As glaciers scour the landscape, they pick up massive boulders and move them far from their point of origin. When the glacier that formed Glacial Lake Missoula's dam burst, uncountable boulders embedded in its ice were carried along with the floodwaters. As these ice blocks melted, the boulders dropped out of the flow. Today, boulders with origins in the mountains of Montana and British Columbia can be found along the flood paths as far away as Oregon's Willamette Valley.

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