90 University of California Publications. [Geology 



CONTENTS. 



PAGE 



Introduction 90 



Petrography and Geological Relationships 92 



The Bedrock Complex 92 



Granodiorite 93 



Schists : 94 



The Irruptive Contact 95 



The Roof of the Batholitk 97 



The Superjacent Series 97 



River Gravels 97 



Volcanics 99 



Rhyolite 100 



Pitchstone 100 



Andesite 100 



Basalt 102 



Other Rocks 102 



Relative Age of the Superjacent Series 102 



Influence of Rocks upon the Geomorphy 103 



Joints 103 



Weathering 104 



Topographic Divisions 106 



Geomorphy 107 



I. The Summit Zone 108 



II. The High Plateau : 110 



Significance of Summits and Plateau Ill 



III. The Fault Zone 112 



Detailed Description of the Fault Zone 114 



The Carson Area 114 



The Franktown Area 125 



The Genoa Area 134 



Summation of Topography 135 



IV. The Valley Zone 136 



Important Features of the Nevada Ranges 139 



Relative Ages of the Faults 143 



Structure and Genesis of Little Valley 153 



Summary of Sequence of Faults 158 



Other Important Structural Features Elsewhere 159 



Carson and Truckee Rivers 159 



INTRODUCTION. 



There exist in that portion of the Sierra Nevada northeast of 

 Lake Tahoe several very peculiar geomorphic features that call 

 for explanation. Of these Little Valley, an elevated longitudinal 

 valley within the range west of Washoe Lake, is at first glance 



