The towns of the Opata were found in the broad valleys of the five north-south trending rivers of northern and eastern Sonora. The rivers, west to east, are the San Miguel, Sonora, Moctezuma, and the two upper tributaries of the Yaqui, the Bavispe and the Arcos. The Opata were not members of a single political entity, but rather organized into a number of “statelets” – several of which may have also been populated by their neighbors to the south, the Pima Bajo. The statelets were characterized by a ruling class, slavery, irrigation agriculture, and emphasis on trade. They featured a central town, functioning as the seat of government, of at least 200 two and three story adobe houses and a population of six per house or 1,200 or more. In the countryside for several miles in every direction from the central town were satellite communities: hamlets of 9 to 25 houses and “rancherías” of less than 9 houses.