Meet Xanthoria parietina, also know as common orange lichen or maritime sunburst lichen. This example is growing on the southwest abutment of Dinely Bridge near the Three Rivers Memorial Building.
Common orange lichen is found in North America, Australia, Africa, Asia, and Europe, growing from seashore to forest. Its presence can be an indicator of high nitrogen levels, presumably meaning higher than the 78% of Earth’s atmosphere.
But this bridge over the Middle Fork of the Kaweah River is not deep in the forest, where decomposing plant litter releases nitrogen, and it’s not covered in bird poop. Perhaps the lichen enjoys this bridge because the water flowing beneath it came from forest lands and as it slows in the relatively calm spot in the river that the bridge spans, particularly when flow is low, nitrous oxide is released below to feed the lichen above.