Sugarloaf is a rhyolite dome located just below the

San Francisco Peaks The San Francisco Peaks (Navajo: , , Hopi: ''Nuva'tukya'ovi'', Western Apache: ''Dził Tso'', Keres: ''Tsii Bina'', Southern Paiute: ''Nuvaxatuh'', Havasupai-Hualapai: ''Hvehasahpatch''/''Huassapatch''/''Wik'hanbaja'', Yavapai: ''Wi:mun Kwa'', ...

Flagstaff, Arizona Flagstaff ( ), known locally as Flag, is the county seat of Coconino County, Arizona, in the southwestern United States. As of the 2020 United States census, the city's population was 76,831. Flagstaff is the principal city of the Coconino Cou ...

. It formed after a

lateral eruption A lateral eruption or lateral blast is a volcanic eruption which is directed laterally from a volcano rather than upwards from the summit. Lateral eruptions are caused by the outward expansion of flanks due to rising magma. Breaking occurs at the ...

of the mountain, which occurred in a similar fashion to the

1980 eruption of Mount St. Helens In March 1980, a series of volcanic explosions and pyroclastic flows began at Mount St. Helens in Skamania County, Washington, United States. A series of Phreatic eruption, phreatic blasts occurred from the summit and escalated until a major ...

References

{{Reflist Mountains of Arizona Cinder cones of the United States Volcanoes of Arizona Flagstaff, Arizona Mountains of Coconino County, Arizona Two-thousanders of the United States Lava domes of the United States