DUBUQUE'S MINES. Post office. Named for its location near the MINES OF SPAIN, the post office was established on May 27, 1833. Since this was five days before the territory was legally opened for settlement, the office was technically a squatter in violation of the government. Milo H. Prentice served as postmaster. The office remained open until January 23, 1837. It was reopened and renamed--Dubuque.