Hanson Bridge — Downieville, CA - U.S. National Register of Historic Places on Waymarking.com

The following information from California State Parks Office of Historic Preservation files:

The Hansen Bridge is a rare surviving example of a single lane low side-panel steel Pratt pony truss bridge that was once common throughout California. The bridge carries automotive and pedestrian traffic over the Downie River connecting Upper Main and Pearl Streets in the community of Downieville. The bridge was constructed and first put into service in 1935. While two bridges downstream were destroyed in a 1937 flood, this bridge sustained major damage to its underpinnings but was repaired and back into service in 1938. While once common throughout California, a relatively small number of low side-panel steel truss bridges survive today within the state. Less common yet are such bridges that are just a single lane wide and still in use carrying automotive traffic.

The Hansen Bridge is a Pratt pony truss steel bridge 80 feet long and 12 feet 4 inches wide, running east-west across the Downie River. The bridge trusses are constructed of steel I-beams secured by riveted steel plates. Steel guardrails extend beyond the edges of the pony truss on either side of the bridge, with a rolled sheet metal safety railing below the steel guardrails. The roadway deck is supported on wooden stringers running the entire length of the bridge, topped with corrugated metal and an asphalt road surface. The bridge is supported by two concrete pilings on each end, resting on concrete footings, with wooden boards between each piling. The boards on the western side appear to have partially collapsed but are still present. Steel struts from the canyon wall to the bridge are located on the eastern side of the bridge behind the pilings. A water pipe runs along the northern edge of the bridge. The remains of a granite retaining wall, possibly from an earlier bridge, are present on the northern side of the western bridge abutment.

The 1937 Downieville Flood

In 1937, Downieville had a total of five bridges. The easternmost (and farthest upstream on the Downie River) was the Hospital Bridge, originally called the Downieville Steel Bridge (due to its status as the town’s first steel truss bridge) constructed in 1908. Next was the Hansen Bridge, a Pratt pony truss bridge completed in 1936. Third was a concrete arch bridge constructed by the State of California to carry traffic on Highway 49. Just downstream of the highway bridge was the Jersey Bridge, a wooden bridge constructed in 1875, and the Durgan Bridge, just downstream of where the Downie River met the Yuba, constructed in 1881. Aside from the highway bridge, all were constructed as single-lane bridges by the county government.

On December 10, 1937, major storms sent a torrent of water through Downieville via both rivers. Nearly ten years had passed since the last high water, and an enormous amount of debris was swept into the river by the storm. State highway crews, aware of the storm’s danger, stood by to clear debris from the bridges, but as the river rose to the point where the highway bridge’s arches were underwater, clearing debris became impossible. The storm passed mostly under the Hospital Bridge and damaged the footings of the Hansen Bridge. The Highway 49 concrete arch bridge, unlike the truss bridges, had several pillars that extended into the river, and once road crews could no longer reach the bridge, debris collected on the piers and blocked the passage of water through the arches. The temporary dam brought the water level high enough to send the river through the streets of Downieville, lifting homes from their foundations and sending them floating downstream. The highway bridge could not withstand the pressure of the water and debris for long, and collapsed after approximately 30 minutes. The catastrophic break-through of water and debris caused more damage to the buildings of Downieville, and utterly destroyed the two wooden bridges downstream from the highway bridge, the Jersey and Durgan Bridges.

When Sierra County officials selected designs to replace the Jersey and Durgan Bridge in 1938, county engineer George Taylor designed two steel truss bridges. Taylor also chose to repair the damaged Hansen Bridge and retain the Hospital Bridge, whose unfashionable steel trusses had survived the disastrous 1937 flood. By the end of 1938, the town of Downieville was again connected by its four traditional single-lane bridges, all of steel truss design. The California Division of Highways rerouted Highway 49 temporarily over the Jersey Bridge as a temporary expedient until a new highway bridge could be constructed to replace the fallen 1936 bridge. As of 2016, no replacement bridge has been constructed, and the temporary expedient of the Jersey Bridge still carries Highway 49 through the city.