Jenson Tunnel

Jenson Railroad Tunnel is the first and only railroad tunnel in the present state of Oklahoma. It was constructed through Backbone Mountain during 1885–86, by the Fort Smith & Southern Railway (FSSR). and has remained in service until the present. At the time it was built, the tunnel was located in the Choctaw Nation in Indian Territory. Since Oklahoma became a state in 1907, the tunnel site has been part of Le Flore County, Oklahoma. It is now primarily used by the Kansas City Southern Railroad (KCS), and is sometimes referred to as the KCS - Jenson Tunnel.

History
Jenson Tunnel is located on private property northeast of Rock Island and is the only known railroad tunnel in Oklahoma. Now used by the Kansas City Southern, it was built by Frisco Railway in 1885–86. The tunnel was created through Backbone Mountain in what is now Le Flore County, Oklahoma.

One blogger reported that the tunnel was built on the east side of the Arkansas-Indian Territory border, but that a subsequent realignment of the border put it entirely inside the present state of Oklahoma.

Description
The tunnel is 1180 feet long and has a single track. The deck width is 14.0 feet and the clearance above the deck is 20.0 feet. Its elevation is 600 feet above mean sea level. The tunnel has various lengths of lining and arching. 624 feet of the interior is unlined and has no arching. About 324 feet at each end are lined with stone and have a brick arch. 62 feet. The rest of the length (118 feet) has timber posts and arches.

NRHP listing
The tunnel was listed on the National Register of Historic Places (NRHP) on May 13, 1976. Reference number is 76001567.