| View from Sheep Mountain Table in Badlands  National Park. A thin frosting of snow highlights a formation boundary between  the Chadron and Brule Formations of the White River Group (of Eocene and  Oligocene age, respectively). Sedimentary formations of the White River Group  extend across western South Dakota, east of the Black Hills into Nebraska in the  Sand Hills region, and correlate with other sedimentary basins in Wyoming. |