Geologic Unit: Frenchman Springs

Usage:

Frenchman Springs Member of Wanapum Basalt of Columbia River Basalt Group (OR*,WA*)
Frenchman Springs Member of Wanapum 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).]

Subunits:

(alphabetical) --all informal flows in OR*,WA*: basalt of Gingko, basalt of Lyons Ferry, basalt of Palouse Falls, basalt of Sand Hollow, basalt of Sentinel Gap, basalt of Silver Falls.

Geologic age:

late Tertiary (middle Miocene)*

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

Type locality: in Frenchman Springs Coulee [Frenchman Coulee], in secs. 19, 20, and 21, and secs. 29 and 30, T. 18 N., R. 23 E., [Evergreen Ridge 7.5-min quadrangle], Grant Co., south-central WA (Mackin, 1961; see also Swanson and others, 1979).
Reference localities (Swanson and others, 1979):
(1) in roadcuts and natural exposures in Devils Canyon, south of Kahlotus, in the Kahlotus and Lower Monumental Dam quadrangles, WA;
(2) on both sides of Wallula Gap, WA;
(3) on the Maryhill grade along Highway 97 north of Biggs, OR;
(4) along the Deschutes River just north of Maupin, OR; and
(5) roadcuts and railroad cuts in Palouse Falls State Park, WA.

AAPG geologic province:

Eastern Columbia basin*