In Borderlands 2, there are many different treasure locations. To find the treasure chest in the Rustyards, look for the "X" to interact with. It will be located within the worn shacks that are full of garbage. These shacks can be found near the west end of the yards. Just make sure you stay close to the cliff side. This is for the mission "Message in a Bottle."
A bug has been hitting the Borderland 2 games, so be careful. It acts very much like a virus, and it erases a players saved game data. It came from players who were hacking the game.