For 3 weeks in Jan/Feb of 2013, I was doing weekly runs between LAX-SFO, and I noticed that the first flight of the day (6 AM) flight was a flatbed 757. (I think continuation onward to EWR each time.) I had fun there for 2 weeks, getting the flatbed for the 50 minute flight.

In the third week, it was the same thing, except the flatbed 757 got subbed at the last second by a 739.