You're on the right track with fighting it.

If you think the speed limit was incorrect take a picture w/i 1/4 mile of where you got caught. That will give you the correct posted speed limit, but you were probably still speeding.

The cop will probably show up. I've helped a lot of people with tickets and my own tickets and the state and local cops always showed up. That's the good news. Assuming you have a fairly clean driving record, plead your case with the cop off the record. Admit that you were out of line but politely ask that they lower the charges to mimimize the effect of the ticket, ie. lower fine, less points whatever they can do in CA.

You'll have to pay a fine but hopefully the cop will be reasonable and they will not throw the book at you.