Minnesota and International Railway Trestle Bridge, Blackduck

The Minnesota and International railway trestle bridge at Blackduck is historically significant for its method of construction and the length of timber required to span Coburn Creek and the surrounding marsh. It is the longest bridge on the former Minnesota & International Railway (M & I) and widely recognized as the railway’s most difficult bridge-building project.

The M & I was a subsidiary of the Northern Pacific Railway that provided a rail link north from Bemidji to Koochiching, Minnesota, on the Canadian border (Koochiching became the town of International Falls in 1903). The area is dense pine forest punctuated by swamp, marshland, and peat bog. The marshland required the erection of timber trestles to span the sinkholes along the route.

A trestle is a rigid frame used as a support; small versions are used to support large tables. A trestle bridge is composed of several short spans supported by such frames. This type of bridge is sometimes called a "trestle" for short, and each supporting frame is generally referred to as a bent. Engineers incorporated timber trestles into designs for wooden roller coasters and, in the nineteenth century, wooden bridges across gorges. Adventure scenes in many Western movies feature trestle bridges.

Veteran engineer Frank H. O’Brien built the bridge at Blackduck according to a timber-stringer design, with rows of wooden beams (stringers) supporting an upper deck, between 1901 and 1902. It is 701 feet (210 meters) long. The trestle itself is made of a timber superstructure and a substructure accessed by gravel approaches on its northeast and southwest ends.

The bridge opened after some delay in the fall of 1902 and boosted local business. Blackduck folk, however, complained about the location of the depot, since it was difficult to reach except on foot. In poor weather conditions, it was even less accessible.

M & I roadmaster W. H. Gemmell agreed and donated $100 to improve the road to the depot. When that did not solve the problem, M & I awarded Foley Brothers a contract to move the depot across Coburn Creek. On November 12, 1902, they jacked up the building and pushed a piece of track and a flatbed car under it. They then pulled the entire building across the trestle to the new site.

The Minnesota Department of Transportation (MNDOT) took over ownership of the bridge in 1992 after the M & I ceased operations. The bridge was then renovated for use by pedestrians and recreational vehicles as part of the Blue Ox Trail (also called the Voyageur Trail). The rail crossing became a favorite among hikers and snowmobilers.

On February 4, 2014, years after the trains had stopped rolling, the bridge was added to the National Register of Historic Places. It was also called the Coburn Creek Trestle and the Blackduck Trestle by various railroads and entities.

Three teenagers burned and severely damaged the bridge on April 13, 2015. About 200 feet of the bridge were charred and destroyed. The bridge was subsequently closed to all traffic. Police placed its value at $500,000.

Due to the condition of the bridge overall, it was determined after two separate studies that it would cost up to $2 million to bring it up to standard. As a result, the bridge was closed. In 2018, cars and pedestrians following the Blue Ox Trail use a half-mile detour through Blackduck that allows them to avoid the bridge and then get back on the trail.