Compilation of Stratigraphic Thicknesses for

Caldera-Related Tertiary Volcanic Rocks,

East-Central Nevada and West-Central Utah

Data Series 271

U.S. Department of the Interior

U.S. Geological Survey
Compilation of Stratigraphic Thicknesses

for Caldera-Related Tertiary Volcanic

Rocks, East-Central Nevada and

West-Central Utah

By D.S. Sweetkind and E.A. du Bray

Prepared in cooperation with the Bureau of Land Management

Data Series 271

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

DIRK KEMPTHORNE, Secretary

U.S. Geological Survey

Mark D. Myers, Director

U.S. Geological Survey, Reston, Virginia: 2008

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Suggested citation:

Sweetkind, D.S., du Bray, E.A., 2008, Compilation of stratigraphic thicknesses for caldera-related tertiary 

volcanic rocks, east-central Nevada and west-central Utah: U.S. Geological Survey Data Series 271, 40 p.
iii

Contents

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

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

Geologic Setting.............................................................................................................................................2

Compilation Methods ....................................................................................................................................4

Stratigraphic Thicknesses from Geologic Maps.............................................................................4

Published Isopach Data.......................................................................................................................5

Comparison of Thickness Compilation Methods......................................................................................6

Summary..........................................................................................................................................................6

References Cited............................................................................................................................................7

Figures

1. Carbonate rock province, BARCAS study area, and associated regional 

ground-water flow systems. .....................................................................................................10

2. Generalized diagram of ash-flow caldera ..............................................................................11

3. Generalized geology map and locations of calderas, eastern Nevada and 

western Utah ...............................................................................................................................12

4. Index of geologic maps in the vicinity of the Indian Peak caldera complex 

used to compile volcanic rock thicknesses ...........................................................................13

5. Thickness (isopach) map of Kalamazoo Tuff..........................................................................14

6. Thickness (isopach) map of Windous Butte Formation .......................................................15

7. Thickness (isopach) map of Monotony Tuff ...........................................................................16

8. Thickness (isopach) map of Shingle Pass Tuff ......................................................................17

9. Thickness (isopach) map of Cottonwood Wash Tuff ............................................................18

10. Thickness (isopach) map of Wah Wah Springs Formation..................................................19

11. Thickness (isopach) map of Lund Formation .........................................................................20

12. Thickness (isopach) map of Isom Formation .........................................................................21

13. Thickness (isopach) map of Leach Canyon Formation.........................................................22

14. Thickness (isopach) map of Condor Canyon Formation.......................................................23

15. Thickness (isopach) map of Harmony Hills Tuff. ...................................................................24

16. Aggregate thickness (isopach) map of all tuffs for caldera-related Tertiary 

volcanic rocks in east-central Nevada and west-central Utah..........................................25

17. Volcanic thickness (isopach) map showing location of valley axes in eastern 

Nevada and western Utah described in tables 1−13 ...........................................................26

18. Comparison of tuff thickness compilation methods, east-central Nevada and 

west-central Utah. Associated table is listed at top of bar.................................................27

Tables

1. Compilation of volcanic-rock thickness from mountain ranges flanking the 

northern part of Dry Lake Valley...............................................................................................28
iv

2. Compilation of volcanic-rock thickness from mountain ranges flanking 

Muleshoe Valley..........................................................................................................................29

3. Compilation of volcanic-rock thickness from mountain ranges flanking 

Cave Valley...................................................................................................................................30

4. Compilation of volcanic-rock thickness from mountain ranges flanking 

southern part of Lake Valley. ....................................................................................................31

5. Compilation of volcanic-rock thickness from mountain ranges flanking 

northern part of Lake Valley......................................................................................................32

6. Compilation of volcanic-rock thickness from mountain ranges flanking 

southern part of Spring Valley. .................................................................................................33

7. Compilation of volcanic-rock thickness from mountain ranges flanking 

the central part of Spring Valley...............................................................................................34

8. Compilation of volcanic-rock thickness from mountain ranges flanking 

southern part of Hamlin Valley. ................................................................................................35

9. Compilation of volcanic-rock thickness from mountain ranges flanking 

northern part of Hamlin Valley..................................................................................................36

10. Compilation of volcanic-rock thickness from mountain ranges flanking 

Snake Valley. ...............................................................................................................................37

11. Compilation of volcanic-rock thickness from mountain ranges flanking 

southern part of Pine Valley......................................................................................................38

12. Compilation of volcanic-rock thickness from mountain ranges flanking 

northern part of Pine Valley. .....................................................................................................39

13. Compilation of volcanic-rock thickness from mountain ranges flanking 

Wah Wah Valley..........................................................................................................................40

Conversion Factors

Multiply By To obtain

inch 2.54 centimeter (cm)

inch 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft)

kilometer (km) 0.6214 mile (mi)

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).
Abstract

The U.S. Geological Survey (USGS), the Desert Research 

Institute (DRI), and a designee from the State of Utah are 

currently conducting a water-resources study of aquifers in 

White Pine County, Nevada, and adjacent areas in Nevada 

and Utah, in response to concerns about water availability and 

limited geohydrologic information relevant to ground-water 

flow in the region. Production of ground water in this region 

could impact water accumulations in three general types of 

aquifer materials: consolidated Paleozoic carbonate bedrock, 

and basin-filling Cenozoic volcanic rocks and unconsolidated 

Quaternary sediments. At present, the full impact of extracting 

ground water from any or all of these potential valley-graben 

reservoirs is not fully understood. A thorough understanding 

of intermontane basin stratigraphy, mostly concealed by the 

youngest unconsolidated deposits that blanket the surface in 

these valleys, is critical to an understanding of the regional 

hydrology in this area. This report presents a literature-based 

compilation of geologic data, especially thicknesses and 

lithologic characteristics, for Tertiary volcanic rocks that are 

presumably present in the subsurface of the intermontane 

valleys, which are prominent features of this area.

Two methods are used to estimate volcanic-rock thickness beneath valleys: (1) published geologic maps and 

accompanying descriptions of map units were used to compile 

the aggregate thicknesses of Tertiary stratigraphic units present in each mountain range within the study areas, and then 

interpolated to infer volcanic-rock thickness in the intervening valley, and (2) published isopach maps for individual outflow ash-flow tuff were converted to digital spatial data and 

thickness was added together to produce a regional thickness 

map that aggregates thickness of the individual units. The 

two methods yield generally similar results and are similar 

to volcanic-rock thickness observed in a limited number of 

oil and gas exploration drill holes in the region, although 

local geologic complexity and the inherent assumptions in 

both methods allow only general comparison. These methods 

serve the needs of regional ground-water studies that require 

a three-dimensional depiction of the extent and thickness of 

subsurface geologic units. The compilation of geologic data 

from published maps and reports provides a general understanding of the distribution and thickness of tuffs that are presumably present in the subsurface of the intermontane valleys 

and are critical to understanding the ground-water hydrology 

of this area.

Introduction

As populations in the southwestern United States 

continued to increase through the 1990s and 2000s, reliance 

on water from the Colorado River basin has become increasingly important. To decrease their dependence on this limited 

surface-water resource, water purveyors in southern Nevada 

have proposed to use the ground-water resources of rural 

basins in eastern and central Nevada to help provide for the 

projected increase in population and associated water supply 

issues in the Las Vegas area. Most of these basins historically 

(prior to 2006) have pumped limited quantities of ground 

water, typically less than 20,000 acre-ft per year. As a result, 

municipal and regulatory agencies have expressed concerns 

about potential impacts from increased ground-water pumping on local and regional water quantity and quality, with 

particular concern for water rights issues and on the future 

availability of water to support natural spring flow and native 

vegetation. Before concerns for potential impacts from pumping can be addressed, municipal and regulatory agencies have 

recognized the need for additional information and improved 

understanding of geologic features and hydrologic processes 

that control the rate and direction of ground-water flow in 

eastern and central Nevada.

In response to concerns about water availability and limited geohydrologic information, Federal legislation was enacted 

in December 2004 (Section 301(e) of PL 108–424, Lincoln 

County Conservation, Recreation, and Development Act of 

2004; short title, Lincoln County Land Act) that directed the 

Secretary of the Interior, through the U.S. Geological Survey 

(USGS), the Desert Research Institute (DRI), and a designee 

from the State of Utah, to conduct a water-resources study of 

the alluvial and carbonate aquifers in White Pine County, Nev., 

and adjacent areas in Nevada and Utah. The main objectives 

Compilation of Stratigraphic Thicknesses for

Caldera-Related Tertiary Volcanic Rocks,

East-Central Nevada and West-Central Utah

By D.S. Sweetkind and E.A. du Bray
2 Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah

of the study, termed the Basin and Range Carbonate Aquifer 

System study, or the BARCAS study, were to evaluate: (1) the 

extent, thickness, and hydrologic properties of aquifers in the 

study area, (2) the volume and quality of water stored in these 

aquifers, (3) subsurface geologic structures controlling groundwater flow, (4) ground-water flow direction and gradients, and 

(5) the distribution and rates of recharge and ground-water 

discharge. Geologic, hydrologic, and supplemental geochemical information were integrated to determine individual basin 

and regional ground-water budgets. A draft report containing 

the preliminary results of the BARCAS study was released for 

public comment in Spring, 2007 (Welch and Bright, 2007); 

final results will be summarized in a USGS Scientific Investigations Report (SIR) that will be prepared in cooperation 

with DRI and the State of Utah, and submitted to Congress by 

December 2007. The BARCAS study final report will be supported by a series of USGS reports, including this report, and 

the DRI Hydrologic Sciences Reports that document, in greater 

detail than the BARCAS study final report, important components of this study.

The BARCAS study area encompasses about 35,000 km2

, 

including about 80 percent of White Pine County, and parts of 

Elko, Eureka, Nye, and Lincoln Counties in Nevada, as well 

as parts of Tooele, Millard, Beaver, Juab, and Iron Counties in 

Utah (fig. 1). The BARCAS study area lies within the Carbonate Rock Province, a relatively large area extending from 

western Utah to eastern California (fig. 1) where ground-water 

flow is predominantly or strongly influenced by carbonaterock aquifers (Winograd and Thordarson, 1975; Bedinger and 

others, 1989; Dettinger and others, 1995; Harrill and Prudic, 

1998). Much of the carbonate-rock aquifer is fractured, and 

these fractured rocks, where continuous, form a regional flow 

system that receives recharge from higher altitude areas in 

White Pine County where these fractured carbonate rocks are 

exposed. Water moving through the carbonate aquifer provides 

some recharge to overlying basin-fill aquifers, sustains many of 

the larger, perennial lower elevation springs in the study area, 

and hydraulically connects similar carbonate-rock aquifers in 

adjacent basins. Most areas in White Pine County, Nev., are 

within four regional ground-water flow systems (fig. 1) — the 

larger Colorado and Great Salt Lake Desert flow systems, and 

the smaller Goshute Valley and Newark Valley flow systems.

Production of ground water from the BARCAS study area 

could impact water accumulations in three general types of 

aquifer materials: consolidated Paleozoic carbonate bedrock, 

and basin-filling Cenozoic volcanic rocks and unconsolidated 

Quaternary sediments. At present, the full impact of extracting 

ground-water from any or all of these potential, valley-graben 

reservoirs is not fully understood. A thorough understanding 

of intermontane basin stratigraphy, mostly concealed by the 

youngest unconsolidated deposits that blanket the surface in 

these valleys, is critical to an understanding of the regional 

hydrology in this area.

The middle Tertiary geologic evolution of east-central 

Nevada is dominated by volcanic events that produced many 

ash-flow tuffs deposited during caldera-forming eruptions 

(Best, Christiansen, and others, 1989). Fractured Cenozoic 

volcanic rocks near the major volcanic fields are locally thick 

enough to be important subregional aquifers that interact with 

the regional flow through the underlying Paleozoic carbonate 

rocks (Dettinger, 1989; Harrill and others, 1988). Eruption 

dynamics cause ash-flow sheets to be distributed as much as 

hundreds of kilometers from their sources, to pond in topographic lows, and to mantle topography. Outflow thicknesses 

of individual ash-flow sheets that form a variety of tuffs can be 

hundreds of meters and the aggregate thickness of the outflow 

deposits that erupted from multiple calderas in east-central 

Nevada can be kilometers thick. Within the BARCAS study 

area, eruption of many of the ash-flow tuffs occurred relatively 

early in the extensional history of the area (Axen and others, 1993). As a consequence, regionally distributed ash-flow 

tuffs are preserved deep in the stratigraphy of the downfaulted 

basins, often covered by thick intervals of younger sedimentary deposits.

Because eruptive events that caused caldera formation 

are such major parts of the geologic framework in east-central 

Nevada, a general understanding of caldera dynamics and 

the distribution and thickness of outflow tuffs is critical to 

understanding the ground-water hydrology of this area. This 

report presents a literature-based compilation of geologic 

data, especially thicknesses and lithologic characteristics, for 

Tertiary rocks (mostly volcanic) that are presumably present in 

the subsurface of the intermontane valleys, which are prominent features of this area. In addition, the calderas themselves, 

as well as their associated structural features, are addressed 

because these features are significant relative to the area’s 

ground-water hydrologic framework. These data are intended 

to support analysis for the extent, thickness, and hydrologic 

properties of volcanic-rock aquifers for the BARCAS study.

Geologic Setting

Processes related to large-volume ash-flow eruptions 

and associated caldera collapses are enumerated by Smith 

and Bailey (1968) and by Lipman (1984) and are summarized below. Calderas can be as much as 120 km in diameter, 

are structurally complex features, and most are bounded by 

a pair of geologic discontinuities, a structural margin and a 

topographic margin (fig. 2), both of which may be obscured 

by subsequent volcanism and erosion. These discontinuities 

are generally concentric and related to the structural collapse 

that is the hallmark of caldera-forming eruptions. Calderas 

form when large volumes of magma are nearly instantaneously erupted from shallowly emplaced magma reservoirs. 

As an eruption of this type ensues, the associated magma 

reservoir is partially evacuated by the eruption of frothy 

magma, and the central block of roof rock that lay above 

the reservoir collapses downward along a series of arcuate faults. The resulting system of faults forms a generally 

circular system of normal faults that constitute the caldera’s 

structural margin. The lithologic discontinuity across the 
Geologic Setting 3

steeply inclined structural margin can be profound and can 

extend to depths of several kilometers. The resulting caldera 

wall begins to retreat outward as landslides calve off the 

oversteepened walls and contribute material to the deepening 

depression caused by the eruption and concomitant central 

collapse of the volcanic edifice (fig. 2). Outward retreat of 

the caldera boundary by subsequent landsliding forms a second, more gently inclined concentric discontinuity known as 

the topographic margin. Simultaneous with central collapse 

and landslide formation, the evolving central depression 

begins to be filled by the volcanic products derived from 

the ongoing eruption. This rapidly evolving intracaldera 

environment is usually filled by a kilometers-thick accumulation of ash-flow tuff and interleaved landslide materials 

(fig. 2). The discontinuity across the caldera’s topographic 

margin, between intracaldera tuff and the country rock that 

host the caldera, can be at least as profound as that across 

the structural margin. Following caldera-forming eruptions, 

some of these igneous systems experience a central upward 

resurgence of unerupted magma from the underlying magma 

reservoir. Resurgence further complicates and disrupts the 

geology within the caldera (fig. 2).

The Cenozoic geologic evolution of east-central Nevada 

is dominated by a broad southward sweep of essentially calcalkaline igneous activity (McKee, 1971; Cross and Pilger, 

1978; McKee and Noble, 1986; Best, Christiansen, and others, 

1989) with volcanic rocks, especially ash-flow tuffs, deposited during caldera-forming eruptions (Best, Christiansen, 

and others, 1989). Between about 30 and 25 Ma, calderarelated eruptions from two major centers, the Indian Peak 

caldera complex (IPCC, fig. 3) and the Central Nevada caldera 

complex (CNCC, fig. 3), formed a broad zone of voluminous 

upper Oligocene–lower Miocene volcanic rocks (Best, Christiansen, and others, 1989) that extended across Nevada and 

Utah. Subsequently, ash-flow eruptions from numerous nested 

calderas of the 23 to 13 Ma Caliente caldera complex resulted 

in regionally extensive ash-flow tuffs that are centered in the 

east-central part of Lincoln County (Scott and others, 1995) 

(fig. 3).

The Indian Peak caldera complex (IPCC, fig. 3), centered on the eastern side of Lake Valley in the northern part 

of Lincoln County, erupted on the order of 10,000 km3

 of 

volcanic rock between about 32 and 27 Ma (Best, Christiansen, and Blank, 1989). At least four major calderas have 

been identified within this complex (fig. 3) based on the 

presence of thick intracaldera tuff sequences and collapse 

breccias; two other calderas are inferred from the presence of 

regionally extensive ash-flow sheets (Best and Grant, 1987; 

Best, Christiansen, and Blank, 1989). Best, Christiansen, and 

Blank (1989) estimated that ash-flow tuffs erupted from the 

Indian Peak caldera complex alone cover about 55,000 km2

in east-central Nevada. The spatial distribution of circular, 

caldera-related ring fracture systems and faults related to the 

Indian Peak caldera complex in east-central Nevada and westcentral Utah were compiled by Loucks and others (1989) and 

Williams and others (1997).

The Central Nevada caldera complex (CNCC, fig. 3), 

in the northern part of Nye County, was even larger than the 

Indian Peak caldera complex. The Central Nevada caldera 

complex may include as many as 12 calderas and there are 

multiple sheets of rhyolite tuff with larger volumes than those 

in the Indian Peak caldera complex (Best, Christiansen, and 

others, 1989; Best and others, 1993). Eruptions from this complex were protracted, beginning at about 35.3 Ma and extending to 22.6 Ma (Best and others, 1993).

The Caliente caldera complex (CCC, fig. 3), about 80 km 

to the south of the Indian Peak caldera complex, erupted several thousand cubic kilometers of volcanic material between 

about 23 and 19 Ma (Williams, 1967). The dimensions of 

the Caliente caldera complex are about 80 km east-west and 

35 km north-south, unusually elongated for a major caldera 

complex. The Caliente caldera complex consists of numerous 

nested calderas of 23–13 Ma, including the Clover Creek caldera, north and east of Caliente, which was the source of the 

densely welded Bauers Tuff Member of the Condor Canyon 

Formation, and the Delamar caldera, which makes up most of 

the western part of the complex and was the main source for 

the 18.3 Ma Hiko Tuff (Rowley and others, 2001).

A smaller volume, but locally important, ash-flow tuff 

called the Kalamazoo Tuff by Gans and others (1989) is 

widely distributed across northern White Pine County, Nev., 

and adjacent areas of Utah. This tuff, and associated overlying 

volcanic rocks, is inferred to have a source area in the northern 

part of Spring Valley (KT, fig. 3); eruptive volume may be 

240–340 km3

 (Gans and others, 1989), an order of magnitude 

smaller than the largest ash-flow tuffs from the caldera complexes described above.

A final consideration concerning the middle Tertiary volcanic stratigraphy of east-central Nevada pertains to the lavas 

(and associated pyroclastic and volcaniclastic deposits) that 

are a significant, though not especially voluminous, part of the 

geologic framework of this area. Best, Christiansen, and others 

(1989) suggested that lavas constitute only about 10 percent 

of the total volume of Cenozoic volcanic rock in this region. 

However, because this is not an inconsequential amount of 

rock, lava flow thicknesses were considered as a possible 

contribution to Tertiary sections in the intermontane valleys 

of east-central Nevada. Most of these lavas are andesitic to 

rhyolitic and are often associated with calderas in the area, 

although there are locally important accumulations that are 

not associated with calderas, such as the volcanic rocks at the 

south end of Butte Valley, 30 km northwest of Ely, Nev. (Feeley and Grunder, 1991). Lava flow eruption dynamics typically 

result in discontinuous deposits that are not as broadly distributed around eruption sources, or as far traveled as ash-flow 

tuffs. The presence and thicknesses of individual lava flow 

sequences in the stratigraphic sections of the intermontane valleys is more difficult to determine than that for ash-flow tuffs, 

and can potentially lead to significantly greater uncertainty 

relative to intermontane valley Tertiary volcanic rock thickness 

estimates. In addition, lava flow rocks may have very different 

porosity, fracture styles, and fracture intensity than adjacent 
4 Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah

rocks in this area, and so may be spatially associated with 

significant ground-water hydrology discontinuities. Consequently, the thicknesses, lithologic character, and hydrologic 

properties of middle Tertiary lava flow rocks, as well as all 

other rock types that constitute parts of the hydrologic framework in east-central Nevada, must be well defined in order to 

accurately define the hydrologic framework for the region.

As a result of pyroclastic eruptions, caldera formation 

processes, and wide distribution of the associated ash-flow 

tuffs, calderas and their erupted products can profoundly influence, in a myriad of ways, ground-water hydrology in terranes 

that host these features. First, in trying to determine the types 

and thicknesses of geologic materials that may be preserved in 

the intermontane valleys of east-central Nevada, one must consider the likelihood that significant accumulations of middle 

Tertiary ash-flow tuff are preserved in many of these valleys. 

The lithologic characteristics of these rocks must be considered with regard to their ability to serve as water reservoirs, 

the extent of their hydraulic conductivity, and their interconnectedness to reservoirs either above in basin-fill sedimentary 

deposits or below in the Paleozoic rock aquifers. Next, the 

role of the topographic and structural margins with regard to 

ground-water hydrology must be considered. Depending on 

the geologic characteristics of these features, they may serve 

as either conduits or impermeable interfaces to ground-water 

flow. Similarly, the nature of the lithologic contrast between 

rocks exposed on either side of these discontinuities must 

be considered. The nature of the lithologic juxtaposition 

can have profound affects on ground-water storage and flow 

frameworks. In addition, the intersections between modern 

intermontane valleys and older intracaldera features must be 

considered. Places where intermontane valleys intersect intracaldera rocks and structures are places where profound geologic 

discontinuities may be present. In particular, structural and 

lithologic discontinuities present in these places can impact 

inferred reservoir geometry as well as ground-water flow. The 

distribution of calderas and associated eruptive products in 

east-central Nevada must be well understood in order to comprehend how they may contribute to the overall ground-water 

hydrology of this area.

Compilation Methods

Stratigraphic Thicknesses from Geologic Maps

Published geologic maps (fig. 4) and descriptions of 

map units were used to compile the aggregate thicknesses of 

Tertiary stratigraphic units present in each mountain range 

within the study areas (tables 1–13). These units are probably 

preserved in down-faulted, Cenozoic graben valleys of eastcentral Nevada and west-central Utah, and probably are about 

as thick in the valleys as they are in the flanking mountain 

ranges. Descriptions of map units contained on the published 

geologic maps almost always include thickness data, although 

usually somewhat generalized, for each unit whose distribution 

is shown on the geologic map. The Tertiary deposits are primarily volcanic rocks but include some interbedded sedimentary deposits. Mapped volcanic rocks are mostly regionally 

distributed ash-flow tuffs but also include significant volumes 

of lava flows. Geologic map units were subdivided into local 

and regional units (tables 1–13). Local units were those units 

with limited spatial extent within a single mapped quadrangle 

or mountain range; typically lava flows and Tertiary sedimentary rocks interbedded with tuff. Regional units were those 

units that occur in several quadrangles or mountain ranges. 

These volcanic-rock units are typically ash-flow tuffs associated with a caldera-forming eruption. Minimum and maximum 

thickness data were compiled for each map unit (tables 1–13), 

although many map unit descriptions indicate only maximum 

thicknesses. Unless minimum thicknesses were explicitly identified in source materials, minimum thicknesses are presumed 

to be zero. In order to estimate the stratigraphic thicknesses of 

Tertiary strata concealed beneath Quaternary deposits in each 

Cenozoic graben valley, we assume that their thicknesses are 

similar to those in the flanking mountain ranges.

The physiography of east-central Nevada is dominated 

by an alternating series of approximately north-trending valleys and mountain ranges. For the purposes of aggregating 

published thickness values, many of these valleys were 

divided into segments along their lengths, to allow consideration of geologic variability along valley lengths. The 

resulting data compilation (tables 1–13) preserves a level of 

detail commensurate with the detail and geologic variability 

portrayed on maps that depict the geology of ranges adjacent 

to each valley.

Stratigraphic thickness data were compiled as a series of 

valley segment components (tables 1–13). In most cases, each 

valley segment component of the tables presents two sets of 

thickness data. The first set presents thicknesses for Tertiary 

strata preserved in the range west of the valley segment, and 

the second for strata in the range east of the valley. In some 

cases, as noted on the tables, volcanic rocks and associated 

geologic data may be available for the range on one side of a 

valley but not on the other (for instance, the northern part of 

Lake Valley, table 5). In these cases, some proxy, as defined on 

the affected tables, is established for the missing information 

so as to enable valley thickness estimates.

Lava flows usually result in limited, near source distributions, whereas tuffs are distributed in a broad, regional 

fashion. Consequently, lava flows present in mountain ranges 

may not have flowed into regions that are now intermontane 

valleys. In contrast, ash-flow tuffs are known to have been 

deposited with much greater continuity over thousands of 

square kilometers. Recognizing these potential distribution 

variations, thickness data for Tertiary lava flow units were 

compiled separately from those for the ash-flow tuff units. An 

additional consideration relative to valley thickness estimates 

relates to whether ash-flow tuffs of east-central Nevada and 

west-central Utah were deposited as intracaldera tuff or as 

outflow tuff sheets. Intracaldera ash-flow tuff accumulations 

are known to be extremely thick (Lipman, 1984; Lipman and 
Compilation Methods 5

Sawyer, 1985) and pertain to the intracaldera setting only. 

Consequently, only outflow ash-flow tuff thicknesses, those 

most likely to be representative of volcanic rocks that are 

presumably present in the subsurface of the intermontane 

valleys, were compiled. However, some valley segments, such 

as southern parts of Hamlin Valley (table 8) and Lake Valley 

(table 4), that are coincident with the intracaldera environment may preserve huge intracaldera ash-flow tuff thicknesses beneath Quaternary deposits.

Using the geologic relationships described above and 

interpolating stratigraphic thicknesses of Tertiary ash-flow 

tuffs between adjacent ranges, the thickness of tuffs potentially 

preserved in the intervening valleys may be estimated. The 

resulting tuff thickness estimates are not biased to the potentially erroneously high thickness estimates that would result 

from assuming that near-source lava flows are continuously 

preserved from adjacent ranges across intervening graben 

valleys. Interpolated thicknesses in valleys, based solely on 

regionally distributed ash-flow tuff thicknesses, are considered 

reasonable estimates of minimum concealed thicknesses of 

Tertiary rocks in the valleys. Accordingly, a highlighted entry 

in the center of each table presents the probable thickness 

range for Tertiary rocks in the associated valley segment. 

Because minimum thicknesses of the constituent stratigraphic 

units are very poorly known in most cases, the low end of 

these thickness ranges is unlikely to be diagnostic. The high 

end of each thickness range represents a value intermediate to 

the total thicknesses of regionally distributed Tertiary strata in 

the flanking mountain ranges.

In addition to thickness data, the data compilation (tables 

1–13) contains additional geologic information. For each intermontane valley segment, stratigraphic units identified in one 

or both of the ranges that flank the valley are identified. One 

list identifies the stratigraphic units (mostly lava flows) that 

are deemed to be of local extent, and the other identifies those 

units (mostly major ash-flow tuffs) that are likely to be regionally distributed. Because the lithologic characteristics of each 

map unit potentially influence the hydrologic properties of 

these deposits, a brief description, including degree of welding, texture, and crystal content of stratigraphic units described 

in each pair of flanking ranges, is included (tables 1–13).

Published Isopach Data

A second method for estimating the stratigraphic thicknesses of Tertiary ash-flow tuffs that might be preserved in 

the intermontane valleys of east-central Nevada and western 

Utah is from published thickness (isopach) maps for individual 

ash-flow tuffs. The voluminous, regionally distributed Tertiary 

ash-flow tuffs have been extensively studied (see, for example, 

Best and Grant, 1987; Best, Christiansen, and others, 1989; du 

Bray, 1995; Scott and others, 1995) and the database derived 

from these studies is quite comprehensive. Consequently, 

synthesis of thickness data for many individual ash-flow tuffs 

is possible. Thickness data have been extremely important in 

identifying the sources of individual ash-flow tuffs and also 

in locating calderas that formed in response to major eruptive 

events. In general, the areas of greatest ash-flow tuff thickness are spatially coincident with calderas. However, mapped 

ash-flow tuffs in east-central Nevada and western Utah greatly 

outnumber identified calderas. In some cases, a caldera may 

be inferred from the volume of an ash-flow tuff unit, yet its 

location may be unknown because it has been subsequently 

disrupted by younger structural or erosional events, or buried 

by younger rocks.

Isopach maps have been compiled for most of the major, 

regionally distributed ash-flow tuffs of east-central Nevada 

and west-central Utah. One of the earliest efforts to compile 

isopach maps for this region was that of Williams (1967), 

who synthesized thickness data for ash-flow tuffs related to 

the Caliente caldera complex, including the Harmony Hills 

Tuff, the Condor Canyon Formation which comprises the 

Bauers Tuff and Swett Tuff Members, and the Leach Canyon 

Formation. Williams also compiled a maximum extent of 

distribution map for the Pahranagat Formation from the central 

Nevada caldera complex. Subsequent mapping of these rocks 

has resulted in refinements to the stratigraphic nomenclature 

(Rowley and others, 1995; Scott and others, 1995), but the 

initial thickness compilations remain valid. Isopach maps for 

some large-volume ash-flow tuffs from the central Nevada 

caldera complex, including the Windous Butte Formation, the 

Monotony Tuff, and the Shingle Pass Tuff were produced by 

Best, Christiansen, and others (1989). Best, Christiansen, and 

Blank (1989) also compiled thickness data for ash-flow tuffs 

of the Indian Peak caldera complex; this compilation includes 

isopach diagrams for the Cottonwood Wash Tuff, Wah Wah 

Springs Formation, Lund Formation, and Isom Formation. The 

distribution and thickness of the Kalamazoo Tuff and associated overlying volcanic rocks across northern White Pine 

County, Nev., and adjacent areas of Utah was portrayed by 

Gans and others (1989). Thickness maps are thus available for 

the majority of the voluminous, regionally distributed ash-flow 

tuffs present in east-central Nevada and west-central Utah.

The published isopach maps were scanned and georeferenced in a Geographic Information System (GIS) and 

the location and thickness values as measured at outcrops of 

individual tuffs were digitized from these published maps. 

In order to preserve the original author’s interpreted contour 

patterns, additional thickness data were created by digitizing a regular series of points along each contour line of 

the isopach maps. For each tuff, these thickness data were 

gridded as 2,500-m square cells within the GIS to produce 

a digital thickness grid as raster data sets. Thickness was 

gridded using either inverse distance or simple kriging algorithms; the gridding methodology was chosen on the basis of 

how closely the digital grid resembled the original published 

contour map. Grids were locally hand-edited in order to recreate abrupt thickness changes at known or inferred caldera 

boundaries. Using this approach, digital thickness grids were 

created for the following ash-flow tuffs: the Kalamazoo Tuff 

(fig. 5), the Windous Butte Formation (fig. 6), the Monotony 

Tuff (fig. 7), the Shingle Pass Tuff (fig. 8), the Cottonwood 
6 Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah

Wash Tuff (fig. 9), the Wah Wah Springs Formation (fig. 10), 

the Lund Formation (fig. 11), the Isom Formation (fig. 12), 

the Leach Canyon Formation (fig. 13), the Condor Canyon 

Formation (fig. 14), and the Harmony Hills Tuff (fig. 15). In 

each of these figures two maps are shown. The larger map 

portrays the thickness of the individual ash-flow tuff contoured using intervals that display most clearly the thickness 

variations of the unit. The smaller map in each figure shows 

the same thickness data, but contoured at intervals consistent 

with those used for the thickest tuffs in the region. Thus the 

reader may see the details of the thickness variations within 

each tuff and also gain an understanding of the thickness of 

the ash-flow tuff as compared to the largest eruptions in the 

study area. In many cases, the thickest intervals do not exactly 

correspond to mapped caldera boundaries. This disparity is 

usually the result of limited outcrop data; in most cases the 

thickness and distribution of the intracaldera fill on published 

isopach maps may be represented by a single data point. 

In a few cases, the caldera boundaries themselves are only 

generally located, or the thickness of the intracaldera volcanic 

rocks is poorly known due to disruption by younger structural 

events, or burial by younger rocks. Thickness data portrayed 

on the individual isopach maps were added together to 

produce a composite isopach map that combines the gridded 

thickness for all of the previously named units (fig. 16). The 

composite isopach map is dominated by the thick intracaldera 

accumulations within the Indian Peak caldera complex and 

the central Nevada caldera complex (fig. 3). The thickness of 

intracaldera rocks within the Caliente caldera complex (fig. 3) 

may be underrepresented in this compilation due to the relative lack of published thicknesses of intracaldera rocks; however, these eruptions were generally much smaller in volume 

than the other two main caldera centers. Using the composite 

isopach map (fig. 16), one can predict the relative thickness of 

outflow tuffs between the caldera complexes.

Comparison of Thickness Compilation 

Methods

The two thickness compilation methods may be compared at specific valley-axis locations by overlaying the 

gridded total thickness map and the predicted valley-axis 

thickness compiled from data contained in published descriptions of map units (fig. 17). A comparison of the two methods 

at these locations (fig. 18) suggests that the two methods yield 

generally similar results. Thickness predicted by the gridded 

data is necessarily generalized because it relies on interpolation between relatively scarce measured sections. Gridded 

thickness maps were created only for those tuffs for which 

published isopach maps were available. Certain regionally 

distributed tuffs, such as those emanating from the Marysvale volcanic field in south-central Utah (Rowley and others, 

1979; Rowley and others, 1998) were not considered in this 

analysis and volcanic-rock thickness may be underestimated, 

especially in the valleys of western Utah. The thickness 

derived from descriptions of map units is principally affected 

by the fact that thicknesses presented in geologic descriptions of map units are somewhat generalized and imprecise in 

most cases. Stratigraphic thicknesses are typically reported as 

ranging from zero to a maximum value (tables 1–13), neither 

of which may be representative of the thickness commonly 

observed in outcrop.

Available subsurface data from oil and gas exploration 

wells drilled in valleys of east-central Nevada (Hess and others, 2004) and west-central Utah (Hintze and Davis, 2003) are 

shown on figures 17 and 18. These data are generally similar 

to the predicted values but also emphasize the degree of local 

variability and the limitations of such general compilations. 

For example, in Lake Valley one well intersected 826 m of 

volcanic rocks (fig. 17) whereas a second well about 15 km 

to the south did not encounter any volcanic rocks (fig. 17), 

even though this well is located within a buried caldera that is 

inferred to underlie Lake Valley. Farther to the east in northern 

Hamlin Valley and southern Snake Valley, one well penetrated 

over 320 m of volcanic rocks and did not penetrate the base of 

the volcanic sequence (fig. 17); another well only 4 km to the 

northeast encountered about 140 m of volcanic rocks before 

penetrating Paleozoic carbonate rocks below. In both of these 

situations, the bedrock exposures on either side of the valleys contain faulted Paleozoic rock outcrops blanketed by the 

Cenozoic volcanic section; projection of this outcrop geology 

into the subsurface would produce a variety of predicted thicknesses of volcanic rocks, depending on the degree of volcanic 

rock preservation and paleogeographic complexity of the 

surface on which they were deposited. These examples emphasize that methods of thickness compilation presented here may 

be of use in defining regional variations in predicted thickness, 

but are not appropriate for site-specific subsurface geology.

Summary

The middle Tertiary geologic history of east-central 

Nevada is dominated by volcanic events, especially emplacement of regionally distributed ash-flow tuffs deposited during 

caldera-forming eruptions. Regional ground-water studies such 

as the BARCAS study require a three-dimensional depiction of 

the extent and thickness of subsurface geologic units that provides a conceptual and numerical framework of the subsurface 

distribution of the aquifer materials. Typically, this requires the 

ability to predict the thickness of a rock unit that is of interest 

across a very large area on the basis of a small number of data 

points. Compilation of geologic data from published maps and 

reports provides a general understanding of the distribution and 

thickness of tuffs that are presumably present in the subsurface 

of the intermontane valleys and are critical to understanding the 

ground-water hydrology of this area. The data compiled in this 

report have been used as direct input in the construction of a 

simplified three-dimensional geologic model of the BARCAS 

study area (Watt and Ponce, 2007) and have also been used in 
References Cited 7

water budget calculations for the BARCAS study area (Welch 

and Bright, 2007). Predicted thicknesses that are based on geologic descriptions of map units may overestimate or underestimate regional thickness trends because such descriptions often 

report a minimum and maximum thickness. It is possible that 

average thicknesses would provide a more likely estimate of tuff 

thickness at any particular location within the area addressed 

by this publication. Predicted thicknesses derived by combining 

isopach maps for individual tuffs are dependent on the availability of such maps and the underlying field data used to create the 

maps. Neither method is accurate for predicting local site-scale 

variability in volcanic-rock thickness, which can only be derived 

from a combination of drilling and geophysical methods.

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MF–2381–B, scale 1:350,000, 1 pl. with pamphlet.
Ely

Mesquite

Las 

Vegas

Salt Lake 

City

Carson City

Reno

Colorado River

Great Salt Lake

Great Salt Lake 

Desert regional

 flow system

Goshute regional

flow system

Newark regional

flow system

Colorado regional

flow system

Death Valley

regional flow

system

120° 118° 116° 114° 112°

36°

38°

40°

42°

44°

EXPLANATION

BARCAS study area

Great Basin boundary

Ground-water flow 

system boundary

Base from USGS 1:100,000-scale digital data, 1979-1984. 

1:1,000,000 scale watershed boundaries from USGS digital data.

Universal Transverse Mercator Projection, Zone 11, NAD83.

Carbonate rock province

AZ

NV

WY

CA

OR ID

UT

ARIZONA

NEVADA

WYOMING

CALIFORNIA

IDAHO

OREGON

UTAH

JUAB .

MILLARD 

BEAVER 

IRON 

LINCOLN 

WHITE PINE 

TOOELE 

ELKO 

EUREKA 

NYE 

Nevada 

Test 

Site

Figure 1. Carbonate rock province, BARCAS study area, and associated regional ground-water flow systems.

10 Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah
2

0

-2

-4

-6

-8

2

0

-2

-4

-6

DEPTH, IN KILOMETERS DEPTH, IN KILOMETERS

Pre-volcanic rocks

Pre-volcanic rocks

Granitic pluton

Granitic pluton

Caldera-collapse

breccia

Intracaldera ash-flow tuff

Ash-flow tuff

Post-caldera sediments Post-caldera lava dome

Structural

margin

Topographic

margin

Intracaldera region

After ash-flow eruption and caldera collapse

After resurgence and post-caldera deposition

Figure 2. Generalized diagram of ash-flow caldera.

No vertical exaggeration; scale approximate.

Diagram modified from Lipman (1984)

Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah 11
Utah

Nevada

California Arizona

Area shown in figure

NYE NYE

LINCOLN LINCOLN

WHITE PINE WHITE PINE MILLARD MILLARD

IRON IRON

EUREKA EUREKA

JUAB JUAB

BEAVER BEAVER

WASHINGTON WASHINGTON

116° 115° 114°

38°

39° Snake Valley Spring Valley Steptoe Valley White River Valley

Tule Valley

Pine Valley

Dry Lake Valley

Newark Valley

Lake Valley

Long Valley

Coal Valley

Butte Valley

Garden Valley

Railroad Valley

Little Smoky Valley

Cave Valley

Pahranagat Valley

Delamar Valley

Wah Wah Valley

Hamlin Valley

Ely

Hiko

Alamo

McGill

Panaca

Pioche

Eureka

Caliente

CCC

CNCC IPCC

KT

EXPLANATION 

Quaternary alluvium

Quaternary playas and fine-grained deposits

Tertiary sedimentary rocks, undivided

Cenozoic lava flows, undivided

Cenozoic ash-flow tuffs, undivided

Intrusive rocks, undivided

Pre-Cenozoic rocks, undivided

Caldera boundary

Nevada geology modified from Stewart and others (2003); 

Utah geology modified from Hintze and others (2000)

Caldera boundaries modified from Williams and others (1997), 

Loucks and others (1989), Raines and others (1996), Workman and 

others (2002), and Gans and others (1989)

Base from USGS 1:100,000-scale digital data, 1979-1984. 

Universal Transverse Mercator Projection, zone 11, NAD83.

Figure 3. Generalized geology map and locations of calderas, eastern Nevada and western Utah.

CCC, Caliente caldera complex; CNCC, central Nevada caldera 

complex; IPCC, Indian Peak caldera complex; KT, inferred 

source of the Kalamazoo Tuff

Roads

BARCAS study area boundary

County boundary

0 10 20 30 40 50 5 MILES

0 20 40 60 80 100 10 KILOMETERS

Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah 12
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah 13

Nevada Utah

California Arizona

Area shown in figure

LINCOLN LINCOLN

MILLARD MILLARD

IRON IRON

WHITE PINE WHITE PINE

BEAVER BEAVER

NYE NYE

Ely

Pioche

7

9

6

17

22 23 3

19

16

10 13

25

8

5

21

11

1

4

2

14

24

18

20

15

12

115° 114°

38°

39°

Snake Valley

Spring Valley

Pine Valley

White River Valley

Lake Valley

Dry Lake Valley

Tule Valley

Steptoe Valley Cave Valley

Wah Wah Valley

Pahroc Valley

Patterson Valley

Hamlin Valley

Muleshoe Valley

Ferguson Desert

Confusion Range

Burbank Hills

Wah Wah Mountains

Indian Peak Range

Mountain Home Range

Limestone Hills

Snake Range

Schell Creek Range

Egan Range

Grassy

Mountain

Fortification

Range

Shingle Pass

Fairview

Range

Bristol Range

West Range

North Pahroc Range

San Francisco Mountains

White Rock Mountains

Wilson Creek Range

Needle Mountains

Schell Creek Range

EXPLANATION 

Quaternary alluvium

Quaternary playas and fine-grained deposits

Tertiary sedimentary rocks, undivided

Cenozoic lava flows, undivided

Cenozoic ash-flow tuffs, undivided

Intrusive rocks, undivided

Pre-Cenozoic rocks, undivided

Caldera boundary

County boundary

Nevada geology modified from Stewart and others (2003); Utah Maps used for thickness compilation geology modified after Hintze and others (2000) 

Caldera boundaries modified from Williams and others (1997), 

Loucks and others (1989), Raines and others (1996), Workman and 

others (2002), and Gans and others (1989)

Base from USGS 1:100,000-scale digital data, 1979-1984. 

Universal Transverse Mercator Projection, zone 11, NAD83.

9

Map 

reference Author 

number

1 Swadley and others, 1994

2 Ekren and Page, 1995

3 Best and others, 1998

4 Page and Ekren, 1995

5 Van Loenen, 1987

6 Drewes, 1967

7 Whitebread, 1969

8 Hose, 1965

9 Hintze, 1974a

10 Loucks and others, 1989

11 Hintze, 1986

12 Hintze, 1981

13 Hintze, 1974b

14 Hintze and Best, 1987

15 Best and Hintze, 1980

16 Willis and others, 1987

17 Best, Toth, and others, 1989

18 Toth, 1986

19 Best, Hintze, and Homes, 

 1987

20 Wheeler, 1980

21 Abbott and others, 1983

22 Best, Morris, and others, 1987

23 Best, Grant, and others, 1987

24 Keith and others, 1994

25 Williams and others, 1997

0 5 10 15 20 25 MILES

0 10 20 30 40 50 5 KILOMETERS

Figure 4. Index of geologic maps in the vicinity of the Indian Peak caldera complex used to compile volcanic rock thicknesses.
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah 14

NYE NYE

LINCOLN LINCOLN

WHITE PINE WHITE PINE

MILLARD MILLARD

EUREKA EUREKA

IRON IRON

JUAB JUAB

BEAVER BEAVER

WASHINGTON WASHINGTON

Ely

Hiko

Alamo

McGill

Panaca

Pioche

Eureka

Caliente

116° 115° 114°

38°

39°

Base from USGS 1:100,000-scale digital data, 1979-1984. 

Universal Transverse Mercator Projection, zone 11, NAD83.

Thickness of Kalamazoo Tuff, in meters, contoured at intervals 

consistent with those used for the thickest tuffs

Thickness, meters

0 - 200

201 - 400

401 - 600

601 - 800

801 - 1,000

1,001 - 1,200

1,201 - 1,400

1,401 - 1,600

1,601 - 1,800

Nevada

Utah

Nevada

Utah

NV UT Kalamazoo Tuff, thickness in meters

0 - 50

51 - 100

101 - 150

151 - 200

201 - 250

251 - 300

301 - 350

Contoured from thickness data in Gans and others (1989)

EXPLANATION

Caldera boundary

Caldera boundaries modified from Williams and others (1997), 

Loucks and others (1989), Raines and others (1996), Workman and 

others (2002), and Gans and others (1989)

Roads

County boundary

0 10 20 30 40 50 5 MILES

0 10 20 30 40 50 5 KILOMETERS

Area shown in figure

Figure 5. Thickness (isopach) map of Kalamazoo Tuff from Gans and others (1989).

Thickness of Kalamazoo Tuff, in meters, contoured at intervals 

that most clearly display the thickness variation of the unit
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah 15

NYE NYE

LINCOLN LINCOLN

WHITE PINE WHITE PINE

MILLARD MILLARD

EUREKA EUREKA

IRON IRON

JUAB JUAB

BEAVER BEAVER

WASHINGTON WASHINGTON

Ely

Hiko

Alamo

McGill

Panaca

Pioche

Eureka

Caliente

116° 115° 114°

38°

39°

Base from USGS 1:100,000-scale digital data, 1979-1984. 

Universal Transverse Mercator Projection, zone 11, NAD83.

Thickness of Windous Butte Formation, in meters, contoured at

intervals consistent with those used for the thickest tuffs

Thickness, meters

0 - 201

201 - 400

401 - 600

601 - 800

801 - 1,000

1,001 - 1,200

1,201 - 1,400

1,401 - 1,600

1,601 - 1,800

Nevada

Utah

Nevada

Utah

NV UT

Figure 6. Thickness (isopach) map of Windous Butte Formation.

Thickness of Windous Butte Formation, in meters, contoured at 

intervals that most clearly display the thickness variation of the unit

Windous Butte Formation, thickness in meters

0 - 200

201 - 400

401 - 600

601 - 800

801 - 1,000

1,001 - 1,200

1,201 - 1,400

1,401 - 1,600

1,601 - 1,800

Contoured from thickness data in Best, Christiansen, and others (1989)

EXPLANATION

Caldera boundary

Caldera boundaries modified from Williams and others (1997), 

Loucks and others (1989), Raines and others (1996), Workman and 

others (2002), and Gans and others (1989)

Roads

County boundary

0 10 20 30 40 50 5 MILES

0 10 20 30 40 50 5 KILOMETERS
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah 16

NYE NYE

LINCOLN LINCOLN

WHITE PINE WHITE PINE

MILLARD MILLARD

EUREKA EUREKA

IRON IRON

JUAB JUAB

BEAVER BEAVER

WASHINGTON WASHINGTON

Ely

Hiko

Alamo

McGill

Panaca

Pioche

Eureka

Caliente

116° 115° 114°

38°

39°

Base from USGS 1:100,000-scale digital data, 1979-1984. 

Universal Transverse Mercator Projection, zone 11, NAD83.

Nevada

Utah

Nevada

Utah

NV UT

Figure 7. Thickness (isopach) map of Monotony Tuff.

Contoured from thickness data in Best, Christiansen, and others (1989) Thickness of Monotony Tuff, in meters, contoured at intervals 

that most clearly display the thickness variation of the unit

EXPLANATION

Caldera boundary

Caldera boundaries modified from Williams and others (1997), 

Loucks and others (1989), Raines and others (1996), Workman and 

others (2002), and Gans and others (1989)

Roads

County boundary

Monotony Tuff, thickness in meters

0 - 200

201 - 400

401 - 600

601 - 800

801 - 1,000

1,001 - 1,200

1,201 - 1,400

1,401 - 1,600

1,601 - 1,800

Thickness of Monotony Tuff, in meters, contoured at intervals 

consistent with those used for the thickest tuffs

Thickness, meters

0 - 200

201 - 400

401 - 600

601 - 800

801 - 1,000

1,001 - 1,200

1,201 - 1,400

1,401 - 1,600

1,601 - 1,800

0 10 20 30 40 50 5 MILES

0 10 20 30 40 50 5 KILOMETERS
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah﻿ 17

NYE NYE

LINCOLN LINCOLN

WHITE PINE WHITE PINE

MILLARD MILLARD

EUREKA EUREKA

IRON IRON

JUAB JUAB

BEAVER BEAVER

WASHINGTON WASHINGTON

Ely

Hiko

Alamo

McGill

Panaca

Pioche

Eureka

Caliente

116° 115° 114°

38°

39°

Thickness of Shingle Pass Tuff, in meters, contoured at intervals

consistent with those used for the thickest tuffs

Thickness, meters

0 - 200

201 - 400

401 - 600

601 - 800

801 - 1,000

1,001 - 1,200

1,201 - 1,400

1,401 - 1,600

1,601 - 1,800

Nevada

Utah

Nevada

Utah

NV UT

Shingle Pass Tuff, thickness in meters

0 - 50

51 - 100

101 - 150

151 - 200

201 - 250

251 - 300

301 - 350

351 - 400

Contoured from thickness data in Best, Christiansen, and others (1989)

EXPLANATION

Caldera boundary

Caldera boundaries modified from Williams and others (1997), 

Loucks and others (1989), Raines and others (1996), Workman and 

others (2002), and Gans and others (1989)

Roads

County boundary

0 10 20 30 40 50 5 MILES

0 10 20 30 40 50 5 KILOMETERS

Base from USGS 1:100,000-scale digital data, 1979-1984. 

Universal Transverse Mercator Projection, zone 11, NAD83. Figure 8. Thickness (isopach) map of Shingle Pass Tuff.
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah﻿ 18

NYE NYE

LINCOLN LINCOLN

WHITE PINE WHITE PINE

MILLARD MILLARD

EUREKA EUREKA

IRON IRON

JUAB JUAB

BEAVER BEAVER

WASHINGTON WASHINGTON

Ely

Hiko

Alamo

McGill

Panaca

Pioche

Eureka

Caliente

116° 115° 114°

38°

39°

Cottonwood Wash Tuff, thickness in meters

0 - 50

51 - 100

101 - 150

151 - 200

201 - 250

251 - 300

Contoured from thickness data in Best, Christiansen, and Blank (1989)

Thickness of Cottonwood Wash Tuff, in meters, contoured at 

intervals that most clearly display the thickness variation of the unit

Thickness of Cottonwood Wash Tuff, in meters, contoured at intervals

consistent with those used for the thickest tuffs

Thickness, meters

0 - 200

201 - 400

401 - 600

601 - 800

801 - 1,000

1,001 - 1,200

1,201 - 1,400

1,401 - 1,600

1,601 - 1,800

EXPLANATION

Caldera boundary

Caldera boundaries modified from Williams and others (1997), 

Loucks and others (1989), Raines and others (1996), Workman and 

others (2002), and Gans and others (1989)

Roads

County boundary

0 10 20 30 40 50 5 MILES

0 10 20 30 40 50 5 KILOMETERS Nevada Utah

Nevada

Utah

NV UT

Base from USGS 1:100,000-scale digital data, 1979-1984. 

Universal Transverse Mercator Projection, zone 11, NAD83. Figure 9. Thickness (isopach) map of Cottonwood Wash Tuff.
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah﻿ 19

NYE NYE

LINCOLN LINCOLN

WHITE PINE WHITE PINE

MILLARD MILLARD

EUREKA EUREKA

IRON IRON

JUAB JUAB

BEAVER BEAVER

WASHINGTON WASHINGTON

Ely

Hiko

Alamo

McGill

Panaca

Pioche

Eureka

Caliente

116° 115° 114°

38°

39°

Nevada

Utah

Nevada

Utah

NV UT

Thickness of Wah Wah Springs Formation, in meters, contoured at 

intervals consistent with those used for the thickest tuffs

Thickness, meters

0 - 200

201 - 400

401 - 600

601 - 800

801 - 1,000

1,001 - 1,200

1,201 - 1,400

1,401 - 1,600

1,601 - 1,800

Thickness of Wah Wah Springs Formation, in meters, 

contoured at intervals that most clearly display the 

thickness variation of the unit

Wah Wah Springs Formation, thickness in meters

0 - 200

201 - 400

401 - 600

601 - 800

801 - 1,000

1,001 - 1,200

1,201 - 1,400

1,401 - 1,600

1,601 - 1,800

Contoured from thickness data in Best, Christiansen, and Blank (1989)

EXPLANATION

Caldera boundary

Caldera boundaries modified from Williams and others (1997), 

Loucks and others (1989), Raines and others (1996), Workman and 

others (2002), and Gans and others (1989)

Roads

County boundary

0 10 20 30 40 50 5 MILES

0 10 20 30 40 50 5 KILOMETERS

Base from USGS 1:100,000-scale digital data, 1979-1984. 

Universal Transverse Mercator Projection, zone 11, NAD83. Figure 10. Thickness (isopach) map of Wah Wah Springs Formation.
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah﻿ 20

NYE NYE

LINCOLN LINCOLN

WHITE PINE WHITE PINE

MILLARD MILLARD

EUREKA EUREKA

IRON IRON

JUAB JUAB

BEAVER BEAVER

WASHINGTON WASHINGTON

Ely

Hiko

Alamo

McGill

Panaca

Pioche

Eureka

Caliente

116° 115° 114°

38°

39°

Thickness of Lund Formation, in meters, contoured at intervals

consistent with those used for the thickest tuffs

Thickness, meters

0 - 200

201 - 400

401 - 600

601 - 800

801 - 1,000

1,001 - 1,200

1,201 - 1,400

1,401 - 1,600

1,601 - 1,800

Lund Formation, thickness in meters

0 - 200

201 - 400

401 - 600

601 - 800

801 - 1,000

Contoured from thickness data in Best, Christiansen, and Blank (1989)

EXPLANATION

Caldera boundary

Caldera boundaries modified from Williams and others (1997), 

Loucks and others (1989), Raines and others (1996), Workman and 

others (2002), and Gans and others (1989)

Roads

County boundary

0 10 20 30 40 50 5 MILES

0 10 20 30 40 50 5 KILOMETERS Nevada Utah

Thickness of Lund Formation, in meters, contoured at intervals 

that most clearly display the thickness variation of the unit Nevada Utah

NV UT

Base from USGS 1:100,000-scale digital data, 1979-1984. 

Universal Transverse Mercator Projection, zone 11, NAD83. Figure 11. Thickness (isopach) map of Lund Formation.
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah﻿ 21

NYE NYE

LINCOLN LINCOLN

WHITE PINE WHITE PINE

MILLARD MILLARD

EUREKA EUREKA

IRON IRON

JUAB JUAB

BEAVER BEAVER

WASHINGTON WASHINGTON

Ely

Hiko

Alamo

McGill

Panaca

Pioche

Eureka

Caliente

116° 115° 114°

38°

39°

Thickness of Isom Formation, in meters, contoured at intervals 

that most clearly display the thickness variation of the unit

Isom Formation, thickness in meters

10 - 50

51 - 100

101 - 150

151 - 200

201 - 250

251 - 300

301 - 350

351 - 400

401 - 467

Contoured from thickness data in Best, Christiansen, and Blank (1989)

EXPLANATION

Caldera boundary

Caldera boundaries modified from Williams and others (1997), 

Loucks and others (1989), Raines and others (1996), Workman and 

others (2002), and Gans and others (1989)

Roads

County boundary

0 10 20 30 40 50 5 MILES

0 10 20 30 40 50 5 KILOMETERS

Thickness of Isom Formation, in meters, contoured at intervals

consistent with those used for the thickest tuffs

Thickness, meters

0 - 200

201 - 400

401 - 600

601 - 800

801- 1,000

1,001 - 1,200

1,201 - 1,400

1,401 - 1,600

1,601 - 1,800

Nevada

Utah

Nevada

Utah

NV UT

Base from USGS 1:100,000-scale digital data, 1979-1984. 

Universal Transverse Mercator Projection, zone 11, NAD83. Figure 12. Thickness (isopach) map of Isom Formation.
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah﻿ 22

NYE NYE

LINCOLN LINCOLN

WHITE PINE WHITE PINE

MILLARD MILLARD

EUREKA EUREKA

IRON IRON

JUAB JUAB

BEAVER BEAVER

WASHINGTON WASHINGTON

Ely

Hiko

Alamo

McGill

Panaca

Pioche

Eureka

Caliente

116° 115° 114°

38°

39°

Base from USGS 1:100,000-scale digital data, 1979-1984. 

Universal Transverse Mercator Projection, zone 11, NAD83.

Figure 13. Thickness (isopach) map of Leach Canyon Formation.

Thickness of Leach Canyon Formation, in meters, contoured at 

intervals consistent with those used for the thickest tuffs

Thickness, meters

0 - 200

201 - 400

401 - 600

601 - 800

801 - 1,000

1,001 - 1,200

1,201 - 1,400

1,401 - 1,600

1,601 - 1,800

Leach Canyon Formation, thickness in meters

10 - 50

51 - 100

101 - 150

151 - 200

201 - 257

Contoured from thickness data in Williams (1967)

EXPLANATION

Caldera boundary

Caldera boundaries modified from Williams and others (1997), 

Loucks and others (1989), Raines and others (1996), Workman and 

others (2002), and Gans and others (1989)

Roads

County boundary

0 10 20 30 40 50 5 MILES

0 10 20 30 40 50 5 KILOMETERS Nevada Utah

Nevada

Utah

NV UT Thickness of Leach Canyon Formation, in meters, 

contoured at intervals that most clearly display the 

thickness variation of the unit
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah﻿ 23

NYE NYE

LINCOLN LINCOLN

WHITE PINE WHITE PINE

MILLARD MILLARD

EUREKA EUREKA

IRON IRON

JUAB JUAB

BEAVER BEAVER

WASHINGTON WASHINGTON

Ely

Hiko

Alamo

McGill

Panaca

Pioche

Eureka

Caliente

116° 115° 114°

38°

39°

Thickness of Condor Canyon Formation, in meters, 

contoured at intervals that most clearly display the 

thickness variation of the unit

Thickness of Condor Canyon Formation, in meters, contoured at

 intervals consistent with those used for the thickest tuffs

Thickness, meters

0 - 200

201 - 400

401 - 600

601 - 800

801 - 1,000

1,001 - 1,200

1,201 - 1,400

1,401 - 1,600

1,601 - 1,800

Condor Canyon Formation, thickness in meters

10 - 25

26 - 50

51 - 75

76 - 100

101 - 125 

126 - 152

Contoured from thickness data in Williams (1967)

EXPLANATION

Caldera boundary

Caldera boundaries modified from Williams and others (1997), 

Loucks and others (1989), Raines and others (1996), Workman and 

others (2002), and Gans and others (1989)

Roads

County boundary

0 10 20 30 40 50 5 MILES

0 10 20 30 40 50 5 KILOMETERS Nevada Utah

Nevada

Utah

NV UT

Base from USGS 1:100,000-scale digital data, 1979-1984. 

Universal Transverse Mercator Projection, zone 11, NAD83. Figure 14. Thickness (isopach) map of Condor Canyon Formation.
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah﻿ 24

NYE NYE

LINCOLN LINCOLN

WHITE PINE WHITE PINE

MILLARD MILLARD

EUREKA EUREKA

IRON IRON

JUAB JUAB

BEAVER BEAVER

WASHINGTON WASHINGTON

Ely

Hiko

Alamo

McGill

Panaca

Pioche

Eureka

Caliente

116° 115° 114°

38°

39°

Thickness of Harmony Hills Tuff, in meters, 

contoured at intervals that most clearly display the 

thickness variation of the unit

Thickness of Harmony Hills Tuff, in meters, contoured at intervals 

consistent with those used for the thickest tuffs

Thickness, meters

0 - 200

201 - 400

401 - 600

601 - 800

801 - 1,000

1,001 - 1,200

1,201 - 1,400

1,401 - 1,600

1,601 - 1,800

Harmony Hills Tuff, thickness in meters

10 - 25

26 - 50

51 - 75

76 - 100

101 - 125 

126 - 152

Contoured from thickness data in Williams (1967)

EXPLANATION

Caldera boundary

Caldera boundaries modified from Williams and others (1997), 

Loucks and others (1989), Raines and others (1996), Workman and 

others (2002), and Gans and others (1989)

Roads

County boundary

0 10 20 30 40 50 5 MILES

0 10 20 30 40 50 5 KILOMETERS Nevada Utah

Nevada

Utah

NV UT

Base from USGS 1:100,000-scale digital data, 1979-1984. 

Universal Transverse Mercator Projection, zone 11, NAD83. Figure 15. Thickness (isopach) map of Harmony Hills Tuff.
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah﻿ 25

116° 115° 114°

38°

39°

EXPLANATION

Combined thickness of all ash-flow tuffs, in meters

0 - 300

301 - 600

601 - 900

901 - 1,200

1,201 - 1,500

1,501 - 1,800

1,801 - 2,100

2,101 - 2,400

2,401 - 2,700

2,701 - 3,000

3,001 - 3,300

Caldera boundary

Caldera boundaries modified from Williams and others (1997), 

Loucks and others (1989), Raines and others (1996), Workman and 

others (2002), and Gans and others (1989)

CCC, Caliente caldera complex; CNCC, central Nevada caldera 

complex; IPCC, Indian Peak caldera complex; KT, inferred 

source of the Kalamazoo Tuff

Roads

BARCAS study area boundary

County boundary

Base from USGS 1:100,000-scale digital data, 1979-1984. 

Universal Transverse Mercator Projection, zone 11, NAD83.

Figure 16. Aggregate thickness (isopach) map of all tuffs for caldera-related Tertiary

 volcanic rocks in east-central Nevada and west-central Utah.

CCC

CNCC

IPCC

KT

Nevada

Utah

NYE NYE

LINCOLN LINCOLN

WHITE PINE WHITE PINE

MILLARD MILLARD

EUREKA EUREKA

IRON IRON

JUAB JUAB

BEAVER BEAVER

WASHINGTON WASHINGTON

Ely

Hiko

Alamo

McGill

Panaca

Pioche

Eureka

Caliente

0 10 20 30 40 50 5 Miles

0 10 20 30 40 50 5 Kilometers

Area shown in figure

Utah

Nevada

California Arizona

Snake Valley

Spring Valley

Steptoe Valley

White River Valley

Tule Valley

Pine Valley

Dry Lake Valley

Newark Valley

Lake Valley

Long Valley

Coal Valley

Butte Valley

Garden Valley

Railroad Valley

Cave Valley

Hamlin Valley
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah﻿ 26

Nevada Utah

California Arizona

Area shown in figure

LINCOLN LINCOLN

MILLARD MILLARD

IRON IRON

WHITE PINE WHITE PINE

BEAVER BEAVER

NYE NYE

Ely

Pioche

7

9

6

17

22 23 3

19

16

10 13

25

8

5

21

11

1

4

2

14

24

18

20

15

12

115° 114°

38°

39°

Snake Valley

Spring Valley

Valley

Lake 

Pine Valley

White River Valley

Dry Lake Valley

Tule Valley

Steptoe Valley

Wah Wah Valley

Cave

 Valley

Pahroc Valley

Patterson Valley

Hamlin Valley

Muleshoe Valley

Ferguson Desert

Confusion Range

Burbank Hills

Wah Wah Mountains

Indian Peak Range

Mountain Home Range

Limestone Hills

Snake Range

Schell Creek Range

Egan Range

Grassy

Mountain

Fortification

Range

Shingle Pass

Fairview

Range

Bristol Range

West Range

North Pahroc Range

San Francisco Mountains

White Rock Mountains

Wilson Creek Range

Needle Mountains

Schell Creek Range

7

10

3 5

4

9

6

8

12

11

1

13

2

EXPLANATION 

Caldera boundary

County boundary

Maps used for thickness compilation

Caldera boundaries modified from Williams and others (1997), 

Loucks and others (1989), Raines and others (1996), Workman and 

others (2002), and Gans and others (1989)

Base from USGS 1:100,000-scale digital data, 1979-1984. 

Universal Transverse Mercator Projection, zone 11, NAD83.

9

Map 

reference Author 

number

1 Swadley and others, 1994

2 Ekren and Page, 1995

3 Best and others, 1998

4 Page and Ekren, 1995

5 Van Loenen, 1987

6 Drewes, 1967

7 Whitebread, 1969

8 Hose, 1965

9 Hintze, 1974a

10 Loucks and others, 1989

11 Hintze, 1986

12 Hintze, 1981

13 Hintze, 1974b

14 Hintze and Best, 1987

15 Best and Hintze, 1980

16 Willis and others, 1987

17 Best, Toth, and others, 1989

18 Toth, 1986

19 Best, Hintze, and Homes, 

 1987

20 Wheeler, 1980

21 Abbott and others, 1983

22 Best, Morris, and others, 1987

23 Best, Grant, and others, 1987

24 Keith and others, 1994

25 Williams and others, 1997

0 5 10 15 20 25 MILES

0 10 20 30 40 50 5 KILOMETERS

Combined thickness of all ash-flow tuffs, in meters

0 - 300

301 - 600

601 - 900

901 - 1,200

1,201 - 1,500

1,501 - 1,800

1,801 - 2,100

2,101 - 2,400

2,401 - 2,700

2,701 - 3,000

3,001 - 3,300

9 General location of valley axis described in tables

1−13; table number indicated

Oil and gas exploration well; number is thickness 

of ash-flow tuff penetrated in meters

230

Nevada well data from Hess and others (2004); Utah well data 

from Hintze and Davis (2003).

0

0

0

159

536

0

>335

140

191

0

826

0

0

0

0

0 0

0

0

Figure 17. Volcanic thickness (isopach) map showing location of valley axes in eastern Nevada and western Utah described in tables 1−13.
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah﻿ 27 CENTRAL SPRING VALLEY SOUTHERN SPRING VALLEY SNAKE VALLEY NORTHERN HAMLIN VALLEY SOUTHERN HAMLIN VALLEY SOUTHERN LAKE VALLEY NORTHERN LAKE VALLEY CAVE VALLEY NORTHERN PINE VALLEY SOUTHERN PINE VALLEY MULESHOE VALLEY WAH WAH VALLEY NORTHERN DRY LAKE VALLEY Table 7 Table 6 Table 10 Table 9 Table 8 Table 5 Table 4 Table 3 Table 12 Table 11 Table 13 Table 2 Table 1

Range of tuff thickness

as computed from map

unit descriptions

(tables 1−13)

Range of tuff thickness

from summed thickness of

published isopach maps

(fig. 16)

Tuff thickness from oil 

and gas exploration wells

EXPLANATION

4,000

3,500

3,000

2,500

2,000

1,500

1,000

 500

 0

THICKNESS OF VOLCANIC ROCKS, IN METERS

GEOGRAPHIC AREA

Figure 18. Comparison of tuff thickness compilation methods, east-central Nevada and west-central Utah. Associated table is listed at top of bar.
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah 28

Table 1. Compilation of volcanic-rock thickness from mountain ranges flanking the northern part of Dry Lake Valley

[Thickness data for North Pahroc Range from Swadley and others (1994) and Ekren and Page (1995); thickness data for the West Range from Page and Ekren (1995); leaders (--), unit not present] 

Description of geologic map units

Mountain range to the west: North Pahroc Range Mountain range to the east: West Range

Local Regional Minimum Maximum Local Regional Minimum Maximum Lithology Lithology Unit1 Unit2 thickness, m thickness, m Unit Unit thickness, m thickness, m

Tts -- 0 200 Lacustrine sandstone and shale; also pebble conglomerate Tfg -- 0 40 Poorly sorted boulder and cobble deposits

Tb -- 0 13 Massive to vesicular basaltic lava flows Tts -- 0 30 Sandstone, ash, shale, and pebble conglomerate; lacustrine limestone 

-- PF 0 20 Weakly to moderately welded rhyolite tuff; 15–35% crystals -- SP 20 60 Densely welded rhyolite tuff; 10–15% crystals

-- CB 20 40 Densely welded rhyolite tuff; 20% crystals Ttu -- 5 30 Tuffaceous sandstone and ash-fall tuff and conglomerate

-- BT 25 75 Weakly welded rhyolite tuff; 15% crystals -- IS 10 20 Densely welded trachydacite tuff; 10–15% crystals

-- SP 20 30 Densely welded rhyolite tuff; 5–12% crystals Ttl -- 0 30 Tuffaceous sandstone and ash-fall tuff and conglomerate

-- IS 0 5 Densely welded trachydacite tuff; 5–15% crystals Tr -- 40 60 Rhyolite lava dome; 1% crystals

Tah -- 0 100 Massive, locally vesicular andesite lava flows; 35% crystals -- 20 200 Weakly to densely welded dacite tuff; 20–28% crystals LF

PC 0 6 Weakly to densely welded trachyte tuff; crystal poor -- DS 0 200 Densely welded rhyolite tuff; 20–25% crystals

Tms -- 0 600 Massive to vesicular andesite lava flows and breccias Tns -- 30 60 Tuff, tuffaceous sandstone, and conglomerate

CW and (or) Tta -- 0 25 Bedded rhyolite ash-fall tuffs, sandstones, and conglomerate -- 0 130 Densely welded dacite tuff; 26–50% crystals WW

Tco -- 0 670 Andesitic mudflows Ta -- 0 30 Andesite lava flows; 28% crystals

Ta -- 0 60 Massive, flow–laminated andesite lava flows; 25–35% crystals

-- RT 0 150 Moderately to weakly welded rhyolite tuff; 25% crystals

-- DS 90 100 Weakly to moderately welded rhyolite tuff; 15–20% crystals

-- WW 0 170 Moderately to densely welded dacite tuff; 20–45% crystals

Tbt -- 0 5 Ash-fall and reworked bedded tuff

-- CW 0 250 Moderately to densely welded dacite tuff; 30–45% crystals

Lacustrine limestone and fluvial siltstone, sandstone, and Tlf -- 0 296 conglomerate

WB 0 115 Weakly to moderately welded rhyolite tuff; 25% crystals

Twg -- 0 140 Andesite lava flows and flow breccias; 5–30% crystals

Compilation of thickness of Tertiary rocks

Mountain range to the west: North Pahroc Range Mountain range to the east: West Range

Minimum Maximum Minimum Maximum 

thickness, m thickness, m thickness, m thickness, m

 Local units 0 2,109 Local units 75 280

 Regional units 155 961 Regional units 50 610

 Total 155 3,070 Total 125 890

Inferred thickness of volcanic rocks beneath valley axis, 50–800 m

1

Local units have limited spatial extent within a single mapped quadrangle or mountain range; typically includes lava flows and Tertiary sedimentary rocks interbedded with tuff. Local units, from uppermost unit downward are: Tfg, Oldest fanglomerate; Tts, Tuffaceous sedimentary rocks; Tb, Basaltic flows; 

Tah, Andesite lava flows of Hamilton Spring; Tms, Andesite lava flows of Mustang Spring; Tta, Bedded tuff and andesitic conglomerate; Tco, Mudflows of Coal Spring; Ttu, Tuffaceous bedded rocks, upper; Ttl, Tuffaceous bedded rocks, lower; Tr, Rhyolite lava dome; Ta, Andesite lava flows; Tbt, 

Bedded tuff; Tlf, Lacustrine and fluvial sedimentary rocks; Tns, Sedimentary rocks above Wah Wah Springs Formation; Twg, Andesite lava flows of Wheatgrass Spring.

2

Regional units occur in several quadrangles or mountain ranges. These volcanic-rock units are typically ash-flow tuffs. Regional units, from uppermost unit downward are: PF, Pahranagat Formation; CB, Bauers Tuff Member, Condor Canyon Formation; BT, Tuff member, Blawn Formation; SP, Shingle 

Pass Tuff; IS, Isom Formation; PC, Petroglyph Cliff Ignimbrite; LF, Lund Formation; RT, Rhyolitic tuff; DS, Tuff of Deadman Summit; WW, Wah Wah Springs Formation; CW, Cottonwood Wash Tuff; WB, Windous Butte Formation. 
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah 29

Table 2. Compilation of volcanic-rock thickness from mountain ranges flanking Muleshoe Valley

[There is no published reference for Tertiary stratigraphic thickness for the Schell Creek Range; thickness data for the Grassy Mountain/Fairview Range area from Best and others (1998); leaders (--), unit not present] 

Description of geologic map units

Mountain range to the west: the southern part of the Schell Creek Range Mountain range to the east: the Grassy Mountain/Fairview Range area

Local Regional Minimum Maximum Local Regional Minimum Maximum Lithology Lithology Unit1 Unit2 thickness, m thickness, m Unit Unit thickness, m thickness, m

Tf -- 0 30 Partly consolidated sandstone, locally conglomeratic; mudflow breccia

The southern part of the Schell Creek Range, at the head of of Muleshoe Valley, includes a significant outcrop area of Ts -- 0 80 Sandstone and conglomeratic sandstone; also limestone and ash-fall tuff

undocumented Tertiary volcanic rock on its east flank. However, further south in the Schell Creek Range, volcanic rocks Tbm -- 0 60 Somewhat porphyritic, aphanitic mafic lava flows

are absent. The Grassy Mountain/Fairview Range area, on the east side of Muleshoe Valley, contains a considerable -- BT 0 10 Weakly consolidated rhyolite tuff; 2–4% crystals

thickness of Tertiary volcanic rocks. Therefore, assuming that volcanic rock distribution was symmetric around -- PF 0 230 Moderately welded rhyolite tuff; 15–35% crystals

Muleshoe Valley, thickness relations in the Grassy Mountain/Fairview Range area are used as a proxy for Tertiary -- CB 0 40 Densely welded rhyolite tuff; 3–5% crystals

volcanic rock thickness in Muleshoe Valley Tr -- 0 200 Aphyric rhyolite lava flows

-- LC 0 75 Partly welded rhyolite tuff; 20% crystals

-- IS 10 20 Densely welded trachydacite tuff; 20% crystals

-- SPU 0 200 Moderately to densely welded rhyolite tuff; 15% crystals

-- SPL 0 200 Moderately to densely welded rhyolite tuff; 15% crystals

-- RAT 0 60 Moderately welded rhyolite tuff; 10% crystals

Tch -- 0 100 Flow-layered dacite lava flow; 15% crystals

-- RT 0 60 Weakly welded rhyolite tuff; 5% crystals

-- PC 0 70 Densely to moderately welded trachydacite tuff; 10% crystals

-- LF 0 1,000 Moderately to densely welded dacite tuff; 55% crystals

-- SK 0 600 Moderately to densely welded dacite tuff; 33% crystals

-- RST 0 30 Rhyolite tuff; 15% crystals

-- DS 0 380 Densely welded rhyolite tuff; 33% crystals

-- WW 0 120 Densely welded dacite tuff; 40% crystals

-- CW 12 280 Densely to moderately welded dacite tuff; crystal rich

-- WB 0 3 Partly welded rhyolite tuff

Ta -- 0 300 Altered, aphanitic andesite lava flows; abundant phenocrysts

Tb -- 0 30 Massive, altered, aphanitic rhyolite lava flows; 15% phenocrysts

-- SW 0 40 Moderately to weakly welded tuff; 40% crystals

Tls -- 0 20 Thinly bedded lacustrine limestone

Compilation of thickness of Tertiary rocks

Mountain range to the west: the southern part of the Schell Creek Range Mountain range to the east: the Grassy Mountain/Fairview Range area

Minimum Maximum Minimum Maximum 

thickness, m thickness, m thickness, m thickness, m

 Local units 0 46 Local units 0 690

 Regional units 144 1,113 Regional units 22 3,418

 Total 144 1,159 Total 22 4,108

Inferred thickness of volcanic rocks beneath valley axis, 23–3,400 m

1

Local units have limited spatial extent within a single mapped quadrangle or mountain range; typically includes lava flows and Tertiary sedimentary rocks interbedded with tuff. Local units, from uppermost unit downward are: Tf, Semi-consolidated alluvium; Ts, Sedimentary deposits; Tbm, Mafic lava flow 

member, Blawn Formation; Tr, Rhyolite lava flows; Tch, Lava flow of Chokecherry Spring; Ta, Andesitic lava flows; Tb, Rhyolite lava flow of Bailey Spring; Tls, Limestone.

2

Regional units occur in several quadrangles or mountain ranges. These volcanic-rock units are typically ash-flow tuffs. Regional units, from uppermost unit downward are: BT, Tuff member, Blawn Formation; PF, Pahranagat Formation; CB, Bauers Tuff Member, Condor Canyon Formation; LC, Leach 

Canyon Formation; IS, Isom Formation; SPU, Upper member, Shingle Pass Tuff; SPL, Lower member, Shingle Pass Tuff; RAT, Rhyolitic tuff; RT, Tuff member, Ripgut Formation; PC, Petroglyph Cliff Ignimbrite; LF, Lund Formation; SK, Tuff of Silver King Well; RST, Tuff member, Ryan Spring 

Formation; DS, Tuff of Deadman Spring; WW, Wah Wah Springs Formation; CW, Cottonwood Wash Tuff; WB, Windous Butte Formation; SW, Tuff of Silverhorn Wash.
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah 30

Table 3. Compilation of volcanic-rock thickness from mountain ranges flanking Cave Valley

[Thickness data for the Egan Range (near Shingle Pass) from Kellogg (1964), Best and Christiansen (1996), and Best, Christiansen, and others (1989); no published reference for Tertiary stratigraphic thickness for the Schell Creek Range; leaders (--), unit 

Description of geologic map units

Mountain range to the west: Egan Range (near Shingle Pass) Mountain range to the east: the southern part of the Schell Creek Range

Local Regional Minimum Maximum Local Regional Minimum Maximum Lithology Lithology Unit1 Unit2 thickness, m thickness, m Unit Unit thickness, m thickness, m

sr -- 0 610 Fluviatile and tuffaceous sedimentary rocks

-- PF 20 21 Weak to moderately welded rhyolite tuff; 20% crystals

-- CB 0 10 Densely welded rhyolite tuff; 15% crystals The Schell Creek Range, east of Cave Valley, includes a significant outcrop area of undocumented Tertiary volcanic rocks, mostly on its east -- SPU 0 40 Moderately welded rhyolite tuff; 5–10% crystals flank. Also, the Grassy Mountain/Fairview Range area, to the southeast of Cave Valley contains a considerable thickness of Tertiary volcanic -- SPL 35 35 Moderately welded rhyolite tuff; 15–20% crystals rock. Therefore, assuming that volcanic rock distribution was symmetric around Cave Valley, thickness relations in the Egan Range were 

-- WW 29 60 Densely welded; dacite tuff; 35–40% crystals used as a proxy for Tertiary volcanic rock thickness in Cave Valley.

-- CW 6 120 Weak to moderately welded crystal-rich dacite tuff

Moderately to weakly welded rhyolite-dacite tuff; 15–30% -- WB 90 165 crystals

Flow-banded biotite dacite lava; locally glassy; 15–30% dl 30 84 crystals

-- SC 0 120 Rhyolite tuff

tts -- Soft, porous, laminated tuffs and tuffaceous sedimentary rocks

ssc -- 0 305 Conglomerate, sandstone, and clay

-- SHP 115 1,013 Lacustrine deposits; limestone, mudstone, and conglomerate

Compilation of thickness of Tertiary rocks

Mountain range to the west: Egan Range (near Shingle Pass) Mountain range to the east: the southern part of the Schell Creek Range

Minimum Maximum Minimum Maximum 

thickness, m thickness, m thickness, m thickness, m

 Local units 30 999 Local units -- --

 Regional units 180 1,584 Regional units -- --

 Total 325 2,583 Total -- --

Inferred thickness of volcanic rocks beneath valley axis, 300–1,600 m

1

Local units have limited spatial extent within a single mapped quadrangle or mountain range; typically includes lava flows and Tertiary sedimentary rocks interbedded with tuff. Sr, sedimentary rocks; dl, dacite lava; tts, tuffs and tuffaceous sedimentary rocks; ssc, Stinking Spring Conglomerate.

2

Regional units occur in several quadrangles or mountain ranges. These volcanic-rock units are typically ash-flow tuffs. Regional units, from uppermost unit downward are: PF, Pahranagat Formation; CB, Bauers Tuff Member, Condor Canyon Formation; SPU, Upper member, Shingle Pass Tuff; SPL, 

Lower member, Shingle Pass Tuff; WW, Wah Wah Springs Formation; CW, Cottonwood Wash Tuff; WB, Windous Butte Formation; SC, Stone Cabin Formation; SHP, Sheep Pass Formation.
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah 31

Table 4. Compilation of volcanic-rock thickness from mountain ranges flanking southern part of Lake Valley

[Thickness data for the Grassy Mountain/Fairview Range area and Bristol Range from Best and others (1998); thickness data for the Wilson Creek Range from Willis and others (1987) and Williams and others (1997); leaders (--), unit not present] 

Description of geologic map units

1 Mountain range to the west: Grassy Mountain/Fairview Range area and Bristol Range Mountain range to the east: Wilson Creek Range

Local Regional Minimum Maximum Local Regional Minimum Maximum Lithology Lithology Unit2 Unit3 thickness, m thickness, m Unit Unit thickness, m thickness, m

Tf -- 0 30 Partly consolidated sandstone, locally conglomeratic; mudflow breccia Tal -- 0 50 Alluvial fan deposits; poorly sorted boulders and cobbles

Tbm -- 0 60 Somewhat porphyritic, aphanitic mafic lava flows Te -- 0 110 Thin bedded, lacustrine silt and sand; some sand, pebbles, and tephra

-- BT 0 10 Weakly consolidated rhyolite tuff; 2–4% crystals Tsr -- 0 250 Aphanitic rhyolite lava flows and domes; 10% crystals

-- PF 0 230 Moderately welded rhyolite tuff; 15–35% crystals -- SR 0 120 Porous volcaniclastic deposits; some sandstone

-- CB 0 40 Densely welded rhyolite tuff; 3–5% crystals Tt -- 0 140 Porous pyroclastic and epiclastic deposits

Tr -- 0 200 Aphyric rhyolite lava flows Tbr -- 0 230 Aphanitic rhyolite lava flows and domes; 10-20% crystals

Ts -- 0 80 Sandstone and conglomeratic sandstone; also limestone and ash-fall tuff -- BT 0 450 Partly welded rhyolite tuff and epiclastic deposits

-- LC 0 75 Partly welded rhyolite tuff; 20% crystals -- BG 0 80 Moderately welded tuff; 20% crystals

-- IS 10 20 Densely welded trachydacite tuff; 20% crystals -- RC 0 1,050 Weakly to densely welded rhyolite tuff; 25-40% crystals

-- SPU 0 200 Moderately to densely welded rhyolite tuff; 15% crystals Ts -- 0 600 Fluvial-lacustrine conglomerate, sandstone, siltstone, and limestone

-- SPL 0 200 Moderately to densely welded rhyolite tuff; 15% crystals Tscl -- 0 300 Dacite and rhyolite lava flows and minor tuff; 25% crystals

-- RAT 0 60 Moderately welded rhyolite tuff; 10% crystals Tn -- 150 250 Dacite to andesite lava flows; 20% crystals; locally vesicular

Tch -- 0 100 Flow-layered dacite lava flow; 15% crystals -- HH 20 150 Densely to moderately welded andesite tuff; 50% crystals

-- RF 0 60 Weakly welded rhyolite tuff; 5% crystals Tf -- 0 100 Rhyolite lava flows

-- PC 0 70 Densely to moderately welded trachydacite tuff; 10% crystals Tlf -- 0 1,000 Trachyandesite to trachydacite flows; 5-25% crystals

-- LF 0 1,000 Moderately to densely welded dacite tuff; 55% crystals -- AFT 0 150 Densely welded tuff; 25% crystals

-- SK 0 600 Moderately to densely welded dacite tuff; 33% crystals Tl -- 0 130 Flow-layered lava flow

-- RST 0 30 Rhyolite tuff; 15% crystals -- CB 10 200 Densely welded rhyolite tuff; 3-5% crystals

-- DS 0 380 Densely welded rhyolite tuff; 33% crystals -- CS 0 200 Densely welded rhyolite tuff; 3-5% crystals

-- WW 0 120 Densely welded dacite tuff; 40% crystals Tcg -- 0 50 Poorly-sorted boulder and cobble conglomerate

-- CW 12 280 Densely to moderately welded dacite tuff; crystal rich -- LC 200 400 Partly welded rhyolite tuff; 20% crystals

-- WB 0 3 Partly welded rhyolite tuff -- IS 0 200 Moderately to densely welded trachydacite; 20% crystals

Ta -- 0 300 Altered, aphanitic andesite lava flows; abundant phenocrysts -- RF 200 650 Partly to densely welded rhyolite tuff; crystal poor

Tb -- 0 30 Massive, altered, aphanitic rhyolite lava flows; 15% phenocrysts -- LF 0 150 Moderately to densely welded dacite tuff; 30-40% crystals

-- SW 0 40 Moderately to weakly welded tuff; 40% crystals -- WW 0 50 Densely welded dacite tuff; 40% crystals

Compilation of thickness of Tertiary rocks

Mountain range to the west: Grassy Mountain/Fairview Range area and Bristol Range Mountain range to the east: Wilson Creek Range

Minimum Maximum Minimum Maximum 

thickness, m thickness, m thickness, m thickness, m

 Local units 0 800 Local units 150 3,210

 Regional units 22 3,418 Regional units 430 3,850

 Total 22 4,218 Total 580 7,060

Inferred thickness of volcanic rocks beneath valley axis, 22–3,400 m

1

The Bristol Range, west of the southern part of Lake Valley, preserves no Tertiary volcanic rock. However, further north along the west side of the southern part of Lake Valley, the Grassy Mountain/Fairview Range area contains a considerable thickness of Tertiary volcanic rocks. Assuming that volcanic rock 

distribution was symmetric around the southern part of Lake Valley, thickness relations in the Grassy Mountain/Fairview Range proxy for Tertiary volcanic thicknesses along the west side of the southern part of Lake Valley.

2

Local units have limited spatial extent within a single mapped quadrangle or mountain range; typically includes lava flows and Tertiary sedimentary rocks interbedded with tuff. Local units, from uppermost unit downward are: Tal, Tertiary fan alluvium; Te, Basin-fill deposits of Eagle Valley; Tsr, Rhyolite lava 

flow member, Steamboat Mountain Formation; Tt, Clastic rocks; Tf, Semiconsolidated alluvium; Tbr, Rhyolite lava flow member, Blawn Formation; Tbm, Mafic lava flow member, Blawn Formation; Tr, Rhyolite lava flows; Ts, Sedimentary deposits; Tscl, Lava-flows member, intermediate-composition rocks 

of Serviceberry Canyon; Tn, Lava flows of Ninemile Rocks; Tch, Lava flow of Chokecherry Spring; Tf, Rhyolite lava flow of Tobe Spring; Tlf, Latite lava flows; Tl, Lava flow; Tcg, Conglomerate; Ta, Andesitic lava flows; Tb, Rhyolite lava flow of Bailey Spring.

3

Regional units occur in several quadrangles or mountain ranges. These volcanic-rock units are typically ash-flow tuffs. Regional units, from uppermost unit downward are: SR, Rhyolite tuff member, Steamboat Mountain Formation; BT, Tuff member, Blawn Formation; BG, tuff of Gold Springs, Blawn 

Formation; RC, Racer Canyon Tuff; HH, Harmony Hills Tuff; PF, Pahranagat Formation; AFT, Ash-flow tuff; CB, Bauers Tuff Member, Condor Canyon Formation; CS, Swett Tuff Member, Condor Canyon Formation; LC, Leach Canyon Formation; IS, Isom Formation; SPU, Upper member, Shingle Pass 

Tuff; SPL, Lower member, Shingle Pass Tuff; RAT, Rhyolitic tuff; RF, Tuff member, Ripgut Formation; PC, Petroglyph Cliff Ignimbrite; LF, Lund Formation; SK, Tuff of Silver King Well; RST, Tuff member, Ryan Spring Formation; DS, Tuff of Deadman Spring; WW, Wah Wah Springs Formation; CW, 

Cottonwood Wash Tuff; WB, Windous Butte Formation; SW, Tuff of Silverhorn Wash.
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah 32

Table 5. Compilation of volcanic-rock thickness from mountain ranges flanking northern part of Lake Valley

[Thickness data for the central part of the Schell Creek Range from Van Loenen (1987); thickness data for the Fortification Range from Loucks and others (1989); leaders (--), unit not present] 

Description of geologic map units

Mountain range to the west: central part of the Schell Creek Range Mountain range to the east: Fortification Range

Local Regional Minimum Maximum Local Regional Minimum Maximum Lithology Lithology Unit1 Unit2 thickness, m thickness, m Unit Unit thickness, m thickness, m

-- SP 0 15 Moderately welded rhyolite tuff; 15% crystals

-- IS 0 6 Moderately to densely welded trachytic tuff; 5–10% crystals

-- WW 0 270 Densely welded dacite tuff; 35–40% crystals The central part of the Schell Creek Range, west of the north part of Lake Valley, includes a significant -- CW 0 220 Weak to moderately welded crystal-rich dacite tuff outcrop area of undocumented Tertiary volcanic rocks on its east flank. However, further north in the Tea -- 0 240 Strongly porphyritic lava flows and flow breccias Schell Creek Range, volcanic rocks are scarce. The Grassy Mountain/Fairview Range area, southwest of

Lake Valley, contains a considerable thickness of Tertiary volcanic rocks, as do the Wilson Creek and -- WB 6 50 Moderately to weakly welded rhyolite to dacite tuff; 15–30% crystals

Fortification Ranges, to the southeast and east, respectively. Therefore, assuming that volcanic rock -- TD 0 670 Member d: weakly to moderately welded rhyolite tuff; 10–15% crystals

distribution was symmetric around the northern part of Lake Valley, thickness relations in the -- TC 0 300 Member c: weakly to densely welded rhyolite tuff; 10% crystals Fortification Range were used as a proxy for Tertiary volcanic rock thickness in the northern part of Ttl -- 0 250 Member l: rhyolite lava; 21% crystals Lake Valley. -- TB 0 450 Member b: weakly welded rhyolite tuff; 8% crystals

-- TA 0 170 Member a: rhyolite air fall ash, surge, and ash flow tuff

Compilation of thickness of Tertiary rocks

Mountain range to the west: central part of the Schell Creek Range Mountain range to the east: Fortification Range

Minimum Maximum Minimum Maximum 

thickness, m thickness, m thickness, m thickness, m

 Local units -- -- Local units 0 490

 Regional units -- -- Regional units 6 2,151

 Total -- -- Total 6 2,641

Inferred thickness of volcanic rocks beneath valley axis, 6–2,100 m

1

Local units have limited spatial extent within a single mapped quadrangle or mountain range; typically includes lava flows and Tertiary sedimentary rocks interbedded with tuff. Local units, from uppermost unit downward are: Tea, Andesite flow member, Escalante Desert Formation; Ttl, Lava flow 

member, formation of the Gouge Eye.

2

Regional units occur in several quadrangles or mountain ranges. These volcanic-rock units are typically ash-flow tuffs. Regional units, from uppermost unit downward are: SP, Shingle Pass Tuff; IS, Isom Formation; WW, Wah Wah Springs Formation; CW, Cottonwood Wash Tuff; WB, Windous 

Butte Formation; TD, Member d, formation of the Gouge Eye; TC, Member c, formation of the Gouge Eye; TB, Member b, formation of the Gouge Eye; TA, Member a, formation of the Gouge Eye.
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah 33

Table 6. Compilation of volcanic-rock thickness from mountain ranges flanking southern part of Spring Valley

[Thickness data for the Fortification Range from Loucks and others (1989); thickness data for the Wilson Creek Range and Limestone Hills from Willis and others (1987); leaders (--), unit not present] 

Description of geologic map units

M 3 ountain range to the west: Fortification Range Mountain range to the east: Wilson Creek Range and Limestone Hills

Local Regional Minimum Maximum Local Regional Minimum Maximum Lithology Lithology Unit1 Unit2 thickness, m thickness, m Unit Unit thickness, m thickness, m

-- SP 0 15 Moderately welded rhyolite tuff; 15% crystals Tbr -- 0 200 Rhyolite lava flows and domes; 10–15% crystals; local vitrophyre

-- IS 0 6 Moderately to densely welded trachytic tuff; 5–10% crystals -- BT 0 200 Weakly to moderately welded rhyolite tuff, ash, and clastics; 10% crystals

-- WW 0 270 Densely welded dacite tuff; 35–40% crystals Tba 0 135 Vesicular, aphyric to strongly porphyritic trachyandesite lava flows

-- CW 0 220 Weak to moderately welded crystal-rich dacite tuff -- BP 0 200 Moderately to weakly welded rhyolite tuff; 25–30% crystals

Tea -- 0 240 Strongly porphyritic lava flows and flow breccias -- SP 0 100 Moderately to densely welded rhyolite tuff; 20% crystals

-- WB 6 50 Moderately to weakly welded rhyolite to dacite tuff; 15–30% -- IS 0 300 Densely welded trachytic tuff; 10–12% crystals

-- TD 0 670 Member d: weakly to moderately welded rhyolite tuff; 10–15% -- RF 0 200 Moderately to densely welded rhyolite tuff; ~3% crystals

-- TC 0 300 Member c: weakly to densely welded rhyolite tuff; 10% Tgs -- 0 130 Weak tuffaceous sandstone and siltstone and conglomeratic sandstone

Ttl -- 0 250 Member l: rhyolite lava; 21% crystals -- RM 0 100 Densely welded rhyolite tuff; 10–15% crystals

-- TB 0 450 Member b: weakly welded rhyolite flow tuff; 8% crystals -- RG 0 200 Moderately welded rhyolite tuff; crystal poor

-- TA 0 170 Member a: rhyolite air fall ash, surge, and ash flow tuff -- WW 0 270 Densely welded dacite tuff; 40% crystals

-- CW 0 200 Dacite tuff; 40% crystals

Tea -- 0 200 Weakly porphyritic lava flows and flow breccias

-- WB 0 100 Moderately to weakly welded rhyolite tuff; 25% crystals

Compilation of thickness of Tertiary rocks

Mountain range to the west: Fortification Range Mountain range to the east: Wilson Creek Range and Limestone Hills

Minimum Maximum Minimum Maximum 

thickness, m thickness, m thickness, m thickness, m

 Local units 0 490 Local units 0 665

 Regional units 6 2,151 Regional units 0 1,870

 Total 6 2,641 Total 0 2,535

Inferred thickness of volcanic rocks beneath valley axis, 0–1,900 m

1

Local units have limited spatial extent within a single mapped quadrangle or mountain range; typically includes lava flows and Tertiary sedimentary rocks interbedded with tuff. Local units, from uppermost unit downward are: Tbr, Rhyolite member, Blawn Formation; Tba, Trachyandesite lava flow 

member, Blawn Formation; Tgs, Sedimentary member, Ripgut Formation; Tea, Andesite flow member, Escalante Desert Formation; Ttl, Lava flow member, formation of the Gouge Eye.

2

Regional units occur in several quadrangles or mountain ranges. These volcanic-rock units are typically ash-flow tuffs. Regional units, from uppermost unit downward are: BT, Tuff member, Blawn Formation; BP, Tuff member of Rosencrans Peak, Blawn Formation; SP, Shingle Pass Tuff; IS, Isom 

Formation; RF, Ripgut Formation; RM, Mackleprang Tuff Member, Ryan Spring Formation; RG, Greens Canyon Tuff Member, Ryan Spring Formation; WW, Wah Wah Springs Formation; CW, Cottonwood Wash Tuff; WB, Windous Butte Formation; TD, Member d, formation of the Gouge Eye; TC, 

Member c, formation of the Gouge Eye; TB, Member b, formation of the Gouge Eye; TA, Member a, formation of the Gouge Eye.

3

The Limestone Hills, directly east of the southern part of Spring Valley, are essentially devoid of Tertiary volcanic rocks; not factored into valley volcanic thickness estimates.
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah 34

Table 7. Compilation of volcanic-rock thickness from mountain ranges flanking the central part of Spring Valley

[Thickness data for the northern part of Schell Creek Range from Drewes (1967); for the Snake Range from Whitebread (1969); leaders (--), unit not present] 

Description of geologic map units

Mountain range to the west: northern part of Schell Creek Range Mountain range to the east: Snake Range

Local Regional Minimum Maximum Local Regional Minimum Maximum Lithology Lithology Unit1 Unit2 thickness, m thickness, m Unit Unit thickness, m thickness, m

-- Fanglomerate Tf 0 91 No Tertiary volcanic rocks present in northern and central parts of the Snake Range

Td -- 0 365 Dacite lava; vitrophyre in part; 15-50% crystals

WW and (or) -- 0 610 Dacite tuff; vitrophyre in part CW Southern part of the Snake Range:

Tl -- 0 100 Latite; includes lava flows, tuff, and small intrusions Tc -- -- -- Conglomerate

WW and Tc -- 0 305 Conglomerate -- 200 300 Dacite tuff; lower member not welded, upper member welded (or) CW

Tco -- -- -- Conglomerate

Compilation of thickness of Tertiary rocks

Mountain range to the west: northern part of Schell Creek Range Mountain range to the east: Snake Range

Minimum Maximum Minimum Maximum 

thickness, m thickness, m thickness, m thickness, m

 Local units 0 861 Local units -- --

 Regional units 0 610 Regional units 200 300

 Total 0 1,471 Total 200 300

Inferred thickness of volcanic rocks beneath valley axis, 0–600 m

1

Local units have limited spatial extent within a single mapped quadrangle or mountain range; typically includes lava flows and Tertiary sedimentary rocks interbedded with tuff. Tf, fanglomerate; Tc, conglomerate; Td, dacite; Tl, latite; and Tco, conglomerate.

2

Regional units occur in several quadrangles or mountain ranges. These volcanic-rock units are typically ash-flow tuffs. WW, Wah Wah Springs Formation; CW, Cottonwood Wash Tuff.
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah 35

Table 8. Compilation of volcanic-rock thickness from mountain ranges flanking southern part of Hamlin Valley

[Thickness data for the southern part of the White Rock Mountains from Toth (1986) and Keith and others (1994); thickness data for the east-central Mountain Home Range from Best, Grant, and others (1987); leaders (--), unit not present] 

Description of geologic map units

Mountain range to the west: the southern part of the White Rock Mountains Mountain range to the east: the southern part of the Indian Peak Range

Local Regional Minimum Maximum Local Regional Minimum Maximum Lithology Lithology Unit1 Unit2 thickness, m thickness, m Unit Unit thickness, m thickness, m

Tp -- 300 400 Weakly bedded clay and silt deposits Tsr -- 0 500 Aphanitic rhyolite lava flows and domes; 0–30% crystals

Tbr -- 0 230 Aphanitic rhyolite lava flows and domes; 10–20% crystals Tbr -- 0 Rhyolite lava flows, domes, and dikes; 25% crystals 100

-- BT 0 150 Weakly welded tuff; crystal poor Tbm -- 0 500 Massive porphyritic mafic lava flows; 10% crystals

-- BG 0 20 Moderately welded tuff; 20% crystals -- T 100 200 Pyroclastic and epiclastic rhyolite deposits

Tscl -- 0 300 Dacite and rhyolite lava flows and minor tuff; 25% crystals Tql -- 0 Flow-layered trachyandesite lava flows, domes, and plugs 500

-- HH 20 150 Densely to moderately welded andesite tuff; 50% crystals -- CB 20 120 Densely welded rhyolite tuff; 10% crystals

Trt -- 0 100 Rhyolite lava flows Tds -- 0 250 Porphyritic dacite lava flow dome

Locally aphyric trachyandesite to trachydacite flows; 5–25% Tlf -- 0 130 -- IS 0 Densely welded trachydacite tuff; 15% crystals crystals 800

-- CB 0 30 Densely welded rhyolite tuff; 20% crystals Tha -- 0 250 Locally vesicular andesite lava flows; 25% crystals

-- CS 10 15 Moderately to densely welded rhyolite tuff; 10% crystals Tla -- 0 400 Porphyritic andesite lava flows; also sandstone and tuff

-- 0 400 Moderately to densely welded trachydacite tuff; 12% crystals -- LF 0 Moderately to densely welded dacite tuff; 45–50% crystals IS 550

-- RF 0 650 Partly to densely welded rhyolite tuff; crystal poor Trr -- 0 200 Flow-layered rhyolite flows and flow domes; crystal poor

-- 0 100 Moderately to densely welded dacite tuff; 25–35% crystals Tra -- 0 Porphyritic andesite lava flows LF 150

-- RG 50 1,400 Moderately welded rhyolite tuff; 10% crystals -- RM 50 500 Moderately welded rhyolite tuff; 20% crystals

-- WW 0 130 Densely welded dacite tuff; 40% crystals -- WW 0 2,000 Densely welded dacite tuff; 40% crystals

-- CW 12 160 Densely to moderately welded dacite tuff; 40% crystals -- CW 0 5 Densely welded dacite tuff; crystal rich

Tea -- 0 350 Weakly porphyritic andesite lava flows -- ST 0 200 Moderately welded tuff; 20–30% crystals

-- ST 0 150 Tuff; crystal rich

Compilation of thickness of Tertiary rocks

Mountain range to the west: the southern part of the White Rock Mountains Mountain range to the east: the southern part of the Indian Peak Range

Minimum Maximum Minimum Maximum 

thickness, m thickness, m thickness, m thickness, m

 Local units 300 1,510 Local units 0 2,850

 Regional units 92 3,355 Regional units 170 4,375

 Total 392 4,865 Total 170 7,225

Inferred thickness of volcanic rocks beneath valley axis, 100–3,500 m

1

Local units have limited spatial extent within a single mapped quadrangle or mountain range; typically includes lava flows and Tertiary sedimentary rocks interbedded with tuff. Local units, from uppermost unit downward are: Tp, Panaca Formation; Tsr, Rhyolite lava flow member, Steamboat Mountain 

Formation; Tbr, Rhyolite lava flow member, Blawn Formation; Tbm, Mafic lava flow member, Blawn Formation; Tql, Quartz latite; Tds, Dacite of Spanish George Spring; Tha, Hornblende andesite lava flows; Tla, Andesite member, Lund Formation; Tscl, Lava flows member, intermediatecomposition rocks of Serviceberry Canyon; Trr, Rhyolite flow member, Ryan Spring Formation; Tra, Andesite flow member, Ryan Spring Formation; Trt, Rhyolite lava flow of Tobe Spring; Tlf, Latite lava flows; Tea, Andesite flow member, Escalante Desert Formation.

2

Regional units occur in several quadrangles or mountain ranges. These volcanic-rock units are typically ash-flow tuffs. Regional units, from uppermost unit downward are: BT, Tuff member, Blawn Formation; BG, tuff of Gold Springs, Blawn Formation; T, Rhyolitic tuffs and related volcaniclastic 

deposits; HH, Harmony Hills Tuff; CB, Bauers Tuff Member, Condor Canyon Formation; CS, Swett Tuff Member, Condor Canyon Formation; IS, Isom Formation; RF, Tuff member, Ripgut Formation; RM, Mackleprang Tuff Member, Ryan Spring Formation; LF, Lund Formation; RG, Greens 

Canyon Tuff Member, Ryan Spring Formation; WW, Wah Wah Springs Formation; CW, Cottonwood Wash Tuff; ST, Sawtooth Peak Formation.
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah﻿ 36

Table 9. Compilation of volcanic-rock thickness from mountain ranges flanking northern part of Hamlin Valley

[Thickness data for the northern part of the White Rock Mountains from Best, Toth, and others (1989); thickness data for the east-central Mountain Home Range from Hintze (1986) and Hintze and Best (1987); leaders (--), unit not present] 

Description of geologic map units

Mountain range to the west: the northern part of the White Rock Mountains Mountain range to the east: east-central Mountain Home Range

Local Regional Minimum Maximum Local Regional Minimum Maximum Lithology Lithology Unit1 Unit2 thickness, m thickness, m Unit Unit thickness, m thickness, m

Tp -- -- -- Tuffaceous mudstone, siltstone, and fine-grained sandstone; Tcg -- 0 600 Weakly cemented conglomerate and sandstone

Ts -- 0 1300 Weakly consolidated fluvial and alluvial deposits -- LF 0 600 Densely welded dacite tuff; 40% crystals

Rhyolite lava flows and domes; 10–15% crystals; local -- 0 300 -- WW 0 300 Weakly to densely welded dacite tuff; 42% crystals Tbr vitrophyre

-- BT 50 120 Moderately welded rhyolite tuff, ash, and volcaniclastics; -- CW 275 400 Weak to densely welded dacite tuff; 40% crystals

Tba -- 0 80 Vesicular, aphanitic trachyandesite lava flows; 15% crystals -- EB 0 10 Weakly consolidated tuff and tuffaceous sediment and conglomerate

-- BP 0 150 Moderately welded rhyolite tuff; 25–30% crystals -- EL 0 90 Moderately to densely welded rhyolite tuff; 12% crystals

-- CB 0 80 Densely welded rhyolite tuff; 15% crystals Tea 0 12 Weakly porphyritic andesite lava flows

-- CS 10 15 Moderately to densely welded rhyolite tuff; 10% crystals -- ST 0 50 Weakly welded tuff; 50% crystals

-- IS 10 350 Moderately to densely welded trachytic tuff; 10–12% crystals Ts -- 0 30 Cobbles and boulders in weakly consolidated tuffaceous matrix

Tif -- 0 100 Lava flows; 15% crystals

-- RF 0 600 Moderately to densely welded rhyolite tuff; ~3% crystals

-- LF 0 600 Densely welded dacite tuff; 40% crystals

-- RM 0 60 Densely welded rhyolite tuff; 10–15% crystals

-- RG 600 1,400 Densely welded rhyolite tuff; 10% crystals

-- WW 0 600 Densely welded dacite tuff; 40% crystals

-- CW 0 200 Dacite tuff; 40% crystals

-- EL 0 100 Moderately to densely welded rhyolite tuff; 10–15% crystals

Tea -- 0 30 Weakly porphyritic lava flows and flow breccias

Compilation of thickness of Tertiary rocks

Mountain range to the west: the northern part of the White Rock Mountains Mountain range to the east: east-central Mountain Home Range

Minimum Maximum Minimum Maximum 

thickness, m thickness, m thickness, m thickness, m

 Local units 0 1,810 Local units 0 642

 Regional units 670 4,275 Regional units 275 1,450

 Total 670 6,085 Total 275 2,092

3

Inferred thickness of volcanic rocks beneath valley axis, 3–3,000 m

1

Local units have limited spatial extent within a single mapped quadrangle or mountain range; typically includes lava flows and Tertiary sedimentary rocks interbedded with tuff. Local units, from uppermost unit downward are: Tp, Panaca Formation; Ts, Sandstone and conglomerate; Tcg, Conglomerate; 

Tbr, Rhyolite member, Blawn Formation; Tba, Trachyandesite lava flow member, Blawn Formation; Tif, Lava flow member, Isom Formation; Tea, Andesite flow member, Escalante Desert Formation; Ts, Sedimentary rocks.

2

Regional units occur in several quadrangles or mountain ranges. These volcanic-rock units are typically ash-flow tuffs. Regional units, from uppermost unit downward are: BT, Tuff member, Blawn Formation; BP, Tuff member of Rosencrans Peak, Blawn Formation; CB, Bauers Tuff Member, Condor 

Canyon Formation; CS, Swett Tuff Member, Condor Canyon Formation; IS, Isom Formation; RF, Ripgut Formation; LF, Lund Formation; RM, Mackleprang Tuff Member, Ryan Spring Formation; RG, Greens Canyon Tuff Member, Ryan Spring Formation; WW, Wah Wah Springs Formation; CW, 

Cottonwood Wash Tuff; EB, Beers Spring Member, the Escalante Desert Formation; EL, Lamerdorf Tuff Member, Escalante Desert Formation; ST, Sawtooth Peak Formation.

3

Thicknesses possibly overstated. Truly adjacent ranges (Limestone Hills, the southern part of the Snake Range, and the western part of the Mountain Home Range) seem to contain only minor amounts of Tertiary rocks.
Table 10. Compilation of volcanic-rock thickness from mountain ranges flanking Snake Valley

[Thickness data for the Snake Range from Hose and others (1976), for the Confusion Range and Burbank Hills from Hose (1965) and Hintze (1974a); leaders (--), unit not present] 

Description of geologic map units

Mountain range to the west: Snake Range Mountain range to the east: Confusion Range and Burbank Hills

Local Regional Minimum Maximum Local Regional Minimum Maximum Lithology Lithology Unit1 Unit2 thickness, m thickness, m Unit Unit thickness, m thickness, m

No Tertiary volcanic rocks present in northern, central, and southeastern parts of the Snake Range Very minimal thickness of Tertiary volcanic rock in Confusion Range

Hintze (1974a) suggests 0–15 m of Cottonwood Wash Tuff and 15 m of Tunnel Spring Tuff

Compilation of thickness of Tertiary rocks

Mountain range to the west: Snake Range Mountain range to the east: Confusion Range and Burbank Hills

Minimum Maximum Minimum Maximum 

thickness, m thickness, m thickness, m thickness, m

 Local units -- -- Local units -- --

 Regional units -- -- Regional units 0 30

 Total -- -- Total 0 30

Inferred thickness of volcanic rocks beneath valley axis, 0–30 m

Thickness of Tertiary volcanic rock in Snake Valley and Ferguson Desert is probably 0 to at most 50 m.

Although the Cottonwood Wash Tuff and Wah Wah Springs Formation are likely to have been deposited in the Snake Valley and 

Ferguson Desert, their scant thicknesses in the adjacent ranges (southern part of Snake Range, northern part of Mountain Home 

Range, Burbank Hills, and Confusion Range) suggests that these rock units were mostly eroded away, presumably prior to Snake 

Valley graben formation.

1

Local units have limited spatial extent within a single mapped quadrangle or mountain range; typically includes lava flows and Tertiary sedimentary rocks interbedded with tuff. 

2

Regional units occur in several quadrangles or mountain ranges. These volcanic-rock units are typically ash-flow tuffs.

Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah﻿ 37
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah﻿ 38

Table 11. Compilation of volcanic-rock thickness from mountain ranges flanking southern part of Pine Valley

[Thickness data for Indian Peak Range from Best, Grant, and others (1987) and Best, Hintze, and Homes (1987); thickness data for the southern part of the Wah Wah Mountains from Best, Morris, and others (1987) and Abbott and others (1983); leaders (--), uni

Description of geologic map units

Mountain range to the west: Indian Peak Range Mountain range to the east: the southern part of the Wah Wah Mountains

Local Regional Minimum Maximum Local Regional Minimum Maximum Lithology Lithology Unit1 Unit2 thickness, m thickness, m Unit Unit thickness, m thickness, m

Ts -- 110 420 Poorly cemented fluvial-lacustrine deposits Tbrp -- 0 100 Porphyritic basaltic trachyandesite lava flows; 10% crystals

Tsr -- 0 500 Massive to flow-layered rhyolite lava flows; 30% crystals Tbra -- 0 100 Aphyric, vesicular trachyandesite lava flows

Flow-layered porphyritic rhyolite lava flows and domes; 10% Tbr -- -- -- Tsr -- 0 500 Massive to flow-layered rhyolite lava flows; 30 percent crystals crystals

Massive to slight vesicular porphyritic mafic lava flows; 10% Tbm -- 0 500 Tbr -- 0 400 Flow-layered porphyritic rhyolite lava flows and domes; 10% crystals crystals

-- CB 3 25 Densely welded rhyolite tuff; 10–15% crystals -- BT 0 400 Weakly welded tuff; 20% crystals; also intercalated volcanic sandstone

Tds -- 0 250 Porphyritic dacite lava dome Tbm -- 0 200 Vesicular trachyandesite lava flows; 30% crystals

-- IS 0 110 Densely welded trachydacite tuff; 10–15% crystals -- BTG 0 150 Weakly welded tuff; 20% crystals; contains a of trace garnet

Tha -- 0 250 Locally vesicular andesite lava flows; 25% crystals Tlt -- 100 200 Crystal-poor tuff and water laid deposits

Tla -- 0 400 Porphyritic andesite lava flows; also sandstone and tuff -- CB 0 30 Densely welded rhyolite tuff; 10–15% crystals

-- LF 55 600 Weakly to densely welded dacite tuff; 30–45% crystals -- IS 10 150 Densely welded trachydacite tuff; 10% crystals

Trr -- 0 200 Flow-layered lava flows and flow domes; crystal poor -- WP 0 200 Weakly welded tuff; 30–45% crystals

Tra -- 0 150 Nonvesicular, porphyritic andesite lava flows -- LF 0 300 Weakly to densely welded dacite tuff; 30–45% crystals

-- RM 0 70 Moderately welded rhyolite tuff; 20% crystals -- WW 0 460 Densely welded dacite tuff; 40–50% crystals

-- RG 0 500 Weakly welded tuff; crystal poor -- CW 0 20 Densely welded dacite tuff; 41% crystals

-- WW 0 520 Densely welded dacite tuff; 40–50% crystals Teb -- 0 40 Volcanic sandstone; also, poorly cemented pebble to cobble gravel

-- CW 0 305 Densely welded dacite tuff; 41% crystals -- EL 0 650 Densely welded dacite tuff; 40–50% crystals

-- EL 100 170 Densely welded rhyolite tuff; 11–18% crystals Tea -- 0 360 Nonvesicular, porphyritic andesite lava flows

Tea -- 0 60 Nonvesicular, porphyritic andesite lava flows Ter -- 0 250 Densely welded dacite tuff; 41% crystals

Ter -- -- -- Flow-layered rhyolite lava; 2% crystals -- EM 0 300 Weakly welded tuff; crystal poor

-- EM 270 500 Weakly welded tuff; crystal poor Toa -- -- -- Nonvesicular andesite lava

-- ST 0 250 Moderately welded tuff; 25% crystals Tcg -- 0 80 Pebble to boulder conglomerate

Compilation of thickness of Tertiary rocks

Mountain range to the west: Indian Peak Range Mountain range to the east: the southern part of the Wah Wah Mountains

Minimum Maximum Minimum Maximum 

thickness, m thickness, m thickness, m thickness, m

 Local units 110 2,730 Local units 100 2,230

 Regional units 428 3,050 Regional units 10 2,660

 Total 538 5,780 Total 110 4,890

Inferred thickness of volcanic rocks beneath valley axis, 10–2,800 m

1

Local units have limited spatial extent within a single mapped quadrangle or mountain range; typically includes lava flows and Tertiary sedimentary rocks interbedded with tuff. Local units, from uppermost unit downward are: Ts, Volcanic sandstone and conglomerate; Tbrp, Porphyritic member, 

formation of Brimstone Reservoir; Tbra, Aphyric member, formation of Brimstone Reservoir; Tsr, Rhyolite lava flow member, Steamboat Mountain Formation; Tbr, Rhyolite lava flow member, Blawn Formation; Tbm, Mafic lava flow member, Blawn Formation; Tlt, Lapilli tuff; Tds, Dacite of 

Spanish George Spring; Tha, Hornblende andesite lava flows; Tla, Andesite member, Lund Formation; Trr, Rhyolite flow member, Ryan Spring Formation; Tra, Andesite flow member, Ryan Spring Formation; Teb, Beers Spring Member, Escalante Desert Formation; Tea, Andesite flow member, 

Escalante Desert Formation; Ter, Rhyolite flow member, Escalante Desert Formation; Toa, Andesitic lava flows; Tcg, Conglomerate.

2

Regional units occur in several quadrangles or mountain ranges. These volcanic-rock units are typically ash-flow tuffs. Regional units, from uppermost unit downward are: BT, Tuff member, Blawn Formation; BTG, Garnet-bearing tuff member, Blawn Formation; CB, Bauers Tuff Member, Condor 

Canyon Formation; IS, Isom Formation; WP, Wallaces Peak Member, Needles Range Formation; LF, Lund Formation; RM, Mackleprang Tuff Member, Ryan Spring Formation; RG, Greens Canyon Tuff Member, Ryan Spring Formation; WW, Wah Wah Springs Formation; CW, Cottonwood 

Wash Tuff; EL, Lamerdorf Tuff Member, Escalante Desert Formation; EM, Tuff of Marsden Spring, Escalante Desert Formation; ST, Sawtooth Peak Formation.
Table 12. Compilation of volcanic-rock thickness from mountain ranges flanking northern part of Pine Valley

[Thickness data for central Mountain Home Range from Hintze (1981), Best and Hintze (1980), and Best, Hintze, and Homes (1987); thickness data for the northern part of the Wah Wah Mountains from Wheeler (1980) and Hintze (1974b); leaders (--), unit not pre

Description of geologic map units

Mountain range to the west: central Mountain Home Range Mountain range to the east: the northern part of the Wah Wah Mountains

Local Regional Minimum Maximum Local Regional Minimum Maximum Lithology Lithology Unit1 Unit2 thickness, m thickness, m Unit Unit thickness, m thickness, m

Ts -- 110 420 Partly consolidated clayey, sandy, and conglomeratic deposits Tb -- 0 500 Volcanic (?) landslide-related breccia masses

Tc -- 0 20 Unconsolidated conglomerate and tuffaceous sandstone Tc -- 0 50 Conglomerate and tuffaceous sandstone

-- CB 0 6 Densely welded rhyolite tuff; 20% crystals Tba -- 0 150 Mafic, aphanitic, vesicular lava flows; some phenocrysts

-- IS 0 6 Densely welded trachytic tuff; 10% crystals -- BT 0 30 Moderately welded rhyolite tuff, ash, and clastics; 10% crystals

-- LF 30 112 Moderately welded dacite tuff; 39% crystals -- IS 0 28 Densely welded trachytic tuff; 10% crystals

-- WW 0 370 Moderately to densely welded dacite tuff; 42% crystals -- WP 0 84 Tuff

-- CW 90 460 Weak to densely welded dacite tuff; 42% crystals -- LF 0 70 Moderately welded dacite tuff; 42% crystals

Weakly consolidated tuff and tuffaceous sediment and -- EB 24 55 -- WW 0 116 Moderately to densely welded dacite tuff; 45% crystals conglomerate

-- EL 0 43 Moderately to densely welded rhyolite tuff; 12% crystals -- CW 20 40 Moderately welded dacite tuff; 37% crystals

Tea -- 0 46 Massive phenocryst-poor andesite lava -- TS 0 61 Rhyolite tuff

-- ST 0 61 Friable, porous, weakly welded tuff; 33–50% crystals Tp -- 0 152 Andesite lava and lava flow domes; also dacite tuff

Compilation of thickness of Tertiary rocks

Mountain range to the west: central Mountain Home Range Mountain range to the east: the northern part of the Wah Wah Mountains

Minimum Maximum Minimum Maximum 

thickness, m thickness, m thickness, m thickness, m

 Local units 110 486 Local units 0 302

 Regional units 144 1,113 Regional units 20 979

 Total 254 1,599 Total 20 1,281

Inferred thickness of volcanic rocks beneath valley axis, 20–1,100 m

1

Local units have limited spatial extent within a single mapped quadrangle or mountain range; typically includes lava flows and Tertiary sedimentary rocks interbedded with tuff. Local units, from uppermost unit downward are: Tb, Breccia; Ts, Sedimentary deposits; Tc, Conglomerate; Tba, Mafic flow 

member, Blawn Formation; Tea, Andesite flow member, Escalante Desert Formation; Tp, Pre-Tunnel Spring volcanic rocks.

2

Regional units occur in several quadrangles or mountain ranges. These volcanic-rock units are typically ash-flow tuffs. Regional units, from uppermost unit downward are: BT, Tuff member, Blawn Formation; CB, Bauers Tuff Member, Condor Canyon Formation; IS, Isom Formation; WP, Wallaces 

Peak Member, Needles Range Formation; LF, Lund Formation; WW, Wah Wah Springs Formation; CW, Cottonwood Wash Tuff; TS, Tunnel Spring Tuff; EB, Beers Springs Member, the Escalante Desert Formation; EL, Lamerdorf Tuff Member, Escalante Desert Formation; ST, Sawtooth Peak 

Formation.

Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah﻿ 39
Tertiary Volcanic Thicknesses, East-Central Nevada and West-Central Utah﻿ 40

Table 13. Compilation of volcanic-rock thickness from mountain ranges flanking Wah Wah Valley

[Thickness data for the southern part of the Wah Wah Mountains from Abbott and others (1983) and Wheeler (1980); thickness data for the San Francisco Mountains from Best, Lemmon, and Morris (1989); leaders (--), unit not present] 

Description of geologic map units

Mountain range to the west: the southern part of the Wah Wah Mountains Mountain range to the east: San Francisco Mountains

Local Regional Minimum Maximum Local Regional Minimum Maximum Lithology Lithology Unit1 Unit2 thickness, m thickness, m Unit Unit thickness, m thickness, m

Tbrp -- 0 100 Porphyritic basaltic trachyandesite lava flows; 10% crystals Tdf -- 0 100 Cobble to boulder volcanic debris flow deposits

Tbra -- 0 100 Aphyric, vesicular trachyandesite lava flows Tsr -- -- -- Vesicular, porphyritic rhyolite lava flows and domes

Tbr -- 0 400 Flow-layered porphyritic rhyolite lava flows and domes; 10% crystals Tsb -- 0 100 Aphyric to porphyritic, vesicular basalt lava flows

Weakly welded tuff; 20% crystals; also intercalated volcanic -- 0 400 Tbr -- -- -- Flow–layered porphyritic rhyolite lava flows and domes; 20–30% crystals BT sandstone

Tbm -- 0 200 Vesicular trachyandesite lava flows; 30% crystals -- BT 0 650 Weakly welded tuff; 20% crystals; also intercalated volcanic sandstone

BTG 0 150 Weakly welded tuff; 20% crystals; contains a of trace garnet Tbm -- 0 200 Vesicular trachyandesite lava flows; 25% crystals

Tlt -- -- -- Crystal-poor tuff and water laid deposits Tsp -- 0 1,000 Flow-layered trachydacite lava flows: 33% crystals

-- CB 0 30 Densely welded rhyolite tuff; 10–15% crystals -- CB 0 18 Densely welded rhyolite tuff; 10% crystals

-- IS 0 28 Densely welded trachydacite tuff; 10% crystals -- IS 0 5 Densely welded trachydacite tuff; 10% crystals

-- WP 0 200 Weakly welded tuff; 30–45% crystals -- TCT 0 200 Densely to moderately welded tuff; 40% crystals

-- LF 350 500 Weakly to densely welded dacite tuff; 30–45% crystals -- LF 0 300 Densely welded dacite tuff; 40% crystals

-- WW 0 460 Densely welded dacite tuff; 30–45% crystals -- WW 0 250 Densely welded dacite tuff; 40% crystals

-- CW 0 20 Densely welded dacite tuff; 30–45% crystals -- CW 0 10 Densely welded dacite tuff; 30–45% crystals

-- 0 40 Volcanic sandstone; also, poorly cemented pebble to cobble gravel -- EL 0 Moderately welded tuff; 15% crystals Teb 200

EL 0 650 Densely welded rhyolite tuff; 10–15% crystals Ths -- 0 700 Porphyritic andesite to dacite lava flows; 10% crystals

Tela -- -- -- Nonvesicular, aphanitic to crystal poor andesite lava flows Tsh -- 0 600 Nonvesicular, andesite lava flows; 20% crystals

EM 0 70 Weakly welded tuff; crystal poor Thr -- 0 10 Pebble, cobble, and boulder conglomerate; siltstone to shale matrix

Toa -- -- -- Nonvesicular andesite lava

Tcg -- 0 80 Pebble to boulder conglomerate

Compilation of thickness of Tertiary rocks

Mountain range to the west: the southern part of the Wah Wah Mountains Mountain range to the east: San Francisco Mountains

Minimum Maximum Minimum Maximum 

thickness, m thickness, m thickness, m thickness, m

 Local units 0 920 Local units 0 2,710

 Regional units 350 2,328 Regional units 0 1,633

 Total 350 3,248 Total 0 4,343

Inferred thickness of volcanic rocks beneath valley axis, 0–1800 m

1

Local units have limited spatial extent within a single mapped quadrangle or mountain range; typically includes lava flows and Tertiary sedimentary rocks interbedded with tuff. Local units, from uppermost unit downward are: Tdf, Volcanic debris flow; Tbrp, Porphyritic member, formation of Brimstone 

Reservoir; Tbra, Aphyric member, formation of Brimstone Reservoir; Tsr, Rhyolite lava-flow member, Steamboat Mountain Formation; Tsb, Basalt lava-flow member, Steamboat Mountain Formation; Tbr, Rhyolite lava flow member, Blawn Formation; Tbm, Mafic lava flow member, Blawn Formation; 

Tlt, Lapilli tuff; Tsp, Quartz latite of Squaw Peak; Teb, Beers Spring Member, the Escalante Desert Formation; Tela, Andesite in Lamerdorf Tuff Member, Escalante Desert Formation; Toa, Andesitic lava flows; Ths, Horn Silver Andesite; Tsh,Andesite of Shauntie Hills; Tcg, Conglomerate; Thr, 

Conglomerate of High Rock Pass area.

2

Regional units occur in several quadrangles or mountain ranges. These volcanic-rock units are typically ash-flow tuffs. Regional units, from uppermost unit downward are: BT, Tuff member, Blawn Formation; BTG, Garnet-bearing tuff member, Blawn Formation; CB, Bauers 

Tuff Member, Condor Canyon Formation; IS, Isom Formation; WP, Wallaces Peak Member, Needles Range Formation; TCT, Three Creeks Tuff Member, Bullion Canyon Volcanics; LF, Lund Formation; WW, Wah Wah Springs Formation; CW, Cottonwood Wash Tuff; 

EL, Lamerdorf Tuff Member, Escalante Desert Formation; EM, Tuff of Marsden Spring, Escalante Desert Formation.