TRIBUTARIES OF THE NORTH FORK. 291 



Grade : 



Bath to Ralston, 8 miles, 72 feet to the mile. 



That Michigan Bluffs is not on the principal channel is also indicate.! 

 by the grades, for from that place to Bath, a distance of three miles, the 

 slope is 140 feet to the mile, while from Michigan Bluffs to Ralston, a 

 distance of five miles, it is only 31 feet to the mile. 



The Damascus and Last Chance Tributaries: General Character. — Mi- 

 Browne has described the Damascus or " white " channel. Its course 

 above Damascus is eroded; it is practically continuous under the lava 

 cap as far down as Gas hill ; from there it is eroded for a long distance, 

 but the characteristic deposits are again found at Michigan Bluffs. It 

 is very different from the Bath channel, being all oust entirely composed 

 of quartz gravel, due to the fact of its flowing for a long distance over a 

 soft clay-slate with a large amount of quartz veins. A short distance 

 below Michigan Bluffs it must have joined the principal Middle fork. 



Tributary to this channel was the Last Chance stream. Coming down 

 from the high country to the northeast of Last Chance, it is preserved 

 under the lava cap for some distance at Last Chance and again at Dead- 

 wood. It scciiis most probable that it joined the main stream some dis- 

 tance north of Michigan Bluffs. The relations of the lava and bed-rock 

 at the two first-named places clearly indicate that this channel flowed 

 in a very distinct depression or valley. Both at Last Chance and at 

 Deadwood there is an older ante-volcanic besides several cement or inter- 

 volcanic channels. 



The important cement channel coming down from the vicinity of 

 Secret canyon by way of Hogsback and Red point under the lava flow 

 very likely followed an ante-volcanic valley; but of the deposits of the 

 latter but little is left. 



Grades : 



Damascus to Michigan Bluffs, SI miles, 73 feet to the mile. 



Deadwood to Last Chance, 5 miles, 136 feet to the mile. 



From the Ralston Mine to Summit Valley. — The divide between Long 

 canyon and the Middle fork of the American river is covered by very 

 deep Neocene deposits and volcanic flows. High bed-rock exists to the 

 north and to the south, forming the sides of a broad and deep depres- 

 sion, the center of which lies buried below the volcanic mass. This 

 deep depression extends in a northeasterly direction up toward Summit 

 valley a distance of about thirty-five miles, in which the deepest channel 

 is only exposed at one point, at the place where the North fork of the 

 American river cuts through it. This is the longest lava-covered stretch 

 of channel in the territory here described. The parallelism with the 



