On examining the structure to ascertain the effect of the protective works of 1892 in staying the destructive processes, particularly the undermining of the walls by spattering rain and drifting sand, it was found that in most cases the results have been excellent.  On the inner side of the middle section of the southern exterior wall sapping is in progress at the ground level, and also along the rows of joist openings for the first and second stories, and in a few other places the protection seems inadequate; but in general the anticipations of the projectors of the protective works seem to have been realized.

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