16 



tlie plains and hills are subjected to almost blistering beat. IJadiation 

 bein<i- equally unobstructed, all objects soon cool at night. 



The high temperature of the day is not oppressive, for it is the direct 

 rays of the sun rather than the stifling heat of a moisture laden 

 atmosphere. Since the atmosphere itself becomes warm only as its 

 moisture accumulates heat in latent form, high temperatures are not 

 reached except in direct sunlight. 



This great ineciuality between day and night temperatures is quite as 

 pronounced in winter as in summer. Very low temperatures are often 

 reached, —40'^ V. being prol)ab]y not unknown. The winter, while in 

 some respects not severe, is long; the summer proper, short. Few, if 

 any, months are wholly exempt from frost, and many a hard freeze 

 occurs during the growing season, which follows close upon the melting 

 of the snows in spring. 



PRECIPITATION. 



The amount of moisture that the region receives is on tlie whole 

 (juite small. During the summer months very little rainlall occurs. 

 Bright, sunny days are the rule. Light showers occasionally fall, but in 

 a few hours afterwards there is little trace of moisture. At this 

 altitude, under the inlluence of the usual winds and the unobscured 

 sun, the evaporation is simply enormous. 



At long intervals occur rainstorms of greater magnitude, sometimes 

 reaching cloudburst proportions. The area covered by them isoften as 

 limited as their force is violent. The downpour along the higher ranges 

 of hills and bluffs becomes flood-like. Torrents rush down the slopes, 

 carrying everything before them, into the usually dry ravines and creek 

 beds that for a few hours overflow with a fluid so turbid that the pro- 

 verbially nnnldy waters of the Missouri would seem clear in compari- 

 son. From this deej), cream-yellow paste there is deposited upon the 

 low banks of the creeks a layer of silt that is pasty and slippery 

 almost beyond belief. This bakes and cracks into hard, irregular 

 bricks, not drying up like ordinary iiind. The showers are of little 

 benefit to the locality; the slopes are so abrupt and the vegetation of 

 such a nature that very little of the nunsture is held back long enongh 

 to penetrate the soil. 



By far the most valuable and available sources of water supply are 

 the snows that may occur at almost any time during the year, uidess it 

 be during one or two of the sumuu'r months. They occur rarely during 

 the early fall, occasionally during the winter, and more frequently 

 during the spring months. These usually melt so gradually that all 

 their moisture, except such as is lost by evaporation, flnds its way into 

 the soil. 



Especially liel])rul to the vegetation of the desert are the snows of 

 late spring. These lie like a wet blanket over everything for a few days 

 at a time, completely saturating the soil and providing an abundance 

 of moisture for the rapidly developing vegetation. 



