High Quality Content by WIKIPEDIA articles! The Bitterroot Valley is located in southwestern Montana in the northwestern United States. It extends over 100 miles (160 km) from remote Horse Creek Pass north to a point near the city of Missoula. To the west is the Bitterroot Range and the large Selway- Bitterroot Wilderness Area, and to the east is the smaller Sapphire Mountains and the Anaconda-Pintler Wilderness Area.