The principal structures are large pueblos handsomely built of stone, and in a pretty good state of preservation. The external walls are composed of yellow Cretaceous sandstone, dressed to a common smooth surface without hammer-marks; in some places they are still 25 feet in height. As usual in buildings of this kind, the walls were unbroken by door or window to a height of 15 feet above the foundation. The interior shows a great number of small rooms, many of which are in a perfect state or preservation, and handsomely plastered. These structures are surrounded by mounds and fragments of masonry, marking the sites of great numbers of subordinate buildings; the whole affording conclusive evidence that a large population once had its home here. [Illustration: Aztec Ruins in 1895.] [Illustration: AZTEC RUINS—GROUND PLAN] White settlement of the valley around the ruins area began in 1876, and from that time on the ruins have been well known. The first scientific investigations of the ruins were made in 1878, when Lewis H. Morgan visited the site and later published a description with a good ground plan. Morgan, sometimes known as “the father of American anthropology,” was one of the most distinguished scientists of the 19th century. He is well known for his ethnological studies of the Iroquois Indians in New York. Though usually thought of as a “social anthropologist,” Morgan had a great and abiding interest in archeology, particularly that of the southwestern part of what is now the United States, Mexico, and Central America. On his trip to the Southwest in 1878, he kept a journal full of observations and notes about the various ruins which he visited. In those days the railroad extended only to Canyon City, Colo., and from there Morgan and his party had to proceed by wagon. One of the ruins which especially seemed to intrigue Morgan was the one on the Animas River, which we now call Aztec. He not only made a ground plan of the entire ruin, but noted that there were other structures of considerable size and interest in the immediate vicinity. He also entered some of the rooms, particularly in the west wing of the larger ruin, which still had their ceilings intact. Even at that time, evidently a good bit of the ruin had already been destroyed by the early settlers, for Morgan records the fact that one man at Animas City, who had lived near the ruins, told him that about one quarter of the stones had been taken away by the settlers to use in building houses, lining wells, or for other construction purposes. Morgan also talks about entering rooms on the second story, so presumably some of these upper stories may still have been intact in 1878.