The Big Horn River Bridge consists of one contributing structure: a riveted Pennsylvania through truss structure that was constructed over a two year period between 1931 and 1933. The bridge consists of 2-spans resting on reinforced concrete abutments and piers. It is 624 feet in length and 21 feet wide. There are two reinforced concrete T-beam approach spans. The bridge crosses the Big Horn River on old US Highway 10 (now an Interstate 94 frontage road) about four miles east of the community of Custer near the river's confluence with the Yellowstone River. The bridge retains integrity of workmanship and feeling and the setting has not significantly changed since the structure's construction during the Great Depression. It is one of only a few Pennsylvania through truss bridges designed and built by the Montana Highway Department during the 1930s

Designer John Morrison checked the plans in June of 1931. Within a month, on July 22, the Montana State Highway Commission awarded the Edward J. Dunnigan Company of St. Paul, Minnesota a $120,211 contract to build a steel truss bridge across the Bighorn River along with six treated timber bridges on US Highway 10 about four miles east of Custer. The company, however, appears to have severely under-bid the project to get the contract. Within a few months, it became clear to Chief Engineer Ralph Rader and Bridge Engineer Ben Ornburn that Dunnigan was not capable of building the 4-span Pennsylvania through truss bridge. Even though Dunnigan promised to take steps which [would] probably result in more satisfactory progress in the future, it never did catch up; the company didn't pay its bills, and the highway commission declared Dunnigan in default of the contract in February 1932. Montana Highway Department workers completed construction of the bridge in late 1933. Interstate 94 bypassed the bridge and this segment of US 10 in 1979. - NRHP, 4 January 2010