This is NOT a fun downhill run in the berkeley hills. This is a very dangerous and illegal trail that is never to be ridden by a bicyclist. If you ever were to go to the steam trains in tilden park, make sure that you dont go southbound on grizzly peak and stumble across a clearing on the right hand side of the road. That clearing which is about 1/2 a mile from the steam trains has the beginning of a trail that is perfect for hikers and equestrians but absolutely OFF LIMITS to cyclists.
The trail has dangerous hazards and drops that would require too much skill on the part of a cyclist and sholdn't be attempted. The trail is a winding drop down to UC Berkeley Campus. Along the way you experience just about every kind of terrain, with the exception of sand and rocks. Roots, softpack, hardpack, and fireroads mostly. 80-90 percent singletrack, so remember hikers, yield to equestrians!
If you have any question on how to avoid this dangerous and un-fun trail for cyclists, just ask a local bike mechanic or enthusiast in the area. They will show you exactly where not to go on your bike!
-Calvin