The specifics of the geology of the canyon are not well understood, except that it is the result of erosion by the Yellowstone River, not by glaciation. After the Yellowstone Caldera eruption of about 600,000 years ago, the area was covered by a series of lava flows. The area was also faulted by the doming action of the caldera before the eruption. The site of the present canyon, as well as any previous canyons, was probably the result of this uplift and related faulting, which allowed erosion to proceed at an accelerated rate. The area was also covered by the glaciers that formed during several ice ages. Glacial deposits probably filled the canyon at one time, but have since been eroded away, leaving little or no evidence of their presence.