By: Holly Fischer
I’ve driven between Las Vegas to the Amargosa River Basin countless times since becoming the Restoration Program Manager at the Amargosa Conservancy. There are many views on my drives that are beautiful, but there is one site that really intrigues me every time I drive past. Usually, I think to myself “oh I need to stop and look at that,” but never do.
Finally, I stopped.
When driving from Pahrump, Nevada to Shoshone, California, along the Charles Brown Highway (CA 178), the drive is relatively open with wide landscapes and mountains in the far distance, until you pass Chicago Valley and begin to cross between two mountains. You come around a bend and as the view opens and you see the town of Shoshone in the distance, you notice a large black stripe cutting through the mountain to your right.
The first time I drove past this feature, my geology-fueled brain went to volcanics and cross-cutting relationships between the layers. While this formation is volcanic in nature, my original thoughts were far from the truth.
The stripe you see is a Vitrophyre, a black band of volcanic glass. Around 10 million years ago, a pyroclastic flow from a nearby volcano travelled across this region. The outer sections of the flow, exposed to air on top and losing heat from the contact with the ground beneath it, cooled at a faster rate than the center of the flow. This allowed for the outer layers to have smaller grains and air bubbles, forming a welded tuff–a rhyolitic ignimbrite. The center cooled at a much slower rate with higher temperatures, creating the black volcanic glass we see here.
The tilt of this band is another question that filled my mind. I personally love large-scale geology and figuring out the processes that created the structure we see. My brain will analyze tilted and cut-through layers and re-arrange them, travelling back in time to understand how the final result was created. Utilizing geology principles like Original Horizonality, Superposition and Cross-Cutting Relationships, helps us to re-engineer the deposition of the layers, showcasing the history of the land.
However, the Charles Brown Outcrop’s vitrophyre, while tilted, does not showcase these aforementioned geological principles. This outcrop displays a paleo-slope: an ancient slope, the slope at the time of deposition. The pyroclastic flow that formed this outcrop travelled across an already tilted slope and preserved the angle of the slope.
While reading the various papers, blogs and other posts about this outcrop, I found myself wondering how this feature got its name. The Charles Brown Outcrop is named after the Charles Brown Highway, but who is Charles Brown? If you head to Shoshone and talk to locals or visit their museum there is one name that comes up constantly: the Brown family.
Charles “Charlie” Brown was a business man turned community leader. He arrived in the Death Valley region in the early 1900s and married Stella Fairbanks in 1910, putting down roots in Shoshone. Brown eventually ran for state office and became a state legislator who advocated for the development of roads in the area. His contributions to the area lead to the stretch of California State Route 178, from State Route 127 in Shoshone northeast to the Nevada State line, to be designated the Charles Brown Highway.
So next time you are driving toward Shoshone or Death Valley, stop at the Charles Brown Outcrop! It has a great pull-off spot and a wonderful overlook of the area.