Officials cautioned that ash in recent burn zones was a toxic mix of incinerated cars, electronics, batteries, building materials, paints, furniture and other household items.

More rain fell Monday on parts of Southern California after causing mudflows over the weekend, helping firefighters but boosting the risk of toxic ash runoff in areas scorched by Los Angeles-area wildfires.

Much-needed rain has begun to fall over Southern California, bringing relief to the drought-stricken region but also the threat of toxic runoff.

Southern California’s first rainy weekend of the winter has arrived. The rain event, months in the making, brought steady storms across the region as the Southland experiences drought conditions. The mostly welcome rain began Saturday night and is expected to sustain until Monday evening.