What is Columbia Plateau?

The Columbia Plateau ecoregion is a Level III ecoregion which the United States Environmental Protection Agency designed it in the U.S. states of Oregon and Washington, with little areas over the Washington state border in Idaho. This ecoregion stretches across a wide swath of the Columbia River Basin from the Dalles, Oregon to Lewiston, Idaho to Okanogan, Washington near the Canadian border. It incorporates nearly 500 miles of the Columbia River, as well as the lower reaches of major tributaries. It’s named for the Columbia River Plateau, a flood basalt plateau created by the Columbia River Basalt Group during the late Miocene and early Pliocene.

The arid sagebrush steppe and grasslands of the region are bordered by moister, predominantly forested, mountainous ecoregions on all sides. The underlying basalt is up to two miles thick and partly covered by thick loess deposits. Where the precipitation amounts are sufficient, the deep loess soils have been extensively cultivated for wheat. Water from the Columbia River is subject to resource allocation debates involving fisheries, navigation, recreation, irrigation and hydropower, and the Columbia Basin Project has considerably transformed much of the area of the region to agricultural use.

This plateau ecoregion includes at least fourteen Level IV ecoregions

1. The Channeled Scablands
2. Loess Islands
3. Umatilla Plateau
4. Okanogan Drift Hills
5. Pleistocene Lake Basins
6. Dissected Loess Uplands
7. Yakima Folds
8. Palouse Hills
9. Deep Loess Foothills
10. Nez Perce Prairie
11. Deschutes/John Day Canyons
12. Lower Snake and Clearwater Canyons
13. Okanogan Valley
14. the Umatilla Dissected Uplands

Image Caption: Alkali Lake in a coulee, Eastern Washington State, United States. Credit: Jami Dwyer/Wikipedia (CC BY-SA 2.0)