The Third and Townsend Depot was the main train station in the city of San Francisco for much of the first three quarters of the 20th century. The station at Third Street and Townsend Street served as the northern terminus for Southern Pacific's Peninsula Commute line between San Francisco and San Jose and long-distance trains between San Francisco and Los Angeles via the Southern Pacific's Coast Line. For service for destinations to the north, such as Seattle, and destinations to the east, such as Chicago, passengers generally needed to travel to Oakland, initially on ferries to Oakland Long Wharf, and later on buses to 16th Street Station. It was demolished in the 1970s and replaced by the Caltrain commuter station a block away at Fourth and King Streets.

The Peninsula Commute, also known as the Southern Pacific Peninsula or just Peninsula, was the common name for commuter rail service between San Jose, California and San Francisco, California on the San Francisco Peninsula. This service ran as a private, for-profit enterprise beginning in 1863. Due to operating losses, the Southern Pacific Railroad (SP) petitioned to discontinue the service in 1977. Subsidies were provided through the California Department of Transportation (Caltrans) in 1980 to continue service, and it was renamed Caltrain.