Abstract

The Henry Mountains area is in an arid region. Little water is visible except in the high part of the mountains. The area, however, has a large amount of ground water stored in several geologic units, of which the Navajo Sandstone (Jurassic) is considered to be the most important regionally.

The Navajo Sandstone extends across the Henry Mountains area, except where it has been removed by erosion. The formation thickens west-southwestward from about 500 ft to more than 1,000 ft. The sandstone commonly is called an eolian deposit, but it may be partly derived from marine tidal-current deposition.

The sandstone is a massive, cross-bedded, very fine to medium grained subarkose that is moderately to well sorted. Samples of the sandstone, especially well cores, exhibit little matrix. Grains exhibit quartz overgrowths and have mainly a siliceous cement.

Based on data from a few sampling points, the Navajo Sandstone appears to have an areal hydraulic conductivity of about 0.5 ft per day which locally is tripled by fracturing. Based on a previous ground-water study in the region, direct recharge to the Navajo from precipitation is a minute quantity when compared with the large volume of ground water in storage. The Navajo receives direct recharge from precipitation in the mountains and the Capitol Reef area. The water moves from these areas generally eastward and southward to discharge areas at the Dirty Devil River and Lake Powell. There probably also is some interformational movement of ground water into and out of the sandstone aquifer. Much of the sandstone aquifer contains confined water; the storage coefficient is estimated to average 0.001.

The Navajo Sandstone can yield several hundred gallons per minute of freshwater to wells where the formation is thick and fully saturated. However, as of 1980, the aquifer has not yet been used much as a source of water.