ply sites where building material was
obtained. Possibly the ground at these points furnished more suitable
material than elsewhere, and, if so, the builders may have taken the
trouble to transport it several hundred yards rather than follow the
usual practice of using material within a few feet of the site. This
hypothesis would explain the large size of the depressions, otherwise an
anomalous feature.

CASA GRANDE RUIN.

_State of Preservation._

The area occupied by the Casa Grande ruin is insignificant as compared
with that of the entire group, yet it has attracted the greater
attention because it comprises practically all the walls still standing.
There is only one small fragment of wall east of the main structure and
another south of it.

The ruin is especially interesting because it is the best preserved
example now remaining of a type of structure which, there is reason to
believe, was widely distributed throughout the Gila valley, and which,
so far as now known, is not found elsewhere. The conditions under which
pueblo architecture developed in the north were peculiar, and stamped
themselves indelibly on the house structures there found. Here in the
south there is a radical change in physical environment: even the
available building material was different, and while it is probable that
a systematic investigation of this field will show essentially the same
ideas that in the north are worked out in stone, here embodied in a
different material and doubtless somewhat modified to suit the changed
environment, yet any general conclusion based on the study of a single
ruin would be unsafe. In the present state of knowledge of this field it
is not advisable to attempt more than a detailed description, embodying,
however, a few inferences, applicable to this ruin only, which seem well
supported by the evidence obtained.

The Casa Grande ruin is located near the southwestern corner of the
group, and the ground surface for miles about it in every direction is
so flat that from the summit of the walls an immense stretch of country
is brought under view. On the east is the broad valley of Gila river
rising in a great plain to a distant range of mountains. About a mile
and a half toward the north a fringe of cottonwood trees marks the
course of the river, beyond which the plain continues, broken somewhat
by hills and buttes, until the view is closed by the Superstition
mountains. On the northwest the valley of Gila