Hershey.] 



Quaternary of Southern. California. 



Upper Pliocene gravel and sand were eroded before the Santa. 

 Clara River and tributaries trenched below the plane of the 

 400-foot terrace, and an estimate for the average of the basin of 

 1,000 feet is quite conservative. More than ten times as much 

 material was removed from the basin down to the completion of 

 the first alluvial plain than has been removed since. This 

 400-foot terrace divides the Quaternary era into a very long- 

 early part and a much shorter late part. To satisfy those critics 

 who plead unknown factors, we will make only the conservative 

 claim that the 400-foot terrace belongs to the last one-fourth of 

 the Quaternary era; for, no reasonable decrease of rainfall could 

 vitiate this estimate. 



On the strength of comparative erosion studies, I correlate 

 the 400-foot terrace of Soledad Canon with the highest of the 

 marine terraces on the coast and with the depression to which 

 the Red Bluff formation in the Great Valley is due. Indeed, I 

 know of no older Quarternary deposit in the State, with the 

 exception of a few limited flood-plain remnants in mountain 

 canons of the Sierran type and a gravel formation at Cajon Pass. 

 The first three-fourths of the Quaternary era in California is 

 represented virtually only by degradation. There is no portion 

 of the State in which this epoch is so clearly defined as on the 

 Upper Pliocene area of the Santa Clara River Valley of the 

 South. Therefore, I suggest for it the name Santa Claran as 

 being eminently appropriate. 



THE RED BLUFF EPOCH AND ITS DEPOSITS. 



The Red Bluff area in the Great Valley of California, as 



usually mapped, includes two formations. The older has a 

 gently undulating surface, due to unequal interstream erosion. 

 Broad, shallow valleys were excavated into its surface, and they 

 were floored with a sheet of alluvium consisting of the same 

 material as the Red Bluff proper. Subsequently, another 

 uplift caused the streams to trench broad, shallow, steep- 

 walled valleys beneath these old flood-plains, leaving them as 

 somewhat discontinuous remnants. They are so near the level 

 of the surface of the Red Bluff proper and so like it in lithologic 

 character as often to escape notice. The surface is flat and 



