The slag is jet black, the silicate rich remains of the furnace used the extract the copper from the host rock.  This molten material was cast aside and grew to this mound, taller than a house.

The men of Rosalie would hold community dances on this slag pile, almost perfectly flat – it made a good dance floor.  Life in the desert, a hundred years ago.

You can see this mound from the I-15, in the desert – if you know where to look.