Geologic Unit: Umtanum

Usage:

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

Informal. The rank or lithologic term should not be capitalized. [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).]

Geologic age:

late Tertiary (middle Miocene)*

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

Reference localities: Umtanum Ridge above Priest Rapids dam, in sec. 12, T. 13 N., R. 23 E., [Priest Rapids 15-min quadrangle, Yakima Co., central southern WA]; and (2) Saddle Mountains, in sec. 2, T. 15 N., R. 23 E., [Beverly 15-min quadrangle, Grant Co., central southern WA] (Reidel and others, 1989).

AAPG geologic province:

Eastern Columbia basin*