I think the signs got put up after someone got killed by a rockfall.

It's a little lesser known, but check out the Edward Lake Cliff area in Lansing. You can follow the gorge up a ways and it ends up in a beautiful waterfall close to 34 with some of the best acoustics I've ever seen. I think you can park just off of Sun Path to get down there, but the Lake Cliff area is a beautiful hike. Bring some boots that are ready for serious mud if you're there in the spring though. We're talking the kind of mud that'll pull normal shoes right off your feet.

Also there are a bunch of wild juniper and Asian pear trees throughout!