Some owners in the area believed in build first and then ask for forgiveness. They believed if they built to County criteria they'g be able to get retroactive approval. The pitfalls for both buyer and seller are that once it is brought to the attention of the County they may red-tag the improvements and/or ask that they be removed. They have even been known to retroactively tax the improvements. There are over a dozen Santa Clara County departments involved in approvals for the building of a residence in County territory, and they may be less likely to approve than they once were. Of particular concerns to the County are fire prevention and access for emergency vehicles, reliable water supply of sufficient quantity, adherence to strict septic system standards, slope control, view shed, ecological impact, and legal subdivision, etc. The County website lists their criteria for development. The mention of a bridge implies access over a waterway. Most waterways in the area are controlled or owned by the Water District who does not like anything to be done in their property/easement without their approval (and a cut of the action - they aren't called the Golden Spigot for no reason). Others have suggested you talk to the County - it is imperative you do so before buying. Buying land should be simpler but in reality can be much more complicated than buying an existing home. Please do not do it without an experienced Realtor at your side. He/she will help you understand the opportunities and pitfalls. BTW - any time you see land for under a hundred thousand there is always a reason - usually location, access and develop-ability issues.
Regards ... Wayne