190 



GEOLOGY 



The outline of some deltas is determined by the surroundings 

 in which they are built. When, for example, a delta is built into 

 a bay, the form of the bay-head determines the shape of the delta. 



Fig. 162. Relief-map of an area about the head of the Gulf of California 

 showing the delta of the Colorado River, outlined, in a general way, l>y 

 dotted lines. The Salton Sink is shown at the north, and the Imperial 

 Valley lies south of the sink. (U. S. Rec. Serv.) 



The normal form of a delta built on an open coast is somewhat 

 semicircular, though there is often a fringe of delta fingers which 

 together have some resemblance to the Greek letter A , which gave 

 these terminal deposits of streams their names. 



