DENVER (KDVR) — Nov. 29 marks the anniversary of a tragedy for the Arapaho and Cheyenne people, with the U.S. military to blame: the Sand Creek Massacre.

The Sand Creek Massacre happened on Nov. 29, 1864, when a U.S. cavalry killed more than 230 peaceful Arapaho and Cheyenne people — most of them women, children and elders. It was the deadliest day in Colorado’s history.

“Cheyenne and Arapaho people continue living with the unresolved trauma the massacre left behind,” according to History Colorado, which shares the Cheyenne and Arapaho stories of the massacre in a new exhibit. “For many Cheyenne and Arapaho people, the Sand Creek Massacre isn’t just history, it’s family history.”

The surprise attack at sunrise happened after the tribes were promised safety and supplies from the military.

“It was genocide. We need to educate the people and heal our people so that something like this won’t happen again,” Chester Whiteman, of the Southern Cheyenne, said in a statement. “I hope this exhibit will get people to understand that we’re all human.”

The legacy of the Sand Creek Massacre

The new History Colorado exhibit shares the story based on the tribal accounts and oral histories of the Cheyenne and Arapaho. Historians say the two tribes have distinct histories but were forever linked by the tragedy.

“The Sand Creek Massacre is sacred,” said Gail Ridgely, of the Northern Arapaho. “Historic remembrance, educational awareness and spiritual healing are very important for the Cheyenne and Arapaho people.”

After the massacre, the tribes were forced to leave the state. Today, they form three sovereign tribal nations in Montana, Oklahoma and Wyoming, according to History Colorado.

An effort is now also close to approval that would rename Mount Evans. The peak is named for Colorado’s second territorial governor, John Evans, who was forced to resign after the Sand Creek Massacre. The mountain was named for him in 1895, decades after his resignation.

A Colorado state panel recently recommended the new name Mount Blue Sky. Gov. Jared Polis will weigh in on the recommendation before a final decision by the U.S. Board on Geographic Names.