...and the private landowner as well. You get a bunch of drunk idiots out there and see what happens: they destroy the terrain and roads, smash bottles everywhere and leave garbage, and spray graffiti? And then there's the potential for somebody to accidentally start a fire (not that difficult out there) or to bring a gun to go "plinking" and accidentally hurt someone (and don't get me wrong- I like guns. In responsible hands, that is). Huge liability for the government. And the private landowner...? Hell, I'd have put up a gate against that douchebaggery if I were them.
Can't say I blame them, really. And remember, I admit to being one of the ones who went over the embankment (although many people had clearly done it before I did). In my defense, I did nothing more than bypass what I consider to be an illegal closure of public lands

, but I'm sure that they don't see it that way. And the bypass of the gate had the exact result that I expected the moment that I saw it: an extended barrier (a very extended one, at that).
A true legal challenge would penetrate the "sensitive species" stuff, but it would take a lot of time, effort, and money. Based on my experience (which is admittedly not encyclopedic), the executive branch of the government doesn't tend to back down when confronted I such a manner; they dig in. Since the government has more resources, they have the advantage in these situations. Thus, the way to handle the legal challenge would be to make it a class-action type of case, bringing in multiple plaintiffs in similar circumstances, affected by the same defendant (i.e. The Forest Service, BLM, SD County, etc.), and illustrate the unconstitutionality of their ongoing actions. A big, big fight that would likely lead to appeals, potentially reaching the Supreme Court. Don't laugh- it happens. That's the way that many of our most contentious laws get created and changed.
By the time it got through litigation, I'd probably be more concerned with not breaking a hip going down on the stairs. I just want to get outside with the kids and enjoy it. The most likelyway of accomplishing that with respect to Pancake Rock would be to (quietly) speak to people in the various clubs and find out what they know. The great thing about the area being "closed to vehicular traffic" because of "sensitive species" is that a registered club could (again, quietly) apply for a special-use permit, taking the liability off of the government and providing the assurance of responsible use.
Any thoughts, suggestions?