The early Holocene in North America was a period still experiencing the aftershocks of the great Pleistocene megafauna extinctions — the loss of mammoths, mastodons, giant ground sloths, American horses and camels, and many other large species that had characterized the late Pleistocene fauna.

By 8,800 years ago, most of these species were already extinct, though some may have persisted in localized refugia for a few more centuries in some regions.

What remained was still a rich fauna by modern standards: bison that were somewhat different in form from modern bison, elk, deer, bighorn sheep, pronghorn, black bears, and the various smaller mammals and birds that characterize the Rocky Mountain fauna.

These animals were present in the high country seasonally, and they represented real and substantial food resources for the communities that could access them.