Ground-water withdrawals in Cuyama Valley (fig. 1) have increased about 500 percent since the early forties, and since about 1947 annual withdrawal has exceeded the estimated perennial yield of the basin. This has caused a general decline of water levels in the valley, and a well-defined cone of depression about 2 by 6 miles in area, reflecting a maximum water-level decline of about 140 feet, has developed near Cuyama. Continued overdraft will increase pumping lifts until pumping costs are no longer economical.
The U.S. Geological Survey, in cooperation with the Santa Barbara County Water Agency, has been engaged in a water-resources investigation of the area during the past year. Preliminary findings are summarized in this progress report, which has been prepared at the request of the Santa Barbara County Water Agency.
Ground water in Cuyama Valley is replenished mostly by rain on a watershed of about 700 square miles (fig. 2). Most of that area, at altitudes from 2,000 to 5,000 feet above sea level, receives less than 14 inches of precipitation a year. Somewhat greater precipitation, about 24 to 30 inches, occurs in the headwater region of the Cuyama River and on the crest of the Sierra Madre Mountains, where altitudes exceed 7,000 feet. However, only a small part of the drainage from these highland areas reaches the Cuyama ground-water basin. In the valley itself the average annual rainfall is less than 10 inches. The average annual rainfall for the 21-year period (1945-65) at Cuyama is 5.79 inches (fig. 3). Most of the rain falls in winter and spring.
