The Denver, South Park, and Pacific Railroad was a historic 3 ft narrow gauge railroad that operated in Colorado in the western United States in the late 19th century. The railroad opened up the first rail routes to a large section of the central Colorado mining district in the decades of the mineral boom. The railroad took its name from the fact that its main line from Denver ascended the Platte Canyon and traversed South Park, hence its popular name "The South Park Line." Despite its lofty goals, the line never connected itself with the Pacific or any transcontinental line, apart from its terminal at Denver Union Station.

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.