Dr. A. E. Douglass, director of Steward Observatory, University of
Arizona, established the tree-ring chronology for dating Southwestern
ruins. This chronology is based upon the facts that solar changes affect
our weather and weather in turn the trees of the arid Southwest, as
elsewhere, and that such affects are recorded in the variation of
tree-ring growth during wet and dry years. Thus the tree-ring record of
living trees has been extended into the past by arranging beams from
historic pueblos in their proper sequence so that the inner diaries of
one dovetailed the outer entries of its predecessor, and in turn
overlapped the diary of the living trees. After completing the series
from living trees and pueblos, of known dates, the record has been
continued through the cross-sections of prehistoric beams of fir and pine
that were chopped with the stone axes. The continuation of this
chronology is only limited by the finding of earlier beams than those
used in the established chronology.
The National Geographic Society tree-ring expedition took, in all, 49
beam sections from ruins within Mesa Verde National Park. During 1932 and
1933 further tree-ring research was carried on in this area and
additional dates have been secured. Presuming that the year of cutting
the timber was the year of actual use in construction, the following
dates have been established for the major cliff dwellings:
Mug House, A. D. 1066
Cliff Palace, A. D. 1073-1273
Oak Tree House, A. D. 1112-84
Spring House, A. D. 1115
Hemenway House, A. D. 1171
Balcony House, A. D. 1190-1272
Long House, A. D. 1204-11
Square Tower House, A. D. 1204-46
Spruce Tree House, A. D. 1230-74
New Fire House, A. D. 1259
Ruin No. 16, A. D. 1261
Buzzard House, A. D. 1273
Since considerable tree-ring material from these ruins remains yet to be
examined, the dates given above are not final. On the basis of present
evidence, Cliff Palace, the largest and most complex cliff house within
the park, shows an occupancy of 200 years.
It is an interesting fact that all of the dates fall just short of the
beginning of the great drought, which the tree-ring chronology shows
commenced in 1276 and extended to 1299, a period of 23 years.