Moses Coulee glaciation on the Waterville Plateau includes polished and striated bedrock, glacial erratics, drumlinoid topography, eskers, moraines, meltwater channels, and glacial till. The Withrow Moraine complex marks the maximum southern extent of the Okanogan Lobe, and a series of recessional moraine complexes represent retreating ice margins. Ice damming of the Columbia River formed Glacial Lake Columbia and Lake Spokane, larger lakes than Lake Roosevelt, which is currently backed up in the same location behind the Grand Coulee Dam. A precursor to glacial-flood-cut Moses Coulee existed prior to the glacial floods as a drainage basin with a number of side streams, draining
Grand Coulee Dam in the newspapers, stating exploratory drilling at the Grand Coulee site found no granite on which a dam's foundations could rest, only clay and fragmented rock. This was later disproved with Reclamation-ordered drilling. Ditchers hired General George W. Goethals, engineer of the Panama Canal, to prepare a report. Goethals visited the state and produced a report backing the ditchers. The Bureau of Reclamation was unimpressed by Goethals' report, believing it filled with errors. In , President Warren G. Harding visited Washington state and expressed support for irrigation work there, but died a month later. His successor, Calvin Coolidge, had little