Basically what you are modeling is Tennessee Pass, or at least part of it. Tennessee Pass runs from Pueblo to Glenwood Springs, crossing the last Class 1 10,000 Foot railroad pass left in America. It was built Narrow gauge, but converted to Standard Gauge early on, dual Gauge existed in Salida until about the 1950's when it was finally removed.
Tennessee was operated by the Denver and Rio Grande Western until 1989, when the Company merged with the Southern Pacific railroad. SP operated it until 1996, when they then Merged with the Union Pacific Railroad. UP crews were not used to the steep grades on Tennessee, and the railroad already had also aquired the Moffat Tunnel route in the D&RGW/SP/UP merger, so in 1997, the last trains ran over Tennessee Pass. UP tried to Abandon the line and tear out the track, but the ICC required them to offer it for sale first. Knowing that BNSF would jump on the chance to buy another route over the Divide, they instead discontinued operations, but left the rails intact, pending reactivation just incase something was to happen to Moffat Tunnel.
I remember some of the last SP trains running over Tennessee around 1995-1997, don't really remember anything earlier then that. I have watched as Tennessee Pass has slowly faded away and rotted.
I'd love to see more then just the Royal Gorge be reactivated as a tourist line, there was a call recently to add Buena Vista to Salida as a tourist line, but the plans were made by people who know nothing about railroads.
There were also plans made in 2005 to dual gauge the Royal Gorge once again, so that Lindsey Ashby, who owns the operations as well as the old Georgetown Loop operation, could bring his ex Loop equipment to the Gorge to return steam to the line once again. UP nixed that idea for maintiance concerns, and the Loop equipment ended up at the Colorado Railroad Museum. That was right after the CHS/Ashby/Railstar disaster, thankfully the Loop still runs, just with different equipment