I flew SNA-CCR for a weekend trip (~$500 r/t, booked about a week prior) and it was cheaper than WN SNA-OAK.
Here are fares for next Fri Jul 18: SNA-OAK/CCR
NK $130 (BE)
JSX $291
WN $337 (and bags don't fly free anymore..)
I don't know what's going on with Southwest on this route but it's making JSX look good by comparison.