As you drove towards the parking lot you passed the entrance to the trail on your right. It's ok; hop out of your car, and backtrack a short ways to the start of the trail.
This trail is wonderful singletrack with pretty easy terrain, but the desert scenery is jaw dropping. The area can be crowded at times, and it is not uncommon to run into many horses and bikers. Trails are well maintained and they have been adding new trails lately (2015). This is one of the more enjoyable trails at the preserve.