The mother of all Novato mountain bike trails must be Big rock ridge. To put it mildly - this is an extremely strenuous ride, it has unpredictable weather, and scary downhills, depending on the route you take.

 I typically start by taking the Alameda del Prado off-ramp and parking on Clay ct. Where Clay meets Alameda del Prado there is a wooden gate at the start of Chicken Shack Fire Road. It starts rather steep, then becomes very steep as it passes some tennis courts. After some distance Chicken Shack FR meets with Big Rock FR. Keep right and go up the mountain (on the way back you can keep going down Big Rock as an alternative).

 After many uphills and some downhills you pass Luiz Fire Road. This is another alternative down and it brings you to Lucas Valley Rd. Luiz is not for the faint hearted and requires very good braking skills! Last time we did Bick Rock the wind was so strong on the ridge that we had to paddle on some of the downhill stretches.

Below is an elevation profile for this ride. It is around 12 miles.