Located just north of Flagstaff, Arizona, the San Francisco volcanic field comprises an area of 1,800 sq miles and contains around 600 volcanoes. These volcanoes range in age from 6 million years old to less than 1,000 years old. Given their location on the Colorado Plateau, many volcanoes have experienced little erosion (like SP Crater seen on the left in the top photo) and younger cones maintain near-original morphology.
The majority of volcanoes in the field are basalt cinder cones, but there are also a number of rhyolite and dacite lava domes. Volcanic activity was likely initiated by a mantle hot spot, with volcanic activity migrating eastward over time.
The most well-known volcano in the San Francisco volcanic field is Sunset Crater. Sunset Crater is one of the youngest volcanoes in the United States, last erupting sometime between 1080 and 1150 CE. The indigenous Sinagua people inhabited the area during this time and were forced to abandon their pueblo for several decades following the eruption.
The San Francisco volcanic field has not experienced an eruption since this time, but geologists do not rule out the possibility of future activity. A future eruption would likely be on the eastern portion of the field (given the eastward migration of activity over time), but hazards would be lessened due to its relatively remote location.
All images by author
Emily Zawacki, Ph.D. 