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CAJON PASS, Calif. () — Concerns are growing among residents of the mountain town of Wrightwood over a proposed rock quarry project near the San Andreas Fault, a region long recognized for its earthquake risk.
During a 2019 tour of the fault through the Cajon Pass, seismologist Dr. Lucy Jones highlighted the area’s seismic potential, noting the fault’s visible path through Lone Pine Canyon.
“These boulders could be thrown into the air at speeds exceeding the speed of gravity,” Jones said at the time about the effects of a magnitude 8.0 or greater earthquake along the fault.
Years later, the same region is the focus of debate as a roughly 300-acre quarry project has been approved, with plans to excavate as deep as 1,600 feet.
Wrightwood resident Melissa Manning, who is part of a citizens group opposing the project, said the use of explosives is a major concern, not only for the potential effects on air quality and wildlife in the area, but the potential effects of mining activity near a major fault line.
“They’re going to be detonating and using high-powered explosives,” Manning said.
While a San Bernardino County document indicated there is a less-than-significant chance the quarry could cause an earthquake, residents remain worried about the broader risks, particularly during a major seismic event.
“This is nearly 300 acres approved for 1,600 feet deep,” Manning said.
Among the concerns is how the quarry could affect evacuation routes in the event of a large earthquake. Wrightwood relies on limited roads for access, and residents fear those routes could be compromised.
“Having two ways to get out of town so fast is imperative. But the steepness of the quarry is like a one-to-one grade,” Manning said. “Our evacuation routes will most likely be cut off.”
Experts say the project is unlikely to trigger an earthquake but agree there are still important questions to consider.
Geophysicist Dr. Ross Stein, CEO of Temblor, said the depth at which earthquakes originate makes it unlikely that surface-level excavation would directly cause seismic activity.
“What are the consequences of a strong shaking event at that site,” Stein said.
“What really matters is what the San Andreas is doing and the stress that it’s experiencing at about six miles depth…so when you’re only talking about a quarter mile down, you’re really not in the area where it counts,” he said.
However, Stein said the presence of the quarry could worsen the effects of a major earthquake.
“This facility doesn’t make an earthquake more likely. What it does, is make the consequences of an earthquake greater,” he said.
In a statement to Eyewitness News, San Bernardino County officials confirmed that the project applicant, Grand Lone Pine Canyon Enterprises, LLC has vested mining rights, but the mine hasn’t been active since the 1960s.
“The submitted reclamation plan is under review by San Bernardino County’s Land Use Services Department, which is responsible for ensuring compliance with federal and state requirements as well as County zoning ordinances. The review process typically takes eight months to a year,” said Janelle Needham, a spokesperson for the department.
A hearing on the item is planning for July 23rd with the San Bernardino County planning commission.
“Land Use Services used a slope stability report provided by the project applicant,” said Needham in response to a question about the evaluation of seismological factors.
“The study used computer modeling to evaluate slope stability under normal conditions and during an earthquake, considering the strength and characteristics of the site’s rock and soil. After reviewing the analysis, the department determined that their conclusions and recommendations were reasonable and consistent with industry standards of care.”
As the debate continues, residents say their concerns center not just on the likelihood of a quake, but on how prepared their community would be if one strikes.
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