Geology in the Parks home NPS home USGS home National Park Service/US Geological Survey banner
Mojave title bar
Click to see map showing field trip stops Hole in the Wall title
Colorful, sculptured volcanic rocks at Hole in the Wall

The last gasp

spacer image The final phase of the volcanic activity that created Hole in the Wall lasted from 17.7 to 17.6 million years ago. Even though this eruptive phase was much more tranquil than the preceding one, its fiery volcanic products once again layed waste to the region.
spacer image Rhyolite lava flows and thick deposits of solid volcanic debris (tephra) were extruded from the caldera soon after the last phase ended. Rhyolite lava flowed out of vents within the caldera, eventually overflowing the rim. Slow-moving lava lobes spread out out over 3 kilometers beyond the caldera.
spacer image During Hole in the Wall’s last volcanic gasp, sticky, viscous, masses of rhyolite lava oozed up from the magma chamber below, bowing up the caldera floor. Some of the viscous lava found its way through vents to the surface, where it squeezed up, toothpaste-like, to form bulbous plugs and domes in and near the caldera rim.
Map showing the original area coverd by the final stage of Hole in the Wall volcanic activity
This map shows the phase of volcanic activity at Hole in the Wall. While most of the volcanic tuff you see at this field trip stop was produced by the previous stage of volcanism, right across the road from the National Park Service visitor center you can see the remains of this final eruptive episode. The bright red area shows the original extent of rock produced by the final phase of volcanism at Hole in the Wall. The brown-colored areas shown on the map represent places where rock from this stage remains. Click here to see enlargement. Adapted from McCurry, 1995.
spacer image Finally, magma that fed Hole in the Wall’s eruptions cooled and solidified, plugging its plumbing for good.
spacer image Although Hole in the Wall was silenced, just a few million years later a different kind of lava began to make its mark on the Mojave National Preserve landscape at Cinder Cones National Natural Landmark...

On to Cinder Cones

Back to field trip menu



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.
| Mojave geology home | Mojave National Preserve home |
| Mojave geology field trip | Education resources | Geologist’s page |
Mojave horizontal bar
| USGS Geology in the Parks home | NPS Park Geology Tour home |

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

Please share your comments and suggestions with us!
parkgeology@den.nps.gov
http://www.nature.nps.gov/grd/usgsnps/mojave/hole1.html
This page was last updated 3/24/99