The Comstock Lode was a fabulous 2½ mile deposit of high-grade ore that produced nearly $400,000,000 in silver and gold. After its discovery in 1859, Virginia City boomed for 20 years, helped bring Nevada into the Union in 1864, and helped build San Francisco. Seven major mines operated during the boom, including the Sierra Nevada, Union, Ophir, Con Virginia, Combination, and the Utah Mines. The lode was worked from both ends, north up Cold Canyon and south from the Sierra Nevada and the Utah Mines.