SnOWLOW AND PiNEDALE RuiNS 

 By Emil W. Haury 



INTRODUCTION 



The year 1923 marks the inception of a new method for ascertaining 

 the actual ages and determining the chronological sequence of South- 

 western ruins — a method devised by Dr. A. E. Douglass and based 

 upon the annual ring-growth of certain coniferous trees. A brief sum- 

 mary of the results of this seven-year investigation has recently been 

 published by him in the National Geographic Magazine.* 



Doctor Douglass has conclusively shown that the width of annual 

 rings of pine in the Pueblo area is conditioned by the amount of 

 precipitation ; thus, in wet or favorable years, ring-growth will be 

 normal, while in drought years the growth will be sub-normal, the 

 width of the rings decreasing with the severity of the drought. He has 

 shown also that practically all trees over a large area record the 

 periodical fluctuations in moisture in identically the same way. Com- 

 menting further on this point. Doctor Douglass says in his recent 

 article : 



The same succession of drought and plenty appears throughout the forest. 

 .... Certain sequences of years become easily recognized from tree to tree, 

 county to county, even from State to State. 



Furthermore, it has been shown to be highly improbable that a 

 given ring-sequence with its characteristic narrow rings will ever be 

 exactly duplicated. In the present continuous calendar which extends 

 over a period of 1,200 years, duplications in even short ring-records 

 have not been discovered. 



With the above facts in mind, it should be possible by a method of 

 cross-dating or over-lapping the inner rings of one beam with the 

 outer rings of another, first in living trees and then in old timbers cut 

 by man before the living trees started their record, to build up a 

 chronology which would extend far into the past. 



In June, 1923, the First Beam Expedition of the National Geo- 

 graphic Society entered the field for the express purpose of recovering 



^ The secret of the Southwest solved by talkative tree rings. Nat. Geogr. Mag., 

 Vol. 56, No. 6, pp. 737-770, December, 1929. Doctor Douglass will elaborate 

 his methods and results in a paper to accompany the report on the Pueblo Bonito 

 explorations, by Neil M. Judd, now in preparation. 



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