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Valley Foothills

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About the Valley Foothills

The Valley Foothills is an irregularly-shaped region that almost entirely surrounds the Williamette Valley, and is also interspersed through its interior in a few places. It can be seen as a transitional region between the Williamette Valley and the surrounding mountains, including the Coast Range to the west and the Cascades to the east.

This region has the highest elevations and most rugged terrain within the Williamette Valley. It consists of rolling hills, with elevations reaching from 10-1,500 feet and local relief of 400 to 1,000 feet. It is underlain by a mix of andesitic basalt, a volcanic rock, and marine sandstone, a relatively erosion-resistant sedimentary rock. Soils here are variable both in their texture and fertility.

The climate is a temperate oceanic climate with a strongly seasonal precipitation pattern. Summers are dry and sunny, and winters are very wet and cloudy. Precipitation varies significantly throughout this region, but includes the areas of the Williamette Valley with the highest average rainfall totals, due to its higher elevations. Although total rainfall is high, many sites have xeric (drought-adapted) plant communities due to the combination of soils that do not hold moisture well, and the prolonged summer dry season.

This area was naturally almost completely forested, with Oregon white oak and Madrone on drier sites, and Douglas-fir more common on moister sites. There was also some western red cedar throughout.

Currently this site has greater forest cover than the bordering lowlands, but less than neighboring mountainous areas. The north of this area has significant suburbanization as part of the Portland, OR metro area, and in the south, also around Eugene, OR. There is significant agriculture, including pastureland, vineyards, orchards, and Christmas tree farms. There is also significant forestry in this region. The McDonald-Dunn Research Forest is located here, and there are also a few smaller protected forests in the north of this region.

Throughout most of this region, it surrounds the Prairie Terraces at lower elevations, and at a few spots it directly borders the bottomlands of the Willamette River and Tributaries Gallery Forest. At the northern end, this region mostly surrounds the Portland/Vancouver Basin. To the east, over its entire length, this region is bordered by the Western Cascades Lowlands and Valleys. At the south, there is a small border with the Umpqua Interior Foothills.

The western border with the Coast Range is more varied. In the south, this region borders the Mid-Coastal Sedimentary, and farther north, the Volcanics, but these borders are irregular and alternate in places. The very northwestern portion of this region is bordered to the north by the Willapa Hills.

References

1. Pater, D.E., Bryce, S.A., Thorson, T.D., Kagan, J., Chappell, C., Omernik, J.M. "Ecoregions of Western Washington and Oregon (Poster)", U.S. Dept., of the Interior, U.S. Geological Survey, Reston, VA (0000) Web.