Re: Sort of narrow gauge puzzle....

Start out with reconnaissance to get an idea of how to approach the terrain and finding a grade. Maybe, take a second recon trip. Use a barometer to find the elevation difference. Figure what your percent of grade will have to be. Go up to the high point (might be the pass you have to go through) and begin surveying down. Do one side and then the other side. Might have to stop and back up to try a different per cent or a different alignment. Repeat as necessary until an alignment is obtained.

With good luck and an experienced location engineer you can get this done without too many problems.

BN