"It is confusing, from McKee's text and fig. 1 whether the tongue is assigned to the Muav formation or to the Bright Angel shale" (GNC note, n.d.). Garnet Canyon tongue of Sanup Plateau member of Muav formation of Tonto group (USGS Bull. 1200); Garnet Canyon tongue [of Bright Angel shale of Tonto group] (USGS DDS-6).
Pg. 14 (fig. 1), 29, 92. Rusty-brown or snuff-colored dolomite unit. (= Noble's, 1922, USGS Prof. Paper 131-B, snuff-brown limestone.) Grades laterally into limestone to the west and into clastic sediments toward the east. Thickness averages about 12 feet. Older than Lava Falls tongue (new); younger than Elves Chasm tongue (new). Carries linguloid brachiopod fauna. [On p. 29 age stated to be Early and Middle Cambrian and on p. 184 (part 2) Middle Cambrian. Age is considered Early and(or) Middle Cambrian.] Report includes cross section.
Type locality not designated. Is upper of two very conspicuous dolomite units which form low but persistent cliffs from Garnet Canyon to Hermit Creek in eastern Grand Canyon [Coconino Co., northwestern AZ].

Source: US geologic names lexicon (USGS Bull. 1200, p. 1474); supplemental information from GNU records (USGS DDS-6; Menlo GNULEX, Denver GNULEX), GNC index card files.