UNIVERSITY OF CALIFORNIA PUBLICATIONS 



BULLETIN OF THE DEPARTMENT OF 



GEOLOGY 



TERTIARY MAMMAL BEDS 



OF 



VIRGIN VALLEY AND THOUSAND CREEK 



IN 



NORTHWESTERN NEVADA 



BY 



JOHN C. MERRIAM. 



PART I. — GEOLOGIC HISTORY. 



CONTENTS. 



PAGE 



Introduction 22 



Acknowledgments 23 



General physical features of the region 24 



Geologic features of the region 25 



Pueblo Range section 26 



Pine Forest Range 29 



Virgin Valley section 30 



Canon Rhyolite 31 



Virgin Valley Beds 33 



Mesa Basalt 36 



History subsequent to outpouring of Mesa Basalt 38 



Thousand Creek Beds 43 



High Rock Canon exposures 51 



Physical conditions obtaining during deposition of Virgin Valley and 



Thousand Creek Beds 51 



Summary of principal events in the geologic history of the Virgin 



Valley region 52 



