Pg. 8, 11, 15, 36 (table 6). Arkill limestone [unranked] in Saavedra member of Lowell formation of Bisbee group. Division 7l, slabby grayish-brown and buff arenaceous limestone. Fossiliferous (ammonites, bivalves). Thickness about 2 feet. Overlain by a soft white, in some places buff, sandstone. A buff sandstone separates the Arkill from underlying Barata limestone (new) in Saavedra member of Lowell formation. [Age is Early Cretaceous (Aptian); DUFRENOYA DUFRENOYI standard ammonite zone.]
[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. 134).