Pg. 15 (table 1), 43-45, pl. 1; USGS Prof. Paper 209, p. 39-40, 1946. Ajo volcanics. Is a waterlaid and volcanic unit; forms Ajo Peaks. Consists of biotite and hornblende andesite tuffs and breccias, passing upward into flows. Thickness 3,500 to 5,000 feet. Unconformably underlies Sneed andesite (new). Tuffaceous sediments of the Ajo interfinger with underlying Locomotive fanglomerate (new). Age is middle(?) Tertiary. Report includes geologic map. (Ajo Volcanics adopted by the USGS.)
Named from exposures at Ajo Peaks, in sec. 32, T. 12 S., R. 6 W., Ajo quadrangle, Pima Co., southwestern AZ. Caps Ajo Peaks; makes up hills west and southwest of Ajo Peaks and extends for about 3 mi in low range of hills southeastward from peaks.

Source: US geologic names lexicon (USGS Bull. 1200, p. 33); supplemental information from GNU records (USGS DDS-6; Denver GNULEX).

Occurs as scattered rounded hills in southeast part of Growler Mountains, Pima Co, AZ in the Basin-and-Range province. Consists of purple to brown altered andesitic flows and minor pyroclastic tuffs. The flows consist of plagioclase and less abundant biotite and hornblende phenocrysts in a matrix of 1-3 mm feldspar and acicular hornblende, devitrified glass, and iron oxide. Fragmental rocks consist of 0.50 to 3 cm fragments largely of feldspar-rich volcanic rocks and lesser amounts of granitic fragments in a glass and iron-rich matrix primarily of quartz phenocrysts. Assignment of an Oligocene and (or) Miocene age based on K-Ar age of 23.8 +/-8 m.y. from biotite in sample from Ajo Peaks and a 25 +/-2.2 m.y. whole rock age from the Ajo about 5 km east of report area.

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