The Santa Susana Pass was at the juncture of the Native American Tongva-Fernandeño, Chumash-Venturaño, and Tataviam-Fernandeño tribal lands and was first crossed by their trail route, and used for an estimated 8,000 years.
Under Spain and Mexico
The first Europeans to use the pass were members of the Spanish Portolà expedition, the first European land entry and exploration of the present-day state of California. The expedition traversed the pass on January 15, 1770, heading east to a campground that later became part of Mission San Fernando Rey de España. After secularization of the mission in 1834, San Fernando Valley rancheros used the trail. A rough wagon road evolved.
Early statehood
American newspapers in California first referred to the pass as Simi Pass from 1857 when the Los Angeles Star wrote of the capture of the outlaw Juan Flores there. That name continued in use, declining from the late 1880s until 1911 in the Eagle Rock Sentinel. It began to be referred to as Santa Susana Pass in the Los Angeles Herald 18 September 1887, being used with increasing frequency thereafter. In 1859, the California Legislature appropriated $15,000 towards improving the old wagon road into a new stagecoach road, now known as the Old Santa Susana Stage Road. The precipitous portion of the route down from the summit on the San Fernando Valley side was called the Devil's Slide; horses were usually blindfolded and chains were used to augment brakes on the steep descent. Passengers debarked and walked. The outbreak of the American Civil War in 1861 disrupted mail service along the Butterfield Overland Mail's southern stagecoach route from St. Louis, Missouri via El Paso, Fort Yuma and Los Angeles and on to San Francisco via the Tejon Pass, which had begun its run in 1858. To compensate, the government contracted the Butterfield Company to carry mail between Los Angeles and San Francisco via the new wagon road over the Santa Susana Pass. The first overland mail stage run through the pass took place on April 6, 1861. The main route climbs through what is now Santa Susana Pass State Historic Park, with a branch in L.A. City Park 'Chatsworth Park South.' It was an important artery linking the Los Angeles Basin and inland Ventura County, and was part of the main route for travel by stagecoach between Los Angeles and San Francisco from 1861 until the opening of rail traffic between the cities in 1876. The Old Santa Susana Stage Road is listed on the National Register of Historic Places. Part of the stage road is also a Historic-Cultural Monument of Ventura County and of the City of Los Angeles under the name 'Old Stagecoach Trail.'
A new wagon route bypassing the deteriorating Devil's Slide was opened in 1895 to the north. Initially called El Camino Nuevo, it was later named the Chatsworth Grade Road, which continued in use until Santa Susana Pass Road was built in 1917. This was the first automobile route between the San Fernando and Simi Valleys. It also was the main northbound 'coast road' to Santa Barbara and San Francisco, until the Conejo Grade in Ventura County between Conejo Valley and the Oxnard Plain on "Camino Real Viejo", was improved. In 1968 State Route 118, the "Simi Valley–San Fernando Valley Freeway" opened, north of the old auto road as the latest route across the Pass. In 1994 it was renamed the "Ronald Reagan Freeway". The pass area became famous from being seen in many movies, primarily Westerns, filmed from the 1920s to the 1950s here at the Spahn, Iverson, Bell Moving Picture, and CorriganvilleMovie Ranches. The area became infamous in the late 1960s with the Manson Family headquartered at the Spahn Ranch, near the top of the stage road's Devil's Slide. To the south of the old stage road is Sage Ranch Park and the Santa Susana Field Laboratory. Immediately to the north of Route 118 at the pass top is Rocky Peak Park, a part of the Rim of the Valley Trail Corridor. The old wagon road and rocky hill environs are part of the Santa Susana Pass State Historic Park, for public exploration. The Southern Pacific Railroad began construction of three railroad tunnels through the pass in 1900 and opened the route in 1904. The railroad built the Santa Susana Depot in Rancho Simi on Los Angeles Avenue at Tapo Street in 1903.
