Named as a member (one of ten) of the Frontier formation for poorly exposed rocks in lower drainage of Grass Creek valley near Echo Reservoir, Summit Co, UT on the Uinta uplift. No type locality designated. Extends north from Coalville area. Intertongues with Hilliard shale south of UT-WY state line. Consists of a basal 600-700 ft thick lenticular coarse-grained sandstone and reddish clay shales of fluviatile origin, and an upper part 275 to 325 ft thick of thin-bedded tan sandstone that alternates with thin layers of gray shale. Overlies Dry Hollow member (new) of Frontier. Has fossils of early Niobrara, middle Coniacian, or Late Cretaceous age. Cross sections. Correlation chart. Shown as equivalent to lower part of Hilliard of the Cumberland Gap area.

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