286 W. LINDGREN — TWO NEOCENE RIVERS OK CALIFORNIA. 



elusion that a stream of considerable magnitude once approximately 



followed the course of the present Webber creek from Diamond Springs 

 to Newtown, and into which the complicated channels of the vicinity of 

 Placerville emptied* His observations did not extend beyond New- 

 town. 



Alter a careful examination of the region I can only confirm his con- 

 clusion, with the addition that this stream without doubt represented 

 the ancient South fork of the American river. It is very distinctly the 

 deepest depression between the highlands of the Georgetown divide on 

 the north and the high ridges on the south separating the Neocene 

 American from the Neocene Cosumnes. The vicinity of Placerville, like 

 the Forest hill divide, is characterized as a broad and flat Neocene de- 

 pression, in which intervolcanic streams have cut a complicated series 

 of channels. It should be noted that the oldest gravels of Placerville, as 

 a rule, are not deep, and that in most of them occasional rhyolite bowl- 

 ders are found. This would seem to indicate that during the earliest 

 part of the gravel period the conditions were not as favorable here for 

 the accumulation of river deposits as further northward. 



About a mile west of Newtown the channel makes a curve, entering 

 the volcanic ridge to the south of Webber creek. It then again turns 

 northward, crossing the south fork of Webber creek about three-quarters 

 of a mile to the northwest ot Newtown. 



Grades : 



Diamond Springs to Webber hill, 2 miles, 71 feet to the mile. 



Webber hill to Newtown. 7 miles, 69 feet to the mile. 



Newtoicn to Pacific House. — After crossing the South fork of Webber 

 creek the deep channel disappears under the volcanic capping of the 

 ridge between the two forks of Webber creek, at a place formerly called 

 Iowa City, but now generally known as Snows ranch. From this point 

 it must continue under the eruptive rocks up to the Pacific house, on 

 the stage road between Placerville and Lake Tahoe, where it crosses the 

 present South fork of the American. The existence of a deep trough is 

 unmistakably indicated by rising bed-rock toward the north and the 

 south, by the pitch of the bed-rock wherever exposed along the margin 

 of the volcanic area, and finally by the heavy flows of rhyolite and 

 rhyolitic tuff with which the old depression, up to a certain level, was 

 filled. A typical cross-section of this channel is shown in K K, with 

 the probable position and depth of the channel indicated ; it is, I believe, 

 sufficiently clear to explain itself. Some extensive mining operations 

 have been and are still carried on to find a deposit under the deep lava- 



* Auriferous Gravels, p. 502. 



