The Apache had relocated to Camp Grant in February and March 1871, when the pressures of white settlement and the complexities of regional land conflicts drove more than five hundred to seek federal security and rations in exchange for a promise of peace. The officer in charge of the facility, Lt. Royal Whitman, described the Indians as quite agreeable and later emerged as their strongest -- if most futile -- defender. Meantime, livestock raids and reprisal killings continued apace in the region, and community leaders elected to blame the Aravaipa, whom they alleged were continuing to harass white settlers in Tucson, San Xavier, Tubac, Sonoita, and San Pedro. In late March, prominent white Tusconans formed the Committee on Public Safety, a citizens' group that unsuccessfully petitioned the federal government for protection and redress. Finding no satisfaction, William S. Oury -- a veteran of the Mexican War and a former delegate to the Confederate Congress -- organized a hunting party and set them loose upon the Indians camped at Fort Grant.
Just after dawn on Sunday, 30 April 1871, the armed posse began firing upon the Aravaipa, who were still sleeping. C. B. Briesly, a surgeon in the US Army, described the aftermath later that year in a sworn affidavit presented to the Bureau of Indian Affairs.
The camp had been fired and the dead bodies of some twenty-two women and children were lying scattered over the ground; those who had been wounded in the first instance, had their brains beaten out with stones. Two of the best-looking of the squaws were lying in such a position, and from the appearance of the genital organs and of their wounds, there can be no doubt that they were first ravished and then shot dead. Nearly all the dead were mutilated. One infant of some ten months was shot twice and one leg nearly hacked off.As with the Chivington Massacre in Colorado less than a decade before, the Eastern public was astonished to hear word of the slaughter. President Ulysses S. Grant denounced the conduct of the vigilantes, while other federal officials called for justice to be served.
In the trans-Mississippi West, the appraisal was considerably more generous to the perpetrators of the massacre. In December 1871, more than 100 defendants were found "Not Guilty" of the crime of murder of 108 people at Camp Grant. After a trial that sensationalized and distorted the record of Apache depredations against whites, the jury took a mere 19 minutes to reach its verdict. Relations between the various Apache bands and the United States degenerated quickly into an open war that would carry into 1873.