Government Seismologist Says the Cajon Pass Earthquake Gate Keeps Him Up at Night After New Study

The last major earthquake on California's deadliest fault system was in 1857.

A new scientific study just revealed why the people who track it most closely are scared.

One government seismologist says the fault junction they're watching keeps him up at night.

The Fault That Runs Through the Heart of Southern California

The San Andreas and San Jacinto fault systems together carry roughly 90% of all tectonic plate movement across Southern California.

They meet 50 miles northeast of downtown Los Angeles at a geographic pinch point called Cajon Pass.

Scientists call this junction the "earthquake gate."

A new study published in the Journal of Geophysical Research – based on computer simulations modeling 1,000 years of rupture history – found that tectonic stress at Cajon Pass has reached its highest level in a millennium.

USGS seismologist Ken Hudnut did not bury the concern.

"Cajon Pass keeps me up at night," Hudnut told National Geographic.

He added: "We all know the San Andreas fault is loaded. It's ready to go."

The study's lead author, University of Bern geophysicist Liliane Burkhard, was equally direct.

"We are primed to have another one in our generation," Burkhard said.

What Happens When That Gate Opens

The earthquake gate works in two directions.

On the better of two bad outcomes, a major rupture on the San Andreas stops at Cajon Pass and does not cross to the San Jacinto.

On the worse, the rupture jumps between fault systems – combining both into a single, longer, more catastrophic event.

With stress at its current level, researchers modeled a potential magnitude 7.5 earthquake.

The projected toll: 1,800 deaths, 50,000 injuries, and $200 billion in damages.

Rail lines severed.

Fiber optic cables cut.

Gas lines combusting.

Every road through Cajon Pass blocked by an estimated 75,000 cubic meters of debris.

Cajon Pass is the primary land corridor connecting Los Angeles to the rest of the American Southwest.

Interstate 15 runs through it.

Shut that route down and 13 million people in the greater Los Angeles basin lose one of their most critical supply arteries overnight.

Lucy Jones, one of the nation's most prominent seismologists and a former USGS scientist, put the stakes plainly: "This earthquake's inevitable. We just don't know exactly when."

The part that frustrates Jones most is not the uncertainty about timing.

"We know exactly where this will happen," she said. "That's the thing that's frustrating."

170 Years and Counting

The last major rupture on the southern San Andreas was January 9, 1857 – the Fort Tejon earthquake, magnitude 7.9.

It toppled chimneys, buckled roads, and shook the ground across hundreds of miles of California.

In the 1,000 years of seismic history the new study examined, the two fault systems produced at least 36 earthquakes of magnitude 6.4 or larger.

That averages to roughly one every 28 years.

Southern California has gone 170 without one.

In 1857, California's entire population was around 380,000 people.

Today, more than 10 million live within 50 miles of the fault segments Burkhard's study examined.

What Burkhard's study adds to the long-running warning is specific, measurable data: the San Jacinto Bernardino segment is showing the highest stress index researchers have recorded for it – 3.6 on the study's scale.

The system is not just overdue on paper.

The measurements show it is loaded.

Who Runs the State With a Loaded Fault 50 Miles From Downtown

California's political class has spent the past decade prosecuting oil companies and pushing multi-billion-dollar high-speed rail projects that have not moved a single passenger at operating speed.

Earthquake preparedness – the kind of infrastructure investment that would actually reduce the $200 billion catastrophe Burkhard's team modeled – has not received the same political energy.

The research is not hedged.

The experts are not speculating.

Hudnut and Burkhard are describing an event they believe is coming, at a location they can pinpoint on a map, in a region they can show is more loaded than it has been in a thousand years.

Gavin Newsom has governed California since 2019.

The seismic retrofit programs for water systems, hospitals, and supply corridors near the fault that would actually reduce Burkhard's projected $200 billion toll remain incomplete.

Newsom signed California's gas stove ban. Earthquake preparedness did not make the cut.

The fault is loaded. Sacramento is not paying attention.

Sources:

• Liliane Burkhard, "Cajon Pass and the Southern San Andreas Fault System: Earthquake Cycle Stress Accumulation and Present-Day Loading," Journal of Geophysical Research: Solid Earth, June 2026.
• Fox Weather, "San Andreas fault hits dangerous 1000-year high, study says," 2026.
• National Geographic, "Why California's 'Earthquake Gate' Keeps Scientists Up at Night," 2026.
• USGS, "M7.9 1857 Fort Tejon Earthquake."