The Clay Deity Head is the fifty-sixth treasure that can be found in Uncharted 2: Among Thieves.
The Clay Deity Head is found in Chapter 17 - Mountaneering. Tenzin will find a rope in the remnants of the campsite at this location, at which point Drake and he can climb back up to the same snowy platform you originally entered the area via. The ability to swing across the campsite to a platform on the other side is now given, but first, why not jump on that rope and simply hang around for a while? Instead of swinging across, the change the rope's momentum so that it swings in the other direction, rightward to leftward and back again. You'll be able to swing to the right side of the room in this way, where an isolated platform containing this treasure can be found. Swing and jump, hang off of this platform, and grab your prize.