The Anaconda Smelter Stack is a brick smoke stack, once part of the Anaconda Copper Mining Company at Anaconda, Montana in the United States. The stack is 585 feet 1 1⁄2 inches (178.346 m) tall, excluding its foundation. The stack contains 2,464,652 locally manufactured perforated tile bricks, each averaging 2.7 times larger by volume than the size of a normal brick. The lowest 80 feet (24 m) is octagonal in cross section while the rest is circular. The vertices of the octagon point to the cardinal and intercardinal directions, north, northeast, east, etc., while its sides face the secondary-intercardinal directions, north-northeast, east-northeast, etc. Two large rectangular openings are in the octagonal portion, both slightly smaller than a side, on the east-southeast and south-southwest sides. Its circular portion is encircled by many large steel rods for reinforcement. The concrete foundation is stated to be 30 feet (9.1 m) tall, but that is its maximum height on its south-southeast side (it is much shorter on the opposite side). The inside diameter of the stack is 75 ft (23 m) at the bottom and 60 ft (18 m) at the top. The wall thickness ranges from six feet at the bottom to two feet at the top.
After the concrete foundation was completed in May 1918, construction of the stack began on May 23, 1918 and was completed on November 30, 1918. It was built by the Alphons Custodis Chimney Construction Company of New York. At the time it was built, it was the tallest masonry, brickwork structure and chimney of any kind in the world and it remains the world's tallest and possibly largest free-standing masonry structure. The Washington Monument would easily fit inside. It is commonly referred to as 'The Stack' and is a well-known landmark in western Montana.
The stack was designed to discharge exhaust gases from the various roasting and smelting furnaces at the smelter. The stack is situated just below the top of a hill. The smelter had a large network of exhaust flues from the furnaces that all fed a main flue. The main flue carried the combined smelter exhaust gases a half-mile up the hill to the stack. The flue system and stack combined to provide a natural draft to carry the smelter exhaust gases, and it was claimed to be capable of handling three to four million cubic feet per minute of gas.
The Anaconda Smelter was demolished after its closure in 1981, and the site underwent environmental cleanup. The stack alone, however, remains standing. After the smelter’s closure, citizens of Anaconda organized to “Save the Stack,” and in 1986 it was designated a state park. The park is known as Anaconda Smoke Stack State Park. The park has two parts: the viewing and parking areas just east of the town of Anaconda and the smoke stack which is about 1.2 miles (1.9 km) southeast of the viewing area.