Final answer:
Deserts are often found on the east side of mountain ranges in the U.S. due to the rain shadow effect, as moist winds from the west lose moisture when ascending the mountain and create drier conditions on the leeward side.
Step-by-step explanation:
In the United States, deserts may be found on the east side of mountain ranges because the air that moves over these mountains from the west, typically from the Pacific Ocean, loses much of its moisture. This process occurs since moist winds prevail from the west, and as these winds rise over mountain ranges, they cool, and their water vapor condenses, leading to precipitation on the windward side. When the winds descend on the leeward side, they are significantly drier, creating a rain shadow effect, which is a key factor in the formation of deserts such as the Mojave and Sonoran deserts in North America.
Based on this understanding, the correct answers to the multiple-choice question are: 'moist winds prevail from the west' and 'the water vapor in the westerlies condenses as it rises over mountain ranges.' Winds from the east are not characteristically dry in this context, and winds originating from the west are not usually dry until they have passed over the mountains, creating the rain shadow effect