La Tuna has some of the Greatest Single Track in Southern CA. It's a great ride...60% of awsome rocky fireroad, and 40% really rocky/rutty singletrack that has a few very technical parts.
Follow the paved road up for .5 miles, and the fire road climb starts. Once you make it to the top (mile 3.45), turn right, and keep going until you get to mile 5.2. Keep looking at your right, you'll see the singletrack (there is no sign...you have to look for it)
How to get there:
Get on the 210 and exit la tuna Canyon. Parking lot is to the south of the 210...can't miss it.