Geologic Unit: Sentinel Bluffs

Usage:

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

Geologic age:

late Tertiary (middle Miocene)*

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

Type locality: along Sentinel Bluffs on east side of Columbia River at Sentinel Gap, in Saddle Mountains, in SE/4 sec. 10, T. 15 N., R. 23 E., Beverly 7.5-min quadrangle, [Grant Co.], Pasco basin, central southern WA (Myers and others, 1979; Reidel and others, 1989; Reidel, 2005).
Reference localities (Reidel and others, 1989): (1) Columbia Hills water gap (Ortley anticline), in secs. 5 and 6, T. 2 N., R. 13 E., Dalles North 7.5-min quadrangle, [Klickitat Co.], southern WA; and (2) Mt. Zion quarry above WA State Highway. 14, in NE/4 sec. 9, T. 1 N., R. 5 E., Bridal Veil 7.5-min quadrangle, [Skamina Co.], southern WA.

AAPG geologic province:

Eastern Columbia basin*