The many canyon exits merge their fans into extensive bajadas and piedmonts. Bare rock and cliff may still outcrop along the crest as a mountain is gradually reduced to alluvium. The Great Basin is effectively cut off from the westerly flow of Pacific moisture. Orographic uplift of crossing air masses by the Sierra and the Cascades provides cooling and precipitates much of the moisture out. The climate is typical of middle latitude, semi-arid lands where evaporation potential exceeds precipitation throughout the year.
Oases occur where highlands generate surface streams or springs.
By the time air masses reach the Basin's eastern edge they get another lift, creating extra moisture and highland climates that support Utah's population corridor below. The vegetation response to the Great Basin's climate, soils, and topography can be generalized in a look at its life zones. Soils grade upslope from Aridisols through Mollisols with occasional young Entisols appearing on the fans, floodplains, and valley bottoms. They are remains from huge Pleistocene lakes filled in an era of melting glaciers and a wetter climate. Government geologist G. K. Gilbert and surveyor Howard Stansbury first mapped and interpreted many of these features.