ied-documents/ufo/what_gov_knows_about_ufos.pdf|author=Peter Gersten, Frontiers of Science|archive-url=https://web.archive.org/web/20210709171322/https://www
(2004); 572 pp excerpt and text search Hawgood, John A. America's Western Frontiers (1st ed. 1967); 234 pp; textbook covering pre-Columbian era through the