This parking lot is notoriously crowded on weekends, often spilling over onto the nearby streets. If you're doing this as a day hike, try to get here as early as possible. If you're backpacking, you may also have better luck waiting until late morning / early afternoon.
Look for the gate on the eastern edge of the parking lot and walk past the ruins of an old resort. Continue east along Icehouse Canyon Creek, passing the ruins of old cabins (and several occupied ones, too!).
Crowds can be an issue on this trail. If you have time to kill, consider leaving the trail and boulder-hopping along the creek - just watch out for stinging nettle.