A pre-winter storm drenched California with rain and dumped nearly three feet of snow to help bolster the vital Sierra Nevada snowpack but also triggered mud flows, street flooding and the dramatic rescue Friday of two homeless women and 10 dogs from a river island near Los Angeles. With thousands of acres of wildfire burn scars all over the state, authorities were warily monitoring barren slopes where parched earth soaked with rain can cause life-threatening mudslides.