Pg. 23 (fig. 1), 40 (table 2), 48. Grouse Creek unit (informal) in Grande Ronde Basalt of Columbia River Basalt Group. Consists of 10+ flows; typically aphyric with rare orthopyroxene. Has reversed magnetic polarity (in R2 magnetostratigraphic unit). Lies above Wapshilla Ridge unit (informal) and below Meyer Ridge unit (informal); both in Grande Ronde Basalt. Age is early Miocene.
Named after exposures described by Ross (1978, Univ. Idaho PhD thesis) on Grouse Creek in Troy basin area of northeastern OR.
Reference locality: Grouse Creek on north side of Grande Ronde River, in T. 7 N., R. 43 E., Troy quadrangle, WA. [Misprint (table 2, p. 40): T. 7 N., R. 43 E. is in Saddle Butte quadrangle, WA; Troy is adjacent quadrangle to south (Twps. 5 and 6) and is almost entirely in OR.]
[Grouse Creek, btw. approx. Lat. 46 deg. 02 min. 02 sec. N., Long. 117 deg. 27 min. 48 sec. W., in SE/4 sec. 31, T. 7 N., R. 43 E., Saddle Butte 7.5-min quadrangle, Asotin Co., southeastern WA, and approx. Lat. 45 deg. 59 min. 12 sec. N., Long. 117 deg. 23 min. 47 sec. W., in NE/4 sec. 23, T. 6 N., R. 43 E., Troy 7.5-min quadrangle, Wallowa Co., northeastern OR (USGS historical topographic map collection TopoView, accessed September 18, 2013).]

Source: Publication.