The rhythmic Touchet Beds in the Walla Walla and lower Yakima valleys resulted from many separate backfloodings by hydraulically ponded glacial Lake Missoula water. At least once this episodic lake briefly contained half the 2130km3 of water that catastrophically drained the largest glacial Lake Missoula. The lack of weathering or soil within the Touchet Beds suggests that all rhythmites are late Wisconsin. Bottom sediment of glacial Lake Missoula in Montana consists of rhythmites each interpreted as the record of a gradually deepening lake. 40 superposed rhythmites record about 40 late-Wisconsin fillings and emptyings of glacial Lake Missoula. -from Author
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About forty last-glacial Lake Missoula jokulhlaups through southern Washington.