It has been called the "Grand Canyon of the North"—a fitting title for the world's largest open pit iron mine. The Hull-Rust-Mahoning pit actually began as separate mines, named for their owners, first dug in 1895, that gradually merged into one. Today this enormous pit measures 1.5 by 3.5 miles with a depth of 600 feet. Because of its size and the important developments that took place here, the Hull-Rust-Mahoning mine played a key role in making Minnesota the leading iron-ore producer in the country.
Setting in the midst of the Mesabi Range, the largest of Minnesota's three iron ore ranges, this mine owed its dominance to its particular iron formations. Here, vast stretches of high-grade, soft ore lay in shallow deposits that could be scooped up with giant steam shovels, machinery perfected at this site. Using the open pit method, mining companies removed huge quantities of iron ore quickly and economically, dumping it into rail cars that were moved out of the mine on tracks circling the slopes of the pit.
Large mining operations required extensive financial resources. Small local developers were soon driven out, and the wealthy ones with names like Rockefeller and Carnegie took over. In 1901 J. P. Morgan consolidated their mining and manufacturing operations as United States Steel, creating what was then the biggest corporation in the world.
The Hull-Rust-Mahoning Mine developed rapidly in the early 1900s, when demand was high for iron and steel to build railroads, bridges, and skyscrapers. In its peak production years during World War I and II, this pit supplied as much as one-fourth of all the iron ore mined in the United States. It was designated a National Historic Landmark in 1966.