The Navajo Indian Reservation in Utah and Arizona is situated in one of the most arid parts of the Western United States. Normal annual precipitation is less than 8 to about 10 in. over much of the region (Cooley and others, 1969). Generally, water supplies for residents on the Reservation come from wells and springs, but locally, these supplies are small and, in some areas, they are slightly to moderately saline and not suitable for domestic purposes (Naftz and Spangler, 1994). One such area where water supply is limited is Monument Valley, along the Utah-Arizona State line, in the northern part of the Navajo Indian Reservation. The main issue identified by the Navajo Nation Department of Water Resources (DWR) concerns adequate water supply for the residents of the Monument Valley area. Additional water sources need to be developed locally to avoid having water piped into the area and to minimize haulage of water for domestic use. In addition, supplemental water supplies need to be developed to meet the demands of an increasing number of tourists. Because of these needs, the Navajo Nation DWR, in cooperation with the U.S. Geological Survey, investigated the hydrology of, and quality of water in, an alluvial aquifer along a tributary of Oljato Wash, near Oljato, Utah.