Debris flows and mudflows are a process of mass wasting, and typically occur in steep mountainside or hillside areas with loose ground cover. Heavy rain or snowmelt is typically required as a catalyst, and hillside areas that are denuded of vegetative cover from wildfires are highly susceptible to debris flows after heavy storms. Debris flows can be terribly destructive and dangerous. AES has performed several studies of areas at risk for debris flows, most commonly in foothill communities of the San Gabriel and Santa Monica Mountains, and devised mitigation systems to minimize the impact of debris flows to structures.