The Behavior of Rivers 41 



would not be carrying waters from the crest of the Sierra Range 

 eastward and leaving it to evaporate in Pyramid Lake if it had 

 not been for the great uplifted mountain range on which snows 

 gather and melt, and the waters seek the easiest way to escape 

 to the lower lands of the Great Plains. The river is subsequent 

 to the uplifting of the mountains. 



The rivers of California offer a fascinating study. A 

 glance at a map of the State showing the rivers suggests at once 

 that the rivers have not developed in the simple manner de- 

 scribed above. The rock structure of California is very com- 

 plex, resulting from the geologic changes that have occurred. 

 The development of drainage systems on a new continent re- 

 cently lifted above the sea has been outlined. The principles 

 of stream action remain valid even though interruptions by 

 geologic forces modify and change the normal development of 

 streams. The streams of California are no exception to the 

 streams of the world. Water runs down hill in California, 

 and running water carries earth materials and erodes the land. 

 Streams in California grow longer by pushing their heads back 

 landward. Young valleys are V-shaped. Far up-stream of 

 the great rivers that serrate the wide western slope of the Sierra 

 Range many examples may be seen of head gullies cutting back 

 into the higher land beyond. Branches or tributaries are de- 

 veloping today just as they may be imagined to develop on an 

 ideal continent newly elevated above sea level. It is apparent, 

 however, that the rivers of California are not generally conse- 

 quent streams. They do not flow from higher land down 

 uniform slopes to the sea. Upheaval of mountains and other 

 movements of the crust of the earth have obstructed streams 

 that had already been established and changed their courses. 

 Thus consequent streams have become subsequent streams, i.e., 

 they have been forced to adopt new courses because of obstruc- 

 tions, such as the upheaval of mountain ranges, the pouring out 

 of lava from volcanoes, and filling of valleys by glacial deposits. 



