People of the Nightland (North America's Forgotten Past, Book Fourteen)

This is the sweeping saga of a visionary boy who leads his people out of the path of one of the worst disasters in the history of the world... It has been a thousand years since Wolf Dreamer led his people up through the dark hole in the ice to a rich, untouched continent bursting with game. Since that time, the world has changed. Most of the magnificent animals are gone, and the last of the great glaciers is melting, forming a huge freshwater lake around the edges of the ice. Over the centuries the People of the Wolf have split into two clans. The People of the Nightland live in the honeycomb of ice caves that skirt the glacier. The People of the Sunpath live in hide lodges to the south, hunting the few remaining mammoths, bison, giant sloths, and short-faced bear. When a young boy named Silvertip receives a vision from Wolf Dreamer that his world is going to end, no one believes him--no one except a jaded war chief and a little girl. Led by Silvertip's dream, the three of them must convince their people to leave the land of their ancestors before the Ice Giants destroy the world.