Chaco Canyon in northwestern New Mexico has been the focus of much recent archaeological research on Pueblo groups who lived during the 9th through 12th centuries in the American Southwest. Here, we examine variation in mortuary patterns in the canyon, focusing in particular on one mortuary crypt, to address questions of social differentiation and the chronology of important sociopolitical processes. Based on new radiocarbon dates as well as reanalysis of the stratigraphy and spatial distribution of materials in the mortuary crypt, we conclude that significant social differentiation began in Chaco ca. 150-200 y earlier than suggested by previous research. We argue that social inequality was sanctified and legitimized by linking people to founders, ancestors, and cosmological forces.