El Rio history:

El Rio is a small unincorporated census-designated town in Ventura County, California, USA, on the northeast side of the 101 Freeway and Oxnard, and south of the Santa Clara River. The population was 6,193 at the time the 2000 census was enumerated.

Early inhabitants of the area were the Chumash, a peaceful tribe who built canoes and milled the acorns. Their region extended from Point Conception to Santa Monica and back into the foothills as far as the Coast Range. One of their largest settlements was at nearby Saticoy, because of the bubbling springs that were found there.

On May 6, 1837, Juan M. Sanchez (1791–1873), a former Santa Barbara Presidio soldier, was granted the Rancho Santa Clara del Norte, which contained 13,989 acres (57 km2) of land extending from the Santa Clara River south to the northern boundary of present day Camarillo, and from the present day 101 Freeway east to the west end of South Mountain. Sanchez and his wife, Ines Guevara de Sanchez (1794–1862), had their adobe home built below the western slope of South Mountain, within a heavy group of eucalyptus trees at the east end of present day Rose Avenue, an avenue that was lined on both sides with tall eucalyptus trees.

The town was founded in 1875 and named New Jerusalem, California, by Simon Cohn (1852–1936), a Prussian Jewish merchant who owned a general store at the location. The postal authority established New Jerusalem Post Office on July 26, 1882, and Cohn was appointed the first postmaster. The first one-room schoolhouse was opened in 1885.

On February 14, 1895, the postal authority changed the name of the town to Jerusalem. Four months later, they changed it to Elrio, one word. In 1905, they changed it to El Rio, two words, which means in Spanish "The River," aptly referring to the nearby Santa Clara.

The El Rio Post Office was discontinued on October 31, 1911. It was reestablished in 1953. Until Rio Mesa High School was built on Central Avenue northeast of El Rio and opened in 1965, El Rio students were bussed to Camarillo High School in Camarillo. The post office was discontinued again in 1966.

http://en.wikipedia.org/wiki/Southern_California