MESOZOIC AND CENOZOIC UPLIFT AND EROSIONAL HISTORY OF THE SOUTHERN MARGIN OF THE COLORADO PLATEAU, YAVAPAI COUNTY, ARIZONA

The uplift and erosion of the southern Colorado Plateau was orchestrated by protracted geologic events that possibly date back to the middle Mesozoic. Widespread but discontinuous outcrops of late Paleozoic strata suggest that most of Arizona was covered by Permian shallow marine deposits. The Mesozoic record suggests that a topographic barrier separated strata on the Colorado Plateau from those of SW Arizona. North and east of the present Mogollon Rim, Late Cretaceous marine and shoreline deposits demonstrate that much of the Plateau was at sea level. The early Cenozoic (Laramide) record documents uplift and erosion SW of the present Mogollon Rim with streams flowing NE onto the Plateau; remaining Paleozoic strata were stripped from most of the Transition Zone. Middle Cenozoic deposits document paleo-relief near the present Mogollon Rim similar to that of modern relief. Integrated SE-flowing streams removed abundant material from along the Mogollon Rim. Late Cenozoic sedimentation and volcanism indicate rapid downcutting and erosion of the entire Plateau region but with little lateral migration of the Mogollon Rim.

Based on regional examination of sub-Cenozoic unconformities, the distribution of present Precambrian-Paleozoic outcrop belts was established during the early and middle Cenozoic. By middle Cenozoic time current relief of the Mogollon Rim was established and most regional uplift had occurred. Modern, dissected topography, strongly influenced by normal faulting, formed late in the Cenozoic and continues to form at present. There is no persuasive evidence for late Cenozoic uplift in the region.