Stratigraphy and NOmenclature 

of Some Upper Cretaceous and 

Lower Tertiary Rocks in 

South-Central Wyoming 

By]. R. GILL, E. A. MEREWETHER, and W. A. COBBAN 

~ GEOLOGICAL SURVEY PROFESSIONAL PAPER 667 

.. 

... 

) 

,:0: 

Regional stratigraphic studies and ammonite 

zonat~·on are used in interpreting complex 

intertonguing and subtle facies changes in· 

rocks of Late Cretaceous and early 

Tertiary age 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1970 
UNITED STATES DEPARTMENT OF THE INTERIOR 

WALTER J. HICKEL, Secretary 

GEOLOGICAL SURVEY 

William T. Pecora, Director 

Library of Congress catalog-card No. 72-604715 

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

Washington, D .. C. 20503- Price 65 cents (paper cover) 

! 

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... 

·<. 
• 

CONTENTS 

Abstract-------------------------------------------

Page 

1 

1 

2 

2 

2 

3 

5 

7 

Mesaverde Group and Mesaverde Formation-Con. 

Introduction and acknowledgments __________________ _ Allen Ridge Formation _______________ - ______ ----

Historical background ______________________________ _ Pine Ridge Sandstone __ - ___ -------_--- ___ --_---_ 

Southwestern Colorado _________________________ _ Almond Formation __________________________ - - - -

Northwestern Colorado _________________________ _ Lew~ Shale _______________________________________ _ 

South-central Wyoming ________________________ _ Fox Hills Formation ____________ - _____ ----- _____ ----

SuminarY--------------------------------------

Medicine Bow Formation __ ---_---------_------ __ ----

Steele Shale _____ -- ___ -_---- ___________ -- ___ - __ --- __ Foote Creek and Dutton Creek Formations ___________ _ Ferris Formation __________________________________ _ 

Mesaverde Group and Mesaverde Formation __________ _ 11 

12 

20 

Hanna Formation ____________________ - __________ ----

Haystack Mountains Formation _________________ _ References cited ________________ -_----_---_--- __ ----

Rock River Formation _________________________ _ Index ____________________________________________ _ 

ILLUSTRATIONS 

FIGURE 1. Index geologic map of south-central Wyoming _______________________ ----_--- ___ - ___ -_ 

2. Stratigraphic diagram showing intertonguing relations of Upper Cretaceous rocks in southcentral Wyoming--------------------------------------------------------------

3-15. Photographs: 

3. Haystack Mountains Formation _____________________________ ---_-- ____ - __ --_ 

4. Hatfield Sandstone Member of Haystack Mountains Formation ________________ _ 

5. Thin-bedded O'Brien Spring Sandstone Member of Haystack Mountains Formation--------------------------------------------------------------------

6. O'Brien Spring Sandstone Member __________________________________________ _ 

7. Allen Ridge Formation at Pine Tree Gulch __________________________________ _ 

8. Outcrop of an unnamed marine member of Allen Ridge Formation ______________ _ 9. Pine Ridge Sandstone _____________________________________________________ _ 

10. Almond Formation--------------------------------------------------------

11. Concretionary sandstone in Lewis Shale _____________________________________ _ 

12. Lewis Shale---------------------------------------------------------------

13. Cliff-forming sandstone of the Dad Sandstone Member of the Lewis Shale_- ____ -_ 

14. Rocks of the Hanna Formation resting unconformably on the Medicine Bow Formation-----------------------------------------------------------------

15. Hanna Formation unconformably overlying the Lewis Shale ___________________ _ 

TABLE 

TADLE 1. Chart showing correlation of Upper Cretaceous rocks in south-central Wyoming and nearby 

areas---------------------------------------~---------------------------------

Page 

4 

8 

12 

13 

14 

14 

25 

25 

30 

33 

36 

37 

38 

44 

48 

Page 

6 

m 

Page 

24 

29 

31 

36 

41 

43 

45 

46 

47 

48 

51 
.,.. 

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STRATIGRAPHY AND NOMENCLATURE OF SOME UPPER CRETACEOUS AND LOWER 

TERTIARY ROCKS IN SOUTH-CENTRAL WYOMING 

By J. R. GrLL, E. A. MEREWETHER, and W. A. CoBBAN 

ABSTRACT 

Upper Cretaceous rocks described and correlated in this report 

are the Steele Shale, Mesa verde Group (consisting of the Rock 

River l!'ormation (new name), Haystack Mountains )formation 

(new name), Allen Ridge Formation, Pine Ridge Sandstone, and 

Almond Formation), Lewis Shale, E'ox Hills Formation, Medieine Bow ll..,ormation, and the lower part of the Ferris Formation. '.rhe lower Tertiary rocks described consist of the upper 

part of the Ferris ll..,ormation of Paleocene age and the overlying 

Hanna ll..,ormation of late Paleocene and Eocene age. 

'l'he oldest unit Jnvestigated, the Steele Shale, consists of 2,300-

8,800 feet of dark-gray marine shale that contains limestone 

concretions, beds of bentonite as much as '5 feet thick, and· thin 

layers of siltstone ami very fine grained sandstone. It becomes 

sandy upward nnd grades into the overlying Mesaverde Group. 

'The Mesaverde Group, in the Rawlins-Medicine Bow area, consists of the following formations, from oldest to youngest: Haystack Mountains Formation, Allen Ridge Formation, Pine Ridge 

Sandstone, and Almond Formation. The Haystack Mountains 

Formation comprises a sequence of mostly shallow-water marine 

sandstone and shale that thins southwestwardly across southcentral 'Vyoming from 2,550 to 850 feet. It contains three persistent ridge-forming sandstone members interpreted as beach and 

barrier-bar deposits. The oldest member, Tapers Ranch Sandstone (new name) , is 270 feet thick ·and forms the base of the 

formation. The second member, O'Brien :Spring Sandstone (new 

name) is 220 feet thick and lies 1,350 feet below the top of the 

formation. The Hatfield Sandstone Member, as much as 167 

feet thick, lies 450 feet ·below the top. 

Nonmarine sandstone, shale, and carbonaceous beds largely 

mal{e up the Allen Ridge Formation, but some sandstone and 

shale of brackish-water and marine origin are included. The 

Allen Ridge is conformable with the underlying Haystack 

Mountains Formation. It is as much as 1,500 feet thick. It intertongues with the Rock River Formation, and in the Laramie 

Basin area, it is replaced by that formation. 

Dlsconformably overlying the Allen Ridge Formation is the 

Pine Ridge Sandstone, a white t<l light-gray nonmarine sandstone 60-450 feet thick. The :formation contains carbonaceous 

shale and impure coal, ·and <lrdinarily f<lrms a conspicuous 

tree-covered ridge. 

The Almond Formation, 30-575 feet thick, conformably overlies the Pine Ridge Sandstone. It is a sequence of sandstone, 

shale, and coal, representing fluviatile, brackish-water, and nearshore marine environments of deposition. 

In the southeastern part of th4~ area (Laramie Basin), the 

Mesaverde Group consists of the Rock River F<lrmation and Pine 

Ridge Sandstone. The Rock River is a 1,500-foot-thick sequence 

of nonresistant sandstone and sandy shale of shallow-water 

marine origin. It grades eastward into the dominantly nonsandy 

Pierre Shale. 

In southeastern Wyoming, the Mesa verde Group is conformably overlain ·by the Lewis Shale. The Lewis, 2,200-2,600 feet 

thick, is chiefly dark-gray marine shale but contains sandy units. 

In the Hanna Hasin, the Lewis is divided into three parts by the 

Dad Sandstone l\Iember, which is as much as 1,400 feet thick. 

·The Fox Hills Formation conformably overlies the Lewis 

Shale. It is chiefly ridge-forming yeJNowish-gray to light-brown 

shallow-water marine sandstone and ranges in thickness from 

less than 200 to more than 700 feet. 

The Medicine Bow Formation, 3,000-6,500 feet thicl{, rests 

conformably on the Fox Hills. Lenticular beds of sandstone, 

siltstone, and shale, ·and persistent beds of coal make up the 

formation. Most <lf the formation is nonmarine, but the lower 

part contains brackish-water beds. 

The Ferris Formation, <lf nonmarine origin, conf<lrmably 

overlies the Medicine B<lw and is divisible into two parts. The 

lower part, 1,100 feet thick, consists of conglomeratic sandst<lne, 

sandstone, siltst<lne, ·and shale. The congl<lmeratic beds contain 

small well-rounded pebbles of resistant rocks such as chert and 

quartzite. The upper part, about 5,400 feet thicl{, is finer grained 

than the lower part and consists of sandstone, shale, and coal. 

The Hanna· F<lrmation unconformably overlies the Ferris or 

older formati<lns. It is as much as 7,000 feet thick and consists 

of nonmarine congl<lmerate, sandstone, shale, and coal. The conglomerates contain large cobbles of locally derived rocks. 

The names Foote Creek and Dutt<ln Creek, recently proposed 

by H. J. Hyden, Harry McAndrews, and R. H. Tschudy (1965), 

are abandoned. The Foote Creek is a remnant of the Medicine 

Bow Formation, and the Dutton Creek is part of the Hanna 

Formation. 

INTRODUCTION AND ACKNOWLEDGMENTS 

Regional stratigraphic and paleontologic studies and 

detailed geologic mapping in south-central Wyoming 

have demonstrated the need for revision of the stratigraphic nomenclature for the rocks of Late Cretaceous 

age. The ammonite zonation of the Upper Cretaceous 

rocks in the Western Interior established by Cobban 

provides a framework for regional stratigraphic studies 

~nd can be used in interpreting the complex intertonguIng and subtle facies changes within these rocks. In this 

report we describe some of these complexities and attempt to make the nomenclature more compatible with 

that used in adjacent areas. 

1 
2 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

We acknowledge the assistance of Drs. D. L. Blackstone, Jr., and R. S. Houston, of the University of Wyoming, in reviewing this report and in discussing pertinent stratigraphic and nomenclature problems. G. H. 

Horn, M. "\¥. R.eynolds, and R. H. Tschudy, of the U.S. 

Geological Survey, also provided valuable assistance. 

N. F. Sohl, of the U.S. Geological Survey, identified 

the marine gastropod collections. 

HISTORICAL BACKGROUND 

SOUTHWESTERN COLORADO 

In 1875, W. H. Holmes studied the geology of the 

San Juan district in southwestern Colorado and contiguous parts of New Mexico, Utah, and Arizona. He 

recognized sedimentary rocks of Cretaceous age and 

determined their thickness to be about 5,000 feet 

(Holmes, 1877, p. 242). He called the lowermost Cretaceous rock unit the Dakota Sandstone, or No. 1, following the nomenclature of Meek a.nd Hayden ( 1862, p. 

419 ; for a summary of Hayden's nomenclature, see Cobban and Reeside, 1952, p. 1014). Holmes thought that 

the overlying marine shale and minor limestone, 1,200'-

1~500 feet thick, represented Hayden's units 2 and 3 and 

part of unit 4 (the Fort Benton Group, Niobrara division, and Fort Pierre Group). Holmes ( 1877, p. 245) 

named stratigraphically higher nonmarine and marine 

rocks the Mesa Verde Group, in which he recognized 

a threefold division-an upper escarpment sandstone, 

a middle coal group, and a lower escarpment sandstone. 

He did not name an overlying 400- to 800-foot-thick 

marine shale, but he called the next higher massive 

marine sandstone the Pictured Cliffs Group. Holmes 

( 1877, p. 243, pl. 15) equated the 1narine shale and overlying Pictured Cliffs Group with Cretaceous units 4 and 

5 of Hayden (Fort Pierre Group and Fox Hills beds). 

The thick marine shale unit between the Dakota Sandstone and the Mesa Verde (Holmes, 1877) was named 

the Mancos Shale by Cross ( 1899) for exposures near 

the town of Mancos, Colo., north of Mesa Verde N ationa! Park. The marine shale between the Mesa Verde 

and the Pictured Cliffs Sandstone was named the Lewis 

Shale by Cross and Spencer (1899) for exposures near 

Fort Lewis, Colo., east of Mesa Verde National Park. 

The current spelling of the name Mesaverde was apparently introduced by Cross and Spencer in 1.899. 

In 1919, A. J. Collier investigated the coal deposits in 

Holmes' middle coal group of the Mesa Verde south of 

the town of Mancos in the region of Mesa Verde. Collier 

(1919, p. 296) recognized Holmes' threefold division of 

the Mesaverde and designated ·the upper escarpment 

sandstone as the Cliff House Sandstone, the middle coal 

group as the Menefee Formation, and the lower escarpment sandstone as the Point Lookout Sandstone and referred the three new formations to the Mesa verde 

Group. 

NORTHWESTERN C'OLORADO 

Geologists of the IGng and the Hayden Surveys 

mapped Cretaceous sedimentary rocks in Routt County, 

northwestern Colorado, a.nd adopted the stratigraphic 

classification previously established in the upper Missouri River region by Meek and Hayden ( 1862, p. 419). 

The classification used in the Missouri River region, 

based on lithology and fossils, was applied to Cretaceous 

rocks throughout much of the Rocky Mountain region. 

Nomenclature used by these surveys is as follows 

(adapted from Fenneman and Gale, 1906, p. 18): 

Tertiary 

6. Laramie 

4. Pierre Montana Group 

5. Fox Hills ) 

Cretaceous 3. Niobrara } 

2. Benton Colorado Group 

1. Dakota 

The early geologists generally assumed that the main 

Cretaceous coal-bearing units were in the Laramie and 

that the minor coal-bearing units were in the Dakota. 

This assumption resulted in the inclusion of the main 

coal-bearing rocks of northwestern Colorado in the 

Laramie Formation. 

In 1905, Fenneman and Gale studied the Yampa coal 

field of Routt Co.unty where they recognized marine and 

nonmarine Cretaceous rocks, about 8,000 feet thick, overlying the Dakota Sandstone. They ( 1906, p. 17-31) were 

unable to apply the classification and nomenclature used 

previously in the area and believed that the established 

nomenclature was incorrect and only generally relevant. 

Concerning this problem they stated (p.19) : 

Below the Laramie and above the Dakota the succession of 

formations as summarized in the foregoing table .is not applicable 

to the Yampa field except in a most general .and indefinite way. 

In the Montana group the Fox Hills sandstone and the Pierre 

shale are not found as distinct formation or lithologic units, and 

similarly the Colorado group cannot be said to be composed of 

the Niobrara limestone and the Benton shale as distinguished in 

other fields. Moreover, the line between the Montana and Colorado groups also becomes an indefinite or abitrary boundary 

as the distinction between Pierre and Niobrara is lost. There is, 

however, a certain fossil fauna which has been recognized as 

characteristic of the Montana formation, and similarly a lower 

fauna which is as characteristic of the Colorado. It is, however, 

more convenient and logical to drop the grouping as Colorado 

and Montana and adopt a new basis for subdivision of the 

combined stratigraphic interval thus represented. This has already been done by the geologists who have worked in southwestern Colorado [Cross, 1899], where the succession shows 

such marked similarity to that of the Yampa field that the names 

there adopted have been incorporated in this report. 

.... 
• 

HISTORICAL BACKGROUND 3 

In summary, Fennemnn and Gale recognized a thick 

unit of marine shale containing fossils of Benton and 

Niobrara age overlying the Dakota Sandstone and underlying a thick unit of marine sandstone and shale containing a fauna of Pierre and Fox Hills age; this latter 

unit grades upward into nonmarine rocks including coal, 

and these, in turn, are overlain by a thick body of marine 

shale. Fenneman and Gale acknowledged the apparent 

homotaxic equivalence of these beds to the Cretaceous 

sequence in southwestern Colorado and, therefore, introduced the names ~1nncos Shale, ~1esaverde Formation, and Lewis Shale into northwestern Colorado. In 

regard to the introduction of the names, Fenneman and 

Gale ( 1906, p. 28) stated "and the na.me is provisionally 

adopted as in the case of the ~1ancos shale and Mesaverde formntion, in the expectation that future geologic 

work will definitely establish the correlation between the 

two." 

The equivalence of the ~1esavercle and Lewis of northwestern and southwestern Colorado anticipated by Fenneman and Gale has not been confirmed. Geologic investigations in western Colorado clearly demonstrate 

a. lack of continuity between the ~1esnverde and Lewis at 

their type localities and the ~1esaverde and Lewis of 

northwestern Colorado and "'\Vyoming. Reeside (1924, 

p. 18) stated that the Lewis Shale of the northern areas 

was definitely not the same age as the Lewis of the 

San Juan district. ~lore recently, "'\~Teimer (1959, p. '11) 

has shown a similar relationship. 

At its type locality in southwestern Colorado, the 

~1esaverde Group is a thick unit of marine sandstone 

and nonmarine rocks. It thins northeastward, becomes 

finer grained, and finally loses its identity within the 

~1ancos Shale. At the lntitude of ·~1ontrose, Colo., the 

entire ~1esaverde Group is represented by the middle 

part of the ~1ancos Shale, and the overlying Lewis Shale 

.is an indistinguishable part of the ~1ancos (Dickinson, 

1965). In this urea the ~1ancos is overlain by the Pictured Cliffs Sandstone, which :in northwestern Colorado 

becomes the bnsal part of the ~1esa verde as defined by 

Fennemnn and Gale ( 1906) and by others. The Lewis 

Shale of the Yampa district of northwestern Colorado 

is not represented by marine rocks in western and 

soutl)'vestern Colorado. 

In 1912 and 1913, I-Iancock ( 1925) investigated the 

geology and coal resources of the Axial and Monument 

Butte quadrangles in ~1offat County in northwestern 

Colorado. IIe divided the ~1esaverde into the lies and 

the overlying vVilliams Fork Formations and elevated 

the Mesaverde to group status (Hancock, 192·5, p. 13-

14). Publication of the report formally describing these 

two new formations was delayed, and the names first 

appeared in the U.S. Geological Survey Press 

Memorandum 16037, October 1,1923. 

SOUTH-CENTRAL WYOMING 

"'\Vhile examining coal deposits in east-central Carbon 

County, "'\Vyo. (fig. 1), in 1906, Veatch (1907) recognized a thick succession of Upper Cretaceous rocks. The 

main difference between these rocks and Upper Cretaceous rocks of northwestern and southwestern 

Colorado was the presence of formations of the 

Colorado and ~1ontana Groups in "'\Vyoming, units that 

had been indistinct or unrecognizable in the southern 

areas. Veatch ( 1907, p. 246) assigned the Da.lmta, 

Benton, and Niobrara Formations to the Colorado 

Group and the Pierre, ~1esaverde, and J.....ewis Formations to the ~1ontana Group. Overlying the ~1ontana 

Group was the "Lower Laramie," a. thick sequence of 

Cretaceous nonmarine rocks. Veatch's Benton, Niobrara., 

and Pierre Formations .are probably equivalent to 

Fenneman and Gale's ~1a.ncos Shale ( 1906), and the 

Mesaverde and Lewis Formations in each a.rea are 

u.pproximately equivalent. Regarding the use of the 

name Pierre in "'\Vyoming, Veatch (1907, footnote on 

p. 246) stated: 

It is the belief of Dr. '1'. \V. Stnnton that the Mesnverde and 

part of the Lewis also belong to the Pierre, ns that formation 

is developed east of the Rocky Mountains. A local name will 

therefore probably be applied to this lowest division of the 

l\fontana in this region. 

The name Steele Shale was introduced by Darton, 

Blackwelder, and Siebenthal ( 1910, p. 10), to re-place 

Pierre as used by Veatch (1907). Their description 

follows: 

The lower portion of the Montana group in the Laramie 

Basin consists of about 3,000 feet of dark shale with some thin 

beds of sandstone and numerous nodular concretions, mostly 

.sandy. These rocks are believed to represent the Steele shale, 

named for the type locality, Fort Steele, on the North Platte 

River. 

In 1918, Bowen reported on the stratigraphy of the 

I-Ianna Basin. l-Ie described the Steele Shale as a 4,000-

foot-thick dark-gray shale with interbedded sandstone 

and shaly sandstone, some of which forms conspicuous 

ledges near the top of the formation (Bowm~, 1918, p. 

229). He described the Mesaverde Formation as 2,700 

feet thick and divisible into three members. The upper 

1nember consists of whitish sandstone interbedded with 

gray and carbonaceous shale and thin irregular beds of 

coal. The middle member is composed of brown to gray 

sandstone, carbonaceous shale, u.nd thin irregular beds of 

coal; it contains a fresh- and brackish·water fauna. The 

lower member is gray to white sandstone and gray shale; 

it lacks coal and contains a. marine fauna. Bowen apparently redefined the upper and lower boundaries of 

the Mesaverde of Veatch and included some of the lower 

part of the Mesaverde in the Steele Shale (Veatch, 1907, 

p. 246; Bowen, 1918, p. 229). 
108' 

42' 

GREAT DIVIDE 

BASIN 

____________ !_¥' 

:., 

BIGHORN BASIN 

------ 106' PaUifinder Res~rvoir ----------~--r---E~PLANATION ______ l 

BASIN 

Saratoga 

~ 

"''!;, 

I D '~"}% , I I Outcrop of Ferris and Outcrop of Mesaverde I 

I Hanna Formations Group 1 

I ~ I 

1 Outcrop of· Lewis Shale, Fox Hills, Lance, I 

I a nd Medicine Bow Formations I 

Includes L ance along east flank of 

o

1

o Wa shakie and Great Divide Basins 1 (.) (.) l sj~ Contact ____ _ 

~I ;:i Dashed where approximately located; 1 

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u...: 6 -<>- Medicine M 

Bow 1 Location of section Oil and gas well I 

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FIGURE 1.-Index geologic map of south-central Wyoming showing location of measured sections. Geology modified from Love, Weitz, and Hose (1955). 

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HISTORICAL BACKGROUND 5 

In south-central Wyoming, the Lewis Shale and overlying "Lower Laramie" were reported by Veatch ( 1907, 

p. 246-249) to consist of marine and continental rocks, 

respectively. Bowen ( 1918, p. 228-230) substituted the 

name Medicine Bow Formation for the "Lower 

Laramie." Dobbin, Bowen, andlloots (1929, p. 22-24) 

described a unit of interbedded 1narine and nonmarine 

rocks, 400-500 feet thick, between the Lewis and Medicine Bow and reassigned n1ost of these rocks from the 

upper part of the Lewis to the basal part of the Medicine 

Bow. They correlated this transitional unit plus •an 

uppermost part of the Lewis Shale with the Fox Hills 

Sandstone of eastern ''rymning. The Fox Hills had 

been named in South Dakota by Meek and Hayden 

(1862, p. 419). Dobbin and Reeside (1929, p. 21-23) 

also recognized .the transitional rocks and stated that 

they were of Fox Hills age. Dorf (1938, p. 4-6) redeHned the ~1edicine Bow assigning the basal 400-+- feet 

in the I-Ia.nna Basin to the Fox Hills Fonnation. 

Bowen ( 1918, p. ·228) also nnmed the Ferris Formation of questionable Tertiary age and the Hanna Fonnation of Tertiary age. Most subsequent workers in the 

area have used the nmnenclature of Bowen (in Dobbin, 

Bowen, and Hoots, 1929, p.17-26). 

The names Foote Creek and Dutton Creek were introduced by Hyden, McAndrews., and Tschudy ( 1965) for 

rocks of Late Cretaceous and Tertiary age in the northern part of the Laramie Basin and southern part of the 

Carbon Basin. Geologic investigations in the area since 

then indicate that these rocks are remnants of the Medicine Bow and Hanna Formations, respectively .. 

SUMMARY 

Nomenclature established for rocks of Late Cretaceous age in southwestern Colorado should not have been 

extended into northwestern Colorado, eastern Utah, and 

Wyoming. Although the stratigraphic sequences are 

homotaxically equivalent, the Mesaverde Formation and 

Lewis Shale are not laterally continuous among the 

areas. It would be desirable to abandon the names Mesaverde and Lewis a way from their type localities, but 

their general use for more than 60 years makes such a 

change impractical. A reasonable solution, based on 

regional geologic studies, is to redefine the Mesa verde 

as a group ·and establish within it lesser stratigraphic 

unit!:\ that are widely mappable and laterally continuous 

(table 1). A similar approach was used by Hancock 

(1925, p. 13-14) in defining the Iles and Williams Fork 

Formations of the ~iesaverde Group in northwestern 

Colorado, by Spieker and Reeside (1925, p. 440); in 

defining the Star Point Sandstone, Blackhawk Fonnation, and Price River Formation of the Mesaverde 

Group in eastern Utah, and by Sears (1926, p. 16); in 

867-863 Q-70-2 

treating the Blair and Rock Springs Formations, the 

Ericson Sandstone, and the Almond Formation o£ the 

Mesaverde Group in southwestern Wyoming. 

We propose a revision of the stratigraphic nomenclature for some of the rocks of Late Cretaceous age in the 

area of the Rawlins uplift and the Hanna, Carbon, and 

Laramie Basins in southern Wyoming. These revisions 

are based on regional stratigraphic and faunal studies 

and on detailed geologic mapping. 

In the area of this report we herein elevate the Mesaverde Formation to the Mesaverde Group and establish 

and accept the following formations within the Mesaverde Group in the Hanna and Carbon Basins (in ascending order) : Haystack Mountains Formation, Allen 

Ridge For1nation, Pine Ridge Sandstone, and Almond 

Form·ation (fig. 2). The Haystack Mount·ains Formation consists o£ thick and persistent units of marine 

sandstone separated by thick units of marine shale. 

Three of the sandstone units have been 1napped ·locally 

and are designated as members of the Haystack Mountains Formation. They are, in .ascending order: Tapers 

Ranch, O'Brien Spring, and Hatfield Sandstone Members. The Hatfield Sandstone Member was proposed by 

Hale ( 1961, p. 134) and is herein adopted. The Allen 

Ridge Formation, proposed by Bergstrom (1959, p. 

114) for the dominantly nonmarine part o£ the Mesaverde underlying the Pine Ridge Sandstone, is herein 

adopted. Dobbin, Hoots, Dane, and Hancock ( 1929, p. 

134) first described the Pine Ridge Sandstone ·as a memher of the Mesaverde Formation. 'V e herein elevate it to 

formation status. The Almond Formation, first described by Schultz (1907, p. 260) is southwestern Wyoming as the Almond coal group, was later called by 

Sears ( 1926, p. 16) the Aln1ond Formation of the Mesaverde Group. This formation confonnably underlies the 

Lewis Shale in much of southern Wyoming. The name 

Almond is hereby extended from southwestern Wyoming into the ·area of this study. 

In the Laramie Basin the ·~iesaverde Group consists 

of the Pine Ridge Sandstone and a thick underlying 

unit of shallow-water marine sandstone and shale. We 

propose that the latter unit be named the Rock River 

Formation (fig. 2). The thick and distinctive marine 

rocks of the Rock River Formation grade westward into 

the mainly nonmarine rocks of the Allen Ridge Formation. The lateral transition between the two formations 

is in the northen1 part of the Laramie Basin. 

The name Lewis Shale is retained in southern Wyoming even though the formation is neither correlative 

with, nor lithologically the same as, the type Lewis 

Shale of southwestern Colorado. The name is perpetuated only because of long-established usage in the region. 

In its upper part the Lewis Shale contains a wide-
6 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

UPPER CRETACEOUS 

STAGES AND 

SUBSTAGES 

.... 

~ 

~ 

0 

...J 

TABLE 1.-Gorrelation of Upper Cretaceous rocks in south-cent1·al Wyonl!ing aml 

WESTERN INTERIOR AMMONITE 

ZONES 

29 Discoscaphites nebrascensis 

28 Hoploscaphites nicolletii 

27 Sphenodiscus (Coahuilites) 

26 Baculites clinolobatus 

2 5 Baculites grand is 

24 Baculites baculus 

ROCK SPRINGS 

UPLIFT 

Lance Formation 

(part) 

Fox Hills Sandstone 

Lewis Shale 

HANNA BASIN 

Medicine Bow 

Formation 

(part) 

Fox Hills Formation 

Upper part 

.c. : - ~ uad Sandstone - ~~~ 

LARAMIE BASIN 

(ROCK RIVER) 

Medicine Bow 

Formation 

(part) 

Fox Hills Formation 

Upper part 

Unnamed 

sandstone 

1--,..--------------J ~ Lower part ~ 1-----------i 

1-----+-----~--------------~ ...J <ll 

·~ 

c: 

ro 

·c: 

ro 

c. 

E 

ro 

(.) 

c: 

ro 

·c: 

0 

c 

ro 

C/) 

.... 

~ 

c. 

c. 

:::> 

Qj 

c. 

c. 

:::> 

2 3 Baculites eliasi 

22 Baculites jenseni 

2 1 Baculites reesidei 

20 Baculites cuneatus 

1 9 Baculites compnssus 

18 Didymoceras cheyennense 

1 7 Exiteloceras jenneyi 

16 Didymoceras stevensoni 

15 Didymocent.s neb1·ascense 

14 Baculites scotti 

13 Baculites gregoryensis 

12 Ba.culites perplexus 

11 Bcwulites sp. (smooth) 

1 0 Ba.culites asperiformis 

9 Baculites mclea.rni 

8 Baculites obtusus 

7 Baculites sp. (weak flank ribs) 

6 Baculites sp. (smooth) 

5 Sca.phites hippocrepis III 

4 Scnphites hippocrepis II 

3 Sca.phites hippocTepis I 

2 De.c;moscaphites bassleTi 

1 Desmoscaphites erdmanni 

c. 

:l 

0 

t5 

~ 

'E 

~ 

> 

ro 

<ll 

~ 

~ 

~ 

c: 

.s 

<ll 

"0 

c: 

ro 

C/) 

c: 

0 

<ll 

u 

;5 

Almond 

Formation 

U;:>per part 

----?--

Middle part 

1--?-

Lower part 

Rock Springs 

Formation 

Blair Formation 

Baxter Shale (part) 

r-L-,..---------~~ 

Almond 

Formation 

Pine Ridge 

Sandstone 

Unnamed marine 

member 

Allen Ridge 

Formation 

Hatfield 

Sandstone 

Member 

.<IJ 1------~ 

c: Middle 

2 unnamed 

5 member 

~ 1----;0""''""B ie=-=n,-,S"p:-r~i n-:-g--i 

~ Sandstone Member 

u .S Lower unnamed 

~ member 

ro ·1-:=----:----l I Tapers Ranch 

Sandstone Member 

Steele Shale 

Lower part 

Pine Ridge 

Sandstone 

Rock River 

Formation 

Steele Shale 

-------------~-------7--------J-------?------~ 

--r 

Airport Sandstone 

Member of 

Smith (1961) 

Niobrara Formation 

(part) 

Niobrara Formation 

(part) 

,._.; 

< 

·• 
nearby m·eas 

SOUTHEASTERN 

WIND RIVER 

BASIN 

ii. 

Lance Formation 

(part) 

Fox Hills Sandstone 

Lewis Shale 

1-

Tongue of Meeteetse 

Formation 

L-------

.•. 

Lewis Shale 

Teapot 

Sandstone 

Member 

1- c: 

0 - :;::; 

<II 

E 

0 

LL.. 

Q) 

"E 

Q) 

> 

<II 

VI ? Q) 

:2 Unnamed middle 

member 

·~ 

Parkman 

Sandstone Member 

~ W!!_llace Creek Tongue of 

Codv-Shale 

Fales Sandstone 

Member 

Shale 

Unnamed sandstone 

Shale 

)-' 

Unnamed sandstone 

)-

t Shale 

<II 

.s Unnamed sandstone 

Q) Shale (ij 

.!: Unnamed sandstone (/) 

>-

"0 

0 

u 

Shale (part) 

.>-

POWDER RIVER 

BASIN 

(SALT CREEK) 

Lance Formation 

(part) 

Fox Hills Sandstone 

Upper part 

(/) 

~~ VI 

'i 

Q) 

.....1 Lower part 

Teapot 

Sandstone 

Member 

c: 

.g 

<II 

E 

0 rLL.. 

Q) 

"0 

Q; 

> 

<II 

VI ? Q) 

:2 Unnamed marine 

member 

Parkman 

Sandstone 

Member 

Shale 

Stray sandstone 

Shale and Q) 

(ij bentonite .!: 

(/) 

Q) Suss~ .. ~~~rstone 

Qi 

Q) Sandy shale 

en Shannon Sandstone 

Member 

Shale 

Fishtooth sandstone 

Shale 

Niobrara Formation 

(part) 

STEELE SHALE 7 

BLACK HILLS 

(RED BIRD) 

Lance Formation 

(part) 

Fox Hills Sandstone 

Upper unnamed 

shale member 

Kara Bentonitic 

Member 

Lower unnamed 

shale member 

(part) 

Ill 

(Absent or 

very thin) 

Q) 

(ij 

.!: 

(/) Lower unnamed 

~ shale member Q) (part) a: 

Red Bird 

Silty Member 

Mitten Black 

Shale Member 

Sharon Springs 

Member 

Gammon 

Ferruginous 

Member 

? 

Niobrara Formation 

(part) 

spread unit of sandstone and shale called the Dad Sandstone l\iembe.r by Hale ( 1961, p. 136). This name is 

herein adopted. 

At the top of the Lewis Shale or ·a.t the base of the 

overlying l\iedicine Bow Formation is ·a. thick unit composed 1nainly of sa.ndstone. Rocks of this unit are transitional from ma.rine shale of the underlying Lewis to 

nonmarine rocks of the overlying l\iedicine Bow Formation and include shallow-water marine sandstone and 

marine to nonmarine siltstone and shale. The name Fox 

Hills Form.ation is used for these rocks. 

The l\iedicine Bow Forma.tion of Late Cretaceous age, 

named and described in the H·anna Basin, is mostly restricted to the Hanna and Carbon Basins. The name is 

herein used-as originally defined. The Ferris Forma.tion 

of Late Cretaceous and early Tertiary age and the 

Hanna Formation of Tertiary age were defined in 

the Hanna Basin and ·are herein adopted as originally 

proposed. 

The Foote Creek Formation of Late Cretaceous and 

early Tertiary age and the Dutton Creek Formation 

of Tertiary -age are exposed a.long the northern m·argin 

of the Laramie Basin and the southern margin of the 

Carbon Basin. Recent studies of the lithology and age 

of these rocks have shown them. to be correlative with 

parts of the Medicine Bow and Hanna Form:ations. 

For reasons given in this report on pages 45-46, we.comInend that the names Foote Creek and Dutton Creek be 

abandoned. 

STEELE SHALE 

T'YPE LOCALITY AND DISTRIBUTION 

The Steele Shale was named by Darton, Blackwelder, 

and Siebenthal ( 1910, p. 10) for Fort Steele on the 

North Platte River, about 15 miles east of Rawlins, Wyo . 

(fig. 1). The name was first used by these authors in the 

Laramie Basin. 

The Steele Shale is recog11ized throughout southcentral and southeastern 'Vyoming, and the name has 

been used in the western part of the Powder River 

Basin in northeastern "Tyoming. In areas where the 

underlying Niobrara Formation is poorly developed or 

not recognized, the marine shale unit beneath the Mesaverde is called Cody Shale. The Cody is equivalent to 

the Carlile Shale, Niobrara Formation, and Steele 

Shale. 
8 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

c 

0 

., 

"' E-

~ t: 0"' 

"' .,~ 0. 

u 

c 

...J "'

Formation 

Almond 

Formation 

c 

~ c c 

:J 0 0 ·- ::;:'ro 

~ E u ~ 

~"- "' 0 

"' " "' I 

1 

en 

z 

...J 

~ 

< 

a:: 

FIGURE 2.-Stratigraphic cliagrwm showing intertongu·ing relations 

2 3 4 5 

wz en_ w~ w a:: 0::< oo w 

< 01- z> a:: I 

...J IZ -0:: i-U 

u O::J ::;:w ...J 

z ...JQ wen W::J 

~::;: enw Zc.!l 

a:: a:: 

f· 

1-

• 
-+ 

STEELE SHALE 

5 6 

!: 

0 

m w I 

w ow a:: I ::;:z ,_u _J ou W:::J u-0 Zc.!l w a: ::;: 

Hatfield Sandstone Member I 

7 

0:: 

w 

~ 

0:: 

:.:: 

u 

0 

0:: 

., c: c: 0 

u 3:"' t :ogE1i 

., ~-

::;: 0 

"-

Fox Hills 

Formatio n 

., 

iii 

r: 

Ul 

Ill 

~ 

., 

_J 

of Upper 01·etaceottS rocks in south-central Wyo•ming 

EXPLANATION 

D 

Marine shale 

D 

Persistent beds of thin-bedded to massive sandstone 

deposited in a marine environment 

D 

Organic-rich black shale, ironstone concretions, and thinbedded sandstone deposited in a lagoonal environment 

Lenticular sandstone and shale, • carbonaceous shale, and coal 

deposited in a fluvatile environment 

.9 

Ammonite coll ection from measured section or nearby locality 

Number refers to 

~ 

arnrnonite sequence shown i1< Wble 1 

Unconformity 

Formation boundary 

Dashed where approximately located 

[ 50: 

l lOOO FEET 

0 10 20 30 MILES 

9 
10 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

LITHOLOGIC CHARACTER 

The Steele Shale consists of dnrk-gray shale that contains sparse layers of gray-weathering limestone concretions and thin beds of very fine grained sandstone 

rmd siltstone. In areas where sandstone beds of the 

overlying Haystack Mountains Formation pinch out 

l . ' t 1e eqtnvalent facies, assigned to the Steele, is very 

sandy shale. 

The Steele Shale is nonresistant and commonly forms 

broad areas of low relief. It is generally poorly exposed, 

bt~t the upper part crops out ·where protected by the 

chff-form1ng sandstone of the Haystack Mountains 

Formation. 

In the nortlnvestern part of the Laramie .Basin, the 

upper part of the Steele includes several persistent 

bentonite beds. One bed, as much as 5 feet thick, has been 

extensively mined a few miles west of Medicine Bow 

'Vyo. This bed and those within a few feet above i~ are probably correlative with the Ardmore Bentonite 

Bed in the Sharon Springs Member of the Pierre Shale 

in the Black Hills region of \'T yoming and South Dakota (Gill and Cobban, 1966a, p. A10). The bentonite 

beds probably also correlate with the thick bentonite 

unit overlying the Sussex Sandstone Member of the 

Steele Shale in the Salt Creek oii field of the western 

Powder River Basin. · 

THICKNESS 

The thickness of the Steele Shale has been reported 

by Veatch (1907, p. 246) as 3,000-3,500 feet; by Darton, 

Black,velder, and Siebenthal (1910, p. 10) as 3,000 feet; 

by Dobbin, Bowen, and Hoots (1929, p. 17) as 4,000-

5,000 feet; and by Bergstrom (1953, p. 59) as 2,600-

3,200 feet. The variation in thickness reported probably 

results mainly from individual preferences in selecting 

the upper and lower boundaries for the formation. No 

type section of the Steele is described in the literature ' and none was measured by us. Electric logs of oil and gas 

wells show that the Steele is about 2,400 feet thick in the 

western part of the Hanna Basin~ where the overlying 

Haystack Mountains Formation is well developed. At 

Hatfield dome, about 10 miles south of Rawlins, Smith 

( 1965, pl. 3) reported the Steele to be about 3 800 feet 

thick. In the Rock River area of the Laramie B'asin the 

formation is about 2,300 feet thick. ' 

RELATION TO ADJACENT FORMATIONS 

The contact of the Steele Shale with the underlying 

Niobrara Formation is gradational. It is located at the 

change from the gray shale of the Steele to the yellowish-orange-weathering calcareous shale of the upper 

part of the Niobrara. The contact of the Steele Shale 

with the overlying Haystack l\tlountains Formation is 

also gradational. The shale of the upper part of the 

Steele becomes increasingly sandy upward and finally 

merges with the sa.ndstone of the Haystack ~iountains 

Formation. 'Ve locate the upper contact at the base of 

the first persistent marine sand.stcne. 

Both the upper and lower boundaries of the Steele 

rise stratigraphically eastwn.rd., and the formatio11 

grades laterally into the lower part of the Pierre Sha,le 

east of the Laramie Mountains. In the type section of 

the Haystack Mountains Formation, about 11 miles 

northeast of Rawlins, the Steele Shale is about 2,400 

feet thick; 22 miles farther south, it is about 3 800 feet 

t~1ic~. This thickness change results from a stratigraphic 

r1se In the Steele-Haystack Mountains contact. 

FOSSILS 

Fossils ·are moderately abundant in limestone concretions and thin sanely beds of the Steele Shale, and 

they have been collected at many localities throughout 

southern \Vyoming. The best documented collections 

with respect to stratigraphic position are those of Smith 

( 1965, p. 21-23) from the Hatfield dome area south of 

Rawlins in Carbon County. Fossils fron1 these collections, which were identified and the names herein updated by W. A. Cobban, are as follows: 

USGS D3293. SEtA, sec. 24, T. 19 N., R. 87 W. From a limestone 

concretion layer 415 ft below the top of the Steele Shale. 

Inoceram1ts cf. I. proximus Tuomey 

Pteria linguaetormis (Evans and Shumard) 

Cytnbophora sp. 

Thyasira sp. 

Baculites obt'ltS'ttS Meek (early form) 

Trachysca-phites pracspiniuer Cobban and Scott 

USGS D3290. SEtA, sec. 12, T. 19 N., R. 88 W. From a limestone 

concretion layer 405 ft below the top of the Steele Shale. 

Inoceram1ts cf. I. proxinws Tuomey 

Pteria sp. 

Lucina subundata Hall and Meek 

Cym,bophora sp. 

Baculites sp. (weal\: flank ribs) 

Trachyscaphites p-raespin·igcr Cobban and Scott 

Placenticems cf. P. meeki Boehm 

Placenticeras cf. P. intercalare Meek 

USGS D3048. N'V% sec. 34, T. 19 N., R. 86 W. From a limestone 

coneretion layer '702 ft .below the top of the Steele Shale 

Inoce-ram1ts sp. 

Pteria sp. 

Ostrea sp. 

Baculites sp. (weak flank ribs) 

Placenticeras cf. P. meeki Boehm 

USGS D3047. NE% sec. 34, T. 19 N., R. 86 W. From a limeston~ 

concretion layer 702 ft below the top of the Steele Shale. 

Inoceramus sp. 

Baculites sp. (weak flank ribs) 

,_.( 

.a..;· 

~. 

•· 

..... 

•-f' 
iJ. 

~- .l. 

~· 

• 

• 

.... 

MESAVERDE GROUP AND MESAVERDE FORMATION 11 

USGS D3046. SW¥.., sec. 3G, T. 19 N., R. 86 \V. From a limestone 

concretion layer 912 ft below the top of the Steele Shale. 

InooemnHtS sp. 

Pte-ria n. sp. 

BaottZites sp. (weak flank ribs) 

'b·achysoaphites 1)raesphvige1· Cobban and Scott 

USGS D3291. NE'It sec. 26, T. 19 N., H. 87 W. From a limestone 

concretion layer 1,73G-1,7GO ft below the top of the Steele 

Shale. 

Lucina, ."'ttbttntlata Hall and Meek 

Baottlites aff. B. aqttilacnsis Reeside 

USG•S D3054. NE¥.., sec. 23, T. 19 N., R. 88 W. From a limestone 

concretion layer 2,320 ft below the top of the Steele Shale. 

Inocemmtts cf. I. proa:inws Tuomey 

Ost1·ea sp. 

GZyptoa:ocm·as sp. 

Scaphites hip7Jocrepis (DeKay) 

USGS D3053. NW:JA, sec. 14, T. 19 N., R. 88 W. From a limestone 

concretion layer 2,332 ft below the top of the Steele Shale. 

InoccramMts cf. I. 1woa:imus Tuomey 

Pte1··ia cf. P. Unguaetormis (Evans and Shumard) 

Ostrea n. sp. 

Drepanochilus sp. 

Bacu.lites sp. 

Glyptoa:ocems sp . 

II m·cs·iceras 1nontanaense ( Reeside) 

Sca.phites hippocrepis (DeKay) I 

USGS D3095. Center of the N% sec. 23, •r. 19 N., R. 88 \V. From 

a limestone concretion layer 2,747 ft below the top of the 

Steele Shale. 

Ost?·ea sp. 

BaculUes sp. 

Sca1Jhites hip1worcpis (DeKay) I 

USGS D3051. NW¥.., sec. 26, T. 19 N., R. 88 \V. From clayey 

limestone concretion layer 3,565 ft below the top of the Steele 

Shale. 

Uintacrinus sooial·is Grinnell 

Ost?·ca oongcsta Conrad 

Inocemn1.1ts cf. I. balticus Boehm 

Bacttlitcs tho1ni Reeside 

Desmoscaphites bassled Reeside 

AGE AND CORRELATION 

The fauna listed above from the Steele Shale in the 

I-Iatfield dome area., south of Rawlins, is common to the 

Telegraph Creek and Eagle Formations and the lower 

part of the Claggett Formation of central Montana 

(Cobban and Reeside, 1952, p. 1019-1020). In the area 

north ·and northeast of Rawlins, the top of the Steele js 

older and apparently does not contain beds younger 

than about the middle part of the Eagle; beds in the 

lower part of the overlying I-Iaystack Mountains Formation contains late Eagle and Claggett fauna. 

The upper part of the Steele Shale in the area north 

of Rawlins correlates with the upper part of the Mancos 

Shale of northwestern Colorado, the upper part of the 

Blair Form·ation of southwestern vVyoming, the upper 

part of the Cody Shale in the vVind River Basin of central V\Tyoming, and the Steele Shale of the western 

Powder River Basin of northeastern 'Vyoming (table 

1). The lower contact of the Steele rises stratigraphically 

toward the east. 

MESAVERDE GROUP AND MESAVERDE FORMATION 

Rocks in south-central V\Tyoming formerly called 

~1esaverde Formation, and hereafter referred to as 

the Mesaverde Group (table 1), are divided into the 

:follmYing formations, in ascending order: Haystack 

~1onntains Form·ation, Allen Ridge Formation, Pine 

Ridge Sandstone, and Almond Formation. The 

~1esaverde Group confonnably overlies, and laterally 

intertongues at the base with, the Steele Shale. It 

conformably underlies, and laterally intertongues at 

the top with, the Lewis Shale (fig. 2). 

In the southeastern part of the area (Laramie Basin), 

the Mesaverde Group comprises the Rock River Formation and the Pine Ridge Sandstone. The absence of 

the Haystack ~1ountains, Allen Ridge, and Almond 

Formations is due to the eastward change in facies from 

rocks typical of these formations to marine beds of the 

Steele and Lewis Shales (fig. 2) . 

The name ~1esaverde Formation is still applied to a 

thick sequence of shallow-water marine and nonmarine 

beds in the Powder River, Bighorn, and 'Vind River 

Basins o:f 'Vyoming. Regional stratigra.phic studies indicate that the formation is composed of severa.l widespread and distinctive units tha.t can be recogt1ized in 

each of the basins. Some of these units, such as the Teapot and Parkman ~Sandstones, a.re formal members of 

the ~1esaverde Formation, but other equally distinctive 

units are unnamed. 

In the southeastern part of the vVind River Basin, 

Barwin ( 1959, p. 141) named the lower regressive 

tongue of the ~1esaverde Formation the Phayles Reef 

~t[e.mber and later modified the name to Phayles Member (Ba.rwin, 1961, p. 174). 'Ve reexa.mined Ba.rwin's 

area and type section in the S'V1.4 sec. 4, T. 33 N., R. 87 

,V., and found that the correct spelling of "Phayles" is 

Fales, as shown on the Garfield Peak 7112-minute quadrangle map. Inasmuch as "Phayles" is not a wellestablished and repeatedly published name, we are accepting the correct spelling of Fales. 

:Marine rocks overlying the Fales were called the 'Vallace Creek Tongue of the Cody Shale (Barwin, 1959, 

p. 142) . The type section of the '~r allace Creek is also in 

the s·"r14 sec. 4, T. 33 N., R. 87 W. The 'Va.llace Creek 

Tongue of the Cody and the Fales ~1ember of the ~1esaverde are distinctive stratigraphic units in the southeastern part of the 'Vind River Basin and are herein 

adopted as formal stratigraphic units. for. that area. 
12 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

FIGURE 3.-Haystack l\Iourutains Formwtion exposed along the west side of the HaystJack Mountains in sec. 18, T. 24 N., R. 86 

W., Oarbon County, Wyo. tr, Tapers Ranch Sandstone Member; ob, O'Brien Spring Sandstone Member; ho, Hatfield Sandstone Member; hm, top of Haystack Mountains Formation. 

HAYSTACK MOUNTAINS FORMATION 

TYPE SECTION AND DISTRIBUTION 

The Haystack Mountains Formation receives its name 

from an imposing range of hills that occupies the west 

half of TS. 22--23 N., R. 86 W., Carbon County, "\Vyo. 

(fig. 3) . These hills, ca.lled the Haystack Mountains, 

form the rugged elevated surface along the east side of 

the Rawlins Northwest 7ljz-minute quadrangle, the 

southern part of the Wild Horse Mountain 7ljz-minute 

quadrangle, and the western part of the Lone Haystack 

Mountain 7ljz-minute quadrangle. 

The type section of the Haystack Mountains Formation was measured a short distance west of the place 

where the Seminoe road passes through the canyon of 

the North Platte River, about 6 miles north of the town 

of Sinclair (fig. 1) . The section was measured by planetable and tape in the NE%NE% sec. 22, NE% sec. 23, 

and SE%SE14 sec. 14, T. 22 N., R. 86 W., Carbon 

County (Sinclair 7ljz-minute quadrangle). The upper 

part of the underlying Steele Shale was measured in the 

NljzSW% sec. 7, T. 22 N., R. 86 W. (Rawlins Northwest 71!z-minute quadrangle). 

Three new distinctive members of the Haystack 

Mountains Formation are recognized and mapped in 

this area (table 1; fig. 2) . These members are, in ascending order: Tapers Ranch Sandstone, O'Brien Spring 

Sandstone, and Hatfield Sandstone. The name Tapers 

Ranch is taken from Tapers Ranch in the Sl!z sec. 3, T. 

24 N., R. 86 W. (Wild Horse Mountain 71!z-minute 

quadrangle), and the name O'Brien Spring is taken 

from O'Brien Spring located in the SWl)!, sec. 9, T. 24 

N., R. 86 W. (Seminoe Dam Southwest 7%-minute 

quadrangle) . Both members are moderately well exposed in the vicinity of these two localities, but they are 

best developed and exposed at the locality of the 'type 

Haystack Mountains Formation which is designated the 

type section of the two new members. 

The Hatfield Sandstone was named a member of the 

"lower (marine) Mesaverde" by Hale (1961, p. 130-

134) for exposures along the flanks of Hatfield dome 

south of Rawlins. The name is here adopted as the 

yotmgest named member of the Haystack Mountains 

Formation. Inasmuch as a type section was not given by 

Hale, we designate as the principal reference section the 

exposure of the Hatfield Sandstone Member on the west 

side of Hatfield dome in the NE%NE% sec. 18, T. 19 N., 

R. 88 W ., Carbon County, Wyo. (Bridger Pass 15-minute quadrangle) (figs. 1, 4). 

The Haystack Mountains Formation is a widespread 

and distinctive unit that can be recognized along the 

east margins of the Great Divide and Washakie Basins, 

on the flanks of the Rawlins uplift, and in the Hanna 

and Carbon Basins (fig. 1). The upper part of the formation is present along the Colorado-Wyoming boundary east of Baggs, "\Vyo. It is not recognizable in the 

Laramie Basin because of a facies change from ridgeforming sandstones to soft sandy sha,le. Rocks in the 

Laramie Basin that are equivalent to the Haystack 

Mountains Formation are part of the Steele Shale. The 

dominant source for the marine sandstones of the Haystack Mountains Formation seems to have been from 
HAYSTACK MOUNTAINS FORMATION 13 

FIGURE 4.-Haystack Mountains Formation at the principal reference section of the Hatfield Sandstone Membe1·, sec. 18, 

T. 19 N., R. 88 W., Carbon County, Wyo. The Ha.tfield Sandstone Member (H) crops out in the middle of the slope. 

the north and northwest inasmuch as brackish-water 

strata occur in association with these beds in that 

direction. 

LITHOLOGIC CHARACTER 

The Haystack Mountains Formation is thick and lithologically diverse, consisting mainly of thick units of 

marine sandstone, deposited in nearshore a11d offshore 

enviroments, interbedded with thick units of marine 

shale, deposited in deeper water environments. The 

sandstone of marine origin in the type section generally 

is pale yellowish gray, very fine to fine grained, very 

thin to thin bedded, a.nd commonly burrowed. Sandstone units generally have a gradational base and ·are as 

much as 275 feet thick. Units of marine shale range in 

thickness from about 25 to 700 feet. The shale is gray 

to brownish gray and consists mostly of clay and sandy 

clay. The shale contains fossiliferous concretions in 

varying abundance, and these may be rusty-weathering 

ironstone, limestone, or argillaceous sandstone. 

At the type section the formation contains eight ledgeforming sandstone beds, three of which ·a.re laterally 

persistent and locailly mapped. The three units are designated members of the Haystack Mountains Formation. The uppermost of the members is the Hatfield 

which is the most diagnostic .and useful for correlation. 

It crops out about 450 feet below the top of the formation north of Sinclair. The Hatfield consists of paleyellowish-gray cliff-forming sandstone about 167 feet 

thick at the principal reference section on Hatfield 

dome. At this locality, it is overlain by a unit of brackish-water and sha.llow-marine carbonaceous shale, siltstone, and sandstone, about 100 feet thick. At the type 

section of the Haystack Mountains Formation, the Hatfield is a cliff-forming marine sandstone, about 120 feet 

thick, that is overlain by rocks of brackish-water origin 

3e7-soo o-70---<3 

.about 55 feet thick. The Hatfield Sandstone Member at 

the type section of the Haystack Motmtains Formation 

is mostly very fine grained, thin bedded, and crossbedded, ·and it is gradational with the underlying marine 

shale. The Hatfield Sandstone Member probably originated as a marine beach and barrier-bar deposit. 

The O'Brien Spring Sandstone Member crops out 

about 1,350 feet below the top of the Haystack Mountains Formation north of Sinclair. It consists of paleyellowish-gray very fine grained and fine-grained thinbedded sandstone (fig. 5) about 220 feet thick, that 

forms a prominent cliff (fig. 6). The lower part of the 

member grades into the underlying marine shale. The 

sandstone contains abundant Ophiomorpha, a fossil 

crustacean burrow indicative of a shallow-water marine 

environment. 

The Tapers Ranch Sandstone Member is the basal 

sandstone of the Haystack Mountains Formation and, 

at the type section north of Sinclair, is about 270 feet 

thick. The member consists of grayish-green fine- to 

coarse-grained glauconitic thin-bedded sandstone containing laminae of dark-gray sandy shale. At the type 

section, a unit about 50 feet thick of gray sandy shale 

containing laminae of sandstone crops out about 75 feet 

above the base of the member. The member has a gradational base. The Tapers Ranch Sandstone Member probably originated in an environment of deeper water than 

either the Hatfield or the O'Brien Spring. 

THICKNESS 

The Haystack Mountains Formation ranges in thickness from 2,550 feet at the type section to 850 feet at Hatfield dome. This thinning toward the southwest results 

from facies changes in the lower part of the formation; 

sandstone at the type section grades into shale at Hat-
14 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

FIGURE 5.-Thin-bedded character of the O'Brien Spring Sandstone Member of the Haystack Mountains Formation at its 

type -section in the NE:i4 sec. 23, T. :::2 N., R. 86 W., Carbon 

County, Wyo. 

field dome. In sees. 2, 3, and 11, T. 24 N., R. 89 \¥., at 

Separation Rim, the formation is 930 feet thick. The 

thickness difference between this locality and the 

type section to the east results from different interpretations of the base of the Mesaverde Group. North 

from Separation Rim, the Haystack Mountains Formation thins to a featheredge, partly by depositional thinning and facies change to nonmarine rocks and partly 

by uplift and erosion before deposition of the Pine 

Ridge Sandstone and the Lewis Shale (Reynolds, 1966). 

The formation thins eastward and is not present in the 

central part of the Laramie Basin. 

RELA'J,'ION TO ADJACENT FORMATIONS 

The contact of the Haystack Mountains Formation 

with the underlying Steele Shale is conformable and 

FIGURE 6.-0'Brien Spring Sandstone Member of the Haystack 

Mountains Formation at its type section in the NE:i4 sec. 23, 

T. 22 N., R. 86 W., Carbon County, Wyo. 

gradational. The basal sandstone of the Haystack Mountains grades into sandy shale in the upper part of the 

Steele. 

The marine shale members of the Haystack Mountains Formation are genetically tongues of the Steele 

Shale. The units of marine sandstone in the Haystack 

Mountains Formation, if traced laterally eastward and 

southward, lose their identity within equivalent parts of 

the Steele Shale. 

The contact of the Haystack Mountains Formation 

with the overlying Allen Ridge Formation is sharp and 

conformable. It is generally located by a change from 

marine sandstone to carbonaceous shale or coal The 

upper part of the Haystack Mountains Formation mn.y 

locally contain a few beds of carbonaceous sha.Ie, but the 

lower part of the Allen Ridge Formation does not contain beds of marine sandstone. The contact of the two 

formations represents a change from a mainly shallowmarine environment to a brackish-water or fluviatile 

environment. The contact descends stratigraphically to 

the west and northwest. 

FOSSILS 

Fossils are moderately abw1dant in the sandstone and 

shale of the Haystack Mountains Formation. Those in 

the shale are commonly enclosed in calcareous, sandy, 

or iron-rich concretions and rarely occur individually. 

Fossils are generally sparse in the sandstone w1its but 

are locally abundant on the upper surfaces of a few 

sandstone beds. The following sequence of index ammonites was established from scattered localities in the 

Haystack Mountains Formation: 

Bacttlites pe1·pleams (youngest) 

asperitormis 

mclearni 

obtusus 

sp. (weak flank ribs) 

sp. (smooth) (oldest) 

Additional fossils are listed with the descriptions of 

the measured sections. 

AGE AND CORRELATION 

At the type section the Haystack Mountarins Formation contains fossils indicative of late Eagle, Claggett, 

and early Judith River ages (Gill and Cobban, 1966a, 

pl. 4; Cobban and Reeside, 1952, p. 1019-1020). The 

Tapers Ranch Sandstone Member contains an undescribed smooth baculite which is also found in the Shannon Sandstone Member of the Steele Shale in the 

Powder River Basin and which is restricted to rocks of 

late Eagle age. The thick shale overlying the Tapers 
.~ 

·~ 

\ 

HAYSTACK MOUNTA,INS FORMATION 15 

H.anch Sandstone l\1e.mber conta.ins an undescribed 

baculite that has. weal~ flank ribs. Thi.s species, which 

is indicative of a, very late Eagle age, has also been 

:found in the shale between the Shannon and Sussex 

Sandstones l\1embe.r in the. Powder River Basin. The. 

O'B1~ien Spring Sandstone Member oontains Baoulites 

obt~t8~t8, n. guide fossil to rocks of ea.rly Claggett age. 

T'his member has the a.ppearance and fossils of the Sus~ 

sex Sandstone Me1111ber of the Steele Shale in the Powder River Basin. Ammonites have not been collected 

from the IIa.tfield Sandstone l\1ember, but they were 

collected from the underlying and overlying shale. ';I'he 

IIatfield apparently was deposited during the time of 

B. a."l]Jerijor1nis or ea.rly during the time of B. per-

]JlermtS. This indicates a late Claggett or early Judith 

River a.ge for these rocks. 

The Hatfield Sa.ndstone Member and the overlying 

rocks of bra.ckish-water origin resulted from a widespread regression of the sea in southern Wyoming, 

northwestern Colorado, and northeastern Utah. This 

regression was followed by an ad vance of the sea represented by the marine rocks of the uppermost part of 

the I-Iaystack Mountains Formation. In the southern 

pa.rt of the vVind River Basin, regressive deposits comparable to the I-Iatfield Sandstone Member are represented by the Fales l\1ember of the l\1esaverde 

Formation, ttnd transgressive deposits equivalent to the 

upperm,ost part of the Haystack Mountains Formation 

are represented by the vVa.llace Creek Tongue of the 

Cody Shale. 

The regression of the sea that resulted in the deposition of the I-Iatfield Sandstone :Member and the overlying brackish-water beds is represented in northwestern Colorado and in the Book Cliffs area of eastern 

Utah ttnd western Colorado by the Castlegate Sandstone. The marine shale overlying the Castlegate Sandstone is called the Buck Tongue of the Mancos Shale 

·and is equivalent to the uppermost part of the Haystack Mountains Forma.tion. The Buck Tongue was 

described by Fisher ( 1936, p. 15) in the Book Cliffs coal 

fi.eld and, more recently, by Cullins (1968) in the 

Rangely ttrea of northwestern Colorado. 

TYPE AND REFERENCE SECTIONS 

The following type and reference sections are descriptions of the lithology and fossil content of the Haystack 

Mountains Formation a.t three. widely separated localities. The I-Iorseshoe Ridge reference section was measured by the late A. D. Zapp, but the section has been 

reexa1nined and additional fossils have been collected 

by us. 

Type section of the Haystack Mountains Fot·mation and its 

O'Bt·icn Spring ancl Ta1wt·s Ran-ch Sandstone Members 

[l\Iensured with plnnetable nnd tape by J. R. Gill and R. L. Fleisher, 

.August 1966. Fossils identified by W. A. Cobban. Measured in the 

NEI,4NEI,4 sec. 22, NEI_4 sec. 2,3, and SEI,4SEI,4 sec. 14, T. 22 N., 

R. 86 W., Carbon C-ounty, Wyo. (S•lnclalr 71JJ-mlnute quadrangle), 

loc. 4, fig. 1.] · 

Allen Ridge Formation: Feet 

36. Sandstone and shale intevbedded ; sandstones 

are lenticular, nonpersistent, and weather 

brown ; shales are gray to brown and 

locally carbonaceous ; ironstone concretions 

common. Unit is dominantly fluviatile in 

origin --------------------------------- 1,475 

35. Shale, 'brown to black, carbonaceous to lignitic ----------------------------------- 50 

Total Allen Ridge Formation _______ 1, 525 

Haystack Mountains Formation: 

Upper unnamed member: 

34. Sandstone, pale-yellowish-gray, fine-grained, 

thin-bedded ; contains clay pebbles and 

Ophiomorpha~· forms ledge_______________ 15 

33. Sandstone ·and shale interbedded, greenishgray to yellowish-gray ; sandstone in beds 

0.1-1 ft thick; forms slope________________ 34 

32. Shale, gray; contains a few thin beds of sand-

·&tone in lower 20 ft_____________________ 85 

USGS D5573, from near base of this unit 

in the SE% sec. 6, T. 23 N., R. 86 W. : 

Lingula subspatulata Halll and Meek 

Pinna sp. 

Inocet·anHts sp. 

Owytoma sp. 

Syncyclonema? sp. 

Modiolus sp. 

Oymella montanensis (Henderson) 

Olisocolus? sp. 

Ethnwcardimn sp. 

Tellina sp. 

Baculites perplemus Cobban 

Hoploscaphites sp. 

Ptace-ntice1·as sp. 

31. Shale, medium-gray_______________________ 15 

30. Sandstone, pale-yellowish-gray, fine-grained, 

medium- to thin-bedded with some flowangle crossbeds ; contains local masses of 

brown-weathering concretionary sandstone 

near top. 01Jhionwrpha abundant________ 65 

29. Sandstone and ·shale interlbedded; san<btone 

is pale yellowish gray and in beds 0.5-2 

ft thick. Unit forms a slope and contains 

a layer of orange-brown-weathering sandstone concretions in middle and locally at 

top ------------------------------------ 65 

USGS D5553, from top of unit in the 

SE%NE%NE% sec. 30, T. 22 N., R. 

85W.: 

N1tcula sp. 

Inoceranws sp. 

Oymbophora sp. 

Baculites sp. 
16 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

Type section of the Haystack Mountains .Formation and its 

O'Brien Spring and Tapers Ranch Sandstone MembersContinued 

Haystack Mountains Formation-Continued 

Upper unnamed member-Continued 

29. Sandstone and shale interbedded-Con. Feet 

USGS D3347, from ·same level as above 

in the NW~NE~NE* ·Sec. 30: 

Inoceramus subcompresiJus Meek and 

Hayden 

Oymbophora sp. 

Baculites cf. B. perpleaJus C'ooban 

28. Shale, medium- to dark-grayish-brown ; contains a few ironstone concretions-------- 25 

USGS D5550: 

Dis'Cinid brachiopod (attached to 

oyster) 

Ostrea sp. 

N1te1tla 1sp. 

27. Sandstone, pale-yellowi,sh-gray, very fine 

grained, thin-bedded; low-angle crossbeds- 5 

USGS D5549: 

Nucula 'sp. 

Ostrea sp. 

26. Shale, medium- to dark-brownish-gray, carbona.ceous in pal'lt ; forms slope. At base n 

1-ft-thick bluish-gray carbonaceous shale 

overlain by a 0.5-ft-thick impure coaJl____ 65 

25. Sandstone, light-gray, very fine grained ; contains a 1-ft-thick 1ignitic shale in middle. 

Pel'lsistent unit but variable in thickness- 4 

24. Shale, dark-grayi,sh-brown to brownish-gray; 

locally carbonaceous at base; jarosiJtic on 

bedding planes__________________________ 50 

Total upper unnamed member________ 428 

Hatfield Sandstone Member: 

23. Sandstone, pale-yeUowish-gray, fine-grained, 

medium- to thick-bedded at base, thinbedded at top with low-angle crossbeds; 

contains abundant Ophiomorpha in mid<lie; 

fornas cliff______________________________ 115 

22. Sandstone and shale interbedded ; sandstone 

i·s pale yeHowish gray, fine grained, and 

in beds 1-2 ft thick; shale is bluish gray 

and sandy. Unit forms slope_____________ 35 

Total Hatfield Sandstone Member____ 150 

Middle unnamed member : 

21. Shale, dark-gray, soft; contains a layer of 

orange-weathering concretions at top____ 160 

USGS D6086, from 40 to 50 ft below top 

in the NE~SE14 ·sec. 30, T. 24 N., R. 

86 W.: 

Calcareous worm tube 

Bryozoan 

Ostrea sp. 

Bamtlites asperlfornvis Meek 

USGS D5564, from 80ft below top in the 

NE1,4NW~ sec. 7, T. 23 N., R. 86 ,V.: 

Bryozoan 

Oymella montanensis (Henderson) 

Bacul~tes mclearni Landes 

Type section of the Haystack Mo1mtains Formation and its 

O'Brien Spring and Ta-pers Ranch Sandstone MembersContinued 

Haystack Mountains Formation-Continued 

Middle unnamed member.....,....Continued Feet 

20. Sandstone, pale-yellowish-gray, fine-grained, 

thin-bedded ; soft at base and harder and 

cliff forming above; contains in middle 

dark-brown-weathering sandstone concretions 1.5 ft thick and 10 ft in diameter ; 

upper few feet contains abundant 

glauconite and a few iron-replaced fossils__ 95 

USGS D6266, from top of unit : 

Baculites mclcarni Landes 

19. Sandstone, like unit 20, sof.t; forms low ridge; 

contains at top dark-brown-weathering 

sandstone concretions 1 ft thick and 6 ft 

in diameter_____________________________ 40 

18. Shale, medium-dark-gray------------------- 40 

17. ·Sandstone, pale-yellowish-gray, fine-grained, 

soft____________________________________ 25 

16. Sandstone, like unit 17, glauconitic; weathers 

in 2 low benches; contains abundant 

Ophiomo·rpha and at top dark-brownweathering sandstone concretions 2 ft thick 

and 8 ft in diameter____________________ 65 

15. Shale, gray, sandy ; weathers yellowish gray ; 

contains 'spa;rse rusty-brown-weathering 

limestone concretions; forms valley------ 85 

14. Sandstone, pale-yellowish-gray, fine-grained, 

cliff former; contains a few Ophionwrpha,_ SO 

13. Shale, medium-dark-gray; poorly exposed but 

contains a 1-ft-thick bentonite at base____ 170 

Total Middle unnamed member________ ·760 

O'Brien Spring Sandstone Member : 

12 . .Sandstone, light-gray, very fine grained, clayey, soft ____________________________ _ 

USGS D5571, from 20 ft below top in 

the S~1,4NE~ sec. 7, T. 23 N., R. 

86W.: 

BacuUtcs obtu.stts Meek 

11. Sandstone, pale-yellowish-gray, fine gra'ined; 

,in beds 0.1-1 ft thick; weathers light 

brown in lower part and light gray at top; 

contains dark-brown sandstone concretions 

and abundant Ophiomorpha. Base poorly 

exposed here, but in other areas it is 

45 

gradational with underlying shale________ 175 

Total O'Brien Spring Sandstone 

Member -------------------------- 220 

Lower unnamed member : 

10. Shale, medium-gray, soft; forms broad 

valley; contains orange-brown-weathering 

gray limestone concretions in the upper part 

and red-weathering ironstone concretions 

in lower part____________________________ 675 

USGS D6100, from 50ft below top in the 

NW*NW% sec. 31, T. 24 N., R. 86 W. : 

Inoceramus sp. 

Baoulites obtusus Meek 

.4. 

..,· 
.,.. 

HAYSTACK MOUNT.A.INS FORMATION 17 

'l'ypo section ot the H aystaok Mountains Formation wnd its 

O'Brien Spring and 'Ta1)01·s Ranch Sandsto'no MembersContinued 

Haystack Mountains Formation-Continued 

Lower unnamed memlJer-Continued 

10. Shale, medium-gray, soft-Continued Feet 

USGS D5548, from 80ft below top on line 

of section: 

Baoulites sp. (weak flank ribs) 

USGS D363, from 2'70 ft below top: 

BQicztUtes sp. (weak flank ribs) 

USGS D2994, from 600 ft below top : 

BQicztZites sp. (w1~ak flank ribs) 

USG.S D364, from 655 f.t below top : 

Bacttlites sp. (weak flank ribs) 

9. Sandstone and shale interbedded; weathers 

yellowish gray and forms slope___________ 40 

USGS D2993, 20 ft below top : 

Bacztlites sp. 

Total lower unnamed member____ 715 

Tapers Ranch Sandstone Member : 

8. Sandstone, pale-greenish-gray, medium- to 

coarse-grained, thin-bedded with low-angle 

cross·beds, calcn.reous, glauconitic, ridge 

forming; contains some reddish-brown iron 

cement--------------------------------- 8 

7. Sandstone, grayish-green to light-yellowishg.ray, fine-grained; contains thin laminae 

and beds of gray shale with the .thicker 

beds of shale forming slopes covered with 

th,in plates of sandstone_________________ 60 

6. Sandstone, gray, fine-grained to very fine 

grained, clayey, thin-bedded with shale 

laminae; cleaner and glauconitic in upper 

part; contains some iron cement ; upper 

part forms a ridge and basal part forms a 

slope --------------..:.-------------------- 78 

5. Shale, medium-dark-gray, sandy; contains 

some sandstone laminae ; poorly exposed__ 50 

4. Sandstone, pale-yellowish-gray to dark-gray, 

glauconitic; contains small dark chert 

granules and limonite-.cemented shale 

pebbles. Upper part medium to coarse 

grained and very glauconitic, weathering to 

a brown cliff ; lower part clayey and slope 

forming -------------------------------- 75 

Total Tapers Ranch Sandstone Member ------------------------------ 271 

Total Haystack Mountains Formation_ 2, 544 

Steele Shale (part) : 

3. Shale, medium- to dark-gray, sandy; contains a few layers of gray sandy limestone 

concretions in upper part and red-weathering ironstone concretions in lower part____ 180 

· 2. Sandstone and shale interbedded ; weathers 

pale yellowish gray ; sandstone in beds 

nbout 0.1 ft thick or less ; forms low ridge_ 8 

Typo section ot the Haystack .Motmtains Formation and its 

O'Bt·ien Spring and Tapet·s Ranch Sandstone .MembersContinued 

Steele Shale (part)-Continued Feet 

1. Shale, medium-dark-gray, soft; contains 

limestone concretion layers 600 ft and 20 ft 

below tOP------------------------------ 600 

USGS D5547, from 20ft ·below top: 

Baoulites sp. (smooth) 

USGS D5554, from 600ft below top: 

Anisomyon sp. 

BacttZites sp. 

Scaphites hippocrcpis (DeKay) III 

H aresiceras natronense Reeside 

Total Steele Shale measured____ 788 

Rete1·encc sect·ion of the Haystack .M01mtains Formation 

[Measured by A. D. Zapp, September 1961. Fossils identified by W . .A. 

Cobban. Measured on the north side of Horsehoe Ridge in the SEIA, 

sec. 36, T. 25 N., R. 84 W., Carbon County, Wyo. (Seminoe Dam 

Southeast 7 %-minute quadrangle), loc. 6, fig. 1.] 

Allen Ridge Formation: 

34. Sandstone and shale interbedded ; lenticular 

ridge-forming units deposited in a fluviatile environment. Thickness estimated 

Feet 

from the topographic map _______________ 1, 120 

Total Allen Ridge Formation (approximate) -------------------- 1, 120 

Haystack Mountains Formation : 

Upper unnamed member: 

33. Sandstone, pale-yellowish-gray, fine-grained, 

massive, soft; weathers light gray to white_ 40 

32. Shale, dark-gray ; contains f?everal 0.2- to 

0.5-ft-thick ledges of hard calcareous siltstone 40-45 ft above base_______________ 200 

USGS D3323, from shale: 

Inoceramus subcornpressus Meek 

and Hayden 

Ethmocardium sp. 

Bacttlites perplemus Cobban 

Placenticeras cf. P. intercalare Meek 

31. Shale, dark-gray, somewhat carbonaceous; 

may be nonmarine----------------------- 3 

30. Sandstone, pale-yellowish-gray, very fine 

grained, hard; cliff former; in beds about 

0.5 ft thick; contains abundant oysters____ 20 

29. Shale, brownish-gray; appears nonmarine__ 13 

28. Sandstone, pale-yellowish-gray, very fine 

grained ro fine-grained, upper surface a 

coquina of clams________________________ 5 

27. Shale, dark-brownish-graY----------------- 22 

26. Sandstone, yellowish-gray, very fine grained, 

thin-bedded, very hard; contains abundant 

burrows, trails, and oysters______________ 2 

25. Shale, dark; appears nonmarine___________ 28 

24. Sandstone, pale-yellowish-gray, fine-grained, 

massive; contains abundant Ophiomorpha 

at tOP---------------------------------- 8 
18 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

Jleference scet·ion of the Haystack 1li ountains Ji'o~nnaHon-Con. 

Haystack Mountains Formation-Continued 

Upper unnamed member-Continued Feet 

23. Shale, purplish-brown, silty; appears nonmarine -------------------------------- 7 

Total upper unnamed member-------- 348 

Hatfield Sandstone Member: 

22. Sandstone, light-gray, fine-g:Pained, ironstained 110-140 ft above base; forms mas- sive ledge______________________________ 140 

21. Shale and siltstone interbedded, dark-gray; 

increasing amounts of thin beds of sandstone in upper part_ ____________________ _ 

20. Sandstone, dull-gray, massive, very resistant; 

contains abundant scattered round phosphate nodules and baculites at top _______ _ 

USGS D3322: 

Inoceramus .sp. 

Ostrea sp. 

Baculites asperiformis Meek 

Total Hatfield Sandstone Member ___ _ 

Middle unnamed member : 

19. Shale, dark-gray; contains large orangeweathering limestone concretions in mid18 

30 

188 

dle; some thin sandstones in lower 5 ft____ 152 

USGS D4770, from concretions: 

Oxytoma nebraseana (Evans and 

Shumard) 

Ostrea sp. 

Modiolus sp. 

Baettlites asperijo1·mis Meek 

Hoploseaphites n. sp. 

18. Sandstone,_ gra:y, fine-grained to very fine 

grained ; clayey and soft in lower ·part, 

cleaner and harder in upper 6 ft; contains 

Ophiomorpha --------------------------- 30 

17. Siltstone and shale, gray; weathers yellowish gray ------------------------------- 80 

16. Sandstone, pale-yellowish-gray, fine-grained; 

.ridge forming for the most part ; lower 80 

ft ·and intervals 80--95 -and 105-120 ft above 

base are soft and may contain some .shale. 

~s.andstone in the interval 35-55 ft ~bove 

the base is clayey .and forms a topographic 

depresSion ----------------------------- 132 

15. Shale, dark-gray ------------------------- 235 

Total middle unnamed member------

O'Brien Spring Sandstone Member : 

14. Sandstone, gray, very fine grained, clayey; 

upper half massive and very concreti-onary, 

629 

top iron cemented and rarely exposed ____ 145 

USGS D3321, from 75 ft a.bove lYase: 

Baculites obt1tSWJ Meek 

USGS D3320, from 5 ft above base : 

Inoceramw~-sp. 

Bacttlites aff. B. obtusus Meek 

Total O'Brien Spring S.andstone 

Member ---------------------- 145 

Reference sect·ion of the Haystack Mountains Formation-Con. 

Haystack Mountains Formation-Continued Feet 

Lower unnamed member: 

13. Shale, brownish-gray, silty to sandy; transitional with overlying sandstone; contains 

brown-weathering gray limestone concretions ---------------------------------- 170 

12. Shale, bl·ack, dayey; contains abundant layers of :ferruginous limestone or ironstone 

-concretions ----------------------------- 320 

USGS D3319, from 15 ft below top: 

Inoceram1ts sp. 

Bamtlites sp. (weak flank ribs) 

USGS D3318, from 150 to 170 ft above 

base: 

Inoceram'lts cf. I. balticzts Boehm 

Baculites sp. (weak flank ribs) 

Placenticet·as sp. 

USGS D3317, near base: 

Inoceranws cf. I. balticus Boehm 

Baculites sp. (weak flank ribs) 

Pla cent-iceras sp. 

11. Shale, gray, sandy and silty, poorly ex-posed._ 165 

Total lower unnamed member ------- 655 

Tapers Ranch Sanclstone Member: 

10. Sandstone, pale-yellow,ish-gray, very fine 

grained to fine-graincil, clayey, soft; a few 

thin ledge formers. Some beds are. glauconitic -------------------------------- 240 

9. San-dstone, brownish-gray, very fine grained 

:to fine-grained, thin-bedded ; clayey and 

.soft in middle; ·contains ·a scattering of 

dark chert granules and pebbles to 0.1 ft in 

diameter. Some beds are very glauconitic__ 60 

Steele Shale (part) : 

Total Tapers Ranch Sandstone 

Member --------------------- 300 

Total Haysback Mountains Formation ------------------------ 2,265 

8. Shale, dark-gray; conta.ins a few very fine 

grained thin sandstone beds; unit is transitional into •the overlying sandstone. Lower 

45 ft contains several discontinuous ledges 

of tan-weathering silty limestone with 

many crushed baculites__________________ 328 

USGS D3316, from limestone concretions 60 ft above base: 

Bac1tlites sp. (·smooth) 

7. Shale and siltstone interbedded, very da1rk 

gray; contains large septa·rioan concretions_ 95 

6. Sand:stone, grayish-green, very glauconitic, 

hard; contains a scattering of dark chert 

granules ------------------------------- 2 

5. Sandstone, greenish-gray, very fine grained., 

glauconitic, clayey----------------------- 105 

... , 
~·· 

~ 

:.l. 

!~ • 

..... 

... 

~· 

~· 

·-

HAYSTACK MOUNTAINS FORMATION 19 

Jlcfc1·enec sect'i,on of the Ilaystack, Mountains li'o1'1nat-ion-Con. 

Steele Shale (part)-Continued Feet 

4. Shnle, mostly coYered; contains some massive 

~iltstone nenr nnd nt the top_____________ 870 

3. 

USGS D3315, from shale 330 ft above 

base: 

bwce1·am.'ns cf I. 1n'OX'lnws 'luomey 

Bac1tlitcs aqud,lacns·is Reeside 

Snncl,stone, gt-eenish-gray, fine-grained with 

some Yery 1ine grained beds ; thin-bedded 

becoming massive in upper part; contains 

nbnnd'ant trails nnd ripple murl\:S on bedcling planes. Capped by a 5-ft-thick bed of 

bnnded silty limestone__________________ 80 

2. 

l. 

Covered; nppears to be shale______________ 125 

Sn ndstoue, pnle-yellowish-g·ray, very fine 

grained, thin-bedded; capped by a 5-ftthick bed of banded silty limestone_______ 55 

Total Steele Shnle measured _________ 1, 660 

Prinoipal 1'Cference scct,ion of the Ilettficl(l San(lstonc Membc1· 

of the Haystack Mounta-ins Ji'onnat'ion 

[Mcnsurcd by .T. H. Gtll nnd G. A. Bergmnn, August 1967, with plnnetnblc null J"ncob's stnlf. :n•osslls identified by W. A. Cobbnn. Measured 

011 the west side or Hn,tfleld dome in the NE~~NEY.t sec. 18 nnd in the 

center nnd N\Vl/.tNW.I/.~ sec. 17, 1'. 1!l N., R. 88 W., Cnrbon County, 

Wy,o. (Brltlgcr Pnss :1'5-mlnute qundrnnglc), Ioc. 2, fig. 1.] 

Allen Ridge l!"'ormation: 

64. Sandstone and shale interbedded; lenticular 

ridge-forming units deposited in a fluviatile 

environment; thiclmess not measured. 

Hnystnck Mountains ll'o.rmation: 

Upper unnamed member: 

03. Snnclstone, pale-yellowish-gray, fine-grained, 

thin-bedded; upper part weathers light 

gray; contains large orange-weathering 

snnclstone concretions in lowe.r part_ ___ _ 

02. Shale, gray, sandy------------------------

61. Sandstone, pale-yellowish-gray, fine-grained, 

thin-bedded; contains 01Jhiomorpha ______ _ 

60. Shale, gray; contains sandstone laminae ___ _ 59. Snndstone, like unit 6L __________________ _ 

58. Shal~ graY------------------------------- 57, Sandstone, like unit 6L _________________ _ 

56. Shale, gray; contains some thin beds of sandstone; poorly exposed __________________ _ 

55. Snndstone, pale-yellowish-gra;\T, very fine 

grained to fine-grained; in beds 0.2-2 ft 

thick in lower part becoming massive in 

upper part; contains a lnyer of pale-oxange 

snndstone. concretions in lower part_ ____ _ 

54. Shale, olive-gray, poorly exposed _________ _ 

G3. Sandstone, pale-yellowish-gray, fine-grained; 

contains 01Jhiomo1'1Jha __________________ _ 

52. Shale, olive-gray--------------------------

51, Sandstone, like unit 53; contains abundant 

01Jhiomorpha and iron-cemented shale 

pebbles -------------------------------- 60. Shale, olive-gray; contains thin-shelled 

oysters -------------------------------- 49. Sandstone, like unit 53 __________________ _ 

48. Shale, olive-gray to brownish-gray; contains 

ironstone concretions ___________________ _ 

17 

15 

2 

8 

2 

14 

2 

22 

75 

40 

1 

1 

34 

23 

5 

8 

Princi.pa.l 1'Cferencc section of the llatficl(l Smulstonc Mcntbe1· 

of tho II etystetclv M omttains F01'1nat-ion-Continued 

Haystack Mountains Formation-Continued 

Upper unnamed member-Continued Feet 

47. Siltstone, pale-yellowish-gray, laminated, carbonaceous; contains many burrows_______ 4 

46. Shale, brownish-gray, flaky ; contains ironstone concretions------------------------ 5 

45. Sandstone, pale-yellowish-gray, fine-grained; 

weathers light gray; contains large Ophio1no1·pha -------------------------------- 2 

44. Shale, like unit 46------------------------- 4 

43. Siltstone, like unit 47---------------------- 5 

42. Shale, lil\:e unit 46------------------------- 10 

41. Siltstone, like unit 47---------------------- 2 

40. Shale, brown, carbonaceous________________ 1 

39. Siltstone, light-brown, carbonaceous, laminated; contains burrows in upper part____ 9 

38. Shale, reddish-brown to black, carbonaceous ------------------------------------ 4 

37. Sandstone and siltstone, interbedded, lightyellowish-gray, very fine grained, ripplelaminated ------------------------------ 5 

86. Shale, olive-gray, poorly exposed; contains 

ironstone concretions____________________ 15 

35. Shale, blacl\:, lignitic_______________________ 1 

34. Sandstone, light-gray to brownish-gray, medium-grained, slightly carbonaceous________ 5 

33. Sandstone, pale-yellowish-gray, fine-grained; 

contains Ophiomorpha___________________ 8 

32. Shale, reddish-brown, carbonaceous, poorly 

exposed -------------------------------- 11 

31. Sandstone, like unit 33-------------------- 6 

30. Sandstone, light-gray, medium-grained; contains abundant oysters__________________ 2 

29. Shale, olive-gray__________________________ 3 

28. Shale, dark-brown, carbonaceous___________ 2 

27. Siltstone, black, coalY---------------------- 1 

Total upper unnamed member________ 374 

Hatfield Sandstone Member: 

26. Sandstone, pale-yellowish-gray, fine-grained; 

weathers yellowish gray to light gray; 

lower 20 ft in . beds 0.5-2 ft thick ; upper 

part forms massive cliff with a slight reentrant 45 ft from top. Contains shale 

pebbles and Ophiom01'1Jha________________ 97 

25. Shale, gray, sanely, poorly exposed________ 30 

24. Sandstone, like unit 26, thin-bedded______ 30 

23. Sandstone and shale ; weathers yellowish 

gray ----------------------------------- 10 

Total Hatfield Sandstone Member___ 167 

Espy Tongue of Hale ( 1961) : 

22. Shale, gray, sandy------------------------ 65 

21. Limestone concretion; weathers orange_____ 1. 5 

USGS D6363: 

B acuUtes sp. 

20. Shale, grayish-brown, flaky________________ 20 
20 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

Principal refet·ence section of the Hatjielcl Sandstone Member 

of the Haystack Mountains Formation-Continued 

Haystack Mountains Formation-Continued 

Espy Tongue of Hale (1961)-Continued Feet 

19. Shale, grayish-brown, flaky; contains sandstone laminae in upper 2 ft_____________ 15 

USGS D6362: 

Ostrea albertensis Landes 

18. Sandstone, yellowish-gray, very fine grained, 

lower 25 ft clayey and friable; contains 6 

layers of orange-weathering sandstone concretions 2 ft thick and 6 ft in diameter. 

Upper 30 ft is glauconitic and contains 

iron-cemented nodules with fossils______ 55 

USGS D6361, from top of unit: 

Calcareous worm tube 

Inocerwrntts sp. 

Ostrea t·usselli Landes 

JJJthmocardi1tm u.rswniense Landes 

Oymbophora sp. 

Baculites cf. B. asperiformis Meek 

17. Shale, gray, sandy; weathers light gray ___ _ 

16. ·Sandstone, pale-yellowish-gray, fine-grained ; 

weathers light brown ___________________ _ 

USGS D6360, from base of sandstone : 

N ucttla? sp. 

Modiolus sp. 

Orenella n. sp. 

Ethmocardium ursaniense Landes 

Oymbophora sp. 

15. Shale, gray, sandY------------------------

14. Sandstone, pale-yellowish-gray, very fine 

grained; capped by a 3-ft-thick bed of 

medium-grained crossbedded sandstone 

containing abundant Ophiomorpha _______ _ 

13. Shale, dark-gray, flaky ___________________ _ 

12. Sandstone, pale-yellowish-gray, very fine 

grained, ripple-laminated; contains at base 

siltstone concretions 1.5 ft thick and 1.5 ft 

25 

6 

19 

12 

17 

in diameter----------------------------- 21 

11. Shale, gray, fl'aky; weathers light gray to 

pale yellowish gray--------------------- 35 

Total Espy Tongue of Hale ( 1961) _- 291. 5 

Deep Creek Sandstone of Hale ( 1961) : 

10. Sandstone, pale-yellowish-gray, fine-grained, 

thin-bedded; weathers yellowish gray to 

dusky yellow in lower part and light gray 

to light brown in upper part; contains a 

few burrows---------------------------- 40 

Total Deep Creek Sandstone of Hale 

(1961) --------------------------- 40 

Total Haystack Mountains Formation (rounded)----------------- 870 

Steele Shale (part) : 

9. Shale, gray, upper part sandy------------- 100 

8. Bentonite, light-greenish-gray, nonswelling__ 1 

7. Shale, gray, poorly expos.ed________________ 75 

Principal reference section of the Hatfield Sandstone Member of 

the Haystack Mountains Formation--Continued 

Steele Shale (part)-Continued 

6. Shale, gray, poorly exposed; contains at top 

tan-weathering silty limestone concretion 

0.5 ft thick and 1.5 ft in diameter________ 150 

5. Shale, gray, with thin laminae of very fine 

grained sandstone; contains at top a 

layer of calcareous sandstone concretions 

0.5 ft thick and 1.5 ft. in diameter. Unit is 

equivalent to the top of the O'Brien Spring 

Sandstone Member of the type Haystack 

Mountains Formation and to Cow Creek 

Member of the Steele Shale of Hale 

(1961) --------------------------------- 35 

USGS D6359, from sandstone concretions: 

Calcareous worm tube 

Inoceramus sp. 

Oymbophora cf. 0. holmesi (Meek) 

Baculites obtusus Meek 

4. Shale, gray, sandy; contains thin sandstone 

laminae, a few gray limestone concretions, 

and at top a 0.2-ft-thick bentonite bed __ _ 

3. Bentonite and yellow fibrous calcite _______ _ 

2. Shale, gray, slightly sandy, poorly exposed __ 

1. Sandstone and shale interlaminated ; forms 

siDall ridge-----------------------------

Total Steele Shale measured 

(.rounded) ---------------------

ROCK RIVER FORMATION 

TYPE SE'CTION AND DISTRIBUTION 

20 

1 

100 

30 

510 

The Rock River Formation of the Mesaverde Group 

is named herein for exposures in the SE% sec. 8, SW14 

sec. 9, and NW14 sec. 16, T. 20 N., R. 76 W., about 2 

miles southeast of the town of Rock River, Albany 

County, Wyo. The Rock River Formation is mainly 

confined to the Laramie Basin and consists of alternating beds of hard and soft fossiliferous sandstone of 

marine origin~ The formation is generally poorly 

exposed and about one-third of the formation is con-

·cealed at the type section. The covered intervals probably contain nonresistant sandstone, but they might 

consist of soft sandy shale. 

Darton and Siebenthal (1909, p. 36-37) first described 

these beds in the Rock River area and related them to 

the lower part of the Montana Formation. Equivalent 

rocks in the southern part of the Laramie Basin were 

called the Mesaverde Formation (Darton and others, 

1910, p. 10). 

The Rock River Formation crops out beneath the 

Pine Ridge Sandstone and overlies the Steele Shale 

along the west margin of the Laramie Basin. The formation grades eastward into the marine Pierre Shale 

........ 

4· 

~ 
·-

··)--

t· 

~· 

,' 

ROCK RIVER FORMATION 21 

nnd does not occur east of the Laramie Range. Westward, the Rock River Formation grades into the dominantly nonmarine rocks of the Allen Ridge Formation. 

One or more thin tongues of the Rock River Formation 

can be identified in the upper part of the Allen Ridge 

in the southeastern part of the Carbon Basin. 

LITHOLOGIC CHARACTER 

The Rock River Formation consists of soft sandstone 

n.nd a few beds of soft sandy shale deposited in a marine 

environment. The sandstone weathers light gray to 

light brown and is generally very fine to fine grained 

and thin bedded to massive. Locally, the sandstone is 

sha.Iy and crossbedded. Large brown-weathering fossiliferous sandstone concretions are abundant in some beds. 

These concretions are harder than the enclosing rocks 

n.nd forn1low ridges where they are numerous. The formation is generally poorly exposed, except for the 

harder concretionary layers. 

THICKNESS 

The maximmn known thiclrness of the Rock River 

Formation, 1,565 feet, is at the type section. The formation has not been measured at other localities, but it 

apparently thins to the east and south. This thinning 

accompanies a facies change from shallow-water marine 

sandstone to deeper water marine shale. 

RELATION TO ADJACENT FORMATIONS 

The basal sandstone of the Rock River Formation 

grades into the sandy shale of the underlying Steele 

Shale. The contact between the two formations is selected where the rocks are dominantly sandstone above and 

dominantly shale below. The Rock River Formation 

grades laterally eastward into marine shale of the Pierre 

and westward into mainly nonmarine rocks of the Allen 

Ridge. 

The Rock River Formation -appears to be overlain unconforinably by nonmarine rocks of the Pine Rirlge 

Sandstone. In the Rock River area, we have little evidence to indicate an angular unconformity at the base 

of the Pine Ridge, but Davis (1966) had sufficient da.ta 

from this area to propose a disconformity. Gill and Cobban ( 1966b) described a widespread unconformity at 

the base of the equivalent Teapot Sandstone Member of 

the Mesaverde Form·ation in northern 'Vyoming, and 

Reynolds (1966, 1967) has reported an unconformity at 

the base of the Pine Ridge Sandstone nlong the east 

margin of the Great Divide Basin. 

FOSSILS 

Marine invertebrate megafossils are abundant at 

several levels in the Rock River Formation. Stanton 

367-863 0-70--4 

(Stanton and J(nowlton, 1897, p. 138-141) identified 

many mollusks from rocks now included in the Rock 

River· Formation. l\1ost of these (with their names updated) and many others are listed in the type section. 

The fossils reveal that the lowest part of the Rock Rive:r 

lies in the :uppermost part of the zone of Baculites per·· 

plexus, and that the formation extends up through the 

zone of Didynwceras stevensoni and probably a little 

higher. One very fossiliferous sandstone (unit 22 of type 

section) contains Trigonia and other fossils characteristic of the Gulf Coast Cretaceous. 

AGE AND CORRELATION 

The Rock River Formation is of Judith River and 

early Bearpaw age. It correlates with about the middle 

part of the Pierre Shale to the east and with the upper 

part of the l\1itten Black Shale l\1ember, the Red Bird 

Silty l\1ember, and the lower part of the lower unnamed 

member of the Pierre Shale in the southern Black I-Iills 

(Gill and Cobban, 1966a, pl. 4). The Rock River is 

equivalent to the Parkman Sandstone Member and overlying unnamed marine member of the Mesaverde ForInation in the western Powder River Basin (table 1). It 

correlates and intertongues with the Allen Ridge Formation in t)le Hanna and Carbon i Basins and is 

equivalent to the lies Formation of northwestern 

Colorado. 

TYPE SECTION 

The type section of the Rock River Formation was 

measured by G. R. Scott and W. A. Cobban, and fossils 

collected from the formation were identified by Cobban 

and N. F. Sohl. A description of the type section follows. 

Type section ot the Rock Rive1· Formation 

[l\Ieasured with a Jacob's staff by G. R. Scott and W. A. Cobban, May 

1957. l\:leasured about 2.5 miles southeast of Rock River tn the S% 

N% and NE:JA,SElJI, sec. 8, NW:JA,NW:!4SW1JI, sec. 9, and NW:I4 

NWlJI, sec. 16, T. 20 N., R. 76 W., Albany County, Wyo. (Rock River 

7%-miruute quadrangle), loc. 8, fig. 1.] 

Pine Ridge Sandstone : 

41. Sandstone, whitish-gray, fine-grained, massive; 

forms conspicuous tree-covered bluff. Not 

measured. 

Rock River Formation : Feet 

40. Concealed ---------------------------------- 3~ 39. Sandstone, light-gray, soft; in massive beds 

separated by darker shale partings_________ 140 

USGS D1390, from 60-90 ft above base: 

Inoceramus sp. 

Ostrea russeZli Landes (bored) 

38. Sandstone, light-brown, soft, massive; contains 

some harder concretionary shaly sandstone 

that weathers darker brown. A few 

Ophiomorpha ----------------------------- 30 

37. Sandstone, gray, soft, shaly; uppermost few 

feet harder and somewhat carbonaceous; 

some parts of unit concretionary___________ 103 
22 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

1'11PC section of the Rock River Formation-Continued 

Rock River Formation-Oontinued 

36. Sandstone, light-brown, soft; contains darker 

brown-weathering concretionary s·a.ndstone 

and, at top, a ridge-forming bed of closely 

spaced sandstone concretions 1-2 ft thick and 

as much as 8 ft in diameter, commonly 

crowded with large Inoce1·am.us ___________ _ 

USGS D1391, from top of unit: 

Membraniporoid bryozoan (attached 

to Inoceramus) 

Inocerwnws cf. I. shikotanensis Nagao 

and Matsumoto 

BacuUtes sp. 

USGS D1389, from rest of unit: 

Inoceramus oonvea:us Hall and Meek 

Ostrea sp. 

TeZlina sp. 

Ba.cuUtes sp. 

Placenticeras sp. 

Eutrephoceras sp. 

Opkiomorpha sp. 

ReptiUan hones 

35. Sandstone, light-gray and light-brown, very fine 

grained, soft; contains closely spaced large 

dark-brown-weathering fossiliferous sandstone concretions that are commonly 3-4 ft 

thick and 8-10 ft in diameter. Unit forms a conspicuous ridge ________________________ _ 

USGS D1388, from concretions : 

Membraniporoid bryozoans 

(on inocerams) 

Inoceram~ts convea:us Hall and Meek 

Pteria linuuaetormis (Evans and 

Shumard) 

Ostrea cf. 0. russelli Landes 

Ostrea cf. 0. plumosa Morton 

Oymella montanensis (Henderson) 

Luoina sp. 

Tellina sp. 

Oymbophora sp. 

Gonioohasma sp. 

Drepanochilus nebrascensis (Evans 

and Shumard) ? 

Euspitra? sp. 

Serritusus n. sp. 

A.nisomyon borealis (Morton) 

Baculites criolcmayi Williams 

Didymooeras stevensoni (Whitfield) 

Solenooeras n. sp. 

Hoploscaphites sp. 

Placentioeras intercalare M~ek 

Crustacean 

Fish scales and teeth 

Carnivorous dinosaur tooth 

Feet 

61 

10 

34. Sandstone, light-brown, soft, very fine grained__ 20 

33. Sandstone, gray, very fine grained, soft, shaly; 

uppermost 1-2ft is harder and forms a low 

ridge -------------------------------------- 24 

Type section of the Rock River Formation-Continued 

Rock River Formation-Continued 

32. Sandstone, like unit 33 ; contains gray- and 

brown-weathering sandy fossiliferous limeFeet 

stone concretions. Thickness estimated________ 30 

USGS D1387: 

M icrabaoia americana Meek and 

Hayden 

Calcareous worm tubes 

Echinoid fragment 

Dysnoetopora demissa (White) 

Websteria-like bryozoan 

Pyriporoid bryozoan (on inocerams 

and ammonite living chambers) 

Solemya n. sp. 

Perrisonota sp. 

Nucula cf. N. pla'fltimarginata Meek 

and Hayden 

Ntteula (Pectinucttla) sp. 

Yoldia? cf. Y.? evansi (Meek and 

Hayden) 

Nemodon sulcatinus (Evans and 

Shumard) 

Limopsis sp. 

Gervillia aff. G. recta Meek and 

Hayden 

Inoceramus convea:ttS Hall and Meek 

Pteria linuuaetormis (Evans and 

Shumard) 

Oa:ytoma aff. 0. nebrascana (Evans 

and Shumard) 

Ostrea cf. 0. plu-nwsa Morton 

Syncyclonema kallii Gabb 

Oklamys nebrascensis Meek and 

Hayden 

A.na.timya n. sp. 

V etericardia? sp. 

Tenea circularis (Meek and Hayden) 

Ottspidaria cf. 0. moreauensis (Meel{ 

and Hayden) 

Ouspidaria cf. 0. variabilis Warren 

Oymbopkora sp. 

Dentalium cf. D. pauperculttm Meek 

and Hayden 

Dentalittm? sp. 

A.cmaea occidentalis (Hall and Meek) 

A.tira? nebrascensis (:1\feek and 

Hayden) 

Drepanochiltts nebrascensis (Evans 

and Shumard) 

Euspira obUquata (Hall and Meek) 

Serritusus aff. S. dako·ten~is (Meek 

and Hayden) 

Oryptorhytis cheyennen~is (Meek and 

Hayden) 

N onactaeonina attenttata (Meek and 

Hayden) 

Oligoptycha sp. 

A.cteon sp. 

A.nisomyon borealis (Morton) 

Baculites criclcntayi Williams 

Didymoceras stevensoni (Whitfield) 

~-· 

_.., 
I 

i' 

.~ 

,\.. 

•· 

ROCK RIVER FORMATION 23 

'l'·mw scct·ion ot the Jl,ock River Formation-Continued 

noel' Ri,·er ]!"'ormation-Continued 

32. Sandstone, like unite 33-Continued 

USGS D1387-Continued 

SoZenoceras n. sp. 

Hoploscaphites n. sp. 

Placenticeras intercalare Meek 

Crustacean 

31. Concealed. Thiclmess estimated--------------

30. Shale, gray, •silty; contains hard gray limestone 

concretions at .tOP-------------------------

29. Sandstone, dark-olive-brown, fine-grained; contains tan-weathering clay pebbles and forms n lo\v ridge _____________________________ _ 

28. Sandstone, soft, massive; weathers tan ___ ., ___ _ 

27. Bentonite, light-gray; contains tan fibrou~ 

calcite ------------------------------~----

26. Sandstone, soft, massi\'e; weathers tan _______ _ 

25. Snndstone, dark-olive-brown, •fine-grained, more 

or less thick bedded and firm ; forms a ridge __ 

24. Sandstone, soft, massive; weathers tan _____ _ 

23. Sandstone, brownish, soft, massive; contains 

large darker brown weathering fossiliferous 

snndstone concretions commonly 2 ft thick 

and G ft in diameter. Uppermost 1ft, which is 

hnrd and ledge forming, locally contains clay 

pellets ----------------------------------- USGS Dl401, from throughout unit: 

Calcareous worm tube (attached to 

haculite) 

Dysnoet01JOra clem.issa (White) 

Pte1·ict Unguaet01·nllis (Evans and 

Shumard) 

Oa:ytoma sp. 

Ost?·ea 1·1tsselli Landes (common in 

upper few feet of unit) 

Syncycloncma? s·im·1Jlicius Conrad? 

Molliolus sp. 

Cymella montanensis (Henderson) 

Ethmocm·clhtm Sl>. 

Lcgumen elH1Jt-icmn Conrad 

Cymbophom sp. 

Dt·c]JanochUus sp. (immature) 

A1Thoges (Lat-ietla) aff. A. (L.) lobatct-

'Vade 

E1tspi1·a sp. 

Gra]Jldclnla cf. G. allenri (White) 

Son·if·ltS1tS '? sp. 

ElU]JSosca]Jha sp. 

0 UgOlJ tycha sp. 

BacuZites n. sp. 

Diclymoceras sp. 

Oa:ybelocc1·as sp. 

Pla.ccnt-icc?·a.s sp. 

22. Sandstone, gray, soft, massive; locally contains 

large brown-weathering sandstone concretions usually 2 ft thicl' and 4 ft in diameter 

and smaller brownish--gray very fossiliferous 

sanely concretions. 'rop is locally baculite-

·bearing brown-weathering concretions containing comminuted pelecypods ____________ _ 

Feet 

280 

8.5 

3 

5 

.5 

80 

4 

57 

28 

27 

Type section ot the Rock Rive1· Formation-Continued 

Rock River Formation-Continued 

22. Sandstone, gray, soft, massive-Continued 

USGS D1400, from throughout unit: 

Calcareous worm tubes (attached to 

baculites) 

Dysnoetopo1·a demissa (White) 

N cnwdon n. sp. 

Pinna lakcs·i White 

Inoceramus cf. I. convca:us Hall and 

Meek 

Ptcria linguactormis (Evans and 

Shumard) 

Oa:ytoma cf. 0. neb1·ascana (Evans and 

Shumard) 

Ost1·ea russelli Landes 

Pycnodonte cf. P. nwtabilis (·Morton) 

T1·igonia cf. '1'. eufaulensis gabbi 

Stephenson 

Syncyclonema? sin"pUciu.s Conrad? 

Lin'!Jatula sp. 

1lnatimya dodclsi, Henderson 

Cymella montanensis (Henderson) 

Astarte sp. 

Protodonaa: n. sp. 

Ethm.ocardi1tm n. sp. 

Legmnen ellipt-icu.m Conrad 

Tenea parilis Conrad? 

Tellina cf. T. munda Stephenson 

Lc.ptosolen sp. 

Scnis sp. 

"Oorbula" n. sp. 

DentaZium sp. 

Baculites n. sp. 

Didymoceras sp. 

AnapachycliscttS n. sp . 

.M enuites n. sp. 

PZacenticeras n. sp. 

Ophiomorpha 

Fish bones, scales, and teeth 

Reptilian bones 

21. Sandstone, light-gray; forms series of small 

ledges of crossbedded sandstone separated by 

shaly sandstone. Top 2 in. is a conglomerate 

of phosphatic pebbles and oyster fragments in 

tan concretionary siltstone ________________ _ 

20. Sandstone, gray and tan, soft_ ______________ _ 

19. Sandstone, gray, soft; at top are brownish-gray 

bard silty concretions about 1 ft ·thick _____ _ 

18. Sandstone, gray and tan, fine-grained, soft ; contains harder limonitic layers---------------

17. Sandstone, light-gray, fine-grained, soft; lower 

part thin bedded and upper part more massive; contains harder masses of tan-weathering concretionary sandstone and some brown 

Feet 

14.2 

16 

74 

32 

carbonaceous partings_____________________ 162 

USGS D1399, from 95-110 ft above base: 

Inoceramus suboom.m·cssus Meek and 

Hayden 

Ostrea cf. 0. subtrigonalis Meek and 

Hayden 

Shark teeth 
24 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. .-4 

Type section of the Rock River Formation-Continued 

Rock River Formation-Continued 

16. Siltstone, gray; contains large tan-weathering 

silty poorly fossiliferous limestone concretions ------------------------------------ 15. Concealed. Thickness estimated ______________ _ 

14. Sandstone, tan,, soft, massive; exposed in railroad cut----------------------------------

13. Sandstone, tan, soft, massive; contains a few 

tan-weathering small silty limestone concretions. Bench mark S318 located here _____ _ 

USGS D1398, from concretions: 

Inoce1·am1ts ,IJubcompressus Meek and 

Hayden 

Baculites perplea:us Cobban (transitional to Baculites gregoryensis 

'Cobban) 

12. Concealed. Thickness estimated _____________ _ 

11. Sandstone, tan, fine-grained ________________ _ 

Feet 

3 

150 

30 

20 

85 

30 

Total Bock River Formation (rounded)_ 1, 565 

Steele 'Shale (part) : 

10. Concealed. Thickness estimated______________ 75 

9. Shale, dark-gray ; contains gray limestone concretions and some baculites---------------- 15 

USGS D3197: 

Pyriporoid bryozoan 

MeDlbraniporoid bryozoan 

Inoceramus sp. 

Baculites perplea:us Cobban 

8. Shale, dark-gray; contains a few iron-stained 

limestone concretions______________________ 85 

7. Shale, dark-gray; contains a few iron-stained 

limestone concretions and, at top, small 

masses of "tepee-butte limestone"---------- 27. 5 

·usGS D1396, from top: 

Pyriporoid bryozoan (in living chaDlbers) 

Inocera/mus sp. 

Baculites perplea:us Cobban 

6. Shale, gray, sandy to silty; contains 7 harder 

layers of tan-weathering very fine grained 

shaly sandstone as much as 1 ft thick______ 72 

5. Shale, dark-gray; contains a few small rusty 

ferruginous concretions and, in upper part, 

a thin layer of bentonite with gray fibrous 

calcite ----------------------------------- 35 

USGS D1395: 

Pyriporoid bryozoans (in living chambers) 

Inoceramus sp. 

Baculites perplea:us Cobban 

Placenticeras sp. 

4. Shale, dark-gray; contains thin rusty ferruginous concretions and sparse layers of tan 

shaly sandstone___________________________ 13 

3. Shale, dark-gray; contains thin rusty ferruginous concretions-------------------------- 80 

USGS D1394: 

Pyriporoid bryozoan 

Membraniporoid bryozoan 

Type section of the Rock River Formation-Continued 

Steele Shale (part)-Continued 

3. Shale, dark-gray-Continued 

USGS D1394-Continued 

Inoceramus subcompress'lts Meek and 

Hayden 

Bac'ltlites perplea:'lts Cobban 

2. Shale, dark-gray; contains rusty-weathering 

thin shaly, sandy concretions, and tan shaly layers of sandstone ________________________ 

1. Shale, dark-gray; contains a few thin layers of 

shaly very fine grained tan-weathering sandstone ------------------------------------

Feet 

30 

30+ 

Total Steele Shale me as u red 

(rounded) ----------------------- 460 

ALLEN RIDGE FORMATION 

PRINCIPAL REFERENCE SECTION AND DISTRIBUTION 

Bergstrom (1959, p. 114) applied the name Allen 

Ridge Form:a;tion to a 1,200-foot-thick sequence of rocks 

underlying the Pine Ridge Sandstone and overlying the 

Steele Sha·le along the northeast flanks of the Hanna 

Basin northeast of Medicine Bow. Bergstrom's description consists of -a composite columnar section accompanied by brief remarks regarding.the lithology of 

the formation. The name was apparently derived from 

the ridge adjacent to the now-abandoned Allen Station 

on the Union Pacific Railroad ; no topographic feature 

by this name is shown on the topographic map of the 

area ( Saddleback Hills 15-minute quadrangle) . According to Bergstrom, part of the Allen Ridge Form-ation was measured in sec. 9, T. 22 N., R. 79 "\V., which is 

near Allen Station, and part was measured in Pine Tree 

Gulch in sec. 18, T. 23 N., R. 79 W. We were una.ble to 

recover Bergstrom's section at these localities, but we 

measured a complete section of the Allen Ridge and adjacent formations along the north and south sides of 

Pine Tree Gulch in the SlhNE~ sec. 19, T. 23 N., R. 79 

W., Carbon County (figs.1 and 7, loc. 7) here designated 

the principal reference section. 

We obtained much the sa.1ne thickness as was reported 

by Bergstrom (1,255 compa.red to 1,200 ft), but we differ radica.lly in our interpretation of rock units composing the forma.tion. "\Ve found the formation to consist of 

a lower nonmarine unit of fluviatile sandstone, shale, 

and carbonaceous beds about 685 feet thick, .a middle 

unit consisting of 195 feet of 1narine shale and sandstone, and an upper unit 375 feet thick consisting dominantly of rocks of brackish-water origin. Bergstrom apparently considered the entire Allen Ridge For1na.tion 

to be nonmarine. 

The Allen Ridge Formation of the Mesaverde Group 

is a ,;idespread and distinctive unit that can be recognized throughout much of south-central Wyoming. It 

.~· 

·--~ 

~ 

" 

.. ·, 

"',-, 

·-4 

·-4 

·• 

'-4 
Pine Ridge 

Sandstone 

ALLEN RIDGE FORMATION 

Allen Ridge Formation Haystack Mountains 

Formation 

25 

...._ FIGURE 7.--Allen Ridge Formation nt its principal reference section in Pine Tree Gulch in the NEJA sec. 19, T. 23 N., R. 79 W., 

I. 

Carbon Uo1mty, Wyo. Contact with the underlying ruassi>e sandstone of the Haystack Mountains Formation is shown on 

the right SJide of the photograph, and the contact with the overlying Pine Ridge Sandstone is shown on the extreme left 

side of the photograph. 

is the main ridge-forming part of the Mesaverde around 

the margins of the Carbon and Hanna Basins and the 

Rawlins uplift, and it is an important part of the Mesaverde along the east margins of the Great Divide and 

Washakie Basins. In the northwestern part of the 

Laramie Basin, the Allen Ridge intertongues on a grand 

scale with marine sandstone and shale of the Rock River 

Formation. At Rock River the facies change is complete, and the entire sequence of beds equivalent to the 

Allen Ridge Formation is represented by rocks of the 

Rock River Formation. The Allen Ridge Formation is 

not present elsewhere in the Laramie Basin. 

LITHOLOGIC CHARACTER 

At its principal reference section, the Allen Ridge 

Formation is a diverse lithologic unit. The lower part 

of the formation is a thick sequence of ridge-forming 

fluviatile sandstones and shales that weather distinctive 

shades of brown ftnd rusty brown. These colors contrast 

sharply with the yellowish-gray-weathering sandstones 

of the underlying Haystack Mountains Formation. The 

fluviatile sequence is about 685 feet thick and contains 

many beds of carbonaceous shale and numerous ironstone concretions but very little coal. 

This nonmarine sequence is interrupted in the eastern 

part of the Hanna Basin by marine strata which are 

included in the Allen Ridge, but which connect laterally 

with the Rock River Formation (fig. 2). This unnamed 

marine member consists of 115 feet of fossiliferous marine shale and siltstone and 80 feet of marine sandstone 

containing abundant 07Jhiomm·pha (fig. 8) . It is overlain by reddish-brown-weathering carbonaceous shale, a 

shallow-water marine sandstone, and a thick unit of 

dark-brownish-gray ironstone-bearing shale. These beds 

367--.863 0-7{}--5 

FIGuRE 8.-0utcrop of an unnamed marine member in the upper 

part of the Allen Ridge Formation at Pine Tree Gulch, in the 

NW1,4SEJA sec. 19, T. 23 N., R. 79 W., Carbon County, Wyo. 

fire nonresistant, poorly exposed, and generally form a 

valley. They were apparently deposited close to the sea, 

perhaps in a lagoon or in some other brackish-water 

environment. The marine member and the overlying 

marginal marine beds change character in a west and 

northwest direction because they grade into nonmarine 

beds typical of the lower part of the Allen Ridge. 

Along the east edge of the Great Divide and Washakie 

Basins, the entire Allen Ridge Format'ion is composed 

of nonmarine beds, except for a small area west of the 

town of Rawlins, where thin shallow-water marine 

sandstones crop out in the upper part of the formation 

(M. W. Reynolds, oral commun., 1968). 
26 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. ~ 

THICKNESS 

The Allen Ridge Formation ranges in thickness from 

a featheredge in the northern part of the Laramie Basin 

to 1,255 feet at its principal reference section on the 

northeast flank of the Hanna Basin; it is as much as 

1,500 feet thick in the Haystack Mountains north of 

Sinclair; and it ranges in thickness from 0 to about 

1,275 feet on the northeast flank of the Great Divide 

Basin. This variation in thickness is due·in part to uplift 

and erosion before .deposition of the Pine Ridge Sandstone, uplift and erosion in early Lewis time, and possibly in part to depositional thinning. The geologic 

history of the Upper Cretaceous rocks of this area is 

discussed in deta.il by Reynolds (1966, 1967). 

RELATION TO A·DJACENT FORM-ATIONS 

The Allen Ridge Formation conformably overlies the 

Haystack Mountains Formation. The contact is sharp 

and is marked by the abrupt change from fine-grained 

yellowish-gray-weathering Inarine sandstone below to 

carbonaceous shale or locally fluviatile channel sandstone above. The contact with the overlying Pine Ridge 

Sandstone probably is unconformable. This unconformity is difficult to document at most localities, but 

regional stratigraphic and faunal studies strongly·suggest its presence (Gill and Cobban, 1966b). This unconformity exists on the northeast flank of the Great 

Divide Basin, as shown by detailed mapping by Reynolds ( 1966, 1967). 

Except for minor marine tongues, the Allen Ridge 

Formation is the landward facies of the m·arine Rock 

River Formation that borders it to the east. To the 

northwest and west the Allen Ridge Formation probably merges into the main mass of the nonmarine Mesaverde Group. In the southern 'Vind River Basin and in 

the Rock Springs uplift, as shown by stratigraphic 

studies, rocks equivalent to the Allen Ridge probably 

have been removed by pre-Teapot or pre-Pine Ridge 

erosiOn. 

FOSSILS 

Fossils in the nonmarine part of the Allen Ridge Formation are scarce. Bone fragments were found at a few 

localities in the Haystack Mountains, and two collections of invertebrates were obtained from widely separated localities in the Hanna Basin. Invertebrate fossils 

from the basal part of the Allen Ridge were collected 

in the S'V1;4SE1;4 sec. 29, T. 24 N., R. 86 W., and were 

identified by W. A. Cobban as follows: 

USGS D6084: 

Oampeloma sp. 

Tttlotomops cf. T. laevibwwlis Yen 

The second collection, which came from a 5-foot-thic:k: 

channel sandstone that crops out 550 feet above the base 

of the Allen R.idge Formation in the center of the NE1;4 

sec. 19, T. 23 N., R. 79 W., is listed in the principal 

reference section. 

The marine tongue included as a part of the Allen 

R.idge Formation at the principal reference section contains abundant marine fossils at 20 and 70 feet above 

the base; these are listed in the section. 

AGE AND CORRELATIOli 

Inasmuch as the Allen Ridge Formation is dominantly nonmarine in most localities, it is difficult to relate the unit to the Western Interior Late Cretaceous 

ammonite sequence, except by comparing it with fossiliferous lateral marine equivalents such as the Rock 

River Formation. At the principal reference section, the 

top of the underlying Haystnck Mountains Formation 

contains Brwulite8 ]Je1•pleayu.s, and we infer that the 

lower part of the Allen R.idge was probably deposited 

late in the range span of this ammonite. Didymooe1·as 

neb1Ytsoen.rse occurs in the lower part of the marine tongue that overlies nonmarine rocks of the lower part of 

the Allen R.idge. A comparison of time-equivalent strata 

at Rock R.i ver shows that these nonmarine beds were 

deposited during the range span. of B. gregoryensis and 

B. sootti. 

Similarly, comparisoi1 of the Rock River section with 

the Allen Ridge section indicates that the marginal marine.beds above the unnamed marine member were probably deposited during, or somewhat later than, the range 

span of Didynwoeras stevensoni. 

The Allen Ridge Formation is Judith River .and 

early Bea.rpaw in age (Gill and Cobban, 196mt, pl. 4) 

in comparison with the central Montana section. The 

formation correlates with the Rock River Formation 

of the Laramie Basin, the Parkman Sandstone Member 

and the lower part of the unnamed marine member of 

the Mesaverde Formation of the western Powder River 

Basin, and the lies Formation of the Mesaverde Group 

of north western Colorado. 'V e are uncertain of the correlation of the Allen R.iclge with rocks of the Mesaverde 

Group in the R.ock Springs uplift and in the southern 

.part of the Wind River Basin. 

PRINCIPAL REFERENCE SECTION 

Inasmuch as we were unable to recover Bergstrom's 

original section ( 1959), we designate the following as 

.the principal reference section for the Allen Ridge 

Formation. 

~-

... , 

·•. 
..... 

... 

.. 

•· 

-,... 

.,. . 

... 

_.,.. 

ALLEN RIDGE FORMATION 27 

Principal1·etc1·cnce section ot the Allen Ri-dge Formation 

[1\:lensurcd in July 1067 with planetable and tape by J. R. Gill and 

R. L. Fleisher. Fossil identifications by W. A. Cobban and N. F. Sohl. 

llensurcd on the not·th nnd south sides of Pine Tree Gulch In the 

NE1/L sec. 19, '1'. 23 N., R. 79 W., Carbon County, Wyo. (Saddleback 

Hills 15-minute quadrangle), loe. 7, fig. 1.] 

Pine Ridge Sandstone : 

57. Sandstone, light-gray, fine-grained, highangle crossbeds; contains thin laminae of 

dark-brown to black carbonaceous shale ; 

forms ridge that supports a moderate 

growth of pine trees; weathers white. 

Not measured. 

Allen Ridge Formation: 

Upper part: 

56. 'Shale, dark-brownish-gray; contains abundant ironstone concretions; poorly exposed 

on line of section but moderately well 

exposed a quarter of a mile to south along 

south side of Pine Tree Gulch____________ 180 

SQ. S·andstone, yellowish-gray to pale-yellow, fineto medium-grained; weathers in three 

ledges 1-2 ft thick at base, middle, and 

top; contains small Ophiomorpha_________ 46 

54. ·Shale,.medium- to dark-brown~ carbonaceous, 

flaky, poorly exposed---------~---------- 80 

53. Sandstone, pale-yellowish-gray, fine- to 

medium-grained, thin-bedded at base, massive at top; capped by a 1-ft-thick bed of 

brown-weathering sandstone_____________ 25 

52. Shale, reddish-brown, very carbonaceous, 

abundant limonite plates and a few ironstone concretions; sandy in upper part____ 43 

Total upper part__________________ 374 

Unnamed marine member : 

51. Sandstone, pale-yellowish-gray, fine- to 

medium-grained, lower part ledge forming, 

upper _part soft; contains Ophiomorpha___ 80 

50. Shale, siltstone and sandstone, dark-gray to 

dull-olive, soft; sandstone and siltstone 

laminae are cemented with limonite; poorly 

exposed on line of section but ·well exposed 

n quarter of a mile to south_______________ 115 

USGS D5000, from limonite concretions 

20ft above base : 

YoZdia·? cvansi (Meek and Hayden) 

NttettZa sp. 

Inoce1·mnus aff. I. turgidus Anderson 

Pte1·ia Unqttaeformis (Evans and 

Shumard) 

Oroytoma sp. 

Ost1·ea sp. 

Goniomya americana Meek and 

Hayden 

Lttcina sp. 

Tenea sp. 

Tellina ntttnda Stephenson 

Oorbttla sp. 

Bacttlites sp. 

Diclymoceras ct. D. nebrascense 

(:Meel.: and Hayden) 

PrinoipaZ reference section·of the Allen Ridge FormationContinued 

Allen Ridge Formation-Continued 

Unnamed maTirie member..:....Continued 

'50. Shale, siltstone and sandstone-Continued 

Lower part: 

USGS D5001, from 70ft above. base: 

Serpttla sp. 

Dysnoetoporoid bryozoan 

Inooeramtts cf. I. pertenuis Meek and 

Hayden 

Oroytoma sp. 

Ostrea sp. 

Syncyclonema sp . 

Pholadomya sp. 

Protocardia? sp. 

Oymella montanensis (Henderson) 

Tellina munaa Stephenson 

Oorbula sp. 

Acmaea? parva (Meek and Hayden) 

Acmaea? cf. A. occiaentalis (Meek 

and Hayden) 

Oerithioderma? sp. 

Tuba.n. sp. 

Aporrhais aff. A. biangulata (Meek 

and Hayden) 

Euspira obliquata (Hall and Meek) 

Gyrodes sp. 

Morea sp. (only apex preserved but 

it belongs in the cancellaria rather 

than marylandica species group) 

Belliftt8U8 sp. (immature) 

Graphidttla cf. G. alleni (White) 

Acteon sp. 

Oligoptycha sp. 

Baculites sp. 

Didymoceras nebrascense (Meek 

and Hayden) 

Placenticeras intercalare Meek 

Fish scales 

Total unnamed marine member-- 195 

49. Sandstone, pale-yellowish-gray, fine-grained, 

·hard; weathers dark reddish brown; contains a few limonite nodules in lower part 

and masses of concretionary-weathering 

sandstone in upper part_________________ 30 

48. Shale, light-gray, interbedded with brown 

carbonaceous s-hale; contains ·a few lightyellowish-weathering 'beds of soft lenticular 1Sandstone. A 1-ft-1hick bed of 

carbonaceous shale at top and a layer of 

reddish-brown-weathering ironstone concre-· 

tions 3 ft below top______________________ 106 

47. Sandstone, pale-yellowish-gray, fine-grained, 

crossbedded, lenticular; forms ridge______ 5 

USG-S D4759: 

Anoaonta propatoris White 

Plesielliptio sp. 

Fusconaia? sp. 

Sphaerittm sp. 

V iviparus sp. 
28 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

Pr·incipaZ 1·eference section of the A.Zlen Ridge FormaUonr-Continued 

Allen Ridge Formation-Continued Feet 

Lower part-Continued 

46. Shale, light- to medium-gray, sandy; oontains 

thin lenses of soft sandstone with layers of 

limonite cement and 2 th.in beds of ca.rbonaceous ·shale in upper part_ ___________ _ 

45. Sandstone, moderate-yellow-brown, finegrained, lenticular; forms ridges; contains numerous limonite nodules ______________ _ 

44. Shale, light-gray, sandy; contains numerous 

layers of iron-cemented siltstone or silty 

konstone. Three 1-ft-thick beds of carbo- naceous •Shale in upper part_ ____________ _ 

43. Sandstone, pale-yellowish-gray, fine-grained; 

crossbedded, lenticular; weathers brown 

and forms ridge ________________________ _ 

42. Shale, as in unit 44; contains a few carbo- naceous streaks ________________________ _ 

41. Sandstone, as above ----------------------

40. Shale, gray and brown interlbedded; in part 

carbonaceous -------------------------- 39. 'Sandstone, pale-yellowish-gray, fine-grained,· 

crossbedded, lenticular; forms ridge; contains 1.5-ft-th'ic.k :by 3-ft-diameter darkyellowish-orange sandstone concretions at 

.base _________________________________ _ 

38. ·Shale, like unit 40; contains some thin beds 

of soft sandstone -----------------------

37. Sandstone, like unit 39, except very fine 

grained ------------------------------- 36. Shale, like unit 40, contains ironstone concretions ------------------------------- 35. S·andstone, pale-yellow, very fine grained, 

thin-bedded, soft; numerous layers are cemented with limonite -------------------

34. Shale, light-gray to reddisrh-brown interbedded; in part carbonaceous; contains tJhin 

lenticul,ar beds of .sandstone _____________ _ 

33. Sandstone, pale-yellowis'h-gray, fine-grained, 

very lenticular; weathers brown and forms 

ridge ----------------------------------

32. 'Shale, like unit 34------------------------

31. Sandstone, like unit 33 ; contains limonite,_ 

cemented shale •pebbles __________________ _ 

30. 1Shale and sandstone inte.rbedded; light-gray 

'shale interbedded with reddisih-·brown carbonaceous shale and lenticular beds of 

reddish.Jbrown-weathering .sandstone. Unit 

capped by a 4-ft-thick 'bed of carbonaceous 

~shale 

29. Sandstone, like unit 33; weathers dusky yellow ----------------------------------- 28. Shale, like unit 34; contains ironstone con- cretions; soft __________________________ _ 

27. Sandstone, like unit 33--------------------

26. Shale, gray; contains thin ironstone layers __ 

25. Shale, dark-brown, carbonaceous-----------

24. 8-andstone, dark~yellowish-orange, very fine 

grained, thin-bedded ____________________ _ 

45 

3 

29 

7 

21 

23 

59 

14 

23 

5 

15 

9 

22 

3 

29 

35 

73 

2 

23 

3 

2 

3 

2 

Pr·indipaZ reference section of the A.Zlen Ridge Formationr-Con tin ned 

Allen Ridge Formation-Continued 

Lower part-Continued Feet 

23. Shale, light-gray ; contains thin beds of soft 

sandstone and cai'bonaceous shale, soft. A 

layer of ironstone concretions 0.8 ft thick 

and 1.5 ft in diameter in middle of unit-___ 15 

22. Sandstone, pale-yellowish-gray, very fine 

grained, thin-bedded ; numerous rusty-

'brown .. wea the ring limonite-cemented layers. Capped by a 1.5-ft-thick bed of hard 

reddish ... brown-weathering sandstone______ 6 

21. Shale, reddish-brown, carbonaceous. Interbedded with light-gray sandy shale; forms 

valley --------------------------------- 35 

20. Sandstone, pale-yellowish-gray, very fine 

grained, thin .. bedded, lenticular; weathers 

dark yellowish orange___________________ 9 

19. Shale, -as above___________________________ 30 

Total lower part____________________ 686 

Total Allen Ridge Formation ________ 1, 255 

Haystack Mountains Formation : 

Upper unnamed member: 

18. Sandstone, pale-yellowish-gray, fine-grained; 

forms massive cliff; contains Ophiomorpha ----------------------------------- 70 

17. Sandstone and shale intel'bedded ; dominantly sandstone in beds 0.1-6 ft thick; 

shale in ·beds less than 0.1-1 ft thick; forms 

valley between 2 cliff-forming sandstones __ 

16. S·andstone, pale-yellowish-gray, fine-grained, 

thin-bedded at 1base to massive at top; 

-abundant limonite-replaced shale pebbles in 

lower part; contains numerous partially 

oxidized small pyrite nodules------------

USGS D5580, from lower part of unit: 

BacuZites perpleams Cobban 

15. S·andstone and shale; weathers yellowish 

gray; poorly exposed--------------------

14. Covered; appears to be dark-gray ·sandy 

shale ------------------------:.-----------

70 

70 

175 

230 

Total upper unnamed member ________ , 475 

Hatfield Sandstone Member: 

13. Sandstone, pale-yellowish-gray, very fine 

grained, thin-bedded, in ·beds 0.1-0.4 ft 

thick, locally cemented with iron -and con- taining fossils; forms ridge _____________ _ 

USGS D5579: 

Pyriporoid bryozoan 

Inooeramus suboompressus 

Meek and Hayden 

Baculites asperiformis Meek? 

Hoploscaphites sp. 

Placenticeras sp. 

55 

Total Hatfield Sandstone Member_ 55 

~· 

... . 

_.. 

...... 

~ 

... 

-4-

-~ -· 
_ .... 

PINE RIDGE SANDSTONE 29 

Prino,lpal 1'ete1·enoe section ot the Allen Ridge FormaNon-Continued 

I-Iaystacl<: Mountains Formation-Continued 

Middle unnamed member : 

12. Covered; appears to be dark-gray shale __ _ 

11. Sandstone, as above; forms massive ridge __ _ 

USGS D5578: 

Inooeranvus sp. 

Baoulites mclea1'ni Landes 

10. Covered; appears to be dark-gray shale ___ _ 

9. Shale and sandstone interbedded, gray, soft, 

poorly exposed; contains thin beds of 

coarse-grained glauconitic sandstone with 

dark phosphate pebbles 50 ft bE!lOw top __ _ 

USGS D5577, from 50ft below top: 

Baculites sp. (phosphatized) 

8. Shale, gray, sandy; weathers yellowish gray; 

poorly exposed--------------------------

USGS D5576, float 190 ft above base of 

unit: 

BaouUtes cf. B. molem-"'~i Landes 

7. Shale, poorly exposed; contains a few thin 

beds of sandstone ______________________ _ 

6. Covered; appears to be sandy shale ______ _ 

Feet 

225 

185 

::l70 

60 

280 

280 

210 

Total middle unnamed member _______ 1, 610 

O'Brien Spring Sandstone Member: 

5. Sandstone, pale-yellowish-gray, very fine 

grained, clayey, soft in lower part becoming slightly resistant in upper part; contains thin beds of sandy shale and sparse 

limestone concretions; poorly exposed____ 250 

USGS D4757, from 150 ft above base of 

unit: 

Oymbopho1·a holmesi (Meek) 

JJaonUtcs obt1ts1ts (Meek) 

4. Bentonite, light-gray, slightly swelling_____ 5 

3. Sandstone, pale-yellowish-gray, very fine 

grained, thin-~bedded, soft ; capped by a 0.3-

ft-thick bed of green glauconitic silicaSteele Shale: 

cemented sandstone______________________ 70 

Total O'Brien Spring Sandstone 

Member ------------------------ 325 

Total Haystack Mountains Formation (rounded)-·---------------- 2, 600 

Total Mesa verde Group measured 

(rounded) --------------------- 3,860 

2. Shale, medium-dark-gray, sandy____________ 175 

1. Bentonite, like unit 4; contains a 0.2-ft-thick 

silicified sandstone at ba:se_______________ 2 

PINE RIDGE SANDSTONE 

TYPE LOCALITY AND DISTRIBUTION 

The Pine Ridge Sandstone wrts designated the upper 

1ne1nber of the ~1esaverde Formn,tion and was na.med by 

Dobbin, I-Ioots, Dane, and Hancock (1929, p. 140) fur 

the exposure on Pine Ridge about, 2 miles southeast of 

tJhe town of Rock River in !{;he northern part of tih.e 

Laramie Basin, but they did not measure a section at 

this locality. The section we measured on Pine E.,idge is 

considered in tlus report as the princi paJ! reference section for the unit. In tJhis report we eleV'ate the Pine 

Ridge Sandstone from a member of the Mesaverde Formation to a formation in the Mesaverde Group. 

The Pine Ridge Sandstone is the most conspicuous 

formation in the Mesaverde Group. It is a white to 

light-gray nonmarine sandstone, more resistant and 

lighter colored than the adjacent forma;tions, and generally crops out 'as ·a distinotive tree-covered ridge. The 

formation can be recognized along the west and north 

margins of the Laramie Basin, t!hroughout tJhe Oarhon 

and Hanna Basins, and along ·the east flank of the Great 

Divide Basin. It is exposed on the nortJlu~ast side of the 

W·ashakie Basin near Rawlins, hut has not been identified on the ·southeast side of the basin near the WyomingColorado State line. 

LITHOLOGIC CHARACTER 

The Pine Ridge Sandstone in much of south-central 

Wyoming consists mainly of pale-yellowish-gray very 

fine grained to fine-grained sandstone that weathers very 

light gray to wihite. It includes beds of light-gray carbonaceous siltstone, sandy carbonaceous sha.le, and thin 

beds of impure coal. Many bedding surfaces are stained 

or ce1nented with iron oxide. High-angle crossbedding 

that resembles torrential bedding is a striking feature on 

1nany outcrops. Some of the sandstone beds in the formation are closely jointed. These joints and the adjacent 

rock have been cemented with secondary silica resulting 

in a raised boxwork pattern on weathered surfaces. 

In most areas, sandstones of the Pine Ridge are fine 

grained, except where the formation has cut deeply 

into the underlying rocks. In these areas the grain size 

of tJhe Pine Ridge ( oalled Tea pot Sandstone Mmnber 

of tJhe Mesaverde iby earlier workers) reaches granulep~bble conglomerate size (Reynolds, 1967, p. D26). 

THICKNESS 

The Pine Ridge Sandstone is 83 foot thick rut the principal reference section (fig. 9). It apparently tluns 

toward the east, grading into shallow -'water marine 

sandstone. This dhange cannot be observed in the Laramie Basin !but has been seen in ibhe Teapot Sandstone 

Men1ber (coextensive with the Pine Ridge) of the 

Mesaverde For1nation in the southern Powder River 

Basin. The Pine Ridge Sandstone is as muoh as 450 

feet thick in the northwestern part of the Rock Creek 

oil field in tlhe northwestern part of the Laramie Basin 

(Dobbin and others, 1929, p. 140), ·and it ranges in 
30 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

FIGURE 9.-Pine Ridge Sandstone at its principal reference section in the NE:t,iSW:t,iNW14 sec. 16, T. 20 N., R. 76 W., Albany 

County, Wyo. Valley to the right side of the area shown in 

photograph is cut in the Lewis Shale, and sage-covered slope 

to the left is formed by the Rock River Formation. 

tJhickness from 250 feet along the east margin of the 

Hanna Basin to about 70 feet in the Kindt Basin south 

of Sinclair (Davis, 1966, p. 68). 

On •the northeast flank of the Great Divide Basin, the 

Pine Ridge is 60-205 feet thick. Reynolds (1967, p. D24) 

attributed this variation to depositional thinning, to intertonguing with tJhe generally overlying Almond Formation, and to local truncation beneath the Lewis Shale. 

Regionally, the Pine Ridge rs a thin widespread unit of 

sandstone deposited by meandering streams upon an 

uplifted and eroded surface of nonmarine and marine 

l'Ocks. South of Rawlins, along the east margin of the 

W a;shakie Basin, the Pine Ridge Sandstone has lost its 

characteristic blanketlike character and is probably 

represented hy thick channel-filling sandstones that 

grade laterally into rocks of Allen Ridge lithology. 

RELATION TO ADJACENT FORMATIONS 

The nonmarine Pine Ridge Sandstone is thought to 

rest unconformably on the Rock River Formation in the 

Laramie Basin an~ on the Allen Ridge Formation in 

the Hanna Basin. The basal beds of the Pine Ridge fill 

channels in the underlying rocks at many places, but the 

relief on this erosion surface can be determined at few 

localities. Apparently, much of central Wyoming was 

subjected to regional uplift and erosion before the deposition of the Pine Ridge Sandstone and the coextensive 

Teapot Sandstone Member of the Mesaverde (Gill and 

Cobban, 1966b). Local areas of intense pre-Pine Ridge 

folding and erosion in south-central Wyoming were described by Reynolds (1966, 1967), and an unconformable 

relationship between the Pine Ridge and older rocks 

in south-central Wyoming was recorded by Davis (1966, 

p. 60-62). 

The Pine Ridge Sandstone is one of the major regressive tongues of the Mesaverde Group and represents an 

eastward retreat of the strand. The formation probably 

thins and changes eastward, first to a shallow-marine 

unit and then to a part of the Pierre Shale. Following 

deposition of the Pine Ridge, the sea again advanced 

westward, and mud of the Lewis Shale was deposited. 

In the Laramie Basin, the Lewis rests comformably on 

the Pine Ridge Sandstone; but in the Oar bon, Hanna, 

Great Divide, and w·ashakie Basins farther west, the 

Pine Ridge is conformably overlain by, and interfingers 

with, coal beds, brackish-water shale, and nearshoremarine sandstone. The name Almond Formation is applied to these rocks which represent the barrier bar or 

barrier island and lagoonal deposits along the western 

shore of the advancing Lewis sea. In the western part 

of south-central w ·yoming, where the uppermost strata 

of the Pine Ridge Sandstone interfinger with the basal 

beds of the Almond, the contact of the two formations 

is placed between the light-gray-weathering nonmarine 

sandstone and the overlying yellowish-gray to brownweathering sandstone or dark-gray brackish-w·ater 

shale. The sandstone of the lower part of the Almond, 

although similar to the sandstone of the upper part of 

the Pine Ridge at many localities, commonly contains 

burrows of marine and brackish-water organisms. The 

shale of the lower palt of the Almond, in contrast with 

the shale of the upper part of the Pine Ridge, contains 

brackish-water fossils and generally occurs in thicker 

units. 

AGE AND CORRELATION 

The age of the Pine Ridge has been extrapolated from 

the ages of overlying and underlying marine rocks because only poorly preserved plant fossils have been 

found in the formation. The youngest marine fossils in 

the underlying Rock River Formation, from 270 feet 

below the top, include Didy11wcem s stevensoni. From 

the kno"-n range span of this species at other localities, 

it appears that the uppermost part of the Rock River 

Formation could have been deposited during the time 

of the next younger index ammonite, E xiteloceras 

jenneyi. 

The lower part of the Lewis Shale, overlying the Pine 

Ridge Sandstone in the Rock River area, contains Baculites ?'eesidei. This ·ammonite is separated from E xiteloceras .ienneyi by, from oldest to youngest, the zones of 

Didymoceras cheyennense, B. compressus, and B. cuneatus in other areas in the Rocky Mountain region. It is 

possible that the Pine Ridge Sandstone was deposited 

during the time span of these three zones, but it is improbable because of the unconformity at the base of the 

formation. The marine equivalent of the Teapot Sandstone Member of the Mesaverde Formation in the Po,,-
~-

.. 

., .. 

... 

..... 

•. 

.y. 

ALMOND FORMATION 31. 

der River Basin contains B. 'l'eesidei (Gill and Cobban, 

1966b, p. B21-B24): vVe believe the. Teapot to be coextensive with the Pine Ridge and, consequently, that the 

Pine Hidge wns deposited early in the time of B. 'l'eesidei. This would indicate that the Pine Ridge Sandstone 

is of middle Bearpaw age (Gill and Cobban, 1966a, 

pl. 4). 

The Pine Ridge Sandstone correlates with an unnamed sandstone unit in the upper part of the Pierre 

Shale at IIorse Creek east of the Laramie. Bange and 

with -an unnamed sandstone and shale sequence below 

the Larimer and Rocky Ridge Sandstone l\1embers of 

the Pierre Shaile along the east side of the Front Range 

in Colorado (Scott and Cobban, 1959, p. 129). It probn,bly nJso correlates wi·th the lower part of the 'i\Tilliams 

Fork Formation of the l\1esa.verde Group in northwestern Colorado and with the Teapot Sandstone l\1ember of the l\1esa.verde Formation in the western Powder 

River Basin, eastern 'i\Tind River Basin, and Bighorn 

Basin of 'i\Tyoming. The Pine Ridge Sandstone. probably is coextensive with the upper part of the Ericson 

Sandstone of the Rock Springs uplift; the two :form·ations luwe similar lithologies, and both underlie the 

Almond Formntion. 

PRINCIPAL REFERENCE SECTION 

The following section, measured about 2 n1iles southeast of the town of Rock River in the area. where the 

formn..tion wn,s named, ·is herein designated the principal 

reference section. 

P·rimci.1mZ 1·ctc1·encc scct·ion of the Pine R·idge Sandstone 

(l\Iensured with n .Tncob's stuff by J. R. Gill in June 1968. Measured 

nbout 2o/.~ miles southenst of the town of Rock River in the NE~­

SWIA,NWlJL sec. l(l, T. 20 N., R. 76 W., Albany County, Wyo. Loc. 

8, fig. 1.] 

Feet 

Lewis Shale: 

18. Shale, dark-gray to black; not measured. 

Pine Ridge Sandstone : 

17. Sandstone, light-gray, very fine grained, very thin 

bedded; contnins some yellow iron .stain______ 1. 0 

16. Shale, reddish-brown, carbonaceous_____________ 2 

15. Sandstone, like unit 17------------------------ 9 

14. Shale, dfH·k-brown to blacl{, coaly in middle; level 

of prospect pit------------------------------ 15. 8 

13. Sandstone, pale-yellowish-gray, fine-grained; 

forms cliff ; contains high-angle crossbeds and 

weathers light gray; weathered surfaces have a boxworl( pattern, in part_ __________________ 20. 5 

12. Coal, blnck, impure---------------------------- 1. 4 

11. Shnle, dark-brown to black, carbonaceous to 

coaly-------------------------------------- 2.0? 

10. Sandstone, like unit 13------------------------- 4. 0 

9. Shale, dark-brown, carbonaceous, silty; contains 

a 1-ft-thick siltstone layer in middle__________ 3. 5 

8. Coni, blncl{, impure____________________________ 2. 8 

Principal 1'ete1·ence section ot the P·ine Ridge SandlltoneContinued 

Pine Ridge Sandstone--Continued Feet 

7. Claystone, light-olive-gray, carbonaceous, very 

silty -------------------------------------- 5.0 

6. Sandstone, like unit 13, but in beds 1-ft thick; 

contains some yellow iron stain______________ 4. 5 

5. Shale, brown to black, coaly in upper foot______ 4. 0 

4. Sandstone, like unit 13, but slightly carbonaceous- 2. 4 

3. Shale, olive-gray, carbonaceous_________________ 4. 5 

2. Sandstone, pale-yellowish-gray, fine- -to mediumgrained, hard; abundant plant and root remains ------------------------------------- .8 

Total Pine Ridge Sandstone (rounded)__ 83. 0 

Rock River Formation (part) : 

1. Sandstone, very light gray, very fine grained, soft, 

clayey; becomes dusky yellow at .top__________ 75 

Rock River Formation measured________ 75 

ALMOND FOR¥ATION 

TYPE LOCALI.TY AND DISTRIBUTION 

The Almond Formation was first called the "Almo11d 

coal group" of the Mesaverde Formation by Schultz 

(1907, p. 262) and later called the Almond Formation 

of the Mesaverde Group by Sears (1926, p. 16). Neither 

geologist designated ·a type locality nor measured a 

type section. 'V e assume that the name was derived 

from the Almond stage station near Point of Rocks, in 

the SW1,4 sec. 27, T. 20 N., R. 101 W., Sweetwater 

County, Wyo. We measured a section nearby, in sec. 25, 

where the Almond is about 585 feet thick and consists of 

two parts. The lower part, 180 feet thick, consists of 

fluviatile sandstone, shale, and coal. The upper part, 

405 feet thick, consists of marine shale, shallow-water 

1narine sandstone, and lagoonal or brackish-water rocks. 

The upper part interfingers with the overlying Lewis 

Shale, and the lower part is in sharp contact with the 

underlying Ericson Sandstone. 

The Almond Formation is well exposed along the 

flanks of the Rock Springs uplift and extends eastward 

in the subsurface through the Great Div.ide and Washakie Basins. The Almond crops out along the east margins of these basins and is also exposed in the Hanna 

and Carbon Basins to the east. The Almond Formation 

is a sequence of fluviatile, brackish-water, and nea~hore 

marine rocks that conformably overlie the Pine Ridge 

Sandstone and conformably underlie, and intertongue 

with, the Lewis Shale in south-central Wyoming. 

LITHOLOGIC CHARACTER 

In south-central Wyoming, the Almond Formation 

consists of a thick sequence of sandstone, shale, and 

minor coal. Sandstone constitutes one-half to one-third 
32 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

of the formation. It is pale yellowish gray to dusky yellow, weathers various shades of brown, and is very fine 

grained and thin bedded. Locally, the sandstone contains Ophiom.orpha, which is evidence of •a shallowwater marine depositional environment, and abundant 

oysters and other fossils from a brackish-water depositional environment. These sandstone units may represent barrier-bar or barrier-island deposits marginal to 

the Lewis Sea. The formation also contains a few sandstone units probably of fluvial origin. The sandstone 

beds of the Almond seem to increase in thickness and 

number seaward (east and southeast). 

Shale units in the Almond are, in a regional sense, 

tongues of the Lewis Shale and likewise increase in 

thickness and number to the east and southeast. The 

Almond contains two types of shale. The first is dark 

gray to olive gray ·and devoid of ironstone concretions 

but, locally, contains limestone concretions with marine 

fossils. Units of this shale thin to the west and northwest and regionally are tongues of the Lewis Shale. 

The second and more typical type is brownish gray to 

brownish black, carbonaceous to coaly, and contains 

many ironstone concretions with abundant oysters and 

other brackish-water fossils. This sha.le was probably 

deposited in a restricted marine or brackish-water environment, possibly behind barrier-bars or islands. In the 

extreme north western part of the area, on the northeast 

flank of the Great Divide Basin, fluviatile sandstone and 

shale form the basal part of the Almond (M. W. Reynolds, oral commun., 1968). 

THICKNESS 

The thickness of the Almond Formation varies considerably in south-central Wyoming. The formation 

generally thins toward the east and southeast. The 

thinning results from an increase in number and thickness of marine shale units and from the nonpersistence, 

in an eastward direction, of the shallow-water marine 

sandstone units chosen to identify the Almond-Lewis 

contact. As the sandstone units beneath the AlmondLewis contact pinch out and the marine shale units in 

the upper part of the Almond thicken to the east and 

southeast, the contact is selected progressively lower in 

the rook sequence. 

Where the Almond Formation crops out along the 

northwestern margin of the Laramie Basin, it consists of 30-40 feet of interbedded carbonaceous shale, 

shallow-marine sandstone, and lenticular coal. The Almond is about 575 feet thick along the south margin 

of the Hanna Basin near the Elk Mountain anticline. 

In this area the Almond contains two tongues of rnarine shale-a lower tongue, 215 feet thick, and an 

upper tongue, 75 feet thick. The remainder of the formati~n consists of slightly carbonaceous shale containing abundant ironstone concretions, interbedded 

sandstone and carbonaceous shale, and beds of shallowwater marine sandstone. About 28 miles northeast of 

this area, in the southern Haystack Mountains, the Almond is about 600 feet thick (fig. 10). Remnants of 

marine tongues are represented there by shallow-water 

marine sandstones and shales containing abundant 

brackish-water fossils. This lithology is described in 

reference section 1 of the Almond Formation. 

Along the northeast flank of the Great Divide Basin 

in the Lamont-Bairoil area, the Almond ranges in 

thickness from 0 to 365 feet. This variation resulted 

from depositional thinning on a growing Late Cretaceous fold and from erosion along a local unconformity 

at the top of the formation (M. 1V. Reynolds, oral 

commun., 1968). 

RELATION TO ADJACENT FORMATIONS 

Dark-gray-weathering shale and sandstone of ·the 

lower part of the Almond are conformable with, and alternate with, lighter colored sandstone of the upper part 

of the Pine Ridge Sandstone. In some areas the contact 

is sharp, and in others it is arbitrarily located within 

gradational rocks. The Almond Formation is generally 

conformable with, and grades laterally into, the partly 

younger Lewis Shale. This contact is generally placed 

at the top of a shallow-marine sandstone unit that overlies dark-colored brackish-water and fluviatile beds and 

underlies a marine shale unit. The Almond Formation 

in south-central Wyoming was deposited along .the margins of the expanding Lewis Sea, which accounts for 

the large-scale intertonguing of the two formations. 

FOSSILS 

The Almond Formation contains 1narine and 

brackish-water faunas. The brackish-water fossils are 

mainly associated with carbonaceous shale and ironstone concretions, but reeflike beds of oysters occur with 

some of the shallow-water marine sandstones. The 

marine fossils are in limestone concretions, within 

tongues of marine shale, or in shallow-marine sandstones. 

At Rock River the part of the Lewis Shale that is 

equivalent to the Almond of the western areas contains 

the following index ammonites, from oldest to youngest : 

B aoulites reesidei, B. ienfleni, and B. eliasi. Of these 

forms, B. reesidei and B. eliasi have been found in 

marine rocks of the Almond at several places. B. jen.seni 

has not been reported in the Almond, probably because 

... 

!._ 

·• 
• 

ALMOND FORMATION 33 

~ ... •< ----·~. ~~-;;·· - ~~ 

... ~ 

FIGURE 10.-Shallow-water marine sandstones and brackish-water shales in the lower part of the Almond Formation near reference section 1, sec. 12, T. 22 N., R. 85 W., Carbon County, Wyo. Dip slope to right is formed by the Pine Ridge Sandstone. 

Looking east. 

the rocks representing this fossil zone are of brackishwater origin in much of the area. 

In the southern part of the Hanna Basin, in the 

NW1,4SW1,4 sec. 27, T. 21 N., R. 81 W., Carbon County, 

the following fossils were collected from 280 feet above 

the base of the Almond : 

USGS D6272: 

Calcareous worm tube 

Solemya? sp. 

Nuou.lana sp. 

Yoldia? evans·i (Meek and Hayden) 

Breviarca sp. 

Inocerarmts sp. 

Orcytoma sp. 

Ethmocm·dittm sp. 

Anisomyon cent1·ale Meek 

Bac1tlites reesidei Elias 

Additional fossils are listed in reference sections 1 

and 2 for the Almond Formation. 

AGE AND CORRELATION 

The Almond Formation in south-central Wyoming 

was deposited during the time range of three ammonites, in ascending order, Baculites ?'eesidei, B. jenseni, and the early ·part of B. eliasi. The type Almond 

in the Rock Springs uplift took longer to accumulate; 

it appears to encompass the preceding zones plus the 

younger zone of B. baculus. The presence of these fossils indicates that the Almond Formation is of late 

Bearpa w age (Gill and Cobban, 1966a, pl. 4). 

The Almond correlates with the lower unnamed shale 

member and the Kara Bentonitic Member of the Pierre 

Shale in the eastern Powder River Basin, with the lower 

part of Meeteetse Formation of the western Bighorn 

and Wind River Basins, and with the upper part of the 

Williams Fork Formation of the Mesaverde Group in 

northwestern Colorado. It also correlates with the lower 

part of the Lewis Shale in the Laramie Basin and 

with the upper part of the Pierre Shale east of the 

Laramie Mountains. 

REFERENCE SECTIONS 

The two following reference sections were measured 

about 11 miles apart and document the southerly (seaward) change in the lithology of the Almond 

Formation. 
34 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

Refe1·ence .<?ect·ion 1 of the r1l1nonll Formation 

[Measured in July 1967 with planetable and tape by J. R. Gill and 

G. A. Bergman. Fossils identified by W. A. Cobban. Measured in the 

SW%SE%SW74, and the SW%NE1~ sec. 12, T. 22 N., R. 85 W., 

Carbon County, Wyo. (Lone Haystack Mountajn 772-minute quadranglet), loc. 4, fig. 1.] 

Feet 

Lewis Shale: 

40. Sandstone, pale-yellow,ish-gray, fine-grained, thinbedded to massive, friable to cliff-forming; contains 3 layers 'Of large brown-weathering sandstone concretions---------------------------- 180 

USGS D5258, from near top of unit: 

Bacu.Utes eliasi Cobban 

39. Shale, olive-gray, flal\:y; ·becomes sandy in upper 

part; contains 4 layers of rusty-weathering 

septarian 1imestone concretions in the lower 30 

ft. Middle of unit contains 2 beds of bentonite 

less than 0.5 ft thick_________________________ 70 

38. Shale, light-olive-gray; weathers yellowish gray; 

persistent bed of red-weathering septarian limestone concretions at tOP--------------------- 30 

Total Lewis 'Shale measured ____________ 280 

Almond Formation: 

37. Sandstone and shale interbedded; weathers yellowish gray ; soft ; nonpersistent layer of brownweathering sandstone concretions at top______ 25 

USGS D6263: 

Calcareous worm tube 

Cymbophora? sp. 

Gastropods 

Baculites eliasi Cobban 

Hoploscaphites sp. (with aptychus) 

36. Shale, reddish-brown, carbonaceous_____________ 7 

35. 'Coal, black, impure---------------------------- 1.5 

34. Sandstone, pale-yellowish-gray, very fine grained; 

thin bedded at base and massive at top________ 5 

33. Shale, brownis·h-gray, flaky, poorly eXlposed; contains tabular masses of orange-weathering ironstone and cone-in-cone limestone concretions. 

Upper 10 ft consists of reddish-brown carbonaceous shale----------------------------- 60 

USGS D6262, from 20 ft below top: 

Corbicula sp. 

USGS D6261: 

Crassostrea glab1·a (Meek and Hayden) 

Corbioula? sp. 

32. Sandstone, pale-yellowish-gray, very fine grained, 

thin-bedded, ripple-laminated; contains small 

vertical burrows----------------------------- 4 

31. Shale, dark-brownisll-gray ; grades into coaly 

shale at toP--------------------------------- 2 

30. Shale, dark-yellowish-orange___________________ 0.5 

29. Sandstone as above---------------------------- 8 

USGS D6264: 

Panopea? sp. 

Corbula undifera (Meek) 

28. Shale, brownish-gray ; olive gray and sandy in 

upper 10ft; contains 3 layers of red-weathering 

ironstone concretions________________________ 55 

USGS D6261: 

Crassostrea glabra (Meek and Hayden) 

Corbicula? sp. 

Reference section, 1 of the Almonll F01·mation--Continued 

Almond Formation-Continued 

27. Sandstone, yellowish-gray to dusky-yellow, fineto medium-grained, ridge-forming; contains 

abundant oyster shells and invertebrate burrows. Locally contains brown-weathering crossbedded sandstone concretions at 10 ft above 

base --------------------------------------- 18 

26. Shale, darl\:-brownish-gray ; contains abundant 

oyster shells and Ophiomorpha_______________ 25 

25. Sandstone, like unit 27------------------------ 5 

24. Shale, like unit 26, but sandy------------------- 13 

23. Sandstone, like unit 27------------------------- 2 

22. Shale, olive-gray; weathers to a yellowish-gray 

slightly bentonitic surface ; contains 4 layers of 

oyster-bearing ironstone concretions___________ 35 

21. Shale, brownish-black, flal{y ; abundant jarosite 

nnd selenite in lower prurt; contains 6 layers of 

small ironstone concretions__________________ 37 

20. Sandstone, pale-yellowish-gray, very fine grained, 

thin-bedded -------------------------------- 2 

19. Shale, dark-gray ; ironstone concretion layer at 

top ---------------------------------------- 10 

18. Shale, black, very carbonaceous________________ 4 

17. Shale, brown, carbonaceous, silty; contains a 0.4-

ft-thick bed of pale-yellowish-gray very fine 

grained sandstone at tOP--------------------- 4 

16. Sandstone, grayish-yellow to dusky-yellow, fine~ 

grained, thin-bedded, diff-forming; contains 

small u~sha.ped burrows and small OphionLorpha ------------------------------------ 17 

15. Sandstone and shale interbedded ; contains a 

1-ft-thick bed of carbonaceous shale at top____ 10 

14. Sandstone, like unit 16------------------------ 10 

13. Shale, dark-gray, flaky; contains at 10 ft above 

base a 0.4-ft-thick uy 1.5-ft-wide orangeweathering lens of limestone with cone-in-cone 

structure ___________________________________ 20 

12. Shale, brownish-gray to brownish-black; con~ains 

2 layers of ironstone concretions. Upper 10 ft 

is reddish-brown carbonaceous shale__________ 29 

11. Sandstone and shale interbedded; grades into 

overlying sandstone_________________________ 10 

10. Sandstone, pale-yellowish-gray; fine-grained, thinbedded, cliff-forming ; contains many smooth 

burrows and a few Opldomo1·pha------------- 60 

9. Sandstone, dusky-yellow to yellowish-gray, finegrained, massive ; ,stained with yellow limonite---------------------------------------- 8 

8. Sandstone, dusky-yellow to light-gray, fine-grained, 

thin-bedded, ripple-marked; contains burrows__ 9 

7. Shale, dark-brown, poorly exposed; contains a few 

thin layers of sandstone______________________ 15 

6. Sandstone, yellow,ish.-gray, fine-g.rained, thinbedded ; lower part weathers dusky yellow and 

upper part weathers light gray; .contains bUirrows ---------------------------------------- 12 

5. Shale, dark-brown ; contains ironstone concretions --------------------------------------- 37 

4. Sandstone, yellowish-gray, very fine grained; 

'veathers light graY-------------------------- 2 

3. Shale, like unit 5------------------------------ 10 

~-

•, 
... ~ 

...... 

..... 

- . 

.... 

ALMOND FJORMATION 35 

llefm·cncc sect·ion 1 of the A.lmoncl Formation--Continued 

Almond ll'ormation-Continued 

2. Sandstone, yellowish-gray to pale-yellowish-gray, 

flue-grained, thb-beclcled to massive, cliff-forming; weathers light gray; contains large Ophion•orpha in upper part________________________ 25 

1. Shale, reddish-brown, carbonaceous______________ 11 

1'otal Almond )!"'ormation __________________ 608 

Pine Ridge Sandstone. Not measured. 

ncte?·cncc sect·ion 2 ot the A.lmona Fo1·mation 

[l\lenslll'ed by .T. n. Gill and G. A. Bergman, August 1967. Fossils 

Identified by W. A. Cobban. Measured in the C SE%, and the SE%,-

SW% sec. a, '1'. 20 N., R. 85 W., Cnrbon County, Wyo. (Savage 

Hanch 7%-mlnute ((\11\d.), loc. G, fig. 1.] 

I.Jewis Shale (.pru,t) : Feet 

54. Shale, clark-grny, poorly exposed; contains 

highly fractured brown-weathering silty limestone concretions nt 100 and 180 ft above 

bnse -------------------------------------- 180 

USGS D6305, from top of unit: 

Bacu-lites eUasi Cobban 

~l'otal Lewis Shale measured________ 180 

AllllOIId lfOI'JliiH t:iOII : 

f.i3. Sandstone, yellowish-gray, fine-grained; cemented with iron ; contains abundant oysters-- 4 

USGS D6310: 

C·mssost1·en ylab1·a (Meek and Hayden) 

G2. Shale, reddish-brown to yellowish-gray; upper 

2 ft very carbonaceous______________________ 9 

Gl. Shale, blacl{, coalY-------------------------- 2 

riO. Sandstone, pale-yellowish-gray, very fine 

grained, ripple-laminatecL__________________ 4 

4!). Shale, clark- to brownish-gray, flal{y; contains 

n layer of ironstone concretions at 10 and 15 

ft above base------------------------------ 36 

48. Sandstone, pale-yellowish-gray, fine-grained, 

soft -------------------------------------- 5 

47. Sandstone, like unit 48; contains numerous 

oyster shells------------------------------ 2 

USGS D6309: 

Cmssost1·ea ylab1·a (Meel{ and 

Hayden)'! 

t.l:6. Sandstone, pale-yellowish-gray, fine-grained ; 

soft in lower part and more resistant near 

top; nt 60 ft nbove base are orange-weathering sandstone concretions 2 ft thick and 4 

ft in diameter; contains Ophionwrpha______ 75 

45. Sh11le, olive-gray at base becoming clark gray at 

top -------------------------------------- 10 

44. Snndstone, pale-yellowish-gray, fine-grained, 

soft ------------------------------------- 3 

43. Shale, dark-gray to blacl{, flaky ; contains a 

layer of ironstone concretions at 10 ft above 

base and at top___________________________ 22 

42. Siltstone, pale-yellowish-gray, ripple-lami-

. nated ------------------------------------ 10 

41. Covered ; appears to be shale ; weathers yellowish graY---------------------------------- 17 

Rcte1·cncc section 2 of the ;llmoncl Fonnation-Continued 

Almond Formation-Continued 

40. Shale and sandstone interbedded; sandstone 

in beds less than 0.2 ft thick weathering yellowish gray to moderate orange with much 

iron stain; outcrop weathers light reddish 

brO\Vn ----------------------------------- 15 

USGS D6308: 

Inoce1·am1t-8 sp. 

39. Shale, olive- to brownish-gray---------------- 13 

38. Sandstone, pale-yellowish-gray, fine-grained; 

weathers light yellow to yellowish gray; contains Ophiom01·pha________________________ 12 

37. Shale, dark-gray, poorly exposed____________ 10 

36. Sandstone, like unit 38, but very thin bedded__ 4 

35. Shale, reddish-brown to black, carbonaceous__ 4 

34. Sandstone like unit 38, but contains at 18 ft 

above base sandstone concretions 2 ft thick 

and 12 ft in diameter______________________ 28 

33. Covered; probably shale_____________________ 20 

32. Shale, medium-gray, platy; contains a few 

ironstone concretions______________________ 30 

31. Sandstone, yellowish- to light-gray, thin-bedded; soft at base and hard at top; weathers 

light graY-------------------------------- 8 

30. Covered; appears to be shale________________ 4 

29. Sandstone, lil{e unit 38, but contains large 

Ophiomo1·pha ----------------------------- 8 

28. Sandstone, like unit 38, but thin to medium 

bedded; forms cliff---------~------------- 4 

27. Shale, .brownish-gray, carbonaceous__________ . 5 

26. Sandstone, like unit 38, but thin beclclecl to massive; forms cliff___________________________ 18 

25. Sandstone, light-brown, fine-grained, very thin 

bedclecl ; contains thin laminae of brownishgray carbonaceous shale__________________ 7 

24. Sandstone, pale-yellowish-gray, very fine 

grained, lenticular_________________________ 3 

USGS D6307: 

Inoceranws sp. 

23. Sandstone, light-brown, very fine grained; 

interlaminated with brownish-gray carbonaceous shale; muddled bedding_____________ 10 

22. Siltstone, pale-yellowish-gray; very thin bedded 

at base to massive at top; contains laminae 

of carbonaceous shale_____________________ 10 

21. Claystone, medium-light-gray_________________ 2 

20. Sandstone, like unit 23; weathers light yellow__ 3 

19. Shale, clark-graY---------------------------- .5 

18. Siltstone, like unit 22------------------------ . 5 

17. Shale, dark- to brownish-gray ; weathers 

splinterY---------------------------------- 2.5 

16. Sandstone, pale-yellowish-gray, fine-grained, 

thin-bedded; local iron-cemented masses of 

sandstone in upper part___________________ 10 

USGS D6306: 

Inoceramus oblongus White 

15. Claystone, dark- to brownish-gray___________ 2. 5 

14. ·Sandstone, yellowish-gray, fine-grained; in beds 

0.1-1.5 ft thick____________________________ 11 

13. Claystone, medium-light-gray_________________ 1 
36 · STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

Reference section 2 ot the Almond Fonnation---Continued 

Almond Formation-Continued 

12. Sandstone, like unit 14---------------------- 4 

11. Coal, black, impure_____ ____________________ 1. 5 

Total Almond Formation______________ 446 

Pine Ridge Sandstone: 

10. Sandstone, light-brown, very fine grained; in 

beds 0.05--0.1 ft thick; contains abundant carbonaceous fragments and carbonaceous shale 

to impure coal laminae; weathers dusky 

yellow to light gray__________________ _____ 17 

9. Shale, brownish-gray, carbonaceous__________ 7 

· 8. Sandstone, like unit 10---------------------- 6 

7. Claystone, dark-brownish-gray, carbonaceous__ 3 

6. Sandstone, like unit 10---------------------- 4 

5. Shale, dark-gray; ironstone concretionary layer 

at base___________________________________ 4 

4. Sandstone, like unit 10---------------------- 13 

Total Pine Ridge Sandstone______ ______ 54 

Allen Ridge Formation : 

3. Shale, medium-dark-gray to brownish-gray; 

contains se1·eral thin layers of sandstone and 

siltstone --------------------------------- 24 

2. Sandstone, pale-yellowish-gray, very fine 

grained, thin•bedded and ripple-marked. 

Weathers dusky yellow to light gray; contains some U-shaped btu'l'OWS-------------- 4 

1. Sandstone and shale interbedded, not measured 

and described in detaiL------------------- 1, 325 

Total Allen Ridge Formation (rounded)_ 1, 350 

Total Mesaverde Group measured 

(rounded) ------------------------- 1,850 

LEWIS SHALE 

TYPE LOCALITY AND DISTRIBUTION 

The Lewis Shale was named by Cross and Spencer 

(1899) for exposures of a thick marine shale near Fort 

Lewis, east of Mesa Verde National Park in southwestern Colorado. The Lewis Shale of southwestern 

Colorado is neither an e~tension of, nor the same age 

as, the Lewis Shale of south-central Wyoming. The 

name is retained in Wyoming only because of longestablished usage in the region. (Seep. 3 and 5.) 

Rocks assigned to the Lewis Shale are widely distributed in Wyoming. The Lewis is recognized in the 

Laramie, Carbon, Hanna, Great Divide, Washakie, 

Powder River Basins, eastern part of the Bighorn and 

vVind River Basins, and around the Rock Springs uplift. In eastern ·wyoming, rocks equivalent to the Lewis 

Shale are in the upper part of the Pierre Shale. 

LITHOLOGIC CHARACTER 

The Lewis Shale of south-central \Vyoming consists 

of 2,200-2,600 feet of shale, siltstone, and sandstone. 

Much of the variation in thickness may result from differences in opinion as to the placement of the upper and 

lower contacts of the formation. Both the overlying 

Fox Hills Formation and the underlying Almond Formation intertongue -with the Lewis Shale on a regional 

scale. In the northern part of the Laramie Basin, the 

Lewis Shale contains many thick beds of sandstone 

that are either tongues of the Fox Hills Formation or 

offshore marine units deposited marginal to the Almond Formation. In this area, Hyden ( 1965) and McAndrews (1965) included the nonresistant sandstones 

of the Fox Hills with the Lewis Shale for mapping. 

\Vhere this procedure was follo'"l·ed, the Lewis Shale 

may contain more than 50 percent sandstone. 

Sandstone of the Lewis is very fine to medium 

grained, thin bedded to massive, and pale yellowish 

gray to brown. It is generally nonresistant, but where 

concretionary, it forms ridges that can be traced for 

many miles (fig. 11). Sandstone units in the lower part 

of the Lewis commonly contain molluscan fossils and 

Ophiomm·pha. The middle and upper parts of the formation contain a distinctive and widespread unit o-f interbedded sandstone and sandy shale that ranges in 

thickness from 300 to at least 700 feet. This unit is assigned in this report to the Dad Sandstone Member of 

the Lewis Shale. 

The shale of the Lewis is dominantly dark gray to 

olive gray, silty to sandy, and nonresistant, and, locally, 

contains fossiliferous limestone or siltstone concretions. 

FIGURE 11.--.Fossiliferous sandstone concretions weathered 

from a soft friable sandstone in the lower part of the Lewis 

•Shale, in the NW% sec. 6, T. 22 N., R. 79 W., Oarbon County, 

Wyo. These distinctive concretions can be traced along the 

entire east side of t'he Carbon and Hanna Basins. 

,

I
.., 

LEWIS SHALE 37 

A distinctive unit of black shale several hundred feet 

thick forms the basal part of the Lewis in the northern part of the Laramie Basin (fig. 12). The siltstone 

of the Lewis is yellowish gray, nonresistant, and poorly 

exposed. 

The Lewis Shale is almost entirely marine in origin. 

The shale of. the Lewis represents a marine depositional 

environment but may contain a few thin units of brackish-water origin. The sandstone in the formation contains Ophiomorpha in places and was probably 

deposited in nearshore marine environments. 

A distinctive unit of interstratified sandstone and 

shale occurs in the middle and upper parts of the Lewis 

Shale in south-central "'Vyomn1g. In the W'ashakie 

Basin, these rocks were called the Dad Member of the 

Lewis by Hale (1961, p. 136-137) and were described 

n.s follows : 

Approximrutely seven miles due west in the Dad area, wells 

have d1illecl ·a to tal of 2,300 feet of Lewis 'but diS<:lose a series of 

sandstones and minor shales 1,000-1,400 feet thick which divides 

the Lewis into upper and lower . hale units. This sanely member is here called the Dad member of the Lewis shale for typical development in the Union Texas Ga s Company Dad Un'it 

2 well between 6,385 feet '!tncl 7,805 f eet. This well is located in 

sec. 13, T. 16 N., R. 93 W. 

We have examined the Lewis Shale along the east 

margin of the ·washakie Basin and can identify the Dad 

Sandstone Member in this and adjacent areas. The Dad 

Sandstone Member is much thim1er where exposed than 

in the subsurface at the Dad Unit well 2. We measured 

a reference section of the Dad Member in the NW1,4 

NE1,4SW1,4 sec. 28, T. 15 N., R.. 91 W ., Carbon County, 

and determined the thickness to be about 585 feet. The 

Dad Sandstone Member can be traced northward along 

the east margin of the Washakie and Great Divide 

Basins, where it has been mapped as the lower part of 

the Lance Formation (Love, and others, 1955). Ten 

miles northwest of Rawlins, the Dad is 735 feet thick. 

(See reference section of the Lewis Shale.) 

The Dad Sandstone Member of the Lewis Shale is 

actually a tongue of the Fox Hills Formation. It can 

be trn.ced from near Rawlins northward along the east 

margin of the Great Divide Basin, where the upper 

shale unit of the Lewis grades into sandstone and the 

1mderlying sandstone beds of the Dad grade into rocks 

of the Fox Hills Formation (M. W. Reynolds, oral 

commun., 1968). 

The Dad Sandstone Member occurs throughout the 

Hanna (fig. 13) and Carbon Basins and is a thick unit 

of poorly exposed sandstone in the northern part of the 

Laramie Basin. The Dad Member probably is a result of 

an uplift in central Wyoming and consequent increase 

in the amount of sediment deposited in the Lewis Sea. 

In the western part of the Powder River Basin, regressive deposits of sandstone, shale, and coaly rocks in the 

upper part of the Lewis Shale represent the same tectonic event that caused deposition of the Dad Sandstone Member. Similar rocks divide the Lewis Shale into 

two parts in the southeasteri1 part of the Wind River 

FIGURE 12.-Dark shale of the lower part of the Lewis Shale exposed along the Pl-atte River, in the NE:IASW:IA sec. 11, T. 20 

N., R. 85 W., Carbon Oounty, Wyo. 
38 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

FIGURE 13.-Ciiff-forming sandstone of the Dad Sandstone Member of the Lewis Shale, in the SWI,i sec. 14, T. 20 N., R. 83 W., 

Carbon County, Wyo. 

Basin. In this area these rocks are called the Meeteetse 

Formation (Rich, 1962, p. 469-4 79). Abundant fossils 

from many localities are evidence that the Dad Sandstone Member of the Lewis Shale, the regressive sandstone tongue in the upper part of the Lewis of the 

Powder River Basin, and the Meeteetse Formation in 

the W"ind River Basin were deposited during the range 

of B aculites grandis. 

THICKNESS 

The thickness of the Lewis Shale is not easily determined at most localities because the formation is poorly 

exposed. Rocks of the Lewis Shale are nonresistant, and 

the contract with the overlying Fox Hills Formation is 

transitional and poorly exposed. Most previous workers 

have included the soft sandstones of the Fox Hills with 

the Lewis Shale (for example, Hyden, 1965; Davidson, 

1966), and this assignment causes the thickness of the 

Lewis to be excessive when compared to its thickness in 

areas where the Fox Hills is recognized. Davidson 

(1966, p. 26) reported tha.t the Lewis is 3,900 feet thick 

in the northeastern part of the Hanna Basin. He included the Fox Hills in the Lewis, and in this area the 

Fox Hills is more than 700 feet thick. Davidson (1966, 

p. 26) also reported that the Lewis is 3,000 feet thick at 

Mill Creek in the southwestern part of the Laramie 

Basin, but he included an unknown thickness of the Fox 

Hills with the Lewis. Hyden (1965) showed the Lewis 

to be about 2,500 feet thick in the northern part of the 

Laramie Basin, but he also included an unknown thickness of the Fox Hills in the Lewis. 

The maximum thicknesses of the Lewis that we have 

measured are 2,600 feet on the southeast flank of the 

Carbon Basin and 2,300 feet on the northwest side of 

the Hanna Basin. These and other measurements are 

evidence that the Lewis thins from south-central 

Wyoming in a north and northwest direction. The Lewis 

is about 2,300 feet thick near Rawlins (see reference 

section) , but, where traced north ward along the east 

flank of the Great Divide Basin, it thins owing to facies 

changes and nondeposition. Thirty miles north of 

Rawlins, near Bairoil, the lower part of the Lewis Shale 

is absent because of nondeposition; the upper part 

changes facies and is represented by beds assigned to 

the Fox Hills and Lance Formations (M. W. Reynolds, 

oral commun., 1968). 

RELATION TO ADJACENT FORMATIONS 

The Lewis Shale gradationally overlies the Almond 

Formation in the area of this report, except in the 

Laramie Basin where it rests sharply on the Pine Ridge 

Sandstone. Locally, as in the Lamont area (fig. 1), the 

Lewis Shale rests unconformably on beds as old as the 

Cody Shale (Reynolds, 1966). The Lewis also grades 

into the overlying sandstone of the Fox Hills Formation. At this contact, sandy shale of the Lewis merges 

gradually into the clayey sandstone of the Fox Hills. 

Northward and northwestward thinning of the Lewis 

is associated with a facies change from marine shale to 

the south to nearshore marine sandstone and to fluviatile 

deposits to the north. 

FOSSILS 

The Lewis Sea sustained a large and varied invertebrate marine fauna. Large collections of fossils from 

many localities show that the Lewis Shale was deposited 

in the eastern part of the area during the range of six 

successive ammonite zones. These ammonites are listed 

below, with the youngest species at the top: 

BacuUtes clinolobatus 

grandis 

bacultts 

eliasi 

jenseni 

reesidei 

.... 
.... 

.. 

~· 

.... 

·~· 

LEWIS SHALE 39 

Many other invertebrate fossils were found in association with these ammonites, and some of these are 

listed in the reference section of the Lewis. 

AGE AND CORRELATION 

In comparison with the classic Cretaceous section of 

central Montana, the Lewis Shale of the Laramie Basin 

.is equivalent to the uppermost Bearpaw Shale, the Fox 

I-Iills Sandstone, and the lower part of the IIell Creek 

Formation. The Lewis Sea remained in south-central 

vVyoming after receding from centrall\{ontana; consequently, the upper part of the Lewis Shale in the report 

area is equivalent to nonmarine rocks of the Hell Creek 

Formation in centrall\{ontana. 

The Lewis Shale correlates with the Meeteetse 

Formation of the western 'iVincl River and Big Horn 

Basins and with the upper unnamed shale member of 

the Pierre Shale in the eastern Powder River Basin 

(Gill and Cobban, 1966a, pl. 4). The Lewis is equivalent 

to the Almond Formation and the Lewis Shale of the 

Rock Springs uplift and approxim·ately equivalent to 

the Lewis Shale of northwestern Colorado. 

REFERENCE SECTIONS 

Two reference sections are described. One is the principal reference section for the newly adopted Dad Sandstone Member of the Lewis, and the other is a reference 

section of the Lewis Shale and Fox Hills Formation in 

the western part of the report area. 

Principal ?'Gfcrcncc sect·ion of the DacZ Sandstone Member of the 

Lewis Sha.le 

[Measured with planetable and Jacob's staff by J. R. Gill and G. A. 

Bergman, August 1067. Measured on the south side of Wild Cow 

Ct·eek from the SW%,SW%NW% sec. 27 to the NW%,NE%,SW1Jl, 

sec. 28, ~'. lu N., R. 01 w., Carbon County, Wyo. (Baggs 15-mlnute 

()tlll<lrlltllgle), loc. 1, fig. 1.) 

T.Jance Formation: Feet 

19. Shale, dark-brown to blacl~, carbonaceous to 

lignitic -------------------------------- 30 

18. Sandstone, light-gray, very fine grained, uplX'.r part cemented with limonite; weathe.t·s white-----------------------·-------- 4 

17. Shale, gray, slightly carbonaceous; weathers light grar--------------------------- 5 

Total Lance Formation measured____ 39 

JJ'ox Hills Formation: 

16. Sandstone, pale-yellowish-gray, very fine 

grained; contains a 1-ft-thick layer of highly fractured siltstone concretions overlain 

by a light-b.rown- to gray-weathering sandstone, concretion 4 ft thick and 20 ft in 

diameter ------------------------------- 70 

15. Shale, gray, very sandy, soft; weathers yellO\vish graY----------------------------- 40 

Principal ?'eference section of the Dad Sandstone M mnbe1· of the 

Lewis Shale-Continued 

Fox Hill Formation-Continued 

14. Sandstone, pale-yellowish-gray, soft; contains local lenses 4 ft thick by 30 ft in diameter of light-brQwn-weathering concretionary sandstone_______________________ 40 

Total Fox Hills Formation___________ 150 

= Lewis Shale : 

Upper pa.rt : 

13. S·hale and sandstone interbedded; shale dominant; sandstone in thin beds 0.1-0.4 ft 

thick; weathers yellowish gray----------- 110 

12. Shale, olive-gray, flaky, sandy near toP---- 220 

Total upper part___________________ 330 

Dad Sandstone Member : 

11. ·sandstone, pale-yellowish-gray, very fine 

grained, soft ; contains shale pebbles in 

lower part and a 0.3-ft-thick bed of platyweathering siltstone at base____________ 60 

10. Shale, olive-gray, sandy; weathers yellowishgray ----------------------------------- 15 

9. Sandstone, pale-yellowish-gray, very fine 

grained, soft ; contains at top light-brownweathering sandstone concretions 4. ft thick 

and 8 ft in diameter-------------------- 25 

8. Shale, olive-gray, sandy ; contains a few sandstone laminae in middle part; weathers 

yellowish graY-------------------------- 150 

7. Sandstone and shale, yellowish-gray, soft; 

contains local masses of concretionary 

sandstone 2-3 ft in diameter ___________ _ 

6. Sandstone, pale-yellowish-gray, very fine 

grained ; contains some tuberous-shaped 

and cannonball-like concretions as much as 

1.5 ft in diameter; forms low ridge _____ _ 

G. Shale, gray ; weathe.rs yellowish gray; contains a few thin beds of fine-grained soft 

40 

40 

sandstone ------------------------------ 105 

4. Sandstone, pale-yellowish-gray, very fine 

grained ; contains brown-weathering cannonball concretions 1.5 ft in diameter and 

large concretionary masses 8 ft thick by 

20 ft in diameter________________________ 50 

3. Shale, gray, sandy; weathers light g~ay_____ 20 

2. Sandstone, paie-yeilowish-gray, very fine 

grained, soft ; upper part poorly exposed 

and may contain some thin beds of sandy 

s'hale; contains some thin tabular masses 

of concretionary sandstone_______________ 80 

Total Dad Sandstone l\1(!mber -------- 585 

·Lower part : 

1. Shale, gray, sandy ; weathers grayish yellow ; 

contains 2 thin layers of yellow limestone 

concretions 50 ft below top ; thickness not 

measured. 
40 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

Reference section of the Fow Hills Formation and Lewis Shale 

(including Dad Sandstone .Member) 

[l\Ieasured with planetable and Jacob's staff by J. R. Glll and G. A. 

.Bergman. Fossils identified by W. A. Cobban. Measured. on the north 

side of Indian Springs Creek starting in the SW~SW~ sec. 1,3 a.nd 

ending in the SE%,SE~ sec. 14, T. 22 N., R. 89 W., Carbon County 

Wyo. (Rawlins Peak 15-minute quadrangle.)] 

Lance Formation : 

40. Shale and sandstone interbedded; sandstone beds are thin and lenticular; shale 

beds are carbonaceous-----------------

USGS D6334, from 10 ft above base of 

unit: 

Oorbiettla fracta (Meek) 

39. Shale, dark-brown to 'black, ca~bonaceous 

38. Coal, lignitic, black _____________________ _ 

Total Lance Formation measured __ 

Fox Hills Formation: 

37. Sandstone, pale-yellowish-gray, very fine 

grained, massive; weathers yellowish 

gray ; contains some concretionary 

Feet 

30 

3 

1.2 

34.2 

masses ------------------------------ 33 

36. Shale and sandstone intef!bedded, ,soft ; 

weathers yellowish gray; contains local 

concretionary ledges of lbrown ... weathering sandstone as much as 2 ft thick____ 32 

35. Sandstone, pale-yellowish-gray, very fine 

grained; contains Ophiomorpha________ 1 

USGS D6333: 

Orassostrea sp. 

Pholadomya n. · sp. 

Tancredia 'I sp. 

Ethmocardium n. sp. 

Legumen sp. 

Oymbophora sp. 

Baculites sp. 

34. Shale, gray, sandY---------------------- 8 

33. Shale, dark-brown, carbonaceous--------- 4 

USGS D6332: 

Orassostrea sp. 

32. Coal, lignitic, impure, black_____________ 1 

31. Sandstone, pale-yellowish-gray, concretionary at base, soft at top; weathers light 

gray ; contains Ophiomorpha___________ 51 

30. Sandstone and shale, interbedded in equal 

amounts, soft; weathers yellowish gray_ 31 

29. Sandstone, pale-yellowish-gray, very fine 

grained, concretionary at top___________ 11 

Total Fox Hills Formation______ 172 

Lewis Shale : 

Upper part: 

28. Shale, gray, silty to sandy, sandier toward 

top; weathers yellowish gray; contains 

three layers of siltstone concretions____ 67 

27. Sandstone, pale-yellowish-gray, very fine 

grained; weathers yellowish gray ; top 

locally cont·ains large masses of concretionary sandstone_____________________ 22 

Reference section of the Fow Hills Formation and Lewis Shale 

(including Dad Sandstone .Member)-Contlnued 

Lewis Shale-Continued 

Upper part--continued 

26. Shale and sandstone; weathers yellowish 

gray; contains orange-brown-weathering 

sandstone concretions 5 ft thick and 15 ft 

in diameter---------------------------

25. Shale, medium-dark-gray; weathers dark 

gray; contains sparse gray limestone con- cretions in middle ____________________ _ 

24. Sandstone, yellowish-gray to dusky-yellow, 

fine-grained, soft; contains numerous 

concretions and Ophiomorpha in upper 

part. Probably represents a northward 

thickening tongue of the Fox Hills 

Sandstone --------------------------- USGS D6248: 

Ora.ssostrea glabra (Meek and 

Hayden) 

23. Shale and s-andstone interbedded, soft; 

55 

33 

85 

weathers yellowish graY--------------- 55 

22. Siltstone and shale interbedded; weathers 

yellowish gray ; contains local lenslike 

concretionary masses of orange-brownweathering siltstone in upper part______ 81 

21. Shale, dark-gray; forms dark band on out-

·crop; contains a 0.1-ft-thick bentonite 

overlain .by a thin layer of dark-gray 

limestone concretions__________________ 37 

USGS D6331, from limestone concretion: 

"Inoceramus" fibrosus (Meek and 

Hayden) 

Baculites sp. 

USGS D558S, from this level in the 

Slh.SWIA, sec. 6, T. 21 N., R. 88 W. : 

"Inoceramus" fibrosus (Meek 

and Hayden) 

Lucina sp. 

Baculites cf. B. clinoZobatus 

Elias 

Hoploscaphites sp. 

20. Shale, yellowish-gray, very sandy; contains small limestone concretions at top__ 20 

USGS D6330: 

Baculites sp. 

19. Shale, medium-gray; weathers light .gray; 

contains a 0.1-ft-thick -bentonite with 

fibrous calcite at 6 ft below top (this 

bentonite is about 2 ft thick a few miles 

to the south)-------------------------- 70 

Total upper part_________________ 525 

Dad Sandstone Member : 

18. Sandstone, yellowish-gray to pale-yellowish-gray, very fine grained, soft, friable; 

contains randomly distributed 5-ft-thick 

by 10 ft in diameter masses of concretionary sandstone_____________________ 56 

17. Shale, gray, sandy; contains thin ·laminae 

of sandstone-------------------------- 34 

\-

•,A_. 

... 
.~ 

.. ~ 

.. )... 

~· 

FOX IDLLS FORMATION 41 

llefet·ence sect·lon of the li'orc Hills Fot·mation and Le'wis Shale 

( inchtcling Dad Sandstone 111 ember) -Continued 

Lewis Shale-Continued 

Dad Sandstone Member-Continued 

16. Shale, gray ; weathers light gray ; contains 

thin siltstone laminae cemented with 

limonite ------------------------------ 89 

15. Siltstone, gray ; weathers yellowish gra.y __ 50 

14. Sandstone, lig·ht- to dusky-yellow, glauconitic, fine-grained, soft; contains sandstone concretions 8 ft thick and 15 ft in 

d-iameter ----------------------------- 77 

USGS D6629: 

Ostrea sp. 

Arctica? sp. 

13. 'Shale, light-gray, sandy in upper half; 

weathers yellowish gray ______________ _ 

12. Sandstone, yellowish-gray, fine-grained, 

soft; contains thin laminae of shale ___ _ 

11. Shale, gray, sandy; weathers pale yellowish 

gray to light gray---------------------

10. Sandstone, yellowish-gray to dark-yellowish-orange, fine-grained, soft, friable ; 

contains abundant burrows and near top 

fossiliferous sandstone concretions 1.5 ft 

thick and 3 ft in diameter-------------

USGS D6328, from top of unit: 

111 icmbacia sp. 

Calcareous worm tube 

Bryozoan 

"lnoceram1ts" fibt·osus (Meek and 

Hayden) 

Pteria linguaeformis (Evans and 

Shumard) 

Ostrea russelU Landes 

Pecten sp. 

Anomia sp. 

111 Olliolus galpiniana (Evans and 

Shumard) 

Pholadomya u. sp. 

Goniomya americana Meek and 

Hayden 

Dt·epanochilus sp. 

BacuUtcs gra.ndi.'l Hall and Meek 

Discosca.phitcs sp. 

9. Poorly exposed. Appears to be sandy shale 

69 

10 

70 

45 

with numerous thin beds of sandstone___ 110 

8. Sandstone and sandy shale interbedded, 

pale-yellowish-gray, thin-bedded, ripplelaminated; weathers in light-brown concretionary and sl·abby ledges 2-5 ft thick 115 

Total Dad Sandstone Member------ 725 

Lower part: 

7. Shale, poorly exposed, .sandy; 15 ft above 

. base is ·a layer of limestone concretions-- 250 

USGS D6327: 11lnocerwmus" fibrosus (Meek and 

Hayden) 

BacuZites sp. 

6. Sandstone, pale-yellowish-gray, very fine 

grained; weathers concretionary locally 5 

5. Shale, gray, sandy, poorly exposed-------- 45 

Reference section of the Fore Hills Formation and Lewis Shale 

(including Dad Sandstone 111 ember) -Continued 

Lewis Shale-Continued 

Lower part---'Continued 

4. Sandstone, pale-yellowish-gray, very fine 

grained, thin-bedded ; locally concretionary ---------------------------------- 15 3. Shale, gray, poorly exposed______________ 405 

2. Shale, dark-gray, flaky; contains several 

layers of dark-reddish.Jbrown-weathering 

limestone concretions, some of which are 

septarian ---------------------------- 340 

USGS D6326, from 50 ft a•bove base: 

BacuZites eliasi Cobban 

Total lower part_ _____________ 1, 060 

Total Lewis Shale _____________ 2, 310 

Almond Formation (part): 

1. Sandstone, yellowish-gray to grayish-yellow, fine- to medium-grained, thinbedded ; contains many oysters in lower 

10 ft and abundant Ophiomorpka in UPper ·part------------------------------ 25 

USGS D6325: 

Orassostrea glabra (Meek ·and 

Hayden) 

FOX HILLS FORMATION 

TYPE LOCALITY AND DISTRIBUTION 

The Fox Hills Formation was named by Meek and 

Hayden ( 1862, p. 419) ror exposures of siltstone and 

sandstone on Fox Ridge between the Grand and 

. Moreau Rivers in central South Dakota. The name has 

been used in South Dakota, North Dakota, Montana, 

Wyoming, and Colorado for rocks that are transitional 

with the underlying marine shale of the Pierre and 

Lewis and with the overlying fluviatile beds of the 

Hell Creek, Lance, and Medicine Bow Formations. 

Early geologists (for example, Dobbin, Bowen, and 

Hoots, 1929, p. 23) recognized rocks equivalent to the 

Fox Hills in south-central Wyoming but included them 

in either the upper part of the Lewis Shale or the lower 

part of the Medicine Bow Formation. Dorf ( 1938, p. 6) 

assigned the name Fox Hills Formation to the marine 

sandstone and 1narine to nonmarine shale that had previously been included in the lower part of the Medicine 

Bow Formation. We accept Dorf's assignment for. the 

area of this report and have identified the Fox Hills in 

the Hanna, Carbon, and Laramie Basins . 

LITHOLOGIC CHARACTER 

The Fox Hills Formation consists dominantly of 

thick units of friable sandstone but includes units of 

shale. Sandstone units are pale yellowish gray, very 

fine to fine grained, weather yellowish gray to light 
42 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. J' 

brown, .and commonly contain fossiliferous sandstone 

concretions. They are thin bedded to massive, crossbedded and ripple bedded, ·and generally nonresistant, but 

loca.Ily they a.re well cemented and cliff forming. The 

shale units are olive gray to dark gray, ma.inly sandy, 

nonresistant, and generally poorly exposed. Thin units 

of carbonaceous shale containing brackish-water fossils 

or thin impure beds of coal crop out in some areas. 

Ophiomorp.ha is common in the sandy rocks, and oysters 

are loca1ly abundant in beds of sandstone or shale. 

THICKNESS 

The Fox Hills l.'anges in thickness from less than 

200 feet along the east side of the Great Divide and 

vVashakie Basins to at least 700 feet along the east side 

of the Carbon Basin near Medicine Bow; ·at other localities it ma.y be thicker. 'Ve interpret the differences in 

thickness to be a result of different rates of subsidence 

and sediment delivery. In areas of maximum thickness, 

the rates of sedimentation and subsidence were probably 

about equal; consequently, the strandline was nearly 

stationary for a long period of time. Where the Fox 

Hills is thin, the strandline probably retreated seaward 

at a relatively rapid rate. 

RELATION TO ADJACENT FORMATIONS 

The sandstone of the Fox Hills Formation intertongues with the m·arine shale of the Lewis and with the 

brackish-water ~and fluviatile shale and sandstone of 

the Medicine Bow Formation. The Fox Hills represents 

a transitional depositional environment between a 

deeper water marine environment ·and the lagoonal and 

continental environments. The formation resulted from 

the deposition of sediments in shallow marine, barrier 

bar, and beach environments as the Cretaceous sea withdrew from the area of the northern Rocky Mountains. 

The contact between the Lewis and Fox Hills is progressively lower in the section in ·a north and northwest 

direction because the marine shale of the Lewis is replaced laterally by the shallow-water marine sandstone 

of the Fox Hills. The lower contact of the Fox Hills 

Formation is placed a.t the horizon below which the 

rocks are predominantly marine shale. The upper contact is located at the horizon above which the rocks are 

predominantly of fresh- and brackish-water origin, 

including coal and carbonaceous shale, a.nd below which 

the rocks a.re predominately of marine origin. These 

criteria are similar to those proposed by Lovering, 

Aurand, Lavington, and Wilson (1932, p. 702) for the 

recognition and delineation of the Fox Hills in northeastern Colorado. 

FOSSILS 

The Fox Hills Formation contains a shallow-water 

marine fauna consisting of a la.rge variety of clams and 

snails. In the area of this report it also contains three 

distinctive types of ammonites which are B aculites clinolobatus, Sphenodiscus ( Ooahuilites) sp., .and Discoscaphites sp. B ar:nr:lites clinolobatus is an index ammonite 

found in the upper part of the Pierre Shale in eastern 

Wyoming, South Da.kota., and eastern Colorado where 

the Fox Hills is younger than in south-centra.! 'Vyoming. The following three collections of fossils, identified 

by W. A. Cobban and N. F. Sohl, are representative of 

the fauna of the Fox HHls in south-central Wyoming: 

USGS D5538. NE*SElA, sec. 16, T. 21 N., R. 79 ,V., Carbon 

County. 

From 215 ft below the top of the Fox Hills Formation. 

Lingula sp. 

Nttet(,la planirnarginata Meek and Hayden 

Oxytorna neb1·ascana (Evans and Shumard) 

Olarnys nebrascensis (Meek and Hayden) 

CreneZla sp. 

Astarte sp. 

Clisocolus sp. 

Protocardia rara (Evans and Shumard) 

Legurnen sp. 

TeZlina sp. 

Dentaliurn sp. 

Euspirasp. 

Ellipsoscapha sp. 

Cylichna volvaria (Meek and Hayden) 

Oligotycha concinna (Hall and Meek) 

Baculites sp. 

Aptychus 

USGS D5539. SE*N\V* sec. 21, T. Z1 N., R. 79 ,V., Carbon 

County. 

From the middle and upper parts of the Fox Hills Formation. 

Dysnoetopora demissa (White) 

Lingt(,la nitida (Meek and Hayden) 

"Inoceranws" fibrosus (Meek and Hayden) 

Pseudoptera n. sp. 

Oxytorna nebrasca1~a (Evans and Shumard) 

Ostrea sp. 

Ethrnocarditm,. sp. 

P1·otocardia sttbquadrata (Ev·ans and Shumard) 

Venerid pelecypod 

Legumen ellipticum (Conrad) 

Gyro des? sp. 

Baculites clinolobatus ,Elias 

Discoscaphites sp. 

·~ 
~-

.. ,).. 

MEDICINE BOW FORMATION 43 

USGS 05540. SWI;.J,NWY.~ sec. 11, T. 21 N., R. 79 ,V,, Carbon 

County. 

From 30 ft above the. bnse of the Fox Hills Formation. 

Bryozoan 

Lingula nitilla Meek and Hayden 

am·vi.lUa sp. 

"Inooer(mws'~ fib1·osn.q (Meek and Hayden) 

P8C1HlOt>tem n. sp. 

Syncyclonema sp. 

PlloZnclomya n. sp. 

Jllthmocan1i·u.m n. sp. 

ProtOC(l1'd·in .mbqua(lrata, (I~ vans and Shumard) 

Venerld pelecypod 

Legnme:;n cZli·1Jt-iowm Conrad 

~J.lclUnn sp. 

Oym.b07>h01'(t 'lt:nrrcnctn(t (:Meek and Hayden) 

Gyrollcs? sp. 

JJaouUtcs sp. 

S1>hcnotUscus sp. 

AGE AND CORRELATION 

'!'he Fox I-Iills in south-central Wyoming is oldest in 

the northern and northwestern pa1~t of the area and 

was probably deposited during the range span of Ba(Yttlites gnundis or possibly during the time of B. bac'Uius. 

In the central and southeastern part of the area, the Fox 

H:ills was deposi,ted within the range span of B. clinolobatus. Nowhere in the area is it as young as at the type 

locality in South Dakota (Gill and Cobban, 1966a, p. 

A35). 

The Fox I-Iills Formation of this area is not necessarily equivalent in age, but it correlates lithologically 

with the Fox I-Iills of North and South Dakota, Montana, ttnd eastern Colorado. It also correlates lithologically with the Fox IIills of the Rock Springs uplift and 

with the Fox I-Iills of the Powder River Basin in Wyolning. It is equivalent to beds in the lower part of the 

Lance Formation in northwestern Colorado, as mapped 

by Bass, Eby, and Campbell ( 1955), and to the 

Lion Canyon Sandstone Member of the Willimns Fork 

Formation, in the area of M:eeker, Colo., as mapped by 

I-Iancock and Eby ( 1930). 

MEDICINE BOW FORMATION 

The Medicine Bow Formation is a thick unit of continental beds that were deposited during and after 

withdrawal of the Cretaceous sea from south-central 

Wyoming. Bowen ( 1918) named and described the formation from exposures ·along the North Platte River 

near the n1outh of the ~1edicine Bow River in the western part of the I-Ianna Basin (fig. 1). The usage of the 

term "Medicine Bow Formation" is restricted to the 

I-Ianna., Laramie, and Carbon Basins. At the type locality and in adjacent areas, the ~1edicine Bow is about 

6,200 feet thick and consists of fluviatile sandstone, siltstone, and shale with persistent beds of coal in the lower 

part. We have studied these rocks in detail only in the 

northwestern pa.rt of the Hanna Basin; consequently, 

our descriptions in this report are more limited than for 

the underlying Cretaceous rocks. 

Marine sandstone and shale included by early workers in the upper part of the underlying Lewis Shale were 

placed by Dobbin, Bowen, and Hoots (1929, p. 22-24) 

in .the Medicine Bow Formation. Dobbin and Reeside 

(1929, p. 21-23) recognized that these rocks represent 

the transition from conditions of marine deposition to 

continental deposition and determined them to be of 

Fox Hills age. Later, Dorf ( 1938, p. 4-6) redefined the 

~1edicine Bow Formation and restricted the several 

hundred feet of marine beds :at the base of the formation to the Fox Hills Formation. We concur with Dorf's 

redefinition. 

We have not measured a complete section of the 

Medicine Bow, but are in general agreement with the 

description given by Bowen ( 1918, p. 229-230) and by 

Dobbin, Bowen, and Hoots (1929, p. 23-24). A brief 

description by the laMer authors follows: 

The Medicine Bow formation ranges from 4,000 to 6,200 feet 

in thickness and consists of yellow, gray, and carbonaceous 

shale, 'beds of coal, .and gray and brown sandstone. * * • The 

lower part of the formation is made up of massive to cross-bedded brown sandstones, which usually ~orm a conspicuous group 

of ledges and contain numerous beds of coal. These sandstones 

are overlain ·by .an 'inter-mediate group of dark-colored shales 

·and thin-bedded fine-grained brown sandSJtones, with some beds 

of massive white sandstone. The sandstones at the top of the 

formation are coarse, massive, friable, and easily eroded and 

are interbedded with thick beds of dnrk-gray shale. 

The Medicine Bow Formation seems to be conformably overlain by coarse-grained to conglmneratic sandstone beds of the Ferris Formation. In the type locality 

of the Ferris, in the central part of the Hanna Basin, 

coarse-grained sandstone of the upper part of the Medicine Bow grades upward into pebble-bearing sandstone 

beds of the Ferris. Locally, along the east side of the 

Hanna and Carbon Basins, the Medicine Bow Formation is overlain in angular unconformity by the Hanna 

Formation (fig. 14). 

The Medicine Bow Formation is of Late Cretaceous 

age, as was suggested by Bowen (1918, p. 230), Dobbin and Reeside ( 1929, p. 22), Dorf ( 1938, p. 6), and 

l(nowlton (1911, p. 369; 1914, p. 328). Dobbin, Bowen, 

and Hoots ( 1929, p. 23) considered that most of the 

Medicine Bow Formation and the lmW-r 1,000 feet of the 

Ferris Formation represented the Lance Formation of 

eastern Wyoming. Dorf (1940, ·p. 223, 233) correlated 

the Medicine Bow with the Lance, the Hell Creek Formation of Montana and the Dakotas, and the Laramie 
44 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

FIGURE 14.-Rocks of the Hanna Formation resting unconformably on the lower part of the Medicine Bow Formation in the 

southeastern part of the Oarbon Basin, in the SEl\4SIDJ4 sec. 20, T. 21 N., R. 79 W., Carbon County, Wyo. 

Formation of Colorado. The Medicine Bow probably is 

equivalent to only major parts of the previously named 

units, as Dobbin, Bowen, and Hoots suggested, because 

the lower part of the Ferris Formation, which conformably overlies the Medicine Bow, is also of Late Cretaceous age (Brown, 1943, p. 81-82; 1962, p. 21). 

Numerous fossil collections from the Medicine Bow 

Formation by earlier workers in the area include 

fresh- and brackish-water invertebrates, ceratopsian 

dinosaur remains, and plants. The geographic and stratigraphic position of many of these earlier collections 

cannot be determined accurately. During the course of 

the present study, invertebrate fossils were collected 

from the Medicine Bow Formation in the Carbon Basin 

and eastern part of the Hanna Basin, as well as from 

the lower and middle parts of the formation near the 

west margin of the Hanna Basin (Seminoe Dam SW 

7%-minute quad.). Representative fossil collections 

from Carbon County, identified by W. A. Cobban, 

follow. 

From middle part of Medicine Bow Formation: 

USGS D6612. NElUNW% sec. 24, T. 24 N., R. 85 W. 

Anodonta aff. A. propatoris White 

Plesielliptio postbiplicata (Whitfield) 

Teredina laramiensis (Whitfield) 

Tulotomops thom.psoni (White) 

Lioplacodes aff. L. temticarinata (Meek and Hayden) 

aampelorna n.eb1·ascensis whitei Russell 

Physa reesidei Stanton 

From lower part of Medicine Bow Formation: 

USGS D5618. Center of the N% sec. 1, T. 22 N., R. 80 W. 

(eastern Hanna Basin). 

Plesielliptio postbiplicata (Whitfield) 

T1tlotomops thompsoni (White) 

Lioplacoaes sp. 

aampeloma neb?·ascensis whitei Russell 

aassiopella tttrricttla White 

USGS D5544. SE%NEJ4 sec. 21, T. 21 N., R. 79 W. (Carbon 

Basin). 

Sphaerittm sp. 

Tttlotomops th01npsoni (White) 

LioplacoiLes sp. 

From S%NE% sec. 1, T. 22 N., R. 80 W.: 

USGS D6241. (eastern Hanna Basin). 

Calcareous worm tube 

USGS D6607. SW%NWl4 sec. 26, T. 24 N., R. 85 W. (western arassostrea sp. 

Hanna Basin)· USGS D6242. 240ft above D6241. 

Proparreysia sp. 

Tttlotornops th01npsoni (White) 

aampeloma neb1·ascensis whitei Russell 

Lioplacodes afl'. L. tenuicarinata (Meek and Hayden) 

USGS D6611. NE% SE% sec. 33, T. 24 N., R. 85 W. 

Proparreysia holmesiana (White) 

cf. verntcositormis (Whitfield) 

Plethobasis aesopiformis (Whitfield) 

aorbicttla cf. a. planum.b01ta Meek 

USGS D6243. 30ft above D6242. 

a01·bula cf. a. mactritormis Meek and Hayden 

Unio sp. 

Gastropods 

USGS D6244. 60ft above D6243. 

aorbula subtrigonalis Meek and Hayden 

•
j 

... 

... 

4 

. '1-. 

. ).• 

FOOTE CREEK AND DUTTON CREEK FORMATIONS 45 

USGS 06245. 215ft above 06244. 

Oorbula cf. 0. mact?·ifO'I-tn-18 Meel{ and Hayden 

Gonio basis sp. 

Vivipcvnts sp. 

USGS 06246.40 ft above 06245. 

.PlesieZUptio sp. 

T1tlOtO?nops thompson:i ( 'Vhite) 

Oam.peloma neb1·asoensis var. 1.vMte·i Russell 

USGS 06247. 45ft above 06246 . 

.PZesieZUptio cf. P. 1)0Stbi.plicata (Whitfield) 

T1tlot01nops thO?nl)SOn·i (White) 

Oant1)elom.a ncb1·ascensis var. 'I.Vhitei Russell 

Li01)lacolles cf. L. tenulicarinata (Meek nnd· Hayden) 

USGS 06080. NE:J,4NE1J.~ sec. 18, T. 24 N., R. 84 W. (western 

Hannn Basin). 

01·assostrea glabra (Meek and Hayden) 

FOOTE CREEK AND DUTTON CREEK FORMATIONS 

The names Foote Creek and Dutton Creek were 

recently introduced in the northern part of the Laramie 

nnd southern part of the Carbon Bnsins by Hyden, 

McAndrews, and Tschudy ( 1965). The names were used 

on several geologic quadrangle maps. The Foote Creek 

Formation was proposed for as much as 400 feet of 

interbedded fine-grained sandstone, carbonaceous shale 

and siltstone, and coal. The Foote Creek (basal Medicine Bow Formation of this report) was reported to be 

of Late Cretaceous and Paleocene age and to conformably overlie the Lewis Shale (Hyden and others, 1965, 

p. 1(1). The Dutton Creek Formation (Hanna Formation of this report) was proposed for 200-500 feet of 

interstratified conglomerate, fine- to coarse-grained 

sandstone, mudstone, carbonaceous shale, and coal. The 

Dutton Creek is of late Paleocene age and unconformably overlies the Foote Creek. These new formation 

names were used for rocks shown on the ·current Wyoming State geologic map (Love and others, 1955) as 

the Medicine Bow and Hanna Formations. 

The Foote Creek Formation at the type section, about 

12 miles west of the town of Rock River, conformably 

overlies the Fox llills Formation, which was included 

by I-Iyden, ~1cAndrews, and Tschudy (1965, p. 1(7) in 

the Lewis Shale. At this locality the Foote Creek contains a thick unit of marine sandstone in its lower part 

and is transitional with the underlying Fox Hills. The 

thickness of the Foote Creek at this locality is 228 feet, 

and its lithology and fossil content are the same as those 

of the Medicine Bow Formation in nearby areas. At the 

type section of the Foote Creek a coal bed, about 7 

feet above the base, contains spores and pollen typical 

of the Hell Creek, Lance, and Medicine Bow Formations of Late Cretaceous age (Hyden .and others, 1965, 

p. 1(5). The beds a few feet above the co~l contain 

01•assostrea glabra (Meek and Hayden), a fossil oyster 

typical of the transitional rocks in the upper part of the 

Fox Hills and lower part of the Medicine Bow. 

The Paleocene age of the Foote Creek was determined 

from plant microfossils in core samples of carbonaceous 

shale and coal. The core was recovered from a hole 12 

miles southeast of the type section of the formation. 

The coal-bearing rocks ·penetrated by the drill are about 

160 feet thick and were interpreted by Hyden, ·McAndrews, and Tschudy ( 1965, p. 1(8) as part of the 

Foote Creek Formation resting confonnably on the 

Lewis Shale. 1V e believe these beds are a fine-grained 

facies of the Hanna Formation. Excellent and wellpreserved pollen assemblages were obtained from five 

beds in the lower part of the Foote Creek and all are 

of late Paleocene age (R. H. Tschudy, oral commun., 

1968). The lowest bed from which pollen was collected 

and identified is 15 feet above the Lewis Shale. 

The basal part of the Foote Creek Formation (Medicine Bow of this report) at the type section contains 

Late Cretaceous plant microfossils, but the basal part 

of the Foote Creek (Hanna Formation of this report) 

at the locality of the drill hole contains plant microfossils now considered to be late Paleocene instead of 

Paleocene in age. 

In the center of the Hanna Basin, about 20 miles 

northwest of the type section of the Foote Creek Formation, rocks of Late Cretaceous age (the lower part of 

the Medicine Bow) are separated from rocks of late 

Paleocene age (the lower part of the Hanna Formation) by as much as 13,000 feet of strata. This thickness contrasts with the reported maximum thickness of 

400 feet between similar rocks of Late Cretaceous and 

late Paleocene (late Paleocene, R. H. Tschudy, oral 

commun., 1968) age in the Foote Creek Formation 

(Hyden and others, 1965, p. 1(3). A major unconformity at the base of the Hanna Formation has been 

described and mapped by Dobbin, Bowen, and Hoots 

( 1929, p. 25 and pl. 27). The Hanna Formation lies 

unconformably on the Ferris Formation and transgresses across all underlying formations at least down to 

the Cloverly and possibly down to Precmnbrian granite 

(Dobbin, Bowen, and Hoots, 1929, p. 25). 'Ve believe 

that the Foote Creek Formation, reportedly of Late 

Cretaceous .to late Paleocene age (Hyden and others, 

1965, p. 1(5), encompasses this unconformity . 

Rocks mapped as Foote Creek by Hyden and McAndrews (1967) along the east margins of the Hanna 

and Carbon Basins (T L Ranch 71h-minute and Saddleback Hills 15-minute quarangles) are at one place 

remnants of the basal Medicine Bow and at other places 

a fine-grained coal-:bearing facies of the Hanna Formation. We have examined the local unconformity at 

the base of the Foote Creek Formation, reported by 

Hyden, McAndrews, and Tschudy (1965, p. K4), and 

conclude that the unc~mformity is not local and that 

the rocks above it are a fine-grained facies of the Hanna 
46 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

Formation. Rocks as thick as 16,000 feet may be represented by the unconformity at this locality. In most 

other quadrangles mapped by Hyden and others in the 

northern ·part of the Laramie Basin, the name Foote 

Creek has been applied to remnants of the lower part 

of the Medicine Bow Formation. 

We believe that the Dutton Creek Formation of late 

Paleocene age is a coarse-grained conglomeratic facies 

of the Hanna Formation and that the name "Hanna" 

should be reinstated for these rocks. Locally, the Dutton Creek is the basal unit of the Hanna which grades 

laterally into a fine-grained facies, as can be demonstrated in the northern part of the T L Ranch quadrangle. Where the lower part of the Hanna is fine 

grained, the Dutton Creek crops out higher in the 

Hanna Formation. 

Our reevaluation of the stratigraphic and paleontologic data from rocks of Late Cretaceous and early 

Tertiary age in the Hanna, Carbon, and Laramie Basins 

results in the conclusion that the F1oote Creek and Dutton Creek Formations have been incorrectly interpreted. The stratigraphic sequence exposed along the 

southeast margin of the Carbon Basin was reexamined 

in the company of H. J. Hyden, and it was concluded 

that the rocks assigned to the Foote Creek Formation 

belong in the lower coal-hearing part of the Medicine 

Bow Formation and in the coal-bearing fine-grained 

parts of the Hanna Formation. 

The Foote Creek Formation as a formal stratigraphic 

name is abandoned in accordance with the wishes of Mr. 

Hyden before his untimely death. This action is taken 

because the lower part of the Medicine Bow Formation 

and the fine-grained facies of the Hanna Formation, 

although similar in appearance, can now be recognized. 

The two formations can be identified on the basis of 

lithology and are separated by a large unconformity. 

The two units are, in addition, of different ages-Late 

Cretaceous and late Paleocene. Inasmuch as most of the 

rocks mapped as Foote Creek are now recognized as 

remnants of the lower part of the Medicine Bow Formation, we recommend that the name ~1edicine Bow be 

reinstated for formal usage in this a.rea. The Dutton 

Creek Formation represents one of the many coarsegrained tongues of the Hanna Formation; consequently, to avoid a duplication of names, the Dutton 

Creek is abandoned and the Hanna is reinstated. 

FERRIS FORMATION 

The Ferris Formation was named by Bowen ( 1918, 

p. 230-231) from exposures between the old Ferris 

Ranch on the North Platte River (sec. 33, T. 23 N., R. 

84 W.) and a hilltop to the east (sec. 28, T. 23 N., R. 

83 V\T.). The formation is about 6,500 feet thick in the 

type locality. It consists of a thick sequence of continental rocks that can be divided into two parts: a lower 

unit of Late Cretaceous age which is about 1,100 feet 

thick and composed of conglomeratic sandstone, sandstone, and shale, and an upper unit of Paleocene age 

which is about 5,400 feet thick and composed of gray, 

brown, and yellow sandstone and many thick beds of 

coal. The two units appear to be conformable, although 

their lithologies are markedly different. 

The conglomerate of the lower unit ·is generally dark. 

It contains pebbles as much as 1 inch in diameter composed of black, red, and yellow chert, red and gray 

quartzite, and sparse rhyolite and quartz latite porphyry (Bowen, 1918, p. 230). Some of the siliceous 

pebbles contain Paleozoic fossils. The pebbles apparently do not consist of rocks exposed locally in mountains adjacent to the basin. Bone fragments are common in the conglomerates, and some have been identified 

by C. W. Gilmore as T1·iceratops, which indicates a 

correlation between the basal part of the Ferris and the 

Lance Formation (Bowen, 1918, p. 231). Plant microfossils collected by us from the dark-brown shales in 

the lower unit of the Ferris were examined by R. H. 

Tschudy, who said (written commun., 1967): "Sample 

D4085 yielded a characteristic late Cretaceous assemblage including the genera P1·oteacidites and A-qu,ilapollenites. There 'is no doubt concerning the age of this 

sa.mple." 

The upper unit of the Ferris differs from the lower 

unit in being much thicker, in containing numerous persistent beds of coal, and in its lack of conglomerate or 

conglomeratic sandstone. Plant microfossils coHected 

· from about the 1niddle of the upper unit were examined 

by R. H. Tschudy, who stated (written commun., 1967) : 

"The few fossils identified indicate a Paleocene age for 

the samples. The absence of 11/ onipites ten1tipol!us 'Suggests early rather than late Pa.leocene." 

The Ferris Formation conformably overlies coarsegrained sandstones of the Medicine Bow Formation and 

unconform·ably underlies locally derived conglomerate 

or conglomeratic sandstone of the Hanna Formation. In 

·the type locality of the Ferris, in the west-central part 

of the Ha.nna Basin, an angular relation between the 

two formations is not apparent. Possibly in the centra.! 

part of the Hanna Basin, the Ferris and Hanna Formations are virtually conformable, as suggested by !{night 

(1961, p. 162). A marked angular unconformity separates the two formations along the east side of the Hanna 

and Carbon Basins. The unconformity is well exposed 

in sec. 14, T. 22 N., R. 80 W., 2 miles north of the old 

town of Carbon. 

In the northern part of the Hanna Basin, Dabbin, 

Bowen, and Hoots (1929, pl. 27) mapped the Hanna un-

~.-
'"" 

.~ 

--~· 

.,.... 

conformably overlying the Ferris. !(night ( 1961, p. 155-

164) measured two sections in the area and found no 

evidence of an angular unconformity, and he did not 

differentiate the Ferris and the I-Ianna. vVe have examined the 11rea and conclude thrut the ma.p of Dobbin, 

Bowen, and I-Ioots is incorrect. The Hanna Formation 

overlies a p11rt of the :Medicine Bow For1nation; the intcrvening upper part of the :Medicine Bow and the Ferris have been removed by pre-IIanna erosion. This accounts for the thinness of the l\1edicine Bow ( 3,950 ft 

.instead of 6,500 ft a few miles to the west) . We, like 

!(night, did not see a measurable angular unconformity 

at the base of the conglomeratic sequence, but it may 

have been overlooked in exposures on the edges of vertical beds. 

'!'he Ferris crops out in the I-Ianna and Carbon Basins, 

but the original areal extent of the for1na.tion is not 

known. Bowen ( 1918, pl. 66) showed ~that the Ferris is 

nt lenst 4,600 feet thick in places along the east flank 

of the llannn. Basin. Probably the formation was also 

deposited in the Laramie Basin. The presence of loc;ally 

derived conglomm~a.te in the basal part of the overlying 

l:In.nna Formation and a marked angular unconformity at the base of this unit indicate that the Hanna and 

Carbon B11sins started to form during the early or Iniddle Paleocene. }(night (1953, p. 67) rep01.ted a loca.lly 

derived conglomerate in the lower part of the l\1edicine 

Bow Fornm.tion, in the southwesten1 part of the Laramie Basin, and he concluded that the IV[edicine Bow 

Mountains were elevated sufficiently in Cretaceous time 

to expose roclrs of Precambrian age. 

HANNA FORMATION 

The I-I anna Formation was named by Bowen ( 1918, 

p. 231) from exposures. north and west of the town of 

I-Ianna (fig. 1). Neither Bowen (1918, p. 231), who proposed the for1nation, nor DolYbin, Bowen, and Hoots 

(1929), who first mapped it, designated a specific type 

locality and described a type section. We have studied 

the formation only in the Hanna and Carbon Basins, 

and our descriptions are limited to general lithology, 

fossil content, and the relation with adjacent fonnations. 

The I-Ianna Formation of continental origin consists 

of conglomerate, sandstone, shale, and coal. Bowen 

(1918, p. 231) reported that the formation was about 

7,000 feet thick, but sections measured subsequently by 

!(night (1961, p. 159-161) on the north flank of the 

I-Ianna Basin and our field observations lead us to believe 

that the Hanna may be a-s much as 13,500 feet thick. 

Bowen reported (1918, p. 231) that the H·anna Formation was "highly feldspathic" and composed of congl01nerate, conglomeratic sandstone, sandstone, shale, 

and many thick beds of coal. The conglomerate is dis47 

tributed throughout the formation, but is most abundant in the lower half. The pebbles in the conglomerate 

are, in general, light colored and consist of chert, granite, quartzite, sandstone, Mowry Shale, oa.nd cong.lomera.te frmn the Cloverly For1nation. The pebbles of 

granite, quartzite, Mowry Shale, and conglomerate are 

believed to represent nearby exposures of these rocks. 

The conglomerates of the Hanna differ from those of the 

Ferris in color and in the size ·and composition of the 

clasts. Apparently, the conglomerates of the Ferris were 

derived from a distant source and those of the Hanna 

from n. nearby source. The basal unit of the Hanna is 

generally composed of coarse conglomerate but may 

locally be finer grained. 

The I-Ia.nna Formation unconfol'lnably overlies the 

Ferris Formation in much of the area, but locally along 

the margins of the basins it rests on rocks us old as Precambrian .age (fig. 15). Bowen ( 1918, p. 232) estimated 

that the unconformity at some localities represented the 

removal of rocks more than 20,000 feet thick. On the 

south flank of the Hanna Basin the I-Ianna and older 

formations are unconfol'lnably overlain by beds na.med 

the North Park Formation of Miocene age by Dobbin, 

Bowen, and Hoots (1929, p. 26) and undivided Pliocene 

and Miocene rocks by 'Veitz and Love ( 1952). 

}(night (1961, p. 160) mapped unnamed continental 

rocks of Eocene age in the northern part of the I-I·anna 

Basin and demonstrated that this unit was in angular 

unconfor1nity with the unded.ying Ha.m1a and older 

formations at the basin margin. He further reported 

that the rocks of Eocene -age became conformable with 

the underlying rocks as they were traced basinward. 

Plant microfossils collected by H. J. Hyden in the lower 

part of }(night's Eocene sequence in the SE% sec. 16, T. 

22 N., R. 81 ,V., Carbon County, were examined by 

R. H. Tschudy, who stated (written commun., 1963) 

"USGS D3232A. Assemblage includes specimens of 

Tiliae]Jollenites and is of late Paleocene or early Eocene 

age." Pl·ant microfossi1ls collected by us fron1 higher in 

the m1it in the center of the SWl!t, sec. 34, T. 24 N., R. 

81 ,V., were described by Tschudy as follows (written 

commun., 1967) : "USGS D4088. Assen1bla.ge includes 

the genera Oarya, Jruglans? Tiliapollenites, and Platyca'rya, and is of Eocene age." }(night's Eocene unit 

was originally m·apped -as part of the Hanna by Dobbin, 

Bowen, and Hoots (1929, pl. 27), but the demonst.ra.ted 

1nappability of the unit (1\:night, 1961, p. 160) and the 

unconformity at its base lead us to conclude that it 

should be excluded from the Hanna and perhaps included in the Wind River Form-ation ·as }(night 

suggested. 

The fossils in the Hanna Formation consist of wellpreserved leaves, spores and pollen, invertebrates, and 
48 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

FIGURE 15.-Hauna Farmation (Th) unconformably overlying the Lewis Sha,le (Kie) in the northeastern part of the Hanna Basin, 

in the NEJA:\fW14 sec. 10, T. 23 N., R. 80 W., Carbon County, Wyo. Sandstones of the Almond Formation (Ko) crop out in 

the area shown in the lower left corner of the photograph, and the soft shales of the Lewis form the valley in the foreground. 

vertebrates. The vertebrate remains described by 

Bowen ( 1918, p. 231) "include fish scales, fragments of 

turtle shells, and a fra.gmentary mammalian jaw identified by J. W. Gidley as a creodont, probably 07-aeonoclon, which may belong to either the Fort Union or 

Wasatch." Bowen also reported that invertebrates from 

the Hanna were identified by T. W. Stanton 'and correlated with those of the Fort Union and Wasatch 

Formations. The plant fossils found by Bowen were referred to the Fort Union by F. H. Knowlton. 

'\iV e collected plant microfossils frorn two localities 

in the lower part of the formation in the eastern part of 

the Carbon and Hanna Basins. These collections were 

described by R. H. Tschudy as follows (written commun., 1967) : 

USGS DW89. NW1,4 sec. 10, T. 23 N., R. 80 W., Carbon County. 

Lower part of Hanna Formation. 

Sparse assemblage, but the presence of Momipites temtipoltts Anderson and the absence of Cretaceous and Eocene 

species indicate that this sample is of late Paleocene age. 

USGS D3939. NE14SEJASE% sec. 20, T. 21 N., R. 79 W., Carbon 

County. Lower part of Hanna Formation. 

Good assemblage of well-preserved fossils ,including Pistillipollenites, of late Paleocene age. 

The age of the Hanna remains in some doubt. The 

upper part of the underlying Ferris Formation is of 

early Paleocene age and the overlying unnamed sequence mapped by Knight (1961) is of possibly latest 

Paleocene and early Eocene age. Fossils from the 

Hanna indicate a late Paleocene age, but the formation 

may be as old as late early Paleocene or middle Paleocene in the center of the Hanna Basin. 

REFERENCES CITED 

Barwin, J. R., 1959, Facies of the Mesaverde formation, eastcentral Wyoming, in Am. Assoc. Petroleum Geologists Rocky 

Mtn. Sec., Geol. record, Feb. 1959: p. 139-142. 

---1961, Stratigraphy of the Mesaverde Formation in the 

southern part of the Wind River Basin, Wyoming, in 

Symposium on Late Cretaceous rocks, Wyoming and adjacent areas-Wyoming Geol. Assoc. [Guidebook] 16th Ann. 

Field Conf., Green River, Washakie, Wind River, and 

Powder River Basins, 1961: Casper, Wyo., Petroleum Inf., 

p.171-179. 

Bass, N. W., Eby, J. B., and Campbell, M. R., 1955, Geology and 

mineral fuels of parts of Routt and Moffat Counties, Colorado: U.S. Geol. Survey Bull. 1027-D, p. 143-250 [1956]. 

Bergstrom, J. R., 1953, The Mesaverde formation of the Laramie 

Basin, in Wyoming Geol. Aswc. Guidebook 8th Ann. Field 

Conf., Laramie Basin, Wyoming, and North Park, Colorado, 

1953 : p. 56-60. 
l 

.~-

... 

_,).. 

REFERENCES CITED 49 

---1959, Generalized composite section of "Mesaverde" rocks 

of southeastern " 7yoming, in Symposium on Cretaceous 

rocks of Colorado and adjacent urens-Rocky M:tn. Assoc. 

Geologists [Guidebook] 11th Ann. Field Conf., ·washakie, 

Sand Wnsh, nnd Picennce Basins, 1959: p. 114. 

Bowen, C. ll'., 1918, Strntigrnphy of the Hanna Basin, Wyoming: 

U.S. Geol. Survey Prof. Paper 108-L, p. 227-235. · 

Brown, R. ,V., 1043, Cretaceous-Tertiary boundary in the Denver 

Basin, Colorado : Geol. Soc. America Bull., v. 54, no. 1, 

p, 65-86. 

---1962, Paleocene florn of the Rocky Mountains and Great 

Plains: U.'S. Geol. Survey Prof. Paper 375,119 p. 

Cobban, ,V, A., nnd Reeside, .T. B., Jr., 1952, Correlation of 

the Cretaceous formations of the Western Interior of the 

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50 STRATIGRAPHY AND NOMENCLATURE, SOME CRETACEOUS AND TERTIARY ROCKS, SOUTH-CENTRAL WYO. 

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Geology. 

-. 

--

~. 
· .... 

._ .... 

.,. 

0. 

- ~-

A Page 

Acknowledgments .. ______ .... ---- ___ ........ 1 

Ago, :nanna Formation .... ------------------- 48 

Ago and cotTCiatlon, Allen JUdge Formation 26 

Almond Formation...................... 88 

Fox .liiiis Formation..................... 48 

Haystack Mountains Formation.......... 14 

J,owls Shale ••......... ---- .... --·----·... 89 

Pine Jtldgo Formation................... 80 

Rock Hlvor Formation................... Sf 

Steele Slmlo.............................. 11 

Allen H.ldgo Formation _________________ 5,11,14,24 

Almond coal group or Mesaverde Formation._ 31 

Almond Formation. _____ ------·- .... 5, 11,90,81, 30 

Amrnonlto zonation ot Uppct· Cretaceous 

rocks In Western Interior.......... 1 

Ammon ito zones •• ___ ..... ·---------......... 38 

Ardmore l3cntonlto Dod In Sharon Springs 

Member or PIOI'l'O Shale__________ 10 

B 

Barwln, J. H .. , cltocl.......................... 11 

Bentonite bods, Steele Shale.................. 10 

Borgman, 0. A., rofcronco section measured 

by---------------------- 1(), 34, 35, 30,40 

Borgstrom, J. H.., cltccL...................... 24 

Bighorn Basin. _______ .......... ____ .. -----_. 11 

Black)H\Wk Formation....................... 5 

Blackwelder, Eliot, cited..................... 3, 7 

Blair Formation _____ ......................... 5, 11 

Bowen, C. F., cited •................. 5,43,40,47,48 

Buck 'l'onguo or M!lncos Slmlo ... -- .. ----.- -·- 15 

c 

Carbon Basin.-------- .. __ ............... 5, 7, 37, 4•1 

Castlcgato Sandstone .... _. ___ .... _ ... _....... 15 

Claggett Formation. ___ ... _ .. _............... 11 

CIIIY House Sandstone .•..... ------ .......... _ 

Coal bod, Foote Crock Formation............ •15 

Fon·is Formation......................... 40 

Cobban, W. A., cited......................... 30 

fossils ldontlfiod by ......... _ ......... _... 10, 

15, 17, 1(), 21, 20, 27, 3<1, 35, 40, •12, •14 

typo section measured by _________ . ___ . 21 Cody Shale __________________________________ 7,11 

Wallace Crook 'l'onguc .................... 11,15 

Collier, A. J., cited........................... 2 

Contact relations, Allen H.ldgo Formation.... 26 

Almond Formation .•• ___ ................ 3S 

Fox Hills Formation_____________________ 42 

J [annn For.tnatlon ........ --- .. --------. __ 47 

Haystack Mountnlns Formation.......... 14 

Lewis Shale •.. ------ .............. ------. 38 

Plno Hldgo Sandstone.................... 30 

Hock H.lvor Formation................... 21 

Steele Shale.............................. 10 

Cross, C. W., cltocL .......................... 2,30 

I) 

Dad Sandstone Moml>or or Lewis Shale ..... 7,36,37 

Dakota Sandstone, coal-bearing units. _____ .. 2 

or No.!.................................. 2 

Darton, N.H., cited......................... 3,7 

Dlllymoceras stevensoni zone .............. ____ . 21 

INDEX 

[Italic page numbers indicate major references] 

Page 

Distribution, Allen Ridge Formation________ 24 

Almond ~,ormation...................... 31 

Fox Hills Formation. ___ ................. 41 

Haystack Mountains Formation._........ 12 

Lewis Shale.............................. 36 

Pine H.idgc Sandstone.................... 29 

Rock H.ivcr Formation................... 20 

Dobbin, C. E., cited ......................... 5,43 

Dorf, Erling, cited............................ 5,41 

Dutton Crock Formation .................... 5,7,45 

E 

Eagle Formation............................. 11 

Ericson Sandstone ____ ........................ 5, 31 

F 

Fales Member of Mesaverde Formation ....... 11, 15 

Fcnneman, N. M., cited...................... 2,3 

Ferris Formation ......................... 5, 7, 43, 40 

Fleisher, R. L., sections measured by _____ ... 15,27 

Foote Crllek Formation. ___ .... __ ........... 5, 7,45 

Fossils: 

Acmaea occillentalis. __ .................... 22,27 

parva................................. 27 

Acteon sp ................................. 22,27 

Allen H.ldgc Formation .. _. __ ... __ ....... 26 

Almond Formation...................... 32 

ammonites .. _............................ 15 

Anapachydiscus sp..... ............ ....... 23 

A.natimya dodllsi. _ ..... ........ ........... 23 

sp. ___ .............................. _. 22 

Anisomyon borealis. _____ ............ __ ... 22 

centrale •.......... _. __ ._.............. 33 

sp ___ ...... __ ..... ___ ........ ___ . .. .. . 17 

Anollonta propatoris. ____ .•........ ------. 27,44 

Anomia sp ___________ ·-------.... .. ... . .. . 41 

Aporrhais biangulata ................. ____ . 27 

A1ltychus. -·--- .•........ ____________ ..... 42 

Aquilapollenites.... .. ...... .. .... .. .. . . ... 40 

Arctica SP-------------------------------- 41 

Arrhogeslobata............................ 23 

Astarte sp. ____ ........................... 23, 42 

Atira nebrascensis ........... _............. 22 

Baculites .............................. 10,11,14 

aquilaensis .... ___ ..................... 11, 19 

asperiformis .................. 14, 10, 18, 20,28 

baculus ___ . . . . . . . . . . . . . .. . .. . . . . .. . 33, 38, 43 

cli~olobatus. _ ...................•.. •10, 42,43 

compressus. __ . _... .. .. . . .... . ... . .... 30 

crickmayi. ___ .. .. . . .. .. .. . . .. . .•... ... 22 

cuneatus __ ..... _ . . . . .. . . . . . .. . .. . . . . . . 30 

eliasi. ____ ............. _ .. 32, 33, 34, 35, 38, 41 

granllis. ___ ........................ 38,41,43 

gregoryensis ....................... _ ... 24, 26 

jensenL ..................•........ 32,33, 38 

mclearni. ....................... ___ 14, 10,29 

obtusus. _ ................. 10, 15, 10, 18, 20,29 

11erplexus ........... 14, 15, 10, 17, 21, 24, 20, 27 

reesillei. .. _ ............ _ ..... 30, 31, 32, 33, 38 

scotti. .. __ ............................ 20 

thomi. -------------------------------· 11 sp __ .... 14, 15, 17, 18, 19, 22, 23, 27, 29, 40, 42, 43 

Fossils-Continued 

Belli/usus sp _____ .................. _____ .. 

Breviarca sp ___ -------- ........... --- ____ . 

bryozoan ....................... __ .....•... 

Calcareous .•....•......................... 

Page 

27 

33 

16 

20 

Campeloma nebrascensis ....•....... ------. 44,45 

whitei.. ...... __ ....................... 44,45 

sp _____ ... . ...... .. .. .. .... .... . . ..... 26 

Cassiopella turricula .• ____ . .. .. .. . . .. .. .. . 44 

Cerithioderma sp. _ ..... .. .... .. ...... .. . . . 27 

Chlamys nebrascensis ____ .................. 22 

Claeonollon. __ ............... -.......... -. 48 

Clamys nebrascensis .• _.................... 42 

Clisocolus sp ___ ------ .... __ ........ -- ..... 15,42 

Corbiculafracta •. .............. ------ ..... 40 

planumbona. ------ ____ ...... .......•. 44 

sp. _ ....................... _.......... 34 

Corbula mactriformis. _ ....... -...... -..... 44, 45 

subtrigonalis. _ .................•. ---.. 44 

undifera. __ ---- .. .... .... . ... . . . . ... . . 34 

sp _ ...... _ ....... _ . . . . .. . . . . . . . . . . . . . . . 23, 27 

Crassostrea glabra ..........••.... 34, 35, 40, 41,45 

sp ____ ................................ 40,44 

Crenella sp. __ ............................ 42 

Cryptorhytis cheyennensis. __ -............. 22 

Cuspidaria moreauensis. _................. 22 

variabilis ... __ .. ............ .. . . .. .. .. . 22 

Cylichna volvaria. _........................ 42 

Cymbophora .• ____ ..... __ . _ 10, 15, 10, 20, 23, 34,40 

holmesi ___ ...................... -..... 20, 29 

warrenana..... .. .... . ... . .. . .... .. .. . 43 

Cymella montanensis ............. 15, 10, 22, 23, 27 

Dentalium pauperculum ....•. .... ---- ..... 22 

sp_ .... _ .......... _ ..... _ .......... 22, 23, 42 

Desmoscaphites bassleri.................... 11 

Didymoceras cheyennense.................. 30 

nebrasense. _ .......................... 26, 27 

stevensoni.. ------ ......•..... ------ 22,26,30 

sp. ____ .... _.......................... 23 

Discoscaphites sp _____ . __ ................... 41,42 

Drepanochilus. ___ ........................ 11 

nebrascensis ______ . ------- ...... ....... 22 

sp __ -·-------..... _________ ........ __ . 23,41 

Dysnoetopora demissa. ___ .............. 22, 23, 42 

Ellipsoscapha sp ................... _ ...... 23, 42 

Ethmocardium ursaniense. __ ......•....... 20 

sp. _ .. ___ .. _. _ .... __ ... 15, 17, 23, 33, 40, 42, 43 

Euspira obliguata ..... __ .................. 22, 27 

sp ................................. 22,23,42 

Eutrephoceras sp __ ........................ 22 

Exiteloceras jenneyi. . _ . . . . . . . . . . . . . . . . . . . . 30 

F'usconaia sp. _____ .. . . .. . . . . .. .. . . . . . .. . . 27 

Fox Hills Formation. __ . __ ............... 42 

Gervillia recta ...........•................. 

SP------------------------------------

Glyptoxoceras ............................ . 

Goniobasis sp. _ ................. ---.---.--

Goniochasma sp .................. -- .. -- .. -

22 

43 

11 

45 

22 

Goniomya americana __ .................... 27,41 

Graphidula alleni. __ ................. -... - 23, 27 

Gyrolles sp ............................. 27, 42, 43 

Hanna Formation........................ 47 

Haresiceras montanaense. _ ........... --... 11 

natronense . .. _ ... _ .... _ . . . . . . .. . . . . . . . 17 

Haystack Mountains Formation .... -..... 14 

51 
52 

Fossils---'Continued Page 

· Hoploscaphites sp __ ... __ .. _ 15, 18, 22, 23, 28, 34, 40 

Inoceramus ___ .. __ .. __ ...... ___________ 10, 11,22 

balticus. _ -----· ____________ ----------- 11,18 

convexus _ . ___ .. _ . _ . _ . __ . _ ... -_ . _ .... -- 22, 23 

fibrosus __ .. ___ .. __ . _______ ..... _ 40, 41, 42, 43 

oblongus __ . _. _ .. __ ..... _ ... --...... _ . . 35 

pertenuis. _ •• _ .. __ ..... _. ---- .. --.. __ - 27 

proximus __________________________ 10, 11,19 

shikotanensis .. ____ . ____ . __ . --. _____ ... 22 

subcompressus ________ .. ___ . _ 16, 17, 23, 24, 28 

turgid us. ______________________ ------· 27 

sp ___ . ___________ 15, 16, 18, 20, 21, 24, 28, 33, 35 

Juglans tiliapollenites. _ .. ________ . __ . _ _ _ _ _ 47 

Legumen ellipticum. ____ . _______ ..... _. 23, 42,43 

sp ______ . __ . ______________ .. _ . _ . _ . _ _ _ _ 40, 42 

Leptosolen sp ______________ .. ____ . _ _ _ _ _ _ _ _ 23 

Lewis Shale._ ... -------------- __ .. _______ 30,38 

Limatula sp. _ ----------------· _____ . ____ __ 23 

Limo psis sp______ _ ___ ____ ____ ___ _______ ___ 22 

Lingula nitida. __________ -------- _________ 42,43 

subspatulata. ___________ .... _. _ _ _ _ _ _ _ _ 15 

SP---------------------------··----- 42 Lioplacodes tenuicarinata ... ____ . __________ 44, 45 

sp __ .. ____ .. ___ . _______ .. ____ .. _____ . _ 44 

Lucina subundata ... ______________________ 10, 11 

sp •.. ___ ... __ .. ____________________ 22, 27, 40 

Menuites sp ________ . _____ ____ ____ __ ____ __ _ 23 

Micrabacia americana______________________ 22 

sp- _ - __ ...... __ . ____________________ . _ 41 

Modiolus galpiniana ____ ---------- ·----- __ _ 41 

sp ••. -- .... --. _. ____________ . ___ 15, 18, 20,23 

mollusks. ____ .___________________________ 21 

Momipites tenuipolus _________ _____________ 46,48 

Morea cancellaria__________________________ 27 

marvlandica_________ _ ____ _____ _ ______ _ 27 

sp. __ .. ____ .. ______ . _________ .. _ _ _ _ _ _ _ 27 

Nemodon sulcatinus ___ _____ ---------- _ ____ 22 

SP---------------------------·--·----- 23 

Nonactaeonina attenuata._________________ 22 

Nucula pectincula sp_ _ ______ ____ _ _ ______ _ 22 

planimarginata _____ ___________________ 22,42 

sp ••. -- .. __ . ____________________ 15, 16, 20,27 

Nuculana SP---·-------------------------- 33 Oligotvcha concinna. _ _________ _____ _ _ _____ 42 

sp •• --- .. __ . ________________ .. _____ 22, 23,27 

Ophiomorpha ••• _ _ _ __ _ _ _ _ _ _ __ _ _ __ _ _ _ _ _ _ _ _ _ 13, 

15, 16, 17, 18, 19, 20, 21, 23, 25, 27, 28, 

32, 34, 35, 36, 37, 40, 41 

sp ••. -- ....... _. _____________ . _ _ _ _ _ __ _ 22 

Ostrea •• ---. ______________________________ 10, 11 

albertensis .•••• _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 20 

congesta. __ • ________________ . _ _ _ _ _ _ __ _ 11 

plumosa. _ --------- ____ ______ _________ 22 

russelli. •• _ .. __ . _____________ 20, 21, 22, 23,41 

subtrigonalis. _ _ __ _ _ _ _ __ _ _ _ _ __ _ _ _ _ __ _ _ _ 23 

sp ________________________ 16, 18,22, 27, 41,42 

Oxybeloceras sp. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 23 

Oxytoma nebrascana ________ _________ 18, 22, 23,42 

sp. --------------------------. __ 15, 23, 27,33 

Panopea sp ________________ --------------- 34 

Pecten SP------------ __ ---------- ______ __ _ 41 

Perrisonota sp_ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 22 

Pholadomya sp ______________________ 27, 40, 41,43 

Physa reesidei________ ____ ____ __ __ __ ____ _ _ _ 44 · 

Pinna lakesi. ______ ---------------- ____ __ _ 23 

sp •• -- ..... -- .. -- ___ . _____ . _. _ _ _ _ _ _ _ _ _ 15 

Pistillipollenites .•.. _______________________ 48 

Placenticeras intercalare _________ . 10, 17, 22, 23, 27 

meekL. __ __ __ ____ ____ __ _ _ ___ _ _ _ ______ _ 10 

sp-.----....... -.. __ .. ___ . 15, 18, 22, 23, 24, 28 

plant microfossils .... _____________________ 47,48 

Ferris Formation_____________________ 46 

Foote Creek Formation._____________ 45 

Platycarya________________________________ .!7 

Plesielloptio postbiplicata. _________________ 44, 45 

sp _______ ------------------------ _____ 27,45 

Plethobasis aesopiformis. _________ . _ _ _ _ _ _ _ _ 44 

INDEX 

Fossils-Continued Page 

PropaJreusia hoiineaiana______ ____ _ _ _ __ _ _ _ _ 44 

verrucosiformis. ________ . ___ .. _ _ _ _ _ _ _ _ _ 44 

SP------------------------------------ 44. Proteacidites. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ 4.6 

Protocardia rara •.• _ _ _ __ __ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ 42 

subquadrata ___ _________ • _ __ _ _ __ _ _ __ _ _ _ 42 

sp. _____________________________ ._ _ _ _ _ _ 27 

Protodonox sp •. ___ • _______ .. ___ . _ _ _ _ _ _ _ _ _ _ 23 

Pseudoptera sp. _______ . ___ . ___ . __________ 42, 43 

Pteria. ____________________ . ______________ 10, 11 

linguaeform·is ___ - ___ . _____ 10, 11, 22, 23, 27, 41 

Pycnodonte mutabilis ..... ---------- ______ _ 23 

Rock River Formation ___________________ 21,30 

Scaphites hippocrepis _________ _____________ 11, 17 

Senis sp. __ ------ __________________ ------- 23 

Serpula sp _____________________ -------- _. _ 27 

Serrifusus dakotensis. ______ . __ . _ ... __ _ _ _ _ _ 22 

sp ___________________________ ---- _____ 22,23 

Solemya sp. ___ ---------- ________ --------- 22,33 

Solenceras sp. ____________________________ 22, 23 

Sphaerium sp ____________ ---------- _______ 27,44 

Sphenodiscus sp. _________________ ------ _ _ 43 

Steele Shale______________________________ 10 

Syncydonema hallii. _ __ ___ _____ ______ _____ 22 

simplicius _____ _____ . ________ . __ _ _ _ _ _ _ _ 23 

sp .. -- _____ . _______ .. __ . ______ .. _. _. 15, 27,43 

Tancredia sp _______ ---------------- _______ 40 

Tellina munda _______ ______ -------- _______ 23,27 

sp. __ . _____________ . ____________ 15, 22, 42,43 

Tenea circularis ___ _____ . _ _ _ _ _ __ _ _ __ _ _ _ _ _ _ _ 22 

parilis. _____________ . _________ . _ _ _ _ _ _ _ 23 

sp.-.---- _______ . __ .... _____ . _ _ _ _ __ _ _ _ 27 

Teredina laramiensis .. _ -------- _______ ____ 44 

Thyasira_________ ___ _ ____ _________ ___ _____ 10 

Tilaepollenites. _ _ _ _ _______ _ ____ _ _ ______ ___ ·47 

Trachyscaphites praespiniger ____ . ____ . ____ 10, 11 

Triceratops_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 46 

Trigonia ... ---- __________________________ . 21 

eufaulensis gabbi. _ _____ ______ _ __ _ _ _ _ _ _ 23 

Tulotomops thompsoni. ..• ____ . ___________ 44,45 

Tuba sp _____ -------- ____ _____ _ ______ ____ _ 27 

Tulotomopslaevibasalis___________ __ __ ____ _ 26 

thompson;__ _________________________ -~ 44,45 

Uintacrinus socialis. _ _ _ _ _ __ _ _ __ _ _ _ _ _ _ _ _ _ _ _ 11 

Unio sp. __ _ _________ __ ____ _ _ __ __ ___ ______ 44 

Vetericardia sp___ _ _ __ __ ______ ____ __ ______ _ 22 

Viviparus sp ___________________ ----------- 27,45 

Westeria. _______________________ . _ _ _ _ _ _ _ _ _ 22 

Yoldia evansL ____________________ _____ 22,27,33 

Fox Hills Formation. ___________________ 7, 36, 38,41 

Fox Hills Sandstone ... _______________________ 5 

G 

Gale, H. S., cited_____________________________ 2,3 

Geology of Sim Juan district.. .. ______________ 2 

Gill, J. R., cited______________________________ 30 

sections measured by ___ 15, 19, 27, 31, 34, 35, 39, 40 

Gilmore, C. W.,fossilidentified by___________ 46 

H Hale, L.A., cited _____________________________ 12,37 

Hancock, E. T., cited ______________ ---------· 3 

Hanna Basin ... 3, 5, 7, 10, 24, 25, 26, 33, 37, 43, 44, 45,46 

lianna Formation .. ___________________ 5, 7, 45, 46,47 

Hatfield dome .. ___________________________ 10, 12, 13 

Hatfield dome area, fossil collections _______ . ___ 10,11 

Hatfield Sandstone Member of Haystack 

Mountains Formation .. _____ 5, 12, 13,15 

Hayden, F. V., cited. __ ---------------------- 41 

Haystack Mountains. ________________________ 12,26 

Haystack Mountains Formation ______ 5, 10,11, 12,25 

Hatfield Sandstone Member _________ 5, 12, 13,15 

Marine shale members ___________________ . 14 

O'Brien Spring Sandstone Member .. 5, 12, 13,15 

Tapers Ranch Sandstone Member ___ 5, 12, 13,14 

Page 

:Hell Creek: Formatioh:..--'~-'-------------C-- 43 

Historical background ••...... _------.________ 2 

Holmes, W. H., cited ________________________ _ 

Hoots, H. W., cited___________________________ 5, 43 

Hyden, H. J., cited ________ ------ ____ ------- 5, 36,45 

fossils collected by _______________________ . 47 

Iles Formation •• ----- ______________ ---- _____ 3, 5, 26 

Introduction ..•• ________________ .. _ .. ____ . __ . 1 

K 

Kara Bentonitic Member of Pierre Shale ..... _ 33 

Knight, S. H., cited •... ---------------------- 46,47 

L 

Lance Formation ... -------------------------- 43 

Laramie Basin. __ --------- _____ 5, 10, 20, 25, 26, 37,43 

Laramie Formation, coal-bearing rocks •.. __ ._ 2 

Lewis Sea ••.. __________ ------------. 30, 32, 37, 38,39 

Lewis Shale •. _____ --------------- 2, 3, 5, 30, 33,36; 45 

Dad Sandstone Member. _______________ 7,36,37 

tongues. _____________ ---- ______ ----------- 32 

Lion Canyon Sandstone Member of Williams 

Fork Formation__________________ 43 

Lithologic character, Almond Formation .••. _ 31 

Allen Ridge Formation___________________ 25 

Fox Hills Formation ____________________ _ 41 

Haystack Mountains Formation ... _ ..... . 13 

Lewis Shale •• --------- ___________ . ______ _ 36 

Pine Ridge Sandstone _____ .. --------. ___ _ 29 

Rock River Formation __________________ _ 21 

Steele Shale----------- __ ----------------. 10 

Lower Laramie Cretaceous nonmarine rocks .. 3, 5 

M 

McAndrews, Harry _________________ . _______ 5, 36,45 

Mancos Shale ... ---------- ____ ------ .. ------- 2, 3, 11 

Buck Tongue .. --------------------------- 15 

Marine shale members of Haystack Mountains 

Formation ________ . ____ ----------. 14 

Marine strata ______________________ ----------. 25 

Allen Ridge Formation___________________ 25 

Medicine Bow Formation ....•... 5, 7, 42, 43, 45, 46, 47 

Meek, F. B., cited.--------------------------- 41 

Meeteetse Formation •• -------------------- 33, 38,39 

Menefee Formation •.... ___ ._. __ .. _ .. _ ....... _ 2 

Mesa Verde Group___________________________ 2 

Mesaverde Formation •• -----------------. 9, 5, 11,29 

Almond coal group.---------------------- 31 

Fales Member. __ -------------------- _____ 11, 15 

Parkman Sandstone Member •. -.-.-...... 26 

Teapot Sandstone Member __ .. _ ..... _ .. _. 29, 31 

Mesaverde Group ____ .-------------- S, 3, 5, 11, 14,29 

Missouri River region, stratigraphic classificacation of Cretaceous rocks .... ___ . I 

Montana Group .... ---------------···-·-----· 3 

N,O 

North Park Formation.---------------·-·-·-· 47 

Northwestern Colorado, stratigraphic classifl· 

cation •• _. ________ . ______ ..... ____ 2 

O'Brien Spring .. ____ .. ---- __ -------.--- .. ---. 12 

O'Brien Spring Sandstone Member of Haystack Mou,ntains Formation .. 5,12, 19,15 

p 

Parkman Sandstone Member of Mesaverde 

Formation ...•... ------------ _____ 11,26 

Phayles Member of Mesaverde Formation.___ 11 

Phayles Reef Member of Mesaverde Forma- tion. ___ . ____ ._. _________ . __ . __ .__ 11 

Pictured Cliffs GroUP---------------·-------- ! 

Pictured Cliffs Sandstone. ___ ---------------. 3 

... 

... , 

r. 

-~ 

•• 

-

. . .J:_ ' 

'-', 
•• 

Page 

Pierro Shale •••...... ------ .......... --------- 39 

Ardmore Bon ton ito Bod In Sharon Springs 

Mombor.......................... IO 

Kara Bon tonltic Mom bcr _................ 33 

Plno Rldgo .............. :.................... 29 

PI no R ldgo Sandstone •..................... 5, 11, £9 

Point Lookout Sandstone ..• _................ 2 

Powder Rlvor Basin .••.•................ 7, IO, n; I4 

Price River Formation....................... 5 

R 

Roosldo, J. B., cited.......................... 3, 5 

Roforonco section, Allen Ridge Formation_ £4, £6. 27 

Almond Formation....................... SS 

Dad Sandstone Member of Lewis Shale... 39 

Hatfield Sandstone Mombor or Haystack 

Mountains Formation............ 19 

Haystack Mountains Formation.......... I7 

Plno Ridge Sandstone.................... 31 

Lewis Shale, Dad Sandstone Member..... 39 

Reynolds, M. W ., cited._ ............ 25, 30, 32, 37,38 

Rock River aroa of Laramie Basin, Steele 

Shale............................. IO 

Rock River Formation ............... 5, 11, £0, 25, £6 

Rock Springs upl!Ct. ___ .................. _ 26, 3I, 39 

s 

San Juan district, geology ____ ................ £ 

Schultz, A. R., cited ••••..................... 5,3I 

Scott, G.R., typosoctionmoasured by ______ _ 

4.- Separation Rim •............................. 

2I 

I4 

Shannon Sandstone Mombor or Steele Shale._ I4 

~ .... 

r' 

INDEX 

Page 

Siebenthal, C. E., cited....................... 3, 7 

Sohl, N .F., fossils identified by ....... _ .... 2I, 27,42 

South-central Wyoming, !ltratigraphic classification............................ S 

Southwestern Colorado, stratigraphic classification •.......... _________________ f 

Smith,J.H.,Cossils collected by______________ IO 

Spencer, A. C., cited ••• --·····-· .... __ ....... 2, 36 

Stanton, T. W., cited_________________________ 2I 

fossils identified by-------- ______ : ....... _ 48 

Star Point Sandstone_________________________ 5 

·Steele Shale _________________________________ S, 7,14 

Shannon Sandstone Member._____________ 14 

Sussex Sandstone Member________________ I5 

Stratigraphic nomenclature, revision.......... 5 

Summary of stratigraphic nomenclature...... 5 

Sussex Sandstone Member or Steele Shale_---- IS 

T 

Tapers Ranch .. --------------····-··-·······- I2 

Tapers Ranch Sandstone Member of Haystack 

Mountains Formation .•..... 5, 1£, 13,14 

Teapot Sandstone Member of Mesaverde Formation._ .......... ___ ........ _ ·II, £9, 31 

Telegraph Creek Formation .... _ .. _.......... II 

Thickness, Allen Ridge Formation._ ... ______ £6 

Almond Formation_______________________ Sf 

Fox Hills Formation_____________________ 4£ 

Haystack Mountains Formation.......... JS 

Lewis Shale______________________________ 38 

Pine Ridge Sandstone____________________ £9 

Rock River Formation................... £1 

Steele Shale ..• ----···-·-······-···-······- 10 

Tschudy, R. H., cited ................... 5,45,46,47 

fossil collections described by_............ 48 

0 

Type locality, Almond Formation ......... _._ 

Lewis Shale ••............................ 

Fox Hills Formation. ____ ......... _ ..... . 

Pine Ridge Sandstone __ .. _._ ............ . 

Type locality and distribution, Steele Shale._ 

Type section, Haystack Mountains Formation. _____ ... _ ....... _ ........... . 

Haystack Mountains Formation and its 

O'Brien Spring and Tapers Creek 

53 

Page 

31 

36 

41 

29 

7 

I2 

Sandstone Members __ . _.......... 15 

Rock River Formation •... __ ..... _._ ... _. £0, £1 

Wallace Creek Tongue of Cody Shale..... 11 

u,v 

Unconformity, at base-or Foote Creek Formation. ___ . __ .. __ .. _ .. _ .. _ ...... __ .. 45 

between Ferris and Hanna Formation_.__ 46 

Veatch, A. C., cited._ ....... __ ........ -- .. _.. 3, 5 

w 

Wallace Creek Tongue of Cody Shale. ___ ._ ... 11, IS 

Williams Fork Formation _________________ 3, 5, 3I, 33 

Lion Canyon Sandstone Member_ .. -_ ... _ 43 

Wind River Basin ............................ 11,26 

Wyoming, uplift in centraL.---------------.-- 37 

Y,Z 

Yampacoalfield............................. f 

Zapp, A. D., reference section measured bv.. I7