Is named as youngest formation of Ash Creek group (new) of Yavapai series for Grapevine Gulch, Yavapai Co, AZ [secs 2, 3, 10, and 11, T14N, R2E], Southwestern Basin-and-Range region. No type locality designated. Is probably 8,000-10,000 ft thick. Contains six map units: 1) coarse-grained tuffaceous sedimentary rock; 2) fine-grained tuffaceous sedimentary rock with chert; 3) volcanic breccia; 4) jasper-magnetite beds; 5) dacite flows and intrusives; and 6) andesite flows. Unit 1 is poorly bedded, layers range from 4 to 50 ft thick, contains gray or greenish-black lithic tuffs. Lithic fragments are rhyolite, dacite, and andesite, and the matrix is dark. Unit 2 is well bedded, locally cross-bedded and channeled. Unit 3 has angular to subangular fragments of lava, 2-4 inches diameter in a matrix of small lava chips and crystals. Unit 4 occurs throughout formation and has no stratigraphic significance. Unit 5 is extensive in eastern exposures. Is dark gray. Rests on and intertongues with Deception rhyolite (new) of Ash Creek group. Top not exposed. Is older Precambrian. Geologic map.

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