The rock of which the canyon walls are formed is a massive sandstone in which the lines of bedding are almost completely obliterated. It is rather soft in texture, and has been carved by atmospheric erosion into grotesque and sometimes beautiful forms. In places great blocks have fallen off, leaving smooth vertical surfaces, extending sometimes from the top nearly to the stream bed, 400 feet or more in height and as much in breadth. In the lower parts of the canyons the walls, sometimes of the character described, sometimes with the surfaces and angles smoothed by the flying sand, are generally vertical and often overhang, descending sheer to the canyon bottom without talus or intervening slopes of debris. The talus, where there is any, is slight and consists of massive sandstone of the same character as the walls, but much rounded by atmospheric erosion. The enlarged map (plate XLIII) shows something of this character. Near its mouth the whole bottom of the canyon consists of an even stretch of white sand extending from cliff to cliff. A little higher up there are small areas of alluvium, or bottom land, in recesses and coves in the walls and generally only a foot or two above the stream bed. Still higher up these areas become more abundant and of greater extent, forming regular benches or terraces, generally well raised above the stream bed. At the Casa Blanca ruin, 7 miles up the canyon, the bench is 8 or 10 feet above the stream. Each little branch canyon and deep cove in the cliffs is fronted by a more or less extended area of this cultivable bottom land. Ten miles up the talus has become a prominent feature. It consists of broken rock, sand, and soil, generally overlying a slope of massive sandstone, such as has been described, and which occasionally crops out on the surface. With the development of the talus the area of bottom land dwindles, and the former encroaches more and more until a little above the junction of Monument canyon the bottom land is limited to narrow strips and small patches here and there. These bottom lands are the cultivable areas of the canyon bottom, and their occurrence and distribution have dictated the location of the villages now in ruins. They are also the sites of all the Navaho settlements in the canyon. The Navaho hogans are generally placed directly on the bottoms; the ruins are always so located as to overlook them. Only a very small proportion of the available land is utilized by the Navaho, and not all of it was used by the old village builders. The Navaho sites, as a whole, are far superior to the village sites.