It's been called the Mad River (Pawhuska) by the Navajo and the River of Lost Souls by the Spanish explorers. Rio de las Animas Peridas was eventually Americanized and shortened to Animas River. The Animas is one of four major rivers that carry San Juan Mountain springtime runoff. This Mad River drops 2,000 feet in a 28 mile stretch near Silverton, Colorado, providing rafters and kayakers class IV and V whitewater. Some portions of the Upper Animas are impassible. However, as it reaches the town of Durango, the class rating drops to Class II and III levels. The Lower Animas still provides fast moving water for novice thrill seekers.