One of the larger buttresses on the east side. In the "middle tier" of the crags on this side. Many high quality all trad & mixed lines.
Getting There
Park in the large lot immediately after crossing the Gallatin River (if coming from Bozeman). Cross the road, aiming for the prominent trail. Follow this trail alongside the river for ~10 minutes until a junction past a large "house-sized" boulder in the river. Head up the hill and pass some smaller buttresses. The trail gets sort of steep and there are a couple switchbacks. Eventually it will deposit you smack dab in the middle of the south face of Black Line Buttress. Allow 20-25 min.