Permian System--Leonardian Series
The oldest rocks exposed at the surface in Harper County are rocks of the Sumner Group of Permian age. The Sumner Group is made up of rocks of the Wellington Formation, Ninnescah Shale, and Stone Corral Dolomite but only the Ninnescah Shale crops out in Harper County.
The Ninnescah Shale is predominantly a blocky brownish-red dolomitic or calcareous silty shale. Its maximum thickness is about 450 feet, but its average thickness is about 300 feet, and probably only about the upper 100 feet crops out in Harper County. The Ninnescah Shale is marked at the top by the Runnymede Siltstone member, which attains a maximum thickness of 8 feet in this area but averages 4 or 5 feet. North of Harper County the upper limit of the Ninnescah Shale is drawn at the base of the Stone Corral Dolomite, but in Harper County the Stone Corral is absent. The beds in the Ninnescah Shale range from chocolate brown to very light gray, but brownish red is their commonest color. The different colors of the beds give the outcrops a banded appearance.
The Ninnescah Shale yields small quantities of water of good to poor quality from the weathered zone near the surface and from fractures at greater depth. Generally, wells in the Ninnescah Shale are relatively shallow, and are dug to provide more storage. In some areas the Ninnescah Shale does not yield enough water for domestic or stock use.
The Nippewalla Group consists of the upper part of the strata that are assigned to the Leonardian Series. It comprises all beds between the top of the Stone Corral Dolomite and the base of the Whitehorse Formation of Permian age and has a total thickness of about 930 feet. Only the Harper Siltstone and Salt Plain Siltstone, having a combined thickness of about 500 feet, crop out in Harper County.
The Harper Siltstone consists of about 180 to 240 feet of reddish-brown argillaceous siltstone and silty shale and a few thin layers of silty sandstone. It has been subdivided into the Chikaskia Siltstone member below and the Kingman Siltstone member above.
The reddish-brown Chikaskia Siltstone member, in Harper County about 140 to 160 feet thick, consists principally of sandstone and siltstone in the lower two-thirds and silty shale in the upper third. Where the Stone Corral Dolomite is absent the base of the Chikaskia is difficult to identify, because of similarity between the lower Chikaskia and the Runnymede Siltstone member of the Ninnescah Shale.
The Kingman Siltstone member is composed of about 80 feet of reddish-brown thin slabby siltstone containing a few beds of silty shale and light-gray to white silty sandstone. The base of the member is marked by a white silty sandstone about 3 feet thick. The top of the member can not be clearly identified. Much of the Kingman Siltstone member is lithologically so nearly identical to the overlying Salt Plain Siltstone that differentiation is not possible or practical, although the Kingman Siltstone generally is more resistant to weathering, and in drill holes the unweathered material in the Kingman generally is slightly coarser and slightly darker than the Salt Plain.
The water-bearing characteristics of the Harper Siltstone are somewhat similar to those of the underlying Ninnescah Shale. Most of the water is obtained from the weathered portion of the formation, and where sandstone is penetrated in the weathered part of the formation good domestic or stock supplies can be obtained. Some wells do not provide adequate water supplies even for stock and domestic use. Many wells in the Harper Siltstone are dug wells, which utilize the added storage space afforded by the large-diameter well. The quality of the water ranges from good to very poor.
Salt Plain Siltstone
The Salt Plain Siltstone includes reddish-brown siltstone, thin sandy siltstone, silty shale, and fine silty sandstone between the Harper Siltstone and the Cedar Hills Sandstone. Its total thickness is about 265 feet, but probably somewhat less than 200 feet of the formation crops out in Harper County. The lower boundary is not clearly defined, whereas the upper boundary in other areas is marked by a white fine-grained sandstone at the base of the Cedar Hills Sandstone. Two prominent sandstones occur in the Salt Plain Siltstone, an unnamed one near the top and the Crisfield Sandstone bed about 100 feet below the top.
Ground water is obtained from the weathered portion of the formation, but generally is not adequate for stock and domestic wells. Dug wells are most common because of their greater storage. The quality of the water from the Salt Plain Siltstone ranges from good to unsuitable for domestic use.
Tertiary(?) System--Pliocene(?) Series
Deposits in four small areas that occupy the highest position on the divide that marks the south edge of the Bluff Creek drainage area in Southeast Harper County probably are remnants of Pliocene deposits. They are lithologically dissimilar to any of the Pleistocene deposits in this general area and resemble deposits of the Pliocene Delmore Formation of Williams and Lohman (1949) in McPherson County. These deposits probably do not exceed 25 feet in thickness in Harper County and generally are much thinner. They are not known to yield water to wells in Harper County.
Quaternary System--Pleistocene Series
The Pleistocene is divided into four main stages, which are related to continental glaciation, and three interglacial stages. Events in each of the periods of continental glaciation follow a cyclic pattern of repetition. Each cycle consists of a glacial and an interglacial interval. The typical cycle in the marginal belt of a glacial area is characterized by a period of downcutting and some local deposition of sediments while the glacier was advancing, then a period of deposition of coarse materials, deposition of progressively finer materials as the glacier retreated, and finally the development of a soil profile over large areas where surface conditions were relatively stable.
Unconsolidated deposits of Pleistocene age unconformably overlie older deposits of Permian age in a large part of Harper County (Pl. 1). The deposits represent all four glacial stages.
Although deposits that represent all the glacial stages are present in Harper County and can be identified locally in the field and in logs of test holes, it is difficult to map some of these units separately. Hence on the geologic map (Pl. 1), deposits of the Lower Pleistocene are not separated in the northern part of the area.
Holdrege Formation--Nebraskan Stage
Deposits of sand, gravel, silt, and some clay classified as Holdrege Formation occur in northern Harper County. Most of the Upland area is underlain by these deposits. The Holdrege Formation was deposited by an aggrading stream that shifted laterally on its alluvial fill. This stream filled its broad, shallow valley and deposited an almost coalescent sheet of sediment over former divides. The deposits range from clay-size particles to coarse gravel, and are as much as 45 feet thick.
The Holdrege Formation yields moderate to large quantities of water to wells in the area. The water is hard but otherwise is of good quality.
Fullerton Formation--Nebraskan and Aftonian Stages
The Fullerton Formation overlies the Holdrege Formation in northern Harper County. The formation is classified as late Nebraskan and Aftonian in age, and was laid down during the retreat of the Nebraskan glacier and, in part, during Aftonian interglacial time. In general the texture of the Fullerton Formation is finer than that of the underlying Holdrege Formation. Silt and clay are the predominant materials composing the deposits but there is also some sand and scattered gravel. The contact between the Fullerton Formation and the Holdrege Formation is placed where the material changes from predominantly coarse to predominantly fine clastic material. This contact is not everywhere clearly seen, for locally the change is gradational and there is interfingering of fine and coarse sediment. The top of the formation in this area is almost everywhere marked by an accumulation of caliche, which is suggestive of soil development during Aftonian time. The deposits of the Fullerton Formation in Harper County range in thickness from 0 to about 20 feet.
As the texture of the Fullerton is predominantly fine, the deposits yield only small quantities of water to wells. The water is hard but otherwise is of good quality.
Grand Island Formation--Kansan Stage
The Grand Island Formation is composed of sand and gravel and some silt. The gravel is principally granitic but in places includes considerable locally derived material. Deposits classified as Grand Island Formation occur in two general areas in Harper County. Those in the Upland area in northern Harper County were laid down by a laterally shifting stream or streams flowing from the west or northwest. Grand Island deposits in the Bluff Creek area in central and southern Harper County were laid down in a broad channel, which is believed to have headed a short distance southeast of the city of Attica. This channel trends south-southeast to about the south line of T. 33 S. and thence eastward, roughly parallel with the present position of Bluff Creek. The deposits range from silt to coarse gravel but contain more fine material than those in the Upland area. Locally a cemented zone occurs near the base of the gravel. In the Upland area the Grand Island Formation ranges in thickness from 0 to about 45 feet, and in the Bluff Creek area it ranges from 0 to about 10 feet.
In the Upland area much of the Grand Island Formation lies above the water table, but where it is below the water table it yields moderate quantities of water to wells. In the Bluff Creek area, it yields small to moderate quantities of water. The water is hard but otherwise of good quality.
Sappa Formation--Kansan and Yarmouthian Stages
Deposits of sand, silt, gravel, and locally, volcanic ash that overlie the Grand Island Formation in the Upland and Bluff Creek areas have been assigned to the Sappa Formation. They comprise the fine clastic deposits of the late glacial stage and the interglacial stage of the Kansan glacial cycle. The diagnostic Pearlette Ash bed was observed in two localities in the county. One deposit, in the NW NE sec. 29, T. 33 S., R. 6 W., in the Bluff Creek area, formerly was mined commercially. The other deposit, in the NW SW sec. 18, T. 31 S., R. 7 W., in the Upland area, is thin and is not of commercial value. The lower boundary of the formation is marked at the change from the coarse clastic material of the underlying Grand Island Formation to the finer texture of the Sappa Formation. At the upper boundary in many places the Sappa is indistinguishable from the present soil, but in extreme northwest Harper County the Sappa Formation is overlain by sand and gravel believed to be of Illinoisan age and here the upper boundary of the Sappa Formation is marked by caliche accumulation.
Most of the Sappa Formation lies above the water table and yields no water to wells. In areas where the formation lies below the water table, little water is obtained from it, because of the fine texture of the deposits.
The upper Pleistocene includes deposits of Illinoisan, Sangamonian, Wisconsinan, and Recent age. All deposits younger than Sappa Formation are included in this group.
Crete Formation--Illinoisan Stage
In extreme northwest Harper County, sand and gravel that lie above the caliche in the upper part of the Sappa Formation are believed to be early Illinoisan in age and are assigned to the Crete Formation. These deposits are small in areal extent and are probably not more than 10 feet thick, and they are not identified on the geologic map (Pl. 1). North and west of this area in central Kansas similar deposits underlie much of the surface but are generally thin.
In Harper County the Crete Formation lies above the water table and yields no water to wells.
Slope Deposits--Illinoisan to Recent Stages
A complex series of deposits lying topographically below deposits of Kansan and Nebraskan age are found in all the ground-water areas except the Upland area. These deposits, called slope deposits in this report, are shown on Plate 1 by the symbol Qsd. Locally they consist of channel deposits of sand and gravel overlain by thick silt, which in turn is locally overlain by silt containing imbedded gravel and sand. Logs record local accumulations of caliche at the top of the thick silt and below the silt containing imbedded gravel and sand. An age ranging from late Illinoisan to Recent is assigned these deposits. It is believed that the deeper channels were cut and at least partly filled during Illinoisan time, for two distinct lower terraces were observed locally in the area. The deposits beneath these terraces probably represent deposition during early and late Wisconsinan time. Also, in the upper part of the East Sand Creek area deep eastward-trending buried channels cross the present drainage system, which trends southward. The upper silt containing the imbedded sand and gravel is believed to be slope-wash material chiefly Recent in age. There is no surface expression of the deposits in the buried channels, which can be located only by test drilling. The sides of the channels are relatively steep, and although a test hole may penetrate only the thin upper silts at one place, another test hole only a very short distance away may penetrate as much as 100 feet of coarse channel deposits. The slope of the surface of these deposits is much steeper than that of the surface of areas underlain by deposits of Kansan or Nebraskan age or the terrace surfaces of Wisconsinan age, which border the present drainage. Moreover, the underlying Permian rocks generally have a much steeper slope than those beneath the deposits of Kansan and Nebraskan age (Pl. 2).
Wells that penetrate sand and gravel in the buried channels yield moderate to large quantities of water. Wells that do not penetrate channel deposits yield little or no water. The thickest channel deposits are in the East Sand Creek area near the city of Harper, and it is from these channel deposits that both Harper and Anthony obtain their water supplies. Three irrigation plants also obtain water from these deposits in the same general area. One irrigation well and three industrial wells obtain water from deposits of the same age in the Big Sandy Creek area in southwest Harper County. The water from the channel deposits is hard but otherwise is of good quality.
Peoria Formation--Wisconsinan Stage
Eolian silts classified as the Peoria Formation overlie older deposits in much of Harper County; where they overlie older Pleistocene deposits it is difficult to differentiate them. Also, in many areas it is difficult to differentiate the eolian silts from silts in underlying Permian "redbeds," and much of the material mapped as Peoria Formation probably is of local origin and has been moved only short distances. In few places does the thickness of the eolian deposits exceed 10 feet.
Wherever present, the Peoria Formation lies above the water table, hence yields no water to wells.
Terrace Deposits--Wisconsinan Stage
Deposits underlying prominent terraces bordering the principal streams in Harper County are assigned a Wisconsinan age (Table 2). Locally, two separate terrace levels probably represent early and late substages of Wisconsinan time, but such localities are few, and therefore the terraces have been mapped as a single unit (Pl. 1). These deposits are composed of clay, silt, sand, and gravel and probably do not exceed 40 feet in thickness.
In areas where a sufficient saturated thickness of sand and gravel is penetrated by a well, moderate supplies of water can be obtained. In areas where only the silt is penetrated, water supplies are inadequate. The old well fields of both Attica and Anthony obtained a part of their water from deposits of this age, but because the aquifer, being confined in a narrow channel, had little storage capacity and recharge was derived principally from the stream, these supplies proved inadequate when the stream ceased to flow. The water from Wisconsinan terrace deposits is hard but generally suitable for most uses.
Dune Sand--Wisconsinan and Recent Stages
Dune sand occurs in three of the ground-water areas in Harper County (Pl. 1). The most extensive deposits are in the Big Sandy Creek area in the western part of the county, where the dune sand overlies older deposits, which are probably of Illinoisan age. In a part of the area the dunes are well stabilized and are cultivated but in much of the area some of the dunes are still active, and the land is suitable only for grazing.
In an area on the east side of Bluff Creek northwest of Anthony, rocks of Permian age and early Pleistocene deposits are overlain by dunes. In general, this dune tract is better stabilized than that in the Big Sandy Creek area and nearly all of it is farmed. In the Chikaskia River area scattered dunes, now semiactive, overlie Wisconsinan terrace and older deposits.
The maximum thickness of the dune sand did not exceed 20 feet in any of the test holes, but a greater thickness probably occurs in the more inaccessible part of the Big Sandy Creek area.
Almost everywhere the dunes lie above the water table and yield little or no water to wells.
Recent alluvium occurs in the modern channels of most of the principal streams in Harper County. It occupies only a narrow strip along these streams and, because of the scale, is not shown on the geologic map (Pl. 1) but is included in the area mapped as Wisconsinan terrace deposits. The alluvium is composed of silt, sand, and gravel and is relatively thin, probably not exceeding 30 feet in thickness. The water-bearing characteristics and yields of wells in the alluvium are similar to those of the Wisconsinan terrace deposits.
Kansas Geological Survey, Geology
Placed on web Feb. 27, 2009; originally published March, 1960.
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