The following comes from:
Duane S. Crowther, "A Study of Eschatological Prophecies
Found in the Scriptures and in the Works of General Authorities of The Church
of Jesus Christ of Latter-day Saints,"
(M.A. Thesis, Brigham Young University, 1960), 18-19:
Luman Shurtliff, upon his arrival in the Great Basin in
1851, also made it clear that the Prophet had definitely contemplated a western
exodus:
We got into the Salt Lake Valley, September 23, 1851,
thankful to the God of Heaven that I and my family were in the valley of the
Rocky Mountains—here where the Prophet Joseph Smith had said thirteen years
before [in 1838] that the Saints would go if the government did not put a stop
to the mobbing and the persecution of them. (“Biographical Sketch of the Life of Luman
Andros Shurtliff,” 1807-1864, under
date)
Orson Pratt also testified that the Prophet had anticipated
the exodus long before it transpired. In a public meeting held on April 26,
1846, in the early days of the exodus, he stated:
It is eight years today since we all came out of Missouri.
Before that time Joseph the Prophet had this move in contemplation and always
said that we would send a company of young men to explore the country and
return before the families can go over the mountains; and it is decidedly my
mind to do so. (“Diary of John D. Lee, 1844, 1846, 1850-1851,” under date
above)
His testimony was corroborated by Lyman Wight, who stated
in a letter to Wilford woodruff that “such a mission was even talked of while
in [Liberty] Jail.” (Letter written by Lyman Wight to Wilford
Woodruff, dated August 24, 1857)
Further Reading:
Resources
on Joseph Smith's Prophecies