Finney and Gray county Geohydrology

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Table of Contents





Geologic History

Ground Water


Quality of Water

Geologic Formations

Records of Typical Wells

Logs of Test Holes





Summary of Stratigraphy

The rocks that crop out in Finney and Gray counties are all of sedimentary origin and range in age from Upper Cretaceous to Recent. Outcrops of the formations are shown on plate 1. The oldest rocks exposed at the surface in this area are Upper Cretaceous in age and comprise parts of the Greenhorn limestone, Carlile shale, and the Niobrara formation. Tertiary deposits of silt, sand, and gravel (Ogallala formation), which overlie the Cretaceous beds over most of Finney and Gray counties, are exposed only along parts of the Arkansas valley, along the Pawnee valley, and on the uplands north of the Pawnee valley. Clay (the Laverne (?) formation and/or the Woodhouse (?) clays of Elms) occurs locally above the Cretaceous beds in northwestern and southern Finney County and in northwestern Gray County.

Undifferentiated deposits of clay, silt, sand, and gravel of Pleistocene age, Pleistocene terrace deposits, and Quaternary alluvium and dune sand cover most of the surface in this area.

Information on the unexposed rocks that lie beneath Finney and Gray counties has been obtained from test holes drilled during the course of the investigation, from logs of oil and gas test wells, and from exposures of these rocks in nearby areas. They include shales and sandstones of Cretaceous age that underlie the Greenhorn limestone over all of this area and Paleozoic limestones and shales with lesser amounts of sandstone, gypsum, anhydrite, and salt that are encountered beneath the Cretaceous deposits.

A generalized section of the geologic formations of this area is given in table 3.

  Table 3--Generalized section of the geologic formations of Finney and Gray counties, Kansas.

System Series Subdivision Thickness (feet) Physical character Water supply
Quaternary Recent and Pleistocene Alluvium and terrace deposits 0-68 Very coarse gravel, sand, and silt comprising stream deposits in the Arkansas Valley, Pawnee valley, and the valleys of other smaller streams. Very coarse gravels occur as terrace deposits along the Arkansas and Pawnee valleys. Terrace gravels occur benea The alluvium yields large supplies of water to wells in the Arkansas valley and lesser amounts in the other stream valleys; supplies many irrigation and a few industrial wells in the Arkansas valley. Some waters from the alluvium are very hard, containing
Unconformable on older formations
Dune sand 0-70 Fine- to medium-grained wind-blown sand. Covers a large area south of the Arkansas valley and occurs in smaller areas north of the Arkansas valley. Occurs above the water table; therefore, it yields no water to wells. The dunes, however, serve as important catchment areas for recharge from local precipitation
  Unconformable on older formations
Pleistocene Undifferentiated deposits 0-300+ Consolidated and unconsolidated lenses of clay, silt, sand and gravel that are lithologically similar to materials of the Ogallala formation. Contain nodules and beds of caliche and locally volcanic ash. The sands and gravels of the Ogallala formation and Pleistocene undifferentiated beds are the most important sources of water in Finney and Gray counties. Most of the domestic and stock wells on the uplands, many of the irrigation and industrial wells, an
    Unconformable on older formations
Tertiary Pliocene Ogallala formation 0-250 Calcareous silts, sands, and gravels, much of which is cross-bedded. Both consolidated and unconsolidated. Contains nodules and beds of caliche.
  Unconformable on older formations
Lower Pliocene and Upper Miocene (?) Laverne (?) formation 0-91.5 Tan, brown, and gray silty blocky clay and clay shale, containing some medium-grained sand to fine gravel. Encountered only in test holes 15 and 16 in southern Finney County. Sands and gravels locally are potential sources of water supply, but they have not been exploited because of their great depth.
    Unconformable on older formations
Cretaceous Gulfian* Smoky Hill chalk member (No rara formation) 0-225 Alternating beds of soft chalky shale and chalk containing some thin beds of bentonite. Not exposed in Finney and Gray counties. Relatively impermeable. Not known to yield water to wells in Finney and Gray counties.
Fort Hays limestone member (No rara formation) 55-80 Thick massive beds of chalk and chalky limestone separated by thin beds of chalky shale. Exposed over wide area in northeastern Finney County. Supplies limited amount of water to few wells and springs in Finney County. Water occurs in fractures and solution openings. Not an important water-bearer.
Codell sandstone member (Carlile shale) 260 +/- Dark gray to black noncalcareous sandy shale and shaly sandstone. Encountered in test holes 1, 3, and 4. Two wells (1 and 8) obtain meager supplies of water from the Codell in Finney County. In most places adequate supplies of water may be obtained from higher formations.
Blue hill shale member (Carlile shale) Dark gray, bluish-black, and black noncalcareous shale containing thin seams of gypsum and in the upper part a zone of septarian concretions. Exposed in wide strip along the Pawnee valley in northeastern Finney County. Three unused wells (46, 47, and 57) tap the Blue Hill shale member. Because of the low permeability of the material the wells were abandoned.
Fairport chalky shale member (Carlile shale) Calcareous shale containing thin beds of chalk or chalky limestone and few thin beds of bentonite. Not exposed in Finney and Gray counties. Not known to yield water to wells.
Greenhorn limestone 130 Light to dark gray, thin, chalky and crystalline limestones separated by thicker beds of light to dark gray chalky shale that contain thin beds of bentonite. Exposed in small area in southeastern Gray County. Reported to yield small supplies of water to wells in southeastern Gray County.
Graneros shale 50 +/- Gray noncalcareous shale containing interbedded lenses of sandstone and sandy shale. Not exposed in Finney and Gray counties. Relatively impermeable. Not known to yield water to wells.
Dakota formation 50-200 (?) Light gray, tan, buff, red, and brown fine- to medium-grained sandstone and light gray, yellow-tan, and brown shale, sandy shale, and clay. Not exposed in Finney and Gray Counties. Sandstones yield moderate supplies of soft water to a few wells in southeastern Gray County.
Comanchean* Kiowa (?) shale 44-100+ Gray, bluish-black, black, and yellowish-gray shale containing a few thin beds of gray limestone and sandstone. Not exposed in Finney and Gray counties. Relatively impermeable. Not known to yield water to wells in Finney and Gray counties.
Cheyenne (?) sandstone 70 +/- Cross-bedded, fine- to coarse-grained, light gray to yellow quartz sandstone, containing interbedded gray to black silty and sandy shale. Not exposed in Finney and Gray counties. Not known to yield water to wells in Finney and Gray counties.
* - Classification of the State Geological Survey of Kansas.

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  Kansas Geological Survey, Finney and Gray County Geohydrology
Comments to
Web version April 2002. Original publication date Dec. 1944.