This is one of my all time favorite places in Arizona. Fortunately, was able to explore before there was a formal trail/parking area, so most times had the place to myself. Eroded cinder cone that you can walk INTO! https://www.alltrails.com/trail/us/arizona/red-mountain https://www.fs.usda.gov/recarea/coconino/recarea/?recid=55160 Red Mountain, located in the Coconino National Forest of northern Arizona, 25 miles northwest of Flagstaff, is a volcanic cinder cone that rises 1,000 feet above the surrounding landscape. It is unusual in having the shape of a "U," and in lacking the symmetrical shape of most cinder cones. In addition, a large natural amphitheater cuts into the cone's northeast flank. Erosional pillars called "hoodoos" decorate the amphitheater, and many dark mineral crystals erode out of its walls. Studies by U.S. Geological Survey (USGS) and Northern Arizona University scientists suggest that Red Mountain formed in eruptions about 740,000 years ago.