Red Mountain is a volcanic cinder cone located in the

Coconino National Forest The Coconino National Forest is a 1.856-million acre (751,000 ha) United States National Forest located in northern Arizona in the vicinity of Flagstaff. Originally established in 1898 as the "San Francisco Mountains National Forest Reserve", th ...

of northern

Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...

, United States, 25 miles northwest of Flagstaff. It rises above the surroundings terrain and is shaped like the letter "U", with its opening towards the west. Geological Survey (

USGS The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, a ...

) and Northern Arizona University scientists suggest that Red Mountain was formed in eruptions nearly 740,000 years ago.

Geology

Red Mountain is a cinder cone in the

San Francisco volcanic field The San Francisco volcanic field is an area of volcanoes in northern Arizona, north of Flagstaff, US. The field covers 1,800 square miles (4,700 km²) of the southern boundary of the Colorado Plateau. The field contains 600 volcanoes rang ...

that is noted for its red color and U shape when viewed from above. The cone was erupted from a

volcanic vent A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates are ...

that now sits under the intact material that comprises the U shape of the mountain. Overall, the pattern of volcanism is not symmetric about the vent suggesting either that

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...

was erupted under conditions of a strong west to east wind or late stage lava flows emanating from the vent may have rafted material out to the east. The origin of the large amphitheater that sits within the U is unclear. Predominate theories suggest it resulted from a steam eruption. This steam eruption may have resulted from the superheating of rainfall on cinders that were still hot. The well cemented cinders that make up the walls of the U may also result from interaction with rainwater. Chemical reactions driven by heated rainwater would also explain the variations in the color of the cinders. The trail into the amphitheater contains small black grains that are often mistaken for Apache's tears ( obsidian). These grains are actually large crystals of pyroxene and amphibole.

References

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External links

Red Mountain trail guide
at

Cinder cones of the United States Landforms of Coconino County, Arizona Volcanoes of Arizona Dormant volcanoes