AQUIFER STRUCTURE REVEALED BY CAVES AND DYE TRACE, GRAND CANYON NATIONAL PARK

Extensive exposures of R Aquifer units in the Grand Canyon creates a unique opportunity to study a geologic cross-section of aquifer structure at depths which are usually inaccessible. A karst aquifer at approximately 2500-3500 feet depth, the R Aquifer is of particular importance because it feeds numerous large springs in the desert environment, including Roaring Springs, the sole source of water for Grand Canyon National Park. Caves in the cliff face are located in geologic units at various depths and display fracture-controlled morphology; therefore, cave maps provide valuable information about structural geometry which is otherwise difficult to discern from typical surface mapping techniques. These structural features allow for significant secondary permeability and are commonly preferential flowpaths for groundwater. Flow along dissolution-enlarged fractures is evident in Grand Canyon caves associated with spring outlets. This project documents a recent dye trace conducted on the Kaibab Plateau which connected surface sinkholes with unexpected springs at the western and eastern edge of the plateau. While the results are unexpected based on previous assumptions, the projected dye pathways follow mapped surface fractures and cave passage orientations. These observations completely re-write earlier assumptions about groundwater flowpaths within the North Rim Kaibab Plateau section of the R Aquifer. A more comprehensive understanding of the underlying structural framework will assist in interpretation of the dye trace results to characterize the aquifer. A robust characterization of the aquifer may be used to assess vulnerability from human use, pollutant spills, and the long term viability of the aquifer as a water source in light of changing conditions such as climate.