Over 30 years ago, I took a steep hike from the banks of Southeastern Utah's San Juan River, to the top of a small volcanic crater. Here, 25-30 million years ago, super-heated water erupted at near hypersonic speed through a fissure deep within the earth, dragging rock debris upward and venting into the atmosphere. This geologic phenomenon is known as a diatreme.

Often, diatremes leave shafts that become hardened from the heat of the explosion, forming blackened spires such as nearby Shiprock in northwestern New Mexico. The Mule Ear Diatreme and its surrounding terrain have become so eroded that all that remains today is a shallow, fifty-foot diameter crater. Standing on its edge, I was surrounded by a field of rock fragments containing serpentine, garnets, and other crystals brought to the surface. Above and behind me, a 400-foot cliff of heat-hardened sandstone resembled its namesake: Mule Ear. Below, a broken brown-yellow rock shelf at the foot of the photograph had also been partially metamorphosed by the eruption's searing temperature.

Before me lay Lime Ridge, the ground eroded into fluted patterns by seasonal monsoons that cut through softer parts of the folded sandstone layers. Dotted by black brush on the tilted terrain and low sagebrush along its ridges and floors, 12,000 years ago, the climate was cooler and wetter, and the area was covered with conifer forests. Today, artifacts are scattered on these desert slopes. Spear tips and pieces of utensils, left behind from mammoth and bison hunts, have been discovered at a place once frequented by seasonally migrating hunter-gatherers.

Location research and commentary by James Baker.