This is just outside Martin (old Beaver Creek) KY on what was once called the Elkhorn and Beaver Valley Railroad (there’s a split in Martin: the E&BV went west, the Long Fork subdivision went south).
It’s supported by wood bracing and framing. This line was built in the 1913-1914 time period, but I don’t know if this wood structural support dates to that time. The timbers are gray with age and have been heavily imbued with creosote. This is an abandoned line.
(I also don’t know who owns the two red plastic balls down on the left)
Blogging the Railroad Tunnels 
This line isn’t abandoned, they run at least a train or two a day here still. This is a non stop railroad to Deane, KY, over some the highest railroad trestles that the C&O built. The line originally ended at Wayland, KY and in the late 1940s was extended to Deane to compete with the L&N railroad at the same mine, the tracks weren’t connected until after the CSX merger. From Deane the line continues on the former L&N on the Rockhouse SD to Hazard, KY. From Hazard on the same former railroad on the Eastern Kentucky (EK) SD to Winchester, KY; there it connects to the mainline of the CC SD. Thanks for sharing, there are a total of four tunnels on the E&BV, all have been gutted and rebuilt at some time.
Thank you very much for this great information!