This is the Mesa Biome at the South (or "Far South") of the map.
It was generated during the world expansion- which was after the 1.8 update, which meant that Mesa's had a giant excess of gold ore to utilise.
The Far South Mesa has however been poached of much of this gold, but still remains relatively unclaimed by the factions of the PirateCraft server. Only if the world border is expanded once more or the area is regenerated, then the gold and it's Mesopotamian-esque ruins will be generated once more.