![An explosion occurs during the construction of the Hoover Dam. Workers, called high-scalers, are suspended from the Black Canyon wall and would drill holes into the rock with 44-pound jackhammer drills. The holes are then loaded with dynamite in order to clear Black Canyon down to bedrock.](http://media.lasvegassun.com/media/img/photos/2008/04/22/scaled.1051_hoover_construction_t653.jpg?214bc4f9d9bd7c08c7d0f6599bb3328710e01e7b)
Sun File Photo
An explosion occurs during the construction of the Hoover Dam. Workers, called high-scalers, are suspended from the Black Canyon wall and would drill holes into the rock with 44-pound jackhammer drills. The holes are then loaded with dynamite in order to clear Black Canyon down to bedrock.