Usage:
Spearfish Formation (MT*,NE*,ND*,SD*,WY*)
Subunits:
(alphabetical): Belfield Member (ND), Pine Member (ND) or Pine Salt Member (MT,ND), Saude Member (ND,SD).
Geologic age:
Permian, Late*
Triassic, Early*
Triassic, Middle
Triassic, Late(?)
Type section, locality, area and/or origin of name:
Not designated. Origin of name not stated by author, but probably named from Spearfish, Lawrence Co., SD (Darton, 1899).
AAPG geologic province:
Williston basin*
Powder River basin*
Chadron arch*
Denver 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 ([ ]).