The Chetco River watershed is covered primarily by temperate coniferous forest, which includes species such as Douglas fir, western hemlock, white fir, Port Orford cedar, California incense cedar, and Sitka spruce. Jeffrey pine, knobcone pine, and golden chinquapin have also been identified. Hardwoods including tanoak, bigleaf maple, red alder, and Pacific madrone are common. Manzanita, hazelnut, vine maple, western skunk cabbage, and multiple species of berries and grasses make up the understory. Kalmiopsis, a flowering evergreen shrub and the namesake of the Kalmiopsis Wilderness, only grows in the Siskiyou Mountains. Several noxious weeds have also been identified, including gorse, Scotch broom, blackberries, and thistles.