Mare Island, a peninsula in the Napa River adjacent to Vallejo, California, was once home to a US Navy shipyard, and thus had a large network of connecting rail lines that spread throughout the facility. A large source of commerce for nearby Vallejo, the shipyard closed down in 1995, leaving abandoned a majority of the buildings and infrastructure there.
The land was subsequently redeveloped into a multi-use area, including a number of industrial customers in need of rail service, which were served by the San Francisco Bay Railroad up until 2008. Only recently has rail service continued to Mare Island, but to only a singular lineside customer (served by Tri-City and Olympia Railroad), despite a number of other industries on the island that still desire rail service. Discussions between T-C&O and the city of Vallejo to resume rail service to these other customers are ongoing.
Today, a majority of the tracks remain, disused.