There are also many rooms in cliffs, possibly used for storage or for some other unknown purposes, but too small for habitations. It is significant that these are identical so far as their size is concerned with the “ledge houses,” near Spruce-tree House, indicating similar or identical uses. The kivas of cliff-dwellings of size in the region considered have the same structural features as those of adjacent ruins, but very little resemblance, save in site, to those of cliff-dwellings in southern Arizona, as in the Sierra Ancha or Verde Valley, the structure of which resembles adjacent pueblos. The absence in the McElmo region of very large cliff-houses is due partly but not wholly to geological conditions, the immense caves of the Mesa Verde not being duplicated in the tributaries of the McElmo; but wherever caverns do occur, as in Sand Canyon, we commonly find diminutive representatives. While differences in geological features may account for the size of these prehistoric buildings, the nature of the site or its size is not all important.[35] [35] Attention may be called to the fact that often we find very commodious caves without correspondingly large cliff-houses, even in the Mesa Verde. Here and there one sees from the road through the McElmo Canyon a few small cliff-houses, and if he penetrates some of the tributaries, he finds many others. The canyon is dominated by the Ute Mountain on the south, but on the north are numerous eroded cliffs in which are many caves affording good opportunities for the construction of cliff-houses. These buildings do not differ save in size from the cliff-houses of the Mesa Verde. Their kivas resemble the vaulted variety and the masonry is identical. Although the existence of cliff-dwellings in the tributaries of the McElmo has long been known, the characteristic circular kivas which occur in the Mesa Verde had not been recognized previous to the present report. The relative age of the pueblos and great towers and the same structures in caves can not be decided by the data at hand, but the indications are that they were contemporary. On account of the similarity in structure of the McElmo cliff-dwellings to those on Mesa Verde, only a few examples from the former region are here considered. It may be worthy of note that while McElmo cliff-dwellings are generally accompanied by large open-air pueblos and towers or great houses on the cliffs above, in the Mesa Verde open-air buildings[36] are generally situated some distance from the cliff-dwellings. CLIFF-DWELLINGS IN SAND CANYON