Pg. 14 (fig. 1), 19, 84-87. Rampart Cave member of Muav formation. This facies is of uniform character over a wide area, but changes abruptly to the east (dolomite) and south (algal). Consists almost entirely of gray or dark-gray aphanitic limestone with small amount of light-brown or tan silty mottling. Mostly thick-bedded and massive, although thin beds found at top and bottom in many sections. In vicinity of Grand Wash Cliffs, maximum thickness about 160 feet. Thins to the east. Basal subdivision of Muav formation; overlies Flour Sack member (new ) of Bright Angel shale. Age is Middle Cambrian, based on fossils (trilobites) identified by C.E. Resser. Report includes measured sections, cross sections, faunal list.
Type locality not designated. Named from a cavern near base of member, a few mi east of Grand Wash Cliffs on south side of Lake Mead, [Mohave Co., northwestern AZ]. In western half of Grand Canyon.

Source: US geologic names lexicon (USGS Bull. 1200, p. 3195); supplemental information from GNU records (USGS DDS-6; Menlo GNULEX, Denver GNULEX), GNC index card files.