Much of the film's dialog and plot points were taken from the writings of President Wilford Woodruff, the fourth President of the Church of Jesus Christ of Latter-day Saints
The fact of the construction materials of the Temple taking 4 days to reach the block from the quarry was, in actuality, one of the biggest problems of construction
Much of the mountainous background is actual scenery from the Salt Lake City, with the current city edited out and the sets filled in at a replacement.
The one part that was not edited was the sceneries around the end of the film where dirt covered actual roadways.
The involvement of Johnston's Army was a result of some rumormongering as the enemies of the church used the fact that the Salt Lake City area was, at the time, not under US control. When the reports came of an army being raised in Salt Lake, the US President sent the army. It was this report coming in that led to the miscommunication which led to the Mountain Meadows Massacre, one of the blackest moments in Church History