Aerial drone view of a roadcut along I-17 northbound south of Anthem, looking at tilted volcanic and sedimentary layers of the Chalk Canyon Formation (Miocene, 23-17 Ma). Layers alternate between dark gray basalt (labeled Tb) and white and tan tuff intermixed with sediment. The youngest layer is on the left, estimated to be about 17 My old, and oldest layer is Tb in the far right, which overlies Early Proterozoic basement rocks (Xv, about 1,700 My old). The rocks exposed are tilted about 20 degrees to the northeast, caused by a southwest-dipping fault (now dormant) concealed beneath younger sediments where houses are seen in far left. Faulting likely would have occurred between 15 and 12 Ma as part of the Basin and Range faulting. Source: Leighty and Huckleberry, 1998, AZGS OFR 98-19, Geologic Map of the Biscuit Flat 7.5’ Quadrangle (http://repository.azgs.az.gov/uri_gin/azgs/dlio/393). Photo and caption by Brian F. Gootee.