John,
The Yucca Mountain Railroad is a 3 foot gauge line. I understand it is several miles in length, although I am not sure. My secretary Connie went on a tour up there some time ago. She said it was Very impressive.
When they get the thing full of radioactive crap from the rest of the country I hear there will be no need to turn on a headlamp.....there's still a lot of energy in them thar rods.
By the way, a several years ago there was another 3 foot narrow gauge line here in the Las Vegas area. It was used also in a long tunnel through the River Mountains from the Las Vegas valley to Lake Mead. I was told it was about 5 miles in length. I saw the track before they took out the line. It was made with 56# iron.
After the project was finished, the entire railroad was taken up and trucked to the Chicago area for another project.
As for the NG line down at Laughlin, Nv. at the Ramada hotel, it is about a mile in length, has signals, bridges, and is built with about 90# rail. It has got to be the most overbuilt railroad for its light use and distance in the world.
So, there you have it. In Southern Nevada alone I know of three narroaw gauge lines in recent years.
I would bet there are a lot of other narrow gauge railroads out there and we have no idea of where they are. They just quietly go about giving reliable service.
Dan