Grand Coulee Dam crane-lifted buckets, each supporting eight tons of concrete. To cool the concrete and facilitate curing, about of piping was placed throughout the hardening mass. Cold water from the river was pumped into the pipes, reducing the temperature within the forms from to . This caused the dam to contract about eight inches in length; the resulting gaps were filled with grout. Until the project began, the stretch of the Columbia River where the dam was to rise was as yet unbridged, making it difficult to move men and materials. In , the Grand Coulee Bridge (a permanent highway bridge) was
Grand Coulee wide as Niagara Falls and three times as high. Steamboat Rock high and a in area, now stands as an isolated rise, but for a time it created two cataract. When the falls passed north of Steamboat Rock, it found a granite base beneath the basal flows. Granite lacks the close vertical joints of basalt, was resisted the erosion from the cataract's plunge. It remains as hills on the broad floor of the Coulee. Some gravel-bar deposits are visible along the Route 155. They provide evidence of eddies in the lee of rock shoulders. Dry Falls is at the head