Honolulu and San Francisco are about 2,395 miles apart by road. Split the difference and you arrive near San Jose, the city closest to the halfway point between them. That puts roughly 50 hr 36 min of driving on the Honolulu side and 1 hr 3 min on the San Francisco side — the fairest single meeting point among the cities near the middle.
Over this distance most people will fly rather than drive the whole way. San Jose still makes a fair, central place for Honolulu and San Francisco to converge, splitting the travel instead of asking one side to cross the country.
If San Jose doesn't have what you're after, Sacramento and Los Angeles are also close to the midpoint and worth a look — each keeps the drive reasonably balanced between Honolulu and San Francisco.
City descriptions adapted from Wikipedia (CC BY-SA); photos via Wikimedia Commons, credited above.