This collection of aerial photographs is intended to show changes over time in the landscape of Colorado; for instance, the appearance of a reservoir in a mountain valley, changes in vegetation or ground cover, or the growth of towns and cities. The online collection, consisting of over 1700 digitized photos, was taken by the U.S. Forest Service from 1938 to 1947 and covers Boulder, Clear Creek, Eagle, Gilpin, Grand, Jefferson, Larimer, and Summit Counties. The photographs can be searched or browsed using a map search or a geographic keyword search. Searches will bring up information and metadata (longitude and latitude, landmark, county, topographic quadrangle, scale, and others) about each photograph and a 150 dpi image that can be downloaded free of charge.