Six Million Years of Volcanoes
Near Williams, Arizona
Williams sits inside one of the most volcanically active landscapes in the continental United States, though you would not necessarily know it from the ponderosa pines and the quiet streets. The San Francisco Volcanic Field covers roughly eighteen hundred square miles of the Colorado Plateau around Williams and Flagstaff, and geologists have identified approximately six hundred cinder cones, lava flows, and related features within it, formed over the past six million years. The mountain that gives Williams its name, Bill Williams Mountain, is itself an eroded volcanic remnant.
The San Francisco Peaks north of Flagstaff, reaching twelve thousand six hundred thirty-three feet, are the remains of a stratovolcano and represent the highest point in Arizona. The most recent eruption in the field occurred at Sunset Crater, a cinder cone about fifteen miles north of Flagstaff, which erupted around ten eighty-five, in the period historians know as the Ancestral Puebloan era. The eruption of Sunset Crater buried nearby Sinagua settlements under ash and lava and triggered migrations of people across the plateau.
The great lava flow from that eruption, called the Bonito Lava Flow, can be visited today at Sunset Crater Volcano National Monument. Geologists consider the San Francisco Volcanic Field still active. The last eruption was less than a thousand years ago, which is, in geological terms, extremely recent.
The peaceful forest around Williams sits on a landscape that has been rearranged repeatedly by fire from below, and may be rearranged again.
