Frontier Formation  search
BTChronostratigraphic Units
 .Phanerozoic
 ..Mesozoic
 ...Cretaceous
 ....Upper Cretaceous
 .....Frontier Formation
RTIdaho
 Utah
 Wyoming
 Montana
 Colorado
 Colorado Group
 Mancos Shale
 Tununk Member
 Wall Creek Member
SNIn Colorado Group or Mancos Shale. S Montana, and W Wyoming, Colorado, Idaho, Utah.