Google Earth is my go to when it comes to mapping former railroad grades. I never assume when mapping the railroads and always use all the maps i can get my hands on. If i see something that looks railroad related but not on the map, I mark it in hopes of getting to explore it someday and proving it out. That is why i asked for help locating the maps for the Gilpin. My mapping projects usually take months and are pretty acccurate and reliable.
We have witnessed valley
and plain and crest,
Canon and pass we've scanned;
We have seen the best
of the glorious West,
by the trail of the Rio Grande
-Author Unknown