Shoshone Falls

On the Snake River in southern Idaho. A gray day, but the falls are in fine form! Later in the season they often go dry because of upstream diversions for irrigation. Some water is also diverted for hydropower, in an installation off the pic to the left (inset).

Shoshone Falls lies in the spectacular Snake River Gorge, which was scoured and deepened around 18K years ago by the so-called Bonneville Flood. Lake Bonneville, an enormous Pleistocene lake covering much of western Utah, overtopped Red Rock Pass in southern Idaho and started spilling into the Snake drainage. The material where the overflow occurred was loose ("unconsolidated", in the jargon) and started eroding very quickly, to yield the natural equivalent of a dam failure. The top few hundred feet of Lake Bonneville spilled out this way in a matter of a few weeks! Geomorphological evidence indicates that at peak flow the gorge was completely filled brim to brim.