Nitrophilous_NearHome_c

A common pattern on rocks in the cold desert, in this case near Reno, Nevada. Birds or rodents (probably pack-rats in this case) often have favorite perches. Over time urin salts accumulate forming a whitish crust. Caloplaca and Xanthoria species often show nitrophilous affinities and are able to tolerate high urin concentrations around these perches.