The crusty deposits on the surfaces of large rocks are lichens (LY-kens), one of the most primitive living organisms in nature. They are excellent examples of symbiosis - a condition where two entirely different organisms live together as one, each contributing to the other’s welfare. One of these partner organisms is a fungus. It cannot manufacture its own food, but it readily absorbs and retains water. The other partner is an alga - a tiny, one-celled organism that can photosynthesize (produce food). These tiny cells are suspended among the microscopic fibers of the fungus. The fungus provides water for itself and the alga while the alga manufactures food for both. In this way, they live together cooperatively, withstanding conditions that neither of the two could survive alone.
Lichens play an important role in nature’s plan. While living on bare rock they release an acid which, over long periods of time, breaks the rock down into soil components.
There are many varieties of lichen. Some produce brilliant colors. The early Pueblo people who lived on the Pajarito Plateau hundreds of years ago would scrape the yellow-orange pigmented lichens off the rocks and mix them with pine pitch to make paint. There are at least three varieties of lichen on these rocks. You may find other kinds of lichen growing on trees, especially on dead branches, and on dead wood on the ground.