The unit type mound uncovered by Doctor Prudden is one of the most instructive examples of this type in Montezuma Canyon, but the author in subsequent pages will call attention to the existence of the same type in Square Tower Canyon. All of these pueblos probably have kivas of the pure type, practically the same in structure as Far View House on the Mesa Verde National Park. MUD SPRING (BURKHARDT) RUIN The collection of mounds (pl. 3, _b_), sometimes called Burkhardt Ruin, situated at Mud Spring, belongs to the McElmo series. This ruin, in which is the “triple-walled tower” of Holmes, for uniformity with Mitchell Spring Ruin and Aztec Spring Ruin, is named after a neighboring spring. Like these, it is a cluster of mounds forming a village which covers a considerable area. The arroyo on which it is situated opens into the McElmo, and is about 7 miles southwest from Cortez, at a point where the road enters the McElmo Canyon. The extension of the area covered by the Mud Spring mounds is east-west, the largest mounds being those on the east. These latter are separated from the remainder, or those on the west, by a shallow, narrow gulch. There are two towers united to the western section overlooking the spring, the following description of one of which, with a sketch of the ground plan, is given by Holmes.[18] [18] Op. cit., pp. 398-399. “The circular structures or towers have been built, in the usual manner, of roughly hewn stone, and rank among the very best specimens of this ancient architecture. The great tower is especially noticeable.... In dimensions it is almost identical with the great tower of the Rio Mancos. The walls are traceable nearly all the way round, and the space between the two outer ones, which is about 5 feet in width, contains 14 apartments or cells. The walls about one of these cells are still standing to the height of 12 feet; but the interior can not be examined on account of the rubbish which fills it to the top. No openings are noticeable in the circular walls, but doorways seem to have been made to communicate between the apartments; one is preserved at _d_.... This tower stands back about 100 feet from the edge of the mesa near the border of the village. The smaller tower, _b_, stands forward on a point that overlooks the shallow gulch; it is 15 feet in diameter; the walls are 3½ feet thick and 5 feet high on the outside. Beneath this ruin, in a little side gulch, are the remains of a wall 12 feet high and 20 inches thick.... The apartments number nearly a hundred, and seem, generally, to have been rectangular. They are not, however, of uniform size, and certainly not arranged in regular order.” Morgan[19] gives the following description of the same ruin which seems to the author to be the Mud Creek village: