Loess
(Holocene to Pleistocene) at surface, covers 92 % of this area eolian silts
Ogallala Formation
(Miocene) at surface, covers 8 % 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
Alluvium
(Holocene to Pleistocene) at surface, covers 0.8 % of this area unconsolidated sand, silt, clay, and gravel
Dune Sand
(Holocene to Pleistocene) at surface, covers < 0.1 % of this area unconsolidated dune sand
Eolian deposits
(Quaternary) at surface, covers < 0.1 % of this area Includes dune sand and silt and Peoria Loess
Ogallala Fm
(Tertiary) at surface, covers < 0.1 % of this area Loose to well-cemented sand and gravel
Niobrara Fm
(Cretaceous) at surface, covers < 0.1 % of this area Calcareous shale and limestone
