We lived in the Silver Valley at Kingston in 1984. The stop light in Wallace on I-90 was still in use. Relocation of the NP depot and construction of the I-90 viaduct over the railroad was in the final design / preconstruction phase.
We later lived in Montana where I visited the Great Northern lift bridge over the Missouri River near Fairview. My understanding is the Corp of Engineers required the GN to build the bridge to allow steam boat traffic on the river. The bridge was operated/opened once to commission it, but never raised for a steamboat after that.
I don't recall how long after the I-90 viadict was open in Wallace that the railroad underneath was abandoned, but sometimes it seems that what comes around, goes around.

Jeff Stabnow