Floodwaters from ancient Lake Missoula uncovered basalt underneath a mixture of sediment and created deep canyons, plunge pools and cataracts. The current was so powerful that some of these depressions are more than 200 feet deep.
REMNANTS OF MASSIVE EROSIONAL ENERGY
Among the widest channels is the Cheney-Palouse Tract, spanning 20 miles wide and 600 feet deep. The south valley wall of the ancestral Palouse River, which flowed through the now dry Washtucna Coulee and onto the Columbia River, was overtopped.
As seen today, the current course of water is from the Snake River to the Palouse Falls. There is an upper fall with a drop around 20 feet, north-northwest of the main drop, 198 feet.