This is the fourth of a series of interpretive reports on the water resources of the major valleys of Santa Barbara County, Calif., prepared by the Geological Survey, United States Department of the Interior, in cooperation with Santa Barbara County. The first three reports described the other major valleys in the county: the south-coast basins, Goleta and Carpinteria, and the Santa Maria and Santa Ynez River valleys. This report deals with the Cuyama Valley in the northeastern part of the county and adjoining parts of San Luis Obispo, Kern, and Ventura Counties. It includes estimates of natural discharge, pumpage, and yield of ground water, and all data on water levels, well records, and water quality that were available up to June 1946.