Tunnel #1 - unofficially but universally called "Mud Tunnel" - was the first of only two tunnels on the D&RGW's San Juan Extension. (The other is Rock Tunnel / Tunnel #2, located four rail miles west.) Located at milepost 311.3, the bore passes 342 feet through a hill made largely of volcanic ash and mud, hence the name. Ever unstable, the entire tunnel is lined with wood.
As is the danger with steam locomotives and wood linings, a spark caught the tunnel liner on fire sometime in the 1920s. Consequently, a shoo-fly? alignment was constructed around the hill until the tunnel could be repaired. That grade is still visible today, though the tunnel was quickly placed back in service.
The liner continues to require maintenance, and was last replaced in 2004.
Maps and Photos
Photos of Mud Tunnel (Tunnel #1)