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

The highest intensity rain was expected between 4 p.m. on Sunday and 4 p.m. on Monday, according to the service. Los Angeles and Ventura Counties were expected to get up to an inch of total rainfall, and up to three inches was forecast in the mountains around Los Angeles.

Rain fell across parts of Southern California, providing relief to firefighters battling wildfires but raising concerns about toxic ash runoff and mudslides. Despite progress in containing major fires,