Nevada County’s road system contains about 80 bridges or box culverts in various states of repair. Recently, the county government put out to bid a project to repaint and rehabilitate one of the more iconic bridges that serves as a recreational focal point for many residents and visitors — Purdon Crossing Bridge. The bridge, a rare surviving example of a pin-connected Pratt Half-Through Truss, which was built in 1889, has a number of functional and aesthetic problems, according to the latest bridge inspection performed by the California Department of Transportation in 2011. The timber railing and rail posts are loose …