Generally, National Weather Service debris-flow warnings are triggered if a quarter-inch of rain falls in 15 minutes, or if one inch falls in an hour, Mickelson said.

One of the worst debris flows in modern California history occurred when a river of mud and rock flowed through Montecito in January 2018, killing 23 people and destroying at least 130 homes.

Debris flows made up of water, mud, boulders, brush and trees emerged from the canyons of the Santa Ynez Mountains, overtopped debris basins and traveled several miles, destroying parts of the ...

As an intense storm moved through Southern California, a debris flow sent mud down Mulholland Drive in Hollywood Hills -- leading to a full closure of the roadway Thursday evening, authorities said.

During intense rainfall, burned slopes become vulnerable to flash floods and debris flows, a threat that can last for years. Conditions in this case are far from the worst case scenario, officials ...