Other than yards, finding track and RoW in Colorado is it fairly easy; I've done it a lot. Usually the grade remains, but sometimes can be fairly minimal. In those cases, I look for small pieces of coal and cinders ... these are dead give-aways.
Using that technique, I've"laid out" track on both Trout Creek and Kenosha Passes, London Junction and other places. On Kenosha, I was surprised to learn that the newly-laid track is nowhere near the original, except one place where it crosses the mainline at an oblique angle. And at London Junction, I found a spur that lead across the Creek to a smelter sure that I didn't know existed.
So when you're up in the high country, and on public land (very important!) try walking down a faint RoW ... great pastime activity.
Mike Conder