The Santa Maria Project is about 150 miles northwest of Los Angeles, California. Authorized in 1954, this water conservation and flood control project also provides full and supplemental irrigation water to approximately 35,000 acres of cropland. Reclamation constructed Twitchell Dam and Reservoir, formerly called Vaquero Dam and Reservoir, and the U.S. Army Corps of Engineers constructed a system of river levees. The Cuyama River, with its principal tributaries Alamo Creek and Huasna River, is the main source of water for the project. The drainage basin, comprising approximately 1,135 square miles above Twitchell Dam, lies along the southern boundary of San Luis Obispo County and the northern edge of Santa Barbara County.
All water used within the area is obtained by pumping from the ground-water reservoir.
The others are the Cachuma and Ventura River Projects. Plan Twitchell Dam is on the Cuyama River about 6 miles upstream from its junction with the Sisquoc River. It stores floodwaters of the Cuyama River, which are released as needed to recharge the ground-water basins to prevent salt water intrusion. The objective of the project is to release regulated water from storage as quickly as it can be percolated into the Santa Maria Valley ground-water basin. Therefore, Twitchell Reservoir is empty much of the time, and recreation and fishing facilities are not included in the project.