I don't know about Colorado, but out here in California the preservation of existing track is the way to go. I work at the Western Railway Museum, where in 1994 we were able to purchase a 22 mile branch line that was ex Western Pacific ex Sacramento Northern ex Oakland, Antioch & Eastern an Interurban electric line. We preserved the 1912 rails and hardware. The museum has so far restored over 5 miles of overhead wire.
I doubt that there is any existing narrow gauge track, so any new new trackage will have to be re-laid such as they are doing at Sumpter Valley railroad Restoration.
It will be interesting to see what developes.