The Delaware mine drew repeated investment during the latter half of the 1800s as companies including the Northwest Company, the Pennsylvania Mining Company, the Delaware Mining Company, and the Conglomerate Mining Company pursued a property encouraged by the success of the nearby Cliff and Central mines. They built substantial infrastructure and blasted to nearly 1,400 feet, yet the mine remained a frustrating failure, as its native copper fissure veins and conglomerate lodes yielded less than they had promised and cost more to work than they returned. In the late 1870s Delaware's population reached 1,150, and its operations were among the largest and most modern in Keweenaw County, with two hundred or more structures, though only a few houses remain today. Since 1977, Delaware Mine Tours amid the ruins has let visitors enter the mine's first level one hundred feet below ground. Horace Greeley had invested there in 1847-48 after a man named Bailey discovered a copper vein and offered him stock in a proposed company, and during three years of involvement Greeley persuaded others to invest as well, but Bailey's discovery proved unlike the rich Cliff and Central deposits, leaving investors disappointed; nearby Mount Horace Greeley bears his name.