The region is a complex topographic basin, the surface of which is broken by numerous fault-block mountains, trending mostly north-south and rising sharply in places to more than 10,000 ft (3,048 m) above dry, sediment-floored basins. Death Valley, 282 ft (86 m) below sea level, is the lowest basin; it is also the hottest (134°F/56.7°C in the shade is the highest temperature ever recorded in the world) and one of the driest (less than 3 in./7.6 cm of rain annually) parts of North America. Throughout the Great Basin rainfall is limited (2–20 in./5.1–51 cm annually) and sporadic.
The region was recognized as an area of interior drainage by J. C. Frémont, who explored (1843–45) and named it. The rivers of the region have no outlet to the sea; they either dry up as they cross the parched terrain, like the Humboldt, or empty into large lakes or into playas that temporarily fill with water after heavy rain. Klamath and Utah lakes contain freshwater; most other lakes are brackish or salty. The lakes are remnants of a much larger system of ancient lakes that occupied the region during the Pleistocene epoch: Great Salt, Sevier, and Utah lakes are remnants of glacial Lake Bonneville (see under Bonneville Salt Flats); North Carson, South Carson, Walker, Honey, Pyramid, and Winnemucca are remnants of glacial Lake Lahontan; and glacial Lake Manly is thought to have occupied Death Valley.