Named as basal formation of five named formations of Libby Creek Group for distinctive outcrops along the Continental Divide and south wall of Cow Creek, Carbon Co, WY, Northern Rocky Mountain region. No type locality designated. Consists of coarse conglomerate of well rounded, 10 to 50 cm granitic, mafic, and quartzite clasts in a quartzitic to amphibolitic matrix. Clasts may be spheroids as in the Cow Creek area to severely stretched ellipsoidal disks at Bridger Peak. The quartzite matrix consists of lenticular grains of quartz + plagioclase +/-microcline +/-biotite, and muscovite. Greater than 300 m thick. Garnet-biotite-hornblende schist, quartz pebble conglomerate, quartzitic and arkosic wacke with graded bedding occur as lenses and interbeds. Is younger than Green Mountain Formation (new). Is older than Bridger Peak Quartzite (new) of Libby Creek Group. Assigned a Proterozoic age. Geologic map; mapped with other formations of the Libby Creek Group. Stratigraphic diagram.

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