Hell Creek Formation  search
BTChronostratigraphic Units
 .Phanerozoic
 ..Mesozoic
 ...Cretaceous
 ....Upper Cretaceous
 .....Hell Creek Formation
RTMontana
 North Dakota
 South Dakota
SNIncludes Bull Creek Sand, Isabel-Firesteal Coal Member. E, N, and central S Montana; SW North Dakota; and NW and N South Dakota.