The mammoths liked to feed in the periglacial areas. By being right up against the glaciers the were shielded fro the north winds, and the face of the glacier reflected sunlight back into the ground. The area near the glacier was much warmer than the surrounding tundra. It was well watered with melt water, and the soil was rich in minerals from the glacial till, and as loose as a well tended garden. Plants that are now exclusively tropical were better adapted to cold and variable day length.
Soooo, a mammoth feeds in the richest local environment, right up next to the glacier, and suddenly there's an avalanche instantly pounding the mammoth into the dirt and packing it in ice...