Sunday, December 6, 2015

Plumas County, California Bridges: Port Wine Road Bridges across Slate Creek

November 2015 (39.66161-120.96432) Port Wine Road Bridges
The Port Wine Road Bridges are two crossings that carry about 50 vehicles a day over Slate Creek. Port Wine Road Bridge #1 (09C0014) is a single span 120 ft long through truss that was built in 1910. Port Wine Road Bridge #2 (09C007) is an 'A' frame supported steel stringer bridge built in 1936. However, it isn't clear how people crossed the creek before the second bridge was built.
The Port Wine Road Bridge #1 is a six panel Pratt truss built by George Brandt 105 years ago. The two center panels have cross members, the second and fifth panels have members sloping down toward the center of the bridge, and the ends are half panels sloping down to far ends of the bridge. The superstructure is only 12 ft wide, with a vertical clearance of only 13.5 ft and is rated in fair condition.
Port Wine Road Bridge #2 is 50 ft long and has sloping legs to support the superstructure at midspan without having to put a pier in the creek. This makes the bridge an unusual hybrid somewhere between a 3 pinned arch and a truss. A problem with this kind of design is that the bridge is rigid (rather than flexible) for longitudinal displacement and the legs are more vulnerable to shear.
The bridges cross Slate Creek on the border between Sierra and Plumas Counties. The creek has a rocky obstruction in the middle that allowed two short bridges (instead of one longer bridge) to be built. When I visited in November of 2015 the creek was only flowing in the deep channel under Port Wine Road Bridge #2 (this was the same as when Craig Philpott visited the site in August 2010).

The name Port Wine came from an abandoned mining town that was formed (but soon abandoned) during the Gold Rush of the 1850s. Since the bridges were built many years later, they may have replaced earlier bridges across Slate Creek. This area (the North Yuba Watershed) has many ghost towns and abandoned mines dotting the landscape. Cemeteries, mine shafts, and building foundations still remain. Today, the town of La Porte is the largest remaining community from that time. It had a population of 10,000 people in the 1880s, a population of 43 in 2000, and a population of 26 in 2010. 
Creative Commons License
Plumas County, California Bridges: Port Wine Road Bridges across Slate Creek by Mark Yashinsky is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

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