BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 

 Vol. 18, pp. 303-324, PLS. 25-30 JULY 16, 1907 



VOLCANIC NECKS OP THE MOUNT TAYLOR EEGION, 



NEW MEXICO* 



BY DOUGLAS WILSON JOHNSON 



{Bead before the Society Deceiaher 29, 1906) 



CONTENTS 



Page 



Introduction 308 



Purpose of the investigation 304 



The conclusions reached 305 



Literature 305 



General geology 307 



Structural details 310 



Possible interpretations 319 



A. As renuiants of laccoliths or sills. 319 



B. As remnants of surface flows , 321 



C. As volcanic necks 322 . 



Resume 324 



References 324 



Introduction 



Several years ago, while studying the geology of tlie Albuquerque 

 quadrangle. New Mexico, I had a distant view of that geological wonder- 

 land made classic by Major Button in his report on the Mount Taylor 

 region. Since that time I have been anxious to visit the district, more 

 especially to get a closer view of the remarkable volcanic buttes in the 

 valley of the Rio Puerco, which Major Button interpreted as remnants 

 of necks formerly connecting with overlying volcanoes which have long 

 since been worn away. 



The buttes are most abundant in an open valley excavated by the 

 Puerco river through the eastern part of the great lava sheets sur- 

 roimding the Mount Taylor volcanic mass, the valley being open to the 

 north and south, inclosed on the west by the ragged escarpment of the 

 larger Mount Taylor mesa and on the east l)y the smaller Prieta mesa. 

 The mesa surface is from one to two thousand feet above the valley floor ; 

 the valley is from 8 to 12 miles wide east and west, and the area studied 

 is about 18 miles north and south. 



* Manuscript receivccl by the Secretary of the Society April 24. 1907. 



XXVI — Bull. Geol. Soc, Am., Vol. 18, 1906 (303) 



