First locate the Dusty Depot Treasure Map.
That map is located at Dusty Depot.
It is located on the south wall of the middle building:
Here it what it looks like:
The map shows the treasure ("X" marks the spot) next to a pine tree. Nearby landmarks include a chair, a big tree atop a hill, and a house with a car on its roof.
All those landmarks can be found in a small complex south of Shifty Shafts. See screenshot below:
The pine tree is on the north side of the complex. Go next to it and a Battle Star item will pop up. Collect the yellow star to complete the challenge:
Location of Treasure Map in Dusty Depot:
Location of where to complete challenge:
- 10 Battle Stars
- You don't have to actually examine the treasure map in Dusty Depot, you can go straight to the location as indicated here.