Located in the northern Rocky Mountains along the Continental Divide, the region is as primitive as any found in the United States outside of Alaska. Indeed, the Bob Marshall region is the most ecologically complete mountain wilderness in the country, according to Wolke. Although renowned for excellent fishing and backpacking opportunities, most of those that enter the wilderness complex do so on horseback and there are outfitters that provide guided pack trips into the region. The Bob Marshall Wilderness Complex is also well known for being prime grizzly bear habitat, with a population density of species considered to be one of the highest in the lower 48 states outside of the Greater Yellowstone Ecosystem according to the National Park Service. Grizzlies migrating from the Complex range well out onto the Great Plains to the east, the only place this still occurs. Every species of mammal indigenous to the Northern Rockies still lives in this area and adjacent Glacier National Park, except bison and woodland caribou. Huge herds of elk, bighorn sheep, and mountain goat roam the region's rugged peaks, big river valleys, large meadows, and vast coniferous forests.