Tahoe National Forest: North Bloomfield and the Hydraulic Mining Disaster

In the eighteen seventies, the most efficient gold mining operation in the world was tearing apart the Sierra Nevada hills above Sacramento with water.

Hydraulic mining worked by directing enormous volumes of water through iron nozzles called monitors, at pressures high enough to slice hillsides apart. The gravel and debris washed through sluice boxes to recover gold, and then moved downstream. The town of North Bloomfield in Nevada County was the center of the Malakoff Diggins operation, the largest hydraulic mining site in California history. The pit it left behind is roughly seven thousand feet long, up to three thousand feet wide, and nearly six hundred feet deep in places, and still there. The walls are layered sediment and gravel exposed like a cross section of the earth.

The problem was the downstream. Billions of cubic yards of debris washed into the Yuba, Bear, and American rivers over two decades of intensive operations. The debris raised riverbeds by as much as eighty feet. Farmland in the Sacramento Valley flooded repeatedly as the rivers, unable to carry the sediment load, spread across their banks. Cities downstream watched their levees fail. Marysville and Sacramento flooded.

The California Debris Commission eventually documented the process that led to the first federal court injunction against an industrial mining practice in American history. In eighteen eighty-four, Judge Lorenzo Sawyer issued an order prohibiting hydraulic mining debris from flowing into navigable waterways. The Malakoff Diggins shut down. The industry that had reshaped an entire watershed ended by court order.

The pit is now part of Malakoff Diggins State Historic Park, inside the Tahoe National Forest. The hills that the monitors eroded are visible from the parking area. They have not recovered. Erosion of that scale does not recover in a century.