I enjoy researching about the bridge. I can not find a published answer. On another web site discussion, someone mentioned Mobridge as well as all the Montana sites Mr. Sol mentioned. The director switched angles a few times while train crossed the
bridge(s).
The different angles could have been at different bridges. The shot coming off of the bridge is Mobridge, because of the sharp right. The Calypso bridge near Terry, and the 2nd bridge over the Yellowstone near Tusler, 16 miles east of Miles City, also have 4 through trusses. The 3rd bridge over the Yellowstone, between Miles City and Lombard, is much smaller.
And nearly get run over by a steam engine in electrified territory.