Acarospora socialis

Acarospora socialis (bright cobblestone lichen) is a usually bright yellow areolate to squamulose crustose lichen in the family Acarosporaceae that grows up to 10 cm wide, mostly on rock in western North America. It is among the most common lichens in the deserts of Arizona and southern California.: 218–9 : 218–219  It grows on sandstone, intrusive and extrusive igneous rock such as granitics, in all kinds of exposures to sunlight, including vertical rock walls. It is found in North America, including areas of the Mojave Desert and Sonoran Desert region, to Baja California Sur. It is the most common yellow member of its genus in southwestern North America. It sometimes, but rarely, grows on other soil crusts. It is a pioneer species. It is variable in its growth pattern. Areoles can be angular to round, sometimes forming lobes. They can be contiguous or scattered. Color is variable - bleached white, green-yellow, and other hades of yellow. It has a lower surface when squamulose, but w......read more on Wikipedia.