Obsidian Dome (Eastern Sierra, CA) 07-Aug-2022

The area between June Lake and Mammoth Lakes has been volcanically active for a long, long time (and still is). Just 672 years ago (in 1350 CE to be exact), screaming hot magma intruded into much colder groundwater to set off phreatic (steam) explosions just south of today’s June Lake.

These blasts formed three domes: Obsidian, Glass Creek, and Deadman Creek. Obsidian Dome is the best known (it has its own sign along Highway 395) and most accessible of these. This dome is neither a volcanic cone nor one giant rock but rather a huge pile of obsidian boulders, most of which sport beautiful striations of different consistencies of obsidian and pumice. 

So, to add some variety to our hiking near June Lake, we decided to explore Obsidian Dome. There are dirt roads that run completely around the dome and it’s these roads that are recommended as a hike. We started hiking counter-clockwise around the dome on Forest Road (FR) 2S10 and then FR 2S11- both of which are also used by motorcycles and 4x4s – but soon decided to divert from FR 2S11 to see the top of the dome – which is actually more of a flat, lumpy pancake shape than that of a smoothly curved dome.

Starting out on FR 2S10
A tumble of obsidian boulders
Striations that look like the spot on Jupiter
More striations
Organic striations

After a short walk, we came to a spur road (FR 2S79A) that was carved up the slope of the dome. We followed it up to where there had been an active pumice mine at some point in the past. All was quiet there today.

Going up FR 2S79A
Wandering around the old pumice mine

Wayne then noticed that there was a road that went south across the dome – presumably back to FR 2S10. It showed on his GPS but not of our maps, so, in the spirit of tough and stupid, we decided to see where it went.

What caught our attention as we walked along were the few, solitary pine trees that were thriving in this vast expanse of arid boulders. Somehow these sturdy conifers have found enough loose dirt and moisture to keep themselves alive. 😊

Following the old, poorly mapped road (note pine tree)
Peak 10009 over the boulder pile that is Obsidian Dome
A lone pine grows in a cracked boulder
Starting our descent
The old road descends from the dome

After less than a mile (1.6 km) on the old road, we were back on FR 2S11, which we followed to an unnumbered old road near Highway 395.

On FR 2S11 again
Layers of obsidian and rock
Still on FR 2S11

We could see and hear cars on Highway 395 when we reached the junction of FR 2S11 and an old 4×4 road going west toward the dome. We went west until it faded away near the dome, then did a little uphill cross-country to connect with yet another old road that took us back into the forest and on to where we’d parked.

We leave FR 2S11 to follow an old 4×4 track toward the dome
The beige wall of the dome comes into view
Climbing out of the valley toward another old road above
A last look at the flat dome
Back through the forest to where we’d parked on FR 2S10

Our wandering route came to 4.8 miles (7.8 km) with 600 feet (183 m) of elevation gain. This was a bit shorter hike than if we’d stayed on the roads around the dome but more interesting – particularly that walk over the top of the dome. 😁

The only thing we missed was a stop at Grass Creek, which we could hear bubbling away below us as we walked along FR 2S11. Still, it was a good walk in great weather around a pretty fascinating piece of the local geology, which (on a geologic time scale) had appeared just yesterday. 😉

Our route over and around Obsidian Dome

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