Named as a tongue of the Mancos Shale for exposures along eastern cliff face of Black Mesa at head of Wind Rock valley, Apache Co, AZ in Black Mesa basin. Type section located at 36 deg 21' 30" Lat N, 109 deg 49' 36" Long W. Is present only in northern part of Black Mesa. Has no subsurface continuation because of Tertiary erosion. Is composed of interbedded gray siltstone, mudstone, and sandstone in lower part and massive gray sandstone in upper part. Ranges from 0-75 ft thick. Thins progressively from north to south. Overlies lower carbonaceous member of Wepo Formation unconformably. Lower contact placed at a color change from dark brown of Wepo to olive gray of Wind Rock. Underlies Rough Rock Sandstone (new) gradationally. Upper contact placed at base of highest mudstone which marks base of massive cliff-forming sandstone of Rough Rock. Is a marine unit that was deposited on a stable platform. Contains fossils of Inoceramus deformis zone of Coniacian, or Late Cretaceous age. Was mapped as part of Wepo in earlier reports.

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