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 and during construction, workers and engineers experienced problems. Contracts for companies to construct the various parts of the dam were difficult to award as few companies were sizable enough to fill them. This forced companies to consolidate. In addition, Native American graves had to be relocated and temporary fish ladders had to be constructed. During construction additional problems included landslides and the need to protect newly poured concrete from freezing. Construction on the downstream Grand Coulee Bridge began in and more considerable earth-moving began in August. Excavation for the dam's foundation required the removal of of dirt and stone. To