Abstract: Geology and Hydrogeology of the Sisquoc Subbasin, Santa Barbara County, California
Brian M. McCord, M. Ali Tabidian
The Sisquoc Valley is a synclinal basin located in the central coast region of California. The valley is drained by the Sisquoc River and its tributaries. It adjoins the Santa Maria Valley at Fugler Point, where the Sisquoc and Cuyama rivers merge to form the Santa Maria River. The Sisquoc River, from its convergence with the Cuyama River to approximately 4.2 mi upstream, is considered a losing stream. The aquifer within the basin has been defined as the Sisquoc Storage Unit (herein referred to as subbasin) of the Santa Maria groundwater basin. All agricultural, domestic, and industrial users depend entirely on water from wells in the Sisquoc and Santa Maria basins.
Geology of the region consists of consolidated and unconsolidated material. Consolidated material is composed predominantly of Tertiary age sedimentary rock. The water-bearing properties of these formations are relatively low to none. The unconsolidated deposits consist of marine and nonmarine Late Tertiary and Quaternary deposits. The water-bearing properties of the unconsolidated deposits is very good, with hydraulic conductivity values ranging from 60 to 3500 gal/day/ft2.
An estimated 250,000 ac-ft of water is stored in the Sisquoc aquifer under unconfined conditions. Inflow to the basin is from rainfall, river water, and return flow. Outflow is through well discharge, evapotranspiration, and subsurface flow.
Historical groundwater level data indicate significant groundwater level fluctuations due to changes in climate and groundwater use. Damming the Cuyama River in 1959 has helped to reduce overdraft and establish a long-term trend in groundwater storage.
AAPG Search and Discovery Article #90981©1994 AAPG Pacific Section Meeting, Ventura, California, April 27-29, 1994