East of Evanston, Wyoming, completion of the Union Pacific's long climb out of Echo Canyon did not mean easy going from there on. In particular, from Piedmont to Leroy the original line encountered steep grades and sharp curves. As part of his general rebuilding of the Union Pacific after becoming head of the bankrupt property in 1897, E.H. Harriman decided to build a new line from Mills to Leroy, completely bypassing Piedmont (which eventually became a ghost town like Sherman) and shortening the mainline by ten miles while drastically reducing grades and curvature. The result was the Aspen Tunnel, located northwest of the original Aspen siding and 5,941 feet long. Begun in 1899, the tunnel was finally opened in 1901 after numerous problems with unstable geology and water seepage.
The single track Aspen tunnel eventually became a severe bottleneck as traffic grew over the following decades, and after World War II UP management finally decided that a second tunnel was essential. The result was the Altamont Tunnel, built parallel to and slightly south of the Aspen Tunnel (whose west portal is seen here).
