Prehistoric Indians of the Southwest

by H. M. Wormington

The astronomer was Dr. A. E. Douglass, who was engaged in the study of the effect of sun spots on climatic conditions. The available meteorological records, of course, went back only a relatively few years and it soon became apparent that a much longer record must be obtained to be of any real value. In searching for information about climatic conditions for past centuries, Dr. Douglass thought of pines, for they may reach a great age and the presence or absence of adequate rainfall, particularly in a climate like Arizona’s, will greatly affect the development of a tree. Every year a new layer of wood is added to the entire living surface of a pine. The size of these layers, which show up as rings when the tree is cut and viewed in cross-section, varies with the amount of food and moisture which the tree has obtained in the course of the year. A dry year will produce a thin ring and a wet year will produce a wide one. By cutting down old trees it was thus possible to learn what the climatic conditions had been during the years of their life. None of the pines which were still living, however, had existed for more than a few hundred years, and the giant sequoias of California which would have covered a longer span did not reflect climatic change in the same way.

Fortunately, through the study of living trees, Dr. Douglass had learned that the tree-rings over a period of years formed a distinct pattern which could be recognized when found on most conifers. Next he began to search for trees which had been cut perhaps many years before, but which contained a pattern which fitted some early portion of that tree whose cutting date was known. This led him to beams made from whole logs which have been a characteristic feature of Southwestern architecture for many centuries. By finding old beams whose outer rings formed the same pattern as the inner rings of living trees the known [chronology] was increased. Through correlating the patterns of progressively older trees with younger ones the pattern was finally established for the period between 1280 and 1929.

Fig. 1—Diagram to illustrate chronology-building with tree rings. Because of space limitation the number of rings in the overlapping specimens has been arbitrarily reduced. (After Stallings.[121] Courtesy Laboratory of Anthropology.)

THE RING PATTERNS MATCH AND OVERLAP BACK INTO TIME A THIS WAS A LIVING TREE WHEN CUT BY US DATE OF LAST RING IS THAT OF YEAR WHEN WE CUT TREE B THIS BEAM CAME FROM A HOUSE THIS DATE OBTAINED BY COUNTING BACK FROM BARK OF A C THIS BEAM CAME FROM AN OLD HOUSE THIS DATE OBTAINED BY COUNTING BACK FROM BARK OF A THROUGH B SPECIMENS TAKEN FROM RUINS WHEN MATCHED AND OVERLAPPED AS INDICATED PROGRESSIVELY EXTEND THE DATING BACK INTO PREHISTORIC TIMES

Next Dr. Douglass began to examine beams from prehistoric sites. From these a continuous sequence of tree-ring patterns was established for a period of 580 years. Unfortunately though, it could not be correlated with the sequence starting in 1280. Relative dates could be obtained and it could be determined how many years had intervened between the occupation of different sites but there was as yet no way of correlating these dates with the Christian calendar. The next step was to seek to bridge the gap between the floating [chronology] of relative dates and that which carried up to the present day and gave absolute dates.

The search for the missing sequence was begun in the Hopi villages in Arizona where one, Oraibi, has been continuously occupied since before the coming of the first white men in 1540. The fact that many of the logs had been cut with stone axes indicated a considerable age. The Hopis, as might be expected, were not overly enthusiastic about the arrival of American scientists who wanted to saw cross-sections from the beams of their buildings and bore holes in other timbers where cutting was not practical. Dr. Douglass did much to solve this problem by presenting the chief with yards and yards of beautiful purple chiffon velvet which delighted him. Dr. Douglass and his associates also did a great deal to mollify the Indians by treating their ancient customs with respect. In many cases, for example, they placed bits of turquoise in holes made in extracting cores in order to “appease the spirit of decay”. One remarkable piece of timber was found which gave an extraordinarily clear series of rings from 1260 to 1344. What made it of particular interest was not only that it lengthened the known [chronology] but that it had been in continuous use from the time it was cut until 1906 when the section of the village in which it was found was abandoned.

Many beams were studied, but no others were found whose inner rings predated 1300. The search was next begun in ruins of villages traditionally occupied by the Hopis prior to moving to their present location. Of particular interest was the Showlow ruin, for pottery finds suggested that it had been the home of Hopis in pre-Spanish times and its proximity to a great pine forest suggested that wood must have been readily available for building purposes. It was here that one of the most famous pieces of wood in the world was found.

The decaying, partially burned, piece of wood to which the field number HH39 was given was not impressive in appearance but it was a treasure, more valuable to those who found it than any buried pirate gold for which adventurers might dig. As it was examined the climatic conditions of year after year were revealed, new ring combinations were established and the [chronology] was carried back to 1237 A.D., the year in which this tree had begun its life. A comparison with the ring patterns of the floating chronology showed that its 551st ring checked with that for 1251 in Beam HH39. June 22, 1929, the date on which this beam was found, is a red letter day in the history of American [archaeology], for from that day it became possible to date many ruins in the Southwest, not only in a comparative sense, but in terms of the Christian calendar. Actually, of course, the floating and the absolute chronology had already overlapped but the evidence had been based on such small fragments as to be unconvincing. Duplication of ring patterns may occur if only a few rings are used. It is only if a pattern covering fifty or more rings is available that one may be assured of correct dating. It was not until the discovery of Beam HH39 that final proof was available.

In the years which have elapsed since 1929 much further work has been done by Dr. Douglass and his associates, who include many brilliant students whom he has trained. The tree ring [chronology] now stretches back to 11 A.D.