The area is presently quiescent, but significant geological activity has occurred in the area over the last 20 million years. The Sangre de Cristo Range lies to the east of the north portion of the rift. The Valles Caldera National Preserve is a huge caldera by the Jemez river, nearby. The Colorado Plateau, to the west, includes the San Juan Volcanic Field and the San Juan Mountains. The Rio Grande river follows the course of the rift from southern Colorado to El Paso; it starts a southeast course out of New Mexico at the pass between the Franklin mountains and the Sierra Juarez, which ends at the Gulf of Mexico.
