Charlie Brown Outcrop
August 03, 2007
Known informally as the Charlie Brown Outcrop, this distinctive road-cut is a popular stop for geologists heading to Death Valley, California. Located along the Charlie Brown Highway (CA 178), northeast of the small town of Shoshone, this road-cut exposes the spectacular vitrophyre (black band of volcanic glass) within the Miocene Resting Spring Pass Tuff. Note the people standing at left for scale.
This tuff formed during a pyroclastic flow that erupted from an unknown nearby volcano. The hot, gaseous flow deposited ash and rock fragments along the ancient irregular topography of the region. This thick deposit of ash cooled relatively quickly at the top and bottom, but the ash in the middle was extremely hot, allowing it to weld together into the present vitrophyre and densely welded tuffs. The evidence for this irregular cooling is in the gradation from vitrophyre in the center, to densely welded tuff surrounding the vitrophyre, to welded tuff on the top and bottom of the outcrop (this gradation can be identified in the photo by the color change from dark to light). Flattened pumice and vesicles are all aligned at a shallower angle than the vitrophyre, indicating that the ash flow was deposited on a paleo-slope. Photo taken on January 30, 2003. The interesting name of this highway isn't a tribute to the hapless but lovable cartoon character but rather to a state legislator who successfully lobbied to have this road added to the state highway system.