Climatic Implications of 

Two Pollen Analyses 

from Newly Recognized 

Rocks of Latest 

Pliocene Age in the 

Washburn Range, 

Yellowstone National 

Park, Wyoming 

By GERALD M. RICHMOND, U.S. GEOLOGICAL SuRVEY and WILLIAM 

MULLENDERS and MADY COREMANS, INSTITUT DE BoTANIQUE, UNIVERSITE CATHOLIQUE DE LOUVAIN 

GEOLOGICAL SURVEY 

Pollen analyses suggest climate about 

2 million years ago was broadly similar 

to that of today 

BULLETIN 1455 

llNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1978 
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary 

GEOLOGICAL SURVEY 

H. William Menard, Director 

Library of Congress Cataloging in Publication Data 

Richmond, Gerald Martin, 1914- i 

Climatic implications of two pollen analyses from newly recognized rocks of latest Pliocene 

age in the Washburn Range, Yellowstone National Park, Wyoming. 

(Geological Survey Bulletin 1455) 

Bibliography: p. 12 

1. Pollen, Fossil. 2. Paleobotany-Pliocene. 3. Palynology-Yellowstone National Park. 

4. Paleoclimatology-Yellowstone National Park. 5. Yellowstone National Park. I. Mullenders, 

W., joint author. II. Coremans, Mady, joint author. III. Title: Climatic implications of two 

pollen analyses ... IV. Series: United States Geological Survey Bulletin 1455. 

QE75.B9 no. 1455 [QE993.2) 557.3'08s [551.7'8] 78-1686 

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

Washington. D.C. 20402 

Stock Number 024-001-03126-4 
CONTENTS 

Page 

Abstract ...................................................................................................................... 1 

Introduction ............................................................................................................... . 

Locality TJ-1 .............................................................................................................. 4 

Locality T J-2 .......... .... ............ .. ......... ........ ......... .. .... ........... .. .......... ............... ........ .... 6 

Palynological evidence for age ............ ... . .. ........... .... .... ........ ................... .. .................. 6 

Geologic evidence for age . ... .......... ..................... ..... ... ... ...................... ................ ....... 7 

Paleoecologic and paleoclimatic inferences . . . . . . .. . . . . . ... . . . . . . . . . . . . .. . . .. . .. . . . . . . .. .. . . . . . . . . . . . . . . . . . . 9 

Acknowledgments ..................................................................................................... 12 

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

ILLUSTRATIONS 

Page 

FIGURE I. Index map of Yellowstone National Park and adjacent areas showing 

known locations of sediments of latest Pliocene age ............. ........ ....... 2 

2. Profile of floor of paleovalley of Yellowstone River between Tower Junction 

and locality TJ-1 ................................................................................... 8 

TABLES 

Page 

TABLE I. Vegetation associations and their altitude limits in Yellowstone National 

Park ...................................................................................................... 10 

2. Comparison of major pollen types and percentages from localities T J-1 and 

T J-2 with those of modern surface samples .......................................... 10 

III 

CLIMATIC IMPLICATIONS OF TWO POLLEN ANALYSES 

FROM ROCKS OF LATEST PLIOCENE AGE 

IN THE WASHBURN RANGE, 

YELLOWSTONE NATIONAL PARK, WYOMING 

By GERALD M. RICHMOND, U.S. GEOLOGICAL SuRVEY, and WILLIAM 

MULLENDERS and MADY COREMANS, INSTITUT DE BoTANIQUE, 

UNIVERSITt CATHOLIQUE DE LOUVAIN 

ABSTRACT 

Pollen analyses of siltstone beds in sedimentary rocks that overlie and closely resemble the 

basal sedimentary unit of the Eocene volcanic sequence in the Washburn Range, north-central 

Yellowstone National Park, have yielded pollen types and percentages indicative of an age no 

older than latest Pliocene. These sedimentary rocks are lithologically similar to others that lie 

conformably beneath the slightly more than 2.0-million-year-old Junction Butte Basalt and are 

therefore no younger than latest Pliocene in age. The geomorphic setting of the sediments in a 

north-trending paleovalley suggests that their source was an upland to the south in an area of 

central Yellowstone Park which has since foundered because of caldera collapse. 

Comparison of the pollen analyses of the sediments at two localities and the altitudes of the 

localities with the modern pollen rain and altitude limits of present day forest associations 

suggests that the vegetation zones and climate in latest Pliocene time were broadly similar to 

present conditions. The sedimentary rocks are correlated with others in and near Yellowstone 

Park on the basis of their overall relation to the Huckleberry Ridge Tuff, which overlies the 

Junction Butte Basalt and is also pottasium-argon dated as slightly more than 2 million years 

old. 

INTRODUCTION 

The Washburn Range, in north-central Yellowstone National Park, is a 

westward projection of the north-trending Absaroka Range along the east 

boundary of the Park (fig. 1). The Washburn Range is underlain chiefly by 

andesitic lava flows, flow breccias, and epiclastic volcanic sedimentary rocks 

of early to middle Eocene age (Smedes and Prostka, 1972). In places, these 

rocks are disconformably overlain by the Junction Butte Basalt, 

Huckleberry Ridge Tuff, and Lava Creek Tuff (Christiansen and Blank, 

1972; U.S. Geological Survey, 1972). The Junction Butte Basalt has been 

K-Ar dated as 2.01±0.05 and 2.15±0.05 million years (m.y.) old (J.D. 

Obradovich, written commun., 1978). The Huckleberry Ridge Tuff, which 

locally overlies the basalt, has been K-Ar dated as about 2.02±0.08 m.y. old 
2 POLLEN ANALYSES, WASHBURN RANGE, WYOMING 

and the Lava Creek Tuff as 0.616±0.08 m.y. old (J.D. Obradovich, written 

commun., 1978). The Junction Butte Basa1tand Huckleberry Ridge Tuff are 

of particular significance to this paper. Christiansen and Blank (1972) 

assigned both units to the Pleistocene. 

I 

I 

·--·--·--·__J 

0 10 20 30 40 KILOMETERS 

FIGURE I.-Index map of Yellowstone National Park and adjacent areas showing known 

locations of sediments of latest Pliocene age. TJ-1 and TJ-2 are localities from which pollen 

analyses were made. Solid circles are localities where gravelly sediments underlie Junction 

Butte Basalt in paleovalley of Yellowstone River. Solid triangle is base of Huckleberry Ridge 

Tuff in same paleovalley. Solid squares are localities where sediments underlie Huckleberry 

Ridge Tuff. 
INTRODUCTION 3 

Any change in this assignment is dependent on the age of the 

Pliocene-Pleistocene boundary at its stratotype section at Le Castella, Italy. 

Berggren (1972) estimated its age as 1.8 m.y. Subsequently, an age of 1.5 

m.y. has been suggested (Haq and others, 1977). However, at Vrica, 16 km 

northeast of Le Castella, a continuous section of marine sediments ranging 

in age from middle Pliocene to lower Pleistocene contains a layer of volcanic 

ash in the zone of sediments that paleontologically records the deterioration 

of climate characterizing the Pliocene-Pleistocene transition (Selli and 

others, 1977). A preliminary age of 2.5±0.1 m.y. (fission track on glass) for 

the ash was determined by Boellstorf (1977). Subsequently, a K-Ar date of 

2.2±0.2 m.y. on glass shards, a fission track date of 2.07±0.33 m.y. on glass, 

and a K-Ar date (whole rock)of2.0±0.1 m.y. on a pumice block in sediments 

immediately above the ash have been determined (Selli and others, 1977). 

The age of the Pliocene-Pleistocene boundary is therefore probably about 2 

million years. In any event, the Huckleberry Ridge Tuff and its correlative 

downwind ash bed, the type B Pearlette ash (Naeser and others, 1973), 

provide a time parallel marker that is essentially, if not actually, at the 

Pliocene-Pleistocene boundary. 

The Eocene volcanic rocks in the Washburn Range include the Sepulcher 

(oldest), Lamar River, and Langford Formations of the Absaroka Volcanic 

Supergroup(Smedes and Prostka, 1972). Nonvolcanic conglomerate in the 

Washburn Range was first described by Shultz(1962, p. 43-57);it underlies 

or interfingers with the lower part of the Sepulcher Formation(Smedes and 

Prostka, 1972, p. C15) both in the Washburn Range and elsewhere (Prostka 

and others, 1975). In places, the nonvolcanic rocks clearly underlie the 

Eocene volcanic rocks (Shultz, 1962, p. 44; Smedes and Prostka, 1972, p. 

C16). In other places, they have been erosionally stripped and now occur at 

the surface. 

In the course of a study qf the Quaternary deposits south of the Washburn 

Range (Richmond, 1974, 1976a, 1976b, 1977), samples for pollen analysis 

were collected from glacial and interglacial lake sediments at a number of 

localities. Analyses of these samples by Mullenders and Coremans revealed 

suprisingly little contamination by Eocene pollen, despite the presence to the 

north and east of widespread Eocene rocks containing an abundant 

described megaflora (Knowlton, 1899; Dorf, 1960) and known Eocene 

pollen (Fisk and DeBord, 1974; Richard A. Scott, oral commun., 1975). To 

insure recognition of possible Eocene pollen contaminants, we collected 

samples of nonvolcanic siltstone and fine-grained sandstone interbedded in 

conglomerate at two readily accessible localities, shown as TJ-1 and TJ-2 in 

figure 1. The rocks at these localities have been mapped as Sepulcher 

Formation (U.S. Geological Survey, 1972; Prostka and others, 1975) and, 

based on their appearance, we had no reason to question their assumed 

Eocene age. At neither locality does the conglomerate contain clasts of 

Junction Butte Basalt or of Huckleberry Ridge Tuff but at neither locality is 

it overlain by Eocene volcanic rocks. 
4 POLLEN ANALYSES, WASHBURN RANGE, WYOMING 

LOCALITY TJ-1 

Locality TJ-1 (fig. l)isjust west of Grand Loop Road, 4.6 km northeast of 

Canyon Village, at a small dam along an unnamed creek that flows southeast 

from a saddle between Dunraven Peak and Hedges Peak. The sedimentary 

rocks crop out on a north-facing slope adjacent to the small dam at an 

altitude of 2,605 m. The outcrops are about 570 m above the Yellowstone 

River in its Grand Canyon to the east. The rocks consist of well-indurated, 

silicified, interbedded greenish-gray and greenish-brown conglomerate and 

sandstones, first described by Shultz (1962). The sandstone beds are 1-130 

em thick, hard, coarse to fine grained, and are locally weakly cross bedded. 

They include numerous thin lenses. of hard siltstone. The conglomerate 

forms considerably thicker and commonly massive beds and lenses of 

well-rounded pebbles and small cobbles. The clasts are mostly 1-4 em in 

diameter, but some are as much as 15 em in diameter. They are chiefly of 

Precambrian granite, gneiss, and schist, but some are of porphyritic, 

medium-grained andesite and basalt of Eocene age and some are of dense 

varicolored quartzite like that of clasts in the Harebell Formation of Late 

Cretaceous age (Love, 1973) or the Pinyon Conglomerate of Late 

Cretaceous and Paleocene age (McKenna and Love, 1970). A small 

percentage are of siltstone, chert, and oolitic limestone. No clasts of rhyolite 

flows or tuffs were found. The matrix of the conglomerate is a silty coarse 

sand composed chiefly of quartz, feldspar, and muscovite. Shultz (1962, p. 

49-51) has described its petrography. He (Shultz, 1962, p. 47-48) also 

reported that "coalified logs and plant fossils" were found in exposures, 

freshly opened at that time, but none of the fossil material could be 

identified. He stated(p. 49)that "some of the carbonaceous material has the 

appearance and texture of charcoal." Owing probably to slumping of the 

exposures, we did not find these organic deposits. 

About 0.3 km southwest of locality TJ-1, in a small quarry along an 

abandoned section of Grand Loop Road, Shultz ( 1962 p. 52-53) found fossil 

leaves in fine- to medium-grained tuffaceous sandstone beds interlayered in 

a pebble conglomerate consisting wholly of andesitic volcanic material. The 

fossil leaves were identified by Erling Dorf (Shultz, 1962, p. 53) as: 

Aralia notata Lesquereux (ginseng) 

Carya culvert Knowlton (hickory) 

(?)Juglans crescentia Knowlton (walnut(?)) 

Quercus weedi Knowlton (oak) 

Quercus yanceyi Knowlton (oak) 

All species are common to the Eocene volcanically derived sedimentary 

rocks in Yellowstone National Park (Dorf, 1960). Shultz ( 1962) recognized 

the lithologic difference between these rocks and those at locality T J-1 but 

considered both to be of Eocene age. 
LOCALITY TJ-1 5 

Pollen analysis' by Mullenders and Coremans of a sample of siltstone 

interbedded in the conglomerate at locality T J -1 yielded the following 

distribution: 

Arboreal pollen (AP) Nonarboreal pollen (NAP) 

1ype Percent 1ype Percent 

Pinus (pine) .......................................... 84.9 Artemisia (sage) ...................................... 5.1 

Picea (spruce) ....................................... 3.8 Chenopodiaceae-Amaranthaceae ............ .4 

Abies (fir) ............. ............... ................. 2. 7 Sarcobarus (greasewood) ........................ .I 

Betula (birch) ....................... ................. 0.1 Compositae (composites) 

Tubuliflorae . ... . . ...... ....... ... . . . ... .... .. . ..... 1.3 

Alnus (willow) ...................................... 0.4 Gramineae (grasses) ................................ .8 

Tha/ictrum (meadow rue) ....................... .I 

Plantago (plantain) ................................. .I 

Umbelliferae ........................................... .I 

Sphagnum (sphagnum moss) .................. .I 

Total AP .................................... 91.9 Total NAP ................................... 8.1 

Pollen sum: 957 

The difference in taxa between the megaflora of Shultz and the pollen 

flora represented in our sample is obvious, and any attempt to equate the two 

on the basis of the absence of megafossils at locality T J -1 is inadequate. The 

absence of leaves of Betula and Alnus in sample TJ-1 is not significant, for, if 

present, their pollen might have been transported from far upslope. The 

same explanation might apply also to the absence of megafossils of Picea 

and Abies. But such an explanation cannot apply to the presence of 85 

percent Pinus pollen in our sample. Clearly, such an abundance of pollen 

indicates the presence of Pinus in the forest, as is further demonstrated by the 

pollen content of modern surface samples discussed below. A differential 

destruction of megafossils similar to that which takes place in bogs might 

explain the absence of megafossils of Pinus at the quarry, but this process is 

unlikely to have taken place in tuffaceous sandstone beds. Furthermore, the 

absence of pollen of Quercus, Juglans, and Carya in the sample from locality 

T J -1, only 300 m from the megafossil site, seems impossible if the rocks at 

both localities are the same age. We therefore conclude that the contrast 

between the megaflora at the quarry and the pollen flora at locality TJ-1 

indicates that deposition of the rocks at the two localities took place at 

different times and in very different environments. The contact between 

these two suites of rocks has not been found, but it probably is a 

disconformity in the form of a valley cut in the Eocene rocks. A fault zone 

recognized by Shultz ( 1962) at the quarry site appears to be restricted to the 

Eocene rocks. 

1The samples from localities TJ-1 and TJ-2 were processed by the method of Frenzel (1964) as modified by Bastin and 

Couteaux ( 1966). The method combines the normal procedure for organic sediments with treatment by a liquid having a density 

of 2 (Cdl+Kl). 
6 POLLEN ANALYSES, WASHBURN RANGE, WYOMING 

LOCALITY T J-2 

The exposures of siltstone at locality TJ-2(fig. l)are along the east side of 

the access road to Petrified Tree, 0.5 km south of its junction with Grand 

Loop Road west of Tower Falls. The rocks crop out on the steep west-facing 

valley wall at an altitude of about 2,025 m, about 210 m above the 

Yellowstone River in its canyon to the east. The deposits are only about 0.3 

km from Petrified Tree, which stands upright in growth position in a 

tuffaceous unit of the Sepulcher Formation. Many specimens of Eocene 

wood and leaves have been collected from exposures in the slopes above 

the tree (Dorf, 1960). 

The sedimentary rocks at locality TJ-2 consist of hard, buff, well-bedded 

siltstone and greenish-gray to buff, locally pebbly, coarse to fine, poorly 

sorted, weakly bedded sandstone derived from andesitic sources. Pollen 

analyses of a sample of the siltstone by Mullenders and Coremans yielded 

the following distribution: 

Arboreal pollen (AP) Nonarboreal pollen (NAP) 

1 ype Percent 1ype Percent 

Pinus (pine) .......................................... 74.5 Artemisia (sage) 5.3 

Picea (spruce) ....................................... 5.3 Chenopodiaceae-Amaranthaceae .......... .7 

Pseudotsuga (Douglas fir) .................... 3.0 Compositae (composites) 

Betula (birch) ....................................... . 

Alnus (willow) ..................................... . 

Fagus (beech) ....................................... . 

Arceuthobium (dwarf mistletoe) ........... . 

Tubuliflorae . ......... ......................... .3 

Liguliflorae . . . . ........ ... . . . . . . ..... .. . .. . ... . . 7 

.3 Graminae (grasses) .............................. 7.3 

.7 Polemoniaceae (polymonium)............... .3 

.3 

.3 Selaginella (selaginella) ......................... .7 

Sphagnum (sphagum moss) ................ .3 

Total AP .................................... 84.4 Total NAP ................................ 15.6 

Pollen sum: 302 

PALYNOLOGICAL EVIDENCE FOR AGE 

The samples from both localities TJ-1 and TJ-2 are very rich in pollen and 

the pollen grains are well preserved. The notable lack of typical Eocene 

species, such as those represented by the leaves collected by Shultz (1962)or 

the flora listed by Dorf(l960), clearly indicate that the rocks from which we 

collected are not of Eocene age. Recent summaries of the evolution of flora 

during the Cenozoic (Leopold, 1969; Leopold and MacGinitie, 1972) show 

that evolutionary modernization of the early Tertiary vegetation in the 

Rocky Mountain region began in late Oligocene time and proceeded so 

rapidly that by middle Miocene time only a few species of trees that are not 

now present in the region remained. A few of these species persisted, in 

decreasing proportion to existing species, until the beginning of Quaternary 

time. For example, rare Carya and Ulmus-Zelkova occur in the Glenns 

Ferry Formation of western Idaho whose abundant molluscan fauna 

suggests a late Pliocene age, but whose rare vertebrate fauna suggests an 
GEOLOGIC EVIDENCE FOR AGE 7 

early Pleistocene age (Malde and Powers, 1962). However, these trees are 

lacking in the overlying middle Pleistocene Bruneau Formation (Malde and 

Powers, 1962; Leopold, 1969; Leopold and MacGinitie, 1972). With the 

exception of a single grain of Fagus, all of the arboreal pollen in our samples 

represent species living in the area today. Of these species, Abies cf A. 

lasiocarpa is reported from rocks as old as early Oligocene and Picea cf P. 

pungens is reported from rocks as old as late Oligocene or early Miocene, 

both from localities in Colorado (Leopold and McGinitie, 1972, p. 195-196). 

Pseudotsuga is reported from beds as old as late Miocene in southern Idaho 

(Leopold and McGinitie, 1972, p. 197). Among the nonarboreal species, the 

most recent to appear were probably the Compositae, in Miocene time, and 

the Polemoniaceae, which occur in beds (Leopold and MacGinitie, 1972, p. 

198) now assignable to the late Miocene on the basis of the recently revised 

age limits of that epoch (Berggren, 1972). However, the absence of relict 

early Tertiary species in our samples strongly suggests that the rocks at 

localities T J -1 and T J -2 are no older than latest Pliocene or earliest 

Pleistocene. 

GEOLOGIC EVIDENCE FOR AGE 

As indicated above, the conglomerate at locality TJ-1 does not contain 

clasts of rhyolite lava flow, or welded tuff, which are abundant in gravels of 

middle and late Pleistocene age (Pierce, 1974; Richmond, 1976a, b, 1977) in 

the Grand Canyon of the Yellowstone River. Such clasts were derived either 

from the Huckleberry Ridge Tuff, no younger than earliest Pleistocene in 

age, or from the Lava Creek Tuff of middle Pleistocene age (Christiansen 

and Blank, 1972). Both tuffs are present in the local bedrock. The absence of 

rhyolite tuff in the conglomerate at locality T J-1 indicates that it is older than 

the Huckle berry Ridge Tuff and therefore no younger than latest Pliocene in 

age. 

Support for such an age is provided by a similar sandy gravel containing 

lenses of sand and silt that is exposed at a number oflocalities in the walls of 

the Grand Canyon of the Yellowstone River from about 1.5 km southwest of 

the mouth of Deep Creek (fig. 1) downstream to Tower Junction 

(Christiansen and Blank, 1972; Pierce, 1974). This gravel is essentially 

identical to the conglomerate lithologically but is less indurated and less 

cemented. The clasts of the gravel, like those in the conglomerate at locality 

T J -1, are chiefly of Precambrian granite, gneiss, and schist, Eocene andesite 

and basalt, and dense quartzite cobbles reworked from rocks of late 

Cretaceous or Paleocene age. An occasional pebble of Paleozoic limestone 

and fine-grained sandstone of unknown age may also be found. Christiansen 

and Blank ( 1972, p. B9) state that the gravel occurs in a paleovalley cut in 

Eocene rocks and that it is overlain by the Junction Butte Basalt which, on 

Mount Everts (fig. 1), directly underlies the Huckleberry Ridge Tuff. As 

indicated above, the Junction Butte Basalt is considered of Pleistocene age, 
8 POLLEN ANALYSES, WASHBURN RANGE, WYOMING 

but may approximate the Pliocene-Pleistocene boundary. The age of the 

underlying gravel, which contains no clasts of rhyolite tuff or Junction Butte 

Basalt, is therefore no younger than latest Pliocene. 

We correlate the conglomerate at locality T J-1 with the gravel beneath the 

Junction Butte Basalt on the basis of their lithologic similarities. Both 

contain similar proportions of clasts of the same rock types, and both lack 

clasts of Huckleberry Ridge Tuff or Junction Butte Basalt. Figure 2 is a 

reconstruction of the profile of the floor of the paleovalley, controlled by 

altitudes at the base of the gravel (Pierce, 1974), the base of the Junction 

Butte Basalt, and the base of the Huckleberry Ridge Tuff (Prostka and 

others, 1975) in the paleovalley, and projected to the altitude of locality T J-1. 

The reconstruction tends to support the above correlation, although a cover 

of middle Pleistocene rhyolite lava flows obliterates the paleovalley in 

places. 

2600 II) 

~ 

t;:j 2400 

·~ 

~ 

z'2200 

0 

i= 

~ 2000 

~ 

s 

0 

..ll: 

., 

., 

u 

"'0 

0 

e 

Ill 

4 

I I 

~ 0 

ID 

., 

ID 

~-> 

0 c: .. 0 1:11 ;::: ._ u ., c: > ~ 0 

------------- Yellowstone River 

8 KILOMETERS 

N 

FIGURE 2.-Profile of floor of paleovalley of Yellowstone River between Tower Junction and 

locality T J-1. Profile is drawn on altitudes at base of gravel beneath Junction Butte Basalt 

(from Pierce. 1974) and at base of Huckleberry Ridge Tuff in paleovalley (from Prostka and 

others, 1975), and is projected upstream, in part beneath younger middle Pleistocene rhyolite, 

to altitude of gravel at locality T J-1. Solid circles and triangle correspond to those in figure I. 

Shultz ( 1962, p. 56) inferred that the source of the clasts of Precambrian 

rock in the conglomerate at locality TJ-1 was probably the Beartooth 

Mountains to the north. However, the similarity of this conglomerate to the 

gravel beneath the Junction Butte Basalt, and the north-sloping profile of 

the paleocanyon in which the basalt and underlying gravels were deposited, 

suggests to us that the source was a former upland to the south. The presently 

known southern limit of the conglomerate is just north of the rim of a large 

caldera complex which formed in the central area of Yellowstone National 
PALEOECOLOGIC AND PALEOCLIMATIC INFERENCES 9 

Park during major eruptions of the Huckleberry Ridge and Lava Creek 

Tuffs (Christiansen and Blank, 1972), 2.02 ±0.08 million years ago and 

616,000±8,000 years ago respectively. The inferred upland source of the 

conglomerate may have been present in this area before collapse of the 

caldera. The paleovalley downstream from locality T J-1 is eroded in Eocene 

rocks north of the caldera rim and is probably cut by the caldera rim fault 

upstream to the southwest. Another paleovalley, tributary from the south, 

may have existed in about the position of the present Grand Canyon of the 

Yellowstone. If so, it was cut by the caldera rim fault about 0.5 km south of 

its confluence with the drainage from locality T J-1. 

The inferred upland source of the paleovalley drainage may have bee lt 

continuous with the Basin Creek uplift, a domal structure truncated by the 

caldera rim fault along the south rim of the caldera in the south-central part 

of the park. Rejuvenation of the domal structure during the onset of 

volcanism in late Cenozoic time has been postulated by Love and Keefer 

(1969) The relatively steeper head ward slope of the paleovalley profile (fig. 

2) suggests that the gravels were deposited on the north slope of the inferred 

uplift immediately before volcanism began. 

The precise age of the deposits at locality TJ-2 is more difficult to 

determine because they are unrelated to datable rocks. The sandy layers at 

TJ-2 are similar to sand in a gravel underlying the Huckleberry Ridge Tuff 

on Mount Everts (Pierce, 1973)in that both deposits are wholly ofandesitic 

material. This implies that both deposits were formed in drainages that 

flowed northward from terrain underlain by andesitic rocks. 

The physiographic setting of these deposits relative to the distribution and 

direction of flow of Pleistocene glaciers in the drainage of the Yellowstone 

River (Pierce, 1974) is such that all glacier-related deposits, and probably 

most interglacial deposits contain Precambrian plutonic and metamorphic 

rocks transported from sources to the northeast. Such material is 

abundantly present in nearby nonindurated ice-contact deposits of the last 

glaciation and scattered glacial erratics (Pierce, 1974). 

Because the deposits at locality TJ-2lack both rhyolitic and Precambrian 

crystalline material, we infer that they are probably preglacial and of latest 

Pliocene age. 

PALEOECOLOGIC AND PALEOCLIMATIC INFERENCES 

A comparison of the pollen analyses from localities T J-1 and T J-2 with the 

modern pollen rain and the present distribution of vegetation provides some 

clues for speculation as to the distribution of vegetation and climatic 

conditions slightly more than 2 m.y. ago in latest Pliocene time. 

Baker (1976, p. El0-E12) has broadly defined the characteristics and 

altitude limits of five modern vegetation associations in Yellowstone 

National Park (table 1) and has described (p. El7-E20 and fig. 13) the 

modern pollen rain from surface samples collected in each. 
10 POLLEN ANALYSES, WASHBURN RANGE, WYOMING 

TABLE 1.-Vegetation associations and their altitude limits in Yellowstone National Park 

[Converted to meters from Baker (1976)] 

Alpine association -----------------------2,800 m to 2,990-3,350 m (summits) 

Picea-Abies-Pinus 

albicau/is forest 

association ----------------------------2,590 m to 2,800-2,990 m 

Pinus contorta .forest association 

(mixed with Picea and 

Abies in upper part) ---------------2,130 m to 2,590 m 

Pseudotsuga ass.ociation-------------1 ,820 m to 2,440 m 

Artemisia steppe 

association -------------------upper limit: approximate 2,075 m 

Comparison of the pollen analyses from sample localities TJ-1 and TJ-2 

with analyses of modern surface samples (table 2) reveals that the pollen 

types and percentages at locality T J-1 are similar to those of both the Pinus 

contorta forest association (mixed with Picea and Abies) and the 

Picea-Abies-Pinus albicaulis forest association. We cannot distinguish 

between these associations because we have not differentiated species of 

Pinus. 

TABLE 2.-Comparison of major pollen types and percentages from localities TJ-1 and TJ-2 

with those of modern surface samples 

[Two of the four surface samples representing the Pseudotsuga association were collected by William Mullenders from moss 

polsters. The other modern surface samples were collected by R. G. Baker( 1976, and written commun., 1977) from pond muds, 

marshes, and organic-rich soils] 

Pollen type 

Fossil 

pollen 

locality 

TJ-1 

Pinus ----------------------------- 84.9 

Picea -------------------------- 3.8 

Abies ------------------------- 2. 7 

Juniperus---------------------- 0 

Pseudotsuga -------------------- 0 

Betula -------------------- 0.1 

Alnus ---------------------------- 0.4 

Ephedra ------------------------ 0 

Artemisia --------------------- 5.1 

ChenopodiaceaeAmaranthaceae -------------- 0.4 

Sarcobatus --------------------- 0.1 

Compositae ------------------- 1.3 

Gramineae -------------- 0.8 

Number of samples ------------

Pollen sum ---------------- 302 

1Minimum pollen sum of all samples analyzed. 

Modern forest surface samples 

Pinus-Abies- Pinus 

albicaulis 

forest anociation 

80.0-87.0 

3.6- 3.8 

1.5 

0 - 0.3 

0 - 0.3 

0 - 0.3 

0 

0 

3 -10.6 

1.5 

0 - 0.3 

0.5- 0.9 

0 - 1.2 

2 

1339 

Pinus contorta 

forest association 

with Picea 

and Abies 

80.0-88.0 

0.5- 4.0 

0.6- 2.8 

0 - 0.6 

0 - 0.5 

0 

0 - 0.5 

0 

4.5-12.5 

0.5- 2.3 

0 - 0.6 

0 - 0.5 

0.3- 4.5 

6 

1228 

Pseudotsuga Fossil association pollen 

52.6-85.0 

0.2- 1.7 

0 - 0.7 

0.5- 2.3 

0.3- 2.8 

0 - 0.6 

0 - 2.3 

0 - 0.1 

4.8-29.7 

0.3- 5.0 

0 - 0.2 

0 - 4.0 

0.5- 6.5 

4 

1296 

locality 

TJ-2 

74.5 

5.3 

0 

0 

3.0 

0.3 

0.7 

0 

5.3 

0.7 

0 

1.0 

7.3 

1 

957 
PALEOECOLOGIC AND PALEOCLIMATIC INFERENCES 11 

All three pollen assemblages contain 80 percent or more Pinus pollen, as 

much as 4 or 5 percent Picea pollen, and as much as about 3 percent Abies 

pollen. The percentage of Artemisia pollen is lower in our sample from 

locality TJ-1 (5 percent) than in some of Baker's (3-12 percent). The 

percentages for Gramineae and Chenopodiaceae-Ameranthaceae are also 

lower in our sample; but that for Compositae is higher. These variances do 

not appear sufficient to suggest major differences in vegetational environment; in fact, the overall similarity is great enough to strongly suggest that 

the local forest during deposition of the rocks at locality TJ-1 was probably 

either the Pinus contorta forest association mixed with Picea and Abies or 

the Picea-Abies-Pinus albicaulis forest association. The altitude of locality 

T J -1 is about that of the modern boundary between the Pinus contorta forest 

association and the Picea-Abies-Pinus contorta forest association (table 1). 

A similarity is apparent also between the pollen types and percentages in 

the sample from locality T J-2 and those of surface samples from the modern 

Pseudotsuga forest (table 2) near and east of Mammoth (fig. 1). Pollen 

counts for individual species in the sample from locality TJ-2 are mostly 

within the range displayed by the surface samples. The percentage of pollen 

of Picea (5.3) at locality TJ-2: is greater than in these surface samples but less 

than in a surface sample (8.3 percent) from open Pseudotsuga forest in 

Jackson Hole, south of Yellowstone National Park. Juniperus pollen is 

more abundant in one surface sample collected near Mammoth where 

Juniperus scopulorum is a major component of the association. Artemisia 

pollen is also more abundant in one surface sample collected east of 

Mammoth where the association is a very open Pseudotsuga forest with 

widespread Artemisia tridentata. Pseudotsuga pollen is slightly more 

abundant in the sample from locality T J -2 than in any ofthe surface samples 

(table 2), all of which are from very open to moderately open Pseudotsuga 

forest. Two samples from dense Pseudotsuga forest, one from Jakcson Hole 

to the south and the other from West Yellowstone Basin, west of 

Yellowstone Park, contained respectively 17.1 percent and 14.6 percent 

Pseudotsuga pollen. We infer therefore that the pollen assemblage from 

locality TJ-2 reflects the presence, at the time of deposition of the rocks, of a 

moderately open Pseudotsuga association, possibly with nearby Picea. 

Locality T J -2 is presently in moderately open Pseudotsuga forest with 

nearby Picea engelmanni on north-facing slopes, and its altitude(2,025 m) is 

in the middle part of the present altitude range of Pseudotsuga forest (table 

1). 

The similarities of the pollen assemblages from the rocks at localities T J-1 

and T J -2 to those of surface samples of modern forest associations, together 

with the relationship of tht! altitudes of localities TJ-1 and TJ-2 to the 

altitude ranges of modern forest associations, suggest that the forest 

associations and their altitude limits during deposition of the rocks at 

localities TJ-1 and TJ-2 did not differ greatly from those of the present. If 

true, the climate in Yellowstone National Park about 2 million years ago in 
12 POLLEN ANALYSES, WASHBURN RANGE, WYOMING 

latest Pliocene time was broadly similar to that of today. 

Other deposits which we correlate with the rocks at localities T J-1 and 

TJ-2 on the basis that all conformably underlie the Huckleberry Ridge Tuff 

include: ( 1) the Heart Lake Conglomerate (Love and Keefer, 1969) which 

underlies the Huckleberry Ridge Tuff in the south-central part of 

Yellowstone National Park; (2) the upper gravel unit of the Bivouac 

Formation (Love, 1956, 1973), which overlies a tuff unit dated as Pliocene 

(Christiansen and Love, 1977) and underlies the Huckleberry Ridge Tuff on 

Signal Mountain in Jackson Hole; and (3) widespread deposits of alluvial 

gravel and lacustrine diatomite, silt, and sand that conformably underlie the 

Huckleberry Ridge Tuff in the area drained by the Teton River and Falls 

River in Idaho, southwest of Yellowstone National Park. 

The Heart Lake Conglomerate was formerly estimated to be of Pliocene 

or Pleistocene age (Love and Keefer, l969)as was the Bivouac Formation 

(Love, 1956, 1973). The Glenns Ferry Formation in Idaho, considered to be 

of Pliocene and Pleistocene(?) age by Malde and Powers (1962), is probably 

mostly older than the rocks at localities TJ-1 and TJ-2 because it contains a 

small relict early Tertiary flora. 

ACKNOWLEDGMENTS 

The writers are grateful to Richard G. Baker for the previously 

unpublished specific pollen percentages of surface samples used in compiling 

table 2. Also, we sincerely thank him and J. Platt Bradbury, William S. 

Scott, and Harold J. Prostka for critically reading the manuscript and 

offering many helpful suggestions for its improvement. 

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