Lucio V. Mansilla (1831-1913), the widely traveled and cultured scion of a famous family, was a colonel in the Argentine army when he undertook an "excursion" to the Argentine interior in 1870 to visit natives in areas then largely unknown. Mansilla's uncle, dictator Juan Manuel de Rosas, dominated most of Argentina from 1829 to 1852 and had led successful military expeditions against the frontier Indians in 1852. Mansilla set out for a reconnaissance...