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.
Mesa Verde National Park
Most Mesa Verdeans practiced dry farming, which relied on rain to water their crops, but others utilized runoff, springs, seeps, and natural collection pools. Starting in the 9th century, they dug and maintained reservoirs that caught runoff from summer showers and spring snowmelt; some crops were watered by hand. Archaeologists believe that prior to the 13th century, springs and other sources of water were considered shared public resources, but as Mesa Verdeans moved into increasingly larger pueblos built near or around water supplies control was privatized and limited to members of the surrounding community.