were again obliterated, along with much else along the San Gabriel River, during the great flood of 1938. Recreational gold mining has continued along the San Gabriel River since then, although it is not legal in many places. Current U.S. Forest Service policy states that "National Forest System lands within the East Fork of the San Gabriel River are not open to prospecting or any other mining operations." However, the ban is rarely enforced and has been subject to much controversy, especially since it does not distinguish between recreational and commercial mining. Farming and irrigation 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. After California became part of the United States in 1846, the ranching economy gradually shifted towards agriculture (a transition quickened by the Great Flood of 1862 and subsequent drought of 1863-64 which killed almost three-quarters of the livestock in Los Angeles County) and the San Gabriel River became a crucial water source for farms. The California Gold Rush brought a huge influx of people to the state, and the high demand for food transformed the San Gabriel River Basin into one of the nation's most productive agricultural regions. The Southern Pacific Railroad arrived in 1876 and the Union Pacific Railroad in the early 1900s, the latter line passing through the Whittier Narrows; this enabled the San Gabriel River region to become a major exporter of agricultural products. Some areas had easy access to permanent water, such as the fertile "island meadow" region between the Rio Hondo and San Gabriel Rivers roughly where El Monte is today. This was one of the most popular destinations for early American settlers; for a time it was