Dry Falls overlook
47.607036°N 119.363455°W

Dry Falls is just a small part of what are referred to as the Channeled Scablands,  These eroded rocks are approximately 3,000 square miles in area. Dry Falls and the Dry Falls Lake can be seen from the Dry Falls overlook here.  The story began in the Pleistocene when ice from the great continental glaciers that once extended into the northern United States formed ice dams.  Lake Missoula filled behind the dams covering 3,000 square miles and 4,350 feet in depth.  The ice dams ruptured several times releasing water at a rates of 200 times that of the Mississippi River in rare flood stages.  Huge potholes and drainage-flood features formed throughout the scablands as well as a temporary falls called Dry Falls here which is 4 miles wide and 400 feet high.  Water poured over the falls during the ensuing floods.  It is now known that there were at least 80 floods over the scablands during a period of 3000 years.  Stop 4 Baker et al.

"Perhaps the most famous cataract in the Channeled Scabland is “Dry Falls,” which is part of a complex that extends over a width of 5.5 km, with a maximum vertical drop of ~120 m (Fig. 24). Dry Falls is at the northern end of Lower Grand Coulee, which was excavated by cataclysmic floodwater from a zone of fractured basalt along the axis of the coulee monocline (Bretz, 1932). It is also at the upstream terminus of an inner channel that receded headward into the Hartline Basin, near Coulee City, Washington. Bretz et al. (1956, p. 1029) hypothesized that the Channeled Scabland cataracts formed subfluvially rather than by the plunge-pool undercutting classically illustrated by Niagara Falls. This hypothesis is supported by high-water mark evidence (Baker, 1973a). Bretz (1932) also described the initiation of a 250 m cataract near Coulee City, which receded more than 30 km upstream to create the Upper Grand Coulee "

Dry Falls

Dry Falls is a 3.5 mile long scalloped precipice in central Washington, on the opposite side of the Upper Grand Coulee from the Columbia River, and at the head of the Lower Grand Coulee. Ten times the size of Niagara, Dry Falls is thought to be the greatest known waterfall that ever existed. According to the current geological model, catastrophic flooding channeled 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. 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.

• http://en.wikipedia.org/wiki/Dry Falls
• Page 202 - Dicka, A. B., 2012, 101 American Geo-sites you've gotta see: Mountain Press Publishing Co., 250p.
• Page 33 - Baker, V. R., 2016, Pleistocene megaflood landscapes of the Channeled Scabland: The Geological Society of America Field Guide 41