Tertiary stratigraphy and nomenclature for western New Mexico and eastern Arizona
— Steven M. Cather, R. M. Chamberlin, and J. C. Ratte

This report delineates new lateral boundaries between lithostratigraphic units of Tertiary age in western New Mexico and eastern Arizona, including the Eocene Baca, Eagar and Mogollon Rim Formations and the Mio-Pliocene Santa Fe Group, Gila Group, Fence Lake Formation, Bidahochi Formation, Quemado Formation and Sheep Crossing Formation. New group-rank units for the upper Eocene to Oligocene rocks of the Mogollon-Datil volcanic field are also proposed. In the proposed nomenclature, all sedimentary rocks of the volcaniclastic apron surrounding the field are subsumed into the Spears Group. Volcanic rocks below a locally prominent disconformity representing a previously recognized 31.4 to 29.0 Ma hiatus in ignimbrite volcanism are assigned to the Datil Group (redefined); volcanic rocks above the disconformity are assigned to the Mogollon Group.