063 N of Copper Mill Yard camp: Use a rope arrow to pull open a cave blocked by roped up boards to find a Strongbox.
064 SE of Copper Mill Yard camp: Pry open the door of the first building by the base camp you for a Relic.
065 SE of Copper Mill Yard camp: A small southern building houses several bunks as well as a Document.
066 SE of Copper Mill Yard camp: Pass the bunkhouse and the train car. A Survival Cache is buried by the wall.
067 SE of Copper Mill Yard camp: A Mural is located on the outside of the first building by the base camp.
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069 SE of Copper Mill Yard camp: Climb the ladder and jump across to get inside the upper levels. A Document is immediately on the left as you enter. Climb the nearby ladder and continue through the building to find a fenced off Strongbox. To get it, simply climb over the nearby wall and drop down behind the fenced off area. You can climb back out, or continue into the nearby Excavation Shaft Tomb.
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077 SE of Copper Mill Yard Camp, in the Excavation Shaft: This Tomb has access to many treasures. This includes three Survival Caches, two Relics, two Documents, and a Mural. Items found inside the Tomb are not shown on the map.
078 SE of Copper Mill Yard camp: In the main building, past the fenced off area with the Excavation shaft, a burnable curtain of cloth and debris hides a small room with a Relic.
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082 SE of Copper Mill Yard camp: the wooden building on the upper floor houses a Relic on the lower floor. Look for a Mural when you’re exploring the building with the breakable wall that slides down to the bottom of the mill. The Mural is across from the rope wall that you break to descend. You can also claim a Strongbox here. If you miss the jump you have to go all the way back up to try again! Once you have it, use the nearby rope pillar to ascend to another Relic.
083 NE of Copper Mill Yard camp: The upper level of the mill requires some climbing, balancing, and swinging on ropes. After climbing the large red fuel tank, Work your way to the top level for a Strongbox, but remember to bring your Lockpicks.
084 E of Copper Mill Yard camp: Continue to rope and climb the upper Mill section. Work your way to the southern section of the upper level to find a Document on nearby tables.
085 E of Copper Mill Yard camp: At the top of the mill, before swinging across on the rope bundle, collect the Document on the table.
086 NE of Copper Mill Yard: You pass through a crusher room before reaching the fiery section that ends the mill portion of this area. A Strongbox is in that room, on the right side.
087 E of Copper Mill Yard camp: The inside of the upper mill is barren of collectibles, but pull down a set of roped up boards overhead to find a ledge that takes you to a slide. At the bottom is a Relic, and a burnable cloth wall.
088 Far NE of Copper Mill Yard Camp: As you reach the next Base Camp (Copper Mill Bridge), you get a Strongbox. This isn’t available until later in the game.
089 NW of Copper Mill Yard Camp: A Survival Cache is buried in the snow underneath the wooden walkway leading to base camp.