Gradually the best placer mines were taken up and the newcomers to the gold fields traced the precious metal up the streams into the gravel of the hillsides. Then was begun hydraulic mining, where water did the work. In the canons great dams were constructed to catch the flow from the melting snows of the mountains, and miles of flumes were built to carry the water to the mining grounds. Immense pipes were laid and altogether millions of dollars were invested in hydraulic mining. The water coming down under heavy pressure from the mountain reservoirs passed through giant hose which would carry a hundred miner’s inches, and, striking the mountain side with terrific force, washed away the earth from the rocks. Down fell the sand and gravel into sluices or boxes of running water where cleats and other arrangements caught and held the gold, which was heavy, while the lighter mixture was carried out into the canyon. The material thus dumped on the mountain side was called debris, and to any one living in the mining region of the state that word means trouble--means fighting, lawsuits, ruin. For the debris did not stay up in the canyon, but was washed down into the rivers, overflowing farm lands, spoiling crops and orchards, and making the streams shallow, their waters muddy. So great was the destruction this process caused that, in 1893, the Congress of the United States enacted a law which provided for the creation of a Debris Commission to regulate the business of hydraulic mining in California. The result of the investigations of this commission was to put a stop to all hydraulic mining in territory drained by the San Joaquin and Sacramento rivers, or any other territory where the use of this form of mining should injure the river systems or lands adjacent. Thus, almost in a moment, the important industry was stopped. It is estimated that over one hundred million dollars were invested in hydraulic mining. Much of this was entirely lost, as the expensive machinery rusted and the water system fell into ruins. It was very hard for the miners, as well as for the commerce of the state, but the act of the government was based upon the principle that one man’s business must not damage another man’s property. Clever engineers in the pay of the government are still trying to find some way by which the debris can be safely disposed of in order that this valuable system may resume operation. Deprived of the use of water as their agent, gold hunters next tried mining by drifts; that is, by tunneling into the mountain’s side until the bed of a buried river is reached. These tunnels are often five thousand to eight thousand feet long. The gold is brought out of the ground before it is washed clean of the gravel. Sometimes it is mixed with cement, when it has to be crushed in rollers before it can be cleared of other material. The counties where drift mining is most in operation are Placer, Nevada, and Sierra.