The Montezuma Creek-Aneth area is in the northeastern part of the Navajo Indian Reservation in southeastern Utah. It is a semiarid area along the San Juan River near the communities of Montezuma Creek and Aneth. Within the Blanding Basin, geologic formations exposed are of Jurassic and Quaternary age. The rock strata are nearly horizontal, dipping gently northeastward. Wells derive small quantities of mater for domestic use from aquifers in the Morrison Formation and the Bluff Sandstone of Jurassic age, but aquifers in deeper formations contain saline mater or brine. Alluvium consisting of sand and gravel along the San Juan River is a potential source of additional moderately large quantities of water to shallow wells for industrial use and public supply. The chemical quality of water in the alluvium is good and varies directly with the discharge of the San Juan River.