The valley of horses - Jean M. Auel (Earth's Children #2)

This is the story of an unforgettable odyssey into a world of awesome mysteries, a novel that carries us back to the exotic, primeval world we encountered in THE CLAN OF THE CAVE BEAR – and to beautiful Ayla, as she leaves the safety of the Clan who raised her and sets out alone on an epic journey of discovery. A hostile land of glacial cold, terrifying beasts and intense loneliness awaits her, and her need for human companionship and love remains unfulfilled.

But in the Valley of Horses she finds refuge and contentment. There, fate brings her a stranger, Jondalar, and Ayla is torn between fear and hope – and carried to an awakening desire that would shape the future of mankind.