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

Water for public use at Pinnacles National Monument has been obtained in the past from tanks which store water yielded from small springs. This spring-water yield is barely adequate to supply the existing camp facilities and therefore, when the National Park Service considered enlarging the camp facilities, it became necessary to obtain a supplementary water supply. The National Park Service, by letter dated April 17, 1959, requested the Geological Survey to make a ground-water reconnaissance of the monument area. Specifically, this investigation included: (a) a reconnaissance of the geology of the monument and its relation to hydrologic conditions in the area; (b) the supervision of drilling one shallow test well and interpretation of the data obtained from this well; (c) a study of the source, occurrence, and movement of ground water; and (d) the preparation of a report outlining the results of items (a) to (c) above.

Pinnacles National Monument, in San Benito and Monterey Counties, Calif., is about 130 highway miles south of San Francisco, 37 miles south of Hollister, and 32 miles north of King City. The monument is in the Gabilan Range on the east side of Salinas Valley and includes about 23 square miles of volcanic spines and crags and rugged topography. Bear Gulch and Chalone Creek, the two major camp grounds, are in the eastern half of the monument and access to them by paved road is only from the east.

Water for public supply at Bear Gulch campground and that for domestic use at the monument headquarters cabins is obtained from a small spring (yield, 2-1/2; quarts per minute) in Bear Gulch and is stored in a 20,000-gallon tank.

Water for public supply at Chalone Creek campground is piped from a small spring to storage tanks and thence into the campground distribution system.

Water for fire protection is obtained from a surface reservoir in Bear Gulch. This water is not suitable for domestic or campground use.