At the end of a dusty dirt road off California’s Highway 395 lies a mountain made of volcanic glass, also known as obsidian. Located just north of Mammoth Lakes, the dome is part of the Mono-Inyo volcanic chain.
Obsidian Dome was formed about 600 years ago during a phreatic blast, when magma hits water on its way to the surface. The heat turns the water into steam and the magma cools into rock. The blast led to the creation of a gigantic pile of obsidian boulders. The dome itself is less one giant rock than a huge pile of those boulders, most of them with beautiful striations of different consistencies of obsidian and pumice.
When obsidian flakes, it can form a sharp edge only a single molecule thick. The naturally occurring sharp fragments may have led to the use of obsidian for weapons and cutting tools. Local native groups used and traded it across a network that spanned hundreds of miles.
The dome is difficult to climb up very far, but there is a nice trail around the base of the dome, where you can admire the mountain and the surrounding forest. There’s a parking lot at the base, and the road is easily traversed by standard passenger cars.
Know Before You Go
Turn onto Obsidian Dome road off of Highway 395 (at some points it is called Glass Flow Rd). It's a short, 1.2 mile drive to the base; follow signs for Obsidian Dome. There is a parking lot at the base of the mountain. The area is part of the Inyo National Forest.