Situated on the summit and south flank of Deer Mountain, the Inyo Craters are a remarkable cluster of three phreatic explosion craters aligned in a north-south direction. Deer Mountain is an approximately 115,000-year-old rhyolite dome located in the western moat of the Long Valley Caldera. These craters, formed in the mid-14th century, emerged shortly after Deadman Creek, Obsidian, and Glass Creek domes erupted in 1350 CE. The two southernmost craters boast an average diameter of around 660 feet and reach depths of about 200 feet, each featuring a small lake within. On the other hand, the summit crater of Deer Mountain is smaller, irregularly shaped, breached on its southern side, and currently dry. Despite variations in shape and vegetation, all three craters originated almost simultaneously, likely within a few hours or days. They erupted successively from north to south, with deposits from the summit crater underlying those of the north crater, which, in turn, underlie the darkest deposits of the south crater. The surrounding terrain bears the marks of numerous north-trending faults and fissures, likely due to uplift and expansion above an intruding magma dike. As the rising magma encountered water, explosive interactions transformed the water into steam. This process led to the formation of vents through the overlying andesitic rocks, giving rise to the Inyo explosion craters and the accompanying phreatic deposits. Interestingly, no fresh rhyolite magma reached the surface during these eruptions, adding to the unique geological character of the Inyo Craters.
