Tuesday, March 31, 2009


Ancient Lake Bonneville covered most of north-central Utah during the Pleistocene Epoch, about 14,000 years ago. The lake was filled by the melting of continental glaciers which were estimated to cover thirty percent of the Earth’s surface. There were severe climatic changes during this time which caused the extinction of mastodons, saber-tooth cats, ground sloths and Neanderthals, (sorry Manny, Diego and Sid).

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.
Most travelers across Idaho only see dry high desert. The state’s beautiful forested mountains, clear deep lakes, lush meadows and herds of big game remain a secret known only to those who leave the beaten path.


The Weaver of Grass said...

Idaho is one of the states i have never visited - but the wide skies and open scenery look wonderful.

Jeannelle said...

Great post, Leenie! The information is very interesting....I had never heard any of that before, about the Bonneville Flood and the resultant formation of the Great Salt Lake. Fascinating!

Your photos are beautiful! Thanks for sharing these scenes along the way to Boise. I love the wind turbine scene.....my son interned at the National Wind Institute in Colorado one summer and he gave us a tour to the top of a turbine!

Anonymous said...

Fascinating post Leenie, thank-you!

Woman in a Window said...

Huh, cool. To see such distinct differences in areas always astounds me. Very cool.

Linda Sue said...

After reading "up from the prairie" I viewed the land differently- before I thought , boring- this is a whole lot of nothing...It is ,in fact, fascinating geology!
My Dad was an amature geologist and lapidarian - taught me some appreciation but growing up in the middle of it didn't impress me until I left... beautiful land great photos.

juliet... said...

Been through that area a number of times. I have family in Idaho Falls, so it has been the "hanging" point for trips to Yellowstone and Jackson. I still want to go back and visit Craters of the Moon. Everytime I'm out that way it is the hottest time of the year, so the hot, hot craters area has been nixed due to heat. Maybe next time!

Egghead said...

Oh but there really are beautiful mountains and green lushness in parts of Idaho. I have visited Boise many times over the years. I grew up in Baker (OR) and was born in Weiser ID. My husbands family is from Idaho, Council to be exact. I have been huckleberry picking off the beaten paths many times with his aunt. Yes the drives can be dry and hot but there is richness hidden as well. Thanks for this post. Brings back memories.