When did major dam construction begin on the Columbia River?

Major dam construction on the main stem of the Columbia River began in the 1930s. This era of multipurpose development was initiated by the federal government with the construction of the Grand Coulee Dam and the Bonneville Dam.1

These projects marked the start of a transformation that eventually saw the river's fall within the United States converted into a series of "stair steps" by 11 major dams on the main river, which provide essential hydroelectric power, irrigation, and flood control for the region.12