General and Engineering 

Geology of the W ray 

Area, Colorado and 

Nebraska 

By DOROTHY R. HILL and JESSIE M. TOMPKIN 

'G E Q_ L 0 G I C A L S U R V E Y B U L L E T I N 1 0 0 1 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1953 
UNITED STATES DEPARTMENT OF THE INTERIOR 

Douglas McKay, Secretary 

GEOLOGICAL SURVEY 

W. E. Wrather, Director 

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

Washi~ton 25, D. C. - Price 90 cents (paper cover) 
CONTENTS 

Page 

Abstract_________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 1 

Introduction______________________________________________________ 2 

Location and accessibility_______________________________________ 2 

Purpose of investigation________________________________________ 3 

Fieldwork____________________________________________________ 4 

Acknowledgments_____________________________________________ 4 

Geography________________________________________________________ 5 

Physiography_________________________________________________ 5 

Drainage and water supply_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 5 

Climate and vegetation_________________________________________ 7 

Culture ________ - ____ - _________ - ___ -__________________________ 8 

Descriptive geology________________________________________________ 8 

General relations ___________________________________________ ~ _ _ 8 

Cretaceous system_______ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 10 

Upper Cretaceous series___ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 10 

Pierre shale________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 10 

Tertiary system_______________________________________________ 12 

Pliocene series_____ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 12 

Ogallala formation_____________________________________ 12 

Quaternary system____________________________________________ 22 

Pleistocene series_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 22 

Grand Island formation________________________________ 23 

Peorian loess ______________________ ·- _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 25 

Late Pleistocene and Recent series___________________________ 28 

Sandy silt and clay ________________ ·- _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 29 

Valley filL___ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 30 

Sand Hills formation____________________________________ 32 

Recentseries______________________________________________ 33 

Alluvium______________________________________________ 33 

Geologic History _________________________________________________ ~ _ 33 

Engineering Geology_______________________________________________ 39 

Engineering problems ______________________ .. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 39 

Foundation conditions _________________ .. _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 39 

Drainage_________________________________________________ 43 

Stability in cuts ______________________ .. ____________________ 43 

Excavation_______________________________________________ 44 

Sources of construction materials_____________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 45 

Surfacing_________________________________________________ 47 

Ballast___________________________________________________ 47 

Base course_______________________________________________ 48 

Binder___________________________________________________ 48 

Mineral filler_________ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 48 

Blending sand____ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 4 8 

Pozzolan_________________________________________________ 49 

Concrete aggregate_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 50 

Fill______________________________________________________ 51 

Well Logs________________________________________________________ 51 

Selected bibliography_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 62 

Index____________________________________________________________ 65 

III 
IV CONTENTS 

IIJLUSTRATIONS 

Page 

PLATE 1. Geologic map and section of the Wray area, Colorado- ~ebraska __________________________________________ Inpocket 

FIGURE 1. Index map showing location of the Wray area_______________ 2 

2. Location of Wray dam___________________________________ 3 

3. Contact between Pierre shale and Ogallala formation_________ 10 

4. Cross-bedded conglomerate at base of Ogallala formation_____ 15 

5. Ledges and slopes of Ogallala formation____________________ 17 

6. Volcanic ash of the Ogallala formation______________________ 19 

7. Exposure of typical "algal limestone" of the Ogallala formation_ 20 

8. Gravel of the Grand Island formation exposed in pit_________ 25 

9. Exposure of valley fill____________________________________ 38 

10. Size analysis graph of construction materials in the Wray area_ 46 

TABLES 

TABLE 1. Geologic formations in the Wray area______________________ 9 

2. Properties and uses of earth materials in the Wray area______ --·40 

3. Summary of tests of construction materials ________ ~ _ _ _ _ Facing 44 

.. 
GENERAL AND ENGINEERING GEOLOGY OF THE WRAY 

AREA COLORADO-NEBRASKA 

By DoROTHY R. HILL and JEssiE M. ToMPKIN 

ABSTRACT 

The Wray area, consisting of the Wray no. 3 and Wray no. 4 15-minute quadrangles, includes part of eastern Yuma County in eastern Colorado, and part of 

southwestern Dundy County in southwestern N ebruska. The North Fork of the 

Republican River flows eastward through the area, joining the Arikaree River 

just east of the Wray no. 4 quadrangle. North of the Republican River are 

northwestward-trending sand hills, alternating with flat, silty, sandy farmlands. 

The Ogallala formation forms steep cliffs along the southern side of the valley of 

the Republican River, and the rolling uplands south of the cliffs are covered with 

loess. 

The Wray quadrangles lie on the eastern flank of the Julesburg Basin, which 

forms a great structural trough extending along the foothills of the Rocky Mountain Front Range from southern Wyoming to southern Colorado, and eastward 

into eastern Wyoming, western Nebraska, and northwestern Kansas. The formations exposed in the Wray quadrangles are flat-lying, or have only a slight dip 

not discernible in outcrops. The oldest formation is the Pierre shale, of Late 

Cretaceous age, which is unconformably overlain by the Ogallala formation, of 

Pliocene age. The Ogallala formation consists of sands, silts, and gravels which 

are cemented to varying degrees by calcium carbonate. The beds are discontinuous; none can be traced more than a few hundred feet. Unconformably 

overlying the Ogallala formation are the Pleistocene Grand Island formation and 

the Pleistocene and Recent sandy silt and clay. South of the Republican River, 

the Grand Island formation and the sandy silt and clay are absent, and the 

Pleistocene Peorian loess rests directly on the Ogallala formation. North of the 

Republican River, where very little loess is present, the Grand Island formation 

and the sandy silt and clay are overlain in some places by sand hills. Valley fill 

chokes the ravines of streams tributary to the Republican River. 

The Pierre shale was deposited in the vast inland Cretaceous sea which covered 

eastern Colorado and much of the surrounding area. After formation of the 

Julesburg Basin at the end of Cretaceous time, the Pierre shale was eroded and 

the Pliocene Ogallala formation was deposited by fresh-water streams flowing over 

the irregular surface of the Pierre shale. During Pleistocene time, streams cut 

deep valleys in the Ogallala formation and deposited the sand and gravel of the 

Grand Island formation in the valleys. After much of the sand and gravel was 

removed by erosion, the valleys were choked with valley fill or with wind-blown 

Peorian loess. South of the Republican River, a thick mantle of undisturbed 

loess covered the surface, and north of the Republican River the loess mantle was 

reworked by streams and covered by sand drifting :into the area from the north. 

In late Pleistocene and Recent time, streams cut terraces in the valley fill. 

Most of the formations in the Wray area are fair foundation materials, although 

good construction materials are scarce. The gravel of the Grand Island formation 

1 
2 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

and the gravels in the Ogallala formation contain large quantities of clay1 silt, 

sand, and calcium carbonate, and have very fe'v pebbles larger than one-half 

inch in diameter. None of the gravel is suitable for concrete aggregate, but it 

may be used for ballast, base- and top-course. Volcanic ash in the Ogallala 

formation may be used as mineral filler, pozzolanic material, and cleansing 

powders. The Pleistocene sandy silt and clay may be used for binder; the Peorian 

loess is a possible source of ceramic slag aggregate and serves as a good mineral 

filler. Blending sand and earth-fill dam material are available in the valley fill. 

INTRODUCTION 

LOCATION AND ACCESSIBILITY 

The Wray area, consisting of the Wray no. 3 and w-ray no. 4 

15-minute quadrangles, includes part of eastern Yuma County in 

eastern Colorado and part of southwestern Dundy County in southwestern Nebraska. The quadrangles cover an area of approximately 

440 square miles, which extends northward from the 40th parallel to 

latitude 40°15' N., and westward from longitude 102° to 102°30' W. 

The location of the area is shown in figure 1. 

Base from U.S.G.S. map of 

United States,1:2,500,000 25 100 Miles 

FIGURE 1.-Index map showing location of the Wray area. 

/ 
INTRODUCTION 3 

The Wray area can be -reached by east-west U. S. Highway 34, 

which is surfaced with oiled gravel. The Chicago, Burlington & 

Quincy Railroad follows a route approximately parallel to this highway. State Highway 51, which is a graded gravel road, extends 

north and south from the town of Wray. State Highway 27 extends 

north and south from the town of Eckley, and State Highway 29 

branches south from U.S. Highway 34, 2 miles west of Wray. Both 

Highways 27 and 29 are graded and graveled. Light-traffic sectionline roads are maintained by grading. 

PURPOSE OF INVESTIGATION 

The Wray area is part of the Missouri River basin, which is now 

being developed. The comprehensive plan for the development of the 

Missouri River basin includes the construction by the Bureau of 

Reclamation of the Wray dam and reservoir on the North Fork of the 

Republican River in the Wray no. 3 quadrangle (S~ Doc. 191, 1944). 

The approximate proposed location of the dam is shown on figure 2. 

Because part of the program of the Engineering Geology Branch of 

the U. S. Geological Survey is to supply background geologic maps of 

areas where construction is proposed by other Federal agencies, the 

mapping of the area surrounding the proposed Wray dam and 

reservoir was undertaken by _the Survey in the summer of 1948. 

T. 

I 

N. 

R.44W. 

\ 

4 

us 34 

15 

\. 

R.44W. 

0 I Mile 

FIGURE 2.-Map showing approximate proposed loeatwn of Wray Dam. 

( \ 

~ 
4 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

The aim of this report is twofold. It is intended to be of value not 

only to persons interested in the geology of the Wray quadrangles, 

but also to anyone who must know the engineering properties of the 

geologic units or who desires to use construction materials. 

The report is divided into two parts. The first, a diseussion of the 

map units shown on the accompanying geologie map, includes descripHve geology and geologic history. The descriptive geology covers the 

extent, distribution, lithology, paleontology, age, and soil development 

of each map unit. The next, a summary of the engineering geology of 

the area, discusses the engineering problems and construction materials 

for each map unit. All geologie materials in the area that might be 

used for construction are considered. Logs for wells shown on the 

gyplogic map are given in an appendix at the end of the report. 

FIELD WORK 

The field work on which this report is based was accomplished by 

the writers during the summer of 1948 under the general supervision 

of E. B. Eckel and E. Dobrovolny of the Engineering Geology Branch, 

U. S. Geological Survey. The geology was mapped directly on aerial 

photographs provided by the Soil Conservation Service of the Department of Agriculture, and culture and drainage were transferred 

from the photographs to the finished m~ (see -pl. 1) by means of a 

vertical sketchmaster. Boundaries of the quadrangles were furnished 

by the Topographic Division of the U. S. Geological Survey; the 

section-line grid was established from Bureau of Land Management 

survey plats. The elevations on which the cross section was based 

were determined by vertieal-angle measurement fron1 bench marks 

established by the U.S. Coast and Geodetic Survey. Other elevations 

were obtained by using an altimeter; these measurements were aceurate only within 10 feet. Units 3 feet or more in thiekness were shown 

on the geologie map. Samples of sand, gravel, silt, voleanic ash, and 

other possible construetion materials were tested by the writers in the 

laboratory at the end of the field season to deter1nine the uses for 

which they were best fitted. 

ACKNOWLEDGMENTS 

The writers are indebted to Mr. R. E. Fincher of the Public Roads 

Laboratory, Denver, who generously supervised the analysis of the 

samples of construction material. The vVray office of the Production 

and ~1arketing Administration furnished aerial photographs which 

were used at the beginning of the field season. Also, many residents 

of the Wray area offered generous cooperation and assistance during 

the course of the field work. 
GEOGRAPHY 

PHYSIOGRAPHY 

5 

The most striking feature of the present physiography of the Wray 

area is the northwest trend of the surface deposits. Two-thirds of the 

area north of the Republican River is covered by sand hills interspersed 

with poorly drained sandy flats. South of the Republican River, 

steep bluffs are cut by rnnnerous northwest-sloping ravines. The 

surface undulations of the loess deposits surn1ounting the bluffs also 

trend northwest. Maxinu1m local relief is 170 feet, which is the height 

of the highest sand hill. The alnwst vertical cliffs south of Wray, are 

the most arresting feature of the relief. These cliffs rise as high as 

150 feet above the flat valley bottom of the Republican River and 

contrast sharply with the rolling topography of the surrounding 

countryside. 

The Wray quadrangles are in the High Plains Section of the Great 

Plains province, on the broad, irregular plain that slopes from the 

Rocky Mountains eastward to the Mississippi Valley. The North 

Fork of the Republican River flows eastward through the southern 

part ·of the area and is bordered on the south by bluffs which are 

highest near the town of Wray, become lower toward the east, and 

finally disappear near the Coloraclo-N ebraska line. South of the 

bluffs are rolling uplands, which are cut by northwestward-heading 

ravines joining the valley of the Arikaree River; both bluffs and uplands are cut by numerous sn1all southward- and southeastwardheading streams tributary to the Republican River. North of the 

Republican River, many long northwestward-trending ridges of sand 

hills, 25 to 170 feet high, alternate with wide, poorly drained flats. 

The northvvesterly trend is repeated in the pattern of ridges and 

hollows in the loess deposits on the uplands south of the Republican 

River. The trend of the loess ridges is quite n1arked on aerial photographs, although it is not easily discerned on the ground. Total relief 

of the area is about 500 feet and the average altitude is 3,750 feet. 

DRAINAGE AND WATER SUP~LY 

The two largest streams in the Wray area are the North Fork Republican River, and the Arikaree River, both of which flow northeastward; many small intermittent streams flow into these rivers from the 

northwest and the south. Wells produce water fron1 gravel 50 to 

.150 feet below the surface. The main aquifers in the area are the 

gravel of both the Grand Island formation and the Ogallala formation. 

At the present tin1e, well water is useclrnostly for domestic purposes 

and stock. Very little irrigation is practiced. 
6 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

The North Fork Republican River heads south of the southern border of Wray no. 3 quadrangle, about 5 miles east of its western boundary. It flows 4 miles northeast, then bends to flow eastward through 

the town of Wray and the Wray no. 4 quadrangle. About 1 mile 

west of Wray, it is joined by Chief Creek which heads in a marshy 

area about 2 miles east of the town of Eckley. The North Fork 

Republican River is fed by many sn1all springs and has an average 

flow of about 22 cubic feet per second. The flow is very uniform and 

is seldom less than 10 cubic feet per second (Colby and Altman, 1948, 

p. 98). Many south-heading inteTmittent streams discharge into the 

river during the spring, but only a few small streams flow into the 

river from the northwest. The ravines formed by the streams extend 

as much as 2 miles from the river valley. Most of the upland area 

has no surface drainage. Although the drainage area of the North 

Fork Republican River upstream from the gaging station near Wray 

contains 650 square miles, only about 40 square miles of this area 

contributes to surface runoff. 

The Arikaree River flows northeast across the southeast corner of 

Wray no. 4 quadrangle a.nd joins the Republican River east of the area 

described in this report. Intermittent streams flow into the Arikaree 

RiveT from the northwest and the southeast. 

Many wells, pumped by windmills, obtain potable water from gravel 

at depths of 50 to 150 feet in quantities adequate for domestic and 

stock use. North of the river, water is obtained from the gravel of 

the Grand Island formation at depths of 50 to 75 feet or from gravel 

of the Ogallala formation at depths of 50 to 150 feet. South of the 

Republican River, it is necessary to drill much deeper for water 

because the loess is very thick and the gravel of the Ogallala formation 

is the only aquifer. There is little or no Grand Island formation south 

of the Republican River. Near Wray and Laird, wells are drilled in 

valley fill. Locations of wells are shown on the geologic map and 

logs are given in an appendix at the end of the report. The water 

table intersects the surface in the valleys near the heads of the Republican River and Chief Creek. Springs and many seeps occur in 

gullies along the contact of the Pierre and Ogallala formations. 

Many intermittent ponds form in slight surface depressions in the 

loess. Because the loess lies above the water table in this area, it 

does not yield water to wells. 

The sand hills north of the Republican River act as reservoirs, 

because the permeability and porosity of the sand make possible the 

accumulation and temporary storage of large amounts of water. 

Seepage of rain water into the dunes prevents high surface runoff. 

The sand is composed of rounded grains, 80 percent of which are 
GEOGRAPHY 7 

between 0.1 and 0.5 Inillimeters in diameter. Because of the uniformity of size and the rounded shape of the grains, the pore space is large, 

and the capacity for water storage is great. Some of the water stored 

in the sand dunes seeps downward into the Grand Island formation 

and the gravels of the Ogallala formation, which are the main aquifers 

in the area. The water that seeps laterally through the sand 

accumulates as temporary ponds in the depressions between the 

dunes; many of these ponds are utilized as stock wallows and watering 

places. Much of the water is discharged to the Republican River by 

lateral seepage through the sand hills. 

At present, irrigation is relatively unimportant in the Wray area. 

In 1944 only 1, 17 5 acres of land were irrigated in Yuma County 

(Crampon, 1949, p. 4). Most of the irrigated land lies in the valley of 

the Republican River east of Wray, where the main irrigation channel, 

the Haigler ditch, runs from the Republican River and flows approxinlately parallel to the river eastward out of the area. 

CLIMATE AND VEGETATION 

The din1ate of the Wray area is semiarid; the average precipitation 

is 18.29 inches a year and is heaviest from April to August, inclusive. 

The region has a typical inland cli1nate, with wide seasonal variations 

in temperature. The average yearly temperature is 51° F.; the highest recorded temperature is 108° F., and the lowest -32° F. During 

the summer months, temperatures higher than 100° F. are not unusual; occasional dust storms and rare violent thundershowers do 

nothing to alleviate the heat. Residents of the area work in their 

fields during the early morning and late afternoon; they make no 

attempt to work out-of-doors during the hot part of the day. In the 

winter, snow covers the area, and sub-zero temperatures continue for 

long periods of time. The prevailing wind is from the northwest, 

although in the summer months the winds shift and blow from the 

southeast.· The average wind velocity is 11 miles pel' hour; winds of 

higher velocities produce dust storms in the summer and drifting 

snow in the winter (U. S. Weather Bureau, Denver, Colo., personal 

communication). 

Trees are scarce in the area except in the town of Wray, along 

streams, and in ravines containing intermittent streams. The rolling 

uplands in the southern part of the area, where not farmed, are covered 

by low grasses, chiefly buffalo, grama, needle, and wheatgrass. Except 

for small blowout areas, the surface of the sand hills and the lowlands 

between them are covered with sparse vegetation, consisting mostly 

of coarse grass, such as redfieldia and stipa, sage, yucca, sand burrs, 

and a few cacti. · 
8 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

CULTURE 

The town of 'Vray, the seat of Yuma County, is located almost in 

the center of the vVray area. The town lies on the :flat bottom land 

of the Republican River, and it is bordered on the south by steep 

cliffs which rise as 1nuch as 150 feet above the valley :floor. Although 

most of the w·ray area is sere and brown during the summer months, 

the town of vVray, with its green lawns and trees, is cool and pleasant 

in appearance. Wray is the largest community in the area; its 

population was reported to be 2,061 in the 1940 census. The town 

of Eckley, population 358, is 14 miles west of Wray and 1 mile north 

of U. S. Highway 34 (the major east-west route through the area). 

Two small unincorporated communities are on U. S. Highway 34: 

Laird, 6 miles east of Wray, and Sanborn, 13 n1iles east of Wray. 

The rest of the area is sparsely populated. 

Dry-land farming and stock raising are the principal industries in 

the region; in 1939 approximately 60 percent of persons 14 years of 

age or older were en1ployed in agriculture in Yuma County (Bur. 

Census 1940, p. 742). The value of farm crops in Yuma County in 

1945 was $2,619,410; sales of livestock and livestock products reached 

$3,808,324 (Bur. Census, 1945, p. 162). vVheat, hay, corn, rye, and 

millet are grown on the rolling uplands south of the valley of the 

Republican River. Hay, corn, Inelons, alfalfa, and truck crops are 

grown in the stream valleys; in the flat areas between the sand hills, 

corn, wheat, alfalfa, and sweet dover are cultivated. The grasscovered uplands and the sand hills are used as grazing land. 

Good production is obtained from crops grown on the loess uplands, 

in the valley botton1s, and in the flats between the sand hills. The 

soil at the edges of the flats, close to the sand hills, is too sandy to 

support crops; when the natural vegetation is reinoved by plowing, 

the fields n1ay become areas of active deflation, because the wind and 

rain quickly erode the sandy soil. During the 1930's many persons 

attempted to farm these sandy, marginal lands; the many small 

abandoned farn1houses in the w·ray area are mute evidence of their 

failure. Some of the fields that were cultivated 15 years ago have 

not yet been recovered by vegetation. 

DESCRIPTIVE GEOLOGY 

GENERAL RELATIONS 

The w·ray quadrangles are on the eastern flank of the Julesburg 

Basin, which lies in a great structural trough formed by the' downwarping of Cretaceous and older formations during the Laramide 

revolution. Flat-lying Cenozoic sediments were deposited on the 

eroded surface of the Cretaceous and older rocks. The great subsurface structural trough extends along thefoothillsof the Rocky Moun-
DESCRIPTIVE GEOLOGY 9 

tain Front Range from southern vVyoming to southern Colorado, and 

eastward into eastern vVyoming, western Nebraska, and northwestern 

Kansas. The basin is asymmetrical, with a steeply dipping western 

side and a gently dipping eastern side. 1\ ear the western edge of 

the basin are many minor folds and flexures, some of which contain 

commercial quantities of oil or gas. South of the "\Vray area, on the 

eastern flank of the basin, is the w ·ray gas field on a small flexure 

called the Beecher Island dome. 

All formations that crop out in the "\Vray area are semiconsolidated to unconsolidated sediments and apparently are horizontal 

except for slight initial dip. X o subsurface data are available and 

structure at depth could not be determined. The oldest formation 

exposed in the w ·ray quadrangles is the Pierre shale of Late Cretaceous age. The Pierre shale is unconformably overlain by the Ogallala 

TABLE 1.-Geolog£c map un£ts in the Wray area 

System Series Map unit Character 1 

Estimated 

maximunl 

thickness 

(feet) 

Construction 

materials 

------ ------------1------------------------ Q,uaternary __ Recent_ _____ Alluvium _____ Unconsolidated silt, sand, 

Pleistocene 

and Re- cent. 

and gravel. 

Sand Hills for- Pale yellowish-brown (10 

mation. YR 6/2), wind-deposited 

quartz sand. 

(?) 30 

100 Blending sand 

mineral filler, 

plaster sand . 

-----------------------------· Valley filL ____ Sandy silt, dark-gray (N 3) to light-gray (N i ); sand, cross-bedded with some lenses of gravel. 

Sandy silt and Yellowish-gray (5 Y 8/1) to clay . pale yellowish-brown (10 YR 6/2), calcareous sandy silt and clay . 

Pleistocene .. . Peorian loess __ Wind-deposited silt (loess), calcareous, yellowish-gray 

(5 y 7/2). 

----- Unconformity Pleistocene __ Grand Island 

formation . 

Unconformity Tertiary_____ Pliocene _____ Ogallala formation. 

Sand and gravel, loosely consolidated, calcareous, pale reddish-brown (10 R 5/4) to light-gray (K i ). 

Sand, gravel, and silt, ce- mented to varying degrees with calcium carbonate; some lenses of limestone, 

volcanic ash, clay . 

75 Road metal, blending sand, binder, 

fine aggregate. 

35 Binder. 

130 Mineral filler. 

20 Aggregate, road 

metal, mineral 

filler. 

220 Aggregate, polishing powder, min- eral filler. 

"C"nconformity ----------- Cretaceous_ _ Upper Cre- Pierre shale ___ Clay shale, thin-bedded, z 1, 500+ taceous. pale-olive (10 Y 6/2) to dark yellowish-orange (10 YR 6/6). Contains thin 

lenses of bentonite and selenite. 

1 Color terms, with the exception of terms used in soil descriptions, are taken from the Rock-color chart. 

distributed by the National Research Council, Washington, D. C., 1918. 'I'hc generalized soil descriptions in this bulletin are based on information from an unpublished report by the Soil Conservation Service 

and the Colorado Agricultural Experiment Station; the soil color terms used in this bulletin are the same a.s those used in the unpublished report. Numbers given after soil color indicate that the term is a Provisional Soil Survey color name, based on Munsell color charts. 2 100 feet exposed. 
10 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

formation of Pliocene age, which is in turn overlain by the Pleistocene Grand Island formation. Peorian loess, Pleistocene and Recent 

sandy silt and clay, late Pleistocene to Recent dune sand, and Recent 

alluvium are also exposed. (See table 1.) 

CRETACEOUS SYSTEM 

UPPER CRETACEOUS SERIES 

PIERRE SHALE 

The Pierre shale, a pale-olive (10 Y 6/2) to dark yellowish-orange 

(10 YR 6/6) clay shale containing some selenite and bentonite, is the 

oldest formation exposed in the Wray area. It is marine in origin 

and Late Cretaceous in age. 

Extent and distribution.- The Pierre shale is exposed in Wray no. 

4 quadrangle and along the eastern edge of no. 3 quadrangle. It 

crops out in the sides of southward-heading ravines on the south 

side of the Republican River and in northwestward-heading ravines 

on the northwest side of the Arikaree River. Only about 100 feet 

of Pierre shale is exposed. Wells drilled in the Beecher Island Dome 

south of the \Vray area show the total thickness of the Pierre shale 

to be about 1,500 feet; one well drilled in the Wray area (see well 

log no. 116) records shale to a depth of 3,275 feet, but the formations penetrated by this well could not be determined because 

the log for the upper 2,410 feet is missing (Barb, 1946, pp. 428-

429). This seems to indicate that the Pierre shale may be more 

than 1,500 feet thick. The Pierre shale is unconformably overlain 

by the Pliocene Ogallala formation. (See fig. 3.) 

FIGURE 3.-0ontact between Pierre shale and Ogallala formation (W}~ SEH. sec., 2 'I'. 1 N., R. 45 W) . 
DESCRIPTIVE GEOLOGY 11 

Previous work.-The Pierre shale was first described and named 

the Fort Pierre group in 1861 by Meek and Hayden (1861, pp. 419·-

424). The Pierre shale is the lowest formation in the Cretaceous 

Montana group, which was named and described in 1889 by Eldridge 

(1889, p. 93). In 1928, ~1:ather, Gilluly, and Lusk (1928) described 

several members of the Pierre shale in northeastern Colorado; in 

1931, Elias (1931, pp. 43- 131) made tentative correlations between 

these members and similar beds in the Pierre shale of Wallace 

County, Kans., and Beecher Island, Colo. (south of the Wray area). 

Only a very small amount of Pierre shale is exposed in the Wray 

quadrangles, and although the lithology is similar to that of the shale 

near Beecher Island, no exaet correlations could be made between 

the shales in the two areas. The shale in the Wray area could not 

be divided into rnembers. 

L1:thology.-The Pierre shale exposed in the "Tray area is thinbedded, pale-olive (10 Y 6/2) to dark yellowish-orange (10 YR 6/6) 

clay shale. It contains thin iron-stained beds and a few thin, lenticular beds of bentonite. vVhere it is exposed in ravines in the southeastern corner of the area, the Pierre shale eontains rnany thin lenses 

and seams of gypsum (selenite and a fibrous variety), frorn oneeighth ineh to 1% inches thick, which weather out on the surface as 

aggregates of crystals. In the SW}~ see. 8, T. 1 N., R. 42 W., the 

shale contains a few in1pure, white (N 9) to yellowish-gray (5 Y 7 /2) 

bentonite sean1s, frorn one-quarter inch to 6 inches thick. These 

seams are remnants of voleanie ash falls. The purest bentonite, 

eonsisting of fine shards of white (N 9) voleanie ash partly altered 

to clay, erops out in a bed about 6 inches thick. The other seams, 

which are from one-quarter inch to one-half inch thiek, consist of 

coarse, only slightly altered glass shards rnixed with grains of fine 

sand and silt. 

Fossils and age.-The only fossil found in the Pierre shale is one 

specimen of Bac·ulite8 sp. The shale eould not be correlated with 

any previously deseribed n1ernbers of the Pierre; eonsequently, it 

was mapped as undifferentiated Pierre shale of Late Cretaceous age. 

Sm:zs.-The soil descriptions in this bulletin are based on information obtained fron1 an unpublished report by the Soil Conservation 

Service and the Colorado Agricultural Experirnent Station. The 

distribution of the soils described in this report is shown on an aeeompanying field n1ap, and by con1paring this n1ap with the geologic 

map of the vVray area, one or more of the described soils was correlated 

with each geologie n1ap unit. Generalized soil profiles and eharacteristies for each map unit were eonclensecl frorn the cleseriptions of the 

one or more soils thus correlated with the geologie map unit. 
12 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

The extremely fine-textured soils developed fron1 the Pierre shale 

are plastic and sticky when wet. Both the soil and the parent 

material shrink greatly while drying; the dry soil is hard and tough, 

and has a blocky texture. A generalized soil profile (top to bottom) 

follows: 

1. Dark-gray (5.0 Y 4/0.5 dry) t.o dark olive-gray (5.0 Y 3/2 moist) heavy clay; 

hard, tough, with medium-blocky structure when dry; plastic and sticky 

when wet; 4 to 10 inches thick. 

2. Olive-gray (5.0 Y 5/1 dry) to dark olive-brown (2.5 Y 4/2 moist) heavy plastic 

clay; may have irregular blocky structure; calcareous in most places; 

may contain gypsum crystals; 4 to 10 inches thick. 

3. Partly weathered gray (5.0 Y 5/0.5) or olive-brown massive to slightly blocky 

clay or clay shale; ealcareous; may contain gypsum crystals; 6 to 12 inches 

thick. 

4. Unaltered parent shale. 

The soil may be developed on a nearly level or steeply sloping 

surface. Surface runoff is mediun1 to high, and permeability is very 

low. In smne plaees wheat, other small grains, and forage are grown 

on the soils developed fron1 the Pierre shale, although the average 

yield is low. Rough areas are used for grazing. Selenium in the 

vegetation grown on some of these soils is poisonous to livestock, 

and appreciably reduces the value of the land. 

TERTIARY SYSTEM 

PLIOCENE SERIES 

OGALLALA FORMATION 

The Ogallala formation of Pliocene age is exposed as bluffs along 

the south side of the Republiean River. Its maximum estimated 

thickness is 220 feet, and it has an estimated initial dip of 12 feet 

to the mile. The formation uneonformably overlies the Pierre shale. 

Lugn (1 939) has suggested that the formation be given the status of 

a group, divided into four formations distinguished by lithology and 

fossil assemblage. Because the Ogallala formation in the W ray 

area could not be divided on the basis of either lithology or fossil 

content, it is mapped as a single formation. 

The bulk of the Ogallala formation eonsists of sand and silt cemented with calcium carbonate; the degree of cementation varies laterally 

and vertically. The formation crops out as a succession of alternating ledges and slopes called "mortar beds"; none of the beds can 

be traced more than a few hundred feet. The only marker bed in 

the formation is the capping layer of algal limestone. 
DESCRIPTIVE GEOLOGY 13 

EJ.tent and distrib·u.tion.-;.;; tmr the tmvn of Wray, the Ogallala 

formation forn"ls pr01ninent cliffs along the south side of the Republican 

River and in ravines of southward-heading streams tributary to the 

valley of the Republican River. In n"lost places on the north side 

of the Republican River valley, the forn"lation is covered by dune 

sand or by Pleistocene sandy silt and clay; south of the Republican 

River, it is mantled by Peorian loess. The greatest thickness of 

the Ogallala formation observed in one continuous vertical exposure 

is 81 feet; the base of the forrnation does not crop out at this place. 

Portions of the section of the Ogallala fonnation are exposed in 

various places; s01ne exposures include the basal eongl01nerate and 

sorne include the capping algal lirnestone, but no single complete 

section including both capping and basal beds was found. The 

maximum thickness of the forn1ation in this area is estirna.tecl to be 

220 feet. East of Wray, the Ogallala forn1ation forms lmv bluff's and 

small outliers, but erosion has cornpletely rernoved the formation 

near the Coloracio-N ebraska bounda.ry. 

Previous work.-The Ogallala forn~ation was first named and defined 

by Darton (1899) who tentatively assigned it to the Pliocene epoch. 

Later, Darton (1920) wrote that the alternating mortar beds and 

fine-grained sediments of the Ogallala formation appear to have been 

deposited by streams in Pliocene and late Miocene time. Elias (1931) 

described the Ogallala as eonsisting of buff to pink unsorted sand and 

gravel, usually mixed in varying proportions with fine sand or silt, 

containing light-green and reddish-brown cla,\r beds in the lower part 

of the formation and lenses of white and pink limestone in the middle 

and upper part. Hesse (1935) assigned the Ogallala formation to the 

Mioeene and Plioeene, on the basis of the vertebrate fossils; Elias 

(1935) established stratigraphie zones in the Ogallala formation by 

the use of fossil plants, and correlated the plant zones with already 

described mamn"lalian zones of known age. In 1936, Lugn (1939), 

working with other geologists of Kansas and K ebraska, redefined the 

Ogallala formation and elevated it to the stntus of a group eonsisting 

of four formations. This division of the Ogallala formation was 

based not only on lithology, but also on fossil evidence. At that 

time the Ogallala group was tentatively assigned to the Pliocene 

epoeh. A brief smnmary of Lugn's subdivision of the Ognllala 

formation is given below. 

The oldest of Lugn's subdivisions is the Valentine forrnation. It 

consists of fine gray unconsolidated sands below the typical nwrtar 

beds of the Ogallala and below the zone containing the fossil seed 

Krym:tzkia coronoform?~8 Elias. The rnortar beds of the Ogallala 

246879-53--2 
14 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

group overlying the Valentine formation are called the Ash Hollow 

formation by Lugn. The formation consists of gravel, sand, silt, and 

fine sandy clay, which are indurated in varying amounts. The 

lowest bed of the Ash Hollow formation contains the li.rynitzkia 

coronoformis Elias seed zones, and the rest of the formation includes 

most of the Biorbia fossilia seed zone described by Elias. The Ash 

Hollow also contains several vertebrate faunal zones. Above the 

mortar beds of the Ash Hollow is the formation called the Sidney 

gravel, which consists of sand and gravel ranging in siz-e from fine 

sand to pebbles and cobbles 4 to 6 inches in diameter. It includes 

the upper part of the Biorbia fossilia seed zone. The Sidney gravel 

is irregular in thickness and is absent in some places. The youngest 

formation of the Ogallala group is the Kimball formation, which 

consists of silt, clay and fine sand partly cemented with calcium carbonate. This forn1ation contains the fossil seeds Echinochloa n. sp., 

Panicum elegans Elias, and Biorbia fossilia. A pinkish, banded, 

pisolitic limestone, which Lugn believes to be identical t,o the "algal 

limestone" described by Elias (op. cit., 1931), is the uppermost bed of 

this formation. 

In the Wray area, no beds are exposed which correspond in lithology 

to the Valentine formation described by Lugn. At the base of the 

Ogallala format,ion is a cross-bedded, calcium carbonate-cemented 

gravel and conglomerate which grades upward into the mortar beds 

section which corresponds to the Ash Hollow formation as defined by 

Lugn. No gravel corresponding to the Sidney gravel is exposed in 

the Wray quadrangles, and the Kimball formation can be distinguished 

only in the few places where the capping algal limestone crops out. 

Although the general lithology of the Ogallala formation is similar to 

that described by workers in other areas, the most striking feature of 

the Ogallala formation in the Wray area is the discontinuity of beds. 

This characteristic makes it very difficult to obtain a lithologic 

correlat,ion of the Ogallala formation near Wray with the formations 

described by Lugn in Nebraska. Elias (1942) cm·related Lugn's 

subdivisions with fossil seed zones in the Wray area. The correlation 

is based on a section measured about a quarter of a mile east of the 

town of W"ray. However, no fossil seeds were found by the writers 

which would enable them to make similar correlations; therefore the 

Ogallala formation in the Wray quadrangles is mapped as a single unit. 

Lithology.-The base of the Ogallala formation is a eross-bedded, 

ealcium carbonate-cemented gravel and eonglon1erate which grades 

upward into the mortar beds. The mortar beds consist of sand and 

silt cemented with caleimn carbonate, and they crop out as alternating 

ledges and slopes. Because the degree of cementation varies later-
DESCRIPTIVE GEOLOGY 15 

ally as well as vertically, none of the beds can be traced more than a 

few hundred feet. A marker bed of banded, pisolitic algal limestone 

is the capping layer of the formation. 

A gravel and eonglomerate bed forms the basal member of the Ogallala formation in the w ·ray area. The maximum thickness of the 

conglomerate is 10 feet, but it varies in thickness and is absent in 

many places. The material varies from moderately well-cemented 

conglomerate to unconsolidated gravel, which is mixed with silt, clay, 

and sand in most places. Channeling and cross-bedding are common. 

(See fig. 4.) The cewenting material is calcium carbonate; the degree 

of cementation varies laterq,lly and vertically. The moderately wellFIGURE 4.-Cross-bedded conglomerate at base of Ogallala formation (SW H sec. 8, T. I N., R. 42 \V .). 

cemented lenses form pronounced ledges, but the conglomerate is 

porous in most places and may be broken easily with a geologic pick. 

The gravel and conglomerate beds are light olive gray (5 Y 6/1) on 

weathered surfaces and grayish orange (10 YR 7 /4) to light brown 

(5 YR 6/4) on fresh faces. 1'he beds contain pebbles and cobbles as 

great as 1 foot in dia1neter, of feldspar, limestone, quartz, basalt, 

granite, diorite, and quart7jte, as well as limonite and clay balls. 

Quartz and feldspar predominate. The pebbles of feldspar and other 

igneous minerals and rocks are subangular to round; the 'pebbles of 

limestone and other soft rocks are angular. Following is a section 

measured in the SW~~ sec. 8, T . 1 N., R . 42 W., which includes the 

upper part of the Pierre shale, the basal portion of the Ogallala formation, and Peorian loess. 
16 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

Section of Pierre shale, Ogallala formation, and Pe01·ian loess in SW?~ sec. 8, 1'. 1 N., 

R. 42 W 

Peorian loess: 

Loess, yellowish-gray ( 5 Y 7 /2) ___ _______ ____ ________________ _ 

Loess, yellowish-gray (5 Y 7/2), contains pebbles from the Ogallala formation _____ ________ ___ __ ___________ ______ __ ____ · 

Tot al of Peorian loess __ __ __ _______________ ___________ _ 

Unconformity. 

Ogallala formation: 

Silt, limy; shaly parting; grades into marl, very pale-orange 

(10 YR 8/2) to whjte (N 9) ____________________ ___________ _ 

Silt, slightly calcareous; indurated, very pale-orange (10 YR 8/2) __ 

Silt, sandy; contains some calcium carbonate; grayish-orange 

( 10 YR 7 I 4) _- -- -------- - - --- - - - -- -- - - -- --- --- - - -- - - - - ---

Conglomerate; moderately well-cemented, some limestone lenses; 

very pale-orange (10 YR 8/2); gray-weathering ______________ _ 

Gravel; unconsolidated; cemented in patches _____ ___ __________ _ 

Conglomerate ; calcareous cement; loosely consolidated at bottom; 

cross-bedded; ledge-forming; contains pebbles and cobbles from 

one-quarter inch to 1 foot in diameter; pebbles are feldspar, 

limestone, quartz, basalt, granite, diorite, and clay balls; feldspars and granites subangular to rounded ; limestone angular ___ _ 

Feet 

5. 0 

2. 0 

7. 0 

6. 0 

3. 0 

.5 

8.0 

8. 0 

5-10. 0 

Total of Ogallala___ ___ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 30. 5-35. 5 

Unconformity. 

Pierre shale: 

Shale, fissile, dark yellowish-orange (10 YR 6/6); some l-inch 

layers of bentonite _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 15. 0 

Tot al of section ________________ ________ ______ __ __ ____ 52. 5-57. 5 

The bulk of the Ogallala formation consists of sand and silt cemented 

with calcium carbonate. The degree of cementation varies from place 

to place, and the formation crops out as a succession of alternating 

ledges and slopes. The most distinctive features of the outcrops of the 

Ogallala formation are the ledges of mortar beds; the ledges are formed 

by beds of poor]y sorted sand, pebbles, and silt cemented with calcium 

carbonate and common]y case-hardened. These cemented beds have 

a mortar-like appearance and feel rough to the touch; hence the name 

mortar bed. The mortar beds are mentioned as a typical feature of 

the lithology wherever the Ogallala formation has been described. 

Following is a section measured in a railroad cut in sec. 31, T . 2 N., R. 

44 W., showing the typical alternation of ledge- and slope-forming 

beds. (See fig. 5.) 
DESCRIPTIVE GEOLOGY 17 

FIGURE 5.-Ledges and slopes of the Ogallala formation in railroad cut (NEH sec. 31, T. 2 N., R. 44 W.), 

showing typica! lensing and alternation of consolidated and unconsolidated "mortar beds." 

Section of Ogallala formation exposed in railroad cu.t in sec. 31, T. 2 N., R. 44 vV. 

Sandstone, calcareous; grayish orange-pink (5 YR 7/2), gray-weathering; 

friable; case-hardened; bluff-forming ___________ ___ ______ ______ ____ _ _ 

Sandstone, calcareous; grayish orange·-pink (5 YR 7/2), friable; contains 

pipes and ·stringers of white calcium carbonate; interbedded with marl, 

impure and porous, white (N 9) to grayish orange-pink (5 YR 7/2) _____ _ 

Sandstone, calcareous; white (~ 9) to grayish orange-pink (5 YR 7/2) ; 

friable and porous ______ _____ ____ _________ _____ ___________ ______ _ _ 

Sandstone; pinkish-gray (5 YR 8/1); friable, very loosely consolidated; 

some calcium carbonate; ledge-forming; grades into underlying layer ____ _ 

Sandstone ; light greenish-gray (5 G Y 8/1) ; friable, loosely consolidated ____ _ 

Sand; grayish orange-pink (5 YR 7/2); slope-forming ___________________ _ 

Sand: grayish-orange (10 YR 7/4) ;slope-forming _______________________ _ 

Sandstone, calcareous cement; coarse with some conglomeratic lenses; 

porou::>in places; very pale-orange (10 YR 8/2); ledge-forming _________ _ 

Sand; very pale-orange (10 YR 8/2); some calcium carbonate stringers ____ _ 

Sandstone; calcareous cement; silicified at top ____________ __ ___________ _ 

Sandstone, argillaceous; very pale-orange (10 YR 8/2); loosely consolidated_ 

Sandstone, calcareous; gray-weathering; case...:hardened __________________ · 

Sandstone, shaly; very fine-grained; grayish-orange (10 YR 7/4); friable __ _ 

Marl, impure; white (N 9) ; punky, soft, breaks into small chunks ________ _ 

Sandstone; fine-grained, loosely consolidated; grayish-orange (10 YR 7/4) ; 

slightly gummy; slope-forming _____________ _______________________ _ 

Clay, shaly; calcareous; white (N 9) to pinkish-gray (5 YR 8/1) __________ _ 

Sandstone; fine-grained, loosely consolidated; grayish-orange (10 YR 7/4); slightly gummy ___________ ______ ______ __ ____________ _______ - _ - - -

Feet 

10. 50 

4. 50 

1. 25 

2. 00 

2. 00 

1. 00 

3. 00 

1. 00 

4. 50 

2. 50 

1. 00 

1. 50 

1. 00 

4. 50 

5. 00 

8. 00 

3. 00 

Total of section __ _____ . _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 56. 25 
18 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

The mortar beds contain very few true limestones. One small 

ledge of dense, fine-grained white limestone crops out in the northeast 

corner of sec. 16, T. 1 N., R. 44 W. This ledge is 3 feet thick and contains many worm holes and external molds of small gastropods identified by Elias (personal communication, March, 1 950) as Gryaulus 

sp. and Pseudosuccinea cf. P. columella (Say). 

The Ogallala formation in this area contains one bed of volcanic ash 

1 to 10 feet thick. It is best exposed where it crops out in the NE}~ 

sec. 16, T. 1 N., R. 44 W., about 26 feet below the white limestone 

described in the preceding paragraph. The fine, white, unconsolidated 

ash, which stands in vertical cuts (see fig. 6), is composed of about 95 

percent slightly altered glass shards, with an index of refraction of 

1.497. The following section, measured in the Ogallala formation in 

the NE}~ sec. 16, T. 1 N., R. 44 W., includes the volcanic ash and the 

limestone layer containing gastropods. 

Section of the Ogallala formation in NE7~ sec. 16, T. 1 N. , R . 44 W 

Limestone, impure; white, (N 9) ____________________________________ _ 

Conglomerate containing pebbles of quartz, feldspar, and calcareous 

sandstone from one-eighth inch to 2 inches in diameter; contains sandy 

lenses; cemented with calcium carbonate; grayish orange-pink ( 5 YR 

7/2) ___________________________________________________________ _ 

Sandstone, calcareous; fine-grained, poorly cemented; very pale-orange 

(10 YR 8/2) to grayish-orange (10 YR 7 /4); very friable _______________ _ 

Sandstone, calcareous; fine-grained; hard ______________________ -- ____ --

Sandstone, C3.lcareous; shaly in places; very pale-orange (10 YR 8/2); friable _________________________________________________________ _ 

Sandstone, calcareous; contains aggregates of light greenish-gr9y (5 GY 

8/ 1) clay; porous; gray-weathering ______ _________________ ----------

Sandstone, calcareous; very pale-orange (10 YR 8/2) to grayish-orange 

(10 YR 7/4), gray-weathering; middle 3 feet loosely consolidated; upper 

7 feet contains calcareous nodules and pipes; ledge-forming ____________ _ 

Limestone; fine-grained; hard; white (N 9); silicified in places; contains 

holes and many casts of small gastropods __________________ -- _- __ -- - -

Sandstone, calcareous; contains worm (?) holes ________________ ---------

Marl; porous, fine-grained, yello'"ish-gray (5 Y 8/ 1); contains numerous 

grains of light greenish-gray (5 G 8/ 1) clay; upper 3 feet less porous, contains less clay _________________________________ --- -- -- - - -- - - - --- -

Silt, sandy; calcareous; slope-forming ______________________ ---- ___ ----

Sandstone, calcareous; coarse-grained, porous; white (N 9) _____ · _________ _ 

Marl, sandy; grayish-orange (10 YR 7 /4) _____________________________ _ 

Sandstone, calcareous cement; fine-grained; white (N 9) ________________ _ 

Volcanic ash; very fine; white (N 9) to very light-gray (N 8); top 4.5 feet 

contains cemented, impure nodules of ash ___________________________ _ 

Sandstone, fine-grained; grayish-orange (10 YR 7/4); friable _____________ _ 

Total of section _____________________________________________ _ 

Feet 

2. 0 

7. 0 

3. 5 

1.5 

3. 5 

5. 0 

12. 5 

3. 0 

3. 0 

9. 0 

2. 0 

2. 0 

1.5 

8. 5 

10. 0 

2. 0 

76. 0 

Lenses of porous, milky-white, brittle chert, mottled with black 

splotches and brown iron stains, are found throughout the mortar beds, 
DESCRIPTIVE GEOLOGY 19 

FIGURE 6.- Volcanic ash of the Ogallala formation exposed in sec. 16, T. 1 N., R . 44 W. 

and in many places sandstones of the formation are cemented with 

secondary silica. Although the chert lenses and silica-cemented sandstones are rarely more than 1 foot thick, they are resistant to erosion 

and in many places are the capping beds of the outcrops of the Ogallala 

formation. · 

Above the mortar beds is a thin and persistent limestone bed. In 

its most distinctive facies it is very pale orange (10 YR 8/2) to grayish 

orange (10 YR 7 /4), compact, dense, and contains light-brown (5 YR 

6/4) pisolitic, concentric, and wavy-banded structures. Wherever 

this bed crops out in the vVray quadrangles it marks the top of the 

Ogallala formation. This capping layer, which averages about 2 feet 

thick, is the only marker bed in the formation. A similar bed at the 

top of the Ogallala formation was found by Elias (1931, pp. 131-163) 

in Wallace County, Kans. He described it as follows: 

The pink concentrically banded limestone usually does not outcrop as a solid 

ledge, but is broken into irregularly oval or angular and somewhat flattened 

cobbles a few inches to a foot or more in horizontal diameter. The texture of the 

bed may be called irregularly pisolitic, the limestone being traversed by a very 

fine more or less concentric rhythmic banding. The fine banding presents an 

alternation of creamy, light-brown, brick red, and otherwise shaded reddishbrown irregularly concentric bands, the cores of which and the matrix between the 

irregularly oval "ovulites" are usually colored in nearly uniform light creamy or 

pinkish shades. The rock is usually full of scattered grains of colorless quartz 

and pink feldspar, the size of which ranges from tens of microns to a few millimeters. Very rarely much larger pebbles of quartz are observed in the rock. 

Some of the sand grains are found in the center of the smaller and more regular 

pisolitic "ovulites," but the vast majority of these grains have no relation to the 
20 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

banding at all and are scattered uniformly through the rock. Many of the larger 

loops of banding embrace groups of smaller concentric structures. A few fragments, also, with nearly parallel banding have an enveloping crust of fine concentric banding. This and other examples of interrupted and resumed growth are 

fairly frequent. The thin section reveals a cryptocrystalline structure, the banding of which is due to the zonal arrangement of nearly opaque calcium carbonate, 

a little more crystallized and more transparent buff-colored bands of the same substance and occasionally still more transparent layers of the same carbonate with 

a faint radial (transverse) structure. The first two kinds of bands are not sharply 

separated, the nearly opaque substance presenting lobate and digitate outgrowths 

jnto the lighter bands. Locally there are much thinner and closer spaced brickred bands of iron oxide and buff-colored calcium carbonate. In the broader bands 

may be noticed a few small spherical bodies with a comparatively thin outer zone 

made of a mosaic of comparatively coarse-grained colorless calcite, much like the 

walls of t he hollow spheres representing the individual cells of Chlorellopsis 

coloniata Reis, the microscopic alga of the Green River formation reefs. Some of 

the spherical bodies from the Ogallala rock are hollow also. The more important 

difference between the spheres from the limestones of the two formations is the 

smaller diameter of the spheres from the Ogallala. 

Elias has named the alga Chlorellopsis bradleyi. 

In megascopic appearance, the grayish-orange (10 YR 7 /4), concentrically banded limestone at the top of the Ogallala formation in the 

Wray area is almost identical with that of the algal limestone described 

by Elias (see fig. 7). Thin sections of the Wray area limestone show 

the same concentric banding as that in the limestone described by 

Elias. The limestone capping the Ogallala formation in the Wray 

FIGURE 7.- Exposure of typical "algal limestone" of the Ogallala formation in the NE~ sec. 30, T. 1 N., 

R. 44 W., showing nodules and banding. 
DESCRIPTIVE GEOLOGY 21 

area has been identified by Elias (personal conununieation, l\,Iarch, 

1950) as Ohlorellops1~s bradley'/~. In Xebraska, the algal limestone is at 

or near the top of the Ogallala formation and was described by Lugn 

(1939) as part of the Kimball fonnation. 

Two sections showing typical algal limestone and underlying beds 

at the top of the Ogallala forrnation follow: 

Section of the Ogallala formation 1:n the center of the north half of 

sec. 86, T. 1 N., R. 45 nT. 

Limestone, "algal bed"; very pale-orange (10 YR 8/2) 'vith concentric 

light-brown (5 YR 6/4) banding; algalike structure; pisolitic _____ _ 

Silt, sandy; light-brmvn (5 YR 6/4); case-hardened in places; contains 

chunks of sandy limestone v.-hich weather out on the silt slope ____ _ 

Sandstone, calcareous; grain size variable with some gravelly lenses; 

pale greenish-yellmv (10 Y 8/2) on fresh face; contains thin calcareous pipes, opalized in the center; alternating friable and massive 

layers form three prominent ledges with slopes beh,,een them ___ _ 

Sandstone, calcareous and conglomeratic; very pale-orange (10 YR 8/2) 

on fresh face weathering light olive-gray (5 Y 6/1); ledge-forming __ 

Sandstone, calcareous; marly with shaly partings; interbedded white 

(N 9) and very pale-orange (10 YR 8/2); very friable ___________ _ 

Sandstone, calcareous; varies to sandy limestone; white (N 9) to very 

pale-orange (10 YR 8/2); very hard; ledge-forming _____________ _ 

Sandstone, more limy and friable than aboYe bed; contains some 

chert nodules; white (N 9) with some very pale-orange (10 YR 8/2) ~nses _____________________________________________________ _ 

Marl; interbedded very pale-orange (10 YR 8/2) to white (N 9); 

Feet 

2-3. 0 

12. 0 

16. 0 

9. 0 

2. 5 

2. 0 

2. 0 

friable_____ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 2. 0 

Limestone, argillaceous; contains limestone nodules which weather out_ 2. 0 

Sandstone, calcareous; very loosely consolidated___________________ 4. 0 

Total of section_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 53. 5-54. 5 

Section of the Ogallala formation £n the NE?~ sec. 80, T. 1 N., R. 44 llT. 

Limestone, "algal bed''; grayish-orange (10 YR 7/4); hard, dense, pisolitic_ 

Limestone, sandy; white (~ 9) to grayish-orange (10 YR 7/4); irregularly 

cemented; contains thin limestone laminae; weathers to nodules _____ _ 

Sand, limy; very pale-orange ( 10 YR 8/2) to pale greenish-yellow (10 Y 8/2); 

unconsolidated, with some limestone lenses_________ _ _____________ _ 

Sandstone, calcareous; very pale-orange (10 YR 8/2l; soft; case-hardened; 

gray-weathering ________________________________________________ _ 

Marl, sandy and porous; 'vhite (N 9); laminated and crumbly __________ _ 

Sandstone, calcareous; medium-grained; very pale-orange (10 YR 8/2), 

gray-weathering; case-hardened in places; bluff-forming ____________ _ 

Sandstone, calcareous; very pale-orange (10 YR 8/2), gray-weathering; 

soft, bluff-forming; upper 2 feet harder, ledge-forming ______________ _ 

Limestone, sandy; white (~ ~1); slope-forming; slope covered with small 

weathered chunks of limestone ___________________________________ _ 

Limestone, sandy; gray-weathering; hard, dense, ledge-forming _________ _ 

Silt, sandy; soft, cemented vdth calcium carbonate in varying degrees; 

grayish-orange ( 10 YR 7 I 4) _______________________________________ _ 

Total of section ____________________________________________ _ 

Feet 

2. 0 

33. 5 

2. 5 

3. 5 

1.0 

9. 0 

10. 0 

5. 0 

2. 5 

12. 0 

81. 0 
22 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

The Ogallala forn1ation has an estimated dip to the east or southeast 

of 12 feet to the mile. Because no evidence of local flexures was found 

in the area the dip is believed to be initial rather than deformational. 

Fossils and age.-No fossils were found by the writers which enabled 

them to date the Ogallala formation. Fragments of the carapace of a 

large turtle were seen, and broken mammalian bones, but none were 

well enough preserved for positive identification. No fossil seeds were 

found. Some external molds of gastropods identified by Elias as 

Gryaulus sp. and Pseudosuccinea cf. P. columella (Say) were found in 

limestone layers in the Ogallala. The combination of these two forms 

is frequently found in limestone beds throughout the Ogallala formation. The Pliocene age of the formation, assigned by other workers 

(Lugn, 1939) in and near the Wray area, has been accepted by the 

writers. 

Soils.-Sandy, grayish-brown loam is developed on the Ogallala 

formation. Soils on near]y level or rolling uplands are 24 to 36 inches 

thick, but those on rough and rolling terrain, especially on eroded 

knobs and the sides of hills, are thin and poorly developed. A generalized profile is given below for a soil developed on a flat upland underlain by the Ogallala formation. 

1. Grayish-brown (10 YR 4/1 dry), massive, noncalcareous loam; 4 to 8 inches 

thick. 

2. Brown, massive, slightly cloddy or prismatic loam; highly calcareous; hard 

when dry; 6 to 8 inches thick. 

3. Light-brown, light grayish-brown (10 YR 6/2 dry), light reddish-brown, or 

nearly white highly calcareous very fine sandy loam or clay loam; contains 

increasing amounts of gravel and sandstone fragments with depth; unmodified sandstone or reddish-brown clay loam or gravelly loam at depths of from 

2 to 3 feet. 

Internal and surface drainage is good on flat uplands; surface drainage may be excessive on steep slopes. Some wheat and corn are grown 

on these soils, although most of the land underlain by the Ogallala 

forn1ation is used as pasture land. 

QUATERNARY SYSTEM 

PLEISTOCENE SERIES 

Formations of Pleistocene age in the Wray area are the Grand 

Island formation and the Peorian loess. The valley fill, the sandy 

silt and elay, and the Sand Hills formation, which are late Pleistocene 

and Recent in age, are discussed in a later part of this report. 

The Grand Island formation, of Kansan age, unconformably overlies 

the Ogallala formation and is the oldest Pleistocene deposit in the 

Wray area. The forn1a:tion consists of pale reddish-brown (10 R 5/4), 

cross-bedded, calcareous sand and gravel which is exposed only in pits 
DESCRIPTIVE GEOLOGY 23 

in the northwest portion of the Wray area. The yellowish-gray 

(5 Y 7 /2) Peorian loess overlies the Ogallala formation south of the 

Republican River. GRAND ISLAND FORMATION 

Extent and distribution.-The Grand Island formation does not crop 

out in natural exposures, and is seen only in 1nan-1nade pits, which 

(with one exception) are in the northwest portion of the Wray area. 

For this reason, the Grand Island for1nation is not shown as a separate 

unit on the geologic map; instead, it is included with the overlying 

sandy silt and clay. The sandy silt and clay and the underlying 

Grand Island formation occupy the flat areas between the long, northwestward-trending sand hills of the Sand Hills formation north of the 

Republican River. The observtld maxinnnn thickness of the Grand 

Island formation is 20 feet. 

Previous work.-The Grand Island formation was first nan1ed and 

described by Lugn, in a paper presented at the forty-fourth annual 

meeting of the Geologica] Society of An1eriea at Tulsa, Okla., in December 1931. He stated that "the Grand Island formation (l{ansan), 

fron1 50 to over 100 feet thick, lies unconformably on the Fullerton 

bed." It is named for exposures at and around Grand Island, Hall 

County, Neb. Lugn (1934, 193.5) further described the formation by 

stating that the upper 30 to 50 feet eonsists of fine sand, of possible 

eolian origin, whereas the lm~ler part contains gravel, "and is clearly 

a fluvial deposit." An exposure about 120 miles east of the Wray area, 

1?~ miles northwest of the town of Arapahoe, is deseribed by Lugn as 

"Grand Island sand and gravel, typical fluviatile n1aterial, bedded 

and cross-bedded, some zones contain smudges of black sooty carbonaceous material"; this is the westernmost exposure deseribed by Lugn. 

The gravel of the Grand Island formation exposed in several other 

places in western Nebraska, is described by Lugn as "buff-pinkish" or 

"pink to reddish" in color; the gravel in eastern Nebraska is deseribed 

as buff colored, gray, or yellowish-gray. 

Because the gravel in the Wray area semns to be of the san1e lithology as the gravel of the Grand Island formation, and apparently is 

of Kansan age, it is called the Grand Island fonnation in this report, 

although the formation could not be traced from exposures in Nebraska 

into the W ray area. 

Lithology.-The Grand Island formation consists of nun1erous lenses 

of pale reddish-brown (10 R 5/4), calcareous sand and gravel, crossbedded in most places, containing rounded pebbles of granite, feldspar, quartz, quartzite, and sandstone, with 90 percent of the fragnlents from 10.0 1nillin1eters to 0.2 mil1in1eters in dian1eter. The 
24 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

gravel is iron-stained, and the pebbles are coated and loosely cemented 

with fine light-brown (5 YR 5/6) silt and calciun1 carbonate. Some 

of the gravel beds contain balls and lumps of day and pipes and stringers of calcium carbonate at or near the top of the gravel. All the 

gravel beds contain large amounts of calcium carbonate near the top. 

(See fig. 8.) In some places the formation contains bands and lenses 

of gravel which are coated with a black stain. Given below are seetions in two pits in the w·ray area where the gravel of the Grand 

Island formation is exposed. 

Section of Grand Island formation in NW;~ sec. 27, T. 2 N., R. 1;.6 TV., pit no. 16 

Feet 

Soil, dark, sandy______________________________________________ 0. 5 

Sand, some pebbles, very calcareous; lime nodules ______________ .... '2. 0 

Sand and graYel, pale reddish-brown (10 R 5/4), grading to silt in 

places; some black-coated material; some white pebbles from Ogallala formation______________________________________________ _ 8. 0 

10. 5 

Section of Grand Island formaf1'on in center E% sec. 10, T. 2 N., R. 4.6 TV. 

Soil, dark, sandy _____________________________________________ _ 

Sandy clay, loess-like, calcareous, very hard, contains root-holes ____ _ 

Sand, very fine, grayish-orange (10 YR 7/4)-----------------------

Gravel, reddish-brown (10 R 5/4), upper 1 foot lime-enriched, contains 

lime nodules and pipes _______________________________ - __ - __ --

Feet 

2-'-3. 0 

.8 

2. 0 

6...:.8. 0 

Total of section _________________________________________ 10.8-13.8 

Foss1~ls and age.-The gravel is believed to be the equivalent of the 

Grand Island formation of Kansan age. The gravels in the Wray area 

everywhere overlie the Ogallala formation, and underlie the Pleistocene 

and Recent sandy silt and the sand dunes. The gravel is exposed in 

a pit in theE% sec. 10, T. 3N., R. 44 W., where it is overlain by a very 

fossiliferous, light olive-gray (5 Y 6/1) sand and slightly clayey silty 

marl. The upper part of the marl is white (N 9) and is overlain by 

6 inches to 4 feet, of clark yellowish-brown (10 YR 4/2) sandy soil. 

This dark sandy soil also fills channels cut into the marl and gravel. 

The fossils found in the light olive-gray (5 Y 6/1) marl are mollusks, 

ostracods, and diatoms. To date, the n1ollusks and diatoms have not 

been identified. Very few Pleistocene freshwater ostracods have been 

described in the literature, and none of the ostracods found in the marl 

could be definitely identified with described forms. Some of the forms 

found in the marl appeared to be similar to dated, but unnamed forms 

in a collection loaned to the authors for study. 1 From comparison 

with the forms in this collection, it seems probable that the light olivel Collection of Pleistocene fresh-water ostracods from Illinois, loaned by Mary R. Hill; fossils obtained by 

courtesy of the lllinois State Geological Survey. 
DESCRIPTIVE GEOLOGY 25 

FIGURE 8.- Gravel of t he Grand Island formation exposed in pit in the~"·~" S\\"H sec. 35, T . 2 X ., H . 

45 \\" .,showing calearcous pipes in gravel. 

gray (5 Y 6/1) marl is pre-Illinoian, probably Yarmouth, in age. The 

lithology of the small amount of marl exposed in this pit is similar to 

the lithology of the Sappa formation described by Reed (1948). The 

light olive-gray (5Y 6/1) rnarl in the \'\ ... ray area is probably a remnant 

of the Sappa formation, and the gravel underlying the marl is probably 

Grand Island formation. The name" Sappa formation" now replaces 

the abandoned name "Upland formation" because of the physiographic implications of the term "Upland. " The new type locality 

of the formation is in Sappa township, Harlan County, X ebr. (Reed, 

1948). PEORIAN LOESS 

The Peorian loess overlies the Ogallala formation south of the 

Republican River; the maximum measured thickness of the loess is 

85 feet. The loess is composed of fine-grained, calcareous, yellowishgray (5 Y 7 /2) silt containing many small rooLlets and vertical root 

holes lined or filled with ealcium. carbonate; it stands in vertical to 

45° cuts. 
26 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

Extent and distribution.-South of the Republican River in the 

Wray area, the yellowish-gray (5 Y 7 /2) Peorian loess overlies the 

Ogallala formation or rests directly on the Pierre shale where the 

Ogallala formation is missing. North of the Republican River, a 

small amount of loess underlying dune sand is exposed in road cuts. 

The maximum thickness of loess measured was 85 feet; total estimated 

thickness is 130 feet, as indicated in the well logs (see log 128). 

Previous work.-Leverett (1898) first described a "Peorian soil and 

weathered zone" and stated that it was of Wisconsin age. The name 

Peorian loess was proposed by Kay and Leighton (1933) for "the 

widespread loess which lies on the Iowan drift and around its border 

and beneath the Mankato (late Wisconsin) drift; and in Illinois for 

the widespread loess which lies above the late Sangamon loess outside of Tazewell drift." In 1934 Lugn (1934) described the Peorian 

loess as" an almost unbroken mantle of yellowish eolian silt and clay 

covering 42,000 square miles of Nebraska." In Kansas, Elias (1931, 

pp. 178-180) described a yellow Pleistocene loess which he included 

with the Sanborn formation. He described it as: "* * * yellowish 

buff, is porous, not stratified and builds perfectly vertical cliffs * * * 

Toward the base it becomes sandy and grades into the gravel * * *." 

He says of the gravels at the base of the loess: 

The average diameter of the round stones of this gravel is from 1 to 6 inches, 

but in many localities there is in addition a considerable number of boulders 

some of which are 1H feet in diameter, and a few boulders have been observed 

that were 2 or 2~ feet in diameter. These large blocks have a more or less angular 

shape, but their angles are smoothly rounded, and all the surface of the blocks is 

smooth and shiny, though at the same time irregularly pitted, as if the surface of 

the blocks had been fused and smoothed by lightning. 

Frye and Fent (1947) reported the results of a field conference of 

geologists from Kansas and Nebraska, who studied the type area of 

the Sanborn formation. On pages 41 and 42 of this report they made 

the following statements regarding the Sanborn, Peorian, and associated Pleistocene deposits: 

Although no specific locality was originally designated as type section of the 

Sanborn, Elias stated that the exposures studied in canyons in the NW}~ sec. 20, 

T. 1 S., R. 41 W., northwestern Cheyenne County, Kansas, occur within this 

type area and constitute a satisfactory type section. In this and adjacent canyons there . is exposed 170 to 180 feet of Sanborn deposits resting on Cretaceous 

Pierre shale. More than half of this thickness is thought to be a stratigraphic 

equivalent to the Peorian loess as defined by the Nebraska Geological Survey in 

southwestern Nebraska. Furthermore, a soil developed on material possessing 

the characteristics of the Loveland formation in Nebraska occurs in the lower 

part of the sections, in the same stratigraphic position as the Loveland soil in the 

Citellus zone of that state. A less well-developed soil that is found near the top 

of the section may be equivalent to the Brady soil which separates Peorian loess 

from Bignell loess in Nebraska. 
DESCIUPTIVE GEOLOGY 27 

Correlations of the various units exposed in the type section of the Sanborn 

have been made eastward across northern Kansas to the glaciated area. During 

the May 1947 field conference, the loesses and buried soils were traced by outcrops and auger holes southward from Jewell County across the uplands of Mitchell and Lincoln Counties to Rice and McPherson Counties. 

In view of these various facts, it is proposed that the late Pleistocene loesses, 

associated deposits, and lateral facies generally occurring in northern and central 

Kansas, be classed as the Sanborn formation, and the several stratigraphic unitsLoveland silt, Peoria silt, and Bignell silt--and their lateral coarse-textured facies 

be assignEd rank as members. It is desirable to retain Sanborn as the stratigraphic unit of formational rank gener.ally in this region because it is a convenie~1t 

mapping unit, whereas the subdivisions, assigned rank as members, are difficult 

or impossible to delineate in suffieient detail to be usable mapping units. It also 

furnishes a general classification for this complex of silts and coarser clastics in 

parts of the region where certain correlation of the several members has not been 

made while allowing the classification to be brought into harmony with regions 

north and east of Kansas. 

The type locality of the Sanborn formation (consisting predonlinantly of the yellowish-gray (.5 Y 7 /2) Peorian loess) adjoins the 

Wray area on the southeast; the loess of this formation extends into 

the Wray quadrangles. Because the gravels at the base of the Sanborn formation (described by Elias) were not found to be underlying 

the loess in the Wray area, and because the Loveland and Bignell 

loesses were not found in the Wray area, the yellowish-gray ( 5 Y 7/2) 

silt has been mapped as Peorian loess. 

Lithology.-In the Wray area, the loess is a fine-grained, calcareous, 

porous, yellowish-gray (5 Y 7/2) silt, composed predominantly of 

quartz grains. It contains many small rootlets and vertical root 

holes lined or filled with caleiurn carbonate. The loess stands invertical to 45° cuts, exhibiting cohm1nar structure. Size analyses show 

that particles fall into the limited size range charaeteristic of loess 

(Russell, 1944); 64 percent of the partieles are between 0.01 and 0.05 

n1illimeters in size. On grass-covered slopes "cat.step" erosion is developed where the rnaterial has slumped and formed "steps.'' 

No Loveland loess was found in the Wray area, nor were gravels 

such as are described by Elias (19:31, pp. 163-178) found beneath the 

loess. In the NW~~NW?~ sec. 13, T. 1 N., R. 44 W., a srnall amount 

of greenish-gray (5 GY 6/1) blocky clay (probably a remnant of the 

Sappa forn1ation) was found directly underlying the loess; under this 

clay are some pebbles and boulders similar to those Elias describes. 

The pebbles are apparently weathered remnants of a lens of silicified 

n1aterial in the Ogallala forrnation; fresh, cherty, iron-stained pebbles 

and unweathered ledges of the sarne material are exposed beneath the 

weathered pebbles and the clay. 

In a few places, buried soil zones overlain by a sn1all an1ount of 

light-gray (N 7) or light olive-gray (5 Y 6/1) silt were observed near 
2g GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

the top of the loess. These soil zones may represent the Brady soil 

described bySchultz and Stout (1948, p. 573), and the silt above them 

Inay be the Bignell loess (Schultz, 1945, p. 241). In most exposures, 

however, the silt overlying the soil zone is indistinguishable from the 

underlying Peorian loess. The soil zones probably represent periods 

of decreased eolian deposition during the Peorian age. Because the 

soil exposures are few and widely separated, they cannot be correlated 

with each other. 

Fossils and age.-No fossils were found in the Peorian loess by which 

it eould be dated. The loess has been described by other workers 

(Condra, Reed, and Gordon, 1947, p. 31) as middle to late Wisconsin 

1n age. 

Soils .-(Soil deseription based on unpublished report by the Soils 

Conservation Serviee and Colorado Agrieultural Experiment Station.) 

The soil developed on the Peorian loess is a silt loam which in most 

plaees has a well-developed zone of lime enrichment 10 to 20 inches 

below the surface with unaltered parent material at a depth of 30 to 

60 inches. A generalized profile of soils as developed on Peorian loess 

is given below: 

1. Grayish-brown (10 YR 4/1 dry), friable silt loam; 1 to 12 inches thick. 

2. Grayish-brown (10 YR 4/1 dry) cloddy or indistinctly prismatic heavy silty 

clay loam; 4 to 10 inches thick. 

3. Light grayish-brown (10 YR 6/2 dry) silt or silt loam containing much lime 

which has been leached from above layers; 24 to 36 inches thick. 

4. Unaltered parent loess. 

In some places a buried surface layer of a former soil (consisting 

of dark grayish-brown (10 YR 3/2 dry) friable silt loam or silty clay 

loam of indistinetly prismatic. structure) is found at depths of 15 to 22 

inches, between units 2 and 3 above. The soil is developed on flat 

upland areas. Surface drainage is good to excessive; on steep slopes 

rapid runoff causes severe erosion. In most places, the soil is cultivated by dry farming methods. 

LATE PLEISTOCENE .AND RECENT SERIES 

The late Pleistocene and Recent deposits in the Wray area are 

sandy silt and clay, valley fill, and the Sand Hills formation. The 

sandy silt and clay lies in the flat areas between northwestward-trending ridges of dune sand north of the Republican River; the valley fill, 

consisting of well-bedded, dark-gray (N 3) to light-gray (N 7) gravel, 

sand, and sandy silt, is exposed in the floodplains and terraces of the 

Republican River and its tributary strean1s. The Sand Hills formation, consisting of well-sorted, pale yellowish-brown (10 YR 6/2), 

unconsolidated sand, constitutes the long northwestward-trending 

r~dges to the north of the Republiean River. 
DESCRIPTIVE GEOLOGY 29 

SANDY SILT AND CLAY 

Extent and di8tn:b~dion.-Calcareous sandy silt and day overlies 

the Pleistoeene gravels, or rests directly on the Ogallala fonnation 

where the gravels are absent. The sandy silt and day, overlain by 

3 inches to 4 feet of dark, sandy silt, lies in the flat areas between 

northwestward-trending ridges of dune sand north of the Republican 

River. The 1naximum thickness observed, 1neasurecl in a gravel pit 

in the "V\i'")~ sec. 13, T. 2 N., R. 44 "\V., was 8 feet. 

L1~thology .-The calcareous sandy silt and clay is yellowish gray 

(5 Y 7 /2) to pale yellowish brown (10 YR 6/2); it stands in vertieal 

to 45° cuts, and in some exposures it is hard and has a "blocky" fracture. It eontains rootholes, lined or filled with calciun1 carbonate, and 

many thin veins of calciun1 carbonate. The pereentage of sand, silt, 

and day in this 1nap unit varies frmn plaee to pla.ee. In some plaees 

it is almost indistinguishable from loess, but in eontrast with loess, it 

eontains n1any clay-sized and sand-sized particles. The bedding is 

indistinct or absent. A n1echanical analysis of sandy silt and clay, 

taken from a pit in the ~vV?~ sec. 2, T. 2 N., R. 46 W., showed 37 percent less than 0.07 1nillimeter in size, and 35 pereent greater than 0.4 

n1illimeter in size. The n1aterial is highly calcareous. 

The dark yellowish-brown (10 YR 4/2) sandy silt, frmn 3 inches to 

4 feet thick, which everywhere overlies the calcareous sandy silt and 

clay is included in this map unit. The percentage of sand in the silt 

varies from place to place, and the contact of the silt and the sand 

hills is gradational. Although in some places the hills rise sharply 

fron1 the flat silt-covered areas, in other places they slope gently and 

grade laterally into the silt. 11apping of the sandy silt was done on 

the basis of both lithology and topography. 

Fo8S1~l8 and a.ge.-No fossils were found in the calcareous sandy silt 

and clay or in the overlying clark sanely silt, and the exact age of these 

beds is unknown. They are younger than the underlying Grand 

Island fonnation. The ealcareous sandy silt and clay, which closely 

resembles the loess in appearance, may be in part a valley phase of the 

loess and probably contains both reworked Peorian loess and sand 

which were laid down in strean1 valleys. The dark sandy silt, containing large quantities of sand undoubtedly derived from the sand 

hills, is probably late Pleistocene to Reeent in age. Deposition of the 

Pleistocene and Recent sandy silt and day was continuous fron1 

Peorian tin1e until Reeent, and the unit is eontemporaneous with 

part or all of the Peorian loess, the valley fill, and the Sand Hills 

forn1ation. 

Soils.-(Soil description based on unpublished report by the Soil 

Conservation Service and Colorado Agricultural Experiment Station.) 

•Q46879-53-3 
30 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

Soils developed on the sandy silt may be divided into two groupsthose which are developed on windblown materials composed largely 

of sand, and those developed on heavier-textured, sandy, calcareous 

material. Given below is a generalized profile of a soil developed on 

sand mixed with a small amount of clay and silt. 

1. Grayish-brown (10 YR 5/2 dry) loamy sand; 5 to 15 inches thick. 

2. Grayish-brown (10 YR 5/2 dry) sandy loam, moderately coherent; 8 to 20 

inches thick. 

3. Light grayish-brown (10 YR~6/2 dry) sandy loam or fine sand; not calcareous; 

goes to depths of more than 4 feet. 

The soil is developed on level to hummocky land. Drainage 1s 

good and precipitation is absorbed rapidly. Some of this land 1s 

farmed, but most of it is used for grazing. 

A generalized profile is given below for soils developed on heaviertextured material. 

1. Grayish-brown (10 YR 5/2 dry), friable sandy loam; noncalcareous, 6 to 24 

inches thick. 

2. Brown (10 YR 4/2 dry), sandy clay loam; 6 to 18 inches thick. 

3. Very pale-brown (10 YR 6.5/3 dry) to nearly white calcareous sandy clay 

loam; weak prismatic structure; in some places contains calcium carbonate 

in soft and hard aggregations; 10 inches to several feet thick. 

4. Tertiary or Quaternary calcareous sandy materials. 

These soils are developed on nearly level or gently rolling plains. 

Permeability is high, internal drainage is good, and surface runoff is 

Inedium to low. Most of these soils produce very high crop yields 

by dry farming methods. 

VALLEY FILL 

The valley fill, which includes the flood plains and terraces of the 

Republican River and its tributary streams, consists of dark-gray 

(N 3) to light-gray (N 7) sandy silt and sand, mixed in some places 

with yellowish-gray loess. The fill contains a few large pockets of 

clean, eross-bedded sand and gravel. In most eases, the fill overlies 

the Ogallala formation, and grades laterally into the loess; it is probably 

younger than or contemporaneous with the loess. The maximum 

estimated thiekness of the fill is 50 feet. 

Extent and distribution.-The material mapped as valley fill includes 

the flood plain of the Republican River, well-defined terraces 40 feet 

above the flood plain along the sides of the valley of the Republican 

River, and as many as three terrace levels in ravines of tributary 

streams. The valley fill has been cut into terraees in 1nany ravines 

which were once completely filled. Due to the faet that no continuous 

terrace level was discernible and the lithology and origin of all the 
DESCRIPTIVE GEOLOGY 31 

valley fill are similar, the flood plain and all the terraces were mapped 

together. In some places, the Republican River flood plain slopes 

gradually up to the bluffs and into the ravines cut into the Ogallala 

formation. Where the Ogallala formation is not exposed, the fill 

grades imperceptibly into sand or loess. The esti1nated maximum 

thickness is 7 5 feet. 

Lithology.-The valley fill consists of dark-gray (N 3) to light-gray 

(N 7) sandy silt and sand, mixed in some places with yellowish-gray 

(5 Y 7 /2) loess, and containing pebbles fron1 the Ogallala fonnation that 

range from one-eighth of an inch to 6 inches in diameter .. The pebbles 

are distributed in bands and lenses, and the silt is finely laminated. 

Pockets of clean, highly cross-bedded sand and gravel occur in a few 

places in the valley fill; smne of the pockets are quite large, containing 

over 50,000 cubic yards of sand and gravel. 

Fossils and age.-The exact age of the valley fill is unknown. lVIany 

fragmental bones resembling those of bison were found in the fill, 

but they were too incmnplete for positive identification. The fill 

overlies the Ogallala fonnation a.nd in some places grades laterally 

into loess. It is probably younger than or contemporaneous with the 

Peorian loess, and contemporaneous with the Pleistocene and Recent 

sanely silt and clay deposited north of the Republican River. 

Soils.-(Soil description based on unpublished report by the Soil 

Conservation Service and Colorado Agricultural Experiment Station.) 

Three distinct types of soil are developed on the valley fill. One of 

these is formed on the valley bottoms, another is formed on the valley 

sides, and a third is developed on the stream terraces. Sandy, lightcolored soils are developed on the sandy alluvial sediments of the 

marshy bottom lands. A generalized soil profile (top to bottom) is 

given below: 

1. Light grayish-brown (10 YR 6/2 dry) fine sand or sandy loam; may be calcareous in places; 4 to 16 inches thick. 

2. Light grayisb-brown (10 YR 6/2 dry), calcareous, incoherent or only slightly 

coherent sand or sand-gravel mixtures; rust-brown and gray stains, spots 

and streaks are numerous below 24 inches; 20 to 60 inches thick. 

The soil is developed on level surfaces, and because the water table 

in most places is 3 c to 5 feet from the surface, drainage is poor. Areas 

mantled by these soils are used for pasture land or for growing truck 

crops. 

The soil formed on the valley sides is a grayish-brown (10 YR 4/2 

dry), friable, n1assive, calcareous silt lomn which is nearly unifonn to 

a depth of about 3 feet. The soil is developed on n1oderate to gentle 

slopes, and drainage is good. 
32 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

A generalized soil profile is given below for the sandy, noncalcareous 

soils on stream terraces. 

1. Grayish-brown (10 YR 4/2 dry) friable, massive, sandy loam; in many places 

breaks into small clods; 6 to 15 inches thick. 

2. Light grayish-brown (10 YR 6/2 dry) slightly coherent fine sandy loam or loamy 

sand; may have some lime spots in lower part; 15 to 30 inches thick. 

3. Grayish-brown (10 YR 4/2 dry) loamy sand, or sand and gravel; at depths of 

36 inches or more. 

The soil is developed on level surfaces, where the drainage is good. 

The stream terraces are usually used as pasture land, although truck 

crops, small grains, and forage may be grown on irrigated terrace soils. 

SAND HILLS FORMATION 

The Sa.nd Hills formation, consisting of well-sorted, pale yellowishbrown (10 YR 6/2), unconsolidated sand, makes up the long northwestward-trending ridges to the north of the Republican River. The 

Sand Hills formation overlies the Grand Island formation and in some 

places covers the Pleistocene and Recent sandy silt and day. Its 

exact age is unknown, and the maximum estimated thickness is 100 

feet. 

Extent and distribution.-North of the Republican River, the Sand 

Hills forn1ation covers a considerable portion of the area. The hills, 

25 to 170 feet high, form northwestward-trending longitudinal ridges 

as much as 10 miles long. They are composed of many sn1all individual ridges and depressions, many of which also trend northwestward. 

Between the sand hills are broad, flat areas underlain by sandy silt 

and day. 

Previous work.-The Sand Hills formation, occupying nearly 20,000 

square miles of north-central and western Nebraska, and parts of western Kansas and Colorado, was named in 1934 by Lugn (1934, pp. 

321, 322, 331, 350). The Sand Hills region of Nebraska is described 

in three publications of the Nebraska Geological Survey (Lugn, 1934; 

Condra and Reed, 1943; Condra, Reed, and Gordon, 194 7). 

Lithology.-The pale yellowish-brown (10 YR 6/2) sand is composed 

of dean grains, rounded and frosted, mostly quartz and smne feldspar 

fragments. The sand is well sorted, 80 percent of the grains falling 

between 0.1 millimeter and 0.5 millimeter in size. No bedding was 

found. The maximum estimated thickness of the Sand Hills formation is 100 feet. 

Fossils and age.-No fossils were found in the Sand Hills formation; 

therefore the exact age of the formation is unknown. Most of the 

sand hills are covered with coarse grass, indicating that the hills are 

mature, although at some places where blowouts are forming in the 

hills, the sand is moving. Lugn (1934, p. 350) suggested that the 
GEOLOGIC HISTORY 33 

source of the sand dunes and the Peorian loess was identical, and that 

they were conten1poraneous. InasnniCh as the authors believe that 

much of the sand in the Wray area \vas deposited later than the loess, 

the age assigned to the 8ancl Hills formation in this paper is late Pleistocene and Recent. The fonnation is probably in part contemporaneous with the valley fill and the Pleistocene and Recent sandy silt and 

clay. 

So,ils.-(Soil description based on unpublished report by the Soil 

Conservation Service and Colorado Agricultural Experi1nent Station.) 

In sonw places, the surface of the sand hills is stabilized by vegetation, 

but no true soil is clcvelo peel. In low spots, and on gently rolling or 

fiat areas within the sand hills, enough organic and fine mineral material has accun1ulatecl to darken and stabilize the surface of the sand, 

thus forn1ing a soil layer 2 to 8 inches thick. 

RECENT SERIES 

ALLUVIUM 

Recent alluvimn in the Republican River valley consists largely of 

reworked valley fill. The Republican River heads in this area, and 

because it is a very small stream, only a sn1all anwunt of fine sand and 

gravel is deposited in the bed. This deposit is too narrow to be 

mapped on the present seale. The alluvimn in the valley of the Arikaree River covers the flood plain with a sheet of sand and gravel 

which is exposed in the extrmne southeast corner of the area. 

GEOLOGIC HISTORY 

The oldest formation exposed in the Wray area is the Pierre shale, 

of Late Cretaceous age. Overlying the Pierre shale is the Pliocene 

stream-laid Ogallala, formation, which is composed of silt, sand, and 

pebbles, irregularly een1cntecl with caleiun1 carbonate. The Pleistocene Grand Island forn1ation, predominantly sand and gravel, overlies 

the Ogalalla formation. l\Iuch of the Grand Island formation was 

eroded before the next formation (the eolian Peorian loess) was laid 

down. The Peorian loess is partly conten1poraneous with the later 

deposits, beeause son1e of the loess (as it was blown into the area) was 

reworked by streun1s and deposited with the Pleistocene and Recent 

sandy silt and clay anll the late Pleistocene and Reeent valley fill. 

Sand from the late Pleistocene and Recent Sand Hills formation was 

also incorporated into the valley fill and the sandy silt and clay. The 

youngest unit exposed in the area is the ulluvimn of Recent age. 

The Pierre shale, the oldest forn1ation exposed in the Wray area, is 

n1arine in origin. It was laid down in the vast Cretaceous inland sea 

which covered eastern Colorado and n1ueh of the surrounding area 
34 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

when the sea was withdrawing from the Rocky Mountain geosyncline. 

The formation thins toward the east, from 5,000 feet near Boulder, 

Colo., to 1,500 feet near the eastern border of the state. The Julesburg Basin was formed during the Laramide uplift, when the Cretaceous and earlier sedimentary rocks were warped and then eroded. 

A long period of erosion ensued between Cretaceous and Pliocene 

times, causing a distinct unconformity between the Cretaceous Pierre 

shale and the overlying Pliocene Ogallala formation. In the southeastern corner of the Wray no. 4 quadrangle, the top of the Pierre 

shale is exposed at elevations near 3,600 feet. About 5 miles northwest of these exposures, the top of the Pierre is at an elevation of 

about 3,500 feet. Whether the high point thus indicated is structural 

or erosional in origin could not be determined, because the observable 

dip of the Pierre is very slight. 

The Ogallala formation was deposited on the irregular surface of 

the Pierre shale. (See fig. 3.) The rounding of pebbles, cross-bedding, 

and channelling indicate its fluviatile origin. The sand and gravel in 

the formation are composed predominantly of quartz and feldspar 

derived from older rocks in the Rocky Mountains, and the greater 

part of the formation was probably deposited in wide, braided streams 

flowing from the west, and in shallow lakes. The calcium carbonate 

in the Ogallala formation was probably derived from limestone beds 

west of the Wray area by streams flowing over l1mestone and dissolving 

considerable quantities of lime, which were subsequently precipitated 

withthesand,siltandgraveloftheOgallalaformation. Thethicknessof 

the Ogallala forn1ationin the western part of the area is estimated at 220 

feet. In the southeastern part of the area, the formation thins and 

disappears and the Peorian loess rests directly on the Pierre shale. 

The thinning of the formation is probably due in part to nondeposition 

over the high point in the underlying Cretaceous Pierre shale; some 

of the Ogallala forrnation may have been removed by erosion. 

It is probable that the Grand Island formation was deposited on 

the Ogallala formation by streams flowing toward the east or southeast 

from the Rocky Mountains during the Kansan stage. The gravel 

contains rounded pebbles of rocks similar to those exposed in the 

Rocky Mountains. The pale reddish-brown (10 R 5/4) silt in the 

gravel may be derived from the Ogallala formation, or it may be 

wind-blown silt which has been reworked and deposited with the 

gravel. In the EYz sec. 10, T. 3 N., R. 44 W., a light olive-gray 

(5 Y 6/1) silty, clayey marl (believed to be identical with the Sappa 

formation of Yarn•outh age) overlies the gravel. This single exposure 

may be a remnant of a formation that once covered the entire area 

and which has been removed by erosion. 
GEOLOGIC HISTORY 35 

The eastward-trending valleys of Chief Creek and the Republican 

River were probably already established at the close of Tertiary time. 

In late Kansas, Yarmouth, and early Illinoian time (prior to the 

deposition of the Peorian loess) the valley of the Republican River 

was enlarged and the steep ravines of tributary strean1s were cut in 

the Ogallala forrnation and in son1e places down to the Pierre shale, 

thus ren1oving all but a few very s1nall re1nnants of the Sappa formation, and leaving some of the Grand Island forrnation on terraces 

above the streams. Present drainage probably roughly follows Pleistocene drainage, although at that tin1e Inany nwre drainage channels 

existed north of the Republican River than at present. 

Many of the ravines tributary to the valley of the Republican River 

and the Arikaree River trend northwestward. In areas underlain by 

flat-lying sedin1ents (as in the Wra.y area) n1ost tributary strean1s 

flow at an angle to n1ain strea1ns, and the acute angle between the 

main strean1 and the tributa.ry is loeatecl upstrean1 frmn their juncture. 

Many of the northwestward-heading tributary streams in the Wray 

area form an obtuse angle with the Inain stream throughout most of 

their length, and bend to fonn the usual acute angle only in their lower 

portion, near the point where they join the main stream. This type 

of drainage is well illustrated in the southeast eorner of the aceonlpanying geolog-ic map. The northwestward trend of the drainage in 

the Wray area is typieal of n1ueh of the drainage in the Great Plains. 

Several hypotheses have been advanced to explain the northwest 

trend of tributary drainage in the Great Plains. W. L. Russell (1929) 

eonsidered and clisearclecl several factors which n1ight influenee the 

trend of drainage, including struetural control and tilting of the surfaee. He suggested that the wind was probably the dominant 

(although indirec.t) faetor in establishing aligned drainag·e south of 

the North Platte in South Dakota, where the streams flow between 

northwestward-trending eolian sand hills. He further suggested that 

aligned drainage over 1nueh of the Great Plains 1nay have been 

established between northwestward-trending dunes formed in sandy 

Tertiary formations whieh were subsequently ren1oved by erosion. 

C. L. Baker (1948, pp. 5-8), working in western South Dakota, 

postulated that drainage was established in elongate northwestwardtrending deflation basins in the Pierre shale. The deflation basins 

beeame filled with water and overflowed into adjaeent basins; the 

streams thus established grew headward along the length of the 

deflation basins. 

D. R. Crandall, 1 working in South Dakota, stated that the longitudinal sand dune hypothesis of drainage orientation does not satis1 Crandall, D. R., 1951. Geology of parts of Hughes and Stanley Counties, South Dakota: Doctorate 

thesis, Yale University. 
36 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

factorily explain drainage alignment in broad areas of the Great 

Plains where no sand dunes are now present and where no indications 

of previous sand deposits have been found. He further stated that 

the northwestward-trending drainage was probably established in 

late Kansas time, and that present drainage is continuing along 

northwestward-trending deflation basins. 

In the Wray area, the drainage was established prior to Peorian 

time; this is proven by the fact that many of the ravines are completely 

filled with Peorian loess. Therefore, drainage must have been established prior to deposition of the Sand Hills formation, which is younger 

than the Peorian loess. Consequently, the northwestward-trending 

sand hills north of the Republican River and the northwestwardtrending depressions and ridges in the Peorian loess south of the river 

had no effect on establishing the trend of pre-Peorian drainage. 

Northwestward-trending sand hills or deflation basins may have 

been formed in the loose sands and silts of the Grand Island and Sappa 

formations during the Yarmouth interglacial stage, before these 

formations were removed by erosion. Northwestward-trending 

drainage established at that time would have become entrenched in 

the underlying Ogallala and Pierre formations and would continue to 

trend northwestward until the present time. 

The wind may also have had a direct as well as an indirect effect in 

establishing drainage patterns, partieularly on the north side of the 

Republican River, where the northwest trend of the drainage is more 

pronouneed than on the south side. When a strong wind blows water 

down a slight slope, the water flows in rivulets down the slope, away 

from the wind; once rainwater blowing down a slope in this 1nanner 

starts to erode the surface and form gullies, the heads of the gullies will 

advance upstream (and upslope) against the wind and will continue 

to erode in this direction. During Pleistocene time, rainwater may 

have been blown by a northwest wind down the slight slope toward 

the Republican River or the Arikaree River, on the north or northwest 

side of the stream, thus forming guJlies which head northwest, although 

the normal headward direction, if uninflueneed by the wind, may have 

been west or southwest. 

During Peorian time, the wind was the dominant depositional agent 

and deposited loess over mueh of the area. It is probable that the 

source of the Peorian loess was the flood plains of rivers north and 

northwest of the Wray area. In glacial stages before Peorian time, 

large quantities of sand and silt, earried by streams from Rocky 

Mountain outwash plains and from Tertiary sandy ,and silty formations in the region (such as the White River, Arikaree, and Oga1lala 

formations) were deposited on the broad flood plains of the Platte and 

other rivers north and northwest of the w·ray area. During Peorian 
GEOLOGIC EUSTORY 37 

time, the wind blowing from the northwest picked up silt from these 

flood plains and from the soft Tertiary formations and dropped it 

later, thus forming deposits of loess. At the same time, loose sand 

was blown from the same formations and formed dunes which moved 

toward the southeast. In the vVray area, in valleys north of the 

Republican River, and in many of the ravines south of the river, the 

loess was reworked or carried away by streams, although thick 

deposits remained on the southern uplands and along the valley sides. 

In stream valleys north of the Republican River, much of the Peorian 

loess was reworked and incorporated in the Pleistocene sandy silt and 

clay. When the valleys became filled, the sandy silt and clay spread 

over the Grand Island formation on the older terraces. A great 

amount of sand from the Sand Hills formation was deposited with 

the silt and clay in late Pleistocene and Recent time. 

The valley fill (which covers the flood plain of the Republican 

River and fills ravines of streams tributary to the valley of the Republican River) consists largely of reworked material from the Ogallala 

formation and some loess. At no place in the area was the valley fill 

seen underlying the Peorian loess, and where the fill and loess are in 

contact at the valley sides they grade into one another. It is probable 

that the valley fi]l is younger than, or contemporaneous with, the 

Peorian loess. The valley fill and the dark surface silts (which overlie the Pleistocene gravels and calcareous sandy clays in many 

places) grade laterally into each other and are probably partly 

contemporaneous. 

Many of the ravines south of the Republican River were completely 

choked with valley fill, and subsequent streams (probably during late 

Wisconsin and Recent time) cut terraces in the fill. In some places, 

these streams cut through the fill and exposed the bottom and sides 

of the old valleys in the Ogallala formation, thus leaving terraces of 

valley fill on the sides of the ravines (see fig. 9). 

During late Pleistocene and Recent time, sand dunes advanced into 

the area north of the Republican River. Lugn (1935) suggested that 

much of the sand in the sand hills of Nebraska and northeastern 

Colorado was derived from the Ogallala formation; however, it seems 

unlikely that this occurred in the vVray area. Although the Ogallala 

formation is very sandy and includes some slightly unconsolidated 

beds, most of the sand in this area is cemented by a large amount of 

calcium carbonate. At no place in the area was a blowout found to be 

developing in the Ogallala beds, but in the SE%NW7~ sec. 3, T. 1 N., 

R. 44 W., along Chief Creek, typical sand dune topography is developed 

on a sand pocket in the valley fill. This sand is now being cut by 

Chief Creek and eroded by the wind. It seems probable that at least 

246879-53-4 
38 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

FIGURE 9.-Exposure of valley fill in the NEt SWi sec.12. T. 1 N., R. 43 W. Outcrops of Ogallala formation on sides of ravine show that this ravine was eroded in the Ogallala formation and then choked with 

valley fill. The fill is now being eroded by a head ward-cutting gully. 

part of the sand of the Sand Hills formation is derived from similar 

Pleistocene stream sediments. 

Sand dunes of the type found in the Wray area usually form with 

their long axis parallel to the direction of the prevailing wind (Bagnold, 1941, pp. 167-207, 222-235). If the trend of the dunes in the 

Wray area represents the prevailing wind direction during Pleistocene 

time, the direction was from the northwest or southeast, and the source 

of the sand must have been from one of these directions. Therefore, 

the most probable sources of the sand comprising the dunes are the 

stream valleys to the north and northwest, and the fine, sandy sediments of the W'hite River and Arikaree formations to the northwest. 

Northwest of the W'ray area, large blowout areas may be seen where 

wind action has developed badland topography in the soft beds of the 

White River. 

The sand and loess probably have the same source, but during 

Peorian time the loess, being lighter, was blown farther south than the 

sand; in late Pleistocene and Recent time the sand migrated southward 

until it covered the Ogallala formation and most of the area north of 

the Republican River. As the small streams which still flowed north 

of the Republican River reworked part of the sand, the dunes piled up 

between the flat areas of the stream beds. Logs of wells (105 and 

111)-drilled in the Sand Hills formation-indicate that some of the 

ridges have rock cores (probably part of the Ogallala formation). The 

dune sand has filled the formerly broad valley of the Republican River 
ENGINEERING GEOLOGY 39 

until it is con1pletely choked with dunes, except for the small flood 

plain of the present Republican River, whieh lies between the eliffs 

formed by the Ogallala for1nation to the south and the dunes which 

encroach frmn the northwest. 

ENGINEERING GEOLOGY 

The dismission of the engineering geology of the W'ray area is divided into two parts: engineering problen1s, and sourees of eonstruction materials. A brief deseription of the 1nap units is ineluded in the 

engineering geology, but 1nore eomplete infor1nation regarding the distribution and physieal eharacteristies of the roeks in eaeh map unit 

1nay be found in the section on descriptive geology and on the aceonlpanying geologic map (pl. 1). 

The following staten1ents in regard to the engineering properties 

(drainage and perrneability, workability, stability, and eeonomic considerations) of the n1ap units are based in part on aetuallaboratory 

tests of representative samples 1nacle by the Colorado State Highway 

n1aterials laboratory, Colorado Agrieultural College road materials 

laboratory, Public Roads materials testing laboratory, or by the U.S. 

Geologieal Survey. In nnwh greater pa.rt, however, they are based on 

field observations of the behavior of the various map units in road 

cuts, bridge abutments and the like, in various parts of the quadrangle 

and in areas nearby. To these field observations have been added infornlation on aetual service records as supplied by several local engineers. It is hoped that these generalized statements in regard to 

engineering properties of the various 1nap units will be of use to engineers and others in laying out preliminary plans and designs. It is 

obvious that they eannot and should not take the place of detailed 

investigations (both field and laboratory) that are required in design 

of speeific engineering structures. 

ENGINEERING PROBLEMS 

The engineering problems to be considered include foundation condit.ions, drainage, stabilit.y in cuts, and ease of excavat,ion. In the 

following text the problems are discussed for each map unit in the 

W'ray area; these data are summarized in table 2. 

FOUNDATION CONDITIONS 

Pierre shale.-The Pierre shale crops out along the eastern part of 

the North Fork of the Republican River and its tributary streams, 

and in northwestward-heading ravines of strean1s tributary to the 

Arikaree River. The shale becmnes very soft and slippery when wet, 

and the weathered near-surface zone, from one-half foot to 25 feet 

deep, is particularly unstable. If possible, foundations of roads or 
FoundaGeologic unit tion condi- Drainage tions 

Sand Hills A if con- A 

formation. fined, 

B-Cif 

unconfined. 

Valley filL _____ B A if water table low, C 

if water 

table high. 

Sandy silt and B A if much 

clay. sand, Cif 

much clay. 

Peorian loess ___ B-C c 

Grand Island A B-C 

formation. 

Ogallala forma- A-B A 

tion. 

Pierre shale ____ B c 

TABLE 2.-Properties and uses of earth materials in the Wray area 

[A indicates good, B fair or adequate, C poor or unsuitable] 

Stability in Removal Surfac- Base Mineral (equipment Ballast Binder cuts required) ing course filler 

c Hand tools ____ c c c c c 

----------------------------- A-C Hand tools to Gravel Gravel Gravel Sandy silt c 

power tools. A B B B 

-------------------

A if little Hand tools to c c c B c 

sand, Cif power tools. 

much 

sand. ------------------

A-C Hand tools ____ c c c c A 

-------------------- A if little Hand tools to B B B c c 

sand, Cif power tools. 

much 

sand. ------------------- A-C Hand tools to Gravel B B c Ash A 

c 

blasting. _B 

1 

___________ 

Hand tool,____ C C C C 

1 

C 

Blending Concrete Pozzolan sand aggregate 

----

B c c 

---------------- Gravel B, c c 

sand B. 

--------------

c c c 

---------------- c c As ceram- icslag B. -------------- B c B 

------ Gravel B. Ash B. Gravel B. 

-----

C May be suitable if 

calcined; not tested; see text. 

----- ---

Fill 

A-B. 

-----

Gravel B, 

sand A- B. 

------

B. 

------

For earth 

dams B. -----

B. 

------

Gravel B. 

C. 

~ 

0 

0 

t:j 

0 

s 

0 

~ 

0 

~ 

8 

~ t:j 

:a 

~ 

> 

~ 

> 

~ 

M 

? 

(1 

0 

t" 

0 

~ t;j 

z 

t:j 

t::d 

~ 
ENGINEERING GEOLOGY 41 

other structures should be constructed on firn1, unweathered rock. 

Roads constructed on the Pierre shale should be well drained and 

surfaced. 

Ogallala formation.-Few foundation problems are encountered 

when building on the Ogallala formation, which underlies the unconsolidated surface deposits in most places and is exposed as bluffs along 

the south side of the Republican River. l\1ost of the rock consists of 

sand cemented with varying amounts of calcium carbonate, and the 

unconsolidated beds alternate with well-cemented beds at short intervals to provide a finn footing. Cementation is so irregular that no 

bedding plane is extensive enough to become a slippage plane and 

cause landslides. 

Grand Island formation and sandy S'ilt and clay.-The Pleistocene 

and Recent sandy silt and clay is exposed in flats between the sand 

hills north of the Republican River and is underlain in some places 

by the Grand Island formation. The fine, reddish-brown (10 R 5/4) 

gravel of the Grand Island fonnation is a fairly stable foundation 

material. The silt and clay content of the pale yellowish-brown 

(10 YR 6/2) sandy silt and clay varies from place to place. The 

sandy silt and clay forms a suitable foundation for small buildings, 

except in small seattered areas where the clay eontent is high. In 

these areas the material may eompact when saturated. 

Unsurfaced roads built on this map unit vary from those built on 

loose non-cohesive sand and silt, which are trafficable when wet but 

offer poor traction when dry, to roads built on clay, whieh become 

impassable in wet weather. 

The distribution of the Grand Island formation is unknown beeause 

it is everywhere eovered by the sandy silt and clay, and is exposed 

only in man-made pits; therefore, the Grand Island formation and 

sandy si1t· and clay have been treated as a single unit in this report. 

Peorian loess.-Deposits of Peorian loess as n1ueh as 130 feet thick 

mantle the rolling uplands south of the Republiean River. It eonsists of yellowish-gray (5 Y 7 /2) ealeareous silt, and is classified by 

Casagrande (1948) as an ML soil, and by the Public Roads Administration as a class A-4 soil (Bollen, 1945, p. 291). The loess presents 

special foundation problems for large structures beeause it tends to 

consolidate under load when wet. However, it is a fair foundation 

material for s1nall buildings and is a fair to poor subgrade material 

for roads. Loess is easily eroded, and roads built near the heads of 

large ravines in loess will be quickly damaged by headward erosion. 

Roads construeted on loess in this area develop small gullies which 

cut into the shoulders during the rainy season and make constant 

filling and maintenance necessary in order to prevent dangerous erosion into the roadbed. Small landslides called "cat-steps" are frequent 
42 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

in the loess (Gwynne, 1950), whieh is unstable and flows easily under 

load when saturated. 

Laboratory tests made on loess by Holland and King (1949), of the 

U. S. Bureau of Reclamation, show that loess is very weak when 

wetted, although it has relatively high compressive strength under 

certain conditions of loading and low moisture content. Permeability 

was found to be greater vertically than horizontally because of the 

large number of small, vertical root holes in the loess, which conduct 

the water. They state: 

* * * loess is composed primarily of silt and sand grains coated with clay 

and sparse calcite which have been deposited in such a manner that the resulting 

texture is a loose, open, framework with only point-to-point contact between the 

grains. This material, therefore, is susceptible to consolidation under load. Clay 

and to a lesser extent calcite, act as binding materials which give the loess a relatively high compressive strength, but as soon as the strength of the clay and 

calcite binder has been exceeded by loading, consolidation takes place rapidly 

until the particles have rearranged themselves into a more dense structure capable of sustaining the load. ·when the dry loess is wetted, the clay softens, cohesion decreases, and only a comparatively small load is necessary to collapse the 

internal structure, with resulting consolidation and differential settlement of the 

loess. 

"Valley fill.-The valley fill, which forms flood plains and terraces 

of the Republican River and its tributary streams, is very irregular 

in composition. In some places it consists largely of loesslike silt, 

and in other places it is composed of sand and gravel. However, 

the major part of the valley fill is a sandy silt which forms a fair 

foundation for roads and small buildings. In areas where the fill is 

loesslike, the same foundation conditions exist as in loess; where it is 

very sandy, the same foundation conditions exist as in dune sand of 

the Sand Hills formation. 

Sand Hills formation.-The sand of the Sand Hills formation, 

which forms long, northwestward-trending ridges north of the Republican River, is a Casagrande (1948) SP construction material. If 

confined, the sand is a good foundation material; if unconfined, it is a 

fair foundation for small buildings, but a poor material for roads. 

Unimproved sand roads are satisfactory in wet weather, when the 

sand is firm and compact, but they become impassable in dry weather, 

when the sand is soft and loose. Roads through the sand hills cannot 

be maintained by grading; they must be surfaced in some manner, 

and even then the road surface is not easily maintained, because the 

sand drifts over the road from cuts. Most of the gravel available 

from other formations in the area is suitable for surfacing roads in 

the sand hills because it contains silt and clay which act as a binder 

to stabilize the sandy soil. 
ENGINEERING GEOLOGY 43 

DRAINAGE 

Pierre shale.-The Pierre shale drains very poorly, and the shale 

becomes a plastic in1pervious clay when saturated. Roads constructed on Pierre shale should have a suitable, well-drained subgrade. 

Ogallala formation.-The Ogallala fonnation is porous and pernleable. 

Grand Island formation and sandy silt and clay.-The gravel of the 

Grand Island forn1ation is well-drained in locations above the water 

table. The sandy silt and clay is permeable in most places because 

it contains a large amount of sand. If roads are built over n1arshy 

places and undrained depressions where the percentage of clay in the 

sandy silt and clay is high, adequate drainage should be provided. 

Peorian loess.-Because reworked loess drains very poorly, low 

places in unsurfaced roads constructed on loess accumulate rainwater, 

and puddles which fonn on the roads do not dry up for severaln1onths. 

A roadbed constructed of loess will absorb a large amount of water; 

freezing causes the loess to heave in the winter and results in a rough 

and dangerous riding surface. In the spring, thawing of the ice makes 

the loess almost fluid; such a condition Inay result in failure of road 

surfaces, and it could make unsurfaced roads almost impassable in 

the spring rainy season. 

"'Valley fill.-Most of the valley fill contains sand; therefore, it is 

~ell drained except in places where the water table is very close to the 

surface. 

Sand Hills format,ion.-The sand hills are porous and permeable. 

STABILITY IN CUTS 

Pierre shale.-The slope angle of eroded cutbanks and gully walls 

in Pierre shale seldom exceeds 45°. Cuts made steeper than this 

angle have a tendency to slump. 

Ogallalaformalion.-The mortar beds of the Ogallala formation will 

stand in vertical cuts, but the poorly consolidated beds between them 

have a natural angle of repose ranging frmn about 30° to almost 

vertical. The an1ount of slun1p, and the angle to which they should 

be cut, vary with the anwunt of eementation of each bed. In a 

railroad cut in sec. 21, T. 2 N., R. 44 W., pole 1natting has been used 

to retain these uneonsolidated beds. 

Grand Island formation and sandy silt and clay.-The Grand Island 

formation and the Pleistocene and Reeent sandy silt and clay will 

stand in aln1ost vertical cuts, except where the percentage of sand in 

the sandy silt is high. In these places, sand drifting across the 

roadbed frmn the cuts is to be expected. 
44 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

Peorian loess.-Construetion experienee indieates that cuts in loess 

should be steep. Backslopes of deep cuts for a canal through silty 

loess in south-central Nebraska were designed to be }~ (horizontal): 

1 (vertical) for slopes whose maximum height did not exceed 55 feet. 

For higher slopes, or sandier loess, baekslope angles of }~: 1, %: 1, 

and 1~:1 were adopted (Turnbull, 1948). If euts are construeted with 

steep slopes, they will stand for a long period of time without much 

slumping, because the natural slope angle of loess is very steep. On 

. ge~tler slopes, however, rainwash and erosion may be severe. In 

19·11:0 the Iowa State Highway Commission used a terrace design for 

deep (80 feet) highway euts in loess; the design is eonsidered reasonably sueeessful (Gwynne, 1950). 

Valley fill.-The eomposition of the valley fill varies widely, and 

the angle of repose varies aecordingly. The angle of slope in euts 

should approximate the natural angle of repose. Where the valley 

fill is silty and loesslike, it will stand in vertical cuts, but where the 

pereentage of sand increases, the angle of slope deereases, until in 

sand pockets the angle of repose is about 30°. 

Sand Hills jormation.-Road cuts in sand hills are very unstable 

because they slump to the natural angle of repose of loose, dry sand 

(approximately 30°). Road cuts in the sand hills are easily eroded by 

wind, and large amounts of sand drift onto the roadway from the 

cuts. Stabilization of banks and cuts in sandy areas is aided by 

seeding and pole matting. 

EXCAVATION 

Pierre shale.-When dry, the Pierre shale may be easily exeavated 

with hand or power tools. However, water-saturated Pierre shale 

beeomes a stieky, plastie elay whieh will stick to tools and be extremely 

heavy and difficult to move. 

Ogallala formation.-All beds of the Ogallala formation may be 

easily excavated with power tools, except for a few very well eemented 

beds. Even these beds can be removed without blasting, 'although 

the work may be somewhat laborious. The extremely hard beds 

are very thin and may be broken with a power shovel and removed 

in blocks. 

Grand Island formation and sandy silt and clay.-The Grand Island 

formation and the sandy silt and elay may be dug with hand or 

power tools. The fairly well consolidated gravel is difficult to dislodge with a spade, but when struck sharply with a piek, the cement 

crumbles, and the loose gravel ean then be seooped up with a shovel. 

Peorian loess.-The loess is easily excavated with hand or power 

tools. 
ENGINEERING GEOLOGY 45 

Valley jill.-The valley fill may be easily dug with hand or power 

tools. 

Sand Hills formation.-The sand is loose and unconsolidated; it is 

easily moved with hand or power tools. 

SOURCES OF CONSTRUCTION MATERIALS 

Possible usage of construction materials found in the Wray area 

during the course of the field investigation was classified in accordance 

with the results of laboratory tests. Not all map units are listed 

under each construction material considered in the text; only those 

rocks are discussed which are recommended for use. The rocks of 

all map units, whether suitable or unsuitable for construction, are 

rated in table 2. The tests and the agency doing the work are noted 

in table 3, which immediately precedes this page. Size analyses of 

all materials are shown on the graph given in figure 10. The size 

analyses and the general characteristics shown in table 3 and figure 10 

for the gravel of the Grand Island formation, the gravel of the Ogallala 

formation, the ash, the loess, and the dune sand, show that material 

from each of these map units varied only slightly from place to place. 

The Pleistocene sandy silt and the sand and gravel from the valley 

fill are variable, and analyses are different for each exposure. 

Good construction materials are scarce. The deposits of gravel of 

the Grand Island and Ogallala formations are small and irregular, 

loosely cemented with clay, silt, and ealcium carbonate, and contain 

very few pebbles larger than one-half inch in diameter. The gravel is 

unsuitable for concrete aggregate, but it may be used for ballast, 

base- and top-course. Existing pits are small, and new deposits are 

difficult to find. The large and readily available deposits of pure ash 

in the Ogallala may be used as Inineral filler, pozzolanic material, 

and cleansing powders. Large amounts of the sandy silt and clay 

may be used for binder. The almost unlimited deposits of Peorian 

loess are a possible source of ceramic slag aggregate and mineral 

filler. Large amounts of blending sand and earth-fill dam material 

are available in the valley fill. 

No deposits of rock for crushed rock aggregate, riprap, or building 

stone were found. Small lenses of limestone in the Ogallala formation 

may be suitable for these uses, but the thick overburden and small 

deposits make them commercially unexploitable. The available 

construction materials in the Wray area are described according to 

use and geologic unit. 
(!) 

z 

(ii 

<h 

it 

1-

z 

w 

(.) 

0:: 

w 

a.. 

i 

z 

w 

:::> 

0 

w 

0:: 

u. 

~ 

~ 5 20 

::!: 

a 10 

FIGURE 10.-Size analysis graph of construction materials in the Wray area. 

Ida Area including oil analyses of grovel 

of Grand Island formation 

Area including ~ oil analyses of grovel 

of Ogollolo formation 

D.S.I Dune sand sample number 

9 Pit number (see table 3 ) 

~ 

~ 

0 

l'=J 

0 

t'l 

0 

~ 

0 

1"'.1 

~ l'=J 

~ 

~ 

> l;lj 

t>;j 

? 

0 

0 

t'l 

~ 

~ t:1 

z 

l'=J 

t::d 

~ 
ENGINEERING GEOLOGY 47 

SURFACING 

Ogallala format,ion.-Gravel suitable for surfacing is found in the 

basal conglmnerate of the Ogallala forn1ation which crops out along 

the south side of the Republican River in the eastern half of the area. 

It is reported that it has been used in the Wray area for surfacing 

with good results. Son1e of the gravel, because of an excessive amount 

passing through the no. 10 screen, is not considered suitable for 

surfacing. The gravel is classified as fine (7 5 percent falling between 

5.0 millin1eters and 0.1 n1illimeter in size); it contains subangular 

to round pebbles of quartz, feldspar, granite, diorite, basalt, quartzite, 

and limestone. Quartz and feldspar predon1inate, and most of the 

feldspar is slightly weathered and moderately sound. Most of the 

gravel contains silt, sand, and calciun1 carbonate, as well as minor 

amounts of limonite and clay balls. 'rhe silt and clay particles may 

be removed by washing. The gravel is 2 to 10 feet thick and is 

overlain by 2 to 10 feet of unconsolidated to sen1iconsolidated sand 

and silt overburden. Calcium carbonate-cemented aggregates in the 

gravel will break down under load; this weakness of cen1entation 

prevents use of crushed Ogallala for aggregate. The location and 

extent of existing pits is shown in table 3. 

Grand Island jormation.-Only a small amount of the gravel of the 

Grand Island formation is suitable for surfacing because too high a 

percentage passes through the no. 200 screen to be acceptable. It 

has been used successfully on sandy roads, where the fine fraction, 

cmnposed of silt and calcium carbonate, acts as a binder for the sand. 

The gravel is fine, 85 percent falling between 5 millimeters and 0.2 

millimeter in size and containing much calcium carbonate, clay, and 

silt. The gravel consists largely of particles of quartz and feldspar, 

which are sound to moderately sound. The gravel is exposed only in 

man-made pits in the northwestern part of the Wray area; the location 

of the pits is shown on the accompanying geologic map and on table 3. 

The gravel is 2 to 15 feet thick and is overlain by 1 to 8 feet of overburden, some of which is hard, calcareous, sandy silt and clay. 

Valleyfill.-Gravel from small pockets containing as much as 15,000 

cubic yards in the valley fill has given good results as surfacing. Sand 

and gravel fron1 the valley fill is free of silt, clay, and organic material. 

The gravel contains son1e large pebbles, but 55 percent of the material 

is between 5.0 millimeters and 0.5 millimeter in size. The gravel is 

about 8 feet thick and is overlain by 2 to 4 feet of sandy silt overburden. 

BALLAST 

Ogallala jormation.-The gravel fron1 the Ogallala formation 1s 

suitable for use as ballast. 
48 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

Grand Islandformation.-The gravel of the Grand Island formation 

is suitable for use as ballast. Some of the gravel has reportedly been 

used for this purpose, but no performance record is available. 

Valley .fill.-Gravel from the valley fill may be used as ballast. 

BASE COURSE 

Ogallala jormation.-Some of the gravel from the basal part of the 

Ogallala formation is recommended for use as base course. (See 

table 3.) 

Grand Island formation.-The gravel of the Grand Island formation 

is recommended for use as base course. 

Valley .fill.-Gravel from the valley fill is suitable for use as base 

course. 

BINDER 

Sandy silt and clay.-The Pleistocene and Recent sandy silt and clay 

is suitable for use as base course binder. Only one pit was found (see 

table 3), but this kind of material is widespread, and the supply is large. 

Material suitable for binder may be found in much of the area shown on 

the map as "sandy silt and clay." Material fron1 the pit located on 

the map has given fair results when used as binder for sandy roads. 

The calcareous sandy silt and clay is overlain by 1 to 3 feet of dark 

yellowish-brown sandy silt. 

Valley .fill.-Sandy silt and clay from the valley fill is suitable for 

use as binder. 

MINERAL FILLER 

Ogallala formation.-Volcanic ash in the Ogallala formation crops 

out a few miles west of the town of Wray and is recommended for use 

as mineral filler. The ash is pure, white, and uniform in particle size. 

The bed of ash is about 10 feet thick; overburden may be as much as 

50 feet of unconsolidated to semiconsolidated Ogallala beds, although 

a large amount of ash is available with little or no overburden. 

Peorian loess.-Loess has been used extensively in Kansas and 

Nebraska as mineral filler, with good results. The supply of loess 

near Wray is practically unlimited (seen by outlining the large area of 

loess shown on the map). The loess has very little overburden except 

sod. 

BLENDING S.AND 

Ogallala formation.-If the gravels of the Ogallala formation are 

washed to remove the silt and calcium carbonate, they may be blended 

with coarse gravels for use as concrete aggregate and surfacing. 

Grand Island formation.-The silt, clay, and calcium carbonate may 

be removed from the gravel of the Grand Island formation by washing. 

This washed gravel is suitable for blending with coarse gravel for use 

as concrete aggregate and surfacing. 
ENG~EER~G GEOLOGY 49 

Valley fill.-One large deposit containing more than 50,000 cubic 

yards of sand (apparently suitable for use as blending sand for mortar, 

surfacing, and concrete aggregate) was found in the valley fill. This 

prospect is shown as pit no. 9 on table no. 3. No performance record 

for this sand is available. The sand is clean, moderately well-sorted, 

and overlain by 6 inches of soil and vegetation. 

Sand Hills jormat1:on.-The sand from the Sand Hills formation is 

suitable for use as blending sand for moftar, surfacing, and concrete 

aggregate. An abundant supply is available north of the Republican 

River. The sand consists largely of rounded grains of quartz and 

feldspar and is free fron1 organic material, silt, clay, and other fine 

materiah. It is unconsolidated and is moderately well sorted; 80 

percent of the sand particles fall between 0.01 millimeter and 0.05 

millimeter in size. 

POZZOLAN 

Pierre shale.-Shales similar to the Pierre have been used, after 

calcination, as pozzolans; if a source of pozzolan is sought in the Wray 

area, the Pierre shale should be considered and tested. 

Ogallala,jormat-ion.-The volcanic ash in the Ogallala formation may 

be suitable for use as a pozzolanic material. Pumicite from the Ogallala formation near Ellis, Kan., which was tested for pozzolanic quality 

by the Bureau of Reclamation (Mielenz, Greene, and Schieltz, 1951), 

was found to reduce mortar expansion and increase mortar strength. 

The ash in the Wray area contains about 95 percent glass, which is 

slightly altered, and has an index of refraction of 1.497. Although many 

satisfactory pozzolans owe their activity primarily to rhyolite glass 

with a refractive index in the range of 1.490 to 1.507, not all volcanic 

glasses of this refractive index are satisfactory pozzolans. Suitability 

of rhyolite glass for pozzolan cannot be predicted by petrographic or 

chemical analyses and must be tested by empirical methods. 

No tests have been made to determine whether the volcanic ash 

of the Ogallala fonnation in the Wray area would counteract the 

reaction of deleterious aggregate with high-alkali cement. Mielenz 

and others (1949), and Mielenz, Witte, and Glantz (1950), of 

the Bureau of Recla1nation, state that only a few pozzolans will 

satisfactorily control alkali-aggregate reactions. ~fost volcanic tuffs 

and ashes, fly ash, siliceous sedi1nentary rocks and calcined clays 

and shales Inay be used as pozzolans to increase the resistance of 

concrete to attack hy sulfate-carrying waters, reduce heat generation 

in massive structures, save portland ce1nent, increase tensile strength 

of concrete, reduce pern1eability of concrete, and in1prove workability 

of the concrete n1ix. However, only the following pozzolans are 

known to control the alkali-aggregate reaction in concrete and mortar: 

(1) Aluminous and siliceous anwrphous n1aterials, such as some opals, 
50 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

certain rhyolitic volcanic glass, diatmnaceous earth, calcined kaolinite, 

and some artificial siliceous glasses; (2) many opals and opaline 

cherts showing a partial X-ray powder diffraction pattern of betacristobalite; and (3) calcined montmorillonite-type clays usually 

inseparably admixed with cristobalite. 

CONCRETE AGGREGATE 

Pierre shale.-The clays of the Pierre shale may be a source of 

ceramic slag aggregate. No tests were made to determine suitability. 

Ogallala formation.-The gravel from the Ogallala formation has 

been used as concrete aggregate, but no perfotmance record is available. It is not recommended for this purpose because of its fine 

particle size and high percentage of silt and calcium carbonate. 

If it is washed to ren10ve the fines, the gravel may be used in concrete 

aggregate after it is blended with coarser material. 

Grand Island formation.-Gravel fron1 the Grand Island formation 

is not recomn1ended for use as concrete aggregate because of its 

fine particle size and high percentage of clay, silt, and calcium carbonate. If the fines are removed by washing, the gravel may be blended 

with coarse n1aterial for use in concrete aggregate. 

Peorian loess.-Ceramic slag suitable for use as concrete aggregate 

has been made fron1 Pleistocene silt in western Kansas by Plummer 

and Hladik (1948) of the Kansas Geological Survey. Because gravels 

in the Wray quadrangles are very poor construction materials, 

and Pleistocene loess (similar to loess in western Kansas) is abundant, 

cera.mic slag n1ade from the loess may provide constructional aggregate 

for the Wray area which would be more satisfactory than the natural 

materials of the region. 

Tests made by Plummer and Hladik indicate that the slag is 

suita.ble for railroad ballast, concrete aggregate, and allied uses. 

The estimated cost of producing it ($1.10 to $1.70 per cubic yard, 

large scale production in a rotary kiln) compares favorably with the 

cost of natural materials used for these purposes in the same area. 

Green and Schieltz (1948) of the Bureau of Reclaination petrographic 

laboratory in Denver, have analyzed these slags and have found them 

to be composed largely of quartz and glass, with minor amounts of 

plagioclase feldspar, n1ullite, and diopside. The glass content ranges 

from 20 to 50 percent and has a relatively high silica content. The 

slag is vesicular, although the size of the pores varies greatly. Tests 

made by the Bureau of Reclamation indicate that because of its 

high glass content the slag would be deleteriously reactive if used as 

concrete aggregate with high-alkali cement, although possibly the 

porosity of the slags would reduce the destructive effect of the re-
WELL LOGS 51 

activity by providing space in which the reaction product could be 

accommodated. No empirical tests have been made to determine 

whether or not this is true. 

FILL 

Ogallala formai'ion.-Smne of the sand and gravel from the Ogallala 

formation is suitable for artificial fill. Although crushed mortar 

beds 1nay be used as fill, the mortar beds are not recommended for 

this use because the loosely cemented rock will gradually disintegrate 

and compact under load when wet. 

Sandy silt and clay.-The Pleistocene and Recent sandy silt and 

clay contains 1naterial suitable for impervious and semipervious zones 

of earth fill dams. The sandy silt is also a fair material for fill in 

low places and swa1npy areas. However, the material should be 

tested before using, because the percentage of sand in the sandy silt 

and clay varies from place to place. 11aterials high in silt and clay 

are unsuited for fill. 

Peorian loess.-Loess is suitable for use in the semipervious layers 

of earth dan1s. It is extremely poor fill1naterial for low or swampy 

areas, as it flows easily under load when wet. 

Valley fill.-The silty portion of the valley fill has been selected by 

Osborn, Dermeyer, and Nesbitt (1947), engineers of the Bureau of 

Reclamation, as suitable impervious material for earth-fill dam 

construction. This material n1ay also be used for other types of fill. 

Sand Hills formation.-The sand from the Sand Hills formation 

is a fair 1naterial for use in the sen1ipervious zone of earth dams. 

It is also a good fill material for low or swampy areas and other types 

of artificial fill. 

WELL LOGS 

With the exception of geologic interpretation, the logs of wells 

included in this appendix are exactly as they were given to the authors 

by the source which is shown as "Authority" at the top oLeach log. 

Logs received fron1 the Bureau of Reclamation were partially interpreted 

when obtained; forn1ations or 1nap units n1entioned in other logs 

were added by the authors. Altitudes for most of the logs are unknown. Tenns used in the logs are those obtained fron1 the original 

source (usually the driller) and they have not been edited. Such 

names as "seep water gravel" and "magnesia" are driller's terms, 

and their exact meaning 1s not always clear. Logs which list the 

Ground Water Branch, Geological Survey, as the authority, are 

also drillers' logs; they were copied fron1 drillers' records by the 

Ground Water Branch, which made then1 available to the authors. 

The na1nes of the drillers who gave these logs to the Ground Water 

Branch are unknown. 
52 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

TV ell 100a, NE;.~ sec. 8, T. 1 N., R. 44 TV. Altitude 3,650. 7 feet 

[Authority, Bureau of Reclamation] 

Depth 

(feet) I 

Thickness 

(feet) 

-----1-----

Sand Hills formation: 

Dune sand, fine, loose, damp, brown _______________________________________ _ 

Valley fill: 

Sand, medium, compact, saturated, brown _________________________________ _ 

Ogallala formation: 

Ogallala clay, clean, plastic, saturated, brown ______________________________ _ Ogallala sand, medium, compact, saturated, clean __________________________ _ 

Pierre shale: 

Pierre shale, soft, rust-coated fractures, saturated, brown ___________________ _ Pierre shale, firm, saturated, black _________________________________________ _ 

45.0 

12.0 

15.0 

10.0 

7.0 

3.5 

TV ell 100b, NE~~ sec. 8, T. 1 N., R. 44 TV. Altitude 3,623. 7 feet 

[Authority, Bureau of Reclamation] 

Valley fill: Silty fine sand, soft, moist, brown __________________________________________ _ Silty fine sand, compact, saturated, brown _________________________________ _ Medium sand, compact, saturated, clean ___________________________________ _ Medium sand, compact, saturated, brown (cross-bedded) ___________________ _ Pierre shale: 

Pierre shale-clay (weathered), plastic, saturated, gray _______________________ _ Pierre shale (a few rust seams), firm, saturated, black _______________________ _ 

Thickness 

(feet) 

15 

17 

14 

7 

6 

8 

Well100c, NE~~ sec. 8, T. 1 N., R. 44 W. Altitude 3,611.4feet 

[Authority, Bureau of Reclamation] 

Valley fill: Loam, sandy, soft, moist, dark-brown ______________________________________ _ Clay, sandy, soft, wet, gray ________________________________________________ _ Sand, fine, compact, saturated, gray ________________________________________ _ Sand, medium, compact, saturated, brown _________________________________ _ Sand, fine, compact, saturated, brown ______________________________________ _ Sand, medium, compact, saturated, brown _________________________________ _ Pierre shale: 

Pierre shale (some silty layers), firm, saturated, black __ ---------------------

I 

Thickness 

(feet) 

.5 

4 

12 

15 

2 

6 

45.0 

57.0 

72.0 

82.0 

89.0 

92.5 

Depth 

(feet) 

Depth 

(feet) 

15 

32 

46 

53 

59 

67 

5 

9 

21 

36 

38 

44 

48 

Well100d, NE~~ SE% sec. 8, T. 1 N., R. 44 TV. Altitude 3,617.5 feet 

[Authority, Bureau of Reclamation] 

Valley fill: Fine sand, soft, moist, dark-brown _________________________________________ _ Silty fine sand, soft, moist, brown __________________________________________ _ Silty fine sand, compact, saturated, gray ___________________________ --------- Medium sand, compact, saturated, clean __________________________________ --

Pierre shale: 

Pierre shale clay (weathered), soft, brown __ --------------------------------- Pierre shale, soft, saturated, black __________________________________________ _ 

Thickness 

(feet) 

3 

7 

10 

25 

2 

6 

Depth 

(feet) 

3 

10 

20 

45 

47 

53 
WELL LOGS 53 

TVell 100e, STY?~ sec. 9, T. 1 N., R. 44 TV. Altitude 3,676.5 feet 

[Authority, Bureau of Reclamation] 

I 

Thickness I Depth (feet) (fe.et) 

-------~------------------1 ·----

Ogallala formation: Loam, silty, compact, moist, brown ________________________________________ _ Ogallala silt, sandy, dry, buff _______________________________________________ _ 

Ogallala fine sand, silty, some lime cementation, firm, dry, gray ____________ _ Ogallala fine sand, partially lime cemented, firm, moist, gray ___________ _ 

Ogallala clay, silty to sand, some lime cementation, firm, saturated, brown_ 

Ogallala fine sand, compact, saturated, some concretions, brown _____________ _ 

Ogallala medium sand, compact, saturated, brown_------------------------_ Pierre shale: Pierre shale (with black shale, weathered), plastic, saturated, green and limonite layers ___________________________________________________________ _ 

Pierre shale, firm, saturated, black _________________________________________ _ 

TVell101, SW7~SE7~ sec. 23, T. 3 N., R. 46 TV. 

[Authority, Ground "\Vater Branch, Geological Survey] 

1 

6 

12 

11 

28 

5 

13 

30 

4 

1 

7 

19 

30 

58 

63 

76 

106 

110 

I 

Thickness I Depth (feet) (feet) 

San~~if~~~-~~~-~~~~~------ Sandy loam ____________________________________________ --------------------- ---- --_-_-_-_-_-_-_-_-_---~~---~~~~--~--- _ 240 1- -~~ Clay strips___________________________________________ __ _ _ __ _ _ ____ _ _ _ _ _ _ _ 8 32 

Ogallala formation: Gravel and sandy clay_______________________________________________________ 28 60 Seep water graveL___________________________________________________________ 73 133 

Well 102, ~Middle of N t£ne of NW7~ sec 26, T. 3 N., R 46 n:r. 

[Authority, Ground Water Branch, Geological Survey] 

Sand Hills formation: SoiL ______________________________________________ -------------------------- Sand _____________________________________________ --------------------------

Ogallala formation: "Magnesia" ________________________________________________________________ _ Gravel, seep water __________________________________________________________ _ Clay _______________________________________________________________________ _ Gravel _____________________________________________________________________ _ 

Thickness (feet) 

2 

48 

20 

10 

20 

42 Bottomed in hard rock ________________________________________________________ _ 

TYeil 103, NTV?~ sec. 26, T. 2 N., R. 46 TV. 

[Authority, City of Eckley (city well)] 

Depth 

(feet) 

2 

50 

70 

80 

100 

142 

I 

Thickness I Depth (feet) (feet) 

----------------~~---~------------ ----------

Sand Hills formation: Sand _________________________________ _ 32 32 

Ogallala formation: Sand rock __________________________________________________________________ _ 10 42 Lime rock __________________________________________________________________ _ 5 47 Lime rock and graveL ______________________________________________________ _ 

Clay ______________ ---------------------------------------------------------- 8 55 3 58 Porous rock ________________________________________________________________ _ 15 73 Sand rock __________________________________________________________________ _ 16 89 Clay _____________ ---- __ ----------------------------------------------------- 35 124 Lime rock __________________________________________________________________ _ 38 162 Sand rock __________________________________________________________________ _ 36 198 GraveL __________________________ . _________________________________________ _ 47 245 Pierre shale: 

[~!~:;~-- - -- - --~-- -! 

-------~-----~-------

:; ! 

257 

268 32 300 

15 315 

246879--53--5 
54 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

Well104, Center NW}~ sec. 21, T. 3 N., R. 45 W. 

[Authority, Ground Water Branch, Geological Survey) 

Sand Hills formation: White sand ________________ ·-- ______________________________________________ _ 

Sandy silt and clay: "Gumbo" __________ --- _______ ----------- ______ ------------------------------ Grand Island formation: Sand _______________________________________________________________________ _ 

GraveL ______ ---- ____ --------- _______ ---- ___ -------------------------------- Ogallala formation: Sand _______________________________________________________________________ _ 

Gravel (14 feet of water) __________________________________ -------------------

Thickness 

(feet) 

6 

10 

10 

53 

Well105, Center NWX sec. 36, T. 3 N., R. 45 W. 

[Authority, Ground Water Branch, Geological Survey) 

Sand Hills formation: SoiL ________________________________________________________________________ _ Sand _______________ -------- ________________________________________________ _ 

Sandy silt and clay: Clay _______________________________________________________________________ _ 

Grand Island formation: 

GraveL ______ ---------------------------- _________ -------------------------- Oga)]a]a formation: Sand _______________________________________________________________________ _ Clay _______________________________________________________________________ _ 

Gravel (12 feet of water) ___________ ----------------"-------------------------

Well106, SE}~ sec. 21, T. 1 N., R. 45 W. 

[Authority, Ground Water Branch, Geological Survey] 

Sandy silt and clay: SoiL ________________________________________________________________________ _ 

Ogallala formation: Rock _______________________________________________________________________ _ 

"Magnesia" _____ ------- ________________ ---------- ___________ ----------------

GraveL ______ ---------- ______ ----------------------------------------------- Stone _______________________________________________________________________ _ 

Thickness 

(feet) 

1 

20 

16 

10 

12 

10 

11 

Thickness 

(feet) 

9 

3 

18 

2 

88 

Well107, SW~SE~ sec. 22, T. 1 N., R. 45 W. 

[Authority, Ground Water Branch, Geological Survey] 

Sand Hills formation and sandy silt and clay: Sand _______________________________________________________________________ _ 

Ogallala formation: Rock _______________________________________________________________________ _ 

GraveL ______ ---------------------------------------------------------------

Thickness 

(feet) 

90 

1 

36 

Depth 

(feet) 

Depth 

(feet) 

Depth 

(feet) 

11 

17 

27 

37 

90 

1 

21 

37 

47 

59 

69 

80 

9 

12 

30 

32 

120 

Depth 

(feet) 

90 

91 

127 
WELL LOGS 

'Well108, Center sec. 27, T. 1 N., R. 45 W. 

[Authority, Ground Water Branch, Geological Survey] 

Sandy silt and clay: 

SoiL-------------------------------------------------------------------------

Ogallala formation: ''Magnesia'' ________________________________________________________________ _ 

Rock and graveL ___________________________________________________________ _ 

Thickness 

(feet) 

20 

73 

55 

Depth 

(feet) 

27 

100 

TYell 109, Center E~NTV7~ sec. 15, T. 3 N., R. 44 TV. 

[Authority, Ground Water Branch, Geological Survey] 

(feet) (feet) 

Thickness I Depth 

----------

Sand Hills formation: Sand ______________________________________________ ------------------------- 40 Grand Island formation: Gravel (20 feet of water) ____________________________________________________ _ 20 

TV ell 110, Center N}~S WX sec. 31, T. 3 N., R. 44 TV. 

[Authority, Ground Water Branch, Geological Survey] 

Sandy silt and clay: SoiL ____ --------- ______________________________________________ -__ -- __ - __ -_-- Sand. ______________________________ --- ____________________________ ----_-----

Ogallala formation: 

"Magnesia" __________________ -____________ ----------------------------------

Clay ____ -------------------------------------------------------------------- GraveL _________ -------_---------------_------------------------------------ Clay ___ --------------------------------------------------------------------- Gravel (16 feet of water) ______________ ----------- __________________ ---- _____ _ 

Thickness 

(feet) 

2 

15 

10 

20 

13 

10 

20 

TV ell 111, Center NWX, sec. 7, T. 2 N., R. 44 TV. 

[Authority, Ground Water Branch, Geological Survey} 

Thickness 

(feet) 

Depth 

(feet) 

Depth 

(feet) 

40 

60 

2 

17 

27 

47 

60 

70 

90 

----------------·----·-------------1----------

Sand Hills formation: 

Sand __________________ ----------------------------------------------------- Ogallala formation: "Magnesia" and clay _________________________________________________ ---- __ - GraveL ________________________________________________________ - _____ -_-- __ - Rock _______________________________________________________________________ _ 20 

15 

35 

2 

20 

35 

70 

72 
56 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

Well112, Middle W line SW% sec. 27, T. 2 N., R. 44 TV. 

[Authority, Ground Water Branch, Geological Survey] 

Thickness 

(feet) 

Sand Hills formation: SoiL _______________________________________________________________________ , 

Sandy silt and clay: I "Magnesia" ________________________________________________________________ _ 

Ogallala formation: "Magnesia" and rock _______________________________________________________ _ 

Brown ~i~~ ~~~~~ porous ~~~ rock ~~ == = (8 === feet = == == of == good = = ==== water) == = = == __ = = ----------------------------------~ = = ===~ == = = = = = = = = = = = = = == = = = = = ====~I 

Well 113, Center lF?~ sec. 33, T. 2 N., R. 44 TV. 

[Authority, Ground Water Branch, Geological Survey] 

15 

19 

15 

18 

5 

14 

j Thickness ---------1 (feet) 

Sand Hills formation: 

~~~(f_-~ ~ = = = ~ ~ ~ = ~ ~ ~ ~ = = ~ ~ ~ = ~ ~ ~ ~ ~ ~ ~ ~ = ~ ~ ~ ~ = ~ ~ ~ ~ = ~ ~ ~ ~ ~ ~ ~ = ~ ~ ~ ~ ~ ~ ~ ~ ~ = ~ ~ = = ~ ~ = = = = = = = = = il

Ogallala formation: 

4 

40 

Clay (12 feet of water) ______________________________________________________ _ 

1Vell114, l\~7~NE7~ sec. 4, T. 1 N., R. 44 lV. 

[Authority, Ground Water Branch, Geological Survey} 

I Thickness 

(feet) 

Depth 

(feet) 

Depth 

(feet) 

Depth 

(feet) 

4 

19 

38 

53 

71 

76 

90 

4 

44 

45 

----1---------

Valley fill: SoiL ________________________________________________________________________ _ 

Clay ____ -------------------------------------------------------------------- Ogallala formation: Gravel _____________________________________________________________________ _ 

Sand-----------------------------------------------------------------.-------

2 

45 

18 

10 

TVell 115, SW corner of NE?~ sec. 6, T. 1 N., R. 44 W. 

[Authority, Ground Water Branch, Geological Survey] 

Soil: Soil _________________________________________________________________________ _ 

Ogallala formation: Rock _______________________________________________________________________ _ GraveL ____________________________________________________________________ _ 

Thickness 

(feet) 

107 

6 

Depth 

(feet) 

2 

47 

65 

75 

2 

109 

115 
WELL LOGS 

Well 116, on sec. l1:ne between sees. 11 and 14, T. 1 N., R. 44 W. 

[Authority, Barb, C. F., (1946, p. 430)] 

Formations unknown (well was taken over by Yuma Valley Land Co. from the 

Hessig Drilling Co., at 2,410 feet): Lime, white ________________________________________________________________ _ Brown shale ________________________________________________________________ _ Brown shale and soapstone _________________________________________________ _ Sand, gray, dark __________________________________________________________ --- Black shale _________________________________________________ - _____ ---_------- Brown shale, sandy _______________________________________________ -- __ ------- Black shale; soapstone ____________________________________________________ --_ Water sand, gray ___________________________________________ -_____ -_- _____ --_ Black shale _________________________________________________________________ _ 

Sandy, ~~~~{ ~g~r:~-~~~e: gray ______________________________________________________ -~~=--~ ~ ~= = = = ~ = = = = = = = == == = = == = = == = = = = = = == = = = = = = = = = = == = = == = = = -----------

Shale, gray _________________________ ----------------------------------------- Sandy, white _________________________________________________________ ------- Shale, gray _________________________________________________________ -_______ _ Shale, black ________________________________________________ -__ -------------- Sandy shelL ________________________________________________________ -_______ _ 

Sandy, gray ___________________________ ------_-------------------------------

Thickness 

(feet) 

125 

40 

125 

8 

32 

20 

135 

10 

25 

12 

8 

10 

10 

10 

15 

20 

Black shale _________________________________________ - _______ ----------------- • 

5 

10 

10 

15 

15 

25 

35 

Sandy, gray ____________________________________ ----------------------------- Gray shale _______________________________________ -_- ___ -_------------------- Sandy shale ____________________________________ ----- ___ --------------------- Gray shale ________________________________________________ ------------------ Black shale, sandy; showing oil and gas _____________________________________ _ Brown shale ________________________________________________________________ _ 

Blue shale, dark _________________ -------------------------------------------- Blue shale, light ____________________________________________________________ _ 

~i~~t~~~Y:, s~:it ~~~1t~;~~~~l_s_-~~= == = == = = = = = == = = == = = == = = = = = = = = = = = = = === = = == = == Sandy lime; lime chalky, gray-white shells __________________________________ _ 

Gray slate ___________________ --- ___ ----_-----_-------------------------------

5 

5 

10 

15 

90 

5 

3 

12 

57 

Depth 

(feet) 

2, 535 

2, 575 

2, 700 2, 708 

2, 740 

2, 760 2, 895 

2, 905 

2, 930 

2, 942 2,950 

2,960 

2,970 

2, 980 

2,995 

3, 015 

3,020 

3,030 

3,040 

3,055 

3,070 

3,095 

3,130 

3,135 

3,140 

3,150 

3,165 

3, 255 

3, 260 3, 263 

3, 275 1----------

Total depth _____________ ---------------------------------------------------- ____________ 3, 305 

lVell 117, SE corner of SW% sec. 24, T. 2 N., R. 44 lY. 

[Authority, Ground Water Branch, Geological Survey] 

Thickness 

(feet) 

Sandy silt and clay: SoiL ________________________________________________________________________ _ 

"Magnesia" _______________________ --- ________ ------------------------------- Clay_______________ --------------------------------------------- Ogallala formation: 

GraveL __________________________________________________________ -- __ ----- Rock _______________________________________________________________________ _ GraveL ___________________________________________________________________ -_ Rock _______________________________________________________________________ _ Gravel (10 feet of good water) _______________________________________________ _ 

Well 118, Center Nlf..NE~~ sec. 12, T. 1 N., R. 44 lV. 

[Authority, Ernest Price, local driller] 

3 

8 

20 

20 

23 

18 

12 

26 

Depth 

(feet) 

3 

11 

31 

51 

74 

92 

104 

130 

----------------------------------------~-------,1-------

Valley fill: 

Topsoil ____ _ Clay _______ _ Gravel_ _____________ _ Clay _______________ _ 

Water-bearing graveL __ _ ---[ 

Thickness 

(feet) 

4 

3 

18 

4 

21 

Depth 

(fee.t) 

4 

7 

25 

29 

50 
58 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

lVell119, NW corner NEI/2 sec. 25, T. 1 N., R. 44 W. 

[Authority, Ernest Price, local driller] 

Thickness 

(feet) 

Peorian loess: 

Brown clay ____ -------------- ________________ -------------------------------- Ogallala formation: 

Gravel and sand __________________________________ -- ______ ------------------- Water graveL ________________________________ -------------------------------

Well120, SW}~NW}~ sec. 33, T. 3 N., R. 43 W. 

[Authority, Ground Water Branch, Geological Survey] 

45 

94 

12 

Thickness 

(feet) 

Sandy silt and clay: Sand ________________________________________________ ------------------------

Ogallala formation: 

"Magnesia" ____________________________________ ----------------------------- Quicksand _________ ! __________________________________________ -------_--- ___ _ 

Clay ____________ ------------------------------------------------------------ Gravel (25 feet of water, hard) ______________________________________________ _ 

Well121, NW corner sec. 9, T. 2 N., R. 43 W. 

[Authority, Ground Water Branch, Geological Survey] 

6 

15 

5 

34 

5 

Depth 

(feet) 

Depth 

(feet) 

45 

139 

151 

6 

21 

26 

60 

65 

: •·' i 

Thickness · Depth ·(feet) (feet) 

----------------------------------------------------------1-·---------------

Sand Hills formation: 

Sand __________________________________________ ------------------------------

Ogallala formation: Quicksand ___________________________________________________ -------------.-- "Magnesia" __________________________________ ---- ____ ---_---_--------------- Rock _______________________________________________________________________ _ GraveL _____________________________________________________________________ _ 

Well122, SWX sec. 9, T. 2 N., R. 43 W. 

[Authority, Ernest Price, local driller] 

45 

5 

10 

3 

9 

Thickness 

(feet) Depth 

(feet) 

45 

50 

60 

63 

72 

---------------------------------------------------------------1-----------------

Sand Hills formation and sandy silt and clay: Top soiL ___________________________________________________________________ _ 

Brown clay _____________________ ----------- ___ ------------------------------- Ogallala formation: 

"Magnesia" __ -------------- ________ - __________ ------------------------------ GraveL _____________________________________________________________________ _ 

Clay ___________ -------------------------------------------------------------- Water-bearing graveL ______________________________________________________ _ 

3 

4 

120 5 

3 

8 

lVell 123, MiddleS. line NWX sec. 17, T. 2 N., R. 43 lV. 

[Authority, Ground Water Branch, Geological Survey] 

Sand Hills formation: 

Sand __ ------------------ _________ ------------------------------------------- Ogallala formation: 

"Magnesia" ______________________ --- __________ ------------------------------ Sand rock ______ ------------- _________________________________________ --- ___ _ GraveL ____ ----------- _______________________________________ ---------------

Thickness 

(feet) 

10 

25 

30 

5 

Depth 

(feet) 

3 

7 

127 

132 

135 

143 

10 

35 

65 

70 
Sand Hills formation: 

WELL LOGS 

1Vell124, NW7~ sec. 17, T. 2 N., R. 43 TV. 

[Authority, Ground Water Branch, Geological Survey] 

Sand ________________________________________________________________________ _ 

Ogallala formation: 

"Magnesia" and sand rock _________________________________________________ _ 

Sand rock _______ .. _____________ --- ____ ---_----------------------------------- Rock ________________________________________________________________________ _ 

GraveL _______________________________ -------- ____________________ -----------

Thickness 

(feet) 

10 

25 

29 

1 

2 

Well125, NTV corner SE7~ sec. 24, T. 2 N., R. 43 TV. 

[Authority, Ground Water Branch, Geological Survey] 

Thickness 

(feet) 

59 

Depth 

(feet) 

Depth 

(feet) 

10 

35 

64 

65 

67 

-----J----------

Sandy silt and clay and Grand Island formation: 

Sand _____________________ -- __ ---- __ ----------------------------------------- Ogallala formation: 

Rock------------------------------------------------------------------------ GraveL ____________________________________________________________________ _ 

22 

2 

1 

lVell126, NW%SW% sec. 31, T. 2 N., R. 43 TV. 

[Authority, Ground Water Branch, Geological Survey] 

Thickness 

(feet) 

I 

Depth 

(feet) 

22 

24 

25 

------------------------ --------1------

Dune sand and sandy silt and clay: Sand _______________________________ _ 

TVell 127, N7~ sec. 2, T. 1 N., R. 43 TV. 

[Authority, Colorado State Highway Department, 3 holes at bridge site] 

101 i 

Depth 

(feet) 

101 

Thickness I 

(feet) 

---------J-------~--------

H-1 

Valley fill: 

No core taken (water at 10.6 feet) ___________________________________________ _ Fine sand ______ . ___________________________________________________________ _ Coarse graveL __ . ___________________________________________________________ _ Fine compacted sand _______________________________________________________ _ 

Pierre shale: Black shale _________________________________________________________________ _ 

H-2 

Valley fill: 

Sandy clay _____ . _______________________________________________ -_____ - ___ ---

Pierre shale: 

Black clay shale .. _______________________________________________ . ___________ _ 

H-3 

Valley fill: Fine sand (water at 0.2 foot) ________________________________________________ _ Clay __________________________________________ ----------------------- ______ _ 

Pierre shale: Black clay shale ____________________________________________________________ _ 

1 

21.51 . 7 

1.3 

l.Oi 

.5 

14.7 

.6 

11.3 

.4 

21.5 

22.2 

23.5 

24.5 

25.0 

14.7 

15.3 

11.3 

11.7 

12.0 
60 GEOLOGY OF THE WRAY AREA, COLO. AND NEBR. 

Peorian loess: 

Well128, Center W~NWX sec. 31, T. 1 N., R. 43 W. 

[Authority, Ernest Price, local driller} 

Thickness Depth (feet) (feet) 

TopsoiL_____________________________________________________________________ 8. 0 8. 0 

Clay loam___________________________________________________________________ 120.0 128.0 

Ogallala formation: 

Sand_---------------________________________________________________________ 10.0 138.0 Gravel and clay_____________________________________________________________ 2. 5 140. 5 

Sand________________________________________________________________________ 7. 5 148.0 Sand________________________________________________________________________ 8. 0 156.0 Brown clay __________________________________________________ . _______ .. _. ___ .. ----------- _ --.--------

Valley fill: 

Well 129, SE corner NW% sec. 6, T. 1 N., R. 43 TV. 

[Authority, Ernest Price, local driller} 

Thickness 

(feet) Depth 

(feet) 

TopsoiL_____________________________________________________________________ 4. 0 4. 0 

Sand (white)_--------------------------------------------------------------- 75.0 79.0 GraveL____________________________________________________________________ . 3 79.3 Sand ________________________________________________________________________ ------------------------

Pierre shale: 

Sand.-----------------------------------------------------------------------------------------------

Well130, MiddleS. line SlV}~ sec. 6, T. 1 N., R. 43 TV. 

[Authority, Ernest Price, local driller] 

Thickness Depth (feet) (feet) 

Valley fill: 

Black soiL__________________________________________________________________ 10 10 Clay________________________________________________________________________ 5 15 

Sand (water)________________________________________________________________ 4 19 

Clay ___________ ------------------------------------------------------------- ------------ ------------ GraveL_____________________________________________________________________ _ _ _ ___ _ ____ _ 63 

Pier~~gal~~Y--- ---------------------------------------------------------------- ----------- -~·- -----------

Shale _________ -__ . ____ ------_-------_---------------------------------------- ------------ ------------

1Vell131, JYiiddle W. line NEX sec. 7, T. 1 N., R. 43 TV. 

[Authority, Ground Water Branch, Geological Survey} 

Ogallala formation: SoiL ________________________________________________________________________ _ Rock _______________________________________________________________________ _ 

Sand ___________ -- ___ --_-----.----_-------. __ -------------------------------- Clay _____________ ----------------------------------------------------------- GraveL ______ -_ .. ___ .. _____ . ____ ._._.-- ____ .--.-.--------------------------- Clay and graveL ____________________________________ ---- ___ ----. ____ .--. __ .- Clay _______________________________________________________________________ _ Rock ______________________________________________________________________ _ Clay _______________________________________________________________________ _ GraveL ______________________________________________ . _____________ --. ___ ._-

Thickness 

(feet) 

1 

9 

10 

11 

27 

15 

10 

10 

4 

2.'3 

Depth 

(feet) 

1 

10 

20 

31 

58 

73 

83 

93 

97 

120 
WELL LOGS 

}Vell132, NTV%SE)~ sec. 7, T. 1 N., R. 43 lV. 

[Authority, Ernest Price, local driller] 

Ogallala formation: 

Rock ("magnesia" and lime) _____________________________________________ _ GraveL _____________________________________________________________________ 'I 

Pierre shale: 

Shale ______________ ----------------------------------------------------------

Thickness 

(feet) 

125 

'"I 

TVell 134, Jl.fiddle S. line 8E7~ sec. 28, T. 1 N., R. 43 TV. 

[Authority, Ground Water Branch, Geological Survey] 

Thickness 

(feet) 

61 

Depth 

(feet) 

Depth 

(feet) 

125 

135 

1-----1----

Peorian loess: SoiL ________________________________________________________________________ _ "Magnesia" ______________________________________________________________ ---

Clay _______________________________________ -------------------------------- Ogallala formation: 

GraveL __________________________________________ -- __ ---- __ -----------------

~~it;:::: 1 

TVell135, SE7~SE7~ sec. 5, T. 1 N., R. 42 W. 

:3 

20 

20 

25 

18 

15 

26 I 

[Authority, Colorado State Highway Department, 3 holes at bridge site] 

H-4 Valley fill: 

Sand (water at 1 foot) __ _ Pierre shale: 

Black clay shale _________________________ _ 

H-5 Valley fill: 

Fine sand _____________________________________________________ - __ ----------- Sandy clay _________________________________________________________________ _ 

Pierre shale: 

Black sandy shale_ 

H-6 Valley fill: 

Sand and sandy clay (water at 8.5 feet) _____ -------------------------------- Pierre shale: 

Black sandy shale _________________________________________________________ _ 

Thickness 

(feet) 

27.9 

.3 

35.2 

1.7 

.6 

360 I 

1.4 

·well136, )~.,fiddleS. line NE% sec. 9, T. 1 N., R. 42 TV. 

[Authority, Colorado State Highway Department, 3 holes at bridge site] 

3 

23 

43 

68 

86 

101 

127 

Depth 

(feet) 

27.9 

28.2 

35.2 

36.9 

37.5 

36.0 

37.4 

I 

Thickness \ Depth 

(feet) (feet) 

-----------------------~-----~-- --------

H-7 Valley fill: 

Sand, streaks of sandy clay (closed at 38.3) _ 38.3 38.3 

H-8 

Valley fill: 

Sand, sand and clay, fine sand ______________________ _ --------------------- -1 

-I 

H-9 Valley fill: 

Sand and sandy clay (water at 9.5 feet) _________ _ 

40.0 40.0 

36.21 3t3. 2