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.: .' ,. ~ .LJ.,() v 12 METROPOLITAN WATER DISTRICT the coastal plain for the 40-year period from IHH9 to 1929 was only 24 per cent of the maximum of record. On the other hand the minimum year of record shows less than 10 per cent of the 40-year mean, and the annual flow for the fh'e-year period from 1924 to 1929 averages only 51 per cent of the same 40-year mean. These large variations in annual run-off might be at least par- tially equalized if sufficiently large storage at strategic points on each stream could be provided. However, except for the Bear Valley reservoir on the Santa Ana River, built in 1883-84, sites do not exist on these streams where reservoirs could have been con- structed in the early days, at a price which the lands could afford and by the time the agricultural development had become suffi- ciently intensive to justify the construction of expensive storage, all stream flow except flood peaks had been appropriated. Spread- ing works and other conservation projects have succeeded in equating these river flows to some extent by providing means of recharging the underground basins, but their operation is likewise subject to prior appropriative rights, The rate of increase in demand can be judged from the data of Table 3 where the increases in irrigated acreage in Los Angeles, Orange, Riverside, and San Bernardinu cuunties are shown for each ten-year period beginning with 1890. TARLE 3 Area. Irrigated in Son Bernardino, Hivenide, Orange, and fA'. Angele8 Counlie. 1889 to 1930 I Irriga.ted fanns __......mm.....m.... Area in irrigated fanns, acreS...m___... Irrigated area per fann, acres..mm.... 1889-90 4,403 139,900 31.8 1899.00 9,215 198.000 21.5 1909.10 1l,S21 .342,400 29.7 1919.20 18,96R S47,300 2B.9 192HO 22.967 549,900 2.3.9 Water supply and regional development In 1870 most of Southern California was still included in enor- mous land holdings, with tens of thousands of acres in single ranchos, and grazing was practically the sole economic activity. Even this industry was unable to survive the vagaries of the region's water supply. One hundred thousand head of cattle were lost in Los Angeles County in the season of 1856-57 because of drought, and in the period from 1862-64 another great drought destroyed even larger numbers, 60,000 head of cattle being re- ported to have been sold at Santa Barbara for 37% cents per head, 1 U. S. Census for IrrigatioD. 1