They changed the west division pairings after 2008, from OAK&SD or DEN&KC to OAK&DEN or SD&KC.
In other words, in the past every 3 years OAK&SD would be on the road, DEN&KC would be at home, and they'd alternate home/away.
But after the complaints in 2008 about the Pats and Jet both having two AFC west games on the coast, they switched the pairings since DEN and KC are same division but not as long a trip.
So now every 3 years OAK&DEN will be on the road, DEN&KC will be at home, alternating home/away. So no more double California trips.