Death Valley's spectacular alluvial fans: explained by a geology professor

Summary

Death Valley’s landscape contrasts steep mountain fronts with the remarkably flat Badwater Basin playa. Alluvial fans form the transition between them: fan-shaped deposits of sediment at the mouths of mountain canyons.

During intense rainstorms and flash floods, water carries material down narrow canyons. When it reaches the flatter valley floor, it loses energy and drops its sediment. Deposits range from boulders near canyon mouths to finer sand and gravel farther out. Beyond the fans, the basin is largely covered by fine mud and salts left behind as water evaporates.

The fans differ in size on opposite sides of Death Valley:

• Black Mountains, east side: The fans are relatively short and steep, generally extending about half a mile from canyon mouth to toe. The steep western mountain front leaves streams with smaller drainage areas, limiting how much sediment they can carry.
• Panamint Range, west side: The fans are much larger, extending for miles. The longer slopes on the range’s eastern side provide larger drainage areas, allowing floods to transport and deposit more sediment.

This contrast reflects the ranges’ faulting and uplift, which shape their slopes and drainage-basin sizes.

Researcher or Source Featured

• Shawn Willsey — geology professor and video presenter.