The date of the so-called "White horse prophecy." Joseph Smith is reported to have said: "The last great struggle that Zion will have to contend with will be when the whole of America will be made the Zion of God. Those opposing will be called Gog and Magog. The nations of the world led by Russia and their power will be great but all opposition will be overcome and this land will then be the Zion of our God."
[Source: On This Day in Mormon History, http://onthisdayinmormonhistory.blogspot.com]