Casa Grande Ruin | Page 4

and it will be further noticed that the irregularity reaches its maximum

in the vicinity of the Casa Grande ruin proper, where the ground
surface was more recently formed, from the fall of walls that were
standing within the historical period.
External appearance is a very unsafe criterion of age, although in some
cases, like the present, it affords a fair basis for hypothesis as to
comparative age; but even in this case, where the various portions of
the group have presumably been affected alike by climatic and other
influences, such hypothesis, while perhaps interesting, must be used
with the greatest caution. Within a few miles of this place the writer has
seen the remains of a modern adobe house whose maximum age could
not exceed a decade or two, yet which presented an appearance of
antiquity quite as great as that of the wall remains east and southeast of
the Casa Grande ruin.
The application of the hypothesis to the map brings out some
interesting results. In the first place, it may be seen that in the lowest
mounds, such as those in the northwestern corner of the sheet, on the
southern margin, and southwest of the well-marked mound on the
eastern margin, the contours are more flowing and the slopes more
gentle than in others. This suggests that these smoothed mounds are
older than the others, and, further, that their present height is not so
great as their former height; and again, under this hypothesis, it
suggests that the remains do not belong to one period, but that the
interval which elapsed between the abandonment of the structures
whose sites are marked by the low mounds and the most recent
abandonment was long. In other words, this group, under the
hypothesis, affords another illustration of a fact constantly impressed
on the student of southwestern village remains, that each village site
marks but an epoch in the history of the tribe occupying it--a period
during which there was constant, incessant change, new bands or minor
divisions of the tribe appearing on the scene, other divisions leaving the
parent village for other sites, and the ebb and flow continuing until at
some period in its history the population of a village sometimes became
so reduced that the remainder, as a matter of precaution, or for some
trifling reason, abandoned it en masse. This phase of pueblo life, more
prominent in the olden days than at present, but still extant, has not

received the prominence it deserves in the study of southwestern
remains. Its effects can be seen in almost every ruin; not all the villages
of a group, nor even all the parts of a village, were inhabited at the
same time, and estimates of population based on the number of ruins
within a given region, and even those based on the size of a given ruin,
must be materially revised. As this subject has been elsewhere[1]
discussed, it can be dismissed here with the statement that the Casa
Grande group seems to have formed no exception to the general rule,
but that its population changed from time to time, and that the extent of
the remains is no criterion of the former population.
[Footnote 1: See pp. 179-261 of this Report, "Aboriginal Remains in
Verde Valley."]
It will be noticed that in some of the mounds, noticeably those in the
immediate vicinity of the Casa Grande ruin, the surface is very
irregular. In this instance the irregularity indicates a recent formation of
surface; for at this point many walls now marked only by mounds were
standing within the historical period. External contour is of course a
product of erosion, yet similarity of contour does not necessarily
indicate either equal erosion or equal antiquity. Surface erosion does
not become a prominent factor until after the walls have fallen, and one
wall may easily last for a century or two centuries longer than another
similarly situated. The surface erosion of a standing wall of grout, such
as these under discussion, is very slight; photographs of the Casa
Grande ruin, extending over a period of sixteen years, and made from
practically the same point of view, show that the skyline or silhouette
remained essentially unchanged during that period, every little knob
and projection remaining the same. It is through sapping or
undermining at the ground surface that walls are destroyed. An
inspection of the illustrations accompanying this paper will show what
is meant by sapping: the external walls are cut away at the ground
surface to a depth varying from a few inches to nearly 2 feet. After a
rain the ground, and that portion of the walls at present below its
surface, retains moisture much longer than the part of the walls which
stands clear; the moisture rises by capillary attraction a foot