In southwest South Dakota and northwest Nebraska, these fossils are characteristic of the White River Badlands (including Badlands National Park), though they can be found far beyond the limits of the White River watershed.
Exposures are less well-investigated in northeast Colorado and scattered sites across western North Dakota.
Animals from the White River Group date from the Eocene and Oligocene epochs.
The fauna is representative of four North American Land Mammal Ages (NALMAs): Indeterminate iguanid, skink, and diploglossine (galliwasp) fossils are also known from the White River Group.
[5] Indeterminate fossils of an anosteirine carettochelyid and a ptychogastrin geoemydid are also known from the White River Group.