Seriously? I was a college history major and from memory could write a pretty long and mostly accurate narrative of the Mormons from Palmyra to the Nauvoo burn-out to the "Reorganized" split to Brigham Young and the seagulls and beehives and unique address-coding in Salt Lake City, but I am stone-cold ignorant of such an event. I better go back to my books.
Here is a fair peice on it from an LDS perspective.
http://www.fairlds.org/FAIR_Conferences/2003_Shining_New_Light_on_the_Mountain_Meadows_Massacre.html
I was LDS. Sixth generation on every side. I am also a descendant of John D. Lee.
There is a side other than that at FAIR. By reading journals and extant writings of participaants in the Massacre, I began seeing LDS history for what it is.
May you have an enlightening journey!
They teach about that in Church History. It is not a secret, the guy responsible was arrested by a Mormon Sheriff, tried by a Mormon prosecutor before a Mormon Judge and Mormon Jury. He was convicted and went to jail.
A lot more is made of this than it deserves. There were other murders that happened in that time frame, but you never hear about them.
People try to blame Brigham Young for this event, but he had sent word to let these people pass through. The message arrived after the event.