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.
Middle Rio Grande Project
The Rio Grande valley from Taos Pueblo downstream to Socorro has been continuously settled for longer than any other part of the United States. The Pueblo Indians diverted water from the river for irrigation. Spanish settlers who arrived in the 17th century established a more extensive system of "acequias", or shared irrigation canals. More settlers arrived after the region was ceded to the United States in 1848, particularly after the American Civil War (1861-1865). Irrigation peaked in 1880 with of cultivated land in the stretch of valley from Cochiti to San Marcial. The extent of cultivation began to decline after this due to water shortage, floods and waterlogging caused by aggradation of the riverbed, a rising water table and poor drainage.