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Geohydrology of Wallace County

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Geologic Formations in Relation to Ground Water

Cretaceous System--Upper Cretaceous Series

Niobrara Chalk

The Niobrara Chalk consists chiefly of about 100 feet of alternating beds of light-gray chalk, chalky limestone, and chalky shale. The lower 50 to 60 feet of the Niobrara is massive-bedded chalk and chalky limestone called the Fort Hays Limestone Member. Most of the Niobrara consists chiefly of thin-bedded chalk and chalky shale called the Smoky Hill Chalk Member, upper member of the Niobrara Chalk.

The Niobrara was named by Meek and Hayden in 1862 from exposures of calcareous marl and chalky limestone near the mouth of the Niobrara River in northeastern Nebraska. Logan (1897, p. 219) described the Niobrara in north-central Kansas and divided it into the Fort Hays limestone member below and the Smoky Hill Chalk Member above. Williston (1891, p. 235) discussed the paleontology and stratigraphy of the Niobrara in western Kansas.

Smoky Hill Chalk Member

The oldest rocks that crop out in Wallace County consist of chalk and chalky shale of the Smoky Hill Chalk Member. Only the uppermost part of the member is exposed in Wallace County, where it crops out along the South side of the South Smoky Hill Valley, in the east-central part of the county. In the rest of the county, these rocks occur in the subsurface.

The Smoky Hill consists principally of chalk and chalky shale, but thin beds of bentonite occur throughout. The Smoky Hill is characteristically thin bedded and platy. Fresh exposures are light to dark gray, but the beds weather colorfully to white, orange, and brown. Concretions of limonite and pyrite are common and they account for the bright colors of the Smoky Hill Chalk Member when weathered.

The Smoky Hill is noted for the abundant fossils it contains. Vertebrate fossils include bones of aquatic reptiles, such as mosasaurs and pIesiosaurs, and many species of fish. Shark teeth are common. Invertebrate fossils characteristically include echinoderms and molluscs, the most numerous of which are the genera Innoceramus, a clam, and Ostrea, an oyster. Minute shells of foraminifers belonging mainly to the families Globigerinidae and Textularidae compose much of the chalk.

The Smoky Hill Chalk is also notable for its effect on topography. Soil development is either thin or absent, vegetation is sparse, and rainwash and erosion produce a badland type of topography.

The Smoky Hill Chalk member is not important as an aquifer in Kansas and is believed to carry but little ground water in Wallace County. As the beds of shaly chalk are relatively impermeable, water within the formation would be transmitted through fractures and joints and would be found only locally. Cave-ins such as the Smoky Hill Cave-in and the Old Maid's Pool attest to solution within the underlying chalk beds and are apparently associated with local faulted areas. Ground water from the Smoky Hill would tend to be more mineralized than other water at comparable depth below the land surface in Wallace County, owning to its association with minerals within the chalk. Although the water probably would be undesirable for household use, it could be used to water livestock.

Pierre Shale

The Pierre Shale was named by Meek and Hayden in 1862 from exposures at old Fort Pierre in South Dakota. The Pierre Shale in northwestern Kansas has been studied and described in detail by Elias (1931). He divided the Pierre into five named members and one unnamed unit. These are, in ascending order: Sharon Springs Shale, Weskan Shale, Lake Creek Shale, Salt Grass Shale, an unnamed shale interval of about 500 or 600 feet, and the Beecher Island Shale. According to Elias, the lithology of the Pierre is fairly uniform and the breaks are based largely on fossils. Only the lower four members, which make up about the lower half of the Pierre, are present in Wallace County, the upper half having been removed by pre-Ogallala erosion. The Pierre Shale ranges in thickness from 0 southeast of the town of Wallace to approximately 600 feet in the northwestern part of the county.

The Pierre Shale conformably overlies the Niobrara Chalk in Wallace County and consists chiefly of dark-gray to black, thin-bedded shale which characteristically weathers to coffee brown and gray. Thin beds of greenish-gray, brown, and orange bentonite occur in much of the Pierre. Pyrite and marcasite are scattered throughout fresh exposures. Outcrops are characterized by limonite concretions and rusty spots, and by thin crystals of selenite, usually found in abundance along the cracks. Except for concretions, the Pierre Shale is concalcareous, thus differing from the chalky shale of the underlying Niobrara Formation. Concretions of varied size and constituents occur commonly but generally consist of calcium carbonate, siderite, and limonite. The concretions characteristically occur in zones along bedding planes and form escarpments and prominent benches in places.

The contact of the Pierre Shale and the underlying Niobrara Formation may be seen southeast of the town of Wallace along the south side of the South Smoky Hill Valley. The Pierre Shale crops out at many localities in the central and northern parts of the county, particularly along stream valleys. It is typically soft and easily eroded, and low rolling slopes characterize its exposures. Because of the uniform hydrologic and lithologic character of the formation, the Pierre Shale is mapped as a single unit on Plate 1.

Following is a section of a part of the Pierre Shale, measured and described by C.R. Johnson and N. W. Biegler (Bradley and Johnson, 1957, p. 20).

Measured section of Pierre SHale in sec. 7, T. 14 S., R. 38 W. Thickness,
Ogallala Formation
Cretaceous--Upper Cretaceous
Pierre Shale
Shale, yellow and brown, mottled; limestone concretions near contact; fish scales interspersed 10.5
Shale, gray, fissile, weathering lighter gray, having white, powdery material in fractures 11.6
Shale, gray and brown, fissile, containing lenticular silty limestone concretions as much as 7 inches in diameter 1.0
Shale, fissile, blue gray 6.5
Bentonite, having yellow limonitic shale partings 0.5
Shale, blue gray, containing lenticular limestone bodies as much as 0.5 foot thick and 6 feet long 3.5
Shale, blue gray, fissile, containing abundant bentonite stringers; a limonitic, resistant, persistent bed 0.5 inch thick lies at base 10.2
Shale, brown, limonitic, containing many limy concretions as much as 3 inches in diameter 0.6
Shale, blue gray, weathering yellow brown and earthy, fissile; bentonite stringers as much as 0.5 inch thick are common; contains fish scales. Gypsum crystals in platy aggregates are numerous 29.0
Total Pierre Shale measured 73.4

The Pierre Shale is of no consequence as an aquifer in Wallace County but serves as an impervious floor below the overlying water-bearing deposits and retards or prevents the downward percolation of water. Although the Pierre generally acts as an aquiclude, confining the ground water above it, at times a small amount of water probably moves along joints and bedding planes; the quantity of water is considered insufficient to supply wells.

Tertiary System--Pliocene Series

Ogallala Formation

The Ogallala Formation was named by Darton in 1899 (p. 732-734) from exposures in Southwestern Nebraska. Darton in 1920 (p. 6) designated the type locality as being near Ogallala Station in western Nebraska. Since his work, the most significant studies of the Ogallala Formation in western Kansas have been by Elias (1931), Smith (1940), and Frye and others (1956). The Ogallala Formation in Kansas is divided by Frye and others into three members which, in ascending order, are the Valentine, Ash Hollow, and Kimball. A thin, discontinuous bed of pisolitic limestone, 1 to 3 feet thick, commonly occurs at the stratigraphic top of the Ogallala Formation.

The Ogallala Formation was deposited upon an erosional surface of Upper Cretaceous rocks, chiefly by eastward-flowing streams whose source of load was igneous and metamorphic rocks of the Rocky Mountains and sedimentary rocks of eastern Colorado. Its lithology varies sharply both vertically and laterally. The Ogallala consists chiefly of a series of valley fillings, overlapping laterally from the axes of the main drainageways onto the gentle erosional slopes of the valley sides.

Thus, the Ogallala Formation consists of a heterogeneous complex of predominantly clastic deposits, the texture ranging from very coarse gravel and pebbles to clay, and the sorting from good to poor. Lentils of volcanic ash, marl or marly limestone, and bentonite contrast with the predominant stream-laid clastics. Throughout this heterogeneous assortment of sediments there is virtually no distinctive bed that can be traced appreciable distances in the field. The formations topographic expression includes flat uplands, gentle erosional slopes, and nearly vertical cliffs. Because of the uniform hydrologic character of the formation, no attempt was made to divide the Ogallala in Wallace County, and it is shown on Plate 1 as a single unit.

Character--The Ogallala Formation in Wallace County is characteristically buff to pinkish in color. It constitutes a widespread mantle of fluvial deposits consisting predominantly of sand, gravel, silt, and clay. The deposits are interbedded and admixed to various proportions and are largely unconsolidated, although cementation of beds occurs to some degree throughout the formation. Also commonly present are thin beds of volcanic ash, fresh-water limestone, and bentonitic clay. Calcium carbonate is a common constituent in almost all the Ogallala. It is distributed both as fine material and as stringers of caliche and small to medium-size nodules. In many places calcium carbonate binds the deposits so firmly as to produce a series of hard ledges, interbedded with only slightly cemented beds. The hard ledges are usually unevenly cemented and form roughly weathered benches and cliffs which resemble mortar and accordingly are often referred to as "mortar beds." Silica also is present as a cementing material in beds of opaline sandstone or as chert deposits, and variously colored chert in the form of nodules and in small irregular lenses and beds is occasionally seen.

Sand is the principal material within the Ogallala Formation and is present at all horizons, the sand typically being light gray or greenish. Beds of uniform sand may occur but generally the sand ranges from fine to coarse and commonly is mixed with gravel, silt, or clay. Gravel beds containing lenses of sand, silt, and clay are common but thick beds of uniform gravel are rare. Beds of sand and gravel with distinct cross bedding occur in places. Silt, sandy silt, and clayey silt are present throughout the Ogallala and are greenish gray, pink, tan, and gray; if the beds contain a large amount of calcium carbonate, they are light gray or white.

Lenses and thin beds of white and pinkish limestone are common in the middle and uppermost parts of the Ogallala. Bluish-gray volcanic ash and light-gray to snow-white diatomaceous marl are locally found in the lower and middle parts of the formation.

Although relatively pure clay beds are not common within the Ogallala, fine plastic, bentonitic clays, greenish and reddish brown, are locally at or near the base of the Ogallala. Elias (1931, p. 153-158) discussed the occurrence of the clays and concluded that for the most part they were the product of weathering of volcanic ash that had been deposited on the surface of the Pierre Shale before Ogallala deposition began, or very early during Ogallala deposition. Subsurface samples of clay of similar appearance at the base of the Ogallala Formation in Thomas County were reported by Frye (1945, p. 67), who suggested that the clay might be a product of weathering of the underlying Pierre Shale. Bentonite lentils occur within the Ogallala, seemingly restricted to the lower member of the formation (Valentine Member). Bentonite was recognized in several test holes drilled in Wallace County, the thickest section being in test hole 14-42-13ccc, where 9 feet of grayish-green bentonite was recorded.

Following is a section of a part of the Ogallala Formation, measured and described by Frye and others (1956, p. 84).

Measured section of the Ogallala Formation in the SE sec. 11, T 13. S., R. 42 W. Thickness,
Ogallala Formation
"Algal limestone" 0.5
Caliche, silt, fine sand, and a few pebbles, gray yo ash gray, distinctly platy structure throughout 9
Sand, fine, some coarse sand and pebbles, massive, densely cemented with calcium carbonate, gray 13
Silt, fine sand, and clay, loose, massive to thin bedded, greenish gray to brown; contains nodules of caliche and small cemented lenses 11
Sand, pebbles of quartz and caliche, and cobbles of red silt, loosely cemented throughout; contains Celtis willistoni 10
Silt and fine sand, well sorted in thin beds, some cross-bedded zones; weathered volcanic ash shards abundant in basal part; discontinuous caliche zone at top 10
Sand, medium, some fine gravel, massive, gray, densely cemented; contains Celtis willistoni
Sand, fine to medium, loosely cemented, gray to pinkish tan 4
Sand and gravel, brown to tan, densely cemented; contains the following fossil seeds: Berrichloa amphoralis, B. tuberculata, Biorbia fossilia, Krynitzkia auriculata Stipidium interimedium, S. variegatum
Silt and sand, loose, local cemented lenses, pinkish to reddish brown. (The Ogallala rests on Pierre Shale) 26
Total Ogallala Formation measured 98.5

Outcrops are characteristically cemented to various degrees and typically are ash gray in color. In spite of the diversity of deposits, the outcrop pattern of the Ogallala presents a uniformity of aspect that makes the formation readily identifiable. Many beds in the Ogallala are cemented or partially cemented with calcium carbonate. Because the cemented beds are more resistant to erosion, many outcrops of the Ogallala form rough benches, hard ledges, and cliffs; exposed surfaces commonly have a knobby, irregular aspect.

Opinions regarding the origin of the thin, discontinuous bed of pisolitic limestone originally called "algal" by Elias (1931, p. 136-141) that marks the stratigraphic top of the Ogallala Formation have been controversial. Elias postulated a lacustrine origin for the capping limestone. Later workers advanced a hypothesis of subaerial origin as a caliche zone. Smith (1940, p. 90-92) discussed the two hypotheses, and more recently Frye and others (1956, p. 13-16) critically discussed the bed, postulating as a mode of origin the development of a mature to senile lime-accumulating soil which was later modified by solution.

Distribution and Thickness--The Ogallala Formation rests on a subaerially eroded surface developed on shales of Late Cretaceous age. This surface has a relief of several hundred feet in Wallace County and slopes generally eastward at a rate of about 10 to 15 feet per mile. Logs of test holes show that the thickness of the Ogallala Formation in Wallace County ranges from 0 to approximately 400 feet, but that the thickness is not uniform because of unconformable contacts at the top and bottom of the formation.

The Ogallala, although generally mantled with eolian silts, underlies the upland plain in the southern, west-central, and northwestern parts of the county. The Ogallala is thickest and most extensive in the Southern part of the county, where it underlies the upland loess in nearly all the area. The Ogallala also occurs extensively in the west-central and northwestern parts of the county and it is locally quite thick. The Ogallala is thin and discontinuous in the central and northeastern parts of the county, where much of it has been removed by erosion. In many parts of this area it only caps the high interstream areas. The Ogallala crops out along the bluffs of the major valleys and locally is well exposed in many of the tributary canyons. The thickness and character of the Ogallala Formation are shown by the logs of test holes and wells at the end of this report and are illustrated in the cross sections on Plate 2.

Water Supply--The Ogallala Formation is the most widespread and important water-bearing formation in Wallace County. It supplies water for most domestic and stock supplies, and 96 irrigation plants were obtaining water from it in the fall of 1960. The yields of the wells range from a few gallons per minute for domestic and stock wells to more than 2,000 gpm for several irrigation wells.

In much of the southern, the extreme western, and the northwestern parts of the county, the saturated thickness of the Ogallala, which yields moderate to large quantities of water, is great enough to store relatively large quantities of ground water. In much of the central and northeastern parts of the county, the Ogallala is either missing or too thin to carry more than a little ground water, if any.

Studies were made to determine the quantity of ground water in storage in the Pliocene and Pleistocene deposits. A contour map (Pl. 3) showing the saturated thickness of the deposits was prepared by superimposing a contour map of the water table upon a contour map of the bedrock surface and connecting points of equal saturated thickness. The area between each pair of contours was measured with a planimeter and was multiplied by the average saturated thickness to give the volume of saturated materials. The total volume of saturated materials and the volume of water, based on an assumed specific yield of 15 percent from the saturated material, are given by townships in Table 10.

Table 10--Volume of saturated water-bearing materials and volume of water available for pumping in Wallace County, based on a specific yield of 15 percent.

Township Volume of
Volume of
T. 11 S., Rs. 38 and 39 W.290,00043,000
T. 11 S., R. 40 W.970,000145,000
T. 11 S., R. 41 W.1,200,000180,000
T. 11 S., Rs. 42 and 43 W.1,300,000195,000
T. 12 S., R. 40 W.90,00013,000
T. 12 S., Rs. 42 and 43 W.1,200,000180,000
T. 13 S., Rs. 41, 42, and 43 W.2,000,000300,000
T. 14 S., R. 38 W.280,00042,000
T. 14 S., R. 39 W.1,000,000150,000
T. 14 S., R. 40 W.1,600,000210,000
T. 14 S., R. 41 W.2,300,000345,000
T. 14 S., Rs. 42 and 43 W.3,700,000555,000
T. 15 S., R. 38 W.1,900,000285,000
T. 15 S., R. 39 W.2,800,000420,000
T. 15 S., R. 40 W.3,700,000555,000
T. 15 S., R. 41 W.2,000,000300,000
T. 15 S., Rs. 42 and 43 W.500,00075,000
Total volume27,000,0004,000,000

The total volume of saturated water-bearing materials in Wallace County, as measured, is about 27 million acre-feet. If the materials have a specific yield of 15 percent, a volume of water equal to 15 percent of the total volume of saturated materials would be available for pumping. Thus, about 4 million acre-feet of water would be available if the deposits were completely drained. From a practical standpoint, much less water than this would be available for pumping.

Quaternary System--Pleistocene Series

Deposits of Quaternary, age, although relatively thin, are the surficial materials in much of Wallace County, as shown by the geologic map (Pl. 1) and cross sections (Pl. 2). The deposits are both eolian and fluvial in origin and are assigned to the Pleistocene Series. The eolian deposits consist of the Peoria and Loveland Formations, and the fluvial deposits consist of alluvium.

Eolian silts cover much of the upland areas and typically extend along the valleys, masking the valley slopes. In places the loess is intermixed with reworked loess and slope wash, and in some areas the upland draws contain several feet of this colluvial material.

Fluvial deposits are associated with the drainage system and consist of alluvial deposits of sand, gravel, and silt along the inner valleys of the principal streams.

Peoria and Loveland Formations

Character and Thickness--Eolian deposits form the most extensive outcrops in Wallace County, blanketing much of the county with a cover of loess ranging from 0 to about 50 feet in thickness. The loess is apparently thicker in the northwestern part of the county. It caps the rolling hills and flat uplands and masks the gentle slopes of the valleys. The loess represents the Loveland Formation of Illinoisan age and the Peoria Formation of early Wisconsinan age. Locally, chiefly in the northwestern part of the county, about 1 or 2 feet of loess, largely incorporated within the modern soil profile and believed to represent the Bignell Formation of late Wisconsinan age, was observed overlying a buried soil believed to be the Brady soil.

The Loveland Formation is a reddish-tan silt, mostly eolian, which characteristically grades into sand in the lower part. The Sangamon buried soil marks the top of the Loveland Formation and separates it from the overlying Peoria Formation. The Peoria is a massive, eolian, tan to gray silt, which covers much of the upland areas of Wallace County and typically masks the valley slopes along the principal stream valleys.

Colluvium, material deposited by slope wash and consisting of reworked loess, sand and gravel derived from the Ogallala Formation, and Cretaceous bedrock fragments, mantles many slopes and characteristically fills the upland draws. Where the colluvium is thick enough to conceal the underlying bedrock it has been included with the Peoria and Loveland Formations on Plate 1.

Water Supply--The deposits mapped as Peoria and Loveland Formations in this report consist mostly of relatively thin, wind-deposited silt, generally well above the water table. In parts of central and northeastern Wallace County, however, where in places ground-water supplies are meager, shallow domestic and stock wells obtain small amounts of ground water from colluvial and slope deposits which in this report are included with the Peoria and Loveland Formations. In these areas where ground-water supplies are meager and difficult to find, the best well sites generally prove to be creek valleys and draws where thin alluvial and colluvial fill and unconsolidated material overlie the bedrock and thus serve as local catchment basins. In periods of ample rainfall these wells generally prove adequate for most domestic or stock use. During extended periods of dry weather, however, the water drains from many of these deposits and wells tend to become dry.

Because ground water in these deposits is generally in contact with the underlying Cretaceous bedrock and with bedrock fragments that are incorporated within the deposits, the water obtained from these wells is generally of inferior chemical quality (Fig. 20).


Character--Alluvium believed to be of late Wisconsinan and Recent age occurs in narrow belts along the principal streams in the county. Thick, coarse alluvial deposits of sand and gravel are restricted to the larger valleys and are derived mostly by erosion of older alluvial deposits and the Ogallala Formation. Thin, poorly-sorted deposits of alluvium lie in the smaller valleys and contain relatively less coarse material, the deposits being predominantly silt and fine sand. These deposits grade headward into colluvium and slope deposits at the edge of the uplands. Their lithology depends chiefly upon the type of rock into which the valley has been incised.

In the South Smoky Hill Valley, the alluvium that underlies the braided stream channel and the narrow floodplain is considered to be Recent in age. Low, relatively narrow terraces, believed to be late Wisconsinan in age, border the floodplain. Although the narrow Recent floodplain and the low terraces are best developed along South Smoky Hill Valley, they are also found to a lesser extent along most of the other principal streams. The alluvium of Recent age and the alluvial deposits of late Wisconsinan age underlying the low terraces are lithologically indistinguishable and are shown together as alluvium on Plate 1.

Distribution and Thickness--Alluvium occurs in narrow belts along the principal valleys. The width and thickness of the alluvium are greatest along the South Smoky Hill Valley, where the alluvium reaches a maximum width of about a mile, averaging about half a mile, and a maximum thickness of 70 feet in the central and eastern parts of the county. Alluvium in the valleys of the North Smoky Hill River and Lake Creek is 40 to 50 feet thick. Alluvium in the smaller valleys is thin and of narrow extent, and headward these deposits grade into colluvium and slope wash.

Water Supply--Alluvial deposits constitute an important source of water in parts of Wallace County where other groundwater supplies are meager or not available. Many domestic and stock wells obtain water from the alluvium, and several irrigation wells obtain water from alluvium along the South Smoky Hill Valley. One irrigation well obtains water from alluvium in the North Smoky Hill Valley and one irrigation plant obtains water from alluvium in the Goose Creek valley.

Moderate to moderately large yields of water can be expected from wells in alluvium along the South Smoky Hill Valley. The areal extent of the alluvium is not great, however, averaging only about half a mile in width. Ground-water yields from wells in alluvium in the smaller valleys can be expected to be considerably less than from those in the larger valleys, because of the finer, less permeable material in the smaller valleys. Since the cross-sectional areas of the smaller valleys also are less, water levels tend to fluctuate more in response to rainfall. Declining water levels, with subsequent drying up of wells in the smaller valleys and upland draws, can be expected during extended periods of below-normal rainfall. In addition, because of the relatively shallow depth to water in the alIuvium, transpiration by deep-rooted plants during the growing season often results in a decline of water levels.

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Kansas Geological Survey, Geology
Placed on web July 9, 2007; originally published November 1963.
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