Willamette Valley

The Willamette Valley ecoregion is a Level III ecoregion designated by the United States Environmental Protection Agency in the U.S. states of Oregon and Washington. Slightly larger than the Willamette Valley for which it is named, the ecoregion contains fluvial terraces and floodplains of the Willamette River system, scattered hills, buttes, and adjacent foothills. It is distinguished from the neighboring Coast Range, Cascades, and Klamath Mountains ecoregions by lower precipitation, lower elevation, less relief, and a different mosaic of vegetation. Mean annual rainfall is 37 to 60 inches , and summers are generally dry. Historically, the region was covered by rolling prairies, oak savanna, coniferous forests, extensive wetlands, and deciduous riparian forests. Today, it contains the bulk of Oregon's population, industry, commerce, and agriculture. Productive soils and a temperate climate make it one of the most important agricultural areas in Oregon.
The ecoregion covers an area of 14,900 square kilometers , lying mostly in Oregon, with a small portion lying across the Columbia River in southern Washington. The ecoregion lies in the Willamette Valley, which runs from south to north between the Oregon Coast Range to the west and the Cascades Range to the east. The ecoregion is drained mostly by the Willamette River and its tributaries, which flows into the Columbia River straddled by Portland, Oregon.

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