Priest Rapids Dam Brochure

The Grant County Public Utility District, based in Ephrata in the dry Columbia Basin of central Washington, built both Priest Rapids Dam and Wanapum Dam on the middle Columbia without federal construction money — an unusual achievement for projects of that scale. Congress authorized the PUD to proceed in 1955; revenue bonds funded groundbreaking in 1956. Priest Rapids began generating power in 1959 and was formally complete in 1961; Wanapum, eleven miles upstream, first generated electricity in 1963 with all ten units running by 1964. The two captions here — one dam done, one under cranes — date this brochure to roughly 1961–1963.

The geology section explains what both dam sites rest on. The "flows" the text references are Columbia River Basalt — thick sheets of flood basalt (lava that spread in flat pulses across the landscape rather than building a cone) that hardened across the plateau in repeated eruptions between roughly 6 and 17 million years ago. The ice-age catastrophes described — glaciers from Canada, "ice-damned lakes northeast of Spokane" breaking loose — are now called the Missoula Floods. When a glacial ice dam holding a lake roughly the size of Lake Erie failed, walls of water swept south and west across the Columbia Plateau and carved the Channeled Scablands. The Grand Coulee and Washtucna Coulee named in the text are coulees (broad dry channels left by those flood surges) that remain the most legible scars of that era on the plateau.

The aerial photograph looking north through Saddle Mountain Gap shows the Columbia River bending through a notch in the Saddle Mountains — a ridge the floods themselves helped cut. The name Wanapum on the upstream dam honors the Wanapum people, the indigenous band long resident along that stretch of river, who were displaced when the reservoir filled.