Leatherbark Run is the name of a stream in Pocahontas County, West Virginia, as well as the name of the gap in the Allegheny Mountains carved by the stream as it flows southeastward toward the Greenbrier River.
The Leatherbark has the distinction of being West Virginia's highest stream. It begins at a natural spring on the south face of Bald Knob on Back Allegheny Mountain in the western half of the county. The elevation of its headwaters is over 4,680 feet above sea level. It then proceeds south down the side of the mountain, then turns eastward near Whittaker and continues in that direction until it flows into the Greenbrier at the town of Cass. The total elevation change from its headwaters to its mouth is approximately 2,230 feet, more than any other stream in the state.
Leatherbark Run was the site of a major logging railroad operation in the early 1900s. Surveyors for the railroad concluded that a railway up alongside of Leatherbark Creek was the only feasible way to cross the Allegheny Mountains to reach the vast spruce forests that thrived above 4,000 feet. Today, Cass Scenic Railroad still uses this route to carry passengers into the mountains via Leatherbark Run. The Leatherbark is crossed twice by the train as it winds into the high country. It is also crossed once by Back Mountain Road, just west of Cass.
The Leatherbark is also noted for its potential to flash flood. The Leatherbark can flood even when it is not raining in Cass because of the location of its headwaters in a very mountainous area that is notorious for its rapidly changing weather.