Onaway Member of Wanapum Basalt of Columbia River Basalt Group. Present in Potlatch River area of the Clearwater embayment, western Idaho and eastern Washington. Consists of several flows of medium- to coarse-grained basalt containing plagioclase phenocrysts extruded from vents extending from Palouse, Washington, to Potlatch, Troy, and Joel, Idaho. Has normal polarity. The informal basalt of Potlatch is the only mappable flow in the member. The Onaway is at the top of the Wanapum and contains flows that lie both below and above the Priest Rapids Member of the Wanapum; hence the Wanapum-Saddle Mountains Basalt contact is redefined at the top of the Onaway. Age is late Miocene.
Type locality: Potlatch River area near and around Onaway, [Potlatch 7.5-min quadrangle], Latah Co., ID. [Extends into Whitman Co., WA.]

Source: US geologic names lexicon (USGS Bull. 1565, p. 230); GNU records (USGS DDS-6; Denver GNULEX).