✯ Yankee Girl Mine, Red Mountain Mining District, Colorado, USA. In 1882, a prospector stumbled over a rock of galena on Red Mountain (galena deposits contain significant amounts of silver), and thus began a very profitable career. The Yankee Girl mine became one of the most profitable mines in the history of silver mining in the United States. At its height, Yankee Girl produced 10 tons of ore on a daily basis. 250 pounds of this was carted out by 75 mules every day.