I notice that there are plenty of bookable on-line taxi and shared-van shuttle services from SFO airport to Sacramento and I would use one of those. We got on very well with them when in Los Angeles, where the public transportation was very strange, to say the least! I would, however, recommend a ride on Amtrak whilst you are there, slow and scenic though it might be. Day trip to Santa Barbara, perhaps, or a longer one to San Diego would be nice on the Californian Zephyr. Watch out though, not all Americans like to be photographed!