I have heard the smallpox blankets story many times and I'm ashamed to say I believed it. It's quite a revelation to learn the source.
Interestingly enough, the well known painter George Catlin visited with and memorialized the Mandans just before they were almost wiped out by the smallpox epidemic. They are one of the best documented Indian groups. Besides, his paintings are gorgeous. We saw an extensive collection in D.C. year before last.
Medicine man Mah-to-he-ha in his ceremonial regalia.