The site is located in an alluvial-filled basin of the Hassayampa River and has been influenced by the nearby river as well as the Quaternary Arlington Mesa basalt flows. A regional aquifer, consisting of basin-fill deposits, underlies the site and comprises the principal source of groundwater to wells in the area. The regional groundwater flow direction is generally to the south-southwest. Wells within three miles of the site provide drinking water for approximately 350 people and irrigation water for an estimated 2,800 acres of farmland. The nearest downgradient domestic well is about 1,000 yards south of the site.

Based on the predominant soil types identified in field studies, the shallow subsurface at the site includes two general units in the vadose zone (unsaturated soils): an upper coarse grained zone (CGZ) and a lower fine-grained zone (FGZ). The CGZ generally extends from ground surface to approximately 30 feet below ground surface (bgs). The FGZ extends from approximately 30 to approximately 60 feet bgs and consists predominantly of silts and fine sands. Beneath the FGZ there is a basaltic lava flow unit that is typically approximately 20 feet thick but tapers out or is not present to the north of the site. This basalt flow unit originated from Arlington Mesa to the south. An unsaturated zone, approximately 10-feet thick, is also currently present beneath the basalt unit.

Two groundwater units, Unit A and Unit B, have been defined at depth. The current water table occurs in silts and fine sands of Unit A at a depth of approximately 80 feet bgs. Unit B is composed of somewhat coarser materials than Unit A and is typically encountered at about 100 feet bgs and has a thickness of over 100 feet. Unit B is a productive aquifer in the region. Piezometric levels in Unit B are 7 to 8 feet lower than those in Unit A, indicating a downward gradient.