Pile of Bison skulls in the 1870’s. They were killed by hunters who were paid by the U.S. government.
“How many of you know the actual context behind this picture? It’s one they certainly don’t teach you in school. The U.S. Army promoted the wholesale extermination of bison herds in order to defeat the Native Americans, as bison were their main food supply. The U.S. government actually paid a bounty for each bison skull recovered. A section of the Royal Museum of Alberta in Canada has a small section dedicated to this, with this very picture.” (Source)
Throughout the 1800’s the North American Bison were hunted to such an extreme that their numbers declined from tens of millions to under less than one thousand.
You can see the pile is in front of a processing plant (it’s in the background). Bison bones were ground up into bone meal fertilizer or charred to make bone black, a substance with several uses (one is refining sugar, bone black can be used to absorb impurities and help give the sugar it’s white color).