Callahan is a common name in this area. There’s a Callahan Avenue in Appalachia and a Callahan Creek that’s near here. I assume that is the origin of the name of this tunnel.
Anyway, this is the other tunnel on that old (1890) Fremont branch of the L&N line that ran from Appalachia to Big Stone Gap. It’s been unused since 1986 or so.
This is Callahan’s Nose tunnel from the Appalachia side:
The short, 135′ tunnel is centered at 36.884670, -82.786329.
This is the south face. The overpassing track is active N&S.
I took these when I was more interested in the pleasant hike from Appalachia to Big Stone Gap than I was the tunnels, but I took one picture because I was surprised at the brick interior of this tunnel (below). I suspected that it showed that the tunnel was an older one and, surprise, I was right. Bricking was an earlier technique of shoring up a tunnel. After the turn of the century, they generally used concrete to ensure the integrity of a tunnel. Enlarge the picture and you can clearly see the brick.
Blogging the Railroad Tunnels 
This is actually on the the old Cumberland Valley main that ran from Corbin, KY to Millers Yard. The Fremont Branch is an old Clinchfield branch in Clint Wood, VA.
I agree, but I wonder which Callahan’s nose this refers to?