NOTES ON THE GEOLOGY OF CARRIZO MOUNTAIN 

 AND VICINITY, SAN DIEGO COUNTY, CAL.^ 



WALTER C. MENDENHALL 

 U. S. Geological Survey 



CONTENTS 



Introduction 

 Geography 

 Earlier Work 

 Geology 

 General 

 Descriptive 



Basal Series 

 Effusives 



Miocene Conglomerates 

 Miocene Shales 

 Superficial Deposits 

 Resume of Geologic History 

 Conclusion 

 Fossil Localities 



INTRODUCTION 



Through the courtesy of Dr. J. C. Merriam, of the University of 

 California, and Dr. Stephen Bowers, of Los Angeles, small collec- 

 tions of fossil corals and mollusks from the vicinity of Carrizo Moun- 

 tain, San Diego County, Cal., were sent to Dr. T. Wayland Vaughan 

 and Dr. Ralph Arnold,^ of the U.S. Geological Survey, during the 

 autumn of 1903. The material in these collections proved to be of 

 exceptional interest to the paleontologists, and in order that a 

 larger amount might be obtained for study and more definite informa- 

 tion secured about the geology of the region. Dr. Bowers and the 

 writer visited the field during the latter part of January, 1904. 



1 Published by permission of the Director, U.S. Geological Survey. 



2 A brief preliminary statement of the conclusions reached by Drs. Vaughan and 

 Arnold after an examination of these collections appears in Science, N.S., XIX, 

 No. 482 (1904), 503. At that time the fauna was regarded as lower Miocene; later 

 conclusions are to the effect that it is upper Miocene. 



