Casa Grande is often referred to as an adobe structure, but this use of the term is misleading. Adobe construction consists of the use of molded brick, dried in the sun, but not baked. The walls here are composed of huge blocks of rammed earth, 3 to 5 feet long, 2 feet high and 3 to 4 feet thick. These blocks were not molded and then laid in the wall, but were manufactured in place.

Plate [CXVI] shows the character of these blocks. The material employed was admirably suited for the purpose, being when dry almost as hard as sandstone and nearly as durable. A building with walls of this material would last indefinitely, provided a few slight repairs were made at the conclusion of each rainy season. When abandoned, however, sapping at the ground level would commence and would in time bring down all the walls; yet in the two centuries which have elapsed since Padre Kino's visit to this place—and Casa Grande was then a ruin—there has been but little destruction from the elements, the damage done by relic hunters during the last twenty years being, in fact, much greater than that due to all causes in the preceding two centuries.

The building was well provided with doorways and other openings, arranged in pairs, one above the other. There were doorways from each room into every adjoining room, except that the rooms of the middle tier were entered only from the east. Some of the openings were not used, and were closed with blocks of solid masonry, built into them long prior to the final abandonment of the structure.

[PLATE CXIV]

GENERAL VIEW OF CASA GRANDE RUIN

CONDITION OF CASA GRANDE IN 1891

The south and east fronts of Casa Grande seem to have suffered, particularly from the weather, and here rainstorms have probably caused some of the damage. The outer faces of the walls are of the same material as the wall mass, all the masonry being composed of earth from the immediate site. In the construction of the walls this soil was laid up in successive courses of varying thickness, whose limits form clearly defined and approximately horizontal joints. The northeast and southeast corners of the building have entirely fallen away, and low mounds of their debris still show many knobs and lumps, parts of the original wall mass.

The destruction of the walls was due mainly to undermining at the ground level. The character of this undermining is shown in many of the illustrations to this report, especially in plate [CXVI], and its extent is indicated on the accompanying ground plan (plate [CXVII]) by dotted lines within the wall mass. Although the material of which the walls are composed is very hard when dry, and capable of resisting the destructive influences to which it has been subjected for a long time, yet under certain conditions it becomes more yielding. The excessively dry climate of this region, which in one respect has made the preservation of the ruin possible, has also furnished, in its periodic sandstorms, a most efficient agent of destruction. The amount of moisture in the soil is so small as scarcely to be detected, but what there is in the soil next to the walls is absorbed by the latter, rising doubtless by capillary attraction to a height of a foot or more from the ground. This portion of the wall being then more moist than the remainder, although possibly only in an infinitesimal degree, is more subject to erosion by flying sand in the windstorms so frequent in this region, and gradually the base of the wall is eaten away until the support becomes insufficient and the wall falls en masse. The plan shows that in some places the walls have been eaten away at the ground level to a depth of more than a foot. Portions of the south wall were in a dangerous condition and likely to fall at any time.

Visiting tourists have done much damage by their vandalism. They have torn out and carried away every lintel and every particle of visible wood in the building. After the removal of the lintels a comparatively short time elapses before the falling in of the wall above. Apparently but a small amount of this damage can be attributed to rainstorms, which, although rare in this region, are sometimes violent. There is evidence that the present height of the walls is nearly the original height, in other words, that the loss from surface erosion in several centuries has been trifling, although numerous opinions to the contrary have been expressed by causal observers. The eastern wall has suffered more from this cause than the others; a belt on the northern half, apparently softer than the remainder of the wall, has been eaten away to a depth of nearly a foot. The interior wall faces are in good condition generally, except about openings and in places near the top.

Evidences of the original flooring are preserved in several of the rooms, especially in the north room. The flooring conformed to the pueblo type in the use of a series of principal beams, about 3 inches in diameter, above which was a secondary series smaller in size and placed quite close together, and above this again a layer of rushes with a coating of clay. All the walls show evidences of the principal series of beams in the line of holes formed by their ends where they were embedded in the walls. In the south wall, in parts of the east wall high up on the level of the upper roof, and in parts of other walls a few stumps of floor beams remained. These specimens of aboriginal woodwork have survived only because they are not in sight from the ground, and their existence therefore was not suspected by the tourists. Evidence of the other features of the floor construction can be seen on the walls in places where they have left an imprint, as described in the memoir previously cited.

No single opening remains intact, as the lintels have been removed from every one of them. This is particularly unfortunate, for openings at their best are an element of weakness in a wall, and here each opening, after the lintel was removed, became, as it were, a center of weakness from which the destruction of the wall mass gradually proceeded further and further.