Geologic Unit: Colorado

Usage:

Colorado Group (CO*,IA*,KS*,MN*,MT*,NE*,NM,ND*,OK*,SD*,UT*,WY*)
Colorado Shale (MT*,NM*,WY*)
Colorado Formation (ID*,MT*,TX*,UT*,WY*)
(†Colorado Shale or †Colorado Formation not used by the CO Geol. Survey.)

Subunits:

GROUP STATUS (alphabetical): Blackleaf Formation (MT*), Belle Fourche Formation (ND) or Belle Fourche Shale (ND,SD), Benton Formation (CO*,MT*,NM*,SD*,WY*) or Benton Shale (CO*,MN*,MT*,NE*,NM,ND*,SD*,WY*), Carlile Shale (CO*,IA*,KS*,MN*,MT*,NE*,NM*,ND*,OK*,SD*,WY*), Coberly Formation (MT*), Dunkleberg Formation (MT), Frontier Formation (MT*,WY), Graneros Shale (CO*,IA*,KS*,MN*,MT*,NE*,NM,ND*,OK*,SD*,WY*), Greenhorn Formation (MN*,MT*,ND*,SD*,WY*) or Greenhorn Limestone (IA*,CO*,KS*,MT*,NE*,NM*,ND*,OK*,SD*,WY*) or Greenhorn Shale (MT*), Holter Sandstone (MT), Marias River Shale (MT*), Mowry Shale (MT*,ND*,SD*,UT,WY*), Niobrara Chalk (KS*) or Niobrara Formation (CO*,KS*,NE*,NM,ND*,SD*,WY*) or Niobrara Marl (SD) or Niobrara Shale (MT*,ND*), Thermopolis Shale (WY), Warm Creek Shale (MT).

FORMATION STATUS (alphabetical): Arrow Creek Member (MT*), Belle Fourche Member (MT*,WY), Big Elk Sandstone Member (MT*), Carlile Member (CO*,MT*,NM*), Fall River Sandstone Member (MT*,WY*), /Greenhorn Bentonite Bed (MT), Greenhorn Limestone Member (MT*), Mosby Sandstone Member (MT*), Mowry Member (MT,WY), Newcastle Sandstone Member (MT*), Niobrara Member (MT*), Skull Creek Member (MT*), Telegraph Creek Member (MT).

Geologic age:

early Late Cretaceous (Cenomanian)*

Type section, locality, area and/or origin of name:

Named from exposures along eastern base of Colorado or Front Range, CO (Hayden, 1876).

AAPG geologic province:

Basin-and-Range province*
Chadron arch*
Williston basin*
Powder River basin*
Montana folded belt*
Central Montana uplift*
Sweetgrass arch*
Denver basin*
Bighorn basin*