A Postglacial Chronology 

For Some Alluvial Valleys 

In Wyoming

By LUNA B. LEOPOLD and JOHN P. MILLER

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1261

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1954
UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary

GEOLOGICAL SURVEY 

W. E. Wrather, Director

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

Washington 25, D. C. - Price 35 cents (paper cover)
PREFACE

This report is one of a series of studies 

of relations between land and water being 

made in the Water Resources Division under the general direction of Royal W. 

Davenport, chief, Technical Coordination 

Branch.

Particular acknowledgment is made to 

C. B. Schultz who identified collections of 

vertebrate fossils and gave his time freely 

in many helpful discussions, and to W. J. 

Clench who identified the invertebrate 

fossils.

L. B. L.

Ill

CONTENTS

Page

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

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

Nomenclature for alluvial terraces.................................................................................... 3

General relations of terraces and alluvial fills in Wyoming.......................................... 6

Arvada formation.................................................................................................. 8

Ucross formation.................................................................................................. 10

Kaycee formation................................................................................................ 10

Lightning formation............................................................................................ 11

Criteria for correlating terraces......................................................................................... 12

Continuity and height.................................................................................................. 12

Physiographic relations to other land forms............................................................ 15

Stratigraphic relations of terrace fills...................................................................... 15

Relations of terraces and alluvial fills in various river basins.................................. 17

Powder River basin.................................................................................................... 17

Powder River near Arvada, Wyo........................................................................ 18

Powder River near Sussex, Wyo........................................................................ 21

Clear Creek south of Ucross, Wyo.................................................................... 23

Clear Creek at Buffalo, Wyo.............................................................................. 26

Belle Fourche River basin........................................................................................ 30

Bighorn River basia................................................................................................... 33

Shoshone River basia................................................................................................. 33

Fivemile and Muddy Creeks...................................................................................... 35

Little Bighorn River basia....................................................................................... 39

Popo Agie River basin................................................................................................ 39

Cheye'nne River basin................................................................................................ 40

North Platte River basin............................................................................................ 44

Regional correlation and its problems.............................................................................. 46

Terraces and glacial features in Clear Creek basin.............................................. 47

Climatic implications of the paleosol...................................................................... 50

The chronology of climatic events............................................................................ 53

Pal eohydrology.................................................................................................................... 60

Stream gradients, past and present, and their hydrologic significance.............. 61

Rate of accumulation of valley alluvium and comparison with modern rivers.... 66

Recent physiographic history and the problem of modern soil erosion........................ 75

Relative ages of erosion features of the present topography................................ 76

The erosion problem in the West.............................................................................. 83

References cited.................................................................................................................. 86

Index...................................................................................................................................... 89

ILLUSTRATIONS

Page 

Figure 1. Block diagrams of cut and fill terraces.......................................................... 4

2. Examples of stratigraphic relations in valley alluvium................................ 5

3. "Inset" and "overlapping" relations of two alluvial fills.......................... 6

4. Location map showing area discussed in this report.................................... 7

5. Generalized relations of alluvial fills in valleys of eastern Wyoming...... 9

6. Cross sections of valley of Powder River showing extension of washslope profiles.................................................................................................. 14

7. Terraces along the Powder River, Wyo.......................................................... 17

, 8. Cross section of valley of Powder River near Arvada, Wyo........................ 18

9. Congeliturbate in alluvial terrace near Arvada, Wyo.................................... 19
VI CONTENTS

Page 

Figure 10. Cross section of valley of Powder River near Sussex, Wyo...................... 21

11. Exposure near top of high terrace near Sussex, Wyo.................................. 22

12. Cross section of valley of Clear Creek near Ucross, Wyo........................ 23

13. Changes in content of calcium carbonate and in pH with depth in

Kaycee terrace alluvium near Ucross, Wyo.............................................. 24

14.. Section through Kaycee and Moorcroft terraces near Clearmont, Wyo...... 26

15. Cross section of valley of Clear Creek near Buffalo, Wyo........................ 27

16. Changes in calcium carbonate content with depth at three positions

on the Kaycee terrace near Buffalo, Wyo.................................................. 28

17. Cross sections of the valley of the Belle Fourche River, Wyo................ 30

18. Cross sections showing stratigraphic and physiographic relations of

alluvial fills in valleys in the Bighorn River basin................................ 36

19. Cross sections of valleys in the Cheyenne River basin............................ 41

20. Valley of Lance Creek near Lance Creek, Wyo.......................................... 42

21. Cross sections showing stratigraphic and physiographic relations of

alluvial fills in valleys in the upper North Platte River basin............ 45

22. Longitudinal profiles of Powder River and Clear Creek............................ 61

23. Cross-sectional area of Kaycee alluvial fill in relation to stream

order, Powder River basin.......................................................................... 70

24. Topographic map, cross section, and block diagram of Revision Draw,

Twentymile Creek, Wyo.............................................................................. 78

25. Topographic map, section, and longitudinal profile of Neardark Draw

near Arvada, Wyo.......................................................................................... 81

TABLES

Page

Table 1. Chronology of events indicated by the alluvial terraces and underlying deposits in Wyoming.......................................................................... 11

2. Heights of terraces on Powder River and tributaries.................................. 29

3. Heights of terraces along Belle Fourche River, Wyo.................................. 33

4. Heights of terraces in Bighorn River basin.................................................. 40

5. Heights of terraces in Cheyenne River basin.............................................. 43

6. Terrace heights along upper reaches of Clear Creek and North Fork

Clear Creek, Wyo.......................................................................................... 48

7. Tentative regional correlation of alluvial deposits.................................... 58

8. Number and length of streams of various orders, Powder River basin

above Arvada, Wyo...................................................................................... 68

9. Computation of volume of alluvium in Kaycee and Lightning fills.......... 71
A POSTGLACIAL CHRONOLOGY FOR SOME ALLUVIAL 

VALLEYS IN WYOMING

By LUNA B. LEOPOLD and JOHN P. MILLER

ABSTRACT

Alluvial terraces were studied in several major river basins in eastern Wyoming. Three 

terraces are present along nearly all the streams and large tributaries. There are several 

extensive dissected erosion surfaces in the area, but these are much older than, and 

stand well above, the recent alluvial terraces with which this report is concerned.

The three alluvial terraces stand respectively about 40, 10, and 5 feet above the present streams. The uppermost and oldest is a fill terrace comprised of three stratigraphic 

units of varying age. The oldest unit is Pleistocene and the youngest unit postdates the 

development of a soil zone, or paleosol, which is characterized by strong accumulation 

of calcium carbonate and gypsum. This paleosol is an important stratigraphic marker. 

The middle terrace is generally a cut terrace and is developed on the material making up 

the youngest alluvium of the high terrace. The lowest is a fill terrace, the surface of 

which is only slightly higher than the present flood plain.

The oldest terrace can tentatively be traced into mountain valleys of the Bighorn 

Range on the basis of discontinuous remnants. The terrace remnants occur far upstream 

from the youngest moraine in the valleys studied. On this basis, the terrace sequence is 

considered to postdate the last Wisconsin ice in the Bighorn Mountains. The paleosol is 

tentatively correlated with Altithermal time, called in Europe the Climatic Optimum. The 

terrace sequence is very similar to that suggested by various workers in the southwestern United States.

Two streams, Clear Creek and the Powder River, deposited comparable silty alluvium, 

the surface of which now comprises the highest alluvial terrace. The gradients of these 

former flood plains differed markedly between the two streams despite the comparability 

in size of material deposited. This difference in gradient is believed to have required 

different relative contributions of water from mountain and plain areas than now exist.

Knowledge of Recent physiographic history of the area is the basis of determining the 

relative ages of some gully features. Certain vertical-walled channels or arroyos that 

might appear to be attributable to postsettlement grazing or other man-induced influences 

are shown to be Recent but pre-Columbian in age. Such differentiation in age of erosion 

features is necessary for proper understanding of present-day soil erosion problems.

1
2 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

INTRODUCTION

There is abundant proof of large-scale climatic changes which 

resulted in the several advances and retreats of Pleistocene ice. 

The erosional and depositional phenomena associated with that 

epoch profoundly affected the landscape, and in many areas were 

primary determinants of present topography.

Since the last retreat of the ice, climatic changes have continued to take place, though of smaller magnitude. Variations in 

climate are even now being experienced, as indicated by recent 

retreats of glacial fronts in many parts of the world, and as shown 

by temperature and precipitation records of historic time.

The changes in climate of the postglacial period have also left 

their marks upon the landscape, and there are many small-scale, 

but nevertheless significant features whose origin can be traced 

to these changes. There are prominent alluvial terraces which 

border the majority of the streams, large and small, in areas 

adjacent to the Rocky Mountains. These terraces are the remnants of former valley floors. Their formation is due to climatic 

changes which produced fluctuations in runoff and in conditions of 

vegetation. These, in turn, caused the streams alternately to fill 

and erode their valleys.

One of the important lines of evidence indicating that the river 

terraces are ultimately due to climatic causes is the similarity of 

the terrace sequence over large areas of the Rocky Mountain region. The present report describes in some detail the alluvial 

terraces of several rivers in Wyoming, and in a less detailed 

manner, of certain rivers in southern Montana, southwestern 

South Dakota, and western Nebraska. There is a remarkable similarity in the sequence of events in river history in Wyoming and 

adjacent areas, and that sequence is comparable to the one worked 

out for streams in the southwestern United States.

Not only do widely separated areas exhibit similar sequences of 

aggradation and degradation, but there is evidence that the respective periods were nearly correlative in time throughout the 

region. Variations in climate provide a logical explanation for 

similar, apparently concordant, alternations of alluviation and 

degradation, and in fact, climatic change is the only agent sufficiently widespread in its effect to account for the observed 

features.

There is evidence that the series of climatic changes which left 

its imprint as well-marked alluvial terraces was quite recent indeed. The youngest alluvial fill in the Southwest contains artifacts 

of Indian cultures which have been dated as only a few centuries
NOMENCLATURE FOR ALLUVIAL TERRACES 3

before the discovery of the New World. The oldest terrace built 

of alluvium, and therefore included in the sequence considered 

here, appears to be related to one of the minor episodes of glacial 

advance at the end of Wisconsin time. It is necessary, then, to 

realize at the outset that climatic changes which characterized 

the Pleistocene have continued even to the present time to play an 

important role in the development of the landscape. Though the 

climatic fluctuations which have occurred since the last major ice 

advance are relatively small in magnitude, they are evidently 

similar in nature to those larger variations which caused the advance and retreat of glaciers.

The arid or semiarid Western States are now undergoing a period of erosion or gully formation. Valleys are now being trenched 

by arroyos, and the alluvial terrace deposits constitute the source 

of much of the sediment carried. This epicycle of erosion has 

widespread and important physical, economic, and social consequences. Because the results of the present erosion are similar 

in many respects to those of past periods of degradation, it is instructive to work out the sequence of climatic and geomorphic 

changes which have marked the late Pleistocene and Recent epochs 

as a background for studying the current erosion problem.

NOMENCLATURE FOR ALLUVIAL TERRACES

By common usage, the terms "cut terrace" and "fill terrace" 

apply to remnants of former floors of alluvial valleys. Terraces 

cut into bedrock are generally called "strath terraces. " The latter 

do occur in the area studied, but this paper is concerned primarily 

with recent alluvium and with cut and fill terraces.

The development of a cut terrace is indicated in diagrams A and 

B of figure 1. It is distinguished from a fill terrace for which the 

developmental stages are indicated in diagrams C, D, and E of 

figure 1.

In C, the initial stage is exactly the same as A of the cut terrace. The stream incised itself into the alluvial valley fill as illustrated in D, which corresponds closely to the final stage B of a 

cut terrace except that the stream is pictured as having cut a 

deeper trench. If, thereafter, degradation ceases and the stream 

deposits material in its valley trench, it may attain the condition 

shown in E, in which the outward form of the terrace may be identical to B of the cut-terrace sequence. Despite the possibility of 

complete similarity in form, the example illustrated by diagrams 

C, D, and E required for its formation an additional change in 

regimen; that is, an aggradational, as well as the degradational, 

phase.
POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

CUT TERRACESEQUENCE OF EVENTS 

 Erosion of valley FILL TERRACE

Deposition of alluvial fill

Erosion of alluvial fill

Deposition of a second 

alluvial fill

Figure 1. Block diagrams illustrating the stages in development of a cut terrace (diagrams A 

and B) and a fill terrace (C, D, and E).

Because a genetic relation exists in a cut terrace between the 

ascending scarp and the plain beneath and in front of it, Davis 

(1902) suggested that this combination be considered the two parts 

of a single-river terrace. This genetic relationship does not exist 

in a fill terrace. As the term "terrace"is used in this report, it is 

made up of the scarp and tread above and behind it. The flood 

plain currently being used by a river is not a terrace according to 

this definition, though it is a surface composed of alluvial 

material.

For present purposes an "alluvial fill" will be considered a deposit of unconsolidated river-laid material in a stream valley, and 

as a single stratigraphic unit. This implies that the mass of material was deposited during a more or less uninterrupted period 

of aggradation.

If incision and aggradation occur repeatedly, it is possible to 

develop any number of terraces. Depending on the magnitude and
NOMENCLATURE FOR ALLUVIAL TERRACES 5

the sequence of deposition or erosion, any number of fills or different stratigraphic units could be deposited. The number of fills 

and terraces constitutes part of a logical classification of alluvial 

valleys.

Figure 2 presents nine possible examples representing different numbers of terraces developed in valleys having various numbers of alluvial fills. The three examples in the group marked A 

show no terraces in valleys having one, two, and three alluvial 

fills. Similarly, the possibilities for valleys with one and two 

terraces are pictured in groups B and C, respectively.

A. NO TERRACE

B. ONE TERRACE

1 

ONE ALLUVIAL FILL

C. TWO TERRACES

TWO ALLUVIAL FILLS THREE ALLUVIAL FILLS

Figure 2. Examples of valley cross sections showing some possible stratigraphic relations in

valley alluvium.

Example 1A will be called a "1-fill, no-terrace alluvial valley, " 

and example 3C will be a "3-fill, 2-terrace alluvial valley. " The 

nomenclature can be extended to include any combination of 

numbers.

Another set of words is needed in order to designate the stratigraphic relations of the alluvial deposits. During the later two 

periods of alluviation, the gully or valley cut in the earlier alluvium may be only partly filled, as pictured in figure 3, cross 

section A, in which the later alluvial fill is "inset" in relation to 

the earlier. In cross section B, the later alluvial fill has an 

"overlapping" relationship to the earlier one; that is, the second 

fill was of sufficient volume to overflow the valley cut into earlier 

alluvium.
POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

A

Second fill "inset" Second fill 'overlapping"

Figure 3. Valley cross sections illustrating "inset" and "overlapping" relations of two

alluvial fills.

Both of the examples in figure 3 represent. 2-fill, 1-terrace 

alluvial valleys. In such a valley, the condition of an inset fill 

implies that following deposition of the first fill there was erosion, 

followed again by deposition which only partly filled the valley. In 

the development of an overlapping second fill, the first deposition 

was followed by erosion, after which occurred a second period of 

deposition, followed again by erosion.

In places where there are several fills and several terraces, the 

permutations possible become large because of the fact that any 

given fill could be either inset or overlapping the preceding one. 

Thus, in figure 2, the stratigraphic relations shown are not the 

only ones which would provide the combinations of multiple terraces 

and multiple fills.

GENERAL' RELATIONS OF TERRACES AND ALLUVIAL FILLS IN WYOMING

The several river basins discussed in this report are shown in 

the map, figure 4. The most detailed work was done in the basins 

of the Powder, Belle Fourche, and upper Cheyenne Rivers, and 

somewhat less detailed work in the Little Bighorn, the middle 

reaches of the Bighorn, and the North Platte Rivers.

The rivers drain, for the most part, undulating plains where 

rainfall is relatively low, 12 to 16 inches a year, and where vegetation is sparse. Semidesert shrub and short-grass prairie associations dominate much of the area, and woodland is next in areal 

extent. The headwaters of nearly all of these rivers are in high 

mountains, but the high country constitutes only a small part of 

the total area.

On the undulating plains remnants of extensive pediment surfaces 

can be seen. Near the mountains particularly, these surfaces, 

generally covered with gravel, are distinct and from a distance 

appear as giant staircases leading spectacularly down toward the
GENERAL RELATIONS OF TERRACES AND ALLUVIAL FILLS IN WYOMING

Figure 4. Location map showing area discussed in this report.

present river bottoms. These surfaces in some areas have been 

described in detail (Blackwelder, 1914; Mackin, 1937) and are not 

considered here.

The present study deals with much younger and smaller features, 

the alluvial terraces which border the present streams. In all of 

the river basins studied, there are generally three such terraces, 

and all three are present so consistently that they are indeed a 

characteristic feature of the valleys. The general aspect of these 

terraces and the sequence of deposits underlying them are pictured 

diagramatically in figure 5. Their topographic characteristics will 

be discussed first.

The highest and oldest alluvial terrace, called the Kaycee, stands 

20 to 50 feet above the present streams. From the scarp of the 

Kaycee terrace, wash-slopes characteristically sweep in gentle 

upward curves toward the drainage divides.
8 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

A middle terrace, called here the Moorcroft, stands commonly 

8 to 12 feet above the streams. It is generally somewhat narrower 

than the lowest terrace and is separated from it by an abrupt scarp.

The lowest terrace, called here the Lightning, stands 4 to 7 feet 

above the streams, and at first glance appears to be the flood plain. 

In some reaches it probably is the modern flood plain, but generally 

there is present a slightly lower, narrow, and relatively inconspicuous flat bordering the stream, which is actually the present 

flood plain. In most reaches the Lightning terrace does not appear 

to be overflowed by modern floods.

These topographic characteristics are shown in the generalized 

cross section of figure 5. In certain places, one or more of the 

features just described are missing, but despite the exceptions, 

the relations are so amazingly consistent that they would attract 

the attention of most observers. There is also a consistency in 

the sequence of deposits forming the respective terraces.

The Kaycee terrace is underlain by more than one stratigraphic 

unit, as can be seen in figure 5, and as will presently be described. 

The surface has a definite soil profile characterized by a columnar 

or cloddy structure and a recognizable B horizon slightly mottled 

with whitish calcium carbonate.

The Moorcroft, the middle of the three terraces, is in most 

places a cut terrace underlain by the same silty formation that 

constitutes the top stratum of the highest, or Kaycee, terrace. 

No soil profile is developed on the Moorcroft terrace, although in 

places some humic darkening can be seenin the upper few inches.

The Lightning terrace is generally composed of an inset fill consisting of silt and fine sand. No evidence of soil formation is 

present near the surface.

A summary of the physical characteristics of these alluvial 

materials follows. It provides a generalized and composite picture 

of the various exposures Which are discussed individually later.

ARVADA FORMATION

The oldest alluvial material found in the valleys which were 

studied is named here the Arvada formation. The material consists 

of highly weathered gravel or gravelly sand, generally stained red 

but containing many cobbles stained with a yellow or yellow-brown 

of limonite. The beds present ample evidence of frost action, including fossil ice wedges and contortions. The formation contains 

bones of late Pleistocene extinct mammals. Where the next younger 

alluvial formation, the Ucross is absent, the carbonate-rich paleosol may be imposed on the upper part of the Arvada formation.
GENERAL RELATIONS OF TERRACES AND ALLUVIAL FILLS IN WYOMING
10 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

The type locality for the Arvada formation is at the west abutment 

of the highway bridge across the Powder River on Highway 16, 3 

miles north of Arvada, Wyo.

UCROSS FORMATION

The gravelly deposits of Recent age discomformably overlying 

the Arvada formation are here designated the Ucross formation. 

Its type locality is in Clear Creek valley, 1 mile south of Ucross, 

Wyo. The deposits consist of fresh, rounded gravel including a 

variety of rocks, mostly igneous and metamorphic, derived from 

mountain areas. The pebbles in the gravel average 1 to 2 inches 

in diameter. The formation contains occasional deeply weathered 

yellow-stained and red-stained pebbles. The upper few feet of the 

formation may locally be composed of silt and may contain lenses 

of clay.

The upper 2 to 3 feet of Ucross formation is characteristically 

impregnated with large amounts of calcium carbonate and gypsum 

in the form of strong white mottlings, concentrically-filled tubules, 

and hard nodules 1/8 to 1 inch in diameter. The carbonate and 

gypsum concentrations on the lower side of cobbles in fibrous or 

crystalline masses are as much as 3/4 of an inch thick. The 

accumulation of carbonate and gypsum is sufficiently great to give 

the zone a whiteness that can be seen even from a distance. The 

carbonate and gypsum are considered to be analogous to a caliche 

crust which accumulates at the ground surface where evaporation 

concentrates the salts brought to the locality by ground water or 

lateral movement of vadose water. A caliche crust by its mode of 

formation will not be associated with a leached A horizon. Though 

such a crust is not a typical soil profile, it is a zone of surface 

weathering and if it were formed at some time in the past rather 

than under present conditions, it would be called paleosol.1

The paleosol is absent in places and the next younger formation, 

the Kaycee, lies unconformably on fresh gravel that is believed to 

be Ucross in age. This sequence is explained by the fact that a 

period of erosion followed the formation of the Ucross and during 

it the carbonate zone was in places removed.

KAYCEE FORMATION

The formation underlying the Moorcroft terrace and comprising 

the upper part of the alluvium of the Kaycee terrace is here called 

the Kaycee formation. As indicated in figure 5, the Kaycee terrace 

characteristically sweeps in smooth wash slopes toward the interstream divides. Slope wash and colluvium interfinger with the

iPaleosol is a term introduced by Hunt and Sokoloff (1950) to describe an ancient soil one 

formed under climatic conditions different from the present.
GENERAL RELATIONS OF TERRACES AND FILLS IN WYOMING 11

contemporaneous river-laid deposits, and both colluvium and river 

alluvium are considered in the Kaycee formation. The type locality 

is designated as the left bank in the reach of the Powder River 

from Kaycee to Sussex, Wyo.

The Kaycee formation is of Recent age. Its surface has a clearly 

defined soil profile characterized by humic darkening through a 

depth of 1 to 2 feet. The soil tends to be columnar or cloddy in 

structure and its B horizon is mottled white by a concentration of 

calcium carbonate. Nodules of calcium carbonate are absent.

The Kaycee formation consists of uniform tan or light-brown 

silt consisting of moderately well sorted grains, predominantly 

quartz. The grains are subrounded but not pitted. The large 

amount of silt suggests the possibility of an aeolian source, but 

the material is not sufficiently well sorted or pitted to assign aeolian processes a major role in its origin. Lenses of sand or fine 

gravel are locally present. In places there is a thin basal gravel. 

Bones of Bison bison are common, and no extinct animal remains 

have been found.

LIGHTNING FORMATION

An alluvial fill of Recent age consisting of light-brown to tan, 

silty, fine or medium sand containing occasional lenses of fine 

gravel or coarse sand but generally devoid of bedding is here 

named the Lightning formation. No bones or artifacts have been 

found in this formation. No soil profile exists at its surface. 

Thickness varies from 3 to 10 feet. The type locality is designated 

as the reach of Lance Creek in the immediate vicinity of the town 

of Lance Creek, Wyo.

The sequence of events leading to the development of the various 

stratigraphic units and the terraces is summarized in table 1.

Table 1. Chronology of events indicated by the alluvial terraces and under/ying deposits

in Wyoming

[Events arranged in order from oldest to youngest] 

Bedrock eroded to form river valleys, strath terraces, pediments, and other features.

Deposition of gravels: Arvada formation. 

Weathering of Arvada formation to deep red. 

Erosion of Arvada formation.

Deposition of gravels near mountains and fine-grained alluvium at distance from mountains:

Ucross formation.

Development of soil (strong calcium carbonate accumulation). 

Erosion.

Deposition of fine-grained alluvium: Kaycee formation.

Trenching of the Kaycee formation, forming the Kaycee terrace and the tread of the Moorcroft 

terrace, cut on Kaycee formation.

Period of stability during which streams flowed at height of Moorcroft terrace tread, which is a

cut terrace. 

Erosion; incision of stream forming the Moorcroft terrace.

Deposition of fine-grained alluvium: Lightning formation.

Slight trenching of Lightning formation forming the Lightning terrace.
12 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

CRITERIA FOR CORRELATING TERRACES

The principles of terrace correlation are generally understood, 

and have been utilized by geomorphologists and archeologists in 

such problems as dating culture horizons and interpreting the alpine glacial sequence. Application of these principles, however, 

involves so many problems that the techniques and criteria are by 

no means uniform. In fact, the differences are so apparent in the 

literature that it seems necessary to consider the problems here, 

and to develop the reasoning which underlies the terrace correlations proposed herein.

Alluvial terraces must be correlated on the basis of terrace 

morphology and stratigraphic characterictics of the alluvial materials of which the terrace is composed. Morphologic characteristics which may be useful in correlation are the continuity and 

.height of terraces, and the physiographic relation of the terrace 

to other land forms, such as higher hills and lower terraces. 

Stratigraphic methods may be employed to determine the depositional characteristics and lithology of the alluvial fills, and the 

relation of the fills to certain horizon markers, such as unconformities, fossil zones, and buried soils. Each criterion used for 

correlation purposes in this report will now be discussed briefly.

CONTINUITY AND HEIGHT

The most important criterion for identifying a stream terrace 

is based on the premise that during a period of relative stability 

the stream cut a surface or built a flood plain, either of which 

was more or less continuous along the valley. When the stream 

cut down below this surface, thus forming a terrace, erosion by 

lateral swinging of the main stream and down-cutting by tributaries partly or completely eliminated the original surface. If 

such erosion has been slight, the terrace remnants will b*e relatively continuous along the valley and will be at a uniform or uniformly changing height above the present stream bed. Terrace 

remnants, furthermore, will in places be of essentially the same 

height on both sides of the streams, or, in other words, paired. 

The continuity of a surface along the valley and a tendency for it 

to have a uniform height above the present stream thus become 

primary criteria for a terrace system.

In contradistinction, a progressively down-cutting stream will 

leave along the valley sides isolated flats which are never paired, 

and are of irregular height because they are not remnants of a 

single continuous surface (Davis, 1902).

A river plain sufficiently continuous to be called a terrace tread 

after the down-cutting of the river usually remained the active 

flood plain for a long enough period of time to form the local base
CRITERIA FOR CORRELATING TERRACES 13

level to which side tributaries and ephemeral washes from the 

valley sides were graded. Mackin (1937) has described how slope 

wash from the valley sides splays over the flood plains of the 

main river and may build a continuous surface sloping toward the 

valley axis» In the Bighorn Basin near Cody, Wyo., where this 

process was described by Mackin, stream-bed gravel covered by 

a thin layer of fine-grained alluvium, -characteristically represents the original flood plain. The difference in texture between 

the gravel and the overlying slope wash was so distinctive that 

differentiation presented no problem. The elevation of the top of 

the gravel was used by Mackin as the height of the river terrace.

Alluvial terraces, generally of more recent origin than those 

described by Mackin, characteristically do not exhibit a sharp 

textural break between deposits of the main stream and slope 

wash. In fact, the materials are generally so nearly identical 

that the criteria usable in the Bighorn Basin cannot be applied. 

The heights of terrace remnants above the present stream are not 

everywhere uniform, but show a range of values, because the 

height measured includes an unknown thickness of slope wash.

It is necessary, then, to restrict measurement of terrace height 

to sections of the valley where a cross profile will provide an intersection of the extension of the wash-slope surfaces. This 

method has been used by Peltier (1949).

Topographic profiles representing three sections across the 

valley of the Powder River near Arvada, Wyo., are presented in 

figure 6. In cross section A, a gently sloping surface extends from 

the hills nearby toward the valley axis and is cut off by a scarp 

near the valley axis. In the field, this scarp is prominent and at 

many places vertical. The top of this scarp stands 60 feet above 

the river. The dashed line representing the projection of the 

wash-slope surface of the left side of the valley intersects the 

right bank well above the present stream level. This example 

demonstrates that the river level to which the wash slope was 

graded stood no less than 35 feet above the present stream at this 

point.

Cross section B of figure 6 is 1.8 miles downstream from cross 

section A. The top of the gently rounded scarp on the left bank 

stands 60 feet above the river and, from field indications, is a 

remnant of the same terrace shown in cross section A. Yet, projecting the wash-slope surface down to intersection with the right 

bank shows that the surface on the left bank could have been developed when the river stood at the level of a lower terrace about 

20 feet above the present stream.

In cross section C a scarp appear son both banks of the river. Each 

wash-slope surface is shown extended toward the valley axis by 

dotted lines which intersect 35 to 40 feet above the present stream.
14 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

3700

3600

3700*^*

MILE 10.6 '* """- xx"

V X- ^ 

3600 

B

3800'

_ =x_ - MILE 24-°

3700' ~~~'"

500 0 1500 Feet

1 I 

Figure 6. Cross sections of the valley of the Powder River near, Arvada, Wyo., showing how 

the extension of the profile of wash slopes to intersection fixes the minimum elevation of the 

master stream to which the wash slopes were graded. (River miles refer to U. S. Geological 

Survey maps, Powder River above Moorhead, Wyo., 1947.)

In two cross sections (A and C) it appears that the river to 

which this particular terrace surface was graded stood at least 

35 feet above the present stream. If many cross sections are 

considered, and if a preponderance of them shows an intersection 

of the extended surfaces well above the present river, one must 

believe that the terrace treads were developed during a time when 

the main stream flowed at a higher elevation than it does at present. If, furthermore, there is a consistency in the height of intersection of the extended surfaces above the present stream, it 

is reasonable to believe that those remnants belong to the same 

terrace and were developed at the same time.

In the present study, considerable reliance was placed on height 

of the terrace remnants as a basis for correlation, but terrace 

height was used in conjunction with other criteria, as will now be 

explained.
CRITERIA FOR CORRELATING TERRACES 15 

PHYSIOGRAPHIC RELATIONS TO OTHER LAND FORMS

Many western stream valleys typically show several alluvial 

terraces standing at different heights above the present stream. 

The highest terrace is oldest and the lower terraces are progressively younger, this being the only age relation possible which 

would result in the preservation of the terrace features.

When the stream stood at the level represented by a particular^ 

terrace, it constituted the local base level to which side tributaries were graded. The longer the period represented by a particular terrace, the better developed should be the drainage pattern graded to that surface. In a valley exhibiting two or three 

alluvial terraces, side tributaries would dissect the terraces 

while the governing" base level (the main stream) was being lowered. It would be expected that the lower and younger terraces 

would have a smaller area graded to them than the higher and 

older ones.

The relative amount of area graded to each of the three terraces studied was useful as corroborative evidence in correlation.

STRATIGRAPHIC RELATIONS OF TERRACE FILLS

Distinguishing alluvial fills of different ages and determination 

of stratigraphic sequence of the fills, as indicated in figure 2, 

follow ordinary stratigraphic principles. The fills may differ in 

color, lithology, texture, consolidation, in contained shells, bones, 

or other vertebrate remains. Actually, however, alluvial materials in any given western valley are amazingly similar. In the 

area described in the present report, uniformity of texture and 

color is a striking characteristic of the fine-grained alluvial deposits. Though local variations in both texture and color may be 

found, fine sand and silt of tan color are most common. Bedding 

is generally not apparent because of uniformity of texture and 

color. The fills are composed largely of detrital quartz grains 

and minor amounts of other minerals. The color varies much 

more in a given fill depending on temporal conditions of moisture 

than between fills of different ages. The color of dry alluvium is 

ordinarily a buff or tan, and wet alluvium is reddish to chocolate.

The degree of consolidation also depends primarily on moisture 

content. When perfectly dry, the alluvium is not only hard but 

tough, and a pick or chisel point penetrates only a fraction of an 

inch, even with a hard blow. When moderately moist, silty alluvium is soft. For this reason, consolidation was not a useful criterion for correlation in this study.
16 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

The banding of many alluvial fills is due either to slight variations in texture in the vertical direction or to varying amounts of 

humic stain. In the area studied, however, these prevalent bands 

are characterized by a lack of continuity in the horizontal direction and were seldom useful for correlation purposes.

Thus, the identification of the different stratigraphic units in 

alluvial deposits along western rivers is difficult, and even a good 

exposure, as for example where the terrace deposits are dissected, may or may not provide conclusive proof of whether the 

terrace was formed by cutting or filling.

Characteristics such as rounding of gravels, size and sorting of 

particles, and nature of bedding aid in determining whether alluvial fills were deposited by the major stream, by slope wash, by 

aeolian action, or by some other means. Because of the interfingering of slope wash with the flood-plain deposits, however, these 

characteristics do not provide a definite field criterion for differentiating alluvium of different ages.

Faunal and floral zones were rare in the alluvium studied, the 

most common fossils being vertebrate bones (Bison especially) and 

snail shells. Such zones, where found, are not useful for correlation purposes because the ranges of species represented have 

not been established. In fact, dating of faunas in alluvial deposits 

at the present time depends on dating of the alluvial terraces by 

whatever methods are available. In general, extinct species of 

vertebrates are not reported in deposits younger than Mankato 

(see Schultz, Lueninghoener, and Frankforter, 1951, table 1; 

Bryan, 1950, p. 122-123).

A horizon useful for correlation in the area studied was the 

paleosol previously mentioned. Where present in materials underlying a terrace, it invariably lay stratigraphically below the 

youngest alluvial fill comprising the high terrace, the Kaycee 

formation.

In summary, correlation in this study depended primarily on a 

combination of three factors: 1. Height of terrace remnants above 

the present stream. 2. Physiographic and topographic relation of 

the terraces to one another and to other land features. 3. The existence of a zone in which there is a concentration of carbonate 

and gypsum, which is interpreted as a paleosol.

No single criterion was sufficient to identify a particular alluvial 

formation or a given terrace or to permit correlation over a wide 

area, but these criteria consisting of topographic andstratigraphic 

relations used in combination allowed correlation with reasonable 

confidence.
RELATIONS OF TERRACES AND ALLUVIAL FILLS IN VARIOUS RIVER BASINS

The authors are well aware of the many possible sources of 

error in such correlation and of the shortcomings of the reconnaissance type of work discussed here. The correlations are for 

that reason considered tentative.

RELATIONS OF TERRACES AND ALLUVIAL FILLS IN VARIOUS RIVER

VALLEYS

POWDER RIVER BASIN

The Powder River basin will be discussed first because more 

detailed work was done in this basin than in any other. Also, 

many of the sites whose names are used for various parts of the 

alluvial sequence discussed herein are along the Powder River or 

its tributaries. The excellent topographic maps of the Powder 

River basin greatly facilitate geologic investigation of this river 

as compared with the other river basins for which relatively few 

maps are available.

There are three prominent terraces along the Powder River, 

which are pictured in figure 7. As will be shown in the following 

description, this is a 4-fill, 3-terrace alluvial valley in which the 

three oldest fills are successively overlapping and now make up 

the deposits of the high terrace.

Figure 7. Terraces along the Powder River, Wyo.
18 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING 

POWDER RIVER NEAR ARVADA, WYO.

A planetable cross section of the Powder River valley near the 

type locality of the Arvada formation is shown in figure 8. There 

are present remnants of three terraces, one standing about 55 feet 

above the stream, another at 17 feet, and the other 7 feet above 

the stream.

3700-

3600-

3500'-1 

U.S.G.S. 

datum

'Bedrock is 

Fort Union formation

Based on planetable survey

Figure 8. Cross section of valley of Powder River near Arvada, Wyo. , (at mile 10.6), 

showing the three alluvial terraces.

A stratigraphic section of the materials making up the high terrace near Arvada follows:

Stratigraphic section of high terrace of Powder River at bridge on Highway 16, 3 miles

north of Arvada, Wyo.

Kaycee formation:

Disconformity. 

Arvada formation:

Unconformity. 

Ft. Union formation: 

(Pal eocene)

Brown sandy silt, comparable to the alluvium of the 

lower terraces; shows profile development of the 

modern soil, consisting of humic darkening of the 

upper 6 to 8 inches, columnar structure in the upper 

24 inches, and caliche mottling in the slightly indurated B horizon.............. ..... .... 

Feet

..1 to 10

Red-brown, rounded, iron-stained, gravel and coarse 

sand, strongly weathered near top and less weathered grading downward. Many cobbles of siltstone 

or sandstone completely uncemented by weathering 

in place. Igneous rocks greatly altered. Rocks 

Strongly coated with crystalline calcium carbonate 

and gypsum on bottom sides. Tooth of horse 

(Eguus) found in gravels...............................................

(Marked by congeliturbation and frost wedges.) 

Sandstone, gray, noncalcareous, soft, uncemented, 

and stained yellow by weathering in upper 20 to 30 

inches, becoming gray and somewhat better cemented below.

.2 to 5
RELATIONS OF TERRACES AND ALLUVIAL FILLS IN VARIOUS RIVER BASINS 19

The red brown gravels, here called the Arvada formation, 

were deposited on bedrock, and then evidently subjected to a period of weathering. Some pebbles of igneous origin are so thoroughly decomposed that they readily break up into small pieces 

when struck with a hammer. The horse tooth suggests a late 

Pleistocene age for those gravels, and it is presumed that the 

weathering which developed the red coloration took place during 

an interglacial or interstadial period. This hypothesis is supported by the fact that the red gravels have been affected by frost 

action which produced frost wedges, contortions, and other features characteristically developed under a frost climate. These 

features are shown in figure 9. The red gravels appear to have

rown streaks along 

bedding contorted 

in the upper part

Base of exposure

Figure 9. Diagram of congeliturbation features in Arvada formation exposed in road cut 

through alluvial terrace near Arvada.

Kaycee 

formation

Arvada 

formation

Fort

Union

formation

1. Colluvium and alluvium, brown silty sand; loose, without caliche.

2. Red-brown and yellow cobbly gravel, weathered; and gypsum in irregular fibrous masses and coating underside of pebbles; grades into 

3. Red-brown and yellow cobbly coarse sand with less caliche and gypsum; fossil ice wedges in contorted lower boundary.

4. Gray-wnite sand streaked with brown stain along bedding; contorted in upper 

part; no caliche or gypsum; grades downward into similar uncontortedpoorly 

cemented sandstone of same color.

slumped into the frost-opened cracks in the sandstone. A distinctive red-brown zone occurs in the sandstone at its contact with 

the overlying gravel but does not edge or line the lower part of the 

frost cracks. This suggests that weathering to the red color preceded the formation of frost wedges.
20 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

Widespread erosion followed, as indicated by the fact that the 

Arvada formation is preserved as small, widely separated remnants. This erosion was generally followed by deposition of the 

Ucross formation, but as will be noted in figure 8, at this exposure (mile 10. 6) the Ucross formation which is the formation next 

younger than the Arvada, (see fig. 5), is absent. In most other 

areas the Arvada formation is absent, but the Ucross formation in 

places contains weathered, iron-stained fragments which are presumed to have been derived from the Arvada formation. The exact 

amount of erosion that occurred is unknown because later deposition buried most remnants of the Arvada formation and very few 

of these have been reexposed.

The marked concentration of calcium carbonate and gypsum in 

the gravelly Arvada formation at mile 10. 6 is interpreted as the 

result of soil-forming processes later than and different in character from those which produced the red color. The carbonate 

and gypsum are characteristic of the post-Ucross paleosol, a 

soil formed earlier than the deposition of the fine-grained Kaycee 

formation. The concentration of carbonate and gypsum extends 

through the entire thickness of the Arvada formation, including the 

frost-heaved zone. The cobbles in and above the frost cracks are 

coated on their lower sides with carbonate and gypsum in the form 

of coarsely crystalline crusts as much as three-quarters of an inch 

thick. There is no evidence of disturbance by frost after the accumulation of carbonate and gypsum. From this it is concluded 

that the carbonate and gypsum deposition occurred after the period 

of frost action. Samples were taken from the site at Arvada and 

analyzed in the laboratory for calcium carbonate. It was found 

that calcium carbonate was essentially absent in the Kaycee alluvium. The amount of it at the top of the Arvada formation was 6.4 

percent, and it decreased downward to none at the gravel and 

sandstone contact. Examination with the petrographic microscope 

and by X-ray techniques showed that gypsum was even more abundant than carbonate, and it also decreased in amount downward 

from the top of the Arvada.

At the end of or after the period of carbonate and gypsum accumulation just described, erosion removed a part of the soil in 

many places and in others destroyed the soil completely. Subsequent deposition of the Kaycee formation buried the ancient soil at 

Arvada and other places where it had not previously been destroyed by erosion. Since deposition of the Kaycee formation, sufficient time has elapsed for a shallow soil profile to develop on the 

smoothly sloping surface of the Kaycee terrace at Arvada. The 

two lower terraces show no distinct soil profile development.

An additional type of evidence regarding age of the high-terrace 

surface was found at the Arvada site. Abundant chips of flint of 

heterogeneous kinds were found scattered over the surface of the 

Kaycee terrace. Most showed definite evidence of having been
RELATIONS OF TERRACES AND ALLUVIAL FILLS IN VARIOUS RIVER BASINS 21

chipped by man, partly by a percussion technique. These worked 

flakes were conspicuously absent from the surface of the middle 

terrace and might pre-date construction of that terrace.

POWDER RIVER NEAR SUSSEX, WYO.

The cliffs along the left 

to Sussex, Wyo., provide 

for the Kaycee formation, 

is reproduced in figure 10. 

53 feet above the stream,

bank of the Powder River from Kaycee

an exposure which is the type locality

The valley cross section at this point

Remnants of the Kaycee terrace stand

and projection of the sloping terrace

4300-1 

U.S.G.S 

datum

/Paleosol Kaycee formation ^ 

-Ucross formation

Lightning formation t^S^r.

Bedrock is - 

Wasatch formation

Based on planetable survey

Figure 10. Cress section of valley of Powder River near Sussex, Wyo., showing the three

alluvial terraces.

surface shows that it was graded to the Powder River when the 

channel was at least 40 feet higher than at present. Relations of 

the deposits that make up the high terrace are shown in the stratigraphic section which follows, and by the photograph in figure 11.

The bulk of the Kaycee formation consists of alluvium laid down 

by the stream as valley fill. Colluvial deposits and slope wash 

that interfinger and were graded to the river deposits are contemporary and are, therefore, included in the Kaycee formation.

The whitened calcareous zone distinctly shown in figure 11 lying 

beneath the Kaycee alluvium and at the top of the Ucross formation 

is interpreted as a paleosol. The paleosolat Sussex differs somewhat in character from the one at Arvada in that no significant 

quantity of gypsum was found. Analysis of the whitened zone 

showed 15. 5 percent calcium carbonate in the upper foot and gradually decreasing concentrations downward in the section. In places
22 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

Figure 11. Exposure near top of Mgh terrace near Sussex, Wyo.

Stratigraphic section of high terrace on Powder River cliff one-quarter miles west

of Sussex, Wyo.

Kaycee formation:

Ucross formation:

Unconformity. 

Wasatch formation: 

(Eocene)

Feet

Fine, tan, silty alluvium consisting primarily of 

quartz grains. Surface soil profile characterized by 

well-developed columnar structure to a depth of 

about 3 feet; no distinct humus zone near the surface; slightly calcareous from a depth of about 10 

inches. Grades downward into Ucross formation...........3 to 6

Gray or white silt, with some gravel in the lower 

part, containing a high concentration of calcium 

carbonate. (Grades into next bed).........................................! to 2

Gravel and sand, calcium carbonate crusts on the 

bottom sides of cobbles and pebbles. Gravel and 

sand, mostly unweathered, except in upper parts, 

but there are a few iron-stained rocks. Grades 

downward into 2 to 3 feet of fine, gray sand containing clay lenses. Shows strongly developed redbrown layers due to iron concentration................................ 7 to 10

Gray to light-green shale.
RELATIONS OF TERRACES AND ALLUVIAL FILLS IN VARIOUS RIVER BASINS 23

where the Kaycee alluvium has been removed, the modern surface 

soil has developed on the paleosoland has in the upper 6 to 8 inches 

partially destroyed the strongly calcareous characteristics of the 

paleosol. Such a soil profile is polygenetic.

In the Sussex area, the two lower terraces stand at 23 feet and 

5 feet, and are composed of light-tan, fine-grained alluvium.

Two important sites on Clear Creek, a tributary of the Powder 

River, will now be discussed. Though there are some differences 

in detail, these two sites indicate a sequence similar to that suggested by the two areas on the Powder River previously described.

CLEAR CREEK SOUTH OF UCROSS, WYO.

A planetable cross section of Clear Creek valley, 1 mile south 

of Ucross, Wyo., (at the ranch of Ike Thomas) is shown in figure 

12. At this point the Kaycee terrace stands 17 feet above the

^Section in figure 13 at this point 

100' i

Ucross formation

Bedrock is 

Wasatch formation' N Lightning formation

Arbitrary 

datum

Based on planetable survey

Figure 12. Cross section of valley of Clear Creek at Thomas's ranch near Ucross, Wyo. 

The three alluvial terraces can be seen.

stream, and is composed of gravel and fine-grained alluvium. The 

upper 50 inches consists of tan, silty alluvium, the upper part of 

which has a columnar structure and a brown color typical of the 

modern soil on the Kaycee formation. Below this depth is a sequence of silt and unweathered gravel which are the type materials 

of the Ucross formation. The stratigraphic relation is interpreted as a calcareous paleosol developed on the upper part of
24 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

the Ucross formation. Overlying the paleosol is the Kaycee 

formation.

Samples taken in the Kaycee and Ucross formation making 

up the 17-foot terrace were studied in the laboratory, with 

results summarized in figure 13. It should be noted that the 

Kaycee alluvium itself is calcareous, but there is a zone of 

markedly increased calcium carbonate concentration at 60 to 75

40

60

120

0 30 

PERCENT CaCO, pH

Figure 13. Changes in cqptent of calcium carbonate and in pH with depth in the Kaycee terrace alluvium at Thomas's ranch near Ucross Wyo. The stratigraphic units are shown in the 

profile at the right of the figure.
RELATIONS OF TERRACES AND ALLUVIAL FILLS IN VARIOUS RIVER BASINS 25

inches. In this zone, which is interpreted as the paleosol layer, 

the carbonate is present as soft, irregular masses dispersed 

through the silt, and also as-hard nodules as much as 1 centimeter 

in diameter and containing as much as 45 percent carbonate. As 

was true at the sites on the Powder River, the paleosol. is an important stratigraphic marker and provides in this section the logical basis for distinguishing the Ucross and Kaycee formations.

The samples consisted of a material dug from a thin horizontal 

groove made with a knife. They were taken every few inches vertically so that the changing relations with depth from the terrace 

surface could be determined. Parts of each sample were examined by the Rolfe technique (Rolfe and Jeffries, 1952) to ascertain the relative amount of weathering with depth.

The results of the analysis indicated moderate hydration of micas 

(an indication of weathering) at the surface, gradually decreasing 

with depth. At a depth of 50 inches the hydration of micas abruptly 

increased to a degree even greater than existed at the surface. 

The indication of weathering provided by the Rolfe technique and 

the coincident stratigraphic evidence of the paleosol provide convincing confirmation of the existence of the paleosol.

Detailed mechanical analyses of the entire sequence of fine alluvium above the basal formation of the Ucross were made. The 

median diameter ranges from 0. 028 to 0. 050 millimeter, and 

averages 0. 037 millimeter. The Trask sorting coefficient ranges 

from 2. 1 to 3. 2 and averages 2. 5. There are no significant differences in size and sorting of the silt above, below, or in the 

paleosol horizon.

Mineral composition was determined by petrographic and X-ray 

techniques. Sixty to 90 percent of the fine alluvium is quartz, and 

the rest is dominantly calcite, though with minor amounts of biotite, chlorite, and clay minerals. The clay size fraction of 2 microns was separated from each sample and analyzed with the X-- 

ray spectrometer. Illite and montmorillonite are the most common clay minerals and are present in nearly equal quantities 

throughout the fine alluvial sequence. Kaolinite is present only as 

traces, except in the lower part of the paleosol horizon, where it 

appears in significant quantities.

The sequence at Ucross seems to be the same as that at Sussex 

and conforms to the generalized section in figure 5 except that the 

Arvada formation is missing. The many highly iron stained pebbles and cobbles in the Ucross formation suggest that stronglyweathered material (Arvada (?) formation) was mixed with relatively 

unweathered gravels during deposition of the Ucross formation. 

The Ucross here and at Sussex consists of basal gravels overlain 

by silt, and the paleosol is developed on the silt. In many places 

the Ucross consists of gravel without any silty strata.
26 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

The middle and low terraces are fairly prominent in the vicinity 

of Ucross and stand 7 feet and 3 feet alSove the stream, respectively. As shown in figure 12, the middle terrace bears a cut rather than a fill relationship to the high terrace.

This cut relationship is well demonstrated by an exposure about 

1 mile upstream from Clearmont, Wyo., pictured in figure 14. The 

terraces shown in the photograph are the Kaycee and Moorcroft surfaces. In figure 14, the gravels of the Ucross formation underlie 

silt of the Kaycee formation, but any soil developed on the gravel 

apparently had been eroded away before the deposition of the silt 

of the Kaycee.

 "* II « sa*-.

Figure 14. Section through Kaycee and Moorcroft terraces near Clearmont. Wyo.

CLEAR CREEK AT BUFFALO, WYO.

A planetable cross section of Clear Creek valley 1 mile east of 

Buffalo, Wyo. , is shown in figure 15. At this point remnants of the 

Kaycee, or high, terrace stand 19 to 23 feet above the stream. The 

stratigraphic section of the Kaycee terrace comprises a gravel 

layer, considered equivalent to the Ucross formation, overlain by
RELATIONS OF TERRACES AND ALLUVIAL FELLS IN VARIOUS RIVER BASINS 27

a fine grained alluvium consisting of a combination of stream deposits and slope wash, both of Kaycee age.

Figure 16 refers to this zone

r

Lightning formation

-- ........................................ Wasatch formation

Kaycee formation 

Arbitrary datum 

^^H 500 0 1000 Feet 

Paleosol ' ' ' ' ' ' ' '

Ucross formation

____ Based on planetable survey

15. Cross section of Clear Creek valley near Buffalo, Wyo. The three alluvial terraces are

well developed.

The Lower terraces are also present at Buffalo, standing 12 

feet and 4 feet, respectively, above the present stream. The 

middle terrace is composed locally of either fine grained alluvium 

or small gravel or both, whereas the low terrace is made up of 

sand and silt except for a short reach near the mountain where it 

is gravel. Here again the paleosol is a conspicuous feature, and 

its relationships are easily recognized.

Laboratory analyses of soil samples collected at three points 

chosen in aline perpendicular to the axis of the valley demonstrate 

the relation of the paleosol to the bedrock and alluvium. Figure 

16 includes a more detailed cross section at the same locality 

shown in generalized form in figure 15. The Kaycee terrace slopes 

toward Clear Creek and ends in an abrupt scarp which rises 23 

feet above the present stream. River valley silt is indistinguishable from slope wash which thins upslope. The slope is a smooth, 

unbroken slightly concave, curve which passes upslope from the 

silty slope wash to bedrock.

As the cross section in figure 16 indicates, the paleosol is developed on the original bedrock surface and passes underneath the 

silt of the Kaycee formation, but is present on the top of the wedge 

of gravel of the Ucross formation. In the upper part of the figure

303189 0-54-3
28 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

Figure 16. Changes in calcium carbonate content with depth at three positions on the Kaycee 

terrace varying in distance from the valley of Clear Creek near Buffalo, Wyo. The depth of 

maximum calcium carbonate accumulation coincides with the field evidence for the position of 

the paleosol.

are graphs showing the variations in amount of calcium carbonate 

with depth; the positions of the samples which the graph represent 

are shown by arrows pointing down to the cross section.

The samples of the paleosol taken farthest downslope showed a 

highly calcareous zone in the upper part of the Ucross formation. 

Midway uphill the Ucross formation has wedged out and silt of the 

Kaycee lies directly on bedrock: shale of the Wasatch formation. 

The strong caliche is in the upper part of the shale. Near the top 

of the hill a sandstone member of the Wasatch formation crops out 

at the ground surface, but in places it is covered by a few inches 

of slope wash. The carbonate has accumulated in the sandstone 

here and attains its greatest concentration 20 inches below the 

ground surface.

These analyses lead to the conclusion that the paleosol was developed on an older topography postdating the deposition of the 

Ucross formation but earlier than Kaycee age. The carbonate accumulation is strongest where the old surface was buried under 

Kaycee silt, thereby protecting the paleosol from further pedogenic
RELATIONS OF TERRACES AND ALLUVIAL FILLS IN VARIOUS RIVER BASINS 29

action. Uphill, where the old surface was covered by little or no 

silt of the Kaycee, the paleosol was exposed to processes different from those which formed it, and as a result, the carbonate 

was leached out in part and the present soil is polygenetic. This 

implies that the climate which followed the development of the 

paleosol was more humid than that under which the carbonate was 

originally deposited.

Terrace heights in the Powder River basin are summarized in 

table 2. Except for sections designated as made in the field by 

plane table mapping or visual estimates, these data represent 

heights determined by cross sections drawn on the Geological 

Survey topographic maps of the Powder River, scale 1:24, 000, 

contour intervals, 10 feet and 5 feet. The terrace heights taken 

from maps are corrected for slope wash by the intersection method discussed in relation to figure 6. Other values are uncorrected.

There is obviously considerable variation in height of remnants 

of a given terrace, but the three terraces are so consistently 

present and so different in average height that height as a basis of 

correlation is useful when combined with other criteria discussed.

Table 2. Heights of terraces, in feet, on Powdet River and tributaries

[Metnods of determining height: A, measured by telescopic alidade; E, estimated; M, from

topographic maps]

Middle Fork Powder at mile 210

Red Fork at mile 206. 5

Middle Fork Powder at mile 203

North Fork Powder, north of Kaycee

at bridge on Hwy. 87................

Sftuth Fork Powder, south of Kaycee

at bridge on Hwy. 87...............

Tributary to South Fork Powder,

south of Kaycee on Hwy. 87.......

Tributary to Salt Creek, 3 miles

east Edgerton, Wyo. , on Rt. 387

Powder River %mile west of Sussex,

Wyo.

Dry Fork Powder River

Middle Fork Crazy Woman Creek,

north of Kaycee on Hwy. 87.......

Poison Creek north of Kaycee on

Hwy. 87 (tributary of Crazy

Waman Creek)

Powder River at mile 19. 4

Powder River at mile 12. 4

Powder River at Arvada

Piney Creek below Kearney

Piney Creek at Ucross (mouth)

Clear Creek at soil site east of

Buffalo

Clear Creek at Thomas ranch

Clear Creek near Clearmont

Clear Creek at Leiter

Method of 

determination

M

M

M

E

E

E

E

M

E

E

E

M

M

A

E

E

A

A

A

A

Kaycee 

(high) 

terrace

9

25

20

22

35

30

55

53

25

20

23 X 32

33

65

12

13

20

17

14

25

Moorcroft 

(middle)

terrace

5

7

10

10

10

10

30

23

12

8

12

12

12

17

5

4

12

7

6

7

Lightning 

(low) 

terrace

4

5

5

3

7

12

5

?

3

7

4

7

2

5

3

3

3

1 Minimum.
30 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING 

BELLE FOURCHE RIVER BASIN

The alluvial terraces of the Belle Fourche River were studied 

from Carlile, Wyo., upstream about 85 miles to the headwater 

area-near the Pumpkin Buttes, which lie about 45 miles southeast 

of Gillette, Wyo.

Although there are three prominent alluvial terraces along the 

Belle Fourche River (see fig. 17), they are appreciably lower than

60-,

Kaycee formation 

i Paleosol 

iia Arvada formation

20

20

140-

Arbitrary datum

300 Feet

J___I

A. NEAR BRIDGE ON U. S. HIGHWAY 14, 7 MILES 

DOWNSTREAM FROM MOORCROFT, WYO.

B. MOORCROFT BRIDGE ON U. S. HIGHWAY 16 

(Based on planetable survey)

C. CARLILE, WYO. (Based on planetable survey)

D. STATE ROUTE 59, SOUTH OF GILLETTE, WYO. 

(Based on planetable survey)

Figure 17. Cross sections of the valley of the Belle Fourche River.
RELATIONS OF TERRACES AND ALLUVIAL FILLS IN VARIOUS RIVER BASINS 31

those on the Powder River. The reason for this difference is not 

well understood but may in part stem from the fact that the Belle 

Fourche is a small stream which rises on the plains east of the 

mountains, whereas the Powder is a major river with its sources 

in the strongly glaciated high mountains.

Figure 17, cross section A, shows the terrace relationships observed near the bridge where Highway 14 crosses the Belle 

Fourche River about 7 miles downstream from Moorcroft, Wyo. 

The exposure is a steep bank 40 feet high, carved by lateral 

swinging of the stream against a slightly rounded hill adjacent to 

the valley. The present surface of the hill slopes smoothly downward 

and is apparently graded to the level of the 20 foot terrace. Details of the stratigraphy at this exposure are given in the following 

stratigraphic section:

Stratigraphic section of exposure of the high terrace along the Belle Fourche River in 

40- foot bijnk neat bridge on Highway 14, 7 miles downstream from Moorcroft, Wyo,

Feat 

Kaycee formation: Brown, sandy silt, slightly stained near the surface (grading into next bed).............................................................Vi

Light-brown silt, columnar structure of modern 

soil profile extends approximately to the bottom 

of this zone. A very small amount of caliche is 

present as small, soft nodules (grades downward 

into next bed)...................................................................................^1/^

Fine, horizontally bedded, olive-colored sand

with no caliche apparent................................................................^1/!

Disconformity.

Arvada formation: Reddish-brown, iron-stained sand in which the 

bedding is markedly contorted. Considerable 

quantities of caliche and gypsum are present as 

large, soft nodules and irregular masses. The 

caliche and gypsum at this depth in the section 

are interpreted as a remnant of an ancient soil 

profile superimposed on the iron-stained Arvada

Unconformity.

Pierre shale: Black clay, with many large white masses of cal-

(Cretaceous) iche and gypsum, grading downward into unaltered bedrock which is brown and black shale

alternating with thin brown sandstone; bedrock

dips about 15° S.

This high terrace, 20 feetabove the present stream, is well defined along the river valley. Because it shows a similar stratigraphic sequence and stands as the third terrace above the stream 

level, it is considered equivalent to the Kaycee terrace in the 

Powder River basin. The Kaycee formation in this section is presumed to have been derived largely by slope wash, and this colluvium overlies a layer of reddish brown sand, here correlated 

with the Arvada formation which in turn rests on weathered bed-
32 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

rock. It would appear that the Ucross formation, which is represented in the Kaycee terrace along the Powder River, has no 

counterpart in the high terrace deposits of the Belle Fourche 

River basin. The distinctive paleosol known to occur at the top 

of the Ucross formation in the Powder River basin, however, is 

apparently present in the Belle Fourche high terrace deposits 

where it is superimposed on the red sand of the Arvada formation.

Near the bridge on Highway 16, 1 mile west of Moorcroft, 

three extensive alluvial terraces stand 18, 12 and 3 feet, respectively, above the level of the river (fig, 14, section B). At 

this locality, however, the stratigraphic sequence in the high 

terrace is different from that described above. Only Kaycee alluvium is exposed in the high terrace, and no exposure showing 

bedrock could be found. The surface soil on the Kaycee alluvium 

at this site had the characteristics of the modern soil described 

for other localities, and neither field examination nor laboratory 

study gave evidence of the existence of a paleosol.

The same stratigraphic sequence was noted at Carlile and near 

Gillette, Wyo., (cross sections C and D), and also at the exposures studied in the headwaters area. At all these localities 

there was no evidence for either the presence of the Arvada and 

Ucross formations or for the .existence of a paleosol. Rather, all 

the terraces were composed of uniform, massive textured silt or 

sandy silt, with no marked textural or compositional variations.

No artifacts were found anywhere in the Belle Fourche River 

basin. Several bones of Dison fcfsonwere collected from the Kaycee 

formation of the high terrace at Carlile and at the site below 

Moorcroft.

Absence of one or more parts of the sequence noted for the 

Powder River basin in several of the exposures studied in the 

Belle Fourche River basin does not necessarily preclude the possibility that these stages occurred. The fact that unequal numbers of stages are shown in various exposures merely emphasizes the role of erosion in eliminating much evidence which 

would otherwise be available. It also shows the dependence on 

raw or unvegetated banks for adequate exposures. The Belle 

Fourche River has very few raw banks, but in the Powder River 

drainage basin they are exceedingly common.

Heights of terrace remnants along the Belle Fourche River are 

summarized in table 3.
RELATIONS OF TERRACES AND ALLUVIAL FILLS IN VARIOUS RIVER BASINS 33

Table 3. Heights of terraces, in ieet, along the Delle Fourche River, Wyo. 

[Methods of determining height: A, measured by telescopic alidade; E, estimated]

About 10 miles northeast of Pine

Near bridge on Hwy. 59 , about 

30 miles south of Gillette, Wyo. 

Near Bridge on Hwy. 16 , 1 mile

Near bridge on Hwy. 14, 7 miles 

downstream from Moor croft, 

Wyo....................................

Method of 

determination

E

A 

A

E

A

Kaycee 

(high) 

terrace

11

34 

18

20

17

Moorcroft 

(middle) 

terrace

6

19 

12

10

12

Lightning 

(low) 

terrace

9 

3

5

3

BIGHORN RIVER BASIN

The alluvial deposits of the Bighorn River and its tributaries 

were studied at several localities from the headwaters downstream as far as Hardin, Mont. Alluvial terraces are exceptionally well developed. The terrace heights and stratigraphic relations of the fills are very similar to those already described 

for other drainage basins. There are, however, differences in 

detail, especially in the lithology of the various fills and the character of buried soil layers in the fills. Also, dunes associated 

with the fills are much more common in this basin than in the 

ones previously described.

SHOSIIONE RIVER BASIN

Terraces in the western part of the Bighorn Basin, and especially those along the Shoshone River, have been described by 

Mackin (1937). The fine grained slope wash overlying gravels of 

the terrace designated by Mackin as Cody is tentatively correlated 

with the Kaycee formation in other river basins. This assignment 

is based primarily on the stratigraphic sequence of basal gravels, 

a buried soil layer, and overlying fine grained alluvium.

Short gullies tributary to the Shoshone River have in several 

places cut headward into the Cody terrace. In a typical gully 10 

miles northeast of Cody, Wyo., and crossed by Highway 14, a 

30 foot cliff exposes the sequence described in the following 

stratigraphic section:
34 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

Stratigraphic section in unnamed gully, tributary to the Shoshone River, 10 miles northeast 

of Cody, Wyo. on Highway 14.

Feet

Kaycee formation: Well-sorted, slightly calcareous, fine sand and silt 

which is light tan in color. Bones of Bison bison 

occur at the base of this deposit. Modern soil, 

developed on upper 2 feet, consists of a slight 

humus darkening at the surface, and caliche mottling in the B horizon............................................................12 to 15

Disconformity.

Ucross formation: Gray zone, composed of about 32 percent calcium 

carbonate and the rest fine quartz sand with 

some organic matter containing many shells............'/2 to 1%

Highly calcareous gray, fine sand and silt (grading downward into next bed)............................................. ...}/2 to 1%

Well-rounded, unaltered stream gravels containing no caliche......................................................................... 8 to 10

Unconformity.

Wasatch formation: Black shale (bedrock).

The areal extent of the bed containing the high concentration of 

calcium carbonate and the snail shells is not great. It pinches out 

a few hundred feet upstream and downstream from the section just 

described, but is exposed along another tributary several hundred 

yards away. The snails were identified in the laboratory of W. J. 

Clench, Museum of Comparative Zoology, Harvard University, as 

species of the genera Oxyloma andSuccina. These are land snails 

which typically live in wet environments, such as are afforded by 

river flood plains. Nearly all members of the assemblage are believed to have been killed in place, but there are a few species 

which must have lived elsewhere and were presumably transported 

by flood water. This leads to the surmise that the snail and carbonate zone probably represents an ephemeral flood-plain pond or 

swamp environment. During floods, a pond or swampy area developed and the snails thrived, but between floods the pond dried 

up completely, killing the snails and causing concentration and 

deposition of calcium carbonate.

About 100 yards downstream from the stratigraphic section just 

described, the snail zone is not present, and the silty Kaycee formation lies in contact with uncalichified gravels. A Bison bison skeleton, complete except for the skull, was found just above the gravel and silt contact. Material composed almost entirely of grass 

stems lay between the rib bones, and was tentatively interpreted 

as stomach remains, pending further study. Laboratory examination by William Spackman, Pennsylvania State University, confirms this belief, though identification of the plants has not been 

attempted. The plant remains are essentially unaltered chemically, and this fact, together with complete absence of pollen and 

spores and the association of the plant remains with the skeleton, 

seems to eliminate the possibility that the plant remains represent 

a peat deposit.
RELATIONS OF TERRACES AND ALLUVIAL FILLS IN VARIOUS RIVER BASINS 35 

FIVEMILE AND MUDDY CREEKS

Fivemile Creek, a minor tributary which enters the Bighorn 

River near River ton, has been studied in detail by R. F. Hadley 

(19502 ). This valley and that of Muddy Creek nearby differ from 

others described in the present study in that the earliest finegrained alluvial fill does not overlap ifhe channel previously cut 

into bedrock as does the Kaycee formation in the Powder River 

basin, for example. Hadley recognizes four surfaces which he 

designated as Slt S2 , S3 , S4 , with average heights above the present stream level of 25 to 30, 15 to 20, 8 to 10, and 2 to 4 feet, respectively (see fig. 18, section A).

The 25 to 30-foot surface (S^ of Hadley) is cut on sandstones 

and shales of Cretaceous and Tertiary age and covered with 2 to 

15 feet of gravel and sand which are considerably calichified in the 

upper parts. This surface is the lowest of a series of gently 

sloping gravel capped terraces, or pediments, which occur in the 

Bighorn Basin. It apparently corresponds to the Lenore terrace, 

named and described by Blackwelder (1914), who believes it to 

have formed during the Bull Lake Pinedale interstadial (late 

Wisconsin). Later, the Lenore surface was dissected and the valley filled with a series of fine grained alluvial deposits.

The 15 to 20 foot surface (S8 ) forms an extensive flat in places 

more than a quarter mile wide. It is composed predominantly of 

light tan, slightly calcareous, fine sand and silt. There are scattered lenses of coarse sand and small gravel which attest to the 

water laid origin of this deposit. The contact of the base of this 

fill and the underlying bedrock is exposed in many places. Hadley 

(personal communication) states that basal gravels can be found in 

some places. The authors found no soil layers or other evidences 

of weathering at the contact or within the alluvium. Soil development at the surface of the fill is of skeletal character, consisting 

of a darkened zone in the top 2 inches and columnar structure extending to depths of 12 to 15 inches. Sand dunes, 6 to 8 feet high 

and now stabilized by salt sage (Ata'p/exsp. ), are common on this 

terrace, especially in the lower course of Fivemile Creek (see fig. 

18, section B). Also there are channels as much as 13 feet deep 

which were cut into the alluvium of this terrace and later were filled 

with windblown sand. Many bones of Bison Wsonwere obtained from 

this earliest alluvium. About a quarter mile below the knickpoint 

known as Little Niagara, a hearth associated with bones was found 

near the base of this S2 fill, but there were no artifacts.

A channel about as deep as the present arroyo and averaging 

about 200 feet wide was cut in the earlier alluvium. Subsequent 

aggradation to a depth of 8 to 10 feet formed a surface (S2 of

zRecent sedimentation and erosional history of Fivemile Creek, Fremont County, Wyo.: 

Master's thesis, Univ. Minnesota.
36 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

 a

£

0) B 

a
RELATIONS OF TERRACES AND ALLUVIAL FILLS IN VARIOUS RIVER BASINS 37

Hadley) inset below the top of the channel. This surface is underlain by slightly calcareous tan alluvium consisting of fine- to 

medium grained sand with many gravel lenses, and is not dissimilar to the earlier fill except for being slightly coarser. There 

is no apparent development of a surface soil profile. Sand dunes 

are present on this terrace in a few places, but in general they 

are smaller and less extensive than those on the higher surface. 

Many bones of Bison bison were collected from this second fill. No 

hearths or artifacts were found. The presence of cockleburs and 

sandburs, showing sharp, well preserved spines, buried more 

than 2 feet below the surface, suggests that the second fill is of 

rather recent age.

After deposition of the second fill, another period of erosion occurred in the valley of Fivemile Creek, again cutting a channel essentially to the level of the present stream bed. Later there was 

aggradation of 2 to 4 feet of coarse, sandy alluvium forming the 

surface Hadley designated as S4 . This level is the present flood 

plain, and it is difficult to say how recent a period of filling this 

surface represents. In some reaches where irrigation return flow 

is large, as for example just below Little Niagara, the stream has 

recently cut down, leaving equivalents of the 2- to 4-foot level 

standing as much as 8 feet above the stream. No soil profile is 

developed on this surface and no bones or artifacts were found.

Hadley found by mechanical analysis that the alluvium underlying the 2- to 4-foot level is coarser than that of the 8- to 10-foot 

terrace which, in turn, is coarser than the deposits of the 15- to 

20-foot level. The bed of the present stream channel is coarser 

than any of the others. In general, the heights of the various terraces above the present stream level increase slightly upstream 

from the mouth. Gradients of the various terrace surfaces are 

nearly the same.

Muddy Creek is tributary to the Bighorn River andflows parallel 

to Fivemile Creek a few miles to the north. The heights and general terrace relationships described for Fivemile Creek also apply 

to Muddy Creek (see fig. 18, section B). The stabilized sand dunes 

as high as 10 feet, which occur on the 15- to 20-foot surface in the 

upper Muddy Creek valley, are considerably more extensive than 

those on Fivemile Creek. Many artifacts, including scrapers and 

grinding stones of modern character, were found associated with 

hearths on or ne.ar the surface of the dunes. They were given to 

William Mulloy, University of Wyoming, director of the Smithsonian archeological party studying the Boysen reservoir area.

Correlation of terraces along Fivemile and Muddy Creeks with 

terraces in other drainage basins is complicated because the 

buried soil horizon, which characteristically occurs in the Kaycee 

terrace, is not present. Also, erosion of the lower reach of channel
38 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

has been greatly accelerated by diversion of return flow from irrigation canals into the channel of Fivemile Creek. This erosion, 

which began in 1926, has considerably altered the downstream 

reaches and formed a flood plain deposit associated with this new 

regimen.

Tentatively, however, the 15- 20-fopt level is correlated with 

the Kaycee terrace, the 8- 10-foot level with the Moorcroft terrace, and the 2- 4-foot level, or flood plain, with the Lightning 

terrace. This is believed to make a perfectly consistent relationship. The Lightning terrace is the flood plain along many minor 

tributaries to the main streams in other drainage basins. If the finegrained alluvium of the 15- 20-foot surface had overlapped the 

gravels on the 25- 30-foot level, the analogy to the Kaycee terrace 

elsewhere would be good; that is, there would be the sequence of 

gravel and fine alluvium making up the high terrace, and silt and 

sand making up the two lower terraces. Because the alluvium of 

the 15- 20-foot terrace actually is inset in relation to the 25- 30- 

foot level and rests upon eroded bedrock, one would not expect to 

find a buried soil at its base. Finally, the Kaycee formation and 

the fill comprising the 15- to 20-foot terrace are both the earliest 

fine grained alluvial deposits, and, as such, both represent a 

marked change in the character of sedimentation. It is not to be 

expected that the Kaycee fill should, in all cases, overflow the 

channel in which it was deposited and provide an overlapping relation as shown by the typical example in figure 5. Indeed, it is 

remarkable that more exceptions to this typical condition were 

not discovered.

Dating the dunes found on the 15- 20-foot (Kaycee) surface along 

Fivemile and Muddy Creeks presents certain difficulties. From 

the lack of definition of dune form, the degree of stabilization by 

vegetation, and the amount of brown-surface staining, it might be 

presumed that the dunes are nearly as old as the terrace on which 

they lie. It is believed by the authors, however, that the stabilized 

dunes either postdate, or are contemporaneous with, the formation 

of the 8- 10-foot level. Figure 18, section B,shows a typical relationship which seems to support this view. The upper 1 to 4 feet 

of the deposits making up the 8- 10-foot level are composed of 

windblown sand which clearly laps onto the 15- 20-foot surface 

where the dunes are.

Evidently, some wind action has continued to the present time, 

as is indicated by the fact that remains of modern habitation, such 

as old automobile springs and pans, are commonly found buried 

by 1 to 3 feet of windblown sand. Also, the fact that the artifacts 

and hearths left by Indians camping on the dunes are now found 

both at and below the surface indicates continuing aeolian activity.
RELATIONS OF TERRACES AND ALLUVIAL FILLS IN VARIOUS RIVER BASINS 39 

LITTLE BIGHORN RIVER BASIN

The Little Bighorn River was studied in the reach from Hardin, 

Mont., where it enters the Bighorn River, upstream to Pass 

Creek near Wyola, Mont. On Pass Creek, 3 miles south of Wyola, 

Mont., are two prominent terraces standing 11 and 4 feet above 

the strccim (see fig. 18, section C). The higher surface, which is 

very extensive, is underlain by 4 feet of fine, gray sand. This 

sand is separated by a disconformity from an organic zone 3 

inches thick, below which are nearly 4 feet of salmon pink silt. 

The upper part of the silt is strongly calichified and contains hard 

nodules as much as one half inch in diameter which are composed 

of about 65 percent calcium carbonate, the rest being mostly sand 

grains. Many shells of land snails OreoheHx sabradis (identification 

by W. J. Clench) were found in the pink zone. A few partly disintegrated bones, probablyd'sonwere also collected from this 

zone. On the basis of physiographic relations and the presence of 

the highly calichified layer, the 11-foot level is tentatively correlated with the Kaycee terrace. The 4 foot level, then, probably 

corresponds to the Moorcroft terrace, and the flood plain of Pass 

Creek with the Lightning terrace.

A-t the junction of the Little Bighorn with the Bighorn River, the 

larger river has impinged on a hill, the summit of which is a 

gravel covered terrace or pediment remnant. The cliff exposed 

by the river's lateral cutting provides a cross section of the materials deposited by the Little Bighorn River and shows their relation to bedrock. The cross section (D) presented in figure 18 is 

a composite diagram based on planetable mapping and soil 

studies. In the lower reaches of the Little Bighorn valley the 

highest and most prominent alluvial terrace stands about 20 feet 

above the stream level. It is tentatively correlated with the Kaycee 

terrace on the basis of its physiographic relationship to the hills 

nearby, and by the fact that a paleosol typical of the sequence in 

other areas occurs in the deposits of this terrace. The only other 

terrace level found near the mouth of the Little Bighorn River is 

one which stands 5 to 7 feet above the stream and forms a broad 

flat. The authors believe that this level corresponds to the Moorcroft surface in other drainage basins. The present flood plain of 

the stream then would be the equivalent of the Lightning terrace.

POPO AGIE RIVER BASIN

Along the Middle Fork Popo Agie River near the eastern limits 

of the city of Lander, Wyo., cross section E of figure 18 was 

studied. There are three alluvial surfaces standing 35 to 40, 20, 

and 3 feet above the stream, respectively. Because of the sequence including gravel, sand and silt, paleosol, and fine alluvium, the high level is correlated with the Kaycee terrace. The
40 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

20 foot level is correlated with the Moorcroft terrace, and the 

3 foot level with the Lightning terrace. The paleosol is well developed, showing concentrations of calcium carbonate as high as 

32 percent. Where the paleosolis exposed at the surface, calcium 

carbonate has been completely leached from the upper 15 to 18 

inches, thus forming a polygenetic soil.

Terraces observed at various localities in the Bighorn Basin 

are typified by elevations shown for specific localities in table 4.

Table 4. Heights of terraces, in feet, in Bighorn River basin 

[Methods of determining height: A, measured by telescopic alidade; E, estimated]

Middle Fork Popo Agie River at

Fivemile Creek 

Sediment station near Pavillion... 

Sediment station near Riverton....

Muddy Creek 

Near Lower Muddy gaging station.

Gooseberry Creek 20 miles

Greybull River, west of Basin, 

Wyo. ...................................

Dry Creek near Emblem, Wyo. ....

Unnamed tributary to Shoshone

Sage Creek east of Cody, Wyo. ... 

Pass Creek near Wyola, Mont. ..... 

Little Bighorn River near LodgeLittle Bighorn River at mouth.......

Method of 

determination

E

E

E

E 

E 

E

E

E 

E

E

E

E

E

E

E

E

£

E

E 

E

A

A

Kaycee 

(high) 

terrace

35

18

15

25 

20 

10

12

12 

15

20

9

12

15

15

10

40 

20

30

18 

11

22

20

Moorcroft 

(middle) 

terrace

20

10

7

10

7

4

7 

6

8

4

4

5

7

4

10

7 

4

7

7

Lightning 

(low) 

terrace

3

3

ft

(J)

0

C1)

(1)

O 

(*)

0

«

(')

(1)

(1)

«

4 

3

4 

«

(t> (*)

Flood plain.

CHEYENNE RIVER BASIN

The terraces of the Cheyenne River basin were studied in the 

triangular area between Newcastle, Wyo., the village of Lance 

Creek, Wyo., and Edgemont, S. Dak. From inspection of the cross 

sections in figure 19, it is apparent that in this drainage basin, as 

in the Powder and Belle Fourche River basins, there are three 

prominent alluvial terraces. However, at only a few sites could 

material be found that is possibly equivalent in age to the earliest
RELATIONS OF TERRACES AND ALLUVIAL FILLS IN VARIOUS RIVER BASINS 41

Tree stump

Bedrock

A. TRAPHAGEN RANCH

B. MOORE RANCH

Bedrock 

Arbitrary datum

C. CLARETON

EXPLANATION

Lightning formation Modern soil Kaycee formation Ucross formation

Figure 19. Cross sections of valleys in the Cheyenne River basin.

fill (Arvada formation) in the Powder River basin. Gravel is much 

less common in the alluvial fills of this area, the usual lithology 

being light-tan, fine sand or sandy silt.

Thehighest terrace, which is considered equivalent to the Kaycee 

terrace, is slightly lower than its counterpart along the Powder
42 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

River. In many exposures the contact of the Kaycee alluvium with 

unweathered bedrock, as shown in figure 19, indicates deep erosion 

before deposition of the Kaycee formation. The two lower terraces, 

especially the Lightning, are well developed along the streams in 

this basin. They stand about the same elevation above the river 

as the equivalent terraces along the Powder and Belle Fourche 

Rivers. The Kaycee and Lightning terraces along Lance Creek 

can be seen in figure 20.

Figure 20. Valley of Lance Creek near Lance Creek, Wyo.

The Lightning formation is named for Lightning Creek, a tributary 

of Lance Creek. It consists of an inset alluvial fill, the top of which 

is covered with cottonwood trees (Populus deltoides Marsh). The surface is only slightly higher than a narrow berm that is immediately 

adjacent to the stream bed and that is the present flood plain. The 

surface of the Lightning formation is called the Lightning terrace. 

Lithologic description of the formation at its type locality follows:

Stratigraphic section of the Lightning formation at its type locality on reach of Lance 

Creek at Lance Creek village, Wyo.

Lightning formation:

Unconformity.

Pierre shale (Cretaceous).

Tan or light-brown, medium to coarse sand consisting primarily of subrounded quartz grains; thin 

lenses of fine gravel occur in places; no evidence of soil profile development; no bones or 

artifacts found in place........................................

Feet

4 to 10
RELATIONS OF TERRACES AND ALLUVIAL FILLS IN VARIOUS RIVER BASINS 43

The estimates and surveyed measurements of terrace heights 

for the Cheyenne River basin appear in table 5. Corrections for 

slope wash have not been applied to data in this table. Even without correction, each of the three terraces is of nearly uniform 

height in the reach studied. In addition, characteristics of the surface soil and physiographic relations provide corroborative evidence for correlation.

Table 5. Heights of terraces, in feet, in Cheyenne River basin 

[Methods of determining height: A, measured by telescopic alidade; E, estimated]

Cheyenne River

Lance Creek 

Tick Bend.....................

Traphagen's ranch ..........

Beaver Creek, 24 miles

Black Thunder Creek..........

Hat Creek, 2 miles above.... 

mouth; sec. 25, T. 9 S., 

R. 4 E. , Sooth Dakota..... 

Hat Creek, south of 

Montrose , Nebr . , sec. 22 , 

T. 33 N. , R. 54 W. .......

Method of 

determination

E

E

E

E

A

E

E

£

A

A

A

E

E

E

E 

E

Kaycee 

(high) 

terrace

Tn

25

28

45

97

25 

40

48

50

40

25

25

30

28

Moorcroft 

(middle) 

terrace

90

12

14

11

12 

10

13

13

12

19

15

17 

15

Lightning 

(low) 

terrace

5

5

6

6

2

5

5 

5

4

5

6

4

7

8

8

7

At most sites examined in the Cheyenne River basin the high 

terrace is composed of the Kaycee fill, and the older fills are 

missing. At one place, however, on Snyder Creek, which is tributary to the Cheyenne River, there is evidence for the existence of 

a paleosol similar to that describedfor severalsites in the Powder 

and Belle Fourche River basins. Here, the calcium carbonate is 

mostly in the form of hard, rounded nodules deposited in a yellow 

sand. Whether the paleosol is developed on Ucross or on Arvada 

deposits is undetermined because of scarcity of exposures.

Bones and artifacts were found in the Kaycee formation at many 

places in the Cheyenne River basin. Insofar as identification of 

individual bones was possible, they are in all cases thought to be 

those of the living species of bison. A large number of flint flakes 

were found in one small area on the top of the Kaycee terrace at

303189 O - 54 - 4
44 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

Moore's ranch (about Smiles south of Lance Creek, Wyo.), and 

are of some significance. Many different kinds of flint, some 

clearly worked by man, are represented. No pottery was present. 

One flint flake was found buried in the surface soil of the Kaycee 

terrace and was considered in place. Chipped flakes of flint were 

also found on the scarp of the Kaycee terrace, but none on the 

lower Moorcroft terrace. This great difference in the number of 

artifacts on the two terraces suggests that they were worked by 

man on the upper terrace before the lower terrace was formed. 

This is the same relation noted at the artifact site on the Powder 

River at Arvada. None of the chipped flint artifacts are sufficiently 

diagnostic to be used for fixing dates, but it cart be inferred that 

they belonged to a prepottery culture.

NORTH PLATTE RIVER BASIN

Alluvial terraces are prominent features along the North Platte 

River and its tributaries. In the upper part of the valley in southcentral and southeastern Wyoming, the several alluvial terraces are 

high enough to be easily recognized, but downstream in western and 

central Nebraska, terrace heights decrease and are less easily 

recognized. Moreover, in the wide valley the terraces are so 

widely separated that recognition is difficult.

Work in the North Platte River basin was of reconnaissance 

nature and was confined principally to the polygonal area bounded 

by Douglas, Sweetwater Crossing, and Laramie, all in Wyoming, 

and Scottsbluff, Nebr. The area covered is considerably upstream 

from that discussed by Lueninghoener (1947), and no correlation 

of the terraces of the two areas is attempted here.

From the cross sections in figure 21, it is apparent that alluvial 

terrace relationships in the upper North Platte River basin are 

similar in many respects to those described in this report for other 

river basins. At many places in the upper North Platte basin there 

are only two alluvial terraces. The information now available is, 

however, too limited to permit more than a tentative correlation 

with other areas studied. Some possible evidence for correlation 

of North Platte terraces with those of other rivers is found at 

Signal Butte near Scottsbluff, Nebr., figure 21, section M. Three 

well-developed terraces are present on Kiowa Creek, but on 

Spring Creek, a tributary of Kiowa Creek, in the vicinity of 

the Scottsbluff bison quarry (Barbour and Schultz, 1932; Schultz 

and Eiseley, 1935), there are only two terraces. In the unweathered gravels at the base of the 15-foot terrace on Spring 

Creek, bones of an extinct species of bison were found by Barbour 

and Schultz. At the top of the silt overlying the bison zone, there 

is a 2- to 3-foot heavily calichified zone which possibly represents 

a buried soil. The top 8 feet of the terrace, consisting of fine, 

buff, sandy silt, with a dark humic zone at the top, contains mollusks which are not extinct but are found in upper Pleistocene
RELATIONS OF TERRACES AND ALLUVIAL FILLS IN VARIOUS RI\ER BASINS 45
46 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

deposits. Tentatively, the calichified zone is considered the equivalentof the paleosol found in the Powder River basin, and the overlying material of the higher terrace is correlated with the Kaycee 

formation. If this is correct, the bison-bearing gravel might be 

correlated with either the Ucross or Arvada formation. Because 

these gravels are unweathered and show no sign of having been 

affected by a warm, moist period, it is supposed more likely that 

they are Ucross equivalents.

REGIONAL CORRELATION AND ITS PROBLEMS

Terraces observed in the valleys of several Wyoming rivers and 

their tributaries are strikingly similar in a number of aspects. 

There are generally three terraces, and in fewer sections, two. 

In nearly all localities where the three are present, the relative 

heights are similar. The highest stands above the river at about 

twice the height of the middle terrace, which is in turn about twice 

the height of the low one (see typical relations, fig. 5).

Remnants of the high terrace are composed of important amounts 

of slope wash, and the remnants slope upward to the adjacent hills 

in long, sweeping curves. The two lower terraces, in contrast, 

are nearly flat and slope wash appears to have contributed so 

little to the form of the terraces that one can characterize the 

materials as having been deposited entirely by the main stream.

These generalizations apply without exception to all the basins 

studied, which include nearly half the State of Wyoming, and it is 

believed that the respective terraces correlate approximately in 

time over the whole area. This belief is strengthened by the close 

analogy to similar sequences throughout a still larger region, as 

will be demonstrated. It becomes important, then, to examine the 

relationship between the sequence of river regimen indicated by 

the alluvial terraces of the plains, and the sequence of events in 

the mountains where a changing climate has left its record in glacial and periglacial phenomena.

The argument for regional correlation will be developed in the 

following sequence^. First, it will be demonstrated that the highest 

alluvial terrace (Kaycee) has, in the mountain valleys, a correlative 

that appears to postdate the youngest moraine. Second, ;the climatic 

implication of the pedocalic paleosol will be examined, and it will 

be argued that the only known climatic period which would account 

for the physical characteristics of the paleosol and for its stratigraphic position is the Altithermal (Antevs, 1948), called in Europe 

the Climatic Optimum. Third, these facts will be compared with 

the sequences in the late Wisconsin and Recent epochs described 

for Texas, New Mexico, Arizona, and Nebraska.
REGIONAL CORRELATION AND ITS PROBLEMS 47 

TERRACES AND GLACIAL FEATURES IN CLEAR CREEK BASIN

In Western United States, Bryan and Ray (1940), Bryan (1950), 

and Moss (1951), have correlated river terraces with alpine glacial moraines in order to provide dates for archeological remains 

associated with the terraces. In Eastern United States, Peltier 

(1949) has related the terraces of the Susquehanna River to continental glacial stages in northern Pennsylvania and New York. 

Each terrace is interpreted as the surface of an outwash train developed during the maximum advance of a" glacial stage or substage. Theoretically, then, correlation is rather simple and consists of tracing a terrace upstream into the mountains until it ends 

at some terminal moraine. In practice, however, this procedure 

may be anything but easy, because (1) the terrace is not a continuous surface but, rather, occurs as dissected remnants; (2) the 

terrace disappears completely in narrow canyons and must be 

picked up again above the canyon on the basis of height, lithology, 

and degree of weathering; (3) the terrace may not show definite 

outwash relations to any terminal moraine.

The present investigation did no-t include extensive work on glacial deposits at the headwaters of the streams studied. Terraces 

were traced headward along several tributaries of Clear Creek, 

itself a tributary to the Powder River. Clear Creek has welldefined alluvial terraces through the length of its reach on the 

plains. Because its headwater area in the Bighorn Mountains has 

been strongly glaciated, it was hoped that by tracing the alluvial 

terraces upstream, the alluvial chronology could be more definitely tied into the glacial sequence than on the basis of general 

argument alone.

In table 6 the terrace heights measured at various points along 

Clear Creek are shown. At the mouth of Clear Creek the three 

terraces along its valley were observed to merge into the three 

terraces already described along the Powder River. Table 6 

shows that the heights of all three terraces above the present Clear 

Creek decrease in the direction of the headwaters. The character 

of the terraces has been described in figures 12 and 15, and these 

descriptions are typical for the whole reach from the mountain 

front to the creek mouth.

In the mouth of the mountain valley the flood plain narrows headward, and there is a marked change in the character of the terrace 

materials. One may walk from the town of Buffalo, which is built 

on the high, or Kaycee, terrace on both sides of Clear Creek, upstream on a continuous flat into the mountain valley.

About 3 miles east of Buffalo a drainage ditch dug in the Moorcroft terrace,*which here is more than one-quarter mile wide, exposes an instructive stratigraphic section. Three to 5 feet of silt
48 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

Table 6. Terrace heights, in feet, along the upper reaches of Clear Creek and North

Fork Clear Creek, Wyo.

[All terrace heights measured with hand level]

Clear Creek: 

Soil site, 1 mile east of 

Buffalo.... ...................

2. 4 miles west of Buffalo..

North Fork Clear Creek:

Above Old Lake upstream 

from Medicine Park......

Kaycee 

(high) 

terrace

20

12 

12

8

10

8

10

7

8

10

8

3

Moorcroft 

(middle) 

terrace

12

4 

4

5

6

4

4

4

3

Lightning 

(low) 

terrace

5

2 

1

2

2

1

2

1

1

Miles upstream from 

mouth of Sand 

Creek near Buffalo

2.4 

3.7

4.6

5.8

6.3

12.1

13.3

18.2

25.2

26.2

27.3'

and sand containing gravel lenses overlies disconformably a 

poorly sorted gravel ranging in size from sand to rounded boulders 

a foot in diameter. The gravel is generally stained a yellowish 

color. The upper surface of the gravel is markedly undulating. At 

the edge of the Moorcroft terrace the gravel can be traced under 

the Kaycee terrace. That the Moorcroft terrace is here cut on material of Kaycee age and older is well demonstrated. The gravel 

underlying Kaycee formation must represent a relation similar to 

that shown in figures 14 and 15, and is considered Ucross in age.

At Buffalo, the Kaycee terrace is predominantly silt, at least in 

the upper few feet, as indicated in figure 15. The present streambed is covered with gravel, probably a thin veneer only. A mile 

upstream from Buffalo, where the width of the Kaycee terrace is 

about one-quarter mile, a long, deep trench excavated for a pipeline provided a good temporary exposure for study. In the trench 

2 to 3 feet of fine sand was interspersed with lenses of sand and 

clay,underlain by gravel. At Fort McKinney, only a mile farther 

upstream, the Kaycee terrace decreases in width to about 100 

yards, and is composed of coarse gravel, including some subrounded boulders as much as 1 foot in diameter. At that point, two 

distinct surfaces stand at levels lower than the Kaycee terrace, 

which is there 12 feet above the stream. Farther upstream the 

terraces, where present, are generally gravel. This transition in 

texture from silt to gravel near the mountain front takes place 

without any break in the topographic continuity of the Kaycee terrace. Whether these relationships are attributable to wedging out 

of the silty Kaycee formation could not be determined from the 

exposures available.
REGIONAL CORRELATION AND ITS PROBLEMS 49

In the narrow canyon the terraces are present only as remnants, and correlation must be based primarily on height above 

the stream and physiographic position relative to other terraces, 

because there are no significant differences inlithology and weathering on the various terraces. Adding to the difficulty of correlation, the terraces themselves are quite low.

Glacial deposits are extremely well developed along Clear 

Creek. Above an altitude of 8, 000 feet (about 20 miles upstream 

from Buffalo) typical glacial forms, including both terminal and 

lateral moraines, kettles, ponds and lakes, are very well preserved. Boulders are strewn over the surface and there is little 

evidence of soil development or weathering. There are two sets 

of we 11-developed lateral moraines; a clearly defined terminal 

moraine is associated with the more extensive and older of the two 

laterals. The older, or higher, lateral moraine rises about 500 

feet above North Fork Clear Creek, and the younger, or lower, 

one stands about 150 feet above the creek.

Just below Florence Lake near the headwater divide, at altitudes of 10, 300 to 11,000 feet (28 miles upstream from Buffalo) 

there are striking deposits of large, angular rock rubble forming 

short ridges which rise 100 to 200 feet above the floor of the valley. These are protalus ramparts of the type described by Bryan 

(1934). Those described by Bryan occur in cirques and form a 

barrier trending normal to the valley. The features in the valley 

of North Fork Clear Creek are composed of blocks frost-riven off 

the cliffs bordering the narrow valley, and for this reason the 

ramparts are essentially parallel to the valley axis.

Individual, boulders in the ramparts are as much as 40 feet in 

the largest dimension, and many of them measure in tens of feet. 

They are fresh in appearance, without lichen coverings, but are 

somewhat darker than the modern talus slopes behind the ramparts. The modern talus is characteristically composed of unweathered angular blocks less than one-fourth the size of those in 

the ramparts.

The relative position of the Kaycee terrace with respect to the 

glacial sequence of Clear Creek will now be discussed. Table 6 

contains datafrom 12 localities along Clear Creek and North Fork 

Clear Creek at which terrace heights were estimated. The 12 

points are designated according to their distance upstream from 

Buffalo. The third locality, Fort McKinney, represents the change 

from the silty surface of the Kaycee terrace, characteristic of the 

plains, to the gravel surface of the mountain valley. The Clear 

Creek localities are arranged in order upstream toward the headwater. The height of the Clear Creek terraces decreases more 

or less continuously upstream, becoming roughly half as high in 

the headwaters as at Buffalo. Terrace remnants occur far up-
50 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

stream from the youngest terminal moraine seen in the valley, 

but disappear downstream from the protalus ramparts. The whole 

length of valley train deposits within the moraine have been subject to surface reworking, at least near the stream.

It will be understood that the remnants of terraces are poorly 

preserved in the mountain valley, and absent in the narrow, steep 

canyon sections. Each of the measured sections presented in table 

6, however, represents clearly developed terrace flats with distinct 

risers. The problem of interpretation is less concerned with the 

existence of terrace remnants, which in the field seemed valid, 

than with the correlation of the remnants. In table 6 assignment 

of the observed remnants to the columns designating age Kaycee, 

Moorcroft, and Lightning is based entirely on the height of the 

remnants above the stream. This assignment derives its primary 

support from the relatively close accordance in height and the 

more or less progressive decrease of height upstream.

By such correlation, the highest terrace in the mountain valley 

is equivalent to the Kaycee terrace downstream. Because there 

are remnants of this terrace upstream from the youngest moraine, 

the Kaycee terrace must postdate the latest phase of glaciation in 

this valley.

Study of two drainage basins adjacent to North Fork Clear 

Creek French Creek and South Piney Creek showed considerable difference in the glacial features. Detailed description of 

these features is considered inappropriate for inclusion in this 

report.

Because of the differences in the valleys studied, the authors 

believe that correlation of moraines in the Bighorn Mountains with 

the glacial sequence of Bryan (1950) and others would be unwarranted in the present state of knowledge. Yet, the existence of 

evidence indicating that the Kaycee terrace postdates the youngest 

moraine is important to an under standing of the alluvial sequence.

CLIMATIC IMPLICATIONS OF THE PALEOSOL

Any series of events proposed to explain the terrace sequence 

and related features must include a period of soil development 

after the deposition of the Ucross formation and before that of the 

Kaycee formation.

Modern surface pedocalic soils are widely distributed geographically and occur in several distinctly different climatic environments. They are commonly characterized by a zone leached of 

soluble salts in the upper part of the profile and concentration of 

these salts, especially calcium carbonate, in a lower layer.
REGIONAL CORRELATION AND ITS PROBLEMS 51

Nikiforoff (1936, 1937) has questioned the pedologic character of 

calcium carbonate accumulations on the grounds that many soils 

that show this feature are derived from lime-rich parent materials; 

however, it is generally agreed (see Robinson, 1949) that soilforming processes are involved. The depth of the zone of accumulation is related to the amount of precipitation; a greater depth of 

the zone is associated with high precipitation, and the zone of 

accumulation is nearer the surface under more arid conditions. 

Furthermore, the largest accumulation of calcium carbonate in 

soils seems to be associated with conditions of aridity. So far as 

the clay complex of pedocal soils is concerned, there would appear 

to be no vertical differentiation due to eluviation and illuviation.

Bryanand Albritton (1943) consider apedocal-type soil, whether 

modern or ancient, to be associated with climatic conditions considerably more arid than those under which pedalfer-type soils 

(in which aluminum and iron are concentrated in the B layer) are 

developed. They point out that climate is one of the most important 

factors in soil formation and that, therefore, a change from a 

relatively arid to a relatively humid climate would cause a change 

in the type of soil produced.

The conspicuous pedocalic paleosol, characterized by a high 

concentration of calcium carbonate, has been described in this 

report at several localities. Were one to rely entirely on the mere 

presence of the calcium carbonate zone, it might be questionable 

whether this zone should be considered of pedologic origin, owing 

to the fact that in no place was a well-defined A horizon of an 

ancient soil found. However, the calcium carbonate zone can be 

traced continuously along buried erosion surfaces which cut across 

several lithic types, as shown in figure 16, a circumstance which 

argues strongly for a pedologic origin. The calcium carbonate 

zone is in some places exposed at the surface, and wherever it is, 

the surface part of the zone is apparently being leached under the 

present climatic regime.

If paleosols are to be interpreted as indicators of periods of 

subaerial weathering, it is the contention of the authors that there 

should be present definite characteristics of profile development. Dark 

bands in alluvial deposits exposed along raw banks of arroyos may 

be mistaken for buried soils. In many places, the dark bands, 

often interpreted as buried carbonaceous A horizons, are merely 

due to textural differences which cause a band of fine-grained material to retain moisture, and hence appear darker in color. Chemical analysis of the dark bands may show no organic matter to be 

present. Unless a particular band shows evidence of profile development that is, horizons of leaching and accumulation no particular stratigraphic significance could be attributed to such a zone 

nor could the zone be considered to represent any appreciable
52 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

period of time during which sedimentation ceased and weathering 

occurred.

In identifying zones of illuviation, it was noted during this investigation that accurate field estimation of amounts of calcium 

carbonate in a soil is very difficult. The authors have not had 

great experience in such matters, but visual estimates of relative 

amounts, whether large or small, often proved wrong, and even 

the use of an acid bottle in the field did not completely eliminate 

this difficulty. Therefore, the soils and paleosols were sampled 

and analyzed for calcium carbonate in the laboratory by a volumetric 

technique depending on liberation of carbon dioxide gas by addition 

of hydrochloric acid. Such an analysis took about 5 minutes a 

sample, and gave results reproducible to within 5 percent. The 

difficulty with estimating relative amounts of calcium carbonate in 

the field, even using an acid, is that the carbonate may be well 

distributed in a particular part of the soil profile, or it may be 

concentrated in nodules, concretions, fibrous threads, and irregular soft masses. Furthermore, in many places the white material 

at first thought to be calcium carbonate was shown actually to include considerable amounts of gypsum.

Another difficulty in the interpretation of buried pedocalic soils 

is the effect of texture. It was noted in many places that the concentration of calcium carbonate in a layer of fine silt or clay was 

much greater than in an overlying or underlying layer of coarser 

material. Such concentrations of calcium carbonate might easily 

be mistaken for significant profile zones.

It may be argued that the position of the ground-water table was 

the critical factor in producing the carbonate soils and crusts 

described. Certainly where carbonate-rich zones are concentrated 

in noncalcareous materials, it must be concluded that those areas 

were under the control of ground water. Also, it might be argued 

that these carbonate zones are being produced under present groundwater conditions. It can be conclusively shown that at Sussex, 

Buffalo, Ucross, and other places, the present water table is far 

below the zone of carbonate concentrations. Furthermore, X-ray 

analysis showed the most weathered mica in the stratum where the 

carbonate accumulation was greatest.

Field examination and laboratory data prove the existence of a 

carbonate-rich zone buried beneath the surface of the Kaycee terrace in many localities. This zone is interpreted as pedogenic, 

despite the fact that no example of a well-defined A horizon has 

been discovered. Under arid conditions, it seems likely that a 

carbonate zone could develop essentially at the surface of the 

ground.
REGIONAL CORRELATION AND ITS PROBLEMS 53

It seems necessary, then, to postulate a period of aridity later 

than the deposition of the Ucross formation and before deposition 

of the Kaycee silt, during which the carbonate-rich zone was 

developed.

High gravel-capped surfaces are present in many of the areas 

studied, but, are not within the scope of this report. These surfaces, 

older than the alluvial terraces, characteristically have thicksurface crusts of calcium carbonate, which may have developed in 

part or wholly during the period when the carbonate zone buried 

beneath alluvium was formed (see fig. 16).

THE CHRONOLOGY OF CLIMATIC EVENTS

A sequence of events which appears to explain the observed facts 

in Clear Creek valley and in the other streams of the area will 

now be postulated.

In late Wisconsin time, glaciers advanced in places in the Rocky 

Mountains. In the Bighorn Range at least two such advances can 

be recognized by moraines. During the earlier of these, large 

volumes of gravel were carried by the streams emanating from 

glaciers out into the valleys of the plains where they were in part 

deposited. The recession from the terminal moraine at an altitude 

of 8, 000 feet was reversed by another advance somewhat less 

strong. More gravel was carried out into the river valleys of the 

plains, but present exposures do not allow a determination of any 

differences in the gravel deposits of these two glacial advances. 

The gravels of the Ucross formation are considered to be related 

in age to one or both of the glacial advances indicated by these 

moraines.

During the glacial period, sedimentary rocks of the plains were 

eroded, and possibly this erosion was accelerated by frost processes; however, the silt derived from the plains could easily have 

been carried by sti earns which were fed by glacial melt water and 

were capable of transporting gravel. For this reason the fine 

material tended to be carried far downstream and the coarser 

gravels were deposited to form the Ucross formation.

During the glacial retreat, the production of gravel by ice abrasion decreased, and the melt waters of the waning ice reworked 

the ground moraine and the valley gravel deposits, eroding some 

of the deposited gravel and carrying it away. When the ice had 

mostly melted under the ameliorated climate, the melt water became a relatively unimportant source of water in the plains 

streams. It is postulated that the trend toward aridity increased 

the importance of summer rainstorms as an agent of erosion on
54 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

the plains, for the Bermuda anticyclone moved northward and in 

summer brought Gulf air into the Middle West much as it does at 

the present time. A condition even more continental than the present 

climate of the area had been reached as the Altithermal time 

approached. Such a climate increased the importance of an anticyclone over the Rocky Mountain area in winter, which gave rise 

to frequent storm passages and accompanying wind, but without 

high precipitation owing to .the lack of development of deep cyclones. 

Such a winter situation is typical of a high-index-pressure pattern; 

that is, one in which there is a large difference in pressure from 

midlatitudes to northerly latitudes.

Summer in the Altithermal time was marked by low pressure 

over the continent, with a strong anticyclonic flow of air aloft 

around the upper air extension of the Bermuda high-pressure cell. 

As at present in the Southwest, considerable moisture derived 

from the Gulf of Mexico passed over the desert aloft, but the dearth 

of strong wave -troughs aloft precluded the precipitation of that 

moisture except as infrequent but intense thunderstorms. Under 

such a climate, flash floods punctuating the hot, dry summers of 

the plains provided a period characterized by erosion of the valleys 

in the plains, but in the form of gullying rather than extensive sheet 

erosion Chemical weathering of the sediments making up the plains 

was not intense, and the flash floods trenched the valleys but did 

not preclude the development of an arid-type soil on the uplands. 

The gravel of the Ucross formation was, therefore, eroded from 

the valleys except in isolated patches, and on these areas paleosol 

developed.

It is postulated that Altithermal time was characterized by an 

increase in the zonal index;*that is, rapidly moving,and frequent 

but weak cyclones in winter and a decrease in the meridional 

exchange of air. This is the concept held by Willett (1949). Such 

a condition would lead to frequent periods of wind during the passage 

of weak fronts. A high-index-circulation pattern is associated with 

intensification of the major anticyclones, and it is agreed by most 

workers that during a period of interglacial climate, the permanent 

high-pressure cells move northward somewhat and expand as well 

as intensify. Such a situation is envisaged as implying a geographic 

expansion of the summer synoptic pattern of New Mexico and 

Arizona in which Gulf moisture aloft is carried northward and thence 

eastward in the anticyclonic flow of high levels. During the infrequent pas sages of low-pressure troughs aloft, strong eonvective 

thunderstorms can break out over a wide area.

It need not be assumed that during Altithermal time the semiarid 

and desert areas experienced a large reduction in the present low 

annual rainfall. Rather, the Altithermal is visualized as a time of

'Mean pressure gradient between two chosen latitudes, usually 35° N. and 50° N.
REGIONAL CORRELATION AND ITS PROBLEMS 55

slight intensification of the conditions which characterized the 

period 1850 70 in New Mexico in which there was a significant 

deficiency in the number of small rains as compared with large 

rains (Leopold, 1951a). Leopold demonstrated that the differential 

change in frequency of large and small rains has characterized the 

present climatic fluctuation in New Mexico without a significant 

change in annual rainfall. He argued that the reduction in frequency 

of small rains, which are important in supporting the vegetal cover, 

and a concomitant increase or lack of decrease of great rains, 

promote gully erosion and the degradation of alluvial valleys.

This conception of the Altithermal in the West would account for 

the general degradation of valley alluvium, the observed efficacy 

of wind action, and the development of an arid-type soil profile 

over large areas adjacent to the Rocky Mountains.

Altithermal time gave way to a period of climate somewhat more 

cold and wet than the present, but only intense enough to cause 

patches of ice to accumulate in the highest mountain valleys. The 

alternation of snow and no snow, typical of present winters but 

slightly intensified, was accompanied by frost action in the mountains and probably to a lesser extent on the plains. The same change 

caused a summer climate more typical of the Middle Western than 

of the Southwestern States, with a decrease in the importance of 

flash storms. Thus, winter conditions were conducive to rapid 

disintegration of the rocks of the plains and the production of large 

amounts of silt and fine sand, but there was insuf fie ient flood volume 

from the mountain streams or from summer storms to carry the 

silt away. The fine-grained materials then accumulated in the 

valleys and Kaycee deposition was in progress. It was mostly during 

such a cold period that the protalus ramparts were formed in the 

mountains.

This post-Altithermal period was marked by two minor fluctuations in climate during Moorcroft and Lightning time. The mechanism of shift was comparable in character, but not in intensity, to 

that which caused the change from the last glacial stage to the 

Altithermal.

These climatic shifts were of a type which must perforce have 

affected wide areas. The climatic mechanism necessary for the 

various shifts in one locality lay in the general atmospheric circulation whose effects were regional.

Some idea of the minimum area which would be affected in a 

similar way by a shift of climate may be gained by study of the 

recent climatic variation for which meteorologic records are 

available.
56 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

Utilizing the Daily Synoptic Map Series of the U. S. Weather 

Bureau covering the period 1899 1939, Petterssen (1949) studied 

changes in certain indices of the general circulation and compared 

winter conditions of the first and second halves of the period. A 

major temperature rise, particularly in northern latitudes, has 

characterized the second half of the 40-year period. Some of his 

conclusions may be summarized as follows:

1. There has been an intensification of the meridional and a 

reduction in the zonal circulation. 2. Over Europe and the Bay of 

Biscay there has been a fairly uniform decrease in the number of 

cyclone centers, with particularly marked decrease over Scandinavia and the Norwegian sea. At the same time, cyclonic activity 

has increased substantially over the Mediterranean and the Balkan 

areas, and also over an area south and east of Newfoundland northward to Greenland.

No cursory discussion can replace actual inspection of Lysgaard' s 

(1949) anomaly maps for the world, presenting summary information on geographic distribution of changes in weather elements 

between 1910 and 1940. In discussing these summary maps of 

temperature variation, Lysgaard says:

The great (January) temperature rises (1910 1940) of more than 3° [C] has taken place 

in Greenland, but Spitzbergen, North Asia and the northern part of North America can 

also show appreciable rises of more than 2°. ***The most extensive [temperature] fall 

appears to faave taken place in East Asia and Australia.

The greatest temperature rise [for July] which is more than 1° [C], has taken place in 

Finland, North Scandinavia and central parts of Canada and the United States. ***The 

most extensive fall has occurred in Central Asia and the Monsoon district of South Asia. 

(P- 33)

Discussing similar charts of precipitation change in the 1910 40 

period, Lysgaard says, in January, the precipitation has increased

***over the greatest part of Algiers, Tunis, North America and Indonesia, while***decreasing in Greenland, Spain, Portugal, West Africa and the Nile.

In July the variation has been positive in the areas around the North Sea, at the Gulf 

of ?<lexico, in South America, South Africa and South East Asia, while it has been negative in most of Europe, the United States [and] West Africa. ***(p. 49).

These climate variations in a 30-year period provide some perspective of the areas of positive and negative anomalies. It need 

not be supposed that variations in climate begin and end simultaneously over large geographic areas. It appears that a lag in the 

effects of recent fluctuations was of such a nature that it caused 

the anomalies to spread geographically in a consistent pattern.

Schove (1950) presents evidence which indicates that between 

1880 and 1915 a zonal ring of high pressure moved progressively 

from the Arctic Arch to the Tropic of Cancer. Preceding and 

following this ring were rings of high rainfall, low pressure, and
REGIONAL CORRELATION AND ITS PROBLEMS 57

high temperature-gradient, suggesting that at any given latitude, 

five phases progressively occur in sequence during a period of 

climatic shift.

Maps showing progressive averages of annual runoff prepared 

by Hoyt (1936) and later by Harbeck and Langbein (1949) indicate 

decreasing runoff for the period of streamflow records (about 50 

years) in the United States. Deer easing runoff was concurrent with 

the generally increasing temperatures. These studies indicate 

that, with many local exceptions, runoff trends tend to be generally 

similar for an area as large as half the United States.

Studies of the present climatic fluctuation indicate an order of 

magnitude of the area over which*similar direction of change is 

probable. Faegri (1950) states as a principle that "the shorter the 

duration of a climatic fluctuation, the smaller is the area similarly 

affected; the longer the cycle, the greater the area within which 

it is felt in the same way. "

It appears, therefore, that an area as large as four or six 

Western States is of the minimum order of magnitude which might 

be expected to react similarly in a given climatic fluctuation. 

Where the boundary of such auniformily affected area might be is 

another question. Also, the effects of altitude might make changes 

in the mountains somewhat different from those of the plains.

A general argument based on meteorologic evidence makes it 

seem probable that streams in the Rocky Mountain area should 

have experienced generally similar sequences of alluviation and 

degradation under the influences of a varying climate. Even if a 

general similarity exists over a region, the same meteorologic 

considerations allow a measure of variability, even within short 

geographic distances.

The major part of a late glacial and Recent regional correlation 

has already been worked out by Bryanin a number of papers (1941^. 

1950, and others). These are summarized with a few additions in 

table 7. The sequence postulated in the present report is tentative, 

but it appears to fit well into that developed for the Southwest, as 

can be seen in the table. In nearly all instances the climatic 

sequence derived from studies of alluvial terraces has been worked 

out for the purpose of dating a particular archeological site. In the 

present study, reconnaissance methods were applied to several 

adjacent major stream systems and, therefore, a somewhat larger 

area was studied than in previous similar investigations.

Reference to table 7 shows that the Jeddito formation (Hack, 

1942), which is correlated with the Ucross formation of the present 

report, is characterized in all localities by a relatively large proportion of gravel, cementation of gravel by carbonate, and by the
58 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

Table 7. Regional correlation

Alluvial 

chronology 

(Bryan,

1941)

Modern 

erosion.

Deposition 

3.

Erosion.

Deposition 

2b.

Erosion.

Deposition 

2a.

Erosion.

Deposition 

1.

Glacial 

chronology

PostAltithermal.

Altithermal

Late 

Wisconsin 

(substage 

unknown).

Wyoming 

^Leopold 

and 

Miller)

Modern 

erosion.

Lightning 

deposi - 

tion.

Erosion.

Moorcroft 

deposition or 

stability.

Erosion.

Kaycee 

deposition; 

modern 

fauna.

Erosion; 

welldeveloped 

paleosol.

Ucross 

gravel.

White water 

Draw, Ariz. 

(Savles and 

^ntevs,1941J

Modern 

arroyo.

Upper silts; 

pottery 

after A. D. 

1300.

Erosion after 

A. D. 1200. 

i

San Pedro 

deposition; 

radiocarbon 

age of 

2,500 years.

Erosion.

Chiricahua 

stage; 

modern 

fauna; 

radiocarbon 

age of4,OOC 

years.

Erosion

Sulphur 

Springs 

stage; Elephant , 

Equus, 

Camelops, 

hickory; 

radiocarbon 

age of 78- 

7200 years.

Hhaco Canyon , 

N. M. 

(Byran, 1941)

Modern 

erosion.

Channel 

deposit; pottery circa 

A. D. 1200.

Erosion.

Main fill; pottery dated 

A. D. 500- 

700

Large arroyo.

San Jon site, 

N. M. 

(Judson, 1953)

Modern dunes 

and channel 

cutting.

Wheatland 

formation; 

after circa 

A. D. 1400.

Channel cutting on 

streams; deflation of 

some depressions; circa 

A. D.13- 

1400.

Upper Sand 

Canyon formation; in 

part later 

than A. D. 1.

Channel cut- 

 ting; wind 

action.

Lower Sand 

Canyon formation; 

"Collateral 

Yum a" projectile point.

Channel cutting; sand 

dunes; deflation of depressions.

San Jon formation; San Jon, 

Folson (?), 

Plainview (?) 

projectile 

points; extinct 

fauna.

Grants, N. M. 

(Bryan and 

VfcCann, 1943)

Modern 

arroyo; dunes.

Upper part of 

'"Late Alluvium."

Erosion; late 

dunes; pottery.

 Late 

Alluvium,"

San Jose 

complex; 

pottery.

"Old Dunes"; 

broad arroyo.

"Intermediate 

Alluvium."1

Following Judson's rearrangement. 

2Along eastern margin of plains.
REGIONAL CORRELATION AND ITS PROBLEMS 59

of alluvial terrace sequence

. Gallup, N. M. 

(Leopold and 

Snyder, 1951)

Modern arroyo.

Late fill in channels.

Erosion.

Upper Nakaibito formation; pottery dated 

A. D. 900-1100.

Erosion.

Lower Nakaibito formation.

Erosion; paleosol.

Gamerco formation.

Hopi country, 

Ariz. 

(Hack. 1942)

Modern dimes 

and channel 

cutting.

Naha formation; after 

A. D. 1300.

Erosion and 

possibly some 

wind action; 

after A. D. 

1200, before 

A. D. 1500.

Tsegi formation (B).

Possible 

erosion.

Tsegi formation (A).

Channel cut* 

ting and 

dunes.

Jeddito formation; proboscidian.

Big Bend area, Tex. 

(AlbrittonandBryan, 1939. 

and Kelley, Campbell, anc 

Lehmer, 1941)

Modern channel cutting.

Kokernot formation.

Channel cutting.

Upper Calamity formation.

Erosion (?).

Lower Calamity formation.

Wind action; broad 

channels.

Neville formation;£/ep/ias 

and IT guns.

High Plains area, Tex. 

(Huffington and 

Albritton, 1941, and 

Evans and Meade, 19451)

Modern channel cutting;2 

Monahans formation 

(upper part) .

Low terrace and recent 

fill.

Channel cutting;2 

Monahans formation 

(main body).

Intermediate 

terrace and Recent fill.

Channel cutting;2 

Judkins formation.

High terrace; 2 late Pleistofill and Tahoka clay; 

Plainview projectile 

point; extinct fauna.

303189 O - 54 - 5
60 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

inclusion of an extinct fauna and a stone culture (prepottery). This 

deposition was followed by a period of wind action, erosion, and 

soil formation during Altithermal time.

The second depositional phase, or phase 2a of Bryan (1941), 

appears to correspond to the Kaycee deposition in valleys in a 

very large area in Wyoming. It is characterized by a generally 

silty or sandy fill, annodern soil, lack of the strong calcification 

imposed on the top of the earlier Deposition 1, by the absence of 

extinct fauna, and by the inclusion of a prepottery culture.

The erosion at the end of this deposition was less marked in 

most areas than that following Deposition 1. Wind action accompanied this erosion in some places.

The third phase (2b of Bryan, 1941) may be represented by a 

period of downcutting only, as indicated by the Moorcroft terrace 

in Wyoming, or it maybe a fill terrace which it appears to be in 

eastern New Mexico (Judson, 1953), on the Puerco River, New 

Mexico (Leopold and Snyder, 1951), in the Hopi country (Hack, 

1942), and in the Big Bend area of Texas (Albritton and Bryan, 

1939). This time unit to which the Moorcroft in Wyoming apparently belongs is characterized by practically no soil development, 

a modern fauna, a pottery culture at least in the upper part of the 

alluvial fill, including pottery types of the Christian era and probably as late as A. D. 1200. It was followed by a period of erosion 

of variable magnitude.

The last phase appears everywhere to represent an alluvial fill, 

the deposition of which began between A. D. 1200 and 1500. Deposition was interrupted by the erosion period which began about 

1880 and was at least partly a result of land use by man. The 

Lightning formation is believed to relate to this phase.

PALEOHYDROLOGY

Consideration of the alluvial chronology brings to mind a host 

of questions concerning a comparison of the present with conditions 

which prevailed in the past. These questions are concerned not so 

much with past climate itself, but with the interaction of climate, 

vegetation, stream regimen and runoff which obtained under climates different from that of the present. That is, with hydrologic 

rather than merely climatic factors. To describe this general 

subject the word "paleohydrology" is introduced.

Two lines of evidence will be explored in the discussion. The 

first concerns the gradients of present and past channels of the 

Powder River and one of its tributaries, Clear Creek. The second
PALEOHYDRQLOGY 6 1

concerns the total volume of alluvium deposited in the river valleys 

and the rate of deposition.

STREAM GRADIENTS, PAST AND PRESENT, AND THEIR HYDROLOGIC SIGNIFICANCE

On figure 22, stream profiles are plotted for Clear Creek and 

the Powder River. The profile of the Powder River could be plotted with accuracy and detail from the excellent topographic maps 

of the river channel. To define the profile of Clear Creek, the Ft. 

McKinney and Sheridan quadrangle maps with 100 -foot contours 

are available, as well as a complete profile published in House 

Document 256, 73d. Congress, 2d Session.

alo, Wyo,

\ \

> 4500 

3000

300 200 

MILES ABOVE MOUTH

Figure 22. Longitudinal profiles of Powder River and Clear Creek.

It is obvious that Clear Creek below Buffalo, Wyo., is about 

three times as steep as the lower Powder River. It has been shown 

by Leopold and Maddock (1953, fig. 5) that despite the difference 

in gradient, the mean velocity, depth, and width of these two 

streams are, respectively, similar at points having equal mean 

annual discharge.

The bed of the Powder River through most of its length consists 

primarily of silt and fine sand. Clear Creek generally has a bed 

of fine gravel. The size of bed material and its effect on bed 

roughness appear to explain in a general way why the slope of Clear 

Creek is greater than that of the Powder River.

While there is a difference in bed material size in the present 

Powder River and Clear Creek, the alluvial terrace representing 

Kaycee deposition in the valley of Clear Creek is composed primarily of silt. The same is true for the corresponding terrace on 

the Powder River. The Kaycee terrace on Clear Creek between
62 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

the towns of Ucross and Leiter slopes 16 feet per mile, as compared with the present stream gradient of 16.4 feet per mile. The 

Kaycee terrace of the Powder River between Sussex and Arvada 

falls 5. 4 feet per mile, compared with the present stream gradient 

of 5. 5 feet per mile. In other words, Clear Creek deposited in 

Kaycee time the same size of material as the Powder River but at 

a much higher gradient, and both streams have gradients at present 

only slightly different from their respective gradients in Kaycee 

time.

Now it might be supposed that during a period of widespread 

alluviation in a river flowing on a bed composed of its own transported sediment and in a self-formed channel, there would be 

ample opportunity for the longitudinal profile to be adjusted to 

conform to the size of the material being carried. If this were so, 

the present Clear Creek, whose bed consists of fine gravel, should 

be far steeper than its channel formed at the end of Kaycee deposition when the stream flowed on an alluvial fill composed primarily of silt. Yet, the gradient of the surface of the silty terrace 

is nearly identical with the gradient of the present stream. It is 

necessary to suppose that when Clear Creek filled its valley with 

tens of feet of silt nearly devoid of gravel it must have had a channel 

bed composed primarily of silt in contrast to the gravel bed observed in the stream today.

Further, it might be expected that for a given discharge, the 

gradient «of the Powder River in Kaycee time was nearly equal to 

that of Clear Creek of Kaycee time because both were carrying 

and depositing nearly the same size of material; however, the 

Kaycee terrace along the Powder River slopes much less steeply 

than the comparable terrace on Clear Creek.

An attempt will be made to account for these apparently anomalous 

facts. Valid comparisons of the gradients of two streams maybe 

made only when the effect of discharge is considered. It is recognized that slopes of rivers are less steep for rivers of large than 

for those of small discharges, sediment sizes remaining the same. 

It will be argued here that in Kaycee time Clear Creek must have 

discharged a much smaller amount of water relative to the discharge of the Powder River than it does today. From this relation 

it would follow that the mountain contribution of water was much 

lower relative to the plains contribution during Kaycee time than 

is observed today. The reasoning supporting this conclusion will 

now be developed.

At a given stage in the physiographic history of a river, the 

elevation of its mouth is essentially fixed by the master stream 

or other base level to which the stream is graded. Also, the 

elevation of the uppermost watershed divide is fixed. That is, the 

difference in elevation between mouth and headwaters is the result
PALEOHYDROLOGY 63

of physiographic history. Between these elevations the stream 

might be considered as adjusting its profile. In the case of the 

Powder River, physiographic events determined that its mouth 

should be a long distance from its headwaters, and for this reason 

the mean gradient is relatively small. In the case of Clear Creek, 

the difference in elevation from mouth to watershed divide is considerable, and the distance relatively short. Its overall slope 

must, perforce, have been steeper than that of the Powder River.

Physiographic history before Kaycee time had seen particular 

profiles developed on the two streams. The Powder River profile 

was characterized by a very long reach of nearly uniform, gentle 

slope. Clear Creek was characterized by a somewhat steeper, 

more concave profile. With these profile conditions existing at the 

beginning of Kaycee time, both streams received an increase of 

sediment of silt size from the plains area, and both began to 

aggrade.

Consider now a point on the Powder River at which the mean 

annual discharge is at present equal to 200 cfs. This point lies 

between the towns of Sussex and Arvada, Wyo. Between these 

towns the Powder River slope is nearly uniform, and has a value 

of 5. 5 feet per mile.

Now consider a point on Clear Creek where the present mean 

discharge is also 200 cfs. This point is somewhere below Ucross 

but upstream from Leiter. In this reach the slope of Clear Creek 

is 16.4 feet per mile.

It has already been stated that the shape factors for Clear Creek 

and the Powder River are nearly identical for the same discharge 

at the present time. Moreover, for the same discharge Clear Creek 

probably now carries a smaller total sediment load than does the 

Powder River.

Therefore, quasi-equilibrium at points of equal discharge but 

different slopes is maintained at present by the different size of bed 

material and not by channel shape. In fact, the larger size of bed 

material in Clear Creek requires a greater slope despite the fact 

that the total load in Clear Creek is not so large as in the Powder 

River for a given discharge. Caliber of load probably overcompensates for the smaller total load.

It follows, then, that if in Kaycee time the streams at the two 

points being considered carried sediment of equal size, the differential in gradient must have been compensated by one or more of 

the following: (1) flattening of slope on Clear Creek; (2) adjustment 

of the channel section of Clear Creek to a wider and more shallow 

stream than at present; and (3) a decrease in discharge in Clear 

Creek relative to that of the Powder River.
64 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

With regard to slope adjustment, the gradient of Clear Creek in 

Kaycee time was about 16 feet per mile, or 0. 4 foot per mile less 

than its present gradient, based on the change in height of the 

Kaycee terrace scarps between Leiter and Ucross. The gradient 

of the Powder River in Kaycee time was about 5. 4 feet per mile, 

or 0.1 foot per mile steeper than its present grade, based on the 

change in height of the Kaycee scarps between the towns of Arvada 

and Sussex. Apparently, the slope-adjustment differential between 

the two streams totaled about 0. 5 foot per mile, but the actual 

gradients still were in the ratio 5.4:16, or 1:3. Thus, it appears 

that the slight adjustment in slope was minor compared with the 

overall difference in gradient of the two streams carrying sediment 

of the same size.

Concerning the second possibility, adjustment of channel section, 

the present shape factors seem to be determined primarily by the 

bank materials which are silt in both streams. Because the materials carried by the streams were more nearly alike in Kaycee 

time than at present, there is no reason to expect a great differential adjustment in channel shape in Kaycee time.

The foregoing argument then leads to the third possibility, that 

the discharge of Clear Creek must have decreased relative to that 

of the'Powder River when comparison is made between two points 

equal in discharge at the present time. A postulated differential 

decrease in discharge of Clear Creek would be in the direction 

necessary to establish equilibrium with the smaller caliber of 

load carried by that stream in Kaycee time.

Clear Creek at present derives its principal flow from the mountain area. Though the stream does receive some ephemeral tributaries from the western edge of the plains at the foot of the Pighorn Mountains, these tributaries contribute only a minor part of 

the total drainage area of Clear Creek.

The Powder River also heads in the mountains. Its course begins 

in the southern end of the Bighorn Mountains where it flows east 

and south, but shortly after leaving the mountains it turns abruptly 

northward and flows parallel to their eastern border more than 

200 miles to its junction with the Yellowstone River. Upstream 

from the mouth of Clear Creek, the Powder River receives the 

drainage of several streams originating in the Bighorn Mountains, 

but none of these taps the high country to the same degree as Clear 

Creek. A large area of the plains to the east and south of the main 

stem of the Powder River drains into that river. Thus, the Powder 

River above the mouth of Clear Creek has a much larger proportion 

of its drainage area in the plains, and a much smaller proportion 

in the high mountains than does Clear Creek.
PA1£OHYDROLOGY 65

If, according to the earlier argument, the discharge of Clear 

Creek must have decreased relative to that of the Powder River, 

it seems logical to suppose that this implies an increased runoff 

from the plains relative to that of the mountains. If the contribution 

from the plains had remained the same and an increase of flow 

from the mountains had occurred, both Clear Creek and the Powder 

would have increased in discharge, Clear Creek somewhat more 

than the Powder. Conversely, if the mountain contribution remained 

unchanged, or even decreased somewhat, and the runoff from the 

plains had materially increased, the flow of the Powder River near 

Arvada would surely increase much more than the flow of Clear 

Creek near Letter. This latter condition is postulated to explain 

the difference in slope of Kaycee deposits of similar texture in the 

two streams.

A climatic mechanism for accomplishing the postulated relations 

will now be discussed.

A trend toward contraction of the circumpolar vortex that is, 

an increase in the zonal index (Willett, 1950) is considered to 

accompany a climatic shift toward an interglacial climate. Just 

such a change has characterized the present climatic fluctuation 

marked by the recession of glaciers, and there has unquestionably 

been a concomitant general trend toward decreased runoff in the 

United States (McDonald and Langbein, 1948). In the Missouri 

River basin the same period shows marked downward trends in 

precipitation(Oltman and Tracy, 1951). The precipitation records 

in the Missouri River basin are predominantly for stations in the 

plains area. These trends in themselves do not, however, demonstrate a differential shift of mountain precipitation in relation to 

plains precipitation. Yet, when there are shifts in the opposite 

direction that is, toward more glacial climate an increase in 

number of light and moderate summer rains relative to heavy 

summer thunderstorm rain in the semiarid climates (Leopold, 

1951a) would affect the plains runoff much more than the mountain 

yield. This follows from the fact that runoff from the mountains is 

derived primarily from winter precipitation, stored temporarily in 

the form of snow which runs off during the spring melt or is stored 

as ground water which supports the flow of mountain streams 

during the summer. On the plains, however, it is clear that storage 

of winter snow is relatively unimportant, and in the moderately 

continental climate of the western plains area the precipitation 

maximum comes in summer. The bulk of the runoff from the plains 

thus occurs in summer.

An increase in winter precipitation affects runoff from mountain 

areas much more than that from the plains. An increase in summer 

precipitation would tend to increase the runoff from the plains 

more than from the mountains.
66 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

A glacial climate probably differs from the present climate 

much more in summer than in the winter, particularly in temperature (Antevs, 1928; Leopold, 1951b), and probably in precipitation. 

On the plains, a lowered summer temperature would tend to provide 

more runoff per unit of precipitation than now occurs.

In summary, these considerations seem to indicate that a trend 

toward a colder and wetter summer climate would produce a 

differential increase in runoff from the plains over runoff from 

the mountains, and that these conditions would cause an aggradation 

of river valleys as occurred in Kaycee time.

Though the argument is roundabout, it at least is a line of 

reasoning independent of previous efforts to ascertain the nature 

of climatic change necessary to cause aggradation in western river 

valleys. This argument supports the hypothesis of Bryan (1941), 

derived from other evidence, that aggradation of alluvial valleys 

is associa'ted with a trend toward a more humid climate, which 

appears to be also a trend toward a more glacial climate. Similarly, a trend toward aridity would be associated with degradation 

of alluvial valleys.

BATE OF ACCUMULATION OF VALLEY ALLUVIUM AND COMPARISON WITH MODERN

RIVERS

Further inference concerning the paleohydrology of the Powder 

River basin may be drawn from consideration of possible rates at 

which the alluvial fills underlying the river terraces were deposited. These estimated rates of sediment movement will be compared with sediment movement in modern streams. The plan of the 

argument is as follows:

The lengths of tributaries of various sizes will be computed for 

the drainage area of the Powder River above Arvada, Wyo. These 

lengths will be multiplied by estimated average cross sections of 

the alluvial fills based on reconstruction of the terrace levels. 

This will provide estimates of the total volume of alluvium deposited 

in all river and tributary valleys at the time of the maximum 

aggradation of the respective terrace systems. A rate of aggradation will be computed by dividing the volume of alluvium by the 

estimated duration of the aggradation process. On such a framework the paleohydrologic conditions implied by the various possible 

sedimentation rates may be examined.

The quantitative description of drainage basin configuration 

devised by Horton (1945) provides an appropriate method of computing the total lengths and the number of tributary streams of 

various sizes. For the Powder River basin above Arvada, two 

30-minute quadrangle maps are available, Ft. McKinney and 

Sheridan, Wyo. Four tributary drainage basins ranging from 27
PALEOHYDROLOGY 67

to 352 square miles in area were studied as samples. All of these 

drain the plains area underlain by Wasatch formation, and though 

three are tributary to the Tongue River, all may be considered 

representative of the greater part of the Powder River basin.

In each sample watershed, the "stream order" of every tributary 

andbranch was determined in the manner outlined by Horton (1945). 

The smallest unbranched tributaries were considered first order; 

streams receiving as tributaries first-order branches were designated second order, and so on. The total number of each order 

of streams was counted, their lengths measured from the map, 

and average lengths computed for the sample areas.

It is not possible to determine the numbers of streams of various order for the whole Powder River basin because detailed topographic maps are not available for a sufficient part of the total 

drainage basin. The data from the sample watersheds could be 

extrapolated, however, to provide an adequate estimate. Three 

graphs were required for determination of average lengths and 

total numbers of tributaries. The number of streams of each order 

was plotted against stream order on semilogarithmic paper for the 

sample watersheds. The lines so determined were essentially 

parallel, as shown by Horton (1945, p. 288).

The average number of first-order streams in each sample basin 

was then plotted against the drainage area of the respective basins, 

and the line so determined was extrapolated to the drainage area of 

the Powder River. This provided an estimate of the number of 

first-order streams in the Powder River basin. The process was 

repeated for higher orders, and thus a curve of stream number 

plotted against stream order was constructed for the Powder River 

above Arvada.

It had been estimated from available maps that the main stem of 

the Powder River had an order of either six or seven. The synthesized curve of number of streams plotted against stream order 

indicated that the Powder River was seventh order, a satisfactory 

agreement.

Curves of average lengths of various orders of streams were 

plotted for the samples, and the mean curve extrapolated to seventh 

order. These curves provided the data listed in the first three 

columns of table 8. It will be recognized that the data in these 

columns were read from smooth, average curves and, therefore, 

the lengths and numbers represent smooth geometric progressions. 

This is in accordance with the Horton analysis based on a much 

larger number of samples.

According to the definition of stream order, the computed length 

of any higher order stream is the whole length from mouth upstream
68 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

to the head of a small tributary. The lengths listed in column 2 of 

table 8 are not, therefore, the lengths of reaches representing an 

approximately uniform volume of alluvial fill per unit length. The 

lengths were corrected as follows:

The seventh order, or largest, stream has a total length of 100 

miles (see column 2). The average length of the next lower is 50 

miles; therefore, the difference represents the length of that downstream segment of the Powder River main stem which is greater in 

size than any other order stream. The number of sixth-order 

streams is thus increased from 3 to 4 (compare columns 3 and 5).

Similarly, 25 miles of the 50-mile length of sixth-order streams 

represents that reach of the sixth-order stream equal or larger in 

size than fifth order. Thus, the number of fifth-order streams is 

increased from 12 to 15. The corrected values of lengths and numbers are listed in columns 4 and 5 of table 8.

When corrected values of stream length are multiplied by corrected numbers of streams, the product represents the total miles 

of segments of streams larger in size than the lower but smaller 

than the next higher order. These segments are considered to be 

uniform in cross section, and the estimated cross-sectional area 

of alluvial fill will be multiplied by total length to approximate the 

total volume of alluvium.

The next problem is estimating the cross-sectional area of the 

reconstructed terrace deposits. The reach of the Powder River 

near Arvada was considered typical of the seventh-order stream 

segment. Field cross sections made by planetable were used in 

connection with sections drawn from detailed topographic sheets to 

arrive at an average cross section. The field conditions along the 

Powder River are nearly ideal for making the required computation 

since the Kaycee fill was deposited in a well-defined valley with

Table 8. Number and length of streams of various orders, Powder River basin above

Arvada, Wyo.

I

orderl

1

2

3

4

5

6

7

2

Average

length 

(miles)

1.4

2.9

5.8

12

25

50

100

3

Number of

streams

Powder River basin 

above 

Arvada

1,400

450

140

40

12

3

1

4 5 6

Corrected to represent

segments of approximately

uniform cross section

Average 

length 

(miles)

1.4

1.5

3

6

12

25

50

Number of 

streams 

above 

Arvada

1,850

590

180

52

15

4

1

Total 

length of 

all streams 

(miles)

2.590

880

540

310

180

100

50

^According to the Horton definition.
PALEOHYDROLOGY 69

steep bedrock walls and, therefore, the valley width could be easily 

determined from the 10-foot contour maps.

Calculation of the volume of slope wash posed a problem. It is 

recognized throughout this study that slope wash graded to the 

Kaycee terrace blankets earlier gravels and bedrock in the areas 

between the rough hilly topography near the drainage divides and. 

the main valley trenches. This blanket of alluvium is in the form 

of a long, thin wedge increasing in thickness toward the river. It 

was decided to eliminate consideration of the volume in these wedges 

because this volume is small compared to that deposited in the 

valley trench. The slope wash within the confines of the valley itself was thought to be of sufficient volume to be included.

The average cross section chosen to represent the Kaycee alluvial 

fill can be seen in comparison with an actual section across the 

Powder River plotted in figure 23, sections A and B. The actual 

section shown at the right is within a reach studied in detail in the 

field. The Kaycee fill, shown in solid black, represents the alluvium of Kaycee age and younger now lying within the valley trench 

and abutting bedrock on the valley sides. It is shown to be only as 

deep as the present stream bed but it probably is somewhat deeper. 

It presumably overlies earlier gravels which partly fill the valley 

cut in bedrock.

On the slopes adjoining the valley, slope wash covers a thin layer 

of gravel, which may be locally absent, and which in turn lies on a 

surface cut on bedrock. As previously explained, the level of the 

stream of Kaycee time was at least as high as a projection of the 

wash slopes to intersection over the valley axis or to the opposite 

valley wall, as in the cross section A of figure 4. It is presumed, 

therefore, that the whole area represented by the solid black, plus 

the crosshatched area, represents an approximation of the cross 

section of Kaycee fill at the end of Kaycee deposition. Of course, 

since Kaycee time, erosion during Moorcroft and Lightning time 

has resulted in loss of part of the Kaycee alluvium and deposition 

of later alluvium in the valley.

Several cross sections were considered in choosing the assumed 

average section (B) shown in figure 23. The average height of 

intersection of the projected Kaycee wash slopes above the present 

stream was about 30 feet. The average width of valley for several 

measured sectio'ns was 2, 500 feet. The average height of the valley 

walls was 50 feet. Thus, the average cross section (B) is in the 

form shown in figure 23, with 30 feet of river terrace alluvium 

covered by two wedges of slope wash.

In a similar manner, cross sections of various sizes of streams 

measured in the field were used as the basis for estimating an 

average cross section for streams of different orders.
70 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

Feet

3800 I 

3700

3600 uU.S.G.S. datum

7TH ORDER STREAM

1000 Feet

I

ASSUMED AVERAGE SECTION, 

KAYCEE FILL ACTUAL ALLUVIAL FILL, 

POWDER RIVER AT MILE 12.4

B

Sqft

100,000 pr

10,000

345 

Stream order

Figure 23. Cross-sectional area of Kaycee alluvial fill in relation to stream order. Diagram 

A shows an actual cross section of alluvium above present stream level (black area), and the 

part of the alluvium eroded away since Kaycee time (hatched area). Diagram B represents the 

assumed average cross section in the same reach of river. Diagram C shows the relation of 

computed cross-sectional area by various sizes of stream valleys to stream order which characterizes the sizes of the valley.

After the average cross sections were determined, the computed 

cross-sectional area of Kaycee fill for each order of stream was 

plotted against stream order. The resulting graph shown as part 

C of figure 23 indicates that the estimated average sections bear 

a consistent relation one to the other.
PALEOHYDROLOGY 71

From the graph of figure 23, then, the area of Kaycee fill for 

each stream order was read and entered in table 9 for the computation of volume of fill, which is expressed finally in acre-feet 

per square mile of drainage area.

The same procedure was used to determine the volume of 

alluvium representing the Lightning fill. It will be noted that for 

each cross section the computed volume does not take into account 

the unknown depths of fill below present stre-am level. The final 

columns, therefore, must be considered minimum values, but the 

error involved in not attempting to estimate the fill between stream 

level and the underlying bedrock or early gravels is probably of 

the same order of magnitude as other errors involved in the 

computation.

During Moorcroft time, erosion resulted in the formation in 

most valleys of a terrace cut on Kaycee alluvium; therefore, no 

attempt has been made to compute the volume of alluvium deposited 

during Moorcroft time.

Figure 9. Computation of volume of alluvium in Kaycee and Lightning fills, Powder

River basin above Arvada

Stream

1

2

3

4

5

6

7

Total

miles 

of

2.590

880

540

310

180

100

50

Kaycee alluvium

Cross-sectional

area of fill

(square feet)

1.000

2,100

4.600

10.000

21,000

46, 000

100,000

Total

volume of fill

(acre-feet)

31x10*

22x10*

30 xlO*

38x10*

46 x 10*

56x10*

60 x 10*

283 x 10*

Lightning alluvium

Cross -sectional

area of fill

(square feet)

150

320

700

1,400

2,900

6,000

12,500

Total volume of

fill

(acre -feet)

47 x 103

34 x 10s

46 x 103

52 x 10s

63 x 10s

73x10*

76 x 10s

391 x 10s

» , ., , , . Kaycee fill Lightning fill Average volume per square mile of drainage area - £- - -= 

470 acre-feet 65 acre-feet

The results may now be examined in the light of other types of 

data. The period of deposition in years for the Lightning fill is 

better known than for the Kaycee fill because of the analogy with 

dated alluvium in the Southwest. Deposition of fills contemporaneous with the Lightning formation probably began about A. D. 1400 

and ended about 1850. The rate of sedimentation of Lightning fill 

based on 450 years would be 0. 14 acre-foot per square mile of 

drainage area per year.

The computation of rate of deposition of the Kaycee fill again 

rests on the assumption that it is correctly correlated with the 

sequence of events elsewhere, but the correlation is probably 

better than the necessary estimate of the span in years representing 

its deposition.
72 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

It is necessary to use a date for the end of the Altithermal time, 

and because no figure is universally agreed upon yet, a round date 

of 4, 000 years ago may be a satisfactory average. This date relies 

in part on the radiocarbon date for the Chiricahua stage of the 

Cochise culture (Flint and Deevey, 1951), and this culture complex 

appears to fit satisfactorily with the end of Altithermal time or the 

beginning of Kaycee time. (See table 7.)

It is also necessary to use a date for the end of Kaycee time. 

For this, one must again lean heavily on the radiocarbon date of 

2,,500 years for the San Pedro phase of the Cochise culture (Flint 

and Deevey, 1951). The span between 4, 000 and 2, 500 years ago 

is the best approximation for the Kaycee period of deposition that 

is possible at present, If, then, 470 acre-feet per square mile of 

drainage area we re deposited in 1, 500 years, the annual rate would 

be 0. 31 acre-foot per square mile.

These estimated rates will now be compared with rates of sediment transportation by modern rivers and rates of accumulation 

of sediment in reservoirs. It must be remembered that during the 

deposition of alluvium in a river valley, sediment is constantly 

being carried out of the valley by the stream. The rate of deposition must then be some fraction of the total sediment production.

Most modern streams in the Middle West and West are either 

degrading somewhat or are relatively stable. Rates of sediment 

movement, therefore, either represent the rate of sediment production from the watershed, as in stable streams; or that rate 

augmented somewhat by erosion of previously deposited valley fill, 

as in degrading streams. Brown (1945) and Brune (1948) compiled 

data on rates of sediment production for the Southwest and Midwest, 

respectively. Their figures for estimated long-term annual sediment production range widely among streams. Roughly, midwestern streams have values of 0.11 to 0. 39 acre-foot per square 

mile per year, and western streams 0. 56 to 1. 10 acre-feet per 

square mile of drainage area per year.

An examination of the difference between total suspended-load 

movement and load deposited will now be made. The Rio Grande 

is aggrading through the middle reaches of its valley, and is an 

example for which good records of both deposition and suspendedsediment load are available. Excluding the reach near the head of 

Elephant Butte Reservoir, the sediment deposited consists of 

roughly one-third of the total load brought into the valley (Thomas 

Maddock, Jr., personal communication).

If, according to this ratio, the estimated rates of deposition 

during Kaycee and Lightning times were increased threefold to 

approximate rates of sediment production, the resultant figures
PALEOHYDROLOGY 73

would be of the same order of magnitude as the rates of sediment 

production observed in present streams, as shown below.

Kaycee fill 

4,000- 2,500 B.C. - 1,500 years..................................

Lightning fill 

A.D. 1,400- 1,850 - 450 years......................................

Modern streams in Midwest................................................

Modern streams in Southwest.............................................

Annual rates (acre-feet per 

square mile per year)

Sediment 

deposition

0.31 

0.14

Sediment production 

from the basin

0.90

0.40 

0.11-0.39 

0.56-1.10

It is admittedly difficult to judge accurately the rates of geologic 

processes because the time span of man1 s observation is so short. 

To judge rates of processes which occurred in a climate different 

from the present is, therefore, even more difficult. The geomorphologist is continually confronted with land forms which would 

be more understandable if relative rates of various processes 

were accurately known.

This explains why an attempt might be made to estimate such 

rates even when computations are frought with many sources of 

possible error. The present computations of rates of deposition 

of the Kaycee and Lightning formations should be viewed with this 

in mind.

One might suppose that the present rates of sediment movement 

in rivers, increased by some unknown amount as a result of man's 

activities, should be relatively high. Particularly in the West, the 

erosion which began in mid-19th century has provided sediment 

from sources inactive for some time previous. It would be conceivable, therefore, that the present rate of sediment movement 

is perhaps of an order many times the geologic norm.

An alternative line of reasoning might lead to a different conclusion. For example, it could be argued that when, at some time 

in the past, deposition of a thick body of alluvium occurred in a 

river valley, it was a result of much larger rates of sediment 

production than are observed today when alluviation of valleys is 

not a dominant process.

Thus, a priori reasoning may result in estimates of sediment 

movement much larger or much smaller than those of the present.

The computation presented here indicates that during alluviation 

under the alternating climate of the Recent period, rates of sediment production are of the same order of magnitude as the rates 

observed in modern streams.
74 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

The relations of rainfall to runoff during the period of accumulation of valley alluvium must have been different from those obtaining at present when some measure of stability appears to 

characterize the rivers of eastern Wyoming. Is it possible, then, 

that rates of sediment production were of the same order as those 

observed at present?

Clearly, when stability is replaced by active gully erosion, as 

when the great valley trenches of the Rio Puerco of New Mexico and 

the Navajo country were being cut, sediment production changed 

from a very low to a very high rate. But in the Rio Puerco where good 

data in the form of successive surveys beginning in 1924 are available, a marked reduction in sediment movement occurred as soon 

as the valley trench had achieved a more or less stable depth. 

After deepening is complete and gradual widening becomes the 

dominant process, sediment production in a period of gully formation rapidly decreases.

Degradationby rapid valley trenching, as has occurred in many 

alluvial valleys of the Southwest, may be considered catastrophic 

as compared to alluviation under different conditions.

Consideration of the present conditions of erosion in New Mexico, 

Arizona, Utah, Colorado, and Wyoming suggest that the catastrophic gullying which began in the middle to late part of the 19th 

century has, to a great extent, run its course. Current extension 

of the small but ramified headwater gullies and gradual widening 

of the main stems are producing sediment at a much lower rate 

than obtained before the first two decades of the present century. 

The quantitative records of sediment movement are, with few exceptions, obtained from reservoirs and stock tanks built later than 

the period of catastrophic gully deepening.

If the computations of sediment production rates in Kaycee time 

have any validity, they suggest that except during the relatively 

short period of maximum arroyo deepening, sediment production 

rates remain of the same order of magnitude during periods of 

valley aggradation, stability, and the long period of headwater 

ramification of gullies constituting the major part of a period of 

valley degradation.

Such an interpretation gains some support from recent work on 

the nature of channel equilibria (Leopold and Maddock, 1953, and 

Wolman, in preparation). These studies suggest that evenduring 

gradual lowering of youthful headwater streams, the alluvial channel retains a quasi-equilibrium. The physical difference between 

a graded stream or reach and one which is not at grade may be 

less than was formerly believed.
RECENT PHYSIOGRAPHIC HISTORY AND THE PROBLEM OF SOIL EROSION 75

This reasoning points to the hypothesis that the physical characteristics of a degrading stream and a stable one are similar. 

Indeed, a truly graded stream can be distinguished only under 

certain conditions, and probably only some time after it has reached 

the condition of grade, as has been suggested by Holmes (1952).

To the extent that these deductions are true, the streams of the 

somewhat cooler and more moist Kaycte time could be pictured 

as very similar to what can be seen in the same area today.

RECENT PHYSIOGRAPHIC HISTORY AND THE PROBLEM OF MODERN SOIL

EROSION

Soil erosion is one of the important agricultural problems of the 

day. The last two decades have seen a change from nearly a total 

lack of appreciation of this problem to a situation in which "accelerated erosion" is a household phrase. The time has come when 

the need for propagandizing the faith is replaced by a need for a 

more fundamental understanding of the erosion process and for 

testing under controlled conditions on large areas various methods 

of control.

It is obvious that the need for food in this country and in the rest 

of the world precludes any possibility of decreasing the total 

acreage of land under plow. As long as land is farmed, it is much 

more vulnerable to the action of erosive forces than it was in 

presettlement eras.

Because it can be so easily demonstrated that removal of vegetal 

cover greatly increases rates of erosion, and because man has so 

obviously affected the protective cover, it is difficult to distinguish 

in detail accelerated from geologic erosion. In fact, a survey of 

the voluminous literature on erosion reveals a great inadequacy 

in our definitions of normal, or geologic, erosion. These words 

are confusing. Normal erosion does not connote vertical-walled 

gullies cutting through a rolling, grassy prairie. Yet there is 

considerable evidence that such conditions were found in some 

places by early settlers in the western High Plains well before 

grazing or other influences of man were important (see Gregg, 

1844, in Leopold, 1951c).

An under standing of our soil erosion problem and of the efficacy 

of control measures requires that we sharpen our tools for distinguishing those features of the modern landscape molded by natural 

forces alone and those related to activities of man. Geomorphology 

can provide techniques that will help us.

The purpose of the following section is to indicate that a study 

of recent physiographic history may aid in separating topographic

303189 O - 54 -
76 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

features developed during the geologically recent but presettlement past from similar features resulting from man's use of the 

land.

RELATIVE AGES OF EROSION FEATURES OF THE PRESENT TOPOGRAPHY

The alluvial valleys of Wyoming, characterized as they are by 

well-developed terrace systems, offer an opportunity for studying 

the relative ages of certain topographic features which are related 

to the terrace system, and for drawing inferences about the processes of aggradation and degradation in a watershed. When a river 

incised itself into the Kaycee fill, the lowered stream bed provided a new base level, represented by the Moorcroft terrace, to 

which tributaries and wash slopes tended to become graded. There 

was initiated, therefore, a period of dissection. Before the dissection had progressed far, the master stream again was lowered 

markedly and then raised a small amount when the Lightning fill 

was inset in the valley trench.

Systems of erosion features developed on the highlands adjacent 

to the streams as a result of this sequence of events. Ascribing a 

relative age to these various erosion patterns is based on the 

premise that lowered base level will induce erosion of tributaries 

which eventually become more or less graded to the new level. 

The practical problem of age determination is one of separating 

the features developed as a result of general lower ing of base level 

following entrenchment of the main stream, from those features 

developed as a result of purely local causes unrelated to the general 

level of the main stream. Two types of erosion features of the 

latter type will now be discussed.

If fora period of time a river flows against one side of the valley 

floor, tributaries entering the valley on the opposite side splay 

detritus on the valley floor, building up a cone or a wash slope 

until the thin edge of the wedge of detritus reaches the master 

stream. If then the stream moves laterally across the valley, 

eroding into the wedge on the original valley floor, the base level 

of the tributary will be effectively lowered and in response it will 

cut down. A new trench will be formed in the valley of the tributary 

which was not caused by a general lowering of the level of the 

master stream, but resulted only from its lateral migration across 

its flood plain. This type of feature has been discussed by Mackin 

(1937).

A second type of erosion feature originating without change in the 

level of the master stream can be cited. For example, a segment 

of wash slope lies far up on the valley side and distant from the 

master stream. It is possible that as a result of a series of heavy
RECENT PHYSIOGRAPHIC HISTORY AND THE PROBLEM OF SOIL EROSION

local storms or local depletion of vegetation, a gully might form, 

which, over a period of time, could erode headward while continuing 

to deposit a fan at its mouth on the original wash slope, in a manner 

characteristic of discontinuous gullies. Such a feature could even 

grow to considerable size. The bed elevation of such a gully would 

be independent of the level of the master stream.

Two examples will now be cited in which a definite relation can 

be established between the erosion features of the tributaries and 

the sequence of events on the master stream.

The first example is a tributary of Twentymile Creek, 12 miles 

west of Lance Creek village. Wyo., in sec. 14, T. 35 N., R. 67 W. 

Twentymile Creek is an ephemeral wash, now characterized in its 

middle reach by an arroyo 15 feet deep and 30 feet wide incised in 

a wide, flat flood plain. The wash is entrenched and has widened 

only little since the last period of degradation. Most of the drainage area is underlain by shale of the Fort Union formation.

There are three terraces along Twentymile Creek, and correlation of these surfaces with the Kaycee, Moorcroft, and Lightning 

formations is based on the criteria discussed earlier. The upper, 

or Kaycee, surface stands 40 feet above the present stream bed. 

This surface grades smoothly to the hills near the watershed divide 

and.thus stands in the same relation to other physiographic features 

as does the Kaycee terrace elsewhere. The upper two terrace 

levels, Kaycee and Moorcroft, are consistently traceable up and 

downstream along Twentymile Creek, but incision of the stream 

into the Lightning surface is discontinuous. The Lightning level 

is, therefore, a terrace in some places but the flood plain in others.

A tributary, called here Revision Draw, was mapped (see fig. 

24)to show its relationship to the terrace features of Twentymile 

Creek.

The Kaycee terrace is lettered K on figure 24. It is dissected 

by long, narrow, flat-floored draws, some extending as far back as 

the hills constituting the divide, but including some short erosion 

channels, such ae Revision Draw pictured here. These flat-floored 

draws enter the valley of Twentymile Creek at the level of a terrace 

(M), remnants of which are traceable along the main valley. This 

is the Moorcroft terrace which stands about 20 feet above the 

stream. The stream is incised about 15 feet below the Lightning 

surface.

In the cross section on figure 24, dotted lines show the extension 

of the Kaycee surface to intersection at the axis of the main valley. 

The intersection occurs 13 feet above the Lightning surface, and 

it is clear that Twentymile Creek could not have been at a lower
78 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

200 0

Figure 24. Topographic map«cross section, and block diagram of Revision Draw, a gully 

system tributary to Twentymile Creek, Wyo.
RECENT PHYSIOGRAPHIC HISTORY AND THE PROBLEM OF SOIL EROSION 79

elevation than that intersection when dissection of the Kaycee 

surface began.

On both sides of the valley, long and short tributary draws cut 

in the Kaycee surface are graded to the Moorcroft terrace level. 

In Revision Draw, the swale (M), accordant with the Moorcroft 

terrace, is about 600 feet long. It is flat-floored, as can be seen 

on the topographic map, and the floor has a grass cover which is 

as dense or more dense than that on the Kaycee surface. The walls 

are concave to the sky and they, too, are covered with grass.

In Revision Draw the Moorcroft surface is incised by a narrow, 

vertical-walled gully (L1 ) 275 feet long, the floor of which is accordant with the Lightning surface. This gully has a vertical raw 

headcut 10 feet in height.

The mouth of this gully is also incised by another very short 

but vertical-walled notch (G) representing the incipient erosion 

feature graded to the present floor of Twentymile Creek.

It is believed that the draw (M)was developed during Moorcroft 

time and represents downcutting in response to the formation of 

the Moorcroft terrace in the valley of Twentymile Creek. The 

Moorcroft is a cut terrace developed on Kaycee formation.

Subsequently, Twentymile Creek incised itself below the Moorcroft surface nearly as deep as the present floor of Twentymile 

Creek. As a result of this lowering of base level, a new erosion 

feature, gully L1 , developed in the floor of Revision Draw. This 

gully was cut about 5 feet below the present level of the Lightning 

surface. The exposure on the gully wall indicates that at maximum 

depth the gully L1 was rounded on the bottom rather than flat. As 

the Lightning fill was inset in the trench, the gully L' was partly 

filled and the present flat floor was developed. During the period 

of stability at the end of Lightning deposition, gully L' widened 

somewhat near its mouth.

It is postulated, therefore, that during the total elapsed time 

since downcutting of Twentymile Creek to the Moorcroft level, 

there has developed in Revision Draw a swale (M) 90Q feetlong. 

Erosion since the dissection of the Moorcroft surface has resulted 

in a gully (L1 ) only 275 feet long. The downcutting into the Lightning 

surface has resulted in an incipient gully only 10 feet long.

The importance of this analysis lies in the use of terraces to 

determine the relative age of erosion features. A striking aspect 

of the example is the small size of features which may, under 

certain conditions, be eroded even in a long period of time. The 

second important feature is that vertical walls of alluvium, com-
80 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

pletely bare of vegetation, may be of considerable age. They need 

not represent erosion in the past 70 years, as a first glance might 

lead one to surmise.

Revision Draw has been chosen as an example because erosion 

features of different ages are so well defined. Many draws nearby 

having flat floors graded to the Moorcroft terrace extend all the 

\vay to the hills, a quarter- to a half-mile away. Gullies graded to 

the Lightning level are commonly nearly as long, terminate in 

head cuts, and have vertical walls in most places.

The amount of headward cutting during these various stages 

appears to depend mostly on the manner in which water is concentrated by the topography of the hills at the watershed divide. Revision Draw lies at the foot of a long sloping tableland, undissected 

by channels, and below a zone where apparently no appreciable 

concentration of water occurs.

In contrast to the example just discussed, there are two types of 

streams not subject to direct base-level control by the mdster 

stream.

In the first, outcrops of bedrock interrupt the grade of numerous 

washes dissecting the hills, and yet conspicuous remnants of what 

might appear to be alluvial terraces occur on the sides of each wash. 

In many washes, remnants of these levels are traceable only short 

distances up or downstream, and therefore no age assignment can 

be given them.

The other type is even more common than the one just described. 

It is typical to see more than a single stage of dissection even on 

ephemeral tributaries far removed from direct base-level effects 

of the main stream. An example, NeardarkDraw, a small tributary 

of the Powder River near Arvada, Wyo., is shown in figure 25. 

From the contours and cross sections, two stages of dissection can 

be recognized. The' surface was once gently rolling and consisted 

of rounded ridges separated by swales having gentle, dish-shaped 

cross sections (dashed line in cross section B-B1,fig. 25). Incised 

in these swales is a system of broad U-shaped channels, with almost flat bottoms and with sides concave to the sky. Over considerable lengths of such channels, the flat-bottomed, U-shaped draws 

meet the earlier, more gently rounded swales in a slight escarpment at an angle of about 60°. The U-shaped channels are generally 

well vegetated both on the floors and sides. The floors are characteristically covered with western wheat grass (Agmpymn smithii).

Cut into the U-shaped channels is a system of active discontinuous 

gullies with bare, vertical head cuts (G in cross section 3 -£?') The 

gullies become more shallow downstream and change to short, flat 

segments of deposition. The aggrading reaches of most of them
RECENT PHYSIOGRAPHIC HISTORY AND THE PROBLEM OF SOIL EROSION 81

400 Feet

DIAGRAMMATIC 

CROSS SECTIONS

100 200 300 400 500 600 700 Feet

Figure 25. Topographic map and profile of Neardark Draw, a small tributary to the Powder 

River near Arvada, Wyo. The draw is graded to an extensive remnant of the Moorcroft terrace which at this place separates by nearly one-half mile Neardark Draw from the main 

Powder River channel.
82 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

are densely covered with wheat grass. The head cuts of the discontinuous channels range from 1 to 10 feet in height. Though 

there is considerable variation from place to place, there are 

many small tributary basins comparable to the one pictured in 

figure 25 in the hills bordering the Powder River valley.

The valley floor of Neardark watershed is graded to the Moorcroft terrace bordering the Powder River. It is possible, therefore, that the earlier stage of erosion represented by the dishshaped channel is the headwater expression of the drainage system 

developed at the time when the Powder River flowed at the level of 

the Kaycee terrace. The U-shaped channels would then represent 

cutting, probably followed by some aggradation which formed their 

flat floors. This occurred during the time when the Powder River 

incised itself into the Kaycee surface toform the Moor croft terrace 

level.

If that is what took place, the present discontinuous gullies 

(like G on fig. 25) could be interpreted as having their beginning 

either during the period of erosion following Moorcroft time, or 

in the last 70 years coincident with the general but slight degradation 

of the main streams into the Lightning surface. According to the 

latter interpretation, dissection of the Moorcroft surface is not 

represented by any remnant feature in the uplands of this locality.

In summary, mention has been made of three types of relationships between erosion features in the uplands and the terrace 

system along the major streams. The first type, Revision Draw, 

indicated a direct relation between tributary draws and the terrace 

system of a moderate sized stream. The relation in that example 

was clearly a direct base-level control. The second type of relation is represented by those headwater draws which exhibit local 

"terrace levels" but in which the "terrace" remnants are not traceable surfaces. In many such tributary valleys, outcrops of bedrock 

in the channel exclude the possibility of any control by the main 

valleys. The third type of relation is represented by Neardark 

drainage basin, a headwater basin removed from direct base-level 

control of the main Powder River. This small drainage exhibits 

a terrace above the present stream bed, and the latter is now 

undergoing degradation by discontinuous gullies.

A question important to an understanding of the mechanism of 

erosion may now be asked: Deposition in the main valleys and in 

major tributaries implies erosion somewhere in the headwaters 

in order to provide a source for the deposited materials. Why, 

then, would deposition downstream not be correlative with erosion 

in the smaller washes and draws of the uplands?
RECENT PHYSIOGRAPHIC HISTORY AND THE PROBLEM OF SOIL EROSION 83

The following discussion of this question is meant to apply to 

the great areas of rolling plains or uplands of moderate relief, and 

it does not involve the processes in mountain valleys.

The authors have dug trenches through the valley alluvium in 

small headwaters draws, and have extended by shovel the cross 

section exposed in the headcuts of discontinuous gullies in the 

uplands. Even headwater valleys only 5 to 15 feet wide consist of 

several feet of alluvium covering the bedrock. This alluvial mantle 

was, everywhere, considered to be of Kaycee age because its 

surface can be traced in a smooth unbroken curve down to merge 

into the Kaycee terrace.

The terraces of the master streams can be traced directly into 

many tributaries of moderate size, indicating that erosion of alluvium in the master streams was accompanied by gully erosion in 

tributaries, even the ephemeral ones.

Erosion of the major valleys was generally accompanied by 

erosion of tributary valleys. Likewise, aggradation in the main 

stream valleys was accompanied by deposition in tributary valleys 

and draws. Probably these deposits were derived by mass movement and sheet erosion on upland slopes.

It seems logical that the shift in relations between runoff and 

vegetation which caused erosion of all major streams would also 

affect the smallest tributary valleys in a similar way at the same 

time. The alluvial material carried and deposited by the river was 

derived from the surrounding hills and slopes leading to the main 

channels. As the deposit in the main valley gradually increased 

in thickness and height and finally more than filled the valley 

trench, the wash slopes that were graded to the main river accumulated material which blanketed all except the most prominent 

hills and uplands. The area of upland from which alluvial materials 

were being derived by erosion shrank, while the area of deposition 

increased. This doubtless had the effect of gradually decreasing 

the rate of rise of the main valley bed. There were both an expanding area of deposition and a contracting area from which the 

materials were ultimately derived.

THE EROSION PROBLEM IN THE WEST

Aperiod of arroyo cutting or valley trenching began in the Southwest about 1885 with serious social and economic consequences. 

It is the view of some writers that the arroyo cutting can be ascribed entirely to the misuse of the land: overgrazing, logging, 

fires, and other misuses (Bailey, 1935; Bailey, Craddock, and 

Croft, 1947; Thornthwaite, Sharpe, andDosch, 1942; and others).
84 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

Another point of view, expressed primarily by Bryan (1925, 1941), 

is that overuse of the land was a triggerpull which timed a change 

about to take place as a result of climatic shift.

With regard to the sequence of aggradation and degradation indicated by stratigraphic studies, Bryan (1941, p. 233) says, 

"Some general causes other than overgrazing must be sought for 

the pre-Columbian episodes of dissection. Whatever the cause of 

recent arroyos, overgrazing by domestic animals can have had no 

influence on the formation of the early arroyos. "

Thornthwaite, Sharpe, and Dosch (1942) deny that climatic shift 

is necessary to explain the alluvial sequence. They hold (p. 89) 

that "***depositionat the lower ends [of headward-cutting arroyos] 

by back-filling of the channels***produced waves of sedimentation 

that migrated up valley. " They believe "***that the explanation of 

successive deposition and removal of fill lies in sedimentary processes and irregular occurrences of heavy storms rather than in 

any change of climate. "

The stratigraphic evidence which has accumulated since that 

discussion has certainly added weight to Bryan's climatic interpretation of the pre-Columbian sequence. The comparability of 

sequences between areas is the basic support for the climatic 

hypothesis.

In explaining the recent epicycle of erosion, the general coincidence between initiation of arroyo cutting and the advent of 

heaviest grazing is agreed upon by all concerned. Moreover, the 

efficacy of intensive land use in promoting soil erosion is not at 

issue. The point of major disagreement is whether climatic change 

or misuse of land has been a greater cause of erosion.

From the assertion that climatic shift has, in part, been responsible for the arroyo problem, the conservationist is prone to 

draw the following inference:

If***a progressive desiccation of climate has brought about the dissection of the western lands, there is little hope that man can stem the quickened erosion. If***misuse of 

the land***has been the cause, there is good possibility of improving the land by improving the land use. (Thornthwaite, Sharpe, and Dosch, 1942, p. 2.)

The implications of the results of geologic studies of postglacial 

climatic variations on current problems of conservation and land 

use might better be viewed in the following light. Climatic variation 

has characterized the postglacial and historic period, as well as 

the Pleistocene epoch. There is in progress at present a climatic 

variation which has affected at least the major part of the Northern 

Hemisphere, and it is discernible in the climatic records of the 

Southwest (Leopold, 1951a)as well as in the geologic record of the
RECENT PHYSIOGRAPHIC HISTORY AND THE PROBLEM OF SOIL EROSION 85

same area. As shown in this report, the configuration of the whole 

landscape bears the imprint of this Recent climatic history.

A shift in climate may act on soil and vegetation in the same 

way as overuse by man, or the shift may act in an opposite way. 

If our present erosion problems are complicated by an interaction 

of land use and a varying climate, in the interest of better use of 

land and water we must recognize the action of both. We should 

study, when possible, the effects of each separately, and design 

our land treatment programs to insure maximum benefits under 

these conditions. Recognition of the current climatic variation does 

not require an abandonment of measures for improvement of land 

use. It should, in fact, spur us to greater effort to protect key 

watersheds from overuse, and currently to balance utilization 

with the varying capacities of watersheds. It should, likewise, 

point to the importance of spending our conservation dollar on areas 

where climatic and land use factors combine to justify reasonable 

hope of success.

Erosion features, such as gullies, observable over great areas 

in Wyoming, are not all of the same age. The present report outlines some of the problems of determining the ages of features 

whose outward aspects are sufficiently similar to suggest that they 

are all related to the recent cycle of arroyo cutting. Evaluation of 

the effects of land use and programs of land use improvement should 

recognize the existence of a difference in age of erosion features. 

Further research of this nature appears desirable.

In the present report, estimates are made of the rate of deposition 

of valley alluvium during the postglacial but pregrazing periods of 

aggradation. These estimates suggest that rates of sediment production during those periods were similar to those of the present 

for the same area. The similarity in rates of sediment production, 

past and present, emphasizes the similarity in the hydrologic 

processes which characterize the effect of a climatic shift and the 

effect of depletion of vegetation by overuse. This similarity of 

rates suggests also similarity in end results. Study of the magnitude of depositional and degradational processes of the past provides some picture of the possible end points of the present erosion 

epicycle.
86 POSTGLACIAL CHRONOLOGY FOR ALLUVIAL VALLEYS IN WYOMING

REFERENCES CITED

Albritton, C. C., and Bryan, Kirk, 1939, Quaternary stratigraphy in the Davis Mountains,

trans-Pecos, Tex.: Geol. Soc. America Bull., v. 50, p. 1423-1474. 

Antevs, Ernst, 1928, The last glaciation: Amer. Geog. Soc., Research ser. 17, 292 p.

 1948, The great basin, with emphasis on glaci.al and postglacial times: part

3, Utah Univ. Bull., v. 38, no. 20, p. 168-191. 

Bailey, R. W., 1935, Epicycles of erosion in the valleys of the Colorado Plateau: Jour.

Geology, v. 43, no. 4, p. 337-355.

Bailey, R. W., Craddock, G. W., and Croft, A. R., 1947, Watershed management for summer flood control in Utah: U. S. Dept. Agri. Misc. Pub. 639. 

Barbour, E. H., and Schultz, C. B., 1932, The Scottsbluff bison quarry and its artifacts:

Nebraska State Mus. Bull., v. 1, no. 34, p. 283-286. 

Blackwelder, Eliot, 1914, Post-Cretaceous history of the mountains of central western

Wyoming: Jour. Geology, v. 23, p. 307-340. 

Brown, C. 3., 1945, Rates of sediment production in Southwestern United States: U. S.

Soil Conserv., SCS-TP-58, 40 p. 

Brune, G. M., 1948, Rates of sediment production in Midwestern United States: U. S. Soil

Conserv., SCS-TP-65, 40 p. 

Bryan, Kirk, 1925, Date of channel trenching (arroyo cutting), in the arid Southwest:

Science, v. 42, no. 1607, p. 338-344.

 1934, Geomorphic processes at high altitude: Geog. Rev., v. 24, p. 655 656.

 ; 1941, Pre-Columbian agriculture in the Southwest, as conditioned by periods 

of alluviation: Assoc. Am. Geogr. Annals, v. 31, no. 4, p. 219-242.

-1950, The geology and fossil vertebrates of Ventana Cave, in Haury, W. W.,

The stratigraphy and archeology of Ventana Cave, Tucson, Univ. Arizona Press, 599 p. 

Bryan, Kirk, and Albritton, C. C., 1943, Soil phenomena as evidence of climatic changes:

Am. Jour. Sci., v. 241, p. 469-490. 

Bryan, Kirk, and McCann, F. T., 1943, Sand dunes and alluvium near Grants, N. Mex.:

Am. Antiquity, v. 8, p. 281-290.

Bryan, Kirk, and Ray, L. L., 1940, Geologic antiquity of the Lindenmeier site in Colorado: Smithsonian Misc. Coll., v. 99, no. 2, 76 p. 

Davis, W. M., 1902, River terraces in New England: Harvard Univ. Mus. Comp. Zoology

Bull., v. 38, p. 281-346. 

Evans, G. L., and Meade, G. E., 1945, Quaternary of the Texas High Plains: Texas

Univ. Pub. 4401, p. 485-507. 

Faegri, K., 1950, On the value of paleoclimatological evidence: Royal Meteorol. Soc.

Centenary Proc., p. 188-195. 

Flint, R. F., and Deevey, E. S., 1951, Radiocarbon dating of late-Pleistocene events:

Am. Jour. Sci., V. 249, p. 257-300. 

Hack, J. T., 1942, Tjie changing physical environment of the Hopi Indians: Peabody Mus.

Nat. History Papers, v. 35, no. 1, p. 3 85. 

Harbeck, G. E., and Langbein, W. B., 1949, Normals and variations in runoff, 1921-45:

Water Res. Rev., supp. 2, U. S. Geol. Survey. 

Holmes, D. C., 1952, Stream competence and the graded stream profile: Am. Jour. Sci.,

v. 250, p. 899-906. 

Horton, R. E., 1945, Erosional development of streams and their drainage basins: Geol.

Soc. America Bull., v. 56, no. 3, p. 275 370. 

Hoyt, W. G., 1936, Studies of relations of rainfall and runoff in the U. S.: U. S. Geol.

Survey Water-Supply Paper 772. 

Huffington, R. E., and Alb'ritton, C. C., 1941, Quaternary sands on the southern High

Plains of western Texas: Am. Jour. Sci., v. 239, p. 325-338. 

Hunt, C. B., and Sokoloff, V. P., 1950, Pre-Wisconsin soil in the Rocky Mountain region,

a progress report: U. S. Geol. Survey Prof. Paper 221 G. 

Judson, S., 1953, Geologic antiquity of the San Jon site, eastern N. Mex.: Smithsonian

Misc. Coll., v. 121, no. 1, 70 p. 

Kelley, J. C., Campbell, T. N., and Lehmer, D. J., 1940, The association of archeological materials with geological deposits in the Big Bend region of Texas: Sul Ross State

Teachers Coll. Bull., v. 21, no. 3. 

Leopold, L. B., 1951a, Rainfall frequency, an aspect of climatic variation: Am. Geophys.

Union Trans., v. 32, no. 3, p. 347-357. 

 1951b, Pleistocene climate in New Mexico: Am. Jour. Sci., v. 249, p. 152-

168 and 399.

-1951c, Vegetation of southwestern watersheds in the nineteenth century:

Geog. Rev., v. 41, p. 295-316.
REFERENCES CITED 87

Leopold, L. B., and Maddock, Thomas, Jr., The hydraulic geometry of stream channels 

and some physiographic implications: U. S. Geol. Survey, Prof. Paper 252.

Leopold, L. B., and Snyder, C. T., 1951, Alluvial fills near Gallup, N. Mex.: U. S. Geol. 

Survey, Water-Supply Paper 1110-A.

Lueninghoener, G. C., 1947, The Post-Kansas geologic history of the Lower Platte Valley area: Nebraska Univ. Studies (new ser.), no. 2, 82 p.

Lysgaard, L., 1949, Recent climatic fluctuations: Folio, Geogr. Danica, torn 5, 85 p.

Mackin, J. H., 1937, Erosional history of the Bighorn Basin, Wyo.: Geol. Soc. America 

Bull. 48, p. 813-894,

McDonald, C. C., and Langbein, W. B., 1948, Trends in runoff in the Pacific Northwest: 

Am. Geophys. Union Trans., v. 29, no. 3, p. 387-397.

Moss, J. H., 1951, Early man in the Eden Valley: Pennsylvania Univ. Mus. Mon., 124 p.

Nikiforoff, C. C., 1936, Some general aspects of chernozem formation: Soil Sci. Soc. 

America Proc., v. 1, p. 333 342.

 1937, General trends of the desert type of soil formation: Soil Sci., v. 43, 

p. 105-125.

Oltman, R. E., and Tracy, H. J., 1951, Trends in climate and in precipitation-runoff relation in Missouri River basin: U. S. Geol. Survey Circ. 98.

Pettier, L. C., 1949, Pleistocene terraces of the Susquehanna River, Pa.: Pennsylvania 

Geol. Survey, 4th ser. Bull. G 23, 158 p.

Petterssen, S., 1949, Changes in the general circulation associated with the recent climatic variation: Geografiska Annaler, HSfte 1-2, p. 212-222.

Robinson, G. W., 1949, Soils, their origin, constitution and classification: New York, 

Wiley and Sons, 573 p.

Rolfe, B. N., and Jeffries, C. D., 1952, A new criterion for weathering in soils: Science, 

v. 116, p. 599-600.

Sayles, E. B., and Antevs, Ernst, 1941, The Cochise culture: Madallion Papers no. 29, 

Gila Pueblo, Globe, Ariz., 81 p.

Schove, D. J., 1950, The climatic fluctuation since A. D. 1850 in Europe and the Atlantic: Royal Meteorol. Soc. Quat. Jour., v. 76, no. 328, p. 147-165.

Schultz, C. B., and Eiseley, L., 1935, Paleontological evidence for the antiquity of the 

Scottsbluff bison quarry and its associated artifacts: Am. Anthropologist, v. 37, no. 2, 

new ser., p. 287-306.

Schultz, C. 3-., Lueninghoener, G. C., and Frankforter, W. D., 1951, A graphic resume of 

the Pleistocene of Nebraska: Nebraska Univ. State Mus. Bull., v. 3, no. 6, 41 p.

Thornthwaite, C. W., Sharpe, C. F. S., and Dosch, E. F., 1942, Climate and accelerated 

erosion in the arid and semiarid Southwest, with special reference to the Polacca Wash 

drainage basin, Arizona: U. S. Dept. Agr. Tech. Bull. 808, 134 p.

Willett, H. C., 1949, Long period fluctuations of the general circulation of the atmosphere: Jour. Meteorology, v. 6, no. 1, p. 34 50.

 1950, The general circulation at the last (Wurm) glacial maximum: Geografiska Annaler, HSfte 3-4, p. 179-187.

Wolman, M. G., in preparation, The channel characteristics of the Brandywine Creek, 

Pa.: U. S. Geol. Survey Prof. Paper.

INDEX

Page 

Aggradation, climatic influence......... 65-66

rate of, by modern streams............... 72

compared with sediment production..................................... 72-73

method of computation...............66-68

Arvada formation, features................ 8, 10

frost action.....................,...........19, 20

Calcium carbonate, concentration in

relation to depth.................... 24-25

concentration related to soil texture. 52 

depth of zone...............................50-51

pedologic origin........................... 50-51

Caliche crust, formation.................... 10

Clear Creek, features of deposition..... 61-65

Climate, fluctuations...................... 55-56

in Altithermal time..................... 54-55

in post-Altithermal time............... 55

regional similarity....................... 57

Deposition, variables of................... 61-66

Erosion, caused by overuse of land. 75, 84, 85 

climatic influence.................. 57, 84, 85

features, ages of.......................... 76-83

in Altithermal time...................... 55

Faegri, K. , quoted.......................... 57

Fills, "inset* relation....................... 5-6

"overlapping" relation................... 5-6

relationship to terraces................... 5

stratigraphic relations..................... 5

Fort Union formation, features............. 19

Glacial activity, late Wisconsin time... 53 

Gravel deposits, late Wisconsin time.... 53

Kaycee formation, aggradation rate.....71-72

contact with bedrock...................... 42

correlation with Cody terrace........... 33

correlation with Fivemile Creek

terrace.................................. 38

correlation with Muddy Creek terrace. 38 

correlation with terrace on Middle

Fork of Popo Agie River............ 39

correlation with terrace on Pass

Creek ................................... 39

deposition..................................... 55

description of.............................. 21-25

mineral composition, analysis.......... 25

relationship to glacial sequence........ 49

size and sorting of alluvium............. 25

terrace height, Belle Fourche River.. 33 

Bighorn River basin.................... 40

Cheyenne River basin................. 43

Powder River basin..................... 29

upper Clear Creek...................... 48

type locality................................ 11

volume...................................... 70-71

Page 

Lenore terrace, correlation............... 35

Lightning formation, aggradation rate.. 71 

correlation with Fivemile Creek

terrace................................ 38

correlation with Muddy Creek

terrace................................ 38

correlation with terrace on Middle

Fork of Popo Agie River.......... 39

correlation with terrace on Pass

Creek................................. 39

description................................. 11

terrace height, Belle Fourche River. 33 

Bighorn River basin................... 40

Cheyenne River basin................ 43

Powder River basin................... 29

upper Clear Creek.................... 48

type locality.............................. 11

volume..................................... 71

Lysgaard, L., quoted...................... 56

Moorcroft formation, correlation with

Fivemile Creek terrace.......... 38

correlation with Muddy Creek

terrace............................... 38

correlation with terrace on Middle

Fork of Popo Agie River......... 40

correlation with terrace on Pass

Creek................................ 39

description............................... 47 -48

terrace height, Belle Fourche

River................................ 33

Bighorn River basin................. 40

Cheyenne River basin.............. 43

Powder River basin................. 29

upper Clear Creek.................. 48

Moraines, correlation of terraces

with................................. 47

Paleohydrology, defined................ 60

Paleosol, defined......................... 10

profile development................... 51

Petterssen, S. , cited..................... 56

Powder River, features of deposition. 61-65

Sand dunes, dating....................... 38

Sediment production, rates............. 72-75

Slope wash, on terraces................. 46

volume................................... 69

Soil, pedalfer-type, significance..... 51 

Stream order, explained................ 68, 71

Terrace deposits, volume............... 68-71

Terraces, age of erosion features..... 76-83

height.....................l2, 14, 15, 46, 47

morphology.............................. 12

regional correlation.................... 58-59

relationship to alluvial fill........... 5

strath...................................... 3

stratigraphic characteristics..... 12, 15-16

89