The Clark Fork River is a river in the U.S. states of Montana and Idaho, approximately 360 mi (579 km). The largest river by volume in Montana, it drains an extensive region of the Rocky Mountains in western Montana and northern Idaho in the watershed of the Columbia River, flowing northwest through a long mountain valley and emptying into Lake Pend Oreille in northern Idaho. The Pend Oreille River, which drains the lake to the Columbia, is sometimes included as part of the Clark Fork, giving it a total length of 479 mi (771 km), with a drainage area of 25,820 sq mi (66,874 km²). In its upper 20 mi (32 km) in Montana near Butte, it is known as Silver Bow Creek. Interstate 90 follows much of the upper course of the river from Butte to northwest of Missoula.

Description

It rises as Silver Bow Creek in southwestern Montana, less than 5 mi (8 km) from the continental divide near downtown Butte, from the confluence of Basin and Blacktail creeks. It flows northwest and north through a valley in the mountains, passing east of Anaconda, where it changes its name to the Clark Fork, then northwest to Deer Lodge. From Deer Lodge it flows generally northwest across western Montana, passing south of the Garnet Range to Missoula, receiving the Blackfoot River from the east 5 mi (8 km) west of the city. Northwest of Missoula it continues through a long valley along the northeast flank of the Bitteroot Range, through the Lolo National Forest . It receives the Bitteroot River from the southeast approximately 20 mi (32 km) northwest of Missoula, and receives the Flathead River from the east near Paradise. It receives the Thompson River from the northeast near Thompson Falls in southern Sanders County.

At Noxon, Montana, along the north end of the Bitteroots near the Idaho border, it is impounded by the Noxon Rapids Dam to form a 20 mi (32 km) long reservoir. It crosses into western Bonner County in northern Idaho near the town of Cabinet, Idaho . Approximately 5 mi (8 km) west of the state line it enters the western end of Lake Pend Oreille near the town of Clark Fork.

History

During the last ice age, from approximately 20,000 years ago, the Clark Fork Valley lay along the southern edge of the Cordilleran ice sheet covering western North America. The encroachment of the ice sheet formed an ice dam on the river, creating Glacial Lake Missoula which stretched through the Clark Fork Valley across central Montana. The periodic rupturing and rebuilding of the ice dam released the Missoula Floods, a series of catastrophic floods down the Clark Fork and Pend Oreille into the Columbia which sculptured many of the geographic features of eastern Washington and the Willamette Valley of Oregon.

In the 19th century the Clark Fork Valley was inhabited by the Flathead tribe of Native Americans. It was explored by Meriwether Lewis of the Lewis and Clark expedition during the 1806 return trip from the Pacific. The river is named for William Clark. A middle segment of the river in Montana was formerly known as the Missoula River.

Since the late 19th century many areas in the watershed of the river has been extensively mined for minerals, resulting in an ongoing stream pollution problem. Many of the worst areas have been designated as Superfund sites. Nevertheless the river and its tributaries are among the most popular destinations for fly fishing in the United States.

See also

• Clarks Fork River
• List of Idaho rivers
• List of Montana rivers

External link

• Clark Fork Coalition
• Upper Clark Fork Restoration Program