Chacoan great houses were constructed with hundreds of thousands of wood timbers. Without extensive forests near Chaco Canyon, the question of where the timbers originated has perplexed archaeologists for over a century. Were trees cut locally, leading to deforestation and associated environmental problems, or were timbers hauled in on peoples’ backs from forested mountain ranges over 50 miles away? Chris will present the findings from several studies that determined probable sourcing of Chacoan timbers via tree-ring methods, using the growth patterns preserved on ancient beams to identify their growth origins. Included in this analysis is one of the most iconic trees of southwestern archaeology, the Plaza Tree of Pueblo Bonito, famously depicted by the Park Service today as a majestic pine growing within the walls of the massive great house. Chris will then describe recent work in which they examined beams from Aztec Ruins National Monument to test if Chacoan construction there relied on locally-sourced wood from the San Juan Mountains to the north.