A distinctive suite of volcanic, sedimentary, structural, and physiographic characteristics permits differentiation of the post-1 2- to 15- Ma Basin-Range disturbance from earlier mid-Tertiary extensional tectonism in Arizona. Basin-Range volcanism comprises basalts or bimodal basalt-rhyolite suites that are concentrated in several fields in central and northern Arizona; the age of volcanism generally decreases northeast and east onto the Colorado Plateau margin.
