He was a member of the Church of Jesus Christ of Latter-day Saints, having been baptized Aug 2, 1840, by Erastus Snow.

[2] He first arrived in California on the ship Brooklyn in 1846 with a group of Mormons led by Sam Brannan.

He was also connected with early agricultural fairs in California designed to encourage others to be involved in growing produce.

[3] Horner was one of the Mormons who were passengers on the ship The Brooklyn that sailed into Yerba Buena (early name for San Francisco) in 1846.

[1][4] By the 1860s Homestead associations were popular in San Francisco as a way for persons of modest means to pool their money and purchase large tracts of land to be subdivided, and for early speculators to acquire groups of lots and even entire blocks for later development.