TREE RECORDS! LENGTH 61 



dating methods are in view. The first is the " bridge" method, by 

 which we start with old living trees and cross-date the early parts of 

 these with late parts of earlier trees, and so on till a real ring record 

 is built back to the age when the ruins were under construction. The 

 other method is the "sequoia comparison" method by cross-dating 

 with the sequoias, whose great age without doubt covers the period of 

 building of these ruins. The best result would be one derived from a 

 complete agreement of these two methods. Perhaps the stronger of 

 the two methods is the first or bridge method, but it promises to 

 require large collections from many different ruins, beginning with the 

 early historic and going back to the period desired. Consequently, 

 in June 1923 an expedition set out for the purpose of making such 

 collections under the charge of Dr. J. A. Jeancon of Denver, assisted 

 by Mr. O. M. Ricketson, of the Carnegie Institution. I went with 

 them for the first 10 days in their visits to the Hopi Indian villages, 

 where some 22 specimens were collected. They then continued the 

 trip, covering generally the southwestern area, including such places 

 as Canyon de Chelly, Chaco Canyon, Mesa Verde, and the Rio 

 Grande Valley. To the present time their collections have not been 

 finally and thoroughly examined (such work will be done in connection 

 with the study of past climates), but it is practically certain that 

 extensive gaps remain in the long interval from the Aztec and Pueblo 

 Bonito chronology to a. d. 1300 or 1400, when the living trees began 

 their record. Nevertheless, this bridge method is probably only 

 delayed, for the collection from Pueblo Bonito reveals the possibility 

 that in some Hopi Pueblo or late prehistoric ruin will be found beams 

 cut in ages different enough to cover the long interval desired.* 



CALIFORNIA AND ARIZONA CROSS-DATING 



In the presence of the gaps above referred to, the sequoia com- 

 parison method becomes of increased importance and has played an 

 important part in directing our effort in the last few years. The visit 

 to the Calaveras Grove in 1924 and to the Springville Grove in 1925 

 were primarily to aid in this problem. The problem itself was stated 

 above in describing the purpose of the fourth sequoia trip, page 52. 



CHARLESTON MOUNTAIN TRIP 



In connection with the dating problem between Arizona and Cali- 

 fornia, the Charleston Mountains, at the southern extremity of Nevada 

 and about midway between the Flagstaff area and the best sequoia 

 region, were visited and collections made. Senator E. W. Griffith, of 

 Las Vegas, Nevada, kindly took me out on July 9, 1924, by automobile 



*At the time of reviewing this chapter a group of 25 beams from " Wupatki" near Flagstaff 

 has shown that this ruin was built some 30 years later than Aztec. It seems very probable that 

 in time the "bridge" method will be successful. 



