The Mesabi Iron Range is a vast deposit of iron ore and the largest of four major iron ranges in the region collectively known as the Iron Range of Minnesota. Discovered in 1866, it is the chief deposit of iron ore in the United States. The deposit is located in northeast Minnesota, largely in Itasca County and St. Louis County. It was extensively worked in the earlier part of the 20th century. Extraction operations declined throughout the mid-1970s but rebounded in 2005. China's growing demand for iron, along with the falling value of the US dollar versus other world currencies, have made taconite production profitable again, and some mines that had closed have been reopened, while current mines have been expanded.
It is theorized that most of the world's iron ore, including that contained in the Minnesota Iron Ranges, was formed during the middle Precambrian period, about two billion years ago. During this period, erosion leveled mountains that were formed during the previous two billion years. This erosion released iron and silica into the waters of a new sea. Marine algae living in this new sea raised the level of atmospheric oxygen, causing the eroded iron to precipitate into the iron formations now found in the Mesabi Iron Range.
The Hull-Rust-Mahoning Mine in Hibbing, Minnesota, is the largest open pit iron mine in the world. The mine, located in the Mesabi Range, supplied as much as one-fourth of all the iron ore mined in the United States during its peak production years of World War I and World War II. The pit is more than three miles long, two miles wide and 535 feet deep.
This area of the Mesabi Range was explored in 1893–1894, shortly after the Mountain Iron Mine was established in 1892. The early development was as an underground mine, but open cast mining soon proved to be a better choice because of the soft, shallow ore deposits. Many open pits in the area soon merged into one large mine, and the consolidation of mines led to the formation of U.S. Steel in 1901. The growth of the mine even resulted in the town of Hibbing being relocated to accommodate expansion. The move started in 1919 and took two years to complete at a cost of $16,000,000. 185 houses and 20 businesses were moved, and some of the larger buildings had to be cut in half for the move. Only a few uninhabited remnants of the original townsite are left near an observational lookout at the edge of the mine.
Over 519 million tons of waste material and 690 million tons of iron ore have been removed from the mine area since ore shipments began in 1895. The mine was listed as a National Historic Landmark, and added to the National Register of Historic Places on November 13, 1966. The mine is still operated today by the Hibbing Taconite Company, and taconite pellets are extracted at the rate of 8.2 million tons annually.