Geologic units in Hanson county, South Dakota

Carlile Shale (Upper Cretaceous) at surface, covers 41 % of this area

Dark-gray to black, silty to sandy shale with several zones of septarian, fossiliferous, carbonate concretions. Contains up to three sandstone units in the upper portion of the formation and sandy calcareous marl at the base. Thickness up to 330 ft (100 m).

Niobrara Formation (Upper Cretaceous) at surface, covers 31 % of this area

White to dark-gray argillaceous chalk, marl, and shale. Weathers yellow to orange. Contains thin, laterally continuous bentonite beds, chalky carbonaceous shale, minor sand, and small concretions. Thickness up to 150 ft (46 m).

Sioux Quartzite (Lower Proterozoic) at surface, covers 27 % of this area

Pink and reddish to tan, siliceous, fine- to coarse-grained, iron-stained orthoquartzite with minor metamorphosed conglomerate and mudstone layers. Estimated thickness greater than 1,000 ft (305 m).