"At the water's edge the walls are perpendicular," writes Doctor G.K. Gilbert, of the U.S. Geological Survey, who first described it, "but in the deeper parts they open out toward the top. As we entered and found our outlook of sky contracted--as we had never before seen it between canyon cliffs--I measured the aperture above, and found it thirty-five degrees. We had thought this a minimum, but soon discovered our error. Nearer and nearer the walls approached, and our strip of blue narrowed down to twenty degrees, then ten, and at last was even intercepted by the overhanging rocks. There was, perhaps, no point from which, neither forward nor backward, could we discover a patch of sky, but many times our upward view was completely cut off by the interlocking of the walls, which, remaining nearly parallel to each other, warped in and out as they ascended." Here he surprises the secret of the making of Zion. "As a monument of denudation, this chasm is an example of downward erosion by sand-bearing water. The principle on which the cutting depends is almost identical with that of the marble saw, but the sand grains, instead of being embedded in rigid iron, are carried by a flexible stream of water. By gravity they have been held against the bottom of the cut, so that they should make it vertical, but the current has carried them, in places, against one side or the other, and so far modified the influence of gravity that the cut undulates somewhat in its vertical section, as well as in its horizontal." [Illustration: _From a photograph by the U.S. Geological Survey_ ZION CANYON FROM THE RIM] [Illustration: THE THREE PATRIARCHS, ZION CANYON These red-and-white structures rise more than two thousand feet above the canyon floor] This, then, is how Nature began, on the original surface of the plateau, perhaps with the output of a spring shower, to dig this whole mighty spectacle for our enjoyment to-day. We may go further. We may imagine the beginning of the titanic process that dug the millions of millions of chasms, big and little, contributing to the mighty Colorado, that dug the Grand Canyon itself, that reduced to the glorified thing it now is the enormous plateau of our great southwest, which would have been many thousands of feet higher than the highest pinnacle of Little Zion had not erosion more than counteracted the uplifting of the plateau. Little else need be said to complete this picture. The rains and melting snows of early spring produce mesa-top torrents which pour into the valley and hasten for a period the processes of decorating the walls and levelling the plateau. So it happens that waterfalls of power and beauty then enrich this wondrous spectacle. But this added beauty is not for the tourist, who may come in comfort only after its disappearance.