Pliocene/Quaternary geology, geomorphology, and tectonics of Arizona

This paper summarizes four decades of my research on the late Cenozoic geology of Arizona that culminated in several maps of late Pliocene and Quaternary geology and neotectonic features of the whole state. Principal conclusions are: (1) Styles of deposition, preservation, and exposure of Pliocene to Holocene deposits differ greatly in various parts of the state. The Colorado Plateau has vast areas of stripped bedrock with local patches of late Quaternary eolian sand and alluvium and also large areas of Bidahochi Formation (Miocene and Pliocene, alluvial-lacustral), as well as the San Francisco, Toroweap, and Springerville-Showlow volcanic fields. South of the Mogollon Rim, a zone 50 to 100 km wide is deeply dissected terrain with a few tiny patches of Quaternary deposits. The main Mexican Highland section of the Basin and Range province contains the fullest, best-exposed Pliocene through Quaternary sequences in the state, in numerous well-dissected intermontane basins, as well as the San Bernardino basalt field. The Sonoran Desert section has widespread alluvium and local eolian sand i n broad, generally little-dissected intermontane basins, and also contains several basalt fields. (2) Quaternary sedimentation shows a primary cyclicity of several hundred thousand years, a dominant rhythm slower than marine oxygen-isotopic glacial cycles, with mainly climatic, not tectonic, control. However, except for the Holocene, many details of depositional chronology still are poorly understood and poorly correlated. (3) We found approximately 144 proven and probable faults less than 3.5 m.y. old, chiefly in a 200-km zone from the northwest to southeast corners of the state. Surface displacements are mostly older than 100,000 years, and we found none younger than 4,000 years. Few faults show multiple displacements. Recurrence intervals are 10 5years for most faults, to 10 4years in some cases; however, parts of northwestern, southwestern, southeastern, and central Arizona have regional recurrence intervals of 10 3years.