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Colorful, sculptured volcanic rocks at Hole in the Wall
Colorful, sculptured volcanic rocks at Mojave National Preserve’s Hole in the Wall.

Hidden violence

Visitors to Mojave National Preserve are fascinated by the brightly colored, fantastically sculpted rocks at Hole in the Wall. Little do they know that these intricate forms hold the key to a devastating and violent episode in Mojave’s geological past.
About 18.5 million years ago, a powerful volcanic eruption blasted outward from the nearby Woods Mountains. Propelled by the force of rapidly rising and expanding gasses, a ground-hugging cloud of ash and rock fragments spread out at near super-sonic speeds across the countryside. Some of the rocks thrown out by the blast are 14-20 meters (60 feet) across - the largest ever documented!
Hot, suffocating ash buried every living thing in the path of the blast. An area of over 600 km2 was covered with ash and rock fragments so hot that they welded together after they reached the ground. The toasted and fossilized remains of birds, mammals, and plants lie entombed beneath the volcanic tuff that forms the colorful cliffs of Hole in the Wall.
Records of many more catastrophic volcanic blasts can be seen as you drive through the Preserve.

Dig deeper into Hole in the Wall’s violent past.

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This site is a cooperative project of the
US Geological Survey Western Earth Surface Processes Team
and the National Park Service.

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This page was last updated 3/24/99

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