A railroad question made it into the Colorado Day quiz offered by the Denver Post.
Spoiler warning: Stop reading unless you want some serious clues as to the answer.
Interesting enough, the Denver & Rio Grande pulled up the narrow gauge rails over this pass as they withdrew from the Blue River basin early on in its history. Few railfans realize that the Rio Grande reached all the way to Summit county, and did so by first going to Pueblo and then up the Arkansas all the way to its source. There would have been no Ski Train to Breckenridge however. Aside from the length of the trip, Breckenridge was still just a mining town and Copper Mountain was still just a hillside above non-descript Wheeler Junction. Nevermind the fact that skiing was relatively unknown in 1923 at the time Rio Grande abandoned the 36 miles of rails on the Blue River Extension.
One final hint: The pass is still reached by rail, although the trains don't quite reach it.