In 1959, what appeared to be the bones of a mastodon were found in a western New York pasture. When researchers began to investigate further in the early 1980s, the site proved to hold far more. Known as the Hiscock Site, it contained an astonishingly rich trove of fossils and artifacts dating from the late Ice Age through the onset of European settlement. For nearly three decades, work at the site--the "Byron Dig"--unearthed new evidence of changing...