Soledad Canyon was a vital part of Los Angeles’ transportation history. Transit between Los Angeles and the Central Valley was always difficult–in the “Gold Rush era” and stagecoach days the ride was extremely difficult, almost straight up-and-down through San Fernando Pass, up San Francisquito canyon, and over Tejon Pass. In 1856, Lieutenant Williamson, on a railroad surveying party, “discovered” that the pass, sometimes named “Williamson Pass”, could provide the lower grades to make Los Angeles–Central Valley train travel possible by the roundabout detour all the way to Mojave, and over Tehachapi Pass, almost 70 miles farther than the direct Interstate 5 used today by trucks and autos. In 1876, seven years after the transcontinental railroad was finished, the rail line was laid down Soledad Canyon, linking LA to the north, after a 6,940 feet (2.12 km) tunnel through San Fernando pass (still used by Metrolink) and the Tehachapi Loop, where trains circle on grades over top of themselves to gain altitude.  Southern Pacific.