One of the most complex sociopolitical systems that developed prehistorically in the American Southwest was centered around Chaco Canyon, New Mexico. At the time of its maximum extent between A.D. 1050–1175, the Chacoan system encompassed more than 50 major settlements that were located throughout the San Juan Basin in northwestern New Mexico and extending into northeastern Arizona and southwestern Colorado (Figure 17.1). The geographic, demographic, and cultural hub of this system was Chaco Canyon, an 80 square kilometer area that contained ten large towns, several smaller towns, and an almost continuous distribution of villages. The large towns were planned, multistory structures whose spectacular appearance and close proximity to one another attracted the first archaeologists to the area in the late nineteenth century. Archaeological investigations have been ongoing in Chaco Canyon ever since; this work has produced some of the most comprehensive evidence available for studying prehistoric social structure and organizational change in the American Southwest.