- Usage in publication:
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- Yankee Fork rhyolite member*
- Modifications:
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- Named
- Dominant lithology:
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- Rhyolite
- AAPG geologic province:
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- Idaho Mountains province
Summary:
Named as an upper member of Challis volcanics for exposures in ridges encircling the head of Yankee Fork (T15N, R13E), Casto quad, Custer Co, ID, Idaho Mountains province. No type locality designated. Is a brown rhyolite and interbedded light-colored tuff. Is much eroded in quad. Thickness: in vicinity of Yankee Fork less than 1,000 ft; south of Cougar Creek ranger station 500 ft; at Castle Rock, about 2 1/2 mi south of Meyers Cove 1,600 ft. Crops out over only about 19 sq mi, but covers extensive area farther east. Is younger than main part of Challis and older than Quaternary glacial units. Regarded as Oligocene? age. Geologic map.
Source: GNU records (USGS DDS-6; Denver GNULEX).
- Usage in publication:
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- Yankee Fork Rhyolite Member*†
- Modifications:
-
- Abandoned
Summary:
†Yankee Fork Rhyolite Member of Challis Volcanics (Eocene) abandoned; name fallen into disuse. Three map units (Tic, intrusive complex; Tdc, dome complex rocks; Tdi, Tdc, dome intrusive rocks) were formerly considered part of the Yankee Fork. In other areas of the Idaho Mountains province, other rhyolitic rocks also assigned to Yankee Fork.
Source: Modified from GNU records (USGS DDS-6; Denver 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 ([ ]).