Livermore KLVK has three and a half flying RV-10s (the half is here only in the winter). Inexpensive tie downs. There are a number of local wineries. Wente has a good golf course and excellent restaurant. Airport has a city run golf course. Rental car is Enterprise. Napa is an hour's drive. Lots of hotels and restaurants within 10 miles, moderately priced. Pleasanton is the end of the BART line in case you want to go to San Francisco.
Napa KAPC is of course at the south end of Napa valley. GA friendly, has rental cars. Hotels are expensive in August. Traffic up the valley is a two lane road, jam packed on summer weekends.
Santa Rosa KSTS is GA friendly, okay restaurant on the field, rental cars.
Mendocino is a great place to visit but the airport (Little River, KLLR) is somewhat lacking in services. Rental cars need to be arranged in advance, I think Hertz or Enterprise in Ft. Bragg will leave a car for you. Highly recommend a drive up to Ft Bragg, or south, on highway 1 along the Pacific. Or, drive south east to Boonville, lots of wineries. Boonville has a vfr only airport but no ground transport.