THE WORK OF RUNNING WATER 



97 



The outline of many deltas is determined by the surroundings 

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

 head of a bay, the outline of the bay determines the shape of the 



Fig. 104. 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, by 

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

 Valley, where many farms were flooded, lies south of the sink. 



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

 semi-circular, though there is often a fringe of delta fingers, which 

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

 gave these terminal deposits of streams their names (Fig. 100). 

 The surfaces of deltas are usually nearly plane (Fig. 98), and the 



