U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2007–5062

Geologic Characterization of Young Alluvial Basin-Fill 

Deposits from Drill-Hole Data in Yucca Flat, Nye County, 

Nevada

This report was produced in cooperation with the Department of Energy through Interagency 

Agreement DE-AI�2-01NV13944.
Geologic Characterization of Young Alluvial 

Basin-Fill Deposits from Drill-Hole Data in 

Yucca Flat, Nye County, Nevada

By Donald S. Sweetkind and Ronald M. Drake II

Scientific Investigations Report 2007–5062

U.S. Department of the Interior

U.S. Geological Survey

This report was produced in cooperation with the Department of Energy 

through Interagency Agreement DE-AI52-01NV13944.
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2007

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Suggested citation:

Sweetkind, D.S., and Drake, R.M. II, 2007, Geologic characterization of young alluvial basin-fill deposits from 

drill-hole data in Yucca Flat, Nye County, Nevada: U.S. Geological Survey Scientific Investigations Report 2007–5062, 

17 p.

This report supersedes the following Open-File Report: Sweetkind, Donald, and Drake II, Ronald M., 2007, Geologic 

characterization of young alluvial basin-fill deposits from drill hole data in Yucca Flat, Nye County, Nevada: 

U.S. Geological Survey Open-File Report 2006-1390.
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................1

Description of the Study Area .....................................................................................................................3

Physiographic Setting..........................................................................................................................3

Geologic Setting....................................................................................................................................3

Interpretation of Drill-Hole Data..................................................................................................................5

3D Lithologic Modeling .................................................................................................................................9

Summary........................................................................................................................................................12

Acknowledgments.......................................................................................................................................12

References Cited..........................................................................................................................................16

Figures

1. Index map of Yucca Flat and the Nevada Test Site, Nevada.................................................2

2. Geologic map of Yucca Flat showing drill-hole locations, cross-section lines and

 boundary of 3D lithology model.................................................................................................4

3. West-east cross sections showing interpreted drill-hole lithologic data...........................7

4. North-south cross section showing interpreted drill-hole lithologic data..........................8

5. Three-dimensional portrayals of drill-hole lithologic data. .................................................10

6. Perspective view of vertical sections cut through 3D lithology model of Yucca Flat. ....11

7. Perspective views of 3D lithologic model showing distribution of lithologic classes. ...13

8. Perspective view of multiple vertical sections cut through 3D lithology mode

of Yucca Flat. ...............................................................................................................................15

Table

1. Generalized lithologic classes based on drill-hole descriptions.........................................5
iv

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

inch 25.4 millimeter

inch 2.54 centimeter

mile 1.609 kilometer

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29).

Horizontal coordinate information is referenced to the Nevada State Plane Coordinate System, 

central zone, North American Datum of 1927 (NAD27), in feet.

Elevation, as used in this report, refers to distance of a point on the Earth’s surface above the 

vertical datum.
Abstract 

Yucca Flat is a topographic and structural basin in the 

northeastern part of the Nevada Test Site in Nye County, 

Nevada, that has been the site of numerous underground nuclear 

tests; many of these tests occurred within the young alluvial 

basin-fill deposits. The migration of radionuclides to the 

Paleozoic carbonate aquifer involves passage through this thick, 

heterogeneous section of Tertiary and Quaternary rock. An 

understanding of the lateral and vertical changes in the material 

properties of young alluvial basin-fill deposits will aid in the 

further development of the hydrogeologic framework and the 

delineation of hydrostratigraphic units and hydraulic properties 

required for simulating ground-water flow in the Yucca Flat 

area. This report by the U.S. Geological Survey, in cooperation 

with the U.S. Department of Energy, presents data and interpretation regarding the three-dimensional variability of the shallow 

alluvial aquifers in areas of testing at Yucca Flat, data that are 

potentially useful in the understanding of the subsurface flow 

system. This report includes a summary and interpretation of 

alluvial basin-fill stratigraphy in the Yucca Flat area based on 

drill-hole data from 285 selected drill holes. Spatial variations 

in lithology and grain size of the Neogene basin-fill sediments 

can be established when data from numerous drill holes are 

considered together. Lithologic variations are related to different 

depositional environments within the basin such as alluvial fan, 

channel, basin axis, and playa deposits.

Introduction

Yucca Flat is a topographic and structural basin in the 

northeastern part of the Nevada Test Site (NTS) in Nye 

County, Nev. (fig. 1). Between the years 1951 and 1992, 659 

underground nuclear tests took place in Yucca Flat; most 

were conducted in large vertical excavations that penetrated 

alluvium and the underlying Cenozoic volcanic rocks (U.S. 

Department of Energy, 2000).

Radioactive and other potential chemical contaminants 

at the NTS are the subject of a long-term program of investigation and remediation by the U.S. Department of Energy 

(DOE), National Nuclear Security Administration, Nevada 

Site Office, under its Environmental Restoration Program. 

As part of the program, the DOE seeks to assess the extent of 

contamination and to evaluate the potential risks to humans 

and the environment from byproducts of weapons testing. To 

accomplish this objective, the DOE Environmental Restoration 

Program is constructing and calibrating a ground-water flow 

model to predict hydrologic flow in Yucca Flat as part of an 

effort to quantify the subsurface hydrology of the Nevada Test 

Site. A necessary part of calibrating and evaluating a model of 

the flow system is to compile and analyze data related to heterogeneity of the component hydrogeologic units. This report 

by the U.S. Geological Survey (USGS), in cooperation with 

the DOE, presents data and interpretation regarding the threedimensional (3D) variability of the shallow alluvial aquifers in 

areas of testing at Yucca Flat, data that are potentially useful in 

the understanding of the subsurface flow system.

Purpose and Scope

The purpose of this study is to develop an understanding of lateral and vertical lithologic variability of Neogene 

sediments that make up the shallow basin fill of Yucca Flat. 

Understanding the configuration and character of the basin-fill 

sedimentary units is critical to delineating hydraulic properties 

and reducing uncertainty in three-dimensional simulations of 

ground-water flow in the Yucca Flat area. Recent stratigraphic 

studies of Cenozoic basins to the south of the NTS, including the Amargosa Desert Basin (Sweetkind and others, 2001; 

Taylor and Sweetkind, 2005) and the Pahrump Valley (Sweetkind and others, 2003) have shown that the three-dimensional 

stratigraphic variability of shallow alluvial sediments can be 

adequately characterized through interpretation of drill-hole 

lithologic data. We hoped that the use of similar techniques 

would yield similar results in the Yucca Flat basin.

Geologic Characterization of Young Alluvial Basin-Fill 

Deposits from Drill-Hole Data in Yucca Flat, Nye County, 

Nevada

By Donald S. Sweetkind and Ronald M. Drake II
116°30'

116°30'

116°15'

116°15'

116°0'

116°0'

115°45'

115°45'

36°45' 36°45'

37°0' 37°0'

37°15' 37°15'

Nevada

California

Area of

figure

Las Vegas

EXPLANATION

Highways

County boundary

Nevada Test Site boundary

Base from U.S. Geological Survey digital 

data, 1:250,000; Universal Transverse 

Mercator projection, Zone 11.

Shaded-relief base from 1:250,000-scale 

Digital Elevation Model; sun illumination 

from northwest at 30o above horizon

Yucca

Flat Halfpint Range

Belted

Range

Yucca Mountain

Nevada

 Test

 Site Frenchman

Flat

Lincoln County

Clark County

Nye County

Lincoln County

Eleana Range

Rainier

Mesa

Figure 1. Index map of Yucca Flat and the Nevada Test Site, Nevada.

0 5 10 15 20 Kilometers

0 5 10 15 20 Miles

Figure 1. Index map of Yucca Flat and the Nevada Test Site, Nevada.

 Characterization of Young Alluvial Basin-Fill Deposits, Yucca Flat, Nevada
This report presents a summary and interpretation of 

alluvial basin-fill stratigraphy in the Yucca Flat area based on 

lithologic data from 285 drill holes that were selected from 

more than 890 available drill holes in Yucca Flat. The drill holes 

that were used in this study were selected on the basis of location (the need to produce a suitable spatial distribution of data) 

and the presence of high-quality lithologic descriptions that 

could be interpreted in terms of depositional environment and 

facies information. Drill-hole lithologic data from the Neogene 

basin-fill sediments are evaluated in terms of lateral and vertical 

lithologic variations. These data are developed as geologic cross 

sections and 3D subsurface interpretations that show lateral and 

vertical changes in young alluvial basin-fill deposits, including 

spatial variations in lithology and grain size.

Description of the Study Area

Physiographic Setting

Yucca Flat is a topographically closed drainage basin 

that occupies much of the eastern part of the Nevada Test Site 

(fig. 1). The valley floor has no perennial surface water; Yucca 

Flat acts as a catchment for surface-water runoff and is a local 

depositional center for sediment. The low-relief topographic 

basin has a playa (seasonally dry lake) at the south end (fig. 2), 

and the basin is surrounded by low ranges of Tertiary volcanic 

rocks and underlying Paleozoic and Late Proterozoic sedimentary rocks (fig. 2) (Slate and others, 2000). In general, 

the valley floor slopes upward toward the surrounding ranges 

on a series of coalescing alluvial fans that ring the margins 

of the basin. Large, active alluvial channels extend into the 

basin from topographic highlands of Rainier Mesa, the Belted 

Range, the Eleana Range, and the Halfpint Range (figs. 1 and 

2). These channels merge and ultimately drain to the playa at 

the south end of the basin.

Geologic Setting

The Cenozoic rocks in Yucca Flat consist of a thick 

alluvial section underlain by Miocene volcanic rocks and 

rare, thin, prevolcanic sedimentary rocks, all of which lie 

unconformably on variably deformed pre-Cenozoic rocks. 

The Miocene volcanic rocks that form the lower part of the 

basin fill were originally erupted from source areas in the 

southwestern Nevada volcanic field (Byers and others, 1976; 

Sawyer and others, 1994). The volcanic rocks include variably welded ash-flow tuff, ash-fall tuff, and reworked tuff; 

the thickness and extent of these rocks vary greatly within 

the basin. The lower part of the sequence of volcanic rocks, 

including pre-Belted Range Group rocks, the Belted Range 

and Crater Flat Groups, and the Wahmonie Formation (stratigraphic designations from Sawyer and others, 1994), consists 

of bedded and reworked, nonwelded, commonly zeolitized 

tuffs. The upper part of the sequence of volcanic rocks, including rocks from the Paintbrush and Timber Mountain Groups, 

consists mainly of welded ash-flow tuff.

The largely postvolcanic sedimentary basin fill that is the 

subject of this report consists of a mixture of loosely consolidated, coarse-grained, alluvial and colluvial deposits that 

were derived from the surrounding Cenozoic silicic volcanic 

and Paleozoic siliciclastic and carbonate sedimentary rocks, 

fine-grained basin axis and playa deposits, and localized eolian 

sand and rare basalt flows. Digital geologic map compilations 

of the Nevada Test Site at 1:120,000 scale (Slate and others, 

2000) and 1:250,000 scale (Workman and others, 2002) have 

defined the map distribution and provided detailed descriptions 

for the surficial geologic units. As described by Workman and 

others (2002), coarse-grained surficial units consist of Holocene 

to Pliocene alluvium, colluvium, and minor eolian and debrisflow sediments associated with alluvial geomorphic surfaces 

(Swan and others, 2001; Potter and others, 2002). In general, 

fluvial deposits are predominantly sandy gravel, whereas 

alluvial fans typically show a gradational decrease in grain size 

from proximal to distal fan with distance from the mountain 

front (Workman and others, 2002). Local eolian accumulations 

consist of sand sheets or dune fields. Sediments generally are 

not cemented but tend to be more indurated with increasing 

depth. The fine-grained alluvial units consist of Holocene playa 

and (or) saltpan deposits that are commonly underlain by older 

playa or lacustrine sequences of middle to early Holocene and 

Pleistocene age (Workman and others, 2002). These rocks typically have coarse material and mixtures of moderately stratified 

to well-stratified silt, clay, and fine sand.

Structurally, the Yucca Flat basin is in general terms a 

simple half-graben dominated by north-striking, east-dipping, 

down-to-the-east normal faults of Cenozoic age such as the 

Yucca fault and the Carpetbag fault (Dockery, 1984; Carr, 

1984) (fig. 2). Gravity models of the Yucca Flat basin define 

a Tertiary-Quaternary basin as much as 8,200 ft deep to the 

east of the Carpetbag fault, a midbasin high to the west of the 

Carpetbag fault, and a shallower basin to the west of the high 

(Phelps and others, 1999; Ferguson and others, 1988). The 

Cenozoic volcanic units have been offset thousands of feet by 

the Carpetbag-Yucca fault system and related smaller faults 

(Phelps and McKee, 1999). The gravity data indicate that the 

Yucca Flat basin is deepest at its south end where it abuts the 

dividing ridge with Frenchman Flat to the south (Dockery, 

1984), although few drill holes penetrate the entire thickness 

of the Tertiary section in this area. Yucca Flat is enclosed at its 

north end, where anticlinally folded Late Proterozoic rocks in 

the Halfpint Range converge with Paleozoic siliciclastic rocks 

near the south end of the Belted Range (Hinrichs, 1968). 

Description of the Study Area 
6

1 3

9 2

4 7

12

17

8

16

11

15

10

14

29

25

Young alluvial depositsUndivided alluvial depositsIntermediate alluvial depositsPlaya depositsTertiary volcanic rocksGranitic rocksPennsylvanian carbonate rocksMississippian and Devonian rocksCambrian to Devonian carbonate rock

Geologic map colors

EXPLANATION

(modified from Slate and others, 2000)

Fault mapped in bedrock O

3L

Fault, concealed

CF, Carpetbag faultYF, Yucca fault N

a

Drill h

A A’

3

Nye County

Lincoln 

Clark C

Nevada Test Site

Area s

in fig

NVCA

116°30' 116°0' 

36°30'

37°0'

37°30'

Figure 2. Geologic map of Yucca Flat showing drill-hole locations, cross-section lines, and boundary of 3D lithology model. 

116° 10' 116° 

37° 37° 10' 

A

A’

B

B’

C

C’

D

D’

CF

CF

YF

YF

0 2 4 6 8 10 Miles

0 2 4 6 8 10 Kilometers

Figure 2. Geologic map of Yucca Flat showing drill-hole locations, cross-section lines, and boundary of 3D lithology model.
Interpretation of Drill-Hole Data

 Subsurface lithologic information was extracted from 

data tabulations from the numerous drill holes in Yucca Flat. 

For most of the holes, no cuttings are preserved for the alluvial 

fill, and the lithologic descriptions represent the primary data 

source. Covington and Berger (1997) produced an extensive 

compilation of lithologic descriptions from depth-specific 

sample intervals of core and cuttings samples collected from 

more than 890 drill holes located in Yucca Flat. These data, 

and additional data from more recently drilled holes, have 

been compiled in recent years in digital form by USGS scientists (David Wood, written commun., 2003) for incorporation in the Ground-Water Site Inventory (GWSI) subsystem 

of the USGS National Water Information System (NWIS). 

The digital compilation of the drill-hole data is available at 

http://nevada.usgs.gov/mercury/core.html. For the purposes 

of this report, the many hundreds of drill-hole lithologic logs 

from Yucca Flat were culled to a total of 285 holes. The holes 

from Yucca Flat that were used represented those that contained the greatest amount of detail in the description of each 

interval, had a large number of downhole intervals described 

(as opposed to a single long interval of “sand and gravel” or 

“alluvium”), were representative of downhole lithology of 

nearby holes, and represented a distribution of holes that were 

not clustered but were approximately equally distributed over 

the Yucca Flat area (fig. 2). The thickness of alluvium penetrated by the selected drill holes ranged from less than 

100 ft to more than 3,000 ft (fig. 2). The thickness of alluvial 

fill for the 285 selected holes varies from about 1,000 ft on the 

alluvial fans near the basin margins to as much as 2,300 ft for 

holes drilled along the axis of the basin (fig. 2). The 285 holes 

selected contained 1,430 lithologic intervals, or an average of 

just over 5 described lithologic intervals per hole.

The original driller’s descriptions were simplified to 

an internally consistent set of 12 general lithologic classes 

(table 1); lithologic classes were similar to, but fewer in 

number than, those generated from recent stratigraphic studies 

of Cenozoic basins to the south of the NTS (Sweetkind and 

others, 2001; Taylor and Sweetkind, 2005). Lithologic descriptions show that subsurface lithology within the alluvial basin 

fill is dominated by generally coarse grained sediments; of the 

1,430 total described lithologic intervals, 1,328 intervals, or 

93 percent, were some combination of sand and gravel. 

However, the lithologic descriptions were sufficiently detailed 

to permit distinguishing cobble and boulder beds from three 

lithologic classes that contain differing proportions of gravel 

and sand (table 1). The relative proportions of sand and gravel 

in these lithologic classes differ from those in standard usage 

(Folk, 1954), but the proportions used gave a satisfactory 

distinction between intervals that were dominated by gravel, 

those where sand and gravel were subequal, and those where 

Lithology class Drill-hole 

intervals Rationale for classification

Gravel 63 Used for cobble beds, boulder beds, and where gravel was reported as having no fine-grained 

matrix.

Sandy gravel 229 Used for sand and gravel mixtures where gravel, clasts, or cobbles were 70 percent or more of 

the total.

Gravelly sand 341 Used for sand and gravel mixtures where gravel, clasts, or cobbles were subequal in abundance 

to the sand component; used where sand was 30 to 70 percent of the total.

Sand and minor 

gravel

360 Used for sand and gravel mixtures where the sand component was much more abundant than 

gravel, clasts, or cobbles; typically sand was 70 to 80 percent of the total, often greater than 

90 percent of the total.

Sand, clay, and 

gravel

42 Used for sand and gravel mixtures where silt or clay was identified as an additional important 

component. Typically these intervals are dominated by the sand-silt component with relatively minor gravels.

Coarse sand 263 Used for sand sizes greater than 0.5 mm, typically greater than 1 mm, often with scattered pebbles up to 1 cm.

Fine sand 44 Used for sand sizes less than 0.5 mm, rare pebbles.

Clay and sand 12 Used for intervals where sands are interbedded with clay layers. Typically explicitly interpreted 

in the description as alluvial material interbedded with playa deposits.

Clay 2 Used for intervals described as almost completely clay. Typically explicitly interpreted in the 

description as playa deposit.

Clay and limestone 4 Used for intervals where clays are interbedded with thin-bedded limestone. Typically explicitly 

interpreted in the description as playa deposits.

Basalt 3 Used for intervals where basalt was specifically identified. 

Nonwelded tuff 9 Used for intervals where nonwelded tuff was specifically identified. 

No data 39 Intervals with no useful lithologic information, such as “alluvium.”

Table 1. Generalized lithologic classes based on drill-hole descriptions.

[mm, millimeter; cm, centimeter]

Interpretation of Drill-Hole Data 
sand was more abundant than gravel (table 1). Of lesser total 

abundance, but important locally, are intervals of nearly 

uniform sand, in places accompanied by a very small amount 

of gravel or individual pebbles. Lithologic descriptions of the 

sand often were sufficiently detailed to distinguish coarse and 

“fine sand” (table 1). Intervals described as containing silt 

were assigned to the lithologic class “fine sand” owing to the 

limited number of reported instances of silt and to the general 

difficulty of identifying truly silt-sized particles without rigorous grain-size analysis.

The uppermost described lithologic intervals from the 

drill holes were compared with the surficial geologic units 

in Yucca Flat (Slate and others, 2000) using a Geographic 

Information System (GIS) in hopes of being able to correlate 

mapped surficial units with subsurface lithologic descriptions. 

No definitive correlation between mapped units and drill-hole 

lithologic descriptions was apparent, in large part because 

surficial units defined by Slate and others (2000) are mapped 

on the basis of deposit age and degree of induration rather than 

strictly by lithologic type or grain size.

The level of subsurface detail present in the drill-hole 

data and the interpreted lithologic classes are portrayed in 

four cross sections that incorporate drill-hole data along three 

generally west-east sections (fig. 3) and one generally northsouth section (fig. 4). The drill-hole data on the cross sections 

are portrayed using general lithologic classes that were derived 

from the original descriptions (table 1). Drill-hole data within 

3,281 ft on either side of the section line are projected onto the 

line of section, such that each cross section integrates drillhole data within a 6,563-ft-wide swath. Portrayal of numerous 

drill holes on a single section is a relatively common way to 

look for overall patterns in subsurface lithologic data (Thorleifson and Pyne, 2004).

Cross section A–A' (fig. 3) at the far north end of Yucca 

Flat portrays a general progression from coarse, gravelly alluvium high on the alluvial fan on the west side of the basin to 

finer grained sediments at the basin axis. The coarse-grained 

alluvium is typically sandy gravel with pebble to cobble-sized 

clasts. Many of the holes drilled on the fan are between 750 

and 1,000 ft deep, yet the alluvial section is described in only 

one or two intervals. The progressive fining toward the basin 

center is represented by an increase in the proportion of sand 

and clay and represents the effects of progressive mechanical abrasion, diminishing depositional energy, and perhaps a 

greater contribution of fine-grained detritus weathering from 

volcanic rocks present to the north and east of Yucca Flat 

(fig. 2). The far eastern end of the cross section portrays an 

increased quantity of gravel as the fan on the east side of the 

basin is approached.

Cross section B–B' (fig. 3) portrays lithologic data from (fig. 3) portrays lithologic data from 

drill holes along a southwest-northeast line near the center of 

the Yucca Flat basin. The drill holes on the east end of the section are shallow and dominated by gravelly sand from a very 

large alluvial fan that dominates this portion of the east side 

of the basin (fig. 2). The lithology reported in holes drilled on 

this fan varies from hole to hole and may represent lithologic 

variability within the fan, such as individual channels. Drill 

holes near the center of the section are at the toe of the fan and 

are dominated by coarse sand or sand with minor gravel, again 

showing a progressive fining trend toward the basin axis. Drill 

holes on the west side of the cross section are dominated by 

relatively coarse grained sediment; these sediments probably 

have their source in alluvial fans on the west side of the basin 

but may also show the influence of a large alluvial channel 

that originates in the northwestern part of Yucca Flat.

Cross section C–C' (fig. 3) portrays lithologic data from (fig. 3) portrays lithologic data from 

drill holes along a west-east line in the southern part of the 

Yucca Flat basin, north of the fine-grained sediments of the 

playa. The center part of section C–C' is characterized by drill is characterized by drill 

holes that have a consistent lithology dominated by coarse 

and fine alluvial sand and sand with minor associated gravels. 

These fine, relatively uniform sands in the south-central portion of the valley must be the result of continued diminishing 

depositional energy within the alluvial system and also the 

result of particularly stable conditions of deposition during 

Late Cenozoic time. On the west side of the section is a drill 

hole that contains one of the rare basalt flows that lie within 

the young alluvial fill.

Cross section D–D' (fig. 4) portrays lithologic data from (fig. 4) portrays lithologic data from 

drill holes along a generally north-south profile along the axis 

of the basin. The northern half of the profile includes drill 

holes that lie to the west of the Yucca fault; the southern half 

of the profile includes drill holes that lie to the east of the 

Yucca fault (fig. 4). Many of the holes possess only one or two 

described lithologic intervals; yet, when the data from multiple 

drill holes are taken as a whole, broad lithologic trends may be 

confidently established. The section displays a broad southward fining from gravel-dominated drill holes in the northern 

one-third of the section to generally more sand-dominated 

intervals in the central and southern parts of the section. The 

north-to-south variation in lithology is complicated by the 

section’s crossing numerous individual alluvial fans and channels. The lithologically homogeneous area of sand portrayed 

in the center of section C–C' is evident on this section as well, is evident on this section as well, 

where a number of holes are dominated by coarse and fine 

sand and sand with minor gravel. The far southern end of the 

section includes intervals of thinly bedded, fine-grained clay 

and limestone that represent the interfingering of the alluvial 

basin fill with the northernmost extent of playa deposits at the 

southern end of the basin.

Figure 5 portrays three views of the interpreted lithologic 

data from the selected drill holes located in 3D space. In these 

views, the location and drilled depth of drill holes are represented as vertical cylinders; the cylinder diameter and color are 

varied for separate lithologic classes. In these figures, only the 

upper portions of the holes are shown in order to emphasize 

the young alluvium; deeper portions of holes that intercepted 

Cenozoic volcanic rocks and Paleozoic rocks are not shown. 

Drill holes are hung at their surface elevations; land surface is 

transparent so that the drill holes appear to hang in space. The 

shortened perspective of the east and south views makes holes 

collared at higher elevations on the west and north side of the 

 Characterization of Young Alluvial Basin-Fill Deposits, Yucca Flat, Nevada
W E

ELEVATION, IN FEET ELEVATION, IN FEET ELEVATION, IN FEET

A A'

3,000 4,000

Vertical exaggeration x5

Vertical exaggeration x5

W B E

B'

3,000 4,000

Vertical exaggeration x5

W C C' E 3,000 4,000

Tiepoint with D–D‘

Tiepoint with D–D‘

Tiepoint with D–D’

Yucca fault

Yucca fault

Carpetbag fault

Carpetbag fault

Yucca fault

Location of cross sections shown in figure 2.

Gravel

Sandy gravel

Gravelly sand

Sand and minor gravel

Sand, clay, and gravel

Coarse sand

Fine sand

Clay and sand

Clay

Clay and limestone

Basalt

Nonwelded tuff

No data

EXPLANATION 

Figure 3. West-east cross sections showing interpreted drill-hole lithologic data. Figure 3. West-east cross sections showing interpreted drill-hole lithologic data.

Interpretation of Drill-Hole Data 
Vertical exaggeration x10

N 

D 

3,000 4,000 2,000

Location of cross section 

ELEVATION, IN FEET

GravelSandy gravelGravelly sandSand and minor gravelSand, clay, and gravelCoarse sandFine sand

EXPLANATION 

Clay and sandClayClay and limestoneBasaltNonwelded tuffNo data

Tiepoint with A–A’

Yucca fault

Tiepoint with B–B’

Tiepoint w

Figure 4. North-south cross section (location, see fig. 2) showing interpreted drill-hole lithologic data.
basin appear anomalously high relative to the majority of drill 

holes. These views emphasize the gravel-dominated sections 

at the northwestern end of the basin and the broad, southwardfining trend to generally more sand-dominated intervals in the 

central and southern parts of the basin. Intervals dominated by 

clay, clay and sand, or clay and limestone are present only in 

the southernmost drill holes in the study region (fig. 5).

3D Lithologic Modeling

Interpreted drill-hole lithologic data were numerically 

interpolated between drill holes by using a cell-based interpolation called horizontal lithoblending within the RockWorks 

2004 software package (Rockware©, 2004). Grid nodes are 

sequentially assigned a value that corresponds to the interpreted lithologic classes based on the proximity to each drill 

hole. The interpolation routine looks outward horizontally 

from each drill hole in search circles of ever-increasing 

diameter. The algorithm assigns the lithology values in each 

vertical interval of the drill hole to cells immediately surrounding each drill hole. Then the interpolation moves out by a 

cell and assigns the next “circle” of cells a lithology value for 

each vertical interval of the drill-hole data. The interpolation 

continues in this manner until the program finds a cell that is 

already assigned a lithology (presumably interpolating toward 

it from an adjacent drill hole), in which case it skips the node 

assignment step. Near the base of the model, all cell values are 

controlled by the few deep drill holes; this modeling artifact is 

removed from the final models by intersecting the solid volume with an arbitrary gridded surface. Cell dimensions for the 

3D interpolation were 3,281 ft in the horizontal dimensions 

and 33 ft in the vertical dimension. We trimmed the resulting 

model at the top by a grid representing land-surface elevations 

and at the base by a grid that represents the smoothed base of 

alluvium present in the selected drill holes. Because there was 

no information regarding stratal dip in the alluvial section, 

strata were assumed to be horizontal in this 3D interpolation. 

The assumption of horizontality is likely more valid for the 

younger, upper parts of the basin fill than for the deeper parts 

of the alluvial section.

The strength of this method is that the interpolated data 

in the resulting 3D grid have the appearance of stratigraphic 

units, with aspect ratios that emphasize the horizontal dimension over the vertical. Also, the method preserves the local 

variability of the lithology in each drill hole with no smoothing or averaging. Thus, where data are abundant, local 

lithologic variability is incorporated. One limitation of this 

numerical interpolation is the sensitivity to the distribution 

of the data, where values from an isolated drill hole tend to 

extrapolate outward to fill an inordinate amount of the model 

area. The effect is particularly noticeable where a small number of deep drill holes are interspersed with shallower holes; 

data from the deepest drill holes tend to overextrapolate over 

the entire model area. We mitigated this effect by trimming the 

base of the model, using a grid that represents the smoothed 

base of alluvium present in the selected drill holes. Faults were 

not explicitly included in the creation of these solid models 

owing to the limitations of the software package used. However, the interpolation methods used here produce lithologic 

variations that approximate fault truncations of lithologic units 

where data density is high.

Six vertical cross sections (fig. 6) cut through the 3D 

model display the results of the numerical interpolation as a 

fence diagram that highlights lithologic variations within the 

basin fill. In the fence diagram, the cross sections are colored according to the interpreted geologic units (fig. 6); land 

surface is transparent so that the sections appear to hang in 

space. The upper surfaces of the six sections are clipped at the 

topographic surface by using a digital elevation model; the 

base of the model is clipped using a generalized surface that 

encloses the drilled intervals of alluvial fill for the drill holes 

used in this study.

The alluvial section on the margins of the basin is represented by relatively thin sections that are dominated by sandy 

gravel, especially on the west and north, and gravelly sand on 

the east side of the basin. Deposition of these coarser grained 

rocks is largely on a series of coalescing alluvial fans that form 

poorly sorted to moderately sorted deposits in which particle 

size may range from clay to boulders. Based on surficial mapping (Slate and others, 2000), the lithologic units within these 

fan complexes tend to be discontinuous and interfingering. 

The limited number of described lithologic intervals in drill 

holes that penetrate these fans reveals only hints of the actual 

lithologic variability. The alluvial fans tend to have a gradational decrease in grain size from proximal to distal fan where 

they interfinger with sandier units toward the basin axis. The 

section at 840,000 ft (fig. 6) displays this trend, with sandy 

gravels on the east and west sides of the basin grading into 

gravelly sand along the basin axis. There is no clear overall 

change in grain-size distribution with depth, although there 

is typically a change in clast lithology. Drill-hole lithologic 

logs typically report a predominance of Paleozoic rock clasts 

in the upper parts of the alluvial sections, whereas volcanic 

rock clasts predominate lower in the alluvial section. Changes 

in clast lithology are probably a reflection of changes in the 

available source-rock types as they are exposed to erosion in 

the surrounding uplands over time.

Several large, active alluvial channels are present around 

the margin of the basin, the most prominent of which is a surface channel as much as a mile wide that drains the highlands 

of Rainier Mesa in NTS area 12 in the northwest corner of 

the Yucca Flat basin (figs. 1, 2). A similar pattern of graveldominated sediment occurs in the subsurface in the northwestern part of the model (fig. 6). A well-defined gravel interval 

extends southeast and then south and brings gravel and sandy 

gravel into the axis of the basin as far south as 860,000 ft 

(fig. 6). Drill-hole data from this subsurface gravel interval 

indicate coarse, boulder gravels with a mixture of Paleozoic 

and volcanic rock clasts. Correspondence of the subsurface 

3D Lithologic Modeling 
820,000

4,000 2,000

840,000 8

Northing (Nevada S

ELEVATION, IN FEET

660,000

4,000 2,000

670,00

Easting (Ne

ELEVATION, IN FEET

820,000

840,000

860,000

880,000

650,000

660,000

670,000

680,000

690,000

700,000

4,000

2,000

Easting (Nevada State Plane, feet) Northing (Nevada State Plane, feet)

ELEVATION, IN FEET

GravelSandy gravelGravelly sandSand and minor gravelSand, clay, and gravelCoarse sand

EXPLANATION 

View from east

View from south

Perspective view from southwest N

Ve

Vertical exaggeration = 15x Cylinders represent the location and interval of drill holes that penetrated young alluvium; colors represent lithologic units intercepted downhole. 

Colors appear variable due to the effects of illumination from below and southeast.Drill holes are hung from their collar elevation at land surface. Land surface is transparent; as a result, the drill holes have the appearance of hanging in space.Location of drill holes and map extent of the upper surface of the 3D volume shown in figure 2.

Vertical e

Figure 5. Three-dimensional portrayals of drill-hole lithologic data.

Figure 5. Three-dimensional portrayals of drill-hole lithologic data.
N

820,000

840,000

860,000

880,000

650,000

660,000

670,000

680,000

690,000

700,000

4,000

2,000

Easting (Nevada State Plane, feet)

Northing (Nevada State Plane, feet)

ELEVATION, IN FEET

6

1 3

9 2

4 7

12

17

8

16

11

15

10

14

29

25

116° 10' 116° 

37° 37° 10' 

0 2 4 6 8 10 Miles

0 2 4 6 8 10 Kilometers

View is from the southeast (145 degrees) looking to 

the northwest from an elevation 20 degrees above

the horizon. Vertical exaggeration is 10x.

Colors appear variable due to the effects of

illumination from below and northeast.

Gravel

Sandy gravel

Gravelly sand

Sand and minor gravel

Sand, clay, and gravel

Coarse sand

Fine sand

Clay and sand

Clay

Clay and limestone

Basalt

Nonwelded tuff

No data

EXPLANATION of colors

shown on sections

EXPLANATION of colors

shown on geologic index map

Young alluvial deposits

Undivided alluvial deposits

Intermediate alluvial deposits

Playa deposits

Tertiary volcanic rocks

Granitic rocks and gabbro dikes

Pennsylvanian carbonate rocks

Mississippian and Devonian rocks

Cambrian to Devonian carbonate rocks

Outer boundary of 3D lithology model

Location of vertical section cut 

through 3D lithology model

Nevada Test Site area boundaries 

(modified from Slate and others, 2000)

8

Figure 6. Perspective view of vertical sections cut through 3D lithology model of Yucca Flat.

Figure 6. Perspective view of vertical sections cut through 3D lithology model of Yucca Flat.

3D Lithologic Modeling 11
gravel interval with the current surface drainage suggests that 

this drainage system is relatively long-lived. 

A uniformly sandy section is present in the southeastern 

part of the simulated area (fig. 6). Drill-hole data from this 

area indicate dominantly coarse and fine sand with rare occurrences of pebbles. Limited coring through this sandy interval 

(A.T. Fernald, written commun., 1983) reveals subhorizontal 

bedding and suggests a long-lived stable depositional environment to allow the accumulation of this thick interval of sand. 

Farther to the south, alluvial sediments interfinger with claydominated intervals (fig. 6) that represent the northern extent 

of sediment associated with the playa at the south end of the 

basin.

The simulated 3D subsurface distribution of each lithologic class is shown in figure 7. In these perspective views, 

only a single lithologic class is portrayed on each view, so the 

data appear to float in space. The basin fill is dominated by 

sandy gravel (fig. 7B) and gravelly sand (fig. 7C), especially 

at the basin margins. The gravel channel in the northwestern 

part of the basin is especially evident when the gravel class 

is viewed separately (fig. 7A); deeper gravel accumulations 

may be the result of older channel systems. Finer grained 

units including sand and minor gravel (fig. 7D) and sand, 

clay, and gravel (fig. 7G) tend to occur along the axis of the 

Yucca Flat basin. The predominance of the uniformly sandy 

section in the southeastern part of the model is well displayed 

by the interpolated lithologic data (fig. 7E). Clay-dominated 

sections occur exclusively at the southern end of the model 

and represent the interfingering of playa sediments with the 

alluvial section. Rare basalts occur within the alluvial section 

(fig. 7H); nonwelded tuffs include airfall units near the base of 

the alluvial section.

Multiple vertical cross sections (fig. 8) cut through the 

3D model display the overall lithologic variations within the 

basin fill. In the fence diagram, the cross sections are colored 

according to the interpreted geologic units (fig. 8); land surface is transparent so that the sections appear to hang in space. 

The upper surface of the model is clipped at the topographic 

surface by using a digital elevation model; the base of the 

model is clipped using a generalized surface that encloses 

the drilled intervals of alluvial fill for the drill holes used in 

this study. The model was not truncated at the elevation of 

pre-Cenozoic bedrock and is allowed to extrapolate into areas 

known to be underlain by pre-Cenozoic bedrock near the 

margins of the model (fig. 8). These sections clearly depict the 

sandy gravels associated with alluvial fan complexes along 

the western and northern margins of the basin; the subsurface 

extent of coarse gravels associated with the channel in the 

northwestern part of the model is also visible.

Deterministic modeling of the limited number of drill 

holes used produces broad lithologic trends, but it does not 

capture the lithologic details of highly discontinuous alluvial 

fan and channel complexes. Additional detail could possibly 

be arrived at through the use of additional drill holes and a 

finer model grid. However, many of the drill holes are as much 

as 1,000 ft deep and may be described in only two or three distinct intervals, so some method of improving the vertical lithologic resolution is needed. Analysis of downhole geophysical 

logs might be of use in defining additional discrete intervals 

that could be based on inferred grain size or sorting characteristics. Alternatively, it may be possible to use a stochastic 

approach where the drill-hole data are used as a guide to the 

subsurface variability (Weissmann and others, 1999). Such an 

approach could incorporate geologic process by evaluating 

the tendency of specific lithologic units to be adjacent to each 

other in specific geologic environments.

Summary

The purpose of this study is to develop an understanding of lateral and vertical lithologic variability of Neogene 

sediments that compose the shallow basin fill of Yucca Flat by 

using a generalized classification of drill-hole lithologic data. 

As shown in previous stratigraphic studies of Cenozoic basins 

to the south of the NTS, including the Amargosa Desert Basin 

(Sweetkind and others, 2001; Taylor and Sweetkind, 2005) 

and the Pahrump Valley (Sweetkind and others, 2003), careful 

classification of lithologic data from drill holes can reveal 

broad subsurface lithologic trends within the basin. Lithologic 

variations are related to different depositional environments 

within the basin such as alluvial fan, channel, basin axis, and 

playa deposits. In the Yucca Flat basin, subsurface trends in 

general mimic the distribution of surficial deposits, suggesting 

that depositional environments within the basin have remained 

stable during Late Cenozoic time.

Acknowledgments

This study was prepared in cooperation with the U.S. 

Department of Energy under Interagency Agreement 

DE–AI52–01NV13944. The authors thank the following 01NV13944. The authors thank the following 01NV13944. The authors thank the following 

individuals who provided data or information for the report: 

David Wood (USGS) compiled the drill-hole lithologic 

descriptions that were interpreted in this report, and Jerry 

Magner (USGS Core Library, Mercury, Nev.) provided access 

to unpublished reports that were invaluable in refining our 

interpretations.

12  Characterization of Young Alluvial Basin-Fill Deposits, Yucca Flat, Nevada
820,000

840,000

860,000

880,000

650,000 660,000 670,000 680,000 690,000 700,000

4,0002,000

Easting (Nevada State Plane, feet)

Northing (Nevada State Plane, feet)

ELEVATION, IN FEET

820,000

840,000

860,000

880,000

650,000 660,000 670,000 680,000 690,000 700,000

4,0002,000

Easting (Nevada State Plane, feet)

Northing (Nevada State Plane, feet)

ELEVATION, IN FEET

820,000

840,000

860,000

880,000

650,000 660,000 670,000 680,000 690,000 

Easting (Nevada State Plane, feet)

Northing (Nevada State Plane, feet)

820,000

840,000

860,000

880,000

650,000 660,000 670,000 680,000 690,000 

Easting (Nevada State Plane, feet)

Northing (Nevada State Plane, feet)

Figure 7. Perspective views of 3D lithologic model showing distribution of lithologic classes.

A, GravelB, Sandy gravel

C, Gravelly sandD, Sand and minor gravel

All views are looking to the degrees abois 10x. Colors  of illuminatio

Figure 7. Perspective views of 3D lithologic model showing distribution of lithologic classes.
Figure 7. Perspective views of 3D lithologic model showing distribution of lithologic classes—Continued

E, Coarse and fine sandF, Clay; clay and sand; clay and limestone

G, Sand, clay, and gravelH, Basalt; nonwelded tuff

Basalt

Nonwelded tuff

Clay Nonwelded tuff Clay and sand

Clay and limestone

Coarse sand

Fine sand

All views are frolooking to the nodegrees above tis 10x. Colors ap of illumination f

820,000

840,000

860,000

880,000

650,000 660,000 670,000 680,000 690,000 

Easting (Nevada State Plane, feet)

Northing (Nevada State Plane, feet)

820,000

840,000

860,000

880,000

650,000 660,000 670,000 680,000 690,000 700,000

4,0002,000

Easting (Nevada State Plane, feet)

Northing (Nevada State Plane, feet)

ELEVATION, IN FEET

820,000

840,000

860,000

880,000

650,000 660,000 670,000 680,000 690,000 700,000

4,0002,000

Easting (Nevada State Plane, feet)

Northing (Nevada State Plane, feet)

ELEVATION, IN FEET

820,000

840,000

860,000

880,000

650,000 660,000 670,000 680,000 690,000 

Easting (Nevada State Plane, feet)

Northing (Nevada State Plane, feet)

Figure 7. Perspective views of 3D lithologic model showing distribution of lithologic classes—Continued.
650,000 660,000 670,000 680,000 690,000 700,000 880,000 860,000

840,000

820,000

4,000

2,000

Easting (Nevada State Plane, feet) Northing (Nevada State Plane, feet)

ELEVATION, IN FEETGrav

SanGravSanSanCoaFine Clay ClayClay BasNonNo d

EXPLANATIOshown on se

EXPLANATIO

shown on ge

Young alluviUndivided aIntermediatPlaya deposTertiary volcGranitic rocPennsylvanMississippiaCambrian to 

(modified from Slate 

Fault mappeFault, conce

Nevada Tes

View is from the southeast (145 degrees) looking to the northwestfrom an elevation 20 degrees above the horizon. Vertical exaggeration is 5x.Colors appear variable due to the effects of illumination from below and southwest.

Vertical sections are cut through the 3D lithology model at1,000-foot intervals in the north-south direction and 5,000-footintervals in the east-west direction. Model was not clippedat the elevation of pre-Cenozoic bedrock and is allowed to extrapolate into areas known to be underlain by pre-Cenozoicbedrock near the margins of the model.

Figure 8. Perspective view of multiple vertical sections cut through 3D lithology model of Yucca Flat.

2

Figure 8. Perspective view of multiple vertical sections cut through 3D lithology model of Yucca Flat.
References Cited

Byers, F.M., Jr., Carr, W.J., Orkild, P.P., Quinlivan, W.D., and 

Sargent, K.A., 1976, Volcanic suites and related cauldrons 

of the Timber Mountain-Oasis Valley caldera complex, 

southern Nevada: U.S. Geological Survey Professional 

Paper 919, 70 p.

Carr, W.J., 1984, Regional structural setting of Yucca Mountain, southeastern 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, 98 p.

Covington, H.R., and Berger, M.A., 1997, Catalogue of 

lithologic and stratigraphic information from drill holes on 

the Nevada Test Site and environs: U.S. Geological Survey 

Open-File Report 97–139, 221 p. 139, 221 p. 139, 221 p.

Dockery, Holly, 1984, Rotation of late Cenozoic extensional 

stresses, Yucca Flat region, Nevada Test Site, Nevada: Houston, Tex., Rice University, Ph.D. thesis, 77 p., 10 plates.

Ferguson, J.F., Felch, R.N., Aiken, C.L.V., Oldow, J.S., and 

Dockery, Holly, 1988, Models of the Bouguer gravity and 

geologic structure at Yucca Flat, Nevada: Geophysics,

v. 53, p. 231–244.

Folk, R.L., 1954, The distinction between grain size and mineral composition in sedimentary rock nomenclature: Journal 

of Geology, v. 62, p. 344–359.

Hinrichs, E.N., 1968, Geologic structure of the Yucca Flats 

area, Nevada, in Eckel, E.B., ed., Nevada Test Site: Geological Society of America Memoir 110, p. 239–246.

Phelps, G.A., and McKee, E.H., 1999, High-angle faults in the 

basement of Yucca Flat, Nevada Test Site, Nevada, based 

on analysis of a constrained gravity inversion surface: U.S. 

Geological Survey Open-File Report 99–383, 6 p. 

Phelps, G.A., Langenheim, V.E., and Jachens, R.C., 1999, 

Thickness of Cenozoic deposits of Yucca Flat inferred from 

gravity data, Nevada Test Site, Nevada: U.S. Geological 

Survey Open-File Report 99–310, 33 p. 

Potter, C.J., Dickerson, R.P., Sweetkind, D.S., Drake II, R.M., 

Taylor, E.M., Fridrich, C.J., San Juan, C.A., and Day, W.C., 

2002, Geologic map of the Yucca Mountain region, Nye 

County, Nevada: U.S. Geological Survey Geologic Investigations Series I–2755, scale 1;50,000, 1 plate with pamphlet. 

Rockware®, 2004, Rockworks 2004 user documentation, 

http://www.rockware.com/, accessed November 2005.

Sawyer, D.A., Fleck, R.J., Lanphere, M.A., Warren, R.G., 

Broxton, D.E., and Hudson, M.R., 1994, Episodic caldera 

volcanism in the Miocene southwestern Nevada volcanic 

field—Revised stratigraphic framework, 40Ar/39Ar geochronology, and implications for magmatism and extension: Geological Society of America Bulletin, v. 106, p. 1304–1318. 

Slate, J.L., Berry, M.E., Rowley, P.D., Fridrich, C.J., Morgan, 

K.S., Workman, J.B., Young, O.D., Dixon, G.L., Williams, V.S., McKee, E.H., Ponce, D.A., Hildenbrand, T.G., 

Swadley, W.C., Lundstrom, S.C., Ekren, E.B., Warren, 

R.G., Cole, J.C., Fleck, R.J., Lanphere, M.A., Sawyer, 

D.A., Minor, S.A., Grunwald, D.J., Laczniak, R.J., Menges, 

C.M., Yount, J.C., and Jayko, A.S., 2000, Digital geologic 

map of the Nevada Test Site and vicinity, Nye, Lincoln, and 

Clark Counties, Nevada, and Inyo County, California: U.S. 

Geological Survey Open-File Report 99–554A, 53 p., scale 

1:120,000; at http://pubs.usgs.gov/of/1999/ofr-99-0554/.

Swan, F.H., Wesling, J., Angel, M., Thomas, A., Whitney, J., 

and Gibson, J., 2001, Evaluation of the location and recency 

of faulting near prospective surface facilities in Midway 

Valley, Nye County, Nevada: U.S. Geological Survey OpenFile Report, 2001–055, 1 disc. 

Sweetkind, D.S., Fridrich, C.J., and Taylor, E.M., 2001, Facies 

analysis of Tertiary basin-filling rocks of the Death Valley regional ground-water system and surrounding areas, 

Nevada and California: U.S. Geological Survey Open-File 

Report 2001–400, 55 p. Available online at http://pubs.usgs.

gov/of/2001/ofr-01-0400/.

Sweetkind, D.S., Taylor, E.M., and Putnam, Heather, 2003, 

Stratigraphic inferences derived from drill hole data of 

Tertiary basin-filling rocks of the Pahrump Valley basin, 

Nevada and California: U.S. Geological Survey Open-File 

Report 2003–051, 30 p. Available online at http://pubs.usgs.

gov/of/2003/ofr-03-051/.

Taylor, E.M., and Sweetkind, D.S., 2005, Using drill hole data 

and three-dimensional models to map the ground-water system in the Amargosa Desert basin, Nevada and California, 

in Thorleifson, L.H., and Berg, R.C., Geological models 

for groundwater flow modeling—Workshop Extended 

Abstracts: Geological Survey of Canada Open-File Report 

5048, p. 93–96. 

Thorleifson, L.H., and Pyne, D.M., 2004, Conversion of lithological data in the Manitoba water well database (GWDrill) 

to a mappable format, in Soller, D.R., ed., Digital Mapping 

Techniques '03 — Workshop Proceedings: U.S. Geological 

Survey Open-File Report 2003–471. 

U.S. Department of Energy, 2000, United States nuclear tests, July 

1945 through September 1992: U.S. Department of Energy, 

Nevada Operations Office, DOE/NV–209 (rev. 15), 162 p. 

16  Characterization of Young Alluvial Basin-Fill Deposits, Yucca Flat, Nevada
Weissmann, G.S., Carle, S.F., and Fogg, G.E., 1999, Threedimensional hydrofacies modeling based on soil surveys 

and transition probability geostatistics: Water Resources 

Research, v. 35, p. 1761–1770.

Workman, J.B., Menges, C.M., Page, W.R., Taylor, E.M., 

Ekren, E.B., Rowley, P.D., Dixon, G.L., Thompson, R.A., 

and Wright, L.A., 2002, Geologic map of the Death Valley 

ground-water model area, Nevada and California: U.S. 

Geological Survey Miscellaneous Field Studies Map MF–

2381–A, scale 1:250,000. Accessed September 1, 2004, at 

http://pubs.usgs.gov/mf/2002/mf-2381/.

References Cited 17
Sweetkind— Characterization of Young Alluvial Basin-Fill Deposits, Yucca Flat , Nevada— Scientific Investigations Report 2007�� � –