Drill, blast, and clear. Drill, blast, and clear. For three months workers repeated this process, carving through 600 feet of solid granite to complete Skyline Drive’s greatest construction challenge, Marys Rock Tunnel.
Mary’s Rock Tunnel is a 610-foot long tunnel blasted through the mountain that Skyline Drive passes through. Constructed in 1932, it is considered one of the engineering feats of Skyline Drive.
In order to eliminate extensive scars and expensive rook retaining walls it was necessary to pierce Mary’s Rook Mountain with a 600-foot tunnel. A sub-contractor completed in a satisfactory manner the job of boring through this solid granite. By careful blasting both portals were preserved in their natural rock settings A little more than three months was required to dig through, and several springs were encountered during the blasting operations. Because some of these still exist there is drippage from the ceiling in the winter and spring seasons.
Twice each day workers drilled 40 holes, each 12 feet deep, into the tunnel’s rock face. Five hundred pounds of dynamite filled the holes, then detonation. A local newspaper described the process:
“After the blast goes off with a mighty roar it requires two or three hours to clear away the loose boulders and stone and to roll them over the side…. Three 8-hour shifts of about 15 men each are on duty… the machinery never being idle except on Sunday…. Every day 15 or more feet of solid rock are eaten away by the blasts.”
In January 1932, they broke through to daylight. Almost immediately venturesome sightseers drove through.
Mary’s Rock is also known as Marys Rock, is a 3,514-foot (1,071 m) tall mountain in Shenandoah National Park. The peak is just south of the Thornton Gap Entrance of the park, and north of the taller Pinnacle. Mary’s Rock is the eighth highest peak in Shenandoah National Park.