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THE CHANNELS: IN PLACER COUNTY. 105 
surfaces, the little furrows and ridges produced by weathering being often from half an inch to an 
inch deep, and running horizontally across the nearly vertical faces of the columns. Many of the 
columnar surfaces are, however, not corrugated ; and some of them are as smooth as if polished ; 
the external crust, in such cases, having its texture entirely changed to a depth varying from an 
eighth of an inch to three quarters of an inch in thickness. This change of texture, which on the 
whole seems most likely to have been produced simply by the chemical action of water, is one 
from the ordinary, sharp, granular condition of volcanic ash, to a peculiar compact, and almost 
opaline, or semi-vitreous state. The rock of this bluff is quite hard, rings sharply in large pieces 
under the hammer, dresses, splits, and chisels easily and well, and is said, probably with truth, to 
furnish the best quality of building-stone of any locality near Placerville. 
The whole crest of the main ridge near and above the “Twelve Mile House,” on the Carson 
road from Placerville, is made up of volcanic debris, and the thickness of this material must be, 
in places, at least, fully 700 or 800 feet. 
Negro Hill, northeast of Placerville, is capped with “ black lava” or volcanic breccia, which 
throughout the hill is generally very hard. The same material extends over all the highest por- 
tions of Cedar and Hangtown hills south of the town. 
The crest of the main ridge between Jackson and Sutter Creek is capped with volcanic gravel. 
The same material frequently caps other ridges in this section of the country, and often has beneath 
it a little metamorphic gravel, which here and there has been worked to some extent by drifting. 
§ 6. The Channels: their Width. 
It is impossible to define with accuracy the width of the deep channel at Iowa Hill, since the 
hydraulic workings, extensive as they are, do not uncover the rims, and high bed-rock is known to 
exist at one or two points so located as to render it more than probable that the width is far from 
uniform. This difficulty is further increased by the great depth of the channel, which appears 
from the barometric observations to be about 200 feet in the bed-rock. But it is evident that at 
the northwest end of Wiessler’s ground the channel was at least from 400 to 600 feet wide, while in 
the central portion of the ridge the strip of ground still standing beneath the town of Iowa Hill is 
so narrow, and the extent of the pits already worked on either side is so great as to render it ex- 
tremely probable that the width of the deeper portion of the channel in its narrowest part is not 
less than 200 feet. 
In the Lebanon Tunnel, on the northeast side of New York Caiion, they have followed a well- 
defined channel in the bed-rock which generally ranges from sixty to eighty feet wide, although 
in places much narrower; it curves somewhat, but its general course is southerly, and it has a 
decided descending grade in that direction. 
At the Tunnel of the Eclipse Company, in Grizzly Caiion, the channel is about 300 feet wide, 
and some fifty or sixty feet deep. 
At the Mountain Gate Tunnel, near Damascus, where the channel has been followed for 4,000 
feet, it has been found to be from 175 to 200 feet in width, and the rise of the rock towards either 
side, so far as they have been worked, is very gentle, the extreme points reached at the sides being 
not generally eighteen or twenty feet higher than the central and lower portions of the channel. At 
the Cement Mill Tunnel, near Damascus, the channel has been worked out to an average width of 
nearly one hundred feet. The bed-rock rises considerably higher on each side of the channel. 
In Yule’s Claim, at Startown, the channel is very wide, but not deep. At Nick Anderson’s 
Claim, just below Last Chance, near Startown, the average width of the outer channel is from 
seventy-five to one hundred feet ; that of the back channel is about 300 feet. 
At the Reed Mine, near Deadwood, the width of the channel is said to be sixty or eighty feet, 
and the Basin Channel at the Devil’s Basin, where the trail from Deadwood to Last Chance begins 
to descend into the cafion of the North Fork of the Middle Fork of the American River, about 
eighty feet. This is the width actually worked in the Basin Channel and rich in gold; but the 
