266 IRRIGATION INVESTIGATIONS IN CALIFORNIA. 



when the water surface rose about 16 feet, increasing in area from about 350 square 

 miles to about 750 square miles — is taken into consideration, it appears that after all 

 the prime cause of the recedence of the lake is not the increased use of water for irri- 

 gation, but the long intei'val between seasons of excessive rainfall and the recent 

 long sequence of seasons with precipitation barelj' normal, or less than normal. It 

 appears, in fact, that the last season in which the streams of San Joaquin Valley were 

 all in extreme flood was that of 1867-68. This is now so remote that a conclusion as 

 to change of climate might almost seem warranted were it not that Indian tradition 

 distinctly points to a still earlier period than that covered by the diagram showing 

 fluctuations, when the lake had all but disappeared, and that the present long sequence 

 of dry 3'ears was almost equaled by that of 1853-1861. There is distinct evidence, 

 too, that at some former period of the lake's history there was a protracted low stage 

 (elevation at or below 200), being a period of suflScient length to permit willows to 

 grow to diameters of from 3 to 1 feet.' 



The occurrence of successive years of scant rainfall, notably the last three 

 seasons, is perhaps serving a good purpose. These seasons afford a better and more 

 satisfactory basis for determining the amount of water that can be relied upon for 

 irrigation, and force upon the water taker the conviction that regulation of use, 

 without expensive and unsatisfactory recourse to the courts, is essential for their 

 protection. 



BAINFALL AND CLIMATE. 



Rainfall in the district under consideration is not overabundant. About 9 inches 

 represent the mean annual fall at Fresno. It is somewhat less farther to the west 

 and considerably more at the base of the Sierra Nevada. Practically no rain falls 

 from May 1 to November 1, if an occasional unwelcome October shower be excepted, 

 which now and then drives the raisin producer under cover. Very wet seasons, with 

 rain at Fresno in excess of 20 inches, are rare. Those with rainfall below the normal 

 are more frequent. About 10 inches, when favorably distributed throughout the 

 winter and spring months, is considered enough to produce fair crops of grain. 

 Failures of grain crops on unirrigated lands are much more frequent than are good 

 crops. 



The summer and fall of the year are dry and hot, temperature frequently rising 

 to about 110^ F. in the shade. The nights are rarely oppressively hot. The heat of 

 the region lacks the oppressiveness of the moister climates of the East. In winter 

 the temperature rarely falls below 22°, though temperatures as low as 12° have been 

 recorded. Late spring frosts are dreaded, but are fortunately of rare occurrence. 

 The splendid results in citrus fruit culture to be noted for the vicinity of Center- 

 ville (Kings River) are sufficient guaranties of the mildness of the winter season. 



As in all copiously irrigated regions, where no effort is made to secure good 

 drinking water, there has been more or less sickness of a malarial type, but in some 

 of the districts which were considered least healthful twentj* years ago, as near Cen- 

 terville, there is now comparatively little complaint. 



' See U. S. Geological Survey, Water-Supply Paper No. 17; also Report of Examining Commis- 

 sion on Rivera and Harbors, California, 1890, page 69. 



