Pg. G6-G7 (fig. 2), G42. Wilbur Creek Member of Saddle Mountains Basalt of Yakima basalt subgroup [informal] of Columbia River Basalt Group. Occurs on Uniontown Plateau and in Lewiston basin, southeastern Washington. Sparsely plagioclase-phyric and fine grained basalt. Conformably overlies Umatilla Member of Saddle Mountains Basalt or unconformably overlies Priest Rapids Member of Wanapum Basalt; unconformably underlies Asotin Member of Saddle Mountains Basalt. Distinguished from Umatilla Member by its somewhat coarser grain size and from Asotin Member by its near lack of olivine phenocrysts. Thickness 45+ m in type area; elsewhere is generally less than 20 m. Has normal magnetic polarity. Age is middle Miocene.
Type locality: series of roadcuts along Wilbur Creek, in sec. 9 and SW/4 SW/4 sec. 4, T. 14 N., R. 44 E., about 7 km west of Pullman, Ewartsville quadrangle, Whitman Co., southeastern WA, [approx. Lat. 46 deg. 43 min. 30 sec. N., Long. 117 deg. 17 min. 20 sec. W.].
Reference locality (Camp, 1976): in roadcuts in the Cloverland Grade section, from 506 to 540 m (1,660 to 1,770 ft) elevation, in NW/4 SW/4 sec. 25 and NE/4 SE/4 sec. 26, T. 10 N., R. 45 E., Asotin quadrangle, Asotin Co., southeastern WA, [approx. Lat. 46 deg. 18 min. 51 sec. N., Long. 117 deg. 07 min. 23 sec. W.]
[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.]
[Additional locality information from ACME Mapper 2.0, accessed February 22, 2011.]

Source: Publication; US geologic names lexicon (USGS Bull. 1564, p. 186); Changes in stratigraphic nomenclature, 1979 (USGS Bull. 1502-A, p. A85).