While I can't confirm that, on the assumption that BoFax is a county road, it would be the Marin Sheriff that would have jurisdiction. I also found this article that starts with the quote "Marin County Sheriff’s Office confirmed that Bolinas-Fairfax Road has been closed to all traffic" so everything points to them.
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I found this article saying construction is ongoing, so looks like that's why they're enforcing the closure now.
http://patch.com/california/petaluma/repairs-begin-marins-fairfax-bolinas-road-closed-winter-mudslide article,