Tri-County Corridor Trail - Amnicon River Bridge

Located near Amnicon Falls, this through girder bridge carries the former Northern Pacific Railway over the Amnicon River. The first bridge at this location likely consisted of a tall timber pile trestle bridge, constructed when the line was first built. In the early 20th Century, the NP decided to upgrade various bridges along this route to support heavier trains and improve maintenance operations. In 1908, it was decided to rebuild the timber bridge with the current structure. The bridge consists of a single 70-foot through plate girder span, approached by timber pile trestle spans on either end. The bridge is set onto timber pile substructures, and the main piers use concrete footings. The timber pile trestle spans were last replaced on 1946 and 1957. Typical of standard NP girders, the main span of this bridge uses rounded girder ends, and a traditionally composed floor.

The main span was reused from Bridge #200 (later Bridge #155) across the West Gallatin River near Belgrade, Montana; which had originally been fabricated in 1897 as a four span bridge. Bridges across the Poplar River, Middle River and West Branch Fish Creek along this line also were constructed using spans from this bridge. Railroads often reused steel and iron spans, as it provided a cost effective way to upgrade bridges along branch lines without requiring significant amounts of new material. A&P Roberts Company (Pencoyd Iron Works) fabricated the main span, and it is believed that railroad labor constructed the concrete footings. Through plate girder spans were commonly used by railroads, as they were durable and easy to construct. Currently, the bridge is owned by Douglas County, and is used as part of the mixed-use Tri-County Corridor. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. The author has ranked this bridge as being locally significant, due to the common design.