Sunset Crater

December 04, 2002


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

Located just north of Flagstaff AZ, Sunset Crater National Monument is one of the best-preserved volcanic cinder cones in the United States. Of the 800 volcanoes in the San Francisco Peaks area, Sunset Crater is the most recent location of volcanic activity in this volcanic field of north-central Arizona. The primary eruptive event that formed this cone was likely observed by the Sinagua or Anasazi native Americans in the year 1064. These people are believed to have moved to the nearby areas of Wupatki and Walnut Canyon.

Frequently steep-sided, cinder cones are formed when volcanic tephra builds up around an active vent. The cinders, also known as scoria, are typically basaltic lava with trapped bubbles of volcanic gasses. Volcanic cinders are usually black in color due to high iron content. The cinders near the top of Sunset Crater were exposed to corrosive volcanic gasses that accelerated the oxidation of the iron. While exploring the southwest, Maj. John Wesley Powell observed that the red and orange oxidized cinders resembled the colors of a western sunset and gave the mountain its name.

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