The Mammoth Lakes Earthquakes – 40th Anniversary

On May 25, 1980–nearly one week after the spectacular eruption of the Mount St. Helens volcano–at 9:33 a.m. PST, a magnitude 6.0 earthquake rocked through Mammoth Lakes, California.

During the next 16 minutes, four more shocks, magnitude 4.1 – 5.5 followed. This seismic activity was the beginning of an earthquake sequence that produced 72 magnitude 4.0 to 6.3 shocks during the next 48 hours. Four of those were in the magnitude 6.0 range.

seismic photo for blog

Damage from earthquake shaking included broken windows and water mains, cracked plaster, and fallen chimneys. Residents reported extensive destruction to breakable household items. Initial calculations of losses to schools and other public buildings and roads in the area were estimated to be $2 million (1980 dollars), which is about $6.2 million today.

Landslides and rockfalls were widespread. Large dust plumes could be seen over the Sierra Nevada immediately following the larger shocks. Two hikers in Yosemite Valley, nearly 45 miles away, were severely injured by rockfall. Roads were closed by debris.

mammoth blog post photo

With the Mount St. Helens eruption fresh on everyone’s mind, strong concerns that the quake sequence would be followed by a volcanic eruption in the Mammoth Mountains spread throughout the community. News media went crazy. Tourism and property values took a hit.

California Geological Survey (CGS) seismologists (then known as California’s Division of Mining and Geology) had been monitoring the area since a 1979 seismic event and had established a small network of sensitive instruments that were in operation when the earthquake sequence occurred.

Five hours after the first shocks, several CGS seismologists from field offices all over the state were dispatched. The team worked feverishly to add six more seismographs to the network, bringing the total to nine. They quickly retrieved film records and reloaded accelerographs with fresh film to monitor the ongoing activity. In all, 14 Strong Motion Instrumentation Program accelerographs were triggered by the three-days of activity. Several CGS geologists were sent out to map fault rupture.

Vintage Cal Geology Photo for Blog

The team also investigated other geologic impacts on the earthquake sequence, including incidents of surface rupture – that is, underground faults breaking the earth’s surface – for Alquist-Priolo Special Studies Zones to protect public safety and property in future events.

An earthquake clearinghouse was established as a base for scientists to gather, share information, and establish priorities for study and mapping. Local government officials, news media, and concerned citizens in the community also frequented the clearinghouse.

Ultimately, the earthquake sequence led to the establishment of the Long Valley Volcano Observatory to monitor the region. That eventually grew into the USGS’ California Volcano Observatory, which monitors the activity of all volcanic areas in California.

Representation of California’s volcanoes monitored by the USGS

Today, the Department of Conservation’s Strong Motion Instrumentation Program has more than 1,000 accelerographs throughout the state monitoring significant seismic activity. The digitally collected data is used to inform future building codes, for earthquake early warning, and to help guide emergency responders to the hardest-hit areas after big earthquakes.

More detailed geologic information can be found in archived California Geology magazine articles on the website.

Cal Geology Cover 1980

Quake sequences such as those in the Mammoth area mentioned in this story are infrequent but can occur in many parts of California. Learn to prepare  at

Prepare for EQ

What to do in an Earthquake

California Department of Conservation administers a variety of programs vital to California’s public safety, environment and economy. The services DOC provides are designed to balance today’s needs with tomorrow’s obligations by fostering the wise use and conservation of energy, land and mineral resources.

5 Comments Add yours

  1. Doris Grinn says:

    Do you see a connection between quakes in East Side CA (like now June 2920) being a precursor to eruptions of Mt St Helens in Oregon?

  2. Hello, thanks for reading! According to our geologists, there is no connection between the recent eastern California earthquakes and volcanic eruptions at Mount St. Helens. These earthquakes are in a very different tectonic environment and at great distances from Mount St Helens.

  3. Frieda Hinkel says:

    I was on the chairlift to ski Mammoth Mountain’s cornice, about 100 ft from the terminus, when the quake hit. It was unlike any I’d felt before. It had been a warm morning but about 5m before the event occurred the wind changed direction/intensity and felt significantly (ten to fifteen degrees) colder. About 10 seconds prior the wind died and everything went muffled, almost silent. I felt a strong jolt then massive shaking/vertical up thrusting that caused the chairlift to swing from the 6 o’clock position to the 8 o’clock and 4 o’clock positions. The lift operator bounced around the cage like a corn kernel in an air popper. We watched the cornice give way in a small avalanche and could see boulders/snow give way. It took ski patrol about 40m to bring us down from the chairlift. We spent the next 3d sharing our room with 10 other skiers (ours was one of the few that was intact plus had a fireplace) while incredibly strong aftershocks hit. Highway 395 was closed due to avalanches so we had no choice but wait until it was cleared. The ground seemed to have a constant vibration that would crescendo and decrescendo rapidly but seemed different then then sound/motion of the aftershocks.
    As people left the ski resort and drove back into town we watched as about 10-15 people stopped at the site of the Park’s Service EQ fault. Everyone swarmed in to see what changes the quake caused until the aftershocks hit. I’ve never heard people scream that loud lol! It seemed a Darwin Test to me-stay out of the railing free fault unless you’re wearing safety gear…..the rangers closed it as we watched.
    I have 2 ???’s:
    Would the P wave cause the apparent wind shift/temperature change?
    Was the sensation of a constant vibration that the aftershocks flowed on top of due to infrasound or ???

    1. Linda Link says:

      That was one crazy day in my quake history as a native So Californian! Never had I felt the ground continuously shaking for hours like that!
      I’m glad I had the experience, though. It taught me to have a deeper respect for Mother Earth than I already had & spurred me on to become more educated about geology.

  4. Linda Link says:

    My ex & our two young children & friends were camping in Iris Meadows campground, just over the hill from Convict Lake. The boys & the friend’s wife went fishing in the creek, while I took the kids & went down the hill to Tom’s Place to call my mom in Huntington Beach. The odd thing about that ride down the mountain was that there was a herd of deer gathered in a clearing. I had never, ever seen that before as a seasoned hiker & camper! They knew instinctively something bad was coming! Pre-shocks? Within a minute on the phone, the ground started to shake. But what was even more frightening was the sound coming from the ground, like a huge, low flying passenger jet; very deep rumble. I jumped out of the old telephone booth in time to see pickup size boulders bumping down the mountains. The kids were naturally scared. Living all of my life in California, I know about & have experienced earthquakes. NO ONE EVER GETS USED TO THEM! But this quake & aftershocks were different in that it seemed as though the ground never stopped shaking. The whole valley down the grade was filled with dust! I thought..Oh God, Hanta Virus! We waited until 9 pm for things to settle down, but that never happened. We packed up & made the long trip home through the desert at night. I was very glad we did as I later heard the quake(s) were due to magma movement. With a place like the Long Valley Caldera, you just never know for sure.
    But man….what an experience that was! My kids who are in their 40s now still talk about it.

Leave a Reply