I blogged at my sonoma.net site today about developing raw land in Sonoma County. It's probably not too different than most places around the country. Everybody needs to have water and take care of their sewage whether they are building in California or Maine, but our hillsides present some unique challenges for fire safety.
One of the requirements that can make a property hard to build on is the need to build a road that is accessible to fire trucks. Whether it's a creek crossing that needs a better bridge or a small building site without enough room to turn trucks around, if you can't meet the fire safe standards you aren't allowed ot build a residence. In the photo, a bridge build on two massive douglas fir logs spans a creek in the Russian River area. It's a strong bridge, but it's hard to demonstrate the strength needed to support a fire truck. Replacing it could be very expensive.
Finding sufficient clean water (1 gallon per minute for a 12 hour period) is a necessary precondition to building. It's great to have more, but a slow, steady supply works great to fill up the required 2,500 gallons of storage needed for fire protection.
The final requirement is for a minimum one bedroom septic system. There are plenty of posts dealing with the details of standard septic systems, but the one thing required is well draining soil (percolation or perc test). If you don't have that, one of the more expensive and maintenance-required alternative systems might be necessary.
Adding a final level of complexity to the process, many of the tests required are dependent on time of year. For instance, you need enough rain to conduct a wet weather perc test. That probably means the December to February time frame. Conversely, you need dry weather to conduct a long duration well test. Probably you're looking at July 15 or later. If the seller of the property hasn't done testing before putting the property on the market, you could be looking at a year or more just to get all of your approvals in place.