San Francisco Peaks

Provided by: Tim Martin, Greensboro Day School
Summary authors & editors: Tim Martin

Rising 12,633 feet (3851 m)above sea level Humphrey’s Peak is the highest point in Arizona. It is also the highest point of the San Francisco volcano, one of over 800 identified volcanoes in the region. Standing tall over Flagstaff AZ, the San Francisco Peaks are a reminder of the intense geologic activity on the Colorado Plateau.

The San Francisco peaks were once believed to be a highly eroded stratovolcano. However, after the 1980 eruption of Mt. St. Helens, scientists re-evaluated many volcanic structures. Horseshoe shaped calderas similar to the one caused by the massive lateral blast on Mt. St. Helens have been found on volcanoes around the world. Most now believe that 400,000 years ago a similar lateral blast devastated the 16,000 ft (4877 m) San Francisco volcano.

This image was taken looking southwest from within Sunset Crater National Monument.

Related Links:

• USGS description of the San Francisco volcanic region
• From USGS virtual field trip of Sunset Crater
• CVO site on the Volcanoes of Northern AZ
• Topo of Humphreys Peak
• Mr. Martin’s Earth Science Page