National Geologic Map Database

Geologic Unit: Fort Union


Fort Union Formation (CO*,MT*,ND*,SD*,WY*)
Fort Union Group (ND,SD)


GROUP STATUS (alphabetical): Bullion Creek Formation (ND), Cannonball Formation (ND,SD), Lebo Formation (SD), Ludlow Formation (ND,SD), Sentinel Butte Formation (ND), Slope Formation (MT,ND), Tongue River Formation (MT,ND), Tullock Formation (MT).

FORMATION STATUS (alphabetical): Badger coal bed (informal) (WY), Badwater unit (informal) (WY), Belfry Member (MT), Blue Gap Member (CO*,WY*), Cannonball Member (ND*,SD*), China Butte Member (CO*,WY*), Fort Kipp Lignite Bed (MT), Fort Peck Lignite Bed (MT), Kingsbury Conglomerate Member (WY), Kleenburn Member (WY), [Lakeside Clay, unranked (MT)], Lebo Member (MT,ND,WY*) or Lebo Shale Member (MT*,SD), Ludlow Member (MT*,ND*,SD*), Overland Member (CO*,WY*), Sentinel Butte Member (MT,ND*,SD), Shotgun Member (WY*), Tongue River Member (MT*,ND*,SD*,WY*), Tullock Member (MT*,SD,WY*), Waltman Shale Member (WY*).

Geologic age:

early Tertiary (Paleocene)*; locally, in SD and MT, Late Cretaceous (Maastrichtian)*

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

Named from exposures at Old Fort Union [later called Fort Buford, and now town of Buford], near mouth of Yellowstone River, McKenzie Co., ND (Meek and Hayden, 1862).
Reference section: measured north of Hoppers Station near abandoned townsite of Cokedale, [in area between Grassy and Canyon Mountains, Gallatin National Forest, Park County, Montana], in secs. 7, 16, 17, 21, 28, 32, and 33, T. 1 S., R. 8 E.; secs. 2, 3, 11, 12, 13, and 23, T. 2 S., R. 8 E.; and secs. 7, 18, 19, and 20, T. 2 S., R. 9 E., [from about Lat. 45 deg. 45 min. 49 sec. N., Long. 110 deg. 47 min. 11 sec. W. to Lat. 45 deg. 38 min. 50 sec. W., Long. 110 deg. 38 min. 32 sec. W., Grassy Mountain and Hoppers 7.5-min quadrangles, Gallatin National Forest], Park Co., MT (Roberts, 1972).

AAPG geologic province:

Bighorn basin*
Central Montana uplift*
Green River basin*
Piceance basin*
Powder River basin*
Uinta basin*
Williston basin*
Wind River basin

For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.

Asterisk (*) indicates published by U.S. Geological Survey authors.

"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).

Slash (/) indicates name does not conform with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005). This may be explained within brackets ([ ]).