I have not camped at Grinnell camp, but unless things have changed, be prepared to lose the trail very soon after crossing the creek at the South Fork. A couple of years ago after the area opened from the lake fire, I hiked all of Grinnell Ridge to its peak beginning from the trail from the South Fork trail. The trail disappeared very soon and I ended up just scrambling up to the ridge through and around dead fall and buck brush. Not sure the trail has been rebuilt since. Maybe someone else knows who can chime in.