US 421, US 23, and US 58 run concurrently with the Appalachia Division rail line through Moccasin Gap, where Moccasin Creek passes through Clinch Mountain. The U.S. Highways enter the town of Gate City; three congruent business routes pass through the center of town while the mainline of the U.S. Highways follows the flank of Clinch Mountain to the south of town. US 421, US 23, and US 58 receive their three business routes at an interchange west of Gate City. The U.S. Highways parallel the railroad and Little Moccasin Creek west between Clinch Mountain to the south and Moccasin Ridge to the north. The highways curve north and parallel the Clinch River to Clinchport, where the road meets the southern end of SR 65 and begins to follow Stock Creek. US 421, US 23, and US 58 pass by Glenita, where the railroad splits north to pass through the Natural Tunnel, the centerpiece of Natural Tunnel State Park. After passing through the Devil's Racepath, US 58 and US 421 split west from US 23 (Orby Cantrell Highway) as Daniel Boone Trail just south of the town of Duffield.