Immediately north of this point lies the Hull-Rust Mahoning Mine, an open pit begun in 1895 that extends about 3½ miles east to west. Over the past 100 years of mining, more than thirty separate companies operated within its perimeter, many of them at the same time, and it was once known as the largest open pit mine in the world. At its maximum depth, the mine reached 600 feet in the Scranton Pit. By the beginning of this millennium, nearly 2 billion tons of iron ore and waste had been removed from this man-made excavation, a volume equivalent to digging a tunnel 24 feet in diameter completely through the earth. The ore shipped from here averaged more than 60% iron and required little processing. The largest year of production was 1942 during World War II, when more than 27 million tons of ore were shipped in the normal nine-month summer season, requiring one train car of ore to leave every 20 seconds on a 90-mile journey to ore docks at the head of Lake Superior. In the 1940s, more than 70 miles of rail line were used within the mine. In 1976, Hibbing Taconite Company (Cliffs Inc.) began taconite mining near the continental divide just north of the Hull-Rust Mahoning, and mining of the higher-grade, hematite-rich natural ores ended in 1984. Taconite mining uses a sophisticated plant to magnetically concentrate lower-grade primary ore containing 30-35% iron, upgrading it to more than 66% iron and producing 3/8-inch furnace-fired pellets. These taconite pellets are now rail-shipped to the Duluth-Superior harbor and transferred to Great Lakes iron ore boats for shipment to blast furnaces. Rainwater and ground seepage once raised the mine's water level to more than 325 feet, but subsequent pumping lowered it to allow continued mining of deeper taconite ores.