Drill, blast, and clear. Drill, blast, and clear. For three months workers repeated this process, carving through 600 feet of solid granite (granodiorite) to complete Skyline Drive's greatest construction challenge, Marys Rock Tunnel.
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.
Was Marys Rock Tunnel really needed or was it built just for show? Area historian Darwin Lambert explained, "the tunnel may have been designed into Skyline Drive partly for show, but it seemed justified to eliminate extensive scars and expensive rock retaining walls."