According to Wikipedia

Sand Creek Massacre National Historic Site is a National Historic Site in Kiowa County, Colorado, commemorating the Sand Creek Massacre that occurred here on November 29, 1864. The site is considered sacred after the unprovoked assault on an encampment of approximately 750 Native people resulted in the murder of hundreds of men, women and children. Near Eads and Chivington, the site is about 170 miles (270 km) southeast of Denver and about 125 miles (200 km) east of Pueblo. A few basic park facilities have been opened at this site.

To be honest, visiting this park was difficult. It didn’t feel like a place to take pictures of and put a pin in a map. I made a stone specifically for the site, but didn’t leave it in the park and instead left it by the entrance sign. I don’t even know if that was right.