Water resources of the Santa Ysabel and Mesa Grande Indian Reservations, San Diego County, California

The Santa Ysabel (consisting of three tracts) and Mesa Grande Indian Reservations are in north-central San Diego County, Calif. On both reservations fractured and weathered igneous and metamorphic rocks and alluvium are water bearing; however, no wells are known to derive their water entirely from alluvium. Well yields range from 2.5 to 250 gallons per minute. Springs occur where saturated fractured or weathered material intersects the land surface. Spring discharge ranged from 0 gallon per minute (November 1979) to 9.4 gallons per minute (November 1979). Few data are available for the surface water characteristics of the study area. One-time measurements of discharge at selected stream sites were made in late November 1979 and late May 1980; discharges ranged from less than 0.01 cubic foot per second to an estimated 3 cubic feet per second. Further study of the surface-water systems would provide a basis for estimating their development potential. The existing water-supply development on the Santa Ysabel Indian Reservation is adequate for the present residents. The Mesa Grande reservation was unoccupied in 1952, was reportedly unoccupied in November 1979, and has no developed water supply. Additional water can be developed for both reservations from the igneous and metamorphic rock, from presently undeveloped springs, and from perennial reaches of the larger streams. Except for excessive iron and sodium at some ground-water sites and excessive sodium at a few surface-water sites, the water is of suitable quality for domestic and agricultural use. (USGS)