Hydraulic mining in the 1870s and early 1880s eroded vast areas of the Sierra Nevada Mountains. The most massive was, and is, at Malakoff Diggins State Historic Park. So much mud was washed down the creeks and rivers that it impeded ship traffic in the San Francisco Bay and raised the Yuba River bottom higher than the surrounding cities of Yuba and Marysville, where today levies still hold back the water.