Side Mission: Uncrate
After freeing the U.S. Auto outpost in John's territory (and part of Merle Briggs' Death Wish mission), talk to the guy with the mission marker for this one.
This will spawn three plot markers inside the U.S. Auto grounds, each one a lost soldier. One of them is in the shop building by the south entrance (right behind the weapon merchant).
The soldier here has just locked herself in the bathroom. The key is on the counter.
Unlock the restroom to free her.
Another plot marker is nearly due north of there. Look for a yellow cargo container stacked on a reddish one.
Shoot off the lock to free another soldier.
The last marker points you to another yellow container, this one off in the far northeast corner of the yard, possibly guarded by a bear.
Kill or drive off the bear, then shoot off the lock again. Unfortunately, this solider has already been mauled to death by the bear that was also locked inside. Despite this mishap, the discovery completes the mission.