The site is located within the Tucson Basin, a northwest trending alluvial valley covering an area of about 750 square miles in the Santa Cruz River drainage basin of southeastern Arizona. The subsurface lithology generally consists of alluvial deposits of sand, silt, clay, and some gravel. The upper portion of the aquifer consists of sandy silt or sand with gravel and silt, and the lower portion of the aquifer begins 190-205 feet below ground surface (bgs) with silty clay or a sandy clay.  Depth to the regional aquifer occurs at 185 to 235 feet bgs. The groundwater flow direction is to the north/northwest. Groundwater has declined by approximately 20 feet since 1988, at an average rate of approximately 0.65 foot per year. However, since approximately 2013, the water table has stabilized and the latest measurements indicate a slight rebound in elevations in several of the monitoring wells.