This assortment of spots are not geographical locations, nor skin irritations, but rather lichen spots, forming different blotch patterns on the tree bark. Some cover the entire trunk, while others are more sparse.
They're an intriguing life form - a combination of a fungus and an algae that live symbiotically on trees (they don't penetrate the bark, or kill the tree. They just use the surface to gain purchase) or rocks.
They're all pretty colorful and have different shaped edges, like moles on our skins!