The answer is: leeward side of the mountain
Mountains consist of two main sides, The windward side and the leeward side. The Windward side of the mountain was constantly hit by air that contain pretty high volume of water that transferred from the sea. Because of this, the windward area tend to be wet.
The leeward side of the mountain on the other hand, does not receive this air. This make the leeward side become extremely dry.
