The tree rings of 52 fallen giant sequoias, Earth's biggest trees, have revealed a 3,000-year-old history of droughts and fires. Hemera/ThinkStock March 29, 2010, 11:49 AM EDT / Source : Discovery ...

Given that the sequoia grew seasonally, each ring marks the passage of another year, and visitors can look at the approximately 260 delineations and think about what such a time span represents.