A rain shadow is a dry area on the leeward side of a mountain range. When moist air rises over the mountains, it cools and loses moisture in the form of precipitation. This process creates lush vegetation on the windward side, while the leeward side receives significantly less rainfall. As a result, the leeward side often becomes arid or semi-arid, leading to unique ecosystems. For example, the Sierra Nevada mountains in the United States create a rain shadow effect, resulting in the dry conditions of the Great Basin region to the east.