Usage:
No current usage.
(Rocks of †Hannan Limestone (MT-local) reallocated to Madison Group. See Madison.)
Geologic age:
Early to Middle Mississippian (Tournaisian to Visean; Kinderhookian to Meramecian)
Type section, locality, area and/or origin of name:
Named from Hannan Gulch where Mississippian rocks form crest of both sides of gulch [Teton Co.]. Almost the complete section of the Hannan is exposed on north side of Sun River Canyon at south end of Castle Reef, which forms east side of Hannan Gulch, [in T. 22 N., R. 9 W., Sawtooth Ridge 7.5-min quadrangle, Teton Co., northwestern MT] (Deiss, 1943).
AAPG geologic province:
Montana folded belt
Sweetgrass arch
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 ([ ]).