The forest stretches for over 100 miles (160 km) along the western slopes of the Cascade Range in Western Oregon. It extends from the Mount Jefferson area east of Salem to the Calapooya Ridge which divides the watersheds of the Willamette and Umpqua rivers. Most of the forest (about 61%) is located in Lane County, but there are large areas in Linn, Marion, and Douglas counties, as well as much smaller areas in Clackamas and Jefferson counties.