A multitude of different lichens on Zuni sandstone near Acoma, New Mexico. Lichen is a mutualistic organism composed of algae or cyanobacteria living in the spaces between fungi stalks. The stuff looks like moldy mushrooms under the micro-scope.

Lichen is bad news for old concrete structures as it literally eats the concrete, creating a pitted and crumbling structure exposed to further erosion by precipitation and temperature changes. The four additional snaps show a concrete 66 bridge west of Old Laguna succumbing to lichen decay.

Lichen is found from low desert zone to high alpine zone elevations.