Recollections of My Life and Reflections on Times and Events During It: A Memoir by Father W. J. Howlett

Sand Creek massacre

On November 29th, 1864, Colonel John Chivington and his men attacked Native Americans in the village of Sand Creek in the Colorado Territory. During the attack, the soldiers mutilated the bodies of the dead Natives, including those of women and children. Accounts of the attack lead to investigations by the Union government as well as reprisal attacks on settlers by Native Americans.

https://www.nps.gov/sand/learn/timeline.htm