DOE/NV/25946--1067-ATT A
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New Name for the 

Nevada Test Site

On August 23, 2010, the U.S. Department 

of Energy, National Nuclear Security 

Administration announced the renaming of 

the Nevada Test Site to the Nevada National 

Security Site. Because this document reports 

on calendar year 2009 activities, the Nevada 

Test Site name has not been changed. Next 

year’s report will be titled the Nevada National 

Security Site Environmental Report.
Editor: Cathy Wills

Technical Editor: Sierra Cory

Graphic Designer: Katina Loo

Geographic Information System Specialist: Ashley Burns

DOE/NV/25946--1067-ATT A

Nevada Test Site

Environmental Report 

2009

Attachment A: Site Description

September 2010

Work performed under contract number:

DE-AC52-06NA25946 

This report was prepared for:

U.S. Department of Energy

National Nuclear Security Administration

Nevada Site Office

By:

National Security Technologies, LLC

P.O. Box 98521

Las Vegas, Nevada 89193-8521
Attachment A: Nevada Test Site Description 

ATT A-ii Nevada Test Site Environmental Report 2009

Table of Contents 

List of Figures ............................................................................................................................................. ATT A-iii 

List of Tables .............................................................................................................................................. ATT A-iii 

Acronyms and Abbreviations .......................................................................................................................ATT A-iv 

A.1 Geology ...............................................................................................................................ATT A-1 

A.1.1 Physiographic/Geologic Setting ......................................................................ATT A-1 

A.1.2 Stratigraphy......................................................................................................ATT A-7

A.1.3 Structural Controls...........................................................................................ATT A-7 

A.2 Hydrology............................................................................................................................ATT A-8 

A.2.1 Surface Water ..................................................................................................ATT A-8 

A.2.2 Groundwater ....................................................................................................ATT A-8 

A.2.3 Hydrogeologic Framework for the NTS and Vicinity ...................................ATT A-12 

A.2.3.1 Hydrogeologic Units ..................................................................ATT A-13 

A.2.3.2 Hydrostratigraphic Units............................................................ATT A-14 

A.2.4 General Hydraulic Characteristics of NTS Rocks .........................................ATT A-15 

A.2.5 Hydrogeology of the NTS Underground Test Areas .....................................ATT A-16 

A.2.5.1 Frenchman Flat Underground Test Area....................................ATT A-19 

A.2.5.2 Yucca Flat/Climax Mine Underground Test Area .....................ATT A-21 

A.2.5.3 Pahute Mesa Underground Test Area ........................................ATT A-26 

A.2.5.4 Rainier Mesa/Shoshone Mountain .............................................ATT A-31 

A.2.6 Conclusion .....................................................................................................ATT A-36 

A.3 Climatology.......................................................................................................................ATT A-36 

A.3.1 Precipitation...................................................................................................ATT A-36 

A.3.2 Temperature...................................................................................................ATT A-38 

A.3.3 Wind ..............................................................................................................ATT A-38 

A.3.4 Relative Humidity..........................................................................................ATT A-38 

A.3.5 Atmospheric Pressure ....................................................................................ATT A-41 

A.3.6 Dispersion Stability Categories .....................................................................ATT A-41 

A.3.7 Other Natural Phenomena..............................................................................ATT A-41 

A.4 Ecology..............................................................................................................................ATT A-42 

A.4.1 Flora...............................................................................................................ATT A-42 

A.4.2 Fauna..............................................................................................................ATT A-42 

A.4.3 Natural Water Sources...................................................................................ATT A-45 

A.5 Cultural Resources ............................................................................................................ATT A-47 

A.5.1 Cultural Resources Investigations on the NTS ..............................................ATT A-47 

A.5.2 Paleo-Indian Period........................................................................................ATT A-49 

A.5.3 Early Holocene Period...................................................................................ATT A-49 

A.5.4 Middle Holocene Period ................................................................................ATT A-49 

A.5.5 Late Holocene Period.....................................................................................ATT A-49 

A.5.6 Ethnohistoric American Indian......................................................................ATT A-51 

A.5.7 Historic Mining on and near the NTS............................................................ATT A-52 

References ...................................................................................................................................................ATT A-55 
 Attachment A: Nevada Test Site Description 

Nevada Test Site Environmental Report 2009 ATT A-iii 

List of Figures 

Figure A-1 Basin and Range Province and Great Basin Province ..........................................................ATT A-2 

Figure A-2 Generalized geologic map of the NTS and vicinity ..............................................................ATT A-3 

Figure A-3 Closed hydrographic subbasins on the NTS .........................................................................ATT A-9 

Figure A-4 Natural springs and seeps on the NTS ................................................................................ATT A-10 

Figure A-5 Groundwater subbasins of the NTS and vicinity ................................................................ATT A-11 

Figure A-6 Location of Corrective Action Units and Corrective Action Sites on the NTS ..................ATT A-17 

Figure A-7 Conceptual east-west cross section through Frenchman Flat..............................................ATT A-20 

Figure A-8 Generalized west-east hydrogeologic cross section through central Yucca Flat ................ATT A-23 

Figure A-9 Generalized hydrostratigraphic cross section through the Silent Canyon complex............ATT A-28 

Figure A-10 Generalized hydrostratigraphic cross section through Aqueduct Mesa ..............................ATT A-32 

Figure A-11 West-east hydrogeologic cross section through Well ER-16-1 ..........................................ATT A-35 

Figure A-12 Mean monthly precipitation at six NTS MEDA stations ....................................................ATT A-37 

Figure A-13 Temperature extremes and normal maximums and minimums at six 

NTS MEDA stations ...........................................................................................................ATT A-39 

Figure A-14 Twenty-year wind rose climatology for the NTS (1984–2004)..........................................ATT A-40 

Figure A-15 Distribution of plant alliances on the NTS..........................................................................ATT A-43 

Figure A-16 Known locations of sensitive plant species on the NTS .....................................................ATT A-44 

Figure A-17 Natural springs and seeps on the NTS ................................................................................ATT A-46 

Figure A-18 Example of prehistoric petroglyphs found on the NTS. This rock art site is in 

Fortymile Canyon ..............................................................................................................ATT A-47 

Figure A-19 DRI archaeologist at an archaeological excavation of a prehistoric site on Pahute Mesa ..ATT A-48 

Figure A-20 Building 400, a camera station for photographing atmospheric tests, 

at Area 6 Control Point. ......................................................................................................ATT A-48 

Figure A-21 Prehistoric projectile points from the NTS (photo by DRI, 1992)......................................ATT A-50 

Figure A-22 Brownware bowl recovered from archaeological excavations on Pahute Mesa.................ATT A-51 

Figure A-23 Overview of the Tippipah Spring area................................................................................ATT A-52 

Figure A-24 Bower cabin on the NTS.....................................................................................................ATT A-54 

List of Tables 

Table A-1 Quaternary and Tertiary stratigraphic units of the NTS and vicinity ..................................ATT A-4 

Table A-2 Pre-Tertiary stratigraphic units of the NTS and vicinity .....................................................ATT A-6 

Table A-3 Hydrogeologic units of the NTS area................................................................................ATT A-13 

Table A-4 Summary of hydrologic properties for hydrogeologic units at the NTS ...........................ATT A-16 

Table A-5 Information summary of NTS underground nuclear tests.................................................ATT A-18 

Table A-6 Hydrostratigraphic units of the Frenchman Flat underground test area ............................ATT A-20 

Table A-7 Hydrostratigraphic units of the Yucca Flat underground test area....................................ATT A-24 

Table A-8 Hydrostratigraphic units of the Pahute Mesa-Oasis Valley area.......................................ATT A-29 

Table A-9 Hydrostratigraphic units of the Rainier Mesa-Shoshone Mountain area...........................ATT A-33 
Attachment A: Nevada Test Site Description 

ATT A-iv Nevada Test Site Environmental Report 2009

A.0 Acronyms and Abbreviations 

AA alluvial aquifer 

AEC Atomic Energy Commission 

a.k.a. also known as 

ATCU argillic tuff confining unit 

ATICU Ammonia Tanks intrusive confining unit 

BA Benham aquifer 

BFCU Bullfrog confining unit 

BMICU Black Mountain intrusive confining unit 

BN Bechtel Nevada 

BP before present 

BRA Belted Range aquifer 

BRCU Belted Range confining unit 

°

C degree Celsius 

ca. circa, meaning “approximately” 

CA carbonate aquifer 

CAS Corrective Action Site 

CAU Corrective Action Unit 

CCICU Claim Canyon intrusive confining unit 

CCU clastic confining unit 

CFCM Crater Flat composite unit 

CFCU Crater Flat confining unit 

CG cloud-to-ground 

CHCU Calico Hills confining unit 

CHICU Calico Hills intrusive confining unit 

CHVCM Calico Hills vitric composite unit 

CHVTA Calico Hills vitric-tuff aquifer 

CHZCM Calico Hills zeolitized composite unit 

cm centimeter(s) 

CP Control Point 

DOE U.S. Department of Energy 

DOE/NV U.S. Department of Energy, Nevada Operations Office 

DRI Desert Research Institute 

DVCM detached volcanics composite unit 

EPA U.S. Environmental Protection Agency 

°

F degree Fahrenheit 

ft foot or feet 

FCCM Fortymile Canyon composite unit 

FCCU Fluorspar Canyon confining unit 

FFACO Federal Facility Agreement and Consent Order 
 Attachment A: Nevada Test Site Description 

Nevada Test Site Environmental Report 2009 ATT A-v 

GCU granite confining unit 

HGU hydrogeologic unit 

HSU hydrostratigraphic unit 

in. inch(es) 

IA inlet aquifer 

IICU intracaldera intrusive confining unit 

IT International Technology Corporation 

KA Kearsarge aquifer 

km kilometer(s) 

kph kilometer(s) per hour 

kt kiloton(s) 

LCA lower carbonate aquifer 

LCA3 lower carbonate aquifer - upper thrust plate 

LCCU lower clastic confining unit 

LCCU1 lower clastic confining unit - upper thrust plate 

LFA lava-flow aquifer 

LPCU lower Paintbrush confining unit 

LTCU lower tuff confining unit 

LTCU1 lower tuff confining unit 1 

LVTA lower vitric tuff aquifer 

LVTA1 lower vitric tuff aquifer 1 

LVTA2 lower vitric tuff aquifer 2 

m meter(s) 

Ma million years ago 

mb millibar(s) 

MEDA Meteorological Data Acquisition 

MGCU Mesozoic granite confining unit 

mi mile(s) 

mph miles per hour 

NNSA/NSO U.S. Department of Energy, National Nuclear Security Administration Nevada Site Office 

NSTec National Security Technologies, LLC 

NTS Nevada Test Site 

OSBCU Oak Spring Butte confining unit 

PBRCM Pre-Belted Range composite unit 

PCM Paintbrush composite unit 

PCU playa confining unit 

PDT Pacific Daylight Time 

PLFA Paintbrush lava-flow aquifer 

PM-OV Pahute Mesa-Oasis Valley 

PST Pacific Standard Time 

PVTA Paintbrush vitric-tuff aquifer 

RMBCU Rainier Mesa breccia confining unit 
Attachment A: Nevada Test Site Description 

ATT A-vi Nevada Test Site Environmental Report 2009

RMICU Rainier Mesa intrusive confining unit 

RM-SM Rainier Mesa-Shoshone Mountain 

RVICU Redrock Valley intrusive confining unit 

SCCC Silent Canyon caldera complex 

SCICU Silent Canyon intrusive confining unit 

SCVCU subcaldera volcanic confining unit 

SNJV Stoller-Navarro Joint Venture 

SWA Stockade Wash aquifer 

SWL static water level 

SWNVF Southwestern Nevada Volcanic Field 

TCU tuff confining unit 

TCVA Thirsty Canyon volcanic aquifer 

THCM Tannenbaum Hill composite unit 

THLFA Tannenbaum Hill lava-flow aquifer 

TMA Timber Mountain aquifer 

TMCC Timber Mountain caldera complex 

TMCM Timber Mountain composite unit 

TM-LVTA Timber Mountain lower vitric-tuff aquifer 

TM-UVTA Timber Mountain upper vitric-tuff aquifer 

TM-WTA Timber Mountain welded-tuff aquifer 

TPA Twin Peaks aquifer 

TSA Topopah Spring aquifer 

TUBA Tub Spring aquifer 

UCA upper carbonate aquifer 

UCCU upper clastic confining unit 

UGTA Underground Test Area 

UPCU upper Paintbrush confining unit 

UTCU upper tuff confining unit 

UTCU1 upper tuff confining unit 1 

UTCU2 upper tuff confining unit 2 

VCU volcaniclastic confining unit 

VTA vitric-tuff aquifer 

WCU Wahmonie confining unit 

WTA welded-tuff aquifer 

WWA Windy Wash aquifer 

YMCHLFA Yucca Mountain Calico Hills lava-flow aquifer 

YMCFCM Yucca Mountain Crater Flat composite unit 

YVCM younger volcanic composite unit 
Attachment A: Nevada Test Site Description

Nevada Test Site Environmental Report 2009 ATT A-1 

A.0 Attachment A: Nevada Test Site Description 

This attachment expands on the general description of the Nevada Test Site (NTS) presented in the Introduction to 

the Nevada Test Site Environmental Report 2009 (National Security Technologies, LLC [NSTec], 2010). Included 

are subsections that summarize the site’s geological, hydrological, climatological, and ecological setting. The 

cultural resources of the NTS are also presented. The subsections are meant to aid the reader in understanding the 

complex physical and biological environment of the NTS. An adequate knowledge of the site’s environment is 

necessary to assess the environmental impacts of new projects, design and implement environmental monitoring 

activities for current site operations, and assess the impacts of site operations on the public residing in the vicinity 

of the NTS. The NTS environment contributes to several key features of the site that afford protection to the 

inhabitants of adjacent areas from potential exposure to radioactivity or other contaminants resulting from NTS 

operations. These key features include the general remote location of the NTS, restricted access, extended wind 

transport times, the great depths to slow-moving groundwater, little or no surface water, and low population 

density. This attachment complements the annual summary of monitoring program activities and dose 

assessments presented in the main body of this report.

A.1 Geology 

A.1.1 Physiographic/Geologic Setting 

The NTS is located in the southern part of the Great Basin, the northern-most sub-province of the Basin and 

Range Physiographic Province (Figure A-1). The NTS terrain is typical of much of the Basin and Range 

Physiographic Province, characterized by mostly tilted, fault-bounded blocks that are as much as 80 kilometers 

(km) (50 miles [mi]) long and 24 km (15 mi) wide. These features are modified locally by the Las Vegas Shear 

Zone (a component of the Walker Lane regional structural belt) in the southern part of the NTS, and by resurgent 

calderas of the Southwestern Nevada Volcanic Field (SWNVF). The land forms and topography of the NTS area 

reflect the complex geology and its location in the arid Mojave Desert. 

The NTS area is geologically complex, with at least seven Tertiary-age calderas nearby, many relatively young 

basin-and-range-style normal faults, and Mesozoic-age thrust faults and intrusive bodies, all superimposed on a 

basement complex of highly deformed Proterozoic- and Paleozoic-age sedimentary and metasedimentary rocks. 

Geologic units exposed at the surface in the NTS area can be categorized as approximately 40 percent alluviumfilled basins and 20 percent Paleozoic and uppermost Precambrian sedimentary rocks, the remainder being 

Tertiary-age volcanic rocks with a few intrusive masses (Orkild, 1983; Slate et al., 1999). A generalized geologic 

map of the NTS area is given in Figure A-2. 

The NTS area is dominated by Tertiary-age volcanic rocks formed from materials that were erupted from various 

vents in the SWNVF, located on and adjacent to the northwestern part of the NTS (Figure A-2). At least seven 

major calderas have been identified in this multi-caldera silicic volcanic field (Byers et al., 1976; NSTec, 2007). 

The calderas formed by the voluminous eruption of zoned ash-flow tuffs between 16 and 7.5 million years ago 

(Ma) (Sawyer et al., 1994). From oldest to youngest, the calderas are Redrock Valley, Grouse Canyon, Area 20, 

Claim Canyon, Rainier Mesa, Ammonia Tanks, and Black Mountain calderas. A comprehensive review of past 

studies and the evolution of concepts on calderas of the SWNVF during the period from 1960 to 1988 is presented 

in Byers et al. (1989). 

The volcanic rocks are covered in many areas by a variety of late Tertiary and Quaternary surficial deposits. 

These younger deposits consist of alluvium, colluvium, eolian (wind-blown sand) deposits, spring deposits, basalt 

lavas, lacustrine (fresh-water lake) deposits, and playa deposits. 

The area includes more than 300 described Tertiary-age volcanic units (Warren et al., 2000a; 2003). As a matter 

of practicality, some units are grouped together, especially those of limited areal extent or thickness. Table A-1 

presents most of the Tertiary volcanic units useful in characterizing the subsurface at the NTS. 
Attachment A: Nevada Test Site Description 

ATT A-2 Nevada Test Site Environmental Report 2009

Figure A-1. Basin and Range Province and Great Basin Province (province boundaries from Fiero [1986]) 
Attachment A: Nevada Test Site Description

Nevada Test Site Environmental Report 2009 ATT A-3 

Figure A-2. Generalized geologic map of the NTS and vicinity
Attachment A: Nevada Test Site Description 

ATT A-4 Nevada Test Site Environmental Report 2009

 Table A-1. Quaternary and Tertiary stratigraphic units of the NTS and vicinity 

Stratigraphic Assemblages and Major Units(a, b) Volcanic Sources(c)

Quaternary and Tertiary Sediments 

 Young alluvium (Qay) 

 Playa (Qp) 

 Quaternary - Tertiary colluvium (QTc) 

 Middle alluvium (Qam) 

 Eolian sand (QTe) 

 Quaternary-Tertiary alluvium (QTa) 

Not applicable

Quaternary Basalts (Qby) Several discrete sources

Pliocene Basalts (Typ) Several discrete sources

Tertiary alluvium (Tgy) Not applicable

Miocene Basalt and Rhyolite 

 Thirsty Canyon and Younger Basalts (Tyb) 

 Rhyolite of Obsidian Butte (Tyr)

Several discrete sources

Tertiary Sediments 

 Late synvolcanic sedimentary rocks (Tgm) 

 Caldera moat-filling sedimentary deposits (Tgc) 

 Younger landslide and sedimentary breccia (Tgyx)

Not applicable

Thirsty Canyon Group (Tt) 

 Gold Flat Tuff (Ttg) 

 Trachyte of Hidden Cliff (Tth) 

 Trachytic rocks of Pillar Spring and Yellow Cleft (Tts) 

 Trail Ridge Tuff (Ttt) 

 Pahute Mesa and Rocket Wash Tuffs (Ttp) 

 Comendite of Ribbon Cliff (Ttc)

Black Mountain Caldera (9.4 Ma)

Volcanics of Fortymile Canyon (Tf) 

 Rhyolite of Boundary Butte (Tfu) 

 Post-Timber Mountain Basaltic Rocks (Tft) 

 Trachyte of Donovan Mountain (Tfn) 

 Rhyolite of Shoshone Mountain (Tfs) 

 Lavas of Dome Mountain (Tfd) 

 Younger intrusive rocks (Tiy) 

 Rhyolite of Rainbow Mountain (Tfr) 

 Beatty Wash Formation (Tfb) 

 Tuff of Leadfield Road (Tfl) 

 Rhyolite of Fleur-de-lis Ranch (Tff)

Several discrete vent areas in and around the Timber 

Mountain Caldera Complex 

Timber Mountain Group (Tm) Timber Mountain Caldera Complex: 

 Trachyte of East Cat Canyon (Tmay) 

 Tuff of Buttonhook Wash (Tmaw) 

 Ammonia Tanks Tuff (Tma) Ammonia Tanks Caldera (11.45 Ma) 

 Bedded Ammonia Tanks Tuff (Tmab) 

 Timber Mountain landslide breccia (Tmx) 

 Rhyolite of Tannenbaum Hill (Tmat) 

 Basalt of Tierra (Tmt) 

 Rainier Mesa Tuff (Tmr) Rainier Mesa Caldera (11.6 Ma) 

 Rhyolite of Fluorspur Canyon (Tmrf) 

 Tuff of Holmes Road (Tmrh) 

 Landslide or eruptive breccia (Tmrx) 

 Rhyolite of Windy Wash (Tmw) 

 Transitional Timber Mountain rhyolites (Tmn)
Attachment A: Nevada Test Site Description

Nevada Test Site Environmental Report 2009 ATT A-5 

Table A-1. Quaternary and Tertiary stratigraphic units of the NTS and vicinity (continued) 

Stratigraphic Assemblages and Major Units(a, b) Volcanic Sources(c)

Paintbrush Group (Tp) Claim Canyon Caldera (12.65 Ma)

 Rhyolite of Benham (Tpb) 

 Post-Tiva Canyon rhyolites (Tpu) 

 Rhyolite of Scrugham Peak (Tps) 

 Paintbrush caldera-collapse breccias (Tpx) 

 Tiva Canyon Tuff (Tpc) 

 Yucca Mountain Tuff (Tpy) 

 Rhyolite of Delirium Canyon (Tpd) 

 Rhyolite of Echo Peak (Tpe) 

 Middle Paintbrush Group rhyolites (Tpm) 

 Pah Canyon Tuff (Tpp) 

 Rhyolite of Silent Canyon (Tpr) 

 Topopah Spring Tuff (Tpt)

Calico Hills Formation (Th; formerly Tac) Unknown

Wahmonie Formation (Tw) Wahmonie Volcanic Center

Crater Flat Group (Tc) Silent Canyon Caldera Complex:

 Rhyolite of Inlet (Tci) 

 Prow Pass Tuff (Tcp) 

 Rhyolite of Kearsarage (Tcpk) 

 Andesite of Grimy Gulch (Tcg) 

 Bullfrog Tuff (Tcb) Area 20 Caldera (13.1 Ma) 

 Rhyolites in the Crater Flat Group (Tcr) 

 Tram Tuff (Tct) 

Belted Range Group (Tb) 

 Deadhorse Flat Formation (Tbd) 

 Grouse Canyon Tuff (Tbg) Grouse Canyon Caldera (13.6 Ma) 

 Comendite of Split Range (Tbgs) 

 Comendite of Quartet Dome (Tbq)

Tram Ridge Group (Tr) 

 Lithic Ridge Tuff (Trl) 

 Dikes of Tram Ridge (Trd) 

 Rhyolite of Picture Rock (Trr)

Uncertain

Tunnel Formation (Tn) 

 Tunnel 4 Member (Tn4) 

 Tunnel 3 Member (Tn3)

Uncertain

Volcanics of Quartz Mountain (Tq) 

 Tuff of Sleeping Butte (Tqs) 

 Hornblende-bearing rhyolite of Quartz Mountain(Tqh) 

 Tuff of Tolicha Peak (Tqt) 

 Early rhyolite of Quartz Mountain (Tqe) 

 Dacite of Mount Helen (Tqm)

Uncertain

Volcanics of Big Dome (Tu) 

 Comendite of Ochre Ridge (Tuo) 

 Tub Spring Tuff (Tub) 

 Comendite of Emigrant Valley (Tue)

Unknown (14.9 Ma)
Attachment A: Nevada Test Site Description 

ATT A-6 Nevada Test Site Environmental Report 2009

Table A-1. Quaternary and Tertiary stratigraphic units of the NTS and vicinity (continued) 

Stratigraphic Assemblages and Major Units(a, b) Volcanic Sources(c)

Volcanics of Oak Spring Butte (To)

Tunnel bed 2 (Ton2) 

Yucca Flat Tuff (Toy) 

Tunnel bed 1 (Ton1) 

Redrock Valley Tuff (Tor) Redrock Valley Caldera (15.4 Ma) 

Tuff of Twin Peaks (Tot) Unknown (15.5 Ma) 

Older Volcanics (Tqo) Unknown

Paleocolluvium (Tl) Not applicable 

(a) Compiled from Slate et al. (1999) and Ferguson et al. (1994). 

(b) Letters in parentheses are stratigraphic unit map symbols. 

(c) Sources and ages, where known, from Sawyer et al. (1994). Sources for Redrock Valley Caldera from NSTec (2007). 

Refer to Table A-2 for lists of Mesozoic, Paleozoic, and Precambrian sedimentary rock formations. 

Underlying the Tertiary volcanic rocks are Paleozoic and Proterozoic sedimentary rocks including dolomite, 

limestone, quartzite, and argillite, some of which form the primary regional aquifer and the regional hydrologic 

“basement” (Table A-2). During Precambrian and Paleozoic time, as much as 10,000 meters (m) (32,800 feet [ft]) 

of marine sediments were deposited in the NTS region (Cole, 1997). The only surface exposure of Mesozoic-age 

rocks in the NTS area are granitic intrusive masses, the Gold Meadows Stock north of Rainier Mesa 

(Gibbons et al., 1963; Snyder, 1977), and the Climax Stock located at the extreme north end of Yucca Flat 

(Barnes et al., 1963; Maldonado, 1977) (Figure A-2). 

 Table A-2. Pre-Tertiary stratigraphic units of the NTS and vicinity 

Stratigraphic Thickness

Map Unit 

Stratigraphic Unit 

Map Symbol Feet Meters Dominant Lithology 

Gold Meadows Stock 

Climax Stock

Kgg 

Kgc N/A N/A Quartz monzonite Granodiorite

Tippipah Limestone (correlative 

with the Bird Spring Formation) PPt 3,500 1,070 Limestone

Chainman Shale and Eleana 

Formation

Mc 

MDe 4,000 1,220 Shale, argillite, and quartzite

Guilmette Formation 

Simonson Dolomite 

Sevy Dolomite 

Laketown Dolomite 

Ely Spring Dolomite 

Eureka Quartzite 

Antelope Valley Limestone 

Ninemile Formation 

Goodwin Limestone 

Nopah Formation 

Bonanza King Formation 

Carrara Formation (upper)

Dg 

Ds 

DSs 

Sl 

Oes 

Oe 

Oa 

On 

Og 

Cn 

Cb 

Cc

1,400 

1,100 

690 

650 

340 

400 

1,530 

335 

685 

2,050 

4,350 

925

430 

330 

210 

200 

105 

125 

466 

102 

209 

620 

1,330 

280

Limestone 

Dolomite 

Dolomite 

Dolomite 

Dolomite 

Quartzite 

Limestone 

Limestone 

Limestone 

Limestone 

Limestone/dolomite 

Limestone

Carrara Formation (lower) 

Zabriskie Quartzite 

Wood Canyon Formation 

Stirling Quartzite 

Johnnie Formation

Cc 

Cz 

CZw 

Zs 

Zj

925 

200 

2,300 

2,900 

3,000

280 

60 

700 

890 

914

Shale/Siltstone 

Quartzite 

Micaceous quartzite 

Quartzite 

Quartzite/siltstone/limestone 

(Stratigraphic units and lithologies adapted from Cole [1992]) 
Attachment A: Nevada Test Site Description

Nevada Test Site Environmental Report 2009 ATT A-7 

A.1.2 Stratigraphy 

In order to confidently characterize the geology at the NTS, geoscientists must start from a well understood 

stratigraphic system. Refinement of the stratigraphy of the area was a continuous process during the decades in 

which geoscientists associated with the Weapons Testing Program worked to understand the complex volcanic 

setting (documented by Byers et al., 1989). The need to develop detailed geologic models in support of the 

Underground Test Area (UGTA) Sub-Project (see Chapter 14 of the main body of this document) intensified this 

process, and the recognition of smaller and smaller distinct volcanic units permitted a greater understanding of the 

three-dimensional configuration of the various types of rocks, which has been incorporated into the geologic 

framework. Efforts to understand the structure and stratigraphy of the non-volcanic rocks (pre-Tertiary) have also 

continued to a lesser degree (Cashman and Trexler, 1991; Cole, 1997; Cole and Cashman, 1999; Trexler et al., 

2003). The most widespread and significant Quaternary and Tertiary (mainly volcanic) units of the NTS area are 

listed in Table A-1. Refer to Table A-2 for a list of Mesozoic (granitic), Paleozoic (sedimentary), and 

Precambrian (sedimentary and metamorphic) stratigraphic units. 

A.1.3 Structural Controls 

Geologic structures are an important component of the hydrogeology of the area. Structures define the geometric 

configuration of the area, including the distribution, thickness, and orientation of units. Synvolcanic structures, 

including caldera faults and some normal faults had strong influence on depositional patterns of many of the units. 

The juxtaposition of units with different hydrologic properties across faults may have significant hydrogeologic 

consequences. Also, faults may act as either conduits or barriers to groundwater flow, depending on the difference 

in permeability between a fault zone and the surrounding rocks and the fault orientation within the present stress 

field. This is partially determined by whether the fault zone is characterized by open fractures, or if it is associated 

with fine-grained gouge or increased alteration. 

Five main types of structural features exist in the area: 

• Thrust faults (e.g., Belted Range and Control Point [CP] thrusts) 

• Normal faults (e.g., Yucca and West Greeley faults) 

• Transverse faults and structural zones (e.g., Rock Valley and Cane Spring faults) 

• Calderas (e.g., Timber Mountain and Silent Canyon caldera complexes) 

• Detachment faults (e.g., Fluorspar Canyon–Bullfrog Hills detachment fault) 

The Belted Range thrust fault is the principal pre-Tertiary structure in the NTS region and, thus, controls the 

distribution of pre-Tertiary rocks in the area. The fault can be traced or inferred from Bare Mountain just south of 

the southwest corner of the NTS area to the northern Belted Range, just north of the NTS, a distance of more than 

130 km (81 mi). It is an eastward-directed thrust fault that generally places late Proterozoic to early Cambrian 

rocks over rocks as young as Mississippian. Several imbricate thrust faults occur east of the main thrust fault. 

Deformation related to the Belted Range thrust fault occurred sometime between 100 and 250 Ma. Lesser thrusts 

of similar age are mapped in the area (e.g., the CP and Spotted Range thrusts). 

Normal faults in the area are related mainly to basin-and-range extension (e.g., Yucca fault in Yucca Flat and 

West Greeley fault on Pahute Mesa). Most of these faults likely developed during and after the main phase of 

volcanic activity of the SWNVF (Sawyer et al., 1994). The majority of these faults are northwest- to northeaststriking, high-angle faults. However, the exact locations, amount of offset along the faults, and character of the 

faults become increasingly uncertain with depth. 

Calderas are probably the most hydrogeologically important features in the NTS area. Volcano-tectonic and 

geomorphic processes related to caldera development result in abrupt and dramatic lithologic and thickness 

changes across caldera margins. Consequently, caldera margins (i.e., faults) separate regions with considerably 

different hydrogeologic character. 
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ATT A-8 Nevada Test Site Environmental Report 2009

A.2 Hydrology 

The hydrologic character of the NTS and vicinity reflects the region’s arid climatic conditions and complex 

geology (D’Agnese et al., 1997). The hydrology of the NTS has been extensively studied for over 50 years 

(U.S. Department of Energy [DOE], 1996); numerous scientific reports and large databases are available (refer to 

cited references for more detailed information). The following subsections present an overview of the hydrologic 

setting of the NTS and vicinity, including summary descriptions of surface water and groundwater, hydrogeologic 

framework, and brief descriptions of the hydrogeology for each of the idle underground test areas on the NTS. 

The reader is directed to Chapter 14 in the main body of this document for a discussion of the hydrogeologic 

modeling efforts conducted through the UGTA Sub-Project. 

A.2.1 Surface Water 

The NTS is located within the Great Basin, a closed hydrographic province that comprises several closed 

hydrographic basins (Figure A-3). The closed hydrographic basins of the NTS (most notably Yucca and 

Frenchman Flats) are subbasins of the Great Basin. Streams in the region are ephemeral, flowing only in response 

to precipitation events or snowmelt. Runoff is conveyed through normally dry washes toward the lowest areas of 

the closed hydrographic subbasins, and collects on playas. There are two playas (seasonally dry lakes) on the 

NTS: Frenchman Lake and Yucca Lake, which lie in Frenchman and Yucca Flats, respectively. While water may 

stand on the playas for a few weeks before evaporating, the playas are dry most of the year. Surface water may 

leave the NTS in only a few places, such as Fortymile Canyon in the southwestern NTS. 

Springs that emanate from local perched groundwater systems are the only natural sources of perennial 

surface water in the region. There are 24 known springs or seeps on the NTS (Hansen et al., 1997; Bechtel 

Nevada [BN], 1999) (Figure A-4). Spring discharge rates are low, ranging from 0.014 to 2.2 liters/second (0.22 to 

35 gallons/minute) (International Technology Corporation [IT], 1997). Most water discharged from springs 

travels only a short distance from the source before evaporating or infiltrating into the ground. The springs are 

important sources of water for wildlife, but they are too small to be of use as a public water supply source. 

Other surface waters on the NTS include man-made impoundments constructed at several locations throughout 

the NTS to support various operations. These are numerous and include open industrial reservoirs, containment 

ponds, and sewage lagoons. Surface water is not a source of drinking water on the NTS. 

A.2.2 Groundwater 

The NTS is located within the Death Valley regional groundwater flow system, one of the major hydrologic 

subdivisions of the southern Great Basin (Waddell et al., 1984; Laczniak et al., 1996). Groundwater in southern 

Nevada is conveyed within several flow-system subbasins in the Death Valley regional flow system (a subbasin is 

defined as the area that contributes water to a major surface discharge area [Laczniak, et al., 1996]). Three 

principal groundwater subbasins, named for their down-gradient discharge areas, have been identified within the 

NTS region: the Ash Meadows, Oasis Valley, and Alkali Flat-Furnace Creek Ranch subbasins (Waddell et al., 

1984) (Figure A-5). 

The groundwater-bearing rocks at the NTS have been classified into several hydrogeologic units (HGUs) 

(see Section A.2.3), of which the most important is the lower carbonate aquifer, a thick sequence of Paleozoic 

carbonate rock. This unit extends throughout the subsurface of central and southeastern Nevada, and is considered 

to be a regional aquifer (Winograd and Thordarson, 1975; Laczniak et al., 1996; IT, 1996a). Various volcanic and 

alluvial aquifers are also locally important as water sources. 
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Nevada Test Site Environmental Report 2009 ATT A-9 

Figure A-3. Closed hydrographic subbasins on the NTS (from State of Nevada Engineers Office, 1974)
Attachment A: Nevada Test Site Description 

ATT A-10 Nevada Test Site Environmental Report 2009

Figure A-4. Natural springs and seeps on the NTS (from Hansen et al., 1997; BN, 1999; Hansen et al., 2010) 
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Nevada Test Site Environmental Report 2009 ATT A-11 

Figure A-5. Groundwater subbasins of the NTS and vicinity (modified from Waddell et al., 1984; Laczniak et al., 

 1996; and Laczniak et al., 2001) 
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ATT A-12 Nevada Test Site Environmental Report 2009

In general, the static water level across the NTS is deep, but measured depths vary depending on the land 

elevation from which each well was drilled. The depth to groundwater in wells at the NTS varies from about 

210 m (690 ft) below the land surface under the Frenchman Flat playa in the southeastern NTS to more than 

610 m (2,000 ft) below the land surface in the northwestern NTS beneath Pahute Mesa (Reiner et al., 1995; 

Robie et al., 1995; IT, 1996b; O’Hagan and Laczniak, 1996; Bright et al., 2001; Locke and La Camera, 2003; 

Fenelon, 2005; 2007). Perched groundwater (isolated lenses of water lying above the regional groundwater level) 

occurs locally throughout the NTS, mainly within the volcanic rocks. 

Recharge areas for the Death Valley groundwater system are the higher mountain ranges of central and southern 

Nevada, where there can be significant precipitation and snowmelt. Groundwater flow is generally from these 

upland areas to natural discharge areas in the south and southwest. Groundwater at the NTS is also derived from 

underflow from basins up-gradient of the area (Harrill et al., 1988). The direction of groundwater flow may 

locally be influenced by structure, rock type, or other geologic conditions. Based on existing water-level data 

(Hale et al., 1995; Reiner et al., 1995; IT, 1996b; BN, 2003; Fenelon et al., 2008) and flow models (IT, 1996a; 

D’Agnese et al., 1997; Stoller-Navarro Joint Venture [SNJV], 2006a; 2006b; 2007), the general groundwater flow 

direction within major water-bearing units beneath the NTS is to the south and southwest. 

Most of the natural discharge from the Death Valley flow system is via transpiration by plants or evaporation 

from soil and playas in the Amargosa Desert and Death Valley. Groundwater discharge at the NTS is minor, 

consisting of small springs that drain perched water lenses and artificial discharge at a limited number of water 

supply wells. 

Groundwater is the only local source of potable water on the NTS. The nine supply wells that make up the NTS 

water system (Gillespie et al., 1996) and the other supply wells for the various water systems in the area (town of 

Beatty, small mines, and local ranches) produce water for human and industrial use from the carbonate, volcanic, 

and alluvial aquifers. Water chemistry varies from a sodium-potassium-bicarbonate type to a calcium-magnesiumcarbonate type, depending on the mineralogical composition of the aquifer source. Groundwater quality within 

aquifers of the NTS is generally acceptable for drinking water and industrial and agricultural uses (Chapman, 

1994) and meets Safe Drinking Water Act standards (Chapman and Lyles, 1993; Rose et al., 1997; BN, 2003). 

A.2.3 Hydrogeologic Framework for the NTS and Vicinity 

When the need for testing nuclear devices underground was recognized in the 1950s, among the first concerns 

was the effect testing would have on the groundwater of the area. One of the earliest nuclear tests conducted 

below the groundwater table (the BILBY test conducted in 1963) was designed in part to study explosion effects 

on groundwater and the movement in groundwater of radioactive byproducts from the explosion (Hale et al., 

1963; Garber, 1971). Since that time additional studies at various scales have been conducted to aid in the 

understanding of groundwater flow at the NTS. The current understanding of the regional groundwater flow at the 

NTS is derived from work by Winograd and Thordarson (1975), which was summarized and updated by Laczniak 

et al. (1996), and has further been developed by the UGTA Sub-Project hydrogeologic modeling team (IT, 1996a; 

BN, 2002a; 2005; 2006; NSTec, 2007; 2009a). See Chapter 14 for a description of the UGTA Sub-Project. 

Winograd and Thordarson (1975) established a hydrogeologic framework, incorporating the work of 

Blankennagel and Weir (1973) who defined the first HGUs to address the complex hydraulic properties of 

volcanic rocks. HGUs are used to categorize lithologic units according to their ability to transmit groundwater, 

which is mainly a function of their primary lithologic properties, degree of fracturing, and secondary mineral 

alteration. Hydrostratigraphic units (HSUs) for the NTS volcanic rocks were first defined during the UGTA 

modeling initiative (IT, 1996a). HSUs are groupings of contiguous stratigraphic units that have a particular 

hydrogeologic character, such as an aquifer (unit through which water moves readily) or confining unit (unit that 

generally is impermeable to water movement). The concept of HSUs is very useful in volcanic terrains where 

stratigraphic units can vary greatly in hydrologic character both laterally and vertically. 
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Nevada Test Site Environmental Report 2009 ATT A-13 

The rocks of the NTS have been classified for hydrologic modeling using this two-level classification scheme in 

which HGUs are grouped to form HSUs (IT, 1996a; NSTec, 2009a). An HSU may consist of several HGUs, but is 

defined so that a single general type of HGU dominates (for example, mostly welded-tuff and vitric-tuff aquifers 

or mostly tuff confining units). 

A.2.3.1 Hydrogeologic Units 

All the rocks of the NTS and vicinity can be classified as one of ten HGUs, which include the alluvial aquifer, a 

playa confining unit, four volcanic HGUs, two intrusive units, and two HGUs that represent the pre-Tertiary rocks 

(Table A-3). 

The deposits of alluvium (alluvial aquifer) fill the main basins of the NTS, and generally consist of a loosely 

consolidated mixture of boulders, gravel, and sand derived from volcanic and Paleozoic sedimentary rocks 

(Slate et al., 1999). The finest sediments can be deposited as playa deposits (or dry lake beds) in some closed 

basins (e.g., Yucca and Frenchman Flats). Because of their silty/clayey nature, these fine-grained units tend to 

behave hydrologically as confining units (restrictive of groundwater flow). 

Table A-3. Hydrogeologic units of the NTS area 

Hydrogeologic Unit 

(Symbol) Typical Lithologies Hydrologic Significance 

Alluvial Aquifer 

(AA) 

Unconsolidated to partially consolidated 

gravelly sand, eolian sand, and colluvium; 

thin, basalt flows of limited extent 

Has characteristics of a highly conductive aquifer, but less so 

where lenses of clay-rich paleocolluvium or playa deposits are 

present. 

Playa Confining Unit 

(PCU) 

Clayey-silt, sandy-silt Surface and near-surface confining unit at Yucca and 

Frenchman Lakes and within the lower portion of the alluvial 

section in the deepest portions of Frenchman Flat. 

Welded-Tuff Aquifer 

(WTA) 

Welded ash-flow tuff; vitric to devitrified Degree of welding greatly affects interstitial porosity (less 

porosity as degree of welding increases) and permeability 

(greater fracture permeability as degree of welding increases). 

Vitric-Tuff Aquifer 

(VTA) 

Bedded tuff; ash-fall and reworked tuff; 

vitric 

Constitutes a volumetrically minor hydrogeologic unit. 

Generally does not extend far below the static water level due 

to tendency to become zeolitized (which drastically reduces 

permeability) under saturated conditions. Significant interstitial 

porosity (20 to 40 percent). Generally insignificant fracture 

permeability. 

Lava-Flow Aquifer 

(LFA) 

Rhyolite, basalt, and dacite lava flows; 

includes flow breccias (commonly at base) 

and pumiceous zones (commonly at top) 

Generally occurs as small, moderately thick (rhyolite) to thin 

(basalt) local flows. Hydrologically complex; wide range of 

transmissivities; fracture density and interstitial porosity differ 

with lithologic variations. 

Tuff Confining Unit 

(TCU) 

Zeolitic bedded tuff with interbedded, but 

less significant, zeolitic, nonwelded to 

partially welded ash-flow tuff 

May be saturated but measured transmissivities are very low. 

May cause accumulation of perched and/or semi-perched water 

in overlying units. 

Intracaldera Intrusive 

Confining Unit 

(IICU) 

Highly altered, highly injected/intruded 

country rock and granitic material 

Assumed to be impermeable. Conceptually underlies each of 

the SWNVF calderas and Calico Hills. 

Granite Confining Unit 

(GCU) 

Granodiorite, quartz monzonite Relatively impermeable; forms local bulbous stocks, north of 

Rainier Mesa and Yucca Flat; may contain perched water. 

Clastic Confining Unit 

(CCU) 

Argillite, siltstone, quartzite Clay-rich rocks are relatively impermeable; more siliceous 

rocks are fractured, but with fracture porosity generally sealed 

due to secondary mineralization. 

Carbonate Aquifer 

(CA) 

Dolomite, limestone Transmissivity values differ greatly and are directly dependent 

on fracture frequency. 

 Note: Adapted from NSTec (2009a). 
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ATT A-14 Nevada Test Site Environmental Report 2009

The volcanic rocks of the NTS and vicinity can be categorized into four HGUs based on primary lithologic 

properties, degree of fracturing, and secondary mineral alteration. In general, the altered (typically zeolitized, but 

hydrothermally altered near caldera margins) volcanic rocks act as confining units (tuff confining unit), and the 

unaltered rocks form aquifers. The volcanic aquifer units can be further divided into welded-tuff aquifers or 

vitric-tuff aquifers (depending upon the degree of welding) and lava-flow aquifers. The denser rocks (welded ashflow tuffs and lava flows) tend to fracture more readily and therefore have relatively high permeability 

(Blankennagel and Weir, 1973; Winograd and Thordarson, 1975; Laczniak et al., 1996; IT, 1996c; 1997; Prothro 

and Drellack, 1997). 

The pre-Tertiary sedimentary rocks at the NTS and vicinity are also categorized as aquifer or confining unit 

HGUs based on lithology. The silicic clastic rocks (quartzite, siltstone, shale) tend to be aquitards or confining 

units, while the carbonates (limestone and dolomite) tend to be aquifers (Winograd and Thordarson, 1975; 

Laczniak et al., 1996). The granite confining unit is considered to behave as a confining unit due to low primary 

porosity and low permeability, and because most fractures are probably filled with secondary minerals (Walker, 

1962). 

A.2.3.2 Hydrostratigraphic Units 

The rocks at the NTS and vicinity are grouped into more than 76 HSUs (NSTec, 2009a). The more important and 

widespread HSUs in the area are discussed separately below, from oldest to youngest. Additional information 

regarding other HSUs is summarized in tables introduced in Section A.2.5 below where the hydrogeology of 

Yucca and Frenchman Flats, and Pahute and Rainier Mesas UGTAs at the NTS is addressed. Additional 

information can be found in the documentation packages for the UGTA Corrective Action Unit (CAU)-scale 

hydrogeologic models (BN, 2002b; 2005; 2006; NSTec, 2007). 

Lower Clastic Confining Unit (LCCU) – The Proterozoic to Middle-Cambrian-age rocks are largely quartzite 

and silica-cemented siltstone. Although these rocks are brittle and commonly fractured, secondary mineralization 

seems to have greatly reduced formation permeability (Winograd and Thordarson, 1975). These units make up the 

LCCU, which is considered to be the regional hydrologic basement (IT, 1996a). The LCCU is interpreted to 

underlie the entire region, except at the calderas. Where it is in a structurally high position, the LCCU may act as 

a barrier to deep regional groundwater flow. 

Lower Carbonate Aquifer (LCA) – The LCA consists of thick sequences of Middle Cambrian through Upper 

Devonian carbonate rocks. This HSU serves as the regional aquifer for most of southern Nevada and, locally, may 

be as thick as 5,000 m (16,400 ft) (Cole, 1997; Cole and Cashman, 1999). The LCA is present under most of the 

area, except where the LCCU is structurally high and at the calderas. Transmissivities of these rocks differ from 

place to place, apparently reflecting the observed differences in fracture and fault densities and characteristics 

(Winograd and Thordarson, 1975; NSTec, 2009b). 

Upper Clastic Confining Unit (UCCU) – Upper Devonian and Mississippian silicic clastic rocks in the NTS 

vicinity are assigned to the Eleana Formation and the Chainman Shale (Trexler et al., 1996; 2003; Cashman and 

Trexler, 1991). Both formations are grouped into the UCCU. At the NTS, this HSU is found mainly within a 

north-south band along the western portion of Yucca Flat. It is a significant confining unit and in many places 

forms the footwall of the Belted Range and CP thrust faults. 

Lower Carbonate Aquifer - Upper Thrust Plate (LCA3) – Cambrian through Devonian, mostly carbonate 

rocks that occur in the hanging wall of the Belted Range and CP thrust faults are designated as LCA3. These 

rocks are equivalent stratigraphically to the LCA but are structurally separated from the LCA by the Belted Range 

thrust fault. The LCA3 is patchily distributed as remnant thrust blocks, particularly along the western and 

southern sides of Yucca Flat (at Mine Mountain and the CP Hills), at Calico Hills, and at Bare Mountain. 

Mesozoic Granite Confining Unit (MGCU) – The Mesozoic era is represented at the NTS only by intrusive 

igneous rocks. Cretaceous-age granitic rocks are exposed at two locations: in northern Yucca Flat at the Climax 
Attachment A: Nevada Test Site Description

Nevada Test Site Environmental Report 2009 ATT A-15 

Stock, and the Gold Meadows Stock, which lies 12.9 km (8 mi) west of the Climax Stock, just north of Rainier 

Mesa (Snyder, 1977; Bath et al., 1983) (Figure A-2). The two are probably related in both source and time and are 

believed to be connected at depth (Jachens, 1999). Because of its low intergranular porosity and permeability, and 

the lack of inter-connecting fractures (Walker, 1962), the MGCU is considered a confining unit. The Climax and 

Gold Meadows intrusives are grouped into the MGCU HSU. 

Tertiary and Quaternary Hydrostratigraphic Units – Tertiary- and Quaternary-age strata at the NTS are 

organized into dozens of HSUs. Nearly all are of volcanic origin, except the alluvial aquifer (AA) and playa 

confining unit (PCU), which are the uppermost HSUs. These rocks are important because (1) most of the 

underground nuclear tests at the NTS were conducted in these units, (2) they constitute a large percentage of the 

rocks in the area, and (3) they are inherently complex and heterogeneous. As pointed out in Section A.2.3.1, the 

volcanic rocks are divided into aquifer or confining units according to lithology and secondary alteration. More 

detailed information can be found in the documentation packages for the UGTA CAU-scale hydrogeologic 

models (BN, 2002b; 2005; 2006; NSTec, 2007). 

Alluvial Aquifer (AA) – The alluvium throughout most of the NTS is a loosely consolidated mixture of detritus 

derived from silicic volcanic and Paleozoic-age sedimentary rocks, ranging in particle size from clay to boulders. 

Sediment deposition is largely in the form of alluvial fans (debris flows, sheet wash, and braided streams), which 

coalesce to form discontinuous, gradational, and poorly sorted deposits. Eolian sand, playa deposits, and rare 

basalt flows are also present within the alluvial section of some valleys. The alluvium thickness in major valleys 

(e.g., Frenchman Flat and Yucca Flat) generally ranges from about 30 m (100 ft) to more than 1,128 m (3,700 ft) 

in the deepest subbasins. The AA HSU is restricted primarily to the basins of the NTS. However, because the 

water table in the vicinity is moderately deep, the alluvium is generally unsaturated, except in the deep subbasins 

of some valleys. These sediments are porous and, thus, have high storage coefficients. Hydraulic conductivity 

may also be high, particularly in the coarser, gravelly beds. 

A.2.4 General Hydraulic Characteristics of NTS Rocks 

Volcanic rocks typically are extremely variable in lithologic character both laterally and vertically. The 

characteristics of rocks that control the density and character of fractures are the primary determinants of their 

hydraulic properties, and most hydraulic heterogeneity ultimately is related to fracture characteristics such as 

fracture density, openness, orientation, and other properties. Secondary fracture-filling minerals can drastically 

obstruct the flow through or effectively seal an otherwise transmissive formation (IT, 1996c; Drellack et al., 

1997). Fracture density typically increases with proximity to faults, potentially increasing the hydraulic 

conductivity of the formation; however, the hydrologic properties of faults, per se, are not well known. Limited 

data suggest that the full spectrum of hydraulic properties, from barrier to conduit, may be possible (Blankennagel 

and Weir, 1973; Faunt, 1998). 

Table A-4 includes a brief summary of the hydrologic properties of NTS HGUs. The lowest transmissivity values 

in volcanic rocks at the NTS are typically associated with non-welded ash-flow tuff and bedded tuff (ash-fall and 

reworked tuffs). Although interstitial porosity may be high, the interconnectivity of the pore space is poor, and 

these relatively incompetent rocks tend not to support open fractures. Secondary alteration of these tuffs (most 

commonly, zeolitization) ultimately yields a very impermeable unit. As described in Section A.2.3.1 and in 

NSTec (2009a), these zeolitized tuffs are considered to be confining units. The equivalent unaltered bedded and 

non-welded tuffs are considered to be vitric-tuff aquifers, and have intermediate transmissivities. 

In general, the most transmissive rocks tend to be moderately to densely welded ash-flow tuffs (welded-tuff 

aquifer), rhyolite lava flows (lava-flow aquifer), and carbonate rocks (limestone and dolomite). Although their 

interstitial porosity is low, these competent lithologies tend to be highly fractured, and groundwater flow through 

these rocks is largely through an interconnected network of fractures (Blankennagel and Weir, 1973; GeoTrans, 

1995). 

Underground nuclear explosions affect hydraulic properties of the geologic medium, creating both long-term and 

short-term effects. Effects include enhanced permeability from shock-induced fractures, the formation of vertical 
Attachment A: Nevada Test Site Description 

ATT A-16 Nevada Test Site Environmental Report 2009

conduits (e.g., collapse chimneys), and elevated water levels (mounding and over-pressurization of saturated 

low-permeability units). However, these effects tend to be localized (Borg et al., 1976; Brikowski, 1991; 

Allen et al., 1997). 

Table A-4. Summary of hydrologic properties for hydrogeologic units at the NTS 

Hydrogeologic Unit(a) Fracture Density(b, c)

Relative Hydraulic 

Conductivity(c)

Alluvial Aquifer Very low Moderate to very high 

Vitric-Tuff Aquifer Low Low to moderate 

Welded-Tuff Aquifer Moderate to high Moderate to very high 

Vitric Low Low to moderate Pumiceous 

Lava Zeolitic Low Very low 

Stony Lava and Vitrophyre Moderate to high Moderate to very high 

Lava-Flow 

Aquifer(d)

Flow Breccia Low to moderate Low to moderate 

Tuff Confining Unit Low Very low 

Intrusive Confining Unit Low to moderate Very low 

Granite Confining Unit Low to moderate Very low 

Carbonate Aquifer Low to high (variable) Low to very high 

Clastic Confining Unit Moderate Very low to low (e)

(a) Refer to Table A-3 for hydrogeologic nomenclature. 

(b) Including primary (cooling joints in tuffs) and secondary (tectonic) fractures. 

(c) The values presented are the authors’ qualitative estimates based on data from published (IT [1996c], Blankennagel and 

Weir [1973], Winograd and Thordarson [1975]) and unpublished sources (e.g., numerous Los Alamos and 

Lawrence Livermore National Laboratories drill-hole characterization reports). 

(d) Abstracted from Prothro and Drellack (1997). 

(e) Fractures tend to be sealed by the presence of secondary minerals. 

Note: Adapted from BN (2002b). 

A.2.5 Hydrogeology of the NTS Underground Test Areas 

Most NTS underground nuclear detonations were conducted in three main UGTAs (Figure A-6; U.S. Department 

of Energy, Nevada Operations Office [DOE/NV], 2000): (1) Yucca Flat, (2) Pahute Mesa, and (3) Rainier Mesa 

(including Aqueduct Mesa). Underground tests in Yucca Flat and Pahute Mesa typically were conducted in 

vertical drill holes, whereas almost all tests conducted in Rainier Mesa were tunnel emplacements. A total of 

85 underground tests (85 detonations) were conducted on Pahute Mesa, including 18 high-yield detonations (more 

than 200 kilotons [kt]). Rainier Mesa hosted 61 underground tests (62 detonations), almost all of which were 

relatively low-yield (generally less than 20 kt), tunnel-based weapons-effects tests. Yucca Flat was the most 

extensively used UGTA, hosting 659 underground tests (747 detonations), 4 of which were high-yield detonations 

(Allen et al., 1997; DOE/NV, 2000). 

In addition to the three main UGTAs, underground nuclear tests were conducted in Frenchman Flat (ten tests), 

Shoshone Mountain (six tests), the Oak Spring Butte/Climax Mine area (three tests), the Buckboard Mesa area 

(three tests), and Dome Mountain (one test with five detonations) (Allen et al., 1997; DOE/NV, 2000). It should 

be noted that these totals include nine cratering tests (13 total detonations) conducted in various areas of the NTS. 

Table A-5 is a synopsis of information about each UGTA at the NTS, and Figure A-6 shows the aerial distribution 

of underground nuclear tests conducted at the NTS. 
Attachment A: Nevada Test Site Description

Nevada Test Site Environmental Report 2009 ATT A-17 

Figure A-6. Location of UGTA Corrective Action Units and historical underground nuclear tests on the NTS 
 

ATT A-18 Nevada Test Site Environmental Report 2009 

Table A-5. Information summary of NTS underground nuclear tests (a) Source: DOE/NV, 2000 (b) High-yield detonations – detonations more than 200 kt. (c) Low-yield detonations – detonations less than 20 kt. (d) JOHNNIE BOY was detonated at a depth of 1.75 ft (essentially a surface burst) approximately 1 mile east of Buckboard Mesa. Total Underground(a) Physiographic Area NTS Area(s) Tests Detonations Test Dates(a) Depth of Burial Range Overburden Media C

Yucca Flat 1, 2, 3, 4, 6, 7, 8, 9, 10 659 747 1951–1992 27–1,219 m (89–3,999 ft) Alluvium/playa, Volcanic tuff, Paleozoic rocks Various test types and 

vertical emplacementlevel; includes four hi

Pahute Mesa 19, 20 85 85 1965–1992 31–1,452 m (100–4,765 ft) Alluvium, (thin) volcanic tuffs and lavas Almost all were large

emplacements above includes 18 high-yield 

Rainier/Aqueduct Mesa 12 61 62 1957–1992 61–640 m (200–2,100 ft) Tuffs with welded tuff caprock (little or no alluvium) Two vertical emplace

horizontal tunnel emplevel; mostly low-yie

Defense weapons effe

Frenchman Flat 5, 11 10 10 1965–1971 179–296 m (587–971 ft) Mostly alluvium, minor volcanic tuff Various emplacement 

and below static wate

Shoshone Mountain 16 6 6 1962–1971 244–640 m (800–2,100 ft) Bedded tuff Tunnel-based low-yie

Uniform tests. Oak Spring Butte (Climax Area) 15 3 3 1962–1966 229–351 m (750–1,150 ft) Granite Three tests above stat

TINY TOT, and PILE 

Buckboard Mesa 18 3 3 1962–1964 < 27 m (90 ft) Basaltic lavas Shallow, low-yield ex

JOHNNIE BOY(d), an

above static water lev

Dome Mountain 30 1 5 03/12/1968 50 m (165 ft) Mafic lava BUGGY (A, B, C, D, 

test using a 5-detonatstatic water level. 
 Attachment A: Nevada Test Site Description

Nevada Test Site Environmental Report 2009 ATT A-19

The location of each underground nuclear test is classified as a Corrective Action Site (CAS). These in turn have 

been grouped into six CAUs, according to the Federal Facility Agreement and Consent Order (FFACO), as 

amended (March 2010), between the DOE and the State of Nevada. In general, the CAUs relate to the 

geographical UGTAs on the NTS (see Figure A-6). 

The hydrogeology of the four main NTS UGTAs is summarized in the following subsections. For detailed 

stratigraphic descriptions of geologic units at the NTS (including each of the UGTAs), see Sawyer et al. (1994) 

and Slate et al. (1999). 

A.2.5.1 Frenchman Flat Underground Test Area 

The Frenchman Flat CAU consists of ten CASs located in the northern part of NTS Area 5 and southern part of 

Area 11 (see Figure A-6). The detonations were conducted in vertical emplacement holes and two mined shafts. 

Nearly all the tests were conducted in alluvium above the water table (BN, 2005). 

Physiography – Frenchman Flat is a closed intermontane basin located in the southeastern portion of the NTS. 

It is bounded on the north by Massachusetts Mountain and the Halfpint Range, on the east by the Buried Hills, 

on the south by the Spotted Range, and on the west by the Wahmonie volcanic center (see Figure A-2). The 

sparsely vegetated valley floor slopes gently toward a central playa lakebed. Ground-level elevations range from 

938 m (3,078 ft) above sea level at the playa, to over 1,463 m (4,800 ft) in the nearby surrounding mountains. 

Geology Overview – The stratigraphic section for Frenchman Flat consists of (from oldest to youngest) 

Proterozoic and Paleozoic clastic and carbonate rocks, Tertiary sedimentary and tuffaceous sedimentary rocks, 

Tertiary volcanic rocks, and Quaternary and Tertiary alluvium (Slate et al., 1999). In the northernmost portion of 

Frenchman Flat, the middle to upper Miocene volcanic rocks that erupted from calderas located to the northwest 

of Frenchman Flat unconformably overlie Ordovician-age carbonate and clastic rocks. To the south, these 

volcanic units, including the Ammonia Tanks Tuff, Rainier Mesa Tuff, Topopah Spring Formation, and Crater 

Flat Group, either thin considerably, interfinger with coeval sedimentary rocks, or pinch out together (BN, 2005). 

Upper-middle Miocene tuffs, lavas, and debris flows from the Wahmonie volcanic center located just west of 

Frenchman Flat dominate the volcanic section beneath the western portion of the valley. To the south and 

south-east, most of the volcanic units are absent, and Oligocene to middle Miocene sedimentary and tuffaceous 

sedimentary rocks, which unconformably overlie the Paleozoic rocks in the southern portion of Frenchman Flat, 

dominate the Tertiary section (Prothro and Drellack, 1997). In most of the Frenchman Flat area, upper Miocene to 

Holocene alluvium covers the older sedimentary and volcanic rocks (Slate et al., 1999). Alluvium thicknesses 

range from a thin veneer along the valley edges to perhaps as much as 1,158 m (3,800 ft) in north central 

Frenchman Flat. 

Structural Setting – The structural geology of Frenchman Flat is complex. During the late Mesozoic era, the 

region was subjected to compressional deformation, which resulted in folding, thrusting, uplift, and erosion of the 

pre-Tertiary rocks (Barnes et al., 1982). Approximately 16 Ma, the region underwent extensional deformation, 

during which the present basin-and-range topography was developed, and the Frenchman Flat basin was formed 

(Ekren et al., 1968). In the immediate vicinity of Frenchman Flat, extensional deformation has produced 

northeast-trending, left-lateral strike-slip faults and generally north-trending normal faults that displace the 

Tertiary and pre-Tertiary rocks. Beneath Frenchman Flat, major west-dipping normal faults merge and are 

probably contemporaneous with strike-slip faults beneath the southern portion of the basin (Grauch and Hudson, 

1995). Movement along the faults has created a relatively deep, east-dipping, half-graben basin elongated in a 

northeasterly direction (Figure A-7). 

Hydrogeology Overview – The hydrogeology of Frenchman Flat is fairly complex but is typical of the NTS area. 

Many of the HGU and HSU building blocks developed for the NTS vicinity are applicable to the Frenchman Flat 

basin. The strata in the Frenchman Flat area have been subdivided into four Quaternary/Tertiary alluvium and 

playa HSUs, nine Tertiary-age volcanic HSUs, and three pre-Tertiary HSUs to serve as layers for the UGTA 

Frenchman Flat CAU groundwater model (BN, 2005). The dominant units are, in descending order, the AA, the 

Timber Mountain welded-tuff aquifer (TM-WTA), the Timber Mountain lower vitric-tuff aquifer (TM-LVTA), 
Attachment A: Nevada Test Site Description

ATT A-20 Nevada Test Site Environmental Report 2009

the Topopah Spring aquifer (TSA), the Wahmonie confining unit (WCU), the lower tuff confining unit (LTCU), 

the volcaniclastic confining unit (VCU), the LCA, and the LCCU (Table A-6). 

Figure A-7. Conceptual east-west cross section through Frenchman Flat 

Table A-6. Dominant hydrostratigraphic units of the Frenchman Flat underground test area 

Hydrostratigraphic Unit 

(Symbol) 

Dominant 

Hydrogeologic 

Unit(a) Typical Lithologies 

Alluvial Aquifer 

(AA) 

AA Alluvium (gravelly sand); also includes relatively thin basalt 

flow in northern Frenchman Flat and playa deposits in southcentral part of basin. Lower permeability layers, such as the 

alluvium and playa deposits, are differentiated as separate 

HSUs in the hydrogeologic models. 

Timber Mountain Welded-Tuff Aquifer 

(TM-WTA) 

WTA, minor VTA Welded ash-flow tuff and related nonwelded and ash-fall tuffs; 

vitric to devitrified 

Timber Mountain Lower Vitric-Tuff Aquifer 

(TM-LVTA) 

VTA Nonwelded ash-flow and bedded tuffs; vitric (unaltered) 

Topopah Spring Aquifer (TSA) WTA Welded ash-flow tuff; vitric to devitrified 

Wahmonie Confining Unit (WCU) TCU, minor LFA Ash-fall and reworked tuffs; debris and breccia flows; minor 

intercalated lava flows. Typically altered: zeolitic to argillic 

Lower Tuff Confining Unit 

(LTCU and LTCU1) 

TCU Zeolitic bedded tuffs, with interbedded but less significant 

zeolitic, nonwelded to partially welded ash-flow tuffs 

Volcaniclastic Confining Unit 

(VCU) 

TCU, minor AA Diverse assemblage of interbedded volcanic and sedimentary 

rocks including tuffs, shale, tuffaceous and argillaceous 

sandstones, conglomerates, minor limestones 

Upper Clastic Confining Unit 

(UCCU) 

CCU Argillite, quartzite; present only in northwest portion of model 

in the CP Basin 

Lower Carbonate Aquifer (LCA) CA Dolomite and limestone; the “regional aquifer” 

Lower Clastic Confining Unit (LCCU) CCU Quartzites and siltstones; the “hydrologic basement” 

(a) See Table A-3 for descriptions of HGUs. 

Note: Adapted from BN, 2005. 

TV

TV TV

TV

TV

TV TV

AA

PZ

NO SCALE

PZ PZ

PZ

PZ

PZ

PZ

PZ

PZ

AA = Alluvial Aquifer

 (Quaternary/Tertiary Alluvium) TV = Volcanic Aquifers and Confining Units

(Tertiary Volcanic Rocks)

PZ = Lower Carbonate Aquifer

(Folded and Faulted pre-Tertiary

Sedimentary Rocks)

 = Movement away from viewer. = Movement toward viewer.
 Attachment A: Nevada Test Site Description

Nevada Test Site Environmental Report 2009 ATT A-21

Water-level Elevation and Groundwater Flow Direction – The depth to the static water level (SWL) in 

Frenchman Flat ranges from 210 m (690 ft) near the central playa to more than 350 m (1,150 ft) at the northern 

end of the valley (SNJV, 2004a; 2006a). The SWL is generally located within the AA, TM-WTA, TSA, WCU, or 

LTCU. In the deeper, central portions of the basin, more than half of the alluvium section is saturated. Water-level 

elevation data in the AA indicate a very flat water table (Blout et al., 1994; SNJV, 2004a; 2006a). 

Water-level data for the LCA in the southern part of the NTS are limited but indicate a fairly low gradient in 

the Yucca Flat, Frenchman Flat, and Jackass Flats areas. This gentle gradient implies a high degree of hydraulic 

continuity within the aquifer, presumably due to high fracture permeability (Laczniak et al., 1996). Furthermore, 

the similarity of the water levels measured in Paleozoic rocks (LCA) in Yucca Flat and Frenchman Flat implies 

that, at least for deep interbasin flow, there is no groundwater barrier between the two basins. Inferred regional 

groundwater flow through Frenchman Flat is to the south-southwest toward discharge areas in Ash Meadows 

(see Figure A-5). An increasing westward flow vector in southern NTS may be due to preferential flow paths 

subparallel to the northeast-trending Rock Valley fault (Grauch and Hudson, 1995) and/or a northward gradient 

from the Spring Mountain recharge area (IT, 1996a; 1996b). 

Groundwater elevation measurements for wells completed in the AA and the volcanic aquifers (e.g., TM-WTA, 

TSA) are higher than those in the underlying LCA (IT, 1996b; BN, 2005; SNJV, 2006a). This implies a 

downward gradient. This apparent semi-perched condition is believed to be due to the presence of intervening 

LTCU and VCU. 

A.2.5.2 Yucca Flat/Climax Mine Underground Test Area 

The Yucca Flat/Climax Mine CAU consists of several hundreds of CASs located in NTS Areas 1, 2, 3, 4, 6, 7, 8, 

9, and 10, and three CASs located in Area 15 (see Figure A-6). These tests were typically conducted in vertical 

emplacement holes and a few related tunnels (see Table A-5). 

The Yucca Flat and Climax Mine UGTAs were originally defined as two separate CAUs (CAU 97 and CAU 100) 

in the FFACO because the geologic frameworks of the two areas are distinctly different. The Yucca Flat 

underground nuclear tests were conducted in alluvial, volcanic, and carbonate rocks, whereas the Climax Mine 

tests were conducted in an igneous intrusion in northern Yucca Flat. However, particle-tracking simulations 

performed during the regional evaluation (IT, 1997) indicated that the local Climax Mine groundwater flow 

system merges into the much larger Yucca Flat groundwater flow system during the 1,000-year time period of 

interest, so the two areas were combined into the single CAU 97. 

Yucca Flat was the most heavily used UGTA on the NTS (see Figure A-6). The alluvium and tuff formations 

provide many characteristics advantageous to the containment of nuclear explosions. They are easily mined or 

drilled. The high-porosity overburden (alluvium and vitric tuffs) will accept and depressurize any gas that might 

escape the blast cavity. The deeper tuffs are zeolitized, which creates a nearly impermeable confining unit. The 

zeolites also have absorptive and “molecular sieve” attributes that severely restrict or prevent the migration of 

radionuclides (Carle et al., 2008). The deep water table (greater than 503 m [1,650 ft] depth) provides additional 

operational and environmental benefits. 

This section provides brief descriptions of the geologic and hydrogeologic setting of the Yucca Flat/Climax Mine 

UGTA, as well as a discussion of the hydrostratigraphic framework. This summary was compiled from various 

sources, including Winograd and Thordarson (1975), Byers et al. (1989), Laczniak et al. (1996), Cole (1997), IT 

(2002), and BN (2006), where additional information can be found. 

Physiography – Yucca Flat is a topographically closed basin with a playa at its southern end. The 

geomorphology of Yucca Flat is typical of the arid, inter-mountain basins found throughout the Basin and Range 

province of Nevada and adjoining states. Faulted and tilted blocks of Tertiary-age volcanic rocks and underlying 

Precambrian and Paleozoic sedimentary rocks form low ranges around the basin (see Figure A-2). These rocks 

also compose the “basement” of the basin, which is now covered by alluvium. 
Attachment A: Nevada Test Site Description

ATT A-22 Nevada Test Site Environmental Report 2009

Ground elevation in the Yucca Flat area ranges from about 1,195 m (3,920 ft) above mean sea level at Yucca 

Lake (playa) in the southern portion to about 1,463 m (4,800 ft) in the northern portion of the valley. The highest 

portions of the surrounding mountains and hills range from less than 1,500 m (5,000 ft) in the south to over 

2,316 m (7,600 ft) at Rainier Mesa in the northwest corner of the area. Yucca Flat is bounded by the Halfpint 

Range to the east, by Rainier Mesa and the Belted Range to the north, by the Eleana Range and Mine Mountain to 

the west, and by the CP Hills, CP Hogback, and Massachusetts Mountain to the south. 

Geology Overview – The Precambrian and Paleozoic rocks of the NTS area consist of approximately 11,300 m 

(37,000 ft) of carbonate and silicic clastic rocks (Cole, 1997). These rocks were severely deformed by 

compressional movements during Mesozoic time, which resulted in the formation of folds and thrust faults 

(e.g., Belted Range and CP thrust faults). During the middle Late Cretaceous, granitic bodies (such as the Climax 

stock in northern Yucca Flat) intruded these deformed rocks (Houser and Poole, 1960; Maldonado, 1977). 

A total of 22 pre-Tertiary formations (including the Mesozoic granitic intrusives) has been recognized in the 

Yucca Flat region (see Table A-2). These rocks range in age from Precambrian to Cretaceous and are the result of 

primarily carbonate and silicic shallow- to deep-water sedimentation near a continental margin. Some of these 

units are widespread throughout southern Nevada and California, though complex structural deformation has 

created many uncertainties in determining the geometric relationships of these units around Yucca Flat. 

During Cenozoic time, the sedimentary and intrusive rocks were buried by thick sections of volcanic material 

deposited in several eruptive cycles from source areas in the SWNVF. The Cenozoic stratigraphy of the Yucca 

Flat area, though not structurally complicated, is very complex. Most of the volcanic rocks of the Yucca Flat area 

were deposited during many eruptive cycles of the SWNVF (see Section A.1.1). The source areas of most units 

(Volcanics of Oak Spring Butte, Tunnel Formation, Belted Range Group, Crater Flat Group, Calico Hills 

Formation, Paintbrush Group, and Timber Mountain Group) are located to the west and northwest of Yucca Flat; 

the Wahmonie source area is located southwest of Yucca Flat. Table A-1 includes the Tertiary stratigraphic units 

common to the Yucca Flat basin. 

The volcanic rocks include primarily ash-flow tuffs, ash-fall tuffs, and reworked tuffs, whose thicknesses and 

extents vary partly due to the irregularity of the underlying depositional surface, and partly due to the presence of 

topographic barriers and windows between Yucca Flat and the source areas to the north and west. 

Over the last several million years, gradual erosion of the highlands that surround Yucca Flat has deposited a 

thick blanket of alluvium on the tuff section. The alluvium in Yucca Flat, and throughout most of the NTS, is a 

loosely consolidated mixture of detritus derived from silicic volcanic and Paleozoic sedimentary rocks, ranging in 

particle size from clay to boulders. Sediment deposition is largely in the form of alluvial fans (debris flows, sheet 

wash, and braided streams), which coalesce to form discontinuous, gradational, and poorly sorted deposits. Eolian 

sand, playa deposits, and rare basalt flows are also present within the alluvium section of Yucca Flat. The 

alluvium thickness in Yucca Flat generally ranges from about 30 m (100 ft) to over 914 m (3,000 ft) (Drellack and 

Thompson, 1990). 

Structural Setting – The structure of the pre-Tertiary rocks in Yucca Flat is complex and poorly known 

(Cole, 1997), but it is important because the pre-Tertiary section is very thick and extensive and includes units 

that form regional aquifers. The main pre-Tertiary structures in the Yucca Flat area are related to the east-vergent 

Belted Range thrust fault, which has placed Late Proterozoic to Cambrian-age rocks over rocks as young as Late 

Mississippian (Cole, 1997; Cole and Cashman, 1999). In several places along the western and southern portions 

of Yucca Flat, east-vergent structures related to the Belted Range thrust were deformed by younger west-vergent 

structural activity (Cole and Cashman, 1999). This west-vergent deformation is related to the CP thrust fault, 

which also placed Cambrian and Ordovician rocks over Mississippian and Pennsylvanian-age rocks beneath 

western Yucca Flat (Caskey and Schweickert, 1992). 
 Attachment A: Nevada Test Site Description

Nevada Test Site Environmental Report 2009 ATT A-23

Large-scale normal faulting began in Yucca Flat in response to regional extensional movements near the end of 

this period of volcanism. This faulting formed the Yucca Flat basin. As fault movement continued, blocks 

between faults were down-dropped and tilted, creating subbasins within the Yucca Flat basin. 

The major basin-forming faults generally strike in a northerly direction, and relative offset is typically down to the 

east (e.g., Yucca, Topgallant, and Carpetbag faults). Movement along the Yucca fault in central Yucca Flat 

indicates deformation in the area has continued into the Holocene (Hudson, 1992). Specific details regarding these 

faults are lacking because of the propensity to avoid inferred and known faults during drilling of emplacement 

holes for underground nuclear tests. 

The configuration of the Yucca Flat basin is illustrated on the generalized west-east cross section shown in 

Figure A-8. The cross section is simplified to show the positions of only the primary lithostratigraphic units in the 

region. This cross section provides a conceptual illustration of the irregular Precambrian and Paleozoic rocks 

overlain by the Tertiary volcanic units, and the basin-filling alluvium at the surface. The main Tertiary-age, 

basin-forming large-scale normal faults are also shown. 

Hydrogeologic Overview – All the rocks of the Yucca Flat underground test area can be classified as one of eight 

HGUs (see Table A-3), which include the AA, four volcanic HGUs, an intrusive unit, and two HGUs that 

represent the pre-Tertiary rocks. 

The strata in Yucca Flat have been subdivided into 11 Tertiary-age HSUs (including the Tertiary/Quaternary 

alluvium), 1 Mesozoic intrusive HSU, and 6 Paleozoic HSUs (BN, 2006). These units are listed in Table A-7, and 

several of the more important HSUs are discussed in the following paragraphs. The alluvium and pre-Tertiary 

HSUs in Yucca Flat are as defined in Section A.2.3.2. 

The hydrostratigraphy for the Tertiary-age volcanic rocks in Yucca Flat can be simplified into two categories: 

zeolitic tuff confining units and (non-zeolitic) volcanic aquifers. 

Figure A-8. Generalized west-east hydrogeologic cross section through central Yucca Flat
Attachment A: Nevada Test Site Description

ATT A-24 Nevada Test Site Environmental Report 2009

Table A-7. Hydrostratigraphic units of the Yucca Flat underground test area 

Hydrostratigraphic Unit 

(Symbol) 

Dominant 

Hydrogeologic 

Units(a) Typical Lithologies 

Alluvial Aquifer 

(AA) 

AA, minor LFA Alluvium (gravelly sand); also includes one or more 

thin basalt flows, playa deposits and eolian sands 

Timber Mountain Upper Vitric-Tuff Aquifer 

(TM-UVTA) 

WTA, VTA Includes vitric nonwelded ash-flow and bedded tuff 

Timber Mountain Welded-Tuff Aquifer 

(TM-WTA) 

WTA Partially to densely welded ash-flow tuff; vitric to 

devitrified 

Timber Mountain Lower Vitric-Tuff Aquifer 

(TM-LVTA) 

VTA Nonwelded ash-flow and bedded tuff; vitric 

Upper Tuff Confining Unit 

(UTCU) 

TCU Zeolitic bedded tuff 

Topopah Spring Aquifer 

(TSA) 

WTA Welded ash-flow tuff; present only in extreme 

southern Yucca Flat 

Belted Range Aquifer 

(BRA) 

WTA Welded ash-flow tuff 

Belted Range Confining Unit 

(BRCU) 

TCU Zeolitic bedded tuffs 

Pre-Grouse Canyon Tuff Lava-Flow Aquifer 

(Pre-Tbg-LFA) 

LFA Lava flow 

Lower Tuff Confining Unit 

(LTCU) 

TCU Zeolitic bedded tuffs with interbedded but less 

significant zeolitic, nonwelded to partially welded 

ash-flow tuffs 

Tub Spring Aquifer 

(TUBA) 

WTA Welded ash-flow tuff 

Oak Spring Butte Confining Unit 

(OSBCU) 

TCU Zeolitic bedded tuffs with interbedded but less 

significant zeolitic, nonwelded to partially welded 

ash-flow tuffs 

Argillic Tuff Confining Unit 

(ATCU) 

TCU Includes the argillic, lowermost Tertiary volcanic 

units and paleocolluvium that immediately overlie the 

pre-Tertiary rocks 

Mesozoic Granite Confining Unit 

(MGCU) 

GCU Granodiorite and quartz monzonite 

Upper Carbonate Aquifer (UCA) CA Limestone 

Lower Carbonate Aquifer - Yucca Flat Upper 

Thrust Plate (LCA3) 

CA Limestone and dolomite 

Lower Clastic Confining Unit - Yucca Flat 

Upper Plate (LCCU1) 

CCU Quartzite and siltstone 

Upper Clastic Confining Unit 

(UCCU) 

CCU Argillite and quartzite 

Lower Carbonate Aquifer 

(LCA) 

CA Dolomite and limestone; “regional aquifer” 

Lower Clastic Confining Unit 

(LCCU) 

CCU Quartzite and siltstone; “hydrologic basement” 

 (a) See Table A-3 for description of HGUs. 

Note: Adapted from BN, 2006. 
 Attachment A: Nevada Test Site Description

Nevada Test Site Environmental Report 2009 ATT A-25

The zeolitic TCUs in Yucca Flat have been grouped into three HSUs: the upper tuff confining unit (UTCU), the 

lower tuff confining unit (LTCU), and the Oak Spring Butte confining unit (OSBCU) (Table A-7). The LTCU and 

OSBCU are important HSUs in the Yucca Flat region (stratigraphically similar to the LTCU in Frenchman Flat) 

because they separate the volcanic aquifer units from the underlying regional LCA. Almost all zeolitized tuff units 

in Yucca Flat are grouped within the LTCU and OSBCU, which comprises mainly zeolitized bedded tuff (ash-fall 

tuff, with minor reworked tuff). The LTCU and OSBCU are saturated in much of Yucca Flat; however, measured 

transmissivities are very low. 

The LTCU and OSBCU are generally present in the eastern two-thirds of Yucca Flat. They are absent over the 

major structural highs, where the volcanic rocks have been removed by erosion. Areas where the LTCU and 

OSBCU are absent include the “Paleozoic bench” in the western portion of the basin. In northern Yucca Flat, the 

LTCU and OSBCU tend to be confined to the structural subbasins. Outside the subbasins and around the edges of 

Yucca Flat, the volcanic rocks are thinner and are not zeolitized. 

The unaltered volcanic rocks of Yucca Flat are divided into three Timber Mountain HSUs. The hydrogeology of 

this part of the geologic section is complicated by the presence of one or more ash-flow tuff units that are quite 

variable in properties both vertically and laterally. 

The Timber Mountain Group includes ash-flow tuffs that can be either WTAs or VTAs, depending on the degree 

of welding (refer to Sections A.2.3.1 and A.2.3.2). In Yucca Flat, these units are generally present in the central 

portions of the basin. They can be saturated in the deepest structural subbasins. 

The AA is confined primarily to the basins of the NTS. However, because the water table in the vicinity is 

moderately deep, the alluvium is generally unsaturated, except in the deep subbasins of some valleys. These 

sediments are porous and, thus, have high storage coefficients. Transmissivities may also be high, particularly in 

the coarser, gravelly beds. 

The more recent large-scale extensional faulting in the Yucca Flat area is significant from both hydrologic and 

containment perspectives because the faults have profoundly affected the hydrogeology of the Tertiary volcanic 

units by controlling to a large extent their alteration potential and final geometry. In addition, the faults 

themselves may facilitate flow of high-pressure gases from nearby explosion cavities and of potentially 

contaminated groundwater from sources in the younger rocks into the underlying regional aquifers. Final 

geometry of formations may be such that rocks of very different properties are now juxtaposed (i.e., a Paleozoic 

carbonate scarp). 

Water-level Elevation and Groundwater Flow Direction – Water-level data are abundant for Yucca Flat, as a 

result of more than 40 years of drilling in the area in support of the weapons testing program. However, 

water-level data for the surrounding areas are scarce. These data are listed in the potentiometric data package 

prepared for the UGTA regional-scale groundwater model (Hale et al., 1995; IT, 1996b) and in the more recent 

Yucca Flat-CAU–specific data reports (Fenelon, 2005; SNJV, 2006b). 

The SWL in the Yucca Flat basin is relatively deep, ranging in depth from about 183 m (600 ft) in extreme 

western Yucca Flat to more than 580 m (1,900 ft) in north-central Yucca Flat (Hale et al., 1995; Laczniak et al., 

1996). Elevation of the water table in Yucca Flat varies from 1,340 m (4,400 ft) in the north (western Emigrant 

Valley) to 730 m (2,400 ft) at the southern end of Yucca Flat (Hale et al., 1995; Laczniak et al., 1996; Fenelon, 

2005). Throughout much of the Yucca Flat area, the SWL typically is located within the lower portion of the 

volcanic section, in the LTCU and OSBCU. Beneath the hills surrounding Yucca Flat, the SWL can be within the 

Paleozoic-age units, while in the deeper structural subbasins of Yucca Flat, the Timber Mountain Tuff and the 

lower portion of the alluvium are also saturated. 

Water levels measured in wells completed in the AA and volcanic units in the eastern two-thirds of Yucca Flat are 

typically about 20 m (70 ft) higher than in wells completed in the LCA (Winograd and Thordarson, 1975; IT, 

1996b; Fenelon, 2005; SNJV, 2006b). The hydrogeology of these units suggests that the higher elevation of the 

water table in the overlying Tertiary rocks is related to the presence of low permeability zeolitized tuffs of the 
Attachment A: Nevada Test Site Description

ATT A-26 Nevada Test Site Environmental Report 2009

LTCU and OSBCU (aquitard) between the Paleozoic and Tertiary aquifers (SNJV, 2006b). Detailed water-level 

data indicate the existence of a groundwater trough along the axis of the valley. The semi-perched water within 

the AA and volcanic aquifers eventually moves downward to the carbonate aquifer in the central portion of the 

valley. Water-level elevations in western Yucca Flat are also well above the regional water level. The hydrology 

of western Yucca Flat is influenced by the presence of the Mississippian clastic rocks, which directly underlie the 

carbonate aquifer of the upper plate of the CP thrust (locally present), AA, and volcanic rocks west of the 

Topgallant fault. This geometry is a contributing factor in the development of higher (semi-perched) water levels 

in this area. The Climax Stock also bears perched water (Walker, 1962; Laczniak et al., 1996) well above the 

regional water level. 

The present structural interpretation for Yucca Flat depicts the LCCU at great depth, except in the northeast 

corner of the study area. The Zabriskie Quartzite and Wood Canyon Formation, which are both classified as 

clastic confining units, are exposed in the northern portion of the Halfpint Range. The high structural position of 

the LCCU there (and in combination with the Climax Stock) may be responsible for the steep hydrologic gradient 

observed between western Emigrant Valley and Yucca Flat. 

Based on the existing data and as interpreted from the UGTA regional-scale groundwater flow model 

(DOE/NV, 1997), the overall groundwater flow direction in Yucca Flat is to the south and southwest (Hershey 

and Acheampong, 1997; see Figure A-5). Groundwater ultimately discharges at Ash Meadows and Alkali Flat to 

the south and Death Valley to the southwest. 

A.2.5.3 Pahute Mesa Underground Test Area 

This section provides descriptions of the geologic and hydrologic settings of the Pahute Mesa UGTA. This 

summary was compiled from various sources, including Winograd and Thordarson (1975), Byers et al. (1976; 

1989), Laczniak et al. (1996), Cole (1997), and BN (2002b). Additional information can be found in 

these documents. For detailed stratigraphic descriptions, see Sawyer et al. (1994) and Slate et al. (1999). 

The Western and Central Pahute Mesa CAUs, encompassing Areas 19 and 20 of the NTS, were the site of 

85 underground nuclear tests (DOE/NV, 2000) (see Figure A-6). These detonations were all conducted in vertical 

emplacement holes (see Table A-5). The Western Pahute Mesa CAU is separated from the Central Pahute Mesa 

CAU by the Boxcar fault and is distinguished by a relative abundance of tritium (DOE/NV, 1999). For 

hydrogeologic studies and modeling purposes, these two CAUs are treated together. 

Hydrogeologically, these CAUs are considered to be part of a larger region that includes areas both within and 

outside the boundaries of the NTS, designated as the Pahute Mesa-Oasis Valley (PM-OV) study area. Because 

most of the underground nuclear tests at Pahute Mesa were conducted near or below the SWL, test-related 

contaminants are available for transport via a groundwater flow system that may extend to discharge areas in 

Oasis Valley. So, like the UGTAs of Frenchman Flat and Yucca Flat, a CAU-scale hydrostratigraphic framework 

model (BN, 2002b) has been developed for the PM-OV study area to support modeling of groundwater flow and 

contaminant transport for the UGTA Sub-Project (SNJV, 2006c; 2009). 

Physiography – Pahute Mesa is a structurally high volcanic plateau in the northwest corner of the NTS 

(see Figure A-2). Ground-level elevations in the area range from below 1,650 m (5,400 ft) off the mesa to the 

north and south, to over 2,135 m (7,000 ft) in eastern Pahute Mesa. Pahute Mesa proper is composed of 

flat-topped buttes and mesas separated by deep canyons. This physiographic feature covers most of NTS Areas 19 

and 20, which are the second-most used testing real estate at the NTS. Consequently, there are numerous drill 

holes that provide a substantial amount of subsurface geologic and hydrologic information (Warren et al., 2000a; 

2000b; BN, 2002b). 

Geology Overview – Borehole and geophysical data from Pahute Mesa indicate the presence of several nested 

calderas that produced thick sequences of rhyolite tuffs and lavas. The older calderas are buried by ash-flow units 

produced from younger calderas. Most of eastern Pahute Mesa is capped by the voluminous Ammonia Tanks and 

Rainier Mesa ash-flow tuff units, which erupted from the Timber Mountain Caldera (11.45 and 11.6 Ma, 
 Attachment A: Nevada Test Site Description

Nevada Test Site Environmental Report 2009 ATT A-27

respectively), located immediately to the south of Pahute Mesa (Byers et al., 1976). The western portion is capped 

by ash-flows of the Thirsty Canyon Group from the Black Mountain caldera (9.4 Ma). A typical geologic cross 

section for Pahute Mesa is presented in Figure A-9. For a more detailed geologic summary, see Ferguson et al. 

(1994), Sawyer et al. (1994), Warren et al. (2000b), and BN (2002b). 

The most widespread and significant Quaternary and Tertiary (mainly volcanic) units of the Pahute Mesa area are 

included in Table A-1. Refer to Table A-2 for a list of Mesozoic (granitic), Paleozoic (sedimentary), and 

Precambrian (sedimentary and metamorphic) stratigraphic units. 

Underlying the Tertiary-age volcanic rocks (exclusive of the caldera complexes) are Paleozoic and Proterozoic 

sedimentary rocks consisting of dolomite, limestone, quartzite, and argillite. During Precambrian and Paleozoic 

time, as much as 10,000 m (32,800 ft) of these marine sediments were deposited in the NTS region (Cole, 1997). 

For detailed stratigraphic descriptions of these rocks, see Slate et al. (1999). The only occurrence of Mesozoic age 

rocks in the Pahute Mesa area is the Gold Meadows Stock, a granitic intrusive mass located at the eastern edge of 

Pahute Mesa, north of Rainier Mesa (Gibbons et al., 1963; Snyder, 1977). 

The Silent Canyon caldera complex (SCCC) lies beneath Pahute Mesa. This complex contains the oldest known 

calderas within the SWNVF, and is completely buried by volcanic rocks erupted from younger nearby calderas. It 

was first identified from gravity observations that indicated a deep basin below the topographically high Pahute 

Mesa. Subsequent drilling on Pahute Mesa indicated that the complex consists of at least two nested calderas, the 

Grouse Canyon caldera and younger Area 20 caldera (13.6 and 13.1 Ma, respectively) (Sawyer et al., 1994). For 

more information on the SCCC, see Ferguson et al. (1994), which is a comprehensive study of the caldera 

complex based on analysis of gravity, seismic refraction, drill hole, and surface geologic data. 

Like the SCCC, the Timber Mountain caldera complex (TMCC) consists of two nested calderas: the Rainier Mesa 

caldera and younger Ammonia Tanks caldera, 11.6 and 11.45 Ma, respectively (Sawyer et al., 1994). However, 

unlike the SCCC, the TMCC has exceptional topographic expression, consisting of an exposed topographic 

margin for more than half its circumference and a well exposed central resurgent dome (Timber Mountain, the 

most conspicuous geologic feature in the western part of the NTS). The complex truncates the older Claim 

Canyon caldera (12.65 Ma) (Sawyer et al., 1994), which is farther to the south. The calderas of the TMCC are the 

sources for the Rainier Mesa and Ammonia Tanks Tuffs, which form important and extensive stratigraphic units 

at the NTS and vicinity. 

The Black Mountain caldera is a relatively small caldera in the northwest portion of the Pahute Mesa area. It is the 

youngest caldera in the area, formed as a result of the eruption, 9.4 Ma, of tuffs assigned to the Thirsty Canyon 

Group (Sawyer et al., 1994). 

Deep gravity lows and the demonstrated great thickness of tuffs in the Pahute Mesa area suggest the presence of 

older buried calderas. These calderas would pre-date the Grouse Canyon caldera and, thus, could be the source of 

some of the pre-Belted Range units. 

Structural Setting – The structural setting of the Pahute Mesa area is dominated by the calderas described in the 

previous paragraphs. Several other structural features are considered to be significant factors in the hydrology, 

including the Belted Range thrust fault (see Section A.1.3), numerous normal faults related mainly to basin-andrange extension, and transverse faults and structural zones. However, many of these features are buried, and their 

presence is inferred from drilling and geophysical data. A typical geologic cross section for Pahute Mesa is 

presented in Figure A-9. For a more detailed geologic summary, see Ferguson et al. (1994); Sawyer et al. (1994); 

and BN (2002b). 
ATT A-28 

Nevada Test Site Environmental Report 2009 See Section A.2.3.2 of this attachment for definitions o

1.5 x vertical exaggeration Figure A-9. Generalized hydrostratigraphic cross section through the Silent Canyon complex, Pahute Mesa 
 Attachment A: Nevada Test Site Description

Nevada Test Site Environmental Report 2009 ATT A-29

Hydrogeology Overview – The hydrogeology of Pahute Mesa is complex. The thick section of volcanic rocks 

comprises a wide variety of lithologies that range in hydraulic character from aquifer to aquitard. The presence of 

several calderas and tectonic faulting further complicate the area, placing the various lithologic units in 

juxtaposition and blocking or enhancing the flow of groundwater in a variety of ways. 

The general hydrogeologic framework for Pahute Mesa and vicinity was established in the early 1970s by 

U.S. Geological Survey geoscientists (Blankennagel and Weir, 1973; Winograd and Thordarson, 1975). As 

described in Section A.2.3, their work has provided the foundation for most subsequent hydrogeologic studies at 

the NTS (IT, 1996a; BN, 2002b). 

All the rocks in the PM-OV study area can be classified as one of nine HGUs, which include the AA, four 

volcanic HGUs, two intrusive units, and two HGUs that represent the pre-Tertiary rocks (see Table A-3). 

The rocks within the PM-OV study area are grouped into 44 HSUs for the UGTA CAU-scale hydrogeology 

framework model (Table A-8; BN, 2002b). The volcanic units are organized into 37 HSUs that include 13 

aquifers, 13 confining units, and 11 composite units (comprising a mixture of hydraulically variable units). The 

underlying pre-Tertiary rocks are divided into six HSUs, including two aquifers and four confining units. HSUs 

that are common to several CAUs at the NTS are briefly discussed in Section A.2.3.2. 

Table A-8. Hydrostratigraphic units of the Pahute Mesa-Oasis Valley area 

Hydrostratigraphic Unit 

(Symbol) 

Dominant Hydrogeologic 

Unit(s)(a) Typical Lithologies 

Alluvial Aquifer (AA) AA Alluvium (gravelly sand); also includes eolian sand 

Younger Volcanic Composite Unit 

(YVCM) LFA, WTA, VTA Basalt, welded and nonwelded ash-flow tuff 

Thirsty Canyon Volcanic Aquifer 

(TCVA) WTA, LFA, lesser VTA Partially to densely welded ash-flow tuff; vitric to 

devitrified 

Detached Volcanics Composite Unit 

(DVCM) WTA, LFA, TCU Complex distribution of welded ash-flow tuff, lava, 

and zeolitic bedded tuff 

Fortymile Canyon Composite Unit 

(FCCM) LFA, TCU, lesser WTA Lava flows and associated tuffs 

Timber Mountain Composite Unit 

(TMCM) 

TCU (altered tuffs, lavas) and 

unaltered WTA and lesser LFA

Densely welded ash-flow tuff; includes lava flows, 

and minor debris flows 

Tannenbaum Hill Lava-Flow Aquifer 

(THLFA) LFA Rhyolitic lava 

Tannenbaum Hill Composite Unit 

(THCM) Mostly TCU lesser WTA Zeolitic tuff and vitric, nonwelded to welded ash-flow tuffs 

Timber Mountain Aquifer 

(TMA) Mostly WTA, minor VTA Partially to densely welded ash-flow tuff; vitric to devitrified 

Subcaldera Volcanic Confining Unit 

(SCVCU) TCU Probably highly altered volcanic rocks and intruded sedimentary rocks beneath each caldera 

Fluorspar Canyon Confining Unit 

(FCCU) TCU Zeolitic bedded tuff 

Windy Wash Aquifer (WWA) LFA Rhyolitic lava 

Paintbrush Composite Unit 

(PCM) WTA, LFA, TCU Welded ash-flow tuffs, rhyolitic lava and minor 

associated bedded tuffs 

Paintbrush Vitric-tuff Aquifer (PVTA) VTA Vitric, nonwelded and bedded tuff 

Benham Aquifer (BA) LFA Rhyolitic lava 
Attachment A: Nevada Test Site Description

ATT A-30 Nevada Test Site Environmental Report 2009

Table A-8. Hydrostratigraphic units of the Pahute Mesa-Oasis Valley area (continued) 

Hydrostratigraphic Unit 

(Symbol) 

Dominant Hydrogeologic 

Unit(s)(a) Typical Lithologies 

Upper Paintbrush Confining Unit 

(UPCU) 

TCU Zeolitic, nonwelded and bedded tuff 

Tiva Canyon Aquifer (TCA) WTA Welded ash-flow tuff 

Paintbrush Lava-Flow Aquifer 

(PLFA) 

LFA Lava; moderately to densely welded ash-flow tuff 

Lower Paintbrush Confining Unit 

(LPCU) 

TCU Zeolitic nonwelded and bedded tuff 

Topopah Spring Aquifer 

(TSA) 

WTA Welded ash-flow tuff 

Yucca Mountain Crater Flat Composite Unit

(YMCFCM) 

LFA, WTA, TCU Lava; welded ash-flow tuff; zeolitic, bedded tuff 

Calico Hills Vitric-tuff Aquifer 

(CHVTA) 

VTA Vitric, nonwelded tuff 

Calico Hills Vitric Composite Unit 

(CHVCM) 

VTA, LFA Partially to densely welded ash-flow tuff; vitric to 

devitrified 

Calico Hills Zeolitized 

Composite Unit (CHZCM) 

LFA, TCU Rhyolitic lava and zeolitic nonwelded tuff 

Calico Hills Confining Unit 

(CHCU) 

Mostly TCU, minor LFA Zeolitic nonwelded tuff; minor lava 

Inlet Aquifer 

(IA) 

LFA Lava 

Crater Flat Composite Unit 

(CFCM) 

Mostly LFA, intercalated with 

TCU 

Lava and welded ash-flow tuff 

Crater Flat Confining Unit 

(CFCU) 

TCU Zeolitic nonwelded and bedded tuff 

Kearsarge Aquifer 

(KA) 

LFA Lava 

Bullfrog Confining Unit 

(BFCU) 

TCU Zeolitic, nonwelded tuff 

Belted Range Aquifer 

(BRA) 

LFA and WTA, with lesser 

TCU 

Lava and welded ash-flow tuff 

Pre-Belted Range Composite Unit 

(PBRCM) 

TCU, WTA , LFA Zeolitic bedded tuffs with interbedded but less 

significant zeolitic, nonwelded to partially welded 

ash-flow tuffs 

Black Mountain Intrusive Confining Unit 

(BMICU) 

IICU 

Ammonia Tanks Intrusive Confining Unit 

(ATICU) 

IICU 

Rainier Mesa Intrusive Confining Unit 

(RMICU) 

IICU 

Claim Canyon Intrusive Confining Unit 

(CCICU) 

IICU 

Calico Hills Intrusive Confining Unit 

(CHICU) 

IICU 

Silent Canyon Intrusive Confining Unit 

(SCICU) 

IICU 

These units are presumed to be present beneath the 

calderas of the SWNVF. Their actual character is 

unknown, but they may be igneous intrusive rocks 

or older volcanic and pre-Tertiary sedimentary rocks 

intruded to varying degrees by igneous rocks. 
 Attachment A: Nevada Test Site Description

Nevada Test Site Environmental Report 2009 ATT A-31

Table A-8. Hydrostratigraphic units of the Pahute Mesa-Oasis Valley area (continued) 

Hydrostratigraphic Unit 

(Symbol) 

Dominant Hydrogeologic 

Unit(s)(a) Typical Lithologies 

Mesozoic Granite Confining Unit 

(MGCU) 

GCU Granodiorite and quartz monzonite; Gold Meadows 

Stock 

Lower Carbonate Aquifer-Thrust Plate 

(LCA3) 

CA Limestone and dolomite 

Lower Clastic Confining Unit Thrust Plate 

(LCCU1) 

CCU Quartzite and siltstone 

Upper Clastic Confining Unit 

(UCCU) 

CCU Argillite and quartzite 

Lower Carbonate Aquifer 

(LCA) 

CA Dolomite and limestone; “regional aquifer” 

Lower Clastic Confining Unit 

(LCCU) 

CCU Quartzite and siltstone; “hydrologic basement” 

(a) See Table A-3 for definitions of HGUs. 

Note: Adapted from BN, 2002c. 

Water-level Elevation and Groundwater Flow Direction – Water-level data are relatively abundant for the 

Pahute Mesa UGTA as a result of more than 30 years of drilling in the area in support of the weapons testing 

program. However, water-level data for the outlying areas to the west and south are sparse. These data are listed 

in the potentiometric data package prepared for the UGTA regional-scale groundwater flow model (IT, 1996b), 

the Pahute Mesa water table map (O’Hagan and Laczniak, 1996), and recent work in support of flow modeling 

(SNJV, 2004b; 2006c). 

The SWL at Pahute Mesa is relatively deep, at about 640 m (2,100 ft) below the ground surface. Groundwater 

flow at Pahute Mesa is driven by recharge in the east and subsurface inflow from the north. Local groundwater 

flow is influenced by the discontinuous nature of the volcanic aquifers and the resultant geometry created by 

overlapping caldera complexes and high-angle basin and range faults (Laczniak et al., 1996). Potentiometric data 

indicate that groundwater flow direction is to the southwest toward discharge areas in Oasis Valley and, 

ultimately, Death Valley (see Figure A-5). 

A.2.5.4 Rainier Mesa/Shoshone Mountain 

The Rainier Mesa/Shoshone Mountain CAU consists of 61 CASs on Rainier Mesa and 6 CASs on Shoshone 

Mountain, which are located in NTS Areas 12 and 16, respectively (see Figure A-6). Together, these two mesas 

constitute the third major area used for underground testing of nuclear weapons at the NTS between 1957 and 

1992. Underground nuclear tests were conducted in horizontal, mined tunnels within these mesas, and two tests 

were conducted in vertical drill holes. All tests were conducted above the regional water table. Underground 

geologic mapping data from the six large and several smaller tunnel complexes, and lithologic and geophysical 

data from dozens of exploratory drill holes, provide a wealth of geologic and hydrologic information for this 

relatively small underground test area. 

Physiography – The Rainier Mesa underground test area includes Rainier Mesa proper and the contiguous 

Aqueduct Mesa. Rainier Mesa and Aqueduct Mesa form the southern extension of the northeast trending Belted 

Range (see Figure A-2). This high volcanic plateau cuts diagonally across Area 12 in the north-central portion of 

the NTS. Ground-level elevations on Rainier Mesa are generally over 2,225 m (7,300 ft). The highest point on the 

NTS, 2,341 m (7,679 ft), is on Rainier Mesa. Aqueduct Mesa has slightly rougher and lower terrain, generally 

above 1,920 m (6,300 ft) in elevation. The edges of the mesas drop off quite spectacularly on the west, south, and 

east sides. 

Shoshone Mountain is located about 20 km (12 mi) south of Rainier Mesa. It is located in the middle of the NTS, 

southwest of Syncline Ridge (see Figures A-2 and A-6). Ground-level elevations range from 1,707 to 2,012 m 
Attachment A: Nevada Test Site Description

ATT A-32 Nevada Test Site Environmental Report 2009

(5,600 to 6,600 ft) but are generally above 1,830 m (6,000 ft). Tippipah Point, above the old Area 16 tunnels, 

has an elevation of 2,015 m (6,612 ft). 

Geology Overview – Both Rainier Mesa and Aqueduct Mesa are composed of Miocene-age ash-fall and ash-flow 

tuffs that erupted from nearby calderas to the west and southwest (NSTec, 2007). As in Yucca Flat, these silicic 

volcanic tuffs were deposited unconformably on an irregular pre-Tertiary (upper Precambrian and Paleozoic age) 

surface of sedimentary rocks (Gibbons et al., 1963; Orkild, 1963) and Mesozoic granitic rocks (at Rainier Mesa 

only). The stratigraphic units and lithologies are similar to those present in the subsurface of Yucca Flat (see 

Section A.2.5.2). The tunnel complexes used for underground nuclear testing at Rainier Mesa and Shoshone 

Mountain were mined in zeolitized bedded tuff, though the upper part of this section is unaltered (vitric) in some 

areas. At both locations, the bedded tuffs are capped by a thick layer of welded ash-flow tuff. The Tertiary 

stratigraphic units and lithologies are similar to those present in the subsurface of Yucca Flat 

(see Section A.2.5.2). 

Structural Setting – The geologic structure of the volcanic rocks of the Rainier Mesa is well documented. 

Several high-angle, normal faults have been mapped in the volcanic rocks. Faults with greater than about 30 m 

(100 ft) of displacement are notably absent in the volcanic rocks of Rainier Mesa. The Rainier and Aqueduct 

Mesa area was minimally extended during Basin and Range tectonism, thus accounting for the absence of larger 

faults and its relatively high elevation (NSTec, 2007). At Shoshone Mountain several faults have been mapped, 

but in general the structure is less well known there than at Rainier Mesa. The structure of the pre-Tertiary section 

at both locations is poorly known, though most workers agree on the framework in general, and that the trace of 

the Belted Range thrust fault is present in the pre-Tertiary rocks beneath Rainier Mesa. A broad synclinal feature 

mapped at the surface and in the tuffs of Rainier Mesa and Aqueduct Mesa roughly overlies the postulated 

location of the Belted Range thrust fault. It may reflect a paleo-topographic low or valley beneath the tuffs (Figure 

A-10), but the exact character of this feature is unknown. 

Figure A-10. Generalized hydrostratigraphic cross section through Aqueduct Mesa 

Hydrogeology Overview – Construction of UGTA CAU-scale hydrogeology model for the Rainier Mesa and 

Shoshone Mountain UGTAs was completed in 2007 (NSTec, 2007). All the rocks in the Rainier Mesa-Shoshone 

Mountain (RM-SM) study area can be classified as one of nine HGUs, which include the AA, four volcanic 

HGUs, two intrusive units, and two HGUs that represent the pre-Tertiary rocks (see Table A-3). The geologic 

units within the RM-SM model area are grouped into 44 HSUs (NSTec, 2007). There are 30 Tertiary-age HSUs, 

including the Tertiary/Quaternary alluvium, older paleocolluvium, two caldera-related collapse breccias, five 

caldera-related intrusives, one Mesozoic intrusive HSU, and six Paleozoic/Precambrian HSUs. HSUs identified in 

the RM-SM CAU are listed in Table A-9. 
 Attachment A: Nevada Test Site Description

Nevada Test Site Environmental Report 2009 ATT A-33

The hydrostratigraphy for the Tertiary-age volcanic rocks in the former UGTAs (Rainier Mesa, Aqueduct Mesa, 

and Shoshone Mountain) can be simplified into two categories: zeolitic, tuff confining units and (nonzeolitic) 

volcanic aquifers. Except for a few nomenclature complications due to embedded welded tuff aquifers, the TCUs 

belong to either the LTCU or the OSBCU HSU (similar to the hydrostratigraphic section in Yucca Flat, see 

Subsection A.2.5.2). The LTCU and OSBCU are important HSUs as they separate the UGTs from the underlying 

regional aquifer. 

The hydrostratigraphy of the pre-Tertiary section at Shoshone Mountain is surmised from a single deep drill hole, 

Well ER-16-1 (U.S. Department of Energy, National Nuclear Security Administration Nevada Site Office 

[NNSA/NSO], 2006a), and from surficial geology (Orkild, 1963). From oldest to youngest, the hydrogeologic 

section for the Shoshone Mountain UGTA consists of the regional carbonate aquifer, the upper clastic confining 

unit, tuff confining units, vitric-tuff aquifers, and welded-tuff aquifers at the surface (Figure A-11). At Rainier 

Mesa, granitic rocks (granite confining unit [GCU], related to the nearby Gold Meadows Stock), carbonate rocks 

(carbonate aquifer [CA]), silicic sedimentary rocks such as siltstone, and metamorphic rocks such as quartzite and 

schist (clastic confining units [CCUs]) have been encountered beneath the tuff section in the few existing drill 

holes that penetrate through the tuff section. This variability is indicative of the complex geology of the preTertiary section, which is a consequence of the Gold Meadows intrusive and the Belted Range thrust fault. 

Most of the tests in Shoshone Mountain and Rainier Mesa tunnels were conducted in the TCU, though a few were 

conducted in vitric bedded tuff higher in the stratigraphic section. 

Table A-9. Hydrostratigraphic units of the Rainier Mesa-Shoshone Mountain area 

Hydrostratigraphic Unit 

(Symbol)

Dominant 

Hydrogeologic 

Units (a) Typical Lithologies

Alluvial aquifer (AA) AA Alluvium: Gravelly sand; also includes colluvium and older 

moat-filling sediments around the Timber Mountain caldera

Fortymile Canyon Composite Unit 

(FCCM)

LFA, TCU, lesser WTA Lava flows, lesser ash-flow and bedded tuffs

Timber Mountain Upper Vitric-Tuff 

Aquifer (TM-UVTA)

VTA, 

minor WTA

Includes vitric nonwelded to partially welded ash-flow and 

bedded tuff

Timber Mountain Welded-Tuff Aquifer 

(TM-WTA)

WTA 

minor VTA

Partially to densely welded ash-flow tuff; vitric to devitrified, 

minor nonwelded tuff

Timber Mountain Lower Vitric-Tuff 

Aquifer (TM-LVTA)

VTA Nonwelded ash-flow and bedded tuff; vitric

Timber Mountain Composite Unit 

(TMCM)

TCU (altered tuffs, lavas) 

and unaltered WTA and 

lesser LFA

Welded ash-flow tuffs, lava flows 

Rainier Mesa Breccia Confining Unit 

(RMBCU)

TCU/AA Landslide breccias

Subcaldera Volcanic Confining Unit 

(SCVCU)

TCU Highly altered pre-Tm volcanic units

Tiva Canyon Aquifer (TCA) WTA Welded ash-flow tuff 

Paintbrush Vitric Tuff Aquifer (PVTA) VTA Bedded tuff, vitric 

Upper Tuff Confining Unit (UTCU) TCU Zeolitized bedded tuff 

Topopah Spring Aquifer (TSA) WTA minor VTA Welded ash-flow tuff 

Lower Vitric-Tuff Aquifer (LVTA) VTA Nonwelded and bedded tuff; vitric 

Calico Hills Vitric-Tuff Aquifer (CHVTA) VTA Nonwelded and bedded tuff; vitric 

Yucca Mountain Calico Hills Lava-Flow 

Aquifer (YMCHLFA) 

LFA Lava flow 
Attachment A: Nevada Test Site Description

ATT A-34 Nevada Test Site Environmental Report 2009

Table A-9. Hydrostratigraphic units of the Rainier Mesa-Shoshone Mountain area (continued) 

Hydrostratigraphic Unit 

 (Symbol)

Dominant 

Hydrogeologic 

Units (a) Typical Lithologies

Kearsarge Aquifer (KA) LFA Lava flow 

Upper Tuff Confining Unit 2 (UTCU2) TCU Zeolitized bedded tuff 

Stockade Wash Aquifer (SWA) WTA minor VTA Weakly welded ash-flow tuff 

Lower Vitric-Tuff Aquifer 2 (LVTA2) VTA Nonwelded and bedded tuff; vitric 

Bullfrog Confining Unit (BFCU) TCU Zeolitic nonwelded tuff 

Upper Tuff Confining Unit 1 (UTCU1) TCU Zeolitized bedded tuff 

Belted Range Aquifer (BRA) LFA and WTA Lava and welded ash-flow tuff 

Lower Vitric Tuff Aquifer 1 (LVTA1) VTA Bedded tuff; vitric 

Belted Range Confining Unit (BRCU) TCU Zeolitized bedded tuff 

Tub Spring Aquifer (TUBA) WTA Welded ash-flow tuff 

Lower Tuff Confining Unit 

(LTCU) 

TCU Zeolitized bedded tuffs with interbedded but less significant 

zeolitized, nonwelded to partially welded ash-flow tuffs 

Oak Spring Butte Confining Unit 

(OSBCU) 

TCU Devitrified to zeolitic non- to partially welded tuffs and 

intervening bedded tuffs 

Redrock Valley Aquifer (RVA) WTA Welded ash-flow tuff, devitrified 

Redrock Valley Breccia Confining Unit 

(RVBCU) 

TCU/AA Landslide breccias 

Lower Tuff Confining Unit 1 (LTCU1) TCU Zeolitized bedded tuffs 

Twin Peaks Aquifer (TPA) WTA Welded ash-flow tuff 

Argillic Tuff Confining Unit (ATCU) TCU Argillic bedded tuffs, minor paleocolluvium 

Ammonia Tanks Intrusive Confining Unit 

(ATICU)

IICU Intrusive (granite?) and altered, older host rocks

Rainier Mesa Intrusive Confining Unit 

(RMICU)

IICU Intrusive (granite?) and altered, older host rocks

Calico Hills Intrusive Confining Unit 

(CHICU)

IICU Intrusive (granite?) and altered, older host rocks

Silent Canyon Intrusive Confining Unit 

(SCICU)

IICU Highly altered older volcanic rocks and pre-Tertiary 

sedimentary rocks and granitic intrusive masses.

Redrock Valley Intrusive Confining Unit 

(RVICU)

IICU Highly altered injected/intruded country rock and granitic 

material

Mesozoic Granite Confining Unit 

(MGCU)

GCU Granodiorite and quartz monzonite

Lower Clastic Confining Unit - Upper 

Thrust Plate (LCCU1)

CCU Quartzite and siltstone

Lower Carbonate Aquifer - Upper Thrust 

Plate (LCA3)

CA Limestone and dolomite

Upper Carbonate Aquifer (UCA) CA Limestone

Upper Clastic Confining Unit (UCCU) CCU Argillite and quartzite

Lower Carbonate Aquifer (LCA) CA Dolomite and limestone

Lower Clastic Confining Unit (LCCU) CCU Quartzite and siltstone 

(a) See Table A-3 for definitions of hydrogeologic units. 

Note: Adapted from NSTec (2007). 
 Attachment A: Nevada Test Site Description

Nevada Test Site Environmental Report 2009 ATT A-35

Figure A-11. West-east hydrogeologic cross section through Well ER-16-1 

Water-level Elevation and Groundwater Flow Direction – Only a few boreholes on or in the vicinity of 

Rainier Mesa are deep enough to tag the regional water table. Most notable are UGTA Wells ER-12-3 

(NNSA/NSO, 2006b) and ER-12-4 (NNSA/NSO, 2006c) located on Rainier Mesa and Aqueduct Mesa, 

respectively. The water levels in these wells are 949 m (3,114 ft) at ER-12-3 and 786 m (2,580 ft) at ER-12-4, or 

1,302 m (4,271 ft) and 1,312 m (4,304 ft) elevation, respectively, in the Paleozoic-age carbonate rocks (LCA3) 

that underlie the volcanic section (Fenelon, 2007). This is approximately 300 m (1,000 ft) below the average 

elevation of test locations in Rainier Mesa. The SWL, where measured in volcanic units at Rainier Mesa, is at an 

elevation of about 1,847 m (6,060 ft). This anomalously high water level relative to the regional water level 

reflects the presence of water perched above the regional aquifer within the tuff confining unit (Walker, 1962; 

Laczniak et al., 1996; Fenelon et al., 2008). Water is present in the fracture systems of some of the tunnel 

complexes at Rainier Mesa. This water currently is permitted to flow from U12e Tunnel (also known as 

E Tunnel); however, water has filled the open drifts behind barriers built near the portals of U12n and U12t 

Tunnels. 

The water level at Shoshone Mountain was measured at 1,248 m (4,093 ft) true vertical depth, or 761.7 m (2,499 

ft) elevation, at UGTA Well ER-16-1 (NNSA/NSO, 2006a) in the Paleozoic-age carbonate rocks (LCA). This is 

the deepest water-level tag at the NTS. No water was encountered during mining at Shoshone Mountain. 

Regional groundwater flow from Rainier Mesa may be directed either toward Yucca Flat or, because of the 

intervening UCCU, to the south toward the Alkali Flat discharge area (Fenelon et al., 2008; see Figure A-5). The 

groundwater flow direction beneath Shoshone Mountain is probably southward. 
Attachment A: Nevada Test Site Description

ATT A-36 Nevada Test Site Environmental Report 2009

A.2.6 Conclusion 

The hydrogeology of the NTS and vicinity is complex and varied. Yet, the remote location, alluvial and volcanic 

geology, and deep water table of the NTS provided a favorable setting for conducting and containing underground 

nuclear tests. Its arid climate and its setting in a region of closed hydrographic basins also are factors in stabilizing 

residual surficial contamination from atmospheric testing, and are considered positive environmental attributes for 

existing radioactive waste management sites. 

Average groundwater flow velocities at the NTS are generally slow, and flow paths to discharge areas or potential 

receptors (domestic and public water supply wells) are long. The water tables for local aquifers in the valleys and 

the underlying regional carbonate aquifer are relatively flat. The zeolitic volcanic rocks (TCU) separating the 

shallower alluvial and volcanic aquifers and the regional carbonate aquifer (LCA) appears to be a viable aquitard 

(non-aquifer). Consequently, both vertical and horizontal flow velocities are low. Additionally, carbon-14 dates 

for water from NTS aquifers are on the order of 10,000 to 40,000 years old (Rose et al., 1997). Thus, there is 

considerable residence time in the aquifers, allowing contaminant attenuating processes such as matrix diffusion, 

sorption, and natural decay of radioactive isotopes to operate. 

A.3 Climatology 

The NTS is located in the extreme southwestern corner of the Great Basin. Consequently, the climate is arid, with 

limited precipitation, low humidity, intense sunlight, and large daily temperature ranges. Meteorological and 

climatological data are collected on the NTS by the Air Resources Laboratory, Special Operations and Research 

Division. Data are collected through the Meteorological Data Acquisition (MEDA) system, a network of 

approximately 30 mobile meteorological towers, which have been located on and near the NTS for many years 

(see Chapter 16 of the main document, Figure 16-2). The climatological data presented below were developed 

from the MEDA system. 

A.3.1 Precipitation 

Two fundamental physical processes drive precipitation events on the NTS: those resulting from cool-season, 

mid-tropospheric cyclones and those resulting from summertime convection. Cool-season precipitation is usually 

light and can consist of rain or snow. Although light, winter precipitation events can last for several days and 

result in significant precipitation totals per winter storm, especially in January and February. Summer is 

thunderstorm season. Precipitation from thunderstorms is usually light; however, some storms are associated with 

very heavy rain, flash floods, intense cloud-to-ground (CG) lightning, and strong surface winds. Thunderstorms 

generally occur in July and August when moist tropical air can flow from the southeastern North Pacific Ocean 

and spread over the desert southwest. This seasonal event is referred to as the southwestern monsoon. The wintersummer precipitation mechanisms produce a bimodal monthly precipitation cycle. Figure A-12 shows these 

patterns of mean monthly precipitation recorded from 6 of the 16 climatological stations on the NTS over the past 

40+ years. Mean annual precipitation totals on the NTS range from nearly 32 centimeters (cm) (12.55 inches [in.]) 

over the high terrain in the northwestern part of the NTS to less than 12.7 cm (5 in.) in Frenchman Flat. However, 

inter-annual variations can be great. For example, 24.6 cm (9.67 in.) occurred in Frenchman Flat in 1998 and 68.2 

cm (26.87 in.) fell on Rainier Mesa in 1983. Annual totals of less than 2.54 cm (1.0 in.) have occurred on the 

lower elevations of the NTS. Daily precipitation totals can also be large and can range from 5 to just over 9 cm (2 

to over 3.5 in.). The greatest daily precipitation event on the NTS was 11.89 cm (4.68 in.), which was measured in 

Jackass Flats on September 26–27, 2007. A storm-total precipitation amount of 8.9 cm (3.5 in.) is a 100-year, 24-

hour, extreme precipitation event. Daily totals of 5.1 to 7.6 cm (2 to 3 in.) have been measured at several sites on 

the NTS (Randerson, 1997). 

Snow can fall on the NTS anytime between October and May. In Yucca Flat, the greatest daily snow depth 

measured is 25.4 cm (10 in.) in January 1974. The greatest daily depth measured at Desert Rock is 15.2 cm (6 in.) 

in February 1987. Maximum daily totals of 38 to 50 cm (15 to 20 in.) or more can occur on Pahute and Rainier 

Mesas. Hail, sleet, freezing rain, and fog are rare on the NTS. Only 24 hailstorms were observed in Yucca Flat 

between 1957 and 1978. Hail and sleet can cover the ground briefly following intense thunderstorms. 
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Figure A-12. Mean monthly precipitation at six NTS MEDA stations 
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A.3.2 Temperature 

As is typical of an arid climate, the NTS experiences large daily, as well as annual, ranges in temperature. 

Moreover, temperatures vary with elevation. Sites 1,524 m (5,000 ft) above mean sea level can be quite cold in 

the winter and fairly mild during the summer months. At lower elevations, summertime temperatures frequently 

exceed 37.7 degrees Celsius (oC) (100 degrees Fahrenheit [oF]). On the dry lakebeds, daily temperature ranges can 

be 22.2oC to 33.3oC (40oF to 60oF) with very cold morning temperatures in the winter and very hot temperatures 

in the summer. These temperature characteristics are clearly shown in Figure A-13. These annual temperature 

plots describe the temperature extremes and normal maximums and minimums throughout the year at different 

locations on the NTS. 

In Frenchman Flat (MEDA 5), the average daily temperature minimum and maximum for January is -4.8oC and 

13.2oC (23oF and 56oF), while in July it is 16.7oC and 38.7oC (62oF and 102oF). By contrast, on Rainier Mesa 

(MEDA 12), the minimum and maximum temperature for January is -4.5oC and 3.2oC (24oF and 38oF) and for 

July is 15.2oC and 26.4oC (59oF and 80oF). The highest maximum temperature measured on the NTS is 46.1oC 

(115oF) in Frenchman Flat near Well 5B in July 1998 and in Jackass Flats near Lathrop Gate in July 2002. The 

coldest minimum temperature measured on the NTS is 28.9oC (-20oF) in Area 19 in January 1970. The 

temperature extremes at Mercury are -11.7oC to 45oC (-11oF to 113oF). 

A.3.3 Wind 

Complex topography, such as that on the NTS, can influence wind speeds and directions. Furthermore, there is a 

seasonal as well as strong daily periodicity to local wind conditions. For example, in Yucca Flat, during the 

summer months, the wind direction is usually northerly (from the north) from 10 p.m. Pacific Daylight Time 

(PDT) to 8 a.m. PDT and southerly from 10 a.m. PDT to 8 p.m. PDT. However, in January, the winds are 

generally from the north from 6 p.m. Pacific Standard Time (PST) to 11 a.m. PST with some southerly winds 

developing between 11 a.m. PST and 5 p.m. PST. March through June tend to experience the fastest average wind 

speeds, 13 to 19 kilometers per hour (kph) (7 to 10 knots or 8 to 12 miles per hour [mph]), with the faster speeds 

occurring at the higher elevations. Peak wind gusts of 80 to 113 kph (43 to 61 knots or 50 to 70 mph) have 

occurred throughout the NTS. Peak winds at Mercury have been as high as 135 kph (73 knots or 84 mph) during a 

spring wind storm. During the same windstorm, Frenchman Flat experienced wind gusts to 113 kph (61 knots or 

70 mph). The peak wind speeds measured on the NTS are above 145 kph (78 knots or 90 mph) on the high terrain 

with maximums of 204 kph (110 knots or 127 mph) at Yucca Mountain Ridge-top (MEDA Station 24), and 185 

kph (100 knots or 115 mph) at MEDA Station 19 during a wind event on February 13, 2008. 

Wind speed and direction data have been summarized for all the meteorological towers (MEDAs) on the NTS. 

These climatological summaries are referred to as wind roses. Annual wind roses for 16 stations on the NTS for 

the years 1989 through 2009 are shown in Figure A-14. This figure describes the strong seasonal and diurnal 

effects on the surface air flow pattern across the NTS. In general, winter and pre-sunrise winds tend to be 

northerly, while summer and afternoon flow tends to be southerly. Terrain also contributes to determining wind 

direction. 

A.3.4 Relative Humidity 

The air over the NTS tends to be dry. On average, June is the driest month with humidity ranging from 10 to 35 

percent. Humidity readings of 35 to 70 percent are common in the winter. The reason for this variability is that 

relative humidity is temperature dependent. The relative humidity tends to be higher with cold temperatures and 

lower with hot temperatures. Consequently, there is not only a seasonal variation but also a marked diurnal 

rhythm with this parameter. Early in the morning the humidity ranges from 25 to 70 percent and in mid-afternoon 

it is in the 10- to 40-percent range, with the larger readings occurring in winter. Humidity readings of more than 

75 percent are not common on the NTS. 
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Figure A-13. Temperature extremes and normal maximums and minimums at six NTS MEDA stations (location 

of numbered stations are shown in Figure A-14) 
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Figure A-14. Twenty-year wind rose climatology for the NTS (1989–2009) 
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A.3.5 Atmospheric Pressure 

On the NTS, atmospheric pressure is measured at many of the sites shown in Chapter 16, Figure 16-2. These 

measurements show that atmospheric pressure has marked annual and diurnal cycles. In addition, pressure 

decreases with elevation. Consequently, stations at high elevations have lower atmospheric pressures than do 

stations at lower elevations. Moreover, because pressure depends on temperature, the larger pressure readings 

occur during the winter months and the smaller readings in the summer months. The diurnal cycle is bimodal: it is 

driven by the diurnal tide of the entire atmosphere and by the diurnal heating/cooling cycle. In general, maximum 

daily surface pressure on the NTS occurs between 8 and 10 a.m. PST (later in winter, earlier in summer), and 

minimum pressure tends to occur between 2 and 6 p.m. PST (earlier in winter, later in summer). Weaker 

secondary maxima occur at approximately midnight PST and minima near 3 a.m. PST. In Yucca Flat (elevation 

1,195 m [3,920 ft]), the atmospheric pressure varies from 857 to 908 millibars (mb), annually; however, the daily 

range is only approximately 3.4 mb in summer and 2.7 mb in winter. 

A phenomenon referred to as atmospheric or barometric pumping can occur as atmospheric pressure decreases. 

When this happens, gases trapped below ground can “vent” or seep upward through the soil and enter the 

atmosphere. Barometric pumping was observed on the NTS following some underground nuclear tests, and small 

concentrations of noble gases from the tests were detected for several months afterwards. Barometric pumping 

also contributes to the release of naturally occurring radionuclides (e.g., radon) from terrestrial sources. 

A.3.6 Dispersion Stability Categories 

Determination of the stability of the atmosphere near the ground is a key input requirement for atmospheric 

dispersion models. Such models are used to estimate the impacts of hazardous materials that might be accidentally 

released into the atmosphere or become airborne from radioactively contaminated soil sites on the NTS. The 

dispersion models commonly used for this purpose are Gaussian plume models that require the specification of 

stability categories to account for effects of atmospheric turbulence on the dispersion process. The mountainvalley topography on the NTS makes it impossible to calculate a single set of values that characterizes 

atmospheric turbulent mixing on the NTS. Consequently, the stability categories for the NTS are calculated from 

the average hourly wind speeds for each MEDA station, the solar angle, and the hourly cloud-cover observations 

reported at the Desert Rock Meteorological Observatory. This procedure follows regulatory guidance provided by 

the U.S. Environmental Protection Agency (EPA) (2000) and the American Nuclear Society (2005). The stability 

category concept makes use of the letters “A” through “F” to define different turbulence regimes. Category “A” 

specifies free convection in statistically unstable air, “D” represents neutral stability, and “F” is very stable 

(dispersion suppressed) with little turbulent mixing. In Yucca and Frenchman Flats, in winter, F-stability tends to 

persist from 4 p.m. PST until 8 a.m. PST the next morning with an abrupt transition to C- or B-stability near 9 

a.m. PST, followed by C- or B-stability during the afternoon. In summer, E- or F-stabilities occur between 7 p.m. 

PST and 6 a.m. the next morning with a rapid change to B-stability at 7 a.m. PST and, generally, C- or 

B-stabilities and some D-stability in late afternoon. 

A.3.7 Other Natural Phenomena 

Wind speeds in excess of 97 kph (60 mph) occur annually. Additional severe weather in the region includes 

occasional severe thunderstorms, lightning, hail, and dust storms. Severe thunderstorms may produce high 

precipitation rates that may create localized flash flooding. Few tornadoes have been observed in the region and 

are not considered a significant threat. 

CG lightning can occur throughout the year but occurs primarily between June and September. Maximum CG 

lightning activity on the NTS occurs between 1 p.m. and 4 p.m. PDT while minimum activity occurs between 

8 a.m. and 9 a.m. PDT. For safety analyses, the mean annual flash density on the NTS is 0.4 flashes per square 

kilometer. Randerson and Sanders (2002) have characterized CG lightning activity on the NTS. 
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A.4 Ecology 

The NTS lies on the transition between the Mojave and Great Basin deserts. As a result, elements of both deserts 

are found in a diverse and complex flora and fauna (Ostler et al., 2000; Wills and Ostler, 2001). 

A.4.1 Flora 

A total of 752 taxa of vascular plants have been collected in ten major vegetation alliances (Figure A-15). Twenty 

vegetation associations from among the alliances have been identified and mapped. Distributions of the Mojave 

Desert, transition zone, and Great Basin Desert ecoregion vegetation alliances and associations are linked to 

temperature extremes, precipitation, and soil conditions. 

Vegetation associations characteristic of the Mojave Desert occur over the southern third of the NTS, on hillsides 

and mountain ranges at elevations below about 1,219 m (4,000 ft) (Figure A-15). Creosote bush (Larrea 

tridentata) is the dominant shrub within these associations. Creosote bush associations are absent from habitats 

where the mean minimum air temperature is below -1.9°C (28.5°F) or the extreme minimum is less than -17.2°C 

(1°F). It is also limited to zones with an average rainfall of 18.3 cm (7.2 in.) or less (Beatley, 1974). Between 

elevations of 1,219 to 1,524 m (4,000 to 5,000 ft), transitional vegetation associations exist. The largest and most 

important is the Blackbrush-Nevada Jointfir (Coleogyne ramosissima-Ephedra nevadensis) Shrubland 

Association, which covers 21.6 percent of the total area of the NTS (Ostler et al., 2000). Above 1,524 m 

(5,000 ft), the vegetation mosaic is characteristic of the Great Basin Desert. Throughout the central and 

northwestern mountains of the NTS, the dominant shrub species are basin big sagebrush (Artemisia tridentata) 

and black sagebrush (Artemisia nova). The distribution of Great Basin Desert associations appears to be limited 

by mean maximum temperature and by minimum rainfall tolerances of the cold desert species (Beatley, 1975). 

Above 1,828 m (6,000 ft), singleleaf pinyon (Pinus monophylla) and Utah juniper (Juniperus osteosperma) mix 

with the sagebrush association where there is suitable moisture for these trees. Tree densities on the NTS are often 

not high enough to create closed canopies but, rather, form an open woodland type with a mix of shrub and tree 

cover. 

None of the plant species on the NTS are listed as threatened or endangered under the Endangered Species Act. 

However, 18 vascular plants and 1 non-vascular plant on the NTS are considered to be sensitive by the Nevada 

Natural Heritage Program (see Chapter 13 of the main document, Table 13-2). Sensitive species are those whose 

long-term viability has been identified as a concern by natural resource experts. Through past field survey efforts 

over multiple years, population locations of sensitive species have been mapped on the NTS (Figure A-16) and 

are monitored under the Ecological Monitoring and Compliance Program (see Chapter 13 of the main document). 

A.4.2 Fauna 

At least 1,163 taxa of invertebrates within the phylum Arthropoda have been identified on the NTS. Of the known 

arthropods, 78 percent are insects. Ants, termites, and ground-dwelling beetles are probably the most important 

groups of insects in regard to distribution, abundance, and functional roles. No native fish species occur on the 

NTS, although non-native goldfish (Carassius auratus), golden shiner (Notemigonus crysoleucas), and bluegill 

(Lepomis machrochirus) have been unofficially introduced into a few man-made ponds. The non-native bullfrog 

(Rana catesbeiana) is the only amphibian that is known to occur on the NTS. 
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Figure A-15. Distribution of plant alliances on the NTS 
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Figure A-16. Known locations of sensitive plant species on the NTS 
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Among reptiles, the desert tortoise (Gopherus agassizii), 16 lizard species, and 17 snake species are known to 

occur on the NTS (Wills and Ostler, 2001). The rich reptile fauna is partly due to the overlapping ranges of plant 

species characteristic of the Mojave and Great Basin Deserts. The most abundant, widely distributed lizards 

include the side-blotched lizard (Uta stansburiana), western whiptail (Cnemidophorus tigris), and desert horned 

lizard (Phrynosoma platyrhinos). The western shovel-nosed snake (Chionactis occipitalis) is the most common 

snake on the NTS. There are four species of poisonous snakes: the Mohave Desert sidewinder (Crotalus cerastes), 

Panamint rattlesnake (Crotalus mitchellii), night snake (Hypsiglena torquata), and Sonoran lyre snake 

(Trimorphodon biscutatus). 

There are records of 239 species of birds observed on the NTS (Wills and Ostler, 2001). Approximately 

80 percent of the bird species are migrants or seasonal residents. To date, 26 species, including 9 raptor species 

(birds of prey) are known to breed on the NTS. Raptors that breed on the NTS include the golden eagle (Aquila 

chrysaetos), long-eared owl (Asia otus), red-tailed hawk (Buteo jamaicensis), Swainson’s hawk (Buteo 

swainsoni), prairie falcon (Falco mexicanus), American kestrel (Falco sparverius), western burrowing owl 

(Athene cunicularia hypugaea), barn owl (Tyto alba), and great-horned owl (Bubo virginianus) (BN, 2002c). 

There are 44 terrestrial mammals and 15 bat species that are known to occur on the NTS. Rodents account for 

about 40 percent of the known mammals and, in terms of distribution and relative abundance, are the most 

important group of mammals on the NTS (Wills and Ostler, 2001). There is an apparent correlation between 

production by winter annual plants and reproduction in desert rodents on the NTS. Larger mammals on the site 

include black-tailed jackrabbit (Lepus californicus), desert cottontail (Sylvilagus audubonii), feral horse (Equus 

caballus), mule deer (Odocoileus hemionus), pronghorn antelope (Antilocapra americana), coyote (Canis 

latrans), kit fox (Vulpes macrotis), grey fox (Urocyon cinereoargenteus), badger (Taxidea taxus), bobcat (Lynx 

rufus), mountain lion (Puma concolor), burro (Equus asinus), and bighorn sheep (Ovis canadensis). Mule deer 

herds occur mainly on the high mesas and surrounding bajadas. Small numbers of feral horses and pronghorn 

antelope range over small areas of the NTS. Bighorn sheep and burros are thought to be rare visitors. 

The desert tortoise is the only resident species found on the NTS that is listed as threatened under the Endangered 

Species Act. Habitat of the desert tortoise is in the southern third of the NTS (see Chapter 13, Figure 13-1). No 

other federally threatened or endangered animal is known to occur on the NTS. All but five birds on the NTS are 

protected by federal legislation under the Migratory Bird Treaty Act and/or by the State of Nevada. Most 

non-rodent mammals of the NTS are protected by the State of Nevada and managed as either game or furbearing 

mammals, and 13 bats on the NTS are considered sensitive species (see Chapter 13, Table 13-3). 

A.4.3 Natural Water Sources 

Important biological communities on the NTS are those associated with springs or other natural sources of water. 

They are rare, localized habitats that are important to regional wildlife and to isolated populations of water-loving 

plants and aquatic organisms. There are 32 natural water sources on the NTS that include 16 springs, 10 seeps, 

4 tank sites (natural rock depressions that catch and hold surface runoff), and 2 ephemeral ponds (Hansen et al., 

1997; BN, 1998; 1999) (Figure A-17). 
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Figure A-17. Natural springs and seeps on the NTS (from Hansen et al., 1997; BN, 1999; Hansen et al., 2010) 
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A.5 Cultural Resources 

A.5.1 Cultural Resources Investigations on the NTS 

Few cultural resources investigations were performed from the 1940s to the 1960s on what is now the NTS. 

Earlier explorers did visit the area, such as O. S. Lodwick in the 1900s and Mark R. Harrington of the Heye 

Museum of the American Indian in the 1920s, but the visits were brief, and no in-depth studies were attempted. 

The work conducted by S. M. Wheeler in 1940 is the first serious investigation, resulting in some prominent sites 

being recorded (Winslow, 1996). Wheeler and a small party, including his wife, supported by the Nevada State 

Parks Commission, were guided by Roscoe J. Wright, also known as (a.k.a.) “Death Valley Curley,” a local 

miner, into the Fortymile Canyon region with the specific purpose of investigating archaeological sites 

(Figure A-18). The party spent only a few days in the area and only briefly described the cultural resources they 

found. In 1955, Richard Shutler (1961), seeking evidence of pueblo ruins, was the next archaeologist to visit and 

record sites in the same general area of Fortymile Canyon as well as on Timber Mountain. He was guided by 

Bill Martin, a Shoshone from Beatty. Frederick C. V. Worman (1965; 1966; 1967; 1969), a zoologist and a 

vocational archaeologist employed by Los Alamos National Laboratory, and Donald Tuohy (1965), an 

archaeologist from the Nevada State Museum, conducted limited surveys and excavations during the 1960s. 

These investigations were typically salvage archaeology in response to an Atomic Energy Commission (AEC) 

directive regarding the preservation and protection of antiquities on AEC lands. It was not until the late 1970s 

with stronger federal laws and regulations concerning cultural resources that systematic archaeological 

investigations on the NTS were carried out on a regular basis. Desert Research Institute (DRI) became the cultural 

resources support contractor at this time, and ever since, has performed numerous surveys and data recovery 

efforts (Figure A-19) as well as recordkeeping and curation of artifacts. Lately, historical evaluations of NTS 

structures and buildings have become part of the program in documenting a significant period in the local and 

national history regarding nuclear testing and the Cold War era (Figure A-20). 

Figure A-18. Example of prehistoric petroglyphs found on the NTS. This rock art site is in 

Fortymile Canyon (photo taken by DRI, 1996). 
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Figure A-19. DRI archaeologist at an archaeological excavation of a prehistoric site on 

Pahute Mesa. The site dates from the middle to late Holocene period 

(photo taken by DRI, 1992). 

Figure A-20. Building 400, a camera station for photographing atmospheric tests, at 

Area 6 Control Point, built in 1951. It is one of the first buildings constructed 

on the NTS to support weapons testing activities (photo taken by DRI, 2003). 
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A.5.2 Paleo-Indian Period 

The oldest cultural remains discovered on the NTS are Clovis-style projectile point fragments dating to the 

Paleo-Indian period, circa (ca.) 12,000 to 10,000 years before present (BP). One was found along an alluvial 

terrace of Fortymile Wash near Yucca Mountain (Reno, 1985) and a second at the upper reaches of the Fortymile 

drainage system near Rattlesnake Ridge at the west base of Rainier Mesa (Jones and Edwards, 1994). The basic 

economic strategy for the Paleo-Indian was hunting of big game and a predominant use of lacustrine-marsh areas 

around late Pleistocene and early Holocene pluvial lakes (Madsen, 1982; Warren and Crabtree, 1986). Pluvial 

lakes were a result of cooler temperatures and higher annual precipitation characteristic of this time (Grayson, 

1993). No evidence is available, however, to indicate that the basins on the NTS supported pluvial lakes as in 

other nearby valleys, such as Groom Lake east of the NTS and the Kawich, Gold Flat, and Mud lakes to the north 

(Grayson, 1993: Table 5-2; Mifflin and Wheat, 1979). The Fortymile Canyon drainage, where the Clovis points 

were found, may have been used as a travel route between highland and lowland areas or, as proposed by Pippin 

(1998), part of a hunting territory where certain animals such as deer and elk could be found. 

A.5.3 Early Holocene Period 

A general broadening in the types of resources being exploited from a variety of environments occurs during the 

early Holocene, ca. 10,000 to 7,500 BP, and includes aquatic and small animals as well as plants (Grayson, 1993). 

Initially, lakes and marshes still abounded overall, but the climate began to change to one more dry, and by 

8,000 BP most of the standing bodies of water were gone (Grayson, 1993). Consequently, the woodlands began to 

move upslope to be replaced by sagebrush or bursage and creosote bush (Grayson, 1993). 

Most cultural activities still appear to be restricted to the lower elevations (Haynes, 1996; Reno et al., 1989); 

however, Pippin (1998) indicates that only short-term hunting forays, originating from the lower elevations, 

occurred in the higher elevations of the NTS. This is similar to the pattern described for the eastern Great Basin 

(Madsen, 1982). 

A.5.4 Middle Holocene Period 

The period from ca. 7,500 to 4,500 BP is marked by increased aridity, and a hotter and dryer climate compared to 

the previous episode and to that of today (Antevs, 1948; Miller and Wigand, 1994). Some evidence suggests that 

entire areas were abandoned. For example, Warren and Crabtree (1986) contend that the people living in the 

Mojave Desert at this time were ill-adapted to the arid conditions because so few sites have been found; of those 

sites, they appear to represent short-term activities with low artifact densities indicative of a highly mobile 

lifestyle. They suggest that the people may have aggregated at the margins of the desert near springs and other 

dependable water sources and only briefly entered the more arid localities during times of greater effective 

moisture. Few sites have been found in the Great Basin dating to this period as well. Grayson (1993) indicates that 

the higher elevation zones were becoming an important part of the subsistence base, and human movements 

coincide with the upward movement in elevation of the woodlands. Pippin (1998) also notes this change on the 

NTS, but he sees the cultural response as an intensification and expansion of the areas previously exploited and 

not in the relocation of residential bases to the uplands. 

A.5.5 Late Holocene Period 

The period from ca. 4,500 to 1,900 BP is generally known for cooler and wetter conditions. Subsequent 

periods fluctuated between dry and wet episodes, with the most notable arid periods from 1,900 to 1,000 BP and 

700 to 500 BP (Miller and Wigand, 1994). A pattern of heavy winter precipitation began after 500 BP, but 

average temperatures have gradually increased since the end of the Little Ice Age about 150 years ago. Culturally, 

there is an increase in the number of sites and a broadening of the subsistence base (Grayson, 1993; Lyneis, 

1982). A shift in the settlement pattern is made in some areas of the southern Great Basin to comparatively large, 
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semi-sedentary communities on valley floors accompanied by a more frequent use of the highlands. An increase 

in the frequency of milling implements indicates a greater reliance on seeds than previously practiced (Warren 

and Crabtree, 1986). Evidence at higher elevations on the NTS supports the contention that highland resources 

were an important part of the subsistence base, and, quite likely, logistical seasonal movements between resource 

zones were being practiced (Pippin, 1998). Rock features interpreted as food caches begin to appear within the 

woodlands (Pippin, 1998). Examples of projectile points from this period found by DRI archaeologists on the 

NTS are shown in Figure A-21. One of the most conspicuous technological changes is the introduction of the bow 

and arrow, ca. 1,500 BP. Madsen (1986a) suggests that the advent of this implement may have led to increased 

efficiency in hunting to where the animal populations were significantly reduced, resulting in a greater 

dependence by the people on plant resources, such as pinyon and other seed plants. Another introduction was 

brownware pottery (Figure A-22), ca. 700 to 1,000 BP (Madsen, 1986b; Pippin, 1986; Lockett and Pippin, 1990; 

Rhode, 1994), indicating a more sedentary lifestyle and a change in the way food was prepared and stored. 

Figure A-21. Prehistoric projectile points from the NTS (photo taken by DRI, 1992) 
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Figure A-22. Brownware bowl recovered from archaeological excavations on Pahute Mesa 

(photo taken by DRI, 1992) 

A.5.6 Ethnohistoric American Indian 

Early explorers and immigrants in the southern Great Basin during the nineteenth century encountered 

widely scattered groups of Numic-speaking hunters and gatherers currently known as Southern Paiute (see 

Kelly and Fowler, 1986) and Western Shoshone (see Thomas et al., 1986). The areas traditionally claimed by 

these tribal entities encompassed a large region and were bound in territories of ethnic or political groups 

(Stoffle et al., 1990). Subsistence strategies revolved around movements between environmental zones within 

their territories (e.g., highlands and lowlands), according to the seasonal availability of food resources 

(Steward, 1938; Wheat, 1967). The normal range was within 32 km (20 mi) of the primary residential base, but 

most resources could be found within a short distance of the main camp. Criteria for the location of the primary 

residential base was nearness to stored or cached foods, availability of water, wood for fuel and house 

construction, and relatively warm winter temperatures like that found in canyon mouths or in the woodlands 

(Steward, 1938). 

The communal group around Rainier Mesa and the southern end of the Belted Range ca. 1875–1880 was known 

as Eso (little hill) and had an estimated population of 42. This locale is at the boundaries of the traditional tribal 

lands for the Southern Paiute and Western Shoshone, and the Eso consisted of members from both tribes. The Eso

were closely linked linguistically with people to the east but maintained close relationships with groups all around 

them, particularly to the north and west. They established winter residential camps at Cane Spring, Captain Jack 

Spring, Oak Springs, Tippipah Springs (Figure A-23), Topopah Spring, White Rock Springs, and on Pahute and 

Rainier Mesas. Another camp, though not located at a spring, was Ammonia Tanks. 
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One of the better known spring sites, Captain Jack Spring, is named after One-eyed Captain Jack, a Paiute who 

resided there at various times with his wife(s) during the late 1800s and early 1900s (Steward, 1938; 

Stoffle et al., 1990). He died in 1928 (Stoffle et al., 1990). At White Rock Springs lived Wandagwana, headman 

for the Eso. He directed the annual fall rabbit drive in Yucca Flat, which was a time of regional interaction 

between the various camps and with more distant people. A fandango was usually held at Wungiakuda off the 

southeast edge of Pahute Mesa (see Johnson et al., 1999) lasting about five days, which provided opportunity for 

the exchange of goods and information. Sweat houses, also serving as places of integration for the local group, 

were located at White Rock Springs and at Oak Springs. They were used by both women and men for smoking, 

gambling, sweating, and as a dormitory. 

Figure A-23. Overview of the Tippipah Spring area (photo taken by DRI, 2004) 

A.5.7 Historic Mining on and near the NTS 

Around the beginning of the twentieth century, when substantial gold and silver deposits were discovered, the 

Euro American culture began to dominate this particular region of Nevada, with strikes at Tonopah, Goldfield, 

and Rhyolite (Elliott, 1966; 1973; McCracken, 1992; Zanjani, 1992). The overall population of Nevada doubled 

(Elliott, 1966; McCracken, 1992). The great mining boom was short-lived, however, and quickly entered the bust 

phase. By 1908, only four years after it began, mining in the Bullfrog district collapsed and the town of Rhyolite 

became one of the many ghost towns in the region. For Goldfield, production fell rapidly after 1911 

(Zanjani, 1992), but the town still survives today, principally because it is the seat for Esmeralda County 

(Elliott, 1966). The decline for the Tonopah mining district was more gradual, and the town had time to transform 

its primary economic base from mining to a supply center, albeit relatively small and limited, for the surrounding 

ranches, remaining mining districts, and military installations. The Las Vegas and Tonopah rail line lasted until 

1918; the rails were removed in 1919 (Myrick, 1963). Still evident on the NTS today are some of the abandoned 

ties reused for the construction of corrals and other structures at a number of the springs. Around the Beatty area, 

the ties were used in some of the later mining operations for shoring (McCracken, 1992). 

As mining explorations continued in the region, fanning out from the earlier strikes, small mining districts were 

founded, such as Tolicha in 1917 at the west end of Pahute Mesa (Lincoln, 1923) and the Bare Mountain district 

just west of the NTS (Cornwall, 1972; Lincoln, 1923; Tingley, 1984). Recorded as an archaeological site by Jones 

et al. (1996), the mining town of Wahmonie in the southern part of the NTS around Mine and Skull Mountains 
 Attachment A: Nevada Test Site Description

Nevada Test Site Environmental Report 2009 ATT A-53

was founded in 1928. The history of Wahmonie spans only a few years and was typical of the boom-and-bust 

cycle of the mining industry. The historic mining camp of Wahmonie is located about 10 km (6 mi) west of 

Cane Spring (McLane, 1995; Quade and Tingley, 1984). It grew to a small town with boarding houses, tent stores, 

and cafes. The Silver Dollar Saloon and the Northern Club were but two of the enterprises (Long, 1950). Most of 

the miners lived in small tents. George Wingfield, a well-known mine owner and banker in Nevada, became 

interested and incorporated the Wahmonie Mining Company. Soon, however, the strike was apparently not as rich 

as had first been thought, and by early 1929 optimism faded and people began leaving Wahmonie. Small amounts 

of prospecting in the Wahmonie district continued into the 1930s and 1940s, but few ore deposits were ever 

discovered. 

The earliest record of prospecting on what is now the NTS is the Oak Spring mining district centered around the 

northern edge of Oak Spring Butte (Drollinger, 2002). Documents at the Recorder’s Office in Tonopah indicate it 

was established by the late 1880s. The main objectives of these early mining activities were gold, silver, and 

chrysocolla, a green to blue mineral resembling turquoise. Lincoln (1923) indicates copper ore containing some 

silver was shipped in 1917 from the Horseshoe claim in the Oak Spring mining district, and minor amounts of 

tungsten were also mined in the district. The Oak Spring district, although having relatively abundant water and 

wood sources, did not prove to be very productive overall. 

B. M. Bower (a.k.a. Bertha Muzzy Sinclair), a noted author, with husband (Bud Cowan) and family, moved to 

Nevada from Los Angeles, California, in 1920 and took up residence (Figure A-24) at a mining camp near 

Oak Spring (McLane, 1996) (see Figure A-17). An accomplished and prolific writer, B. M. Bower published a 

number of short stories and novels over a 40-year career, with some of them becoming the basis for early 

western-themed movies in Hollywood. She also served as a screenwriter on a couple of them. While living at 

the camp, Bower wrote 11 novels, incorporating some of the surrounding geographic features, such as 

Oak Spring Butte and the camp itself, into a few of the stories. (Copies of several of her books have been made 

electronically available to the public by Project Gutenberg as eText and can be downloaded at 

http://www.thalasson.com/gtn/gtnletB.htm#bowerbm). The family also formed the El Picacho Mining Company, 

with B. M. Bower serving as the president, and filed assessment work for the claims from 1922 to 1928. The 

family moved to Las Vegas around 1926 but still worked the mining claims sporadically over the next couple 

years. 

They eventually returned to California. Fittingly, in keeping with the theme for some of the novels, the abandoned 

camp was used in the early 1930s by outlaws from Utah and Arizona whose escapades were later featured in a 

Death Valley Days radio episode narrated by Ronald Reagan. B. M. Bower died in 1940 and was inducted into 

the Western Writers of America Hall of Fame in 1994. 

Historically, demand of tungsten for use in weaponry was high during times of war (World Wars I and II, the 

Korean War) and fell during times of peace (Stager and Tingley, 1988). Correspondingly, so did the mining of 

tungsten in Nevada. Tungsten was discovered in the Oak Spring district and located as the Climax group in 

1937 by V. A. Tamney (Kral, 1951; Stager and Tingley, 1988). Most operations ended when the area was 

closed with the founding of the bombing and gunnery range by the federal government (Kral, 1951; Quade and 

Tingley, 1984; Stager and Tingley, 1988). Production was never fully established for these claims, however, and 

only samples totaling some 15 tons were processed in a nearby dry concentrating mill serving the Oak Spring 

district. The last known mining operation at the Climax claims was from December 1956 to May 1957 involving a 

co-use agreement between George Tamney, W. A. Kinney, A. J. Wright, owners of the Climax Tungsten 

Corporation, and the AEC (McLane, 1996; Quade and Tingley, 1984). The agreement was terminated and no 

legal mining has since been conducted on the NTS. 
Attachment A: Nevada Test Site Description

ATT A-54 Nevada Test Site Environmental Report 2009

Figure A-24. Bower cabin on the NTS (photo taken by DRI, 2001) 
Attachment A: Nevada Test Site Description

Nevada Test Site Environmental Report 2009 ATT A-55

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U.S. Department of Energy

National Nuclear Security Administration

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