Geologic Unit: Grande Ronde

Usage:

Grande Ronde Basalt of Columbia River Basalt Group (ID*,OR*,WA*)
Grande Ronde Basalt of /Yakima basalt subgroup [informal] of Columbia River Basalt Group (ID*,OR*,WA*)

[Yakima basalt subgroup considered informal and should not be capitalized. "Subgroup" not recognized as a formal stratigraphic rank term (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). Columbia River Basalt Group adopted by the ID, OR, and WA Geol. Surveys, and the USGS (rules suspended).]

Subunits:

(alphabetical): Field Springs member (informal) (WA*), Sentinel Bluffs Member (OR*,WA*), Slack Canyon member (informal) (OR*,WA*), Teepee Butte Member (ID*,OR*,WA*), Umtanum member (informal) (OR*,WA*), Winter Water member (informal) (OR*,WA*).

Geologic age:

late Tertiary (early to middle Miocene)*

Type section, locality, area and/or origin of name:

Type locality: prominent west-trending spur ridge, extending from NW/4 sec. 23 across N/3 sec. 22 to NE/4 sec. 21, T. 7 N., R. 46 E., Black Butte quadrangle, in the lower part of Grande Ronde River Valley, Asotin Co., extreme southeast WA (Swanson and others, 1979).
Reference localities (Swanson and others, 1979):
(1) in cliffs along Yakima River south of Ellensburg, in western part of Columbia Plateau, south-central WA;
(2) Crescent Bar, WA;
(3) Divide Ridge and Windy Point, Tieton River area, WA;
(4, 5) sections w/ minor faulting in Cow Canyon and Tygh Ridge, in southwest part of plateau, Wasco Co., northeast OR;
(6, 7) sections structurally undisturbed at Sherars Bridge, along Deschutes River (in T. 3 S., R. 14 and 15 E.), and Beef Hollow, northeast OR;
(8) along Butte Creek where interlayered contact of Grande Ronde and Picture Gorge is well exposed; and
(9) Ortley anticline, east of White Salmon, in the Columbia River Gorge, WA.

AAPG geologic province:

Eastern Columbia basin*