A clonal colony of Quaking Aspen trees, known as Pando or the Trembling Giant, covers 105 acres in Fishlake National Forest in Utah and is tied together by a single root system. Pando is estimated to be at least 80,000 years old and dates back to when our human ancestors were still exploring the Great Rift Valley. Taken as a whole, all the individual trunks, branches and leaves of these genetically identical trees weigh in at an estimated 6,615 tons - the heaviest known organism on earth.
Pando's current 80,000 year designation is based the evidence indicating that there are few if any naturally occurring new aspens in most of the western U.S. since a climate shift took place 10,000 years ago and eliminated favorable soil conditions for seedling. Successful seeding has not occurred in the western United States since the last glaciation, some 10,000 years ago due to the rarity of a favorable suite of conditions in semiarid environments.