Final answer:
The majority of American iron ore, approximately 80% of American iron ore passed through Soo Locks, during the 20th century, which was crucial for shipping on the Great Lakes.
Step-by-step explanation:
The Soo Locks were a system of locks located on the St. Marys River in Michigan, which allowed ships to bypass the rapids and travel between Lake Superior and the lower Great Lakes. In terms of iron ore, the Soo Locks were a crucial transportation route.
During the 20th century, the majority of American iron ore passed through the Soo Locks. This was because the locks provided a direct and efficient way to transport iron ore from the mines in Minnesota to the steel mills in the lower Great Lakes. The exact percentage of iron ore that passed through the Soo Locks would vary over time, but it was a significant amount.
For example, during the 1960s, the Soo Locks handled around 75% of the iron ore produced in the United States. This shows just how important the locks were in facilitating the iron ore trade and supporting the country's steel industry.