Cenozoic paleogeography of the central Mogollon Rim-southern Colorado Plateau region, Arizona, revealed by Tertiary gravel deposits, Oligocene to Pleistocene lava flows, and incised streams

Eocene to Pleistocene paleogeography of the Mogollon Rim-southern Colorado Plateau region in central Arizona is interpreted by use of Tertiary sedimen tary deposits and mafic lavas that have been correlated on the bases of pro venance of pebbles, stratigraphic sequence, geomorphic positions of deposit s and flows, published K-Ar ages, tracing of lava flows to vents, and lava textures and structures. Five categories of Tertiary sedimentary deposits a re (1) Paleocene(?) to Oligocene(?) fluvial and lacustrine deposits on the margin of the Colorado Plateau that were derived from local and distant sou thern sources; (2) Oligocene(?) to Miocene deposits in valleys at the base of the Mogollon Rim that were derived from local and distant southern sourc es; (3) Oligocene(?) to Pliocene locally derived gravel on pediments and in canyons along the rim; (4) Miocene locally derived lag gravel beneath shee t flows on the plateau; and (5) Miocene to Pleistocene locally derived chan nel-filling gravel on the plateau. Mafic lavas used are (1) upper Oligocene to lower Miocene basalt and minette in the Transition Zone; (2) Miocene pa hoehoe sheet flows on the Colorado Plateau and draped over the Mogollon Rim ; (3) middle Miocene to Pleistocene cones and flows of basalt scattered acr oss the region; and (4) Pliocene to Pleistocene basalts of the Mormon and S an Francisco volcanic fields. Basalt sheet flows in ten middle (ca. 12 Ma) and upper (ca. 6 Ma) Miocene flow fields, traced to 12 low-profile vent str uctures, cover nearly 30% of a 9000 km(2) area of the central Mogollon Rim region and depict the paleogeography at the times of eruption. Principal conclusions are: (1) the Mogollon Rim developed near its present position after Precambrian rocks in central Arizona had been unroofed durin g the Paleocene to Eocene Epochs, and before late Oligocene to early Miocen e mafic volcanism; (2) after erosional quiescence during the Paleogene, Tri assic strata were stripped off the southern Colorado Plateau in a Miocene t o Pleistocene erosional sweep from the southwest to the northeast; (3) inci sion of meanders on the Mogollon Slope occurred in the late Pliocene to Ple istocene Epochs as a result of integration of the Little Colorado River wit h the Colorado River in the Grand Canyon.