CONCEPTUAL EVALUATION OF

REGIONAL GROUND-WATER FLOW

IN THE CARBONATE-ROCK PROVINCE

OF THE GREAT BASIN, NEVADA,

UTAH, AND ADJACENT STATES

UTAH

_J

ARIZONA I

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1409-D
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ERRATA

U.S. Geological Survey Professional Paper 1409-D

The original version of this report was published in September 

1991 as a Professional Paper with the same title and number 

(1409-D). In November 1991, an error in the model was 

discovered. As a result, the model was corrected and 

recalibrated. This report, published in 1995, presents the 

revised model.

Conceptual Evaluation of Regional Ground-Water 

Flow in the Carbonate-Rock Province of the 

Great Basin, Nevada, Utah, and Adjacent States

By DAVID E. PRUDIC, JAMES R. HARRILL, and THOMAS J. BURBEY 

REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1409-D

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1995
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director

Any use of trade, product, or firm names in this publication

is for descriptive purposes only and does not constitute endorsement

by the U.S. Government

Library of Congress Cataloging-in-Publication Data

Prudic, David E.

Conceptual evaluation of regional ground-water flow in the carbonate-rock province of the Great Basin, 

Nevada, Utah, and adjacent states / by David E. Prudic, James R. Harrill, and Thomas J. Burbey. Rev.

p. cm. (Regional aquifer system analysis Great Basin, Nevada-Utah) (U.S. Geological Survey 

professional paper ; 1409-D)

Burbey's name appears first on the earlier edition. 

Includes bibliographical references (p. ). 

Supt. of Docs, no.: I 19.16:1409-D

1. Groundwater flow Great Basin. 2. Rock, Carbonate Great Basin. I. Harrill, James R. II. Burbey, 

Thomas J. III. Title. IV. Series. V. Series: U.S. Geological Survey professional paper ; 1409-D. 

GB1197.7.B87 1995

551.49'0979 dc20 95-23686

CIP

For sale by U.S. Geological Survey, Information Services, 

Box 25286, Federal Center, Denver, CO 80225
FOREWORD

THE REGIONAL AQUIFER-SYSTEM ANALYSIS PROGRAM

The Regional Aquifer-System Analysis (RASA) Program was started in 

1978 following a congressional mandate to develop quantitative appraisals of 

the major ground-water systems of the United States. The RASA Program 

represents a systematic effort to study a number of the Nation's most 

important aquifer systems, which in aggregate underlie much of the country 

and which represent an important component of the Nation's total water 

supply. In general, the boundaries of these studies are identified by the 

hydrologic extent of each system and accordingly transcend the political 

subdivisions to which investigations have often arbitrarily been limited in the 

past. The broad objective for each study is to assemble geologic, hydrologic, 

and geochemical information, to analyze and develop an understanding of the 

system, and to develop predictive capabilities that will contribute to the 

effective management of the system. The use of computer simulation is an 

important element of the RASA studies, both to develop an understanding of 

the natural, undisturbed hydrologic system and the changes brought about in 

it by human activities, and to provide a means of predicting the regional 

effects of future pumping or other stresses.

The final interpretive results of the RASA Program are presented in a series 

of U.S. Geological Survey Professional Papers that describe the geology, 

hydrology, and geochemistry of each regional aquifer system. Each study 

within the RASA Program is assigned a single Professional Paper number, 

and where the volume of interpretive material warrants, separate topical 

chapters that consider the principal elements of the investigation may be 

published. The series of RASA interpretive reports begins with Professional 

Paper 1400 and thereafter will continue in numerical sequence as the interpretive products of subsequent studies become available.

Gordon P. Eaton 

Director

CONTENTS

Page

Abstract..................................................................................... Dl

Introduction.............................................................................. 2

Purpose and scope ............................................................. 5

Previous investigations.................................................... 5

Description of the carbonate-rock province................. 7

Physiography................................................................. 7

Climate............................................................................ 7

Surface water................................................................ 9

Acknowledgments .............................................................. 10

Ground water in the carbonate-rock province................. 11

Hydrogeology....................................................................... 11

Occurrence and movement of ground water................ 13

Conceptual evaluation of ground-water flow................... 15

General assumptions ........................................................ 15

Model development............................................................ 17

Application of finite-difference equations .............. 18

Model grid................................................................. 18

Representation as a two-layer system ............... 18

Boundary conditions.................................................... 18

Modeling approach ............................................................ 22

Estimates of recharge....................................................... 26

Initial estimates of transmissivity and leakance ...... 28

Model calibration............................................................... 28

Limits of calibration ......................................................... 38

Simulation results .................................................................. 39

Estimated transmissivities ............................................. 39

Correlation of simulated ground-water flow to

regional geologic features............................................. 43

Distribution of flow into regions ................................... 49

Flow regions ............................................................................. 56

Death Valley region........................................................... 56

Inflow............................................................................... 57

Outflow............................................................................ 58

Description of subregions........................................... 59

Big Smoky subregion ............................................. 59

Clayton subregion................................................... 59

Mesquite subregion ................................................ 61

	Page

Flow region Continued

Death Valley region Continued

Description of subregions Continued

Pahrump-Amargosa subregion ............................ D61

Ground-water flow to Furnace Creek ........... 62

Ground-water flow to Ash Meadows.............. 62

Colorado River region....................................................... 64

Inflow............................................................................... 65

Outflow............................................................................ 65

Description of subregions........................................... 65

Penoyer subregion .................................................. 65

Las Vegas subregion .............................................. 67

Virgin River subregion .......................................... 69

White River subregion........................................... 70

Bonneville region............................................................... 73

Inflow............................................................................... 73

Outflow............................................................................ 76

Description of subregions........................................... 76

Escalante subregion ............................................... 76

Spring-Steptoe subregion ..................................... 78

Ruby subregion........................................................ 79

Clover-Independence subregion .......................... 80

Utah Lake subregion ............................................. 81

Great Salt Lake Desert subregion ..................... 82

Railroad Valley region...................................................... 85

Inflow............................................................................... 85

Outflow............................................................................ 85

Description of ground-water flow ............................ 87

Upper Humboldt River region ........................................ 89

Inflow............................................................................... 89

Outflow............................................................................ 89

Description of subregions........................................... 89

Diamond subregion................................................. 89

Humboldt subregion............................................... 92

Potential uses of model ......................................................... 93

Summary and conclusions .................................................... 93

References cited....................................................................... 97

ILLUSTRATIONS

FIGURE 1. Map showing location and geographic features of study areas for Great Basin Regional Aquifer-System

Analysis (RASA) and carbonate-rock province............................................................................................................

2. Map showing hydrographic areas and location of Nevada Test Site ...........................................................................

3. Graph showing population growth in study area between 1900 and 1990 ................................................................

4. Map showing distribution of average annual precipitation ...........................................................................................

5. Map showing distribution of rivers and lakes in and adjacent to study area for Great Basin Regional

Aquifer-System Analysis....................................................................................................................................................

6. Geologic sections of Precambrian and Paleozoic rocks in carbonate-rock province.................................................

7. Map showing principal source areas for ground-water recharge, areas where ground water is consumed by 

evapotranspiration, and regional springs .....................................................................................................................

8. Map showing distribution of estimated ground-water withdrawals by hydrographic areas for 1975 ................

9. Map showing finite-difference grid network......................................................................................................................

Page

D3

4

5

8

10

12

14

16

19
VI CONTENTS

Page

Figure 10. Diagrams showing simulations of evapotranspiration as a function of water level............................................... D21

11-20. Maps showing:

11. Cells used to simulate spring discharge from lower model layer ......................................................................... 23

12. Wells tapping basin fill for which water-level data are available........................................................................ 24

13. Wells, test holes, and mine shafts tapping consolidated rocks for which water-level data are available.. 25

14. Distribution of recharge assigned to cells in upper model layer, and simulated recharge from rivers

and lakes through general-head boundaries ......................................................................................................... 27

15. Principal rock types assigned to cells in upper model layer, and initial transmissivities used .................. 29

16. Estimated vertical leakance between cells in upper and lower model layers ................................................... 31

17. Simulated evapotranspiration rates in cells in upper model layer, and simulated discharge from

rivers, lakes, and Death Valley through general-head boundaries................................................................. 34

18. Areas where ground water is consumed by evapotranspiration............................................................................ 35

19. Simulated steady-state ground-water levels, upper and lower model layers .................................................... 36

20. Estimated transmissivities, upper and lower model layers.................................................................................... 40

21. Graphs showing frequency distributions of estimated transmissivities for cells in upper model layer on

basis of principal rock type, and for all cells in lower model layer....................................................................... 42

22-25. Maps showing:

22. Relation between selected geologic features and simulated ground-water levels, areas of

evapotranspiration, and location of springs simulated in model..................................................................... 46

23. Distribution of shallow-flow regions delineated in upper model layer in relation to areas where

ground water is consumed by evapotranspiration, simulated water levels in upper model layer,

and outcrops of low-permeability rocks .................................................................................................................. 48

24. Distribution of deep-flow regions and subregions delineated in lower model layer in relation to 

metamorphic core complexes, low-permeability rocks, and magnetic source bodies; and 

generalized directions of deep ground-water flow ............................................................................................... 50

25. Distribution of high transmissivities in lower model layer in relation to springs simulated in

model and to boundary of central corridor of thick carbonate rocks in south-central Nevada ................ 52

26. Schematic diagrams showing conceptualization of ground-water flow from recharge areas in mountains 

to discharge areas on basin floors, same conceptualization of ground-water flow but represented in 

finite-difference computer model, and summary of water budget within area encompassed by a 

deep-flow region on basis of computer-model output................................................................................................. 54

27-35. Maps showing:

27. Distribution of vertical flow between model layers .................................................................................................. 55

28. Areas of assigned recharge, simulated discharge from upper model layer, and simulated discharge

from regional springs in Death Valley region....................................................................................................... 57

29. Simulated direction of ground-water flow for both upper and lower model layers in Death Valley

region ...........................................................................................................................................................................^ 60

30. Areas of assigned recharge, simulated discharge from upper model layer, and simulated discharge

from regional springs in Colorado River region ................................................................................................... 66

31. Simulated direction of ground-water flow for both upper and lower model layers in Colorado River

region ...........................................................................................................................................................................^ 68

32. Areas of assigned recharge, simulated discharge from upper model layer, and simulated discharge

from regional springs in Bonneville region ........................................................................................................... 74

33. Simulated direction of ground-water flow for both upper and lower model layers in Bonneville region ... 77

34. Areas of assigned recharge, simulated discharge from upper model layer, simulated discharge from 

regional springs, and simulated direction of ground-water flow for both upper and lower model 

layers in Railroad Valley region .............................................................................................................................. 86

35. Areas of assigned recharge, simulated discharge from upper model layer, simulated discharge from 

regional springs, and simulated direction of ground-water flow for both upper and lower model 

layers in upper Humboldt River region.................................................................................................................. 90

TABLES

Page

TABLE 1. Estimated discharge of regional springs compared with simulated discharge following model calibration........ D33

2. Selected statistics of estimated transmissivities in both model layers ........................................................................ 42

3. Summary of estimated transmissivities for model cells corresponding to selected rock types in both

model layers................................................................................................................................................................. 43

4-9. Simulated ground-water flow budgets for:

4. Death Valley region .............................................................................................................................................................. 58

5. Colorado River region........................................................................................................................................................... 67

6. Bonneville region................................................................................................................................................................... 75

7. Railroad Valley region.......................................................................................................................................................... 87

8. Upper Humboldt River region............................................................................................................................................ 91

9. Five deep-flow regions of modeled area .......................................................................................................................... 96
CONTENTS

CONVERSION FACTORS AND VERTICAL DATUM

VII

Multiply By To obtain

acre-foot (acre-ft) 0.001233

acre-foot per year (acre-ft/yr) 0.001233

cubic foot per second (ft3/s) 0.02832

foot (ft) 0.3048

foot per mile (ft/mi) 0.1894

gallon per day per foot (gal/d/ft) 0.01242

inch (in.) 25.40

inch per year (in/yr) 25.40

mile (mi) 1.609

foot squared per second (ft2/s) 0.0929

foot squared per day (ft2/d) 0.0929

square mile (mi2) 2.590

cubic hectometer

cubic hectometer per year

cubic meter per second

meter

meter per kilometer

square meter per day

millimeter

millimeter per year

kilometer

meter squared per second

meter squared per day

square kilometer

Temperature: Degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) by

using the formula 

°C = 0.5556 (°F-32).

Sea level: In this report, "sea level" refers to the National Geodetic Vertical Datum 

of 1929 a geodetic datum derived from a general adjustment of the first-order level 

nets of the United States and Canada, formerly called Sea Level Datum of 1929.

REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN 

THE CARBONATE-ROCK PROVINCE OF THE GREAT BASIN, NEVADA,

UTAH, AND ADJACENT STATES

By DAVID E. PRUDIC, JAMES R. HARRILL, and THOMAS J. BURBEY

ABSTRACT

The carbonate-rock province of the Great Basin, mainly 

in eastern Nevada and western Utah, is characterized by thick 

sequences of carbonate rocks of Paleozoic age. These rocks 

overlie clastic and crystalline rocks of Cambrian and Precambrian age, respectively. Since the carbonate rocks were deposited, structural compression and extension, intrusive and 

volcanic episodes, and erosion have greatly modified their distribution and thickness, and a variety of younger rocks and 

deposits have been emplaced within and above them. The most 

notable present-day physiographic features in the area are 

associated with normal faults caused by tensional forces during 

Tertiary time. The faulting has formed the north- to northeast-trending mountain ranges and adjacent sedimentary basins that characterize the terrane. The 100,000-square-mile 

study area, with its abundant carbonate rocks, is referred to 

in this report as the carbonate-rock province of the Great 

Basin.

Regional ground-water flow in the province has been studied as part of the Great Basin Regional Aquifer-System Analysis. The flow system is conceptualized as having (1) a relatively 

shallow component, moving primarily from mountain ranges 

to basin fill beneath adjacent valley floors, which is superimposed upon (2) a deeper component, moving primarily 

through carbonate rocks. A computer model has been developed to simulate and thereby evaluate the regional flow. Two 

model layers are used to simulate the two components. The 

layers are divided into cells with dimensions of 5 miles by 

7.5 miles, elongate in a north-northeastward direction. The 

maximum depth of flow in the province is unknown, but freshwater has been detected at depths as great as 10,000 feet.

The conceptualization and simulation of regional groundwater flow includes several simplifying assumptions: Flow 

through fractures and solution openings in consolidated rocks 

is approximately equivalent to flow through a porous medium; 

Darcy's Law is applicable from a regional perspective; steadystate conditions exist, in which estimates of present-day recharge equal natural discharge prior to ground-water 

withdrawals; transmissivity is heterogeneous over the region 

but is homogeneous and isotropic in each 37.5-square-mile 

model cell; recharge is from precipitation in the mountain 

ranges and percolation from rivers and lakes; and discharge 

is by evapotranspiration, seepage to rivers and lakes, and 

flow from regional springs. Although the assumptions are probably valid for parts of the province, the validity of each assumption is unknown for the province as a whole. Therefore,

the simulation results do not completely replicate actual 

ground-water flow throughout the province; rather, the intent of the simulations is to provide a conceptual evaluation 

of regional ground-water flow.

The model was calibrated by adjusting the transmissivities of cells in both model layers and the vertical leakance of 

cells between layers during repeated simulations. Calibration 

proceeded until simulated water levels and simulated discharge 

as evapotranspiration and regional-spring flow generally agreed 

with available water levels, the mapped distribution and estimated quantity of evapotranspiration, and the estimated flow 

at regional springs. Because of (1) the scarcity of available 

water-level data, particularly for the carbonate-rock aquifers, 

(2) the uncertainty in the extent and thickness of the carbonate-rock aquifers, and (3) the uncertainty in the estimates 

of ground-water recharge and evapotranspiration, other distributions and estimates of transmissivities and vertical 

leakances than those calibrated may also adequately simulate water levels and discharge in the province. Nonetheless, 

several inferences can be made regarding ground-water flow 

in the province from the model results.

Transmissivities in the upper model layer are generally 

greater in cells corresponding to basin fill and carbonate rocks, 

and are less in cells corresponding to other consolidated rocks 

(clastic, metamorphic, igneous, and volcanic). In the lower 

layer, transmissivities are greatest near regional springs and 

in the vicinity of basins where ground-water discharge is considerably more than the estimated recharge from the immediately surrounding drainage area.

Simulated inflow to the modeled area is about 1.5 million acre-feet per year, which is only 3 percent of the estimated total precipitation. This inflow does not include recharge 

that discharges locally (that is, within the same 37.5-squaremile model cell). Most ground-water flow is simulated in the 

upper model layer; it moves from mountainous recharge areas to adjacent valley lowlands where it discharges by evapotranspiration. A total of 45 shallow-flow regions is identified 

on the basis of horizontal flow between model cells.

In the lower layer, simulated flow is 428,000 acre-feet 

per year, or only 28 percent of the total inflow. About half of 

the flow is discharged to regional springs that represent the 

discharge of deep flow through carbonate rocks. Seventeen 

deep-flow subregions are identified on the basis of horizontal 

flow between model cells. These subregions are further grouped 

into five deep-flow regions on the basis of water-level patterns. Simulated flow in the lower layer is generally southward and northward from a large, topographically high area

Dl
D2 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

in east-central Nevada and southwestern Utah. Southward 

flow is toward Death Valley and the Colorado and Virgin Rivers; 

northward flow is toward the Great Salt Lake Desert and 

the upper Humboldt River. However, only small quantities of 

deep flow are simulated as discharge to the Death Valley playa, 

the Colorado and Virgin Rivers, the Humboldt River, and the 

Great Salt Lake Desert. Instead, most of the flow is discharged 

upgradient from these sinks. Within the topographically high 

area of east-central Nevada, some deep ground water flows 

to a land-surface depression in Railroad Valley.

In conclusion, most ground-water flow is relatively shallow, 

moving from recharge areas in the mountain ranges to discharge areas in adjacent valleys. Directions of shallow groundwater flow do not correspond everywhere to directions of deep 

flow. Deep ground-water flow mostly discharges at regional 

springs or in areas of evapotranspiration upgradient from the 

terminal sinks (the Great Salt Lake, the Great Salt Lake 

Desert, the Railroad Valley and Death Valley playas, and the 

Colorado, Virgin, and Humboldt Rivers). Interbasin movement 

of ground water to the larger regional springs is through permeable carbonate rocks in areas where the rocks are thick 

and continuous; elsewhere, consolidated rocks beneath the valleys and surrounding mountains are not highly transmissive, 

suggesting that not all carbonate rocks are highly permeable 

or that not all valleys and surrounding mountains are underlain by carbonate rocks.

INTRODUCTION

Ground-water flow within an area dominated 

by basin-fill and carbonate-rock aquifers was studied as part of the Great Basin Regional AquiferSystem Analysis (RASA). The Great Basin RASA 

project began in 1980 as a component of a national program designed to systematically study 

large aquifer systems that constitute a major part 

of the Nation's water supply (Harrill and others, 

1983, p. 2). Results of the Great Basin RASA 

project, in addition to those described in this report, include detailed studies of ground-water flow 

in selected basins and analyses of regional 

hydrogeology and geochemistry.

The area of the Great Basin RASA project is 

about 140,000 mi2 and includes most of Nevada, 

westernmost Utah, and small parts of California, 

Oregon, Idaho, and Arizona (fig. 1). The project 

area is characterized by northeast-trending mountains and adjoining basins that are partly filled 

with sediments derived from the mountains. 

Ground-water flow in this area is typically from 

recharge areas in and adjacent to the mountains 

to discharge areas in the valley lowlands. Carbonate rocks, deposited in a shallow sea during 

the Paleozoic Era, underlie large areas in the eastern two-thirds of the Great Basin. These rocks 

can be highly permeable where thick sequences 

are present, thereby providing conduits for the

interbasin movement of ground water (Eakin, 1966; 

Mifflin, 1968; Winograd and Thordarson, 1975; 

Gates, 1984, 1987; Dettinger, 1989).

Ground water is pumped primarily from unconsolidated deposits that partly fill each of the 

240 hydrographic areas (Harrill and others, 1983, 

p. 5), most of which are topographically closed 

or nearly closed basins (fig. 2). The hydrographic 

areas usually contain a ground-water reservoir 

in the basin fill and include the drainage area of 

adjacent mountains. These hydrographic areas are 

used by State and local agencies for planning and 

management of water resources.

The general area underlain by carbonate rocks 

is defined in this report as the carbonate-rock 

province of the Great Basin and is bounded on 

the east, south, and north by boundaries of the 

Great Basin RASA project (Harrill and others, 

1983; fig. 1). These boundaries include the Wasatch 

Range and the Colorado Plateau to the east, the 

Snake River drainage divide to the north, and 

the predominantly Precambrian rock exposures in 

the mountains to the south. The southern boundary also includes hydrologic boundaries of the Virgin and Colorado Rivers and Death Valley (fig. 

1). The western boundary is generally the easternmost extent of transitional-assemblage sedimentary rocks of Paleozoic age (Plume and 

Carlton, 1988, fig. 2). The transitional-assemblage 

rocks are composed of limestone, shale, siltstone, 

and quartzite (Stewart, 1980, p. 20). These rocks 

separate coeval carbonate rocks deposited on a 

broad shelf to the east from marine sedimentary 

rocks of shale, chert, and quartzite and volcanic 

rocks deposited in a deep-water basin to the west. 

The province encompasses an area of about 

100,000 mi2 .

As of 1990, population in the province was 

more than 2.3 million (U.S. Bureau of the Census, 1991a, 1991b). Most of these people live along 

the eastern border where perennial streams flow 

from the Wasatch Range into the adjacent valleys, or near other sources of surface water such 

as the Humboldt River and Lake Mead (fig. 1). 

Almost three-quarters of a million people live in 

the Las Vegas metropolitan area, and more than 

a million people live in the vicinity of Salt Lake 

City. Population densities averaged over the land 

area in each county range from 2 to 980 people 

per square mile in Utah and from less than one 

person to 94 people per square mile in Nevada.

Population in the province at the turn of the 

last century was less than 300,000 (fig. 3), and 

most of the people lived in the vicinity of Salt
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE 

120° 115°

D3

35

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000,1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30'. central meridian -114°

EXPLANATION

I I Carbonate-rock province study area Boundary is approximate

 Boundary of Great Basin Regional Aquifer-System Analysis 

(RASA) study area

 Approximate boundary of carbonate-rock province Within 

province, at least 60 percent of measured sections are 

composed of more than 50 percent carbonate rock (from 

Mifflin and Hess, 1979)

=? = = Approximate boundary of Roberts overthrust belt Queried 

where uncertain

Note: Lakes and rivers clashed where ephemeral

FIGURE 1. Location and geographic features of study areas for Great Basin Regiona Aquifer-System Analysis

(RASA) and carbonate-rock province.
D4 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

Lake City where surface-water supplies are plentiful. The number of people living in the province increased slowly until after World War II. 

Since World War II, the population has increased

fivefold. The marked increase in the number of 

people living in Nevada (fig. 3) is largely in the 

Las Vegas area, where the population increased 

from about 16,000 people in 1940 to more than

120° 115°

40°

35°

CALIFORNIA

ARIZONA

100 MILES

100 KILOMETERS

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000, 1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°

EXPLANATION

I I Carbonate-rock province study area Boundary is approximate 

^^| Nevada Test Site

 Boundary of Great Basin Regional Aquifer-System Analysis 

(RASA) study area

 Boundary of hydrographic area or subarea

FIGURE 2. Hydrographic areas and location of Nevada Test Site. Hydrographic-area boundaries from Harrill

and others (1988J.
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D5

770,000 in 1990. As the number of people in the 

province increases and surface-water supplies become less available, additional sources of water 

will be needed. One such source that has been 

proposed (Hess and Mifflin, 1978) is the water 

stored in the carbonate rocks beneath much of 

western Utah and eastern Nevada.

In most other RASA studies, enough information exists for comprehensive model simulations and evaluations of ground-water flow in 

regional aquifer systems. Although numerous wells 

have been drilled within the carbonate-rock province, most have been drilled into unconsolidated 

deposits in the valleys and usually to shallow 

depths, except at the Nevada Test Site. Thus, little 

is known about the deeper and more regional 

ground-water flow in the carbonate rocks. However, because of the greatly increased demand for 

water and because of the potential for contamination of ground water from underground testing of nuclear weapons at the Nevada Test Site 

(fig. 2) and from the possible storage and disposal of nuclear and hazardous wastes, an improved understanding of ground-water flow in the 

province is needed.

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 

YEAR

FIGURE 3. Population growth in study area between 1900 and 

1990. Data from U.S. Bureau of Census (1913, 1921, 1952, 

1983, 1991a, b).

PURPOSE AND SCOPE

The purpose of this report is to present a conceptual evaluation of ground-water flow in the 

carbonate-rock province, mainly in Nevada and 

Utah. The evaluation is based on simulation results using the three-dimensional ground-water 

flow model of McDonald and Harbaugh (1988). 

The basic conceptual model for the province includes relatively shallow flow from recharge areas in the mountains to discharge areas in the 

adjacent valley lowlands, superimposed over 

deeper, more regional flow through carbonate 

rocks. The concept is based on theoretical analyses of regional flow by Freeze and Witherspoon 

(1967, p. 623-634) where, in regions of hummocky 

terrain, numerous relatively shallow flow systems 

are superimposed over fewer deeper flow systems. 

Results of the model analysis include: transmissivity distributions, identification of shallow and 

deep flow systems, and comparisons of simulated 

flow and discharge to estimates presented in previous reports.

The original version of this report was published in January 1991 as a U.S. Geological Survey interim Open-File Report and in September 

1991 as a U.S. Geological Survey Professional 

Paper. In November 1991, an error that resulted 

from an inadvertent coding transposition of the 

cell-dimension variables DELR and DELC 

(McDonald and Harbaugh, 1988, chap. 5, p. 8) 

was discovered. This error produced an unintended 

regional anisotropy in the model transmissivities 

(Stillwater and others, 1992). As a result, the 

model grid cell dimensions have been corrected 

and the model recalibrated. David E. Prudic did 

the recalibration and, along with James R. Harrill, 

has revised the report to reflect changes resulting therefrom. In addition, Donald H. Schaefer 

and James R. Harrill assisted in checking information used in the model.

PREVIOUS INVESTIGATIONS

Surveys of geologic features in the Great Basin began in the late 1860's under the leadership of Clarence King, J.W. Powell, G.K. Gilbert, 

A.R. Morvine, and E.E. Howell. Nolan (1943) summarized available geologic information pertaining to the entire Great Basin. Between 1938 and 

the late 1970's, numerous geologic investigations 

were completed in the Great Basin region. The 

results of all these studies and studies before 1938
D6 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

are summarized on a map of Nevada by Stewart 

and Carlson (1978), a publication about Nevada 

by Stewart (1980), and a map of Utah by Hintze 

(1973). Since 1980, numerous articles have been 

published that pertain generally to metamorphic 

core complexes, geophysics, and geologic structure. 

The hydro geologic framework of the Great Basin 

has been described by Plume (1995) as another 

part of the Great Basin RASA project.

Ground-water investigations within the carbonate-rock province began in the early 1900's. 

Mendenhall (1909, p. 13) suggested that many of 

the desert springs in southern Nevada are not 

dependent on rainfall in the area immediately 

surrounding the springs but that their source is 

from distant mountains. Carpenter (1915, p. 18) 

noted that rocks exposed in the mountains in 

southeastern Nevada generally act to close the 

adjacent valleys by making the sides and bottoms 

of the valleys practically impervious. He did, however, state that several topographically closed valleys higher in altitude than adjacent valleys lose 

water through fissures in the rocks because water levels in the higher valleys are far below land 

surface. Meinzer (1917, p. 150) reported that water 

from a valley near Tonopah, Nev. (fig. 1), leaks 

through a mountain range into an adjacent valley. These are some of the earliest reports that 

suggest the possibility of interbasin flow of ground 

water within the carbonate-rock province.

Few additional ground-water investigations 

were done until after World War II, when several studies of selected basins commenced. These 

studies generally focused on recharge and discharge of ground water in individual basins. In 

the early 1960's, the State of Nevada and the U.S. 

Geological Survey began systematic reconnaissance 

studies of all unstudied basins in Nevada to determine potential ground-water supplies. A similar series of investigations began in Utah in 1964. 

The results of these investigations have been published by the Nevada Department of Conservation and Natural Resources and the Utah 

Department of Natural Resources, and most are 

summarized in Eakin and others (1976). These 

reports provide the basic estimates of recharge 

and discharge used in this report.

Detailed discussion of interbasin flow also 

began in the 1960's. Hunt and Robinson (1960) 

discussed the possibility of interbasin flow into 

the Death Valley (fig. 1) area on the basis of chemical analysis of water samples from springs and 

wells. Loeltz (1960) discussed the source of water issuing from springs at Ash Meadows in the

Amargosa Desert near Death Valley (fig. 1). 

Winograd (1962) discussed interbasin movement 

of ground water at the Nevada Test Site. Winograd

(1963) also summarized ground-water flow between 

Las Vegas Valley and the Amargosa Desert and 

presented evidence for fault compartmentalization 

of the aquifers in the region. Eakin and Moore

(1964) presented information about the uniformity 

of discharge at Muddy River Springs in southeastern Nevada (fig. 1) and related it to interbasin 

movement of ground water. Winograd and Eakin

(1965) and Eakin and Winograd (1965) presented 

evidence and some economic implications of 

interbasin flow of ground water in south-central 

Nevada. Hood and Rush (1965) discussed the possibility of interbasin flow of water to and from 

Snake Valley in western Utah (fig. 1). Eakin (1966) 

presented information that described interbasin 

flow in an area in southeastern Nevada that he 

named the White River area. Shortly afterward, 

Mifflin (1968) delineated ground-water basins for 

all Nevada and concluded that interbasin flow of 

ground water occurs wherever the consolidated 

rocks in the mountains and beneath the valleys 

are permeable or wherever the basins are connected by unconsolidated deposits. The area of 

interbasin flow through permeable consolidated 

rocks is primarily within the carbonate-rock province. Mifflin and Hess (1979) discussed regional 

carbonate flow systems in Nevada. Gates and 

Kruer (1981) discussed regional flow in west-central Utah, and Gates (1984, 1987) discussed regional flow in northwestern Utah and adjacent 

parts of Idaho and Nevada.

The U.S. Geological Survey began a study in 

1981 to evaluate potential hydrogeologic environments for isolation of high-level radioactive waste 

in the Basin and Range physiographic province 

of the southwestern United States. The study includes a much larger area than is described in 

this report. Bedinger and others (1989, 1990) characterized the geology and hydrology of the Death 

Valley region and the Bonneville region; both areas are included in this study.

The most detailed information regarding 

ground-water flow in carbonate rocks is at the 

Nevada Test Site (fig. 2). Detailed studies began 

in 1957 and included the drilling of several deep 

test holes into carbonate rocks beneath the unconsolidated and volcanic deposits in the vicinity of the Test Site during 1962-64. Numerous 

reports have been written about the area. Most 

of the work from 1957-64 is summarized by 

Winograd and Thordarson (1975), which is the
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D 7

most detailed description of ground-water flow 

through carbonate rocks in the province. Some 

of the more recent reports that pertain to groundwater flow near the Test Site include Winograd 

and Pearson (1976), Waddell (1982), Claassen 

(1983), and Waddell and others (1984).

In addition to test wells drilled in the vicinity of the Nevada Test Site, many wells have been 

drilled in the province for other purposes, including 

several into carbonate rocks as part of the U.S. 

Air Force MX missile-siting program in the Great 

Basin. Selected hydrologic data collected for the 

Air Force by the contractor, ERTEC, Inc. (or Earth 

Technology, Inc., formerly FUGRO) are presented 

by Bunch and Harrill (1984). Geochemical studies as a part of the Great Basin RASA project 

and more recent studies of the carbonate-rock aquifers in eastern and southern Nevada provide additional evidence of interbasin flow (Welch and 

Thomas, 1984; Thomas, 1988; Dettinger, 1989; Kirk 

and Campana, 1990). Also, regional ground-water flow in the vicinity of Fish Springs (fig. 1) in 

western Utah was analyzed using a computer 

model as part of the Great Basin RASA project 

(Carlton, 1985).

DESCRIPTION OF THE CARBONATE-ROCK 

PROVINCE

PHYSIOGRAPHY

The carbonate-rock province of the Great Basin 

is characterized by a series of generally north- to northeast-trending mountain ranges composed predominantly of carbonate rocks of Paleozoic age. The 

intervening valleys are partly filled with detritus from 

the mountains. Both the mountain ranges and the 

valleys are generally 5 to 15 mi wide and are typically elongate, commonly 40 to 80 mi long. The mountain ranges rise from 1,000 ft to more than 7,000 ft 

above the adjacent valleys.

Altitudes of valley floors in the southern part 

of the province range from below sea level to 3,000 

ft above sea level. Death Valley (fig. 1) is the 

lowest point in the province, as well as the Nation, and at its lowest point is 282 ft below sea 

level. Altitudes of valley floors in the province 

exceed 6,000 ft in north-central Nevada, whereas 

valley floors in western Utah are between 4,000 

and 5,000 ft. Several of the mountain ranges in 

the province exceed 10,000 ft in altitude. The highest mountains in the southern part are the Spring 

Mountains west of Las Vegas with altitudes exceeding 11,000 ft. The Ruby Mountains in northern Nevada exceed 12,000 ft, but the highest point 

in the province, at 13,063 ft, is Wheeler Peak in 

the Snake Range (fig. 1), which is in Nevada near 

the border with Utah. The Wasatch Range in Utah, 

which has several peaks that exceed 11,000 ft, 

forms the eastern boundary of the study area.

CLIMATE

Climate in the province is highly variable, 

ranging from arid to semiarid on most of the valley 

floors to humid alpine in the higher mountains. 

Average annual precipitation on the valley floors 

ranges from less than 3 in. in the Amargosa Desert 

and Death Valley to about 16 in. in some of the 

higher valleys in north-central Nevada and northern Utah. Average annual precipitation in the 

mountains ranges from about 8 in. in some of 

the lower southern mountains to more than 60 

in. in some parts of the highest mountains. Estimated annual precipitation in the province is 

shown in figure 4. Approximately 54 million acreft of precipitation annually falls in the province. 

The regionally averaged annual precipitation for 

the province is less than 10 in., making it one of 

the drier regions in the United States.

Houghton (1967) reported three sources of 

precipitation in the province: (1) moisture from 

the Pacific Ocean, (2) moisture from the Gulf of 

Mexico, and (3) moisture evaporated within the 

Great Basin. Much of the precipitation falls between October and May from storm fronts that 

begin in the subpolar North Pacific Ocean. Generally, these storm fronts are much less frequent 

in the southern part than in the northern part 

of the province (north of latitude 40°). However, 

unusually heavy quantities of precipitation from 

Pacific storms can fall in the southern part of 

the province (south of latitude 40°) when secondary 

lows develop south of the subpolar fronts and move 

inland.

Houghton (1967) also suggested that precipitation from moisture that moves inland from the 

Gulf of Mexico happens only during the summer, 

when southeasterly winds carry moist tropical air 

into the southern and eastern parts of the province and produce scattered convective showers. 

More recent information (Brenner, 1974) suggests 

that these convective showers are from moisture 

which moves northward from the Gulf of California along the Colorado River and that no precipitation is derived from the Gulf of Mexico. In
D8 REGIONALAQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

118° 117' 112°

Precipitation zones In inches per 

year

Oto4

Boundary of carbonate-rock province 

study area

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000,1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D9

addition, the source of most of the precipitation 

in the southern part of the province is from tropical storms that originate in the Pacific Ocean near 

Central America. These storms generally move out 

to sea but occasionally move inland near northern Mexico and southern California and dissipate 

over Arizona, southern Nevada, and Utah (K.P. 

Smith, University of Arizona, Tucson, oral 

commun., 1986). The storms are most common 

from late August to November but do not necessarily occur every year.

Precipitation from water evaporated over the 

Great Basin is associated with surface cyclones 

(Houghton, 1967, p. 6) that usually develop in 

the spring and fall. The storms are most frequent 

from March until mid-June and gradually shift 

from south to north but generally provide little 

moisture.

Average annual temperature ranges from about 

30°F in some high northern valleys to about 60°F 

in the extreme southern valleys (Eakin and others, 1976, p. 3). Temperatures are subject to large 

daily and seasonal fluctuations. Daily fluctuations 

in most valleys exceed 30°F, and 40°F changes 

are not uncommon. Large variations in temperature are observed within short distances due to 

the topography. Summer temperatures can exceed 

100°F, particularly in the south, where the maximum summer temperatures can reach 120°F. Minimum temperatures can drop below 0°F in the 

northern part of the province.

Average annual humidity ranges from about 

30 to 40 percent over most of the region and is 

about 20 percent in the extreme south. Low humidity, abundant sunshine, and light to moderate winds result in rapid evaporation. Average 

annual lake evaporation ranges from about 40 in. 

in the north to more than 70 in. in the extreme 

south (Kohler and others, 1959, pi. 2).

SURFACE WATER

The Great Salt Lake, in northwestern Utah, 

has the largest area of any body of surface water in the province (fig. 5). The size of the lake

FIGURE 4. Distribution of average annual precipitation. 

Precipitation zones for Nevada from Hardman (1965); zones 

for Utah and Idaho from U.S. Weather Bureau (1963 and 

1965, respectively); zones for California from Rantz (1972). 

Precipitation zones near Death Valley and Amargosa Desert 

modified from those of Winograd and Thordarson (1975, 

p. 8).

varies considerably depending on the altitude of 

the water surface in the lake, which has fluctuated about 20 ft during 1847-1982 (Arnow, 1984, 

p. 1). The average size of the lake during this 

period has been 1,700 mi2 , and the average lake 

volume has been 16 million acre-ft. The lake is 

unique in North America in that it is considerably saltier than the oceans.

Most of the water that enters the Great Salt 

Lake is surface runoff that originates as precipitation in the nearby Wasatch Range. The major 

rivers that feed the lake are the Bear, Weber, and 

Jordan. Surface inflow to the lake averaged 1.9 

million acre-ft/yr during 1931-76, whereas groundwater inflow is estimated at 75,000 acre-ft/yr 

(Arnow, 1984, p. 15, 16).

Lake Mead borders the south end of the province and was formed after Hoover Dam was built 

on the Colorado River near Las Vegas in the 1930's. 

The lake supplies water to parts of Nevada, California, and Arizona. Tributary streams that discharge into Lake Mead, and that begin within or 

border the province, include (1) the Virgin River, 

which borders the southeastern edge of the province, (2) the Muddy River, which begins at the 

Muddy River Springs about 50 mi northwest of 

Lake Mead, and (3) Las Vegas Wash, which discharges 

water from Las Vegas Valley (fig. 5).

In addition to the rivers and streams that 

drain into the Great Salt Lake and Lake Mead, 

a few other river systems either begin within the 

province or enter it from bordering mountains and 

discharge into terminal sinks. The Sevier River 

drains several high-altitude basins along the western margin of the Colorado Plateau and discharges 

into ephemeral Sevier Lake (fig. 5). Its average 

annual flow near where the river enters the province is about 190,000 acre-ft for a 73-year period, 1913-85 (ReMillard and others, 1986, p. 320). 

The Humboldt River begins in northeastern Nevada, flows westward, and exits the province near 

Palisade (fig. 5) on its way to the Humboldt and 

Carson Sinks. The average annual flow near Palisade is about 290,000 acre-ft for a 77-year period, 1902-06 and 1911-84 (Frisbie and others, 

1985, p. 134). The Amargosa River, which is 

ephemeral over most of its course, begins in southwestern Nevada (fig. 5) and flows south, west, 

and then north on its way to Death Valley, which 

is the terminus for both surface- and ground-water flow in southwestern Nevada and southeastern California.

Streams are considerably less common within 

the interior of the province, however, than over
DIG REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

the rest of the Great Basin (fig. 5), suggesting 

that the carbonate rocks exposed in the mountains allow for more recharge into and through 

the mountain blocks than do other types of rocks.

ACKNOWLEDGMENTS

We give special thanks to Catherine KraegerRovey of Water & Environmental Systems Tech1200 115°

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000,1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°

EXPLANATION

I I Carbonate-rock province study area Boundary is approximate

 Boundary of Great Basin Regional Aquifer-System Analysis 

(RASA) study area

Note: Lakes and rivers dashed where ephemeral

FIGURE 5. Distribution of rivers and lakes in and adjacent to study area for Great Basin Regional AquiferSystem Analysis.
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D11

nology, Inc., Denver, Colo., who discovered the 

model-grid coding transposition discussed in the 

section "Purpose and Scope." Within the U.S. Geological Survey, we are grateful to Russell W. Plume, 

who, along with Michael D. Dettinger, helped define the regional geologic features that may affect ground-water flow in the province.

GROUND WATER IN THE CARBONATEROCK PROVINCE

A detailed discussion of the hydrogeology in 

the Great Basin, which includes the study area, 

is presented in a companion report by Plume 

(1995). A brief description of the rocks in the province and their water-transmitting properties is 

presented in the following section and provides 

a basis for understanding the occurrence and 

movement of ground water within the carbonaterock province.

HYDROGEOLOGY

The geologic features of the province are complex and involve rocks that range in age from 

Precambrian to Holocene. Its history includes 

major episodes of sedimentation, volcanic activity, and tectonic deformation by both compressional 

and extensional forces.

The oldest exposed rocks are Precambrian in 

age and consist mostly of gneiss, schist, and granite. The province is part of an area in which marine sediments accumulated in a shallow sea near 

the margin of western North America (referred 

to as the miogeosynclinal belt of the Cordilleran 

geosyncline) from late Precambrian time through 

the Paleozoic Era and into the early Mesozoic Era. 

During that period, more than 30,000 ft of marine sedimentary rocks accumulated in parts of 

the province. These rocks include sequences of 

clastic rocks that are mostly sandstone, quartzite, and shale, and carbonate rocks that are mostly 

limestone and dolomite. Rocks of late Precambrian 

to Middle Cambrian age are dominantly clastic, 

and those of Middle Cambrian to early Mesozoic 

age are dominantly carbonates. The thickness of 

carbonate rocks varies within the province. The 

general distribution of clastic and carbonate rocks 

from late Precambrian to early Mesozoic age are 

shown in two geologic sections through the middle 

of the province (fig. 6).

Beginning in Mesozoic time, the environment 

of deposition of the rocks changed from marine 

to continental. Rocks of this period include (1) 

shale, sandstone, and conglomerate and lesser 

quantities of freshwater limestone and evaporite 

that range in age from Middle Triassic to middle 

or late Tertiary; (2) volcanic rocks of middle Tertiary to Quaternary age that range in composition from basalt to rhyolite; (3) intrusive rocks 

of Jurassic to Tertiary age that are predominantly 

granodiorite and quartz monzonite; and (4) since 

about middle Miocene time, clastic deposits, referred to as basin fill, that consist of unsorted to 

well-sorted clay, silt, sand, gravel, and boulders.

Geologic structure in the province is complex. 

Thrust faulting during the Paleozoic and Mesozoic Eras superimposed older rocks on top of 

younger rocks. Extensional (normal) faulting since 

about middle Miocene time formed the north- to 

northeast-trending mountains and basins that are 

characteristic of the entire Great Basin. Strikeslip faults found in parts of the Great Basin add 

to the structural complexity of the region and probably are directly associated with compressive and 

extensional events. Wernicke and others (1984) 

suggest that the strike-slip faults are mostly related to extension. Estimates of their age range 

from Early Jurassic to late Tertiary (Stewart, 1980, 

p. 86). Two major sets of strike-slip faults are 

present in the province: right-lateral faults in 

southwestern Nevada and southeastern California that form a zone referred to as the Walker 

belt (Stewart, 1980, p. 86), and left-lateral faults 

in southern and southeastern Nevada (Stewart 

and Carlson, 1978).

Isolated complexes of metamorphic rocks of 

possible Mesozoic age (termed metamorphic core 

complexes by Coney, 1980) have been identified 

at four locations in the province: the Ruby Mountains just south of Elko, the Snake Range east 

of Ely, the Deep Creek Range north of the Snake 

Range, and the Grouse Creek Mountains in northwestern Utah at the northern boundary of the 

Great Basin with the Snake River drainage (fig. 

1). The complexes generally consist of a mobile 

metamorphic-plutonic basement terrane, overlain 

by unmetamorphosed rocks that are deformed by 

low-angle extensional faults. The two zones are 

separated by a decollement, which is a surface 

of dislocation (Coney, 1980, p. 15). Such complexes 

probably act as barriers to deep ground-water flow.

The depositional thickness and lithology of the 

Paleozoic sedimentary rocks are notable in their
D12 REGIONALAQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

1 2345

New Pass Simpson Sulphur Butte

Range Park Spring Eureka Mountains

Range Range

Permian

Pennsylvanian

Mississippian

100 MILES

_I

0 100 KILOMETERS 

Vertical exaggeration x35

FEET METERS 

0-rO

L 5,000

B

Toiyabe 

Range

8 9 10 11 12

Dugway Sheeprock East Long

Range Mountains Tintic Range Provo

Ordovician

Upper and Middle 

Cambrian

Lower Cambrian and 

Precambrian

EXPLANATION

Conglomerate

Quartzite or sandstone

Siltstone or shale

Limestone

Silty or clayey limestone

Dolomite

Shale

Metamorphic rocks

Geologic contact Dashed where 

approximately located. Dotted 

where unconformity exists
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D13

homogeneity over large areas in the province. Since 

deposition, however, compression, extension, intrusive and volcanic episodes, and erosion have 

greatly modified their distribution and thickness. 

The actual thickness and distribution of the various rock types at depth are not well known because the region is structurally complex and 

because granitic rocks are more extensive at depth 

than indicated by outcrops. The existence of intrusive and other crystalline rocks in the subsurface may act as barriers to regional 

ground-water flow. The distribution of these rocks 

in the carbonate-rock province was estimated from 

aeromagnetic anomalies by Plume (1989, 1995).

Near the south end of the province a large 

gravity gradient exists (Hildenbrand and Kucks, 

1982; Saltus, 1984), which suggests that either 

the depth to Precambrian basement is much less 

or the rocks are more dense than in surrounding 

areas. This gradient is referred to as the transverse crustal boundary (Eaton, 1975; Eaton and 

others, 1978). The possible effects of major structures and changes in rock types on ground-water 

flow within the province are discussed in detail 

in the section "Correlation of Simulated GroundWater Flow to Regional Geologic Features."

OCCURRENCE AND MOVEMENT OF GROUND 

WATER

Ground water is present in all the rock types 

in the province. Basin-fill aquifers are the primary ground-water reservoirs. Most of the water 

pumped from wells is from these aquifers. Carbonate-rock aquifers that underlie much of the 

study area are also significant ground-water reservoirs, particularly where the rocks are fractured 

or where openings have been enlarged by dissolution. Most of the larger springs in the area issue from carbonate rocks or from basin fill 

overlying or adjacent to carbonate rocks. The other 

types of consolidated rocks and the fine-grained 

basin fill generally transmit only small quantities of water and act as barriers to ground-water 

flow. However, there are some exceptions to this 

generalization. Some volcanic rocks, namely

FIGURE 6. Geologic sections of Precambrian and Paleozoic rocks 

in carbonate-rock province (from Stewart, 1980, figs. 10 

and 25). A, Northern section of Mississippian through 

Permian rocks. B, Southern section of Precambrian through 

Devonian rocks.

basalts and welded tuffs, can yield significant 

quantities of water to wells where the rocks are 

fractured over relatively large areas. Winograd 

(1971) presents evidence that the welded tuffs are 

aquifers in the vicinity of the Nevada Test Site 

and in parts of Idaho. The welded tuffs are not 

as extensive as the basin fill or the carbonate 

rocks but where present could allow for the 

interbasin movement of ground water. The Precambrian and Lower Cambrian clastic, metamorphic, and granitic rocks beneath the carbonate 

rocks are relatively impermeable and probably 

provide a lower limit to ground-water circulation. 

The source of ground water in the province is 

precipitation that falls directly onto the province 

or in adjacent areas whose surface waters drain 

into the province (for example, the Sevier River 

in Utah, fig. 5). Most of the precipitation is lost 

by evaporation or transpired by plants. Eakin and 

others (1976, p. 6) estimated that only about 5 

percent of the total precipitation in the Great 

Basin becomes ground-water recharge. Much of 

the recharge is from winter and spring storms 

that produce heavy snows in the mountains; during 

spring melt, the water seeps into permeable bedrock or flows off to adjacent valleys where some of 

the water seeps into the basin fill. Areas estimated 

to recharge ground water are shown in figure 7.

Much of the ground water in the carbonaterock province is discharged by evapotranspiration 

(a combination of direct evaporation and transpiration by plants) on the valley floors where the 

ground water is near land surface. Figure 7 shows 

areas in the province where ground water is consumed by evapotranspiration. In addition to evapotranspiration, ground water is discharged by 

numerous springs. Usually, this water seeps back 

into the ground, is consumed by evapotranspiration, or flows to a river that ends in a terminal 

sink or leaves the study area. Many small springs 

are present in the mountains. These springs typically represent perched local systems that are not 

connected to surrounding and underlying ground 

water. Numerous small springs are also present 

in the valleys. These springs represent shallow 

ground-water flow through basin fill that originates in the adjacent mountains or associated alluvial fans. Large springs that issue from 

carbonate rocks or from basin fill overlying carbonate rocks are present in several of the valleys. 

These springs discharge ground water that has 

moved through the regional flow systems in the 

carbonate-rock aquifers from distant source areas.
D14 REGIONALAQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

118° 116° 115 113°

I I Principal source area for ground-water 

recharge

^^| Area where ground water is consumed by 

evapotranspiration Approximately 

located

Boundary of carbonate-rock province 

study area

 Regional spring or spring area

35° 

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000,1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D15

Mifflin (1968) classified springs in Nevada as 

local, intermediate, and regional on the basis of 

water chemistry, water temperature, and fluctuation of flow from the springs. Regional springs 

presumably represent the discharge of deep flow 

through carbonate rocks. Locations of the regional 

springs, as delineated by Thomas and others (1986) 

using similar criteria, are shown in figure 7. The 

largest concentration of regional springs is in a 

small area at Muddy River Springs. The flow of 

these springs totals about 36,000 acre-ft/yr (Eakin 

and Moore, 1964).

Most ground-water withdrawals in the province are from wells drilled into the basin fill beneath the valley floors because (1) people settled 

in the valleys where the climate is less severe 

than the mountains and where the land is more 

suitable for agriculture, (2) ground water in many 

of the valleys is generally within a few feet to 

several tens of feet below land surface in contrast to generally deeper water levels in mountain areas, and (3) the basin fill generally yields 

large quantities of water to wells. Eakin and others 

(1976, p. 15) reported yields as much as 8,600 

gallons per minute from large-capacity wells in 

north-central Utah.

Prior to World War II, most of the groundwater withdrawals were from flowing wells drilled 

into basin fill. Areas of flowing wells were concentrated largely along the eastern side of the 

province in valleys adjacent to the Wasatch Range, 

although several other valleys, including Las Vegas Valley, also had flowing wells. Ground-water 

withdrawals were generally small and constant 

until after World War II, when more efficient 

pumps and inexpensive energy greatly increased 

the quantity of ground water withdrawn to irrigate crops and to supply a rapidly increasing population. The total quantity of ground water 

withdrawn in the province during 1975 was approximately 1 million acre-ft. Major areas of 

ground-water withdrawals during 1975 are shown 

in figure 8.

FIGURE 7. Principal source areas for ground-water recharge, 

areas where ground water is consumed by evapotranspiration, and regional springs (discharge exceeds 100 gallons per minute; water chemistry indicates long flow time, 

mostly within carbonate rocks). Recharge and evapotranspiration areas from Mifflin (1988, pi. 3); spring locations 

and criteria from Thomas and others (1986, pi. 2).

CONCEPTUAL EVALUATION OF 

GROUND-WATER FLOW

Computer models are tools that can be used 

effectively to help understand complex groundwater flow systems. However, rarely are computer 

models used to simulate ground-water flow over 

such a large and geologically complex area as the 

carbonate-rock province. Endless arguments could 

be invoked as to the validity of the assumptions 

and hydrologic values used in simulating groundwater flow within the carbonate-rock province. For 

this reason, it must be stressed that the computer simulation discussed in this report is conceptual in nature. Only broad concepts and 

large-scale features can be inferred from the results of this study. Although a fairly detailed analysis of ground-water flow will be discussed, it does 

not intend to indicate that the study results presented here are adequate; in fact, the objective 

in presenting a detailed analysis of ground-water flow is to examine the possibility of the relatively shallow flow regions being interconnected 

by deep flow through carbonate rocks, and how 

regional geologic features might affect the direction of flow and water levels.

GENERAL ASSUMPTIONS

In the carbonate-rock province, ground-water 

flow takes place through the pores of basin-fill 

sedimentary deposits and through the fractures 

and solution openings of consolidated rocks. On 

a regional scale, flow through fractures and solution openings in the consolidated rocks is assumed to be the same as flow through a porous 

medium; that is, it was assumed that Darcy's Law 

is applicable. This assumption may be reasonable 

because the model grid used to simulate regional 

flow results in the averaging of hydraulic properties over 37.5-mi2 areas. However, not enough 

information is available for the study area to substantiate the assumption.

Model simulations assume steady-state conditions prior to development, in which estimates 

of current recharge (1950-80) equal estimates of 

natural discharge prior to ground-water development. That is, the model does not include groundwater withdrawals. Whether current recharge 

equals natural discharge is unknown. During the 

late Wisconsin glaciation (from about 20,000 to 

10,000 years ago), ground-water flow in the prov-
DIG REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

118° 117° 116° 115' 114° 113° 112°

Estimated ground-water withdrawals 

for 1975 In acre-feet

Less than 1,000 

1,000 to 5,000 

5,000 to 20,000 

20,000 to 80,000 

Greater than 80,000

Boundary of carbonate-rock province 

study area

Boundary of hydrographic area or 

subarea

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000,1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D17

ince may have been more than that of the present 

day because the climate was significantly wetter, with numerous lakes in the closed basins 

(Hubbs and Miller, 1948). Ground-water levels and 

spring discharge may not be in equilibrium with 

the present-day recharge because of the long distances between areas of recharge and discharge. 

That is, the water levels and spring flows may 

still be declining in response to the drier climate 

of today relative to that of 10,000-20,000 years 

ago.

Evidence of a long-term water-table decline 

at Ash Meadows, in the southern part of the province near Death Valley (fig. 1), is presented by 

Winograd and Szabo (1986). They estimated a slow 

rate of decline 0.07 to 0.26 ft per 1,000 years. 

This range of rates is based on (1) uraniumdisequilibrium dating of calcitic veins as much 

as 160 ft (reported as 50 meters) higher than the 

highest present-day water level at Ash Meadows 

and as much as 8.7 mi (reported as 14 kilometers) up the hydraulic gradient, and (2) the assumption that the rate of decline has been constant 

for the past 510,000 to 750,000 years. The calcitic veins are associated with other features indicative of paleo-ground-water discharge. Further 

evidence for a slow rate of water-table decline 

near Ash Meadows is presented by Jones (1982) 

in which he reports the water table beneath an 

alluvial fan at the Nevada Test Site has been 

within 160 ft (reported as 50 meters) of the present 

level through most of Quaternary time. In contrast, the water table in some of the northern 

valleys and, in particular, the Great Salt Lake 

Desert must have declined at least several hundred feet over the past 10,000-20,000 years as 

ancestral Lake Bonneville shrank to the present 

level of the Great Salt Lake.

The assumption of steady-state conditions cannot be validated. However, the lack of long-term 

trends in measured water levels in basin fill (in 

areas not influenced by pumping) suggests that 

a dynamic equilibrium or steady state exists (at 

least prior to pumping) in many of the basins. 

Because estimates of hydraulic properties and the 

length of flow through the consolidated rocks are 

generally unknown, deeper flow through carbonFIGURE 8. Distribution of estimated ground-water withdrawals 

by hydrographic areas for 1975. Hydrographic areas from 

Harrill and others (1988); estimates of ground-water withdrawals for Utah from Sumison and others (1976); estimates for Nevada from Bedinger and others (1984).

ate aquifers may not be in equilibrium throughout the province. If deeper flow is not in equilibrium, then present-day discharge may be 

responding to residual water levels related to recharge from previous wet periods, such as the last 

glacial epoch, and the analysis of flow presented 

herein may not represent actual flow everywhere.

Transmissivity in the province is assumed 

heterogeneous because horizontal hydraulic conductivities can change abruptly as a result of 

changes in lithology. Heterogeneity is simulated 

by varying the transmissivity among the model 

cells. Transmissivity within a model cell, however, 

is assumed homogeneous and isotropic, and is assumed to represent an average for the cell. Abrupt 

changes in transmissivities within a model cell 

are not simulated in the model. Consequently, the 

model is designed to simulate flow across regional 

changes in transmissivity.

The assumption of isotropy within a model 

cell is reasonable for cells corresponding to basin fill, but may be unreasonable for cells corresponding to consolidated rocks. Where flow is 

through fractures, the fractures may have a preferred orientation that could produce a greater 

transmissivity in one direction. However, anisotropic conditions may not be the same throughout the province because the orientation of 

fractures in consolidated i _>cks is not the same 

everywhere. Even though some types of consolidated rock may be anisotropic, there is no compelling reason to assume a regional anistropy for 

the entire modeled area, and the model is not 

capable of simulating anistropy in individual cells. 

Furthermore, data is lacking to calibrate a model 

whereby every cell corresponding to consolidated 

rocks could have a greater value of transmissivity in one direction.

MODEL DEVELOPMENT

A three-dimensional finite-difference groundwater flow model developed by McDonald and 

Harbaugh (1988) was used for the computer simulations. The model uses the basic partial differential equation for ground-water flow in an 

anisotropic, heterogeneous porous medium with 

a constant water density:
D18 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

where Kxx, Kyy, Kzz = hydraulic conductivity along x, 

y, and z coordinate axes (units 

of length per time); 

h = hydraulic head, referred to as 

simulated water level in this 

report (units of length); 

W= volumetric flux per unit volume representing sources and 

(or) sinks (units of per time); 

Ss = specific storage of the medium

(units of per length); and 

t = time.

For simulation of steady-state (equilibrium) 

conditions that do not include changes in simulated water level with respect to time, the right 

side of the equation is equal to zero and estimates of specific storage are not needed. This is 

the case for simulations used to conceptualize 

ground-water flow in the carbonate-rock province.

APPLICATION OF FINITE-DIFFERENCE EQUATIONS

The partial differential equation for groundwater flow can be closely approximated by finitedifference equations, which are sets of algebraic 

expressions that are solved simultaneously by using, in this model, the strongly implicit procedure (McDonald and Harbaugh, 1988, chap. 12). 

The solution of this algorithm involves designing 

a three-dimensional grid system in which each 

model cell within the grid exhibits specific hydrologic properties that best approximate the 

physical setting of that area. The model solves 

for unknown water level at the center of each 

cell (called a node) by iterating through the finite-difference equations until the simulated water-level change between the previous iteration 

and the current iteration is less than a specified 

quantity for all nodes. The original model used a 

closure criterion of 5 ft; the value was reduced 

to 0.1 ft during the recalibration process. This 

closure criterion resulted in computed mass-balance errors of less than 0.05 percent. In addition 

to the closure criterion, the acceleration parameter (a value that increases or decreases the simulated water-level change at each iteration) was 

adjusted and a value of 0.8 chosen, following repeated trial simulations.

MODEL GRID

The grid system used to simulate ground-water 

flow in the province contains 60 columns, 61 rows,

and two layers (fig. 9). The grid, oriented parallel to the generally north-northeastward trend of 

the fault-block mountains and adjacent valleys 

in the province, has rectangular cells of uniform 

dimension. The width of each cell is 5 mi along 

the row direction (perpendicular to the fault-block 

mountains), and the length is 7.5 mi along the 

column direction (parallel to the fault-block mountains). The length of each cell is greater than its 

width because the mountain ranges and valleys 

are typically longer than they are wide. The dimensions chosen for the grid are large enough to 

minimize the number of cells in the model, yet 

small enough to simulate the variation in topography and physiography characteristic of the province. Cells in the grid that are outside the 

carbonate-rock province are not used in the model 

simulation; each layer contains 2,456 active cells.

REPRESENTATION AS A TWO-LAYER SYSTEM

Commonly, different model layers are used to 

simulate different hydrogeologic units on the basis of permeability contrasts between units. However, due to the complexity of the geologic 

structures in the province, the uncertainty in the 

thickness of the hydrogeologic units, and the lack 

of data, the province is simply divided into two 

layers. The upper model layer is used to simulate relatively shallow flow primarily through basin 

fill and adjacent mountain ranges to depths of a 

few thousand feet. The lower model layer is used 

to simulate deep flow through consolidated rocks 

beneath the basin fill and mountain ranges. The 

actual depth to the base of deep flow is unknown, 

but marine sedimentary rocks containing thick 

sequences of carbonate rocks may be more than 

30,000 ft thick (Stewart, 1980), and freshwater 

has been identified from oil-exploratory wells in 

Railroad Valley to depths as great as 10,000 ft 

(Van Denburgh and Rush, 1974, p. 31). Calculated depths of ground-water flow in the province range from about 3,700 to 10,000 ft, on the 

basis of temperatures and silica concentrations 

of water collected from selected wells and springs 

(Carlton, 1985, p. 34-37; Thomas and others, 1990, 

p. 56). A maximum depth for the lower model layer 

may be, therefore, about 10,000 ft.

BOUNDARY CONDITIONS

In general, the model boundaries of the carbonate-rock province extend to mountain ranges
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D19

118°

42°

38° 

37° 

115' 114° 113'

 i _L x - ^ 5

EXPLANATION

| | | Active model cells

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000, 1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°

General-head boundary cells in upper 

model layer

Boundary of carbonate-rock province 

model Model grid superimposed 

over carbonate-rock province study 

area (shown in white)

FIGURE 9. Finite-difference grid network.
D20 REGIONALAQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

consisting mostly of low-permeability consolidated 

rocks, which are assumed to be no-flow boundaries. Carbonate rocks may extend northward beneath the basalts of southern Idaho. The 

topographic divide between the Snake River drainage area in southern Idaho and the Great Basin 

is assumed to act as a divide not only for nearsurface ground-water flow but also for deep flow. 

Ground-water flow to the north of the Great Salt 

Lake is not simulated in the model because the 

lake is used as a hydrologic boundary for groundwater flow in the model. The Great Salt Lake 

occupies a low area with no surface outflow, and 

it presumably is a sink for ground-water flow in 

the northern part of the province. Carbonate rocks 

may also extend westward from where the rocks 

are exposed in the mountains. The western boundary of the modeled area is along mountain ranges 

in which the Paleozoic strata consist mostly of 

transitional-assemblage sedimentary rocks (Plume 

and Carlton, 1988, fig. 2). Although small quantities of ground water may flow across these mountain ranges, the western boundary is simulated 

as a no-flow boundary. A no-flow boundary is also 

simulated beneath the lower model layer. The 

boundary represents the depth below which there 

is little ground-water flow. The depth of the noflow boundary beneath the lower layer is unknown 

because the depth below which flow ceases is generally unknown. Presumably, ground water does 

not flow through the underlying Precambrian and 

Lower Cambrian rocks.

Hydrologic boundaries are also used in three 

other places along the edge of the modeled area: 

Utah Lake, the Virgin River and Lake Mead, and 

Death Valley (see figs. 5 and 9). These hydrologic boundaries are simulated as head-dependent 

flow boundaries to the upper model layer, using 

the general-head package of McDonald and 

Harbaugh (1988, chap. 11). Flow across the headdependent flow boundaries is computed by multiplying the water-level difference across the 

boundary with a hydraulic conductance term. The 

water-level difference is determined by comparing a specified head assigned to the boundary with 

a simulated water level in the upper layer cell. 

The hydraulic conductance term is the hydraulic 

conductivity times the cross-sectional area of the 

boundary through which flow is simulated divided 

by the length of the flow path.

The head-dependent flow boundary allows flow 

either to or from the model cell depending on 

whether the simulated water level in the cell is 

less than or greater than the specified head. The

boundary is applied above the upper model layer, 

thus the conductance term used for each model 

cell is in the vertical direction. An initial estimate of vertical conductance was determined for 

each cell by multiplying an approximate vertical 

hydraulic conductivity with the planimetric area 

of the model cell and then dividing by an estimate of the vertical flow-path length. The length 

of the flow path is assumed to be half the estimated thickness of the basin fill, which probably 

represents the average value of the flow length. 

The conductance terms were adjusted during model 

calibration.

The same type of boundary is used to simulate the interaction of ground-water flow with the 

Sevier and Humboldt Rivers and selected tributaries to the Humboldt River, where rivers flow 

into or out of the modeled area (see figs. 5 and 

9). The area used to compute the conductance term 

for each model cell is the area of the river within 

the cell.

Specified heads for the head-dependent flow 

boundaries were estimated by overlying the model 

grid onto U.S. Geological Survey l:250,000-scale 

topographic maps corresponding to the modeled 

area. Specified heads for lakes are based on values listed on the maps, specified heads for dry 

lakes are based on the land-surface altitudes of 

the dry lakes, and specified heads for rivers were 

estimated by approximating the average stream 

altitude for each reach corresponding to a model 

cell. Specified heads for the Humboldt River range 

from 4,650 ft (cell: row 14, column 9) to 5,500 ft 

above sea level (cell: row 7, column 21). Specified heads of 4,200 ft and 4,475 ft were assigned 

to cells corresponding to the Great Salt Lake and 

Utah Lake, respectively. A specified head of 4,519 

ft was assigned to Sevier Lake, and specified heads 

for the Sevier River range from 4,525 ft (cell: row 

24, column 49) to 5,100 ft (cell: row 22, column 

60). Specified heads for the Virgin River range 

from 1,400 ft (cell: row 48, column 41) to 1,650 

ft (cell: row 45, column 45). Specified heads for 

Lake Mead range from 1,200 ft near the dam (cell: 

row 53, column 37) to 1,205 ft near the 

confluence with the Virgin River (cell: row 49, 

column 41). A specified head of 800 ft above 

sea level was assigned to the Colorado River 

below the dam (cell: row 54, column 38). Specified heads for Death Valley range from 270 ft 

below sea level in the central part (cell: row 

54, column 14) to 10 ft above sea level at the 

north and south ends (cells: row 50, column 10, 

and row 58, column 18).
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D21

Recharge to the model is simulated as a constant flux to the upper model layer in cells that 

correspond to mountain ranges. Recharge is not 

simulated in model cells that correspond to valleys, because much of that recharge does not infiltrate into the deep part of the aquifer system. 

Recharge in the valley is assumed to discharge 

within the same general area, either as evapotranspiration or as flow to small springs.

Evapotranspiration is the principal mode of 

ground-water discharge in the study area. This 

discharge is simulated as a head-dependent flow 

boundary in the upper model layer using the 

evapotranspiration package of McDonald and 

Harbaugh (1988, chap. 10). The simulation is based 

on a discontinuous function related to land surface (fig. 10A). Information required includes the 

land-surface altitude of each model cell, the evapo01

o

01

01

tr 01

I

Land surface

Maximum 

RET

Slope = Maximum RET 

Extinction depth

Extinction depth

B

Land surface

Slope = RET at land surface 

Extinction depth

_Extjnctjpn_de2th

EVAPOTRANSPIRATION RATE

FIGURE 10. Simulations of evapotranspiration as a 

function of water level in a model cell, where 

RET is evapotranspiration rate. A, Discontinuous function given by McDonald and Harbaugh 

(1988, chap. 10). B, Modified function used herein 

to reduce numerical oscillation (see text section 

titled "Boundary Conditions").

transpiration rate at land surface, and the depth 

below land surface where evapotranspiration 

ceases (extinction depth).

The equation used to simulate evapotranspiration was modified because numerical oscillations 

developed in some cells during initial simulations 

as a result of the discontinuous function at land 

surface. To alleviate the oscillations, the equation was changed so evapotranspiration rates continued to increase even when the simulated water 

level in a cell was above land surface (fig. 1(XB). 

Although this reduced the numerical oscillations 

in the model, the simulated water level in cells 

with evapotranspiration were compared with land 

surface following each simulation to determine if 

the water level in a cell exceeded land surface 

and produced an unrealistic discharge. Where it 

did, transmissivities and vertical leakances were 

changed to lower the simulated water level.

Land-surface altitude, evapotranspiration rate 

at land surface, and extinction depth are specified for all active cells in the upper layer. A uniform extinction depth of 20 ft is assumed. 

Evapotranspiration rates at land surface vary from 

42 in. in the northern part of the study area to 

72 in. in the extreme southern part, and generally follow the distribution of annual lake-evaporation rates for the period 1946-55 presented by 

Kohler and others (1959, pi. 2). A lower rate of 

12 to 25 in/yr is assumed in the Great Salt Lake 

Desert because, in areas where ground water has 

a high salinity, the rate of evaporation and transpiration is less (van Hylckama, 1974, p. 28). Landsurface altitude for all model cells was determined 

from digital elevation data obtained from the National Geophysical Data Center (National Oceanic 

and Atmospheric Administration, Boulder, Colo.). 

These data represent a regular sampling of landsurface altitudes at an interval of 1 minute in 

geographic coordinates. This corresponds to a spacing between values of about 4,800 ft in an eastwest direction and about 6,000 ft in a north-south 

direction. Approximately 35 altitude values were 

used to compute the average land-surface altitude of each model cell.

Only a few of the numerous springs discharging in the study area are specifically simulated 

by discharge cells in the model. Most small springs 

in the study area are assumed to be discharging 

from the upper model layer. This springflow is 

included in the simulated evapotranspiration. All 

large springs, and several smaller springs listed 

by Thomas and others (1986, pi. 2), are herein 

termed "regional springs." The flow of these
D22 REGIONALAQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

springs is simulated as discharge from the lower 

model layer, and therefore is not a component of 

simulated evapotranspiration from the upper layer. 

Model cells corresponding to springs or a group 

of springs simulated as discharging from the lower 

layer are shown in figure 11. In Death Valley, 

spring flow from Texas, Nevares, and Travertine 

Springs near Furnace Creek is not simulated as 

discharge from the lower layer, because it is included in the discharge from the head-dependent 

flow boundary.

The drain package (McDonald and Harbaugh, 

1988, chap. 9) is used to simulate spring discharge 

from cells in the lower model layer that correspond to the location of selected regional springs. 

Discharge from these cells is simulated whenever 

the water level in the cell exceeds a specified head 

for the drain. No discharge is simulated whenever the water level is below the specified head. 

Land-surface altitudes of the springs, listed by 

Thomas and others (1986, pi. 2), are used as the 

specified head. A representative altitude is used 

in cells that include more than one spring. Discharge from the drain (spring) is also dependent 

on a conductance term (McDonald and Harbaugh, 

1988, chap. 9, p. 5). A single conductance value 

is used for all springs. Initially, a value of 3 ft2/s, 

large enough that discharge from the cell was not 

controlled by the conductance term but rather by 

transmissivity of cells in the lower layer, was used. 

The value was increased to 10 ft2/s during model 

calibration without any effects to simulated spring 

discharge.

MODELING APPROACH

Simulation of ground-water flow in the carbonate-rock province required a slightly different 

approach from that used for most modeled areas, 

because all the variables in the ground-water flow 

equation (eq 1) either are unknown over large 

parts of the area or are only approximately known. 

The locations of recharge and discharge areas are 

generally known, although the quantities of recharge and discharge are only approximately 

known. Water levels in the upper part of the basin fill are generally known (Thomas and others, 

1986), but water levels in the consolidated rocks 

beneath the basin fill are known only at a few 

locations. Also, the existing water-level measurements represent only the uppermost part of the 

basin fill and the consolidated rocks, because wells 

penetrate only a small part of their total thicknesses. Water levels are generally unknown in 

the mountains because only a few wells exist there. 

Hydraulic properties of shallow basin fill are generally known because numerous wells have been 

drilled into the basin fill. Estimates of hydraulic 

properties of the various consolidated rocks are 

largely unknown, except at a few locations such 

as the Nevada Test Site. In addition, the subsurface geology is largely unknown, as is the depth 

of ground-water flow.

The general approach used to simulate regional ground-water flow in the province was to 

adjust transmissivities and vertical leakances until 

(1) water levels in both model layers approximated 

the estimated water levels, (2) evapotranspiration in the upper layer approximated the quantity and distribution of ground-water 

evapotranspiration estimated for each hydrographic area, and (3) simulated discharge from 

the lower layer approximated the discharge at 

regional springs.

Estimated water levels used to compare with 

simulated values are based on contours by Thomas and others (1986) in both the basin fill and 

consolidated rocks. Water-level data are concentrated in the basin fill because these deposits generally yield at least moderate quantities of water 

at shallow depth. The locations of measured wells 

in basin fill are shown in figure 12. In contrast, 

water-level data in consolidated rocks are sparse. 

These data include measurements from wells, test 

holes, or mine shafts that penetrate consolidated 

rocks in the mountains or beneath the basin fill, 

and land-surface altitudes at regional springs (Thomas and others, 1986, pi. 2). The locations of measured wells, test holes, and mine shafts completed 

in consolidated rocks are shown in figure 13.

For initial model calibration, a water-level 

altitude was estimated for each cell in the upper 

model layer and for selected cells in the lower 

layer. A water-level altitude was estimated for 

cells in the upper layer by superimposing the 

model grid over the map of water levels in basin 

fill (Thomas and others, 1986, pi. 1) and determining an average water level for each cell in 

an area where water-level contours had been 

drawn. Water-level contours drawn by Thomas and 

others for some basins, in particular Las Vegas 

Valley, show the effects of ground-water withdrawals. In these basins, water levels measured prior

FIGURE 11. Cells used to simulate spring discharge from lower 

model layer. Cells correspond to selected springs shown 

in figure 7.
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D23

115' 113°

Cells used to simulate spring 

discharge from lower model 

layer

37° 

36° 

35° 

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000,1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°

1. Manse Springs

2. Ash Meadows area (several springs)

3. Rogers and Blue Point Springs

4. Muddy River Springs

5. Grapevine and Stainigers Springs

6. Pahranagat Valley (several springs)

7. Panaca Warm Spring

8. Hot Creek Ranch Springs

9. Lockes (several springs)

10. Blue Eagle and Tom Springs

11. Moon River and Hot Creek Springs

12. Mormon Hot Spring

13. Northern White River Valley (several springs)

14. Duckwater (Big and Little Warm Springs)

15. Fish Creek Spring

16. Twin Spring

17. Campbell Ranch Spring

18. Shipley Hot Spring and Bailey Spring

19. Fish Springs

20. Nelson Spring

21. Blue Lake and Little Salt Springs

22. Warm Springs

Boundary of carbonate-rock province 

model
D24 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

116° 115'

Well tapping basin fill Water-level 

data available

I | Area where wells are too numerous 

to show

Boundary of carbonate-rock province 

model

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000,1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°

FIGURE 12. Wells tapping basin fill for which water-level data are available (modified from Thomas and others, 1986, pi. 1).
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D25

118' 117° 113°

42' J. OREGON IDAHO

NEVADA

* I 

.L___L___--±

i* 'R I' r v, '

-T 7

P

40°

39°

38C

37°

36°

35C

*

i

1

- \

T~

Well, test hole, or mine shaft tapping 

consolidated rocks Number is water 

level, in feet above sea level at selected 

site. Additional water levels are shown by 

Thomas and others (1986, pi. 2)

Area where wells are too numerous 

to show

Boundary of carbonate-rock province 

model

100 MILES

100 KILOMETERS

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000,1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°

FIGURE 13. Wells, test holes, and mine shafts tapping consolidated rocks for which water-level data are available

(modified from Thomas and others, 1986, pi. 2).
D26 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

to the withdrawals were used. Water-level altitudes in cells corresponding to basins with sparse 

data were estimated from the measurements at 

individual wells, from the altitude of springs discharging on the valley floor, or from an average 

altitude of areas of evapotranspiration. Water-level 

altitude for cells corresponding to mountainous 

regions was interpolated from adjacent valleys and 

from the average land-surface altitude estimated 

for the cell. A water-level altitude was estimated 

for some cells in the lower model layer by superimposing the model grid over the map of waterlevel contours for consolidated rocks (Thomas and 

others, pi. 2). The value assigned to a cell corresponded to the average altitude indicated by the 

contours. Most cells in the lower layer do not have 

an estimated water level.

For final model calibration, the estimated 

water-level altitudes of only selected cells were 

used to compare with simulated water levels. Cells 

in the upper model layer were selected if they 

corresponded to (1) an area where water-level contours in basin fill had been drawn by Thomas 

and others (1986, pi. 1) or (2) a measured water 

level in a well. Cells in the lower layer were selected if they corresponded to a measured water 

level in a well, test hole, or mine shaft, or the 

land-surface altitude of a regional spring. In the 

upper layer, 773 cells out of a total 2,456 active 

cells had an estimated water level, whereas in 

the lower layer, only 144 cells out of 2,456 had 

an estimated water level.

ESTIMATES OF RECHARGE

The method used to estimate recharge in Nevada and Utah is reported by Maxey and Eakin 

(1949, p. 40, 41) and Eakin and others (1951, p. 

26, 27). Their method assumes that recharge is 

principally from precipitation in the mountains. 

The quantity of recharge is based on a percentage of the total volume of annual precipitation 

that falls within a selected altitude interval. Percentages range from 0 percent for areas where 

annual precipitation is less than 8 in. to as much 

as 40 percent in the highest parts of the Wasatch 

Range, where annual precipitation is more than 

40 in. The original percentages listed by Maxey 

and Eakin (p. 40, 41) are based on trial-and-error calculations in which estimates of recharge 

are set equal to estimates of ground-water discharge from natural losses. Although recharge is 

estimated by this empirical method in Utah, the

percentage of recharge applied to each precipitation zone varies considerably between hydrographic 

areas. The reason for the variation is that the 

estimates of recharge are adjusted to match estimates of discharge. The original percentages of 

recharge applied to each precipitation zone have 

also been adjusted subjectively when applied to 

other hydrographic areas in Nevada. Thus, the 

percentage of precipitation estimated to become 

recharge for a particular precipitation zone may 

vary by several percent among different hydrographic areas in both Nevada and Utah. Watson 

and others (1976) quantitatively evaluated the 

method for estimating recharge and concluded that 

the method could not reliably predict recharge 

other than provide an approximation.

Estimates of recharge for a given mountain 

range were obtained by determining the areas 

within each precipitation zone from maps of average annual precipitation for Nevada and Utah 

(Hardman, 1936, 1965; U.S. Weather Bureau, 

1963). The estimate of recharge for each mountain range was then compared and revised to be 

consistent with the estimated recharge for individual hydrographic areas or selected groups of 

areas. Finally, the distribution of recharge areas 

was compared with areas of principal recharge 

as delineated by Mifflin (1988, pi. 3). The distribution of recharge assigned to cells in the model 

is shown in figure 14.

Total annual recharge within the modeled area 

is about 1.5 million acre-ft. The quantity of precipitation that is estimated to recharge the aquifers in the province is about 3 percent of the 

estimated total annual precipitation. This approximation is slightly less than the 5 percent reported 

by Eakin and others (1976, p. 6). However, they 

include hydrographic areas that receive water from 

the much wetter Sierra Nevada, the mountains 

in extreme northern Nevada, and areas along the 

north and east sides of the Great Salt Lake that 

receive some water from the Wasatch Range. They 

also exclude several hydrographic areas in the 

much drier southeastern Nevada. Thus, the 3-percent estimate is probably reasonable. Also, the 

estimates of recharge presented herein, and in 

most of the numerous reconnaissance reports, do 

not include water that locally recharges ground 

water only to be discharged nearby.

FIGURE 14. Distribution of recharge assigned to cells in upper model layer, and simulated recharge from rivers and 

lakes through general-head boundaries.
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D27

118 116° 112°

36° 

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000,1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°

Recharge rates for cells in upper model 

layer In acre-feet per year

No recharge 

Less than 1,000 

CTl 1,000 to 5,000 

5,000 to 10,000 

Greater than 10,000

Recharge at general-head boundary 

Flow exceeds 40 acre-feet per year

Boundary of carbonate-rock province 

model
D28 REGIONALAQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

INITIAL ESTIMATES OF TRANSMISSIVITY AND 

LEAKANCE

Initial estimates of transmissivity for the upper model layer are grouped into three geologic 

units. The estimates were made to provide a starting point for the calibration process in which transmissivities were modified. The geologic units 

within the modeled area are grouped into three 

principal types (Harrill and others, 1988; Plume 

and Carlton, 1988): (1) basin fill, which includes 

Tertiary tuffs, terrigenous sediments, and Quaternary stream, alluvial fan, and lacustrine deposits; (2) thick sequences of carbonate rocks of 

Paleozoic and early Mesozoic age; and (3) other 

consolidated rocks, which include clastic sedimentary rocks, intrusive and extrusive igneous rocks, 

metamorphic rocks, and locally thick units of Tertiary clay and silt. Figure 15 shows how the principal rock types are distributed in the upper layer. 

The basin-and-range physiography can be easily 

distinguished with the resolution provided by the 

5-mi by 7.5-mi grid.

Carbonate rocks are assumed to have the highest transmissivity. The initial transmissivity assigned to cells in the upper model layer 

representing carbonate rocks was 0.25 ft2/s, within 

the range of values reported by Winograd and 

Thordarson (1975, table 3 and p. 73), Bunch and 

Harrill (1984, p. 119), and Plume (1989). Reported 

values range from about 0.002 ft2/s (200 ft2/d) to 

about 9 ft2/s (800,000 ft2/d). Initial transmissivity assigned to cells representing other consolidated rocks was 0.002 ft2/s; the initial value 

assigned to cells representing basin fill was 0.02 

ft2/s, within the range of values presented by 

Winograd and Thordarson (1975, table 3) and 

Bunch and Harrill (1984, p. 115). A uniform value 

of 0.25 ft2/s was initially assigned to all cells in 

the lower layer.

Transmissivities of each rock type actually 

vary widely due to either changes in thickness 

or differing hydrologic properties of the rocks. The 

transmissivities for each model cell changed during 

model calibration. The vertical resistance to 

ground-water flow is simulated in the model with 

a vertical leakance term. Vertical leakance is defined as the vertical hydraulic conductivity divided by length of flow path (Lohman, 1972, p. 

30). A vertical leakance of 1 x 10"11 per second 

was initially assumed for all cells. No attempt 

was made to distinguish leakance values according to hydrogeologic conditions because of the uncertainty of the geologic units at depth and because

of uncertainties in estimating the vertical hydraulic conductivity and the length of the flow path. 

The vertical leakances also changed during model 

calibration.

MODEL CALIBRATION

Initial model calibration began by assigning 

an estimated water level to each model cell. In 

many cells, particularly in the lower layer, the 

assigned water levels were interpolated and extrapolated from data many miles away. Transmissivities of cells in the upper and lower model layers 

and vertical leakances of cells between layers were 

initially adjusted on the basis of comparing simulated water levels to those assigned to the model 

cells. Two computer programs were written and 

used to automatically adjust both transmissivities and vertical leakances. The first program adjusted transmissivities in cells where the simulated 

water levels were either too high or too low compared to the assigned water levels. Transmissivities were increased or decreased depending on the 

ratio of the simulated water level to the assigned 

water level. The method worked reasonably well 

because simulated heads were either too high or 

too low over large regions of the model.

The second program adjusted vertical 

leakances between adjacent cells in the upper and 

lower model layers during alternate simulations. 

Vertical leakances were adjusted using the ratio 

of the simulated water-level difference to the assigned water-level difference as expressed in the 

following equation (Williamson and others, 1989, 

p. 32):

Lnew = Lold * FAC * (AHVmod/AHVas)

where Lnew = the adjusted vertical leakance

value; 

Lold = the previous vertical leakance

value;

AHVmod = the simulated water-level difference of adjacent cells between the 

upper and lower model layers; 

AHVas = the assigned water-level difference 

of adjacent cells between the upper and lower model layers; and 

FAC = 0.9 when the ratio of AHVmod to 

AHVas is less than 1, 1.1 when the 

ratio is greater than 1, and 1.0 

when the ratio is 1.

The computer programs do not correctly adjust 

transmissivities or vertical leakances on the first
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D29

118° 117° 115' 114° 113°

36'

Rock type assigned to cells in upper model 

layer, with initial transmissivity (T) In

feet squared per second

Carbonate rocks, T = 0.25

Basin fill, T = 0.02

Other consolidated rocks, T = 0.002

Boundary of carbonate-rock province 

model

35'

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000, 1987

Alters Equal-Area Conic projection

Standard parallels 29C30' and 45°30', central meridian -114°

FIGURE 15. Principal rock types assigned to cells in upper model layer, and initial transmissivities used.
D30 REGIONALAQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

computation because flow to and from a cell may 

change after adjusting the vertical leakance and 

the transmissivities in adjacent cells. Thus, the 

process involved numerous simulations that alternately adjusted transmissivities and vertical 

leakances. The use of these programs ceased once 

the simulated water levels over the entire model 

generally matched the water levels presented by 

Thomas and others (1986).

The final part of model calibration involved 

(1) testing the range in transmissivities and vertical leakances calculated from the initial calibration by comparing the simulated water levels 

in 773 selected cells in the upper layer and 144 

cells in the lower layer where water levels had 

been estimated from the maps by Thomas and 

others (1986), (2) making regional and local 

changes to transmissivities and vertical leakances 

until simulated discharge as evapotranspiration 

in the upper model layer and regional spring flow 

in the lower layer approximated estimated values, and (3) adjusting conductance values at headdependent flow boundaries.

Transmissivities following the initial calibration ranged from 2.5 x 10~4 to 2.5 ft2/s in the 

upper layer and from 2.5 x 10~4 to 2.5 x 10"1 ft2/s 

in the lower layer. During the final phase of model 

calibration, both transmissivities and vertical 

leakances were rounded to the nearest exponent 

(1 x 10~4; 1 x 10-3 ; 1 x ICT2 ; and so forth) without affecting the simulation results. The rounding of both transmissivities and vertical leakances 

is reasonable because of the lack of information 

on the extent and distribution of aquifers, their 

hydraulic properties, and the lack of ground-water levels in many areas. Such groupings also simplified the final calibration while reasonably 

duplicating regional ground-water levels, and the 

distribution and quantity of discharge. The best 

match with estimated water levels and discharge 

was simulated when the grouped transmissivities 

were multiplied by a factor of 2.2 in the upper 

layer and when the values were multiplied by a 

factor of 3.3 in the lower layer. In a few areas, 

transmissivities were further multiplied by a factor 

ranging from 2 to 5. Even though transmissivities are generally grouped by a factor of 10, the 

range in simulated transmissivities did not change 

greatly from the initial calibration. In the upper 

layer, transmissivities following final calibration 

ranged from 2.2 x ICT5 to 2.2 x lO" 1 ft2/s; both 

the minimum and maximum values are about 10 

times less than the initially calibrated values. In 

the lower layer, transmissivities following model

calibration ranged from 3.3 x 10~5 to 6.6 x 10"1 

ft2/s.

Vertical leakances following initial calibration 

ranged from 1 x 10~16 to 3 x 10~9 per second. 

During final calibration, increasing vertical 

leakances of less than 1 x 10~13 to that value 

produced little difference in simulated water levels 

and discharge. Similarly, decreasing values greater 

than 1 x 10"11 to that value also produced little 

differences. Finally, all other leakance values were 

rounded to values of 1 x 10" 11 , 1 x 10~12 , or 1 x 

10~13 per second. The distribution of vertical 

leakances is shown in figure 16.

The average vertical leakance for all model 

cells is 4 x 10~12 per second. Overall, 62 percent 

of cells (1,517 of 2,456) have a value of 1 x 10~12 

per second, 34 percent (833 cells) have a value 

of 1 x 10"11 per second, and only 4 percent (106 

cells) have a value of 1 x 10~13 per second. Most 

of the cells (95 out of 106) having the lowest vertical leakances are in or adjacent to the Great 

Salt Lake Desert. More than half of the cells having the highest leakances (455 out of 833) are in 

the central third of the modeled area (rows 21 to 

40). In contrast, only 17 percent of the cells having the highest leakances (140 out of 833) are in 

the southern third of the modeled area (rows 41 

to 61). In the central part, about half of the highest 

leakances correspond to mountain ranges, whereas 

in the southern third, 60 percent correspond to 

mountain ranges.

The magnitudes of the computed transmissivities and vertical leakances are dependent on 

the quantity of assigned recharge. Increasing recharge results in a corresponding increase in discharge and requires a proportional increase in 

transmissivities and vertical leakances to maintain the same head gradients. The estimates of 

recharge are only approximations; thus, recharge 

was increased by a factor of 2 and decreased by 

a factor of 2 during model calibration to evaluate its effect on transmissivities and vertical 

leakances.

Conductances used for the head-dependent 

flow boundaries range from 0.005 to 0.5 ft2/s and 

average 0.13 ft2/s for the 94 cells. Only one cell 

has a value of 0.005, and three have a value of 

0.5. Conductances are slightly different between 

the different areas. Conductances for the Humboldt 

River range from 0.1 to 0.5 ft2/s and average 0.24 

ft2/s; more than half of the cells (11 of 20) have 

a value of 0.3 ft2/s. Conductances for the Great 

Salt Lake and Utah Lake are 0.1 ft2/s, except 

for four cells along the Great Salt Lake, which
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D31

116° 115 113° 112°

_ -_ A. L _,_ _ _L I -r' 1 ^ \ 

coinJ..- V «>

38

37°

Estimated leakance between cells in 

upper and lower model layers, per 

second

36° 

Boundary of carbonate-rock province 

model

35'

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000, 1987

Albers Equal-Area Conic projection

Standard parallels 29C 30' and 45°30', central meridian -114°

FIGURE 16. Estimated vertical leakance between cells in upper and lower model layers.
D32 REGIONALAQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

have a value of 0.15. Conductances range from 

0.01 ft2/s for the upstream reaches of the Sevier 

River to 0.15 for Sevier Lake; conductances for 

the Sevier River average 0.07 ft2/s. Conductances 

for the Virgin River are 0.01 ft2/s, except for the 

northernmost cell, which is 0.02 ft2/s. Conductances 

for Lake Mead are also 0.01 ft2/s, except for the 

two cells nearest the dam, which are 0.5 ft2/s. The 

conductance for the one cell representing the Colorado River below the dam is 0.005 ft2/s. Conductances for Death Valley are 0.1 ft2/s.

Because flow to and from the head-dependent 

boundaries are generally controlled by the estimated transmissivities of the model cells, changing conductances does not greatly affect the 

simulation results. For example, decreasing the 

conductances for cells that have a value of 0.5 

ft2/s to 0.1 ft2/s resulted in a slight decrease (0.1 

ft3/s) in discharge and recharge along the 

Humboldt River and no change to discharge at 

Lake Mead. Increasing the conductances for nine 

cells along the Sevier River which had values less 

than 0.1 ft2/s by a factor of 10 resulted in a 10- 

percent increase in discharge (5 ft3/s increase) to 

the Sevier River, a corresponding decrease in simulated evapotranspiration, and consequently, no 

change in the simulated discharge from the area.

Total simulated spring discharge from the 

lower model layer is only 0.5 percent greater than 

the total estimated discharge (table 1). However, 

the percentage difference between simulated and 

estimated discharge for individual springs is generally more. For example, simulated discharge at 

Warm Springs (table 1) is 152 percent of the estimated discharge.

During final model calibration, conductance 

values used to simulate spring discharge were 

changed to test their sensitivity. Initially, a uniform value of 3 ft2/s was assigned to each spring. 

This value is more than two orders of magnitude 

greater than the initial conductance value assigned 

between layers (vertical leakance multiplied by 

cell area\ Increasing the conductance value for 

springs to 10 ft2/s did not affect discharge from 

the lower layer, indicating that the discharge was 

dependent on flow from adjacent model cells. The 

higher conductance values resulted in slightly reduced water levels in cells where spring discharge 

was simulated, because not as much head difference was needed to simulate flow through the 

springs. A value of 10 ft2/s was used during final model calibration. Spring discharge was extremely sensitive to changes in both transmissivity 

and vertical leakance.

Land-surface altitude assigned to each model 

cell in the upper layer controlled the distribution of evapotranspiration and water levels in cells 

where evapotranspiration was simulated. Initially, 

land-surface altitudes assigned to each cell were 

averaged values. This did not produce a reasonable distribution of evapotranspiration and water levels in some areas of the model. Adjusting 

transmissivities and vertical leakances did not 

always improve results. Areas of evapotranspiration are generally confined to the lowest parts of 

a valley. Consequently, minimum land-surface altitudes from the one-minute data were used in 

areas of known evapotranspiration.

Because evapotranspiration did not reach a 

maximum rate when water levels exceeded land 

surface (fig. 10.B), simulated water levels in cells 

with evapotranspiration were compared with the 

assigned land-surface altitude. Whenever water 

levels exceeded land surface, transmissivity and 

leakance values in that cell, and sometimes in 

surrounding cells, were changed to lower heads 

below land surface. Evapotranspiration of ground 

water was assumed to occur only from basin fill 

in the valley lowlands. Thus, the transmissivity 

and leakance values were increased in a model 

cell corresponding to consolidated rocks whenever 

evapotranspiration was simulated in such a cell. 

Final distribution of simulated evapotranspiration 

is shown in figure 17. The simulated distribution generally corresponds to areas mapped by 

Harrill and others (1988, pi. 2). Areas mapped 

by Harrill and others are shown in figure 18.

The model was deemed calibrated when simulated discharge approximated the mapped distribution and estimated discharge in each hydrographic 

area. In addition, computed water levels were matched 

as closely as practical with estimated values. For the 

best-fit simulation, 86 percent of the simulated water levels (666 out of 773 model cells) were within 

250 ft of the estimated water levels for the upper 

layer and 76 percent (109 out of 144 cells) were within 

250 ft for the lower layer.

The 250-ft criterion used for calibration purposes is only 3 percent of the total water-level 

difference in the model. The maximum simulated 

water level is more than 7,000 ft above sea level, 

along the eastern side of the model; in contrast, 

the minimum is below sea level, in Death Valley. 

Water-level differences between adjacent model 

cells commonly exceed 250 ft; in a few locations, 

they exceed 500 ft. The distribution of water levels 

in both model layers for the best-fit calibration 

is shown in figure 19.
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D33

13

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D34 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

118° 117° 116° 115° 114° 113° 112° 111°

Evapotranspiration rates for cells in 

upper model layer In acre-feet 

per year

No evapotranspiration 

Less than 5,000 

5,000 to 10,000 

Greater than 10,000

Discharge at general-head boundary 

Flow exceeds 40 acre-feet per year

Boundary of carbonate-rock province

model r^^-LO]

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000,1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°

FIGURE 17. Simulated evapotranspiration rates in cells in upper model layer, and simulated discharge from rivers, lakes, and

Death Valley through general-head boundaries.
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D35

He'- 116° 115 113°

Area where ground water is consumed 

by evapotranspiration Approximately 

located

Boundary of carbonate-rock province 

model

35

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000, 1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°

FIGURE 18. Areas where ground water is consumed by evapotranspiration ( from Harrill and others, 1988, pi. 2).
D36 REGIONALAQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

116° 115' 112°

42°

 5000 Potentiometric contour Shows

altitude of simulated ground-water level 

in upper model layer. Interval 500 feet. 

Hachures indicate depression. Datum is 

sea level

Boundary of carbonate-rock province 

model

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000,1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°

FIGURE 19. Simulated steady-state ground-water levels. A, Upper model layer. B, Lower model layer.
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D37

116

I i

I ' 

5000 Potentiometric contour Shows

altitude of simulated ground-water level 

in lower model layer. Interval 500 feet. 

Hachures indicate depression. Datum is 

sea level

Boundary of carbonate-rock province 

model

35° 

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000,1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°

FIGURE 19. Continued.
D38 REGIONALAQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

Conductance values used to simulate the interaction of ground water with surface water (general-head boundaries in fig. 9) were changed 

during model calibration until the simulated water-level gradients near the boundaries approximated the estimated gradients.

LIMITS OF CALIBRATION

Results from the model simulation are only 

approximate because uncertainties exist in the 

distribution and quantity of recharge and because 

water levels in the consolidated rocks are unknown 

over much of the area. Although discussed in detail, the model results are conceptual because actual values are not known for any of the variables 

in the ground-water flow equation. In particular, 

other, equally valid, distributions of transmissivity 

may be found that permit the model to be calibrated to the existing information. Model results 

are also dependent on the general assumptions 

discussed previously.

Transmissivities estimated for both model layers are in part dependent on the quantity and 

distribution of recharge used in the model, particularly for model cells that correspond to mountains. Recharge is simulated in the mountains 

except where head-dependent flow boundaries are 

used to simulate the interaction of ground water 

with surface water. Simulating all recharge in 

mountains that consist of carbonate rocks is probably reasonable because little surface water flows 

to the nearby valleys. But in mountains that consist of low-permeability rocks, much of the water 

flows into nearby valleys where recharge occurs 

mostly on the adjacent alluvial fans. Thus, the 

transmissivities estimated for model cells that 

represent these mountains are probably higher 

than the actual transmissivities.

Transmissivities in the upper model layer are 

highly sensitive to changes in both the quantity 

and location of recharge. Transmissivities for the 

lower model layer are not as sensitive to changes 

in recharge, because recharge is not added directly to cells in this layer. Recharge to the lower 

layer is dependent on the leakage between the 

upper and lower layers, which is controlled by 

the vertical leakance.

Errors in the estimates of recharge are unknown but locally could be well in excess of 100 

percent. If recharge is increased in the model by

100 percent, a similar distribution of water levels 

could be simulated by proportionately increasing 

transmissivities and vertical leakances. Because the 

model assumes steady-state conditions, discharge 

would also increase by 100 percent. However, a different distribution of transmissivity and vertical 

leakance near regional springs would be needed if 

the additional recharge was forced to discharge as 

evapotranspiration instead of allowing spring discharge to increase as well.

Estimates of water levels used to calibrate 

transmissivities in the lower model layer are based 

on limited data. Locally, transmissivities could be 

changed an order of magnitude, and model results might still be reasonable with respect to 

areas of estimated water levels and quantities of 

simulated discharge. Large cell sizes and the generalization of transmissivities result in a more 

gradual change in simulated water levels than 

might be expected from abrupt lateral and vertical changes in geologic units observed in the study 

area. Where geologic structures are barriers to 

flow in south-central Nevada, water-level differences between adjacent valleys are as much as 

2,000 ft (Winograd and Thordarson, 1975, p. 63). 

With cell sizes of 5 mi by 7.5 mi, the model tends 

to smooth such large differences.

The model is designed to simulate groundwater flow at a regional scale. Orientation of the 

columns in the model grid corresponds to the general trend of range-front faults. These faults are 

thus parallel and perpendicular to the two directions of horizontal transmissivity. However, rangefront faults are not the only faults present in the 

province. The mountains are extensively faulted, 

as presumably are the rocks beneath the basin 

fill. Orientation of the model grid to coincide with 

the range-front faults therefore may be unnecessary. Also, transmissivity in one of the two principal directions could be changed with respect to 

the other direction over the entire modeled area, 

although no compelling reason was discovered to 

simulate such a condition. Anisotropy probably 

exists on a more localized scale, but available computer programs do not allow anisotropy to be specified by individual model cells. Localized anisotropic 

conditions could be simulated by reducing the dimensions of the model cells. The simulation of 

ground-water flow with smaller cell dimensions 

is not beyond the scope of this study. However, 

insufficient data over large areas preclude such 

a detailed simulation.
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D39

SIMULATION RESULTS

Discussion of the simulation results has been 

divided into three sections: (1) estimated transmissivities, (2) correlation of ground-water flow 

to regional geologic features, and (3) distribution 

of flow into regions.

ESTIMATED TRANSMISSIVITIES

Transmissivities in both model layers were 

estimated by adjusting the initial values until 

simulated water levels generally agreed with estimated water levels and the quantity and distribution of simulated discharge approximated 

those of the estimated discharge. The transmissivities are also dependent on the quantity and 

distribution of recharge assigned to cells corresponding to mountain ranges. Estimated transmissivities for the upper and lower model layers 

are shown in figure 20.

Errors in transmissivities are unknown, but 

the estimates could be off by a factor of 5 or more. 

Other uncertainties used in the model also result in unknown errors, especially the assumption of isotropy in each 37.5-mi2 model cell in an 

area of complex geology. Consequently, transmissivities are discussed using the qualitative terms 

listed as follows:

Qualitative 

term

Lowest..................

High......................

Highest ................

Transmissivity range 

(feet squared per second)

............ <0.0006

............ 0.0006-0.006

............ 0.006-0.18

............ 0.18 0.66

In the upper model layer, no distinct pattern 

of transmissivities is simulated (fig. 20A), perhaps because of areal variability in the quantity 

and distribution of recharge. Highest transmissivities are scattered in small groups of cells 

throughout much of the province. Lowest transmissivities are concentrated in the Great Salt Lake 

Desert, in the vicinity of Death Valley, and in 

the extreme southern part of the province. Low 

values are assigned in the Great Salt Lake Desert 

to match estimated ground-water discharge. Circulation of fresh ground water in this area is assumed minimal because the area is underlain by 

an extensive body of saline ground water. Low 

values are assigned in the vicinity of Death Valley and in the southern part of the province to 

simulate large hydraulic gradients between Death 

Valley and adjacent basins. Outcrops of Cambrian 

and Precambrian clastic rocks, assumed to be 

poorly permeable, are common in the mountains 

surrounding Death Valley.

In the lower model layer, high transmissivities are generally grouped in areas associated with 

regional springs or in the vicinity of basins where 

ground-water discharge is considerably more than 

the estimated recharge from tributary drainage 

areas (fig. 20.B). Highest values are simulated in 

narrow bands near regional springs in the White 

River Valley in eastern Nevada, near the Muddy 

River Springs area in southern Nevada, and near 

Fish Springs in west-central Utah. Elsewhere in 

the province, low transmissivities are simulated. 

Lowest transmissivities are simulated in the Great 

Salt Lake Desert, Death Valley, and the extreme 

southern end of the province, with an areal distribution similar to that of the upper layer.

Transmissivities in the upper and lower model 

layers are summarized in table 2.

The geometric mean transmissivity of the upper layer is greater than that of the lower layer 

even though the minimum, median, and maximum 

values in the upper layer are less than those in 

the lower layer. However, the 25th-and 75th-percentile values are nearly an order of magnitude 

greater in the upper layer. The reason for this 

seeming disparity is that the estimated transmissivities in the model cells are assigned values that 

generally differ by an order of magnitude. In the 

upper layer, about 40 percent of the active cells 

(979 of 2,456 cells) are assigned an estimated 

transmissivity of 0.022 ft2/s, whereas in the lower 

layer approximately half of the active cells (1,187 

of 2,456 cells) are assigned an estimated transmissivity of 0.0033 ft2/s.

As a result of model calibration, estimated 

transmissivities in both model layers are generally less than the initially assigned values. Initially, one of three transmissivity values was 

assigned to groups of model cells in the upper 

layer on the basis of surficial geology (that is, 

carbonate rocks, basin fill, or consolidated rocks 

of low permeability; fig. 15), and one value representing carbonate rocks was assigned to all cells 

in the lower layer. The frequency distribution of 

estimated transmissivities for the three groups 

of rocks in the upper layer is shown in figure 

21. Also shown is the frequency distribution for
D40 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

118° 116 112°

36° ~

Estimated transmissivity of cell in upper 

model layer In feet squared per second

Less than 0.0006

0.0006 to 0.006 

I f 0.006 to 0.18 

d] 0.18 to 0.66

Boundary of carbonate-rock province 

model

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000,1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45C30', central meridian -114°

FIGURE 20. Estimated transmissivities. A, Upper model layer. B, Lower model layer.
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D41

118

39° 

38° 

36° 

116° 115° 114° 113° 112°

Estimated transmissivity of cell in lower 

model layer In feet squared per second

Less than 0.0006 

0.0006 to 0.006 

0.006 to 0.18 

0.18 to 0.66

Boundary of carbonate-rock province 

model

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000.1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°

FIGURE 20. Continued.
D42 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH 

TABLE 2. Selected statistics of estimated transmissivities in both model layers

Transmissivity (feet squared per second)

Model Number of Geometric 25th

layer cells mean Minimum percentile

Upper 2,456 0.0048 0.000022 0.0022

Lower 2,456 .0030 .000033 .00033

600

500 

400 

300

200

w 

ZJ 100

LLJ 

O

g 0

O

^

OF NUMBERI

400

300

200

100 

n

Upper layer, carbonate rocks

-

: 01 :

_ n .

-4.75 -3.75 -2.75 -1.75 -0.75 0.75

Upper layer, consolidated rocks 

of low permeability

-

 

_ 

HrL."

600

500 

400 

300

200 

100 

0

1,400 

1,200 

1,000

800 

600

400 

200 

n

75th

Median percentile Maximum

0.0022 0.022

.0033 .0033

0.22

.66

Upper layer,

basin fill

-

-

-4.75 -3.75 -2.75 -1.75 -0.75

-

-

0.75

Lower layer, all rock types

i i n 1 i

-4.75 -3.75 -2.75 -1.75 -0.75 0.75 -4.75 -3.75 -2.75 -1.75 -0.75 0.75 

LOGARITHM OF TRANSMISSIVITY, IN FEET SQUARED PER SECOND

FIGURE 21. Frequency distributions of estimated transmissivities for cells in upper model layer on 

basis of principal rock type, and for all cells in lower model layer. Shades correspond to transmissivity 

ranges in figure 20.
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D43

TABLE 3. Summary of estimated transmissivities for model cells corresponding to selected rock types in both model layers

Transmissivities 

(feet squared per second)

Percentage of model cells having transmissivities (in feet squared per second) within 

the following ranges

UPPER LAYER

Carbonate rocks

Basin fill

Number of 

cells

480

1,316

Initially 

assigned 

value

0.25

.02

Geometric

mean of estimated postcalibration 

values

0.0057

.0060

Less than 

0.0006

12

15

0.0006- 

0.006

39

31

0.006- 

0.18

43

46

0.18-0.66

6

8

Consolidated rocks of low

permeability 660 .002

LOWER LAYER

All rock types 2,456 .25

.0027

.0030

28

30

37

48

33

20

all rock types (all model cells) in the lower layer. 

Estimated transmissivities for each group of rocks 

are log-normal distributions. The geometric mean 

transmissivities for each group of rocks in the 

upper layer and all rock types in the lower layer, 

and the percentage of model cells within the transmissivity ranges shown in figure 20, are listed 

in table 3.

The geometric means of estimated transmissivities for cells representing carbonate rocks and basin 

fill are only 3 and 30 percent, respectively, of the 

initially assigned values (0.25 and 0.02 ft2/s), whereas 

the geometric mean for cells representing consolidated rocks of low permeability is 135 percent of 

the initially assigned value. The geometric mean 

of estimated transmissivities for all rock types 

in the lower layer is only 1 percent of the initially assigned value. Overall, this mean closely 

approximates the geometric mean for cells representing consolidated rocks of low permeability, 

rather than that of carbonate rocks.

In the upper model layer, the distribution of 

estimated transmissivities for cells representing 

carbonate rocks and basin fill are nearly the same 

(table 3). In contrast, a greater percentage of cells 

representing consolidated rocks of low permeability 

have an estimated transmissivity of less than 

0.0006 ft2/s (28 percent compared with 12 and 

15 percent for cells representing carbonate rocks 

and basin fill, respectively). In the lower model 

layer, the distribution of estimated transmissivities for all cells is similar to the distribution for 

cells representing consolidated rocks of low permeability in the upper layer, except that the lower 

layer has a greater percentage of cells with estimated transmissivities of less than 0.006 ft2/s (78

percent compared with 65 percent for cells representing consolidated rocks of low permeability).

CORRELATION OF SIMULATED GROUNDWATER FLOW TO REGIONAL GEOLOGIC 

FEATURES

The most striking geologic structures in the 

study area are the normal faults that separate 

the basins and mountains. These faults are the 

result of extension that has been occurring over 

the past 17 million years. Normal faulting (mainly 

the juxtaposition of basin fill and consolidated 

rocks) is indirectly incorporated in the model, because columns in the grid are oriented parallel 

to the general strike of the mountain ranges and 

adjacent basins. Thus, differences in transmissivities between cells representing basin fill and consolidated rocks may indirectly simulate the effects 

of these normal faults on ground-water flow.

Faults may provide vertical conduits for flow 

or act as barriers to horizontal flow by offsetting 

permeable rocks against low-permeability rocks. 

Discontinuities in rock types along a fault would 

cause a marked change in the hydraulic gradient across the fault (referred to as fault compartmentalization by Winograd and Thordarson, 1975, 

p. 119). In addition, broken rock adjacent to faults 

could act as a conduit if the rubble is porous and 

not cemented, but could act as a barrier if the 

rocks are highly cemented. The model simulates 

average transmissivities and water levels for each 

cell, thus water-level or permeability changes due 

to faults within a cell cannot be represented. However, a step function of water-level change can
D44 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

be simulated across model-cell boundaries whenever adjacent cells have different transmissivities. Unfortunately, such changes can be masked 

because water levels for each model layer are contoured using an averaging technique that draws 

contours on the basis of a linear interpolation of 

water levels between adjacent model cells and 

because the large contour intervals (500 ft) were 

chosen to show regional trends. Thus, marked 

changes in water levels between individual cells 

are generally not evident.

Several east-west-trending lineaments that 

generally are at right angles to the north- to northeast-trending normal faults have been discussed 

in the literature (Roberts, 1964, 1966; Eaton, 1975; 

Stewart and others, 1975, 1977; Ekren and others, 1976; Rowley and others, 1978; Rowan and 

Wetlaufer, 1981). These lineaments are usually 

several tens of miles to a hundred miles long and 

one to several miles wide. The lineaments tend 

to be associated with disruption and termination 

of mountain ranges, stratigraphic discontinuities, 

east- to east-northeast-trending faults, mineral 

belts, caldera boundaries, volcanic deposits, and 

changes in both gravity and aeromagnetic gradients. Rowan and Wetlaufer (1981, p. 1414) proposed that the east-west lineaments are conjugate 

shears formed during and after middle Miocene 

extension. Ekren and others (1976, p. 1) suggest 

that the east-west lineaments are caused by deepseated crustal control. However, they are uncertain whether the lineaments are partly the result 

of conjugate shears or are caused by a continentwide fracture system.

Stewart and others (1977, p. 67) noted that 

the Cenozoic igneous rocks crop out in generally 

east-west-trending belts and that the rocks become successively younger southwestward. The 

oldest igneous rocks are about 34 to 43 million 

years old near latitude 40°, and the youngest rocks 

are about 6 to 17 million years old along an eastwest belt near latitude 37°. They postulated that 

the volcanic front is related to igneous activity 

localized along a southward propagating transverse break or structural warp in a subducting 

plate. A similar conclusion was reached by Ekren 

and others (1976, p. 15), but they also noted that 

the faulting along the lineaments became younger 

toward the west and southwest ends, which agrees 

with a southwestward decrease in the age of silicic volcanism.

The east-west lineaments could act as barriers to ground-water flow because the features usually extend across many tens of miles to a hundred

miles, are several miles wide, and may disrupt 

the continuity of Paleozoic carbonate rocks by the 

repositioning of less permeable intrusive and (or) 

extrusive rocks, or by movement along left-lateral strike-slip faults. The lineaments are shown 

superimposed on the simulated water levels in 

the upper and lower model layers in figure 22. 

One lineament, the Oregon-Nevada lineament described by Stewart and others (1975), trends in 

a northwesterly direction essentially parallel to 

the Walker belt, a zone of right-lateral shears. 

The Oregon-Nevada lineament (also referred to 

as the Cortez rift) is characterized by a northnorthwest-trending belt of closely spaced faults, 

centers of volcanic activity during the late Miocene, and a conspicuous aeromagnetic anomaly. 

Also shown in figure 22 are reported metamorphic core complexes and east-west-trending mineral belts.

Of the lineaments in figure 22, only the transverse crustal boundary of Eaton (1975) corresponds 

to a change in simulated water levels. Water levels 

decrease southward, suggesting southward flow 

across the lineament. Near the lineament, the 

simulated water-level gradient ranges from about 

40 ft/mi in the central part to 200 ft/mi at the 

western end and near Death Valley. South of the 

lineament, the water-level gradient generally decreases in the central part; the gradient from the 

boundary to Ash Meadows is about 20 ft/mi. The 

lineament is nearly coincident to the axis of the 

southern part of the intermountain seismic belt 

(Rowley and others, 1978) and generally marks 

the southern limit of Cenozoic igneous activity. 

The lineament is also coincident with a considerable decrease in altitude of the valley floors; 

north of the lineament, valley floors are generally 4,000 ft or more above sea level, whereas 

south of the lineament, valley floors are 2,000 ft 

or less above sea level. Water levels in the basin 

fill generally follow changes in land-surface altitudes of the valley floors. Except for a relatively 

narrow band of high transmissivities in east-central Nevada, low transmissivities are estimated 

along the lineament (fig. 20).

The other lineaments shown in figure 22 do 

not correspond as well as the transverse crustal 

boundary to changes in simulated water levels, 

although many of the regional springs (discharge 

points in the lower model layer shown in fig. 22B) 

may be controlled at least in part by structures 

related to the lineaments. Transmissivities (fig. 

20) are generally lower in model cells that correspond to lineaments, although there is no con-
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D45

sistent pattern. The Oregon-Nevada lineament 

(feature 6 in fig. 225) corresponds to a discontinuous zone of low transmissivities in the lower 

model layer (compare figs. 205 and 225). This 

lineament also corresponds to springs and areas 

of phreatophytes where ground water is near land 

surface.

The Warm Springs lineament in Nevada (feature 1 in fig. 225) and the Blue Ribbon lineament (feature 5 in fig. 225) generally cut across 

the study area at latitude 38°. The Blue Ribbon 

lineament in Utah is associated with the Pioche 

mineral belt, which has abundant volcanic deposits 

that are elongate in an east-west direction 

(Stewart and others, 1977; Rowley and others, 

1978, p. 180), and generally corresponds with a 

ground-water divide between northward flow toward the Great Salt Lake Desert and southward 

flow toward the Virgin River and Lake Mead.

The lack of pronounced changes in simulated 

water levels, and transmissivities along the lineaments north of the transverse crustal boundary could be due to younger normal faults 

disrupting the lineaments. Accordingly, the older 

lineaments may be leaky barriers to ground-water flow. In contrast, igneous activity along the 

transverse crustal boundary began at about the 

same time as the normal faulting. Perhaps the 

structures and emplaced intrusions along this lineament have not been disrupted, so structures 

along the lineament still act as barriers to flow.

Some structures that might affect ground-water flow could not be correlated with the simulated water levels and transmissivities. In general, 

major thrust faults could not be correlated with 

simulated and estimated water levels or with 

transmissivities at the scale of the model. Perhaps this is due to masking by other features or 

due to the size of the model cells used in the 

simulations; or perhaps the effects of these features on regional ground-water flow are minimal. 

Thrust faults might act as barriers to flow, particularly to vertical flow, where less permeable 

rocks have been thrust over more permeable rocks 

or where gouge along the thrust has been altered 

to clay. However, thrust faults could also increase 

the transmissive properties of rocks due to fracturing of brittle rocks, particularly near the center of folds or along the margins of the thrust 

plates.

Shear zones also could not be correlated with 

simulated water levels and transmissivities. 

Winograd and Thordarson (1975, p. 67) discussed 

evidence that the Las Vegas Valley shear zone

(fig. 22A) acts as a barrier to flow. Evidence for 

a barrier is based on a water-level difference of 

600 ft measured from two wells that are 3 mi 

apart. They assumed that most of this difference 

takes place in the vicinity of the shear zone instead of assuming a more gradual gradient between the two wells. The Pahranagat shear zone 

(fig. 22A) may also restrict ground-water flow. The 

Walker belt (fig. 22A) may restrict flow, but the 

zone is an area of abundant volcanic activity (Carr, 

1984) and also corresponds to the approximate 

area where exposures of Precambrian and Cambrian clastic and crystalline rocks are common 

in the mountain ranges. Thus, on a regional basis it is not possible to determine if strike-slip 

faults along the Walker belt act as barriers or if 

flow is restricted by some other geologic feature.

The lack of correlation of simulated water levels and transmissivities with strike-slip faults 

could reflect how the model averages water levels and transmissivities within each cell. A steep 

drop across a small distance of a mile or so could 

not be simulated with model cells that are 5 mi 

by 7.5 mi. Instead, a smoother gradient and a 

less severe change in transmissivity was simulated, thus possibly masking any local effects that 

could be related to a series of strike-slip faults.

Shear zones might act as barriers to flow but 

also could act as conduits along the direction of 

strike. This possibility could not be simulated in 

the model because anisotropy of selected cells could 

not be simulated without simulating anisotropy 

in every cell of a model layer. Increasing transmissivity in the direction of strike along the shear 

zones for all model cells could not be justified, 

because most normal faults in the study area are 

at right angles to the shear zones and could just 

as easily act as conduits along their strike.

Perhaps more important than the lineaments 

as ground-water barriers are the distribution of 

low-permeability rocks. Low-permeability rocks 

include intrusive rocks, metamorphic rocks that 

may be associated with the intrusives, and Precambrian and Cambrian igneous, metamorphic, 

and clastic rocks (Plume, 1995). The distribution 

of these rocks is shown in figure 23 along with 

simulated water levels, areas of ground-water 

evapotranspiration, and estimated boundaries of 

ground-water flow for the upper model layer. Lowpermeability rocks south of the transverse crustal 

boundary (south of latitude 36°) are generally Precambrian and Cambrian clastic and crystalline 

rocks; this suggests that carbonate rocks are not 

very thick or are absent over parts of the area.
D46 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

118° 116° 115° 113° 112°

36'

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000,1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°

Metamorphic core complex Approximately 

located. From Coney, 1980; Stewart, 1980

^^j Aeromagnetic ridge of Pioche mineral belt 

From Stewart and others, 1977

^^| Area where ground water is consumed by

evapotranspiration Approximately located. 

From Harrill and others, 1988

 sooo Potentiometric contour Shows altitude of 

ground-water level. Interval 1,000 feet. 

Hachures indicate depression. Datum is sea 

level

Boundary of carbonate-rock province model

Shear zone Arrows indicate direction of relative 

movement. From Stewart, 1980

 ="^~ Las Vegas Valley shear zone

 ^ Pahranagat shear zone

Note: explanation continued on figure 22B

FIGURE 22. Relation between selected geologic features and simulated ground-water levels, areas of evapotranspiration, and 

location of springs simulated in model. A, Upper model layer. B, Lower model layer.
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D47

118" 117° 115' 113° 112°

____j__2?EGON__ I _-_ '___^

36°

35° 

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000,1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°

EXPLANATION (continued)

Walker belt From Ekren and others, 1976

 Axis of southern part of intermountain seismic 

belt From Rowley and others, 1978

Transverse crustal boundary From Eaton, 1975

 4 ~~ Lineament and number Dashed where projected 

farther than in cited literature

1 Warm Springs (Ekren and others, 1976)

2 Pancake Range (Ekren and others, 1976)

3 Pritchards Station (Ekren and others, 1976)

4 Timpahute (Ekren and others, 1976)

5 Blue Ribbon (Rowley and others, 1978)

6 Oregon-Nevada (Stewart and others, 1975); 

also referred to as Cortez rift

11 = Axis of mineral belt and number

7 Hamilton-Ely (Roberts, 1964, 1966)

8 Cherry Creek (Roberts, 1964, 1966)

9 Deep Creek-Tintic (Shane and Stewart, 1976)

10 Oquirrh-Uinta (Shane and Stewart, 1976)

11 Delmar-lron Springs (Shane and Stewart, 1976)

12 Pioche (Shane and Stewart, 1976)

 Spring simulated in model

FIGURE 22. Continued.
D48 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

117° 116° 114° 113° 112°

42°

41° 

40'

39° 

38°

37° - 

\

36° 

I 

I

__(__OREG OREGON

^ 

NEVADA

i1 V

r\ F

,c-s **v/ ^ <

nSaltVake\ J\ / :iM"^ N^"'

\

\1

\

EXPLANATION

Area where ground water is consumed by 

evapotranspiration Approximately 

located

Low-permeability rocks

ouuu Potentiometric contour Shows altitude of

simulated ground-water level in upper model 

layer. Interval 1,000 feet. Hachures indicate 

depression. Datum is sea level

 Boundary of carbonate-rock province model

100 MILES

Boundary of flow region, upper model layer 

Approximately located

100 KILOMETERS

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000,1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D49

Transmissivities in the upper model layer (fig. 

20A) are generally low in model cells that correspond to outcrops of these rocks.

The distribution of low-permeability rocks in 

the subsurface may be more extensive than indicated by outcrop. Where present, these rocks could 

act as effective barriers to deep ground-water flow. 

Aeromagnetic data indicate that several subsurface magnetic bodies are present in the province; 

these are interpreted as low-permeability intrusive and igneous rocks (Plume, 1995). Large magnetic bodies are most prevalent in Utah, extreme 

eastern Nevada, and southern Nevada (fig. 24A). 

These bodies correspond to outcrop areas of intrusive and other crystalline rocks. A long, linear magnetic body in north-central Nevada is 

associated with the Oregon-Nevada lineament (fig. 

22.B). Only a few small magnetic bodies are present 

in east-central Nevada, an area devoid of extensive outcrops of low-permeability rocks. Transmissivities in the lower model layer are generally 

less than 0.006 ft2/s in areas associated with the 

subsurface magnetic bodies (figs. 20.B and 24A). 

Consequently, only small quantities of flow are 

simulated in these areas. Several regional springs 

are upgradient from outcrop areas of low-permeability rocks or subsurface magnetic bodies (fig. 

24A, B\ further suggesting that intrusive and 

other crystalline rocks are effective barriers to 

deep ground-water flow.

Ground-water flow also may be affected by 

the presence of metamorphic core complexes in 

the Ruby Mountains and the Deep Creek and 

Snake Ranges (fig. 24). These complexes include 

a metamorphic-plutonic basement terrane, an overlying transition zone of abrupt change in lithology and structure characterized by intense strain, 

and an unmetamorphosed cover characterized by 

low-angle detachment faults (Stewart, 1980, p. 80; 

Coney, 1980). Generally, transmissivities in the 

lower model layer are low in the vicinity of the 

metamorphic core complexes (fig. 20.B), causing 

mounding effects at these locations. Simulated 

ground-water flow in areas of the core complexes 

is radially outward. Estimated recharge in mountains associated with the core complexes is higher 

than in adjacent mountains because the mounFIGURE 23. Distribution of shallow-flow regions delineated in 

upper model layer in relation to (1) areas where ground 

water is consumed by evapotranspiration (Harrill and others, 

1988, pi. 2), (2) simulated water levels in upper model layer, 

and (3) outcrops of low-permeability rocks (modified from 

Plume, 1995).

tains are higher in altitude, thus contributing to 

the radial flow pattern.

The areas of high transmissivities (values exceeding 0.006 ft2/s) in the lower model layer correspond to areas near regional springs or to areas 

where estimated water budgets indicate interbasin 

flow. Elsewhere, the quantities of simulated deep 

flow are small, perhaps because the carbonate 

rocks are thin, are present as isolated blocks, or 

are buried beneath low-permeability rocks. High 

transmissivities may reflect areas where the carbonate rocks are thick and generally continuous 

An area of high transmissivities extending from 

east-central Nevada into southern Nevada (fig. 

25) generally corresponds to an area defined by 

Dettinger (1989, p. 13-16) as the central corridor (shown in figure 251 This corridor of carbonate 

rocks may be the principal conduit for regional 

flow from east-central Nevada into southern Nevada. High transmissivities in west-central Utah 

(fig. 25) also correspond to an area where carbonate rocks are continuous and relatively thick 

(Carlton, 1985, p. 11). This area is simulated as 

a major conduit for northward flow from western 

Utah into the southern end of the Great Salt Lake 

Desert. The high transmissivities adjacent to regional springs is consistent with the results of 

aquifer tests of carbonate rocks in eastern and 

southern Nevada. Results from aquifer tests indicate that the carbonate rocks are, on the average, 25 times more transmissive within 10 miles 

of regional springs than farther away (Dettinger, 

1989, p. 16).

DISTRIBUTION OF FLOW INTO REGIONS

Ground-water flow in the carbonate-rock province is generally from recharge areas in the mountains to discharge areas on the valley floors. Much 

of this is shallow flow from a local recharge area 

to an adjacent valley floor. However, in areas 

where permeable consolidated rocks (primarily 

fractured carbonate rocks) exist, ground water can 

flow at greater depths beneath mountains and 

valley floors. The deeper water can originate in 

distant recharge areas outside the topographic 

drainage basin in which it is discharged. Groundwater flow through deep permeable consolidated 

rocks is best exemplified by large springs or spring 

groups, from which the discharge greatly exceeds 

the estimated local recharge. Examples include 

the springs in Ash Meadows (Winograd and 

Thordarson, 1975, p. 75-78), the Muddy River
D50 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

118° 117° 115° 113°

DEATH \N, 

VALLEY ' 

'REGION

I I Low-permeability rocks

35°

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000,1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°

Metamorphic core complex Approximately 

located

Subsurface magnetic body Inferred lowpermeability rocks that could act as a barrier 

to deep flow. Approximately located

 5000 Potentiometric contour Shows altitude of 

simulated ground-water level in lower model 

layer. Interval 1,000 feet. Hachures indicate 

depression. Datum is sea level

Boundary of carbonate-rock province model

 Boundary of flow region in lower model layer 

Approximately located

Note: explanation continued on figure 24B

FIGURE 24. Distribution of deep-flow regions and subregions delineated in lower model layer in relation to (A) metamorphic 

core complexes (Coney, 1980; Stewart, 1980), low-permeability rocks and magnetic source bodies (modified from Plume, 

1995); and (B) generalized directions of deep ground-water flow
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D51

118° 116° 115° 113° 112°

EXPLANATION (continued)

37° 

- - - - Boundary of flow subregion in lower

model layer Approximately located

Generalized direction of deep groundwater flow

Spring simulated in model

36'

35° 

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000,1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°

FIGURE 24. Continued.
D52 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

118° 116° 115'

41° 

40'

39° 

High transmissivity zone Shows area 

where estimated transmissivities in 

lower layer exceed 0.006 feet squared 

per second

Boundary of central corridor of thick 

carbonate rocks Approximately 

located. Queried where not delineated. 

(From Dettinger, 1989, p. 14)

Boundary of carbonate-rock province 

model

Spring simulated in model

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250.000, 1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45°30', central meridian -114°

FIGURE 25. Distribution of high transmissivities in lower model layer in relation to springs simulated in model and to 

boundary of central corridor of thick carbonate rocks in south-central Nevada.
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D53

Springs (Eakin, 1966, p. 251), and the Fish Springs 

(Bolke and Sumsion, 1978, p. 13). A schematic 

depiction of shallow flow overlying deep regional 

flow, which is based on concepts presented by Toth 

(1962, 1963) and Freeze and Witherspoon (1966, 

1967), is shown for the carbonate-rock province 

in figure 26.

The delineation of flow regions in both model 

layers is based on a graphical plot of horizontal 

flow across common boundaries between model 

cells, which are referred to as cell faces (fig. 26). 

The flow-region boundaries in each model layer 

were hand drawn on l:l,000,000-scale maps considering only horizontal flow within each layer. 

Vectors were machine drawn on the maps at the 

center of each cell face in the direction of horizontal flow; the length being proportional to the 

base 10 logarithm of the simulated flow across 

the cell face. Cells having inward, horizontal flow 

from adjacent cells in each layer were first identified, then the area contributing horizontal flow 

to these cells was determined from flow vectors 

in surrounding cells. In some areas, as in the 

Great Salt Lake Desert, groups of cells having 

inward flow are considered a single sink.

Flow regions in the upper model layer are 

referred to as shallow-flow regions. Forty-five regions are delineated in the model (fig. 23).

Active cells in the lower model layer are 

grouped into deep-flow regions (fig. 24A). The regions are delineated for terrain in which water 

levels generally decline toward one of five major 

discharge areas. Four of the flow regions are 

named for the geographic area of lowest land-surface altitude and lowest ground-water level within 

that region. Thus, the flow region in which water levels and land surface generally decrease toward Death Valley is called the Death Valley 

region. Other regions named this way are the Colorado River, Railroad Valley, and upper Humboldt 

River regions. The huge area that includes Great 

Salt Lake and the Great Salt Lake Desert is 

named the Bonneville region because most of it 

was inundated by pluvial Lake Bonneville during the Pleistocene epoch. Not all horizontal flow 

in the lower layer reaches one of the major regional discharge areas. Thus, deep-flow regions 

are further divided into subregions. Seventeen 

subregions are delineated in the lower layer (fig. 

24B).

The number of subregions in the lower layer 

is the same as the number of flow systems delineated by Harrill and others (1988, pi. 2), although 

the boundaries between subregions do not everywhere correspond to those of the flow systems.

Flow-system boundaries drawn by Harrill and others (1988) are along topographic divides between 

hydrographic areas and are based on water-level 

gradients and flow budgets in each hydrographic 

area. In contrast, the subregion boundaries delineated herein are not constrained by topographic 

divides and hydrographic areas. Instead, they are 

based on the area within the lower layer that 

contributes horizontal flow to model cells having 

inward flow.

Boundaries of deep-flow regions (fig. 24A) do 

not everywhere correspond to boundaries of shallow-flow regions (fig. 23). For example, the Colorado River deep-flow region (fig. 24A) underlies 

several shallow-flow regions that also overlap the 

adjacent Bonneville and Death Valley deep-flow 

regions. Similarly, the Railroad Valley deep-flow 

region underlies several shallow-flow regions that 

also overlap the adjacent upper Humboldt River 

and Death Valley deep-flow regions. This results 

in the simulation of upper-layer flow that moves 

across underlying boundaries of deep-flow regions 

(fig. 26JS). Although model results indicating differences in the horizontal directions of shallow 

flow and deep flow are simulated on the basis of 

limited data, such differences have been reported 

in central Nevada (Dinwiddie and Schroder, 1971). 

The general patterns of ground-water flow in both 

model layers shown in figure 26B depend on (1) 

the configuration of the water table simulated in 

the upper layer and (2) the hydraulic properties 

assigned to model cells in both layers. The effect 

of these two factors in combination with a third 

factor the ratio of depth to lateral extent for a 

basin is discussed by Freeze and Witherspoon 

(1967, p. 625-632).

Vertical flow between model layers is illustrated in figure 27. Vertical flow between layers 

for each cell is depicted as being predominantly 

upward, predominantly downward, or negligible 

(less than 0.01 ft3/s over a cell area of 37.5 mi2 ). 

Downward flow is generally simulated in model 

cells corresponding to areas of recharge. Upward 

flow is generally simulated in areas of discharge. 

Little vertical (as well as horizontal) flow is simulated in the Great Salt Lake Desert because little 

ground water is estimated to discharge there. Consequently, estimated transmissivities and vertical leakances of cells in the area are among the 

lowest in the model.

A total of 428,000 acre-ft/yr (28 percent of 

total recharge to the model) is simulated as downward flow from the upper layer to the lower layer. 

Discharge at regional springs accounts for 211,000 

acre-ft/yr of the flow out of the lower layer (which
Not to scale

B

4

Fault zone

Evapotranspiration Boundary of shallow Spri/n9 dischar9e 

/ flow region.

Recharge Model cell

/

Upper model 

- layer *

\

Lower model

~ layer "*

Not to scale

C

t|

- 1 - i

\

\ r ' "

1 

* «*

*/

- 1 - HI * t ... T ,<* 

1

^*

.

T

»l

1 - 1

\

Spring discharge

Evapotranspiration 4 

Recharge 4 1 

i 1 "

\

*> - 1

1 n

I

Cell face -___^

* *-

**

Boundary of deep flow region

i f j EXPLANA1K

Subsurface flow

Not to scale

Simulated direction of 

ground-water flow

 ^ Upper model layer 

_». Lower model layer

Boundary of flow region 

..... water table

FIGURE 26 Schematic diagrams showing (A) conceptualization of ground-water flow from recharge areas in mountains to discharge areas on basin floors; (B) 

same conceptualization as in A but represented in finite-difference computer model; and (C) summary of water budget within area encompassed by a 

deep-flow region on basis of computer-model output.

OI-Ho

&

c!C/3S!C/3

V

Hi
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D55

118° 117° 116° 115° 114° 113°

Vertical flow between model layers

36° 

Downward from upper layer to lower layer 

(greater than 0.01 cubic feet per second, 

per cell)

Upward from lower layer to upper layer 

(greater than 0.01 cubic feet per second, 

per cell)

Negligible (less than 0.01 cubic feet per 

second, per cell)

Boundary of carbonate-rock province 

model

35

Base modified from U.S. Geological Survey digital linegraph data, 1:100,000 and 1:250,000,1987

Albers Equal-Area Conic projection

Standard parallels 29°30' and 45C30', central meridian -114"

FIGURE 27. Distribution of vertical flow between model layers.
D56 REGIONALAQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

is equivalent to 49 percent of the downward flow 

into the lower layer). The remaining 217,000 acreft/yr (51 percent) is upward leakage to the upper 

layer.

Results of model simulations are summarized 

in a separate section for each of the five deepflow regions. Flow in each region is compared with 

flow described by other investigators. A simulated 

ground-water budget is presented for each deepflow region and subregion. The budget, calculated 

using a computer program written by Harbaugh 

(1990), includes the flow through corresponding 

cells in the upper model layer that is, the budget includes all recharge and discharge in both 

model layers within each deep-flow region and 

subregion. Although flow-region boundaries do not, 

in theory, have flow across them, the budget for 

each deep-flow region and subregion includes subsurface flow to or from adjacent regions or subregions. This cross-boundary flow is included for 

two reasons. First, the boundaries of deep-flow 

regions and subregions commonly are drawn within 

model cells (fig. 26B), but the cells that straddle 

a boundary are assigned to only one of the two 

regions or subregions for water-budget calculations (fig. 26C). Second, upper-layer flow in a shallow-flow region can cross the underlying boundary 

of a deep-flow region or subregion in places where 

the shallow-flow and deep-flow boundaries do not 

coincide (fig. 26JB, C). Most of the cross-boundary flow takes place in the upper layer.

The simulated ground-water budget for each 

deep-flow region and subregion is summarized in 

terms of inflow and outflow components. Inflow 

includes recharge assigned to the upper model 

layer beneath mountain ranges, leakage to the 

upper layer from head-dependent flow boundaries, 

and subsurface flow from adjacent regions and 

subregions in both layers. Outflow includes evapotranspiration and leakage to head-dependent flow 

boundaries from the upper layer, regional spring 

discharge from the lower layer, and subsurface 

flow to adjacent regions and subregions in both 

layers. The evapotranspiration and leakage components of outflow include spring flow that is not 

assigned to regional springs in the lower model 

layer. Head-dependent flow boundaries are used 

in the model to simulate leakage of ground water to or from the principal rivers, lakes, and sinks 

(including Death Valley) that border or are within 

the model area. These boundaries allow either 

inflow to or outflow from the upper layer. Thus, 

leakage components are included as both inflow 

and outflow for the budget of each deep-flow region 

and subregion.

Recharge areas contributing flow to regional 

springs are determined on the basis of a computer program that tracks ground-water flowpaths 

backward (upgradient) from the model cells that 

represent the springs (Pollock, 1989). The program is not used to determine the increment of 

flow from each contributing area, because porosities and cell thicknesses in the model area are 

largely unknown. The areal distribution of incoming flow to each regional spring is indicated in a 

general way by comparing the flow quantities computed for each face of the cell that represents 

the spring.

Although the directions of ground-water flow 

and the quantities of inflow and outflow are described in quantitative detail for each deep-flow 

region, the uncertainties in estimating recharge 

and evapotranspiration, and the lack of information on hydraulic properties and extent of rock 

units in the subsurface, result in several alternatives regarding directions and quantities of 

ground-water flow within the carbonate-rock province. Thus, the conceptualization presented herein 

is but one of several possible scenarios. Some alternative scenarios particularly with regard to 

the flow of ground water to major discharge areas are also discussed.

FLOW REGIONS 

DEATH VALLEY REGION

The Death Valley region, in the southwestern part of the study area (fig. 24A), encompasses 

about 19,000 mi2 . It includes four deep-flow subregions in the lower model layer Big Smoky, 

Clayton, Pahrump-Amargosa, and Mesquite (fig. 

28) and all or part of eight shallow-flow regions 

in the upper model layer (fig. 23). Little groundwater flow is simulated between deep-flow subregions even though water levels generally decline 

toward Death Valley.

The Death Valley region includes some of the 

most intensively studied terrane in the Great Basin. With the inception of underground nuclear 

explosions at the Nevada Test Site in 1957, detailed investigations were begun to determine the 

occurrence and movement of ground water within 

and adjacent to the Test Site, thereby permitting 

an assessment of ground-water contamination 

(Winograd and Thordarson, 1975, p. Cl). Results 

of these investigations have been summarized in 

several reports (Winograd and Eakin, 1965; 

Winograd and Thordarson, 1968, 1975; Rush, 1970;
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D57

Winograd and Friedman, 1972; Blankennagel and 

Weir, 1973; Naff and others, 1974; Winograd and 

Pearson, 1976; Waddell, 1982; Czarnecki and 

Waddell, 1984; Waddell and others, 1984).

INFLOW

Total inflow to the Death Valley region is 

177,000 acre-ft/yr, of which recharge assigned to

cells in the upper model layer totals about 161,000 

acre-ft/yr (table 4). Principal recharge areas include the Toquima Range and eastern slope of 

the Toiyabe Range in the north, and the Spring 

Mountains in the south (fig. 28). Small quantities of recharge are also simulated in several other 

mountain ranges. The remaining 16,000 acre-ft/yr 

of simulated inflow enters the region as subsurface 

flow in both layers from adjacent regions (table 

4): About 6,000 acre-ft/yr is simulated to the Big

117°

I BIG SMOKY 

SUBREGION

39'

CLAYTON 

SUBREGION

38°

PAHRUMP

EXPLANATION

I 3 I Generalized area of recharge Number is assigned 

recharge in thousands of acre-feet per year. Values 

less than 500 acre-feet per year are not shown

B9 Generalized area of discharge from upper model layer 

Number is simulated evapotranspiration and (where present) 

leakage to head-dependent flow boundaries, in thousands of 

acre-feet per year. Values less than 500 acre-feet per year 

are not shown

'' Regional spring and simulated discharge Number is 

simulated discharge in thousands of acre-feet per year

Approximate simulated boundary of Death Valley region 

Approximate simulated boundary of subregion

AMARGOSA 

SUBREGION

'LN

ARK

LOCATION MAP

0

1 

0 

\.

\ MESQUITE 

SUBREGION

50 MILES

I 1

I 

50 KILOMETERS

FIGURE 28. Areas of assigned recharge, simulated discharge from upper model layer, and simulated discharge

from regional springs in Death Valley region.
D58 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

TABLE 4. Simulated ground-water flow budgets, Death Valley region

[All amounts are in acre-feet per year (acre-ft/yr), rounded to nearest 1,000 acre-ft/yr. Amounts of mountain recharge are assigned, 

as described in text section title "Estimates of Recharge"; all other listed amounts are determined from model simulation]

Budget component and Pahrump-

(in parentheses) Big Smoky Clayton Mesquite Amargosa Entire Death

primary model layer involved subregion subregion subregion subregion Valley region

INFLOW

Mountain recharge (upper) 75,000

Subsurface inflow from adjacent

regions (both) °6,000

Subsurface inflow from adjacent

subregions (both) 0

25,000 

a 1,000 

C5,000

1,000

minor

0

60,000 

*9,000

161,000

16,000 

(d)

Total inflow

OUTFLOW

Evapotranspiration* (upper) 

Regional springs (lower) 

Subsurface outflow to adjacent 

regions (both)

Subsurface outflow to adjacent 

subregions (both) 

Leakage (upper)

Total outflow'

81,000

77,000

0

A,000

/I4,000 

0

82,000

31,000

31,000

0

31,000

1,000

2,000

0

2,000

69,000

37,000

22,000

"1,000 

'8,000

70,000

177,000

147,000

22,000

3,000 

(d)

8,000

180,000

From Railroad Valley region.

Includes 8,000 acre-ft/yr from Colorado River region and 1,000 acre-ft/yr from Railroad Valley region. 

c Includes 4,000 acre-ft/yr from Big Smoky subregion and 1,000 acre-ft/yr from Pahrump-Amargosa subregion.

Net flow among subregions within Death Valley region is zero.

e Includes evapotranspiration of flow from small springs that are assumed to be discharging from upper layer; does not include 

evapotranspiration of flow from regional springs that are simulated to be discharging from lower layer. 

 'To upper Humboldt River, region. 

8 To Colorado River region.

To Clayton subregion. 

\ To Death Valley playa. 

J Total outflow does not always equal total inflow due to rounding of individual values.

Smoky subregion from the Railroad Valley region, 

about 8,000 acre-ft/yr to the Pahrump-Amargosa 

subregion from the Colorado River region, and 

1,000 acre-ft/yr each to the Clayton and PahrumpAmargosa subregions from the Railroad Valley 

region.

OUTFLOW

Simulated outflow from the Death Valley region is 180,000 acre-ft/yr, of which 147,000 acreft/yr is evapotranspiration from the upper model 

layer (table 4). Principal areas of simulated evapotranspiration are in Big Smoky Valley, Monitor

Valley, and Clayton Valley in the north, and Ash 

Meadows in Amargosa Desert, Pahrump Valley, 

and Death Valley in the south (fig. 28). In addition, 22,000 acre-ft/yr is simulated as discharge 

from regional springs in the lower layer, 8,000 

acre-ft/yr as discharge to the Death Valley playa 

through head-dependent flow boundaries in the 

upper layer, and 3,000 acre-ft/yr as subsurface 

flow to adjacent regions in both layers. Simulated 

discharge from regional springs includes 17,000 

acre-ft/yr at Ash Meadows, 3,900 acre-ft/yr at 

Manse Springs in Pahrump Valley, and 720 acreft/yr at Grapevine and Stainigers Springs at the 

north end of Death Valley (table 1). Spring discharge at Furnace Creek in Death Valley (Nevares,
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D59

Texas, and Travertine Springs) is included in the 

discharge to Death Valley playa.

DESCRIPTION OF SUBREGIONS

BIG SMOKY SUBREGION

The Big Smoky subregion, at the extreme 

northern end of the Death Valley region (fig. 28), 

encompasses about 2,400 mi2 . The boundary of 

the subregion differs from that of Harrill and others (1988) in that it extends to the east side of 

Monitor Valley instead of following the crest of 

the Toquima Range. Recharge assigned to cells 

in the upper model layer totals 75,000 acre-ft/yr 

(table 4); most of the recharge is from the Toiyabe 

Range. In addition to recharge, another 6,000 acreft/yr of subsurface flow enters the subregion from 

the Railroad Valley region, primarily through the 

upper model layer on the east side of Monitor 

Valley. Evapotranspiration from the upper layer 

accounts for most of the simulated outflow and 

totals 77,000 acre-ft/yr. Principal areas of evapotranspiration are northern Big Smoky Valley and 

Monitor Valley. A small quantity (about 1,000 acreft/yr) leaves as subsurface flow to the upper 

Humboldt River region in the upper layer. About 

4,000 acre-ft/yr leaves as subsurface flow to the 

Clayton subregion.

Low transmissivities are simulated in both 

model layers in cells corresponding to the Toquima 

Range and to mountains east of Monitor Valley 

(fig. 20). The low transmissivities are needed in 

the model to simulate evapotranspiration in Monitor Valley. Because of the low transmissivities in 

the Toquima Range, flow is simulated mostly in 

the upper layer from the mountain crest east to 

Monitor Valley and west to Big Smoky Valley. Most 

of the shallow and deep flow from the Toiyabe 

Range is simulated as moving to the large discharge area in northern Big Smoky Valley (fig. 

29), where evapotranspiration from the upper layer 

is 62,000 acre-ft/yr. In comparison, 64,000 acreft/yr of evapotranspiration was estimated by Rush 

and Schroer (1970, p. 37-39), who also estimated 

another 5,000 acre-ft/yr as spring discharge but 

noted that part of the spring discharge was included in their estimate of evapotranspiration.

Flow at the north end of the Toquima Range 

is from Monitor Valley to Big Smoky Valley; the 

combined flow in both model layers is 700 acreft/yr. The potential for flow exists between Monitor Valley and Big Smoky Valley because water 

levels in the former are higher than those in the

latter. Thermal water discharges from springs at 

the north end of Big Smoky Valley, which indicates deep circulation of flow along faults or permeable rock. Volcanic rocks are common in the 

Toquima Range, but carbonate rocks crop out at 

a few locations. The sequence of carbonate rocks 

has been thickened as a result of westward movement and overthrusting along the Roberts Mountain thrust fault (McKee, 1976, p. 44-46). Where 

present, the carbonate rocks may provide an avenue for interbasin flow. However, enough precipitation falls in the drainage basin of Big Smoky 

Valley to account for the estimated discharge there 

(E.H. Handman, U.S. Geological Survey, written 

commun., 1992). Thus, if water does flow from 

Monitor Valley to Big Smoky Valley through the 

Toquima Range, the quantity must be small.

CLAYTON SUBREGION

The Clayton subregion, between the Big Smoky 

subregion and the Pahrump-Amargosa subregion 

(fig. 28), encompasses about 3,800 mi2 . The boundary of the Clayton subregion approximates the 

flow-system boundary delineated by Harrill and 

others (1988). Basins contributing subsurface 

ground-water inflow to Clayton Valley include 

southern Big Smoky Valley (Tonopah Flat) to the 

north, and Ralston and Stone Cabin Valleys to 

the northeast. Recharge assigned to cells in the 

upper model layer totals 25,000 acre-ft/yr (table 

4). Most of the recharge is in the southern end 

of the Toiyabe and Toquima Ranges. An additional 

6,000 acre-ft/yr enters the subregion as subsurface flow, primarily in the upper layer (table 4): 

4,000 acre-ft/yr from the Big Smoky subregion, 

and 1,000 each from the Pahrump-Amargosa subregion and Railroad Valley region. Subsurface flow 

out of the Clayton subregion is minimal. Flow in 

both model layers follows the same general path 

to Clayton Valley (fig. 29).

Major discharge areas include southern Big 

Smoky Valley (Tonopah Flat area) and Clayton 

Valley. Simulated evapotranspiration in the upper layer is 31,000 acre-ft/yr (table 4). Evapotranspiration in the Tonopah Flat area is about 8,000 

acre-ft/yr, which is 2,000 acre-ft/yr more than that 

estimated by Rush and Schroer (1970, p. 38). However, simulated evapotranspiration in the model 

is concentrated in the northern part of Tonopah 

Flat, in an area of observed evapotranspiration, 

but not at the southern end, where additional 

evapotranspiration occurs. Evapotranspiration in 

Clayton Valley is about 20,000 acre-ft/yr 4,000
D60 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

acre-ft/yr less than the 24,000 acre-ft/yr estimated 

by Rush (1968a, p. 29).

Simulated flow from Tonopah Flat into Clayton 

Valley is about 11,000 acre-ft/yr, which is slightly 

less than the 13,000 acre-ft/yr ascribed as subsurface flow through carbonate rocks (Rush, 1968a, 

p. 26). Another 7,600 acre-ft/yr is simulated as 

subsurface flow from the northeast, which is 

slightly more than the 5,000 acre-ft/yr reported

by Rush (1968a, p. 27). Simulated subsurface flow 

into Clayton Valley is thus about equal to that 

previously estimated. The possibility of subsurface 

flow from adjacent basins into Clayton Valley was 

first mentioned by Meinzer (1917, p. 144).

During model calibration, transmissivities were 

increased in a narrow band from Big Smoky Valley to Clayton Valley in both model layers until 

they were generally in the range of 0.006 to 0.18

'LANDER IBIG SMOKY 

JSUBREGION

CLAYTON 

SUBREGION

38

PAHRUMP-AMARGOSA 

SUBREGION

i. I* T/II %,%, *? vn^H-g g :V

EXPLANATION

Nevada test site

Simulated direction of ground-water flow

Upper model layer 

Lower model layer

Approximate simulated boundary of Death Valley region 

Approximate simulated boundary of subregion

LOCATION MAP

50 MILES

_| I I I

0 50 KILOMETERS

MESQUITE 

SUBREGION

FIGURE 29. Simulated direction of ground-water flow for both upper and lower model layers in Death Valley

region.
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D61

ft2/s (fig. 25). By increasing transmissivities, simulated evapotranspiration was decreased in northern 

Big Smoky Valley and Tonopah Flat, and increased 

in Clayton Valley, resulting in a better agreement 

with the estimated water levels. The simulated 

transmissivities bracket an estimated transmissivity of 0.09 ft2/s (60,000 [gal/d]/ft) reported by 

Rush (1968a, p. 27) for the area between Tonopah 

Flat and Clayton Valley.

MESQUITE SUBREGION

The Mesquite subregion, at the extreme southern end of the Death Valley region (fig. 28), encompasses only 490 mi2 . The subregion generally 

coincides with the Mesquite Valley hydrographic 

area and with a shallow-flow region delineated 

in the upper layer (fig. 23). The subregion boundaries generally correspond to boundaries of a flow 

system delineated by Harrill and others (1988). 

Inflow in the subregion is about 1,000 acre-ft/yr 

and is recharge assigned to cells in the upper 

model layer. A minor quantity (less than 500 acreft/yr) is simulated as subsurface flow from the 

Colorado River region in the upper layer. Discharge, simulated as evapotranspiration in Mesquite Valley from the upper layer, is about 2,000 

acre-ft/yr (table 4), approximating the 2,200 acreft/yr estimated by Glancy (1968b, p. 26). The subregion does not contribute flow to either the 

Pahrump-Amargosa subregion or the Colorado 

River region. Most of the flow simulated in the 

subregion is within the upper layer. Transmissivities in the lower layer are among the lowest 

in the entire modeled area (fig. 20B); they correspond to an area of low-permeability rocks delineated by Plume (1995) and shown in figure 23.

PAHRUMP-AMARGOSA SUBREGION

The Pahrump-Amargosa subregion encompasses about 12,700 mi2 ; it is the largest subregion delineated in the Death Valley region (fig. 

28). The subregion extends from Stone Cabin Valley and the Kawich Range to the Ivanpah Mountains in California. The northern and southern 

boundaries of the subregion generally correspond 

to the flow-system boundary delineated by Harrill 

and others (1988). The eastern boundary of the 

subregion does not extend as far eastward as that 

of Harrill and others (1988). Hydrographic areas 

included by them but excluded herein are Tikaboo 

Valley, southern Railroad Valley, both parts of

Three Lakes Valley, and northern ends of Groom 

Lake and Kawich Valleys.

Recharge assigned to cells in the upper model 

layer totals 60,000 acre-ft/yr, of which nearly twothirds is in the Spring Mountains. An additional 

8,000 acre-ft/yr enters the subregion as subsurface flow from the Colorado River region in both 

layers. Most of this ground-water inflow is in the 

Spring Mountains, but about 700 acre-ft/yr enters the subregion near the Pintwater Range. 

About half of the simulated inflow along the Spring 

Mountains is in the lower model layer. Subsurface inflow in these mountains is the result of 

assigning cells along the crest, where flow is both 

eastward and westward, to the Colorado River 

region. About 1,000 acre-ft/yr enters the subregion as underflow from the Railroad Valley region (table 4).

Simulated outflow from the subregion totals 

70,000 acre-ft/yr (table 4), including 37,000 acreft/yr as evapotranspiration from the upper model 

layer, 22,000 acre-ft/yr as regional-spring discharge 

from the lower layer, 8,000 acre-ft/yr as leakage 

to head-dependent flow boundaries in the upper 

layer associated with the Death Valley playa, and 

2,000 and 1,000 acre-ft/yr as subsurface flow in 

both layers to the Colorado River region and 

Clayton subregion, respectively. Areas of evapotranspiration of shallow ground water in the subregion include those of Sarcobatus Flat, Oasis 

Valley, Amargosa Desert near Ash Meadows, 

Pahrump Valley, the lower Amargosa River near 

Shoshone, and Death Valley (Harrill and others, 

1988). The only area of evapotranspiration not 

simulated is in Oasis Valley, where Malmberg and 

Eakin (1962, p. 25) estimated 2,000 acre-ft/yr of 

discharge along the channel of the Amargosa River. 

Simulated ground-water flow in the area of Oasis Valley is southward into Amargosa Desert and 

then to Death Valley.

Total simulated discharge in Death Valley is 

about 14,000 acre-ft/yr, which includes the flow 

of Grapevine and Stainiger Springs at the north 

end (fig. 28), leakage to the head-dependent flow 

boundary cells associated with the playa, evapotranspiration at both the north and south ends 

of the playa, and evapotranspiration near Furnace Creek. Not including ground-water flow from 

the Panamint Mountains to the west, estimated 

discharge from the Death Valley playa is about 

8,300 acre-ft/yr (Hunt and others, 1966, p. B38, 

table 25). This value includes the flow of Nevares, 

Texas, and Travertine Springs near Furnace Creek, 

for which Hunt and co-workers estimated a total
D62 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

of 4,100 acre-ft/yr. Later, Miller (1977, p. 27) reported a combined discharge of 2,700 acre-ft/yr.

Evapotranspiration also occurs in a marsh area 

north of the playa, in Mesquite Flat, and at Grapevine and Stainiger Springs. Discharge in these 

areas is not part of the 8,300 acre-ft/yr. Estimated 

evapotranspiration from the marsh area is 3,000- 

5,000 acre-ft/yr; at Mesquite Flat, it is a "few 

thousand acre-ft/yr"; and the combined discharge 

of Grapevine and Stainiger Springs is about 1,000 

acre-ft/yr (Miller, 1977, p. 25, 33). Thus, total estimated discharge is greater than 12,000 acre-ft/yr 

and is similar to the quantity simulated in the model.

Flow in the Pahrump-Amargosa subregion is 

generally from recharge areas toward Death Valley (fig. 29), although much of the recharge generated in the Spring Mountains is discharged 

between the Spring Mountains and Death Valley. In the southern part of the subregion, south 

of Pahrump Valley, flow is generally westward. 

Evapotranspiration is simulated in several model 

cells south of Shoshone (fig. 28), but the quantity is small. The cells correspond to the channel 

of the Amargosa River, where only small, localized areas of evapotranspiration are mapped by 

Harrill and others (1988). Increasing the transmissivities in these cells would reduce the simulated evapotranspiration and thereby allow more 

ground-water flow to Death Valley. Little flow is 

simulated in the area south of Shoshone because 

estimated recharge is minor and transmissivities 

in both model layers are low (fig. 20). Consolidated rocks in this area have low transmissivities because the proportion of carbonate rocks is 

small (fig. 23; Plume, 1995).

Westward flow is simulated in both model layers from the Spring Mountains to destinations 

in Pahrump, Shoshone, and Death Valleys (fig. 

29). Simulated evapotranspiration and regionalspring discharge in Pahrump Valley is about 

15,000 acre-ft/yr. This total is within the range 

of 10,000 to 19,000 acre-ft/yr reported by Harrill 

(1986, p. 46). Another 9,000 acre-ft/yr is simulated as discharging near Shoshone (fig. 28). Estimated subsurface flow from Pahrump Valley to 

the area near Shoshone is 6,000 to 18,000 acreft/yr (Harrill, 1986, p. 46). The quantity simulated in the model is 10,000 acre-ft/yr, of which 

about 1,400 acre-ft/yr is simulated as flow from 

Shoshone into Death Valley.

GROUND-WATER FLOW TO FURNACE CREEK

Flow to the springs at Furnace Creek, along 

the east side of Death Valley, has been postulated to originate in Ash Meadows, or in Pahrump 

Valley, with the flow passing through Ash Meadows (Hunt and others, 1966, p. B39, B40), although 

Winograd and Thordarson (1975, p. C96) asserted 

that flow from Pahrump Valley to Ash Meadows 

is unlikely. Discharge through head-dependent flow 

boundaries in the Furnace Creek area is about 

2,900 acre-ft/yr. An additional discharge of 2,600 

acre-ft/yr is simulated as evapotranspiration in 

two adjacent cells, making a total of 5,500 acreft/yr. This discharge is only 400 acre-ft more than 

that estimated by Hunt and others (1966, p. B38).

Flow to springs at Furnace Creek is simulated from recharge areas in the Kawich Range, 

Pahute Mesa, Yucca Mountain, the Belted Range, 

and, to a much lesser extent, the Funeral Mountains. Generally, flow is south from the recharge 

areas to just west of Ash Meadows, then west 

through the Funeral Mountains. No flow is simulated directly from Ash Meadows to Furnace Creek.

Carbonate rocks crop out in a nearly continuous band in the Funeral Mountains west of Ash 

Meadows and provide an avenue of flow through 

the mountains. Postulated sources of spring discharge at Furnace Creek are direct flow from Ash 

Meadows or downward leakage from the basin fill 

beneath the central and south-central Amargosa 

Desert (Winograd and Thordarson, 1975, p. C96). 

Water in the basin fill may be from spring runoff at Ash Meadows, from southward flow through 

the Nevada Test Site, or from southeastward flow 

through the upper Amargosa Desert. The chemistry of water from each of these areas is similar 

to the water discharged at Furnace Creek 

(Winograd and Thordarson, 1975, pi. 3).

Although no water is simulated as flowing directly from Ash Meadows to Furnace Creek, model 

results do not rule out the possibility of underflow 

between the two spring areas. Transmissivities 

used in the model are averaged over a large area, 

and only general trends have been simulated. Although transmissivities could be adjusted to attain underflow from beneath Ash Meadows directly 

to Furnace Creek, existing data are as yet insufficient to justify such an adjustment.

GROUND-WATER FLOW TO ASH MEADOWS

Ash Meadows is the largest discharge area 

in the Pahrump-Amargosa subregion and has been 

studied for many years because of its proximity 

to the Nevada Test Site, because of its close relation to Devils Hole (habitat of an endangered 

species of pupfish), and, more recently, because 

of hydrologic studies regarding the feasibility of
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D63

nuclear-waste storage at Yucca Mountain. Among 

the studies discussing flow in the vicinity of Ash 

Meadows are those of Winograd (1962, 1963), 

Winograd and Thordarson (1975), Winograd and 

Pearson (1976), Dudley and Larson (1976), Waddell 

(1982), Czarnecki and Waddell (1984), Waddell and 

others (1984), and Dettinger (1989). The most detailed discussion on the possible sources of ground 

water at Ash Meadows is presented by Winograd 

and Thordarson (1975, p. C85-C92 and p. C108- 

C113).

Simulated discharge in the vicinity of Ash 

Meadows totals about 26,000 acre-ft/yr, including 17,000 acre-ft/yr of regional spring discharge 

from the lower layer and 9,000 acre-ft/yr as evapotranspiration from the upper layer (fig. 28). The 

simulated distribution of evapotranspiration approximates the distribution mapped by Harrill and 

others (1988), except that areas of simulated 

evapotranspiration extend farther upgradient from 

the springs, whereas mapped areas extend farther downgradient. Estimated discharge in this 

area is 24,000 acre-ft/yr (Walker and Eakin, 1963, 

p. 21-27), including 17,000 acre-ft/yr from regional 

springs (table 1).

Recharge areas contributing flow to Ash Meadows include mountain ranges as far north as the 

southern ends of the Kawich and Belted Ranges 

and as far east as the Pintwater Range and Spring 

Mountains. The Spring Mountains account for 

much of the recharge in southern Nevada. Consequently, a large ground-water mound is simulated beneath the mountains, from which flow is 

radially outward. Northward flow from the Spring 

Mountains is simulated to the Spotted Range (fig. 

29), where the direction changes to westward flow 

beneath Frenchman Flat and eventually southwestward to Ash Meadows. Flow in the upper layer 

from recharge in the Pintwater Range is simulated as entering the subregion near Indian Spring 

Valley.

Subsurface flow from Pahrump Valley, excluding direct flow from the north end of the Spring 

Mountains, to the adjacent Amargosa Desert also 

is simulated, but the quantity is only 1,400 acreft/yr. None of this ground water is simulated as 

discharging at Ash Meadows. Instead, the flow 

moves southwestward toward Death Valley. Estimates of flow between Pahrump Valley and Ash 

Meadows range from as little as 3,000 to as much 

as 13,000 acre-ft/yr, as summarized by Winograd 

and Thordarson (1975, p. C90-C92). However, they 

concluded that only a small percentage of Ash 

Meadows discharge may actually originate in 

Pahrump Valley. They based their conclusion on

(1) the presence of low-permeability rocks between 

the basins, (2) differences between the quality of 

water discharging at Ash Meadows and ground 

water in Pahrump Valley, and (3) the estimated 

water-level gradient between the two areas.

Most of the water simulated as discharging 

from Ash Meadows originates in the Spring Mountains. Flow southward from Yucca Flat through 

the Nevada Test Site to Ash Meadows is about 

3,000 acre-ft/yr through the lower layer and 1,000 

acre-ft/yr through the upper layer. This accounts 

for about 15 percent of the total simulated discharge at Ash Meadows. Subsurface outflow to 

Death Valley from the two model cells representing the regional springs at Ash Meadows is only 

200 acre-ft/yr.

The area contributing flow to Ash Meadows 

differs from that of Winograd and Thordarson 

(1975, pi. 1 and p. C85-C90) to the east and northeast. They include recharge from the Desert and 

Sheep Ranges east of the Pintwater Range and 

subsurface flow from Pahranagat Valley, but do 

not delineate the northern extent of the area. Their 

boundary on the east side of the Sheep Range is 

drawn on the basis of low-permeability clastic 

rocks exposed along a thrust fault in the southern (and highest) part of the Sheep Range 

(Winograd and Thordarson, p. C87). More recent 

evidence (Dettinger, 1989, p. 13) suggests that a 

thick section of carbonate rocks is present beneath 

the Sheep Range and that the underlying clastic 

rocks are sufficiently high in altitude on the west 

side of the Sheep Range to impede westward flow 

of water recharging in the Sheep Range. This evidence supports geochemical balances indicating 

that nearly all recharge generated in the Sheep 

Range may flow north and east toward Muddy 

River Springs (Thomas, 1988).

The Desert Range, between the Pintwater and 

Sheep Ranges, may be a more logical location for 

a divide between the Death Valley and Colorado 

River regions. Precambrian and Cambrian clastic rocks are exposed in the central part of the 

Desert Range (Winograd and Thordarson, 1975, 

pi. 1). Dettinger (1989, p. 13) noted two areas 

underlain by relatively thick sequences of carbonate rocks near the boundary between Clark and 

Lincoln Counties: the Pintwater-Spotted Range 

area (Guth, 1988) and the Coyote Spring Valley 

area (Guth, 1988; Wernicke and Axen, 1988, p. 

1749). These two areas are connected to a similar area of thick carbonate rocks to the north and 

may represent the principal conduits for regional 

flow from east-central Nevada to Ash Meadows 

and Muddy River Springs (Dettinger, 1989, p. 13).
D64 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

Although no flow is simulated in the model from 

areas north of the Pintwater Range to Ash Meadows, geologic evidence indicates that such flow 

is possible.

The current boundaries of the deep-flow region are determined from model calibrations based 

on measured water levels at a few sites and estimated discharges for each hydrographic area. 

During model calibration, changing the hydraulic properties near any one of the principal discharge areas (for example, Las Vegas Valley, 

Pahrump Valley, Ash Meadows, and Muddy River 

Springs) resulted in changed flow quantities at 

the other discharge areas. Such changes suggest 

that the flow boundary between the Colorado River 

and Death Valley regions is sensitive to hydraulic properties near areas of discharge. Because 

boundaries of flow regions are dependent on flow 

from recharge areas to discharge areas, changing the flow quantity at a discharge area results 

in a shift of flow-region boundaries. For example, 

a five-fold transmissivity increase in two lowerlayer cells representing the regional springs at 

Ash Meadows increased the simulated discharge 

at Ash Meadows by about 3,000 acre-ft/yr and decreased the discharge at Muddy River Springs by 

about 1,400 acre-ft/yr, indicating that the simulated boundary between the two regions shifted 

eastward. Similarly, a transmissivity increase in 

five upper-layer cells on the east side of Las Vegas Valley increased evapotranspiration in the 

valley and reduced the simulated flow to Ash 

Meadows and Pahrump Valley, suggesting that the 

flow-region boundary moved westward in the 

Spring Mountains.

Model results present but one possibility of 

flow to Ash Meadows. Flow from Pahranagat Valley 

to Ash Meadows is suggested by Winograd and 

Friedman (1972, p. 3700), Thomas (1988), and Kirk 

and Campana (1990). To simulate such flow in 

the model, transmissivities could be increased 

between the two areas. However, this would increase the total discharge at Ash Meadows unless some of the flow currently simulated to the 

springs is diverted elsewhere.

Northward flow from the Spring Mountains 

may be inhibited by the Las Vegas Valley shear 

zone (fig. 22). Evidence for this in one area is 

presented by Winograd and Thordarson (1975, p. 

C67). If the shear zone does block northward flow, 

more water from the Spring Mountains may flow 

toward Las Vegas Valley, and less to Ash Meadows, than is simulated herein. Reducing flow to 

Ash Meadows would allow for the simulation of

flow from the Pahranagat Valley area to Ash 

Meadows.

In summary, current boundaries of deep-flow 

regions and subregions are based on limited estimates of water levels and on the distribution 

of estimated recharge and discharge. The model 

simulation provides one concept of flow from areas of recharge to areas of discharge. If the estimates of recharge and discharge used in model 

calibration are grossly incorrect, then the flow 

boundaries as delineated in this report are also 

incorrect. Model results suggest that the Death 

Valley deep-flow region can be divided into subregions that are virtually separate, compartmentalized flow systems. Model results also suggest 

that estimated discharge at Ash Meadows can be 

accounted for by flow from the Spring Mountains 

and from recharge areas in and north of the Nevada Test Site. If water from east-central Nevada 

also discharges to Ash Meadows, as indicated from 

geochemical evidence (Winograd and Friedman, 

1972, p. 3700; Thomas, 1988), then either the estimates of discharge are too low or some (or all) 

of the water currently simulated as flowing to 

Ash Meadows actually flows elsewhere.

COLORADO RIVER REGION

The Colorado River region, in the southeastern part of the study area (fig. 24A), encompasses 

about 19,000 mi2 . It includes four deep-flow subregions in the lower layer Penoyer, Las Vegas, 

Virgin River, and White River (fig. 30) and all 

or part of 11 shallow-flow regions in the upper 

layer (fig. 23). Little ground-water flow is simulated between the deep-flow subregions, even 

though water levels generally decline toward the 

Virgin and Colorado Rivers.

Las Vegas Valley is the most intensively studied area in the Colorado River region of the study 

area. A rapidly increasing population since World 

War II has resulted in severe ground-water overdrafts in the basin-fill aquifers. Several detailed 

studies have been undertaken to assess the 

ground-water resources in Las Vegas Valley and 

to ascertain the changes caused by development 

(Maxey and Jameson, 1948; Domenico and others, 1964; Malmberg, 1965; Harrill, 1976; Morgan and Dettinger, 1994). Several other studies 

have been undertaken in an effort to explain 

the origin of flow from large springs along the 

course of the White River and at Muddy River 

Springs (Eakin, 1966; Winograd and Friedman,
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D65

1972; Welch and Thomas, 1984; Thomas, 1988; 

Kirk and Campana, 1990). These studies, along 

with hydrologic reconnaissance investigations 

elsewhere in the region, form the basis for comparison of ground-water flow with the model 

results.

INFLOW

Simulated inflow to the Colorado River region is about 207,000 acre-ft/yr, of which recharge 

to cells in the upper model layer totals about 

202,000 acre-ft/yr (table 5). Principal recharge 

areas include the White Pine, Egan, and Schell 

Creek Ranges in the north; the Wilson Creek, 

Bristol, and Quinn Canyon Ranges in the central part; and the Spring Mountains and Sheep 

Range in the south (fig. 30). Small quantities of 

recharge are also assigned to several other mountain ranges. In addition, about 5,000 acre-ft/yr 

enters the region as subsurface flow in both layers from adjacent regions: about 1,000 acre-ft/yr 

is simulated as subsurface flow to the White River 

subregion from the Railroad Valley region, about 

2,000 acre-ft/yr to the Penoyer subregion from the 

Death Valley region, and about 2,000 acre-ft/yr 

to the Virgin River subregion from the Bonneville 

region v table 5).

OUTFLOW

Simulated outflow from the Colorado River 

region is about 205,000 acre-ft/yr (table 5). In contrast to the other regions, simulated discharge 

from regional springs (97,000 acre-ft/yr) in the 

lower model layer exceeds discharge from evapotranspiration (91,000 acre-ft/yr) in the upper model 

layer. Regional-spring discharge is simulated in 

White River Valley (25,000 acre-ft/yr), at Panaca 

Warm Spring near Panaca (9,900 acre-ft/yr), in 

Pahranagat Valley (24,000 acre-ft/yr), at Muddy 

River Springs (37,000 acre-ft/yr), and at Rogers 

and Blue Point Springs south of Overton (1,200 

acre-ft/yr). Major areas of simulated evapotranspiration are in White River in the north, 

Pahranagat Valley in the central part, and Las 

Vegas Valley and the Muddy River Springs area 

in the south (fig. 30). The remaining simulated 

outflow includes 7,000 acre-ft/yr of leakage to the 

Virgin River and Lake Mead from the upper layer, 

and 10,000 acre-ft/yr of subsurface flow in both 

layers to adjacent regions.

DESCRIPTION OF SUBREGIONS

PENOYER SUBREGION

The Penoyer subregion, on the westernmost 

margin of the Colorado River region (fig. 30), encompasses about 1,200 mi2 . The deep-flow subregion generally coincides with two shallow-flow 

regions in the upper model layer (fig. 23). The 

subregion boundaries do not correspond to the 

flow-system boundaries delineated by Harrill and 

others (1988). The subregion includes Penoyer, 

southern Railroad, and northern Kawich Valleys 

(fig. 30), whereas Harrill and others classify 

Penoyer Valley as a hydrologically closed basin 

and include all of Kawich and southern Railroad 

Valleys in a flow system that drains toward Death 

Valley.

Simulated inflow is primarily from recharge 

assigned to cells in the upper model layer. Recharge totals 12,000 acre-ft/yr, principally in the 

Kawich, Reville, and Quinn Canyon Ranges (fig. 

30). The remaining 2,000 acre-ft/yr of inflow is 

subsurface flow from the Death Valley region, primarily in the upper layer.

Simulated outflow from the subregion (table 

5) is primarily by evapotranspiration from the upper model layer in southern Railroad Valley (2,000 

acre-ft/yr) and Penoyer Valley (9,000 acre-ft/yr; 

fig. 30). These rates are considerably greater than 

those estimated by Van Denburgh and Rush (1974, 

p. 24) 200 acre-ft/yr in southern Railroad Valley and 3,800 acre-ft/yr in Penoyer Valley [the 

latter is only 60 percent of the 6,400 acre-ft/yr 

estimated earlier by Eakin and others i!951, p. 

156)]. Subsurface flow to the White River subregion of 2,000 acre-ft/yr accounts for the remaining simulated outflow.

In the subregion, low transmissivities (generally less than 0.006 ft2/s) are simulated in the 

lower layer (fig. 20.B), whereas higher values 

(0.006-0.18 ft2/s) are simulated in the upper layer 

(fig. 20A). Consequently, only 17 percent of the 

simulated inflow to the subregion is inflow to the 

lower layer. Most of the flow in the lower layer 

is simulated as leaking back to the upper layer 

in Penoyer Valley. Subsurface flow from southern Railroad Valley to Kawich Valley has been 

suggested by Blankennagel and Weir (1973, p. 

B20). In contrast, ground-water flow is simulated 

from southern Railroad Valley and northern 

Kawich Valleys to Penoyer Valley (fig. 31). Regionally, model results replicate areas of evapotranspiration and regional spring discharge.
D66 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

Locally, the model results might be improved by 

increasing transmissivities in northern Kawich 

Valley to simulate southward flow from southern 

Railroad Valley. This might reduce simulated 

evapotranspiration in Penoyer Valley and increase 

subsurface flow to the Death Valley region. However, locally changing transmissivities during

model calibration did not always result in expected 

changes in simulated discharge. Observations 

made during the model calibration indicate that 

increasing the transmissivities in southern Railroad Valley results in a northward shift of the 

subregion boundary, with an accompanying increase in simulated flow to the south.

EXPLANATION

115°

PENOYER 

SUBREGION

WHITE RIVER 

SUBREGION

| 3 | Generalized area of recharge Number is assigned 

recharge in thousands of acre-feet per year. Values 

less than 500 acre-feet per year are not shown

Generalized area of discharge from upper model layer 

Number is simulated evapotranspiration and (where present) 

leakage to head-dependent flow boundaries, in thousands of 

acre-feet per year. Values less than 500 acre-feet per year 

are not shown

Regional spring and simulated discharge Number is 

simulated discharge in thousands of acre-feet per year

Approximate simulated boundary of Colorado River region 

Approximate simulated boundary of subregion

WASHINGTON

50 MILES

j______I

VIRGIN RIVER ° 

SUBREGION

I I

50 KILOMETERS

LAS VEGAS 

SUBREGION

LOCATION MAP

FIGURE 30. Areas of assigned recharge, simulated discharge from upper model layer, and simulated discharge

from regional springs in Colorado River region.
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D67

TABLE 5. Simulated ground-water flow budgets, Colorado River region

[All amounts are in acre-feet per year (acre-ft/yr), rounded to nearest 1,000 acre-ft/yr. Amounts of mountain recharge are assigned, 

as described in text section title "Estimates of Recharge"; all other listed amounts are determined from model simulation]

Budget component and

(in parentheses) Penoyer Las Vegas Virgin River White River Entire Colorado 

model layer involved subregion subregion subregion subregion River region

INFLOW

Mountain recharge (upper)

Subsurface inflow from adjacent

regions (both)

Subsurface inflow from adjacent

subregions (both)

12,000

fl2,000

0

35,000

0

0

9,000

*2,000

rf3,000

146,000

c l,000

e3,000

202,000

5,000

(f)

Total inflow 14,000 35,000

OUTFLOW

Evapotranspiration (upper) 8 11,000 25,000

Regional springs (lower) 0 0

Subsurface outflow to adjacent regions

(both) minor A7,000

Subsurface outflow to adjacent

subregions (both) ^.OOO A,000

Leakage (upper) 0 '2,000

Total outflow" 13,000 35,000

14,000

8,000

1,000

0

0 

m5,000

14,000

150,000

47,000

96,000

'3,000

*3,000 

0

149,000

207,000

91,000

97,000

10,000

(f) 

7,000

205,000

a From Death Valley region.

From Bonneville region. 

c From Railroad Valley region.

Primarily from White River subregion.

e Includes 2,000 acre-ft/yr from Penoyer subregion and 1,000 acre-ft/yr from Las Vegas subregion. 

 * Net flow among subregions within Colorado River region is zero.

& Includes evapotranspiration of flow from small springs that are assumed to be discharging from upper layer; does not include 

evapotranspiration of flow from regional springs that are simulated to be discharging from lower layer.

To Death Valley region.

1 Includes 2,000 acre-ft/yr to Bonneville region and 1,000 acre-ft/yr to Death Valley region. 

J To White River subregion.

To Virgin River subregion.

To Lake Mead and Colorado River. 

m To Virgin River. 

n Total outflow does not always equal total inflow due to founding of individual values.

LAS VEGAS SUBREGION

The Las Vegas subregion, at the southern end 

of the Colorado River region, encompasses about 

3,300 mi2 . The western boundary of the subregion generally corresponds to a flow-system boundary by Harrill and others (1988). However, the 

northern boundary does not coincide with their 

flow-system boundary because they consider flow 

to the Colorado and Virgin Rivers as one flow 

system. Thus, their flow system also includes the 

White River and Virgin River subregions.

Las Vegas Valley, at the northern end of the 

subregion, is one of the most densely populated 

areas in the carbonate-rock province, and ground 

water is an important source of municipal supply. Ground-water withdrawals, which began in 

the early 1900's, exceed 60,000 acre-ft/yr (fig. 8; 

Morgan and Dettinger, 1994X The model simulations herein assume predevelopment conditions 

and, therefore, do not include changes in groundwater flow caused by pumping or by recharge associated with the use of ground water and 

imported surface water.
D68 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

Simulated inflow to the subregion, which consists entirely of recharge assigned to cells in the 

upper model layer, totals 35,000 acre-ft/yr (table 

5). All but 2,000 acre-ft/yr of the recharge is from 

the Spring Mountains, which are the highest in 

southern Nevada. Estimates of predevelopment 

recharge to Las Vegas Valley, the principal area 

of discharge in the subregion, range from 25,000 

acre-ft/yr (Malmberg, 1965, p. 57) to about 35,000 

acre-ft/yr (Maxey and Jameson, 1948, p. 108). The

115°

PENOYER 

SUBREGION *°

WHITE RIVER 

SUBREGION

difference in estimates is due in part to differences in the boundaries selected to define the Las 

Vegas Valley hydrographic basin.

Simulated outflow from the subregion is 35,000 

acre-ft/yr, of which evapotranspiration (including 

spring discharge) from the upper model layer in 

Las Vegas Valley is 25,000 acre-ft/yr (table 5). 

Estimates of predevelopment discharge are assumed to equal those of predevelopment recharge. 

Thus, simulated evapotranspiration is at the low

EXPLANATION

Simulated direction of ground-water flow

" * Upper model layer 

«==> Lower model layer

Approximate simulated boundary of Colorado River region 

Approximate simulated boundary of subregion

50 MILES

I

VIRGIN RIVER 

SUBREGION

i I

50 KILOMETERS

LAS VEGAS 

SUBREGION

LOCATION MAP

FIGURE 31. Simulated direction of ground-water flow for both upper and lower model layers in Colorado River

region.
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D69

end of the range of 25,000 to 35,000 acre-ft/yr 

estimated for predevelopment discharge from Las 

Vegas Valley. Only 2,000 acre-ft/yr is simulated 

as subsurface leakage to Lake Mead and the Colorado River in the upper layer. This total includes 

about 1,000 acre-ft/yr from Las Vegas Valley and 

another 1,000 acre-ft/yr from the area south of 

Las Vegas Valley. The simulated quantity of leakage from Las Vegas Valley is similar to the 1,200 

acre-ft/yr simulated by Harrill (1976, p. 50) and 

the 2,000 acre-ft/yr simulated by Morgan and 

Dettinger (1994). The quantity of eastward subsurface outflow from the area south of Las Vegas 

Valley is comparable to the 1,100 acre-ft/yr from 

Eldorado Valley estimated by Rush and Huxel 

(1966, p. 17). Discharge also is simulated to Lake 

Mead southeast of the Muddy Mountains, but the 

combined flow in several cells there is less than 

500 acre-ft/yr.

Subsurface flow to the White River subregion 

and the Death Valley subregion account for the 

remaining outflow from the Las Vegas subregion. 

A small quantity of outflow (less than 1,000 acreft/yr) is simulated to the White River subregion 

from an area near the Muddy Mountains. Subsurface flow is simulated to the PahrumpAmargosa subregion of the Death Valley deep-flow 

region along the crest of the Spring Mountains, 

where boundaries of both the shallow-flow and 

deep-flow regions are drawn across model cells. 

Because cells are not subdivided when determining flow budgets for each subregion, those along 

the crest of the Spring Mountains are assigned 

to the Las Vegas subregion. As a result, subsurface outflow is used to account for the westward 

component of flow from the crest. Of the 7,000 

acre-ft/yr simulated to the Pahrump-Amargosa subregion, about half is in the lower layer.

Simulated flow in the subregion is mostly in 

the upper model layer. About 76 percent of the 

total inflow to the subregion is simulated through 

the upper layer. Transmissivities in the upper layer 

typically range from 0.006 to 0.18 ft2/s (fig. 20A), 

whereas in the lower layer, they range from 0.0006 

to 0.006 ft2/s (fig. 20B). In Las Vegas Valley, the 

transmissivities in the upper layer encompasses 

the range of 0.02 to 0.12 ft2/s for basin fill reported by Harrill (1976, p. 15, 16) and Morgan 

and Dettinger (1994). Low transmissivities in the 

lower layer south and east of Las Vegas Valley 

correspond to an area where carbonate rocks are 

thin or isolated (Dettinger, 1989, p. 14) and where 

outcrops in the mountains are generally rocks of 

low permeability (fig. 23; Plume, 1995).

VIRGIN RIVER SUBREGION

The Virgin River subregion, on the east side 

of the Colorado River region (fig. 30), encompasses 

about 2,000 mi 2 . Simulated inflow totals 14,000 

acre-ft/yr (table 5). Recharge assigned in the upper layer is about 9,000 acre-ft/yr, primarily in 

the Bull Valley Mountains and Beaver Dam Mountains. In addition, 2,000 acre-ft/yr is simulated 

as subsurface inflow from the Bonneville deepflow region at the southern end of the Escalante 

Desert (of which 800 acre-ft/yr is in the lower 

layer), and about 3,000 acre-ft/yr is simulated as 

flow from the White River subregion, mostly in 

the upper layer.

Simulated outflow from the subregion totals 

about 14,000 acre-ft/yr, of which 8,000 is evapotranspiration in the upper model layer, 5,000 is 

leakage to the Virgin River from the upper layer 

and 1,200 is discharge to Rogers and Blue Point 

Springs south of Overton in the lower layer (table 

5 value in table differs slightly from table 1 due 

to rounding). Simulated evapotranspiration in 

Beaver Dam Wash is about 5,000 acre-ft/yr (fig. 

30). An additional 1,200 acre-ft/yr is simulated 

as leakage at the head-dependent flow boundary 

cell corresponding to the confluence of Beaver Dam 

Wash and the Virgin River. Thus, total simulated 

discharge along Beaver Dam Wash is 6,200 acreft/yr. Estimated ground-water discharge in Beaver Dam Wash includes about 150 acre-ft/yr as 

evapotranspiration and 3,600 acre-ft/yr as leakage to the Virgin River for a total discharge of 

about 3,800 acre-ft/yr (Glancy and Van Denburgh, 

1969, p. 36, 47). Evapotranspiration simulated 

along the lower Muddy River near Overton is about 

3,000 acre-ft/yr considerably less than the 11,000 

acre-ft/yr estimated by Rush (1968b, p. 35; he refers to the area as lower Moapa Valley). Much of 

the ground-water recharge in this area is from 

downward seepage of streamflow in the Muddy 

River, and little is thought to enter the area either as direct recharge from precipitation or as 

underflow from adjacent areas (Rush, 1968b, p. 

23-26). Secondary recharge to the upper model 

layer of spring flow from Muddy River Springs 

is not simulated in the model and may account 

for the difference between simulated and estimated 

evapotranspiration along the lower Muddy River.

The Virgin River below Beaver Dam Wash also 

is simulated as a discharge area for ground water flowing from recharge areas north of the river 

(fig. 31). Some ground water probably seeps into 

the Virgin River from recharge areas northwest
D70 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

and southeast of the river, but the location and 

magnitude of this seepage is unknown (Glancy 

and Van Denburgh, 1969, p. 36). The river reach 

from Beaver Dam Wash to Lake Mead is generally a losing stream that supplies water to underlying aquifers (Glancy and Van Denburgh, 1969, 

p. 37). Much of the seepage from the river in this 

reach is to the adjacent and underlying alluvium, 

where most of it is discharged by evapotranspiration. Shallow ground water not lost to evapotranspiration moves parallel to the river, and 

therefore is not included in the model because it 

is considered local flow.

The principal contribution of ground water to 

the Virgin River in or near the modeled area is 

about 50,000 acre-ft/yr of moderately saline water from springs in the channel of the river along 

a 7-mile reach near Littlefield, Arizona (Glancy 

and Van Denburgh, 1969, p. 33, 36). These springs 

were not specifically included in the model because they are at the model boundary. Furthermore, most of the water discharging at the springs 

is Virgin River water that seeps into the underlying alluvium and carbonate rocks 9 to 15 mi 

upstream and local recharge of precipitation 

(Trudeau and others, 1983, p. 328).

Transmissivities in both model layers generally range from 0.0006 to 0.006 ft2/s. Because 

transmissivities are nearly the same for both layers, about half of the recharge is simulated as 

flow to the lower layer. Discharge from the lower 

layer is primarily to the upper layer along Beaver Dam Wash, the Muddy River, and the Virgin 

River. Transmissivities assigned to model cells in 

the vicinity of Beaver Dam Wash perhaps could 

be increased slightly to reduce the quantity of 

discharge as evapotranspiration along the wash 

and increase upward leakage to the Virgin River. 

Another alternative is to increase the vertical conductance in the head-dependent flow boundary 

used to simulate leakage to the river.

A zone of higher transmissivities is simulated 

along the western margin of the subregion, from 

Rogers and Blue Point Springs (fig. 11, No. 3) 

northward to an area between the Mormon Mountains and Beaver Dam Wash (fig. 20). Transmissivities in this zone are based on calibration of 

spring discharge at Rogers and Blue Point Springs. 

During model calibration, transmissivities in the 

lower layer were increased in cells at and north 

of Rogers and Blue Point Springs. The springs 

issue from carbonate rocks near the contact with 

basin fill. Recharge in the adjacent Muddy Mountains (fig. 31) is insufficient to supply all the flow

to the springs. Simulated flow to the springs is 

from the northern part of the subregion. Ground 

water could potentially flow from Muddy River 

Springs to Rogers and Blue Point Springs because 

land surface at the latter springs is about 200 

feet less in altitude than that at Muddy River 

Springs (Thomas and others, 1986, pi. 2). However, differing isotope values for the two spring 

systems (Thomas and others, 1991, p. 14, 19) and 

the presence of low-permeability rocks near land 

surface downgradient from Muddy River Springs 

(Michael D. Dettinger, U.S. Geological Survey, oral 

commun., 1987) suggest that underflow from those 

springs is an unlikely source.

WHITE RIVER SUBREGION

The White River subregion, the largest delineated in the Colorado River region, encompasses 

about 12,800 mi2 (fig. 30). The subregion boundary generally corresponds to a shallow-flow-region boundary delineated in the upper model layer 

(compare figs. 23 and 24). The White River subregion extends farther east and west of the flow 

system defined by Eakin (1966), but does not extend as far north. The subregion includes Tikaboo 

Valley and the Pintwater and Desert Ranges to 

the west, and Lake and Patterson Valleys, Meadow 

Valley Wash, and western Escalante Desert to the 

east. The northern boundary extends to southern Jakes Valley, whereas Eakin includes all of 

Jakes Valley as well as Long Valley (Long Valley 

is included in the Railroad Valley deep-flow region; see figure 34). The northern part of the flow 

system delineated by Harrill and others (1988) 

is the same as Eakin's. Their flow system differs 

to the east and south because they extend their 

eastern boundary to the Virgin and Colorado Rivers and their southern boundary to the boundary of the study area.

Inflow to the subregion totals 150,000 acreft/yr, of which recharge assigned to model cells 

in the upper model layer is 146,000 acre-ft/yr 

(table 5); the latter is more than 70 percent of 

the total for the entire Colorado River region. Principal areas of recharge include the White Pine, 

Egan, and Schell Creek Ranges in the northern 

part of the subregion; the Wilson Creek, Bristol, 

and Quinn Canyon Ranges in the central part; 

and the Sheep Range in the southern part (fig. 

30). The remaining inflow is simulated subsurface flow from adjacent regions and subregions: 

about 1,000 acre-ft/yr from the Railroad Valley 

region, 2,000 acre-ft/yr from the Penoyer subre-
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D71

gion, and 1,000 acre-ft/yr from the Las Vegas 

subregion (table 5).

Outflow from the subregion is primarily discharge to regional springs in the lower model layer, 

which totals 96,000 acre-ft/yr. Discharge as evapotranspiration from the upper layer is only 47,000 

acre-ft/yr. Discharge is simulated in three general areas of the subregion that correspond to 

mapped areas of ground-water evapotranspiration 

and to regional spring discharge (Harrill and others, 1988). The three areas are: Patterson and 

southern Lake Valleys and Panaca Warm Spring 

in the upper Meadow Valley Wash drainage, White 

River and Pahranagat Valleys in the White River 

drainage, and Muddy River Springs (fig. 30). Subsurface outflow to the Bonneville region simulated 

through the upper layer from the Egan, Schell 

Creek, and Wilson Creek Ranges (fig. 31) totals 

about 2,000 acre-ft/yr (table 5). An additional 3,000 

acre-ft/yr is simulated as outflow to the Virgin 

River subregion, and 1,000 acre-ft/yr flows to the 

Death Valley region near the Pintwater Range 

(table 5; fig. 31).

Ground-water flow in the subregion is generally from north to south in both model layers (fig. 

31), paralleling the Meadow Valley Wash and 

White River drainages. Simulated flow is west 

to east near the Sheep Range. More ground-water flow is simulated in the lower layer in the 

White River subregion than in any other in the 

study area. Ground-water flow in most other subregions is generally in the upper layer from recharge areas in the mountain ranges to discharge 

areas in adjacent valleys. In contrast, about 69 

percent of the total inflow to the subregion is simulated as inflow to the lower layer. Downward flow 

from the upper layer to the lower layer totals 

113,000 acre-ft/yr. Discussion of flow and comparison of simulated to estimated discharge is separated into three areas flow along the Meadow 

Valley Wash and White River drainages, and flow 

to Muddy River Springs.

Ground-water flow in the lower model layer 

is simulated from southern Lake Valley into 

Patterson Valley, then southward to Panaca (fig. 

31). Recharge areas contributing flow to Panaca 

Warm Spring are primarily the Bristol and Wilson Creek Ranges. Overall, simulated discharge 

in Patterson Valley and at Panaca Warm Spring 

is about 13,000 acre-ft/yr, which is greater than 

the 8,500 acre-ft/yr estimated by Rush (1964, p. 

19, 22). Minor quantities of evapotranspiration 

(totaling about 3,000 acre-ft/yr), which have been 

estimated elsewhere along the axis of Meadow Valley Wash, are not simulated in the model. Simulated evapotranspiration in southern Lake Valley is 3,000 acre-ft/yr. Not all of the simulated 

discharge in Lake Valley is included in the White 

River subregion because the valley is bisected by 

the boundary between the Colorado River and 

Bonneville regions. When the additional 6,000 acreft/yr of evapotranspiration simulated in northern 

Lake Valley is added to that in southern Lake Valley, 

total simulated discharge in Lake Valley is approximately the same as the 8,500 acre-ft/yr estimated 

by Rush and Eakin (1963, p. 13).

South of Panaca, flow is toward Muddy River 

Springs (fig. 31). Additional flow is added from 

recharge areas in the Clover, Delamar, and Mormon Mountains (fig. 30). A total of 13,000 acreft/yr of underflow is simulated from lower Meadow 

Valley Wash to the area near Muddy River Springs, 

of which 9,000 acre-ft/yr is simulated in the upper layer. Estimated shallow underflow from 

Meadow Valley Wash into the Muddy River drainage just downstream from Muddy River Springs 

is 7,000 acre-ft/yr (Rush, 1968b, p. 26, 27).

Simulated ground-water flow along the White 

River is generally southward in both model layers from White River Valley to Pahranagat Valley, then southeast to Muddy River Springs. This 

flow is consistent with water levels in the area 

(Eakin, 1966, p. 258; Thomas and others, 1986). 

Less ground-water flow is simulated through Jakes 

Valley into White River Valley than was estimated 

by Eakin (1966, p. 265). He estimated that about 

25,000 acre-ft/yr may enter the White River Valley from as far north as Long Valley (location 

shown on figure 34). Although recharge in mountains adjacent to Jakes Valley is included herein, 

only 7,000 acre-ft/yr is simulated as underflow 

from the Jakes Valley drainage basin into the 

upper end of White River Valley, and no flow is 

simulated from Long Valley. Simulated flow to 

White River Valley is from the White Pine and 

Egan Ranges. Discharge along the White River 

includes about 25,000 acre-ft/yr from three groups 

of regional springs simulated in the lower layer 

near the axis of the valley and 14,000 acre-ft/yr 

from evapotranspiration simulated in the upper 

layer (fig. 30). Evapotranspiration from the upper layer includes the flow of small springs not 

considered part of the regional group in the lower 

layer. Simulated flow to the northern group of 

springs and to Mormon Hot Spring is from the 

Egan Range, whereas flow to the southern group 

is from both the White Pine and Egan Ranges. 

Estimated discharge in White River Valley is
D72 REGIONALAQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

37,000 acre-ft/yr (Eakin, 1966, p. 261), which is 

only 2,000 acre-ft/yr less than the total simulated 

discharge from regional springs and evapotranspiration.

Simulated underflow from White River Valley and adjacent Cave Valley (fig. 31) to the south 

is about 27,000 acre-ft/yr, which is 13,000 acreft/yr less than that estimated by Eakin (1966, p. 

265). This underflow is toward Pahranagat Valley, where discharge from three regional springs 

in the lower layer is 24,000 acre-ft/yr and evapotranspiration in the upper layer is 10,000 acreft/yr. Estimated spring flow in Pahranagat Valley 

is about 25,000 acre-ft/yr (table 1; Eakin, 1966, 

p. 261), nearly all of which is consumed by evapotranspiration in the valley. Although simulated 

discharge from springs is nearly the same as the 

reported spring flow, total discharge from 

Pahranagat Valley is 9,000 acre-ft/yr more than 

previously reported. Flow to the northern two 

springs in Pahranagat Valley is simulated from 

the White Pine, Egan, and Schell Creek Ranges. 

Flow to the southern spring (Hiko Spring of Thomas and others, 1986, pi. 2) is simulated from 

the Quinn Canyon, Seaman, and Schell Creek 

Ranges.

Simulated underflow from Pahranagat Valley 

and adjacent Tikaboo Valley (fig. 31) to Muddy 

River Springs is about 24,000 acre-ft/yr. This flow 

is about 11,000 acre-ft/yr less than the 35,000 

acre-ft/yr estimated as underflow from Pahranagat 

Valley by Eakin (1966, p. 265). Tikaboo Valley 

was not included in his conceptualization of flow 

to Muddy River Springs. More recent studies based 

on geology, water levels, and deuterium concentrations of water from regional springs in 

Pahranagat Valley, at Muddy River Springs, and 

at Ash Meadows (location shown in figure 28) indicate that some ground water from within or near 

Pahranagat Valley may flow southwest through 

northern Tikaboo Valley to the regional springs 

in Ash Meadows (Winograd and Friedman, 1972; 

Thomas, 1988; Dettinger, 1989; Kirk and Campana, 

1990). Estimates of underflow to Ash Meadows 

range from about 4,000 acre-ft/yr (Kirk and 

Campana, 1990, p. 385) to 7,000 acre-ft/yr (Thomas, 1988). Perhaps flow in southern Tikaboo 

Valley is toward the Muddy River Springs, whereas 

flow in northern Tikaboo Valley is toward Ash 

Meadows. Such a possibility is suggested by Harrill 

and others (1988, pi. 2). Although no flow is simulated from Pahranagat Valley to Ash Meadows, 

such flow might be simulated by increasing transmissivities between the two places. However, to

simulate the estimated spring flow at Ash Meadows, some of the flow from the Spring Mountains 

to Ash Meadows would need to be diverted either to Las Vegas Valley or Pahrump Valley by 

decreasing transmissivities in model cells at the 

north end of the Spring Mountains.

Ground-water flow in the subregion that is 

not discharged upgradient from the Muddy River 

Springs is discharged as regional spring flow in 

the lower layer or as evapotranspiration in the 

upper layer. Simulated spring flow at Muddy River 

Springs is 37,000 acre-ft/yr and evapotranspiration along the Muddy River from the springs to 

the confluence with Meadow Valley Wash is about 

18,000 acre-ft/yr. The measured aggregate spring 

flow is about 36,000 acre-ft/yr (Eakin, 1966, p. 

261). The reach of the Muddy River between its 

source at the springs and Lake Mead (fig. 31) is 

perennial, but only part of the flow reaches Lake 

Mead. The average annual flow of the Muddy River 

near its confluence with Lake Mead is about 6,600 

acre-ft/yr, which is based on a 12-year period, 

1979-83 and 1985-91 (Garcia and others, 1992, 

p. 72). Much of the streamflow is consumed by 

evapotranspiration from phreatophytes and irrigated crops or is used for industrial and public 

supply. A small percentage of the streamflow may 

seep back into the ground.

Simulated ground-water discharge near Muddy 

River Springs is about 19,000 acre-ft/yr more than 

estimated. Perhaps some or all of extra discharge 

can be accounted for in the uncertainty of estimated evapotranspiration along the river. Another 

possibility is that some ground water flows through 

consolidated rocks beneath the river to discharge 

into Lake Mead. This does not seem likely, however, because low-permeability rocks that are near 

land surface downstream from the springs probably inhibit significant underflow to the lake 

(Michael D. Dettinger, U.S. Geological Survey, oral 

commun., 1987).

Simulated upper-layer flow to the area of 

evapotranspiration at Muddy River Springs includes: 9,000 acre-ft/yr from Meadow Valley Wash; 

5,000 acre-ft/yr from the southern Sheep Range; 

3,000 acre-ft/yr from Pahranagat and Tikaboo 

Valleys and the northern Desert, Pintwater, and 

Sheep Ranges; and 1,000 acre-ft/yr from the Las 

Vegas subregion. Simulated flow in the lower layer 

to Muddy River Springs is mainly underflow from 

Pahranagat and Tikaboo Valleys, and the Sheep, 

Las Vegas, and southern Desert Ranges. Contributions to regional springs include: 23,000 acreft/yr from Pahranagat and Tikaboo Valleys; 8,000
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D73

acre-ft/yr from the Sheep, Las Vegas, and southern Desert Ranges; 4,000 acre-ft/yr from Meadow 

Valley Wash; and 2,000 acre-ft/yr from Delamar 

Valley.

The sources of water discharging at Muddy 

River Springs simulated in the model differs from 

the sources described by Eakin (1966, p. 265). 

Using imbalances in estimated water budgets for 

hydrographic areas north of the springs, he estimated only 2,000 acre-ft/yr of flow from the Sheep 

Range; the rest was ground-water flow through 

Pahranagat and Delamar Valleys from recharge 

areas to the north. A difference in concentrations 

of the deuterium isotope between spring water 

in Pahranagat Valley and at Muddy River Springs 

suggests that not all the discharge at Muddy River 

Springs is from Pahranagat Valley (Winograd and 

Friedman, 1972). Deuterium concentrations in 

water from Muddy River Springs are nearly the 

same as those in high-altitude springs in the Sheep 

Range and Spring Mountains, which led Winograd 

and Friedman (1972, p. 3705) to propose that the 

principal source of water to the Muddy River 

Springs is the Sheep Range, the Spring Mountains, or both. On the basis of chemical balances 

of ground water, Thomas (1988) proposed that 

nearly all recharge in the Sheep Range may discharge at Muddy River Springs and that ground 

water beneath the southernmost reach of Meadow 

Valley Wash may also flow to the springs. Similar conclusions were reported by Kirk and 

Campana (1990), except they did not suggest as 

much flow from the Sheep Range to the Muddy 

River Springs. Because of (1) lack of knowledge 

regarding the extent of the carbonate-rock aquifers contributing flow to Muddy River Springs, 

(2) lack of hydraulic properties and water-level 

gradients in the aquifers, and (3) uncertainties 

in deuterium concentrations over time and at the 

different source areas, several areas remain candidate sources of flow to the Muddy River Springs.

Simulated flow to the regional springs is sensitive to the distribution of transmissivities in 

the lower layer. During model calibration, transmissivities in the lower layer were increased along 

an axis that generally corresponds to the location of springs in White River and Pahranagat 

Valleys, and at Muddy River Springs. Transmissivities for the lower layer generally range from 

0.006 to 0.18 ft2/s, but in White River Valley and 

near Muddy River Springs the values range from 

0.18 to 0.66 ft2/s (fig. 20B). The highest transmissivities are concentrated near regional springs; 

this may be related to locally high flow rates that

enhance or maintain openings in the carbonate 

rocks (Dettinger, 1989, p. 16). Eakin (1966, p. 251) 

estimated a regional transmissivity value of 200,000 

(gal/day)/ft (equivalent to about 0.3 ft2/s) on the 

basis of estimated flow across three vertical sections. The zone of higher transmissivities in the 

lower layer (fig. 25), which acts as a drain for 

ground water from adjacent areas, generally corresponds to an area of thick carbonate rocks that 

may be considered the principal aquifers in central and southern Nevada (Dettinger, 1989, p. 13).

BONNEVILLE REGION

The Bonneville region, in the northeastern 

part of the study area (fig. 24), encompasses about 

39,000 mi2 largest of the five regions. It includes 

six deep-flow subregions in the lower model layer 

Escalante, Spring-Steptoe, Ruby, Clover-Independence, Utah Lake, and Great Salt Lake Desert 

(fig. 32) and all or part of 23 shallow-flow regions in the upper layer (fig. 23). Ground-water 

flow is from recharge areas in the mountains to 

topographically low parts of basins within each 

subregion. Little flow is simulated between adjacent subregions, even though water levels in most 

of the Bonneville region generally decline toward 

the Great Salt Lake Desert or Great Salt Lake.

INFLOW

Inflow to the Bonneville region totals about 

889,000 acre-ft/yr (table 6), which is considerably 

more than inflow to the other four deep-flow regions. Recharge assigned to cells in the upper 

model layer, which constitutes most of the inflow, 

totals about 855,000 acre-ft/yr. The eastern boundary of the flow region is along mountain ranges 

that supply large quantities of water to both the 

southeastern Great Salt Lake area and the Sevier 

Desert area (fig. 32). Other principal recharge 

areas include fault-block mountains in extreme 

eastern Nevada and western Utah. Subsurface flow 

in both layers from adjacent regions, which totals about 34,000 acre-ft/yr, accounts for only 4 

percent of the inflow to the Bonneville region. 

Much of the subsurface inflow is from the upper 

Humboldt River region, where about 25,000 acreft/yr is simulated along the Ruby Mountains and 

East Humboldt Range; another 5,000 acre-ft/yr 

is simulated from the Colorado River region, and 

4,000 acre-ft/yr is from the Railroad Valley region.
D74 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

Inflow from the upper Humboldt River region is 

simulated along the crest of the Ruby Mountains, 

where boundaries of both the shallow-flow and 

deep-flow regions are drawn across model cells. 

Because cells are not subdivided when determining flow budgets for each region, those along the 

crest of the mountains are assigned to the upper 

Humboldt River region. As a result, subsurface 

inflow is used to account for the eastward component of flow from the crest.

EXPLANATION

114°

115

| 3 I Generalized area of recharge Number is assigned 

recharge in thousands of acre-feet per year. Values 

less than 500 acre-feet per year are not shown

E9 Generalized area of discharge from upper model layer 

Number is simulated evapotranspiration and (where present) 

leakage to head-dependent flow boundaries, in thousands of 

acre-feet per year. Values less than 500 acre-feet per year 

are not shown

Regional spring and simulated discharge Number is 

simulated discharge in thousands of acre-feet per year

Approximate simulated boundary of Bonneville region 

Approximate simulated boundary of subregion

CLOVERINDEPENDENCE 

SUBREGION"

RUBY

SUBREGION' UTAH LAKE 

SUBREGION

ESCALANTE 

SUBREGION

SPRING-STEPTOE 

SUBREGION '

50 MILES

50 KILOMETERS

FIGURE 32. Areas of assigned recharge, simulated discharge from upper model layer, and simulated discharge from regional

springs in Bonneville region.
TABLE 6. Simulated ground-water flow budgets, Bonneville region

[All amounts are in acre-feet per year (acre-ft/yr), rounded to nearest 1,000 acre-ft/yr. Amounts of mountain recharge are assigned, as described in text 

of Recharge"; all other listed amounts are determined from model simulation]

Budget component and 

(in parentheses) 

model layer involved

INFLOW

Mountain recharge (upper)

Subsurface inflow from

adjacent regions (both)

Subsurface inflow from

adjacent subregions (both)

Total inflow

OUTFLOW

Evapotranspiration (upper)

Regional springs (lower)

Subsurface outflow to

adjacent regions (both)

Subsurface outflow to

adjacent subregions (both)

Leakage (upper)

Total outflow9

Escalante 

subregion

138,000

0

d 3,000

141,000

139,000

0

'2,000

0

0

141,000

Spring-Steptoe 

subregion

93,000

a 4,000

d 4,000

101,000

91,000

7,000

'3,000

0

0

101,000

Ruby 

subregion

14,000

* 16,000

e 4,000

34,000

32,000

0

J 2,000

0

0

34,000

CloverIndependence 

subregion

33,000

* 9,000

d 2,000

44,000

36,000

5,000

0

1 3,000

0

44,000

Utah Lake 

subregion

53,000

0

0

53,000

18,000

0

0

m 13,000

0 22,000

53,000

Great Salt 

Lake Desert 

subregion

524,000

c 5,000

As.ooo

542,000

442,000

52,000

k 1,000

" 10,000

P 37,000

542,000

a From Railroad Valley region.

From upper Humboldt River region. 

c From Colorado River region.

From Great Salt Lake Desert subregion.

* Includes 3,000 acre-ft/yr from Clover-Independence subregion and 1,000 acre-ft/yr from Great Salt Lake Desert subregion.

' From Utah Lake subregion.

& Net flow among subregions within Bonneville region is zero.

Includes evapotranspiration of flow from small springs that are assumed to be discharging from upper layer; does not include evapotranspiration of flow from r

simulated to be discharging from lower layer.

To Colorado River region. 

' To Railroad Valley region. 

To upper Humboldt River region. 

To Ruby subregion.

m To Great Salt Lake Desert subregion.

n Includes 3,000 acre-ft/yr to Escalante subregion, 4,000 acre-ft/yr to Spring-Steptoe subregion, 1,000 acre-ft/yr to Ruby subregion, and 2,000 acre-ft/yr to Clove

subregion.

0 To Utah Lake, through head-dependent flow boundaries.

p Includes 3,000 acre-ft/yr to Great Salt Lake and 34,000 acre-ft/yr to Sevier River and Sevier Lake.

* Total outflow does not always equal total inflow due to rounding of individual values.
D76 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

OUTFLOW

Simulated outflow from the Bonneville region 

totals 889,000 acre-ft/yr and includes discharge 

as evapotranspiration and leakage to Utah Lake, 

Great Salt Lake, Sevier River, and Sevier Lake 

from the upper layer; discharge to regional springs 

in the lower layer; and subsurface flow to adjacent regions in both layers (table 6). Many areas 

of discharge are simulated in the Bonneville region (fig. 32). Large parts of the region are occupied by three deserts the Great Salt Lake Desert 

in the north, the Sevier Desert in the middle, 

and the Escalante Desert in the south in which 

considerable ground water is discharged. Simulated evapotranspiration for the entire region is 

758,000 acre-ft/yr, which represents about 85 percent of the total outflow. The remaining outflow 

is to regional springs (64,000 acre-ft/yr), to headdependent flow boundaries representing leakage 

to surface water bodies (59,000 acre-ft/yr), and 

to adjacent regions (8,000 acre-ft/yr).

DESCRIPTION OF SUBREGIONS

ESCALANTE SUBREGION

The Escalante deep-flow subregion, in the 

southern part of the Bonneville region (fig. 32), 

encompasses about 4,000 mi2 . The subregion approximately coincides with three shallow-flow regions (compare figs. 23 and 24B). It also coincides 

with the southern half of a flow system delineated by Harrill and others (1988) that includes 

the Sevier Desert. Simulated ground-water flow 

in the subregion is from recharge areas in the 

mountain ranges to discharge areas in adjacent 

valleys. Inflow to the subregion totals about 

141,000 acre-ft/yr. Recharge assigned to cells in 

the upper model layer is 138,000 acre-ft/yr (table 

6) and accounts for nearly all the inflow. The remaining 3,000 acre-ft/yr of simulated inflow is 

subsurface flow from the Great Salt Lake Desert 

subregion, primarily in the upper layer. Principal recharge areas include the Tushar Mountains 

and Markagunt Plateau on the east side, Kolob 

Terrace on the south side, and The Needles on 

the west side (fig. 32). The mountains on the east 

side of the subregion generally have more precipitation and runoff than most mountains in the 

interior of the overall study area.

Outflow from the subregion is mostly evapotranspiration from the upper model layer. Simulated evapotranspiration in the subregion is about 

139,000 acre-ft/yr (table 6), mostly in Beaver Valley, the southern half of the Milford area, Parowan 

and Cedar City Valleys, and the Escalante Desert 

(fig. 32). Areas of simulated evapotranspiration 

generally coincide with mapped areas of groundwater evapotranspiration (Harrill and others, 

1988). About 2,000 acre-ft/yr is simulated as subsurface flow to the Colorado River region, of which 

about 800 acre-ft/yr is from the lower layer.

Most simulated flow in the Escalante subregion is in the upper model layer. About 88 percent of the total inflow to the subregion is 

simulated through the upper layer. Transmissivities in the lower layer are generally less than 

0.006 ft2/s except beneath the Escalante Desert 

(fig. 20.B), whereas values in the upper layer generally exceed 0.006 ft2/s (fig. 20A). Ground-water 

flow is from the Tushar Mountains and Markagunt 

Plateau on the east side toward the Escalante 

Desert and southern Milford area (fig. 33). However, much of the simulated flow is discharged 

in Beaver, Parowan, and Cedar City Valleys (fig. 

32). Simulated evapotranspiration in these valleys is about 91,000 acre-ft/yr, which is considerably less than the estimated discharge of at least 

126,000 acre-ft/yr (Mower, 1978, p. 30; Bjorklund 

and others, 1978, p. 17, 41). Estimated discharge 

in these valleys includes water recharged locally 

from streams crossing the valley floor. This local 

recharge is not simulated in the model, which accounts for at least part of the difference between 

simulated and estimated discharge in the valleys.

Simulated underflow from Beaver, Parowan, 

and Cedar Valleys westward to the southeastern 

part of the Milford area and the eastern part of 

the Escalante Desert is about 12,000 acre-ft/yr. 

In contrast, less than 1,000 acre-ft/yr is estimated 

as underflow to the Milford area and the Escalante 

Desert (Mower, 1978, p. 33; Bjorklund and others, 1978, p. 45). Estimated transmissivities in 

this area are generally in the range of 0.0006 to 

0.006 ft2/s in the lower model layer (fig. 205) and 

0.006 to 0.18 ft2/s in the upper layer (fig. 20A). 

Decreasing transmissivities in the upper layer immediately west of Beaver, Parowan, and Cedar 

City Valleys would increase evapotranspiration in 

the two valleys and decrease flow to the southern Milford area and Escalante Desert. Decreasing westward flow to the Escalante Desert is 

reasonable because the simulated evapotranspiration of 33,000 acre-ft/yr is about 7,000 acre-ft/ 

yr more than the quantity estimated by Mower 

(1982, p. 34). Simulated flow to the Escalante
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D77

Desert is from recharge areas in the Kolob Terrace (referred to as Pine Valley Mountains by 

Mower) and The Needles, and from Parowan and 

Cedar Valleys (fig. 33). Instead of subsurface flow 

from Parowan and Cedar Valleys, Mower (1982, 

pi. 13) assumed ground-water recharge in the 

mountains between the Escalante Desert and those

115'

two valleys. These mountains are relatively low 

in altitude and, thus, no recharge is assigned to 

them in the model.

The hydraulic gradient of ground water at the 

north end of the Escalante Desert indicates northward flow from the Escalante Desert to the southern end of the Milford area. The estimated

EXPLANATION

Simulated direction of ground-water flow

-^- Upper model layer 

Lower model layer

Approximate simulated boundary of Bonneville region 

Approximate simulated boundary of subregion

CLOVER- /* 11 

INDEPENDENCE "'" 

SUBREGION^

RUBY 

SUBREGION 40'

UTAH LAKE 

SUBREGION

0

GREAT SALT LAKE« 

lyrOESERT SUBREGION

I A ^ «= > ' <% *5 "* !__"* «2?» *V.

A c Jf v^ *j^1ilfor(f*-ge %

I l ^ * S BErfVFR l% Va»eyr . <

ESCALANTE 

SUBREGION

SPRING-STEPTQE 

SUBREGION

50 MILES

0 50 KILOMETERS 

FIGURE 33. Simulated direction of ground-water flow for both upper and lower model layers in Bonneville region.
D78 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

quantity of flow is about 2,100 acre-ft/yr (Mower, 

1982, p. 35;. Subsurface flow simulated in the 

model from the Escalante Desert to southern 

Milford area is about 2,400 acre-ft/yr, two-thirds 

of which is in the upper layer.

The Milford area is split between the 

Escalante and the Great Salt Lake Desert subregions (fig. 32). Simulated evapotranspiration for 

all of the Milford area is 32,000 acre-ft/yr of which 

about 15,000 acre-ft/yr is simulated in the 

Escalante subregion. Estimates of ground-water 

discharge in the entire Milford area prior to development range from 27,000 acre-ft/yr (Mason, 

in press) to 33,000 acre-ft/yr (Mower and Cordova, 

1974, p. 22). Subsurface flow from the Milford 

area to the Sevier Desert has been postulated by 

these authors on the basis of water-level gradients between the basins. In the model, all flow 

in the southern part of the Milford area is discharged there as evapotranspiration, rather than 

moving northward. Simulated flow to the northern part of the Milford area is from recharge in 

the San Francisco Mountains to the west and the 

Mineral Mountains to the east (fig. 33).

The simulated subregion boundary that splits 

the Milford area may be an artifact of the relatively large size of model cells. The principal direction of ground-water flow simulated in the 

Milford area is from east to west. With the large 

size of model cells, ground-water flow simulated 

in the lower layer is upward beneath the valley 

to the upper layer, where most of it is discharged 

as evapotranspiration.

SPRING-STEPTOE SUBREGION

The Spring-Steptoe subregion, on the west side 

of the Bonneville region (fig. 32), encompasses an 

area of 2,100 mi2 . It includes the northern half 

of Spring Valley, the southern half of Steptoe Valley, and part of southern Butte Valley. Superimposed on the deep-flow subregion are parts or all 

of five shallow-flow regions in the upper layer 

(fig. 23). The subregion boundary differs from those 

delineated by Harrill and others (1988) in that 

they include the southern two-thirds of Butte 

Valley and all of Steptoe Valley as one flow system and Spring Valley as part of a large system tributary to the Great Salt Lake Desert. 

Altitudes of the mountains and valleys in the 

subregion are generally higher than those in 

the surrounding subregions. Consequently, 

ground-water levels in the subregion also are 

generally higher (fig. 24B).

Simulated inflow to the subregion totals 

101,000 acre-ft/yr (table 6), of which 93,000 acreft/yr is recharge assigned to model cells in the 

upper model layer. Principal recharge areas include the Snake, Schell Creek, Egan, and Cherry 

Creek Ranges (fig. 32). Subsurface inflow totals 

8,000 acre-ft/yr about 4,000 acre-ft/yr is simulated from the Railroad Valley region and 4,000 

acre-ft/yr from the Great Salt Lake Desert subregion, primarily in the upper layer (table 6). 

Outflow from the subregion is primarily from 

evapotranspiration, which totals about 91,000 acreft/yr (table 6). Simulated regional-spring discharge 

at Campbell Ranch Spring (fig. 11) in southern 

Steptoe Valley is 7,400 acre-ft/yr (table 1, fig. 32). 

Subsurface flow to the Colorado River region is 

3,000 acre-ft/yr and accounts for the rest of the 

simulated outflow.

Estimated transmissivities for the lower layer 

in the Spring-Steptoe subregion are generally less 

than 0.006 ft2/s; as a result, most of the simulated flow is in the upper layer. About 82 percent of the total inflow to the subregion is 

simulated through the upper layer. Flow from the 

upper layer into the lower layer is about 17,000 

acre-ft/yr. Nearly half (44 percent) of the downward flow from the upper layer is discharged from 

the lower layer at Campbell Ranch Spring in 

southern Steptoe Valley (table 1, fig. 32).

A topographic divide of low relief in the central part of Spring Valley corresponds to the approximate subregion boundary between the 

Spring-Steptoe and Great Salt Lake Desert subregions. In northern Spring Valley, simulated flow 

is eastward from the Schell Creek Range and westward from the Snake Range (fig. 33) to the valley floor. Flow is simulated mostly in the upper 

model layer. Low-permeability rocks are widely 

exposed in these mountains, and the rocks may 

extend to great depth, as inferred from subsurface magnetic bodies (fig. 24). In southern Spring 

Valley, ground-water flow is simulated through 

the Snake Range into Hamlin Valley (fig. 33). An 

estimated 4,000 acre-ft/yr of subsurface flow is 

thought to move from Spring Valley into Hamlin 

Valley through the Snake Range (Rush and Kazmi, 

1965, p. 19). This estimate is based on a hydraulic gradient in basin fill in southern Spring Valley that is toward the Snake Range. Simulated 

discharge in Spring Valley is 75,000 acre-ft/yr (fig. 

32), of which 39,000 acre-ft/yr is in the SpringSteptoe subregion. Estimated discharge by evapotranspiration for the entire valley is 70,000 

acre-ft/yr (Rush and Kazmi, 1965, p. 22). The es-
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D79

timate includes the discharge of numerous small, 

nonregional springs and seeps near the margin 

of the valley floor.

In southern Steptoe Valley, simulated flow is 

westward from the Schell Creek Range and eastward from the Egan and Cherry Creek Ranges 

(fig. 33). Simulated evapotranspiration and regional-spring discharge for the entire valley totals 75,000 acre-ft/yr. In comparison, estimated 

evapotranspiration in the valley, which includes 

the discharge from regional springs, is 70,000 acreft/yr (Eakin and others, 1967, p. 24). Simulated 

evapotranspiration and regional spring discharge 

in the southern part of Steptoe Valley (within the 

Spring-Steptoe subregion) is 45,000 acre-ft/yr.

The simulated subregion boundary that splits 

Steptoe Valley between two deep-flow subregions 

does not correspond to either a topographic divide of low relief or a water table divide in the 

basin fill. The boundary may be an artifact of 

the relatively large size of the model cells. The 

principal directions of simulated flow in both layers 

are east and west from the adjacent mountains 

to areas of evapotranspiration on the valley floors. 

Reducing the size of model cells might allow for 

a small northward component of flow through the 

valley that is not simulated with the larger cell 

size.

Simulated flow in Butte Valley is westward 

from the Egan and Cherry Creek Ranges and eastward from Butte Mountains (fig. 33). Simulated 

evapotranspiration is 20,000 acre-ft/yr, the same 

as that estimated by Glancy (1968a, p. 32). Within 

the Spring-Steptoe subregion, simulated evapotranspiration in the southern part of Butte Valley is 7,000 acre-ft/yr. A ground-water divide in 

the basin fill is present near a topographic divide that separates the northern one-third of the 

valley from the southern two-thirds (Glancy, 1968a, 

p. 11). In the model, the divide between deepflow subregions is south of the actual ground-water 

divide, but a shallow-flow region divide in the 

upper layer approximates the observed divide.

Depth to ground water beneath the playa at 

the southern end of Butte Valley exceeds 50 ft. 

The reason for the depressed water table is unknown; phreatophytes in the central part of the 

valley may consume enough ground water to keep 

the water table depressed, or the ground water 

in southern Butte Valley may flow generally southward through underlying carbonate rocks to discharge areas in adjacent valleys (Glancy, 1968a, 

p. 11). Although Butte Valley could be a source 

area for water discharging at Campbell Ranch

Spring on the east side of the Egan Range (fig. 

32), shallow ground-water flow is considered doubtful because of a low hydraulic gradient between 

Butte Valley and the springs and because a 

ground-water mound from recharge in the Egan 

Range would be a barrier to shallow flow between 

the two valleys (Eakin and others, 1967, p. 21).

Deeper ground-water flow from Butte Valley 

to Steptoe Valley beneath the Egan Range may 

be possible. The rocks are largely carbonates and 

may extend to great depth. In the model, a groundwater mound is simulated beneath the Egan 

Range, yet outflow in the lower layer is simulated as deep flow from the southern end of Butte 

Valley to Campbell Ranch Spring. In this area, 

transmissivities computed in the lower layer correspond to a zone of relatively high values (greater 

than 0.006 ft2/s) that extends to the southern end 

of the study area (fig. 25). The quantity of subsurface flow simulated in the lower layer from 

southern Butte Valley to Campbell Ranch Spring 

is 2,100 acre-ft/yr. The remaining 5,300 acre-ft/yr 

of simulated flow to the spring is from nearby, in the 

Egan Range.

Geochemical evidence seems to support the 

concept of both long and short flow paths to 

Campbell Ranch Spring. Detectable concentrations 

of tritium in the spring water indicates that some 

of the water discharging at the spring is from 

recent (post-1952) precipitation (James M. Thomas, U.S. Geological Survey, oral commun., 1986), 

perhaps from the Egan Range. In contrast, the 

carbon-14 content of the spring water (17 percent of modern carbon) indicates that some of the 

water may be several thousand years old, a reasonable travel time for water from Butte Valley.

Whether ground water actually flows from 

southern Butte Valley to Campbell Ranch Spring 

is uncertain. Discharge simulated at the spring 

is sensitive to relatively small transmissivity 

changes in the lower layer. For example, increasing 

transmissivities of model cells in White River Valley results in decreased flow to Campbell Ranch 

Spring because more water is diverted into White 

River Valley.

RUBY SUBREGION

The Ruby subregion, in the western part of 

the Bonneville region (fig. 32), encompasses only 

550 mi2 the smallest of the six deep-flow subregions. It includes the southern two-thirds of a 

shallow flow region (fig. 23). The extent of the 

subregion differs from a flow system delineated
D80 REGIONALAQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

by Harrill and others (1988) in that their system 

includes all of Ruby Valley and the northern third 

of Butte Valley. Simulated ground-water flow in 

the Ruby subregion is from the adjacent Ruby 

and Butte Mountains to the floor of southern Ruby 

Valley (fig. 33).

Simulated inflow to the subregion totals 34,000 

acre-ft/yr, of which only 14,000 acre-ft/yr is from 

recharge assigned to cells in the upper model layer 

(table 6) the rest is subsurface flow from adjacent subregions and regions. Most of the subsurface flow into the subregion is from the upper 

Humboldt River region, where simulated inflow 

along the Ruby Mountains is 16,000 acre-ft/yr 

(11,000 acre-ft/yr of which is in the upper layer). 

Inflow from the upper Humboldt River region is 

the result of model discretization. Cells along the 

crest of the Ruby Mountains (where simulated 

flow is both east and west) had to be included in 

either the Ruby subregion or the upper Humboldt 

River region. Cells along the crest are assigned 

to the upper Humboldt River region; thus, in the 

simulated water budgets, flow eastward from the 

crest is accounted for as subsurface outflow from 

the upper Humboldt River region to the adjacent 

Ruby subregion.

Simulated outflow from the Ruby subregion 

is 34,000 acre-ft/yr, of which 32,000 acre-ft/yr is 

evapotranspiration from the upper model layer 

and 2,000 acre-ft/yr is subsurface flow to the Railroad Valley region, primarily in the lower layer 

(table 6). In comparison, estimated evapotranspiration in the southern half of Ruby Valley, which 

approximately coincides with the Ruby subregion, 

is about 30,000 acre-ft/yr (Eakin and others, 1951, 

p. 82).

Within the Ruby subregion, transmissivities 

in the upper layer mostly range from 0.18 to 0.66 

ft2/s beneath the valley floor, but are less than 

0.006 ft2/s in the Ruby Mountains (fig. 20A). Values in the lower layer follow a similar trend 

higher beneath the valley floor than beneath the 

mountain block (fig. 20B).

The Ruby Mountains constitutes one of the 

highest ranges in northeast Nevada and, consequently, receives more precipitation, on the average, than all other nearby ranges. In the 

northern Ruby Mountains, where metamorphic and 

igneous rocks of low permeability are exposed (fig. 

24A; Plume and Carlton, 1988, pi. 1), numerous 

streams flow from the mountains to the neighboring valley floors, because little precipitation 

percolates into the rocks. Contrastingly, in the 

southern Ruby Mountains, where carbonate rocks

are exposed, few streams are present because most 

of the precipitation percolates into these more 

permeable rocks. Considerable ground water flows 

locally through the carbonate rocks to the neighboring valleys. For example, Ruby Lake, at the 

southern end of the Ruby Valley, is fed by springs 

and seeps discharging from carbonate rocks at 

the base of the mountains.

The simulated division of Ruby Valley into 

two separate subregions may be a result of the 

large size of the model-grid cells. Available groundwater levels in the basin fill do not indicate a 

divide in Ruby Valley (Thomas and others, 1986, 

pi. 1), although a topographic divide of low relief 

separates Ruby Lake from the northern part of 

the valley. The principal directions of simulated 

ground-water flow in the model are eastward from 

the Ruby Mountains and westward from the Butte 

Mountains (fig. 33) to areas of evapotranspiration on the valley floor. These flow directions are 

accentuated in the model by the rectangular grid.

CLOVER-INDEPENDENCE SUBREGION

The Clover-Independence subregion, north of 

the Ruby subregion on the west side of the 

Bonneville region (fig. 32), encompasses about 

1,400 mi2 . The subregion incorporates all or part 

of three shallow-flow regions in the upper layer. 

The subregion includes Clover and Independence 

Valleys and the northern parts of Butte and Ruby 

Valleys. This subregion is slightly different from 

the flow system delineated by Harrill and others 

(1988), as they do not include northern Butte and 

Ruby Valleys.

Simulated inflow to the subregion is 44,000 

acre-ft/yr, of which recharge assigned to model 

cells in the upper model layer totals 33,000 acreft/yr (table 6). Principal recharge areas include 

the Ruby Mountains, East Humboldt Range, and 

Pequop Mountains (fig. 32). Subsurface inflow from 

the upper Humboldt River region, simulated 

through the lower layer along the Ruby Mountains, is about 9,000 acre-ft/yr. An additional 2,000 

acre-ft/yr is simulated as subsurface inflow through 

the upper layer from the Great Salt Lake Desert 

subregion.

Simulated evapotranspiration in the subregion 

is 36,000 acre-ft/yr (table 6), including 10,000 acreft/yr in northern Ruby Valley, 2,000 acre-ft/yr at 

the north end of Butte Valley, and 24,000 acreft/yr in Clover and Independence Valleys (fig. 32). 

Regional-spring discharge simulated from the 

lower layer in southern Clover Valley is 5,000 acre-
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D81

ft/yr, at Warm Springs (table 1; figs. 11, 32). An 

additional 3,000 acre-ft/yr is simulated as subsurface outflow to the Ruby subregion, about half 

through the lower layer.

Ground-water flow is generally from recharge 

areas in the mountains to discharge areas on the 

valley floors (fig. 33). About 71 percent of the total inflow to the subregion is simulated through 

the upper layer. In the lower layer, simulated flow 

to Warm Springs is from the Ruby Mountains and 

East Humboldt Range (fig. 33).

Estimated evapotranspiration in Clover and 

Independence Valleys is about 29,000 acre-ft/yr 

(Eakin and others, 1951, p. 110, 112), which is 

the same quantity simulated in the model when 

discharge from Warm Springs is included. However, estimated evapotranspiration in northern 

Ruby Valley about 38,000 acre-ft/yr (Eakin and 

others, 1951, p. 82) is 28,000 acre-ft/yr more than 

the simulated quantity. Increasing the simulated 

evapotranspiration in northern Ruby Valley by 

reducing subsurface flow to Clover and Independence Valleys would result in a similar decrease 

in simulated evapotranspiration in the latter valleys. One alternative would be to adjust transmissivities in the Clover-Independence subregion 

until more flow is from recharge areas to the east 

and south. However, simulated flow from northern Ruby Valley is not enough to account for the 

28,000-acre-ft/yr discrepancy. The only logical area 

where more flow can be simulated to northern 

Ruby Valley is in the Ruby Mountains, either by 

increasing recharge in model cells corresponding 

to the mountain block or by adjusting transmissivities in the area to divert more recharge from 

the Ruby Mountains into northern Ruby Valley. 

Perhaps some of the estimated evapotranspiration is related to surface water. Many streams 

flow from the east flank of the northern Ruby 

Mountains onto the adjacent valley floor. These 

streams are used for irrigation of meadow lands, 

but some streamflow probably seeps into the 

ground, where it is then discharged locally as 

evapotranspiration. Local flow of this type is not 

simulated in the model, because recharge and discharge is not simulated in the same model cell.

UTAH LAKE SUBREGION

The Utah Lake subregion, in the northeast 

corner of the Bonneville region (fig. 32), encompasses 1,400 mi2 . The southern boundary of the 

subregion generally corresponds to a flow-system 

boundary by Harrill and others (1988) that separates ground-water flow to the Sevier Desert from 

flow to the Great Salt Lake. Elsewhere, the subregion does not correspond to their flow system 

because they consider Utah Lake a part of a larger 

flow system that includes all tributary valleys 

surrounding the Great Salt Lake. Some ground 

water flows northward from Utah Lake toward 

the Great Salt Lake; however, this was not simulated in the conceptual model because both lakes 

are treated separately.

Utah Lake, in Utah Valley, lies at the base 

of the Wasatch Range, which is east of the lake 

and outside of the modeled area. Streams that 

head in the Wasatch Range are the major source 

for irrigation water and one of the major sources 

of recharge to ground water in Utah Valley 

(Cordova and Subitzky, 1965, p. 12; Cordova, 1970, 

p. 23). Because only areas west of Utah Valley 

are simulated in the model, much of the estimated 

ground-water recharge to the valley is not included 

therein. Estimated ground-water discharge from 

the northern part of Utah Valley exceeds 200,000 

acre-ft/yr (Cordova and Subitzky, 1965, p. 19), and 

discharge from southern Utah Valley exceeds 

125,000 acre-ft/yr (Cordova, 1970, p. 30). Both 

estimates do not include discharge from wells. 

Only a small part of the estimated discharge in 

Utah Valley is subsurface flow from areas west 

of Utah Lake. Simulated discharge to Utah Valley in the model includes only the ground-water 

flow from areas west of Utah Valley. Estimates 

of underflow from west of Utah Valley range from 

10,000 acre-ft/yr (Feltis, 1967, p. 18) to 24,000 

acre-ft/yr (Harrill and others, 1988).

Simulated inflow to the Utah Lake subregion 

is 53,000 acre-ft/yr, all of which is recharge assigned to cells in the upper model layer (table 

6). Principal recharge areas are the Oquirrh Mountains and the East and West Tintic Mountains 

(fig. 32). Simulated outflow from the subregion 

includes 18,000 acre-ft/yr as evapotranspiration 

from the upper layer, 22,000 acre-ft/yr as flow to 

Utah Lake, and 13,000 acre-ft/yr as subsurface 

flow, primarily through the upper layer, to Tooele 

Valley in the Great Salt Lake Desert subregion. 

In Utah Valley, total simulated discharge is 33,000 

acre-ft/yr (fig. 32), which includes 11,000 acre-ft/yr of 

evapotranspiration.

Flow in both model layers is generally from 

recharge areas to Utah Lake (fig. 33). About 87 

percent of the total inflow to the subregion is simulated through the upper layer. Simulated underflow 

to Utah Valley from areas to the west is more than 

the estimated underflow of 24,000 acre-ft/yr (Harrill
D82 REGIONALAQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

and others, 1988). Because the model boundary 

north of the lake is along the northern Oquirrh 

Mountains, some of the simulated underflow to 

the valley may actually move east from the mountains to the Jordan River (Waddell and others, 

1987, p. 7). In the model, ground-water flow from 

the Oquirrh Mountains is to Utah Lake, Rush 

Valley, and Tooele Valley (fig. 33).

GREAT SALT LAKE DESERT SUBREGION

The Great Salt Lake Desert subregion extends 

over much of western Utah and extreme eastern 

Nevada (fig. 32) and has an area of about 29,500 

mi2 . It is the largest subregion delineated in the 

entire study area. The subregion includes all or 

most of 13 shallow-flow regions (fig. 23). The subregion differs from the flow system delineated by 

Harrill and others (1988) in that it includes the 

Sevier Desert and valleys adjacent to the Great 

Salt Lake in Utah, and Goshute and northern 

Steptoe Valleys in eastern Nevada (fig. 32). Although the Great Salt Lake Desert and the Great 

Salt Lake are delineated by Harrill and others 

(1988) as separate flow systems, the topographically lowest discharge areas in the two flow systems constitute one virtually continuous area that 

can be considered a single large system (Gates, 

1987, p. 83). Sparse water-level data suggest that 

some ground water may flow from the Sevier 

Desert and Goshute Valley to discharge areas in 

the Great Salt Lake Desert (Gates, 1987, p. 84; 

Harrill and others, 1988), implying that these areas also could be included with the Great Salt 

Lake Desert as part of a single flow system.

Inflow to the subregion is 542,000 acre-ft/yr, 

of which 524,000 acre-ft/yr is from recharge assigned to cells in the upper model layer. Principal mountain ranges, where recharge exceeds 

30,000 acre-ft/yr apiece, are the Pavant Range, 

Oquirrh Mountains, Stansbury Mountains, and 

Deep Creek Range in Utah, and the southern 

Schell Creek and Snake Ranges in Nevada (fig. 

32). Simulated inflow from adjacent regions and 

subregions, primarily through the upper layer, 

includes 13,000 acre-ft/yr from the Utah Lake subregion and 5,000 acre-ft/yr from the Colorado River 

region (table 6). Underflow from the Utah Lake 

subregion is in the vicinity of Oquirrh Mountains 

and Rush Valley, whereas underflow from the Colorado River region is near Hamlin Valley (fig. 33).

Simulated outflow from the subregion includes: 

442,000 acre-ft/yr as evapotranspiration from the 

upper model layer; 37,000 acre-ft/yr as leakage

through head-dependent flow boundaries to the 

Great Salt Lake, the Sevier River, and Sevier Lake 

in the upper layer; 52,000 acre-ft/yr as regionalspring discharge from the lower layer; and 11,000 

acre-ft/yr as subsurface flow to adjacent subregions and to the upper Humboldt River region 

(table 6). Principal areas of ground-water discharge 

include: Rush, Skull, and Tooele Valleys at the 

south end of the Great Salt Lake; the Sevier River 

drainage, Pavant Valley, and northern Milford area 

in the southeastern part of the subregion; the Great 

Salt Lake Desert, Tule Valley, and Snake Valley 

in western Utah; and the south end of Spring Valley, the north end of Steptoe Valley, and all of 

Goshute Valley in eastern Nevada (fig. 32). Regionalspring discharge is from two areas on the margin 

of the Great Salt Lake Desert Fish Springs and 

Blue Lake and Little Salt Springs and from Twin 

Spring in Snake Valley, and Nelson Spring in northern Steptoe Valley (figs. 11, 32; table 1).

Simulated flow in the subregion is primarily 

in the upper layer from recharge areas in the 

mountains to discharge areas on the adjacent valley floors. About 78 percent of the total inflow is 

simulated through the upper layer. Flow entering the lower layer from the upper layer is about 

115,000 acre-ft/yr. Much of the flow in the lower 

layer is concentrated in three general areas where 

estimated transmissivities exceed 0.006 ft2/s: a 

relatively small area at the south end of the Great 

Salt Lake, extending to Rush Valley; a relatively 

long and narrow area extending from the south 

end of the Great Salt Lake Desert to Wah Wah 

Valley; and a relatively small and narrow area 

extending southwestward from Blue Lake and 

Little Salt Springs in extreme western Utah (fig. 

25). Of the simulated flow entering the lower layer 

from the upper layer, 45 percent is discharged 

at regional springs.

Most of the simulated flow toward Great Salt 

Lake is discharged before reaching it. Simulated 

leakage to Great Salt Lake is only about 3,000 

acre-ft/yr. Much of this (about 2,700 acre-ft/yr) 

is at the north end of Tooele Valley. The remaining 300 acre-ft/yr is simulated along the shore of 

the Great Salt Lake north of Skull Valley (fig. 

32). Estimated ground-water leakage to the Great 

Salt Lake from Tooele Valley is 3,000 acre-ft/yr 

(Razem and Steiger, 1981, p. 17). The area along 

the Great Salt Lake northwest of Tooele Valley 

discharges little, if any, ground water directly to 

the lake (Arnow, 1984, p. 16).

Simulated flow at the south end of the Great 

Salt Lake is primarily from recharge areas in the
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D83

Oquirrh, West Tintic, Stansbury, and Cedar Mountains to areas of discharge in Rush, Tooele, and 

Skull Valleys (fig. 33). Simulated discharge in 

these valleys is 99,000 acre-ft/yr (fig. 32), which 

is within the range estimated by previous investigators. The estimates range from 94,000 acreft/yr to 113,000 acre-ft/yr, as follows: Rush Valley, 

27,000 acre-ft/yr (Hood and others, 1969, p. 28); 

Tooele Valley, 23,000 as evapotranspiration and 

17,000 as spring discharge (Razem and Steiger, 

1981, p. 16); and Skull Valley, 27,000 to 46,000 

acre-ft/yr (Hood and Waddell, 1968, p. 29). About 

16,000 acre-ft/yr is simulated as ground-water flow 

from Rush Valley into Tooele Valley, of which 6,000 

acre-ft/yr is by way of the lower layer.

Simulated flow in the Sevier Desert area is 

generally toward the Sevier River and Sevier Lake 

(fig. 33). About 89 percent of the total inflow to 

this area is through the upper layer, because estimated transmissivities in the lower layer are 

less than 0.006 ft2/s (fig. 205). Simulated discharge 

as evapotranspiration from Sevier Desert and as 

leakage to the Sevier River and Sevier Lake is 

44,000 acre-ft/yr, which is considerably less than 

estimated by previous investigators. Estimated 

ground-water discharge, excluding subsurface outflow, in the Sevier Desert ranges from 83,000 acreft/yr (Holmes, 1984, p. 27) to 175,000 acre-ft/yr 

(Mower and Feltis, 1968, p. 52). Some of the difference between the quantity of discharge simulated herein and that reported by Holmes (1984, 

p. 27) is due to an additional 24,000 acre-ft/yr of 

recharge he estimated as seepage from canals, 

reservoirs, and unconsumed irrigation water. Recharge from irrigation water is not included in 

the model because it is assumed to be local flow 

and because only a net recharge or discharge is 

simulated for each cell. Another reason for the 

difference is that Holmes (1984, p. 27) simulated 

about 27,000 acre-ft/yr of underflow from Pavant 

Valley to the Sevier Desert. This value is considerably higher than the 3,400 acre-ft/yr simulated 

herein and the 14,000 acre-ft/yr estimated by 

Mower (1965, p. 54).

Evapotranspiration is simulated over a large 

area of the Great Salt Lake Desert (fig. 32); however, the total is about 14,000 acre-ft/yr. More 

evapotranspiration actually occurs in this area 

than is simulated in the model, but much of the 

additional discharge is derived from local precipitation on the desert floor. Estimated evapotranspiration from the Great Salt Lake Desert is 84,000 

acre-ft/yr. It includes about 69,000 acre-ft/yr of 

local evaporation from mud and salt flats (Gates,

1984, p. 244). If this local discharge is not included, the model-simulated quantity is about the 

same as the estimated quantity. The combination 

of only small quantities of ground-water discharge 

and low hydraulic gradients results in transmissivities that are generally very low less than 

0.0006 ft2/s (fig. 20). Whether these values are 

representative of the actual transmissivities is 

uncertain because the model results in this area 

are insensitive to changes in assigned transmissivities in either model layer and vertical 

leakances between the layers.

Simulated flow in the southwestern part of 

the subregion is generally toward a band of high 

transmissivities (between 0.18 and 0.66 ft2/s; fig. 

20) estimated in both layers that extends from 

Wah Wah Valley to Fish Springs Flat at the south 

end of the Great Salt Lake Desert (fig. 33). The 

band of high transmissivities correlates to a zone 

of relatively thick, flat-lying carbonate rocks that 

acts as a major conduit for ground-water flow 

(Carlton, 1985, p. 53).

Simulated outflow as evapotranspiration and 

as regional-spring discharge in the southwestern 

part of the subregion totals 144,000 acre-ft/yr, exclusive of southern Spring Valley. Simulated evapotranspiration includes 36,000 acre-ft/yr in southern 

Spring Valley; 12,000 acre-ft/yr in Hamlin Valley; 5,000 acre-ft/yr in Pine Valley; 56,000 acreft/yr in Snake Valley; 32,000 acre-ft/yr in Tule 

Valley; and 9,000 acre-ft/yr in Fish Springs Flat 

(fig. 32). Simulated regional-spring discharge from 

the lower layer totals 30,000 acre-ft/yr: 4,000 acreft/yr from Twin Spring in Snake Valley and 26,000 

acre-ft/yr from Fish Springs (fig. 32).

The simulated outflow in this part of the subregion, exclusive of southern Spring Valley, is 

about 12,000 to 20,000 acre-ft/yr less than the 

estimated discharge of 156,000 to 164,000 acreft/yr. Estimated discharge by valley is as follows: 

Snake and Hamlin Valleys, 80,000 acre-ft/yr 

(Hood and Rush, 1965, p. 24, 25); Pine Valley, 

7,000 acre-ft/yr (Stephens, 1976, p. 17); Tule 

Valley, 32,000 to 40,000 acre-ft/yr. (Stephens, 

1977, p. 19; Gates and Kruer, 1981, p. 36); Wah 

Wah Valley, 1,500 acre-ft/yr (Stephens, 1974b, 

p. 27); and Fish Springs Flat, about 35,000 acreft/yr, including the flow from Fish Springs 

(Bolke and Sumsion, 1978, p. 13). Most of the 

difference between simulated and estimated discharge is in Snake, Hamlin, and Tule Valleys, 

where the simulated quantity is 12,000 to 20,000 

acre-ft/yr less than the estimated quantity. Perhaps a larger area than that simulated contributes
D84 REGIONALAQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

flow to this part of the Great Salt Lake subregion.

As with many of the relatively large springs 

in the study area, discharge at Fish Springs 

greatly exceeds the quantity of recharge estimated 

for the topographic drainage area. Estimated recharge in Fish Springs Flat is only 4,000 acre-ft/yr 

(Bolke and Sumsion, 1978, p. 9), suggesting that most 

of the spring flow is from adjoining basins. Evidence 

for interbasin flow to Fish Springs Flat is based 

on the presence of carbonate rocks that crop out 

in several mountain ranges to the south; the imbalance in water budgets (Gates and Kruer, 1981, 

p. 31), where recharge exceeds discharge in Snake, 

Pine, and Wah Wah Valleys; and the indication 

from water-level data that ground-water flow is 

eastward from Snake Valley, northward from Pine 

and Wah Wah Valleys, and perhaps westward from 

Sevier Desert toward Fish Springs (Gates, 1987, 

p. 85).

Simulated flow entering Fish Springs Flat 

from adjacent areas differs between model layers. Simulated flow in the upper layer is primarily from the east and southeast, whereas 

simulated flow in the lower layer is primarily from 

the south and west (fig. 33). Total inflow to the 

upper model layer is about 10,300 acre-ft/yr, including 1,700 acre-ft/yr as recharge from mountain ranges, 4,200 acre-ft/yr as underflow from 

areas to the east, 1,600 acre-ft/yr as northward 

flow from Tule Valley, 900 acre-ft/yr as 

northwestward flow from Sevier Desert, 300 acreft/yr as eastward flow from Snake Valley, and 1,600 

acre-ft/yr as upward flow from the lower layer. 

Total outflow equals inflow and includes 8,700 

acre-ft/yr as evapotranspiration and 1,600 acreft/yr as northward flow to the Great Salt Lake 

Desert. Total inflow to the lower layer is about 

27,200 acre-ft/yr, including 19,700 acre-ft/yr as 

northward flow from Tule Valley, 6,500 acre-ft/yr 

as eastward flow from Snake Valley, and a combined 1,000 acre-ft/yr as westward and 

northwestward flow from areas to the east and 

Sevier Desert. Total outflow equals inflow and includes 25,700 acre-ft/yr as regional flow at Fish 

Springs and 1,600 acre-ft/yr as leakage to the upper layer. Eastward flow in the lower layer from 

Snake Valley to Fish Springs is mostly from recharge in the Deep Creek Range (fig. 33) a source 

area suggested by Gates and Kruer (1981, p. 32).

At least half of the simulated flow to Fish 

Springs Flat from Tule Valley originates in the 

Snake Valley drainage basin. Of the 23,000 acreft/yr simulated as entering Tule Valley in the lower

layer, 14,000 is underflow from Snake Valley 

through the Confusion Range and 9,000 is from 

Wah Wah Valley.

Available water-level data suggest that subsurface flow from Sevier Desert to Tule Valley 

and, thence, Fish Springs Flat is likely (Gates, 

1987, p. 85). Not counting northward flow from 

Wah Wah Valley through the extreme western side 

of Sevier Desert, about 1,200 acre-ft/yr is simulated as subsurface flow from Sevier Desert to 

Tule Valley and, thence, Fish Springs Flat. Combining the 1,200 acre-ft/yr with the 1,600 acreft/yr simulated as direct underflow from Sevier 

Desert to Fish Springs Flat results in 2,800 acreft/yr as underflow from Sevier Desert to adjoining areas along the westside. This quantity is less 

than the 8,800 acre-ft/yr simulated by Holmes 

(1984, p. 27). Although the quantity of flow from 

Sevier Desert to Tule Valley and Fish Springs Flat 

is different in the conceptual model than that determined by Holmes, both values are considered 

approximate because the hydraulic properties of 

rocks west of the Sevier Desert are largely unknown.

Ground-water levels along the west and north 

sides of the subregion generally decrease toward 

the Great Salt Lake Desert (figs. 19, 23, and 24). 

Simulated flow in this part of the subregion is 

primarily through the upper layer from recharge 

areas in the mountains to discharge areas in adjacent valley floors. In general, simulated evapotranspiration in valleys west and north of the 

Great Salt Lake Desert (fig. 32) approximates estimated values. Estimates of discharge are as follows: Goshute Valley, 10,000 acre-ft/yr (Eakin and 

others, 1951, p. 28); Deep Creek Valley, 14,000 

to 17,000 acre-ft/yr (Hood and Waddell, 1969, p. 

25; Gates and Kruer, 1981, p. 26, 36); Pilot Creek 

Valley, 4,600 acre-ft/yr (Harrill, 1971, p. 29); Thousand Springs Valley, 5,700 acre-ft/yr (Rush, 1968c, 

p. 35); Pilot, Grouse Creek, and Park Valleys, 

7,400, 11,000, and 16,000 acre-ft/yr, respectively 

(Stephens, 1974a, p. 30). A small quantity of 

ground-water flow (less than 2,000 acre-ft/yr) is 

simulated between several hydrographic basins. 

For example, about 1,700 acre-ft/yr is simulated 

from Goshute Valley to Pilot Creek Valley. This 

is slightly more than the 1,000 acre-ft/yr estimated 

by Harrill (1971, p. 28).

More than half of the flow simulated in the 

lower layer on the west side of the Great Salt 

Lake Desert is discharged at Blue Lake and Little 

Salt Springs (fig. 32). Ground-water flow to these 

springs, as simulated in the model, is mostly from
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D85

the Deep Creek Range to the south and the 

Goshute Mountains to the west (fig. 33). During 

model calibration, transmissivities were increased 

south and west of the springs to increase spring 

discharge and to decrease discharge by evapotranspiration in valleys between the springs and Spring 

Valley. Perhaps other combinations of transmissivities in and upgradient from the spring area 

could just as reasonably simulate discharge at the 

springs and in the adjacent valleys. The actual 

quantity of flow from the Deep Creek Range to 

Blue Lake and Little Salt Springs may be less 

than the simulated quantity, because simulated 

discharge in Deep Creek Valley (fig. 32) is less 

than the estimated discharge.

RAILROAD VALLEY REGION

The Railroad Valley region, in the west-central part of the study area (fig. 24), encompasses 

about 7,200 mi2 . It contains no deep-flow subregions in the lower model layer (fig. 34) but includes all or part of 10 shallow-flow regions in 

the upper layer (fig. 23). The Railroad Valley region differs from the flow system delineated by 

Harrill and others (1988) in that it includes most 

of Long Valley, northern Jakes Valley, and southern 

Newark Valley to the north; and northern and 

central parts of Little Smoky Valley, most of Antelope Valley, and northern Stone Cabin Valley 

to the west.

Railroad Valley is the terminal discharge area 

for ground-water flow within the region and also 

is the principal area for oil production in Nevada. 

The oil, which is produced primarily from traps 

in Tertiary volcanic rocks overlying the Paleozoicage carbonate rocks (French and Freeman, 1979, 

p. 487), is probably derived from the Chainman 

Shale of Paleozoic age (Poole and Claypool, 1984, 

p. 201). Locally, the Chainman Shale confines 

ground-water flow in the underlying carbonate rock 

aquifers. Regionally, however, the shale may not 

confine ground-water flow in these aquifers because it is disrupted by numerous faults.

INFLOW

Simulated inflow to the Railroad Valley region is 134,000 acre-ft/yr, of which 132,000 acreft/yr is recharge assigned to cells in the upper 

model layer and 2,000 acre-ft/yr is subsurface flow 

from the Bonneville region, primarily in the upper layer (table 7). Principal recharge areas include the Butte Mountains and White Pine Range 

in the northeast, the Grant and Quinn Canyon 

Ranges in the southeast, and the Hot Creek and 

Monitor Ranges in the west (fig. 34). Several other 

mountain ranges are also assigned small quantities of recharge.

OUTFLOW

Outflow from the Railroad Valley region is 

simulated as discharge by evapotranspiration in 

the upper model layer, as discharge from regional 

springs in the lower layer, and as subsurface flow 

to adjacent regions. Simulated discharge by evapotranspiration includes flow from small springs that 

is not simulated as regional-spring flow from the 

lower layer. Simulated outflow from the region 

is 133,000 acre-ft/yr, including 86,000 acre-ft/yr 

as evapotranspiration, 24,000 acre-ft/yr as regional-spring discharge, and 23,000 acre-ft/yr as 

subsurface flow to adjacent regions (table 7). Areas of evapotranspiration, shown in figure 34, are 

simulated in Railroad Valley, Hot Creek Valley, 

the northern part of Little Smoky Valley, and the 

northern part of Long Valley. Regional-spring discharge is simulated at Duckwater in northern 

Railroad Valley (13,000 acre-ft/yr, from Big and 

Little Warm Springs, table 1), on the east and 

west sides of Railroad Valley (6,000 acre-ft/yr, from 

Lockes, Blue Eagle, and Tom Springs, table 1), 

in Little Smoky Valley (2,800 acre-ft/yr, from Fish 

Creek Spring, table 1), and in Hot Creek Valley 

(2,000 acre-ft/yr, from Hot Creek Ranch Springs, 

table 1). Subsurface outflow includes: 10,000 acreft/yr to the upper Humboldt River region along 

the east side of Newark Valley and at the north 

end of Antelope Valley, 8,000 acre-ft/yr to the 

Death Valley region on the west side of the Monitor 

Range, 4,000 acre-ft/yr to the Bonneville region on 

the north end and east side of Long Valley, and 

1,000 acre-ft/yr to the Colorado River region at the 

southern end of Jakes Valley (table 7, fig. 34).

Simulated evapotranspiration and regionalspring discharge in Railroad Valley total about 

84,000 acre-ft/yr (fig. 34). This compares closely 

with an estimated evapotranspiration of 80,000 

acre-ft/yr (Van Denburgh and Rush, 1974, p. 24), 

which includes evapotranspiration of flow from 

the regional springs. Simulated evapotranspiration and regional-spring discharge in Hot Creek 

Valley is about 15,000 acre-ft/yr (fig. 34). This 

discharge is about 10,000 acre-ft/yr more than the
D86 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

evapotranspiration from phreatophytes and from 

areas irrigated with spring flow estimated by Rush 

and Everett (1966a, p. 27). The difference in simulated to estimated discharge in Hot Creek Valley 

represents simulated ground-water flow from Stone 

Cabin and Little Fish Lake Valleys (fig. 34). No 

evapotranspiration is simulated in Little Fish Lake 

Valley, even though 10,000 acre-ft/yr is estimated

for the valley (Rush and Everett, 1966a, p. 27). 

However, the combined quantity of simulated discharge from Hot Creek and Little Fish Lake Valleys (15,000 acre-ft/yr) agrees with the combined 

quantity of estimated discharge from the two valleys. The simulated distribution of discharge probably would agree more closely with the distribution 

observed by Rush and Everett (1966a, pi. 1) if

EXPLANATION

I 3 I Generalized area of recharge Number is assigned 

recharge in thousands of acre-feet per year. Values 

of less than 500 acre-feet per year not posted

Generalized area of discharge from upper model layer 

Number is simulated evapotranspiration in thousands of 

acre-feet per year. Values of less than 500 acre-feet per 

year not posted

Regional spring and simulated discharge Number is 

simulated discharge in thousands of acre-feet per year

Simulated direction of ground-water flow

~^- Upper model layer 

=£> Lower model layer

 Approximate simulated boundary of Railroad Valley region

116°30'

30 MILES

i 

30 KILOMETERS

38°30'

LOCATION MAP

FIGURE 34. Areas of assigned recharge, simulated discharge from upper model layer, simulated discharge 

from regional springs, and simulated direction of ground-water flow for both upper and lower 

model layers in Railroad Valley region.
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D87

TABLE 7. Simulated ground-water flow budget, 

Railroad Valley region

[All amounts are in acre-feet per year (acre-ft/yr), rounded to 

nearest 1,000 acre-ft/yr. Amounts of mountain recharge are 

assigned, as described in text section title "Estimates of 

Recharge"; all other listed amounts are determined from model 

simulation]

Budget component and

(in parentheses) 

model layer involved

INFLOW

Mountain Recharge (upper) 

Subsurface inflow from

adjacent regions (both) 

Subsurface inflow from

adjacent subregions (both)

Total inflow

OUTFLOW

Evapotranspiration (upper) 

Regional springs (lower) 

Subsurface outflow to

adjacent regions (both) 

Subsurface outflow to 

adjacent subregions (both)

Total outflow**

132,000

a 2,000

0

134,000

86,000

24,000

c 23,000 

0

133,000

a From Bonneville region.

Includes evapotranspiration of flow from small springs 

that are assumed to be discharging from upper layer; does 

not include evapotranspiration of flow from regional springs 

that are simulated to be discharging from lower layer.

c Includes 8,000 acre-ft/yr to Death Valley region, 1,000 

acre-ft/yr to Colorado River region, 4,000 acre-ft/yr to 

Bonneville region, and 10,000 acre-ft/yr to upper Humboldt 

River region.

Total outflow does not equal total inflow due to rounding 

of individual values.

model cells in the Hot Creek Range were assigned 

lower transmissivities. This was not done because, 

during model calibration, the discharge in Little 

Fish Lake Valley was grouped with the discharge 

of Hot Creek Valley to reduce the number of comparisons between simulated and estimated discharge.

The simulated areal distribution of evapotranspiration in Little Smoky and Long Valleys agrees 

with the mapped areas of evapotranspiration 

(Harrill and others, 1988). In Little Smoky Valley, simulated evapotranspiration is at the north 

end of the valley (fig. 34), adjacent to the discharge from Fish Creek Spring. Simulated discharge in this area is about 6,000 acre-ft/yr (fig. 

34), which is slightly more than the 5,200 acreft/yr estimated by Rush and Everett (1966a, p. 

27). In Long Valley, simulated evapotranspiration 

is also at the north end (fig. 34); however, the 

quantity is about 3,000 acre-ft/yr more than the 

2,200 acre-ft/yr estimated by Eakin (1961a, p. 23). 

The additional discharge in northern Long Valley represents flow from the adjacent Butte and 

Ruby Mountains.

No evapotranspiration is simulated in Antelope Valley (fig. 34), west of Little Smoky Valley, 

even though 4,200 acre-ft/yr is estimated by Rush 

and Everett (1964, p. 21). During model calibration, estimated discharge in Antelope Valley was 

grouped with that in Kobeh Valley. The model 

distribution of discharge in Antelope and Kobeh 

Valleys probably would agree more closely with 

the observed distribution if upper-layer cells in 

Antelope Valley were assigned lower values of 

transmissivity.

DESCRIPTION OF GROUND-WATER FLOW

Simulated ground-water flow is generally in 

the upper layer from recharge areas in the mountains to the adjacent valley floors (fig. 34). In 

the Railroad Valley region, about 68 percent of 

the total inflow is simulated through the upper 

layer. Downward flow from the upper layer to the 

lower layer totals 41,000 acre-ft/yr. Most of the 

flow in the lower layer is to regional springs and 

leakage to the upper layer on the floor of Railroad Valley. Of the simulated flow entering the 

lower layer from the upper layer, about 60 percent is discharged at regional springs.

In Railroad Valley, estimated discharge is 

27,000 acre-ft/yr greater than estimated recharge, 

which led Van Denburgh and Rush (1974, p. 28) 

to suggest additional ground-water inflow from 

adjacent valleys west and north of Railroad Valley. The imbalance between recharge and discharge 

in Railroad Valley is also reflected in the model, 

where assigned recharge in the drainage basin 

is less than the simulated discharge. The difference is balanced by subsurface inflow from adjacent areas. Flow is simulated from the Monitor 

and Hot Creek Ranges toward southern Railroad 

Valley (fig. 34). This flow direction is consistent 

with the orientation of deep flow in both carbonate and volcanic rocks as reported by Dinwiddie 

and Schroder (1971, p. 62-64). Simulated underflow 

entering Railroad Valley from the west is about 7,600 

acre-ft/yr, of which 4,900 acre-ft/yr is in the lower
D88 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

layer. Estimated flow from Hot Creek and southern Little Smoky Valleys to Railroad Valley is 

about 3,000 acre-ft/yr (Rush and Everett, 1966a, 

p. 26). Discharge to springs on the west side of 

Railroad Valley is simulated as flow from recharge 

in the Hot Creek Range, by way of southern Little 

Smoky Valley. Discharge to springs on the east 

side of Railroad Valley is simulated from the adjacent Grant Range (fig. 34).

In the model, flow to the large regional springs 

at Duckwater is mostly from the north (fig. 34). 

This flow is controlled by a zone of high transmissivities in the lower layer that extends from the 

north end of Long Valley to Muddy River Springs 

in southern Nevada (transmissivities there range 

from 0.006 to 0.66 ft2/s, as shown in fig. 25). About 

16,000 acre-ft/yr is simulated as southward flow 

to the springs at Duckwater. More than 90 percent of this flow is from the northern White Pine 

Range. Simulated flow from the Pancake Range 

west of the springs is only 600 acre-ft/yr. Not all 

flow entering the model cell that represents the 

Duckwater regional springs is discharged as spring 

flow. Some deep flow (about 3,800 acre-ft/yr in the 

lower layer) continues southward to the playa in 

Railroad Valley There, flow in the lower layer leaks 

upward into the upper layer near the north end of 

the playa where it is discharged as evapotranspiration. Whether deep flow through carbonate rocks 

continues southward from Duckwater Springs to 

the playa in Railroad Valley is unknown. In the 

model, southward flow from areas to the north is 

needed to balance simulated evapotranspiration with 

estimated evapotranspiration.

In Long Valley, estimated recharge exceeds estimated discharge (Eakin, 1961a, p. 1). Subsurface 

flow from Long Valley is postulated as moving either south to White River Valley (Eakin, 196la, p. 

1) or west to Newark Valley (Mifflin, 1968, p. 42). 

Both flow directions are shown by Harrill and others 

(1988). Simulated flow from Long Valley to Newark Valley is 12,700 acre-ft/yr; about 8,800 acreft/yr is simulated through the lower layer. In the 

lower layer, much of the ground-water flow is from 

Long Valley through eastern Newark Valley to the 

regional springs at Duckwater. Actual flow may differ from simulated flow because of uncertainties 

in the estimation of recharge and because hydraulic properties of the rocks are largely unknown.

The boundary between Railroad Valley region 

and upper Humboldt River region extends across 

northern Newark Valley to the western edge of 

Long Valley. Simulated flow from the Railroad Valley region to the upper Humboldt River region 

in Newark Valley through the upper and lower

layers is 5,400 and 1,600 acre-ft/yr, respectively. 

Simulated flow moving across this boundary is 

mostly discharged as evapotranspiration in Newark Valley.

The boundary between Railroad Valley and 

upper Humboldt River region also extends across 

northern Antelope Valley and southern Fish Creek 

Range (fig. 34). Ninety-eight percent of the flow 

across this part of the boundary is simulated in 

the upper layer. Outflow of 4,900 acre-ft/yr from 

the Railroad Valley region is simulated from Antelope Valley to Kobeh Valley. Inflow of 1,800 acreft/yr is simulated in the Fish Creek Range.

Simulated flow to Fish Creek Spring in northern Little Smoky Valley is mostly from the west 

and south (fig. 34), where transmissivities in the 

lower layer are greater than 0.006 ft2/s (fig. 25). 

Simulated flow from the west is 1,600 acre-ft/yr, 

mostly from Antelope Valley. (Rush and Everett 

[1966a, p. 23, 25] have postulated that Antelope 

Valley is the source of the spring flow.) Simulated flow from the south is 1,100 acre-ft/yr, mostly 

from the northern Hot Creek Range. Only 50 acreft/yr of spring flow is simulated from the north 

and the northeast in the adjacent Fish Creek 

Range. In Antelope Valley, ground-water flow in 

the upper layer of about 4,900 acre-ft/yr is simulated northward to Kobeh Valley.

The simulated flow to the spring from the west 

and south, although consistent with the general 

directions of ground-water flow on the basis of 

available water-level data, must cross the OregonNevada lineament that trends southeastward 

through at least part of the Railroad Valley region (the lineament is shown in fig. 225). Areas 

of observed ground-water discharge in Antelope 

and Kobeh Valleys begin upgradient from this lineament, suggesting that it may act as a barrier 

to ground-water flow northwest of the springs. 

The lineament is marked by a zone of closely 

spaced northwest-trending faults that are segmented by many northeast-trending basin-andrange faults (Stewart and others, 1975, p. 266). 

Northwest of Antelope Valley, the lineament is 

associated with a subsurface magnetic body that 

may be related to low-permeability rocks (fig. 24A; 

Plume, 1995). The degree to which the lineament 

impedes eastward and northward flow from Antelope Valley and northern Hot Creek Range, respectively, is unknown. If structures along the 

lineament are a barrier to flow, then the most 

likely alternative source for discharge at Fish 

Creek Spring is the Fish Creek Range, and the 

distribution of transmissivities in the lower model 

layer would be different from those simulated.
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D89

UPPER HUMBOLDT RIVER REGION

The upper Humboldt River region, in the 

northwestern part of the study area (fig. 24), encompasses about 7,200 mi2 . It includes two deepflow subregions in the lower layer Diamond and 

Humboldt (fig. 35) and all or part of 10 shallow-flow regions in the upper layer (fig. 23). The 

region described herein does not coincide with the 

upper basin of the Humboldt River drainage as 

discussed by Eakin and Lamke (1966, p. 17); their 

area incorporates the entire 5,000 mi2 drainage 

basin of the river east of Palisade and does not 

include the area corresponding to the Diamond 

subregion.

Discussion of ground-water flow in this region is limited to the simulation of (1) flow from 

mountains to adjacent valley floors, including those 

in the Humboldt River Valley, and (2) interbasin 

flow. Head-dependent flow boundaries (fig. 9) are 

used in the model to represent the Humboldt River 

and the major tributaries that enter the model 

area from the north. These boundaries are used 

to simulate net leakage, either as discharge to 

the river or as recharge from the river. Net flow 

depends on the relation of simulated water levels in the upper layer to a specified head that 

represents the river stage. Tributaries that originate within the region (most of which are south 

of the Humboldt River) are not simulated as headdependent flow boundaries because they are generally gaining streams and ground-water seepage 

to them is simulated in the model as evapotranspiration. Most of the net leakage at the headdependent flow boundaries is simulated as 

ground-water discharge (table 8). For areas along 

the Humboldt River, this discharge is combined 

with simulated evapotranspiration from the upper layer, as shown in figure 35. The percolation 

of surface water from the Humboldt River and 

its tributaries to the shallow ground-water body 

in the alluvium is not generally included in the 

model, because much of this percolation is discharged as nearby evapotranspiration and, thus, 

is considered local flow.

INFLOW

Simulated inflow to the upper Humboldt River 

region is 189,000 acre-ft/yr, including 174,000 acreft/yr as recharge assigned to cells in the upper 

model layer, 3,000 acre-ft/yr from head-dependent 

flow boundaries in the upper layer associated with 

the river and major tributaries to the north, and

12,000 acre-ft/yr as subsurface inflow in both layers from adjacent regions (table 8). Major recharge 

areas for the region include the East Humboldt 

Range, Ruby Mountains, and Diamond Mountains 

in the east; the Roberts Mountains and Sulphur 

Spring Range in the central part; and the Simpson 

Park and Cortez Mountains in the west (fig. 35). 

Small quantities of recharge also are assigned to 

several other mountain ranges. Of the subsurface 

flow simulated from adjacent regions, most (10,000 

acre-ft/yr) is from the Railroad Valley region, primarily through the upper model layer.

OUTFLOW

Simulated outflow from the upper Humboldt 

River region is 188,000 acre-ft/yr, including 

131,000 acre-ft/yr as evapotranspiration from the 

upper layer, 28,000 acre-ft/yr as discharge to headdependent flow boundaries from the upper layer 

associated with the Humboldt River, 4,000 acreft/yr as flow to regional springs in the lower layer, 

and 25,000 acre-ft/yr as subsurface flow in both 

layers to the Bonneville region (table 8). Areas 

of simulated discharge are shown in figure 35. 

The major areas are along the Humboldt River 

in the north; in Huntington and Newark Valleys 

in the east; in Kobeh, Diamond, and Pine Valleys in the central part; and in Grass and Crescent Valleys in the west. Subsurface flow to the 

Bonneville region is along the crest of the Ruby 

Mountains. Discharge to regional springs is on 

the west side of Diamond Valley in the Diamond 

subregion (fig. 35).

DESCRIPTION OF SUBREGIONS

DIAMOND SUBREGION

The Diamond subregion, in the southern part 

of the upper Humboldt River region (fig. 35), encompasses about 2,100 mi2 . It differs from the 

flow system delineated by Harrill and others (1988) 

as their system includes the drainage areas of 

Monitor and Antelope Valleys and excludes Newark Valley. Although Monitor and Antelope Valleys are not part of the Diamond subregion, flow 

is simulated through the upper layer from these 

valleys to Kobeh Valley. The subregion includes 

all or part of three shallow-flow regions in the 

upper layer (fig. 23). The shallow-flow regions 

generally correspond to drainage areas for Newark, Kobeh, and Diamond Valleys.
D90 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

Inflow to the subregion is from recharge assigned to cells in the upper model layer and subsurface inflow from the Railroad Valley region. 

Recharge totals 61,000 acre-ft/yr (table 8), mostly 

in the Diamond and Roberts Mountains and the 

southern half of the Sulphur Spring Range. An

additional 10,000 acre-ft/yr is simulated as subsurface flow from the Railroad Valley region, and 

1,000 acre-ft/yr from the Death Valley region. Of 

the subsurface flow from Railroad Valley, about 

6,400 acre-ft/yr is along the east and south sides 

of Newark Valley and about 4,900 acre-ft/yr is

115°

HUMBOLDT 

SUBREGION

EXPLANATION

Generalized area of recharge Number is assigned 

recharge in thousands of acre-feet per year. Cells with 

net recharge totaling 3,000 acre-feet per year along 

Humboldt River not shown. Values of less than 500 

acre-feet per year not posted

Generalized area of discharge from upper model layer 

Number is simulated evapotranspiration in thousands of 

acre-feet per year. Includes leakage to head-dependent 

flow boundaries along Humboldt River. Values of less 

than 500 acre-feet per year not posted

Regional spring and simulated discharge Number is 

simulated discharge in thousands of acre-feet per year

Simulated direction of ground-water flow

Upper model layer 

Lower model layer

 Approximate simulated boundary of upper Humboldt River region 

...... Approximate simulated boundary of subregion

FIGURE 35. Areas of assigned recharge, simulated discharge from upper model layer, simulated discharge from regional 

springs, and simulated direction of ground-water flow for both upper and lower model layers in upper Humboldt 

River region.

DIAMOND 

SUBREGION
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D91

TABLE 8. Simulated ground-water flow budget, Humboldt River region

[All amounts are in acre-feet per year (acre-ft/yr), rounded to nearest 1,000 acre-ft/yr. Amounts of mountain recharge are 

assigned, as described in text section title "Estimates of Recharge"; all other listed amounts are determined from model 

simulation]

Budget component and

(in parentheses) 

model layer involved

Diamond 

subregion

Humboldt 

subregion

Entire upper

Humboldt River

region

INFLOW

Mountain recharge (upper) 

Subsurface inflow from adjacent regions (both) 

Subsurface inflow from

adjacent subregions (both) 

Leakage

Total inflow

OUTFLOW

Evapotranspiration (upper/ 

Regional springs (lower) 

Subsurface outflow to

adjacent regions (both) 

Subsurface outflow to

adjacent subregions (both) 

Leakage (upper)

Total outflow'

61,000 

a 11,000

0

0

72,000

61,000

4,000

0

h 6,000 

0

71,000

113,000 

* 1,000

c 6,000 

e 3,000

123,000

70,000

0

25,000

0 

'28,000

123,000

174,000

12,000

(d) 

e 3,000

189,000

131,000

4,000

25,000

(d) 

'28,000

188,000

a Includes 10,000 acre-ft/yr from Railroad Valley region and 1,000 acre-ft/yr from Death Valley region.

Includes 600 acre-ft/yr from Bonneville region and 400 acre-ft/yr from Death Valley region. 

c From Diamond subregion.

Net flow among subregions within upper Humboldt River region is zero. 

' From Humboldt River and selected tributaries.

' Includes evapotranspiration of flow from small springs that are assumed to be discharging from upper layer; does not include 

evapotranspiration of flow from regional springs that are simulated to be discharging from lower layer. 

& To Bonneville region.

To Humboldt subregion. 

1 To Humboldt River and selected tributaries. 

 J Total outflow does not always equal total inflow due to rounding of individual values.

simulated as flowing northward from Antelope 

Valley into Kobeh Valley in the upper layer (fig. 

35); about 1,200 acre-ft/yr is simulated as southward flow from the Fish Creek Range at the south 

end of Diamond Valley into the Railroad Valley 

region.

Total simulated outflow from the subregion 

is 71,000 acre-ft/yr. Simulated evapotranspiration 

from the upper model layer and discharge to regional springs in Diamond Valley from the lower 

layer total about 65,000 acre-ft/yr, which is approximately the same as the estimated discharge 

of 61,000 to 63,500 acre-ft/yr from Newark, Kobeh, 

and Diamond Valleys: 16,000 to 18,500 acre-ft/yr 

in Newark Valley (Eakin, 1960, p. 15, 16), 15,000

acre-ft/yr in Kobeh Valley (Rush and Everett, 1964, 

p. 20), and 30,000 acre-ft/yr in Diamond Valley 

(Harrill, 1968, p. 33).

Ground-water flow in the subregion is primarily from recharge areas in the mountains to discharge areas on the valley floors. About 83 percent 

of the total inflow to the subregion is simulated 

through the upper layer. Downward flow from the 

upper layer to the lower layer totals 9,500 acreft/yr. Of the flow in the lower layer, 4,400 acreft/yr is discharged at Shipley Hot Spring and 

Bailey Spring on the west side of Diamond Valley (fig. 35, table 1). Transmissivities simulated 

in the lower layer are less than 0.006 ft2/s throughout most of the subregion (fig. 20J3); southwest
D92 REGIONALAQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

of the regional springs, in contrast, values range 

from 0.006 to 0.18 ft2/s (fig. 25). Simulated transmissivities in the upper layer are generally less 

than 0.18 ft2/s, except in Kobeh and Diamond Valleys where they range from 0.18 to 0.66 ft2/s (fig. 

20A). Estimated transmissivities for basin fill, 

based on pumping tests at six water wells in southern Diamond Valley, range from 0.04 to 0.4 ft2/s 

(27,000 to 250,000 gal/d/ft; Harrill, 1968, p. 15). 

These values are in the same range as those simulated in the model.

Simulated ground-water flow to Shipley Hot 

Spring and Bailey Spring on the west side of 

Diamond Valley (table 1, fig. 35) is from the 

Roberts Mountains southwest of the springs. 

This is the same source area for an estimated 

9,000 acre-ft/yr of subsurface flow from Garden Valley (Harrill, 1968, p. 25, 26) a small 

basin on the west flank of the Roberts Mountains that is tributary to Pine Valley (not shown 

in fig. 35). The estimate is based on an imbalance between recharge and discharge in Garden Valley and a hydraulic gradient of 25 to 

120 ft/mi from that valley to Diamond Valley.

HUMBOLDT SUBREGION

The Humboldt subregion encompasses about 

5,100 mi2 . It includes all or part of six shallowflow regions in the upper layer (fig. 23). The subregion generally corresponds to the flow system 

of Harrill and others (1988) along the east and 

south boundaries, except they exclude Grass Valley. 

To the north and west, their flow system includes 

basins tributary to the Humboldt River that extend beyond the modeled area. Simulated inflow 

to the subregion is 123,000 acre-ft/yr, of which 

113,000 acre-ft/yr is recharge assigned to cells in 

the upper model layer, 3,000 acre-ft/yr is flow from 

head-dependent flow boundaries in the upper layer, 

6,000 acre-ft/yr is subsurface flow from the Diamond subregion, and 1,000 acre-ft/yr is flow from 

the Bonneville and Death Valley regions (table 

8). Simulated outflow from the Humboldt subregion includes 70,000 acre-ft/yr as evapotranspiration from the upper layer, 28,000 acre-ft/yr as 

leakage to head-dependent flow boundaries in the 

upper layer, and 25,000 acre-ft/yr as subsurface 

flow to the Bonneville region. The latter is from 

model cells along the crests of the Ruby Mountains, where horizontal flow in both layers is eastward and westward (fig. 35). Model cells along 

the crests are included in the water-budget computation for the upper Humboldt River region.

Thus, eastward flow along the crests of these 

ranges is accounted for as simulated subsurface 

outflow to the Bonneville region; about 11,000 acreft/yr is simulated through the upper layer, the 

remaining 14,000 acre-ft/yr is simulated through 

the lower layer.

Ground-water flow in the subregion is simulated from recharge areas in the mountain ranges 

to discharge areas on the adjacent valley floors 

and to the Humboldt River (fig. 35). About 73 

percent of the total inflow to the subregion is simulated through the upper layer. Transmissivities 

in the lower layer are less than 0.006 ft2/s throughout the subregion, with values less than 0.0006 

ft2/s on the west side (fig. 20B). Transmissivities 

in the upper layer are generally less than 0.006 

ft2/s in the northern Ruby Mountains and East 

Humboldt Range, which corresponds to the lowpermeability rocks that crop out in these mountains (Plume, 1995), and between 0.006 and 0.18 

ft2/s in the valley lowlands and areas north of 

the Humboldt River (fig. 20A).

The generally low transmissivities in the lower 

layer may be related to thinning of the Paleozoic 

carbonate rocks. Outcrops of deep-water clastic 

rocks, chert, and volcanic rocks of Triassic to Cambrian age become increasingly abundant west of 

the Ruby Mountains, and correspondingly, outcrops of Paleozoic carbonate rocks become less 

abundant (Plume and Carlton, 1988). Locally, however, volcanic and carbonate rocks in the subregion may be highly permeable and may transmit 

moderate quantities of ground water to discharge 

points near the river. The springs near Carlin 

may be an example of this.

In valleys south of the Humboldt River, simulated evapotranspiration is 47,000 acre-ft/yr, including: 14,000 acre-ft/yr for two areas in 

Huntington Valley, 22,000 acre-ft/yr in Pine Valley, 6,000 acre-ft/yr from Crescent Valley, and 5,000 

acre-ft/yr in Grass Valley (fig. 35). Estimated 

evapotranspiration in these valleys totals 57,000 

acre-ft/yr: 21,000 acre-ft/yr in Huntington Valley 

area (Rush and Everett, 1966b, p. 21, 22), 24,000 

acre-ft/yr in Pine Valley (Eakin, 196Ib, p. 22, includes 5,000 acre-ft/yr as leakage to Pine Creek), 

12,000 acre-ft/yr in Crescent Valley (Zones, 1961, 

p. 21), and 12,000 acre-ft/yr in Grass Valley 

(Everett and Rush, 1966, p. 16). Crescent and 

Grass Valleys are on the edge of the modeled area 

and recharge from mountain ranges on the west 

sides of the valleys is not simulated. Consequently, 

the simulated discharge in these valleys is appreciably less than the estimated quantity.
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D93

Total simulated discharge (as evapotranspiration 

and leakage to head-dependent flow boundaries) along 

the Humboldt River is 52,000 acre-ft/yr (fig. 35). This 

quantity represents only a fraction of the total 

estimated evapotranspiration and streamflow in 

the Humboldt River valley above Palisade (Eakin 

and Lamke, 1966, p. 59, 60). Simulation of regional ground-water flow with the model did not 

account for the local circulation of water adjacent to the Humboldt River; rather, the model is 

designed to assess the potential for regional flow 

from distant sources to regional discharge areas. 

In the upper Humboldt River region, the quantity of simulated deep flow (flow through the lower 

model layer) to the Humboldt River is small (a 

few thousand acre-ft/yr) compared to local flow 

between the river and its alluvium.

POTENTIAL USES OF MODEL

The ground-water flow model of the carbonate-rock province is unlike most models in that 

the extent of aquifers and their hydraulic properties are generally unknown in the province; thus, 

the model greatly simplifies flow through a complex geologic region. Simulation results are based 

on assuming recharge to the province is known 

with the distribution of transmissivities simulated 

to match the general distribution of water levels 

and estimates of discharge. However, water levels in consolidated rocks are generally unknown, 

and estimates of recharge and discharge are known 

only approximately. Consequently, other, equally 

valid distributions of transmissivities may be found 

that permit the model to be calibrated to the existing water-level data and estimates of recharge 

and discharge. The model may be best suited for:

 Simulating alternative transmissivity distributions to evaluate potential source areas of 

regional springs,

 Simulating the effects of differing recharge 

rates on regional ground-water flow, and

 Simulating the effects of changing location 

of discharge on regional ground-water flow.

Therefore, the potential uses of the model are 

limited. The model is not suited to predict accurate water-level declines that would result from 

pumping ground water in the province. Also, the 

model is not suited to predict the accurate rate 

of change in natural discharge caused by pumping, because the model has not been calibrated 

to any transient simulations.

SUMMARY AND CONCLUSIONS

This report describes the results of a computer-model-based analysis of regional groundwater flow in the eastern Great Basin, a 

100,000-mi2 area that lies mostly in eastern Nevada and western Utah, with small parts in northwestern Arizona, eastern California, and southern 

Idaho. The original version of this report, published in 1991, presented results that subsequently 

proved to be adversely affected by a transpositional error in the computer data files that define the model-cell dimensions. This error produced 

an unintended regional anisotropy in hydraulic 

conductivity. The results reported herein constitute a reanalysis of regional flow after the transposition was corrected and the computer model 

recalibrated.

Ground-water flow in the eastern Great Basin has been evaluated as part of the U.S. Geological Survey's Great Basin Regional 

Aquifer-System Analysis. The area is referred to 

as the carbonate-rock province because, during 

the Paleozoic era, thick sequences of limestone 

and dolomite were deposited in a shallow sea that 

inundated the area. Since then, many episodes 

of sediment deposition, volcanic activity, erosion, 

and tectonic deformation by both compressional 

and extensional forces have altered the extent and 

thickness of the carbonate rocks. The present-day 

physiography, which is characterized by north- to 

northeast-trending mountain ranges separated by 

intervening valleys that are partly filled with sedimentary deposits eroded from the adjacent mountains, is the result of normal faulting caused by 

extension that began about 20 million years ago. 

Relief between the block-faulted mountains and 

the adjacent valley floors ranges from 1,000 ft to 

more than 7,000 ft.

Shallow ground-water reservoirs in the basin fill supply most of the current (1992) pumpage 

from wells in this geologically complex terrain. 

Aquifers in the underlying carbonate rocks are 

largely undeveloped; regionally, however, these 

aquifers are important because they provide an 

avenue for interbasin ground-water flow. The 

source of ground water in the province is precipitation, most of which falls in the higher mountain ranges. Ground-water discharge is mostly by 

evapotranspiration in the low parts of the many 

valleys. Some ground water also discharges from 

small, local springs. Such springs are fed by recharge that originates nearby. In contrast, ground 

water discharging at larger, regional springs
D94 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

issuing from the carbonate-rock aquifers originates 

in distant mountain ranges.

Ground-water flow in the province is conceptualized as consisting of two components: a relatively shallow one in which the flow is from 

mountain ranges to adjacent valleys, and a deeper 

one in which the ground water is transmitted 

through carbonate rocks beneath mountain ranges 

and valleys to discharge areas at distant springs 

or terminal sinks. The maximum depth of flow 

in the province is unknown, but freshwater has 

been detected at depths as great as 10,000 ft. A 

three-dimensional ground-water flow model was 

used to simulate the concept of shallow flow systems superimposed over deeper flow systems and 

to evaluate regional flow. The modeled area is 

divided into rectangular cells, 5 mi wide and 7.5 

mi long, that are elongate in a northnortheastward direction. Two model layers are 

used to simulate the shallow and deeper flow 

systems.

The conceptualization and simulation of regional ground-water flow includes the following 

simplifying assumptions: (1) Fractures and solution openings in consolidated rocks can be represented on a regional scale as a porous medium. 

(2) Darcy's Law is applicable on a regional scale 

to flow through the fractures and solution openings and across abrupt changes in lithology. (3) 

Steady-state conditions exist, in which estimates 

of present-day recharge equal estimates of discharge (the discharge estimates used for each valley are based on conditions prior to ground-water 

development). (4) Horizontal transmissivity is 

heterogeneous in the region, but it is homogenous 

and isotropic within each 37.5-mi2 model cell. (5) 

Recharge is from precipitation in the mountain 

ranges and is based on previously published estimates. (6) Rivers and lakes that border the province, as well as the Death Valley playa, can be 

either a source or a sink for ground-water flow.

(7) Discharge from regional springs is known, and 

flow to the springs is through carbonate rocks.

(8) Spring flow not simulated as discharging from 

carbonate rocks is included as part of the discharge from shallow ground water. Although these 

assumptions are probably valid for parts of the 

province, the validity of each assumption for the 

entire area is not known. Because of the uncertainty of these assumptions and because the extent, thickness, and hydraulic properties of the 

carbonate aquifers throughout most of the province are largely unknown, simulation results do 

not perfectly replicate actual ground-water flow

in the province. The results do, however, provide 

a simplified concept of the distribution of recharge, 

discharge, and flow in the province within the 

limitations of current understanding and the limitations of the model simulations.

The computer model was calibrated by adjusting transmissivities of cells in both model layers 

and vertical leakances between layers during repeated simulations. Calibration proceeded until 

simulated water levels and simulated discharge 

as evapotranspiration and regional-spring flow 

agreed with available water levels in most places, 

with the mapped distribution and estimated quantity of evapotranspiration, and with the estimated 

flow at regional springs. The magnitude of the 

estimated transmissivities and vertical leakances 

in the model is dependent upon the quantity of 

recharge used in the simulation. Estimates of recharge are approximate and could differ from actual recharge by 100 percent or more. Therefore, 

the estimated transmissivities and leakances include an uncertainty equal to or greater than that 

of the estimated recharge. Additional uncertainty 

in the distribution of transmissivities and 

leakances results from the scarcity of available 

water-level data (particularly for the carbonaterock aquifers), the lack of information on the extent and thickness of the basin-fill and 

carbonate-rock aquifers, and the lack of knowledge on the distribution of recharge. Because of 

the uncertainty in the transmissivities and vertical leakances, other distributions may adequately 

simulate water levels and discharge in the province. In addition, the estimated transmissivities 

should be considered only on a regional basis because the values represent an average for all rocks 

and deposits included within the 37.5-mi2 area 

of a model cell. The hydraulic properties of the 

various rocks and deposits within even a single 

cell can vary by several orders of magnitude.

In the upper model layer, transmissivities 

range from 0.000022 to 0.22 ft2/s. Transmissivities are generally greater than 0.006 ft2/s for cells 

corresponding to basin fill and carbonate rocks 

and are less than 0.006 ft2/s for cells corresponding 

to other consolidated rocks (which are assumed 

to be of low permeability). Lowest transmissivities are simulated in the Great Salt Lake Desert, 

where an extensive body of ground water is saline and the circulation of freshwater is minimal.

In the lower model layer, estimated transmissivities range from 0.000033 to 0.66 ft2/s. Transmissivities greater than 0.006 ft2/s are simulated 

in the vicinity of regional springs or in areas where
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D95

ground-water budgets indicate interbasin flow. 

These zones of higher transmissivity may be related to places in the province where thick sequences of Paleozoic carbonate rocks are still 

present. The highest transmissivities are simulated in narrow bands associated with regional 

springs in the White River Valley in eastern Nevada, the Muddy River Springs in southern Nevada, and Fish Springs in west-central Utah. 

Transmissivities less than 0.006 ft2/s are simulated throughout much of the province. Lowest 

transmissivities are simulated for the Great Salt 

Lake Desert, for Death Valley, and for the extreme southern end of the province.

Only one of several extensive east-west-trending lineaments could be correlated with a marked 

change in the simulated and measured water-level 

trends. This lineament, called the transverse 

crustal boundary, extends across southern Nevada. 

It generally corresponds to the southern extent 

of Cenozoic volcanism in the province, to a considerable southward decline in the altitude of the 

valley floor, to a change in gravity, and to the 

location of left-lateral shears. Except for a narrow zone of high transmissivities in eastern Nevada, assigned values in the lower model layer 

are less than 0.006 ft2/s along the lineament.

The lack of correlation of marked changes in 

simulated water levels and transmissivities, as 

well as observed water-level trends, across other 

lineaments north of the transverse crustal boundary might be due to disruption of the lineaments 

by younger faulting. However, several regional 

springs are near the lineaments, which suggests 

that segments along some of the lineaments may 

restrict regional ground-water flow.

The model simulates the concept of numerous shallow-flow regions superimposed upon fewer 

deep-flow regions. A total of 45 shallow-flow regions are identified in the upper model layer on 

the basis of horizontal flow between cells. In the 

lower layer, flow is grouped into deep-flow regions 

and subregions. A total of 17 deep-flow subregions 

are delineated, also on the basis of horizontal flow 

between cells. The subregions are, in turn, grouped 

into five deep-flow regions on the basis of areas 

having simulated water levels that generally decline toward one of five regional discharge areas. 

These are named the Death Valley, Colorado River, 

Bonneville, Railroad Valley, and upper Humboldt 

River regions. Simulated water levels are generally highest in southwestern Utah and east-central Nevada, where altitudes of the valleys floors 

are highest. From this area, water levels generally decrease northward toward discharge areas 

in the upper Humboldt River and Bonneville regions and southward toward discharge areas in 

the Colorado River and Death Valley regions. 

Within the area of high water levels in east-central Nevada, some of the ground water flows to 

a terminal sink in Railroad Valley.

Water budgets for each of the deep-flow regions are summarized in table 9. The budgets include flow within the overlying shallow-flow 

regions. The budgets list cross-boundary flow between regions because cells that straddle a flowregion boundary are assigned to only one of the 

two regions and because simulated flow in the 

shallow-flow regions is not everywhere in the same 

direction as that in the underlying deep-flow 

regions.

Most of the simulated flow is in the upper 

model layer. Total simulated inflow is about 1.5 

million acre-ft/yr (about 3 percent of the total precipitation), with all but 3,000 acre-ft/yr assigned 

as recharge to the mountains (table 9). This inflow does not include recharge that is discharged 

locally that is, within the same 37.5-mi2 model 

cell. If this recharge were included, the estimated 

total inflow would be considerably more. Simulated outflow is mostly from the upper layer as 

evapotranspiration (about 1.2 million acre-ft/yr) 

and as leakage to surface-water bodies and to the 

Death Valley playa (about 100,000 acre-ft/yr). Most 

of the simulated flow in the lower layer is in areas of high transmissivities. Flow is downward 

in recharge areas, then lateral to regional springs 

or to areas of discharge from the upper layer. Total 

simulated flow in the lower layer is 428,000 acreft/yr, or only 28 percent of total inflow. About half 

the flow through the lower layer (211,000 acreft/yr) is simulated as discharge to regional springs. 

This simulated total is only 0.5 percent more than 

the estimated total for the regional springs.

Simulated regional-spring flow is extremely 

sensitive to changes in transmissivities in both 

layers and to changes in vertical leakance between 

layers. For example, increasing transmissivities 

in the lower layer between Ash Meadows in 

Amargosa Desert and Death Valley results in less 

spring flow at Ash Meadows and greater flow to 

Death Valley. Similar results are simulated at 

Muddy River Springs in southern Nevada and Fish 

Springs in west-central Utah when transmissivities are increased downgradient from the springs. 

Even minor changes to the assigned hydraulic 

properties can result in changes to the discharge 

at regional springs. The final assigned distribution
D96 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

TABLE 9. Simulated ground-water flow budgets for five deep-flow regions of modeled area

[All amounts are in acre-feet per year (acre-ft/yr), rounded to nearest 1,000 acre-ft/yr. Amounts of mountain recharge are 

assigned, as described in text section title "Estimates of Recharge"; all other listed amounts are determined from model 

simulation]

Budget component and

(in parentheses) 

model layer involved

Death 

Valley 

region

Colorado 

River 

region

Bonneville 

region

Upper

Railroad Humboldt Entire 

Valley River modeled 

region region area

INFLOW

Mountain recharge (upper) 

Subsurface inflow from 

adjacent regions (both) 

Leakage (upper)

161,000 202,000

a 16,000 

0

5,000

0

855,000

c 34,000 

0

132,000 174,000

2,000

0

e 12,000 

# 3,000

1,524,000

(f) 

3,000

Total inflow

OUTFLOW

Evapotranspiration (upper) 

Regional springs (lower) 

Subsurface outflow to

adjacent regions (both) 

Leakage (upper)

177,000 207,000

147,000

22,000

'3,000 

"8,000

91,000

97,000

10,000

0 7,000

889,000

758,000

64,000

* 8,000 

59,000

134,000 189,000 1,527,000

86,000

24,000

131,000

4,000

1,213,000

211,000

1 23,000 m 25,000 ® 

0 q 28,000 102,000

Total outflow1" 180,000 205,000 889,000 133,000 188,000 1,526,000

a Includes 8,000 acre-ft/yr from Colorado River region and 8,000 acre-ft/yr from Railroad Valley region.

b Includes 2,000 acre-ft/yr from Bonneville region, 1,000 acre-ft/yr from Railroad Valley region, and 2,000 acreft/yr from Death Valley region.

c Includes 4,000 acre-ft/yr from Railroad Valley region, 25,000 acre-ft/yr from upper Humboldt River region, and 

5,000 acre-ft/yr from Colorado River region. 

From Bonneville region.

e Includes 10,000 acre-ft/yr from Railroad Valley region, 1,400 acre-ft/yr from Death Valley region, and 600 acreft/yr from Bonneville region.

' Net flow among regions within modeled area is zero.

g From Humboldt River and selected tributaries.

Includes evapotranspiration of flow from small springs that are assumed to be discharging from upper layer; does 

not include evapotranspiration from regional springs that are simmulated to be discharging from lower layer.

1 Includes 1,000 acre-ft/yr to upper Humboldt River region and 2,000 acre-ft/yr to Colorado River region.

J Includes 2,000 acre-ft/yr to Bonneville region and 8,000 acre-ft/yr to Death Valley region.

* Includes 5,000 acre-ft/yr to Colorado River region, 2,000 acre-ft/yr to Railroad Valley region, and 1,000 acre-ft/yr 

to upper Humboldt River region.

Includes 8,000 acre-ft/yr to Death Valley region, 10,000 acre-ft/yr to upper Humboldt River region, 4,000 acre-ft/yr 

to Bonneville region, and 1,000 acre-ft/yr to Colorado River region.

m To Bonneville region.

" To Death Valley playa.

0 Includes 5,000 acre-ft/yr to Virgin River and 2,000 acre-ft/yr to Lake Mead and Colorado River.

p Includes 34,000 acre-ft/yr to Sevier River and Sevier Lake, 22,000 acre-ft/yr to Utah Lake, and 3,000 acre-ft/yr to 

Great Salt Lake.

* To Humboldt River and selected tributaries.

r Total outflow does not always equal total inflow due to rounding of individual values.

of transmissivities and vertical leakances results 

in simulated water levels, regional-spring flows, 

and evapotranspiration rates that reasonably duplicate measured and estimated values. However, 

other combinations of transmissivities and vertical leakances may be possible that also would
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D97

reproduce measured water levels and estimated 

discharge in the province, but would result in different patterns of ground-water flow and different configurations of flow-region boundaries.

The simulation results presented in this report are only approximate because of uncertainties in the quantity of recharge to and 

evapotranspiration from the aquifers in the province and because the extent, thickness, and hydraulic properties of the carbonate aquifers are 

largely unknown. Nonetheless, several general conclusions can be made on the basis of available 

information and the model simulations:

 Most ground-water flow in the province is 

relatively shallow, moving from recharge areas in the mountain ranges to discharge areas in the adjacent valleys.

 Directions of shallow ground-water flow do 

not everywhere correspond to the directions 

of deep ground-water flow.

 Most consolidated rocks beneath the valleys 

and surrounding mountains are not highly 

transmissive, suggesting either that not all 

carbonate rocks are highly permeable or that 

not all valleys and surrounding mountains 

are underlain by carbonate rocks.

 Ground-water flow to the larger regional 

springs is through permeable carbonate rocks 

that transmit water from distant recharge 

areas beneath intervening mountains and 

valleys.

 Only small quantities of deep flow discharge 

at the terminal sinks (the Great Salt Lake, 

the Great Salt Lake Desert, the Railroad Valley and Death Valley playas, and the Colorado and Virgin Rivers); rather, most of the 

deep flow discharges at regional springs and 

in areas of evapotranspiration upgradient 

from the terminal sinks.

 Only small quantities of deep flow are simulated in the upper Humboldt River region, 

because most of the ground water discharging along the river is from local flow associated with the river.

The model is a simplification of flow through 

a geologically complex region, in which hydraulic properties can change abruptly because of 

changes in lithology. The lack of information on 

the extent of aquifers, their hydraulic properties, 

and the distribution of water levels in the aquifers precludes developing a model in which only 

one distribution of transmissivity is possible. The 

model, therefore, may not reliably predict waterlevel declines that would result from pumping 

ground water in the province nor simulate the 

rate of change in natural discharge caused by 

pumping. The model may be best suited for simulating different transmissivity distributions to 

evaluate potential source areas of regional springs 

and for simulating long-term effects of changing 

recharge and discharge on regional ground-water 

flow.

REFERENCES CITED

Arnow, Ted, 1984, Water-level and water-quality changes in 

Great Salt Lake, Utah, 1847-1983: U.S. Geological Survey Circular 913, 22 p.

Bedinger, M.S., Harrill, J.R., and Thomas, J.M., 1984, Maps 

showing ground-water units and withdrawal, Basin and 

Range province, Nevada: U.S. Geological Survey WaterResources Investigations Report 83-4119-A, 10 p., 2 plates, 

scale 1:500,000.

Bedinger, M.S., Sargent, K.A., and Langer, W.H., 1989, Studies 

of geology and hydrology in the Basin and Range province, southwestern United States, for isolation of highlevel radioactive waste Characterization of the Death 

Valley region, Nevada and California: U.S. Geological Survey Professional Paper 1370-F, 49 p.

 1990, Studies of geology and hydrology in the Basin 

and Range province, southwestern United States, for isolation of high-level radioactive waste Characterization 

of the Bonneville region, Utah and Nevada: U.S. Geological 

Survey Professional Paper 1370-G, 38 p.

Bjorklund, L.J., Sumsion, C.T., and Sandberg, G.W., 1978, 

Ground-water resources of Parowan-Cedar City drainage 

basin, Iron County, Utah: Utah Department of Natural 

Resources Technical Publication 60, 93 p.

Blankennagel, R.K., and Weir, J.E., Jr., 1973, Geohydrology 

of the eastern part of Pahute Mesa, Nevada Test Site, 

Nye County, Nevada: U.S. Geological Survey Professional 

Paper 712-B, 35 p.

Bolke, E.L., and Sumsion, C.T., 1978, Hydrologic reconnaissance of the Fish Springs Flat area, Tooele, Juab, and 

Millard Counties, Utah: Utah Department of Natural Resources Technical Publication 64, 30 p.

Brenner, I.S., 1974, A surge of maritime tropical air Gulf 

of California to the southwestern United States: Monthly 

Weather Review, v. 102, p. 375-389.

Bunch, R.L., and Harrill, J.R., 1984, Compilation of selected 

hydrologic data from the MX missile siting investigation, 

east-central Nevada and western Utah: U.S. Geological 

Survey Open-File Report 84-702, 123 p.

Carlton, S.M., 1985, Fish Springs multibasin flow system, 

Nevada and Utah: University of Nevada, Reno, Mackay 

School of Mines, M.S. thesis, 103 p.

Carpenter, Everett, 1915, Ground water in southeastern Nevada: U.S. Geological Survey Water-Supply Paper 365, 86

PCarr, W.J., 1984, Regional structural setting of Yucca Mountain, southwestern Nevada, and late Cenozoic rates of tectonic activity in part of the southwestern Great Basin, 

Nevada and California: U.S. Geological Survey Open-File 

Report 84-854, 114 p.
D98 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

Claassen, H.C., 1983, Sources and mechanisms of recharge 

for ground water in the west-central Amargosa Desert, 

Nevada A geochemical interpretation: U.S. Geological 

Survey Open-File Report 83-542, 66 p.

Coney, P.J., 1980, Cordilleran metamorphic core complexes 

An overview, in Crittenden, M.D., Jr., Coney, P.J., and 

Davis, G.K., eds., Cordilleran metamorphic core complexes: 

Geological Society of America Memoir 153, p. 7-31.

Cordova, R.M., 1970, Ground-water conditions in southern 

Utah Valley and Goshen Valley, Utah: Utah Department 

of Natural Resources Technical Publication 28, 72 p.

Cordova, R.M., and Subitzky, Seymour, 1965, Ground water 

in northern Utah Valley, Utah A progress report for the 

period 1948-63: Utah State Engineer Technical Publication 11, 41 p.

Czarnecki, J.B., and Waddell, R.K., 1984, Finite-element simulation of ground-water flow in the vicinity of Yucca Mountain, Nevada-California: U.S. Geological Survey 

Water-Resources Investigations Report 84-4349, 38 p.

Dettinger, M.D., 1989, Distribution of carbonate-rock aquifers in southern Nevada and the potential for their development Summary of findings, 1985-88: Carson City, 

Nev., Program for the Study and Testing of CarbonateRock Aquifers in eastern and southern Nevada, Summary 

Report No. 1, 37 p.

Dinwiddie, G.A., and Schroder, L.J., 1971, Summary of hydraulic testing in and chemical analyses of water samples 

from deep exploratory holes in Little Fish Lake, Monitor, 

Hot Creek, and Little Smoky Valleys, Nevada: U.S. Geological Survey Report USGS 474-90, 70 p. [Available only 

from National Technical Information Service, U.S. Department of Commerce, Springfield, VA 22161.]

Domenico, P.A., Stephenson, D.S., and Maxey, G.B., 1964, 

Ground water in Las Vegas Valley: University of Nevada, 

Desert Research Institute Technical Report H-W 7, 53 p.

Dudley, W.W., Jr., and Larson, J.D., 1976, Effect of irrigation pumping on desert pupfish habitats in Ash Meadows, Nye County, Nevada: U.S. Geological Survey 

Professional Paper 927, 52 p.

Eakin, T.E., 1960, Ground-water appraisal of Newark Valley, White Pine County, Nevada: Nevada Department of 

Conservation and Natural Resources, Ground-Water Resources - Reconnaissance Report 1, 33 p.

 1961a, Ground-water appraisal of Long Valley, White 

Pine and Elko Counties, Nevada: Nevada Department of 

Conservation and Natural Resources, Ground-Water Resources - Reconnaissance Report 3, 35 p.

 1961b, Ground-water appraisal of Pine Valley, Eureka 

and Elko Counties, Nevada: Nevada Department of Conservation and Natural Resources, Ground-Water Resources 

- Reconnaissance Report 2, 41 p.

 1963, Ground-water appraisal of Pahranagat and Pahroc 

Valleys, Lincoln and Nye Counties, Nevada: Nevada Department of Conservation and Natural Resources, GroundWater Resources - Reconnaissance Report 21, 36 p.

-1966, A regional interbasin ground-water system in the

White River area, southeastern Nevada: Water Resources 

Research, v. 1, no. 3, p. 251-271.

Eakin, T.E., Hughes, J.L., and Moore, D.O., 1967, Waterresources appraisal of Steptoe Valley, White Pine and Elko 

Counties, Nevada: Nevada Department of Conservation 

and Natural Resources, Water Resources - Reconnaissance 

Report 42, 48 p.

Eakin, T.E., and Lamke, R.D., 1966, Hydraulic reconnaissance of the Humboldt River Basin, Nevada: Nevada Department of Conservation and Natural Resources, Water 

Resources Bulletin 32, 107 p.

Eakin, T.E., Maxey, G.B., Robinson, T.W., Fredericks, J.C., 

and Loeltz, O.J., 1951, Contributions to the hydrology of 

eastern Nevada: Nevada State Engineer, Water Resources 

Bulletin 12, 171 p.

Eakin, T.E., and Moore, D.O., 1964, Uniformity of discharge 

of Muddy River Springs, southeastern Nevada, and relation to interbasin movement of ground water, in Geological Survey Research 1964: U.S. Geological Survey 

Professional Paper 501-D, p. D171-D176.

Eakin, T.E., Price, Don, and Harrill, J.R., 1976, Summary 

appraisals of the Nation's ground-water resources Great 

Basin region: U.S. Geological Survey Professional Paper 

813-G, 37 p.

Eakin, T.E., and Winograd, I.J., 1965, Interbasin movement 

of ground water in south-central Nevada Some implications, in Abstracts for 1964: Geological Society of America 

Special Paper 82, p. 52.

Eaton, G.P., 1975, Characteristics of a transverse crustal 

boundary in the Basin and Range province of southern 

Nevada: Geological Society of America Abstracts with Programs, v. 7, no. 7, p. 1062.

Eaton, G.P., Wahl, R.R., Prostka, H.J., Mabey, D.R., and 

Kleinkopf, M.D., 1978, Regional gravity and tectonic patterns: Their relation to late Cenozoic epeirogeny and lateral spreading in the western Cordillera, in Smith, R.B., 

and Eaton, G.P., eds., Cenozoic tectonics and regional geophysics of the western Cordillera: Geological Society of 

America Memoir 152, p. 51-92.

Ekren, E.B., Bucknam, R.C., Carr, W.J., Dixon, G.L., and 

Quinlivan, W.D., 1976, East-trending structural lineaments 

in central Nevada: U.S. Geological Survey Professional 

Paper 986, 16 p.

Everett, D.E., and Rush, F.E., 1966, A brief appraisal of water 

resources of Grass and Carico Lake Valleys, Lander and 

Eureka Counties, Nevada: Nevada Department of Conservation and Natural Resources, Water Resources - Reconnaissance Report 37, 27 p.

Feltis, R.D., 1967, Ground-water conditions in Cedar Valley, 

Utah County, Utah: Utah Department of Natural Resources 

Technical Publication 16, 34 p.

Freeze, R.A., and Witherspoon, PA., 1966, Theoretical analysis 

of regional groundwater flow 1. Analytical and numerical solutions to the mathematical model: Water Resources 

Research, v. 2, no. 4, p. 641-656.

 1967, Theoretical analysis of regional groundwater 

flow 2. Effect of water-table configuration and subsurface permeability variation: Water Resources Research, 

v. 3, no. 2, p. 623-634.

French, D.E., and Freeman, K.J., 1979, Tertiary volcanic 

stratigraphy and reservoir characteristics of Trap Spring 

field, Nye County, Nevada, in Newman, G.W., and Goode, 

H.D., eds., Basin and Range symposium and Great Basin 

field conference: Denver, Colo., Rocky Mountain Association of Geologists, Guide Book, p. 487-502.

Frisbie, H.R., La Camera, R.J., Riek, M.M., and Wood, D.B., 

1985, Water resources data, Nevada, water year 1984: U.S. 

Geological Survey Water-Data Report NV-84-1, 247 p.

Garcia, K.T., Gortsema, G.C., Pennington, R.N., and Preissler, 

A.M., 1992, Water resources data, Nevada, water year 1991: 

U.S. Geological Survey Water-Data Report NV-91-1, 481 p.

Gates, J.S., 1984, Hydrogeology of northwestern Utah and 

adjacent parts of Idaho and Nevada: Utah Geologic Association Publication 13, p. 239-248.
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D99

 1987, Ground water in the Great Basin part of the 

Basin and Range Province, western Utah: Cenozoic geology of western Utah Site for precious metal and hydrocarbon accumulations: Utah Geological Association, 

Publication 16, p. 75-89.

Gates, J.S., and Kruer, S.A., 1981, Hydrologic reconnaissance 

of the southern Great Salt Lake Desert and summary of 

the hydrology of west-central Utah: Utah Department of 

Natural Resources Technical Publication 71, 55 p.

Glancy, PA., 1968a, Water-resources appraisal of Butte Valley, Elko and White Pine Counties, Nevada: Nevada Division of Water Resources, Reconnaissance Report 49, 50 p.

 1968b, Water-resources appraisal of Mesquite-Ivanpah 

Valley area, Nevada and California: Nevada Division of 

Water Resources, Reconnaissance Report 46, 57 p.

Glancy, P.A., and Van Denburgh, A.S., 1969, Water-resources 

appraisal of the lower Virgin River Valley area, Nevada, 

Arizona, and Utah: Nevada Division of Water Resources, 

Reconnaissance Report 51, 87 p.

Guth, PL., 1988, Superposed Mesozoic thrusts and Tertiary 

extension, northwestern Clark County, Nevada [abs.]: Geological Society of America, Abstracts with Programs, v. 

20, no. 3, p. 165.

Harbaugh, A.W, 1990, A computer program for calculating 

subregional water budgets using results from the U.S. 

Geological Survey modular three-dimensional finite-difference ground-water flow model: U.S. Geological Survey Open-File Report 90-392, 46 p.

Hardman, George, 1936, Nevada precipitation and acreages 

of land by rainfall zones: University of Nevada-Reno, Agriculture Experiment Station mimeograph paper, 10 p.

 1965, Nevada precipitation map: University of NevadaReno, Agriculture Experiment Station, Bulletin 183, 57 p.

Harrill, J.R., 1968, Hydrologic response to irrigation pumping in Diamond Valley, Eureka and Elko Counties, Nevada, 1950-65: Nevada Department of Conservation and 

Natural Resources, Water Resources Bulletin 35, 85 p.

 1971, Water-resources appraisal of the Pilot Creek Valley 

area, Elko and White Pine Counties, Nevada: Nevada Division of Water Resources, Reconnaissance Report 56, 46 p.

 1976, Pumping and ground-water storage depletion in 

Las Vegas Valley, Nevada, 1955-74: Nevada Division of 

Water Resources, Bulletin 44, 70 p.

-1986, Ground-water storage depletion in Pahrump Valley, Nevada-California, 1962-75: U.S. Geological Survey 

Water-Supply Paper 2279, 53 p.

Harrill, J.R., Gates, J.S., and Thomas, J.M., 1988, Major 

ground-water flow systems in the Great Basin region of 

Nevada, Utah, and adjacent States: U.S. Geological Survey Hydrologic Investigations Atlas HA-694-C, 2 sheets.

Harrill, J.R., Welch, A.H., Prudic, D.E., Thomas, J.M., 

Carman, R.L., Plume, R.W., Gates, J.S., and Mason, J.L., 

1983, Aquifer systems in the Great Basin region of Nevada, Utah, and adjacent states A study plan: U.S. Geological Survey Open-File Report 82-445, 49 p.

Hess, J.W, and Mifflin, M.D., 1978, A feasibility study of 

water production from deep carbonate aquifers in Nevada: 

University of Nevada, Desert Research Institute Publication 41054, 125 p.

Hildenbrand, T.G., and Kucks, R.P., 1982, A description of 

colored gravity maps of the Basin and Range Province, 

southwestern United States: U.S. Geological Survey OpenFile Report 82-500, 18 p.

Hintze, L.F., 1973, Geologic map of Utah: Utah Geologic and 

Mineralogic Survey, scale 1:500,000.

Holmes, W.R., 1984, Ground-water hydrology and projected 

effects of ground-water withdrawals in the Sevier Desert, 

Utah: Utah Department of Natural Resources Technical 

Publication 79, 54 p.

Hood, J.W., Price, Don, and Waddell, K.M., 1969, Hydrologic 

reconnaissance of Rush Valley, Tooele County, Utah: Utah 

Department of Natural Resources Technical Publication 

23, 63 p.

Hood, J.W., and Rush, F.E., 1965, Water-resources appraisal 

of the Snake Valley area, Utah and Nevada: Nevada Department of Conservation and Natural Resources, Water 

Resources - Reconnaissance Report 34, 43 p.

Hood, J.W, and Waddell, K.M., 1968, Hydrologic reconnaissance of Skull Valley, Tooele County, Utah: Utah Department of Natural Resources Technical Publication 18, 54 p.

 1969, Hydrologic reconnaissance of Deep Creek Valley, Tooele and Juab Counties, Utah, and Elko and White 

Pine Counties, Nevada: Utah Department of Natural Resources Technical Publication 24, 54 p.

Houghton, J.G., 1967, Characteristics of rainfall in the Great Basin: University of Nevada, Desert Research Institute, 205 p.

Hubbs, C.L., and Miller, R.R., 1948, The Great Basin with 

emphasis on glacial and postglacial times, II The zoological evidence: University of Utah Bulletin, v. 36, no. 

20, p. 17-166.

Hunt, C.B., and Robinson, T.W, 1960, Possible interbasin 

circulation of ground water in the southern part of the 

Great Basin, in Geological Survey Research 1960: U.S. 

Geological Survey Professional Paper 400-B, p. B273-B274.

Hunt, C.B., Robinson, T.W, Bowles, W.A., and Washburn, 

A.L., 1966, Hydrologic basin, Death Valley, California: U.S. 

Geological Survey Professional Paper 494-B, 138 p.

Jones, B.F., 1982, Mineralogy of fine grained alluvium from 

borehole U11G, expl. 1, northern Frenchman Flat area, 

Nevada Test Site: U.S. Geological Survey Open-File Report 82-765, 10 p.

Kirk, S.T., and Campana, M.E., 1990, A deuterium-calibrated 

groundwater flow model of a regional carbonate-alluvial 

system: Journal of Hydrology, v. 119, p. 357-388.

Kohler, M.A., Nordenson, T.J., and Baker, D.R., 1959, Evaporation maps for the United States: U.S. Department of 

Commerce, Weather Bureau Technical Paper 37, 13 p.

Loeltz, O.J., 1960, Source of water issuing from springs in 

Ash Meadows Valley, Nye County, Nevada [abs.]: Geological 

Society of America Bulletin, v. 71, no. 12, part 2, p. 1917- 

1918.

Lohman, S.W, 1972, Ground-water hydraulics: U.S. Geological 

Survey Professional Paper 708, 70 p.

Malmberg, G.T., 1965, Available water supply of the Las Vegas 

ground-water basin, Nevada: U.S. Geological Survey Water-Supply Paper 1780, 116 p.

Malmberg, G.T., and Eakin, T.E., 1962, Ground-water appraisal of Sarcobatus Flat and Oasis Valley, Nye and 

Esmeralda Counties, Nevada: Nevada Department of Conservation and Natural Resources, Ground-Water Resources 

- Reconnaissance Report 10, 39 p.

Mason, J.L., (in press), Ground-water hydrology and simulated effects of development in the Milford area, an arid 

basin in southwestern Utah: U.S. Geological Survey Professional Paper 1409-G.

Maxey, G.B., and Eakin, T.E., 1949, Ground water in White 

River Valley, White Pine, Nye, and Lincoln Counties, Nevada: Nevada State Engineer, Water Resources Bulletin 

8, 59 p.

Maxey, G.B., and Jameson, C.H., 1948, Geology and water
D100 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

resources of Las Vegas, Pahrump, and Indian Springs Valleys, Clark and Nye Counties, Nevada: Nevada State Engineer, Water Resources Bulletin 5, 292 p.

McDonald, M.G., and Harbaugh, A.W., 1988, A modular threedimensional finite-difference ground-water flow model: U.S. 

Geological Survey Techniques of Water-Resources Investigations, Book 6, Chapter Al, 586 p.

McKee, E.H., 1976, Geology of the northern part of the Toquima 

Range, Lander, Eureka, and Nye Counties, Nevada: U.S. 

Geological Survey Professional Paper 931, 49 p.

Meinzer, O.E., 1917, Geology and water resources of Big 

Smoky, Clayton, and Alkali Spring Valleys, Nevada: U.S. 

Geological Survey Water-Supply Paper 423, 167 p.

Mendenhall, W.C., 1909, Some desert watering places in southeastern California and southwestern Nevada: U.S. Geological Survey Water-Supply Paper 224, 86 p.

Mifflin, M.D., 1968, Delineation of ground-water flow systems in Nevada: University of Nevada, Desert Research 

Institute Technical Report H-W 4, 112 p.

 1988, Region 5, Great Basin, in Back, W., Rosenshein, 

J.S., and Seaber, PR., eds., Hydrogeology: Boulder, Colo., 

Geological Society of America, The Geology of North 

America, v. O-2, p. 69-78, pi. 3, scale 1:1,000,000.

Mifflin, M.D., and Hess, J.W, 1979, Regional carbonate flow 

systems in Nevada, in Back, William, and Stephenson, D.A., 

eds., Contemporary hydrogeology, the George Burke Maxey 

memorial volume: Journal of Hydrology, v. 43, p. 217-237.

Miller, G.A., 1977, Appraisal of the water resources of Death 

Valley, California-Nevada: U.S. Geological Survey OpenFile Report 77-728, 68 p.

Morgan, D.S., and Dettinger, M.D., 1994, Ground-water conditions in Las Vegas Valley, Clark County, Nevada Part 

II, Geohydrology and simulation of ground-water flow: U.S. 

Geological Survey Open-File Report 90-179, 151 p.

Mower, R.W., 1965, Ground-water resources of Pavant Valley, Utah: 

U.S. Geological Survey Water-Supply Paper 1794, 78 p.

 1978, Hydrology of Beaver Valley area, Beaver County, 

Utah, with emphasis on ground water: Utah Department 

of Natural Resources Technical Publication 63, 90 p. 

-1982, Hydrology of the Beryl-Enterprise area, Escalante

Desert, Utah, with emphasis on ground water: Utah Department of Natural Resources Technical Publication 73, 66 p.

Mower, R.W., and Cordova, R.M., 1974, Water resources of 

the Milford area, Utah, with special emphasis on ground 

water: Utah Department of Natural Resources Technical 

Publication 43, 105 p.

Mower, R.W., and Feltis, R.D., 1968, Ground-water hydrology of the Sevier Desert, Utah: U.S. Geological Survey 

Water-Supply Paper 1854, 75 p.

Naff, R.L., Maxey, G.B., and Kaufmann, R.F., 1974, Interbasin 

ground-water flow in southern Nevada: Nevada Bureau 

of Mines and Geology Report 20, 28 p.

Nolan, T.B., 1943, The Basin and Range Province in Utah, 

Nevada, and California: U.S. Geological Survey Professional Paper 197-D, 55 p.

Plume, R.W., 1989, Use of aeromagnetic data to define boundaries of a carbonate-rock aquifer in east-central Nevada, 

in Subitzky, Seymour, ed., Selected papers in the hydrologic sciences: U.S. Geological Survey Water-Supply Paper 2330, p. 1-10.

 1995, Hydrogeologic framework of the Great Basin region of Nevada, Utah, and adjacent States: U.S. Geological Survey Professional Paper 1409-B, 64 p.

Plume, R.W., and Carlton, S.M., 1988, Hydrogeology of the 

Great Basin region of Nevada, Utah, and adjacent States:

U.S. Geological Survey Hydrologic Investigations Atlas HA694-A, 1 sheet.

Pollock, D.W., 1989, Documentation of computer programs 

to compute and display pathlines using results from the 

U.S. Geological Survey modular three-dimensional finitedifference ground-water flow model: U.S. Geological Survey Open-File Report 89-381, 188 p.

Poole, F.G., and Claypool, G.E., 1984, Petroleum source-rock 

potential and crude-oil correlation in the Great Basin, in 

Woodward, Jane, Meissner, F.F., and Layton, J.L., eds., 

Hydrocarbon source rocks of the Greater Rocky Mountain 

region: Denver, Colo., Rocky Mountain Association of Geologists, p. 179-229.

Rantz, S.E., 1972, Mean annual precipitation in California 

region: U.S. Geological Survey Open-File Map, scale 

1:1,000,000.

Razem, A.C., and Steiger, J.I., 1981, Ground-water conditions in Tooele Valley, Utah, 1976-78: Utah Department 

of Natural Resources Technical Publication 69, 95 p.

ReMillard, M.D., Andersen, G.C., Birdwell, G.A., and 

Sandberg, G.W, 1986, Water resources data, Utah, water 

year 1985: U.S. Geological Survey Water-Data Report UT85-1, 400 p.

Roberts, R.J., 1964, Economic geology, mineral and water 

resources of Nevada: U.S. 88th Congress, second session, 

Senate Document 87, p. 39-48.

 1966, Metallogenic provinces and mineral belts in Nevada, in AIME Pacific Southwest Mineral Industry Conference, Sparks, Nevada, 1965, Papers, part A: Nevada 

Bureau of Mines Report 13, p. 47-52.

Rowan, L.C., and Wetlaufer, P.H., 1981, Relation between 

regional lineament systems and structural zones in Nevada: American Association of Petroleum Geologists Bulletin, v. 65, no. 8, p. 1414-1432.

Rowley, P.O., Lipman, P.W., Mehnert, H.H., Lindsey, D.A., 

and Anderson, J.J., 1978, Blue Ribbon lineament, an easttrending structural zone within the Pioche Mineral Belt 

of southwestern Utah and eastern Nevada: U.S. Geological Survey Journal of Research, v. 6, no. 2, p. 175-192.

Rush, F.E., 1964, Ground-water appraisal of the Meadow Valley area, Lincoln and Clark Counties, Nevada: Nevada Department of Conservation and Natural Resources, 

Ground-Water Resources - Reconnaissance Report 27, 43 p.

 1968a, Water-resources appraisal of Clayton ValleyStonewall Flat area, Nevada and California: Nevada Department of Conservation and Natural Resources, Water 

Resources - Reconnaissance Report 45, 54 p.

 1968b, Water-resources appraisal of the Lower MoapaLake Mead area, Clark County, Nevada: Nevada Division 

of Water Resources, Reconnaissance Report 50, 66 p. 

-1968c, Water-resources appraisal of Thousand Springs

Valley, Elko County, Nevada: Nevada Division of Water 

Resources, Reconnaissance Report 47, 61 p.

-1970, Regional ground-water systems in the Nevada

Test Site area, Nye, Lincoln, and Clark Counties, Nevada: 

Nevada Division of Water Resources, Reconnaissance Report 54, 25 p.

Rush, F.E., and Eakin, T.E., 1963, Ground-water appraisal 

of Lake Valley in Lincoln and White Pine Counties, Nevada: Nevada Department of Conservation and Natural 

Resources, Ground-Water Resources - Reconnaissance Report 24, 29 p.

Rush, F.E., and Everett, D.E., 1964, Ground-water appraisal 

of Monitor, Antelope, and Kobeh Valleys, Nevada: Nevada 

Department of Conservation and Natural Resources, Ground-
CONCEPTUAL EVALUATION OF REGIONAL GROUND-WATER FLOW IN THE CARBONATE-ROCK PROVINCE D101

Water Resources - Reconnaissance Report 30, 42 p.

-1966a, Water-resources appraisal of Little Fish Lake,

Hot Creek, and Little Smoky Valleys, Nevada: Nevada 

Department of Conservation and Natural Resources, Water Resources - Reconnaissance Report 38, 38 p.

-1966b, Water-resources appraisal of the Huntington Valley area, Elko and White Pine Counties, Nevada: Nevada 

Department of Conservation and Natural Resources, Water Resources - Reconnaissance Report 35, 37 p.

Rush, F.E., and Huxel, C.J., Jr., 1966, Ground-water appraisal 

of the Eldorado-Piute Valley area, Nevada and California: 

Nevada Department of Conservation and Natural Resources, 

Water Resources - Reconnaissance Report 36, 30 p.

Rush, F.E., and Kazmi, S.A.T., 1965, Water resources appraisal of Spring Valley, White Pine and Lincoln Counties, Nevada: Nevada Department of Conservation and 

Natural Resources, Water Resources - Reconnaissance 

Report 33, 36 p.

Rush, F.E., and Schroer, C.V, 1970, Water resources of Big Smoky 

Valley, Lander, Nye, and Esmeralda Counties, Nevada: Nevada 

Division of Water Resources, Bulletin 41, 84 p.

Saltus, R.W., 1984, A description of colored gravity and terrain maps of the southwestern Cordillera: U.S. Geological Survey Open-File Report 84-95, 16 p.

Shane, D.R., and Stewart, J.H., 1976, Ore deposits as related to tectonics and magnetism, Nevada and Utah: 

American Institute of Metallurgical and Petroleum Engineers Transactions, v. 260, p. 225-232.

Stephens, J.C., 1974a, Hydrologic reconnaissance of the northern Great Salt Lake Desert and summary of hydrologic 

reconnaissance of northwestern Utah: Utah Department 

of Natural Resources Technical Publication 42, 55 p.

 1974b, Hydrologic reconnaissance of the Wah Wah Valley 

drainage basin, Millard and Beaver Counties, Utah: Utah 

Department of Natural Resources Technical Publication 

47, 53 p.

 1976, Hydrologic reconnaissance of the Pine Valley 

drainage basin, Millard, Beaver, and Iron Counties, Utah: 

Utah Department of Natural Resources Technical Publication 51, 38 p.

-1977, Hydrologic reconnaissance of the Tule Valley

drainage basin, Juab and Millard Counties, Utah: Utah 

Department of Natural Resources Technical Publication 

56, 37 p.

Stewart, J.H., 1980, Geology of Nevada A discussion to accompany the geologic map of Nevada: Nevada Bureau of 

Mines and Geology Special Publication 4, 136 p.

Stewart, J.H., and Carlson, J.E., 1978, Geologic map of Nevada: U.S. Geological Survey, scale 1:500,000.

Stewart, J.H., Moore, W.J., and Zietz, Isidore, 1977, Eastwest patterns of Cenozoic igneous rocks, aeromagnetic 

anomalies, and mineral deposits, Nevada and Utah: Geological Society of America Bulletin, v. 88, p. 67-77.

Stewart, J.H., Walker, G.W, and Kleinhampl, F.J., 1975, Oregon-Nevada lineament: Geology, v. 3, no. 5, p. 265-268.

Stillwater, R., Kraeger-Rovey, C., and Scott, P., 1992, Technical note on MODFLOW notation: Ground Water, v. 30, 

no. 4, p. 613.

Sumsion, C.T., and others, 1976, Ground-water conditions 

in Utah, spring of 1976: Utah Division of Water Resources 

Cooperative Investigations Report 15, 69 p.

Thomas, J.M., 1988, Delineation of regional ground-water 

flow systems in southern Nevada using isotopic and chemical data [abs.]: Geological Society of America, Abstracts 

with Programs, v. 20, no. 7, p. A363.

Thomas, J.M., Lyles, B.F., and Carpenter, L.A., 1991, Chemical 

and isotopic data for water from wells, springs and streams 

in carbonate-rock terrane of southern and eastern Nevada and southeastern California, 1985-1988: U.S. Geological Survey Open-File Report 89-422, 24 p.

Thomas, J.M., Mason, J.L., and Crabtree, J.D., 1986, Groundwater levels in the Great Basin region of Nevada, Utah, 

and adjacent States: U.S. Geological Survey Hydrologic 

Investigations Atlas HA-694-B, 2 sheets.

Thomas, J.M., Schaefer, D.H., and Dettinger, M.D., 1990, 

Use of geochemical data to trace ground-water flow which 

could affect oil migration in carbonate-rock aquifers of 

eastern Great Basin, Nevada and Utah [abs.], in Flanigan, 

D.M.H., Garside, L.J., and Hansen, Mike, eds., Oil fields 

and geology of the Pine Valley, Eureka County area, Nevada: Reno, Nev., Nevada Petroleum Society, Inc., 1990 

Fieldtrip Guidebook, 74 p.

Toth, J., 1962, A theory of ground-water motion in small 

drainage basins in central Alberta, Canada: Journal of 

Geophysical Research, v. 67, no. 11, p. 4375-4387.

 1963, A theoretical analysis of ground-water flow in 

small drainage basins: Journal of Geophysical Research, 

v. 68, no. 16, p. 4795-4812.

Trudeau, D.A., Hess, J.W., and Jacobsen, R.L., 1983, 

Hydrogeology of the Littlefield Springs, Arizona: Ground 

Water, v. 21, no. 3, p. 325-333.

U.S. Bureau of the Census, 1913, General report and analysis: U.S. Government Printing Office, Population 1910, 

v. 1, 1369 p.

 1921, Number and distribution of inhabitants: U.S. Government Printing Office, Population 1920, v. 1, 695 p.

 1952, Number of inhabitants: U.S. Government Printing 

Office, Census of population 1950, v. 1, 1351 p.

 1983, United States summary: U.S. Government Printing Office, 1980 Census of Population, v. 1, chap. A, pt. 

1, 284 p.

-1991a, Summary, population and housing characteristics, Nevada: U.S. Government Printing Office, 1990 Census of Population and Housing, 1990 CPH-1-30, 94 p. 

-1991b, Summary, population and housing characteristics, Utah: U.S. Government Printing Office, 1990 Census of Population and Housing, 1990 CPH-1-46, 141 p.

U.S. Weather Bureau, 1963, Normal annual precipitation, 

normal May-September precipitation, 1931-1960, State of 

Utah: Utah State Engineer map, scale 1:500,000.

 1965, Mean annual precipitation, 1930-57, State of 

Idaho: U.S. Soil Conservation Service in cooperation with 

the U.S. Weather Bureau.

Van Denburgh, A.S., and Rush, F.E., 1974, Water resources 

appraisal of Railroad and Penoyer Valleys, east-central 

Nevada: Nevada Division of Water Resources, Reconnaissance Report 60, 61 p.

van Hylckama, T.E.A., 1974, Water use by saltcedar as measured by the water budget method: U.S. Geological Survey Professional Paper 491-E, 30 p.

Waddell, K.M., Seiler, R.L., Santini, Melissa, and Solomon, 

O.K., 1987, Ground-water conditions in Salt Lake Valley, 

Utah, 1969-83, and predicted effects of increased withdrawals from wells: Utah Department of Natural Resources 

Technical Publication 87, 69 p.

Waddell, R.K., 1982, Two-dimensional steady-state model of 

ground-water flow, Nevada Test Site and vicinity, NevadaCalifornia: U.S. Geological Survey Water-Resources Investigations Report 82-4085, 72 p.

Waddell, R.K., Robison, J.H., and Blankennagel, R.K., 1984,
D102 REGIONAL AQUIFER-SYSTEM ANALYSIS GREAT BASIN, NEVADA-UTAH

Hydrology of Yucca Mountain and vicinity, Nevada-California Investigative results through mid-1983: U.S. Geological Survey Water-Resources Investigations Report 

84-4267, 72 p.

Walker, G.E., and Eakin, T.E., 1963, Geology and ground water 

of Amargosa Desert, Nevada-California: Nevada Department 

of Conservation and Natural Resources, Ground-Water 

Resources - Reconnaissance Report 14, 57 p.

Watson, Phil, Sinclair, Peter, and Waggoner, Ray, 1976, Quantitative evaluation of a method for estimating recharge 

to the desert basins of Nevada: Journal of Hydrology, v. 

31, p. 335-357.

Welch, A.H., and Thomas, J.M., 1984, Aqueous geochemistry and isotope hydrology of the White River system, eastern Nevada [abs.]: Geological Society of America, Abstracts 

with Programs, v. 16, no. 6, p. 689.

Wernicke, Brian, and Axen, G.J., 1988, Basin and Range extensional tectonics at the latitude of Las Vegas, Nevada: 

Geological Society of America Bulletin, v. 100, p. 1738-1757.

Wernicke, Brian, Guth, PL., and Axen, G.J., 1984, Tertiary 

extension in the Sevier thrust belt of southern Nevada, in 

Lintz, Joseph, Jr., ed., Western geological excursions [in conjunction with the 1984 annual meetings of Geological Society of America and affiliated societies]: University of Nevada, 

Reno, Mackay School of Mines, v. 4, p. 473-510.

Williamson, A.K., Prudic, D.E., and Swain, L.A., 1989, Groundwater flow in the Central Valley, California: U.S. Geological Survey Professional Paper 1401-D, 127 p.

Winograd, I.J., 1962, Interbasin movement of ground water 

at the Nevada Test Site, Nevada, in Short papers in geology, hydrology, and topography: U.S. Geological Survey 

Professional Paper 450-C, p. C108-C111.

 1963, A summary of the ground-water hydrology of the

area between the Las Vegas Valley and the Amargosa 

Desert, Nevada, with special reference to the effects of 

possible new withdrawals of ground water: U.S. Geological Survey Open-File Report TEI-840, 79 p.

-1971, Hydrogeology of ash-flow tuff A preliminary statement: Water Resources Research, v. 7, no. 4, p. 994-1006.

Winograd, I.J., and Eakin, T.E., 1965, Interbasin movement 

of ground water in south-central Nevada The evidence, 

in Abstracts for 1964: Geological Society of America Special Paper 82, p. 227.

Winograd, I.J., and Friedman, Irving, 1972, Deuterium as a 

tracer of regional ground-water flow, southern Great Basin, Nevada and California: Geological Society of America 

Bulletin, v. 83, no. 12, p. 3691-3708.

Winograd, I.J., and Pearson, F.J., Jr., 1976, Carbon 14 

anomaly in a regional carbonate aquifer Possible evidence 

for megascale channeling, south-central Great Basin: Water 

Resources Research, v. 12, no. 6, p. 1125-1143.

Winograd, I.J., and Szabo, B.J., 1986, Water-table decline 

in the south-central Great Basin during the Quaternary 

period Implications for toxic waste disposal: U.S. Geological Survey Open-File Report 85-697, 18 p.

Winograd, I.J., and Thordarson, William, 1968, Structural control 

of ground-water movement in miogeosynclinal rocks of southcentral Nevada, in Eckel, E.B., ed., Nevada Test Site: Geological Society of America Memoir 110, p. 35-48.

 1975, Hydrogeologic and hydrochemical framework, 

south-central Great Basin, Nevada-California, with special reference to the Nevada Test Site: U.S. Geological 

Survey Professional Paper 712-C, 126 p.

Zones, C.P., 1961, Ground-water potentialities in the Crescent Valley, Eureka and Lander Counties, Nevada: U.S. 

Geological Survey Water-Supply Paper 1581, 50 p.

* U.S. GOVERNMENT PRINTING OFFICE: 1995-686-511


SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS

Periodicals

Earthquakes & Volcanoes (issued bimonthly). 

Preliminary Determination of Epicenters (issued monthly).

Technical Books and Reports

Professional Papers are mainly comprehensive scientific reports 

of wide and lasting interest and importance to professional scientists 

and engineers. Included are reports on the results of resource studies 

and of topographic, hydrologic, and geologic investigations. They also 

include collections of related papers addressing different aspects of a 

single scientific topic.

Bulletins contain significant data and interpretations that are of lasting scientific interest but are generally more limited in scope or geographic coverage than Professional Papers. They include the results of 

resource studies and of geologic and topographic investigations, as well 

as collections of short papers related to a specific topic.

Water-Supply Papers are comprehensive reports that present significant interpretive results of hydrologic investigations of wide interest 

to professional geologists, hydrologists, and engineers. The series covers 

investigations in all phases of hydrology, including hydrogeology, availability of water, quality of water, and use of water.

Circulars present administrative information or important scientific information of wide popular interest in a format designed for distribution at no cost to the public. Information is usually of short-term 

interest.

Water-Resource Investigations Reports are papers of an 

interpretive nature made available to the public outside the formal 

USGS publications series. Copies are reproduced on request unlike 

formal USGS publications, and they are also available for public 

inspection at depositories indicated in USGS catalogs.

Open-File Reports include unpublished manuscript reports, maps, 

and other* material that are made available for public consultation at 

depositories. They are a nonpermanent form of publication that may 

be cited in other publications as sources of information.

Maps

Geologic Quadrangle Maps are multicolor geologic maps on topographic bases in 7 %- or 15-minute quadrangle formats (scales mainly 

1:24,000 pr 1:62,500) showing bedrock, surficial, or engineering geology. Maps generally include brief texts; some maps include structure 

and columnar sections only.

Geophysical Investigations Maps are on topographic or planimetric bases at various scales; they show results of surveys using 

geophysical techniques, such as gravity, magnetic, seismic, or radioactivity, which reflect subsurface structures that are of economic or geologic significance. Many maps include correlations with the geology.

Miscellaneous Investigations Series Maps are on planimetric or 

topographic bases of regular and irregular areas at various scales; they 

present a wide variety of format and subject matter. The series also 

includes 7 %-minute quadrangle photogeologic maps on planimetric 

bases that show geology as interpreted from aerial photographs. Series 

also includes maps of Mars and the Moon.

Coal Investigations Maps are geologic maps on topographic or 

planimetric bases at various scales showing bedrock or surficial geology, stratigraphy, and structural relations in certain coal-resource 

areas.

Oil and Gas Investigations Charts show stratigraphic information for certain oil and gas fields and other areas having petroleum 

potential.

Miscellaneous Field Studies Maps are multicolor or black-andwhite maps on topographic or planimetric bases on quadrangle or irregular areas at various scales. Pre-1971 maps show bedrock geology 

in relation to specific mining or mineral-deposit problems; post-1971 

maps are primarily black-and-white maps on various subjects, such as 

environmental studies or wilderness mineral investigations.

Hydrologic Investigations Atlases are multicolor or black-andwhite maps on topographic or planimetric bases presenting a wide range 

of geohydrologic data of both regular and irregular areas; principal 

scale is 1:24,000, and regional studies are at 1:250,000 scale or smaller.

Catalogs

Permanent catalogs, as well as some others, giving comprehensive 

listings of U.S. Geological Survey publications are available under the 

conditions indicated below from the U.S. Geological Survey, Books 

and Open-File Reports Sales, Federal Center, Box 25286, Denver, CO 

80225. (See latest Price and Availability List.)

"Publications of the Geological Survey, 1879-1961" may be purchased by mail and over the counter in paperback book form and as a 

set of microfiche.

"Publications of the Geological Survey, 1962-1970" may be purchased by mail and over the counter in paperback book form and as a 

set of microfiche.

"Publications of the Geological Survey, 1971-1981" may be purchased by mail and over the counter in paperback book form (two 

volumes, publications listing and index) and as a set of microfiche.

Supplements for 1982, 1983, 1984, 1985, 1986, and for subsequent years since the last permanent catalog may be purchased by mail 

and over the counter in paperback book form.

State catalogs, "List of U.S. Geological Survey Geologic and 

Water-Supply Reports and Maps For (State)," may be purchased by 

mail and over the counter in paperback booklet form only.

'Trice and Availability List of U.S. Geological Survey Publications," issued annually, is available free of charge in paperback booklet form only.

Selected copies of a monthly catalog "New Publications of the 

U.S. Geological Survey" are available free of charge by mail or may 

be obtained over the counter in paperback booklet form only. Those 

wishing a free subscription to the monthly catalog "New Publications 

of the U.S. Geological Survey" should write to the U.S. Geological 

Survey, 582 National Center, Reston, VA 22092.

Note. Prices of Government publications listed in older catalogs, 

announcements, and publications may be incorrect. Therefore, the prices 

charged may differ from the prices in catalogs, announcements, and 

publications.