4.50 FORESTRY AND IRRIGATION Octobei 



currence, volume, and the laws govern- These high groups protect the lands on 

 ing their replenishment since in parts their Pacific slope from the climatic ex- 

 of the arid and semi-arid West these are tremes of the deserts, and at the same 

 important sources of supply for domes- time wring from the ocean winds the 

 tic purposes and for irrigation. Such moisture with which they are laden and 

 studies had been carried out especially which in the form of perennial streams 

 along the eastern slope of the Rocky makes possible the high state of culti- 

 Mountains and the adjacent parts of the vation which has given some of the adja- 

 Great Plains by the Hydrographic cent agricultural lands values of $2,000 

 Branch previous to the organization of or even $3,000 per acre, 

 the Reclamation Service ; but soon after Previous to man's occupancy of this 

 its organization this work was segre- region the streams, issuing from the 

 gated into a separate division, known as mountain canyons as perennial flows, 

 the Division of Hydrology, with east- sank at once, except in cases of rare 

 ern and western sections, under sepa- floods, into the alluvial gravels and 

 rate chiefs. sands, which have been piled up about 

 Por the actual field work in this the canyon mouths as evidences of the 

 division, geologists have usually been deliberate, but unceasing, erosional pro- 

 detailed from the Division of Geology, cesses of the past ages. Percolating 

 with which, and the Reclamation Serv- slowly seaward through this alluvium, 

 ice, the new division is closely affiliated, the waters encountering subterranean 

 Its problems are largely geologic prob- obstructions are forced to the surface at 

 lems, since the distribution, the circula- certain points in their courses, only to 

 tion, and the quantities of underground sinkagainonce theobstruction is passed, 

 waters depend upon geologic facts. Its Thus, some of the rivers disappear and 

 relations with the hydrographic work reappear several times in their passage 

 are most intimate, as the questions of to the sea. 



replenishment of underground reser- When white men first entered the re- 



voirs and drafts upon them are in many giou they settled about these areas of 



cases questions whose answers depend rising waters, points where the streams 



upon water and rainfall measurements. were forced out as springs by some im- 



One of the first important fields in penetrable body of rock or clay. In 

 which work was undertaken by the new these damp lands irrigation was unnec- 

 division is that of the valley of southern essary, and if it became desirable to ex- 

 California, long well known throughout tend the cultivated area slightly beyond 

 the United States as the center of orange them a short ditch sufficed to carry the 

 culture, and as possessed of a mild and water to the desired spot, so that the 

 equable climate which is rapidly mak- few irrigation projects were of the shn- 

 ing it to America what the south of plest sort. Average rainfall in the val- 

 France is to Europe, a region of beau- ley is from 10 to 20 inches, the greater 

 tiful homes and a center of wealth, amount near the mountains, the lesser at 

 culture, and pleasant leisure. This some distance from them, and practically 

 work is now well under way, its results all of it falls in the winter months, from 

 are rapidly being made available, and October to May. Irrigation, therefore, 

 they promise to be of great interest and except on these moist " cicnega " lands, 

 value to the people of this part of the is necessary to mature the majority of 

 Southwest. crops. 



Thegreatestpopulationandthehighest With the slow settlement of the re- 

 cultural interests of southern California gion by Americans after the Mexican 

 are distributed through a wide, beauti- cession and the gold discoveries in Cali- 

 fully diversified valley that extends 80 fornia, the desire to extend the culti- 

 miles inland from the Pacific at Port Los vated areas led to the building of 

 Angeles, and is effectually separated ditches, either from the ricnegas, the 

 from the Mohave and Colorado deserts areas of springs, or from the streams 

 by the San Gabriel and San Bernardino which flow out of the mountains. 

 mountain ranges on the north and east. These systems were rapidly extended 



