Keeper of the Stone — Margaret Allan

Maya was born to be keeper of the Mammoth Stone, the age-old talisman believed to protect the People of the Mammoth in their struggle for survival in the vastness of the prehistoric American West. But now another woman has taken her place, and Maya was in exile with the mighty hunter who loved her, Black Caribou.
Then her most fearful dreams of prophecy came to pass. Two brutal warriors with an injured youth as captive took her prisoner as well, to use for their pleasure and torture. But they did not suspect what Maya learned about the captive boy and his secret possession. He, like Maya had one blue eye and one green. He, like Maya, was keeper of a stone--a stone that was the match and mate of the Mammoth Stone.
Now Maya was sure that they had to come together--no matter what odds she had to overcome. And she trembled to imagine what might happen when the mightiest magic of all burst like a flaming dawn across the land...