Changes in Arapaho Glacier, Front Range, Colorado, are determined using historical maps, aerial photography, and field surveys using ground penetrating radar (GPR) and Global Positioning System data. Arapaho Glacier lost 52% of its area during the 20th century, decreasing from 0.34 to 0.16 km². Between 1900 and 1999 glacial area loss rates increased from an average of 1500 m² yr^–1 to 2400 m² yr^–1. Average glacial thinning between 1900 and 1960 was 0.76 m yr^–1, but slowed to 0.10 m yr^–1 between 1960 and 2005. Its maximum thickness is approximately 15 m. If recent trends in area loss continue, Arapaho Glacier may disappear in as few as 65 years. However, the decline in thinning rate suggests that the glacier is retreating into a corner of its upper cirque in which increased inputs of snow from direct precipitation and avalanching, and decreased insolation will greatly slow its rate of retreat. This may be generally true for many temperate-latitude cirque glaciers.