The Valles caldera lies within the Jemez volcanic field in New Mexico, at the northern end of the north-south trending Rio Grand rift. It is one of three resurgent calderas in the U.S. that erupted less than 1.5 million years ago; the other two being the Long Valley caldera of California and the Yellowstone caldera. The Valles caldera developed above the site of an earlier eruption associated with the collapse of the Toledo caldera. Both eruptions took place between 1.4 and 1.0 million years ago. Collapse of the Valles caldera produced a circular depression 23 km (14 miles) in diameter. Eruption and collapse of the Toledo caldera generated pyroclastic flows of the Lower Bandelier tuff, which can be seen along the canyon walls west of the caldera. Eruption and collapse of the Valles caldera generated the overlying pyroclastic flows of the Upper Bandelier tuff.

Valles Caldera -- The lowlands in this shaded elevation map of the Valles caldera are shown in blue and the highlands in orange. The circular depression and the resurgent dome of the caldera are evident in the center of the image. The prominent radial valleys along the outer rim of the caldera are incised into the ouflow facies of the Bandelier tuff. Copyright Calvin J. Hamilton.