On December 28, 2025, a natural gas transmission line explosion occurred on a hillside above the 5 Freeway in Castaic, California, leading to the complete closure of the freeway and a shelter-in-place order for local residents. The Los Angeles County Fire Department received reports of the explosion and a gas leak around 4:20 PM, prompting immediate traffic diversions and warnings for residents to remain indoors due to safety concerns.

The California Highway Patrol issued a SigAlert shortly after 5 PM, closing both northbound and southbound lanes of the 5 Freeway, which is a critical transportation route, especially during the holiday travel season. Traffic congestion extended for miles as vehicles were redirected to alternative routes.

Residents in the Santa Clarita Valley reported feeling their homes shake from the explosion, which was described as producing a sound similar to a jet engine. The shelter-in-place order, issued around 5:40 PM, affected a one-mile radius around the explosion site, instructing residents to close doors, windows, and vents, and to turn off HVAC systems to minimize exposure to gas.

As of the evening of the incident, no formal evacuation orders were issued, and fire officials reported no injuries. Emergency crews were cautious in approaching the rupture site until utility technicians secured the gas line. By approximately 6 PM, gas company personnel had shut off both sides of the affected line, significantly reducing gas leakage, although responders continued to monitor the area for residual hazards.

The cause of the explosion remains under investigation, with preliminary reports suggesting a potential link to a recent mudslide in the area. Authorities have not confirmed this connection, and the investigation is ongoing to assess the infrastructure risks associated with such incidents.