1 64 OSCAR H. HERSHEY 



great folding of the Coast Range region. This occurred at the 

 close of deposition of the Merced series and was the opening 

 event of the Quaternary era. Last winter I recognized' in Piru 

 canyon in southern California a valley definitely comparable in 

 size to Sierran canyons of the Sierra Nevada region that have 

 been eroded under like conditions. This canyon dates entirely 

 from a time succeeding the deposition of a late Pliocene forma- 

 tion, apparently an equivalent of the Merced series. 



The erosion of the Sierran valleys of the Klamath region has 

 continued practically uninterrupted to the present day. With a 

 few unimportant exceptions, there are no well-marked terraces 

 in the lower mountain valleys to indicate halts in the down- 

 cutting, although locally, through the vicissitudes of erosion, 

 remnants of the alluvial deposits are left for a time at some 

 height above the streams. They are commonly known as "old 

 channels," and many of them have been opened as hydarulic 

 mines. Naturally, they are most abundant at low levels, but 

 occasionally one may be found as much as 500 feet above a 

 stream. Sooner or later all will succumb to the undermining of 

 the slopes, and new ones will be formed at yet lower levels. 



The exceptions worth noting are in the vicinity of Hawkins' 

 Bar on the lower Trinity river and at the junction of the north and 

 south forks of the Salmon river. These streams there flow, at 

 present, in very narrow rocky canyons trenched in the bottom 

 of much broader, flat-bottomed, gravel-floored valleys. The 

 latter remain intact over comparatively extensive areas and the 

 trenching is quite recent. Whether this is purely a local devel- 

 opment or a persistent feature in the direction of the coast I am 

 unable to say. 



Late in the Quaternary era there was developed by subaerial 

 agencies on the northern border of the Sacramento valley a plain 

 several miles in width, which traverses the edges of highly 

 inclined pre-Cretaceous strata. Some disturbance, probably a 

 slight and temporary depression, mantled this plain with stream 

 gravel, forming the Red Bluff formation. The Red Bluff grade 

 level is traceable at several points for a distance of several miles 



"■Bull. Dept. Geol, Univ. Calif., Vol. Ill, No. i, p. 9. 



