Bearing around the Mesa to the west, the party encamped upon the site of the most extensive mass of ruins yet found in United States territory, “known as the Aztec Springs.” As Mr. Jackson’s description is but partial, we defer the treatment of this locality until we take up the explorations of Mr. Holmes, already mentioned. Four miles distant from “Aztec Springs,” the party reached a river-bed, dry during most of the year, and known as the McElmo, which, when it flows at all, empties into the San Juan farther to the west. On the _mesa_, above this river-bed, a tower resembling that first met in the Mancos was observed, but of much greater size, having a diameter of fifty feet. Adjoining the tower were the ruins of large subdivided buildings resembling the community dwellings of the Moquis and the old ruins of the Chaco. This group of ruins was very extensive and complicated, literally occupying all the available space in the vicinity. [Illustration: Watch-Tower of the Cañon of the Mancos.] Half a dozen miles down the cañon of the McElmo, several of the little nest-like dwellings peculiar to the Mancos were seen perched forty or fifty feet above the valley. A couple of miles beyond these, the tower shown in the cut (p. 301) was discovered standing on the summit of a great block of sandstone forty feet high, and detached from the bluff back of it. [Illustration: Square Tower on the McElmo.] The building which surmounts this rocky pedestal is square and about fifteen feet high at present. Windows open toward the north and east, the directions from which the enemies of this people, according to tradition, came down upon them. A wall at the base of the rock is mostly in ruins and covered with débris from the building above. Immediately beyond this point the boundary line into Utah was crossed, and two or three miles distant the party came upon a very interesting group, a historic spot in the career of this ancient race. In the centre of the widening valley stands a solitary butte of dark-red sandstone, upon a perfectly smooth floor of the same, dipping gently towards the centre of the valley. This butte or _cristone_ is about one hundred feet high and three hundred feet in length, of irregular form. All around the rock are remains of stone walls which indicate an extensive structure and complicated system of walls and towers. At the back of the rock two remains attract special attention. One wall forming the corner of a building near the base of the rock, seems to have served as an approach to the larger house up in the side of the butte. This structure is about eighteen feet in length and twelve feet in height, nearly reaching to the top of the rock. Part of the walls have fallen, but those standing show a finish surpassing those of any structure previously discovered in the region. In front is a single aperture eighteen by twenty-four inches. On top of the rock are remains of masonry, but too badly ruined to indicate their original form. All