While your question is not particularly specific, I'm assuming you're trying to attack the city blocking your way through the pass. This is not something that you're supposed to do; rather, you're supposed to go hunt down three groups of Urxen sitting on little villages and kill them off. Once you've done that, you should be able to pass the city. Two of the groups should be slightly to the Northwest of Redstone (following the road that leads in that direction will bring you close to them), while the third should be roughly directly South of Redstone, on the dead-end road that leads into the forested valley, if I recall correctly.