Pg. 14 (fig. 1), 29, 101-102. Boucher tongue of [see below]. Composed of thin beds of rusty-brown dolomite. On fresh surface, dolomite appears steely gray and typically even grained, with crystals averaging 0.25 or 0.30 mm. In places, grades into brownish siltstone. Younger than Parashant tongue (new). [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.]
Extends southeastward from vicinity of Garnet Canyon at least as far as Cottonwood Canyon, a distance of 25 mi, Grand Canyon area [Coconino Co., northwestern AZ].
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GNC note (n.d.): "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";
US geologic names lexicon (USGS Bull. 1200, p. 438, 1966): Boucher tongue [of Muav formation];
GNU records (USGS DDS-6; Denver GNULEX, 1989, Menlo GNULEX, 1990): Boucher tongue [of Bright Angel shale].

Source: US geologic names lexicon (USGS Bull. 1200, p. 438); supplemental information from GNU records (USGS DDS-6; Menlo GNULEX, Denver GNULEX), GNC index card files.