OEOG1UPHICAL FEATURES. 427 



at some places, to an absence of rain, and a well marked maximum 

 late in December. Eange excessive. &quot; 



Other tables could be produced to illustrate a characteristic in the 

 winter rain-falls, namely, that during the season there is a marked 

 cessation of rain, ranging from one to four weeks. 



This cessation does not occur at any regular epoch, so that its 

 effect is not seen in a chart constructed only upon average quantities, 

 but it has occurred nine years out of ten. Very frequently during 

 this cessation of rain, the cold winds from the north, accompanied 

 by a clear sky, blow fiercely, and blast the young growing crops; or 

 when this dry interval is prolonged, even without these cold north 

 ers, the weather is usually clear and fine, perhaps hot, and the young 

 grain withers and may be w r holly lost, even for fodder, if the last 

 rains of the season come late. 



In some years the rains cease suddenly in February, and the crop 

 is lost. This was notably so in the Great Valley in the spring of 

 1873, where a most promising harvest was blighted by the ceasing 

 of the rains, and only those few fields that were irrigated yielded a 

 crop; those that had been sammer-f allowed yielded about half an 

 average crop; the remainder, especially on the southern half of the 

 valley, yielded, probably, an average of six or eight bushels. 



Southward of the Great Valley, to the Mexican boundary, the 

 necessity for irrigation increases, and the problem becomes more 

 intricate, because the extensive arable sections have a limited sup 

 ply of water, and the country is not so easily watered. In the San 

 Diego river no w r ater flowed through its lower parts for about five 

 years, ending November, 1873. 



Although the commission has not been required to examine any 

 other than the Great Valley, the foregoing fact is stated in confirma 

 tion of the peculiar climatic conditions of the coast. 



The orographical features of the Pacific slope are such that were 

 other conditions equal, the uniformity of rain-fall can nowhere take 

 place. 



Speaking generally, the Coast Kange of mountains and the Sierra 

 Nevada run parallel with the coast line, and the Great Valley lies 

 between them. The Coast Range of mountains maintains an average 

 elevation of over two thousand feet, reaching as much as six thou 

 sand two hundred feet a few miles south of Monterey, and three 

 thousand eight hundred feet to the peninsula of San Francisco. 



The southerly storms of winter bring up rain north of latitude 

 28 to 30, and drive the moisture-laden air against the southwest 

 erly, or seaward-flanks of these mountain ranges, and the precipita 

 tion of rain amounts to two and a half times the quantity that falls 

 upon the eastern flanks. This has been established by measurement 

 at the reservoirs of the Spring Valley Water Company, and confirms 

 the reports of the farmers and stockmen. 



Nine years observations at Pillarcitos Dam, give an average of 58 

 inches of rain, while San Francisco, distant only fourteen miles, has 

 23.5 inches. The same law holds good along the western flank of 

 the Sierra Nevada, which chain averages nine thousand five hundred 

 feet elevation. From several years observations on the line of the 

 Central Pacific railroad, the fall of rain at Summit station is three 

 times that between Eocklin and Auburn, and many times greater 



