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Multnomah Falls, Oregon, on the Columbia River Plateau just below the Bonneville Dam. Seventeen million years ago, lava began to pour out of huge fissures across an area of 200,000 square kilometers (80,000 square miles) in the northwestern United States and eventually formed a basalt plateau with an average thickness of more than 1 kilometer (half a mile). The rock is now deeply cut by the Columbia River and its tributaries. See page 663. [Michael R. Rampino, New York University, New York, NY 10003]


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Science. ISSN 0036-8075 (print), 1095-9203 (online)