On this day in 1915, Rocky Mountain National Park in Colorado officially became a national park. Even in cold weather, you can explore the park’s spectacular mountain environments by snowshoeing, cross-country skiing, sledding and wildlife watching. In fact, winter is an especially good time to look for elk, mule deer, moose and other large mammals. Sunrise photo of Dream Lake in 2014 by C. Brindle, National Park Service.