Clan of the Cave Bear
It is 30,000 years ago, the final Ice Age of the Pleistocene Epoch. The earth is peopled by Neanderthals -- squat, bow-legged, nonverbal, they live in clans, exist by foraging, and are ruled by taboos. The Cro-Magnons, the people who will replace them, are just emerging.
When an earthquake destroys a Cro-Magnon dwelling, they tame the prairie, to the sudden fortune of a lucky few.
"A ripping yarn...a gorgeous piece of work." (Saturday Review of Literature)