THE RELATION OF IRRIGATION TO HUMIDITY IN A 

 RECENTLY RECLAIMED DESERT 



e. a. McGregor 



El Centro, California 



The Imperial Valley of California, which is the subject of this 

 paper, offers many very interesting studies. It comprises the 

 major portion of the Salton Basin, an area which is below sea 

 level, and at the lowest portion of which lies the Salton Sea. 

 The water of this sea is strongly alkaline through the age-long 

 concentration by the excessive evaporation of the periodic 

 inundations occasioned by the overflowing of the Colorado 

 River. 



The Imperial Valley is geographically a part of the great Colo- 

 rado Desert. As recently as 1900 it was a desolate uninhabited 

 waste of typical southwestern desert which supported only creo- 

 sote bush, mesquite, salt bush, arrow-weed and a few similar 

 characteristic desert plants. The average total annual rainfall 

 for the Imperial Valley is probably less than two inches. 



Geologically the Salton Basin or Sink possesses a very inter- 

 esting history. We are told that in comparatively recent times, 

 as reckoned by geologists, the Gulf of California extended north- 

 westward to where Indio now lies. At that time the Colorado 

 River did not flow into the head of the gulf, as now, but emptied 

 laterally on its eastern shore at a point not far south of the pres- 

 ent location of Yuma, Arizona. Little by little a delta was built 

 out across the gulf, opposite the river mouth, by the vast quan- 

 tities of silt carried by the river's flood waters. In time this 

 delta spread, fan-like, until it reached and fused with the western 

 shore of the gulf. Owing to the fact that the apex of the delta 

 was some 40 feet above sea level, this silt deposition gradually 

 elevated itself above sea level. The final result was that the 

 upper (northwestern) portion of the former Gulf of California be- 



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THE PLANT WORLD. VOL. 22, NO. 2 



