On siliceous rocks on ground. I collected a large selection on pebbles from the general area but chemistry and form differed subtly across all the samples, so there's no knowing for sure which species this particular photo is. X. cumberlandia was one of the most common (medulla K+y/o, fertile, rounded flat unmarked lobes, no lobulae, brown underneath), but X. somloensis (same but weakly maculate lobe tips) was also there, and X. lineola (K+y-r) is to be expected. (X. coloradoensis was also present, but it looks different, with somewhat divided lobes and "tattered" appearance toward the interior of the thallus where the highly-divided interior lobes grow all over one another in an imbricate mat, and rarely has so many apothecia.)