The Hassayampa River Canyon, located near Wickenburg, Arizona, is a riparian ecosystem and a popular recreational area in the arid Sonoran Desert of central Arizona. The canyon hosts well-exposed middle Cenozoic volcanic and sedimentary sequences, an underlying crystalline basement, and the unconformity that separates the two packages of rocks. The crystalline basement includes Proterozoic metamorphic and granitic rocks, and a Cretaceous granodiorite intrusion. The area features extension-related normal faults, major associated tear faults, evidence for faulting during accumulation of the mid-Cenozoic sequence, and known mineral deposits, including those of manganese, gold, and copper. New geologic mapping provides the city of Wickenburg with scientific and societal information for future land-use and resource-management decisions, and improves the understanding of the geologic history of the region. New geologic mapping in the southern half of the Sam Powell Peak 7.5' Quadrangle highlights (1) mid-Cenozoic volcanism and extension that formed the main geologic features of the area, including Hassayampa River Canyon; (2) relationships between Neogene sedimentation and late Neogene basin-fill deposits, and (3) the development of the modern Hassayampa River system onto pre-existing bedrock topography. Geologic mapping was conducted under the joint State-Federal USGS National Cooperative Geologic Mapping program, and was jointly funded by the Arizona Geological Survey and USGS under EdMap award G18AC00230.