Marin County, California Bridges: The Richardson Bay Bridge
There aren't too many long bridges in Marin County. The Richardson Bay Bridge is a 873 ft long precast girder bridge (with a few box girder and T girder spans) that was built in 1957 and widened in 1973. It carries busy US-101 north of the Golden Gate Bridge through the affluent Mill Valley. Like a lot of other long bridges, the Richardson Bay Bridge has mostly flexible piers that alternate with occasional stiff lateral restraining piers. Despite or because of this kind of seismic design, the bridge suffered moderate damage during the 1989 Loma Pieta earthquake, but that didn't result in closure. After the earthquake, Caltrans provided a retrofit that consisted of infill walls to resist the lateral load.