Roll On, Columbia, Roll On near Cascades Rapids, in The Dalles, and on Memaloose Isle. The final three verses describe the construction of two Columbia River dams: Bonneville Dam and Grand Coulee Dam. Bonneville Dam, the first dam built on the Columbia, had locks built into it so ships could navigate past it, alleviating worries that a dam would prevent the shipment of goods and passengers along the length of the river. Guthrie's lyrics describe Grand Coulee Dam as "the mightiest thing ever built by a man"; when it was built it was the largest concrete dam in the world, and as of 2012 it
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