I'm not sure about Pacifica, but I'm guessing you won't get many replies in this thread otherwise. While I'm more of a xc kind of rider, it is my impresson that most of the potential shuttles in the bay area have some issues around them - private roads, illegal trails, sometimes both issues at the same spot; issues with neighbors near legal trailheads; conflicts with other users on multi-use trails; even battles over trail access with local clubs. I think that has a lot to do with the prevalence of long travel trail bikes in this area.
My advice is look, listen, be sensitive to the various local trail politics / access issues. And folks more in the know than I may be able to help you via word of mouth or via private message.