​er·rat·ic:

​noting or pertaining to a boulder or the like carried by glacial ice and deposited some distance from its place of origin.

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Most erratics in SE Washington were rafted in on icebergs after the breakup of the Glacial Lake Missoula ice dam.

An erratic boulder enveloped in ice at the base of the Omoo Glacier, British Columbia.

Erratic Rock Types

A granodiorite erratic boulder lies 700 ft above the Columbia River at Wallula Gap.

An argillite boulder as it melted out of a grounded iceberg in Oregon's Willamette Valley.

Painting by Stev Ominski and Brian Swaren

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Erratics

Bergmounds

Two bergmounds

of ice-rafted debris on Rattlesnake Mountain (RM). Note large erratic (circled)