This illustration from Harper’s Weekly on March 15, 1879 depicts the railroad’s crossing of the Missouri River on ice.
Due to bankruptcy in the aftermath of the Panic of 1873, a bridge was not completed until 1883 – ten years after the line reached Bismarck
Source: Institute for Regional Studies, NDSU, Fargo (Folio 102.TrR34.1a)
Main Post: Pre-1871: Early History