Ground-water resources of the Yucca Valley-Joshua Tree area, San Bernardino County, California

The southeastern part of the Mojave Water Agency area included in this report comprises about 600 square miles. Recharge into the area is almost exclusively from precipitation in the San Bernardino and Little San Bernardino Mountains. About 500 acre-feet per year of recharge enters the western part of the area as underflow through Pipes Wash. Little direct recharge occurs as a result of precipitation directly on the unconsolidated deposits.

Presently about 11,000 persons reside in the area and current gross pumpage is about 1,600 acre-feet annually. By the year 2000 the population is estimated to be 62,000 and annual gross pumpage is expected to be nearly 11,000 acre-feet. Although over 1,200,000 acre-feet of ground water are presently in storage, most of the population is centered in the southern part of the area around the towns of Yucca Valley and Joshua Tree. About 70 percent of the population resides in the vicinity of Yucca Valley and is supplied by ground water pumped from the Warren Valley basin. Of the 96,000 acre-feet of ground water in storage in that basin in 1969, about 80,000 acre-feet will be necessary to sustain projected growth there until 2000. Assuming negligible recharge and only about 50 percent recovery of the ground water in storage, if imported water from northern California is not available before about 1990, additional local supplies will have to be developed, possibly in the adjacent Pipes subbasin to the north.

Ground water in the southern part of the study area generally contains less than 250 mg/l (milligrams per liter) dissolved solids and 1.0 mg/l fluoride. A general degradation of ground-water quality occurs northward toward the dry lakes where the concentrations of dissolved solids and fluoride approach 2,000 and 5.0 mg/l, respectively. In Reche subbasin some isolated occurrences of fluoride exceeding 1.5 mg/l were noted. The chemical character of ground water in Johnson Valley and Morongo Valley basins differs from well to well and, in general, water from these basins is less desirable for use.