UNIVERSITY OF CALIFORNIA PUBLICATIONS 

 Bulletin of the Department of Geology 



A CONTRIBUTION TO THE PETROGRAPHY 



OF THE 



JOHN DAY BASIN. 



BY 



Frank C. Calkins. 

 CONTENTS. 



PAGE 



Introduction 110 



The Geological Section Ill 



Geological Features of the Region Ill 



Geographical Limits Ill 



Pre-Tertiary Geology 112 



Clarno Eocene 112 



John Day Miocene : 113 



Miocene Basalt 113 



Mascall Formation 114 



Rattlesnake Formation 114 



Quaternary and Recent Deposits 115 



Petrographical Descriptions 115 



Pre -Eocene Rocks 115 



General Classification 115 



Granodiorite of the Middle Fork 115 



Granite-porphyry of Spanish Gulch 117 ' 



Pyroxenites of Spanish Gulch and Beach Creek lis 



Serpentine of Beach Creek 12(1 



Serpentine of Desolation Creek 121 



Rocks of the Clarno Eocene 122 



General Classification 122 



Pyroxene Andesites 122 



Hornblende Andesite of Hald's Canon 128 



Hornblende -hypersthene Andesite of Clamo's Ferry 129 



Andesitic Tuff of Clamo's Ferry 131 



Andesitic Tuff of Cherry Creek 133 



Quartz Basalts of Cherry Creek .• 134 



Andesite from Volcanic Neck at Cherry Creek 136 



Spherulitic Rhyolites of Currant Creek Hill 137 



Rhyolites of Clamo's Ferry 141 



