In 1924 Mahan, as a junior, helped the Mountaineers post an 8–1 overall record, totaling 302 points in nine contests, the most of any Eastern squad, and outscored the opposition by nearly a 7–1 margin. Mahan was a first team All-American pick by Midweek Pictorial and Metropolitan News. Mahan was also named as a third team All-American right guard by Walter Camp, and was selected to the all-Eastern team.
In 1925, Mahan captained the Mountaineers to another 8–1 mark. Mahan is also a member of the West Virginia all-time team for 1919 to 1929. He was inducted into the West Virginia University Sports Hall of Fame in 1999.