Hi Logan, I am the recreation manager on the Lost River Ranger District in Mackay, Idaho, and I have been asked to answer your question on the King Mountain Hang glider site. The launch site is located on public land, so a membership in a club or organization is not necessary to hang glide there. However, King Mountain is an advanced flying site known for strong thermal conditions, moderate turbulence, and occasional high winds that can develop quickly. Several passes/gaps exist in the Lost River Mountain Range to the north that will compress and multiply the existing wind speed. Rams Horn Canyon, Pass Creek, and Double Springs Pass are examples of these features. Take extra care to approach these locations with sufficient altitude and upwind clearance such that a forced landing in the canyons/pass is avoided. It’s also a good idea to contact a local pilot prior to flying here for the first time. Thanks! -=Melissa=
This matches what I got from Utah DNR:
The rules at the park are as follows. We do not require flyers to be members of the local club or USHPA to fly at the flight park. We encourage and think it's a good idea to be members and receive training with a group, as from what I have found, offers some good insurance coverage if you are, but it is not required to be a member.
As far as I can tell, the National Park Service is the only public land entity that doesn't understand Federal Law.
Logan