The Calapooya Mountains are a mountain range in Lane and Douglas counties of southwestern Oregon in the United States. The range runs for approximately west from the Cascade Range between Eugene on the north and Roseburg on the south.
Geology
The Calapooya Mountains are composed of volcanic rocks and newer sedimentary strata. The mountains have been deeply eroded by the Coast Fork Willamette River and its tributaries. In the southern drainage, the tributaries of the North Umpqua River have cut into the southern slopes. The soil is silty, clay loam formed from sandstone, sediment, and igneous rocks.
Topography
The Calapooya Mountains and the Calapooya Divide are two parts of a spur of the Western Cascade mountains in the U.S. state of Oregon that form the divide between the watersheds of the Willamette and Umpqua rivers. At its southeastern end, the spur joins the Cascade Range near Cowhorn Mountain near the headwaters of the Middle Fork Willamette River and the North Umpqua River. A topographic map in the Atlas of Oregon shows the Calapooya Mountains curving northwest from near Potter, McGowan, and Balm mountains past Bohemia Mountain to Holland Point, south of Oakridge. From near Bohemia Mountain, a block of mountains connected to the Calapooya Mountains runs due west along the border between Lane and Douglas counties to the vicinity of Interstate 5 (I-5) near Rice Hill. This block is known as the Calapooya Divide. To the north along I-5 are Cottage Grove and Eugene and to the south are Sutherlin and Roseburg.
Streams flowing south from the Calapooyas into the North Umpqua River include Steamboat, Canton, and Rock creeks, while Calapooya Creek flows west from the divide into the Umpqua main stem. Streams flowing north or east into the Middle Fork Willamette River include Tumblebug, Staley, Coal, and Packard creeks. Flowing northwest or west into the Coast Fork Willamette River or its major tributary, the Row River, are Brice, Layng, and Mosby creeks and Big River. The Umpqua flows west through the Oregon Coast Range to the Pacific Ocean at Reedsport, while the Willamette flows north to the Columbia River, which flows northwest to the Pacific Ocean at Astoria.