Southern California residents in Glendora and other foothill communities were bracing Monday for potential disaster after Sunday's rain-triggered mudslide on Pacific Coast Highway. Here's how hillsides that have been burned by wildfire become prone to flash floods and dangerous mudslides during heavy rains.
Step 1: Fire burns through growth
Step 2: Rainfall
Step 3: Mudslide
Source: University of Idaho, "After the Fires: Hydrophobic Soils" by Randy Brooks