The Arizona Basin and Range Province consists of broad alluvial valleys that separate low but rugged mountain ranges. The broad expanses of dry alluvial deposits and ephemeral streams that characterize the basin areas belie their importance as water sources and their geologic complexity. These basins are geologically interesting as the record of late Cenozoic deformation in southwestern North America. They are economically interesting because of contained salt, anhydrite, manganese, uranium, clay, and zeolite resources, as well as the potential for metallic mineral deposits concealed beneath their sedimentary fill. The alluvial basins contain reservoirs of groundwater that are a vital resource for human occupants. An accurate geologic framework model of these basins is fundamental to scientific understanding of geologically recent continental tectonics, and to the discovery and managed development of the resources contained in the basins. This report provides a snapshot of current understanding of the subsurface geometry of the boundaries of Tertiary basin fill, which is a major component of the necessary geologic framework model.