MOVEMENT AND AGE OF GROUND WATER IN THE NAVAJO SANDSTONE AND KAYENTA FORMATION IN THE AREA OF PIPE SPRING NATIONAL MONUMENT, NORTHERN ARIZONA

Pipe Spring National Monument is on the Arizona Strip, an area between the Utah border to the north and the north rim of the Grand Canyon to the south. Four springs at the base of Winsor Point on Winsor Mountain discharge from the Navajo Sandstone and Kayenta Formation. The relation between declining discharges from springs in the monument and ground-water development north of the monument was studied to provide information that could be used for management of the monument resources (Truini, 1999). The Navajo Sandstone and Kayenta Formation are the primary water-bearing units on the west side of the fault. Ground-water elevations from wells indicate that ground water in the Navajo Sandstone and Kayenta Formation moves from north to south along the west side of a branch of the Sevier Fault. The Chinle and Moenkopi Formations on the east side of the fault are poorly permeable and inhibit ground-water movement from the west side of the fault to the east side (Truini,1999). Ground water south of Moccasin Canyon is higher in total dissolved solids than ground water north of Moccasin Canyon. Wells north of Moccasin Canyon are open primarily in the Navajo Sandstone, and wells south of Moccasin Canyon are open primarily in the upper sandstone facies of the Kayenta Formation. (Truini,1999). The estimated water budget for the study area indicates a recharge deficit of 780 acre-feet per year. This deficit suggests that some recharge may be occurring outside the study area. Oxygen and hydrogen stable-isotopic data suggest no isotopic variation in recharging waters in the study area and surrounding region. Radiocarbon and tritium activities indicate that apparent ground-water ages at wells and springs are between 45 and 9,000 years (Truini,1999).