It is more than four times as long as all of recorded Western history.

It encompasses the rise and fall of multiple civilizations about which we know nothing because they left no written record.

It represents approximately 350 to 400 human generations — enough for substantial genetic, linguistic, and cultural change.

In that span of time, the landscape around Hourglass Cave has changed.

Tree lines have shifted up and down with climate fluctuations.

Species have moved through their ranges.

The glaciers that still decorated some high peaks during the early Holocene have come and gone with the climate.