Posted by: Brad Nixon | September 21, 2018

On the Glass Mountain: Obsidian Dome

As a kid, I was enthralled by legends of Medieval knights, giants and ogres.

A Polish story tells of a princess put under enchantment and imprisoned in a castle atop a mountain of sheer glass — the Glasberg. A tree bearing golden apples grew beside the castle. The knight who could scale the mountain and pluck a golden apple would break the enchantment and win the princess.

Countless knights-errant endured risk and privation crossing a vast plain to the mountain and attempted to ride up it. All failed, sliding to their doom, and the skeletons of armor-clad knights and their steeds littered the ground at the base of the Glasberg.

Eventually, someone succeeded — or it wouldn’t be much of a story. But that iconic setting is what caught my attention: a mountain of diamond-hard glass!

A Childhood of Deprivation

I grew up in a part of the world sorely lacking in knights-errant, ogres or mountains of any kind, bereft as well of oceans, yawning canyons, arid deserts, or one single lava-spewing volcano. We had a vast plain, all right — bulldozed by glaciers 12,000 years earlier, stretching from our border with Pennsylvania to somewhere out in Illinois or Iowa. But it was limited in its provision of risk and privation, covered as it was by corn, soybeans and dairy farms.

Go West!

After several decades, I wised up and headed southwest. The American west, finally, had it all: soaring mountains, the planet’s biggest ocean, immense canyons and deserts, not to mention any number of volcanoes that might erupt at any minute. Cool!


Mom Nature has been at work out here creating an inexhaustible supply of lava flows, craters, cones and other great-looking volcanic features that meet or exceed the requirements of the doofiest prepubescent imagination. Years ago, I visited one of the best: Devil’s Postpile National Monument, in the Sierra Nevada of California.

Devils Postpile Marcy Vincent 004 (576x640)

To the Glass Mountain: Obsidian Dome.

Preparing for a recent trip to the Eastern Sierra, I discovered a startling fact: There is a genuine glass mountain. It’s not diamond-clear and sheer-faced as I pictured that Glasberg, but it’s glass — obsidian: volcanic glass.

Obsidian Dome Brad Nixon 1285 680

Obsidian Dome is a mile-long, mile-wide mound of obsidian piled up by a volcanic eruption in the year 1350 C.E. It’s in a volcanic caldera that includes some smaller obsidian deposits, craters and other features kids in Ohio, Indiana and Illinois can’t reach on even their longest bike ride.

Obsidian Dome Brad Nixon 1288 680

Reaching the site at the end of a long day, we hadn’t left time to drive to the trailhead and make the hike that circles around to the top of the dome. There, Obsidian Dome is 400 feet high. From the spot I reached, it was still an immense mass of glassy rock over 100 feet tall.


Because of the specific forces that created Obsidian Dome, the lava solidified full of trapped gas bubbles. The scientific term is vesicles. They keep this obsidian from being the intensely black substance prized by ancient craftspeople for making tools and weapons with razor-sharp edges. The vesicles show the “banding” that resulted as flowing lava cooled and hardened.

Obsidian Dome Brad Nixon 1301 680

To the touch, it has exactly the cold, hard smoothness of glass.

There I stood, on a mountain of glass — my very own Glasberg, at last.

BN on Obsidian M Vincent 3902 680

Some Eastern Sierra Geology

Much of the Owens Valley has volcanic features. As you drive along U.S. Route 395, you’ll see rugged, black lava near the roadside, a small portion of extensive prehistoric flows, and evidence of volcanic evidence continues as you travel. There are a number of large craters and cones visible throughout the valley. Here’s Red Hill, a cinder cone near Coso Junction to the East of 395.

Coso Cone M Vincent 1639 680

It’s one of 38 dome and flow features in the Coso Volcanic Field. The field includes large obsidian deposits that were mined by natives from 3,000 to 1,000 years ago to make knives, projectile points, etc. That’s the jet-black obsidian, not like the banded glass at Obsidian Dome.

Southeast of Obsidian Dome, down in the valley, is a large area of geothermal activity including hot springs and geysers. The center is near Whitmore Springs, east of Route 395 (map below, lower right).

The volcanic features of the Eastern Sierra are far too many for me to list, and there’s a lot to explore.

Seeing Obsidian Dome

Obsidian Dome is relatively easy to reach on U.S. Route 395, 310 miles north of Los Angeles. Five miles north of Mammoth Scenic Loop Road, just after you top Deadman Summit (8,036 feet, and, no, I’m not making that up) Obsidian Dome Road crosses the highway. Turn left with caution. From the north, the turn’s about 3 miles south of June Lake Junction.

Obsidian Dome Map Google

The road is graded gravel, so conditions vary by season and maintenance. Most conventional vehicles will manage it, but don’t take the Lamborghini.

Obsidian Dome Rd M Vincent 3910 680

We stopped short of the trailhead, which is 2.5 miles from 395. I encourage you to go the full way there for your hike, because the relatively easy one mile trail (according to reports) offers you the opportunity to get on top of the dome and see more of the feature, overall.

There are campgrounds nearby. You’re on the lower edge of the Headwaters Wilderness, and it’s gorgeous country, so take time to enjoy.

Safety Caveats

The top of Obsidian Dome is 8,556 feet (2,608 meters) above sea level. Pace yourself. The air can be fiercely dry, so TAKE MORE WATER THAN YOU THINK YOU NEED.

I strongly urge you to take the trail and not attempt to scale a slope, as I did. It’s not all rock; it’s a loose, perilous scree of pumice, sand, gravel and boulders. Climbing up is one thing. Descending that nearly 45-degree slope is harrowing, and I do not recommend it. Don’t spend your Sierra holiday in the Mammoth Hospital.

Your favorite volcanic feature, anywhere in the world? Leave a comment.

Licensable, high resolution versions of some photographs in this post, and select images from other Under Western Skies posts are available on Click on the linked photos, or CLICK HERE to view the Underawesternsky photo portfolio.

© Brad Nixon 2018. Some photographs © M. Vincent 2018, used by kind permission. Map © Google.


  1. When I saw the title I assumed you were talking about the Glass Mountain I had been to in Northern California near Medicine Lake. It was stunning to walk up to the edge of the shiny flow that towered above us. I hadn’t heard of the one in the Eastern Sierra.

    Liked by 1 person

    • Thank you. I, in turn, was unaware of Looking Glass Rock. Spectacular. Also volcanic in origin, but granite instead of obsidian. I’ve been through Asheville, but know little about the surrounding area. Thanks for dropping in and commenting. Happy trekking!

      Liked by 1 person

  2. Probably Lassen Volcanic in the Cascades – we were there about 20 years ago but the memories are still vivid !

    Liked by 1 person

    • Great. A place in California I have NOT visited, and would very much like to. Thanks!

      Liked by 1 person

  3. We’ve been to Obsidian Dome! A week’s vacation to that area in 2000 yielded our visit there as well as many of the other geological, geographic, historical and educational sites to see.

    Liked by 1 person

    • Obviously, I should’ve checked with you first. Thanks. I found it PREhistorical and educational.


  4. Very interesting picture of the glass mountain, It looks very crystallized. Or like they could form diamonds.


    • That’s beyond my knowledge of physics, but I love the shininess of obsidian.


  5. My favorite volcanic feature has to be the baked potato sized chunk of pure black obsidian I picked up in the 1950s while vacationing with my parents. We were west, I know that; I have a photo of my dad and I at the continental divide, and for years I had a collection of vintage Colorado post cards. So, I don’t know exactly where I picked it up, but it was stunningly beautiful.

    Liked by 1 person

    • Exactly. There’s nothing else like that black, glassy rock. Prized and traded across hundreds of miles of territory for thousands of years, and easy to see why.


  6. I’m not sure if this is the same place I went to about 1969 with my dad. I remember climbing a steep hill of black rock in tennis shoes and shorts. Sharp pieces of obsidian were everywhere. When we made it to the top we could see a huge flow that changed to flat flow at least a 1/4 mile ahead. It was super hot and my dad asked if I wanted to walk along the unstable ridge to flat ground and then down. Or just head back down the way we came. I chose the dangerous, slippery, knife sharp but quicker way down. I carried one large piece of glass sharp edged obsidian glass with me. I had dozens of cuts on my legs, arms and hands but it was well worth it. It disappeared into my childhood but I remember reading the some edges were as sharp as a scalpel. We traveled as a family of rockhound photographers over every dirt, gravel and side road my dad could find for years. Ice caves, strange tiny town museums and ghost towns. In un- air conditioned Ford station wagon, mom, dad and 3 kids. I loved it all. But by the time I hit high school most places were becoming too busy. Huge RVs with generators running all night. We stuck to a tent and the basics. What a gift we’ve both had.

    Liked by 1 person

    • Jan, you could have been at a number of obsidian deposits in the Sierras, but Obsidian Dome certainly matches your description. Yes, those pieces of volcanic glass are razor-sharp, and would slice you to pieces if you tripped and fell. And, yes, “camping” has evolved from families in tents to monster RVs, but we’re all out after the same thing: some look at the world.


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