“V-901   SOUTH ENTRANCE TO NATURAL TUNNEL, SHOWING THE APPROACH OF A MIGHTY SOUTHERN RAILWAY DEISEL ENGINE, NATURAL TUNNEL, VA.”  Yeah, they misspelled “diesel”.
The plate number is E-10246

On the reverse:

The Natural Tunnel, located on U.S. Highway 23, 14 miles west of Gate City, Virginia, in Scott County, is said to be the only Natural Tunnel in the world used by a railroad.  Through it the Southern Railroad has hauled many million tons of coal from the rich deposits of Southwest Virginia.

(Kodachrome by Robert Suttle)

In pencil:  1951

Published by Asheville Post Card Co., Asheville, N.C.