Gregory Natural Bridge is one such wonder. The 137-foot arch of Navajo sandstone spans Fiftymile Canyon and was fully submerged under Lake Powell when the reservoir filled in 1969.

The 26-inch by 40-inch "Butte, Montana, Richest Hill on Earth: 100 Years of Underground Mining" map is available in the Montana Bureau of Mines and Geology's publications office in Room 200 of ...