War with the state of Ohio over the location of their mutual border. Meanwhile, the people of Michigan approved a constitution in May 1835 and elected state officials in late autumn 1835. Although the state government was not yet recognized by the United States Congress, the territorial government effectively ceased to exist. President Andrew Jackson's government offered the remainder of the Upper Peninsula to Michigan if it would cede the Toledo Strip to Ohio. A constitutional convention of the state legislature refused, but a second convention, hastily convened by Governor Stevens Thomson Mason, consisting primarily of his supporters, agreed in December 1836 to the deal. In January 1837, the U.S. Congress admitted Michigan as a state of the Union. At the time, Michigan was considered the losing party in the compromise. The land in the Upper Peninsula was described in a federal report as a "sterile region on the shores of Lake Superior destined by soil and climate to remain forever a wilderness." This belief changed when rich mineral deposits (primarily copper and iron) were discovered in the 1840s. The Upper Peninsula's mines produced more mineral wealth than the California Gold Rush, especially after shipping was improved by the opening of the Soo Locks in 1855, and docks in Marquette in 1859. The Upper Peninsula supplied 90% of America's copper by the 1860s. It was the largest supplier of iron ore by the 1890s, and production continued to a peak in the 1920s, but sharply declined shortly afterward. The last copper mine closed in 1995, although the majority of mines had closed decades before. Some iron mining continues near Marquette. The Eagle Mine, a nickel-copper mine, opened in 2014. Thousands of Americans and immigrants moved to the area during the mining boom, prompting the federal government to create Fort Wilkins near Copper Harbor to maintain order. The first wave were the Cornish from Great Britain, with centuries of mining experience; followed by Irish, Germans, and French Canadians. During the 1890s, Finnish immigrants began settling there in large numbers, forming the population plurality in the northwestern half of the peninsula. In the early 20th century, 75% of the population was foreign-born. From 1861 to 1865, 90,000 Michigan men fought in the American Civil War, including 1,209 from the Upper Peninsula. Houghton County contributed 460 soldiers, while Marquette County, Michigan sent 265. There was a boundary dispute over the border with Wisconsin.