[This photo confirms BNSF has
trackage rights over what is
now a UP line.]
Until trains started using the tunnel in February 1928, they had to travel 27 miles over the 12,000-foot Rollins Pass. [ColoradoRailfan] Some of the grades over the pass exceeded 4%. The tunnel was 6.21 miles long. [American-Rails] (American-Rails indicates the route over the pass was 23 miles.) David Moffat intended to build a railroad to Salt Lake City, but it didn't get past Craig, CO. However, he was instrumental in getting the Colorado Legislature to allow the tunnel to be built, and construction began in 1922. One reason it took six years to build the tunnel is that they encountered "bad rock" on the west end. 28 workers died during construction.
The Denver & Rio Grande assumed control of the route in 1931, but the ICC required that they build a connection between the Moffat route and their mainline so that the Moffat Tunnel didn't remain just a long, expensive hole in a mountain. In 1934, they finished the 30-mile "Dotsero Cutoff" between Dotsero, CO and Orestod. [drgw] Note that Orestod is Dotsero spelled backwards. It took me a while to find the junction because it is in Bond, CO. Later, I came across a reference that stated Orestod was renamed to Bond. The Dotsero Cutoff provided the competitive transcontinental route that the ICC wanted. The California Zephyr passenger train between Chicago and the San Francisco bay area was jointly run by Chicago, Burlington & Quincy; Denver & Rio Grande; and Western Pacific jointly. Amtrak still uses this route to run the California Zephyr.
The Union Pacific now owns the D&RG and WP, and they discontinued service on the 175-mile [TrainOrders] circuitous Pueblo + Tennessee Pass route in 1997 [Wikipedia]. I read an article that because of the reduction of coal shipments on this former DR&G line, UP may abandoned this route as well. This would jeopardize the California Zephyr because Amtrak could not afford the heavy maintenance expenses that a mountain route requires. (Update: a railfan video shows that at least some coal trans are still running on this route.)