D&C 116

After the Prophet Joseph Smith visited Spring Hill, he recorded -

"SPRING Hill is named by the Lord Adam-ondi-Ahman, because, said he, it is the place where Adam shall come to visit his people, or the Ancient of Days shall sit, as spoken of by Daniel the prophet." (Doctrine and Covenants Section 116:1)

What Daniel saws was -

"I beheld till the thrones were cast down, and the Ancient of days did sit, whose garment was white as snow, and the hair of his head like the pure wool: his throne was like the fiery flame, and his wheels as burning fire.
10 A fiery stream issued and came forth from before him: thousand thousands ministered unto him, and ten thousand times ten thousand stood before him: the judgment was set, and the books were opened.
11 I beheld then because of the voice of the great words which the horn spake: I beheld even till the beast was slain, and his body destroyed, and given to the burning flame.
12 As concerning the rest of the beasts, they had their dominion taken away: yet their lives were prolonged for a season and time.
13 I saw in the night visions, and, behold, one like the Son of man came with the clouds of heaven, and came to the Ancient of days, and they brought him near before him.
14 And there was given him dominion, and glory, and a kingdom, that all people, nations, and languages, should serve him: his dominion is an everlasting dominion, which shall not pass away, and his kingdom that which shall not be destroyed." (Old Testament Daniel 7:9 - 14)

Of this event, President Joseph Fielding Smith wrote that it would be -

"...of the greatest importance to this world. At that time there will be a transfer of authority from the usurper and impostor, Lucifer, to the rightful King, Jesus Christ. Judgment will be set and all who have held keys will make their reports and deliver their stewardships, as they shall be required. Adam will direct this judgment, and then he will make his report, as the one holding the keys for this earth, to his Superior Officer, Jesus Christ. Our Lord will then assume the reins of government; directions will be given to the Priesthood; and He, whose right it is to rule, will be installed officially by the voice of the Priesthood there assembled. This grand council of Priesthood will be composed, not only of those who are faithful who now dwell on this earth, but also of the prophets and apostles of old, who have had directing authority. Others may also be there, but if so they will be there by appointment, for this is to be an official council called to attend to the most momentous matters concerning the destiny of this earth.

When this gathering is held, the world will not know of it; the members of the Church at large will not know of it, yet it shall be preparatory to the coming in the clouds of glory of our Savior Jesus Christ as the Prophet Joseph Smith has said. The world cannot know of it. The Saints cannot know of it—except those who officially shall be called into this council—for it shall precede the coming of Jesus Christ as a thief in the night, unbeknown to all the world." (Way to Perfection, pp. 290–91.)

I've wondered at times if this event has already taken place.