The site of Caltonac is located in the state of Puebla, at the eastern edge of the Mexican Central Altiplano. A major rhyolite flow is located ca. 10 kilometers northwest of the site. Elemental analysis by x-ray fluorescence and emission spectroscopy for Rb, Sr, Zr, Y, Nb, Ba, La, Mn, Ni, Be, Co and Ga, Si, Ti, Al, Fe, Mg, Ca, Na, K, P, F, and Cl shows the glassy portions of this flow to be the source of the D or Zaragoza type obsidian form in Formative to Postclassic Mesoamerican sites, whose provenance was until now uncertain. The chronology of the site is unknown, but an increase during the Classic of the number of sites in which D-type obsidian artifacts are found suggests that by this time local control of the source had been established.