The level "benches" on th opposite hillsides were the bottom of a huge lake that filled the Okanagan Valley when the Ice Ages created a ice dam that blocked the valley below. Stream runoff brought sand and gravel down side valleys, and when it hit the lake, it spread to form nearly-level lake bottom. Eventually the dam failed, unleashing a tremendous flood that scoured the lower valley and the Columbia basin downstream. Thr process repeated several times with recurring ice ages, leaving several layers of level benches.
The much larger and more famous ice dams at Missoula, Montana created floods that washed over northern Idaho and eastern Washington in roaring torrents hundreds of feet deep and almost as wide as the state, digging the Grand Coulee and other canyons in a matter of weeks.
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