The karstic groundwater basins of the Kaibab Plateau, Arizona

The Kaibab plateau north of the Grand Canyon is characterized by the absence of live surface streams because most of the surplus water drains through the groundwater system. Over 95% of the primary porosity that can be attributed to the 4000‐ft sequence of Paleozoic sediments under the plateau occurs in the upper 900 ft of the section. However, almost all the water that discharges from the region exits through perennial karst springs developed in carbonates 3000 ft below the rims of the Grand Canyon and the Marble Canyon. The locations of these springs are fault‐ and joint‐controlled, and they drain between 65 and 97% of the area underlying the Kaibab plateau. The relatively permeable upper Paleozoic rocks in the section collect and transmit water to fault zones where the water enters regional drains dissolved along fractures in the lower carbonates. Flow in the fault zones is largely unconfined and perched above an impermeable shale unit that underlies the lower carbonates. Consequently, the areal extent of the groundwater basins that drain the Kaibab plateau as well as potential saturated zones along the faults can be delineated by using gradients taken from a structural contour map of the top of the shale.