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GEOLOGY OF THE COAST RANGES. 15 
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, raising that stream several feet in the course of half an hour, while 
its effects 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 
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 cafions 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 farther on in this 
volume, in the chapter devoted to glacial phenomena. 
Section II. — Geological Age and Structure of the Coast Ranges. 
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 
Great Valley, since occasional reference will have to be made to these in 
