Washington State Route 17 Coulee City–Brewster branch of PSH 10 was codified in 1931 as a branch of State Road 10 and re-codified in 1937, during the creation of the primary and secondary state highways; however, the highway was not built between Sims Corner and Bridgeport until the 1950s. The Soap Lake–Coulee City branch of PSH 7 was established in 1937 to serve as an alternate route to SSH 2F, avoiding the Grand Coulee Dam. In 1951, the PSH 10 branch between Bridgeport and Brewster was moved north of the Columbia River via the newly built Columbia River Bridge on the present route of
Grand Coulee Dam Clapp were pumpers, while many influential businessmen in Spokane associated with the Washington Water and Power Company (WWPC) were staunch ditchers. The pumpers argued that hydroelectricity from the dam could cover costs and claimed the ditchers sought to maintain a monopoly on electric power. The ditchers took several steps to ensure support for their proposals. In 1921, WWPC secured a preliminary permit to build a dam at Kettle Falls, about upstream from the Grand Coulee. If built, the Kettle Falls Dam would have lain in the path of the Grand Coulee Dam's reservoir, essentially blocking its construction. WWPC planted rumors