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Table of Contents

Abstract

Introduction

Geography

Geology

Ground Water

Geologic Formations

Water Levels

Well Records

Logs of Test Holes

References

Plates

Geologic Formations and Their Water-bearing Properties

Tertiary System--Pliocene Series

Character--The Ogallala formation is composed of silts, sands, and gravels and contains layers of sandstone and conglomerate, much of which is crossbedded and cemented with lime. In general, the fine-grained sediments alternate with the coarser lime-cemented beds at different horizons. The Ogallala sediments are generally buff colored to pinkish, although some of the more limy silts and sands are white to whitish gray. The coarser sediments are present at all horizons but are most prominent in the lower part of the formation, and it is this part that yields water most freely to wells. Locally, the lower part of the Ogallala formation may be composed of bentonitic clays of bright mottled colors ranging from reddish brown to olive green. These basal clays represent a local lateral change in lithology in the lower part of the Ogallala formation and may be equivalent to the Woodhouse clays of either Miocene or Lower Pliocene age of Wallace County, Kansas, described by Elias (1931, pp. 155-158).

Sand constitutes the principal material of the Ogallala formation and ranges in texture from fine- to coarse-grained, some of the coarser material containing scattered pebbles and thin beds of pebbles (Pl. 8A). The finer-textured materials of the Ogallala formation are composed chiefly of silt that generally is intermixed with fine sand. Lenses or beds of sandy silt occur in all parts of the formation, but principally in the upper part. The color of the silt ranges from gray to buff to light tan. Some of the beds of silt are impregnated with lime giving them a white to light-gray color. Gradations from one lithologic type to another may take place both laterally and vertically--sometimes within relatively short distances.

Plate 8A--View of north face of gravel pit in Scott County State Park showing cross-bedding of deposits of sand and gravel of Tertiary age.

The Ogallala formation is characterized by lenticular bedding; thus, individual beds of sand or gravel are not continuous over wide areas, but generally are discontinuous lenses that may grade laterally into finer materials such as silt or clay, in some places within relatively short distances. The deposits range from those that show definite bedding to those that show no bedding whatever. The structureless layers are commonly found in the upper part of the formation, are rather fine-grained, and contain some silt and small amounts of clay and lime. Irregular limy concretions are abundant in these layers, typical exposures of which occur in the bluffs on both sides of Beaver (Ladder) Creek in the vicinity of Scott County State Park. They are well displayed in both sides of the road cut that was constructed through the "Devil's Backbone," about 1 mile south of the south entrance to Scott County State Park (Pl. 5A). The color of this structureless part of the Ogallala ranges from buff tan to light reddish brown.

Plate 5A--Lime concretions in the Ogallala formation in a road cut through the Devil's Backbone at the south end of Scott County State Park.

Plate 6--A, Series of many thin parallel "mortar beds" resting on structure-less cemented sandy silt of the Ogallala formation. East side of Salt Creek in the NE sec. 24, T. 16. S., R. 31 W. B, "Caliche" of the Ogallala formation exposed in County quarry in the SW sec. 28, T. 18 S., R. 32 W.

Section of Ogallala formation on the east side of Lake McBride in Scott County State Park near the NE cor. NW 1/4 sec. 12, T. 16 S., R. 33 W.		Thickness (feet)
	Surface covered with unconsolidated sand and gravel
Tertiary--Pliocene
	11. Silt, sandy, lime-cemented, hard, gray to white; contains scattered coarse gravel and some pebbles; grades upward into a lime-cemented silt and becomes whiter in color near top; resembles a true "caliche"	28
	10. Sand, silty, lime-cemented, dirty gray, extremely hard and resistant; contains pebbles up to 1 inch in diameter and larger imbedded firmly in the coarse sandy matrix; forms distinct caprock ledge	2
	9. Silt, sandy, cemented, hard, gray to buff	1
	8. Sand and silt, cemented, gritty, irregular ("mortar bed"); into lighter gray structureless sandy silt	6
	7. Sand, silty, lime-cemented, dirty gray; grades upward into white limy silt	5
	6. Sand, silty, cemented, buff colored; contains pebbles up to 1/2-inch in diameter and larger imbedded in sandy matrix; forms resistant ledge	8
	5. Sand, silty, cemented, massive, hard, somewhat siliceous, dark gray to buff; contains a seam of extremely hard dense blue chert ranging from about 1 to 8 inches in thickness at top	4
	4. Sand, silty, cemented, brown to buff; forms distinct smooth-faced bench in bordering bluffs	7
	3. Sand, silty, cemented, hard, gray; contains scattered coarse gravel; also contains some rather thin-bedded layers in the lower part that tend to break off in thin slabs ranging in thickness from about 1 to 3 inches	17
	2. Sand, cemented, gritty, gray; contains coarse gravel and scattered pebbles; grades upward near the top to a hard cemented silty sand, brownish-buff in color; forms a resistant ledge at the top that stands out in the bluffs bordering the lake	47
	1. Clay, plastic, brown to chocolate brown, mottled in part with pale-green splotches (Woodhouse clays?)	16
Total thickness of Ogallala exposed		141
CRETACEOUS (Upper)
	Niobrara formation

Section of Ogallala formation at the north end of Scott County State Park in the NW 1/4 SE 1/4 sec. 2, T. 16 S., R. 33 W. (Measured by H. T. U. Smith, H. A. Waite, and L. P. Buck.)		Thickness (feet)
Tertiary--Pliocene
	11. "Limestone," sandy, cemented ("mortar bed"); weathers chunky, somewhat porous, harder near the top	11
	10. Sand, cemented, calichiferous (covered interval)	9.5
	9. Sand, cemented, hard, resistant ("mortar bed"); weathers very knobby and irregular; cavernous throughout	6
	8. Sand and silt, cemented, gritty, irregular ("mortar bed"); slabby in lower part, cavernous in upper part; contains some pebbles and limy concretions that look like reworked caliche nodules	6
	7. Gravel, cemented, sandy, gritty, structureless	4.5
	6. Sand and gravel (covered interval)	35
	5. Silt, sand, and gravel, cemented, hard, gritty ("mortar bed"), weathers cavernous in lower part and slabby above; contains some short vertical concretions	6
	4. Caliche, massive, gritty, structureless; contains small scattered pebbles and irregular limy concretions, some having root shape - weathers irregularly knobby; contains fossil grass seeds Biorbia fossilia (middle Pliocene)	11
	3. Sand, covered interval	29.5
	2. Sand and gravel, crossbedded, locally cemented; fossil bone found at a point 14 feet above bottom. (Sand and gravel have been excavated at this interval for use in the State Park.) View of gravel pit in Plate 8A	20
	1. Clay, buff, massive; contains some gray layers and is somewhat silty in upper part (Woodhouse clays?)	23
Total thickness of Ogallala exposed		161.5
Cretaceous (Upper)
	Niobrara formation

Distribution and thickness--Exposures of the Ogallala formation occur along Beaver (Ladder) Creek and in tributary draws in the northwestern part of the county (Pl. 1). The Ogallala formation is also exposed in the northern part of the county along the sides of draws tributary to Chalk Creek, which flows eastward across the southern part of Logan County to the north. Exposures of the Ogallala formation occur above the Cretaceous rocks in the northeastern part of the county along draws tributary to Hell Creek which flows eastward near the southeastern boundary of Logan County and along the southern boundary of Gove County. Outcrops of the Ogallala formation occur along Lion Creek from near Modoc to a point about 4 miles west of Scott City and along Rocky Draw from the west county line to a point about 5 1/2 miles south of Modoc. Isolated exposures of the Ogallala formation have been noted near the heads of draws tributary to Dry Lake in the southeastern part of the county. Most of the upland surface in Scott County is underlain by deposits of Pleistocene age. The Ogallala formation, however, is found beneath younger deposits over most of the area. It is thin to practically absent in the Dry Lake vicinity near the southeastern corner of Scott County occupied by the buried Cretaceous hill shown in Figure 2.

The Ogallala formation was not encountered in test holes 13, 16, 17, and 19 (logs 13, 16, 17, and 19), all of which are situated in the deepest part of the buried trough (Fig. 5, sections B-B' and C-C'). It is probable that the Ogallala formation was removed by erosion and in its place 'sediments of Pleistocene age were deposited. Section B-B' shown in Figure 5 shows that the Ogallala formation is very thin in the vicinity of test holes 12, 14, 15, and 18 in the eastern part of the county east of Shallow Water. In certain areas in the southeastern part of the county deposits of dune sand overlie the Ogallala formation.

The Ogallala formation ranges in thickness from a few feet to about 160 feet. The variable thickness of the Ogallala formation is shown in the three profile sections in Figure 5. The thickness of the Ogallala in the 23 test holes drilled during the investigation ranges from about 6 feet in test hole 12 in the eastern part of the county to 159 feet in test hole 1 situated about 6 miles north of Scott City. In general, the test drilling revealed that the Ogallala becomes progressively thinner from north to south and in a southeasterly direction toward the southeastern corner of the county. The thickness of the Ogallala formation ranges within wide limits because of the uneven surface on which the sediments were deposited and also in part because of the fact that all or part of the sediments were removed during post-Ogallala erosion. At one time the Ogallala formation probably was much thicker in the vicinity of the buried trough in the vicinity of Scott City and Shallow Water but most of it was removed by post-Ogallala erosion.

Origin--As pointed out under Geologic History the sediments comprising the Ogallala formation were deposited by heavily laden streams that flowed from the Rocky Mountain region. The pebbles of igneous and metamorphic rocks in the gravels and abundance of quartz and feldspar in the sands are believed to have been derived from the Rocky Mountains. Locally, the basal gravels also contain some reworked material from less distant sources, including water-worn fragments derived from Cretaceous rocks in or just west of the county. Smith (1940, pp. 85-86) describes the mode of deposition of the Ogallala formation as follows:

"The deposition of the Ogallala was mainly of the channel and floodplain type. The coarser beds of sand, gravel, and grit represent channel deposits. ... The finer materials are best interpreted as representing flood-water deposits formed by the overflow of shallow channels, perhaps approaching the character of sheet-floods locally. No recognizable deposits of eolian sand or silt have been found in the Ogallala in the area studied, but the presence of ventifacts indicates that there must have been appreciable wind action.

"The deposition of the Ogallala formation began with the change from stream degradation to aggradation. ... During the early stages of deposition, there was a topography of moderate relief. The main valleys were occupied by through-going streams from the Rocky Mountains, and the valley bottoms were mantled by normal floodplain deposits. ... Deposition probably began with the filling of stream channels, leading to more frequent overflow and thus to the up-building of the floodplains. This soon led to shifting of the channels themselves, and probably to the development of anastomosing patterns. As filling progressed, the valley flat overlapped farther and farther on the slopes of the bordering hills. ... Relief was lowered, the valley plains grew broader, and finally the divides were overtopped, and there followed overlapping and coalescing of the depositional zones of individual streams."

"The transported calcareous matter in the Ogallala originated mainly, if not only, in the Rocky Mountain area from weathering of Paleozoic limestone and calcic minerals in the crystalline rocks. ... Additional lime may have been provided also by weathering in situ after deposition."

Age and correlation--The Ogallala formation originally was named and described by Darton (1899, pp. 732, 734) and its age was given as late Tertiary, or Pliocene (?). Darton later (1920, p. 6) designated the type locality near Ogallala station in western Nebraska. The conclusions of later workers regarding the age and correlation of the Ogallala formation in western Kansas have been summarized by Smith (1940, pp. 73-74).

Smith (1940, pp. 75-76) concluded that the Ogallala of southwestern Kansas, insofar as it is represented by exposures at the surface, may be assigned to middle Pliocene age. According to this definition, the top of the Ogallala formation is marked by the top of the capping limestone. No upper Pliocene beds were recognized in Scott County, and no attempt has been made to subdivide the Ogallala formation.

So far as is known, no vertebrate fossils have been taken from the Ogallala formation in Scott County. In Ford County, a horse tooth was recovered from the Ogallala at a depth of 113 feet during the drilling of an irrigation well in the SW 1/4 sec. 6, T. 27 S., R. 26 W. The tooth was identified by C. W. Hibbard as a right molar of Pliohippus cf. interpolatus (Waite, 1942, p. 160). Schoff (1939, pp. 61-62) reported that large collections of vertebrate remains taken from excavations in the vicinity of Optima and Guymon, Texas County, Oklahoma, were considered by Stovall to be middle Pliocene in age. According to Schoff, the fossils were found in the upper 100 feet of the formation.

Fossil grass and hackberry seeds collected from the Ogallala formation have been described by Elias (1932, pp. 333-340). In a later paper (Chancy and Elias, 1936) it was shown that certain of the fossil seeds are of widespread occurrence and have a short vertical range making them useful as guide fossils. Fossil grass and hackberry seeds were collected by me from the Ogallala formation in Scott County, notably from exposures in the bluffs just west of the dam at the north end of Lake McBride near the center sec. 2, T. 16 S., R. 33 W. (Pl. 13A) and from exposures in the bluffs on the east side of Lake McBride below the McBride monument in the NW 1/4 NE 1/4 sec. 12, T. 16 S., R. 33 W. In both localities the seeds were collected from massive layers of cemented grit and coarse sand from 5 to 10 feet in thickness that formed prominent benches along the sides of the valley. Fossil grass and hackberry seeds were also collected from exposures of the Ogallala formation in the northeastern part of the county in the SE 1/4 NE 1/4 sec. 1, T. 16 S., R. 32 W. Fragments of grass and hackberry seeds were found in test hole 23 in the southwestern corner of Scott County between depths of 103.5 and 119 feet. From comparisons with forms described by Elias, the grass seeds are believed to be Biorbia fossilia and the hackberry seeds are believed to be Celtis willistoni.

Plate 13A--Cluster of Biorbia fossilia seeds in Ogallala formation at north end of Scott County State Park in the NW SE sec. 2, T. 16 S., R. 33 W.

In recent years there has been an increase in the number of wells tapping the Ogallala formation in Scott County, largely as a result of increased demands for irrigation and industrial supplies.

The water from the Ogallala formation is hard. The analyses of typical waters from the Ogallala formation are shown in Figure 16. Samples of water were collected from 19 wells that derived water from the Ogallala formation, from six wells that derived water from the Ogallala formation and/or undifferentiated Pleistocene deposits, and from three wells that derived water from the Ogallala and/or Niobrara formations. Analyses of the 19 samples of water collected from the Ogallala formation indicate that the hardness ranged from 162 to 319 parts per million and averaged about 221 parts. The analyses also indicate that the amount of iron contained in these samples of water from the Ogallala ranged from 0.0 to 2.9 parts per million. The fluoride content of these 19 samples ranged from 0.3 to 3.0 parts per million. Three samples of water from this group contained less than 1 part per million of fluoride, six contained more than 1 part, nine contained between 2 and 3 parts, and one contained 3 parts. Because the fluoride content of some of the water from the Ogallala formation is relatively high, some water derived from this source may be harmful to children's teeth. The analyses show also that the amount of sulfate contained in these 19 samples of water from the Ogallala ranged from 8.4 to 84 parts per million and averaged about 44 parts. The analyses indicate that the water from the Ogallala is well within the suggested safe use for irrigation. The water in the Ogallala is generally softer than the water in the overlying undifferentiated Pleistocene deposits.

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