662 PROCEEDINGS OF THE CORDILLERAN SECTION 



Diablo are discnssed. The presence of Horsetowu in northern California and 

 the absence in southern California is taken as proof of a differential land 

 movement on the west coast during mid-Cretaceous times. 



PHYSIOGRAPHIC FEATURES OF SOUTH CESTRAL OREGON 

 BY G. A. WARING* 



[Ahstracn 



This paper deals with the region forming the northwestern end of the Great 

 basin. The basin range type of structure described by Gilbert and Russell is 

 here well developed, the main features of the relief being the fault-scarps of 

 the tilted monoclinal blocks. These, together with their associated undrained 

 basins, now occupied by remnants of more extensive Quaternary lakes, and the 

 peculiar lack of well defined drainage over much of the area are the three dis- 

 tinctive physiographic features. Low folding has also taken place and has 

 resulted in certain definite topographic effects. In addition to the major 

 scarps, there are numerous minor scarps, some of which may be faults, but 

 others of which have evidently been produced by weathering agencies. The 

 rock masses observed within the region are representative of various igneous 

 effusive series exclusively. Here and there bosses of older rocks of medium 

 basicity occur, but by far the greater part of the area is floored by a series of 

 sheets of basalt and associated tuffs, which have been affected by the struc- 

 tures that have given rise to the striking physiographic features of the region. 



The next paper was read by title : 



THE ilETAMORPHIC AXD CRYSTALLINE ROCKS OF THE SANTA CRUZ 



MOUNTAINS 



BY SOLON SHEDD 



The following were then read and discussed : 



GENERAL GEOLOGICAL FEATURES OF THE TRUCKEE REGION EAST OF THE 



SIERRA NEVADA 



BY GEORGE D. LOUDERBACK 



[Ahstract] 



Contents 



Page 



Area described 663 



Bedi'ock complex 663 



The great unconformity 664 



The Tertiary lavas 604 



Andesites 664 



Rhyolites 605 



Basalts 665 



Distribution of types 665 



Tertiary sediments 665 



Post-Tertiary orogenic movements 666 



Laiie Dahontan 66S 



The Truckee river 66S 



* Introduced by W. C. Mendenhall. 



