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University of California. 



[Vol. 2. 



prior depression, the conditions would tend to grow more and 

 more unfavorable to the production of bars. 



Since bars are usually formed at the mouths or in the lower 

 stretches of the stream valleys, if these valleys are narrow and com- 

 paratively steep-graded, the bars will soon be removed by the ero- 

 sion of the streams, on elevation, just as the deposits made by the 

 streams themselves during depression are removed on elevation. 

 As the valleys broaden and their grade decreases, the bars formed 

 will tend to preserve their character for a longer time. As their 

 destruction will be due largely to the cutting of the stream which 

 occupies the valley, the length of time during which they will be 

 preserved will depend on the corrasive power of the stream, and on 

 the extent of its wandering to and fro over the valley floor. 



The general conditions governing the formation and preserva- 

 tion of other wave- and current-built features (spits, hooks, &c), 

 are similar to those for the features already described, and need not 

 be considered separately. 



Along the California coast the present conditions are in general 

 unfavorable to bar construction. Large embayments are not 

 numerous, the majority of the drainage lines reaching the ocean 

 being minor ones. Most of the larger openings are too wide and 

 the water of too great depth for the bay to be spanned by a bar; 

 wave- or current-built features may, however, be found in such 

 bays, along the curving shore line, partially or completely closing 

 the mouth of some stream emptying into the bay. San Francisco 

 Bay has its entrance kept open by the powerful tidal currents flow- 

 ing through the Golden Gate. In a few instances where the cir- 

 cumstances have been favorable well-developed bars have formed, 

 as, for example, at Humboldt Bay and San Diego Bay. Most of the 

 minor valleys have probably not been flooded; but where bays 

 have been formed at their mouths they have in most cases been 

 destroyed, either by rapid cutting back of the cliffs, or by filling in 

 with the deposits of the stream. Some of the larger and more 

 open of these minor valleys are now drowned, without being 

 barred; while a comparatively small number have bars formed at 

 their mouths. Similar conditions to these for the minor valleys are 

 found among the rugged islands off the coast, bars being uncom- 



