The Western Cascades Lowlands and Valleys ecoregion comprises a network of steep ridges and narrow valleys on the lower slopes of the Cascade Mountains. Elevation varies from . Its mild, wet climate promotes lush forests dominated by western hemlock and Douglas-fir, with western redcedar, bigleaf maple, red alder, vine maple, salal, rhododendron, Oregon grape, huckleberry, thimbleberry, swordfern, oxalis, hazel, and blackberry. Soils are warmer here than in higher elevation ecoregions, and it is one of the most important timber producing areas in the Pacific Northwest. The steep valleys trending to the west contain high and medium gradient rivers and streams that support cold water salmonids, including the threatened Chinook salmon, steelhead, and bull trout. Notable river drainages in Oregon include the North Umpqua, North and Middle Forks of the Willamette, McKenzie, North Santiam, South Santiam, Clackamas, Salmon and Bull Run River watersheds; and in Washington, the Lewis, Cowlitz, Nisqually, Puyallup, White, and Green River watersheds. Reservoirs store winter snowmelt for irrigation and municipal water supply in the Willamette Valley. The Westerns Cascades Lowlands and Valleys is the largest of the Cascades subregions, covering in Oregon and in Washington.