The towers of Hill Canyon bear a close likeness to those in the region mentioned, except that their masonry is poorer and their walls are more dilapidated. This can be ascribed in part to the material out of which they are built, for whereas the stone in the southern part of the area is soft and easily worked, that in the Hill Canyon region is hard but can readily be split into slabs which did not require much manipulation to bring them into desired shapes for use. The tall and better built towers of the San Juan (pl. 14, _a_) and its tributaries are sometimes single rooms without connections with other buildings, but are more often surrounded at their bases by rooms not unlike those of pueblo ruins. Thus at Cannon Ball ruin the towers rise from the midst of secular rooms and the same is true of the tower in Cliff Palace and elsewhere. This leads to the supposition that these buildings were constructed for some purpose other than as lookouts: they bear all the outward appearance of sacred rooms called kivas of pueblos and cliff dwellers. If we accept this explanation[20] that the McElmo towers are round kivas, as suggested by Holmes, Morgan, and others we can explain why several are united in a cluster, for it would seem that each room in such a cluster belonged to a family or clan. The use of these towers as here suggested can not, however, be proven until excavations of them are made and the signification of the banquette constantly found annexed to their inner wall is determined. Several structural remains in Ruin Canyon (pl. 14, _b_), a tributary of the Yellow Jacket, especially those at the head of the South Fork, give a good idea of the relation of the tower to surrounding rooms. Here we find towers constructed of fine, well preserved, masonry rising to almost their original height, but crowded into the midst of rectangular rooms imparting to the whole ruin a compact rectangular form. Several towers in this canyon are without surrounding rooms, others have rectangular, square or D-shaped ground plans, but the author studied none with two or three concentric surrounding walls. The form of one of the largest ruins in Ruin Canyon situated near the fork of the canyon, closely resembles Far View House, in the Mesa Verde National Park. It has a central tower around which are rooms with straight walls, the intervals between which and the circular wall of the tower having a roughly triangular shape. While there is but one tower in this ruin, its similarity in form and position to the large central kiva of Far View House indicates that towers in the McElmo are practically ceremonial rooms, as has been long suspected.