From 1864 to 1875, early pioneers in Butte used placer mining, or gold panning, relying on water to separate waste rock from heavier gold, with tools such as the rocker box, sluice, dredge, shaker table, and pan, while hydraulic mining used high-pressure water to wash away waste and expose gold; this easy-to-get ore ran out quickly, and Butte almost became a ghost town in 1875. From 1875 to 1979, vein mining extracted silver, copper, lead, zinc, and manganese using picks, shovels, drills, and dynamite, with horizontal stations cut every 100, 135, or 200 feet below the surface, drifts driven from each station, and crosscuts excavated to intersect ore veins; ore was hoisted through vertical shafts attached to massive iron head frames, 13 of which remain today, and research indicates about 10,000 miles of underground workings in the Butte area, including 4,200 miles of vertical shafts and 5,600 miles of main horizontal openings, now filling with returning groundwater. From 1948 to 1967, block cave mining provided a low-cost way to extract small pockets of ore by dividing the ore body into 80 by 120 foot blocks undercut from below until caving crushed the ore into removable fragments, which then flowed by gravity through chutes into ore cars or slasher drifts before being pulled by compressed-air-operated motors to central loading points and hoisted to the surface; daily production at the Kelley Mine northwest of the Berkeley Pit reached 15,000 tons. From 1955 to 2000, open pit mining stripped away waste to expose ore, then used dynamite blasting and electric or diesel shovels to load haul trucks; in 1963 the Weed Concentrator southeast of the Berkeley Pit was built to process the ore, chiefly copper and molybdenum with by-products of gold, silver, lead, and zinc, and after the Berkeley Pit closed in 1982, mining resumed at the Continental Pit east of the Berkeley in 1986, was suspended in 2000, and resumed again in fall 2003.