The "basalt of Shumaker Creek." Informal unit in Eckler Mountain Member of Wanapum Basalt of Yakima basalt subgroup [informal] of Columbia River Basalt Group. Named for a flow prominently exposed in roadcuts above the "basalt of Dodge" at the head of Shumaker Creek (see fig. 1, loc. 12), in extreme southeast corner of sec. 11, T. 7 N., R. 45 E., Black Butte quadrangle, Asotin County, Washington. Consists of one or two aphyric flows that are also low in Fe and Ti but considerably higher in alkalis and lower in Mg than the Dodge. Is similar in appearance to many flows of the Grande Ronde Basalt, however, is distinctly lower in Mg than the Grande Ronde chemical type. Its distribution is poorly known; [thickness not stated]. Age is middle Miocene. Has normal magnetic polarity (citing McKee and others [abs.], 1977, GSA Abs. with Prog., v. 9, no. 4, p. 463-464).
[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.]

Source: Publication; US geologic names lexicon (USGS Bull. 1564, p. 53); Changes in stratigraphic nomenclature, 1979 (USGS Bull. 1502-A, p. A24).