ABSTRACT This field trip will visit the southern Black Mountains volcanic center (SBMVC) and its associated products in northwestern Arizona. Post-volcanic extension and erosion of this semi-arid area afford the opportunity to examine a Miocene-aged (ca. 19–17 Ma) volcanic terrain in detail, using an approach that integrates fieldwork, petrography and geochemistry, and remotely sensed data. This approach was recently used in a three-year National Science Foundation Research Experience for Undergraduate (NSF REU) program, from which some results will be highlighted. This integrated approach can provide insight into the amounts and types of information that can be gleaned from various types of remotely sensed data of a volcanic terrain. Over three days, we will work our way through the volcanic section associated with the SBMVC as exposed near Oatman and Kingman, Arizona, to observe: (1) felsic to mafic shallow intrusions; (2) deposits from felsic to intermediate explosive and effusive eruptions; (3) deposits from sedimentary processes; and (4) the results of subsequent extensional faulting. The petrologic, physical volcanic, and morphologic characteristics of observed outcrops will be discussed at each field stop, and will be used as points of discussion while in the field, for observations of presumably volcanic terrains on other planetary bodies. An appended road log serves as a geologic guide to this volcanic center and associated rocks.

ABSTRACT The Colorado River extensional corridor, which stretched by a factor of 2 in the Miocene, left a series of lowland basins and intervening bedrock ranges that, at the dawn of the Pliocene, were flooded by Colorado River water newly diverted from the Colorado Plateau through Grand Canyon. This water and subsequent sediment gave birth, through a series of overflowing lakes, to an integrated Colorado River flowing to the newly opened Gulf of California. Topock Gorge, which the river now follows between the Chemehuevi and Mohave Mountains, is a major focus of this field guide, as it very nicely exposes structural, stratigraphic, and magmatic aspects of the Miocene extensional corridor, a core complex, and detachment faults as well as a pre-Cenozoic batholith. Topock Gorge also is the inferred site of a paleodivide between early Pliocene basins of newly arrived Colorado River water. Overspilling of its upstream lake breached the divide and led the river southward. The Bouse Formation in this and other basins records the pre–river integration water bodies. Younger riverlaid deposits including the Bullhead Alluvium (Pliocene) and the Chemehuevi Formation (Pleistocene) record subsequent evolution of the Colorado River through a succession of aggradational and re-incision stages. Their stratigraphic record provides evidence of local basin deepening after river inception, but little deformation on a regional scale of the river valley in the last 4 m.y. except in the Lake Mead area. There, faults interrupt both the paleoriver grade and incision rates, and are interpreted to record 100’s of m of true uplift of the Colorado Plateau. Warren Hamilton’s insightful work beginning in the 1950s helped set the stage for interpretation of Mesozoic orogeny and Cenozoic extension in this region, as well as the record of the Bouse Formation.