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Williamette Valley

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NameColor on MapEPA Code‡
Portland/Vancouver Basin3a
Willamette River and Tributaries Gallery Forest3b
Prairie Terraces3c
Valley Foothills3d

† Status: ✓ = Complete ○ = Needs Image … = Incomplete ∅ = Stub Only

This code refers to the US EPA's Level 4 ecoregion codes for the continental U.S., see here.


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About the Williamette Valley

The Williamette Valley is a level III ecoregion of the U.S., running north-south, located mostly in northwestern Oregon and extending slightly into Washington. The Williamette river is the central feature of this valley, which is surrounded by mountains to the west, east, and south.

The climate here is a marine west coast climate, tending towards Mediterranean, with wet winters and drier summers, and more moderate temperatures than is typical for a climate of this high a latitude. Relative to the Puget Lowlands to the north, this area is slightly drier and has slightly more unpredictable weather.

Naturally this area was covered by a mix of vegetation types. Like the areas to the north, there was significant coniferous forest, wetlands, and deciduous forests in riparian areas, but there were also more open habitats including prairies and oak savannahs.

This area is heavily utilized for cropland, industry, and urban development. The bulk of Oregon's population lives here, mostly in the metro area of Portland, with some in the Salem metro area as well. This is one of the primary agricultural areas.


1. Wiken, E., Griffith, G. "North American Terrestrial Ecoregions - Level III", Commission for Environmental Cooperation, (2011) Web.