Vast quantities of sediment were removed from hillslopes, transported by streams and rivers through the Delta, and finally deposited in 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. Beginning in the early 1900s, state and federal water projects built dams on many rivers in the Sierran foothills, Central Valley, and Coastal Ranges. Large canals were built to transport the stored water to farms in the Central Valley and to urban areas throughout the state.
Dams collect sediment as well as fresh water carried by rivers.
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. A group of scientists at the U.S. Geological Survey used bathymetric surveys in San Pablo Bay to estimate the amount of sediment accumulation during the past 150 years. In the middle 1900s, San Pablo Bay lost about 7 million cubic meters of sediment, probably because of California water projects.