Fall Canyon Tuff of Oligocene age named for Fall Canyon, Shelley Peak quad, Catron Co, NM in the Basin-and-Range province. Has a 29.4 +/-l.4 Zr F-T date. Type section selected in W1/2 sec 23, T13S, R17W, where it is a single cooling unit. Is a high-silica phenocryst-rich rhyolite ash-flow tuff. Phenocrysts (10-40 percent) are sanidine cryptoperthite, quartz and sodic plagioclase. Biotite commonly 1-2 percent. Accessory minerals include opaque oxide, zircon, sphene, oxyhornblende, and apatite. About 150 m thick at type; overlies unnamed lava flows; underlies unnamed lava flows.

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

May be the correlative in Catron and Grant Cos, NM, Basin-and-Range province, of the Hells Mesa Tuff of the northern part of the Mogollon-Datil volcanic field and older than 32 m.y. Has yielded ages of 34.7 +/-1.2 m.y. (biotite), 30.8 +/-3.4 and 29.4 +/-3.1 m.y. (zircon), 15.8 +/-1.0 m.y. (sanidine). [These ages, except for 15.8 +/-1.0 m.y. are regarded as Oligocene.] Is the same general age as the Hells Mesa Tuff.

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