Leidy Formation New Name for a Pleistocene 

Glacio-Fluviatile-Lacustrine Sequence in 

Northwestern Wyoming

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 932-D

Prepared in cooperation zvith the Geological Survey 

of Wyoming and the Department of Geology of the 

University of Wyoming
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Leidy Formation New Name for a Pleistocene 

Glacio-Fluviatile-Lacustrine Sequence in 

Northwestern Wyoming

By].V. LOVE

GEOLOGY OF THE TETON-JACKSON HOLE REGION, 

NORTHWESTERN WYOMING

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 932-D

Prepared in cooperation with the Geological Survey 

of Wyoming and the Department of Geology of the 

University of Wyoming

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1994
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Robert M. Hirsch, Acting Director

Any use of trade, product, or firm names in this publication is

for descriptive purposes only and does not imply endorsement

by the U.S. Government.

Library of Congress Cataloging-in-Publication Data

Love, J.D. (John David), 1913-

Leidy Formation new name for a Pleistocene glacio-fluviatile-lacustrine sequence in 

northwestern Wyoming / by J.D. Love.

p. cm. (U.S. Geological Survey professional paper; 932-D. 

(Geology of the Teton-Jackson Hole region, northwestern Wyoming)

Includes bibliographical references.

Supt. of Docs, no.: I 19.16:932D

1. Geology, Stratigraphic Pleistocene. 2. Geology Wyoming Gros Ventre River 

Valley. 3. Leidy Formation (Wyo.) I. Title. II. Series. III. Series: Geology of the TetonJackson Hole region, northwestern Wyoming.

QE697.L765 1994 93-34982 

551.7'92'09787 dc20 CIP

For sale by U.S. Geological Survey, Map Distribution

Box 25286, MS 306, Federal Center

Denver, CO 80225
CONTENTS

Page

Abstract......................................................................................... Dl

Acknowledgment............................................................................ 1

Name and definition...................................................................... 1

Distribution and thickness............................................................ 1

Lithology......................................................................................... 3

Type section............................................................................ 3

Devils Elbow locality.............................................................. 8

Red Hills locality.................................................................... 8

West Crystal Creek locality................................................... 8

East Crystal Creek locality ................................................... 9

Page

Lithology Continued

Cottonwood Creek locality.................................................... D9

South Fork Fish Creek locality ............................................ 10

North Fork Fish Creek locality............................................ 10

Sources of sediment and conditions of deposition...................... 10

Environmental significance.......................................................... 11

Stratigraphic and structural relations........................................ 12

Age and correlation....................................................................... 12

References cited............................................................................. 12

ILLUSTRATIONS

FIGURE 1. Map showing localities of Leidy Formation in northwestern Wyoming................................................................................... D2

2-4. Photographs of Leidy Formation at type section:

2. General view................................................................................................................................................................ 4

3. Concentration of selenium-converter plants on unit 26........................................................................................... 5

4. Lower part................................................................................................................................................................... 6

5. Diagram showing intertonguing relations of Leidy Formation and glacial deposits at Devils Elbow locality..................... 9

6. Photograph of upper part of Leidy Formation at Devils Elbow locality.................................................................................. 9

in

GEOLOGY OF THE TETON-JACKSON HOLE REGION, NORTHWESTERN WYOMING

LEIDY FORMATION NEW NAME FOR A PLEISTOCENE

GLACIO-FLUVIATILE-LACUSTRINE SEQUENCE IN

NORTHWESTERN WYOMING

ByJ.D. LOVE1

ABSTRACT

The Leidy Formation (new name) consists of about 400 ft to perhaps 900 ft of intertonguing till, fluviatile gravel, very fine sand, 

sandstone, and tan to red-brown lacustrine clay, claystone, and 

shale. The formation was deposited along at least 40 mi of the 

Gros Ventre River valley and adjacent tributaries in and adjacent 

to a lake impounded behind an ice dam at the mouth of the Gros 

Ventre canyon. Subsequent erosion and glaciation have removed 

the deposit from all but a few isolated localities. No conspicuous 

volcanic debris and no diagnostic fossils have been found. The 

presence of abundant, coarse, granitic till from the Wind River 

Range, 25-50 mi to the southeast, and normal magnetic polarity of 

the fine-grained strata suggest a Pleistocene age for the sequence. 

The fine-grained strata are environmentally significant because 

they support abundant selenium-converter plants that probably 

have an adverse affect on livestock and wildlife.

ACKNOWLEDGMENT

This paper has been greatly improved by Ann Coe 

Christiansen whose help and skill in editing are 

acknowledged with gratitude.

NAME AND DEFINITION

The Leidy Formation is here named after Mount 

Leidy, the highest peak (elevation 10,323 ft) in the 

Mount Leidy Highlands, Teton County, Wyoming. 

The type section is on the north side of the Gros

'U.S. Geological Survey, Laramie, Wyoming.

Ventre River (fig. 1), 12 mi south-southwest of the 

peak. In an earlier publication (Love, 1956), the 

strata were lumped together as landslide and glacial 

deposits. Detailed geologic field work that started in 

1955 and roadcuts made by the U.S. Forest Service 

in the late 1970's demonstrated that an unnamed 

glacio-fluviatile-lacustrine sequence more than 400 ft 

thick was present, remnants of which occur along the 

valley of the Gros Ventre River and its tributaries 

over a distance of at least 30 mi (Love, 1977, p. 592, 

depositional event 19). Therefore, a formal name for 

these strata is justified.

DISTRIBUTION AND THICKNESS

The mapped areas of outcrop of the Leidy Formation are along the Gros Ventre River valley and the 

North and South Forks of Fish Creek, tributaries of 

the Gros Ventre River (fig. 1). The Leidy Formation 

is preserved only in isolated outcrops, rarely more 

than 1.5 mi long, so correlation of individual beds is 

difficult except for the basal, rather homogeneous, 

quartzite gravel. The formation tilts westward at 

about 35 ft per mi. In the absence of specific data 

to the contrary, one interpretation of the deposit as 

a whole could be that the poorly consolidated and 

generally fine-grained strata overlying the basal 

gravel were laid down in "layer-cake" fashion, with 

the older units at the base and the younger at the 

top. Another interpretation is that some units low 

in the center of the valley may be inset and thus

Dl
D2 GEOLOGY OF THE TETON-JACKSON HOLE REGION, NORTHWESTERN WYOMING

R114W 110°30' R113W

R114W 110°30' R113W

FIGURE 1 (above and facing page). Localities of Leidy Formation described in text, showing selected elevations, in feet, of top and base 

of Leidy Formation. DE, Devils Elbow; HC, Horsetail Creek; TS, type section of the Leidy Formation; RH, Red Hills; WCR, West 

Crystal Creek; ECR, East Crystal Creek; CO, Cottonwood Creek; SF, South Fork Fish Creek; NF, North Fork Fish Creek. Light 

shading on index map indicates Precambrian rocks; dark shading indicates Tertiary and Quaternary volcanic rocks. Base from U.S. 

Geological Survey l:100,000-scale Jackson Lake quadrangle, 1981; contour interval 50 m.

are younger than those high on the valley margins. 

If the latter is true, the actual original thickness of 

the Leidy Formation may never have been the 

cumulative thickness from the basal strata on the

valley floor to the highest strata on the valley margins. If the first interpretation of thickness and 

depositional mechanics is accepted, the formation 

would be about 440 ft thick at the type section in
LEIDY FORMATION NEW NAME FOR GLACIO-FLUVIATILE-LACUSTRINE SEQUENCE IN NW. WYO. D3

R112W R111W

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Mountains _ _J .

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NORTHWESTERN WYOMING SHOWING REPORT AREA

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R112W R111 W

10 KILOMETERS

5 MILES

sees. 1 and 12, T. 42 N., R. 114 W. (fig. 2). The 

westernmost exposure, at the Devils Elbow locality, 

is a partial section that may be nearly 300 ft thick. 

At the South Fork Fish Creek locality (SF, fig. 1), 

the top of the Leidy Formation is at 8,600 ft and 

the bottom is at 7,680 ft.

LTTHOLOGY 

TYPE SECTION

The lithology of the Leidy Formation is described 

in detail in the type section. The type section was
D4 GEOLOGY OF THE TETON-JACKSON HOLE REGION, NORTHWESTERN WYOMING

FIGURE 2. Type section of Leidy Formation, sees. 1 and 12, T. 42 N., R. 114 W, Teton County, Wyoming. View is to the north, across 

Gros Ventre River (lower left corner). Dotted line indicates line of section; solid lines indicate formation contacts. Qls, Quaternary 

landslide debris derived from Leidy Formation; Qly, Leidy Formation; arrow, till in unit 24; Jm, Morrison(?) Formation; J"En, 

Nugget Sandstone; "Sc, extensive outcrops of Chugwater Formation. Note the two roads across Leidy outcrops in middle of photograph; measured section is tied to them. Photograph by J.D. Love, June 1963.

described, sampled for pollen, and photographed in 

1955, 1957-58, 1967, 1969, and 1984 by the author 

(figs. 2-4). It is poorly exposed and extensively 

slumped, partly because of the unlithified nature of 

the strata. Intertonguing with the fine-grained 

strata are several tills, some with erratics as much 

as 5 ft in diameter. These are chiefly of Paleozoic 

rocks from the Gros Ventre Range (6 mi to the 

south), Precambrian igneous and metamorphic rocks 

from the Wind River Range (40 mi to the southeast), 

and volcanic rocks from the Absaroka Range (25 mi 

to the northeast) (fig. 1).

The type section was hand-trenched wherever possible. The dark-gray shale marker bed (unit 9) 

strikes about 45° NE. and dips about 1° NW. This 

dip could be depositional or could perhaps be the 

result of regional westward tilting of this part of the 

Jackson Hole area. Samples for pollen, collected in 

1958, were identified by E.B. Leopold (written commun., 1960). No megafossils were found except for 

sparse, unidentifiable leaf fragments at the Devils 

Elbow locality. Several samples for paleomagnetic 

determination were collected by D.W. Burbank, University of Southern California. In the type section 

below, unit 1 is oldest.
LEIDY FORMATION NEW NAME FOR GLACIO-FLUVIATILE-LACUSTRINE SEQUENCE IN NW. WYO. D5

Type section of the Leidy Formation

[Measured with hand level and steel tape on the north side of the 

Gros Ventre River in sees. I and 12, T. 42 N., R. 114 W., Mount 

Leidy and Grizzly Lake 7 1/2-minute quadrangles, 1965, Teton 

County, Wyoming]

Thickness 

(feet)

Leidy Formation (Pleistocene):

28. Claystone, reddish- to chocolate-brown, tough, containing 10 to 20 percent sand; pebbles of quartzite, chert, and red siltstone from Triassic 

Chugwater Formation in clay matrix. Unit overlaps a surface of high relief on north side of paleovalley cut in Chugwater Formation. Younger 

strata that may have once been present have been 

scoured away by ice and later erosion. Scattered 

clumps of Astragalus bisulcatus grow on unit but 

are not abundant. Pollen samples from 38 ft above 

base, from 35 ft above base, and from a chocolatebrown claystone in middle of unit are chiefly 

forms reworked from Cretaceous rocks.......... 45

27. Claystone, cocoa- to reddish-brown, soft, poorly exposed; mantled with much glacial debris. Probably no significant lithologic changes were missed 

because pits were dug about every 5 ft to in-place 

strata. In upper part, many angular, grit- to 

pebble-size clasts, chiefly of Precambrian quartzite and Paleozoic limestone and sandstone, 

embedded in claystone. Astragalus bisulcatus is 

abundant in lower 10 ft, sparsely present 

throughout remainder of unit. Top of unit is 30 ft 

north of wooden power pole................... 42

26. Claystone and shale, dark-lead-gray, soft, fissile in 

part, very finely sandy; light gray near top. Four 

pollen samples are forms chiefly reworked from 

Cretaceous rocks. Main seleniferous unit; about 

15 Astragalus bisulcatus bushes are in each 10-ftsquare area (fig. 3); another unidentified vetch 

also grows selectively on unit................. 31

25. Claystone, dark-gray, very fine grained, soft, plastic; 

thin partings of salmon-pink, very fine sand; lower part poorly exposed....................... 16

24. Till interbedded with sand and claystone, poorly exposed. Till is of angular erratics of Paleozoic rocks 

and some Precambrian granite that are as much 

as 6 ft in diameter. Sand is salmon pink and loose. 

Claystone is brick red and pebbly in upper part, 

gray brown in middle, and brick red at base. Pollen samples are reworked from Cretaceous shale. 

Astragalus bisulcatus grows on lower and middle 

parts but not on till.......................... 50

23. Claystone and clay, dull-reddish-brown to gray, soft; 

monotonous sequence with only a few very fine 

sand and silt partings. Because of poor exposures, 

pits were dug at 3-ft intervals down to in-place 

strata. Pollen samples show forms reworked from 

Cretaceous rocks............................ 33.5

22. Sand, greenish-gray, very fine, homogenous; many 

dark grains; moderately clean. Concentration of 

plants having chevron-shaped leaves, unidentifiable without flowers......................... 5.5

FIGURE 3. Concentration of selenium-converter plant Astragalus 

bisulcatus on gray claystone of unit 26, type section of Leidy 

Formation. Note abrupt decrease in abundance of these plants 

at lithologic change marking top of unit (arrow). Photograph by 

J.D. Love, August 1984.

Thickness 

(feet)

Leidy Formation (Pleistocene) Continued:

21. Claystone, dark-red-brown to green, plastic, soft, 

very fine grained, very limy; contains white, clear 

crystals of gypsum(?)......................... 24

20. Claystone, dark-reddish-brown to green; appears 

wet on surface; very limy; abundant secondary 

clear crystals of gypsum(?)................... 3

19. Claystone, dark-reddish-brown and green, mottled, 

very soft, plastic, limy, possibly gypsiferous; has 

hard crust on surface, poorly vegetated; supports 

some Astragalus bisulcatus. .................... 8

18. Sand, tan, containing pea gravel in upper 2 ft; darkbrown and green, mottled plastic claystone in 

middle; tan at base........................... 5

17. Gravel, chiefly gray and red quartzite in rounded 

clasts 0.25-2 inches in diameter, rarely larger; 

has appearance of river gravel with little clay and 

silt........................................ 6.5

16. Sand, rusty-brown, very soft, very fine; contains 

sporadic small, rounded quartzite pebbles. Lower 

1 ft has white, salty bloom on outcrop that is 

licked by animals.............................. 2

15. Claystone, dark-reddish-brown to brownish-gray, 

soft, plastic. Top is at top of abandoned upper 

road (fig. 2)................................. 11

14. Sand, gray, fine, clean, sparkly, loose; abundant 

black grains; 3-in-thick lens of coaly granules in 

middle.................................... 26
D6 GEOLOGY OF THE TETON-JACKSON HOLE REGION, NORTHWESTERN WYOMING

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.-;-" <S&> '*-" . ,*" " -*» S
LEIDY FORMATION NEW NAME FOR GLACIO-FLUVIATILE-LACUSTRINE SEQUENCE IN NW. WYO. D7

FIGURE 4 (above and facing page). Lower part of type section of 

Leidy Formation exposed near lower road shown on figure 2. 

Numbers refer to units of measured type section. 6, quartzite 

gravel; 7, sand with lenses of coaly debris; 8, sand (too thin to 

show in figure 4A); 9, shale and claystone; m, dark-gray shale 

marker bed; cl, laminated pink, yellow, and gray claystone; 

10, sand and silt. Photographs by J.D. Love: A and B, September 26, 1969; C, August 26, 1955. A, Lacustrine and fluviatile strata; B, locality shown in figure 4B; Ab, seleniumconverter plants of Astragalus bisulcatus; hammer shows 

scale. B, Detail of dark-gray shale marker bed, m; c, dark 

coaly debris; cl, claystone. C, Closeup of coarser laminae (as 

many as 20 per inch) and graded bedding in pink claystone of 

unit 9.

Leidy Formation (Pleistocene) Continued:

13. Partly covered interval between two roads. Tan silt 

and gray and pale-purple, silty, very fine sand 

was dug out. Upper part may have some pebbble 

beds, but this can be determined only by deeper 

excavation. Abundant Astragal us bisulcatus. ....

12. Claystone, chocolate-brown to pink, soft, plastic,

evenly bedded; thin silt and very fine sand partings. Upper 1 ft has white salty bloom; deer and 

elk have licked it so extensively that the top forms 

an overhanging ledge. Top of unit is at top of lower roadcut (fig. 2"> ...........................

11. Gravel, gray; com^oed chiefly of rounded quartzite 

clasts, but some are of fresh granite, probably 

from Wind River Range because no granite is exposed on north flank of Gros Ventre Range; size of 

clasts rarely as much as 6 in; angular blocks of 

Paleozoic sandstone as much as 3 ft in diameter; 

lithified and limy at top. .....................

Thickness 

(feet)

16

Thickness 

(feet)

Leidy Formation (Pleistocene) Continued:

10.

9.

8.

7.

6.

5.

4.

3.

2.

Sand and silt, brown, fine, thin-bedded. Top transitional. See figure 4A......................... 3

Shale and claystone, lead-gray to chocolate-brown 

and pink; thin interbeds of gray, very fine sand 

(fig. 4B). Laminated pink, yellow, and gray claystone with silty partings is shown in figure 4C. At 

base is a 1-in-thick, dark-gray, ripple marked 

shale marker bed (m, fig. 4A, B) that is continuous 

for 100 ft and dips 1° NW..................... 3.5

Sandstone, olive-drab, hard, ripple marked, very

limy, fine-grained; forms thin ledge (fig. 4B)...... 0.1

Sand, light-tan, soft, fine, mostly clean; lenses of 

black coaly debris in upper part (fig. 4B); 

scattered pebbles of quartzite in lower 2 ft....... 4

Gravel, gray; chiefly quartzite clasts 1-2 inches in 

diameter, very few larger than 4 in; some clasts of 

gray granite, probably from Wind River Range, 

have disintegrated in place. Top of unit is just 

above road level of lower road (figs. 4A, 2)........ 20.+

Sand, light-tan, clean in part, silty and clayey in 

part, soft. Pollen samples from thin, pink clay 

2 ft below top of unit, from 1-in-thick, pink, 

waxy claystone 6 ft above base, and from 

clayey sand containing carbon chunks that do 

not look like coal, 5 ft above base. A 4-in-thick 

layer of sandy siltstone, licked by animals for 

salt, is 3 ft above base................... 11

Gravel, gray, unlithified; chiefly of rounded quartzite redeposited from the Pinyon Conglomerate, 

but sparse angular clasts of Paleozoic and Mesozoic rocks are rarely larger than 1 ft in diameter; 

is more till-like than the basal gravel (unit 2)..... 28

Sand, light-brown, silty, evenly bedded; partings of 

very fine grained, dark-brown to pink claystone... 2

Gravel, gray, unlithified; smaller clasts are predominantly quartzite from the Pinyon Conglomerate; 

larger clasts of Mesozoic sandstone from Cretaceous formations (including Mowry Shale) and 

the Jurassic Sundance Formation; larger clasts 

also of Paleozoic limestone and Precambrian 

granite, probably from Wind River Range; many 

clasts larger than 2 ft in upper part; those in lower 

part are 1-2 inches in diameter. Looks more like 

a fluviatile deposit than till (no striated boulders 

seen). Contains some very small gold flakes...... 52

Total measured thickness of Leidy Formation 438.7

[Contact between Leidy Formation, which is essentially horizontal, and Morrison(?) Formation, which strikes N. 55° W. and 

dips 45° NE., is very sharp. The gravel of unit 2 was deposited 

on a very irregular surface.]

Thickness 

(feet)

Morrison(?) Formation (Jurassic?)

1. Sandstone, greenish-gray, porous, nonglauconitic, 

nonsparkly. Forms prominent 50-ft-high cliff 

above Gros Ventre River, 100 ft east of Leidy type 

section, the sandstone is overlain by 15 ft of red 

and green nonglauconitic claystone, also part of 

the Morrison(?) Formation..................... 50.+
D8 GEOLOGY OF THE TETON-JACKSON HOLE REGION, NORTHWESTERN WYOMING

DEVILS ELBOW LOCALITY

At the Devils Elbow locality (DE, fig. 1), the Leidy 

Formation is about 300 ft thick but is too poorly 

exposed to be described in detail except for the basal 

part, which was well exposed in a roadcut in 1984 

when the data for figure 5 were collected. The roadcut was extensively modified in 1988 by the U.S. Forest Service and no longer appears as diagrammed. 

This exposure was especially important because it 

showed the intertonguing of till with the fluviatilelacustrine strata. The till consists of large and small 

erratics, chiefly of highly rounded quartzite derived 

from the Pinyon Conglomerate but also includes 

angular fragments as much as 5 ft in diameter of 

Paleozoic and Mesozoic rocks that are embedded in a 

structureless, hard, limy matrix of pebbles, granules, 

and sand. Soled and striated erratics are common.

The clay and pebble sequence shown in figure 5 is a 

poorly bedded deposit of small, rounded pebbles in a 

matrix of dull-brown to gray, colloidally fine, plastic 

clay; this combination is characteristic of the Leidy 

Formation at all outcrops. The clay sequence is brown, 

reddish brown, and greenish gray, invariably fine, 

waxy, and plastic. The sand is tan and fine and forms 

a moderately continuous bed that dips about 7° NW.; 

it has not been determined if this is an initial attitude 

or one acquired by westward tilting of the Jackson 

Hole area in Pleistocene and Holocene time.

Overlying the strata exposed in the roadcut is 

nearly 100 ft of brown and gray clay and possibly 

some sand and gravel. Astragalus bisulcatus is 

abundant. Above this interval is 35 ft of sand (fig. 6) 

that is gray, medium, moderately well sorted, and 

homogeneous; it contains abundant sparkly grains 

and numerous chunks of coaly debris. This sand has 

been extensively quarried. It does not support 

Astragalus bisulcatus,

The remainder of the section overlying the sand is 

mostly brown and pink clay and silt that support 

abundant Astragalus bisulcatus. A 10-ft zone of clay, 

about 50 ft above the sand, contains some fossil leaf 

impressions too poor to be identified. The uppermost 

part of the Leidy Formation at this locality overlaps 

the Triassic Chugwater Formation; the Leidy was 

deposited on a surface of much higher relief than is 

now present but, despite this, very little locally 

derived coarse clastic debris from the adjacent slope 

is incorporated in it.

RED HILLS LOCALITY

The remnant of the Leidy Formation at the Red 

Hills locality is plastered on the east face of the Red 

Hills (RH, fig. 1); the relief on the base of the Leidy 

is about 560 ft in a horizontal distance of 2,200 ft. If 

the Leidy is essentially horizontal, its thickness here 

would be a minimum of 560 ft. The lowest part of 

the formation is at or slightly below the present Gros 

Ventre River valley floor, and the top is eroded away. 

Exposures are poor, and the formation is heavily 

mantled with glacial debris. Most of the sequence 

here is apparently soft, plastic, colloidally fine, gray 

to pink clay. Pollen samples were collected from near 

the top but yielded reworked Cretaceous forms. 

There are probably coarse elastics in the basal part 

but, if present, they are difficult to distinguish from 

younger glacial debris. An active landslide has 

stripped much of the Leidy claystone from the steep 

slope on the Chugwater Formation against which it 

was deposited. Astragalus bisulcatus is so abundant 

at some horizons in the middle and upper parts that 

it is difficult to walk without stepping on individual 

plants.

WEST CRYSTAL CREEK LOCALITY

The Leidy Formation, 1-2 mi south of the Red 

Hills locality, on the west side of Crystal Creek 

(WCR, fig. 1), consists largely of glacial debris and 

gravel having a maximum thickness of about 400 ft. 

Below the bare surface of till and gravel, about 10 ft 

of gray to dull-pink, plastic, soft, very fine clay is 

exposed in a pull-away landslide scar on the east 

side of the outcrop. The entire formation is poorly 

exposed in broad, rounded slopes; the base is everywhere hidden by slump or younger glacial debris. 

The till and gravel in the Leidy Formation are chiefly 

of subrounded clasts of Madison Limestone (Mississippian) from the Gros Ventre Range to the south, 

but there are also large erratics of Permian chert and 

Pennsylvanian Tensleep Sandstone, very sparse Precambrian granite from the Wind River Range to the 

southeast, and rounded quartzite cobbles and boulders from the Pinyon Conglomerate across the Gros 

Ventre River valley to the north. No volcanic rocks 

from the Absaroka Range to the northeast were 

found. Some of the boulder beds are pink and support sparse stands of Astragalus bisulcatus. The 

zone of waxy, soft clay is at an elevation of about 

8,080 ft, 350 ft higher than the top of the clay at the 

Red Hills locality. The strata at the West Crystal
LEIDY FORMATION NEW NAME FOR GLACIO-FLUVIATILE-LACUSTRINE SEQUENCE IN NW. WYO. D9

FIGURE 5. Diagram of south-facing roadcut at Devils Elbow locality (DE, fig. 1) showing the intertonguing relations of the lacustrinefluviatile strata and glacial deposits in the Leidy Formation. The till contains abundant striated and soled erratics, chiefly of 

quartzite from the Pinyon Conglomerate and Paleozoic and Mesozoic rocks. Approximately 70 ft of strata are exposed above road 

level. Diagram sketched from a photograph taken August 6, 1984; roadcut extensively modified in 1988 by the U.S. Forest Service.

Creek locality were deposited on a very irregular terrain cut into Paleozoic and Mesozoic rocks.

EAST CRYSTAL CREEK LOCALITY

On the east side of Crystal Creek (ECR, fig. 1), the 

Leidy Formation is at approximately the same elevation as on the west side and, likewise, is almost 

entirely gravel and till, but there are also tiny exposures of soft, plastic, red and gray clay. The till and 

gravel contain considerably more quartzite clasts 

from the Pinyon Conglomerate than the strata at 

West Crystal Creek; otherwise, the composition here 

is comparable to that at the West Crystal Creek 

locality.

COTTONWOOD CREEK LOCALITY

Seven miles to the east of the East Crystal Creek 

locality, on the west side of Cottonwood Creek (CO, 

fig. 1), the Leidy Formation unconformably overlies 

the Upper Cretaceous Sohare Formation and consists 

of about 75 ft of fluvial gravel containing clasts generally less than 1 ft in diameter but with a maximum 

size of about 3 ft. These clasts, chiefly from the 

Pinyon, are rounded quartzite clasts but include

_,

FIGURE 6. Leidy Formation at Devils Elbow locality (DE, fig. 1). 

Upper part of gray, medium sand, 35 ft thick, about 100 ft 

above roadcut shown in figure 5. Dark layers near base of photograph are concentrations of coaly debris. Photograph by J.D. 

Love, September 6, 1962.
DIG GEOLOGY OF THE TETON-JACKSON HOLE REGION, NORTHWESTERN WYOMING

lesser amounts of Eocene Absaroka Volcanic Supergroup rocks, Mesozoic sandstone, and Precambrian 

rocks from the Wind River Range. Overlying this fluvial gravel is about 60 ft of till containing huge, 

angular erratics, 4 ft or more in diameter; the erratics are mainly Paleozoic rocks in an unsized and 

unsorted matrix of many rock types. Overlying the 

till is 2 ft of dark-gray-brown, very fine, plastic clay 

similar to that in the type section. The clay is overlain by 20-30 ft of gray, fine, soft, loose, even-textured sand. Above the sand is 10 ft of lead-gray to 

tan, soft, plastic clay and silt. Overlying the clay is 

50 ft or more of tan, fine, loose sand. Astragalus 

bisulcatus is common on many of the beds.

SOUTH FORK FISH CREEK LOCALITY

The composition of the Leidy Formation on the 

South Fork of Fish Creek (SF, fig. 1) is especially significant. The basal strata rest unconformably on the 

Sohare Formation (Upper Cretaceous) on a spur 

about 150 ft topographically above the adjacent flood 

plain at the junction of the North and South Forks of 

Fish Creek (at elevation 7,680 ft, fig. 1). Here, the 

basal bed consists of about 5 ft of highly rounded 

granite boulders, more like stream boulders than glacial erratics, as much as 4 ft in diameter, intermixed 

with highly rounded quartzite gravel from the Pinyon. Above the basal boulder bed are 15 ft of soft, 

tan clayey sand, overlain by 5 ft of angular boulders 

of black basalt scoria and andesitic rocks that are as 

much as 3 ft in diameter. These boulders are overlain by a 10-ft unit of tan, clayey sand.

About 250 ft higher on this spur is a remnant of the 

upper part of the Leidy Formation. Cretaceous sandstone occupies the interval between these outcrops. 

At the base of the upper section is about 100 ft of 

quartzite gravel derived from the adjacent Pinyon 

Conglomerate that is exposed to the east and north. 

This gravel is intermixed with boulders of gray to 

pink granite, as much as 4 ft in diameter, which 

become more abundant and larger near the top of the 

section. One 4-ft boulder of hard, tuffaceous sandstone from the Aycross Formation (middle Eocene), 

which crops out 15 mi to the northeast, was observed. 

Above this boulder bed is 30-40 ft of tan to pink, 

loose, medium sand and some clay beds. Capping 

these is a till of giant granite boulders, one of which 

measured 8x6x5 ft, and sparse, much smaller, Paleozoic clasts. No volcanic clasts were seen. The granitic 

debris at this locality was carried 20-25 mi northwestward by ice and water from the Wind River 

Range. No granite source is exposed on the north

side of the Gros Ventre Range. The debris from the 

Wind River source merged with volcanic debris that 

was brought by ice and water 10 mi southwestward 

from Lava Mountain and the Absaroka Range. (See 

discussion of the deposit on the North Fork Fish 

Creek.)

NORTH FORK FISH CREEK LOCALITY

One remnant of the Leidy Formation, about 120 ft 

thick, is preserved on the west end of a narrow spur 

between Squaw and Papoose Creeks east of the 

North Fork of Fish Creek (NF, fig. 1). At the base is 

about 10 ft of carbonate-cemented, quartzite pebble 

conglomerate with clasts of only 1-2 in; this conglomerate unconformably overlies coaly strata in the 

Wind River Formation (lower Eocene). Above this is 

25 ft or more of bright-red, green, and gray clay, silt, 

sand, and tuff reworked from middle Eocene rocks. 

Overlying these strata is a 13-ft layer of jumbled, 

angular, red and black basalt boulders, some as 

much as 5 ft in diameter, which were probably 

derived from basalt flows on Lava Mountain, 10 mi 

to the northeast, and dated at about 500,000 years 

B.P. (Love and Love, 1983, p. 15). This boulder bed 

has characteristics typical of till, but it could be a 

debris flow. Above the boulder bed to the top of the 

deposit is about 65 ft of pale-green, very fine, sticky 

clay and pebbly sand containing sporadic boulders of 

basalt.

SOURCES OF SEDIMENT AND 

CONDITIONS OF DEPOSITION

A preliminary attempt was made to compile an isopach map using the data on figure 1 and using 19 

points from the exposed base and top of the Leidy 

Formation along 30 mi of the Gros Ventre River valley and the North Fork of Fish Creek. This isopach 

map shows that the river that deposited the basal 

fluvial gravel followed the present course of the Gros 

Ventre River between the junction of the North and 

South Forks of Fish Creek and the Devils Elbow 

locality. Most quartzite clasts were probably derived 

from the Paleocene and Upper Cretaceous Pinyon 

Conglomerate, which is extensively exposed north 

and east of the Gros Ventre River in the Mount Leidy 

area and along Fish Creek. However, Lagas (1984), 

who studied the glacial deposits in the lower part of 

the Gros Ventre valley, thought that the source of the 

basal quartzite gravels was Jackson Hole and that 

they backfilled the valley.
LEIDY FORMATION NEW NAME FOR GLACIO-FLUVIATILE-LACUSTRINE SEQUENCE IN NW. WYO. Dll

Glacial erratics indicate that ice flowed into the 

Fish Creek drainage from granitic terrain in the 

Wind River Range to the southeast and from the 

Paleozoic rocks of the Gros Ventre Range to the 

south (fig. 1). Precambrian rocks are not exposed 

north of the topographic crestline of the Gros Ventre 

Range (Simons and others, 1988). Ice also advanced 

southwestward from the Eocene volcanic terrain of 

the Absaroka Range and the Quaternary basalt of 

Lava Mountain, crossed the drainage divides at the 

heads of Cottonwood Creek and North Fork Fish 

Creek, and flowed down the Fish Creek valley. It 

then merged with ice from the Wind River and Gros 

Ventre Ranges.

The base of the Leidy Formation on the South 

Fork Fish Creek is at an elevation of about 7,740 ft, 

whereas 15 mi downstream, to the west at the Red 

Hills locality, the base is at 7,160 ft. This indicates 

that the paleovalley at the beginning of Leidy deposition had a gradient only slightly steeper along this 

stretch of the Gros Ventre valley than exists today 

(40 ft vs. 35 ft per mi).

What happened in the deeper part of Jackson Hole 

during deposition of the Leidy Formation is not well 

understood, but it seems likely that a glacier more 

than a thousand feet thick occupied the area between 

the Devils Elbow locality and the Teton Range, 10 mi 

to the west, and almost certainly dammed the Gros 

Ventre River valley west of the Devils Elbow locality. 

If the "layer-cake" interpretation, described previously, is correct, perhaps 800 ft or more of very fine 

clay and associated glacio-fluviatile deposits composing the Leidy Formation were deposited upstream 

from (east of) that ice dam. The clay probably was 

derived in large part from Cretaceous and Tertiary 

shale and claystone to the east. The presence of 

abundant Late Cretaceous pollen at several horizons 

in the type section of the Leidy helps substantiate 

this interpretation.

The sediments at the top of the Leidy Formation 

and incorporated glacial debris deposited in and adjacent to the lake had approximately the same maximum elevation. The maximum elevation of remnants 

at the West Crystal Creek locality is 8,400 ft, at 

Cottonwood Creek 8,400 ft, at South Fork Fish Creek 

8,600 ft, and 6 mi farther north, on North Fork Fish 

Creek, 8,700 ft. The top of the Leidy Formation 

farthest to the west is probably somewhat lower now 

than when originally deposited because of the westward downtilting of the Jackson Hole area along the 

Teton fault (Love, 1977) later in Quaternary time.

The eastern remnants of the Leidy Formation contain more glacial debris and less lacustrine sediment 

than their western counterparts. The top of the

glacio-fluvatile deposit probably increased in alt; tude 

toward the source in the Wind River Range due to 

normal stream gradients. Although many cubic 

miles of debris were removed by later glaciatior and 

erosion when the valley was reexcavated, there 

apparently was no more than 150 ft of deepening of 

the pre-Leidy valley floor in post-Leidy time.

The number of ice advances from the Gros Ventre 

Range to the south, from the Wind River Range to 

the southeast, and from the Absaroka Range to the 

northeast, and the thickness of ice at any given time 

during deposition of the Leidy Formation are not easily determined because of poor exposures and discontinuous remnants of Leidy deposits. Two conspicuous 

tills from the Wind River Range merge near the 

South Fork Fish Creek locality, but it is not known 

how they correlate with other tills in the region.

ENVIRONMENTAL SIGNIFICANCE

Astragalus bisulcatus is the only seleriumconverter plant on the Leidy Formation. This species requires selenium to grow well. Most of the 

selenium is probably recycled from the Sohare Formation and Cody Shale, although lesser amounts 

may have come from the Mowry Shale, Cloverly and 

Morrison(?) Formations, and the Eocene strata east 

of the forks of Fish Creek. In addition to indicating 

the presence of selenium, this plant has important 

environmental significance. One question that has 

been raised is whether this species is indigenous to 

the area. During the summer of 1933, O.A. Beath, 

the selenium chemist at the University of Wyoming, 

assigned the author to search for selenium-converter 

plants of any species along the Gros Ventre River 

valley. After a week of looking, H.F. Eppson, chemist, University of Wyoming, and the author found 

only a few plants of Astragalus bisulcatus, all on the 

Sohare Formation near the mouth of Cottonwood 

Creek. None was observed on sediments recognized 

in this report as the Leidy Formation. The seeds 

were probably brought into the region from some 

other seleniferous area by way of baled hay, cars, or 

cattle because the plants themselves cannot spread 

across broad natural nonseleniferous barriers. During the next 57 years, this species spread progressively along seleniferous strata, laterally from v^nere 

these strata cross the U.S. Forest Service access road 

along the Gros Ventre River valley. Each seleniumconverter plant converts a halo of selenium from a 

chemical form that is unavailable to most of the common, normally nonseleniferous plant types to a 

chemical form that is available to nearly all plants
D12 GEOLOGY OF THE TETON-JACKSON HOLE REGION, NORTHWESTERN WYOMING

(Beath, 1982). Thus, the originally nonseleniferous 

plants at these sites became secondarily seleniferous. 

Each June, about 3,000 cattle are driven across the 

Leidy Formation at the Devils Elbow and Horsetail 

Creek (DE, HC, fig. 1) localities (Fred Kingwill, U.S. 

Forest Service, oral commun., 1985) and spread out 

from there eastward into the headwaters of Fish 

Creek. The cattle return across the same downstream localities in September and October. Chronic 

selenium poisoning, as indicated by "sledrunner" 

hoofs, weight loss, patchy hair, and low birth rate, 

have been observed in some of the cattle that have 

spent the summer on this range (correspondence 

from O.A. Beath to Rod Lucas, January 1957). The 

area east of the type section of the Leidy Formation 

is winter range for elk. The type section and the Red 

Hills locality are likewise winter range for bighorn 

sheep. The elk in this area have an unusually low 

birth rate, and some exhibit greater nervousness and 

a higher incidence of ulcerated livers and tooth decay 

than elk in nonseleniferous areas (Dr. Margaret Altmann, University of Wyoming, oral commun., 1955). 

The effect of selenium on humans in this area has 

not been documented.

STRATIGRAPHIC AND STRUCTURAL 

RELATIONS

The Leidy Formation rests with angular unconformity on strata ranging in age from Pennsylvanian to 

early Eocene. The relief on this unconformity is 

steeper than the present land surface. The only 

deposits known to overlie the Leidy Formation along 

and adjacent to the Gros Ventre River valley are 

younger tills of Pleistocene age.

AGE AND CORRELATION

The Leidy Formation is of Pleistocene age. No 

diagnostic megafossils or microfossils have been 

found. The ice-margin environment may have been 

too harsh to permit extensive development of fauna 

and flora. Samples from units 5-26 of the type section contain the following palynomorphs, as identified by E.B. Leopold (Report F-58-32-D, written 

commun., April 28, 1960):

Sporites arcifer Thiergart

Triplanosporites sinuosus Pflug

Gleicheniidites senonicus Ross

Deltoidospora halli Miner

Foveosporites canalis Balme

Inaperturopollenites dubius Potonie 

Pityosporites labdacus Potonie 

Classopollis cf. torosus Reiss 

Triporopollenites endoplicatus (Stanley, 1960 

dissert.).

"Units C, D, and E [units 15, 21, and 23 in type 

section] contain substantial amounts of these pollen 

about 60 to 100 grains per 20-gram sample of sediment. Only 6 or 8 grains that could be interpreted as 

Quaternary pollen forms were found among these 7 

samples. Because the stratigraphy indicates a Quaternary(?) age [for the Leidy Formation], the contained pollen must be interpreted as rebedded. The 

assemblage listed above suggests a Lance age for the 

source sediments."

Paleomagnetic determinations by D.W. Burbank, 

University of Southern California (oral commun., 

1985) of samples from the type section of the Leidy 

Formation have normal magnetic polarity, compatible 

with an age of less than about 750,000 years B.P. No 

volcanic ash has been found in the Leidy Formation.

The till intertonguing with the fluviatile-?acustrine 

strata (fig. 5) in the Leidy Formation represents a 

glaciation that is younger than the Pliocene till 

(Love, 1989; also called diamicton by Pichmond, 

1986, p. 86) under the Huckleberry Ridg^ Tuff at 

Signal Mountain in Grand Teton National Park and 

is older than, or perhaps contemporaneous with, 

some of the ice that dammed the mouth of the Gros 

Ventre River valley. The correlation of this and other 

Pleistocene glaciations in Jackson Hole with the Bull 

Lake glaciation at Bull Lake, Wyoming, the Pinedale 

glaciation at Pinedale, Wyoming, and old^r glaciations in the Wind River Range to the southeast has 

not been firmly established.

REFERENCES CITED

Beath, O.A., 1982, The story of selenium in Wyoming: Laramie, 

University of Wyoming Agricultural Experiment Station 

Bulletin 774, 31 p.

Lagas, P.J., 1984, The glacial geology of the Gros Vertre Canyon, 

Teton County, Wyoming: Bethlehem, Pennsylv? nia, Lehigh 

University, unpub. M.S. thesis, 150 p.

Love, J.D., 1956, Geologic map of Teton County, Wyoming, in Jackson Hole: Wyoming Geological Association Guidebook, llth 

Annual Field Conference, map in pocket.

 1977, Summary of Upper Cretaceous and Cenozoic stratigraphy and of tectonic and glacial events in Jrokson Hole, 

northwestern Wyoming, in Rocky Mountain Thrust Belt Geology and Resources: Wyoming Geological Association Guidebook, 29th Annual Field Conference, p. 585-593.
LEIDY FORMATION NEW NAME FOR GLACIO-FLUVIATILE-LACUSTRINE SEQUENCE IN NW. WYO. D13

 1989, Names and descriptions of new and reclassified formations in northwestern Wyoming: U.S. Geological Survey Professional Paper 932-C, 45 p.

Love, J.D., and Love, J.M., 1983, Road log, Jackson to Dinwoody 

and return: Geological Survey of Wyoming Public Information 

Circular 20, 32 p.

 1988, Geological road log of part of the Gros Ventre River 

valley, including the Lower Gros Ventre slide: Geological 

Survey of Wyoming Reprint 46, 14 p.

Love, J.D., Reed, J.C., Jr., and Christiansen, A.C., 1992, Geologic map of Grand Teton National Park, Teton County,

Wyoming: U.S. Geological Survey Miscellaneous Inve^tigations Map 1-2031, scale 1:62,500.

Richmond, G.M., 1986, Stratigraphy and chronology of glaciations 

in Yellowstone National Park, in Sibrava, V, Bowen, D.Q., 

and Richmond, G.M., eds., Quaternary Glaciations in the 

Northern Hemisphere: New York, Pergamon Press, p. 82-98.

Simons, F.S., Love, J.D., Reefer, W.R., Harwood, D.D., and 

Bieniewski, Carl, 1988, Mineral resources of the Gros Ventre 

Wilderness Study Area, Teton and Sublette Counties, Wyoming: U.S. Geological Survey Bulletin 1591, 65 p.

Published in the Central Region, Denver, Colorado 

Manuscript approved for publication August 10,1993 

Edited by Richard W. Scott, Jr. 

Graphics prepared by Wayne Hawkins 

Photocomposition by Marie Melone

*'U.S- QOVEHNMHSIT PRINTING OFFICE: 1993-573-038/86011

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