Glaze-decorated pottery of the Classic Period from the Rio Grande Valley and environs was analyzed using a scanning electron microscope with an x-ray fluorescence detector (SEM-XRF). A cluster analysis of element composition data obtained on the decoration and slip of 57 sherds indicated that intrusive wares could be identified, that trading patterns could be illucidated, and that a source of glaze components appears to have been located near the Cerrillos Mining District of New Mexico.