248 0. H. Hershey — River TerrOyCes of California. 



also consider to have been approximately San Pedran in age. 

 At the close of the San Pedran epoch there seems to have 

 been a land disturbance practically co-extensive with the State. 

 The coast line and Great Valley were slightly uplifted and 

 some of the main mountain masses, as the Klamath, were dis- 

 tinctly bowed. In tlie incoherent strata of the Great Yalley, 

 broad, shallow canon-shaped valleys were excavated, bat in the 

 hard rocks of the Klamath region tiny canons were eroded. 

 With the exception of a more recent local subsidence on the 

 coast and west of the center of the Great Yalley, this first 

 post-San Pedran orogenic activity is the last of which we have 

 any record in California. 



After studying the small present canon of the lower Trinity, 

 Klamath and Salmon Pi vers as far up as Summerville, one is 

 able to arrive at a fairly definite conclusion as to what would 

 be the character and amount of the erosion of the same period 

 in the glaciated valleys had not glaciation intervened to com- 

 plicate matters. Pecently the writer has recognized evidence 

 of glacial deposits earlier in age than those usually described 

 from the California mountains. Part of the evidence of age 

 consists of certain rock gorges on Coifee Creek and the South 

 Fork of Salmon Piver. Higher in the glaciated valleys are 

 much smaller rock gorges (tiny canons) which have been eroded 

 practically since the complete disaj^pearance of the Quaternary 

 glaciers. It is not possible at the ]3resent time to accurately 

 fix upon the time relation of the erosion of the caiion from 

 Summerville downstream and the different stages of the gla- 

 ciation. Put comparison, and the connection by direct tracing 

 of one of the upper terraces in the Summerville basin with 

 the product of one of the earlier stages of the glaciation, 

 make it faiily certain that the inception of the canon cutting 

 from Summerville downstream considerably antedated the 

 close of the glaciation, but certainly did not occur earlier than 

 its beginning. If there were no inter-glacial stages, the uplift 

 which inaugurated the last canon cutting from Summerville 

 downstream, was contemporary Avith some stage of the glacia- 

 tion, probably a later one. At any rate, it is safe to assert 

 that the uplift did not occur before the beginning of glaciation 

 and apparently has not occurred since its close. 



The axis of deformation or line of greatest elevation, is 

 somewhere centrally situated between Summerville in the 

 Salmon Piver valley and Trinity Center in the upper Trinity 

 valley. Petween these points is the group of high mountains 

 which were most extensively glaciated. These mountains 

 apparently rose to the extent of between 2,000 and 3,000 feet 

 at some time between the beginnino^ and close of the glacia- 



