| System |
Series |
Subseries |
Stratigraphic
units
used in
this report |
Max
thick.,
feet |
Physical character |
Water supply |
| Neogene |
Pleistocene |
Upper
Pleistocene |
Dune sand
(Recent) |
5 |
Composed of fine to medium, silty sand. |
Lies above the water table and thus yields no water to wells. |
Alluvium and
terrace deposits
(Wisconsinan
to Recent) |
45 |
Composed of fine to coarse sand and fine to very coarse arkosic gravel containing
only minor amounts of silt and clay that grade upward into clayey silt. Clay
balls up to one foot in diameter are common in the sand and gravel. |
Comprises the most widely used aquifer in the County and yields large supplies of very
hard water to many wells. Well yields up to 2,000 gpm can be developed locally.
Adjacent to the Arkansas River the water is too highly mineralized for many
uses. |
Colluvium (Illinoisan
to Recent) |
30 |
A heterogeneous mixture of silt, clay, sand, gravel, and bedrock fragments deposited by
slope processes. |
Generally above the water table and thus yields no water to wells. Where deposits are
thick and contain sand and gravel lenses, wells yielding a few gpm may be
possible but would be subject to failure in dry years. |
Loess (Illinoisan
to Recent) |
74 |
Wind-deposited tan to pink-tan, calcareous silt, containing zones of caliche nodules and
some sandy zones. |
Generally above water table, but locally the basal part is saturated and sandy zones
may yield some water to wells. |
Terrace deposits
(Illinoisan) |
75 |
Composed of fine to coarse sand and fine to coarse arkosic gravel that grades upward
into sandy silt. Sand and gravel beds locally contain silt and clay lenses, and
clay balls up to one foot in diameter are common. |
Well yields of 500 gpm of good quality water are generally available from the deposits,
and locally yields up to 1,000 gpm can be obtained. |
Lower
Pleistocene |
Undifferentiated
deposits
(Nebraskan
and Kansan) |
157 |
Composed of light tan to light gray, commonly sandy, silt and clay, fine to coarse sand,
and fine to coarse arkosic gravel. Locally contains a lenticular bed of volcanic
ash, the Pearlette ash bed of late Kansas age. |
Yield large quantities of good quality water to wells in the Arkansas Valley that are
screened in multiple porous zones and penetrate the complete section of
unconsolidated rocks. The water is highly mineralized locally near the Arkansas
River. Where present in the uplands west of the Arkansas Valley, well yields up
to 50 gpm are possible locally. |
| Pliocene |
|
Ogallala (?)
Formation |
150 |
Composed of lenticular beds of calcareous, gray to pink-tan silt and clay, fine to coarse
sand, and fine to coarse gravel. The sediments reflect two sources; arkosic sand
and gravel beds derived from the west are interfingered in the northern part of
the County with sand and gravel beds composed of gray to tan quartz and
ironstone derived from Cretaceous rocks to the north. In subsurface only. |
Contributes large supplies of good quality water to many municipal, irrigation, and
industrial wells screened in multiple porous zones and penetrates the complete
section of unconsolidated rocks. |
| Permian |
Lower
Permian |
|
Ninnescah
Shale |
175 |
Composed of alternating beds of brownish-red silty shale and siltstone, and a few thin
beds of gray-green silty shale in lower part. Some gypsum is present as thin,
cross-cutting and intersecting vein fillings. |
Yields small quantities of water to many stock and domestic wells in the western part
of the County. Water obtained from the weathered zone in the formation is
generally of good quality. Water from deeper zones is generally highly
mineralized but usable. |
Wellington
Formation |
550 |
Calcareous gray and blue shale containing several thin beds of impure limestone and
thin beds of gypsum and anhydrite. Some beds of maroon and gray-green
shale near top of Formation. The thick Hutchinson Salt Member is present near
the middle of the Formation in the western part of the County. |
Yields small quantities of highly mineralized water to many stock and domestic wells
east of the Arkansas River valley and in south-central part of County.
Moderately large water supplies of as much as 350 gpm are available from
solution zones in gypsum beds near east County line. The water is highly
mineralized but usable |
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