West Montalvo Oil Field

While parts of the oil field are within the city of Oxnard, California, most of it is within an unincorporated region east of the intersection of Harbor Boulevard and Gonzales Road, a mixed-use area of agricultural fields interspersed with oil wells and associated production and processing facilities.

[5] Mandalay Beach Park consists of 94 acres (38 ha) of land left in its natural state, without amenities, and contains habitat for the endangered snowy plover.

[7] The climate in the region is Mediterranean, with cool, rainy winters and warm, rainless summers, in which the heat is moderated by frequent morning coastal low clouds and fog.

Beneath the McGrath, and separated by an unconformity, portions of the Miocene-age Santa Margarita and Monterey Formations show in drilling logs; yet another unconformity marks the top of the Colonia Zone, of Oligocene age, which contains more lenticular and pinched-out reservoirs of oil sands containing crude oil with an API gravity of around 15-18.

[2] Standard Oil Company of California discovered the field in April 1947 by drilling into the McGrath producing horizon.

In 1951, the Colonia Pool was found at 11,500 feet (3,500 m), which had a heavier oil with high sulfur content, and following the trend west, discovered the offshore portion of the field in June 1953 by drilling into the Oligocene-age Sespe Formation, where they also found oil at the 11,500-foot (3,500 m) depth.

[2] By the end of 2008, the field was one of the top ten in California by largest production increase of the preceding year.

In 1977, Standard Oil Company of California became Chevron Corporation, and the field was run under that logo.

Bush Oil ran the field for only two years, selling it to Berry Petroleum Company in 1992.

In the McGrath pool, gas injection was used from 1956 to 1968, and the zone has been waterflooded since 1963, in an attempt to boost reservoir pressure.