The Mountain Meadows Massacre Memorial is a memorial that was built by the Later Day Saints in rememberance of the 120 men and women and childeren that were ambushed and killed by Mormon militia on Sept. 11, 1857. It's an amazing story told in great detail in the book American Massacre: The Tragedy at Mountain Meadows, September 1857 by Sally Denton (on Amazon). It was a terrible event in American history. For years the Mormon Church denied any involment in the massacre going as far as blaming the Indians for the attack. In 1858 the Unided States Army investigated and found no evidence Indians played any involvement in the attack. Seventeen childeren under the age of 8 were spared and dispersed among Mormon families in Salt Lake City. The history of the Mormon Church is a fascinating one and I recommend the reading of American Massacre.
http://en.wikipedia.org/wiki/Mountain_Meadows_Massacre