0. H. Hershey — River Terraces of Cahfornia. 245 



3. That decreased rainfall caused the erosion of the tiny 

 canons has in its favor the probability as derived from other 

 sources of such a lessening in the precipitation during their 

 development, but hardly explains the sudden trenching with- 

 out even destroying the meanders. Further, a lessened preci- 

 pitation would yield smaller streams which would be less able 

 to carry away the products of weathering and would reach a 

 stable grade with a higher angle of slope and aggradation 

 would result. 



4. That the tiny canons are the result of a general uplift, 

 without tilting, of the entire region is vitally defective for the 

 reason that dissection should begin at the coast line and 

 advance inland. The canons would be older and consequently 

 larger near the sea than far up on the streams. ISTow, it is a 

 characteristic of these canons that they are equally developed 

 proportionate to the streams far up on Salmon River as low 

 down on the Trinity and Klamath Rivers. The recency of the 

 beginning of the canon erosion low down on the streams as 

 clearly shown by their small size, implies that with uplift 

 without tilting, in order to abrade the stream-bed at all, there 

 should be such an increase of grade near the coast that the 

 canons would soon run out and the middle and upper courses 

 of the streams retain their low-grade condition. 



5. The hypothesis which I can unreservedly accept, is that 

 along with general uplift there has been a tilting of the region 

 toward the coast. The main rivers have been converted from 

 low-grade to high-grade streams. They began to erode their 

 beds at the same time throughout the area and the canons 

 resulting are everywhere approximately equal. The present 

 high-grade character of the streams is evident. They flow 

 swiftly in the canons within the basins as well as in the gorges. 

 They move considerable bowlders with ease and there is little 

 more tendency for the debris to lodge in the canons in the 

 basins than in the gorges. The bottoms of these canons will 

 be reduced far below their present level before the energy of 

 the streams will be largely devoted to widening of the basins 

 as it once was. Indeed, I am of the impression that this uplift 

 and tilting of the region was one of the most pronounced 

 which has effected it in Quaternary time, but has been so recent 

 that its products are yet insignificant and likely to be over- 

 looked. 



In the absence of accurate surveys, distances on these rivers 

 may be roughly determined by the trails. The Klamath River 

 at "Weitchpec, about 45 miles from tlie sea, has an altitude of 

 scarcely 300 feet. Taking this point as a base, the Salmon 

 and Klamath Rivers fall from Summerville to Weitchpec (a 

 distance of about 80 miles), 2,800 feet or 35 feet per mile. 



