Four Seattle-based news photogs covering the construction of the Mud Mountain Dam in early 1941. Left to right: Charles Perryman of News of the Day, Chalmer Sinkey of Fox Movietone, Earl Nelson of Universal Newsreel and Bill Hudson of Pathe News.

Charles Perryman wrote about covering the dam’s construction:

One of the world’s strangest engineering undertakings is now under way at Mud Mountain Dam in the State of Washington. They are covering a deep canyon with one of the largest known tents so they can build a dam under it, all the while keeping everything nice and dry, they hope.

Thirteen thousand square yards of heavy waterproof canvas was cut to fit the zig-zag edges of the canyon, where an area 196 by 328 feet will be covered. The canvas weighs 30,000 pounds dry and will be suspended by overhead cables. A series of pulleys and cables make it possible to clear the snow from the top of it and around the canyon walls has been constructed gutters into which the huge tent can drain.

Under this huge protecting canvas men and machinery will work for many months to come on the earthen core of Mud Mountain dam.

Newsmen were not permitted to ride up and down into the canyon on the “skip” and, as you can see by the photograph, the walls are straight up and down, making it a tough job getting outfits in or out, hence the Eyemos.