Later in the 1847 trek, Harmon was left with 9 other men to construct and operate a ferry across the North Platte river located near present-day Casper, Wyoming. After settling in Salt Lake City in 1848 he prospered, living in downtown Salt lake city, building one of the first sawmills and farming near the present location of Sugar House Park. Harmon kept detailed journals of his trek west and his 1850-1853 mission to England that have been published. On the trail heading east for his missionary service in 1850, he saw throngs of gold miners heading west in the second year of the California gold rush, and he was an eye-witness to, and a survivor of, the tragic cholera epidemic that decimated the participants. In 1851 he visited the famous Crystal Palace Exposition in London. He had success on his mission and led a company of about 300 Latter-day Saints from England to Salt Lake City on his return in 1853. In 1862 he was called to settle southern Utah. After experiencing floods of the Virgin river in Grafton, he settled in Toquerville where he built a lumbermill, farmed and made furniture. In 1865 Brigham Young called him to oversee the design, construction and equipping of a factory for producing cotton fabric. Cotton and Woolen fabrics were produced until 1904, although interest in cotton diminished after the civil war and the coming of the railroad. The building that housed the factory, located in Washington near St. George Utah, still stands. In 1870 Harmon moved to Holden, Utah, where he built another lumbermill. He and Elmeda had 12 children.