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Eastern Divide Mountains

Ecoregion in Rocky Mountains, MT

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The semiarid to subhumid, largely forested Eastern Divide Mountains ecoregion is underlain by Precambrian Belt formations and is lithologically distinct from the Big Snowy-Little Belt Carbonate Mountains (17q), Scattered Eastern Igneous-Core Mountains (17r), Elkhorn Mountains-Boulder Batholith (17ai), and Southern Garnet Sedimentary-Volcanic Mountains (17al). Ecoregion 17aj lies east of the Continental Divide where it receives 12 to 25 inches of precipitation per year, less than farther west. The climax vegetation is mapped as Douglas-fir and ponderosa pine forests, with subalpine fir occurring at the highest elevations; it is distinct from the nearby, treeless Ecoregions 42r, 42q, and 43u .

— EPA

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Ecoregion