SMITHSONIAN EXPLORATIONS. I929 169 



digging factors that may actually be correlated with known human 

 events. Especially is this so in the New World where only the Maya 

 erected datable monuments. 



Within the United States divers Indian civilizations had taken root, 

 blossomed, and disintegrated before Columbus was born. To mention 

 l)ut two, there are the so-called Mound Builders of the Mississippi 

 \ alley and the pre-Hispanic Puelilos of the Southwest. From frag- 

 ments of their material culture, we have learned much of these dis- 

 similar peoples and their individual accomplishments ; we have even 

 pieced together bits of information i)ertaining to their religious con- 

 cept.s — the very hub on which their daily life revolved. l-)Ut until the 

 close of 1929 we had no means of knowing accurately the ye^rs during 

 which these native cultures flourished. 



From 192 1 to 1927 it was my privilege to conduct cx[)lorations for 

 the National Geographic Society at Pueblo Bonito, most famous, per- 

 haps, of the great communal centers which mark the very apex of 

 Pueblo civilization. The architectural development of Pueblo Bonito ; 

 the material culture of its, 1,200 or more inhabitants ; their conquest of 

 a semi-arid environment and their defeat, in turn, l)v forces quite 

 l)ey'ond their control have been briefly presented in earlier numbers of 

 this series.* But the age of Pueblo Bonito, the years of its rise and 

 fall, remained until recently a matter of conjecture only. 



Of course there were relative dates, determined by a lialancing of 

 the evidence in hand. We knew, for example, that Pueblo P>onito was 

 older than the now ruined Hopi settlements visited by Pedro de Tobar 

 and Fray Juan de Padilla, of Coronado's command, in 1540 ; we knew 

 it was younger than hundreds of small communities throughout the 

 San Twan drainage, and elsewhere. This knowledge acted merely as a 

 spur toward more precise information. We wanted at least one defi- 

 nite year. And we finally got it, and much more, after seven years' 

 painstaking research along dim trails that led us far from our starting 

 point. 



It was on December 8. 1922, at a conference called by the Carnegie 

 Institution of Washington to consider cyclic phenomena that I first 

 heard Doctor Douglass describe his use of tree rings in tracing 

 sun-spot influence. As a mere by-product of his studies, Doctor 

 Douglass mentioned the fact that in examining sections of prehistoric 

 beams sent him from Pueblo Bonito and Aztec ruins, in New Mexico, 



'Smithsonian Misc. Coll., Vol. 72, Nos. (> and 15; Vol. 74, No. 5; Vol. 76, 

 No. 10; Vol. 77, No. 2; Vol. 78, Nos. I and 7; Explorations and Field-Work of 

 the Sniitlisonian Institution in 1927. 



