Level IV: (3a) Portland/Vancouver Basin

Level IV (3a) Portland/Vancouver Basin

The Portland/Vancouver Basin ecoregion (named for the cities of Portland and Vancouver) is a geological depression at the base of the Portland Hills fault-block.  The region covers 305 square miles (790 km2) in Washington and 269 square miles (697 km2) in Oregon, including the northern and eastern suburbs of the Portland metropolitan area.

It contains the confluence of the Willamette and Columbia Rivers and is composed of deltaic sands and gravels deposited by Pleistocene floods, notably the Missoula Floods.

Elevation varies from 0 to 300 feet (0 to 90 m), with buttes as high as 650 feet (200 m).

Historically, the basin was characterized by Oregon white oak groves and Douglas-fir forests on the uplands; black cottonwood groves on riverbanks and islands; Oregon ash, red alder, and western redcedar in riparian areas; and prairie openings maintained by Native American burning, with camas, sedges, tufted hairgrass, fescue, and California oatgrass. Numerous wetlands, oxbow lakes, and ponds can still be found, but today the region is dominated by urban and suburban development, pastures, cropland, and tree farms.

The climate is usually marine-influenced, but easterly winds from the Columbia River Gorge periodically bring continental temperature extremes.  It contains several National Wildlife Refuges within the Ridgefield National Wildlife Refuge Complex.[2][3]

Source: Wikipedia

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