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.
Water in California
California recognizes water rights granted to pueblos (settlements) under the Spanish and Mexican governments, prior to the Treaty of Guadalupe Hidalgo. Under the doctrine, pueblos organized under the laws of Mexico or Spain have a water right to the yield of all streams and rivers flowing through the city and the groundwater aquifers lying below. Pueblo water rights are superior to all riparian and appropriative rights and cannot be lost by a failure to assert an interest or use the water. In addition, the pueblo's claim expands with the needs of the city and may be used to supply the needs of areas that are later annexed to the city. Los Angeles and San Diego are the only original pueblos to exercise their pueblo water rights in the courts.