452 



FORESTRY AND IRRIGATION 



October 



Thus, as the San Bernardino Moun- 

 tains were uplifted and the valley to the 

 south of them sank, the streams rising in 

 the high range carried quantities of de- 

 tritus, boulders, gravel, sand, and clay 

 into the lowland, and there deposited it. 

 The rock floor of this valley is below 

 sea-level, while its present surface is 

 i ,000 to i , 500 feet above. This surface 

 has been thus raised by the accumulation 

 of material brought in by the mountain 

 streams loose, porous detritus, satu- 

 rated by the mountain waters, and so 

 constituting a great underground res- 

 ervoir. 



Similarly, while the ridge, which in 

 various parts is known as the San Jose 

 Hills, the Puente Hills, and the Santa 

 Ana Mountains, has been uplifted, an 

 area north of it has been depressed until 

 its bedrock bottom, in places at least, 

 lies below sea-level. This valley has 

 also been filled by the loose material 

 brought in by the San Antonio, the 

 Santa Ana, and other streams, until the 

 valley level is now several hundred feet 

 above the sea. This great mass of loose 

 debris, like that in the San Bernardino 

 Valley, has been saturated by water sup- 

 plied by the rainfall of the past, and 

 serves as a storage reservoir. 



Between the Santa Ana Mountains 

 and their extension on the one side and 

 the Pacific Ocean on the other lies the 

 coastal plain of southern California, 10 

 or 20 miles wide and with a northwest- 

 southeast dimension of 40 or 50 miles. 

 This again is a lowland, built up largely 

 of sands and gravels contributed by the 

 various rivers which flow across it . The 

 waves and currents of the ocean have 

 probably contributed to the supply and 

 have certainly aided in its distribution. 

 These alluvial and marine deposits are 

 saturated, as are the exclusively alluvial 

 deposits farther inland, and constitute a 

 very large underground reservoir of 

 fresh water. 



In portions of all of these basins, 

 whose origin has been thus roughly 

 sketched, the alteration of coarse and 

 fine deposits, pervious and impervious 

 beds, representing more or less rapid 

 deposition, has been such that some of 

 the waters, percolating along the easiest 

 channel, have passed beneath sloping, 



overlying beds of clay, and, accumulat- 

 ing there under pressure, flow when the 

 impervious bed above them is pierced. 

 Practically all of the artesian waters in 

 the valley and they are of great im- 

 portance and wide distribution occur 

 under these conditions. The synclinal 

 rock basins, which have come to be rec- 

 ognized as typical of regions in which 

 artesian waters are found, are of little 

 importance here. 



These special artesian conditions, 

 which are characteristic of the alluvial 

 fans and the Coastal Plain deposits, pos- 

 sess certain definite attributes, some of 

 which are advantageous and others of 

 which are disadvantageous, from the 

 point of view of the water- user. 



In the first place, the gravels are 

 loose, free, and coarse, so that they have 

 a high transmission capacity, the water 

 passing through them readily. Under 

 these conditions there is no possibility 

 of failure from the cause effective in the 

 Denver basin, for example, namely, an 

 inability on the part of the water-bearing 

 rock to transmit the waters as fast as 

 the}- are withdrawn by the wells. But 

 this very openness creates another dan- 

 ger, that of exhaustion of the stored 

 waters, which flow so freely to the point 

 of exit that shallow wells of lo-inch 

 bore have yielded as much as 400 miner's 

 inches. 



Again, in the majority of the basins 

 the first water-bearing stratum is found 

 at a very moderate depth, often less than 

 100 feet. Small wells may be sunk to such 

 depths at very slight cost so slight, 

 indeed, that ranchers have found it more 

 economical to sink a number on a small 

 tract than to distribute the water from a 

 central well. This condition has en- 

 couraged larger drafts upon the supply 

 than would be made in an artesian basin, 

 where the waters were farther from the 

 surface and less readily accessible. 



In its preliminary work upon the un- 

 derground waters of southern Califor- 

 nia, the U. S. Geological Survey has 

 mapped the principal artesian areas in 

 their present and their original outlines. 

 The results which are shown in the ac- 

 companying illustration are of consider- 

 able interest, and reveal the rather aston- 

 ishing fact that at one time this semi-arid 



