The passage of the steamer Illinois through the locks at Sault Ste. Marie marks the opening of unobstructed shipping between Lakes Superior and Huron. Ships were no longer forced to stop at Sault Ste. Marie and portage their cargoes around the rapids of the St. Mary’s River, which drops 12 feet from Lake Superior to Lake Huron. The canal was the result of a long-sought 1852 grant by Congress to Michigan of 750,000 acres of public land. Construction, begun in mid-1853, had progressed despite cost overruns, food shortages, a hostile climate and a cholera epidemic. The mile-long canal and two 350-foot locks arranged in tandem were completed in two years. The Sault locks provided new impetus to Michigan’s fledgling mining industry. Copper mining on the Keweenaw Peninsula began in the early 1840s, and Michigan led the nation in copper production for many years. In 1844, surveyor William A. Burt discovered iron ore deposits near Negaunee. Iron ore mining expanded gradually, but by the late 19th century, Michigan produced more iron ore than any other state. Michigan also produced significant amounts of salt, gypsum, oil and natural gas.
Source : June 22, 1855 : Michigan Department of Natural Resources
Note : some sources prefer June 18 as the date that the Steamer Illinois first passed through he locks.