Geologic units in Sheridan county, Kansas

Loess (Phanerozoic | Cenozoic | Quaternary | Pleistocene Holocene) at surface, covers 78 % of this area: eolian silts
Lithology: silt
Alluvium (Phanerozoic | Cenozoic | Quaternary | Pleistocene Holocene) at surface, covers 6 % of this area: unconsolidated sand, silt, clay, and gravel
Lithology: gravel; sand; silt; clay or mud
Ogallala Formation (Phanerozoic | Cenozoic | Tertiary | Miocene) at surface, covers 16 % of this area: massive to cross-bedded, generally arkosic sand, silt and gravel, locally cemented with calcium carbonate; also contains limestone, volcanic ash, diatomaceous marl, opaline sandstone and bentonitic clay
Lithology: arkose; limestone; volcanic ash; carbonate; sandstone; claystone