About 26 miles north of Nevada City on Tyler Foote Road, Malakoff Diggins is the largest hydraulic gold mine ever operated in California, and one of the most visually striking landscapes in the Sierra foothills. The monitors — water cannons fed by an elaborate flume system — carved a vast canyon out of the hillside, exposing layers of ochre, rust, and white rock that look almost like a Bryce Canyon in miniature.
The park preserves the old mining town of North Bloomfield, with a handful of restored buildings and a small museum explaining the technology and its consequences. The consequences were significant: hydraulic mining sent millions of tons of sediment downstream into the Sacramento Valley, burying farmland and clogging rivers. The legal fight to stop it produced the country's first environmental injunction against industrial pollution.
The drive alone is worth it. Allow at least three hours for the round trip from Nevada City, more if you want to walk the rim trail around the diggings. The canyon changes colour with the light — late afternoon is dramatic.