A good rule of thumb is that "almost" all the properties that are East of 101 fall into the flood zone. The only way to make sure is to read the reports.
When you purchase a home, there a many dislcosures that the seller will provide and one of them is a natural hazard disclosures and advisories which will tell you all you need to know. This report is mandatory in the state of California.
If you are looking for an agent who knows that area reall well, call Mac McCarthy 650-245-1005. Mac works and lives in the area.
Dave Tap Tapper