12 



University of California. 



[Vol. 3. 



distinctly lower than the undulating' areas of the main Red 

 Bluff. 



The Red Bluff formation belongs to the last one-fourth of 

 the Quaternary era. On the northern border of the Sacramento 

 Valley, in Shasta County, there are flats one to two miles wide, 

 consisting of the Red Bluff gravel resting on the truncated 

 edges of the highly inclined mef amorphic formations. They are 

 elevated one hundred to two hundred feet above the present 

 streams, as Clear Creek and the Sacramento River, which have 

 trenched narrow canons below them. The Red Bluff terrace can 

 be traced for several miles up into the mountain valleys of such 

 main streams as those mentioned above, and it is thus made 

 evident that at the very least three-fourths of the erosion of 

 the Sierran valleys had been accomplished by the time of the 

 opening of the Red Bluff epoch. 



Since the uplift of the Red Bluff formation, it has been 

 eroded to about the same extent under approximately similar 

 conditions as the Illinoian drift sheet of the Mississippi Basin. 

 In the same manner I arrive at the conclusion that the trenching 

 of the old alluvial plains, or second formation of the Red Bluff 

 area, as mapped, dates from about the Iowan epoch of the 

 classification adopted in the Eastern States. I do not wish to 

 convey the idea that I consider them chronologic equivalents, 

 respectively, of the Illinoian and Iowan drift sheets of the 

 Mississippi region. The Red Bluff formation may have been 

 deposited entirely during the interglacial epoch preceding the 

 Illinoian epoch or that succeeding it. I mean simply that the 

 erosion on the Red Bluff formation has been very much less 

 than that on the Kansan drift area of Northern Missouri and 

 Southern Iowa, and very much greater than that on the Iowan 

 drift area of Northwestern Illinois and Northeastern Iowa, but 

 that it has been remarkably alike, in general character and 

 amount of material removed, that accomplished on the Illinoian 

 drift area of Western Illinois and Southwestern Iowa, so that if 

 there could be any particular object in referring the Red Bluff 

 formation (or, rather, the time of its uplift and inception of 

 erosion) to one of the glacial epochs, the Illinoian would 

 undoubtedly be the one fixed upon. 



