Gold occurs as fine grains in the black sands on the beach at San Francisco. From 1938 to 1950, gold was produced at the beach by people who used small washing plants. From 1938 to 1941, the recorded production was valued at about $13,000. The most productive part of the beach was south of the Fleishhacker Zoo, and the gold was most plentiful immediately after heavy winter storms. Several narrow goldbearing quartz veins have been found in metamorphic rocks in the general area.