Pg. 12, 27, 36 (table 6). Black Knob dolomite [informal, unranked] in Patcheta member of Lowell formation of Bisbee group. Division 9b, yellow dolomite, pinkish when fresh, in places silicified. Thickness in Ninety One Hills area 30 feet; on Black Knob Ridge 56 feet. Overlies Cienda limestone (new); underlies Black Knob quartzite (new). Fossils (reptilian remains). 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. 366).