Obsidian Dome

The road to the top of the dome

Mammoth Mountain is as renowned for being part of a volcano as it is for its skiing. The Long Valley Caldera, a colossal volcano in the eastern Sierra Nevada region, is an area of extreme volcanism. Volcanoes have been erupting here since long before its last climactic eruption 750,000 years ago, and the last eruptions are as young as a few hundred years. This final eruption erupted approximately 600 cubic kilometers of material and resulted in the subsidence of the crust between 2 and 3 kilometers to create the current caldera. This particular feature, Obsidian Done, is related to the volcanics here but is from a different system: the Mono-Inyo crater chain. 

Fossil Falls

Fossil Falls with the Sierra Nevada backdrop.

Ancient Owens Valley had a bustling population center here, at Fossil Falls. Fossil Falls is a series of cascades along the ancient Owens river, when it was fed by a series of melting glaciers from the Sierras and by a much larger Owens Lake. At this point along the river, a series of basaltic lava flows impounded the valley between 400 and 10 thousand years ago. During the most recent period of glacial Owens River, the waterfall poured over the lava flows and slowly eroded upstream, and an increase in eruptions from nearby Red Hill may have spurred pothole formations in the upper falls. These potholes, formed when rocks or sand get caught in a hole and spin around in a vortex that gradually bores a hole in the rock, are what Fossil Falls are best known for today. Some of them form chimneys over twenty feet deep that open up at the bottom, and many interconnect. The upper falls today is a convoluted maze of these potholes. When the river flowed here, the noise would have been cacophonous and the mist blinding.