Ore-processing facilities known as "stamp mills" operated near gold mines in California and Nevada. "Stamping" mechanisms, typically comprised a water wheel, cams, and hammers, could crush or "pulverize" the ore into smaller lumps to allow for further processing. In Californian facilities, Cornish-style stamp mills were used to pound ore into sand. Gold stamping, in particular, was used to separate the valuable material from the worthless chunks of rock. The mills often required water for processing and were therefore located near rivers or lakes. While the use of chemicals and other processing practices have changed over the years, some stamp mills are still in use today.