Idaho Geology The Plateau Regions

Parts of the greater volcanic Columbia Plateau of Washington

The Clearwater Plateau is the second region of Idaho formed like the Columbia Plateau Clearwater Plateau

Area drained by the Clearwater River, including the Palouse Hills

Tall rolling hills and gently sloping prairies A lot of it is ideal for farming for many reasons

Clarkston-Lewiston Moscow Post Falls Snake River Clearwater River WA ID Potlatch River Dworshak Clearwater and tributaries like the Potlatch

Snake River on border Clearwater joining from the east The Clearwater joins the Snake at the western edge of Idaho

Lowest point in Idaho – 738 feet at Lewiston

Originally formed by basalt flows

Granite peaks – Cottonwood Butte and Craig Mt.

Exposed as hills uplifted and basaltic lava eroded away

Much of the region formed by wind and water erosion. Covered by a thick layer of rich topsoil of eroded volcanic material mixed with clay-like glacial sediment blown in from Puget Sound (loess). This makes up the Palouse Hills.

Wheat farms of the Palouse with rich water- holding soil called loess

Clearwater Climate Fairly mild Summer temp. averages 89 degrees with cool evenings Winter temp. averages degrees Precipitation 20+ inches (25-55 in higher elevations) 4-6 month growing season! (the Banana Belt)

Irrigation not needed because of clayey glacial loess

The grasslands originally covering much of the region have now been generally replaced by domesticated grasses (wheat, oats, barley) and legumes (alfalfa, peas, lentils) Crop rotation and fallow fields help offset the loss of nutrients and water

Palouse

Camas Prairie

At higher elevations through the plateau and as the plateau in the east rises to meet the Rockies, evergreen forests are found. These are mainly………

Pine forests

Owyhee- Bruneau Plateau 3 rd Volcanic region in Idaho

Rolling hills and mountains; dry and sparsely populated

Mountains Jump Creek Hills Poison Creek Hills French John Hills Owyhee Mts.

Rivers Owyhee River Bruneau River Jarbridge River Salmon Falls Creek

Bruneau Gorge

Columbia Plateau lava flows included Owyhee- Bruneau

Lava layers from the many preceding fissure flows Owyhee-Bruneau becoming a plateau through uplifting forces. This is the main difference between it and the Snake River Plain

feet above the SRP; some peaks rising to 8000 feet

WA, OR, CA ID Why is it so dry? Rainshadow Effect

Climate Extreme and semi-arid Precipitation inches Summer average temp. = 88 degrees Winter average = 12 degrees

Southern Idaho Vegetation

O-B Summary Hostile environment and climate Ranching is main industry Low population density (more cows and sheep than people) Few towns Murphy is the county seat of Owyhee County (pop. 600)