374 



University of California. 



[Vol. i. 



that the water is said to flow from the latter river into the lake dur- 

 ing high freshets. Prof. E. W. Hilgard informs the writer that the 

 Kings River, which is tributary to the lake on the north through a 

 plexus of mouths, sometimes sends a portion of its water northward 

 to join the San Joaquin. All of this goes to show that the actual 

 divide is very slight, and must lie somewhere between the San Joa- 

 quin River and the mouths of the Kings River. It is possible, too, 

 that there may be no constant direction of flow, but that it may 

 depend upon a rather delicate adjustment of the water carried by 

 the two rivers, and upon the level of the lake, which is known tc 

 be subject to considerable fluctuations. 



The name San Joaquin Valley is frequently used to embrace not 

 only that middle portion of the Great Valley drained by the San 

 Joaquin River, but also the shallow basin in which Tulare Lake lies. 

 It seems preferable, however, in view of the threefold natural divi- 

 sion outlined above, to retain for the latter the name of Tulare Valley, 

 as was done by Blake and the earlier explorers, while recognizing, 

 as they did, that it is really a portion of the Great Valley separated, 

 from the northern portions merely by an accident of drainage. 



The whole Great Valley is completely walled in by mountains, 

 except at one point, near latitude 38 , where the Sacramento and 

 San Joaquin Rivers become confluent, and pour their united waters 

 through the Straits of Carquinez into San Francisco Bay. 



Having briefly sketched in outline the general features of the 

 Great Valley, and indicated its convenient natural division into three 

 parts, it will now be necessary to consider each of these sections in 

 greater detail. 



The Sacramento Valley. — The broad, flat, alluvial plain, having a 

 width of about fifty miles near the point where the Sacramento and 

 San Joaquin Rivers come together, gradually diminishes in breadth 

 to the northward, and may be said to terminate near the town of 

 Red Bluff, at an altitude of about 300 feet above the sea. For some 

 15 miles further north, however, the Sacramento River, with a 

 grade increased to about 25 feet per mile, continues to be bordered 

 by alluvial plains, which rise very gently toward the mountains on 

 the west and east. This modern alluvium of the upper portion of 

 the valley is evidently formed by the coalescence of the low alluvial 



