Out on the Ebb Tide Achievement
Out on the Ebb Tide15
Take down Shelby Cross in Copper Mountain QuarryThis achievement is mutually exclusive with The Great Escape (15G). At the end of the Bounty Hunter chapter, you will be tasked with saving your husband. Save when you reach him so you can reload and get the other option, which is the one you will want to carry forward as your "true" choice.
For this achievement, you'll need to access three levers to open the unbreakable door and confront Shelby Cross. The first one is across a gap from the broken railroad tracks, jump across to reach it. The second is hidden inside the red curtain behind where your husband was imprisoned, you'll need to jump over to the ledge on the right to get there. The last one is on top of a high ledge, so carry a barrel to it and jump up. Once you have hit all three levers you can go through the door, kill Shelby, and escape to unlock the achievement.