Wow -- I went to LA expecting to be in car-smog city. But because we are on the outskirts of the sprawl, it turns out that there's heaps of good mountain biking available. Chino Hills state park is just a couple of miles from the client. It has 60 miles of trails, including about 30% of single track. I've brought the old Toyota down and the old Specialized to take advantage of the dirt.