The hook
The Gold Rush ran on mercury, and the mercury came from here: California's oldest and richest mine, with its company town still intact in a San Jose canyon.
01Why it's worth it
Before anyone found gold, New Almaden was already the most valuable mine in California — cinnabar ore the Ohlone used for pigment became the quicksilver that processed the Mother Lode's gold and silver; by some accounts this single district produced more wealth than any California gold mine. The village survives as a drowsy one-road historic district: the 1854 Casa Grande mansion now houses an excellent free county mining museum (working models, the eerie story of the miners' mercury exposure), and the hills above — Almaden Quicksilver County Park — are laced with 34 miles of trails past rotting tramways, the San Cristobal mine portal, chimneys, and the hilltop English Camp ghost settlement where Cornish miners lived. It's the Bay Area's most complete industrial-history landscape, and almost nobody outside South San Jose knows it exists. Pairs perfectly with Mt Umunhum, whose road starts nearby.
02How to experience it
Almaden Rd through the village; museum first (free, closed some weekdays — check), then hike from the Hacienda entrance: the Mine Hill loop past English Camp is the classic. No shade to speak of once you climb — spring and fall. The mercury stays in the ground; don't collect rocks, and heed the fishing warnings on the reservoirs.