The White Mountains in east-central Arizona were the site of middle to late Cenozoic volcanism. The lava flows, volcaniclastic, and epicIastic rocks can be separated into two age groups: the first of Oligocene and Miocene age and a later one of late Miocene-Pleistocene age. The first period of activity preceded the delineation of the Colorado Plateau and Basin and Range geologic provinces, and is contemporaneous with volcanism in the Mogollon Plateau region of New Mexico.