Soap Lake and the Dam mark either end of the Grand Coulee. The Falls are a 3.5 mile (5,600 m) long semi-circular scalloped precipice. Unlike other waterfalls in the USA called Dry Falls, this one is actually dry. From Wikipedia: "According to the current geological model, catastrophic flooding channelled water at 65 miles per hour through the Upper Grand Coulee and over this 400-foot (120 m) rock face at the end of the last ice age. It is estimated that the falls were five times the width of Niagara, with ten times the flow of all the current rivers in the world combined." Geological and climate changes around 20,000 years ago eventually dried up the water sources.