I stumbled upon this at work researching something unrelated. California has what is referred to as "Hazardous Recreational Activity" laws that protect public entities from lawsuits related to extreme sport injuries at public facilities. An excerpt:
Neither a public entity nor a public employee is liable to any person who participates in a hazardous recreational activity, including any person who assists the participant, or to any spectator who knew or reasonably should have known that the hazardous recreational activity created a substantial risk of injury to himself or herself and was voluntarily in the place of risk, or having the ability to do so failed to leave, for any damage or injury to property or persons arising out of that hazardous recreational activity.
I feel it no mystery that this legislation coincides with the mass proliferation of funding and support for public skate/bike parks in western states. I could not find any similar laws in Michigan. It goes without saying, but passing this type of law in Michigan would be a HUGE first step in getting more official support for adding freeride features to trails. Who’s in the know? How to get it started?
Here's the link to the whole law: http://law.onecle.com/california/government/831.7.html