 Nearly all of the national forest is mountainous and includes parts of the Southern Oregon Coast Range, the Klamath Mountains, and the Cascade Range.The largest river in the national forest is the Rogue River, which originates in the Cascade Range and flows through the Klamath Mountains and Coast Range.The Illinois River is a major tributary of the Rogue in the Klamath Mountains, while the Sixes, Elk, Pistol, Chetco, and Winchuck rivers drain the Coast Range directly to the Pacific Ocean.