Depends on how much time you have. I would put both SF and Charleston as primo tourist destinations, however, Charleston has soooo much more history to explore. I think a west coaster (if raised there) would be fascinated with our salt/tidal marshes. As mentioned, a drive from Murrels inlet through Pawley's, McClellanville, Shem Creek, Ace Basin, Beaufort, Hilton Head. Or do a Charleston and Savannah excursion. The Columbia trip is a easy drive, like mentioned, State house, state museum, Riverbanks & Botanical Gardens, etc. Upstate, Lake Jocassee, Hagood's Mill, Blue Ridge parkway, Cowpens and King's Mountain battle sites, and Biltmore should be entertaining to a west coaster.
Again, depends on how much time. You might consider them flying into Charleston, pick them up there, tour there, maybe spend the night, next day drive to Columbia and tour, then drive home, next day do the upstate, if you have the time.