On September 19, 2025, Southern California, especially San Bernardino County and its surrounding areas, was suddenly hit by heavy rainfall driven by the residual moisture of Tropical Storm Mario, causing severe floods and mudslides, resulting in significant damage and casualties.
Floods and mudslides came with great force
According to the latest report, from the night of September 18th to September 19th, the residual moisture of Tropical Storm Mario from the Pacific Ocean accumulated over Southern California, causing intermittent heavy rain in some mountainous areas. Communities such as Yucaipa, Forest Falls, Oak Glen, and Potato Canyon were the first to be hit by mudslides and floods. The intensity of the rainfall far exceeded what the local area could usually tolerate during the dry season.
In the San Bernardino Mountains area, the stability of the slopes has been severely weakened due to the burn marks left by previous wildfires (loose soil structure and sparse vegetation). After encountering sudden heavy rain, silt and gravel quickly wash down the mountains, submerging or burying the paths and blocking the roads. The section of State Route 38 near Jenks Lake was filled with mud, stones, and gravel. Many cars were trapped, and people were forced to wait for rescue. The local fire department said that at least six vehicles and more than ten people were trapped on that mountain road.
Casualties and property losses
In the flood caused by the heavy rain, a car carrying a father and his two-year-old son was washed off the road by the flood. The father was rescued, but the young son was swept away by the flood in the car and was confirmed to have drowned several hours later. The location is in Barstow, which belongs to SAN Bernardino County. The local police, fire department, and water rescue team jointly participated in the search and rescue operation.
In addition, mudslides and floods have caused damage to many houses, destroyed roads, cut off water and electricity in many mountain communities, and paralyzed traffic in many places. The clean-up work is very difficult. Temporary evacuation or alert orders have been issued in some areas, urging residents to take refuge.
Government and emergency response
In the face of sudden disasters, many counties in Southern California, especially SAN Bernardino County, have urgently activated their emergency response mechanisms. The fire department and local government jointly carried out inspections and rescue operations in the affected areas. Meanwhile, the road management and transportation departments blocked some damaged sections of the road to prevent more vehicles from being trapped. Clearing the ruins and rebuilding the roads have become top priorities.
Health and public safety agencies have reminded the public that mountainous areas and burned areas (surfaces that have been destroyed by wildfires) are highly vulnerable to mudslides caused by heavy rain, and residents living in these areas must be vigilant. Relevant departments also dispatched rescue teams, including air or water rescue operations, to deal with trapped vehicles and people besieged by floodwaters.
Terrain, fires, and rainfall interact to intensify disasters
The terrain and past wildfires are the key factors that have exacerbated the severity of this disaster. The slopes in mountainous areas are steep. After the soil layer is damaged by wildfires, the vegetation coverage is low, and the soil cannot be effectively maintained. When heavy rain comes, it is easy to form loose stones and soil flow. At some stations, the rainfall reached nearly two inches within just two hours, which is extremely rare in dry areas. Compared with normal seasons, this type of intense rainfall exceeds the carrying capacity of the soil and drainage systems.
Follow-up and outlook
After the disaster, the local government focused on assessing the damage, rebuilding infrastructure, and preventing secondary hazards caused by disease vectors and landslides. The maintenance of schools and public facilities, as well as the restoration of power and water supply, have also been listed as top priorities. The clearance and reconstruction of the passageways may take several days or even weeks. The weather forecast indicates that the main impact of this storm has passed, but there are still risks of rainfall and landslides in some highlands and burn marks. The authorities continue to issue warnings for these areas.
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