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Geohydrology of Grant and Stanton Counties

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General Geology

Summary of Stratigraphy

[Note: The classification and nomenclature of the rock units described in this report follow that of the State Geological Survey of Kansas as of publication date and differ somewhat from the classification and nomenclature of the U. S. Geological Survey.]

The rocks that crop out in Grant and Stanton counties range in age from Lower Cretaceous to Recent. Large expanses of the older deposits are masked by a thin mantle of dune sand and loess (eolian silt) of Recent age. The surficial geology is shown on Plate 1. The geologic formations of the Grant-Stanton area and their water-bearing properties are given in Table 1.

Table 1--Geologic formations and their water-bearing properties, Grant-Stanton area.

System Series Subseries Stage Stratigraphic
Character Water Supply
Neogene Pleistocene Upper(?)
eolian and
0 to
Soil, loess, dune sand, alluvium on surface. Clay, silt, sand, and gravel in subsurface. Where saturated, known to yield 750 gpm from sand and gravel; higher yields may be possible. (Most deposits lie above water table and yield no water to wells.)
0 to
300 ±
Coarse sand and gravel deposits in channel fill; silt, fine sand, and clay in backwater and inter-stream deposits. Wells screened only in Lower Pleistocene(?) deposits yield up to 2,000 gpm.
Pliocene     Ogallala
0 to
Silt, clay, sand, and gravel. (Sand and gravel lenses may contain large amounts of inter-bedded silt and clay.) Yields up to 1,000 gpm obtained in areas of coarse channel-fill deposits.
Cretaceous Lower     Dakota
(L. ? Cret.)
0 to
Fine- to medium-grained sandstone with shale beds. Yields small supplies of water for stock and domestic wells. Yields water to multiple-aquifer irrigation wells.
0 to
Gray to black silty shale; may contain some thin sandstone beds. Yields little or no water to wells.
0 to
White to yellow fine to coarse quartzose sandstone. Yields up to 500 gpm possible. Yields water to multiple-aquifer irrigation wells.
Triassic (?) Upper     Dockum
in Kansas)
0 to
Fine to medium gravel, quartzose sandstone. Contains red sandstone and siltstone. Yields up to 1,000 gpm reported. Yields water to multiple-aquifer irrigation wells.
Permian Upper     Big Basin
160± Dark-red mudstone and orange-red siltstone. No information available.

All deposits that yield water of a chemical quality suitable for irrigation lie above the Permian red beds. These deposits are of sedimentary origin and are composed of consolidated and unconsolidated materials which range in age from Triassic (?) to Recent. The pre-Pliocene surface and the Pliocene (Ogallala) drainage pattern developed on this surface are shown on Plate 2A. The general drainage pattern of the early Pleistocene streams and the eroded surface of the Ogallala Formation and, in places, the pre-Ogallala surface are shown on a contour map (Pl. 2B). The buried stream valleys shown on the maps contain deposits that are coarser grained and thicker than those in the interstream areas. Wells which yield large quantities of water are obtained from the channel phase of these buried-valley deposits.

Geologic cross sections (Pl. 3-7) show the stratigraphic units and the depth of erosion. The configuration of the top of the bedrock (Permian to Cretaceous) and the top of the Ogallala Formation (Pliocene) between wells shown on the cross sections was derived from Plates 2A and 2B. Offset wells were added to the sections in some places to show the approximate depths of the sandstone aquifers.

Structural Geology

The Grant-Stanton area is on the eastern flank of the broad, regional Las Animas Arch (Lee and Merriam. 1954.). The Syracuse Anticline (Darton, 1918), the dominant structural feature in this area, is only a minor flexure upon the regional arch. This local flexure is a southeast-northwest-trending faulted fold which extends from Kearny County, Kansas, through northwestern Grant County and across the northeastern part of Stanton County into Hamilton County. Bass (1926) modified Darton's generalized structure map for Hamilton County and further described the flexure.

From a study of the physiographic data, Smith (1940) concluded that the rectilinear pattern of the north branch of Bear Creek indicated the presence of a fault on the southern margin of the Syracuse flexure. This fault was mentioned by Latta (1941) as being present in Stanton County, and it was mapped by McLaughlin (1943) in Kearny and Hamilton counties.

The prominent fault or fault system in Grant and Stanton counties (T. 27 S., R. 37-40 W.) is shown on Plates 2A and 2B and on the geologic cross sections (Pl. 5-7). The throw of the fault ranges from 100 to 200 feet. The exact structural relationships of the pre-Tertiary rocks are not clear from existing data. Along a northeast-southwest-trending fault in T. 30 S., R. 42-43 W. outcrops of the Dakota Formation occur at the same elevation as those of the Ogallala Formation. Minor faults also are found in the surface and subsurface, but information is not available to locate them precisely.

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Kansas Geological Survey, Geology
Placed on web July 17, 2007; originally published December 1964.
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