12 CLIMATIC CYCLES AND TREE GROWTH 



a highly sensitive sequence of rings with immense and sudden changes from 

 one ring to the next. (See Plate 10B.) A certain questionable ring in these 

 trees — namely, 1904 — was settled by cross-identification with Flagstaff 70 

 miles away. The twenty-five Flagstaff tree sections used at that time gave 

 less pronounced correlations among themselves, for their ring records were 

 relatively complacent. This was later recognized as a different ring type, 

 namely, the "forest interior" type showing rings of low sensitivity, though 

 not really complacent; the thin rings used for identification were there, but 

 were not often highly conspicuous because of their smallness. In 1919 a col- 

 lection was made at Aztec, New Mexico. In 1922 a large collection of ancient 

 specimens was begun from the Indian country located on the Colorado Plateau 

 between Flagstaff and the Rio Grande Valley. It is very obvious to one who 

 knows this region that the Indians selected residence locations at the lower 

 forest border and from there on down into the desert and cut their building 

 timbers from the trees of the neighboring forest edge. Many of their ruined 

 villages, now miles from the forest, contain thousands of pine logs. Many 

 ring specimens have been secured from these logs, and in 1927 serious work on 

 them began. By 1929, with the aid of field trips financed by the National 

 Geographic Society, dated sequences were carried back to A.D. 700. 



The character of the prehistoric ring sequences used in constructing this 

 early chronology was at once noted as different from the general character 

 previously observed at Flagstaff in modern tree growth (Plate 10 A). There 

 were sudden and pronounced differences in ring thickness from year to year. 

 This made cross-dating almost infallible if conducted with care in the selection 

 of uninjured and sensitive specimens. It was at first thought that this 

 difference was a climatic change during the centuries. But that idea was 

 quickly destroyed by finding highly sensitive modern trees in the Pueblo area 

 and complacent records from ancient trees near Flagstaff. 



In connection with the early attempts to date this prehistoric material, 

 this difference in ring type was investigated more carefully. Between 1922 

 and 1927 many individual collections were made around the Pueblo area for 

 the purpose of establishing in modern trees the existence or non-existence of 

 cross-dating over that area. Obviously it would be of little use to spend large 

 sums of money in excavating prehistoric ruins only to find that the process 

 failed and left us without results for the money expended. We were able to 

 see as a result of these collections that such dating was highly reliable between 

 Flagstaff, the Hopi Villages, Black Mesa, Kayenta, Mesa Verde, Chaco 

 Canyon, Chin Lee, Fort Defiance, and the "Rim" eighty miles south of 

 Flagstaff. Ease of its application was found to increase as one left the forest 

 center and worked nearer the desert. At the very desert edge the trees may 

 become difficult from absence of rings. This area outlined forms a rough 

 circle about the Chuska-Lukachukai mountain range, and has therefore come 

 to be called the "Central Pueblo Area." 



Effect of Local Topography — There still remained characters in the ring 

 sequences found that were not explained thus simply by geographical location 



