Dry Falls is thought to be the greatest known waterfall that ever existed. Where is it?

Dry Falls is a 3.5 mile long scalloped precipice in central Washington. According to the current geological model, catastrophic flooding channeled water over this 400-foot (120 m) rock face at the end of the last ice age. At this time, it is estimated that the flow of the falls was ten times the current flow of all the rivers in the world combined.