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.
Irrigation in Bolivia
The Spanish colonists, soon after their arrival in the central Andes in the 16th century, appropriated the best farmlands on the coasts and valleys and pushed the indigenous population to the more inhospitable highlands. The highlands had been grazing grounds for llamas and alpacas, but had not been used for agriculture because of their low productivity and high climatic risks. Under the new circumstances, the highlands became the center of Bolivia’s subsistence agriculture.