Analysis of a collection of lithic artifacts from recent INAH salvage excavations in Azcapotzalco, Mexico, contributes to our understanding of lithic procurement and manufacturing processes, other economic activities, intersite relations, and the decline of Classic civilization in the Basin of Mexico. The results of NAA conducted at the Missouri University Research Reactor on a small sample of obsidian artifacts from the site support the conclusions of visual analysis and growing evidence from other central Mexican sites that at the end of the Classic Period obsidian exchange networks utilizing the Pachuca, Hidalgo, sources were largely replaced by a widespread dependence on the considerably more distant obsidian source of Ucareo, Michoacan. It appears likely that Ucareo obsidian was imported primarily in the form of large polyhedral cores used to produce prismatic blades. Obsidian from the Otumba, State of Mexico, source was also identified by NAA in biface and blade form.