Recent lichenological investigations of Fox Hills Formation sandstone outcrops in Colorado resulted in the discovery of three populations that represent an undescribed member of the Lecanora dispersa group (=Myriolecis). This new species is different from all others in the group in its production of usnic acid, which yields apothecia that are yellowish-green in color in fresh field material. The new species, here formally described as Lecanora lendemeri, is further characterized by its relatively large ascospores, endolithic thallus, presence of POL+ granules, and apparent restriction to this sandstone formation. We conducted molecular phylogenetic analyses to place the new species into the context of other members of Lecanora using new shotgun sequence data generated for this study in tandem with previously published rDNA data, and found that the new species is resolved as nested within the L. dispersa group, which was a strongly supported clade in our analysis. Using IUCN criteria including a known occurrence of only three populations, the largest of which is under conservation threat, we herein formally rank this new species as Endangered. This discovery comes on the heels of several other recent lichen discoveries on Fox Hills Sandstone, all species that are, so far as known, restricted to this rock type, suggesting that substrate endemism may be a common element of the biotic communities of the Fox Hills Formation. From the results of this and prior studies, it is clear that sandstone outcrops serve as important, yet still incompletely documented, habitats for cryptogamic diversity. This discovery further highlights the significance of conservation areas, even tiny units (e.g., 40 ha or less) that represent mere islands in a sea of urban development, such as in the Front Range of Colorado.