The boulder forming the substrate for these lichens was part of the Hope Slide forty years ago. Unless this rock was previously exposed as part of mountainside (which I doubt), forty years of lichen colonization and growth have led to this mosaic containing six species or more.
As pioneers, these crustose lichens play an important role in the establishment of succeeding (i.e., sequentially following) organisms such as mosses or vascular plants. The bulky tissue of the lichen (particularly the thallus, or body) slowly traps air-borne dust and silt, while the fungal hyphae of the lichen penetrates and helps etch a thin layer of the rock’s surface. The fine particles of soil in combination with dead or decaying lichen tissue form a medium where moss spores or vascular plant seeds can establish and grow. Over a long period of time (assuming no mechanical disturbances), a layer of mosses and herbaceous plants will replace these lichens. Although the period of time may be measured in decades or centuries, it is essentially instant in the scale of geologic time.
Botany resource link: Plant Talk magazine.