Geologic units in Campbell county, South Dakota

Pierre Shale (Upper Cretaceous) at surface, covers 86 % of this area

Blue-gray to dark-gray, fissile to blocky shale with persistent beds of bentonite, black organic shale, and light-brown chalky shale. Contains minor sandstone, conglomerate, and abundant carbonate and ferruginous concretions. Thickness up to 1,000 ft (305 m).

Fox Hills Sandstone (Upper Cretaceous) at surface, covers 14 % of this area

Bluish-green to green, white to dark-gray, and yellow to tan, carbonaceous and iron-stained, cross-bedded, very fine- to coarse-grained, glauconitic sandstone and siltstone. Interbedded with gray and green to brown shale and siltyshale. Thickness up to 200 ft (61 m).

Pierre Formation (Upper Cretaceous) at surface, covers < 0.1 % of this area

Dark-gray shale; marine offshore sediment; as thick as 700 metres (2,300 feet).

Fox Hills Formation (Upper Cretaceous) at surface, covers < 0.1 % of this area

Olive-brown sand, shale, and sandstone; marine shoreline and off-shore sediment; as thick as 120 metres (400 feet).