Disclosure Be Damned!!!
California State law does not require a developer to disclose to the home buyer the fact the home has been constructed right on top of a landslide if the dangerous soils condition was 'mitigated' before the home was built.

Prospective home buyers are forced to go through the arduous task of checking soil and grading reports filed with their city's planning department.  Reports should show what, if anything at all, has been done to rectify the landslide-prone slopes.  The problem is that tract numbers and lot numbers are very hard to correlate with street numbers, thereby making the process difficult or even impossible for the average layman.  And that's the idea -- to keep the dangers a secret!

For homes in unincorporated landslide-prone areas of Orange County, reports can be found at the Orange County Planning and Development Services Department, 300 N. Flower St., Santa Ana.

State laws theoretically require developers to do the following before building on our tenuous hillsides:
The builder must get soil and geologic reports from geotechnical consultants who analyze hillside geology. The problem here is that the builders shop around for the geotechnical consultant who gives him the cheapest construction guidelines that have to be implemented.  And if the hill slides, the consultant just says that he is just as surprised as the homeowner -- except it is the homeowner that unknowingly has been living on the edge of disaster.
If there is an existing landslide, the grader hired by the builder must 'mitigate' the slope problems. The most common method of stabilizing a hillside before development is buttressing, which involves cutting away a portion of the soil and recompacting it.  Since the compacting process acts as a plug stopping all natural drainage, water will build up within the hill causing mudslides -- even though the landslide has been 'mitigated'.  The necessary solution to this compaction problem is the construction of numerous gravity drains within the hill.  Now, the next problem is that these drains always get plugged by mineral deposits, dead rodents, etc., plus breaks in the drains are equally common -- all of which necessitates costly ongoing monitoring and repairs till the end of time. 

When mitigation is complete and the slopes meet safety standards for building, the approval process for construction begins. Since the builders donate big-bucks to all of the politicians, any delays in construction approval are frowned upon by such builder-financed politicians as Anaheim's Mayor Daly -- who once actually lobbied on behalf of the Orange County Builders Association.

If development is in an unincorporated area, the county issues approvals. City developments go to city planning departments.

Once the homes go on the market, the builder is under no obligation to disclose the previous landslide condition.

Right about now you're thinking: "Well, if no one is told about the existing landslide,  who is going to take care of the gravity drains?  Who will be monitoring them against clogs and breaks till the end of time?"

No one!

Hey, don't worry about it... You'll be dead!