Pg. 14 (fig. 1), 29, 94-95. Spencer Canyon member of Muav formation of Tonto group. Medium- to dark-gray aphanitic limestone, mottled with red-brown siltstone. Average thickness about 40 feet. Beds comprising basal 20 feet are thick, massive, and cliff-forming; next 10 feet is thin-bedded and frequently weathers into a slope; uppermost 10 feet resembles bottom part and is also cliff-forming. Youuger than Sanup Plateau member (new); older than Peach Springs member (new). Interfingers with Bright Angel shale. No fossils found. Age is Middle Cambrian, based on stratigraphic position. Report includes measured sections, cross sections.
Type locality not designated. Extends eastward from Grand Wash Cliffs almost to Diamond Creek; in Grand Canyon [Mohave and Coconino Cos., northwestern AZ].

Source: US geologic names lexicon (USGS Bull. 1200, p. 3682); supplemental information from GNU records (USGS DDS-6; Menlo GNULEX, Denver GNULEX), GNC index card files.