There are two large mounds comprised of enormous quantities of construction debris and discarded household debris associated with rapid growth of the Pueblo Bonito great house in Chaco Canyon between ca. CE 1040 and 1100. There is some debate among specialists as to whether these features were expedient refuse middens or constructed platform mounds or something in between, and thus whether they index political processes linked to control of labor by elites. Although originally investigated by archaeologists between 1896 and 1927, this study presents the first detailed formation history for each mound, based on recent fieldwork by the University of New Mexico. We argue that the mounds were not the product of institutionalized political power as assumed for platform mounds in other parts of North America but rather reflect local landscape changes associated with complex social negotiations during a period of rapid social transformation.