SIERRA N VALLEYS OF THE KLAMATH REGION I 59 



Neocene grade level of about 1,300 feet. The tributary streams 

 on the west kept pace with the main river in cutting channels 

 through the rock barrier between the old and new valleys, and 

 they have eroded deep canyons into the gravel deposit of the 

 latter. Stewart's Fork and Rush creek have each cut down 

 about 1,600 feet. Weaver creek was especially active and was 

 favored by finer material in the broad portion of the old valley, 

 so this small stream excavated a basin three or four miles in 

 diameter and at least 1,000 feet in average depth. As a means 

 of draining this basin it excavated in micaceous quartz schist and 

 serpentine, a narrow, crooked canyon valley five miles in length 

 and over 1,000 feet in depth. 



From Junction City to North Fork, six miles, the present 

 course of Trinity river seems to coincide with the old course. It 

 is directly in line with the last mile of the old channel deposit of 

 the Weaverville area, and there is no other apparent outlet among 

 the hills for the old valley. But between Weaverville and the 

 La Grange hydraulic mine (the latter at the extreme western 

 end of the gravel deposit), as already mentioned, the bed-rock 

 floor of the channel rises rapidly, and westward from the mine it 

 is so elevated above the present drainage level that erosion has 

 completely destroyed the gravel deposit. Yet the influence of 

 the old channel on the present valley is still apparent as far as 

 North Fork ; for the Pleistocene river, being favored in this 

 portion of its course by a broad valley filled with easily eroded 

 gravel, and having cut down deeply among the bed-rock hills, 

 although not nearly to the present water-level, has been enabled 

 to greatly widen its present valley. Such abnormal widening of 

 the present Trinity valley does not occur except at the few 

 points where independent evidence indicates clearly that there 

 the old and new courses coincide. 



One mile below North Fork, the Trinity river enters a narrow 

 gorge five miles in length and perhaps 1,500 feet in depth. The 

 extreme narrowness of the gorge is explained by the fact that 

 the river is traversing a resistant formation, a great gabbro 

 batholith. However, it is beyond dispute that this gorge does 

 not represent the Neocene valley which, even in this hard 



