Chadron Formation  search
BTChronostratigraphic Units
 .Phanerozoic
 ..Cenozoic
 ...Paleogene
 ....Chadron Formation
RTWyoming
 Colorado
 Nebraska
 South Dakota
 White River Group
 upper Eocene
 lower Oligocene
 Chadronian
SNUpper Eocene to lower Oligocene. In White River Group. NE Colorado, W Nebraska, W South Dakota, and E Wyoming. Age was previously considered lower Oligocene. Indexed with upper Eocene and/or lower Oligocene as applicable.