Sonoma County and Santa Rosa are fortunate to have a small but nice, very convenient and easy-to use airport. This is the Charles M. Schulz-Sonoma County Airport just on the NW edge of Santa Rosa, between Santa Rosa proper and Windsor. Horizon Air, a subsidiary of Alaska Airlines, operates daily flights directly to Los Angeles, Las Vegas, Seattle, and Portland. There is only one terminal and everything is easy to use. It also has a pretty good restaurant right in the building, with patio seating. I find this incredibly convenient and easy to use if flying to or from the above cities and everyone I know who has flown to or from here agrees. This is the only airport in the North Bay Area that has commercial passenger flights.
It's at the very western end of Airport Blvd, which cross Hwy 101 just north of Santa Rosa and south of Windsor. From Hwy 101, just take Airport Blvd west until the end.
One can get information from the airport and its website and one can make reservations directly at the Horizon Air/Alaska Airlines website.
Considering the sorry state of public transit in California, Santa Rosa is actually well served by a good by network. It is the focal point for bus transit in Sonoma County.
The central focus is the Transit Mall downtown along 2nd Street between B Street and Santa Rosa Ave. Three bus systems converge on the Transit Mall: Santa Rosa CityBus, Sonoma County Transit, and Golden Gate Transit. The latter is primarily useful for getting between Santa Rosa, San Francisco, and any town in between. The others are best for getting around the Sonoma County area.
The key system is Santa Rosa CityBus. This operates an extensive network of lines going all over Santa Rosa and connecting downtown to all other areas. As a result, on can easily get to within walking distance of any part of Santa Rosa by taking the bus.
The main problem is that, as often with such systems, one may need to take a few different lines to get between areas, especially between two stops not in downtown. This can make a trip a lot longer and less convenient.
A good aspect, though, is that since all the bus lines end up at the downtown transit mall, it is very easy to get between downtown and other parts of town on one bus.
Although we live on the edge of downtown and almost always walk to and through downtown, and although we do have cars, sometimes we find the bus to be convenient and enjoyable to use.
You must have access to an automobile due to the fact that Santa Rosa and Sonoma County have the worst public transportation ever. I know, I used to ride the bus and it was not a good experience. United Airlines used to have a quick hop to SF and LA but cancelled it due to lack of riders. That's sad.
I used www.picharters.com and chartered a jet for 15 from LA to Santa Rosa. Great people, great time, great wine!