There are many different things that you have to consider when you are going to build a structure in California. One of the very important points is the soil stability. If there is an adverse soil condition in the area, it would need to be addressed before you could build your structure. People who aren't familiar with this issue usually turn to a knowledgeable person to help them come up with a plan and execute that plan.
When you have a house or other structure built, you assume that the contractor has taken proper steps to ensure that the structure is going to be stable. The last thing that you expect is to find out that there are foundation problems that could have been prevented if the area had been properly prepared.