This is the mecca of NorCal off-roading. Huge place with wonderful trails. Be aware that it is a *challenging* place to ride; most trails have long Black Diamond sections and demand your best skill. But that's what makes it Awesome!!!

If you have newbies, they can do a 30 mile loop on M5. The nice thing is that this forest road is criss-crossed by challenging trails, and so both experienced and inexperienced riders can kinda do a loop together.