The Middle Fork South Platte River is a tributary of the South Platte River, approximately 50 miles long,located in central Colorado in the United States. The river provides part of the drainage of South Park, the intermontane grassland basin located between the Front Range and the Mosquito Range in the Rocky Mountains southwest of Denver. The river was a significant source of placer gold during the Colorado Gold Rush of 1859, leading to the first large influx of white settlers into South Platte, previously inhabited principally by the Ute
people. The river bed near Fairplay continued to be a productive gold
source for many decades and was the location of mining and milling
operations up through the middle 20th century.