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National Geologic Map Database

Geologic Unit: Fergus

Usage:

Fergus Group (MT)


Subunits:

(alphabetical) --all in MT: Alaska Bench Formation, Bear Gulch Formation, Cameron Creek Formation, Tyler Formation.


Geologic age:

Late Mississippian (Chesterian)


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

Type section (composite), in ascending order: lower Tyler Formation, in NE/4 sec. 25, T. 13 N., R. 21 E. (Mundt, 1956); Bear Gulch Formation, in Bear Gulch, in SW/4 sec. 22, T. 14 N., R. 21 E.; upper Tyler Formation, in NE/4 sec. 30, T. 14 N., R. 21 E.; Cameron Creek Formation, in Cameron Creek, in sec. 31, T. 11 N., R. 21 E. (Gardner, 1959); and Alaska Bench Formation, near Beacon Hill, in SW/4 sec. 36, T. 13 N., R. 19 E., in Fergus Co. or adjacent Golden Valley Co., central MT. Named from Fergus Co. (Shepard, 1993).


AAPG geologic province:

Central Montana uplift


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 ([ ]).