There are three main airports that we would recommend looking for flights into: San Francisco, Oakland, and Santa Rosa.

The Santa Rosa Airport is, as the name suggests, in Santa Rosa itself, so travel to your accommodations will be quick. However, it is a very small airport, so it is likely you won't be able to find flights directly into Santa Rosa, though you may be able to connect through Los Angeles.

The San Francisco and Oakland Airports are each about an hour and half drive from Santa Rosa. There is a bus that runs from SFO to Santa Rosa; the details and the schedule can be found here: http://airportexpressinc.com/schedule.php. If you plan on doing some sightseeing while you're in California, it may be easier to rent a car from the start and drive to Santa Rosa instead.

We recommend using sites like Kayak to search for the best flight options.