Gravity surveys and depth to bedrock in the Truxton basin, northwestern Arizona

The volume of available groundwater and the effect of groundwater pumping in an alluvial basin is influenced in part by the shape and depth of the basin boundary, which commonly consists of low-permeability bedrock. To better understand the shape and depth of basin fill in the Truxton valley in Arizona, new gravity data were collected at 149 stations in 2017 and 2018. These data, combined with historical data, show a gravity low consistent with deep basin fill near the community of Truxton, west of the Hurricane Fault, which crosses the study area from northeast to southwest. Depth to bedrock was estimated quantitatively through a three-dimensional gravity inversion, a process that identifies the most likely position of a contact between two units with different densities (in this case, high-density bedrock and low-density basin-fill material). Maximum basin-fill thickness near Truxton is about 500 meters (m). East of the Hurricane Fault, basin fill is generally thin (less than 100 m) and groundwater availability within basin-fill material in this area is likely limited. Few boreholes exist in the study area, but depths to bedrock are consistent with geologic logs from boreholes east and west of Truxton.