3. Moenkopi sandstone.
Notice how this rock breaks down into good building stones. The banded layers of sandstone, developed as silt in an ancient shallow sea, split along horizontal planes, and for this reason it was easily quarried and used by the Indians in construction of their dwellings.
The gray material on the sandstone is a lichen (ly-ken) which produces an acid that assists in the breakdown of rock, the first step in producing soil.