

360 32 

304 28 

99 9 

total 190 430 215 1,100 

Percentage ==================================================================== 

in each 

areal 

subunit ________ 17 25 39 19 100 

46 
TABLE 4.-Sumnw?·y of usable and 1·ecoverable water in sto1·age de1·ived [?·om the Colo•rado Rive1· mzd local sources 

[Estimates in millions of acre-feet] 

Storage in m·eal ~ubunits Percentage Vertical 

depth zone Sand Hills East Mesa 

Zone 1: 

Local ---------------- 16 6 

Colorado River ------- 110 97 

Zone 2: 

Local ---------------- 2.6 4.7 

Colorado River ------- 25 84 

Zone 3: 

Local ---------------- 5.3 4.8 

Colorado River ------- 32 63 

Zone 4: 

Local ---------------- 0 0 

Colorado River ------- .1 19 

Totals: ------------ 191 279 

Local 24 , -------- 16 

Colorado River __ 167 263 

Percentage of total: 

Local ---------------- 13 6 

Colorado River ------- 87 94 

The vertical distribution (fig. 9) of the usable and recoverable water in storage is about 

as follows: vertical depth-zone 1 (from the 

water table to a depth of 3,000 ft in most of 

the area), about 350 million acre-feet; depthzone 2 (fron1 3,000 ft to a water-temperature 

depth of 100°C in most of the area), about 360 

million acre-feet; depth-zone 3 (from a watertemperature depth of 100°C to a depth of 

8,000 ft in most of the area), about 300 million 

acre-feet; and depth-zone 4 (at a depth greater 

than 8,000 ft), about 100 million acre-feet. 

Preliminary estimates of total usable and recoverable water in storage derived from local 

sources and the Colorado River are summarized 

in table 4. Of the approximate total 1.1 billion 

acre-feet in storage, about 420 million acre-feet 

or about 38 percent was probably derived from 

local sources and about 690 million acre-feet or 

about 62 percent was probably derived from 

the Colorado River. 

RELIABILITY OF THE ESTIMATES 

The probable percentage error for the estimates compiled in this report cannot be determined. Data are not available on which such 

error estimates could be based. In fact, if it 

had been required at this stage that such estimates be based on standard methods of computation, using only data that would ordinarily 

be termed of minimum acceptable accuracy, in 

in each Main valley West Mesa Total depth zone 

47 

31 

0 119 141 

0 .9 208 

32 

75 63 145 

106 0 215 

28 

68 29 107 

102 0 197 

9 

24 2.4 26 

53 0 72 

428 214 1,112 

167 213 420 38 

261 .9 692 62 

39 100 38 

61 0 62 

the amount ordinarily acceptable, and having 

the usually required pattern of distribution 

throughout the system, it would have been impossible to compile the estimates. 

The logic on which the great extrapolations 

could be b,ased had to be developed by formulating a c6nceptual model of the sedimentary 

basin, considering the elements and mechanisms of the hydrothermal system. Both models had to take into consideration all available 

data and information available at the present 

time (June 1971). Therefore, the accuracy of 

the estimates of usable and recoverable water 

in storage in the system is directly related to 

how adequately the conceptual model of the 

system represents the prototype. How nearly 

the conceptual model agrees with the prototype 

cannot be determined until considerable additional data are collected and much further research is completed. Until additional data are 

generated and much new research is done, the 

estimates must be considered usable engineering approximations; all planning, including development of the resources, research, and future data-collection programs, should be based 

on that understanding. 

SIGNIFICANCE OF PRODUCTION METHODS 

Although the estimates of recoverable water 

(tables 2, 3, and 4) in the Imperial Valley area 

were based on an assumption that all water in 
t+:o. 

00 

116°00' 

1J5°oo• ------.,., ;;,~~T:;:.J --~ ~ i ~ ' ( 

t-"'<"~ ! \ I 

., ~~J :_,__ __ {71. 

-.... !!1 --1 -~- (_~_. ~-

t 

•I 

.. 

--~+-. -.--,, ~. ~- ::,;.f"1,, . \ 

t M,w. ''"[ o) 

' "~ 2."o.:J~,.'' --t----;-~- I ~,' 

3J'oo'l ~~r~~ll"~ 1·~ 1\· 'ij L-1' '\1 ~{·"' :r ] JJ'oo· •·l&H . . •- · '-' Ia - '17.>.1 1 '~*- ~'"T I 1 =~ ,- · 7 . \ - I 

EXPLANATION 

Ground-wale r basin boundary 

---?-··· Fault 

Dashed where approximate I y I ocat ed, 

do !ted where concealed, queried 

where doubt fu I 

----3-?--

Line of equal thickness of usable 

water of mo 1 e than 150°C, in 

thousands a f feel. Ouer i ed 

where doubt fu I. Interval, 

500 feet and va r i ab I e, in 

thousands of feet. 

Usable water, less than 35,000 milligrams per I iter d1 sso I ved so I ids 

Fo rmat1on po rasi ty, 5 and 20 percent 

Recoverab I e wale r, I 0 percent 

:. ,v·; ., ~ ~ 

~ ~ 

APPRO X I MATE MEAN 

OECLINATICN 1971 

0 5 I 0 15 20 MILES 

Base from U.S. Geolog1cal Survey State of 

Caloforn>a (south half) 1:500,000,1970 

FIGURE 20.-Thickness of deposits with usable water of more than 150°C, 

114°30 1 

CONTOUR INTERVAL 500 FEET 

DATUM IS MEAN SEA LEVEL 
storage would be recoverable through wells by 

some means, production of much of the water 

may not be economically feasible. For example, 

average yields of wells penetrating depth-zone 1 

beneath the East and West Mesa areas where 

water temperatures are less than 100°C may 

be a few hundred gallons per minute with 

large drawdowns (many tens of feet). The 

problem of small yields may also occur where 

wells penetrate depth-zone 2. 

Large-scale subsidence of the land surface 

following production might require reinjection 

of water from the ocean or other sources to 

maintain reservoir pressures, adding further 

to the costs. Only further drilling, testing, and 

experiments can provide a basis for determining whether or not the water can be recovered 

economically. 

Furthermore, the problem of preventing 

large-scale subsidence will probably be compounded by a need to recharge the deep aquifers by using injection wells. On the basis of 

available geologic data and estimates of aquifer transmissivity and rock permeability, it is 

very unlikely that the deep parts of the system 

can be recharged by spreading water in surface basins. The vertical permeability is probably much too low in most of the basins. Recharging the deep aquifers using injection 

wells will greatly increase costs over those experienced in other areas where recharge can be 

accomplished through use of water-spreading 

basins on the surface. 

In addition to the economic and environmental problems, there are many legal factors to 

be considered that might influence utilization 

of the resource. The significant legal factors 

are summarized in a report by the California 

Geothermal Resources Board ( 1971). 

The cost of pumping water from wells increases with lift. The electric power, in kilowatthours (kwhr), required to lift 1 acre-foot 

of water 1 foot can be calculated from the formula: 

weight of 

gallons in X 1 gallon 

1 acre-ft of water 

kwhr I acre-ft/ft = -:------,-----,=-----:---

foot-pounds per minute 

for 1 kilowatthour 

49 

X 

100 

pumping plant 

efficiency, in 

percent 

325,850 X 8.336 

44,254 X 60 

100 

X pmnping plant 

efficiency, in 

percent 

=1.02X .100 

pumping plant 

Conversion factors: 

efficiency, in 

percent 

1 acre-ft= 325,850 gallons (gal) 

1 gal water= 8.336 pounds (lbs) 

1 kilowatt (kw) =44,254 foot-pounds per 

minute (ft-lbs/min) 

1 kilowatthour (kwhr) = 44,254 X 60 

Estimating prospective pumping-plant efficiency for future wells is not presently possible. 

Pumping costs, however, would be very high 

if a large percentage of the total estimated 

usable and recoverable water in storage in the 

basin were pumped from wells. An example of 

such costs, using a pumping-plant efficiency of 

50 percent, probably a very optimistic estimate 

if pumps are set at great depth, is included below to illustrate the economics of dewatering 

deep aquifiers. 

The power requirements to pump 1 acre-foot 

at a rate of 1 cfs (cubic foot per second) at a 

5,000-foot head for the wire-to-water efficiency 

of 50 percent, using electrical energy cost of 

$0.01 per kilowatthour, would be about as follows: 

kwhr I acre-ft/ft = 1.02 X 100/50 = 2.04 

Cost/acre-ft = 2.04 x 5,000 X $0.01 = 

about $100.00 

Cost of wells and pumps should also be considered. Mean costs of deep 8- to 12- inch wells 

in sandstone can be crudely estimated using an 
empirical formula derived by the Illinois State 

Water Survey (written commun., 1968): 

Well cost=0.029d 1.s7 

where d is depth of well, in feet. Thus, a 

3,000-foot well would cost about $90,000. Wells 

8,000 feet deep might cost more than $210,000 

each. 

If as much as 1,000 feet of pumping lift 

could be economically justified, about 100 million acre-feet of water, all in depth-zone 1 beneath the Sand Hills and East and West Mesa 

areas, might be economically recoverable. Of 

course, at high temperatures ( > 150°C) wells 

do produce steam and water without being 

pumped, if the initial hydrostatic head is removed by gas lifting or other means. Production of all such water and steam, however, presumably will be from zones greater than 1,000 

feet beneath the surface. If deep wells produce 

both water and steam without being pumped, 

additional water would be recoverable if high 

well costs, repressurization costs, and air and 

water pollution prevention measures do not 

prevent such production. 

In summary, economic studies are needed to 

determine the feasibility of recovering the 1.1 

billion acre-feet of water estimated in this report as being recoverable. Such studies may indicate that recoverable water is only about 100 

million acre-feet at a temperature less than 

100°C, less than 100 million acre-feet at higher 

temperature, and less than 200 million acrefeet from all sources. 

POSSIBLE CHANGES IN THE FLOW REGIME 

Another objective of this report was to describe briefly and in general terms the possible 

changes in the water inflow-outflow relations 

that might result from large-scale extraction 

of the recoverable water in storage. Depending 

on where wells are located, their yields, drawdowns, and duration of pumping, several 

changes in the flow regime could be induced as 

follows: 

1. Ground-water flow might change in quantity or be induced to reverse direction 

across the international boundary. 

2. More water might be induced to percolate 

50 

from the large irrigation canals to the 

underlying ground-~ater body. 

3. Ground water derived from local sources 

might b~ induced to flow into or toward 

producing wells in areas formerly containing only 'water derived from the Colorado River. 

4. Ground water. derived from the Colorado 

River might be induced to flow into or 

toward producing wells in areas formerly 

containing. only water derived from local 

sources. . 

5. Ground wat~r,. which under natural or 

present-day conditions flows upward to 

enter the drainage systems on the surface, might be diverted to enter pumping 

wells. 

6. Water that now presumably flows downward to recharge ~deep water-convection 

systems might be diverted by production 

wells and thus cause changes in the deep 

inflow-outflow systems. 

7. Changes in chemical quality of water might 

occur as a result of disturbing waterquality interfaces by pumping. 

8. Ground water might be diverted downward 

from the land surface, rivers, or drainage channels in the irrigated area, and 

thus be diverted from the Salton Sea. 

Other and unforeseen changes in the ground 

water inflow-outflow relations might also occur. The point is that any large-scale water 

production will induce changes in the system 

and these are now impossible to predict 

quantitatively. A very large additional quantity of special data would be required before it 

would be possible to make a quantitative prediction of the nature and magnitude of the 

changes that would result if specified production stresses are imposed on the system. 

POSSIBLE ENVIRONMENTAL HAZARDS 

We have not attempted to foresee or analyze 

the consequences of all possible practices that 

might result in environmental hazards. The 

most serious problems may result from land 

subsidence, induced seismic activity, and air, 

water, and noise pollution. These are briefly 

discussed in the following sections of the report. 
LAND SUBSIDENCE 

One of the potential hazards of ground-water extraction in Imperial Valley, either for 

geothermal power or for water supply, is the 

threat of land subsidence. Whenever fluids are 

mined from a ground-water reservoir-that is ' withdrawals exceed the recharge rate and reservoir pressures continue 'to decline-land 

subsidence may occur. Throughout much of the 

developed area of Imperial Valley~ subsidence 

would cause costly damages; in outlying undeveloped areas, subsidence might be tolerated. 

In either setting, the likelih~od of subsidence 

resulting from the extraction of reservoir 

fluids must be fully considered, and the hydrogeologic parameters affecting the magnitude, 

extent, and rate of subsidence should be understood. 

Subsidence results from the compaction of 

compressible beds of the aquifer system as 

effective st,resses are increased by fluid-pressure reduction (Lofgren, 1968). The magnitude of the subsidence is dependent on the 

effective stress increase caused by the pressure 

dr?p, the compressibility of the deposits, the 

thickness of the compressible beds, the time 

the increased stress has been applied, and also 

on the past stress history-whether the increased stress is being applied for the first 

time or has been attained or exceeded previously. Although a small part of the subsidence may be elastic in nature and tend to rebound when the stress is removed, most of the 

change is nonelastic and nonrecoverable. 

Water-level fluctuations in a ground-water 

reservoir cause effective stresses in the following two ways (Lofgren, 1968, p. B225) : 

1. A rise of the water table increases the buoyant support of the sand grains in the 

zone of the change, and a decline decreases the buoyant support; these 

changes in gravitational stress are transmitted downward to all underlying deposits. 

2. A change in position of the water table or 

in the fluid pressure in a confined system, 

or both, may induce vertical hydraulic 

gradients across confining or semiconfining beds and thereby produce seepage 

stresses. These stresses are algebraically 

51 

additive to the gravitational stress that 

is transmitted downward to all underlying deposits. 

Land subsidence caused by the exploitation 

of oil and gas resources and by intensive 

pumping of ground water is relatively common 

throughout the world (Poland and Davis, 

1969). As in oil-field or artesian ground-water 

production, a direct relation exists between 

subsidence and fluid-pressure decline in a 

geothermal field. Subsidence can be minimized 

or prevented by maintaining fluid pressures by 

either natural or artificial recharge. Also, the 

lateral extent of subsidence effects is sometimes defined by faults that are barriers to 

fluid flow. Recently, subsidence has been related to the extraction of geothermal waters in 

Wairakei, New Zealand (Hatton, 1970; Hunt, 

1970) and Cerro Prieto, Mexico (Eduardo 

Paredes, oral commun., 1971). Although the 

geologic setting at these locations varies considerably, the basic cause of the subsidence is 

the same-the reduction of fluid press11re causing a marked increase in effective stress. 

At Wairakei (Hatton, 1970) the area affected 

by subsidence exceeds 25 square miles, and the 

maximum subsidence rate is about 1.3 feet per 

year. Total subsidence exceeds 10 feet and, of 

particular significance, ·the area of maximum 

subsidence occurs outside the production field. 

At Cerro Prieto subsidence has been measured 

7 miles outside the well field even though extensive production has not begun (Eduardo 

Paredes, oral commun., 1971) . Corresponding 

effects could occur in Imperial Valley, unless 

provisions are made to maintain reservoir 

pressures. 

Most of the parameters for predicting subsidence in Imperial Valley-such as anticipated pressure declines, thickness and compressibilities of the water-bearing deposits, 

and lateral ~xtent of fault blocks-are not well 

known. Both fluid pressures and surface bench 

marks should be carefully monitored to measure the effects of production. Because Imperial 

Valley is tectonically active and may be subsid:-

ing naturally, provision should be made in the 

monitoring program to differentiate tectonic 

subsidence and also surficial compaction of 

shallow deposits from subsidence caused by 

geothermal development. 
One of the considered proposals of the Imperial Valley development, and the principal reason for this ground-water storage appraisal, is 

the extensive production of ground water. Water-bearing deposits extend from near land 

surface down to practicable pumping depths 

and have a large storage capacity. Can this 

shallow reservoir be exploited without causing 

subsidence? 

Experience in many areas of intensive 

pumping, particularly in the San Joaquin 

(Lofgren and Klausing, 1969; Poland and 

Davis, 1969) and Santa Clara (Poland, 1969) 

Valleys of California, indicates that ground 

water cannot be mined from these unconsolidated or semiconsolidated deposits without 

causing land subsidence. Particularly in the 

confined aquifer systems a direct relation exists between pumpage and land subsidence. 

Water pumped from a confined reservoir not 

recharged at the same rate by natural or artificial recharge is mined from the formation 

and causes subsidence. 

In areas studied, the ratio of subsidence to 

head decline varies considerably, depending on 

the parameters discussed above. In general, 1 

foot of surficial subsidence occurs for each 

10-5p feet of long-term artesian-head decline. 

In ~everal interior areas of heavily pumped 

basins, the volume of water pumped about 

equals the volume of subsidence it produces. 

This suggests that little or no recharge is getting to these parts of the reservoir. 

As. in other heavily pumped basins of the 

arid West, extractions in Imperial Valley that 

cause water levels to decline to new low levels 

each year will cause continuing subsidence. In 

parts of the valley long-term subsidence might 

be of little consequence; in other areas damages would probably be prohibitive. 

SEISMIC ACTIVITY 

Much scientific literature has accumulated in 

recent years on problems related to the disposal of liquid wastes underground. Pi per 

(1969) has reviewed the overall subject, and 

his report included an extensive list of references on the subject. In regard to the hazard 

of induced seismic activity by either fluid withdrawal or injection, however, experience is 

52 

much more limited. That fluid pressure and 

temperature changes caused by water removal 

or injection in systems such as the Salton 

Trough hydrothermal system can cause earthquakes or seismic activity has not been proved. 

However, earthquakes have resulted from such 

temperature and pressure changes in other 

rock-water systems. This was experienced at 

the Rocky Mountain Arsenal near Denver, 

Colo. (Hoover and Dietrich, 1969; Healy and 

others, 1968) . 

Snow (1968) described fracture deformation 

and changes in permeability and storage upon 

change in fluid pressure. Pickett ( 1968) described fractured rocks and the relation of 

these properties to the earthquakes at Derby, 

Colo., and Birch (1958) described some results 

of temperature changes in deep systems. 

As a result of research still in progress at 

the Rangely oil field in Colorado, preliminary 

data indicate that seismic activity can be both 

induced and then reduced by changing fluid 

pressures in some deep rock-water systems 

(Raleigh and others, 1971). 

Little or no seismic activity is anticipated 'in 

the Imperial Valley area in response to pumping from the unconsolidated aquifers to depths 

of several thousand feet. The threat of earthquakes being induced by deep fluid withdrawals or injections, particularly if large stress 

differentials are produced and consolidated formations are involved, must be considered a 

definite possibility. Apparently no significant 

earthquakes have been reported at the heavily 

developed W airakei, New Zealand, geothermal 

field (Hunt, 1970). 

In summary, it must be anticipated that 

large-scale water production from deep hightemperature fractured rocks of the Salton 

Trough geothermal system or high-pressure 

injection of fluids, or both, might constitute a 

seismic hazard. Extensive research will be 

needed to determine the extent of the hazard 

and the operating procedures that would reduce or overcome the possibility of any such 

induced seismic activity. 

AIR, WATER, AND NOISE POLLUTION 

Air, water, or noise pollution could result 

from production of water and steam from the 
Salton Trough hydrothermal system unless adequate engineering is p~ovided and effective 

production practices are invoked to prevent 

such pollution. Of the three hazards, the water-pollution potential is the best known; Federal, State, and local regulations adequately 

control the operating procedures and practices 

that are permissible. Proper practices should 

make it possible to prevent water pollution in 

the area. However, prevention of water pollution will materially add to production costs 

and consequently may affect the economic feasibility of development programs. 

Air pollution might possibly take two forms 

(1) an increased humidity burden caused by 

releasing vapor to the atmosphere, or (2) release of mineral vapor and gases to the atmosphere. Because evapotranspiration associated 

with irrigation in the area exceeds 3 million 

acre-feet annually, the moisture burden that 

could be expected to result from geothermal 

power production probably would be below expected natural variations in the humidity. 

Therefore, the increased humidity burden 

probably will not constitute a hazard. Detailed 

engineering estimates should be compiled, however, to confirm this preliminary conclusion. 

Serious air pollution might result from noxious gases, such as hydrogen sulfide, and mineral vapors if these are released to the 

atmosphere with steam. Mercury vapor may 

constitute a hazard. Barnes ( 1970) described 

anomalous waters from much of the Pacific 

margin of the United States and included 

water from the Wister mudpots near Salton 

Sea. He attributed the anomalous waters to 

deep metamorphism of marine sedimentary deposits and pointed out their association with 

mercury ores. Because marine rocks are almost 

certainly present in the deepest part of the 

Salton Trough and thus are being metamorphosed, detailed analyses should be made of 

steam produced before large-scale release of 

vapors to the atmosphere during tests and production. If mercury vapor is detected, the concentration and hazard should be determined. 

Noise is produced at high levels during 

geothermal production. Experiments for noise 

reduction should be carried out to provide engineering designs to keep noises to environmentally acceptable levels. 

53 

ADDITIONAL DATA NEEDS 

Many private and public agencies have 

worked, drilled, and tested to provide data 

needed to determine the magnitude of the 

water and geothermal-power resources of the 

area and its quality. Still a paucity of data exists. 

Although the lack of existing data is a serious problem, an equally serious one is encountered by all workers who seek to study the 

system. The available data that have been accumulated over the years are in files of numerous public agencies, private individuals, and 

commercial firms. These data, for the most 

part, are unorganized and in various formats. 

The lack of a systematic tabulation of the data 

and an analysis of the accuracy and usability 

of the data is at present the greatest handicap 

to effective study of the hydrothermal system. 

An analysis and systematic tabulation of all 

the available data should be given a high priority as additional studies are planned. 

Available data from wells in the Imperial 

Valley area are mainly from deep test wells 

drilled during exploration for oil or high-temperature water and steam. For these wells few 

data have been obtained at shallow and intermediate depth as drilling progressed. This results in a gap in our knowledge of the vertical 

variation in temperature and pressure in the 

shallow zones. It also leaves a gap in geologic 

data relative to permeability and porosity of 

the rocks and deposits, and type, distribution, 

and extent of cementation or other chemical or 

physical alteration of the original deposits. 

Data from some recently drilled shallow test 

wells partly compensate for this general lack 

of data for shallow zones, but even these holes 

have not provided all the data needed. Few of 

these shallow wells have been drilled on the 

margins of the high heat-flow anomalies where 

temperatures decrease rapidly and chemical cementation presumably occurs. Data on pressure (or head), temperature, cementation, porosity, permeability, and water quality in such 

areas would prove useful in achieving a full 

understanding of the hydrothermal elements 

and mechanisms. 

Data of the type needed for accurately estimating rock porosity and permeability are al-
most completely lacking. Insofar as can be determined, only well 92 (U.S. Bur. Reclamation 

127) has both a gamma-gamma log and a neutron log. This combination of logs provides the 

most dependable means of estimating porosity 

and permeability of the deposits. Future research would be greatly enhanced if such logs 

were provided for all new deep and shallow 

wells drilled. 

Water-quality data and water-level measurements in wells 1,000-3,000 feet deep are 

scarce; for deeper test wells they are virtually 

lacking. In fact, preproduction water-level altitudes in deep wells are not commonly recorded. 

Such data would be very useful. 

Many additional water-quality data are 

needed to adequately define the system. Of particular importance, oxygen and hydrogen isotope data should be obtained routinely for all 

water sources until the three-dimensional distribution of water from the Colorado River 

and local soucres is clearly defined. Oxygen isotope data should also be obtained for the reservoir rocks penetrated in test wells. 

Many additional geologic data will be needed 

if a clear understanding of the hydrothermal 

system is ever to be obtained. Accurate data on 

three-dimensional distribution of porosity, 

permeability, and thickness will be particularly 

important if quantitative predictions are to be 

made of the effects of proposed development. 

The ground-water recharge-discharge relations have not yet been determined with sufficient accuracy to predict the possible system 

changes that might result from large-scale 

water production. Rates and areal variations 

of water losses from the canals should be determined. A better understanding of rates and 

areal distribution of ground-water discharge to 

the drainage canals should be obtained. 

Subsidence resulting from ground-water developments in Imperial Valley could be a limiting restraint. Long before actual withdrawals 

occur, a surveillance program should be implemented to monitor fluid-pressure and land-surface changes that might take place. Also consideration should be given to a measuring 

program to differentiate tectonic changes and 

surficial compaction of shallow deposits resulting from the effects of ground-water production. 

54 

A complete analysis of the data-collection 

program needed for planning, developing, and 

eventually operating a large-scale water-production program in the Imperial Valley area is 

beyond the scope of this report. Needless to 

say, such comprehensive plans would require 

decisions by management that could only be 

based on a much more accurate and extensive 

knowledge of the system than now exists. 

Therefore, as plans for development of the 

water resources progress, the need for data 

will increase. The types and kinds of data that 

will be needed must be determined in advance 

of need, accuracy standards for the data must 

be established, and the program must be timed 

to provide the data as they are needed. 

SELECTED REFERENCES 

Allison, E. C., 1964, Geology of areas bordering Gulf 

of California, in VanAndel, 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. 

Alonso Espinosa, Hector, and Mooser, Federico, 1964, 

El pozo M-3 del campo geotermico del Cerro 

Prieto, Baja California, Mexico: Assoc. Mexicana 

Geologos Petroleros Bull., v. 16, nos. 7-8, p. 

163-178. 

Anda, L. F., de, and Paredes, Eduardo, 1964, La falla 

de San Jacinto y su influencia sobre la actividad 

geotermica en el valle de Mexicali, Baja California, Mexico: Assoc. Mexicana Geologos Petroleros 

Bull., v. 16, nos. 7-8, p. 179-181. 

Arnal, R. E., 1961, Limnology, sedimentation, and microorganisms of the Salton Sea, California: Geol. 

Soc. America Bull., v. 72, p. 427-478. 

Bailey, T. L., and Jahns, R. H., 1954, Geology of the 

Transverse Range province, southern California, 

in Geology of southern California: California Div. 

Mines Bull. 170, chap. 2, p. 83-106. 

Barnes, Ivan, 1970, Metamorphic waters from the Pacific tectonic belt of the west coast of the United 

States: Science, v. 168, p. 973-975. 

Beal, C. H., 1948, Reconnaissance of the geology and 

oil possibilities of Baja California, Mexico: Geol. 

Soc. America Mem. 31, 138 p. 

Berry, F. A. F., 1966, Proposed origin of subsurface 

thermal brines, Imperial Valley, California [abs.]: 

Am. Assoc. Petroleum Geologists Bull., v. 50, no. 

3, p. 644-645. 

---1967, Role of hyperfiltration on origin of thermal 

brine, Imperial Valley, California [abs.]: Am. 

Assoc. Petroleum Geologists Bull., v. 51, p. 454-455. 

Biehler, Shawn, 1964, Geophysical study of the Salton 

Trough of south~rn California: Pasadena, Calif., 

California Inst. Technology, unpub. Ph.D. thesis, 

139 p. 
Biehler, Shawn, Kovach, R. L., and Allen, C. R., 1964, 

Geophysical framework of northern end of Gulf of 

California structural province, in VanAndel, 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. 

Biehler, Shawn, and Rex, R. W., 1971, Structural geology and tectonics of the Salton Trough, southern 

California: Riverside, Calif., California Univ., 

Dept. Geol. Sci., rept. Field Trip 2, p. 30-42. 

Birch, Francis, 1958, Thermal considerations in deep 

disposal of radioactive waste: Natl. Acad. Sci.-

Natl. Research Council Pub. 588 (Report for 

Comm. on Waste Disposal, Div. Earth Sciences). 

Bradshaw, G. B., and Donnan, W. W., 1952, Groundwater investigations of Imperial County, California: U.S. Dept. Agriculture Soil Conserv. Service 

Research, rept., 61 p. 

Brown, J. S., 1920, Routes to desert watering plq.ces in 

the Salton Sea region, California: U.S. Geol. Survey Water-Supply Paper 490-A, p. 1-86. 

---1923, The Salton Sea region, California, a geographic, geologic, and hydrologic reconnaissance, 

with a guide to desert watering places: U.S. Geol. 

Survey Water-Supply Paper 497, 292 p. 

Bullard, E. C., 1940, The disturbance of the temperature gradient in the earth's crust by inequalities 

of height: Royal Astron. Soc. Monthly Notices, 

Geophysics S-c:pp., v. 4, p. 360-362. 

---1947, Time necessary for a facehole to attain 

temperature equilibrium: Royal Astron. Soc. 

Monthly Notices, Geophysics Supp., v. 5, p. 

125-130. 

California Department of Conservation, Division of 

Mines and Geology, 1962, San Diego-El Centro 

Geologic Map Sheet. 

---1965, Santa Ana Geologic Map Sheet. 

---1967, Salton Sea Geologic Map Sheet. 

California Department of Public Works, Division of 

Water Resources, 1954, Ground water occurrence 

and quality, Colorado River basin region, water 

quality investigations: Rept. no. 4, 55 p. 

C~lifornia Department of Water Resources, 1970, 

Geothermal wastes and the water resources of the 

Salton Sea area: Bull. 143-7, 123 p. 

California Geothermal Resources Board, 1971, The economic potential of geothermal resources in California: California Resources Agency rept., 35 p. 

Clayton, R. N., Muffler, L. J. P., and White, D. E., 

1968, Oxygen isotope study of calcite and silicates 

of the River Ranch no. 1 well, Salton Sea geothermal field, California: Am. Jour. Sci., v. 266, p. 

968-979. 

Craig, Harmon, 1966, Isotopic composition and origin 

of the Red Sea and Salton Sea geothermal brines: 

Science, v. 154, no. 3756, p. 1544-1547. 

-·--1969, Source fluids for t'he Salton Sea' geothermal system: Am. Jour. Sci.; v. 267, p. 249-255. 

Craig, Harmon, and Gordon, L. I., 1965, Deuterium 

and oxygen-18 variations in the ocean and the marine atmosphere, in Spolito, Stable isotopes in 

55 

oceanographic studies and paleotemperatures: 

Consiglio N acionale delle Richerche, Pisa, Italy, p. 

9-130. 

Crowell, J. C., 1962, Displacements along the San Andreas fault, California: Geol. Soc. America Spec. 

Paper 71. 

Dibblee, T. W. Jr., 1954, Geology of the Imperial Valley 

region, California, Pt. 2 in Chap. 2 of Jahns, R. 

H., eel., Geology of southern California: California 

Div. Mines Bull. 170, p. 21-28. 

Doe, B. R., Hedge, C. E., and White, D. E., 1966, Preliminary investigation of the source of lead and 

strontium in deep geothermal brines underlying 

the Salton Sea geothermal area: Econ. Geology, v. 

61,no.3,p.462-483. 

Downs, Theodore, and Woodard, G. D., 1961, Middle 

Pleistocene extension of the Gulf of California 

into the Imperial Valley: Geol. Soc. America, San 

Diego, paper presented annual meeting Cordilleran 

section. 

Durham, J. W., and Allison, E. C., 1961, Stratigraphic 

position of the Fish Creek gypsum at Split Mountain gorge, Imperial County, California: Geol. Soc. 

America, San Diego, paper presented annual meeting Cordilleran section. 

Elders, W. A., and Robinson, P. T., 1970, Possible seafloor spreading in the Imperial Valley of 

California IV: A model for magma generation 

[abs.]: EOS Trans. Am. Geophys. Union, v. 51, 

no. 4, p. 422. 

Fenneman, N. M., 1931, Physiography of western 

United States: New York, McGraw-Hill Book Co., 

Inc., 534 p. 

Griscom, Andrew, and Muffler, L. J. P., 1971, Aeromagnetic map and interpretation of the Salton 

Sea geothermal area, California: U.S. Geol. Survey Geophys. Inv. Map GP-754. 

Grubbs, D. K., 1964, Ore-bearing magmatic and metamorphic brine from the Salton Sea volcanic domes 

geothermal ar~a, Imperial County, California 

[abs.]: Virginia Jour: Sci., v. 15, new ser., no. 4, 

p. 333; also, 1963, Charlottesville, Va., Virginia 

Univ., unpub. M.S. thesis. 

Hatton, J. W., 1970, Ground subsidence of a geothermal field during exploitation: United Nations 

Symposium on the development and utilization of 

geothermal resources, Pisa, Italy. 

Healy, J. H., Rubey, W. W., Griggs, D. T., and Raleigh, C. B., 1968, The Denver earthquakes: Science,v. 161,n~ 3848,p. 1301-1310. 

Helgeson, H. C., 1967a, Silicate metamorphism in sediments and the genesis of hydrothermal ore 

solutions: Genesis of stratiform lead-zinc-baritefluorite deposits, Mississippi Valley type deposits 

-Symposium, New York, 1966: Econ. Geology 

Mon. no. 3, p. 333-338. 

---1967b, Solution chemistry and metamorphism, in 

Abelson, P. H., ed., Researches in geochemistry, v. 

2: New York, John Wiley and Sons, Inc., p. 

362-404. 

---1968, Geologic and thermodynamic characteris-
tics of the Salton Sea geothermal system : Am. 

Jour. Sci., v. 266, no. 3, p. 129-166. 

Rely, 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. 

Rely, A. G., and Peck, E. L., 1964, Precipitation, runoff and water loss in the lower Colorado RiverSalton Sea area: U.S. Geol. Survey Prof. Paper 

486-B, p. B1-B16. 

Holmes, J. G., and party, 1903, Soil survey of the Imperial area, California: U.S. Dept. Agriculture 

rept., p. 1219-1248, 2 maps. 

Hoover, D. B., and Dietrich, J. A., 1969, Seismic activity during the 1968 test pumping at the Rockey 

Mountain Arsenal disposal well: U.S. Geol. Survey 

Circ. 613, 35 p. 

Hubbs, C. L., Bien, G. S., and Suess, H. E., 1963, LaJ olla natural radiocarbon measurements 3: Radiocarbon,v. 5,p. 254-272. 

Hunt, T. M., 1970, Gravity changes at Wairakei geothermal field, New Zealand: Geol. Soc. America 

Bull., v. 81, p. 529-536. 

Jaeger, J. C., 1956, Numerical values for the temperature in radial heat flow: Jour. Math. Physics, v. 

34, p. 316-321. 

Jaeger, J. C., and Sass, J. H., 1963, Lee's topographic 

correction in heat flow and the geothermal flux in 

Tasmania: Geofis. Pura. Appl., v. 54, p. 55-63. 

Jahns, R. H., 1954, Geology of the Peninsular Range 

province, southern and Baja California, in Jahns, 

R. H., ed., Geology of southern California: Calif. 

Div. Mines Bull. 170, chap. 2, p. 29-52. 

Jeffrys, H., 1940, The disturbance of the temperature 

gradient in the earth's crust by inequalities of 

height: Royal Ash·on. Soc. Monthly Notices, Geophysics Supp., v. 4, p. 309-312. 

Keith, T. E. C., Muffler, L. J. P., and Cremer, Marcelyn, 1968, Hydrothermal epidote from the Salton 

Sea geothermal field, California: Am. Mineralogist, v. 53, no. 9-10, p. 1635-1644. 

Kelley, U. C., and Soske, J. I., 1936, Origin of the Salton volcanic domes, Salton Sea, California: Jour. 

Geology, v. 44, p. 496-509. 

Kocher, A. E., Carpenter, E. J., Dean, W. C., Smith, 

Alfred, Cosby, S. W., and Wank, M. E., 1923, Soil 

survey of the Brawley area, California: U.S. 

Dept. Agriculture rept., p. 641-716. 

Koenig, J. B., 1967, The Salton-Mexicali geothermal 

province: California Div. Mines and Geology, Mineral Inf. Service, v. 20, no. 7, p. 75-81. 

---1969, The Geysers geothermal field: California 

Div. Mines and Geology, Mineral Inf. Service, v. 

22, p. 123. 

---1970, Geothermal exploration in the western 

United States: United Nations Symposium on the 

development and utilization of geothermal resources, Pisa, II/19-III/38. 

Kovach, R. L., Allen, C. A., and Press, Frank, 1962, 

Geophysical investigation in the Colorado delta region: Jour. Geophys. Research, v. 67, no. 7, p. 

2845-2871. 

56 

Lachenbruch, A. H., 1957, Thermal effects of the ocean 

on permafrost: Geol. Soc. America Bull., v. 68, p. 

1515-1530. 

Lachenbruch, A. H., and Brewer, M. C., 1959, Dissipation of the temperature effect of drilling a well in 

Arctic Alaska: U.S. Geol. Survey Bull. 1083-C, p. 

73-109. 

Lang, W. B., 1959, The origin of some natural carbon 

dioxide gases: Geophys. Research Jour., v. 64, no. 

1, p. 127-131. 

Larsen, E. S., Jr., 1948, Batholith and associated rocks 

of Corona, Elsinore and San Luis Rey quadrangeles, southern California: Geol. Soc. America 

Mem. 29, p. 1-182. 

Lofgren, B. E., 1968, Analysis of stresses causing land 

subsidence: U.S. Geol. Survey Prof. Paper 600-B, 

p. B219-B225. 

Lofgren, B. E., and Klausing, R. L., 1969, Land subsidence due to ground-water withdrawal, TulareWasco area, California: U.S. Geol. Survey Prof. 

Paper 473-B, 103 p. 

McBirney, A. R., 1963, Conductivity variations and 

terrestrial heat flow distribution: Geophys. Research Jour., v. 68, p. 6323-6329. 

McNitt, J. R., 1963, Exploration and development of 

geothermal po\ver in California: California Div. 

Mines and Geology Spec. Rept. 75, 45 p. 

---1965, Review of geothermal resources in terrestrial heat flow: Am. Geophys. Union, pub. no. 

1288,chap. 9,p. 240-266. 

Menard, H. W., 1960, The East Pacific rise: Science, v. 

132,no. 3441,p. 1737-1746. 

Mendenhall, W. C., 1909, Some desert watering places 

in southeastern California and southwestern N evada: U.S. Geol. Survey Water-Supply Paper 224, 

98 p. 

Merriam, Richard, 1958, Geology and mineral resources of Santa Ysabel quadrangle, San Diego 

County, California: California Div. Mines Bull. 

177, 42 p., 2 pis. 

Merriam, Richard, and Bandy, 0. L., 1965, Source of 

upper Ceneozoic sediments in Colorado River delta 

region: Jour. Sed. Petrology, v. 35, no. 4, p. 

911-916. 

Morton, P. K., 1972, Geology and mineral resources of 

Imperial County, California: California Dept. 

Conserv., Div. Mines and Geology, rept. (In press.) 

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, no. 2, p. 384-399. 

Muffler, L. J. P., and White, D. E., 1968, Origin of C02 

in the Salton Sea geothermal system, southeastern 

California, U.S.A.: Internat. Geol. Cong., 23rd, 

Prague, August 1968, Genesis of mineral and thermal waters, v. 17, p. 185-194. 

---1969, Active metamorphism of upper Cenozoic 

sediments in the Salton Sea geothermal field and 

the Salton T1·ough, southeastern California: Geol. 

Soc. America Bull., v. 80, p. 157-182. 

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, 0. J., and Irelan, Burdge, 1972, 

Geohydrology of the Yuma area, Arizona and California: U.S. Geol. Survey Prof. Paper 486-H. (In 

press.) 

Paredes, Eduardo, 1964, Someras consideraciones sobre 

el origen de la energia y su posible utilizacion en 

el valle de Mexicali, Baja California, Mexico: 6 p. 

Pickett, G. R., 1968, Properties of the Rocky Mountain 

Arsenal disposal reservoir and their relation to 

Derby earthquakes: Colorado School Mines Quart., 

v. 63,no. l,p. 73-100. 

Piper, A. M., 1969, Disposal of liquid wastes by injection underground-neither myth nor millennium: 

U.S. Geol. Survey Circ. 631, 15 p. 

Poland, J. F., 1969, Land subsidence and aquifer-system compaction, Santa Clara Valley, California, 

U.S.A.: lASH-UNESCO, Internat. Conf., Tokyo, 

1969, Land subsidence, v. 1, pub. 88, p. 285-294. 

Poland, J. F., and Davis, G. H., 1969, Land subsidence 

due to withdrawal of fluids: Geol. Soc. America, 

Revs. in Eng. Geology 2, p. 187-269. 

Raleigh, C. B., Healy, J. H., Bredehoeft, J. D., and 

Bohn, J. P., 1971, Earthquake control at Rangely, 

Colorado [abs.]: EOS Trans Am. Geophys. Union, 

v. 52, no. 4,p. 344. 

Randall, Walter, Meidav, Tsvi, Rex, R. W., and Coursey, Leonard, 1968, Electrical resistivity and geochemistry of aquifers in the Durnival Dome, Imperial Valley [abs.]: Am. Geophys. Union Trans., 

v. 49,no. 4, p. 759. 

Rex, R. W., 1966, Heat flow in the Imperial Valley of 

California [abs.]: Am. Geophys. Union Trans., v. 

7 4, no. 1, p. 181. 

---1968, Geochemical water facies in the Imperial 

Valley of California [abs.]: Am. Geophys. Union 

Trans., v. 49, no. 4, p. 758. 

---1970, Investigation of geothermal resources in 

the Imperial Valley and their potential value for 

desalination of water and electricity production: 

Riverside, Calif., California Univ., Inst. Geophysics and Planetary Physics rept., no. 92502, 14 p. 

Robinson, P. T., and Elders, W. A., 1970, Possible seafloor spreading in the Imperial Valley of California III: Xenoliths in rhyolite volcanoes as samples 

of the basement [abs.]: EOS Trans. Am. Geophys. 

Union, v. 51, no. 4, p. 422. 

Rogers, J. J. W., 1961, Igneous and metamorphic rocks 

of the western portion of Joshua Tree National 

Monument, Riverside and San Bernardino Counties, California: California Div. Mines, Spec. Rept. 

68, 26 p. 

Rook, S. H., and Williams, G. C., 1942, Imperial carbon dioxide gas field: California Div. Oil and Gas, 

California Oil Fields-Summ. Operations, v. 28, 

no. 2, p. 12-33. 

Schlumberger, Ltd., 1969, Log interpretation charts: 

Houston, Tex., 76 p. 

Skinner, B. J., White, D. E., Rose, H. J., and Mays, R. 

E., 1967, Sulfides associated with the Salton Sea 

57 

geothermal brine: Econ. Geology, v. 62, no. 3, p. 

316-330. 

Snow, D. T., 1968, Fracture deformation and change 

of permeability and storage upon change of fluid 

pressure: Colorado School Mines Quart., v. 63, no. 

1, p. 201-244. 

Strahorn, A. T., Watson, E. B., Kocher, A. E., Eckmann, E. C., and Hammon, J. B., 1922, Soil survey 

of the El Centro area, California: U.S. Dept. Agriculture rept., 59 p., 2 maps. 

Sykes, Godfrey, 1937a, The Colorado delta: Carnegie 

Inst. Wash. Pub. 460, 193 p. 

---1937b, Delta, estuary, and lower portion of the 

channel of the Colorado River, 1933 to 1935: Carnegie Inst. Wash. Pub. 480, 70 p. 

Tarbet, L. A., 1951, Possible petroleum provinces of 

North America, Imperial Valley: Am. Assoc. Petroleum Geologists Bull., v. 35, p. 260-263. 

Tarbet, L. A., and Homan, W. H., 1944, Stratigraphy 

and micropaleontology of the west side of the Imperial Valley [abs.]: Am. Assoc. Petroleum Geologists Bull., v. 35, p. 1781-1782. 

U.S. Bureau of Reclamation, 1971, Geothermal resource investigations, Imperial Valley, California: 

Status report, 47 p. 

Von Herzen, R. P., 1963, Geothermal heat flow in the 

Gulfs of California and Aden: Science, v. 140, no. 

3572,p. 1207-1208. 

White, D. E., 1965a, Saline waters of sedimentary 

rocks in Fluids in subsurface environments: Am. 

Assoc. Petroleum Geologists Mem. 4, p. 342-366. 

---1965b, Metal contents of some geothermal fluids: 

Symposium, Problems of postmagnetic ore deposition, Prague, Czechoslovakia, v. 2, p. 432-443. 

---1968, Environments of generation of some basemetal ore deposits: Econ. Geology, v. 63, no. 4, p. 

301-335. 

White, D. E., Anderson, E. T., and Grubbs, D. K., 

1963, Geothermal brine well-Mile-deep drill hole 

may tap ore-bearing magmatic water and rocks 

undergoing metamorphism: Science, v. 139, no. 

3558, p. 919-922. 

White, D. E., Hem, J. D., and Waring, G. A., 1963, 

Chemical composition of subsurface waters: U.S. 

Geol. Survey Prof. Paper 440-F, 67 p. 

White, D. E., and Muffler, L. J. P., 1965, Metamorphism of upper Cenozoic sediments to greenschist 

miner assemblages, Salton Sea geothermal area, 

California [abs.]: Geol. Soc. America Spec. Paper 

82, p. 221-222. 

White, D. E., Muffler, L. J. P., and Truesdell, A. H., 

1971, Vapor dominated hydrothermal systems compared with hot-water systems: Econ. Geology, v. 

66, no. 1, p. 75-97. 

Woodard, G. D., 1961, Stratigraphic succession of the 

west Colorado desert, San Diego and Imperial 

Counties, southern California: Geol. Soc. America, 

San Diego, paper presented annual meeting Cordilleran section. 

trU.S. GOVERNMENT PRINTING OFFICE:l972 721-362/406