Permian System (Leonardian Series)
The Wellington Formation underlies all of Cloud County but is not exposed at the surface anywhere in the county. The thickness of the Wellington Formation where the sequence is complete and the upper surface is not eroded is about 700 feet, but the maximum thickness in Cloud County is about 400 feet. This formation consists chiefly of gray shale but contains some red and green shale in the lower part. The most conspicuous of several thin limestone beds in the Wellington is the Hollenberg Limestone member, which lies about 40 feet above the base of the formation. It is somewhat dolomitic and locally cherty. Massive beds of gypsum are exposed in Saline, Dickinson, and Clay counties and are buried in the subsurface of Cloud County. To the west and South of Cloud County thick beds of salt (Hutchinson Salt member) occur near the middle of the formation, but they are nowhere exposed at the surface.
The Wellington Formation is a very poor aquifer because of its low permeability and the large amount of mineral matter that can be taken into solution by ground water.
Cretaceous System (Gulfian Series)
Character and subdivisions--The Dakota Formation includes the nonmarine material between the base of the marine Graneros Shale and the top of the marine Kiowa Shale. In areas where the Kiowa Shale is absent the base of the Dakota Formation is marked by a persistent cobble zone, as much as 3 feet thick, composed of polished pebbles and cobbles of quartzite, chert, and quartz embedded in sand and clay, which probably represents the time interval between the end of Permian deposition and the beginning of Cretaceous deposition. Where the Kiowa Shale is present, this cobble zone separates Permian rocks from the Kiowa Shale. The base of the Dakota Formation and the underlying beds are not exposed in Cloud County, but the Dakota Formation probably is underlain by the Kiowa Shale throughout much of the county. Because of the lithologic similarity of the Dakota Formation and the Kiowa Shale, the contact between the two formations was not recognized in test holes, and the entire sequence is logged as the Dakota Formation.
Because of the conspicuous outcrops formed by resistant beds or lenses of sandstone, it is popularly believed that the Dakota Formation is composed chiefly of sandstone. Test drilling has revealed, however, that it consists chiefly of clay of various colors interspersed with pyrite, limonite, and hematite and contains numerous thin beds of lignite.
The sandstone beds in the Dakota Formation are not continuous over large areas, and irregular beds or lenses of sandstone may be present in any part of the formation, but massive sandstone beds are most common in the upper half of the lower third and the lower half of the upper third of the formation. A quartzitic phase of the sandstone is common in the lower part of the formation. The quartzitic rock is not well exposed in Cloud County but has been extensively quarried in Lincoln County. Plummer and Romary (1947) divided the Dakota Formation into two members, the Terra Cotta Clay member, which comprises approximately the lower two-thirds of the formation, and the Janssen Clay member, which constitutes the upper part of the formation. A fairly persistent bed of lignite about 2 feet thick, lying about 12 feet below the top of the formation, has been mined in the area of the old community of Minersville, northeast of Concordia.
Distribution and thickness--The Dakota Formation underlies all of Cloud County except possibly the most deeply scoured parts of the Republican River valley east of Clyde and of the Chapman Creek valley southeast of Miltonvale. The Dakota Formation is overlain by younger beds in much of the western part of the county. The thickness of the Dakota Formation in Cloud County ranges from a few feet, at most, beneath the deep valleys at the east side of the county to a known maximum thickness of about 400 feet in the northwestern part of the county.
Water supply--The Dakota Formation is the only aquifer of major consequence in the uplands of Cloud County. In the outcrop area of the formation it yields an abundance of good water for domestic and stock use. In west-central Cloud County, where the formation is most deeply buried under younger formations, and in some other areas, where wells must be drilled to the lower part of the formation because there is no sandstone in the upper part, the water is somewhat mineralized.
In general, the area of greatest salt concentration lies west of the saddle or trough in the piezometric surface (Pl. 2) trending southwest from the west side of T. 6 S., R. 4 W. In this area, as elsewhere, the salinity increases with depth, but at a much higher rate than average. A water sample from test hole 5-3-15ab drilled into the Dakota Formation contained 32,000 ppm of dissolved solids, of which 16,000 ppm was chloride. It is believed that this mineralized water is moving southeast and is being discharged into the alluvial fill in the deepest part of the Republican River valley in the vicinity of Concordia.
Character--The Graneros Shale consists of blue-black fissile noncalcareous clay shale that weathers olive drab. Selenite crystals may be present throughout the formation, and very thin rusty-colored lenses of sandstone are exposed in most weathered outcrops. The Graneros Shale weathers to a heavy clay and forms a gentle slope from the base of the Greenhorn Limestone to the top of the Dakota Formation.
Distribution and thickness--The Graneros Shale underlies most of the western half of Cloud County except along the valleys of Republican and Solomon Rivers and Buffalo Creek. The thickness of the Graneros Shale in Cloud County ranges from 20 to 40 feet.
Water supply--No wells are known to yield water from the Graneros Shale in Cloud County. The shale is impermeable and yields little or no water.
Character and subdivisions--The Greenhorn Limestone is divided into four members. They are, in ascending order, the Lincoln Limestone member, Hartland Shale member, Jetmore Chalk member, and Pfeifer Shale member. The Lincoln Limestone member is composed chiefly of thin-bedded fossiliferous limestone, dark-gray to brown shale, and thin bentonite beds. The limestone beds of the Lincoln member are characterized by a strong petroliferous odor when freshly broken. The Hartland Shale member is composed of light-colored calcareous shale and beds of bentonite. The Jetmore Chalk member is composed of alternating beds of chalky limestone and calcareous shale and some thin bentonite beds. The top of the Jetmore Chalk member is marked by the very persistent 11 shell rock" bed. This bed is composed of a mass of invertebrate fossils in a matrix of chalky limestone. The Pfeifer Shale member, like the underlying Jetmore Chalk member, is composed of alternating beds of limestone and calcareous shale and some thin bentonite beds. The limestone beds of the Pfeifer Shale member are more massive and not as chalky as those of the Jetmore Chalk member. The top of the Pfeifer Shale member (top of the Greenhorn Limestone) is marked by the conspicuous Fencepost Limestone bed. This limestone bed is about 0.7 foot thick, contains Inoceramus shells, and has a persistent iron-stained layer in the middle. It is easily quarried into rectangular blocks about 6 feet long, and these blocks are used widely throughout central Kansas for fence posts.
Distribution and thickness--The Greenhorn Limestone crops out on or underlies much of the western part of Cloud County. The areal distribution of the Greenhorn Limestone is shown on Plate 1. The average thickness of the formation in Cloud County is about 85 feet.
Water supply--A few wells in Cloud County yield small quantities of water from the Greenhorn Limestone. Most of the water in the Greenhorn Limestone occurs in cracks above impervious layers, and dug wells of large diameter are constructed because of the greater infiltration area offered by this type of well. Most of the water from the Greenhorn Limestone is hard.
Character and subdivisions--The Carlile Shale is the youngest Cretaceous formation in Cloud County. Because of its high topographic position and nonresistant nature, the Carlile Shale is poorly exposed in Cloud County. The formation is divided into the Fairport Shale member below and the Blue Hills Shale member above. Only the lower member, the Fairport, is present in Cloud County.
Distribution and thickness--The Carlile Shale has been removed by erosion from all but the highest divides in west-central Cloud County, and nearly all outcrops are completely mantled by younger silt deposits. The maximum thickness of the formation in Cloud County probably does not exceed 30 feet.
Water supply--The Carlile Shale does not yield water to wells in Cloud County.
Tertiary System (Pliocene Series)
Character and subdivision--The Ogallala Formation, which was deposited by streams flowing eastward from the Rocky Mountains, is the only Tertiary rock in Cloud County. The Ogallala Formation in Kansas is divided into three members, in ascending order the Valentine Member, Ash Hollow Member, and Kimball Member. The Kimball Member, the top of the Ogallala Formation, is commonly capped by the "Algal limestone." The "Algal limestone" is pink-white or gray-green concentrically layered sandy limestone and in Cloud County constitutes the entire Ogallala Formation.
Distribution and thickness--The Ogallala Formation was recognized in only two places in Cloud County (Pl. 1). These localities are on high divides, and the Ogallala Formation is probably buried under younger silt deposits in similar topographic Position throughout the western part of the county. The maximum observed thickness of the Ogallala Formation in Cloud County was about 1 foot.
Water supply--The Ogallala Formation is above the water table in Cloud County and does not yield water to wells.
Quaternary System (Pleistocene Series)
Character and subdivisions--Prior to February 1958 the State Geological Survey of Kansas classified the Holdrege and Fullerton as members of Nebraskan and Aftonian age, Meade Group, and the Grand Island and Sappa as members of Kansan and Yarmouthian age, Meade Group. Since February 1958 the Holdrege and Fullerton have been regarded as formations of Nebraskan and Aftonian age and the Grand Island and Sappa have been regarded as formations of Kansan and Yarmouthian age.
In the area studied for this report only deposits of Meade Group--Kansan age were recognized, and the Sappa and Grand Island Formations were not differentiated. In much of north-central Kansas the Meade Group consists of discontinuous terrace remnants along the major streams. These valley-fill deposits are composed principally of material transported from the west, but near the margin of glacial advance the deposits are composed of outwash materials. In eastern Kansas, south of the glacial outwash deposits, Kansan deposits consist principally of chert gravels and some pebbles of limestone and sandstone, nearly all locally derived. In other local areas in Kansas in which Meade deposits occur they are composed entirely of locally derived materials. In Cloud County, deposits that are in a high-terrace position and are associated with the Solomon River drainage system are thought to be Kansan in age. These deposits consist of a thin veneer of locally derived limestone gravel resting on a bedrock bench about 45 feet higher than the bedrock underlying the next lower terrace. Deposits near Kirwin, Phillips County, which lie in the deepest part of the Solomon River channel, underlying younger Illinoian deposits, have been identified as Kansan in age (Frye and Leonard, 1954). Kansan deposits near Kirwin occupy the lowest part of the valley, whereas the deposits in southwestern Cloud County that are believed to be Kansan occupy a high position, but these deposits probably are associated with a tributary stream rather than with the main stream. Deposits in the deepest parts of the valleys of Republican River and Buffalo Creek in northern Cloud County are classified in this report as being of Kansan age and as belonging to the Meade Group. These deposits underlie the younger Wisconsinan and Recent alluvium, and in some areas they probably are overlain by Illinoian deposits, but Kansan deposits could not be differentiated from Illinoian materials from test-drilling information. The Kansan deposits consist chiefly of locally derived limestone and sandstone gravel in the lower part and silt and clay in the upper part. They are believed to be equivalent in age to the arkosic Kansan deposits in the ancestral Republican valley in Republic County, which probably were deposited prior to the capture or spilling over of the ancestral Republican River, but they differ lithologically because the source materials of the deposits in the two valleys differ.
Distribution and thickness--The Kansan deposits associated with the Solomon drainage were observed at the surface in only one locality, about 3 miles north of Simpson, where they are about 15 feet thick. This small outcrop was not mapped.
The Kansan deposits in the Republican River valley occupy the deepest part of the valley and extend entirely through the county along both Republican River and Buffalo Creek, but do not crop out. Thickness ranges from a featheredge to as much as 60 feet.
Water supply--The Kansan deposits along Solomon River are above the water table and do not yield water to wells. As previously mentioned, salt water is entering the basal alluvial fill (Kansan) of the Republican River valley in the vicinity of Concordia from the Dakota Formation. The fairly persistent silt and clay bed that forms the upper part of the Kansan deposits in this area acts as a seal to prevent the salty water from entering the overlying younger beds. In that part of the Republican River valley from a few miles west of Concordia to the east side of Range 2 West, wells should not be drilled through this clay layer, because salty water is likely to be encountered below it. East of the east side of Range 2 West, the clay layer at the top of the Kansan deposits is discontinuous or absent, and the salty water in the Kansan deposits is diluted by mixing with the fresh water in the overlying younger deposits, hence is not objectionably salty.
Nearly all the Pleistocene deposits of Cloud County, with the exception of the Kansan deposits, Recent alluvium, and dune sand, are part of the Sanborn Group. The Sanborn, as used by the Kansas Geological Survey, includes deposits of two glacial stages (Illinoian and Wisconsinan) and the several substages of the Wisconsinan; also it includes two unconformities and represents three distinct cycles of deposition. The Sanborn Group includes, in ascending order, the following formations: Crete, Loveland (containing the Sangamon buried soil in its upper part), unnamed early Wisconsinan alluvial deposits, Peoria (containing the Brady buried soil in its upper part), unnamed late Wisconsinan alluvial deposits; and Bignell. For the purpose of discussing the water-bearing characteristics, the eolian silt units of the Sanborn Group are considered together.
The Crete Formation is present in two general areas of Cloud County, in a terrace position along Solomon River, and a unit identified as the Crete and Loveland Formations undifferentiated in a terrace position along Buffalo Creek and Republican River. Along Solomon River the top of the Crete is about 50 feet above the floodplain level. These deposits consist of both arkosic and locally derived gravel and minor amounts of interbedded silt and clay. In general, the sand and fine gravel of these deposits are arkosic, but the coarse gravel and cobbles are locally derived. In few places does the thickness of Crete deposits along Solomon River exceed 30 feet. The Crete Formation in the Solomon valley lies above the water table and does not yield water to wells. There are numerous gravel pits in Crete deposits, particularly along U. S. Highway 24 west of Glasco.
Deposits of the Crete and Loveland Formations adjacent to Republican River and Buffalo Creek are as a rule much thicker than those along Solomon River and are composed chiefly of silt and clay. A fairly persistent bed of almost entirely locally derived gravel was penetrated in test holes at the base of the Crete along Republican River and Buffalo Creek. There, the Crete-Loveland unit yields quantities of water suitable for domestic and stock uses, and locally the basal gravel may be thick enough to permit development of small irrigation supplies.
Loveland and Peoria Formations
Large parts of the upland as well as the Kansan and Crete terrace surfaces in Cloud County are blanketed with wind-deposited silt. The oldest of these eolian (loess) deposits, the Loveland Formation, of Illinoian age, was deposited immediately after or contemporaneous with the deposition of the Crete Formation. In unweathered exposures the Loveland consists of compact reddish-yellow silt and clay, but in many places in Cloud County almost its entire thickness is included within the Sangamon buried soil profile. The Sangamon soil formed during the period between the end of Loveland deposition and the beginning of Peoria deposition.
The Early Wisconsinan alluvial deposits, which are usually regarded as a part of the Sanborn Group in Kansas, were not recognized in Cloud County. The Peoria Formation (Wisconsinan age) is a massive calcareous buff to yellow silt and clay, locally containing many fossil snails. The upper surface of the Peoria, where it is overlain by the Bignell (late Wisconsinan) Formation, is marked in most places by the Brady buried soil. The Bignell Formation, which is the youngest formation of the Sanborn Group, was not recognized in Cloud County. No differentiation between the silts of the Sanborn Group was made in geologic mapping. They are above the water table in Cloud County and do not yield water to wells.
Wisconsinan Terrace Deposits
After the deposition of the Peoria Formation and prior to and in part contemporaneous with the deposition of the Bignell Formation, thick deposits of sand and gravel were laid down along the valleys of Solomon River, Republican River, Buffalo Creek, and other streams in the county. These deposits, now in a low-terrace position, are late Wisconsinan in age and are included in the Sanborn Group. To differentiate these deposits from the silts of the Sanborn Group, they have been mapped separately and are designated as Wisconsinan terrace deposits on Plate 1.
Wisconsinan terrace deposits in the valley of Buffalo Creek are about 40 feet thick and along Republican River are as much as 125 feet thick. Along Buffalo Creek the Wisconsinan terrace deposits are composed chiefly of silt and clay and contain only a minor amount of locally derived gravel. Yields of wells almost anywhere in the Wisconsinan terraces of Buffalo Creek are adequate for domestic and stock use, but generally are not large enough for irrigation. Owing to subsurface movement of mineralized water downstream from the salt marsh northwest of Jamestown and recharge of the terrace deposits from the Dakota Formation, the quality of water from the Wisconsinan terrace deposits of Buffalo Creek is not uniform. The ground water in both the Buffalo Creek and Salt Creek valleys is strongly mineralized where these two streams enter the county. The deepest part of the Buffalo Creek channel intersects sandstone beds in the Dakota Formation that yield salt water, and as the water in the Dakota is under a greater head than the water in the terrace deposits, the salty water moves upward into the terrace deposits. Shallower parts of the channel are receiving fresh water from the upper part of the Dakota Formation and from downward percolation of local precipitation. Depending on several very local geologic and recharge conditions, a well at a given location in Buffalo Creek valley terraces may yield fresh water whereas a nearby well may yield salt water.
The Wisconsinan terrace deposits along Republican River are composed of sand and silt in the upper part and almost entirely of sand and gravel in the lower part. The deposits supply water to many domestic and stock wells in the valley and yield abundant supplies to irrigation wells. The quality of water from the Wisconsinan terrace deposits of Republican River is generally good, but when-a well is drilled care should be taken not to penetrate the silt and clay at the top of the underlying Kansan deposits where the Kansan deposits are known to contain salt water, as the water in the Kansan deposits is probably under a higher hydrostatic head than that in the overlying Wisconsinan and alluvial deposits, and salt water will flow upward into those deposits.
The thickness of the Wisconsinan terrace deposits along Solomon River and the minor streams in Cloud County does not exceed 50 feet. The terrace deposits along these streams are composed chiefly of silt and clay and contain only minor amounts of sand and gravel. Yields adequate for domestic and stock supplies are obtained from these deposits, and irrigation supplies may be developed in some areas from Wisconsinan terrace deposits along Solomon River.
The areas mapped as alluvium (Pl. 1) consist of the flood plains of streams. The alluvium consists of coarse sand and gravel intermixed with a small amount of silt and in places contains thin clay layers. Because of the similarity of material, alluvium cannot readily be distingushed from Wisconsinan terrace deposits, and there is no difference in their water-bearing characteristics. The present distribution of alluvium coincides in most places with the position of the deepest part of the channel, and as a result, wells drilled therein penetrate a greater thickness of permeable material, and hence have somewhat higher yields, than wells dug or drilled in Wisconsinan terrace deposits. Locally the alluvium of Republican River may be as much as 130 feet thick.
At several places in Cloud County, the wind has piled up sand from the alluvium into dunes. These dunes are of Recent age, and some are semiactive, the sand being somewhat ineffectually held in place by a sparse cover of vegetation. The thickness of dune sand in Cloud County does not exceed 50 feet. The sand dunes are generally above the water table and yield only small supplies of water to wells, but are important areas of recharge because they absorb and transmit water so readily.
Kansas Geological Survey, Geology
Placed on web June 29, 2009; originally published May 1959.
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