The valley extends approximately from Lost Trail Pass in Idaho, where it is narrow, to a point near the city of Missoula along Interstate 90 where it is wider and flatter. To the west is the Bitterroot Range and its large Selway-Bitterroot Wilderness Area, and to the east is the smaller Sapphire Mountains and their Anaconda-Pintler Wilderness Area. The Bitterroot Range has steep faces, deep canyons, is heavily forested, and is within the Bitterroot National Forest. The Sapphire Mountains are more rounded, drier, and much less forested.