Geologic units in Wallace county, Kansas

Loess (Holocene to Pleistocene) at surface, covers 74 % of this area

eolian silts

Ogallala Formation (Miocene) at surface, covers 13 % 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

Pierre Shale (Late Cretaceous) at surface, covers 10 % of this area

Thin bedded gray to brownish gray shale; contains concretions, selenite crystals, thin beds of bentonite and locally chalky beds.

Alluvium (Holocene to Pleistocene) at surface, covers 3 % of this area

unconsolidated sand, silt, clay, and gravel

Niobrara Chalk (Late Cretaceous) at surface, covers 1 % of this area

Interbedded, soft, light-gray calcareous shale and chalk

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