Evidence left behind by mastodons, mammoths, giant sloths and huge bison — along with insects, plants, pollen and other animals — offers a glimpse at how ancient animal adapted to climate change.

Among their findings: The warmer weather allowed forests to reach about 2,500 feet farther up the mountainside than today's tree line, which is about 11,500 feet above sea level at the Snowmass site. Forests also may have been denser, and smaller trees and grasslands might have been more widespread amid drier conditions.

A team of 47 scientists has been studying material unearthed four years ago near Snowmass, a town just outside Aspen, when a bulldozer was enlarging a reservoir. The researchers published their first big batch of data in the journal Quaternary Research in November.