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

A portion of the Pacific Coast Highway in Los Angeles County was closed on Sunday afternoon due to mudflows as rain fell in parts of Southern California.

If the rain falls at a steady, lighter rate, Southern California could be in good shape. That could mean enough rain to help ease the firefighting strain, but not enough to trigger another potential disaster. Heavier rain could mean the chance for flash flooding or mudslides over fresh burn scars.