In 1859-60, thousands of people drawn by the promise of gold crossed the passes into South Park, where towns such as Tarryall, Fairplay, and Buckskin sprang up. That first boom receded by 1864, but the discovery of silver in 1870 spurred another mining rush. Coal found near Como supported the operation of the Denver, South Park & Pacific Railway, which hauled ore, gold, silver, coal, and passengers between Denver and Leadville over Boreas Pass. In the 1920s, dredge boats began mining for gold on the South Platte River, producing huge tailings, or piles of discarded gravel. By the 1950s, the high cost of mining in a harsh landscape forced most operations to close, and only a few mines operate in South Park today. The amount of soil and rock removed from South Park equaled about 3.3 million dump trucks filled with gravel, and 115,000 ounces of gold was extracted, enough to fill about 8 grocery bags.