Poston returned to the United States in time for the Centennial Exposition in Philadelphia. Through his acquaintance with John Bigelow, he then became a campaign worker for Samuel J. Tilden during the U.S. presidential election of 1876. Poston expected a consul position in London if Tilden had won the election, but instead was made Registrar of the United States land office at Florence, Arizona from July 1877 till June 1879. During his time in Florence he became interested in building a Parsi fire temple on a nearby hill, paying for construction of a road to the summit. The temple itself was decorated with a blue and white flag depicting a red sun and built upon the ruins of an older Indian structure. Construction ended when Poston ran out of funds. He attempted to raise additional money, even writing to the Shah of Iran, but his efforts failed and the temple's eternal flame failed shortly thereafter. This unusual interest led to Poston being criticized as a crank and eccentric.