Tennessee Pass Railroad Tunnel West Portal, Colorado

Tennessee Pass is mostly remembered as an important railway route over the Continental Divide. A narrow gauge railway was built over the pass from Leadville in 1881. At that time Leadville had a population of around 30,000, and was among the largest cities between St. Louis and San Francisco. A few years later a tunnel was bored through the mountain, and the rails were converted to standard gauge. The line connected to Aspen, and was a busy route between Denver and the West for a few decades.  A new and larger tunnel opened next to the old one in 1945, though traffic was already diminishing, favoring the shorter route through the Moffat Tunnel, which opened in 1928. The last train through Tennessee Pass came through in 1997, and the tracks have been quiet ever since. In 2012, part of the older train tunnel collapsed, creating a sinkhole in the highway above it. That tunnel was sealed off. The 1945 tunnel remains open, and the route has recently been considered as a potential backup for transcontinental freight—if the Moffat Tunnel were to close, Union Pacific would have to reroute traffic out of the state into Wyoming.