sky island n. an isolated ecosystem occurring at a high altitude, such as on a mountain top, which shows evolutionary tendencies similar to those occurring on islands surrounded by water. (source: Double-Tongued Dictionary)
Further reading
After our conversation about the expression dingle day, a term used by workers at a research station in Antarctica to denote bright, sunny weather, a listener offers a possible explanation for this term. It may derive from the idea of the skies...