State Parks Access Restrictions?

Okay...long story short.

So, I live in Missouri, and there is a state park nearby that is building a bike trail...after several months, the trail is built. However, the state park says that no one is allowed to go onto the trail until they declare it "open". They advise us that tickets will be issued if we use the trail.

This is not a natural or wilderness area, btw.

Is this even legit? I thought that if state parks and public lands were open, then you could enter as they are public land...within reason of course. But can they restrict and write tickets for trail use on a trail built for bike use once it is in place?