The Great Basin is defined by hydrology and physiography. It is a region of interior drainage bounded prominently on the west by the Sierra Nevada and the Cascade Range and on the east by the middle Rocky Mountains and the Colorado Plateau. Less distinct are its northern boundary with the Columbia Plateau and the southern transition with other subdivisions of the Basin and Range province. It encompasses most of the state of Nevada, while its Utah portion is set off physiographically by the Wasatch Mountains and the high plateaus, particularly the Pavant, Tushar, and Markagunt sections.
In terms of geological plate tectonics, the Great Basin may be viewed as a series of north-south trending, linear, fault-block mountain ranges occupying the distance between the Sierra crest and the Wasatch Front. They may have rumpled up in response to the impact of the Pacific plate on the continental California coast. The block faulting began in the middle and late Tertiary period and still continues. Abrupt front slopes and more gentle back slopes are typical; and the intervening valleys are structural rather than erosional.