The Dotsero volcano, or crater, near Dotsero.
"The most recent lava flow in Colorado occurred in Eagle County. This was approximately 4,000 years ago (think Stonehenge) as determined by radiocarbon dating of a tree found in the ash in 1962. Local historians weren’t available for documentation purposes, however, according to an article written by Allen Best in 1990 (Vail Trail Dec. 7, 1990).