The Rocky Mountains are one of the Earth's most spectacular geological features, containing vast stretches that remain wild and untamed. Hikers on mountain trails often see the wilderness just as Lewis and Clark saw it almost 200 years ago. The diversity of life found along the Rockies' 2000-mile range is so varied that the mountains are divided into three regions: the Northern, Central, and Southern Rocky Mountains. Scott A. Elias discusses the unique features of each region in his comprehensive natural history of the backbone of the continent.