In addition to the explorations of Mr. Jackson and party, Mr. W. H. Holmes of the Geological and Geographical Survey, was also assigned the duty of examining ancient remains in the valley of the Upper San Juan, during the summer of 1875.[479] Mr. Holmes and party examined an area of nearly six thousand square miles, chiefly in Colorado on the San Juan and its tributaries. Most of the ruins met with were of the same general character and description as those examined by Mr. Jackson, and to repeat in detail the majority of descriptions contained in Mr. Holmes’ memoir, would be to weary the reader with repetitions without affording additional advantage. However, a few remarkable ruins described by Mr. Holmes command our attention. The first of these which may be pronounced unique in this section of the country, and quite unlike anything met with thus far in the exploration, is situated on the Rio La Plata, about twenty-five miles above its junction with the San Juan. The remains of an extensive village with structures of various forms, are scattered upon a terrace some twenty feet above the river-bed. The distribution of the works viewed in connection with plans upon which they were constructed are suggestive of the remains of the mound-builders of the Ohio valley. The forms are chiefly rectangular and circular, one or two seem to have been elliptical while a number have consisted of irregular groups of apartments. All now lie in ruins with their outlines marked by ridges of débris composed of earth, water-worn pebbles, and small fragments of sandstone. The walls of the main structure are still prominently defined, while those of a circular enclosure, used probably as an estufa, are standing to the height of four feet. Three hundred feet directly north of this enclosure is a truncated rectangular mound nine feet high, measuring fifty by eighty feet. In one of the angles of the east end are the remains of what may have been a tower rising above the platform of the mound. One hundred feet north of this mound is a rectangular enclosure measuring sixty by one hundred feet. Its wall ranges from four to six feet in height. The ruins of a wall extending between the mound and the enclosure, indicate that they were once connected. A system of works joined these to a range of low hills, lying to the north. Southward from the large central circle are earthworks and ruins covering an area of fifteen thousand square feet. A large number of small circles and mounds occupy the southern extremity of the terrace. It is impossible to account for the sudden change in the plan of works so contiguous to those of a well-marked pueblo origin. On the San Juan River, thirty-five miles below the mouth of the La Plata and ten miles above the Mancos, Mr. Holmes observed an interesting combination of cave-shelters and towers united in a system for giving signals upon the approach of the enemy. In the face of a vertical bluff thirty-five feet