While the sections known as the old quarter, the plaza quarter, and much of the tower quarter are protected by the roof of the cave, even here there has been exposure and destruction from the same cause. Torrential rains on the mesa in the late summer form streams of water which, following depressions,[18] flow over the rim of the cave roof and are precipitated into the trees beyond the lowest terrace of the ruin. The destruction of walls from these flows is much less than that from smaller streams which, following the edge of the cave roof, run under the roof and drip on the walls, washing the mortar from between the component stones, and eventually undermining their foundation and leading to their fall. The former presence of these streams is indicated by the black discoloration of the cave roof shown in photographs. [Footnote 18: In some of these waterways are found good examples of "potholes," some of considerable size, which often retain water for a long time. Their capacity was increased in prehistoric times by the construction of dams.] A visitor to Cliff Palace in the dry season can hardly imagine the amount of rain that occasionally falls during the summer months, and it is difficult for him to appreciate the destructive force it exerts when precipitated over the cliff. When Cliff Palace was occupied, damage to walls could be immediately repaired by the inhabitants after every torrent, but as the ruin remained for centuries uninhabited and without repair, the extent of the destruction was great. The torrents falling over the ruin not only gain force from the distance of the fall, but sweep everything before them, bringing down earth, stones, small trees, and bushes. At such a time the bottom of the canyon is filled with a roaring torrent fed by waterfalls that can be seen at intervals far down the gorge. The observer standing in Cliff Palace during such a downpour can behold a sheet of water falling over the projecting cliff in front of him. These cataracts fortunately are never of long duration, but while they last their power is irresistible.[19] [Footnote 19: While there has probably been considerable erosion in the bed of the canyon since Cliff Palace was constructed, this does not mean that "the action of the water carved out the valley, leaving at an inaccessible height buildings originally constructed on almost level land." See History N. Y. State Chapter, Colorado Cliff Dwellings Assoc., p. 11.] VANDALISM