In studying human/environment interaction, geographers look at the positive and negative effects that occur when people interact with their environment.
Due to the circulation of the Bermuda high which creates a humid south wind that blows to the Mexican gulf along the terrain in east of the Rockies while the pacific high creates a dry northerly circulation over east of the Sierras. This results in the very dry region which is blocked by the Pacific moisture and blocked by the Gulf moisture forming a rain shadow over the Rockies.