Durango to Silverton Coloado (still running) is a narrower gauge, built that way because of the terrain, for mining.
Of course, the ONLY time I was in Durango I actually had tickets for this, but starting THAT DAY the railway was closed due to fire threat. We drove up, saw flames maybe about 1 mile from the raod; fear was that a coal could spark another fire (early 2000s). So we went on a 4-hour "City Slickers" cattle round-up with the refund money (the girls all ride super well, I'm the greenhorn).
In late 2019, we went on the Verde Canyon Railroad in Arizona, also a narrow gauge railroad built for mining because of the terrain. The Perkinsville train station was used in How the West was Won (Eli Wallach, George Peppard there for that scene) and for the beginning scene of The Sons of Katie Elder.
