Wapiti" Formation and 

Trout Peak Trachyandesite 

Northwestern Wyoming

By WILLIS H. NELSON and WILLIAM G. PIERCE

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 1254-H

Description of two new formations

in the Absaroka Mountains, If^yoming
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

U.S. GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1968

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 - Price 10 cents (paper cover)
CONTENTS

Page

Abstract--___-___-_-__--_-_--------------------------------------- HI

Introduction _____-_______-____-____--_--_------------------------- 1

Wapiti Formation__________________----_---_--__------------------ 1

Trout Peak Trachyandesite___----_-----_--------------------------- 9

References cited._____________-_-_____-__--_----------------------- H

ILLUSTRATIONS

Page

FIGUKE 1. Map showing generalized distribution of the Wapiti Formation and the Trout Peak Trachyandesite in the northeastern Absaroka Mountains, northwestern Wyoming_____- H2 

2. Generalized stratigraphic sections______________---_--_---_ 4

TABLE

Page

TABLE 1. Chemical and normative analyses of rocks of the Wapiti Formation and the Trout Peak Trachyandesite-______________ H5

in

CONTRIBUTIONS TO STRATIGRAPHY

WAPITI FORMATION AND TROUT PEAK 

TRACHYANDESITE, NORTHWESTERN WYOMING

By WILLIS H. NELSON and WILLIAM G. PIERCE

ABSTRACT

The volcanic rocks of the northeastern Absaroka Mountains consist of lava 

flows that are interbedded with breccia, sandstone, siltstone, and conglomerate 

composed, wholly or in part, of volcanic detritus. The name Wapiti Formation is 

given to the lower 1,500 to 4,000 feet of this heterogeneous assemblage, excluding 

the Cathedral Cliffs Formation, which locally underlies the Wapiti Formation in 

the northwestern part of the area. Over part of its extent the formation includes, 

near the middle, as much as 1,100 feet of lava flows herein called the Jim 

Mountain Member.

A sequence of lava flows 150 to 1,000 feet thick that overlie the Wapiti Formation is named the Trout Peak Trachyandesite.

The Wapiti Formation is of early or middle Eocene age, or botli. The Trout 

Peak Trachyandesite is considered to be of Eocene (probably late Eocene) age, 

although potassium-argon dates conflict with this age assignment.

INTRODUCTION

The names Wapiti Formation and Trout Peak Trachyandesite are 

introduced for slightly deformed rocks of Eocene age that were 

heretofore informally called early basic breccia and early basalt sheets 

respectively (Hague, 1899). These informal names have been useful 

in reconnaissance studies that have shown the general distribution of 

rocks in the volcanic pile that makes up much of the northern Absaroka 

Mountains. The names a,re not suitable for use as formal names, 

however, because they are not descriptively accurate, they are not 

geographically derived, and they are not consistently used.

WAPITI FORMATION

The Wapiti Formation is here named from, exposures between about 

6,800 and 10,300 feet altitude in the mountains north and south of the 

Wapiti Post Office located about 18 miles west of Cody, Wyo. Stratigraphic section G north of the Wapiti Post Office is designated the 

type section (figs. 1 and 2).

Hi
H2 CONTRIBUTIONS TO STRATIGRAPHY

44"45' 109°30' 109°

44°15'

FIGUKE 1. Generalized distribution of the Wapiti Formation and the Trout Peak 

Trachyandesite in the northeastern Absaroka Mountains, northwestern 

Wyoming. Circled numbers show the locations of the analyzed specimens in 

table 1. Stratigraphic sections A, B, and C are shown in figure 2.
WAPITI FORMATION, TROUT PEAK TRACHYANDESITE, WYO. H3

The Wapiti Formation is composed of volcanic breccia, standstone, 

siltstone, conglomerate, and lava flows. The relative abundance of 

these rock types varies both vertically and horizontally (fig. 2). 

Individual layers that range from a few feet to a few hundreds of 

feet in thickness are dominated by one rock type and interfinger and 

are interbedded with layers dominated by other rock types.

The volcanic breccia is somber shades of brown, reddish brown, 

gray, and rarely greenish gray. Most of the breccia occurs as lenticular 

masses a few to many tens of feet in thickness and many hundreds of 

feet in lateral extent. Most of the thicker masses of breccia consist of 

numerous irregular beds, but some of them seem to be a single thick 

bed. Most of the breccia is believed to have been deposited as mudflows, 

as indicated by poor sorting, and each bed of such breccia seems to 

represent a single mudflow. Better sorting in some of the beds of 

breccia suggests that those beds were deposited by streams. Other beds 

have intermediate textural characteristics which suggest that there was 

virtually a complete transition between very fluid water-rich mudflows 

and fluvial transport and deposition. Most of the material comprising 

the breccia is volcanic detritus, either pyroclastic material or material 

derived from fragmentation of preexisting solid volcanic rocks. The 

matrix of the breccia is fine grained and is composed dominantly of 

silt to coarse-sand-sized detritus. It contains larger fragments that 

range from coarse-sand size to several feet across, but which are 

commonly from 1 to 12 inches across. The size of these larger fragments varies from bed to bed and also laterally within a given bed.

The individual fragments in the breccia are fine-grained volcanic 

rocks that contain phenocrysts of plagioclase, pyroxene, and local 

olivine or hornblende. Many of the fragments are vesicular. An 

analysis of a specimen of breccia that seems to be typical of the darkcolored breccia (table 1, specimen 1) suggests that the breccia is 

trachyandesite and similar to most of the flows in the formation.

A small proportion of the breccia in the formation is rich in hornblende and has a light-colored matrix. Both features suggest that this 

breccia is somewhat more felsic than the more abundant, darker breccia 

described above. This is also indicated by a chemical analysis of a 

specimen of light-colored breccia (table 1, specimen 2), which indicates 

a dacitic composition. The texture of the detritus in the light-colored 

breccia suggests that most of it is pyroclastic; most of the deposits of 

light-colored breccia seem to have been reworked but some seem to be 

unmodified aerial deposits.

Volcanic sandstone and siltstone, along with lesser amounts of volcanic conglomerate, commonly occur together in sequences that range 

from a few feet to many tens of feet in thickness. Most of these rocks
NW

Jim Mountain 

Stratigraphic section C

5000' 

4000' 

3000' 

2000' 

1000'-

Ptarmigan Mountain 

Stratigraphic section B

FIGURE 2. Generalized stratigraphic sections of the Wapiti Formation and 

sections are shown in figure 1; circled numbers indicate stratigraphic p

ologies of the Wapiti Formation and Trout Peak Trachyandesite: f, lav

siltstone, and conglomerate; u, lava flows and volcanic clastic rocks, un
TABLE 1. Chemical and normative analyses of rocks of the Wapiti Form

Chemical analyses by P. Elmore, S. Botts, L. Artis, D. Taylor, G. Chloe, H. Smith, and J. Glen by rapid 

by atomic absorption. CIPW norm computed using U.S. Geol. Survey general rock norms comp

Wapiti Formation

2 3 4 5 6 7 

Chemical analyses

SiOj..... ....................... 51.4

AljOs- _ ................... 16.2

FeO _____ . __ .... __ . __ 2.2

MgO...... ..................... 4.2

CaO. .......................... 7. 7

NajO ______ ..... _ ....... 3.0

KaO....... ..................... 3. 6

HaO- . ...................... 2.4

HjO+ _________ . __ ..... 1.3

TiOa- - ..................... .99

PaO5 . ....................... .48

MnO... ..................... . 17

CO».............. .............. . 12

Sum... ___ ... ___ .. 100

60.6 

17.4 

40 

.38 

2.5 

48 

3.7 

1.9 

2.1 

1.2 

.49 

.20 

.05 

.12

99

54.3 

17.5 

3.1 

45 

4.1 

7.2 

3.5 

2.3 

.95 

.85 

.90 

.43 

.13 

.08

100

56.2 

17.3 

4.3 

2.9 

3.3 

5.2 

4.0 

3.2 

.81 

.69 

.98 

.66 

.16 

.07

100

54.3 

15.8 

5.0 

3.6 

4.8 

6.6 

3.2 

2.6 

1.4 

.70 

1.0 

.60 

.15 

.07

100

544 

17.1 

6.2 

1.2 

2.9 

5.4 

3.8 

3.5 

1.6 

1.0 

.98 

.63 

.09 

.11

100

545 

18.3 

4.6 

1.9 

2.9 

6.2 

3.9 

40 

.89 

1.0 

.89 

.62 

.13 

.12

100

CIPW norm

q......... ...................... 2.22

or.-..........-.... ...-...... 21.8

ab _______ __________ 26.0

an __________________ 20. 6

wo.. ________________ 6.08 .

en...... ..... .......... 10. 7

fa.......... ....... ............. ........ .

fo.- . .... .............. ........ .

fa.............................. ........ . mt... - ... ...... . 4.90 .

hm.. 2.88

il.............-- ..... ..... 1.93

ap .. 1. 16

1. Dark-colored breccia fragment. 

2. Lieht-colored breccia.

19.2 

1.32

11.5 

32.2 

22.3

6.40

4.11 

.93 

.01

.49 

.38

460

13.7 

29.9 

25.5

3.02 

10.3 

4.51

4.55

1.73

1.03 

.18

6.81

19.1 

34.2 

20.0

.53 

8.31 

.46

6.30

1.88

1.58 

.16

7.52

15.6 

27.5 

21.4

3.10 

12.1 

1.13

7.37

1.93

1.44 

.16

6.79

21.0 

32.7 

19.6

1.15 

7.35

1.34 

5.38 

1.89

1.52 

.25

2.15

23.9 

33.3 

20.8

2.25 

7.29

401 

1.88 

1.71

1.48 

.28

3-14. Lavas.
H6 CONTRIBUTIONS TO STRATIGRAPHY

are well bedded and locally crossbedded which suggests that they are 

stream deposits. A few of the beds of sand- and silt-sized material are 

so thin, widespread, and poorly sorted that they are thought to be 

aerially deposited tuffs. The volcanic sandstone, siltstone, and conglomerate consist of medium-brown and gray volcanic detritus including pyroclastic material, fragments of lava flows, detritus derived from 

volcanic breccia deposits, and quartz and quartzite. Quartzite pebbles 

and cobbles abound in some of the conglomerate, and petrified wood is 

sparsely scattered through all the rocks. Some beds are lighter colored 

and probably somewhat more felsic than the dark-colored rocks just 

described.

Lava flows, either singly or in sequences of several flows, occur 

sporadically within the Wapiti Formation. Trachyandesite flows are 

the most abundant, and dacitic flows, much less so.

The trachyandesite flows within the Wapiti Formation are identical 

to those of the Trout Peak Trachyandesite, and the description of the 

flows in the Trout Peak Trachyandesite, which is given below, is 

applicable to them. These flows commonly are less than 120 feet thick 

except where they fill channels. Along the creek near section B one of 

these channel fills is about 400 feet thick; this is illustrated diagrammatically in section 5, figure 2.

The name Jim Mountain Member is here given to the prominent 

sequence of trachyandesite lava flows that occur near the middle of 

the Wapiti Formation throughout the map area (fig. 1) north of the 

South Fork of the Shoshone River. Its type section is designated as 

stratigraphic section O in the vicinity of Jim Mountain (fig. 2). This 

member consists of a maximum of 8 to 10 flows in the central part of 

the area; it thins southward, so that in the area between the forks of 

the Shoshone River, locally only one flow is present at this horizon. 

As many as three superimposed trachyandesite flows occur within the 

Wapiti Formation on the north slope of Carter Mountain, but none 

of them can be confidently correlated across the South Fork valley 

with the Jim Mountain Member. Specimens 3 through 6, table 1, are 

of flows from the Jim Mountain Member.

Dacitic lava flows occur mainly in the upper part of the Wapiti 

Formation. They generally seem to be thinner and less extensive than 

individual trachyandesite flows, but this may be an illusion that results 

from the fact that the dacitic flows do not crop out as prominently as 

the trachyandesite flows. In addition to the plagioclase and pyroxene 

phenocrysts that occur in the trachyandesite flows, the dacitic flows 

all contain abundant black acicular amphibole phenocrysts. Specimen 

8, table 1, is from a dacitic flow.
WAPITI FORMATION, TROUT PEAK TRACHYANDESITE, WYO. H7

Roughly the lower 800 feet of the Wapiti Formation in stratigraphic 

section C, the type section, consists of well-bedded light-colored volcanic sandstone, siltstone, and conglomerate that enclose wedge- or 

lenticular-shaped masses of irregularly bedded somber-colored volcanic 

breccia. These masses are as much as 400 feet thick and occur discontinuously at the base of the formation. The next higher part of the 

formation consists of about 1,000 feet of somber-colored breccia in 

irregular beds that range from a few feet to several tens of feet in 

thickness and that grade into and are interbedded with volcanic sandstone. Above this are eight trachyandesite flows totaling about 1,000 

feet thick which comprise the Jim Mountain Member of the Wapiti 

Formation. The upper 1,000 feet of the Wapiti Formation above the 

Jim Mountain Member consists of interbedded volcanic breccia, sandstone, siltstone, and discontinuous lava flows. Somber-colored breccia 

is the predominant rock; light-colored breccia, in layers up to a few 

tens of feet in thickness, is sporadically distributed throughout the 

upper 1,000 feet of the formation. The somber- and light-colored volcanic sandstone and siltstone and trachyandesite and dacite lava flows 

are interbedded with the breccia.

Away from the type section, only the Jim Mountain Member and 

the sandstone and siltstone at the base of the formation can be recognized. Light-colored volcanic sandstone and siltstone form a discontinuous but widespread unit at the base of the formation. This unit is 

commonly only a few feet to a few tens of feet thick, but locally it is 

much thicker; for example, on Pat O'Hara Mountain it is more than 

300 feet thick, and near stratigraphic section B all the volcanic 

breccia beneath the Jim Mountain Member locally pinches out at the 

same place, so that the entire formation beneath the Jim Mountain 

Member locally consists of volcanic sandstone, siltstone, and conglomerate. In the type section, as already noted, volcanic sandstone, siltstone, 

and conglomerate locally make up the entire lower 800 feet of the 

formation.

The distribution of rock types within the Wapiti Formation varies 

from the distribution of rock types at the type locality, and 

although most of the variations are erratic, the overall thickness of the 

formation, the thickness of the Jim Mountain Member, and the proportion of breccia in the formation all decrease, somewhat systematically, from north to south. The overall thickness of the formation 

ranges from at least 3,800 feet in the northern part of the area to about 

1,700 feet at the southern edge; this is shown diagranmiatically in 

figure 2. The Jim Mountain Member, which is about 1,000 feet thick 

in the northern part of the area, is thinner and may be locally absent 

in the southern part. In the northern part volcanic sandstone and silt-
H8 CONTRIBUTIONS TO STRATIGRAPHY

stone occur only as thin wedges and lenses interbedded in volcanic 

breccia, but in the southern part the relationships are reversed breccia 

occurs as wedges and lenses within volcanic sandstone, siltstone, and 

associated conglomerate.

The three trends that have just been noted suggest that much of the 

material in the Wapiti Formation came from a volcanic source or 

sources in or near the northwestern part of the area of figure 1. However, no volcanic centers have been identified within this area, and 

although several are known to the northwest, none of these have as 

yet been identified specifically as a source of material in the Wapiti 

Formation.

The Wapiti Formation is in part stratigraphically equivalent to the 

middle Eocene Pitchfork Formation which Hay (1956) proposed for 

a sequence of volcanic sandstone and siltstone in the area south of 

figure 1. The Pitchfork Formation is a facies of the sequence of volcanic rocks that Hague (1899) had informally termed "early basic 

breccia." Hay noted that the volcanic sandstone and siltstone, which he 

called the detrital facies, interfingered with breccia, and he assigned 

the detrital tongues to the Pitchfork Formation and continued to use 

the term early basic breccia for the breccia beds. Thus, the Pitchfork 

Formation was set up to distinguish the part of the sequence composed 

predominantly of volcanic sandstone and siltstone from the brecciarich part of the sequence. If the Pitchfork Formation were extended 

to include the rocks here defined as the Wapiti Formation, this distinction would be obliterated, an extensive revision of the description of 

the rocks composing the Pitchfork Formation would be required, and 

it would defeat the purpose for which the Pitchfork was named. Therefore, we believe that the name Pitchfork Formation should be restricted to the breccia-poor sequence of rocks in the area south of figure 

1, and that it is useful to introduce the new name Wapiti Formation for 

the breccia-rich sequence of rocks in the area of figure 1. Thus, the 

usage of Pitchfork, as originally proposed and as used up to the present time, remains unchanged. Because of inadequate exposures, it is 

impossible to map the details of the transition between these two formations. Instead the mutual boundary is arbitrarily defined as the 

place that separates areas wherein breccia is the dominant rock type 

from areas wherein it is the subordinate rock type. This change occurs 

within a fairly narrow zone near, and approximately parallel to, the 

southern boundary of figure 1.

The Wapiti Formation in much of the area shown in figure 1 overlies 

the Will wood Formation of early Eocene age and in a lesser area overlies older rocks, with slight to locally strong discordance. Also, in a 

number of places the Wapiti Formation surrounds and buries blocks
WAPITI FORMATION, TROUT PEAK TRACHYANDESITE, WYO. H9

of Paleozoic rock, mostly carbonate, some of them hundreds of feet 

thick and thousands of feet across. These blocks were dispersed on the 

early Eocene land surface by the Heart Mountain detachment fault 

before deposition of the Wapiti Formation (Pierce, 1957,1963). During the deposition of the lower part of the "Wapiti Formation, these 

blocks were topographic highs, which shed fragments up to many feet 

across that became sparsely distributed in the lower part of the formation. In the north-central part of the Wapiti quadrangle, and locally 

elsewhere, blocks of bedded sedimentary rocks of both the Willwood 

and Wapiti Formations have been incorporated in the lower 500 feet of 

the Wapiti Formation, probably by small-scale gliding tectonics. Many 

of these blocks are steeply and randomly tilted. In the northwestern 

corner of the Pat O'Hara Mountain quadrangle, the Wapiti Formation 

locally overlies light-colored tuff, volcanic sandstone, siltstone, and 

breccia of the Cathedral Cliffs Formation, of late early or early middle 

Eocene age (Pierce, 1963). These rocks are discordant beneath the 

Wapiti Formation and lie on Heart Mountain detachment blocks on 

which they seem to have been deposited before the Heart Mountain 

faulting.

As noted above, the Wapiti Formation correlates in part with the 

Pitchfork Formation. Vertebrate remains of middle or late Eocene age 

were collected by Jepsen (1939) and Van Houten (1944) from the 

lower part of the Pitchfork Formation. Jepsen restudied these two 

collections and he reported (in Hay, 1956, p. 1883-1884) that three of 

the species "all indicate early Bridgerian age" and one "suggests late 

Wasatchian (Wind River)." Dorf (1939) reports that the flora near 

Valley, Wyo. (which is from the Wapiti Formation of this report) is 

of late Green River to early Bridger age, which he considers early 

middle Eocene. From the Wapiti Formation within or near the Wapiti 

quadrangle, fossil plant collections identified by R. W. Brown and 

Jack A. Wolfe and reported in Pierce (1963) indicate a probable 

middle Eocene age for four collections, and a late early or early 

middle Eocene for one collection. Thus, the Wapiti Formation is 

assigned an age of early or middle Eocene or both.

TROUT PEAK TRACHYANDESITE

The Trout Peak Trachyandesite is here named from exposures on 

Trout Peak (fig. 1) about 10 miles northwest of Wapiti Post Office. 

The type section extends from the top of Trout Peak at an altitude of 

12,244 feet down to about 11,400 feet. Figure 1 shows the distribution 

of the formation in the area that we have studied.

The Trout Peak Trachyandesite consists of lava flows locally interbedded with subordinate amounts of volcanic clastic rock. The flows 

are gray and weather brown and reddish brown; they commonly have
H10 CONTRIBUTIONS TO STRATIGRAPHY

a maximum thickness of about 150 feet and are locally columnar 

jointed. The tops and bottoms of the flows are commonly vesicular and 

brecciated owing to flowage of the central parts after the outer parts 

had solidified. They have aphanitic groundmasses which contain 

plagioclase and pyroxene, and locally olivine or hornblende phenocrysts. Analyses 9 through 14, tafale 1, are of specimens of these flows, 

and show them to be trachyandesite.

Five lava flows, each slightly more than 100 feet thick, cap the upper 

part of Trout Peak; the lowest flow is separated from the overlying 

flows by about 150 feet of light-colored, moderately well-bedded 

volcanic sandstone and siltstone. Nine flows cap the ridge about halfway between Trout Peak and the northwest corner of the Wapiti 

quadrangle. Flows of the Trout Peak Trachyandesite occur on a northeast-trending spur of Ptarmigan Mountain (fig. 1). There the formation is about 1,000 feet thick and consists of 9 or 10 flows of which the 

second and third from the base are separated by about 150 feet of 

orange lapilli tuff.

The continuity of the Trout Peak Trachyandesite in the area of figure 1 is interrupted by the valleys of both the North and South Forks of 

Shoshone River. Correlation across these valleys is suggested first by 

the similarity of the flows that make up this f omiation throughout the 

area. This is not conclusive, however, because similar flows also occur 

at various levels in the underlying Wapiti Formation. Correlation 

across the North Fork is based with considerable confidence on the 

continuity of similar sequences of rocks within the Wapiti Formation, 

especially the Jim Mountain Member, on the two sides of the valley. 

Correlation across the South Fork valley is supported by the fact that 

the Trout Peak Trachyandesite flows are overlain by light-colored 

rocks of the Wiggins Formation on Carter and Ptarmigan Mountains. 

Correlation across both the North and South Forks of the Shoshone 

River is further confirmed by the widespread occurrence of the Trout 

Peak Trachyandesite at about the same altitude for several miles west 

of the mapped area (fig. 1).

In the area of figure 1 the contacts between the Trout Peak Trachyandesite and the Wapiti Formation below and the Wiggins Formamation above seem to be conformable and gradational. The lower part 

of the Wiggins Formation consists of light-colored tuffaceous sandstone, siltstone, conglomerate, and breccia that are similar to material 

that occurs between some of the Trout Peak Trachyandesite flows and 

also locally within the upper part of the Wapiti Formation.

The Trout Peak Trachyandesite lies between the Wapiti Formation, 

which may be as young as middle Eocene, and the Wiggins Formation, 

which Love (1939, p. 83) considered to be Oligocene in age based on
WAPITI FORMATION, TROUT PEAK TRACHYANDESITE, WYO. Hll

vertebrate fossils from about 40 miles south of the area of figure 1. 

Wilson (1963, p. 19) reported that volcanic ash near the base of the 

Wiggins Formation on the south side of Carter Mountain has provided a potassium-argon date that indicates, "an early Oligocene age 

possibly latest Eocene (K. S. Houston, oral commun., 1962)," whereas 

vertebrate fossils from immediately below the ash "suggest an Eocene 

age (E. L, Simons, oral commun., 1962)," J. D. Love (oral commun., 

1965) believes that the rocks containing the vertebrate fossils are distinctly different from most of the rocks of the "Wiggins Formation, 

and he has suggested that there may be an unconformity between the 

rocks that contain the vertebrate fossils and the Wiggins Formation. 

H. L. Prostka (written commun., May 23,1967) has collected samples 

both from a welded tuff and from a dike. The tuff is interbedded with, 

and the dike cuts, rocks that are probably equivalent to the Trout 

Peak Thachyandesite about 20 miles west of the map area (fig. 1) J. D. 

Obradovich, U.S. Geological survey, has obtained potassium-argon 

dates of 51.3 and 52.6 ±1.6 m.y. from these samples. These dates are 

too old to- be reconciled with the possible middle Eocene age indicated 

by fossils for part of the underlying Wapiti Formation; we therefore 

consider the Trout Peak Trachyandesite to be late Eocene age, at least 

until further data are available.

REFERENCES CITED

Dorf, Erling, 1939, Middle Eocene flora from the volcanic rocks of the Absaroka 

Range, Park County, Wyoming [abs.]: Geol. Soc. America Bull., v. 50, no. 

12, pt. 2, p. 1906-1907.

Hague, Arnold, 1899, Description of the Absaroka quadrangle (Crandall and 

Ishawooa quadrangles) [Wyoming]: U.S. Geol. Survey Geol. Atlas, Folio 

52, 6 p.

Hay, R. L., 1956, Pitchfork Formation, detrital facies of early basic breccia, 

Absaroka Range, Wyoming: Am. Assoc. Petroleum Geologists Bull., v. 40, 

no. 8, p. 1863-1898.

Jepson, G. L., 1939, Dating Absaroka volcanic rocks by vertebrate fossils [abs.]: 

Geol. Soc. America Bull., v. 50, no. 12, pt. 2, p. 1914.

Love, J. D., 1939, Geology along the southern margin of the Absaroka Range, 

Wyoming: Geol. Soc. America Spec. Paper 20, 134 p.

Pierce, W. G., 1957, Heart Mountain and South Fork detachment thrusts of 

Wyoming: Am. Assoc. Petroleum Geologists Bull., v. 41, no. 4, p. 591-626.

 1963, Cathedral Cliffs Formation, the early acid breccia unit of northwestern Wyoming: Geol. Soc. America Bull., v. 74, no. 1, p. 9-22.

Shapiro, Leonard, and Brannock, W. W., 1962, Rapid analysis of silicate, carbonate, and phosphate rocks: U.S. Geol. Survey Bull. 1144-A, 56 p.

Van Houten, F. B., 1944, Stratigraphy of the Willwood and Tatrnan Formations 

in northwestern Wyoming: Geol. Soc. America Bull., v. 55, no. 2, p. 165-210.

Wilson, W. H., 1963, Correlation of volcanic rock units in the southern Absaroka 

Mountains, northwest Wyoming: Wyoming Univ., [Laramie] Contr. Geology, 

v. 2, p. 13-20.

U.S. GOVERNMENT PRINTING OFFICE: 1968