From the character of the remains it seems probable that the site of the ruins here designated as the Casa Grande group was occupied a long time, not as a whole, but piecemeal as it were, one part being occupied and abandoned while some other part was being built up, and that this ebb and flow of population through many generations reached its final period in the occupation of the structure here termed the Casa Grande ruin.  It is probable that this structure did not exist at the time the site was first occupied, and still more probable that all or nearly all the other sites were abandoned for some time before the structure now called the Casa Grande was erected.  It is also probable that after the abandonment of the Casa Grande the ground about it was still worked by its former population, who temporarily occupied, during the horticultural season, farming outlooks located near it.

[Illustration:  Pl.  LX:  Circular Opening in North Room.]

The methods employed in the construction of the buildings of the Casa Grande were thoroughly aboriginal and characteristically rude in application.  A fair degree of adaptability to purpose and environment is seen, indicating that the Casa Grande was one, and not the first, building of a series constructed by the people who erected it and by their ancestors, but the degree of skill exhibited and amount of ingenuity shown in overcoming difficulties do not compare with that found in many northern ruins.  As architects, the inhabitants of the Casa Grande did not occupy the first rank among pueblo-builders.

It is probable that the Casa Grande ruin as we see it today shows very nearly the full height of the structure as it stood when it was abandoned.  The middle tier of rooms rose to a height of three stories; the others were but two stories high.  It is also probable that the building was enlarged after being once completed and occupied.  At one time it probably consisted of four rooms on the ground plan, each two stories high.  The northern tier, of rooms was added afterward, and probably also the third room in the central tier.

The Casa Grande was undoubtedly built and occupied by a branch of the Pueblo race, or by an allied people.  Who these people were it is impossible to determine finally from the examination of one ruin, but all the evidence at hand suggests that they were the ancestors of the present Pima Indians, now found in the vicinity and known to have formerly been a pueblo-building tribe.  This conclusion is supported by the Pima traditions, as collected by Mr. Bandelier, who is intimately acquainted with the documentary history of the southwest, and whose knowledge of the Pima traditions is perhaps greater than that of anyone else now living.  In his various writings he hints at this connection, and in one place he declares explicitly that the Casa Grande is a Pima structure.  None of the internal evidence of the ruin is at variance with this conclusion.  On the contrary, the scanty evidence is in accord with the hypothesis that the Casa Grande was erected and occupied by the ancestors of the Pima Indians.