Usage:
Fort Rock Formation (OR*)
Subunits:
Pettus Lake Member (OR).
Geologic age:
Pliocene*
Type section, locality, area and/or origin of name:
Type section: in NE/4 SW/4 sec. 33, T. 27 S., R. 17 E., on west side of Seven Mile Ridge, Lake Co., south-central OR. Named from Fort Rock, a remnant of an eruptive center of this unit, which rises above valley plains as mesalike butte in secs. 29 and 30, T. 25 S., R. 13 E. Characteristic exposures also at Table Rock Butte and Fandango Canyon-St. Patrick Mountain area (Hampton, 1964).
AAPG geologic province:
Southern Oregon 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 ([ ]).