6.4 SAND WASH BASIN
Sedimentary rocks of Paleozoic, Mesozoic, and Cenozoic age are represented within the Sand Wash Basin. Tertiary-age geologic formations lie at or near the surface throughout most of the basin, and as such the Wasatch-Fort Union aquifer is the uppermost regional aquifer in the Sand Wash Basin. The thickness of Tertiary rocks in the Sand Wash Basin increases from a feather edge at the margins to about 12,000 feet in the center of the basin. A generalized cross-section of the basin is presented as Figure 6.4-2 and details on the hydrogeologic units are presented in Table 6.4-1.
The Wasatch-Fort Union aquifer overlies a group of rocks composing the Mesaverde aquifer, and then the Dakota aquifer (lower Cretaceous). Because of the extensive outcrop area of Cretaceous rocks in the Sand Wash Basin (Figure 6.4-2), the Mesaverde and Dakota are likely to be the principal aquifers along the southern, southeastern, and eastern margins of the basin. In these areas, the Cretaceous-age target aquifers exist at depths less than 2,000 feet and their outcrop areas are exposed to recharge from precipitation, resulting in good water quality.