Heushkv.] 



The River Terraces of the Orleans Basin 



473 



probably of the terrace over Channel E of the Summerville 

 Basin. I cannot correlate these lower terraces with the glacial 

 series except in a general way. It is my impression that the 

 seventy-foot terrace represents an early sub-stage of the Wis- 

 consin glacial stage, and the forty-five-foot terrace a late sub- 

 stage of the same epoch. 



Throughout the Klamath region the highest terrace is char- 

 acterized by fineness of materials and the red color. It seems 

 to attain to its greatest height along the Klamath River between 

 the mouth and a point above Happy Camp. In the valley of 

 the Trinity River it rarely reaches 300 feet above the stream. 

 In Scott Valley it is very low and indefinite. On Clear Creek 

 and the Sacramento River above Redding it is fairly well repre- 

 sented, but at heights usually less than 200 feet above these 

 streams. 



I wish to call particular attention to one fact in connection 

 with this upper terrace, namely, that it marks an important line 

 of division of the Sierran Canons into a comparatively broad, 

 upper non-terraced portion and a narrow, lower terraced por- 

 tion. The contrast between the two portions is great enough to 

 point to a change in conditions. The latter portion of the 

 period during which the upper division was being eroded was 

 a time of quiescent conditions. There were no important changes 

 of level or of climate, and the streams had long cut to low grade 

 and greatly widened their valleys. The upper terrace is simply 

 a portion of the valley floor at the close of that quiet period. 

 The remainder of the Quaternary Era has been one of repeated 

 earth movements and changes of climate, and the terrace system 

 is the result. 



In much softer formations than those of the Klamath region, 

 the broad upper canon would be represented by very broad, 

 basin-like valleys, or even, on incoherent late Pliocene strata, 

 by small peneplains. In the softer rocks of the Coast Range 

 province, the Klamath River could probably have excavated a 

 valley 2,000 feet deep and fifteen miles wide in the time which 

 has occupied it in eroding the upper division of the Sierran 

 Canon. This fact must be taken into account in correlating 

 valleys and terraces throughout the State. 



