File:Rhyolitic pumice (El Cajete Pumice, Upper Pleistocene, 55-60 ka; Rt. 4 roadcut, southern margin of Valles Caldera, northern New Mexico, USA).jpg

English: Rhyolitic pumice from the Pleistocene of New Mexico, USA. (specimen at left is 3.4 cm from top to bottom)

Northern New Mexico’s Valles Caldera (a.k.a. Jemez Caldera) formed 1.1 million years ago, during the Early Pleistocene, after significant explosive ash & pyroclastic eruptions. The large, ~empty magma chamber under the volcano collapsed, resulting in a very large surface depression. The Valles Caldera is just the latest caldera to form in this area. Volcanic activity at this locality has been ongoing since the Late Miocene, and has continued since the most recent caldera collapse. The samples shown above were produced by a post-caldera volcanic event during the Late Pleistocene.

The pumice samples shown above are from the El Cajete Pumice. Material from this unit represents air-fall pumice deposits and pyroclastic surge deposits. The El Cajete Pumice was deposited during the Late Pleistocene, at about 55 to 60 thousand years ago, from a volcanic center in the Valles Caldera.

Stratigraphy: El Cajete Pumice, Upper Pleistocene, 55-60 ka

Locality: roadcut along the northern side of Rt. 4, ~3.9 miles east of the Three Rhyolites Roadcut, near the southern margin of the Valles Caldera, northern New Mexico, USA (35° 48’ 55.94” North latitude, 106° 32’ 40.64” West longitude)