Blowdown zone

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The lateral blast stripped away and knocked down trees. Two to three feet of blast material stripped away all trees and covered the ground. A few small patches of understory vegetation survived in places shielded by ridges or other natural features or protected by late-lying snow. The lateral blast also knocked down trees on about 143 square miles. Fragmented rock and ash blanketed the ground in a layer 4 to 78 inches thick.