Tourism influences the growth of Mammoth Cave and Cave City Kentucky post offices from 1842 to 1915The American Philatelic Congress72–87
Lera, Thomas M. 2009. "Tourism influences the growth of Mammoth Cave and Cave City Kentucky post offices from 1842 to 1915." In The Congress Book 2009. Trettin, Kenneth, editor. 72–87. The American Philatelic Congress.