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

Rain and cooler temperatures will bring relief to Southern California this weekend, after a prolonged stretch of dry, breezy weather that allowed wildfires to thrive.

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.