From abstract: Carnotite-bearing sandstone and claystone have been found in the Chadron formation of the White River group of Oligocene age in the southern part of the Slim Buttes area, Harding County, S. Dak. The carnotite is an efflorescent yellow coating on lenticular silicified sandstone. Locally, the mineralized sandstone contains 0.23 percent uranium. The uranium and vanadium ions are believed to have been derived from the overlying mildly radioactive tuffaceous rocks of the Arikaree formation of Miocene age. Analyses of water from 26 springs issuing from the Chadron and Arikaree formations along the margins of Slim Buttes show uranium contents of as much as 200 parts per billion. Meteoric water percolating through tuffaceous rocks is thought to have brought uranium and other ions into environments in the Chadron formation that were physically and chemically favorable for the deposition of carnotite.