Erosion and Deposition in 

the Loess-Mantled Great 

Plains, Medicine Creek 

Drainage Basin, Nebraska

GEOLOGICAL SURVEY PROFESSIONAL PAPER 352-H

Prepared as part of a program of the 

Department of the Interior for development 

of the Missouri River basin and part of the 

soil and moisture program
Erosion and Deposition in 

the Loess-Mantled Great 

Plains, Medicine Creek 

Drainage Basin, Nebraska

By JAMES C. BRICE

EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

GEOLOGICAL SURVEY PROFESSIONAL PAPER 352-H

Prepared as part of a program of the 

Department of the Interior for development 

of the Missouri River basin and part of the 

soil and moisture program

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1966
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEW ART L. UDALL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

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

Washington, D.C. 20402 Price 55 cents (paper cover)
CONTENTS

Abstract ______.___ _ __ _____..____ _____. ,___-_-____ ___

Introduction __ __________..___._____- .__.___.___..___-__. ____ -__

Climate, by Cloyd H. Scott _.__._.._._._.____ _....._..

Vegetation and paleoclimate ___.._______ ___ ___ ___ __ ____-____

Climax plant communities ______________-__ ___-__-____ _

Characteristics of native grasses _____________________________

Effects of drought ________.._.._______________________________....

Effects of land use ______________________________________________________

Native trees and dendrochronology _ __ _._-__

Pre-Pleistocene rocks ______ _________ _ __________________________

Unexposed rocks _____-__________.________________________________ ______

Exposed rocks - ___ _______________________________________________

Niobrara Formation __________________________________________

Ogallala Formation ________________________________________

Pleistocene and Recent deposits ________________________________

Terraces -___ ____--________________ __ ____________________________

General stratigraphy of the Pleistocene and 

Recent _ _ ._ ____-__ ____________ _______________ ____ 

Stratigraphy on Cedar Creek near Stockville ________

Stratigraphy on Cut Canyon near Curtis ______________

Stratigraphy on Elkhorn Canyon near Maywood _ 

Loveland Formation and Sangamon soil ________________

Peorian Loess, Brady soil, Bignell Loess, and 

modern soil ______________________________

Stockville terrace deposits ________________________________

Mousel terrace deposits ________________________________________

Recent alluvium ________________ .________________________ ______

Significance of carbonized fragments of grass ________

Sand dunes _______________.______________________________________.__ 

Archeology and human occupation ________________________

Results of archeologic investigations ________________________

Settlement and land use __________________________________

Page 

255 

255

258

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268

270

271

272

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275

278

278

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-i .'. Page 

Drainage system ______.L__£ L_____ - _ - 282

Evolution of the drainage system ___._______-_ - 282

Morphometry ___ ___ _ __ _ _.__ - ~ 284 

Drainage transformation and variations in drainage texture _______________. __ 288

Gully erosion __._._ __.._.__..________-____ 290 

Definition and classification of gullies __________- _- 290

Age and activity of erosional scarps __ _____ 291

Channel scarps and valley-bottom gullies .__ ___ 291 

Development of valley-bottom gullies ____________ 295

History of late Recent gullying on Dry Creek ______ 300

Valley-head and valley-side gullies ________ __ 301

Measurement of valley-head and valley-side gullies

on Dry Greek ____.__ __ 304

Areal distribution of gullies _.._-__ - 307

Formation of valley-head and valley-side gullies ___ 309 

Gullying and land use ______-__ _ _ 313

Control of gullies __________ ___ -_-_--- _ __- 314

Suspended sediment and the hydraulic geometry of 

channels, by Cloyd H. Scott __ __ _ 315

Hydraulic relations at a section and in a downstream direction ___________________ 315

Suspended-sediment discharge relations ___ 321

Particle-size distributions of suspended sediment

and bed material _._____.__- _ __ . - 322

Relative sediment contributions of the major tributaries _________________ -___ _ _ -_ _ 325

Geomorphic properties in relation to water and sediment discharge _ _____________________ _ ^_ __ _ 328

Summary and conclusions ____-___ __ 332

References __-_-____-_____ __ 333

Index .. _____._ ..__._______ __ 337

ILLUSTRATIONS

Page 

FIGURE 175. Regional physiographic map _ ________-._______-______ _ _ - __ __ __ - 256

176. Location map _____________________________ _______________-,,___-__ ____-_ - _ __- 257

177. Photograph of typical relief in southern part of basin _ __________ _ _ - 258

178. Graph of average monthly temperature and maximum, average, and minimum

monthly precipitation at Curtis, Nebr., 1931-55 ____ ________ _ __ 259

179-180. Graph of annual precipitation, 1895-1960 

179. Curtis, Nebr. _ ___ _._____ __ _ _________________________________________ 260

180. McCook, Nebr. .. _._._._. __ _. ____.._.______.__ ________.___._ 261

181. Graph of rainfall intensity-duration-frequency curves for Curtis, Nebr., 1951-58 ____ 262

182. Photographs showing effect of land use on native vegetation _______________________ 264

183. Geologic section across lower tip of basin ___________________________________________________._._.._ 266

184. Geologic section across the basin _______________________________________________________________________________ 267

185. Section showing general topographic and stratigraphic relations of Pleistocene and

Recent deposits .__________ ____________ _______________________________________________________________ 268

186. Channel profile, valley flat profile, and terrace profiles along the main course of

Medicine Creek ________ _________________ ___.-________ ___________________.________________________.___.... 270

ill
IV CONTENTS

Page FIGURES

187-189. Profile and geologic section 

187. On Cedar Creek _______________________________________________________ 271

188. Along road entering Cut Canyon _ __ __ ____________ ________ _...__ 272

189. On Elkhorn Canyon ______ __________._ ___ __ ___ __ _ ______________.___ 273

190-193. Photographs showing 

190. Terrace sequence and valley fills along Elkhorn Canyon ____ _.____________ 273

191. Valley fill of the Peorian Loess set unconformably against Sangamon soil

and Peorian Loess _ _-___ __ __ _-_ _________._.__-______-____ 274

192. Peorian Loess overlying A horizon of Sangamon soil ___ _ _ ___________ _ 276

193. Banding in Recent alluvium, Dry Creek ____________________________.___ __ 279

194. Block diagram showing evolution of the relief since deposition of the Peorian Loess... - 283

195. Photographs of remnants of the side slopes and valley flats of former drainage

systems ____________________ ____-______ ___________.______________ 284

196. Map showing area of capture of North Plum Creek by Deer Creek _________________. 285

197. Maps showing variations in drainage texture ________________- ____________ __ __ 287

198. Graph showing mean channel length in relation to channel order ____________________ 289

199. Graph showing number of channels of each order in relation to channel order __ __ _ 290

200. Composite sketch showing varieties of valley-bottom gullies ______________________ 292

201. Map of head scarps in major valley-bottom gullies ____________________________________ 293

202. Profiles of valley and channel for some major tributaries __ ____ ___ _____ . 295

203. Graph showing local valley slope in relation to drainage area ___ __ 296

204. Photographs of typical valley-bottom gullies ________________________ ________________ 297

205. Profile showing changes in a large valley-bottom gully on Dry Creek ________ __ __ 298

206. Profiles of a large valley-bottom gully in a tributary of Curtis Creek Canyon ___ . 299

207. Profile showing changes in a gullied tributary of Dry Creek ___ _. _____ __ ____ - 300

208. Profiles of channel, valley flat, and terraces on Dry Creek ________________ ___ 301

209. Cross profiles of Dry Creek ___________ _________________________ __________________________-_ 302

210. Photographs showing downstream changes in channel of Dry Creek _____ __ ______ 303

211. Composite sketch showing varieties of valley-head and valley-side gullies ________ 304

212. Photographs of valley-head and valley-side gullies __ __ _.___________________ ____-__- 305

213. Graph of cumulative frequency distribution of enlargements of valley-head and valleyside gullies on Dry Creek _ ._ _ ________ _ _ __-___ ___.__ __ _ ___ __ 306

214. Aerial photograph of a severely gullied area on upper Dry Creek ___________________ 308

215. Map showing areal frequency distribution of active valley-head and valley-side

gullies _ _____._-_______ ______ ______________________ __-__-________________ 310

216. Graph showing frequency of active valley-head and valley-side gullies in relation to

area of upland and adjusted frequency of first-order channels _____ _ ______. 311

217. Profiles and plan view of a large valley-head gully ______________________________ _ _ 312

218. Profile of a large valley-head gully _______________________________________________________ 313

219. Photograph of the head scarp of a small valley-head gully on Dry Creek ________________ 314

220. Hydrographs of daily mean flows equaled or exceeded about 1 percent of time _________ 316

221. Graph showing change of width, depth, and velocity with increasing discharge at a

section, Dry Creek near Curtis _- _ -_-__ .__________ ___________ _ ___ __ -__ 317

222-223. Graph showing change of width, depth, and velocity in a downstream direction for 

channels of 

222. Perennial streams ____-_-_______ -______ ________-__ _____________..._ 319

223. Ephemeral streams _____-____._________________________________^______________ 320

224-225. Graph showing change of suspended-sediment load with increasing discharge at a 

section 

224. Perennial streams ___ _ ______-________.______________________________________ 323

225. Ephemeral streams ____ _____________________________________________________________ 324

226-231. Graph showing 

226. Size distribution of suspended sediment ______________________________________ 325

227. Size distribution of bed material ______ ________ _ __ _ _____________... 326

228. Cumulative water discharge and sediment discharge per square mile _________ 327

229. Mean channel slope in relation to channel order ______________________________ 328

230. Adjusted frequency of first-order channels in relation to mean valley-side 

slope, mean slope of first-order channels, and mean length of firstorder channels _-_ _ ________ ___ ___ ____________ ______________ 329

231. Slope of first-order channels in lower Dry Creek subbasin in relation to

length ____ _-___ . ______ ________ _____________________________ 330

232. Trial graph showing multiple linear regression of sediment discharge in relation to 

relief ratio, percentage of upland, and adjusted frequency of first-order channels ______ _______________ __._________________________________________ __ 331
CONTENTS

TABLES

Page

TABLE 1. Thickness and percentage of each rock type in seven exposed sections of the Ogallala

Formation .______...._..___._.._.._......_......._......_ __ _ _____-______-_ 265

2. Correlation of stratigraphic units and terraces of the Pleistocene and Recent in Nebraska and Wyoming. ._ .____._ __.........................._ _._._..... _ _ _.__....._.. 269

3. Measured and derived properties for the Medicine Creek basin and its major subbasins...... 288

4. Drainage system properties, listed according to channel order, for major subbasins of

the Medicine Creek basin ._.___..._......_._....._....... ._.._. ._...__- __ .-..__... .____ 294

5. Measurements relating to the size and topographic setting of major valley-bottom gullies ___ 299

6. Number of gullies according to type and size in the Medicine Creek basin and in major

subbasins ___________________-_________-_. .______________ 307

7. Gully frequencies and related data for subbasins of the Medicine Creek basin . _______ 309

8. Values of 6, /, and m for streams in Medicine Creek basin ..._._.._ .._.... ...-.__...._.._. 321

9. Areas in upland and valley flat in comparison with areas in two categories of land use 330

EROSION AND DEPOSITION IN THE LOESS-MANTLED GREAT PLAINS 

MEDICINE GREEK DRAINAGE BASIN, NEBRASKA

By JAMES C. BRICE

ABSTRACT

The Medicine Creek basin is representative of the loessmantled Great Plains in climate, surface materials, and 

relief forms, but its relief, degree of dissection, and rate 

of erosion are higher than average. In operation, if not in 

rate, processes of erosion and deposition in the basin are 

considered to be representative of loess-mantled regions in a 

semiarid or subhumid climate.

About 12,000 years ago, the valley fill of the Peorian 

Loess was incised and the drainage system was ramified to 

approximately its present extent. During the subsequent 

episode of deposition (about 1,000-5,000 yr ago), the deposits 

of the Stockville terrace accumulated and the valley sides 

were graded. The formation of the Stockville terrace was 

followed by a minor episode of deposition, another of valley 

incision, and finally the accumulation of the late Recent 

alluvium, which has been intermittently incised during the 

past 500 years.

The property of the drainage system that is most useful 

in accounting for the areal distribution of gullies is called 

adjusted channel frequency, in the derivation of which the 

drainage basin area is adjusted by subtracting the area of 

upland. The slope of the exponential curves, relating mean 

channel length to channel order, changes at the lower channel 

orders because of drainage transformations, in late Recent 

time, that affected only channels of low order.

Gullies in the basin are widened, lengthened, and deepened 

mainly by scarp erosion. They are classified on the basis of 

topographic location as valley-bottom, valley-side, and valleyhead gullies. Trenching of a valley reach to bedrock takes 

place not only by coalescence of discontinuous gullies but also 

by the successive upstream migration of several channel 

scarps. Many large valley-bottom gullies have evidently 

originated on locally steepened valley reaches, but the ratio 

of local slope to drainage area that is critical for the initiation of a gulley is not sharply denned. Valley-bottom gullies 

advance mainly because of plunge-pool action, but this 

mechanism is less important in the advance of valley-side 

and valley-head gullies. The areal frequency distribution of 

valley-head and valley-side gullies is correlated with two 

geomorphic properties: percentage of area in upland and 

adjusted frequency of first-order channels.

Hydraulic geometry of the channels is expressed by the 

slope of curves relating width, depth, and velocity to discharges equaled or exceeded 1, 2, and 25 percent of the time. 

At the gaging stations on Dry, Mitchell, and Brushy Creeks, 

the flow is categorized as ephemeral; at the others, as perennial. In a downstream direction, an increase in discharge 

of ephemeral streams is accommodated by relatively large 

changes in depth and velocity, but the increase in discharge 

of perennial streams is accommodated by a relatively large

change in width. Curves relating suspended-sediment load 

to water discharge for the perennial streams are characterized 

by a break in slope at water discharges above normal but 

below the bankfull stage.

In general, the concentration of measured suspended sediment is higher in wet years than in dry, and the ephemeral 

streams have higher concentrations than the perennial 

streams. Differences in runoff and sediment discharge among 

five subbasins are attributed mainly to differences in relief 

ratio, adjusted frequency of first-order channels, and percentage of area in upland.

Active valley-head and valley-side gullies, and all but a 

few of the active valley-bottom gullies, are attributed to 

land use since settlement rather than to climatic change. 

Restoration of native vegetation to the heads of valleys, 

together with conservation measures on the upland, would be 

effective in the control and prevention of valley-head gullies, 

which are the most numerous in the basin.

INTRODUCTION

The purpose of this report is to give an integrated 

account of the geologic and hydrologic factors that 

are pertinent to erosion and deposition in a part of 

the loess-mantled Great Plains and to evaluate the 

major factors involved in gully erosion, channel 

deposition, and the discharge of water and sediment 

through channels. Climatic change as a cause of 

modern erosion is evaluated in the light of ecologic, 

stratigraphic, and archeologic evidence from terrace 

deposits of late Pleistocene and Recent age. Processes of scarp erosion are analyzed, gullies are 

classified, and the areal distribution of gullies is 

correlated with morphologic properties of the basin. 

Generalizations are made as to the hydraulic geometry of the channels and the relations between discharge and suspended-sediment load. Differences in 

runoff and sediment discharge among five subbasins 

are attributed mainly to differences in specific morphologic properties among the subbasins.

The Medicine Creek basin was selected by several 

cooperating agencies (U.S. Bur. of Reclamation, U.S. 

Agr. Research Service, and the Univ. of Nebraska) 

as a suitable area in which to investigate erosion 

and runoff. Collection of data, which was begun in 

1951 and ended in 1958, was directed toward an

255
256 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

evaluation of soil and water conservation practices 

and also toward an understanding of the processes 

and causes of rapid erosion in this region, which 

is the major subject of the present report.

The regional setting of the Medicine Creek basin, 

which is in the loess-mantled part of the Great 

Plains, is shown in figure 175. The processes of 

erosion and deposition in the basin are characteristic 

of loess-mantled regions in a semiarid or subhumid 

climate, and they apply specifically to an area of 

about 115,000 square miles that is within the Missouri River basin and is mantled with 8 feet or 

more of loess. Most of this area is within the Great 

Plains, although part is in the Interior Plains. The 

Medicine Creek basin is dissected to a much greater 

degree than many parts of the Great Plains, and 

the local relief is greater than average. Nevertheless, nearly all the relief forms typical of the Great 

Plains occur within the basin, including areas of 

nearly flat upland and sharply dissected areas of 

narrow divides and flat-bottomed valleys. Gullies

of all types and sizes occur, and the frequency of 

gullies ranges from high in some places to low in 

others.

Medicine Creek, which is a tributary to the 

Republican River, has a drainage area of about 

690 square miles that lies between the Platte and 

the Republican Rivers. Major subbasins and general geographical features are shown in figure 176. 

Remnants of the upland surface reach a maximum 

altitude of about 3,150 feet in the northern part 

of the basin and descend gradually to an altitude of 

about 2,400 feet at the bluffs of the Republican 

River. The maximum local relief, about 200 feet, 

is in the northern part of the basin. In general, 

the upland is more sharply dissected in the northern 

part, and the divides tend to be flat but narrow; 

in the central and southern parts, the divides are 

broader and slope gently toward the valleys. The 

general aspect of the relief in the southern part of 

the basin is shown in figure 177, which is an oblique 

aerial view southwest from a point above Medicine

EXPLANATION

 Sand dunes Mantled by 8-16 feet 

of loess

Mantled by 16-64 feet Mantled by more than 

of loess 64 feet of loess

Medicine Creek basin

FIGURE 175. Map showing the regional physiographic setting of Medicine Creek basin. Distribution and thickness of loess generalized from Thorpe

and others (1952).
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 257

L__ ] i^ 

L=rC^I\«^- 

\Area. of this report

R. 31 W

 40°30r

EXPLANATION

Boundary of report area 

Boundary of subbasin

Stream-gaging station

FIGURE 176. Location map of Medicine Creek basin.
258 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

FIGURE 177. Oblique aerial photograph of typical relief in southern part of 

Medicine Creek basin. Medicine Creek at lower left. Photograph by River 

Basin Surveys, Smithsonian Institution, 1948.

Creek and about 7 miles north of the town of 

Cambridge.

Fieldwork for geomorphic purposes was begun in 

the summer of 1953 and continued during the summers of 1954-56. Special hand-level and stadia-rod 

equipment was devised to permit the measurement 

of slopes without an assistant. Field studies, as well 

as office work, were facilitated by excellent topographic map and aerial photographic coverage of 

the entire basin. On the 1 :24,000-scale topographic 

maps, prepared by photogrammetric methods and 

published by the jGeological Survey in 1957-58, even 

minor topographic features are accurately represented. The Munsell color system was used for field 

description of loess and soil.

Data contributed by the cooperating agencies have 

been used in the preparation of this report. The 

detailed surveys necessary to measure rates of 

channel erosion on Dry Creek were made by the 

Bureau of Reclamation, who also contributed data 

on precipitation. Land use was tabulated by the 

Agricultural Research Service and the Soil Conservation Service. Runoff and suspended sediment were 

measured by the Geological Survey.

Many persons contributed to this report, which 

was prepared under the successive supervision of 

P. C. Benedict, regional engineer, and D. M. Culbertson, district engineer, U.S. Geological Survey. 

The section on native vegetation was read by E. J. 

Dyksterhuis, range conservationist for the Soil Conservation Service. Fossil snails were identified and 

information on snail ecology was given by W. J. 

Wayne of the Indiana Geological Survey. One carbon-14 age determination was made by Meyer Rubin, 

geochemist of the U.S. Geological Survey, and another by J. L. Kulp of Columbia University.

CLIMATE

By CLOYD H. SCOTT

The climate of the Medicine Creek basin is typical 

of the interior of continents of the middle latitudes 

with rather light rainfall, hot summers, cold winters, 

large variations in precipitation and temperature 

from year to year, and frequent changes in weather 

from day to day.

The mean annual temperature at Curtis, near the 

center of the basin, is about 52°F. Maximum and 

minimum temperatures above 100° and below 0°F 

occur occasionally. The coldest month is January 

when the average temperature is about 27° F, and 

the warmest month is July when the average temperature is about 78°. The monthly mean temperature at the U.S. Weather Bureau Station at Curtis 

for the years 1931-55 is shown in figure 178.

Much of the precipitation occurs during April 

through September, generally as thunderstorms. On 

the average, more than half the total annual precipitation occurs from May through August. Precipitation varies widely from the average (fig. 178); 

7 months had no precipitation at least once during 

the period 1931-55, and some months had no precipitation several times during that period. Maximum amounts exceeded the averages by about two 

to seven times.

The annual precipitation also varies widely from 

year to year (fig. 179). The minimum annual 

amount of slightly less than 11 inches was recorded 

in 1934, and the maximum of about 38.2 inches was 

recorded in 1915. The 66-year average (1895-60) 

was about 21.5 inches, but the 25-year average 

(1931-55) was only 19.1 inches.

The 5-year moving averages (figs. 179 and 180) 

show the general trends of precipitation at Curtis 

and McCook from 1895 to 1960. The annual totals 

are highly variable from one year to another, but the 

5-year moving averages show a somewhat cyclic 

trend. Even though the high- and low-precipitation 

years tend to be grouped somewhat, about half of 

the years have above-average precipitation amounts. 

However, during 1951-58 at Curtis, 5 years had 

precipitation below average; 4 of the years had 

more than 6 inches below average.

The 5-year moving average for Curtis indicates 

a long-term trend toward decreasing annual precipitation. The consistency of the precipitation data 

at Curtis was checked by plotting a double-mass 

curve of data at Curtis and at McCook. A pattern 

composed of data for McCook, Cambridge, and 

North Platte was first used; but the data for North 

Platte and Cambridge were inconsistent with the
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 259

100

90

I 80

LU 

CC. 

I 

<

^ 70

CO 

LU 

LU

o: 

O 

g 60

LU

o: 50

40

30

20 L

Average monthly 

temperature

Annual average 

temperature

FIGURE 178. Average monthly temperature and maximum, average, and minimum monthly precipitation at Curtis, Nebr., 1931-55

pattern, whereas the data for McCook seemed to be 

consistent. The double-mass curve showed a trend 

toward more precipitation at Curtis beginning about 

1908 but returned to about the original slope in 

1914. There is no record that the gage was moved 

in 1908, although the location was changed in 1914 

(U.S. Weather Bureau, 1955a).

The pattern of the 5-year moving average for 

Curtis (fig. 179) is generally similar to the pattern 

for McCook (fig. 180) except that the precipitation 

for the period 1908-18 was higher at Curtis than at 

McCook and for the period 1940-52 was lower at 

Curtis than at McCook. The apparent secular decrease in annual precipitation at Curtis is probably 

a result of uneven areal distribution and is not 

considered to be representative of the region. As 

shown by the double-mass curve, the data at Curtis 

may have been somewhat biased for the years 

1908-14.

Precipitation at Curtis averaged about 18.77 

inches for the years 1951-58, or somewhat below 

the 66-year average of about 21.5 inches. Extremes 

of annual precipitation for this period ranged from 

31.61 inches in 1951 to 12.36 inches in 1952. The 

occurrence of a high and a low in consecutive years 

is not unusual owing to the large variations in rain-
260 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

40

38

36

34

32

30

28

£ 26

z 

g

5,4

22

20

18

16

14

12

10

5-year moving average (plotted at 

middle of 5-year period)

/66-year average

1895 1900 05 10 15 20 25 30 35 40

FIGURE 179. Annual precipitation at Curtis, Nebr., 1895-1960.

45 50 55 1960

fall over much of the central part of the continent. 

At Curtis, only 2 of 6 years since 1895 that had in 

excess of 30 inches of precipitation, were followed 

by years that had more than the long-term average 

amount. An extreme occurred in 1915-16 when the 

difference between precipitation amounts exceeded 

20 inches.

Although averages and extremes give some indication of precipitation, a more meaningful description of rainfall can be obtained through the use of 

rainfall intensity-duration-frequency curves. Such 

curves (fig. 181) were developed for Curtis for 

return periods of 2 and 5 years based on the annual 

series of 1-, 6-, and 24-hour amounts. The California 

method of plotting positions, Tr = n/m, was used; 

a log normal distribution was assumed. Tr is the 

return period in years of item having order number 

m in, a decreasing series, and n is the period of 

record in years.

An empirical factor of 1.13 (U.S. Weather Bureau, 

1957) was used to convert the clock-hour amounts

of rainfall to maximum 60-minute values. An inspection of the 6- and 24-hour amounts indicated 

that conversion for these periods was unnecessary.

The plot of rainfall intensity versus return period, 

which was used to define the curves of figure 181, 

showed little scatter from the average curve, which 

indicated that no extreme storms had occurred during the period.

The U.S. Weather Bureau (1955b) gives rainfall 

intensity-duration-frequency curves for about 200 

stations, including North Platte, for the years 

1906-51. Comparison of the curves for Curtis with 

those for North Platte shows that differences are 

minor between the two stations for both the 2- and 

5-year return periods, even though only 8 years of 

record was used to define the curves for Curtis. 

The similarity between the short- and long-term 

curves and the fact that no extreme amounts of 

precipitation fell during the short period indicate 

that the rainfall regimen was well represented at 

Curtis during the years 1951-58, even though the
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 261

40

38

36

32

30

co 28

LJ 

I

o

^ 26

22

20

18

10

66-year average.

5-year moving average 

(plotted at middle 

of 5-year average)

1895 1900 05 10 15 20 25 30 35 40

FIGURE 180. Annual precipitation at McCook, Nebr., 1895-1960.

45 50 1960

average precipitation for the period was somewhat 

lower than the long-term average.

Evaporation is also variable from year to year, 

although the variations probably are not as extreme 

as those of rainfall. The only evaporation data 

available are for a few years at Medicine Creek 

Dam, and these data were used to check evaporation 

maps in a technical paper by the U.S. Weather 

Bureau (1959a). According to the maps the average 

annual evaporation from a class A pan in Medicine 

Creek basin is about 75 inches, or about S1/^ times 

the average annual precipitation; and lake evaporation is about 50 inches, or nearly 21/2 times the average annual precipitation. Evaporation increases 

from north to south in the basin, but the average 

difference is only about 3 to 4 inches per year.

Data on wind speed and direction nearest Medicine Creek basin are those at North Platte. Because

North Platte is in the valley of the Platte River, 

the wind speeds and directions may not be entirely 

representative of conditions in the Medicine Creek 

basin. The average wind speeds at North Platte 

range from about 12 to 13 miles per hour March 

through July and from a little less than 10 to 

slightly more than 11 miles per hour for the remainder of the year. December and January have 

the lowest average speeds with 9.8 and 9.7 miles 

per hour, respectively, and April has the highest 

average with 13.1 miles per hour. The prevailing' 

direction is from the southeast April through August; south-southeast in September and January; 

northwest in February, October, and November;' 

north in March; and west-northwest in December. 

The annual prevailing direction at North Platte is 

considered to be from the southeast (U.S. Weather 

Bureau, 1959b).
262 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

0.01

RAINFALL DURATION, IN HOURS

FIGURE 181. Rainfall intensity-duration-frequency curves for Curtis, Nebr.,

1951-58.

VEGETATION AND PALEOCLIMATE

CLIMAX PLANT COMMUNITIES

The Medicine Creek basin lies in a transitional 

zone between the tall-grass region to the east (prairie 

grassland) and the short-grass region to the west 

(plains grassland). Trees are restricted to valley 

bottoms, except where they have been artificially 

planted.

Some information regarding the history of plant 

communities appears in the notes of surveyors for 

the General Land Office who made brief reference 

to the grasses they saw while laying out the landdivision grid in 1869-72. 1 Their comments also 

indicate the condition of the vegetal cover before 

white settlement. The following excerpts are from

1 Field notes of survey are on file at the Dept. of Educational Lands and 

Funds, State Capitol Bldg., Lincoln, Nebr.

the notes of Deputy Surveyor D. V. Stephenson, 

made in the Medicine Creek basin during the summer 

of 1872: "land broken by steep ravines running in 

almost every direction, in bottoms of some of which 

there is some blue grass. The upland is about threefourths covered with short buffalo grass. * * * grass 

almost entirely short buffalo, growing in bunches." 

Deputy Surveyor J. L. Slocum made the following 

notes, also in the summer of 1872: "Soil is dry and 

sandy, produces only short buffalo grass in scattering bunches unfit for cultivation or grazing. * * * 

Considerable good grass in bottom of ravines, upland 

is sparsely covered with short buffalo grass." Deputy Surveyor Charles Wimpf wrote as follows, in 

August of 1869: "Bottoms of ravines filled with a 

thick very good grass which gives an excellent hay. 

The hills are covered with a short sweet grass." 

Although the term "buffalograss" may have been 

used loosely by the early surveyors, their comments 

do indicate that during 1869-72 the uplands and 

valley-side slopes were covered with a rather sparse 

growth of short grass, and the valley bottoms with 

a thicker growth of tall grass.

E. J. Dyksterhuis( writen commun. 1958), range 

conservationist for the Soil Conservation Service, 

considers that the climax community on the uplands 

in regions of climate and soils like those of the Medicine Creek basin contains a dominance of midgrasses 

with an understory of short grasses. He also says 

that the dominant midgrasses include western wheatgrass, needlegrasses, and little bluestem; little bluestem, side-oats grama, and blue grama dominate on 

the valley sides, and big bluestem and switchgrass on 

the valley bottoms.

CHARACTERISTICS OF NATIVE GRASSES

Characteristics of native grasses are summarized 

in this section from Weaver and Albertson (1943, 

1944), U.S. Department of Agriculture (1948), and 

Phillips Petroleum Co. (1956).

Big bluestem is a coarse perennial native bunchgrass that reaches a height of 6 feet under favorable 

conditions. The root system is extensive; it may 

penetrate to a depth of about 8 feet and form a 

dense mat to a depth of 1 foot. Under favorable 

conditions it, together with other species of its 

community, will form a continuous sod; under less 

favorable conditions it forms separate, scattered 

bunches. Both rainfall and dust are largely intercepted by the foliage before reaching the ground. 

According to Clark (1937), a prairie covered by big 

bluestem may intercept as much as 53 tons of water 

per acre during a rainfall of 1 inch per hour, 

whereas a prairie covered by buffalograss will inter-
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 263

cept about 28 tons per acre. Such intercepted rainfall commonly evaporates from the leaves of the 

plant without reaching the ground.

Buffalograss is native, sod forming, fine leaved, 

and perennial and typically grows to a height of 

4 to 6 inches. The roots of well-developed buffalograss extend to a depth of 4 to 5 feet and form a 

very thick mat to a depth of 1 foot. Blue grama is 

a low native perennial grass whose flowering stems 

reach a height of about 18 inches. It is the most 

drought resistant of all the native prairie grasses, 

and it spreads, even during drought, mainly by means 

of seedlings. The root system is similar to that of 

buffalograss.

All these native grasses may form a dense thick, 

continuous sod, although the bluestems and blue 

grama are more likely to form separate bunches than 

buffalograss. The taller grasses intercept a greater 

amount of rainfall, which is usually lost to the soil; 

but a corresponding decrease in erosion by raindrop 

impact is effected. Windblown dust is retained more 

effectively by the taller grasses.

EFFECTS OF DROUGHT

Some insight into the influence of ancient arid 

climatic regimes on native grasses and on the 

ability of these grasses to prevent erosion may be 

gained by study of the effects of the drought of 

1933-40 in Kansas and Nebraska. Such study was 

made by Weaver and Albertson (1943, 1944). These 

authors took for a base station Hays, Kans., which 

has an average annual precipitation of about 22.9 

inches and which is located about 120 miles south 

of the Medicine Creek basin. Total precipitation 

at Hays for the 6 years preceding 1933 was below 

normal. Precipitation during each of the 4 driest 

years was about 16 inches.

According to Weaver and Alberston, decrease in 

grass cover as a result of drought varied with the 

intensity of grazing and of burial by dust and also 

with the type of grass cover, as grasses with shorter 

roots underwent greater destruction. The basal 

cover of short grasses in Kansas ranged between 

80 and 95 percent in 1932, and this cover was commonly reduced to 20 percent or less during the worst 

years of the drought. In some localities, particularly 

those that had been overgrazed or covered by blown 

dust, the native plant population was reduced almost 

to zero. Where the effects of drought were moderate, 

the sod was interrupted by patches of bare ground, 

a square foot or less in area, that formed an irregular 

but continuous network. Where the effects of 

drought were more severe, the patches of bare 

ground were larger, up to several square yards in

area; and in the most severely affected localities, 

the grass was so decimated that nearly all the ground 

was bare. These bare patches, described by Weaver 

and Albertson and noted by the writer (Brice, 1958) 

throughout the Medicine Creek basin in 1953-56, are 

important in slope erosion because erosion scarps 

commonly form at their edges. ,

The influence of ancient droughts and ancient 

episodes of aridity on the grasses of the Medicine 

Creek basin can be inferred from Weaver and 

Albertson's study. Short-term droughts would have 

reduced the cover of climax grasses, but erosion 

would not have been severe because these grasses 

are replaced by weeds during drought and recover 

rapidly after drought. Sheet-wash and raindrop 

impact would have removed soil from the irregular 

patches of bare ground between sod-covered areas, 

and low sod scarps would have formed on the slopes. 

During ancient episodes of aridity that lasted for 

hundreds or thousands of years, a climax community 

of grasses adapted to prevailing climate and rainfall 

distribution would have become established. Such 

a community would probably have consisted of an 

association of short grasses similar to the association 

now in eastern Colorado, where the average annual 

precipitation is about 15 inches. If this short-grass 

association were significantly different from that 

established before the arid episode, stream profiles 

and slopes would have been regarded by gullying and 

other erosional processes.

EFFECTS OF LAND USE

The pronounced effect of land use is strikingly 

shown by the contrast in vegetation on either side 

of a fence that follows the north-south section line 

between sections 15 and 16, T. 9 N., R. 27 W. 

("See-fig. 182, upper.) The heads of two tributaries 

to" East Fork of Dry Creek are isolated by this fence, 

and the aspect of the vegetation in these tributary 

heads is unlike that observed at any other place in 

the Medicine Creek basin. Although no information 

on the land-use history of the tributary heads was 

obtained, the contrast in vegetal cover at the fence 

is evident on both the 1937 and the 1952 aerial 

photographs. Therefore, the fence had divided areas 

of contrasting land use for at least 15 years, and 

the aspect of the vegetation in the tributary heads 

in 1953 suggested that it may have been disturbed 

in no important way since white settlement. Besides 

the much greater thickness of the sod and the dominance of tall grasses in the tributary heads, the 

thickness of brush such as wild plum, sumac, buckbrush, and wild rose is exceptional (fig. 182, 

middle). A few ash trees were observed on the
264 , EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

FIGURE 182. Photographs showing effect of land use on riative vegetation, 

East "Fort Dry Creek, August '1953. Upper, Areas separated by a fence 

and contrasting sharply in vegetal cover. Denser vegetation is at right of. 

fence. Although sparse, the vegetation at left of fence was better than 

average for the Medicine i Creek basin in 1953. Middle, Dense cover of 

grass and brush in ungrazed valley head. View looking west. Vegetation 

more dense on south side of valley. Lower, Sparse cover of short grass, 

yucca, and Weeds in heavily grazed5 valley head, 1.5 miles southeast of 

valley head shown, in middle. ,Valley is oriented in north-south direction.

valley bottoms. The termination of the small valleybottom gullies (fig. 182,,,upper) before reaching the 

fence may be fortuitous, but no gullies were observed 

in the tributary heads. By contrast, gullies are in 

most tributary heads in this part of. Dry Creek (fig. 

182, lower). Step scarps occur on the steep slopes 

of the heavily vegetated area, but they are much 

subdued and seem to be inactive. The upland draineci, 

by the tributary heads is planted in row crqps orr 

small grain, as elsewhere in the basin. t .,

NATIVE TREES AND DENDROCHRONOLOGY '

During the period 1869-72 General Land Office, 

surveyors reported that trees in the Medicine Creek, 

basin were confined to stream valleys, in which they 

identified cottonwood, ash, boxelder, elm, hackberry, 

and cedar. These same kinds of trees now grow 

from place to place in the valleys, but the wider 

valley flats have been mostly cleared of trees.

A tree-ring indication of precipitation during the. 

past 400 years in western Nebraska, including the 

vicinity of North Platte, was reported by Weakly 

(1940, 1943). According to his interpretation, the 

climate has been characterized by frequent dry years 

and by less frequent droughts that lasted 5 years 

or more. The 13 droughts (period of five or more 

successive dry years) had an average duration of 

13 years, and the average interval between droughts 

was about 20 years. The longest drought lasted 

from 1539 to 1564 (26 yr), but other lengthy' 

droughts were from 1587 to 1605 (19 yr) and from 

1688 to 1707 (20 yr).

PRE-PLEISTOCENE ROCKS 

UNEXPOSED ROCKS

Neither the lithology nor the structure of unexposed rocks in the Medicine Creek basin has any 

apparent direct influence on the present relief. The 

Paleozoic and Mesozoic formations that overlie thei 

Precambrian basement dip gently to the west and 

are overlain unconformably by Tertiary formations 

that dip gently to the east.

EXPOSED ROCKS 

NIOBRARA FORMATION

The Niobrara Formation of Late Cretaceous age 

crops out along the banks of Harry Strunk Lake and 

from place to place along Medicine Creek downstream from the lake, but it is not exposed elsewhere 

in the basin. Where exposed, the Niobrara consists 

mainly of orange or white chalk interbedded with 

thin layers of altered volcanic ash. ,
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 265

O GALL ALA FORMATION

Outcrops of the Ogallala Formation of Tertiary 

(Pliocene) age are mainly restricted to valley sides 

and channels of larger streams in the Medicine 

Creek basin, and the best exposures are along Medicine Creek and Cedar Creek in the vicinity of Stockvine. No outcrops were observed in the northern 

parts of the basin where the loess cover is thickest. 

Available well logs indicate that the Ogallala underlies most of the basin and that its thickness increases 

from about 200 feet in the southern part to about 

400 feet in the northern part. (See figs. 183 and 184.)

Exposed sections of Ogallala at seven localities 

were measured and described in detail. Thicknesses 

of described sections ranged from 6 feet at one locality on Cedar Creek to 73 feet at another locality 

downstream, and the total thickness of described 

sections was 290 feet. In general, the Ogallala consists of clay, silt, volcanic ash, sand, and gravel, 

poorly sorted into different beds that are cemented 

with (and partly replaced by) different amounts 

of carbonate. Five rock types were distinguished, 

and the total thickness of each type as represented 

in the seven measured sections is given in table 1.

TABLE 1. Thickness and percentage of each rock type in 

seven exposed sections of the Ogallala Formation

Sand, pebbly, and silt; loosely cemented, locally

Limestone, sandy, rather uniformly cemented . _ _

Clay; alternating beds of fine-grained limestone _._. __

Thickness

(ft)

22

156

62

26

24

Percent

of total

thickness

7.5

54.0

21.4

9.0

8.1

With regard to the origin of the Ogallala, Frye 

and others (1956) have presented convincing eyidence that it was deposited by streams flowing eastward from the Rocky Mountain region. In the 

earlier part of their history these streams occupied 

broad, relatively shallow valleys eroded into Cretaceous bedrock. However, as alluviation proceeded, 

the deposits progressively overlapped the gentle 

valley sides, most divides were buried, and eventually 

a coalescent alluvial plain was formed.

PLEISTOCENE AND RECENT DEPOSITS 

TERRACES

Three terraces were identified along Medicine 

Creek and its tributaries. The highest of these is 

named the Wellfleet terrace after the village of 

Wellfleet, Nebr., which is on Medicine Creek. Although Wellfleet is not built on the terrace surface, 

conspicuous flat-topped remnants of the terrace 

stand about 125 feet above the valley flat at intervals 

of a mile or more between Wellfleet and Maywood, 

Nebr. For example, the remnant in the SE*4 sec. 8, 

T. 8 N., R. 29 W., about 1 mile north of Maywood, 

is well defined both in the field and on the Curtis 

NW quadrangle sheet. There are similar flat-topped 

remnants along Well Canyon and other major tributaries, but the originally flat surface of the terrace 

has been dissected in most places.

The best preserved and most continuous terrace 

in the Medicine Creek basin is named the Stockville 

terrace after the town of Stockville, Nebr., which 

is built on a remnant of the terrace, along the west 

side of Medicine Creek. The Stockville terrace is 

represented along Medicine Creek by broad remnants that stand above the valley flat at a height 

of about 50 feet in the lower course of the creek 

and about 30 feet in its upper course. The Stockville 

terrace can be traced almost continuously along 

most tributary channels in the basin. Moreover, the 

sides and heads of valleys are broadly graded to the 

level of the Stockville terrace.

The lowest terrace of general importance in the 

Medicine Creek basin is named the Mousel terrace 

after the Mousel School, which is in sec. 25, T. 5 N., 

R. 26 W., on the east side of the valley of Medicine 

Creek.' (See fig. 176.) The Mousel terrace is represented'along Medicine Creek by widely scattered 

remnants that stand 15 to 20 feet above the valley 

flat. Similar remnants are along most major tributaries, such as Well Canyon, Cedar Creek, and Fox 

Creek; but the Mousel terrace cannot be traced along 

most minor tributaries because its surface has been 

buried by late Recent alluvium. Even where the 

terrace; is well defined, there has been little grading 

of the ivalley sides to the level of the terrace; the 

slope that forms the riser of the Stockville terrace 

rises abruptly above the tread of the Mousel terrace.

A sequence of well-defined terraces appears along 

most streams in Nebraska, but general agreement 

has not been reached as to terrace nomenclature. 

Condra and others (1950) describe a sequence of 

six terraces in central Nebraska; and Schultz and 

others (1951) describe a sequence of five terraces 

that applies to Nebraska generally. Neither sequence 

would be expected to apply to all Nebraska streams 

because of complications, such as overlap of an older 

terrace deposit by a younger terrace deposit, that 

may be peculiar to a single stream.

Schultz and others (1948, 1951) have specifically 

applied their terrace sequence to alluvial terraces
266 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

X

Z

o

H

CL 

X

u

AdVNd3_LVnO

UB!OUHII
Pleistocene

Wisconsin Illinoian

g K

.

5. S fi 

*£& 

«?§

QUATERNARY

Creiaceoits

1

CRETACEOUS

m

X

D

> 

Z 

> 

H

o

z

Nebr Indianola, 

River Republican 

2,93 aaTLNvw-ssaoi xvano 's^[Iv^J aMioiaan naaao 'Nisva 
268

in the southern part of the Medicine Creek basin, 

in particular along Lime Creek. According to their 

nomenclature, alluvial terraces in Nebraska are numbered upward from the youngest and lowest, which 

is called Terrace-0, to the highest and oldest, which 

is called Terrace-5. Although their numerical system of terrace nomenclature is not used, the terrace 

sequence in this report is based on, and in general 

agreement with, the work of Schultz and others. 

Correlation of terrace deposits with Pleistocene time 

units is uncertain, particularly in view of the present 

controversy about the units. A tentative correlation 

of the Medicine Creek terrace sequence with other 

terrace sequences and with the Pleistocene time 

units is given in table 2.

The Stockville terrace of this report corresponds 

physiographically to Terrace-2 of Schultz and others 

(1948, 1951), and the Stockville terrace deposits 

correspond to fill A of Terrace-2. No terrace deposits corresponding to fill B of Terrace-2 were 

observed in the Medicine Creek basin by the writer.

The Wellfleet terrace, which is underlain by the 

upper part of the valley fill of the Peorian Loess, 

corresponds physiographically with the Terrace-3 

of Schultz and others and with the Terrace no. 3 

of Condra and others (1950, p. 35). No physiographic expression of the Terrace-4 of Schultz and 

others nor of the Terrace no. 4 of Condra and others 

was recognized in the Medicine Creek basin. At a 

locality on Medicine Creek (sec. 11, T. 5 N., R. 26 

W.), Schultz and others (1948, p. 36) have identified a surface as the tread of Terrace-3. This surface 

is interpreted by the writer as a long valley-side 

slope graded to the level of the Stockville terrace. 

At this same locality the surface identified as Terrace-4 by Schultz and others is interpreted as the 

tread of Terrace-3, or the Wellfleet terrace. A terrace equivalent to Terrace-4 was doubtless once

present in the Medicine Creek basin, but the physiographic expression has been obliterated by deposition of the upper part of the Peorian Loess and by 

grading of the valley sides during the time that the 

Stockville terrace deposits were accumulating.

GENERAL STRATIGRAPHY OF THE 

PLEISTOCENE AND RECENT

Stratigraphy of the Pleistocene deposits in Nebraska is well established, and satisfactory correlations have been made with the deposits of Kansas 

and other adjoining States, although nomenclature 

differs somewhat from State to State. For regional 

descriptions of the stratigraphic units the reader is 

referred to publications of the Nebraska Geological 

Survey (Condra and others, 1950; Lugn, 1935) and 

of the Kansas Geological Survey (Frye and Leonard, 

1952). Leonard (1950, 1952) has established the 

ranges of land snails that are generally abundant 

in the Pleistocene deposits of Kansas.

The general relations of Pleistocene and Recent 

stratigraphic units in the Medicine Creek basin are 

shown in figure 185, and in table 2 correlation is 

tentatively made with formally named units in Nebraska and Wyoming. Long profiles of terrace deposits along the course of Medicine Creek are shown 

in figure 186. Correlation of the upper Wisconsin 

and Recent units is based on carbon-14 age determinations and on physiographic expression as terraces. Correlation of the older units is based on 

fossil evidence, on soil markers such as the Sangamon 

soil, and on lithology. Pleistocene and Recent deposits in the Medicine Creek basin consist of dune 

sand, loess, and alluvium, overlying a pre-Pleistocene 

(or lower Pleistocene) surface cut into the Ogallala 

Formation. The deposits of Nebraskan or Kansan 

age are mainly of alluvial silt and sand; gravel, in 

lesser amounts, is confined to the bottoms of former

Q

! 25

50 -

75 -

100 -

Mouse! terrace . 

deposits

Sappa Formation

jpgallala Formation

VERTICAL EXAGGERATION X8

FIGURE 185. General topographic and stratigraphic relations of Pleistocene and Recent deposits in the Medicine Creek Basin. Differences in stratigraphy and relief on either side of the figure represent the range of differences among valleys in the basin.
TABLE 2. Correlation of stratiyraphic units and terraces of the Pleistocene and Recent in Nebraska 

Age

S0)

-?-

V

C

V

101

£

-

 ? ? 

Wisconsin

Altithermal

Mankato

Gary

Tazewell

lowati

Sangamon

Illinoian

Yarmouth

Kansan

Aftonian

Nebraskan

Central Nebraska 

(Condra and others, 1950)

~\

\ 

\

\ Terrace 

Bignellsilt \ na2

WWWWWVWWWVW i *-

Brady soil \

_ . .,1 Terrace 

Upper Peorian silt I no 3

Soil development

Middle Peorian silt \

Soil development \

Lower Peorian silt \ no. 4 

Todd Valley sand \

- vwwwwvwvwvwwww L

Loveland soil

Loveland fm 

Crete fm

Sappa soil

Upper Sappa fm 

Pearlette ash lenticle 

Lower Sappa fm 

Grand Island fm

Soil development

Fullerton fm 

Holdrege fm "' :

Nebraska 

(Schultz and others, 1951)

WWWWWWWVWWWW -i 

Wisconsin "VI" silt \ 

Soil Z \Terrace-0 

Late Cochrane silt \ wvwwwwwwwww -\ >-

Early Cochrane silt \ 

(2,140±150^ 1

Soil Y I Terrace-1

Late Mankato silt \

WWWVWWVWWWWV -i *-

Early Mankato silt \

Soil YY \ Terrace-2 

(9,880+670)^ \ fill A

Late Gary silt \

WWWWIAWWWVWWV -i \r 

Early Gary silt P '2

Brady soil \

Late Tazewell silt \

WWWWWVWWWWWW -i L 

Early Tazewell silt I

Soil W \Terrace-3

Todd Valley fm \

wwwvwwwwwwv . L

Early lowan silt I

Sangamon soil \

Loveland fm Terrace-4 

Crete fm

Yarmouth soil \ 

Sappa f m \

Grand Island fm \

wwwwwwwwvwwvww L

Red Cloud fm

Fullerton f m

Holdrege fm

Wyoming 

(Leopold and Miller, 1954)

 wvwvwwwwwvw -i 

Lightning fm lightning 

\ terrace

wwwwwwwww _-\ Moorcroft-deposition Mooror stability \ crof t

wfwwww* -, terrace

Kaycee fm I \

wwwwwwww \

Paleosol \

I Kaycee

TT ,. \ terrace Ucross fm I

Medicine Creek, Nebraska 

(This report)

 WWWVWWVWWWWWVWVWWV -i - 

 , . Recent va

Recent alluvium \ fl te 

(420±160)^ , \ terrace

wwwwwvvvvvvwvwvvvwvww i L

Mousel terrace deposits \ Mousel 

(U43±240)^ \ terrace 

(2,200±200)^ I

wwvvvwwvwvvwwwwwvwv -\

Soil development \

\ Stockvill

\ terrace 

Stockville terrace deposits \

vvvwwwwwwwwvwwwvww -\

Brady soil \ 

v \ Wellfle

\ terrace 

Peorian Loess \

Peorian Loess

Sangamon soil

Loveland Formation

Yarmouth soil

Sappa Formation

Years B.P., C dates reported by Schultz and others (1951)

Years B.P., C 14 dates given in this report

Dates from pottery and dendrochronology

Years B.P., C 14 dates from various localities

Years B.P., C 14 date reported by Wedel and Kivett (.1956)

MWVWW Denotes major periods of 

\

Encloses the units under

expressed terrace. 

subsequently on terrace 
270 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

2800

2700

Z 2600

2500

2400

2300

2200

70 60 50 40 30 

DISTANCE FROM CONFLUENCE, IN MILES

20 10

FIGURE 186. Channel profile, valley flat profile, and terrace profiles along the main course of Medicine Creek.

valleys (figs. 183 and 184). Although loess may 

have been deposited during either Kansan or Nebraskan time, no loess of Kansan or Nebraskan age 

has been identified with certainty either on Medicine 

Creek or elsewhere in Nebraska. At two localities 

in the Medicine Creek basin, a paleosol was identified as the Yarmouth soil on the basis of snail fauna 

and high content of volcanic ash. Silts beneath the 

Yarmouth soil are correlated with the Sappa Formation. No deposits of ash of the Pearlette Ash 

Member of the Sappa Formation were seen in the 

Medicine Creek basin, but deposits up to 30 feet 

in thickness crop out in areas adjacent to the basin. 

No Pleistocene deposits older than the Sappa were 

recognized with certainty in the Medicine Creek 

basin.

The thickness and areal distribution of pre-Wisconsin stratigraphic units cannot be determined 

without data from drilling. Moreover, the logs must 

include full and accurate descriptions of the rocks 

that are penetrated, because the different Pleistocene 

stratigraphic units are similar in rock type to one 

another and to the Ogallala Formation. Two geologic sections (figs. 183 and 184) have been compiled 

from logs of test holes that were drilled by the

Nebraska Conservation and Survey Division in cooperation with the U.S. Geological Survey. Figure 

183 is simplified from an unpublished section by 

J. L. Deffenbaugh, based on his interpretation of 

logs of test holes drilled in 1948. On his original 

section, Deffenbaugh distinguishes the Loveland, 

Sappa, and Grand Island Formations. Figure 184 

represents an interpretation, made by the writer, 

of logs of test holes drilled in 1960. Although the 

logs include full descriptions of the rocks penetrated, 

the writer was not able to distinguish with confidence any formational boundaries beneath the Sangamon soil and above the Ogallala Formation. To 

facilitate comparison of figures 183 and 184, some 

of the stratigraphic units distinguished by Deffenbaugh were combined in order that they correspond 

with the units shown on figure 184.

STRATIGRAPHY ON CEDAR CREEK NEAR 

STOCK VILLE

Along Cedar Creek, about 3 miles southwest of 

the village of Stockville (Bartley NW quad., NE^4 

sec. 18, T. 6 N., R. 27 W.), several sections have been 

exposed by lateral cutting of the creek, and the 

terrace sequence is more complete and distinct than
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 271

SOUTH

Mousel /*' st°ckvil|e 

terrace

2500'

VERTICAL EXAGGERATION X3

DATUM IS MEAN SEA LEVEL

FIGURE 187. Profile and geologic section on Cedar Creek.

usual for the Medicine Creek basin. The section 

described below applies to the right-hand (south) 

side of figure 187: Depth

(ft) Peorian Loess:

Silt, pale-yellow (2.5F 7/3 dry, 2.5F 6/3 moist),

calcareous. Surface soil not present _. .. .. . 0-15 

Loveland Formation:

Silt, very pale brown (WYR 7/4 dry, 10F# 5/4 

moist); a few streamers of fine sand near base 15-20

Gravel, sand, and silt, crossbedded, calcareous, 

locally cemented with carbonate ________________________ 20-22

Silt, pale-brown (WYR 6/3 dry, WYR 4/2 

moist), noncalcareous; indistinct sedimentary 

lamination .. -..--...._.__....__.. ......_._._.._..._.... 22-26

Yarmouth soil:

Silt, clayey, gray-brown (WYR 5/2 dry, 10F.R 

4/2 moist). Weak columnar structure, columns irregular, 2 to 5 in. wide; noncalcareous. 

Upper contact gradational ______^__-__^_ _____________ 26-28.9

Sappa Formation:

Sand, fine, and ashy light-gray (2.5F 7/2 moist) 

silt; a few thin white irregular seams of volcanic ash. Upper 0.5 ft mottled with darker 

gray, gradational with unit above. Upper 2 

ft is Cca horizon of Yarmouth soil; contains 

meshwork of fine carbonate veinlets ____ ___________- 28.9-32

Sand, fine, and ashy silt; a few streamers of 

sand and fine gravel near base; noncalcareous 32-35

Gravel and other debris from Ogallala Formation ; crossbedded; a few streamers of fine sand 35-37 

Ogallala Formation: 37-53

A snail fauna was collected from the lower part of 

the soil identified as Yarmouth and from the upper 

part of the unit identified as Sappa, and identification was made by Dr. W. J. Wayne of the Indiana 

Geological Survey. In the following table, the number of individuals of each species is given in the 

right-hand column.

Gastrocopta tappaniana (C. B. Adams) _^_______- 2

proarmifera Leonard _._._. ._..-..._-_.__..__ 3

Gyraulus tircumstriatus (Tryon) ___________________ 21

Helicodiscus parallelus (Say _- _ _ . 3

Physa anatina Lea ~ _ _._ ~_ _______ 2

Retinella electrina (Gould) 

Lymnaea [Fossaria] parva ________

Vallonia gracilicosta Reinhardt 

Valvata tricarinata (Say)

3

2

15

4

According to Leonard (1950), G. proarmifera is 

restricted to the Yarmouth, and none of the species 

in the collection is restricted to deposits younger 

than the Yarmouth. Correlation of the soil with the 

Yarmouth and of the underlying silt with the Sappa 

is, therefore, supported by the faunal evidence. 

V. tricarinata is aquatic, and the fauna as a whole 

indicates a moist environment such as would be 

afforded by a^valley.

The stratigraphic and topographic relations shown 

in figure 187 indicate that the valley of Cedar Creek 

was cut not later than Kansan time and that at 

least five episodes of valley alluviation, each followed by cutting, have taken place since Yarmouth 

time.

STRATIGRAPHY ON CUT CANYON NEAR CURTIS 

Near the confluence of Cut Canyon with Fox 

Creek, a significant section of Pleistocene deposits 

is exposed along the county road that descends 

eastward from the upland and crosses Cut Canyon 

in the NWi/4 sec. 29, T. 9 N., R. 28 W. The presence 

of deposits of the Sappa indicates that the canyon 

was cut not later than Kansan time, and the Pleistocene sequence of pre-Wisconsin age seems to be 

complete. Both the Yarmouth and the Sangamon 

soils are well developed. Of the terrace deposits of 

late Wisconsin and Recent age, however, only the 

Stockville is exposed (fig. 188).

A stratigraphic section along the road, beginning 

1,500 feet west of Cut Canyon bridge and ending 

1,150 feet west of the bridge, is as follows:

_ . T : , Depth Peorian Loess: , ~> - (ft) 

Silt, yellowish-gray, massive, homogeneous ________ 0-30
272 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

WEST EAST

2800' -i

2600'

VERTICAL EXAGGERATION X3

DATUM IS MEAN SEA LEVEL

FIOUBE 188. Profile and geologic section along road entering Cut Canyon.

Depth 

(ft)

Sangamon soil and Loveland Formation:

Silt, yellowish-brown (10YR 5/4 when moist),

friable; no distinct structure ._____________________ 30-32

Silt, light-yellowish-brown (10YR 6/4 when

moist); weak prismatic structure, noncalcareous -_-_I____________________________________________ 32-38

Silt, clayey, approximately same color as unit

above, but has pinkish cast ___._-______.______ 38-38.5

Silt, streaked and veined with abundant soft

carbonate ____ ____________________________________ 38.5-43

Yarmouth soil:

Silt, light-brownish-gray (5Y 7/2 when dry, 

WYR 6/2 when moist), clayey; streaked with 

carbonate from unit above, but otherwise noncalcareous. Breaks into irregular small, polyhedrons (5 to 10 mm in diameter) that fit together. Contact with unit above sharp but 

irregular ___J_____-___i____.._______ _____________ 43-46.5

Silt, yellowish-brown (10YR 5/4 when moist); 

contains abundant small iron concretions ________ 46.5-47

A stratigraphic section 800 feet west of the bridge 

is similar to that described above, except the Sappa 

Formation is exposed and the Yarmouth soil is 

somewhat different, as shown below:

Depth 

(ft)

Yarmouth soil:

Silt, olive-gray (SYR 4/2 when moist) ____________ 0-1

Silt, light-gray (WYR 7/2 when moist) ; crumb

structure __________________________________________________________ 1-2.5

Silt, light-gray, mottled with rust color; structure weakly prismatic, prisms have irregular 

sides, 1 to 3 cm wide _________________________,_: 2.5-4.1

Silt, light-gray; no distinct structure _._...__v_ 4.1-7.5 

Sappa Formation:

Sand, fine-grained, and silt; cross-laminated ___ 7.5-9.5 

< i

No fossils were found at this section, but fossils

were found in gray ashy silt, correlated with the

Sappa, about 600 feet to the east. The faunas were

^identified by the writer, and the identification was

checked and corrected by Dr. W. J. Wayne of the 

Indiana Geological Survey. The number of each 

species found is indicated in column at right in the 

following list:

Carychium exile canadense Clapp ____._ ____ 2

perexiguum Baker ______ _ ___________________ 2

Gastrocopta pentodon (Say) ______________________ 6

proarmifera Leonard ______-____ __- _ -_ 2

Gyraulus circumstriatus (Tryon) _ ______________ 19

Pupilla muscorum (Linne) __________________ 1

muscorum sinistra Franzen ______-______-_ _ 1

Retinella electrina (Gould) ___.___ ___._ _.__-___-_. 1

Vallonia gracilicosta Eeinhardt _______-_-_ ___ 10

Valvata tricarinata (Say) ________ ___ __ _ _ 24

Vertigo nylanderi Sterki __________ ______-_____ _ 3

According to Leonard (1950), G. proarmifera and 

P. muscorum sinistra are restricted to the Yarmouth 

and (7. perexiguum is restricted to deposits of Nebraskan and Yarmouth age; none of the species 

found is restricted to deposits younger than Yarmouth age. Therefore, correlation of the ashy silt 

with the Sappa Formation is reasonable.

STRATIGRAPHY ON ELKHORN CANYON NEAR 

MAYWOOD

The Peorian Loess, Stockville terrace deposits, 

and late Recent alluvium are exposed along Elkhorn 

Canyon about 2 miles southwest of the village of 

Maywood, near a bridge where the county road 

crosses the canyon (Curtis SW quad., center of 

section line between sees. 31 and 32, T. 8 N., R. 29 

W.). The exposure was studied after it had been 

thoroughly moistened by rainfall and runoff, because 

moistening greatly increases visibility of the sedimentary structures and textures. The relations between the different units are shown .in figure 189, 

and a general view of the locality is shown in figure 

190. Evidence was found in the late Recent alluvium 

for two episodes of cutting and filling, which took
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 273

SOUTH 

2730' -i

2720' -

2710' -

2700' -

2690' -

NORTH

2680' -

Peorian 

Loess

Stockville terrace

Numbers refer to parts of 

Recent deposits

\,

Flow line of Elkhorn Canyon

Layer from which

Cu sample W-754 \ 

was collected \

Recent deposits

2670'

Ogallala Formation

VERTICAL EXAGGERATION X2V2

DATUM IS MEAN SEA LEVEL

FIGURE 189. Profile and geologic section on Elkhorn Canyon.

place (according to a carbon-14 age determination) 

within the past 300 to 400 years.

The late Recent alluvium consists of four parts, 

which are designated by the numbers 1 through 4 

on figure 189. Part 1 is oldest, lightest in color, and 

most compacted, whereas the younger parts are 

successively darker in color and less compacted. 

The contact between part 1 and part 2, which lies 

at a depth of about 12 feet below the ground surface, 

is conformable and nearly horizontal. Beneath the 

contact, the deposits of part 1 show no evidence of 

erosion or of leaching. Part 2 is characterized by 

light brownish gray bands of fine sand and silt 

(2.5Y 6/2 moist) alternating with darker grayish 

brown bands of clayey silt (2.5Y 4/2 moist), whose 

darker colors result from a finer texture and a

FIGURE 190. View of terrace sequence and valley fills along Elkhorn Canyon. 

Prominent scarp marks front of Stockville terrace; lower scarp marks contact between parts 3 and 4 of late Recent alluvium.

higher content of organic matter. Part 1 is also 

banded, but the banding is inconspicuous because 

of the relatively lighter color of the clay-rich layers. 

Part 2 is riddled with worm burrows, which are 

partly filled with castings and dark silt, and many 

of which terminate in a round cavity partly filled 

with castings. The darker clay-rich bands seem to 

have been preferred by the worms, for these bands 

contain castings in greatest abundance. Worm castings are much less apparent in part 1, although 

dark vertical streaks, which probably represent the 

filled burrows of worms, were seen from place to 

place, and the bedding is apparently riddled by worm 

burrows. A lens of charcoal and wood ashes, mixed 

with silt and containing a single large fragment of 

charred bone, was found interbedded in part 2 at 

a depth of about 7.5 feet below the ground surface 

and 3 to 4 feet above the contact with part 1. 

Charcoal (Geol. Survey sample W-754; analysis by 

Meyer Rubin) from the lens yielded a carbon-14 

date of 420±160 years B.P. (before present).

Parts 1 and 2 of the late Recent alluvium are described here because the contact between these parts 

is considered to mark a distinct change in the rate 

of accumulation of the late Recent alluvium; the-rate 

of accumulation of part 2 is considered to be much 

the more rapid. Furthermore,-the more rapid accumulation of part 2 probably reflects an increase in 

rate of erosion on the uplands and valley1 sides.' 

Part 1 is lighter in color because its slower rate of 

accumulation permitted a greater degree of oxida-' 

tion of finely divifled organic matter, which was 5 

originally intermixed with the silt and clay. A 

slower rate of accumulation of part 1 is also indi-
274 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

cated by the greater destruction of its sedimentary 

structures by earth worms. If the described changes 

from part 1 to part 2 do in fact reflect a change in 

rate of accumulation, this change took place about 

500 years ago, as indicated by the position of the 

radiometrically dated charcoal. According to archeologic evidence, a period of drought may have begun 

about 500 years ago, when the region was apparently 

evacuated by people of the Upper Republican 

Culture.

Parts 3 and 4 of the late Recent alluvium are dark 

gray brown (WYR 5/2 moist) and show rather distinct banding. Carbonized fragments of grass stems, 

having an average length of about 0.5 mm, are scattered throughout, but they are more abundant in 

the darker, clay-rich bands. Dark laminae formed 

of ashes and charcoal, which probably represent the 

debris from grass fires, were seen from place to 

place. Much of the alluvium seems to have passed 

through the digestive tracts of earth worms, whose 

castings dominate the texture and account for the 

loose consolidation.

The steeply dipping erosional contact that separates parts 1 and 2 from part 3 is attributed to the 

passage of a major gully head scarp along the valley 

of Elkhorn Canyon. Part 3 of the late Recent alluvium, which was deposited in the gully left by this 

head scarp, was in turn trenched by a second head 

scarp following consecutively behind the first. The 

former sides of the trench made by the second head 

scarp are represented by a pair of low terraces that 

were traced (on aerial photographs) to their terminus about 3 miles upvalley. Deposits formed 

behind the second head scarp (part 4) were in turn 

trenched by a third head scarp following consecutively behind the second. In 1952 the third head 

scarp was 13,300 feet upvalley from this locality, 

and it advanced about 500 feet during the period 

1937-52.

Relatively little time is required for the formation 

of a series of low terraces by the passage of consecutive gullies, because deposition is rapid on the floor 

of a gully and the head scarps travel rapidly as a 

result of concentration of flow on the gully bottom. 

The average rate of advance of the third head scarp 

during the period 1937-52 is probably conservative, 

partly because the head scarp has reached bedrock. 

An average advance of about 200 feet a year, attained by some head scarps in the Medicine Creek 

basin during the period 1937-52, would be adequate 

to account for passage of the events described during 

a period of about 350 years. On the other hand, 

these events would not likely be compressed into a 

period of much less than 350 years.

LOVELAND FORMATION AND SANGAMON SOIL

The most useful and distinctive soil marker within 

the Pleistocene deposits is the Sangamon soil, which 

is developed on the Loveland Formation. No other 

soil in the region, including the modern soil, approaches the Sangamon in depth of profile or in 

degree of development of the Cca horizon. On the 

uplands the Loveland consists of loess, which mantles 

the valley sides and merges into contemporaneous 

valley-fill deposits of silt and sand. The maximum 

observed thickness of Loveland in the Medicine Creek 

basin is 35 feet (along Cedar Creek), and the average thickness is about 20 feet. At some exposures 

in valleys, the Loveland is missing and the Sangamon 

soil is developed on the Ogallala Formation.

Moist loess of the Loveland is typically light yellowish brown (WYR 6/4), but darker colors (WYR 

5/3 and WYR 5/4) were observed at some localities. 

The Sangamon soil, as observed from a distance, is 

a distinct dark-brown humus-rich band that separates loess of the Loveland from the distinctly lighter 

colored loess of the Peorian. (See fig. 191.) This 

band ranges from about 4.5 to about 2 feet in thickness and from yellowish brown (WYR 5/4) where 

the soil is weakly developed to very dark gray brown 

(WYR 4/3) where it is strongly developed. A Cca 

horizon is nearly everywhere present in the soil, 

but its depth below the dark band ranges from 

about 2 feet in some localities to about 25 feet in 

others, and its thickness is also variable. The variations indicate that development of the Sangamon 

in some localities was nearly continuous, whereas 

in other localities the developing soil was intermittently buried by fresh accumulations of silt.

In spite of the conspicuous development of the 

humus-rich part of the Sangamon soil profile, it 

contains an abundance of fresh ferromagnesian minFIGURE 191. Valley fill of the Peorian Loess set unconformably against 

Sangamon soil and Peorian Loess. Steeply dipping unconformity, indicated by arrows, is exposed on either side of the small valley, and the 

valley fill of the Peorian is between the arrows.
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 275

erals and hence has undergone little chemical weathering. About 20 species of heavy minerals were 

identified under the petrographic microscope; of 

these, clinozoisite, green hornblende, apatite, and 

brown hornblende are by far the most abundant. In 

addition, calcic feldspar (labradorite) was identified 

among the light minerals.

PEORIAN LOESS, BRADY SOIL, BIGNELL LOESS, 

AND MODERN SOIL

An account of the involved history of the terms 

"Peoria" and Peorian has been given by Leonard 

(1951, p. 323). In this report, the term Peorian 

Loess is applied to deposits that are stratigraphically 

above the Sangamon soil and terminate in the Brady 

soil. The absolute time at which the Sangamon 

Interglaciation ended has not been determined, but 

a reasonable estimate can be made by extrapolating 

from existing carbon-14 dates; the estimate of Frye 

and Willman (1960, p. 2) is between 50 and 70 

thousand years B.P., as measured by carbon-14. 

The Brady soil has been dated, by means of a carbon14 age determination on organic carbon from the 

A horizon of the soil, at 9,160±250 years B.P. 

(Rubin and Suess, 1956, p. 443). This date is probably too young because of root hairs in the sample.

In general, the Peorian Loess mantles the whole 

of the Medicine Creek basin except the modern 

valley flats and the Stockville and Mousel terraces. 

On the uplands the Peorian consists of massive silt, 

which grades laterally (at least at the surface) to 

fine sand in the vicinity of dune areas. This massive 

silt is called loess because its topographic position 

indicates that it is eolian and because the snails that 

it contains are not aquatic. In valley locations also, 

the greater part of the thickness of the Peorian 

consists of massive silt, except in the valleys in the 

vicinity of dune areas, where it consists of silt and 

fine sand. The lowermost 10 to 20 feet of the Peorian 

in the valleys commonly consists of silt interbedded 

with fine gravel, silty clay, or sand; and this lowermost part contains, in some localities, aquatic snails 

or pelecypods. The massive silt of the valleys is not 

called loess because its agent of deposition is not 

apparent. Where a vertical face cut in this silt is 

exposed to wind and rainwash, it commonly shows 

well-defined lamination that could be attributed 

either to wind or to water. Eolian deposition of silt 

on the uplands was probably accompanied by an 

equal or greater amount of eolian deposition in the 

valleys, but the silt in the valleys was probably 

reworked by water before final deposition. Deposits 

of the Peorian in valley locations, whether of massive

silt or of some other sediment type, are called the 

valley-fill deposits of the Peorian.

Leonard (1951) recognizes three biostratigraphic 

zones in the Peorian Loess of Kansas, but these 

zones are not marked by any physical discontinuities 

in the loess. The basal zone, which is devoid of 

molluscan fossils, is overlain by a lower molluscan 

faunal zone and an upper molluscan faunal zone. 

Between the upper and lower faunal zones is a 

transitional faunal zone, which bears elements of 

both the lower and upper faunal assemblages.

A snail fauna was collected about 25 feet stratigraphically above the Sangamon soil at a locality 

on Dry Creek to ascertain the approximate position 

of these faunal zones relative to the total thickness 

of the loess of the Peorian in the Medicine Creek 

basin. The locality is in the NW^4 sec. 16, T. 9 N., 

R. 27 W. The stratigraphic position of the fauna 

is about midway of the total thickness of the loess 

on Dry Creek. A sample of loess weighing about 

25 pounds was collected, and the contained snails 

were obtained by washing the loess through a sieve. 

Identification of the snails was made by Dr. W. J. 

Wayne of the Indiana Geological Survey, and the 

faunal list is as follows (the number of individuals 

of each species is given in right-hand column) :

Columella alticola (Ingersoll) ___ _ - 2

Discus cronkhitei (Newcomb) ___. __ ._-._ 2

shimeki (Pilsbry) ._.____-__________ __ _- 24

Euconulus fulvus (Miiller) __ ____ -_ 2

Pupilla vmiscorum (Linne) _ ______ 4

Succinea grosvenori Lea _._-_ _-_ - 16

Vallonia gracilicosta Reinhardt ._ - ___ 2

Vertigo modesta (Say) __________________________ 3

tridentata Wolf .._____________ 10

Of the nine species listed, five belong to the upper 

and transitional zones of Leonard, and four occur 

in all three zones. Because of the absence of S. avara 

and the numerical dominance of D. shimeki and 

S. grosvenori, which are upper zone species, the 

assemblage is assigned by the writer to the upper 

zone. The fauna in this single locality indicates that 

at least half of the total thickness of the Peorian 

in the Medicine Creek basin was deposited during 

the time represented by the upper faunal zone of 

Leonard. Leonard correlated his upper zone with 

the Tazewell Stade of the Wisconsin Glaciation.

During accumulation of the Peorian on the uplands, a period of incision to bedrock took place in 

the valleys. Valley fill of the Peorian that accumulated after this incision is set unconformably against 

the Loveland Formation, the Sangamon soil, and 

the Jower part of the Peorian. (See figs. 185 and 

191, both of which show valley fill of the Peorian 

set unconformably against the Sangamon soil and
276 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

the lower part of the Peorian.) From a distance the 

valley fill of the Peorian looks almost white, whereas 

the loess of the Peorian that overlies the Sangamon 

soil has a yellowish cast. On the uplands no physical 

discontinuity within the Peorian was discerned.

Molluscan fauna collected from the base of the 

valley fill of the Peorian at two localities indicates 

that deposition of the valley fill began in Tazewell 

time. The first locality is on the bank of Dry Creek, 

about 700 feet upstream from the gaging station, 

in the SE^4 sec. 24, T. 8 N., R. 28 W. Here the 

valley fill rests unconformably on the Ogallala Formation. Identification of the fauna was made by 

the writer, with the assistance of Dr. W. J. Wayne. 

The faunal list is as follows:

Columella alticola (Ingersoll) 

Discus cronkhitei (Newcomb)

shimeki (Pilsbry) 

Gyraulus circumstriatus (Tryon) 

Physa anatina Lea 

Pupilla muscorum (Lirme) 

Retinella electrina (Gould) 

Succinea grosvenori Lea 

Vallonia gracilicosta Reinhardt 

Vertigo gouldi coloradensis Cockerell

modesta (Say) 

Zonitoides arboreus (Say)

According to Leonard (1952, p. 19), D. shimeki 

and D. cronkhitei are reliable indexes to the upper 

(Tazewell) faunal zone of the Peorian. None of the 

other species in the assemblage is restricted to deposits either older or younger than this upper faunal 

zone.

A second fauna from the valley fill of the Peorian 

was collected at the side of Mitchell Creek, near a 

county road in the NW1/^ sec. 9, T. 6 N., R. 26 W. 

Identification was made by the writer, with the assistance of Dr. W. J. Wayne. The faunal list is as 

follows:

Discus cronkhitei (Newcomb) 

'Euconulus fulvus (Muller) 

'Gcfstrocopta armifera (Say) 

Lymnaea (Stagnicola) pahistris (Muller) 

, Retinella electrina (Gould) 

., Succinea grosvenori Lea 

Vallonia gracilicosta Reinhardt 

Vertigo tridentata Wolf

Although this Assemblage is different from the assemblage collected from the valley fill of the Peorian 

on. Dry 'Creek, a correlation with the upper molluscan faunal zbne of Leonard (1951, 1952) is indicated 

by the presence of D. cronkhitei and £. grosvenori., 

The,average tnickness of the loess of the Peorian, 

in the Medicine Creek basin is about 50 feet, and the, 

maximujp thickness is,about 80 feet. Thicknesses' 

were measured at'exposures in upland'localities and.

from the logs of test wells drilled by the Nebraska 

Conservation and Survey Division. (See figs. 183 

and 184.) The thickness of the loess reaches a maximum in the vicinity of the Platte River, gradually 

decreases southward to a minimum in a belt which 

is about 30 miles south of the Platte River and 10 

miles north of the Republican River, then again increases in thickness in the direction of the Republican. A well near the north side of the Republican 

River valley penetrated a thickness of 60 feet of 

loess, whereas a well near the south side of the 

valley penetrated a thickness of only 30 feet. About 

50 feet of loess of the Peorian is exposed in the 

vertical wall of a deep pit, 1.5 miles west of Eustice, 

Nebr. (fig. 192).

The valley fill of the Peorian is thicker than the 

loess. The exposed thickness of valley fill of the 

Peorian on the main stem of Medicine Creek, as 

measured from the surface of the Wellfleet terrace 

to the modern valley flat, is about 125 feet. On the 

assumption that the valley fill extends to bedrock, 

as it does on Dry Creek, the total thickness on 

Medicine Creek is about 200 feet. On the same 

assumption, the total thickness on Well Canyon, 

at a locality about 7 miles north of Curtis, is 180 

feet. The exposed thickness in the upper reaches 

of Dry Creek is 42 feet, and the total thickness is 

about 65 feet.

Loess of the Peorian in the Medicine Creek basin 

is a massive friable light-colored silt, similar to 

loess that has been described in other regions. The 

loess when dry is typically light gray (WYR 7/2) 

and when moist is light brownish gray or pale

f^^^, ~+

FIGURE 192. Peorian Loess (50 ft thick) overlying a horizon of Sangamon 

soil (upper dark band, marked S). Units beneath Peoriah Loess are 

Lpveland Formation (20 ft), Yarmouth soil (lowermost 'dark band,, 

marked Y), Sappa Formation (33 ft), and Pearlette A§h Member of 

S'aJppa' Formation'(20 ft): Excavation, made for removal of Pearlette, 

is 1.5 miles west of,'Eustice, Nebr. Photographed by C. H. Hembree, 1956.,
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 277

'brown (10YR 6/2 or 6/3). Although the loess appears to be homogeneous when viewed from a distance, closer inspection reveals abundant hollow 

'tubules made by rootlets, worm burrows, and small 

botryoidal structures which are worm castings. 

Within 5 feet of the ground surface, the loess may 

show such an abundance of these botryoidal structures as to indicate that all of it has passed through 

the digestive tracts of earth worms. Snail shells 

are generally present and are locally abundant. 

Lamination, although not usually observable, may 

appear where erosion by wind and raindrops has 

been sufficiently delicate to etch the laminae into 

relief.

Thin sections of seven samples of loess of the 

.Peorian, collected at different localities in the Medicine Creek basin, were studied under the petrographic microscope. The most distinctive textural 

features of loess, when viewed at high magnification, 

are the rather close packing arrangement and the 

presence of biref ringent clay coatings around detrital 

silicate grains. Grains larger than 125 microns in 

maximum diameter constitute less than 1 percent by 

volume of the samples, and grains larger than 31 

microns constitute 55 to 75 percent by volume. 

Particles larger than 31 microns may be regarded 

as the framework or skeleton of the loess, and particles smaller than 31 microns may be regarded as 

the matrix. The clay grain coatings, which are evidently authigenic, may be regarded as cement. The 

framework grains are mainly separated by their 

clay coatings and by the matrix. Contacts between 

framework grains are mainly tangential or long, 

and an average of about two contacts per grain was 

observed.

The birefringent clay coatings around detrital 

silicate grains consist of crystalline flakes oriented 

parallel with the surface of the coated grain. These 

coatings merge with the matrix and probably account 

in considerable part for the coherence of the loess 

and for the ability of loess to maintain a vertical 

face. Clay coatings on flat grains, such as mica 

flakes and glass shards, are in general thicker than 

coatings on equant grains. Clay coatings on grains 

are not characteristic of siltstones deposited under 

water. In loess the coatings are probably formed 

by wetting and drying qf th'q surface layer during 

deposition. Kubiena (1938, p. 134) has attributed 

the formation of grain coatings in soils to such 

wetting and drying. After rainfall, the soil solution 

may-fill'all pore spaces in the soil, but evaporation 

at the ground surface causes the soil solution to 

retreat to the angles of the intergranular spaces and 

to the surfaces of grains. As the soil dries, substances that were peptized or dissolved in the soil 

solution are left as coatings on grains. Although 

the grain coatings described by Kubiena 1 were of 

humus, coatings of clay also probably form by 

'wetting and drying. ' '

In this region loess of the Peorian is generally 

"calcareous, but the calcium carbonate is not uiiiformly disseminated. Calcium carbonate in the loess 

occurs in the form of silt-sized grains, which are 

doubtless primary; as powdery streaks and vein 

fillings; as fine-grained aggregates that line or fill 

rootlet tubules, worm burrows, or other openings; 

and as concretions. Many loess outcrops show zone's 

up to several feet thick that are noncalcareous'. 

Frankel (1957) has reported vertical variations in 

the distribution and concentration of secondary 

calcareous concretions and in the abundariee "and 

state of preservation of fossil mollusks in the loess 

in Nebraska. He attributes the"s£ variations 'to an 

intermittent rate of loess depositibn. S16w: deposition of loess is accompanied by solution of snail 

shells and by accumulation of secondary carbonate 

at depth. Rapid accumulation of loess is _ indicated 

by unaltered snail shells. Frankel suggests that 

many phantom soils are present. The writer has 

observed that massive silt, accumulated as1 Valley 

fill and indistinguishable from upland wind-laid 

loess, is more commonly noncalcareous than upland 

loess.

The Brady soil' was named and described by 

Schultz and Stout (1948) from a locality on the 

steep south side of the Platte Valley near Bignell, 

Nebr. This locality is also the type section for the 

overlying Bignell Loess (Schultz and Stout, 1945). 

According to the writer's observations, the huinic 

zone of the type Brady soil is about 1.3' feet thick, 

and the soil is weakly calcareous throughout; soft 

streaks and films of carbonate appear to a depth of 

2.2 feet from the top of the soil, and these are conspicuous from 1.3 to 2.2 feet. Overlying the Bratjy 

soil is a thickness of 8 to 10 feet of Bignell Loe'sS, 

on which the modern soil is developed. This modern 

soil is noncalcareous to a depth of 3.2 feet and shows 

a distinctly columnar structure to a depth of 1.3 feet. 

Above the modern soil is about 1 foot of] lighter silt, 

evidently colluvial and related to cultivation; of fields 

upslope from this locality. The modern sorf appeal's 

to be more strongly developed than the Bra&y soil. 

1 In spite of the fact that Medicine^ Creek* basin is 

adjacent tb the type locality 6f both the 'Brady soil 

and the overlying Bignell'Loess, the Brady soil, as 

separately developed from the riioderii soil, wa4 opserved at only three exposures, all in the northern 

part of the basin. " ' -
278 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

< General deposition of a thin layer of Bignell Loess 

over the uplands of the Medicine Creek basin is 

indicated by abnormally thick A horizons that commonly appear in the modern soil. The modern soils 

of Lincoln County, Nebr., have been mapped and 

described by Goke and others (1926); and the soils 

of Frontier County, Nebr., by Bacon and others 

(1939). The Medicine Creek basin lies within these 

two counties. Principal soils of the loess-mantled 

areas are the Holdredge very fine sandy loam and 

the broken phase of the Colby very fine sandy loam. 

The Holdredge soil, which is developed mainly on 

areas of flat or rolling upland, is mature. The B 

horizon of the Holdredge lies between 10 and 24 

inches in depth and shows an imperfectly developed 

columnar structure; and the Cea horizon, which 

contains a concentration of carbonate in the form 

of streaks, splotches, or threads, lies between 3 

and 4 feet in depth. A dark-brown zone, probably 

representing the Brady soil, lies between the B 

horizon and the Cca horizon at many localities.

STOGKVILLE TERRACE DEPOSITS

Typical relations of the Stockville terrace deposits 

to other stratigraphic units are shown, in figure 185. 

Along major valleys, the unconformity between the 

Stockville terrace deposits and older units is rarely 

marked by a scarp; if one were originally present, 

it has been obliterated by erosion on the valley-side 

slopes. Along minor valleys, the unconformity is 

usually marked by a distinct scarp.

The Stockville terrace deposits consist mainly of 

calcareous silt. In minor valleys the silt is less 

compact, the color is darker, and the bedding is less 

well defined than in major valleys. Dark humus-rich 

bands, beneath which the silt is leached to a depth 

of a foot or two, are observable at most exposures 

of the Stockville terrace deposits. The depth of 

burial of the uppermost band ranges, in different 

parts of the basin, from about 2 to 20 feet; and 

the number of bands varies from one exposure to 

the next. These bands, together with the underlying 

leached zone, .probably represent immature soils that 

formed during periods of slow deposition. The Stockville terrace deposits occur in nearly all valleys of 

the present drainage system, including valleys of 

first order.* The thickness, which depends on the 

size of the valley, is about 100 feet along Medicine 

Creek and Well Canyon, about 60 feet along Lime 

Creek, and about 30 feet along Dry Creejc. 

. A fauna of t snails and pelecypods was collected 

from the StocJkyiHe terrace deposits exposed along 

Medicine Cre^k ija the Np cor. sec, 13, T, 6 N., R. 27 

W. According to Dr. W. J. Wayne, who identified

the fauna, none of the species is extinct, and all are 

fresh-water species that now inhabit parts of central 

United States. Leonard (1952, p. 16) concludes, 

from his study of Bignellian molluscan faunas in 

Kansas, that the environment of Bignell Loess deposition was very much like present conditions in the 

Great Plains. The Bignell Loess is considered by the 

writer to be the upland counterpart of the Stockville 

terrace deposits.

MOUSEL TERRACE DEPOSITS

The Mousel terrace deposits consist mainly of silt 

and differ from the Stockville terrace deposits only 

by being somewhat darker in color and more compact. In some localities the Mousel terrace deposits 

contain fragments of carbonized grass stems, which 

are rare in the Stockville terrace deposits. Along 

the main course of Medicine Creek, two buried 

humus-rich bands, which are interpreted to be 

immature soils, were observed in deposits of the 

Mousel terrace.

Charcoal suitable for carbon-14 age determination 

was collected from the Mousel terrace deposits on 

Dry Creek in the NW^NEi/4 sec. 1, T. 7 N.,' R. 

28 W. The charcoal was in a lens of wood ashes 

and silt, buried at a depth of 14.5 feet below the 

ground surface. The age was reported as 2,200±200 

years (J. L. Kulp, Lamont No. 239C).

RECENT ALLUVIUM

Where valley trenching has exposed the full thickness of the late Recent alluvium as at localities on 

Dry Creek, Cedar Creek, Elkhorn Canyon, and Lime 

Creek the alluvium rests on the bedrock floor of the 

valley. Therefore, at these localities the valleys were 

incised to bedrock during the episode of incision that 

followed accumulation of the Mousel terrace deposits. 

Incision to bedrock may have been confined tq 

localities where the bedrock is high beneath the 

valley floor. In some valleys, such as Dry Creek and 

Elkhorn Canyon, accumulation of the late Recent 

alluvium has been interrupted by one or more 

episodes of incision during which the valley was 

trenched for part of its length by the upstream, 

migration of intermittently spaced channel scarps. 

In other valleys, such as Well Canyon and Fox Creek,, 

accumulation of the late Recent alluvium has evidently proceeded without the interruption of valley 

incision.

In the upper reaches of Dry Creek, where the 

previously untrenched valley flat is being trenched 

by head ward migration of a major channel scarp, 

the silty late Recent alluvium consists of a banded
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 279

FIGURE 193. Banding in late Recent alluvium, Dry Creek. 

(SW%NE% Sec. 29, T. 9 N., R. 27 W.)

upper part, about 14 feet thick, and a lower part 

that is indistinctly banded and lighter in color. 

(See fig. 193.) The dark bands of the upper part 

are somewhat more clayey than the light bands, 

and the dark color is a result of a finer texture and 

a higher content of organic matter. Both light and 

dark bands are composed mostly of loosely consolidated silt, through which abundant fragments of 

carbonized grass stems are scattered. Earth-worm 

castings are a conspicuous feature of the upper 

banded part, but they are less apparent in the more 

compact silt of the lower part.

A similar division of the late Recent alluvium of 

Elkhorn Canyon into an upper part that is banded 

and a lower part that is indistinctly banded has 

already been described. The banded fill is attributed 

to a rate of accumulation so rapid that time has not 

been available for oxidation of finely divided organic 

matter in the clayey bands. If the accumulation of 

banded fill began at the same time on Dry Creek as 

on Elkhorn Canyon, the banded fill shown in figure 

193 has accumulated during the past 500 years, 

approximately. This corresponds to an average rate 

of accumulation of about 0.34 inch per year, although the appearance of the banding indicates that 

the rate of accumulation was not uniform.

The banded alluvium seems to be characteristic of 

valleys that are being actively trenched, whereas 

the more compact unbanded alluvium is characteristic of more stable valleys. For example, the alluvium beneath the valley flats of Well Canyon and 

Fox Creek, which are not being actively trenched, 

is unbanded. On the other hand, distinctly banded

alluvium is exposed in the walls of rapidly advancing 

trenches on Dry Creek and Curtis Creek Canyon.

The present rate of accumulation of alluvium on 

valley flats must be known in order to relate sediment discharge by streams from the drainage basin 

(sediment yield) to the amount of sediment that is 

eroded from uplands and valley-side slopes (gross 

erosion). In spite of a thorough search, exposures 

of the late Recent alluvium yielded no artifacts 

nor other materials that would give an accurate 

indication of the rate of accumulation. Valley flats 

in many localities were examined after runoff events, 

and the depth of accumulation of freshly deposited 

sediment was measured. The thickness of the freshly 

deposited silt layer ranges widely (from a fraction 

of an inch to about 6 in.) from one locality to another, and almost as great a range was observed 

from place to place at a single locality. Moreover, 

freshly deposited alluvium may either remain at its 

place of deposition or be removed during the next 

runoff event. Farmers were asked about the time 

required for fenceposts on the valley flat to become 

wholly or partly buried. In the upper part of Dry 

Creek, two farmers estimated independently that 

5 or 6 feet of sediment had accumulated on the valley 

flat between 1920 and 1953. On Well Canyon one 

farmer estimated an accumulation of 2 feet on the 

valley flat in the past 40 years (1916-56) and another estimated an accumulation of 2 feet in the 

past 30 years (1926-56). On Medicine Creek, about 

4.5 miles north of Cambridge, a farmer reported 

that the wire of a hogpen, last used before the 1935 

flood on Medicine Creek, was buried to a depth of 

6 feet by 1957. An average rate of accumulation 

of about 1 inch per year on the valley flats of the 

drainage basin is probably of the right order of 

magnitude. A range between ^ inch and 3 inches is 

estimated, and this range would be found not only 

from valley to valley but also from place to place 

within the same valley.

The rate of accumulation of alluvium within a 

trenched channel, downstream from an actively advancing channel scarp, must be considered separately 

from the rate of accumulation on an untrenched 

valley flat. Examination of freshly deposited alluvium on the floor of trenched channels, several hundred feet downstream from an actively advancing 

channel scarp, indicates that 0.5 foot or more of 

alluvium can be deposited during a single runoff 

event. At several localities on Dry Creek, tin cans 

and wire were found buried to a depth of several 

feet in alluvium that had accumulated on the floor of 

the trench. Evidently, alluvium accumulates rapidly
280 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

in trenched channels but is susceptible to removal 

by a second episode of trenching.

SIGNIFICANCE OF CARBONIZED FRAGMENTS 

OF GRASS

In this region the younger a fluvial deposit is, 

the darker is its color. The dark color is due in 

part to finely divided organic matter and in part 

to fragments of carbonized grass stems, which are 

more abundant in the younger deposits. The carbonized fragments are attributed to grass fires, inasmuch as uncarbonized plant fragments would 

decay in this environment. The scarcity of carbonized stems in the older deposits might mean that 

grass fires were uncommon during the deposition 

of these deposits, or it might mean that any fragments originally present have been destroyed by 

oxidation or by the activities of earth worms. In an 

effort to decide between these alternatives, five thin 

sections of the Stockville terrace deposits, one thin 

section of the Mousel terrace deposits, and two thin 

sections of the late Recent alluvium were examined. 

In mineralogy, degree of development of clay coatings around grains, and packing of particles, all 

these thin sections were similar to thin sections of 

loess. However, the upper Recent alluvium shows 

many open spaces, which are attributed mainly to 

the activity of earth worms. Although carbonized 

fragments in the Stockville terrace deposits are 

small, they show no signs of partial oxidation. The 

tentative conclusion is that grass fires were more 

common during deposition of the Mousel terrace 

deposits and the upper Recent alluvium than during 

deposition of the Stockville terrace deposits. A 

greater incidence of grass fires might reflect a drier 

climate, or it might reflect a greater use of fire 

drives as a method of hunting game. The extent to 

which fire drives were used by prehistoric man on 

the Great Plains is largely speculative (Wedel, 

1961, p. 76).

SAND DUNES

The sand dunes within the Medicine Creek basin 

are part of a much larger dune area that is an outlier 

of the Sandhills of Nebraska. The geomorphology of 

the Sandhills has been briefly described by Smith 

(1955). In general, the dune relief in the Medicine 

Creek basin is irregular and hummocky, dominated 

by innumerable blowouts, most of which are stabilized by grass. However, an indistinct linear pattern 

was observed in aerial photographs of areas about 

7 miles north and 10 miles northwest of Wellfleet. 

The pattern is made by low, discontinuous longitudinal dunes in subparallel arrangement. The dunes

have a maximum length of about one-fourth of a 

mile, an average width of about 200 feet, and heights 

ranging from 10 to 30 feet; they show the furrowed 

crest that is typical of longitudinal dunes in the 

Sandhills. They are probably relicts of a more extensive dune system that has in most places been 

destroyed by blowouts but has in some places been 

modified into U-shaped dunes. Although the longitudinal dunes are oriented about N. 65° W., the ends 

of most of the U-shaped dunes are oriented more 

northerly. Elongated blowouts tend to be oriented 

at about N. 20°-30°W. Evidently, the prevailing 

wind direction has shifted since the formation of 

the longitudinal dunes. Most of the blowouts are 

clearly man induced, for they are associated with 

areas that formerly were or currently are cultivated.

The stream-dissected relief of the loess-mantled 

part of the basin is separated from the sand-dune 

relief by a transitional belt of ground that is intermediate both in relief and in particle size of underlying materials. The relief of this transitional belt 

is characterized by broad undrained depressions, 

generally elongated northward and separated by 

nearly level ground or by broad, rounded elevations. 

The underlying material, which is intermediate in 

particle size between dune sand and loess, is restricted to upland locations. The mixture of dune 

sand and loess, on which the Anselmo fine sandy 

loam and the Colby fine sandy loam are developed, 

is generally less than 3 feet thick and is underlain 

either by dune sand or by loess (Goke and others, 

1926; Bacon and others, 1939). Because of seasonal 

shifts in wind direction, silt from the loess-mantled 

areas has become mixed with sand from the dune 

areas.

In general, the dune sand does not seem to have 

transgressed very much over the loess-mantled areas 

since the end of deposition of the Peorian that is, 

within the past 12,000 years. In areas bordering 

the Sandhills, the surface of the Wellfleet terrace is 

generally free of windblown sand.

ARCHEOLOGY AND HUMAN OCCUPATION 

RESULTS OF ARCHEOLOGIC INVESTIGATIONS

Archeologic investigations have been made in the 

Medicine Creek basin by the Nebraska State Historical Society, by the Nebraska State Museum, and 

by the River Basin Surveys of the Smithsonian 

Institution. Three cultural aspects have been distinguished. These are represented by the Early 

Lithic sites, which are buried about 35 feet beneath 

the surface of the Stockville terrace (Terrace-2) ; 

by Woodland sites on the Mousel terrace (Terrace-
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 281

1) ; and by Upper Republican sites on the Stockville 

terrace.

Personnel of the University of Nebraska State 

Museum have excavated two sites on Lime Creek, 

designated Ft-41 and Ft-42, and one site on Medicine Creek about a half a mile downstream from the 

mouth of Lime Creek (Ft-50). All these sites are 

in the lower part of the Stockville terrace (Terrace2) at occupation levels marked by abundant artifacts 

and many hearths. No human remains were found. 

Schultz and others (1951), who investigated both 

the geologic and archeologic aspects of the sites, 

report dates of 9,167±600 years B.P. and 9,880± 

670 years B.P. from two charcoal samples taken 

from the bone-artifact zone of site Ft-41. A charcoal sample from the lower occupation zone of Ft-50 

yielded a date of 10,493±1,500 years B.P.

Two Woodland sites in the Medicine Creek Dam 

area are described by Kivett (1949). Habitation 

areas (marked by shallow basins, post molds, shallow 

pits, flint tools, and scant pottery fragments) were 

on the Mousel terrace (Terrace-1) and were covered 

by about 18 inches of silt. The remains give Wedel 

(1949) the impression of a rather uncertain hold 

on the region by a culturally simple group. According to Kivett, calcite-tempered ware found at the 

site is a marker for the Keith focus, which is one 

of several western Woodland cultural complexes. 

Although no radiocarbon dates were obtained at the 

Woodland sites on Medicine Creek, a radiocarbon 

date of 1,343±240 years B.P. has been obtained 

from a Keith-focus site on Prairie Dog Creek in 

northern Kansas, about 60 miles southeast of the 

Medicine Creek sites (Wedel and Kivett, 1956).

The Upper Republican Aspect represents the latest 

wholly prehistoric culture on Medicine Creek and is 

the most abundantly represented by archeologic remains, which are on the Stockville terrace and are 

buried under a silt mantle 6 to 18 inches thick 

(Kivett, 1949). The date of the culture is estimated 

to be about 500 to 600 years B.P. (Kivett, oral 

commun., 1957).

The geologic significance of these archeologic researches may now be considered. Radiocarbon dates 

on charcoal from occupation levels in the lower part 

of the Stockville terrace indicate that deposition of 

the Stockville terrace deposits began about 10,000 

years ago. If the Woodland sites on the Mousel terrace do indeed belong to the Keith focus and if this 

focus is correctly dated, then the terrace is older 

than 1,300 years. The silt mantle ranging in thickness from 6 to 18 inches covers Woodland sites on 

the Mousel terrace and Upper Republican sites on 

the Stockville terrace. Most of the sites are not

adjacent to upland areas from which colluvium 

might be readily derived, and no fluvial sedimentary 

structures were observed. Probably most of the silt 

was deposited on both cultural sites by the wind 

after the passing of the Upper Republican Aspect 

that is, during the past 500 years. Conditions under 

which the silt was deposited were of more than local 

magnitude, as the silt mantle appears on Upper 

Republican sites throughout the Republican River 

basin in southern Nebraska from Frontier County 

eastward to Webster County (Wedel, 1941). Probably the Upper Republican people inhabited the 

region during a wet period and emigrated about 

500 years ago at the onset of a dry period. During 

the wet period a humic zone developed, which was 

buried by windblown silt accumulated during one 

or more later dry periods.

SETTLEMENT AND LAND USE

One of the first settlers of the basin came to the 

Stockville area in 1860. His dwelling was used for 

the formal organization of Frontier County in 1872, 

when the population of the county consisted of a 

few stockraisers and only two permanent settlers. 

Through the later 1870's, settlers gradually entered 

Frontier County, and a little village arose at Stockville. By 1880 farmers had begun to claim; land and 

to settle on the divides. Until the Free Range Law 

was repealed in 1885, farming on the uplands was 

of little consequence. By 1900 most of the desirable 

land had been taken under the Homestead, Timber 

Claim, and Preemption Acts.

Bacon and others (1939) note that corn has beeri 

the main crop since farming began. The first'settlers 

did not understand how to adjust their farming 

methods to the highly variable precipitation, and 

their practices were crude and wasteful. A series 

of dry years, accompanied by plagues of grasshoppers, culminated in the disastrous droughts of 1893 

and 1894. Many of the early farmers were forced 

to leave the region, and agricultural development 

was delayed. The farmers who remained acquired 

larger holdings and gradually adjusted their farming 

methods to local conditions. Although corn remained 

the most important crop, increasing amounts of 

wheat, oats, rye, barley, and sorghums were grown;

Census figures have not been published for the 

basin as a unit, but satisfactory approximations df 

the population may be made from the precinct 

census. The total population was 7,750 in 1930, 

6,400 in 1940, and 5,900 in 1950. The total popular 

tion of the basin decreased by 23 percent between 

1930 and 1950, and the proportion of persons living 

in the towns has increased from 42 percent in 1930
282 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

to 51 percent in 1950. Population density of the 

basin in 1950 was 8.7 persons per square mile.

The number of settlers and domestic animals in 

the basin before 1875 was too small to have any 

significant effect on erosion and deposition. The 

sparseness of the grass cover on the uplands during 

1869-72 reported by surveyors cannot be attributed 

to grazing by livestock. According to the Federal 

census, cattle and horses in Frontier County increased from about 30,000 in 1890 to about 43,000 

in 1935. Farming could have had little geologic 

importance before 1879, when, according to the 

Federal census, only about 600 acres in Frontier 

County had been plowed. Only about 104,000 acres 

of plowed land was reported in Frontier County in 

1889, whereas about 425,000 acres was reported in 

1929.

DRAINAGE SYSTEM

EVOLUTION OF THE DRAINAGE SYSTEM

According to the stratigraphic evidence presented 

in this report, major valleys of the Medicine Creek 

basin, such as Cut Canyon and Cedar Creek, were 

in existence during- the Kansan Glaciation, and their 

bedrock floors were at about the same depth as at 

present. In the Republican River valley also, the 

bedrock floor has not been deepened since Kansan 

time according to a geologic section of the river 

valley near McCook, Nebr. (Bradley and Johnson, 

1957 pi. 38). Drilling along two traverses between 

the Republican and the Platte Valleys (figs. 183 and 

184) revealed buried valleys, cut into the Ogallala 

Formation and filled with pre-Wisconsin deposits. 

These valleys, which evidently had an eastward 

trend, were probably filled with alluvium and abandoned in Nebraskan or early Kansan time. Plum 

Creek, which flows eastward into the Platte River, 

is probably a relic of the early Pleistocene drainage. 

Deposits of Pearlette Ash Member of the Sappa Formation of Kansan age are distributed along the 

valley of Plum Creek and its former westward extension, which was captured by Deer Creek after 

deposition of the Peorian.

The valleys of most major tributaries (fifth and 

higher order) were established by incision and probably by extension of the drainage system during 

the episode of incision that followed deposition of 

the Sappa Formation. These incised valleys were 

subsequently filled with the Loveland Formation to 

levels that are generally 10 or 20 feet above the 

modern valley flats. Most valleys of lower order 

than fifth were probably not in existence in Sangamon time, for the Sangamon soil does not dip toward 

them.

There is no evidence of extension of the drainage 

system between the end of Sangamon time and the 

initial deposition of loess of the Peorian, although 

the valleys may have been incised. After about half 

of the total thickness of the Peorian had accumulated 

on the uplands, the valleys were incised to bedrock. 

The incision was followed by an episode of deposition 

during which the upper part of the Peorian accumulated in the valleys and on the uplands.

The landscape as it existed at the end of deposition 

of the Peorian can be reconstructed (fig. 194) from 

remnants such as those shown in figure 195 (upper) . 

In a few places, as for example at the eastern tip 

of Dry Creek, the valley heads of Peorian time have 

been preserved. Deposition of the Peorian Loess 

and development of the Brady soil are tentatively 

assigned to the interval 60,000 to 12,000 years B.P.

The drainage system was developed to approximately its present pattern and extent during the 

episode of incision that followed deposition of the 

Peorian (fig. 1945). The incision is perhaps associated with a rapid retreat of late Wisconsin ice 

sheets and a rather abrupt climatic warming about 

11,000 years B.P., the evidence of which is presented 

by Broecker and others (1960). Valleys were probably incised to about the same bedrock altitudes as 

during previous erosional episodes, but drainage 

was gradually increased. The extent of incision and 

increase in drainage density is strikingly shown in 

an area just outside the Medicine Creek basin, 

where the head of North Plum Creek was captured 

by Deer Creek. Although the Deer Creek drainage 

was incised about 100 feet below the surface of the 

Peorian, the North Plum Creek drainage just east 

of the point of capture was not incised, and the 

surface of the Peorian has been preserved almost 

intact. (See fig. 196.)

The lengthy duration of the episode during which 

the Stockville terrace deposits accumulated is indicated by extensive grading of valley-side slopes and 

valley heads to the level of the Stockville terrace. 

In profile, the valley-side slopes that join the Stockville terrace to the upland are straight for most of 

their length, gently convex upward at their intersection with the upland and gently concave upward 

at their intersection with the terrace. Most of the 

slopes are graded across the Peorian, but some are 

graded across older rock units, including the Ogallala. Accumulation of the Stockville terrace deposits 

and grading of slopes are assigned tentatively to 

the interval between the climatic warming of about 

11,000 years B.P. and the middle of the Altithermal, 

about 5,000 B.P. The Stockville terrace and slopes 

graded to the terrace can be identified nearly every-
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 283

- :""K'u**

 -' .' ' iV"-'**

FIGURE 194. Evolution of the relief since deposition of the Peorian Loess. A, Valleys were broad and valley sides gently sloping at end of 

deposition of the Peorian, about 12,000 years B.P. B, Drainage system was incised, extended, and branched during episode that lasted from 

about 12,000 to 11,000 years B.P. C, Valley sides and valley heads were graded during accumulation of Stockville terrace deposits, from about 

11,000 to 5,000 years B.P. D, Relief was modified during the several episodes of incision and deposition that occurred during the past 5,000 years.
284 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

FIGURE 195. Remnants of the side, slopes and valley flats of former drainage 

systems. Upper, Looking south from the Platte-Republican drainage 

divide (in the NE^ sec. 31, T. 11 N., R. 28 W.) along a fourth-order 

tributary to Fox Creek. Remnants of the valley sides of Peorian time are 

preserved on the divides between side tributaries, and these remnants show 

the general aspect of the former valley. Middle, Looking north along 

Well Canyon in the SW% sec. 27, T. 10 N., R.. 29 W. Gentle slope on horizon (left) is slope of valley side of Peorian time. Steeper converging 

slopes on horizon (left center) are slopes of valley side of Stockville time. 

Remnant of the valley flat of Stockville time is in middle distance, and 

below this is a remnant of the valley flat of Mousel time. Narrow trench 

on modern valley flat showed little or no change from 1937 to 1952. Lower, 

Looking southeast from the upper end of a fifth-order tributary to Cut 

Canyon, in the NEVi sec. 26, T. 10 N., R. 29 W. Crest of interstream 

divides between side tributaries in background indicate approximate level 

of valley flat of Peorian time. Valley head in foreground was graded 

in Stockville time, as were the steep side slopes leading to it.

where in the basin and constitute a reference surface 

to which the incision of later erosional episodes can 

be related.

The Stockville terrace was formed at some time 

before 2,200 years_B.P., which is the carbon-14 date 

obtained from Mousel terrace deposits on Dry Creek. 

Tentatively, the Stockville terracing is placed at 

about 5,000 years B.P., and the cause is assigned 

to drought during the Altithermal, which was a 

well-established warm-dry climatic episode that 

lasted from about 6,000 to 4,000 B.P. In minor 

valleys (of fifth and lower order) the effects of this 

terracing cannot generally be distinguished from 

the effects of the Mousel terracing. During one or 

the other of these two episodes of erosion, trenching 

extended to the heads of many minor valleys. Other 

minor valleys were trenched for only part of their 

length, and still others escaped being trenched.

Deposition of the Mousel terrace deposits began 

at some time before 2,200 years B.P. and ended at 

some time before 420 years B.P. (carbon-14 date 

from late Recent alluvium on Elkhorn Canyon). 

Tentatively, this deposition is assigned to the interval 4,000 to 1,000 years B.P., which corresponds 

roughly with the dates of the "Deposition 2" described by Miller (1958, p. 38) in his generalized 

alluvial sequence in Western United States. (See 

table 2.) The terracing of the Mousel terrace must 

have been brief, inasmuch as the thickness and properties of the late Recent alluvium indicate that not 

much less than a thousand years would be required 

for its accumulation.

A tentative chronology of post-Sangamon depositional and erosional episodes in the Medicine Creek 

basin is summarized below:

Tears B.P.

Local incision of valley bottoms ______. __.__ Present to 500.

Accumulation of late Recent alluvium _.______ Present to 900.

Terracing of Mousel terrace . ___ ___ 900 to 1,000.

Accumulation of deposits of Mousel terrace 1,000 to 4,000.

Terracing of Stockville terrace .__ ______._.____ 4,000 to 5,000.

Accumulation of deposits of Stockville terrace. 5,000 to 11,000.

Incision and extension of the drainage system to approximately its present pattern. 11,000 to 12,000.

Accumulation of Peorian Loess and development of Brady soil., 12,000 to 60,000.

MORPHOMETRY

Detailed measurements were made of the drainage 

basins of six major tributaries of the Medicine Creek 

basin, the locations of which are shown in figure 

176. The purpose of the measurements was to determine the drainage-basin characteristics that correlate most closely with water and sediment yield 

and with the development of gullies. Where gaging
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA

100° 30'

285

40°35'20'

T.9N.

FIGURE 196. Capture of head of North Plum Creek by Deer Creek. In inset, which is reproduced from the Stockville NE quadrangle, relict topography of the depositional surface of Peorian time is shown at right.
286 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

stations (also shown on fig. 176) are not at the 

mouth of a basin, only that part of the basin upstream from the station was measured.

Ordering of the drainage system was carried out 

according to the method of Strahler (1952, p. 1,120), 

which is a modification of the method of Horton 

(1945, p. 281). Strahler's method is not only more 

objective and convenient, but it is also more valuable for many hydrologic purposes. A channel segment of third or higher order obtained by Strahler's 

method is of approximately uniform cross-sectional 

area throughout its length, but this is not true of 

channels obtained by Horton's method. The word 

"channel" is used here in the same sense that the 

word "stream" is used by Horton and Strahler in 

connection with ordering. A channel is an established 

watercourse that may transmit water continuously, 

intermittently, or ephemerally. The flow of water 

in most channels of the Medicine Creek basin is 

ephemeral, and the term "stream" is inappropriate 

for them.

Properties of fluvially eroded landforms and recommended symbols for these properties are summarized by Strahler (1958, p. 282-283). The properties discussed in this report and the symbols used 

are listed below. Measured properties are those 

that can be directly measured or counted, and derived properties are those that cannot be directly 

measured but must be computed from measurements.

Measured properties:

Total area of drainage basin, A

Area of upland in drainage basin, Act

Area of valley system in drainage basin, A* (A* = A 

Aa) 

Channel order, u (for examples: u-i, first order; Ua, second order)

Number of channels of order u, Na 

Channel length, L

Channel length, mean length of segments of order u; Lu 

Basin relief, H 

Basin length, L&

Derived properties: 

Channel slope, Se 

Valley slope, S, 

Bifurcation ratio, Rb

Channel length ratio, RL

Channel frequency, Fu

Drainage density, D

Relief ratio,

Elongation ratio, Re

r> Re =

diameter of a circle

Adjusted channel frequency, F*

For practical purposes first-order channels in the 

Medicine Creek basin are defined as the lowest order 

of channels represented by V-shaped bends in contour lines on the available topographic maps. Fortunately, the accuracy of the topographic maps in 

representing small drainage channels is excellent, 

and the scale (1:24,000) and contour interval (10 

ft) are also favorable for representation of small 

channels. Drainage patterns of several fifth-order 

basins were plotted both on aerial photographs and 

on topographic maps, and comparison showed that 

results obtained by the two methods were very 

similar.

Nearly all the first-order channels represented by 

V-shaped bends in contour lines are channels that 

formed immediately before or during accumulation 

of the Stockville terrace deposits, and the valley 

sides leading to these channels show some degree of 

grading. In only a few places has modern gullying 

proceeded far enough to form channels where no 

channels had existed previously.

Each of the six major subbasins was separately 

outlined on the topographic maps, and each subbasin 

area was measured with a polar planimeter. In 

addition, the area of upland in each subbasin was 

measured. Upland is defined as undissected remnants 

of the land surface that existed at the end of deposition of the Peorian. For practical purposes upland 

is distinguished on topographic maps by smooth 

contour lines that is, by contour lines that do not 

have V-shaped indentations. Where areas of upland 

are continuous around the periphery of a drainage 

system as in basins 1-1', A', 0-4', and C-2' of 

figure 197 the area of upland was determined by 

measuring with a polar planimeter the area actually 

occupied by the drainage system and subtracting 

this area from total basin area.

For Dry Creek and Lime Creek, every channel of 

every order was drawn in color on topographic maps, 

counted, and measured individually. Sampling procedures, similar to those described by Leopold and 

Miller (1956, p. 16), were tested for the approximation of number, mean slope, and mean length of 

first- and second-order channels in the other subbasins. These procedures were used for Mitchell 

Creek, Well Canyon, Fox Creek, and Brushy Creek.
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 287

CONTOUR INTERVALS 10 AND 20 FEET

DATUM IS MEAN SEA LEVEL

FIGURE 197. Variations in drainage texture in the Medicine Creek basin. Basins shown are fourth or fifth order.
288 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

Two derived properties drainage density and 

channel frequency commonly are used but are ambiguous for so-called immature or youthful basins 

in which areas of undissected upland remain. For 

such basins a distinction must be made between the 

properties of the drainage system and the properties 

of the drainage basin. If a particular drainage system were transferred without any change in properties to a larger drainage basin, the values of 

drainage density and channel frequency would 

change regardless of the constancy of the drainage 

system. Drainage density is also ambiguous for 

another reason: a drainage system consisting of 

short channel segments may have the same total 

channel length as another drainage system that 

consists of fewer but longer segments. Melton 

(1958, p. 36) has proposed that the ratio of F/D2 

is constant for mature drainage basins, but this is 

not true of Medicine Creek, which for the most 

part is immature. To compare the channel frequency 

of two immature drainage systems whose drainage 

basins differ in percentage of upland, drainage basin 

area must be adjusted by subtracting the area of 

upland. Channel frequency, expressed as number 

of channels per square mile of area actually occupied 

by the valley system, is here called adjusted channel 

frequency.

Relief ratio was defined by Schumm (1956, p. 612) 

as the ratio between H, basin relief, and L6, the 

longest dimension of the basin as measured parallel 

to the principal drainage channel. Basin relief is 

the difference in altitude between the highest and 

lowest points in the basin. A measure of basin

shape, also devised by Schumm, is the elongation 

ratio, which is derived by dividing the diameter of 

a circle having area equal to that of the basin by 

the basin length, L6.

A measure of mean valley-side slope is difficult to 

obtain because the side slopes leading to low-order 

channels are steeper than side slopes leading to 

high-order channels. For example, measurements 

on topographic maps indicate that slopes leading 

to first-order channels on the lower part of Dry 

Creek have a mean angle of about 25°, whereas 

slopes leading to the main channel (which is seventh 

order) have a mean value of about 12°. Slopes leading to the main channel of lower Dry Creek were 

measured in the field during the preparation of 12 

transverse valley profiles. Of 23 slopes, 13 ranged 

from 8 to 11°, only 2 were greater than 15°, and 

none were less than 6°. The mean angle was 11.5°; 

the mean deviation, 3.3°; and the mode, 10°. Mean 

side slopes of third- and fourth-order channels probably represent the best approximation to mean 

values for the drainage system as a whole and are, 

therefore, quoted in table 3.

DRAINAGE TRANSFORMATION AND 

VARIATIONS IN DRAINAGE TEXTURE

Variations in drainage texture are accompanied by 

variations in most drainage-basin characteristics. 

The major variations in drainage texture within the 

Medicine Creek basin are illustrated by the representative fourth- and fifth-order drainage basins in 

figure 20. Basins 0-2' and K-l' are typical of the 

upper part of Medicine Creek; 1-1' and 0-4', of the

TABLE 3. Measured and derived properties for the Medicine Creek basin and its major subbasins

Drainage basin

Mitchell Creek __ ... ... .. ._

Brushy Creek

Dry Creek (above gage) : 

Total _______.. ___ ..

Lower only

Fox Creek: 

Total.... ___ .. . __ . ._

Lower only

Well Canyon: 

Total ___ ....... ___ .. ___ 

Upper only ____

Medicine Creek above

Total 

area, A 

(sq mi)

11.6 

52.1

73.8

21.1 

12.6

8.5

72.5 

57.0 

15.5

53.3 

22.7 

30.6

549.0

Area of 

upland,

Aa

(percent)

37.0 

51.8

25.9

34.8 

25.0 

49.5

16.5 

12.6 

30.4

20.4 

12.3 

26.5

30.0

Area of 

valley 

flat 

(percent)

14.0 

11.5

16.0 

14.2

27.2

22.6

Valley 

slope of 

main 

segment 

(ft per ft)

0.00299 

.00367

.00550 

.00366

.00360 

.00386 

.00310

.00286 

.00290 

.00284

Mean 

valley 

side 

slope 

(ft per ft)

0.179 

.200

.412 

.360

.363

_______

Mean 

upland 

slope 

(ft per ft)

0.026 

.013

.022 

.032

.037

.036

Relief 

ratio, 

Rh

0.0114 

.0050

.0064 

.0079

.0059

.0052

.00435

Elongation 

ratio,

Re

0.662 

.416

.734 

.475

.445

.335

First-order channels

Mean 

length, 

L 

(ft)

410 

370

192

267 

260

287

250

245

Mean 

slope,

Sc

(ft per ft)

0.110 

.100

.234

.187 

.195 

.160

.241

.251

Adjusted 

freaueney, 

F*u 

(channels 

per sq 

mi)

140 

165

260

203 

214 

185

250

235 

260 

220

200
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 289

central part; and A' and C-2', of the lower part. 

Major differences in these small basins, as in the 

larger subbasins of which they are representative, 

lie in the percentage of upland, the length and frequency of first-order channels, and relief ratio. 

These differences can be conveniently related to 

differences in geomorphic history.

In basins A' and C-2' valleys at the end of Peorian 

deposition were broad and shallow, and the gently 

sloping valley sides were graded all the way to the 

interstream divides. Divides were rounded, and no 

areas of flat upland remained. These valleys were 

deeply incised during the episode of erosion that 

preceded deposition of the Stockville terrace deposits, and channel frequency was increased. During 

accumulation of the Stockville terrace deposits, the 

transformed drainage system was smoothly graded, 

and the gently sloping tips of first-order tributaries 

were extended nearly to the former drainage divides. 

Basin C-2' represents a less advanced stage of 

grading than Basin A', which is nearer the mouth 

of Medicine Creek; it was incised first, and consequently underwent a longer period of grading during accumulation of the Stockville terrace deposits.

Basins 1-1' and 0-4' are representative of the 

central part of the Medicine Creek basin, where the 

valleys at the end of deposition of the Peorian were 

more narrow than those in the lower part and were 

separated by broad, nearly flat uplands. Later, 

these valleys were deeply incised, and the drainage 

was extended into the upland; however, large areas 

were left undissected. The sides and heads of firstand second-order valleys were smoothed and somewhat reduced in angle during deposition of the 

Stockville terrace deposits, but they remained rather 

steep. The surface into which basin 0-4' was incised 

is unusually flat, because it represents the valley 

flat and gently sloping valley side of Medicine Creek 

at the end of deposition of the Peorian.

In basin 0-2', valleys at the end of deposition of 

the Peorian were narrow and steep sided (average 

slope angle about 14°). The channel frequency, already considerably higher than that in the lower 

part of Medicine Creek, was greatly increased during the episode of incision preceding deposition of 

the Stockville terrace deposits. Moreover, the newly 

incised valleys, although somewhat graded during 

Stockville time, retained their steep sides and heads. 

Later episodes of incision have further increased the 

frequency of first- and second-order channels. Basin 

K-l' is similar in history, but it formed on a less 

steeply sloping surface and underwent a greater 

degree of grading during the deposition of the 

Stockville terrace deposits.

500,000

100,000 -

10,000 -

1000 -

100

CHANNEL ORDER 

FIGURE 198. Mean channel length in relation to channel order.

In summary, variations in the modern drainage 

pattern are related to two conditions that existed at 

the end of deposition of the Peorian the extent of 

drainage transformation that preceded deposition 

of the Stockville terrace deposits and the amount of 

grading that took place during deposition of the 

Stockville terrace deposits. To a minor extent, the 

drainage pattern has been modified by episodes of 

incision that followed deposition of the Stockville 

terrace deposits. At the end of Peorian deposition, 

valleys were broad and shallow in the lower part of 

the basin, narrow and separated by flat divides in 

the central part, and narrow but separated by narrow divides in the upper part. Grading during 

deposition of the Stockville terrace deposits reached 

an advanced stage in the lower part of the basin, 

and in general the stage of grading decreases in an 

upstream direction.

The curves representing the relation of mean channel length to channel order (fig. 198) can be arranged in a sequence that illustrates some of the 

major variations in drainage texture. The length 

of channel segments (of orders one through five) 

shows a consistent decrease from Lime Creek, in 

the lower part of the basin, to Brushy Creek, in the 

central part. Also, RL between orders one and two, 

as well as between orders two and three, is less than 

RL between higher orders. The change in slope at 

the lower end of the curves applies only to orders 

one and two for Lime Creek, but it applies to orders 

one through four for Dry Creek and to orders one 

through three for Well Canyon, Fox Creek, and 

Brushy Creek.

An upward concavity of the curves representing 

the relation of mean channel length to channel order,
290 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

CHANNEL ORDER 

FIGURE 199. Number of channels of each order in relation to channel order.

as plotted on semilogarithmic paper with channel 

order as independent variable, was noted by Strahler 

(1952) and Broscoe (1959, p. 5). Broscoe concluded 

that Horton's (1945) "law of stream lengths" may 

not apply when Strahler's method of ordering the 

drainage system is used. However, the basins analyzed by Strahler and Broscoe were of fourth or 

smaller order; basins of larger order must be analyzed for proper definition of the relation. In the 

Medicine Creek basin the relation is exponential, 

but the exponent changes at second or third order 

(fig. 21).

If a drainage system having low density of channels is transformed by the growth of new first- and 

second-order channels without extension of the 

higher order channels, a marked absolute shortening 

of lower order channels can take place without much shortening of higher order channels. The 

order of higher order channels may change, but the 

absolute length remains nearly constant. A transformation of this kind took place in the Medicine 

Creek drainage basin at the end of deposition of the 

Peorian. Furthermore, the transformation can take 

place without much change in the bifurcation ratio. 

The bifurcation ratios of the same subbasin, as well 

from one subbasin to another, are remarkably constant. (See fig. 199.) One result of a transformation of the kind described is a change in slope, at 

lower channel orders, of the curve relating mean 

channel length to channel order. The major subbasins that have undergone the greatest drainage 

transformation and, consequently, have the highest 

frequency of first-order channels are those that 

show the change in slope extending to third or even

fourth order. In a sense the change in slope of the 

curve relating mean channel length to channel order 

is a measure of disequilibrium of the drainage 

system.

GULLY EROSION 

DEFINITION AND CLASSIFICATION OF GULLIES

In a region such as the Medicine Creek basin, 

where many of the drainage channels have steep, 

unvegetated sides and are incised in massive silt, 

the distinction of a gully from other drainage channels is difficult. According to general usage, the 

essential features of a gully are its size (which is 

larger than a rill), recency of extension in length, 

steepness of sides and head, incision into unconsolidated materials, and ephemeral transmission of flow. 

Gullies in the Medicine Creek basin are incised into 

the sides, head, or bottom of previously established 

drainageways, which are deepened or extended by 

development of the gully. The lower limit of depth 

for a gully is placed at about 2 feet because channel 

head scarps that are less than 2 feet in height show 

a very slow rate of advancement. Most of the actively 

advancing head scarps in the Medicine Creek basin 

are greater than 6 feet in height. The lower limit 

of width is arbitrarily placed at about 1 foot. The 

criterion of recency of extension requires that some 

evidence be obtained for extension within a period 

of a few years. Extension can be established by comparison of aerial photographs, by comparison of 

field measurements made at intervals of a few years, 

or by indirect evidence observed in the field. If the 

sides and head of a drainage channel have a slope 

less than about 45°, the channel is probably not actively advancing and hence would not be considered 

a gully. In this report the following definition of a 

gully is followed: A gully is a recently extended 

drainage channel that transmits ephemeral flow, has 

steep sides, a steeply sloping or vertical head scarp, 

a width greater than about 1 foot, and a depth 

greater than about 2 feet.

The sides and heads of gullies in the Medicine 

Creek basin are steep slopes, straight in profile, 

that are here called erosional scarps or simply scarps.

In addition to the erosional scarps at the sides 

and heads of gullies, other erosional scarps are 

conspicuous elements of the landscape. These include 

step scarps on slopes (Brice, 1958), scarps that form 

the fronts of terraces, and scarps at the base of 

valley-side slopes. The inclination of a scarp ranges 

from about 45° to nearly 90°, and the height ranges 

from a foot to about 40 feet. Generally, the top of 

a scarp meets the surface into which it is cut at a 

sharp angle, but the base of the scarp decreases in
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 291

slope as it merges with the surface below. The term 

"channel scarp" is appropriate for a. scarp that 

forms a break in the long profile of a well-defined 

channel. If a particular channel scarp is the headward terminus of a gully and attention is to be 

drawn to this fact, the channel scarp may be called 

a head scarp. Not all gully head scarps are channel 

scarps. The term "head cut," although commonly 

applied to the headward terminus of a gully, is unsatisfactory because it may refer either to the scarp 

at the head of a gully to to the whole gully head. 

Moreover, a channel may have many scarps along its 

length, and the designation of several of these as 

head cuts is confusing. The scarps that form the 

sides of a gully along its length are here called side 

scarps.

Study of gullies in the field and on aerial photographs of the Medicine Creek basin has shown that 

the depth of a gully, its areal pattern, and its rate 

of growth are more closely related to the topographic 

position of the gully head than to any other single 

factor. Of particular significance is the location 

of the gully head in relation to the previously established drainage system. On the basis of location, 

gullies are classified as valley-bottom gullies, valleyhead gullies, and valley-side gullies. Inasmuch as 

valley bottoms grade smoothly into valley heads and 

valley sides, the distinction among the different 

classes of gullies is arbitrary. Moreover, a valleybottom gully becomes a valley-head gully as its head 

scarp migrates into the valley head. The valley-head 

gullies are by far the most numerous kind, and 

nearly all of these are in steep valley heads that 

border areas of upland.

The size of a gully depends on its depth and areal 

dimensions; but because of the irregular shape of 

gullies, the areal dimensions cannot be expressed 

simply and consistently. For complexly branching 

gullies, it is not clear whether or not the unconsumed area between the branches should be considered part of the gully. The best approximation 

to an expression of gully size seems to be the maximum width of the gully head. Inasmuch as gully 

depth increases roughly in proportion to width of 

gully head, the width of the gully head is an indirect 

expression of gully depth. In an arbitrary ranking 

of gullies according to width of gully head, valleyside and valley-bottom gullies must be considered 

separately from valley-head gullies, which are relatively wider in proportion to depth.

AGE AND ACTIVITY OF EROSIONAL SCARPS

Obviously, a scarp is younger than the surface 

into which it is cut. All the scarps in the Medicine

Creek basin are considered to be younger than the 

Stockville terrace deposits. Some of the slopes 

graded to the level of the Stockville terrace are 

steep, especially those in the upper parts of the 

drainage basin; but these slopes are not regarded 

as scarps because they have an inclination less than 

45°. Also, the steepest part of these slopes (in a 

particular area of the basin) is graded to about the 

same angle, and the upper parts of the slopes decrease in angle as they merge with the older Peorian 

surfaces.

Regardless of the age of the surface it cuts, a 

scarp may be either active or inactive. A scarp is 

considered to be active if it has migrated a distance 

that can be measured by comparing of aerial photographs made in 1937 and in 1952 or if it shows field 

evidence of recent movement. In the field, inferences 

as to activity were made from the type of vegetation 

on the scarp, from the degree of inclination, or from 

evidence of recent or imminent slumping. A thick 

sod of native grass indicates an inactive scarp; a 

cover of brush (such as wild rose, buckbrush, or 

currant) indicates a moderately active scarp; and 

lack of vegetal cover, or a cover of weeds, indicates 

an active scarp. In general, the more nearly vertical 

a scarp, the more likely it is to be active. However, 

many scarps that were bare and nearly vertical 

showed little or no migration during the interval 

1937-52. Even a bare and nearly vertical scarp was 

not regarded as active unless recently slumped silt 

was observed at the scarp base or unless fissures were 

observed on the ground surface beyond the scarp.

CHANNEL SCARPS AND VALLEY-BOTTOM 

GULLIES

Varieties of valley-bottom gullies are distinguished 

on the basis of position with respect to one another 

and to different topographic levels produced by 

trenching of the drainage system. The main varieties are indicated by numerals in figure 200. The 

two gullies at upper left (1), which are in the same 

valley bottom but are separated by a reach of undissected valley, are of the sort called discontinuous 

by Leopold and Miller (1956, p. 29). When the 

head scarp of a downvalley gully reaches the tail of 

an upvalley gully, a stage of coalescence is reached; 

and the two gullies are integrated into a single 

trench as the downvalley scarp advances. Similarly, 

the advance of a major scarp in a large valley is 

commonly preceded by the advance of a minor scarp 

(2). A scarp may be initiated on the floor of a 

trench, where it may advance either into freshly 

deposited sediment (3) or into previously undisturbed alluvium. Channel scarps on the floor of a
292 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

:§< ^irnw'X- ?^^^$$*

^^S^S^^^^-' ">s

^^^ffejj^^^J^. W L^T~ "" " >^^^

^/////T/T^^^^^^'.^-^-^^^r

'^rtifei^f^fc

_ " *7~ T- -« _ VXy'- '*!.>'' >^ ^ "^ ^*". m*?*?2r''Zl

l ...

^^V^

:

FIGURE 200. Composite sketch, based on field sketches and photographs, showing the different varieties of valley-bottom gullies. Actively eroding

scarps are indicated by darker shading. Numbered features are described in text.

trench are here described as inset. Remnants of the 

original gully floor, left along the gully sides after 

passage of an inset scarp, constitute an inset terrace 

(4). Another variety of valley-bottom gully is illustrated by the two gullies (5) in the middle ground of 

figure 200. Unlike the discontinuous gullies, which 

have no relation to the topographic level formed by 

trenching elsewhere in the drainage system, these 

gullies were initiated at the side scarps of the gully 

in the foreground and are accordant with its floor.

The location of the head scarps of major valleybottom gullies in the Medicine Creek basin is shown 

in figure 201. Most of the gullies are in the size 

category of. very large, but some are in the category 

of large. The scarps range in height from 10 to 25 

feet and are in valleys of fourth or higher order. 

Advance of the scarps during the period 1937-52 

ranges from a maximum of about 3,400 feet (for 

gully B4 on fig. 201) to a minimum of about 200 feet. 

Two significant facts relevant to the origin of the 

scarps are indicated by their areal distribution:

Scarps are most numerous in the central and lower 

part of the basin, and scarps in large valleys are 

commonly upstream from the confluence of a large 

tributary.

The greater abundance of the scarps in the central 

and lower part of the basin is attributed to the 

relative narrowness of the valley bottoms there. 

(See table 4.) In general, the width of a valley 

bottom is much affected by the degree of trenching 

both before and after deposition of the Stockville 

terrace deposits. The branching valley at upper left 

(6) in figure 200 was represented by a relatively 

narrow and shallow trench before deposition of the 

Stockville terrace deposits. During deposition of 

the Stockville terrace deposits the valley sides were 

graded, and the valley has been little affected by 

post-Stockville trenching. By contrast, the valley 

at upper right (7) was represented by a relatively 

deep and wide trench before deposition of the 

Stockville terrace deposits. Post-Stockville trenching has extended to the valley head, and only narrow
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 293

EXPLANATION

Heavy transverse 

line indicates position of head scarp

B8

Numbered gully

See text for description

FIGURE 201. Head scarps of major valley-bottom gullies.
294 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

TABLE 4. Drainage system properties, listed according to

channel order, for major subbasins of the

Medicine Creek basin

Subbasin

Mitchell Creek 

Dry Creek................

Well Canyon ..........

Fox Creek . _ .. 

Brushy Creek .... .

Channel 

order

1

2 

3 

4 

5 

6 

1 

2

3

4

5

6

1

2 

3 

4 

5 

6 

7 

1

2

3

4

5

6

1

2 

3 

4 

5 

6 

7 

8 

1 

2

3

4

5

6

7

Number 

of 

channels

1,020

233 

42 

9 

2 

1 

3,940 

950

172

31

6

1

2,824

725 

153 

30 

4 

2 

1 

10,310

2,460

545

104

24

1

15,900 

4,250 

904 

177 

35 

6 

2 

1 

12,400 

3,500

729

147

29

6

2

Mean 

channel 

length 

(ft)

410

670 

1,600 

4,110 

9,200 

26,000 

370 

537

1,170

4,970

3,320

114,000

267

458 

1,023 

1,816 

8,830 

8,600 

25,500 

245

480

772

2,195

5,375

126,000

250 

460 

725 

2,040 

4,085 

14,850 

32,000 

45,000 

192 

370

674

2,040

5,450

12,833

40,500

Mean 

channel 

slope 

(ft per ft)

0.1100

.0517 

.0185 

.0111 

.00545 

.00384 

.100

.187

.0673 

.0343 

.0155 

.0088 

.00576 

.00296 

.251

.241 

.100 

.0465 

.0215 

.0101 

.0055 

.00406 

.00274 

.234

Mean 

width 

of valley flat 

(ft)

25

50 

105 

120 

150 

500 

35 

55

90

140

160

400

35

60 

96 

125 

160 

200 

260 

35

70

110

140

190

545

35 

70 

120 

150 

190 

270 

440 

880 

35 

60

95

135

165

240

300

Area of 

valley 

flat 

(sq mi)

0.37

.28 

.25 

.16 

.10 

.47 

1.83 

1.00

.68

.77

.11

1.63

.95

.71 

.54 

.24 

.20 

.12 

.24 

3.17

2.85

1.75

1.23

.88

2.18

4.98 

4.90 

2.82 

1.94 

.97 

1.71 

1.01 

1.40 

2.99 

3.39

1.67

1.44

.93

.66

orr

remnants of the Stockville terrace remain along 

the valley sides. The valley at right in figure 200 

is typical of the upper part of the Medicine Creek 

basin; and the valley at left, of the central and 

lower part.

The association of major channel scarps with 

the confluence of a large tributary is notable on 

Fox Creek, Cut Canyon, Curtis Creek Canyon, and 

Well Canyon. Although the present scarps are upvalley from the tributary confluence, the possibility 

is good that the scarps were initiated at the confluence, where the slope of the main valley may be 

locally steepened. After a valley floor has been 

trenched, its long profile cannot be accurately reconstructed ; however, long profiles drawn from contours at 10-foot intervals on the topographic maps 

indicate that the main valley profile is generally, 

but not everywhere, steepened upstream from the

confluence of a large tributary. (See fig. 202.) On 

Curtis Creek Canyon a conspicuous steepening of 

the valley profile just upstream from the confluence 

of a large tributary is indicated on the topographic 

map. The steepening is probably due to deposition 

of a fan at the mouth of a tributary. This fan ponds 

the drainage in the main valley and leads to deposition upstream from the fan. Schumm and Hadley 

(1957) have shown that, in small drainage basins 

in eastern Wyoming and northern New Mexico, 

discontinuous gullies can form on locally steep valley 

reaches.

The proposal that gullies are initiated at a local 

steepening of the valley slope has as a corollary the 

proposal that local slope in an ungullied valley reach 

may be adjusted to water discharge. In the absence 

of discharge measurements for most valley reaches, 

the assumption may be made that the discharge in 

a reach is proportional to the upstream drainage 

area. The relation of local valley slope to drainage 

area for reaches along three valleys is shown in 

figure 203. Cut Canyon and Dry Creek are free 

of major channel scarps in their uppermost reaches, 

as shown in figure 202, but Coyote Creek has channel 

scarps throughout most of its length. In spite of 

the fact that the floors of all three valleys are well 

above bedrock, local slope is not constant in a given 

valley reach several hundred feet in length. The 

values of local slope plotted in figure 203 represent 

the best approximation obtainable from topographic 

maps for mean local slope in a reach bounded by 

contours and having a fall of 20 feet.

A general relation between local valley slope and 

drainage area is apparent from figure 203. Slope 

values applying to gullied reaches tend to plot above 

the average curve representing this relation, but 

some slope values applying to ungullied reaches also 

plot above it. Aside from chance, factors other than 

local slope and drainage area seem to be involved 

in the initiation of gullies, and the most important 

of these is probably valley width. The upstream 

reaches of Coyote Creek have a greater susceptibility 

to gullying than reaches of Cut Canyon because of 

the relative narrowness of the valley bottom of 

Coyote Creek.

The main valley of Well Canyon is relatively free 

of gullies, and the few gullies present have grown 

slowly. The channel scarps in the long profile of 

Well Canyon (fig. 202) did not advance during the 

interval 1937-52 by an amount measurable on aerial 

photographs nor did the intricate small-scale meanderings of the trenched channel reaches show any 

observable change. The aspect of a trenched channel 

on Well Canyon is shown in figure 195 (middle).
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 295

700 -r600 --

500 --

- 400 - -

uT

< 300 O

200 --

100 --

0 -L20 15 10 

HORIZONTAL SCALE, IN MILES

FIGURE 202. Long profiles of valley and channel for some major tributaries to Medicine Creek. A break in the channel profile represents a channel 

scarp, and an arrow on the valley profile indicates the point of confluence of a large tributary. Profiles drawn from topographic maps.

The general slope of the valley profile, although 

somewhat less than that of Dry and Curtis Creeks, 

is not significantly different from that of Mitchell 

and Fox Creeks. The tributaries received by Well 

Canyon are relatively short, however, and the valley 

of Well Canyon is relatively wide at the point of 

confluence of the two largest tributaries. Upstream 

from the confluence of the northernmost of these 

tributaries, the valley profile of Well Canyon shows 

local steepening and the presence of a channel scarp. 

Neither local steepening nor a channel scarp occurs 

at the confluence of the other tributary. The inactivity of channel scarps in the main valley of Well 

Canyon is attributed to the lack of large tributaries, 

to relatively great valley width, and to the generally 

low valley slope.

DEVELOPMENT OF VALLEY-BOTTOM GULLIES

Photographs of typical valley-bottom gullies are 

reproduced in figure 204. After a gully has become 

large, neither the exact way in which it was initiated 

nor the point of initiation can be established. However, study of small gullies in various stages of development indicates that valley-bottom gullies may 

begin as small depressions scoured by flowing water 

on the valley bottom. Breaks in the sod cover such 

as might result from an animal burrow, a trail, or 

an excavation by man are likely spots at which 

scour can take place. The upstream side of a depression can evolve into a scarp and advance upvalley, meanwhile growing in height. Although most 

scarps in major valleys have apparently been ini-
296 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

I I I I I I I l_ 

EXPLANATION

Upper Cut Canyon

0.01

0.001

1 10 

DRAINAGE AREA, IN SQUARE MILES

FIGURE 203. Local valley slope in relation to drainage area for reaches along upper Cut Canyon, upper Dry Creek, and Coyote Creek.

100

tiated in a locally steepened valley reach, a scarp, 

once initiated, can continue to advance into reaches 

where the value of local slope is conservative in 

relation to drainage area (water discharge). Moreover, many gullies occur in valleys of fourth or 

smaller order in which no evidence of local steepening can be found. The value of the ratio of slope to 

drainage area that is associated with the initiation 

and rapid growth of a gully is not sharply defined.

Advance of a head scarp takes place as the massive silt at the base of the scarp becomes saturated 

and disintegrates. In this region the permeability 

of undisturbed dry loess in place is only about 0.8 

foot per day (Holtz and Gibbs, 1952), but this value 

has no significance for a vertical face of loess that 

is immersed in water, as at the edges of a plunge 

pool. The loess in contact with the water continually 

sloughs along vertical joints and is removed by the 

turbulent water of the pool. In figure 204 (upper 

left) the recently collapsed base of a scarp may be 

seen at right of plunge pool. The cohesiveness of 

massive silt depends to a considerable extent on a 

cement formed by clay minerals that coat the silicate 

grains, and when wet the clay coatings have little

or no cohesive effect. Gully side scarps regress by 

the same process. For a distance up to 12 feet from 

the edges of a gully, the ground is broken by cracks 

marking the boundaries of large blocks that have 

slumped because of saturation of the silt at their 

base. These blocks will eventually slump into the 

gully, as illustrated in figure 200. Head scarps can 

be maintained in massive silt whether or not they 

are capped by sod or some other resistant layer. 

Drainage is conveyed to many head scarps by a 

narrow channel, the bottom of which is bare of 

vegetation and is cut below the soil profile. A deep 

notch is formed by the intersection of this channel 

with the head scarp. The notch in the head scarp of 

gully Bl on Dry Creek changed very little between 

1953 and 1957.

Downstream from a head scarp, long profiles of 

gullies change from year to year; the change depends on the amount of runoff. V. I. Dvorak (written commun., 1962) has compiled measurements of 

the long profiles of three major gullies on Dry Creek, 

which are designated gullies Bl, B2, and B3 in 

figure 201. Changes in the long profile of gully 

B2 are typical and are represented in figure 205.
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 297

Upper left. Gully in main channel of Dry Creek, designated gully Bl in 

figure 201. Photographed on July 5, 1956. Lower left, Oblique aerial 

photograph of gully Bl, September 4, 1965. Upper right, Center, valleybottom gully below large valley-head gully, which is designated by numeral 

3 on figure 214. Note cowpath erosion on side slope of valley. Oblique 

aerial photograph, September 4, 1965. Lower right, Discontinuous valleybottom gullies of a tributary to East Curtis Creek Canyon, SE% sec. 31. 

T. 10 N., R. 27 W. Oblique aerial photograph, September 4, 1965.

FIGURE 204. TYPICAL VALLEY-BOTTOM GULLIES

According to Dvorak, the relatively high runoff in 

1951 was accompanied by gully slopes distinctly less 

than valley slopes, but during the succeeding drier 

years the gully slopes increased. Gully slope was 

steeper than valley slope for gully B2 in 1956 and 

for gullies Bl and B3 in 1960.

The maximum height attained by a head scarp is 

evidently controlled mainly by the steepness of the 

slope into which the head scarp is advancing. The 

highest head scarps in the basin, which reach a 

maximum of about 35 feet, are all in steep valley 

heads, whereas head scarps on the gently sloping 

valley bottoms all range from 10 to 25 feet in height. 

The height that a scarp can attain is also limited 

by the rate of deposition at, and downstream from, 

its base.

The cross profile of a valley-bottom gully changes 

in a direction downstream from the head scarp, but 

the nature of the change is not consistent from gully 

to gully. Typically, gully depth decreases very 

gradually in a downstream direction, whereas gully 

width reaches a maximum within a thousand feet 

of the head scarp and then decreases in a downstream direction. Downstream changes in the cross 

profile of a typical rapidly advancing valley-bottom 

gully (gully B4 in fig. 201) are shown in figure 206. 

The width of gully B4 remains nearly constant for 

about 5,000 feet downstream, but for other gullies 

the width decreases downstream at a much faster 

rate than depth. For example, in 1952 the width 

of a large valley-bottom gully on Curtis Canyon 

(gully B6) decreased from about 105 feet at a
298 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

500 1000 1500 

DISTANCE FROM ARBITRARY REFERENCE POINT, IN FEET

2000

FIGURE 205. Changes in long profile of a large valley-bottom gully on Dry Creek, 1951-60. Gully is designated B2 in figure 201. From V. I. Ovorak.

point 900 feet downstream from the head scarp to 

about 45 feet at a point 5,000 feet from the head 

scarp. Through this 5,000-foot distance, the depth 

of the gully changed little. Neither gully B4 nor 

B6 has a well-defined downstream terminus at which 

the gully floor merges with the valley floor; each 

merges downstream with a narrow but apparently 

stable channel that continues for miles along the 

valley bottom.

From his study of valley-bottom gullies on Dry 

Creek, Dvorak (written commun., 1962) concluded 

that widening downstream from the head scarp 

effectively ceased when the width-depth ratio was 

in the range of 3.5 to 5. At great width, the depth 

and velocity of flowing water would be insufficient 

to remove material that accumulated from bank 

slumping, and the channel bottom would assume a 

parabolic shape.

As is generally the case with channels in nature, 

the width-depth ratio that can be maintained for a 

gully probably depends on the magnitude of water 

discharge. Small gullies in the Medicine Creek basin 

have low values of the width-depth ratio, and large 

gullies have larger values. In 1956 none of the large 

valley-bottom gullies had attained a width-depth

ratio greater than 6, which was the value measured 

for gully B5 at a point 390 feet downstream from 

its head scarp. However, none of these gullies had 

a drainage area greater than about 16 square miles. 

Gully B9, the drainage area of which was about 

1.5 square miles, had in 1956 a width-depth ratio 

that did not exceed a value of 1 for a distance of 

1,000 feet downstream from its head scarp.

The advance of major valley-bottom gullies during 

the period 1937-52 is given in table 5, together with 

pertinent information as to gully size and topographic setting. Gully advance and width of valley 

bottom were measured on aerial photographs; drainage area was measured on topographic maps; and 

height of head scarp was measured in the field. 

Slope of the valley bottom, which applies to the 

slope upvalley from the 1952 position of head scarps, 

was measured by field surveys for some of the gullies 

and on topographic maps for others. In general, 

the maximum depth of a gully is about equal to, or is 

greater than, the height of its head scarp. No correlation is apparent between the rate of advance 

and any of the other measurements. The estimate 

of the year at which active advance of the gully 

began is made by dividing gully length by average
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 299

TABLE 5. Measurements relating to the size and topographic 

setting of major valley-bottom gullies

[Gully locations are indicated on fig. 201]

Gully

Bl

B2 __.___.__._____

B 3 ___. ___

B4.. ____

B5

B6.____ _____

B7._ _______

B9._... _____

Drainage

area

in 1952

(sq mi)

6.1

5.6

.8

3.4

Q «7. 71

9.8

15.9

9.5

1.4

Width

of

valley

bottom

(ft)

215

210

120

140

200

160

180

150

120

Slope

of

valley

bottom

(ft per ft)

0.0056

.0055

.0105

.0082

.0058

.0062

.00415

.0050

.0125

Height

of head

scarp

in 1956

(ft)

24

22

20

16

18

18

18

20

23

Advance

of head

scarp,

1937-52

(ft)

900

750

610

3,400

2,400

1,750

2,800

2,100

2,100

Esti-

 mated

year of

activation

1850

?

1900

1920

1920

1910

1920

annual rate of advance during 1937-52. For Dry 

Creek, which has a continuous channel downstream 

from the head scarp, the point of origin is assumed 

to be at the confluence of East Fork.

Valley-bottom gullies advance only during periods 

of runoff. As a result of rainfall on July 4 and 5, 

1956, which totaled about 1.9 inches, gully B5 advanced about 15 feet and gully Bl advanced 20 feet. 

The year 1937 was preceded by a period of relatively

low rainfall (fig. 179) and, as observed on aerial 

photographs, most of the gullies were inactive in 

1937 and were partly filled with sediment. A substantial part of the advance during the period 1937- 

52 took place in 1951 as a result of high runoff. 

For example, of the 750-foot advance made by gully 

B2 during the period 1937-52, about 350 feet was 

made during 1951. Differences in rate of gully advance (table 5) are probably in part due to unequal 

distribution of rainfall during 1951.

The development of a locally continuous channel 

by the coalescence of two discontinuous valley-bottom gullies, as described by Leopold and Miller 

(1956, p. 31), is illustrated in figure 207. Only the 

upper reach of the gullied valley bottom is shown 

in the illustration. The shallow channel shown at 

left continues downvalley for 1,300 feet and terminates at the head scarp of gully B3. No evidence of 

downvalley extension of gullies during the period 

1937-56 was observed at this locality, and in general 

downvalley extension of a gully is uncommon. The 

long profile of a single discontinuous gully is rarely 

smooth, but it is ordinarily broken by one or more 

inset scarps.

20 40 60 80 100 120 FEET

VERTICAL AND HORIZONTAL SCALE OF CROSS PROFILES 

IN \ / J1000 2000 3000 

DISTANCE, IN FEET

4000 5000 6000

FIGURE 206. Long profile and cross profiles of a large valley-bottom gully in a tributary to Curtis Creek Canyon. Gully is designated B4 in figure

201. Based on a field survey, 1956.
300 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

160

120

80

EXPLANATION

Profile of valley in 1956

Profile of channel in 1956

Probable profile of channel in 1937

40

4000 3500 3000 2500 2000 1500 

DISTANCE FROM VALLEY HEAD, IN FEET

1000 500

FIGURE 207. Changes in long profile of a gullied tributary to Dry Creek, 1937-56. For the long profile in 1937, the position of head scarps was taken 

from aerial photographs, and other parts of the profile were estimated. Long and cross profiles in 1956 are based on a field survey.

The gradient of a discontinuous gully is less steep 

than the gradient of the valley floor into which it is 

advancing, and Leopold and Miller attribute this to 

the narrower width of the gully. As gullies coalesce 

and widen, a continuous channel is finally formed 

that has a gradient nearly parallel to the original 

valley floor. The gullies of the Medicine Creek 

basin, however, have not reached this final stage; 

channel scarps are advancing in succession along 

the valleys, and final regrading of a given reach will 

probably involve the passage of many channel scarps.

HISTORY OF LATE RECENT GULLYING ON 

DRY CREEK

Dry Creek was selected for detailed study of gully 

erosion by agencies involved in the Medicine Creek 

Watershed Investigations because the rate of erosion 

there seemed to be more severe than elsewhere in the 

basin. Periodic surveys were made of selected 

reaches of valley-bottom gullies to provide a basis 

for calculation of gross erosion by these gullies. A 

detailed geomorphic study of the Dry Creek channel 

and terraces was made by the writer, with the 

objective of deciphering the history of gullying in 

late Recent time and relating this history to white 

settlement and occupation.

A detailed long profile of Dry Creek, based on a 

field survey made by personnel of the Bureau of 

Reclamation in 1951, is shown in figure 208. The 

terrace profiles in figure 208 and the cross profiles 

in figure 209 are also based on this survey, supplemented with field surveys made by the writer. 

Station references used in the text and in figure

209 refer to distances in feet from the mouth of 

Dry Creek, are represented in figure 208.

In general, the upper reaches of Dry Creek are 

ungullied (fig. 210, upper left), the middle reaches 

(as represented in fig. 210, lower left and upper 

right) have been twice gullied in late Recent time, 

and the lower reaches (as represented in fig. 210, 

lower right) were ungullied until about 1937. The 

inset terrace (figs. 209 and 210, lower left) provides 

evidence for the two episodes of gullying. The inset 

terrace deposits accumulated in the wake of a major 

channel scarp, and the inset terrace was formed 

as these deposits were trenched by the advance of a 

second scarp. The first channel scarp probably began 

at about station 10,000 for the inset terrace becomes 

indistinct at this point. A reasonable date for the 

beginning of this first scarp is about 350 years ago, 

which is the date suggested (on the basis of a 

carbon-14 age determination) for gullying on Elkhorn Canyon.

The approximate age of the inset terrace deposits 

can be inferred from a cottonwood stump rooted 

on the terrace at station 43,300 (fig. 210, lower left) 

and from a tobacco tin buried to a depth of 5 feet 

in the deposits at station 43,700. The growth rings 

on the cottonwood stump indicate that it was about 

40 years old at the time of cutting (1950) ; therefore, 

the inset terrace deposits had already accumulated 

in 1910. The tobacco tin, which is about 400 feet upvalley from the stump, was perhaps buried about 

this time or somewhat later. Because the inset 

terrace deposits accumulate in the wake of an advancing head scarp, their age decreases in an upvalley
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 301

2900

EXPLANATION

Stockville terrace

Mousel terrace

Valley flat

East Fork Dry Creek

Flow line, 1951 channel

1111ii ii 

Bedrock outcrops in channel

Position of channel scarp in 1937

VERTICAL SCALE IS EXAGGERATED 100 TIMES

2450

30 40 50 60 

CHANNEL LENGTH, IN THOUSANDS OF FEET

FIGURE 208. Long profiles of channel, valley flat, and terraces on Dry Creek.

direction. The channel scarp that is trenching the 

deposits and thus forming the inset terrace was at 

station 37,400 in 1937 and had advanced 8,300 feet 

by 1951.

A new channel scarp began at or near the mouth 

of Dry Creek at a time not long before 1937, according to its position on the 1937 aerial photographs. 

This scarp had reached station 6,000 (fig. 210, lower 

right) by 1952, and it is moving rapidly upvalley 

at present.

VALLEY-HEAD AND VALLEY-SIDE GULLIES

Varieties of valley-head and valley-side gullies 

are distinguished mainly on the basis of shape of 

gully head in plan view. The main varieties in their 

characteristic topographic situations are illustrated 

in figure 211. A gully head that is on a relatively 

steep slope and receives a concentration of flow 

from a single direction, as from a narrow channel, 

tends to be narrow and pointed (gully 1, fig. 211). 

If the slope is less steep or the flow less concentrated, 

the gully head will be broadly lobed (2). If, on 

the other hand, the slope is gentle and the flow comes 

from diverse directions, the gully head will be complexly branching (3).

Situations favorable for the initiation of a gully 

are related to valley shape (as determined by past 

erosional history of the valley), to the presence of

cultivated upland at the valley head, and to the 

activities of man and livestock. The valley at right 

has steep sides and head because it was deeply 

trenched both before and after deposition of the 

Stockville terrace deposits. The steep valley head, 

which receives heavy runoff from a field planted in 

row crops, is a favorable place for the formation of 

a gully. A large valley-head gully (gully 3, fig. 211), 

which began on the upper part of the valley head, 

has branched along the fence and into the field. The 

step scarps (4) on the steep valley sides began at 

animal trails along the slope contour and have grown 

in height as they slowly migrated upslope. The step 

scarp at extreme right has evolved into a valley-side 

gully (5). At the left side of the valley, two narrow 

valley-side gullies (1) are forming from cowpaths, 

and another valley-side gully (8) is advancing along 

a road ditch.

The valley at center is shallow and has a relatively 

gently sloping head because it was trenched to shallow depth before deposition of the Stockville terrace 

deposits, and post-Stockville trenching has not extended far upvalley. In addition, the valley head 

borders a divide rather than a tract of upland and, 

therefore, has a small drainage area. The three 

gullies in the valley head (6) are lobed and have 

grown slowly. In the background beyond the center 

valley, two gullies (7) in another valley head are
302 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

STA 30,760

STA_24,210

1 I I I | I I I I I I I I I "NyT" ~ ~~ ~

20 20 40 60 80 100 FEET

VERTICAL AND HORIZONTAL SCALE

EXPLANATION

Stockville terrace Valley flat Inset terrace

Dashed lines represent valley profiles restored 

by projection of terrace slopes

FIGURE 209. Cross profiles of Dry Creek. Station numbers are distances in feet from mouth of creek.
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 303

Upper left. Upper reach of East Fork Dry Creek, 1953. Narrow incised 

channel is shown in middle ground. Lower left, Channel and inset terrace at station 43,300 in 1956. Cottonwood stump, near center, is rooted 

at outer edge of inset terrace. Upper right, at gaging station (sta. 

17,660), August 17, 1953. Discharge about 300 cfs. Lower right. Channel 

at station 6,000 in 1953, looking downstream. On downstream side of 

cottonwood tree is a large channel scarp, advance of which has since 

felled the tree.

FIGUGE 210. DOWNSTREAM CHANGES IN CHANNEL OF DRY CREEK

advancing rapidly one in the direction of drainage 

from the road and the other in the direction of drainage from the barnyard.

The two valleys at extreme left are typical of 

many valleys in the upper part of the basin. Severe 

post-Stockville trenching has removed most of the 

deposits of Stockville age and left the valley sides 

raw and steep. The valley-side and valley-head 

gullies (2), which are lobed in plan view and have 

head scarps tens of feet in height, are advancing 

very slowly because their drainage area is small.

Photographs of valley-head and valley-side gullies 

are shown in figure 212. The valley-head gullies in 

figure 212 (upper left and upper right) are among

the largest in the basin. As is typical, these gullies 

border areas of cultivated upland. The gully in figure 

212 (upper left) extends for about 900 feet along 

a fence line. A narrow but deep valley-head gully, 

whose head scarp attains a height of 31 feet, is 

shown in figure 212 (lower left). Valley-side gullies 

typical of the sharply dissected upper part of the 

basin are shown along the sides of the three valleys 

in figure 212 (upper right). Some are moderately 

active and others are inactive. The growth rate of 

such gullies is slow because they border narrow 

divides and hence have small drainage areas. The 

valley-side gullies in figure 212 (lower right) originated from cowpaths and an old field road.
304 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

 - V < *.- jn /W» IJ** I'm V'.IV/ * 

FIGURE 211. Composite sketch, based on field sketches and photographs, showing different varieties of valley-head and valley-side gullies. Actively

eroding scarps are indicated by dark shading. Numbered features are described in text.

MEASUREMENT OF VALLEY-HEAD AND 

VALLEY-SIDE GULLIES ON DRY CREEK

In the summer of 1953 measurement of the volume 

increase of valley-head and valley-side gullies during 

the period 1937-52 was made by field surveys and 

comparison of aerial photographs. On aerial photographs enlarged to a scale of 1 inch to 660 feet, 

reference lines across or near gully Heads were 

drawn between fixed points, such as trees, fence 

corners, houses, or other landmarks. The position 

of gully head in 1937 was marked on a 1952 aerial 

photograph, which was then taken into the field to 

facilitate measurement of the volume increase. 

Changes in gully depth could not be determined from 

aerial photographs; but this is probably not a significant source of error, inasmuch as neither height 

of head scarp nor gully depth changes very much 

during a moderate advance. The horizontal dimensions of gullies were measured by pacing, and the 

depths were measured with a steel tape. Determination of volume was complicated by the irregular 

shape of most gullies. No volume increases less than 

about 30 cubic yards are reported because increases 

less than this amount are considered to be unrecognizable by comparison of aerial photographs. Volume increases, however, were measured for nearly 

all the gullies on Dry Creek that seem to be active, 

and erosion from gullies that seem to be inactive is 

probably not quantitatively important.

According to these measurements, the enlargement 

of all active valley-head and valley-side gullies on 

Dry Creek (216 gullies) for the period 1937-52 

totaled 106,500 cubic yards. A plot of the frequency 

distribution of gully enlargements on logarithmic 

probability paper indicates a logarithmically normal 

distribution, and the skewness at the lower end of 

the curve is attributed to the omission of perhaps 

10 gully enlargements less than 30 cubic yards. 

(See fig. 213.) The median enlargement is about
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 305

FIGURE 212. Valley-head and valley-side gullies. Upper left. Center, large valley-head gully in Curtis Creek subbasin, NE*4 sec. 10. T. 8 N., R. 

28 W. Oblique aerial view, September 4, 1965. Lower left. Valley-head gully in Dry Creek subbasin, center sec. 33, T. 9 N., R. 27 W., September, 

1953. Upper right, Large valley-head gullies and smaller valley-side gullies in Curtis Creek subbasin, SW */4 sec. 30, T. 10 N., R. 27 W. Oblique 

aerial view, September 4, 1965. Lower right, Valley-side gullies in Well Canyon subbasin, SW *4 sec. 13, T. 9 N., R. 29 W.

200 cubic yards, and the range is from 28 to about 

4,200 cubic yards.

A satisfactory approximation to the measured 

gully enlargement was reached by another method, 

which is based on the premise that active gullies 

can be recognized on aerial photographs and also 

on the premise that small gullies have small volume 

increases and large gullies have large volume increases. Several years after the gully measurements were made on Dry Creek, active gullies in the 

Medicine Creek basin were studied on aerial photographs and ranked into four categories according 

to size (not according to enlargement). On the 

basis of the measured gully enlargements on Dry 

Creek, each size category was assigned an enlargement range, according to the following scheme:

Enlargement range, 

1937-52 (cu yd)

50-100

100-600

600-3,600

3,600-7,200

Geometric mean of 

enlargement range 

(cu yd)

63

245

1,470

5,100

GuUy size

Small _____ 

Medium _____ 

Large ___ 

Very large

The number of gullies in each category on Dry 

Creek is shown in table 6. By multiplying the number of gullies in each category by the geometric 

mean of the enlargement, a total enlargement of 

97,300 cubic yards was obtained, which is a reasonable approximation to the measured enlargement. 

Although this method is obviously subjective, no 

means of applying rigorously objective sampling 

methods to such irregular objects as gullies is
CO

o

O5

PERCENTAGE ENLARGEMENT PERCENTAGE ENLARGEMENT

§ vi 01 on £» w ro o o o o o o p p fo *- 

m o2

OM

8

H 

2{ 

H

ss2 

i i 

2502

H

§

^ 

H 

2!

H3
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 307

TABLE 6. Number of gullies according to type and size in the Medicine Creek basin and

in major subbasins

Gully type

Valley head ____..._____

Valley side __ __ _

Valley bottom __ ___

Size

Small __ _ _____

Medium _______

Large _____ _

Very large _ _ . ___

Small ......

Medium ____ __ ._

Large __ _ __

VPT v 1 s T* &{*

Small . _______

Medium .___ ______

Large _____ ._

Very large ______

gully head

(range in

feet)

1-15

16-60

61-180

>180

1-10

11-25

26-50

>50

1-10

11-25

26-50

>50

Number of gullies

Mitchell

(subbasin C)

47

99

28

1

22

21

6

56

33

} »

Dry

(subbasin I)

70

110

35

2

3

14

2

38

27

10

Fox

(subbasin K)

39

90

16

_ ______

7

17

2

11

23

9

Brushy

(subbasin N)

36

302

90

3

10

66

7

24

82

19

Medicine

(subbasins

A-O)

417

1,357

360

20

112

279

44

563

477

152

apparent. In the ranking of gullies into categories, 

a particularly difficult subjective decision lies in 

deciding whether the complex branches of a severely 

eroded valley head should be regarded as one gully 

or several. In the Dry Creek measurements, most 

of the branching valley heads were divided into 

several gullies, whereas in the later ranking of 

gullies according to size, the branching valley heads 

were regarded as one gully. For this reason the 

geometric mean of the largest size category (5,100 

cu yd) is larger than the largest measurement reported (4,200 cu yd).

The topographic situations of gullies, as well as 

most of the topographic features characteristic of 

the Medicine Creek basin, are illustrated by the 

vertical aerial photograph reproduced as figure 214. 

Sec. 17, T. 9 N., R. 27 W., is approximately in the 

center of the area, and the valley of Dry Creek crosses 

it from left to right. Gullies numbered 3 and 5 on 

the photograph are in the very large category and 

have complexly branching heads. Total enlargement 

of all branches amounted to about 6,950 cubic yards 

for gully 3 during the period 1937-52 and about 

5,610 cubic yards for gully 5. Figure 204 (upper 

right) is a view of gully 3 as seen from the air. 

Gullies 1 and 4 are in the large category, and the 

lobed shape of their heads indicates that they have 

not advanced beyond the steeper parts of the valley 

heads, although the head of gully 4 is beginning to 

branch. Enlargement during the period 1937-52 

was 1,320 cubic yards for gully 1 and 2,250 cubic 

yards for gully 4. The group of four gullies indicated by the numeral 2 are in the medium category, 

and their enlargements ranged from 107 to 225 

cubic yards.

Discontinuous valley-bottom gullies of small size 

are indicated by the two arrows at left of the numeral 4, and others of medium size are indicated by 

arrows in the lower left corner of the photograph. 

Small discontinuous valley-bottom gullies are also 

indicated by arrows on the valley flat of Dry Creek. 

The major valley-bottom gully on Dry Creek begins 

about 1 mile downstream (to the right) from this 

locality. A valley-side gully of medium size, which 

is advancing along a fence, is indicated by the 

numeral 6.

Among the notable relief features shown on the 

photograph are the differences among valleys in 

flatness of bottom and steepness of side. The valleys 

at right of numeral 4 have flat bottoms and steep 

sides because post-Stockville trenching extended to 

the valley heads; the valleys at left and below 

numeral 4 have narrow bottoms and gentle sides 

because their trenching was incomplete. Also notable, in the field at right center on the photograph, 

is a dark round spot that indicates a depression. 

Depressions of this sort, sometimes called buffalo 

wallows, are common on the Great Plains. Many 

hypotheses have been proposed as to itheir origin, 

but they probably originate in more th&n one way, 

and no hypothesis has been established as generally 

valid. In the Medicine Creek basin, many of the 

depressions probably mark the positions of sinkholes in the underlying Ogallala Formation.

AREAL DISTRIBUTION OF GULLIES

Experience in the recognition of Dry Creek gullies 

on aerial photographs and in the estimation of their 

size and activity was used in the collection of information on the distribution of gullies in the Medicine
308 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

FIGURE 214. Vertical aerial photograph of a severely gullied area on upper Dry Creek. Numbers indicate gullies described in text. Arrows indicate 

small- and medium-size discontinuous valley-bottom gullies described in text. Photograph by U.S. Commodity Stabilization Service.
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 309

Creek basin as a whole. Aerial photographs of the 

whole basin were studied stereoscopically, and all 

gullies in the basin that seemed to be active were 

plotted on topographic maps. Decisions as to the 

activity of a gully were checked by reference to 

1937 aerial photographs. The gullies were grouped 

according to type (valley head, valley side, or valley 

bottom) and according to size (small, medium, large, 

very large). (See table 6.)

A map showing the frequency distribution of 

gullies according to subbasin was prepared (fig. 

215). The basin was divided into 24 subbasins, 

corresponding generally to subbasins used by the 

Agricultural Research Service in their land-use tabulations, that are reasonably homogeneous in texture 

of relief. The frequencies of valley-head, valley-side, 

and valley-bottom gullies (excepting large and very 

large valley-bottom gullies) in each subbasin are 

given in table 7. Gully frequency refers to number 

of gullies per square mile of valley system rather 

than to number per square mile of drainage area. 

Gullies are directly related to the valley system and 

are not present in the upland except at its edges. 

Area of upland and characteristics of the valley 

system should be regarded as independent variables 

in their relation to gullying.

The frequency of active valley-head and valleyside gullies is low in the lower and upper part of 

the basin and ranges from moderate to high in the

TABLE 7. Gully frequencies and related data for subbasins of 

the Medicine Creek basin

Subbasin

A ______

B-l _ . __

B-2 _____

C-l _____

C-2 ____ _ 

D

E

F

G .

H ___ __

1-1 _____

1-2 ______

J-l ____

J-2 _____

K-l._._ ___

K-2 _____

L-l __ _

L-2_ ___ .

M ______

N _____ 

0-1 __ - -

O-2 _____

O-3 _____ 

O-4 _____

Drainage 

area 

(sq mi)

27.2

43.4 

11.6

22.3

29.8 

74.4

10.9

58.9

23.2

16.5

12.6

8.5

17.6

22.6

57.0

15.5

,22.7

30.6

27.5

73.8 

14.6

15.0

35.4 

22.0

Area in 

upland 

(percent)

45

38 

37

50

52 

45

42

34

42

48

40

49

12

45

12

30

12

26

30

26

10

12

55

Area of 

vallev 

system 

(sq mi)

15.0

26.4 

7.3

10.8

14.4 

40.9

6.3

35.3

13.4

7.4

9.5

4.3

15.5

12.6

49.8

10.8

19.9

22.5

19.3

52.4

13.5

31.1 

9.9

Frequency 

of firstorder 

channels

113

150 

140

190

150 

160

165

170

195

185

214

185

275

200

260

200

260

220

180

260

450

350 

350

Frenuency 

of valleyhead and 

vallev-side 

gullies

3.2

2.9 

3.7

16.0

3.5

5.7

5.2

6.9

12.4

11.7

18.5

14.2

3.3

16.4

1.5

9.1

.5

5.2

6.8

10.0

.7

2.1

10.8

Frequency 

of 

valleybottom 

gullies

5.3

4.2 

5.5

4.3

3.4 

2.6

6.1

4.1

5.0

4.2

5.1

5.3

3.0

4.6

4.2

1.6

,2

.9

1.6

2.3

.4

.4 

1.8

central part (fig. 215). The frequency ratio of 

valley-head and valley-side gullies to valley-bottom 

gullies ranges from about 0.6 in the lower part of 

the basin (subbasin A) to about 6 in the central 

part of the basin (subbasin 0-4). The distribution 

of gullies according to type and frequency is controlled mainly by the steepness of valley heads, the 

narrowness of valley bottoms, and the amount of 

upland drained by a valley head. In general, the 

steepness of valley heads is directly proportional, 

and the narrowness of valley bottoms is inversely 

proportional, to first-order-channel frequency.

Gully frequency in relation to percentage of area 

in upland and to adjusted frequency of first-order 

channels is shown in a semiquantitative way in 

figure 216. Moderate to high frequencies of valleyhead and valley-side gullies are associated with 

values of first-order-channel frequency and percentage of area in upland that plot to the right of the 

dashed line. On the other hand, values that plot to 

the left of the dashed line tend to have a higher 

frequency of small and medium valley-bottom gullies.

Points representing high gully frequency would 

probably be more widely separated from points representing low gully frequency were it not for the 

fact that the subbasins are not entirely homogeneous 

in topographic character. The severity of postStockville trenching not only varies from the upper 

to the lower part of the basin, but also from one 

minor side tributary to the next (fi£. 214). The point 

indicated by a gully frequency of 10.8 and representing subbasin 0-4, at upper right in figure 216, 

is most anomalous. In spite of the relatively low 

gully frequency in this subbasin, it includes an area 

of exceptionally severe erosion that is about 3 miles 

northeast of Maywood. This area is also exceptional 

in that its drainage was greatly extended by postStockville erosion. Several large gullies there made 

advances ranging from 60 to 180 feet during the 

period 1937-52.

FORMATION OF VALLEY-HEAD AND 

VALLEY-SIDE GULLIES

The head scarps of many valley-head gullies originate on the steep upper part of the valley head and 

advance toward the upland. This is indicated by the 

position of short gullies and by the shape in plan 

view of long gullies. The width of many large valleyhead gullies decreases sharply toward the lower part 

of the valley head, and the gullies are connected to 

the valley flat by a narrow trench. (See fig. 217 

and gully 5 in fig. 214.) Gully 5 narrowed downvalley (in 1956) to a particularly deep trench about 

25 feet deep, 15 feet wide at the top, and 5 feet wide
310 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

« fill. Ill

Frequency of gullies per square 

mile of valley system

FIGURE 215. Areal frequency distribution of active valley-head and valley-side gullies in the Medicine Creek basin. Subbasins illustrated in figure

197 are shown by heavy outlines. See table 7.
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 311

60

' \ 

\H.2Q0

\

o 117 (

o52 \ 124o

I

3.7 O2' \

o \

 .. \

6.8 \

°\

GULLY FREQUENCY \ 

LOW TO MODERATE \

\

4.4 

A

EXPLANATION

o2- 1

 Subbasin

A1 ' 2

Small basins less than 2

square miles in area

Number beside symbol refers to gully frequency 

per square mile of valley system 

1

1

16.4

9.1 

O

5.2 10 

0 0

^

^^ _____ Al,3

"o 83- 3

1.5

1

1

10.8 

O

30.4 

A

34.6 

A

GULLY FREQUENCY 

MODERATE TO HIGH

'.

- ___ ____ <

2.1 

1.2

i

1

I

-

,

23.2 

A

o°'7 -

A2

i

50

40

i 30

20

10

0

100 150 200 250 300 

ADJUSTED FREQUENCY'OF FIRST-ORDER CHANNELS

350 400 450 500

FIGURE 216. Frequency of active valley-head and valley-side gullies in relation to area of upland and adjusted frequency of first-order channels.

at the bottom. Set in the bottom of this trench was 

a winding notch, sections of which passed underground.

Other valley-head gullies begin at an upvalley 

riser of the Stockville terrace, such as the one shown 

in the valley at center in figure 211, or as discontinuous valley-bottom gullies, such as the ones shown 

in the valley at upper left in figure 200. In the tabulation of all active gullies in the basin, valley-head 

gullies that are connected by a continuous, rather 

wide trench to the valley flat were given a separate 

designation because they probably began on the 

valley bottom rather than in the valley head. The 

percentages of valley-head gullies that fall in this 

category are as follows for several subbasins: Dry 

Creek, 7 percent; Brushy Creek, 22 percent; Mitchell

Creek, 9 percent; Fox Creek, 6 percent; Lime Creek, 

45 percent; and subbasin A, 65 percent. Thus, in 

the narrow valleys of the lower part of the basin, a 

greater percentage of valley-head gullies begins on 

the valley bottoms.

The head scarps of valley-head gullies reach a 

maximum height of about 35 feet, a value about 

10 feet higher than the maximum height of head 

scarp measured for large valley-bottom gullies. This 

greater height is evidently related to the steeper 

slopes into which the valley-head and valley-side 

gullies are advancing and to the correspondingly 

steeper slopes at the bsise of their head scarps. (See 

figs. 217 and 218.) Material does not tend to accumulate at the -base of the head scarp as it does in 

large valley-bottom gullies. In long profile, the head
312 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

190

pproximate profile o 

Stockville valley fill

100

100 200 300 400 500 600 

DISTANCE ALONG GULLY, IN FEET

700 800 900

HORIZONTAL AND VERTICAL SCALE

Cross profiles

FIGURE 217. Long profile, plan view, and cross profiles of a large valley-head gully, designated gully 4 in figure 214. Shaded area on plan view 

indicates enlargement during the period 1954-57. Based of field surveys. Location of cross profile H is beyond limit of area shown in plan .view.

scarps are nearly vertical or even overhanging at 

the rim, and the channel profile downstream from 

the head scarp is typically broken by several channel 

scarps. The channel scarps deepen the gully as they 

advance and probably increase the height of the 

head scarp by merging with it. The modal value for 

height of head scarps of active valley-head and 

valley-side gullies on Dry Creek is about 10 feet.

The mechanism of head-scarp advance is not 

identical with that described for large valley-bottom 

gullies. Most valley-head gullies are advancing into 

surfaces underlain by a well-developed soil profile 

and, except for gullies advancing into cultivated 

upland, protected by a sod > cover. The rills or 

trenches that lead to the gully head have not been 

incised through this profile; hence, the head scarp 

has a resistant rim. On the other hand, plunge 

pools are not conspicuous at the base of the head 

scarps, and saturation of the massive silt by plunge 

pool action is less important tjian that for large 

valley-bottom gullies. The water flowing over the

rim of the head scarp has relatively small volume 

and velocity, and silt beneath the resistant rim is 

disintegrated by back trickle of water. Underground 

drainage, which probably enters the ground through 

rodent burrows upslope from the head scarp, is conveyed into the gully head at some point below the 

resistant rim. The abundance of rodent burrows 

intersected by some head scarps, as well as the overhanging of the resistant rim, is shown in figure 219. 

Head scarps less than 4 feet high do not advance 

rapidly because the resistance of the soil profile and 

the sod cover extend to about this depth. !

Material that slumps from the head scarps and 

side scarps accumulates on the gully floor arid is 

gradually removed by runoff. Deposition is uncommon in the trench that drains the gully head, but 

much deposition takes place where this trench enters 

the valley flat. The number of valley-head and 

valley-side gullies that discharge directly into the 

channels of major tributaries is insignificant, and
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 313

no

100

1937 profile of gully (approximate)

100 200 300 400 500 

DISTANCE, IN FEET

600 700 800 900

FIGURE 218. Long profile of a large valley-head gully, designated gully 1 in figure 214.

most of the material eroded is probably deposited 

on valley flats.

Although the general conditions of topography and 

vegetation that are conducive to the formation of 

valley-head gullies can be stipulated, the localization 

of a gully in a particular valley head rather than 

in an adjoining valley head depends on events that 

cannot be reconstructed. Such events include the 

past methods of cultivation of the upland and the 

past land use of the valley head, as well as such 

fortuitous events as the digging of burrows by 

animals. Moreover, no correlation whatever is apparent between the size of a gully and its topographic situation. Study of the topography of seven 

of the largest valley-head gullies in the basin showed 

that the drainage areas ranged from 4 to 37 acres 

and1 that the slope of the upland draining into the 

valley head ranged from 0.02 to 0.06 foot per foot. 

The slope of the valley heads could not be accurately 

reconstructed, but all appeared to have been relatively steep. Other valley heads, similar in drainage 

area and steepness to the severely gullied valley 

heads, contain small gullies or none.

GULLYING AND LAND USE

That most of the active valley-head and valley-side 

gullies in the Medicine Creek basin are man induced 

is highly probable. Many of the valley-side gullies 

are directly associated with cultural features such 

as roads, buildings, and fences and nearly all the 

valley-head gullies have begun in valley heads that 

drain areas of cultivated upland. During past naturally induced episodes of erosion, gullying does not 

seem to have begun in valley heads. The two postStockville episodes of trenching stopped short of 

the valley heads or else progressed from downvalley 

to the valley heads. The drainage system is presently 

extending itself beyond the valley heads and into 

the upland, a process that last took place before 

accumulation of the Stockville terrace deposits. The 

lack of gullying in two tributary heads on Dry 

Creek, densely vegetated because of protection by 

fences, indicates that land use has caused gullying 

elsewhere. (See fig. 182.)

The role of land use in the initiation and growth 

of large valley-bottom gullies is uncertain. Geologic 

evidence indicates that valley-bottom gullying has 

taken place on Elkhorn Canyon and probably, on-;
314 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

FIGURE 219. Head scarp of a small valley-head gully on Dry Creek. Note 

animal burrows and overhanging rim of head scarp.

Dry Creek within the past 350 years and before the 

arrival of settlers. There is no evidence of late 

Recent valley-bottom gullying elsewhere in the basin, 

except that valley-bottom gullies, probably formed 

since settlement, are advancing rapidly at one or 

more localities in the valleys of major tributaries 

to Medicine Creek. The formation of these large 

valley-bottom gullies entirely from natural causes 

is improbable. The condition of the vegetal cover 

in relatively undisturbed areas indicates that the 

climate since settlement has not been particularly 

conducive to the formation of gullies.

Antevs (1952) concludes that arroyo cutting and 

filling in the semiarid southwest are controlled mainly by vegetation, which is in turn controlled naturally by climate. Channeling is a result of drought; 

filling takes place during climatic transitions; and 

soil development takes place during relatively moist 

periods. Arroyo cutting was caused mainly by

drought in the past and by overgrazing since 1875. 

Bryan (1941) also concludes that a slight change 

in climate from the dry toward the less dry is adequate to convert ephemeral streams from a condition 

of erosion to alluviation.

These conclusions are reasonable, although the 

specific climatic conditions that prevailed during 

past episodes of cutting and filling cannot be reconstructed by any presently known method. During 

dry years in the Medicine Creek basin, gully advance 

has been negligible and alluviation has taken place 

in large valley-bottom gullies. Gullying does not 

literally take place during dry years, but rather 

during the wet years that occur from time to time 

during a general period of drought. A temporary 

effect of drought may be an increase in the rate of 

accumulation of valley fill, as is suggested by the 

character of the terrace deposits on Elkhorn Canyon; 

but valley fill accumulated during drought is subject 

to almost immediate incision. As to the climatic 

conditions that prevailed during episodes of filling, 

good faunal evidence indicates that the Stockville 

terrace deposits accumulated during a climatic regime very similar to the present climate. Past episodes of cutting are probably due to a series of 

droughts more rigorous than any recorded since 

white settlement.

CONTROL OF GULLIES

Valley-head gullies of moderate to large size have 

been stabilized in some parts of the basin. The most 

effective methods of stabilization have involved the 

construction of an arcuate ditch above the gully 

head and the diversion of drainage along grassed 

waterways on either side of the gully. As is true of 

gully control structures generally, these must be 

maintained; and lack of maintenance has resulted 

either in renewed activity of the gully head scarp or 

in trenching of the grassed waterways.

A heavy vegetal cover in a valley head inhibits 

formation of new gullies because gullies begin on 

the valley head rather than on the upland. The cultivation of upland to the very edges of valley heads 

has been unfortunate. Restoration of native vegetation in the valley heads and in the area of upland 

adjoining the valley head would probably be effective 

in preventing new gullies and in stabilizing gullies 

of small to moderate size.

No large valley-bottom gully in the Medicine 

Creek basin has been effectively controlled, and only 

one effort toward control was noted. Concrete blocks 

were placed in the head of the main gully on Dry 

Creek, but these had no apparent effect. The control 

problem is complicated by the fact that a given head
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 315

scarp may have in its wake a series of channel 

scarps, all of which must be controlled. A reduction 

of runoff on the valley bottom is the only apparent 

solution to the problem, and this can probably be 

achieved by construction of terraces on the upland, 

restoration of native vegetation of some parts of the 

valley bottoms, and more moderate grazing.

SUSPENDED SEDIMENT AND THE HYDRAULIC 

GEOMETRY OF CHANNELS

By CLOYD H. SCOTT

Medicine Creek has a well-sustained low flow. 

Fox Creek and Brushy Creek also receive groundwater inflow, although the volume is not so great 

as the volume received by Medicine Creek. Fox 

Creek has a well-sustained low flow, but Brushy 

Creek usually stops flowing for some time during 

the summer months. The other gaged tributaries, 

Dry Creek and Mitchell Creek, and most of the 

ungaged streams in the basin flow only after rainfall. 

Typical hydrographs of large flows are shown in 

figure 220. The magnitude of these flows was such 

that the daily mean discharge was equaled or exceeded about 1 percent of the time. Medicine Creek 

at Maywood rises and falls more slowly than the 

others because of reservoir regulation upstream.

Medicine Creek and its tributaries tend to be 

"flashy" streams; that is, the discharges increase 

rapidly in response to rainfall, and peaks are of 

short duration. This flashy condition is probably 

the result of several factors, the most important of 

which is the intensity of thunderstorms. One storm 

produced 1.70 inches of rain in 45 minutes at 

Tobiassen gage. Such intense storms do not occur 

often, but storms that produce as much as threefourths of an inch of precipitation in an hour or less 

are common.

The thunderstorms result in runoff having moderately high suspended-sediment concentrations. The 

maximum observed concentration in the basin during 

the approximately 37 years of combined station 

record was 192,000 ppm (parts per million), and 

the maximum observed suspended-sediment concentration was more than 100,000 ppm in 5 of the 37 

years of combined station record. All the annual 

maximum observed concentrations were in excess 

of 10,000 ppm for the period of record. Maximum 

concentrations in excess of those observed undoubtedly occurred during most years. Because concentrations do not remain high for very long, the maximum daily suspended-sediment concentrations are 

much less than the maximum observed concentrations. The maximum daily concentration during the 

period of record was 37,600 ppm at the Fox Creek

station, but the maximum exceeded 20,000 ppm during only 3 years of combined station record. The 

maximum daily concentrations were larger than 

about 1,000 ppm for the combined record, and about 

one-third were between 10,000 and 20,000 ppm.

The material that makes up suspended sediment 

is relatively fine because of the general lack of 

sources of coarse material in the basin. The percentages of clay (finer than 0.004 mm) and silt 

(0.004 to 0.062 mm) are variable, but clay and silt 

together make up 90 percent or more of the suspended sediment. Ten percent or less of sand 

(0.062 to 2.00 mm) is generally finer than 0.125 

mm except at the two stations on Medicine Creek, 

where a few samples contain 1 or 2 percent of sand 

ranging from 0.125 to 0.250 mm.

Stream-channel cross-sectional shapes are rather 

diverse within the basin, particularly the shapes of 

channels of ephemeral streams. In cross section, 

the channels of ephemeral streams range from shallow swales on the valley floor to deeply incised 

trenches, either wide or narrow. Figure 210 (upper 

left} illustrates a broad valley floor in which a narrow channel is forming. In figure 204 (upper left) 

a narrow trench is shown upstream from the head 

of a gully, and this trench is being widened and 

deepened by the advance of the gully head scarp. 

The broad trench formed by advance of the head 

scarp is only about twice as deep as the narrow 

trench, but a short distance downstream from the 

head scarp the width of the broad trench is several 

times that of the narrow trench. Head scarps are 

advancing in some valley floors where narrow channels are poorly defined or do not exist at all. As a 

result of the advance of these head scarps, the shape 

of the channel is changed from broad and shallow 

to broad and deep.

Dry Creek (fig. 210, upper riqht) and Brushy 

Creek both have broadly incised channels at the 

gaging stations, and Brushy Creek has a poorly defined low-flow channel in the broadly incised channel. 

Medicine Creek and Fox Creek, which are perennial 

streams, have well-defined low-flow channels at the 

gaging station.

HYDRAULIC RELATIONS AT A SECTION AND 

IN A DOWNSTREAM DIRECTION

As the discharge at a particular cross section 

(called "at a station" by Leopold and Maddock, 1953, 

p. 4) in a stream increases, the width, depth, and 

velocity increase. Previous investigators (Leopold 

and Maddock, 1953; Wolman, 1955; and Leopold 

and Miller, 1956) have shown that, within limits of
316 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

1400

1300

1200

1100

1000

900

-Medicine Creek above Harry Strunk Lake

O 700

uj 600

I

O 

CO 

O 500

400

300

200

100

-Fox Creek

/

 Medicine Creek at Maywood

Dry Creek12! ,=t

0.2 4 6 8 10 12 14 16 18 20 22 24

TIME, IN HOURS

FIGURE 220. Typical hydrographs of large flows.

bankfull discharge, these variables are simple power The product of mean velocity, width, and mean

functions of the water discharge of the form depth must equal discharge; therefore, the sum of

uaQm the exponents b, f, and m must equal 1.00.

daQf Points on graphs of width, depth, and velocity

waQ^ versus discharge for the gaging stations in the Mediwhere u is mean velocity (fps),: cine Creek basin scatter rather widely from the

d is mean depth (ft), . mean, particularly for Brushy, Dry (fig. 221), and

w is width,(ft), and ; % Mitchell Creeks. Scatter at the lower values of

Q is water discharge (cfs). discharge is caused, in part, by natural variations
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 317

10 100 600

DISCHARGE, IN CUBIC FEET PER SECOND 

FIGURE 221. Change of width, depth, and velocity with increasing discharge at a section, Dry Creek near Curtis.
318 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

in channel shape at the different sections used for 

making discharge measurements by wading. Flows 

too deep to be waded were measured at a single 

section at each of the stations, and the scatter on 

the plots is somewhat reduced at the higher discharges. There would be some scatter on the plots 

even if all measurements were made at a single 

cross section.

The slopes of curves relating width, depth, and 

velocity to discharge at each gaging station were 

fitted by eye and adjusted so that the values of 

b, f, and m summed to 1.00. The adjustments were 

small for all sections. The relations of width, depth, 

and velocity to water discharge at the individual 

sections have little meaning; therefore, the curves, 

without the defining points, were placed on one 

graph, and the discharges that were equaled or exceeded 1, 2, and 25 percent of the time were indicated on each of the curves. Discharges equaled or 

exceeded 1, 2, and 25 percent of the time were 

selected because the 1-percent discharge represents 

approximately bankf ull flow at the Fox Creek station 

but less than bankfull flow for the other stations. 

The 25-percent discharge is approximately the modal 

discharge for the Fox Creek and both Medicine 

Creek stations, and the 2-percent discharge is about 

the lower limit for which reliable measurements of 

width, depth, and velocity are available for the Dry, 

Brushy, and Mitchell Creek stations.

The slopes of width-discharge relations for Dry 

and Brushy Creeks are greater than those for the 

other sections, and lines joining points of equaldischarge frequency indicate that the sections should 

be divided into two groups (figs. 222 and 223). The 

fact that Mitchell Creek does not fit with either 

group is attributed to the presence of a concrete 

control at the section and to a low-water road crossing a short distance downstream, which causes backwater at the section. Therefore, the Mitchell Creek 

section will not be considered further.

Lines that join points of equal frequency of discharge on the curves of the at-a-station relations 

represent the downstream relations of width, depth, 

and velocity to discharge, if the assumption is made 

that the relation at sections not on the same stream 

is representative of relations at different sections 

on the same stream. This assumption may be justified for two reasons. First, the discharges of equal 

frequency for the two Medicine Creek stations and 

the Fox Creek station plot about on a straight line 

even though the uppermost section on Medicine 

Creek, at Maywood, is somewhat affected by reservoir regulation. Second, the gaging sections are

on reaches where flows are over loess, which covers 

much of the basin. The assumption implies that the 

channels of two streams are similar at the points 

along their lengths where the discharges are the 

same at equal frequencies of occurrence.

The values of b, f, and m for changes of width, 

depth, and velocity in a downstream direction obtained from figures 222 and 223 cannot be considered 

reliable because too few stations are available to 

establish averages. The values can be used to show 

general differences between the types of streams 

represented by the two groups.

The downstream relations of width, depth, and 

velocity to discharge could best be defined by measurements along a stream at several stations for which 

at-a-station relations of width, depth, and velocity 

to water discharge and flow-duration curves are 

available, tiowever, gaging stations of the number 

required for such a study are found on few if any 

streams. When better data are lacking, discharge 

measurements might be made at several sections in 

a downstream direction at discharges of unknown 

frequency at each of the sections. Even though the 

frequency of the discharges were the same at all 

the sections measured, the plot of width, depth, and 

velocity against discharge would scatter from the 

average line because of variations in shape that exist 

from place to place in a natural channel. Of course, 

it would not be possible to obtain measurements of 

discharges of the same frequency at all sections, 

especially for channels of ephemeral streams.

Assume that a series of measurements are to be 

made in a downstream direction on Dry Creek at discharges that are equaled or exceeded about 2 percent 

of the time at each of the sections. Further assume 

that the downstream relation of width to discharge 

for Dry Creek is the same as that shown on figure 

223 for discharges equaled or exceeded 2 percent of 

the time. If a measurement is made at the gaging"* 

station at a discharge assumed to be equaled or 

exceeded 2 percent of the time, but the discharge 

is actually the one equaled or exceeded 1 percent 

of the time, then the width will be greater than that 

indicated by the downstream relation at discharges 

equaled or exceeded 2 percent of the time by about 

40 percent plus or minus the deviation from the 

at-a-station relation (fig. 221). About two-thirds 

of the points that defined the at-a-station relation 

for the Dry Creek station were within plus 35 and 

minus 35 percent of the mean line. As the difference 

between the slopes of the lines for the at-a-station 

relations and the downstream relations of width, 

depth, and velocity to discharge becomes less, the 

scatter from the average line attributable to differ-
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 319

100

I I I I I I I I

100

DISCHARGE, IN CUBIC FEET PER SECOND 

EXPLANATION

1000

Medicine Creek above 

Harry Strunk Lake

A 

Medicine Creek at Maywood

O

Percentage of time daily flow 

equaled or exceeded:

1

Fox Creek at Curtis 25 

FIGURE 222. Change, of width, depth, and velocity in a downstream direction for channels of perennial streams.
320 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

10

DISCHARGE, IN CUBIC FEET PER SECOND 

EXPLANATION

100

Dry Creek near Curtis

Percentage^ time daily flow 

equaled or exceeded:

Brushy Creek near Maywood 2 

FIGURE 223. Change of width, depth, and velocity in a downstream direction for channels of ephemeral streams.
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 321

ences in frequency of discharge at the various stations becomes less. Establishing fairly reliable 

downstream relations of width, depth, and velocity 

to discharge is possible if a sufficient number of sections are selected to provide a reliable average and if 

measurements of extremely high or low discharges 

are avoided.

The slopes of the relations of width, depth, and 

velocity to discharge (table 8) indicate differences

TABLE 8. Values of b, f, and m for streams in Medicine 

Creek basin

b.

f

m . _ __ ____

Perennial streams

At a station 1

0.24 

.56 

.20

Downstream 2

0.69 

.12 

.19

Ephemeral streams

At a station 1

0.35 

.43 

.22

Downstream 2

0.03 

.48 

.45

1 Unweighted average.

2 At discharge equaled or exceeded 1 percent of time.

between the perennial and ephemeral streams in the 

Medicine Creek basin. The at-a-station slope values 

may be considered reliable, but slopes for the downstream relations probably only indicate the correct 

order of magnitude. The differences between the 

at-a-station relations for the perennial and ephemeral 

streams reflect the differences in channel shapes. 

The channels of the perennial streams have fairly 

steep banks, and the width does not increase as 

rapidly as the depth. The channels of the ephemeral 

streams also have steep banks; but the bottoms of 

the channels are somewhat parabolic, and the width 

can increase rapidly as discharge increases until the 

limits of the steep confining banks is reached. However, a relatively large discharge is required for the 

width of water surface to reach the confining limits 

of the steep banks in the broadly incised channels of 

ephemeral streams. The changes of velocity with 

increasing discharge are about the same for perennial and ephemeral streams; therefore, the change 

of width is less and the change of depth is greater 

with increasing discharge for perennial streams than 

for the broadly incised ephemeral streams.

Depths of water in a channel normally do not 

increase very rapidly in a downstream direction. 

That is, it would not be expected that the depth at 

a cross section on a stream would be much greater 

than the depth at another section several tens of 

miles upstream. The downstream change in depth 

for perennial streams in Medicine Creek basin is 

relatively small, and the downstream change in 

velocity is about the same as the change in velocity

at a station. Because the discharge at a constant 

frequency increases downstream, the width must 

increase rapidly. However, the width for the broadly 

incised ephemeral streams increases very little downstream. 'The increase in discharge is accommodated 

by relatively large changes in both depth and velocity in a downstream direction. The downstream 

change in width of the broadly incised ephemeral 

streams may be greater than that indicated on 

figure 223, but the change still would not be so large 

as the change of the perennial streams. Figure 204 

(upper left) shows the main-stem channel of Dry 

Creek just below the gully scarp that forms the end 

of the broadly incised channel, and figure 210 (upper 

right) shows the main-stem channel at the gaging 

section. The top widths of the channel just below 

the gully scarp and in the vicinity of the gaging 

section are 40 to 50 feet. The distance is too short 

and the measurements are too rough to indicate 

the change in width along the Dry Creek channel; 

but if the width increased as rapidly as the indicated 

change of about 5 percent per mile on Medicine 

Creek between Maywood and the gage above Harry 

Strunk Lake, the width at the gage on Dry Creek 

should be more than 10 feet wider than the width in 

the vicinity of the head scarp.

SUSPENDED-SEDIMENT DISCHARGE RELATIONS

The curves relating suspended-sediment load to 

water discharge for the perennial streams (fig. 224) 

have breaks in slope at water discharges that are 

higher than normal but below bankfull stage. The 

curves applying to ephemeral streams show no corresponding breaks in slope (fig. 225), and in value 

of slope they are generally similar to the upper part 

of the curves applying to perennial streams. The 

breaks in the suspended-sediment rating curves result from a rather complex and uncertain set of 

conditions. The concentrations, peak and mean, for 

runoff periods are highly variable. Even two events, 

which may be very similar with respect to peak 

discharge and total discharge, may have very differpeak suspended-sediment concentrations and mean 

concentrations. The peak concentration generally 

occurs before the peak water discharge for stations 

in the Medicine Creek basin, but the length of lead 

is variable. The length of lead may be from 1 to 3 or 

or more for the perennial streams and is generally 

an hour or less for the ephemeral streams. The 

shorter lead time, in general, occurs with a small 

peak discharge. The variability in concentration 

of suspended sediment and in' length of lead results 

because the suspended-sediment load is made up 

principally of fine material derived from sources
322 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

other than the streambed. The amount of fine material that is transported by the streams during a 

given storm depends on intensity and duration of 

rainfall, soil conditions at the time of the storm, 

antl tjt&er factors. The leading1* coneentratitHtf indicates that the sediment rating curve should describe 

a loop, but because of the variability of concentration 

from storm to storm and the variability of the lead 

time of concentration, the loop would not be defined 

by an average of many measurements for many 

storms. Instead, the points defined by the measurements would scatter with increasing discharge. (See 

fig. 224.) The measurements that define the points 

of figures 224 and 225 are somewhat biased, however, 

because only a few measurements were obtained 

before peak water discharge and practically none 

were obtained near peak sediment concentration. 

The generally rapid rises and mud roads prevented 

arrival of workers at the stations much before the 

occurrence of the peak water discharge, particularly 

on the ephemeral streams. Nearly all the measurements at those stations were obtained after the peak 

water discharge; therefore, the scatter of points is 

fairly uniform throughout the range of water discharge.

The lower part of the curves for the perennial 

streams is represented mostly by measurements made 

during small rises. A small increase in water discharge is accompanied by a relatively large increase 

in sediment concentration, and the lead time for 

smaller rises is generally short. As a result, the 

slope of the relation of water discharge to sediment 

discharge increases more rapidly for low water discharges than for the high water discharges.

The fact that the slope of the water-sediment discharge relation is slightly less than unity for the 

ephemeral streams indicates that the concentration 

remains about the same or decreases slightly in a 

downstream direction, but the fact that the slope 

of the water-sediment discharge relation is slightly 

greater than unity for perennial streams indicates 

that the concentration increases in a downstream 

direction. Because so few records are available to 

establish good average downstream relations, it is 

not possible to state that an actual difference exists 

between the slopes of the water-sediment discharge 

relations in a downstream direction for perennial 

and ephemeral streams.

PARTICLE-SIZE DISTRIBUTIONS OF SUSPENDED 

SEDIMENT AND BED MATERIAL

Average particle-size distributions of suspended 

sediment were obtained from unweighted averages 

of all size analyses at each of the stations. The size

analyses were not weighted because a plot of water 

discharge against percentage of suspended sediment 

finer than 0.004 mm and coarser than 0.062 mm 

indicated no relation between instantaneous water 

 diseharge-gilfd ^article-size distribution. -The average 

size distributions for each year for each of the 

stations did show an inverse relation to annual water 

discharge; that is, the percentage finer than a given 

size decreased as water discharge increased. The 

relation was not very well defined, and the indicated 

change was not large; but the relation of annual 

water discharge to the average percentage finer than 

a given size does indicate the possibility of a relation 

between the percentage finer than a given size and 

instantaneous water discharge. The large variability of particle-size distributions for a given water 

discharge, however, prevent detection of a relation. 

Average particle-size distributions of suspended 

sediment and bed material (figs. 226 and 227) indicate little difference between size distributions of 

suspended sediment and a large difference between 

size distributions of bed material for Medicine Creek 

at Maywood and Medicine Creek above Harry Strunk 

Lake. Medicine Creek above Harry Strunk Lake 

has a small percentage of material in the 0.125- to 

0.250-mm range in suspension; such material is 

normally not in suspension at Maywood. Although 

the size distributions of suspended sediment are 

similar at the Medicine Creek stations, the distributions of bed material are very different. The bed 

material at Maywood has 36 percent of the material 

finer than 0.062 mm, 44 percent between 0.062 and 

2.0 mm, and 20 percent coarser than 2.0 mm; at the 

station above Harry Strunk Lake only 8 percent is 

finer than 0.062 mm, 80 percent is between 0.062 

and 2.0 mm, and only 12 percent is coarser than 

2 mm. The increase of material in the 0.062- to 2.0- 

mm range is probably from the tributaries draining 

the area to the southwest of Medicine Creek. There 

are, however, no analyses of bed-material samples 

from any of these tributaries. The average distribution of only three samples, each of bed material 

from the low-flow channels of Brushy and Fox Creeks 

(fig. 50), indicates that the bed material at those 

stations is similar to bed material at Medicine Creek 

at Maywood, especially for the sizes finer than about 

1.0 mm. Suspended-sediment size distributions for 

Brushy, Fox, Dry, and Mitchell Creeks (fig. 226) 

show that there is an apparent increase in fine 

material available for transport as suspended sediment from the west to the east side of the basin. 

Brushy Creek, on the west side of the basin, has a 

median suspended-sediment particle size of about 

0.014 mm, whereas Mitchell Creek, on the east side
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 323

100,000

100 1000 

WATER DISCHARGE, IN CUBIC FEET PER SECOND

10,000

FIGURE 224. Change of suspended-sediment load with increasing discharge at a section, perennial streams.
324 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

100,000

10,000

1000

Mitchell Creek above Harry Strunk Lake 

I I I I I I I I I I I I I I I I

100

10 100 

WATER DISCHARGE, IN CUBIC FEET PER SECOND

1000

FIGURE 225. Change of suspended-sediment load with increasing discharge at a section, ephemeral streams.
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 325

Medicine Creek at Maywood

en 99.0 -

0.002

x:Medicine Creek above 

Harry Strunk Lakei

0.01

DIAMETER, IN MILLIMETERS 

FIGURE 226. Size distribution of suspended sediment at gaging stations in Medicine Creek basin.

of the basin, has a median particle size of about 

0.004 mm. The decrease in median particle size 

from west to east reflects the increasing distance 

from the sand-dune area of the extreme western and 

northwestern parts of the basin.

The measured loads for all the stations are nearly 

the total loads because the suspended sediment contains little sand and the fine suspended sediment 

should have fairly uniform distribution in the vertical. Computations of total load were made by the 

Colby method (Colby, 1957) for the two stations 

on Medicine Creek, both of which have sand beds. 

Not many sets of data are available for computation 

of total loads, but the average percentage of measured load to total load is indicated. At low flow the 

measured load amounts to alkmt 90 percent of the 

total load, but at high flow it 'amounts to more than 

95 percent. Because all the' suspended sediment at 

the Dry Creek gage results from storm runoff and 

a large part of the suspended sediment at the Brushy 

and Fox Creek gages results from storm runoff, the 

measured suspended sediment for those stations.

probably represents 95 percent or more of the total 

load for the period of record.

RELATIVE SEDIMENT CONTRIBUTIONS OF THE 

MAJOR TRIBUTARIES

In any basin or subbasin, erosion and deposition 

are taking place simultaneously, and sediment data 

collected at any point along a stream represent the 

net of erosion and deposition upstream from that 

point.

A measure of the net erosion and deposition in 

a basin is the discharge-weighted mean concentration of suspended sediment. This is the concentration 

that .would result if all the water passing a point 

during some period of time were mixed with the 

suspended sediment passing during the same period. 

If the cumulative water volume is plotted against 

cumulative weight of sediment, the slope of a line 

that joins points of the graph defines the dischargeweighted mean concentration for the period of time 

for which the data are cumulated. The annual sediment loads and storm runoff for the station were 

reduced to a per-square-mile basis and are shown
326 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

Medicine Creek at Maywood

Medicine Creek above Harry Strunk Lake

10

5 -

2 -

1.0

0.05

DIAMETER, IN MILLIMETERS 

FIGURE 227. Size distribution of bed material at gaging stations in Medicine Creek basin.

on figure 228. Reducing the values to a per-squaremile basis does not change the constant of proportionality and presents a comparison of storm runoff 

and sediment yields. Such a comparison is valid if 

precipitation over the entire basin is assumed to be 

uniform in amount. Because of the relatively small 

size of the basin and the low relief, the assumption 

of uniform precipitation probably is valid if several 

years record are considered. The" differences in total 

precipitation for the years 1951-58 recorded at the 

Wellfleet, Curtis, and Stockville rain gages were less 

than 10 percent. As the time period is shortened, 

however, the probability of uniform precipitation 

becomes less.

Each of the stations shows a definite break in 

slope following the 1951 water year. The break in

the curve probably occurs because the ratio between 

the variables is not constant at all rates of cumulation. If the ratio were constant at all rates of 

cumulation, the break would have to be explained 

by a physical change that would cause a greater 

reduction in sediment yield than in water yield 

(Searcy and Hardison, 1960). A break in the curve 

is drawn at the 1956 water year for the Dry Creek 

data; and breaks at the same year are indicative 

for Fox and Mitchell Creeks, but they are not drawn. 

For hydrologic data plotted in this manner, breaks 

that persist for less than about 5 years should be 

attributed to chance and ignored unless there is 

definite reason for believing that such a break should 

occur. The high rainfall and runoff during the 1951 

water year explains the break at the end of that
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 327

Slopes of lines representing 

discharge-weighted concentrations

Data for 1951-58 water years 

except Mitchell Creek which 

is for 1952-57 water years

reek above Harry Strunk Lake

40 60 80 100 120 140 160 

WATER DISCHARGE, IN CUBIC FEET PER SECOND DAYS PER SQUARE MILE

180 20C

FIGURE 228. Cumulative water discharge and sediment discharge per square mile at gaging stations in Medicine Creek basin. Year at which a curve

changes in slope is indicated.
328 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

year. Data are available for only the part of the 

year when rainfall was extremely heavy. The reason 

for the break at the end of the 1956 water year is 

obscure. Runoff for the 1957 water year was generally greater than normal, but the break is in the 

wrong direction on the basis of the experience for 

the 1951 water year. Land-conservation work was 

being actively carried on during the period of the investigation, but there are too few data to evaluate 

the significance of the break.

The ephemeral streams Brushy, Dry, and Mitchell Creeks have higher discharge-weighted mean 

concentrations and generally yield larger amounts 

of sediment per square mile for storm runoff than 

the perennial streams.

GEOMORPHIC PROPERTIES IN RELATION TO WATER 

AND SEDIMENT DISCHARGE

One major objective of quantitative geomorphic 

measurements is to select drainage-basin properties 

that have the highest possible degree of correlation 

with runoff and sediment yield. If runoff and sediment yield are known for a large number of drainage 

basins in the same region, statistical methods can be 

used to evaluate the significance of different drainage-basin properties. If, as in the Medicine Creek 

basin, runoff and sediment yield are known for only 

five subbasins, evaluation of the properties cannot 

be made rigorously by statistical methods. Ideally, 

the properties selected should be independent of one 

another, unambiguous, and not unduly time consuming to obtain. For the Medicine Creek basin, 

properties that meet these qualifications and offer 

promise of good correlation with runoff and sediment 

yield are relief ratio, adjusted frequency of firstorder streams, and percentage of area in upland.

Relief ratio was shown to correlate with mean 

annual sediment accumulation for small drainage 

basins in the upper Cheyenne River basin by Hadley 

and Schumm (1961, p. 173). Maner (1958) reports 

that relief ratio correlated more closely with sediment delivery rates than did size of sediment contributing area, drainage density, basin shape, or 

weighted-average land slopes. The drainage basins 

studied by Maner, which are in the Red Hills area 

of Oklahoma and Texas, range from 332 to 0.036 

square miles. For these basins, relief ratio showed a 

correlation, as based on inspection of scatter diagrams, with basin size, basin shape, average land 

slopes, and drainage density. Maner concludes that 

sediment delivery rate in the Red Hills area is a 

function of several drainage-basin properties that 

evidently are expressed adequately by relief ratio.

For drainage basins that are incised in a level or 

gently sloping upland surface to approximately the 

same local relief, a correlation of relief ratio with 

size and shape properties is apparent. Basin relief 

increases at a much slower rate than basin length; 

therefore, relief ratio is reduced both by increase 

in basin size and by increase in basin length. Because 

of the decrease in valley-side slope with increasing 

channel order, the lower relief ratio of high-order 

basins is accompanied by a lower mean value of side 

slope. Similarly, because of the decrease in channel 

slope with channel order (fig. 229), the lower relief 

ratio of higher order basins is accompanied by a 

lower mean channel gradient. However, the relation of channel slope to channel order may not be 

consistent; therefore, relief ratio may not express 

adequately the slopes of low-order channels.

In a discussion of the interrelations of drainagebasin characteristics, Gray (1961) presents evidence 

to show that, for small basins, the properties of 

area, length of main stream, and length to center 

of area are highly correlated. In a region of homogeneous relief, a correlation also exists between these 

properties and the slope of the main stream. Although not discussed by Gray, relief ratio probably 

will express adequately all the above interrelated 

properties for some regions. In addition, relief ratio 

will express differences in relief between basins of 

about the same size. The effectiveness of relief ratio 

as a property probably depends on, among other 

things, the constancy in shape of long profile among 

the basins being compared. A basin whose main

o.oi -

0.001

CHANNEL ORDER

FIGURE 229. Mean channel slope in relation to channel order for Lime, 

Dry, and Fox Creek subbasins.
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 329

stream is strongly concave upwards in long profile 

may have the same relief ratio as another basin, of 

equal size, whose main stream is nearly straight in 

long profile. However, such differences in long profile surely affect runoff and sediment yield.

Frequency of first-order streams was found by 

Morisawa (1959) to give a high correlation with 

peak intensity of runoff for drainage basins in the 

Appalachian Plateaus. The properties used by Morisawa in multiple regression analysis were relief 

ratio, basin circularity, and first-order channel frequency. She considers that these three properties 

express the shape, relief, and network composition 

of a drainage basin, that they vary independently of 

each other and of area, and that they do not duplicate any other geomorphic factor. For the Medicine 

Creek basin, relief ratio is considered to be an adequate expression of basin shape, but first-order 

channel frequency is an important property not only 

in relation to runoff and sediment yield but also in 

relation to gully erosion.

Frequency of first-order channels expresses the 

small-scale properties of a drainage basin and thereby complements relief ratio, which expresses the 

larger scale properties. Channel frequency must be 

adjusted for immature basins according to their 

differing percentages of upland area. In figure 230 

scatter diagrams show the relation of adjusted frequency of first-order channels to mean valley-side 

slope, slope of first-order channels, and mean length 

of first-order channels. The number of points is too 

small to warrant the calculation of correlation coefficients, but the existence of a relation is apparent 

not only from the scatter diagrams but also from 

examination of the topographic maps. In addition, 

the reason for the correlation is apparent from geomorphic history. In subbasins where post-Peorian 

dissection was most intense, first-order channels are 

shorter, steeper, and more numerous. Much of the 

scatter of points in figure 230 is due to the fact that 

some of the subbasins are less homogeneous than 

others in texture of drainage.

The relation of length to channel slope for firstorder channels in the lower part of Dry Creek is 

shown in figure 231. Each point represents the 

mean slope and mean length of 10 channels in a 

particular length group. Noteworthy is the fact 

that the shorter channels have relatively steeper 

slopes than the longer channels. In addition, the 

shorter channels have steeper valley heads and more 

concave profiles. This is of particular importance 

in gully erosion because steep valley heads promote 

the formation of new gullies.

In combination, relief ratio and frequency of firstRAGE LENTHFIRST-ORD OF

CHANNELS, IN FEET

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ADJUSTED FREQUENCY OF FIRST-ORDER CHANNELS,

IN CHANNELS PER SQUARE MILE

EXPLANATION

Brushy 

O 

Creek Fox 

- - 

Creek Dry Creek 

AX

Mitchell Creek

+ A V 

Well Canyon Upper Dry Creek Lower Dry Creek Lime Creek

FIGURE 230. Adjusted frequency of first-order channels in relation to mean 

valley-side slope, mean slope of first-order channels, and mean length of 

first-order channels.

order streams should give indirect expression to 

another important variable the percentage of area 

in valley flat. An unusual geomorphic feature of 

the Great Plains generally is the flatness of valley
330 EROSION AND SEDIMENTATK

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100 300 500 700

MEAN LENGTH OF FIRST-ORDER CHANNELS, IN FEET

FIGURE 231. Slope of first-order channels in lower Dry Creek subbasin 

in relation to length.

bottoms along channels of both low and high order. 

The percentage of area in valley flat for each channel 

order in each major subbasin has been calculated 

from the product of average width of valley flat and 

average length of channel. (See table 4.) The percentage distribution of valley flat according to channel order differs considerably from one subbasin to 

the next and depends mainly on the distribution of 

channel length according to order. In Well Canyon 

subbasin, for example, about 18 percent of the total 

area of valley flat is in the wide bottom along the 

main channel, whereas in Dry Creek subbasin only 

8 percent is along the main channel. The probability 

of deposition of sediment on the main valley flat 

seems greater for Well Canyon than for Dry Creek, 

and the probability of rapid runoff is less because 

of the lower slope angle of the Well Canyon valley. 

The relief ratio gives an indication of the percentage 

of valley flat along channels of fourth and higher 

order, whereas the frequency of first-order channels 

gives an indication of the percentage along channels 

of first, second, and third orders. (See fig. 198, in 

which the slope of the curve relating channel length 

to channel order changes at about third order.)

Because of the immaturity of drainage in the 

Medicine Creek basin, a variable is needed to express 

the difference among subbasins in percentage of 

upland. The slope of the upland, which shows variation from one subbasin to the next, is related to 

the slope of channels. In general, the slope of the 

upland is less than the slope of first- and secondorder channels, about equal to the slope of third-order 

channels, and greater than the slope of fourth-order 

and higher order channels. (See tables 3 and 4.) 

The percentage of upland gives a reasonably good 

indication of land use. (See table 9.) Similarly, the 

percentage of area in side slope and valley flat shows 

a correspondence with the percentage of area used 

for hay and pasture.

The probable effect of the selected properties 

(relief ratio, frequency of first-order streams, and 

percentage of area in upland) on runoff and sediment yield can be inferred. On the premise that 

lower slopes, wider valley flats, and larger (or 

longer) drainage basins all tend toward reduction of 

runoff and sediment yield because of greater opportunity for infiltration and for deposition of sediment, 

runoff and sediment yield should be positive functions of relief ratio. According to the graphs of 

Hadley and Schumm (1961), the function is exponential where mean annual sediment accumulation 

in reservoirs is the dependent variable. According 

to the graph of Maner (1958, fig. 3), the function is 

exponential where sediment delivery rate is the 

dependent variable. Sediment delivery rate is the 

ratio, expressed as a percentage, between annual 

rate of sediment yield and annual gross erosion rate.

An increase in frequency of first-order channels 

is associated with an increase in both valley slope 

and side slope for lower order channels; therefore, 

increase in water and sediment discharge should be 

a positive function of frequency of first-order channels. For drainage basins whose main channel is 

very long and bordered by wide valley flats, a high 

yield of water and sediment from lower order channels may be largely dissipated along the main 

channel.

TABLE 9. Areas in upland and valley flat in comparison with 

areas in two categories of land use

[Land-use percentages are mean values from inventories taken in 1954, 

1955, and 1957]

Subbasin

Mitchell Creek 

Dry Creek ____ ....

Well Canyon .

Fox Creek _________

Brushy Creek __._

Area in

side slope

and

valley flat

(percent)

48.2

65.2

79.6

83.5

74.1

Area in

hay and

pasture

(percent)

51.3

69.7

83.4

86.2

77.7

Area in

upland

(percent)

51.8

34.8

20.4

16.5

25.9

Area in

row crops,

small

grain, and

fallow

(percent)

46.6

28.7

15.6

12.7

21.7

Ratio of

row crops

to small

grain

1.72

1.43

1.34

1.57

.98
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 331

The effect of percentage of area in upland depends 

on the land use of the upland. If the upland is used 

mainly for row crops, runoff and sediment yield 

probably would be a positive function of percentage 

of area in upland. If, on the other hand, the upland 

were thickly sodded, the function probably would be 

negative. A positive function would be expected for 

the Medicine Creek basin.

The preceding inferences as to the geomorphic 

properties most highly correlated with runoff and 

sediment yield cannot, unfortunately, be rigorously 

tested for Medicine Creek because of the small 

number of subbasins for which data are available. 

Nevertheless, a trial multiple linear regression of 

sediment discharge in relation to the three selected 

variables (fig. 232) is given in order to illustrate 

the numerical effects of these variables. The trial 

regression is based on data in table 3 and figure 228. 

The uncertainties involved in correlation are apparent from the graphs in figure 232, and clearly 

no quantitative significance can be attached to the 

results.

In figure 232 the assumption is made that the 

sediment discharge of each subbasin for the period 

1952-58 is correctly represented by the data. Data 

for 1951 were not used because no measurements 

for Mitchell Creek were made during that year. The 

1958 suspended sediment for Mitchell Creek is estimated. Relief ratio is plotted against sediment discharge on semilogarithmic paper because previous 

work has indicated that this relation is exponential. 

Percentage of upland and adjusted frequency of 

first-order streams are plotted against sediment 

discharge on rectangular coordinate paper. When 

only relief ratio is considered (top graph, fig. 232), 

the sediment discharge of Fox Creek is very low and 

that of Mitchell Creek is high relative to the trial 

curve. This is perhaps accounted for by the fact 

that the percentage of upland on Fox Creek is lower 

than the average, and the percentage on Mitchell 

Creek is higher. When relief ratio and percentage 

of upland are held constant (bottom graph), a reasonably good correlation with adjusted frequency of 

first-order channels can be obtained for all the subbasins except Medicine Creek above Harry Strunk 

Lake, which shows a high sediment discharge not 

only for this trial regression curve but for the other 

two as well.

The relatively high sediment discharge of Medicine Creek above Harry Strunk Lake is attributed 

to yet another factor the presence of raw vertical 

banks along a continuous incised channel for a distance of several miles upstream from the gaging 

station. In general, the banks along Mitchell, Fox,

10

0.6

0.003 0.005 0.007 

RELIEF RATIO

0.009

+ 2

+1

I- O Z U.

-2

10 30 50 

PERCENTAGE OF UPLAND

70

140 180 220 260

ADJUSTED FREQUENCY, FIRST-ORDER CHANNELS

EXPLANATION 

O X A

Brushy Creek Fox Creek Dry Creek

A 

Mitchell Creek Medicine Creek

FIGURE 232. Trial graphic multiple linear regression of sediment 

discharge in relation to relief ratio, percentage of upland, and 

adjusted frequency of first-order channels.
332 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

and Brushy Creeks upstream from the gaging stations are more sloping and more protected by vegetation than the banks along Dry and Medicine 

Creeks. But Dry Creek is ephemeral, whereas the 

continuous flow along Medicine Creek obtains a continuous supply of sediment from bank erosion.

A trial graphical linear regression, in which water 

discharge was plotted as a dependent variable against 

the three geomorphic factors used in the sediment 

discharge regression, yielded results similar to those 

of the sediment yield regression. As with the sediment discharge, the water discharge of Medicine 

Creek above Harry Strunk Lake is much higher than 

expected. Probably, Medicine Creek receives a larger 

proportion of its water discharge from ground water 

than do Fox and Brushy Creeks. In addition, the 

assumption of uniform distribution of rainfall over 

the various subbasins during the period 1952-58 

may be incorrect.

SUMMARY AND CONCLUSIONS

Annual precipitation at Curtis for the period 

1895-1960 averaged 21.5 inches but ranged from 11 

to 38.2 inches. More than half of the precipitation 

falls during 4 summer months, and much of this is 

thunderstorm rainfall. The 5-year moving average 

for Curtis indicates a long-term trend toward decreasing annual precipitation. Rainfall intensityduration-frequency curves indicate that the rainfall 

regimen was satisfactorily represented at Curtis 

during the years 1951-58, although precipitation 

was lower than the long-term average. Potential 

evaporation is about three times average annual 

precipitation. The Medicine Creek basin lies in a 

transitional zone between prairie and plains grassland; the climax plant community consists of a 

dominance of midgrasses and an understory of short 

grasses.

The immediate effects of drought, as during the 

years 1933-40, are to reduce the grass cover in such 

a way as to leave bare patches of ground, but grasses 

are rapidly replaced by weeds. As a result of a 

secular climatic shift toward dryness, a climax community of short grasses would become established. 

Climatic change since the arrival of settlers has had 

little effect on the climax community, as indicated 

by the character and abundance of vegetation in 

areas that are neither grazed nor cultivated.

Geomorphic and stratigraphic evidence indicates 

that the drainage system grew to approximately its 

present pattern and extent during the episode of 

erosion (tentatively assigned to the interval 12,000 

to 11,000 years B.P.) that followed deposition of the 

Peorian Loess. During the subsequent episode of

deposition (about 11,000 to 5,000 years B.P.), deposits of the Stockville terrace accumulated in the 

valleys and the valley sides were graded. The deposits were incised (about 5,000 to 4,000 years B.P.) 

to form the Stockville terrace, and the deposits that 

subsequently accumulated in the valleys (4,000 to 

1,000 years B.P.) were later incised (about 1,000 to 

900 years B.P.) to form the Mousel terrace. Mousel 

terracing was followed by accumulation of the upper 

Recent alluvium that underlies the present valley 

flats. In some valleys the late Recent alluvium has 

been incised intermittently during the past 350 

years. Thus, within the past 12,000 years, the valleys 

were trenched three times prior to the trenching 

that is taking place in some valleys at present. No 

clear evidence was obtained as to the causes of past 

episodes of erosion or of deposition. However, snails 

from the Stockville terrace deposits probably lived 

under climatic conditions similar to the present, 

and the terracing of the Stockville terrace corresponds approximately with the Altithermal, a wellestablished dry climatic period that lasted from 

about 6,000 to 4,000 years B.P.

Morphometric analysis of the drainage system 

shows that the slope of the exponential curves relating mean channel length to channel order changes 

at the lower channel orders, whereas the curves relating number of channels to channel order have a 

nearly uniform slope. This change in slope of the 

curve relating channel length to channel order is 

attributed to post-Peorian drainage transformation 

in which the lengths of first- and second-order channels were reduced relative to third-order channels. 

In order to compare the channel frequencies of immature drainage systems whose drainage basins 

differ in percentage of undissected upland, drainage 

basin area is adjusted by subtracting the area of 

upland. Channel frequency, expressed as number 

of channels per square mile of area actually occupied 

by the valley system, is called adjusted channel 

frequency.

Erosion by scarp retreat takes many forms in the 

basin, and gullies are regarded as a type of scarp 

erosion. Gullies are defined and are classified as 

valley-bottom, valley-side, and valley-head gullies. 

Many large valley-bottom gullies apparently originate on valley reaches that are locally steepened at 

the entrance of a major tributary. However, the 

ratio of local slope to drainage area that is critical 

for the initiation of a gully is not sharply defined 

because other factors (such as width of valley bottom) are important. In general, trenching of a 

valley reach to bedrock does not take place by the 

coalescence of two discontinuous gullies, but by the
LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 333

passage of several channel scarps in succession. 

Saturation of massive silt at the edges of a plunge 

pool is the most important factor in the advance of 

channel scarps.

Steep-sided valleys that drain areas of cultivated 

upland are most susceptible to valley-head and 

valley-side gullying. The most significant geomorphic factors in the areal frequency distribution of 

valley-head and valley-side gullies are percentage of 

area in upland and adjusted frequency of first-order 

channels.

Generalizations regarding suspended sediment and 

the hydraulic geometry of channels are based on 

data from six gaging stations, two of which are on 

the main channel of Medicine Creek and four on 

tributaries. At the gaging stations on Dry, Mitchell, 

and Brushy Creeks the flow is categorized as ephemeral ; at the others, as perennial. Water discharge 

tends to increase rapidly in response to rainfall, 

much of which falls during summer thunderstorms; 

and the discharge peaks are of short duration.

Hydraulic geometry of the channels is expressed 

by the slope of curves relating width, depth, and 

velocity to discharges equaled or exceeded 1, 2, and 

25 percent of the time. At a station, the low-flow 

channels of perennial streams are well defined and 

have steep banks; with increasing discharge, width 

does not increase as rapidly as depth. By contrast, 

the low-flow channels of ephemeral streams are 

shallow and transient, and width increases rapidly 

with discharge until the steep sides of the incised 

trench are reached. In a downstream direction, the 

incised trenches of ephemeral streams do not widen 

appreciably, and increase in discharge is accommodated by relatively large changes in depth and velocity. The increase in discharge of perennial streams 

is accommodated by relatively rapid increase in 

width and by a slow increase in depth and velocity.

Curves relating suspended-sediment load to water 

discharge for the perennial streams are characterized by a break in slope at water discharges above 

normal but below the bankfull stage; curves for the 

ephemeral streams show no corresponding break. 

Peak sediment concentrations usually occur before 

peak water discharge, but the length of lead is variable and is generally shorter for smaller discharge 

events. In general, 90 percent or more of the suspended sediment is silt and clay, and the measured 

(suspended) load represents 90 to 95 percent of the 

total load. No relation was discerned between instantaneous water discharge and particle-size distribution. In general, the concentration of measured 

suspended sediment is higher in wet years than in

dry, and the ephemeral streams have higher concentrations than the perennial streams.

An evaluation of geomorphic properties indicates 

that relief ratio, adjusted frequency of first-order 

channels, and the percentage of area in upland would 

be expected to have the highest correlation with 

runoff and sediment discharge. No rigorous 

statistical correlation can be made because of the 

small number of subbasins for which data are available, but a trial graphic multiple regression indicates 

that differences in runoff and sediment discharge 

can be accounted for reasonably well by differences 

in these three properties. They are not only important in themselves, but they also give indirect expression to other important properties. For example, 

the percentage of area in upland is related to area in 

row crops, small grain, and fallow.

Active valley-head and valley-side gullies, and all 

but a few of the active valley-bottom gullies, are 

attributed to land use since settlement. During the 

past two naturally induced episodes of erosion, gullying was mainly confined to valley bottoms. Although 

some valley incision has taken place within the past 

500 years and before settlement, major episodes of 

the past are probably associated with droughts more 

severe than any since settlement. Restoration of 

native vegetation to the heads of valleys, together 

with conservation measures on the upland, would 

be effective in the control and prevention of valleyhead gullies, which are the most numerous in the 

basin. These steps, if accompanied by more moderate 

grazing in the vallevs, would probably prevent the 

initiation of new valley-bottom gullies; but no economically feasible means for arresting the present 

large valley-bottom gullies is apparent.

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334 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

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LOESS-MANTLED GREAT PLAINS, MEDICINE CREEK BASIN, NEBRASKA 335

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INDEX

A Page

Acknowledgments _._ _ __. 258

Adjusted channel frequency _. 286, 288

Aerial photographs, use - . .. 274,

280, 286, 291, 298, 299, 304, 305, 309

Agricultural development of

basin _____._.__________ _ .___ ________________ 281

Alluvial fan .._.__ _.__.____ 294

Alluvium _____________________________________ 268

Rates of accumulation

compared _____________________ 273,279

See also Banded alluvium; 

Recent alluvium; Unhanded 

alluvium. 

Altithermal, warm-dry climatic

eposide _________ ___ ___ 284, 332

Annual temperature __..____ _____..____.. 258

Anselmo loam ______.______ ____...______ 280

Archeology ..._...._____....____...____.._.... 280

Arroyo cutting and filling _______ 314

Artifacts _.__..._._______ 279, 281

B

Banded alluvium ____-._-____....__ ^_____. 279

Basin, circularity .___ .____________..___... 329

length ________...____....______....__________ 286

measurement of areas ___.... ___ 286

properties ____.-..________ -. ......___ 288

relief _____________ 286,288

shape -_....____....____ ..______. 288, 328

Bed material _______....______ ._______._._. 322

Bibliography ._..______._____..____._______...___ 333

Bifurcation ratio ____ ___ ___ _ 286

Big bluestem ____......___-...____-____-..-_____. 262

Bignell Loess ____ _._____.. 277, 278

Blowouts .____-_____-________....__....______ 280

Blue grama _______ . .._____......... 262, 263

Blue grass _ _._ ______-_____ _. 262

Brady soil -______ __-___ 277,282

Branched gully head ___._.______ 301,307

Broscoe, A. J., cited __ _ ___ 289 

Brush, examples of thick ._________.. 263

indicator of scrap activity .... 291

Brushy Creek . . .. 286,289,315,

322,331 

Buckbrush .__________.._.____.___..._....____.... 263

Buffalograss .._______.______ _... 262, 263

Bunchgrass ____. .___.__________________._______ 262

Buried valleys -_ _____ _________ 282

California method of

plotting TT .. . .. _.... . ..._... 260 

Cambridge ________-_ ____________ 279

[Italic page numbers indicate major references]

Page

Carbon 14 age determinations .... 268,

272, 273, 278, 281, 284, 300 

Carbonates in loess, significance __ 277 

Carbonized grass _________ 274, 279, 280

Castings, worm ____-___-__.-__ 273,274

Cedar Creek _________ 265,278,282

Ogallala exposures in ____ _ 265

terrace sequence __________ - 270

Census ____ __ _______ ___ 281

Channel, cross-sectional shapes __ 315 

definition __________________ 286

frequency ___ 286,288,289,329,

332 

geometry ______ _.__.-_____ 315

hydraulics __ __ _ 315

length ________ 286, 329, 330, 332

order _____ 286,289,328,330,332

scarp _____ 278,279,290,25^,332

shape ___ ____________ 321

slope __________ 286, 328, 329, 330

See also Trenched channel. 

Charcoal samples ___________ 273, 281

Class A pan evaporation ___ .______ 261

Climate _______ 258, 260, 314, 332

archeological evidence . .._.._ 281 

effect on by Wisconsin Ice 

retreat _________________ 282

Climax plant community __ __._ 262,

263,332 

Colby loam ______________ .. 278,280

Colluvial soil __ ______ _. _________ 277

Conclusions __ _______ ___________ 332

Correlation of terraces ____. _ 268

Cowpaths _________________ 301, 303

Coyote Creek ______________________ 294

Cretaceous bedrock __ ____-______ 265

Crops, area in _______________ 333

Curtis, climatic data __ __ ___ 258 

Curtis Canyon ________________ 279,294,297

Cut Canyon _____________ 272,282,294

D

Deer Creek _ ____________ _______ 282

Deffenbaugh, J. L., cited _______________ 270

Dendrochronology -_ ______.264, 300

Depth, relation to discharge ________ 316

Discharge-weighted mean 

concentration of suspended 

sediment...._____________________ 325

Discontinuous gullies _ 291,294,299 

Downstream hydraulic relations _ 315 

Drainage-basin characteristics, 

interrelations _______ ____- 328

Page

Drainage-basin measurements ___ 286 

Drainage, density _______ 286,288,328

evolution _____ _._ _ _ 282

ordering _____.__ _ __ 285

properties _______ _ - 294

texture variation _ __. 288 

transformation _ .___ 288

Droughts ________________ 281, 314

ancient _ __ __.._ 263,264,274 

effects ___________________ 263

Drought-resistant grass _______ _ _ 263

Dry Creek ____ 278,279,282,286,289,

294, 296, 298, 300, 315, 330,332 

Dunes ____________ 268,250,325

Dust interception __ _____ - 262, 263

Dyksterhuis, E. J., cited _ .___ 258,262

E

Earth worms ________ 274,277,280

East Fort ________.___ - 263

Elkhorn Canyon .____ 272,278,284

head scarp -_._ _ 274

Recent alluvium __ _ _ _ ._ 279 

terrace sequence and valley 

fills ______________ 273

Elongation ratio ._____.__ _ 286,288

Eolian silt, Peorian Loess _ - 275 

Ephemeral streams _ _ 321,322,328,

333 

channels ________________ - _ 315, 318

Erosion rate ___._______ ____- -___ ._ 330

Erosional scarps ._____-.____ 263,290,25i

Evaporation ____ __..____.__ 261,332

Exposed rocks ^ __,__ _ ___ . 264

Fence posts, rate of burial - 279 

Fire drives, use by 

prehistoric man ____-__ _- 280

First-order channels _ ___ 309,331 

Flashy streams ___ _ _ 315

Flats __________________ 332

Formulas, landform _ _ _ 286 

Fossils, list _____________ 271, 276

See also Index fossils. 

Fox Creek _____ 265,271,278,279,286,

289, 294, 315, 322, 331 

Frye, J. C., and others, cited .__ 265

G

Gaging stations _________ 315,318,333

Geologic section, Cut Canyon .._ 272

337
338 EROSION AND SEDIMENTATION IN A SEMIARID ENVIRONMENT

Page

Geometric differences of ephemeral 

and perennial streams ____________ 321

Geomorphic properties in relation 

to water and sediment 

discharge ______________________ 328

Grading _______.__._______ ______ 282, 289

Grand Island Formation __________ 270

Grass -_.-_-_-___.____.___ _ ____ _ __ 332

ability to prevent erosion ___ 263

characteristics of native ~ 262

indicator of scarp activity ___ 291

Gray, D. M., cited ________ 328

Gross erosion ____-_ _-___ __ _ 279

Growth rings of trees __-______ ___ 300

Gullies _-______ 264, 291, 300, 313

advance ______________________ ______ 315

areal distribution -___ __ ___ 307 

coalescence _____________ 291, 299, 332

control of ____________________ 314.

Gully, definition and 

classification ____._____.______ _ 290

erosion _ __._________ ____ _ 290

formation _____________ __________ 301

frequency distribution ___________ 309

man induced _______________________ 313

measurement of advance _._.__ 298 

profile changes _______________________ 296

size categories ________ ________ 305

slumping _________________________ 296

See also Discontinuous gullies; 

Valley-bottom gullies; 

Valley-head gullies; . 

Valley-side gullies. 

Gully head, branched ___ ____... 301, 307

lobed _______________________ 301, 307

H

Harry Strunk Lake _______ 331, 332

Niobrara Formation . ________ 264

Head cut, use of term ______ 291

Head scarps ____ 274, 297, 298, 303, 309

advance -_-_____ __ 274, 290, 312

maximum height __________________ 311

Heavy minerals, Sangamon soil ___ 274 

Holdredge soil ___________________________ 278

Horton, R. E., cited __________ 285,289

Human occupation ____-_ ____ ___ 280

Hydraulic geometry _______________ 333

Hydraulic relations at a section 

and in a downstream 

direction ________________ _ _ _ _ _ 315

Index fossils ________ 268,271,272,275,

276 

Inset terrace -_____ _____________________ 300

K

Kansan deposits ___-___i_-_________ 268

Kansan Glaciation __,-______. 271,282

Kulp, J. L., quoted _______________ 258,278

Page

Land use _......_..._. 25J, £7.?, 330, 331

effects _______________ #03, 264, 301

Landform properties ____________ 286

Leonard, >A.B., cited -. . - 268,271, 

275, 276, 278 

Leopold, L. B., and Maddock,

Thomas,, quoted _________ . . __ _ 315

Lime Creek __ ______ 278, 281, 286, 289

Little bluestem ____ _____'.____.____ __ 262

Load computations, B. R. Colby's

- method ________________________________ . 325

Lobed gully head ...... ... ___ 301, 307

Loess ___..__..___._........ 256, 268, 274

deposition rate ... _ _ ._.__. 277 

See also Bignell Loess. 

Loveland Formation ... 271,274,275,

282

M

Maywood _ _______ _________ __ __ 265

McCoqk, climatic data __ _ _ 258 

Mean channel length _ __ 289 

Mean valley-side slope __ 288 

Medicine Creek _.__.____ 256, 270,278,

, 279, 315, 331, 332

Medicine Creek basin, climate 258

Niobrara Formation ____ __ 264

Ogallala Formation _ _ __ 265

Melton, M. A., cited :__ __ 288

Midgrass' _L _________ ___ 262,332

Mitchell Creek 286, 294, 315, 322, 331 

Modern soil ______ ... L___ __...__ _______ 277

Molluscan fauna, Peorian 275, 276 

Morisawa, M. E., cited _ ... .____. 329

Morphometric analysis ___________ _ 332

Morphometry ________ _.___ _ __ 284.

Mousel terrace __. _. _ _ 265, 278, 280,

284, 332 

carbon-14 dating _ ____. __ __ _ 284

Woodland sites ___________ 280

Multiple linear regression of 

sediment discharge ___________ 331

Multiple regression analysis, 

properties used by Morisawa . 329,

333

N

Native grasses ___________________________ 262

Nebraskan deposits ___-_______ - 268

correlation with ________________ 272

Needlegrass ____________________________ 262

Niobrara Formation ____.___ _ ___ 264

North Platte. ancient

droughts at _____________________ 264

climatic data ___ _-____________ 260

North Plum Creek ___________ 282

Page

0

Ogallala Formation ______________ 265,

270, 271, 274 

buried valleys in ___.____ - 282

Overgrazing _________________________ 263

Oxidation _______________________ 280

Paleoclimate _-___-_--__ __ - 262 

Paleosol __...__-_-_____- _ 270 

Parabolic channel shape _ _ _ 321 

Particle-size distributions of

suspended sediment and bed

material ____-___- 322, 333 

Pearlette Ash Member of the

Sappa Formation _____________ 270, 282

Pelecypod fauna _________ _ _ 278

Peorian Loess __.___._ 268,271,272 

275, 276, 277, 282, 332 

Peorian postdepositional landscape

reconstructed ________________ 282

Peorian valley heads _____ _.___ - 282

Percentage of area, in side slope . 330 

in upland ______________ 328, 331, 333

in valley flat __________ ______ 330

Perennial streams _____ 315,321,333

Petrographic features, Peorian

Loess _______________________.... 277

Platte Valley ____.._..... _..... -__--__ 282

Pleistocene and Recent

deposits _______ __.__.__ __ 265,268

Pleistocene deposits ______ _______ 271

Pleistocene drainage, relic ______ 282

Plum Creek ___ __________ .___.____ 282

Plunge pools .__ _____ _.. 296, 312, 333

Polar planimeter, use _______ _____ 286

Population _________________________________ 281

Post-Sangamon, chronology _____ 284

Prairie _______________________________ 332

Precipitation _ _ 258, 263, 315, 326, 332 

Pre-Pleistocene rocks ________ 264,268

Profile, Cut Canyon _..__ __ _______ _ 272

main course of Medicine

Creek _____ ___________ 270

Purpose of report _____ _____________ _ 255

R .

Radiocarbon dating. See Carbon-14

age determination. 

Raindrop impact _______________________ 263

Rainfall, intensity-durationfrequency curves __-___-_ 260, 332 

interception __ _ _______ 262,263

Ravines ____________________________ 262

Recent alluvium ______ 265,272,273,

278, 279, 280, 284, 332 

Recent deposits. See Pleistocene and

Recent deposits. 

Relief ratio _______________ 286,288,328,

329, 331, 333 

Republican River valley _________ 282
INDEX 339

Page

Reservoir regulation _ 315,318

Rodent burrows __________________. 312

Rubin, Meyer, cited _______ 258,273

Runoff _____ 326,328,329,330,331

Runoff, reduction ..._________________ 314

S

Sand dunes ________________ 268,250,325

Sangamon soil _______ 271,274,282

Sappa Formation _________ 270,271,282

Saturation ____________________. 296, 312

Scarps ____________________________ 290

See also Channel, scarp; 

Erosional scarps; Head 

scarps; Step scarps; Side 

scarps.

Schultz, C. B., and others, cited __ 265 

Schumm, S. A., cited ________________ 288

Scour __________________ 295

Settlement __________________ 281

Short grass ___ _-___ _____ 262,332

Side-oats grama _ ___ __ _-___-_ 262 

Side scarps -._ __ ______ ______ 291

Silt ___________________ 333

Slocum, J. L., quoted ___________________ 262

Slumping ____________ 298, 312

Snails ______ 268,271,275,276,278,

332 

Sod _____________________ 263

effects of breaks in ___.___. 295 

scarps ___________-_-___ _ 263

Soil marker _____ ______ 268, 274

Station hydraulic relations __________ 315

Step scarps ______________ 264,290

Stephenson, D. V., quoted ______ 262

Stockville terrace ______ 265, 268, 272,

978, 282, 286, 291, 292,311, 313, 332 

age ________________ 281

carbon-14 dating ________ _ 284

Early Lithic sites ___________ 280

Strahler's, A. N., method of 

stream ordering ____ 285,286,289

Stratigraphy, Cedar Creek near 

Stockville ________________ 270

Cut Canyon near Curtis - 271 

Pleistocene and Recent _ 268

Page

Stream, capture by Deer Creek _.__ 282 

hydraulics ____________________ 315

ordering method _._ '285, 286, 289 

Stream lengths, R. E. Horton's 

law of ___________________ 289

Upland, definition _________________ 286

Summary _______________________ 332

Sumac ____________________ 263

Suspended sediment - - 279, 315,321, 

325, 328, 329, 330, 331, 333 

affect on hydraulic geometry

of channels . ___ ___ ___ 315 

contributions of major

tributaries ___________________ 325

particle-size distributions ___ 322 

Switchgrass ____________________ 262

Tall grass ______________________ 262

Tazewell Stade, Wisconsin

Glaciation __________________ 275

Temperatures __________________ 258

Terraces, Cedar Creek __________ 270

Elkhorn Canyon ____________________ 273

rate of formation ________ _ 274

sequence ___ _______________ 265

See also Inset terrace; 

Mousel terrace; Stockville 

terrace; Wellfleet terrace. 

Topographic maps, use _____ 258,286,

288,294,298 

Trees ____________________ 262, 264

Trenched channel _______________ 279

U

Unbanded alluvium .__.__.__ ____ 279

Unexposed rocks __ ____________ 264

Upland ___________ 286, 288, 330

slope _________________ 330

Upper Republican Culture __ 274, 281 

U-shaped dunes ______________ 280

Valley-bottom gullies __ 264,291,295,

297, 298,307, 309, 313, 314, 332, 333

Valley bottoms __________________ 264

Page

Valley fill, Elkhorn Canyon ________ 273

Peorian __ ____________ ___ 276

Valley flat ___________ 279, 329, 330

Valley-head gullies _______ 291, 301,

303, 307, 313,332,333 

formation _________ ____ 309

measurement ___________ 304, 309

Valley incision, Ogallala

Formation ______________ ._ 282

Valley-side gullies _____ 291,501,303,

307,313,332,333 

formation ___,_______ __ 309

measurement ____ _______ __ 304

Valley, slope ___________ ___.._____-_ 286, 329

trenching ___ _________________ 278

Vegetation ________________ 262, 314, 332, 333

role of, in gully control _____ 314

Velocity, relation to discharge __ 316

V-shaped contour lines _______________ 286

W

Water-discharge functions .__ _ 316 

Water-sediment discharge

relation _____________ _______ 322

Wayne, W. J., cited _ 258,271,275,

276

Weakly, H. E., cited ___.___.__ 264 

Weaver, J. E., and Albertson,

F. W. cited ____________________ _ 263

Well Canyon ... ... 265,278,279,286,

289,294, 330 

Wellfleet terrace ______ 265,268,280

Wheatgrass _________________ 262

Width of stream, relation to

discharge _____._ _ ___ _ ____ 316

Wild plum -___ ______ _______ 263

Wild rose ___________ ______. 263

Wimpf, Charles, quoted _._ _______ 262

Wind speed and direction __. ___ 261 

Windblown dust ________.. .__ _ 263

Wisconsin deposits _.__ __-_____. __ 268

Wisconsin ice, retreat _______________ 282

Worm burrows and casting _.__ 273, 277

Yarmouth soil _________ 270,271

U.S. GOVERNMENT PRINTING OFFICE: 1966 O 2I7-S78