Columbia Plateau Ecoregion

Description & Physiography

The Columbia Plateau is a broad expanse of sagebrush covered volcanic plains and valleys, punctuated by isolated mountain ranges and the dramatic river systems of the Snake, Owyhee, Boise and Columbia. Covering 301,329 km2, the Columbia Plateau stretches across the sagebrush steppe of southern Idaho, connecting the Columbia Basin of eastern Washington and Oregon to the northern Great Basin of Nevada, Utah and California. State representation in the ecoregion is varied with Oregon having the largest percentage of the area at 32%, followed closely by Idaho. Nevada and Washington have similar representations (17-18%) but California, Utah and Wyoming have only minor area within the ecoregion.


Elevations range from near sea level at the western end of the ecoregion to over 3000 meters on the highest mountain peaks. Precipitation occurs on a declining gradient from west to east with forest vegetation being supported only at higher elevations. In the rain shadows of mountain ranges there are alkali deserts that receive less than 15 cm of precipitation a year. Geologically and ecologically speaking, much of the ecoregion has quite modern origins dating back only a million years to the Pleistocene.

Plants & Animals

At least 239 vulnerable plants and animals (species that are considered to be globally threatened with extinction), including approximately 72 endemic plant species, are found in the Columbia Plateau ecoregion. The vulnerable species occur in all habitats and sections of the ecoregion but they are not distributed equally across it. There are concentrations of endemism in unique habitats and there are also concentrations of vulnerable species found in habitats that have been significantly altered by human activities. Some of the most threatened species are invertebrates which are only beginning to be taxonomically defined by experts.

In this semi-arid land it is instructive to be reminded that the ecoregion’s fisheries are an important part of its diversity. The Columbia River system, first bisecting the ecoregion between Oregon and Washington and then forming the core of its extent in Idaho and stretching all the way into northern Nevada, at one time sustained one of the largest salmon runs in the world.

Today, the salmon runs have declined to less than a tenth of their former size due to the effects of dams, diversions, over-fishing and upland habitat degradation. The fisheries in those portions of the ecoregion not in the Columbia River basin are made up of numerous isolated desert fishes that are threatened throughout the ecoregion. The sagebrush steppe ecosystem supports huge herds of pronghorn that still have seasonal migrations and numerous species of birds of prey nest here at higher densities than anywhere else on earth. Approximately 46 plant community alliances (according to the Gap Analysis Program (GAP) of U.S. Geological Survey) and approximately 450 plant community associations (according to TNC/Heritage classification) occur in the Columbia Plateau. These plant communities are representative of the incredible biological diversity present in the ecoregion. Over 20% of these plant associations (105 plant community associations) are considered vulnerable by Heritage Programs in the ecoregion. Riparian and aquatic natural communities, that are only now beginning to be classified, represent along with their resident species another aspect of diversity that is yet be fully realized.

Humans & History

The Columbia Plateau’s economic base remains firmly rooted in agriculture and commodity extractive related businesses and industry, although there are strong indications that extractive sectors of the economy are declining in importance. Irrigated agriculture is the most significant economic force in the ecoregion with crops ranging from potatoes and peas to wheat and alfalfa. Agriculture is prominent throughout the Snake River Plains of Idaho and the Columbia Basin which dominates portions of three states: Oregon, Washington, and Idaho.

Throughout much of the rest of the ecoregion ranching is the dominant industry. Small family ranches mixed in with larger corporate ranches dot vast areas of the Basin & Range country and the Owyhee Uplands. Industrial development is limited mostly to Boise and the Tri Cities of Washington. One of the largest employers in the ecoregion is the federal government which is tied to its prominent land ownership. Population centers are widely dispersed in the ecoregion with only one metropolitan area, Boise, Idaho, exceeding 100,000 in population. Other cities are growing rapidly, however, with the Tri Cities of Washington (Kenniwick, Pasco, Richland); Bend, Oregon; Moscow, Twin Falls and Idaho Falls, Idaho all likely to become major centers in the near future. Growth is occurring in these population centers but it has not dramatically affected much of the ecoregion which still retains its rural character.


Only 3% of the ecoregion has formal management designation that gives priority to maintaining biological diversity. To put this figure in perspective, approximately 3% of the terrestrial land base world-wide is managed for biodiversity. Biodiversity designations include Research Natural Area (RNA), Area of Critical Environmental Concern (ACEC), National Wildlife Refuge, TNC Preserve, National Park, Wild & Scenic River, and established Wilderness Area. Of the 3% that is designated for biodiversity protection, a much smaller percentage are adequately designed and managed to maintain that diversity. Many of the existing conservation areas are small, continue to support competing and unbalanced management goals (such as cattle grazing and recreation), and receive only minimal management and monitoring.

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Links to Completed Ecoregional Assessments

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