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Geology of Mojave National Preserve: Hole in the Wall

Woods Mountains volcanic center sputters to life

Colorful, sculptured volcanic tuff at Hole in the Wall. Photo by M. Moreno, USGS
Layer upon layer of volcanic tuff and ash make up the mesas that surround Hole in the Wall.

The intriguing volcanic rock formations of Hole in the Wall are but a small remnant of the devastating volcanic episode that began in this region about 18.5 million years ago. Geologist Mike McCurry and others have pieced together evidence that tells the story of this exciting period in Mojave National Preserve.

The first hint of what was to come may have been earth-shaking tremors. As magma made its way from deep in the crust toward the surface it nudges the rock, creating earthquakes. The first magma to reach the surface exploded from several vents. Initial eruptions blanketed the region with up to 200 meters of volcanic flows and tuff. Great masses of sticky (viscous) rhyolite lava oozed up and solidified to form volcanic domes and flows (Hackberry Spring volcanics).

Map showing the original area coverd by the first stage of Hole in the Wall volcanic activity

This map shows the first stage of Hole in the Wall volcanic activity. The bright red area shows the original extent of the lava flows and domes that covered the area during this early stage of Hole in the Wall's volcanic history. Much of the rhyolite and tuff have since eroded away, but you can still see rocks of this event in the brown-colored areas shown on the map. Geologists call the entire area within the blast zone, including Hole in the Wall, the Woods Mountains volcanic center.

Although these thick volcanic deposits would have wiped out virtually all life beneath them, they had relatively mild effects compared with what was to come next...

Citation: McCurry, M., Lux, D. R., and Mickus, K. L., 1995. Neogene Structural Evolution of the Woods Mountains Volcanic Center, East Mojave National Scenic Area: San Bernadino County Museum Association Quarterly, v. 42, no. 3, p.75-80.

 

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