A few miles south of the California-Oregon border, up a remote canyon on the Klamath River, the hum of heavy machinery marks the start of the largest dam removal project in U.S. history.

Hundreds of workers and scores of trucks and wrecking vehicles last month began dismantling a nearly century-old concrete dam, the first of four hydroelectric dams slated for demolition in an ambitious bid to restore one of the great rivers of the West.

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