South Park is a grassland flat within the basin formed by the Rocky Mountains' Mosquito and Park Mountain Ranges within central Colorado. This high valley ranges in elevation from approximately 9,000 to 10,000 ft. It encompasses approximately 1,000 square miles around the headwaters of the South Platte River in Park County approximately 60 mi (100 km) southwest of Denver. It is the largest and southernmost of three similarly named high altitude basins in the Front Range of Colorado, the others being North Park and Middle Park. The largest town in the basin is Fairplay, with a population of 724.

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.