LAX-STS on a DH-8 Q400. Takeoff was 50 minutes late due to a "mechanical problem." Upon beginning the descent, the pilot announced that Santa Rosa Airport was closed due to fog. After circling for 30 minutes the flight was diverted to Oakland. Passengers were unceremoniously dumped off the plane into the terminal, and the only thing Horizon Air bothered to do was arrange for a shuttle from Oakland to Santa Rosa - 3 HOURS after the plane touched down. Flight attendants and ground crew couldn't be bothered to even apologize. I booked a return flight with them, but I will be flying Southwest out of Oakland instead. Horizon Air did a disgraceful job and I will NEVER fly with them again.