A couple of miles east of San Elijo on Harmony Grove Road. It is a short, steep trail - about a mile of trail and 1000 feet of vertical. So it can be moderate to strenuous, depending on your pace. At the top is more flat trails, some picnic areas, and the Olivenhain Reservoir - sorry, no swimming! I have done this trail a few times early in the morning. It gets pretty crowded as the day goes on.