The San Ramon Valley Branch of the Southern Pacific entered service in 1891 to serve the abundant agriculture interests of the San Ramon Valley. The line extended from the SP's West Side line at Avon south through Concord, Walnut Creek, Danville, San Ramon, and Alamo. In 1909 it was extended to the original Central Pacific transcontinental railroad alignment through the Livermore Valley at Radum. This part of Contra Costa County never realized industrial development to support use of the railroad beyond a secondary branch line, and much of the area was developed into a residential area with single family homes. By the mid-1970s, the southern section of the branch was used for surplus car storage, and the line was abandoned in 1978.

Today (2004), most of the line has been converted to a bike trail, the very popular Iron Horse Trail. Most of the right-of-way can be easily followed south of Concord. The Danville and Walnut Creek depots have been preserved, although both have been moved short distances from their original locations. The line's undercrossing of Interstate 580 in Dublin is now part of a major transit center for the Bay Area Rapid Transit (BART) system and local bus lines. In Walnut Creek, just south of Ygnacio Valley Road, a through truss bridge of 1923 vintage serves to support the bike trail (see photo at right). At Dublin, spur tracks into the former Santa Rita federal depot still remain (also at right). The northernmost portion of the branch is still intact and visible at Avon, although completely within the confines of a Valero oil refinery.