Landslides impact California’s terrain often.
The Californian Geological Survey released a new map in 2011 showing the susceptibility to deep-seated landslides across the whole of the state. This map does not take into consideration the occurrence of triggers of the potential landslides, which of course in this area are both intense rainfall and earthquakes.
In an area where earthquakes are common, we recently had two events happening: numerous wildfires in the area and a few big storms. In a burned area, a wildfire can make the soils repellent to water, creating a flood like flow on the ground that picks up rock and debris. In an area that has not burned, soil can become saturated. Pressure builds up underground, and soil starts moving and begins picking up mud and debris as it starts flowing downhill, creating mudflows or debris flows.
No surprise mudslides, rockslides, and landslides occurrences are in the news often these days, cutting main traffic arteries, wreaking havoc in busy roads, or isolating populations like Big Sur. The map from Caltrans show all the problems along 61 miles of highway.
There is a USGS page with information on how to identify landslides and what to do if one happens: http://landslides.usgs.gov/learn/prepare.php
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