Late Miocene to Pliocene Paleogeography of Arizona (7-4 Ma).
The final stages of extension begin to form the modern landscape. Late Miocene "Rim Basalts" form north of the Mogollon Rim but spill down large valleys carved perpendicular to the Rim into Verde and Chino Valleys. There they intertongue with Late Miocene and Pliocene fluvial and lacustrine deposits. Contrast Rim basalt location with that of the older Hickey Basalt (shown in light gray). To the north, lacustrine and volcanic deposits form the upper part of the Bidahoche Formation. Late in the interval, the early stages of Grand Canyon begin to form. When the Verde and Colorado Rivers tap sea level, the modern, steep, dissected landscape forms.