Dakota Formation(Phanerozoic | Mesozoic | Cretaceous-Early)at surface, covers 0.4 % of this area
White, gray, red, brown and tan kaolinitic claystone, mudstone, shale and siltstone interbedded with grayish to yellowish brown thick lenticular sandstone beds. It also contains lignite and sandstone is commonly well cemented with iron oxide and calcite.
Ogallala Formation(Phanerozoic | Cenozoic | Tertiary | Miocene)at surface, covers 1 % 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