I love the detail in these old USBR photos. If you zoom in on them, you can see some pretty cool stuff. This one is no exception. It gives us a good downstream look at the temporary coffer dam. You are looking upstream toward what would eventually become Lake Powell. The coffer dam was built to divert the Colorado River water into the two spillway tunnels that routed the water through the canyon walls to the downstream side of the dam site. The right side tunnel (the Visitor Center side) was the primary tunnel and it handled most of the diversion water.
The excavation going on in this picture is prep work for laying the base of the dam. I remember reading or hearing somewhere that the base concrete for Glen Canyon Dam was poured 135 feet below bedrock. This picture captures that excavation. Some of the dirt and rock that was Continue reading