The Rio Grande rift is intersected in northern New Mexico by the NE-SW trending Jemez Lineament which extends well into Arizona. The lineament is defined by aligned volcanic fields and several calderas in the area, including the Valles Caldera National Preserve in the Jemez Mountains. The Jemez Lineament is thought to be a hydrous subduction zone scar, separating Precambrian basement rock of the Yavapai-Mazatzal transition zone from the Mazaztl Province proper. Also on the Colorado Plateau but further north lies the San Juan volcanic field in the San Juan Mountains of Colorado.