Nevada Test Site 

Environmental Report 2006 

Attachment A: Site Description 

 

Northern Harrier (Circus cyaneus)

DOE/NV/25946--259 

September 2007
 

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DOE/NV/25946--259 

Nevada Test Site 

Environmental Report 2006 

Attachment A: Site Description 

Senior Author: Cathy A. Wills 

Technical Editor: Fina Martinez-Myers 

Graphics Arts/Desktop Publisher Specialist: Angela McCurdy 

Geographic Information System Specialist: Ashley Cushman

September 2007 

Work Performed Under 

Contract No. DE-AC52-06NV25946 

Prepared for: 

U. S. Department of Energy 

National Nuclear Security Administration 

Nevada Site Office 

Prepared by: 

National Security Technologies, LLC 

P. O. Box 98521 

Las Vegas, NV 89193-8521
 Nevada Test Site Description 

Nevada Test Site Environmental Report 2006 A-i

Table of Contents 

List of Figures.............................................................................................................................................................A-ii

List of Tables .............................................................................................................................................................A-ii 

Acronyms and Abbreviations..................................................................................................................................A-iii

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

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

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

A.1.3 Structural Controls ......................................................................................................A-8 

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

A.2.1 Surface Water...............................................................................................................A-9 

A.2.2 Groundwater ................................................................................................................A-9 

A.2.3 Hydrogeologic Framework for the NTS and Vicinity .........................................A-13 

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

 A.2.3.2 Hydrostratigraphic Units.........................................................................A-15 

A.2.4 General Hydraulic Characteristics of NTS Rocks ................................................A-16 

A.2.5 Hydrogeology of the NTS Underground Test Areas...........................................A-17 

 A.2.5.1 Frenchman Flat Underground Test Area .............................................A-20 

 A.2.5.2 Yucca Flat/Climax Mine Underground Test Area..............................A-22 

 A.2.5.3 Pahute Mesa Underground Test Area...................................................A-27 

 A.2.5.4 Rainier Mesa/Shoshone Mountain ........................................................A-32 

A.2.6 Conclusion..................................................................................................................A-34 

A.3 Climatology.....................................................................................................................................A-35 

A.3.1 Precipitation ...............................................................................................................A-35 

A.3.2 Temperature ...............................................................................................................A-35 

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

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

A.3.5 Atmospheric Pressure...............................................................................................A-38 

A.3.6 Dispersion Stability Categories................................................................................A-40 

A.3.7 Other Natural Phenomena.......................................................................................A-40 

A.4 Ecology............................................................................................................................................A-41 

A.4.1 Flora.............................................................................................................................A-41 

A.4.2 Fauna...........................................................................................................................A-41 

A.4.3 Natural Water Sources..............................................................................................A-44 

A.5 Cultural Resources .........................................................................................................................A-46 

A.5.1 Cultural Resources Investigations on the NTS.....................................................A-46 

A.5.2 Paleo-Indian Period...................................................................................................A-48 

A.5.3 Early Holocene Period..............................................................................................A-48 

A.5.4 Middle Holocene Period...........................................................................................A-48 

A.5.5 Late Holocene Period ...............................................................................................A-48 

A.5.6 Ethnohistoric American Indian...............................................................................A-50 

A.5.7 Historic Mining on and near the NTS....................................................................A-51 

 References .................................................................................................................................................................A-54
 Nevada Test Site Description 

A-ii Nevada Test Site Environmental Report 2006 

List of Figures 

Figure A-1. Basin and Range Physiographic Province and Great Basin Hydrologic Province...................A-2 

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

Figure A-3. Closed hydrographic subbasins on the NTS ...............................................................................A-10 

Figure A-4. Natural springs and seeps on the NTS.........................................................................................A-11 

Figure A-5. Groundwater subbasins of the NTS and vicinity .......................................................................A-12 

Figure A-6. Location of Corrective Action Units and Corrective Action Sites on the NTS.....................A-19 

Figure A-7. Conceptual east-west cross section through Frenchman Flat...................................................A-21 

Figure A-8. Generalized west-east hydrogeologic cross section through central Yucca Flat....................A-24 

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

Pahute Mesa......................................................................................................................................A-28 

Figure A-10. Generalized hydrostratigraphic cross section through Aqueduct Mesa ..................................A-33 

Figure A-11. Mean monthly precipitation at six NTS MEDA stations..........................................................A-36 

Figure A-12. Temperature extremes and normal maximums and minimums at six NTS 

MEDA stations................................................................................................................................A-37 

Figure A-13. Twenty-year wind rose climatology for the NTS........................................................................A-39 

Figure A-14. Distribution of plant alliances on the NTS..................................................................................A-42 

Figure A-15. Known locations of plant species of sensitive plant species on the NTS...............................A-43 

Figure A-16. Natural water sources on the NTS................................................................................................A-45 

Figure A-17. Example of prehistoric petroglyphs found on the NTS. This rock art site is in Fortymile 

Canyon. .............................................................................................................................................A-46 

Figure A-18. DRI archaeologist at an archaeological excavation of a prehistoric site on 

 Pahute Mesa......................................................................................................................................A-47 

Figure A-19. Building 400, a camera station for photographing atmospheric tests, at 

Area 6 Control Point, built in 1951. One of the first buildings constructed on 

 the NTS to support weapons testing activities............................................................................A-47 

Figure A-20. Prehistoric projectile points from the NTS .................................................................................A-49 

Figure A-21. Brownware bowl recovered from archaeological excavations on Pahute Mesa.....................A-50 

Figure A-22. Overview of the Tippipah Spring Area........................................................................................A-51 

Figure A-23. Bower cabin on the NTS................................................................................................................A-53 

List of Tables 

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

Table A-2. Pre-Tertiary stratigraphic units of the NTS and vicinity ..................................................................A-7 

Table A-3. Hydrogeologic units of the NTS area ...............................................................................................A-14 

Table A-4. Summary of hydrologic properties for hydrogeologic units at the NTS......................................A-17 

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

Table A-6. Hydrostratigraphic units of the Frenchman Flat underground test area .....................................A-21 

Table A-7. Hydrostratigraphic units of the Yucca Flat underground test area...............................................A-25

Table A-8. Hydrostratigraphic units of the Pahute Mesa-Oasis Valley area ...................................................A-30 

 
 Nevada Test Site Description 

Nevada Test Site Environmental Report 2006 A-iii

A.0 Acronyms and Abbreviations 

AA alluvial aquifer 

AEC Atomic Energy Commission 

ATICU Ammonia Tanks intrusive confining unit 

BA Benham aquifer 

BCU Bullfrog confining unit 

BMICU Black Mountain intrusive confining unit 

BN Bechtel Nevada 

BP before present 

BRA Belted Range aquifer 

BRCU Belted Range confining unit 

BRT Belted Range thrust 

°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) 
 Nevada Test Site Description 

A-iv Nevada Test Site Environmental Report 2006 

CP Control Point 

DOE U.S. Department of Energy 

DRI Desert Research Institute 

DVCM detached volcanics composite unit 

EPA U.S. Environmental Protection Agency 

°F degree Fahrenheit 

ft foot or feet 

FCCU Fluorspar Canyon confining unit 

FFACO Federal Facility Agreement and Consent Order 

GCU granite confining unit 

HGU hydrogeologic unit 

HSU hydrostratigraphic unit 

in. inch(es) 

IICU intracaldera intrusive confining unit 

IT International Technology Corporation 

KA Kearsarge aquifer 

km kilometer(s) 

kmh kilometer(s) per hour 

kt kiloton(s) 

LCA lower carbonate aquifer 

LCA3 lower carbonate aquifer, upper thrust plate 

LCCU lower clastic confining unit 

LFA lava-flow aquifer 

LPCU lower Paintbrush confining unit 

m meter(s) 

Ma million years ago 

mb millibar(s) 

MEDA Meteorological Data Acquisition 

MGCU Mesozoic granite confining unit 
 Nevada Test Site Description 

Nevada Test Site Environmental Report 2006 A-v

mi miles 

mph miles per hour 

NTS Nevada Test Site 

PDT Pacific Daylight Time 

PLFA Paintbrush lava-flow aquifer 

PM-OV Pahute Mesa-Oasis Valley 

PST Pacific Standard Time 

PVTA Paintbrush vitric-tuff aquifer 

RMICU Rainier Mesa intrusive confining unit 

SCCC Silent Canyon caldera complex 

SCICU Silent Canyon intrusive confining unit 

SCVCU subcaldera volcanic confining unit 

SWL static water level 

SWNVF Southwest Nevada Volcanic Field 

TCA Tiva Canyon aquifer 

TCU tuff confining unit 

TCVA Thirsty Canyon volcanic aquifer 

THCM Tannenbaum Hill composit unit 

THLFA Tannenbaum Hill lava-flow aquifer 

TMA Timber Mountain aquifer 

TMCC Timber Mountain caldera complex 

TM-LVTA Timber Mountain lower vitric-tuff aquifer 

TM-UVTA Timber Mountain upper vitric-tuff aquifer 

TM-WTA Timber Mountain welded-tuff aquifer 

TSA Tonopah Spring aquifer 

TUBA Tub Spring aquifer 

UCA upper carbonate aquifer 

UCCU upper clastic confining unit 

UGTA Underground Test Area 
 Nevada Test Site Description 

A-vi Nevada Test Site Environmental Report 2006 

UPCU upper Paintbrush confining unit 

VCU volcaniclastic confining unit 

VTA vitric-tuff aquifer 

WCU Wahmonie confining unit 

WTA welded-tuff aquifer 

WVCU Wahmonie volcanic confining unit 

WWA Windy Wash aquifer 

YF-LCU Yucca Flat lower confining unit 

YF-UCU Yucca Flat upper confining unit 

YMCFCM Yucca Mountain Crater Flat composite unit 

YVCM younger volcanic composite unit 
 Nevada Test Site Description

Nevada Test Site Environmental Report 2006 A-1

A.0 Attachment A: Nevada Test Site Description 

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

Nevada Test Site Environmental Report 2006 (NSTec, 2007). 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 which 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 appendix 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 Southwest 

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 six Tertiary-age calderas nearby, many relatively young basin-andrange-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 alluvium-filled basins and 

20 percent Paleozoic and uppermost Precambrian sedimentary rocks, the remainder beingTertiary-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 six major 

calderas have been identified in this multi-caldera silicic volcanic field (Byers et al., 1976). 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: 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. 
 Nevada Test Site Description 

A-2 Nevada Test Site Environmental Report 2006 

Figure A-1. Basin and Range Physiographic Province and Great Basin Hydrologic Province 
 Nevada Test Site Description

Nevada Test Site Environmental Report 2006 A-3

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

A-4 Nevada Test Site Environmental Report 2006 

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 (Snyder, 1977; 

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

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

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

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

Quaternary or Tertiary Sediments 

 Young alluvium (Qay) 

 Playa (Qp) 

 Quaternary - Tertiary colluvium (QTc) 

 Middle alluvium (Qam) 

 Eolian sand (QTe) 

 Quaternary-Tertiary alluvium (QTa) 

Quaternary Basalts (Qby) 

Pliocene Basalts (Typ) 

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 

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 
 Nevada Test Site Description

Nevada Test Site Environmental Report 2006 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)

Timber Mountain Group (Tm) 

 Trachyte of East Cat Canyon (Tmay) 

 Tuff of Buttonhook Wash (Tmaw) 

 Ammonia Tanks Tuff (Tma) 

 Bedded Ammonia Tanks Tuff (Tmab) 

 Timber Mountain landslide breccia (Tmx) 

 Rhyolite of Tannenbaum Hill (Tmat) 

 Basalt of Tierra (Tmt) 

 Rainier Mesa Tuff (Tmr) 

 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) 

Timber Mountain Caldera Complex 

Ammonia Tanks Caldera 

Rainier Mesa Caldera 

Paintbrush Group (Tp) 

 Rhyolite of Benham (Tpb) 

 Post-Tiva Canyon rhyolites (Tpu) 

 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) 

Claim Canyon Caldera 

Claim Canyon Caldera 

Unknown 

Unknown 

Calico Hills Formation (Th; formerly Tac) Unknown 

Wahmonie Formation (Tw) Wahmonie Volcanic Center 

Crater Flat Group (Tc) 

 Rhyolite of Inlet (Tci) 

 Prow Pass Tuff (Tcp) 

 Rhyolite of Kearsarage (Tcpk) 

 Andesite of Grimy Gulch (Tcg) 

 Bullfrog Tuff (Tcb) 

 Rhyolites in the Crater Flat Group (Tcr) 

 Tram Tuff (Tct) 

Belted Range Group (Tb) 

 Deadhorse Flat Formation (Tbd) 

 Grouse Canyon Tuff (Tbg) 

 Comendite of Split Range (Tbgs) 

 Comendite of Quartet Dome (Tbq) 

Silent Canyon Caldera Complex 

Area 20 Caldera 

Grouse Canyon Caldera 
 Nevada Test Site Description 

A-6 Nevada Test Site Environmental Report 2006 

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

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

Tram Ridge Group (Tr) 

 Lithic Ridge Tuff (Trl) 

 Dikes of Tram Ridge (Trd) 

 Rhyolite of Picture Rock (Trr) 

Uncertain 

Tunnel Formation (Tn) 

 4 Member (Tn4) 

 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 

Volcanics of Oak Spring Butte (To) 

 Tunnel bed 2 (Ton2) 

 Yucca Flat Tuff (Toy) 

 Tunnel bed 1 (Ton1) 

 Redrock Valley Tuff (Tor) 

 Tuff of Twin Peaks (Tot) 

Unknown 

Older Volcanics (Tqo) Unknown 

Paleocolluvium (Tl) N/A 

(a) Compiled from Wahl et al. (1997) and Ferguson et al. (1994). 

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

(c) Sources, where known, from Sawyer et al. (1994). 

Refer to Table A-2 for lists of Mesozoic, Paleozoic, and Precambrian sedimentary rock formations. 
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Nevada Test Site Environmental Report 2006 A-7

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) 

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) Project (see Chapter 14) 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 (Cole, 1997; Cole and 

Cashman, 1999; Cashman and Trexler, 1991; 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. 
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A-8 Nevada Test Site Environmental Report 2006 

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 of groundwater flow, depending on the difference in 

permeability between a fault zone and the surrounding rocks. 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 principle 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 them 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 northeast-striking, 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. 

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 40 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 Project. 
 Nevada Test Site Description

Nevada Test Site Environmental Report 2006 A-9

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 below), 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. 

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 (Locke and LaCamera, 2003; Bright et al., 2001; IT, 1996b; Reiner et al., 

1995; O’Hagan and Laczniak, 1996; Robie et al., 1995). 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 (Reiner et al., 1995; 

Hale et al., 1995; IT, 1996b; DOE, 2003) and flow models (IT, 1996a; D’Agnese et al., 1997), the general groundwater 

flow direction within major water-bearing units beneath the NTS is to the south and southwest. 
 Nevada Test Site Description 

A-10 Nevada Test Site Environmental Report 2006 

Figure A-3. Closed hydrographic subbasins on the NTS
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Nevada Test Site Environmental Report 2006 A-11

Figure A-4. Natural springs and seeps on the NTS
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A-12 Nevada Test Site Environmental Report 2006 

Figure A-5. Groundwater subbasins of the NTS and vicinity 
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Nevada Test Site Environmental Report 2006 A-13

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 which 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 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-magnesium-carbonate 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; DOE, 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 Project hydrogeologic modeling team (IT, 1996a; BN, 2002a; 2005). See 

Chapter 14 for a description of the UGTA 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. 

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). 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). 
 Nevada Test Site Description 

A-14 Nevada Test Site Environmental Report 2006 

Table A-3. Hydrogeologic units of the NTS area 

Hydrogeologic Unit 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. 

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 lava flows; includes flow 

breccias (commonly at base) and 

pumiceous zones (commonly at 

top) 

Generally a caldera-filling unit. Hydrologically 

complex; wide range of transmissivities; fracture 

density and interstitial porosity differ with lithologic 

variations. 

Tuff Confining Unit 

(TCU) 

Zeolitized bedded tuff with 

interbedded, but less significant, 

zeolitized, 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 BN (2002a). 

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 ash-flow 
 Nevada Test Site Description

Nevada Test Site Environmental Report 2006 A-15

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 roughly 60 HSUs. 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 CAU-scale hydrogeologic models (IT, 1996a; Gonzales and Drellack, 1999; 

BN, 2002a; 2005). 

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). 

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 northsouth 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 

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-5). 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. 
 Nevada Test Site Description 

A-16 Nevada Test Site Environmental Report 2006 

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, which is the uppermost HSU. 

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 (IT, 1996a; Gonzales and Drellack, 1999; BN, 2002a; 

2005). 

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 (Drellack et al., 1997; IT, 1996c). 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 (air-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, 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 

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). 
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Nevada Test Site Environmental Report 2006 A-17

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 (i.e., 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 (2002c). 

A.2.5 Hydrogeology of the NTS Underground Test Areas 

Most NTS underground nuclear detonations were conducted in three main UGTAs: (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). 

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). It should be noted that these totals 

include 9 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. 
 Nevada Test Site Description n 

 summary of NTS underground nuclear tests 

– detonations more than 200 kt. 

– detonations less than 20 kt. 

tonated at a depth of 1.75 ft (essentially a surface burst) approximately one mile east of Buckboard Mesa. 

7.

Total Underground(a)

NTS 

Area(s) Tests Detonations

Test 

Dates(a)

Depth of 

Burial Range

Overburden 

Media Comments 

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 yields; almost all were vertical emplacements above and below static water level; includes 4 high-yield(b) detonations.

19, 20 85 85 1965 - 1992 31 – 1,452 m 

(100 – 4,765 ft) 

Alluvium, (thin) volcanic tuffs and lavas 

Almost all were large-diameter vertical emplacements above and below static water level; includes 18 high-yield detonations. 

12 61 62 1957 - 1992 61 - 640 m 

(200 – 2,100 ft) 

Tuffs with welded tuff caprock (little or no alluvium) 

Two vertical emplacements; all others were horizontal tunnel emplacements above static water level; mostly low-yield(c) U.S. Department 

of Defense weapons effects tests. 

5, 11 10 10 1965 - 1971 179 - 296 m 

(587 - 971 ft) 

Mostly alluvium,minor volcanic tuff 

Various emplacement configurations, both above and below static water level. 

16 6 6 1962 - 1971 244 - 640 m 

(800 – 2,100 ft) 

Bedded tuff Tunnel-based low-yield weapons effects and 

Vela Uniform tests. 

 

15 3 3 1962 - 1966 229 - 351 m 

(750 – 1,150 ft) 

Granite Three tests above static water level. (HARD 

HAT, TINY TOT, and PILE DRIVER). 

18 3 3 1962 - 1964 < 27 m 

(90 ft) 

Basaltic lavas Shallow, low-yield experiments (SULKY, 

JOHNNIE BOY(d) and DANNY BOY); all were 

above static water level. 

30 1 5 03/12/1968 50 m 

(165 ft) 

Mafic lava BUGGY (A, B, C, D, and E); Plowshare cratering 

test using a 5-detonation-horizontal salvo; all above static water level. 
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Nevada Test Site Environmental Report 2006 A-19

Figure A-6. Location of Corrective Action Units and Corrective Action Sites on the NTS 
 Nevada Test Site Description

A-20 Nevada Test Site Environmental Report 2006 

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) of 1996 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. 

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-5). 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 southeast, 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 five Tertiary-age HSUs (including the 

Quaternary/Tertiary alluvium) and three pre-Tertiary HSUs to serve as layers for the UGTA Frenchman Flat CAU 

groundwater model (BN, 2005). In descending order, these units are: the AA, the Timber Mountain aquifer (TMA), 

the Wahmonie confining unit (WCU), the TCU, the volcaniclastic confining unit (VCU), the LCA, and the LCCU 

(Table A-6). 
 Nevada Test Site Description

Nevada Test Site Environmental Report 2006 A-21

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

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

Hydrostratigraphic Unit 

(Symbol) 

Dominant 

Hydrogeologic Unit(a) Typical Lithologies 

Alluvial Aquifer (AA) AA, minor LFA Alluvium (gravelly sand); also includes relatively 

thin basalt flow in northern Frenchman Flat and 

playa deposits in south-central part of basin 

Timber Mountain Aquifer 

(TMA) 

WTA, VTA Welded ash-flow tuff and related nonwelded and 

air-fall tuffs; vitric to devitrified 

Wahmonie Volcanic Confining 

Unit (WVCU) 

TCU, minor LFA Air-fall and reworked tuffs; debris and breccia 

flows; minor intercalated lava flows. Typically 

altered: zeolitic to argillic 

Tuff Confining Unit (TCU) 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.
 Nevada Test Site Description

A-22 Nevada Test Site Environmental Report 2006 

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. The SWL is generally located within the AA, TMA, WVCU, or TCU. 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; Stoller-Navarro, 2004). 

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 TMA are higher than those in the 

underlying LCA (IT, 1996b; BN, 2005a). This implies a downward gradient. This apparent semi-perched condition is 

believed to be due to the presence of intervening TCUc and VCUs. 

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 which 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 which severely restrict or prevent the migration of radionuclides. 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 BN (2002c), IT (2002), Gonzales and Drellack (1999), Winograd and Thordarson (1975), 

Laczniak et al. (1996), Byers et al. (1989), and Cole (1997) 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-5). These rocks also compose the 

“basement” of the basin, which is now covered by alluvium. 
 Nevada Test Site Description

Nevada Test Site Environmental Report 2006 A-23

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 (Maldonado, 1977; Houser and Poole, 1960). 

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 represent 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.4.1). 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 lists 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 which 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). 

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. A fault movement continued, blocks between faults 

were down-dropped and tilted, creating subbasins within the Yucca Flat basin. 
 Nevada Test Site Description

A-24 Nevada Test Site Environmental Report 2006 

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 thickness of the alluvium in the Yucca Flat basin varies as a function of 

the topography of the underlying deposits and due to continuing movements along faults during alluvium deposition. 

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 (Gonzales and Drellack, 1999). These units are listed in 

Table A-7, and several of the more important HSUs are discussed in the following paragraphs. The alluvium and preTertiary 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
 Nevada Test Site Description

Nevada Test Site Environmental Report 2006 A-25

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 

Yucca Flat Upper Confining Unit 

(YF-UCU) 

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 

Tub Spring Aquifer (TUBA) WTA Welded ash-flow tuff 

Yucca Flat Lower Confining Unit 

(YF-LCU) 

TCU Zeolitic bedded tuffs with interbedded but 

less significant zeolitic, nonwelded to 

partially welded ash-flow tuffs 

Mesozoic Granite Confining Unit 

(MGCU) 

GCU Granodiorite and quartz monzonite 

Upper Carbonate Aquifer (UCA) CA Limestone 

Lower Carbonate Aquifer - Yucca Flat 

Upper 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 Gonzales and Drellack, 1999. 
 Nevada Test Site Description

A-26 Nevada Test Site Environmental Report 2006 

The YF-LCU is an important HSU in the Yucca Flat region (stratigraphically similar to the TCU in Frenchman Flat) 

because it separates the volcanic aquifer units from the underlying regional LCA. Almost all zeolitized tuff units in 

Yucca Flat are grouped within the YF-LCU, which comprises mainly zeolitized bedded tuff (air-fall tuff, with minor 

reworked tuff). The YF-LCU is saturated in much of Yucca Flat; however, measured transmissivities are very low. 

The YF-LCU is generally present in the eastern two-thirds of Yucca Flat. It is absent over the major structural highs, 

where the volcanic rocks have been removed by erosion. Areas where the YF-LCU is absent include the “Paleozoic 

bench” in the western portion of the basin. In northern Yucca Flat, the YF-LCU tends 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 might 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 sub-basins 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 30 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 (IT, 1996b; Hale et al., 1995). 

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 (Laczniak et al., 1996; Hale et al., 1995). 

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 (Laczniak et al., 1996; Hale et al., 1995). Throughout much of the 

Yucca Flat area, the SWL typically is located within the lower portion of the volcanic section, in the YF-LCU. 

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). 

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 YF-LCU (aquitard) between the Paleozoic and 

Tertiary aquifers. Detailed water-level data indicate the existence of a groundwater trough along the axis of the valley. 

The semi-perched water within the alluvial aquifer and volcanic aquifers eventually moves downward to the carbonate 

aquifer in the central portion of the valley. 
 Nevada Test Site Description

Nevada Test Site Environmental Report 2006 A-27

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, 1997), 

the overall groundwater flow direction in Yucca Flat is to the south and southwest (see Figure A-5). Groundwater 

ultimately discharges at Franklin Lake Playa 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 BN (2002a and 2002b), Winograd and Thordarson (1975), Laczniak et 

al., (1996), Byers et al. (1976; 1989), and Cole (1997). 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, 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 by 

the Boxcar fault and is distinguished by a relative abundance of tritium (DOE, 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 has been developed for 

the PM-OV study area to support modeling of groundwater flow and contaminant transport for the UGTA Project 

(BN, 2002c). 

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

(see Figure A-5). 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 utilized testing real estate at the NTS. Consequently, there are numerous drill holes which provide a 

substantial amount of subsurface geologic and hydrologic information (BN, 2002a; Warren et al., 2000a and 2002b). 

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

calderas which 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, 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. 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 (2002a).
A-28

Nevada Test Site Environmental Report 2006 Figure A-9. Generalized hydrostratigraphic cross section through the Silent Canyon complex, Pahute Mesa 
 Nevada Test Site Description

Nevada Test Site Environmental Report 2006 A-29

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

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 (Snyder, 1977; Gibbons et al., 1963). 

The 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 (13.7 and 13.25 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 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 (12.7 Ma) (Sawyer et al., 1994) which is further 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-and-range 

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 (2002c). 

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 USGS 

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, 2002c). 

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

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

A-30 Nevada Test Site Environmental Report 2006 

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

framework model (Table A-8). 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 6 HSUs, including 2 aquifers and 4 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 

Upper Paintbrush Confining Unit 

(UPCU) TCU Zeolitic, nonwelded and bedded tuff 
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Nevada Test Site Environmental Report 2006 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 

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 (BCU) 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 
 Nevada Test Site Description

A-32 Nevada Test Site Environmental Report 2006 

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

Hydrostratigraphic Unit 

(Symbol) 

Dominant Hydrogeologic 

Unit(s)(a) Typical Lithologies 

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 preTertiary sedimentary rocks intruded to varying 

degrees by igneous rocks. 

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) and the 

Pahute Mesa water table map (O’Hagan and Laczniak, 1996). 

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 utilized 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 
 Nevada Test Site Description

Nevada Test Site Environmental Report 2006 A-33

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

mapping data from the numerous 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-5). 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 edge 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, at 

the west end of Syncline Ridge (see Figure A-5). Ground-level elevations range from 1,707 to 2,012 m (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 Rainer Mesa and Aqueduct Mesa are composed of Miocene-age air-fall and ash-flow tuffs, 

which erupted from nearby calderas to the west and southwest. As in Yucca Flat, these silicic volcanic tuffs were 

deposited unconformably on an irregular pre-Tertiary (upper Precambrian and Paleozoic) 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). Most of Rainier 

Mesa and Shoshone Mountain consist of 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. 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 some workers speculate that the trace of the BRT 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/Aqueduct Mesa may reflect a paleo-topographic low 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
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A-34 Nevada Test Site Environmental Report 2006 

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

Shoshone Mountain UGTAs is scheduled to begin in fiscal year 2006. However, HGUs and HSUs in the Rainier 

Mesa and Shoshone Mountain area are expected to be similar to those defined for the Yucca Flat area (see Table A-7). 

The hydrostratigraphy of the pre-Tertiary section is unknown at Shoshone Mountain, and is poorly known at Rainier 

Mesa. At Rainier Mesa, granitic rocks (related to the nearby Gold Meadows Stock), carbonate rocks, silicic 

sedimentary rocks such as siltstone, and metamorphic rocks such as quartzite and schist 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 pre-Tertiary section. 

Most of the tests in Shoshone Mountain and Rainier Mesa tunnels were conducted in the tuff confining unit, though a 

few were conducted in vitric bedded tuff higher in the stratigraphic section. 

Water–level Elevation and Groundwater Flow Direction – The regional water level at Rainier Mesa is not well 

known, but is estimated to be at an elevation of approximately 1,280 m (4,200 ft) in the pre-Tertiary carbonate rocks 

that underlie the volcanic section. This is approximately 300 m (1,000 ft) below the average elevation of test locations 

in Rainier Mesa. The SWL, where measured in a few drill holes 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). Abundant 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 elevation at Shoshone Mountain is not known. 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 (see Figure A-5). The groundwater flow 

direction beneath Shoshone Mountain is probably southward. 

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 table for local aquifers in the valleys and the 

underlying regional carbonate aquifer are relatively flat. The zeolitic volcanic formation (TCU) separating the 

shallower alluvial and volcanic aquifers and the regional carbonate aquifer (LCA) appears to be a viable aquitard. 

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 to 

operate. 
 Nevada Test Site Description

Nevada Test Site Environmental Report 2006 A-35

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, 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, midtropospheric 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 south-eastern North Pacific Ocean and spread over the desert 

southwest. This seasonal event is referred to as the south-western monsoon. The winter-summer precipitation 

mechanisms produce a bi-modal monthly precipitation cycle. Figure A-11 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 33 centimeters (cm) (13 inches [in.]) over the high terrain in the 

north-western 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 cm (26.79 in.) fell on Rainier 

Mesa in 1978. 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 (2.0 to over 3.5 in.). The greatest daily 

precipitation event on the NTS was 9.32 cm (3.67 in.), which was measured in Mid-Valley on October 19-20, 2004. 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. 

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 

Centigrade (oC) (100 degrees Fahrenheit [oF]). In the dry lakebeds, daily temperature ranges can be 22.2 to 33.3oC 

(40 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-12. 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, the average daily temperature minimum and maximum for January is -4.4 to 13.3 oC 

(24 to 56oF), while in July it is 16.7 to 38.9oC (62 to 102oF). By contrast, on Pahute Mesa, the minimum and 

maximum temperature for January is -3.9 to 5oC (25 to 41oF ) and for July, 16.1 to 28.9oC (61 to 84oF .) 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 -11.7 to 45oC (11 to 113oF). 
 Nevada Test Site Description

A-36 Nevada Test Site Environmental Report 2006 

40-MI Canyon (40MN) Average Monthly Precipitation, 1960-2003 

Average Annual Precipitation = 7.81 inches

0

0.2

0.4

0.6

0.8

1

1.2

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Inch

Desert Rock (DRA) Average Monthly Precipitation, 1964-2003 

Average Annual Precipitation = 5.72 inches

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Inch

Frenchman Flat (W5B) Average Monthly Precipitation, 1963-2003 

Average Annual Precipitation = 4.77 inches

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Inch

Jackass Flats (4JA) Average Monthly Precipitation, 1958-2003 

 Average Annual Precipitation = 5.45 inches

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Inch

Pahute Mesa (PM1) Average Monthly Precipitation, 1964-2003

Average Annual Precipitation = 7.54 inches

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Inch

Yucca Flat (BJY) Average Monthly Precipitation, 1960-2003

Average Annual Precipitation = 6.17 inches

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Month

Inch

Figure A-11. Mean monthly precipitation at six NTS MEDA stations 
 Nevada Test Site Description

Nevada Test Site Environmental Report 2006 A-37

Figure A-12. Temperature extremes and normal maximums and minimums at six NTS MEDA stations 
 Nevada Test Site Description

A-38 Nevada Test Site Environmental Report 2006 

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 11:00 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 (kmh) (8 to 12 miles per hour [mph]) with the faster speeds occurring at the higher elevations. Peak wind 

gusts of 80 to 113 kmh (50 to 70 mph) have occurred throughout the NTS. Peak winds at Mercury have been as high 

as 84 mph during a spring wind storm. Frenchman Flat experienced wind gusts to 113 kmh (70 mph) during the 

same windstorm. The peak wind speeds measured on the NTS are above 145 kmh (90 mph) on the high terrain with 

maximums of 146 kmh (91 mph) at Yucca Mountain Ridge-top, 148 kmh (92 mph) at the Monastery (MEDA 

Station 10) in Area-6, and 151 (94 mph) in Area-12 on Radio Hill. 

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 six stations on the NTS are shown in 

Figure A-13. 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 percent 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. 

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 those stations at 

lower elevations. Moreover, since 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 and 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), 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 phenomena 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. 
 Nevada Test Site Description

Nevada Test Site Environmental Report 2006 A-39

Figure A-13. Twenty-year wind rose climatology for the NTS 
 Nevada Test Site Description

A-40 Nevada Test Site Environmental Report 2006 

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 mountain-valley 

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 (2000). 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 kmh (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.
 Nevada Test Site Description

Nevada Test Site Environmental Report 2006 A-41 

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 10 major vegetation alliances (Figure A-14). A total of 

20 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-14). 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, an open woodland type with a mix of shrub and tree cover. 

There are no plants on the NTS which are listed as threatened or endangered under the Endangered Species Act. 

However, there are 18 plant species and 1 moss species on the NTS considered to be sensitive by the Nevada Natural 

Heritage Program (see Chapter 13, 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 14 sensitive species have been mapped on the NTS (Figure A-15), and many of these species as well as 

new species continue to be monitored under the Ecological Monitoring and Compliance Program (see Chapter 13). 

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 as regards distribution, abundance, and functional roles. No native fish species occur on the NTS, 

although non-native goldfish, golden shiners, and bluegills have been unofficially introduced into a few man-made 

ponds. The non-native bullfrog is the only amphibian that is known to occur on the NTS. 

Among reptiles, the desert tortoise, 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), desert horned lizard (Phrynosoma platyrhinos), and desert 

spiny lizard (Sceloporus graciosus). 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). 
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A-42 Nevada Test Site Environmental Report 2006

Figure A-14. Distribution of plant alliances on the NTS 
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Nevada Test Site Environmental Report 2006 A-43 

Figure A-15. Known locations of sensitive plant species on the NTS
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A-44 Nevada Test Site Environmental Report 2006

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. The raptors which breed on the NTS include the golden eagle (Aquila chrysaetos), longeared 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, 2002b). 

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, desert and Nuttall’s cottontail rabbits, feral horses, mule deer, pronghorn antelope, coyote, kit fox, badger, 

bobcat, and mountain lion. Mule deer herds occur mainly on the high mesas and surrounding bajadas. Small 

numbers of wild horses and pronghorn antelope range over small areas of the NTS. Bighorn sheep and burros are 

thought to be rare visitors. 

The desert tortoise (Gopherus agassizii) is the only resident species found on the NTS which 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). The bald eagle is a threatened bird which is a rare migrant on the site. No other 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 12 bats on the NTS are 

considered sensitive species (see Chapter 13, Tables 13-2 and 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 30 natural water sources on the NTS which include 15 springs, 9 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-16). 
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Figure A-16. Natural water sources on the NTS 
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A-46 Nevada Test Site Environmental Report 2006

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, a.k.a. “Death Valley Curley,” a local miner, into the Fortymile Canyon region with 

the specific purpose of investigating archaeological sites (Figure A-17). The party spent only a few days in the area, 

how, 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-18), as well as records keeping 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-19). 

Figure A-17. Example of prehistoric petroglyphs found on the NTS. This rock art site is in 

Fortymile Canyon (photo by DRI, 1996). 
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 Figure A-18. DRI archaeologist at an archaeological excavation of a prehistoric site on

 Pahute Mesa. The site is probably from the middle to late Holocene period

 (photo by DRI, 1992). 

Figure A-19. Building 400, a camera station for photographing atmospheric tests, at 

Area 6 Control Point, built in 1951. One of the first buildings constructed 

on the NTS to support weapons testing activities (photo 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, 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, however (Haynes, 1996; Reno et al., 1989); 

and 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, and 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 are becoming 

an important part of the subsistence base and coincides 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, semi-sedentary 

communities on valley floors accompanied by a more frequent use of the highlands. An increase in the frequency of 
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Nevada Test Site Environmental Report 2006 A-49 

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-20. 

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-21), ca. 700 to 1,000 BP 

(Lockett and Pippin, 1990; Madsen, 1986b; Pippin, 1986; Rhode, 1994), indicating a more sedentary lifestyle and a 

change in the way food was prepared and stored. 

Figure A-20. Prehistoric projectile points from the NTS (photo by DRI, 1992) 
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Figure A-21. Brownware bowl recovered from archaeological excavations on Pahute Mesa 

(photo 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-22), 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, and 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-22. Overview of the Tippipah Spring Area (photo 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 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. 
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A-52 Nevada Test Site Environmental Report 2006

(1996), the mining town of Wahmonie in the southern part of the NTS around Mine and Skull mountains 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 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 that 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-23) at a mining camp near Oak Spring 

(McLane, 1996) (see Figure A-16). 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 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. 
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Nevada Test Site Environmental Report 2006 A-53 

Figure A-23. Bower cabin on the NTS (photo by DRI, 2001) 
References – Nevada Test Site Description

A-54 Nevada Test Site Environmental Report 2006

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