The dryness of the Great Basin in Nevada is mainly caused by the rain shadow effect from the Sierra Nevada mountains.

The Great Basin in Nevada is dry due to the rain shadow effect from the Sierra Nevada mountain range. As moist air from the Pacific Ocean moves eastward, it is forced to rise over the Sierra Nevada. This rising air cools and loses moisture as precipitation on the western slopes of the mountains. By the time the air descends into the Great Basin, it is dry, creating arid conditions in Nevada and much of the surrounding area. This phenomenon is a key factor contributing to the desert-like climate of the Great Basin, making it one of the driest regions in the U.S.