Miners aimed monster hoses with high-pressure water at hillslopes to wash ancient sediments into sluices and remove gold pieces. Vast quantities of sediment were removed from hillslopes and entered into streams, rivers, the Delta, and finally into San Francisco Bay. Farmers downstream from the mining activities began to complain loudly, as their fields became covered and the streams became clogged with sediment. The hydraulic mining practice was soon outlawed, but the badlands topography that was created by this destructive method can still be seen today along Interstate 80. Large canals were built to transport the stored water to farms in the Central Valley and to urban areas throughout the state.
Dams collect sediments as well as fresh water carried by rivers.
Whereas the effect of hydraulic mining was to increase the amount of sedimentation in the Bay, the effect of water projects has been to decrease sedimentation in the Bay. Timeline of activities in the San Francisco Bay watershed. The period of hydraulic mining is shown in light brown. The solid blue area shows the increased capacity of water storage created by damming of rivers in the Bay's watershed. For more information about their methods, see Jaffe's web site .