The ancient Snowmass clock was measured in the untold lives of the creatures that roamed and roared in a place and period poorly recorded in the scientific record: The high reaches of Rocky Mountains during the Sangamonian interglacial, a time of very warm weather around the globe, 75,000 to 125,000 years ago.
Other well-known ice age fossil sites, by contrast, like the La Brea Tar Pits in California and Hot Springs, S.D., have been dated to between 10,000 and 40,000 before present, and no well-preserved site has ever been found, scientists said, at this altitude in North America.