"Although gold v/a% mined in California in the late 18th and early 19th Centuries, the gold rush did not begin until after Marshall's discovery at Sutter's Mill in 1848. Thou- sands of gold seekers soon arrived, and in a few years much of the state was permanently settled. Gold production attained an all-time high of $81 million in 1852 but then declined because of the exhaustion of the rich surface placers. At the last government-set price of $35 per ounce, the 1852 amount would have been about $138 million.
Hydraulic mines became the largest sources of gold until curtailed by court order in 1884. Lode mines and dredges were the principal sources after that date. During the depression years of the 1930s, gold output in the state was nearly as high as it had been during the gold rush. Gold mining was curtailed during World War II end has not recovered since.
A number of spectacular nuggets and masses of pure gold were recovered in Cali- fornia during the early days. The most famous were the 195-pound mass of gold from Carson Hill and the 54-pound Willard nugget from Magalia. Small high-grade ore shoots or pockets have been found in many districts, but the richest and most numerous have been in the Alleghany district of Sierra County." end
This excerpt from Mining Districts of California
There are pictures of the scars left on the mountains. I think it was above Lytle creek. Somewhere I have a book with the pictures and descriptions. Still looking, but if you search hydraulic mining/sluicing Lytle Creek or San Gabriel Mountains you might get some photos.
I spent a few years prospecting gold and checked it out. The entire valley is filled with sediment from the hydraulic sluicing.