The Fort Mason tunnel runs east-west beneath historic Fort Mason, which is located on the bay just west of Fisherman's Wharf in San Francisco, CA. Spanning the Fort Mason grounds, the tunnel is approximately 1500 ft long. The tunnel, built in 1914, runs less than 60 ft beneath a number of buildings within the Fort Mason complex, several of which are historic structures. The project included assessment of the entire tunnel structure, both portals and portal approaches. Primary concerns for the tunnel are potential of liquefaction and/or lateral spreading during a major seismic event, significant crack in the crown within the cut and cover section, and water inflow. Our research showed that during the 1989 Loma Prieta earthquake, no liquefaction damage was observed at Ft. Mason while significant liquefaction damage occurred in the Marina District, immediately west of Ft. Mason. Additionally, during the 1906 earthquake, refugee camps were located on the lawn west of the tunnel, suggesting this area was considered relatively safe. Our scope also included developing the seismic design criteria for this project based on the probabilistic and deterministic seismic hazard analyses. The results of our investigation and analyses also show that liquefaction and lateral spreading is not a concern for this tunnel. However, settlement of uncompacted fills below and around the tunnel can have impact on the tunnel stability. The structural analyses indicate that portal retaining walls are adequate for static loading but FOS for overturning under seismic loading is less than 1. Tension in existing tunnel lining due to static compression and bending exceeds the allowable stress levels. This paper will present an assessment of the existing tunnel conditions, the results of our investigation and analyses, and our recommendations.