Can geologists really know all this just by looking across this landscape? For thousands of years, layer after layer of slow moving lava spread out over great plains.  As it cooled it contracted and fractured creating vast expanses of columnar basalt.  Icefields expanded covering the region grinding channels and blocking rivers. Colossal Lake Missoula formed behind ice dams.  Ice dams broke and flood waters raged.  Ice advanced.  Lakes refilled.  Ice dams broke and flood waters raged.

Each time, Wallula Gap was the restriction that held back a wall of water some 1250ft high and like a nozzle it generated a powerful stream that eroded enormous basins and flow streams in the basalt fields.

The Columbia River flows through that gap now.  We hiked to the top of its craggy cliffs for a pretty fantastic view of this handiwork.