The Okanogan lobe of the Cordilleran Glacier moved down the Okanogan River valley, covering 500 mi2 of the Waterville Plateau and blocked the ancient route of the Columbia River, backing up water to create Glacial Lake Columbia and Lake Spokane.
The Okanogan lobe of the Cordilleran Glacier slid down the Okanogan River valley, encompassing 500 square miles of the Waterville Plateau and impeding the old path of the Columbia River. This movement caused water to back up and form Glacial Lake Columbia and Lake Spokane.