Petroleum Potential of 

Wilderness Lands in 

Nevada 

By Charles A. Sandberg 

PETROLEUM POTENTIAL OF WILDERNESS LANDS IN THE 

WESTERN UNITED STATES 

GEOLOGICAL SURVEY CIRCULAR 902-H 

This chapter on the petroleum 

geology and resource potential of 

Wilderness Lands in Nevada is 

also provided as an accompanying 

pamphlet for Miscellaneous Investigations Series Map 1-1542 
j 
CONTENTS 

Page 

Abstract---------------------------------------------------------------------- Hl 

Introduction------------------------------------------------------------------- 1 

Area, purpose, and scope of report ---------------------------------------------- 2 

Sources of data and acknowledgments------------------------------------------- 4 

Geologic framework ------------------------------------------------------------ 4 

Conodont biostratigraphic and geothermal studies------------------------------------ 4 

Petroleum geology-------------------------------------------------------------- 5 

Oil fields and oil and gas seeps ------------------------------------------------- 6 

Sourcerocks---------------------------------------------------------------- 6 

Previous qualitative appraisals------------------------------------------------ 7 

Evaluation of Wilderness Lands by clusters ----------------------------------------- 7 

Eastern Basin and Range province --------------------------------------------- 7 

Western Basin and Range province --------------------------------------------- 9 

Summary------------------------------------------------------------------ 9 

Referencescited---------------------------------------------------------------- 9 

ILLUSTRATION 

Page 

FIGURE 1. Index map ofN evada showing petroleum provinces, Wilderness Lands and clusters, "cold spots" of Sandberg and 

Gutschick (1977), oil fields, and other evidence of petroleum generation------------------------------- H3 

III 

PETROLEUM POTENTIAL OF WILDERNESS LANDS IN THE WESTERN UNITED STATES 

Petroleum Potential of Wilderness Lands in Nevada 

By Charles A. Sandberg 

ABSTRACT 

Wilderness Lands in the Eastern and Western Basin and 

Range petroleum province~ are evaluated by application of 

plate-tectonic concepts to innovative regional-biostratigraphic 

and source-rock studies and by use of a unique geothermometry technique based on temperature-induced color 

changes in phosphatic microfossils called conodonts. Structural 

and stratigraphic complexities are thus deciphered and the 

thermal maturation of possible petroleum source rocks is interpreted. Wilderness Lands having oil and gas potential were 

grouped into 10 clusters in the Eastern Basin and Range province and into two clusters in the Western Basin and Range 

province. Of these, only two clusters have been evaluated to 

have a high potential, and two other clusters have been 

evaluated to have a medium potential. All four of these higher 

rated clusters are located in the Eastern Basin and Range province. The remaining eight clusters are considered to have low 

potential. Many Wilderness Lands, which were not clustered, 

are considered to have zero petroleum potential because they 

comprise terranes composed solely of intrusive igneous rocks, 

thick piles of extrusive igneous rocks, or metamorphic rocks. 

Although such terranes may be highly favorable to nonorganic 

mineral exploration, they contain no original or surviving hydrocarbons in petroleum sour~e or reservoir rocks because of 

the high geothermal temperatures to which they were subiected. 

INTRODUCTION 

The resource evaluation of frontier petroleum 

provinces, such as the Eastern and Western Basin 

and Range provinces, presents problems quite distinct from those of already developing petroleum 

provinces. In developing provinces, such as the 

Williston basin, producing oil and gas fields provide analogs for predicting where and how similar 

accumulations might have formed under matching 

sedimentary and structural controls elsewhere in 

the basin. In the Basin and Range provinces, however, where subsurface well control is extremely 

sparse (Garside and Schilling, 1977; Garside and 

Hl 

others, 1977), the controls necessary for petroleum accumulations-source rocks, reservoir 

rocks, traps, and hydrocarbon maturation--can be 

analyzed only by field (surface) lithostratigraphic 

and biostratigraphic investigations. At present, 

there are in Nevada only three, or possibly four, 

producing oil fields (Bortz and Murray, 1979; 

Duey, 1979; Veal, 1983), plus several deep abandoned wells that had good hydrocarbon shows and 

one area of significant oil and gas seeps (Foster 

and others, 1979). These widespread indicators of 

petroleum potential are located on figure 1.· In addition, many small oil and gas seeps occur in and 

around areas of hot and cold springs (although 

some of these may yield only shallow biogenic 

gas); thin veins of solid hydrocarbons (dead oil) 

cutting sedimentary rocks are widespread, and 

some fossils such as cephalopods contain liquid petroleum (live oil). 

Complicating the whole procedure of resource 

evaluation is the fact that the name Great Basin, 

which is popularly applied to the area of Nevada 

and western Utah, does not connote a single 

sedimentary or structural basin, but rather a 

large region of present-day interior drainage, 

wherein streams die out in the desert rather than 

feeding into larger and larger rivers that eventually reach the sea. In fact, the Great Basin represents the former northwest margin of the North 

American continent during the Paleozoic Era 

(Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, and Permian Periods) 

and Mesozoic Era (Triassic, Jurassic, and Cretaceous Periods) of geologic time. Thus, the deposited 

sedimentary rocks, which are sources of hydrocarbons that generate oil and gas, represent many 

different ancient environments that have modern 
analogs-carbonate platforms similar to the present Bahamas Bank and Florida Bay but many 

times broader; continental shelves bathymetrically 

similar to the Atlantic Coastal Shelf; continental 

slopes and rises; and deep ocean basins like the 

Gulf of Mexico. Adding greatly to the complexity 

is the fact that this former margin of North America has been subjected to several plate-tectonic 

(oceanic plate against continent) collisions. These 

collisions not only have caused the continental 

margin to migrate progressively westward 

through accretion of orogenic highlands produced 

by the collisions but also have caused thin sheets 

of previously deposited sedimentary rocks to be 

obducted or pealed off as nearly horizontal thrust 

sheets and to be pushed landward across the surface of the continent. The net result is that most 

mountain ranges in Nevada contain rocks that 

have moved at least 200 kilometers (120 miles) 

generally eastward from their original sites of deposition. Consequently, the rocks in thrust sheets 

encountered by drilling below the thrust sheets 

closest to the surface may represent totally different depositional settings from those at the surface. Additionally complicating the structural 

scenario is the fact that following relaxation of 

compressional plate-tectonic forces, extension took 

place and produced nearly vertical faults that 

broke up the horizontal thrust sheets and allowed 

parts of them to be downdropped to form the desert basins between the mountain ranges. These 

high-angle extension or normal faults now parallel 

the steep fronts of ranges. Because of the many 

northward- and northeastward-trending, long 

rows of alternating ranges and basins, Nevada is 

more properly referred to as part of the Basin and 

Range province. A further complexity is that extension also permitted the upwelling of magmas 

through fractures and the outpouring of sheets of 

volcanic rocks, which have covered and obscured 

broad areas of sedimentary rocks. 

Because of these structural complexities and extensive volcanic cover, most major oil companies 

almost totally dismissed Nevada as a petroleum 

province after conducting cursory field stratigraphic and source-rock studies during the 1950's 

and 1960's. A few hydrocarbon indications, such 

as the Bruffey oil and gas seeps, which were first 

reported in 1927, and the Eagle Springs oil field, 

which was discovered in 1954, were passed over 

as mere anomalies or curiosities related to 

Cenozoic Era (Tertiary Period) lake-basin source 

H2 

rocks. As discussed by Sandberg (1975) and 

Sandberg and Poole (1975), the myth developed 

that the sources of hydrocarbons in Paleozoic 

rocks of the Eastern Basin and Range province 

had been pervasively overmatured by geothermal 

processes and that any oil or gas that might have 

been generated from them had leaked to the surface along faults and fractures and long ago had 

been dissipated. Recent biostratigraphic and 

geothermometric studies of phosphatic marine 

microfossils known as conodonts, however, have 

helped to dispel these myths and to unravel the 

depositional and structural complexities. Studies 

by Sandberg (1975), Sandberg and Poole (1975), 

Sandberg and Gutschick (1977), and Poole, Fouch, 

and Claypool (1979), moreover, have suggested 

that oil and gas are still being generated today 

from Paleozoic source beds such as those in the 

Mississippian Chainman Shale and equivalent formations. This generation is occurring presumably 

after many of the faults and fractures that could 

have leaked oil and gas to the surface have been 

sealed. The Bruffey seeps (Foster and others, 

1979), however, are an example of currently generated oil and gas. 

AREA, PURPOSE, AND SCOPE 

OF REPORT 

This report qualitatively evaluates the petroleum potential of 76 wilderness tracts, comprising 

about 4. 9 million acres in the State of Nevada. An 

additional 3.1 million acres of Wilderness Lands 

have zero petroleum potential Potential is rated 

as zero, low, medium, or high based on parameters that are unique tQ frontier provinces in 

Nevada and adjoining States. Such ratings are not 

quantitatively or qualitatively comparable to similar adjectival ratings for highly developed petroleum provinces. Ratings are based partly on thermal maturation of source rocks, as evidenced by 

geothermometry from conodonts in Paleozoic and 

Triassic source rocks and from spores and 

palynomorphs (microscopic plant remains) in Cretaceous and Tertiary source rocks. Potential 

source rocks were identified as such on the basis 

of organic carbon content greater than 0.5 percent. A few actual hydrocarbon analyses 

(Sandberg and Poole, 1975; Poole, Fouch, and 

Claypool, 1979) were used to substantiate the 

thermal maturation derived from conodont color 

alteration index (CAl) values (Epstein, Epstein, 
0 

EXPLANATION 

• HIGH POTENTIAL 

~ MEDIUM POTENTIAL 

• LOW POTENTIAL 

D ZERO POTENTIAL 

/ ........ 

/12 I CLUSTER AND l_/ NUMBER 

ww 

CJC) azz 

<(<( 

a: a: It 

Q Q /i Zzo 

<( <( It 

~z oo- <(oo 

(D<( (D 

Zz 

a: a: Ww 

1-tC/)C/) w<( 

~w 

FIGURE 1.-Index map of Nevada showing petroleum provinces, Wilderness Lands and clusters, "cold 

spots" of Sandberg and Gutschick (1977), oil fields, and other evidence of petroleum generation. 

H3 
and Harris, 1977). Ratings are also based on proximity to areas of known production or oil and gas 

shows and to areas of potential source and reservoir rocks. Trapping mechanisms were not considered because of a paucity of data. However, because of the great volume of source rocks, oil and 

gas accumulations could be expected even if all 

but a few percent of available hydrocarbons had 

leaked to the surface. Time did not permit an onthe-ground field check of most of the areas being 

evaluated. 

SOURCES OF DATA AND 

ACKNOWLEDGMENTS 

This report builds on 15 years of experience 

studying Paleozoic (mainly Devonian and Mississippian) rocks in Nevada. The knowledge gained 

through this experience was then applied to other 

areas-mainly in the Western Basin and Range 

province and Nevada Test Site-that are covered 

by the geologic literature but have not been visited personally. This report would not have been 

possible without benefit of the even greater experience of my Geological Survey colleague, Forrest G. Poole, who introduced me to the complexities of the Great Basin during parts of the 

1968-1973 field seasons and coauthored many publications. 

GEOLOGIC FRAMEWORK 

A geologic map of Nevada by Stewart and 

Carlson (1977) is at the same 1:1,000,000 scale as 

the Miscellaneous Investigations Series Map I1542 (in press), showing the color-coded qualitative petroleum evaluation of Nevada Wilderness 

Lands, and thus can be used to relate them to the 

geographic locations of basins and ranges and to 

the surface distribution of geologic formations. An 

excellent accompanying text by Stewart (1980) 

fully describes the geology of Nevada. A correlation chart by Langenheim and Larson (1973), although somewhat outdated in light of recent biostratigraphic advances, gives an overall picture of 

the distribution of geologic formations in the various mountain ranges of Nevada. Correlation 

charts by Poole, Sandberg, and Boucot (1977) and 

by Poole and Sandberg (1977) present the updated 

distribution of sedimentary formations of Silurian, 

Devonian, and Mississippian ages. Similar regional 

studies have been performed by other geologists 

for rocks of Cambrian, Ordovician, and Permian 

ages. Reconstruction of discrete depositional comH4 

plexes or packages of rocks deposited at the same 

time in the geologic past, as exemplified by the reconstruction of Upper Devonian cratonic-platform 

and continental-shelf rocks (Sandberg and Poole, 

1977), have been accomplished despite the previously described complexities. Moreover, even the 

ancient oceanographic and bathymetric setting of 

Nevada during a brief span of Mississippian time 

has been interpreted as part of a continentwide 

reconstruction by Gutschick and Sandberg (1983). 

CONODONT BIOSTRATIGRAPHIC AND 

GEOTHERMAL STUDIES 

Conodonts are the fossilized toothlike, phosphatic hard parts of enigmatic, soft-bodied organisms 

that lived in most marine environments during 

Paleozoic and Triassic times, but are now extinct. 

Because of their mineralogic composition (carbonate apatite), lack of internal permeable canal 

structures such as fish teeth possess, and imperviousness to most types of chemical alteration, they 

are generally preserved even in rocks that have 

been subjected to high-temperature metamorphism or hydrothermal solutions that destroyed other 

(mainly calcitic) fossil remains. The only notable 

change that occurs in conodonts when they are 

subjected to increasing geothermal temperatures, 

most commonly caused by increasing depth of rock 

burial, is a series of progressive and irreversible 

color changes. On the basis of color differences observed in the field and produced through hightemperature experiments in the laboratory, Epstein, Epstein, and Harris (1977) proposed a scale 

of conodont color-alteration index (CAl) values, 

numbered 1 to 8, that readily tell the maximum 

temperatures to which rocks have been subjected. 

In other words, their work established conodonts 

as virtual geothermometers with a scale of 1 to 8. 

The observed conodont CAl values can then be related to the thermal maturation of hydrocarbons 

contained in the rocks. The utility of conodonts as 

geothermometers, as virtual time planes for determining precise dates (within 0.5 million years) 

and rates of sedimentation, and for making 

biofacies interpretation of rocks deposited in 

greatly different paleotectonic settings in the 

Great Basin, was discussed by Sandberg and 

Poole (1977). Similar usages in nearby areas were 

discussed by Sweet, Harris, Sandberg, and 

Wardlaw (1981). The utility of conodonts to petroleum exploration in identifying source rocks and 
determining their thermal maturation was discussed by Sandberg and Gutschick (1977) and 

Sandberg (1980). Conodonts have proven to be almost infallible in determining precise ages of 

Paleozoic and Triassic rocks. The worldwide standard Late Devonian and Early Mississippian conodont zonations have been recognized throughout 

the Great Basin (Sandberg, 1979). Conodonts are 

also abundant and widespread in rocks of the 

other systems in the Great Basin and provide useful zonations, as desCribed in a number of papers 

in a symposium volume edited by Sandberg and 

Clark (1979). The utility of Carboniferous (Mississippian and Pennsylvanian) conodonts for zonation, biofacies, and intercontinental correlation has 

been discussed by Sandberg, Lane, and Matthews 

(1979). 

Because of the multiplicity of their usages, conodonts have proven to be the most valuable tool 

for evaluating the petroleum potential of Paleozoic 

and Triassic rocks in the Eastern and Western 

Basin and Range frontier petroleum provinces. On 

the basis of conodont CAl values, two "cold 

spots," wherein Paleozoic source rocks were abnormally cool and still within the oil-generation 

window, were delineated in Nevada by Sandberg 

and Gutschick (1977). These cold spots (CAl 

values of 2.5 or less) were based on conodonts contained in source rocks within the Mississippian 

Chainman Shale and equivalents and within the 

Late Devonian lower member of the Pilot Shale, 

whose richest source-rock area had earlier been 

identified and delineated by Sandberg and Poole 

(1975). The cold spots and the area of rich Pilot 

source rocks are located in relation to Wilderness 

Lands in figure 1. Large-scale thermal maturity 

maps that give the CAl values for Ordovician 

through Triassic rocks on a systemic rather than 

formational basis were compiled from many 

sources by Harris, Wardlaw, Rust, and Merrill 

(1980). These maps are invaluable in rating the 

wilderness tracts of Nevada. 

PETROLEUM GEOLOGY 

The petroleum resource appraisal of Wilderness 

Lands in Nevada, as elsewhere, is dependent on 

the four major parameters that govern accumulation-the presence of source rocks, maturation 

history, reservoir rocks, and traps. Because of the 

complex shuffling of many different rock types by 

several types of faulting, reservoir rocks and 

traps are considered to be broadly distributed 

throughout the State. Consequently, the prime 

parameter for consideration in frontier petroleum 

provinces, such as the Eastern and Western Great 

Basin and Range provinces, devolves to the presence or absence of source rocks and their maturation. 

H5 

Additionally, of special importance in Nevada 

are present and ancient geothermal temperatures, 

which control the maturation of hydrocarbons in 

source rocks and the state of preservation of oil 

and gas that has already migrated into reservoir 

rocks. Because of the extremely complex geology, 

actual geothermal temperature measurements 

cannot be extrapolated for a:ny great distance 

from their points of measurement in wells or hot 

springs. Consequently, geothermal-gradient and 

subsurface-temperature maps of North America 

(American Association of Petroleum Geologists 

and U.S. Geological Survey, 1976a, 1976b) do not 

map any part of Nevada except in the vicinity of 

the Eagle Springs oil field, and they show only 

data points and temperature values. Hence, conodont CAl values, which provide numerous additional data points, are of prime importance in determining the total effect of present and past 

geothermal temperatures on source and reservoir 

rocks. In areas where such rocks are slightly overmatured (CAl 3.5 to 4) at the surface, less heated 

rocks still may be encountered at depth in lower 

thrust plates. However, in broad regions that 

have been pervasively overheated (CAl values of 

5 or greater), hydrocarbons are interpreted to 

have been destroyed from the surface down to 

great depth. Care must be taken not to extrapolate CAl values downward, however, without considering the local geologic structure. For example, 

in some areas, western facies rocks that have 

never been deeply buried (CAl 2.5 or less) occupy 

thin horizontal thrust sheets that veneer totally 

overmatured terranes (CAl 5 or greater). 

In addition to the distribution of source rocks 

and their maturation, two other subjects must be 

addressed in making petroleum resource appraisals. One is the availability of a few analogs that 

are provided by evidence of hydrocarbon distribution from existing oil fields and known oil and gas 

seeps. The other is the consideration of previous 

qualitative appraisals that have been made by 

other qualified petroleum geologists. 
OIL FIELDS AND OIL 

AND GAS SEEPS 

At present there are in Nevada at least three 

producing oil fields-Eagle Springs field (Bortz 

and Murray, 1979) and Trap Spring field (Duey, 

1979), which lie close together in Railroad Valley, 

and a newly discovered, unnamed, single-well field 

(Veal, 1983) in Pine Valley, which lies some distance north of the other two fields and west of the 

Roberts Mountains thrust (fig. 1). A possible 

fourth field, Currant oil field was discovered in 

1978 (Foster and Dolly, 1980), but whether this 

field is still producing is not known. It lies north 

of Eagle Springs field in Railroad Valley and is 

the third field near the cluster shown on figure 1. 

The source of oil in the older Eagle Springs field 

commonly has been attributed to Cretaceous or 

Tertiary (Paleogene) lacustrine source rocks, but 

some workers, beginning with Picard (1960), have 

suggested that both Tertiary and Paleozoic 

affinities of the oil are possible, inasmuch as 

Paleozoic rocks enclose the Tertiary basin from 

which the oil is produced. A great difference 

exists between the characteristics of the oil produced at the Eagle Springs field and at the nearby, newer Trap Spring field, as discussed by Duey 

(1979). Thus, if one of these fields is largely from 

a Tertiary source, the other must be largely from 

a Paleozoic source, the Mississippian Chainman 

Shale. As pointed out in several presentations 

since 1975 (Sandberg, 1975; Sandberg and 

Gutschick, 1977), one key to characterizing oil 

types is the time of generation. Thus, if the major 

organic constituent of both the Tertiary and Mississippian rocks is somewhat similar and the Mississippian source rocks have been kept abnormally 

cool through most of geologic time, as indicated by 

low conodont CAl values, the oils being generated 

today from either source would be difficult to separate on the basis of physical and chemical characteristics. In fact, geochemical evidence has now 

documented that source rocks in the Chainman 

Shale have undergone two major cycles of generation and that one of these is taking place at present (Poole, Fouch, and Claypool, 1979). 

Little is known about the recently discovered 

producing oil well that lies west of the leading 

edge of the Roberts Mountains thrust system (fig. 

1). The source of oil could be the Ordovician Vinini 

Formation or Cretaceous-Tertiary lacustrine beds, 

as suggested by Veal (1983) or just as likely the 

Mississippian Chainman Shale or its lateral equiH6 

valents, the Diamond Peak and Webb Formations. 

This field lies close to the Bruffey oil and gas 

seeps (Foster and others, 1979), which suggest 

that petroleum in the vicinity is either migrating 

or being generated today. It also lies close to the 

smaller of the two cold spots of Sandberg and 

Gutschick (1977) and to a deep well that had significant oil shows in highly fractured or faulted 

rocks (fig. 1). 

SOURCE ROCKS 

In the Eastern Basin and Range Province, the 

Mississippian Chainman Shale and locally the 

equivalent part of the Woodman Formation contain the thickest, richest, and most widespread 

source rocks in the area (fig. 1) between the 

Sevier and Roberts Mountains thrust systems and 

for a short distance to the west (Sandberg, 1975; 

Poole and Sandberg, 1977; Poole and others, 

1979). Locally, however, in east-central Nevada, 

the lower member of the Pilot Shale contains even 

richer source beds in the area outlined on figure 1 

and equally rich source beds in an aureole to the 

northwest, west, and south. Source beds within 

the Chainman and Pilot are generally at the optimum maturation for oil generation within the 

larger cold spot of Sandberg and Gutschick (1977). 

This cold spot lies in the general area of, but extends farther east than, the Prichards Station, 

Pancake Range, and Warm Springs lineaments of 

Ekren and others (1976). In fact, the southern 

limit of the cold spot appears to be an eastward 

continuation of their independently hypothesized 

Warm Springs lineament. The Permian Meade 

Peak Tongue of the Phosphoria Formation 

(Maughan, 1979) may be a source rock in the extreme northern part of the province. The Ordovician Valmy and Vinini Formations and Devonian 

Woodruff Formations almost certainly are extremely rich source rocks in the area west of the 

Roberts Mountains thrust (fig. 1). The organiccarbon content of Mississippian source rocks in adiacent States and the difficulties encountered in 

estimating the organic-carbon and hydrocarbon 

values from outcrop samples were discussed by 

Sandberg, Grogan, and Clisham (1979). 

Throughout the Eastern Basin and Range province, Cretaceous to Tertiary (Paleogene) lacustrine oil shales that were deposited in former lake 

basins between the mountain ranges may act as 

source rocks (McDonald, 1973; Fouch and others, 

1979). Such rocks cover at least half the surface 
area of the province. In most areas, the hydrocarbons in these source rocks are regarded as immature. Locally, however, where they have been additionally heated by deeper burial, intrusive igneous rocks, or hydrothermal solutions, the contained hydrocarbons could be well within the oilgeneration window. 

In the Western Basin and Range province, 

Paleozoic rocks are no longer believed to contain 

source rocks because of broad areas of pervasive 

high geothermal temperatures, as exemplified by 

the Battle Mountain heat-flow high (Hyde, 1979). 

Cretaceous and Tertiary (Paleogene) lacustrine 

rocks in some parts of this province may be at or 

near optimum maturation at least at depths below 

2,500 meters, as suggested by analyses reported 

by Hastings (1979). Possible Tertiary source rocks 

are present throughout most of the province 

(McDonald, 1973; Warner, 1980). Cretaceous 

source rocks may be present in the northern part 

of the province (Willden, 1979). However, a possible connection between the Sierra Nevada and 

Idaho batholiths has been postulated in that area 

by Taubeneck (1971). If such connecting igneous 

rocks exist at depth, any overlying s'ource rocks 

would have been overmatured. 

PREVIOUS QUALITATIVE APPRAISALS 

In addition to my earlier evaluations of the petroleum potential of the Eastern Basin and Range 

province based on Paleozoic source rocks 

(Sandberg, 1975; Sandberg and Poole, 1975; 

Sandberg and Gutschick, 1977), three othe.r evaluations have been presented at meetings of the 

American Association of Petroleum Geologists. 

Meissner (1978) discussed possible source rocks, 

existing oil fields, and dry (biogenic) gas accumulations. Foster and Dolly (1980) discussed methods 

of exploration, oil and gas indications, and possible 

stratigraphic and structural traps. Veal (1983) discussed possible Paleozoic and Cretaceous to Tertiary source rocks, mainly west of the Roberts 

Mountains thrust (fig. 1). The only evaluation of 

oil and gas possibilities based on wells drilled at 

the south end of the Eastern basin and Range province, adjacent to the Sevier thrust system (fig. 

1), was made by Bissell (1973). Some of the exploration techniques employed by the petroleum industry in searching for a new prospect, as discussed by Dolly (1979), are highly relevant to the 

present evaluation of the petroleum potential of 

Nevada Wilderness Lands. 

H7 

EVALUATION OF WILDERNESS 

AREAS BY CLUSTERS 

The State of Nevada is arbitrarily divided into 

the Eastern and Western Basin and Range provinces by the 117° meridian (fig. 1). This province 

boundary projects the Oregon-Idaho State line 

southward from its junction with Nevada. It was 

selected because of the difference in source rocks 

between the two parts of the State and because 

the area of greatest heat flow lies generally west 

of the 117° meridian. This is exemplified by the 

maps of geothermal areas presented by Hyde 

(1979). Within each province, for ease of treatment, wilderness tracts are grouped into clusters 

on the basis of similar petroleum potential, inferred from matching geologic settings, source rocks, 

organic maturation, and distance from known oil 

production or oil and gas shows. 

EASTERN BASIN AND RANGE 

PROVINCE 

This province contains 10 clusters (fig. 1): clusters 1, 2, 4, 7, 9, and 10 are rated to have low petroleum potential; clusters 5 and 8 are rated to 

have medium potential; and clusters 3 and 6 are 

rated to have high potential. All Wilderness 

Lands outside these clusters are rated to have 

zero potential. 

Cluster 1.-This cluster is identical in its 

geologic setting to Idaho wilderness cluster 4 discussed by C. A. Sandberg, chapter F, in this circular. Both clusters are underlain by Tertiary lake 

beds of the Lake Bruneau basin (Warner, 1980) 

but are covered at the surface mainly by slightly 

younger volcanic rocks. Little is known about the 

few small windows of presumably overmatured 

Paleozoic rocks that poke out from the extensive 

volcanic cover. Because the heating by volcanic 

rocks and minor areas of intrusive rocks may have 

raised the temperatures of some of the Tertiary 

source beds to optimum maturity, this cluster is 

rated to have a low potential. Quantitative resource estimates discussed by B. M. Miller, chapter A, in this circular were made using the IdahoSnake River Downwarp province as an analog, instead of the Eastern Basin and Range province. 

Cluster 2.-Wilderness Lands in this cluster lie 

in the mountain ranges that border the Steptoe 

Valley, where there has been some recent shallow 

exploratory drilling for reservoirs in Cretaceous 
to Tertiary lacustrine beds. The ranges themselves are composed mainly of Paleozoic rocks, 

which are largely overmatured thermally (CAl 

greater than 4). Some conodont samples (Harris 

and others, 1980) have CAl values that are within 

the oil- and gas-generating range, however. Because of the proximity to economically interesting 

lacustrine beds and the possibility of some 

Paleozoic source beds being at optimum maturity, 

this cluster is rated to have a low potential. 

Cluster 3.-This cluster lies on or close to the 

buried trace of the leading edge of the Roberts 

Mountains thrust system (fig. 1). Cretaceous to 

Tertiary tuffaceous lacustrine beds and upper 

Paleozoic rocks that underlie the wilderness tracts 

are partly obscured by alluvial cover. Because this 

cluster is situated within one of the cold spots of 

Sandberg and Gutschick (1977), within a few miles 

of two deep wells that had excellent petroleum 

shows and less than 25 miles from a producing oil 

well and significant oil and gas seeps, it is a prime 

area for petroleum exploration and is rated to 

have a high potential. 

Cluster 4-Wilderness Lands in this cluster are 

situated in the Roberts and Simpson Park Mountains. They are underlain mainly by Paleozoic 

sedimentary rocks and partly by Tertiary volcanic 

rocks. Rocks of the lower fault plate exposed at 

the surface generally are thermally overmatured 

(CAl 3.5 to 4), but those on the upper plate of the 

Roberts Mountains thrust, which contain rich 

source rocks, may have CAl values as low as 1 

(Harris and others, 1980). Because lower temperature rocks, at optimum maturation for oil and gas 

generation, form a veneer on higher temperature 

rocks and because there is little indication of 

which temperature range might be encountered in 

rocks of lower fault slices at depth, this cluster is 

rated to have a significant but low potential. 

Cluster 5.-Wilderness Lands in this cluster are 

situated in the Cherry Creek, Snake, Schell 

Creek, southern Egan, and Grant Ranges. They 

are underlain by Paleozoic sedimentary rocks that 

include the Chainman Shale in all five ranges and 

the lower member of the Pilot Shale in all but the 

Grant and southern Egan Ranges (fig. 1). All but 

one of these tracts lie within the larger cold spot 

of Sandberg and Gutschick (1977), and hence 

source rocks in the Chainman and Pilot are regarded to be at optimum maturation for oil and 

gas generation. Additionally, some of these tracts 

lie close to Railroad Valley, which is currently the 

H8 

main oil- producing area in Nevada. Because of 

the optimum maturity of source rocks and moderate proximity to oil fields, this cluster is rated to 

have a medium potential. --

Cluster 6.-The single wilderness tract that 

constitutes this cluster lies in the Grant Range 

and is underlain by Paleozoic sedimentary rocks 

and Tertiary volcanic rocks. This cluster is regarded to have high petroleum potential because 

it directly borders the three oil wells in Railroad 

Valley and because Cretaceous to Tertiary source 

rocks in the valley and Paleozoic source rocks in 

the range are at optimum maturation for oil and 

gas generation. 

Cluster 7.-Wilderness Lands in this cluster are 

underlain almost entirely by Tertiary volcanic 

rocks except for several small patches of Paleozoic 

sedimentary rocks. Nothing is known about the 

maturation of source beds in the Paleozoic rocks. 

However, because of the presence of volcanic 

rocks, some of the Cretaceous to Tertiary source 

beds in adjacent valleys may be thermally mature. 

Hence, this cluster is rated to have a low petroleum potential. 

Cluster 8.-The five tracts that compose these 

clusters are situated in the Mormon, Muddy, and 

Meadow Valley Mountains, and Arrow Canyon 

and Las Vegas Ranges. On the basis of my own 

field work, I am familiar with both the local geology and conodont CAl values. Most of the tracts 

are underlain by Paleozoic sedimentary rocks that 

have CAl values of 2.5 to 3.5, but the southernmost tract also includes some Cretaceous to 

Tertiary lacustrine beds. A recent dry hole drilled 

just east of this cluster (fig. 1) had significant oil 

and gas shows, which I interpret to have been 

generated from Mississippian source rocks farther 

west, within cluster 8. Because the CAl values indicate organic maturation that is close to the 

upper limit for oil generation but in the optimum 

range for gas generation and because of significant 

nearby oil and gas shows, this cluster is rated to 

have a medium potential. 

Cluster 9.-Tracts in this cluster are situated in 

several low mountain ranges bordering Lake 

Mead and south of the city of Las Vegas. They are 

partly underlain by areas of Precambrian 

metamorphic and intrusive rocks that have zero 

petroleum potential, partly by Tertiary volcanic 

rocks, and partly by Paleozoic, Mesozoic, and Tertiary sedimentary rocks. This cluster lies east of 

the Sevier thrust system, so Paleozoic source 
. . 

rocks, such as the Chainman Shale, are not present. The Mesozoic rocks are not believed to contain source beds, but some of the Tertiary rocks 

may. Because of nearby oil and gas shows, one of 

which was described by Bissell (1973), and recent 

exploratory drilling in the area just to the north, 

this cluster is regarded to have low petroleum potential, despite the thinness of the sedimentary 

sequence and the scarcity of source rocks. 

Cluster 10.-This cluster comprises mainly the 

Nevada Test Site (fig. 1, large square group of 

tracts) and several smaller tracts in mountain 

ranges to the west. Most of these tracts are underlain by Paleozoic sedimentary rocks covered by 

small patches of Tertiary volcanic rocks and Cretaceous to Tertiary lacustrine rocks. A large part 

of this cluster has been thermally overmatured 

(CAl 4 to 5), but many conodont CAl values reported by Harris and others (1980) have a range 

of 2.5 to 3.5. Because such values are at the upper 

end of the oil-generation window and well within 

the gas-generation window, the cluster is regarded to have a low petroleum potential. 

WESTERN BASIN AND RANGE 

PROVINCE 

Because of widespread pervasive geothermal 

heating, only two clusters of Wilderness· Lands 

have potential in this province. Both clusters, 11 

and 12, have a low petroleum potential. 

Cluster 11.-Tracts in this cluster are situated 

in the Stillwater and Tobin Ranges and Augusta 

Mountains. The tracts are underlain mainly by 

upper Paleozoic and Mesozoic sedimentary rocks, 

the source-rock potential of which is not known. 

However, Carson Sink, which is underlain by 

rocks of the Tertiary northern Fallon basin (Hastings, 1979), lies just west of the southern two 

tracts in this cluster. The Fallon basin has been 

explored by a large number of shallow (less than 

1,000 meters) wells (Garside and Schilling, 1977), 

some of which recovered dry (biogenic) gas. At 

least one deep test, just west of cluster 11 (fig. 1), 

cores of which were analyzed for source-rock potential by Hastings (1979), gave indications that 

thermal maturation was occurring at about 2,500 

meters depth. Similar Cretaceous to Tertiary basins lie among the tracts in this cluster. Consequently, this cluster is regarded to have a low 

petroleum potential. 

Cluster 12.-Tracts in this cluster are situated 

in the Black Rock Desert and in ranges on either 

side of it. Little is known about the rocks in the 

Black Rock Desert because of an extensive alluvial cover. However, Willden (1979) has speculated that it is underlain by potential source and 

reservoir rocks and that it appears highly favorable for exploration. On the other hand, Taubeneck 

(1971) has speculated that the area may be underlain by intrusive igneous rocks forming a connection between the Sierra Nevada and Idaho 

batholiths. Because of these conflicting interpretations the cluster is regarded at this time to have 

a low petroleum potential. 

SUMMARY 

Of the 7,980,608 acres covered in this assessment of the petroleum potential of Wilderness 

Lands in Nevada, the potential acreage can be 

summarized as follows: high potential, 132.4 

thousand acres; medium potential, 1,099.1 

thousand acres; low potential, 3,631.2 thousand 

acres; and zero potential, 3, 117.9 thousand acres. 

The petroleum potential by acreage of all Wilderness Land categories in the Western United 

States is shown in this circular by B. M. Miller in 

table 1, chapter P. 

REFERENCES CITED 

American Association of Petroleum Geologists and U.S. 

Geological Survey, 1976a, Geothermal gradient map of 

North America: U.S. Geological Survey Geological Maps 

of North America Series, scale 1:5,000,000. 

--1976b, Subsurface temperature map of North Ameri~a: 

H9 

U.S. Geological Survey Geological Maps of North America 

Series, scale 1:5,000,000. 

Bissell, H. J., 1973, Oil and gas possibilities in southern 

Nevada: Brigham Young University Geology Studies, v. 

20, no. 1, p. 65-77. 

Bortz, L. C., and Murray, D. K., 1979, Eagle Springs oil field, 

Nye County, Nevada, in Newman, G. W., and Goode, H. 

D., eds., Basin and Range Symposium: Rocky Mountain 

Association of Geologists and Utah Geological Association, 

p. 441-453. 

Dolly, E. D., 1979, Geological techniques utilized in Trap 

Spring field discovery, Railroad Valley, N ye County, 

Nevada, in Newman, G. W., and Goode, H. D., eds., 

Basin and Range Symposium: Rocky Moutain Association 

of Geologists and Utah Geological Association, p. 455-467. 

Duey, H. D., 1979, Trap Spring oil field, Nye County, Nevada, 

in Newman, G. W., and Goode, H. D., eds., Basin and 

Range Symposium: Rocky Mountain Association of 

Geologists and Utah Geological Association, p. 469-4 76. 
Ekren, E. B., Bucknam, R. C., Carr, W. J., Dixon, G. L., and 

Quinlivan, W. D., 1976, East-trending structural lineaments in central Nevada: U.S. Geological Survey Professional Paper 986, 16 p. 

Epstein, A. G., Epstein, J. B., and Harris, L. D., 1977, Conodont color alteration-an index to organic metamorphism: 

U.S. Geological Survey Professional Paper 995, 27 p. 

Foster, N. H., and Dolly, E. D., 1980, Petroleum potential of 

Great Basin [abs.]: American Association of Petroleum 

Geologists Bulletin, v. 64, no. 3, p. 442. 

Foster, N. H., Howard, E. L., Meissner, F. F., and Veal, H. 

K., 1979, The Bruffey oil and gas seeps, Pine Valley, 

Eureka County, Nevada, in Newman, G. W., and Goode, 

H. D., eds., Basin and Range Symposium: Rocky Mountain Association of Geologists and Utah Geological Association, p. 531-540. 

Fouch, T. D., Hanley, J. H., and Forester, R. M., 1979, Preliminary correlation of Cretaceous and Paleogene lacustrine and related nonmarine sedimentary and volcanic 

rocks in parts of the eastern Great Basin of Nevada and 

Utah, in Newman, G. W., and Cooke, H. D., eds., Basin 

and Range Symposium: Rocky Mountain Association of 

Geologists and Utah Geological Association, p. 305--312. 

Garside, L. J., and Schilling, J. H., 1977, Wells drilled for oil 

and gas in Nevada through 1976: Nevada Bureau of Mines 

and Geology Map 56, scale 1:1,000,000. 

Garside, L. J., Weimer, B. S., and Lutsey, I. A., 1977, Oil and 

gas developments in Nevada, 1~1976: Nevada Bureau 

of Mines and Geology Report 29, 32 p. 

Gutschick, R. C., and Sandberg, C. A., 1983, Mississippian 

continental margins of the conterminous United States, in 

The shelfbreak; critical interface on continental margins: 

Society of Economic Paleontologists and Mineralogists, 

Special Publication 33, p. 79-96. 

Harris, A. G., Wardlaw, B. R., Rust, C. C., and Merrill, G. 

K., 1980, Maps for assessing thermal maturity (conodont 

color alteration index maps) in Ordovician through Triassic 

rocks in Nevada and Utah and adjacent parts of Idaho and 

California: U.S. Geological Survey Miscellaneous Investigations Series Map I-1249, 2 sheets. 

Hastings, D. D., 1979, Results of exploratory drilling, northern Fallon basin, western Nevada, in Newman, G. W., 

and Goode, H. E., eds., Basin and Range Symposium: 

Rocky Mountain Association of Geologists and Utah 

Geological Association, p. 515-522. 

Hyde, Joy, 1979, An overview of geothermal exploration and 

development in Nevada, in Newman, G. W., and Goode, 

H. D., eds., Basin and Range Symposium: Rocky Mountain Association of Geologists and Utah Geological Association, p. 381-386. 

Langenheim, R. L., Jr., and Larson, E. R., 1973, Correlation 

of Great Basin stratigraphic units: Nevada Bureau of 

Mines and Geology Bulletin 72, 36 p., 3 charts. 

Maughan, E. K., 1979, Petroleum source rock evaluation of the 

Permian Park City Group in the northeastern Great 

Basin, Utah, Nevada, and Idaho, in Newman, G. W., and 

' . 

Goode, H. D., eds., Basin and Range Symposium: Rocky 

Mountain Association of Geologists and Utah Geological 

Association, p. 523--530. 

McDonald, R. E., 1973, Great Basin Tertiary has potential: Oil 

and Gas Journal, v. 71, no. 33, 34, 35, p. 146-158, 86-90, 

132--134. 

Meissner, F. F., 1978, Petroleum geology of Great Basin, 

western Utah and Nevada [abs.]: American Association of 

Petroleum Geologists Bulletin, v. 62, no. 5, p. 888-889. 

Picard, M. D., 1960, On the origin of oil, Eagle Springs field, 

Nye County, Nevada, in Geology of east central Nevada: 

Intermountain Association of Petroleum Geologists, 11th 

Annual Field Conference Guidebook, p. 237-244. 

Poole, F. G., Fouch, T. D., and Claypool, G. E., 1979, Evidence for two major cycles of petroleum generation in Mississippian Chainman Shale of east-central Nevada [abs.]: 

American Association of Petroleum Geologists Bulletin, v. 

63, no. 5, p. 838. 

Poole, F. G., and Sandberg, C. A., 1977, Mississippian 

paleogeography and tectonics of the Western United 

States, in Stewart, J. H., Stevens, C. H., and Fritsche, 

A. E., eds., Paleozoic paleogeography of the Western 

United States: Society of Economic Paleontologists and 

Mineralogists, Pacific section, Pacific Coast Paleogeography Symposium 1, p. 67-85. 

Poole, F. G., Sandberg, C. A., and Boucot, A. J., 1977, Silurian and Devonian paleogeography of the Western United 

States, in Stewart, J. H., Stevens, C. H., and Fritsche, 

A. E., eds., Paleozoic paleogeography of the Western 

United States: Society of Economic Paleontologists and 

Mineralogists, Pacific section, Pacific Coast Paleogeography Symposium 1, p. 39-65. 

Sandberg, C. A., 1975, Petroleum geology of Paleozoic rocks of 

Cordilleran miogeosyncline: U.S. Geological Survey OpenFile Report 75-96, 7 p., 6 figs. 

--1979, Devonian and Lower Mississippian conodont zonation of the Great Basin and Rocky Mountains, in 

Sandberg, C. A., and Clark, D. L., eds., Conodont biostratigraphy of the Great Basin and Rocky Mountains: 

Brigham Young University Geology Studies, v. 26, pt. 3, 

p. 87-106. 

--1980, Use of Devonian conodonts in petroleum exploration, Western United States [abs.]: American Association 

of Petroleum Geologists Bulletin, v. 64, no. 5, p. 780. 

Sandberg, C. A., and Clark, D. L., eds., 1979, Conodont biostratigraphy of the Great Basin and Rocky Mountains: 

Brigham Young University Geology Studies, v. 26, pt. 3, 

190 p. 

Sandberg, C. A., Grogan, D. R., and Clisham, T. J., 1979, 

Mississippian source rocks in Utah and Idaho: U.S. 

Geological Survey Professional Paper 1150, p. 2~29. 

Sandberg, C. A., and Gutschick, R. C., 1977, Paleotectonic, 

biostratigraphic, and economic significance of Osagean to 

early Meramecian starved basin in Utah: U.S. Geological 

Survey Open-File Report 77-121, 16 p., 5 figs. 

HlO 
Sandberg, C. A., Lane, H. R., and Matthews, S. C., 1979, 

Utility of Carboniferous conodonts for zonation, biofacies, 

and intercontinental correlation [abs.]: International Congress of Carboniferous Stratigraphy and Geology, 9th, 

Abstracts of Papers, p. 189-190. 

Sandberg, C. A., and Poole, F. G., 1975, Petroleum source 

beds in Pilot Shale of eastern Great Basin-Talk for Oil 

and Gas Session I, Rocky Mountain Section Meeting, 

American Association of Petroleum Geologists, Albuquerque, New Mexico, June 2, 1975: U.S. Geological Survey 

Open-File Report 75--371, 13 p., 4 figs. 

--1977, Conodont biostratigraphy and depositional complexes of Upper Devonian cratonic-platform and continental-shelf rocks in the Western United States, in Murphy, 

M.A., Berry, W. B. N., and Sandberg, C. A., eds., Western North America; Devonian: California University, 

Riverside, Campus Museum Contribution 4, p. 144-182. 

Stewart, J. H., 1980, Geology of Nevada: Nevada Bureau of 

Mines and Geology Special Publication 4, 136 p. 

Stewart, J. H., and Carlson, J. E., 1977, Million-scale geologic 

map of Nevada: Nevada Bureau of Mines and Geology 

Map 57. 

Sweet, W. C., Harris, A. G., Sandberg, C. A., and Wardlaw, 

B. R., 1981, Conodonts; guides to biostratigraphy and 

geothermometry in the western United States, in Montana Geological Society Field Conference and Symposium 

Guidebook to Southwest Montana, p. 133-137. 

Taubeneck, W. H., 1971, Idaho batholith and its southern extension: Geological Society of America Bulletin, v. 82, no. 

7, p. 1899-1928. 

Veal, H. K., 1983, Relationship of Roberts Mountains thrust to 

oil and gas exploration in Nevada [abs.]: American Association of Petroleum Geologists Bulletin, v. 67, no. 3, p. 564. 

Warner, M. M., 1980, S. Idaho, N. Nevada, southeastern Oregon-prime exploration target: Oil and Gas Journal, v. 78, 

no. 18, p. 325-341 (not inclusive). 

Willden, Ronald, 1979, Petroleum exploration possibilities in 

northwestern Nevada, in Newman, G. W., and Goode, H. 

D., eds., Basin and Range Symposium: Rocky Mountain 

Association of Geologists and Utah Geological Association, 

p. 541-548. 

Hll 
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