STATE AGRICULTURAL SOCIETY. 257 



oonfident that it will bo found tliat the southwest return trades i)rcvail in Winter north of Capo 

 Corrientes, and are turned by the mountains and tlie coast uj) tlie Gulf of California, and so 

 over this State as our southeast winds. It comes from tliis gulf warm and laden with moist- 

 ure, and passes over the Colorado and Mojave deserts. These deserts, as shown by tlie meteor- 

 ological records of the Smithsonian Institute, have a mean Winter temj)erature of from 

 forty-eight to fifty -six degrees. This is not sufficiently low to precijiitate its moisture, and it 

 passes on until it meets the Sierra Nevada and Coast Range. In ascending these it rises into 

 cooler regions, finds a mean Winter temperature of forty degrees, and gives up some of its moist- 

 ure. When it flows down into the southern end of the great valley of the Tulare, it meets a 

 mean Winter temperature of forty-eight degrees, which is higher than that of the mountains 

 it has just passed. It therefore retains its moisture and passes on, until it meets a cold polar 

 wind, and has another portion of its moisture condensed in a rainstorm, or, failing to meet 

 this, passing still further north, until its moisture is condensed by the i)revailing low tempera- 

 ture of a higher latitude. It is of frcrpient occurrence in Winter that a gentle soutlieast wind 

 will blow for days, giving no rain south of the latitude of San Francisco, but cloudy weather at 

 the northern end of the Sacramento Valley, and light showers and rains from Red Bluff to 

 Oregon. Therefore, the northern part of the State should receive more rain than the southern, 

 and the mountains more than the valleys. The least rain should be in the hot deserts and on 

 those sides of valleys most sheltered by mountains from the moisture-bearing winds. 



Meteorological observations, taken since the writing of the above, 

 fully confirm the assertion made respecting the rainfall, however 

 phenomenal it may appear to be, and show, conclusively, that the 

 precipitation in all the territory tributary to the influence of the above 

 factors of climate, is subservient to meteorological laws, the same as 

 in other parts of the M^orld, differing only as the physical causes differ 

 that produce the resultant effects. The average annual rainfall at 

 Crescent City, in the extreme northern part of the State of California, 

 is thirty-six inches, and diminishes about two inches for every degree 

 of latitude towards the south, until, at San Diego, it is but ten inches. 

 In altitude, it is found to increase about one inch for every one hun- 

 dred feet in elevation in ascending the windward side of the Sierra 

 Nevada range of mountains. Local causes have influences bearing 

 upon the amount of rainfall in different localities, but they are nearly 

 all topographical; and, wiien carefully studied, are easily explained, 

 either for the small or great amount of average rainfall they receive. 



17"*' 



. I 



