Obsidian Dome, California is one of several Recent rhyolite domes that erupted north of Long Valley caldera. The photograph shows the steep northern front of the dome and the topographic map shows its semicircular outline. This dome is almost entirely obsidian (volcanic glass). Volcanic domes have diameters from a small as a fraction of a kilometer to as much as 5 to 10 km.

Carmichael (1967) inferred the oxygen pressures in several salic volcanic magma chambers from the compositions of the iron titanium oxides (magnetite and ilmenite). Some of his samples came from the Mono and Inyo Craters of which Obsidian Dome is one. He found that biotite and pyroxene crystallized at higher oxygen pressures than olivine.