As noted earlier, the sandstone beds and lenses of the Kayenta generally are coarser grained (some even contain small pebbles) and much harder than the underlying Wingate Sandstone—particularly the lower beds of the Kayenta, which serve as a protective capping, as shown in figure 13 and in many of the other photographs. Unlike the dominantly fine grained, well sorted, windblown sands of the Wingate, the coarser stream-laid sands of the Kayenta are angular and poorly sorted, so that small grains fill spaces between larger ones. Moreover, in addition to the calcite cement (which also holds together the sand grains in the Wingate and Entrada Sandstones), most of the sand grains and pebbles in the Kayenta are covered by interconnected “overgrowths” of silica (SiO₂), which make up about 10 percent of the rocks and serve as a nearly insoluble hard cement.[20] The combination of the coarse and fine grains and interlocking silica “overgrowths” makes the Kayenta one of the most resistant rocks in the Colorado Plateau. In distant views of weathered outcrops the Kayenta appears to consist mainly of thin beds or lenses of sandstone, which indeed it does, but in some fresh exposures, such as roadcuts, the highly lenticular red flood-plain deposits form striking features which may wedge out from 3 or 4 feet thick to a featheredge within horizontal distances of only a few feet (fig. 14). The Kayenta has yielded fossil bones of dinosaurs and other reptiles in northeastern Arizona and freshwater shells in eastern Utah. As yet, however, no fossils have been reported from it in or near the Monument. Another Gap in the Rock Record Following the wet interval when the Kayenta Formation was deposited over wide areas of the Colorado Plateau by streams, the Plateau once again became a vast desert, and this time the dry climate persisted from the Late Triassic into the Jurassic. The howling winds piled up enormous sand dunes, layer upon layer, to a total thickness of more than 2,200 feet at Zion National Park, and as much as 500 feet remains in eastern Utah and parts of southwestern Colorado. This immense sandpile eventually was cemented by calcite into the Navajo Sandstone. [Illustration: KAYENTA FORMATION, showing lenses of hard channel sandstones and wedge of red siltstone and mudstone. Along road cut of Rim Rock Drive near head of main stem of Ute Canyon. Vertical grooves remain from drill holes used in blasting roadcut. (Fig. 14)]