Obsidian artifact sourcing studies performed over the last 25 years have identified obsidian from outcrops around the communities of Zinapecuaro and Ucareo, Michoacan, at sites widely distributed in time and space. Recent data indicate that Zinapecuaro and Ucareo constitute distinct obsidian sources, although their proximity to each other and their similar chemical compositions merit their consideration as collectively comprising part of an obsidian source area. Sourcing studies that used Ucareo as well as Zinapecuaro source reference samples provide strong evidence of considerably greater pre-Hispanic utilization of the Ucareo source, and raise the possibility that at least some artifacts attributed to Zinapecuaro in studies that did not use Ucareo reference samples may be from the Ucareo source. These findings are supported by recent archaeological evidence of considerably greater exploitation of the Ucareo source, including what is probably one of the largest known pre-Hispanic quarries. Preliminary data provide a tentative chronology for settlement and exploitation of the source area.