William M. Thomas of Thomas and Post Consulting Engineers designed the 685-foot-long Parks Bar Bridge for Yuba County in 1912, and the Portland Concrete Pile Company constructed the original 16-foot-wide bridge with four 140-foot-long arch spans in 1912-13. The bridge was widened to 22 feet in 1924 and removed in 1994 after a new bridge was built downstream. Thomas established himself as a leader in early reinforced concrete bridge design by developing the Thomas System, which used precast construction, three-hinge arches, and open spandrels. Each arch had three flexible connections, one on each base and one joining the arch halves in the middle, and the open spandrels, the triangular spaces between the arches and the deck, added to the bridge's beauty. Over time, the river bed lowered and eroded the bridge's base, and undermining of the footings hastened replacement of this impressive early example of the Thomas System. The bridge was determined eligible for the National Register of Historic Places in 1984.