3G4 Transactions of the 



not now remember which, and have not tlio notes before me). Professor 

 Blake, In speaking of the rocks in one of these passes, notes that they 

 contain large numbers of garnets, and as these arc much harder than 

 the rock in which they arc embedded, they have resisted in a greater 

 degree erosive action of these storms, which have worn the face of the 

 rocks, so to speak, into long fingers, each tipped with a garnet, and all 

 pointing in the direction from which these winds usually blow. Hero 

 we have a practical illustration of the power of tin; sand blast, and if 

 its effect has been such upon the rocks, it is not difficult to imagine 

 what it must he on the tender Spring vegetation. 



Their temperature and drying capabilities require no further or more 

 complete illustration than a simple statement of the fad that during 

 their prevalence at San Diego, the merchants are compelled to keep 

 their books in presses to prevent the hacks from curling up, as they do 

 if unprotected, in exactly the same manner as if placed before a hot fire. 

 That these winds acquire their baleful properties on the desert is easily 

 shown. They are essentially southeast winds, more or less modified by 

 the topography of the region over which they blow. They reach tho 

 desert as cool winds from the Gulf of California. On the desert they 

 acquire the temperature and lose their moisture by evaporation, at the 

 same time acquiring their burden of sand from the ridges on the north 

 of the desert, and in their altered character find their way through tho 

 mountain passes on the north and west, into the fertile plains of Kern 

 and Los Angeles Counties. 



Seccnd — It would also seem that the presence of this desert is a prac- 

 tical far to the rainfall in the region occupied by it, and diminishes to a 

 serious extent that in the surrounding region to the north and west. A 

 large portion of the desert, so called, is a desert only because of the ab- 

 sence of rainfall. The vegetation on the desert, whenever it exists, is 

 due to the overflow of the Colorado River, and its rapid growth to the 

 fertility of the soil, which is a deep alluvium, ami the warm temperature 

 of the nights, which in Summer rarely falls below sevent}' degrees Fah- 

 renheit. This vegetation derives no nourishment from any rainfall; it 

 is due solely to the effects of the overflow, and if no overflow occurs, is 

 wanting. The absence of rain is well illustrated by the meadows near 

 New River Station. In these meadows the grass which was standing 

 on them at the time of Mr. James' visit, grew and matured three years 

 ago, and yet is good feed for stock. Had any rain fallen upon it, it 

 would have been quickly destroyed, as are all the dry pastures of Cali- 

 fornia at the commencement cf the rainy season. These facts are noth- 

 ing more than might be expected. The rain-bearing clouds of California 

 come from the soul beast and southwest. Those from the southeast fol- 

 low the Gulf of California, and on reaching the desert, as shown by Mr. 

 James, have their temperature so increased that their rain is dissipated 

 or carried by the upward current and rarefaction into higher regions, to 

 be deposited partially further to the northward. In the same way tho 

 westerly winds drawing in to supply the vacuum caused by the rarefac- 

 tion of the air above the desert are brought into contact with these warm 

 currents, and, instead of releasing their contents, are dissipated in a 

 similar manner. Now, a large portion of the San Joaquin Valley is de- 

 pendent on these southeast winds for its rainfall, and it is necessary 

 thattbese rain -laden winds should not be interrupted. The southwestern 

 rain winds -deposit most of their rainfalls on the Coast Range which lies 

 between the San Joaquin Valley and the ocean, and must ever do so, on 

 accounjt of the structural peculiarities of California, hut the mountain 



