After entering the Fissure of Sorrow you creep along the dam until you get to third vehicle. On the right before you get there is a gated access way. In the back of the vehicle is a 308 sniper rifle and a bunch of ammo. Beyond the trunk on its side in front of you are several super mutants. You can kill the master with the sniper rifle from the out cropping, up to you, or you can retreat like Annai Oran suggests. Going forward brings more to the story. This is as far as I have gone this round.