Type section located in Lemitar Mountains, about 8 mi northwest of Socorro in a tributary canyon on north side Canoncito de Puertocito del Lemitar, NW/4 SE1/4 SE1/4 sec 12, T2S, R2W, Socorro Co, NM, Orogrande basin (described by Chamberlin, 1980, in open-file report). Occurs in San Mateo, Magdalena, Lemitar, and Chupadera Mountains, Joyita Hills and northern Jornada del Muerto. Replaces term Potato Canyon Rhyolite Tuff (abandoned). Composed of 0-400 ft outflow and 800-2,000 ft ash-flow tuff in Sawmill Canyon-Magdalena cauldrons. Is a simple to compound cooling unit of densely welded tuff showing strong compositional zoning. Divisible into lower, middle, and upper members. Is above Vicks Peak Tuff and below South Canyon Tuff. Can also be overlain and underlain by tongues of La Jara Peak Basaltic Andesite. Source area probably in northern or central San Mateo Mountains. Has a 28.4 m.y. age on an average of four K-Ar biotite dates. Assigned to the Oligocene.

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