A Report to the Central Arizona Water Conservation District...on Geophysical Investigations of Butler Valley, Arizona

Abstract

Summary: Recent (1984) geophysical investigations of Butler Valley, Arizona, included gravity and seismic refraction surveys to estimate depth to and describe general configuration of bedrock underlying the basin outlet at the narrows into the Ranegras Plain. Interpretation and correlation of geophysical data collected from these surveys indicates a depth to bedrock at the basin outlet ranging from about 55 to 90 feet along a profile between bedrock outcrops, a distance of approximately 3,800 feet (see Figure 3, Profile A -A'). Such a bedrock configuration appears favorable to closing the lower end of the basin to eliminate possible ground-water underflow into the Ranegras Plain, using different engineering or management techniques. In addition, these data were correlated with available data from previous gravity surveys and geologic well logs to produce three other cross-basin profiles, which together were used to develop a generalized depth to bedrock map of the entire Valley (see Figure 7). Geophysical information presented in this report can be used to estimate alluvial thickness, define storage volume and boundaries of the aquifer and describe configuration of the shallow bedrock saddle beneath the narrows of the Valley. This information is useful in developing and evaluating technical or management solutions to eliminate potential ground-water outflow from the basin.