U.S. Department of the Interior

U.S. Geological Survey

Professional Paper 1757

The Inskip Formation, the Harmony Formation, and the 

Havallah Sequence of Northwestern Nevada—An 

Interrelated Paleozoic Assemblage in the Home of the 

Sonoma Orogeny

The Inskip Formation, the Harmony 

Formation, and the Havallah Sequence of 

Northwestern Nevada—An Interrelated 

Paleozoic Assemblage in the Home of the 

Sonoma Orogeny

By Keith B. Ketner

Professional Paper 1757 

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:

Ketner, Keith B., 2008, The Inskip Formation, the Harmony Formation, and the Havallah Sequence of Northwestern 

Nevada—An Interrelated Paleozoic Assemblage in the Home of the Sonoma Orogeny: U.S. Geological Survey 

Professional Paper 1757, 21 p.
iii

Contents

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

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

Geologic Setting ...................................................................................................................................1

Early Work..............................................................................................................................................2

Purpose and Method............................................................................................................................3

East Range ......................................................................................................................................................3

Preble Formation...................................................................................................................................3

Valmy Formation....................................................................................................................................3

Chert Couplet of Table Mountain...............................................................................................4

Inskip Formation....................................................................................................................................4

Lower Unit.....................................................................................................................................4

Upper Unit .....................................................................................................................................4

Base of the Inskip ........................................................................................................................4

Triassic Rocks........................................................................................................................................5

Nomenclatural Problems in the East Range ....................................................................................5

Northern Exposures ....................................................................................................................5

Southern Exposures ....................................................................................................................5

Metamorphism ......................................................................................................................................5

Megastructures of the East Range....................................................................................................5

Petrologic Features of the Inskip Formation .............................................................................................7

Source of Data.......................................................................................................................................7

Metasedimentary Rocks......................................................................................................................7

Metaigneous Rocks..............................................................................................................................9

Metabasalt ...................................................................................................................................9

Metafelsite..................................................................................................................................10

The Felsite Problem...................................................................................................................10

Depositional Conditions of the Inskip..............................................................................................11

Hot Springs Range.......................................................................................................................................11

Source of Data.....................................................................................................................................11

Strata in the Hot Springs Range Underlying the Inskip-Equivalent Rocks................................13

Stratigraphic Units Equivalent to the Inskip in Age and General Aspect..................................13

Harmony Formation ...................................................................................................................13

Home Ranch Subterrane ..........................................................................................................13

Lower Poverty Peak Sequence ...............................................................................................13

Upper Poverty Peak Sequence ...............................................................................................13

Poverty Peak–Golconda Mélange ..........................................................................................14

Phyllite and Shale Sequence...................................................................................................14

Triassic and Jurassic Rocks .............................................................................................................14

Megastructures of the Hot Springs Range.....................................................................................14

Osgood Mountains.......................................................................................................................................14

Sonoma Range .............................................................................................................................................14

Stratigraphic and Structural Issues ................................................................................................14
iv

Havallah Sequence.............................................................................................................................15

Triassic Rocks......................................................................................................................................15

Battle Mountain............................................................................................................................................15

North Slope..........................................................................................................................................15

South Slope..........................................................................................................................................15

The Havallah Sequence.....................................................................................................................16

Unconformities....................................................................................................................................16

Relation of the Inskip and the Harmony Formations to the Havallah Sequence in the Arkosic 

Triangle ............................................................................................................................................16

Sonoma Orogeny and Golconda Thrust...................................................................................................16

Conclusions...................................................................................................................................................17

Acknowledgments.......................................................................................................................................18

References Cited..........................................................................................................................................18

Figures

1. Map showing northwestern Nevada the locations of figures 2 and 11. Also 

shown, in the inset outline of Nevada, are the locations of the arkosic 

triangle and the area shown in figure 1 ....................................................................................2

2. Map showing the central part of the East Range modified from Whitebread 

(1994), Whitebread and Sorensen (1983), and Johnson (1977) .............................................6

3–10. Photographs showing:

 3. Sheared arkosic sandstone from the lower Inskip Formation. Clasts are

quartz, quartzite, K-feldspar, and plagioclase ..................................................................7

 4. Unpolarized view of figure 3 ................................................................................................7

 5. Coarse arkosic sandstone from a massive bed in the lower Inskip Formation. 

This specimen shows no evidence of shear. Crossed polarizers .................................7

 6. Chert from the uppermost part of the Inskip Formation. The carbon-rich 

stylolites are preserved in this specimen, and radiolarians are sporadically 

preserved in others. The only effect of the relatively slight metamorphism 

was to slightly increase the grain size. Unpolarized .......................................................8

 7. Metabasalt from the upper member of the Inskip Formation. Megacrysts 

are magnesian hornblende, groundmass is albite and ilmenite. This 

specimen shows slight evidence of shear. Crossed polarizers.....................................8

 8. Relatively unsheared porphyritic felsite from the upper part of the Inskip 

Formation. Megacrysts are albite, groundmass is quartz and biotite. Crossed

polarizers ................................................................................................................................8

 9. Sheared felsite from the lower part of the Inskip Formation. Light bands are 

albite and quartz, medium bands are muscovite, dark bands are biotite. 

Uncrossed polarizers............................................................................................................8

 10. Sheared porphyritic felsite from the Rochester Rhyolite at the base of the 

Triassic sequence immediately overlying the Inskip Formation. 

Megacrysts are albite, groundmass is albite, quartz, and muscovite. 

Crossed polarizers.................................................................................................................9
v

11. Generalized and simplified map showing part of the Hot Springs Range 

modified from Jones (1997a, b) showing the Hot Springs Range syncline 

and the northern Hot Springs Range anticline ......................................................................12

Tables

1. Chemical composition of metabasalt of the Inskip Formation, East Range, Nevada......10

2. Chemical composition of metafelsites of the Inskip Formation and the 

Triassic Rochester Rhyolite, East Range ................................................................................11

Abstract

An area between the towns of Winnemucca and Battle 

Mountain in northwestern Nevada, termed the arkosic triangle, 

includes the type areas of the middle to upper Paleozoic Inskip 

Formation and Havallah sequence, the Upper Devonian to 

Mississippian Harmony Formation, the Sonoma orogeny, 

and the Golconda thrust. According to an extensive body 

of scientific literature, the Havallah sequence, a diverse 

assemblage of oceanic rocks, was obducted onto the continent 

during the latest Permian or earliest Triassic Sonoma orogeny 

by way of the Golconda thrust. This has been the most 

commonly accepted theory for half a century, often cited 

but rarely challenged. The tectonic roles of the Inskip and 

Harmony Formations have remained uncertain, and they have 

never been fully integrated into the accepted theory. New, and 

newly interpreted, data are incompatible with the accepted 

theory and force comprehensive stratigraphic and tectonic 

concepts that include the Inskip and Harmony Formations as 

follows: middle to upper Paleozoic strata, including the Inskip, 

Harmony, and Havallah, form an interrelated assemblage that 

was deposited in a single basin on an autochthonous sequence 

of Cambrian, Ordovician, and lowest Silurian strata of the 

outer miogeocline. Sediments composing the Upper Devonian 

to Permian sequence entered the basin from both sides, 

arkosic sands, gravel, limestone olistoliths, and other detrital 

components entered from the west, and quartz, quartzite, 

chert, and other clasts from the east. Tectonic activity was 

expressed as: (1) Devonian uplift and erosion of part of the 

outer miogeocline; (2) Late Devonian depression of the same 

area, forming a trough, probably fault-bounded, in which the 

Inskip, Harmony, and Havallah were deposited; (3) production 

of intraformational and extrabasinal conglomerates derived 

from the basinal rocks; and (4) folding or tilting of the east 

side of the depositional basin in the Pennsylvanian. These 

middle to upper Paleozoic deposits were compressed in the 

Jurassic, causing east-verging thrusts in the eastern part of 

the depositional basin (Golconda thrust) and west-verging 

thrusts and folds in the western part. Hypotheses involving a 

The Inskip Formation, the Harmony Formation, and 

the Havallah Sequence of Northwestern Nevada—An 

Interrelated Paleozoic Assemblage in the Home of the 

Sonoma Orogeny

By Keith B. Ketner

far-traveled allochthon that was obducted from an ocean or 

back-arc basin are incompatible with modern observations and 

concepts.

Introduction

Geologic Setting 

This report concerns middle to upper Paleozoic rocks 

in an area of northwestern Nevada, between the towns of 

Winnemucca and Battle Mountain, termed the “arkosic 

triangle” (Ketner and others, 2005). This area (fig. 1) includes 

the type section of the Inskip Formation, the Harmony 

Formation, the Havallah sequence, the type Sonoma orogeny, 

and the type area of the Golconda thrust. For many years, 

tectonic theories regarding middle to upper Paleozoic rocks 

of this area have held that the Havallah sequence, a mostly 

deepwater deposit, comprises a far-traveled allochthon that 

was displaced from basins to the west by way of the Golconda 

thrust in the Late Permian or Early Triassic. A link between 

the Golconda thrust and the Sonoma orogeny was commonly 

assumed. The enigmatic Inskip and Harmony Formations were 

not fully integrated into stratigraphic and tectonic concepts.

The present report uses new and old evidence to integrate 

the three named stratigraphic units, to downgrade the regional 

importance of the Sonoma orogeny, to reduce the extent of the 

Golconda thrust, and to revise the age of that thrust.

The Inskip Formation, the Harmony Formation, and 

the Havallah sequence constitute a structurally disrupted 

stratigraphic assemblage that records a history of extreme 

tectonic and igneous activity from the Devonian to the 

Permian. Only recently have their ages become reasonably 

accurate as cited in the present work. Therefore, only recently 

has it become possible to construct a tectonic theory that 

involves all the middle to upper Paleozoic sequences and is 

applicable both to the arkosic triangle and regionally.

An understanding of the stratigraphy and structure of 

the East Range, including the Inskip Formation, is essential 
2 Inskip Formation, Harmony Formation, and Havallah Sequence of Northwestern Nevada

NEVADA

118° 117°

41 41° °

117°30’

117° 117°30’

40°15’ 40° East Range15’

Fig. 2 Battle

Mountain

Battle

Mountain

Edna Mountain Sonoma

Range

Winnemucca

Osgood Mountains

Arkosic Triangle

Fig. 2 Fig. 11

Fig. 11

Hot Springs Range

0

0

10 20 MILES

10 20 KILOMETERS

Figure 1. Northwestern Nevada 

showing the locations of figures 

2 and 11. Also shown, in the inset 

outline of Nevada, are the locations 

of the arkosic triangle and the area 

shown in figure 1.

for an understanding of the stratigraphy and tectonics of 

the region; consequently, the rocks of this range, especially 

the Inskip Formation, are herein described in detail. Other 

areas in the arkosic triangle have been well described in 

numerous publications, some of which are cited. The Upper 

Devonian to Mississippian parts of the Inskip Formation 

and of the correlative sequences described here have a very 

conspicuous feature in common—coarse-grained arkosic 

sedimentary strata. These coarse-grained arkosic rocks are 

unique in Nevada and call for a unique explanation of origin. 

The ages of detrital zircons in these rocks point to an origin 

in northwestern Canada (Gehrels and Dickinson, 2000; 

Gehrels and others, 2000). That fact plus the coarse grain size 

and immaturity of the arkosic deposits led to the theory that 

the arkosic sediments were eroded from a part of the North 

American plate that rifted away from the continent at the 

latitude of northern British Columbia and drifted southward 

to the latitude of Nevada. From this position it shed coarse 

arkosic sediments eastward to the arkosic triangle in Late 

Devonian to Mississippian time (Ketner and others, 2005). 

Supporting this theory is the presence, at the base of the 

arkosic deposits, of large olistoliths that contain Cambrian 

Archaeocyathids endemic to northwestern Canada and other 

distant northern locations (DeBrenne and others, 1990). The 

dimensions of some of these olistoliths, measured in meters, 

imply a very close source area.

Early Work

The standard regional model of Paleozoic tectonism, 

including the Sonoma orogeny and Golconda thrust, evolved 

in northwestern Nevada and was published in the form of 

reconnaissance maps and commentary by Ferguson and others 

(1951, 1952) and Muller and others (1951). Their pioneering 
East Range 3

efforts, made difficult by a scarcity of reliable paleontological 

dating, were supplemented later by frequently quoted papers 

by Roberts and others (1958) and Silberling and Roberts 

(1962). Subsequent pertinent maps and accounts are cited in 

the following sections.

Purpose and Method

The purpose of this report is to describe the lithic composition of the Inskip Formation of the East Range, establish its 

relation to correlative strata of the Hot Springs Range, and integrate those two sequences into the regional stratigraphy and 

structure. In addition, an attempt is made to reduce the Sonoma “orogeny” to a minor, local event and to revise the age 

of the Golconda thrust. More than 150 samples of the Inskip 

were collected and sectioned for petrologic examination, and 

X-ray diffraction diagrams were made of almost all of them. 

Eleven samples of igneous rocks were analyzed chemically. In 

the following paragraphs, the stratigraphy and structure of the 

East Range are discussed, followed by a detailed description 

of the Upper Devonian to Permian Inskip Formation. 

East Range

Preble Formation

The oldest rocks exposed in the East Range are predominantly carbonate strata, here correlated with the type Preble 

Formation of Cambrian and Early Ordovician age (fig. 2). 

Lower beds have been altered so intensely by a combination of regional and contact metamorphism that the original 

composition and bedding features are obscure. Upper beds are 

graded and consist of interbedded limestone, quartzose detrital 

sediments, and tabular bodies of metabasalt near the boundary 

with the overlying Valmy Formation. 

The uppermost beds of the Preble, just below the Valmy 

Formation, contain conodonts that, in two places, have been 

dated at the boundary between latest Cambrian and earliest 

Ordovician age (Whitebread, 1994) and a collection from SE 

1/4, sec. 12, T. 30 N., R. 36 E., Bartomes Spring quadrangle, 

identified by John Repetski (written commun., 2000). Lower 

beds are paleontologically undated but are interpreted, from 

their stratigraphic position and general resemblance to the type 

Preble Formation (Hotz and Willden, 1964), to be of Middle 

to Late Cambrian age. The Preble Formation is regarded as 

autochthonous, as it overlies the Osgood Mountain Quartzite 

with a sedimentary contact in the Osgood Mountains (Hotz 

and Willden, 1964). This quartzite unit is generally correlated 

with the Prospect Mountain Quartzite, a well-established formation of the miogeocline.

On some published maps of the East Range, the Preble 

is designated as being of Triassic age (Ferguson and others, 

1951; Muller and others, 1951; Johnson, 1977; Stewart and 

Carlson, 1978). This resulted in long-lasting misinterpretations 

of the tectonic history of the region because it seemed to 

mandate a major thrust fault separating the Preble from the 

overlying Valmy Formation. A fault is no longer necessary; 

the two formations are in sequential stratigraphic order and, in 

fact, the contact is depositional and gradational as described in 

the next section.

Valmy Formation

The term Valmy Formation has been applied by many 

authors to relatively deepwater, siliceous deposits of known 

Ordovician age in northern Nevada. In the East Range, lower 

strata of the Valmy consist mainly of argillite, chert, greenstone, and limestone. Middle strata are mainly quartzite and 

minor interbedded chert, argillite, and greenstone. Upper strata 

are mainly shale, siltstone, greenstone, and chert.

In the East Range, conodonts from the older beds are of 

Early to Middle Ordovician age (Whitebread, 1994; Ketner 

and others, 2000). Massive quartzite beds in the middle of the 

formation are regarded as Middle Ordovician on the basis of 

their stratigraphic position and lithic correlation with dated 

strata elsewhere. The boundaries of Lower, Middle, and Upper 

Ordovician in terms of their paleontological content, as used 

here and in earlier publications on the Inskip Formation by 

Ketner and others (2000, 2005), are longstanding and are comparable with usage in older publications. Readers should note, 

however, that boundaries between these intervals worldwide 

have been changed in terms of their paleontological content as 

described by Webby and others (2004). The principal result, 

locally, is to move the massive quartzite unit of the Valmy 

from the Middle to the Upper Ordovician.

The Valmy Formation has been wholly or partly displaced by low-angle faults in many parts of Nevada, but in 

the East Range the Valmy is autochthonous as it overlies the 

Preble Formation with a depositional, gradational contact. 

This contact is clearly exposed 2 km east of Kyle Hot Springs 

in the Bartomes Spring 7.5-minute quadrangle and somewhat 

less clearly near the center of sec. 6, T. 31 N., R. 37 E., in the 

Dun Glen quadrangle (Whitebread, 1994). The East Range is 

not unique in this respect, as indicated by the following examples. In northern Nevada, gradational, depositional contacts 

between autochthonous Cambrian carbonate strata and the 

Valmy Formation are well exposed in the Bull Run Mountains 

(Ketner and others, 1993) and at Bearpaw Mountain (Ketner and others, 1995) where the contact zone is dated at the 

Cambrian-Ordovician boundary by conodont collections. In 

southern Nevada the gradational contact between a Cambrian 

carbonate unit and the Valmy-equivalent Palmetto Formation 

is exposed in the Montezuma Range at Railroad Pass where 

the gradational nature of the contact is confirmed by numerous conodont collections (Repetski and Ketner, unpub. data, 

1993). The precise locations of these and other exposures are 

recorded in a previous publication (Ketner, 1998).
4 Inskip Formation, Harmony Formation, and Havallah Sequence of Northwestern Nevada

Chert Couplet of Table Mountain

A conspicuous bedded chert couplet exposed on the east 

side of Table Mountain in the central part of the East Range 

(Ketner and others, 2000) is composed of a lower member 

of black chert and an upper member of thickly bedded white 

chert. The combined members, commonly less than 10 m 

thick, lie at the top of the Valmy Formation regionally. The 

age of the couplet, where it is well represented in northeastern 

Nevada, is latest Ordovician and Early Silurian (Ketner, 1991; 

Ketner and Ross, 1990; Noble and others, 1997). In many 

exposures regionally, the upper member of this couplet is 

mineralized and discolored by oxidation of sulfides. On many 

published maps, the chert couplet has been included in the 

Valmy Formation, and that practice is continued here.

Inskip Formation

The name Inskip Formation is used exclusively in the 

East Range and, on most published maps, is applied only to 

a thick marine sequence of strata exposed on the west side of 

the range where it overlies the Ordovician Valmy Formation 

disconformably (Whitebread, 1994). The significance of the 

Inskip Formation was not understood at first, owing to scarcity 

of paleontologic dating and lack of accurate petrologic data. 

The formation therefore did not figure significantly into the 

early formulation of stratigraphic, structural, and tectonic 

concepts.

The thickness of the Inskip is somewhat uncertain owing 

to incomplete exposure, internal folding, possible inconspicuous faults, and bedding-parallel shearing strain. In this 

report, the Inskip is divided into the same lower and upper 

stratigraphic units designated by Whitebread (1994).

Lower Unit

The lower unit of the Inskip consists of arkosic 

conglomerate and arkosic sandstone, shale, limestone, 

basalt, and felsite. Basalt and felsite are scarce relative to 

their presence in the upper unit. Composition of clasts in the 

conglomerate and sandstone, roughly in order of abundance, 

are quartz, quartzite, feldspar, arkosic sandstone, siltstone, 

shale, and radiolarian chert. Sparse limestone sequences, 

commonly a few meters thick, are recrystallized, and all 

contain abundant siliceous detrital grains. A rough estimate of 

the thickness of the lower unit based on Whitebread (1994) is 

about 1 km.

Corals and conodonts from limestone beds, the only 

fossils that have been reported, are extremely rare. One 

limestone sample collected from the lowest beds of the 

Inskip contains conodonts of Late Devonian to Mississippian 

age (locations shown in Whitebread, 1994, and Ketner and 

others, 2000). Those fossils recovered from the lower but not 

lowest part of the Inskip, formerly thought to be long-ranging 

(Whitebread, 1978), have been reevaluated and are now 

regarded as indicating an Osagean, late Early Mississippian 

age (Ketner and others, 2000). Corals collected from the lower 

part are of Meramecian age, early Late Mississippian (Sando, 

1993). No direct evidence exists of beds of Pennsylvanian age 

in the Inskip, possibly due to the general scarcity of fossils or 

a depositional hiatus.

Upper Unit

The upper unit of the Inskip consists of abundant 

tabular and irregular bodies of basaltic and felsitic rocks 

interstratified with quartzite, shale, and sparse arkosic and 

limy beds. High in the upper unit are fine-grained, highly 

quartzose strata containing abundant stylolites. These strata, 

which are minimally sheared, are interpreted to be somewhat 

recrystallized bedded chert. The thickness of the upper unit, 

in spite of the uncertainties listed above, is at least 1 km. 

One limestone outcrop, high in the sequence, among strata 

interpreted to be altered chert, yielded Permian and reworked 

Early Pennsylvanian conodonts (Ketner and others, 2000).

Base of the Inskip

As originally mapped and described by Ferguson and 

others (1951), the Inskip lies with a concordant sedimentary 

contact on the Ordovician Valmy Formation (then called 

Leach Formation). Later, this contact was stated by 

Silberling and Roberts (1962, p. 13) to be “for the most 

part steeply faulted” and was shown on their sketch map as 

entirely faulted. Whitebread (1994) mapped it in detail as 

a sedimentary contact. I concur with Whitebread and with 

Ferguson and others because the contact of the Inskip with 

the Valmy Formation is remarkably parallel with bedding, 

above and below, along its entire exposed length of 20 km, 

and the stratigraphic base of the Inskip is in contact with the 

stratigraphic top of the Cambrian-Ordovician sequence, a 

perfectly normal disconformable depositional succession. 

Moreover, pebbles and cobbles of quartzite in the Inskip 

are lithically identical to quartzite beds in the underlying 

Valmy. The concept of Hargett and others (2000) that 

the Valmy has been thrust over the Inskip is structurally 

impossible, given that the stratigraphic base of the Inskip is 

in concordant contact with the stratigraphic top of the Valmy. 

The disconformity between these two units, and the coarsegrained arkosic beds of the Inskip, are local expressions of 

the Late Devonian to Early Mississippian Antler orogeny. 

The disconformable nature of the contact indicates uplift 

and erosion, but structural evidence of folding and thrust 

faulting during that event are entirely lacking here. Because 

such a relationship is contrary to generally accepted beliefs, 

additional support is offered. The East Range is not unique 

in this respect. Several other exposures in Nevada display 

concordant depositional contacts between lower Paleozoic 

deepwater sequences and overlying Late Devonian to 

Mississippian strata. The precise locations of some of these 
East Range 5

exposures are recorded in a previous publication (Ketner, 

1998).

Triassic Rocks

In the East Range, a thick sequence of Triassic strata lies 

concordantly on Paleozoic strata. Most of these are sedimentary rocks, but the basal unit is the Rochester Rhyolite, 

a member of the Koipato Group. It lies concordantly on the 

uppermost exposures of the Inskip Formation.

Nomenclatural Problems in the East Range

Northern Exposures

The terms Inskip and Havallah have been applied 

inconsistently to upper Paleozoic deepwater strata in the East 

Range. Immediately north of Rockhill Canyon in the Dun Glen 

quadrangle (Whitebread, 1994), a small area of limestone, 

chert, basalt, felsite, and arkosic rock was originally mapped 

as Inskip by Ferguson and others (1951) and as Havallah 

Formation by subsequent authors (Silberling and Roberts, 

1962; Johnson, 1977; Stewart and Carlson, 1978; Whitebread, 

1994). Most of these rocks appear to be somewhat less 

metamorphosed than strata assigned by all of those authors 

to the Inskip Formation, and these rocks are separated from 

the uncontested Inskip by a reverse or thrust fault, the Willow 

Creek thrust of Whitebread (1994). Collections of conodonts 

from these strata range from Mississippian to Permian in age, 

and fusulinids are of Permian age (Whitebread, 1994). The 

random pattern of ages of these fossil collections suggests the 

presence either of unmapped faults or possibly of reworked 

conodonts. In any event, the age range of these beds as 

indicated by fossils, their lithic composition (especially 

the arkosic rocks), and the position of the beds adjacent to 

uncontested exposures of the Inskip suggest their original 

assignment to the Inskip Formation by Ferguson and others 

is reasonable; therefore, these beds are here reassigned to the 

Inskip Formation. However, for the purpose of discussion, this 

unit is shown in figure 2 as Havallah.

Southern Exposures

In the southern East Range, on both sides of Hot 

Spring Canyon, strata similar in lithic composition and 

general appearance to typical beds of the Inskip Formation 

originally were mapped by Muller and others (1951) as Inskip 

Formation. These same strata subsequently were designated 

Havallah by Johnson (1977) and by Stewart and Carlson 

(1978). Because the lower strata consist largely of arkosic rock 

and overlie the Valmy Formation concordantly, the original 

assignment to the Inskip Formation by Muller and others is 

reasonable; therefore, the strata are here reassigned to the 

Inskip Formation. As in the northern exposures, this unit, for 

the purpose of discussion, is shown in figure 2 as Havallah.

Metamorphism

The Inskip Formation was subjected to two phases of 

metamorphism: the first was at the time of deposition and 

the second was in the Jurassic or later. In the first phase, the 

plagioclase of the basaltic rocks was converted to albite by 

contact with seawater, and ferromagnesian minerals were 

altered to hornblende. Plagioclase of the felsites was also converted to albite. This process could be considered as alteration 

rather than metamorphism; but, by whatever name, the process 

produced a profound change in the mineralogy of the igneous 

rocks. While the sedimentary rocks do contain a small percentage of albite, their much more abundant K-feldspar apparently 

escaped unchanged. Albitized basalt and felsite were termed 

respectively spilite and keratophyre in older publications, and 

their origins were not understood.

In the second phase, most of the igneous and nearly 

all sedimentary rocks were mylonized by shearing stress 

parallel to bedding. (Note: In this report, the term “mylonize” 

is used rather than the equivalent “mylonitize.” The 

equivalent textural term is flaser or flasered.) The intensity 

of mylonization varied according to the rock type and 

stratigraphic position. The more massive bodies of basalt 

and felsite appear to have been relatively resistant to the 

mylonizing process, and sedimentary strata of Permian age 

appear to have been relatively little affected compared with the 

more deeply buried Mississippian and Devonian rocks.

The superposition of the two phases of metamorphism 

complicates the assignment of the Inskip to established 

metamorphic facies. Neither the term greenschist facies nor 

the term amphibolite facies is strictly appropriate because the 

end product of alteration of the original basaltic components is 

albite, characteristic of the greenschist facies, and hornblende, 

characteristic of the amphibolite facies.

The age of the dynamic metamorphism is uncertain. 

Although the degree of metamorphism decreases upward, 

the Rochester Rhyolite, regarded as at least partly Triassic, is 

distinctly metamorphosed.

Megastructures of the East Range

In the East Range, detailed mapping by Whitebread 

(1994) indicates that Cambrian, Ordovician, and upper 

Paleozoic strata form an anticline that is overturned to the 

northwest. Separated from this anticline by a northwestverging reverse or thrust fault, upper Paleozoic and Triassic 

strata form a syncline also overturned to the northwest. 

If the folded strata in the East Range were to be restored 

to their original horizontal attitude, they would form a 

concordant stack in which an upright sequence of Cambrian 

and Ordovician age is overlain disconformably by an upright 

sequence of late Paleozoic and Triassic ages. The northwest 

vergence of folds and faults in the East Range may seem 
6 Inskip Formation, Harmony Formation, and Havallah Sequence of Northwestern Nevada

118° 117°45’

118° 117°45’

41°

40° 40°

EXPLANATION

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Contact 

Fault

Axis of overturned

syncline 

Axis of overturned

anticline

Oep

0 1 2 3 4 5 MILES

0 2 4 6 8 KILOMETERS

Figure 2. Central part of the East Range modified from Whitebread (1994), Whitebread and Sorensen (1983), 

and Johnson (1977). Paleozoic rocks form an anticline overturned to the west and northwest; Triassic rocks 

and a sliver of Paleozoic rocks form a syncline overturned to the northwest. The anticline and syncline are 

separated by a reverse or thrust fault. Strata of the anticline are: (1) the Cambrian to Lower Ordovician Preble 

Formation (Oep), (2) the Ordovician to lowest Silurian Valmy Formation (SOv), (3) the Upper Devonian to 

Permian Inskip Formation (PDi), (4) the Devonian to Mississippian Harmony Formation (MDh), and (5) Devonian 

to Permian Havallah sequence (PDh). Strata of the syncline are: (1) the Devonian to Permian Havallah 

sequence (PDh), (2) the Permian? to Triassic Rochester Rhyolite (dPr), (3) the Triassic Star Peak Group (ds), 

and (4) the Auld Lang Syne Group (da). Units labeled Harmony (MDh) and Havallah (PDh) on this and most 

published maps of the East Range are reassigned to the Inskip Formation in this report. Post-Triassic units are: 

Jurassic granitic rocks (Jg) and Tertiary and Quaternary units undifferentiated (QTu). 
Petrologic Features of the Inskip Formation 7

counterintuitive, but such structures in several areas of 

northwestern Nevada including the East and Hot Springs 

Ranges were recognized long ago (Wallace and Silberling, 

1964) and more recently with respect to the Hot Springs 

Range (Jones, 1993).

Petrologic Features of the Inskip 

Formation

Source of Data

All samples pertaining to the Inskip Formation in this 

report are derived from strata universally assigned to the 

Inskip exposed between Rock Hill Canyon on the north and 

Hot Spring Canyon on the south. Many of the finer grained 

rocks cannot be identified in the field with certainty and 

require microscopic examination and X-ray diffraction. 

Laboratory work was based on more than 150 thin sections, 

150 whole-rock X-ray diffraction patterns, and 11 chemical 

analyses. The Inskip is extremely heterogeneous, and the 

photomicrographs shown in figures 3 to 10 are samples of the 

more common lithic types.

Almost all the arkosic rocks are in the lower part of the 

Inskip, most of the igneous bodies and quartzite are in the upper part, and all of the fine-grained, pure quartz rocks interpreted as metacherts are high in the upper part. Because the 

proportions of lithic types vary in the extreme, both laterally 

and stratigraphically within the Inskip, precise estimates of 

relative abundances have not been attempted.

Figure 3. Sheared arkosic sandstone from the lower Inskip 

Formation. Clasts are quartz, quartzite, K-feldspar, and 

plagioclase. Megacrysts were abraded, and fine-grained quartz 

has crystallized syntectonically in pressure shadows. Crossed 

polarizers.

Figure 4. Unpolarized view of figure 3.

Figure 5. Coarse arkosic sandstone from a massive bed in 

the lower Inskip Formation. This specimen shows no evidence 

of shear. Crossed polarizers.

Metasedimentary Rocks

Interlayered beds of mylonized sandstone and conglomerate form much of the lower unit of the Inskip and a 

smaller part of the upper unit. Less common are limestone and 

inconspicuous, poorly exposed beds of siltstone and shale. 

Beds of sandstone range from a few centimeters to several 

meters in thickness. Most are tabular at the outcrop scale, but 

some have been deformed into lenses. The original thickness 

and internal features of the beds have been altered by beddingparallel mylonization, which affected some beds more than 

others. Some of the thicker beds that are relatively unaffected 
8 Inskip Formation, Harmony Formation, and Havallah Sequence of Northwestern Nevada

Figure 6. Chert from the uppermost part of the Inskip Formation. 

The carbon-rich stylolites are preserved in this specimen, and 

radiolarians are sporadically preserved in others. The only effect 

of the relatively slight metamorphism was to slightly increase the 

grain size. Unpolarized.

Figure 7. Metabasalt from the upper member of the Inskip 

Formation. Megacrysts are magnesian hornblende, groundmass is 

albite and ilmenite. This specimen shows slight evidence of shear. 

Crossed polarizers.

Figure 8. Relatively unsheared porphyritic felsite from the upper 

part of the Inskip Formation. Megacrysts are albite, groundmass is 

quartz and biotite. Crossed polarizers.

Figure 9. Sheared felsite from the lower part of the Inskip 

Formation. Light bands are albite and quartz, medium bands are 

muscovite, dark bands are biotite. Uncrossed polarizers.
Petrologic Features of the Inskip Formation 9

Figure 10. Sheared porphyritic felsite from the Rochester 

Rhyolite at the base of the Triassic sequence immediately 

overlying the Inskip Formation. Megacrysts are albite, 

groundmass is albite, quartz, and muscovite. Crossed polarizers. 

by mylonization display graded bedding. Relatively thin beds 

commonly are strongly mylonized and have lost most of their 

original texture and sedimentary structure as a result of abrasion, recrystallization, and segregation of minerals into lenses. 

The relative thinness of the intensely mylonized beds may be 

an original feature, may be due to the mylonizing process, or, 

more likely, both. Clasts range from cobble size to fine sand 

size, rarely boulder size. The larger clasts are composed of 

quartzite, arkosic sandstone, and rarely chert, some of which 

display the faint outlines of radiolarians. The smaller clasts 

are quartz, quartzite, albite, K-feldspar, and mica, rarely chert, 

shale, and basalt (figs. 3–5). The cobble- and boulder-size 

clasts are elongated and flattened as a result of recrystallization under shearing stress. Many small pebbles and large sand 

grains appear, in thin section, to have been reduced in size by 

abrasion and are commonly rotated.

Some cobbles are composed of quartzite similar to that 

of the Valmy Formation, on which the Inskip lies. Boulders 

in intraformational conglomerate are composed of arkosic 

rock similar to arkosic sandstone beds of the Inskip. Much of 

the quartz of sand size and the chert clasts could have come 

from the Valmy Formation, but many quartz grains are much 

too large to have originated from the Valmy. Based on studies 

of thin sections of Valmy quartzite from many locations in 

Nevada, the quartz grains of that formation rarely exceed one 

millimeter in diameter (Ketner, 1966), whereas a major component of the Inskip consists of quartz grains that are several 

millimeters in diameter in spite of metamorphic size reduction. 

Some beds in the uppermost part of the Inskip may be weakly 

recrystallized cherts. These are composed wholly of fine sandsize quartz grains and, in spite of recrystallization, display 

stylolites like those typically present in bedded chert (fig. 6). 

Such beds are stratigraphically close to limy beds that yielded 

Permian conodonts.

As described in subsequent sections, correlatives of the 

Inskip include olistostromes, mélanges, and very large limestone clasts. Such components may be present in the Inskip 

but have escaped notice because of the pervasive beddingparallel shearing. The effect of shearing would be to elongate 

such deposits to the point of making them resemble beds or 

lenses of more conventional sedimentary origin.

Metaigneous Rocks

Igneous rocks throughout the Inskip Formation range 

from fractions of one meter to several meters in thickness and 

are generally tabular and parallel to bedding, although some 

are of irregular shape. Some tabular layers transect bedding at 

the outcrop scale at very low angles, and some appear to have 

altered the sedimentary rocks above and below. Such bodies 

are clearly intrusives. Tabular bodies that do not appear to cut 

bedding and have not altered overlying beds are regarded as 

flows or possibly tuffs.

Metabasalt 

Irregularly shaped bodies and tabular layers of basalt 

are present in the lower unit of the Inskip and are abundant 

in the upper unit. The tabular bodies, which are parallel or 

nearly parallel with bedding of intercalated sedimentary strata, 

range from a few centimeters to a few meters in thickness. 

The irregularly shaped bodies and thick tabular bodies display 

relatively little internal structure, but thin tabular bodies commonly display internal planar structure parallel with bedding. 

Pillow structures were not observed in any of the metabasalts, 

and deformed amygdules were observed in very few.

In thin sections of the basalts, the cataclastic texture 

characteristic of the sedimentary rocks is either relatively 

subtle or absent. Typically, slightly oriented blades, sheaves, 

and lenticular clusters of hornblende are embedded in a matrix 

of smaller, equant grains of albite (fig. 7). A few thin sections 

display good evidence of shear stress including boudinage, 

rotated clusters of hornblende, and pressure shadows adjacent 

to megacrysts.

Microscopic study and X-ray diffraction patterns indicate 

that the metabasalts consist almost entirely of albite and bluegreen, magnesian hornblende. Minor components are brown 

hornblende, biotite, epidote, sphene, ilmenite, and quartz. Pyroxene, olivine, K-feldspar, and plagioclase more calcic than 

albite are very scarce or absent. In some basalts, albite is more 

abundant than hornblende; in most, hornblende is dominant. 

Chemical analyses of a variety of basalts in the Inskip indicate 

a subalkaline basaltic composition (table 1), but these analyses 

may not accurately reflect the original compositions because 

the rocks have been subjected to metamorphic processes.

In the field, basaltic tabular bodies resemble some finegrained metasediments but can commonly be identified as 
10 Inskip Formation, Harmony Formation, and Havallah Sequence of Northwestern Nevada

basalt by their somewhat greenish cast. The metabasalts must 

have originated as basaltic magma but were altered by contact 

with seawater either within saturated sediments or in the sea 

itself, in either event resulting in the complete alteration of 

calcic plagioclase to albite and mafic minerals to hornblende.

Metafelsite

The felsites are porphyritic, quartz-bearing rocks of 

igneous origin. Although some of these rock bodies are of 

irregular shape, most are tabular layers parallel, or nearly so, 

with beds of mylonized sedimentary rocks and tabular bodies 

of basalt. They are sparsely present in the lower part of the 

Inskip and abundant throughout the upper part.

The felsites are composed of quartz, albite, muscovite, 

and biotite as determined microscopically and by wholerock X-ray diffraction (fig. 8). Scattered opaque minerals, 

including ilmenite, and a trace of microcline are present 

in some of them. The megacrysts are albite; none is quartz 

although exsolved quartz blebs are common in the albite. 

Microscopic examination and X-ray diffraction patterns of the 

fine-grained matrix indicate it is composed largely of quartz. 

Texture varies from unflasered porphyry of thick bodies that 

have large, notably sericitized, subhedral albite megacrysts to 

the relatively equigranular mylonites in which the megacrysts 

have been rotated, reduced to small lenses, or almost 

completely destroyed (fig. 9). In these, the biotite is commonly 

segregated into thin lenses. The mineralogical composition 

indicates they have been albitized, presumably by contact with 

seawater, either within saturated sediments or in the sea itself. 

The chemical composition of the felsites suggests they are of 

rhyolitic to andesitic origin (table 2).

In the field, tabular felsite bodies can be mistaken for mylonized sandstone beds. Microscopically, however, the felsites 

differ from sandstones in the presence of intensely sericitized 

albite megacrysts, in the absence of quartz megacrysts, in the 

relative abundance of biotite that is commonly segregated into 

thin lenses, and in the near absence of K-feldspar.

The Felsite Problem

In the East Range, felsite bodies are in beds ranging from 

Mississippian to Triassic in age. Were they intruded into saturated sediments or erupted on the sea floor contemporaneously 

with deposition of the enclosing sediments, or were they 

intruded into consolidated Paleozoic rocks in Triassic time? 

The irregular bodies, some of which do not display evidence 

of shear, probably are intrusives too massive to have been 

mylonized. The tabular layers, some of which are as thin as a 

few centimeters, may represent original sills, flows, or tuffs, 

their thinness partly due to the metamorphic process. The 

abundance of quartz and albite together with the near absence 

of K-feldspar suggest that these rocks may have originated 

as rhyolitic, dacitic, or andesitic magma but that K-feldspar, 

oligoclase, and andesine were altered to albite by contact with 

seawater.

Triassic formations of the East Range are mainly 

sedimentary rocks. However, the basal unit of the Triassic 

sequence is the Rochester Rhyolite, a member of the Koipato 

Group, which sits disconformably on uppermost beds of the 

Inskip. The Rochester, at this location, is undated and may be 

partly of Permian age. An X-ray diffraction pattern and thin 

sections from the Rochester indicate that this rock is flasered 

and is composed of quartz and muscovite, with sericitized 

albite megacrysts—practically the same texture and mineral 

composition as that of the felsitic rocks in the underlying 

Inskip Formation (fig. 10). The chemical composition is also 

similar. Conceivably, the Rochester Rhyolite and the felsites 

of the Inskip are all intrusives of latest Permian to Early 

Triassic age, but this would not account for the universally 

albitic composition of their feldspars, which implies direct 

contact with seawater. Tentatively, the Inskip bodies and the 

Rochester Rhyolite are interpreted to be contemporaneous 

with the sedimentary rocks with which they are interlayered. 

If this interpretation is correct, basalt and felsite emplacement 

alternated frequently from Late Devonian to Early Triassic 

time.

Table 1. Chemical composition of metabasalt of the Inskip 

Formation, East Range, Nevada.

Sample

number 13655 13705 13706 13707 13708

Major-oxide composition1

SiO2 49.8 48.3 49.1 55.4 51.7

Al2O3 15.2 16.0 14.3 11.8 17.0

FeTO3 10.5 11.1 13.7 8.84 8.49

MgO 7.74 8.54 6.30 8.59 7.26

CaO 9.96 10.2 9.63 9.45 9.89

Na2O 3.24 2.65 2.93 2.96 3.43

K2O 0.40 0.21 0.30 0.38 0.26

TiO2 1.25 1.39 2.48 0.88 0.82

P2O5 0.16 0.19 0.35 0.25 0.13

MnO 0.17 0.20 0.21 0.21 0.18

LOI 1.05 0.79 0.48 0.45 0.50

1

Method of analysis: WDXRF, weight percent.

DESCRIPTION OF SAMPLES

13655: fine-grained; magnesium-sodium hornblende, albite; flasered.

13705: coarse-grained; very massive; magnesium hornblende, albite; not 

flasered.

13706: coarse-grained; magnesium hornblende, albite, ilmenite; not 

flasered.

13707: fine-grained; magnesium hornblende, albite, biotite, quartz veins 

and amygdules; flasered.

13708: coarse-grained; magnesium hornblende, albite; flasered.
Hot Springs Range 11

Depositional Conditions of the Inskip

The Inskip was deposited in a marine environment under 

conditions that varied from time to time throughout its long 

history. The graded bedding observed in some exposures 

of the sedimentary rocks suggests deposition by turbidity 

currents, but most sedimentary structures have been obliterated 

by metamorphic processes. The large size of most of the 

clasts, including boulders in intraformational conglomerate, 

indicates proximity to sources. Feldspathic and large quartz 

clasts must have been derived from a nearby granitic terrane, 

and other components probably were derived from sources 

such as the Valmy Formation exposed to the east (Ketner and 

others, 2005). The presence of intraformational conglomerate 

composed of feldspathic sandstone clasts low in the Inskip 

suggests tectonic instability and intervals of elevation and 

erosion within the depositional basin. An additional indication 

of tectonic instability is the presence of cobbles and even 

boulders of arkosic rock in Lower Mississippian strata of 

eastern Nevada. These, by their petrographic features as 

revealed in numerous thin sections, were derived from the 

Inskip or other arkosic rocks in northwestern Nevada. The 

picture that emerges is of a vertically oscillating basin or 

trough, bound on the west by granitic highlands and on the 

east by highlands composed of Paleozoic siliceous rocks such 

as the Valmy Formation, as discussed by Ketner and others 

(2005).

Hot Springs Range

Although they have been structurally disrupted, the 

Paleozoic stratigraphic components of other ranges in the 

arkosic triangle are similar to those of the East Range. Starting 

with the Hot Springs Range, stratigraphic and structural issues 

pertaining to these ranges are discussed in the following 

sections for the purpose of establishing the hypothesis that 

all Upper Devonian to Permian units in the arkosic triangle, 

by whatever name, are parts of a single genetic assemblage, 

deposited on a similar substrate, in a single depositional basin, 

and have the same tectonic history.

Source of Data

The Hot Springs Range, 80 km northeast of the East 

Range (fig. 11), was mapped in detail by Jones (1991a). 

Table 2. Chemical composition of metafelsites of the Inskip Formation and the Triassic Rochester 

Rhyolite, East Range.

Sample 

number

Formation

13649

Inskip

Formation

13652

Inskip

Formation

13656

Inskip

Formation

13780

Inskip

Formation

14040

Inskip

Formation

15049

Rochester

Rhyolite

Major oxide composition1

SiO2 69.4 66.3 64.1 60.4 65.5 69.4

Al2O3 14.2 14.4 15.3 15.3 14.5 14.1

FeTO3 01.70 02.97 04.66 06.65 03.48 1.92

MgO 00.17 00.42 01.90 02.77 00.84 0.23

CaO 01.30 01.33 01.37 04.89 02.02 0.11

Na2O 03.78 03.93 04.49 02.55 04.12 3.21

K2O 03.93 03.44 03.72 03.09 02.86 5.08

TiO2 00.25 00.27 00.57 01.12 00.40 0.16

P2O5 00.04 00.08 00.14 00.23 00.12 0.04

1

Method of analysis: ICP–AES, weight percent.

DESCRIPTION OF SAMPLES

13649: interlayered with limestone; quartz, albite, muscovite; flasered; equigranular; x-ray diffraction pattern 

 identical to that of 15049.

13652: interlayered with conglomerate; quartz, albite, muscovite, biotite; flasered; equigranular.

13656: interlayered with arkosic sandstone; quartz, albite, much biotite; flasered; prominent feldspar megacrysts.

13780: cuts bedding at small angle; quartz, albite, much biotite; variably flasered; prominent feldspar megacrysts;

 amygdules.

14040: quartz, albite, muscovite; intensely flasered; prominent feldspar megacrysts.

15049: Rochester Rhyolite at base of Triassic sequence; quartz, albite, much muscovite; flasered; rotated 

 megacrysts; X-ray diffraction pattern identical to that of 13649.
12 Inskip Formation, Harmony Formation, and Havallah Sequence of Northwestern Nevada

117°30’ 117°22’ 30”

41°22’ 30”

41°15’

41°22’ 30”

41°15’

QTu

Pm

Ppp

Ppp

Pm

Pps

QTu

Pm

Cpp

EXPLANATION

Ppp

Cpp Mhr

Mhr

Pps

SOv

Mhr

MDh

SOv

QTu

SOv

SOv SOv

MDh

Contact 

Thrust fault

sawteeth on upper plat

Fault

Axis of syncline

Dashed where concealed 

Axis of anticline

QTu

SOv

SOv

MDh

TR

TR

TR

0 1 2 3 MILE

0 1 2 3 4 KILOMETERS

Figure 11. Generalized and simplified map of part of the Hot Springs Range modified from Jones (1997a, 

b) showing the Hot Springs Range syncline and the northern Hot Springs Range anticline. Strata of the 

syncline are (from oldest to youngest): the lowest Silurian and Ordovician Valmy Formation (SOv), the 

Harmony Formation (MDh), and the Home Ranch subterrane (Mhr). Areas shown as Valmy Formation on 

the west and northeast sides of the range may include some Harmony limestone. Strata of the anticline 

are (from oldest to youngest): the carboniferous lower Poverty Peak subterrane (Cpp), the Permian upper 

Poverty Peak subterrane (Ppp), the Permian Poverty Peak–Golconda mélange (Pm), the Permian Phyllite 

and shale subterrane (Pps), and the Triassic and Jurassic (?) Jungo terrane (Ö). Post-Triassic strata are 

Tertiary and Quaternary units undifferentiated (QTu).
Hot Springs Range 13

Except for the Valmy and Harmony Formations, my 

knowledge of that range is based entirely on her published 

work (Jones, 1991b, 1993, 1997a, b), discussions with her, and 

on thin sections of rocks that she lent me. Her interpretation of 

the structure that the various formations were brought together 

tectonically from differing environments is entirely plausible. 

However, as a result of my study of the East Range, I here 

offer an alternative theory: that the formations of the Hot 

Springs Range, prior to faulting, formed an intact stratigraphic 

sequence similar to that of the East Range.

The East Range and Hot Springs Range exhibit similar 

stratigraphic, petrologic, and structural features. Both ranges 

lie at the western margin of the Paleozoic miogeocline. In 

both ranges the exposed strata range from lower Paleozoic to 

Triassic. In both, most of the Silurian and Devonian systems 

are missing. In both, the middle Paleozoic strata are notably 

arkosic and the upper Paleozoic strata are rich in basalt, felsite, 

and chert. In both, as here interpreted, two large northeasttrending, northwest-vergent folds are separated by northwestvergent faults. In the following sections the tectonostratigraphic units recognized by Jones (1997a,b) are briefly described in 

stratigraphic order from older to younger.

Strata in the Hot Springs Range Underlying the 

Inskip-Equivalent Rocks

In this section, the generally accepted stratigraphy and 

Cambrian age of the Paradise Valley Chert are radically 

reinterpreted on the basis of local and regional relations. The 

Ordovician Valmy Formation and the overlying Paradise 

Valley Chert, as here interpreted, concordantly underlie Inskipequivalent strata of the Hot Springs Range and constitute the 

oldest exposed rocks of the Hot Springs Range syncline.

Since it was first described, the Paradise Valley Chert of 

the Hot Springs Range has been considered to be of Cambrian 

age (Hotz and Willden, 1964). The formation, as described 

by Hotz and Willden and by Jones (1997a, b), consists of 

two lithic units: chert and limestone. Trilobite fragments 

and conodonts extracted from the limestone unit indicate a 

Cambrian age, but the chert unit is not directly dated and its 

age could be different from that of the limestone. Complex 

structure and poor exposures have resulted in uncertainty 

as to the stratigraphic relations of the limestone and chert 

beds to each other and to overlying and underlying units. In 

the present interpretation based on observed field relations, 

the limestone unit of the Paradise Valley Chert is part of the 

Harmony Formation. The chert part of the Paradise Valley 

Chert, where it is well exposed on the west side of the range, 

is quite distinctive, being composed of a lower black chert unit 

and an upper mineralized white chert unit. As here interpreted, 

this chert couplet is equivalent to the “chert couplet of Table 

Mountain” in the East Range. This couplet is at the top of the 

Valmy Formation in the East Range (Ketner and others, 2000) 

and in numerous exposures across Nevada. In the northern 

Adobe Range of northeastern Nevada, the chert couplet was 

determined, by means of contained graptolites and radiolarians 

(Ketner and Ross, 1990; Ketner, 1991; Noble and others, 

1997), to be close to the Ordovician-Silurian boundary in age 

and probably straddles that border. In subsequent discussions, 

the term Valmy Formation includes the chert part of the 

Paradise Valley Chert.

Stratigraphic Units Equivalent to the Inskip in 

Age and General Aspect

In the following paragraphs the tectonostratigraphic units 

of Jones (1997b) are treated as stratigraphic units, essentially 

formations, and described from oldest to youngest. If, as here 

interpreted, the upper Paleozoic rocks of the Hot Springs 

Range are parts of a formerly intact stratigraphic sequence 

comparable to the Inskip Formation, the various depositional 

environments indicated by its components represent changing 

tectonic conditions through time.

Harmony Formation

The Harmony Formation, composed of mainly coarsegrained arkosic sandstone and lesser amounts of calcarenite 

and shale, is of Late Devonian to Mississippian age and is 

therefore similar to, and correlative with, the lower, arkosic 

part of the Inskip Formation. A detailed description was given 

in Jones (1997a, b), and its age was discussed in Ketner and 

others (2005), and Crafford (2007).

Home Ranch Subterrane

This unit, composed of mafic and felsic volcanic rocks, 

limestone, and chert, is of Mississippian age (Jones, 1997a, b). 

As such, it is equivalent to strata just above the arkosic part of 

the Inskip Formation, and it constitutes the youngest stratigraphic unit of the Hot Springs Range syncline.

Lower Poverty Peak Sequence

This unit, largely chert and basalt, is of Carboniferous age 

and, prior to faulting, overlay the Home Ranch subterrane. It is 

the oldest unit in the northern Hot Springs Range anticline.

Upper Poverty Peak Sequence

This unit of principally sedimentary rocks contains Permian conodonts and is exposed in two parallel belts overlying 

the Lower Poverty Peak sequence on the northern Hot Springs 

Range anticline.
14 Inskip Formation, Harmony Formation, and Havallah Sequence of Northwestern Nevada

Poverty Peak–Golconda Mélange

The two Permian mélanges of Jones (1997b) are here 

combined into a single stratigraphic unit slightly younger than, 

and overlying, the Upper Poverty Peak sequence. Although the 

two mélanges differ in components of blocks, this difference 

could represent spatial variation within a single unit and is so 

interpreted here. The mélange is exposed in two parallel belts, 

one on each flank of the northern Hot Springs Range anticline. 

Mélanges were not identified in the Inskip Formation, but if 

present, they would be hard to identify as such because of the 

pervasive dynamic metamorphism.

Phyllite and Shale Sequence

This unit is the stratigraphically highest Paleozoic unit. It 

is exposed only on the south flank of the northern Hot Springs 

Range anticline, presumably because on the north flank it 

was cut out by the fault that separates Paleozoic from Triassic rocks. The notable chert content of this unit allies it with 

metachert beds in the uppermost part of the Inskip Formation.

Triassic and Jurassic Rocks

Triassic and Jurassic stratigraphic units of shelf and 

basin facies, isolated from the Paleozoic rocks by a fault, are 

equivalent to some of the Triassic and Jurassic shelf and basin 

units overlying the Inskip Formation. The Rochester Rhyolite, 

or equivalent felsic rock normally at the base of the Triassic 

sequence regionally, is not exposed, probably owing to this 

fault.

Megastructures of the Hot Springs Range

The Paleozoic rocks of the Hot Springs Range are here 

interpreted as a once-coherent stratigraphic sequence similar 

to that of East Range but one that has been dismembered by 

high- and low-angle faults of small displacement. As depicted 

in figure 11, the Valmy Formation, the Harmony Formation, 

and the Home Ranch subterrane form a broad syncline or 

synclinorium. The Poverty Peak subterrane, the Golconda 

and Poverty Peak mélanges, and the phyllite-shale unit form 

a nearly isoclinal anticline. The syncline and anticline are 

separated by a northwest-directed thrust fault. This thrust fault, 

as mapped by Jones (1997a) and as here interpreted, places 

the Home Ranch Formation of the syncline over the phylliteshale and mélange units on the southeast limb of the anticline. 

Therefore, as here interpreted, the East Range and the Hot 

Springs Range are similarly constructed of northeast-trending 

folds separated by west-vergent thrust faults, but the older 

strata of the Hot Springs Range form a syncline rather than an 

anticline as in the East Range, and the younger strata form an 

anticline rather than a syncline.

Osgood Mountains

The Osgood Mountains are about 100 km northeast 

of the East Range and just east of the Hot Springs Range. 

Cambrian and Ordovician rocks and formations that appear 

to be contemporaneous with the Inskip Formation are present 

in highly faulted relations to one another. Formations correlative with the Inskip include units named Harmony, Goughs 

Canyon, Farrel Canyon, and Adam Peak Formations (Hotz and 

Willden, 1964). McCollum and McCollum (1991) contributed 

much valuable data on the Osgood Mountains, but further 

work is required to settle persistent stratigraphic and structural 

problems.

Sonoma Range

The Sonoma Range is adjacent to the East Range on the 

east and northeast. The highly dismembered stratigraphic components of the Sonoma Range generally resemble the stratigraphic sequence of the East Range. As reconstructed here, 

the Harmony Formation and the Havallah sequence, which 

together correlate with the Inskip Formation, are underlain 

by Cambrian, Ordovician, and lowest Silurian strata similar 

to strata in the East Range and are overlain by Triassic rocks 

similar to those of the East Range.

Stratigraphic and Structural Issues

The oldest strata in the Sonoma Range, as in the East 

Range, are the mainly Cambrian Preble Formation and the 

mainly Ordovician Valmy Formation. Although separated 

by faults, they are here assumed to have been in normal 

stratigraphic sequence originally, as they are in the East 

Range. As interpreted by Gilluly (1967), who mapped much 

of the range in considerable detail, the Harmony Formation 

is of Cambrian age and therefore normally would underlie 

the mainly Ordovician Valmy Formation. As mapped, contact 

relations between these two units in many areas unequivocally 

place the Harmony above the Valmy. This was confirmed by 

my detailed observations in Bacon Canyon in the southern 

part of Gilluly’s map area. In Bacon Canyon, arkosic strata 

clearly overlie the uppermost beds of the Valmy Formation 

with a concordant contact. To accommodate the seeming 

reversal of normal stratigraphic order, Gilluly separated the 

two units with a thrust fault, the “Clear Creek thrust.” In the 

present interpretation, the Harmony is of latest Devonian 

to Mississippian age, partly based on lithic correlation with 

dated beds in the East Range and Hot Springs Range and 

partly on conodonts collected from a mass of limestone 

embedded in arkosic rocks of the Harmony Formation as 

mapped by Silberling (1975). Therefore there is no need 

for a thrust fault separating the Valmy from the Harmony, 

nor is there any physical evidence to support the concept. 
Battle Mountain 15

The simplest interpretation is that they form a normal, 

disconformable, depositional sequence, as the true age of the 

Harmony permits, and as contact relations in Bacon Canyon 

and in the East Range indicate. It should be noted that Gilluly 

(1967) apparently assigned coarse-grained arkosic sequences 

conspicuously interlayered with greenstone to the Valmy 

Formation, whereas he assigned coarse-grained arkosic 

sequences without interlayered greenstone to the Harmony 

Formation. This is inconsistent with mapping elsewhere; the 

lower part of the Inskip Formation in the East Range and the 

Harmony Formation of Battle Mountain include both arkosic 

rocks and greenstone. 

Havallah Sequence

The Havallah sequence, present in the southern part of 

the Sonoma Range and which correlates with the upper parts 

of the Inskip Formation, is discussed in a subsequent section 

on the relation of the Inskip and the Harmony Formation to the 

Havallah Sequence.

Triassic Rocks

Similar Triassic formations are present in both the East 

Range and Sonoma Range. In both ranges they form northwest-vergent synclines (Gilluly, 1967; Whitebread, 1994).

Battle Mountain

Battle Mountain lies about 65 km east of the East Range. 

As originally interpreted by Roberts (1964), the Paleozoic 

stratigraphy bears little resemblance to that of the East Range. 

However, recent revisions of the ages of important units and 

their relations to each other, as here interpreted, bring the stratigraphy of the two areas much closer together. More detailed 

descriptions of the formations are given by Roberts (1964) and 

by Doebrich (1994).

North Slope

On the north slope of Battle Mountain, the “Cambrian” 

Harmony Formation is mainly underlain by the Valmy 

Formation and less extensively by Devonian chert (Theodore, 

1994). Where the contact is fairly well exposed, it does not 

appear to be significantly angular. The Valmy consists of 

quartzite, shale, chert, and greenstone. Here, as elsewhere, the 

Harmony consists mainly of arkosic sandstone. The contact 

between the Harmony and the Ordovician and Devonian rocks 

was mapped originally by Roberts (1964) and subsequently 

by Theodore (1994) as the Dewitt thrust fault. This was 

logical because the relation appeared to be one of older strata 

superposed on younger strata. The Harmony is undated in 

the Battle Mountain area, but because it correlates lithically 

with Late Devonian to Mississippian parts of the Inskip 

Formation in the East Range and with the latest Devonian to 

Mississippian Harmony Formation of the Hot Springs Range, 

its age is here assumed to be within the latest Devonian to 

Mississippian range. This permits the interpretation that the 

lower contact of the Harmony Formation is depositional and 

not a fault.

South Slope

On the south slope of Battle Mountain, contacts in 

relation to topography clearly indicate that the Harmony 

Formation is underlain by heterogeneous strata assigned to 

the “Cambrian” Scott Canyon Formation (Doebrich, 1994). 

These strata include quartzite, shale, chert, and greenstone, 

all of which are similar to strata of the Valmy Formation as 

exposed on the north side of Battle Mountain. In addition, 

olistostromes are present sporadically just below the Harmony 

Formation (McCollum and others, 1985; Doebrich, 1994).

Ordovician conodonts identified by John Repetski 

were collected from two localities in the Scott Canyon 

Formation (McCollum and others, 1987), and Devonian 

radiolarians were obtained from chert beds at two locations 

(Jones and Wrucke, 1978; Murchey, in Theodore, 1994). 

Cambrian archaeocyathids and trilobites were obtained from 

limestone clasts in some of the olistostromes (Roberts, 1964; 

McCollum and others, 1985; DeBrenne and others, 1990). 

The dimensions of some of these clasts are several meters. 

The quartzite, shale, and greenstone components of the Scott 

Canyon are not dated by fossils. However, the quartzite 

strata are lithically identical to quartzite strata of the Valmy 

Formation and were mapped as Valmy by Roberts (1964). 

The general lithic aspect and paleontological data indicate 

that a large part, if not most, of the Scott Canyon should be 

assigned to the Valmy Formation. An unknown portion of the 

chert is of Devonian age and could be regarded as the oldest 

component of the heterogeneous Harmony Formation and as 

only locally present at the base of that unit. In addition to the 

chert deposits, the olistostromes are here considered to be 

basal components of the Harmony Formation for two reasons: 

(1) they consistently occur just below arkosic strata of the 

Harmony, and (2) limestone olistoliths of Cambrian age are 

present near the base of the Harmony Formation in the Hot 

Springs Range (Ketner and others, 2005). The archaeocyathids 

in these olistostromes have been intensively studied by 

DeBrenne and others (1990). These authors state that some 

of the forms “***suggest a paleogeographic relationship with 

northwestern Canada***” and other areas extremely remote 

from Nevada. This information led McCollum and McCollum 

(1989) to the conclusion that the Antler orogeny was “a 

transpressional orogen within a transcurrent fault system” 

and it tends to confirm the conclusion of Ketner and others 

(2005) and Crafford (2008), based entirely on other data, that 

the provenance of Cambrian limestone olistoliths, as well 

as arkosic clasts of the Harmony Formation, was an exotic 
16 Inskip Formation, Harmony Formation, and Havallah Sequence of Northwestern Nevada

terrane transported tectonically to Nevada from northwestern 

Canada. Olistostromes bearing large clasts of limestone were 

not identified in the Inskip Formation. However, some lenses 

of limestone observed in the Inskip may actually be such 

clasts, elongated by the dynamic metamorphism to the point of 

resembling normally deposited strata or lenses.

The Havallah Sequence

These upper Paleozoic rocks in fault contact with lower 

to middle Paleozoic strata on the west side of Battle Mountain 

are discussed in a subsequent section on the relation of the 

Inskip and the Harmony Formation to the Havallah Sequence. 

Unconformities

The disconformity, or unconformity with only slight angular discordance, between the Valmy and the Harmony Formations represents the Antler orogeny currently defined as a 

Late Devonian to Early Mississippian event. A younger unconformity is present in the same area: the Battle Conglomerate 

of mid-Pennsylvanian age lies with angular unconformity on 

the Valmy and Harmony Formations, thus recording an event 

of folding or tilt, uplift, erosion, and a return to deposition of 

post-Harmony and pre-Battle age. This unconformity commonly has been regarded as evidence of the Antler orogeny, 

but because the Harmony is Late Devonian to Mississippian 

in age, it represents a distinctly younger tectonic event, the 

Humboldt orogeny of mid-Pennsylvanian age.

Relation of the Inskip and the Harmony 

Formations to the Havallah Sequence 

in the Arkosic Triangle 

The Havallah sequence, which crops out in several 

mountain ranges of the arkosic triangle, is a series of mainly 

deepwater deposits ranging from Late Devonian to Permian 

in age and is therefore correlative with the Inskip Formation. This discussion argues that the Havallah is similar to the 

Inskip in general lithic composition and that it is part of the 

same genetic assemblage as the Inskip and the upper Paleozoic 

rocks of the Hot Springs Range, in agreement with Crafford 

(2007). 

On maps dated in the 1950s, certain upper Paleozoic, 

relatively deepwater strata were divided between the mostly 

sedimentary Havallah Formation and the largely igneous 

Pumpernickel Formation. Now both units are subsumed under 

the name Havallah sequence, as detailed by Stewart and others 

(1977, 1986), and are commonly considered to be a major 

component of the Golconda allochthon or Golconda terrane.

The Inskip Formation is lithically comparable to, and 

correlative with, the Havallah sequence as now defined. Muller 

and others (1951) stated in their original description of the 

type occurrences of both the Havallah and Inskip Formations, 

that the Inskip is “***assumed equivalent to Havallah***” and 

“***may represent marginal facies of the more widespread 

Havallah.” It would have been more accurate to say that the 

Inskip may represent a facies of the combined Havallah and 

Pumpernickel. Jones (1997a) applied the term Golconda terrane to middle to upper Paleozoic rocks of the Hot Springs 

Range, suggesting that they also are comparable to the Havallah as now defined. As interpreted here, the Inskip and the 

middle to upper Paleozoic rocks of the Hot Springs Range do, 

indeed, constitute a facies of the Havallah sequence because: 

(1) they occur close to the principal exposures of the Havallah; (2) like the Havallah, both sequences range from Late 

Devonian to Permian in age; (3) like the Havallah, both are 

predominantly deepwater deposits; (4) like the Havallah, both 

include igneous bodies of basaltic and felsic composition; and 

(5) like the Havallah, both are overlain by Triassic rocks.

Most exposures of the Havallah sequence do not include 

arkosic rocks, but in the southern East Range, an extensive 

area designated as Havallah on most published maps (for 

example, Johnson, 1977) includes basal arkosic strata disconformable on the Valmy Formation. In the Sonoma Range, 

the basal unit of the Havallah termed the “clastic unit of the 

Havallah sequence” by Silberling (1975) is, for the Havallah, 

an unusually coarse-grained sandstone and includes a small 

percentage of feldspar. The lack of arkosic deposits in other 

exposures of the Havallah could be due to incomplete exposure (most exposures of the Havallah are of the Pennsylvanian 

and Permian parts of the sequence), to nondeposition due to 

topographic relief in the depositional basin, to distance from 

the western source area, or to structural elimination during 

thrust faulting. In the present interpretation, the Inskip, upper Paleozoic rocks of the Hot Springs Range and sequences 

designated by various modern authors as Havallah constitute a 

genetically related assemblage that was deposited in the same 

basin, on the same substrate (the Valmy Formation), and was 

overlain by similar sequences of Triassic rocks.

Sonoma Orogeny and Golconda Thrust

For many years, contact relations near the boundary 

between Permian and Triassic rocks of the arkosic triangle 

have been interpreted as representing an orogenic event known 

as the Sonoma orogeny, and a thrust fault juxtaposing upper Paleozoic rocks of different facies has been known as the 

Golconda thrust (Silberling and Roberts, 1962). The relation 

between the “orogeny” and the thrust is uncertain; they could 

be the same age and genetically related, or the thrust could be 

younger.

The purposes of this discussion are to propose downgrading the Sonoma orogeny to a relatively minor tectonic event 

and to propose establishing the age of the Golconda thrust as 

Jurassic rather than Late Permian or Early Triassic. The result, 

to the extent it is successful, would be to unify the tectonic 
Conclusions 17

histories of the various mountain ranges in the arkosic triangle 

and reconcile the tectonic history of the area with modern field 

observations.

Although the contact between the Havallah and overlying 

volcanic rocks at the base of the Triassic sequence has been 

asserted to be a major unconformity representing the Sonoma 

orogeny in numerous publications, clear evidence supporting 

that concept in the form of detailed maps or descriptions of 

the contact is scarce. Maps by Ferguson and others (1952) and 

Muller and others (1951) lack sufficient detail to prove a major 

unconformity, and my reconnaissance of several areas where 

the contact between Havallah and Triassic rocks is shown on 

those maps did not reveal convincing structural evidence of 

a major tectonic event. Significant deposits of coarse-grained 

orogenic sediments of Late Permian to Early Triassic age are 

nowhere to be found.

According to Silberling and Roberts (1962) “Evidence 

for orogeny during Permian time is best illustrated in the 

China Mountain area ***where the Havallah Formation 

of Pennsylvanian and Permian age has been tightly folded 

and thrust-faulted and is overlain unconformably by the 

Koipato Formation***.” However, according to Stewart and 

others (1977, 1986) the Havallah on the southeast side of 

the mountain is not tightly folded but is a structural package 

composed of northwest-dipping, nearly homoclinal strata 

that are sliced by numerous, inconspicuous, undated faults 

subparallel to bedding. Stewart and others (1986) state that 

“No folds of sufficient size to duplicate the map subunits 

have been observed, and no major overturned successions 

can be identified***.” These authors do not discuss the 

basal contact of the overlying Koipato except to say that it 

is unconformable, but that might also be an inconspicuous 

undated fault. Figure 2 of Stewart and others (1986) showing 

the contact as a “sedimentary or fault contact” implies that 

possibility.

In the East Range where the base of the Rochester 

Rhyolite member of the Koipato Formation was mapped in 

some detail by Whitebread (1994), the base of the Koipato 

is shown to follow faithfully the bedding in underlying 

Permian strata that he assigned to the Havallah sequence. 

Also, the close similarity between felsites of the Inskip and 

the overlying Rochester Rhyolite indicates that felsitic magma 

generation and emplacement continued across the PaleozoicTriassic boundary. It is therefore hard to believe that this 

contact represents a major tectonic event characterized by 

folding and thrust faulting. 

The substrate of the Koipato is also pertinent to the 

nature of the Sonoma orogeny. According to Silberling 

and Roberts (1962), “***beds depositionally underlying 

the Koipato sequence, wherever exposed, belong to the 

Havallah sequence***.” If the contact between the Koipato 

and Havallah represents a major tectonic event, why does 

the Koipato not overlap the contact in many places and lie 

directly on pre-Havallah units? In one area in the eastcentral East Range, Ferguson and others (1951) showed the 

Koipato directly overlying the Leach Formation (now the 

mainly Ordovician Valmy Formation), and they state that this 

demonstrates a major unconformity in which the Havallah 

has been entirely eroded away. On later maps, however, 

Silberling and Roberts (1962), Johnson (1977), Stewart and 

Carlson (1978), and Crafford (2007) interpreted the formation 

underlying the Koipato at that location as the Havallah 

sequence, thereby eliminating a major unconformity in an area 

where it seemed imperative. 

The age of the Golconda thrust is even more uncertain 

than the existence of the Sonoma orogeny, and this uncertainty 

has been explored by many authors without the development 

of a consensus. Silberling and Roberts (1962) express this 

uncertainty in their often-cited report defining the Sonoma 

orogeny and exploring its relation to the Golconda thrust. 

“Until more reliable information is available the ages of the 

Koipato sequence and the Edna Mountain Formation do not 

preclude development of the Golconda thrust during the 

Sonoma orogeny.” They leave the question of linkage between 

the Golconda thrust and the Sonoma orogeny open to the 

possibility that the Golconda is of post-Triassic age. Gabrielse 

and others (1983) expressed the same degree of uncertainty: 

“All evidence on the age of the Golconda thrust, however, is 

equivocal, and the issue is unresolved.”

Arguments for the distance traveled by the Golconda 

allochthon are also open to reinterpretation. The close 

proximity of contrasting deepwater Havallah and the partially 

contemporaneous shallow-water deposits (Antler sequence) 

separated by the Golconda thrust at Battle Mountain, 

Edna Mountain, and the Osgood Mountains has led to the 

hypothesis that the Havallah is a far-traveled allochthon 

(for example, Brueckner and Snyder, 1985). An alternative 

explanation is that the depositional basin of the Havallah 

and correlatives was bounded on the east by a high-angle 

fault and that the contrasting deep and shallow depositional 

environments were therefore originally possibly close together. 

In any event, the distance traveled by the allochthon is a matter 

of opinion in the absence of any convincing evidence.

In contrast to the apparent weakness of the evidence for 

intense deformation of Late Permian or Early Triassic age 

and lack of evidence for thrusting of that age, several detailed 

maps of local areas show unequivocally that the entire Triassic 

sequence was intensely folded and faulted in Jurassic or later 

time. Examples of such maps are those by Gilluly (1967), 

Whitebread (1994), Wallace, Silberling, and others (1969), 

Wallace, Tatlock, and others (1969), and Silberling and 

Wallace (1967).

Conclusions

Cambrian, Ordovician, and lowest Silurian strata of the 

arkosic triangle form a depositionally continuous part of the 

outer miogeocline and are indigenous to that area. Sequences 

variously termed Inskip, Havallah, and Harmony lie on those 

lower Paleozoic miogeoclinal strata depositionally and are 

therefore indigenous to the area also. The Inskip Formation, 
18 Inskip Formation, Harmony Formation, and Havallah Sequence of Northwestern Nevada

equivalent strata in the Hot Springs Range, and arkosic strata 

termed Harmony in several ranges constitute a facies of the 

Havallah sequence exposed widely within the arkosic triangle, 

and the entire assemblage was deposited in the same faultbounded basin or trough within the outer miogeocline. This 

assemblage therefore constitutes a single genetic stratigraphic 

unit (the Harvallahskip assemblage?) that has since been structurally disrupted.

Sediments composing this assemblage came from both 

sides of the depositional basin. Arkosic sands, olistoliths, and 

probably other detrital components, came from the west as 

argued by Ketner and others (2005). Clasts of quartzite, chert, 

and other components probably came from the east. The giant 

size of some olistoliths indicates the western source of these 

clasts was very close to the depositional basin.

Throughout the Late Devonian to Permian interval, basaltic and felsic magmas repeatedly erupted into sediments still 

saturated with seawater and into the sea itself. The Cambrian 

to Permian sequence was topped depositionally with mild 

structural discordance by Triassic rocks and was strongly 

folded with those Triassic rocks in Jurassic or later time.

Paleozoic tectonic activity within the arkosic triangle 

was expressed as: (1) Devonian elevation and erosion of part 

of the outer miogeocline; (2) Late Devonian depression of the 

same area, forming a trough, probably fault-bounded, in which 

the middle to upper Paleozoic assemblage was deposited; 

(3) Mississippian partial erosion of the arkosic deposits and 

deposition of resulting intraformational and extrabasinal 

conglomerates derived from those deposits; and (4) midPennsylvanian uplift and folding, or tilting, of the east side of 

the depositional basin resulting in an angular unconformity 

beneath certain Pennsylvanian to Permian strata.

The middle to upper Paleozoic basinal assemblage was 

compressed in the Jurassic or later, producing east-vergent 

thrusts in the eastern part of the depositional basin (Golconda 

thrust) and west-vergent thrusts and folds in the western part.

Stratigraphic and tectonic concepts dating from the 

early 1970s involving subduction and a far-traveled Golconda 

allochthon that was obducted onto the continent in the 

Early Triassic from a distant oceanic or back-arc basin are 

incompatible with modern observations as cited in the present 

report.

Acknowledgments

For geologic information on the Hot Springs Range, 

I have relied almost entirely on the published work of A. 

Elizabeth Jones Crafford and on conversations with her. 

Thanks to Linda and Michael McCollum for steering me to 

olistoliths and other important features of the Scott Canyon 

Formation in the Battle Mountain area. For paleontological 

support, I relied on John Repetski, Anita Harris, and Bruce 

Wardlaw all of the U.S. Geological Survey. Reviews by A. 

Elizabeth Jones Crafford and Patricia Cashman have improved 

the manuscript and are greatly appreciated.

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Manuscript approved for publication August 18, 2008.

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Keith B. Ketner—The Inskip Formation, the Harmony Formation, and the Havallah Sequence of Northwestern Nevada—Professional Paper 1757

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