Aspen (ăsˈpən) [key], city (1990 pop. 5,049), alt. 7,850 ft (2,390 m), seat of Pitkin co., S central Colo., on the Roaring Fork River; founded c.1879 by silver prospectors, inc. 1881. Declining after an 1880s–90s boom, it was transformed in the 1930s into a ski resort. Affluent, cosmopolitan Aspen is now noted for its Aspen Institute for Humanistic Studies and Aspen Music Festival and School (see Aspen Music Festival). The summer music festival was the progenitor (1949) of similar arts festivals throughout the mountain states.