These colorful rock coatings are produced by lichens, a remarkable symbiotic relationship between algal cells and fungal filaments.
Neither the algae nor fungi would be able to survive on their own in this harsh desert environment. The algae are photosynthetic and provide the fungus with carbohydrate nutrients.
The fungi provide a dense mesh-work of fungal filaments which helps the algae attach to the rock and gives the embedded algae protection from the heat and aridity of the desert.
Rock lichens come in a variety of bright colors from red, orange, and yellow to brilliant shades of green. A dozen or so species may grow on a single rock.