hmmm... seems like you're new to the flight booking business....
If you book a flight in the off-season (always round-trip !!! btw !! always!)
which in SF probably is Jan - April and you book it at least 3 months in advance, you'll be able to get the price down even more.
Oct - Dec is also worth a try with Oct being the best month to visit California hands down.
But you have to watch out for holidays in that time frame (Thanksgiving, Halloween, and so on)
For example:
If I was to book my annual flight to Austria on the 20 -23rd of December it would cost me $2000 USD because everybody wants to be home before Christmas.
Since we don't have little kids in the family and it doesn't matter if we celebrate a day late, I fly out on the 24th.
There are no lines at the counters and the flight is only $500 to $600 . . .
See?