<Tr> <Td_colspan="2"> The Boise River watershed </Td> </Tr> <Tr> <Td_colspan="2"> Boise River's mouth in Idaho </Td> </Tr> <P> The Boise River is a 102 - mile - long (164 km) tributary of the Snake River in the northwestern United States . It drains a rugged portion of the Sawtooth Range in southwestern Idaho northeast of Boise, as well as part of the western Snake River Plain . The watershed encompasses approximately 4,100 square miles (11,000 km) of highly diverse habitats, including alpine canyons, forest, rangeland, agricultural lands, and urban areas . </P> <P> The Boise River rises in three separate forks in the Sawtooth Range at elevations exceeding 10,000 feet (3,050 m), and is formed by the confluence of its North and Middle forks . The North Fork, 50 miles (80 km) long, rises in the Sawtooth Wilderness Area, along the Boise - Elmore county line, 60 miles (100 km) northeast of Boise . It flows generally southwest through the remote mountains in the Boise National Forest . The Middle Fork, approximately 52 miles (84 km) in length, rises within 12 miles (19 km) of the North Fork in the southern Sawtooth Wilderness Area in northeastern Elmore County . It flows west - southwest near the town of Atlanta, joining the North Fork to form the Boise River, approximately 15 miles (24 km) southeast of Idaho City . The main stream flows southwest into Arrowrock Reservoir joining the South Fork from the Anderson Ranch Dam . </P>

Where does the boise river start and end
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