Original caption Grand Coulee Dam the worlds largest concrete structure under construction by the Bureau of Reclamation on the Columbia River in eastern Washington Three quarters of a mile long this gigantic barrier will be when completed feet high and will control for irrigation flood control navigation and power generation the second largest river in the nation Concrete is being poured in the east section in the foreground while the bedrock in the central section where the river formerly flowed is being laid bare The huge block of concrete in the west section towers in the background
