Calaveras Big Trees / South Loop Mountain Bike Trail.
Take Memorial Parkway to the end past Beaver Creek Picnic Area. A fire road starts on other side of the gate. Stay right on road until your past the bridge. Then go right at first crossing, right at second crossing, and left at the second crossing. Then just stay left for the loop, very, very rustic, no tracks, nothing for 100 miles south of you.