The Early Pleistocene (Latest Blancan-Earliest 

Irvingtonian) Froman Ferry Fauna and History of 

the Glenns Ferry Formation, Southwestern Idaho 

U.S. GEOLOGICAL SURVEY BULLETIN 2105 
Cover.-Late 19th- or early 20th-century Idaho ferry, from photograph in James L. 

Huntley, "Ferry boats in Idaho" (1979), redrawn by Rob Wells. 
The Early Pleistocene (Latest Blancan-Earliest 

Irvingtonian) Froman Ferry Fauna and History of 

the Glenns Ferry Formation, Southwestern Idaho 

By Charles A. Repenning, Ted R. Weasma, and George R. Scott 

U.S. GEOLOGICAL SURVEY BULLETIN 2105 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1995 
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary 

U.S. GEOLOGICAL SURVEY 

Gordon P. Eaton, Director 

For sale by U.S. Geological Survey, Information Services 

Box 25286, Federal Center 

Denver, CO 80225 

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 

Repenning, Charles Albert, 1922-

The early Pleistocene (latest Blancan-earliest Irvingtonian) Froman Ferry fauna and 

history of the Glenns Ferry formation, southwestern Idaho I by Charles A. Repenning, Ted 

R. Weasma, and George R. Scott. 

p. em.- (U.S. Geological Survey bulletin; 2105) 

Includes bibliographical references and index. 

Supt. of Docs. no.: I 19.3:2105 

I. Paleontology-Pleistocene. 2. Animals, Fossil-Idaho. 3. Geology-Idaho. 

4. Glenns Ferry Formation (Idaho) I. Weasma, Ted R. II. Scott, George R., 1946- . 

III. Title. IV. Series. 

QE75.B9 no. 2105 

[QE741.2] 

557.3 s-dc20 

[560'.178] 94-30229 

CIP 
CONTENTS 

Abstract .......................................................................................................................... . 

Introduction..................................................................................................................... 2 

Organization of This Report . .. . . . . . . .. . . . . . . . . . . .. . . . . .. . . . . . .. .. . . . . . . . . . . . . . .. . . . . . .. . . .. . . . .. . . . . .. . . . . . . 6 

Age Assignments and Age of the Froman Ferry Faunas .. . . .... ....... ... ....... ......... ... . 8 

Mammal Ages and Provincialism . .. .. .. .. . . . .. . .. ... . . . . . .. .. . . .. . . . .. . . . . . . . . . .. . .. .. ... . . .. .. . ... . . . . . . 10 

Dispersal................................................................................................................ 13 

Dispersal Events and Faunal Changes ..................... ... ...... .. .... ........ .......... ............ 16 

Collections . .. .. . . . . . . .. .. .. . . . . . . . . .. .. . . . . . . .. . . .. . . . . . . . . . .. . .. . . . . . . .. . . .. .. . . . . . . . . . . . . . . . . . . .. . . . . . . .. . . . .. . . . . . . 18 

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

The Froman Ferry Fauna................................................................................................. 18 

Genus Sorex Linnaeus, 1758 ................................................................................. 19 

Genus Ischyrosmilus Merriam, 1918 ........ ........... ........... ... .......... .......... ........... .... 20 

Genus Puma Jardine, 1834 .................................................................................... 20 

Genus Hypo fagus Dice, 1917.................... ... . . . . . . . . . . . . . . . . . .. . .. .. . . . . .. .. . . . . . . . . .. . . .. . . . . . . .. . . . 25 

Genus Castor Linnaeus, 1758 ............................................................................... 26 

Genus Mictomys True, 1894 .. . ...... ........ ........... ...... ........ .. ......... ......... .. . .......... ... ... 27 

Genus Mimomys Major, 1902 ............................................................................... 30 

Genus Phenacomys Merriam, 1889 ...................................................................... 32 

Genus Ondatra Major, 1902 ................................................................................. 33 

Genus Stegomastodon Pohlig, 1912...................................................................... 35 

Genus Plesippus Matthew, 1924........................................................................... 35 

Specific Nomenclature.................................................................................... 43 

Subgeneric Nomenclature ............................................................................... 44 

Phylogenetic Summary ................................................................................... 46 

Genus Gigantocamelus Barbour and Schultz, 1939 .. ......... ................ ......... ......... 4 7 

Family Cervidae Gray, 1821 ................................................................................. 47 

Historic Setting of the Froman Ferry Faunal Succession ............................................... 47 

Youngest Glenns Ferry Lake Beds . ............ ............. ..... .... . ....... ........ .......... .......... 4 7 

Correlation of Youngest Lake Beds................................................................ 50 

Snake River and the Glenns Ferry Formation ....................................................... 52 

Glenns Ferry Formation ........................................................................................ 53 

Glenns Ferry Formation Near Hagerman and King Hill ................................. 55 

Lake, Marsh, and Stream Facies, Longitudinal Relationships ........................ 57 

Lake, Marsh, and Stream Facies, Transverse Relationships........................... 59 

Chattin Hill.............................................................................................. 59 

Jackass Butte........................................................................................... 60 

Birch Creek ............................................................................................. 61 

Regional Facies Relationships .......... ............ ............ ............ ...................... ... 62 

Incision of the Lake Beds and Canyon Damming ... .. ..... ....... ..... .... .. ........... ... 64 

Adjacent Areas of Significance ............................................................................. 66 

Pre-Glenns Ferry Drainage . . ............. .... .. .. . . . . . ... ..... . . . . ............. .... .... . ..... ... . . . . . .. 66 

Glenns Ferry Lake Drainage .. . .. .. .. .. .. . .... .. .. .. .. .. . .. .. .. .. .. .. .. .. . .. .. .. .. .. .. .. .. . .. .. .. . .. .. . 69 

Conclusions .. . . .. .. .. .. .. . . .. .. . .. . .. . . . . .. .. .. . . . . . . .. .. .. .. .. . . .. . .. .. . . . . . .. .. .. .. .. . . . . .. .. .. .. . . . . .. .. .. .. . . .. .. .. .. . . . . .. . 71 

References Cited .. . .. . . .. .. .. .. . .. . . . . .. .. .. . . . . .. . .. .. .. . . . . . .. .. .. .. . . . . .. .. . .. . .. . . . .... .. . . . . . .. .. .. .. .. . . .. .. .. .. . . . . .. . 7 4 

Correction........................................................................................................................ 79 

Index ................................................................................................................................ 80 

III 
IV CONTENTS 

FIGURES 

1. Map of southern Idaho and adjacent areas, showing the route of the Snake River, the western Snake River 

Plain, and some localities mentioned in the text...................................................................................................... 3 

2. Map of the Froman Ferry area, Idaho...................................................................................................................... 4 

3. Generalized composite stratigraphic column of the Glenns Ferry Formation at Froman Ferry area, with 

paleomagnetic determinations . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . .. . . . . . . . . . ... . . . . . . . . . ... . . . . . . . . . . ............ ...... 7 

4. Correlation chart of paleomagnetic polarity chrons with events, time, deposits, faunas, and mammal ages.......... 9 

5-11. Sketches showing: 

5. Sorex (Otisorex) palustris USNM 264328 from GS-225, lower dentition and mandibular condyles............ 19 

6. Modem specimens of Puma concolor and Panthera tigris calcanea and astragali........................................ 21 

7. Third lower premolar of Hypo lag us gidleyi USNM 264338 from locality GS-232 ...................................... 25 

8. Dentition of microtine rodents, Froman Ferry faunal succession.................................................................. 28 

9. Upper cheek teeth of Plesippus idahoensis and P. simplicidens .................................................................... 36 

10. Upper and lower cheek teeth of Plesippusfromanius, P. shoshonensis, and P. idahoensis .......................... 39 

11. Second upper molar and incomplete third lower molar of P. fromanius.... ... . . . . . . . . . . .. .. . . . . . . .. .............. ............. 40 

12. Map of Snake River area between Sand Point and Walters Ferry, Idaho, showing localities discussed................. 48 

13. Map of Idaho and adjacent areas showing approximate location of some localities discussed............................... 66 

To convert 

Feet (ft) 

Miles (mi) 

Pounds (lb) 

METRIC CONVERSIONS 

To 

Meters (m) 

Kilometers (km) 

Kilograms (kg) 

Multiply by 

0.3048 

1.609 

0.454 
THE EARLY PLEISTOCENE (LATEST BLANCANEARLIEST IRVINGTONIAN) FROMAN FERRY FAUNA 

AND HISTORY OF THE GLENNS FERRY FORMATION ' SOUTHWESTERN IDAHO 

By Charles A. Repenning, Ted R. Weasma, 1 and George R. Scott2 

ABSTRACT 

The Froman Ferry fauna of south-central western 

Idaho was discovered in about 1897 during an early survey 

of the mining districts in the mountains to the west and 

north of the western Snake River Plain. This survey was 

made by Waldemar Lindgren and party of the U.S. Geological Survey. The Froman Ferry fossil locality was visited 

next by John C. Merriam of the University of California in 

1916, but seems not to have been examined again until 

1988, when the Boise District Office, Bureau of Land Management, was conducting an inventory of fossil localities. 

Much of the neglect of this fauna appears to have resulted 

from an error in recording its locality description as "section 7 ," rather than "section 17 ," in the files of the University of California Museum of Paleontology; moreover, the 

construction of a bridge across the Snake River at the town 

of Marsing in 1921 resulted in the abandonment of the 

nearby Froman Ferry, the closest geographic reference in 

the description of the locality. 

Most subsequent mention of the locality has assumed 

that the age of the Froman Ferry fossil fauna was that of the 

better known "Grand View" fauna from Jackass Butte, more 

than 50 miles to the southeast and near the city of Mountain 

Home. The recent collecting here described has established 

the age of the Froman Ferry fauna as being about half a million years younger than the Jackass Butte fauna. 

The two faunas are quite similar. but have some differences that reflect this age difference. The Jackass Butte 

fauna is late Pliocene and typical of the Blancan V mammal 

age of Repenning (1987); the Froman Ferry fauna is Pleistocene and spans the boundary between the Blancan and 

Irvingtonian mammal ages in the Pacific Faunal Region of 

1

Bureau of Land Management, Roseburg. Oregon. 

2 BLM Volunteer Program. Nampa, Idaho. 

the United States, as herein recognized; both are in the 

Glenns Ferry Formation of Mal de and Powers ( 1962), 

which is present throughout the western Snake River Plain. 

Although primarily characterized by faunal elements 

that are also known from Jackass Butte, the Froman Ferry 

fauna differs in the appearance of an immigrant microtine 

rodent in the lower third of the fossiliferous section (a 

rodent known earlier from the Beringian Faunal Region 

adjacent to the Arctic Ocean), in a more evolved horse of 

intermediate condition between the Pliocene genus 

Plesippus (known from the older parts of the Glenns Ferry 

Formation) and the Pleistocene and Recent genus Equus, 

and in the oldest known record of the North American 

puma, although its ancestors are believed to be represented 

in the older Glenns Ferry faunas. 

The Froman Ferry fauna also seems to lack some taxa 

that would be expectable, to judge by the older Jackass 

Butte fauna. These taxa include the cold-water stream 

sculpin Cottus (first known from Jackass Butte) and the 

giant beaver Procastoroides (known from most older fossiliferous horizons of the Glenns Ferry Formation); the first 

seems to be lacking in the Froman Ferry fauna because of 

environmental reasons (the Froman Ferry fauna represents 

warmer water than does Jackass Butte fauna) and the second appears to represent the extinction of the giant beaver 

because it is unknown from all other faunas of the same or 

younger age in the Pacific Faunal Region. 

In addition, the archaic rabbit Hypolagus gidleyi was 

found high in the Froman Ferry faunal succession (perhaps 

little more than 1.5 million years old). This rabbit has not 

been found at Jackass Butte and was previously thought to 

have become extinct before the time of that fauna, perhaps 

by 3.0 million years ago. 

The fossiliferous section containing the Froman Ferry 

fauna is, in places, nearly 500 feet thick and consists of 

abundant marsh and pond deposits with fluvial deposits that 

become increasingly prominent toward the top of the 
2 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

section. An overlying lava flow provides a minimum age of 

> 1.5 Ma and paleomagnetic polarity determinations provide 

a maximum age of <1.67 Ma. As such, the fauna is the 

youngest known from the Glenns Ferry Formation of Malde 

and Powers (1962), and enables determination of the timing 

and history of the final drainage of the western Snake River 

Plain and the relationship of the formation to Hells Canyon, 

which now drains the area to the Columbia River in southcentral Washington. Hells Canyon appears to be at least 3 

Ma old and may have a history that dates back to the 

Miocene. 

INTRODUCTION 

To our knowledge nothing has been published indicating that vertebrate fossils have been collected from the Froman Ferry area, along the western margin of Canyon 

County and 14 miles west of Nampa, Idaho, since J.C. Merriam visited there in 1916 (Merriam, 1918). In 1988 

Weasma, then in the Boise District Office of the Bureau of 

Land Management, was compiling an inventory of Idaho 

fossil localities and noted that the Froman Ferry area 

seemed not to have been examined in perhaps 72 years. 

Weasma inspected the area and found a few fossils, and 

suggested that Scott try to collect more under the sponsorship of the U.S. Government Volunteer Program. The locality was first collected, apparently by N .F. Drake, in 1897 

(Lindgren, 1900). 

Scott prospected the area and discovered fossils in and 

near the Chalk Hills on the Marsing 7.5 minute quadrangle 

(USGS) and in the area of the Cucumber vertical angle 

benchmark on the Lake Lowell 7.5 minute quadrangle to 

the east (figs. 1 and 2). The area includes the original Froman Ferry fauna of Lindgren, which is at the base of the 

fossiliferous section near the Snake River. These are not the 

Chalk Hills for which the Miocene Chalk Hills Formation 

was named (Malde and Powers, 1962); those Chalk Hills 

are about 75 miles to the southeast. 

The only exposure of fossiliferous deposits along the 

Snake River about "two mi. plus NW of Froman Ferry 

[actually about 1.4 miles NW.], 7-8 mi. SW of Caldwell, 

Idaho, and in T.3N, R.4W, Sec. 7 [actually sec. 17]" (University of California Museum of Paleontology [UCMP] 

Locality 3036), is at a point along the Snake River that is 

closest to Chalk Hills of the present report. We believe that 

this exposure is probably the locality UCMP 3036C of Merriam (1918) in the upper 75-100 feet of the section; this 

locality has been renumbered in the UCMP locality files as 

3036 and is the type locality of Ischyrosmilus? idahoensis 

Merriam and Equus idahoensis Merriam. Merriam ( 1918) 

and the UCMP locality records indicate two lower 

localities: (1) 3036A, from the base of the section 50-75 

feet above the Snake River flood plain (now numbered 

V75043); and (2) 3036B in the middle of the section (now 

numbered V75044). These elevations are estimates made by 

the person recording the locality in the UCMP records, 

probably J.C. Merriam; the river bluff is no more than 140 

feet high. 

Although the UCMP localities are not exactly recoverable, as both the ferry and the road leading to it no longer 

exist, Scott found fossils at the highest horizon, apparently 

geographically and stratigraphically close to UCMP locality 

3036 (Merriam's 3036C), and assigned his field locality 

number GS-211 to it. Thus old UCMP 3036C, renumbered 

UCMP 3036, and Scott's field number GS-211 are, in our 

opinion, the same or nearly the same locality. Scott found 

no fossils in the stratigraphically lower horizons, despite the 

UCMP locality records indicating that Merriam had. Examination of the fragmentary material in UCMP that Merriam 

collected in the two lower localities suggests that it may 

have been slope wash from the fossiliferous highest horizon. 

These, or this, locality is the lowest fauna of the Froman Ferry faunal succession. Original records in the 

National Museum of Natural History [USNM] with the original material collected in 1897 and later by N.F. Drake (and 

W. Lindgren?) are located only in terms of distance from the 

ferry along the no-longer evident road to Caldwell and may 

or may not have also been slope wash, as the road would 

have crossed the highest fossil horizon at some point within 

2 miles of the ferry. The former location of the ferry is here 

taken to be that indicated by Huntley ( 1979). 

The bluff in which these localities occur is downsection 

and separate from the exposures in Chalk Hills a mile and 

less to the northeast of the Froman Ferry localities (fig. 2). 

The paleomagnetic polarity section made by Van Domelen 

and Rieck (1992) ran from the base of the Froman Ferry 

bluffs up to the top of Chalk Hills; it indicated that this 

entire section was reversely polarized. The paleomagnetic 

section was taken from the lowest exposures (below locality 

UCMP 3036 ±=GS-211) to locality GS-203, which are 

shown in figures 2 and 3. 

Scott found fossil mammals about 25 feet below the 

top of the bluff adjacent to the Snake River near UCMP 

3036, and we believe that this must be close to the original 

locality of Drake (Lindgren, 1900; Lindgren and Drake, 

1904, p. 86), and essentially the same horizon as UCMP 

locality 3036. The bluff is not steep but is rather hummocky 

and now overgrown with vegetation, possibly shaped by a 

series of small slumps; cultivated and irrigated fields are on 

the surface above it. 

The ferry, first built in about 1886 by G.W. Froman, 

hasn't been in existence for many years (since about 1921) 

and is not located on recent maps; it was located about 3 

miles downstream (north) of the present bridge across the 

Snake River at Marsing, Idaho (Huntley, 1979). The bluff 

containing locality GS-211 is about 7,400 feet northwest of 
INTRODUCTION 3 

HIGHLANDS 

OF 

f 

I 

r 

\. ,.-:\ 

0 25 

I I II I I 

50 

I 

MONTANA 

75 MILES 

I 

CENTRAL IDAHO \ 

:------~--

\. _ veNIIo~ston1 e ~ 

\Centennial Mtns \' ·~ . at1ona{ . 

.------- ·I Park ( 

,.·--

·-·J 

Fig. 12 

Figure 1. Southern Idaho and adjacent areas, showing the route of the Snake River, the western Snake River Plain, and some localities 

mentioned in the text. Areas of figures 2 and 12 are outlined. 

the ferry site, in the NW I/4 sec. 17, T. 3 N., R. 4 W. (Boise 

base and meridian) and at present is largely covered by 

vegetation. 

The many fossil localities found by Scott in the Froman 

Ferry area are here included under the more inclusive name 

"Froman Ferry faunal succession,'' enlarging the geographic 

and stratigraphic coverage of the original locality name, and 

including the field names: Froman Ferry (includes UCMP 

3036), Chalk Hills, Cucumber, Lizard Butte, and Homedale 

areas (fig. 2). Most of these field area names include several 

individual localities that are fairly close together. The individual localities are distributed over about 13.5 miles, 

extending from east of Homedale on the north (downstream) 

to Pickles Butte, at the southern (upstream) limit of the 

Cucumber area. The mammal-bearing part of the Glenns 

Ferry Formation is at least 255 feet thick in the Froman 

Ferry-Chalk Hills area and appears to be nearly 500 feet 

thick in the Cucumber area; the difference appears to result 

from erosion that formed an overlying unconformity. 

All localities were found on the east side of the Snake 

River; we have found only lake deposits of the Glenns Ferry 

Formation on the west side of the river, and these only south 

of Marsing. The fossiliferous deposits are essentially a single stratigraphic zone of the Glenns Ferry Formation; this 

zone appears to be more than 214 feet thick everywhere 

except near Homedale to the north. Except for the 

Homedale and Lizard Butte areas, all exposures are in 

nearly continuous outcrops. 

The stratigraphically lowest specific locality here discussed is that bearing the field name Froman Ferry area 

(field locality GS-211, ?=UCMP 3036), which appears to 

be the locality, or at least the horizon, of most of the earlier 

published fossil records. GS-211 is also the topographically 

lowest locality and is about 2,398 feet above sea level and 
4 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

43° 

45' 

43° 

30' EXPLANATION 

1. Cucumber area 

2. Lizard Butte area 

3. Froman Ferry site 

4. Froman Ferry area 

5. Chalk Hills area 

6. Homedale area 

;z; 0 

0 :c 

ffi <t: ~ 9 

0 

2600 

-¢-Test hole in Deadhorse 

Canyon 2,400 foot and 2,600 foot contours shown 

Figure 2. The Froman Ferry area, Idaho, showing localities mentioned in the text and the various fossil areas included under the name 

Froman Ferry faunal succession. The paleomagnetic section (fig. 3) was made from UCMP-3036 northeast to GS-203. Map is continued to 

south (at a different scale) in figure 12. 

about 178 feet above the Snake River. This is the youngest 

horizon previously reported as the Froman Ferry locality in 

the University of California Museum of Paleontology 

records (UCMP 3036). All our localities are designated by 

the prefix GS-, and their descriptions are on file in the 

National Museum of Natural History (USNM) in Washington and in the Idaho Museum of Natural History (IMNH) in 

Pocatello. 

Scott's collections from the Froman Ferry faunal succession consist largely of microtine rodents, fish, and 

amphibians, although a few remains of large mammals are 

present. There exists the possibility that local residents have 

picked the area clean; one of us (Scott) has seen some 

material in private hands. However, no privately owned collections that have been found appear to be extensive or significant. 

The depositional nature of the fossil accumulation, in 

light-colored, flat-bedded silts and fine sands of shallowwater marsh deposits (containing abundant impressions and 

carbonized reeds and rushes) interbedded with less frequent, darker gray and siltier lake and crossbedded, sandy 

to pebbly sluggish stream deposits of a browner hue, suggests that rodents were actually the most abundant 

mammals present, and that the rarity of large mammals, and 

rodents other than microtines, reflects the environment of 

the fauna. Larger mammal remains are most often 
INTRODUCTION 5 

associated with stream deposits, and these are most common in the higher parts of the section, particularly in the 

Cucumber area. The absence of other rodents is taken as an 

environmental indication; as will be discussed, the climate 

appears to have been cloudy and cool, and ice may have 

formed locally in the marshes during the winter. 

Pollen from the Glenns Ferry Formation, much farther 

upstream (from Bruneau and Hagerman), shows an alternation of pine and fir (with some spruce) forests and sage 

steppe (Thompson, 1992). These pollen records are, however, from an older part of the formation and pollen was not 

found in the Froman Ferry area. 

The topographically and stratigraphically highest specific localities in the Froman Ferry faunal succession are 

from the area of Pickles Butte and near the Cucumber vertical angle bench mark on the Lake Lowell quadrangle. These 

are as much as 2,890 feet above sea level and are in deposits 

that have been elevated by slight tilting at the time of, and 

shortly before, the volcanic activity that formed Pickles 

Butte. Stratigraphically, they appear to be little higher than 

the top of Chalk Hills (2,630 feet above sea level). 

Except in the area of Pickles Butte (where the strata are 

slightly tilted), the deposits are essentially flat lying, 

although dipping slightly southward toward the Snake River. 

They are composed of fine-grained lacustrine, paludal, and 

fluvial deposits that contain abundant marsh vertebrates and 

fresh-water mollusks, as well as plant remains (primarily of 

reeds and rushes); the nonmammalian fossils have not been 

studied, although Gerald R. Smith (University of Michigan 

Museum of Paleontology) has examined about 1,000 fish 

bones from the Cucumber area and Terrance Prest (Seattle, 

Wash.) is currently working on the mollusks. 

The marsh deposits are highly diatomaceous, and the 

diatoms indicate shallow marshy environments (J.P. Bradbury, oral commun., 1990-1993). The diatoms were found 

in matrix containing fossil microtine rodents and in other 

deposits throughout the section. Small lake and pond 

deposits are abundantly interbedded with marsh deposits in 

the Froman Ferry sequence, as are less common lenticular 

bodies of medium-scale crossbedded fine fluvial sand. 

Although the section overlies typical Glenns Ferry lake 

beds, there is no depositional record of extensive or longlasting lakes within the fossiliferous zone, suggesting that 

the Glenns Ferry lake was no longer present in this most 

downstream area of the western Snake River Plain. In the 

stratigraphically highest part of the deposits, near Pickles 

Butte, fluvial sands and gravels are more common and represent a large part of the formation. These, it seems, have 

resulted from the initial fluvial activity that later formed the 

eroded surface upon which the Pickles Butte basalt was 

deposited. 

The deposits are typical of the "floodplain" facies of 

the Glenns Ferry Formation found farther upstream 

(southeast) at well-known localities, such as Grand View 

and Hagerman, although they have fewer channel sand 

deposits; they have been included in the Glenns Ferry Formation by Malde and Powers (1962) and Othberg and Stanford (1992). A generalized stratigraphic section, compiled 

by Van Dome len and Rieck ( 1992) while collecting samples 

for the magnetic polarity section, is shown in figure 3. 

Although no deposits of large lakes are present in the 

outcrops of the Glenns Ferry Formation containing the Froman Ferry faunal succession, outcrops of the formation to 

the west of the Snake River in the Froman Ferry area are 

entirely lacustrine in origin and dip a few degrees northeastward toward the river. That these lacustrine deposits are 

lower in the Glenns Ferry section than the marsh deposits 

on the northeast side of the river is indicated by regional 

relationships and by one test hole that was drilled through 

the marsh beds and into the lake beds in the Cucumber area. 

The lake beds are also present beneath the capping basalt 

upstream from (south of) Pickles Butte in the high bluffs 

along the northeast side of the Snake River opposite Givens 

Hot Springs (fig. 2); but their relationship to the marsh 

deposits is obscured by cover where these bluffs disappear 

west of Pickles Butte. Downstream (north) of this area the 

basal contact of the fossiliferous marsh beds is covered by 

the more modem deposits of the Snake River and the lake 

beds are not known on the west side of the river. 

At the Pickles Butte Sanitary Landfill of Canyon 

County, Idaho, located in Dead Horse Canyon on the north 

side of Pickles Butte, a test hole (at elevation 2,930 feet) 

drilled through the entire fossiliferous zone (marsh deposits) and entered lake beds of the Glenns Ferry Formation at 

a depth of 505 feet; the test hole bottomed at 520 feet in 

lacustrine silt (Bill Stroud, Holladay Engineering Co., Payette, Idaho, oral commun., 1992). In this area much later 

Pleistocene sands and silts, some probably eolian, are 

deposited on top of the Glenns Ferry Formation. 

From a cursory inspection of the lake beds exposed 

southwest of the river, it is our opinion that the northeastward dips, which appear to be regional, result from regional 

uplift of the Owyhee Mountains some 4 miles west of the 

Snake River opposite the southern limit of the Froman 

Ferry faunal localities. Here, near Elephant Butte some 5.8 

miles south-southwest of Marsing (fig. 2), the Glenns Ferry 

lake beds lap out against much more intensely deformed 

older Miocene rocks-the Chalk Hills Formation and an 

overlying unit of rust-colored medium- to coarse-grained 

sandstone that is oolitic in some places and relatively resistant to weathering in this area. 

These deposits between Elephant Butte and the hills 2 

miles south of Marsing are the most northerly exposures of 

the Glenns Ferry Formation on the southwest side of the 

Snake River. On the northeast side, Glenns Ferry deposits 

are present northward nearly to the Boise River south of 

Parma, Idaho, and perhaps 16 miles farther north than 

Marsing, Idaho (Othberg and Stanford, 1992). This would 
6 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

be about 9 miles north of the northernmost fossil localities 

here included in the Froman Ferry faunal succession. The 

formation in this northernmost area is thin and apparently 

all marsh deposits, but is poorly exposed. 

Deposits in the region of Adrian, Oregon, containing 

fossil fish described by Kimmel (1975), were called the 

Deer Butte Formation by Kittleman and others (1965, 1967) 

and were then believed to be of early Pliocene age. At the 

time of these publications, the correlation of these ages to 

North American vertebrate faunal events was being reevaluated to late Miocene because of better age control of the 

Miocene-Pliocene boundary in Italy and newly developed 

radiometric age determinations. What was called early and 

middle Pliocene in the United States by vertebrate paleontologists in the mid 1960's is now called late Miocene 

(beginning, perhaps, with Repenning, 1968, and finalized, 

perhaps, by Tedford and others, 1987). Formations of this 

age are much older than the Glenns Ferry Formation. 

Neither the Deer Butte Formation of Kittleman and 

others (1965, 1967), the Chalk Butte Formation of Corcoran 

and others ( 1962), nor the Payette Formation of Lindgren 

(1898) contains Pliocene deposits by modem correlations, 

and all three are part of the structurally deformed rocks in 

the foothills of the Owyhee Mountains (fig. 1) and the 

Salmon River Mountains of central Idaho to the north of the 

modem Boise River. These formations are traceable southward more than 70 miles, along the west side of the Snake 

River Plain, into the Chalk Hills Formation of Malde and 

Powers (1962; Ekren and others, 1981). 

On the west side of the Snake River, the next extensive 

exposure of Tertiary sediments to the north is between Vale, 

Oregon, and Weiser, Idaho (fig. 1). These deposits, exposed 

in the region called Moores Hollow, contain upper Miocene 

mammals (Repenning, unpub. data, 1975) and seem to 

overlie older lake beds exposed opposite the town of Weiser 

that contain a diatom flora unrelated to that of the Glenns 

Ferry Formation (J.P. Bradbury, oral commun., 1993). On 

the northern rim of Moores Hollow, in a gravel quarry west 

of Interstate Highway 84, these deposits are overlain by a 

coarse, rusty sand with abundant fish remains that appears 

to be the oolitic rusty sand that separates the Glenns Ferry 

Formation from the underlying Miocene Chalk Hills Formation along the entire west edge of the Snake River Plain. 

The Moores Hollow sediments are close in geography 

and age to the Payette Formation of Lindgren (1898), 

exposed to the east in Idaho along the Payette River valley, 

and they were included in this formation by Lindgren. 

Extension of the name "Payette Formation" from 

Lindgren's original definition, without sufficient justification, has led to considerable confusion; and the name has 

fallen into disuse. It has been replaced by a variety of other 

formation names, in part or entirely synonymous. It should 

be noted that Lindgren (1898) specifically separated the 

Payette Formation from the overlying Idaho Formation of 

Cope (1883), which was defined on the basis of fossil fish 

collected at Castle Creek, about 12 miles northwest (downstream) of Grand View (this report, fig. 12) and is clearly 

within the unit now called the Glenns Ferry Formation 

(Malde and Powers, 1962, p. 1201-1202). The history of 

stratigraphic nomenclature is discussed in the third major 

section of the present report, under the heading "Glenns 

Ferry Formation." 

ORGANIZATION OF THIS REPORT 

The purpose of this report is to record the mammalian 

fauna of the Froman Ferry faunal succession and to indicate 

its significance in the history of the Glenns Ferry Formation. The Froman Ferry faunal succession appears to be in 

the youngest part of this formation; it is very close to 1.6 

million years old (> 1.5 Ma and <1.67 Ma) while the oldest 

Glenns Ferry mammal faunas, from the world-famous 

Hagerman faunal succession 112 miles to the southeast, 

are as old as 3.6 million years. The oldest deposits of the 

formation are lake beds that seem to be nearly 4 million 

years old. Thus the formation was deposited over a period 

of nearly 2.5 million years. 

The significant aspects of the Froman Ferry faunal 

succession are many, and to demonstrate these one must not 

only explain the contents of the fauna and its stratigraphic 

position within the Glenns Ferry Formation, but also outline ( 1) the history of the entire formation; (2) the relationships of the formation to older and younger stratigraphic 

units; (3) the prior and subsequent history of the western 

Snake River Plain that relates to the Glenns Ferry Formation; and ( 4) the records outside the area that have a bearing 

on these interpretations. 

In order to do this, we divide this report into four 

major sections. The first is an enlarged introduction containing several sections that explain, primarily, various 

aspects of biochronologic, paleomagnetic, and climatic 

methods of correlation. Some of the concepts presented 

are relatively poorly known, and their explanation is 

Figure 3 (facing page). Generalized composite stratigraphic column. Measured section of the Glenns Ferry Formation at Froman Ferry 

area (Marsing 7.5 minute quadrangle, Idaho; sees. 8, 9, 17, T. 3 N., R. 4 W.). Measured by David J. Van Domelen and Hugh J. Rieck and 

reproduced from their U.S. Geological Survey Open-File Report, 1992. Items notedby the prefix GS- are fossil localities discussed in the 

present report (those followed by an asterisk [*] have been projected into the section). Fifty-three samples were taken from 12 localities 

(FrohA to FrohL) and all were determined to have primary reversed polarity (Van Domelen and Rieck, 1992). Most were taken from fossiliferous marsh deposits (marked by GS- locality numbers), and some of these were examined by J.P. Bradbury and found to contain diatoms 

indicative of marsh deposits. 
ELEVATION 

(METERS) (FEET) 

800 

2,620 

2,600 

790 

2,580 

780 2,560 

2,540 

770 

2,520 

2,500 

760 

2,480 

750 2,460 

2,440 

740 

2,420 

2,400 

730 

2,380 

720 

2,360 

2,340 

710 

2,320 

700 2,300 

675 1'2,2 15 

INTRODUCTION 

GS203 - Frohl 

Lenses of thin flaggy fine to - GS207* 

medium sand, some crossbedding 

Mostly covered steep wash slope; regular 

5-10ft cyclic variation of fine to medium 

silty sand and very fine sandy silt to 

minor silty clay; mostly very fine 

sandy silt 

GS205* 

GS206* 

GS208* 

GS204 

GS202 

FrohK 

FrohJ 

~~~~~~~:-o~~~~:J"rT;\J~~~""""D:;;:;:;~- GS201- Frohl 

+- Silt and clayey silt 

f---- Medium sand lenses not apparent 

everywhere 

Silt 

Dark-olive-brown to medium-gray silt clay; 

organic-rich base 

Mostly covered; silty sand with some layers 

of silty clay (from slope morph.) 

Covered interval; mostly sand forming 

broad bench of gentle slope 

----,--~·--'::....---------- Hoskins Road 

Cong lomerate; cobble base grading upward 

to pebbles, about 5 em thick . GS211 _ 

ream to lt. gray, un rm, some silt and clay 

Reworked basaltic ash layer, dark gray to 

black, 0-4 em thick, overlying silicic ash 

Ia r, 2-6 em thick 

Olive-gray clay; minor Fe blebs 

Interval covered by grassy slopes 

FrohH 

FrohG 

FrohF 

Fro hE 

FrohD 

FrohC 

FrohB 

FrohA 

Approximate level "Frohman" Wasteway Canal 

Interval covered by Pleistocene and 

Holocene Snake River gravels 

Approximate level of Snake River 

Samples 49-50 

Samples 53-55 

Samples 44-46 

Samples 38-43 

Samples 24- 27 

Samples 28- 32 

Samples 33- 37 

Samples 21-23 

Samples 16-20 

Samples 11-15 

Samples 1-5 

Samples 6-10 

EXPLANATION 

7 

Reversed polarity 

Reversed polarity 

Reversed polarity 

Reversed polarity 

Reversed polarity 

Reversed polarity 

Reversed polarity 

Reversed polarity 

Reversed polarity 

Reversed polarity 

Reversed polarity 

Reversed polarity 

Fine to medium sand 

Silt, sandy silt, and silty sand 

Silty clay and clayey silt 

needed before they can be used in the sections to follow. 

A great many of the former differences of interpretation 

of the late Cenozoic history of the western Snake River 

Plain have arisen because of a lack of understanding of 

the meaning, and limitation, of age interpretations 

implicit in the use of fossil mammals. 
8 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

The second major section is the discussion of fauna 

from the Froman Ferry faunal succession. This section is 

primarily a listing of specimens, including locality and 

elevation, and a discussion of the features that are 

pertinent to identification. In this discussion some wellestablished practices, primarily in taxonomic nomenclature, are discussed and modified. And in some places considerable space is used to discuss the history of particular 

taxa and varying nomenclature. 

The third major section is of the geologic history of 

the Glenns Ferry Formation, in which age and depositional facies figure prominently. Also included is evidence 

of faunal affinity and history that goes as far afield from 

the western Snake River Plain as the States of California 

and Washington. Suggested climatic events of presumed 

significance to the timing of observed conditions within 

the Glenns Ferry Formation are introduced from as far 

away as Scandinavia. We point out that these are global 

climatic events that had an effect everywhere and that the 

choice of evidence is not so much dependent upon geographic position but on greatest temporal precision. A similar question of relevance could be made for 

paleomagnetic evidence; although the Olduvai Normalpaleomagnetic Subchron may have been named and identified in East Africa, for example, its recognition in North 

America is not alarming because it was a global event. 

The fourth and final section, "Conclusions," is mercifully brief and consists only of a listing of those conclusions of the report that seem most significant to the authors. 

This treatment, while logical in sequence, requires 

repeated mention of the same evidence. When this is 

done, an effort has been made to mention the page where 

the evidence is first or most completely discussed to eliminate as much duplication as possible. Yet the reader will 

usually recall its prior mention and be impressed by duplication of statements. For this we apologize. 

The greatest deficiency of this study is the lack of 

complete coverage of the western Snake River Plain by 

adequate geologic mapping. H.E. Malde has spent the 

past 40 years in this effort, but the Snake River Plain is 

very large and major parts of the area discussed remain 

without adequate published geologic maps. The immediate area of the Froman Ferry faunal succession is covered 

by the excellent map of Othberg and Stanford ( 1992). A 

large part of the area discussed is covered by the fine map 

of Owyhee County, Idaho, by Ekren and others ( 1981 ), 

but unfortunately the attention of this work was not 

directed at the Glenns Ferry Formation, and its several 

facies are not recognized, although the recognition of 

these facies is the substance of the present report. To overcome this shortage of detailed geologic mapping, all of 

the area discussed has been covered in reconnaissance; 

positive statements have a basis in observation, and 

qualified statements are the most reasonable interpretation 

in the authors' minds or are approximations. 

AGE ASSIGNMENTS AND AGE OF THE 

FROMAN FERRY FAUNAS 

In this report, the ages of the faunas of the Snake River 

Plain are given in radiometric years and are correlated to 

established mammalian biochronology and magnetic polarity stratigraphy. These assignments and correlations are 

shown in figure 4. The temporal correlations of polarityreversal events are those of Mankinen and Dalrymple 

( 1979), which have been used in prior reports by Repenning. Minor changes in the age of the beginning of the 

Brunhes Normal-polarity Chron (lzett and Obradovich, 

1991), the beginning of the Olduvai Normal-polarity Subchron (McDougall, 1985), and the addition of the Cobb 

Mountain event (Mankinen and others, 1978) have been 

made in consideration of more recent information. 

We emphasize that in the following discussion the correlations of biochronologic and geologic evidence to geomagnetic polarity events are those reported in the references 

cited, but the ages of these events are basically those of the 

magnetic stratigraphy of Mankinen and Dalrymple (1979). 

In one example (Multi-ash section south of Oreana, Idaho; 

p. 49-51) we have revised the correlations originally made 

by Neville (1981) on the basis of new age information in the 

area (including the Birch Creek fauna). 

In the past, the temporal calibration of magnetopolarity reversals has been made on the basis of three distinctly 

separate criteria: ( 1) radiometric age measurements; (2) 

Earth orbital parameters correlated with climatic events as 

inferred from oceanic isotope records; and (3) the assumption of uniform rates of sea floor spreading. Although surprisingly close in agreement, these different approaches to 

determining the ages of the magnetic events have resulted in 

somewhat different calibrations. The assumptions of an 

·exact correlation of sea level change with orbital variations 

and of uniform rates of sea floor spreading have been disproved in detail and are based upon questionable assumptions (Repenning, 1992, 1993). 

While not applicable in marine environments and 

while also subject to errors, those calibrations based upon 

radiometric age determinations are the least contradictory 

and are most useful in nonmarine environments, as they can 

be integrated directly with independent radiometrically 

measured dates where suitable rocks are stratigraphically 

related to fossils. As a result, only the radiometrically dated 

magnetopolarity chronology of Mankinen and Dalrymple 

( 1979, and later revision by other authors) has been used in 

calibrating micro~ine rodent history in past reports (Repenning, 1987; Repenning and others, 1990; Repenning, 1992). 

For consistency, and because its use does not require the 
INTRODUCTION 9 

1-

a: 

w 

m 

...I 

a 

§ 

-

8 

t;j 

tE 

BIRCH 

CREEK 

EXPlANATION 

Basalt ~ Fossil 

mammals 

Lake 

~ Radiometric 

River dates 

Marsh ? Not exposed 

? 

JACKASS 

BUTTE 

FROMAN 

FERRY 

PASCO 

BASIN ALTURAS 

z 

<( 

z 

0 

1-

(!) 

z 

> Q:; 

> 

Figure 4. Correlation of deposits in areas discussed, showing paleomagnetic polarity chrons and events correlated with time, deposits, 

faunas, and mammal ages of the United States. 

added uncertainties of correlating radiometric age determinations to marine evidence, the direct radiometric 

calibration of magnetopolarity stratigraphy is used in the 

present report. 

The magnetic polarity of the section containing the Froman Ferry faunal succession was made (by Van Domelen and 

Rieck, 1992) from what we take to be the original Froman 

Ferry locality to the top of Chalk Hills, including most of the 

fossiliferous section. It was entirely of reversed polarity and, 

in combination with the radiometric age of the overlying 

Pickles Butte basalt (also of reversed magnetopolarity), indicates that the possible. age of the fossil sequence is between 

1.5 and 1.67 million years (fig. 4). Absence of the Olduvai 

event in the lower part of the Froman Ferry section and the 

unknown duration of the erosional interval disconformably 

separating the dated Pickles Butte lava from the Froman 

Ferry marsh beds further restrict this age to more than 1.5 and 

less than 1.67 million years ago. 

Only one radiometrically determined date is available in 

the Froman Ferry area, taken from the basalt on the Snake 

River rim south of Pickles Butte and derived from the lava 

flow forming this butte (K.L. Othberg, written commun., 

1993 ). Where the sample was taken, the Pickles Butte basalt 

overlies the Glenns Ferry lake beds (older than the fossiliferous marsh beds), but the basalt is continuous to Pickles Butte 

where it overlies the Froman Ferry marsh deposits of the 

Glenns Ferry Formation; a pre-basalt erosional unconformity 

is obvious but of unknown duration. 

The Pickles Butte basalt was dated as 1.58±0.085 million years old by 40 Ar-39 Ar age determination at the Berkeley Geochronology Center, University of California, 

Berkeley (K.L. Othberg, written commun., 1993). The minimum date is here used throughout, as the maximum date 

would indicate the presence of the Olduvai event in the 

underlying Froman Ferry faunal succession, and this was 

not found in the magnetic section by Van Domelen and 

Rieck (1992). This basalt unconformably overlies both the 

marsh deposits, containing the Froman Ferry faunal succession, and the underlying lake beds of the Glenns Ferry 

Formation. 

Although, from the preceding, erosion obviously separates the Pickles Butte basalt from the Glenns Ferry 
10 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

Formation in this area, it is not possible at present to estimate the missing time; one of us (Weasma) has examined 

areas to the east of the Froman Ferry area and is of the opinion that in this direction the basalt, or its debris, is interbedded with Glenns Ferry deposits (apparently younger than 

the formation underlying the basalt in the Froman Ferry 

area). The entire Froman Ferry area was uplifted and eroded 

prior to the eruption; the beginning of this fluvial activity is 

incorporated in the deposits of the youngest parts of the 

Glenns Ferry Formation of the Cucumber area. This fluvial 

gravel contains a greater variety of large mammals than the 

marsh beds, as at locality GS-232 on the north side of Dead 

Horse Canyon. 

The maximum age span of the Froman Ferry faunal 

succession is thus less than the 170,000 years between 1.5 

million years ago (the age of the overlying basalt) and 1.67 

million years ago (the age of the end of the Olduvai 

Normal-polarity Subchron of the Matuyama Reversedpolarity Chron, which lies an undetermined stratigraphic 

distance below the lowest fossil horizon). This time span 

must be reduced by the unknown time involved in the erosion that separates the youngest fossil deposits from the 

overlying lava and by the unknown time involved between 

the oldest fossil deposits and the unlocated top of the Olduvai event. The Olduvai event seems to have lasted 230,000 

years itself, longer than the time involved in the Froman 

Ferry faunal succession, and thus is clearly not present in 

the paleomagnetic section of Van Domelen and Rieck 

(1992). That the record of the 01duvai event was not 

removed by the erosion separating the dated lava from the 

Froman Ferry faunal succession is indicated by the differences between the Froman Ferry fauna and the Jackass 

Butte fauna, which is as young as about 2 million years old, 

as will be discussed. 

The Froman Ferry faunal succession is thus between 

>1.5 and <1.67 million years old. By interpolation of stratigraphic thickness, the arrival of the new immigrant Phenacomys gryci in the Froman Ferry faunal succession is thus 

believed to have been about 1.60 million years ago. This 

arrival marks the beginning to the Irvingtonian mammal age 

in the Pacific Faunal Region of the United States. 

MAMMAL AGES AND PROVINCIALISM 

Most of the mammal faunas of the Glenns Ferry Formation are representative of the Blancan mammal age of 

the United States. The Blancan mammal age is approximately equal to the Pliocene, as Blancan is defined by 

fauna and calibrated in radiometric years. The Blancan 

(defined by its mammals) began a bit more recently (4.8 

Ma; Repenning, 1987; Repenning and others, 1990) than 

did the Pliocene (defined by the age of its type section), 

which began about 5.3 Ma. 

Twenty years ago a difference of half a million years 

might have been disregarded as being within the margin of 

error in mammalian biochronology or any other chronology, but recent work (Repenning, 1992) has shown that, 

with ideal evidence, some mammalian groups indicate a 

biochronologic sensitivity approaching 5,000 to 10,000 

years, and the entire Froman Ferry faunal succession was 

deposited in less than 170,000 years and contains at least 

one prominent and previously unknown faunal change 

within this time span: the immigration of a new taxon. 

In most of the United States (east of the Rocky Mountains, the Eastern Faunal Region of Fejfar and Repenning, 

1992), the Blancan mammal age ended a bit earlier than did 

the Pliocene. In this faunal region the Blancan ended at the 

beginning of the Olduvai Normal-polarity Subchron (1.9 

Ma) with the immigration of the microtine genus Allophaiomys (Repenning, 1992), whereas the Pliocene is approximated as ending with the end of the Olduvai event ih its 

type section ( 1.67 Ma; Aguirre and Pasini, 1985). 

Allophaiomys is unknown west of the Rocky Mountains (in the Pacific Faunal Region; called Western Faunal 

Region by Fejfar and Repenning, 1992), and there is no 

faunal change upon which to base the end of the Blancan 

until after the beginning of the Pleistocene (beginning with 

the end of the Olduvai event). Thus the first faunal change 

(immigration of Microtus and Phenacomys) upon which the 

Irvingtonian mammal age could be basefl appears about 

1.6 million years ago in the Pacific Faunal Region (age control from the Vallecito Creek faunal succession of the AnzaBorrego Desert, California, and, more precisely, from this 

discussion of the Froman Ferry faunal succession). 

This date for the Blancan-Irvingtonian faunal age 

boundary is 300,000 years later than this mammal age 

boundary is recognized in the Eastern Faunal Region 

because this boundary is defined upon the immigration of 

distinctive Irvingtonian mammalian taxa, and the histories 

of immigration differ between the Eastern Faunal Region 

and the Pacific Faunal Region. 

Available age control for the immigration into the 

Vallecito Creek faunal succession indicates a possible 

range that includes the age indicated in the Froman Ferry 

faunal succession. Because the immigration (from the Arctic) of these two new taxa appears to have been climatically controlled and because only one major, Northern 

Hemisphere climatic change is included in the possible 

time range, it is presumed that the two dispersing microtine rodents (Microtus and Phenacomys) appeared at the 

same time in the Pacific Faunal Region (Repenning, 

1992). However, Phenacomys is missing farther south, in 

the Anza-Borrego Desert of southern California (the area 

is south of any record of Phenacomys), and Microtus is 

not present in the marsh beds of the Froman Ferry area. 

Thus the end of the Blancan mammal age, and the 

beginning of the following Irvingtonian mammal age, varied 
INTRODUCTION 11 

between the east (late Pliocene) and west (early Pleistocene) 

sides of the Rocky Mountains because the times, and composition, of the first immigration of an Irvingtonian form varied 

by about 300,000 years between the two faunal regions 

(Repenning, 1992). Neither of the immigrants marking the 

beginning of the Irvingtonian mammal age in the United 

States is yet known at so early a date in the Mexican Faunal 

Region, and there the beginning of the Irvingtonian age (if 

these terms are to be used in that region) is yet to be discovered and the age boundary can only be approximate. Conversely, the immigrants are known (Phenacomys) or are 

assumed (Microtus) to have been present in the Arctic area 

(Beringian Faunal Region) at an earlier date. 

This difference in the age of the first Irvingtonian faunas on either side of the Rocky Mountains will be disturbing 

to those who think of the Irvingtonian and Blancan mammal 

ages as time terms, rather than as faunal terms; but they are 

defined in faunal terms (Savage, 1951; Wood and others, 

1941). One can hardly select a mammal age boundary at a 

time when there is no change in the mammal fauna. And, 

except for the immigrant microtine, the Froman Ferry fauna 

is a Blancan fauna between 1.5 and 1.67 million years old, 

based upon the minimum possible age given for the overlying Pickles Butte basalt and the 1985 approximation of the 

end of the Olduvai event by Aguirre and Pasini; neither date 

would claim a possible sensitivity of 5,000 years, as suggested for micro tine biochronology on page 10 and again on 

page 13 (although the lava date was rather precise and 

claimed a possible laboratory error of only 85,000 years). 

Although the genus Microtus was listed from the Irvington fauna (Pacific Faunal Region) by Savage (1951) when 

naming the Irvingtonian mammal age, no form of Microtus is 

known east of the Rocky Mountains before 0.83 million 

years ago (Repenning, 1992). Thus, if the arrival of Allophaiomys east of the Rocky Mountains is not used for the beginning of the Irvingtonian age in the Eastern Faunal Region, 

the difference in age for the beginning of the Irvingtonian 

mammal age (based upon the first Microtus) would be even 

greater in the two faunal regions. The genus Phenacomys 

may have arrived in both Pacific and Eastern Faunal Regions 

at the same time, but the earliest record east of the Rocky 

Mountains is in the Java fauna of South Dakota (Martin, 

1989; as Hibbardomys zakrzewskii), which has no external 

(nonbiochronologic) age control. 

A similar regional difference is associated with the 

beginning of the Blancan mammal age of the United States. 

West of the Rocky Mountains it is marked by two immigrant 

species of the microtine genus Mimomys (Wood and others, 

1941; Repenning and others, 1990): Mimomys (Cosomys) 

sawrockensis and Mimomys (Ophiomys) mcknighti. These 

obviously followed a route down the Pacific coast from Beringia and are dated in the upper Alturas fauna of northeastern 

California at 4.8 million years ago. But at the beginning of 

the Blancan, no new microtine immigrants had arrived east 

of the Rocky Mountains; the first Pliocene use of a dispersal 

route from the Arctic region to the Eastern Faunal Region 

(east of the Rocky Mountains) was not until 2.56 million 

years ago, and marks the beginning of the fifth faunal age of 

the Blancan, Blancan V. This was the arrival of the genus 

Plioctomys (Repenning and Brouwers, 1992, p. 15), which 

coincides with the arrival of the closely related genus Mictomys in the Pacific Faunal Region at the beginning of the late 

Blancan (Blancan V). 

One of the earliest Blancan immigrants, Mimomys 

(Cosomys) sawrockensis, is present to the south of the Alturas area in earliest Blancan faunas, in the Maxum fauna of 

the San Francisco area (May, 1981; May and Repenning, 

1982; Repenning, 1987), and seems to have dispersed rapidly around the south end of the Rocky Mountains to the 

Great Plains, where it was named by Hibbard (1949) from 

the Saw Rock Canyon fauna of Kansas, but where its age 

can only be approximated by associated fauna; there is no 

paleomagnetic control of its type locality (Repenning, 

1987, p. 254 ). Within the limits of available biochronologic 

resolution, the age of the type locality (Saw Rock Canyon 

fauna) seems to be about the same as the age in California 

so that there is thought to have been little age difference, 

and the beginning of the Blancan age is assumed to be the 

same on either side of the Rocky Mountains (about 4.8 Ma; 

Repenning, 1987). 

The other earliest Blancan immigrant, Mimomys 

(Ophiomys) mcknighti (Gustafson), is not present south of 

the well-dated Alturas fauna in northern California, but is 

present in the White Bluffs fauna of Washington (type 

locality; 4.3+ Ma in Repenning, 1987), where some question exists of the correlation of magnetic events (Gustafson, 

1985). Mimomys mcknighti moved southward and eastward 

from northern California slowly, and evolved into Mimomys 

(Ophiomys) magilli as it did so. This species is known in 

later faunas in the Kettleman Hills and Buttonwillow, 

California; Panaca, Nevada; Duncan, Arizona; Beck 

Ranch, Texas (Repenning, 1987); and Sand Draw, 

Nebraska, where it was named by Hibbard (Skinner and 

others, 1972). By the time that Mimomys (Ophiomys) had 

reached the Great Plains, Mimomys (Cosomys) had evolved 

into the new subgenus Mimomys (Ogmodontomys) in the 

Great Plains, the later history of which is documented by 

Zakrzewski (1967). 

The Blancan mammal age was defined (Wood and others, 1941) long before its age (and that of the Pliocene) was 

known in terms of radiometric years. In addition, when the 

Blancan mammal age was first defined, it was believed to 

be only of late Pliocene age, and a three-part Pliocene 

(including the Clarendonian, Hemphillian, and Blancan 

mammal ages) was recognized in the mammalian faunas of 

the United States. Before the availability of radiometric age 

determinations, some had even considered the Blancan to 

be Pleistocene (McGrew, 1944) or had considered some 
12 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

deposits of the western Snake River Plain (Grand View and 

younger deposits) to be of late Pleistocene age (Hibbard, 

1959). By the modem definition of Pliocene and Pleistocene, the Grand View deposits are clearly of Pliocene age 

and older than 1.67 million years (end of the Olduvai 

event). Such concepts are the subject of constant debate, 

and this is not to say that future agreement between international "authorities" will not change these statements. 

In 1964 potassium/argon radiometric dates were first 

systematically correlated with North American mammal 

ages (Evemden and others, 1964). In 1968, the earlier correlation of North American mammalian faunas with the 

type Pliocene (in Italy) was first questioned by vertebrate 

paleontologists (Repenning, 1968). Those correlating by 

means of marine invertebrates had, for many years, disagreed with the mammalian correlations (see Repenning 

and Vedder, 1961 ). The Pliocene is now considered as 

beginning about 5.3 million years ago (rather than about 12 

Ma in former mammalian paleontology usage). 

As used herein, the Blancan is considered as beginning 

4.8 million years ago based upon the age of the youngest 

Alturas fauna of California (Repenning, 1987; Repenning 

and others, 1990). The youngest Alturas fauna is considered 

to be of Blancan age because it contains the earliest United 

States record of Mimomys, perhaps the only taxon listed as 

first appearing in the Blancan in the original definition by 

Wood and others ( 1941) that appears so early but not in 

older Hemphillian faunas. Determination of the age of the 

beginning of the Blancan has been difficult to make because 

nearly all of the first appearances listed in Wood and others 

( 1941) have been found to "first appear" at different times 

in the faunas of the United States, either in earlier faunas 

that Wood and others called Hemphillian, or much later 

within the Blancan than Mimomys. 

By these definitions, the Hagerman fauna of the 

Glenns Ferry Formation in the western Snake River Plain, 

about 3.6 to 3.1 million years old, is roughly mid-Blancan 

(and mid-Pliocene) in age. In many reports it has been 

called "early Blancan" (for example, Neville and others, 

1979), however, and in others it has been called "late Blancan" (for example, Repenning, 1967b; Hibbard, 1958). 

The faunas of the Glenns Ferry Formation in the Froman Ferry area are herein considered as representing latest 

Blancan and earliest Irvingtonian. These mammal faunal 

terms are of latest Pliocene and earliest Pleistocene geochronologic age as herein dated in the United States west of the 

Rocky Mountains. The paleomagnetic determinations of Van 

Dome len and Rieck ( 1992) eliminate the possibility that 

Pliocene deposits are present in the Froman Ferry faunal succession: the Olduvai Normal-polarity Subchron is not 

present in the Froman Ferry faunal succession and by current 

modem convention the Pliocene ends with the end of the 

Olduvai event. 

Originally defined as North American mammal ages 

by Wood and others (1941) and by Savage (1951 ), these 

mammal ages are here used as ages of only the 

conterminous United States, south of the Canadian border, because faunal criteria in North America (as elsewhere) are provincial in nature and vary greatly between, 

for example, Mexico and Alaska. The "North American 

mammal ages" cannot be used in Alaska without complete redefinition. This point is illustrated by the elephant 

Mammuthus, first appearing in Irvingtonian faunas in the 

conterminous United States, and by the bovid Bison, first 

appearing in the younger Rancholabrean faunas of the 

contiguous United States; both are present in the faunas 

of Alaska that correlate in time with the Blancan mammal 

age as defined by Wood and others (1941). 

Although the position is here taken that a difference 

of 300,000 years can exist in the timing of mammal ages 

within the conterminous United States, because of varying regional faunal history, it does not seem that this position can be extended to differences as great as 2 million 

years for the same reason. With time differences this 

great, faunal differences become too great for the practical application of one faunal name. Instead, it is believed 

that Beringian (nonglaciated northeastern Siberia and 

northwestern North America) mammal ages merit their 

own system of regional mammalian ages. Sher ( 1986) has 

suggested such a set of regional mammal ages for Beringia, which indicates the need for the terms, but these ages 

have some weaknesses in definition and correlation 

(Repenning and Brouwers, 1992, p. 2). 

Perhaps only because more attention has been paid 

to it, provincialism is most prominent in the history of 

microtine rodents and exists within the conterminous 

United States, on either side of the Rocky Mountains 

(Repenning, 1987), as well as between Alaska and Mexico. (See discussion in Repenning, 1992.) Hence the 

microtine (and to a varying extent other mammalian) faunal criteria for the recognition of mammal ages differ in 

time and taxa on either side of the Rockies-in the 

Pacific Faunal Region to the west, and in the Eastern Faunal Region to the east. (These are called "regions" 

because they also can be subdivided into faunal provinces 

by examining the less widely ranging, and more environmentally specific, taxa. Greater subdivision is not 

attempted here, however.) 

Following the logic of defining the beginning of 

mammal ages by the earliest appearance of immigrants 

(expressed by Repenning, 1967b to the present), the southward dispersal of Phenacomys gryci and Microtus californicus from Beringia into the Pacific Faunal Region of the 

conterminous United States is considered the first indication of the beginning of the Irvingtonian mammal age in 
INTRODUCTION 13 

the Pacific Faunal Region, which includes the Snake 

River Plain, as discussed previously. 

Both the Froman Ferry faunal succession of Idaho 

and the comparable part (Natural History Museum of Los 

Angeles County (LACM), California, locality LACM 6683) 

of the much longer sequence of the Vallecito Creek faunal 

succession in the Anza-Borrego Desert of southern 

California are otherwise characterized by typical Pacific 

region Blancan V microtines at the beginning of the Irvingtonian mammal age. Only the immigrant microtines are 

present to mark a change in the faunas and to provide a 

basis for the recognition of the Irvingtonian mammal age 

(at about 1.6 million years ago). 

But even such a simple (and precise) definition of the 

beginning of a mammal age can have complications. From 

the beginning of the Blancan, 4.8 million years ago, until 

2.56 million years ago, when the Blancan V age began, 

microtines followed only one dispersal route from Beringia 

to the conterminous United States; it was down the Pacific 

Coast and new immigrants can be nicely first recorded in 

faunas of the Pacific Northwest. But 2.56 million years ago 

immigrants first came south on both sides of the Rocky 

Mountains, and, also for the first time, immigrants began 

appearing first in the Great Plains, some never to disperse 

westward to the Pacific Faunal Region west of the Rocky 

Mountains. 

This differing history of microtine immigration on 

either side of the Rocky Mountains causes the problem in 

the definition of the beginning of the Irvingtonian mammal 

age-the end of the Blancan mammal age. One can hardly 

consider faunas west of the Rocky Mountains to be of Irvingtonian age if they differ in no way from late Blancan faunas, even though they may be younger than earliest 

Irvingtonian faunas to the east of the Rocky Mountains. 

Thus, mammal ages, based upon faunal composition, 

can represent different times in different faunal regions that 

happen to have different histories of immigration and, in 

fact, of evolution. As they do not indicate exactly the same 

times in different faunal regions, they must be defined separately in each region. If we find this situation disturbing it is 

because we were educated under the outmoded concepts of 

instantaneous global evolution and of global biohistoric 

events (biochronology). The biochronologic terms "First 

Appearance Datums" (FADs) and "Last Appearance 

Datums" (LADs) were generalities that became outmoded 

with the development of radiometric dating and recognition 

of globally synchronous events as changes in the Earth's 

magnetic polarity and climate, and, on a smaller geographic 

scale, ash falls and immigrations. FADs and LADs are of 

use in correlation only within specific faunal regions, and 

these regions have been only recently, and approximately, 

defined for microtine rodents (Fejfar and Repenning, 1992), 

and have not been defined for other fossil mammals in most 

parts of the world. 

DISPERSAL 

Evolution is broadly sequential and, within varying 

limits of precision, can indicate geologic time; but evolution 

is mostly mosaic in the sense that the same, or similar, 

events can happen in different regions at different times, at 

least within the present approximate taxonomic classification. Time and geography are important considerations of 

phylogeny and taxonomy, as well as of biochronology. 

Genetic potential is inherited and evolves, but its realization 

in new morphotypes is opportunistic, and opportunity to 

develop depends upon regional environmental conditions. 

Mammalian biochronology is not lost, because regional 

environmental changes result from climatic changes that are 

the result of global conditions; biochronology becomes 

more complicated but at the same time much more precise. 

And with this, evolution is better understood and taxonomy 

improved. 

"Global" mammalian biochronology has relied upon 

the concept of simultaneous evolution for a century or 

more, with the help of other methods of indicating or correlating time when they become available (that, since 1964, 

can more precisely determine time). But no great attempt 

has been made to improve mammalian biochronology by 

documenting the greater detail of evolution that is available 

on a provincial or regional scale. Repenning ( 1992) has 

documented such intraregional detail for a few lineages of 

microtine rodents and has shown that it can detect age differences as brief as 5,000 years; this is an age discrimination so precise that there exists no external method of 

checking its precision beyond the effective range of carbon 

isotopes. Confirmation can come only by matching such a 

biochronology against similarly precisely determined biochronologies. 

To merge provincial records into a global, or even continental, average is to lose detail that more precise methods 

of age determination, external to existing biochronology, 

provide. It "smooths out'' the record of evolution and hides 

its detail. Because different biologic events occur at different 

times in different regions, documenting, rather than averaging, these can produce biochronologies that are more sensitive to time differences than current measurement of 

radioactive decay. With such a time-sensitive biochr~nology, 

dispersal history must be known to correlate the biochronology across faunal barriers between adjacent faunal regions. 

And an awareness of climate changes that may eliminate or 

modify faunal barriers or stimulate morphologic change 

(that has become potential because of genetic evolution) is a 

most valuable tool. 

A number of microtine and other mammalian taxa have 

crossed the Rocky Mountain ecologic barrier between the 

Pacific and Eastern Faunal Regions, and most of the microtine crossings are well enough known that the route of a 

given dispersing taxon can be traced. They have dispersed 
14 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

either around the south end of the Rocky Mountains (through 

Arizona), or across Wyoming and through the Yellowstone 

pass, between the Snake River drainage of Idaho and the 

Great Plains of southern Wyoming. 

Depending upon the region of their source, microtine 

taxa have moved either east or west along these avenues 

around or through the Rocky Mountains. These movements coincide with climatic events that have made these 

avenues environmentally acceptable to the specific constraints of individual taxa. They have also made these avenues filter barriers which some microtine taxa have never 

penetrated. Climate changes are difficult to correlate, 

because conditions vary with location, and one of the easiest ways to correlate them is by interregional correlation of 

microtine dispersals that have happened because environmental corridors have opened or closed. 

Southward dispersal from Beringia down both sides of 

the Rocky Mountains to the conterminous United States has 

also occurred at particular times of climatically forced environmental conditions (Repenning, 1984, 1987, 1990, and 

1992; Repenning and others, 1990; and Repenning and 

Brouwers, 1992). No immigrant microtine rodent can be 

demonstrated to have appeared in the United States both 

east and west of the Rocky Mountains at the same time. 

This fact speaks for a mountainous provincial barrier that 

continued westward beyond the Rocky Mountains, across 

the Bering Strait, and into Asia as the mountains of eastern 

Siberia, which separates the Asian part of the Beringian 

Faunal Region from the Oriental Faunal Region just as it 

separates the Eastern Faunal Region from the Pacific Faunal 

Region of the United States. (See discussion in Repenning, 

1992.) However, some closely related forms have appeared 

at the same time on opposite sides of this mountain chain, 

as, the first Mictomys in the Pacific Faunal Region and the 

first Plioctomys (ancestral to Mictomys) in the Eastern Faunal Region, or different subgenera of the genus Phenacomys. 

Immigrants dispersing from Beringia down the Pacific 

Coast route west of the Rocky Mountains to the Pacific Faunal Region of the contiguous United States usually are first 

recorded in the Pacific Northwest, often in the Snake River 

or Columbia River areas (late Miocene Promimomys [perhaps at 5.6 Ma], the early Pliocene smaller subgenus 

Mimomys (Ophiomys) [at 4.8 Ma], the late Pliocene bog 

lemming Mictomys [at 2.56 Ma], and the Pleistocene subgenus Phenacomys (Paraphenacomys) [at 1.6 Ma]). But, 

apparently, some crossed the Columbia River along the 

coast (before the Snake River was diverted into it at about 

3.5 Ma) and left the Pacific Coast by dispersal up the Sacramento River system in the present State of California (the 

Pliocene larger subgenus Mimomys (Cosomys) [4.8 Ma], the 

muskrats [at 4.2 Ma] and perhaps the vole Microtus [at 1.6 

Ma]). The Pacific Coast route seems to have been closed 

after 1.6 million years ago, but the route east of the Rockies 

opened 2.56 million years ago and the primitive bog lemming Plioctomys [2.56 Ma], the voles Allophaiomys and a 

more modernized Mimomys [1.9 Ma], the subgenus Phenacomys (Phenacomys) [perhaps 1.6 Ma], the vole 

Lasiopodomys and pine vole Terricola [0.85 Ma], and 

finally the modern vole Microtus [possibly 0.4 Ma] took 

advantage of it and first appeared in the Eastern Faunal 

Region. Details behind most of these dates appear later in 

this report. 

For microtine rodents, these dispersals began in the 

late Hemphillian (Promimomys; latest Miocene), and 

some endemically derived North American microtines 

(Microtoscoptes) apparently dispersed in the opposite 

direction into Eurasia at the same time. The arrival of 

Mimomys early in the Pliocene defines the beginning of 

the Blancan mammal faunas of the United States (Wood 

and others, 1941; discussed in the previous section, p. 

11). As will be discussed later, the muskrats appeared in 

the Pacific Faunal Region about 4.2 million years ago. 

Immigrants dispersing down the east side of the Rockies 

(to the Eastern Faunal Region) appear first in the Great 

Plains; this route was opened by Plioctomys at the beginning of the late Blancan (Blancan V), followed by Allophaiomys and a second immigration of Mimomys (1.9 

Ma). Probably because of tectonic activity in the area of 

the Canadian Rockies near the Gulf of Alaska (Repenning, 1990), the Pacific coastal route was: closed shortly 

after the immigration of Phenacomys and Microtus ( 1.6 

Ma); all later microtine immigrations (Terricola and 

Lasiopodomys at 0.85 Ma and Old World Microtus perhaps at 0.45 Ma) appear to have come down the east side 

of the Rocky Mountains to the Great Plains and the Eastern Faunal Region. 

The immigration of Mictomys (to the Pacific Region of 

the contiguous United States) and Plioctomys (to the Eastern Region) was about 2.56 million years ago (both marking the beginning of the Blancan V mammal age in their 

respective faunal regions). Repenning (1987) considered 

these immigrations as being 2.6 million years ago (on the 

basis of their earliest records about 15 feet below the end of 

the Gauss Normal-paleomagnetic Chron in Idaho, Arizona, 

and Texas), but the age was revised to 2.56 million years by 

Repenning and Brouwers (1992, p. 15) on the basis of better age control of the dispersal-controlling climatic change. 

This climatic change was the inception of the first recognized Neogene continental glaciation of the Northern 

Hemisphere, best dated by the activity of the Scandinavian 

Ice Sheet (Jansen and others, 1988; Repenning and Brouwers, 1992). 

Mictomys, the immigrant to the Pacific Faunal Region, 

dispersed rapidly through the western Snake River Plain 

(Grand View faunas), southern Utah (Beaver fauna), and 

central Arizona (Tusker fauna) 2.56 million years ago, and 

onto the Great Plains (Borchers fauna) by 2.0 million years 
INTRODUCTION 15 

ago (Repenning, 1987). It also dispersed (with Microtus) to 

the Anza-Borrego Desert of southern California by 1.6 million years ago, presumably because climatic conditions had 

not earlier allowed it into this extreme southwestern area. 

Plioctomys first appeared in the Cita Canyon fauna of the 

Texas Panhandle in the same paleomagnetic position as Mictomys (about 15 feet below the end of the Gauss); the genus 

is known earlier from Hungary to Beringia in Eurasia and 

Alaska. (Where statements regarding the age of occurrence 

in specific faunas are made without reference, the reader is 

referred to the Appendix in Repenning, 1987.) 

These dispersals suggest cool and rainy summers if one 

presumes that the modem environmental controls of these 

taxa apply to the earliest forms. And, indeed, continental glaciation began to accumulate 2.56 million years ago in both 

Laurentia and Scandinavia and reached a climax 2.1 million 

years ago when till was deposited in Iowa (Boellstorff, 1978; 

Repenning and Brouwers, 1992). At the same time, the 

Glenns Ferry lake of the Snake River Plain had a rise in water 

level, presumably a result of glaciation in Yellowstone, as is 

discussed on page 60. 

Current information about the flora of the Glenns Ferry 

Formation (Bradbury and Krebs, 1982; Thompson, 1992) 

indicates pine and fir forests alternating with sage steppes in 

the western Snake River Plain, and a distinctive diatom flora 

in the Glenns Ferry lake. But the pollen record extends only 

to deposits as young as about 2.5 million years ago, about as 

young as the beginning of Blancan V faunas (Grand View 

faunas), and the floral environment at the glacial peak 2.1 

million years ago is unknown, but presumed to be a continuation of fir forests because of contemporaneous hemispheric 

accumulation of continental ice. The diatom flora in the lake 

is known to persist to about 2.1 million years ago without 

change, and is assumed to extend to about 1.67 million years 

ago in the Froman Ferry area, although no evidence of the 

age of the lake beds is known in this area. The fluvial environment appears to change by 2.1 million years ago, as the 

modem cold water stream sculpin Cottus makes its earliest 

appearance in the Jackass Butte section (G.R. Smith, written 

commun., 1992). The Jackass Butte section includes 2.1 million years ago, as will be discussed; the arrival of the sculpin 

may reflect the glacial origin of the Snake River in the 

Yellowstone area. 

Younger lake beds farther downstream (northwest, near 

the mouth of Sinker Creek; fig. 12) contain a diatom flora 

that is typical of the not-well-dated Bruneau Formation (J.P. 

Bradbury, oral commun., 1993). The Bruneau Formation is 

younger than the Glenns Ferry Formation at Froman Ferry 

on superpositional evidence, that is, younger than 1.5 Ma, as 

will be discussed. In all locations where the Bruneau Formation has been sampled (from the town of Bruneau northwest 

to Froman Ferry; figs 1, 2, 12), its diatom flora is distinct 

from that of the Glenns Ferry lake, and is like that found in 

modem lakes of the Pacific Northwest (J.P. Bradbury, oral 

commun., 1993). The formation contains only sage steppe 

pollen (Thompson, 1992), suggesting drier and, hence, interglacial climate with hotter summers and colder winters. 

At the beginning of Blancan V time (Ninefoot 

Rapids-early Grand View faunas; Conrad, 1980) the 

microtines Pliophenacomys osborni, a genus known almost 

entirely from the Eastern Faunal Region, and Ondatra idahoensis dispersed to the Snake River Plain from the Great 

Plains, along with Mictomys from the Arctic. The westward 

dispersal route of Pliophenacomys and Ondatra idahoensis 

appears to have been by way of the Yellowstone pass, as 

Bamosky (1985; as "Pliophenacomys primitivus, 

advanced" and "Pliopotamys near meadensis"; also Repenning, 1987, under "Boyle Ditch, Wyoming") reported them 

from that area on the Continental Divide at this time. This 

glacial period correlates in time with the Praetiglian floras 

of the Netherlands. Whatever the environmental changes 

during the early part of this first continental glaciation of 

the N orthem Hemisphere, they seem to have allowed 

Pliophenacomys and Ondatra to cross the Rocky Mountains from the Great Plains. The emigration of Pliophenacomys to the Pacific Faunal Region does not seem to have 

been successful, however, as the genus is not known from 

any other fauna in this region. 

The immigration from the Great Plains of Ondatra idahoensis near the beginning of Blancan V faunas (Repenning, 

1987) is discussed in more detail beginning on page 34-5. 

Subsequently discovered faunas (Conrad, 1980, and unpublished records of ours) in the Glenns Ferry Formation of an 

age intermediate between the Hagerman faunas and the late 

Grand View faunas (Jackass Butte) make the conclusions of 

Wilson (1934) and Zakrzewski (1969), that the Hagerman 

Pliopotamys minor evolved locally into the Grand View 

Ondatra idahoensis, seem improbable. If these muskrats 

represent the same lineage, these records show an inexplicable and abrupt increase in the animal's size shortly following 

the beginning of Blancan V faunas (seep. 34-5 ). The abrupt 

size difference seems most easily explained by an immigration of Ondatra idahoensis from the Great Plains and by the 

coincident extinction of Pliopotamys minor in earliest Blancan V faunas, as suggested by Repenning (1987). 

By about 3 million years ago, Pliopotamys had dispersed southward to Nevada, Arizona, and the Great Plains 

(apparently with Mimomys (Ophiomys)) and evolved into the 

species P. meadensis. Advanced forms of P. meadensis are 

difficult to distinguish from Ondatra idahoensis; hence it is 

not possible to say that 0. idahoensis did not evolve from 

Pliopotamys in the Great Plains. 

The period of global cooling and initiation of continental ice that was contemporaneous with the Grand View faunas until about 2.0 million years ago (high in the Jackass 

Butte sequence) is called the Praetiglian in the fossil floras of 

Holland, and was followed by the Tiglian warm floras. The 

Tiglian floras ended late during the Olduvai Normal-polarity 
16 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

Subchron and were followed, in tum, by the "cooler" floras 

of the Eburonian (van Kolfschoten, 1990). 

Matching these cycles with the records of activity of the 

Scandinavian Ice Sheet (Jansen and others, 1988) indicates 

that the Eburonian floras ended about 1.6 million years ago, 

but with a maximum peak in Scandinavian ice activity 

(Repenning and Brouwers, 1992, fig. 2). This maximum 

peak appears to correlate with the immigration of Phenacomys gryci in the Froman Ferry faunal succession at 1.6 

Ma, with Microtus californicus (and the arrival of Mictomys 

vetus) in the Anza-Borrego Desert record, and, presumably, 

with the arrival of Phenacomys zakrzewskii in the Java fauna 

of South Dakota (Martin, 1989) at about the same time. 

The later history of Mictomys is abundantly recorded 

both east and west of the Rocky Mountains. There is no 

later record of Plioctomys, from which Mictomys evolved, 

after Mictomys reached the east side of the Rocky Moun!. 

tains 2.0 million years ago, and Plioctomys is presumed to 

have become extinct (Repenning and Grady, 1988). Mictomys is abundant in the Froman Ferry faunal succession, 

both before and after the arrival of Phenacomys. 

The same circumstance of related forms appearing on 

the opposite sides of the Rocky Mountains occurred with 

immigration of Phenacomys 1.6 million years ago. Phenacomys (Paraphenacomys) gryci, then appearing in the 

middle of the Froman Ferry faunal succession, is of a different subgenus (Repenning and Grady, 1988) than that which 

first appeared in the Great Plains, Phenacomys (Phenacomys) zakrzewskii (Martin). This earliest record of the 

genus in the Great Plains (Java fauna, South Dakota, as 

Hibbardomys zakrzewskii; Martin, 1989) is of uncertain 

age, as the locality lacks paleomagnetic polarity determination or any other age approximation evidence external to the 

fauna, but the fauna contains Allophaiomys and is unquestionably of an early Irvingtonian age with a high percentage 

of Blancan holdovers (Martin, 1989). These holdovers are 

of different taxa than the holdovers in the Froman Ferry 

faunal succession of the Pacific Faunal Region. 

Because of the number of Blancan holdovers, the 

Java fauna appears to be about the same age as the Froman Ferry fauna, even without external age control; it 

seems likely that its magnetic polarity would be reversed 

and younger than the Olduvai event, should it be determined. But Microtus, immigrant with Phenacomys in the 

Pacific Faunal Region, did not yet exist in the Eastern 

Faunal Region. The microtine genus Allophaiomys, also 

in the Java fauna, immigrated (from Asia) to the Eastern 

Faunal Region 1.9 million years ago to provide a faunal 

basis for recognizing the beginning of Irvingtonian faunas, as has been mentioned, and is abundantly present in 

the faunas of the Eastern Region from then until about 

830,000 years ago (Repenning, 1992). 

Allophaiomys never dispersed west of the Rocky 

Mountains; one of its environmental preferences was a 

warm temperate environment, unlikely to have been present 

in the Yellowstone pass area at the peak of glaciation. This, 

however, says something about Beringian climate about 2 

million years ago when Allophaiomys must have crossed 

the land bridge to North America (Repenning and 

Brouwers, 1992). 

DISPERSAL EVENTS AND FAUNAL CHANGES 

The history of dispersals of microtine rodents from 

Asia and through the Arctic region to the conterminous 

United States is strengthened by the age and composition of 

the Froman Ferry faunal succession. The fauna closely 

dates an immigration event at about 1.60 Ma, that is in the 

lower one-third of a section between the dates of <1.67 and 

> 1.5 million years old. This immigration event was not recognized by Repenning (1987, fig. 8.1). It was not then recognized that a difference existed in the ages of dispersal to 

the regions east and west of the Rocky Mountains, but the 

event recorded in the Froman Ferry faunal succession 

shortly follows (by 300,000 years) dispersal event 7 of that 

reference, and marks the beginning of Irvingtonian faunas 

in the Pacific Faunal Region, as does dispersal event 7 in the 

Eastern Faunal Region. 

Repenning ( 1987) assigned numbers to the microtine 

dispersal events as a matter of convenience, and these numbers have been followed in his later publications (for example, Repenning and others, 1990). The number to assign to 

this newly recognized dispersal event, evident in the Froman Ferry faunal succession by the arrival of Phenacomys, 

in the Vallecito Creek faunal succession by the arrival of 

Microtus, and in the Eastern Faunal Region at the Java 

fauna of South Dakota by the arrival of a different subgenus 

of Phenacomys, presents a problem to this numbering 

system. 

As discussed later in the third section of this report 

("Historic Setting of the Froman Ferry Faunal Succession"), the recognition of the primitive muskrat Dolomys 

in the Etchegoin Formation of California eliminates the 

evidence of dispersal event 4, formerly believed to be 

dated by the arrival of the more advanced muskrat Pliopotamys in the Hagerman fauna (Repenning, 1987). Thus 

the muskrats appear in North America during dispersal 

event 3, not 4 (which is now recognized as not being a 

dispersal event). Dispersal event 5 thus becomes event 4; 

dispersal event 6 (at the beginning of the Grand View faunal succession) becomes event 5, dispersal event 7 (beginning the Irvingtonian mammal age in the Eastern Faunal 

Region) becomes event 6, and the immigration of Phenacomys and Microtus to the Pacific Faunal Region may be 

considered dispersal event 7, also evident in the Eastern 

Faunal Region by the immigration only of Phenacomys. 

Present information does not exclude the possibility that 
INTRODUCTION 17 

Phenacomys dispersed up the Columbia River route from 

the Pacific Coast, and that Microtus did not venture 

inland until reaching the Sacramento River farther south. 

The date of this new dispersal event 7 derives from 

(1) the 1.5-million-year minimum age of the overlying 

Pickles Butte basalt flow; (2) the entirely reversed polarity of the Froman Ferry faunal succession and of the overlying Pickles Butte basalt; (3) the probable correlation of 

the dispersal event, as recorded in the Froman Ferry succession, to the less well dated Vallecito Creek faunal succession of California; ( 4) the history of climatic change in 

the Northern Hemisphere, and the dependence of dispersals on these climatic changes; and (5) the faunal differences between the Froman Ferry faunas and the faunas of 

other known ages, which indicate a change related to 

time. These changes include the modernization of the lineage of Plesippus and that leading to Puma throughout 

the records of Glenns Ferry faunas, the new immigrant, 

and the extinction of Procastoroides, all to be discussed. 

Minor differences in the microtine Mimomys (Ophiomys) 

parvus will also be noted. 

The age of the underlying lacustrine deposits of the 

Glenns Ferry Formation is unknown in the Froman Ferry 

area, but the history of deposition of other known marsh 

deposits overlying lake beds (Hagerman, Sand Point, Poison and Birch Creeks, and Jackass Butte, to be discussed) 

suggests that no hiatus is present between the lake beds 

and the fossiliferous marsh deposits. In all but one of 

these localities (Jackass Butte), marsh deposition immediately follows the disappearance of the lake and can be 

seen to grade basinward into lake beds. The marsh dep_osits in the middle of the Jackass Butte faunal succession 

have fluvial deposits above and below them and thus 

appear to have resulted from a temporary rise in lake 

level, as will be discussed (p. 60-61 ). 

Consideration of these factors suggests that the immigrant microtine, Phenacomys gryci, appeared about 1.60 

million years ago, and that the entire faunal sequence 

lived between less than 1.67 (end of the Olduvai event) 

and more than 1.5 (unconformably capping Pickles Butte 

basalt) million years ago. 

From the correlations made by Repenning and Brouwers ( 1992) between the activity of the Scandinavian Ice 

Sheet and the pollen floras of Holland, this date for the 

immigration of Phenacomys (1.60 Ma) would seem to 

have been near the end (and in the most glacially active 

part) of the Eburonian cold flora of northwestern Europe 

(Zagwign and de J ong, 1984 ). It might thus be assumed 

that summers were cool and winters warm (because of 

cloud cover). Evidence cited in Repenning and Brouwers 

(1992) indicates that the Arctic Ocean was not ice covered at this time. These conditions were needed for 

growth of continental ice fields, but at present the only 

evidence of ice sheet expansion at this time is from Scandinavia. 

The presence of Phenacomys and that of the northern 

bog lemming Mictomys in the Froman Ferry faunal succession support this interpretation of climate. Living Mictomys 

avoids the hot summers of the modem temperate climate by 

now living to the north in Canada, but does not appear disturbed by the modem severity of the winters in this area. 

Living Phenacomys (Paraphenacomys) is more environmentally restricted and can endure neither hot summers nor 

severe winters of today and lives only in the forests of 

coastal Oregon, in perhaps the most equable climate in 

North America--even the severity of winters of coastal 

Washington now limits its range. In combination, the two 

common forms of microtines in the Froman Ferry faunas 

suggest cool winters, possibly cool enough to freeze at 

times, and cool rainy summers about 1.6 million years ago. 

The cold winter temperatures of the modem Canadian 

forests are ruled out by the subgenus of Phenacomys in the 

fauna, and hot sunny summer days, as are now typical of the 

Snake River Plain, are ruled out by both genera. In addition, 

the absence of subtropical mice, as Sigmodon, suggests that 

winters were cool enough to include some freezing temperatures. 

The Froman Ferry faunal succession contains microtine and other taxa that are typical of the Blancan V age 

throughout the Pacific Faunal Region, including the Grand 

View faunas (2.5 to 2.0 Ma) of the Snake River Plain and 

the Vallecito Creek faunal succession (Natural History 

Museum of Los Angeles County (LACM) localities 6683 

and 1357) of southern California (approximately 1.6 Ma 

and 2.1 Ma). These Blancan V microtine rodents are 

Mimomys parvus, Mictomys vetus, and Ondatra idahoensis. 

Thus, the older part of the Froman Ferry faunal succession, 

prior to the arrival of Phenacomys, is considered a Blancan 

V fauna, but younger than other known Glenns Ferry Formation faunas. 

Only the introduction of the immigrant microtine, 

Phenacomys (Paraphenacomys) gryci (from the Arctic), 

marks a change in the higher parts of the Froman Ferry faunal succession, a change that is here used to identify the 

beginning of the Irvingtonian mammal age in the Pacific 

Faunal Region of the United States, close to 1.6 million 

years ago. 

We point out that none of the large mammals from the 

Froman Ferry faunas are indicative of an Irvingtonian mammal age; most are usually thought of as being indicative of a 

Blancan age. The arrival of Phenacomys gryci is the first 

faunal change in the Snake River Plain of Idaho that would 

separate Irvingtonian faunas from Blancan faunas. But the 

age of this faunal change is not at all consistent with the age 

of the beginning of Irvingtonian mammals to the east of the 

Rocky Mountains in the Eastern Faunal Region of the 

United States, as has been discussed under the headings 
18 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

"Mammal Ages and Provincialism" and "Dispersal" (pages 

10 and 13). 

COLLECTIONS 

Very few large mammals and small mammals other 

than microtines are present in the Froman Ferry faunal 

succession, although an aquatic shrew is present in several localities, and leporids and a beaver are present, but 

rare. The scarcity of large mammals and the absence of 

many types of small mammals are thought to be a result 

of the environmental constraints of the ancient marsh. 

Scott's collections were made by prospecting for 

marsh plant remains (reeds and rushes, usually visible 

only in freshly exposed material), and collecting and 

washing at least three burlap sacks of matrix (about 75 lb 

each) when these were found. As collecting proceeded, it 

became apparent that the great majority of small mammals were in those deposits that appeared as dark-gray 

layers because they were rich in carbonized plant matter 

and that were visible hundreds of feet away. Fragmented 

large mammals were most common in fluvial gravel beds, 

as at locality GS-232 in the Cucumber area. As judged by 

the scarcity of large mammal remains, however, the area 

would be considered sparsely fossiliferous. 

The specimens from the Froman Ferry faunas here discussed are cataloged in the National Museum of Natural 

History, Smithsonian Institution, Department of Paleobiology, Vertebrate Paleontology Catalog (USNM). Only the 

most significant specimens described herein (figured or 

described in detail) have been assigned USNM numbers in 

this report; the others are designated only by George Scott 

locality field numbers (GS-XXX), which will also be on file 

at the USNM; these specimens will be cataloged in USNM 

at a later date. 

Specimens collected by Scott subsequent to writing 

this report are being placed in the Museum of Natural History, Idaho State University, Pocatello, Idaho. 

ACKNOWLEDGMENTS 

We are particularly in debt to Harold E. Malde, Colleen A. Neville, and Gregory S. Conrad for taking the 

time to show C.A.R., Platt Bradbury, and Richard Forester the Snake River Plain and Glenns Ferry Formation 

in the summer of 1978. Hugh J. Rieck and David J. Van 

Domelen made the paleomagnetic section of the Froman 

Ferry section at our request. Gerald R. Smith (fish), John 

A. White (lagomorphs), J. Platt Bradbury (diatoms), and 

Robert S. Thompson (pollen) were kind enough to share 

their knowledge of the fossils and stratigraphy of the 

Glenns Ferry Formation. G. Dallas Hanna was first to call 

our attention to the microtine rodents of the Alturas Formation in northeast California. Mark L. Ferns, Oregon 

Department of Geology and Mineral Industries, provided 

useful discussion and constructive thought. And James 

and Neil Morgan provided information about the Taunton 

fauna in eastern Washington, as well as years of discussion of the fauna and biochronology. Richard H. Tedford 

provided valuable information about the specimens from 

the Blanco fauna, Crosby County, Texas, in the American 

Museum of Natural History. G.A. Izett and J.G. Honey 

permitted the examination of undescribed specimens from 

Rock Creek, Texas, and from the Aries fauna of Mead 

County, Kansas. W. Tony Bryant and W.C. Repenning 

helped in the field work, and Patricia Holroyd in the preparation of illustrations and general discussion of the 

fauna. Elaine Anderson, W.A. Akers ten, J .H. Hutchison, 

Cheri A. Jones, S.A. McLeod, Carron Meaney, K.L. Othberg, Julia Sankey, and Bill Stroud permitted examination 

of specimens or samples in their care and (or) provided 

information of value to the study. Lorna Carter, editor for 

the U.S. Geological Survey, once again assisted greatly in 

making the wording more understandable. This study was 

supported in part by a Gilbert Fellowship from the U.S. 

Geological Survey, Project 1-9590-09250 from April 

1992 to April 1993 and in part by the U.S. Government 

Volunteer for Science Program through the Boise District 

Office, Bureau of Land Management, and the Geologic 

Division, U.S. Geological Survey. 

THEFROMANFERRYFAUNA 

Fish remains are abundant throughout the Froman 

Ferry faunal succession; Gerald R. Smith (University of 

Michigan Museum of Paleontology) examined about 

1,000 from the Cucumber area and identified the following forms (G.R. Smith, written commun., 1992): 

Family Cyprinidae 

Acrocheilus latus, chiselmouth chub; derived from the 

Columbia River drainage (common). 

?Gila sp., chub. 

Mylopharodon hagermanensis, minnow; derived from 

the Sacramento River drainage (abundant). 

Family Catostomidae 

Catostomus macrocheilus, sucker; derived from the 

Columbia River drainage (rare). 

Chasmistes sp., lake sucker; derived from the Snake 

River drainage (not Columbia River) (rare). 
THE FROMAN FERRY FAUNA 19 

~ 2mm Mental foramen 

OCCLUSAL 

MEDIAL 

POSTERIOR 

Figure 5. Sorex (Otisorex) palustris USNM 264328 from locality GS-225, Cucumber area, 

Froman Ferry faunal succession, Canyon County, Idaho. Medial, occlusal, and labial views of 

the lower dentition, and posterior view of the mandibular condyles. Scale as shown. 

Family Ictaluridae 

/ctalurus sp., catfish; now found only east of the 

Rocky Mountains (uncommon). 

Smith (written commun., 1992) noted that all of the 

lake species and also the Columbia River fluvial species 

(sturgeon, peamouth chub, sculpins, rainbow trout, mountain whitefish) are missing, and that the fish fauna is a distinctly warm water one. The presence of stunted catfish 

and the absence of sunfish suggest a short growing season. He stated that "The fauna is most similar to that at 

Jackass Butte, but lacks the cold-water stream sculpin Cottus." As has been mentioned and is further discussed 

beginning on page 60, most of the Jackass Butte faunal 

sequence is from stream deposits apparently draining a 

glaciated headwaters in the Yellowstone Park area, and 

marsh deposits are lacking except in the middle part of 

the section that contains the older normal event of the 

Reunion Subchron (2.12-2.14 Ma), which also is present 

in glacial till in Iowa. 

Smith and Patterson (1994) have recently published a 

summary of the temperature conditions in the Glenns Ferry 

lake, based upon the nature of the fish fauna and oxygen 

isotopic evidence. Although it is concerned mainly with 

the environment of the lake, the results are in good agreement with the climatic interpretations here made from the 

mammalian faunas. 

Surprisingly few bird bones were found in the Froman 

Ferry faunal succession, and only the tarsometatarsus of a 

pintail, Anas sp. cf. A. acuta, was identified from GS-220 

(2,630 feet elev., in the Cucumber area). 

Abundant herpetofaunal and molluscan remains were 

not identified. 

Order INSECTIVORA 

Family SORICIDAE Gray, 1821 

Subfamily SORICINAE Fisher von Waldheim, 1817 

Genus SOREX Linnaeus, 1758 

Subgenus OTISOREX De Kay, 1842 

SOREX (OTISOREX) PALUSTRIS Richardson, 1828 

FigureS 

Localities and material.-CHALK HILLS AREA: 

GS-209 (2,470 ft elev.): mandible fragment with M/1-2; 

mandible fragment with part of Mil and M/2. LIZARD 

BUTTE AREA: GS-213 (2,440 ft elev.): mandible with M/ 

1-3. CUCUMBER AREA: GS-217 (2,480 ft elev.): mandible fragment with M/3. GS-220 (2,630 ft elev.): partial 

mandible with P/4-M/3; mandible with M/1. GS-221 

(2,650 ft elev.): mandible with M/1; mandible fragment 

with posterior structures; two mandible frags with M/1-2. 

GS-225 (2,640 ft elev.): five mandibles (one· USNM 

264328) and a maxillary with P\4-M\2. GS-230 (2,760 ft 

elev.): mandible with P/4-M/3. GS-234 (2,770 ft elev.): 

mandible fragment with M/1-2. 

Eight localities; 2,440 to 2,770 feet elevation (uncorrected for structural uplift in the Pickles Butte area). 

Discussion.-The genus So rex has a rather large number of species and has been subdivided into subgenera in various ways; the presence of "postmandibular foramen" is 

possibly the most questionable criterion, as it has many 

exceptions and can result from ossification failure at the base 
20 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

of the internal temporal fossa. Nevertheless, it is here used as 

a character of the subgenus Otisorex (see Hall, 1981, p. 27) 

as all specimens (N=13) preserving this part of the mandible 

lack the postmandibular foramen. In contrast, those shrews 

belonging to the genus Sorex described from the Hagerman 

fauna (three species; Hibbard and Bjork, 1971) all have both 

a mandibular foramen and a postmandibular foramen. 

Sorex palustris, a living species, appears to be present 

throughout the Froman Ferry faunal succession. There is 

only a single mandibular foramen, which may (N=4) or may 

not occur in a shallow depression or groove. A single unicuspid is present anterior to P/4. The mental foramen is below 

the paraconid of Mil and slightly below and behind the 

labial flange of P/4. The talonid of M/3 is not greatly reduced 

and pigmentation is moderately variable in extent, but well 

developed. The mandibular condyles are typically soricine 

(Repenning, 1967a). 

In size the Froman Ferry material seems to be slightly 

small for the species, and the length of M/1-M/3 averages 

3.1 mm (N=13; range=2.7-3.5 mm). Modem specimens in 

the Denver Natural History Museum from Archuleta 

County, Colorado, average about 3.7 mm in this dimension 

but from Chaffee County, Colorado, about 3.2 mm in this 

dimension. 

The specimens do not resemble any shrew species 

from the Hagerman faunas that Hibbard and Bjork (1971) 

assigned to the genus. These belong to the subgenus 

Sorex on the basis of the presence of a single postmandibular foramen. Sorex palustris is a more or less generalized 

species of the genus, but has exceptional aquatic adaptations; it is not surprising to find it in fair abundance in the 

Froman Ferry marsh beds. 

Order CARNIVORA Bowdich, 1821 

Family FELIDAE Gray, 1821 

Subfamily MACHAIRODONTINAE Gill, 1872 

Genus ISCHYROSMILUS Merriam, 1918 

ISCHYROSMILUS IDAHOENSIS Merriam, 1918 

This species was originally described from the Froman Ferry fauna (locality UCMP 3036, old 3036C) on 

the basis of a badly abraded and incomplete left mandibular ramus. Nothing more of the taxon has been recovered 

from the Froman Ferry area, but material from Grand 

View has been referred to the species (Shotwell, 1970; 

Conrad, 1980). A large and poorly preserved calcaneum 

(USGS locality M 1346, unpublished) and a fourth metacarpal (Bjork, 1970) have been referred to the genus from 

Hagerman. Machairodont affinities and size, of course, 

are the only basis for these assignments, as the type is 

known only from the mandibular ramus. 

The species is larger than Ischyrosmilus ischyrus from 

the Asphalto fauna of California (Merriam, 1905), probably 

of Irvingtonian I age Uudging from its association with an 

advanced p1esippine horse) and roughly the same age as the 

Froman Ferry fauna. I. idahoensis is slightly larger than 

Ischyrosmilus johnstoni Mawby (1965) from the Cita Canyon fauna of Texas (about the same age as the oldest part of 

the Grand View faunal succession), and Kurten (in Kurten 

and Anderson, 1980) noted a considerable range in size of 

these two species, apparently considering both synonymous 

under the prior name /. idahoensis. 

Ischyrosmilus idahoensis from the Froman Ferry fauna 

has an elongate diastema between the stout lower canine 

and P/3 with a more sloping chin (hence a less blunted rostrum), and appears to have had a less prominent flange on 

the lower jaw for the upper canine than some sabertooth 

cats; the synonymy apparently intended by Kurten (in 

Kurten and Anderson, 1980) seems reasonable. 

Subfamily FELINAE Trouessart, 1885 

Genus PUMA Jardine, 1834 

PUMA CONCOLOR (Linnaeus), 1758 

Locality and material. -CUCUMBER AREA: GS222 (2,650 ft elev.): left calcaneum. GS-221 (2,650 ft elev.): 

USNM 264337: two patellae, left and incomplete right 

astragali, incomplete left calcaneum, left and right cuboids, 

left navicular, left entocuneiform with typically reduced 

first metatarsal, incomplete left metatarsal II, distal half of 

right metatarsal III, head of left metatarsal IV, proximal 

third of right metatarsal V; right scapholunar, left trapezoid, 

left and right magnum, left and right unciform, left 

cuneiform, proximal half of right metacarpal II, complete 

left and head of right metacarpal III, heads of left and right 

metacarpal IV, heads of right first and third metacarpals; 18 

sesamoids; 10 distal and many intermediate phalanges; 

last(?) caudal vertebra (elongate) and many vertebral fragments; distal articulations of fibula, ulna, and humerus; 

proximal articulation of radius; fragment of mandibular 

ramus at diastema with P/2 roots, two mental foramina, and 

worn canine; fragment of left premaxillary with alveoli for 

1\1,2,3 and C; GS-232, Sample 14 (2,815 ft elev. and 60ft 

uphill from GS-232): proximal third of ulna. 

Three localities; 2,650 to 2,815 feet elevation. 

Comparison.-The generic allocation of species of 

cats is unstable. The cheetah Acinonyx and the unrelated 

and extinct North American cheetah Miracinonyx are 

almost always considered as genera separate from Felis; the 

large, roaring cats (lion, tiger, leopard, jaguar) are often 

considered separately in the genus Panthera; the bob-tailed 

intermediate-sized cats are often placed in the genus Lynx; 

and the large puma and small cats that do not clearly belong 

in any of the above are usually left in the genus Felis. 

Living Lynx rufus, L. canadensis, and L. caracal, 

Puma concolor, Panthera tigris (two subspecies), P. onca, 

P. pardus, and P. uncia, Felis pardalis, F. serval, and 

domestic cat, as well as Acinonyx jubatus and the fossil 
THE FROMAN FERRY FAUNA 21 

~ 3 

B 

Figure 6. Modem specimens of Puma concolor and Panthera tigris, calcanea and astragali, showing 

differing articulations on the sustentaculum. Scale as indicated. A, Puma concolor, articulated left astragalus and calcaneum, medial aspect. B, Panthera tigris, articulated left astragalus and calcaneum, medial aspect. C, Puma concolor, calcaneum in tibial aspect. D, Panthera tigris, calcaneum in tibial aspect. 

X, posteroplantar articular facet on the sustentaculum. 

Miracinonyx inexpectatus, were compared with the fossil 

material. 

Although the comparisons made to identify the puma 

from the Froman Ferry faunal succession were by no 

means complete for the subfamily Felinae, they did lead 

to the observation that in most bones of the body of the 

puma, the genus is distinct, in varying degrees, from other 

cats, and that the puma is as logically considered as a separate genus as are any of the other often-recognized genera (see Honacki and others, 1982, p. 277-283). We 

therefore follow this reference with the exception that we 

also treat Puma as a full genus (Honacki and others 

included it in Felis). 

The living Lynx canadensis and Lynx rufus are very 

similar in skull size but differ in body size, Lynx canadensis having relatively larger body and longer legs than 

Lynx rufus. The difference between these two species is 

comparable to that between Miracinonyx inexpectatus and 

Puma con color. Yet the lynxes are left in one genus (or 

subgenus) and the puma and the extinct North American 

cheetah (often considered as being closely related to the 

puma) are put in separate genera. However, in this review 

we do not advocate placing Puma and Miracinonyx in the 

same genus, although a comparison of the heads of these 

two does favor such a similarity (Savage, 1960). Many 

consistent differences exist in the postcranial skeleton and 

in their biogeographic history (Van Valkenburgh and others, 1990). 

A single calcaneum of Puma was found at GS-222; it 

is unmistakably identical to that bone of the living Puma 

concolor. The bone is less similar to that of Felis lacustris 

from older faunas of the Glenns Ferry Formation, which is 

smaller (Gazin, 1933; Bjork, 1970; Conrad, 1980) and less 

similar to living puma. Length of the fossil calcaneum=61.4 

mm (cuboid facet to lateral posterior process, the longer 

medial posterior process is missing because of damage). 

The specimen from GS-221 (USNM 264337), about 

150 feet from GS-222, is obviously the remains of a single 

individual, completely disarticulated and with the larger 

bones fragmented but not worn or weathered. Several bones 

are represented by both left and right elements and those that 

are preserved are sharply defined morphologically. The single calcaneum of this individual is smaller than that from 

GS-222 and measures 52.3 mm in the same dimension 

(cuboid facet to lateral posterior process; 85 percent the size 

of that from GS-222). In comparison with the calcaneum 

from GS-222, this is the same size difference as may be 

present in the sexual size difference of living Puma concolor 

(Hall, 1981, v. 2, p. 1 039), although individual variability 

may exceed sexual variability. The size difference of the two 
22 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

Froman Ferry individuals is interpreted as being a sexual difference, however. Considered together, both specimens seem 

possibly small in comparison with living puma, but within its 

size range. But the sample is small. 

CALCANEUM.-The male and female calcanea from 

Froman Ferry have little similarity to that of the living Old 

World cheetah, Acinonyx jubatus; they also are not very similar to the calcaneum of the North American cheetah, Miracinonyx inexpectatus, as follows: 

1. Like Puma concolor, the calcaneum is much 

smaller than that of Miracinonyx. 

2. Like Puma concolor, the sustentacular articular 

facet on the male calcaneum from Froman Ferry has a distinct caudal (proximal) crestlike edge above the more prominent groove (for interosseous ligaments with the astragalus) 

that separates the two articular surfaces for the astragalus 

(noted by VanValkenburgh and others, 1990). 

In Miracinonyx, as in most living cats except puma, 

the caudal part of the sustentacular articular surface is varyingly bent, in a plantar-caudal direction, but is less developed in Miracinonyx than in most. Viewed in medial aspect 

this articulation between the calcaneum and the astragalus 

is distinctly an angled surface (about 130° between facets) 

in all cats (best developed in the tiger, see fig. 6), except 

Puma. In Puma and Lynx rufus only the primary facet is 

present and a caudal-plantar-directed portion of the surface 

is lacking. The caudal-plantar flexure is minimally developed in the Afroasian caracal (sometimes included in the 

subgenus Lynx), and is also weakly present in some individuals of North American Lynx canadensis, but not Lynx 

rufus. The articular surface in the Froman Ferry specimen is 

like that of puma, and has only the primary facet. 

The lack of this downward flexure at the caudal limit 

of the sustentacular articulation is the strongest single feature that distinguishes the calcaneum of North American 

puma and lynx from other cats of the world, including jaguar. One calcaneum of M. inexpectatus from the Cheetah 

Room fauna, West Virginia (USNM 401092), and two unassociated calcanea from Cita Canyon, Texas (JWT 1950 and 

608), were made available by B. VanValkenburgh. On the 

West Virginia specimen the downward (caudal) flexure of 

the articular surface is clearly present, although weakly 

developed in comparison with many modern Old World 

cats, as tiger. It is even more weakly developed in the two 

specimens from Cita Canyon. 

The calcaneum is not known from the specimen of 

Miracinonyx inexpectatus from Santa Clara County, California (USNM 184064 ), but the opposing articular surface on 

the plantar surface of the astragalus clearly shows this flexure, as is the case with the astragalus of the Old World cats. 

This downward, caudal bend of the articular surface on the 

calcaneum appears to be consistently absent in Puma and 

very weak in Lynx and Miracinonyx; it is weak to pronounced in other living felids. 

On the Froman Ferry specimens, the sustentacular 

astragalar articulation is preserved only in the male from 

GS-222, but this specimen shows no sign of this downwardflexed caudal part of the articulation, comparing favorably 

with living puma. 

3. The body of the Miracinonyx calcaneum, posterior 

to the astragalar articulations, is thickened dorso-plantarly, 

as though to provide additional strength to resist the strain 

of extension of the pes. This thickening is not evident on 

Puma, Old World Acinonyx, or other cats examined. 

The calcanea of Puma, Miracinonyx, and Acinonyx are 

similar in having a more massive sustentacular process than 

do those of most Old World cats. In medial aspect of the calcaneum (fig. 6: Puma) of these forms, the entire sustentaculum is, relatively, thicker in a plantar-tibial direction and the 

plantar groove for the tendon of the flexor digitorum profundus is variably narrow and more sharply defined than on 

many (but not all) Old World cats. 

The sustentaculum itself is not transversely elongate in 

puma, Miracinonyx, or Lynx, and its articular surface is 

approximately equidimensional, rather than transversely 

elongate as in some (but not all) Old World cats (fig. 6: 

tiger). 

In summary, the Puma calcaneum from GS-222 

resembles that of Miracinonyx about as much as does living 

Puma, and is identical to living Puma. Unlike Miracinonyx 

and like Puma it is smaller, has a less robust calcaneal tuber 

behind the astragalar articulations, has a deeper and more 

sharply rimmed trench between the sustentacular 

articulation and the body of the calcaneum, and shows no 

tendency toward a plantar-caudal flexure of its sustentacular 

articular facet. Disregarding size, there is no felinid that has 

a calcaneum which could be confused with Puma except 

within the genus Lynx. 

ASTRAGALUS.-The downward fold of the astragalar 

articulation of the calcaneal sustentaculum in all but puma 

and lynx is matched on the opposing articular surface of the 

astragalus by a downward (plantar) bend at its caudal (proximal) limit. Thus the articular surface for the calcanear sustentaculum extends a short distance onto the base of the 

tibial trochlea of the astragalus in Old World cats. The available astragalus of Miracinonyx inexpectatus (USNM 

184064) shows the Old World pattern. There are some individual exceptions, however, in the astragalus of both living 

puma and the Froman Ferry fossil from GS-221 (USNM 

264337). In the astragalus of these a small posterior-plantardirected surface is present at the back of the articular surface for the sustentaculum of the calcaneum. This small surface is not reflected on the opposing calcaneum in these 

individuals, but its presence on the plantar surface of the 

astragalus makes the character less reliable when judged by 

the astragalus than when judged by the calcaneum. 

Similarly, the trench is narrower between the two 

astragalar articular surfaces for the calcaneum, on the 
THEFROMANFERRYFAUNA 23 

plantar side of the astragalus, of puma and lynx than in 

some individuals of Panthera. This parallels the lack of 

transverse elongation of the sustentaculum, and the presence of a narrower, more sharply defined groove between 

the articulations for the astragalus on the calcaneum in 

puma and lynx. The trench of the astragalus and the 

groove of the calcaneum are relatively wide in some Old 

World cats, as, tiger and snow leopard, but not so in leopard and jaguar. Evaluation of puma characters of the 

astragalus is less certain than evaluation of the calcaneum. 

ULNA.-As shown by Van Valkenburgh and others 

( 1990, fig. 8) the distal radial articulation on the ulna of 

puma and Canadian lynx is pedestaled, it is on a process 

that holds it above the anterior surface of the ulna: this 

elevation of the articular facet above the ulna shaft is not 

so obvious in bobcat (Lynx rufus). Although apparently 

always present in Puma, the pedestaled radial articulation 

on the ulna seems to be a random condition in all other 

cats and not particularly diagnostic of species groups, 

except that it is remarkably reduced in the cheetahs and 

Miracinonyx and so its lack is presumably related to running. 

A comparable structure is present on the distal end of 

the radius for the opposing articulation with the ulna in 

puma and other cats having the pedestal on the ulna. The 

result is that the radius and the ulna of puma, Canadian 

lynx, and some other cats are relatively more separated at 

their distal ends, suggesting a more massive wrist. 

The distal radial articulation on the ulna of Miracinonyx trumani (not seen; VanValkenburgh and others, 1990, 

fig. 8) appears intermediate, and the living cheetah appears 

almost not to have the articulation. The partial ulna from the 

female puma specimen of the Froman Ferry succession 

exactly matches living puma, and it bears no resemblance to 

the North American cheetah. The more proximal parts of 

the ulna were not found at GS-221, but an isolated proximal 

third of an ulna of Puma was found in the fluvial gravel of 

GS-232, Sample 14. It is well preserved, although the individual was a bit arthritic. In the region of the humeral 

socket, the posterior (ventral) margin of the puma ulna is 

straight or even a bit convex, whereas it is concave in some 

cats (as, tiger) because of a posterior curve of the olecranon 

process, and the humeral socket (semilunar notch) is deeper 

and nearly semicircular in puma. In these respects the proximal part of the Lynx ulna matches that of Puma. 

RADIUS.-Only the proximal head of this bone was 

found with the female specimen. In puma and lynx the 

ringlike proximal articulation for the ulna does not completely circle the head of the radius but is incomplete at 

the most anterior point (on the side opposite the ulna); in 

all other cats seen the articular band completely circles 

the head, suggesting greater pronation-supination of the 

manus in most cats. 

HUMERUS.-Only the distal articulation of a humerus 

was found with the female specimen from GS-221(USNM 

264337). Orientation of the bridge for the entepicondylar 

foramen seems to vary in different cat lineages. In medial 

aspect of the humerus of the tiger, the internal epicondyle, 

and the bridge of the foramen proximal to it, originate centrally on, and lie in line with, the shaft axis. The bridge continues proximally, terminating in a more or less central 

position on the medial side of the shaft. In puma, lynx, leopard, snow leopard, and many others, the medial epicondyle 

is located more posteriorly-the bridge of the foramen 

begins at the flexor origins, and is oriented anteroproximal 

so that the foramen bridge is directed anteriorly as well as 

proximally up the shaft: at its proximal termination it is 

essentially at the anterior face of the shaft, not medial on the 

shaft as in tiger and a few other largest cats. Again, the condition seems variable in most cats except Puma. 

Miracinonyx and Acinonyx have the puma-lynx pattern 

except that the bridge is remarkably broad. The distal articulation of the humerus from GS-221 clearly shows the pumalynx pattern, and is not a relatively broad bridge as in Miracinonyx. The character seems intraspecifically variable and 

not diagnostic at the generic level, except that within Puma 

the condition is consistent in all individuals (N=6). 

METACARPALS.-In the manus of all cats, the first 

metacarpal is reduced and has a uniform morphology, 

although varying in size. The fossil first metacarpal from the 

female specimen is identical to living felids and its size is 

that of a small female puma; as are all other bones, it is conspicuously larger than this bone of Lynx. The first metacarpal 

of Miracinonyx appears to be considerably larger (150 percent) than in male puma (Van Valkenburgh and others, 1990, 

p. 441, fig. 10). 

The third metacarpal from GS-221 (female) is 6.7 em 

long, and the same bone in a modem (wild) male puma is 

7.8 em long. Van Valkenburgh and others (1990, table 5) 

listed an average of 8.35 em based upon eight specimens in 

the Natural History Museum of Los Angeles County. Their 

specimens are very large and may be animals from a zoo; 

the same greater size is evident in zoo animals in the Denver Natural History Museum. Captive puma grow to larger 

sizes than wild puma (Betty Mulcahy, Denver Zoo, oral 

commun., 1994); however, we know of no published size 

comparison between zoo and wild puma. (One of our wild 

specimens was killed by a bow hunter in southern Arizona 

and, by skull length, was said to be the seventh largest puma 

killed by a bow in Arizona; it cannot be considered a small 

puma.) 

PEs.-In addition to the astragalus and calcaneum, 

the tarsal elements from the Froman Ferry locality GS221 include the cuboid, entocuneiform, and rudimentary 

first metatarsal of the right pes. Except that they are 

small, these also seem identical to Puma concolor but differ only slightly from those of other cats compared. The 

calcaneal facet of the cuboid is almost rectangular in 

tiger; in Lynx rufus it is rectangular but its posteromedial 
24 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

comer is enlarged in this direction, which is above the buttress that forms the groove for the peroneus longus. This 

expansion of the posteromedial comer of the calcaneal 

articulation of the cuboid is more pronounced in puma so 

that the articular surface could be described as a trapezoid, and this pattern is identical on the smaller cuboid 

from GS-221. There seems to be little consistency to the 

individual variation of this facet, however, and the jaguar 

and ocelot cuboids examined are like puma in this feature. 

The fossil entocuneiform is rather narrow, conspicuously narrower (plantar-dorsally) than the first metatarsal 

at their articulation, but these conditions do not seem significantly different than in other cats. The distal phalanges 

are typically feline, and little can be said about the elongate caudal vertebra, except that the animal had a long 

tail, apparently as elongate as in living puma; the vertebra 

is 17.7 mm long and 6.5 mm thick at its proximal articulation and appears to have been nearly terminal by comparison with living puma. 

Discussion.-Although the characters separating 

Puma concolor from other living cats are variable in other 

cats, they seem consistent within Puma. The elements preserved in the Froman Ferry fauna at localities GS-221 and 

GS-222 show the puma condition in all of them. The fossils from GS-222, GS-221, and GS-232 represent three 

individuals that are within the size range of the living 

(wild) form of the species, but apparently slightly smaller 

than the average, if our comparisons have not been influenced by the size difference between captive and wild 

individuals. The male calcaneum is larger than that of 

Felis lacustris from the older parts of the Glenns Ferry 

Formation, but even this population is within the rather 

large size range of the living species. 

Both the fossil cats from the Glenns Ferry Formation 

and the living puma are morphologically dissimilar to and 

smaller than the North American cheetah, Miracinonyx 

inexpectatus, which lived contemporaneously with Puma 

from about 2.56 million years ago until at least 600,000 

years ago and in all parts of the United States. 

From the present fossil record, M. inexpectatus 

appears fully developed about 2.56 million years ago at 

Cita Canyon, Texas, and has no earlier North American 

record. It appears to have changed little over the following 2 million years that it is recognized as a species (Van 

Valkenburgh and others, 1990), suggesting that when it 

arrived in North America it was fully adapted and morphologically stable. 

The time of arrival of Miracinonyx in North America 

was a time of conspicuous faunal dispersal from Eurasia to 

North America (beginning of Blancan V). This was also the 

time of the beginning of the first Tertiary buildup of 

continental ice in the Northern Hemisphere, as well as the 

first development of permafrost in Beringia (see Repenning 

and Brouwers, 1992, for a climatic summary). Glacial 

buildup was accompanied by the retraction of forests from 

the shores of the Arctic Ocean and the expansion of great 

areas of steppe grassland and of tundra environments in the 

Arctic region (because of the increasing development of the 

Arctic low over the Arctic Ocean and lowered summer temperatures). It is reasonable to expect the dispersal of steppeadapted cats and other mammals at this time. There is, however, some basis for questioning the steppe adaptation of 

Miracinonyx, both because it was so very widespread across 

the United States (California to the Appalachian Mountains) 

and because the differences in body proportions between it 

and the puma are comparable to those between Canadian 

lynx and bobcat, the Canadian lynx being larger bodied and 

longer legged, but not generally considered a steppe cat. 

Van Valkenburgh and others noticed no skeletal difference between the oldest specimens of the North American cheetah (Cita Canyon, Texas, 2.56 Ma) and the 

youngest (Cheetah Room, West Virginia, 0.84 Ma, and 

the undated Conard Fissure, Arkansas, which is, perhaps, 

as young as 0.61 Ma), suggesting that they were preadapted to take advantage of this climatic change and 

were relatively fixed morphologically. As Van Valkenburgh and others (1990, p. 452) noted, this evolutionary 

stasis of the cheetah-like cat seems to have ended during 

the possibly 600,000 years following its youngest record, 

if the late Pleistocene Miracinonyx trumani actually 

derives from M. inexpectatus as has been suggested. This 

departure from stasis also might be expected, as the 

youngest record, although· undated, was during a time of 

global climate fluctuations: the beginning of the later, and 

most intense, part of the Ice Ages. This climatic instability could have forced major changes in adaptation, and 

may have stimulated renewal of morphologic evolution 

toward M. trumani. Although not so well known, M. trumani appears to have been restricted to steppe environments, and is known only from modem plains and desert 

areas whereas M. inexpectatus has been found from Florida to Pennsylvania and westward to California. 

Not only was the Froman Ferry puma different in morphology and size from the contemporaneous immigrant, M. 

inexpectatus, it was not in morphologic stasis but was evolving in both size and morphology toward modem puma during deposition of the Glenns Ferry Formation, from Felis 

lacustris of the Hagerman fauna (about 3 Ma) and of the 

Jackass Butte fauna (about 2.2 Ma) to Puma concolor of the 

Froman Ferry fauna. The skeletal evolution seems to have 

been nearly complete by the time of the Froman Ferry faunal 

succession. 

In the patterns of the limb skeletal elements 

described previously, the New World jaguar and ocelot 

appear to be like Old World cats and less similar to North 
THE FROMAN FERRY FAUNA 25 

0 2 mm 

Figure 7. Occlusal enamel pattern 

of the third lower premolar of 

Hypolagus gidleyi from the right 

mandibular ramus ofUSNM 264338; 

locality GS-232, Sample 14, high in 

the section in the Cucumber area, 

Froman Ferry faunal succession, 

Canyon County, Idaho. Scale as 

shown. Enamel shown as black. 

American puma, suggesting a later immigration to North 

America, possibly 840,000 years ago from the evidence in 

the Cheetah Room fauna of West Virginia (Van Valkenburgh and others, 1990). This also was at a time of major 

immigration to North America from Asia and the beginning of the "official" Ice Ages (Nebraskan glaciation). At 

this time Eurasia experienced the "End-Villafranchian" 

dispersal event of Azzaroli ( 1983 ), in which Arctic large 

mammals spread southward. 

But the North American puma, dating back to the Froman Ferry fauna (close to 1.6 Ma, Phenacomys gryci was 

collected at the site of the female specimen) and evolving in 

the Glenns Ferry Formation from the Hagerman Felis lacustris (3.6 Ma) and from still earlier faunas in the Great 

Plains, appears to have entered North America possibly at 

the beginning of the Blancan faunas, 4.8 million years ago. 

Thus, the fossil record seems to show at least three 

invasions of Old World Felidae into the Western Hemisphere: (1) The puma-lynx lineage appeared perhaps at the 

beginning of the Blancan mammal age of the United States 

(4.8 Ma). The time of division of these two genera appears 

to have been perhaps 3.4 Ma but is not well documented in 

the fossil record. (2) The North American cheetah appeared 

in North America in late Blancan time (2.56 Ma). (3) The 

Panthera lineage, in possibly several stages during the 

Pleistocene, begins with the jaguar (possibly 0.84 Ma ago), 

the only living New World species of Panthera. Only those 

of the most recent immigration seem identical to the living 

Old World cats. The North American cheetah is cheetahlike only in convergent adaptation; a number of features 

suggest a closer relationship to puma than to Old World 

cheetah, as has been noted by others, but if so, it evolved 

out of an Asian, not a North American, puma-like cat. 

Although Savage (1960) and Bjork (1970) believed 

that Felis lacustris from the Hagerman fauna was not 

directly related to modem puma, the progressively increasing similarity to puma in younger parts of the Glenns Ferry 

Formation suggests that the cats of the Glenns Ferry Formation are the previously unknown origin of Puma concolor, a 

suggestion made much earlier by Glass and Martin ( 1978). 

If so, the frequently suggested relationship between P. concolor and Miracinonyx inexpectatus is not as close as has 

been thought; P. concolor was still evolving out of F. lacustris while M. inexpectatus was fully evolved and morphologically stable, with a head the size of P. concolor but 

much longer limbs. 

As listed by Kurten (1976), most fossil records of P. 

concolor are of late Pleistocene or younger age. The Reddick lA, Florida, record may be of Irvingtonian age (but late 

rather than beginning Irvingtonian). The judgment of where 

the genus Puma should first be recognized is a hypothetical 

consideration, but here Puma concolor is recognized as 

having evolved before the Froman Ferry faunal succession 

(before the Irvingtonian mammal age in the Pacific Faunal 

Region). 

Surprisingly, no other records of carnivores are identifiable from the Froman Ferry faunal succession, although a 

bear-like (agriotherine/tremarctine?) canine and partial 

radius (having a strong resemblance to the radius of Agriotherium sp. from the Hemphillian Edson fauna of Kansas 

(Harrison, 1983, fig. 10) and, somewhat less, to living 

Tremarctos) and a mandibular fragment of a small carnivore 

have been found in the fluvial gravel of GS-232. 

Order LAGOMORPHA Brandt, 1855 

Family LEPORIDAE Gray, 1821 

Subfamily ARCHAEOLAGINAE Dice, 1929 

Genus HYPOIAGUS Dice, 1917 

HYPOIAGUS GIDLEY/ White, 1987 

Figure7 

Locality and material.-CVCVMBER AREA: GS232, Sample 14 (2,815 ft elev. and 60 feet uphill from GS232) USNM 264338 right mandibular ramus, incomplete, 

with P/3 to M/2. 

Although a few leporid molars have been found 

throughout the Froman Ferry faunal succession, this is the 

only specimen containing a P/3, diagnostic in identification. 

Discussion.-This specimen was recovered from the 

gravel deposits of a fluvial channel high in the Glenns 

Ferry Formation of the Cucumber area. The channel 
26 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

forms a band on the south-facing slope of the north side 

of Dead Horse Canyon and contained many fragmentary 

specimens of various mammals not otherwise common in 

the marsh deposits, including parts of an ursid (tremarctine?), puma, Plesippus fromanius n. sp., camel, and 

cervid, all of which have not been identified unless mentioned under the proper taxon. It is believed that these fluvial deposits high in the Glenns Ferry Formation of the 

Froman Ferry area represent the initial part of the fluvial 

regimen that ultimately resulted in the unconformity separating these deposits from the overlying Pickles Butte lava. 

The specimen is from a large leporid. The length of 

the tooth row (P/3 to M/2) is 14.3 mm and the anteroposterior length of P/3 is 3.42 mm. John White, author of the 

species, has kindly examined a drawing of the P/3 of this 

specimen (fig. 7) and has confirmed its identification, saying (oral commun., 1994) that it was in the middle of the 

variation of about 50 specimens of the species. He also 

noted that this is a major revision in the known age range 

of both the species in North America, which had previously been considered as terminating before 2.5 million 

years ago, and of the genus in the United States, which 

was not believed to have survived beyond the end of the 

Blancan mammal age (J.A. White, oral commun., 1994). 

The presence of this species and genus in deposits so 

young is surprising and contradicts the prior opinion that 

the genus did not survive the Pliocene in North America 

(the type locality is in the Hagerman faunal sequence). 

Although the species can no longer be considered as confined to mid-Blancan age and earlier deposits, the scarcity 

of its later records certainly indicates that the genus (and 

species) was not very common in the North American 

record of early Pleistocene date. 

This may not be the first record from the Irvingtonian, however; Lucas and others (1993) also reported the 

genus, questionably referring it to the species H. gidleyi, 

from a possible Irvingtonian fauna in the Sierra Ladrones 

Formation (Tijeras Arroyo fauna) on the south side of 

Albuquerque, New Mexico. Based upon the preconception of the Blancan age significance of Hypolagus cf. H. 

gidleyi and associated Equus cf. E. cumminsii in the basal 

8 m of their faunal sequence, they referred this part of the 

section to the Blancan. The overlying 64 m of the section 

contains a distinctly Irvingtonian mammal fauna, and, 

beginning above the basal 8 m (about 4 m above the 

Hypolagus), they reported clasts of pumice from the Bandelier Tuff (1.6-1.1 Ma). Lucas (written commun., 1994) 

reported that hand specimen examination of the pumice 

clasts suggests the oldest of this time range, but no mineralogic identification has been made. 

Although Lucas and others ( 1993) inferred an unconformity to explain the Blancan age of the earliest 

mammals in their fauna'! sequence, they also noted that 

John Hawley (New Mexico Bureau of Mines and Mineral 

Resources) had informed them of pumice clasts believed 

to represent the Bandelier Tuff ( <1.6 Ma) in water well 

cuttings stratigraphically well below the Tijeras Arroyo 

outcrop. More field study is required to resolve the question, but, at present, it is possible that the Tijeras Arroyo 

fauna is the latest record of Hypolagus gidleyi (and Equus 

cumminsii). 

The mammalian fauna from the overlying, pumicebearing zone in Tijeras Arroyo is a typical early Irvingtonian assemblage and contains two species of primitive 

Mammuthus; as such these may be the oldest known 

record of this genus in the United States. 

Order RODENTIA Bowdich, 1821 

Family CASTORIDAE Gray, 1821 

Subfamily CASTORINAE Gray, 1825 

Genus CASTOR Linnaeus, 1758 

CASTOR CALIFORNICUS Kellogg, 1911 

Localities and material.-FROMAN FERRY AREA: 

USNM 11607: exact locality uncertain. (USNM records 

indicate that it was collected by N.F. Drake in 1897 along 

the road from Froman Ferry to Caldwell, but not how far 

along the road or above the river; the road no longer 

exists; Hay ( 1927) cited only the Froman Ferry locality of 

Merriam (1918) and Lindgren (1900), both of whom 

listed the taxon as "Castor, possibly new species: P/4.") 

CUCUMBER AREA: GS-226 (2,690 ft elev.): incomplete 

P/4. 

Apparently only these two teeth have been found in 

the area in the past 98 years. They are from near the top 

and near the bottom of the Froman Ferry faunal succession. 

Discussion.-F.A. Lucas of the U.S. National 

Museum identified the fossil specimens collected by 

Lindgren and Drake in 1897 and later, and he assigned 

the single beaver P/4 (USNM 11607) to "Castor, possibly 

new species." Merriam (1918) followed this identification. 

Based upon no additional material, Hay (1927) provided 

the specific name Castor accessor. Shotwell ( 1970) stated 

that the single tooth from Froman Ferry could not be separated from other fossil or living species, and therefore 

selected one of the Castor specimens from Jackass Butte 

(youngest of the Grand View faunas) as the pleisiotype of 

Castor accessor, thinking that the geographic and temporal proximity of the Froman Ferry fauna to the Grand 

View faunas probably indicated specific identity. Shotwell 

did not know the age of the Froman Ferry fauna and 

apparently assumed that it was the same age as the fauna 

from Jackass ·Butte. In fact it is only about half a million 

years different in age, whereas the oldest fauna of the 
THE FROMAN FERRY FAUNA 27 

Glenns Ferry Formation at Hagerman is as much as 1.3 

million years older than the Jackass Butte faunas. These 

time differences were not known to Shotwell, however, 

when he studied and compared these faunas. 

This same assumption of a similar age and fauna at 

Jackass Butte and Froman Ferry was made for the horses 

both earlier (Schultz, 1936) and later (Conrad, 1980; 

Azzaroli and Voorhies, 1993). In the case of the horses, 

however, Shotwell (1970) thought the horse from Jackass 

Butte was more like that from Hagerman. It was not until 

1993 that Azzaroli and Voorhies indicated that at least 

two horses were present in the fauna from Jackass Butte. 

Shotwell (1970, p. 39) stated, in his diagnosis of the 

referred material of Castor accessor from the Jackass 

Butte faunas, that the opposition of the hypostriid and the 

mesostriid on the Grand View beaver was dissimilar to 

that in living Castor canadensis, but this is not always 

true, and he stated that the stria and striids of the cheek 

teeth are longer than in the older fossil species Castor californicus, which does not seem true in the available material (N=4 P/4) of the older species from the type locality 

in Kettleman Hills, California. 

Conrad (1980) compared a good sample of the beaver from Hagerman (which he referred to Castor californicus) with that from Jackass Butte, and concluded that 

they do not differ more than one would expect from the 

tooth variability of any species of Castor, and that both 

belong to the prior species name Castor californicus. He 

suggested that when enough material is known from Froman Ferry, this population will also appear assignable to 

Castor californicus. Not enough material is yet known to 

determine the variability of the Froman Ferry population 

(and recognition of proper specific assignment seems obviously defendable only upon differences in population composition), but the two known first lower premolars from 

the Froman Ferry faunal succession fall within the range 

of variability of Castor californicus, and there thus seems 

to be no reason to recognize Hays' species, or Shotwell's 

referral of the Jackass Butte population to it. Following 

Conrad (1980), we assign all of the Glenns Ferry samples 

of Castor to the species Castor californicus Kellogg, 

largely on the basis of priority. 

This species remains separable· from the living species on the basis of its external striae on the upper teeth 

and internal striids on the lower cheek teeth, which are of 

unequal length and average (on the basis of all assigned 

populations) shorter in length than in Castor canadensis 

(Stirton, 1935, p. 445). These grooves are cement-filled 

and often hard to see. The type of Castor californicus 

Kellogg is from the "Pecten bed" of the San Joaquin Formation in the Kettleman Hills of California, and is about 

3 million years old, intermediate in age between the 

Hagerman and the Jackass Butte faunas. 

Family CRICETIDAE Rochebrune, 1883 

Subfamily LEMMINAE Gray, 1825 

Tribe SYNAPTOMYININI Von Koenigswald and Martin, 1984a 

Genus MJCTOMYS True, 1894 

MICTOMYS VETUS (Wilson, 1934) 

Figure 8 

Localities and material.-HOMEDALE AREA: GS212 (2,430 ft elev.): three-fourths of an M/1. CHALK 

HILLS AREA: GS-209 (2,470 ft elev.): M/1, M/2, M\3. 

GS-201 (2,477 ft elev.): two partial M/1, M/2. GS-208 

(2,550 ft elev.): M/1. FROMAN FERRY AREA: GS-211 

(2,398 ft elev.; =UCMP 3036?): incomplete M/1. CUCUMBER AREA: GS-215 (2,540 ft elev.): three ~vf\2, four M/1 

(one USNM 264331), M\3 (USNM 264:,J2). GS-230 

(2,750 ft elev.): four M/1, three M/2, M\1, five M\2. GS232 (2,810 ft elev.): M/2, M/3, M\3. GS-233 (2,890 ft 

elev.): M/1, M\3, two partial M/1. 

Nine localities; 2,398 to 2,890 feet elevation. The distinctive form of all cheek teeth of the genus enables their 

inclusion in the list of specimens, although the specific 

identification of those teeth other than the first lower and 

the last upper molars could not be verified. 

Discussion.-Mictomys vetus (Wilson, 1934) was 

originally described as a species of Synaptomys, in which 

genus Mictomys had been placed, as a subgenus, since 

Miller ( 1896). This concept of the genus Synaptomys was 

so entrenched that, when an ancestral form of this otherwise 

North American genus group was found in lower Pliocene 

deposits of Bashkir (now Bashkiria), Russia, Suchov (1976) 

placed it in a new subgenus as Synaptomys (Plioctomys) 

mimomiformis. S. (P.) mimomiformis was subsequently recognized throughout much of Eurasia, usually as Suchov's 

species, and its youngest records are found in Beringia 

(Sher and others, 1979; Repenning and others, 1987). 

In a detailed consideration of the forms included in 

Synaptomys, von Koenigswald and Martin ( 1984a) also recognized Synaptomys (Plioctomys) rinkeri (Hibbard, 1956) 

in the upper Pliocene deposits of the lower latitude United 

States. They removed Mictomys from the genus Synaptomys 

as a separate genus on the basis of differences in the 

Schmelzmuster (arrangement of the prisms or rods in the 

tooth enamel)~ but left Suchov's Plioctomys as a subgenus 

within Synaptomys." This was· done because of the 'thenprevailing beliefthat S. (P.) rinkeri was ancestral to the 

living Synaptomys cooperi. 

However, in 1988 Repenning and Grady discovered 

the surprising origin of living Synaptomys cooperi out of 

Mictomys in an 840,000-year-old fauna from the Cheetah 

Room of Hamilton Cave, West Virginia. They concluded 

that, despite morphologic similarities (not exact), it was 

misleading to put forms as old as 4 million years in a 

genus that is known to have evolved out of Mictomys 
28 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

,CAP B 

c 

only 840,000 years ago, and they consequently raised the 

subgenera Synaptomys and Plioctomys to generic rank. As 

such, the oldest record of the genus Synaptomys is 

840,000 years ago. The genus Mictomys, removed from 

Synaptomys by von Koenigswald and Martin ( 1984a), is 

known back to 2.56 million years ago and the genus 

Plioctomys, removed from Synaptomys by Repenning and 

D 

0 1 ---·-1 

E 

2mm 

I 

Grady (1988), is known back to about 4 million years ago 

in Eurasia (Repenning and others, 1990). Plioctomys 

appears to have become extinct more than 2.0 mr!Jion 

years ago, but Synaptomys and Mictomys remain as a part 

of the living fauna of North America. 

The fossil record of Mictomys is rather abundant during 

the 1.15 million years when nothing called Synaptomys 
THE FROMAN FERRY FAUNA 29 

Figure 8 (facing page). Microtine rodents of the Froman Ferry 

faunal succession, Canyon County, Idaho. Occlusal views and two 

buccal views. Dentine shown as black, cementum stippled, and 

enamel unpatterned in occlusal views. Scale the same for all drawings and as indicated. A and B, Mictomys vetus from locality GS215, Cucumber area. A, USNM 264331: Right first lower molar in 

occlusal view; B, USNM 264332: Left last upper molar in occlusal 

view. C. D, and E, Mimomys (Ophiomys) pan1us from locality GS212, Homedale area. C, USNM 264333: Left first lower molar with 

little wear in buccal view. D, USNM 264333: Same as last, in occlusal view. E, USNM 264334: Left last upper molar in occlusal 

view. F, G, and H, Phenacomys (Paraphenacomys) gryci from locality GS-232, Cucumber area. F. USNM 264335: Left lower first 

molar with moderate wear in occlusal view. G, USNM 264336: Left 

upper last molar in occlusal view. H, Same as F but in buccal view. 

ACC, anteroconid complex; BR, buccal reentrant; LR, lingual reentrant; AL, anterior loop; PL. posterior loop; on last upper molars PL 

B, bell-shaped posterior loop; PL H, hooked posterior loop; and PL 

M, globular posterior loop of Mictomys; T, triangle (numbered from 

the back of the tooth), triangles 4 and 5 form from the primary 

wings; LPW, lingual primary wing; BPW, buccal primary wing; 

BSW, buccal secondary wing; x, "Mimomys Kante," present only 

on FandH. 

existed in the world fauna. The recognized morphologic differences, that had been assigned subgeneric significance, 

assumed generic significance when it was realized that the 

earliest Plioctomys and the earliest Synaptomys were separated by almost 3.2 million years. 

As the evolution of the group is now considered, 

Plioctomys is the ancestral form of about 4 million years 

ago (Simbugino fauna, Bashkir, Russia); its origin is 

unknown but apparently was in western Eurasia; Plioctomys dispersed to Beringia by 2.6 million years ago 

(Kutuyakh faunas, Yakutia, Russia; 2.4 Ma Fish Creek 

fauna of the Alaskan North Slope). Along the Pacific 

Coast of North America in the south-Alaskan Beringian 

Faunal Region (assumed; possibly farther south), 

Plioctomys evolved into Mictomys by about 2.6 million 

years ago and dispersed southward in North America west 

of the Rocky Mountains to the Pacific Faunal Region of 

the United States by 2.56 million years ago as Mictomys 

vetus (Grand View faunas, Idaho). At the same time 

Plioctomys remained unchanged in the north-Alaskan 

Beringian Faunal Region (Fish Creek fauna, Alaskan 

North Slope, 2.4 Ma) and dispersed southward on the east 

side of the Rocky Mountains, arriving in the United 

States in the Eastern Faunal Region as the slightly modified species Plioctomys rinkeri (Cita Canyon fauna, 

Texas, and other faunas); Mictomys rapidly dispersed 

southward from the Pacific Northwest and eastward 

around the south end of the Rocky Mountains (Beaver 

fauna, Utah; Tusker fauna, Arizona), and also possibly 

through the Yellowstone pass (Boyle Ditch, Wyoming) to 

the Great Plains before 2.0 million years ago (Borchers 

fauna, Kansas); Plioctomys became extinct by this time; 

Mictomys then occupied the entire United States until 

about 0.84 million years ago when Synaptomys evolved 

out of an Appalachian population (Cheetah Room fauna, 

West Virginia). 

The primitive bog lemming, Mictomys vetus, occurs 

throughout the fossiliferous section in the Froman Ferry 

area. Plioctomys was extinct by this time (and is not 

known to have dispersed west of the Rocky Mountains) 

and Synaptomys had not yet evolved. The type locality of 

Mictomys vetus is at Jackass Butte of the Grand View faunas (Wilson, 1934; as Synaptomys vetus), and the genus is 

known in the Pacific Faunal Region of the United States 

from 2.56 million years ago (when it first immigrated to 

the United States from the Arctic) until the presently living fauna. The genus is, however, now known only from 

Alaska, Canada, and areas just south of the Canadian 

border in the States of Washington and Montana (and presumably Idaho, more than 350 miles north of the Froman 

Ferry area). It also crosses the border into the United 

States in northernmost Minnesota and the New England 

States of Maine and New Hampshire (Hall, 1981). The 

genus now clearly thrives in moist areas with cool summers, and its history is marked by repeated southward dispersal into the United States when these climatic 

conditions prevailed, which was during continental glacial 

accumulations that are also favored by this climate 

(Repenning, 1993). 

Mictomys, and the related Lemmus and apparently 

unrelated Dichrostonyx, are the oldest extant microtine 

genera, depending upon how one classifies the primitive 

muskrat Pliopotomys. 

Two million fifty-six hundred thousand years ago Mictomys vetus lived less than 50 miles from the Mexican border 

in Arizona (Tusker fauna; Repenning, 1987), and 1.6 million 

years ago it lived a similar distance north of the Mexican border in what is now the Anza-Borrego Desert of California 

(LACM locality 6683, Vallecito Creek faunal sequence; 

Zakrzewski, 1972, as Metaxiomys anzaensis; with the earliest Microtus); both times were presumably characterized by 

cool and cloudy summers during Northern Hemisphere glaciation, although Canadian ice did not, at these times, flow 

southward as far as the United States (Repenning and Brouwers, 1992). Canadian ice did extend into the United States, 

and left till in Iowa, about 2.1 million years ago, when Mictomys appeared in the Borchers fauna on the Great Plains, 

but Mictomys (apparently) still did not enter southern California, although the Grand View species Mimomys parvus 

did appear there at this time. The irregularity of the times 

when these species of Mictomys and Mimomys, seemingly 

constantly present in the Grand View and Froman Ferry 
30 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

faunas of Idaho, appeared in the Anza-Borrego Desert of 

southern California is not fully explainable, but it must 

record a difference in climatic patterns of these times. 

Later, Mictomys moved northward as hot (interglacial) summers developed, but it returned southward repeatedly, during each glacial period. The obvious implication 

is that similar cool, cloudy summers prevailed in the 

Snake River Plain during the final episode of the Glenns 

Ferry deposition at Froman Ferry, as well as during the 

Grand View faunal succession. Faunas intermediate in age 

(between about 2.0 and 1.7 Ma) are not yet known in the 

Snake River Plain; drier climates (with hotter summers) 

prevailed during this time in many parts of the Northern 

Hemisphere (the Tiglian floras of northwestern Europe), 

and it is possible that Mictomys had, at this time, withdrawn from the Snake River Plain, after the Grand View 

faunas, and returned before the Froman Ferry faunas 

came into existence. 

Before 2.0 million years ago Mictomys vetus (as M. 

landesi) dispersed eastward onto the Great Plains (Borchers fauna, Kansas); Plioctomys was by then, or as a consequence, presumably extinct as no later records are known. 

In the Great Plains (or to the north during a withdrawal), 

Mictomys evolved into the species Mictomys kansasensis 

by 1.2 million years ago and into Mictomys meltoni by 

610,000 years ago. The salient evolutionary change consisted primarily of a shallowing of the buccal reentrants 

on the lower cheek teeth, particularly that reentrant immediately behind the anteroconid complex of the first lower 

molar so that the connection between this structure and 

the alternating triangles shifted buccally, with a corresponding deepening of the lingual reentrants (see fig. 6 of 

Repenning and Grady, 1988; and, for dental nomenclature, fig. 10 of Repenning, 1992). It is not certain that 

these species recognized east of the Rocky Mountains 

were present west of the Rocky Mountains, but similar 

changes also took place in the Pacific Faunal Region. The 

genus is a sensitive climate indicator, but one is inclined 

to wonder if its range was restricted to the north with the 

evolution of the living Synaptomys cooperi 840,000 years 

ago, which could have assumed the southern part of its 

former range; the modern distribution of Mictomys may 

not precisely reflect its climatic constraints before this 

time when Mictomys alone may have had the environmental range of both Mictomys and Synaptomys in the living 

fauna. 

Despite a later, well-established trend in modernization of its morphotype, the specimens of Mictomys vetus 

from the Froman Ferry fauna show no difference from 

the older type population in the Grand View faunal 

succession. 

Subfamily ARVICOLINAE Boneparte, 1837 

Tribe ARVICOLINI Kretzoi, 1954 

Genus MIMOMYS Major, 1902 

Subgenus OPHIOMYS Hibbard and Zakrzewski, 1967 

MIMOMYS (OPHIOMYS) PARVUS Wilson (1934) 

Figure 8 

Localities and material.-HOMEDALE AREA: GS212 (2,430 ft elev.): seven M/1 (one USNM 264333), seven 

M\3 (one USNM 264334). CHALK HILLS AREA: GS-210 

(2,464 ft elev.): two M/1. GS-201 (2,477 ft elev.): four M/1. 

GS-208 (2,550 ft elev.): five M/1, M\3. GS-204 (2,560 ft 

elev.): five M/1. FROMAN FERRY AREA: GS-211 (2,398 

ft elev.; =UCMP 3036?): Mil, M\3. LIZARD BUTTE 

AREA: GS-213 (2,440 ft elev.): M/1. GS-214 (2,470 ft 

elev.): 11 M/1, M\3. CUCUMBER AREA: GS-218 (2,460 

ft elev.): 11 M/1, 9 M\3. GS-217 (2,480 ft elev.): four M/1. 

GS-216 (2,485 ft elev.): four M/1, two M\3. GS-215 (2,540 

ft elev.): 12 Mil, 8 M\3. GS-220 (2,630 ft elev.): six M/1, 

M\3. GS-223 (2,630 ft elev.): 14 Mil, 3 M\3. GS-219 

(2,640 ft elev.): M/1. GS-221 (2,650 ft elev.): 13 Mil, 4 

M\3. GS-222 (2,650 ft elev.): six M/1, four M\3. GS-229 

(2,750 ft elev.): three Mil, two M\3. GS-232 (2,810 ft 

elev.): 6 Mil, 12 M\3. GS-233 (2,890 ft elev.): 11 M/1, 6 

M\3. 

Twenty localities: 2,398 to 2,890 feet elevation. This is 

the entire Froman Ferry faunal succession. 

Discussion.-This is the youngest, and possibly the 

most northern, dated record of this species. The species is 

possibly the most abundant mammal in the faunal sequence. 

Mimomys parvus is present in the Vallecito Creek faunal 

succession of the Anza-Borrego Desert in southern California, but not at 1.6 million years ago (LACM locality 6683), 

the temporal equivalent of the immigration of Phenacomys 

gryci in the Froman Ferry faunal succession; this was the 

time of a rather mild glacial period with no known flow of 

ice into the United States. Mimomys parvus has been collected in the Vallecito Creek succession only at LACM 

locality 1357, which is well below the Olduvai event in the 

paleomagnetic section, representing an age that is comparable to that of some part of the Jackass Butte section of the 

Grand View faunas, possibly 2.2 to 2.3 million years old; 

this would have been during the time of the first major 

North American ice accumulation that climaxed 2.1 million 

years ago with till in Iowa. Unfortunately the position of the 

Reunion Normal-polarity Subchron was not identified in the 

paleomagnetic section of the Vallecito Creek faunal succession (Opdyke and others, 1977). 

That Mictomys did arrive in southern California 1.6 

million years ago with Microtus, whereas Mimomys parvus 

did not and only appeared this far south during the earlier 

and more extreme glacial buildup between 2.5 and 2.1 million years ago (but apparently without Mictomys), suggests 
THE FROMAN FERRY FAUNA 31 

that the species of Mimomys may have been even more 

climatically sensitive than Mictomys. 

But, as just noted on pages 29-30, there seems to be 

some difference in climatic, or other, patterns that are not 

fully understood, as Mictomys vetus and Mimomys parvus 

lived together, sharing the same environment in the Snake 

River Plain from 2.56 to nearly 1.5 million years ago, yet 

Mimomys parvus is only known about 2.2 million years ago 

and Mictomys vetus only about 1.6 million years ago in the 

Anza-Borrego Desert area of southern California. 

Mimomys ( Ophiomys) parvus has a long history of differing generic assignments. Wilson (1934) questionably 

assigned it to Mimomys when describing it from Jackass 

Butte; Hibbard (1950, p. 157) assigned it to Pliophenacomys; Kretzoi (1955, p. 354) assigned it to the European 

genus Pliomys, to which its first lower molar bears a strong 

resemblance because of the well-developed primary wings 

(triangles 4 and 5); the M\3 (fig. 8£) does not so closely 

resemble Pliomys; Hibbard (1959) again assigned it to 

Pliophenacomys; Hibbard and Zakrzewski ( 1967) assigned 

it to the new genus Ophiomys; and Repenning ( 1980, 1987) 

returned it to the genus Mimomys but recognized it as 

belonging to a separate, North American subgenus Ophiomys that had been separated from Eurasian species since 

the beginning of the Blancan. 

Von Koenigswald and Martin ( 1984b) examined the 

Schmelzmuster (arrangement of the prisms or rods in the 

tooth enamel) of a few North American species that Repenning (1980) had included in Mimomys and found differences (in the Schmelzmuster) between them and European 

species; they concluded that the genus Mimomys is 

unknown in North America. Later Repenning and von 

Koenigswald had the opportunity to discuss their concepts 

of the evolution of Mimomys and the forms from North 

America; they discovered that their opinions were essentially identical. The differences in published classification 

resulted only from differing taxonomic procedure. Von 

Koenigswald considered a genus to be monophyletic; 

Repenning as paraphyletic. (See Repenning, 1992.) 

The oldest known Mimomys isM. antiquus (Zazhigin, 

1980; as Promimomys antiquus) from the upper Miocene 

Pavlodar Series (Peshnovo Formation and locality, upper 

mollusk horizon) of Western Siberia. This species has a 

primitive, and, at this primitive stage, basically universal 

Schmelzmuster that cannot be used to define affinity. From 

this central Eurasian region the genus dispersed westward 

to Europe and eastward to North America, arriving at about 

the same time in both areas (early Pliocene), and both 

immigrant lineages retained the primitive Schmelzmuster. 

The two lineages that dispersed in opposite directions 

around the Northern Hemisphere never again had contact 

with each other and evolved in separate patterns, which 

included Schmelzmuster patterns. 

Von Koenigswald and Martin ( 1984b) have assumed 

that, as European and North American immigrants represent 

different lineages, they also represent different genera. 

Repenning ( 1980) assumed that as long as the common 

ancestral group in central Eurasia was placed in the genus 

Mimomys, the two derived lineages should be placed in 

Mimomys but should be recognized by separate subgenera; 

this procedure is adopted in the present discussion of the 

Froman Ferry faunal succession. Article 42c ("Collective 

Groups") of the International Code of Zoological Nomenclature (revision of 1961) is not specific on this point. Some 

of the earlier North American forms, less derived than 

Mimomys parvus, could be mixed with a sample from 

Europe, and could not be separated back out without 

recourse to a scanning electron microscope (to examine the 

Schmelzmuster), and even this examination would reveal 

only the primitive, nondiagnostic Schmelzmuster. 

There is ample reason to suspect a second invasion of 

Mimomys from Asia to North America in late Pliocene time 

(Mimomys monohani (Martin) from the Blancan V Mullen 

fauna, Nebraska) that persisted through early Pleistocene 

time (Mimomys dakotaensis Martin, 1989, from Irvingtonian I Java fauna, South Dakota; and Mimomys virginianus 

Repenning and Grady, 1988, from Irvingtonian II Cheetah 

Room fauna, West Virginia). More invasions of the genus 

dispersed from Asia to Europe than to North America. 

Morphologically Mimomys (Ophiomys) parvus from 

the Froman Ferry faunal succession is very similar to the 

older (±2.2 Ma) type material from the Jackass Butte of the 

Grand View faunas. The material from Jackass Butte here 

used for comparison (N=12 M/1) was collected at the southwestern base of the butte (elevation 2,475 ft; USGS loc. 

Ml361), about 125 feet below the marsh beds and the first 

event of the Reunion Subchron (2.1 Ma). The Mils are 

quite uniform in morphology, but, as do all rooted microtine 

taxa, vary with wear. 

In comparison with the species from the Froman Ferry 

localities, this Grand View sample has distinctly wider dentinal confluences between the three basic alternating triangles, not between basic triangle 3 and confluent triangles 4 

and 5 (primary wings; dental nomenclature shown in fig. 8; 

also see Repenning, 1992, fig. 10; fig. 8). The type population also has a much lower percentage (about 15 percent) of 

individuals with a noticeable reduction of the confluence 

between triangles 4 and 5 (the primary wings of the anteroconid complex) than does the material from the Froman 

Ferry faunas (about 66 percent). This narrowness between 

the primary wings, in combination with a persistent teardrop shape of the anterior cap, results in a first lower molar 

dental pattern in the Froman Ferry specimens that is 

remarkably similar to that of living C!ethrionomys rutilus, 

although tooth and dentine tract height and the most distinctively complex last upper molar of Clethrionomys 
32 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

make any thought of close relationship seem improbable. 

The M\3 of Mimomys ( Ophiomys) parvus is the same in 

both Idaho localities and is quite simple, consisting of an 

anterior loop, two alternating triangles and a posterior loop 

of an upside-down-bell shape (Wilson, 1934, fig. 5a; this 

report, fig. 8£). 

Genus PHENACOMYS Merriam, 1889 

Subgenus PARAPHENACOMYS Repenning and Grady, 1988 

PHENACOMYS (PARAPHENACOMYS) GRYCI Repenning, 1987 

Figure 8 

Localities and material.-CHALK HILLS AREA: 

GS-204 (2,526 ft elev.): mandible w. Mll-2, two M/1, M\3. 

GS-205 {2,550 ft elev.): mandible in matrix w. all teeth. 

LIZARD BUTTE AREA: GS-213 (2,440 ft elev.): two M/1. 

CUCUMBER AREA: GS-215 (2,540 ft elev.): two Mil, 

M\3. GS-223 (2,630 ft elev.): Mil, two M\3. GS-221 (2,650 

ft elev.): mandible frag. w. Mil, M/1. GS-224 (2,650 ft 

elev.): 14 Mil, 5 M\3. GS-232 (2,650 ft elev.): two Mil 

(one USNM 264335), seven M\3 (one USNM 264336). 

Eight localities; from 2,440 to 2,650 feet elevation. 

The species is unknown in the lower 42 feet of the succession. Its first record is considered as marking the beginning 

of Irvingtonian faunas. 

Discussion.-The primitive species Phenacomys (Paraphenacomys) gryci was described by Repenning (Repenning and others, 1987) from the Fish Creek fauna of the 

Alaskan North Slope. The Fish Creek section was deposited 

early (about 2.4 Ma) in the first recognized Neogene glacial 

cycle of the Northern He~isphere (2.56 to 2.00 Ma). The 

Fish Creek records of Phenacomys (Paraphenacomys) gryci 

were interpreted as being very close to 2.4 million years old 

(Repenning and others, 1987; Repenning and Brouwers, 

1992) largely on the basis of: 

1. The stage of climatic change represented by older 

deposits in the Fish Creek area and by the fauna and flora in 

the Fish Creek section; 

2. A continuous regressive marine sequence showing 

Arctic climates changing from much warmer than today to 

a climate comparable to that of today (in terms of water 

temperatures in the Arctic Ocean and the development of 

permafrost on land; Repenning and others, 1987); 

3. The paleomagnetic polarity changes from the 

Gauss Normal-polarity Chron to the Matuyama Reversedpolarity Chron in exposures older than the Fish Creek section; 

4. The correlation of climatic, floral, and faunal 

changes to a similar section in eastern Siberia; finally, 

5. The Arctic Ocean was not covered by ice at the 

time of the Fish Creek mammal fauna, and permafrost, 

causing the development of wet (herb) tundra, first developed at this time and latitude in the Arctic Ocean Borderland (Repenning and others, 1987), both suggesting a 

preliminary climatic condition prior to the glacial maximum 

of 2.1 million years ago. Permafrost developed earlier at 

higher latitudes (Repenning and Brouwers, 1992). 

One last upper third molar, apparently of Phenacomys 

(Paraphenacomys) gryci, the only record of the genus from 

Eurasia (but within the same Beringian Faunal Region), has 

been reported from the Krestovka sections of Yakutia (Sher 

and others, 1979; Repenning and others, 1987) in a very 

similar climatic and paleomagnetic sequence that is correlated with the Fish Creek fauna (Repenning and others, 

1987; Repenning and Brouwers, 1992). This Siberian locality preserves a record of somewhat later and more severe 

climate change. 

Repenning and Grady (1988) discussed the history and 

diversity of Phenacomys and established the subgenus Paraphenacomys (including the living white-footed tree vole 

Phenacomys (Paraphenacomys) albipes), lowered the genus 

Arborimus (Taylor, 1915; including the living red or longtailed tree vole Phenacomys (Arborimus) longicaudus) to 

subgeneric rank within Phenacomys, and placed the living 

species Phenacomys intermedius (heather vole) in the subgenus Phenacomys (Phenacomys) as well. 

All three subgenera have a fossil record (subgenus 

Paraphenacomys is the oldest), and all still live, but they 

represent markedly different environments, a factor usually 

not considered in interpretation of the late Pleistocene 

records of Phenacomys in the United States. 

The immigration of Phenacomys (Paraphenacomys) 

gryci from the Arctic to the conterminous United States is 

first recorded in the Froman Ferry faunal succession of the 

Glenns Ferry Formation; the age of this immigration is 

approximated at 1.6 million years ago, as discussed on page 

8 and following. The subgenus Phenacomys (Phenacomys) 

first immigrated to the conterminous United States on the 

east side of the Rocky Mountains at about the same time 

and is first known there from the Java fauna of South 

Dakota (Martin, 1989; as Hibbardomys zakrzewskii). The 

subgenus Phenacomys (Arborimus) appears to be a fairly 

recent innovation, based upon unpublished records of Phenacomys in the Booth Canyon fauna of eastern Idaho (Idaho 

Museum of Natural History collection) that show a population variation of morphotypes including those of both Phenacomys (Phenacomys) and Phenacomys (Arborimus). This 

subgenus appears to have developed during the Rancholabrean mammal age and in the Rocky Mountains; the Booth 

Canyon locality is close to the Continental Divide along the 

Snake River near the Wyoming border. 

P. (Phenacomys) now lives in Canadian forest from the 

Atlantic to the Pacific, southward down the Rocky Mountains in the Canadian life zone of the United States, and in 

western Washington. P. (Paraphenacomys) and P. (Arborimus) now live in the southern coastal forests of the Pacific 

Northwest, avoiding colder winters in the State of Washington and hot summers in central California. During glacial 
THEFROMANFERRYFAUNA 33 

periods, when seasonal equability was more pronounced, 

these two southern subgenera lived in areas that are now dry 

and have hot summers and cold winters from eastern Washington to central Nevada (Repenning and Grady, 1988). 

Cool summers are indicated in the earliest Pleistocene 

of western Snake River Plain (Froman Ferry fauna) and in 

the late Pleistocene of eastern Washington (Kenniwick 

fauna; Rensberger and others, 1984) and central Nevada by 

the presence of Mictomys as well as that of Phenacomys 

(Paraphenacomys) and P. (Arborimus) (Mead and others, 

1982; Grayson, 1983). The two coastal subgenera of Phenacomys (Arborimus and Paraphenacomys) also indicate 

warm winters. Although these two subgenera of Phenacomys are usually found in fossil faunas with Mictomys 

spp., their modem ranges are separate because these subgenera of Phenacomys are intolerant of cold winters and 

Mictomys is not. 

Caution must be exercised in evaluating tolerance to 

cold winters of the subgenera Paraphenacomys and Arborimus in view of the earliest records of the former in areas of 

permafrost, and of the latter within a population of the subgenus Phenacomys (Phenacomys); it seems that the modern 

intolerance to cold winter temperatures may have evolved 

during the history of these subgenera. The absence of the 

subgenus Phenacomys in the late Pleistocene faunas of 

Nevada and eastern Washington is probably as climatically 

significant as is the presence of the subgenera Arborimus 

and Paraphenacomys. Furthermore, the evolution of living 

Synaptomys out of Mictomys about 840,000 years ago suggests that prior to that time the genus Mictomys may have 

had a range of environmental tolerance that included that of 

both living genera, which would make the presence of Mictomys within 50 miles of the Mexican border in Arizona and 

California a bit more understandable. Modem environmental preferences may not reflect those of any particular animal throughout the time of its existence. 

To judge from the Alaskan (and Siberian) records of 

Phenacomys (Paraphenacomys), which are associated with 

developing permafrost but an unfrozen Arctic Ocean, this 

cool summer and warm winter environment in the Froman 

Ferry area 2.6 million years ago could have had a mean 

annual temperature as low as freezing (measured below any 

snow cover). It thus seems that only the extreme winter cold 

of the Canadian forests, tolerated by modem Mictomys and 

Phenacomys (Phenacomys), may have been missing during 

deposition of the Glenns Ferry Formation. 

In contrast with this suggestion of the annual average 

temperature in Beringia, based upon the associated permafrost 2.5 million years ago, Smith and Patterson (1994) have 

recently defended the interpretation that the fish fauna of the 

Glenns Ferry lake indicates that water temperature seldom 

got below freezing in the winters nor above 69° F in the 

summers. They have also suggested that the large lake may 

have influenced the local climate near it toward this 

temperature equability, which would be more similar to the 

modem annual temperature range of the subgenus of Phenacomys present in the Froman Ferry fauna. 

The Froman Ferry fauna, therefore, suggests that 

although winters may have reached freezing temperatures, 

very cold winter temperatures (comparable to modem central Canada) did not occur in the Snake River Plain during 

deposition of the Froman Ferry faunal succession; at the 

same time summer temperatures were cooler than now. 

Although Phenacomys (Paraphenacomys) lives today in 

coastal northern California and Oregon, coastal Washington 

appears to be too cold in the winter for the subgenus and it 

is replaced by Phenacomys (Phenacomys) of the modem 

Canadian forests. The Canadian heather vole, Phenacomys 

(Phenacomys) intermedius, was not present in the Pleistocene faunas of the Great Basin or the Snake River Plain, 

although present in the higher parts of the Continental 

Divide to the east and in the higher mountains and the 

Sierra Nevada to the west. 

The suggestion of cool, not cold, winters and cool, not 

hot, summers is also based upon the assumption that the 

Canadian heather vole also has not changed in its environmental constraints. This assumption seems contradicted by 

the earliest record of this subgenus on the Great Plains, in 

the Java fauna of South Dakota. In this fauna the ancestor of 

the Canadian heather vole is associated with Allophaiomys 

sp. cf. A. pliocaenicus, a taxon whose every record throughout the Northern Hemisphere appears to indicate a warm 

temperate preference (Repenning, 1992, p. 6). The environmental constraints of fossil mammals merit considerably 

more study. 

Phenacomys gryci is superficially similar to Mimomys 

parvus (fig. 8D, F). Its secondary wings are not so well 

developed, and the labial one (triangle 4) always has the 

slight flexure of enamel called a "Mimomys Kante" 

(Repenning and others, 1987, fig. 6; this report, fig. SF); the 

cap of the anteroconid complex is not so uniformly teardrop-shaped as in M. parvus, and the dentine tracts are not 

nearly so highly developed. The last upper molar (M\3) has 

a posterior loop in the form of a "hook" rather than being 

the shape of an inverted bell (fig. 8G). They are related; 

Repenning and others ( 1987) speculated that Pherwcomys 

gryci was derived from the Asiatic subgenus Mimomys 

( Cromeromys). 

Subfamily ONDATRINAE Repenning, Fejfar, and Heinrich, 1990 

Tribe ONDATRINI Kretzoi, 1954 

Genus ONDATRA Major, 1902 

ONDATRA IDAHOENSIS (Wilson, 1934) 

Localities and material.-HOMEDALE AREA: GS212 (2,430 ft elev.): 3/4 and 1/4 M/1. CHALK HILLS AREA: 

GS-201 (2,477 ft elev.): three M/1, M\3, two matrix slabs 

with frags. GS-204: (2,526 ft elev.): shattered jaw w. cheek 
34 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

teeth missing, three Mil, M\3. GS-208 (2,550 ft elev.): part 

M/1. GS-209 (2,470 ft elev.): mandible w. Mll-2, M\3. GS210 (2,464 ft elev.): M/1, M\3. CUCUMBER AREA: GS215 (2,540 ft elev.): two Mil, M\3. GS-218 (2,460 ft elev.): 

M/1. GS-221 (2,650 ft elev.): six Mil, two M\3. GS-224 

(2,650 ft elev.): mandible ramus w. Mll-3. GS-225 (2,650 

ft elev.): M/1. GS-232 (2,650 ft elev.): M/1. GS-230 (2,750 

ft elev.): M/1. 

Thirteen localities with first lower and last upper 

molars~ other localities contain the taxon on the basis of 

other teeth (much larger than other microtine teeth), but 

were not counted; 2,430 to 2,750 feet elevation. 

Discussion.-Although not so indicated above, 

because only those localities with first lower or last upper 

molars are listed and faunas containing only other teeth 

were not counted, the Idaho muskrat is a common taxon in 

the Froman Ferry faunal succession, about as common as 

Mimomys parvus. An initial impression was that the sample 

averaged somewhat larger in individual size than that from 

Jackass Butte (mid-Blancan V age; perhaps 2.3 to 2.0 Ma); 

however, measurement of 19 first lower molars from the 

Froman Ferry faunas indicates an average length of 4. 7 mm, 

similar to that of Jackass Butte (4.79 mm, N=26; Conrad, 

1980). The range of variation in length of the first lower 

molars at Froman Ferry was 4.4 mm to 5.1 mm, about the 

same as at Jackass Butte (4.19 mm to 5.30 mm; Conrad, 

1980, whose sample presumably included specimens from 

all parts of the Jackass Butte section). Other characters of 

the species from the Froman Ferry faunas (for example, 

height of dentine tracts and degree of cementation) also 

appear similar to the Jackass Butte population. 

This lack of noticeable change in the Froman Ferry 

muskrat from the condition of the taxon in the Jackass Butte 

localities of the Grand View faunal succession (the two are 

separated by as little as 400,000 years) contrasts strongly 

with the difference between the muskrat population from 

Jackass Butte and the early Blancan V Poison Creek and 

Birch Creek faunas, less than 100,000 years older than the 

estimated age of the oldest Jackass Butte faunas. We have 

only a few muskrat teeth from Birch Creek, but several first 

lower molars (N=5) from the Poison Creek localities. These 

have an average length of 4.46 mm, indicating a size 

increase of 0.2+ mm between 2.4 million years ago (Poison 

and Birch Creek) and an estimated 2.3 (older Jackass Butte) 

million years ago, but no increase between 2.0 (youngest 

Jackass Butte) and 1.6 million years ago (Froman Ferry). 

No attempt has been made to see if there is a size increase 

within the Jackass Butte faunal sequence, and there may be. 

The smaller size of M/1 in the Poison Creek population appears to continue back in time to the Hagerman faunas (3.2-3.6 Ma), where the muskrat has an average first 

lower molar length of 4.1 mm in the available sample (N=4; 

Zakrzewski, 1969). The dentine tract on the buccal face of 

the anteroconid complex of the Hagerman population is 

very low, hardly higher than the more posterior tracts on the 

salient angles, and very high in the Jackass Butte population~ those from Poison Creek are intermediate in height. 

These two time spans, between Poison Creek and 

Jackass Butte and between Jackass Butte and Froman Ferry 

faunas, are marked by different climatic environments. Cool 

and cloudy continental glacial conditions were present during the first time period (early Blancan V: Poison Creek to 

early Jackass Butte faunas), which shows easily recognized 

size increase in the muskrats~ warmer and sunny conditions 

were present during the last time period (later Blancan V: 

late Jackass Butte to Froman Ferry faunas), which shows no 

size change in the muskrats, but which is not recorded by 

intermediate faunas from the Glenns Ferry Formation. The 

last period ended with a global summer cooling and with 

the immigration of Phenacomys at the beginning of Irvingtonian faunas in the Froman Ferry succession, a climate 

more like that of the early Blancan V Grand View faunas. 

Continental glaciation was not evident in temperate 

regions (in the United States) at either the beginning of the 

Pleistocene ( 1.67 Ma) or the beginning of Blancan V (2.56 

Ma), but it is evident at these times in the Arctic Ocean 

region and is evident in the Mississippi River valley 

between them, by the end of the Grand View faunas at about 

2.1 million years ago (Repenning and Brouwers, 1992). 

From this varied climatic record, it is difficult to infer climatic cause for the marked difference in size change in the 

muskrat lineage. 

Speculation about the apparent cause of different rates 

of size increase may be pointless. In 1987 Repenning (p. 

245) suggested that the Jackass Butte muskrat, Ondatra 

idahoensis, was an immigrant from the Great Plains, there 

derived from Pliopotamys meadensis, and that the Hagerman species Pliopotamys minor became extinct with this 

immigration. If so, the smaller muskrats, whose youngest 

records are in the Poison and Birch Creek faunas, may be 

the last, and most advanced, Pliopotamys minor~ the larger 

mid to late Blancan V and early Irvingtonian I Glenns Ferry 

Ondatra idahoensis may be a derivative of the Great Plains 

Pliopotamys meadensis. Barnosky (1985) described "Pliopotamys near meadensis" from the Blancan V deposits of 

the Yellowstone Park area, suggesting such an immigration 

from the Great Plains. Thus the rapid increase in size of 

Blancan V muskrats between Poison Creek-Birch Creek 

populations (2.4 Ma) and earliest Jackass Butte.populations 

(2.3 Ma) may result from immigration, not from some 

unusual ecologic stimulation. 

These climatic changes between the early and late 

Blancan V are global climatic changes and well dated east 

of the Rocky Mountains and in the Arctic Ocean area 

(Repenning and Brouwers, 1992). The Snake River Plain 

probably followed a different weather pattern (in response 

to changes in the North Pacific Ocean) than the Great Plains 

(in response to the Bermuda High), but the times of change 
THEFROMANFERRYFAUNA 35 

were the same, and the change in muskrat size took place 

during increasing continental glaciation in the N orthem 

Hemisphere. As discussed on page 60, there appears to have 

been increased mountain glaciation in the Yellowstone Park 

area at this time which increased flow down the Snake River 

to the Glenns Ferry lake, and must have done so to the east 

as well, permitting Great Plains muskrats to disperse up the 

former North Platte River to the Continental Divide and 

down the Snake River to the west. 

The available samples are small for all compared muskrat populations except that from the Froman Ferry faunal 

succession, but it seems reasonable that the size data approximate reality, and inferring a reason for the change in rate of 

size increase from the presumed climatic change is difficult. 

Thus, the suggestion of an immigration across the Rocky 

Mountains, rather than one of abrupt size increase in the 

local population of muskrats, is favored. 

Order PROBOSCIDEA Illiger, 1811 

Suborder ELEPHANTOIDEA Osborn, 1921 

Family GOMPHOTHERIIDAE Cabrera, 1929 

Subfamily ANANCINAE Hay, 1922 

Genus STEGOMASTODON Pohlig, 1912 

STEGOMASTODON MIRIFICUS (Leidy), 1858 

Localities and material.-CHALK HILLS AREA: Locality number unassigned, near point of eastern of two southward-running ridges, NE I/4SE I/4 sec. 8, T. 3 N., R. 4 W., 800 

ft W. and 2,200 ft N. of SE. section comer (2,500 ft elev.): M/ 

2, nearly complete and little worn, other bones were associated but not collected. CUCUMBER AREA: GS-231 (2,750 

ft elev.): patella. GS-232 (2,810 ft elev.): proximal articulation of ulna. 

Three localities: 2,500 to 2,810 feet elevation; essentially from the upper part (Irvingtonian) of the Froman 

Ferry faunal succession. 

Discussion.-The M/2 has strong internal proversion 

of lophids (terminology of Osborn, 1936, p. 1545-1549, 

and Savage, 1955, especially p. 59), indicating a lower 

tooth, but the roots are not preserved. The tooth is slightly 

worn; wear cuts through the enamel only on the top of the 

internal hemilophid of the protolophid, but wear facets are 

prominent on the enamel of the metalophid and the anterior 

faces of the tritolophid. One (posterior) entotrefoil is on 

the internal protolophid (the external protolophid is broken 

off), and moderately developed posterior entotrefoils are 

developed on all internal lophids, but are most sharply 

defined on the proto lop hid. No ectotrefoils are evident on 

the metalophid or tritolophid. The metalophid is the only 

loph with both anterior and posterior entotrefoils, and the 

tritolophid has only an anterior entotrefoil. A low tetartolophulid is present, formed by a central external cusp and an 

internal hemiloph, lacking trefoils but forming a heel on the 

tooth. Except that it appears less ptychodont, the tooth is 

similar to those described by Savage ( 1955) from the Cita 

Canyon fauna of Texas; it more resembles those described 

by Woodbume (1961, pl. IV) from the Pliocene of Kansas 

(especially KUMNH 4637). 

The Froman Ferry tooth measures 108.6 mm in length 

and 65.2 mm across the tritolophid; this is somewhat 

smaller than those described by Savage (1955) from Cita 

Canyon, Texas, but within the range of the material Woodbume ( 1961) described from Kansas. 

The proximal portion of the ulna from locality GS-232 

is smaller than that of Elephas or Mammuthus, yet larger 

than that of any other possible taxon of the fauna. The 

semilunar notch is not nearly so deep as in these other proboscidians (the missing radius presumably bearing more of 

the weight of the animal than in the compared specimens). 

The facets for humeral articulation form a more openly 

curved surface that is not so deeply notched as in E. and M.; 

these facets form an angle close to 120° in the fossil, rather 

than about 100° as in E. and M. The articular facets for the 

radius are not evident on the specimen. The individual was 

young and the epiphysis for the olecranon process is missing 

at its unfused suture. 

The patella from locality GS-213, is large and thick 

and can only belong to a proboscidean in this fauna. It does 

not seem otherwise distinctive. 

Most students express the belief that all records of Stegomastodon in the United States represent the single, quite 

variable species, Stegomastodon mirificus (Leidy). (see Savage, 1955; Kurten and Anderson, 1980), and this small 

sample from the Froman Ferry succession can contribute 

little to this opinion. Shotwell ( 1970) attributed most of the 

material from Jackass Butte to this species, while Conrad 

(1980) expressed the belief that two and possibly three species may be present in the Jackass Butte faunas; he questionably referred a large scapula from the youngest part of 

the Jackass Butte sequence to Stegomastodon arizonae 

Gidley, 1926. 

Order PERISSODACTYLA Owen, 1848 

Family EQUIDAE Gray, 1821 

Genus PLESIPPUS Matthew, 1924 

PLESIPPUS IDAHOENSIS (Merriam), 1918 

Figures 9 and 10 

Localities and material.-FROMAN FERRY AREA: 

UCMP 3036 [old UCMP 3036C; =GS-211 ?] (2,398 ft 

elev.): Third upper premolar UCMP 22348 [type specimen] and UCMP 22347 lower fourth premolar. CUCUMBER AREA: GS-228 (Sample 4, which was collected 620 

feet W. of the locality; 2,740 ft elev.): right P\3 (USNM 

264329) and M\2? (USNM 264330). A fragment of an 

upper cheek tooth, preserving the complete prefossette, 

was found on the surface about 100 yards south of locality GS-221 (elev. 2,650 ft). 
36 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

A B c D 

.. 

4cm 

I 

I 

I 

I 

I 

: 

I 

I 

I 

I 

I 

I 

: 

I 

: I 

.. \ 

~ ' \\. 

'I 

'I 

~ :,: 

Figure 9. Plesippus cheek teeth. A, B, and C, Plesippus idahoensis (Merriam) teeth showing short protocones, simple fossettes, and minimal crown curvature, from Froman Ferry faunal succession, Canyon County, Idaho. A and B show occlusal, lingual, and anterior views 

from locality GS-228, Sample 4, Cucumber area; Cis occlusal, buccal, and anterior views of type specimen from locality UCMP 3036 (= 

GS-211 ?) in Froman Ferry area. A, USNM 264330: Moderately worn second(?) right upper molar. B, USNM 264329: Moderately worn 

third right upper premolar. C, Type specimen, UCMP 22348: Very worn third left upper premolar (drawn from cast).D, Plesippus simplicidens (Cope) [as Equus simplicidens], type, Blanco fauna, Blanco Canyon, Crosby County, Texas, University of Texas specimen, copied 

from Osborn (1918, pl. 24-5), which was drawn from a cast; little-worn upper molar, probably a first molar, occlusal, buccal, and anterior 

views. Showing slight anteroposterior length of protocone at this stage of little wear, relatively simple fossettes, and smaller size in comparison with Plesippus idahoensis. This is one of the very few published illustrations of the species. 

Three localities; 2,398 to 2,740 feet elevation. This 

is essentially the entire thickness of the fossiliferous section as the highest specimens were found only about 150 

feet beneath the highest known fossil locality. 

Discussion.-Most authors follow Opinion 271 of the 

International Commission on Zoological Nomenclature in 

placing the living species of equids (about seven) in the 

genus Equus, recognizing as subgenera several previously 

named genera that cover the variety of living domestic and 

wild species of Asia and Africa: the domestic horse (and 

wild tarpan), the asses (and wild African ass), and the still 

extant wild onager, kiang, and zebras. 
THE FROMAN FERRY FAUNA 37 

When Morris Skinner (Skinner and others, 1972) 

decided that the North American Pliocene genus Plesippus (of Matthew, 1924) was the same as the living African zebra (subgenus Equus (Dolichohippus)), he was 

obliged to either follow the minority or to put the North 

American fossil species, which he assigned to the living 

subgenus Dolichohippus, in the genus Equus; he chose to 

follow the majority. Our recognition (to follow) of the differences, both morphologic and historic (pointed out earlier by others), between the North American Pliocene 

fossil forms and the living African Grevy zebra (Equus 

(Dolichohippus) grevyi) permits us to recognize Matthew's extinct taxon Plesippus as a full genus; it is not a 

living horse. 

As far as the present fossil record reveals, not only the 

Grevy zebra but all living horses derive from North American Plesippus, as was believed by Matthew when erecting 

the genus in 1924 and as recently reinforced by Azzaroli 

and Voorhies ( 1993). The living Grevy zebra (subgenus 

Dolichohippus) may differ less than the other living horses 

from this ancestral Plesippus, but this does not indicate that 

they are the same. The later evolution of the Grevy zebra is 

fairly well documented in Africa (for example, Churcher 

and Richardson, 1978; Azzaroli and Voorhies, 1993), and 

certainly the several species of Plesippus have a much earlier record in North America. 

The type specimen of Plesippus idahoensis, UCMP 

22348, is a very worn upper premolar with less than an 

inch (Merriam gives 24.7 mm) of the enamel crown left 

above the roots (and this only at the least worn corner). The 

type tooth is distinctly more worn anteromedially relative 

to its vertical axis (J.H. Hutchison, oral commun., 1993) 

and appears, therefore, to be most likely a third upper premolar, although Merriam ( 1918, fig. 3) supposed that it was 

a P\4. As noted by Merriam (and Shotwell, 1970, p. 91), 

the tooth is so worn that it is not possible to approximate 

buccal curvature from base to top of the crown (but some is 

evident). The tooth is quite large, and Merriam measured it 

as 35.5 mm in anteroposterior length (presumably across 

the ectoloph), and 34.8 mm in transverse width (which is 

its width across the enamel, discounting the great thickness of cement at the protocone). The mesostyle has a conspicuously anteromedial slope to its external enamel face 

(fig. 9C). 

The two upper teeth from near Cucumber locality GS228 (fig. 9A and B) are equally large, and less worn; they 

confirm Merriam's inferences made from the well-worn 

type tooth. In addition they show that the short protocone of 

the type is not a result of its great wear but is short even 

with less wear, and that it has a prominent lingual groove at 

all stages of wear (at least on P\3 and M\2?). The protocone 

column does not taper toward the tooth base, reducing its 

anteroposterior length (fig. 9A and B). The upper tooth fragment found 100 yards south of Cucumber locality GS-221 

shows a prefossette equal in size to that of the type tooth, 

and exhibits only slightly less wear than the type, further 

suggesting that Plesippus idahoensis is a consistently large 

species. However, the fossettes of the less worn teeth are 

only slightly more crenate than the type specimen, contradicting Merriam's inference, made from the very worn type 

specimen, that these would have been quite plicate with less 

wear. 

All horses are rare in the Froman Ferry faunal succession, making the distinction between morphologic 

characters and individual variation vague. But the two 

teeth collected in the Cucumber area near GS-228 (a right 

P\3 and apparently a M\2) clearly are Plesippus idahoensis, and not the other horse known from the Froman Ferry 

faunal succession (figs. 10 and 11 ), although they may be 

500,000 years younger than Merriam's type specimen. P. 

idahoensis had distinctly less buccal crown curvature than 

the other horse, P. fromanius (n. sp., discussed next), from 

the same fauna, had protocone columns with a short protocone and of a uniform anteroposterior length down the 

height of the crown, had less plicate fossettes, and the teeth 

were large (anteroposterior dimension across the ectoloph 

of P\3 is about 35 mm) and heavily cemented. The occlusal 

enamel pattern of the younger teeth is essentially identical 

to the that of type specimen (fig. 9B compared with 9C). 

These two new teeth clearly show that the size and enamel 

pattern of P. idahoensis are characters of the species and 

differ from those of P. fromanius n. sp. discussed next. 

Except for greater size, possibly more persistent protocanal gutter, thicker cement, and less curvature, the cheek 

teeth of P. idahoensis do not differ greatly from the type of 

Plesippus simplicidens (Cope) from the Blanco fauna near 

Lubbock, Texas (fig. 9D). They also show that the protocone column does not taper toward the roots and that the 

crown curvature is less than in the contemporaneous and 

older Glenns Ferry horses. 

The curvature of the mesostyle column of M\2 (above 

the point where it flattens to merge with the crown base) is 

2.5 mm across a 48.6 mm height of the column on the M\2 

of Plesippus idahoensis (ratio for M\2xl00=5.14). The 

mesostyle curvature is 6.85 mm across a 64.8 mm height of 

the column on the left M\2 mesostyle of P. fromanius from 

the Chalk Hills (ratioxl00=10.57). The amount of curvature clearly varies with the tooth position and also varies 

between the mesostyle and the protocone of the same tooth 

(protocone curvature of P. fromanius on the same tooth has 

a ratioxlOO of 12.89). The type P\3 of P. idahoensis has an 

occlusal length across the ectoloph of 35.5 mm and transverse width of 34.8 mm (enamel to enamel), compared to 

34.4 mm and 31.3 mm of the P\3 of P. fromanius from 

Chalk Hills. The referred P\3 of Plesippus idahoensis 

(USNM 264329 from locality GS-228) is nearly as large as 

the type specimen and measures 35.1 mm in length and 

33.2 mm in width. 
38 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

The only lower cheek tooth known of Plesippus idahoensis is still the paratype described by Merriam (1918), 

UCMP 22347. It is large and heavily cemented in comparison with the lower tooth of the other horse from the Froman 

Ferry faunal succession (fig. 10£). 

RELATIONSHIPS.-This is not the only record of a plesippine horse having these characters in the Glenns Ferry 

Formation. Horses of this nature, with a short, nontapering 

protocone, are inferred to have been an immigrant to the 

Snake River Plain before 2.1 million years ago. 

Azzaroli and Voorhies (1993) have recently recognized two horses from the Glenns Ferry Formation 

exposed in Jackass Butte (their "Jackson Butte") northwest of Grand View, Idaho (the usual concept of the 

Grand View fauna; see p. 59). One of these was a large 

horse (USNM 23903, male skull and mandible; USNM 

264281, female partial skull and mandible; and nine cataloged postcranial elements (others, mainly carpal and tarsal bones, are in the collection)). Except for the male 

skull and mandible, none were in articulated position as 

buried. All were collected in the same excavation with no 

other horse in association, although a few other mammal 

remains, as a Stegomastodon tooth and a badger mandible, were found. These horses were collected from a horizon estimated to be about 2.2 million years old from 

paleomagnetic control and supporting climatic evidence 

discussed later (p. 60). Azzaroli and Voorhies (1993) 

named this larger horse a new subspecies of Old World 

Equus stenonis, E. (Dolichohippus) stenonis anguinus, but 

for reasons discussed later in this report (on p. 44-46), 

we place the species in the genus Plesippus in North 

America. Although not mentioned by Azzaroli and 

Voorhies, some of the upper cheek teeth of this horse 

have protocones that taper toward the base of the tooth so 

that the anteroposterior length of the protocone decreases 

as the tooth wears. 

The second horse that Azzaroli and Voorhies recognized in the Jackass Butte faunal succession was a slightly 

smaller species with a shorter and stouter muzzle, more 

massive premaxillaries, shallower narial notch, and more 

anteriorly located posterior palatine foramina (LACM 

(CIT) 118/892; the partial skull and jaw were discussed in 

1936 by J.P. Schultz). Schultz (1936) referred this specimen 

to Merriam's Equus idahoensis (apparently on geographic 

grounds) and Azzaroli and Voorhies (1993) followed this 

assignment, although the distinguishing features of the 

skull are not known for Merriam's type material from Froman Ferry and the teeth from Jackass Butte are noticeably 

smaller. 

Although Azzaroli and Voorhies ( 1993) mentioned 

Merriam's type material as being "obviously inadequate" 

for a species type, they cited dental similarities that suggest a relationship; the protocones on the upper teeth are 

short at the early stage of wear of the specimen (7-8 years 

old according to Azzaroli and Voorhies), especially on the 

P\3. This suggests that the protocone column does not taper 

toward the crown base. The teeth are also massively 

encased in cement, but the mesostyle of the upper teeth, 

especially the premolars, lacks the pronounced anteromedial slope of the external enamel surface found on the 

known topotypic specimens of Equus idahoensis. (The consistency of this feature is difficult to evaluate with so little 

topotypic material; it does not appear consistent in other 

horses, including Plesippus fromanius.) 

The lower cheek teeth from Jackass Butte are very 

similar to the single topotypic lower premolar from Froman 

Ferry, except for their smaller size; and they have a heavy 

coat of cement. 

Thus it seems probable that the new horse lineage 

leading to Plesippus idahoensis appeared in the Snake 

River Plain during deposition of the Grand View faunas, 

during the Blancan V mammal age of the United States. 

The decision of whether the form described by Schultz 

(1936) and Azzaroli and Voorhies (1993) from the Jackass 

Butte section should be assigned to the Froman Ferry species of Merriam (1918) probably should wait until more 

material has been found in both areas. Based upon the 

known teeth, Plesippus idahoensis is larger than the 

referred horse from Jackass Butte, seems to have slightly 

shorter protocones, and has a forward slant of the enamel 

forming the mesostyle; these may represent evolutionary 

trends during the 400,000 years that separate the two localities, or individual variations. 

The Jackass Butte section is as young as about 2.0 

million years based upon the presence of the older. of the 

Reunion normal events (2.14 Ma) found in the marsh beds 

in the middle of the section and as old as possibly 2.3 million years based upon the thickness of the deposits and the 

absence of exposures of the 2.4-million-year-old Birch 

Creek fossil horizon in the immediate area. No attempt has 

been made to discover any faunal difference over this possibly 300,000 years of deposition at Jackass Butte. 

The type and referred skulls of Plesippus stenonis 

anguinus were collected a short distance below marsh beds 

on Jackass Butte that contain the earlier event of the 

Reunion Normal-polarity Subchron (2.1 Ma), but the horizon of discovery of LACM (CIT) 118/892, referred to 

Plesippus idahoensis, is unknown to us. 

PLESIPPUS FROMAN/US n. sp. 

Figures 10 and 11 

Localities and material.-HOMEDALE AREA: GS212 (2,430 ft elev.): two left cuboids (fourth tarsal bones). 

CHALK HILLS AREA: GS-203 (2,613 ft. elev.): (USNM 

264339) the type left and right upper tooth rows, with 

fragments of the palate; the left side of the palate shows a 

minute (2.3 mm) alveolus for a P\1 (the palate is missing 

in this area on the right side). GS-208 (2,550 ft elev.): 
THE FROMAN FERRY FAUNA 

A 

B 

c 

Upper teeth 

~ 2 4cm 

E 

Lower teeth 

3cm 

Figure 10. Plesippus fromanius from Froman Ferry faunal succession, Canyon County, Idaho; P. 

shoshonensis from Hagerman faunal succession, Gooding County, Idaho; and Plesippus idahoensis from 

Froman Ferry faunal succession. A, type Plesippus fromanius, USNM 264339: Right upper tooth row of 

type palate, locality GS-203, Chalk Hills area. Drawing reversed. Band C, Plesippus shoshonensis, left upper tooth rows showing change with wear. Copied from Gazin (1936, fig. 21 ). B, little worn: C, well worn. 

Note shortening of the protocone with wear. D, Plesippus fromanius, USNM 264340: little-worn right P/4 

in occlusal and buccal views, from Cucumber area locality GS-221. E, Plesippus idahoensis, UCMP 22347: 

modestly worn right P/4 in occlusal and buccal views, referred by Merriam ( 1918), UCMP 3036, Froman 

Ferry area. Lower teeth shown larger, as indicated by different scales. 

39 
40 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

3 4 5cm 

Figure 11. Plesippusfromanius second upper and third 

lower molars. Top: Plesippus fromanius, USNM 264339: 

left M\2 of the type specimen, locality GS-203, Chalk 

Hills area, Froman Ferry faunal succession, Canyon 

County, Idaho; occlusal, posterior, and lingual aspects. 

Showing buccal curvature of crown. Bottom: USNM 

264341: Plesippus fromanius, occlusal surface of incomplete and well-worn M/3 from locality GS-232 Sample 

15, Cucumber area, very high in the Froman Ferry faunal 

succession. Showing Equus-like enamel pattern in worn 

condition. 

medial condyle of distal articulation of femur. CUCUMBER AREA: GS-221 (2,650 ft elev.): (USNM 264340) 

unrooted P/4. GS-229 (2,750 ft elev.): astragalus, metapodial splint. GS-234 (2,770 ft elev.): unerupted P/2 

(onager?). GS-228 (2,770 ft elev.): distal epiphysis of 

radius, and proximal and middle phalanges (subadult). GS232, Sample 15 (a rusty gravel bed 175 feet east of the 

locality, 2,810 ft elev.): M\3 and incomplete M/3 (USNM 

264341 ), and miscellaneous postcranial elements. 

Eight localities: 2,430 to 2,810 feet elevation; essentially throughout the Froman Ferry faunal succession. 

Although all postcranial elements found have been included 

here, there is no assurance that some do not belong to Plesippus idahoensis. 

Etymology.-The species name fromanius (Latin; 

commemorative masculine) is in honor of George W. Froman who established, in the 1880's, a roadhouse on the road 

to Jordan Valley, Oregon, that was called Poison Creek Station. Mr. Froman built a ferry south of Chalk Hills in about 

1886 to provide a more direct route to Caldwell, Idaho. The 

ferry operated until 1921, when a bridge was built across 

the Snake River at Marsing, 3 miles upstream (to the south) 

(Huntley, 1979, p. 170-176). According to Huntley, a Mrs. 

Velda Swinney, resident of the area, often crossed on the 

ferry with her horse and buggy and the horse always 

stopped in the middle of the ferry without command. When 

the bridge was built, Mrs. Swinney used it, and the horse 

stopped in the middle of the bridge as well. 

Diagnosis.-A species of Plesippus with a protoconal 

column that tapers only at the base of P\4, M\1, and the M\2 

(fig. 11), and that has strong buccal curvature of the crown 

(present but variably developed on the other cheek teeth 

except P\1-2), differing from Equus; differing from Plesippus shoshonensis from the Hagerman fauna (Gazin, 1936) 

and P. stenonis anguinus from the Grand View fauna 

(Azzaroli and Voorhies, 1993) in having a more elongate 

protocone (so that the cheek teeth resemble some species of 

the genus Equus ), with tapering restricted to a very minor 

part (near the base) of the protocone column of only P\4 to 

M\2 to produce a Plesippus pattern with great wear; buccal 

curvature of the upper cheek teeth prominent and much 

greater than in Plesippus idahoensis or species of Equus. 

Lower teeth plesippine in having a V-shaped gutter between 

the metaconid and metastylid (fig. IOD), possibly excepting 

M/3 (fig. 11). This is a large horse; the complete cheek 

tooth row measures 198 mm in length. 

Discussion.-USNM 264339 is the most complete 

specimen of this horse. It is a broken and incomplete palate 

with right and left dental rows (missing P\ls, although a 

very small alveolus for one is present on the left side). Casts 

of the right toothrow have been deposited with the material 

collected from Froman Ferry by Merriam in 1916 in the 

University of California Museum of Paleontology (UCMP) 

and in the Idaho Museum of Natural History (IMNH 1105/ 

11890). 

Although this horse is here believed to have evolved 

directly out of Plesippus stenonis anguinus (Azzaroli and 

Voorhies) from the Jackass Butte faunal succession, these 

authors based the specific identity of the Jackass Butte species on features of the skull (deep narial notch, preorbital 

pit) not known from the Froman Ferry species, as well as 
THE FROMAN FERRY FAUNA 41 

the teeth. Azzaroli and Voorhies (1993, p. 183) mentioned 

that E. (D.) stenonis anguinus has more posteriorly placed 

posterior palatine foramina, which is also true of P. fromanius, in which the foramina appear to have been behind the 

midpoint of M\3 (the foramina are broken away on the 

specimen and this statement is based upon projection from 

the limits of the breaks). This position appears to be slightly 

more posterior than in the Grand View and Hagerman specimens. Otherwise, these characters of the skull are not preserved in Plesippus fromanius, but the differences in the 

teeth from Froman Ferry are sufficient to show that P. fromanius is distinct from P. stenonis anguinus of Jackass 

Butte. 

This North American lineage appears to have evolved 

the characters of Eurasian E. stenonis about 2.5 million 

years ago and dispersed to Eurasia, where the oldest forms 

are of about this age (Azzaroli and Voorhies, 1993, p. 183). 

Thus it also seems that the "stenonine" characters were relatively short lived in North America, but existed during the 

time that the lineage dispersed to Eurasia (although this is 

about 400,000 years earlier than the records from Jackass 

Butte). Although the "stenonine" characters persisted in the 

Eurasian clade, in North America the dental characters continue evolving toward the "caballine" condition. Thus, the 

species stenonis is not recognized again in later North 

American horses. 

In North America the lineage evolved toward the modem horse while the Eurasian branch trended toward the 

modem zebras. The combination of Plesippus fromanius 

from Froman Ferry, of an evolutionary stage comparable 

with Old World zebras (and so named) from the Jackass 

Butte faunal sequence, and the more primitive Plesippus 

shoshonensis from Hagerman, all having dental features 

that suggest a single lineage (as will be discussed), presents 

a peculiar nomenclatorial situation: the evolution of the 

Glenns Ferry lineage appears to have lacked diversification 

and to have been Plesippus shoshonensis > Equus (Dolichohippus) stenonis anguinus > Plesippus fromanius. 

Because of this change in generic and sub generic attribution 

in the middle of this sequence and because of arguments 

following as to the validity of these names in North America, we refer to the Jackass Butte species as Plesippus stenonis anguinus without comment regarding the proper 

nomenclature in Eurasia. 

But there exists a peculiar circumstance in the last 

record, the species from Froman Ferry. As here interpreted, 

in Plesippus fromanius evolution has produced upper teeth 

that resemble Equus (Equus) species, especially Equus 

scotti of the early Irvingtonian faunas of the United States, 

although the lower teeth still appear to be those of Plesippus. The alternative interpretation is to recognize three 

horses from the Froman Ferry fauna: ( 1) a Plesippus idahoensis; (2) a species with Equus-like upper teeth and no 

known lower teeth; and (3) a species with Plesippus-like 

lower teeth, but no known upper teeth. The lower teeth here 

attributed to Plesippus fromanius have the character of the 

genus Plesippus (V-shaped metaconid-metastylid gutter: 

McGrew, 1944; Skinner in Skinner and others, 1972), even 

though the upper teeth have those of Equus (elongate protocone). 

This situation of mixed "generic" characters between 

the upper and lower teeth is not unique to the Froman Ferry 

fauna, although the stratigraphic succession in the Glenns 

Ferry Formation showing the transition from Plesippus into 

this form may be unique in the stratigraphic record. The 

mixture of characters exists in some living horses (Asinus, 

Dolichohippus) that Opinion 271 places in the genus Equus, 

and in other fossil records. 

For example, Akersten ( 1972), in describing the Red 

Light fauna of Texas, assigned only upper teeth (with the 

exception of one lower tooth, listed but not discussed) to 

Equus scotti and only lower teeth to Plesippus simplicidens. 

Akersten (1972, p. 36) recognized this problem and, in discussing the differences between his Red Light fauna and the 

nearby Hudspeth local fauna, having only Plesippus-like 

lower teeth (Strain, 1966), said, "There are two possible 

explanations for this situation. These two faunas [Red Light 

and Hudspeth] of equivalent age and separated only hy a 

minor mountain range may have had a different species of 

large horse in each, or both may have had a single species 

of large horse in which the upper cheek teeth were similar 

to E. scotti and the lowers similar to E. (P.) idahoensis." He 

followed with, "I favor the latter explanation" but did not 

follow this in his identification. Had he done so, he would 

have recognized neither Equus aff. Scotti nor Plesippus cf. 

simplicidens in the Red Light fauna, nor Strain's Plesippus 

idahoensis from the Hudspeth fauna on the other side of the 

mountains from Red Light. 

The same mixture of Equus-like upper teeth and 

Plesippus-like lower teeth appears to be present in the oldest faunal horizon at Rock Creek, Texas (the type Equus 

scotti is from the middle horizon), and in the Aries fauna of 

southwestern Kansas according to G.A. Izett and J.G. 

Honey (oral commun., 1994). 

During nearly all stages of tooth wear the Froman 

Ferry horse has a distinctly elongate protocone that is like 

that of species of the subgenus Equus (Equus) and quite 

similar to Equus scotti (?=E. excelsus). But, with great 

wear, the length of the protocone is shorter, most noticeably 

on the P\4 and M\1, and more like that of Plesippus. This is 

to say that the protocone is tapered near the base of the 

tooth, and this tapered protocone is also present, but extends 

farther down the tooth toward the occlusal surface, in Plesippus stenonis anguinus (Azzaroli and Voorhies) from 

Jackass Butte and in P. shoshonensis Gidley from the 

Hagerman fauna, in which Gazin ( 1936, fig. 21) illustrated 

a shortening of the protocone throughout wear. 
42 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

The upper teeth on the type palate of Plesippus fromanius from Chalk Hills locality GS-203 (fig. lOA), 1.3 miles 

northeast of and about 215 feet higher in the section than 

the type locality of P. idahoensis, are only moderately worn 

(figs. 1 OA and 11 ), although roots had begun to form. The 

P\3 ectoloph measures 34.1 mm and the fossettes are amply 

plicated, more so than the little-worn teeth of P. idahoensis 

(fig. 9A and B). The mesostyles of the P\3 are strongly modified in the same way as those of P. idahoensis, with a conspicuous anterior slope of the ectoloph enamel, but this is 

not very evident in the other teeth of the type specimen. The 

crown of P\3 is 53.8 mm tall at the protocone on the type of 

Plesippus fromanius (avoiding root development). 

Even with great wear, the protocone of P\3 is more 

elongate in P. fromanius than in P. stenonis anguinus from 

Jackass Butte, which is little altered from the condition in P. 

shoshonensis from Hagerman. Except for P\2, the protocone of P\3 is, however, the shortest of the tooth row, as is 

generally the case in all horses. The protocones of P. 

shoshonensis, P. stenonis anguinus, and Plesippus fromanius taper (shorten in anteroposterior length) toward their 

base; that of the P\3 of Plesippus fromanius is most 

advanced in that the protocone measures 13.1 mm in length 

at the occlusal surface of the type specimen, but is about 

10.3 mm at the base; that of the P\4 has an anteroposterior 

length of 15.1 mm on the occlusal surface, and 13.6 mm at 

the base. As :can be seen in Gazin's (1936, fig. 21) illustration of enamel patterns of P. shoshonensis from the Hagerman horse quarry (two reproduced here in fig. lOB and C), 

the same shortening of the protocone toward its base is 

found in the type population of this species. However, the 

elongation of the protocones in early wear is not so extreme 

in this population, and, as noted, the tapering of the protocone of P. shoshonensis is evident through the entire length 

of the column. The protocones of all three taxa have a moderate gutter running down their lingual surface which disappears before reaching the base of the tooth; it is, however, 

not so prominent as in Plesippus idahoensis. 

The type and referred P\3 of P. idahoensis have 

ectoloph lengths of 35~5 mm and 35.2 mm, respectively, 

somewhat larger than the P\3 of P. fromanius (34.1 mm). 

Although the size of the type and referred upper teeth of P. 

idahoensis is great, it is little larger than P. fromanius; and 

Gazin ( 1936) noted that this ectoloph length is equalled or 

exceeded by two specimens of P. shoshonensis from Hagerman, although certainly the average from Hagerman is 

smaller. Both Plesippus idahoensis and P. fromanius are 

large horses. 

All upper teeth but the P\2 of Plesippus fromanius 

from the Froman Ferry succession are moderately curved 

buccally; the amount of curvature of the protocone column 

is greatest in M\2 (fig. 11 ), as noted on page 37, and is 6.1 

mm at its midpoint, and the protocone is 47.3 mm tall 

(ratiox100=12.89). The total occlusal-surface length of the 

cheek tooth row, P\2 to M\3, on the type specimen from 

Chalk Hills is 198 mm. There is a small ( ::::2 mm) alveolus 

for a P\1 on the type (left side only preserved), and Plesippus fromanius may also be more advanced in the reduction 

of this tooth than P. shoshonensis from Hagerman and P. 

stenonis anguinus from Jackass Butte, as well as in its more 

elongate protocone (the small alveolus is not shown in fig. 

lOA). 

Of the lower teeth, the P/4 from locality GS-221 in the 

Cucumber area is shorter in crown height than the P/3 

referred by Merriam (1918, fig. 5) to Equus idahoensis 

(UCMP 22347 from UCMP locality 3036). Although the 

Cucumber P/4 of P. fromanius is similar in generic characters, it is at a younger stage of growth and wear and smaller 

than the lower premolar of P. idahoensis, again illustrating 

the size difference (fig. lOD and E). Measured at the enamel 

boundaries (to avoid differences in cement thickness) the 

Cucumber P/4 is 33.5 mm long and 14.8 mm in transverse 

width at the occlusal surface (fig. lOD) and Merriam's 

referred P/3 is 34.6 mm long and 19.5 mm wide (fig. 10£). 

The base of the Cucumber tooth is not preserved and it is 

not possible to determine whether roots had yet formed, as 

they had begun to do in the tooth that Merriam described. 

Like the specimen from the Froman Ferry area referred 

to Plesippus idahoensis, on the P/4 of Plesippus fromanius 

from the Cucumber area the metaconid-metastylid gutter is 

distinctly V-shaped, but the enamel plications, including the 

plicaballinid, are greater (fig. lOD). The occlusal surface of 

the Cucumber lower tooth of Plesippus fromanius has a 

remarkable amount of plication of the hypoconid wall of 

the posterior fossettid, which is not present at the broken 

base of the tooth; this also is evident in early wear of the 

lower teeth of the Grevy zebra as well as on the lower premolars of Plesippus shoshonensis and P. stenonis anguinus. 

A shallow gutter on the posterior face of the hypoconulid 

becomes more prominent toward the base of the tooth, and 

the tooth is so little worn that the hypoconulid is represented on the occlusal surface by two cusps. This hypoconulid groove is unusual in all Plesippus specimens seen 

and may only be an individual variation. 

The incomplete M/3 from Cucumber locality GS-232 

is a mature tooth with well-developed roots and is more 

than half worn (fig. 11). The buccal valley does not separate 

the fossettids, which are reduced in size because of wear, 

and the metaconid-metastylid gutter is shallow and broadly 

open because of wear. The tooth does not look particularly 

plesippine, but this is a variable and unreliable tooth for 

identification. It may show a tendency in the lower dentition 

toward an Equus tooth pattern. 

The unerupted P/2 from locality GS-234, questionably 

assigned to Plesippus fromanius, is 41.1 mm long (in line 

with the tooth row), completely unworn, and of course has 

not developed roots. It is not possible to separate this tooth 
THE FROMAN FERRY FAUNA 43 

with certainty from the same tooth of the subgenus 

Hemionus. 

We point out that the few available specimens of the 

horse from the nearly 1 million-years-older Birch Creek 

and Poison Creek areas of the Grand View faunal succession are considerably smaller (P\2 to M\2=144.7 mm; 

P\2-P\4=93.4 mm; P/2=37.7 mm; P/4=32.7 mm) and close 

to the average size of the tooth rows from Hagerman. 

Jonena He~st (University of Kansas), currently studying 

the Birch Creek and Poison Creek faunas, has a more complete record of this horse, which may indicate that the small 

size we have seen is primarily an individual variation. 

In summary, the teeth of Plesippus fromanius from the 

Froman Ferry faunal succession differ from the coeval Plesippus idahoensis in slightly smaller size, more elongate 

protocone, and greater buccal curvature of the upper tooth 

crowns; it differs from later species of Equus in this greater 

upper tooth crown curvature, in the shortening of the protocone of P\4 and M\1 with extreme wear, and in the retention 

of a V-shaped metaconid-metastylid gutter on the lower 

teeth, although this feature is not lost in all later Equus species. 

Because the tapering of the protocone toward the roots 

and the crown curvature are also increasingly or equally 

evident in Plesippus stenonis anguinus from Jackass Butte 

of the Grand View faunas and in Plesippus shoshonensis 

from the Hagerman succession, the Froman Ferry species is 

considered part of a single horse lineage that was native to 

the western Snake River Plain throughout the history of the 

Glenns Ferry Formation. The Froman Ferry species differs 

from older populations of this lineage of the Glenns Ferry 

Formation in having greater elongation of the protocone, 

restriction of the protoconal tapering to the very base of the 

tooth, and in the reduction of P\1. The intermediate form of 

the lineage, Plesippus stenonis anguinus (Azzaroli and 

Voorhies) of the Jackass Butte faunas, had developed skull 

characters of this Eurasian lineage at the time that it dispersed to that supercontinent, and evidence indicates that 

subsequent evolution was not parallel in the two areas. In 

Eurasia E. (D.) stenonis continued to evolve in the direction 

of the living zebras, while, in North America, Plesippus fromanius evolved in the direction of living horses (and 

asses?). 

The postcranial bones (listed on p. 38 and 40) provide 

little information and are not certainly assigned to Plesippus fromanius. The size indicated by all specimens is within 

the range of those tabulated by Shotwell ( 1970, table 22) for 

the Grand View faunal succession (Jackass and Wild Horse 

Butte areas), and larger than the range for those he tabulated 

for Plesippus shoshonensis from the Hagerman fauna. A 

large horse is indicated, but none are larger than the maximum Shotwell indicates for the horses in the Jackass Butte 

faunas. We do not know that the postcranial bones of P. idahoensis from Froman Ferry are as enlarged as are the teeth, 

although Azzaroli and Voorhies (1993) suggested, from evidence in other areas, that the species may also have had 

massive postcranial bones. 

The ulna is fused to the radius as in modem horses and 

zebras and in the genus Plesippus; this is indicated on the 

radial epiphysis from GS-228, listed previously. This is the 

condition in all horses from the Glenns Ferry Formation. 

Skinner (in Skinner and others, 1972, p. 118) stated that the 

radius and ulna are not fused in the living E. (Dolichohippus) grevyi, which would be a very distinctive and primitive 

(or juvenile) feature, but his statment is not supported by 

the observation of others, as Gazin ( 1936, p. 308). We have 

not examined the postcranial skeleton of the Grevy zebra. 

SPECIFIC NOMENCLATURE 

That two horses are present in the Froman Ferry fauna 

seems clear, but what should they be called? Following 

Skinner (in Skinner and others, 1972), nearly every plesippine horse in North America has been assigned to the African zebra subgenus Dolichohippus of Heller (1912) and to 

the species simplicidens of Cope (1892), named from the 

Blanco fauna near Lubbock, western Texas (northern 

Crosby County), as has been mentioned (p. 37). 

Cope's type, in the University of Texas collection, was 

a single incomplete upper tooth, reproduced here in figure 

9D from Osborn (1918). Skinner assigned additional fossil 

horse specimens in the American Museum of Natural History (AMNH) from the Blanco fauna to E. (Dolichohippus) 

simplicidens with no explanation other than that they were 

topotypic. All these additional specimens from the Blanco 

fauna, collected by W.D. Matthew and G.G. Simpson in 

1924, have quite worn teeth but give a much better idea of 

the nature of the species. In establishing the genus Plesippus Matthew had these specimens at hand, and this additional material was also assigned to Cope's species by 

Gidley (1930) and Gazin (1936): Skinner (Skinner and others, 1972) may have thought that an explanation of the 

assignment was not needed. 

Unfortunately, the anterior portion of the protocone of 

Cope's type is missing and has been variously inferred; 

Cope (1892, fig. 1) inferred an anterior projection of the 

protocone as in Equus, and Osborn (1918, pl. 24-5, reproduced here in fig. 9D) inferred a Pliohippus-like anterior 

part of the protocone. However, it is evident from the illustrations of the type that it is a little-worn tooth (probably an 

M\1) and that, at this early stage of wear, even the posterior 

portion of the protocone is short in comparison with the 

tooth of little-worn Plesippus shoshonensis (compare fig. 

9D with the M\ls of fig. lOB [little worn] and C [well 

worn]). If Cope's Plesippus simplicidens had a tapered protocone, as does Gidley's Plesippus shoshonensis, with great 

wear the protocone must have been very Pliohippus-like. 
44 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

This is not evident in the worn teeth collected by Matthew 

and Simpson from the type locality. 

Skinner (Skinner and others, 1972) stated that Plesippus shoshonensis Gidley, from the Hagerman faunal succession, was the same species as that described by Cope from 

the Blanco fauna, but without explanation and without mentioning the characters that Gazin (1936) gave as being different between the two species. Gazin, noting that the 

topotypic teeth were quite worn, believed that the strongest 

differences between P. simplicidens and the Hagerman 

horses were those of the skull and limb proportions. 

The Glenns Ferry horse lineage (Plesippus shoshonensis > P. stenonis anguinus > P. fromanius) is not Plesippus 

simplicidens (figs. 9 and 10). Possibly the most conspicuous 

difference is that their upper cheek teeth have a protocone 

that resembles that of Equus in at least early wear. This feature gradually increases in development during deposition 

of the Glenns Ferry Formation until the representative from 

Froman Ferry has a Plesippus-like protocone only in the 

final stages of wear. P. idahoensis is possibly the most similar to Cope's species, but is much larger, its upper teeth are 

less curved, and it has a lingual gutter running down the 

protoconal column (fig. 9A, B, and C), a feature developed 

in a few teeth from the Blanco fauna. 

From Shotwell's work, relative limb proportions seem 

to change from P. shoshonensis to P. stenonis anguinus 

(Hagerman to Jackass Butte). Although complete skeletons 

are known only from Hagerman, major elements of the 

postcranial skeleton were recovered with the two USNM 

skulls from Grand View (P. stenonis anguinus (Azzaroli and 

Voorhies) from Jackass Butte); and Shotwell (1970, table 

22) had a large number of isolated postcranial elements 

from there, but did not recognize the presence of two 

horses. Without individual associated skeletons, determining whether the differences in limb sizes represent individual proportions, population variation, or different species is 

difficult. 

Most importantly, dental characters change over this 

time (at least 2 million years), and the youngest population 

of the native Glenns Ferry lineage, Plesippus fromanius 

from Froman Ferry, had developing dental features in the 

upper teeth, particularly the elongate protocone, that would 

ordinarily cause them to be included in the subgenus Equus, 

rather than Plesippus. In contrast, P. idahoensis, also from 

the Froman Ferry faunal succession, developed a straighter 

crown, but retained a primitive protocone. On the other 

hand, P. simplicidens (Cope) from the Blanco fauna, Texas, 

seems to retain all primitive dental characters, a plesippine 

(almost pliohippine) protocone and a strongly curved upper 

cheek tooth (fig. 9D). The material of P. simplicidens, collected later by Matthew and Simpson from the type locality, 

is all rather well worn, but none have an elongate protocone 

like little-worn Plesippus shoshonensis. 

Shotwell (1970) and Conrad (1980) assigned the 

Grand View horse material (Jackass Butte) to Merriam's 

species (E. idahoensis) from Froman Ferry, but to different 

subgenera (depending upon whether Skinner's statements 

had been published at the time of each one's writing); their 

assignments were hesitant because of the limited material 

available from Froman Ferry (then only Merriam's type 

material), and neither recognized two different horses from 

the Grand View faunas. Dalquest (1978) followed Skinner 

in accepting Equus (Dolichohippus) simplicidens as the 

name for most Blancan horses, and Kurten and Anderson 

( 1980, p. 285) apparently followed Dalquest and assigned 

Merriam's two teeth from Froman Ferry, as well as all other 

Glenns Ferry horses, to E. (Dolichohippus) simplicidens. 

Beyond the generic definition for Plesippus provided 

by Matthew (1924), Merriam's type specimen of Equus idahoensis from Froman Ferry (fig. 9C) bears little resemblance to Cope's Equus simplicidens (fig. 9D) from Blanco, 

Texas. Of the material from the Blanco fauna of Texas, only 

the type of Plesippus simplicidens is not greatly worn, and 

it has a Pliohippus-like short protocone on its occlusal surface at this early stage of wear, as does Equus idahoensis. 

This is quite different from the elongate protocone of littleworn Plesippus fromanius of the Froman Ferry faunal succession (fig. lOA) or P. shoshonensis from Hagerman (fig. 

1 OB and C), end members of the lineage present throughout 

the Glenns Ferry Formation. 

SUBGENERIC NOMENCLATURE 

As with the felids (and many other mammalian groups 

such as the micro tine rodents) the generic allocation of 

species of horses is unstable. There exist many concepts of 

the definition of a genus. We follow what seems to be current convention by considering many living taxa, initially 

considered as genera, to be subgenera of the genus Equus; 

however, we do not believe that this treatment should be 

carried back into fossil horses, as it tends to conceal 

biostratigraphic and phylogenetic significance. This is an 

approach similar to that taken with the cats (p. 20). But if 

the species Equus (Dolichohippus) simplicidens is recognized, why isn't the species Equus (Dinohippus) mexicanus 

recognized as well? 

The upper dentition is the most critical in consideration of these species, as the lower teeth maintain a more 

uniform Plesippus pattern, a feature that may have led Skinner to such extensive synonymy, thus minimizing the usefulness of Blancan and early Irvingtonian horses in 

biochronology. 

Although horse lower teeth are scarce in the Froman 

Ferry faunal succession, those that are known would indicate a biochronologic age spanning the Blancan United 

States mammal age and extending into the early 

Irvingtonian mammal age (4.8 to 1.5 Ma). The upper teeth, 
THE FROMAN FERRY FAUNA 45 

however, show a strong difference across the 400,000 years 

between the youngest horse whose age can be approximated at Jackass Butte (Plesippus stenonis anguinus) and 

the related horse in the Froman Ferry faunal succession 

(Plesippus fromanius); the upper teeth also seem most distinctive in comparing the Grand View P. stenonis anguinus 

to the Hagerman P. shoshonensis. It certainly is easier to 

use the lower teeth and call all Blancan horses "Equus 

(Dolichohippus) simplicidens," but it certainly is more 

informative to recognize the differences in the upper teeth 

of these horses and their biochronologic significance. 

We note that if the upper teeth of the horses are considered, the di~erence over the span of time between Jackass 

Butte and Froman Ferry is more conspicuous than the difference observed in the native microtine rodent fauna. The 

lower horse teeth, however, appear inseparable, with the 

present limited number of specimens from Froman Ferry. 

Except for the immigration of a new microtine lineage 

(Phenacomys), the apparent extinction of Procastoroides, 

and the differences in the upper teeth of Plesippus fromanius, the two faunas are essentially identical. 

According to Gazin (1936, p. 292), the horse from 

Hagerman, which Gidley (1930) named Plesippus 

shoshonensis, had many similarities to the living Grevy 

zebra, Equus (Dolichohippus) grevyi. (It is not indicated 

in Gazin's report whether other living zebras were available for comparison, but it can be so assumed, as he was 

working out of the National Museum of Natural History 

and also visited the American Museum of Natural History 

in New York.) He devoted about 18 pages to descriptive 

comparison of the Hagerman horse with the Grevy zebra 

and with domestic horse. 

This morphologic comparison does not indicate that 

Gazin thought the Hagerman horse was a zebra any more 

than it indicates that he thought it was a domestic horse. 

Classification is based upon the interpretation of evolutionary history, which, in tum, is based on both morphologic 

similarities and the temporal and geographic distribution 

of these similarities. The temporal record of these morphologically similar forms indicates that Equus (Dolichohippus) grevyi evolved out of African Equus stenonis, which, 

in tum, had evolved out of North American Plesippus 

shoshonensis. These taxa lived during a sufficiently brief 

span of time that their morphologic similarity is great, 

and careful morphologic, temporal, and geographic consideration is needed to distinguish their fossil forms. The 

fauna of the world is not everywhere the same at any single instant, and the differences are what are important to 

interpretation. What both McGrew (1944) and Skinner (in 

Skinner and others, 1972) did was to rely entirely upon 

morphology, and in doing so they failed to note morphologic differences that are in agreement with, and made 

apparent by, the temporal and geographic record. 

Matthew ( 1924) had introduced the generic name 

Plesippus for North American (geography) forms that 

appeared to be intermediate between the late Miocene 

(time) horse Dinohippus (included in Pliohippus before 

Quinn, 1955) and Pleistocene (time) Equus. Gazin (1936) 

followed Gidley (1930) and assigned the Hagerman horse 

to Matthew's extinct genus. That the Plesippus grade in 

horse evolution is little modified in the modem (time) 

zebra is coincidental; modem zebras certainly are not 

ancestral to modem Equus, and yet classification is supposed to reflect evolution. 

The difference in approach is the difference between 

basing taxonomy upon evolutionary history and basing it 

on morphologic similarity. However, McGrew and Skinner misunderstood this point and said that Plesippus was 

a zebra because it was so morphologically similar (in 

their comparison) to the living forms. They compared the 

3-million-year-old North American fossils with the living 

African Grevy zebra, but did not look for differences that 

this amount of time and geography might have produced. 

Skinner, citing Heller (1912), stated that the correct 

generic (in original usage) assignment of Blancan plesippine horses was Dolichohippus, but otherwise was following McGrew's thinking. Skinner also used the zebrine 

genus as a subgenus following the International Commission on Zoological Nomenclature (mentioned on p; 36), 

and he recognized only one North American species, 

Equus (Dolichohippus) simplicidens (Cope), the type of 

Matthew's genus Plesippus. Although using Cope's name 

for a horse from Texas, Skinner described E. (Dolichohippus) simplicidens from Gazin's specimens of Plesippus 

shoshonensis from Hagerman, not from the type material, 

which was hardly mentioned in his report. Since then, 

Matthew's genus Plesippus has dropped from usage, its 

nature as an intermediate form between the. late Miocene 

Dinohippus and the Pleistocene and modem horses 

(Matthew might have added "and zebras") has been 

ignored, and the similarity of Plesippus to the modem 

Grevy zebra has been emphasized. Dolichohippus, usually 

as a subgenus of Equus, has become the standard usage in 

North America, yet Dolichohippus evolved in Africa out 

of Equus stenonis, which evolved in North America out 

of Plesippus shoshonensis. Historically, Skinner's nomenclature is difficult to describe; it places extinct horses 

around the world in a living genus and subgenus. 

Skinner's (in Skinner and others, 1972, p. 118) morphologic discussion in defense of his use of the subgenus 

Dolichohippus in North America, in preference to Plesippus, consisted of five paragraphs (in comparison with 

Gazin's 18 pages of comparison with Dolichohippus), and 

stressed its similarity with the living African species E. (D.) 

grevyi, with little comparison to any other horse, although 

he asserted that he had compared the fossil material to 

many species. His discussion completely ignored 

Matthew's concept of Plesippus as an intermediate between 

Dinohippus and modem horses (it has never been suggested 
46 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

that the Grevy zebra evolved out of Dinohippus and into 

domestic horse). And the morphologic similarity is not 

exact, as pointed out by Bennett (1980) and Azzaroli and 

Voorhies (1993). Most of Skinner's consideration was 

directed to the structure of the lower teeth, yet no discussion 

of the lower teeth of topotypic material of Cope's Pliohippus simplicidens from Blanco, Texas, was given. Skinner 

illustrated only lower dentitions from Nebraska and Idaho, 

with no defense of identification. As has been mentioned, 

lower teeth of Dolichohippus (Matthew's Plesippus) differ 

little throughout the Blancan United States mammal age, 

and the result has been that very little horse evolution has 

been recognized. 

Not surprisingly, because of his strictly anatomical 

evaluation, Skinner also made no effort to explain any historical evidence that would suggest that the North American 

form dispersed to Africa to become the living species. Most 

disturbing, he made no mention of Equus stenonis, the thenwell-known fossil plesippine of Asia, Europe, and North 

Africa. Equus stenonis has been favorably compared with 

both the living zebras and with North American horses at 

least since Lydekker (1887) and Boule (1899). 

According to Churcher and Richardson ( 1978) the 

oldest African records of living Dolichohippus equate 

with the time between the youngest part of Jackass Butte 

and the Froman Ferry faunal succession (Ethiopia: 

Shungura members G-J; Tanzania: Olduvai Beds I-IV). 

Azzaroli and Voorhies (1993, p. 185) added additional 

data about the earliest records of Equus stenonis in Asia, 

Europe, and Africa, and noted that the living Grevy zebra 

"has progressed very little beyond the evolutionary stage 

of these [fossil] species; it is however apomorphic in its 

widely open facial angle and, to a lesser degree, in its dentition." 

Bennett ( 1980) undertook an analysis of late Cenozoic 

and modem equids and came up with perhaps the most reasonable (at that time) hypothesis of their evolutionary history. Her discussion sparkled with logic, and her characters, 

several new to the literature, were interesting. Her cladistic 

analysis led to a phylogenetic diagram (her fig. 6) that has 

some very sensible aspects, which have not been sufficiently considered in some American literature (for example, that E. grevyi derives from European [or African] E. 

stenonis, rather than from the very similar North American 

"E. simplicidens"). In general, Bennett ( 1980) presented the 

same interpretations as Azzaroli and Voorhies (1993 ), but 

lacked as detailed a history of the lineage in Eurasia. 

Regrettably, the completion of her study, mentioned in her 

publication, has never been published. 

Skinner's use of the African subgenus Dolichohippus 

in North America, as a replacement for Matthew's Plesippus, was based upon similarities in dental and cranial morphology which later authors (and earlier, as Gazin, 1936) 

have limited. The similarities are not complete: North 

American Plesippus is more primitive than African Dolichohippus in having a less open facial angle and much 

greater buccal curvature of the upper teeth; in addition the 

Glenns Ferry lineage, Plesippus shoshonensis > P. stenonis anguinus > P. fromanius, has more elongate protocones on their upper teeth in at least early stages of wear. 

We elect to restore Matthew's intermediate genus, Plesippus, in North America and to restrict Dolichohippus to 

Africa, following Gazin (1936) and Bennett (1980), and 

reversing Skinner (in Skinner and others, 1972) and 

McGrew (1944). 

PHYLOGENETIC SUMMARY 

Although specific assignment is a matter of opinion, 

there appears at present to be no great similarity, within 

Plesippus, between Cope's (1892) Plesippus simplicidens 

of Lubbock, Texas, and Gidley's (1930) Plesippus 

shoshonensis of Hagerman, Idaho, an appearance strengthened by Skinner's omission of an explanation when he 

placed them in synonymy. Thus, reinstatement of the 

Hagerman species appears reasonable to us on the basis 

of available information. 

Figure 9D shows Plesippus simplicidens to be a more 

primitive taxon than Plesippus shoshonensis (fig. lOB and 

C) by virtue of its short (Dinohippus-like) protocone in 

little-worn teeth, lack or weak development of a lingual 

protoconal gutter, lack of a tapering protocone, and, possibly, greater crown curvature. 

Merriam's Plesippus idahoensis (fig. 9A, B, and C) is 

more advanced toward modem horses than P. simplicidens 

in less crown curvature, presumably persistent lingual protoconal groove, heavy cementum, and larger size. Plesippus 

shoshonensis from Hagerman, P. stenonis anguinus from 

Jackass Butte, and Plesippus fromanius from Froman Ferry 

have tapering protocones, which are more elongate, at least 

with little wear, than P. simplicidens; in the youngest species (from Froman Ferry) they approach Equus scotti of the 

Irvingtonian faunas of the United States. 

From the material now available, there appears to 

have been a new horse lineage (Plesippus idahoensis) 

introduced to the western Snake River Plain during the 

Blancan V United States mammal age; the lineage 

remained present during at least the earliest Irvingtonian I 

part of the Froman Ferry faunal succession, but no recognized record of this lineage appears in the Glenns Ferry 

faunas earlier than about 2.3 million years ago. 

At the same time that the Plesippus idahoensis lineage appeared in the Snake River Plain, during the Blancan V mammal age, the Glenns Ferry native horse lineage 

dispersed to Eurasia as Plesippus stenonis anguinus (at 

which time it must assume the generic assignment of 

Equus to conform to Eurasian usage), and shortly thereafter to Africa, where it evolved into the living Grevy zebra, 
HISTORIC SETTING OF THE FROMAN FERRY FAUNAL SUCCESSION 47 

Equus (Dolichohippus) grevyi. In North America, however, the nondispersing branch of the lineage evolved in 

the direction of species that have been placed in Equus 

and by the end of the deposition of the Glenns Ferry Formation (> 1.5 Ma) had come close to resembling later 

Pleistocene Equus scotti, as shown by Plesippus fromanius from the Froman Ferry faunal succession. In addition 

to the Froman Ferry record, this latest Blancan and earliest Irvingtonian transition from Plesippus into Equus is 

also recorded in the Red Light-Hudspeth faunas of westem Texas (Akersten, 1972; Strain, 1966), the lower horizon of Rock Creek, Texas, and the Aries fauna of 

southwestern Kansas (J.G. Honey and G.A. Izett, oral 

commun., 1994). 

As the fossil record indicates (Churcher and Richardson, 1978; Azzaroli and Voorhies, 1993), living Equus 

(Dolichohippus) grevyi evolved out of Equus stenonis in 

Africa about the same time that Plesippus stenonis anguinus evolved into P. fromanius in the Glenns Ferry Formation. Phylogenetic history might be better illustrated by 

the name Plesippus stenonis in Eurasia (rather than Equus 

stenonis), which would clearly indicate that it was an 

immigrant from North America, rather than from Africa. 

Order ARTIODACTYLA Owen, 1848 

Family CAMELIDAE Gray, 1921 

Subfamily CAMELINAE Zittle, 1893 

Genus GIGANTOCAMELUS Barbour and Schultz, 1939 

GIGANTOCAMELUS SPATULUS (Cope), 1893 

Localities and material.-CUCUMBER AREA: GS234 (2,770 ft elev.): lateral condyle of the distal articulation 

of a radius-ulna, complete unciform. GS-227 (2,750 ft 

elev.): proximal phalanx. 

Two localities: 2,750 to 2,770 feet elevation. 

Discussion.-These few remains of the giant camel are 

much larger (and stouter) than comparable elements of other 

genera, as Camelops, and the proximal suspensory ligament 

scars on the posterior side of the proximal phalanx are W 

shaped and identical to those of Gigantocamelus spatulus 

(Cope) (Voorhies and Comer, 1986, fig. 5A). This appears 

to be the first Irvingtonian record of this typically Blancan 

species; it is earliest Irvingtonian and clearly higher in the 

section than the first record of Phenacomys, marking the 

first of the Irvingtonian mammal age in the Pacific Faunal 

Region of the United States. 

Skeletal elements and teeth fragments of smaller camels have been found throughout the Froman Ferry faunal 

sequence, including unpublished material in the UCMP collected by Merriam. These are not identifiable. 

Family CERVIDAE Gray, 1821 

Unidentified cervid postcranial elements, largely phalanges, have been found from the lowest to the highest part 

of the Froman Ferry faunal succession. The size range 

varies from that of small elk to deer, but no effort has been 

made to improve this identification. One medial phalanx of 

near elk size was in Merriam's collection in UCMP, number 

113695. 

HISTORIC SETTING OF THE FROMAN 

FERRY FAUNAL SUCCESSION 

The marsh beds containing the Froman Ferry faunal 

succession are the final known depositional record of the 

2.5-million-year history of the Glenns Ferry Formation (and 

lake) of the western Snake River Plain. To the east of the 

Froman Ferry area, near the then-existing (to be discussed) 

Snake River, lake, marsh, and fluvial deposition may have 

continued while erosion in the Froman Ferry area and the 

volcanic eruption of Pickles Butte took place, but this has 

not been confirmed. 

The Froman Ferry marsh beds were not the first to 

form in the Glenns Ferry Formation as the lake withdrew. 

Repeatedly, throughout the history of deposition of the formation, marsh or stream deposits covered the lake beds as 

the lake withdrew from particular areas, and the marsh beds 

of the Froman Ferry area are only the most recent example. 

To explain the historic setting of the Froman Ferry faunal 

succession, it is necessary to record the 2.5-million-year 

history of deposition of the formation, of which the Froman 

Ferry fauna is only the final example. Also needed is some 

discussion of areas beyond the western Snake River Plain 

and events that preceded the deposition of the Glenns Ferry 

Formation in explanation of the origin and the end of the 

Glenns Ferry lake. 

This discussion is compli~ated by many published 

interpretations of this history that must be considered in 

evaluating the most probable history of the Glenns Ferry 

lake and contiguous areas of deposition. Most critical to 

interpretation is the age of the youngest deposits of the 

Glenns Ferry lake; the age of these is not known but only 

suspected as being immediately older than the Froman 

Ferry faunal succession. The relationship of the Glenns 

Ferry Formation to the ancient Snake River, which has a 

prior history of major changes in its route, is also important 

in understanding the depositional history of the formation. 

These records are part of the consideration of history that 

the Froman Ferry faunal succession terminates. 

YOUNGEST GLENNS FERRY LAKE BEDS 

No evidence exists that lake deposition persisted later 

than about 2.1 million years ago-the approximate youngest known age of the "typical" Glenns Ferry lacustrine diatom flora with age control (Multi-ash paleomagnetic section 

south of Oreana; Neville, 1981; paleomagnetic correlation 

revised). In a test hole drilled near the town of Bruneau 
42°45' 

~11\,__ I <'t.jlf'~:~ ~,~f'L / L Smker :i"J.\ 

Murphy~~r e I Butte 'l~J --·,:_~-- ~- ? r~·~-) 

-. ---c:1-ee\<-'-~~( \ \ I 

o.bb\t lr' \\ 

~ 

c;'el' '{ ' 

/-r::~0 .- 'e,_ 

c-. rL~ 

20 s_--~~0 ' ~~\ 

-cj Oreana 'Q}' ' ,-,'. ' ' Q.i 0 )-!' _,1:,,/' v' 0 ~ ( '~'j I 00 /'- ,sMulti-ash: ~Q.I (j\ , ,, , ":> - I 

'l\(~ 'c.f' ~~(}' 

ft.. 

)-

~ 

~ 

~ 

,, I·~ 

~ p 

EXPLANATION 

Fossil localities 

Marsh deposits and faunas 

Paleomagnetic section 

o: 

(/I 

~ ,>-

--<? 

/ 

/f, 

~ 

EAST 

~ Mountain Home 

5 10 15MILES I I I 

_-

1

3ooo\ 

~:¢. . B Flat1ron utte 

-¢- Bruneau core 

B ~ 'j """ e runea_u _ ) '>,· ~, ~ \ r·-- 1 cJ [1 ,1_ 

~ , ( lr-j ll.) "? ' I 

~9 I 

~~~~ ) 

/6 \ I I 

~.... (/~ 

1)\ Chalk Hills 

..j:::., 

00 

~ 0 

~ 

> z 

tB 

:::0 

;;o 

>-< 

'Tl 

> 

~ > 

> 

~ a 

r 

~ C/.l 

tB 

;;o 

;;o 

>-< 

25 

;;o 

~ 

> ...., 

0 

~ 

C/.l 

0 

Si 

C/.l 

~ @ 

~ 

s 

> 

::c: 

0 
HISTORIC SETTING OF THE FROMAN FERRY FAUNAL SUCCESSION 49 

(Thompson, 1992), the youngest Glenns Ferry lake beds are 

about 2.5 million years old, based upon their normal magnetic polarity and the assumption that the time of their 

replacement by fluvial deposits in the Bruneau core was 

about the same throughout the Bruneau area. The closeness 

to Bruneau of the 2.4-million-year-old Poison Creek marsh 

beds (to be discussed; fig. 12) indicates that if this assumption is in error, it cannot be greatly so. In addition, the earliest Grand View (Blancan V) Ninefoot Rapids fauna is even 

closer to the core site (fig. 12) and believed to be slightly 

older than the Poison Creek marsh beds; it is nonlacustrine 

and about 2.56 million years old (p. 59). Hypothetically, 

because the area of the Bruneau core is a short distance 

upstream from these and the filling of the basin of the Snake 

River Plain was in a downstream direction (as will be discussed), the initiation of fluvial deposition in the Bruneau 

core should be slightly older than the Ninefoot Rapids 

fauna. The youngest paleomagnetic sample from the lake 

beds in the core is normally polarized, indicating that it is 

older than the termination of the Gauss Chron (2.48 Ma). 

The late Blancan IV Flatiron Butte fauna is upstream from 

the Bruneau core a distance somewhat less than the Ninefoot Rapids fauna is downstream (fig. 12), and indicates that 

fluvial deposition began before 2.56 million years ago at 

this position in the Snake River Plain, as the section is all 

normally polarized (Neville, 1981) but does not contain the 

immigrant microtine Mictomys. 

The youngest known Glenns Ferry lake diatoms in the 

Grand View area are in a paleomagnetic section termed 

"Multi-ash" (Neville, 1981, p. 119) about 3 miles south of 

Oreana (fig. 12). This polarity section is the only one in the 

Glenns Ferry Formation in which the original polarity 

assignment is changed due to later information, as mentioned on page 8. The Multi-ash polarity section has the top 

of the Gauss Chron at least 59 feet above its base; above the 

Gauss is a long sequence (perhaps 132 feet) of reversely 

polarized lacustrine deposits of the Glenns Ferry lake, 

obviously representing the early part of the Matuyama 

Chron; the "typical" Glenns Ferry lacustrine diatom flora 

(p. 58) is present to the top of the section (J.P. Bradbury 

locality 13 IX 89-5A), and is unconformably overlain by 

fluvial deposits presumably of the Bruneau Formation (H.E. 

Figure 12 (facing page). Snake River area between Sand Point 

and Walters Ferry, Idaho, showing some localities mentioned in the 

text, and fossil localities. Marsh beds of the Birch Creek and Poison 

Creek-Shoofly Creek areas are patterned; 3,000 foot contour shown 

to suggest relief. A generalized west to east section of the Glenns 

Ferry Formation in the central Snake River Plain, through Birch 

Creek, Jackass Butte, Chattin Hill, and Mountain Home, is shown 

inset at the upper right. Horizontal scales are different and the cross 

section has great vertical exaggeration. In the section dashed lines 

approximate the position of known or inferred faults; barb, direction 

of relative movement. 

Malde, oral commun., 1979). These overlying deposits also 

contain some lake beds that have the typical Bruneau diatom flora (J.P. Bradbury, oral commun., 1992). 

According to Neville (1981), the Multi-ash section is 

close above the locally oolitic rusty sand unit that is found 

beneath the Glenns Ferry Formation along the southwest 

side of the Snake River Plain. This unit had been included 

in the Glenns Ferry Formation, as the basal unit, and its 

presence shortly below the Multi-ash section led Neville 

( 1981, p. 141) to assume that the lake beds in the Oreana 

area were the oldest part of the Glenns Ferry Formation. 

Her assumption was strongly supported (Neville, 1981, p. 

141) by the local occurrence of the primitive rabbit Hypo/agus vetus (later renamed H. gidleyi White, 1987). Although 

not clearly correlated to the Multi-ash section, the presence 

of this rabbit suggested, in 1981's state of knowledge, that 

the deposits of the Oreana area were rather old. Neville and 

associates were not aware that ( 1) the locally oolitic rusty 

sand unit lay unconformably beneath the Glenns Ferry lake 

beds (and thus had little bearing on the age of the lake 

beds); (2) the lake beds were transgressive against the 

underlying rocks (oolitic unit) toward the southwest side of 

the Snake River Plain (thus the oldest parts of the Glenns 

Ferry Formation were increasingly younger in this direction); (3) the rabbit Hypolagus gidleyi would be found high 

in the Froman Ferry faunal succession in post-Blancan 

deposits little more than 1.5 million years old (p. 25); (4) 

fossils in the vicinity of the Multi-ash section (the Birch 

Creek fauna, less than 5 miles to the southeast across almost 

continuous exposures) dated the lake beds as being the 

youngest so far discussed in the Glenns Ferry Formation (p. 

61); and ( 5) the lacustrine diatoms at the base of the Hagerman section and associated with the Cochiti Normal-polarity Subchron (the obvious youngest possible correlation of 

the normal polarity at the base of the Multi-ash section in 

her thinking) were distinctly different ("oldest" diatom 

flora; p. 56, 58) than the diatom flora in the lake beds of the 

Multi-ash paleomagnetic section ("typical" and youngest 

diatom flora; p. 58). 

These more recently learned facts completely invalidate Neville's reasoning for the correlation of the magnetic 

events in the Multi-ash polarity section and indicate that the 

polarity pattern can only be that of the top of the Gauss 

Chron overlain by a good thickness of reversed deposits of 

the early Matuyama Chron. She did not detect any brief 

normal events that would represent the Reunion Subchron, 

and thus the section seems to be older than 2.14 million 

years. The possibility is good, however, that her sampling 

missed these brief events, as 30-40 feet separate the two 

highest paleomagnetic samples of the Multi-ash section; the 

absence of the Reunion events cannot be positively 

demonstrated. Based upon relative thicknesses, and the 

assumption that the rate of deposition of lake beds at the 

Multi-ash section was about the same as nonlacustrine 
50 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

deposition at Jackass Butte, the upper, reversely polarized, 

lake beds of the Multi-ash section would seem not young 

enough to contain a record of the Reunion events, although 

almost so. The rise in lake level that brought marsh deposition into the middle of the Jackass Butte section (shortly 

before the earlier Reunion event; p. 60) may correlate with 

part of the lacustrine deposition in the upper part of the 

Multi-ash section. 

Probably the first published recognition of the unconformity between the oolitic unit and the Glenns Ferry lake 

beds was the map of Owyhee County by Ekren and others 

(1981), which shows the oolitic unit dipping basinward 

more steeply than the modem drainages whereas the overlying Glenns Ferry lake beds (not separated from the Glenns 

Ferry marsh and fluvial deposits on their map) dipped basinward at a flatter gradient than the modem drainages. In 

every major drainage from Shoofly Creek northwest nearly 

to Murphy, this relationship was mapped, and the relationship continues northward to the Marsing area-although 

Ekren and others changed their mapping detail at about the 

position of Murphy and ceased recording this contact. Thus 

this structural implication is present along the southwest 

margin of the Snake River Plain for a distance of more than 

70 miles. 

This relationship between the oolitic unit and the 

Glenns Ferry lake beds, in combination with our own observations that the lake bed units gradually lap out against the 

top of the oolitic unit toward the southwest margin of the 

Snake River Plain, forms the major reason for removing the 

oolitic unit from the Glenns Ferry Formation (p. 54). 

Neville (1981, p. 141) was following Malde and Powers (1962) in considering the oolite to be the basal unit of 

the Glenns Ferry Formation. The 2.4-million-year-old fauna 

from Birch Creek, about 5 miles to the southeast of the 

Multi-ash section, was undiscovered when she worked in 

the area, and the fact that it lay directly on top of the oolitic 

unit in the upstream part of Birch Creek was not known. 

Her (Neville, 1981, p. 141) only basis for fossil control of 

the age of the lake beds was the occurrence of the extinct 

rabbit Hypolagus gidleyi (called H. vetus when Neville did 

her work) in the Oreana area to the north of the Multi-ash 

section, which then was thought to indicate an age older 

than the Jackass Butte fauna of the Grand View area, a 

belief shattered by its discovery high in the Froman Ferry 

fauna (p. 25-26). She therefore considered Glenns Ferry 

lake beds in the Multi-ash section to be the oldest part of the 

formation and suggested that the long reversed section correlated with the Gilbert Reversed-polarity Chron (Neville, 

1981' p. 121 ). 

The diatom flora in the lake beds of the Multi-ash 

polarity section indicates otherwise, however, as will be 

noted in discussing the diatom flora of the oldest known 

lake beds of the Glenns FetTy Formation at the base of the 

Hagerman section (p. 56). The diatoms associated with 

these oldest lake beds at Hagerman (and with the Gilbert 

Chron) are very unusual and do not resemble the "typical" 

diatom flora present in the Multi-ash area and in the bottom 

of Birch Creek, some 200 feet below the Birch Creek marsh 

beds (2.4 Ma) (J.P. Bradbury, oral commun., 1993). These 

lake beds all pinch out against the oolitic unit upstream 

from this point, leaving the 2.4-million-year-old marsh beds 

lying directly on top of the oolitic unit in both Birch Creek 

and Shoofly Creek. 

In fact, the ash beds, which are the source of the name 

of the "Multi-ash section," occur in the middle of the polarity section about 10-20 feet above the most probable position of the top of the Gauss Chron (Neville, 1981, fig. 5.5) 

and are the lacustrine equivalent of the ash beds found in 

the Birch Creek marsh deposits containing the Birch Creek 

fauna a short distance to the southeast; the Birch Creek 

fauna is a Blancan V fauna and is younger than 2.56 million 

years. From the position of the ash beds in the Multi-ash 

section above the top of the normal magnetozone, these ash 

beds are estimated as being 2.4 million years old, the Gauss 

Chron ending 2.48 million years ago. This age is, accordingly, also that of the ash beds in the Birch Creek marsh 

beds and of the fauna, 5 miles to the southeast. 

We therefore revise Neville's identification of the 

polarity chrons by virtue of evidence unavailable to her: the 

normal magnetozone at the base of the Multi-ash section is 

the younger part of the Gauss Chron, and the overlying long 

section of reversely polarized lake beds (with a "typical" 

diatom flora to its very top) represents the early part of the 

Matuyama Chron. With the possible exception of the lake 

beds of unknown age underlying the Froman Ferry faunal 

succession, the Glenns Ferry lake beds in the Multi-ash 

(Oreana) area are the youngest known, rather than the oldest, as suggested by Neville ( 1981 ). The biochronologic 

suggestion of the age of the Multi-ash section (Neville, 

1981, p. 141; also Conrad, 1980, p. 1 09) does not contradict 

this correlation because of more recently gained information about Hypolagus gidleyi from the Froman Ferry fauna. 

The diatoms in the lake beds of the Multi-ash polarity 

section, and the age of the ashes where present in the Birch 

Creek fauna, do contradict an age as old as the Gilbert 

Chron. 

CORRELATION OF YOUNGEST LAKE BEDS 

About 4.3 miles to the southeast of the Multi-ash 

paleomagnetic section, on the divide between Birch Creek 

and Castle Creek, the marsh beds of Birch Creek (about 

2.4 Ma old and correlative to those of Poison Creek 10 to 

15 miles farther to the southeast, as will be discussed on 

p. 62) grade to the northwest into the Glenns Ferry lake 

beds (fig. 12). Their horizon is not recognizable in the 

lake beds of the Multi-ash section except as a 
HISTORIC SETTING OF THE FROMAN FERRY FAUNAL SUCCESSION 51 

continuation of the associated ash beds for which the 

paleomagnetic section was named. Fine-grained fluvial 

deposits above the marsh beds near Birch Creek overlie 

the lake beds beyond the limit of marsh deposits in the 

Castle Creek area, but 4 miles farther northwest, at the 

Multi-ash paleomagnetic section, 125 feet of lake beds 

separate the fluvial deposits from the ash beds that correlate with the Birch Creek marsh deposits. Fluvial deposits 

of either the Glenns Ferry Formation or the younger 

Bruneau Formation overlie the lake beds throughout the 

Oreana area to the north. 

The overlying 125 feet of lake beds in the reversely 

polarized part of the Multi-ash section can represent only 

the older part of the Matuyama Reversed-polarity Chron, 

and this correlation strongly suggests that the younger parts 

of the lake beds at the section are equivalent in age to part 

of the largely fluvial deposits of the Jackass Butte section 

of the Grand View area, estimated to be from about 2.3 to 

2.0 million years old. The normal events of the Reunion 

Subchron were not found in the Multi-ash section, however, 

and the youngest lake beds of the Multi-ash section may be 

younger, or older, than 2.14 million years. 

It is between 100 and 125 feet from the lowest fossils 

found at the base of Jackass Butte up to the first brief normal event of the Reunion (2.14-2.12 Ma). The end of the 

Gauss Chron, the multi-ashes, and a Birch-Creek-type 

fauna are not found at Jackass Butte, but 7.5 miles northwest of Jackass Butte, at an unnamed butte about a mile 

northwest of Wild Horse Butte, the end of the Gauss Chron 

was found about halfway up the section of sediments (Neville, 1981, p. 137-138; this report, p. 63). In 1979 G.S. 

Conrad (oral commun.) had found Mictomys vetus, 

Mimomys parvus, and Ondatra sp. at this section; the 

Ondatra is small, suggesting the Birch Creek fauna. The 

highest normal polarity of the Gauss Chron on this 

unnamed butte is at about the same elevation as the oldest 

of the Reunion events on Jackass Butte; obviously the two 

localities are separated by structure. Note. however. that the 

same time span as the Multi-ash polarity section, but no 

lacustrine deposits, occurs at "unnamed butte" (p. 63); the 

Glenns Ferry lake lay entirely west of this area during the 

time of Blancan V faunas. 

A striking difference between the diatom flora of the 

Glenns Ferry lake and those of the lakes in which the 

Bruneau Formation was deposited is seen at the top of the 

Multi-ash polarity section, as well as at many other locations, and suggests that deposition of the Glenns Ferry lake 

had ended, in this area, well before the Pleistocene Bruneau 

beds were deposited. This is easily believed in most areas, 

where the youngest Glenns Ferry lake beds are of Pliocene 

age and the disconformably overlying Bruneau lake beds 

are of Pleistocene age. Whether this change in diatom flora 

is an ecologic or a time signal, or a combination of the two, 

is not known. 

The youngest dated diatom floras of the Glenns Ferry 

lake beds are in the Multi-ash section and may or may not 

be as young as 2.14 million years; the lake beds beneath the 

Froman Ferry marsh beds contain the same "typical'' diatom flora and could be this old or as young as the Olduvai 

Normal-polarity Subchron (<1.67 million years), to judge 

from the age of the overlying Froman Ferry faunal succession. As much as 4 70,000+ years may separate these two 

time possibilities. 

The diatom flora of the Bruneau Formation at Guffey 

Butte is like that of the formation elsewhere, and like that of 

modern lakes in the Pacific Northwest (J.P. Bradbury, oral 

commun., 1994); and it lived at the time that the Pickles 

Butte lava dammed the Snake River ( 1.5 Ma) to form this 

Bruneau lake. The Bruneau diatom flora is thus little more 

than 170,000 years younger than the youngest possible age 

of the Glenns Ferry lake beds in the Froman Ferry area 

south of Marsing; it is little more than 640,000 years 

younger than the youngest age of the Glenns Ferry lake 

beds in the Multi-ash polarity section. Evolution of the Bruneau type of diatom flora in either time span seems out of 

the question as this extant flora has lived 1.5 million years 

without change since it existed at Guffey Butte and the 

"typical" Glenns Ferry lake diatom flora existed at least 

1.36 million years before its youngest record in the Multiash section-both without significant change. It must be 

assumed that the Bruneau type of diatom flora existed elsewhere contemporaneous with the "typical" flora of the 

Glenns Ferry lake. Adam and others ( 1990) have reported 

the same diatom floral change, from a "typical" Glenns 

Ferry flora to a modern Bruneau-like flora in the Tule Lake 

basin of northern California nearly 3 million years ago. 

Apparently the "Bruneau-like'' diatom flora has 

existed with little change for at least the past 3 million 

years; its entry into the Snake River Plain marks only the 

end of a long stable Glenns Ferry lake environment and the 

beginning of a period of short-lived Bruneau lake basins. In 

contrast, the "typical" Glenns Ferry lake diatom flora may 

have lived with no change for about 2 million years, but in a 

single Glenns Ferry lake without interruption and with no 

basin dislocation (although there was some basin shifting 

without breaking the continuity of the lake). It seems more 

probable that the continued existence of the Glenns Ferry 

lake was the primary cause for the continued existence of 

the "typical" Glenns Ferry diatom flora, and that its presence in the lake beds beneath the Froman Ferry faunal succession has no bearing on the age of the lake deposits, only 

on the continuing presence of the lake until the time that the 

Froman Ferry marsh beds covered the area. Apparently the 

"typical" diatom flora of the Glenns Ferry lake was, at least 

in the later history of the lake, a relict flora that survived 

only because the Glenns Ferry lake persisted, and could not 

survive the disappearance of this lake. It was replaced, in 

later, short-lived lakes, by the Bruneau Formation type of 
52 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

diatom flora that can survive in relatively temporary lakes 

and that lives in such lakes today. 

Although the presence of the "typical" Glenns Ferry 

lake diatom flora in the lake beds beneath the Froman Ferry 

faunal succession suggests that these lake beds can be no 

younger than their youngest dated record in the Multi-ash 

polarity section, its age significance is unclear. The alternate assumption, that no hiatus exists between the Froman 

Ferry marsh beds and the underlying lake beds of the 

Glenns Ferry Formation, is based upon four separate 

considerations: 

1. The essential continuity of deposition between 

lake beds and overlying marsh beds at earlier times in the 

history of the Glenns Ferry lake makes a similar history 

seem more likely in the Froman Ferry area. 

2. The contrast between the cool, cloudy and wet 

summers indicated by the Froman Ferry fauna (p. 29, 

32-33) and the sage-steppe pollen flora of the Bruneau Formation (p. 15) does not favor contemporaneity-the immigrant Phenacomys gryci and the endemic Mictomys vetus 

suggest a climate other than the dry, moderately hot summers of a sage-steppe, implied by the pollen known from 

the Bruneau Formation. But no climatically informative 

fossil mammals have been found in the Bruneau. 

3. It is difficult to model a situation in which the 

Glenns Ferry lake could disappear for 470,000 years with 

no record of desiccation, erosion, or subsequent marsh or 

fluvial deposition, and then be covered by marsh deposition. When the lake finally disappeared, it seems to have 

done so because a sufficient drain had been cut; but it was 

not at first cut so deeply that marsh beds could not form for 

perhaps another 100,000 years in the Froman Ferry area. 

4. Although the youngest dated record of the 

"typical" Glenns Ferry diatom flora is about 2.14 million 

years, its survival, at the scale of time here discussed, 

seems not to depend so much on time as on constancy of 

its habitat. The distinctly different Bruneau diatom flora 

appears to overlap in time the "typical" Glenns Ferry 

flora in records outside the Snake River Plain, and it 

appears too quickly after the draining of the Glenns Ferry 

lake to be a result of evolving lake diatom floras. 

SNAKE RIVER AND THE GLENNS FERRY 

FORMATION 

The history of the Glenns Ferry lake began about 4.0 

million years ago with the diversion of the Snake River, 

most likely near Twin Falls, Idaho, into the rift valley that 

now contains the western Snake River Plain. It ended, as 

we assume the age of the youngest lake beds, about 1.67 

million years ago when deepening of Hells Canyon had 

become great enough to drain the last of the lake. The 

Froman Ferry marshes then formed on top of these lake 

beds until they too were drained. This interpretation 

involves much other evidence within and beyond the western Snake River Plain, and a synthesis of the history of 

the Glenns Ferry lake will put the Froman Ferry faunal 

succession into this historical scenario. This synthesis contains new information. 

The boundaries of the State of Idaho appear to have 

been drawn to include as much of the Snake River as possible (fig. 1 ). Beginning at the Continental Divide in the 

Centennial Mountains at the northeast comer of southern 

Idaho, and in Yellowstone Park in adjacent northwest 

Wyoming, the Snake River drainage area incorporates all 

Pacific drainage until, two-thirds of the way down the 

Idaho-Wyoming border, the river and its drainage basin 

pass entirely into Idaho. South of this point westward 

drainage from the Continental Divide flows into the Great 

Salt Lake basin, and, farther south, into the Colorado 

River. 

The Idaho and Wyoming headwaters of the Snake 

River join upstream from the city of Idaho Falls, still in 

the northeast quarter of the southern part of the State (fig. 

1 ). The combined headwaters flow southwest from there 

through the eastern Snake River Plain to Twin Falls. Here, 

marching to a different drum, the Snake River abruptly 

turns about 90° and flows northwest, down the graben 

now filled by the western Snake River Plain, past the Froman Ferry area, and to the Idaho-Oregon State line west 

of Boise (fig. 1). 

At the Oregon State line, the river turns again and 

flows north for about 200 miles, the longest northward 

course of any river in the United States. Along this northward route the Snake River first forms the Idaho-Oregon 

State boundary, and then the Idaho-Washington boundary. 

It turns west at Lewiston, Idaho, to join the Columbia 

River at Pasco, Washington (figs. 1 and 13). At the point 

where the Snake River leaves Idaho, it is 320 miles north 

of its most southerly point, near Twin Falls, and nearly 

160 miles north of its headwaters in Yellowstone Park. 

Over most of its course along the Idaho-Oregon 

State line, the Snake River flows through Hells Canyon, 

up to 1.5 miles deep (half again deeper than the Grand 

Canyon of Arizona). Hells Canyon cuts through the highland between the Salmon River Mountains of central 

Idaho and the Wallowa Mountains of northeastern Oregon 

(fig. 13). The Glenns Ferry Formation of the western 

Snake River Plain laps against these highlands, and its 

deposition was halted when Hells Canyon was cut to a 

level below the base level of the western Snake River 

Plain, beginning erosion of the Glenns Ferry Formation at 

its northwestern limit of deposition, the Froman Ferry 

area, and ending its deposition. 
HISTORIC SETTING OF THE FROMAN FERRY FAUNAL SUCCESSION 53 

GLENNS FERRY FORMATION 

The Glenns Ferry Formation was named by Malde and 

Powers (1962), and was at first thought to have formed in a 

large lake filling the entire basin of the western Snake River 

Plain. Earlier, Cope ( 1883) had called the lake Lake Idaho, 

and the deposits that formed in it the Idaho Formation. As 

originally conceived by Cope, Lake Idaho may have 

included more than just the lake in which the Glenns Ferry 

Formation was deposited, although he published no indication that he was aware of older lake beds. Although Cope 

was not specific about geographic extent, his information 

was based upon fossil fish collected at Castle Creek (fig. 13; 

Malde and Powers, 1962, p. 1201), 10 miles northwest of 

Grand View and unquestionably within the Glenns Ferry 

Formation, as used by Malde and Powers. 

Lindgren ( 1898) believed that Cope intended the 

names "Idaho formation" and "Lake Idaho" to apply essentially to the Pliocene deposits that Malde and Powers later 

called the Glenns Ferry Formation (and the Glenns Ferry 

lake). He therefore put older (Miocene) lake and stream 

deposits above the Columbia River Basalt Group and 

beneath what is now called the Glenns Ferry Formation in 

his Payette Formation. The Payette Formation is present 

within, and deformed with, the highlands of central Idaho. 

On the misconception that Lindgren's Payette Formation lay entirely within and beneath the Columbia River 

Basalt Group, Kirkham (1931) redefined Cope's Idaho Formation to include all deposits above the Columbia River 

Basalt Group, including, actually, both Cope's Idaho Formation and Lindgren's Payette Formation, although 

Kirkham thought that his usage separated the Idaho Formation from the Payette. Kirkham's error may have resulted, in 

part, from the erroneous correlation of some younger basalt 

units to the Columbia River Basalt Group, but he was primarily misled by earlier errors published by Buwalda 

(1923) who, in naming the Poison Creek Formation, stated 

that this formation contained Pliocene mammals (as they 

had come to be correlated by vertebrate paleontologists at 

this time) and overlay the "Payette" Formation of Miocene 

age (as originally and correctly dated by Lindgren). Earlier 

Miocene sediments are interbedded with the volcanic units 

of the Columbia River Basalt Group, but these are much 

older than what Lindgren called the Payette Formation. 

This statement of Buwalda's was based upon the thinking of Merriam (1917, p. 432) who stated that "The Idaho 

formation is not yet satisfactorily separated from the Payette Eocene or Miocene, and from a Miocene or Pliocene 

stage which may intervene between the Payette and the 

Idaho," a statement that clearly reflected the uncertainty of 

mammalian biochronology in the region of the western 

Snake River Plain at that time, as well as the chronostratigraphic significance of the few fossils known from these 

units. Actually, all fossil mammals that appear to have come 

from the Payette Formation, and those that clearly do, are 

late Miocene in age; the Payette Formation probably 

includes the Poison Creek fauna, in its older part, now 

known to be of early late Miocene age. These faunas contain mammals that were all called early Pliocene by vertebrate paleontologists up until about 1970, although 

paleobotanical records from the Payette were placed in the 

Miocene. 

Since about 1970, and certainly since Tedford and others (1987), these faunas have been recognized as being of 

late Miocene age; the recognition has been strongly reinforced by radiometric dates that became generally available 

in 1964 (Evernden and others, 1964 ). As the Miocene and 

Pliocene are now defined, the Payette Formation of 

Lindgren is of late Miocene age, older than the Pliocene 

Glenns Ferry Formation ofMalde and Powers (equals Idaho 

Formation of Cope) and much younger than the Columbia 

River Basalt Group of middle Miocene age. 

Malde and Powers (1962) were caught in the middle of 

this series of conflicting age claims and also thought that 

Cope applied his term (Idaho Formation) to more than the 

Glenns Ferry Formation, despite their statement that what 

Cope originally referred to was deposits from Castle Creek 

northwest of Grand View; and they thought that the Payette, 

because it was Miocene, must underlie the Pliocene Poison 

Creek deposits. They followed Kirkham ( 1931 ), Buwalda 

(1923 ), Merriam (1918), and Russell (1902), but not 

Lindgren (1898 and 1900), by including in Cope's Pliocene 

Idaho Formation the Miocene Chalk Hills and Poison Creek 

Formations-deposits that had been included in the concept 

of the Payette Formation by Lindgren. 

Malde and Powers (1962) elevated Cope's Idaho Formation to the Idaho Group, which included the Poison 

Creek and Chalk Hills Formations (±Payette Formation), 

the Glenns Ferry Formation (± the Idaho Formation), and 

the newly named units Tuana Gravel, Bruneau Formation, 

and Black Mesa Gravel. Thus defined, the Idaho Group 

spanned at least the upper Miocene, the Pliocene, and the 

lower Pleistocene. But, at the time that they did this, all of 

these units were called Pliocene by vertebrate paleontologists. The group also includes the Banbury Basalt (between 

the Poison Creek and the Chalk Hills Formations). 

As a result of this varied usage of geologic names, 

considerable confusion has developed about the stratigraphic contents of Lindgren's Payette Formation, and 

Cope's Idaho Formation. The name Glenns Ferry Formation 

has become firmly entrenched in usage as a replacement for 

Cope's Idaho Formation, but no suitable name is in general 

use that would replace the Payette Formation, and this name 

is seldom used in recent studies. The names "Poison Creek 

Formation," "Sucker (or Succor) Creek Formation," "Chalk 

Hills Formation" (equals the "Chalk Butte Formation" of 

Corcoran and others, 1962 and "Deer Butte Formation" of 

Kittleman and others, 1965), "Drip Spring Formation," and 
54 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

"Bully Creek Formation" have sprung up in the place of 

parts of the Payette Formation of Lindgren, but each has a 

different meaning not matching the Payette Formation as 

defined by Lindgren. New names are still being proposed 

(see Othberg and Stanford, 1992, under "Sand and mudstone of stream and lake sediments"). Of these many names, 

only the unit called Chalk Hills Formation is exposed in the 

Snake River Plain, and it underlies the Glenns Ferry 

Formation. The Poison Creek Formation is exposed in the 

margins of the mountains to the southwest of the Snake 

River Plain. There are complicating duplications in names: 

the Poison Creek fauna of the Glenns Ferry Formation is 

not related to the Poison Creek Formation, and the Chalk 

Hills faunas of the Froman Ferry area have nothing to do 

with the Chalk Hills Formation. "Chalk" and "Poison" 

seem to be common features of the western Snake River 

Plain. 

An intervening unit between the Glenns Ferry Formation and the underlying Chalk Hills Formation, a locally 

oolitic rusty sandstone, has been considered the basal unit 

of the Glenns Ferry Formation. (See p. 49 and following.) 

In terms of its relative thinness, different distribution, 

greater tectonic disturbance, and different lacustrine environment (Swirydczuk and others, 1979) than the Glenns 

Ferry Formation, this locally oolitic, rusty sand unit that 

Mal de and Powers ( 1962) considered the basal member of 

the Glenns Ferry Formation is here considered a separate 

and older depositional sequence unconformably underlying 

the Glenns Ferry Formation. It also is unconformable on the 

still older Chalk Hills Formation and has a different magnetic polarity (Conrad, 1980, p. 76-77; Swirydczuk and 

others, 1979), and thus appears to be equally distinct from 

this unit. Thus the locally oolitic, rusty-stained sandstone 

seems, to the authors, to deserve separate formational recognition. It is a very extensive unit, separating the Chalk 

Hills and Glenns Ferry Formations, for over 110 miles 

along the entire southwest side of the Snake River Plain 

from southwest of the town of Bruneau to the northern limit 

of Moores Hollow, north of Vale and Ontario, Oregon. 

The Chalk Hills Formation may be the lacustrine 

equivalent of the Payette Formation in the Moores Hollow 

area, an area that Lindgren included in the type definition 

of the Payette. Both formations are more severely deformed 

by tectonic activity than the Glenns Ferry Formation to the 

south. We are not aware of any published identification of 

exposures of the oolitic unit in the Moores Hollow area, 

although a rusty, coarse sand deposit, rich in fossil fish and 

exposed in a quarry west of Interstate 84 on the crest of the 

divide between Moores Hollow and Farewell Bend of the 

Snake River, appears to represent it. About 35 miles of little 

exposure or cover separates the Moores Hollow exposures 

from those of the Chalk Hills Formation and the overlying 

oolitic unit south of Marsing. Kimmel (1975) has 

described the fossil fish from these small exposures of the 

Chalk Hills (referred to the Deer Butte Formation) near 

Adrian, Oregon, and within this area of few exposures or 

cover. 

Malde and Powers identified as "floodplain" deposits 

many marsh deposits (flat-bedded, lighter colored silt containing prominent diatomaceous beds and some ash) and 

stream deposits (cross bedded, browner colored, fine to pebbly sand and conglomerate). These "floodplain" deposits 

overlie the Glenns Ferry lake beds, and Malde and Powers 

included them in the Glenns Ferry Formation. In these 

marsh and stream deposits, many fossil mammals have 

been found, and they form the principal basis for the age 

assignment of the formation. 

Although the three-dimensional, spatial relationships 

of lake and "floodplain" deposits have been difficult to recognize (Malde, 1972), a general picture has emerged that 

suggests that the Snake River Plain graben had ( 1) a deeper 

trench at the east end of the northeast side of the Snake 

River Plain (King Hill area) in which the lake first formed, 

followed by (2) progressive filling of the trench (by both 

sediment and lava) and displacement of the lake to the west 

across the Snake River basin; (3) deposition of younger lake 

beds against the basement rocks forming the west side of 

the Snake River Plain (the locally oolitic rusty sandstone 

beds overlying the Chalk Hills Formation), with (4) progressive filling, in a downstream direction, of the lacustrine 

basin to the west and northwest toward Hells Canyon; and 

(5) low-gradient stream sediments, brought into the graben 

by the Snake River and other drainages. These covered the 

lake and marsh beds as the lake basin filled. 

Marsh beds seem to have accumulated in areas with no 

great stream inflow, and some persisted for nearly 170,000 

years, as in the Froman Ferry area. All these depositional 

facies are included in the Glenns Ferry Formation. Marsh 

and fluvial deposition was followed by incision (by the 

Snake and other rivers) into the Glenns Ferry Formation. 

The entire sequence of deposition and erosion was a result 

of both filling of the structural basin and lowering of its 

base level at the outlet, Hells Canyon. 

With canyon cutting of the Glenns Ferry Formation, 

gravel deposits of higher gradient (or lower silt and sand 

load) streams, derived both from northeastern and southwestern sources, blanketed parts of the low-gradient stream 

deposits. This "higher gradient" stream action progressed 

northwestward down the length of the Snake River Plain as 

the lake withdrew in the same direction. The oldest covering gravels are in the southeast end of the western Snake 

River Plain, and Malde ( 1991) has followed ancient, filled 

canyons from the Hagerman area, which was the upstream 

limit of the lake about 3.9 million years ago, to Jackass 

Butte, near Grand View, which was near the upstream limit 

of the lake about 2.1 million years ago. He followed one 

canyon northward nearly to the Nampa area. Upstream 

from the Grand View area the covering gravels, as well as 
HISTORIC SETTING OF THE FROMAN FERRY FAUNAL SUCCESSION 55 

the modem Snake River, have a steeper gradient than exists 

downstream from Grand View to the Froman Ferry area. 

The depositional filling of the basin of the western 

Snake River Plain by the Glenns Ferry Formation took 

place over a long period of time, roughly 2.4 million years. 

It is inconceivable that a permanent Glenns Ferry lake could 

exist for 2.4 million years as an enclosed basin, having no 

outlet or through-flowing waters, without becoming saline. 

Yet evaporates are not conspicuous in any part of the 

Glenns Ferry lake deposits (they are more common in the 

Miocene lake deposits of the Chalk Hills Formation, 

underlying the Glenns Ferry Formation). 

The biota of the Glenns Ferry lake beds also indicates 

fresh water throughout its existence. Because of the long 

life of the Glenns Ferry lake, most lacustrine biota developed specialized, endemic forms, particularly noticeable in 

the fish (Smith, 1975), mollusks (Taylor, 1966 ), ostracodes 

(Forester, 1991 ), and diatoms (Bradbury and Krebs, 1982). 

Moderately saline faunas and floras of the Glenns Ferry 

Formation have been found only in deposits of small lakes, 

marginal to Glenns Ferry lake and separated from its influence, so that evaporation could increase their salinity without dilution by waters of the main lake or inflowing 

streams. 

The lack of abnormally saline deposits in the Glenns 

Ferry lake beds and the varied fauna and flora of the Glenns 

Ferry lake, both indicating normal salinity, certainly also 

indicate through-flowing waters during the entire existence 

of the lake (Middleton and others, 1985). A drain thus 

appears to have been present essentially from the beginning 

of the Glenns Ferry lake, perhaps 3.9 million years ago, but 

with a higher sill at the lake outlet than now exists, thus 

containing the lake. The basin is still entirely enclosed 

today and would still contain a lake except for the Hells 

Canyon drain. 

Before, during, and after the Glenns Ferry lake, basaltic volcanic activity was prominent for many miles 

upstream from the lake (in the eastern Snake River Plain) 

and was also present along the south and north sides of the 

western Snake River Plain near the head of the Glenns 

Ferry lake. About 2 million years ago volcanic vents began 

developing along the axial part of the Snake River basin and 

became prominent features of the area during the late history of the lake and later (Mal de, 1991, fig. 8). 

GLENNS FERRY FORMATION NEAR HAGERMAN AND 

KING HILL 

The oldest known parts of the Glenns Ferry Formation 

are lake beds in the Hagerman and King Hill region (figs. 1 

and 13 ). At Hagerman, 40 miles down the Snake River from 

Twin Falls (fig. 13), the formation is nearly as old as 3.9 

million years (older part of the Cochiti event of the Gilbert 

Chron; Neville and others, 1979). Hagerman is close to the 

east end of the northeast side of the Snake River Plain (and 

the Glenns Ferry lake). In the King Hill area, 25 miles 

northwest of Hagerman, the Clover Creek lava is believed 

to lie within the oldest known part of the Glenns Ferry Formation (Malde, 1972) and to be older than the Cochiti event 

(Neville and others, 1979; more than 3.9 Ma). Following 

the discussion by Neville and others ( 1979), Conrad ( 1980), 

and Repenning ( 1987), the Hagerman mammal faunas 

range in age from about 3.6 to 3.3 Main age. Although considered as being of early Blancan age in many reports (and 

late, in others), the Hagerman faunas lived midway through 

the Blancan mammal age of the United States (Blancan is 

4.8 to 1.6 Ma old in the Pacific Faunal Region; see section 

on mammal ages, p. 1 0). Throughout the western Snake 

River Plain the youngest replacement of lake beds by overlying marsh or stream deposits is in the Froman Ferry area, 

and these are about I. 7 million years younger than the 

youngest marsh deposits at Hagerman and 2.1 million years 

younger than the oldest. 

Both nonlacustrine and lacustrine deposits at Hagerman are included in the Glenns Ferry Formation by Malde 

and Powers (1962). The higher and major part of the Hagerman section consists of stream and marsh deposits (deltaic, 

with fossil mammals). Although rarely found in large lake 

deposits (and then mostly in marginal facies), mammal 

remains are relatively common in the paludal and fluvial 

deposits of the Glenns Ferry Formation. Many individual 

fossil localities in the bluffs across the Snake River from the 

town of Hagerman have been combined under the name 

''Hagerman fauna"; all are in the marsh and stream deposits. 

Glenns Ferry lake deposits form the lowest part of the 

bluffs opposite Hagerman, near the pump station that lifts 

irrigation water from the Snake River 528 feet to the top of 

the bluffs. The lake beds are more extensive downstream 

(northwest) near the towns of Glenns Ferry and King Hill, 

where only lake beds represent the time of the Hagerman 

delta; here the lake beds extend well into the Gauss 

Normal-polarity Chron and, in part, are younger than any 

part of the Glenns Ferry Formation exposed near Hagerman 

(Neville and others, 1979). 

Deposits in the high bluff on the west side of the Snake 

River across from Weiser, Idaho, are older, but are not well 

dated and appear to have no relationship to the Glenns Ferry 

Formation. They, and adjacent Miocene fluvial deposits, 

were included in Lindgren's (1898) Payette Formation. The 

lake beds contain a diatom flora that is different than any 

known from the Glenns Ferry lake deposits and that is 

known elsewhere only in the subsurface at the Idaho 

National Engineering Laboratory (INEL, fig. 1) in the eastem Snake River Plain north of Pocatello, and in the Klamath Lake basins of south-central Oregon and adjacent 

California. In the INEL core this diatom flora is of a greater 

age than floras similar to those known from the Glenns 
56 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

Ferry lake, but younger than diatom floras that are also 

known from the Chalk Hills Formation (J.P. Bradbury, oral 

commun., 1992). 

Deposits at Hagerman are essentially the easternmost 

deposits of the formation, and are at the head of the Glenns 

Ferry lake basin. To the east (upstream), deposits of the 

Glenns Ferry Formation are covered by, and interbedded 

with, extensive basalt flows. A test hole drilled north of 

Wendell, Idaho, less than 15 miles east of Hagerman (where 

the formation is perhaps 600 feet thick), shows that the 

Glenns Ferry Formation rapidly pinches out between lava 

flows (Whitehead and Lindholm, 1985; Malde, 1991). 

Deposits of approximate Glenns Ferry age are known 

farther upstream only from drilled cores, such as at INEL; 

these are interbedded with lava flows and are presumed to 

represent deposition in local basins, rather than in the 

Glenns Ferry lake. Up the Snake River from Twin Falls 

there may have been, at times, a string of lakes, constrained 

by lava flows, of which the Glenns Ferry lake was only the 

most downstream and largest. 

Because of the relationship of the Hagerman section to. 

the apparent upstream limit of the Glenns Ferry lake basin, 

and because the marsh and stream deposits making up most 

of the Glenns Ferry section at Hagerman are, by far, the oldest nonlacustrine deposits of the formation and are 

restricted to a relatively small area near Hagerman, those 

deposits are believed to be deltaic and to have formed at the 

mouth of the ancient Snake River where it entered the 

Glenns Ferry lake. The deltaic environment was local: lake 

beds in the King Hill area, 25 miles northwest of Hagerman, are of an equal age as well as both older and younger 

than the Hagerman section, but they contain almost no 

marsh and stream deposits. 

Insofar as published dates, based upon fossil mammals, are concerned, there seems to be no record of deposition between perhaps 8 and 4 million years ago in the 

western Snake River Plain. The sequence of diatom floras in 

the INEL cores suggests that the beds at Weiser (included in 

the type definition of the Payette Formation) may have been 

deposited during this hiatus. Some of the fission-track dates 

cited by Kimmel ( 1982, table 1) suggest a younger age for 

these pre-Glenns Ferry deposits. It is beyond our interests in 

the Froman Ferry faunal succession to try to clarify these 

uncertainties regarding the pre-Glenns Ferry deposits. 

Sediments older than the Glenns Ferry Formation are 

exposed in Clover Creek, upstream from the oldest known 

Glenns Ferry Formation, at Strout Claim (the usual spelling 

"Stroud" is incorrect according to Mr. LeRoy Strout, of 

Gooding, Idaho). They are diatomite and contain early 

Hemphillian mammals; interbedded ash falls have been 

radiometrically dated at 10 Ma (Evernden and others, 1964; 

not corrected for revised decay constants), although the fossil mammals suggest an age of 9 million years or somewhat 

less. The Strout Claim diatomite may represent part of the 

Miocene Chalk Hills Formation, which underlies the 

Glenns Ferry Formation in most areas, but the deposits are 

not demonstrably the same unit because of tectonic scrambling and basalt cover. 

The diatoms at the base of the Hagerman section suggest a smaller lake than that indicated for most of the 

Glenns Ferry lake beds (J.P. Bradbury, oral commun., 

1992), and the associated ostracodes include few endemic 

forms, suggesting a lake with a briefer history than the 

later Glenns Ferry lake (Forester, 1991 ). Neither the ostracodes nor the diatoms resemble the fauna and flora of 

later stages of the Glenns Ferry lake, including those 

from the Multi-ash paleomagnetic section south of Oreana (p. 49-50). Thus the lake beds at Hagerman record 

different conditions early in the existence of the Glenns 

Ferry lake, than when the lake reached maximum size. 

This was roughly the time of the Cochiti event of the Gilbert Normal-polarity Chron. 

The ostracodes and diatoms in the deltaic deposits of 

the Hagerman section differ from those in the lake beds at 

the base of this section ("oldest" flora) and from the temporally equivalent Glenns Ferry lake ("typical" flora) in 

other areas as the King Hill and Bruneau areas. The ostracodes and diatoms of the deltaic deposits reflect changing 

water levels, salinity, and temperatures in locations sufficiently isolated from the Glenns Ferry lake to reflect more 

varied environments (Forester, 1991). 

As in all deltas, the sediments represent interbedded 

marsh, stream, and tongues of lacustrine deposits (marking high water stands). The indicated fluctuating environments agree with the deltaic origin suggested by the 

geographic restriction of these deposits and their proximity to the head of the Glenns Ferry lake and mouth of the 

ancestral Snake River. Although the lake beds in younger 

parts of the Glenns Ferry Formation have a unique and 

endemic fauna and "typical" flora, the associated marsh 

deposits contain a conventional biota little different than 

that found in similar environments today (Forester, 1991; 

Bradbury and Krebs, 1982). 

To judge from the data in Neville and others ( 1979), 

the change from the small lake deposits at the base of the 

Hagerman section to deltaic marsh deposits was about 23 

feet higher in the section than the end of the Cochiti event 

of the Gilbert Chron; this is interpolated to have been 

about 3.6 Ma ago. The oldest mammalian fauna was 

found as low as the very base of the delta beds. These are 

by far the oldest mammal faunas and marsh deposits in 

the Glenns Ferry Formation. 

Although the oldest lake beds (about 3.8 Ma) in the 

Hagerman section contain evidence (diatoms and ostracodes) of only a small and juvenile lake, by the time of 

the youngest fluvial-deltaic deposits of the Hagerman section (Horse Quarry and younger, possibly as young as 3.2 

Ma), the Glenns Ferry lake had filled most of the Snake 
HISTORIC SETTING OF THE FROMAN FERRY FAUNAL SUCCESSION 57 

River graben and extended from the King Hill area to 

beyond Bruneau, and possibly to the Froman Ferry area. 

This is indicated by the uniformly present "typical" diatom flora in the lake beds of these areas downstream from 

Hagerman and by the development of an endemic ostracode fauna in the Glenns Ferry lake. Once the basin was 

filled to the preexisting sill level, drainage began. Downcutting of the sill then continued at a rate greater than the 

prior headwater drainage that had cut the embryonic Hells 

Canyon to sill depth; for then the headwaters of the Hells 

Canyon tributary to the Columbia River had the Snake 

River flowing down it. 

LAKE, MARSH, AND STREAM FACIES, 

LONGITUDINAL RELATIONSHIPS 

As lake level dropped, nonlacustrine deposits, usually 

called "floodplain" deposits, covered the exposed Glenns 

Ferry lake deposits. In the main channels of the Snake and 

other rivers, thick beds of crossbedded fine to medium sand 

accumulated. Between stream mouths marsh deposits were 

laid down, and these grade laterally into stream deposits or 

lake beds. Ash falls are common in the flat-bedded and finer 

grained marsh deposits, as the lack of significant currents in 

this environment did not disperse the tephra. Whitish diatom-rich beds are also common in the marsh beds, but they 

are less concentrated and widely dispersed in the lake 

deposits. As the lake withdrew, these marsh and finegrained river deposits progressively extended to the northwest, down the Snake River graben, filling the basin with 

the locally youngest Glenns Ferry Formation. 

Continued filling of the basin and drainage of the 

lake extended the marsh and low-energy fluvial cover 

downstream to the Froman Ferry area. Although this combination of filling and draining lasted 2 million years (earliest Hagerman delta deposits to latest Froman Ferry 

marsh beds), after the time of the marshes in the vicinity 

of Birch Creek (2.4 Ma; fig. 12), its history is not well 

recorded in existing exposures. Northwest of Oreana the 

belt of Glenns Ferry outcrop narrows between the Snake 

River and the southwest margin of the Snake River graben and consists only of fluvial deposits; it would seem 

that a major drainage from the west (across the modern 

Owyhee Mountains) entered the basin in this area. In the 

vicinity of Guffey Butte, along the Snake River north of 

Murphy (fig. 12), only a little of the lake beds are 

exposed beneath fluvial deposits, and younger lake beds, 

related to later canyon damming, overlie the fluvial deposits; these younger lake beds are included in the Bruneau 

Formation (Malde, 1985, p. 45-46) and have the distinctly different diatom flora (J.P. Bradbury, oral 

commun., 1993). 

As mentioned, the oldest deposits of the Glenns Ferry 

Formation are both lacustrine (perhaps 4 Ma) and deltaic 

(about 3.6 Ma) in the King Hill-Hagerman area (fig. 1 ). At 

the Sand Point locality (Hibbard, 1959; Hibbard and 

Zakrzewski, 1967), on the south side of the Snake River 

opposite the town of Hammett (fig. 12), the fossiliferous 

marsh deposits apparently represent the margin of the delta 

about 3 million years ago (Repenning, 1987; Conrad, 

1980). The marsh beds change to lake beds in the outcrop 

and are about the age of the youngest deltaic deposits at 

Hagerman (C. Neville, oral commun., 1978). They are also 

the same age as part of the lacustrine deposits in the King 

Hill area, 17 miles to the east. 

Thirty to thirty-five miles west of Sand Point, on the 

east and west sides of Shoofly Creek ( 10 miles south of 

Grand View; fig. 12), lacustrine deposition persisted until 

2.4 million years ago before the lake beds were covered by 

marsh and fluvial deposits. Lacustrine deposits as old as the 

older deltaic part of the Hagerman section are present some 

17 miles closer to Sand Point in the Bruneau area (Neville 

and others, 1979, fig. 8) to the east of these marsh beds 

along Shoofly Creek. About 9 miles to the northwest of 

Bruneau, at Ninefoot Rapids (about 2.56 Ma), and about 

the same distance to the east, at Flatiron Butte (perhaps 2.6 

Ma), deposits are deltaic and fluvial. 

Eleven miles northwest of Shoofly Creek, the same 

marsh beds as at Shoofly Creek are present along Birch 

Creek, from about 13 to 6 miles west of Grand View (fig. 

12; p. 49-50, 61 and following). Northwest of this point, 

from the vicinity of Oreana essentially to the Walters Ferry 

area, 22 miles farther northwest (fig. 12), marsh beds are 

not present and only fluvial deposits overlie the Glenns 

Ferry lake beds; at present these fluvial sediments have little 

age control. In this area lake beds are increasingly confined 

to the area close to the modern Snake River. In the Guffey 

Butte area north of Murphy, Glenns Ferry fluvial deposits 

lie on Glenns Ferry lake beds in the canyon of the Snake 

River and underlie Bruneau Formation lacustrine deposits 

in adjacent buttes. A major concern in correlating across 

this distance from Guffey Butte to Oreana is the possible 

presence of fluvial deposits correlative to the lake beds of 

the younger Bruneau Formation lying on top of similar beds 

of the Glenns Ferry Formation. Just north of Guffey Butte, 

the canyon of the Snake River opens out and Glenns Ferry 

lake beds are exposed over a somewhat wider area. 

Between Walters Ferry and the Froman Ferry area 

there are no deposits of the Glenns Ferry Formation on the 

southwest side of the Snake River, and the northeast side of 

the river is marked by a high, lava-capped scarp composed 

of Glenns Ferry lake beds. At the north end of this scarp, 

the Glenns Ferry lake beds again are present on the west 

side of the Snake River, opposite the Froman Ferry area. 

Wherever these lake beds between Guffey Butte and the 
58 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

Froman Ferry area have been sampled, they contain the 

"typical" diatom flora of the Glenns Ferry Formation. 

Thus there are no marsh deposits for about 46 miles 

between Birch Creek and Froman Ferry, and only stream 

deposits overlie the Glenns Ferry lake beds. About 700,000 

years also separate these two series of marsh deposits. 

These sites of transition from lacustrine to marsh environments within the Glenns Ferry Formation, beginning 3.6 

million years ago in the Hagerman area, advancing to Sand 

Point about 3.1 million years ago, to Shoofly and Birch 

Creeks 2.4 million years ago, and to Froman Ferry about 

1.6 million years ago, rather clearly indicate a northwestward advance of nonlacustrine deposition down the western 

Snake River Plain. They also suggest that the mouth of the 

Snake River at the head of the lake was first near Hagerman 

and advanced, with the nonlacustrine deposits, to the foot of 

the lake at Hells Canyon. Fossil canyons, traced by Malde 

(1991), indicate that as the mouth of the Snake River 

advanced to the northwest down the Snake River Plain, the 

upstream part of the river incised the older deposits of the 

Glenns Ferry Formation. 

Individual units of marsh deposits extend only short 

distances to the northwest, "downstream'' toward the thenexisting lake and the lake outlet; they are not continuous in 

this direction but are replaced, down-basin, by lake beds, as 

between Birch Creek and the Multi-ash paleomagnetic section (p. 50-51). Transverse to the axis of the basin and 

upsection upstream, marsh deposits are replaced by fluvial 

deposits. It seems probable that the development of marsh 

deposits was localized and that all grade into low-energy 

stream deposits where stream flow into the Glenns Ferry 

lake was prominent. Because of their proximity to the lake, 

the marsh deposits show no excessive salinity, although 

small-lake deposits that are removed from the Glenns Ferry 

lake do contain saline organisms, as will be discussed. Each 

of these different environments, large lake, marsh, and 

small lake or pond, has its own distinctive diatom flora, 

making depositional interpretations easily determinable. 

Although the work, so far, has been of a reconnaissance nature, J.P. Bradbury has established a rough 

sequence of the lacustrine diatoms in the Glenns Ferry lake 

beds. In summary, this "sequence" is: ( 1) an "oldest" flora 

(about 3.8 Ma) found only at the base of the Hagerman section and associated with the Cochiti event of the Gilbert 

Chron (but other locations where this flora might be 

expected, as the oldest beds in the King Hill area, have not 

been examined); (2) an "intermediate" diatom flora that has 

been found at the base of the lake beds in areas where it was 

transgressing against the "basement," as west of Bruneau on 

top of the locally oolitic rusty sandstone and in the same 

position at the base of the lake beds at Elephant Butte in the 

Marsing area (fig. 2); and (3) a "typical" flora that has been 

found in many exposures (possibly older than 3.4 Ma in the 

Bruneau area, as young as 2.2 Main the Oreana area, and 

assumed to be as young as 1.67 Ma in the Froman Ferry 

area (p. 51, 52). This flora has been found about 200 feet 

stratigraphically below the 2.4-million-year-old marsh beds 

at Birch Creek and Poison Creek (fig. 12) and more than 

100 feet above the Gauss Chron in the perhaps 2.1-millionyear-old top of the Multi-ash paleomagnetic section south 

of Oreana (p. 51). It has not been looked for in deposits 

older than the Gauss Chron (>3.4 Ma) but is suspected to be 

that old. In the Froman Ferry area the flora occurs in the 

lake beds, underlying the marsh beds of less than 1.67 million years age, 2.5 miles south of Marsing on the west side 

of the Snake River, 7 miles southeast of Marsing in the 

bluffs along the east side of the river, and in a test hole 

drilled through the marsh beds to the lake beds in the 

Cucumber area of the Froman Ferry fossil localities. 

In many areas, such as high in the King Hill area, 

and in the Oreana area only the "typical" diatom flora has 

been found. Although preliminary in nature, the determination of these different diatom floras has assisted in evaluating what part of the lake bed sequence is under 

consideration; for example, these data speak against Neville's correlation of the Multi-ash paleomagnetic section 

with the Gilbert Chron, as they provide no indication of 

the "oldest" diatom flora in the Multi-ash section (p. 50). 

The age significance of these floras is questionable. 

The "oldest," at the base of the Hagerman section, is distinct and indicates a much smaller lake than the others; 

the "intermediate" flora has been found .only at the base 

of the Glenns Ferry lake beds near the southwest side of 

the Snake River Plain and may represent an environmental condition associated with the transgressing lake as it 

was forced across the Snake River graben; and the youngest flora is that "typical" of most outcrops of the Glenns 

Ferry lake beds and indicates a large and stable lake environment for perhaps as much as 1.8 million years. This 

has been discussed on page 49, 50. 

On the east side of the Snake River, the Glenns 

Ferry Formation is covered by extensive basalt flows, but 

Malde ( 1985 and 1991) reported that the longest fossil 

canyon dissecting the Glenns Ferry lake beds is identifiable beneath the lava cover in well records in the area to 

the northeast of Walters Ferry. This indicates the probability of the Glenns Ferry lake having existed mainly to the 

east of the present Snake River between Murphy and the 

Froman Ferry area, and being now largely covered by 

younger basalt flows. Examination of the facies relationships between Oreana and Froman Ferry is accordingly 

hampered. 

In at least some areas the trench along the northeast 

side of the Snake River graben was filled both by volcanic flows and by the Glenns Ferry Formation. Parts of the 

trench (evident near Mountain Home, Idaho, and eastward; Lewis and Stone, 1988; Arney and others, 1984) 

are largely filled with volcanic flows, presumably both 
HISTORIC SETTING OF THE FROMAN FERRY FAUNAL SUCCESSION 59 

older and younger than the Glenns Ferry Formation, a situation comparable to that evident in the Wendell area a 

short distance east of and upstream from Hagerman. 

This persistent lava source area along the northeast 

side of the Snake River Plain appears to have caused the 

Snake River to be confined to the central part of the basin 

in most areas upstream from the Oreana-Sinker Butte 

area. Its modern route along the western structural margin 

of the graben below Sinker Butte (fig. 12) appears to be 

the result of repeated damming by lava flows as described 

by Malde ( 1985). 

Thus the Snake River basin was filled both from the 

northeast side by lava flows, and from its head by the 

Snake River. Possibly, streams entered the lake basin 

from the southwest side also. Lake bed deposition continued until the outlet of the basin was cut deep enough to 

drain the lake at its lowest point, in the Froman Ferry 

area, and Snake River sediment was then carried through 

the basin and down Hells Canyon. 

LAKE, MARSH, AND STREAM FACIES, 

TRANSVERSE RELATIONSHIPS 

The relationships of the depositional facies (lake, 

marsh, and stream) of the Glenns Ferry Formation across 

(rather than down) the Snake River Plain are well displayed in the vicinity of the town of Grand View (fig. 12). 

They represent conditions at the time of the Grand View 

faunal succession (early Blancan V; 2.56-2.0 Ma). At this 

time, and in this position within the graben, the marsh 

deposits first extended across the Snake River Plain from 

the underlying older rocks along the southwest side of the 

graben (Chalk Hills Formation and the overlying locally 

oolitic and rusty sand unit) to the fluvial deposits of the 

Snake River in the center of the basin. The Snake River 

was then, and in this area, essentially in its modem position, at the foot of the basaltic ramp flooding the east half 

of the basin from the northeastern margin of the graben in 

the vicinity of Mountain Home. By this time basaltic 

flows had filled the eastern part of the graben in the 

Grand View area and forced the Snake River to an axial 

position, and the Glenns Ferry lake to the west half. Farther downstream, the lake seems to have remained in the 

axial and northeastern part of the basin. 

The Grand View faunas are about 130 miles downstream from Twin Falls (fig. 1) and the initial head of the 

Glenns Ferry lake. At many Grand View localities in the 

vicinity of the modern Snake River, the underlying Glenns 

Ferry lake beds, if present, are not exposed. They are 

exposed beneath Grand View faunas to the east (upstream), 

south, and west of the town of Bruneau (fig. 12), where the 

oldest exposed lake beds are older than the Hagerman horse 

quarry and the Gauss Chron (>3.4 Ma), although lake beds 

as old as the oldest part of the Hagerman section are not 

known (Neville and others, 1979, fig. 8, Bruneau section). 

Glenns Ferry lake beds are also present to the south of 

Grand View (below the Poison Creek fauna along Shoofly 

Creek), west (below the Birch Creek fauna), and northwest 

(below fluvial deposits in the Oreana area). A short distance 

north of the Bruneau area (toward Mountain Home), Glenns 

Ferry lacustrine and fluvial deposits disappear. They are 

replaced by increasing volumes of basaltic flows interbedded with pond deposits that had no connection with the 

then-existing Snake River. Glenns Ferry fluvial deposits of 

the ancient Snake River in this area are confined to the area 

of the modem Snake River, and it appears that the Snake 

River of that time ran along the east side of the lake basin 

and at the foot of the basaltic ramp from the Mountain 

Home area (fig. 12). 

Many localities, as old as the Ninefoot Rapids fauna of 

Conrad ( 1980; probably about 2.56 Ma old although 

paleomagnetic control is lacking for this fauna), are here 

included in the late Pliocene Grand View faunal succession-used in a broad sense. This use of a Grand View faunal succession differs from that of Shotwell ( 1970), Conrad 

( 1980), and all other previous writers, who included only 

the Jackass Butte faunas in the Grand View fauna. A minimum of 10 fossiliferous areas are here included in the 

Grand View faunal succession, each with one to many individual localities. These include Jackass Butte, Birch Creek, 

Chattin Hill, Black Butte, Castle Butte, Ninefoot Rapids, 

Oreana area, Poison Creek (Shoofly Creek of Shotwell, 

1970), "unnamed butte" (of Conrad, 1980; p. 62-63), and 

Wild Horse Butte. Discussion of the first three, Chattin Hill, 

Jackass Butte, and Birch Creek, will suffice to illustrate the 

Glenns Ferry transverse-basin facies relationships at this 

time (in a northeast-southwest direction across Snake River 

Plain, see cross section of fig. 12). Jackass Butte is about 10 

miles northwest of the town of Grand View and is the best 

known area of the Grand View faunal succession (Stirton, 

1936). 

CHATTIN HILL 

Nearly 8 miles southeast of Jackass Butte, near the 

topographic feature called Chattin Hill 4 miles north and 

2-3 miles east of the town of Grand View along the road to 

Mountain Home, the Glenns Ferry Formation is correlative 

to some part of the Jackass Butte section (unpublished, fossil mammals collected by H.E. Malde in 1979) and connected to it by nearly continuous exposures. But near 

Chattin Hill the Glenns Ferry Formation contains basaltic 

flows, most of which are not present at Jackass Butte. As 

mentioned, in the Mountain Home area the northeast side of 

the Snake River Plain graben is largely filled with basaltic 

flows. 

The sediments in the Chattin Hill area appear to have 

been deposited in small, at least to some degree saline, 
60 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

lakes, possibly dammed behind lava flows; no Glenns Ferry 

lake, marsh, or fluvial deposits have been recognized. Both 

diatoms (J.P. Bradbury, oral commun., 1992) and ostracodes 

(Forester, 1991, as the Grand View locality) indicate varying salinity and temperatures, with no moderating influence 

from the Glenns Ferry lake or from the ancient Snake River. 

The diatom flora is characteristic of small ponds and not 

large lakes. The significant features of the Glenns Ferry 

Formation in the Chattin Hill area are the interbedded lavas, 

and pond deposits showing temperature and salinity variability, thus indicating no influence from either the thenexisting Snake River or the Glenns Ferry lake. 

JACKASS BUTTE 

Marsh deposits are present in the middle part of the 

section at Jackass Butte, northwest of Chattin Hill. From a 

distance they stand out as white deposits in the middle of 

the section and, like the Birch Creek fauna, they contain the 

marsh-inhabiting giant beaver Procastoroides idahoensis, 

which is only found in this middle part of the section at 

Jackass Butte (Shotwell, 1970; Conrad, 1980). The lowe; 

and upper parts of this section are fluvial, with many crossbedded and sandy channel deposits, containing all the taxa 

of the fauna except for Procastoroides. In these respects the 

Jackass Butte section differs from the older deposits at 

Birch Creek farther west: the latter are marsh deposits overlying lake beds and underlying fluvial deposits of a finer 

grained composition than at Jackass Butte. The Jackass 

Butte section also differs _from the deposits of the Chattin 

Hill area, which are largely pond deposits and lava flows. 

The entire section exposed on Jackass Butte is between 

100,000 and 400,000 years younger than the Birch Creek 

fauna, as mentioned on page 51. 

From a sample collected high in the Jackass Butte section, near the locality where a Stegomastodon scapula was 

collected (Conrad, 1980, p. 236-241) and above the marsh 

deposits, Forester ( 1991) indicated that the ostracode fauna 

from Jackass Butte section consists of eurythermal taxa of 

unspecialized morphology, suggesting a modem-like seasonality and a lack of contact with the then nearly 2-million-year-old Glenns Ferry lake. This ostracode fauna is like 

that of Chattin Hill but lacks the suggestion of varying 

salinity, suggesting that it may have been flushed by the 

Snake River and thus subject to seasonal changes in water 

temperature, but not seasonal salinity. Forester saw no 

ostracodes from the underlying marsh deposits on Jackass 

Butte, and the seasonality that he detected applies to the fluvial deposits above the marsh beds. 

Diatoms also were found only very near the top of the 

Jackass Butte section, about 20 feet lower than the ostracode sample and possibly also in the fluvial deposits. They 

were of modem aspect and, like those in the Chattin Hill 

section, indicated pond environments but did not suggest 

increased or varying salinity (J.P. Bradbury, oral commun., 

1993). 

A brief normal paleomagnetic event midway up the 

Jackass Butte section (elevation 2,600 feet and in that part 

composed of marsh deposits) is reported by Conrad (1980); 

it was also detected in the work of C.A. Neville (oral commun., 1978), but not reported in Neville and others (1979) 

or Neville (1981). In Neville's work the normal event was 

supported only by one sample, and its normal polarity was 

discredited because it was unconfirmed by other samples. 

But Conrad did further sampling and found the normal zone 

in other parts of the butte in the same apparent stratigraphic 

position. The event can only represent one of the two normal events of the Reunion Normal-polarity Subchron; the 

earlier (2.13 Ma) has been suggested by Conrad (1980), and 

the suggestion fits the climatic history of the Northern 

Hemisphere. 

Two million one hundred thousand years ago preNebraskan glacial till was deposited in Iowa, and the earlier 

of the two Reunion excursions occurs within this till (Easterbrook and Boellstorff, 1984 ). Although age control is 

poor, there appears to have been mountain glaciation in the 

Yellowstone Park area at about the same time that continental glaciation extended to Iowa (Richmond, 1986). Glaciation in the Yellowstone area, marking a period of increased 

precipitation, would have increased the flow of the Snake 

River that drained into the Glenns Ferry lake. G.R. Smith 

(written commun., 1992) noted that the modem cold-water 

stream sculpin Cottus makes its earliest appearance at Jackass Butte. Possibly the rise in the level of the Glenns Ferry 

lake, indicated by the return of marsh deposits to the Jackass Butte area, reflects this glacial period. 

But by 2.0 million years ago, the time of the second 

brief normal excursion of the Reunion (not found at Jackass 

Butte), the Northern Hemisphere was experiencing a different climate with marked warmth (Repenning and Brouwers, 

1992); the second event of the Reunion is found in deposits 

above the till in Iowa (Easterbrook and Boellstorff, 1984 ). 

This climatic change seems to be reflected in the renewed 

lowering of the Glenns Ferry lake level and the return of 

fluvial deposition to Jackass Butte, from which the ostracodes and diatoms were collected. Presumably the reduction of glaciation in the Yellowstone Park area resulted in 

this lowering of lake level, and in the seasonality indicated 

by the ostracodes found in the fluvial deposits overlying the 

marsh beds in the upper part of the Jackass Butte section. 

The significance of seasonality is that it results from less 

cloud cover, producing hotter summers and colder winters, 

and less runoff from precipitation. 

The age of the Jackass Butte fauna has been erroneously indicated as Pleistocene. Hibbard (1959, p. 35-38) 

indicated that the Grand View fauna of Jackass Butte and 

younger deposits of the Glenns Ferry Formation as far north 

as the Froman Ferry fauna were of middle Pleistocene age, 
HISTORIC SETTING OF THE FROMAN FERRY FAUNAL SUCCESSION 61 

"most probably of Yarmouth age." His opinion was based 

upon two correlations: ( 1) the presence in the Grand View 

fauna of Ondatra idahoensis, Mictomys vetus, and 

Mimomys parvus correlated best with the Borchers fauna of 

Kansas; and (2) the Borchers fauna was in the top of the 

Cudahy ash (thus thought to be 0.61 Ma), which Hibbard 

considered to be of Yarmouth age. Later, it was determined 

that three separate ash beds, all derived from the Yellowstone area, were assigned to the Cudahy ash that Hibbard 

had found associated with the Great Plains mammal faunas 

he described. The ash containing the Borchers fauna was 

2.01 million years old, rather than 0.61 million years old 

(Naeser and others, 1973 ). 

Certain other considerations also suggested a Pleistocene age to Hibbard, such as the belief that Blancan 

was Pleistocene, but subsequent work (Shotwell, 1970; 

Neville and others, 1979; Conrad, 1980, and Repenning, 

1987 ), and the refinement of the definition of the beginning of the Pleistocene (Aguirre and Pasini, 1985) have 

clearly shown that the Grand View faunal succession is 

late Pliocene in age and belongs in the Blancan V mammal age. The Grand View faunas were included in the 

Blancan mammal age in the original definition of that age 

(Wood and others, 1941, p. 20). 

Hibbard's correlation of the Grand View fauna with 

the Borchers fauna of Kansas is reasonable in terms of faunal evolution and the age it indicates. Unknown to Hibbard 

(in 1959), the Borchers fauna is in close association with 

the second event of the Reunion Subchron and thus correlates closely with the fluvial deposits above the first 

Reunion event in the medial marsh beds of the Jackass 

Butte section. This rather remarkable biochronologic correlation by Hibbard was confirmed 21 years later by Conrad's 

(1980) paleomagnetic studies. The only difference between 

the Jackass Butte faunas of the Grand View faunal succession and the Borchers fauna is that the Jackass Butte section includes a considerable span of time (perhaps as much 

as 300,000 years), from early during the Matuyama 

Reversed-polarity Chron to the Reunion events, while the 

Borchers fauna of Kansas represents only one horizon in 

the reworked top of the Borchers ash and, essentially, one 

time (2.0 I Ma). The two faunas are in different faunal 

regions and have different taxa, making Hibbard's correlation even more difficult. 

The marsh deposits in the middle of Jackass Butte 

seem to indicate that this was the approximate limit of the 

river 2.1 million years ago. 

BIRCH CREEK 

Extending from 17 miles southwest to about 7 miles 

south of Jackass Butte (about 13 to 6 miles west of Grand 

View), the marsh beds containing the Birch Creek fauna 

overlie typical Glenns Ferry lake beds. The Birch Creek 

fauna is a part of the Grand View faunal succession of Blancan V age, but represents only an early part of that mammal 

age; it is 2.4 million years old based upon the correlation of 

its associated ash beds to the Multi-ash paleomagnetic section between 4 and 5 miles to the northwest (p. 50). This 

age is also indicated by the small size (in comparison with 

the Jackass Butte fauna) of the horse, Plesippus sp. aff. P. 

shoshonensis, of the giant beaver Procastoroides idahoensis, and of the muskrat Pliopotamys minor; and by the presence of the immigrant lemming Mictomys vetus ( <2.56 

Ma). These indicate an age between that of Hagerman and 

Jackass Butte and younger than 2.56 million years ago. The 

positioning of the ash above the top of the Gauss Chron in 

the Multi-ash paleomagnetic section sharpens this age 

assignment to about 2.4 million years. The advancement of 

the vole subgenus Mimomys (Ophiomys) to the species M. 

( 0.) parvus is also suggestive, but represents a stage in a 

graded series that has been recognized in pre-Mictomys 

(late Blancan IV) faunas (as at the Flatiron Butte fauna). 

Jonena Hearst, University of Kansas, is currently (1994) 

studying the Birch Creek and Poison Creek faunas. 

One of the outstanding features of the beaver genus 

Dipoides is the little size variation of its species. In fact, 

size varies little from its Clarendonian ancestor Eucastor so 

that the size remained stable in the lineage for about 6 million years. Thus the beginning of a trend toward larger size, 

appearing in Blancan faunas, marks the divergence of the 

large but similar genus Procastoroides. On this basis, 

Zakrzewski's (1969) large species Dipoides intermedius 

from the Hagerman fauna is here included in Procastoroides. Procastoroides intermedius (Zakrzewski) from the 

Hagerman fauna is smaller than P. idahoensis from the 

Grand View faunas (Zakrzewski, 1969), and for this reason 

Zakrzewski's species name is retained. The Procastoroides 

sp. from the Birch Creek fauna is intermediate in size. 

The taxa in the Birch Creek fauna indicate an age 

younger than the Glenns Ferry faunas of Hagerman, Sand 

Point, and Flatiron Butte, but distinctly older than the faunas of Jackass Butte. They most closely resemble those of 

the Ninefoot Rapids fauna of Conrad ( 1980), but the Birch 

Creek fauna lacks the microtine Pliophenacomys osborni, 

an immigrant from the Great Plains. Ninefoot Rapids is a 

fluvial deposit, rather than a marsh deposit, and Conrad 

noted the lack of Procastoroides and the scarcity of the 

muskrat, which is of small size but which he referred to 

Ondatra idahoensis. 

The Ninefoot Rapids fauna has no paleomagnetic 

polarity determinations; the biostratigraphic interpolation 

of its age, intermediate between the Flatiron Butte fauna in 

the younger part of the Gauss and the Birch Creek fauna 

just above the Gauss, suggests that it should be close to the 

top of the Gauss Normal-polarity Chron, and very close to 

the time of dispersal of Mictomys vetus 2.56 million years 

ago. The fact that it contains the only record in the Pacific 
62 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

Faunal Region of Pliophenacomys, an obviously unsuccessful immigrant from the Great Plains, seems to favor this 

interpretation of an age very close to dispersal event 5. Barnosky (1985) reported Pliophenaconzys from the Yellowstone area on the Continental Divide between the Snake 

River and the Great Plains. In all faunal elements, Barnosky's fauna seems to represent a record of this dispersal 

event in the Yellowstone pass area, a most remarkable 

record. 

The marsh beds that contain the Birch Creek mammal 

fauna are coeval with (and can be traced into) the marsh 

beds containing the Poison Creek fauna, 10 miles south to 

south-southwest of Grand View (fig. 12). These marsh beds 

extend to the east across Shoofly Creek, and, as far as they 

are exposed (fig. 12), seem to be marking the northwestern 

limit of the Snake River 2.4 million years ago (southeastern 

limit of the Glenns Ferry lake at this time). The Poison 

Creek fauna was first mentioned by Shotwell ( 1970, in connection with Procastoroides idahoensis) as a locality along 

Shoofly Creek. Kimmel (1982, table 1, sample 19-A-02) 

cited a 2.5± 1.0 million year fission-track date for an ash 

(one of the ''multi -ashes") in the lower part of the Poison 

Creek marsh deposits in the vicinity of Shoofly Creek. This 

is permissive of the correlation but carries such a wide margin of error that it certainly does not provide confirmation. 

Both fossiliferous marsh deposits (Birch Creek and Poison 

Creek) overlie Glenns Ferry lake beds containing a "typical" diatom flora (of an uncertainty in age significance 

greater than that of the fission-track date). 

Both Birch Creek and Poison Creek marsh deposits 

extend across the Snake River Plain from the vicinity of the 

Snake River (middle of the basin) to the southwest margin 

of the Glenns Ferry lake, where they lap against pre-Glenns 

Ferry Tertiary rocks: the now-familiar, locally oolitic rusty 

sand unit above the Chalk Hills Formation. The Glenns 

Ferry lake beds underlying the marsh deposits pinch out 

against the unconformity before the marsh beds do. 

The marsh deposits of Birch Creek and Poison Creek 

appear to be the same age on the basis of mammalian fauna, 

outcrop tracing, ash deposits, underlying lake beds, and fission-track date, but are not continuous. Both are overlain by 

fine-grained and crossbedded fluvial deposits and, between 

Birch Creek and Poison Creek (a distance of about 10 

miles), the marsh beds disappear and their stratigraphic 

position is marked only by the overlying fluvial deposits, 

which lie directly on the Glenns Ferry lake beds. 

The outcrop pattern of the marsh deposits may represent sinuosity of the limits of marsh deposition, as between 

the two areas small exposures of marsh beds have been 

found at locations more marginal (to the southwest) within 

the basin (fig. 12); in these areas the marsh beds are also 

below the fluvial deposits. It seems probable that, as the 

lake drained, it was covered with marshes for a time great 

enough to accumulate a recognizable deposit only locally, 

and that fluvial deposits were left directly on the lake beds 

where there were streams entering the lake. 

REGIONAL FACIES RELATIONSHIPS 

To judge by the distribution of these nonlacustrine 

deposits, it seems evident that continuous, open waters of 

the Glenns Ferry lake did not extend southeast and east 

(upstream toward the Hagerman area) much farther than 

Shoofly Creek about 2.4 million years ago. The head of the 

lake was in the position of Oreana and the Multi-ash polarity section about 2.1 million years ago, at the time that shallow, marsh water had backed up some river channel to 

Jackass Butte. No lake deposits are known along the present 

route of the Snake River as far downstream as the unnamed 

butte north of Wild Horse Butte, although near-lake marsh 

deposits are present in the area of "unnamed butte" until 

about the time of the Birch Creek fauna; the oldest marsh 

deposits at ''unnamed butte" are at river elevation and 

would seem, from the paleomagnetic pattern, to be correlative to some part of the lake beds beneath the Birch Creek 

fauna and the base of the Multi-ash polarity section. They 

must approximate the age of the Ninefoot Rapids fauna. 

The Glenns Ferry lake was clearly restricted to areas southwest of the modern river in the Oreana area during the 

approximate time span between Ninefoot Rapids, Birch 

Creek, and Jackass Butte faunas. 

It is unknown whether the fluvial deposits in the. Jackass Butte-Wildhorse Butte area, at the foot of the basalt 

ramp in the eastern parts of the Snake River Plain, were 

deposited by the Snake River or by streams flowing into the 

lake from the northeast basin margin. The basaltic composition is not conspicuous, but has not been carefully looked 

for. 

Downstream (northwest) from the Birch Creek area, 

the marsh deposits feather out into lake beds before reaching the next modem drainage, Castle Creek, as noted on 

pages 50-51; but the continuation of the ash beds of the 

Birch Creek-Poison Creek marsh beds into lake beds, with 

132 feet of lake beds overlying them at the Multi-ash paleomagnetic section, provides a convincing correlation of these 

localities. The youngest Glenns Ferry lake beds in the 

Multi-ash paleomagnetic section appear, on the basis of 

thickness, to be about the same age as the stream deposits at 

Jackass Butte; this assumes similar rates of deposition in 

stream and lake deposits. 

Northwest from the Multi-ash section, in the vicinity 

of Oreana ( 16 miles northwest of Grand View) and farther, 

only fluvial deposits appear on top of the lake beds, and 

these may be of either Glenns Ferry or Bruneau Formations, 

although scattered fossils found in them in the Oreana area 

appear to represent a Glenns Ferry fauna (Conrad, 1980; 

Anderson, 1965, UCMP specimens). At the top of the 
HISTORIC SETTING OF THE FROMAN FERRY FAUNAL SUCCESSION 63 

Multi-ash section, and possibly elsewhere, Bruneau deposits overlie the Glenns Ferry lake beds, apparently because 

of pre-Bruneau erosion that becomes more conspicuous farther downstream. 

Although the 2.4-million-year-old Birch Creek marsh 

beds do not extend into the contemporaneous lake basin 

much more than a mile northwest of Birch Creek, they 

extend about 7 miles in a northeast direction from the 

southwest margin of the Snake River Plain nearly to Grand 

View. With the exception of exposures at Jackass Butte of 

younger age and those at Wild Horse Butte and the 

unnamed butte farther downstream, 6-8 miles northwest of 

Jackass Butte and as old as and older than Birch Creek, 

marsh beds are not again known to be present until the Froman Ferry area, where they are less than 500,000 years 

younger than those at Jackass Butte and, possibly, the 

youngest Glenns Ferry lake beds in the Oreana-Multi-ash 

area. 

The marsh beds midway in the Jackass Butte section, 

and centering on the 2.1-million-year-old first normal event 

of the Reunion Subchron, lie about midway in the time 

interval separating Birch Creek and Froman Ferry. But, as 

discussed, in those areas downstream from Oreana (north, 

between Sinker Butte and Walters Ferry; fig. 12) the lake 

basin appears to have been largely east of the exposures 

along the Snake River, and the deposits are now covered by 

basalt flows. 

A fauna comparable to that from Birch Creek has not 

been found at the heavily collected Jackass Butte exposures, 

which, because of regional dip (and bas inward faulting), are 

topographically lower but stratigraphically higher than 

Birch Creek (fig. 12, section); the Jackass Butte faunas are 

too young to be identical to the Birch Creek fauna. Six 

miles northwest of Jackass Butte, at Wild Horse Butte, 

Shotwell ( 1970) collected fossil mammals, including Procastoroides, that he included with his Grand View fauna. 

These are more like the Birch Creek fauna (unknown to 

Shotwell) than the Jackass Butte faunas. 

At the unnamed butte north of Wild Horse Butte, Neville ( 1981) measured a paleomagnetic section that included 

the younger part of the Gauss Chron and the overlying oldest part of the Matuyama Chron, nearly matching in its 

polarity record the Multi-ash section. Although Neville 

(1981) called the section the "Wildhorse Butte" section, 

because this was the closest named feature on the topographic map, Conrad ( 1980) referred to the locality as 

"unnamed butte" because Neville's section was actually 

collected on the south face of a butte having no name on the 

topographic quadrangle and about 1 mile north of Wild 

Horse Butte. 

At "unnamed butte," however, the lake beds, if 

present, are well down in the Gauss magnetozone and are 

not exposed within the canyon of the adjacent Snake 

River; marsh beds with abundant carbonized plant remains 

are present at river level. Fossil mammals were found at 

"unnamed butte" both above and below the Gauss/ 

Matuyama polarity reversal (2.48 Ma; about at the 2,542 ft 

elevation on "unnamed butte") in whitish marsh beds and 

in fluvial deposits above these. The fauna collected 

included Mictomys vetus, Mimornys parvus, and Hypo/agus sp. from localities GS-236, Sample 1, and GS-237, 

Sample 2, both of which were in marsh deposits less than 

25 feet below the top of the Gauss Chron. In the reversed 

part of the section (Matuyama Chron and fluvial deposits), 

Hypolagus, a peccary, and a fairly large camel were found. 

The specimens, collected by both Conrad and Scott, are 

accessioned in IMNH, and this locality was the basis for 

the statement of Repenning ( 1987) that the immigration of 

Mictomys was older than the end of the Gauss Chron in 

Idaho. 

The Wildhorse Butte-"unnamed butte" deposits indicate that the lake was restricted to the west before the time 

of the Birch Creek section and the ash beds of the Multi-ash 

section. The Glenns Ferry lake was, at about 2.48 million 

years ago, less than 6 miles wide in the vicinity of 

Oreana-Wild Horse Butte. 

Lowering of the Glenns Ferry lake level was reversed 

about 2.1 million years ago when marsh deposits appeared 

in the Jackass Butte area, marking the highest lake level 

recorded there. The 132 feet of lake beds above the Gauss 

Chron in the Multi-ash paleomagnetic section may include 

deposits reflecting this deepening. As has been noted (p. 

60), this rise in lake level was contemporaneous with the 

other evidence of Northern Hemisphere continental glaciation, which began about 2.4 million years ago (to judge 

from oceanic oxygen isotope records and recorded activity 

of the Scandinavian Ice Sheet), and peaked about 2.1 million years ago (to judge from glacial deposits in Iowa and 

Yellowstone). The Birch Creek-Poison Creek marsh beds 

may easily owe their extensive nature to a resulting stasis in 

lowering of the level of the Glenns Ferry lake, and then the 

peak of glacial activity brought a temporary rise in lake 

level and the marsh environment upstream to Jackass Butte. 

As the Jackass Butte marsh beds overlie fluvial deposits, it would seem possible that this marsh deposition was 

confined to a preexisting river valley at that point, but must 

represent a considerable rise in lake level, as they are the 

only marsh beds in the section. Considerable effort has been 

made to find possible lake deposits above the Birch Creek 

marsh deposits, with negative results. If the Birch Creek 

marsh beds represent a stasis in lake draining, it was 

resumed again before the rise recorded in Jackass Butte; 

this is not inconsistent with the pattern of ice activity of the 

Scandinavian Ice Sheet at this time (Jansen and others, 

1988 ), although well removed from Scandinavia in terms of 

regional weather patterns. 

In summary, a transverse section of the Glenns Ferry 

Formation in the vicinity of Grand View (fig. 12, section), 
64 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

midway down the axis of the western Snake River Plain, 

shows 2.4-million-year-old lake beds grading southward 

into Birch Creek marsh beds and lapping out against the 

underlying locally oolitic rusty sand at the southwest structural margin of the graben. At this time the lake beds did 

not extend as far to the northeast as the present position of 

the Snake River at "unnamed butte" north of Wild Horse 

Butte, but appear to have extended to the southeast, in the 

vicinity of the present Snake River, as far as Shoofly Creek. 

Marsh beds of Birch Creek extend a great distance to the 

northeast, across the basin toward the town of Grand View, 

in the center of the basin; they also extend to the southeast 

(up the basin) as far as Shoofly Creek, where the outcrop 

band of marsh beds swings northeast toward the Snake 

River and appears to mark the then-existing upstream limit 

of the Glenns Ferry lake. In this area the lake may have 

been more of an estuary of the main lake, extending 

upstream from Sinker Butte to the position of Oreana and 

Shoofly Creek, but largely to the west of the present 

position of the Snake River. 

From the southwest side of the basin toward the 

present Snake River, the oldest lake beds are increasingly 

older; they are nearly 3.5 million years old in the lowest 

exposures near Bruneau (Neville and others, 1979, fig. 10), 

which is about 15 miles to the east of their closest exposures along Shoofly Creek, but are little older than the overlying marsh beds (2.4 Ma) where they pinch out against the 

locally oolitic rusty sand unit along Shoofly and Birch 

Creeks. The entire sequence dips toward the center of the 

basin, roughly at the modem Snake River, but the locally 

oolitic unit does so more steeply. 

To the northwest of Birch Creek, the marsh beds 

feather out into lake deposits. Farther in this direction, at the 

Multi-ash paleomagnetic section 3 miles south of Oreana, 

these lake beds contain the ash beds found in marsh deposits 

at Birch Creek and extend upsection (about 132 feet in 

stratigraphic thickness) well into the Matuyama Chron 

(Neville, 1981, reinterpreted), but they may or may not contain the first normal event of the Reunion Subchron. 

Because this brief normal event of the Reunion was not 

found in the Multi-ash section, these reversed-polarity lake 

beds may be more than 2.1 million years old at their youngest point. However, Neville's paleomagnetic sampling was 

very widely spaced in that part of the Multi-ash section 

where the Reunion Subchron might be expected, and the 

normal events could easily have been missed; that the lake 

existed this recently is indicated by the appearance of highwater marsh beds on Jackass Butte. The Multi-ash section 

of Glenns Ferry lake beds is overlain by marginal lacustrine 

deposits of the Bruneau Formation, also of reversed geopolarity according to Neville (1981), and contain both fluvial 

gravels with fossil horses (unpub. data, collected by H.E. 

Malde, 1976) and lacustrine clays with a "Bruneau" diatom 

flora. The youngest Glenns Ferry lake beds may have been 

removed by pre-Bruneau erosion. 

The youngest fluvial deposits at Jackass Butte are as 

young as about 2 million years, and, northeast of the town of 

Bruneau at the Ninefoot Rapids fauna, the fluvial deposits 

are as old as about 2.56 million years. Fluvial deposits are 

still older at Flatiron Butte to the east of Bruneau, and about 

3.1 million years old at Sand Point. At Hagerman, the easternmost marsh and fluvial beds are as old as 3.6 million 

years. 

The brief rise in lake level recorded in Jackass Butte 

appears to have been coincident with glaciation in Yellowstone Park; it was followed by renewed lowering of the 

level of Glenns Ferry lake. The lake did not rise high 

enough to deposit lake beds on top of marsh deposits in any 

examined exposure. 

Although extending for some 7 miles across the 

basin from its southwest side toward the town of Grand 

View, the Birch Creek marsh beds extend to the northwest 

("downstream" into the lake) only about a mile before 

grading into lake beds. In other directions they are 

replaced or overlain by fine-grained fluvial deposits. Farther to the northwest, beyond the Oreana area and continuing as far as Guffey Butte, fine-grained fluvial deposits 

overlie the Glenns Ferry lake beds in the exposures west 

of the Snake River; to the east they are covered by lava 

flows. 

Northeast of Grand View (north of Bruneau), a ramp 

of multiple lava flows, interbedded with local ponds that 

appear to have had no contact with either the former 

Snake River or the Glenns Ferry lake, leads up to the 

northeast side of the Snake River basin in the direction of 

Mountain Home (fig. 12). 

INCISION OF THE LAKE BEDS AND 

CANYON DAMMING 

Incision began first in the more upstream parts of the 

Snake River Plain, where the gradient of the covering gravels (and of the modem river) is greater than in the lower half 

of the basin. Incision thus followed the Snake River delta 

downstream to the northwest. Several times the incised 

channel of the Snake River was obstructed by lava flows, 

forcing ponding and overflow down a new channel (Malde, 

1985, 1991 ). In water impounded behind these dams, the 

sediments of the Pleistocene Bruneau Formation were 

deposited, making that formation a collection of several 

separate, but similar, depositional events. 

Mal de ( 1991, p. 263-266) has plotted the course of 

four former channels and provided dates of their damming, 

as all dams are composed of volcanic rocks. As tabulated by 

Mal de ( 1991 ), these dates have a wide temporal range (2.06 

to 0.78 Ma, with a range of 340,000 years for four samples 

from one locality), suggesting a problem with precision. We 
HISTORIC SETTING OF THE FROMAN FERRY FAUNAL SUCCESSION 65 

are unable to judge which is correct, and thus to infer a 

history. 

The dates for the dams also suggest that some of the 

channels were dammed during deposition of Glenns Ferry 

lake beds farther downstream. But all impounded lakes 

apparently contained identical diatom floras of the Bruneau 

Formation type, and these differ distinctly from those 

known from the Glenns Ferry Formation, including those 

immediately underlying the Froman Ferry faunal succession. The Bruneau diatom flora resembles that of modem 

lakes in the Pacific Northwest (J.P. Bradbury, oral commun., 

1993 ), but the deposits consistently show a reversed polarity and so must be older than the Bruhnes Normal-polarity 

Chron (> 790,000 years). The modem character of the Bruneau diatom flora suggests a different and younger age for 

the Bruneau Formation in comparison with the Glenns 

Ferry lake flora, but records outside the Snake River Plain 

suggest that environmental differences, rather than age differences, may be responsible (p. 51). In the core drilled near 

Bruneau, the pollen flora found in the lake beds of the Bruneau Formation indicated only a sage-steppe environment, 

whereas the underlying Glenns Ferry Formation showed an 

alternation of conifer forests and sage steppes (Thompson, 

1992). This would seem to suggest an environmental difference that was time-related. The problem of the relationship 

of the Bruneau Formation to the Glenns Ferry Formation is 

unresolved. 

The present route of the Snake River from Walters 

Ferry to the junction with the Boise River, north of the Froman Ferry area (fig. 2), resulted from the damming of the 

Snake River by the eruption of Pickles Butte (and related 

volcanic centers) 1.5 million years ago (p. 9, minimum date 

here selected, as the maximum date would indicate the presence of the Olduvai Normal-polarity Subchron, which was 

not found in the measured polarity section of the underlying 

marsh beds). This eruption forced the river to the southwest 

structural boundary of the Snake River Plain; its overflow 

down a new route to the west of the Pickles Butte lava flows 

removed earlier deposits of the Glenns Ferry Formation, as 

well as the capping Pickles Butte basalt. In some areas it 

seems to have also removed parts of the underlying 

Miocene Chalk Hills Formation, although in others it 

appears to have scoured its bed across the resistant locally 

oolitic rusty sandstone that lies between the Chalk Hills and 

the Glenns Ferry Formations. 

At Guffey Butte, south of Walters Ferry (fig. 12), there 

is exposed a considerable section of the Bruneau Formation 

downstream from the dams considered by Malde (1985, 

1991 ); the Pickles Butte lava dam is the only known damming feature that would account for the Bruneau deposits at 

Guffey Butte. These deposits contain a Bruneau Formation 

diatom flora (J.P. Bradbury, oral commun., 1993). 

No exposures of the Glenns Ferry Formation are 

present on the southwest side of the river from south of 

Walters Ferry (fig. 12) to north of Givens Hot Springs (fig. 

2), although thick exposures of Glenns Ferry lake beds are 

present in the steep scarp that is capped by lava on the 

northeast side of the river in this area. The geographic distribution of sediments and lava clearly indicates that overflow, to initiate the modem drainage route in this area, was 

around the southwest edge of Pickles Butte lavas extending 

to (or nearly to) the structural boundary of the Snake River 

Plain. The relationships of preserved deposits in this area 

indicate that subsequent erosion by the Snake River has 

brought the river course eastward (and basinward) into the 

area formerly covered by the lava. The Glenns Ferry lake 

beds have been stripped off older deposits west of the 

present river course, and it was not until the Snake River 

reached the Marsing-Froman Ferry area that Glenns Ferry 

Formation again is present on both sides of the river, marking the approximate northwestern former limit of the Pickles Butte lava. This is close to the downstream part of the 

Boise River, north of which there are no preserved parts of 

the Glenns Ferry Formation. 

In the Froman Ferry area, between the Snake and 

Boise Rivers, the lake beds have marsh beds above them, 

containing the Froman Ferry faunal succession, that are 

about 800,000 years younger than the Birch Creek marsh 

beds and about 500,000 years younger than the youngest 

marsh deposits of Jackass Butte in the Grand View area. 

The Glenns Ferry Formation of the Froman Ferry area was 

dissected by the modem Snake River following its overflow 

down a route west of the Pickles Butte lava field, and was, 

therefore, deposited in a basin into which the Snake River 

flowed farther east than its present route, possibly in the 

Nampa area, as suggested by the canyon traced beneath the 

lava surface by Malde (1991). 

When the Glenns Ferry lake formed, the Snake River 

entered the lake in the Hagerman area (beginning perhaps 

about 4.0 Ma). By the time of the Sand Point fauna (about 

3.1 Ma), the mouth of the Snake and head of the lake had 

moved downstream to the vicinity of Hammett. By the time 

of the earliest Grand View faunas (2.56 Ma), the Glenns 

Ferry lake was restricted to areas southwest of the modem 

Snake River (southwest half of the Snake River Plain) 

downstream from Bruneau and, by 2.4 million years ago, 

the lake was restricted to areas downstream from the marsh 

deposits containing the Poison Creek and Birch Creek faunas. By the time of the youngest Grand View faunas (2.0 

Ma) the mouth of the Snake River was downstream from 

Jackass Butte, or the fluvial deposits along the river 

between Jackass Butte and "unnamed butte" derive from 

streams that entered the lake down the basalt ramp covering 

the east half of the basin. 

At the Multi-ash section, 4 miles northwest of the point 

where the marsh deposits containing the Birch Creek fauna 

grade into lacustrine deposits of the Glenns Ferry lake, lacustrine deposition continued until perhaps 2.1 million years 
66 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

OREGON 

Jordan Valley 

25 50 75 1 DO MILES 

I""' 

0 __ T Lakeview ______ _ Alturas NEVADA 

I ~ Alturas I «,~ 

<i#" ~ <::J<; «'-\ ">~ <( I 0'{;- Winnemucca 

<(0 ~0 

~<( 0 1 v'{;-

V5~ ~ I <o~ • 

u 

SALMON 

MOUNTAINS 

IDAHO 

Figure 13. Idaho and adjacent areas showing approximate location of some localities discussed. Solid dot, Blancan locality. 

ago, to judge by the 132 foot thickness of reversed lake beds 

above the top of the Gauss magnetozone. The youngest 

lacustrine deposits in the Froman Ferry area may be close to 

1.67 million years old, but the end of the Olduvai event is not 

recorded in the paleomagnetic section of the fossiliferous 

marsh beds and no paleomagnetic section was made of the 

underlying lake beds. 

According to Jan sen and others (1988 ), evidence of the 

activity of the Scandinavian Ice Sheet began to abruptly 

increase 2.56 million years ago (the time of the immigration 

of Mictomys and the beginning of Blancan V), and reached a 

climax about 2.1 million years ago (glaciation in Iowa, presumably in Yellowstone, and rise in Glenns Ferry lake level 

at Jackass Butte). The first part of the Blancan V mammal 

age was a time of developing continental glaciation which 

would have been marked by increased precipitation. But, 

except for the brief rise in lake level 2.1 million years ago 

(Jackass Butte marsh beds) and a possible halt in the lowering of the lake level 2.4 million years ago (extensive Birch 

Creek-Poison Creek marsh beds), the water level of the 

Glenns Ferry lake was dropping. It is difficult to believe that 

the lake was not draining. 

The assumption that the Glenns Ferry lake was draining 

down Hells Canyon to the Columbia River during most of its 

existence seems to follow from the records in the Hagerman, 

Sand Point, Grand View, and Froman Ferry areas. Although 

the Glenns Ferry lake seems to have been present for perhaps 

2.5 million years, evaporates are not conspicuous in its 

deposits and the lacustrine fauna and flora indicate no saline 

waters; these conditions also suggest that the Snake River 

and the Glenns Ferry lake were parts of a through-flowing 

drainage system during all of this time. If so, there could be 

evidence of this drainage beyond the limits of the western 

Snake River Plain. 

ADJACENT AREAS OF SIGNIFICANCE 

From the preceding age and geographic data, this discussion assumes that the Snake River drained into the 

Glenns Ferry lake from the time of its inception and that the 

lake drained down Hells Canyon as soon as the basin filled 

to sill height. Hells Canyon is thus assumed to have been a 

pre-Glenns Ferry Formation feature that was further incised 

to completely drain the lake by the time of the Froman 

Ferry faunal succession. 

There have been suggestions of drainage by other 

routes during the time that the Glenns Ferry lake was in 

existence. In addition, it is evident that the Snake River did 

not always drain down the western Snake River Plain, but 

was once connected to the Sacramento River drainage of 

California (see fig. 13 ). These points require consideration to 

complete the history of the Glenns Ferry Formation. 

The hydrologic connection between the Glenns Ferry 

lake and the Sacramento River is defended on the basis of 

fossil fish and mollusks of the Sacramento drainage that are 

similar to those of the Glenns Ferry Formation. Diatoms and 

one mammal also suggest a connection. But much of this evidence of a connection is older than the Glenns Ferry lake. 

PRE-GLENNS FERRY DRAINAGE 

Wheeler and Cook (1954; followed by Miller, 1965; 

Taylor, 1966-his "Fish Hook" pattern, 1985; Middleton 

and others, 1985; and Mal de, 1991) have suggested a 

former drainage of the Glenns Ferry lake up the course of 

the Owyhee River in southeast Oregon (fig. 13), then either 

westward to Klamath Falls (Taylor) or southward to Nevada 

(Miller), and then south or southwest to the Sacramento 

River. This route has also been suggested for the Snake 

River before the formation of the Glenns Ferry lake, as 

many of the faunal similarities are older than the lake. 

No deposits of Glenns Ferry age (Blancan) are found 

anywhere in southeast Oregon, from the junction of the 

Boise River with the Snake River in Idaho, up the present 

Owyhee River in eastern Oregon, and west to Lakeview, 

Oregon. The area was a highland in the middle Miocene, 

when great sheets of ignimbrite flowed off it to the south 

into Nevada (almost exactly opposite the direction of flow 

of the modem Owyhee River); these welded tuffs have been 
HISTORIC SETTING OF THE FROMAN FERRY FAUNAL SUCCESSION 67 

broken up by north-south Basin-and-Range block faulting 

since then (at right angles to the proposed Snake River 

drainage to California), and in none of the resulting basins 

have any Blancan (Pliocene) age deposits been found 

(Walker and Repenning, 1965, 1966). The lack of Blancan 

deposits extends southward (with the ignimbrites) into 

northwesternmost Nevada. Southeast Oregon and adjacent 

Nevada were a highland well before the existence of the 

Glenns Ferry lake, and remain so today. 

Deposits claimed to be of Pliocene age from the Danforth Formation southeast of Harney Lake, Oregon (Taylor, 

1966; Taylor and Bright, 1987), are of Miocene age by 

modern correlations, as are all deposits of southeastern Oregon that were called "Pliocene" in the 1960's by Malde and 

Powers (1962), Walker and Repenning (1965, 1966), and 

Shotwell ( 1970). (See "Mammal Ages and Provincialism,'' 

p. 10-13.) 

Informed discussion of the drainage route from southern Idaho before the Glenns Ferry lake formed and of the 

earliest flow of the Glenns Ferry lake down Hells Canyon to 

the Columbia River requires consideration of evidence 

beyond the limits of the western Snake River Plain. These 

drainages should have left records in other areas. 

Drainage of southern Idaho, prior to the Glenns Ferry 

lake, is speculative; most evidence of the actual drainage 

route seems to have been destroyed by elevation of Basin 

and Range mountains and covered by volcanic flows; whatever the route, it was across the much older path of the Yellowstone "hot spot" and is likely to have been affected by 

both tectonism and volcanism. However, similarities in fossil and living freshwater fish (Miller, 1965, p. 576 and fig. 

3) and mollusks (Taylor, 1966, p. 17-27) have long suggested a possible late Miocene route out of southern Idaho 

and into northern California, to join the Sacramento River 

drainage. 

To a degree, the interpretation of this drainage route is 

also supported by diatom similarities in the Klamath Lake 

area of southern Oregon (J.P. Bradbury, oral commun., 

1992) and a questionable record of the primitive muskrat 

Dolomys in central California; Dolomys was ancestral to 

Pliopotamys from the Glenns Ferry Formation. This record 

of Dolomys is a damaged lower jaw (UCMP 57958) from 

the uppermost part of the upper Miocene and lower 

Pliocene Etchegoin Formation (UCMP locality V3520) in 

the Kettleman Hills, California. The locality is stratigraphically near the Lawlor Tuff, which lies within the Nunivak 

event of the Gilbert Chron (Sarna-Wojcicki, 1991) and has a 

date of 4.1 million years; it is thus older than the earliest 

mammalian record from Hagerman. 

The muskrats originated in Eurasia and this date is in 

the earlier, but not the earliest, part of their record there. 

The earliest record is in western Asia (Kazakhstan) and 

appears to be of latest Miocene age (Repenning and others, 

1990). 

The presence of a muskrat in the Etchegoin Formation 

suggests a surface-water connection between the Sacramento River system and the Snake River and Glenns Ferry 

lake, in which its descendant, Pliopotamys minor, is first 

known from the earliest faunas at Hagerman. The lack of 

the Ondatrinae (the muskrats) in the Columbia River basin 

until about 2.9 million years ago (to be discussed), but their 

presence in the oldest Hagerman faunas (3.6 Ma) and in the 

Sacramento River basin ( 4.1 Ma) suggests that the lineage 

arrived in Idaho up the Sacramento River drainage and that 

its later introduction to the Columbia River basin was down 

the Glenns Ferry lake-Snake River drainage (Hells Canyon). The record of the muskrats, as well as of mollusks and 

fish of the Sacramento area, thus suggests a connection with 

the Sacramento River drainage basin before the time that 

the Snake River first flowed into the Glenns Ferry lake; 

once the river flowed into the western Snake River Plain it 

could no longer flow to the Sacramento basin without crossing the southeast Oregon highland. 

It is well known that this part of Oregon was uplifted 

by middle Miocene time, as just discussed (p. 66-67), 

and a series of late Miocene (pre-Glenns Ferry) basins are 

preserved, at progressively lower elevations, down the 

modern northward course of the Owyhee River from the 

southwesternmost corner of Idaho, through the Jordan Valley area, around the north end of the Owyhee Mountains 

of Oregon, and to the modern Snake River north of the 

Froman Ferry area near the junction of the Boise River. 

These basins correlate, but were not depositionally continuous, with Lindgren's Payette Formation. Although all 

these basins contain late Miocene deposits, only the 

Rome basin in the Jordan Valley area contains later deposits, and these are Irvingtonian in age, younger than the 

Glenns Ferry Formation. The Owyhee drainage has been 

flowing north since well before the deposition of the 

Glenns Ferry Formation. 

To the west of the Owyhee River, across southeastern Oregon at least as far as Lakeview, modern topography is marked by Basin and Range mountains and basins, 

trending roughly north-south, at right angles to the trace 

of the proposed former route of the Snake River. No 

deposits of Blancan age have been found in any of these 

basins, as would be expected if the Snake River formerly 

drained westward across them (Walker and Repenning, 

1965, 1966). 

A more probable route, which at least has early Blancan deposits along it, runs from the present position of 

the Snake River near Twin Falls, Idaho, south through the 

eastern part of northern Nevada to the Humboldt River 

area, westward to Winnemucca and the Black Rock 

Desert in Nevada, and then to the Alturas lake basin and 

the Pit River in California (fig. 13 ). This route traverses 

several basins with upper Miocene and, particularly, some 

pre-Glenns Ferry Pliocene deposits that are entirely 
68 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

missing between Marsing, Idaho, and Klamath Lake, Oregon; it also detours the highland of southeastern Oregon. 

This Nevada route also crosses the eastern scarp of the 

Sierra Nevada west of the Black Rock Desert and constrains this uplift to an age no older than early Pliocene 

(after about 4.7 Ma). The faunal and floral similarities of 

the Klamath Lake area, a strong point in the argument for 

the southern Oregon route, may indicate that the area was 

then tributary to the Sacramento River drainage, and not 

necessarily a part of the former Snake River. 

The modern Pit River follows a series of lacustrine 

basins in northeast California, including that containing the 

lake beds of the Alturas Formation, and drains into the Sacramento River. These lacustrine basins may have been part 

of the former drainage route from southern Idaho, or may 

have been tributary to it. The history of these basins is 

poorly known, but they appear to have resulted from the 

damming of drainage by lava flows and faulting. 

The lake beds in the vicinity of Alturas, California, 50 

miles south of Lakeview, Oregon (fig. 13), are best exposed 

and best known; all other basins are downstream along the 

Pit River and, essentially, not dissected. All deposits in the 

Alturas basin are of an age that is older than the known age 

of the Glenns Ferry Formation, although they may equal 

the age of at least part of the older formations of the Snake 

River Plain. The youngest faunas of the Alturas lake basin 

are of earliest Blancan age (4.8 Ma: Repenning and others, 

1990, p. 395-396). The oldest faunas in the Alturas basin 

are of Miocene age (greater than 5.3 Ma; Evernden and others, 1964). The presence of the diatom Mesodictyon in 

these older deposits of the Alturas basin suggests an age 

similar to that of the Chalk Hills Formation, underlying the 

Glenns Ferry Formation of the western Snake River Plain 

(J.P. Bradbury, written commun., 1993). 

The earliest Blancan fauna of the lake beds of the 

Alturas Formation occurs in marsh deposits (fiat-bedded, 

diatomaceous, silty deposits, with reed and rush remains 

and containing a prominent ash bed) that were marginal to 

the lake. The fauna contains the ancestors of the Glenns 

Ferry microtines, Mimomys (Ophiomys) taylori and 

Mimornys (Cosomys) primus, both known from the oldest 

marsh beds at Hagerman (Repenning, 1987). This Blancan 

fauna is well dated at 4.8 Ma by (1) a 4.7±0.5 Ma potassium/argon date of a lava flow on top of the lake beds and 

about 70 feet above the fauna (M.L. Silberman, written 

commun., 1978; three samples were run with good agreement); (2) paleomagnetic correlations (S.R. May, written 

commun., 1985); the early Blancan faunas lie about 15 feet 

above the Thvera event of the Gilbert Chron (younger than 

4.85 Ma); and (3) a directly associated ash bed (the fauna is 

found both above and below the ash) that has been fingerprint -correlated with a tephra in a core off the California 

coast and there dated by marine biochronology at about 4.8 

million years (A.M. Sarna-Wojcicki, written commun., 

1985). These age controls are in addition to ( 4) the 

biochronologic correlation provided by the microtine 

rodents (Repenning and others, 1990, p. 396), which indicates an age about as old as the other evidence. 

Deposits of a slightly younger age are known from the 

Ringold Formation in the Columbia River drainage basin 

near Pasco, Washington (fig. 13; White Bluffs fauna, ::::4.3 

Ma; Gustafson, 1978; Repenning, 1987), but the mammalian similarity is weaker as the fauna contains no ancestor 

of Mimomys (Cosomys) primus, which became extinct in 

the Pacific Faunal Region about 3.0 million years ago and 

never appears, as a result, in the Columbia River basin. 

Mimomys (Ophiomys) mcknighti, found in the Alturas 

fauna, was named from the White Bluffs fauna by 

Gustafson (1978). In the White Bluffs section there are 

overlying transitional faunas that show evolution of M. ( 0.) 

mcknighti into an intermediate form, informally called 

Mimomys (Ophiomys) mcknighti-taylori, that is present in 

abundance in the Blufftop faunas (Repenning, 1987; ::::3.9 

Ma). M. (0.) taylori (the slightly younger species from 

Hagerman) is present in the younger Taunton fauna (::::2.9 

Ma) of the Pasco basin. Here is a nice demonstration of an 

evolutionary sequence that bridges the time between the 

dated record from Alturas to the early Hagerman records 

and roughly to the Sand Point record in the Glenns Ferry 

Formation. 

But there is no record of the lineage of Mimomys 

( C osomys) at any time in the Pasco basin, nor any muskrat 

until the Taunton fauna (2.9 Ma). 

Although both subgenera of Mimomys appear as 

immigrants from Eurasia 4.8 million years ago (Alturas 

fauna), from these fossil records Mimomys ( Cosomys) 

seems to have followed the Pacific Coast from Beringia 

(and Eurasia) to the San Francisco area (where it alone is 

first found in UCMP locality V6869-Maxum fauna; 

Repenning, 1987, p. 254; May, 1981). It then appears to 

have moved up the Sacramento River to the Snake River, to 

be diverted into Glenns Ferry lake area at Hagerman with 

the primitive muskrat Pliopotamys minor, which arrived 

from Eurasia (as Dolomys) with the next dispersal event 

about 4.1 million years ago (Etchegoin fauna). 

Mimomys ( Ophiomys) immigrated at the same time 

but appears to have moved inland up the then-existing 

Columbia River, where it is later known from the White 

Bluffs fauna and can be stratigraphically followed upward 

as it evolved into the more advanced species of the Hagerman fauna. But before the White Bluffs fauna this immigrant moved southward as far as Alturas, California; its 

further dispersal southward in the Pacific Faunal Region 

was greatly delayed, presumably because Alturas was then 

at the southern limit of its temperature tolerance. 

There is no recognized indication in the fossil record 

of why Mimomys (Ophiomys) was able to move southward 

from the Columbia River area to northern California, when 
HISTORIC SETTING OF THE FROMAN FERRY FAUNAL SUCCESSION 69 

Mimomys (Cosomys) did not move northward over the 

same route. Both are present in the oldest faunas of the 

Glenns Ferry Formation of Idaho and in the Alturas Formation of northern California, and in no other known fauna of 

North America. By the time that Mimomys (Ophiomys) is 

known farther south than Alturas, Mimomys (Cosomys) had 

become extinct in the Pacific Faunal Region. 

Mimomys (Cosomys) also moved southward from the 

San Francisco area, obviously down the San Joaquin River 

drainage, where it is known from the Kettleman Hills, in 

the "Pecten Bed" of the San Joaquin Formation-an 

approximate Hagerman equivalent (Repenning, 1987, p. 

256). The species (M. (C.) primus) continued southward to 

the type locality in the Coso Mountains near what is now 

the Mojave Desert. But it is unknown in the Columbia 

River basin at any time, and was extinct by the time the 

muskrats entered that area from the Glenns Ferry lake. 

Early Pliocene tectonic and volcanic activity of the 

Owyhee Plateau south of Twin Falls, Idaho (and along the 

older path of the Yellowstone "hot spot"), could have 

blocked flow of the Snake River southward into Nevada, 

and to the Sacramento drainage. This blocking could only 

direct the Snake River into the western Snake River Plain 

near Hagerman. Interestingly, this model would suggest 

the temporary creation of a pre-Glenns Ferry lake 

upstream from Twin Falls (possibly extending to INEL; 

fig. 1 ). Little direct evidence of a route southward from the 

area of Twin Falls (into northern Nevada) exists other than 

scattered basins with deposits of the proper late Miocene 

and early Pliocene age, and containing microtine faunas 

that were ancestral to those from the Glenns Ferry Formation. To our knowledge, the fish and mollusks of the Alturas lake beds have not been examined. 

Presumably after 4.7±0.5 Ma (date of the lava 

capping the Alturas lake beds) and before 4.0 Ma (oldest 

known Glenns Ferry Formation near King Hill), the disruption of a southwestward drainage of the Snake River 

into Nevada and diversion to the northwest into the Snake 

River basin and the Columbia River took place. The 

Glenns Ferry lake then flooded parts of the western Snake 

River Plain until it reached the sill height of a preexisting 

Hells Canyon tributary of the Columbia River. 

Formation, or deepening, of the Snake River graben 

happened either at the same time that activity on the Owyhee Plateau obstructed flow to Nevada, or the diverted 

Snake River flowed into preexisting small lakes within the 

graben. That these lakes existed seems indicated by the 

locally oolitic rusty sand unit and the underlying and 

saline Chalk Hills Formation. Both are more tectonically 

deformed than the Glenns Ferry Formation and are found 

unconformably beneath the Glenns Ferry Formation along 

the southwest side of the Snake River Plain as far northwest as Marsing and the northern limit of the Glenns 

Ferry Formation. The greater deformation of these earlier 

lake beds suggests that the Snake River graben was further deepened just before the Snake River was diverted 

into it. The pre-Glenns Ferry lake beds extend farther 

north than does the Glenns Ferry Formation, to the 

approximate latitude of Weiser, Idaho, and, west of the 

Snake River, Moores Hollow, Oregon. 

From the delta deposits at Hagerman, it seems obvious that the Snake River drained into the Snake River 

Plain graben to form the Glenns Ferry lake before about 

3.6 million years ago, possibly because of diversion of 

earlier flow through Nevada and into California. That 

diversion took place earlier is suggested by the inferred 

age of the oldest Glenns Ferry Formation in the King Hill 

area (>4.0 Ma) and by the youngest deposits of the Alturas lake beds (4.7±0.5 Ma). 

There remains a gap of possibly 700,000 years 

between flow of the Snake River into California and the 

earliest record of flow into the Snake River Plain. Much 

of it could disappear into the "±" estimate of the radiometric ages involved, but not in the biochronology of the 

microtine rodents involved; fossil records are not, however, found in every foot of section under consideration. 

A lake along the Snake River upstream from Twin Falls, 

Idaho, could be responsible for only part of this time. During this time deposits are known in the Ringold Formation in the area of Pasco, Washington, but the faunas of 

this time in this area do not contain Sacramento River faunal elements. A delay occurred between flooding of the 

Snake River Plain and outflow to the Columbia River; in 

the same way, there was a delay between the Snake River 

flowing into Nevada and then into the Snake River basin. 

GLENNS FERRY LAKE DRAINAGE 

From the development of marsh cover across the 

Snake River Plain in the vicinity of Grand View 2.4 million 

years ago (p. 61-62) and from the lack of evidence of significant salinity in the lake beds, it seems obvious that the 

Glenns Ferry lake was draining somewhere and had 

reduced its area to less than half the area of the Snake River 

Plain by this time (it has not been established that the 

Glenns Ferry lake ever covered, at one time, the entire area 

of the western Snake River Plain). 

The proposed route up the Owyhee River and across 

southeastern Oregon to the Sacramento River drainage is 

implausible, as this area shows all signs of being a drainage 

divide during the late Miocene and Pliocene, and contains 

no evidence of deposits of the appropriate age. One other 

drainage route of the Glenns Ferry lake has been suggested: 

into Oregon and west of the Wallowa Mountains to the 

Columbia River (Wheeler and Cook, 1954 ), but this route 

also contains no Blancan deposits, although middle and 

upper Miocene deposits are known. This route would also 
70 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

cross a highland between the Wallowa and Blue Mountains 

(fig. 13) to follow the Grande Ronde to the Columbia River, 

a highland that developed with the Blue Mountains and is 

much older than any drainage of the Snake River here considered. No outlet for the western Snake River Plain other 

than Hells Canyon seems possible. 

Downstream from Hells Canyon, in the area of Pasco, 

Washington, where the Snake River now joins the Columbia 

River, extensive lacustrine and fluvial deposits are included 

in the Ringold Formation. This formation contains (fig. 4) 

( 1) the River Road fauna (Gustafson, 1977) that is near the 

following fauna and is of Miocene age, possibly the age of 

the Chalk Hills Formation that underlies the Glenns Ferry 

lake beds and of the older part of the Alturas Formation of 

northeast California (the River Road fauna is in a coarse 

conglomerate rather than lake beds); (2) the White Bluffs 

fauna (Gustafson, 1978) that may be 4.3 Ma old (Repenning, 1987), older than any mammalian fauna in the Glenns 

Ferry Formation but of Blancan (Pliocene) age and younger 

than the youngest part of the Alturas lake beds of northeast 

California; (3) the Blufftop faunas (Gustafson, 1985; 

including Haymaker's Orchard locality of Repenning, 

1987) that are about 3.9 Ma old (a little older than the oldest 

Hagerman mammals but possibly a bit younger than the 

oldest lake beds included in the Glenns Ferry Formation 

near King Hill); and (4) the Taunton fauna (Tedford and 

Gustafson, 1977; Morgan and Morgan, 1995) about 2.9 Ma 

old, younger than the Hagerman faunas and about the age of 

the Sand Point fauna of Idaho. Repenning ( 1987) assigned 

too old an age to the Taunton fauna, and an age of about 2.9 

Ma has become evident with further collecting of the locality by James and Neil Morgan of Othello, Washington. 

Pliopotamys minor, the small muskrat named from the 

Hagerman fauna (Wilson, 1934 ), is the oldest North 

American muskrat except for Dolomys (p. 16, 67) from the 

Kettleman Hills, California. Its first record at Hagerman is 

from the base of the deltaic deposits, above the lake beds in 

the oldest part of the Glenns Ferry section. Here it is about 

3.6 Ma old and appears about 23 feet above the 3.8-millionyear-old top of the Cochiti Normal-polarity Subchron of the 

Gauss Chron (Neville and others, 1979). In Idaho, this 

primitive muskrat is also known from the Sand Point and 

Birch Creek faunas; it was replaced by Ondatra idahoensis 

in Blancan V faunas of Jackass Butte ( <2.4 Ma), and Pliopotamys minor has no younger record. 

In the Ringold Formation of the Pasco basin, Pliopotamys is clearly not present in the White Bluffs fauna ( 4.3 Ma, 

older than any North American muskrat) or the Blufftop 

faunas (3.9 Ma, younger than the California record but 

older than the oldest Glenns Ferry record). Its first appearance in the Taunton fauna of the Ringold Formation (2.9 

Ma), as an advanced form, is 700,000 years younger than 

the oldest Hagerman records, but no fauna of an intermediate age is known between the Blufftop faunas and the 

Taunton fauna of the Ringold Formation; Pliopotamys 

could have entered the Pasco basin any time between 3.6 

and 2.9 million years ago. 

The presence of the little muskrat from the Taunton 

fauna seems to indicate that the Glenns Ferry lake was 

draining down Hells Canyon at least by 2.9 million years 

ago. The lake may have been draining by this route since 

the earliest Glenns Ferry mammal records, because no older 

faunas are known from the Ringold Formation that postdate 

Pliopotarnys' oldest Hagerman record. 

As has been mentioned, the oldest Glenns Ferry Formation appears to be in the King Hill area, and is 

believed to be older than the oldest record of Pliopotamys 

minor at Hagerman. The King Hill record is reversely 

polarized and is presumed to be older than the Cochiti 

event recorded at the base of the Hagerman section (Neville and others, 1979). If it is this age, then the paleomagnetic position of the oldest Glenns Ferry lake beds seems 

to be about the same as that of the Blufftop fauna in the 

Pasco basin. No Pliopotamys has been found this old in 

the Glenns Ferry Formation, but the right environment is 

not involved: a muskrat finds little food in a large lake. 

Thus the oldest record of the Glenns Ferry lake is about 

contemporaneous with the Ringold Formation Blufftop 

fauna, and the absence of Pliopotamys in Blufftop may be 

due to delay of the muskrat in entering the Glenns Ferry 

lake, or to delay caused by the time involved in filling the 

western Snake River Plain to the then-existing sill at the 

head of the ancestral Hells Canyon. As has been noted (p. 

56-57), the oldest lake beds at Hagerman appear to have 

been of limited extent, suggesting that the Snake River 

Plain basin had not yet filled to sill depth. 

It is not likely that the little muskrat took an overland 

route, across the Salmon River Mountains of central Idaho 

from the Snake River Plain to the Pasco basin. The less 

aquatically adapted Mimornys (Cosomys) primus did not do 

so earlier (p. 68-69), and muskrats are closely tied to their 

habitat and seem to have little sense of direction. Erickson 

( 1963) found that when he moved living muskrats about 2.5 

miles from their home range, only 15 percent found their 

way back, whereas if he moved them only I mile, 57 percent found their way back to their former home area. A 

sense of direction is not important when dispersal routes 

are closely tied to water routes. 

The record of Pliopotamys in the Taunton fauna is permissive of a through-flowing Snake River to the Columbia 

River system from the beginning of the Glenns Ferry lake 

almost 4 million years ago, and is indicative of such a 

drainage by nearly 3 million years ago. 

The Taunton fauna also has the first (and only) record 

of the giant beaver Procastoroides idahoensis (small form) 

in the Columbia River basin. Expectably, because of the 

age of the fauna, the Taunton giant beaver is very similar in 

size to that from the Birch Creek fauna of the Glenns Ferry 
CONCLUSIONS 71 

Formation (p. 61 ); it is larger than P. intermedius from the 

Hagerman fauna, but smaller than typical P. idahoensis 

from Jackass Butte. Like the muskrats, Procastoroides 

appears to have been closely tied to standing water, and 

nearly all records are from marsh deposits (Kurten and 

Anderson, 1980, for Castoroides), and all are associated 

with muskrats. 

The history of origin of Procastoroides is not so certain, however, and it may have derived from Dipoides in 

several areas-the Great Plains, the Snake River Plain; and 

Gustafson ( 1978) described a suitable ancestor from the 

White Bluffs fauna in the Ringold Formation. 

Several other forms occurring in the Taunton fauna 

suggest a Glenns Ferry fauna of about the same age, but 

these aquatic mammals are most convincing of a hydrologic connection. 

CONCLUSIONS 

I. Because of the suggested prior history of the 

muskrat lineage in the Sacramento River drainage basin, 

Pliopotanrys appears to have been introduced to the Snake 

River Plain by the diversion of the Miocene and early 

Pliocene Snake-Sacramento River drainage. Similarity in 

the fish and mollusk faunas has indicated, for over a quarter 

of a century, a probable early connection between the Snake 

and Sacramento Rivers. 

2. The route of the Snake River to the Sacramento 

River system is not clear, but a route across southeast Oregon does not seem possible because this area has been a 

highland since about 15 million years ago. A route south 

from the present position of the Snake River near Twin 

Falls, Idaho, across northeastern Nevada (and the former 

path of the Yellowstone "hot spot") to the general area of 

the modern Humboldt River, west to the Black Rock Desert 

of western Nevada, through the Alturas lake basin and down 

the Pit River to the Sacramento River is suggested. This 

proposed route skirts the highlands of southeastern Oregon 

(which extend into northernmost western Nevada). Lacustrine basins in the Black Rock Desert, Nevada, and in the 

Alturas basin, California, contain deposits that range in age 

from late Miocene into early Pliocene, favoring this hypothesis of the earlier drainage of the Snake River. 

The youngest lake beds in the Alturas basin, California, are about 4. 7 (±0.5) million years old and (70 feet 

lower in the section) contain the ancestors of two microtine 

rodents that are first known in the Snake River Plain from 

the oldest nonlacustrine Glenns Ferry Formation (3.6 Ma). 

The oldest Glenns Ferry fossils also include the giant beaver Procastoroides (place of origin uncertain) and the first 

muskrat (derived from ? Dolomys of the Sacramento drainage). The youngest fossils of the Alturas lake beds are too 

old to contain the ancestor of the Glenns Ferry muskrat, 

first known about 4.1 million years ago in the Sacramento 

River basin. 

Although the two subgenera of the microtine Mimom.vs 

from the Hagerman delta deposits are known by ancestral 

species from the Alturas faunas, only one, M. (Ophiomys), 

is also known from the Ringold Formation of the Columbia 

River basin, in the White Bluffs fauna that is 4.3 million 

years old. The other subgenus known from Hagerman, 

Mimomys (Cosomys), has never been reported from the 

Columbia River basin, but is first known from the San Francisco area and the Sacramento River system; it became 

extinct in the Pacific Faunal Region before the time of the 

Taunton fauna of the Ringold Formation. 

The history of the dispersal of the subgenus Mimomys 

( Ophiomys) suggests that it dispersed from Asia, through 

Beringia, down the Pacific coast and up the Columbia 

River, south to the former Snake-Sacramento River drainage as far as the Alturas lake basin. Its earliest records in 

central and southern California, south of the Alturas area, 

are much younger than the earliest records in the Pacific 

Northwest. There is a suggestion that this subgenus was 

more inclined toward cooler climates than its associates in 

the Glenns Ferry Formation; for example, the subgenus (as 

Mimomys (Ophiomys) parvus) did not reach southern California except during a period of maximum glaciation in the 

United States (p. 30-31 ). 

The other subgenus, Mimomys ( Cosomys), that is 

present in the Alturas ( 4.8 Ma) and Hagerman faunas 

(3.6-3.2 Ma, youngest record is in the Hagerman horse 

quarry), is unknown in the Columbia River basin, as has 

been noted. This subgenus appears to have crossed the 

Columbia River drainage when dispersing southward down 

the Pacific Coast (about I million years before the Snake 

River was diverted into the Columbia) and moved on to the 

Sacramento drainage where its earliest records are among 

the oldest known. Its record in the San Francisco area (from 

the Maxum fauna; Repenning, 1987) is probably the oldest 

Blancan fauna in the United States (Blancan being defined 

by the arrival of Mimomys), but has only weak evidence of 

age. The subgenus appears to have become extinct about 3 

million years ago in the Pacific Faunal Region; earlier it 

dispersed to the Great Plains where it evolved into the 

subgenus Ogmodontomys and persisted throughout the 

Pliocene. 

The early muskrats followed the same route as 

Mimomys (Cosomys) perhaps 4.2 million years ago. But 

they did not become extinct so quickly and, with the giant 

beaver, appeared in the Columbia River basin by 2.9 million 

years ago. 

From these two points, we believe that the Snake 

River was diverted from its route through northern Nevada, 

California, and the Sacramento River drainage, and into its 

present route down the Snake River Plain to the Columbia 

River drainage, between 4 and 3 million years ago. Insofar 
72 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

as records indicate, the Glenns Ferry lake began to drain 

down a preexisting Hells Canyon as soon as the Glenns 

Ferry lake filled to sill depth; this may have been by 3.9 

million years ago and certainly was before 2.9 million years 

ago. Judging from the Bruneau paleomagnetic section of 

Neville and others ( 1979; typical Glenns Ferry lake deposits before 3.4 million years ago), the Glenns Ferry lake was 

fully developed to sill depth well before 3.4 million years 

ago. 

3. Earlier lakes existed in the position of the Snake 

River Plain that appear not to have been entirely confined 

to that area, as defined by the modem topography. The 

most widespread deposits of these lakes are those of the 

Chalk Hills Formation of Malde and Powers (1962), 

which are exposed along the southwest side of the plain, 

and beyond, for more than 100 miles. This unit of late 

Miocene age is characterized by saline lake deposits 

(abundant gypsum, saline diatoms) and thus does not suggest as large an input of fresh water as that provided by 

the Snake River, nor through-flowing water. It also is 

more tectonically deformed and in many places is found 

beyond the boundary faults of the Snake River graben. 

The Chalk Hills Formation lies unconformably beneath 

the unnamed, locally oolitic · rusty sandstone unit which, 

in tum, unconformably underlies the Glenns Ferry 

Formation. 

Both of these older units are believed to predate the 

diversion of the Snake River into the Snake River Plain 

from its prior route to the Sacramento River system. Age 

control is not well defined at present, but the Chalk Hills 

Formation appears to be separated from the Glenns Ferry 

Formation by at least 4 million years, based upon published 

information. 

Deposits of the approximate age of the Chalk Hills 

Formation are present beneath the lower Pliocene beds in 

the Black Rock Desert and in the Alturas basin along the 

proposed former route to the Sacramento River; in these 

areas there appears to have been continuous deposition 

from late Miocene time into earliest Pliocene time. Late 

Miocene deposits are also widely distributed in eastern 

Oregon and adjacent Washington and in Idaho beyond the 

limits of the western Snake River Plain, unlike the Glenns 

Ferry deposits of Pliocene age. 

4. Filling of the Snake River Plain structural basin 

was by deposits brought into the Glenns Ferry lake by the 

Snake and apparently other rivers and by lava flows from 

the northeast flank of the graben. Apparently lava filling 

was less significant in the downstream part of the basin as 

the center of the lake, downstream from Oreana nearly as 

far as Walters Ferry, is progressively farther to the northeast 

and fluvial deposits are dominant along the southwestern 

margin. This situation abruptly changed downstream from 

Walters Ferry and lake beds again were deposited to the 

western margin of the Snake River Plain for the remaining 

distance to the Froman Ferry area and the head of Hells 

Canyon. 

The age difference of the oldest lake deposits of the 

transgressing lake, from location to location, is marked; 

ages vary from perhaps 4 million years old in the King 

Hill-Hagerman area (supported by paleomagnetic 

determinations), to about 2.4 million years old at the southwest margin of the basin west of Bruneau and Grand View 

(supported by fossils in the overlying marsh beds and 

paleomagnetic determinations at the Multi-ash section). The 

youngest possible age of known lake deposition is about 1. 7 

million years old near the southwest margin of the basin in 

the Froman Ferry area, an age supported only by the age of 

the overlying marsh beds. 

Along the southwest margin of the basin, from Oreana 

northwest to the Murphy-Guffey Butte area, Glenns Ferry 

lake beds are not present or are of only limited exposure; the 

formation is nonlacustrine in this area. Apparently a major 

source of fluvial material lay to the west of the Glenns Ferry 

lake in this area, perhaps an ancient Owyhee River passing 

through an embryonic Owyhee Mountains. These deposits 

have not been carefully prospected for fossils, and their age 

is uncertain. They overlie the Glenns Ferry lake beds that are 

little more than 2.1 million years old in the Oreana area and 

at Guffey Butte (not dated, but apparently less than 2.5 Ma). 

They were mapped as the Glenns Ferry Formation by Ekren 

and others ( 1981 ), but in part they could be a facies of the 

Bruneau Formation. 

We believe it probable that the center of the Glenns 

Ferry lake was east of the modem Snake River in this downstream area north of Murphy-Guffey Butte and that its 

deposits are now covered by basalt flows. It is obvious from 

these relationships that the entire structural basin of the 

Snake River Plain did not fill completely once the Snake 

River had been directed into it. Shifting of the lake to the 

southwest margin of the graben in the Grand View area 

resulted from filling along the northeast margin; restriction 

of the lake to the northeast side of the structural basin in the 

Murphy-Guffey Butte area could have taken place because 

of filling from the southwest side. 

5. In areas away from the lake and the then-prevailing 

Snake River, pond deposits indicate a lack of association 

with the river or lake because of the seasonal fluctuations in 

salinity and temperature they display. Only seasonal temperature changes are recorded in deposits of the Snake River, 

and deposits of the Glenns Ferry lake are uniform in both 

temperature and salinity. Marsh deposits, because of their 

close association with the lake, are also relatively free of 

indication of variation in both temperature and salinity, but 

(because they were covered by shallow water) the marshes 

were warmer than the open lake and were avoided by cold 

water fish. Their diatom flora and ostracode fauna were distinctly different than those of the open lake and they were the 

habitat of mammalian faunas. 
CONCLUSIONS 73 

6. As the lake receded from the head of the basin, 

either fine-grained fluvial or marsh deposits were deposited 

on top of the lake beds. Marsh deposits appear to have been 

deposited only in areas where tributary drainage into the lake 

was minimal, and are absent in the area of the mouth of the 

Snake River except as part of the deltaic deposits, where 

shifting distributaries left lenticular bodies of marsh 

deposits. 

7. Marsh beds are not known for all stages of lake 

withdrawal, and thus their recognizable presence may 

record periods of stasis in lowering the level of the Glenns 

Ferry lake. They, and the overlying fluvial deposits, contain 

mammalian fossils and therefore are the best source of evidence for dating the stages of withdrawal of the lake. The 

known marsh deposits were formed 3.6-3.2 Ma (Hagerman; 

magnetic and faunal age control), 3.1 Ma (Sand Point; magnetic and faunal age control with a weak correlation to oceanic oxygen isotope records), 2.4 Ma (Poison and Birch 

Creeks; magnetic, climatic, and faunal age control), 2.1 Ma 

(mid-Jackass Butte; magnetic, climatic, and faunal age control), and <1.67-> 1.5 Ma following the last withdrawal of 

the Glenns Ferry lake (Froman Ferry; magnetic, radiometric, climatic, and faunal age control). 

Except for the oldest of these marsh deposits, which 

was a result of the Snake River delta when the lake first 

formed and presumably was tectonically timed, these 

times of marsh deposition are the same as those of known 

or suspected increasing Northern Hemisphere glaciation, 

and a climatic cause is suggested for their development. 

(Compare with figure 2 of Repenning and Brouwers 

( 1992) to correlate with events in the Arctic Ocean 

region.) Times of increasing or maximum glaciation were 

times of increased precipitation, and the increased flow 

from the Snake River headwaters may have produced the 

stasis in the overall rate of lake drainage that allowed 

marsh deposits to accumulate in recognizable units. 

8. The return of marshes to the Jackass Butte area 

around 2.0 Ma ago suggests that the outlet of the Glenns 

Ferry lake was sufficiently restricted that increased flow 

of the glacial Snake River could not be fully accommodated, forcing a rise in lake level. It seems possible, from 

hemispheric records, that the region became more arid 

after this rise in lake level, but the lake deposits did not 

become saline, suggesting that drainage continued. 

The lake seems to have persisted until perhaps 1. 7 

million years ago in the Froman Ferry area. Hells Canyon 

must have been incised below the base level of the western Snake River Plain by the end of the Froman Ferry 

marsh deposition, and subsequent lacustrine deposition of 

the Bruneau Formation was dependent on the development of local basins behind lava dams across the Snake 

River. 

9. Evidence from the Columbia River basin, near 

Pasco, Washington, indicates a through-flowing drainage 

of the Glenns Ferry lake down Hells Canyon after about 3.9 

million years ago (after the Blufftop faunas) and before 

about 2.9 million years ago (before the Taunton fauna). 

Critical to this interpretation is the dispersal patterns of 

rodents (especially the dispersal of muskrats along 

streams), persistent lack of evidence of saline conditions 

throughout the 2.5 million year life of the Glenns Ferry 

lake, and the documentation of progressive filling of the 

western Snake River Plain throughout its history. 

10. We postulate that initial drainage down Hells 

Canyon was by way of a preexisting tributary of the 

Columbia River and that consideration of the modern elevation of the Glenns Ferry Formation suggests that possibly 

one-third of the modern depth of Hells Canyon was 

already cut before the Glenns Ferry lake overflowed a sill 

and started draining down it. In view of the more limited 

flow available to cut Hells Canyon before overflow of the 

Glenns Ferry lake and drainage of the Snake River down it, 

Hells Canyon may well have begun to form in the Miocene. 

11. In correlation with the climatic significance of 

marsh beds in the Glenns Ferry lake, listed in "7" above, 

the first record of the cold water stream sculpin is found in 

the Jackass Butte section, at a time marked by continental 

glaciation that advanced as far south as Iowa. Not surprisingly, this fish is absent in the younger and warmer marsh 

beds of the Froman Ferry area. 

12. Although several authors have suggested otherwise, a relationship seems indicated between the North 

American puma and the cat known from the Hagerman faunas, Felis lacustris. Minor increase in size and minor morphologic changes throughout the deposition of the Glenns 

Ferry Formation culminate in a remarkably complete 

(although fragmented) skeleton from the Froman Ferry 

sequence indicating that this was the ancestor of the living 

puma. The Froman Ferry records are by far the oldest fossil 

puma so far published. 

Comparisons of the Froman Ferry puma, and other 

records, suggest that the puma lineage was the first of the 

Old World cats to disperse to North America, at the beginning of the Blancan (4.8 Ma ago). The North American 

cheetah, Miracinonyx, was next, at about 2.56 million years 

ago; it arrived full size with larger limbs than the Froman 

Ferry (or modern) puma. The genus Panthera arrived last, 

by 840,000 years ago. 

A number of features suggest that the living lynx may 

also have derived from the lineage, although by 1.6 million 

years ago the Glenns Ferry lineage was already too large 

(and still had a long tail and too many teeth) to be ancestral 

to the lynx. Savage (1960, p. 337) suggested that the 

subgenus Felis (Lynx) had been established by the time of 

the Cita Canyon fauna of Texas (about the age of the earliest of the Grand View faunas, ""2.56 Ma), and Stephens 

( 1959) indicated that the cat from the Rexroad fauna of 

Kansas (Cochiti event, ""3.8 Ma; Repenning, 1987) was 
74 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

losing its P\2 in maturity; total loss of this tooth is a distinctive lynx character. 

13. Unexpectedly, the only identifiable leporid was a 

specimen of Hypolagus gidleyi from very high in the 

Cucumber area, close to being the youngest horizon of the 

Froman Ferry faunal succession and associated with Plesippus fromanius. An Irvingtonian age is beyond doubt, and an 

estimated age of 1.55 million years seems reasonable, 

although made uncertain by lack of evidence to estimate the 

duration of the hiatus involved in the overlying unconformity beneath the dated basalt (minimum age 1.5 Ma). 

This species has been believed to be no younger than 

about 2.6 million years old (Flatiron Butte), and the genus 

is generally considered to have become extinct by the end 

of the Blancan mammal age of the United States. This 

belief was a major factor in the erroneous correlation of the 

polarity pattern at the Multi-ash polarity section south of 

Oreana. 

14. Two horses are present in the Froman Ferry 

fauna: Plesippus idahoensis (Merriam) and Plesippus fromanius n.sp., a descendant of the well-known Glenns Ferry 

horse P. shoshonensis Gidley. P. fromanius represents direct 

evolution from the Hagerman horse, through the Jackass 

Butte horse, Plesippus stenonis anguinus (Azzaroli and 

Voorhies) with persistent direction of changes in the dentition throughout the Glenns Ferry Formation. These evolving characters are in the direction of the subgenus Equus 

(Equus) in the upper teeth; the lower teeth retain a simple 

Plesippus-like enamel pattern throughout the Blancan. 

The mixed characters (Equus-like upper teeth with 

Plesippus-like lower teeth) have been noted elsewhere in 

the Red Light fauna of western Texas (Akersten, 1972), in 

the lowest horizon of the type locality of Equus scotti at 

Rock Creek, Texas, and in the Aries fauna, southwestern 

Kansas (Rock Creek and Aries data from G.A. Izett and 

J.G. Honey, unpub., oral commun., 1993). According to 

Izett, the Rock Creek record has been dated close to 1.5 

million years old, similar to the Froman Ferry record. 

P. idahoensis appears to be a newly introduced lineage 

to the Snake River Plain in the Jackass Butte fauna, which 

preserved some plesippine characters but is advanced in its 

increased size and reduced upper tooth curvature. Both 

horses appear to be typically plesippine in their lower teeth. 

The application of Cope's species Plesippus simplicidens to these horses is undefended, and the Glenns Ferry 

species do not resemble Cope's species. No attempt to 

defend the synonymy has ever been published and published illustrations show major differences. The use of the 

species name Plesippus simplicidens is here restricted to 

Cope's type, and to topotypic material collected by 

Matthew and Simpson in the AMNH. 

The use of the genus-group name, Dolichohippus, for 

North American plesippine horses is poorly and, in part, 

incorrectly defended and biogeographically improbable as 

defended. It is not used here, and North American species 

are returned to Matthew's genus Plesippus. The subgenus 

Dolichohippus is restricted to the living and fossil African 

Grevys zebra. This is not to deny that they are closely 

related, but to emphasize the more advanced stage of evolution shown by the living form and to reflect phylogeny. 

15. The realization that the Ondatrini (muskrats) 

probably arrived in North America about 4.1 million years 

ago nullifies the evidence of intercontinental dispersal event 

4 of Repenning ( 1987) and Repenning and others ( 1990). 

Reevaluation of correlations based upon it is also needed. 

At present there appears to have been no intercontinental 

microtine dispersal event at 3.7 million years ago. The 

event had been only questionably recognized in Europe at 

the beginning of the Arondellian European small-mammal 

age (formerly referred to as the small-mammal Villafranchian age or, because of an erroneous assumption by Steininger and others, 1989, p. 24, earliest Villanyian). 

Microtine dispersal event 3 is prominently recognized 

in Europe at the beginning of the Csarnotan small-mammal 

age, but did not seem to be present in North America 

(Repenning, 1987). However, if the ondatrine from the Kettleman Hills of California does represent this group (which 

is not seriously doubted although it is a damaged specimen), it indicates immigration during dispersal event 3 (at 

the base of the Nunivak Normal-polarity event, 4.2 Ma) and 

not dispersal event 4 (near the end of the Cochiti event, 3.7 

Ma; Repenning and others, 1990). The original dispersal 

event 4 is not real, and, as in Eurasia, is not recognizable in 

the North American record. With renumbering because of 

this change, dispersal event 7 becomes dispersal event 6 

( 1.9 Ma, at the beginning of the Olduvai event and marking 

the Blancan/Irvingtonian faunal change in the Eastern Faunal Region of the United States [p. 10]). And the dispersal 

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and Microtus, to the Pacific Faunal Region becomes the 

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Olduvai event; not previously recognized and not evaluated 

outside of the United States). Dispersal event 7 is recognized in the Eastern Faunal Region as well, by the immigration of Phenacomys (but not Microtus), as has been 

discussed (p. 10, 16, and 32). 

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CORRECTION 

Julia T. Sankey (1991, ''A late Blancan-early Irvingtonian vertebrate fauna and magnetic stratigraphy from the upper Glenns 

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the oldest part of the Matuyama Chrons. The difference in interpretation equals nearly a million years and can only be clarified by the 

associated fauna. 

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However, Sankey reported Ondatra idahoensis from the 

lower, normally polarized magnetozone of Tyson Ranch (oral and 

written commun., 1995). Her material suggests a slightly larger size 

than at the type locality, Jackass Butte; clearly not representing the 

much smaller Pliopotamys minor found shortly above the top of the 

Gauss in the Birch Creek and Poison Creek faunas (see p. 34 ). It 

seems reasonable to assume that the immigration of Ondatra 

resulted in the rapid extinction of Pliopotamys, but a period of different environmental preferences may have existed in the two muskrats during which the smaller was restricted to marsh environments 

(Poison Creek and Birch Creek) while the immigrant Ondatra was 

restricted to fluvial environments (Jackass Butte, Tyson Ranch, 

"unnamed butte"). This possibility cannot yet be evaluated; present 

evidence indicates only that the oldest Ondatra is younger than 

Birch Creek and the Gauss Chron. 

The Tyson Ranch and "unnamed butte" sections can be 

approximately correlated by tracing a basaltic tuff (the Montini Tuff 

of Malde (1985)). Therefore, it seems probable that the normally 

polarized deposits at "unnamed butte'' and Tyson Ranch represent 

the Olduvai event, as inferred by Sankey, and not the top of the 

Gauss Chron, as inferred by Neville. Statements made in the present 

report (p. 51 and 64) that suggest that "unnamed butte" appears to 

be the same age as the Multi-ash polarity section farther to the west 

seem to be incorrect. In addition, Repenning's statements ( 1987 and 

following) that Mictom_vs is found just below the top of the Gauss 

Chron in Idaho also seem to be incorrect. The oldest known Mictomys in Idaho therefore is in the Birch Creek fauna (with an advanced 

Pliopotamys minor) shortly above the top of the Gauss Chron, or in 

the Ninefoot Rapids fauna of Conrad ( 1980), which has no paleomagnetic control. 
INDEX 

A 

Age 

Birch Creek fauna ....................................................................... 50, 61 

Eocene .............................................................................................. 53 

Fish Creek, Alaska, 2.4 Ma................ ...... ...... .......................... ...... .. 32 

fission-track...................................................................................... 62 

Froman Ferry faunal succession ........ ...... ...... ................ .................. 10 

Glenns Ferry lake beds, youngest dated ................................ 15, 47-51 

Miocene ........................................................................... 53-56. 65-70 

late ............................................................................ 31, 45, 53. 69 

Pleistocene ...... 5, 10-12, 14, 24-26, 31-34, 45, 46, 51, 53, 60, 61, 64 

Pliocene ...... 6, 10, 12, I4, 26, 27, 31, 37, 51,53-55,59,61, 67,68-72 · 

radiometric years...................................................................... II 

three parts . .. .... .. .... .. .. .. .. . .. .... .. .. .. . .... .. .... .. . .. .... .. .... .. .. . .... .. .. . .. .... . II 

Yarmouth .................................................................................. 61 

American Museum of Natural History (AMNH) ......................... 18, 43,45 

B 

Boundaries, age of 

Blancan-Irvingtonian............................................................... 10, II 

Miocene-Pliocene ............................................................................ I2 

Pliocene-Pleistocene ................................................................... II, I2 

Bradbury, J.P. ............................. 5, 6, 15, 49, 50. 51,56-58,60, 65, 67,68 

Bureau of Land Management, Boise District Office .................. ............... 2 

c 

California 

Alturas ........................................................................ II, 12, 18, 67-7I 

Anza-Borrego Desert ................................................. 10, 13, 30. 31,67 

Kettleman Hills .......................................................... II, 27, 67, 70,74 

Klamath Lake basins ............................................................ 55, 67,68 

Mojave Desert .................................................................................. 69 

San Francisco ........................................................................ II, 68, 7I 

Tule Lake .. ...... ... ...... ... ...... ... ... .............. .... .. . .. ............ ......... ............. 51 

Climatic implications 

Allophaiomys ............................................................. 10, II, I4, I6. 33 

Mictomys ........................................................ 14, 17, 29, 30-33, 52, 66 

Vallecito Creek......................................................................... 29 

Phenacomys and Mictomys .. .................................................. 17, 32, 33 

Phenacomys subgenera ................................................................ 32, 33 

Sorex palustris .................................................................................. 20 

Blancan V ............................................................ 15, 24, 34, 35, 61,66 

Bruneau Formation, interglacial ............................................ 15, 52,65 

Canadian ice in Iowa, 2.I Ma ........................ 15, 19, 30, 60, 63, 66, 73 

fish .................................................................................... 19, 33, 55, 72 

Fish Creek, Alaska........................................................................... 32 

Froman Ferry succession ..................................... 17, 29, 30, 33, 34, 51 

Glenns Ferry Formation .................................................... 5, 33, 55, 65 

microtine dispersals ......... 11-17, 24, 25, 29, 61, 62, 68, 69, 70, 73-74 

oxygen isotopic evidence ....................................................... 19, 64, 73 

questionable, based on modem ranges .. .. ..................... ................... 30 

80 

seasonality ................................................................................... 60, 6I 

second Reunion event 2.0 Ma ...... 19, 30, 31, 38, 50, 51, 60, 61, 63, 64 

unfrozen Arctic Ocean, permafrost .................................................. 33 

wet (herb) tundra ......................................................................... 24, 32 

Collections 

in marsh beds.................................................................................... 4 

National Museum of Natural History ............................................... 18 

Conrad, Gregory S ............................................................................... 15, 18 

Correlations 

biochronologic ................................. 6, 8, 10-13, 14, 17, 32, 53, 6I, 68 

climatic ................................................................ 14-17, 32, 60, 66,73 

mammals versus mollusks ........................................................... 12, 67 

Oreana lake beds to Jackass Butte fluvial beds .......................... 62-63 

paleomagnetic ................................................. 8, 49, 50, 51, 62, 63, 68 

Pliocene versus Miocene ............................................................. 53, 54 

to eastern Siberia ......................................................................... 14, 32 

Creeks 

Birch .................................. 8, 17, 34, 38, 43, 50, 51, 57, 58, 61-65, 73 

Castle ......................................................................... 6, 50, 51, 53, 62 

Poison ............................. 34, 40, 43, 47, 50, 58, 59, 61, 63, 65, 66,73 

Shoofly ..................................................................... 50, 57, 59, 62, 64 

Sinker ................................................................................................ 15 

D 

Diatom floras 

Birch and Poison Creek marsh beds overlie "typical" ...................... 62 

Bruneau ............................................................... 15, 49, 51, 52, 64, 65 

Guffey Butte .............................................................................. 65 

living in Pacific Northwest .................................................. 51, 65 

Sinker Creek .. .. .. .. .. .. .. .. . .. .. . .... .. . .. ... ... .... .. . .. .... .. ...... .. ... .... .. .... .. .. 15 

Chalk Hills ........................................................................................ 56 

Glenns Ferry 

"intermediate" ........................................................................... 58 

"oldest" ......................................................................... 49, 52, 58 

"typical" ....................................................... 15, 44,47-52, 56-59 

ecologic versus time significance ............................................. 51 

lake, youngest dated and possible ....................................... 49-51 

oldest, Hagerman lake beds .......................................... 50, 55, 56 

Glenns Ferry versus Bruneau ...................................................... 51, 52 

Hagerman 

basal lacustrine .......................................................................... 55 

delta deposits ............................................................................ 56 

Jackass Butte pond beds ................................................................... 60 

Multi-ash lake beds ...................................................................... 49, 58 

small, saline ponds ................................................................ 59. 60, 72 

Weiser lake beds ..................................................................... 5. 55, 56 

Dispersal events 

Allophaiomys from Asia to Eastern region, 1.9 Ma ......................... l 0 

Microtus, variation in different regions ............................................ II 

Mictomys from Arctic to Pacific region ................................. 14, 15,61 

Mimomys (Ophiomys) with Pliopotamys to Great Plains ................. 15 

Mimomys, beginning Blancan ........................................................... ll 

second invasion from Asia ........................................................ 31 
INDEX 81 

Ondatra and Pliophenacomys from Great Plains, 2.56 Ma ......... .... 15 Multi-ash, youngest dated ............................................. 47-52, 62 

Panthera lineage from Asia perhaps 0.84 Ma .................................. 25 overlain by fluvial deposits ................................................. 49-51 

Phenacomys (Paraphenacomys) gryci 1.6 Ma ................................. 32 Weiser ............................................................................. 6, 55, 69 

Phenacomys (Phenacomys) to Great Plains 1.6 Ma? ............ 11, 17, 32 Jake, marsh, and stream ............................................ 47, 55, 57, 58, 62 

Phenacomys and Microtus, Pacific region Irvingtonian ........ 10, 12-13 longitudinal relationships .......................................................... 57 

Plesippus idahoensis to Snake River Plain ...................................... 38 transverse relationships ................................................. 59, 62-64 

P. stenonis to Eurasia ....................................................... .41, 43, 45,46 marsh and river beds ......................................................................... 47 

Plioctomys to Eastern region, Blancan V .................................... 15,29 Wild Horse Butte- "unnamed butte" .................................. 62-64 

Pliophenacomys from Great Plains, 2.56 Ma .............................. 61-62 marsh beds 

Pliopotamys south to Nevada, Arizona, Great Plains .................. 15, 34 Alturas, Calif ............................................................................. 68 

"climatic control" ...................................................... 10, 13-17,24-25 ash beds ............................................................. 50, 51. 57, 62, 68 

"First Appearance Datums" (FADs) ................................................. 13 Birch and Poison Creeks overlie lake beds ......................... 62-64 

"Last Appearance Datums" (LADs) ................................................ 13 Birch Creek ....................................................... 47. 49. 50, 60, 63 

North American cheetah from Asia 2.56 Ma ................................... 25 Cucumber area .......................................................................... 10 

numbered dispersal events ........................................................... 16, 17 diatoms, Glenns Ferry Formation............................................. 5 

puma-lynx lineage from Asia, perhaps 4.8 Ma ................................ 25 extended across Snake River plain, Grand View area ............... 59 

Dispersal routes fresh water, distinctive .............................................................. 58 

climatically opened (or forced) and closed ........................... 14-17, 25 Froman Ferry faunal succession ................................. 5, 9, 47, 65 

different taxa followed different routes ................................. 10, 11, 13 Glenns Ferry, repeated development.. ........................... 49, 55, 73 

Pacific Coast to Pacific Northwest ........................................ 14, 68, 69 grade into lake beds ............................................................ 58, 65 

Pacific route, closed tectonically after 1.6 Ma ................................. 14 Hagerman.................................................................................. 57 

Pacific Region Jackass Butte, rise in lake level... ................ 17, 50, 60, 63, 66, 73 

from coast up Columbia ................................................ 14, 68, 71 pinch out against oolitic rusty sandstone ............................ 49, 64 

from coast up Sacramento ................................................... 14, 68 Poison Creek ........................................................................ 62,63 

through Arizona to Great Plains-south of Rockies ..................... 29, 69 narrow downstream, wide across .............................................. 58 

through Rockies to Great Plains-Yellowstone pass ........ 29, 30, 35, 62 "unnamed butte" ..................................................... 51, 62, 63, 79 

Drake, N.F. ............................................................................................ 2, 26 Faunal regions 

Duplication of statements......................................................................... 8 Beringian ........................................................................ II, 14, 29, 32 

Eastern ............................................................................ 10-17,29,74 

E Mexican ............................................................................................ II 

Pacific ............ tO, 11.13-17,25,29,30,47,55,61-62,69, 71, 72,74 

Evolution ............................ 13, 29, 30, 33, 38, 41, 45, 46, 51, 68, 69, 73, 74 separated by dispersal barriers .................................................... 13, 14 

Extinctions "western faunal region" .................................................................... 10 

Hypolagus ........................................................................ 26, 49, 50, 74 Faunal successions 

Mimomys (Cosomys) ................................................................... 69,71 Froman Ferry ............ 2-5, 8-20, 23-27,29-35, 37, 38, 40,43-52,56, 

Pliocto1nys ....................................................................... 16, 28, 30, 34 65-67, 74 

Pliopotamys 1ninor ........................................................................... 15 age ....................................................................................... 10, 17 

Procastoroides .................................................................................. 45 highest part................................................................................ 5 

versus Jackass Butte sequence .................................................. 10 

F Grand View ....................................... 16, 20, 30, 34, 38, 43, 51, 59, 61 

in Blancan definition ................................................................. 61 

Facies minimum 10 faunas .................................................................. 59 

ash beds Hagerman ............................................. 5, 6, 12, 20, 26, 34, 43, 55, 57 

Alturas ...................................................................................... 68 Jackass Butte .......................... 15, 17,19, 30, 34, 35, 38, 40, 51,60-64 

Borchers .................................................................................... 61 as young as about 2.0 Ma ........................................................ 38 

Cudahy ...................................................................................... 61 possibly as old as 2.3 Ma .......................................................... 38 

Glenns Ferry Formation .................................... 50, 51, 57,61-64 two horses ................................................................................. 27 

Multi-ash or Birch Creek.. ........................... 50, 51, 60, 61, 64, 65 Krestovka sections, Yakutia .............................................................. 32 

Strout Claim ............................................................................. 56 Rock Creek, Texas ........................................................... 18, 41, 47, 74 

Yellowstone .............................................................................. 61 Vallecito Creek, Calif ......................................... 10, 13, 16, 17, 24,30 

"floodplain'' "unnamed butte" ............................................................. 51,"62, 63, 64 

Glenns Ferry Formation .................................................. 5, 54, 57 Faunas 

fluvial .................................................................................... 55, 57,58 Aries, Kans ........................................................................... 18, 41, 47 

Birch and Castle Creeks, Oreana, and Guffey Butte .......... 57-59, Alturas, Calif .................................................................. 11, 18, 68,69 

61-63, 72 Asphalto, Calif. ................................................................................. 20 

Froman Ferry area ............................ 5, 10, 18, 19, 25, 26, 57, 65 Beaver, Utah ..................................................................................... 29 

Glenns Ferry Formation ............................. 50, 52, 55-57, 59, 73 Beck Ranch, Texas ............................................................................ 11 

Grand View area, center of the basin ................ 49, 51, 57-63, 65 Birch Creek ............................................... 8, 34, 43, 50, 51, 59-63, 70 

Jackass Butte........................................ 15, 17, 51, 59-61, 63, 64 correlation to Multi-ash section .......................................... 50, 61 

"unnamed butte" ........................................................... 62-64, 65 Black Butte ................................................................................. 59, 60 

lake beds Blanco, Texas ........................................................................ 18,43,44 

Alturas, Calif ...................................................................... 68, 69 Blufftop, Wash ...................................................................... 68, 70, 73 

Bruneau ......................................................................... 15, 51,65 Booth Canyon, Idaho ........................................................................ 32 

Glenns Ferry Formation ...... 3-6, 9, 17, 47, 49-52, 55-62, 65-69 Borchers, Kans ..................................................................... 14, 29, 61 

Glenns Ferry, beneath Birch Creek fauna ............................ 61. 62 Boyle Ditch, Wyo. (Yellowstone pass) ....................................... 15, 29 

Hagerman ............................................................................ 55-58 Buttonwillow, Calif ........................................................................... II 
82 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

Castle Butte ...................................................................................... 59 Alturas (California) ............................................................... 18, 68-71 

Chattin Hill .................................................................................. 59-60 Banbury Basalt ................................................................................. 53 

Cheetah Room, W.Va ............................................................. 27-29, 31 Black Mesa Gravel ........................................................................... 53 

Cita Canyon, Texas .......................................................... 15, 20, 35,73 Bruneau .................................... 5, 15, 49, 51, 52-54, 57, 62, 64, 65, 72 

Duncan, Ariz. .. . .. .. . . .. . .. . .. .... .. . .. ... .. . .. . .. . .. .... .. .. . .... .. .... .. ... ... .. .. .. .. . .. .. . .. I I Bully Creek ....................................................................................... 54 

Fish Creek, Alaska ........................................................................... 32 Chalk Butte ................................................................................... 6, 53 

Flatiron Butte .................................................................. 49, 57, 61,64 Chalk Hills ............................. 2, 5, 6, 53-56, 59, 62, 65, 68, 69, 70, 72 

Hagerman horse quarry ........................................................ 42, 59, 71 Clover Creek lava ............................................................................. 55 

Hudspeth, Texas.............................................................. II, 16, 41, 4 7 Columbia River Basalt. ..................................................................... 53 

Java, S.Dak .................................................................... 11,16,31,32 Danforth (Oregon) ............................................................................ 67 

Kettleman Hills, Calif.. ....................................... II, 27, 67, 69, 70, 74 Deer Butte ..................................................................................... 6, 54 

Maxum, Calif. (earliest Blancan) ......................................... 11, 68, 71 

Ninefoot Rapids ............................................ 15, 49, 57, 59, 61, 62, 64 

Oreana area ..................................................................... 49, 58, 59, 62 

Panaca, Nev ...................................................................................... 11 

Poison Creek (Shoofly Creek) .................................. 34, 54, 59, 61,65 

Red Light, Texas ......................................................................... 41,47 

Reddick lA, Fla ................................................................................ 25 

River Road, Wash ............................................................................. 70 

Sand Draw, Nebr .............................................................................. II 

Sand Point... .............................................................. 57, 61, 65, 68, 70 

Saw Rock Canyon, Kans .................. .............. .................................. II 

Strout Claim ..................................................................................... 56 

Drip Spring ....................................................................................... 54 

Etchegoin (California, first Nearctic muskrat) ...................... 16, 67, 68 

GlennsFerry .............. 3-10, 12, 15, 17,18,25-27,29-30,33,43,44, 

47-66,68-74 

easternmost outcrops .... .. ... .... .. .... .. .... .. .. . .... .. ... ... .. ... ... .. . .... .. .... . 56 

oldest ................................................................................... 55, 69 

removal of oolitic unit.. ............................................................. 50 

youngest .......................................................................... 6, 51,74 

Idaho ....................................................................................... 6, 53, 54 

elevated to group ....................................................................... 53 

Lawlor Tuff (California) ................................................................... 67 

Taunton, Wash ........................................................... 18, 68, 70, 71, 73 oolitic rusty sandstone .............. 5, 6, 49-50, 54, 58, 59, 62, 64, 69, 72 

Tijeras Arroyo, N.Mex .................................................................... 26 Payette ........................................................................ 6, 53, 54-56, 67 

Tusker, Ariz .. .. . .... .. . .. .... .. . .. .. .. .. . .. . .. .. . .. ... .. .. .. ... .. . ... .. . .... .. . .. ... .. .. .. .. . .. .. 29 Moores Hollow area.................................................................. 6 

White Bluffs, Wash......................................................... 11, 68, 70, 71 Pickles Butte basalt, dammed Snake River ................................ 51, 65 

Wild Horse Butte .................................................................. 43, 60, 63 erosion surface ................................................ 5, 9, I 0, 26, 65, 66 

Field localities.......................................................................................... 18 Poison Creek ............................................................................... 53, 54 

GS-201 ................................................................................... 27, 30,33 Ringold (Washington) ................................................................. 70, 71 

GS-203 .......................................................................................... 2, 38 San Joaquin (California) ................................................................... 27 

GS-204 .................................................................................. 30, 32, 33 Sucker (or Succor) Creek ................................................................. 54 

GS-205 .............................................................................................. 32 Tuana Gravel ..................................................................................... 54 

GS-208 ............................................................................. 27, 30, 34, 38 Fossil areas 

GS-209 .................................................................................. 19, 27, 33 Chalk Hills ......................................................................... 2, 3, 5, 9, 54 

GS-21 0 ........................................................................................ 30, 33 Cucumber ..................................................... 2, 3, 5, 10, 18, 19, 58, 74 

GS-211 .................................................................................... 2, 27,30 Froman Ferry .............................................................................. 2, 3, 9 

GS-211? ............................................................................................ 35 Homedale .......................................................................................... 3 

GS-212 ............................................................................ 27, 30, 34,38 Jackass Butte ....... 13, 15, 26, 29-31, 35, 38, 40, 41, 43-46, 50, 51, 54, 

GS-213 ................................................................................... 19, 30,32 59,60-62,71,73 

GS-214 .............................................................................................. 30 Lizard Butte...................................................................................... 3 

GS-215 .................................................................................. 27, 30,32 Wild Horse Butte .............................................................................. 63 

GS-216 .............................................................................................. 30 

GS-217 ......................................................................................... 19,30 

Froman, George W .. .. .. ... .. .... .. .. .. .. .. .. .. .. ... .. .. ... .. .... .. .... .. .. .. .. .. . .. .... .. .. .. ... 2, 40 

GS-218 ......................................................................................... 30,33 

GS-219 .............................................................................................. 30 G,H 

GS-220 ......................................................................................... 19, 30 

GS-221.. ...................................... 19, 20, 24, 30, 32, 34, 35, 37, 40,42 

GS-222 ............................................................................ 20, 21, 24, 30 

GS-223 ........................................................................................ 30, 32 

GS-224 ........................................................................................ 32, 34 

GS-225 ........................................................................................ 19, 34 

GS-226 .............................................................................................. 26 

Generic allocation, many definitions ........................................................ 44 

of felids .... .. .. . .... .. ... ... .... .. .. . .. .... .. .... .. .. . .... .. .... .. . .. ... .. .. .. .. . .. .... .. .. . .. 20, 44 

of horses ............................................................................................ 44 

of microtines ..................................................................................... 44 

Genetic, opportunistic morphologic expression ....................................... 13 

evolving potential ............................................................................. 13 

GS-227 .............................................................................................. 47 Geologic mapping 

GS-228 ............................................................................ 35, 37, 40,43 

GS-229 ......................................................................................... 30, 40 

Froman Ferry area . .... .. . .. .. .. . .... .. . .. ... .. . ... .. . .... .. . .. .... .. ...... .. .... .. .. . .... .. . . 8 

Snake River Plain .. .... .. .... .. .. .... .. . ........ ...... ...... . .. .... .. ........ ... ...... ...... . . 8 

GS-230 ................................................................................... 19, 27, 34 Glaciation 

GS-231 .............................................................................................. 35 beginning, Northern Hemisphere ..................................................... 14 

GS-232 ................................... 10, 20, 24, 25, 27, 30, 32, 34, 35, 40,42 first Neogene, Alaska ....................................................................... 32 

GS-233 ........................................................................................ 27, 30 marsh beds, Jackass Butte 2.1 Ma .................................................... 60 

GS-234.. ................................... ....................................... 19, 40, 42, 4 7 Iowa till, 2.1 Ma ..................................................................... 15, 60, 64 

GS-236 .............................................................................................. 63 Scandinavian Ice Sheet, peak 2.1 Ma .................. 15, 16, 17, 25, 63, 66 

GS-237 .............................................................................................. 63 Yellowstone till, 2.1 Ma? ....................................................... 15, 60, 63 

Weasma unassigned .......................................................................... 35 Globally synchronous events 

Floral ages (Europe: Praetiglian, Tiglian, Eburonian) ........................ 15-16 geopolarity, climate, ash falls ........................................................... 13 

Formations Hearst, Jonena .................................................................................... 43, 61 
INDEX 83 

I 

Idaho 

Ada County 

Boise ................................................................................ 2, 18, 52 

Bannock County 

Pocatello .......................................................................... 4, 18, 55 

Bonneville County 

Idaho Falls ................................................................................ 52 

Canyon County 

Caldwell ........................................................................... 2, 26,40 

Chalk Hills ....................................................................... 2, 3, 5, 9 

Dead Horse Canyon ......................................................... 5, 10, 26 

Froman Ferry ....... 2, 4, 5, 8-10, 12, 15, 26, 27, 29, 30, 33,42-47, 

51-59,63,65,66, 72, 73,74 

Nampa ............................................................................ 2, 55, 65 

Pickles Butte ..................................................... 3, 5, 9, 19, 47,65 

Walters Ferry .................................................... 57, 58, 63, 65, 72 

Elmore County 

Chattin Hill............................................................................... 59 

Glenns Ferry............................................................................. 55 

Hammett ............................................................................. 57, 65 

King Hill ........................................................... 55-58, 69, 70, 72 

Mountain Home ............................................................ 58, 59,64 

Gooding County 

Hagerman ........... 5, 17, 20, 25, 27, 41-46, 50, 55-59, 61, 64-72 

Wendell ............................................................................... 56,59 

Nez Perce County 

Lewiston . .. .. ...... ............ .... ......... ............. ............ ... ...... ....... ...... 52 

Owyhee County 

Bruneau ................................ 5, 15, 47, 49, 54, 57-59, 64-66, 73 

Chalk Hills................................................................................ 2 

Elephant Butte ...................................................................... 5, 58 

Grand View ................................... 5, 6, 20, 38,47-50,54-65, 72 

Guffey Butte ..................................................... 51, 57, 64, 65, 72 

Homedale .................................................................................. 3 

Jackass Butte .... 13, 17, 19, 26, 27, 29-31, 34, 35, 38, 40-46, 49, 

50,51,54,66, 70, 71,73 

Marsing ..................................... 2, 3, 5, 40, 51, 54, 58, 65, 68, 69 

Murphy ................................................................... 50, 57-59, 72 

Oreana .................................. 8, 49, 50, 51, 57-59, 62-64, 72, 74 

Oreana-Sinker Butte area ......................................................... 59 

Poison Creek Station . . .. . .. . . . . .. . .. . .. . .. .. . .. . .. . . . . .. . .. . . . . .. . .. . . . . .. . .. . .. . . . . 40 

Sinker Butte ................................................................... 59, 63, 64 

Wild Horse Butte............................................. 43, 51, 59, 60-64 

"unnamed butte" ......................................... 51, 59, 62-64, 65, 79 

Payette County 

Parma........................................................................................ 5 

Twin Falls County 

Twin Falls ............................................. 52, 53, 55, 56, 59, 67, 71 

Washington County 

Weiser ............................................................................. 6, 55, 69 

age of Payette lake beds ...................... ......... ...... .................. 6, 55 

Idaho Museum of Natural History (IMNH) .................................... 4, 18, 32 

specimen I 105/11890 ....................................................................... 40 

specimens ............... .............. ... ...... ... ......... ........ ......... ...................... 63 

Idaho National Engineering Laboratory (INEL) .......................... 55, 56, 69 

Idaho-Oregon, Hells Canyon ............... 2, 52, 54, 55, 57-59, 66-70, 72, 73 

International Code of Zoological Nomenclature ..................................... 31 

International Commission on Zoological Nomenclature, 

opinion 271 ..................................................................................... 36, 41 

L 

Lakes 

Bruneau ............................................. 15, 49, 51, 52, 57, 63, 64, 65, 73 

Glenns Ferry ............................... 3, 5, 9, 15, 17, 19, 33, 35, 47,50-73 

draining ..................................... 47. 55, 57, 61, 66, 67, 70. 71,73 

filling history ........................................................... 57, 59, 64, 65 

head ............................................................. 55-59,62, 63, 66, 73 

lake to west in Oreana area ........................................... 49, 51, 64 

mainly east in Canyon and Ada Counties ................................. 58 

normal salinity .............................................................. 55, 70, 72 

renewed lowering .................................................... 61, 64, 66,73 

restricted to southwest of modern river .............................. 60, 64 

southeastern limit 2.4 Ma ......................................................... 62 

temperature ................................................. 19, 33, 49, 53, 57, 72 

water level....................................... 15, 17, 51, 57, 60, 62-66, 73 

<6 miles wide, Oreana area ...................................................... 63 

Great Salt (Utah) ............................................................................... 52 

Harney (Oregon) ............................................................................... 67 

Idaho .............................................................................. 19, 33, 53, 73 

Klamath (California and Oregon) ......................................... 55, 67, 68 

small and marginal to main Glenns Ferry lake, saline ... 55, 58, 59-60 

Tule (California) ............................................................................... 51 

Lucas, F. A................................................................................................. 26 

M 

Malde, Harold E ....................................................... 5, 8, 18, 49, 58, 59, 64 

Mammal ages .... ...... ............ ....... .. ....................... ......... ...... ...... ..... ..... I 0-13 

begin with immigrants ...................................................................... 12 

Blancan .......... I0-13, 14, 16, 17,24-26,31,34,35,38,44-47,55,59, 

61,62,66-68,70,74 

beginning ............................................................................ 11-14 

definition ................................................................................... 11 

end ....................................................................................... 10, II 

latest, and earliest Irvingtonian ...... 12, 13, 16, 17, 26, 32, 34, 41, 

44,47, 74 

Blancan V: 2.56 Ma .............................................................. 13, 14,65 

Blancan=Pliocene ....................................................................... 10,61 

Clarendonian ................................................................................ II, 61 

conterminous United States .................................................. 12-13, 32 

defined separately in each faunal region ........ ... .......... ... ....... ... .. 12, 13 

faunal, not time, terms . . .. . .. . .. . .. . . . . . . .. . . . . .. . .. . .. . .. .. . . .. . .. . .. . .. . .. . .. . I I, 12, 13 

Hemphillian .................................................................... II, 12, 14, 56 

Irvingtonian ..................... ! 0-13, 16, 17, 20, 25, 26, 31, 32, 35, 41, 44, 

46,47,67 

Blancan holdovers in Eastern region ........................................ 16 

Eastern region, beginning 1.9 Ma ........................... 10, 14, 16, 17 

originally three in Pliocene ............................................. II, 12, 53, 54 

Mammalian biochronology 

global simultaneous evolution.......................................................... 13 

greater precision in regional scale.................................................... 13 

margin of error.................................................................................. I 0 

precision .......... ............... ...... ......... ........ .... .. . ..................... ............... 13 

usefulness minimized by synonymy ................................................. 44 

Merriam, J.C ............................................................................. 2, 26, 47, 53 

Mountains 

Blue (Oregon) ................................................................................... 70 

Centennial ......................................................................................... 52 

Coso (California) .............................................................................. 69 

Owyhee ......................................................................... 5, 6, 57, 67, 72 

Owyhee plateau ................................................................................ 69 

Salmon River .......................................................................... 6, 52, 70 

Wallowa (Oregon) ................................................................. 52, 69, 70 

N 

National-Museum of Natural History (USNM) .......................... 2, 3, 18, 45 

specimen 11607 ................................................................................ 26 

23903 ························································································ 38 
84 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

184064 ...................................................................................... 20 end ........................................................................... 10--12, 17,74 

264281 ...................................................................................... 38 Reunion ........................................ l9, 30, 31, 38, 50, 51, 60, 61, 63,64 

264328 ...................................................................................... 19 second event .............................................................................. 60 

264329 ................................................................................ 35, 37 Thvera ............................................................................................... 68 

264330 ...................................................................................... 35 Paleomagnetic sections 

264331 ...................................................................................... 27 Alturas (California) .......................................................................... 68 

264332 ...................................................................................... 27 Bruneau ........................................................................... 48, 59, 64, 72 

264333 ...................................................................................... 30 Fish Creek (Alaska) .......................................................................... 32 

264334 ...................................................................................... 30 Flatiron Butte .................................................................................... 49 

264335 ...................................................................................... 32 

264336 ...................................................................................... 32 

26433 7 ..... ... .... .. . ...................... ... .... ........... ............ ... ......... 20--23 

264338 ...................................................................................... 25 

264339 ................................................................................ 38, 40 

264340 ................................................................................ 39, 40 

264341 ...................................................................................... 40 

Natural History Museum of Los Angeles County (LACM) ......... 13, 17, 23, 

29,30 

locality 1357 ................................................................................ 17, 30 

locality 6683 ................................................................... 13, 17, 29, 30 

specimen (CIT) 118/892 ................................................................... 38 

Nevada 

Froman Ferry ................................................................ 2, 9, 10, 12, 18 

Hagerman .......................................................... , .................. 50, 55-56 

Jackass Butte .................................................................. 38, 51, 60, 63 

King Hill........................................................................................... 55 

Multi-ash .......................................................... 8, 47-52, 56, 58, 61-66 

="unnamed butte" ......................................................... 51, 63,79 

Sand Point ................................................................................. 57 

"unnamed butte" ................................................. 51, 59, 62, 63-65, 79 

Vallecito Creek (California) ................................ 10, 13, 16, 17, 29,30 

White Bluffs (Washington)............................................................... 11 

Pollen floras 

Bruneau ................................................................................. 15, 52, 65 

Black Rock Desert .......................................................... 67, 68, 71, 72 Glenns Ferry Formation .......................................................... 5, 15, 65 

Winnemucca . . .. . . . . .. . .. . . . . .. . .. . . . . .. . . . . .. .. . .. . . . . .. . . . . .. . .. . . . . .. . . . . .. . . . . .. . .. .. . . . . .. . . 68 Provincialism 

Neville, Colleen A ........................................... 18, 49, 50, 55, 57, 60, 63,64 between Alaska and Mexico............................................................. 12 

opposite sides of Rockies (U.S.A.) ................................................... 12 

0 prominent in microtine rodents .... .................................................... 12 

varying faunal criteria of age ........................................... 10, 11, 53,54 

Oregon 

Lakeview ..................................................................................... 67, 68 R 

Malheur County 

Adrian . .. ... . .. . .. ... .. . .... .. .. . .... .. ... .. ... ... .... .. . .. .... .. ... .. . .... .. .. . ...... .. . 6, 54 Radiometric age ........................................................ 6, 8, 20, 53, 54, 56, 69 

Jordan Valley ....................................................................... 40, 67 Alturas Formation (California) ....................................... II, 68, 69, 71 

Moores Hollow ............................................................... 6, 54, 69 first correlated to mammal ages........................................................ 12 

Ontario ...................................................................................... 54 Pickles Butte basalt.. .................................................. 9, II, 17,51,65 

Vale ....................................................................................... 6, 54 Rivers 

Ostracode faunas Boise ....................................................................................... 6, 66, 67 

endemic by ca. 3.2 Ma ................................................................ 55, 56 Colorado ........................................................................................... 52 

Hagerman Columbia (Washington) ........................... l4, 17-19,52,57,66-71,73 

basal lacustrine ......................................................................... 56 Humboldt (Nevada) .................................................................... 67,71 

delta deposits ............................................................................ 56 

Jackass Butte ............................................................................. 60, 61 

marsh ................................................................................................ 72 

small, saline ponds ..................................................................... 55, 60 

Owyhee ........................................................................... 66, 67, 69, 72 

Pit (California) ...................................................................... 67, 68, 71 

Sacramento (California) ..................................... 14, 17, 18,67-69,71 

Snake .................. 2-6, 9, 14, 15, 18, 29, 30, 32, 35, 38, 40, 43, 47, 52, 

54-60,62-74 

p delta at Hagerman .. .. .. .. . .. .... .. . .. . .. ... .... .. . .. .... .. .. .. .. .. . .. .... .. . .. .... .. .. 56 

Paleomagnetic events 

age ................................................................................................ 8, 13 

radiometric.............................................................................. 8, 9 

Brunhes Normal-polarity Chron...................................................... 8 

calibration criteria, temporal ...... ........ .................. ............ ............ .... 8 

Cobb Mountain................................................................................. 8 

diversion ........................................................................ 52, 69-73 

Farewell Bend .... .. .... .... .. . ... ... .... .. ... ... ... .... .. . .. .... .. ... . .. ... .. . .. . .. .. .. . 54 

former ........................................................................... 47, 59, 65 

in modem position, Grand View area 2.5 Ma ........................... 59 

northwestern limit 2.4 Ma ......................................................... 62 

restricted to west by lava flows ................................................. 59 

Cochiti ................................................................ 49, 55-56, 58, 70, 73 Russia 

correlation to biochronologic evidence ............................ 8, 10, 50,61 Bashkiria ........................................................................................... 27 

to earth orbital parameters .. ........... ....... ... .................... ............. 8 

to geologic evidence ...................................................... 60, 61, 66 s to microtine evidence ................................................................ 61 

to uniform sea floor spreading ................................................ 8, 9 Schmelzmuster ................................................................................... 27, 31 

Gauss Chron ................................................. 14, 15, 49, 58, 61,63-64 Stratigraphic test hole 

Gauss/Matuyama boundary .......................... 32, 49-51, 55, 59, 61, 63 Bruneau, near town of ......................................................... 48-49, 65 

Gilbert Chron ...................................................... 49, 50, 55, 58, 67, 68 INEL ........................................................................................... 56,69 

Matuyama Chron... ...... ............ ......... ........ ...... .......... 10, 32, 51, 61, 63 Mountain Home .......................................................................... 58, 59 

Nunivak ............................................................................................ 67 Pickles Butte..................................................................................... 5 

Olduvai ............................................... 8-12, 15-17,30,51,65, 66,74 Wendell ....................................................................................... 56, 59 

beginning ........................................................................ 8, 10, 74 Stroud, Bill............................................................................................... 5 
INDEX 85 

T 

Taxa 

Allophaiomys ............................................................ 10, 11, 14, 16, 33 

immigrant, earliest Irvingtonian............................................... 10 

unknown in Pacific Faunal Region........................................... 16 

warm temperate . .. . .. . . . . .. . .. . . . . .. . . . . .. . .. .. . . . . .. . . . . .. . .. . .. . . . . . . . .. . .. . . . . .. . . . . 16 

Castor 

accessor .................................................................................... 26 

californicus ......................................................................... 26, 27 

canadensis................................................................................ 27 

Clethrionomys rutilus ....................................................................... 31 

Cottus, first appearance ......................................................... 15, 19, 61 

Dichrostonyx ..................................................................................... 29 

Dipoides intennedius ....................................................................... 62 

Dolonzys .................................................................... 16, 67, 68, 70, 71 

Equus .............................................................................. 36,40-47,74 

(Dolicholzippus) ........................................... 37, 41, 43, 44, 45-4 7 

stenonis anguinus .............................................. 30,40-47, 74 

(Hemionus) ............................................................................... 43 

excelsus ..................................................................................... 41 

idahoensis .................................................................. 2, 38, 42, 44 

scotti ....................................................................... 41, 46, 47,74 

sirnplicidens. ... .. ......... ...... ............... .. ... ... ... .... .. ......... ...... ....... ... 4 7 

Eucastor ...... .. ......... ......... ........ ... .... .. . .............. .. ....... ................. ....... 61 

Felis lacustris ................................................................. 21, 24, 25, 73 

Gigantocamelus spatulus ................................................................. 47 

Hibbardomys z.akrz.ewskii ...................................................... 11, 16, 32 

Hypolagus ....................................................................... 25, 26, 50, 63 

gidleyi ............................................................... 25, 49, 50, 51, 74 

vetus .......................................................................................... 50 

lschyrosmilus idahoensis............................................................. 2, 20 

Lasiopodomys. .. .. ................ .. .... ..... ...... ......... ...... ................. .... .. ....... 14 

Le1nmus ............................................................................................ 29 

Metaxionzys anz.aensis ...................................................................... 29 

Microtus ........................................................ 10-12, 14-17,29,30,74 

earliest . . . . .. .. . .. . . . . .. . .. . . . . .. . . . . . . . .. . . . . .. . .. .. . . . . .. . . . . .. . .. . .. . .. . . . . .. . .. . . . . .. . . . . 29 

immigrant only to Pacific region.................................. 10-12, 16 

Mictomys ......................... 11, 14-17,27-31,33,49,51,52,61, 63,66 

kansasensis . . . . . .. . .. . . . . .. . . . . .. . .. . . . . .. . .. . . . .. . .. . . . . .. . . . . .. . .. . . . . .. . .. . .. . . . . . . . .. . 30 

me/toni ...................................................................................... 30 

vetus ................................................ 16, 17,27-31,51,52, 61,63 

late Blancan immigrant ......................... 11, 14, 16, 17, 29, 61,63 

later record in S. California...................................................... 16 

Mimomys (Cosomys) ...................................................... 11, 14, 69,71 

sawrockensis .. ....... ...... .. ............... ... .. .... .. ...... ... ............ ... ...... .... 11 

Mimomys (Ophiomys) mcknighti ................................................ 11,68 

parvus ..................................................................... 17,30-32,71 

M. antiquus ....................................................................................... 31 

dakotaensis ........ .. . ...... .. .... .................... ..... ... ...... ......... ............. 31 

1nonolzani .................................................................................. 31 

parvus, youngest and most northerly dated .............................. 30 

virginianus ................................................................................ 31 

Miracinonyx inexpectatus ..................................................... 20, 22-25 

trunzani ............................................................................... 23, 24 

Ondatra idahoensis ............................................ 15, 17, 33-35, 61,70 

immigrant ........................................................................... 15, 34 

Phenacomys.............. 10-12, 14, 16, 17, 25, 30, 32, 33, 45, 47, 52, 74 

(Arborinzus) .............................................................................. 32 

(Paraphenacomys) .......................... 10, 12, 14, 16, 17,32-33,52 

gryci .................................... 10, 12, 16, 17, 25, 30,32-33,52 

gryci, Siberia ...................................................................... 32 

(Phenacomys) .................................................... 14, 16, 21, 32, 33 

z.akrzev.·skii.......................................................................... 16 

immigrant Eastern and Pacific regions..................................... 16 

Plesippus ............................................................. 17, 26,35-47,61,74 

=Equus (Dolichohippus) ........................................................... 37 

fronzanius ................................................................ 26, 37-47, 74 

idalzoensis ............................................... 2, 35-38, 40, 42-44, 46 

shoshonensis ........................................................... 40-46, 61, 74 

simplicidens, type ......................................................... 37, 43, 74 

sp. aff. P. shoshonensis ............................................................. 61 

stenonis anguinus .................................................... 38,40-47, 74 

Plesippus slwshonensis > Equus (Dolichohippus) stenonis anguinus > 

Plesippus fromanius ................................................ 41, 42, 44, 46 

Plesippus, evolution in North America ........ 35, 38,41, 43,45-47, 74 

Plioctomys ................................................................ 11, 14-16, 27-30 

extinction ...................................................................... 16, 29, 30 

Pliophenacomys osborni ............................................................ 15, 62 

Pliopotamys ............................................. 15, 16, 34, 61, 67, 68, 70, 79 

nzeadensis ............................................................................. 15, 34 

minor ........................................................... 15, 34, 61, 67, 70, 79 

near meadensis, Boyle Ditch, Wyo ..................................... 15, 34 

Procastoroides .......................................................... 17, 45, 60-63. 71 

idahoensis ..................................................................... 60-62, 70 

intermedius ............................................................................... 62 

Promimomys antiquus (Kazakhstan) ................................................ 31 

Puma ...................................................................................... 17,20-25 

concolor .............................................................................. 20-25 

captive animals larger ........................................................... 23 

So rex ( Otisorex) palustris ........................................................... 19-20 

Stegomastodon mirificus .................................... ................... 35, 38, 60 

Synaptomys ........................................................................... 27-30, 33 

(Plioctomys) mimomiformis ...................................................... 27 

rinkeri .................................................................................. 27 

Terricola ........................................................................................... 14 

agriotherine/tremarctine? .................................................................. 25 

birds .................................................................................................. 19 

camel ..................................................................................... 26, 47, 63 

cervid ................................................................................................ 47 

fish ........................................ 3, 5, 6, 18, 19, 33,53-55,67,69, 71,73 

peccary .............................................................................................. 63 

tremarctine? ...................................................................................... 25 

Taxonomic nomenclature .............. ..... .. ...... ... ...... ..................... ... .. ....... .. .. 8 

approximate in present form............................................................. 13 

difficulties, North America versus Eurasia ....................................... 41 

time and geography important.. ................................................... 13, 45 

Type localities 

Castor accessor ................................................................................ 26 

californicus. .. .... .. ....... ... ................ ....... ...... ......... ................... .. 27 

Equus idahoensis .......................................................................... 2, 37 

SCOtti. ....................................................................•.•....... 41, 74 

Hypo fagus gidleyi .............. ...... ... .. ... . .. ............ ... ....... ..... ... ...... .. ... ..... 26 

/schyrosmilus? idahoensis ................................................................ 2 

Mictomys vetus ........................................................................... 29-30 

Mimomys (Cosomys) primus ............................................................ 69 

sawrockensis .. .................. ........ ...... ............... ... ... ......... .. ... ........ 11 

(Ophiomys) magilli ................................................................... 11 

mcknighti.............................................................................. 11 

parvus .................................................................................. 31 

Ondatra idahoensis. .. . . . . .. . .. . . . . .. . .. .. . .. . .. . . . . .. . . . . .. . .. . . . . .. . . . . .. . .. . . . . . . .. . .. . .. . . 34 

Phenacomys (Paraphenacomys) gryci .............................................. 32 

Plesippus fromanius .................................................................... 38-43 

idahoensis ............................................................... 35-38, 42, 44 

shoshonensis ....................................................................... 40-46 

simplicidens ............................................................ 37, 43, 44, 46 

stenonis anguinus .................................................... 38, 40-44, 46 

Payette Formation ....................................................................... 53, 54 

Pliocene, Italy ................................................................................... 12 
86 FROMAN FERRY FAUNA AND GLENNS FERRY FORMATION, SOUTHWESTERN IDAHO 

U-Z 

U.S. Government Volunteer Program....................................................... 2 

Unconformities 

Bruneau Formation/ Glenns Ferry Formation .......... 15, 49, 63, 64, 72 

Glenns Ferry Formation/oolitic rusty sandstone ...... 50, 54, 62, 64, 69 

oolitic rusty sandstone/ Chalk Hills Formation .......................... 54, 72 

Pickles Butte basalt/ Glenns Ferry Formation .......................... 5, 9, 10 

University of California Berkeley Geochronology Center....................... 9 

University of California Museum of Paleontology (UCMP) 

locality 3036 ..................................................... 2-4,20, 27, 30, 35,42 

locality 3036C .................................................................................. 35 

Published in the Central Region, Denver, Colorado 

Manuscript approved for publication June 21, 1994 

Edited by Lorna Carter 

Photocomposition by Norma J. Maes 

locality V3520 .................................................................................. 67 

locality V6869 .................................................................................. 68 

specimen 113695 .............................................................................. 47 

specimen 22347 .................................................................... 35, 38,42 

specimen 22348 .......................................................................... 35, 37 

specimen 57958 ........ .................................................. ..... ...... .......... 67 

specimens . . . .. . .. . .. . .. . .. . .. . .. . .. .. .. . . .. . .. . .. . .. ... . .. . . . . .. . .. . .. . .. . .. .. ... . .. ... . .. . . . . .. . 63 

U.S. Geological Survey (USGS) locality Ml361.. ................................... 31 

Washington, Franklin County 

Pasco ............................................................................... 52, 68-70, 73 

West Virginia, Hamilton Cave .................................................................. 27 

Wyoming, Yellowstone ........................ 14-16, 19, 29, 34, 35, 62,60-64,66 

Graphics by C.A. Repenning, Gayle M. Dumonceaux, and Patricia Holroyd 

U.S. OOVERNMI!NI' PIUNriR; OFFICE: 1995-673-046/86101