A pile of American Bison Skulls (Circa 1892)

A pile of American bison skulls waiting to be ground for fertiliser (circa 1892) unknown photographer taken outside of Michigan Carbon Works in Rougeville, Mich., in 1892.

At the close of the 18th century, there were between 30 and 60 million bison on the continent. By the time of this photograph, that population was reduced to only 456 wild bison.