Report of the Hydraulic Mining commission and large regional map illustrating the region where the restart of hydraulic mining was being contemplated in California in the 1920s.
The report was prepared at a time period when California was considering the resumption of hydraulic mining.
On February 17, 1927, the Commission submitted its report to the Legislature. Unlike Gilbert's extensive report published just a decade earlier, the limited Jarman report suggested that hydraulic mining could indeed be resumed, "not only without fear of damage to farming and other interests, but with positive benefit to them, provided that impounding dams be constructed at strategic points. It was pointed out that an expenditure of about two and a half million dollars would be needed for the erection of three dams and the purchase of storage in a fourth would enable mining to be resumed on the American, Bear, and Yuba Rivers. However, Jarman reported that the available water will only suffice for one-fourth of the activity of the early eighties and the shortage of water will mainly restrict works on gravels above the average gold content. His forecast is an annual output of gold only one-seventh of that formerly obtained from the district described. Approximately 10,000,000 cubic yards estimated to field $1,156,000 would be mined annually compared with 38,610,000 cubic yards in 1880, estimated to have yielded $8,000,000.
By the 1930s, the lobbying effort succeeded and hydraulic mining resumed.