lyi INTRODUCTION. 



more and more parched and sterile as they near the head of 

 the Gulf of California. 



The Eio Gila does much the same thing : it cuts througli 

 the Pina-leno Mountains north of Camp Grant by means of 

 a succession of canons. Its bottom-lands are extensive and 

 fertile ahove these canons for a distance which at present is 

 not ascertainedj and heloiv them for about fifty miles in the 

 Pima country. But, further west^ it enters the sterile region 

 known as the Gila Desert^ the continuation northward of the 

 Great Sonora Desert, and passes thi'ough it for the remaining 

 150 miles of its course until it reaches the Colorado. 



This completes our rapid sun^ey of the Colorado Basm. 

 We will now pass oyer the Wahsatch Mountains^ forming its 

 western boundary, and take a bird's-eye yiew of the country 

 beyond. - . 



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