Geology and availability of ground water on the Ute Mountain Indian Reservation, Colorado and New Mexico

The geology and availability of ground water on the Ute Mountain Indian Reservation were studied to determine the possibility of developing additional water for domestic and stock purposes. The reservation is in the southwest corner of Colorado and a part of northwestern New Mexico; it has an area of about 900 square miles and includes part of Mesa Verde and the laccolithic Ute Mountains. The climate is semiarid, and the average annual precipitation generally ranges from 10 to 15 inches. The streams are tributary to the San Juan River; the Mancos River is the main tributary. Most of the rocks exposed are of Cretaceous age. The oldest formation exposed is the Navajo Sandstone of Jurassic and Triassic(? ) age. Pre-Cretaceous rocks younger than the Navajo are, in ascending order: the Entrada Sandstone, the Summerville Formation, the Junction Creek Sandstone, and the Morrison Formation. The Cretaceous rocks are: the Burro Canyon Formation, the Dakota Sandstone, the Mancos Shale, the Point Lookout Sandstone, the Menefee Formation, the Cliff House Sandstone, the Lewis Shale, the Pictured Cliffs Sandstone, the Fruitland Formation, the Kirtland Shale, the McDermott Formation, and the Ojo Alamo Sandstone. Some of the pediment deposits are of Tertiary (? ) and Quaternary age. Quaternary deposits include: alluvium and terrace, pediment, and talus deposits. Laccoliths, sills, and stocks of Cretaceous or Tertiary age intruded into and between sedimentary rocks form the Ute Mountains. The regional dip is away from the mountains. There had been little development of water resources before the early 1950's. With the establishment of the Ute Mountain Indian rehabilitation program, ground-water studies were started in an attempt to alleviate shortages of domestic and stock water supplies. The major factors controlling the occurrence and movement of ground water are climate, lithology, structure, and erosion. The principal occurrence of ground water is in the sandstone formations, although surficial deposits are significant aquifers near the Ute Mountains. Shale, the dominant rock type, inhibits or precludes the movement of ground water. Thus, artesian conditions generally prevail in the sandstone beds confined by the shale. Most of the wells yield water from artesian sandstone aquifers. The major artesian aquifers are the Dakota Sandstone, the Burro Canyon Formation, the Junction Creek Sandstone, and the Entrada Sandstone. Gl G2 WATER SUPPLY OF INDIAN; RESERVATIONS During this investigation, several stock wells were drilled in the western part of the reservation, and three deep public-supply wells were drilled at Towaoc. Stock wells tapped the Dakota Sandstone; the deep wells at Towaoc tapped the Junction Creek, Entrada, and Navajo Sandstones. Pumping tests at Towaoc indicate that yields of as much as 100 gallons per minute are possible from pumping the three wells. Water from the bedrock aquifers generally is highly mineralized, and most of it contains one or more constituents that exceed limits recommended by the U.S. Public Health Service. Water from alluvial sources in the mountain area is generally of better quality than that from the deeper aquifers. Shallow supplies are unreliable the year round, and it is necessary to depend on water from the deeper aquifers for a continuous supply. In general, ground water is not available in large quantities. However, adequate stock supplies are available from the Dakota Sandstone in the western part of the reservation. The Mesa Verde and New Mexico areas are not favorable for extensive ground-water development. Springs are an adequate source of water in the mountains. Public supplies for Towaoc are adequate for the present needs (1962). INTRODUCTION PURPOSE AND SCOPE OF INVESTIGATION This investigation was made to determine the water resources of the Ute Mountain Indian Reservation and to aid in the development of additional water supplies for domestic use in the Towaoc area and for stock use throughout the reservation. The investigation was made by the U.S. Geological Survey in cooperation with the Ute Mountain Ute Tribe of Indians, Towaoc, Colo. , and with the approval of the U.S. Bureau of Indian Affairs. The project was established by the Ute Mountain Tribal Council as a part of the Ute Mountain Indian Rehabilitation Program. The location of water supplies and development of the meager supply to serve the Indian population throughout their semiarid lands have long been critical problems. The investigation included a study of the geology and the ground-water resources to ascertain the occurrence of ground water and to insure its proper development. The investigation was begun in 1955 and was under the direct supervision of Thad G. McLaughlin and Edward A. Moulder, successive district chiefs, Ground Water Branch, U.S. Geological Survey, in charge of ground-water investigations in Colorado. Details of scope and methods of procedure were established in conferences with Messrs. Robert O. Bennett and James F. Cannon, successive Superintendents of the consolidated Ute Agency, U.S. Bureau of Indian Affairs, Ignacio, Colo. , and with the Ute Mountain Tribal Council. LOCATION AND EXTENT OF THE AREA The Ute Mountain Indian Reservation includes the southwesternmost part of Colorado and a small part of northwestern New Mexico (fig. 1). The southwest corner is coincident with the "Four Corners," UTE MOUNTAIN RESERVATION, COLORADO, NEW MEXICO G3