South Platte

South Platte River
South Platte River in Douglas County, Colorado,
Basin features
Main source	Confluence of South Fork and Middle Fork 39°00′40″N 105°44′25″W / 39.01111°N 105.74028°W / 39.01111; -105.74028
River mouth	Confluence with North Platte River 2,762 ft (842 m) 41°06′50″N 100°40′33″W / 41.11389°N 100.67583°W / 41.11389; -100.67583Coordinates: 41°06′50″N 100°40′33″W / 41.11389°N 100.67583°W / 41.11389; -100.67583
Progression	Platte—Missouri—Mississippi
Physical characteristics
Length	439 mi (707 km)
Discharge	Average rate: 174 cu ft/s (4.9 m3/s)
Discharge range	0 to 4,640 cu ft/s (0 to 131 m3/s)

The South Platte River is one of the two principal tributaries of the Platte River. Flowing through the U.S. states of Colorado and Nebraska, it is itself a major river of the American Midwest and the American Southwest/Mountain West. Its drainage basin includes much of the eastern flank of the Rocky Mountains in Colorado; much of the populated region known as the Colorado Front Range and Eastern Plains; and a portion of southeastern Wyoming in the vicinity of the city of Cheyenne. It joins the North Platte River in western Nebraska to form the Platte, which then flows across Nebraska to the Missouri. The river serves as the principal source of water for eastern Colorado. In its valley along the foothills in Colorado, it has permitted agriculture in an area of the Colorado Piedmont and Great Plains that is otherwise arid.

The river is formed in Park County, Colorado, southwest of Denver in the South Park grassland basin by the confluence of the South Fork and Middle Fork, approximately 15 miles (24 km) southeast of Fairplay. Both forks rise along the eastern flank of the Mosquito Range, on the western side of South Park, which is drained by the tributaries at the headwaters of the river. From South Park, it passes through 50 miles (80 km) of the Platte Canyon and its lower section, Waterton Canyon. Here, it is joined by the North Fork before emerging from the foothills southwest of the Denver suburb of Littleton. At Littleton, the river is impounded to form Chatfield Reservoir, a major source of drinking water for the Denver Metropolitan Area.