DC electrical resistivity and ground-penetrating radar (GPR) data were integrated to help map shallow groundwater contamination due to releases of hydrocarbons from underground storage tanks at a site in northern Arizona. These data also were used to help strategically locate monitoring wells at the site. Soil and groundwater quality data from these wells were compared and correlated with the resistivity and GPR data. DC resistivity sounding data were obtained with a Bison Offset Sounding System, using the Wenner electrode configuration. The resistivity data were reduced and modeled to generate isoresistivity contour maps. A GSSI SIR SYSTEM-3 radar system was used to collect vertical, two-dimensional, continuous profiles along traverse lines at the site. These profiles were analyzed for structure, stratigraphy, and fluid dispersion. Soil and water samples from strategically located monitoring wells were chemically analyzed for contaminants. Contamination contours based on these data typically correlate very well with the geophysical data. The source and general geometry of the contaminant plume appear to be mapped by these data sets.