Usage:
No current usage.
(†Agency zone (informal) (SD) combined with overlying and partly equivalent †Oacoma zone (informal) (SD) to form the †Agency-Oacoma zone (informal) of †Sully Member of Pierre Shale (SD); this unit was later replaced with DeGrey Member of Pierre Shale. See DeGrey.)
Geologic age:
Late Cretaceous
Type section, locality, area and/or origin of name:
Named from Cheyenne River Agency [in T. 12 N., R. 31 E., Dewey Co., SD], where it is well exposed. Unit extends up Missouri River to within a few mi of mouth of Moreau River, down the Missouri below mouth of Cheyenne River [in Armstrong Co., SD], and some distance up Cheyenne River (Russell, 1930).
Type section: measured at highway bridge across the Missouri River, below Whitlocks Crossing and Cheyenne Agency, southeastern Dewey Co., SD (Searight, 1937).
AAPG geologic province:
Sioux uplift
Williston 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 ([ ]).