BEDROCK AND QUATERNARY GEOLOGY OF THE HASSAYAMPA RIVER CANYON, WICKENBURG, ARIZONA

The Hassayampa River Canyon, Wickenburg, central Arizona, is a riparian ecosystem and a popular recreational area in the arid Southwest desert. The canyon hosts well-exposed middle Cenozoic volcanic and sedimentary sequences, evidence for faulting during accumulation of these sequences, mines and mineral prospects, and exposures of Proterozoic basement rocks and the overlying unconformity beneath the mid-Cenozoic sequence. New geologic mapping of the canyon and adjacent areas provides the city of Wickenburg with scientific and societal infrastructure for future land-use and resource-management decisions, and improves the understanding of the geologic history of the region.

Rock units in the mapping area have been affected by mid-Cenozoic faulting, displaying steep dips and numerous low- to high-angle normal faults. The south-central portion of the Sam Powell Peak Quadrangle contains a newly discovered large normal fault responsible for the down-dropping and tilting the rocks in Hassayampa Box Canyon. This fault terminates to the southeast against a left-lateral tear fault with hundreds of meters of displacement. For the rocks to the west, the tear fault is a lateral ramp that offsets an oblique-slip reverse fault.

The record of early erosion of granitic basement and deposition of this material by local streams is recorded in the exposures of conglomerate in the Hassayampa Box Canyon. The highest exposure of conglomerate is at the top of Box Canyon, overlying lower basalt in a fanning dip sequence. As the conglomerate grades upward, it becomes loosely consolidated and flat-lying. New mapping reveals that the integration of the Hassayampa River in the area is likely due to superimposition after the shut off of mid-Cenozoic volcanism and faulting. Flat-lying conglomerate may be part of the basin fill sequence in the area.