New Cretaceous Formations in the 

Western Wyoming Thrust Belt

GEOLOGICAL SURVEY BULLETIN 1372-1
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New Cretaceous Formations in the 

Western Wyoming Thrust Belt

By WILLIAM W. RUBEY

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 1372-1

Westward equivalents of Bear River and Aspen 

Formations are divided into Jive new 

formations by two red-bed tongues of the 

Wayan Formation. The Milliard Shale changes 

northward to sandstone of the upper part of 

the new Blind Bull Formation

UNITED STATES GOVERNMENT PRINTING OFFICE, WASH INGTON : 1973
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress tatalog-tarti No. 73-600205

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

Washington, D. C. 20402 - Price 50 cents (paper cover) 

Stock Number 2401-02402
CONTENTS

Page

Abstract ___________________________________________ II

Introduction _____________________________________ 1

Lower Cretaceous _____________________________________ 3

Smiths Formation __________________________________ 5

Thomas Fork Formation ______________________________ 10

Cokeville Formation _________________________________ 14

Quealy Formation__________________________________ 17

Sage Junction Formation ______________________________ 19

Upper Cretaceous ____________________________________ 23

Blind Bull Formation _________________________________ 25

References cited _________________________________________ 34

ILLUSTRATIONS

Page

FIGURE 1. Map showing central part of thrust belt of western Wyoming,

southeastern Idaho, and northeastern Utah ______________ 12

2. Northwest-southeast sections, showing lateral relations of Cretaceous

rock units above the Gannett Group _________________ 4 

3 6. Geologic maps showing type localities:

3. Smiths Formation __.____________________ 7

4. Thomas Fork Formation __________________ 12

5. Cokeville and Quealy Formations _________________ 16

6. Sage Junction Formation __________________ 20

7. Sections showing lateral relations of Upper Cretaceous formations in the

Kemmerer, Cokeville, and Afton quadrangles ___________ 26

8. Geologic map, showing location of type section of the Blind Bull

Formation and of the upper and lower tongues of the Milliard Shale 28

CONTRIBUTIONS TO STRATIGRAPHY

NEW CRETACEOUS FORMATIONS IN THE 

WESTERN WYOMING THRUST BELT

By WILLIAM W. RUBEY

ABSTRACT

Six new formations are named and defined for distinctive rock sequences mapped in several 

quadrangles in the central part of the western Wyoming thrust belt. Previously recognized 

rock-stratigraphic units in the region are inapplicable to the sequences.

A western sequence of Lower Cretaceous rocks is divided into five formations by two units of 

variegated mudstone regarded as southeastward-extending tongues of the Wayan Formation 

red beds. The basal formation, the Smiths Formation, directly above the Gannett Group and 

about 750 feet thick near the type section, consists of ferruginous black shale and tan quartzitic 

sandstone. The overlying Thomas Fork Formation, about 1,000 feet thick, consists of banded 

and variegated red, purple, brown, and green mudstone and some gray to tan sandstone. The 

middle formation, the Cokeville Formation, about 1,600 feet thick, consists of gray sandstone, 

siltstone, and claystone, tan limestone, and porcelanite, bentonite, and coal. The Quealy Formation, about 1,000 feet thick, consists of red and variegated pastel-tinted mudstone and pink, 

gray, and tan sandstone. The Sage Junction Formation, at the top of the Lower Cretaceous 

sequence, is more than 3,000 feet thick and consists mainly of gray and tan siltstone, sandstone, 

and quartzite but also contains porcelanite, limestone, conglomerate, and some coal. The 

Smiths, Thomas Fork, and lower part of the Cokeville Formations are approximately correlative with the Bear River Formation in the eastern part of the thrust belt, although parts of 

the Smiths may be older. The upper part of the Cokeville and Quealy Formations and most of 

the Sage Junction Formation are correlative with the Aspen Shale. The uppermost several hundred feet of the Sage Junction Formation may contain beds equivalent in age to parts of the 

Frontier Formation.

In the eastern part of the thrust belt, the marine Milliard Shale, which separates the underlying Frontier Formation from the Adaville Formation, becomes increasingly sandy northward 

and northwestward until divisions of the Upper Cretaceous sequence can no longer be mapped. 

The Blind Bull Formation, more than 5,000 feet thick, is the name proposed for this Upper 

Cretaceous sequence; the formation is separated into the lower and upper parts by the mappable lower and upper tongues of the Milliard Shale on the east, but not on the west. The Blind 

Bull consists of partly conglomeratic sandstone, siltstone, claystone, coal, and bentonite. It is 

directly underlain by the Aspen Shale and overlain, where mapped thus far, by thrust plates of 

older rock. The Shurtliff Sandstone Member of the Milliard Shale near Kemmerer is regarded 

as a southward-extending tongue of the Blind Bull Formation.

INTRODUCTION

Geologic mapping in the central part of the thrust belt of western Wyoming revealed some new rock-stratigraphic units that differ from

II
12 CONTRIBUTIONS TO STRATIGRAPHY

Cretaceous formations formerly described (Veatch, 1907; Schultz, 1914; 

Mansfield, 1927) and still commonly recognized within the region. These 

new formations are depicted on the geologic map of the Afton quadrangle

112°00' HO-OO'

FIGURE 1. Map showing central part of thrust belt of western Wyoming, southeastern 

Idaho, and northeastern Utah, and quadrangles mentioned in this report. Principal thrust 

faults indicated by sawteeth, which are on upper plate; dotted where concealed.
NEW CRETACEOUS FORMATIONS, WESTERN WYOMING 13

(Rubey, 1973) and on geologic maps that are being prepared on the 

Cokeville quadrangle (W. W. Rubey, J. I. Tracey, Jr., and S. S. Oriel) and 

on the Sage and Kemmerer quadrangles (W. W. Rubey, S. S. Oriel, and J. 

I. Tracey, Jr.) (fig. 1).

The purpose of this contribution is to describe these new formations and 

the type sections upon which they are based so they might serve as a basis 

for future studies of the Cretaceous tectonostratigraphic history of the 

region. My understanding of these units was helped immeasurably by discussions with, and contributions by, the late John B. Reeside, Jr. We examined numerous sections of these rocks together, and many of the fossils 

found supporting the physical relations were identified by Reeside. In fact, 

the present report was to have been a joint paper by the two of us, and we 

were both working on it at the time of his unfortunate death in 1958. The 

companionship in the field, during the later years of this study, of Joshua I. 

Tracey, Jr., and Steven S. Oriel was both helpful and stimulating, and I especially thank Oriel for preparing a draft of this report that encouraged me 

to return to an earlier draft that I had set aside after John Reeside's death. I 

also thank Daniel A. Jobin and Donald E. Trimble, whose suggestions substantially improved the report.

LOWER CRETACEOUS

Sedimentary rock sequences above the Gannett Group in the western part 

of the region differ markedly in composition and thickness from those in the 

eastern part which have been assigned to the Bear River and Aspen Formations. These differences are so marked that the same rock-stratigraphic 

designations cannot logically be applied to both. The eastern sequence is exposed east of the trace of the Absaroka fault, whereas the western sequence 

is present in the several thrust plates west of and above the Absaroka fault. 

Although parts of the western sequence resemble lithologies assigned to the 

Bear River and Aspen Formations, accounting for previous use of these 

names west of the Absaroka fault, an entirely new division has proved more 

practical in mapping and is more expressive of the facies relations that merit 

formal recognition. Informal brief descriptions of the divisions have been 

published previously (as in Moritz, 1953, p. 69).

At no place are the eastern and western sequences exposed in lateral contact. Everywhere they are separated by areas from a few to several miles 

wide where these beds either have been eroded away or are buried under 

higher thrust plates. The inferred lateral relations of the formations in the 

two sequences are shown in figure 2.

The Gannett Group directly beneath the new units has been sufficiently 

well described in recent reports (Eyer, 1969; Purer, 1970) that repetition in 

this report is unnecessary.

The western sequence of Lower Cretaceous rocks above the Gannett 

Group is divided here into five new formations. These formations are 

named, in ascending order, the Smiths, Thomas Fork, Cokeville, Quealy,
14 CONTRIBUTIONS TO STRATIGRAPHY

op IIO'OO' 110°30' 

SE 43°. 

Smiths Formation

Gannett Group

Gannett Group FEET

 4000

on____ C

Aspen Shale 

Bear River Formation

Thomas Fork Formation 

Smiths Formation*5'"""""^" 3

Gannett Group

FIGURE 2. Northwest-southeast sections, showing the probable lateral interflngering 

relations of Cretaceous rock units above the Gannett Group at their westernmost exposures 

near the western border of Wyoming with the eastern facies of rocks formed at the same time 

over wide areas in western Wyoming. Dark patterns indicate location of measured sections.

and Sage Junction Formations for geographic features in the areas in which 

they have been mapped.

The bottom, middle, and top formations consist mainly of strata that 

resemble somewhat those assigned on the east to the Bear River and Aspen
NEW CRETACEOUS FORMATIONS, WESTERN WYOMING 15

Formations. The intervening Thomas Fork and Quealy Formations, 

however, consist mainly of variegated mudstones and sandstones that have 

no recognized counterparts in the east. These variegated units may be 

regarded as south- and southeastward-extending tongues of the mainly red 

Wayan Formation described by Mansfield (1927, p. 105) for the Lanes 

Creek and Freedom quadrangles. The intervening Cokeville Formation 

pinches out northwestward toward the Freedom quadrangle, where a 

threefold division the Smiths, Wayan, and Sage Junction Formations 

has been mapped by S. S. Oriel and L. B. Platt (unpub. data, Dec. 6, 1971). 

However, because Mansfield (1927, pi. 5) initially mapped many rocks as 

Wayan in the Freedom quadrangle that belong instead to the Gannett 

Group, his understanding and description of the Wayan (p. 105 108) were 

less than clear and accurate, according to my own observations and those of 

J. B. Reeside, Jr., which are confirmed by S. S. Oriel and L. B. Platt 

(written commun., Dec. 6, 1971). Redefinition of the Wayan Formation is 

clearly necessary but lies beyond the scope of this report.

The proposed Smiths Formation, which contains abundant black shale, 

and the proposed Cokeville Formation, which contains beds of highly 

fossiliferous and Pyrgulifera-bearing limestone, are not treated here as 

simply tongues of the Bear River Formation interfingering northwestward 

into time-equivalent red and variegated strata. Abundant beds of quartzitic 

sandstone and of the highly distinctive Kootenai-Cloverly fauna (which has 

not been found in typical Bear River) and the absence of the characteristic 

coquinas and fossils of the Bear River in the proposed Smiths Formation 

make it inadvisable to consider these beds as simply a northwestern tongue 

of the Bear River Formation; rather, they should be ranked as an independent formation. Similarly, the presence of numerous coaly beds and of 

fossils of post-Bear River age and the absence of characteristic black shale 

of the Bear River Formation make the Cokeville Formation compositionally distinctive from the Bear River.

In general, the Smiths, Thomas Fork, and lower part of the Cokeville 

Formations are approximately the same age as the Bear River Formation, 

although parts of the Smiths may be somewhat older. The upper part of the 

Cokeville, and Quealy, and much of the Sage Junction Formations are 

probably the same age as the Aspen Shale. The uppermost beds of the Sage 

Junction Formation may represent parts of the Frontier Formation.

SMITHS FORMATION

The Gannett Group is directly overlain, in the hills along Smiths Fork, by 

a unit here named the Smiths Formation. Its lower unnamed member consists mainly of ferruginous black shale, and the upper unnamed member, of 

tan very fine grained quartzitic sandstone, although these rock types are interbedded and are present throughout the formation. The formation is particularly well exposed farther north, close to the Smiths Fork Guard Station 

of the U.S. Forest Service, for which it is named, in the Cokeville 30-minute 

quadrangle.
16 CONTRIBUTIONS TO STRATIGRAPHY

The noncalcareous black fissile shale and the tan fine-grained quartzitic 

sandstone beds of the Smiths Formation are readily distinguished from the 

gray limestone and calcareous red, purplish, and gray siltstone beds of the 

underlying Gannett Group and from the variegated mudstone and 

sandstone and nodular limestone of the overlying Thomas Fork Formation.

The upper member of the formation, the tan fine-grained quartzitic 

sandstone, is the same as that which was called the Tygee Sandstone by 

Mansfield and Roundy in their paper (1916, p. 83) in which the formations 

of the Gannett Group and the overlying Wayan Formation were first 

described. The upper, sandstone member of the Smiths Formation is exposed on the ridge along the Idaho-Wyoming boundary (Mansfield, 1927, 

pi. 7) near the type locality of the Draney Limestone (sec. 10, T. 8 S., R. 46 

E., Idaho), with which it is locally in fault contact. As a result of this juxtaposition, the sandstone was inadvertently included by Mansfield and 

Roundy in their Gannett Group.

A respectable but not convincing case can be made for retaining the name 

Tygee Sandstone for what is here called the upper, sandstone member of the 

Smiths Formation and restricting the name Smiths to the lower, shale 

member. However, the two rock types, black fissile shale and tan quartzitic 

sandstone, are interbedded with one another, and both are present 

throughout the formation.

At some localities the dark shale is intercalated with thin beds of quartzitic sandstone like that in the thicker beds above, and where exposures are 

sufficiently good, the thick beds of sandstone in the upper part commonly 

alternate with thinner beds of dark shale and siltstone. At a few places the 

thin sandstones in the lower part thicken and the thicker beds of sandstone 

in the upper part grade laterally into shale and siltstone and so the main 

sandstone development is in the lower rather than the upper part of the unit. 

For these reasons and because the black shale is the most persistent and 

diagnostic lithology for this part of the section, it seems best and simplest 

for economy of stratigraphic nomenclature to propose, albeit reluctantly, 

that the name Tygee Sandstone be abandoned and that Smiths Formation 

be used to include both of the two dominant lithologic types.

The type section of the Smiths Formation (fig. 3) is designated as that 

measured across a ridge 1.1 1.4 miles N. 68° W. of the Smiths Fork Guard 

Station in the NWKNEW sec. 27 of the unsurveyed T. 29 N., R. 118 W., 

where the formation is about 700 feet thick. The formation is thicker, about 

755 feet thick, where it is poorly exposed along the north bank of Smiths 

Fork, directly east of the guard station. This somewhat more accessible exposure, along a road, is here designated as one of two nearby reference sections. The formation is thinner, 300-400 feet thick, in the Sage and 

Kemmerer quadrangles. Fossils collected from the formation and reported 

on by J. B. Reeside, Jr., establish its Early Cretaceous age.
NEW CRETACEOUS FORMATIONS, WESTERN WYOMING 17

R. 118 W.

1 KILOMETER 

J

EXPLANATION

Qa Alluvium and colluvium QUATERNARY 

Tsl Salt Lake Formation - TERTIARY 

Kq Quealy Formation 

Kck Cokeville Formation 

Ktf Thomas Fork Formation 

Ks Smiths Formation 

Kg Gannett Group 

Jsp Stump Sandstone and

Contact

u

LOWER 

CRETACEOUS

Preuss Red Beds

UPPER 

JURASSIC

D

Fault

U, upthrown side 

D, downthrown side

38

Strike and 

dip of beds

# 

Coal prospect

FIGURE 3. Geologic map of the southeastern part of T. 29 N., R. 118 W., showing locations 

of type section (line with crossbars) and two reference sections (straight lines) of the Smiths 

Formation (stippled) in the Cokeville 30-minute quadrangle. Contour interval, 200 feet.
18 CONTRIBUTIONS TO STRATIGRAPHY 

Type section of the Smiths Formation

[1 '/4 miles west-northwest of Smiths Fork Guard Station, NWWNEW sec. 27, T. 29 N., R. 118 W. Measured by W. W. Rubey,

June 25, 1936]

Smiths Formation: Thickness 

Upper, sandstone member (part): ifeet) 

12. Sandstone, hard, fine-grained, somewhat olivaceous; brown -at base

of ledge that makes prominent ridge ___ 5+ 

Lower, shale member:

11. Covered________________________________ 21 

10. Shale, black clay with few hard ferruginous concretions and sandy

layers; no fossils found______________ _____ 250 

9. Shale, tan clay ___________________________ 29 

8. Limestone, hard; fossils abundant but difficult to collect ____ 1 

7. Shale, tan clay; like unit 5, but no fossils noted ________ 27 

6. Limestone, like unit 8 __________ '/£ 

5. Shale, tan clay; with highly fossiliferous ferruginous concretionary 

and more or less hardened layers of brown siltstone, particularly 

in upper half; fossil colln. 36 1 (Unios and gastropods): 

USNM

Unio aff. U. hamili McLearn 

Unio sp., triangular form 

Goniobasisl aff. G.I ortmanni Stanton 

Campeloma cf. C. harlowtonensis Stanton

"Kootenai" fauna (J. B. Reeside, Jr., written commun., 1937) 74 

4. Shale, tan.clay, poorly exposed_______ 38 

3. Limestone, light-gray-weathering; much like Draney, but black on

fresh surface and has bituminous odor ____ 1 

2. Poorly exposed. Red soil in upper two-thirds, grading to tan clay 

soil in lower third; very fine grained tan calcareous sandstone 1 Vi 

ft thick, approximately at middle of unit _ 108 

Total lower, shale member 549 VS 

Total Smiths Formation measured__________ _ 554'/£+

Draney Limestone (part):

1. Limestone, medium-gray, fine-grained; weathers to very light gray.

Makes low hogback _______________________ 10+

Reference section of the Smiths Formation

[East of Smiths Fork Guard Station, SEW sec. 23 and SWW sec. 24, T. 29 N., R. 118 W. Measured by W. W. Rubey, Aug. 24,

1938]

Thickness

Thomas Fork Formation (part): (feet) 

12. Shale, poorly exposed, light-purplish-gray and pinkish variegated, 

sandy. Fragments of sandstone and conglomerate in tan to faintly 

pinkish sandy shale soil _____________________ HO

Smiths Formation:

Upper, sandstone member:

11. Poorly exposed. Medium-gray soil with abundant fragments of tan

and buff-gray quartzite and small light-gray limestone nodules 185 

10. Block of white quartzite float, not more than 25 ft below true position and possibly less than 5 ft; fossil collns. 38 18B (scales of 

gar pike) and 38-18C (dicotyledonous leaves) ________ 2
NEW CRETACEOUS FORMATIONS, WESTERN WYOMING 19

Smiths Formation Continued Thickness 

Upper, sandstone member Continued <feet> 

9. Poorly exposed. Shaly soil, medium gray to black _______ 25± 

8. Limestone; concretionary bed; sandy, fossiliferous; fossil colln.

38 ISA (Unios and gastropods) ________________ 1 

7. Shale, buff, gray, sandy, poorly exposed ______________ 2'/2 

6. Quartzite, olive-brown, very hard, massive, noncalcareous, and 

well-sorted sandstone. Grains show some recrystallization; 

uniformly '/6 '/4 mm in diameter. Medium pale buff and gray 

where fresh, weathering to pale to medium buff. Individual beds 

2-5 ft thick. Abundant rich brown and black lichens on 

weathered surfaces. Unit makes prominent ridge with abundant 

quartzite talus ___________________________ 14

Total upper, sandstone member ________________ 229'/2 

Lower, shale member:

5. Shale, black, fissile, poorly exposed; surface strewn with blocks of

tan sandstone from above ___________________ 520 

4. Shale, gray to black, fissile, thin-bedded; contains medium-gray 

limestone nodules which weather medium buff gray. Fossil colln. 

38-19 ("Kootenai-Cloverly" fauna. Field identification by J. B. 

Reeside, Jr.) ___________________________ 6 

Total lower, shale member" __________________ 526

Total Smiths Formation ___________________ 755 Vi

Smoot Formation of Eyer (1969, p. 1383):

3. Covered _____________________________ 25

2. Shale, calcareous, pink and variegated _______________ 15 

Total Smoot Formation _____________________ 40

Draney Limestone (part):

1. Shale, light- to medium-gray, calcareous; a few 6- to 12-in.-thick

limestone beds ___________________________ 25 +

Reference section of the Smiths Formation

[3'/4 miles southwest of Smiths Fork Guard Station, south-central part of sec. 33, T. 29 N., R. 118 W. Measured by W. W.

Rubey, Aug. 9, 1938]

Thickness

Thomas Fork Formation (part): (feet)

9. Mudstone and sandstone, variegated _______________ 35 + 

Smiths Formation:

Upper, sandstone member:

8. Soil, tan sandy; alternating with 1- to 2-ft-thick beds of hard finegrained pale-buff-gray sandstone ________________ 100+

7. Sandstone, hard-white, fine-grained, calcareous; weathers pale buff

gray ________________________________ l'/2

6. Soil, tan, sandy clay; contains small sandstone and white limestone

chips _______________________«________ 36

5. Limestone, medium-gray; weathers light gray; dense; has fetid odor.

Fossils abundant but difficult to collect; colln. 38-22_____ ¥2

4. Quartzite, olive-brown; pale-tan hard fine-grained sandstone with 

numerous buff, brown, and red stains on joint surfaces; brown impressions of plant stems (reeds) _________________ 17

3. Poorly exposed. Tan sandy soil and fragments of olive-brown quartzite _____________________________ 46

Total upper, sandstone member _______________ 201 +
110 CONTRIBUTIONS TO STRATIGRAPHY

Smiths Formation Continued 'j*"e" 

Lower, shale member (part):

2. Poorly exposed. Abundant black shale chips in soil 10 

1. Shale, black; makes steep slope; fossil colln. 38 23 (bone

fragments) about 60 ft below top ______ 100+ 

Total lower, shale member measured _____ _ __ 110+ 

Total Smiths Formation measured 311 +

THOMAS FORK FORMATION

Also exposed in the hills along Smiths Fork is a unit here named the 

Thomas Fork Formation, for exposures along the Thomas Fork in the 

Cokeville quadrangle. The unit consists of banded and variegated red, 

purple, brown, and green mudstone and gray, tan, and buff sandstone which 

is conglomeratic in part with pebbles as much as 4 inches in diameter. The 

formation is characterized by pastel shades of the colors mentioned and 

abundant gray to brown limestone nodules as much as several inches in 

diameter.

The variegated mudstone and gray to buff sandstone beds of the Thomas 

Fork Formation may be easily distinguished from the beds of gray to tan 

abundantly fossiliferous sandstone and limestone and of gray sandstone, 

mudstone, and claystone of the overlying Cokeville Formation.

The type section (fig. 4) is that measured along the north bank of Thomas 

Fork, from the SEttNEMNWtt sec. 26 to the SWttSWMNWVi sec. 25, T. 

28 N., R. 119 W. Evident here are not only strata typical of the Thomas 

Fork Formation but also the intertonguing relation between the upper part 

of the formation and the overlying unit. The main body of the Thomas Fork 

is about 1,080 feet thick at the type section, but it is overlain by the 573- 

foot-thick lower tongue of the Cokeville Formation, described in the following measured section, and a 72-foot-thick upper tongue of th.e Thomas 

Fork. Although the Thomas Fork is about 2,000 feet thick farther north, on 

the southwest side of Star Valley, it thins southward to 350 feet in the Sage 

quadrangle. Its Early Cretaceous age is established by fossils in underlying 

and overlying units.

Type section of the Thomas Fork Formation

[At Thomas Fork, 2W miles above mouth of Salt Creek, from SEKNEJ4NWV4 sec. 26 to SWMSWMNWJ4 sec. 25, T. 28 N., 

R. 119 W. Measured by W. W. Rubey, Oct. 6 and 9, 1947]

Thickness

Cokeville Formation upper tongue (part): (feet) 

58. Sandstone, medium-hard, massive to thin-bedded; weathers pale 

gray; medium grained; calcareous; abundant dark grains; 

crossbedded (from north) ____________________ 28 

Thomas Fork Formation: 

Upper tongue:

57. Siltstone, red to almost chocolate-brown, calcareous; weathers 

fairly bright red. Red limestone nodules 3 in. across in upper 1 ft 

of unit ___________________-_-----_-__- 11

56. Sandstone, gray, medium-hard, calcareous, medium-grained; abundant dark grains _____________________ __ 2
NEW CRETACEOUS FORMATIONS, WESTERN WYOMING 111

Thomas Fork Formation Continued Thickness 

Upper tongue Continued \feet) 

55. Siltstone; in alternating red and gray beds 1 4 ft thick. Gray beds 

contain soft coarse-grained medium-gray sandstone with abundant dark grains _________________________ 59

Total upper tongue of Thomas Fork Formation 72

Cokeville Formation: 

Lower tongue:

54. Siltstone, pale-greenish-gray; 12 ft above base unit contains 1-ftthick bed of sandstone like unit 53 _______________ 38 

53. Sandstone, distinctly olive-green, medium-hard, massive, fine- to

medium-grained, calcareous; weathers medium brown _____ 3 

52. Siltstone, pale-greenish-gray ____________________ 31 

51. Sandstone, medium-hard, brownish-gray-weathering, fine-grained,

calcareous; abundant dark mineral grains ____________ 3 

50. Siltstone, light-gray; surface strewn with sandstone blocks from

above ________________________________ 80 

49. Siltstone, light-gray _________________________ 80 

48. Siltstone, gray; like unit 47, but poorly exposed ___________ 35

47. Siltstone, pale-greenish-gray, blocky, highly calcareous _____ 15 

46. Sandstone; like unit 44, but more massive and less hard ____ 12 

45. Siltstone, gray, poorly exposed ___________________ 8 

44. Sandstone, hard, ledge-making, medium-grained, calcareous; abundant dark mineral grains. Thin bedded but hard throughout;

weathers pale tan gray; lichens are on surface_________ 3 

43. Soil, gray, poorly exposed; like unit 42, but has abundant chips and

blocks of sandstone from above _________________ 116

42. Siltstone, medium- to light-greenish-gray, poorly exposed 130

41. Covered_________________________________ 17

40. Sandstone, medium-gray, hard, massive, fine-grained, calcareous 2

Total lower tongue of Cokeville

Formation __________________________ 573

Thomas Fork Formation: 

Main body:

39. Poorly exposed. Alternate layers 2 5 ft thick of (1) mediumgreenish-gray calcareous siltstone (weathers light gray) and (2) 

dull-red calcareous siltstone with a few thin (!/4 2 in.) beds of 

brown calcareous fine-grained sandstone. Whole unit weathers to 

a distinctly red soil. Red 2-ft-thick siltstone bed at top ____ 47

38. Sandstone, medium-gray, thin-bedded, fine- to medium-grained,

calcareous; abundant dark mineral grains___________ 9

37. Poorly exposed. Light-gray sandy soil in upper part, red soil in middle, abundant fragments of sandstone like unit 36 in lower part 18

36. Sandstone, medium-gray, thin-bedded, medium-grained,

calcareous; abundant dark minerals _______________ 8

35. Siltstone; light gray in upper half, medium gray in next one-sixth,

dull pinkish gray in lower third ________________ 26

34. Sandstone, faintly greenish-gray, crossbedded, fine-grained; abundant dark grains. Contains limestone pebbles as much as % in. in 

diameter in thin layers and along a few bedding surfaces __ 9

33. Siltstone, pale-gray; upper 3 ft darker gray with faint lavender cast 44

32. Sandstone, pale-gray, medium-hard, fine-grained, calcareous,

crossbedded; many dark grains ________________ 2
112 CONTRIBUTIONS TO STRATIGRAPHY

110°55'

R. 119 W.

1 MILE 

I

1 KILOMETER

J

EXPLANATION

Qa Alluvium and colluviurn-QUATERNARY 

Ksj Sage Junction Formation 

Kq Quealy Formation 

KckCokeville Formation 

Ktf Thomas Fork Formation 

Ks Smiths Formation 

Kg Gannett Group

LOWER 

CRETACEOUS

Jsp Stump Sandstone and 

Preuss Red Beds

I UPPER 

[JURASSIC

Contact

Fault 

Dotted where concealed

Inclined Vertical Overturned 

Strike and dip of beds

K 

Coal prospect

FIGURE 4. Geologic map of the southeastern part of T. 28 N., R., 119 W., showing location 

of type section (line with crossbars) of the Thomas Fork Formation (stippled) in the 

Cokeville quadrangle. Contour interval, 200 feet.
NEW CRETACEOUS FORMATIONS, WESTERN WYOMING 113

Thomas Fork Formation Continued Thickness 

Main body Continued <feet>

31. Soil, dull-reddish-gray; red siltstone bed, a few feet thick, about 10

ft below top _____________________________ 38

30. Poorly exposed. Most of interval is covered by dull-red soil; in basal

few feet a gray thin-bedded sandstone ______________ 25

29. Siltstone, brick-red; contains nearly spherical light-gray sandy 

limestone nodules commonly 2 4 in. in diameter. This red unit 

overlain by conspicuous pale-gray siltstone and that by faintly 

pinkish-gray, then light-gray siltstone with 1 ft of medium-soft 

white sandstone at top ______________________ 25

28. Sandstone, hard, thin-bedded, fine-grained, calcareous, 

crossbedded (from northwest); many dark grains. Abundant red 

clay pellets Vt l/i in. in diameter on some bedding surfaces. 

Becomes softer above and contains red sandstone in middle_ 15

27. Siltstone, red; abundant limestone nodules. Light-gray shale bed, a

few feet thick, just below middle ________________ 55

26. Sandstone, thin-bedded, medium-grained, calcareous; many dark

grains ________________________________i. 4

25. Siltstone; light gray in upper half, red in lower half ________ 10

24. Sandstone, medium-soft, thin-bedded, medium-grained, highly

calcareous; abundant dark grains _______________ 5

23. Siltstone, pale-greenish-gray; and pinkish-tan soil _______ 28

22. Poorly exposed. Dull-red soil with unusually abundant limestone 

nodules as much as 4 in. in diameter. Surface of nodules very 

irregular _____________________________ 86

21. Siltstone, pale-pinkish-gray, deep-maroon, and pale-lavender. 

Fossil colln. C15 47 (gastropods, fish scales, and bone 

fragments) ____________________________ 40

20. Sandstone, pale-buff _____________________________ 4

19. Siltstone; lavender in upper part, dull red in middle, and pale

greenish gray in lower part; abundant limestone nodules ___ 30

18. Sandstone, massive, buff-weathering; pale buff gray, both fresh and

weathered. Fine grained, calcareous; few dark grains _____ 2

17. Siltstone; lavender and medium gray in upper third, alternating red 

and light gray in lower two-thirds. A 2-ft-thick bed near middle is 

dull maroon. Limestone nodules, 3/8 5 in. in diameter, especially 

abundant, the larger ones consisting of limestone pellets or 

fragments. The individual pellets are light gray, medium gray, 

and red and are Vi l/i in. in diameter ____________ 26

16. Sandstone, pale-greenish-gray, medium-grained, massive, buffweathering; relatively few dark grains. Almost noncalcareous _ 2

15. Siltstone; dominantly red but with medium-gray to lavender beds,

each 2 3 ft thick, just below middle and at top _______ 38

14. Sandstone, medium-hard, thin-bedded, fine-grained, calcareous _ 4

13. Shale, sandy, pale-tan-gray; greenish-gray calcareous siltstone with

abundant sandstone chips ____________________ 25

12. Shale, dark-gray-red; weathers to lavender; succeeded by red soil 

above, then lavender again. Abundant limestone nodules in red 

soil. Discontinuous 2-ft-thick sandstone beds_________ 85
114 CONTRIBUTIONS TO STRATIGRAPHY

Thomas Fork Formation Continued Thickness 

Main body Continued (feet> 

11. Sandstone, hard, medium-grained, calcareous, crossbedded; saltand-pepper aspect; weathers light buff gray; forms ledge ___ 1 

10. Siltstone, red _____________________________ 2 

9. Sandstone, like unit 11 ____________ _______ 2 

8. Siltstone, gray ____________________________ 4 

7. Sandstone, like unit 11 _______________________ 8 

6. Siltstone, gray-red, calcareous; weathers to light lavender. Lower

part of unit dull pinkish gray; upper part, pale greenish gray _ 54 

5. Siltstone, reddish-brown, sandy, blocky, highly calcareous. Poorly 

exposed. Sandstone fragments only in lower part. Red soil and 

abundant small limestone nodules ________________ 244 

4. Sandstone, hard, massive, fine-grained, calcareous; weathers

pinkish brown __________________________ 3 

3. Shale, sandy, variegated; and limestone nodules _________ 52 

Total main body of Thomas Fork

Formation ___________________________ 1,080 

Total main body and upper tongue 

of Thomas Fork Formation ________________ 1,152

Smiths Formation (part):

Upper, sandstone member:

2. Shale, medium-gray; brown sandstone chips ___________ 36 

1. Sandstone, hard, noncalcareous; sparkly salt-and-pepper aspect;

forms ridge. Grains '/6 '/3 mm in diameter _____ 25 

Total Smiths Formation measured_ _______ 61 +

COKEVILLE FORMATION

Above the variegated beds of the Thomas Fork Formation lies a mainly 

gray and tan unit here named the Cokeville Formation. The formation consists of light-gray- to tan-weathering medium-gray fossiliferous sandstone 

and sandy siltstone, light- to dark-gray claystone and mudstone, calcareous 

concretions, abundantly fossiliferous tan limestone, and some beds of lightgray, tan, and pink porcelanite and bentonite. In the upper part of the formation are a few beds of coal which were mined one-half mile west of Sage.

The beds of gray to tan fossiliferous sandstone and limestone and of gray 

sandstone, mudstone, and siltstone of the Cokeville Formation may be distinguished, north of the latitude of Cokeville, from the poorly exposed red 

and variegated mudstone and sandstone of the overlying Quealy Formation. 

From Cokeville southward the reddish-colored Quealy Formation is absent, 

and the Sage Junction Formation directly overlies the Cokeville Formation. 

In this southern area the two formations may be differentiated by the 

generally greater abundance of fossiliferous limestone and tan thin-bedded 

sandstone in the Cokeville and the greater abundance of porcelanite beds in 

the Sage Junction. The exact boundary is drawn at the base of the lowest 

thick interval of porcelanite and bentonite beds, which is continuous 

throughout the area and which, in the southernmost part, is more than 50 

feet thick.
NEW CRETACEOUS FORMATIONS, WESTERN WYOMING 115

The Cokeville Formation is moderately well exposed in the low hills east 

of Cokeville Butte, 2 miles northeast of the town of Cokeville for which it is 

named. The section here designated as the type (fig. 5) is that measured 

from the SEttSEttSWtt to the NWttSWttSWM sec. 36, T. 25 N., R. 119 

W., east of Cokeville Butte.

The formation is about 1,609 feet thick at the type section, but precise 

thicknesses are difficult to determine because the formation intertongues 

with and grades into both underlying and overlying units which thicken 

northward at the expense of the Cokeville; formational boundaries, 

therefore, are arbitrary. Fossils from this type locality have been described 

by Yen (1954, his locality 10, p. 46, and division 2, p. 48, 49). In the Sage 

quadrangle the formation is 1,900-2,500 feet thick. Fossils from the formation are similar to those in the Bear River Formation east of the Absaroka 

fault and are assigned an Early Cretaceous age (Cobban and Reeside, 1951. 

See, however, Yen, 1954, p. 49, 50).

Type section of the Cokeville Formation

[2 miles northeast of Cokeville along the north side of Smiths Fork, SWW sec. 36, T. 25 N., R. 119 W. Measured by W. W.

Rubey, Sept. 24, 1949]

Thickness

Quealy Formation (part): (feet) 

48. Soil, grayish-red; distinctly different from underlying units. Alternation in beds Vi ft to several feet thick of dull-gray-red and lightgreenish-gray calcareous siltstone ________________ 35 

Cokeville Formation:

47. Faintly pinkish gray soil at base, then light-gray sandy soil like unit

46, but also some pale-green soil ________ 195 

46. Soil, light-gray, sandy; obscure exposures of pale-tan-gray siltstone

in upper third___________________________ 235 

45. Dark-gray shale in upper part. Light-gray silty calcareous shale and 

soft thin-bedded gray iron-stained sandstone in middle part; unit 

has been prospected for coal. Dark-gray soil in lower part includes black shale dump ______________ _ 22 

44. Soil, light-tan, sandy ________________________ 122 

43. Sandstone, hard, thin-bedded _______________ _ 7 

42. Soil, tan, sandy; abundant sandstone fragments _________ 60 

41. Coquina of oyster shells ______________________ 1 

40. Soil, light-tan-gray; contains sandstone fragments, several thin

zones of dark-gray shale __________________ _ 188 

39. Sandstone, light-gray, hard; weathers tan ____________ 2'/2 

38. Soil, light-tan-gray, sandy ______________________ 29 

37. Porcelanite, dark-gray, hard __________________ _ 8 

36. Covered_________________________________ 11 

35. Sandstone, tan, medium-grained, hard; some clay pellets ____ 32 

34. Covered. Old coal prospect in lower part _______ _ 80 

33. Sandstone, tan, hard, calcareous, medium-grained _______ 6 

32. Covered _________________________________ 45 

31. Sandstone, tan ______________________________ 4

30. Covered by coal dump ________________________ 32 

29. Sandstone, gray, thin-bedded, carbonaceous______________ 8
116 CONTRIBUTIONS TO STRATIGRAPHY

R.119 W. 110°55' R. 118 W.

R.119 W.

1 KILOMETER 

J

Qa

Tf

Ksj

Kq

Kck

Ktf

Ks

Kts

Kg 

Jsp

Jt

"Rw 

 Rd 

Pp 

PIPw

EXPLANATION

Alluvium and colluvium O U ATE R N A R Y

Fowkes Formation - TERTIARY

Sage Junction Formation

Quealy Formation

Cokeville Formation

Thomas Fork Formation

Smiths Formation

Thomas Fork and

Smiths Formations

Gannett Group

Stump Sandstone and

Preuss Red Beds

Twin Creek Limestone

Nugget Sandstone-JURASSIC*?) AND TR1ASSIC(?)

Ankareh Red Beds

Thaynes Limestone

Woodside Red Beds

Dinwoody Formation

Phosphoria Formation PERMIAN

Wells Formation - PERMIAN AND PEN NSYLVAN I AN

CRETACEOUS

JURASSIC

TRIASSIC

Contact 

Dotted where concealed

"Fault 

Dotted where concealed

H

Thrust fault

Dotted where concealed

T, on upper plate

45 80, 

I ~D~ 

Inclined Overturned 

Strike and dip of beds

^ 

Coal prospect

FIGURE 5. Geologic map of the Cokeville area, showing location of type sections (line with 

crossbars) of the Cokeville (light stipple) and Quealy (heavy stipple) Formations. Contour 

interval, 200 feet.
NEW CRETACEOUS FORMATIONS, WESTERN WYOMING 117

Cokeville Formation Continued Thickness

(feet)

28. Sandstone, thin-bedded. Main mine portal enters eastward through

these beds _____________________________ 25

27. Soil, light-tan, sandy. Dump with bony coal fragments in middle of

unit ________________________________ 54 

26. Sandstone, light-tan, soft, thin-bedded ______________ 14 

25. Soil, tan, sandy; abundant sandstone fragments. Dark-gray to black

carbonaceous zone in lower 5 ft. Dump with bony coal fragments 40 

24. Limestone, tan, thin-bedded, silty, soft ______________ 4 

23. Soil, light-tan, sandy ________________________ 41 

22. Carbonaceous zone, dark-gray __________________ 1 

21. Limestone, brown, silty, concretionary, fossiliferous _______ 1 

20. Siltstone, medium-gray, soft; silty sandstone. A tan zone 6 in. thick

near middle ____________________________ 20 

19. Sandstone, soft, thin-bedded, dirty ____________________ 2'/2

18. Siltstone, soft, gray, tan, calcareous________________ 3 

17. Limestone, tan-weathering, silty; coquina beds with Pyrgulifera _ 2 

16. Siltstone, light-tan-gray, calcareous _______________ 28 

15. Carbonaceous and coal zone. Main prospect. Fossil colln. R49 49

(Pyrgulifera) _____________________________ 13

14. Limestone, tan-weathering, silty. Fossil colln. R49-50

(Campeloma. Field identification by J. B. Reeside, Jr.)____ 3 

13. Siltstone, light-gray _________________________ 22 

12. Limestone, tan, sandy, hard __________________ 2V4

11. Shale, light-gray, calcareous ____________________ 5 

10. Limestone, tan, sandy ________________________ '/2 

9. Carbonaceous zone and coal. Minor prospect entry _______ 6 

8. Limestone, hard, like unit 6; fossiliferous (large gastropods) __ 3 

7. Shale, medium-gray _________________________ 28 

6. Limestone, medium-brownish-gray, hard, silty; weathers very light

gray _________________________________ 8

5. Soil, light-gray, sandy _______________________ 195

Total Cokeville Formation _________________ 1,609

Thomas Fork Formation (part):

4. Soil, light-gray, sandy; 1-ft-thick red zones 16 ft above base and at

top of unit _________________________ ____ 45 

3. Soil, red, sandy ____________________________ 2 

2. Soil, light-gray, sandy; limestone nodules as in unit 1. Contains 6-ftthick very light gray, soft, calcareous sandstone just below middle. Numerous pale-salmon-pink calcite vein fragments ____ 117 

1. Siltstone, soft; alternating pale-gray-red and light-gray with abundant small limestone nodules ('A 1 in. in diameter) ______ 197 

Total Thomas Fork Formation measured __________ 361 +

QUEALY FORMATION

The Cokeville Formation is directly overlain in the northern part of the 

region but not in the south by a unit of red beds here named the Quealy Formation for the exposures 114 miles south of Quealy Reservoir in the SE'/4 

sec. 35 and the SWtt sec. 36, T. 25 N., R. 119 W., in the Cokeville 

quadrangle, here designated the type section (fig. 5). Some other 

moderately well exposed sections of the formation are along First, Second, 

and Third Creeks in the westernmost part of T. 26 N., R. 118 W. A section
118 CONTRIBUTIONS TO STRATIGRAPHY

of about 1,200 feet of beds between the Cokeville and Sage Junction Formations 1 mile north of Quealy Reservoir is designated as a reference section. The unit consists of red and variegated pastel-tinted mudstone and 

pink, gray, and tan sandstone.

The red-tinted soils of the poorly exposed Quealy Formation contrast 

with, and distinguish it from, the better exposed beds of the overlying Sage 

Junction Formation, which is dominantly gray sandy siltstone and 

sandstone but which includes many thin beds of white, gray, green, and pink 

porcelanite.

The formation is about 1,000 feet thick in the northern part of the 

Cokeville quadrangle, but it grades out southward and is absent south of the 

latitude of Cokeville; it is regarded as a southward-extending tongue of the 

Wayan Formation (Mansfield, 1927, p. 105). The formation is very 

probably equivalent to the lower part of the Aspen Shale, for it includes 

fossil trunks of Tempskya1 at numerous localities. It is of Early Cretaceous 

age, as shown by fossiliferous strata above and below.

Type section of the Quealy Formation

[1W miles south of Quealy Reservoir, Sfc'/4 sec. 35 and SWW sec. 36, T. 25 N., R. 119 W. Measured by W. W. Rubey, Sept. 24,

1949]

Thickness

Thaynes Limestone (part): (feet)

13. Siltstone, hard, calcareous _____________________ 15 

Crawtbrd thrust fault. 

Quealy Formation (part):

12. Soil, very faintly pink; covered with chips of Thaynes tan siltstone

and gray sandstone from immediately above __________ 46

11. Soil, red________________________________ 73

10. Poorly exposed; largely red soil __________________ 97

9. Soil, light-gray, sandy. Contains green siltstone beds ______ 65

8. Sandy soil; distinctly red zone __________________ 3

7. Soil, light-gray, sandy. Includes one red zone 3 ft thick 30 ft below

top_________________________________ 98 

6. Soil, light-gray, sandy; alternating with five dull-pinkish-gray zones 78 

5. Two red zones, each about 4 ft thick, separated by very light gray

weathering siltstone ________________________ 26 

4. Soil, very light gray, sandy; faintly reddish zone near middle.

Siltstone very light distinctly greenish gray ___________ 70 

3. Soil, grayish-red; distinctly different from underlying units. Alternation in beds l/2 ft to several feet thick of dull-gray-red and lightgreenish calcareous siltstone ___________________ 35

Total Quealy Formation below Crawford thrust fault ___ 591 

Cokeville Formation (part):

2. Faintly pinkish gray soil at base, then light-gray sandy soil like unit

1, but also some pale-greenish soil _______________ 195 

1. Soil, light-gray, sandy; obscure exposures of pale-tan-gray siltstone

in upper third___________________________ 235 

Total Cokeville Formation measured ____________ 430+

'Tempskya is a fossil fern that forms readily recognizable false trunks and in western North America is narrowly restricted 

in stratigraphic range (Brown, 1936; Read and Brown, 1937, p. 124-129).
NEW CRETACEOUS FORMATIONS, WESTERN WYOMING 119 

SAGE JUNCTION FORMATION

The Quealy Formation north of Cokeville and the Cokeville Formation 

south of Cokeville are directly overlain by the Sage Junction Formation, 

named here for exposures at the highway junction 1 !/2 miles west of Sage. 

The formation consists of light-gray and locally tan calcareous sandy 

siltstone and fine to very fine but partly medium-grained sandstone and 

quartzite; light-gray, tan, and grayish-red mudstone and claystone; some 

thin beds of grit and conglomerate in the upper part; numerous thin beds of 

white, gray, and green to pink porcelanite through all but the uppermost 

several hundred feet of the formation; and a few beds of brown to gray 

fossiliferous limestone. A few beds of coal are present in the lower part and 

have been mined at several localities along Boulder Ridge from near Sage to 

Antelope Creek.2

The section measured along the south end of Boulder Ridge, on the north 

side of U.S. Highway 30N at Sage Junction, from the NEMNWMSEM to 

the NWWSWKNWtt sec 7, T. 21 N., R. 119 W., is here designated the type 

(fig. 6). Preserved unconformably beneath Tertiary strata is 2,270 feet of 

beds; on the west, the unit is overlain by Quaternary sediment. The formation is overlain with angular unconformity by Tertiary and Quaternary 

strata everywhere else that it has been examined. Total thicknesses 

deposited, therefore, are not known. An additional 1,100 feet of beds, "higher 

than those at the type section, is preserved 4 miles north-northeast, along 

the unnamed northwest-flowing stream in sec. 20, T. 22 N., R. 119 W.; this 

approximately 3,400-foot-thick section is here designate^ a reference section. Fossils indicate that the Sage Junction Formation is Early Cretaceous 

in age. That the formation is correlative in large part with much of the 

Aspen Shale is suggested by the abundance of porcelanite beds in both as 

well as by invertebrate fossils (J. B. Reeside, Jr., oral commun.; Yen, 1951, 

1952, 1954).

It is distinctly possible that the uppermost several hundred feet of the formation may be equivalent in age and lithologic character to parts of the 

Frontier Formation, which overlies the Aspen Shale farther east. At places 

where the greatest thicknesses of the formation are exposed (at discontinuous exposures from sec. 29, T. 22 N., R. 119 W., northward for 6 miles 

to sec. 28, T. 23 N., R. 119 W., Wyoming; from Third Creek in sec. 12, T. 

26 N., R. 119 W., northward for 5 miles to sec. 13, T. 27 N., R. 119 W., 

Wyoming; and near the head of Tincup Creek in Idaho, 50 miles farther to 

the northwest) the porcelanite beds characteristic of most of the formation 

do not extend higher than about 2,600 feet above the base. Furthermore, 

layers of grit and conglomerate are more numerous in these upper beds than 

in those below, and dicotyledonous leaves were noted at several localities 

(NW'/4 sec. 20 and NEtt sec. 17, T. 22 N., R. 119 W., Wyoming; SEM sec.

!The coal bed mined at Sage may have been the origin of the name for the town of Cokeville. Mr. Albert Mau, a stockman 

in the region, believes that signs for the railroad sidings Sage and Cokeville along the Oregon Short Line were inadvertently 

reversed when the railroad was being built.
120 CONTRIBUTIONS TO STRATIGRAPHY

12, T. 26 N., R. 119 W., Wyoming, and sec. 19, T. 5 S., R. 44 E., Idaho, 

about 2 miles southeast of Wayan Post Office). The leaves from the locality 

near Wayan Post Office are in strata near the top of an approximately

110°55'

R. 120 W. R. 119 W.

1 MILE

0 1 KILOMETER

EXPLANATION

Qa Alluvium and colluvium-QUATERNARY 

Tf Fowkes Formation

Contact

Tg Green River Formation 

Tw Wasatch Formation 

Ksj Sage

Kck Cokeville Formation 

Kg Gannett Group

TERTIARY

CRETACEOUS

Fault

Dotted where concealed 

U, upthrown side

35

Strike and 

dip of beds

K 

Coal prospect

FIGURE 6. Geologic map of the Sage area, in the southwestern part of the Sage quadrangle, 

showing location of type section (line with crossbar) of the Sage Junction Formation (stippled).
NEW CRETACEOUS FORMATIONS, WESTERN WYOMING 121

2,000-foot-thick section of light-gray siltstone, shale, sandstone, and 

porcelanites which yield numerous Tempskya trunks and which are in many 

respects similar to the Sage Junction Formation as it is exposed to the 

southeast in western Wyoming. The leaves from this locality were identified 

by the late R. W. Brown (written commun., Nov. 8, 1940) as follows: 

USNM 8589

Nilssonial sp.

Platanus sp.

Artocarpus sp.

Liriodendron sp.

Fragments of other species of dicotyledons

Stems or roots

His interpretation was that "this group of fossils indicates an age between 

that of the Dakota sandstone and the Mesaverde formation." Although this 

age assignment certainly does not prove that these uppermost beds of the 

Sage Junction Formation are equivalent in age to the Frontier Formation, 

they are at least consistent with that interpretation.

These uppermost beds of the Sage Junction Formation are especially conglomeratic north and south of Third Creek, in sees. 12 and 18, T. 26 N., R. 

119 W.

The Sage Junction Formation is not simply another name for the Aspen 

Shale. The two formations differ in several significant respects. (1) 

Although the total number and thickness of porcelanite beds may be 

roughly the same in the two formations, these beds make up a much smaller 

part of the Sage Junction because of its greater thickness. (2) The Quealy 

Formation, which underlies the Sage Junction in the northern part of the 

region, is very probably equivalent in age, though not in composition, to 

part of the Aspen. (3) Farther south, where the Quealy has pinched out, the 

Cokeville Formation underlies the Sage Junction and very probably includes beds equivalent to part of the Aspen. (4) The absence of porcelanite 

beds and the presence of gritty sandstone and dicotyledonous leaves suggest 

that the upper several hundred feet of the Sage Junction may be equivalent 

to the lower part of the Frontier Formation.

Type section of the Sage Junction Formation

[Sage Junction (of U.S. Highways 30N and 89), NWWSEW and SViNWVi sec. 7, T. 21 N., R. 119 W. Measured by W. W. 

Rubey, Aug. 30, 1949, and Sept. 17, 1949]

Top of exposure. Thickness

Sage Junction Formation: (feet)

63. Siltstone, light-tan, sandy; faintly greenish tint _____________ 25±

62. Siltstone, faintly reddish-gray _______________________ 5

61. Siltstone, light-tan, sandy ________________________ 115

60. Siltstone, faintly reddish-gray _______________________ 1

59. Siltstone, light-tan, sandy; relatively common tan sandstone blocks _ 145

58. Clay, medium-gray, bentonitic-weathering ________________ 6

57. Siltstone, light-tannish-gray ________________________ 18
122 CONTRIBUTIONS TO STRATIGRAPHY

Thickness

Sage Junction Formation Continued Vee') 

56. Sandstone, tan ______________________________ 1 

55. Siltstone, gray, tan, sandy; a few thin sandstone beds and a few thin

dark-gray siltstone beds ___________ ____ 175 

54. Bentonite and porcelanite. Bentonitic-weathering clays in upper and

lower fourths; abundant porcelanite chips in middle half of unit _ 11 

53. Siltstone, light-tan, sandy; several 6-in.-thick beds of brown-weathering 

sandstone. Fossil collns. R49 69 and Y16A (leaves) from 6 ft above 

base of unit _______________________________ 62 

52. Sandstone, fine-grained, calcareous, hard; weathers dark brown. Fossil 

collns. R49-68 and Y16B (Unios, a molluscan fauna of six species 

described by Yen, 1952, p. 349) ___________________ l'/2 

51. Siltstone, light-tan, sandy ________________________ 90 

50. Soil, light-tan, sandy. Poorly exposed______________ 200 

49. Sandstone, crossbedded, calcareous, tan, medium-hard, mediumgrained (V* mm in diameter) _____ __ 8 

48. Siltstone, sandy, light-tan-gray. Old coal prospect in upper part shows

only light-gray siltstone ________________________ 36 

47. Sandstone, brown-weathering; contorted bedding at top and bottom,

2'xi-ft-thick bed of soft light-tan-gray sandy shale in middle 4 

46. Siltstone, light-tan-gray, sandy; poorly exposed ____________ 36 

45. Sandstone, light-tan-gray, hard, massive to thin-bedded; weathers

medium brown _____________________________ 9 

44. Covered __________________________________ 10 

43. Siltstone, dark-gray; in dump of old coal prospect _____ 5 

42. Covered __________________________________ 128 

41. Clay, dark-gray, slightly silty, slightly calcareous ___________ 2 

40. Covered __________________________________ 30 

39. Porcelanite, light-tan-gray; coarser grained above __ 9 

38. Soil, light-gray, silty ____________________________ 26 

37. Sandstone, hard, brown-weathering _____ _____ 1 

36. Covered __________________________________ 105 

35. Porcelanite; very light gray thin chips _________________ 1 

34. Soil, light-gray, sandy ___________________________ 25 

33. Porcelanite, slightly calcareous, medium-gray; weathers light gray. 

Minute gastropods and fragments of larger mollusks. Fossil collns. 

Y24A and Y24B (a nonmarine molluscan fauna of 20 species in 14 

genera described by Yen, 1952) ________________ l'/z 

32. Sandstone, silty, light-gray, soft calcareous ______________ 2 

31. Sandstone, brownish-gray, hard, calcareous; scattered black chert 1%

pebbles as much as Vi in. in diameter 

30. Soil, light-tannish-gray, sandy; fragments of poorly consolidated sand 23 

29. Siltstone, calcareous, blocky to chippy __ 15 

28. Sand, tan, poorly consolidated, calcareous, medium-grained (average

diameter '/3 mm) __________ 26 

27. Soil, light-tannish-gray, sandy ______ 21 

26. Covered __________________________________ 27 

25. Porcelanite, fine- and medium-grained; abundant biotite flakes in the 

medium-grained material. The fine material strikingly banded by 

alternation of thin light- and dark-gray layers ____ 28 

24. Soil, light-gray, sandy __________________ 104 

23. Sandstone, hard, tan ____________ 1
NEW CRETACEOUS FORMATIONS, WESTERN WYOMING 123

Thickness

Sage Junction Formation Continued (feet) 

22. Soil, light-gray, sandy ___________________________ 24 

21. Covered __________________________________ 295 

20. Siltstone, light-gray; poorly exposed_________________ 25 

19. Covered __________________________________ 100 

18. Soil, light-tan; sandy; a few outcrops of light-gray siltstone _____ 50 

17. Sandstone, tan, crossbedded, fine-grained ____________ 8 

16. Sandstone, crossbedded and contorted, fine-grained, calcareous; alternating with light-tan sandy shale ___________________ 41 

15. Soil, light-gray, sandy ______________________ 25 

14. Sandstone, medium-hard, medium-grained; in beds '/2-2 ft thick that 

alternate with soft sandy siltstone in beds 1 2 ft thick. Fossil colln. 

R49-67 from basal bed (Unio and dicotyledon leaf. Field identification by J. B. Reeside, Jr.)_______________________ 10 

13. Soil, light-gray, sandy ___________________________ 38 

12. Covered ___________________________________ 56 

11. Poorly exposed. Contains light-tan and pink bentonitic-weathering soil 

and abundant fragments of porcelanite and fine-grained tan slightly 

calcareous sandstone __________________________ 24 

10. Sandstone, white, regularly bedded, noncalcareous; probably contains 

volcanic ash. Apparently grades laterally into dense pink and light-tan 

porcelanite_____________________________ l'/2 

9. Soil, light-gray, bentonitic-weathering __________________ 9 

8. Porcelanite, light-gray, hard, blocky, noncalcareous; weathers light

greenish tan _____________________________ l /3 

1. Soil, light-gray, bentonitic-weathering__________________ 10 

6. Tuff, pink, coarse-grained, thin-bedded, fairly soft. Beds '/IQ V4 in. thick 3 

5. Soil, light-gray, bentonitic-weathering; abundant fragments of mediumto dark-gray to pale-grayish-pink porcelanite in lower part. Tempskya 

fragments _____________________________ ^ 

NOTE. The lowest thick zone of porcelanite and bentonite is represented in this

section by the 58 ft of units 5-11. 

Total Sage Junction Formation ________________ 2,270'A±

Cokeville Formation (part):

4. Soil, light-gray, sandy; like unit 2 ____________________ 6 

3. Sandstone, medium-gray, hard, calcareous; weathers dark brown __ '/2 

2. Soil, conspicuous light-gray, fine sandy __________ 10 

1. Alternating (1) sandstone, light-tan, fine-grained (average diameter '/20 

mm); black grains and small white flecks, crossbedded, somewhat 

contorted; beds Vi-l'/i ft thick, and (2) light-tan sandy siltstone; beds 

2-10 ft thick. Some dense light-tan-gray calcareous concretions, 

slightly septarian_____________________________ 122 

Total Cokeville Formation measured _______________ 138V4 +

UPPER CRETACEOUS

Upper Cretaceous rocks in the central and southern parts of the western 

Wyoming thrust belt have commonly been assigned to the Frontier Formation and the overlying Milliard Shale and Adaville Formation (Veatch, 

1907, p. 65-67; Schultz, 1914, p. 60-68). In the northern part of the 

region, however, differences in composition make a threefold division so
124 CONTRIBUTIONS TO STRATIGRAPHY

difficult that the hyphenated designation "Adaville-Frontier formation" 

was used for the Bedford quadrangle (Rubey, 1958). The clues to understanding the regional relations have emerged from recognition of facies changes 

within the Milliard Shale.

The Frontier Formation is about 2,200 feet thick at its type locality and 

consists dominantly of interbedded white and brown sandstone, tan 

siltstone, and dark-gray claystone; layers of lignite, coal, and some 

porcelanite are also present. The Milliard Shale, about 6,600 feet thick in 

the Kemmerer area, consists dominantly of dark- to medium-gray and tan 

marine claystone and somewhat lighter siltstone and includes some laminae 

and beds of white to dark-gray sandstone and white to gray bentonite. The 

Adaville Formation, about 2,900 feet thick at its type locality, consists, 

somewhat like the Frontier, of interbedded yellow, brown, and gray 

sandstone, siltstone, partly carbonaceous claystone, and layers of coal.

Near the middle of the Milliard Shale along Hams Fork is a comparatively thin but ledge-forming tongue of mainly sandstone that was 

recently named the Shurtliff Member of the Milliard Shale by Smith (1965, 

p. 14). This sandstone unit pinches out within 7 miles south of Hams Fork, 

which probably explains why it was not given greater attention by Veatch 

(1907, p. 70 and pi. 3). Where exposed at the type locality along Hams 

Fork, in sec. 27, T. 22 N., R. 116 W., the Shurtliff Member, here adopted as 

the Shurtliff Sandstone Member, is about 800 feet thick and consists of 

sandstone ledges in the lower 264 feet, dark-gray claystone and siltstone in 

the middle 367 feet, and sandstone ledges in the upper 173 feet. As the 

member is traced northward along strike, the middle shale intertongues 

with sandstone, and large fossil oyster shells increase in abundance. Shale 

beds above and below the member along Hams Fork also intertongue 

northward with sandstone beds so that increasingly greater proportions of 

Milliard are assigned to the middle sandstone unit northward. Uppermost 

beds of the Hilliard also intertongue northward with sandstone beds 

assigned to the Adaville Formation (fig. 7). Recognition of these relations 

(Andrews, 1944; Cobban and Reeside, 1952, p. 1934) resulted in the 

designation in the Bedford quadrangle (Rubey, 1958) of the "AdavilleFrontier formation," a sequence of sandstone, siltstone, claystone, and coal 

which contains no recognizable Hilliard Shale. It is now proposed (in the 

following section) to assign these rocks to the Blind Bull Formation.

Northward decrease in the abundance of claystone is accompanied by increase in the number and clast size of grit and conglomerate beds. The clasts 

are composed mainly of medium- to dark-gray chert. Grit beds are present 

as far south as the southeastern part of the Kemmerer quadrangle. The 

coarsest material noted is in the SE1A sec. 19, T. 25 N., R. 115 W., in a bed 

22 feet thick, approximately 1,630 feet above the base of the Shurtliff 

Sandstone Member of the Hilliard Shale. The pebbles and boulders in this 

bed range in diameter from less than 1 inch to 15 inches, but are chiefly 3 6
NEW CRETACEOUS FORMATIONS, WESTERN WYOMING 125

inches, and consist of subrounded to well-rounded clasts of white, tan, red, 

and brown quartzite and white, gray, red, and black chert.

BLIND BULL FORMATION

Formal definition of a new term to replace the unsatisfactory hyphenated 

designation "Adaville-Frontier formation" (Rubey, 1958) seems desirable 

to promote understanding of regional stratigraphic relations and to provide 

for forthcoming maps. The sequence of partly conglomeratic sandstone, 

siltstone, claystone, coal, and bentonite above the Aspen Shale is here 

named the Blind Bull Formation for exposures 3 miles north of the Blind 

Bull coal mine in the northeastern part of the Afton quadrangle (Rubey, 

1973).

New names are not proposed here for the greatly thinned remnants of the 

Milliard Shale in the northeastern part of the region. These remnants differ 

in no significant way from the typical Milliard Shale of the southern part of 

the region and therefore they are designated as upper and lower tongues of 

the Milliard.

The question remains as to how best to treat the sequence of beds of gray 

to buff calcareous sandstone and sandy siltstone and some black carbonaceous shale and coal which, in the northeastern part of the area east of 

the Wyoming Range, lies above the Aspen Shale and below the lower 

tongue of the Milliard. In this area this sequence could be assigned accurately to the Frontier Formation. In the exposures west of the Wyoming 

Range, however, no tongues of the Milliard Shale have been recognized, and 

therefore this treatment is not feasible. Consequently, I propose to apply, 

somewhat arbitrarily perhaps, the name Blind Bull Formation to the sequence of Cretaceous sandstone, sandy siltstone, and coal beds lying above 

the Aspen Shale, both west and east of the Wyoming Range.

One of the best exposed sequences of these strata is that measured along 

the divide between Horse Creek and the Hoback River, along the north 

margin of the Afton quadrangle3 from the SW1A sec. 18, T. 35 N., R. 115 

W., to the SV2 sec. 23, T. 35 N., R. 116 W., here designated the type section 

(fig. 8). Preserved in this section east of and beneath the trace of the Darby 

thrust fault is about 6,200 feet of beds that contain not only fossils but also 

two tongues of the Milliard Shale which document the regional relations of 

the unit. The base of the lower tongue of the Hilliard, 975 feet thick, lies 

about 1,143 feet above the base of the Blind Bull Formation; that of the upper tongue of the Hilliard, more than 135 feet thick, lies about 6,058 feet 

above the base of the Blind Bull.

Fossils were collected from a bed about 250 feet above the base of the upper tongue of the Hilliard Shale at a locality 3 J/2 miles south of Deadman 

Mountain, in the SWttSEVi sec. 3, T. 34 N., R. 116 W. They were identified

'The sequence of Cretaceous rocks exposed at this locality has also been measured by Ross and St. John (1960, p. 50-51) 

and Frerichs and Steidtmann (1971, p. 163-165).
126 CONTRIBUTIONS TO STRATIGRAPHY

15'

Upper member of 

Milliard Shale

Frontier Formation -< Middle part

 t

Aspen Shale

EXPLANATION 

LITHOLOGIC SYMBOLS

Conglomerate Sandstone Siltstone Shale

Coal Porcelanite Covered Poorly exposed

->-North

42°00' 

111-00'

KEMMERER 

QUADRANGLE

41-45'\ 

110-45'I \ 

110-30'

43°00'

COKEVILLE 

QUADRANGLE

La Barge Meadows 

Fontenelle /^ 

basin.

20

"Snider Basin 

30 40 50 MILES 

I____I____|

Deadman 

Mountain 

BLIND BULL MINE

FIGURE 7. Lateral relationships of Upper Cretaceous formations in the Kemmerer,

heavy lines, thrust faults above
NEW CRETACEOUS FORMATIONS, WESTERN WYOMING 127

43°00' 

I

Lower tongue of 

/Milliard Shale

Aspen Shale Aspen Shale

43°00'

Lower tongue of Milliard Shale

Lower part of Blind Bull Formation 

Aspen Shale

Cokeville, and Afton quadrangles. Lithologic symbols indicate sites of measured sections; 

preserved Upper Cretaceous rocks.
128 CONTRIBUTIONS TO STRATIGRAPHY

HOMO'

1 KILOMETER

EXPLANATION 

Qa Alluvium and colluvium QUATERNARY

Khu Upper tongue of 

Hilliard Shale

Kbb Blind Bull Formation CRETACEOUS

Khl Lower tongue of 

Hilliard Shale

PIPw Wells Formation -PERMIAN AND

PENNSYLVAN I AN

PMa AmsdenFormation- PENNSYLVANIAN AND 

MISSISSIPPIAN

Contact

Thrust fault 

T, on upper plate

30 65

-1- -dInclined Overturned 

Strike and dip of beds

-ftOverturned anticline

Overturned syncline

Adit Coal 

prospect

FIGURE 8. Geologic map of the Blind Bull mine area in the northeastern part of the Afton 

quadrangle, showing location of type section (line with crossbars) of the Blind Bull Formation (heavy stipple) and of the lower and upper tongues (light stipple) of the Hilliard Shale.
NEW CRETACEOUS FORMATIONS, WESTERN WYOMING 129

by J. B. Reeside, Jr. (written commun., Aug. 21, 1933) as follows: 

USNM 15889

Inoceramus sp.

Ostrea sp.

Pholadomya cf. P. papyracea Meek and Hayden

Cardium curtum Meek

Legumen wyomingensis (Meek)

Mactra arenaria Meek 

Niobrara fauna.

More than 1,300 feet of shale and siltstone of the upper tongue is 

preserved beneath the Darby fault on the east side of Mount McDougal in 

sees. 18, 20, and 29, T. 34 N., R. 115 W., where coaly beds in the upper 250 

feet might be regarded as an upper part of the Blind Bull Formation rather 

than part of the Milliard Shale tongue.

Mollusks, plants, and the tongues of the Milliard Shale establish that the 

Blind Bull Formation is correlative with the Frontier Formation and the 

Milliard Shale to the south and southeast and thus is of Late Cretaceous 

age. Whether beds as young as those in the lower part of the Adaville Formation are present in the Blind Bull anywhere in the region has not been 

determined. Tongues of Billiard Shale have not been recognized in the 

Blind Bull Formation in the relatively poor exposures west of the Wyoming 

Range, where as much as 3,500 feet of post-Aspen beds (Rubey, 1958) is 

preserved beneath the Absaroka thrust fault (Rubey, 1973); thus, division 

into Frontier and Milliard equivalents is impractical.

From these relations, therefore, the Shurtliff Sandstone Member of the 

Milliard Shale may be regarded as a southward-extending tongue of the 

Blind Bull Formation.

Type section of the Blind Bull Formation

[Along the divide between Horse Creek and Hoback River, east of Deadman Mountain and 3 miles north of head of Blind Bull

Creek, from the SW'/i sec. 18, T. 35 N., R, 115 W., through the SW sec. 24 to the Sto sec. 23, T. 35 N., R. 116 W. Measured

by W. W. Rubey and J. Steele Williams, Aug. 25 and 26, 1931]

Thickness

Wells Formation (part): (feet) 

83. Quartzite, light-gray, fine-grained, calcareous; weathers pale buff;

regularly bedded; clear quartz grains _.__________ 75 

Darby thrust fault. 

Milliard Shale:

Upper tongue (part):

82. Siltstone and shale, poorly exposed ___.___________ 135 

Blind Bull Formation: 

Upper part:

81. Sand, uniformly light-gray, poorly exposed, soft, loose, calcareous, 

poorly sorted, coarse-, medium-, and fine-grained; many coarse 

grains; contains very light yellowish gray siltstone ______ 90 

80. Sandstone, gray, calcareous; weathers brown __ 4 

79. Siltstone, brownish-gray; weathers light yellowish gray. Some dark

shale beds ________________.____________ 100
130 CONTRIBUTIONS TO STRATIGRAPHY

Blind Bull Formation Continued Thickness 

Upper part Continued (fa') 

78. Sandstone, white to gray, massive. Near base a 3-in.-thick coaly 

bed. Fossil colln. AW 191: 

USNM 15886 

Ostrea sp.

Cardium cf. C. curium Meek 

Tellina isonema Meek? 

Mactra arenaria Meek 

Baculites sp.

Halymenites major Lesquereux

Niobrara fauna (J. B. Reeside, Jr., written commun., Aug. 21, 

1933) _______________________________ 75 

77. Limestone, brown, sandy; alternating with sandy siltstone.

Limestone beds 2 ft thick ____________________ 17 

76. Sandstone, light-gray, massive, soft; dark chert pebbles to 15 mm in

diameter in lower part ______________________ 15 

75. Gradational sequence, in ascending order: black fossiliferous shale, 

nonfossiliferous black shale, coal pebbles and worn oyster shells, 

sandstone _____________________________ 5 

74. Shale, gray ______________________________ 4 

73. Shale, carbonaceous, highly fossiliferous. Fossil colln. AW190: 

USNM 15885

Cardium pauperculum Meek 

Corbula sp.

Colorado fauna (J. B. Reeside, Jr., written commun., Aug. 21, 

1933) _______________________________ 2 

72. Siltstone________________________________ 12 

71. Sandstone, fossiliferous. Fossil colln. AW189: 

USNM 15884 

Ostrea sp.

Modiola multilinigera Meek 

Neritina, n. sp. aff. N. bellatula Meek 

Colorado fauna (J. B. Reeside, Jr., written commun., Aug. 21, 

1933) _______________________________ 2 

70. Siltstone_______________________________ 10 

69. Shale_________________________________ 1 

68. Coal _________________________________ Vs 

67. Shale_________________________________ 1 

66. Sandstone, regularly bedded; weathers yellow brown __ __ 25 

65. Sandstone and siltstone. Sandstone soft (almost a loose sand), 

medium to coarse grained; abundant dark grains, very 

calcareous. Siltstone weathers light gray ___ __ __ 85 

64. Alternating sandstone, shale, and siltstone, poorly exposed. 

Sandstone is medium gray, weathers yellowish, greenish, and 

brownish gray, averages 2-3 ft thick. Shale is dark gray, gritless, 

noncalcareous. Siltstone is gritty, greenish gray, weathers 

yellowish gray, noncalcareous _________________ 450 

63. Sandstone and siltstone alternating with some coal. Upper 30 ft 

poorly exposed and mostly sandy siltstone. Sandstone: massive to 

thin bedded, clay pellets, crossbedded, calcareous, yellow gray, 

weathers grayish yellow, beds lenticular and as much as 15 ft
NEW CRETACEOUS FORMATIONS, WESTERN WYOMING 131

Blind Bull Formation Continued Thickness 

Upper part Continued <Seet> 

thick. Siltstone: calcareous, dark brown, weathers medium gray. 

Also some bluish-gray shale; weathers light gray. Sandstone, 

shale, and siltstone contain plant fragments. A coal bed, P/io ft 

thick, 42 ft above base of unit. Bones in calcareous concretions in 

somber gritless shale. Fossil colln. AW138 __________ 90 

62. Covered. At base is a blossom from a black carbonaceous shale or 

coal. Soil looks like that of carbonaceous clay rather than sandy 

shale except in upper 50 ft where loose sandstone slabs cover surface ______._____________._____________ 200 

61. Sandstone and siltstone, alternating and poorly exposed coaly 

streaks. Sandstone white and thin bedded. Siltstone medium 

greenish gray, weathers light gray. Two 3-in.-thick coal beds 4 ft 

apart about 135 ft above base ______.____________ 205

60. Covered. Sandy soil, has some medium-gray siltstone and soft white

thin-bedded sandstone _________.____________ 90 

59. Sandstone, light-buff, calcareous, hard; in beds 2 ft thick; weathers 

gray and yellow. Poorly sorted, largest grains 3/4 mm in diameter. 

Numerous clay pellets, highly contorted beds in lower part. 

Sandstone beds alternate with beds of veiy light gray loose sand 

which in places are cemented into large loglike concretions. A 2- 

in.-thick coal bed near top. Unit is well exposed and makes a 

prominent ridge ._____________.____________ 290 

58. Covered ___________________._______________ 45

57. Clay, buff-gray, plastic, noncalcareous; resembles bentonite __ 2 

56. Coal, black, soft _._____________.____________ 3 /5 

55. Clay, brown, carbonaceous, gritty, noncalcareous _________ 2

54. Poorly exposed except for thin sandstone slabs _________ 150 

53. Siltstone, sandstone, and shale; poorly exposed. Siltstone, sandy; 

sandstone, brown calcareous; shale, black carbonaceous 2-ftthick layer near middle of unit. Abundant large pieces of petrified 

wood about 175 ft above base _____ ____________ 495

52. Covered except for a few thin-bedded gray friable sandstone ledges

2-5 ft thick __.____________..______________ 170

51. Sandstone, light-gray to brown, thin-bedded to massive, some very

calcareous, fine- to medium-grained (clear quartz, white opaque

chert, black grains, and clay pellets). Beds l-2'/2 ft thick. Unit

contains subordinate poorly exposed lighl-buff-gray sandy shale 100

50. Clay, brown carbonaceous; grades upward into yellowish-gray

sandy shale __.____________.____________ 4 

49. Coal ________________________..____________ I'/,

48. Clay, medium-dark-brown, gritty; weathers very light gray ___ 4 

47. Coal _____________________..____________ 1710 

46. Shale, gray, gritless, platy ________.___________ P/5

45. Coal ____________________._____________ 7,0 

44. Clay, black carbonaceous ________.______________ 72

43. Sandstone, light-yellowish-gray _______.____________ 7z

42. Covered _______._____________._____________ 107

41. Sandstone, calcareous, medium-grained (clear quartz, opaque white 

chert, black grains, and clay pellets), sabrounded to angular. 

Regularly bedded in beds 1 6 in. thick.___________ 10
132 CONTRIBUTIONS TO STRATIGRAPHY

Blind Bull Formation Continued Thickness 

Upper part Continued <feet> 

40. Siltstone, medium-brownish-gray noncalcareous gritty; weathers 

light buff gray. Thin coaly layers. Yellowish-gray sandy limestone beds !/2 l'/2 ft thick; some have contorted bedding _ 120 

39. Sandstone, yellowish-gray, calcareous, heavily iron-stained, 

medium-grained; weathers grayish yellow. Irregular ripple 

marks______________________ _______ 6

38. Shale, sandy; several sandstone beds IVi 5 in. thick ______ 10 

37. Coal; mostly glance; units 35 and 37 are the coal mined at the Blind

Bull and Vail mines ________________________ 5'/s 

36. Clay; brown parting _________________________ '/io 

35. Coal; mostly glance _________________________ l l/2 

34. Claystone, gray; like unit 30 ____________________ 3

33. Coal, bony ______________________________ '/2 

32. Claystone and shale with ironstone masses and harder irregular

oolitic ironstone concretions ___,__________ _ ! 4 /5

31. Coal, impure_____________________________ 1 

30. Claystone, gray, somewhat gritty _________________ 2V2 

29. Siderite; nodular concretionary masses, septarian ________ '/ 2 

28. Sandstone and shale; a few beds of coal less than 2 ft thick. 

Sandstone greenish gray, salt and pepper grains at base. Irregular 

bedding and current marks. Yellowish-brown sandy limestone at 

top_________________________________ 110 

27. Sandstone, greenish-gray to yellowish-gray, hard. Salt and pepper 

grains as much as V4 mm in diameter, average Vs mm. Much 

crossbedding (from south and from northwest). Bed near top has 

abundant clay pellets which weather out, leaving conspicuous 

holes ________________________________ 100 

26. Sandstone, hard, massive, regularly bedded; forms ridge; alternates 

with subordinate sandy shale and dark-gray clay. Sandstone beds 

are mostly 4 10 ft thick, but a few are thin. At top of unit 

sandstone is irregularly bedded and ripple marked. Conspicuous 

black grains. Fossil colln. AW166 from near base of unit: 

USNM 15881

Barbatia micronema Meek 

Inoceratnus cf. /. deformis Meek 

Ostrea [Crassostrea] soleniscus Meek 

Ostrea [Crassostrea] cf. O. coalvillensis

Meek

Anomia propatoris White 

Cardium curium Meek 

Tellina isonema Meek? 

Mactra arenaria Meek 

Gyrodes cf. G. depressa Meek 

Gastropods, undet.

Early Niobrara age (J. B. Reeside, Jr., written commun., Aug. 

21, 1933). Fossil colln. AW 187 (Inoceramus, baculite, and 

plant fragments) from just below middle of unit ______ 105 

25. Shale and sandstone, alternating; both calcareous. Sandstone beds

as much as 1V4 ft thick, most less than 4 in __________ 210 

24. Sandstone and sandy siltstone, calcareous, gray to blue-gray;

sandstone beds 3 8 in. thick __________________ 140
NEW CRETACEOUS FORMATIONS, WESTERN WYOMING 133

Blind Bull Formation Continued Thickness 

Upper part Continued <feet> 

23. Sandstone and siltstone, sandy. Sandstone is soft, thin bedded, light 

yellowish gray. Oscillation ripple marks 1 1/2 in. wide, Vi in. deep, 

trend N. 30° W. ______________.____________ 25 

22. Poorly exposed. Yellowish-gray sandy soil; abundant slabs of brown

sandstone on surface ___________.______ 230 

Total upper part of Blind Bull

Formation ______________.____ 3,940 

Milliard Shale: 

Lower tongue:

21. Shale, dark-brownish-gray, fissile, slightly gritty, calcareous, wellexposed; a few thin calcareous sandstone beds ________ 260 

20. Shale, dark-brownish-gray, slightly gritty, calcareous; weathers

medium dark gray; poorly exposed ______________ 180 

19. Poorly exposed. A few thin beds of sandstone, pale buff gray, nonfossiliferous ___________________________ 85

18. Sandstone, highly calcareous, fetid odor, highly fossiliferous. Fossil 

colln. AW186: 

USNM 15883

Barbatia micronema Meek 

Inoceramus cf. /. gilberti White 

Ostrea [Crassostrea] soleniscus Meek 

Modiola multilinigera Meek 

Cardium cf. C. pauperculum Meek 

Volutoderma cf. V. plicatula Dall

Niobrara fauna (J. B. Reeside, Jr., written commun., 

Aug. 21, 1933) _________________________ 75 

17. Sandstone, medium- to light-gray, highly calcareous; weathers 

brown; fetid odor. Grains subrounded, average l /3 mm, many 

dark minerals. Highly fossiliferous at base and at three 

calcareous zones above. Fossil colln. AW 185: 

USNM 15882

Inoceramus deformis Meek 

Ostrea congesta Conrad 

Pseudomelanial sp. 

Gyrodes sp. 

Tumtellcfl sp. 

Volutoderma plicatula Dall

Lower Niobrara fauna (J. B. Reeside, Jr., written commun., 

Aug. 21, 1933) _________________________ 80 

16. Poorly exposed; a few layers of thin-bedded fine-grained calcareous

sandstone exposed. Fossil colln. AW184 (plant fragments)__ 100 

15. Siltstone, medium-gray, sandy, platy, calcareous. Fragments of

fossiliferous sandstone (pelecypods) ____ . 195 

Total lower tongue of Milliard Shale _ __ _________ 975 

Total upper and lower tongues of

Milliard Shale ________________________ 1,110+

Blind Bull Formation: 

Lower part:

14. Largely covered but has some exposures of hard calcareous siltstone

and sandstone like those in unit 13 ______________ 285
134 CONTRIBUTIONS TO STRATIGRAPHY

Blind Bull Formation Continued Thickness 

Lower part Continued <foet> 

13. Siltstone, medium-greenish-gray, soft, calcareous; weathers light 

yellow gray. Includes numerous 2-ft-thick ledges of harder 

siltstone and fine- to medium-grained sandstone. Near top are 

brownish-gray calcareous concretions _____________ 200 

12. Siltstone, medium-gray; weathers light buff gray. Includes a few 6-

in.-thick beds of very ferruginous sandstone and siderite ___ 190 

11. Soil, light-yellow, sandy, poorly exposed _____________ 175 

10. Siltstone, yellow-weathering, sandy, poorly exposed; nodular

masses of ferruginous sandstone _ _ 40 

9. Siltstone, medium-gray, very calcareous; weathers brownish to

greenish gray ________________ _ l'/2 

8. Siltstone, gray; hard 7-in.-thick bed of greenish-gray porcelanite

with biotite flakes ______________________-_ 30 

7. Limestone, medium-buff-gray, hard, silty; weathers dark to light

brown ___________________________ __ l'/2 

6. Covered. Probably carbonaceous shale _______ _ __ 35 

5. Siltstone and subordinate shale. Siltstone is sandy, medium brownish gray; weathers buff gray. Petrified wood abundant. Fossil 

colln. AW 165. Black gritless highly calcareous siltstone in beds 2 

ft thick at several levels. Hard concretionary dark-brown silty 

limestone near middle. Black carbonaceous shale about 4 ft thick 

at top ________________________________ 70 

4. Siltstone, sandy; chiefly gray but includes gray to brown friable 

poorly sorted sandstone. All highly calcareous. Sand grains 

average 2 /3 mm in diameter but are as much as 1V4 mm. Chiefly 

quartz but also white opaque chert, dark minerals, and pale-green 

grains ________________________ _ 35 

3. Alternating silty sandstone and sandy siltstone, brown to greenishgray. Grains as much as Vi mm in diameter, angular, many dark 

grains. Beds are very soft and friable. A dark-gray gritless noncalcareous clay with a thin bony coal 8 in. thick about 3 ft below 

top of unit _____________________________ 45 

2. Siltstone, soft, sandy, poorly exposed _______________ 35 

Total lower part of Blind Bull Formation __________ 1,143 

Total upper and lower parts of Blind Bull

Formation __________________________ 5,083 

Total of Blind Bull Formation and two 

Hilliard Shale tongues measured _____________ 6,193 +

Aspen Shale (part):

1. Porcelanite beds, hard, medium-bluish-gray to black. Some soft

blue-gray shale and a few 6- to 8-in. thick beds of sandstone _ 60

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NEW CRETACEOUS FORMATIONS, WESTERN WYOMING 135

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Creek area, Lincoln County, Wyoming, pt. 2 of Fresh-water mollusks of Cretaceous age

from Montana and Wyoming: U.S. Geol. Survey Piof. Paper 233-A, p. 11-18. 

____1952, Freshwater molluscan fauna from an Upper Cretaceous porcellanite near Sage

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____1954, A fauna from western Wyoming, pt. 1 of Nonmarine mollusks of Late

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* U.S. GOVERNMENT PRINTING OFFICE: 1973 O 543 576/4