sg Geology of the Atomic

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5 GEOLOGICAL SURVEY BULLETIN 1021-K

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A CONTRIBUTION TO GENERAL GEOLOGY

GEOLOGY OF THE ATOMIC ENERGY COMMISSION 

NEVADA PROVING GROUNDS AREA, NEVADA

By MIKE S. JOHNSON and DONALD E. HIBBARD

ABSTRACT

The Nevada proving grounds area in Nye and Clark Counties, Nev., is about 

700 square miles in size and lies about 70 miles northwest of Las Vegas in southern 

Nevada. It consists essentially of two large valleys, Yucca and Frenchman Flats, 

both surrounded and separated from one another by hills and mountains of variable 

relief.

Seventeen Paleozoic formations and one of Tertiary age have been recognized in 

the Nevada proving grounds area. The Paleozoic formations are Early Cambrian 

to probable early Permian in age and consist of 22,000 feet of limestone, dolomite, 

quartzite, shale, and conglomerate beds. The predominantly volcanic Oak Springs 

formation of Tertiary age is at least 2,000 feet thick and is the most widespread 

formation in the area. A granitic intrusion of probable Late Cretaceous to early 

Tertiary age has metamorphosed and mineralized some of the Paleozoic rocks, and 

dikes of middle Tertiary or later age occupy normal faults along the northeastern 

margin of the area. Quaternary deposits reaching a maximum thickness of more 

than 800 feet are mostly a heterogeneous mixture of detritus derived from bedrock 

areas. This fill contains some caliche and fanglomerates. Playas made up wholly 

of impermeable fine, silt and clay are present.

During the Mesozoic era uplift and attendant folding and contemporaneous 

thrust faulting occurred, probably in Cretaceous time. Normal faulting began in 

early Tertiary time, followed by volcanic deposition and later by continued normal 

fault displacement.

INTRODUCTION

The Nevada proving grounds area is in southeastern Nye County 

and along the extreme northwest margin of Clark County, Nev., about 

70 miles northwest of Las Vegas (fig. 57). The area is about 42 miles 

long and from 16 to 18 miles wide, comprising a total of about 700 

square miles. The proving grounds lie in the Great Basin section of 

the Basin and Range physiographic province.

The proving grounds area consists of two major valleys, Yucca Flat 

to the north and Frenchman Flat to the south. These valleys are 

bordered by hills and ridges of moderate relief.

The geologic study of the Atomic Energy Commission Nevada proving grounds area, Nye and Clarke Counties, was made and the present

333
334 CONTRIBUTIONS TO GENERAL GEOLOGY

118°

CLARK

®lndion 

] Springs LAKE§

Areas referred to in this report

1. Pioche district

2. Groom district

118° 116°

FIQTTKE 67. lnd$x mao showing areas (cross ruled) described In this report and other areas.

report was written while the writers were in the U. S. Army stationed 

at the Mercury Test site. The report is being published by the 

Geological Survey so that geologic data for an area that is now inaccessible will be available to those interested in the geology of 

southern Nevada.
GEOLOGY, ATOMIC ENERGY COMMISSION PROVING GROUNDS 335 

PREVIOUS INVESTIGATIONS

A brief mention of part of the Nevada proving grounds area is included in Ball's report (1907) on the geology of southwestern Nevada 

and eastern California. In 1951 A. M. Piper carried out reconnaissance 

investigations of Yucca Flat. The writers, who served as assistants to 

Piper on this project, have incorporated many of the results of his 

work in this report.

The southeastern part of the area lies within the Las Vegas quadrangle, which is being mapped by C. R. Longwell, who kindly supplied 

important information on parts of the area. Nolan (1929) has mapped 

the northwestern part of the Spring Mountains, about 15 miles south 

of the proving grounds. Hazzard (1937) has described the Paleozoic 

stratigraphy hi the Nopah-Resting Springs Mountains, Inyo County, 

Calif., about 40 miles to the south. Ten miles northeast of the proving 

grounds, Humphrey (1945) reported on the geology of the Groom lead 

and silver mining district.

PRESENT INVESTIGATION

Reconnaissance was done in the Nevada proving grounds area in 

the fall of 1951 under the direction of A. M. Piper. The writers did 

the detailed mapping between February and mid-August, 1952.

ACKNOWLEDGMENTS

The writers wish to thank Col. Gordon B. Page, U. S. Army, 

who was in charge of the project, for his critical analysis of the written 

report. . . We are indebted to the following for their contributions to this report: T. B. Nolan, C. W. Merriam, Allison Palmer, Helen Duncan, 

Josiah Bridge, Raymond Douglass, J. Steele Williams, J. Brookes 

Knight, Edwin Kirk, Arthur Boucot, and T. C, Yen of the U. S. 

Geological Survey and the U. S. National Museum, for identification 

of fossil collections and for assistance in the field; C. R. Longwell for 

his criticism and aid in the field and for his review of the manuscript; 

and C. W. Merriam and J. H. Wallace for revision of the manuscript.

STRATIGRAPHY

The exposed rocks in the Nevada proving grounds include a wide 

variety of sedimentary rocks of Paleozoic age, as well as Tertiary 

volcanic rocks and Quaternary valley fill (pi. 32).

The Paleozoic rocks have an aggregate thickness of about 22,000 

feet of which more than 16,000 feet is limestone and dolomite. The 

rest is dominantly conglomerate, quartzite, and shale. Fossils occur 

in many beds of limestone, dolomite, and shale but are absent in the 

other rocks. These sedimentary rocks range in age from Early 

Cambrian to probable early Permian.
336 CONTRIBUTIONS TO GENERAL GEOLOGY

The Tertiary rocks have a minimum thickness of about 2,000 feet. 

They consist mostly of rhyolite and tuff but include many other 

igneous types. Locally, near the base, these rocks are interbedded 

with layers of conglomerate and fresh-water, marly limestone containing fossils of probable Miocene age.

Quaternary rocks form the valley fill of Yucca and Frenchman 

Flats. These rocks consist of a heterogeneous mixture of detritus 

derived from adjacent bedrock areas.

A stratigraphic column showing the exposed rocks in the area is 

included (pi. 33). This column is a composite of 10 partial sections 

measured at different localities in the area. It was not possible to 

obtain a stratigraphic section to include all units between the Cambrian 

and Permian (?), the oldest and youngest pre-Tertiary rocks exposed, 

because of faulting and cover by alluvium or Tertiary volcanic rocks. 

Correlation between the partial sections is based on distinctive 

paleontological and lithologic characteristics.

CAMBRIAN ROCKS

STIRLING QUARTZITE

The Stirling quartzite is restricted to several high hills northeast of 

Yucca Flat. The outcrops range in width as much as 3,000 feet and 

are traceable northwestward for about 4 miles. The type locality

of the Stirling is in the northwest Spring Mountains, where it was 

originally denned by Nolan (1929).

That part of the Stirling quartzite exposed in the area consists of

quartzite interbedded with a few layers of shale. The quartzite is 

light gray, lead gray, and brown but includes some beds exhibiting 

distinct color-banding. It is generally poorly bedded, granular in 

texture, and shows indistinct crossbedding. In a few zones, quartz 

pebble conglomeratic beds are interbedded with the quartzite. The 

shale is generally gray, brown, and greenish, Where examined,

these shale beds are also hard micaceous thin-bedded and slopeforming. Characteristically, the Stirling forms hills of moderate to

high relief that, in places, have talus-covered slopes.

The Stirling is well set off irom, and conformably overlain by the 

Pioche shale. The nature of the lower contact is not known because 

the Stirling is the oldest formation recognized in the area.

This formation is only partly exposed. The exposure was not 

measured but the thickness was estimated to be at least SOO feet, 

of which 95 percent is quartzite. This figure is considerably less than

the 3,700 feet exposed at the type locality south of the area (Nolan,
GEOLOGY, ATOMIC ENERGY COMMISSION PROVING GROUNDS 337

1929) or less than the 7,855 feet reported at the Groom district 

(Humphrey, 1945). ^

The Stirling quartzite is probable Early Cambrian in age for it 

conformably underlies shale beds containing late Early Cambrian 

fossils. It is similar in age and lithologic characteristics to the Stirling 

of the northwest Spring Mountains and hence is correlated with it. 

The Prospect Mountain quartzite of the Groom district also corresponds in lithologic characteristics and stratigraphic position to this 

unit and is considered as the probable correlative of the Stirling.

PIOCHE SHALE

The Pioche shale is recognized in several small hills and gullies 

about iy2 miles east of Banded Mountain in northeastern Yucca Flat. 

These exposures are separated by alluvium or Tertiary volcanic rocks 

making correlation between outcrops difficult. Many of these outcrops are not shown on the map because of their small size. However, 

in the field they may be recognized at a distance by their buff color 

and sharp contrast to the other beds. Walcott (1908) defined this 

formation from the Pioche district, Nevada.

The Pioche consists of buff to reddish-brown, highly micaceous 

shale containing thin interbedded limestone. The shale is generally 

flaky, slope forming, fossiliferous, and contains some silty beds. A 

few beds are ripple marked and some are foliated because of the large 

amount of mica in the shale. In places, the Pioche contains several 

beds of dark-gray hard micaceous, quartzitic shale in layers a few 

inches thick.' Elsewhere, limestone is interbedded with the shale in 

layers a few feet or less thick. The beds are generally dark gray, buff 

weathering, thin bedded, fossiliferous limestone containing much buff 

to red clastic material. Because of faulting and incomplete exposures, 

the stratigraphic position of these limestone beds within the Pioche 

was not definitely established. However, they appear to be more 

common in the middle and lower parts of the formation.

Distinct lithologic breaks separate the Pioche from the overlying 

and underlying formations. The lower contact is at the base of the 

lowermost buff-colored shale bed, and the upper boundary is at the 

break between shale and overlying limestone.

Only the upper 150 feet of the Pioche was measured in the area 

because of faulting and inability to correlate between outcrops. At 

the Groom district, the Pioche shale is 961 feet thick (Humphrey, 

1945). This figure probably approximates the thickness of this formation in the Nevada proving grounds.

Trilobites were found in the lower and middle parts of the Pioche

398882 57 2
338 CONTRIBUTIONS TO GENERAL GEOLOGY

shale. These fossils were examined by A. R. Palmer (written communication) who reports:

Olenellus gilberti Meek 

fremonti Walcott 

Paedumias transitans Walcott 

Peachella sp.

This is a typical Lower Cambrian assemblage. Peachella is a striking olenellid 

trilobite that seems to be widespread in the Great Basin in the upper part of the 

Lower Cambrian.

Some of the same fossils are reported in the Pioche from the Groom 

district where fossils of Middle Cambrian age have also been found 

(Humphrey, 1945). By fossils, stratigraphic position, and lithologic 

similarity, the Pioche in the Nevada proving grounds is correlated 

with the Pioche of the Groom district and consequently is considered 

of Early and Middle Cambrian age.

I^TNDON LIMESTONE

Exposures of the Lyndon limestone are limited to a discontinuous, 

faulted, narrow band about 1^ miles east of Banded Mountain. 

These outcrops are about 300 feet wide and are traceable northward 

for about 2K miles. Westgate (1927) originally defined the Lyndon 

at the Pioche district, Nevada.

The Lyndon consists of light to medium-gray, mottled, generally 

finely crystalline, resistant limestone. Characteristically, it contains 

many oval and elongate, concentric algal masses, commonly an inch

or more in size. These "Giruanella" beds occur throughout the 

formation. In some places the Lyndon contains pink to reddishbrown silty limestone and at those places may be less resistant. Some

buff to reddish-brown oolitic material also occurs in a few of the beds.

The contact of the Lyndon limestone with the underlying and 

overlying formations is conformable and at both places is at the lithologic break between limestone and shale. 

A total thickness of 245 feet was measured for the Lyndon limestone

in the area.

Fossil fragments from the upper part of the Lyndon limestone

establish it as Middle Cambrian. These fossils were examined by 

A. R. Palmer (written communication) who identified them as:

Kosknfa sp.

Ptarmigania? sp.

pOSition; UtholOgiO aimilarities and tb.e

" Girvanella" beds, the Lyndon of the Nevada proving grounds area 

is correlated with the Lyndon limestone of the Groom district,
GEOLOGY, ATOMIC ENERGY COMMISSION PROVING-GROUNDS 339 

CHISHOLM SHALE

The Chisholm shale is exposed about 2 miles east of Banded Mountain. The outcrop extends for about 2^ miles as a narrow, northwardtrending, discontinuous band a few hundred feet wide. Because of 

its nonresistant character, it forms gently sloping low hills.. This 

formation was originally defined by Walcott (1908) at the Pioche 

district, Nevada.

The Chisholm consists of brown, buff-weathering, slightly micaceous shale. In places, the shale beds are silty. Some of the shale 

layers break into small, sharp, angular pieces and others weather into 

flat, platy fragments. One or two dark-gray, resistant limestone 

beds, a few feet or less thick, are exposed about 110 feet above the 

base of this formation.

The Chisholm shale is sharply set off from, and lies conformably 

over the Lyndon limestone and under the Jangle limestone. Each 

contact is at the lithologic break between shale and limestone. A 

complete thickness of this formation was obtained and measured as 

320 feet.

No fossils were found in the Chisholm shale in the area. However, 

in the Groom district, the Chisholm is Middle Cambrian in age because it is underlain and overlain by beds containing Middle Cambrian 

fossils (Humphrey, 1945). The Chisholm shale of the Nevada proving grounds area is correlated with the Chisholm shale of the Groom 

district by lithologic similarities and stratigraphic position and is thus 

considered as Middle Cambrian in age.

JANGLE LIMESTONE

The section of beds which is here named the Jangle limestone crops 

out on Jangle Ridge and also occupies several of the hills a few miles 

to the south. The name Jangle limestone is substituted for the 

Peasley limestone of Wheeler (1940) in the Pioche and Groom districts 

because of differences in thickness, lithologic characteristics, and 

possibly in formational boundaries. In the field the Jangle may be 

identified by its prominent, ledge-forming upper and lower units and 

generally slope forming middle unit. ' .

The Jangle is subdivided into three units, each of which consists of 

limestone.

The lower unit is 80 feet thick and consists of dark smoky-gray to 

steel-gray, prominent, ledge-forming limestone containing buff irregular silty partings. The lower 40 feet of this unit includes some wellbedded resistant finely crystalline limestone beds a few inches thick. 

The remaining 40 feet of the unit is dominantly resistant, calcitic, 

poorly to fairly well bedded limestone.
340 CONTRIBUTIONS TO GENERAL GEOLOGY

The middle unit is 115 feet thick. The beds consist of dark-gray 

limestone containing much buff to reddish-brown silty material which 

is distinctive for its slope-forming character.

The upper unit of the Jangle is 80 feet thick and consists of darkgray to smoky-gray ledge-forming limestone containing a few buff 

silty partings and round, concentric algal masses. This formation is 

completely exposed on Jangle Ridge where it is 275 feet thick.

The Jangle limestone lies in conformity with the underlying Chisholm shale and with the overlying Yucca Flat formation. The lower 

boundary is at the lithologic break between shale and overlying limestone. The upper contact is at the break between the dark-gray 

limestone of the Jangle and the lowest, light-gray limestone bed of 

the Yucca Flat formation.

" Crirvanella" were_the only fossils found in the Jangle limestone. 

However, in the Groom district, the Jangle is lithologically similar to 

most of the Peasley limestone of Wheeler. At that locality, the 

Peasley of Wheeler directly overlies the Chisholm shale and is listed as 

Middle Cambrian in age (Humphrey, 1945). Because of the relationship, the Jangle is correlated for the most part with the Peasley limestone of Wheeler in the Groom district, and is assigned a Middle 

Cambrian age.

YUCCA FLAT FORMATION

The name Yucca Flat formation is hereby given to all beds lying 

between the Jangle limestone and the Dunderberg shale on the east

side of Yucca Flat in the Nevada proving grounds area.

This formation is the most widely distributed Cambrian unit in 

the area. It crops out boldly along the northeast margin of Yucca 

Flat and occupies many hills and ridges of great relief. Banded 

Mountain obtains its name from the alternating beds of dark and lightcolored limestone and dolomite so characteristic of parts of this formation. The most complete section of the Yucca Flat is exposed from 

Jangle Ridge to Banded Mountain. However, owing to faulting, 

this section is not continuous.

The Yucca Flat formation consists of limestone and dolomite and 

is subdivided into two parts. The upper part contains four recognizable units, A through D in ascending order.

The lower part is 395 feet thick, nearly all of which is limestone.

The limestone beds are generally light to medium gray and weather a 

mottled buff to gray. Characteristically they form prominent ledges

which weather into a rough, sharp surface. Commonly they contain 

stringers and specks of calcite. The upper portion of this part

includes an alternating sequence of light and dark-gray, fine to medium

crystalline limestone beds which have a subdued banded appearance, 

Interbedded with these banded beds are a few thin dark and light-gray
GEOLOGY, ATOMIC ENERGY COMMISSION PROVING GROUNDS 341

finely laminated dolomite beds totaling about 15 feet in thickness. 

Sixty feet from the base of this part is a dark-gray and buff, silty 

limestone, 30 feet thick, similar lithologically to the underlying Jangle 

limestone.

About 355 feet of black to dark-gray, finely crystalline, fairly well 

bedded limestone comprise unit A, which overlies the lower part. 

This unit is easily recognized in the field by its sharp contrast to the 

lighter colored limestone beds directly above and below.

The basal 20 feet of unit B is made up of light-gray limestone. 

These beds are separated from the remainder of the unit by a large 

fault. Because of this faulting, the total thickness of this unit 

was not established but at least 1,450 feet of section was measured 

and the total thickness probably exceeds this figure by hundreds of 

feet. That part of unit B lying above the fault is made up dominantly of an alternating sequence of dark limestone and light dolomite. 

At a distance, these interbedded dark and light beds form a diagnostic 

banded color effect. The limestone is commonly dark gray to black 

finely crystalline and resistant. Many of the limestone beds emit a 

fetid odor upon being struck by a hammer. The dolomite beds are 

generally several .shades of gray and buff. They are nonresistant 

finely crystalline to cryptocrystalline and many weather into tabular 

fragments or spalls. Some fragments ring like china when struck. 

Many rocks of this unit are of dark limestone and light dolomite in 

an alternating series of fine laminations, a fraction of an inch thick.

Unit C consists of 380 feet of light-gray to light-buff finely crystalline 

to cryptocrystalline very well bedded aphanitic limestone. It 

occurs in beds about 1-2 feet thick and is well exposed in bold, bare 

outcrops. The lower part of the unit weathers to a light yellowish 

brown which is easily identifiable on Banded Mountain. The 

remainder of this unit weathers light gray and lies in sharp contact 

with the overlying dark unit.

Unit D, the uppermost 235 feet of the Yucca Flat formation, is 

a dark-gray to black well-bedded fossiliferous resistant limestone. 

Generally it is finely crystalline but contains much calcite and in 

places has been recrystallized, probably from dolomite.

The underlying and overlying contacts of the Yucca Flat formation 

are conformable and are placed at distinct lithologic breaks. The 

lower contact is at the base of the lowermost, light-gray limestone 

bed of the Yucca Flat and the upper boundary is at the contact 

between dark-gray limestone and overlying Dunderberg shale.

The measured thickness of the Yucca Flat formation, including 

the lower member, the partial section of unit B, and the complete 

sections of the other three units, is at least 2,815 feet. The total 

thickness is considerably more.
342 CONTRIBUTIONS TO GENERAL GEOLOGY

The only faunal evidence for the age of the Yucca Flat was obtained 

from unit D. A. K. Palmer (written communication) reported on 

fossils collected from two zones within this unit as follows:

Collection from the upper part of the dark limestone unit below the 'Dunderberg' : 

Micromitra sp. 

Pseudagnostus sp. 

Acrotretid brachiopods 

Two undescribed trilobite genera

This collection is late Dresbach (early Late Cambrian) in age. The fauna has 

never been reported from the Great Basin although it is now known to be present 

at several localities.

In the lower portion of the dark limestone unit below the 'Dunderberg', representatives of Meteoraspis and Crepicephalus, characteristic Dresbachian trilobites, 

were seen.

Although no fossils were collected in the units underlying unit D, 

their stratigraphic relationship with overlying and underlying fossilbear ing beds indicates these units are mostly Middle Cambrian in age.

Lithologically, the lower part of the Yucca. Flat is similar to the 

Burrows dolomite of Wheeler (1940) in the Groom district. However, 

the lower part is much thicker and the lower contact is at a lithologic 

break unlike the lower contact of Wheeler's Burrows in the Groom 

district (Humphrey, 1945). Unit A is also lithologically similar to the

basal part of the Highland Peak limestone, which overlies Wheeler's 

Burrows at Groom, and the color-banded beds of unit B are found in 

higher units of the same formation.

For these reasons, the stratigraphic interval represented by the 

Yucca Flat formation corresponds to most of Wheeler's Burrows and 

the Highland Peak limestone as used by Humphrey (1945) at Groom,

and is assigned a Middle Cambrian to early Late Cambrian age,

The Dunderberg shale is recognized on the lower slopes of the west 

side of Banded Mountain and is also exposed about a mile east of

Palute Ridge. It characteristically forms low, gently sloping hills or 

a break in slope below the resistant limestone beds of the overlying

formation. This shale is generally exposed as a narrow northwardtrending band. The Dunderberg was originally called Hamburg shale

l?y Hague (1892) a,t tHo Evu-cko. district, Nevada.. La-ter-, it was renamed Dunderberg stale by Wfllcott (1908) to eliminate COnfUSlOH 

with the underlying Hamburg dolomite in that district.

THe D under berg consists of brown and reddist -brown Hard, fissile,

nonreslstant stale and several thin beds of dark-gray and reddish-gray

argillaceous fine-grained fossiliferous limestone. The limestone commonly forms resistant ledges between the slope-forming shale beds.

Where measured on the west side of Banded Mountain, the Dunderberg is 195 feet thick.
GEOLOGY, ATOMIC ENERGY COMMISSION PROVING GROUNDS 343

The age of the Dunderberg is well established as Late Cambrian by 

a fossil collection from limestone in the upper part of that unit. Concerning the fossil collection, A. R. Palmer (written communication) 

reports as follows:

Four trilobites are quickly recognizable "Pterocephalina," Pseudagnostua, 

Geragnostus, and Dunderbergia. This is the same association found in the Dunderberg at Eureka. In that area, this association1 is considered to be latest Dresbach 

or earliest Franconia in age.

Palmer's findings indicate that this formation is correlated with the 

Dunderberg of the Eureka district and is assigned an early Late 

.Cambrian age. Fissile green shale and limestone containing a similar 

Late Cambrian fauna are also found in the Las Vegas quadrangle 

(C. R. Longwell, oral communication).

UPPER CAMBRIAN ROCKS

In the Yucca Flat area post-Dunderberg, pre-Pogonip strata have 

a thickness of about 2,660 feet, part of which can be closely correlated 

with like strata in the Eureka district, Nevada. In redefining the 

"Pogonip limestone" at Eureka, Hague (1892) retained these rocks 

in that division. More recently they have been described (Nolan 

and others, 1956) as an independent Upper Cambrian formation 

comprising two members, and are excluded from the Ordovician 

Pogonip group. At Yucca Flat the limestone and dolomite of this 

interval are provisionally referred to as Upper Cambrian rocks. 

Four units, A through D, are described in ascending order.

Contact between Upper Cambrian rocks and overlying Pogonip is 

provisionally drawn at a break between dolomite and overlying limestone. (At this boundary limestone and dolomite are interbedded, 

the contact being placed at the top of the uppermost dolomite bed of 

the Upper Cambrian rocks.) The lower contact of Upper Cambrian 

rocks is conformable, being drawn at a break between limestone and 

the underlying Dunderberg shale.

Units A, B, and C of the Upper Cambrian rocks crop out on the high 

hill west of Banded Mountain. Southward, nearly all the overlying 

units are exposed on Paiute Ridge. Because of faulting at this 

locality the lower contact of unit D is not exposed. As it does not 

.crop out elsewhere in the area, this division constitutes the only incompletely measured part of the Upper Cambrian strata.

Unit A consists of 80 feet of brownish-gray limestone containing 

buff to reddish-gray silty partings. These beds are fossiliferous, 

cherty, and nodular. They generally occur in well-defined beds a few 

feet thick which form alternating resistant and nonresistant ledges.

Unit B is a dark- to smoky-gray aphanitic limestone, 360 feet thick, 

containing many thin bands of reddish-gray silty material. It is
344 CONTRIBUTIONS TO GENERAL GEOLOGY

characterized by extremely well defined beds 1-2 inches thick. 

Typically, the lower 150 feet weathers into a talus slope of thin flat 

plates which have a light-gray sandy surface. Localty these surfaces 

display indications of trilobites. The remaining upper 210 feet of 

limestone contains lenses and nodules of gray chert which weathers 

orange brown. Because of the chert, these beds are resistant and 

are prominent ledge formers.

At least 1,115 feet of poorly bedded massive gray, dark-gray, and 

black mottled limestone containing many thin calcite veinlets composes unit C. It is generally finely crystalline although some mediumcrystalline beds are in the upper part. The lower 260 feet also contains many gray chert lenses a few inches thick and in places several 

feet long.

Unit D is 1,105 feet or more thick. This unit consists chiefly of 

medium-gray and dark-gray dolomite. The dolomite is finely crystalline and fairly well to poorly bedded. Characteristically, it contains 

thin bands of white to pink coarse dolomite crystals. Some beds are 

cherty and others show distinct crossbedding. In other places, the 

unit displays a rough, pitted sandy surface. About 200 feet from the 

top is a 55-foot bed of dark-gray finely crystalline calcitic limestone. 

Other thin dark-gray limestone layers, interbedded with the dolomite, 

are also in the lower part of this unit.

Unit A, basal division of the Upper Cambrian undesignated, contains fossils examined by A. R. Palmer (written communication), who 

reports as follows:

Irvingella major TJlrich and Resser

Qeragnostus sp. 

Pseudagnostus sp. 

Kinbladia sp. 

Litocephalus sp.

Pterocephalia sp.

Elvinia sp. 

Dunderbergia sp.

Meosp.

This large fauna is characteristic of the Elvinia zone of Franconia age. Except

for Delka and Kinbladia the assemblage is the same as that in the basal beds of

ivlae (ixew post-JDunclerloerg, r>ire !*ogonir> formation) *>-"t Eureka..

Unit B contains an unusual trilobite fauna and concerning them; 

A. R. Falmer states:

B-ienvillia sp>.

Loganellus sp.

Geragnostus sp.

Inasmuch as this collection is bracketed by fossiliferous beds of FraHCOnia ag6,

primarily from boulders in the Levis conglomerate in Quebec. BminUia also 

occurs in the Eureka district (near the middle of the new Upper Cambrian formationed mentioned above).
GEOLOGY, ATOMIC ENERGY COMMISSION PROVING GROUNDS 345

Float from an unknown zone in the lower 100 feet of unit C yielded 

fossils concerning which A. K. Palmer reports:

Pseudagnostus 

Idahoia sp. 

Wilbernia sp.

This collection represents a horizon in the Ptychaspis zone from the upper part 

of the Franconian stage indicating that there is still Upper Cambrian in the 

section [above unit B].

Fossils were not collected from the thick remaining part of unit C 

nor from unit D. Some doubt therefore remains as to the age assignment of these units.

CAMBRIAN ROCKS UNDIFFERENTIATED

Immediately west of Yucca Pass, the exposed rocks consist of strata 

assignable to the Lower, Middle, and Upper Cambrian formations. 

These rocks have been intensely deformed and in most places are not 

recognizable as mappable units. For this reason, these formations 

are grouped together and are mapped as Cambrian rocks, undifferentiated.

OBDOVICIAN ROCKS 

POGONIP GROUP

King (1878) originally defined Pogonip as beds that conformably 

underlie the "Ogden quartzite" (later named Eureka quartzite) and 

conformably overlie "Cambrian quartzite" (Prospect Mountain 

quartzite). Hague (1892) later redefined "Pogonip limestone" as 

the beds overlain by the Eureka quartzite and underlain by "Hamburg 

shale" (later named Dunderberg shale).

In recent years the term "Pogonip" has been applied mainly to 

strata of Ordovician age. As redefined in the Eureka mining district, 

Nevada (Nolan and others, 1956), Cambrian strata have been excluded 

from the lower part of the group. Considered as a group the Pogonip 

of the Eureka area embraces several mappable formations falling 

between the top of the Cambrian system and the base of the Eureka 

quartzite. In the Nevada proving grounds area the latter definition 

is applied arbitrarily.

Reconnaissance of the present stratigraphic study does not favor 

the formal naming of new formational divisions within the Pogonip, 

though such procedure may eventually be called for. Accordingly a 

provisional subdivision is employed with nine minor units designated 

as units A through / in ascending order.

Rocks of the Pogonip group are exposed over large areas in the 

mountains surrounding Yucca and Frenchman Flats. East of Yucca 

Flat the section is essentially complete. Small outcrops are found 

along the southwest margin of Yucca Flat where the Pogonip is

898882 67 8
346 'CONTRIBUTIONS TO GENERAL GEOLOGY

involved in complex thrust faulting. A single small exposure occurs 

in the northern part of the same valley. It is entirely surrounded by 

alluvium and lies about 1,000 feet from strata of Carboniferous age, 

offering one of the more puzzling structural problems in the area.

About 2 miles northeast of Oak Spring Butte unit / is exposed in 

steeply-dipping, northward-trending beds that are terminated on the 

east by Butte fault.

The west front of Ranger Mountains is made up entirely of Pogonip 

units F, G, H, and /. Except for G, these units are all very prominent 

and cliff forming,

The Pogonip is also exposed several miles northwest of Camp 

Mercury in the vicinity of Red Mountain. As elsewhere, these beds 

are resistant and are easily identifiable by their cliff-forming character 

and bluish-gray color.

Pogonip unit A comprises the lower 610 feet of the group. It 

consists of mottled and dark-gray finely crystalline fossiliferous 

limestone. The lower 175 feet contains a few interbedded layers of 

dolomite near the base and is massive. The remainder of the unit 

is made up of thin-bedded, silt or shale-parted, buff-weathering 

limestone. Some beds contain orange-brown weathering chert and a 

few near the top are platy bedded. Intraformational breccia occurs 

in some of the limestone indicating shallow water deposition.

Unit B comprises about 105 feet of medium- to dark-gray nodular 

fossiliferous, silty and shale-parted limestone and is interbedded 

with thin layers of buff flaky shale.

Unit C, the next unit, is 615 feet thick. The lower 250 feet is a 

light- to medium-gray, well-bedded limestone in beds that range from 

a few inches to 2 feet in thickness. It contains stringers and masses 

of dark-brown chert as much as 6 inches in diameter and forms a 

resistant ledge above unit B. These lower beds are separated from 

the next 270 feet of the unit by a resistant, 2-foot bed of gray chert 

that weathers dark brown to black. These beds are gray, thin-bedded 

limestone containing a few layers of interbedded brownish-gray

limestone and a few stringers and masses of dark-brown chert. Above

these beds are about 65 feet of gray, yellowish-buff weathering, shaleparted, nodular limestone layers 6 inches thick. The uppermost 30

feet of this unit is a brownish-gray limestone containing a few darkbfOWn Chert masses. It is uniformly bedded in 6-incK layers and

weathers into a rough sandv surface.

Unit D is a distinctive shale, 265 feet thick. It is a buff paper-thin

flaky shale interbedded throughout with 1-inch layers of gray to

reddish-buff highly fossiliferous clayey nodular limestone. This unit 

is recognized at a distance by its characteristic slope-forming 

appearance. , , ,
GEOLOGY, ATOMIC ENERGY COMMISSION PROVING GROUNDS 347

The shale is overlain by unit E which consists of 235 feet of gray 

limestone. This limestone along the east side of Yucca Flat contains 

irregular layers of buff silty and muddy material that weathers 

dark brown. This material gives these beds an alternating buff and 

gray appearance. The limestone occurs in beds 6 inches to a few feet 

thick and forms a resistant slope above the underlying shale unit. 

However, along the east side of Frenchman Flat, this unit is somewhat 

different lithologically. The unit contains a few shale-parted layers 

but lacks the characteristic silty and muddy material found in the 

area to the north.

Unit F comprises about 135 feet of gray to dark-gray finely crystalline limestone. It is characterized by large straight-coned cephalopods 

and prominent ledges which set it off from the slope-forming unit 

above and from the less resistant unit below. Commonly, fragments 

of this limestone emit a fetid odor if struck by a hammer.

Unit G consists of 195 feet of gray thin-bedded fossiliferous silty 

limestone and many buff to pink lenses of silty material. It is nonresistant and at a distance is recognized as the slope-forming unit lying 

between the cliff-forming beds above and below. Some beds contain 

abundant small brachiopods.

The overlying 535 feet of gray to dark-gray calcitic resistant, 

massive and cliff-forming limestone makes up unit H. The lower 300 

feet contains many large gastropods as much as a few inches in diameter. These fossils seldom weather out but are generally seen in 

cross section.

Unit /, which is 455 feet thick, is the uppermost unit of the Pogonip. 

It is made up of interbedded limestone and dolomite and is characterized by alternating color bands. Shades of buff, gray, and brown are 

common and many of the beds weather an unusual rusty brown ^or 

bluish gray. This unit is uniformly bedded in layers 1 to 2 feet thick 

and contains many thin silty siliceous partings.

Contacts of the Pogonip group with underlying and overlying 

divisions are conformable. As drawn at the base of Pogonip unit A 

the lower boundary is somewhat arbitrary and provisional. Future 

work may demonstrate the desirability of including older rocks at 

present assigned without fossil evidence as unit D and upper unit C 

of the Upper Cambrian rocks.

The total thickness of the Pogonip is about 3,150 feet. This figure 

was obtained by combination of separate sections measured along the 

east side of Yucca and Frenchman Flats. Sections were correlated 

by lithologic characteristics and fossils.

Lowermost Ordovician fossils were found 185 feet above the base 

of Pogonip unit A. Faunas of unit A so far obtained apparently 

correlate with those from the Nanorthis-Kainella zone (lowermost
348 'CONTRIBUTIONS TO GENERAL GEOLOGY

Ordovician) near the base of the lowest Pogonip of Eureka, Nev., as 

currently understood. However, before definite conclusions can be 

reached it will be necessary to collect distinctive fossils immediately 

above and below the base of Pogonip unit A in the Yucca Flat area. 

Pogonip unit A yielded several fossil collections which were examined by Josiah Bridge (written communication) who states that these 

collections

contain a well-preserved pygidium of Xenostegium sp. together with spines and 

other fragments presumably belonging to the same form; poorly preserved 

brachiopods tentatively identified as Nanorthis sp.; a single well-preserved specimen of Tetralobula sp., and a large species doubtfully referred to Nanorlhis.

Bridge also examined a collection from unit B and reports that this 

collection contains "the pygidium of a large but undescribed trilobite 

that is known from the Manitou formation of Colorado." Bridge 

further states that

all of the forms seen in these collections are characteristic of the lowest Lower 

Ordovician rocks in other parts of Nevada and adjoining states, and Palmer and 

I are convinced that the collections are of Lower Ordovician age.

A fossil collection from the lower part of unit D was also examined 

by Josiah Bridge. He comments that this collection "contains 

numerous specimens of Protopliomerops and is correlated with zone G 

of Eoss's Garden City sections."

Fossils were also collected from unit F. They were examined by 

C. W. Merriam, who identified them as follows:

Orthidiella

Mitrospirat

Large holochoanate cephalopod

Merriam (written communication) considers these forms to be

Early Ordovician in age.

Unit G yielded abundant small brachiopods. Concerning these, 

Bridge (written communication) remarks 

the boundary between the Lower and Middle Ordovician is tentatively placed

at the top of (unit G). This is done largely on the presence of the brachiopod 

Orthidiella, a very late Lower Ordovician form. (Unit G) is still Lower Ordovician,

approximately equivalent to the Roubidoux or a slightly younger horizon in

Missouri.

Unit H contains a fauna which C. W. Merriam places in the upper 

i. He identified these forms as:

Maclurites sp. 

Mitrospira longwelli Kirk

Girvanella si>.

lit

mammillaris Walcott
GEOLOGY, ATOMIC ENERGY COMMISSION PROVING GROUNDS 349

Bridge's comments concerning these fossils are: [This collection] 

"was not seen, but from the list on the columnar section, it is undoubtedly Chazy, Middle Ordovician of most geologists."

From the abundant fossil evidence, the Pogonip is placed as Early 

to Middle Ordovician in age.

EUREKA QUARTZITJE

The Eureka quartzite is well exposed in the southeastern part of 

the area. Its nonresistant character in this area is well displayed 

in the Ranger Mountains where it has been eroded back from the 

steep cliffy outcrops of the underlying limestone of the Pogonip 

group. It crops out high in these mountains and can be easily traced 

as a complete unit northwestward across the entire length of the 

mountains.

The Eureka is also exposed in the high areas capping some of the 

hills in the vicinity of Red Mountain and may also be observed along 

Mercury Highway in the southernmost part of Frenchman Flat.

In the northern part of the area, the Eureka quartzite occupies a 

small area south of Paiute Ridge and occurs in small, patchy outcrops 

near the Mine Mountains. About a mile northeast of Oak Spring 

Butte, it crops out in steeply dipping beds and can be traced as a 

complete unit beyond the north margin of the area. The Eureka was 

originally defined by Hague (1892), at Eureka, Nev.

This formation is divisible into two lithologic units. The lower 

unit is 155 feet thick and consists of varicolored quartzite. Common 

colors of these beds are several shades of gray and brown which 

generally weather to darker tones and which sometimes are desert 

varnished. The formation is poorly bedded, well jointed vitreous 

nonresistant and fine grained. Near the middle of this unit are beds 

of mottled gray and buff finely crystalline thin-bedded dolomite 

about 5 feet thick.

The upper unit is 130 feet thick and consists of white to light-gray 

fine-grained quartzite which grades to medium gray at the top. It is 

characteristically nonresistant and lacks bedding. Many beds 

weather into small, thin chips an inch or less in size.

Carbonate rocks conformably underlie and overlie the Eureka 

quartzite. The lower contact is placed at the lithologic break between 

limestone and quartzite and the upper contact is at the break between 

quartzite and dolomite.

As measured in the Ranger Mountains, the Eureka is about 285 

feet thick.

Although unfossiliferous, the age and correlation of the Eureka is 

well established by the underlying fossiliferous limestone of Chazyan 

age and by the overlying fossiliferous dolomite of Late Ordovician
350 -CONTRIBUTIONS TO GENERAL GEOLOGY

age. This relationship, in addition to lithologic similarity, allows 

little question as to the age and correlation with the Eureka quartzite 

of the Eureka district, Nevada. Kirk (1933) divided the Eureka into 

three units; a thin basal unit which he considered as Chazyan in age; 

a middle unit which constitutes the bulk of the Eureka and which is 

Middle Ordovician; and an upper unit only a few feet thick which he 

considered to contain the basal beds of the Upper Ordovician. Owing 

to the lack of definite evidence of this relationship, the Eureka quartzite in the Nevada proving grounds area is considered as Middle 

Ordovician in age.

ORDOVICIAN TO DEVONIAN ROCKS

DOIX>MITE OF MIDDLE PALEOZOIC AGE, UNDIFFERENTIATED

In the Yucca and Frenchman Flats areas a dolomitic sequence more 

than 1,500 feet thick occupies the interval between Middle Ordovician 

Eureka quartzite and the Nevada formation of Devonian age. Comparison with similar sections in central Nevada leads to the conclusion 

that the dolomite in question includes time-stratigraphic intervals of 

Late Ordovician, Silurian, and possibly Early Devonian age. At 

Eureka, Nev., Hague (1892) described similar rocks as the "Lone 

Mountain limestone."

Middle Paleozoic rocks of central Nevada have more recently been 

reclassified (Merriam, 1940, p. 13-16) by restricting the name Lone 

Mountain dolomite to the higher part of this column. To the basal 

or Upper Ordovician part the term Hanson Creek formation was 

applied. The name Roberts Mountains formation was given to

limestone and dolomitic limestone beds between Hanson Creek 

formation and Lone Mountain dolomite. Whereas both Hanson 

Creek and Roberts Mountains are commonly not dolomitized, the 

Lone Mountain is dolomitic throughout.

Except where detailed stratigraphic work has been done, the subdivision and correlation of this part of the Great Basin Paleozoic

column is difficult, especially where it is mainly dolomitic and contains

few determinable fossils. Such appears to be the case in the Yucca

Flat area where for purposes of this report it seems desirable provisionally to employ the noncomittal term dolomite of middle Paleozoic age, undifferentiated.

Dolomite of middle Paleozoic age, undifferentiated is best exposed

in the southeastern part of the area. It crops out in a large part of

tlie Hanger iviountains wliere it is recognized as the dark- and. light" 

COlOred, Cliff-forming teds above the Eureka quartzite. The dolomite

beds are also well displayed in the pass north of Camp Mercury as

resistant hills consisting of poorly bedded dolomite which is typical Qf

this division throughout the area. Elsewhere, a small outcrop is
GEOLOGY, ATOMIC ENERGY COMMISSION PROVING GROUNDS 351

present about 2 miles east of Yucca playa and many hills north and 

.northeast of Oak Spring Butte consist of this dolomite.

Seven unnamed lithologic units are recognized within the undifferentiated dolomite of middle Paleozoic age in the area.

Unit A, the basal unit, consists of 95 feet of dark-gray to black 

aphanitic cherty gritty dolomite including some beds that contain thin 

veinlets of white dolomite crystals. This unit is easily recognized at 

a distance by the striking contrast to the light-colored beds of the 

underlying Eureka quartzite.

Unit B is made up of 130 feet of light- to medium-gray dolomite and 

a few darker beds of aphanitic hard dolomite. It occurs hi beds several 

inches thick and in places contains veinlets of coarse dolomite crystals.

The overlying unit C is lithologically similar to unit A. It consists 

of 115 feet of dark-gray to black, gritty, aphanitic dolomite containing 

chert and dolomite veinlets.

About 270 feet of mottled-gray poorly bedded finely crystalline to 

cryptocrystalline, strong cliff-forming dolomite makes up unit D. It 

weathers to a light-gray sandy surface and at a distance is identified 

as the light-colored resistant ledges which overlie the dark dolomite 

beds of unit C.

Where seen, unit Eis poorly exposed. The part measured is 365.feet 

thick, the upper beds are covered by alluvium. It generally consists 

of light- and dark-gray and some black beds of dolomite. Dark-brown 

and tan chert occurs in a few beds and others contain dolomite veinlets 

typical of many of the underlying units.

Unit F consists of about 340 feet of light-gray vuggy, medium to 

coarsely crystalline poorly bedded resistant dolomite. Characteristically, it weathers to a rough, saccharoidal surface and forms hills of 

high relief with prominent ledges.

Unit G is lithologically similar to unit F but is finer textured. The 

unit is made up of about 250 feet of medium to finely crystalline 

dolomite and a few interbedded coarsely crystalline beds.

The undifferentiated dolomite of middle Paleozoic age conformably 

overlies the Eureka quartzite and underlies the Nevada formation. 

The lower boundary is one of the most striking lithologic breaks in 

the area. It is placed at the contact between the light-colored quartzite beds of the Eureka and the black dolomite which forms the lowermost unit of the dolomitic sequence. The upper contact is placed at 

the top of the uppermost light-gray dolomite bed.

In the Ranger Mountains the undifferentiated dolomite of Paleozoic 

age was measured as 1,565 feet thick. This thickness represents the 

total for this division, except for a faulted interval of about 100 feet.

In the Pioche district (Westgate and Knopf, 1932) and the Death 

Valley region (McAllister, 1952) the lower part of a similar dolomitic
352 CONTRIBUTIONS TO GENERAL GEOLOGY

sequence has been assigned to the Ely Springs dolomite. The Hanson 

Creek limestone of the Eureka district, Nevada (Merriam, 1940; 

Nolan and others, 1956) is about the same age.

The upper contact of the Ely Springs dolomite has elsewhere been 

placed at a lithic break between dark-gray to black dolomite and 

light-colored beds of the overlying Silurian. This procedure could 

not be followed hi the Nevada proving grounds area, however, because 

of the interbedded and lenticular character of these dark- and lightcolored beds.

Unit B yielded a few fossils which were examined by Josiah Bridge 

(written communication). He states that these fossils are 

possibly of Upper Ordovician age, but might be Silurian. Insoluble residues 

have yielded numerous brachiopods (and) a few silicified bryozoa belonging to the 

genus Rhinidictya, and several specimens of Tentaculites. Although this last 

named form has been reported from rocks of Richmond age, it is not common 

below the Silurian.

The brachiopods in this collection were examined by G. A. Cooper, 

who considers that they are Ordovician and Silurian types.

Although the evidence is not conclusive, the fossils and the Late 

Ordovician age generally assigned to the Ely Springs in other localities 

indicate that the lower part of the dolomitic sequence in question is

probably Late Ordovician.

Poorly preserved colonial corals were collected from the upper part 

of unit E. These fossils were studied by Helen Duncan (written 

communication), who reports:

The specimens of halysitid corals have mesopores and belong either to the subgenUS HQ>lysties or to the subgenus Cystihalysites, neither of which is known to 

occur in the Ordovician. The phaceloid coral has dissepiments and apparently 

is related to the post-Ordovician disphyllid or columnarid corals and not to the

Ordovician favistellids, which have no dissepiments. The form characterized by 

a massive corallum and very small corallites is a squamulate favositid. According 

to two authorities on the tabulate corals, squamulae are not known to have developed, in the favositids until 'upper' Silurian time (Wenlock, or approximately 

Niagaran Which is Considered to be Middle Silurian in the American classification).

It is not particularly desirable tO base an age determination on fossils that cannot

be accurately identified. The corals in this assemblage, however, exhibit a stage

of morphologic development that was not attained in the Ordovician. Further,

at present it is believed tnat taie naiyeitid. oo.ro.ia u.r-0 ^^^n^^A *<, i=,ro-T3o,^oi»;a.i» rocks. It is therefore reasonable to conclude that this particular corai assemblage

IS Of Silurian age.

-A.oooriine to tt,is report, tkese fossil-bearing: beds are no older than 

Silllriafl in age. However, no attempt is made to locate tne omcmCian-Silurian boundary in tKe area because fossils were not lOUnd 111 

the interval between unit B and tKe Upper part of Ultit E. In central Nevada finely crysuaumo aoi^v- ^~ ^^^

in lithology to unit G are considered as Middle to possible Early 

Devonian in age (Merriam, oral communication). This unit was
GEOLOGY, ATOMIC ENERGY COMMISSION PROVING GROUNDS 353

examined in the field by Nolan and Merriam who consider it similar 

to beds at the base of the Nevada formation in the Eureka district. 

This fine-grained dolomite is also lithologically similar to the Sevy 

dolomite of western Utah. Presence of a distinctive lower Middle 

. Devonian fauna 20 feet above the top of the undifferentiated dolomite 

of middle Paleozoic age further augments the possibility of Lower 

Devonian strata occurring between the Nevada formation and unit E 

of the dolomitic sequence which contains Silurian corals.

DEVONIAN BOCKS

NEVADA FORMATION

As defined by Hague (1892) in the Eureka district, Nevada, the 

Nevada limestone comprised Devonian strata occupying the interval 

between his Lone Mountain limestone and his Mississippian White 

Pine shale. In the original definition the Nevada included likewise 

an upper limestone later proposed as an independent formation, the 

Devils Gate limestone (Merriam and Anderson, 1942; Nolan and 

others, 1956). Both the Nevada formation (restricted) and the overlying Devils Gate limestone have been recognized in the Yucca Flat 

area.

The Nevada formation is recognized at several localities in the area. 

About 2 miles northwest of Captain Jack Spring, dolomite and limestone beds of this unit are well exposed. These beds form prominent, 

dark-colored, cliff-forming ledges unconformably overlain by Tertiary 

volcanic rocks.

At the Mine Mountains, the Nevada and overlying rocks have been 

thrust over Mississippian strata. The beds are exposed about 3 miles 

southwest of the Mine Mountains along the west margin of the area. 

They form areas of high relief and are recognized by their alternating 

dark- and light-colored steplike ledges. Tertiary volcanic rocks 

overlie these Devonian strata with angular unconformity.

The highest part of the southern Ranger Mountains is developed 

on the Nevada formation.

The Nevada comprises three units designated as unit A through 

unit C in ascending order.

Unit A consists of about 460 feet of dolomite, limestone, and 

quartzite. The basal 15-20 feet is a distinctive gray finely crystalline 

limestone which weathers bun7 to reddish brown. A few feet of darkgray to black highly fossiliferous limestone overlies the basal limestone. 

Interbedded gray and dark-gray finely crystalline fairly well bedded 

limestone and dolomite beds comprise the next 175 feet of the member. 

It is slope forming except for the upper 50 feet which contains thin 

beds and nodules of tan and gray chert. These cherty beds are 

prominent and stand out as resistant ledges. Overlying these cherty

398882 57 4
354 'CONTRIBUTIONS TO GENERAL GEOLOGY

beds are 95 feet of light-gray, brown-weathering, fine-grained, crossbedded quartzite. Some beds are desert varnished and others are 

calcareous and sandy textured. A few thin black limestone layers 

occur near the top of these beds. The uppermost 175 feet of unit A 

consists of thin beds of black, gray, and brown dolomite. These beds 

are generally finely crystalline, well bedded and appear strikingly 

banded. Near the base and at the top, thin quartzite beds are interbedded with these carbonate rocks.

Unit A is overlain by unit B which consists of about 260 feet of 

interbedded light-gray and black dolomite. The. light-gray dolomite 

makes up about 80 percent of this unit. It is a medium to coarsely 

crystalline, vuggy poorly bedded cliff-forming dolomite that weathers 

into a sugary texture. The black dolomite beds are finely crystalline 

poorly bedded and contain dolomite veinlets. Where struck by a 

hammer these beds emit a strong fetid odor.

About 350 feet of interbedded limestone and dolomite make up 

unit C, the next overlying unit. These beds are characterized by 

many poorly preserved twiglike fossils which have produced a spaghettilike white mottling in these beds. According to information 

received from Helen Duncan, many of the so-called spaghetti limestones that occur in the Devonian of the West were formed by concentrations of the rodlike stromatoporoid Amphipora, which flourished 

all over the world in Devonian tune. These strata also contain other 

stromatoporoids that form concentric masses that range from a few 

to several inches in diameter. The limestone of this unit is dark gray 

to black, finely crystalline, well bedded, cherty and weathers to an 

irregular, sharp, rough surface. The dolomite is differentiated from 

the limestone by a generally lighter color and by weathering to a 

SffiOOth sandy surface. At a distance this unit is recognized by

prominent, dark-colored, steplike ledges, usually 5-10 feet truck.

Where measured the three units comprising the Nevada formation 

total 1,070 feet.

The lower age of the Nevada formation in this area is well established 

as early Middle Devonian by the presence of a highly fossiliferous 

limestone about 20 feet from the base of the formation. A cursory 

examination of fossils collected from this limestone was made by C. W.

Merriam, who identified the following forms:

Large cyathophyiiid coral

Favosites sp.

Syringopora sp,

Tenta.c-u.Utes sr>-

Meristtlla sp,

Leptaena sp.

Chonetes macrostriata Walcott 

Stropheodonta sp.
GEOLOGY, ATOMIC ENERGY COMMISSION PROVING GROUNDS 355

Atrypa sp.

Oypidula sp.

Platyceras sp.

Large Loxonema-like gastropod

Dalmanites meeki Walcott

Merriam (written communication) considers these fossils as early 

Middle Devonian in age.

The lower part of unit C yielded fossils reported on by Edwin Kirk 

and A. J. Boucot (written communication). They state that these 

beds "contain an unidentified cyrtinid brachiopod and finely plicated 

brachiopods belonging to the genus Atrypa. [The Atrypas] resemble 

forms elsewhere found in the Middle and Upper Devonian."

Unit C contains forms identified as Cladopora (a name also applied 

to Amphipora in other reports), Stromatoporoidea, and Striatopora, 

fossils commonly found in the Nevada formation in other localities 

(Nolan, oral communication).

From this faunal evidence the Nevada formation of the Yucca Flat 

area is considered as Middle Devonian.

DEVILS GATE(?) UDMESTONE

The Devils Gate limestone (Merriam, 1940) of the Eureka area, 

Nevada, was formerly included in the original "Nevada limestone" of 

Hague (1892). Because of distinctive lithologic characteristics and 

faunas it is now considered a separate formation. The formation is 

predominantly limestone, though it is locally dolomitized in parts of 

Nevada. Beds and lenses of dolomite or magnesian limestone are 

sometimes found in the lowermost part near the boundar}7 with the 

dolomite of the underlying Nevada formation.

The Devils Gate(?) limestone about 1,380 feet thick is made up of 

limestone containing several quartzite interbeds. Whereas the beds 

are similar in surficial appearance to those in the topmost division 

(unit C) of the underlying Nevada formation, they differ in being all 

limestone. Within the upper 750 feet, the Devils Gate(?) limestone 

is sandier, containing sandy limestone, a few lenticular sandstone 

layers and several beds of quartzite. The sandstone, totaling about 

10 feet in thickness, is tan to light brown medium to coarse grained 

crossbedded and has a "salt and pepper" appearance. The quartzite 

beds are light buff to orange brown and weather dark brown. They 

are fine to coarse grained, and include some sandy lenses. Characteristically they form a break in slope between the ledge-forming 

limestone layers.

Where observed, the contact of the Devils Gate(?) limestone with 

the overlying and underlying formations is conformable and is placed 

at distinct lithologic changes. The upper contact is conspicuous, 

owing to the slope-forming nature of the overlying formation< This
356 'CONTRIBUTIONS TO GENERAL GEOLOGY

contact is at the base of the lowermost buff nonresistant platy limestone of the Narrow Canyon.

This formation, like the underlying Nevada, contains fossils resembling cladoporoid corals (many of these are probably Amphipora) 

and stromatoporoids in some abundance. Its most distinctive fossil, 

however, is the gastropod Orecopia mccoyi Knight which characterizes 

a widespread zone in the upper part of the Devils Gate of the Great 

Basin. Orecopia mccoyi Knight probably indicates an early Late 

Devonian age. In the type area, however, a large part of the Devils 

Gate below this zone is considered late Middle Devonian.

DEVONIAN AND MISSISSIPPIAN BOCKS

NARROW CANYON LIMESTONE

The strata which are here named Narrow Canyon limestone crop 

out in Narrow Canyon, at the southeast margin of the area. These 

beds are well exposed about a half mile from the mouth of the canyon 

in a narrow, northeastward-trending band and are characterized by 

their typical buff-colored slope-forming appearance. This formation 

is not recognized elsewhere in the area.

The Narrow Canyon limestone consists of dark-gray silty limestone 

well defined in beds less than an inch thick. It weathers into thin 

buff-colored plates and forms talus-covered slopes.

The Narrow Canyon limestone conformably overlies the Devils 

Gate(?) limestone in sharp contact. The contact of the Narrow Canyon with the overlying formation is also conformable but is interbedded 

for an interval of about 10-20 feet.

At the type locality, the measured thickness of the entire formation

is 175 feet.

No fossils were collected from this formation. However, in eastcentral Nevada, beds of lithologic similarity and stratigraphic position

have been noted in the Narrow Canyon, These feeds have been

termed Pilot shale and are considered as Late Devonian to early

Mississippian in age (Nolan, T. B. and Merriam, C. W., oral communication) . 

Because of lithologic similarities in these formations the Narrow

Canyon is considered, as a, probable correlative of tne Pilot sHale.

MISSISSIPPIAN ROCKS

MERCURY LIMESTONE

TIxo name IVEereviai-y l^nvestonci is Hero eSvoTn to tiro beds exposed On

Mercury Ridge that overlie tne Narrow Canyon limestone, about

5 miles east of Camp Mercury, Tnis formation is not recognized

elsewiiere in the area. It is traceable northeastward for about a mile

as a prominent gray ledge W ifl terminated in totn (fectidflS fey H 

reverse fault.
GEOLOGY, ATOMIC ENERGY COMMISSION PROVING GROUNDS 357

In the small part of the area where the Mercury limestone is exposed, 

it consists of dark-gray, buff-weathering crinoidal limestone. It is 

generally poorly bedded cherty and forms resistant ledges above the 

slope-forming Narrow Canyon limestone.

The basal beds of the Mercury are interbedded with the buff platy 

limestone of the formation below and the upper contact is not exposed 

owing to faulting.

The complete thickness of the Mercury limestone in the area is not 

known. At the type locality, only the lower 115 feet of this formation 

was measured. The remaining part has been dropped under alluvium 

by faulting.

The Mercury contains fossils identified by C. W. Merriam in the 

field as Syringopora and Spirifer centronatus? Winchell. This species 

of Spirifer is considered to be early Mississippian in age and is also 

found in the Joana limestone of east-central Nevada and in the Tin 

Mountain limestone of the Death Valley region (Merriam, C. W., 

oral communication).

J. Steele Williams (written communication) examined a collection 

obtained from the Mercury limestone and made the following report 

on the brachiopods:

Collection 28 contains several specimens of a Spirifer that I believe is Spirifer 

centronatus Winchell as generally recognized in the West. It also has the brachial 

valve of a productid of the type Girty in 1899 referred to Produclus scabriculus 

Martin. Fragments of brachiopods representing other productids, other Spirifers, 

possibly a Chonetes and a Rhynchopora are present. I believe that the most 

probable age of the collection is early Mississippian.

A few corals in the same collection were examined by Helen Durican 

(written communication) who reports:

This lot includes several pieces of Syringopora cf. S. aculeata Girty and fragments of clisiophyllid and caninoid horn corals. The specimens of Syringopora 

are recrystallized, but the characters of the coralla indicate that the species is 

comparable to a species that is very common in the lower Mississippian of the 

West. The horn corals, likewise, are Carboniferous types.

The faunal evidence indicates that the Mercury limestone is of 

early Mississippian age and a probable correlative of the Joana and 

the Tin Mountain limestone of nearby areas.

EIJEANA FORMATION

The beds in the area to which the name Eleana formation is here 

given crop out in the Eleana Range and in other mountainous areas 

bordering Yucca Flat on the west. These beds are exposed on Quartzite Ridge, which topographically, is one of the highest peaks in the 

area. These strata are also present in the Mine Mountains where 

they consist mostly of reddish-brown shale. In the Mine Mountains, 

light-colored carbonate rocks of Devonian age have been thrust over
358 CONTRIBUTIONS TO GENERAL GEOLOGY

these shale beds and hi places the thrust-fault relationship between 

the Devonian rocks and the Eleana is well displayed and easily identified by the striking contrast of the beds.

Lithologically, the Eleana formation is the most diverse unit 

in the area. Abrupt facies changes from north to south prevent 

correlation of beds. However, the Eleana generally consists of a 

conglomerate, quartzite, and shale facies in the northern part of the 

area. Southward these grade into finer grained sediments.

On Quartzite Ridge, where the section was measured, the Eleana 

is subdivided into three units.

The lower unit consists of 1,000 feet or more of dark-brown to buff 

hard poorly bedded slope-forming argillite and shale. These beds 

break into small irregular flat fragments and contain a few thin beds 

of quartzite and conglomerate in the upper 100 feet. The base of this 

unit was not observed in the area.

The middle unit is composed of about 1,050 feet of interbedded 

quartzite, conglomerate, and argillite. The quartzite is generally 

brown, fine to medium grained, well cemented and fairly well bedded. 

The conglomerate is also brown and characteristically contains 

subrounded varicolored chert pebbles about one-fourth to one-half 

'inch across, well cemented in a quartzite matrix. Generally, the 

quartzite and conglomerate beds do not form cliffy ledges. However, 

locally they may be cliff forming. The argillite is brown to reddish 

brown, platy, bedded, hard and makes up only about 100 feet of this 

unit. Many beds show evidence of cyclic deposition by the interbedded relationship and gradational change from one lithic type to 

another. They are probably the result of an oscillating Sea that, while 

advancing and receding, deposited these alternatingly fine- and 

coarse-grained sediments.

The upper unit consists Of about 760 feet of varicolored argillite. 

Generally it is slope forming and breaks into platy and blocky fragments. The colors are highly diverse and include shades of gray, 

brown, red, and yellow, which have a conspicuous color banding in

the upper part.

These three units of the Eleana are traceable Southward into

the Eleana Range where they grade laterally into finer grained sediments. The most noticeable facies change is in the middle lUlit which 

is split by a shale tongue. The tongue thickens southward where it

also contains interbedded thin limestone beds and OCCUplCS about a 

third Of the middle Unit. The remainder is conglomerate and quartzite. similar changes occur in the upper unit, Whereas it is composed 

entirely of argillite on Quartzite Ridge, in the southern part of the

Range the Upper unit consists of an interbedded sequence of
GEOLOGY, ATOMIC ENERGY COMMISSION PROVING GROUNDS 359

argillite and limestone. The lower unit is exposed only as far south 

as Captain Jack Spring and does not exhibit, in the area exposed, 

radical facies changes similar to the other units of the Eleana. South 

of the Eleana Range and in the Mine Mountains, the middle and 

upper units are not recognizable as units owing to abrupt lithologic 

changes, and are not differentiated on the geologic map. In these 

areas, this formation consists of interbedded conglomerate, quartzite, 

shale, and some limestone.

The lower contact of the Eleana formation was not observed in the 

area. The upper contact on the margins of Syncline Ridge, is placed 

at the lithic break between interbedded quartzite, argillite and 

overlying limestone and appears to be conformable.

The Eleana was measured on Quartzite Ridge where it is 2,810 

feet thick. However, this figure does not represent a total thickness 

because the lower unit was not completely measured.

No fossils were collected from the Eleana formation in the area. 

However, clastic sedimentary rocks similar in lithologic characteristics and stratigraphic position to the Eleana are exposed in central 

Nevada. In the Eureka district, these beds are referred to as the 

Chainman shale and Diamond Peak formation and generally are 

assigned a Mississippian age. The White Pine shale of Hague (1893) 

has been subdivided in the Eureka district by Nolan, Merriam, and 

Williams (1956) into a lower unit, the Pilot shale; a middle unit, the 

Joana limestone; and an upper unit, the Chainman shale, formations 

originally defined by Spencer (1917) for the Ely district. As previously 

stated, the Narrow Canyon and Mercury formations of the Nevada 

proving grounds area probably correlate with the Pilot shale and 

Joana limestone of central Nevada. The lower unit of the Eleana is 

lithologically similar to the Chainman shale, considered as probable 

late Mississippian in age, and may correspond, at least in part, with 

that unit. Likewise by lithic similarities, the middle unit of the Eleana 

is considered as probably the approximate equivalent of the Diamond 

Peak formation.

From this reasoning, the Eleana is considered as probable Late 

Mississippian in age. The exact age limitation of the Eleana is not 

known owing to the absence of fossils in the upper unit and the inability 

to correlate it with known formations in other areas.

Of striking significance, are the radically different lithologic characteristics of strata of supposedly equivalent age in the Spring Mountains, less than 50 miles to the south. Whereas the strata are dominantly clastic in the Nevada proving grounds area, they are represented 

in the Spring Mountains entirely by limestone and dolomite. It is 

inferred that the sedimentary facies changed abruptly to the south.
360 CONTKIBUTIONS TO GENERAL GEOLOGY

The radical changes in lithology might be due in part to shortening 

of the earth's crust by thrust faulting (C. R. Longwell and T. B. 

Nolan, oral communication).

PENNSYLVANIAN AND PERMIAN (?) BOCKS 

TIPPIPAH LIMESTONE

The name Tippipah limestone is hereby assigned to the beds of 

Pennsylvanian and probable Permian age that overlie the Eleana 

formation on Syncline Ridge, about a mile east of Tippipah Spring. 

These rocks are also exposed about one-half mile north of Syncline 

Ridge in a single outcrop which is surrounded by alluvium, and in a 

few small areas along the north end of the Mine Mountains. Also 

correlated with this unit are the beds that overlie the Eleana in the 

southern part of the Eleana Range and on the eastern slopes of 

Quartzite Ridge. At a distance, the Tippipah is recognized by its 

light-buff color and for the most part by slope-forming limestone 

zones 20-50 feet thick which are separated from one another by thin, 

resistant ribs of limestone 5-10 feet thick. West of Yucca Pass, the 

Tippipah is exposed on several hills which are entirely surrounded and, 

in places overlain by strata of Cambrian age in a thrust-fault relationship. The Tippipah exposures are interpreted as being fensters or the 

exposed parts of the underthrust block.

The Tippipah limestone is subdivided into four distinct units, A 

through D in ascending order, all of which consist of limestone.

Unit A, 295 feet thick, consists of four zones of alternating resistant 

and nonresistant limestone. The lower 95 feet is poorly exposed but 

generally consists of dark smoky-gray medium-bedded slope-forming 

limestone. It is overlain by about 130 feet of interbedded gray to

dark-smoky-gray limestone in beds 1-3 feet thick, which contain thin 

buff and light-gray silty limestone partings. This zone is resistant 

and stands out as a prominent, gray cliff between the slope-forming 

units above and below. These resistant beds are overlain by 50 feet 

of light-gray and buff-colored nonresistant finely crystalline limestone. 

This Z0n6 iS in turn OVerlain by the uppermost 20 feet of unit A, which 

is a dark smoky-gray well-bedded, resistant limestone containing large

masses and lenses of brown chert.

Unit B consists of about 58O feet of light-gray, buff, lavender, and

light-purplish silty limestone. The beds are slope forming and weather

intO Small plates. These platy fragments generally have a gritty 

surface and a few ring when struck by a hammer.

About 2,035 feet of limestone make up unit (7, THIS unit) is an

alternating sequence of resistant and nonresistant light- to mediumgray and brown limestone. The nonresistant zones are generally 

20-50 feet thick and are separated by 5-10 foot ribs of resistant
GEOLOGY, ATOMIC ENERGY COMMISSION PROVING GROUNDS 361

limestone. The resistant beds are medium to finely crystalline and 

are uniformly bedded in layers 2-4 feet thick. This unit contains 

many beds of pebbly limestone, the pebbles of which are made up of 

varicolored chert generally one-fourth to an inch across, cemented in 

a limestone matrix. The brown color prevalent in some of the beds 

is a result of the large amount of clastic material contained in the 

limestone. A few buff and lavender platy, silty limestone beds are 

exposed in this section.

Unit D is 1,195 feet thick. Like unit C, it consists of alternating 

resistant and nonresistant strata. The principal difference is that the 

beds of unit D are considerably thicker and definitely more massive 

than the beds of unit C. The resistant, ordinarily massive beds of 

unit D are light to medium gray, and some beds show a slight olive 

green tint on the fresh fracture. Some zones contain a few conglomeratic limestone beds and others are cherty or contain calcite stringers. 

The nonresistant zones are generally silty, thin bedded and often 

weather into platy fragments.

Collection 29A of W was taken from the Tippipah strata exposed 

west of Yucca Pass. Knight also examined these fossils and reports:

There are two very interesting species here from which very tentative conclusions may be drawn. The most significant is Neilsonia. Poor preservation prevents close identification, but the species is very close indeed to an undescribed 

species from the Smithwick shale (early middle Pennsylvanian) of central and 

west Texas. Similar species are found as low as the New Providence shale 

(Mississippian) of Indiana, but I have never met with any specimens in beds 

higher than the Smithwick.

There is in the same collection a euomphalid of undescribed genus and species. 

The genus is also best known in the Smithwick although the species seems to be 

different.

There is a third gastropod, a high-spired one with a shape identical with an 

undescribed genus and species of murchisonid that I know only from the Smithwick and a little higher. Unfortunately the poor preservation of the growth lines 

does not permit confirmation of the identity suggested by the shape.

Fusulinids and corals were collected 750 feet from the base of unit C. 

The foraminifera were identified by Raymond Douglass (written communication) who reports:

Fusulinids and smaller foraminifera occur abundantly in this sample but are 

poorly preserved due to silicification and distortion. Textularians, Bradyina sp. 

and Staffella sp. were recognized among the smaller foraminifera and tPseudofusulinella sp., Triticites sp. and ? Schwagerina sp. among the fusulinids. This 

assemblage does not allow an age determination closer than late Pennsylvanian 

or early Permian.

Concerning the corals from this collection, Helen Duncan (written 

communication) states:

The coral-bearing rock is a limestone conglomerate and from the condition of 

the corals, I infer that the specimens must have been broken and worn before they
362 CONTRIBUTIONS TO GENERAL GEOLOGY

were incorporated in the conglomerate. All the pieces appear to have been derived 

from caninoid forms. Caninoid corals occur throughout the Carboniferous and 

range into rocks that are classed as Permian.

The collection also contains a single specimen of the bryozoan Rhabdomeson. 

This genus also occurs throughout the Carboniferous and ranges into the Permian.

A collection of fusulinids was made from a zone located about 1,060 

feet from the base of unit C. Douglass (written communication) 

reported on these forms as follows:

This sample contains Tolypamminids, Calcitornellids, Textularians and 

Bradyina sp. among the smaller foraminifera. The fusulinids include an undescribed genus resembling Fusulinella and Wedekindellina and a Triticites aff. 

T. notus Thompson. Forms similar to this Triticites have been reported from the 

lower Wolfcamp equivalents in several areas.

Another fusulinid collection, located about 500 feet higher stratigraphically than the preceding one, was identified by Douglass who 

states:

This collection contains Calcitornellids, Climacammina sp., Textrataxis sp., 

Bradyina sp., Endothyra? sp., Millerella sp., Pseudofusulinella? sp., and Triticites 

sp. aff. T. subventricosus Dunbar and Skinner. This assemblage suggests lower 

Wolfcamp age.

Limestone beds about 200 feet above the base of unit D yielded the 

next fossil collection. The fauna obtained consists of several classes 

of fossils, which were examined by several specialists.

J. S. Williams (written communication) comments:

Although I have not studied this collection in detail, in general appearance its 

brachiopods resemble some of the Wolfcamp and Permian brachiopod faunules of 

the West. Contained in it are productoids of several types, including forms related 

to species of 'Productus' and Marginifem. Also represented are types suggesting

species of Composita?, perhaps Martinia, and Choneles. Few specimens can be 

identified specifically and some not even generically. The basis for considering 

the collection to be of Wolfcamp or of Permian age is not very firm, but I believe

it belongs in one of these divisions. More detailed study would be necessary before

such assignment could be confirmed if the brachiopods would warrant a definite 

conclusion.

Concerning the bryozoans Duncan (written communication) states:

The single specimen of the bryozoan Polypora in this lot is specifically indeterminate. Representatives of this genus are common throughout the Pennsylvanian 

and Permian of the West. The coarse meshwork of this particular specimen suggests a form, that occurs in rocks of Wolfcamp age in Nevada, but the actual ranges

of comparable species are not well established in the West.

The gastropods were studied by J. B. Knight (written communication) who reports: 

This collection contains Straparollus (Euomphalus) undescribed species. Although

too imperfect for close work, this specimen resembles a species as yet undescribed 

that ranges through beds of Leonard to lower Word age in the west Texas

I know of no similar species in any older beds.
GEOLOGY, ATOMIC ENERGY COMMISSION PROVING GROUNDS 363

Douglass, who examined the fusulinids, reports, "Triticites sp. 

advanced type resembling T. ventricosus but more elongate and with 

fewer volutions. Age: Virgil or younger."

The next fossil collection was made about 400 feet higher hi unit D. 

It consists of fusulinids and corals. Douglass studied the fusulinids 

and states:

"This sample contains Tolypamminids, Bradyina sp., and Triticites 

sp. aff. T. ventricosus (Meek and Hayden). Lower Wolfcamp age is 

indicated."

Duncan's report on the corals is as follows:

A fragment of a syringoporoid coral was found in this collection. The specimen is 

not well preserved, but sections suggest that it may be a species of Pseudoromingeria. This genus was described originally from the late Upper Carboniferous of 

Asia (approximate equivalent of the Wolfcamp in America), but it apparently 

ranges well down in the Carboniferous in this country.

The highest fossil collection was taken from beds that occur about 

450 feet from the top of unit D. This collection was reported on by 

Douglass as follows:

This collection includes Bradyina sp. and Triticites sp. aff. T. subvenlricosus 

Dunbar and Skinner. Lower Wolfcamp age is indicated.

The fossil evidence establishes the approximate age of the Tippipah. 

However, because of the absence of diagnostic fossils at the top and 

base of this formation, its range is indefinite. From the paleontologic 

data at hand, it is here considered to be as old as early Pennsylvanian 

and probably as young as early Permian.

The apparent absence of earliest Pennsylvanian fossils (Morrow 

equivalents) in the Tippipah may appear surprising as strata of that 

age are reported in the Nopah Range (Hazzard, 1937) and in the 

Spring Mountains (Hewett, 1931). It is entirely possible that the 

earliest part of the Pennsylvanian may be represented in these lower 

beds as no fossils were found hi the lower 775 feet of the Tippipah.

Hewett (1931) assigned the name Bird Spring formation to rocks 

of Pennsylvanian age in the Goodsprings quadrangle, where the section 

is about 2,500 feet thick. Also rocks of early Pennsylvanian age in 

the Nopah Range have been correlated with the Bird Spring (Hazzard, 

1937). Longwell and Dunbar (1936) reported fusulinids of Wolfcamp 

and probable Leonard age in the upper 2,950 feet of the much thicker 

section (5,000 feet) of Bird Spring formation in the Las Vegas quadrangle, thereby extending the age span of the Bird Spring.

At present, no detailed correlation of the Tippipah with the Bird 

Spring can be attempted. However, the Tippipah generally is comparable in age and lithology to the Bird Spring and probably correlates, 

at least in part, with that formation.
364 CONTRIBUTIONS TO GENERAL GEOLOGY

QUATERNARY ROCKS 

ORIGIN

The fill which forms and underlies Yucca and Frenchman Flats is 

made up of detritus transported by the intermittent streams which 

flow only during and following torrential storms.

The size and amount of detritus that the intermittent streams of 

the area can carry depends upon the gradient and the amount of 

precipitation. Thus, during rains, the carrying power is great along 

the margins of the valleys where the alluvial fans have relatively 

steep slopes, about several hundred feet per mile, and gradually diminishes progressively towards the middle of the valley where slopes are 

only about 10 feet per mile.

Only a crude sorting of the debris takes place anywhere in the 

alluvial fans. However, a larger amount of coarse debris generally 

is deposited along the flanks of the valleys, where streams are more 

turbulent, than in the central part of the valley where carrying power 

of the streams is less.

COMPOSITION OP THE FILL,

Large excavations and four test holes, dug in the northern part of

Yucca Flat offered the writers an excellent opportunity to study in

detail the valley fill in that area. Elsewhere in Yucca and Frenchman 

Flats, information was collected as it became available but was not 

equal in amount nor in detail, to the data compiled from northern 

Yucca Flat. This information was obtained from well logs, excavations dug in several parts of the valleys, and observations made at

the surface.

The valleys are generally composed of an assemblage of interfingering and lenticular beds of unconsolidated detrital material. This

material is unsorted and consists of the several lithic types exposed

in the bedrock areas which border the valleys. The dominant rock

types are limestone, dolomite, quartzite, conglomerate, shale, tuff,

rhyolite, and other igneous rocks. From pebble counts made in parts 

of the valleys, it was determined that a direct relationship exists

between, tne dominant li.th.ic type of th.e aUuvium. in. any part of the

valley, and the immediately adjacent bedrock areas. For example,

the dominant rock types present in the alluvium in the northern part 

of Yucca Flat are tuff and rhyolite, "which also is the composition of the bedrock bordering Yucca Flat to tne nortn. By tms analogy, it

would be possible to predict the composition of tne valley nil by determining the rock types of nearby bedrock exposures. Thus, the 

west side of Frenchman Flat) which is bordered onttreij *>y volcanic

outcrops, is probably made up of alluvium containing mostly volcanic 

rocks; the northwest side of Yucca Flat, which is commonly bordered
by exposures of the Eleana formation, consists of shale, quartzite, 

and conglomerate.

The texture of the alluvium is variable. It ranges from clay and 

silt-sized particles to cobbles and boulders. In northern Yucca Flat 

60 alluvial samples were collected at random from depths of 5-35 feet 

and analyzed for particle-size distribution (Piper, oral communication). 

Fifty percent of the material ranges in grain size from 0,009 to 0.39 

inch; the average is 0.082 inch. The corresponding range of largest 

particles is from 1 to 12 inches. The percentage of particles passing 

a 100-mesh sieve (size of opening 0.0058 inch or 0.15 mm) ranged from 

3 to 31 and averaged 13. These variations in particle size appear to be 

random in geographic position and in depth below land surface within 

the area spanned by the data.

At a few localities in the western and northwestern part of Yucca 

Flat, many large boulders of quartzite and conglomerate lie directly 

beneath a thin surface veneer of finer textured alluvium. These 

boulders are particularly evident along the Five Mile road, west of the 

Jangle area, where they are more than a foot in diameter and lie only a 

few inches below ground surface.

The playas in Yucca and Frenchman Flats are lithologically different 

from the rest of the valley fill. They consist generally of compact 

fine silt and clay and are uniform, both laterally and vertically. The 

thickness of the playa deposits is probably variable. At one place, 

in the playa at Frenchman Flat, it was calculated by seismic methods 

to be about 175 feet thick (Farnham, oral communication).

THICKNESS OF VALLEY FELL

Only general limiting facts concerning the thickness of the valley 

fill in Yucca and Frenchman Flats are known. Along the valley 

margins and over many reentrants, the fill is only a veneer and locally, 

as in the washes, it has been removed, exposing the underlying bedrock. Away from the valley margins, the valley fill is hundreds of 

feet thick. A part of northern Yucca Flat was surveyed by a seismograph crew of the United Geophysical Co. (Rugg, oral communication) . In this area, they report that the alluvial fill thickens towards 

the central part of the valley to about 800-1,000 feet. Elsewhere in 

the valleys, wells drilled in search of water have cut through hundreds 

of feet of valley fill before reaching bedrock.

Seismic survey (Farnham, oral communication) determined a depth 

to bedrock of about 650 feet in the playa in Frenchman Flat, which 

is the only other area where depth to bedrock is known.

Notwithstanding the lack of conclusive evidence, it is probable
366

that the major part of Yucca and Frenchman Flats away from the 

valley margins contains alluvial fill exceeding 500 feet in thickness.

CAUECHE

The term caliche is of Spanish origin and is commonly applied to 

a porous, earthy, calcium carbonate deposit containing soil, sand, and 

coarser rock fragments. There has been much speculation in regard 

to the'origin of caliche. One of the early theories is the one expounded 

by Blake (1902). He considers caliche deposits the result of upward 

capillary flow of calcareous water, induced by constant and rapid 

evaporation at the surface in a comparatively rainless region. In the 

formation of caliche, two essential factors are necessary; a constant 

Supply of phreatic calcareous water and a continuous dessicating 

atmosphere. Desert regions are characterized by the unusual dryness 

of the air and its capacity for absorbing moisture, and by maintenance 

of continued evaporation from the soil which determines a constant 

upward movement of the phreatic water. However, the great depth 

to water in the Nevada proving grounds area, at least several hundred 

feet, and the presence of caliche at the surface leaves some question 

as to whether capillary action could cause the rise of water from such 

a great depth. A more suitable explanation would be to consider 

the caliche as forming from evaporation of water which occupies the 

valley during infrequent downpours. The water, which contains 

calcium carbonate in solution, is absorbed by the upper few feet of

the alluvium soon after the rains. Later, it evaporates and leaves

the calcium carbonate as a deposit in the interstices of the valley fill. 

The caliche in the area is generally chalky white to cream colored 

amorphous dull soft and very well cemented- It seldom OCCUTS in 

beds more than a foot thick. More commonly it occurs as 1- to 2-inch 

stringers. Often it is indicated only by the firmly consolidated

character of the alluvial fill. The caliche distribution vertically and 

horizontally is irregular, and the deposits may occur from the surface 

downward. However, wells dug in other parts of the area indicate 

that the vertical spacing between caliche zones increases with depth. 

In the excavations examined in the northern part of Yucca Flat, 

caliche is not present to a depth of about 18 feet.

INTRUSIVE BOCKS 

Intrusive rocks are represented in the Nevada proving grounds area

by a granitic intrusive mass south of Oak Spring Butte, and by many

generally northward-trending dikes in the mountains bordering Yucca 

Mat on the east.

The granitic intrusive mass is bordered on the north by Tertiary

volcanic rocks which lie in normal contact with the intrusion. East

and west, the intrusion is bordered by Paleozoic rocks which have been
GEOLOGY, ATOMIC ENERGY COMMISSION PROVING GROUNDS 367

altered and intruded by the granitic rocks, and to the south it is 

bordered by Butte fault.

The dikes are all dark colored which makes them easily identifiable 

on aerial photographs. They are generally 25-50 feet wide and in 

most places occupy preexisting normal fault zones.

The intrusion at Oak Spring Butte is a pink highly biotitic, granite 

porphyry which contains quartz and large phenocrysts of orthoclase. 

Typical of granite, it weathers to a sandy granular texture and 

into rounded jointed knobs or smooth-sloping hills. Wyant (oral 

communication) also reports granite pegmatite and diorite in this 

intrusion.

The dikes are aphanitic, and probably basic in composition. Generally, they are more resistant than the rocks which they intrude and 

stand out in thin resistant outcrops.

Age of the intrusion is not definitely known. However, Nolan 

(1943, p. 177) has suggested that granitic intrusive masses apparently 

marked the end of major compressional diastrophism in the Great 

Basin. Major compressional deformation in the area is dated as 

probably occurring between Cretaceous and early Tertiary time and 

thus conceivably the intrusion may lie within these time intervals. 

The dikes on the other hand, cut the Tertiary volcanic rocks and 

consequently are considered much younger, probabty Miocene or 

younger in age.

METAMOBPHIC ROCKS

Metamorphic rocks are recognized south of Oak Spring Butte 

where they occupy an area of a few square miles. The granitic intrusion separates the metamorphic rocks into an eastern and western 

block, both of which are highly folded, faulted, and intruded.

These rocks are made up dominantly of light-colored coarsely 

crystalline calcitic and dolomitic beds of marble. The western outcrop of metamorphic rocks contains, in addition to marble, a few 

quartzite and several conglomerate beds lithologically similar to the 

Eleana formation. Thus they are considered as possibly belonging 

to the younger Paleozoic rocks of the area.

In all probability, metamorphism of these Paleozoic rocks was 

contemporaneous with intrusion of the granite and therefore is considered as occurring in late Mesozoic or early Tertiary time.

EXTRUSIVE ROCKS 

OAK SPRINO FORMATION

The name Oak Spring formation is hereby assigned to the rocks 

exposed at Oak Spring Butte and to corresponding rocks in other 

parts of the area. These rocks are Tertiary in age, and nearly all are 

volcanic in origin. At one time, they probably masked the entire 

area, but subsequent faulting and erosion has exposed the older strata.
368 CONTRIBUTIONS TO GENERAL GEOLOGY

Many geographic landmarks in the area are evident on these beds. 

North of Yucca Flat, Oak Spring Butte and Twin Peaks, prominent 

topographic features are visible from great distances. In the mountains west of Frenchman Flat, where only volcanic rocks are exposed, 

prominent high peaks such as Skull Mountain, Hampel Hill, and 

Mount Sayler are easily identified.

In places the variations in color and lithology of the Oak Spring 

formation within a short stratigraphic distance makes them quickly 

recognizable. At French Mountain, white, gray, and black beds are 

interbedded and juxtaposed by faulting into several separate, colorbanded blocks. In other places, the hills are composed of white slopeforming tuffaceous beds, interbedded with, or capped by, thin dark, 

resistant extrusive masses. At Tippipah Springs, the tuff beds, the 

color of which is unlike that of any other rocks in the area, form steep, 

high picturesque, white cliffs. Elsewhere, a thick series of dark lava 

flows blankets the area.

The Oak Spring formation consists of rhyolitic lava flows, tuff beds, 

and many other volcanic rock types. A few sedimentary rocks were 

noted near the base. No attempt was made to subdivide these rocks 

nor to correlate them for great distances. This was rendered impossible by the abrupt lateral changes of many of the units and by the 

interfingering with, and lensing out against, volcanic units derived 

from other "centers" of volcanism.

The tuff beds are generally chalky white, cream or light gray and 

highly variable. In places they may be noncrystalline earthy dull, 

porous tuff beds, whereas in other places the beds may consist of

compact, hard, dense, welded tuff containing glassy quartz phenocrysts. Most of the tuff layers, indicate deposition in water, probably 

large lakes or basins which existed at the time of volcanism. Biotitic 

tuff, tuff breccia, and tuff containing shards of pumice are a few of the

many tuffaceous rock types.

The extrusive rocks are also diverse in appearance and composition.

These rocks are dominantly acidic although rocks of basic composition

also occur. Colors are dominantly several shades of red, brown,

black, or gray. Textures range from aphanitic to phaiieritic, Some

Of the lavas are vesicular indicating rapid cooling at the time of extravasation. Dark schlieren and flow banding occur in some of these

rocks. Rhyolites are probably the dominant extrusive type although 

dacite, latite and other more basic rocks are also present. Pumice and a few beds of obsidian were also ouseirea D\M tue&e ro^s «,ie <,*

abundant.'

Some of the extrusive masses are resistant and form steep ledges 

that can be traced for several miles. The rhyolite beds which form 

the cap and shoulder of Oak Spring Butte are so distinctive and
GEOLOGY, ATOMIC ENERGY COMMISSION PROVING GROUNDS 369

widespread in the northern part of the area that the tops of these two 

flat-lying flows are shown on the geologic map (pi. 32) as mappable 

units.

A few sedimentary rocks are present near the base of the Oak Spring 

formation. These include some fanglomeratic deposits and wellcemented gravels. A few cream to light-gray fossiliferous, marly 

limestone beds are exposed at the base of the Oak Spring section in a 

few of the low hills along the south margin of Frenchman Flat.

About 2,000 feet of Oak Spring rocks were measured at Oak Spring 

Butte. However, this does not represent a maximum figure for this 

formation. Thicker sections of these rocks are exposed west of 

Frenchman Flat but were net measured because of faulting.

Gastropods were collected from the fresh-water, marly, limestone 

beds. These fossil-bearing beds were found along the south margin 

of Frenchman Flat. Although restricted in distribution, the age of 

these beds, and consequently the age of the overlying volcanic rocks 

at that locality, seems to conform with age assignment given to similar 

rocks in other areas.

Teng-Chien Yen (written communication) examined these fossils 

and reports as follows:

Valvata sp. undet.

Lymnaea cf. L. meekiana Evans and Shumard

cf. L. shumardi Meek 

Menetus cf. M. retulus Meek and Hayden

The fossil specimens are represented by internal molds, and they are not well 

enough preserved to yield desirable features to establish identification of species. 

Therefore, a definite age assignment cannot be given at present. Judged by the 

fossil findings available in comparison with the known records of freshwater 

molluscan faunas in the Western Interior, the fossil-bearing beds are probably of 

late Tertiary age and possibly of Miocene deposition.

According to Nolan (1943, p. 165), beds of Miocene age appear to 

be the most widely distributed of the Tertiary sedimentary rocks in 

the California and Nevada parts of the Great Basin. Thick accumulations of surficial volcanic rocks and local small intrusive bodies are 

commonly associated with these sedimentary beds.

No definite age assignment can be given to the Oak Spring formation 

owing to the lack of diagnostic fossils. However, evidence indicates 

that it is probably Miocene or younger in age.

STRUCTURAL GEOLOGY

The Nevada proving grounds area is structurally complex, corresponding to other areas in southern Nevada where intense crustal 

deformation has been the rule. Six significant folds, five in the 

Paleozoic rocks and one in the Tertiary volcanic rocks, and several 

thrust faults, and many normal faults have been mapped. Most of
:370 'CONTRIBUTIONS TO GENERAL GEOLOGY

the folds and all the thrust faults are exposed in the bedrock areas

-surrounding Yucca Flat. The Paleozoic bedrock of the Yucca Flat 

.area is broken into two main blocks; a western block consisting of 

folded upper Paleozoic rocks and an eastern block of westwarddipping lower Paleozoic strata. The lower Paleozoic rocks of the

-eastern block are believed to overlie the upper Paleozoic rocks in a 

thrust-fault relationship. A small granitic mass has been intruded 

into the north end of the western block.

Normal faults occur in almost every part of the area. They cut 

the Paleozoic sedimentary rocks and Tertiary volcanic rocks, producing in several localities, a series of tilted, repeated, fault blocks. This 

is strikingly displayed at French Peak, where light, varicolored tuffaceous sedimentary rocks and dark extrusive masses are repeated many 

times by faulting. Northwest of Yucca Flat, postvolcanic normal 

faults have broken the bedrock into two structurally different areas; 

.an eastern area which has been thoroughly cut and broken by faulting 

and a western stabilized area, which has remained almost completely 

uncut by faulting. The bedrock of the Frenchman Flat area is

-extensively broken by normal faults into a series of fault blocks. 

Several dikes, which occupy preexisting normal fault zones, crop out 

northeast of Paiute Ridge.

The valley fill of Yucca and Frenchman Flats is broken by faulting.

Yucca Flat is cut by a southward-trending normal fault which extends

throughout the valley. Frenchman Flat contains many southward 

to southwestward-trending small faults of an indeterminate structure.

After deposition of the Paleozoic sedixnentary rocks compression

produced an uplift of the land surface with concurrent formation of

fOldS and Contemporaneous thrust faults. Tke fold aXGS and tuTUSt

traces trend southward, and conform to the general pattern of Great

Basin Structure. To produce this pattern, compression was applied

along an east-west plane, perpendicular to the resulting fold and fault

trends. Evidence, Such as the overturned limb of the syncline north 

of Oak Spring Butte and overturned beds of the overthrust block north

 Of TiPPlPah SprinffS. Indicates that the active compression was applied

from the west. This evidence is further corroborated by the westward-dipping surfaces of the thrust faults west of the Eleana Range

and. llUlbti viC'Tippi-po-ia. Spx-i^,cs. TKo one anomalous example is the

-syncline southeast of Frenchman Flat, the overturned southeastern

limb of which indicates an active application of compression from the

j39\itKea,st. This latter overturned, northeastward-plunging syncline

is one of the most conspicuous folds in tie area teOT 01 iB ffilp

 structural, transition in a northeasterly direction from a normal,
symmetrical syncline to an asymmetrical, axial-faulted syncline with 

an overturned southeastern limb to a gently-dipping syncline with a 

small anticline formed on the southeastern limb. Still farther northeast the two folds die out, and the projected trend of the two axes is 

represented by a gently to steeply southeastward-dipping homocline. 

This syncline is exposed in the bold, prominent outcrops of Mercury 

Ridge, a high dark-colored ridge 1 mile east of Camp Mercury, and 

is in limestone of Devonian age.

Almost all the folds of the Yucca Flat area are in the Carboniferous 

Tippipah and Eleana formations exposed west of that valley. In the 

Mine Mountains, clastic rocks of the Eleana formation are folded into a 

northward-plunging anticline. Although the fold is largely covered 

by a thrust plate of limestone of Devonian age, both anticlinal limbs 

are exposed on either side of the thrust plate. Moderate dips have 

been recorded on these limbs, which extend about 1 mile from the axis 

before being covered by volcanic rocks.

Two miles to the northwest of the Mine Mountains is Syncline 

Ridge, where rocks of the Tippipah limestone have been folded into 

one of the two longer folds hi the area. This fold is a northeastwardtrending syncline, 5 miles long and symmetrical in cross section. An 

axial fault drops the western limb with a displacement of about 1 GO200 feet. A later cross fault transects the synclinal axis and the axial 

fault, and drops the northern part of the fold. The northernmost part 

of the syncline is overturned, possibly by a smaller unexposed thrust 

fault.

Quartzite Ridge, a prominent topographic feature north of Yucca 

Flat, is on the eastern flank of a southward-plunging anticline where 

clastic rocks of the Eleana formation are present. It is the second of 

the two longer exposed folds in the area, and has an axial length of 5 

miles. This fold is broad at the northern limit, where it appears 

from beneath the volcanic rocks. To the south, the fold becomes 

more compressed before disappearing beneath the alluvium.

In the small mineralized area just south of Oak Spring Butte, 

metamorphosed Paleozoic rocks are folded and faulted into a sharp, 

northward-plunging syncline. The possible northern extension of 

this structure is a northward-plunging syncline, which reappears from 

beneath the volcanic rocks north of Oak Spring Butte. The western 

limb is overturned. Uiimetamorphosed limestone of the Pogonip 

group, Eureka quartzite, and dolomite of middle Paleozoic age have 

been recognized on the limbs of this possible synclinal extension. 

From there, the syncline is traceable beyond the northern boundary of 

the area.

. One long northeastward-trending syncline in Tertiary volcanic 

rocks is hi the Belted Range in the northwest corner of the area.
372 CONTRIBUTIONS TO GENERAL GEOLOGY

The flank dips are no more than 5°-10°. Also several small folds 

are present in the volcanic rocks.

FAULTING 

THRUST FAULTS

The thrust faults of the area appear to be concentrated in the 

vicinity of Yucca Flat where at least four thrusts have been observed. 

The first thrust indicates that Carboniferous strata have been thrust 

from the west over younger Carboniferous rocks. Two widelyseparated thrust faults reveal limestone and dolomite of Devonian 

age resting on clastic rocks of Carboniferous age. The fourth thrust 

fault reveals Cambrian .sedimentary rocks thrust on Carboniferous 

strata. Contact relationship in the vicinity of the Mine Mountains,, 

combined with evidence from this fourth thrust and the areal distribution of lower and upper Paleozoic rocks surrounding Yucca Flat 

indicate that at least two of the above mentioned thrusts may besegments of a very large thrust fault in that area. Almost all the 

Paleozoic rocks which make up the western bedrock rim of the valley 

are Devonian to Carboniferous in age. Most of the Paleozoic sedimentary rocks bordering the valley on the east are of Cambrian and 

Ordovician age, and the writers believe that these rocks comprise a, 

thrust plate which rests on the Carboniferous rocks cropping out west

of the valley.

Four miles north of Tippipah Springs, the first thrust relationship

reveals overturned quartzite and conglomerate Of the Carboniferous 

Eleana formation thrust from the west over shale of the same age on

the east, One-half mile east of Tippipah Springs, overturned clastic 

rocks of the Eleana and limestone of the Tlppipak Lave teen thrust 

over limestone higher in the Carboniferous section. The relationship

Of these tWO thrUStS is not definitely known. However, fcKey ar&

probably partS Of the Same fault because of the similarity of rocks

displaced Ul the thrusting and the similarity in thrust trends.

.A nortHeastward-trending thrust fault, which dlpS 45° W., IS

immediately west of the Eleana Range. Fractured, westwarddipping dolomite beds of Devonian age are thrust against folded,

clastic rocks of the Eleana. The minimum displacement is 2,800 feet,

ThiS thTUSt IS traceable for Only 1 mile. THo soutKem extension is

covered by volcanic rocks and the northern extension IS COVG1M by 

alluvium. A crOSS fault Ul the northern part Of the Eleana Range and 

DUO DOUUlitMr oo^^-rc^^ of Devonian rocks in this vicinity indicate

that the northern part of this thrust IB ofet h) the GESt Dj 016 CfOSS 

fault.

The most apparent thrust in the area is the low-angle Mine Mountains thrust fault. It may be easily detected by the conspicuous
GEOLOGY, ATOMIC ENERGY COMMISSION PROVING GROUNDS 373

contrast between the overthrust plate and underlying block. The 

Devonian rocks of the overthrust plate are resistant, highly distorted 

dark to light-gray dolomite, limestone, and quartzite. In contrast, 

the underlying block is made up of anticlinally folded relatively 

nonresistant reddish-brown clastic rocks of the Eleana formation. 

The overthrust plate crops out for more than half the area occupied 

by the Mine Mountains. Evidence indicating the direction of thrusting in this area is lacking.

Southeast of the Mine Mountains is a northeastward-trending 

normal fault. It displaces the clastic rocks of Mississippian age and 

overlying thrust plate of Devonian strata, which crop out at the Mine 

Mountains, and is downthrown on the southeast. The downthrown 

block is almost completely covered by alluvium in that vicinity except 

for small protruding bedrock "islands." The highest strata exposed 

in these "islands" are Devonian in age, thus revealing the probable 

existence of the Mine Mountains overthrust plate southeast of the 

normal fault. No Eleana rocks crop out in this vicinity.

On the largest of these "islands," a few patches of the thrust plate 

of Devonian rocks lie, not on the underlying block of the clastic rocks 

of the Eleana as at the Mine Mountains, but on limestone of the 

Ordovician Pogonip group and on Eureka quartzite. Although the 

contacts are by no means clear cut, the presence of another thrust 

fault displacing Ordovician rocks is indicated. The clastic rocks of the 

Eleana are dropped from the Mine Mountains along the normal fault, 

but are not exposed in the area to the southeast. Thus they conceivably may underlie the Ordovician rocks in a thrust relationship. 

If this is true, two overlapping thrust faults may exist in this area as 

follows:

1. A lower thrust, in which a plate of Ordovician sedimentary rocks has been 

thrust over an underlying block of Carboniferous rocks.

2. An upper thrust, in which a plate of Devonian strata has been thrust over the 

clastic rocks of Carboniferous age (Mine Mountains thrust fault) and onto 

the lower thrust plate of Ordovician sedimentary rocks.

In the bedrock area southeast of the Mine Mountains and west of 

Yucca Pass, the exposed formations are of Cambrian age but are undifferentiated because of the extreme structural complexity and lithologic changes from other known Cambrian formations in the area. This 

undifferentiated Cambrian section and the Ordovician section of the 

"islands" are essentially continuous stratigraphically from Yucca Pass 

northwestward to the normal fault southeast of the Mine Mountains, 

where the section abuts against clastic rocks of the Carboniferous 

Eleana formation. These Cambrian and Ordovician sedimentary 

rocks therefore probably make up the lo.wer thrust plate which overlies
374 CONTRIBUTIONS "TO GENERAL : GEOLOGY .

Carboniferous sedimentary rocks, as postulated in the precedingparagraph.

Positive evidence for the existence of this thrust plate of Cambrian 

and Ordovician rocks lies in the fensters about 2 miles west of Yucca 

Pass. Normal faults have brought rocks containing fossils of very 

probable Carboniferous age (Knight, written communication) against 

fractured Lower Cambrian strata. The lithology and fossil content 

of the rocks in the fensters and units A and B of the Tippipah formation 

are almost identical. If this thrust fault of Cambrian on Carboniferous 

rocks is continuous northwestward from these fensters to the Mine 

Mountains, as is postulated, the movement along the fault would be 

at least 8 miles.

The area adjacent to the Quartzite Ridge in northern Yucca Flat acts 

as a focal point for all the structure of the Paleozoic rocks in the northern part of that valley. The western mountainous run of the valley

from the Mine Mountains to Quartzite Ridge is almost completely 

composed of clastic rocks and limestone of Carboniferous age. On the 

contrary, the Paleozoic bedrock east of the valley is Early Cambrian 

to Silurian in age. The Eleana and Tippipah (?) formations of ^ 

Quartzite Ridge are separated from limestone beds of the Pogonip 

group, about 10,000 feet lower in the section, by only a 1,000-foot 

interval of alluvium. Butte fault cuts this interval but its relative 

displacement is exactly opposite that necessary to produce this 10,000- 

foot displacement in the Paleozoic rocks. It is postulated that a thrust

plate of Cambrian and Ordovician sedimentary rocks is dropped on

the southeast along Butte fault against Carboniferous rocks of the ^

underthrust block on the west.

This structural relationship is analogous to that of the Mine Mountains, where a known thrust plate of Devonian strata is dropped on the 

southeast along a normal fault against the xmderlying block of clastic

rock of the Eleana. Thus all the lower Paleozoic formations exposed 

east of Butte fault and east of the Mine Mountains probably make up

a large thrust, plate, which has been thrust over the Carboniferous

strata that crop out only west of the yalley.

The displacement of this.thrust fault would be along at least an 18

mile front from Quartzite Ridge to Yucca Pass. The direction of

thrusting is not positively Isnown, although, evidence indicates it was

from the west. The overthrust plate is exposed in the bedrock areas (

north, east, and south, of Yucca Flat, and the underlying block occupies

the areas only to the west, but this evidence does not imply that the

thrust originated from the east. Many normal fault blocks in this

area are dropped on the east. Consequently, the overthrust plate has

been repeatedly dropped to the east along these normal faults, thus 

explaining its eastern exposure.
GEOLOGY, ATOMIC ENERGY COMMISSION PROVING GROUNDS 375-

Whether this large thrust is related to the thrust fault north of 

Tippipah Springs and to the one west of the Eleana Range is unknown,

NORMAL FAUI/TS

Almost every part of the Nevada proving grounds area has been 

affected by normal faulting. Most of these faults have a southerly 

trend similar to most of the Great Basin normal faults, and the trend 

of the mountain ranges in the area has been largely determined by this; 

faulting. Consequently the Great Basin ranges have been likened to> 

a group of "caterpillars crawling southward." This pictorial comparison holds true for most of the Nevada proving grounds area except 

in the southern part where the trend gradually changes westward. 

South of the area the mountain ranges and normal faults resume their 

southerly trend.

One of the most conspicuous structural features of the area is in the 

vicinity of western Yucca Flat. A line drawn from Butte fault 

trending S. 20° W. and passing just west of the Mine Mountains would 

divide the Yucca Flat area into two postvolcanic structural blocks. 

West of this line, the volcanic rocks remain essentially unfaulted. 

This area of structural stability is separated by Butte fault from an 

area of instability east of this line, where the normal fault pattern is 

extremely detailed and complex.

The pattern of the normal faults east of Yucca Flat is uniform. 

The faults generally dip to the east and are downthrown on the east. 

The displacements, about ten to several hundred feet, produce a series 

of tilted fault blocks in which Paleozoic and Tertiary rocks dip westward. Much repetition of strata is thus produced. The general 

fault trend is southward.

Another pattern of normal faults occurs 6 miles southwest of Yucca 

Pass. The pattern is opposite that east of Yucca Flat. Western 

fault blocks are dropped relative to eastern blocks along westwarddipping faults, producing a series of repeated, eastward-dipping, tilted 

fault blocks. Displacements as much as 100-200 feet occur, and 

again repetition of strata is caused.

In the area southwest of Frenchman Flat, no definite pattern of 

fault trends or displacements is present. A change in trend of the 

faults to the southwest may be seen.

Butte fault, as mentioned previously, is a major fault which separates areas of structural stability and instability in northern Yucca 

Flat. A displacement of 1,200 feet has been measured from two 

prominent extrusive flows, which form the cap and shoulder of Oak 

Spring Butte, to their dropped counterparts east of the fault. The 

fault trends northward beyond the limits of the area and southwestward along the southeast side of Quartzite Ridge. Displacement
376 CONTRIBUTIONS TO GENERAL GEOLOGY

.along this fault resulted in the dropping of the eastern block which 

is made up of the granitic intrusion, the mineralized and metamorphosed rocks, and the Tertiary volcanic rocks. The downthrown

 extension of the tungsten-bearing strata, should be present beneath 

the volcanic tuff extrusive mass east of Butte fault. Further to the 

southwest Butte fault disappears beneath the alluvium.

Yucca fault is the major structural feature of Yucca Flat. This 

fault has the largest displacement and is the longest normal fault in 

the Nevada proving grounds area. This southward-trending normal 

fault divides the valley about in half. The fault block is downthrown

 on the east and at one locality dips 60° to the east.

By its well-defined scarp in the valley deposits Yucca fault is 

traceable southward across most of Yucca Flat. In the northern part

 of the valley, the height of the scarp is greatest and exceeds 75 feet. 

Unconsolidated valley fill on the east is faulted against compact 

fanglomerate on the west. Northward, Yucca fault terminates 

.against the northeastward-trending Butte fault at the boundary of 

the valley and bedrock areas.

From the point where the scarp attains its maximum height, Yucca 

fault is traceable southward by its gradually diminishing scarp for 

about 12 miles. It is then impossible to recognize the fault farther 

to the south in the valley deposits. However, if the fault trend were 

projected southward 2 miles, it would cut Yucca Pass. Geologic 

mapping in this vicinity has proved the existence of a normal fault, 

which has dropped volcanic rocks on the east against limestone of

 Cambrian age on the west with a displacement of about 1,000 feet. 

This relationship indicates that Yucca fault extends across the entire 

18-mile length of Yucca Flat, cuts the bedrock of Yucca Pass, and

 continues into Frenchman Flat.

No evidence of Yucca fault was uncovered south of Yucca Pass in

 either the alluvial deposits of Frenchman Flat or in the adjacent hms

 and ridges. However, because Yucca fault has displaced the bedrock

 of Yucca Pass, it most probably continues from the pass into Frenchman Flat but is covered by alluvium.

Other normal faults may exist along mountain fronts which rise

.abruptly from the alluvium. One example is the Ranger Mountains, 

east of Frenchman Flat. The homoclinal strata of these mountains

.are remarkably unbroken by faults, However, tne abrupt na& f^m

the alluvium, the linear front of the mountains, and the dip 01 the

^trata away from the valley strongly indicate a typical Basin and

Range block fault,

Several faults have displaced the playa and alluvial fan deposits in

 eastern and southern Frenchman Flat. These faults are generally

 small, extending only short distances laterally and apparently do not
GEOLOGY, ATOMIC ENERGY COMMISSION PROVING GROUNDS 377

have large displacements. All the faults in the alluvial fans areupthrown to the southeast. When the sun is at the right angle in the 

late afternoon, these faults may easily be detected even from considerable distances by their sunlit scarps and by the shadows cast on thedissected upthrown block.

Probably the most recent valley fault is one which strikes S. 20° W. 

for about one-half mile across the extreme eastern margin of Frenchman 

playa. The fault trace is a crevice in the silt and clay playa sedimentsabout 15 feet deep and 10 feet wide. No vertical displacement is 

apparent. This crevice represents the fault's surface displacement, 

which probably has been produced as a result of relatively large displacement in the compact underlying bedrock.

Several linear sagebrush growths on Frenchman playa trend aboutparallel to this recent playa fault crevice and suggest the existence of 

similar faults in that vicinity. The growth of some type of vegetation 

along fault traces seems a natural consequence. Any fault rift in 

the playa surface would act as an ideal collecting trough for plant 

seeds and for water. These factors lead to the belief that the linear 

sagebrush growths across Frenchman playa are probably along recent 

faults, but older than the fault crevice at the eastern edge of the playa..

The pattern of valley faulting shows a gradual change of trend from 

S. 20° W. in the eastern part of Frenchman Flat to S. 60° W. in the 

southern part. This pattern is parallel to the normal faulting of the 

Paleozoic and Tertiary rocks of the adjacent mountainous rim. The 

relative fault displacement of the valley and bedrock areas is generally 

the same, the southeastern blocks are upthrown in relation to thenorthwestern blocks.

DATING OF STBUCTUBAL DEFOBMATION

Owing to the absence of reliable reference features in the Nevada 

proving grounds area, only generalized age determinations of thestructural events may be made. In succession, the compressional 

deformation, intrusion of the granitic mass, and initiation of normal 

faulting followed upper Carboniferous or early Permian (?) time and 

preceded Miocene(?) time. The localized intrusion of dikes followed 

the Miocene(?) or later deposition of tuff beds and extrusions of flow 

rock, and also followed the faulting of the volcanic section in that area. 

Normal faulting has continued to the present day.

Dating of the compressional orogeny within the Nevada proving 

grounds area is impossible. However, detailed mapping in adjacent 

southern Nevada areas has provided an approximate dating for the 

thrust faulting. In the Muddy Mountains (Longwell, 1949) about 

90 miles southeast of the area, a thick fanglomerate was deposited in 

front of the Glendale thrust as the thrust plate advanced. The age-
378 'CONTRIBUTIONS TO GENERAL GEOLOGY

of the fanglomerate is Late Cretaceous. However, because it was

 deposited while the thrusting was in progress, the beginning of the 

.thrust faulting may date back to middle Cretaceous or earlier. Final 

stages of the thrusting in the Muddy Mountains occurred sometime 

near the end of the Cretaceous. Possibly thrust faulting in the 

Nevada proving grounds area, although not definitely dated, can be 

correlated with Cretaceous thrusting. However compressional deformation resulted, in its early stages, in the uplift of the land surface and 

subsequent folding before the formation of thrust faults. Thus the 

inception of deformation was probably earlier in the Mesozoic era 

than the Cretaceous dating of the thrusting.

As in many other localities in the Great Basin, a granitic mass 

has been intruded into the Paleozoic county rock north of Yucca 

Flat. The age relationship of this intrusion is not clear. However, 

Nolan (1943) states, "the emplacement of these granitic bodies

 everywhere in the Great Basin appears to have marked the end of 

major (compressional) diastrophism" and thus the intrusion conceivably could be of Late Cretaceous or early Tertiary age.

Normal faults have displaced the folds and thrust faults exposed 

in the Paleozoic rocks, and the granitic mass which has intruded them. 

'The normal faulting had therefore been initiated subsequent to the

-compressional deformation and the intrusion. Three evidences for 

'the upper age limitation of the inception of the faulting exist within

-the Nevada proving grounds area.

.1. An unconformity of Tertiary age occurs within the tuffaceous section at four 

localities from Twin Peaks to French Peak in the Yucca Flat area. The 

strata underlying these unconformities are not folded, but are merely tilted, 

and beveled by erosion before continued deposition of the volcanic rocks 

of the Oak Spring formation. As disruption of the Tertiary strata by simple 

compression during this period was unlikely, possibly the tilting of the strata 

underlying the unconformities was produced as a result of normal faulting,

This is analagous to the tilting of normal fault blocks as observed in the

area today. Normal faulting, which was in progress during deposition of

the Tertiary volcanic rocks, is thus implied.

:2, Immediately east of the southern part of Paiute Ridge, the Paleozoic formations 

are cut Dy a large normal fault. This fault projects into an area where

Tertiary volcanic rocks come in contact with Paleozoic rocks, and form a

scarplike feature in the volcanic rocks along the line of projections. However, where this scarp was studied, evidence indicates that the Tertiary 

volcanic rocks merely lap onto and dip in the same direction as the scarp.

Also in one smaU outcrop, tuff beds lie on the Paleozoic rocks of the scarp in 

a sedimentary contact and no fault relationship between the two exists,

At least some of the normal faults in this locality, therefore, appear to have

been formed before deposition of the Tertiary volcanic rocks, 

3. The Tertiary Oak Spring formation in most of the Nevada proving grounds

area, and adjacent areas ie composed of tviff and extrusive rocks. Time,
 GEOLOGY, ATOMIC ENERGY COMMISSION PROVING GROUNDS 379

exception occurs in southern Frenchman Flat, where interbedded tuff and 

fresh-water limestone beds of Miocene (?) age unconformably overlie the

 eroded Paleozoic rocks and make up the basal 100 feet of the Tertiary 

section. Overlying this are 100-200 feet of interbedded volcanic tuff and 

conglomerate layers bearing cobbles of quartzite and limestone of Paleozoic

 ageSimilarly, the major exception.to the southerly trend of the fault pattern.

 occurs in the mountainous areas south of Frenchman Flat, where the fault 

traces swing abruptly to the southwest and almost attain a westerly trend. 

This coincidence in structure and stratigraphy suggests the following hypothesis: Normal faulting attained a southwesterly trend in the vicinity of 

southern Frenchman Flat, and created a bedrock "dam" before Miocene 

time. The drainage of surface waters was impeded resulting in a fresh 

water lake, in which a few limestone beds were deposited in an interbedded 

sequence with volcanic tuff. Continued uplift along the southwestwardtrending normal faults transformed the "dam" into a high area of Paleozoic 

rock subject to erosional forces. From this bedrock high area, cobbles and 

boulders of limestone and quartzite were eroded and washed into the basin 

where a predominance of volcanic rocks was being deposited. Thus, if this 

hypothesis is valid that faulting actually preceded the limestone and conglomerate deposition, a pre-Miocene(?) age of the inception of normal 

faulting is implied. Normal faults, which cut the valley alluvial deposits, 

attest to the recency of some of the faulting.

References from literature concerning dating of normal faulting 

substantiate an even earlier pre-Miocene inception of the faulting. 

Nolan (1943) presents a summary of the several publications concerning this subject and states:

Ferguson (1926) and Ferguson and Cathcart (1924) . . . found that . . . (block 

faults) both preceded and followed the deposition of sediments belonging to the 

Esmeralda formation (late Miocene and early Pliocene) . . . Westgate (1927, p. 44) 

has also found evidence for block faulting of pre-Pliocene(?) age in southeastern 

Nevada, and Longwell (1936, p. 1456) has described block faulting in the Boulder 

Dam region that preceded, accompanied, and followed the deposition of his 

Muddy Creek formation, of questionable Pliocene age.

. . . The evidence provided by the Tertiary sedimentary rocks, however, 

appears to be conclusive that the block-faulting movements started early in the 

Tertiary period, probably in late Eocene or early Oligocene time, and were 

widespread through the later Miocene and early Pliocene.

In the Muddy Mountains, Nevada (Longwell, 1949) and Gold Hill, 

Utah (Nolan, 1935) the stage of normal faulting is not distinctly 

separated from the compressional phase, as evidence of contemporaneous normal faulting and thrusting has been found.

Nolan (1943) also writes:

Finally, there appears to be a suggestive connection in time between the block 

faulting and preceding folding and thrusting. Thus, block faulting is believed to
380 'CONTRIBUTIONS TO GENERAL GEOLOGY

have been in progress in early Oligocene time and thrusting seems to have continued well into the Eocene epoch, a relation that may be interpreted as sequential 

and implying continuity in action of the same causative forces . . . the block 

faults thus represent the final and declining stages of (the- compressional) 

revolution.

Thus, the foregoing discussions and references indicate that normal 

faulting in the Nevada proving grounds area began at least as early 

as Miocene time and probably as early as early Tertiary time, soon 

after the completion of folding and thrusting, and the intrusion of the 

granitic body. The normal faulting has continued to recent time.

One of the latest structural developments of the area is the localized 

intrusion of a series of dikes in the Paleozoic and Tertiary country 

rocks northeast of Paiute Ridge. Dating was made possible by the 

linear alinement of some of the dikes along preexisting normal faults, 

which cut the Tertiary volcanic rocks. In places the dikes have completely occupied the fault zone. Thus, intrusion of dikes in this 

locality followed the Miocene (?) or later volcanic deposition and the 

normal faulting.

ECONOMIC GEOLOGY

The tungsten mine at Oak Spring and the Hornsilver mine west of 

Frenchman Flat, now abandoned, are the largest mines in the area. 

Many smaller abandoned mines are in other parts of the area, particularly in the Mine Mountains, but information concerning them is 

not available. No mines are operating in the area.

The tungsten mine has been described by Wyant (1941), He states 

that scheelite (CaW04) and powellite (CaMoW04) occur in large 

masses of tactite, formed by granitic intrusion into limestone, and 

occupy premineral faults and dikes. Most of the tactite masses have

been found parallel to bedding or premineral faults from 100 to 500

feet from any granite contact. Minerals found in the tactite in approximate order of abundance are garnet, quartz, pyroxene (?), calcite,

idocrase, scheelite, powellite, and epidote. Control of the scheelite

concentrations with tactite bodies is obscure; probably cross fractures

and irregularities of the contact are factors in localization.

The original discovery of scheelite at Oak Spring was made in 1930

by individuals who immediately interested Goldfield Consolidated

Mining Co. in the claim. This company optioned the claim to U, 5,

"Vanadium. Corp. for exploitation. However, XJ. S. Van axliuiM. Oorr>.,

after thoroughly sampling the tactite masses dropped their option, 

Later, exploratory work was done by Goldfield Consolidated Mining

Co.7 Pacific Bridge Co., Nevada Massachusetts Co., and I. Foster

Smith. Returns were small and further work was frustrated by the 

incorporation of the Oak Spring area into an Air Force gunnery range. 

Total extraction of ore amounted to about 7 to 8 tons of concentrate
GEOLOGY, ATOMIC ENERGY COMMISSION P30VING GROUNDS 381

containing 50 percent W03 . Estimated tungsten reserves include 

35,000 tons of probable and possible ore containing 0.5 percent or 

higher of W03 and 60,000 tons of possible marginal and submarginal 

ore containing 0.1 to 0.49 percent W03 .

Very little is known concerning the Hornsilver mine. Minerals 

occur in volcanic rocks and probably include gold as well as silver. 

Production figures for the mine are not known, however, judging from 

the size of the shafts, the mine operated on a fairly large scale at one

time.

LITERATURE CITED

Ball, S. EL, 1907, A geologic reconnaissance in southwestern Nevada and eastern

California: U. S. Geol. Survey Bull. 308. 

Blake, W. P., .1902, The caliche of southern Arizona; an example of deposition

by the vadose circulation: Am. Inst. Min. Metall. Eng. Trans., v. 31, p. 220-

226. 

Ferguson, H. G., 1926, Late Tertiary and Pleistocene faulting in western Nevada

labs.]: Geol. Soc. America Bull., v. 37, p. 164. 

Ferguson, H. G., and Cathcart, S. H., 1924, Major structural features of some

western Nevada ranges [abs.]: Washington Acad. Sci. Jour., v. 14, p. 376-379. 

Hague, Arnold, 1892, Geology of the Eureka district, Nevada: U. S. Geol. Survey

Mon. 20.

Hazzard, J. C., 1937, Paleozoic section in the Nopah and Resting Springs Mountains, Inyo County, Calif.: Calif. Jour. Mines and Geology, v. 33, p. 273-339. 

Hewett, D. F., 1931, Geology and ore deposits of the Goodsprings quadrangle,.

Nevada: U. S. Geol. Survey Prof. Paper 162. 

Humphrey, F. L., 1945, Geology of the Groom district, Lincoln County, Nev.:

Nev. Univ. Bull., v. 39, no. 5, Geol. and Mining, ser. 42. 

King, Clarence, 1878, Systematic geology. U. S. geological exploration of the

fortieth parallel: Prof. Papers Eng. Dept. U. S. Army, no. 18, v. 1. 

Kirk, Edwin, 1933, The Eureka quartzite of the Great Basin region: Am. Jour.

Sci., 5th ser., v. 26, p. 27-44. 

Longwell, C. E., 1936, Geology of the Boulder Reservoir floor, Arizona-Nevada:

Geol. Soc. America Bull., v. 47, p. 1393-1476.

 1949, Structure of the northern Muddy Mountain area, Nevada: Geol.

Soc. America Bull., v. 60, p. 923-968. 

Longwell, C. R., and Dunbar, C. 0., 1936, Problems of Pennsylvanian-Permian

boundary in southern Nevada: Am. Assoc. Petroleum Geologists Bull., v.

20, p. 1198-1207. 

McAllister, J. F., 1952, Rocks and structure of the Quartz Spring area, northern

Panamint Range, California: Calif. State Div. Mines Spec. Rept. 25. 

Merriam, C. W., 1940, Devonian stratigraphy and paleontology of the Roberts

Mountains region, Nevada: Geol. Soc. America Spec. Paper no. 25. 

Merriam, C. W., and Anderson, C. A., 1942, Reconnaissance survey of the Roberts

Mountains, Nevada: Geol. Soc. America Bull., v. 53, p. 1675-1728. 

Nolan, T. B., 1929, Notes on the stratigraphy and structure of the northwest

portion of Spring Mountain, Nevada: Am. Jour. Sci., 5th ser., v. 17, p. 461-

472.

 1935, The Gold Hill mining district, Utah: U. S. Geol. Survey Prof. Paper 

177.

 1943, The Basin and Range province in Utah, Nevada, and California: 

U. S. Geol. Survey Prof. Paper 197-D, p. 141-196.
382 ! ONTRIBj[JTIQNS TO GENERAL GEOLOGY

Nolan, T. B., Merriam, C. W., and Williams, J. S., 1956, The stratigraphic section in the vicinity of Eureka, Nev.: U. S. Geol. Survey Prof. Paper 276.

Walcott, C. D., 1908, Nomenclature of some Cambrian Cordilleran formations: 

Smithsonian Misc. Coll., v. 53, no. 1, p. 1-12.

 1916, Cambrian geology and paleontology Cambrian trilobites: Smithsonian Misc. Coll., v. 64.

Westgate, L. G., 1927, Geology of Pioche, Nevada and vicinity, pt. 1, General 

geology: Am. Inst. Min. Metall. Eng. Trans., v. 75, p. 816-828.

Westgate, L. G., and Knopf, Adolph, 1932, Geology and ore deposits of the Pioche 

district, Nevada: U. S. Geol. Survey Prof. Paper 171.

Wheeler, H. E., 1940, Revisions in the Cambrian stratigraphy of the Pioche 

district, Nevada: Nev. Univ. Bull., v. 34, no. 8, Geol. and Mining, ser. 34.
INDEX

A Page

Area, location of._ _________ 333 

size of..... . 333

B

Banded Mountain.... . 338,342 

Belted Range..... . .. . 371 

Bird Spring formation. . ..... 363 

Bridge, Josiah, quoted... ... ... 348,352 

Burrows'dolomite.. 342 

Buttefault.............. ......... .... 374,375

0 

Caliche, depth___........___ ___ 366

description.__ . ________ 366 

Camp Mercury...._ . ______... 346,350

Captain Jack Spring........ ....-..--.. 353

Centers of volcanism.. 367

Ohainman shale._.. ___ - 359

Chisholm shale, age.. 339

extent of outcrops.... .. 339

lithologic description.._____...__ 339

thickness_____-..--..____ ... 339

Correlation of stratigraphic sections, lithologic- 336,

pi. 33 

paleontological.. 336, pi. 33

D

Dating compressional orogeny__.. 377

Death Valley region. ___ 351

Devils Gate (?) limestone, age . 356

fossils...._______.-___ 356

lithologic description.. 355 

thickness....... 355

type locality....-------- ... 356

Diamond Peak formation ... 359

Dolomite, undifferentiated, age._ 351

contact with Eureka quartzite.. 351

lithologic units... 351

description.___-.____ 351-353

thickness. 351

Douglass, Raymond, quoted...__... 361,362,363

Duncan, Helen, quoted....__ 352,357,361,362,363

Dunderberg shale, age. 343 

composition.. 342 

fossils......___-_......__......... 343

thickness___ ____ 342

E

Eleana formation, age.. 359 

correlation with Chainman shale 359 

folds............... .............. 371

lithologic units... __.. 358-359 

description... ................... 358-359

thickness_ .________ 358-359 

thrust faults..----- 372

Page

Eleana Range________________ 357,372'

Ely Springs dolomite._________^_t... 352:

Eureka district________...____... 334

Eureka quartzite, age_.___________ 349

lithologic units..._____________ 349

description.______________ 349 1

thickness_._____________ 349

Qlendale thrust...._________..____ 377

Groom district...___.......--.....- 334,335,337

lead and silver mining.__________ 335>

Hamburg shale. See Dunderberg shale. 

Hanson Creek formation..._________ 350' 

Highland Peak limestone.___ ... __ 342 

Hornsilver mine.. __ ...__ 380,381

Jangle limestone, age... __ ..___ 340 

correlation with Peasley limestone of

Wheeler.........._....__..... 340-

fossils_._ __ _____ 340 

lithologic units........__........ .. 339

description... __ .. 339'

structural features . 339

thickness of lower unit___ ____ 339'

middle unit.. .............. . 340

upper unit.. ..... .. 340

Jangle Ridge... __ 339,340 

Joana limestone.. 357,359

K

Knight, J. B., quoted....- ............. 361,362'

Location of wells in area...__ .. 365-

Lone Mountain dolomite... 350-

Lyndon limestone, age..... ...... 338

fossils...._...-- --...-----.-.. .. 338

lithologic description...--..... . 338

occurrence of "Girvanella" beds . 338

thickness__.__....__ .... 338-

M

Mercury limestone, age 357' 

fossils... ........ .-... 357

lithologic description 357'

type locality . . 367

Mercury test site. 331

Merriam.'C. W., quoted..... .. . 348,354

Mine Mountains...._...__ 353,372,373,374

Muddy Mountains....... . 334,377,378,379»

383
I r384 CONTRIBUTIONS TO GENERAL GEOLOGY

N Page

.Nanorthis-Kainella zone of Eureka, Nev_.__ 348

.Narrow Canyon limestone, age..-______ 356

^ contact with Devils Qatet?) limestone__ 356

thickness- 356

Nevada formation, age... 353

fossils_-___--. . __.__ 354-355

lithologic units..- .. -. 353

description..______________ 353-354

thickness.... ......---- 353-354

structure.... . 353 

Nolan, T. B., quoted._...-._____..... 379,380

^Nopah-Resting Springs Mountains, California... . 334,335

Oak Spring Butte.............. 366-367,370,371,375

Oak Spring formation, age__________ 366 

lithologic description... ____ 367 

structure.. . 370

Paiute Ridge. ................... 342,343,370,380

Paleozoic rocks, composition .. -.-.... 335

fossils..__...-.----.- . -..--....-.. 335

range in age of..-- ... ... 335

thickness__ 335

Palmer, A. R., quoted.......... 338,342,343,344,345

Pattern of normal faults. 375,377 

Peasley limestone of Wheeler... _....- 339

Pilotshale. .................. 356,359

Pioche district. .. . . 334,338,339

Pioche shale, age.. 338

fossils 337,338

lithologic description..--.-. 337 

size of outcrops.-.-- . 337 

thickness...-.---_------- . . 337

Pogonip group, age. 345

areas exposed._____________ 345,346 

folds. ----------------__-------__ 371

fossils.. . 347-348

lithologic units..______________ 345,346 

description.........__..__.--. 345,346

thickness_______---__---- 345-347

structure.-_---_------------------------ 346

thickness... ........ ............. 347

Production of ore--------------- -------- 380

Prospect Mountain quartzite 337

Q

Quartzite Ridge. - 357,358,375

Quaternary rocks. ........... 336,364

R Page

Ranger Mountains. _________ 349,351,353,376 

Red Mountain.....-.-..---_._______ 346,349 

Roberts Mountains formation.________ 350

S

Sevy dolomite. . _________ 353 

Spring Mountains. ....._____ 335,336,359

Stirling quartzite, age.-.. _________ 337 

composition..______________ 336

lithologic description....._________ 336

thickness_------ _________ 336

type locality_.. . ...___ 336 

width of outcrops_ ....______ 336

Stratigraphic sections_ .... 336, pi. 33

Syncline Ridge....__ ______ 371

T

Tertiary rocks, age... 336 

composition...... ..__ 336

fossils.- . 336

thickness...--..... . . . . 336

Tin Mountain limestone...________ 357

Tippipah limestone, age.___________ 360

folds--... 371

fossils "_______________.__. 361 

lithologic units.. 360-361

description.___________.__ 360-361 

thickness..-.---.--------.-----__. 360-361

Tippipah Springs..-.______________ 372 

Tungsten mine_________________ 380 

Tungsten reserves, estimated. ...____ 381

V 

Valley fill, composition.....-...-..-- 364

faults in..---..-------..- 370

thickness____--______ 365

W

White Pine shale............. . ........ . 353,359

Williams, J. Steele, quoted.. 357,362

Yen, Teng-Chien, quoted...___._____ 369

Yucca fault.. - ... . 376

Yucca Flat formation, age.--.---.--- 340

composition----.--------------------..--. 340

contact with Jangle limestone.--...----.. 340

distribution.........................._ 340

fossils.-.-___________-________ 342

lithologic units--..--------.....---------- 340

thickness of unit A ____________ 341

unit 13....------- ---- 341

unit C--------------------- 341

unit D................................ 34J

U. S. GOVERNMENT PRINTING OFFICEl 1957