The Mountain Meadows Massacre was a series of attacks which resulted in the mass murder of 120 members of the Baker–Fancher emigrant wagon train. The massacre occurred September 7–11, 1857 at Mountain Meadows in southern Utah, and was perpetrated by Mormon settlers belonging to the Utah Territorial Militia (officially called the Nauvoo Legion)....

The wagon train, mostly families from Arkansas, was bound for California on a route that passed through the Utah Territory... The Baker–Fancher party made their way south along the Mormon Road, eventually stopping to rest at Mountain Meadows.

The leaders of the militia, wanting to give the impression of tribal hostilities, persuaded some Southern Paiutes to join with a larger party of militiamen disguised as Native Americans in an attack. During the militia's first assault on the wagon train, the emigrants fought back, and a five-day siege ensued. Eventually fear spread among the militia's leaders that some emigrants had caught sight of white men and had likely discovered the identity of their attackers. As a result, militia commander William H. Dame ordered his forces to kill the emigrants. By this time, the emigrants were running low on water and provisions, and allowed some members of the militia - - who approached under a white flag - - to enter their camp. The militia members assured the emigrants they were protected, and after handing over their weapons, the emigrants were escorted from their hasty fortification. After walking a distance from the camp, the militiamen, with the help of auxiliary forces hiding nearby, attacked the emigrants. The perpetrators killed all the adults and older children in the group, sparing only seventeen young children under the age of seven.

[en.wikipedia.org]