John Milner was tasked by the State of Alabama in 1858 to survey a route across Shades Mountain for the S&N Railroad. The S&N was intended to connect the mineral resources south of Shades Mountain, coal, limestone, and iron ore, with the developing industries in the area of Jones Valley that would become Birmingham around the junction of the S&N Railroad and the Alabama and Chattanooga Railroad. Brock Gap was selected and the rail line north was constructed between 1858 and 1871, interrupted by the Civil War. At Brock Gap, workers used nitroglycerin to blast a cut 75 feet deep through limestone bedrock.