Usage:
Grinnell Formation of Ravalli Group of Belt Supergroup (MT*-local)
Grinnell Argillite (MT*-local)
Exposures in the U.S. confined to Glacier National Park and adjacent areas, Glacier Co., MT.
Geologic age:
Mesoproterozoic*
Type section, locality, area and/or origin of name:
Type locality: Mount Grinnell, at head of Swift Current Valley, Glacier National Park, Glacier Co., northwestern MT, where it is 1,800 feet thick. Also well exposed on Appekunny and Robertson Mountains (Willis, 1902).
AAPG geologic province:
Northern Rocky Mountain region*
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 ([ ]).