Sunset Crater is a volcanic cinder cone located north of Flagstaff in U.S. State of Arizona. The crater is within the Sunset Crater Volcano National Monument.
Sunset Crater is the youngest in a string of volcanoes (the San Francisco volcanic field) that is related to the nearby San Francisco Peaks.
The eruptions forming the 340-meter-high cone (1,120 ft) were initially considered from tree-ring dating to have begun between the growing seasons of 1064–1065 AD; however, more recent paleomagnetic evidence places the onset of the eruption sometime between about 1080 and 1150 AD. The largest vent of the eruption, Sunset Crater itself, was the source of the Bonito and Kana-a lava flows that extended about 2.5 kilometers (1.6 mi) NW and 9.6 kilometers (6 mi) NE, respectively. Additional vents along a 10-kilometer-long fissure (6.2 mi) extending SE produced small spatter ramparts and a 6.4-kilometer-long lava flow (4 mi) to the east. The Sunset Crater eruption produced a blanket of ash and lapilli covering an area of more than 2,100 square kilometers (810 sq mi) and forced the abandonment of settlements of the indigenous Sinagua Indians. The volcano has partially revegetated, with pines and wildflowers. The crater has given its name to the Sunset Crater Beardtongue (Penstemon clutei).
Damage from hikers forced the National Park Service to close a trail leading to the crater, but a short trail at the base remains.
The hiking trail below the summit skirts the substantial Bonito Lava Flow. This hardened lava is black and appears fresh as it has devastated the forest in its path. The lava flow also created an ice cave or tube that is now closed to the public after a partial collapse.