3rd Colorado Cavalry The Third Colorado Cavalry was formed in the mid - 1860s when increased traffic on the United States emigrant trails and settler encroachment resulted in numerous attacks against them by the Cheyenne and Arapaho . The Hungate massacre and the display in Denver of mutilated victims raised political pressure for the government to protect its people . Governor John Evans sought and gained authorization from the War Department in Washington to found the Third . More a militia than a military unit , the " Bloodless Third " was composed of " 100 - daysers , " that is , volunteers who signed on for 100 days to fight against the Indians . ( Its nickname came from its lack of battle experience . ) The unit ' s only commander was Col . George L . Shoup , a politician from Colorado . The regiment was assigned to the District of Colorado commanded by Col . John M . Chivington . At the Camp Weld Council of September 28 , 1864 , Evans and Chivington met with five chiefs , including Black Kettle of the Cheyenne and White Antelope of the Arapaho . They had been brought to Denver to parlay for peace under military escort by Major Edward W . Wynkoop , commander of Fort Lyon . The chiefs agreed to peacefully settle their people on the reservation on Big Sandy Creek about 40 miles northwest of Fort Lyon . The reservation was created under the Fort Wise Treaty of 1860 . With Wynkoop ' s assuring their safety , the chiefs settled their bands in a large village at the curve of Sand Creek . Some Indians set up lodges closer to Fort Lyon . On November 5 , Major Wynkoop was removed from command and replaced by an ally of Chivington , Major Scott Anthony . He ordered all Indians camped around the fort to the reservation . On November 26 , Wynkoop departed for reassignment to Fort Riley , Kansas . Two days later , Chivington arrived at Fort Lyon , having traveled in great secrecy with 700 Third Colorado Cavalry . Encouraged by Governor Evans and spurred by his own ambitions , Chivington felt pressure to use the " Bloodless Third " before the volunteers ' terms expired . He sealed off the fort . Officers loyal to Wynkoop were held at gunpoint . That night , reinforced by artillery from the fort and 125 troops of the First Cavalry , Chivington set off for the Cheyenne - Arapaho village at Sand Creek . The Sand Creek Massacre . Arriving at dawn on November 29 , 1864 , the volunteer militia attacked . Although Black Kettle had flown an American flag on his tipi to signal peace ( as directed by Wynkoop ) , the volunteers killed indiscriminately . Historians have not agreed on the number killed , but they often cite 150 , mostly women and children , as the warriors had gone out on a hunt . The militia mutilated some of the corpses , taking body parts as souvenirs . Now called the " Bloody Third , " the regiment returned to Denver in December . It mustered out on December 31 , 1864 . For months the men displayed the body parts as trophies in Denver saloons . Although Chivington and his forces were lauded by many at the time for a heroic " battle , " critics complained about the conduct of him and his men . Aftermath . The US Congress investigated the attack . The hearings were widely covered , leading to national shock and outrage about the brutality of the attack and the betrayal of promises made to the Cheyenne and Arapaho . Because the Native Americans believed the Cheyenne had been targeted by the US , major Sioux and Arapaho bands allied with them from 1865 on to attack the " Vehos " ( whites ) and try to drive emigrant settlers out of their lands .