Here's a place to start.

http://www.conservation.ca.gov/cgs/geologic_hazards/landslides/Pages/index.aspx

Clairebear, that slide didn't 'just happen.' It occurred because the cracks in the rock, the slope of the bedding, and (possibly) a slick clay layer under them allowed thousands of tons of rock to slip downslope rapidly and violently. It could happen again.

You and your neighbors need to know where else this might happen and to make plans so you are not in the way.

Somebody said 'this is the cost of living in a tranquil place.' That is pure BS, you know.