The Behavior of Rivers 45 



Castroville. The streams which enter the basin from the adja- 

 cent mountains are torrential, as is the Salinas during the season 

 of heavy rainfall. The annual precipitation is light, probably 

 not more than 10 inches. The river is a raging torrent during 

 the flood season, but its bed is dry so far as any active stream is 

 concerned during much of the year. Gullies are cut into the 

 mountain sides at the headwaters of the tributary streams. At 

 these headwater sources the principles of stream development 

 for consequent streams apply. The Salinas itself, however, does 

 not conform to the simple law of drainage development. In 

 fact the Salinas is not a drainage stream but is what is known 

 as a superimposed stream. In other words, it has inherited its 

 present course from a series of geologic events that go back 

 through a long series of changes. 



The river does not follow the valley to which it would seem 

 to belong. North and east of San Luis Obispo the stream leaves 

 the flat open valley bottom and flows through a canyon eroded 

 into the hard granite rocks of the mountains that border the 

 valley on the northeast. This canyon has been cut by the river 

 to a depth of 500 to 700 feet. The river continues in this can- 

 yon for three miles when it approaches the flat bottom of the 

 valley, only to again turn back into the hard granite, and 

 emerges again upon the broad valley bottom northeast of Mar- 

 garita. Three principal tributaries enter from the west across 

 the broad valley bottom. These are the Rinconnaida, the 

 Trout, and the Santa Margarita. These streams cross the broad 

 valley in a generally northerly direction. The Rinconnaida 

 joins the Salinas at a point where the latter emerges from the 

 granite and touches the edge of the valley. From this point 

 the Salinas again turns away from the valley and pursues its 

 course through the granite. The Trout and the Santa Mar- 

 garita flow across the flat valley bottom, being separated only 

 by a low divide. These enter the Salinas about three miles 

 apart, about three miles northeast of Santa Margarita, where 

 the main river again emerges from the granite canyon. The 



