Late Cenozoic vertebrate faunas, southeastern Arizona
— Everett Lindsay

Fossil vertebrates are relatively common and widespread in late Cenozoic deposits of southeastern Arizona (fig. 1). Perhaps the best known vertebrate sites from this area are those of San Pedro Valley. Fossil mammals were first described from San Pedro Valley by J. W. Gidley (1922). Since that time, numerous fossil sites have been found in San Pedro Valley, primarily between Benson and the Mexican border. Another area in southeastern Arizona where vertebrate fossils are well known is San Simon Valley, near Safford. Knechtel (1936) described the Gila Conglomerate in San Simon Valley, including a list of fossils collected from Red Knolls and 111 Ranch. Faunal lists for vertebrate sites in Arizona are given in Lindsay and Tessman (1974).

 

Late Cenozoic terrestrial sediments in southeastern Arizona are good recorders of paleomagnetism. This fact, plus the occurrence of numerous fossils in these deposits, provide an excellent opportunity for correlation of vertebrate biochronology with the magnetic polarity time scale. Johnson and others (1975) demonstrated the first direct correlation of a vertebrate faunal sequence in North America with the polarity time scale. This work, on both late Pliocene and early Pleistocene deposits in San Pedro Valley, has continued on older deposits (early Pliocene) to the north, between Redington and Mammoth.

 

Four North American Land Mammal Ages are recognized in the late Cenozoic. A land mammal age is a biochronological unit, characterized by the association of several mammalian genera, and differing from earlier and later land mammal ages in a different characterizing assemblage. The late Cenozoic land mammal ages of North America are: Hemphillian (early Pliocene), Blancan (late Pliocene), lrvingtonian (early Pleistocene) and Rancholabrean (late Pleistocene). Each of these ages is relatively well represented in southeastern Arizona.