Charles G. Graf- Hydrogeology of Kartchner Caverns State Park, Arizona. Journal of Cave and Karst Studies 61(2): 59-67. HYDROGEOLOGY OF KARTCHNER CAVERNS

each in fault contact with the other two. The southeastern corner and eastern edge of the park is part of the large graben that formed the San Pedro Valley during Miocene Basin and Range faulting. A thick alluvial sequence fills this graben and contains a regional aquifer covering 1000 km. One well in the park pen-etrates this aquifer. The groundwater level measured in this well was 226 m below land surface (1167 m msl), which is 233 m lower than the lowest measured point inside of Kartchner Caverns (1400 m msl). A pediment occupies a small part of the southwestern corner of the park. Structurally, this feature is part of the Whetstone Mountains horst rising above the park to the west. The pediment consists of a bedrock surface of Precambrian Pinal Schist overlain by a few tens of meters of “granite wash ” sediments. Groundwater occurs at depths of 4-18 m below land surface in wells tapping the granite wash sediments. Data from these wells indicate that the zones of saturation within the granite wash sediments are proba-bly of limited lateral extent and yield little water to wells. At the boundary between the pediment and the carbonate ridge containing Kartchner Caverns, the water table in the granite wash aquifer is 20 m high-er than the bottom of the nearest known cave passage, located about 200 m to the east. The arid carbonate hills occupying the northwestern part of the park are the erosional remnants of a faul