Named as one of seven members of Twin Creek Limestone for Rich Co, UT on Wasatch uplift. Type section designated on north side Birch Creek 8 mi west of Woodruff near line of secs 18 and 19, T9N, R6E. Is 425 ft thick at type. Previously called member C of Twin Creek. Base marked topographically by shallow depression at top of thick-bedded limestone of Sliderock Member (new) of Twin Creek. Top marked by change from gray silty, shaly limestone to red siltstone, gray limestone or siltstone of Boundary Ridge Member (new) of Twin Creek. Weathers to pencil-like splinters. Thickens west from less than 100 ft in eastern exposures in western WY, Greater Green River basin to about 380 ft at Willow Creek, Bonneville Co, ID, Snake River basin, and in UT from 40 ft on Whiterocks River, Uintah Co, Uinta basin to 500+ ft near Devils Slide, Morgan Co on Wasatch uplift. Thins south in UT to 180 ft near Thistle, Utah Co. Is 425 ft thick at type. Composed mostly of gray shaly limestone that is soft at base, becoming hard upward. Is clayey and fossiliferous to east; calcareous and poorly fossiliferous to west. Detailed listing of fossils (pelecypods, gastropods, cephalopods). Probably late Bajocian, Middle Jurassic shallow sea deposit. Correlation with Sawtooth, Piper, Gypsum Spring, and Carmel Formations shown on chart and cross sections.

Source: GNU records (USGS DDS-6; Denver GNULEX).

Is one of seven members of Twin Creek Limestone. Conformably overlies Sliderock Member of Twin Creek and conformably underlies Boundary Ridge Member in Snake River basin, ID, Yellowstone province, WY, Wasatch uplift, Uinta basin and Uinta uplift, UT. Correlation charts include information on thickness and lithology. Wedges out between Whiterocks River Canyon and Vernal, Uintah Co, UT in the Uinta basin. Correlates with middle part, Twelvemile Canyon Member of Arapien Shale. Of late Bajocian, Middle Jurassic age.

Source: GNU records (USGS DDS-6; Denver GNULEX).