Is the top of the mountain at the top of the gully?
No, but almost. Once you finish the class 3 portion at the top of the gully, the hardest parts of the climb are over. After the gully you have about 200 feet of easy talus climbing on an open slope.
Just a little more info. The class 3 portion is to the right of the cliff at the top of the chute. After about 60 feet of climbing you are on the summit plateau.