  Sunset
Crater Volcano was originally named Sunset Mountain by that intrepid explorer
of the Colorado River, John Wesley Powell, for the bright sunset reds
and yellows of its summit. Of all the cinder
cones of the San Francisco volcanic field, Sunset Crater Volcano is
one of the most colorful and pristine.
  Most of the rock you see at Sunset Crater Volcano National Monument
is dark gray to black basalt.
Basalt is rich in iron and magnesium-bearing minerals, which give it its
dark color. While the base of Sunset Crater Volcano is mantled with dark
gray cinders,
the summit of the cinder cone is a striking rusty red. Although you might
speculate that the rocks at the top are of a different type, they are
not! What makes these basalt cinders red? |
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 Searing basalt lava was not the only material
to erupt from Sunset Crater Volcano! The cinder cone also belched forth
hot gasses. The cinders on the rim of the cinder cone were bathed in
these vapors and chemically reacted with them to form iron oxide (rust),
sulfur compounds, and gypsum. The resulting red, yellow, purple, and
green-colored basalt cinders decorate Sunset Crater Volcano’s summit.
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In
addition to these materials, strange pieces of rock, not created
by this eruption, were also erupted. These pieces of rock can be
seen within the lava flows and are called xenoliths, xeno
meaning strange and lith referring to rock. These pieces
of rock were ripped up from the sides of the eruption conduit. This
xenolith is a piece of Kaibab limestone, a rock unit found as far
as 1 kilometer under the present ground surface. |
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Many visitors to the National Monument notice splotches
of greens and yellows on the basalt surface. These splotches
are actually lichen. Continue on to the next
stop to learn about these early colonizers of lava flows.
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