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Long Valley Caldera Field Guide - Mammoth Mountain

Hike, ski, or bike on a series of domes. A good vantage point for seeing entire Caldera. 

Geologic Summary

Mammoth Mountain summit from McCoy Station (halfway up) in the late...
Mammoth Mountain summit from McCoy Station (halfway up) in the late summer.(Public domain.)

Mammoth Mountain is a collection of 25–30 overlapping domes that were erupted on the southwest caldera rim between 111 and 57 thousand years ago (Hildreth, 2004). The summit dome is the youngest extrusion on the mountain and has a composition that is typical of other high silica rocks erupted after the formation of the Long Valley Caldera. Research on the chemical compositions of the lava that erupted to form Mammoth Mountain shows that it is not the same as the lava that erupted to form either the Long Valley Caldera or the Mono–Inyo chain.

Ride up the Gondola

Almost everything that can be seen from the summit can be seen on the gondola ride up except for Mammoth Lakes Basin and areas to the south. Facing away from the mountain provides a view of the Inyo-Mono domes, Earthquake Dome, and the entire caldera (all discussed in the "View of Long Valley Caldera" section below). Facing the mountain when it's free of snow provides a view of the rocks that make up the multiple domes. Above McCoy station (midpoint on gondola ride) and to the east of the gondola path, is the Mammoth Mountain fumarole. CO2 (carbon dioxide) is emitted from this fumarole which is monitored and fenced off. Analysis of the CO2 indicates that it is magmatic in origin (see the Horseshoe Lake field guide stop for more information on CO2). Three members of the Mammoth ski patrol died in April of 2006 when they dropped into a snow cave while moving the safety fences even farther away from the fumarole to protect visitors during an unusually snowy year. The warm gases had melted the snow forming a large snow cave that could not be seen from the surface and contained toxic levels of carbon dioxide.

Long Valley Caldera and domes viewed from the top of Mammoth Mounta...
Long Valley Caldera and domes viewed from the top of Mammoth Mountain. Mono Lake visible in upper left of photo.(Public domain.)

View of Long Valley Caldera

On a clear day the entire expanse of Long Valley caldera can be seen from the summit. Climb to the summit following the path to the east of the gondola station (a sign with the elevation marks the summit). Look north (a little to the left behind the sign) for an excellent view of the Mono Inyo Craters and a section of Mono Lake. The flat area below with no trees is called Crater Flat; behind that is Deer Mountain, where the Inyo Craters erupted - you can see the Deer Mountain summit crater. Continuing to the north behind Deer Mountain is Deadman Dome, then a patch of trees followed by Glass Creek Dome and Obsidian Dome. Glass Creek Dome is darker than Obsidian Dome. Behind Obsidian Dome are the Mono Craters (really domes) and behind the domes is Mono Lake.

Directly behind the summit sign in the near distance is Earthquake Dome, which erupted before the formation of Mammoth Mountain, about 86,000 years ago (Hildreth, 2004) with lavas of similar composition. Behind Earthquake Dome is Lookout Mountain and behind that is Bald Mountain (no trees), which is on the north rim of the caldera. In the foreground to the right is the Resurgent Dome (the area that is elevated compared to the flatter areas around it). The Resurgent Dome is somewhat of a misnomer since it was named for its dome-like topographic expression and not because it is a volcanic dome. The Resurgent Dome is comprised of uplifted volcanic deposits that erupted during the first 100,000 years after formation of Long Valley Caldera.

The Resurgent Dome has been uplifted an additional 2.5 feet since 1980. The uplift may have been caused by either magma or geothermal water. Ground deformation (uplift and subsidence) is a common phenomenon in calderas and Long Valley Observatory scientists monitor the area for this type of activity. Behind the Resurgent Dome is a kaolinite mine (bright white rocks), and far beyond the mine is Glass Mountain. Glass Mountain (~ 50 high-silica rhyolites) erupted 2.1- 0.8 Ma years ago and forms the northeast boundary of Long Valley Caldera.

Looking to the east (right) of the summit is the airport and Doe Ridge. Hot Creek flows through a gorge cut through Doe Ridge (tree covered finger-shaped ridge). Behind Doe Ridge is Lake Crowley followed by the Volcanic Tableland. On the horizon in the distance are the White Mountains.

To the west (left) is the gondola station and visitor center. Enter the visitor center for viewfinders and more information about the area. Above the visitor center are satellite dishes for relaying monitoring data and communications.

Mammoth Lakes Basin including the treekill area next to Horseshoe L...
The gray area along the edge of Horesehoe Lake (lower right) is one of several areas around Mammoth Mountain where trees were killed recently by high concentrations of carbon dioxide gas in the soil. Mary Lake (left of center) is the 2nd largest in the basin. The largest lake, Duck Lake, is accessible only by foot and is hidden from view.(Credit: Brantley, S. R.. Public domain.)

Hike to view Horseshoe Lake

Walk from the summit down and to the south (left) following signs to a scenic view. Keep hiking to a small summit at the end of the path. Near the summit is USGS benchmark MMTN 1989 that was installed during the earthquake swarm of 1989 to increase monitoring capabilities in the area. To the east (left) is the Mammoth Lakes Basin, which bordered on its west by Mammoth Crest (10,640 ft, 3243 m), a granite headwall carved by glaciers that receded 15,000 years ago. The basin is a cirque around the lakes. To the west of Horseshoe Lake is an area of dead trees and barren ground killed by carbon dioxide (CO2) emissions that began following the 1989 earthquake swarm (See the Horseshoe Lake page for more information about CO2).

To the south and behind Mammoth Crest are Red Cones, two reddish 8,000 year old basaltic cinder cones. Behind Red Cones is the San Joaquin river valley and Yosemite National Park. The mountain that resembles Half Dome, is called Balloon Dome. Yosemite Valley is not visible from here.

To the southeast is Lake Crowley, Doe Ridge, the southern edge of the Resurgent Dome, and Glass Mountain. To the west are the Minarets, Ritter, Banner, and Mount Lyell. Viewfinders and more information about the peaks to the east, south, and west can be found in the Summit Interpretive Center, above the gondola.

The White Mountains, on the distant skyline, bound the eastern side of the Owens Valley rift and rise to 4,373 m (14,347 ft)-nearly 300 m (1,000 ft) higher than the local Sierran peaks; they are underlain by Mesozoic granitic plutons (magma storage areas that formed below the surface but are now exposed) and Paleozoic roof-pendant rocks.


Hildreth, Wes, 2004, Volcanological perspectives on Long Valley, Mammoth Mountain, and Mono Craters: several contiguous but discrete systems, Journal of Volcanology and Geothermal Research, Vol. 136, p. 169–198.

Field Stop Location: Mammoth Mountain

Quadrangle: Mammoth Mountain, California 7.5 minute topographic quadrangle 
Coordinates: parking lot-37°39.062' N, 119°02.217' W, summit-37°37.829' N, 119°01.941' W
Approximate Elevation: parking/lodge-8,891 ft (2710 m), summit- 11,030 ft (3,362 m)

Directions to Mammoth Mountain:

Riding the gondola requires a ticket, even for hikers, and it only runs during ski and bike seasons. Please call ahead to check on hours. This stop provides excellent views on clear days.

Directions from Mammoth Lakes exit U.S. 395 and CA-203 Go this distance
1. Start at Mammoth Lakes exit from U.S 395 and head west on CA-203 W/Minaret Rd toward Sawmill Rd. and Mammoth Mountain Ski Lodge. Continue to follow CA-203 W. Go 3.7 miles
2. Turn right onto Minaret Road [Start here if you are already in Mammoth Lakes]. Go 4.2 miles
3. Park in the parking lot and walk up to the Gondola station to purchase tickets. Take the gondola (check hours for ski and bike seasons) to Mammoth Mountain summit (3362 m) and walk about 200 m southeast along the crest.