Drilling jumbos (aka Williams Jumbo) mounted on the back of a truck for starting construction of lower portal No. 4, Arizona side of Black Canyon. 9-26-31. (This first wood-frame jumbo was experimental - the jumbos later were steel pipe)
Looking up Black Canyon from a point below all the lower portals, showing the Government pumping plant (lower left), the Six Companies' compressor plant (middle left), the location of the lower portals, & the highway loop above the canyon wall (upper center) - 7/30/31.