The Santa Maria Valley is an American Viticultural Area (AVA) which straddles the boundary of Santa Barbara and San Luis Obispo counties in California's multi-county Central Coast AVA. It was established on August 5, 1981, by the Alcohol and Tobacco Tax and Trade Bureau (TTB) as California's second oldest AVA. A portion of the AVA crosses the Cuyama River into the southernmost corner of San Luis Obispo County. The east–west orientation of the 152.3 square miles (97,483 acres) with a wide, open valley and rolling hills means cool winds and fog flow in freely from the Pacific Ocean, settling most noticeably in lower-lying areas. The result is a mild Mediterranean climate that lengthens the growing season and contributes to the eventual sugar/acid balance in the grapes from Santa Maria Valley