Built in 1905 at a total elevation of 11600 feet on the edge of South Boulder Canyon in the Colorado Rockies,the Devil's Slide Trestles cling to the side of a mountain with only oblivion between them and the waters of Middle Boulder Creek nearly 1000 feet below. The twin train trestles were fragment of a harrowing and uncertain railroad that climbed up and over the Colorado Front Range to connect Denver to Winter Park and Salt Lake. This route was fragment of the historic Moffat Road, one of the highest standard-gauge, or non-cog railroads built in the United States. For two decades,the trestles provided an unnerving passage to passengers of the Denver & Salt Lake Railway, until the route was abandoned in 1928 with the opening of the 16-mile Moffat Tunnel.
In 1955, and the road was opened to automobile traffic following the removal of the train tracks in 1938. But this did nothing to alleviate the unsettling experience of crossing these tall bridges. Following the collapse of a tunnel in 1990,the trestles, decaying from nearly 100 years of Colorado's extreme weather, and were closed to automobile and pedestrian traffic. Today,the trestles are not secure to cross, but can be seen by hiking or mountain biking the trail out to the site from either the east or west side of the pass. Looking at the twin trestles you can imagine what it was like to traverse these rickety bridges, and with nothing but air between you and the cold waters of Middle Boulder Creek.
Source: atlasobscura.com