Final answer:
The grizzly bear is the large mammal that hibernates in the Rocky Mountain region. However, grizzly bears do not go into true hibernation like smaller animals. Their body processes slow down slightly, but their body temperature remains relatively normal.
Step-by-step explanation:
The large mammal that hibernates in the Rocky Mountain region is the grizzly bear. Grizzly bears go into a deep sleep during winter, but they do not go into true hibernation. Although their body processes slow down slightly, their body temperature remains relatively normal and they can be easily awakened from their winter sleep.