Belton Bridge (East end of Old River Bridge Road)
Built in 1920, the Belton Bridge was the western entrance to Glacier National Park from 1920 to 1938, and was one of the park’s first major construction projects. Between 1933 and 1938, the bridge was also a vital link on Going-to-the-Sun Road, a 51-mile stretch of scenic road across the park. The road is significant as a unique engineering accomplishment of the early 20th century, and as the first product of a 1925 cooperative agreement between the National Park Service and the Bureau of Public Roads.
In 1964, an extraordinary flood destroyed all of the bridge except the reinforced concrete arch. Down the river, a highway bridge built in 1938 to replace this one was completely destroyed. As a temporary measure, the park hired E.F. Matelich Construction Company to build a timber superstructure on the bare arch to carry traffic for the tourist season of 1964. [i]
[i] Historic American Engineering Record-Benton Bridge; Kathryn Steen,
HAER Historian, 1990; http://lcweb2.loc.gov/pnp/habshaer/mt/mt0200/mt0243/data/mt0243data.pdf
Historic Highway Guides 
I will never forget my first year on the GNP trail crew, and having to watch the West Glacier Bridge buckle as huge logs and parts of houses crashed into the undercarriage of the bridge. The year was 1964, and our crew of four was diverted to flood control for a few weeks before we could head up to the Northfork to live and work on Bowman and Kinta Lakes.
Thank you for your comment. I am very envious of your experience at Glacier National Park.