Here's a link to point you to some resources.
The geologist for Santa Clara County is your best source of information with respect to that issue.
I have spoke with the County Geologist with respect to that very issue for a client who I represented on the purchase of a home in that area. The information from the county Geologist was very good.
I recommend that you get that information from the County Geologist rather than second hand from me or someone else.
If you are represented by a REALTOR I recommend that you ask your REALTOR to get that information for you.
If you are not represented by a REALTOR you may call me on my cell phone: (408)509-6218, and I will help you get that information.
You have received some very good information from my fellow Realtors. I would also recommend that you call the county health department and maybe the state health department regarding the naturally occurring asbestos rock. I would also Google it to check for more info. A few years ago their was some press about this very issue in the El Dorado Hills above Sacramento and the health effects. Check out this article http://www.ucdmc.ucdavis.edu/synthesis/issues/fall_winter_06 Their should be lots of info for you so you can make an informed decision. Be sure you have all the facts before you decide what to do. If you have an agent already they should also be able to help you. I hope this was of some help to you.
Realty World/Blue Property Group