From the book "The Redwood Country" by Lynwood Carranco.
Fortuna has had three legal names: Slide, Springville and Fortuna. The book 'California Place Names' by Professor Erwin P. Gudde states: "The place was opened for settlement in the late 1870's by a minister named Gardner, who owned the land. He named it Fortune because he believed it was an ideal place in which to live. Later, for the sake of euphony, he changed its appellation to Fortuna."
On March 20, 1888, Gardner's addition of fifty-two lots were added to the town, already comprised of eighty-eight lots, but no documentation was found that mentioned that Gardner was responsible for naming the town "Fortuna."
The town was first recognized by the United States Government when a post office was established in 1874 under the name of Slide. This popular name was derived from the hill just north of town called Slide Hill. On October 12, 1874, Henry Rohner, Alexander Masson, M. N. Weber and G. F. Gushaw organized the Springville Mill Company, which helped to establish a permanent community. This name was used because of the many springs in the surrounding hills. On May 5, 1875, the town of Springville was filed with sixteen lots. Although the town was called Springville, the post office continued to be known as Slide. On April 5, 1880, Postmaster W. J. Swortzel tried to have the post office changed from Slide to Springville, but was refused because there was another Springville in Ventura County. On July 3, 1888, the post office was changed to Fortuna (fortune), and the name was also adopted for the town.
-- From W. H. Jewett, Humboldt County Historical Society News Letter, March-April, 1964 --
"Another popular story on the naming of Fortuna concerns a certain Jack Hosier. In the early days there were two Odd Fellows Lodges in Eureka called Humboldt Lodge, No. 77, and the Fortuna Lodge, No. 221. Jack Hosier, an active worker in the Fortuna Lodge, moved from Eureka to Springville. As Springville increased in population, a movement was started to give the town a different name. Jack Hosier, who was very popular, suggested the name of 'Fortuna,' and it was selected from many names either because of Hosier's popularity or because of the attractiveness of the name."