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Frenchman Coulee is one of the most beautiful features left behind by the great Ice-Age floods. Frenchman Coulee is a dual coulee and cataract system. Like its neighbor to the north, Potholes Coulee, Scabland floods created Frenchman Coulee. During the first stages of flooding, the water levels between the flood-filled Quincy Basin and the Columbia River immediately west of Evergreen Ridge approached 700 feet over just a few miles.
This incredible difference in water levels caused floodwaters to relentlessly eat away the underlying rock layers. Erosion continued for at least as long as it took for the water level in the Columbia Valley to rise to about 1200 feet, or until the floodwater supply was exhausted.