

^^^■^^^^^^H 



498 



FORMER TOPOGRAPHY OF THE SIERRA. 









excavated to depths ranging from 1,500 to 2,500 feet below the ancient surface, leaving a series of 

 ridges whose crests (wherever the space between adjacent canons is wide enough to allow of it) 

 almost invariably rise to nearly a uniform plane, and over a considerable area of country never rise 

 much above it. These ridges are now almost everywhere heavily timbered, and so, when this 

 region is seen from a favorable point of view to-day, as, for example, from the Canada Hill Bald 

 Mountain, which overlooks it and is near enough to give a good view of it, and yet too far re- 

 moved to enable us to see down into the canons, it presents far more the appearance of the ancient 

 basin-plain than it does of the series of narrow riclges and tremendous canons which it really is 

 to-day. There is perhaps no point from which so good an idea can be obtained of the general 

 appearance of this portion of the country at the close of the volcanic period as from the summit of 

 this mountain. 



From here the Georgetown ridge — that is, the ridge which forms the divide between the main 

 South Fork and the South Fork of the Middle Fork of the American River — is very conspicuous, 

 bounding the basin of the Middle Fork, and limiting the view in that direction in the form of a great 

 spur of the Sierra Nevada, running far southwesterly from high up towards the summit of the range 

 down almost to Georgetown, itself, with a crest which is not smooth like those of the ridges in the 

 basin of the Middle Fork, but rough and peaky with bed-rock hills, and whose general height 

 all the way to Georgetown is considerably greater than that of the adjacent country for a long 

 distance either to the northwest or southeast of it on a line parallel with the axis of the range. 



It was when I caught this view from the Canada Hill Bald Mountain that my previous suspicion 

 first deepened into conviction that, in this portion of the country at least, the outlines of the larger 

 drainage basins were essentially the same in the gravel period as now. I felt confident, even then, 

 that the higher parts of that Georgetown ridge were bed-rock hills, and so it proved. 



As in the basin of the Middle Fork the volcanic-capped ridges do not rise above a certain level, 

 so in the ridge between the South and Middle Forks the volcanic matter does not rise above a 

 certain level on the sides of the higher hills. Wherever I went for a distance of thirty miles east 

 from Georgetown in this ridge I found everything above a certain horizon to consist of bed-rock 



I do not think these hills have ever been covered either with gravel or volcanic matter, 



hills. 



unless indeed by possible showers of ashes dropped in the air, which were readily washed away by 

 rains to lower ground. 



This distribution of the volcanic matter here, together with the fact that the total quantity both of 

 gravel and of volcanic matter scattered over this ridge, (though the aggregate, especially of the 

 volcanic matter, is large) is yet far less than it is in the country to the north — both seem to be 

 necessary consequences of these features of the ancient topography of the region. 



Strong additional evidence in favor of the view above presented of the general topography of the 

 country here in the gravel period is furnished by the courses of the ancient channels in the region 



i 



immediately north and northeast of Georgetown, and between it and the river, wherever sucl 

 channels were excavated to a sufficient depth in the bed-rock to make them unmistakable, and 

 have been since preserved, and at last definitely traced and exposed by mining operations. 



The Castle Hill channel, near the Clipper Mill, runs about K 20° W. (magnetic). The 

 Roanoke Channel, near Bottle Hill, runs about K 50° W. (magnetic) for more than a mile through 

 the ridge. It then zigzags for some little distance in a general westerly direction, and from the last 

 point seen of it here to Jones's Hill (if in reality the latter be, as I think it probably is, a con- 

 tinuation of the same channel) the course is about S. 80° W. (magnetic), — still a little north of 

 west {true course), — while in Jones's Hill it seems to make, for a short distance at least, 

 another bend to the north, and pass out northwesterly from that hill over the present canon of the 

 American. Moreover, the little branch of this channel, which has been drifted entirely through 

 the ridge beneath or just west of Bottle Hill, comes into the main channel from the south. 



Moreover, the channel upon which Flora's mine is situated, though a considerable portion of it has 

 indeed gone down the river canon, seems to have been pretty well defined, and to have had, from 

 a point a little northeast of Volcanoville, a course somewhat to the south of west, for some distance 





