Conclusions
Deposit 1, at the bottom of the cut, was sterile of cultural material.
This was cut by Erosion Surface 1, likewise sterile. In Deposit 2 were
shards of Escavada Black on White, indicating that the period of erosion
represented by Surface 1 probably came sometime before, or early
in, the tenth century.
Erosion Surface 2 was apparently caused by a period of cessation
of deposition if not of extreme erosion, antedating the deposition of
Gallup and of Chaco Black on White shards in Deposit 3, directly above
it. The date for Erosion Surface 2, then, would appear to be somewhere
in the eleventh century.
This approximate chronology of dry and wet periods
in the Chaco as indicated by the profile of erosion and of deposition
surfaces and as dated by the incorporated potsherds coincides
with the tree ring chronology for the area. Much of Chetro Ketl
remains to be excavated, but it seems probable, from the evidence of
wall types and pottery, that it was occupied some time before the
extreme drouth of 900 to 907 A. D. This drouth may be that responsible
for the erosion of Surface 1, after which the shards of Escavada Black
on White made in the pueblo were carried or washed onto the surface
now listed as Deposit 2 but which was the ground level about 950 A. D.
Between then and 1035 the years, as indicated by the tree rings,
were of average rainfall, with some dry seasons, but between 1035 and
41 there was another drouth, less severe than the one in the early 900's.
It does not appear to have affected the expansion of the pueblos. Erosion
Surface 2 is probably representative of this period.
Deposit 3 represents a post-drouth period, probably from about
1059 or 1100 A. D. onward. It contains the Gallup and the Chaco Black
on White, which were both being made at the end of the century.
The successive erosion and deposition surfaces suggest increasing
dryness in the canyon, although the tree ring growth indicates that
there was no change in weather but merely a succession of wet and of
dry periods. The increasing denudation of the canyon floor was, perhaps,
because of deforestation and of farming, perhaps because of farming
alone. Interpretation of the profiles on the cut of the canyon floor
accords with the Douglass theory of recession of the forest border, after
human despolation, and of consequent erosion of the light soil by wind
and water.[5]
