[7] These domes formed in a long series of eruptions from 110,000 to 57,000 years ago, building a volcano that reaches 11,059 feet (3,371 m) in elevation.

[3][11][12] Mammoth Mountain is composed primarily of dacite and rhyolite,[13] part of which has been altered by hydrothermal activity from fumaroles (steam vents).

[14] Mammoth is outgassing large amounts of carbon dioxide out of its south flank, near Horseshoe Lake, causing mazuku in that area.

Measurements of the total discharge of carbon dioxide gas at the Horseshoe Lake tree-kill area range from 50 to 150 short tons (45 to 140 t) per day.

As of 2003, the concentration of carbon dioxide in soil gas at Mammoth Mountain is being monitored on a continuous, year-round basis at four sites—three at Horseshoe Lake and one near the base of the previous Chair 19 at the ski area.

[15] Measurements of helium emissions support the theory that the gases emitted in the tree kill area have the same source as those discharged from Mammoth Mountain Fumarole.

[25] In the summer months the ski gondolas are used by mountain bikers and tourists who wish to get a summit view of Long Valley Caldera directly to the east and Sierra peaks to the west, south and north.