San Francisco Mountain (12,633 feet),
near Flagstaff, Arizona. The
individual peaks are erosional remnants of a compound stratovolcano with lava
domes. Approximately 121 km of rhyolite, dacite, and andesite were erupted since
the birth of the volcano in late Pliocene times. Photograph by R. Forrest Hopson.
West-looking view into the inner basin of the San Francisco Peaks
stratovolcano. Sugarloaf Mountain, the small dome-shaped hill in the
foreground, is a rhyolite dome. Quarries at the base of the dome
(bottom-right) mine pumice. The quarries are in an older dome that
predates Sugarloaf Mountain by about 500,000 years. Photograph by
Wendell Duffield, U.S. Geological Survey.
San Francisco Mountain is the most prominent volcano in the San Francisco volcanic field. The volcanic field covers 1,935 square miles (5,000 square km) and includes more than 600 vents. Most of the vents erupted basalt lava flows. Basaltic scoria cones are scattered throughout the field. Intermediate to silica-rich eruptions formed a few localized volcanic centers.
Sources of Information
Holm, R.F., 1987, San Francisco Mountain: A late Cenozoic composite volcano in northern Arizona, in Beus, S.S., ed., Centennial Field Guide Volume 2 Rocky Mountain Section of the Geological Society of America, p. 389-392.
Wood, C.A., and Kienle, J., 1993, Volcanoes of North America: Cambridge University Press, New York, 354 p.
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