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

So far, many clues to the origins of the deadly Eaton fire, which started in the area just after 6 p.m. that evening and went on to kill 17 people, have pointed to the brushy hillside where a tangle of electrical lines stretch up Eaton Canyon.

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.