- Status: Mammoth Mountain is monitored by the Long Valley Observatory and is at a background level of activity.
- Volcanic History Overview: Mammoth Mountain, a trachydacitic lava-dome complex, lies on the SW topographic rim of Long Valley caldera. The 3369-m-high volcano lies west of the structural rim of the caldera and is considered to represent a magmatic system distinct from Long Valley caldera and the Inyo Craters (Hildreth, 2004). The latest magmatic eruptions at Mammoth Mountain took place about 57,000 years ago. Mammoth Mountain is surrounded by at least 35 mafic vents that are part of the same magmatic system and include Red Cones, two closely spaced basaltic cinder cones located SW of Mammoth Mountain and SE of Devils Postpile National Monument. The cones, whose name derives from colorful mantling scoria deposits, are unglaciated and were radiocarbon dated at about 8900 years ago. Phreatic eruptions, distinct from those at South Inyo Craters, took place about 700 years ago from vents on the north side of Mammoth Mountain. Recent unrest, including seismicity, gas emission, and tree kill, is thought to be related to dike intrusion beneath Mammoth Mountain in 1989.
- Location: Western US, CA
Elevation: 3369 m
Recent Eruption: Red Cones - radiocarbon date of 8900 years ago, phreatic eruption 700 years ago.
- Hazard Assessments: Miller, C. Dan; Mullineaux, D. R.; Crandell, D. R.; Bailey, R. A., 1982, Potential hazards from future volcanic eruptions in the Long Valley-Mono Lake area, east-central California and southwest Nevada; a preliminary assessment, USGS Circular 877, 10 p. :ill., maps.
- Link to monitoring data: LVO Web Site
Volcanic Alert Level: NORMAL Aviation Color Code: GREEN