GEOLOGY OF THE COAST RANGES 



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Sierra is very large in certain years, and probably quite irregular; but there 

 is an entire want of statistics extending over any considerable number of 

 years at any one point. The snow-fall in some winters near the summit of 

 the range must amount to as much as sixty or seventy feet, and it accu- 

 mulates to a depth of from fourteen to twenty feet in the more elevated 

 valleys. After a winter of large precipitation, the snow lies in the passes 

 until midsummer, and a considerable amount remains over until the next 

 year on the highest peaks and ridges, especially on their northern slopes. 

 When two or three dry seasons succeed each other, the crest of the Sierra 

 becomes, apparently, almost entirely denuded of snow, as seen from a dis- 

 tance ; still, even then, quite large patches would be found high up among 

 the depressions and ravines near the summit. 



Although, as before remarked, almost the whole precipitation, in the 

 higher part of the Sierra, is in the form of snow, there are, even on the 

 western slope, occasional heavy rain-falls, accompanying violent thunder- 

 storms. Such a one occurred in June, 1867, at the head of the Yosemite 

 Creek, raisins; that stream several feet in the course of half an hour, while 

 its eflects were also very perceptible in the South Fork of the Merced, as 

 far down as Clark's Ranch. On the eastern slope, near the summit, such 

 summer thunder-showers are not very infrequent; but their range seems 



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to be quite limited. Farther down on that side, and generally through the 

 very dry portions of the mountainous regions of the State there are occa- 

 sional exceedingly heavy rain-falls over very small areas ; these are popu- 

 larly known as "cloud-bursts," and their effects are sometimes disastrous to 

 persons caught in them, dry canons being converted for a few minutes into 

 raging torrents which sweep everything before them. Additional remarks 

 on the snow and rain-fall of the High Sierra will be found further on in this 

 volume, in the chapter devoted to glacial phenomena. 



Section II. — Geological Age and Structure of the Coast Ranges. 



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It is not intended in this place to give anything like an exhaustive 

 account of the geology of the Coast Ranges; it would require more than 

 one volume to do the subject justice. It will be convenient, however, for the 

 Purposes of the present work, that the reader should have a general idea, of 

 the geological peculiarities of the elevated border of the western side of the 

 weat Valley, since occasional reference will have to be made to these in 



