Comparison of properties of laharic (volcanic mudflow) and pyroclastic breccias leads to the conclusion that two described volcanic breccias near Mt. Rainier, Washington originated as lahars. The two volcanic-breccia deposits are typical of many breccias within a thick andesitic series (Eocene-Oligocene), suggesting that rapid denudation of nearby volcanoes was an important process in the accumulation of the lower Tertiary andesitic material within the southern Cascade Mountains of Washington.

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