This is my favorite trail in Southern California because of the variety it offers. It is a mix of doubletrack and singletrack. Some parts of the trail has quite a bit of climbing, and some is fairly flat.
The easiest route is to take the Sulpher Springs/Cheeseboro Canyon Trail out as far as y ou want from the parking lot, and turn around when you get tired. Other trails may be short, but make sure you read the descriptions before you ride them. The Modello trail may be short, but there's a bit of climbing involved.
If you're looking for something a bit tougher, you can always take the Palo Comado Canyon trail, which has a significant amount of climbing.