A vital transportation corridor in Southern California is situated above two major fault lines experiencing tectonic stress at its highest level in 1,000 years, prompting concerns about a potentially devastating earthquake. The Cajon Pass, a key route through the San Bernardino and San Gabriel Mountains north of Los Angeles, lies at the convergence of the San Andreas and San Jacinto fault systems.
Scientists have labeled this area an "earthquake gate," a junction where a seismic rupture could either be contained or propagate across both fault systems, resulting in a significantly larger earthquake. "We all know the San Andreas fault is loaded. It’s ready to go. For years the scientific community has been saying so," Ken Hudnut, who previously assisted the U.S. Geological Survey in developing seismic resiliency initiatives for California, told National Geographic. He added, "Cajon Pass keeps me up at night."
Research indicates that during past periods of simultaneous stress on these faults, the Cajon Pass acted as a conduit, allowing ruptures to spread across both systems. While these findings do not predict the timing of the next major earthquake, they suggest that an event at this junction could reach approximately magnitude 7.5. "We are primed to have another one in our generation," said Liliane Burkhard, lead author of a study and a geophysicist at the University of Bern.
The strategic importance of the Cajon Pass amplifies the potential impact of such an event. The corridor hosts critical infrastructure connecting Southern California to the rest of the region. An estimated 160,000 vehicles traverse this route daily, and it also carries vital rail lines, power infrastructure, fiber optic cables, aqueducts, and high-pressure natural gas pipelines.
Previous earthquake modeling, such as the 2008 ShakeOut Scenario, has projected severe consequences for a magnitude 7.8 event, including over 1,800 fatalities, 50,000 injuries, and approximately $200 billion in damages. The ShakeOut Scenario specifically highlighted potential destruction of rail lines, damage to highways, severed communication links, and ruptured gas infrastructure within Cajon Pass. Earthquake-triggered landslides could also topple transmission towers, bury utility lines, and block roadways with an estimated 75,000 cubic meters of debris.
"This earthquake’s inevitable. We just don’t know exactly when," stated former USGS seismologist Lucy Jones, warning that "any sort of lifeline crossing the fault will be cut off."
California officials have acknowledged the vulnerability of the Cajon Pass, recognizing that its disruption could severely impact transportation, supply chains, communications, and power systems. The California Governor’s Office of Emergency Services has formed a task force to coordinate government and private sector efforts for restoring critical infrastructure after a disaster.
Utilities are also implementing measures to reinforce their systems. Southern California Edison has invested approximately $300 million in seismic hardening between 2016 and 2025. SoCalGas has installed automated and fault-isolation valves along its transmission pipelines in the Cajon Pass area. "We know exactly where this will happen. That’s the thing that’s frustrating," Jones added regarding the predictable location of the seismic threat.