I got tired of waiting for the local DFG/CDFW to call me back, so I called their main enforcement division number in Sacramento.
The warden I spoke with could not tell me what the violation would be, exactly, and I'm no lawyer or expert on CA code sections either. He explained that it's hard to know what the violation would be without knowing precisely who was responsible for the region of Back Bay in question: county or state. He reckoned it was a county thing, but was not sure. In any case, if it really is a violation at the state level, it is an infraction, probably of section 550 (b) of the CCR:
(b) Area Regulations:
[...]Permit Requirements. No person shall enter any State wildlife area or portion thereof where the department has limited public entry without a valid entry permit in their immediate possession. [See subsections 551(f), (g), and (h) for regulations regarding general requirements and costs for individual entry permits.[...]
There is no bail listed for this in the
OC Bail & Penalties Schedule that I could find, but according to
this:
(b)Notwithstanding subdivision (a), any person who violates any of the following statutes or regulations is guilty of an infraction punishable by a fine of not less than one hundred dollars ($100), or more than one thousand dollars ($1,000), or of a misdemeanor:[...]
(9)Sections 505, 507 to 510, inclusive, and 550 to 553, inclusive, of Title 14 of the California Code of Regulations.
Now, using the Uniform Bail and Penalties schedule as a guide, infractions with a base fine of $100, like fishing without a license, have (in the 2013 schedule) a total bail of $485. There are other infractions which have higher base fines, but the total bail is not quite proportional. I found at least one example with a base fine of $250, which gets you a total bail in excess of $1100, but the vast majority of infractions listed have a total bail of $485. So my guess would be that getting caught riding the CDFW-administered portion of Back Bay without a pass or appropriate license would prolly get you a $485 citation.