I can’t believe that they slapped you with a misdemeanor; I could see a summary offense? Do they have an ARD program? I would also consider writing an editorial for the local paper. Surfing is part of the USA coastal cultural. Placing a black mark on a young person’s record for something like this is way too much government interference with freedom. Local governments can often be the worst!
read the rules and regs at that website. it sounds like you were in a no surfing zone and therefor trespassing. either you are full of it about getting a misdemeanor or you literally have no common sense/lawyer. go down to sweetwater and cry about it.
Did you mug someone while you were in the lineup? 6 months probations for surfing beside a pier? The cop must either be a fisherman or you were out at his spot while he had duty and was angry at the fact. I could see that happening. Sad.