The Henry Mountains of southeastern Utah were one of the last-surveyed and last-named mountain ranges in the lower forty-eight United States. The Henrys are located in the middle of the Colorado Plateau, a sea of sandstone cut by deep canyons. The surrounding country for miles is arid and supports little vegetation; the very ruggedness of their setting left the Henry Mountains isolated and unknown until after the Civil War. Even today the Henrys and the surrounding regions remain isolated and sparsely settled. Ironically, however, among geologists the Henrys are known world-wide because of a classic study of their geology done during the 1870s.

The Henry Mountains are about sixty miles long by about twenty miles wide, and are located in Garfield County, Utah. The nearest settlement is the town of Hanksville to the north. The range is bounded on the east and south by the Colorado River and its tributary, the Dirty Devil River; on the west by the Waterpocket Fold; and on the north by the San Rafael Swell. The vertical relief between the Henrys and the surrounding plateau regions ranges from 6,000 to 8,000 feet. From north to south the highest peaks of the Henrys are as follows: Mount Ellen (the northernmost and also the highest peak), having an elevation of 11,506 feet above sea level; Mount Pennell, with an elevation of 11,371 feet; Mount Hillers, 10,723 feet; Mount Holmes, 7,930 feet; and Mount Ellsworth, at 8,235 feet. The latter two peaks are separated from the main range by a valley, and are sometimes referred to as the Little Rockies because of their rugged appearance. All of these names were given to the peaks by U.S. government surveying parties in the 1870s.