9 84 



SUPPLEMENTARY INVESTIGATIONS IN THE GRAVEL REGION. 





data given me by Mr. Pearl, shows all there is to be known about this deposit at present. The 

 position of the bed-rock under the gravel is hypothetical. 



It cannot be said with certainty that the old channel flowed directly from French Corral to 

 Mooney Flat ; but the evidence is very much in favor of the hypothesis that those two places once 

 lay upon the same stream. If this hypothesis is not accepted, two difficult questions arise for 

 solution, namely : Where was the outlet for the French Corral channel ? and, Where were the sources 

 of the Mooney Flat channel? The two points are about nine miles apart in a direct line, and the 

 bed-rock at French Corral is 822 feet higher than that at Mooney Flat. This allows a grade of 

 ninety-one feet to the mile, a grade only four feet less than the average grade of the old channel 

 between French Corral and Snow Point. The subject is complicated somewhat by the position of 

 the gravel seen on the hill above Fiene's toll-house and of that at Pearl's tunnel. Both these 

 masses of gravel are too high to belong to the old French Corral-Mooney Flat channel, unless there 

 were irregularities of grade so extraordinary as to be almost inadmissible in theory, though they 

 are very nearly in the line of the supposed stream. It is possible that they represent some tribu- 

 tary stream, or lateral ravine. 



Section III. — The Divide between the South and Middle Yuba Elvers. 



For the purposes of this report this region can be conveniently subdivided into five parts, which 

 will be considered in the following order : — 



A. From French Corral to North San Juan, 



B. Lone Ridge and Montezuma Hill, 



C. From North San Juan to North Bloomfield, 



D. From North Bloomfield to Eureka, and 



E. Above Eureka. 



Before passing to the details, however, a few words may be introduced of a more general character. 



Upon showing the Gravel Map to Mr. N. C. Miller, of French Corral, I learned that there were 

 errors upon it which could not be corrected without great expenditures of time and money. Some 

 of these errors may be due to inaccuracies of the original survey, and some of them are undoubtedly 

 chargeable to the persons who ran the United States section lines in 1873. Certain it is that the 

 relative positions of the section lines and the towns, as given on the map, are not the same as they 

 are on the ground. The discrepancy amounts in some cases to as much as half a mile, saying 

 nothing about those cases in which the error is even greater in amount but of such a character that 

 it can be easily corrected.* Moreover, there is always room for considerable uncertainty as to the 

 precise site of a town in the gravel mining districts. Take the town of Moore's Flat, for instance ; 

 built originally upon the gravel, the rapid advance of the hydraulic washing has made at least one 

 removal necessary, and, after the recent fire, the town was rebuilt in a still different place. At 

 Woolsey Flat, also, two different towns have been washed away since hydraulic mining began. 

 Columbia Hill has been moved from an uncertain gravel foundation to its present site upon the 

 bed-rock. The town of Omega, on the Washington ridge, has been moved once, and will have to 

 be moved again, before many years, if mining continues without interruption. 



There is another class of errors, difficult to correct except at great expense. These relate to the 

 positions of the mining ditches, and to the line of demarcation between the volcanic stratum and 



* Some corrections in manuscript have been made upon the copy of the map left at Cambridge. Other errors 

 may as well remain uncorrected until such time as more trustworthy and detailed surveys can he made. For 



example, it is known that the section corner, — — , T. 18 N., R. 10 E., is a few rods only to the south of the 



hotel at Moore's Flat, and that the section line runs just in front of the hotel door. But to make that correction 

 by itself, without making any change in the position of other places in the vicinity, would introduce confusion of 

 a different kind. 



