The most serious of the destructive processes was sapping, and this process has been nearly checked by the protective works. The second was the desurfacing and subsequent eating away of the walls by beating rains and frost, and this is still in progress at a moderate rate. The least serious process was the wearing away of the crests of the walls by rain and winds, and this is still going on at a perceptible rate. It is impossible to determine, and difficult even to approximate, the rate of destruction quantitatively, especially so since it goes on cumulatively, with constantly increasing rapidity, as the cemented surfaces are destroyed and the crevices widen and deepen; but judging from the history of the ruin, and from the rate of destruction indicated by comparing the photographs of 1892 with the present aspect, it would seem safe to conclude that, if protected completely from vandalism, the ruin will be comparatively little injured during the next five years, and will stand perhaps half a century, without further protective works, before moldering into dust. In view of the slow yet ever increasing rate of destruction of the ruin, and of its great interest as a tangible record of the prehistoric inhabitants of this country, no hesitation is felt in recommending that the structure be further protected, and practically perpetuated, by a suitable roof, so designed as to shield the walls from rain and sun and at the same time permit an unobstructed view of the ruin from any direction. * * * * * I have the honor to be, sir, yours, with great respect, J. W. Powell, _Director_. Secretary of the Interior. INDEX Adobe construction, what constitutes 323 Burrell, H. H., Casa Grande photographed by 343 Clauton, M. E., bid of, for repair of Casa Grande 339 Colton, A. T., on Casa Grande reserve 340 Contract for repairing Casa Grande 333-335 Doran, A. J., affidavit of 335 contract with, for Casa Grande repair 334 Eaman, C. B., witness to Casa Grande contract 334 Garlick, C. A., cooperation of, in repair of Casa Grande 327 Henry, C. D., bids of, for repair of Casa Grande 338-339 Hoar, G.F., interest of, in Casa Grande 346 Hunt, Jeff, witness to Casa Grande contract 334 Kebbey, F. C., witness to Casa Grande contract 334, 335 Kebbey, J. H., affidavit of 335 Kino, Eusebius, Casa Grande visited by 323, 345