c. 2 Million BCE

Death Valley

The melted remains of the Farallon tectonic plate under western North America are buoyant, rising blobs of magma that push upward on and bulge the overlying continental plate. Especially in the Southwest—from northern Nevada through northwest Mexico—the extensional (stretching) forces on the bulging North American plate have caused deep, nearly vertical (“normal”) fault cracks to form, aligned roughly north–south. Over the past few million years, the crustal blocks between adjacent normal faults have down-cropped, creating deep valleys that geologists call graben, with high parallel ridges on either side that geologists call horst. The undulating, semi-regular repeated patterns of horst and graben across much of the Southwest defines a region known as the Basin and Range.

The deepest graben among the Basin and Range is a 140-mile-long (225-kilometer), 5- to 15-mile-wide (8–24 kilometer) crustal block just west of Las Vegas known as Death Valley. The block has dropped so much that even though the valley floor has been filled by a large volume of sediments from the surrounding mountains, Death Valley is still the lowest elevation point in North America, at just under 300 feet (90 meters) below sea level. Ample fossil and geologic evidence (such as huge salt and borax deposits) reveal that there used to be abundant surface water (rivers, lakes, and small inland seas) in what is now the Mojave Desert, but continued regional uplift and changing climate conditions have driven that water away. The result is a spectacular landscape of rocky sediments and colorful mineral deposits eroding from rugged, barren mountains onto an expansive, relatively flat valley floor.

Multiple mountain ranges to the west of the Mojave Desert effectively siphon water vapor out of the air, and decreasing snowfall in mountains to the north and east contributes to dwindling river and groundwater flows, making Death Valley among the driest places in the world, with average annual rainfall of only around 2 inches (50 millimeters). It also has the dubious distinction of holding the record for highest reliably recorded air temperature at the surface of the Earth: 134°F (57°C).

SEE ALSO The Sierra Nevada (c. 155 Million BCE), The Rockies (c. 80 Million BCE), Cascade Volcanoes (c. 30–10 Million BCE), The Andes (c. 10 Million BCE), The Dead Sea (c. 3 Million BCE), Basin and Range (1982)

Sand dunes and parched mountains within Death Valley National Park.