Ryan is correct to suggest talking to an insurance agent. Choose a local Insurance agent as well who is familiar with the area. Alot of Mill Valley as I'm sure you've figured out by now, is in a zone 4, espciallly if you are looking at the hills surrounding downtown. A good home inspector will or should also let you know if further investigations are necessary, especially when dealing with retaining walls, steep driveways, the foundation of the home, he/she will recommend getting an engineer if necessary. Home Inspecters should look at water drainage on the property. I would walk the property and neighborhood to check out where the culverts are. In heavy rains, the culverts can get clogged with debris. It is good to know where they are and who is responsible for keeping these clear. Ask your agent, I'm sure he/she has the name of a good home inspector as well as insurance agent. If you would like me to give you some names, I'd be happy to do so as well. Just drop me an email.