• Aaron initially traveled to the Salt Lake Valley with his parents and siblings in 1847. Sometime after this, the Thatcher family moved to California, settling near Salmon falls (near present day Folsom CA) by 1850. In 1857, heeding the call for the Saints to return to Utah, Aaron's family headed East, while he and his brother Moses stayed in California. Their brother John later returned, and they are seen with him to San Bernardino, and then back up into Utah. Further research is needed to determine which company they left San Bernardino with.

  In 1868 he acted as "assistant captain" of the Simpson M. Molen out-and-back train sent out to collect emigrants from the terminus of the rail line in Laramie, Wyoming. 

Daniel Spencer/Perrigrine Sessions Company (1847)

• Age at Departure: 10

Company Unknown (1857)

• Age at Departure: 19

Simpson M. Molen Company (1868)

• Age at Departure: 31

Sources

• 1850 California Census, Eldorado County.
• "Aaron D. Thatcher Joins His Brother," Deseret News, 8 Sep. 1909, 3.
• Frederick W. Hurst autobiography and diaries, 1855-1877, Journal, 1857 April-1860 April. 
• Hyde, William, “Correspondence,” Semi-Weekly Telegraph , 6 July 1868, 2.
• Journal History of The Church of Jesus Christ of Latter-day Saints, 21 June 1847, 11.
• Missionary Department Missionary Registers, 1860-1959, Volume 1.
• Smith, Mercy Livermore, Autobiography, in Dorothy Streeper, Family Histories, [ca. 1983].
• Utah, Early Mormon Missionary Database
• Utah Death Certificates.