The Green Loop is a short loop on the north side of Ontario County Park. It's short and sweet, without any extended climbs or descents. The Green Loop makes for an excellent warm-up, and many group rides and races start with this humble trail. It's also great introduction for beginners to the OCP trail system, with enough rocks and roots to keep them on their toes.
From the pavement leading from the pavilions, the Green Loop is usually entered by crossing Gannet Hill Park Rd onto a gravel path and making an immediate left turn, riding the Green Loop counter-clockwise. As a bonus, this shoots you back out on the road directly across from the Violet Trail, which takes you towards the rest of the trail system.
That said, the Green Loop is fun in either direction. Try it!