Tree-ring dating burst into Southwestern archaeology on June 22, 1929, when Andrew Ellicott Douglass of the University of Arizona and his colleagues discovered specimen HH-39, the piece of charcoal that “bridged the gap” in his tree-ring chronology and allowed him to date, for the first time in history, archaeological sites at Mesa Verde, Chaco Canyon, and elsewhere. Over the last nine decades, tree-ring dating has been refined, expanded, and matured into a full-blown science in its own right, with near world-wide application. In this wide-ranging presentation, Denver Museum of Nature & Science curator of archaeology Stephen E. Nash will examine the development and application of tree-ring dating in Southwestern archaeology and beyond.