38 THE CLIMATOLOGY OF THE UNITED STATES. 



like Nevada and Arizona is subject to occasional cloud 

 bursts when the water comes down in a deluge carrying 

 everything before it. These generally occur in the moun- 

 tain canyons and small valleys and have not been known 

 near the large towns, though the railroads and towns suffer 

 from the rapidly rising streams at such times. Sand 

 storms also occur here as they do in the San Joaquin 

 valley. To the east of southern California lies the Ari- 

 zona meteorological region in which the small rainfall oc- 

 curs in summer ; this season is excessively hot except 

 in the mountains. The mercury in a few places some- 

 times reaching 120 in the shade, and the hot days are 

 followed by hot nights ; the southern part, however, has 

 a fine winter climate the mountain districts being cold. 

 The mean July temperature of Yuma, which is in the low- 

 lands, is one hundred and four degrees and the rainfall 

 at this place is only four inches. Between this region 

 and southern California lies a desert which is influenced 

 by the dry winters of the former and the dry summers 

 of the latter. A year or more has often passed without 

 rain, but an occasional cloud burst supplies the country 

 with an unwelcome amount in a few minutes ; coming in 

 this way little good is done, and no vegetation is pro- 

 duced here. As I have stated Nevada and Utah differ 

 somewhat from California in climate, so also Colorado and 

 the western parts of Texas partake somewhat of the climate 

 of the Arizona region, but the classification of the three 

 principal regions of the United States already made is 

 sufficient in a general way. 



It remains to be stated that the above characteristics and 

 statistics refer to the weather in its normal condition, but 

 a change has been taking place throughout the world during 

 the last five or six years, which the majority of meteorolo- 



