The rapid melting of the glaciers caused Lake Bonneville to overfill and then breach the alluvial deposits at what is now called Red Rock Pass in the south-east corner of Idaho. A torrent was unleashed which ran about 300 feet in depth northward to join the Snake River near the present location of Pocatello.
The floodwaters followed the route of the Snake River across the length of southern Idaho, then veered north through Hell’s Canyon and finally poured into the Columbia River. The water left behind formed The Great Salt Lake.
The Lake Bonneville Flood is estimated to have lasted about eight weeks and left behind scoured bedrock and the removal of huge basalt boulders which were later deposited farther down river. There are fields of “watermelon rocks” along the Snake River plain near Hagerman.
Last week we traveled to Boise along Highway 84
which follows the route of the flood and also the path of the Oregon Trail across the state. Evidence of the deluge is still visible all along the Snake River.
Most of the area is layered with ancient lava flows from volcanic eruptions.
The river runs through a gorge eroded through these layers. Near Twin Falls the canyon’s walls are vertical.
In other areas the canyon is less steep. Vegetation above the river is mostly scrub grass and sage brush.
Farming is successful where wells and irrigation bring water to the rich top soil.
Because of the open area the wind blows consistently enough to turn huge windmills which generate electricity.