Hello. Celebrity's MERCURY sails from LA to Mexico Rivera (11 nights) around October to March then heads up to San Francisco for April and May 7 nights California and Baja Mexico.
RCI's MONARCH OF THE SEAS sails year round 3 and 4 nights Baja Mexico from LA and so does Carnival's ECSTASY (which wiill be replaced by a newer but same class PARADISE in the fall of this year)se
There are a few repositioning cruises in the spring and fall times.
All the ships offered are great.