THE CLIMATOLOGY OF THE UNITED STATES. 31 



few productive spots like the great Salt Lake Valley, which 

 lies in the eastern part at an elevation of about 4000 feet 

 above sea level. This Valley is about the only locality 

 here, capable of supporting at present any large popula- 

 tion. Passing on to the west, we cross the great Alkali 

 Desert ; aregion producing very little in the way of Vege- 

 tation but sage brush. The rainfall in this section of 

 the country is very light, ranging from eighteen inches 

 at Ogden to four inches at Humboldt per annum, as com- 

 pared with an annual precipitation in Boston of forty-eight 

 inches ; and as more water is lost here by evaporation than 

 is furnished by the rainfall, the lakes, inckiding Great 

 Salt Lake, are gradually diminishing in size. The winters 

 here are cool and the summers quite warm, but the ex- 

 tremes are not so great as in much of the country east of 

 the Kocky Mountains, nor are the changes in temperature 

 as great or as sudden. This condition appears to be the 

 result of the relative position of the plateau with regard 

 to the Rocky Mountains and the Pacific Ocean. We should 

 expect to find it somewhat cooler than the lowlands of tlie 

 great Mississippi Valley, but we also find that it is less 

 subject to the violent fluctuations of temperature which we 

 experience when warm areas of barometric depression are 

 rapidly followed by cold waves from the west or northwest. 

 The majority of these cold waves sweep down into the 

 United States in a southeasterly and easterly direction 

 from the northwest states and the reo^ion to the north, alons; 

 the eastern slopes of the Rocky Mountains which here trend 

 in a southeasterly direction. The region to the west of 

 these mountains is subject to more or less change, but in 

 a less degree ; and again, the character of atmospheric 

 changes, advancing from the west, would be inÜuenced by 

 the proximity of the Pacific Ocean which is milder than 

 the Atlantic in the same latitudes, a matter which will be 



