9 94 



SUPPLEMENTARY INVESTIGATIONS IN THE GRAVEL REGION. 



I have dwelt thus in detail upon a question which may seem to be unimportant, on account of 

 the bearing which it has upon any estimate of the probable depth of the gravel at Columbia Hill, 

 and upon the view which is to be taken as to the relations of the gravels on the north to those on 

 the south side of the South Yuba River, at Gopher Hill and Blue Tent. 



The position of the deep channel between Columbia Hill and Lake City is not known ; but 

 the superficial area and the outline of the gravel deposit are given on the General Gravel Map 

 with a pretty close approximation to accuracy, and I do not think it will be necessary to make any 

 changes upon the lithographic stones until more detailed surveys are made. Local maps giving 

 accurate information are few in number.* 



For the ground between Columbia Hill and Lake City I have no fresh information to give. So 

 far as I could judge from a couple of trips over the ground, the outlines of the gravel are given 

 correctly on the Gravel Map. Above Lake City the gravel is not indicated quite as it should be, 

 though the errors are not serious. The principal ones are in regard to Lake City, which stands 

 upon lava and not upon gravel, and to the boundary lines between gravel and lava, or gravel and 

 country-rock, respectively, in the neighborhood of Bloomfield. The gravel exposed to the south of 

 Lake City is extremely narrow. Lake City itself stands upon a high spur of the lava ridge, being 

 over four hundred feet higher than Columbia Hill, and nearly five hundred feet above the bed°- 

 rock at Malakoff. Standing at the hotel at Lake City I saw no higher point on the horizon 

 through an arc of 160°, between the directions N. 80° W. and S. 60° E. (magnetic). In the latter 

 direction the view was obstructed by a high hill of bed-rock, about half a mile distant, while in the 

 former the level line strikes a point on the northern branch of the lava, flow. To the north of 

 the hotel the lava rises rather abruptly for about two hundred feet. Gravel begins to be seen at 

 the surface in a southwesterly direction from the town at an altitude about two hundred feet lower. 



Slate bed-rock is seen on both sides of Virgin Creek and in the stage road near the hotel at 

 Malakoff, although there are extensive bodies of gravel for a considerable distance to the south of 

 the creek and of the stage road. This high southern gravel has been worked in several places, but 

 has no great depth. It is probably an overflow, or the result of the lateral expansion of the 

 stream as the deep bed filled up. 



Attention should be called to the occurrence of high bed-rock to the north and northwest of 

 Malakoff between the gravel and the lava capping. I did not go to the spots myself where it is 

 said to be seen in the beds of brooks or in ravines, but have given their positions on the Bloom- 

 held map on the authority of Mr. Perkins. These spots are of importance in determining the 

 probable position of the northwestern rim-rock. 



The principal points at which regular mining has been carried on are at Badger Hill, Columbia 

 Hill, and Malakoff, or Bloomfield. 



The lower end, or outlet, of Badger Hill, as has already been stated, overlooks the canon of the 

 Middle Yuba. The descent from the mine to the river is exceedingly steep, almost precipitous. 

 The bed-rock at the mine has been uncovered for a distance of nearly half a mile towards the 

 south, and shows a very slight grade indeed. With the aneroid and hand-level alone it was not 



Hill and its 



possible to make accurate measurements. This flatness of the channel at Badger 

 known steepness in the vicinity of Bloomfield lend some support to the view that there is an un- 

 usual change of grade at some intermediate point, and that the bed-rock at Columbia Hill may be 

 low enough to admit a tributary from Grizzly Hill. 



The deepest part of the channel at Badger Hill is quite narrow, being not over 200 feet in width, 

 and the bed-rock rises rapidly both to the oast and the west. The total width of the deposit at 

 the outlet is scarcely more than 500 feet. The high bank at the south end of the mine I made to 

 be 165 feet in height. The top gravel to a depth of eighty or a hundred feet is composed mainly 

 of a fine quartz, well-rounded, white or reddish in color. The lower gravel for a thickness of from 

 sixty to seventy-five feet is of a bluish cast of color, and contains, relatively to the upper gravel, a 



* A comparison of the Eureka Lake Company's plats of their ground, as kid down by the United States sur- 

 veyors, shows the general accuraey of the Gravel Map for the region near Columbia Hill. 



