I'm presuming from the sign that this metal, pyramidal object once contained explosives. It's location seemed random: it sat on uneven ground amongst some rabbit brush and sagebrush, near one small juniper tree and some scattered, irregular mine dumps.
Set of rungs or handholds going up one side.
It was sturdily built: notice the rivets or bolts lining the edges of the metal sheets. This type of structure is atypical compared to the usual sorts of powder magazines or powder houses I've run across in the field before, which are more often dug into the side of a hill, sometimes consisting of a short adit with a sturdy metal or wooden door, and sometimes being a small, dug-in room or building like this one found in Tonopah or this one from the Matchless Mine in Colorado.
No rungs on the opposite side.
Inside, the metal can be seen to be riveted or bolted to sturdy, wooden crossbeams. The wooden floor was a bit worn, and pack rats had been using the area.