Isolated, rugged, and remote, the Henry Mountains became the last mountain range to be surveyed in the lower 48 states. In 1872, on John Wesley Powell's second expedition to the area, Powell's brother-in-law, Almon H. Thompson, led a survey party through the mountains and named the highest peak, Mount Ellen (11,506 feet), after his wife. The range is named after Joseph Henry, Powell's friend and supporter. The Henry Mountains formed between 24 and 28 million years ago, when sedimentary rock layers were pushed up and infused with magma that never reached the surface, like a volcano that never erupted. The resulting cluster of dome-topped mountains offers spectacular views of canyon country, including the San Rafael Swell to the north, the Waterpocket Fold of Capitol Reef National Park to the west, the canyons of the Dirty Devil River to the east, and Glen Canyon/Lake Powell to the south. A small herd of 18 bison were transplanted to the Henry Mountains in 1941, and the range is now home to about 200 free-roaming bison.