Geologic units in Cheyenne county, Nebraska

White River Group (Phanerozoic | Cenozoic | Tertiary | Oligocene) at surface, covers 10 % of this area: Clay, some claystone, silt and siltstone. Predominantly greenish gray and volcaniclastic. Other occurrences are greenish gray to white and bentonitic. Local channel sandstone at base. Aprox thickness 195 ft.
Lithology: clay or mud; claystone; silt; siltstone
Ogallala Group or Formation (Phanerozoic | Cenozoic | Tertiary | Miocene) at surface, covers 90 % of this area: Silt, sand, sandstone, gravel and conglomerate. Predominantly interfingered fine- to coarse grained, poorly sorted, arkosic, fluvial deposits of light-gray, light-olive-gray, and grayish-green calcareous silt and sand, and locally poorly consolidated conglomerate, sandstone, and siltstone.
Lithology: mudstone; sandstone; volcanic ash