The Zaca Oil Field is an oil field in central Santa Barbara County, California, about 20 miles southeast of Santa Maria. One of several oil fields in the county which produce heavy oil from the Monterey Formation, the field is hidden within a region of rolling hills, north of the Santa Ynez Valley. As of 2011, the principal operator of the oil field is Greka Energy and the operator of the "Zaca Field Extension Project" is Underground Energy. The field is known to contain heavy crude oil and Underground Energy has recently discovered a lower sub-thrust block in the field, which was not previously produced by the field's historical operators. The field was discovered in 1942, reached peak production in 1954, and remains active with more than thirty oil wells and continues to grow. Geographic setting The Zaca oil field is about four miles long by a quarter-mile across, running from northwest to southeast, paralleling U.S. Highway 101, which is about two miles to the southwest. Its southern extent is about four miles north of the town of Los Olivos, not counting the eastern "Zaca Field Extension Project", which surrounds the existing oil field and increases the southern extent by another three miles. Underground Energy acquired the acreage which circles the existing Zaca Oil Field in an acquisition completed in November of 2011. Total productive area of the oil field is approximately one square mile. The oil field lies perpendicular to a series of ridges which form the foothills of the San Rafael Mountains, and from northwest to southeast is dissected by San Antonio Creek, Canada del Comasa, and Zaca Creek. Drainage is to the southwest, and out to the Pacific Ocean via San Antonio Creek to the west, for San Antonio Creek and Canada del Comasa, and the Santa Ynez River to the southwest, for Zaca Creek. Terrain is rolling to steep, with flat bottomlands along Zaca Creek. Most of the oilfield operations are invisible from public rights-of-way with the exception of oil pumps and a water evaporation pond along Foxen Canyon Road. Native vegetation is a mix of chaparral and oak woodlands (California montane chaparral and woodlands), with vineyards and agricultural land uses interspersed with oilfield operations (the Firestone Vineyard is adjacent to the southeastern end of the oil field; some of the oil pumps are on Firestone-owned land). The region has a Mediterranean climate, with cool and