Agriculture in the prehistoric Southwest
After the Hohokam disappeared, Spanish explorers of the 16th century noted the use of canal irrigation in only two areas of the Southwest: eastern Sonora, primarily practiced by the Opata and Lower Pima, and among the Pueblos of northern New Mexico. Irrigation by the Opata and Pueblos had different objectives. In Sonora, with a long growing season, two crops of maize a year were grown in river valleys. The spring crop during the dry season was dependent upon irrigation; the summer and fall crop during the rainy season utilized irrigation to supplement rainfall. The necessity of irrigation probably required a high level of social organization. In New Mexico, with only one crop of maize per year possible, irrigation was supplemental and the lesser dependence on irrigation implies less social organization than in Sonora.
Aztec society
In the valleys of the empire, irrigation farming was used. Dams diverted water from natural springs to the fields. This allowed for more regular harvests because the prosperity of an irrigated field was not dependent upon the rain. Irrigation systems had been in place long before the Aztecs. However, they built canal systems that were longer and more elaborate than any previous irrigation systems. They even managed to divert a large portion of the Cuauhtitlan River to provide irrigation to large areas. The network of canals was very complex and intricate.