Anvil Rock is a massive tabletop mesa on the moon Choss.
In 2393, a group known as the Anaranjado Noventa arrived at Anvil Rock and decided that it was a place of spiritual significance. This was the birth of the colonization of Choss. The inhabitants of Choss came back every centennial to celebrate their arrival on the moon.
After the troubles, the Terran Dominion declared that Choss had been purified of zerg, but missed a spire of mutalisks hidden at Anvil Rock. They fed on the surrounding game bats and range boars, but after their population began to dry up they began attacking human tourists.
Breg Shaw, Marshal Rin Shearon and Professor Brad Champlain tracked the mutalisks to Anvil Rock, but the mutalisks trapped them and killed Shaw. Shearon was able to lure the flock over their spire, and hit it with a punisher grenade, killing the entire flock and destroying the spire.