On January 23, 1870, United States Army forces under Major Eugene Mortimer Baker attacked a Piegan Blackfeet camp on the Marias River in Montana Territory, killing approximately 200 Native people, most of whom were women, children, and older men. The attack was intended to punish Mountain Chief's band of Piegan Blackfeet, but the soldiers instead struck a different band led by Chief Heavy Runner, whom the U.S. government had previously promised protection.
The events leading to the massacre began with the murder of rancher Malcolm Clarke on August 17, 1869, by Owl Child, a young Piegan warrior, and his companions. The killing followed a prior dispute in which Clarke and his son Horace had beaten and humiliated Owl Child, and accounts from Blackfeet sources describe Clarke assaulting Owl Child's wife. After Clarke's death, the U.S. Army demanded that the Blackfoot Confederacy execute Owl Child within two weeks; when this deadline passed, General Philip Sheridan ordered Major Baker to "strike them hard" against Mountain Chief's band.
Baker's command, comprising four companies of the 2nd U.S. Cavalry and a mounted detachment of the 13th U.S. Infantry, left Fort Ellis on January 6, 1870, and moved north from Fort Shaw on January 19 in search of Mountain Chief. On January 22, they captured a small camp whose occupants directed them to nearby camps. Baker's forces located a camp of 32 lodges and positioned themselves on high ground before dawn on January 23. Scout Joe Kipp identified the camp as belonging to Heavy Runner, a chief considered peaceful, but Baker ordered the attack regardless, reportedly threatening to have Kipp shot if he warned the camp. Heavy Runner was shot and killed while approaching the soldiers holding a safe-conduct paper. Soldiers then fired into lodges, killed occupants, and burned the camp, according to survivor accounts including those of Spear Woman, Buffalo Trail Woman, Long Time Calf, and Bear Head.
Casualty counts varied significantly among sources. Baker's men reported approximately 173 dead; scout Joe Kipp later reported 217 dead; and Blackfeet agent William B. Pease, after interviewing officers and survivors, reported a breakdown of eighteen older men, ninety women, fifty children, and fifteen young men killed. Pease's report, publicized via a letter from Vincent Colyer of the Board of Indian Commissioners that was published by The New York Times and read in the House of Representatives, sparked national outrage. Military officials, including Colonel Philippe Régis de Trobriand and Major General Winfield Scott Hancock, defended the attack and disputed the proportion of non-combatant casualties. No formal military investigation was conducted, and Baker's reports became the official record. Baker continued his military career, later commanding Fort Ellis and leading Yellowstone survey expeditions, before his 1872 arrest for drunkenness; he died in 1884.
The massacre contributed to a shift in federal policy, as President Ulysses S. Grant moved toward a "Peace Policy" and appointed Indian agents recommended by religious organizations. The Blackfeet Reservation was subsequently reduced through executive orders in 1872 and 1873 and further diminished by the 1887 Dawes Act. A memorial has been held annually at the site since organized by Blackfeet Community College, and the Baker Massacre Memorial was erected in 2010.