The Taos Plateau volcanic field in northern New Mexico is the largest volcanic field in the Rio Grande Rift, covering about 7,000 square kilometers and preserving a vast outpouring of lava. Its sheet flows, cinder cones, and shield volcanoes formed mostly between about 1.8 and 4 million years ago, with some older vents around 22 million years old. Near the meeting of the Jemez Lineament and the Rio Grande Rift, mantle upwelling helped generate lavas ranging from tholeiitic basalt to rhyolite. The Rio Grande Gorge dramatically exposes these layered volcanic rocks, and rhyolite at No Agua supplies economically important perlite.