I've heard good things about Almaden Quicksilver County Park (located near San Jose). Anyone up for a last minute hike? Meet at the Hacienda Trailhead, off Almaden Road at 9 am, I'll wait near the portable toilets on the north side of the parking area (hopefully they're not too smelly...).
This is a 7.6 mile, moderate loop trail: http://www.bahiker.com/southbayhikes/almadenquicksilver.html
Estimated hiking time is 4 hours, so bring a snack and plenty of water. The trail is mostly exposed, sunscreen and a hat are recommended.