Geological Survey Water-Supply Paper 1475-K Ground-Water Reconnaissance at Pinnacles National Monument, California

Abundant ground water for the Pinnacles National Monument can be obtained from wells, less than 50 feet deep, drilled in the alluvium of Chalone Creek. The yield of properly constructed wells in the alluvium should exceed 10 gpm, because test well 35R1 yielded 11 gpm at a pumping level of 14 feet below the top of casing. The low yield of this well probably was due to the fact that much of the water-yielding formation was sealed off by the drilling fluid.

Supplemental water, if desired, can be obtained by drilling additional wells in the alluvium of Chalone Creek, or by deepening the existing dug well from 17 feet to 20 or 35 feet. To avoid the possibility of introducing drilling mud into the permeable gravel, the deepening could be done by the cable-tool method. Care should be taken to see that the annular space between the casing and the dug well is backfilled with gravel below the water level and with clay above the water level.

It is suggested that the water levels in all wells be measured periodically (preferably monthly) and that records be kept of the measurements. Also, it would be desirable to make chemical and bacteriological analyses of the water at least semiannually. These basic records would provide the necessary data for periodic appraisal of the adequacy of the ground-water supply.