The Henry Mountains were the last mountain range to be explored and mapped in the lower 48 United States. Due to their remoteness and surrounding terrain of infinitely complex canyons and mesas, the Henrys weren’t mapped until 1872 by Major John Wesley Powell and his US Geological Survey of the Colorado River, known before only as the “Unknown Mountains”, in both English and Navajo. Named after Joseph Henry, the first secretary of the Smithsonian Institution, these mountains are actually volcanic in nature, created by laccoliths forcing rock layers upward into the shape of the mountains we now see. Administered by the Bureau of Land Management, the Henrys also are home to one of Earth’s last free-roaming bison herds. The herd usually has a population of around 300 animals, but this varies from year to year due to weather events, hunting lotteries, disease and predation.