Sky Islands, as mysterious as special The highs and lows of Sky Islands 'Sky Islands' are a rare geological phenomenon where a group of lone mountains tower above the desert or the clouds, supporting multiple biospheres of life at different heights. Each mountain is inhabited by uniquely evolved endemic species that cannot cross the scorching desert lowlands or the foggy cloudy area in between the mountains. Sky Islands would have been formed during the ice age, with creatures literally running for the hills!