GENERAL DISTRIBUTION OF THE GRAVELS 



*05 



type of the uncovered deposits, spread over broad areas, and with difficulty 

 to be connected together into any one continuous channel, those between 

 the South and Middle Yuba furnish, probably, the finest example to be found 

 anywhere of a detritai mass possessing all those peculiar characteristics 

 which mark the work of ancient rivers in the Sierra. The deposits of gravel 

 are of great thickness, and may be traced almost continuously from high up 

 in the range down almost to its very base. Large portions of it are un- 

 covered, so that the banks can be washed by the hydraulic method; the 

 auriferous particles are probably more uniformly scattered through the de- 

 tritai masses than anywhere else on the slope of the Sierra ; and the topo- 

 graphical conditions at and near the summit are favorable for securing large 

 and permanent supplies of water. Hence we have in this region the largest 

 and most important hydraulic mines in the world, which promise to hold 

 their own for a considerable number of years to come. From Snow Point, 

 at an elevation of 4,200 feet, to French Corral, 1,579 feet, the gravel has 

 been traced not continuously, but sufficiently so to make it certain that it 

 belongs essentially to one channel, although not without lateral branches, 

 the position of which has not yet been clearly made out. This channel is 

 extensively covered in its upper portion by volcanic materials, but below 

 Columbia the gravel is entirely free from any lava capping ; and although 

 there is a break in its continuity, between Cherokee and North San Juan, of 

 a little over three miles, yet there can be no doubt of the former existence 

 of a connecting deposit, which has been washed away and disappeared. It 

 is not necessary, however, to dwell on the peculiar features of this great 

 deposit on the summit between the Yubas, because it has already been quite 

 fully described in the preceding pages.* Certain questions connected with 

 it will come up for consideration further on, after the present general sketch 

 of the occurrence of gravels has been completed. 



The divide between the Middle and North forks of the Yuba is very differ- 

 ently situated, with reference to the gravel deposits, from that between the 

 Middle and South branches of the same river. There are two quite decidedly 

 marked channels, and possibly a third; but we have them now for the first 

 time exhibiting a direction not, in the main, coincident with that of the 

 present lines of drainage ; but, on the other hand, decidedly transverse to it. 

 "he gravel deposits occur on this divide in quite isolated patches, which are 

 not of extensive area; but their position with regard to each other is such 





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* See ante, pp. 196-208, and Appendix A. 



