The Mississippian Redwall Limestone is the deepest water-producing unit in the study area. It unconformably overlies the Devonian Martin Formation, and is primarily a massive, coarse-grained, crystalline limestone. The thickness of the unit in the study area is unknown due to the lack of wells drilled to sufficient depth. However, the thickness generally ranges from 0 feet to 300 feet in the region. Bed thickness ranges from thinly bedded in the lower one-third, to thickly bedded in the upper two-thirds. Some beds are highly fractured and contain solution channels and caverns that have formed along joints, bedding planes, or at random (Owen-Joyce and Bell, 1983).

Overlying the Redwall Limestone is the Supai Formation. The Supai Formation is exposed at the surface throughout the study area. The Supai is divided into three members. The lower member, which is approximately 1,100 feet thick, contains alternating beds of sandstone, siltstone, and some limestone. This member was deposited on the karst-type erosional surface on the Redwall Limestone. Lenticular beds of basal conglomerate contain pebbles derived from the Redwall Limestone. The middle member, which is approximately 300 feet thick, contains alternating beds of siltstone, mudstone, and sandstone, overlying a basal limestone unit. In the upper section of this member, lenticular beds of dolomitic intraformational conglomerate contain well-rounded limestone pebbles in a siltstone matrix. Some siltstone beds are calcareous. The dolomitic and calcareous beds are subject to solutioning, as indicated by sinkholes in the Sedona area. The upper member of the Supai Formation is approximately 625 feet thick, and is a sequence of very fine to coarse-grained sandstone beds with some interbedded siltstones. The sandstone is friable and calcareous, and the bedding is thick and massive (Owen-Joyce and Bell, 1983).

Review of the Well Driller’s Reports in the study area indicate that the depth to the base of the Supai formation in the study area ranges from 623 feet to over 740 feet below ground surface (bgs). Estimating from three BPWC Wells (#3, #4, and #5) that appear to penetrate the Redwall Limestone, the average depth to the base of the Supai formation is about 650 feet bgs.