Passenger train service through San Clemente is set to resume again following several shutdowns caused by a sliding slope under Casa Romantica. A temporary wall has been placed to protect the rail line from falling debris. Experts like Brett Sanders, who's a professor of civil and environmental engineering, urban planning and public policy at UC Irvine, are studying the shifting landscape and said the slope is made up of materials that loosen up when moisture sets in. "It's more of like a mixture of soil," Sanders said. "A mixture of sand, and gravel and silts that when wetted, starts to flow like a liquid." He said people across Southern California live on hillsides just like the one in San Clemente. Sanders said residents need to be aware that this could happen to them. Watch More