The Madison River originates in Yellowstone National Park at the junction of the Firehole and Gibbon rivers and flows in a northerly direction for 140 miles to Three Forks, Montana, where it joins the Jefferson and Gallatin rivers to form the Missouri River. From its source in the park, the Madison flows across a high conifer-forested plateau, its journey interrupted by two man-made impoundments: Hebgen Reservoir, located one and one-half miles below the park boundary, and Ennis Reservoir, 58 miles downstream from Hebgen. Just below Hebgen, the Madison feeds Quake Lake, a natural lake formed by an earth slide during a major earthquake in 1959. From Ennis Reservoir the Madison flows through Bear Trap Canyon before entering the lower Madison River Valley for its final 18 miles. The Madison is one of Montana's premier wild trout rivers. Due to its national reputation, heavy fishing pressure, good access, high scenic value, and excellent wild trout populations, it has been classified as a Blue Ribbon trout stream. The Madison is also the home of wild trout management, where the results of a controversial study in the early 1970s introduced a shift in management emphasis nationwide, from stocking trout to population monitoring, harvest regulation, and habitat protection. A number of challenges exist to wild trout fisheries in the Madison River, such as whirling disease, increased angling pressure, and drought.