1904 



FORESTRY AND IRRIGATION 



45 



and improved, until practically all of 

 the flowing mountain and valley waters 

 were appropriated and made useful for 

 irrigation or as a source of domestic 

 supply for the growing villages and 

 cities. 



The next step taken to increase the 

 water resources was usually in the di- 

 rection of attempts to intercept the sub- 

 surface seepage by systems of shafts 

 and tunnels, or to increase the flow of 

 the large cicncgas by similar means. 



In two or three instances storage res- 

 ervoirs have been built, whose object is 

 to save those excess waters which pass 

 to the sea during the exceptional floods 

 of winter, and thus are entirely lost. 

 Notable among reservoirs of this type 

 is the Bear Valley dam, in the San Ber- 

 nardino Mountains, at an elevation of 

 6,500 feet. Its waters furnish the main 

 supply for the flourishing colony tribu- 

 tary to Redlands, in the eastern end of 

 the valley. Similarly the Hemet dam, 

 in the San Jacinto Mountains, stores 

 the winter rains for use during the irri- 

 gating season on the plains in the vicin- 

 ity of Hemet. Other unique features 

 in hydraulic engineering are the sub- 

 merged dams in the Pacoima Wash, 

 San Fernando Valley, and in the can- 

 yon of Santiago Creek, Orange county. 

 These are concrete structures, built 

 across the underground channels of the 

 streams to intercept the percolating 

 waters as they find their way seaward 

 through the porous sands and gravels 

 of the stream bed. The waters thus 

 intercepted are forced to the surface by 

 the dam or are pumped from its upper 

 side and distributed in the usual man- 

 ner by main pipes and laterals to the 

 lands which it is desired to irrigate. 



In no part of the United States have 

 the methods of irrigation engineering 

 been so highly developed as here. A 

 few of the less important old canals are 

 cut in earth and are unlined, with irreg- 

 ular grades and leaky beds ; but all the 

 more important systems have been built 

 by engineers after careful surveys, are 

 cement lined or of concrete construc- 

 tion, many of them covered and sup- 

 plied with most effective headworks and 

 distributing systems. Recent practice 

 has been in the direction of using con- 



crete pipe for the main lines, thus pre- 

 venting all loss of water from leakage 

 or evaporation in transit from its source 

 to the point of distribution. 



In late years, because of the com- 

 plete appropriation of all the surface 

 streams and a natural desire to extend 

 the areas so profitably cultivated, water- 

 users have turned their attention more, 

 and more to the subterranean supplies- 

 and in some cases flourishing commu- 

 nities have been built up which de- 

 pend entirely upon these for their irri- 

 gation water. 



As a result of the geologic and cli- 

 matic processes which have given the 

 picturesque combinations of mountain 

 and plain that make up the landscape 

 and much of the charm of southern 

 California, a number of 'deep and ca- 

 pacious underground reservoirs have 

 formed, which through the past centu- 

 ries have been charged with the waters 

 flowing from the mountains, and are 

 now yielding these waters that the 

 tributary lands may be made fruitful. 



The origin of these basins in its broad 

 outlines is simple, although the details 

 may often be most complex. In general 

 the high mountains are areas which have 

 been uplifted during the crustal move- 

 ments that have been so marked a feat- 

 ure of the later geologic history of the 

 region, and the valleys are areas which 

 have been depressed during the same 

 processes. These furnish unusual types 

 of valleys, whose width and extent bear 

 no particular relation to the streams that 

 flow through them. The normal stream 

 valley, unlike these California valleys, 

 has been cut by the stream which occu- 

 pies it, is broad and flat where the stream 

 is large, constricted where the stream is 

 small, and is in every way adjusted to 

 the stream that has produced it. But 

 these basins, which together constitute 

 the region known as the Valley of South- 

 ern California, owe their origin to earth 

 movements instead of stream action, and 

 the principal function of the streams has 

 been not to deepen and broaden them , 

 but to fill them up, smoothing them and 

 partially burying the inequalities which 

 resulted from the crinkling and buckling 

 of the earth's crust, to which they are 

 due. 



