Kings Mountain - Skyline Boulevard - Canada Road Loop is a 23 mile loop trail located near Redwood City, CA and is rated as difficult. The trail is primarily used for hiking, trail running, and road biking and is accessible year-round.
I really like this route. It's has very very few cars, quiet, serene and quite smooth. Yes, it's all uphill which requires some normal level of fitness. The bends are awesome going downhill.