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.
San Gabriel River (California)
Although the Southern California climate is well suited to most types of agriculture, the seasonality of rainfall made it almost impossible to grow crops without irrigation. After the founding of Mission San Gabriel, the Spanish built and gradually expanded a system of "zanjas" (canals) and reservoirs to irrigate crops, power mills, and water livestock. The earliest historic record of a water diversion for the mission appears around 1773. Irrigation systems were also built on some of the Mexican ranchos, such as in 1842 when Don Luis Arenas, owner of the Rancho Azusa, constructed a "zanja" from the mouth of San Gabriel River to his homestead, a distance of about one mile (1.6 km). This would later be expanded in to the Azusa Ditch, one of the more important canals of the region.