THE MAKE OF THE DESEBT 



29 



desert is far from being a permanent afEair. 

 There is hardly enough vegetation to hold the 

 sands in place. With little or no restraint npon 

 them they are transported hither and yon at 

 the mercy of the winds. 



Yet the desert winds hardly blow where they 

 list. They follow certain channels or " draws " 

 through the mountain ranges ; and the reason 

 for their doing so is plain enough. During the 

 day the intense heat of the desert, meeting with 

 only a thin dry air above it, rises rapidly sky- 

 ward leaving a vast vacuum below that must be 

 filled with a colder air from without. This 

 colder air on the southern portion of the Colo- 

 rado Desert comes in from the Gulf region. 

 One can feel it in the passes of the mountains 

 about Baboquivari, rushing up toward the 

 heated portions of Arizona around Tucson, 

 And the hotter the day the stronger the inward 

 rush of the wind. Some days it will blow at 

 the rate of fifty miles an hour until sunset, and 

 then with a cessation of radiation the wind 

 stops and the night is still. 



On the western portions of the Colorado the 

 wind comes from the Pacific across Southern 

 California. The hot air from the desert goes 

 up and out over the Coast Range, reaching sea- 



Destrt 

 vjinds. 



Eadiation 

 qfheaL 



