In the late 1870s, the Osage Nation was displaced from its Kansas roots and moved to an Oklahoma reservation—land that turned out to be sitting on an oil goldmine. As told in David Grann's piece for the New Yorker (an excerpt from his upcoming book, Killers of the Flower Moon: The Osage Murders and the Birth of the FBI, to be published in April), Mollie Burkhart and her family were among those Native Americans on an official register who started receiving royalty checks and lease fees from oil prospectors, to the point where Osage members racked up millions of dollars and were deemed to be, per capita, the richest people on Earth. Newspapers at the time reported on both the exorbitant wealth of these "red millionaires"—complete with expensive furs and jewelry, mansions, and servants—as well as any indication of the "primitive" way of life that white people assigned to "wild" Indians.
But then the mysterious disappearances and deaths started: One of Burkhart's sisters, for example, died in 1918 from a "peculiar wasting illness" (she'd been just fine up to that point), and in 1921, another sister, Anna Brown, simply vanished. By 1923, dozens of the Osage had been found dead—and the DOJ office that eventually became the FBI picked up the case, one of its first big murder investigations. Meanwhile, about a week after Brown's disappearance, a teenager made a discovery while squirrel hunting near a local creek that brought closure to Burkhart's family, as well as the "first hint of the darkness" about what was to come down on her tribe. More on the Osage saga here. (This is the "lost site" of the biggest Native American massacre in history.)