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Napa-Sonoma-Lake Volcanic Highlands

Ecoregion in Coast Ranges, CA

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The Napa-Sonoma-Lake Volcanic Highlands ecoregion has two separate units. In the north, in Lake County, the region includes the volcanic terrain around Mount Konocti and the mostly volcanic terrain that extends to the southeast. Its Quaternary volcanic geology of rhyolite, andesite, and dacite differs from the Franciscan Complex geology of Ecoregion 6j to the west and from the abundance of ultramafic rocks of adjacent Ecoregion 6g. The unit in the south in Napa and Sonoma Counties has mostly Tertiary volcanic geology. Elevations in the ecoregion range from about 500 feet in the south to the high points of 4,286-foot Mount Konocti, 4,343-foot Mount St. Helena, and 4,722-foot Cobb Mountain. Soil temperature regimes are mostly thermic, but are mesic on some north-facing slopes and at high elevations. Soil moisture regimes are xeric. The vegetation mosaic includes mixed chaparral, mixed hardwoods (including coast live oak, madrone, and California bay), and some areas of Douglas-fir or pines and cypress.

— EPA

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