Sand Creek Massacre National Historic Site preserves the place in southeastern Colorado where about 750 Cheyenne and Arapaho people were encamped when hundreds of men, women, and children were killed in the Sand Creek massacre on November 29, 1864. Regarded as sacred, the landscape was identified and protected through modern archaeological work and collaboration with Native American observers. Authorized by Congress in 2000 and added to the National Park System in 2007, it continues to expand through federal, tribal, and preservation efforts. The site honors the massacre’s national historical significance while also protecting land important to descendants and an unusually intact shortgrass prairie ecosystem.