Tongue River Member  search
BTChronostratigraphic Units
 .Phanerozoic
 ..Cenozoic
 ...Paleogene
 ....Paleocene
 .....Tongue River Member
RTWyoming
 Montana
 North Dakota
 South Dakota
 Fort Union Formation
SNIn Fort Union Formation. In Montana and North Dakota, composed of light-yellow, tan, and gray sandstones and shales; thin lenses of limestone; and numerous beds of lignite. Found in E Montana, SW North Dakota, South Dakota and NW Wyoming.