Geologic units in Decatur county, Kansas

Loess (Holocene to Pleistocene) at surface, covers 69 % of this area

eolian silts

Ogallala Formation (Miocene) at surface, covers 18 % 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 13 % of this area

unconsolidated sand, silt, clay, and gravel

Ogallala Group or Formation (Miocene) at surface, covers 0.3 % 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.

Pierre Shale (Late Cretaceous) at surface, covers < 0.1 % of this area

Mostly medium to dark-gray, brownish-gray, and black, fissle clay shale. Locally grades to thin beds of calcareous, silty shale or claystone, marl, shaly sandstone, and sandy shale. Locally contains thin seams of gypsum and sparse selenite crystals. Approx. max thickness 1970 ft.