Cumberland Rock-shield (Xanthoparmelia cumberlandia), photographed on a rock wall at hte Crystal Sprins Roadside Rest Area in San Mateo County, CA (near Burlingame). The lead shot (Shot 1) shows this lichen's upper surface, whereas the second shot (Shot 2) shows a bit of its underside. Identification is quite tentative, based on the following: 1) Foliose structure of the lichen. Part of the lichen can be lifted or removed without affecting the substrate underneath. (See Shot 2.) 2) Substrate consists of rock, some of which contains quite a bit of silica. (Note the abundance of small quartz granules in the exposed rock.) 3) Thallus pale bluish-green in color, generally smooth and shiny, with no pruina, spots, or markings. 4) Thallus forming more or less rounded lobes that are tightly appressed to the underlying surface. Margin of lobes varyies from entire to crenate. 5) Apothecium present, with a somewhat in-rolled margin, a dark center, and no pruina. (Note, however, this specimen does not seem to be as well-laden with apothecia as is typical for X. cumberlandia. This may or may not be a problem for this analysis.) 6) Pycnidia common, forming small, black bumps and tiny, crater-like structures on the upper surface of the thallus. Thallus lacking isidia, soredia, or pustulae. 7) Lower surface (Shot 2) pale tan in color, with simple, pale brown rhizines. (The rhizines in Shot 2 appears to be a light grayish-brown in color, which seems 'pale' to me. However, if they are not light enough to be considered 'pale,' this would probably invalidate my analysis here and therefore my indentification of this lichen.) References: 1) A Field Guide to California Lichens, Stephen Sharnoff, Yale University Press, 2014. See especially the description and picture of Xanthoparmelia cuberlandia on p. 136. 2) Consortium of North American Lichen Herbaria, https://www.lichenportal.org. Description of Xanthoparmelia cumberlandia is available at http://lichenportal.org/portal/taxa/index.php?taxon=54737 3) Ways of Enlichenment, http://www.waysofenlichenment.com. Description of Xanthoparmelia cumberlandia available here: http://www.waysofenlichenment.net/lichens/Xanthoparmelia%20cumberlandia