91 \ I E AGRICULTURAL SOCIETY. 31 7 



\\ .I age 

 Rainfall, 

 in inches. 



Santa Barbara - 



Loa Angeles 



San Diego 



San Bernardino 

 Yuma 



15.8 

 17.fi 

 10.6 

 L5.9 

 2.3 



In general the rainfall of the western part of Southern California is 

 sufficient to produce as much as the soil will stand without '"wearing out." 

 This, on the average, will hold good six years in seven. In the eastern 

 region, wherever water can be obtained for irrigation, vegetation grows 

 with wonderful luxuriance, as may be seen in the ease of the railway sta- 

 tion at Indio, in the Colorado Desert. Without artificial irrigation, scarcely 

 anything beyond a few species of cactus and agave will grow. 



From the preceding it will he seen that the habitable portions of South- 

 ern California receive hut a trifle less of rain than the lower Sacramento 

 Valley, and considerably more than the San Joaquin Valley.* 



A more important factor than the rainfall is the relative humidity of the 

 air. This is a matter somewhat difficult to presenters the atmosphere may 

 be extremely "moist" one day and very •'dry" on another, and yet in both 

 cases contain exactly the same amount of aqueous vapor. The cause, it is 

 hardly necessary to state, is due to a difference in temperature. In the one 

 ease the air, because of its low temperature, contains nearly or quite all the 

 vapor it can possibly hold. In the second case, while the air may contain 

 the same amount or even more of moisture, the air seems dry, because its 

 high temperature enables it to hold three or four times as much vapor as it 

 appears to contain. In Southern California the seasons of dry air and moist 

 air are well marked. Aside from these there are belts of country especially 

 liable to heavy fogs. 



From the time of the first rains, the belt of country next the coast is 

 bathed in an atmosphere which is tolerably moist. At a distance of a few 

 miles inland the relative humidity increases — not because there is more 

 moisture but because the temperature is apt to range lower. Here the fogs 

 are heaviest and the deposition of dew is greatest. Beyond this belt, as the 

 distance from the coast increases, the relative humidity decreases; until, at 

 the crest wdiich separates the Pacific Slope from the Great Basin, the air 

 throughout the year is dry, pure, and invigorating. During the Summer 

 months the relative humidity is much less than in Winter. The deposi- 

 tion of dew ceases altogether, and the atmosphere becomes very dry. There 

 is no decomposition of organic matter, because there are no Summer rains. 

 As a result, the atmosphere is so pure and free from organic germs, that 

 meat exposed to the air cures, or "jerks," but does not putrify. In the 

 Colorado Desert, and even in the high mesa lands west of the divide, cul- 

 ture fluids, such as are used in cultivating bacteria, if properly sterilized, 

 often evaporate without "breaking down." It must be borne in mind, 

 however, that this condition, although a prevalent one, is by no means 

 universal. There are many days during the rainy season when the atmos- 

 phere is damp, chilly, and depressing. There may also be occasional 

 localities where on account of excessive irrigation and imperfect drainage, 

 etc., the atmosphere is liable to be unwholesome, and malarial diseases 



* Sacramento, 19.7 inches; Stockton, 10.7 inches; Visalia, 9 inches. 



