Approximately 740000 years ago,a volcanic eruption blasted out the side of a cinder cone volcano in what is now northern Arizona. The volcano is fraction of the San Francisco Volcanic Field, an 1800-square-mile area that is crowded with evidence of volcanic activity as recent as 1000 years ago.
There are over 600 volcanoes in the area between Flagstaff, or Arizona,and the Grand Canyon. What makes Red Mountain unique is that its eruption blew out the side of the mountain, leaving it as an odd U-shape and presenting an impressive amphitheater of otherworldly pillars of stone and volcanic materials.
Passed by unnoticed by most tourists en route to the Grand Canyon, and the trail up to the core of Red Mountain gently climbs up 300 feet in elevation and presents hikers with views of the transition in ecosystems from pinyon and juniper desert scrubland to high-elevation ponderosa pine forests.
Source: atlasobscura.com