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National Geographic : 1911 Nov
Contents
THE GREAT RAINBOW NATURAL BRIDGE yon wall on its downward curve. The opening, augmented by a gorge cut by the stream to a depth of 80 feet below the level of the supporting bench, meas ures a vertical distance of 267 feet; but the total height from stream-bottom to the top of the arch is 309 feet, while the abutments at their base stand 278 feet apart. The causeway, upon which one may be lowered from an adjacent cliff, but whose sides are too steep to serve for a complete passage, is 33 feet wide by 42 feet thick at its keystone point; and the limbs are not greatly in excess of these dimensions. A mere recitation of figures must fail to convey an adequate idea of the im posing nature of the bridge. It is not the size alone, though this far exceeds the greatest masonry arches constructed by engineering skill; nor is it solely the graceful lines or curvature of maximum stability, but rather all of these, that com bine to make this the most remarkable single arch now known. It would easily span, with room to spare, the dome of the Capitol at Washington; or, if hung .over the Flatiron Building of New York, its limbs would come within a few feet of the ground, though to the west of Fifth Avenue on the one hand and to the east of Broadway on the other. The arch is carved from a buff-colored, fine-grained sandstone, brick-red upon its surface and stained with vertical streaks of a darker shade. Mostly massive, though in part oblique-bedded, the rock is only moderately firm, and is easily crushed beneath the blows of a hammer. Geologically it is a part of the Upper La Plata sandstone, a formation of great thickness, deposited in Jurassic time over a large portion of southeast Utah, south west Colorado, and northeast Arizona. The origin of the arch is simple and evident. It was caused by the progres sive narrowing of the neck of a meander intrenched between high and steep walls, until an opening was made through the tongue of intervening rock, permitting the stream to cut off its meander by flow ing beneath the arch thus formed. The hole, once made, has been enlarged and given its present shape by the combined action of weathering, expansion, and contraction due to changes in tempera ture, and the carving effect of wind blown sand, all of which unite to produce the rounded rock-forms so characteristic of this region. The abandoned arm of the meander is present and unmistakable, indicating the former course pursued by the stream. Though doubtless requiring many years for its formation, the arch is nevertheless a very recent geological feature, and des tined to withstand the forces that gave it being for only a brief period as geologic time is reckoned. The bridge was first visited by white men and its existence made definitely known on August 14, 1909. It was then reached by a party consisting of W. B. Douglass, of the United States General Land Office, with four assistants; Byron Cummings, of the University of Utah, with three students; John Wetherill, of Oljato, Utah; and two Piute Indians, Jim and Nasjabegay. Douglass was act ing under instructions from the Depart ment of the Interior, dated October 20, 1908, to investigate a reported natural bridge in southeast Utah, with a view to making it a national monument if found of sufficient interest. An attempt was made in December, 1908, to locate the oridge, but was abandoned on account of snow. The search was renewed in Au gust, 1909, the party being joined at Oljato by Cummings, Wetherill, and the three students. The arch was surveyed by Douglass, and the figures herein used, as well as the details of its discovery, are taken from his official report to the Land Office. The bridge was undoubtedly known to the Indians prior to its discovery by white men; but as to the actual knowl edge of it there is uncertainty. Douglass relates that Whitehorsebegay, his guide, on a second visit to the bridge, would not go beneath the arch, but laboriously clam bered around one side whenever it was necessary to pass. Later Mrs. John Wetherill, an accomplished Navaho lin guist, ascertained from an old Navaho that the arch is supposed to represent the rainbow, or sun-path, and one who 1053
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