RockfallHazard RainfallInducedFailure HighwaySafety CaliforniaStorms

Rainfall triggered rockfall disrupts on Highway 18 in Southern California

*Rockfall Incident on Highway 18 Highlights Mountain Slope Risks. Source: CBS (IMAGE BY San Bernardino County Fire Department)*

A recent rockfall incident on Highway 18 in San Bernardino County has highlighted the geotechnical vulnerabilities of steep mountain corridors subjected to prolonged rainfall. Following intense winter storms in late December 2025, a massive boulder detached from a saturated slope and rolled onto the roadway near Big Bear Lake, triggering a two-vehicle collision and injuring five occupants, including two children. All reported injuries were minor, but the event underscores the latent hazards associated with storm-driven slope failures.

Rockfall incidents on steep slopes are commonly triggered by intense rainfall, groundwater infiltration, and weathering processes that reduce rock mass stability. Effective rockfall management therefore focuses on controlling both rock detachment and post-failure movement in order to protect roads, infrastructure, and public safety. Rockfall control measures typically include:

Draped high-tensile wire mesh systems to contain falling blocks and prevent free-fall onto roads
Rockfall barriers or catch fences to intercept and dissipate impact energy
Rock bolts or anchors to stabilise fractured rock masses at the source
Scaling and removal of unstable blocks from slope faces
Hybrid attenuator systems combining mesh and barriers for high-energy rockfall zones

When selected through site-specific geological assessment and rockfall trajectory modelling, these measures provide an effective and durable solution for managing rockfall hazards in mountainous terrain.

Rockfall mitigation system with draped wire mesh installed over a steep rock cut to control block detachment and protect infrastructure below. Source: GSI

Emergency crews cleared the debris within hours, allowing traffic to resume. However, forecasts indicate further rainfall events, which may elevate the likelihood of additional rockfalls and shallow slope failures.