- Usage in publication:
-
- Gunsight Formation*
- Modifications:
-
- Named
- Dominant lithology:
-
- Quartzite
- AAPG geologic province:
-
- Northern Rocky Mountain region
Summary:
Named for exposures on south and west sides of Gunsight Peak in T14N, R24E in the central part of the Lemhi Range, Patterson quad, ID in Northern Rocky Mountain region. These exposures are the type locality. Upper formation (of 5) of Lemhi Group. Composed of brownish-gray, fine-grained, feldspathic quartzite with silty or muddy partings throughout; has abundant magnetite concentrated as laminae and cross-laminae; some beds deformed by penecontemporaneous slumping. Maximum thickness 6,000 ft (1,830 m). Overlies Apple Creek Formation gradationally; underlies Swauger Formation, or where Swauger eroded underlies Kinnikinic Quartzite. Exposed across Lemhi Range and south toward Gilmore mining area. Tentatively correlated with upper Helena and Wallace Formations and lower Missoula Group, all of Belt Supergroup.
Source: GNU records (USGS DDS-6; Denver GNULEX).
- Usage in publication:
-
- Gunsight Formation*
- Modifications:
-
- Age modified
- AAPG geologic province:
-
- Idaho Mountains province
Summary:
Age of the Gunsight Formation of the Lemhi Group is Middle Proterozoic.
Source: GNU records (USGS DDS-6; Menlo GNULEX).
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 ([ ]).