The first Devil’s Slide tunnel was built as a corridor for the Ocean Shore Railroad. Construction began in 1905, with plans to lay 73 miles of track from Mission Street in San Francisco to Santa Cruz. The 1906 earthquake caused extensive destruction and delays. Tracks were completed from San Francisco to Tunitas Creek, south of Half Moon Bay, and from Santa Cruz to Swanton, but were never connected. The northern route and tunnel closed in 1920 because of costs related to earthquake damage and competition from trucking as roads were built. Travel between Pacifica and Montara had no easy route, and all roads over San Pedro Mountain were treacherous. In 1879, Half Moon Bay-Colma Road carved the path the Ocean Shore Railroad later followed. In 1915, construction of Coastside Boulevard over the east slope of the mountain allowed farmers to take produce to market. Steep grades and hair-raising curves caused many accidents before State Route 1 was completed in 1937. California Route 1, renamed Highway 1 in 1964, was first closed at Devil’s Slide in 1940 and has been plagued by erosion and landslides ever since.