Here's another picture from my trip to the Keweenau peninsula in Michigan's Upper Peninsula last weekend.
This is the Lake Superior shoreline at the site of the Mohawk Stamp Mill.
Stamp mills processed ore removed from mines by pulverizing it with a series of machines to remove the copper. Copper was shipped to a smelting facility, while the rest, ground and smashed into a coarse-grained sand, was washed down into a body of water (Superior in this case).
This sand reaches about half a mile out past the original shoreline, sits in ten to fifteen foot dunes, and stretches literally miles down the shore, millions of tons of what used to be the underground rocks of the Keweenau, now become fill for artificial land. This material is completely inorganic; nothing grows in it. Standing here is uneartly, like being in a moonscape. And this mill hasn't operated in seventy years.
The concrete tunnel is the structure that once held a wooden launder, the chute that the stamp sand and water mixture from the mill was sluiced downward into Lake Superior through. As the shore of the lake filled up with waste sand, the chute was just extended further and further out over what had once been the lake waters.
Much fascinating information about this site is here at The Copper Country Explorer