Interesting that you never see an electric locomotive, although you do see plenty of catenary (and the derrick clearing the rock slide has wooden sheathing around the boom to prevent it touching the wire). There's a scene shot inside the roundhouse where you can clearly hear an electric going by outside. I guess steam is more dramatic. Based on that and views of other locations (such as Lombard), I believe the terminal scenes were shot in Harlowton, Montana. Some have suggested Othello, Washington but I doubt it.