Pajarito Plateau

The Pajarito Plateau is a volcanic plateau in north central New Mexico, United States. The plateau, part of the Jemez Mountains, is bounded on the west by the Valles Caldera and on the east by the White Rock Canyon of the Rio Grande. The plateau is occupied by several notable entities, including Bandelier National Monument, the town of Los Alamos and its remote suburb White Rock, and Los Alamos National Laboratory. Elevations range from about 5600 feet (1700 meters) at the river to about 7800 feet (2300 meters) where the plateau merges into the mountain range.

The Pajarito Plateau is primarily composed of ignimbrite, a voluminous deposit of volcanic tuff laid down in an explosive eruption — in this case, a pair of eruptions from the nearby Valles Caldera. The two ignimbrite-forming eruptions occurred about 1.6 million and 1.2 million years ago and ejected about 300 cubic kilometers of rock each. The orange-pink rock formations constituting the resulting ignimbrites are known as the Otowi and Tshirege Members of the Bandelier tuff. The tuff lies on top of a volcanic field, exposed to the east, which used to be continuous with the Caja del Rio (now across the Rio Grande).

Erosion has created a maze of canyons up to 800 feet (240 meters) deep that dissect the plateau into mesas. Many of these mesas climb on the western side rather than descending on all sides, thus sometimes are referred to as potreros. Rock climbing is popular here with locals and visitors alike, and is done in the canyons on basalt cliffs that lie within and below the tuff, which itself is too soft to be climbed safely.

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