Red Mountain is a volcanic

cinder cone A cinder cone or scoria cone is a steep, volcanic cone, conical landform of loose pyroclastic rock, pyroclastic fragments, such as volcanic ash, clinkers, or scoria that has been built around a volcanic vent. The pyroclastic fragments are forme ...

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, with elevations ranging from 2,600 feet to the highest point in Arizona at 12,633 feet (H ...

of northern

Arizona Arizona is a U.S. state, state in the Southwestern United States, Southwestern region of the United States, sharing the Four Corners region of the western United States with Colorado, New Mexico, and Utah. It also borders Nevada to the nort ...

, 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), founded as the Geological Survey, is an government agency, agency of the United States Department of the Interior, U.S. Department of the Interior whose work spans the disciplines of biology, geograp ...

) and

Northern Arizona University Northern Arizona University (NAU) is a public research university based in Flagstaff, Arizona, United States. Founded in 1899, it was the third and final university established in the Arizona Territory. It is one of the three universities gove ...

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 rangi ...

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 commonly defined as a vent or fissure 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 fo ...

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 Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

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 In thermodynamics, superheating (sometimes referred to as boiling retardation, or boiling delay) is the phenomenon in which a liquid is heated to a temperature higher than its boiling point, without boiling. This is a so-called ''metastable state ...

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 An amphitheatre ( U.S. English: amphitheater) is an open-air venue used for entertainment, performances, and sports. The term derives from the ancient Greek ('), from ('), meaning "on both sides" or "around" and ('), meaning "place for vie ...

contains small black grains that are often mistaken for Apache's tears (

obsidian Obsidian ( ) is a naturally occurring volcanic glass formed when lava extrusive rock, extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock. Produced from felsic lava, obsidian is rich in the lighter element ...

). These grains are actually large crystals of

pyroxene The pyroxenes (commonly abbreviated Px) are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents ions of calcium (Ca), sodium (Na), iron ( ...

and

amphibole Amphibole ( ) is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is ...

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 Pleistocene cinder cones