Usage:
Big Snowy Group (MT*,ND*)
Big Snowy Formation (ID*,MT*)
Subunits:
GROUP STATUS (alphabetical): Heath Formation (MT*,ND*) or Heath Shale (MT*), Kibbey Formation (ND,MT*) or Kibbey Limestone (ND) or Kibbey Sandstone (MT*,ND*), Otter Formation (MT*,ND*).
Geologic age:
Late Mississippian (Chesterian)*
Type section, locality, area and/or origin of name:
Named from extensive distribution and excellent exposures in Big Snowy Mountains, central MT (Scott, 1935).
Standard section, a composite of Stonehouse Ranch and State Road No. 25 sections: (1) upper part of section measured in secs. 31 and 32, T. 11 N., R. 21 E.; and (2) lower part of section measured in sec. 30, T. 11 N., R. 21 E., and sec. 25, T. 11 N., R. 20 E., Big Snowy Mountains, central MT (Gardner, 1959).
Type section (=reference section of Tyler Formation): along prominent cliff forming Alaska Bench (locally called Beacon Hill) extending secs. 25 through 36, T. 13 N., R. 19 E., and sec. 1, T. 12 N., R. 19 E., Fergus Co., central MT (Maughan and Roberts, 1967, citing Easton, 1962; Maughan, 1967).
AAPG geologic province:
Central Montana uplift*
Idaho Mountains province*
Montana folded belt*
Powder River basin*
Snake River basin*
Sweetgrass arch*
Williston 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 conflicts with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). May be explained within brackets ([ ]).