Pg. 12, 27, 36 (table 6). Black Knob quartzite [informal, unranked] in Patcheta member of Lowell formation of Bisbee group. Division 9a, greenish quartzite in places overlain with buff and white speckled sandstone. Contains large silicified tree trunks (ARAUCARIOXYLON). Whitish-gray limestone at base. Thickness in Ninety One Hills area 30 feet; on Black Knob Ridge, where it consists of buff and white quartzite beds, 412 feet. Top division of Pacheta member. Underlies Joserita member (new) and overlies Black Knob dolomite (new). Age is Early Cretaceous (Aptian); PARAHOPLITES MELCHIORIS standard ammonite zone.
[Occurs in southern Mule Mountains (Black Knob Ridge section), north of International Monument No. 89, in N/2 sec. 14, T. 24 S., R. 25 E., Bisbee 15-min quadrangle, Cochise Co., southeastern AZ. Also occurs in the Ninety One Hills area, local name for hills in secs. 14 and 23, T. 24 S., R. 24 E., immediately north of International border in vicinity of International Monument No. 91, southeast of Bisbee Junction on Southern Pacific RR, Bisbee 15-min quadrangle, Cochise Co., southeastern AZ; area includes type locality and standard section of Lowell Formation.]

Source: Publication; US geologic names lexicon (USGS Bull. 1200, p. 367).