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.
Ciénega
Ciénaga habitat in an otherwise arid, resource constrained landscape was the first source of water to be used by Hispanics and Anglos for their livestock. As early as the 1680s, Pima Indians in Sonora were complaining that Spanish livestock were so common that watering places were drying out. The effects of long-term, sustained grazing — particularly during drought episodes — caused reduced plant cover and vigor; increased runoff and sediment transport; fostered desertification, which worsened the deepening of incised channels; triggered water table declines and further loss of wetland vegetation, thereby making ciénagas and their surrounds among the most abused sites on earth.