426 



SUPPLEMENT AEY INVESTIGATIONS IN THE GRAVEL PEG ION. 



are discharged, a dam has formed, which holds the water back for nearly a mile in the canon of 

 Steep Hollow. At the time I was there, the 21st of November, a part of the water from the mines 

 was flowing " up stream " into this lake. A similar lake has been formed in Greenhorn Creek 

 above the mouth of Gas Canon ; and if the mines at Hunt's Hill are worked, a similar dam will 

 form, near the junction of Greenhorn and Little Greenhorn creeks, which will work to the injury 

 of Gas Canon as a natural outlet for the Quaker Hill mines. 



The rapid accumulation of tailings in the present canons, in spite of their steep grade, shows 

 conclusively that a comparatively short time will be sufficient for the formation of extensive de- 

 posits of gravel, provided only the conditions are favorable. 



Section VI. — The Forest City Divide, between the Middle and North Yuba Rivers, and the 



Vicinity of Sierra City. 



On the divide between the Middle and the North forks of the Yuba Piver the relations of the 

 old gravel channels to the present topographical features of the country are radically different from 

 those which prevail on the ridge between the Middle and the South forks. On the latter ridge, 

 as has been seen from the preceding pages of this volume,* an old channel can be traced almost 

 without interruption from Snow Point to French Corral, sometimes on the northern and again on 

 the southern slope of the divide, but following in the main the same direction as the ridge. On 

 the former the old channels are transverse to the ridge and cross it nearly at right angles, as if 

 they were occupying the places of northern tributaries to the main northeasterly and southwesterly 

 stream (on the ridge lying to the south), very nearly parallel to the course followed by the present 

 North Fork, from a point southerly from Strawberry Valley to its junction with the Middle Fork, 

 a couple of miles below North San Juan. This is true of the principal and best-defined channels, 

 which are two in number. In addition to the gravel of these two channels there are other depos- 

 its, some large and some small, whose relations both to each other and to the old channels are a 

 matter of considerable doubt. In the opinion of some there is a third channel, nearly parallel to 

 the other two, the existence of which, however, I cannot regard as proven. 



Any attempt to portray the topographical and geological features of this section will be to some 

 extent unsatisfactory on account of the lack of good and trustworthy maps, to which the reader 

 can be referred. A portion of the ridge lies in Yuba County, of which the most recent map bears 

 date of 1861, and the remainder in Sierra County. Mr. Hendel's map of the latter county, though. 

 " compiled from official surveys" and dated 1874, still leaves much to be desired. Its errors, espe- 

 cially in those portions which have not been surveyed by Mr. Hen del in person, make the map 

 practically unavailable as a background upon which to represent the geology of the county. Had 

 Mr. Hendel been able to extend his instrumental surveys more generally over the county, there is 

 no doubt that the most serious of the errors would have been detected and eliminated. My 

 acquaintance with Mr. Hendel's work in Plumas County warrants me in making this assertion. 



The detailed description of this ridge falls naturally into three parts. I will take up first the 

 vicinity of Camptonville ; second, the region near Forest City ; and third, the higher portions of 

 the ridge in the neighborhood of Sierra City. 



A. Camptonville and Vicinity. 



This region, lying partly in Yuba County and partly in Sierra County, does not fall within the 

 limits of any published map that is constructed on a scale sufficiently large to be of practical value 

 as a map of reference. For the western portion, the old Yuba County map may be used, though 

 it is in some particulars inaccurate. I cannot state precisely what corrections should be made 

 upon this map, for I had neither the time nor the means for making the necessary instrumental 

 surveys. According to the information I received from several sources, and to the hasty observa- 



* See ante, pp. 196-208. 





