A vast desert formed in Earth's prehistoric past when the supercontinent of Pangaea straddled the equator and stretched to the poles. Pangaea's position influenced ocean circulation patterns, and its huge size meant that there were vast areas where moist air from the oceans never penetrated. The north east of the continent, coastal areas and the poles had water aplenty, but elsewhere deserts ruled supreme. Many of the bright red rocks of the Late Permian and Triassic are from this desert period. They often contain chunks of gypsum and other salts left by evaporating lakes since, when rain came, it was likely to be as monsoon-type deluges.