In this closed hydrological system, there are many mountain ranges that operate like islands, isolated by oceans of sage. There is literally no other place like the Great Basin in the United States, and very few places like it in the world. The boundaries defined by these various definitions are not identical. The most commonly used definition is the hydrographic one. The Great Basin is an approximately 200,000 square mile area that drains internally.
Surface water leaves the Great Basin only by evaporation.
No creeks, streams, or rivers find an outlet to either the Gulf of Mexico or the Pacific Ocean. The boundaries to the east and west, are the Wasatch Mountains of Utah and the Sierra Nevada Mountains of eastern California, respectively. The northern boundary is the Snake River Plain of Idaho and Oregon. The south rim is less distinct. In fact, John Fremont, the explorer who named the Great Basin, postulated a nonexistent mountain range to the south.